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J/A+A/531/A155     HST photometry in six M31 globular clusters   (Perina+, 2011)

HST/ACS color-magnitude diagrams of candidate intermediate-age M 31 globular clusters. The role of blue horizontal branches. Perina S., Galleti S., Fusi Pecci F., Bellazzini M., Federici L., Buzzoni A. <Astron. Astrophys. 531, A155 (2011)> =2011A&A...531A.155P
ADC_Keywords: Galaxies, nearby ; Clusters, globular ; Photometry, HST Keywords: galaxies: individual: M31 - galaxies: star clusters: general - techniques: photometric Abstract: We present deep (V∼28.0) BV photometry obtained with the wide field channel of the Advanced Camera for Surveys on board HST for four M31 globular clusters that were identified as candidate intermediate-age (age∼1-9Gyr) by various authors, based on their integrated spectra and/or broad/intermediate-band colors. Two of them (B292 and B350) display an obvious blue horizontal branch, indicating that they are as old as the oldest Galactic globulars. On the other hand, for the other two (B058 and B337), which display red horizontal branches, it was not possible either to confirm or disconfirm the age estimate from integrated spectra. The analysis of the distribution in the spectral indices Mg2 and Hβ of the M31 and Milky Way clusters whose horizontal branch can be classified as red or blue based on existing CMDs, strongly suggests that classical age diagnostics from integrated spectra may be significantly influenced by the HB morphology of the clusters and can lead to erroneous age-classifications. We also provide the CMD for another two clusters that fall into the field of the main targets, B336, an old and metal-poor globular with a significant population of RR-Lyrae variables, and the newly discovered B531, a cluster with a very red red giant branch. Description: Tables b058.dat, b292_531.dat, b350.dat, b336.dat, b337.dat present the photometry of the individual stars of six M31 globular clusters. The observations were carried out with the ACS on board of the HST, employing the WFC+F435W/F606W filters. The data reduction has been performed using the ACS module of DOLPHOT, a point spread function-fitting package specifically devoted to the photometry of HST data, that provides as output the magnitudes and the pixel positions of the detected sources, and a number of quality parameters for a suitable sample selection. The tables present, for the chip holding the cluster, all the stars with valid measurements in both passbands, global quality flag=1, crowding parameter <0.5, chi-square parameter <2.5 and sharpness parameter between -0.3 and 0.3. The x,y coordinates, the magnitudes in the Vegamag system, the errors on the magnitudes and the ACS_WFC chip number are listed for each of the selected stars. Objects: -------------------------------------------------------------------------- RA (2000) DE Designation(s) (file) -------------------------------------------------------------------------- 00 36 14.70 +40 57 56.6 Bol 531 = M31GC J003615+405757 (b292_531.dat) 00 36 16.59 +40 58 26.6 Bol 292 = M31GC J003617+405827 (b292_531.dat) 00 40 47.60 +42 08 41.4 Bol 336 = M31GC J004048+420841 (b336.dat) 00 40 48.45 +42 12 11.5 Bol 337 = M31GC J004048+421211 (b337.dat) 00 41 53.01 +40 47 08.6 Bol 058 = M31GC J004153+404709 (b058.dat) 00 42 28.33 +40 24 50.2 Bol 350 = M31GC J004228+402450 (b350.dat) ---------------------------------------------------------------------------- File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file clusters.dat 62 6 Cluster list b058.dat 50 21883 *Stellar Photometry of the M31 GC B058 b292_531.dat 50 9896 Stellar Photometry of the M31 GCs B292 and B531 b336.dat 50 13235 Stellar Photometry of the M31 GC B336 b337.dat 50 16150 Stellar Photometry of the M31 GC B337 b350.dat 50 32279 Stellar Photometry of the M31 GC B350
Note on b058.dat: The photometry of B058 is limited to a sub-section of the chip having an area of ∼3000 square arcseconds.
See also: J/AJ/114/1488 : Globulars in M31 (Holland+ 1997) J/AcA/48/455 : Globular Clusters in M31 and M33 (Mochejska+, 1998) J/AJ/119/727 : M31 globular clusters photometry (Barmby+, 2000) J/AJ/122/2458 : M31 globular clusters from HST (Barmby+, 2001) J/A+A/416/917 : M31 globular clusters revised Bologna Catalog (Galleti+ 2004) J/A+A/471/127 : New globular clusters in M31 (Galleti+, 2007) J/AJ/133/2764 : M31 globular clusters structural parameters (Barmby+, 2007) J/ApJS/173/643 : GALEX UV photometry of M31 Globular Clusters (Rey+, 2007) J/MNRAS/392/L55 : M31 globular clusters from K-band photometry (Peacock+, 2009) J/A+A/507/1375 : HST/ACS VI data of M31 globular clusters (Perina+, 2009) http://www.bo.astro.it/M31 : Revised Bologna Catalogue of M31 globular clusters Byte-by-byte Description of file: clusters.dat
Bytes Format Units Label Explanations
1- 4 A4 --- Name Cluster name 6- 7 I2 h RAh Right ascension (J2000) 9- 10 I2 min RAm Right ascension (J2000) 12- 16 F5.2 s RAs Right ascension (J2000) 18 A1 --- DE- Declination sign (J2000) 19- 20 I2 deg DEd Declination (J2000) 22- 23 I2 arcmin DEm Declination (J2000) 25- 28 F4.1 arcsec DEs Declination (J2000) 30- 49 A20 --- SName Simbad name 51- 62 A12 --- FileName Name of the file with cluster photometry
Byte-by-byte Description of file: b*.dat
Bytes Format Units Label Explanations
1- 5 I5 --- ID Identification number 7- 12 F6.3 mag F435W HST/ACS F435W band magnitude (Vegamag system) 14- 18 F5.3 mag e_F435W rms uncertainty in F435W 20- 25 F6.3 mag F606W HST/ACS F606W band magnitude (Vegamag system) 27- 31 F5.3 mag e_F606W rms uncertainty in F606W 33- 39 F7.2 pix Xpos X pixel coordinates (1) 41- 48 F8.2 pix Ypos Y pixel coordinates (1) 50 I1 --- Chip ACS/WFC chip number
Note (1): Output coordinates corrected for the ACS geometrical distortions.
Acknowledgements: Sibilla Perina, sibilla.perina2(at)unibo.it
(End) Patricia Vannier [CDS] 03-Jun-2011
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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