Observations shed more light on the atmosphere of white dwarf GD 424

Observations shed more light on the atmosphere of white dwarf GD 424

Mean spectrum of the white dwarf GD 424 obtained with WHT / ISIS on 26 August 2017. Credit: Izquierdo et al., 2020.

Astronomers have made spectroscopic observations of a newly spotted white dwarf star known as GD 424. Results of the observation campaign provide more insight into the atmosphere of this object. The study was presented in a paper published on arXiv.org on December 23rd.

White dwarfs remain compact nuclei of low-mass stars that have depleted their nuclear fuel. Although their atmosphere consists mainly of hydrogen or helium, between 25 and 50 percent of all known white dwarfs show traces of metals in their spectra. These metals are believed to have originated in the growth of tidal disturbed planetary bodies. Spectroscopic observations of metal-contaminated white dwarfs can be an essential tool to measure the large compositions of the parent bodies.

Therefore, a team of astronomers led by Paula Izquierdo of the University of La Laguna, Spain, made spectroscopic observations of GD 424 – a metal-contaminated, helium-atmosphere white dwarf of the spectral type DB with a large amount of trace hydrogen. For this purpose they use the Intermediate dispersion Spectrograph and Imaging System (ISIS), mounted on the 4.2 m William Herschel Telescope (WHT) and the high resolution Echelle Spectrometer (HIRES) of the 10 m Keck I telescope.

“We presented the discovery and chemical abundance analysis of GD 424, a metal-contaminated DBA white dwarf with one of the largest amounts of trace hydrogen ever measured among white dwarfs with similar temperatures,” the scientists wrote in the newspaper.

The researchers used a hybrid method to align synthetic spectra, photometry and data of the ESA Gaia DR2 parallax with the WHT optical spectrum, enabling them to determine the photospheric parameters of GD 424. The white dwarf has been found to have an effective temperature of about 16,560 K, mass of about 0.01 solar masses, radius of about 0.0109 sunbeams and cooling age is about 215 million years.

Analyzing the spectra of WHT and Keck, the team identified 11 metals in the atmosphere of GD 424, namely oxygen, sodium, manganese, chromium, nickel, silicon, iron, magnesium, titanium, calcium and aluminum. The astronomers assumed that the presence of these elements was due to the growth of a planetary body on the white dwarf.

They added that GD 424 is likely to collect dry, rocky debris in the increasing or steady state. The photometric results also enabled the researchers to estimate the composition of the parent body.

“The estimated composition of the parent body corresponds to both CI chondrites and the largest earth. (…) The composition of the parent body did not reveal an excess of oxygen. This suggests that the large amount of trace hydrogen is probably the result of the earlier growth of water-rich planetary animals, ‘the authors of the paper concluded.

Further observations of GD 424, focused on measuring the abundance of volatile elements, are needed to gain more insight into the nature of the parent object.


First contaminated white dwarf found in Gaia DR2


More information:
GD424 – a helium-atmosphere white dwarf with a large amount of trace hydrogen in the process of digesting a rocky planetesimal, arXiv: 2012.12957 [astro-ph.EP] arxiv.org/abs/2012.12957

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Quotation: Observations shed more light on the atmosphere of white dwarf GD 424 (2020, 30 December) obtained on 31 December 2020 from https://phys.org/news/2020-12-atmosphere-white-dwarf-gd.html

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