Wide-Field Survey of Globular Clusters in M31. I. A Catalog of New Clusters
We present the result of a wide-field survey of globular clusters (GCs) in M31 covering a field centered on M31. We have searched for GCs on CCD images taken with Washington filters at the KPNO 0.9 m telescope using the following steps: (1) inspection of morphological parameters given by the SExtractor package such as stellarity, full width at half-maximum, and ellipticity; (2) consulting the spectral types and radial velocities obtained from spectra taken with the Hydra spectrograph at the WIYN 3.5 m telescope; and (3) visual inspection of the images of each object. We have found 1164 GCs and GC candidates, of which 605 are newly found GCs and GC candidates and 559 are previously known GCs. Among the new objects there are 113 genuine GCs, 258 probable GCs, and 234 possible GCs, according to our classification criteria. Among the known objects there are 383 genuine GCs, 109 probable GCs, and 67 possible GCs. In total there are 496 genuine GCs, 367 probable GCs and 301 possible GCs. Most of these newly found GCs have magnitudes of mag, [ mag assuming ], and colors in the range .
Subject headings:galaxies: star clusters — galaxies: spiral — galaxies: individual (M31, NGC 224) — Local Group
Globular clusters (GCs) are an ideal tool for studying the formation and evolution of nearby galaxies for several reasons. First, GCs are one of the brightest objects in galaxies, so it is relatively easy to observe them even in the outer parts of the galaxies where individual stars are too faint to be observed. Second, GCs are believed to be among the oldest objects in galaxies (see, e.g., Salaris & Weiss (2002); De Angeli et al. (2005)) giving a lower limit to the ages of their parent galaxies. Third, the stars in GCs are believed to be born essentially at the same time and with the same chemical composition, which makes GCs an ideal laboratory for the study of stellar evolution. Fourth, GCs are distributed much more widely than stars, so they can be used for the study of the halo of their parent galaxy. Finally, since the present GCs have survived since the formation of their parent galaxies, they give information on the formation and evolution of both the clusters and the galaxies.
The GCs in M31 are especially important, since M31 is the nearest spiral galaxy and has an abundant population of GCs. There have been numerous studies of the GCs in M31 starting as early as 1932. Table 1 shows a list of the previous studies on M31 GCs, focusing primarily on the number of GCs and candidate GCs found. Examples of the most extensive GC surveys are those of Sargent et al. (1977, the M31 Consortium), Crampton et al. (1985, the DAO group), and Battistini et al. (1987, the Bologna group). However, these surveys are mostly based on visual searches of the photographic plates.
Since the use of CCD detectors in astronomy, there have been efforts to use them for deep photometry to search for new GCs in M31. However, the small field of view (FOV) of the first generation CCDs enabled previous investigators only to perform GC surveys for a limited region of M31, and there has not yet been any wide-field survey of GCs using CCD cameras. It is clear from Table 1 that our new GC survey presented in this study is the first systematic one for the largest area of 3° 3° centered on M31.
Recently several new extended GCs were found in the halo located at kpc (where is the projected radius) from the center of M31 (Huxor et al., 2005; Martin et al., 2006; Mackey et al., 2007), and Mackey et al. (2006, 2007) presented deep photometry of stars in these clusters based on Hubble Space Telescope (HST) ACS images. Kodaira et al. (2004) found 49 compact star clusters with mag and in the south-west field () of the M31 disk from CCD images taken at the Subaru 8 m telescope, some of which may be GCs.
This paper is the first in a series on our wide-field survey of M31 GCs. In this paper we present a catalog of new GCs in M31, and the analyses of the photometric and spectroscopic data of the new and known GCs in M31 will be presented in separate papers. Brief progress reports of this study were given in Lee et al. (2002), Kim et al. (2002), and Seguel et al. (2002), which are superseded by this series of papers.
This paper is organized as follows: §2 describes the photometric and spectroscopic observations and data reductions, and §3 the GC search method. Section 4 presents the catalog of new GCs found in this study and some properties of newly found GCs, and finally, a summary is given in §5.
2. Observations and Data Reduction
We carried out two kinds of observation for the survey of M31 GCs. First, photometric observations were made using the CCD camera at the KPNO 0.9 m telescope. Second, spectroscopic observations were performed using the Hydra multifiber spectrograph at the WIYN 3.5 m telescope. We describe the details of these observations below.
We obtained Washington and and broadband Kron-Cousins images using the T2KA CCD camera at the KPNO 0.9 m telescope on the nights of UT 1996 October 14 – 25 and UT 1998 October 19. The pixel scale of the CCD chip is pixel, and the CCD has 2048 2048 pixels, corresponding to on the sky. We used the Kron-Cousins filter as an alternative to the filter, since the filter accurately reproduces the photometry with 3 times greater efficiency (Geisler, 1996). The resulting calibrated magnitudes and colors will therefore be in the Washington system. Geisler (1996) gave a transformation relation between and , , with an rms of only 0.02 mag derived from the data of 53 standard stars.
We observed 53 fields covering the central region of M31. Figure 1 shows the location of the observed fields, the names of which are labeled in the upper left corner of each solid box. For most of the fields, one exposure per filter was made. Typical exposure times for the 1996 run were 1500 s for and 600 s for and , while those for the 1998 run were 1200 s for and 500 s for and . The seeing was mostly 1.1″– 2.0″(1.6 – 2.9 pixels in our CCD frames) during the observations, although a few fields have a seeing of 2.0″– 3.0″. Table 2 lists the journal of observation, where column (1) is the night number, column (2) the observation date in UT, column (3) the field numbers, and column (4) the weather condition. Of the total of 11 nights of observation, four nights (N5, N8, N9 and Oct98) were photometric, three (N3, N4, and N11) were semi-photometric, and the remaining four nights were non-photometric or even cloudy. The standard star observations were made in the photometric and semi-photometric nights indicated in Table 2.
2.1.2 Data Reduction
We processed all the CCD images to apply overscan correction, bias subtraction and flat fielding using the IRAF111IRAF(Image Reduction and Analysis Facility) is distributed by the National Optical Astronomy Observatory, which is operated by AURA, Inc., under cooperative agreement with the National Science Foundation./CCDRED package. We derived the calibration transformation using the Washington standard stars (Geisler, 1996) observed during the observing runs. We obtained the aperture magnitudes of the standard stars using a radius aperture (the same as in Geisler (1996)) from the images of the standard stars. Then we used the IRAF PHOTCAL package to derive the calibration equations.
For three out of the four nights of photometric conditions, all three standard calibration coefficients (zeropoint, color term, and airmass term) were derived. For the three nights of semi-photometric conditions, we adopted the mean values of the color and airmass term coefficients of the three photometric nights to derive the zeropoints. Although the night of UT 1996 October 22 was believed to be photometric, there were not enough standard stars to derive all three calibration coefficients independently, so we adopted the color and airmass term coefficients of the previous photometric night.
For the fields observed on the nights without standard stars, we derived secondary standard transformations using the neighboring fields. Since we initially arranged our target fields to overlap adjacent fields by – , we could easily identify the stars in common between two neighboring fields. On the image of each filter, we first identified the positions of the common stars in the two adjacent fields, calculated the mean magnitude offsets between the standardized magnitudes and instrumental magnitudes, and then applied this magnitude offset (together with the color and atmospheric coefficients of the standardized field) to transform the instrumental magnitudes of the nonphotometric frames. There are 14 fields for which this secondary transformation method is applied. The typical errors of the standard star calibration are 0.020, 0.022, and 0.019 mag for , , and , respectively.
We have derived the photometry of the objects in the target images using the SExtractor package (Bertin & Arnouts, 1996). SExtractor performs detection of objects in the images and gives position, aperture magnitude, stellarity, the full width at half-maximum (FWHM), ellipticity, position angle, quality of the photometry, and some other parameters. We used the SExtractor parameters DETECT_MINAREA = 5 pixel and DETECT_THRESH = above the local background. The results for new GC searches do not depend strongly on the choice of these values. The instrumental magnitudes of the objects obtained using the SExtractor package were transformed into the standard system using the calibration equations.
We have obtained plate solutions for each of the CCD images for astrometry of objects using the Guide Star Catalogue (GSC) provided by the Space Telescope Science Institute (STScI) and the IRAF tasks ccxymatch and ccmap. These plate solutions transform the and coordinates of our images to/from the celestial equatorial coordinates of epoch J2000.0 by using the IRAF cctran task. The mean rms errors in right ascension and declination are and , respectively.
For most of the GC candidates selected from the photometric list of the objects to be described in the next section, we carried out spectroscopic observation using the Hydra multifiber bench spectrograph and T2KC CCD at the WIYN 3.5 m telescope on the nights of UT 2000 September 7–9 and UT 2001 November 2–4. Table 3 lists the journal of spectroscopic observations. Table 3 shows the observation date in UT, the number of target objects, and the exposure time for each Hydra configuration marked in Figure 1.
For both the 2000 and 2001 observations, almost the same instrumental setup was used. The email@example.com grating and Simmons camera were used. This combination with the blue fiber cable covers a wavelength range of Å in the first order and gives a 7.07 Å spectral resolution and 1.56 Å pixel dispersion.
During the observing run of 2000, all three nights were clear and a total of eight Hydra configurations were used for spectroscopy. However, in the run of 2001 only the first night was clear, while the two subsequent nights were cloudy or rainy. Only three Hydra configurations were obtained during this run. The total number of targets observed during the observing runs was 748, including 106 previously known GCs observed in order to quantify our errors and compare our values with previous studies.
2.2.2 Data Reduction
First we performed overscan correction, image trimming, bias subtraction, and flat combining on the spectroscopic data using the IRAF ccdred package. We removed cosmic rays in the object images and combined the resulting object images. For the reduction of the Hydra spectroscopic data, we used the Hydra data reduction task, IRAF dohydra, which was specifically designed for multifiber spectral reduction (Valdes, 1995).
Before doing the main data reduction part, DOHYDRA first performs aperture finding using the apfind task, and performs fitting and subtracting of the scattered light using the apscatter task. Then DOHYDRA performs aperture extraction, flat-fielding, fiber throughput correction, wavelength calibration, and sky subtraction. Dome-flat images were used as a template to extract the one-dimensional object and calibration spectra from the two-dimensional images. Cu/Ar calibration lamp spectra were used for wavelength calibration. The rms error of the wavelength calibration is estimated to be typically 0.2–0.3 Å. Finally, we calibrated the flux of the spectra of the targets using the spectra of the flux standard star BD +40 4032 (R.A.(B1950), Dec.(B1950), B2 III, m mag; Strom (1977)) using the calibrate task.
We determined the radial velocity of the targets by cross-correlating their spectra against high signal-to-noise ratio (S/N) template spectra using the IRAF fxcor task (Tonry & Davis, 1979; Huchra, Brodie, & Kent, 1991). We used two bright GCs in M31 as a reference. GCs 020-073 and 158-213 are relatively bright clusters with mag and and mag and , respectively, and have well-determined radial velocities of and km s, respectively (Barmby et al., 2000). We used the wavelength range of 3900 – 5400 Å for velocity measurement, excluding the noisy region of Å due to some sky lines not completely eliminated even after sky subtraction. Measuring errors of the radial velocity are typically km s. For the objects with successfully measured velocity values, we measured the S/N values at Å, obtaining S/N. The peak S/N values are 6 – 10 for all these spectra, and 10 – 20 for newly found, highest probability GCs.
3. Cluster Search Method
We have used both photometric and spectroscopic information to select GCs in M31. First, using photometric data, we investigated various photometric parameters and morphological properties of the objects in the CCD images. Then we assigned spectral classes to bright objects, and used the radial velocities to determine the M31 membership of the objects with measured radial velocities. Finally, we performed the final classification by careful visual inspection of the image of each object, after training our eyes with images of the previously known GCs, stars, and galaxies in our own data. Details of these steps are described below.
Before starting a survey of M31 GCs, we tried to find the suitable parameter space to select M31 GC candidates using the photometric data of the known M31 GCs. We matched our photometric catalog of the objects with the previous catalogs of Galleti et al. (2006) (Revised Bologna Catalog ver. 2.0 [RBC2] – their confirmed and candidate GCs), Huxor et al. (2005), and Mackey et al. (2007). There are 861 objects (347 confirmed GCs and 514 GC candidates) common between the previous catalogs and our catalog of photometry derived from our CCD images.
Figure 2 shows the distributions of three SExtractor parameters (stellarity, FWHM and ellipticity) based on the images, and Figures 3 and 4 show the photometric diagrams of these objects. In Figure 2 (a), (b), and (c), the crosses and the open solid histograms show the distributions of all 861 objects with good photometry, and the filled circles and hatched histograms show those of the confirmed GCs in common between this study and the papers above. As stellarity of 1 corresponds to a point-source (star), and a stellarity of 0 to a resolved object. The distribution of stellarity in Figure 2 shows that most objects have stellarity of 1, few objects have stellarity between 0.1 and 0.8, and the rest have stellarity . Figure 2 (d) shows the histogram of the normalized FWHM, which is the measured FWHM divided by the seeing value of each image.
In Figure 2 several features are noted: (1) the distribution of the stellarity of the confirmed GCs shows a strong peak around 1 with a broad tail extending to about 0.8, and a weak peak around 0. There are relatively much fewer GCs in the range between 0.1 and 0.8; (2) the distribution of the ellipticity of the confirmed GCs shows a broad peak around 0.1 with a tail extending to 0.5; and (3) the distribution of the normalized FWHM of the confirmed GCs shows a strong peak around 1.4, which is significantly larger than that of the stars, 1.0. Considering the pixel scale of our CCD chip, typical seeing of 2 pixels (), and the linear size of at the distance of M31 ( pc), it is expected that most of the GCs in M31 will appear point-source-like. Even for these star-like GCs, Figure 2 (d) shows that the normalized FWHM is greater than 1.
Considering the features in Figure 2, we have set up two kinds of criteria for the selection of GC candidates: (1) criteria for “all candidates” are (a) all values of stellarity, (b) FWHM/seeing , and (c) ellipticity ; and (2) criteria for “good candidates” are (a) stellarity of , (b) FWHM/seeing , and (c) ellipticity . “Good candidates” are candidates with higher probability among “all candidates.” Figure 3 shows the color-magnitude (CM) diagram (Fig 3 (a)), the histograms of color (Fig 3 (b)) and magnitude (Fig 3 (c)) of the 861 objects matched with the previous catalogs. Figure 4 shows the – color-color (CC) diagram of the same objects. Notable features in Figures 3 and 4 are that (1) the colors of the confirmed GCs are mostly in the range , (2) the luminosity function (LF) of the confirmed GCs shows a peak at mag, (3) the CM diagram shows a dominant vertical plume of GCs with extending up to , and (4) the CC diagram shows a well-defined linear sequence of star clusters.
In Figures 3 and 4 we also plotted the data for “all candidates” and “good candidates”. It is striking that the general properties of these candidates seen in these figures are very similar to those of the confirmed GCs, noting that no information of color and magnitude was used for selecting these candidates. This indicates that a significant fraction of these candidates may be GCs.
We selected the candidates in the best-seeing image among the and images, which are predominantly the -band images. We used objects at least mag brighter than the limiting magnitude where the stellarity cannot be used to separate stellar/non-stellar objects. The typical limiting magnitude of the images is mag, varying from field to field due to the seeing and the crowding in the field. We set the magnitude cut-off value for the candidate selection 1 – 2 mag brighter than the limiting magnitude of the images, depending on the seeing and the crowding in the images. The magnitude cut-off value for the candidate selection ranges from mag (for the center field) to mag (for halo fields or good seeing), mostly mag. Therefore our search is considered to be incomplete at mag for most fields (at mag for the central field). Figure 5 shows an example of our application of the above criteria to one of the KPNO fields (F56) with a seeing of pixels. In this field, there are 4894 measured objects with good photometry. Among these we selected 362 “all GC candidates” according to criterion (1), and 277 “good GC candidates” according to criterion (2).
Finally we marked the “all” and “good” GC candidates selected above on the images, and visually inspected their images to finalize the GC candidates. We checked contour maps and radial profiles of the objects as well as the images themselves. In the contour map, we classified irregular, significantly elongated, asymmetric, and loosely concentrated objects as galaxies, and round, slightly elongated, strongly concentrated objects as star clusters. Although some faint galaxies look round in the displayed images, in the contour maps their outer areas look irregular, while star clusters look very smooth and round. Inspection of the contour maps was very efficient in selecting galaxies. In the radial profile, the objects with FWHM larger than the seeing size are considered as GCs, those with FWHM similar to seeing size as stars, and those with a large excess in the wing as galaxies. Checking color, position, and/or velocity information was also included. There are some confusing cases: compact elliptical galaxies versus GCs, compact GCs versus stars, and compact star clusters in H ii regions versus galaxies. For these cases spectroscopic information was needed for classification. In the outer areas close to the edge of each CCD image, the FWHMs get larger due to image degradation. Therefore, we carefully compared potential targets in these areas with other nearby objects to see whether they are really extended.
Spectral information was also used for the classification of bright objects. We have visually classified the flux-calibrated spectra into stars, star clusters, and galaxies, comparing them with the template spectra of the spectral library of Santos et al. (2002). We used the continuum of the wavelength range as well as various spectral features: Balmer lines between 4000 and 5000 for early-type objects; absorption lines like Ca ii H and K, CH (G band), MgHMgb, and TiO for late-type objects; and emission lines for galaxies. Figure 6 displays sample spectra for confirmed GCs, young star clusters, foreground stars (F, G, and K types), and three galaxies (M31, M32 and a background galaxy).
The radial velocities were used as a strong constraint on the membership of the objects belonging to the Galaxy, M31, or the distant universe. Most of the objects with radial velocities less than km s are probably M31 members, while those from to km s could be M31 members or Galactic foreground stars. We considered all the objects with km s to be M31 members. The objects with km s were classified as background galaxies. For objects with km s km s, we classified each object consulting its spectral class.
Combining both image and spectral inspections was very efficient and accurate in classifying the objects. For our fields F08–F42, we used both image inspection and spectral inspection methods, while for the fields without spectroscopic data (F1–F7, F43–F52, and F56) we used only the image inspection method.
We have classified the final GCs/GC candidates into three classes according to probability as follows: (1) class 1, genuine GCs that were confirmed by either spectral types and radial velocities or high resolution images (mostly images); (2) class 2, probable clusters that are probably GCs from imaging data but without spectral information; and (3) class 3, possible clusters that are possibly GCs, but may be other kinds of objects like background galaxies.
4.1. The Catalog of New Globular Clusters in M31
By applying the cluster search method described in the previous Section to the 53 KPNO fields of M31 covering a 3° 3° area, we have found a total of 1164 GC candidates. Among these there are 605 new GC candidates found in this study and 559 previously known GCs in the catalogs of previous studies (e.g., Huxor et al. (2005); Galleti et al. (2006); Mackey et al. (2007)). Table 4 lists a summary of the numbers of the GCs and GC candidates for each class. Among the new 605 GC candidates there are 113 genuine GCs (class 1), 258 probable GCs (class 2) and 234 possible GCs (class 3). Among the known GCs in previous studies we find 383 genuine GCs, 109 probable GCs and 67 possible GCs. In total there are 496 genuine GCs, 367 probable GCs and 301 possible GCs.
Tables , , and present the lists of the GCs and GC candidates newly found in this study for genuine GCs, probable GCs, and possible GCs, respectively. In these tables the columns give the running number (col. ), the coordinates in right ascension and declination (J2000.0; cols.  and ), magnitudes (col. ), and colors (cols.  and ), and the radial velocities derived in this study (col. ). The magnitudes and colors here are from the simple aperture photometry derived using SExtractor with an aperture of radius 5″. Figures 7, 8, and 9 show the -band mosaic images of genuine GCs (class 1) with identifications in Tables labeled.
Tables and 18 present the lists of 111 stars and 21 galaxies, respectively, identified in the present study. The columns are the same as those of Tables , except the last column of Table 18, whithc gives the identification matched with the RBC2 of Galleti et al. (2006). These lists of stars and galaxies were obtained from the spectral classification described in Section 3. We found that 13 objects in these lists were already identified as galaxies or GC candidates without measured velocities in the RBC2 catalog.
4.2. Properties of New Globular Clusters
Although the detailed properties of the newly found GCs/GC candidates as well as those of the whole M31 GC system including the previously known GCs will be presented in separate papers, we show a few salient features of the newly found objects here.
Figure 10 shows the CM diagram (Fig. 10 (a)), color distributions (Fig. 10 (b)), and LF (Fig. 10 (c)) of the newly found GCs/GC candidates in Tables , , and Figure 11 shows the CC diagram of the same objects. Most of the class 1 GCs have magnitudes of mag, which would be mag assuming (see below) and using the Geisler (1996)’s transformation coefficients between photometry and photometry. Figure 12 shows the direct comparison of the confirmed, previously known GCs and newly found, class 1 GCs in the CM diagram, and it is noted that most of the class 1 GCs newly found in this study are fainter than most of the confirmed, previously known GCs. The brightest object among the newly found class 1 GCs has () mag and the faintest one has () mag. We checked the color distributions of the previously known GCs and newly found GCs, confirming that they are quite similar.
Figure 10 (b) shows that the color distributions of all three classes encompass the color range of [; Geisler (1996)], in which most of the class 1 objects reside. There are a rather large number of very red objects with , which could be reddened GCs or intrinsically red clusters.
Figure 13 shows the spatial distribution and histograms of the newly found GCs and GC candidates. Open circles and filled histograms are for class 1 GCs in this study, crosses are for class 2 GCs in this study, and dots and open solid histograms are for GCs in the catalogs of Galleti et al. (2006, their class 1), Huxor et al. (2005), and Mackey et al. (2007). Most of the newly found, class 1 GCs are located in the disk area of M31. Higher spatial resolution imaging and spectroscopy, and possibly in the near-infrared wavelength band, would be needed to search for GCs in the central region of M31 where we missed many faint GCs, as seen in Figure 13 ().
We have presented the results of a new systematic wide field CCD survey of M31 GCs. Using Washington CCD images obtained at the KPNO 0.9 m telescope and spectra obtained using the WIYN 3.5 m telescope and Hydra multifiber bench spectrograph, we have investigated the photometric and morphological parameters of the objects, visually checked their images, and obtained their spectra and radial velocities. Finally, we have found 1164 GCs and GC candidates, of which 559 are previously known GCs and 605 are newly found GC candidates. Among the new objects there are 113 genuine GCs (class 1), 258 probable GCs (class 2), and 234 possible GCs (class 3). Among the previously known objects there are 383 genuine GCs, 109 probable GCs and 67 possible GCs. In total there are 496 genuine GCs, 367 probable GCs and 301 possible GCs.
The magnitudes and colors of most of the newly found class 1 objects are mag and . The faintest part of the M31 GC LF is mostly filled with these new GC candidates, although the intrinsically very faint GCs like AM 4, Palomar 1, E 3, and Palomar 13 in the Galaxy (see, e.g., van den Bergh & Mackey (2004); Sarajedini et al. (2007)) may remain to be detected.
We would like to thank the anonymous referee for providing prompt and thoughtful comments that helped improve the original manuscript. The authors are grateful to the staff members of the KPNO for their warm support during our observations and data reduction. The WIYN Observatory is a joint facility of the University of Wisconsin-Madison, Indiana University, Yale University, and the National Optical Astronomy Observatory. M. G. L. was supported in part by a Korean Research Foundation grant (KRF-2000-DP0450) and ABRL (R14-2002-058-01000-0). D. G. gratefully acknowledges support from Chilean Centro de Astrofísica FONDAP grant 15010003. A. S. was supported by NSF CAREER grant AST 00-94048.
- Alloin, Pelat, & Bijaoui (1976) Alloin, D., Pelat, D., & Bijaoui, A. 1976, A&A, 50, 127 (Erratum 1977, A&A, 54, 321)
- Aurière, Coupinot, & Hecquet (1992) Aurière, M., Coupinot, G., & Hecquet, J. 1992, A&A, 256, 95
- Baade & Arp (1964) Baade, W., & Arp, H. C. 1964, ApJ, 139, 1027
- Barmby et al. (2000) Barmby, P., Huchra, J. P., Brodie, J. P., Forbes, D. A., Schroder, L. L., & Grillmair, C. J. 2000, AJ, 119, 727
- Barmby & Huchra (2001) Barmby, P., & Huchra, J. P. 2001, AJ, 122, 2458
- Battistini et al. (1987) Battistini, P., Bònoli, F., Braccesi, A., Federici, L., Fusi Pecci, F., Marano, B., & Börngen, F. 1987, A&AS, 67, 447
- Battistini et al. (1993) Battistini, P., Bònoli, F., Casavecchia, M., Ciotti, L., Federici, L., & Fusi Pecci, F. 1993, A&A, 272, 77
- Bertin & Arnouts (1996) Bertin, E., & Arnouts, S. 1996, A&AS, 117, 393
- Crampton et al. (1985) Crampton, D., Cowley, A. P., Schade, D., & Chayer, P. 1985, ApJ, 288, 494
- De Angeli et al. (2005) De Angeli, F., Piotto, G., Cassisi, S., Busso, G., Recio-Blanco, A., Salaris, M., Aparicio, A., & Rosenberg, A. 2005, AJ, 130, 116
- Galleti et al. (2004) Galleti, S., Federici, L., Bellazzini, M., Fusi Pecci, F., & Macrina, S. 2004, A&A, 416, 917
- Galleti et al. (2006) Galleti, S., Federici, L., Bellazzini, M., Buzzoni, A., & Fusi Pecci, F. 2006, A&A, 456, 985
- Geisler (1996) Geisler, D. 1996, AJ, 111, 480
- Hubble (1932) Hubble, E. P. 1932, ApJ, 76, 44
- Huchra, Brodie, & Kent (1991) Huchra, J. P., Brodie, J. P., & Kent, S. M. 1991, ApJ, 370, 495
- Huxor et al. (2005) Huxor, A. P., Tanvir, N. R., Irwin, M. J., Ibata, R., Collett, J. L., Ferguson, A. M. N., Bridges, T., & Lewis, G. F. 2005, MNRAS, 360, 1007
- Karachentsev et al. (2004) Karachentsev, I. D., Karachentseva, V. E., Huchtmeier, W. K., & Makarov, D. I. 2004, AJ, 127, 2031
- Kim et al. (2002) Kim, S. C., Lee, M. G., Geisler, D., Seguel, J., Sarajedini, A., & Harris, W. E. 2002, in IAU Symp. 207, Extragalactic Star Clusters, ed. D. Geisler, E. K. Grebel, & D. Minniti, 143
- Kodaira et al. (2004) Kodaira, K., Vansevicius, V., Bridzius, A., Komiyama, Y., Miyazaki, S., Stonkute, R., Sabelviciute, I., & Narbutis, D. 2004, PASJ, 56, 1025
- Lee et al. (2002) Lee, M. G., Kim, S. C., Geisler, D., Seguel, J., Sarajedini, A., & Harris, W. E. 2002, in IAU Symp. 207, Extragalactic Star Clusters, ed. D. Geisler, E. K. Grebel, & D. Minniti, 46
- Mackey et al. (2006) Mackey, A. D., Huxor, A., Ferguson, A. M. N., Tanvir, N. R., Irwin, M., Ibata, R., Bridges, T., Johnson, R. A., & Lewis, G. 2006, ApJ, 653, L105
- Mackey et al. (2007) Mackey, A. D., Huxor, A., Ferguson, A. M. N., Tanvir, N. R., Irwin, M., Ibata, R., Bridges, T., Johnson, R. A., & Lewis, G. 2007, ApJ, 655, L85
- Martin et al. (2006) Martin, N. F., Ibata, R. A., Irwin, M. J., Chapman, S., Lewis, G. F., Ferguson, A. M. N., Tanvir, N., & McConnachie, A. W. 2006, MNRAS, 371, 1983
- Mayall & Eggen (1953) Mayall, N. U., & Eggen, O. J. 1953, PASP, 65, 24
- Mochejska et al. (1998) Mochejska, B. J., Kaluzny, J., Krockenberger, M., Sasselov, D. D., & Stanek, K. Z. 1998, Acta Astronomica, 48, 455
- Morrison et al. (2003) Morrison, H. L., Harding, P., Hurley-Keller, D., & Jacoby, G. 2003, ApJ, 596, L183
- Perrett et al. (2002) Perrett, K. M., Bridges, T. J., Hanes, D. A., Irwin, M. J., Brodie, J. P., Carter, D., Huchra, J. P., & Watson, F. G. 2002, AJ, 123, 2490
- Racine (1991) Racine, R. 1991, AJ, 101, 865
- Salaris & Weiss (2002) Salaris, M., & Weiss, A. 2002, A&A, 388, 492
- Santos et al. (2002) Santos, J. F. C., Jr., Alloin, D., Bica, E., & Bonatto, C. 2002, in Extragalactic Star Clusters, IAU Symp. 207, eds. D. Geisler, E. K. Grebel, & D. Minniti, 727
- Sarajedini et al. (2007) Sarajedini, A., Bedin, L. R., Chaboyer, B., Dotter, A., Siegel, M., Anderson, J., Aparicio, A., King, I., Majewski, S., Marín-Franch, A., Piotto, G., Reid, I. N., & Rosenberg, A. 2007, AJ, accepted (astro-ph/0612598)
- Sargent et al. (1977) Sargent, W. L. W., Kowal, C. T., Hartwick, F. D. A., & van den Bergh, S. 1977, AJ, 82, 947
- Seguel et al. (2002) Seguel, J., Geisler, D., Lee, M. G., Kim, S. C., Sarajedini, A., & Harris, W. E. 2002, in IAU Symp. 207, Extragalactic Star Clusters, ed. D. Geisler, E. K. Grebel, & D. Minniti, 146
- Seyfert & Nassau (1945) Seyfert, C. K., & Nassau, J. J. 1945, ApJ, 102, 377
- Strom (1977) Strom, K. M. 1977, Standard Stars for IIDS Observations, Kitt Peak National Observatory
- Tonry & Davis (1979) Tonry, J. T., & Davis, M. 1979, AJ, 84, 1511
- Valdes (1995) Valdes, F. 1995, Guide to the HYDRA Reduction Task DOHYDRA
- van den Bergh & Mackey (2004) van den Bergh, S., & Mackey, A. D. 2004, MNRAS, 354, 713
- Vetešnik (1962) Vetešnik, M. 1962, Bull. Astr. Inst. Czech, 13, 180
- Wirth, Smarr, & Bruno (1985) Wirth, A., Smarr, L. L., & Bruno, T. L. 1985, ApJ, 290, 140
|Reference||Plate vs. CCD||CCD FOV||N(GC)||Comments|
|Hubble (1932)||plate||140||M31’s disk only|
|Seyfert & Nassau (1945)||plate||101||W. Baade’s discovery, no coordinates|
|Vetešnik (1962)||plate||(241)aaNot new discoveries, but studies on the objects found by Hubble (1932) and Seyfert & Nassau (1945).||coordinates, magnitudes and colors|
|Baade & Arp (1964)||plate||30|
|Mayall & Eggen (1953)||plate||4||outer parts of M31|
|Alloin, Pelat, & Bijaoui (1976)||plate||5||nuclear region of M31|
|Sargent et al. (1977)||plate||355||KPNO 4 m|
|Crampton et al. (1985)||spectra plates||109||CFHT 3.6 m, A catalog of total 509 GCs|
|Battistini et al. (1987)||plate||353bbWith 254 class A, 99 class B, 152 class C, and 218 class D objects, where class A objects are very high-confidence objects, class B objects are high confidence objects, class C objects are plausible candidates, and class D miscellaneous non-stellar objects with an expected percentage of actual clusters of the order of a few percent.||Bologna 1.52 m|
|Wirth, Smarr, & Bruno (1985)||video camera||bulge region|
|Aurière, Coupinot, & Hecquet (1992)||CCD||16ccWith 12 reliable, 4 possible.||field centered on M31|
|Battistini et al. (1993)||CCD||pixel||4ddWith 3 class A, 1 class B, 20 class C, and 20 class D objects.||( kpc)|
|Mochejska et al. (1998)||CCD||4eeWith 2 class A, 2 class B, 28 class C, and 36 class D objects.||four fields in the M31’s disk|
|Barmby et al. (2000)||CCD||(435)ffObservations of 13 fields centered on M31, but no GC search. Of the 435 objects, 268 have optical photometry in four or more filters, 224 have near-infrared photometry, 200 have radial velocities, and 188 have spectroscopic metallicities.||A new catalog of “best” photometry|
|Barmby & Huchra (2001)||HST/WFPC2||32||157 images|
|Perrett et al. (2002)||spectroscopy||(288)ggSpectroscopy for 288 previously known objects. They presented a spectroscopic database of 321 velocities and 301 metallicities.||WHT 4.2 m + WYFFOS|
|Galleti et al. (2004)||2MASS/NICMOS3||all sky||(693)hh2MASS near-infrared photometry for 693 known and candidate GCs. Of 1035 objects, 337 are confirmed GCs, 688 are GC candidates, and 10 are objects with controversial classification.||Revised Bologna Catalogue of 1035 objects|
|Huxor et al. (2005)||CCD||deg||3||INT 2.5 m + WFC|
|Galleti et al. (2006)||spectroscopy||(42)iiConfirmed GC nature from spectroscopy of 76 candidates.||Revised Bologna Catalogue V2.0|
|Mackey et al. (2006, 2007)||HST/ACS||14||HST Program GO 10394 (Cycle 13)|
|This study||CCD||605jjWith 113 class 1, 258 class 2, and 234 class 3, where classes 1, 2, and 3 are similar to classes A, B, and C, respectively, in Battistini et al. (1987).||mapping field centered on M31|
|Night||Obs. Date (UT)||Field||Weather|
|N1||1996 October 14||23() 26||cloudy|
|N2||1996 October 15||16 17 18(long) 19 20 23() 24 25(long) 27||cloudy|
|N3||1996 October 16||18(short) 25(short) 30 31 32 33 34 35||semi-photometric|
|N4||1996 October 17||28 36||semi-photometric|
|N5||1996 October 18||09 10 37 38 39 40 41||photometric|
|N6||1996 October 19|
|N7||1996 October 20|
|N8||1996 October 21||11 12 13 14 15 29 42 43()||photometric|
|N9||1996 October 22||43() 44 45||photometric|
|N10||1996 October 23||(45) 46 47 48 49 50||non-photometric|
|N11||1996 October 24||01 02 03 04 05||semi-photometric|
|N12||1996 October 25||06||non-photometric|
|Oct98||1998 October 19||07 08 21 22 51 52 56||photometric|
Note. – The fields with standard transformation data (photometric and
semi-photometric nights) are represented with bold letters.
For the field of F18, which is just the northern field of F25, we took two sets of data; long exposures (1500s in , 600s in , and 600s in ) and short exposures (300s in , 100s in , and 100s 2 in ).
For the field of F25, which includes the M31 central region, we took of data; long exposures (1500s in , 600s in , and 300s 2 in ) and short exposures (300s in , 200s in , and 200s 2 in ).
Field 45 was observed both on N9 and N10 with the same exposure time setups. Even though the seeing of N10 for F45 was slightly better than that of N9 ( versus ), we primarily used the N9 data for the utilization of N9 standard transformation information.
|Hydra||N(observed)aaNumber of all observed objects.|
|Obs. Date (UT)||Configuration||(=newbbGC candidates found from the photometric criteria in this study. + oldccPreviously known GCs.)||N(vel)ddNumber of objects for which successful velocities were measured.||Exposure Time|
|2000 September 7||1||68 (=66+2)||38||1800 s 4 = 7200 s (2)|
|2000 September 7||2||73 (=56+17)||66||1800 s 3 + 900 s = 6300 s (1 45)|
|2000 September 8||3||64 (=64+0)||47||1800 s 4 = 7200 s (2)|
|2000 September 8||4||62 (=59+3)||34||1800 s 3 = 5400 s (1 30)|
|2000 September 8||5||71 (=59+12)||56||1800 s 4 = 7200 s (2)|
|2000 September 9||6||75 (=74+1)||36||1800 s 4 = 7200 s (2)|
|2000 September 9||B||70 (=67+3)||56||1800 s 4 = 7200 s (2)|
|2000 September 9||E||70 (=60+10)||57||1800 s 3 + 1041 s = 6441 s (1 47 21)|
|2001 November 2||11||69 (=54+15)||35||2400 s 3 = 7200 s (2)|
|2001 November 2||12||79 (=45+34)||60||2400 s 3 = 7200 s (2)|
|2001 November 2||17||47 (=38+9)||20||2400 s 1 = 2400 s (40)|
|Class||Previously found by othersaain Huxor et al. (2005); Galleti et al. (2006); Mackey et al. (2007) and references there in.||New GCs||Sum|
|R.A.aaRight ascension in units of hours, minutes, and seconds.||Decl.bbDeclination in units of degrees, arcminutes, and arcseconds.|
Note. – Table 5 is published in its entirety in the electronic edition of the Astronomical Journal. A portion is shown here for guidance regarding its form and content.
|R.A.aaRight ascension in units of hours, minutes, and seconds.||Decl.bbDeclination in units of degrees, arcminutes, and arcseconds.|