Spectroscopic Analysis of Hot, Hydrogen-Rich White Dwarfs: The Presence of Metals and the Balmer-Line Problem

Gianninas, A.; Bergeron, P.; Dupuis, J.; Ruíz, M. T.

doi:10.1088/0004-637x/720/1/581

Cited by 80 publications

(153 citation statements)

References 63 publications

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“…The synthetic spectra are convolved at a resolution of 1.0 Å. a practical recipe for computing some sort of saturated metallicity in model atmospheres, namely multipling the solar abundances of metals by a factor 10, for example. This is the same as the suggestion previously made by O'Toole & Heber (2006), Geier et al (2007), and Gianninas et al (2010), but with the added justification of the saturation effect. Figure 3 furthermore reveals that the saturation effect is verified over the full range of parameters displayed in the plot.…”

Section: Exploring Metallicity Effects On Spectral Linessupporting

confidence: 82%

“…In this temperature range, the mismatch between observed and model spectra is not so much in the Balmer lines themselves, but rather in the helium ones, for which the lines originating from both ionization stages cannot be correctly reproduced without this artifact. The Balmer line problem is also seen in hot white dwarfs, and a few of those analyzed in Gianninas et al (2010) were much better reproduced with NLTE model atmospheres including C, N, O with ten times their solar abundances. It is thought that this approach compensates, at least partially, for some unknown opacity sources to the point where the atmospheric structure is affected in the correct way.…”

Section: Discussionmentioning

confidence: 92%

“…In this way, consistent and acceptable spectral fits could be obtained. Likewise, and more recently, Gianninas et al (2010) concluded that using a boosted metallicity consisting of ten times the solar values of C, N, and O in NLTE models of hot DAO white dwarfs might be a practical approach to the analysis of optical spectra of such stars.…”

Section: Exploring Metallicity Effects On Spectral Linesmentioning

confidence: 99%

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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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Section: Exploring Metallicity Effects On Spectral Linessupporting

confidence: 82%

Section: Discussionmentioning

confidence: 92%

Section: Exploring Metallicity Effects On Spectral Linesmentioning

confidence: 99%

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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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“…First, there are the hot DA and DAO stars exhibiting the socalled Balmer line problem. A comprehensive and detailed analysis of these stars has already been presented by Gianninas et al (2010) and those results will be included in our analysis. Second, we have DA+dM binary systems whose Balmer line profiles are contaminated, to varying degrees, by the spectrum of the dM secondary.…”

Section: Introductionmentioning

confidence: 99%

A Spectroscopic Survey and Analysis of Bright, Hydrogen-Rich White Dwarfs

Gianninas¹,

Bergeron²,

Ruíz³

2011

ApJ

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358

477

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We have conducted a spectroscopic survey of over 1300 bright (V ≤ 17.5), hydrogen-rich white dwarfs based largely on the last published version of the McCook & Sion catalog. The complete results from our survey, including the spectroscopic analysis of over 1100 DA white dwarfs, are presented. High signal-to-noise ratio optical spectra were obtained for each star and were subsequently analyzed using our standard spectroscopic technique where the observed Balmer line profiles are compared to synthetic spectra computed from the latest generation of model atmospheres appropriate for these stars. First, we present the spectroscopic content of our sample, which includes many misclassifications as well as several DAB, DAZ, and magnetic white dwarfs. Next, we look at how the new Stark broadening profiles affect the determination of the atmospheric parameters. When necessary, specific models and analysis techniques are used to derive the most accurate atmospheric parameters possible. In particular, we employ M dwarf templates to obtain better estimates of the atmospheric parameters for those white dwarfs that are in DA+dM binary systems. Certain unique white dwarfs and doubledegenerate binary systems are also analyzed in greater detail. We then examine the global properties of our sample including the mass distribution and their distribution as a function of temperature. We then proceed to test the accuracy and robustness of our method by comparing our results to those of other surveys such as SPY and Sloan Digital Sky Survey. Finally, we revisit the ZZ Ceti instability strip and examine how the determination of its empirical boundaries is affected by the latest line profile calculations.

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“…The fact that no PN is present around these stars is rather unexpected, since in our canonical understanding each star that evolves through the AGB should produce a PN. A simple explanation for their missing PNe could be that their post-AGB times are longer than the time it took for the PNe to disappear Heber & Hunger (1987); (b) Fontaine et al (2008); (c) this work; (d) Chayer et al (2015); (e) Heber & Kudritzki (1986); ( f ) Bauer & Husfeld (1995); (g) Napiwotzki (1999); (h) Ziegler (2012); (i) Rauch et al (2007); ( j) Gianninas et al (2010).…”

Section: H-rich Starsmentioning

confidence: 99%

Radial velocity variable, hot post-AGB stars from the MUCHFUSS project

Reindl¹,

Geier

Kupfer

et al. 2016

A&A

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In the course of the MUCHFUSS project we recently discovered four radial velocity (RV) variable, hot (T eff ≈ 80 000−110 000 K) post-asymptotic giant branch (AGB) stars. Among them, we found the first known RV variable O(He) star, the only second known RV variable PG 1159 close binary candidate, as well as the first two naked (i.e., without planetary nebula (PN)) H-rich post-AGB stars of spectral type O(H) that show significant RV variations. We present a non-LTE spectral analysis of these stars along with one further O(H)-type star whose RV variations were found to be not significant. We also report the discovery of a far-infrared excess in the case of the PG 1159 star. None of the stars in our sample displays nebular emission lines, which can be explained well in terms of a very late thermal pulse evolution in the case of the PG 1159 star. The "missing" PNe around the O(H)-type stars seems strange, since we find that several central stars of PNe have much longer post-AGB times. Besides the non-ejection of a PN, the occurrence of a late thermal pulse, or the re-accretion of the PN in the previous post-AGB evolution offer possible explanations for those stars not harbouring a PN (anymore). In the case of the O(He) star J0757, we speculate that it might have been previously part of a compact He transferring binary system. In this scenario, the mass transfer must have stopped after a certain time, leaving behind a low-mass close companion that may be responsible for the extreme RV shift of 107.0 ± 22.0 km s −1 that was measured within only 31 min.

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Spectroscopic Analysis of Hot, Hydrogen-Rich White Dwarfs: The Presence of Metals and the Balmer-Line Problem

Cited by 80 publications

References 63 publications

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

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

A Spectroscopic Survey and Analysis of Bright, Hydrogen-Rich White Dwarfs

Radial velocity variable, hot post-AGB stars from the MUCHFUSS project

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