Mode Identification of BPM 37093 with the HST
Abstract
Theoretical calculations indicate that the massive pulsating white dwarf BPM 37093 has a crystallized interior (Winget et al. 1997, Kanaan 1996, Montgomery 1998). Crystallization was predicted theoretically about 40 years ago (Abrisokov 1961, Kirshnitz 1960; Salpeter 1961), but in spite of its importance in astrophysics, there is no direct observational evidence of the theory. Uncertainties in the nature and extent of crystallization, as well as its associated effects, are the largest sources of uncertainties in calculating the ages of the coolest white dwarf stars -- important chronometers for the Galactic disk. The Whole Earth Telescope and the Hubble Space Telescope simultaneously observed BPM 37093 in April 1999 in hopes of using asteroseismology to measure its crystallized mass fraction. The first step is correct mode identification, principally the spherical harmonic index l. Kanaan et al. (1999) explain the attempt to identify the modes from only the optical WET data, using mainly the periods of the modes. Here we present our preliminary results of applying the Robinson et al. (1995) l identification method which uses a comparison of amplitudes of the modes in the UV and in the optical spectrum.
- Publication:
-
Baltic Astronomy
- Pub Date:
- 2000
- DOI:
- 10.1515/astro-2000-0116
- Bibcode:
- 2000BaltA...9...97N
- Keywords:
-
- STARS: INTERIORS;
- WHITE DWARFS;
- OSCILLATIONS;
- INDIVIDUAL: BPM 37093;
- ZZ CETI