The Formation of Subdwarf A-type Stars

Yu, Jinlong; Li, Zhenwei; Zhu, Chengliang; Wang, Zhaojun; Liu, He-Lei; Guo, Sufen; Han, Zhanwen; Chen, Xuefei

doi:10.3847/1538-4357/ab44b5

Cited by 14 publications

(9 citation statements)

References 53 publications

(71 reference statements)

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“…We find that stellar atmospherederived luminosity estimates are in excellent agreement with Gaia parallax measurements at effective temperatures T eff > 9,500 K. However, many of the coolest <9,000 K objects, where the hydrogen Balmer lines lose their sensitivity to temperature and gravity (Strom 1969), are subdwarf A-type stars (Kepler et al 2015(Kepler et al , 2016. Gaia parallax shows that most subdwarf A-type stars are mis-identified metal poor halo stars Pelisoli et al 2017Pelisoli et al , 2018aPelisoli et al ,b, 2019Yu et al 2019); at these temperatures, such stars are also called field blue stragglers (e.g. Bond & MacConnell 1971;Preston & Sneden 2000).…”

Section: Introductionmentioning

confidence: 99%

The ELM Survey. VIII. Ninety-eight Double White Dwarf Binaries

Brown

Kilic

Kosakowski

et al. 2020

ApJ

105

156

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We present the final sample of 98 detached double white dwarf (WD) binaries found in the Extremely Low Mass (ELM) Survey, a spectroscopic survey targeting <0.3 M ⊙ He-core WDs completed in the Sloan Digital Sky Survey footprint. Over the course of the survey we observed ancillary low mass WD candidates like GD 278, which we show is a P = 0.19 d double WD binary, as well as candidates that turn out to be field blue straggler/subdwarf A-type stars with luminosities too large to be WDs given their Gaia parallaxes. Here, we define a clean sample of ELM WDs that is complete within our target selection and magnitude range 15 < g 0 < 20 mag. The measurements are consistent with 100% of ELM WDs being 0.0089 < P < 1.5 d double WD binaries, 35% of which belong to the Galactic halo. We infer these are mostly He+CO WD binaries given the measurement constraints. The merger rate of the observed He+CO WD binaries exceeds the formation rate of stable mass transfer AM CVn binaries by a factor of 25, and so the majority of He+CO WD binaries must experience unstable mass transfer and merge. The shortest-period systems like J0651+2844 are signature LISA verification binaries that can be studied with gravitational waves and light.

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Section: Introductionmentioning

confidence: 99%

The ELM Survey. VIII. Ninety-eight Double White Dwarf Binaries

Brown

Kilic

Kosakowski

et al. 2020

ApJ

105

156

View full text Add to dashboard Cite

show abstract

“…Low-mass WDs at <9000 K temperatures exist, but subdwarf A-type stars are 100 times more common at these temperatures (Kepler et al 2015(Kepler et al , 2016. Subdwarf A-type stars are mostly field blue stragglers and metal-poor halo stars (Brown et al 2017;Pelisoli et al 2017Pelisoli et al , 2018aPelisoli et al , 2018bYu et al 2019).…”

Section: Elm Wd Target Selectionmentioning

confidence: 99%

The ELM Survey. IX. A Complete Sample of Low-mass White Dwarf Binaries in the SDSS Footprint

Brown

Kilic

Kosakowski

et al. 2022

ApJ

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We present the discovery of 17 double white dwarf (WD) binaries from our ongoing search for extremely low mass (ELM) < 0.3 M ⊙ WDs, objects that form from binary evolution. Gaia parallax provides a new means of target selection that we use to evaluate our original ELM Survey selection criteria. Cross-matching the Gaia and Sloan Digital Sky Survey (SDSS) catalogs, we identify an additional 36 ELM WD candidates with 17 < g < 19 mag and within the 3σ uncertainties of our original color selection. The resulting discoveries imply the ELM Survey sample was 90% complete in the color range −0.4 < (g − r)0 < −0.1 mag (approximately 9000 K < T eff < 22,000 K). Our observations complete the sample in the SDSS footprint. Two newly discovered binaries, J123950.370−204142.28 and J232208.733+210352.81, have orbital periods of 22.5 and 32 minutes, respectively, and are future Laser Interferometer Space Antenna gravitational-wave sources.

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“…These stars are most consistent with subdwarf A-type stars (sdAs). sdA stars have hydrogen-rich spectra and surface gravities between those of main-sequence stars and isolated WDs, but their effective temperatures are below the zero-age horizontal branch (Kepler et al 2016;Bell et al 2018;Yu et al 2019). J1355+1956 is a composite spectrum binary, which we decomposed into its components, and here we report the parameters only for the hot star.…”

Section: Comparison To the Elm Surveymentioning

confidence: 99%

Extremely Low-mass White Dwarf Stars Observed in Gaia DR2 and LAMOST DR8

Wang

Németh

Luo

et al. 2022

ApJ

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We present the first results from our ongoing project to study extremely low-mass (ELM) white dwarfs (WDs) (M ≤ 0.3M ☉) with the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) spectra. Based on the LAMOST DR8 spectral database, we analyzed 136 ELM WD candidates selected from Gaia DR2 data and 12 known objects previously identified by the ELM Survey. The atmospheric parameters and radial velocities of these stars were obtained by fitting the LAMOST low-resolution spectra. After comparing the atmospheric parameters of the 12 known objects from this work to the results reported by the ELM Survey, we demonstrated the potential of LAMOST spectra in probing into the nature of ELM WDs. Based on the atmospheric parameters and Gaia EDR3 data, we identified 21 new high-probability ELM WDs with masses M ≤ 0.3M ☉ and parallax estimates that agree to within a factor of 3. Two of them, J0338+4134 and J1129+4715, show significant radial velocity variability and are very likely to be binary systems containing at least one ELM WD.

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The Formation of Subdwarf A-type Stars

Cited by 14 publications

References 53 publications

The ELM Survey. VIII. Ninety-eight Double White Dwarf Binaries

The ELM Survey. VIII. Ninety-eight Double White Dwarf Binaries

The ELM Survey. IX. A Complete Sample of Low-mass White Dwarf Binaries in the SDSS Footprint

Extremely Low-mass White Dwarf Stars Observed in Gaia DR2 and LAMOST DR8

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