J/A+A/589/A1 Extreme Horizontal Branch stars in ω Cen (Randall+, 2016)
Pulsating hot O subdwarfs in omega Cen: mapping a unique instability strip on
the extreme horizontal branch.
Randall S.K., Calamida A., Fontaine G., Monelli M., Bono G., Alonso M.L.,
Van Grootel V., Brassard P., Chayer P., Catelan M., Littlefair S.,
Dhillon V.S., Marsh T.R.
<Astron. Astrophys. 589, A1 (2016)>
=2016A&A...589A...1R 2016A&A...589A...1R (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, globular ; Stars, horizontal branch ; Photometry ;
Spectroscopy
Keywords: stars: oscillations - stars: horizontal branch - subdwarfs -
globular clusters: individual: omega Cen - stars: variables: general
Abstract:
We present the results of an extensive survey for rapid pulsators
among Extreme Horizontal Branch (EHB) stars in ω Cen. The
observations performed consist of nearly 100 hours of time-series
photometry for several off-centre fields of the cluster, as well as
low-resolution spectroscopy for a partially overlapping sample. We
obtained photometry for some 300 EHB stars, for aro und half of which
we are able to recover light curves of sufficient quality to either
detect or place meaningful non-detection limits for rapid pulsations.
Based on the spectroscopy, we derive reliable values of logg, Teff and
logN(He)/N(H) for 38 targets, as well as good estimates of the
effective temperature for another nine targets, whose spectra are
slightly polluted by a close neighbour in the image. The survey
uncovered a total of five rapid variables with multi-periodic
oscillations between 85 and 125s. Spectroscopically, they form a
homogeneous group of hydrogen-rich subdwarf O stars clustered between
48000 and 54000K. For each of the variables we are able to measure
between two and three significant pulsations believed to constitute
independent harmonic oscillations. However, the interpretation of the
Fourier spectra is not straightforward due to significant fine
structure attributed to strong amplitude variations. In addition to
the rapid variables, we found an EHB star with an apparently periodic
luminosity variation of ∼2700s, which we tentatively suggest may be
caused by ellipsoidal variations in a close binary.
Description:
We make available the reduced spectra for the 47 EHB stars in omega
Cen that we derived atmospheric parameters for in Table 5. Each star
is associated with two files (the flux-calibrated and the
non-flux-calibrated spectrum), where the filename takes the format
s_xxxxxxx or fc_xxxxxxx, where xxxxxxx is the star's ID as listed in
Table 5. Filenames with s_ refer to non-flux calibrated spectra, while
the fc_ files are flux calibrated. The format of all the files is the
same, the first column being the wavelength in Angstroms, and the
second the relative flux for the s_ files and the absolute flux for
the fc_ files.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table5.dat 122 47 Atmospheric parameters inferred for our FORS2
spectroscopic sample of 47 EHB stars with
clean or slightly polluted spectra.
spfc/* . 47 Individual flux-calibrated spectra
sps/* . 47 Individual non-flux-calibrated spectra
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Byte-by-byte Description of file: table5.dat
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Bytes Format Units Label Explanations
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1- 7 I7 --- Name Star identification number
8 A1 --- n_Name [*] Note on Name (1)
10- 11 I2 h RAh Right ascension (J2000)
13- 14 I2 min RAm Right ascension (J2000)
16- 21 F6.3 s RAs Right ascension (J2000)
23 A1 --- DE- Declination sign (J2000)
24- 25 I2 deg DEd Declination (J2000)
27- 28 I2 arcmin DEm Declination (J2000)
30- 35 F6.3 arcsec DEs Declination (J2000)
37- 41 I5 K Teff Effective temperature
43- 46 I4 K e_Teff rms uncertainty on Teff
48- 52 F5.3 [cm/s+2] logg Suface gravity
54- 58 F5.3 [cm/s+2] e_logg rms uncertainty on logg
60- 65 F6.3 [-] log(He/H) Abundance He/H
67- 71 F5.3 [-] e_log(He/H) rms uncertainty on log(He/H)
73- 75 A3 --- r_Bmag [ACS/WFI] Instrument for Bmag and Rmag
77- 82 F6.3 mag Bmag ACS/WFI B magnitude
84- 88 F5.3 mag e_Bmag rms uncertainty on Bmag
90- 95 F6.3 mag Rmag ACS/WFI R magnitude
97-101 F5.3 mag e_Rmag rms uncertainty on Rmag
103-108 A6 --- Phot Instrument used for photometry
110-113 F4.2 % Det ? Detection limit above which pulsations
would have been detected for the targets
that overlap with our time-series
photometry sample
115-120 A6 --- OName Other name (2)
121-122 A2 --- n_OName [** ] Note on OName (1)
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Note (1): Notes as follows:
* = spectrum polluted by cooler star. The estimate of logg should be seen as
a lower limit only.
** = ID from Moehler et al. (2011A&A...526A.136M 2011A&A...526A.136M, [MDL2011] NNNNNN in Simbad)
Note (2): The rapid variables V1-V5 are indicated, as is the slow variable (SV).
V1-V4 = [RCF2011] V1-[RCF2011] V14 in Simbad
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Byte-by-byte Description of file: spfc/*
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Bytes Format Units Label Explanations
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1- 7 F7.2 0.1nm lambda Wavelength
9- 21 E13.7 10mW/m2/nm Flux Absolute flux (erg/cm2/s/Å)
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Byte-by-byte Description of file: sps/*
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Bytes Format Units Label Explanations
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1- 7 F7.2 0.1nm lambda Wavelength
9- 20 E12.7 --- Flux Relative Flux
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Acknowledgements:
Suzanna Randall, srandall(at)eso.org
(End) Suzanna Randall [ESO], Patricia Vannier [CDS] 19-Feb-2016