arXiv subjects

M. R. Burleigh

Publications and source records attributed to M. R. Burleigh.

95 records · Page 6Linked to original sources

arXiv1999

Optical spectroscopy of the candidate luminous white dwarf in the young LMC cluster NGC1818

An optical spectrum of the Elson et al. (1998) candidate luminous white dwarf in the young LMC cluster NGC1818 shows conclusively that it is not a degenerate star. A model atmosphere fit gives T=31,500K and log g=4.4, typical of a garden-variety main sequence B star. However, if it is a true LMC member then the star is under-luminous by almost three magnitudes. Its position in the cluster colour-magnitude diagram also rules out the possibility that this is an ordinary B star. The luminosity is, however, consistent with a ~0.5 solar mass post-AGB or post-EHB object, although if it has evolved via single star evolution from a high mass (7.6-9.0 solar masses) progenitor then we might expect it to have a much higher mass, $\sim0.9\Msun$. Alternatively, it has evolved in a close binary. In this case the object offers no implications for the maximum mass for white dwarf progenitors, or the initial-final mass relation. Finally, we suggest that it could in fact be an evolved member of the LMC disk, and merely projected by chance onto NGC1818. Spectroscopically, though, we cannot distinguish between these evolutionary states without higher resolution (echelle) data.

astro-ph↗

arXiv1999

Opacities along the line of sight to and in the atmosphere of the white dwarf in the close detached DAO+dM binary RE J0720-318 (V* IN CMa)

We present the results from a multi-wavelength study of the mixed H+He composition DAO white dwarf RE J0720-318. A detailed analysis of UV and EUV spectroscopic data with state-of-the-art non-LTE photospheric models demonstrates that the observed opacity to EUV radiation probably results from a more complex structure than a simple H+He, chemically layered atmosphere. Instead, EUV photometry and phase resolved EUV spectroscopy indicate a likely spatial non-uniformity in the surface distribution of helium, which is consistent with a model in which material is accreted from the wind of the dM secondary. The rotational modulation of the spatially inhomogeneous EUV opacity allows us to estimate the rotation period of the white dwarf (0.463 +/- 0.004 days). We have also reviewed two plausible origins proposed by Burleigh et al. (1997) and Dupuis et al. (1997) to account for the unusual N(HI)/N(HeI)~1 along this line of sight. We conclude that it is probably due to the presence of a cloud of ionized gas along this line of sight, rather than a circumbinary disk. The cloud, residing between 123-170pc distant in the direction of the CMa ISM tunnel, may be >40pc in length.

astro-ph↗

arXiv1998

Theta Hya: Spectroscopic identification of a second B star + white dwarf binary

We report the identification, in an Extreme Ultraviolet Explorer (EUVE) spectrum, of a hot white dwarf companion to the 3rd magnitude late-B star Theta Hya (HR3665, HD79469). This is the second B star + white dwarf binary to be conclusively identified; Vennes, Berghofer and Christian (1997), and Burleigh and Barstow (1998) had previously reported the spectroscopic discovery of a hot white dwarf companion to the B5V star y Pup (HR2875). Since these two degenerate stars must have evolved from main sequence progenitors more massive than their B star companions, they can be used to place observational lower limits on the maximum mass for white dwarf progenitors, and to investigate the upper end of the initial-final mass relation. Assuming a pure hydrogen composition, we constrain the temperature of the white dwarf companion to Theta Hya to lie between 25,000K and 31,000K. We also predict that a third bright B star, 16 Dra (B9.5V), might also be hiding an unresolved hot white dwarf companion.

astro-ph↗

arXiv1998

Phase-resolved far-ultraviolet HST spectroscopy of the peculiar magnetic white dwarf RE J0317-853

We present phase resolved FUV HST FOS spectra of the rapidly rotating, highly magnetic white dwarf RE J0317-853. Using these data, we construct a new model for the magnetic field morphology across the stellar surface. From an expansion into spherical harmonics, we find the range of magnetic field strengths present is 180-800MG. For the first time we could identify an absorption feature present at certain phases at 1160A as a ``forbidden'' 1s_0 -> 2s_0 component, due to the combined presence of an electric and magnetic field.

astro-ph↗

arXiv1998

A search for hidden white dwarfs in the ROSAT EUV survey II: Discovery of a distant DA+F6/7V binary system in a direction of low density neutral hydrogen

We report the results of our final search for hot white dwarfs in unresolved, Sirius-type, binary systems with IUE. One new system, RE J0500-364 (DA+F6/7V), has been identified. This star appears to lie at a distance of between 500-1000pc, making it one of the most distant white dwarfs, if not the most distant, to be detected in the EUV surveys. The very low line-of-sight neutral hydrogen volume density to this object could place a lower limit on the length of the Beta CMa interstellar tunnel of diffuse gas, which stretches away from the Local Bubble in a similar direction to RE J0500-364.

astro-ph↗