Spectral analysis of sdB stars from the Hamburg Quasar Survey

Edelmann, H.; Heber, U.; Hagen, H. J.; Lemke, Michael; Dreizler, S.; Napiwotzki, R.; Engels, D.

doi:10.1051/0004-6361:20030135

Cited by 147 publications

(233 citation statements)

References 55 publications

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“…The hotter stars tend to have a higher He abundance than their cooler counterparts, as expected (e.g. Edelmann et al 2003), and as such are predominantly the p-mode pulsators. There are two stars that do not follow the general trend in the plot: the g-mode pulsator LS IV-14 116 which has both high helium abundance and a high temperature, and the cool g-mode pulsator KIC 1718290.…”

Section: Introductionsupporting

confidence: 67%

Three new pulsating sdB stars discovered with SuperWASP

Holdsworth

Østensen

Smalley

et al. 2017

Mon. Not. R. Astron. Soc.

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We present an analysis of three new pulsating subdwarf B stars discovered in the SuperWASP archive. Two of the stars, J1938+5609 and J0902-0720, are p-mode pulsators; J1938+5609 shows a pulsation at 231.62 d −1 (P = 373 s; 2681 µHz) with an amplitude of 4 mmag, whereas J0902-0720 pulsates at frequencies 636.74 d −1 (P = 136 s; 7370 µHz) and 615.34 d −1 (P = 140 s; 7122 µHz), with amplitudes 7.27 and 1.53 mmag, respectively. The third star, J2344-3427, is a hybrid pulsator with a p-mode frequency at 223.16 d −1 (P = 387 s; 2583µHz) and a corresponding amplitude of 1.5 mmag, and g modes in the frequency range 8.68 − 28.56 d −1 (P = 3025 − 9954 s; 100 − 331µHz) and amplitudes between 0.76 and 1.17 mmag. Spectroscopic results place J1938+5609 and J2344-3427 among the long-period or hybrid pulsators, suggesting there may be further modes in these stars below our detection limits, with J0902-0720 placed firmly amongst the p-mode pulsators.

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Section: Introductionsupporting

confidence: 67%

Three new pulsating sdB stars discovered with SuperWASP

Holdsworth

Østensen

Smalley

et al. 2017

Mon. Not. R. Astron. Soc.

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“…In an ongoing project Green et al (2008) analyse all hot subdwarfs from the PG survey down to 14.0 mag. The sample of hot subdwarf stars analysed in the course of the SPY survey reaches down to 16.5 mag Ströer et al 2007), quite similar to the sample of sdBs from the Hamburg Quasar Survey analysed by Edelmann et al (2003).…”

Section: Final Target Samplementioning

confidence: 54%

The MUCHFUSS project – searching for hot subdwarf binaries with massive unseen companions

Geier

Hirsch

Tillich

et al. 2011

A&A

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104

109

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The project Massive Unseen Companions to Hot Faint Underluminous Stars from SDSS (MUCHFUSS) aims at finding sdBs with compact companions like supermassive white dwarfs (M > 1.0 M ), neutron stars or black holes. The existence of such systems is predicted by binary evolution theory and recent discoveries indicate that they are likely to exist in our Galaxy. A determination of the orbital parameters is sufficient to put a lower limit on the companion mass by calculating the binary mass function. If this lower limit exceeds the Chandrasekhar mass and no sign of a companion is visible in the spectra, the existence of a massive compact companion is proven without the need for any additional assumptions. We identified about 1100 hot subdwarf stars from the SDSS by colour selection and visual inspection of their spectra. Stars with high velocities have been reobserved and individual SDSS spectra have been analysed. In total 127 radial velocity variable subdwarfs have been discovered. Binaries with high RV shifts and binaries with moderate shifts within short timespans have the highest probability of hosting massive compact companions. Atmospheric parameters of 69 hot subdwarfs in these binary systems have been determined by means of a quantitative spectral analysis. The atmospheric parameter distribution of the selected sample does not differ from previously studied samples of hot subdwarfs. The systems are considered the best candidates to search for massive compact companions by follow-up time resolved spectroscopy.

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“…Numerous analyses were made on various samples of sdB stars and their global properties (helium content, metal content, rotational velocity, binary population, etc.) are now well documented (e.g., Edelmann et al 2003;Geier et al 2010;Geier & Heber 2012;Geier 2013;Fontaine et al 2014). However, the situation is different when speaking of the hotter sdOs; they are distributed among a much larger region in the HR diagram, and this distribution is not as homogeneous as in the case of the sdBs.…”

Section: Astrophysical Contextmentioning

confidence: 99%

A non-LTE analysis of the hot subdwarf O star BD+28°4211

Latour

Fontaine

Green

et al. 2015

A&A

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We present the second part of our detailed analysis of the hot subdwarf O (sdO) and spectroscopic standard star BD+28 • 4211, in which we focus on the optical spectrum. This target was selected to revisit the more general question of how reliably the atmospheric parameters of a very hot star can be inferred from optical spectroscopy alone. Given its status as a spectrophotometric standard, spectral data of exceptional quality are available for BD+28 • 4211. In the first part of our study, we determined the abundances of some 11 metals detected in the atmosphere of BD+28 • 4211 using UV and far-UV spectra of the star and corroborated the fundamental parameters estimated in past studies (T eff ∼ 82 000 K, log g ∼ 6.2, and solar N(He)/N(H)). In this work, we aim at rederiving these secured parameters on the sole basis of high-quality optical spectra. A first grid of non-LTE line-blanketed model atmospheres, including C, N, O, Mg, Si, S, Fe, and Ni with the abundances derived from the UV spectrum, does not give satisfactory results when we apply a standard simultaneous fitting procedure to the observed H and He lines of our optical spectra. The line profiles are not finely reproduced and the resulting effective temperatures, in particular, are too low by ∼10 000 K. We next investigate the probable cause of this failure, that is, the importance of missing opacity sources on the atmospheric stratification. We thus compare line profiles computed from models with artificially boosted metallicities, from solar abundances to 15× these values. We find that the structural effects saturate for a metallicity of ∼10× solar, and use this to compute a second full grid of models and synthetic spectra. This metal-enriched grid allows us to achieve significantly improved spectral fits with models having the expected parameters. As an a posteriori test, we compared the detailed profiles of several model spectral lines with high-resolution spectra culled from archived HIRES observations. The agreement between our synthetic lines and the observed lines is very convincing. Our test case thus reveals that there is still a need for models with enhanced metallicity for better estimating the atmospheric parameters of objects such as hot subdwarfs and hot white dwarfs if only optical spectra are available.

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Spectral analysis of sdB stars from the Hamburg Quasar Survey

Cited by 147 publications

References 55 publications

Three new pulsating sdB stars discovered with SuperWASP

Three new pulsating sdB stars discovered with SuperWASP

The MUCHFUSS project – searching for hot subdwarf binaries with massive unseen companions

A non-LTE analysis of the hot subdwarf O star BD+28°4211

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