SALT discovers new hot white dwarf and pre-white dwarf stars

SALT discovers new hot white dwarf and pre-white dwarf stars

SALT/RSS spectra of hot white dwarfs and pre-white dwarfs. The identifiers are on the left, and the spectral classes are on the right. Credit: Jeffrey et al., 2023

Using the South African Large Telescope (SALT), an international team of astronomers has discovered eight new super-hot white dwarf and pre-white dwarf stars with effective temperatures over 100,000 K. Monthly Notices of the Royal Astronomical Society.

White dwarfs (WDs) are stellar cores that are left behind after a star has exhausted its nuclear fuel. Because of its high gravity, it is known to have atmospheres of either pure hydrogen or pure helium. However, only a small fraction of WDs show traces of heavier elements.

Although WDs have a relatively small size, comparable to Earth’s, they are only a few million times larger than our planet. Pre-white dwarfs (PWDs) are a few times larger and are set to shrink in size, eventually becoming WD within a few thousand years.

Now, a group of astronomers led by Simon Jeffrey of Armagh Observatory and Planetarium, UK, have reported the discovery of new WDs and PWDs with extreme heat. the New stars They were discovered using SALT’s Robert Stobie Spectrograph (RSS) while searching for hot, helium-rich dwarfs.

“Serendipitously, the SALT survey of helium-rich sub-dwarfs led to the discovery of eight hot white dwarfs and pre-white dwarfs with effective temperatures exceeding 100,000 K,” the researchers wrote in the paper.

According to the study, two of the newly discovered SPs turned out to be stars PG 1159 – precursors to DO or DA white dwarfs. white dwarfs, while retaining some hydrogen in its shell, which is named after its prototype. The sample also includes one white dwarf, three O (He) stars and two O (H) stars.

It was found that one of the two O(H) stars is the central star of the newly discovered planetary nebula (PN), while the other is the hotter O(H) star without PN. The star PG 1159 designated SALT J213742.6−382901 (or J2137 for short) appears to be the hottest of the eight newly discovered – its effective temperature has been estimated to be around 180,000 K. Furthermore, the white dwarf DO, with effective temperature Of 130,000 K, it is the highest temperature yet detected.

J2137, along with another PG 1159 star designated SALT J172411.7−632147 (or J1724) were found to be variables, with more than one period detected in the 600 to 1200 s range. Astronomers have designated these two stars as GW Vir variables, making SALT J213742.6−382901 the most important GW Vir variable known to date.

Summarizing the results, the paper’s authors stress that further studies of J2137 and J1724 could be crucial for testing theoretical models of stability in GW Vir stars. They suggest more extensive observations, likely using space observatories, that would help reveal its stellar properties in detail.

more information:
CS Jeffery et al, Hot white dwarfs and pre-white dwarfs detected using salt, Monthly Notices of the Royal Astronomical Society (2023). DOI: 10.1093/mnras/stac3531. on me arXiv: DOI: 10.48550/arxiv.2301.03550

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