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  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., et al. (2018). The McDonald Observatory search for pulsating sdA stars: Asteroseismic support for multiple populations. Astronomy and Astrophysics, 617: A6. doi:10.1051/0004-6361/201833279.

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Item Permalink: http://hdl.handle.net/21.11116/0000-0003-BA6C-3 Version Permalink: http://hdl.handle.net/21.11116/0000-0003-BA6D-2
Genre: Journal Article

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 Creators:
Bell, Keaton J.1, Author              
Pelisoli, I., Author
Kepler, S. O., Author
Brown, W. R., Author
Winget, D. E., Author
Winget, K. I., Author
Vanderbosch, Z., Author
Castanheira, B. G., Author
Hermes, J. J., Author
Montgomery, M. H., Author
Koester, D., Author
Affiliations:
1Max Planck Research Group in Stellar Ages and Galactic Evolution (SAGE), Max Planck Institute for Solar System Research, Max Planck Society, ou_2265636              

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Free keywords: stars: oscillations / stars: variables: general / subdwarfs / white dwarfs / Galaxy: stellar content
 Abstract: Context. The nature of the recently identified “sdA” spectroscopic class of stars is not well understood. The thousands of known sdAs have H-dominated spectra, spectroscopic surface gravity values between 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. Aims. Stellar eigenfrequencies revealed through time series photometry of pulsating stars sensitively probe stellar structural properties. The properties of pulsations exhibited by sdA stars would contribute substantially to our developing understanding of this class. Methods. We extend our photometric campaign to discover pulsating extremely low-mass white dwarfs from the 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. Results. Out of 23 sdA stars observed, we clearly detect stellar pulsations in 7. Dominant pulsation periods range from 4.6 min to 12.3 h, with most on timescales of approximately one hour. 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. Conclusions. 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.

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Language(s): eng - English
 Dates: 2018
 Publication Status: Published online
 Pages: -
 Publishing info: -
 Table of Contents: -
 Rev. Type: Peer
 Identifiers: DOI: 10.1051/0004-6361/201833279
 Degree: -

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Title: Astronomy and Astrophysics
  Other : Astron. Astrophys.
Source Genre: Journal
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Publ. Info: Les Ulis Cedex A France : EDP Sciences
Pages: - Volume / Issue: 617 Sequence Number: A6 Start / End Page: - Identifier: Other: 1432-0746
ISSN: 0004-6361
CoNE: https://pure.mpg.de/cone/journals/resource/954922828219_1