相关论文: Rotation velocities of white dwarfs determined fro…

Previous investigations on hydrogen-rich white dwarfs generally yield only very small rotational velocities (v_rot sin i). We have analyzed line profiles in high-resolution optical spectra of eight hydrogen-deficient (pre-) white dwarfs and…

White dwarfs rotate. The angular momentum in single white dwarfs must originate early in the life of the star, but also must be modified (and perhaps severely modified) during the many stages of evolution between birth as a main--sequence…

Context. Knowing the rotation rates and masses of white dwarf stars is an important step towards characterising the angular momentum transport mechanism in their progenitors, and coupling the cores of red giants to their envelopes. However,…

We have obtained projected rotation velocities (vsini) of a sample of 19 ultracool dwarfs with spectral types in the interval M6.5-T8 using high-resolution, near-infrared spectra obtained with NIRSPEC and the Keck II telescope. Among our…

I discuss and consider the status of observational determinations of the rotation velocities of white dwarf stars via asteroseismology and spectroscopy. While these observations have important implications on our understanding of the…

Context: Rotation plays a key role in the life cycles of stars with masses above 8 Msun. Hence, accurate knowledge of the rotation rates of such massive stars is critical for understanding their properties and for constraining models of…

Using patterns in the oscillation frequencies of a white dwarf observed by K2, we have measured the fastest rotation rate, 1.13(02) hr, of any isolated pulsating white dwarf known to date. Balmer-line fits to follow-up spectroscopy from the…

We demonstrate that the peculiar line profiles observed in DA white dwarfs in the temperature range of the ZZ Ceti variables can be explained by the surface velocity fields associated with the pulsations.

We continue our studies on stellar latitudinal differential rotation. The presented work is a sequel of the work of Reiners et al. who studied the spectral line broadening profile of hundreds of stars of spectral types A through G at high…

The location of the red edge of the ZZ Ceti instability strip is defined observationally as being the lowest temperature for which a white dwarf with a H-rich atmosphere (DA) is known to exhibit periodic brightness variations. Whether this…

We have examined the relationship between rotation and activity in 14 late-type (M6-M7) M dwarfs, using high resolution spectra taken at the Keck Observatory and flux-calibrated spectra from the Sloan Digital Sky Survey. Most are inactive…

We present observations of 36 late-M dwarfs obtained with the KeckII/NIRSPEC in the J-band at a resolution of \sim20,000. We have measured projected rotational velocities, absolute radial velocities, and pseudo-equivalent widths of atomic…

We present our findings on the spectral analysis of seven magnetic white dwarfs that were presumed to be double degenerates. We obtained time-resolved spectroscopy at the Gemini Observatory to look for evidence of binarity or fast rotation.…

We present the results of a radial velocity survey designed to measure the fraction of double degenerates among DA white dwarfs. The narrow core of the H-alpha line was observed twice or more for 46 white dwarfs yielding radial velocities…

We present a synthetic spectral analysis of IUE archival and FUSE FUV spectra of the peculiar dwarf nova WW Ceti. During the quiescence of WW Ceti, a white dwarf with Twd=26,000K can account for the FUV flux and yields the proper distance.…

Stability of the r-modes in rapidly rotating white dwarf stars is investigated. Improved estimates of the growth times of the gravitational-radiation driven instability in the r-modes of the observed DQ Her objects are found to be longer…

We present photometry and spectroscopy for 27 pulsating hydrogen-atmosphere white dwarfs (DAVs, a.k.a. ZZ Ceti stars) observed by the Kepler space telescope up to K2 Campaign 8, an extensive compilation of observations with unprecedented…

We have examined the relationship between rotation and activity in 14 late-type (M6-M7) M dwarfs, using high resolution spectra taken at the W.M. Keck Observatory and flux-calibrated spectra from the Sloan Digital Sky Survey. Most were…

The white dwarf stars WD1614+136 and WD1353+409 are not sufficiently massive to have formed through single star evolution. However, observations to date have not yet found any evidence for binarity. It has therefore been suggested that…

With an aim of getting information on the equatorial rotation velocity (v_e) of Sirius A separated from the inclination effect (sin i), a detailed profile analysis based on the Fourier transform technique was carried out for a large number…