Hot Subdwarf Atmospheric Parameters, Kinematics, and Origins Based on 1587 Hot Subdwarf Stars Observed in Gaia DR2 and LAMOST DR7

Luo, Yangping; Németh, P.; Wang, Kun; Wang, Xi; Han, Zhanwen

doi:10.3847/1538-4365/ac11f6

Cited by 28 publications

(55 citation statements)

References 86 publications

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“…The main reason is that the atmospheric parameters of those double-lined binaries are more complicated to be determined and they are therefore often removed from analyses of larger samples (e.g. Luo et al 2021). Only few composite sdB binaries have been analysed in detail so far (e.g.…”

Section: Sample Selectionmentioning

confidence: 99%

“…The atmospheric parameters effective temperature T eff , surface gravity log g, and helium abundance log n(He)/n(H) for the hydrogen-rich sdB and sdOB stars (log n(He)/n(H) < −1.0) have been taken from the literature (Heber et al 1987;Saffer et al 1994;Maxted et al 2001;Edelmann et al 2003;Lisker et al 2005;Ströer et al 2007;Charpinet et al 2008;Hirsch 2009;Østensen et al 2010a, 2010bNemeth et al 2012;Geier et al 2013aGeier et al , 2014Geier et al , 2015bGeier et al , 2017cLuo et al 2016Luo et al , 2019Luo et al , 2021Lei et al 2018Lei et al , 2019Lei et al , 2020Kepler et al 2019;Hogg et al 2020), if available.…”

Section: Atmospheric Parametersmentioning

confidence: 99%

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Radial velocity variability and evolution of hot subdwarf stars

Geier,

Dorsch,

Pelisoli

et al. 2022

Preprint

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Hot subdwarf stars represent a late and peculiar stage in the evolution of low-mass stars, because they are likely formed by close binary interactions. Here we performed a radial velocity (RV) variability study of a sample of 646 hot subdwarfs with multi-epoch radial velocities from Sloan Digital Sky Survey (SDSS) and Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST) spectra. Atmospheric parameters and RVs were taken from the literature. For stars with archival spectra but without literature values, we determined the parameters by fitting model atmospheres. In addition, we redetermined the atmospheric parameters and RVs for all the He-enriched sdO/Bs. This large sample allowed us to study RV-variability as a function of the location in the T eff − log gand T eff − log n(He)/n(H) diagrams in a statistically significant way. As diagnostics we used the fraction of RV-variable stars and the distribution of the maximum RV variations ∆RV max . Both indicators turned out to be quite inhomogeneous across the studied parameter ranges. A striking feature is the completely different behaviour of He-poor and He-rich hot subdwarfs. While the former have a high fraction of close binaries, almost no significant RV variations could be detected for the latter. This led us to the conclusion that there likely is no evolutionary connection between these subtypes. Intermediate He-rich-and extreme He-rich sdOB/Os on the other hand are likely related. We conclude further that the vast majority of this population is formed via one or several binary merger channels. Hot subdwarfs with temperatures cooler than ∼ 24 000 K tend to show less and smaller RV-variations. These objects might constitute a new subpopulation of binaries with longer periods and late-type or compact companions. The RV-variability properties of the extreme horizontal branch (EHB) and corresponding post-EHB populations of the He-poor hot subdwarfs match and confirm the predicted evolutionary connection between them. Stars found below the canonical EHB at somewhat higher surface gravities show large RV-variations and a high RV-variability fraction, which is consistent with most of them being low-mass EHB stars or progenitors of low-mass helium white dwarfs in close binaries.

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Section: Sample Selectionmentioning

confidence: 99%

Section: Atmospheric Parametersmentioning

confidence: 99%

Radial velocity variability and evolution of hot subdwarf stars

Geier,

Dorsch,

Pelisoli

et al. 2022

Preprint

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“…We checked the obtained candidates by cross-validating with the catalog of Hot subdwarfs published by Luo et al (2021) and Geier et al (2017) and manually validating. Manual validation results of the 2393 Hot subdwarf candidates are presented in Table 4.…”

Section: Modelling and Performance Analysismentioning

confidence: 99%

“…Following the works of Luo et al (2016) and Luo et al (2021), atmospheric parameters (Effective temperature T ef f , surface gravity log(g), and He abundances log(nHe/nH)) for the 25 newly identified Hot subdwarf stars were obtained by fitting the LAMOST spectra with TLUSTY/SYNSPEC non-LTE synthetic spectra (Hubeny & Lanz 1995. All the parameters of the 25 newly discovered Hot subdwarfs are listed in Table 5, which includes the LAMOST designation, right ascension, declination, effective temperature, surface gravity, He abundance, the SNR in the µ-band, apparent magnitudes in the µ-band and g-band of SDSS DR9, and apparent magnitudes in the g-band of Gaia DR2.…”

Section: Modelling and Performance Analysismentioning

confidence: 99%

“…Scientists have experimented with other methods to identify HOT subdwarfs from the LAMOST catalog. Luo et al (2021) identified 1587 Hot subdwarfs using the spectra released by the LAMOST and the catalog of Hot subdwarf candidates released by Gaia DR2. With the development of machine learning techniques, especially the deep learning techniques, Bu et al (2017) used machine learning methods to search for Hot subdwarf candidates from the LAMOST DR1 and obtained 10,000 candidates, and Lei et al (2019) further identified 56 Hot subdwarfs from these candidates.…”

Section: Introductionmentioning

confidence: 99%

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A Robust Hot Subdwarfs Identification Method Based on Deep Learning

Tan¹,

Mei²,

Liu³

et al. 2022

Preprint

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Hot subdwarf star is a particular type of star that is crucial for studying binary evolution and atmospheric diffusion processes. In recent years, identifying Hot subdwarfs by machine learning methods has become a hot topic, but there are still limitations in automation and accuracy. In this paper, we proposed a robust identification method based on the convolutional neural network (CNN). We first constructed the dataset using the spectral data of LAMOS DR7-V1. We then constructed a hybrid recognition model including an 8-class classification model and a binary classification model. The model achieved an accuracy of 96.17% on the testing set. To further validate the accuracy of the model, we selected 835 Hot subdwarfs that were not involved in the training process from the identified LAMOST catalog (2428, including repeated observations) as the validation set. An accuracy of 96.05% was achieved. On this basis, we used the model to filter and classify all 10,640,255 spectra of LAMOST DR7-V1, and obtained a catalog of 2393 Hot subdwarf candidates, of which 2067 have been confirmed. We found 25 new Hot subdwarfs among the remaining candidates by manual validation. The overall accuracy of the model is 87.42%. Overall, the model presented in this study can effectively identify specific spectra with robust results and high accuracy, and can be further applied to the classification of large-scale spectra and the search of specific targets.

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A seven-Earth-radius helium-burning star inside a 20.5-min detached binary

Lin,

Wu,

Xiong

et al. 2024

Nat Astron

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Binary evolution theory predicts that the second common envelope (CE) ejection can produce low-mass (0.32 − 0.36 M ⊙ ) subdwarf B (sdB) stars inside ultrashort-orbital-period binary systems as their helium cores are ignited under nondegenerate conditions. With the orbital decay driven by radiation of gravitational waves (GWs), the minimum orbital period that an sdB binary formed in this channel can reach before the Roche-lobe overflow is ∼ 20 minutes. However, only four sdB binaries with orbital periods below an hour have been reported so far, while none of them has an orbital period approaching the above theoretical limit. This leads to an unclear role of the second CE ejection in forming ultracompact sdB binaries and a blocked link between detached helium-burning-star binaries AM CVn stars. Here we report the discovery of a 20.5-minute-orbital-period ellipsoidal binary, TMTS J052610.43+593445.1, in which the visible helium-burning sdB star is being tidally deformed by an invisible carbon-oxygen white dwarf (WD) companion. This sdB star is inferred to have a mass of ∼ 0.33 M ⊙ , approaching that of the helium-ignition limit. Owing to the low-mass sdB star, WD companion, and extremely short orbital period, this system provides the first clear case to justify the formation of sdB binaries through the nondegenerate channel of second CE ejection. In particular, the radius of this low-mass sdB star is only 0.066 R ⊙ , about seven Earth radii, representing the most compact nondegenerate star ever known. As the shortest-orbital-period single-degenerate detached binary discovered up to date, TMTS J052610.43+593445.1 provides a crucial bridge to map the binary evolution scheme from the second CE ejection to the formation of AM CVn stars having a helium-star donor, and will serve as a crucial verification binary of space-borne gravitational-wave detectors in the future. −0.24 E(B −V ) SED (mag) 0.387 +0.008 −0.009 T eff,sd,re (K) 25410 ± 370 log(g) sd,re (cm s −1 ) 6.352 ± 0.068 Light-curve analysis i (deg) 68.2 +3.7 −5.2 M WD (M ⊙ ) 0.735 +0.075 −0.069 M sd,re (M ⊙ ) 0.360 +0.080 −0.071 R sd,re (R ⊙ ) 0.0661 ± 0.0054 T 0,re (BJD TDB ) 2459933.175697 +0.000016 −0.000017 a (R ⊙ ) 0.255 ± 0.011 Derived parameters (ν sd sin i) cal (km s −1 ) 216 +18 −19 Ṗorb /P orb (yr −1 ) −1.72 +0.40 −0.47 ×10 −7 A 2.49 +0.72 −0.60 ×10 −22 4-year LISA SNR 33.6 +9.7 −8.0 3-month LISA SNR 3.3 +1.

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Hot Subdwarf Atmospheric Parameters, Kinematics, and Origins Based on 1587 Hot Subdwarf Stars Observed in Gaia DR2 and LAMOST DR7

Cited by 28 publications

References 86 publications

Radial velocity variability and evolution of hot subdwarf stars

Radial velocity variability and evolution of hot subdwarf stars

A Robust Hot Subdwarfs Identification Method Based on Deep Learning

A seven-Earth-radius helium-burning star inside a 20.5-min detached binary

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