J/AJ/140/1500 RR Lyrae variables in the central region of M54 (Montiel+, 2010)
A search for RR Lyrae variables in the central region of M54.
Montiel E.J., Mighell K.J.
<Astron. J., 140, 1500-1505 (2010)>
=2010AJ....140.1500M 2010AJ....140.1500M
ADC_Keywords: Clusters, globular ; Stars, variable ; Photometry, HST
Keywords: globular clusters: individual (M54) - methods: statistical -
stars: variables: RR Lyrae - techniques: photometric
Abstract:
We have analyzed archival Hubble Space Telescope (HST) Wide Field
Planetary Camera 2 (WFPC2) observations of the central region of the
globular cluster M54. The 12 irregularly timed observations (6 F555W,
6 F814W) were reduced using the HSTphot stellar photometry package.
Our statistical analysis of the HSTphot photometry yielded 50 variable
stars that are likely RR Lyrae candidates. These candidates were
missed by previous ground-based searches for RR Lyraes due to the
extreme crowding in the core of M54. We performed two checks on our
sample of RR Lyrae candidates to determine how different they were
from the other variable candidates.
Description:
WFPC2 observations of M54 were taken as part of HST Program GO-6701
(PI: Ibata) to study the Sgr field. The first observations, U37GA401R
through U37GA406R consisted of six images in the F814W filter. A
second set of observations, U37GA407R through U37GA40CR, was made up
of six images in the F555W filter.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 41 12 Observation Log
table2.dat 72 50 RR Lyrae candidates
table3.dat 36 580 Photometry
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See also:
J/AJ/109/1086 : VI Photometry in M54 and Sgr Dwarf Galaxy (Sarajedini+ 1995)
J/AJ/118/1245 : Elemental abundances in five stars in M54 (Brown+, 1999)
J/AJ/119/1760 : M54 and Sgr dSph VI photometry (Layden+, 2000)
J/A+A/520/A95 : Abundances of red giants in M54 & Sgr dSph (Carretta+, 2010)
J/MNRAS/406/329 : Variable stars in M54 (Sollima+, 2010)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 9 A9 --- Set Data Set
11- 15 A5 --- Filt Filter name
17- 21 F5.1 s Texp Exposure time
23- 33 F11.5 d MJD Modified Julain Date
35- 38 A4 "h:m" Dt1 Difference in time between the first
observation and subsequent observations
40- 41 A2 --- OID Observation ID
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 4 A4 --- Name Star name, VCNN
6- 14 I9 --- ID Identification number (1)
16- 17 I2 h RAh Right ascension (J2000)
19- 20 I2 min RAm Right ascension (J2000)
22- 26 F5.2 s RAs Right ascension (J2000)
28 A1 --- DE- Declination sign (J2000)
29- 30 I2 deg DEd Declination (J2000)
32- 33 I2 arcmin DEm Declination (J2000)
35- 38 F4.1 arcsec DEs Declination (J2000)
40- 45 F6.3 mag <Vmag> Mean V magnitude
47- 51 F5.3 mag e_<Vmag> rms uncertainty on <Vmag>
53- 58 F6.3 mag <Imag> Mean I magnitude
60- 64 F5.3 mag e_<Imag> rms uncertainty on <Imag>
66- 72 F7.3 --- chi2 chi2 VI
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Note (1): The leftmost digit of the identification gives the WFPC2 CCD number
(1, 2, 3, or 4, for cameras PC1, WF2, WF3, or WF4, respectively).
The rightmost four digits give the x-coordinate of the star multiplied by 10.
The remaining four digits give the y-coordinate of the star multiplied by 10.
For example, the first star has an ID of 158546257, indicating that it is
found on the PC1 image at the (x, y) location of (625.7, 585.4).
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 4 A4 --- Name Star name
6- 7 A2 --- OID Observation identification; see Table 1
9- 14 F6.3 mag mag Observed magnitude in band
16- 20 F5.3 mag e_mag The 1σ error in mag
23 A1 --- Band [IV] Observed band (I for F814W, V for F555W)
26- 36 F11.5 d MJD Modified Julian Date of observation
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Patricia Vannier [CDS] 07-Jul-2012