J/A+A/463/589 Variables stars in NGC 362 (Szekely+, 2007)
RR Lyrae stars in the southern globular cluster NGC 362.
Szekely P., Kiss L.L., Jackson R., Derekas A., Csak B., Szatmary K.
<Astron. Astrophys. 463, 589 (2007)>
=2007A&A...463..589S 2007A&A...463..589S
ADC_Keywords: Clusters, globular ; Stars, variable ; Radial velocities ;
Photometry, CCD
Keywords: stars: variables: general - stars: variables: RR Lyr -
globular clusters: individual: NGC 362
Abstract:
NGC 362 is a bright southern globular cluster in the foreground of the
Small Magellanic Cloud (SMC), for which no extensive variability
survey has ever been done. Finding regularly pulsating RR Lyrae stars
in the cluster can lead to improved metallicity and distance estimates
of the system, while other types of variable objects may be used to
confirm the results. Time-series CCD photometric observations have
been obtained. Light curves have been derived with both profile
fitting photometry and image subtraction. We developed a simple method
to convert flux phase curves to magnitudes, which allows the use of
empirical light curve shape vs. physical parameters calibrations.
Periods and light curve parameters of the detected variable stars have
been determined with Fourier analysis, phase dispersion minimization
and string-length minimization. Using the RR Lyrae metallicity and
luminosity calibrations, we have determined the relative iron
abundances and absolute magnitudes of the stars. The color-magnitude
diagram has been fitted with Yale-Yonsei isochrones to determine
reddening and distance independently. For five RR Lyrae stars we
obtained radial velocity measurements from optical spectra.
We found 45 RR Lyr stars, of which the majority are new discoveries.
While most of them are cluster members, as shown by their radial
velocities and positions in the color-magnitude diagram, we also see a
few stars in the galactic field and in the outskirts of the SMC. About
half of the RR Lyraes exhibit light curve changes (Blazhko effect).
The RR Lyrae-based metallicity of the cluster is [Fe/H]=-1.16±0.25,
the mean absolute magnitude of the RR Lyrae stars is
M_V=0.82±0.04mag implying a distance of 7.9±0.6kpc. The mean
period of RRab stars is 0.585±0.081days. These properties place NGC
362 among the Oosterhoff type I globular clusters. The isochrone fit
implies a slightly larger distance of 9.2±0.5kpc and an age of
11±1Gyr.
We also found 11 eclipsing binaries, 14 pulsating stars of other
types, including classical Cepheids in the SMC and 15 variable stars
with no firm classification.
NGC 362 hosts a large number of RR Lyrae stars, which makes the
cluster a potentially important test object for studying the Blazhko
effect in a chemically homogeneous environment.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
stars.dat 65 6895 Celestial coordinates and standard V and V-I of
NGC 362 stars (only the central CCD segment)
varstars.dat 54 84 Variables coordinates
isis/* . 41 Flux light curves obtained using ISIS 2.1 software
for variable stars in NGC362
psf/* . 44 Magnitude light curves from IRAF PSF photometry
for some variable stars in NGC362
rv/* . 3 Radial velocities for 3 RR Lyr stars (HJD, RV)
rvp/* . 3 Radial velocities for 3 RR Lyr stars (phase, RV)
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See also:
J/A+AS/93/311 : Relative proper motions in NGC 362 (Tucholke 1992)
J/AJ/106/1508 : Dynamics of globular cluster NGC 362 (Fischer+ 1993)
J/AJ/122/2569 : VI photometry of NGC 288, 362 and 1851 (Bellazzini+, 2001)
J/MNRAS/351/1204 : IR Photometry of 10 Galactic Globular Clust. (Valenti+ 2004)
Byte-by-byte Description of file: stars.dat
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Bytes Format Units Label Explanations
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1- 2 I2 h RAh Right ascension (J2000)
3 A1 --- --- [:]
4- 5 I2 min RAm Right ascension (J2000)
6 A1 --- --- [:]
7- 12 F6.3 s RAs Right ascension (J2000)
14 A1 --- DE- Declination sign (J2000)
15- 16 I2 deg DEd Declination (J2000)
17 A1 --- --- [:]
18- 19 I2 arcmin DEm Declination (J2000)
20 A1 --- --- [:]
21- 25 F5.2 arcsec DEs Declination (J2000)
27- 31 A5 --- --- [J2000] Epoch
33- 40 F8.3 pix xpos x coordinate
42- 49 F8.3 pix ypos y coordinate
51- 57 F7.4 mag Vmag standard V magnitude
59- 65 F7.4 mag V-I standard V-I magnitude
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Byte-by-byte Description of file: varstars.dat
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Bytes Format Units Label Explanations
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1- 3 A3 --- VName Variable number
5- 6 I2 h RAh Right ascension (J2000)
7 A1 --- --- [:]
8- 9 I2 min RAm Right ascension (J2000)
10 A1 --- --- [:]
11- 16 F6.3 s RAs Right ascension (J2000)
18 A1 --- DE- Declination sign (J2000)
19- 20 I2 deg DEd Declination (J2000)
21 A1 --- --- [:]
22- 23 I2 arcmin DEm Declination (J2000)
24 A1 --- --- [:]
25- 29 F5.2 arcsec DEs Declination (J2000)
31- 34 A4 --- isis Name of file in isis subdirectory (Flux vs HJD)
36- 39 A4 --- psf Name of file in psf subdirectory (dmag vs HJD)
41- 46 A6 --- rv Name of file in rv subdirectory (RV vs HJD)
48- 54 A7 --- rvp Name of file in rvp subdirectory (RV vs phase)
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Byte-by-byte Description of file: isis/*
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Bytes Format Units Label Explanations
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1- 14 F14.6 d HJD Heliocentric Julian Date
16- 28 F13.5 --- Flux Flux values calculated by ISIS 2.1
30- 37 F8.6 --- --- ? some unknown value from ISIS...
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Byte-by-byte Description of file: psf/*
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Bytes Format Units Label Explanations
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1- 8 F8.6 --- Phase Pulsational phase (roughly calculated)
10- 14 F5.3 mag dmag Differential magnitude
16- 20 F5.3 mag e_dmag Error of PSF photometry
22- 33 F12.4 d HJD Heliocentric Julian Date
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Byte-by-byte Description of file: rv/*
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Bytes Format Units Label Explanations
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1- 12 F12.4 d HJD Heliocentric Julian Date
14- 21 F8.4 km/s RV Radial velocity
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Byte-by-byte Description of file: rvp/*
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Bytes Format Units Label Explanations
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1- 8 F8.6 --- Phase Pulsational phase
10- 17 F8.4 km/s RV Radial velocity
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Acknowledgements:
Peter Szekely, pierre(at)physx.u-szeged.hu
(End) P. Szekely, [Univ. of Szeged, Hungary], P. Vannier [CDS] 30-Nov-2006