The zoomed Lomb-Scargle periodogram of J1718 for 20 s exposures by TESS in 2022. The horizontal red dashed line is the 4.0σ threshold. Red text arrows are frequencies identified above 4.0σ, while green text arrows are frequencies identified below but near the 4.0σ threshold. Details of three possible splitting frequency regions are shown in separate inset figures. Credit: Guo et al, 2024
Astronomers have made spectroscopic and photometric observations of a peculiarly pulsing variable white dwarf known as TMTS J17184064+2524314. Results of the observation campaign, published on January 26 on the preprint server arXivprovide essential information regarding the properties and behavior of this object.
White dwarfs (WDs) are stellar cores left behind after a star has exhausted its nuclear fuel. Due to their strong gravity, they are known to have atmospheres of pure hydrogen or pure helium. However, a small fraction of WD shows traces of heavier elements.
In pulsating white dwarfs, brightness varies due to pulsations of non-radial gravitational waves within these objects. A subtype of pulsating WDs is known as DAV stars, or ZZ Ceti stars. They are white dwarfs of spectral type DA, having only hydrogen absorption lines in their spectrum.
At a distance of approximately 228.5 light years, TMTS J17184064+2524314 (or J1718 for short) is a DA white dwarf with a mass of approximately 0.63 solar masses and an effective temperature of 11,361 K. As of 2020 , J1718 was classified as one of several new ZZ Ceti WDs, with a main pulse period of 731 seconds.
Today, a team of astronomers led by Jincheng Guo from the Beijing Planetarium in China combed through data obtained mainly by the Tsinghua-Ma Huateng University Survey Telescope (TMTS) and the survey satellite of Transiting Exoplanets (TESS) from NASA, to find out more. about the properties of this particular variable star.
By performing extensive asterosesimological analysis, Guo’s team managed to derive precise parameters for J1718. In total, they identified 10 pulsation periods and three combination periods of this variable.
The rotation period of J1718 was calculated to be approximately 25.12 hours. The age of the white dwarf was found to be around 510 million years, while its effective temperature was measured to be somewhat higher than previously thought, at a level of 11,640 K .
The mass of J1718 was estimated to be around 0.75 solar masses, so the star turned out to be more massive than previously suggested. The study also found that the abundances of carbon and oxygen in the core of J1718 were found to be approximately 0.43 and 0.57, respectively.
According to the authors of the article, the results obtained confirm that J1718 is a relatively massive DAV with a slightly thick hydrogen atmosphere.
“From the asteroseismological results, it can be inferred that J1718 is a relatively massive pulsing WD with a slightly thick hydrogen atmosphere. The final results are consistent with the parameters derived from the spectral fitting of our tracking spectrum,” they said. concluded the researchers.
More information:
Jincheng Guo et al, Variable white dwarfs in TMTS: asteroseismological analysis of a ZZ Ceti star, TMTS J17184064+2524314, arXiv (2024). DOI: 10.48550/arxiv.2401.14692
Journal information:
arXiv
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Quote: Astronomers inspect a peculiar variable and pulsating white dwarf (February 5, 2024) retrieved on February 5, 2024 from
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