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

Reindl, N.; Geier, S.; Kupfer, Thomas; Bloemen, S.; Schaffenroth, V.; Heber, U.; Barlow, B. N.; Østensen, R. H.

doi:10.1051/0004-6361/201527637

Cited by 32 publications

(24 citation statements)

References 82 publications

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“…1 shows that the shape of the light curve of J0146+3236 could be explained with a bright spot model assuming an inclination of i = 50 • . The synthetic light curve was calculated with a surface brightness distribution that provides the 1 For this, we obtained FUV, NUV (Bianchi et al 2014), u, g, r, i, z (Ahn et al 2012, J, H (Cutri et al 2003), and W1 (Cutri & et al 2014) magnitudes of J0146+3236 and converted them into fluxes as outlined in Reindl et al (2016); Verbeek et al (2014). We applied a reddening of E B−V = 0.05 (Schlafly & Finkbeiner 2011) to the flux of our TMAP model mentioned above.…”

Section: Discussionmentioning

confidence: 99%

Unravelling the baffling mystery of the ultrahot wind phenomenon in white dwarfs

Reindl

Bainbridge

Przybilla

et al. 2018

Monthly Notices of the Royal Astronomical Society: Letters

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The presence of ultra-high excitation (UHE) absorption lines (e.g., O VIII) in the optical spectra of several of the hottest white dwarfs poses a decades-long mystery and is something that has never been observed in any other astrophysical object. The occurrence of such features requires a dense environment with temperatures near 10 6 K, by far exceeding the stellar effective temperature. Here we report the discovery of a new hot wind white dwarf, GALEX J014636.8+323615. Astonishingly, we found for the first time rapid changes of the equivalent widths of the UHE features, which are correlated to the rotational period of the star (P = 0.242035 d). We explain this with the presence of a wind-fed circumstellar magnetosphere in which magnetically confined wind shocks heat up the material to the high temperatures required for the creation of the UHE lines. The photometric and spectroscopic variability of GALEX J014636.8+323615 can then be understood as consequence of the obliquity of the magnetic axis with respect to the rotation axis of the white dwarf. This is the first time a wind-fed circumstellar magnetosphere around an apparently isolated white dwarf has been discovered and finally offers a plausible explanation of the ultra hot wind phenomenon.

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Section: Discussionmentioning

confidence: 99%

Unravelling the baffling mystery of the ultrahot wind phenomenon in white dwarfs

Reindl

Bainbridge

Przybilla

et al. 2018

Monthly Notices of the Royal Astronomical Society: Letters

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“…We identified spectroscopically in our sample a total of 12 PG 1159 and O(He) stars and 36 DOs with spectra dominated by He II lines. Furthermore, we found one O(H) star (Reindl et al 2016) and 48 DAO stars, with spectra showing both H and He II lines as well as 310 hot DAs, showing only H lines. All these stars are hotter than T eff = 45 000 K, where NLTE effects are important in the spectral analysis.…”

Section: Hot White Dwarfsmentioning

confidence: 76%

White dwarf and subdwarf stars in the Sloan Digital Sky Survey Data Release 16

Koester

Pelisoli

Romero

et al. 2021

Monthly Notices of the Royal Astronomical Society

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White dwarfs are the end state of the evolution of more than 97% of all stars, and therefore carry information on the structure and evolution of the Galaxy through their luminosity function and initial-to-final mass relation. Examining the new spectra of all white or blue stars in the Sloan Digital Sky Survey Data Release 16, we report the spectral classification of 2410 stars, down to our identification cut-off of signal-to-noise ratio equal to three. We newly identify 1404 DAs, 189 DZs, 103 DCs, 12 DBs, and 9 CVs. The remaining objects are a mix of carbon or L stars (dC/L), narrow-lined hydrogen-dominated stars (sdA), dwarf F stars and P Cyg objects. As white dwarf stars were not targeted by SDSS DR16, the number of new discoveries is much smaller than in previous releases. We also report atmospheric parameters and masses for a subset consisting of 555 new DAs, 10 new DBs, and 85 DZs for spectra with signal-to-noise ratio larger than 10.

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“…The black dots indicate filteraveraged fluxes that were converted from observed magnitudes. GALEX FUV and NUV magnitudes were taken from Bianchi et al (2014) and converted to fluxes as outlined in Reindl et al (2016). B, V, g, r, and i magnitudes were taken from Henden et al (2015), 2MASS J, H, and K magnitudes from Cutri et al (2003).…”

Section: Radii Luminosities Masses and Agesmentioning

confidence: 99%

An extremely hot white dwarf with a rapidly rotating K-type subgiant companion: UCAC2 46706450

Werner¹,

Reindl

Löbling³

et al. 2020

A&A

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The subgiant UCAC2 46706450 is a late-type star with an ultraviolet (UV) excess. It was considered as a candidate to establish a sample of stars of spectral type F, G, and K with white dwarf (WD) companions that could be used to test binary evolution models. To verify the WD nature of the companion, UV spectroscopy has previously been performed by other authors. Via a detailed model-atmosphere analysis, we show that the UV source is an extremely hot WD with an effective temperature of Teff = 105 000 ± 5000 K, mass of M∕M⊙ = 0.54 ± 0.02, radius of R/R⊙ = 0.040−0.004+0.005, and luminosity of L/L⊙ = 176−49+55, meaning that the compact object is just about to enter the WD cooling sequence. Investigating spectra of the cool star (Teff = 4945 ± 250 K), we found that it is a K-type subgiant with M∕M⊙ = 0.8−2.4, R/R⊙ = 5.9−0.5+0.7, and L/L⊙ = 19−5+5 that is rapidly rotating with vsin(i) = 81 km s−1. Optical light curves reveal a period of two days and an o-band peak-to-peak amplitude of 0.06 mag. We suggest that it is caused by stellar rotation in connection with star spots. With the radius, we infer an extremely high rotational velocity of vrot = 151−13+18 km s−1, thus marking the star as one of the most rapidly rotating subgiants known. This explains chromospheric activity observed by H α emission and emission-line cores in Ca II H and K as well as NUV flux excess. From equal and constant radial velocities of the WD and the K subgiant as well as from a fit to the spectral energy distribution, we infer that they form a physical, wide (though unresolved) binary system. Both components exhibit similar metal abundances and show iron-group elements with slightly oversolar (up to 0.6 dex) abundance, meaning that atomic diffusion in the WD atmosphere is not yet active due to a residual, weak radiation-driven wind. Kinematically and from its height above the Galactic plane, the system belongs to the Galactic thick disk, indicating that it is an old system and that the initial masses of both stars were close to 1 M⊙.

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

Cited by 32 publications

References 82 publications

Unravelling the baffling mystery of the ultrahot wind phenomenon in white dwarfs

Unravelling the baffling mystery of the ultrahot wind phenomenon in white dwarfs

White dwarf and subdwarf stars in the Sloan Digital Sky Survey Data Release 16

An extremely hot white dwarf with a rapidly rotating K-type subgiant companion: UCAC2 46706450

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