J/ApJ/748/91 Blue straggler stars in M75 (Contreras+, 2012)
The unimodal distribution of blue straggler stars in M75 (NGC 6864).
Contreras Ramos R., Ferraro F.R., Dalessandro E., Lanzoni B., Rood R.T.
<Astrophys. J., 748, 91 (2012)>
=2012ApJ...748...91C 2012ApJ...748...91C
ADC_Keywords: Clusters, globular ; Photometry, HST ; Stars, blue
Keywords: binaries: close - blue stragglers -
globular clusters: individual (M75, NGC 6864) - stars: evolution
Abstract:
We have used a combination of multiband high-resolution and wide-field
ground-based observations to image the Galactic globular cluster M75
(NGC 6864). The extensive photometric sample covers the entire cluster
extension, from the very central regions out to the tidal radius,
allowing us to determine the center of gravity and to construct the
most extended star density profile ever published for this cluster. We
also present the first detailed star counts in the very inner regions.
The star density profile is well reproduced by a standard King model
with core radius rc∼5.4" and intermediate-high concentration c∼1.75.
The present paper presents a detailed study of the blue straggler star
(BSS) population and its radial distribution. A total of 62 bright
BSSs (with mF255W≲21, corresponding to mF555W≲20) have been
identified, and they have been found to be highly segregated in the
cluster core. No significant upturn in the BSS frequency has been
observed in the outskirts of M75, in contrast to several other
clusters studied with the same technique. This observational fact is
quite similar to what has been found in M79 (NGC 1904) by Lanzoni et
al. (2007ApJ...663.1040L 2007ApJ...663.1040L). Indeed, the BSS radial distributions in the
two clusters are qualitatively very similar, even if in M75 the
relative BSS frequency seems to decrease significantly faster than in
M79: it decreases by a factor of five (from 3.4 to 0.7) within 1rc.
Such evidence indicates that the vast majority of the cluster heavy
stars (binaries) have already sunk to the core.
Description:
The high-resolution (HR) data set: The inner and most crowded region
of the cluster has been sampled using the exquisite-quality images
from the Wide Field Planetary Camera 2 (WFPC2) on board HST. These
data were obtained under program GO 11975 (PI F. Ferraro) on 2009
March.
The wide-field (WF) data set. The HST/WFPC2 data were complemented
with a set of WF images acquired in the V and I bands during an
observing run at the 2.2m ESO-MPI telescope at ESO (La Silla) in 2002
June using the Wide Field Imager (WFI).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 65 62 The blue straggler star (BSS) population of M75
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See also:
B/hst : HST Archived Exposures Catalog (STScI, 2007)
J/A+A/554/A81 : Abundances of 16 giants in M75 (Kacharov+, 2013)
J/A+A/483/183 : Catalogue of Blue Stragglers (Moretti+, 2008)
J/ApJ/681/311 : Blue stragglers in NGC 2419 (Dalessandro+, 2008)
J/A+A/469/529 : UBVI photometry of NGC 6864 (Kravtsov+, 2007)
J/ApJ/663/267 : Blue straggler population of M5 (Lanzoni+, 2007)
J/ApJ/522/983 : M80 blue straggler stars (Ferraro+, 1999)
J/A+A/324/915 : Blue stragglers in M3 (Ferraro+ 1997)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 3 A3 --- --- [BSS]
4- 5 I2 --- Seq Running sequence number
7- 17 F11.7 deg RAdeg [301.49/301.56] Right Ascension (J2000) (1)
19- 29 F11.7 deg DEdeg [-21.95/-21.90] Declination (J2000) (1)
31- 37 F7.3 arcsec Dist [0.401/143.024] Distance from cluster center
39- 44 F6.3 mag F225W [19.50/21.34]? HST/WFPC2 F255W filter magnitude
46- 51 F6.3 mag F336W [19.19/20.61]? HST/WFPC2 F336W filter magnitude
53- 58 F6.3 mag F555W [18.65/20.21] HST/WFPC2 F555W filter magnitude
60- 65 F6.3 mag F814W [18.34/19.23]? HST/WFPC2 F814W filter magnitude
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Note (1): The position residuals are of the order of ∼0.2" in both right
ascension and declination. See section 2.3 for further explanations.
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 11-Oct-2013