Rotation velocities of white dwarfs determined  from the Ca II K line

Berger, L.; Koester, D.; Napiwotzki, R.; Reid, I. Neill; Zuckerman, B.

doi:10.1051/0004-6361:20053340

Cited by 71 publications

(68 citation statements)

References 30 publications

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“…Figure 10 shows a close-up of three Fe I lines, along with models for v sin i = 0, 15, and 30 km s −1 , and suggests that the white dwarf in LTT 560 is a very slow ( < ∼ 15 km s −1 ) rotator, similar to the majority of single white dwarfs (Koester et al 1998;Karl et al 2005;Berger et al 2005). This is an interesting result, as it suggests that the evolution of angular momentum of white dwarfs in PCEBs is similar to that of field white dwarfs, with current theories requiring magnetic torques to explain the observed low rotation rates (e.g.…”

Section: Discussionmentioning

confidence: 87%

Accretion in the detached post-common-envelope binary LTT 560

Tappert

Gänsicke

Schmidtobreick

et al. 2011

A&A

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In a previous study, we found that the detached post-common-envelope binary LTT 560 displays an Hα emission line consisting of two anti-phased components. While one of them was clearly caused by stellar activity from the secondary late-type main-sequence star, our analysis indicated that the white dwarf primary star is potentially the origin of the second component. However, the low resolution of the data means that our interpretation remains ambiguous. We here use time-series UVES data to compare the radial velocities of the Hα emission components to those of metal absorption lines from the primary and secondary stars. We find that the weaker component most certainly originates in the white dwarf and is probably caused by accretion. An abundance analysis of the white dwarf spectrum yields accretion rates that are consistent with mass loss from the secondary due to a stellar wind. The second and stronger Hα component is attributed to stellar activity on the secondary star. An active secondary is likely to be present because of the occurrence of a flare in our time-resolved spectroscopy. Furthermore, Roche tomography indicates that a significant area of the secondary star on its leading side and close to the first Lagrange point is covered by star spots. Finally, we derive the parameters for the system and place it in an evolutionary context. We find that the white dwarf is a very slow rotator, suggesting that it has had an angular-momentum evolution similar to that of field white dwarfs. We predict that LTT 560 will begin mass transfer via Rochelobe overflow in ∼3.5 Gyr, and conclude that the system is representative of the progenitors of the current population of cataclysmic variables. It will most likely evolve to become an SU UMa type dwarf nova.

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Section: Discussionmentioning

confidence: 87%

Accretion in the detached post-common-envelope binary LTT 560

Tappert

Gänsicke

Schmidtobreick

et al. 2011

A&A

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“…Because of their higher atomic weight, the NLTE line cores of the metal lines have smaller instrisic thermal widths than those of the hydrogen lines, facilitating the measurement of rotational broadening. Among 38 DAZ WDs, Berger et al (2005) measured projected rotation speeds for 10 WDs, and upper limits of v sin i < 10 km s −1 for the other 28 objects.…”

Section: Wd Rotationmentioning

confidence: 99%

Kepler and the seven dwarfs: detection of low-level day-time-scale periodic photometric variations in white dwarfs

Maoz

Mazeh

McQuillan

2014

Monthly Notices of the Royal Astronomical Society

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We make use of the high photometric precision of Kepler to search for periodic modulations among 14 normal (DA-and DB-type, likely non-magnetic) hot white dwarfs (WDs). In five, and possibly up to seven of the WDs, we detect periodic, ∼ 2 hr to 10 d, variations, with semi-amplitudes of 60-2000 ppm, lower than ever seen in WDs. We consider various explanations: WD rotation combined with magnetic cool spots; rotation combined with magnetic dichroism; rotation combined with hot spots from an interstellar-medium accretion flow; transits by size ∼ 50-200 km objects; relativistic beaming due to reflex motion caused by a cool companion WD; or reflection/reradiation of the primary WD light by a brown-dwarf or giant-planet companion, undergoing illumination phases as it orbits the WD. Each mechanism could be behind some of the variable WDs, but could not be responsible for all five to seven variable cases. Alternatively, the periodicity may arise from UV metal-line opacity, associated with accretion of rocky material, a phenomenon seen in ∼ 50% of hot WDs. Nonuniform UV opacity, combined with WD rotation and fluorescent optical re-emission of the absorbed UV energy, could perhaps explain our findings. Even if reflection by a planet is the cause in only a few of the seven cases, it would imply that hot Jupiters are very common around WDs. If some of the rotation-related mechanisms are at work, then normal WDs rotate as slowly as do peculiar WDs, the only kind for which precise rotation measurements have been possible to date.

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“…Bergeron et al (2001) suspected that shallow line cores which they found for these objects might indicate low-strength magnetic fields. The line cores of both objects have since been fitted with rotationally broadened line profiles, corresponding to projected rotation velocities of 36 +14 −7 km s −1 for WD 2253−081 ) and 4.5 ± 2 km s −1 for WD 1344+106 (Berger et al 2005). The Hα line cores in the SPY spectra of both objects neither show Zeeman triplets nor flat bottoms that could indicate the presence of a B field.…”

Section: Objects With Magnetic Fields or Helium Contaminationmentioning

confidence: 99%

High-resolution UVES/VLT spectra of white dwarfs observed for the ESO SN Ia Progenitor Survey

Koester¹,

Voß

Napiwotzki

et al. 2009

A&A

Self Cite

158

231

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Context. The ESO Supernova Ia Progenitor Survey (SPY) took high-resolution spectra of more than 1000 white dwarfs and pre-white dwarfs. About two thirds of the stars observed are hydrogen-dominated DA white dwarfs. Here we present a catalog and detailed spectroscopic analysis of the DA stars in the SPY. Aims. Atmospheric parameters effective temperature and surface gravity are determined for normal DAs. Double-degenerate binaries, DAs with magnetic fields or dM companions, are classified and discussed. Methods. The spectra are compared with theoretical model atmospheres using a χ 2 fitting technique. Results. Our final sample contains 615 DAs, which show only hydrogen features in their spectra, although some are double-degenerate binaries. 187 are new detections or classifications. We also find 10 magnetic DAs (4 new) and 46 DA+dM pairs (10 new).

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Rotation velocities of white dwarfs determined from the Ca II K line

Cited by 71 publications

References 30 publications

Accretion in the detached post-common-envelope binary LTT 560

Accretion in the detached post-common-envelope binary LTT 560

Kepler and the seven dwarfs: detection of low-level day-time-scale periodic photometric variations in white dwarfs

High-resolution UVES/VLT spectra of white dwarfs observed for the ESO SN Ia Progenitor Survey

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