The Halo White Dwarf WD 0346+246 Revisited
نویسنده
چکیده
The extreme helium-rich atmospheric composition determined for the halo white dwarf WD 0346+246 is reexamined. This solution is shown to be improbable from an astrophysical point of view when accretion of hydrogen and metals from the interstellar medium is taken into account. An alternate solution is proposed where hydrogen and helium are present in the atmospheric regions in equal amounts. The best fit at Teff = 3780 K, log g = 8.34, and N(He)/N(H) = 1.3 is achieved by including in the model calculations a bound-free opacity from the Lyman edge associated with the so-called dissolved atomic levels of the hydrogen atom, or pseudo-continuum opacity. Subject headings: stars: atmospheres — atomic processes — stars: individual (WD 0346+246) — white dwarfs
منابع مشابه
Discovery of High Proper-Motion Ancient White Dwarfs: Nearby Massive Compact Halo Objects?
We present the discovery and spectroscopic identification of two very high proper-motion ancient white dwarf stars, found in a systematic proper-motion survey. Their kinematics and apparent magnitude clearly indicate that they are halo members, while their optical spectra are almost identical to the recently identified cool halo white dwarf WD 0346+246. Canonical stellar halo models predict a w...
متن کاملObservations of Ultracool White Dwarfs
We present new spectroscopic and photometric measurements of the white dwarfs LHS 3250 and WD 0346]246. Along with F351[50, these white dwarfs are the coolest ones known, all with e†ective temperatures below 4000 K. Their membership in the Galactic halo population is discussed, and detailed comparisons of all three objects with new atmosphere models are presented. The new models consider the e†...
متن کاملThe Chemical Residue of a White Dwarf-Dominated Galactic Halo
Halo initial mass functions (IMFs), heavily-biased toward white dwarf (WD) precursors (i.e. ∼ 1 → 8 M ), have been suggested as a suitable mechanism for explaining microlensing statistics along the line of sight to the LMC. Such IMFs can apparently be invoked without violating the observed present-day WD luminosity function. By employing a simple chemical evolution argument, we demonstrate that...
متن کاملSimulating a White Dwarf-dominated Galactic Halo
Observational evidence has suggested the possibility of a Galactic halo which is dominated by white dwarfs (WDs). While debate continues concerning the interpretation of this evidence, it is clear that an initial mass function (IMF) biased heavily toward WD precursors (1<m/M⊙<8), at least in the early Universe, would be necessary in generating such a halo. Within the framework of homogeneous, c...
متن کاملOn the Interpretation of High Velocity White Dwarfs as Members of the Galactic Halo
A detailed analysis of 32 of the 38 halo white dwarf candidates identified by Oppenheimer et al. is presented, based on model atmosphere fits to observed energy distributions built from optical BV RI and infrared JHK CCD photometry. Effective temperatures and atmospheric compositions are determined for all objects, as well as masses and cooling ages when trigonometric parallax measurements are ...
متن کامل