Observations and light curve solutions of theeclipsing stars CSS J075205.6+381909 and NSVS 691550

Observations and light curve solutions of the
eclipsing stars CSS J075205.6+381909
and NSVS 691550

D. Kjurkchieva Department of Physics and Astronomy, Shumen University, 115 Universitetska, 9700 Shumen, Bulgaria IRIDA Observatory, Rozhen NAO, Bulgaria    V. Popov Department of Physics and Astronomy, Shumen University, 115 Universitetska, 9700 Shumen, Bulgaria IRIDA Observatory, Rozhen NAO, Bulgaria    D. Vasileva Department of Physics and Astronomy, Shumen University, 115 Universitetska, 9700 Shumen, Bulgaria    Y. Eneva Department of Physics and Astronomy, Shumen University, 115 Universitetska, 9700 Shumen, Bulgaria Medical University, Varna, 84 Tcar Osvoboditel str.
d.kyurkchieva@shu.bg
   S. Ibryamov Department of Physics and Astronomy, Shumen University, 115 Universitetska, 9700 Shumen, Bulgaria
Abstract

The paper presents observations and light curve solutions of the eclipsing stars CSS J075205.6+381909 and NSVS 691550. As a result their initial epochs were determined. The target periods turned out almost equal to the previous values. We found that NSVS 691550 is overcontact system whose components are close in temperature while CSS J075205.6+381909 has almost contact configuration and temperature difference of its components is around 2000 K. Both targets undergo partial eclipses. Their stellar components seem to obey the relations mass-temperature of MS stars.

binaries: eclipsing binaries: close binaries: contact stars: fundamental parameters; individual (CSS J075205.6+381909, NSVS 691550)
\tocauthor

D. Kjurkchieva \papertypeSubmitted on xx.xx.xxxx; Accepted on xx.xx.xxxx

Introduction

Most of the W UMa stars consisting of solar-type components have orbital periods within 0.25 d 0.7 d. They are recognized by continuous brightness variations and nearly equal minima depth. The short orbital periods of these binaries mean small orbits and synchronized rotation and orbital revolution.

The investigation of the contact binary systems is important for the modern astrophysics because they are natural laboratories for study of the late stage of the stellar evolution connected with the processes of mass and angular momentum loss, merging or fusion of the stars (Martin et al., 2011).

The huge surveys ROTSE, MACHO, ASAS, Super WASP, Catalina, Kepler increased significantly the number of stars classified as W UMa type but small part of them are studied in details.

This paper presents our follow-up photometric observations of two W UMa stars, CSS J075205.6+381909 (further CSS 0752+38) and NSVS 691550, and their modeling. Table 1 presents the coordinates of our targets and available preliminary information for their light variability from VSX database (www.aavso.org/vsx/).

Target RA DEC mag ampl type
CSS 0752+38 07 52 05.68 38 19 09.8 14.35(CV) 0.17 0.5493 EW
NSVS 691550 08 08 40.32 70 29 24.4 11.74(R1) 0.26 0.334562 EB/EW
Table 1: Parameters of variability of the targets according to VSX database

1. Observations

Our CCD photometric observations of the targets in Sloan bands were carried out at Rozhen Observatory with the 30-cm Ritchey Chretien Astrograph (located into the IRIDA South dome) using CCD camera ATIK 4000M (2048 2048 pixels, 7.4 m/pixel, field of view 40 x 40 arcmin). Information for our observations is presented in Table 2.

Target Date Exposure () Number () Error ()
[sec] [mag]
CSS 0752+38 2016 Feb 8 180, - 4, - 0.006, -
2016 Feb 9 180, 240 40, 40 0.007, 0.014
2016 Feb 15 180, 240 63, 62 0.008, 0.017
2016 Feb 28 180, 240 36, 32 0.009, 0.018
2016 Mar 6 180, 240 35, 35 0.007, 0.016
2016 Feb 17 180, 240 48, 48 0.011, 0.017
2016 Feb 18 180, 240 50, 52 0.014, 0.023
NSVS 691550 2014 Dec 19 60, 90 82, 81 0.003, 0.004
2014 Dec 20 60, 90 192, 187 0.003, 0.004

Table 2: Journal of the Rozhen photometric observations
Label Star ID RA Dec
Target CSS 0752+38 07 52 05.68 +38 19 09.8 14.692 14.346
Chk UCAC4 643-044185 07 51 20.51 +38 34 24.58 14.121 13.686
C1 UCAC4 643-044208 07 51 47.59 +38 35 55.44 14.120 13.657
C2 UCAC4 643-044212 07 51 49.87 +38 35 24.70 14.660 13.681
C3 UCAC4 643-044217 07 51 54.27 +38 32 17.07 14.572 13.818
C4 UCAC4 643-044225 07 52 03.85 +38 32 23.81 14.709 14.018
C5 UCAC4 643-044233 07 52 15.03 +38 31 48.84 13.911 13.311
C6 UCAC4 643-044248 07 52 40.64 +38 32 08.27 14.134 13.686
C7 UCAC4 643-044271 07 53 09.97 +38 31 21.83 13.671 13.366
C8 UCAC4 643-044218 07 51 54.46 +38 29 44.02 14.346 13.859
C9 UCAC4 643-044228 07 52 07.68 +38 27 03.01 13.635 13.310
C10 UCAC4 643-044235 07 52 19.56 +38 25 59.02 14.447 13.755
C11 UCAC4 643-044258 07 52 55.66 +38 24 46.13 14.096 13.712
C12 UCAC4 642-042689 07 52 04.30 +38 21 25.15 14.479 13.864
Target NSVS 691550 08 08 40.32 +70 29 24.4 11.91 11.280
Chk UCAC4-803-018811 08 08 11.10 +70 31 24.30 13.893 12.897
C1 UCAC4-803-018819 08 08 35.27 +70 27 34.33 12.235 11.135
C2 UCAC4-803-018792 08 07 14.92 +70 29 38.18 13.617 13.227
C3 UCAC4-803-018788 08 06 53.73 +70 24 34.73 13.703 13.357
C4 UCAC4-803-018845 08 09 52.06 +70 26 47.75 12.788 12.350
C5 UCAC4-803-018826 08 08 56.41 +70 25 32.22 13.536 12.918
C6 UCAC4-803-018829 08 09 05.15 +70 24 34.93 13.981 13.230
C7 UCAC4-802-017856 08 09 29.07 +70 23 33.50 13.721 13.218
C8 UCAC4-802-017853 08 09 27.67 +70 21 39.78 12.754 12.180
Table 3: List of the standard stars
Target -2450000 Period T
[d] [mag] [mag] [mag] [K]
CSS 0752+38 7428.30337(7) 0.549284(4) 0.283 0.281 0.306 6420(180)
NSVS 691550 7011.31650(4) 0.334562(2) 0.338 0.308 0.419 5650(80)
Table 4: Parameters of variability of the targets according to the Rozhen data

The photometric data were reduced by AIP4WIN2.0 (Berry, Burnell 2006). We performed aperture ensemble photometry with the software VPHOT using more than eight standard stars in the observed field of each target. Table 3 presents their coordinates and magnitudes from the catalogue UCAC4 (Zacharias et al., 2013).

We performed periodogram analysis of our data by the software PerSea. It led to determination of initial epochs of the targets (Table 4) while the periods turned out almost equal to the previous values (Table 1). The amplitudes of variability of our observations (Table 4) are considerably larger than the preliminary values (Table 1). This is a result of higher precision of Rozhen observations.

Figure 1: The folded light curves of targets with their fits and the corresponding residuals (shifted vertically by different amount to save space).
Figure 2: 3D configurations.

2. Light curve solutions

We carried out the modeling of our data by the package PHOEBE (Prsa Zwitter 2005) based on the Wilson–Devinney code (Wilson Devinney 1971). It is appropriate for our task because allows to model data in various filters, including Sloan ones. The observational data (Fig. 1) show that our targets are contact systems. That is why we modelled them using the mode ”Overcontact binary not in thermal contact”.

The target temperatures were determined in advance (Table 4) on the basis of their infrared color indices (J-K) from the 2MASS catalog and the calibration color-temperature of Tokunaga (2000).

The procedure of the light curve solutions consists of several steps. Firstly, we adopted primary temperature = and assumed that the stellar components are MS stars. Then we calculated initial (approximate) values of secondary temperature , mass ratio , relative stellar radii and , based on the empirical relation of MS stars (Ivanov et al. 2010): , , .

Further we searched for best fit varying: and around their initial values; orbital inclination in the range 60-90 (appropriate for eclipsing stars); potentials in such way that the ratio to correspond to the initial value . We adopted coefficients of gravity brightening 0.32 and reflection effect 0.5 appropriate for late stars (Table 4). The limb-darkening coefficients were chosen according to the tables of Van Hamme (1993).

After reaching the best solution (corresponding to the minimum of ) we adjusted the stellar temperatures and around the value by the formulae (Kjurkchieva Vasileva 2015)

(1)
(2)

where the quantities (the ratio of the relative luminosities of the stellar components) and are determined from the PHOEBE solution.

Star
CSS 0752+38 58.5(0.2) 0.36(0.01) 4477(250) 2.59(0.02)
NSVS 691550 60.4(0.1) 0.845(0.001) 5370(50) 3.448(0.002)
Table 5: Fitted parameters
Star
CSS 0752+38 6525(195) 4580(250) 0.472(0.003) 0.294(0.004) 0.057(0.017)
NSVS 691550 5650(90) 5370(50) 0.404(0.002) 0.374(0.002) 0.681(0.077)
Table 6: Calculated parameters
star
[] [] []
CSS 0752+38 90(5) 110(2) 10(1) 0.9(0.02)
NSVS 691550 90(5) 11(2) 12(1) 0.87(0.02)
Table 7: Parameters of the surface spots

Although PHOEBE works with potentials, it gives a possibility to calculate directly all values (polar, point, side, and back) of the relative radius of each component ( is linear radius and a is orbital separation). Moreover, PHOEBE yields as output parameters bolometric magnitudes of the two components in conditional units (when radial velocity data are not available). But their difference determines the true luminosity ratio .

The formal PHOEBE errors of the fitted parameters were unreasonably small. That is why we estimated the parameter errors manually based on the following rule (Dimitrov Kjurkchieva 2017). The error of parameter corresponded to that deviation from its final value for which the mean residuals increase by 3 ( is the mean photometric error of the target).

Table 5 contains the final values of the fitted stellar parameters and their uncertainties: inclination i; mass ratio q; potentials ; secondary temperature . Table 6 exhibits the calculated parameters: stellar temperatures ; relative stellar radii (back values); ratio of relative stellar luminosities . Their errors are determined from the uncertainties of fitted parameters used for their calculation.

The synthetic curves corresponding to the parameters of our light curve solutions are shown in Fig. 1 as continuous lines while Figure 2 exhibits 3D configurations of the targets. Table 7 shows the parameters (latitude , longitude , angular size and temperature factor ) of the spots which were necessary to reproduce the light curve asymmetries.

4. Analysis of the results

The analysis of the light curve solutions led us to several conclusions.

(a) NSVS 691550 is overcontact system while CSS 0752+38 is almost contact binary (Fig. 2).

(b) The components of CSS 0752+38 and NSVS 691550 are F – K stars.

(c) The difference between the component temperatures of the overcontact system is around 300 K, while that of CSS 0752+38 reaches almost 2000 K.

(d) The two targets undergo partial eclipses.

(e) The mass ratio of NSVS 691550 is near 0.84 while that of CSS 0752+38 is 0.35. This result means that the stellar components of our targets almost obey the relations mass-temperature of MS stars.

(f) Light curve asymmetries of the targets were reproduced by cool spots on their primary components.

Acknowledgements. This work was supported partly by projects DN 08/20 and DM 08/02 of the Foundation for Scientific Research of the Bulgarian Ministry of Education and Science as well as by project RD 08-102 of Shumen University.

References

  • [2006] Berry R., Burnell J., 2006, The Handbook of Astronomical Image Processing with AIP4WIN2 software, Willmannn-Bell.Inc., WEB
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  • [2017] Dimitrov D., Kjurkchieva D., 2017, Mon. Not. R. Astron. Soc., accepted
  • [2010] Ivanov V., Kjurkchieva D., Srinivasa Rao, 2010, BASI,
  • [2015] Kjurkchieva, D., Vasileva, D., 2015, PASA, 32, 23
  • [2011] Martin E.L., Spruit H.C., Tata R., 2011, A A, 535, A50
  • [2005] Prsa A., Zwitter T., 2005, Astrophys. J. Suppl. Ser., 628, 426
  • [1992] Rucinski, S.M., 1992, AJ., 103, 960
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  • [1971] Wilson R. E., Devinney E. J., 1971, Astrophys. J., 166, 605
  • [2013] Zacharias N. et al., 2013, AJ, 145, 44
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