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OGLE-GD-WD-0001 is an extremely hot pulsating pre-white dwarf, observations find

Astronomers from Poland and Germany have performed photometric and spectroscopic observations of a blue variable object designated OGLE-GD-WD-0001. As a result, they found that the investigated object is an extremely hot pulsating pre-white dwarf of PG 1159 spectral type. The findings were detailed in a research paper February 24 on the arXiv preprint server.

White dwarfs (WDs) are stellar cores left behind after a star has exhausted its nuclear fuel. Due to their high gravity, they are known to have atmospheres of either pure hydrogen or pure helium. However, a small fraction of WDs shows traces of heavier elements.

Although WDs have a relatively small size, comparable to that of Earth, they are a few million times more massive than our planet. Pre-white dwarfs (PWDs) are a few times larger and slated to shrink in size, eventually becoming WDs within a few thousand years.

OGLE-GD-WD-0001 was first spotted in 2013 as a blue object exhibiting sinusoidal light variations with an amplitude of about 0.01 mag in the I-band at a period of about 18.34 minutes. The object was initially classified as a pulsating white dwarf.

However, subsequent studies have put the WD status of OGLE-GD-WD-0001 into question. The latest observations of this object, made by a team of astronomers led by Paweł Pietrukowicz of the University of Warsaw, Poland, provide evidence that OGLE-GD-WD-0001 is a pulsating pre-white dwarf.

The observations found that OGLE-GD-WD-0001 showcases brightness variations and properties typical for pulsating PG 1159 stars. The so-called PG 1159 stars, or GW Virginis pulsators, are hot hydrogen-deficient precursors of white dwarfs, retaining some hydrogen in their envelope, named after their prototype.

The study found that the atmosphere of OGLE-GD-WD-0001 is composed of helium and carbon in equal proportions, with a 0.005 mass fraction of oxygen. The effective temperature of OGLE-GD-WD-0001 was found to be about 160,000 K, while its luminosity was estimated to be at a level of 2,000 solar luminosities. The astronomers noted that there are no traces of a planetary nebula around this PWD.

The authors of the paper concluded that OGLE-GD-WD-0001 is therefore among the hottest GW Virginis pulsators known to date. Moreover, it is close to the blue edge of the GW Virginis instability strip.

Further observations of OGLE-GD-WD-0001 are required, focused on obtaining a higher resolution spectrum of this pre-white dwarf, which would allow a more accurate determination of its physical parameters.