A Tables of results

Chromospheric activity and rotation of FGK stars in the solar vicinity1 2

An estimation of the radial velocity jitter
Key Words.:
Galaxy: solar neighbourhood – Stars: late-type – Stars: activity – Stars: chromospheres – Stars: rotation – Stars: planetary systems
3

Abstract

Context:Chromospheric activity produces both photometric and spectroscopic variations that can be mistaken as planets. Large spots crossing the stellar disc can produce planet-like periodic variations in the light curve of a star. These spots clearly affect the spectral line profiles and their perturbations alter the line centroids creating a radial velocity jitter that might “contaminate” the variations induced by a planet. Precise chromospheric activity measurements are needed to estimate the activity-induced noise that should be expected for a given star.

Aims:We obtain precise chromospheric activity measurements and projected rotational velocities for nearby (d 25 pc) cool (spectral types F to K) stars, to estimate their expected activity-related jitter. As a complementary objective, we attempt to obtain relationships between fluxes in different activity indicator lines, that permit a transformation of traditional activity indicators, ., Ca ii H & K lines, to others that hold noteworthy advantages.

Methods:We used high resolution ( 50000) optical spectra. Standard data reduction was performed using the IRAF echelle package. To determine the chromospheric emission of the stars in the sample, we used the spectral subtraction technique. We measured the equivalent widths of the chromospheric emission lines in the subtracted spectrum and transformed them into fluxes by applying empirical equivalent width and flux relationships. Rotational velocities were determined using the cross-correlation technique. To infer activity-related radial velocity () jitter, we used empirical relationships between this jitter and the index.

Results:We measured chromospheric activity, as given by different indicators throughout the optical spectra, and projected rotational velocities for 371 nearby cool stars. We have built empirical relationships among the most important chromospheric emission lines. Finally, we used the measured chromospheric activity to estimate the expected jitter for the active stars in the sample.

Conclusions:

1 Introduction

Exoplanetary science is living a golden era characterized by the enormous rate at which new exoplanets are being discovered. This impressive advancement would not have been possible without parallel technological developments. Improved precision in both radial velocity and photometric measurements has extended the area around the star in which a planet can be found and has increased the probability of detecting low mass exoplanets. These improvements have created, however, a new and noteworthy problem, .., the possibility of misidentifying planets. Chromospheric activity, in particular, the presence of spots and/or alteration of the granulation pattern in active regions, create a time-variable photometric and spectroscopic signature (Saar & Donahue 1997; Santos et al. 2000; Saar 2003) that might be misinterpreted as an exoplanet. Moreover, the minimum detectable mass of a planet orbiting a star is limited by the velocity jitter caused by stellar sources (Narayan et al. 2005). Therefore, a thorough analysis of activity levels, as only different activity indicators can provide, must be performed for those stars that constitute the natural targets of planet-search surveys.

When searching for exoplanets using the radial velocity () technique, the possibility of jitter caused by chromospheric activity must be considered. When modeling stellar activity, Saar & Donahue (1997) were the first to quantitatively estimate the impact of stellar spots on the curve and showed that they could produce peak-to-peak amplitudes of up to a few hundred  m s, depending on spot size and the rotational velocity of the star. Subsequent studies (Santos et al. 2000; Saar et al. 2003; Paulson et al. 2004; Desort et al. 2007) obtained similar results. Several attempts to reduce noise levels by using an activity-based correction have been made (Saar & Donahue 1997; Saar et al. 1998; Santos et al. 2000; Saar & Fischer 2000; Saar et al. 2003; Wright 2005). To use these corrections and to test and calibrate the relations, high precision, homogeneous chromospheric activity measurements are needed.

Transit searches for exoplanets are also affected by the temporal evolution and modulation of active regions across the stellar disc. The amplitude of variations can reach more than 1 when a large spot crosses the solar disc at activity maximum. This decrease in signal, combined with the modulation caused by stellar rotation can mimic the signal of a planet orbiting the star. Therefore Sun-like variability, not to mention that of stars more active than the Sun, can significantly affect the detection performance of photometric planet searches (Henry et al. 1997; Baliunas et al. 1997; Henry et al. 2000; Aigrain et al. 2004).

Hence, chromospheric activity is a proxy for predicting variability levels expected for a star, therefore allowing the estimation of a lower limit for planet detections in its vicinity. In this paper, we present spectroscopic-based chromospheric activity measurements for 371 nearby (d 25 pc), cool (spectral types F to K) stars. These stars are the natural targets for exoplanet searches: their proximity ensures the ability to get an adequate signal-to-noise ratio (hereafter S/N), and solar-like stars are more likely to host so-called habitable planets (Kasting et al. 1993; Doyle et al. 1998; Turnbull & Tarter 2003). In this study, we considered not only the traditional chromospheric activity indicators, .., or H, but also other less common indicators, such as the Ca ii IRT lines, which allow us to exploit peak-to-peak amplitude variations caused by spots being less significant at longer wavelengths (Desort et al. 2007; Reiners et al. 2009).

2 The stellar sample

The stellar sample comprises 371 cool stars in the solar vicinity, constrained to be at distances closer than 25 pc (see Table 6). Distances were obtained from the Hipparcos Catalogue (ESA 1997) and the New Reduction of the Raw Data (van Leeuwen 2007). The spectral type distribution of the sample is 56 F type stars, 126 G type stars, 186 K stars, and 3 M type stars. Since our study is based on solar-like stars, only F, G and K spectral types stars with trigonometric parallax 40 mas were retrieved. To avoid misclassified stars, we used colour index as a complementary criteria, .., colour index in the range 0.25-0.58 mag (F stars), 0.52-0.81 mag (G stars), and 0.74-1.40 mag (K stars). To establish the main-sequence character of the stars, we used a cutoff of 1 mag from the main sequence (Wright 2005). Finally, stars in multiple systems were removed from the sample. We used the CCDM (Dommanget & Nys 1994, 2002) and SB9 (Pourbaix et al. 2004) catalogues to identify astrometric and spectroscopic binaries, respectively.

These stars are potential targets for present and future projects that aim to detect Earth-like planets or exo-solar analogues to the Edgeworth-Kuiper Belt. In this context, most of our stars will be observed in the framework of DUNES (DUst around NEarby Stars), an approved Herschel Open Time Key Project with the aim of detecting cool faint dusty disks, at flux levels as low as the Solar EKB. Some preliminary results can be found in Martínez-Arnáiz et al. (2009), Maldonado et al. (2010), and Montes et al. (2010).

3 Observations and data reduction

The present work is based on data extracted from high resolution echelle spectra. Most of the spectra were obtained in several observing runs but we also used spectra (Allende Prieto et al. 2004). The latter have similar spectral resolution ( 45000) to those obtained by us and were consequently used in an analogous manner to measure and analyse the stellar parameters and properties of the stars.

Observations were obtained at two different observatories: the German-Spanish Astronomical Observatory, CAHA, (Almería, Spain) and La Palma Observatory (La Palma, Spain). Observations were taken at the former.2 m telescope using the Fibre optics Cassegrain Echelle Spectrograph (FOCES) (Pfeiffer et al. 1998) with a 20482048 24 m SITE1d-15, and at the latter with the 3.5 m Telescopio Nazionale Galileo (TNG) using the Spectrografo di Alta Resoluzione Galileo (SARG), the grid R4 (31.6 lines/mm), the red cross-dispersor (200 lines/mm), and a CCD detector mosaic of total surface 20484096 and 13.5 m pixels.

We carried out four observing runs at CAHA (July 2005, January 2006, December 2006 and February-May 2007). FOCES spectra have a wavelength range from 3600 to 10700 Å in 106 orders with a typical resolution of 40000 (reciprocal dispersion from 0.08-0.13 Å/pixel in the red and blue region of the spectrum, respectively). The total number of stars observed using this spectrograph is 198. At La Palma Observatory, we performed three observing runs (February 2006, April 2007 and, November 2008). SARG spectra have a wavelength range from 5540 to 7340 Å in 50 orders with a resolution of 57000 (reciprocal dispersion from 0.01 to 0.04 Å/pixel in the red and blue region of the spectrum, respectively). We observed 129 stars using the SARG spectrograph.

As mentioned before, we used (Allende Prieto et al. 2004) spectra. These spectra were taken between October 2000 and November 2001 in six observing runs at the Harlan J. Smith 2.7 m telescope (McDonald Observatory) and two at the 1.52 m telescope at La Silla (Chile). At McDonald Observatory, the 2dcoudé (Tull et al. 1995) spectrograph with the Tektronix 20482048 24 m CCD detector was used. The spectral coverage was 3600-5100 Å  with a typical resolution of 50000. At La Silla Observatory, the Fiber-fed Extended Range Optical Spectrograph (FEROS) (Kaufer et al. 2000) with the CCD detector EEV 20482048 15 m was used. The wavelength coverage in this case is 3500-9200 Å  and the resolution 45000. The total number of studied stars is 106. Of them, 79 were observed at McDonald Observatory, while the rest were observed with FEROS at La Silla Observatory.

All the observed stars and the corresponding spectrograph used are listed in Table 6. We note that some stars were observed more than once and using different spectrographs.

For the reduction, we used the standard procedures in the IRAF (Image Reduction and Analysis Facility) package (bias subtraction, extraction of the scattered light produced in the optical system, division by the normalized flat-field, and wavelength calibration). After the reduction process, the spectrum was normalized to the continuum order by order by fitting a polynomial function to remove the general shape of the aperture spectra.

4 Analysis and results

4.1 Rotational velocities

The determination of rotational velocities for stars in exoplanet surveys is crucial. Radial velocity variations induced by chromospherically active regions on the stellar surface are modulated by the rotation period of the star (Baliunas et al. 1997; Henry et al. 1997, 2000). Obtaining the rotational velocity of the star is thus essential to test whether detected variations have a stellar or a planetary origin.

FOCES 2dcoudé FEROS SARG
Name SpT A Name SpT A Name SpT A Name SpT A
HIP 104217 K7V 0.500 0.130 HIP 67422 K2V 0.550 0.009 HIP 99461 K3V 0.640 0.015 HIP 98698 K4V 0.523 0.007
HIP 117779 K5V 0.436 0.095 HIP 3765 K2V 0.610 0.008 HIP 10138 K1V 0.620 0.008 HIP 3765 K2V 0.605 0.005
HIP 3765 K2V 0.616 0.100 HIP 7981 K1V 0.580 0.008 HIP 99825 K0V 0.600 0.008 HIP 88972 K2V 0.501 0.003
HIP 7981 K1V 0.574 0.100 HIP 3093 K0V 0.570 0.008 HIP 84720 G8V 0.640 0.008 HIP 3093 K0V 0.607 0.006
HIP 3093 K0V 0.557 0.100 HIP 56997 G8V 0.630 0.016 HIP 57443 G5V 0.660 0.008 HIP 64924 G5V 0.606 0.010
HIP 95319 G8V 0.648 0.100 HIP 10798 G5V 0.620 0.008 HIP 91438 G5V 0.650 0.008 HIP 23835 G4V 0.646 0.008
HIP 9269 G5V 0.581 0.224 HIP 64924 G5V 0.600 0.008 HIP 71683 G2V 0.640 0.008
HIP 48113 G0.5V 0.680 0.280 HIP 7918 G1V 0.640 0.008 HIP 1599 F9V 0.680 0.007
= 0.574 0.004 = 0.598 0.003 = 0.643 0.003 = 0.581 0.082
Table 1: A constant for FOCES, 2dcoudé (McDonald), FEROS and SARG spectra.

The widths and shapes of spectral lines contain information that allow us to deduce physical information about the star, including its rotation rate. To measure this width, the most commonly used parameter is the the line FWHM (Full Width Half Maximum) because it can be easily measured. The Fourier domain offers, however, some advantages over the wavelength one. Signatures of certain physical processes, such as the Doppler-shift distribution produced by rotation or macroturbulence, are more readily detected in that domain. The cross-correlation function (CCF) was therefore used to measure rotational velocities. The width () of the CCF peak for a star when correlated with itself depends on the instrumental profile and several broadening mechanisms such as gravity, effective temperature, or rotation. To measure the rotational contribution, and hence determine the star’s projected rotational velocity, the contribution of other broadening mechanisms has to be modelled. For   50  km s, the CCF is well approximated by a Gaussian (Soderblom et al. 1989) and consequently the rotational broadening corresponds to a quadratic broadening of the CCF. In that case, the observed width of the CCF can be written as (see Queloz et al. 1998, and references therein)

(1)

where is the rotational broadening and is the width of the CCF of a similar non-rotating star. Projected rotational velocities, v , can be derived from the above expression as

(2)

where is a coupling constant that depends on the spectrograph and its configuration. To determine for each spectrograph, non-rotating stars were used4. Their spectra were broadened from  =1  km s to 50  km s using the program jstarmod5. The value of was then determined as the equivalent width of the first peak in the CCF. The constant was found by fitting the relation   vs . The stars used to compute , the measurements, and the mean values for each spectrograph are shown in Table 1.

It is well known that is a function of the broadening mechanisms present in the atmosphere of the star, except rotation (Melo et al. 2004). Since the broadening mechanisms are a function of the temperature and gravity, we may expect the colour index, to depend on , for stars in the main sequence. To determine this dependence, we created morphed spectra with no rotational velocity using the ATLAS9 code by Kurucz (1993) adapted to operate on a linux platform by Sbordone et al. (2004) and Sbordone (2005). Temperatures vary from 3500 K to 6500 K (in intervals of 250 K). Since the stars were selected to be on the main sequence, was fixed to be 4.5. Solar metallicity was assumed. The morphed spectra were broadened to match the instrumental profile of the real spectra using the FWHM of the calibration arc lines, which is a good approximation of the broadening for the instruments used. Given that each spectrograph has a different resolving power, different instrumental broadenings were applied to obtain a calibration curve for each instrument. These curves are shown in Fig. 1.

Color indices, , were obtained from the Tycho-2 Catalogue (Høg et al. 2000) using the transformation from and to Johnson indices (see Sect. 1.3 from Hipparcos Catalogue, ESA 1997) and are listed in Table 6.

Figure 1: Calibration between and colour index , where represents the “natural” broadening of the spectrum lines and was obtained from synthetic spectra covering the spectral range of the observed stars. Given that the instrumental profile also contributes as a broadening mechanism and considering that each spectrograph has a different one, we had to derive a calibration relationship for each of them.

Once and were known for each star,   could be directly derived by measuring , .., width of the CCF of the star when correlated with itself. Values for stars in the sample can be found in Table 6. For slow rotating stars, it is important to mention that sometimes, the value of is larger than that of . In that case,   cannot be measured using this method and we only provide an upper limit. This value was chosen by considering the minimum   that could be measured with the same spectrograph for a star of the same spectral type, , the same .

4.2 Chromospheric activity

We analyse different activity indicators throughout the optical spectra (from Ca ii H&K to Ca ii IRT). These lines form at different heights in the chromosphere hence provide information about different stellar properties. Some lines are present only during high energy processes such as flares. As shown in previous work (see Montes et al. 2000, 2001, and references therein), by performing a simultaneous analysis of different optical chromospheric activity indicators, a detailed study of the chromosphere’s structure can be achieved and it becomes possible to discriminate between structures such as plages, prominences, flares, and microflares. The spectra used in this work have a spectral range that covers plages from Ca ii H & K to Ca ii IRT lines, including the Balmer lines.

Equivalent widths and fluxes

To determine the chromospheric contribution to the spectrum, and thus the chromospheric activity, the contribution of the photosphere must be removed. In order to achieve this, we used the spectral subtraction technique, described in detail by Montes et al. (1995a, 2000). This technique has been extensively used before because it permits the detecion of weak emission features in the cores of chromospheric lines. In addition, it is the most effective means of identifying other chromospheric activity indicators such as the Balmer lines or the Ca ii IRT, where no calibrations of the photospheric minimum flux exists (Barden 1985; Huenemoerder et al. 1989; Hall & Ramcey 1992; Frasca & Catalano 1994; Gunn & Doyle 1997; Lázaro & Arévalo 1997; Montes et al. 1995a, 1996b, 1997, 2000, 2001; Gálvez et al. 2002, 2007, 2009; López-Santiago et al. 2003, 2010). Inactive, slowly rotating stars, observed in the same observing run as the active stars, were used as reference to construct a morphed spectrum for each active star, using the program jstarmod. The program builds the morphed spectrum by shifting and broadening the reference spectrum to match that of the target star. This implies that the reference star must have a lower rotation rate than but a similar spectral type to the target star. A compilation of the inactive, slowly rotating stars used as references can be found in Table 2. Reference stars were initially chosen from the literature but some inactive, slowly rotating stars of the sample were also used as reference after confirming that they did not show chromospheric activity. To ensure that those stars were inactive, their values of total flux in Ca ii H & K were compared to the lower boundary defined by Rutten (1984), which is traditionally used to correct flux measurements from the basal chromospheric flux (see Fig. 3). Maximum differences of 0.25 (F type stars), 0.3 (G type stars) and 0.35 (K type stars) in values between the stars used as references and the lower boundary of Rutten (1984) were allowed. The morphed spectrum was subtracted from that of the active star, obtaining a spectrum in which only the chromospheric contribution is present, .., the subtracted spectrum. The excess emission of the activity indicator lines were obtained from that spectrum. To estimate the errors in the measured , we followed Montes et al. (2001) and considered jstarmod’s typical internal precisions (0.5-2 km s in velocity shifts and 5 km s in  ), the in regions outside the chromospheric features (typically 0.01-0.03), and the standard deviations. The estimated errors for relatively strong emitters are in the range of 10-20% but for low activity stars errors are larger. Taking into consideration that S/N is lower in the blue spectral region, errors in the chromospheric features at these wavelengths are larger.

HIP SpT   Obs. HIP SpT   Obs.
(km s) (erg cm s) (km s) (erg cm s)
37279 F5V 0.420 5.38 Mc 0.76 8102 G8V 0.730 8.00 Mc 0.15, 0.14
910 F5V 0.489 4.88 S 79492 G8V 0.756 2.68 FO 0.12, 0.11
78072 F6IV 0.480 11.42 FO 0.57 95319 G8V 0.805 0.60 FO -0.05, 0.01
22449 F6V 0.475 19.22 Mc 0.71 101997 G8V 0.730 3.50 S 0.16
40035 F7V 0.495 11.26 S 47080 G8V 0.779 6.97 FO/S/Mc 0.30
27072 F7V 0.498 FE 63366 G9V 0.780 FE 0.12
17147 F9V 0.538 9.70 FO 0.48 74537 K0V 0.761 2.12 S
57757 F9V 0.558 3.41 Mc 0.44 40693 K0V 0.766 6.79 Mc 0.09
16852 F9V 0.568 2.67 Mc 0.39, 0.37 84195 K0 0.940 8.58 FO -0.20
1599 F9V 0.576 3.23 FE 0.45 112190 K0 0.968 3.35 FO -0.12
64394 F9.5V 0.588 4.72 Mc 0.48 3093 K0.5V 0.853 9.38 FO/S/Mc -0.05, -0.11
61317 G0V 0.589 2.00 Mc 0.43, 0.41 7981 K1V 0.834 6.50 FO/S/Mc -0.01, -0.02
77257 G0IV 0.596 3.00 Mc 0.37 70016 K1V 0.867 8.15 S -0.13, -0.07
14632 G0V 0.606 3.15 Mc 0.33, 0.32 79190 K1V 0.843 3.97 FE
77801 G0V 0.624 FO/S 0.37 71681 K1V 0.900 3.52 FE
1499 G0V 0.680 4.18 FO 0.21 3765 K2V 0.885 6.71 FO/S/Mc -0.04
67904 G0V 0.697 FE 0.27 88972 K2V 0.886 4.82 S -0.11, -0.13
10644 G0.5V 0.603 3.93 Mc 0.52, 0.50 105152 K2V 1.028 3.69 FO -0.33
29860 G0.5V 0.611 2.98 S 0.34 114886 K2V 0.898 3.18 FO -0.07
48113 G0.5IV 0.624 2.93 FO/S 0.23, 0.27 12114 K3V 0.918 6.45 S -0.11, -0.04
15371 G1V 0.600 2.64 FE 0.42 114622 K3/K4 V 1.000 2.10 FO/S -0.29
53721 G1V 0.613 2.80 Mc 0.31, 0.35 78843 K3/K4V 1.059 6.24 S -0.38
24813 G1.5IV 0.613 2.00 Mc 0.31 73184 K4V 1.110 FE -0.20
7918 G1.5V 0.620 2.10 FO/S/Mc 0.30 113718 K4V 0.948 6.22 FO
52369 G2/G3V 0.629 7.22 S 12929 K5 1.170 8.11 FO 0.01, -0.07
79672 G2Va 0.648 4.07 Mc 0.31, 0.30 50125 K5V 1.122 2.85 S
27435 G4V 0.639 2.61 S 0.32 54651 K5V 1.089 0.53 S
50505 G5 0.686 1.72 S 0.22 83591 K5V 1.120 3.70 FO/S -0.20
64924 G5V 0.709 4.09 S 0.16, 0.15 93871 K5V 1.050 4.07 FO
171 G5V 0.660 3.00 Mc 0.30 104214 K5V 1.160 4.72 FO/S -0.22
5336 G5V 0.700 8.00 Mc 0.19 80644 K6V 1.209 3.68 FO -0.25, -0.26
62523 G7V 0.706 10.60 S 0.42 104217 K7V 1.360 1.70 FO/S -0.50
2941 G7V 0.717 5.54 S 0.23, 0.19 54646 K8V 1.345 5.83 S -0.37
58576 G8IV-V 0.757 Mc 0.03, 0.11 60661 M0V 1.451 FO
14150 G8V 0.715 4.08 S 0.22

Spectrograph used: Mc: Mc Donald; S: SARG; FO: FOCES; FE: FEROS

Duncan et al. 1991

Henry et al. 1996

Jenkins et al. 2006

Wright et al. 2004

Table 2: Inactive stars used as references in the subtraction technique to measure chromospheric activity

In Fig. 2, we plot an histogram for the total number of stars of each spectral type and the number that could be classified as active (displaying chromospheric features in the spectrum) or not active.

Figure 2: Number of active (black) and inactive (grey) stars in the sample for each spectral type.

In Table 7, we give the excess emission and its error for the active stars in the sample. Of the complete sample of stars analysed (371 stars), 173 presented chromospheric activity features in their spectra. Of them, 8 were F type stars (14% of the analysed F stars), 38 G type stars (30% of the G type stars), 126 K type stars (68% of the analysed K stars) and 1 M star (33% of the analysed M stars). From the remaining, 193 could be classified as inactive because of the lack of any chromospheric activity feature in their spectra. Of them, 48 are F type stars (86% of the analysed F stars), 88 G type stars (70% of the total G type stars), and 57 K stars (31% of the analysed K type stars). The remaining 5 stars could not be classified as either active or inactive because of the low S/N of their spectra. We have included a column (Col. # 8) in Table 6 to specify whether the star can be considered as active or not active. In 6 cases (5 K stars and 1 M star), we could not measure chromospheric activity due to the lack of a suitable non-active reference star to perform the subtraction technique, but chromospheric activity features were clearly present in the spectra. These stars were classified as active (and indicated with * in Table 6) but chromospheric activity was not measured. It is also important to mention that due to the configuration used with the SARG spectrograph the spectral range corresponding to Ca ii H & K was not covered and these lines could not be measured.

We must comment on eight special cases: HIP 3093, HIP 3765, HIP 7981, HIP 54646, HIP 60866, HIP 62523, HIP 77408 and HIP 85810. These stars were observed more than once and with different instruments. Chromospheric activity features were detected in at least one of the observations, but not in all of them. Therefore, the stars are labelled as active and inactive depending on the observing run. In six of the cases (HIP 3093, HIP 3765, HIP 54646, HIP 60866, HIP 77408 and HIP 85810), the level of activity (when measured) is very low, which points to the use of a different reference star as the explanation for the inability to detect emission features in the subtracted spectrum. Two of these stars (HIP 3093 and HIP 3765) show levels of chromospheric activity so low that are generally considered inactive and used as reference stars to subtract the photospheric contribution from the spectrum. In the remaining cases, HIP 7981 and HIP 62523, variability appears to be the cause. The star HIP 7981 was previously classified as variable by Hall et al. (2007). Both stars were observed in three observing runs, two of them closer in time than the other. The stars exhibit no chromospheric emission features in observations carried out during the same epoch, whereas they do in data for other epoch. This indicates that the lack of features appears to be real and not attributable to a different choice of the reference star. Variability therefore presents itself as a plausible explanation of the lack of detected activity in two of the observations. These stars are marked with in Table 6. Fluxes can be derived from the measured by correcting the continuum flux

(3)

where the continuum flux, , is obviously dependent on the wavelength and must therefore be determined for the region where the activity indicator line appears. We used the empirical relationships between and colour index, , (Hall 1996) to compute for each line and star. We note that the aforementioned relationships are linear for the spectral type range of the sample stars. In Table 8, we give the absolute flux at the stellar surface and its error for the active stars in the sample.

index

Chromospheric activity has been traditionally studied using the index, defined as the ratio of the emission from the chromosphere in the cores of the Ca ii H & K to the total bolometric emission of the star, where the prime denotes that subtraction of the photospheric contribution has been performed.It was first used by Noyes et al. (1984). This index was first measured using observed flux indices in the core of Ca ii H & K (corrected from the continuum signal) with the Mount Wilson H-K spectrophotometer (Vaughan et al. 1978). These fluxes were corrected from the photospheric contribution using an empirical calibration with the colour index (Noyes et al. 1984). Finally, the Ca ii H and K line-core flux measurements were corrected from the minimum surface flux using a calibration with the colour index (Rutten 1984), thus providing a measurement of the chromospheric contribution associated with magnetic activity. In principle, we could derive directly from the measured fluxes in Ca ii H & K lines using the subtraction technique

(4)

When the subtraction technique is applied, the residual chromospheric contribution of the reference star is also subtracted from the spectrum of the target star. The source of possible differences between the fluxes obtained using the subtraction technique and those obtained with the traditional method, is the difference in chromospheric emission between our reference stars and those used by Rutten (1984) to compile his calibration. In Fig. 3, we have plotted the total surface flux in the Ca ii H & K lines for the reference stars used in this work, and the Rutten (1984) calibration for main sequence stars. The values of total surface flux in the Ca ii H & K lines for the reference stars have been obtained from Duncan et al. (1991), Henry et al. (1996), Wright et al. (2004), and Jenkins et al. (2006) and are included in Table 2. We note that all our reference stars have Ca ii H & K fluxes close to the lower boundary defined by Rutten (1984) adopted in subsequent studies. The maximum difference between the surface fluxes of the stars used as references in the present study and the Rutten (1984) calibration is 0.2 dex, with the exception of K5 to K7 stars for which it is 0.35 dex. Since these differences account for differences of only 0.2 dex (0.35 dex for K5 to K7 stars) in R’, we can assume that the values of obtained using the subtraction technique are comparable to those obtained with the traditional method.

Figure 3: Ca ii H & K surface flux colour index . Small dots represent Duncan et al. (1991) and Wright et al. (2004) data. To represent the stars considered as reference in this work, we have used different symbols according to the source of F+F values: circles for Duncan et al. (1991) data, squares for Henry et al. (1996) data, crosses for Wright et al. (2004) data, and triangles for Jenkins et al. (2006) data. The curve represents the surface flux boundary obtained by Rutten (1984).

To determine the effective temperatures needed to convert total flux in Ca ii H & K into , we used the empirical calibrations with the colour index provided by Gray (2008), which holds for the spectral type range of the target stars (0.00 1.5).

Dataset # of common stars # of coincidences
Active Inactive Active Inactive
Duncan et al. (1991) 52 90 40 75
Strassmeier et al. (2000) 37 21 31 20
Wright et al. (2004) 34 92 30 84
Hall et al. (2007) 21 35 14 31
Mamajek & Hillenbrand (2008) 27 54 23 47
Table 3: Comparison of the classification of the stars as active or inactive with previous results.
Figure 4: Comparison of index obtained in this paper and that obtained with the Mount Wilson H-K spectrophotometer (Vaughan et al. 1978) and similar techniques. Different symbols are used for Duncan et al. (1991), Strassmeier et al. (2000), Wright et al. (2004), Hall et al. (2007), and Mamajek & Hillenbrand (2008) data. In the lower panel, we have plotted (as described in the text).

4.3 Comparison with previous results

To test whether the transformation is consistent with those values of computed using photometry (or a technique to mimic photometric results using spectroscopic data), we compared our data to those obtained by Duncan et al. (1991), Strassmeier et al. (2000), Wright et al. (2004), Hall et al. (2007), and Mamajek & Hillenbrand (2008). The comparison is plotted in Fig. 4, where

(5)

The dispersion observed in Fig. 4 is compatible with variations in activity levels with time. To determine if there are systematic differences between our data and any of the five data sets analysed, we have plotted in Fig. 4. The closer the value of to 0, the smaller the difference between our values and those from other authors. In addition, we performed a Kolmogorov-Smirnov test to determine whether our data and those obtained by other authors are equivalent. The values of the estatistical estimator obtained when applying the Kolmogorov-Smirnov test with Mt. Wilson ( = 59), Strassmeier ( = 37), Wright ( = 38), Hall ( = 19) and Mamajek ( = 31) data are 0.152, 0.351, 0.236, 0.263 and 0.322, respectively. These results indicate that the null hypothesis, . ., both samples are equivalent, could not be rejected at a level of significance less than 65 % in the Mt. Wilson, Wright, and Hall cases. This clearly means that values obtained using the traditional method are equivalent to those obtained in this study. As might be expected, discrepancies are larger when we compare our results with those presented in Mamajek & Hillenbrand (2008), because the latter constitutes a compilation of values obtained from different sources. Differences between our results and Strassmeier et al. (2000) are also larger than the rest. Again this is not surprising, taking into account that the method used to correct from the photospheric contribution is different than in the rest of the cases. The Strassmeier et al. (2000) values therefore do not necessarily reproduce the original values. It is also important to note that discrepancies are larger for less active stars, in particular for stars with measured . This result is again expectated considering that for stars with low activity levels, errors in the photospheric contribution correction become more apparent.

HIP HD This work Previous results
Activity Activity Activity
3765 4628 active -5.40 inactive -4.89
5286 6660 active -4.57 inactive -4.76
7751 10360 active -4.94 inactive -4.90
7981 10476 active -5.19 inactive -4.95,-4.98,-4.91
10644 13974 inactive active -4.64, -4.71, -4.69
12929 17230 inactive active -4.55
15442 20619 active -4.75 inactive -4.83
15457 20630 inactive active -4.41, -4.71, -4.40
17420 23356 inactive active -4.69
19422 25665 inactive inactive -4.86 active -4.69
19849 26965 active -5.38 inactive -4.87, -4.90
20917 28343 active -4.62 inactive -4.76
22449 30652 inactive inactive -4.79 active -4.65
23311 32147 active -5.29 inactive -5.75
36551 59582 active -4.44 inactive -4.88
40693 69830 active* inactive -4.95
42173 72946 inactive active -4.46
41484 71148 inactive inactive -4.95, -4.94 active -3.65
43726 76151 inactive active -4.59, -4.66
46509 81997 inactive active -4.67
46853 82443 inactive active -4.01, -4.05
49699 87883 inactive active -5.00
56452 100623 active* inactive -4.89
56997 101501 inactive active -4.54, -4.55, -4.62
64394 114710 active -5.06 inactive -4.75, -4.76 active -4.74
64792 115383 inactive active -4.45, -4.40, -4.47
67275 120136 active -4.89 inactive -4.86, -4.79 active -4.73
68337 122120 active -4.68 inactive -4.82
69701 124850 inactive inactive -4.75 active -4.69
72875 131582 active -4.45 inactive -4.75
73695 133640 inactive active -4.62, -4.64
81375 149806 inactive inactive -4.83 active -4.70
84195 155712 inactive active -4.69
85810 159222 active -4.48 inactive -4.92, -4.90
86400 160346 active -4.76 inactive -4.83
88622 165401 inactive active -4.61
96285 184489 active -5.08 inactive -4.88
97649 187642 inactive active -4.47
99461 191408 active -5.39 inactive -4.99
101955 196795 inactive inactive -4.78 active -5.00
104092 200779 active -5.14 inactive -5.14
108156 208313 active -4.68 inactive -4.76
114886 219538 active -4.84 inactive -4.84
Duncan et al. (1991)
Strassmeier et al. (2000)
Wright et al. (2004)
Hall et al. (2007)
Mamajek & Hillenbrand (2008)
* Activity features in the spectrum but values not measured due to the lack of a suitable reference star.
Table 4: Stars for which our classification as active or inactive differs from that of other authors.

We also compared our results with those obtained by the mentioned authors (Duncan et al. 1991; Strassmeier et al. 2000; Wright et al. 2004; Hall et al. 2007; Mamajek & Hillenbrand 2008). In Table 3, we summarise the number of active and inactive targets that we share with the mentioned authors as well as the number for which our classification is convergent. As mentioned in Sect. 4.2.1 we classified a star as active when chromospheric features were present in the spectrum. To classify the stars observed by other authors, we used Saar & Brandenburg (1999) criterion to differentiate between active ( - 4.75) and inactive ( -4.75) stars with the exception of Strassmeier et al. (2000) data, for which the author provides his own classification. For Duncan et al. (1991), we obtained similar results for 84% of the inactive and 77% active stars. We obtained similar results to Strassmeier et al. (2000) data for 95% of the inactive stars and 84% of the active ones. Concerning Wright et al. (2004) and based on the Saar & Brandenburg (1999) criterion, we reached agreement for 88% of the active stars and 91% of the inactive ones. For the Hall et al. (2007) data, we obtained similar results for 89% of the inactive stars and 67% of the active ones. Finally, when comparing our results to those of Mamajek & Hillenbrand (2008), we reached an agreement for 87% of the common inactive stars, and for 85% of the actives ones.

In Table 4, we give details of the values of found for those stars for which our classification as active or inactive differs from that of Duncan et al. (1991), Strassmeier et al. (2000), Wright et al. (2004), Hall et al. (2007), or Mamajek & Hillenbrand (2008). We note that with the exception of HIP 41484, which was classified as a high-activity variable by Hall et al. (2007), in all cases the measured values correspond to the low activity domain ( -4.40). It is important to mention that we classify a star as active or inactive after inspecting the spectrum from which the photospheric contribution has been subtracted. This means that every star showing chromospheric activity features will be considered active, regardless of the weakness of the activity levels that we measure. On the other hand, Saar & Brandenburg (1999) criterion is based on the value obtained after measuring the activity. This implies that some of the stars that we have considered as active (because they show emission features in the spectrum) should be reclassified as inactive after applying the aforementioned criterion. We prefer to maintain our criterion, and consider inactive only those stars that did not exhibit emission features in the subtracted spectrum. Taking this into account, we can consider the agreement between data obtained in the present work and that previously reported as fairly good.

4.4 Spectral types

As mentioned in Sect. 4.2.1, when performing the subtraction technique to measure chromospheric activity the use of a reference non-active star with similar physical properties (temperature and surface gravity) to those of the target star is necessary. Therefore, we were able to determine the spectral types of the target stars by comparing their spectra with those of the reference stars. The process began by assuming a spectral type for each star and applying the subtraction technique using as a reference an inactive star of similar spectral type and luminosity class. We then compared the non-chromospheric lines of the original and morphed spectra to test whether the spectral types of the star and that of the reference were really the same. In this way, we could correct the assumed spectral type of each star. We estimate the errors to be of one spectral subtype.

In theory, if both stars have the same spectral type, the resultant (subtracted) spectrum should be null. In reality, the subtracted spectrum exhibit some noise, because of the small differences in metallicity and/or gravity and when the S/N of one of the spectra is low. Nevertheless, small differences in metallicity (only population I stars were observed) and gravity (the cutoff of 1 mag from the Main Sequence (see Sect. 2) corresponds to variations of 0.2 in ) are lower than those produced by the difference of one spectral subtype, which is the estimated error in the spectral type determination. Our results are shown in Table 6.

5 Discussion

5.1 Flux-flux relationships

Although chromopsheric activity has been traditionally studied using the index, we have already pointed out that longer wavelengths provide noteworthy advantages when exoplanet searches are to be performed. The impact of chromospheric active regions on radial velocity variations appear to be smaller when the red region of the spectrum is considered (Desort et al. 2007). Moreover, the S/N in the red region of the spectrum is higher for cool stars. We have measured activity levels using activity tracers throughout the optical spectrum, including the IRT Ca ii lines.

After measuring chromospheric activity in different indicator lines, we have analysed the relationships between their fluxes. This approach was first introduced to study the magnetic structure of cool stars (Schrijver 1987; Rutten et al. 1991) by comparing fluxes in chromospheric and coronal indicator lines. Subsequent studies generalised the method and analysed the relationship among different chromospheric indicators. The most widely studied relationship is that between H core emission and the total surface flux in Ca ii H & K lines (Strassmeier et al. 1990; Robinson et al. 1990; Cincunegui et al. 2007; Walkowicz & Hawley 2009). Several studies have obtained fluxes in other chromospheric indicators lines, such as the Ca ii infrared triplet, for binary (Montes et al. 1995b, 1996b, 1996a) and single (Thatcher & Robinson 1993; López-Santiago et al. 2005; Busà et al. 2007) stars. The aforementioned studies were either centred on a specific spectral type range (Thatcher & Robinson 1993; Walkowicz & Hawley 2009) or analysed the relation between total fluxes, instead of that between each of the indicator lines.

We have obtained empirical power-law relations between pairs of chromospheric indicator lines by fitting the data shown in Figs. 5 and Table 6 to an equation

(6)

where F and F are the fluxes of two different lines. We present the coefficients and the correlation coefficient () of such relationships in Table 5.

In this context, the present study represents a significant extension in terms of spectral type range and number of stars. Moreover, we present relationships between each pair of chromospheric indicator lines in the optical range. These relationships have an enormous potential given that they permit the transformation between any pair of chromospheric activity indicator lines, in particular the transformation of Ca ii H & K fluxes to other more convenient ones. They might be extremely useful when using traditional photometric activity data, .., similar to that obtained by Vaughan et al. (1978), or when using spectroscopic data in which not all the chromospheric features are present. We have used them to obtain when Ca ii H or K lines could not be measured (see Sect. 5.2).

c c R
Ca ii H Ca ii K -0.16 0.20 1.01 0.03 0.897
Ca ii H H 1.95 0.29 0.69 0.05 0.736
H Ca ii K -0.14 0.44 0.95 0.08 0.775
Ca iiIRT (8498Å) Ca ii IRT (8542 Å) -0.15 0.16 1.01 0.03 0.894
H Ca ii IRT (8542 Å) -0.06 0.29 0.98 0.05 0.818
Ca ii H Ca iiIRT (8542 Å) 1.27 0.30 0.80 0.05 0.830
Ca ii (H + K) Ca ii IRT (8489 Å+ 8542 Å+8662 Å) 1.30 0.32 0.80 0.05 0.852
Ca ii (H + K) H 2.37 0.30 0.68 0.06 0.748
Table 5: Linear fit coefficients for each flux-flux relationship
Figure 5: Flux-flux relationship between the total flux in H&K Ca ii and Ca ii IRT (left) and the total flux in H&K Ca ii and Ca ii IRT (right). Symbol sizes increase with increasing rotational velocity (triangles are used when   could not be determined). Colors are used to discern different spectral types.

5.2 Predicted radial velocity jitter

The most fruitful technique for detecting extrasolar planets has been the radial velocity method. As instrumental improvements and technique refinements have improved precisions in the m s domain, the analysis and minimization of the impact of noise sources has become more important. There are two different kinds of perturbations: the random and systematic measurement effects, and the intrinsic stellar variations. The former can be reduced by improving spectrographs and performing robust statistical analysis. The latter, however, includes several phenomena (Saar 2009) and must be handled carefully. The noise sources can lead to a false planet detection (if they produce a periodic signal over a few orbital periods) or prevent planet detection (if the perturbation is larger than the orbital variation). Following Narayan et al. (2005), the minimum detectable exoplanet mass with the method is

(7)

where is the planet mass, is the stellar mass, is the number of observations, is the orbital period, and and are the instrumental error and velocity jitter caused by stellar sources, respectively. Therefore, for a given system, the minimum detectable mass will be limited by the number of observations and the dominant noise source, or . Since spectrographs have been improved to achieve 1 m s, the true limiting factor in Eq. 7 is the intrinsic stellar noise.

Stellar variations are produced by different magnetic-activity-related phenomena: convection (Saar 2009), starspots (Saar & Donahue 1997), magnetic plage/network (Saar 2003) and flares (Saar 2009; Reiners 2009). Although bisector analysis may sometimes lead to the confirmation of a planet orbiting a star even when jitter is present (Sozzetti et al. 2006; Setiawan et al. 2007, 2008), the latter technique is not always successful (Huélamo et al. 2008; Figueira et al. 2009). Several authors have studied the impact of activity on jitter using as a (Saar et al. 1998; Santos et al. 2000; Paulson et al. 2002; Saar et al. 2003; Wright 2005; Paulson & Yelda 2006; Santos et al. 2009). In particular, Saar et al. (1998) and Santos et al. (2000) compiled empirical relationships between and for stars in the Lick survey (Marcy & Butler 1998) and the Geneva extrasolar planet search programme. We used these relationships to obtain the expectable jitter for the active stars in the sample. Results are given in Table 9. We note that, while Santos et al. (2000) obtained individual relationships for G and K stars, Saar et al. (1998) found that both type of stars exhibited similar trend. Agreement between the values obtained using each method is therefore fairly good except for K stars, which present larger values for Saar et al. (1998) than for Santos et al. (2000) relationships.

It is important to mention that both relationships were obtained using stars with moderate activity levels (-5.0 -4.0). We assumed that the linear fit holds for more active stars and applied the relations to five stars that have -4.0. Whether this is valid or not is an open question that must be studied by recalibrating these relations by including a wider variety of activity levels. In our study, we considered chromospheric activity measurements in spectral ranges that contain some advantages for cool stars, the Ca ii IRT lines. New calibrations with different indices would be very beneficial to the community. In the context of this aim, our sample represents a large and varied (in terms of activity levels and activity indicators) set of stars but due to the unavailability of data (not public) we could not perform this analysis.

By applying the aforementioned empirical relationships and the derived values of , we calculated the expected jitter for the stars in the sample, which we present in Table 9. For stars for which both Ca ii H and Ca ii K could be measured, could be directly derived as described in Sect. 4.2.2. However, in some cases, measurement of one of the Ca ii lines (or both) was not possible due to low S/N or the presence of cosmic rays. In these cases, we used the empirical relationships obtained in Sect. 5.1 to transform the total flux in Ca ii IRT into Ca ii (H + K) flux. We chose to use the Ca ii IRT index because the dispersion between both indices is clearly lower than in the relation between the Ca ii (H + K) and H fluxes. However, when one or more lines in the triplet could not be measured, we used the flux in H to infer that in Ca ii (H + K). It is important to mention that the stars observed with the SARG spectrograph constitute a special case. With the configuration of the spectrograph we used, the spectral range containing Ca ii H & K is not available in the spectrum. The photospheric contribution correction for the orders containing the Ca ii IRT lines was also less accurate than in the H order. Consequently, we chose to use the empirical relationship between Ca ii (H + K) and H for these stars. The values obtained are given in Table 8. As mentioned in Sect. 4.3, discrepancies between our derived values of and those obtained using a traditional method become important for stars with low activity levels. Given that the Saar et al. (1998) and Santos et al. (2000) relationships were obtained using traditional data, the results obtained when applying them to the least active stars should be interpreted carefully. We have marked all stars with in Table 8 with the symbol ‡.

We cross-correlated our sample with the exoplanet database6 and found that out of the total sample of 371 stars, 17 have confirmed exoplanets orbiting around them. As expected, all of them are either inactive stars, , HIP 1499 (HD 1461 b), HIP 7513 ( And b), HIP 43587 (55 Cnc b), HIP 49699 (HD 87833 b), HIP 53721 (47 UMa b), HIP 64924 (61 Vir b), HIP 65721 (70 Vir b), HIP 109378 (HD 210277 b) and HIP 116727 ( Cephei b); or have very low activity levels, , HIP 3093 (HD 3651 b), HIP 10138 (Gl 86 b), HIP 16537 ( Eri b), HIP 71395 (HD 128331 b), HIP 80337 (HD 147513 b), HIP 99711 (HD 192263 b) and HIP 113357 (51 Peg b). For HIP 40693 (HD 69830 b), chromospheric activity could not be measured because of the lack of an inactive reference star to apply the subtraction technique, but chromospheric features were visible in the spectrum. The stars with known extrasolar planets are marked with †  in Table 6.

5.3 Applicability to transit searches

Transit searches for exoplanets are also affected by the presence of active regions on the surface of a star (Henry et al. 1997; Baliunas et al. 1997; Henry et al. 2000). Aigrain et al. (2004) used a Sun-based model to predict the “stellar background” using chromospheric activity (as given by ). In the solar case, the noise spectrum for chromospheric irradiance variations at frequencies lower than 8 mHz, commonly referred to as “solar background”, is frequently modelled by a sum of power laws, in which the number of terms, , varies from one to five depending on the frequency coverage (Andersen et al. 1994), ,

(8)

where is frequency, is the amplitude of the th component, is its characteristic timescale, and is the slope of the power law. For a given component, the power remains approximately constant on timescales longer than , and declines for shorter timescales. Each power law corresponds to a separate class of physical phenomena with a different characteristic timescale. The fitting of solar data (Aigrain et al. 2004) uncovers three components. The first component corresponds to active regions ( 1.3 x 10 s), whose amplitude both increases and correlates with the Ca ii K-line index (Andersen et al. 1994; Aigrain et al. 2004). The second component is related to super- and meso-granulation with typical timescales of hours, but no detailed models of these phenomena have been developed to date. The third component is the superposition of variability on timescales of a few minutes, related to granulation and higher frequency effects, such as oscillations and photon noise.

This model can be applied to other stars (Aigrain et al. 2004) to predict the expected “stellar background”. According to Aigrain et al. (2004), the amplitude of the first power law A is correlated with emission in the Ca ii H & K lines, .. , and can be written as follows

(9)

We refer the reader to Aigrain et al. (2004) for a detailed derivation of the aforementioned formula and the other two parameters ( and ). Chromospheric activity measurements, such as those presented in this work, can be therefore used as a proxy to infer the expected amplitude variation of active stars and thus to establish a lower limit to planet detection.

6 Summary and conclusions

We have used high resolution spectroscopic observations to measure the chromospheric activity and the projected rotational velocities for 371 nearby cool stars. For the fraction presenting chromospheric activity (173 stars out of 371), we have analysed the relationship between pairs of chromospheric activity indicator lines, compiling empirical relations to be used when not all the chromospheric features are included in the spectral range. We have applied these relationships to obtain values of when the Ca ii H & K spectral region was not available in the spectrum.

To test the applicability of the results to planet searches, we have calculated the jitter one should expect for each of the active stars in the sample. As previously pointed out, those values must be applied carefully because magnetic activity is variable and a simple subtraction of the activity-related “signal” is not possible. They have to be used as an estimation of the activity-related noise one should expect for a star and thus used to set the minimum detectable mass for a planet orbiting the star or to determine the minimal amplitude variation that could indicate the existence of a planet. Our results represent an important resource in terms of target selection for exoplanet searches surveys.

Acknowledgements.
R. Martínez-Arnáiz acknowledges support from the Spanish Ministerio de Educación y Ciencia (currently the Ministerio de Ciencia e Innovación), under the grant FPI20061465-00592 (programa nacional Formación Personal Investigador) and projects AYA2008-00695 (Programa Nacional de Astronomía y Astrofísica), AYA2008-01727 (Programa Nacional de Astronomía y Astrofísica), AstroMadrid S2009/ESP-1496. This research has made use of the SIMBAD database and VizieR catalogue access tool, operated at CDS, Strasbourg, France. We also thank the anonymous referee for his/her valuable suggestions on how to improve the manuscript.

Appendix A Tables of results

The stellar and line parameters are published in electronic format only. available at CDS, Table 6, contains the Hipparcos number (Col. #1), the spectrograph used to observe the star (Col. #2), the modified julian date (MJD) of the observation (Col. #3), the right ascension and declination (Col. #4 and #5), colour index () (Col. #6), spectral type (Col. #7), and projected rotational velocity,   (Col. #8). Col. #9 specifies whether the star may be classified as active or non active. We note that for some stars in Col. #8, only upper limits are given. As mentioned in the text, for very slowly rotating stars, the value of can be higher than that of . In those cases, we give the minimum value that could be measured with the same spectrograph and for a star of the same spectral type.

The chromospheric activity results are listed in two different tables. Table 7 contains the excess emission EW as measured in the subtracted spectrum, whereas Table 8 includes the excess fluxes derived in this work. In both tables, Cols. #1 , #2, and #3 contain the Hipparcos number of the star, the spectrograph used to observe it, and the modified julian date of the observation, respectively. In Cols. #4, #5, #6, #7, #8, and #9, excess emission (or fluxes) for Ca ii K, Ca ii H, H, and Ca ii IRT 4898Å, Ca ii IRT 8542Å  and Ca ii IRT 8662Å  are given. Table 8 has an additional column containing . As mentioned in the text, for those stars with measured values of both Ca ii H and Ca ii K lines, was derived directly as described in Sect. 4.2.2. When it was not possble to measure one or both of the Ca ii lines, we used the empirical relationships between the total flux in Ca ii (H + K) and H or Ca ii IRT obtained in the present work (see Fig. 5 and Table 5). Given that the relationship between Ca ii (H + K) and Ca ii IRT clearly exhibits lower dispersion, we used it when possible, when measuring the three lines in the Ca ii infrared triplet was possible. In the remaining cases, including all the stars observed with SARG (infrared orders are strongly affected by fringing), we used the relationship between Ca ii (H + K) and H.

Predicted radial velocity variations, ., jitter (based on Saar et al. 1998; Santos et al. 2000), are given in Table 9. It contains only those stars for which could be derived. Columns #1, #2, and #3 contain the same information as that of Tables 7 and 8. The spectral type and for each star are listed in Cols. #4 and #5. Columns #6 and #7 contain the values (within 1) obtained using Saar et al. (1998) and Santos et al. (2000) relationships, respectively.

As online material we have also included Fig. 6 with plots of the flux-flux relationships among different chromospheric activity indicators.

HIP Spectrograph MJD RA DEC SpT ACTIVE
(days) (J2000) (J2000) (mag) (km s)
171 McDonald 52164.3858 00 02 09.65 +27 05 04.2 0.690 G5Vb 4.07 Not Active
544 McDonald 52031.3248 00 06 36.53 +29 01 19.0 0.749 G8V 5.72 Active
544 SARG 54780.9561 00 06 36.53 +29 01 19.0 0.749 G8V 8.07 Active
910 SARG 54777.8430 00 11 15.91 -15 28 02.4 0.489 F5V 4.88 Not Active
1499† FOCES 53578.1286 00 18 41.62 -08 03 09.5 0.680 G1.5V 4.18 Not Active
1532 FOCES 54089.7731 00 19 05.58 -09 57 50.8 1.305 K5V 0.53 Not Active
1598 FOCES 53576.1488 00 20 00.51 +38 13 41.0 0.625 G0V 3.74 Not Active
1599 FEROS 52030.4120 00 20 01.91 -64 52 39.4 0.576 F9V 3.23 Not Active
1803 SARG 54777.9856 00 22 51.55 -12 12 34.5 0.675 G3V 9.94 Active
2021 FEROS 52030.2567 00 25 39.20 -77 15 18.1 0.618 G0V 2.64 Not Active
2941 SARG 54777.9574 00 37 19.79 -24 46 02.0 0.717 G5V 5.54 Not Active
3093† FOCES 53577.1854 00 39 22.09 +21 15 04.9 0.850 K0.5V 11.97 Active
3093† McDonald 51880.1295 00 39 22.09 +21 15 04.9 0.850 K0.5V 6.79 Not Active
3206 FOCES 53579.0491 00 40 49.00 +40 11 19.7 0.956 K3/K4V 9.16 Not Active
3418 FOCES 53580.1213 00 43 33.00 +33 50 43.6 1.058 K5V 0.53 Active*
3535 FOCES 53579.1710 00 45 04.92 +01 47 12.9 1.005 K3V 3.35 Not Active
3765 McDonald 52164.3977 00 48 22.53 +05 17 00.2 0.885 K2V 6.30 Active
3765 FOCES 53747.7686 00 48 22.53 +05 17 00.2 0.885 K2V 9.04 Active
3765 SARG 54107.8938 00 48 22.53 +05 17 00.2 0.885 K2V 4.78 Not Active
3821 McDonald 52164.4538 00 49 05.10 +57 48 59.6 0.582 G0VSB 3.15 Not Active
3979 FOCES 53579.1354 00 51 10.69 -05 02 20.4 0.668 G1.5V 13.97 Not Active
3998 FOCES 53577.0654 00 51 21.72 +18 44 23.6 1.237 K3V 3.35 Not Active
4148 FEROS 51834.1339 00 53 00.72 -30 21 25.2 0.911 K2V 3.52 Active
4845 SARG 54778.9878 01 02 21.12 -10 25 24.3 1.177 K7V 3.21 Active
5286 FOCES 53576.1601 01 07 37.81 +22 57 22.2 1.114 K3V 3.35 Active
5336 McDonald 51789.1451 01 08 12.92 +54 55 27.2 0.704 G5Vb 4.17 Not Active
5799 FOCES 53577.1530 01 14 23.97 -07 55 24.6 0.713 F6V 13.04 Not Active
5944 FOCES 53576.1764 01 16 29.34 +42 56 22.2 0.583 G0V 8.78 Active
5957 FOCES 53577.0880 01 16 39.08 +25 19 54.2 1.372 K7V 3.68 Low S/N
6290 SARG 54107.9171 01 20 41.06 +57 19 36.7 1.437 K7V 3.21 Active
7235 SARG 54780.9662 01 33 15.63 -24 10 39.3 0.766 G8V 4.88 Active
7339 SARG 54779.9914 01 34 33.88 +68 56 52.3 0.682 G7V 3.27 Not Active
7513† McDonald 51883.1803 01 36 47.98 +41 24 23.0 0.544 F8V 10.73 Not Active
7576 FOCES 53577.1583 01 37 35.37 -06 45 36.7 0.793 G8V 0.45 Active
7751 FEROS 51834.1456 01 39 47.24 -56 11 47.2 0.895 K0V 5.64 Active
7918 McDonald 52206.3054 01 41 46.52 +42 36 49.7 0.620 G2V 4.07 Not Active
7981 SARG 54779.9355 01 42 29.95 +20 16 12.5 0.836 K1V 5.98 Not Active
7981 FOCES 53578.1869 01 42 29.95 +20 16 12.5 0.836 K1V 1.20 Active
7981 McDonald 51880.1781 01 42 29.95 +20 16 12.5 0.836 K1V 7.01 Not Active
8102 McDonald 51880.1671 01 44 05.13 -15 56 22.4 0.727 G8V 3.26 Not Active
8275 FOCES 54086.7647 01 46 38.70 +12 24 43.0 1.012 K3/K4V 9.01 Active
8362 McDonald 51883.2217 01 47 44.06 +63 51 11.2 0.797 K0V 2.67 Active
8486 FOCES 53748.8161 01 49 23.43 -10 42 11.9 0.639 G1V 3.34 Active
8768 SARG 54778.0142 01 52 48.64 -22 26 05.5 1.376 K7V 3.21 Active
9269 FOCES 53748.8369 01 59 06.46 +33 12 37.9 0.786 G8V 14.54 Not Active
9269 SARG 54779.9417 01 59 06.46 +33 12 37.9 0.786 G8V 3.87 Not Active
10138† FEROS 51834.1664 02 10 24.00 -50 49 31.1 0.812 K0V 0.18 Active
10337 SARG 54780.0100 02 13 11.93 -21 11 47.7 1.362 K7V 3.21 Active
10416 FOCES 54086.7855 02 14 13.58 -03 38 04.8 1.073 K3/K4V 8.12 Active
10644 McDonald 51880.1997 02 17 02.42 +34 13 29.4 0.606 G0.5V 3.93 Not Active
10798 McDonald 52206.3310 02 18 58.65 -25 56 48.4 0.726 G8V 3.26 Not Active
11072 SARG 54780.0327 02 22 32.42 -23 48 58.7 0.613 G2V 4.22 Not Active
11452 FOCES 54087.9694 02 27 45.81 +04 25 53.6 1.394 K7V 10.18 Low S/N
11565 SARG 54780.2041 02 29 01.31 -19 58 46.6 1.186 K5V 5.30 Active
12110 SARG 54780.0623 02 36 00.72 -23 31 16.9 1.061 K3V 10.85 Active
12114 FOCES 54086.7803 02 36 03.83 +06 53 00.1 0.918 K3V 3.35 Not Active
12114 SARG 54778.0541 02 36 03.83 +06 53 00.1 0.918 K3V 6.45 Not Active
12843 McDonald 52164.4842 02 45 05.98 -18 34 21.5 0.486 F5/F6V 28.02 Not Active
12929 FOCES 54086.8010 02 46 17.12 +11 46 32.7 1.170 K5V 8.11 Not Active
13258 FOCES 54086.8172 02 50 36.69 +15 42 39.2 1.198 K5V 9.26 Active
13402 McDonald 52207.4006 02 52 31.89 -12 46 09.3 0.876 K1V 7.74 Active
13402 SARG 54779.0488 02 52 31.89 -12 46 09.3 0.876 K1V 9.96 Active
13976 SARG 54778.0715 03 00 02.62 +07 44 58.9 0.933 K3/K4V 8.86 Active
14150 SARG 54779.0891 03 02 25.87 +26 36 34.7 0.715 G8V 4.08 Not Active
14286 FOCES 53747.8359 03 04 08.75 +61 42 27.1 0.653 G1.5V 16.48 Not Active
14632 McDonald 51880.2222 03 09 02.88 +49 36 48.6 0.606 G0V 3.15 Not Active
14879 McDonald 51883.2713 03 12 04.28 -28 59 20.8 0.511 F8IV 4.41 Not Active
15099 FOCES 53747.8508 03 14 46.99 +08 58 54.4 0.896 K0V 1.20 Active*
15330 FEROS 51834.2315 03 17 44.47 -62 34 36.8 0.641 G1V 2.64 Active
15371 FEROS 51834.2390 03 18 11.14 -62 30 28.6 0.600 G1V 2.64 Not Active
15442 SARG 54780.1170 03 19 01.75 -02 50 34.6 0.647 G4V 3.20 Active
15457 McDonald 51880.2509 03 19 21.54 +03 22 11.9 0.674 G5Vvar 5.86 Not Active
15510 FEROS 51834.2471 03 19 53.22 -43 04 17.6 0.711 G8V 0.18 Not Active
15673 FOCES 54086.8639 03 21 55.05 +52 19 55.8 1.032 K2V 3.04 Active
15919 FOCES 53747.8508 03 24 59.87 -05 21 42.8 1.145 K5V 0.53 Active
16134 SARG 54779.0552 03 27 52.07 -19 48 18.8 1.337 K7V 3.85 Active
16134 FOCES 54091.9052 03 27 52.07 -19 48 18.8 1.337 K7V 3.21 Active*
16537† McDonald 51833.9938 03 32 56.42 -09 27 29.9 0.887 K2V 4.08 Active
16852 McDonald 51883.2557 03 36 52.52 +00 24 10.2 0.573 F9V 2.67 Not Active
17147 FOCES 53748.8576 03 40 21.66 -03 12 59.3 0.538 G0V 9.70 Not Active
17378 McDonald 52206.3787 03 43 14.96 -09 45 54.7 0.922 K0IV 6.79 Not Active
17420 McDonald 52207.4446 03 43 55.15 -19 06 40.6 0.915 K2V 3.03 Active
17496 FOCES 54086.8866 03 44 50.94 +11 55 10.9 1.194 K5V 7.33 Active*
17651 SARG 54778.0619 03 46 50.99 -23 14 54.4 0.731 F7V 16.25 Not Active
18324 FOCES 53748.9323 03 55 03.31 +61 10 02.7 0.858 K1V 10.29 Not Active
18774 SARG 54779.1053 04 01 18.81 +76 09 38.5 1.129 K4V 8.41 Active
18859 SARG 54780.1408 04 02 36.66 -00 16 05.9 0.520 F7V 20.24 Active
19076 SARG 54780.1482 04 05 20.15 +22 00 33.2 0.646 G5V 5.52 Active
19335 SARG 54780.1552 04 08 36.49 +38 02 24.8 0.529 F7V 20.81 Active
19422 SARG 54778.1206 04 09 34.92 +69 32 31.6 0.957 K3/K4V 6.26 Not Active
19832 FOCES 54087.9871 04 15 09.48 -04 25 05.1 1.149 K5V 8.14 Active
19849 McDonald 51880.2760 04 15 17.64 -07 38 40.4 0.820 K0V 4.06 Active
20917 FOCES 54086.9422 04 29 00.17 +21 55 20.2 1.357 K5V 1.11 Active
22263 McDonald 52207.4280 04 47 36.21 -16 56 05.5 0.638 G1V 4.07 Active
22449 McDonald 51883.3250 04 49 50.14 +06 57 40.5 0.477 F6V 19.22 Not Active
23311 McDonald 52207.4662 05 00 48.68 -05 45 03.5 1.069 K3V 5.18 Active
23693 FEROS 51834.2547 05 05 30.69 -57 28 22.8 0.518 F7V 18.34 Active
23786 FOCES 53747.9144 05 06 42.05 +14 26 48.5 0.804 K0V 1.20 Active
24786 SARG 54780.1623 05 18 50.24 -18 07 48.7 0.574 G0.5V 4.38 Not Active
24813 McDonald 51880.3379 05 19 08.08 +40 06 02.4 0.627 G0V 3.15 Not Active
24819 FOCES 53748.9549 05 19 12.25 -03 04 26.9 1.021 K3V 3.69 Active
24874 FOCES 54086.9907 05 19 59.47 -15 50 24.5 1.014 K3V 7.37 Active
25220 FOCES 53748.9746 05 23 38.23 +17 19 26.9 1.121 K5V 0.53 Active
25623 FOCES 54087.0273 05 28 26.28 -03 29 51.4 1.182 K4V 3.35 Active
26505 FOCES 53747.9719 05 38 12.38 +51 26 43.7 0.827 K0V 1.20 Not Active
26779 McDonald 52030.0849 05 41 20.33 +53 28 56.4 0.844 K1V 4.06 Active
27072 FEROS 51834.2811 05 44 27.97 -22 26 51.0 0.498 F7V 9.84 Not Active
27207 SARG 54779.1315 05 46 01.53 +37 17 09.2 0.846 K5V 4.00 Not Active
27207 FOCES 53749.0129 05 46 01.53 +37 17 09.2 0.846 K5V 12.05 Not Active
27435 SARG 54194.8500 05 48 34.90 -04 05 38.7 0.639 G5V 2.61 Not Active
27913 McDonald 51882.3464 05 54 23.08 +20 16 35.1 0.599 G0V 10.79 Active
28103 SARG 54107.0756 05 56 24.32 -14 10 04.9 0.833 F1V 16.99 Not Active
29067 FOCES 54088.0550 06 07 55.33 +67 58 37.5 1.258 K5V 0.53 Active
29271 FEROS 51834.2617 06 10 14.20 -74 45 09.1 0.730 G5V 0.32 Not Active
29432 FOCES 54086.0365 06 12 00.45 +06 47 01.3 0.635 G4V 1.49 Not Active
29525 FOCES 53747.9540 06 13 12.46 +10 37 40.3 0.667 G1.5V 12.09 Active
29568 SARG 54778.1689 06 13 45.33 -23 51 43.9 0.702 G5V 9.63 Active
29650 SARG 54193.8451 06 14 50.94 +19 09 24.8 0.709 F6V 5.67 Not Active
29800 SARG 54193.8509 06 16 26.57 +12 16 18.2 0.730 F5IV-V 20.92 Active
29860 SARG 54193.8555 06 17 16.25 +05 05 58.9 0.611 G0.5Vb 2.98 Not Active
32010 FOCES 54086.0581 06 41 15.58 +23 57 30.2 1.028 K2V 7.40 Active
32423 FOCES 54086.0836 06 46 05.37 +32 33 19.6 0.989 K3V 3.35 Active
32439 SARG 54778.1944 06 46 14.47 +79 33 58.6 0.517 F8V 6.63 Not Active
32480 FOCES 54086.0365 06 46 44.34 +43 34 37.3 0.570 G0V 5.03 Not Active
32919 FOCES 54086.0995 06 51 32.60 +47 22 10.2 1.206 K5V 10.46 Active
32984 FOCES 54088.0194 06 52 18.37 -05 10 25.3 1.067 K3V 8.07 Active
33277 FOCES 54087.0522 06 55 18.69 +25 22 32.3 0.599 G0V 1.89 Not Active
33373 FOCES 54086.1177 06 56 28.03 +40 04 31.4 1.113 K3/K4V 6.91 Active
33537 FOCES 54087.0571 06 58 11.72 +22 28 32.3 0.633 G5V 3.01 Not Active
33560 SARG 54193.8607 06 58 26.02 -12 59 29.3 1.115 K5V 7.97 Active
33852 FOCES 54087.0680 07 01 38.11 +48 22 47.0 0.997 K3/K4V 6.59 Active
33955 SARG 54192.8556 07 02 43.04 -06 47 54.5 1.159 K5V 6.72 Not Active
34017 FOCES 54087.0835 07 03 30.35 +29 20 20.7 0.601 G4V 1.92 Not Active
35136 FOCES 54088.0145 07 15 50.11 +47 14 25.5 0.583 G0V 1.89 Not Active
36357 FOCES 54164.9213 07 29 01.66 +31 59 36.3 0.946 K2V 7.14 Active
36357 SARG 54107.0827 07 29 01.66 +31 59 36.3 0.946 K2V 7.38 Active
36366 FOCES 54133.0217 07 29 06.61 +31 47 02.7 0.333 F0V 56.66 Not Active
36366 SARG 54778.2122 07 29 06.61 +31 47 02.7 0.333 F0V 42.32 Not Active
36366 FOCES 54088.1352 07 29 06.61 +31 47 02.7 0.333 F0V 50.74 Not Active
36439 FOCES 54088.1291 07 29 55.86 +49 40 21.6 0.696 F6V 5.88 Not Active
36551 FOCES 54086.1369 07 31 07.67 +14 36 53.5 1.141 K2V 3.04 Active
36827 SARG 54193.8830 07 34 26.21 -06 53 47.7 0.871 K2V 8.76 Active
37279 McDonald 51880.3830 07 39 18.54 +05 13 39.0 0.432 F5IV-V 5.38 Not Active
37288 SARG 54780.1812 07 39 23.12 +02 11 03.3 1.397 M0V Low S/N
37349 McDonald 51883.3603 07 39 59.29 -03 35 48.6 0.944 K1V 9.50 Active
37349 FOCES 53748.0933 07 39 59.29 -03 35 48.6 0.944 K1V 4.63 Active
37349 SARG 54193.8960 07 39 59.29 -03 35 48.6 0.944 K1V 7.31 Active
38657 FOCES 54087.1403 07 54 54.01 +19 14 14.8 0.979 K2 6.36 Not Active
38784 SARG 54778.2232 07 56 18.87 +80 15 55.2 0.732 G8V 4.27 Not Active
38931 FOCES 53749.0318 07 57 57.88 -00 48 51.9 1.021 K5V 0.53 Not Active
39157 FOCES 54088.0799 08 00 32.24 +29 12 54.7 0.714 G8V 5.65 Not Active
40035 SARG 54778.2756 08 10 39.98 -13 47 57.7 0.495 F7V 11.26 Not Active
40118 FOCES 54087.2768 08 11 38.96 +32 27 31.3 0.657 G4V 1.49 Not Active
40170 FOCES 54158.0979 08 12 14.55 +51 54 27.3 1.497 K5V 0.53 Active
40375 SARG 54192.8698 08 14 36.17 +13 01 21.3 1.192 K5 4.38 Not Active
40671 FOCES 54086.1612 08 18 10.97 +30 36 10.1 1.077 K4V 8.45 Low S/N
40671 FOCES 54164.9814 08 18 10.97 +30 36 10.1 1.077 K4V 3.81 Active
40693† McDonald 51880.4285 08 18 23.78 -12 37 47.2 0.771 K0V 6.79 Active*
40843 FOCES 54088.1499 08 20 03.87 +27 13 07.0 0.479 F6V 4.45 Not Active
41484 FOCES 54164.9640 08 27 36.80 +45 39 13.8 0.624 G5V 12.37 Not Active
41926 McDonald 52030.1102 08 32 52.26 -31 30 09.7 0.774 K0V 6.79 Not Active
42074 FOCES 54087.1283 08 34 31.76 -00 43 34.0 0.791 G8V 5.60 Active
42074 SARG 54193.9536 08 34 31.76 -00 43 34.0 0.791 G8V 6.34 Active
42173 FOCES 53748.1111 08 35 51.34 +06 37 23.2 0.695 G5V 3.23 Not Active
42333 FOCES 53749.0569 08 37 50.47 -06 48 25.2 0.654 G1.5V 9.44 Active
42438 McDonald 51883.5354 08 39 11.74 +65 01 14.5 0.617 G1.5Vb 11.21 Active
42499 FOCES 53574.9531 08 39 50.86 +11 31 26.0 0.836 K1V 3.18 Not Active
42808 FEROS 52046.9654 08 43 18.26 -38 52 59.5 0.926 K2V 9.63 Active
43557 FOCES 53749.0723 08 52 16.30 +08 03 48.6 0.627 G0 1.89 Active
43587† McDonald 51880.5005 08 52 36.13 +28 19 53.0 0.873 G8V 2.27 Not Active
43726 SARG 54193.9604 08 54 18.19 -05 26 04.3 0.671 G3V 3.66 Not Active
43726 FOCES 54086.1561 08 54 18.19 -05 26 04.3 0.671 G3V 3.58 Not Active
44248 FOCES 54091.1468 09 00 38.75 +41 47 00.4 0.705 F5V 21.17 Not Active
44897 SARG 54779.1457 09 08 51.20 +33 52 57.0 0.604 F9V 5.86 Active
45038 SARG 54779.1571 09 10 23.53 +67 08 03.3 0.498 F6IV 7.55 Not Active
45170 FOCES 53748.1456 09 12 17.87 +14 59 43.6 0.750 G9V 16.32 Not Active
45333 SARG 54779.1643 09 14 20.55 +61 25 24.2 0.602 F9V 5.59 Not Active
45383 FOCES 53748.1605 09 14 53.72 +04 26 34.4 1.010 K0V 41.20 Active
45617 FOCES 53748.1832 09 17 53.42 +28 33 42.3 1.002 K0V 1.20 Active
45839 FOCES 54087.1669 09 20 44.53 -05 45 13.3 1.191 K5V 7.73 Not Active
46509 SARG 54779.2324 09 29 08.84 -02 46 08.2 0.411 F6V 30.56 Not Active
46509 FOCES 54164.9473 09 29 08.84 -02 46 08.2 0.411 F6V 14.04 Not Active
46580 SARG 54193.9665 09 29 55.12 +05 39 17.5 0.994 K3V 8.39 Active
46580 FOCES 54087.1896 09 29 55.12 +05 39 17.5 0.994 K3V 8.85 Active
46816 FOCES 54161.0253 09 32 25.72 -11 11 05.0 0.911 K0V 29.03 Active
46816 SARG 54193.9734 09 32 25.72 -11 11 05.0 0.911 K0V 30.42 Active
46843 SARG 54193.9834 09 32 43.86 +26 59 20.9 0.783 K0V 10.57 Active
46843 FOCES 54161.0562 09 32 43.86 +26 59 20.9 0.783 K0V 29.71 Active
46853 McDonald 51880.4889 09 32 52.33 +51 40 43.0 0.487 K0V 8.77 Not Active
47080 McDonald 52031.1226 09 35 40.03 +35 48 38.8 0.779 G8V 6.72 Active
47080 FOCES 53749.1406 09 35 40.03 +35 48 38.8 0.779 G8V 7.22 Active
47592 SARG 54779.2669 09 42 14.67 -23 54 58.4 0.538 G0V 7.08 Not Active
48113 SARG 54192.8958 09 48 35.18 +46 01 16.4 0.624 G2V 3.97 Not Active
48113 FOCES 54086.0303 09 48 35.18 +46 01 16.4 0.624 G2V 1.89 Not Active
48411 SARG 53785.1132 09 52 11.61 +03 13 18.5 1.162 K5 1.90 Active*
49081 FOCES 54086.2050 10 01 01.02 +31 55 29.0 0.675 G1V 3.08 Not Active
49366 SARG 53786.1106 10 04 37.77 -11 43 46.7 0.913 K0 8.22 Active
49699† SARG 54194.0124 10 08 43.18 +34 14 32.7 0.964 F6V 3.67 Not Active
49699† FOCES 53749.1488 10 08 43.18 +34 14 32.7 0.964 F6V 1.20 Not Active
49908 SARG 54194.0217 10 11 23.36 +49 27 19.7 1.319 K7V 3.21 Active
49908 FOCES 54086.2131 10 11 23.36 +49 27 19.7 1.319 K7V 5.21 Low S/N
49986 SARG 54779.2385 10 12 17.76 -03 44 42.3 1.359 M1.5 Active*
50125 SARG 53785.1372 10 13 57.30 +52 30 30.9 1.122 K5 2.85 Not Active
50384 FOCES 54088.1414 10 17 14.80 +23 06 23.2 0.503 F8Vbw 2.16 Not Active
50505 SARG 53786.1322 10 18 51.90 +44 02 56.6 0.686 K0V 1.72 Not Active
51459 McDonald 51880.5129 10 30 37.76 +55 58 50.2 0.532 F8V 3.41 Not Active
51502 SARG 54780.2195 10 31 05.02 +82 33 30.7 0.783 F2V 41.65 Not Active
51525 SARG 53786.1408 10 31 24.69 +45 31 39.0 1.339 K7V 3.21 Active
51933 FOCES 54164.9551 10 36 32.22 -12 13 42.6 0.523 F7V 31.06 Not Active
52369 SARG 54106.1490 10 42 13.18 -13 47 14.3 0.629 G2/G3V 3.80 Not Active
52369 FOCES 54167.9622 10 42 13.18 -13 47 14.3 0.629 G2/G3V 10.64 Not Active
53486 SARG 53786.1585 10 56 30.95 +07 23 19.2 0.924 K0 7.85 Active
53721† McDonald 52031.1341 10 59 28.22 +40 25 48.4 0.622 G0V 3.15 Not Active
54155 SARG 53786.1684 11 04 41.58 -04 13 15.0 0.837 G8V 9.46 Active
54155 FOCES 54158.1320 11 04 41.58 -04 13 15.0 0.837 G8V 0.45 Active
54426 FOCES 54087.2019 11 08 14.17 +38 25 35.5 0.964 K0V 5.74 Active
54646 FOCES 54086.2260 11 11 04.77 +30 26 47.4 1.344 K8V 5.83 Active
54646 SARG 54780.2266 11 11 04.77 +30 26 47.4 1.344 K8V 3.21 Not Active
54646 FOCES 54159.0846 11 11 04.77 +30 26 47.4 1.344 K8V 0.53 Not Active
54651 FOCES 54167.9786 11 11 11.26 -10 57 08.4 1.089 K5V 1.90 Not Active
54651 SARG 54106.1567 11 11 11.26 -10 57 08.4 1.089 K5V 0.53 Not Active
54745 FOCES 54086.2729 11 12 32.53 +35 48 52.0 0.620 G1V 7.74 Active
54810 SARG 54106.1858 11 13 13.42 +04 28 56.7 1.228 K5V 5.31 Active
54906 FOCES 54087.2432 11 14 33.23 +25 42 37.0 0.824 K1V 3.18 Not Active
55210 FOCES 54087.2567 11 18 21.55 -05 04 01.0 0.756 G8V 1.52 Not Active
56242 FOCES 54087.2704 11 31 45.14 +14 21 53.9 0.581 G0V 3.59 Not Active
56452 McDonald 52030.1374 11 34 29.95 -32 50 00.0 0.804 K0V 6.79 Active*
56997 McDonald 52031.1440 11 41 03.03 +34 12 09.2 0.737 G8Vvar 3.26 Not Active
57443 FEROS 52045.9778 11 46 32.25 -40 30 04.8 0.664 G3/G5V 0.32 Not Active
57494 FOCES 54156.0187 11 47 03.96 -11 49 26.0 1.196 K3/K4V 7.27 Active
57757 McDonald 52030.1547 11 50 41.29 +01 45 55.4 0.563 F8V 3.41 Not Active
57939 SARG 54780.2555 11 52 55.82 +37 43 58.1 0.745 G8Vp 3.26 Not Active
57939 FOCES 54156.0864 11 52 55.82 +37 43 58.1 0.745 G8Vp 9.28 Not Active
58576 McDonald 52030.1657 12 00 44.37 -10 26 41.4 0.772 G8IV-V 3.26 Not Active
59000 FOCES 54158.1703 12 05 50.67 -18 52 28.1 1.403 K7V 3.68 Low S/N
59000 SARG 54194.0305 12 05 50.67 -18 52 28.1 1.403 K7V 3.21 Active
59280 FOCES 54156.0998 12 09 37.50 +40 15 07.8 0.786 K0V 1.20 Active
60866 FOCES 54228.9530 12 28 31.49 -18 17 48.7 1.165 K5V 0.53 Active
60866 SARG 54194.0543 12 28 31.49 -18 17 48.7 1.165 K5V 3.19 Not Active
61317 McDonald 52030.1888 12 33 45.09 +41 21 24.4 0.595 G0V 3.15 Not Active
61901 SARG 54108.2284 12 41 06.41 +15 22 39.3 1.095 K5V 3.60 Low S/N
61941 McDonald 52031.1932 12 41 40.00 -01 26 58.3 0.368 F0V 31.36 Not Active
62207 FOCES 54156.1221 12 44 59.68 +39 16 42.9 0.557 G0V 8.11 Not Active
62523 SARG 54194.1269 12 48 47.26 +24 50 25.7 0.706 G7V 6.24 Not Active
62523 FOCES 53575.8536 12 48 47.26 +24 50 25.7 0.706 G7V 11.97 Active
62523 FOCES 54132.2376 12 48 47.26 +24 50 25.7 0.706 G7V 13.60 Not Active
63257 SARG 54108.2639 12 57 44.17 -14 27 48.8 1.109 K5V 6.91 Not Active
64241 McDonald 52030.2129 13 09 59.55 +17 31 44.8 0.455 F5V 21.47 Not Active
64394 McDonald 52030.2579 13 11 52.92 +27 52 33.7 0.588 G1V 4.72 Active
64792 McDonald 51883.2234 13 16 46.71 +09 25 25.3 0.587 G0Vs 10.64 Not Active
64797 McDonald 52030.2286 13 16 50.67 +17 01 04.1 0.910 K2V 2.86 Active
64924† SARG 54195.0981 13 18 24.97 -18 18 31.0 0.709 G5V 4.09 Not Active
64924† McDonald 52030.2464 13 18 24.97 -18 18 31.0 0.709 G5V 1.35 Not Active
65352 SARG 53786.1888 13 23 39.15 +02 43 22.2 0.780 G5 3.34 Not Active
65515 FOCES 54132.1649 13 25 45.76 +56 58 13.7 0.804 K0V 1.20 Active
65721† FOCES 54156.1333 13 28 25.95 +13 46 48.7 0.711 G5V 4.83 Not Active
66147 SARG 53786.1989 13 33 32.70 +08 35 11.5 1.028 K3/K4V 8.66 Active
66252 FOCES 54168.0938 13 34 43.38 -08 20 30.5 1.196 K5V 0.53 Active
66886 SARG 53786.2148 13 42 26.20 -01 41 09.2 1.223 K5V 1.90 Not Active
67105 SARG 53786.2384 13 45 14.76 +08 50 10.4 1.042 K2 6.76 Active
67275 SARG 54108.3087 13 47 16.04 +17 27 24.4 0.501 F6IV 17.86 Active
67422 McDonald 52030.2748 13 49 04.28 +26 58 48.5 1.104 K2 6.27 Active
67927 McDonald 52030.3480 13 54 41.12 +18 23 54.9 0.607 G0IV 15.43 Not Active
68030 SARG 54106.2362 13 55 50.17 +14 03 23.3 0.510 F6V 3.66 Not Active
68184 McDonald 52030.3291 13 57 32.10 +61 29 32.4 1.037 K3V 7.43 Not Active
68337 FOCES 53577.8595 13 59 19.50 +22 52 11.0 1.149 K5V 0.53 Active
68682 FOCES 53578.8527 14 03 32.30 +10 47 15.1 0.737 G8V 0.45 Not Active
69357 FOCES 53578.0216 14 11 46.32 -12 36 40.8 0.861 K0V 11.71 Active
69414 FOCES 53578.8591 14 12 45.33 -03 19 09.5 0.747 G8V 18.16 Not Active
69526 FOCES 53578.9125 14 13 57.35 +30 13 00.3 1.053 K2V 9.43 Active
69701 FOCES 54156.1416 14 16 00.88 -05 59 58.3 0.521 F7V 4.39 Not Active
69962 SARG 54108.2822 14 18 58.28 -06 36 09.3 1.316 K7V 3.21 Active
69962 FOCES 54156.1471 14 18 58.28 -06 36 09.3 1.316 K7V 9.38 Active*
69972 FEROS 52177.0088 14 19 05.36 -59 22 37.4 1.020 K3V 3.97 Not Active
70016 SARG 53786.2551 14 19 35.23 -05 09 03.2 0.867 K1V 8.15 Not Active
70218 SARG 53786.2988 14 21 57.64 +29 37 49.3 1.238 K5V 1.90 Active
70218 FOCES 54159.1693 14 21 57.64 +29 37 49.3 1.238 K5V 10.40 Active
70319 FOCES 54156.1724 14 23 15.15 +01 14 33.8 0.637 G1V 3.08 Not Active
71284 SARG 54108.3110 14 34 40.69 +29 44 41.3 0.803 F3Vwvar 7.32 Not Active
71395† SARG 54194.1338 14 36 00.44 +09 44 49.7 0.965 K2V 9.22 Active
71395† FOCES 53577.8799 14 36 00.44 +09 44 49.7 0.965 K2V 9.39 Active
71681 FEROS 52045.1062 14 39 39.39 -60 50 22.1 0.900 K1V 3.52 Not Active
71683 FEROS 52045.1030 14 39 40.90 -60 50 06.5 0.710 G2V 2.64 Not Active
71743 SARG 54193.0776 14 40 31.17 -16 12 32.9 0.709 G8V 6.19 Active
72146 FOCES 53575.8597 14 45 24.32 +13 50 48.7 0.929 K0V 7.68 Active
72146 FOCES 54132.2205 14 45 24.32 +13 50 48.7 0.929 K0V 12.04 Low S/N
72146 SARG 54194.1582 14 45 24.32 +13 50 48.7 0.929 K0V 6.00 Active
72237 FOCES 54159.2162 14 46 23.35 +16 29 56.2 1.358 K5V 1.90 Active
72237 SARG 53786.2752 14 46 23.35 +16 29 56.2 1.358 K5V 0.53 Active
72567 FOCES 54168.1225 14 50 15.72 +23 54 42.4 0.592 G2V 8.54 Active
72603 SARG 54193.0831 14 50 41.26 -15 59 49.5 0.763 F4V 5.95 Not Active
72659 McDonald 52030.3731 14 51 23.28 +19 06 02.3 0.764 G8V 3.26 Active
72848 McDonald 52164.0668 14 53 24.04 +19 09 08.2 0.844 K1V 6.35 Active
72875 FOCES 53577.8968 14 53 42.09 +23 20 42.6 0.961 K0V 4.00 Active
72981 SARG 54193.0870 14 54 53.67 +09 56 40.1 1.377 M1 Low S/N
73184 SARG 54194.1436 14 57 27.35 -21 24 40.6 1.092 K4V 7.68 Active
73457 FOCES 54156.1866 15 00 43.42 -11 08 02.3 1.472 K7V 3.68 Not Active
73695 McDonald 52030.3967 15 03 47.68 +47 39 14.5 0.641 G0V 3.15 Not Active
73786 FOCES 53577.9150 15 04 53.88 +05 38 21.6 1.333 K7V 3.68 Not Active
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75277 FOCES 53576.9457 15 22 46.98 +18 55 07.6 0.804 G8V 0.45 Not Active
75542 SARG 54195.1035 15 25 59.04 -26 42 20.7 1.117 K3/K4V 6.80 Active
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76779 SARG 54195.1198 15 40 34.47 -18 02 57.3 1.337 K7V 3.21 Active
77052 FOCES 54158.2301 15 44 01.85 +02 30 55.9 0.678 G2.5V 11.01 Not Active
77257 McDonald 52032.2461 15 46 26.75 +07 21 11.7 0.609 G0Vvar 3.15 Not Active
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77408 FOCES 53575.9293 15 48 09.57 +01 34 19.7 0.796 G8V 0.45 Active
77408 SARG 54193.1507 15 48 09.57 +01 34 19.7 0.796 G8V 7.48 Active
77952 FEROS 52045.1226 15 55 08.81 -63 25 47.1 0.324 F1V 69.63 Not Active
78072 FOCES 53579.9391 15 56 26.99 +15 39 53.0 0.478 F6V 11.13 Not Active
78072 McDonald 52030.4041 15 56 26.99 +15 39 53.0 0.478 F6V 11.71 Not Active
78709 SARG 54193.1431 16 04 04.03 +25 15 11.3 0.760 G8V 4.35 Not Active
78775 McDonald 52030.4155 16 04 57.22 +39 09 23.0 0.738 G8V 3.26 Not Active
78843 SARG 54194.1958 16 05 40.29 -20 26 57.1 1.059 K3/K4V 6.24 Not Active
79190 FEROS 52180.0646 16 09 42.94 -56 26 45.5 0.837 K1V 3.97 Not Active
79492 FOCES 53575.9778 16 13 18.34 +13 31 40.5 0.756 G8V 2.24 Not Active
79672 McDonald 52164.0986 16 15 37.13 -08 22 05.7 0.658 G1V 4.07 Not Active
80337† FEROS 52045.1772 16 24 01.24 -39 11 34.8 0.633 G3/G5V 0.32 Active
80366 SARG 54193.2128 16 24 19.94 -13 38 28.2 0.974 K2V 5.89 Active
80644 FOCES 53574.8662 16 27 57.05 +07 18 21.9 1.209 K7V 3.68 Not Active
80686 FEROS 52045.2054 16 28 27.80 -70 05 04.8 0.556 F9V 3.23 Active
80725 FOCES 53579.9305 16 28 52.88 +18 24 47.2 0.834 K2V 4.12 Active
81300 McDonald 52164.1210 16 36 21.18 -02 19 25.8 0.844 K0Vk 4.12 Active
81375 FOCES 53574.8765 16 37 08.37 +00 15 15.0 0.827 K0 5.66 Not Active
81693 McDonald 52030.4342 16 41 17.48 +31 36 06.8 0.652 G0IV 3.11 Not Active
82588 FOCES 53576.9600 16 52 59.22 -00 01 22.1 0.751 G8V 10.60 Active
83591 SARG 54195.2015 17 05 03.93 -05 03 49.5 1.120 K5V 1.90 Not Active
83601 SARG 54195.2462 17 05 16.83 +00 42 12.1 0.578 F9V 8.00 Active
84195 FOCES 53579.9452 17 12 37.56 +18 21 05.3 0.940 K0V 10.77 Not Active
84195 SARG 54195.2119 17 12 37.56 +18 21 05.3 0.940 K0V 6.40 Not Active
84405 McDonald 52208.0394 17 15 21.29 -26 36 00.2 0.861 K2V 5.12 Active
84720 FEROS 52048.1876 17 19 02.95 -46 38 11.4 0.764 G8V Not Active
84862 McDonald 52030.4428 17 20 39.47 +32 28 13.0 0.616 G0V 3.15 Not Active
85235 McDonald 52030.4468 17 25 00.90 +67 18 24.1 0.773 K0V 6.79 Not Active
85295 SARG 54193.2589 17 25 45.57 +02 06 51.5 1.354 K7V 3.21 Active
85561 SARG 54194.2041 17 29 06.74 -23 50 09.4 1.324 K5V 1.90 Active
85810 SARG 54193.2741 17 32 01.16 +34 16 15.6 0.648 G5V 5.12 Active
85810 FOCES 54132.2478 17 32 01.16 +34 16 15.6 0.648 G5V 3.01 Not Active
86036 McDonald 52030.4566 17 34 59.25 +61 52 33.0 0.601 G0Va 5.61 Active
86400 McDonald 52032.3071 17 39 17.02 +03 33 19.7 0.957 K3V 3.37 Active
86722 FOCES 53574.8860 17 43 15.72 +21 36 38.6 0.755 K0V 1.20 Not Active
86974 McDonald 52030.4693 17 46 27.72 +27 43 21.0 0.751 G5IV 5.86 Not Active
87579 FOCES 53574.8992 17 53 29.98 +21 19 30.5 0.950 K0V 15.78 Active
88175 SARG 54195.2729 18 00 28.92 -03 41 24.6 0.770 F3V 51.51 Not Active
88601 McDonald 52164.1787 18 05 27.21 +02 30 08.8 0.860 K1V 4.06 Active
88622 FOCES 53578.9512 18 05 37.47 +04 39 28.6 0.593 G0V 13.90 Not Active
88972 McDonald 52030.4780 18 09 37.65 +38 27 32.1 0.886 K2V 4.06 Not Active
88972 SARG 54195.2463 18 09 37.65 +38 27 32.1 0.886 K2V 4.82 Not Active
89937 McDonald 52030.4614 18 21 02.34 +72 44 01.3 0.509 F7V 6.01 Not Active
90656 FOCES 53574.9158 18 29 52.31 -01 49 03.5 1.072 K3V 11.33 Not Active
90790 McDonald 52208.0867 18 31 19.05 -18 54 30.0 0.864 K1V 4.06 Active
91009 SARG 54779.8159 18 33 55.60 +51 43 11.7 1.183 K6Ve 8.81 Active
91438 FEROS 52046.2542 18 38 53.45 -21 03 05.4 0.664 G5V 0.32 Not Active
92043 FOCES 53574.9531 18 45 39.73 +20 32 49.6 0.475 F6V 14.08 Not Active
92200 FOCES 53574.9577 18 47 27.33 -03 38 21.0 1.226 K7V 3.68 Active
92283 FOCES 53578.9782 18 48 29.15 +10 44 47.4 1.128 K3/K4V 3.35 Active
93017 SARG 54779.8858 18 57 01.47 +32 54 05.8 0.590 F9V 6.80 Not Active
93871 FOCES 53574.9827 19 07 02.23 +07 37 03.8 1.050 K5V 4.07 Not Active
95319 FOCES 53576.0730 19 23 33.96 +33 13 17.7 0.805 G8V 0.00 Not Active
96085 FOCES 53578.0463 19 32 06.56 -11 16 29.9 0.923 K2V 3.04 Active
96100 McDonald 52030.4861 19 32 20.59 +69 39 55.4 0.804 K0V 6.79 Not Active
96285 FOCES 53575.0438 19 34 39.53 +04 34 54.3 1.355 K7V 3.68 Active
98036 McDonald 52164.2366 19 55 18.77 +06 24 28.6 0.850 G9.5V 22.28 Not Active
98677 FOCES 53575.0687 20 02 34.25 +15 35 36.6 0.723 G0V 10.87 Not Active
98819 FOCES 53575.0956 20 04 06.47 +17 04 16.2 0.609 G1V 8.06 Not Active
98819 SARG 54195.2659 20 04 06.47 +17 04 16.2 0.609 G1V 5.38 Not Active
98819 FOCES 54228.1518 20 04 06.47 +17 04 16.2 0.609 G1V 8.27 Not Active
98828 FOCES 53575.0823 20 04 10.09 +25 47 25.2 0.934 K0V 1.20 Active
99240 FEROS 51834.9776 20 08 41.86 -66 10 45.6 0.751 G5IV-Vvar 0.32 Not Active
99316 FOCES 53578.0824 20 09 34.30 +16 48 19.2 0.825 K0 4.06 Not Active
99452 FOCES 53575.1133 20 11 06.33 +16 11 13.3 0.837 K1V 6.41 Not Active
99461 FEROS 51833.9874 20 11 11.61 -36 05 50.6 0.868 K3V 3.97 Active
99711† FOCES 53575.9912 20 13 59.88 -00 52 03.1 0.936 K4V 5.72 Active
99764 FOCES 53576.0317 20 14 28.18 -07 16 52.8 1.291 K6V 3.85 Active
99825 FEROS 51834.0083 20 15 16.58 -27 01 57.1 0.878 K2V 3.97 Not Active
101345 FOCES 53578.9946 20 32 23.51 -09 51 13.1 0.698 G2.5IV 1.91 Not Active
101955 FOCES 53579.9626 20 39 37.20 +04 58 18.7 1.219 K5V 0.53 Not Active
101997 SARG 54779.7904 20 40 11.44 -23 46 30.0 0.729 G8/K0V 3.50 Not Active
102422 McDonald 52030.4905 20 45 17.27 +61 50 12.5 0.912 K0IV 6.79 Not Active
102485 SARG 54779.8091 20 46 05.77 -25 16 13.9 0.725 F5V 34.94 Not Active
103256 FOCES 53576.0317 20 55 06.53 +13 10 33.1 1.025 K2V 3.04 Active
104092 FOCES 53576.0519 21 05 19.70 +07 04 14.4 1.215 K6V 14.33 Active
104214 SARG 54777.8548 21 06 50.84 +38 44 29.4 <