Astronomers Investigate a Unique Oscillating Variable White Dwarf

A team of astronomers led by Jincheng Guo of Beijing Planetarium in China has conducted detailed spectroscopic and photometric observations of a peculiar, pulsating variable white dwarf named TMTS J17184064+2524314, also known as J1718. The team’s findings, published on the preprint server arXiv, offer critical insights into the properties and behavior of this celestial object.

White dwarfs are remnants of stars that have exhausted their nuclear fuel. They are characterized by high gravity and atmospheres of either pure hydrogen or helium, with a small fraction showing traces of heavier elements. Pulsating white dwarfs exhibit luminosity variations due to non-radial gravity wave pulsations within them. One subtype of these is DAVs or ZZ Ceti stars, which are white dwarfs having only hydrogen absorption lines in their spectra.

Located approximately 228.5 light years away, J1718 is a DA white dwarf with a mass of around 0.63 solar masses and an effective temperature of 11,361 K. It was classified as a ZZ Ceti WD in 2020, with a main pulsation period of 731 seconds.

The astronomers utilized data primarily from the Tsinghua University-Ma Huateng Telescope for Survey (TMTS) and NASA’s Transiting Exoplanet Survey Satellite (TESS) to learn more about this unique variable star. They carried out an extensive asteroseismological analysis, identifying 10 pulsating periods and three combination periods of this variable.

The team estimated J1718’s rotation period to be about 25.12 hours and its age approximately 510 million years. They found its effective temperature to be slightly higher than previously thought, at around 11,640 K. The star was also found to be more massive than previously suggested, with an estimated mass of about 0.75 solar masses. Additionally, the carbon and oxygen abundances in J1718’s core were found to be approximately 0.43 and 0.57, respectively.

This research confirms that J1718 is a relatively massive DAV with a slightly thick hydrogen atmosphere. The findings are consistent with the parameters derived from spectral fitting of the follow-up spectrum. These insights could potentially contribute to our understanding of white dwarfs and stellar evolution.

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