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J/A+A/533/A37       VI HST photometry of VV124 = UGC4879     (Bellazzini+, 2011)

HST-ACS photometry of the isolated dwarf galaxy VV124=UGC4879. Detection of the blue horizontal branch and identification of two young star clusters. Bellazzini M., Perina S., Galleti S., Oosterloo T. <Astron. Astrophys. 533, A37 (2011)> =2011A&A...533A..37B
ADC_Keywords: Galaxies, photometry ; Photometry, UBVRI ; Photometry, HST Keywords: galaxies: dwarf - Local Group - galaxies: structure - galaxies: stellar content - galaxies: individual: UGC4879 - galaxies: ISM Abstract: We present deep V and I photometry of the isolated dwarf galaxy VV124=UGC4879, obtained from archival images taken with the Hubble Space Telescope - Advanced Camera for Surveys. In the color-magnitude diagrams of stars at distances larger than 40" from the center of the galaxy, we clearly identify for the first time a well-populated old Horizontal Branch (HB). We show that the distribution of these stars is more extended than that of Red Clump stars. This implies that very old and metal poor populations becomes more and more dominant in the outskirts of VV124. We also identify a massive (M=1.2±0.2x104M) young (age=250±50Myr) star cluster (C1), as well as another of younger age (C2≲30±10Myr) with a mass similar to classical open clusters (M≤3.3±0.5x103M). Both clusters lie at projected distances smaller than 100pc from the center of the galaxy. Description: Magnitudes (in the ACS-WFC VEGAMAG system), positions and crowding parameter (CRO) for 69795 stars in the considered HST ACS-WFC field (dwarf galaxy VV124). In the paper the analysis is limited to the subsample of 44894 stars having CRO<0.3. However we relaxed this limit to CRO<1.0 to study the two star clusters, that are affected by extra-crowding. Hence, to allow the full reproducibility of our analysis, all stars with CRO<1.0 have been included in the present catalog. See the paper for the other selections applied on the original photometric sample. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file vv124.dat 78 69795 Stellar photometry in the dwarf galaxy VV124
Byte-by-byte Description of file: vv124.dat
Bytes Format Units Label Explanations
1- 6 I6 --- Seq Identification number 7- 13 F7.3 mag F606W HST/ACS F606W magnitude 14- 19 F6.3 mag e_F606W Error of the F606W magnitude 20- 26 F7.3 mag F814W HST/ACS F814W magnitude 27- 32 F6.3 mag e_F814W Error of the F814W magnitude 33- 38 F6.3 mag Cro DOLPHOT crowding parameter (see Dolphin, 2000PASP..112.1383D) (1) 39- 46 F8.2 pix Xpos x coordinate 47- 54 F8.2 pix Ypos y coordinate 55- 66 F12.7 deg RAdeg Right ascension in decimal degrees (J2000.0) 67- 78 F12.7 deg DEdeg Declination in decimal degrees (J2000.0)
Note (1): the crowding parameter tells how much brighter the star would be if nearby stars would not be fit simultaneously. The value is zero for an isolated star.
Acknowledgements: Michele Bellazzini, michele.bellazzini(at)
(End) Patricia Vannier [CDS] 20-Jul-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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