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 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:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
vv124.dat 78 69795 Stellar photometry in the dwarf galaxy VV124
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Byte-by-byte Description of file: vv124.dat
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Bytes Format Units Label Explanations
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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 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)
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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.
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Acknowledgements:
Michele Bellazzini, michele.bellazzini(at)oabo.inaf.it
(End) Patricia Vannier [CDS] 20-Jul-2011