J/A+A/617/A6 Seven new pulsating sdA stars (Bell+, 2018)
The McDonald Observatory search for pulsating sdA stars.
Asteroseismic support for multiple populations.
Bell K.J., Pelisoli I., Kepler S.O., Brown W.R., Winget D.E., Winget K.I.,
Vanderbosch Z., Castanheira B.G., Hermes J.J., Montgomery M.H., Koester D.
<Astron. Astrophys. 617, A6 (2018)>
=2018A&A...617A...6B 2018A&A...617A...6B (SIMBAD/NED BibCode)
ADC_Keywords: Stars, variable ; Stars, subdwarf ; Photometry
Keywords: stars: oscillations - stars: variables: general - subdwarfs -
white dwarfs - Galaxy: stellar content
Abstract:
The nature of the recently identified "sdA" spectroscopic class of
star is not well understood. The thousands of known sdAs have
H-dominated spectra, spectroscopic surface gravities intermediate to
main sequence stars and isolated white dwarfs, and effective
temperatures below the lower limit for He-burning subdwarfs. Most are
likely products of binary stellar evolution, whether extremely
low-mass white dwarfs and their precursors, or blue stragglers in the
halo.
Stellar eigenfrequencies revealed through time series photometry of
pulsating stars sensitively probe stellar structural properties. The
properties of pulsations exhibited by any sdA stars would contribute
importantly to our developing understanding of this class.
We extend our photometric campaign to discover pulsating extremely
low-mass white dwarfs from McDonald Observatory to target sdA stars
classified from SDSS spectra. We also obtain follow-up time series
spectroscopy to search for binary signatures from four new pulsators.
Out of 23 sdA stars observed, we clearly detect stellar pulsations in
seven. Dominant pulsation periods range from 4.6 minutes to
12.3 hours, with most on hour timescales. We argue specific
classifications for some of the new variables, identifying both
compact and likely main sequence dwarf pulsators, along with a
candidate low-mass RR Lyrae star.
With dominant pulsation periods spanning orders of magnitude, the
pulsational evidence supports the emerging narrative that the sdA
class consists of multiple stellar populations. Since multiple types
of sdA exhibit stellar pulsations, follow-up asteroseismic analysis
can be used to probe the precise evolutionary natures and stellar
structures of these individual subpopulations.
Description:
This work identifies seven new photometrically variable pulsating
stars among the targets classified as "sdA" from Sloan Digital Sky
Survey spectroscopy. We provide the light curves of these new
variables. All data we obtained with a Princeton Instruments ProEM
camera on the McDonald Observatory 2.1-meter Otto Struve Telescope.
Circular aperture photometry was measured for the targets and
comparison stars with the IRAF script ccd_hsp (2002A&A...389..896K 2002A&A...389..896K).
The target flux was divided by the mean comparison star flux and a
low-order polynomial fit, and a barycentric correction was applied to
the timestamps with the Wqed tools (2013ascl.soft04004T). These light
curves are in the format output by Wqed, with headers defined in
2009JPhCS.172a2081T 2009JPhCS.172a2081T.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
stars.dat 63 7 List of studied stars
list.dat 65 30 List of light curves
lc/* . 30 Individual light curve files
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See also:
J/ApJ/839/23 : Subdwarf A stars vs ELM WDs radial velocities (Brown+, 2017)
Byte-by-byte Description of file: stars.dat
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Bytes Format Units Label Explanations
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1- 4 A4 --- --- [SDSS]
6- 24 A19 --- SDSS SDSS designation (JHHMMSS.ss+DDMMSS.s)
26- 27 I2 h RAh Right ascension (J2000)
29- 30 I2 min RAm Right ascension (J2000)
32- 36 F5.2 s RAs Right ascension (J2000)
38 A1 --- DE- Declination sign (J2000)
39- 40 I2 deg DEd Declination (J2000)
42- 43 I2 arcmin DEm Declination (J2000)
45- 48 F4.1 arcsec DEs Declination (J2000)
50- 63 A14 --- SName Short name
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Byte-by-byte Description of file: list.dat
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Bytes Format Units Label Explanations
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1- 14 A14 --- SName Short name
16- 25 A10 "date" Obs.date Observation date
27- 28 I2 s ExpTime Exposure time
30- 32 F3.1 h Dur Duration
34- 65 A32 --- FileName Name of the light curve file in subdirectory lc
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Byte-by-byte Description of file (#): lc/*
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Bytes Format Units Label Explanations
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1- 10 F10.3 s Time Time since start of run
12- 24 E13.10 --- RFlux Relative flux
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Acknowledgements:
Keaton J. Bell, bell(at)mps.mpg.de
(End) Keaton J. Bell [MPS], Patricia Vannier [CDS] 04-Jun-2018