BPM 37093: The Way to the Interior of Crystallized Stars (original) (raw)

The effects of crystallization on the pulsations of white dwarf stars

2004

The theory of white dwarf crystallization lias been around for over forty years, yet there exists few direct observational tests to verify it. A littie over a decade has past since a possible testing-ground for the theory lias been discovered, the star BPM 37093, yet our ability to proceed with such tests using current methods is stiil under debate. This DAV star lias the cliaracteristic pulsations of tlie otliers of its type, yet it also lias a mass high enougli so that, by theoretical calculations, we expect tlie center to already be in tlie process of crystallizing, leading some to propose that the pulsations could serve as indicators of the crystallized fraction of tlie star. The validitidy of this daim, tlie use of current tecliniques and stellar knowledge. to determine tlie exact fraction of the star whicli is crystallized is tlie basis of this research. Using extensive, and careful modeling techniques, the relative importance of the crystallization as a parameter of pulsation...

The Crystal Method: Asteroseismology of BPM 37093

2004

More than 40 years have passed since Ed Salpeter and others predicted that the carbon/oxygen cores of the coolest white dwarf stars in our Galaxy will theoretically crystallize. This effect has a dramatic impact on the calculated ages of cool white dwarfs, but until recently we have had no way of testing the theory. In 1992, pulsations were discovered in the massive potentially crystallized white dwarf BPM 37093, and in 1999 the theoretical effects of crystallization on the pulsation modes were determined. Observations from two Whole Earth Telescope campaigns in 1998 and 1999, combined with a new model-fitting method using a genetic algorithm, are now giving us the first glimpse inside of a crystallized star.

Constraining the physics of carbon crystallization through pulsations of a massive DAV BPM37093

Proceedings of the International Astronomical Union, 2015

We are trying to reduce the largest uncertainties in using white dwarf stars as Galactic chronometers by understanding the details of carbon crystalliazation that currently result in a 1–2 Gyr uncertainty in the ages of the oldest white dwarf stars. We expect the coolest white dwarf stars to have crystallized interiors, but theory also predicts hotter white dwarf stars, if they are massive enough, will also have some core crystallization. BPM 37093 is the first discovered of only a handful of known massive white dwarf stars that are also pulsating DAV, or ZZ Ceti, variables. Our approach is to use the pulsations to constrain the core composition and amount of crystallization. Here we report our analysis of 4 hours of continuous time series spectroscopy of BPM 37093 with Gemini South combined with simultaneous time-series photometry from Mt. John (New Zealand), SAAO, PROMPT, and Complejo Astronomico El Leoncito (CASLEO, Argentina).