Elements found in two hydrogen atmosphere white dwarfs

White dwarf (Image Credit: Jonathan Saurine/Science Vault)Main Points:

Astronomers have reported the chemical composition of two white dwarfs, G29-38 and GD 133, outside the solar system. Oxygen, magnesium, Silicon and Calcium are found in both planetesimals.

Published in:

The Astrophysical Journal

Study Further:

White Dwarf:

It is a small, dim, extremely dense star that has collapsed on itself and is in the final stages of its evolution.

Elements in white dwarfs:

Calcium is the most easily noticed element and has been found in more than 200 white dwarfs. Scientists utilized high-resolution spectroscopic observations and have found about 19 heavy elements in the atmosphere of white dwarfs. These 19 elements include C, O, Na, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Sr.

Until now scientists have found three hydrogen dominated white dwarfs having more than 8 elements. These are as follows:

  • 11 for WD 1929+012
  • 10 for WD 0843+516
  • 9 for NLTT 43806

Moreover, 10 white dwarfs are known to have at least O, Mg, Si, and Fe in the atmosphere.

Planetesimal:

It is a small rocky celestial object thought to have orbited the Sun in the early stages of the solar system before coalescing with others to form the planets. They can be of different sizes ranging from several meters to hundreds of kilometers.

You can think that these are small planets but actually the term occupies a number of different characteristics.

G29-38 (WD 2326+049) and GD 133 (WD 1116+026) are two extrasolar planetesimals having hydrogen atmosphere. These are pulsating ZZ Ceti hydrogen white dwarfs.

Present Study:

In the present study, astronomers spectroscopically analyzed G29-38 and GD 133 with the High Resolution Echelle Spectrometer (HIRES) on the Keck telescope and the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope (HST).

Scientists found abundance of eight elements including C, O, Mg, Si, Ca, Ti, Cr, and Fe in G29-38, and elements including O, Si, Ca, and marginally Mg have been found in GD 133. After this finding, G29-38 is the forth known white dwarf having 8 or more elements.

Scientists have also reported that extrasolar planetesimals have almost the same elemental compositions as that of bulk Earth regardless of their evolutionary history.

“We continue to find that a variety of extrasolar planetesimals all resemble to zeroth order the elemental composition of bulk Earth,” Scientists wrote in the paper.

Reference:

S. Xu (许偲艺), M. Jura, D. Koester, B. Klein, B. Zuckerman (2014). Elemental compositions of two extrasolar rocky planetesimals The Astrophysical Journal DOI: 10.1088/0004-637X/783/2/79

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