ND: Astrophysicists Release New Study of One of the First Stars

[bystander]

Astrophysicists Release New Study of One of the First Stars
University of Notre Dame | 2016 June 20

No one has yet observed the first stars that formed in the Milky Way. In all likelihood, they will never be directly observed, because the first stars are massive, ending their lives only a few millions years after their birth.

But, astronomers can study those oldest stars by examining the elements these stars produced through nuclear fusion and the supernova explosions that mark the spectacular ends of their short lives.

Timothy Beers ... is part of a team that has used the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope to study key regions of the ultraviolet (UV) spectrum of a star thought to have been enriched by elements from one of the first generation of stars. This star, named BD+44 493, is the brightest known second-generation star in the sky. ...

Beers and his team detected phosphorus and sulphur, which had never been seen previously, and zinc, which had only been seen in one such second-generation star. They compared the amounts of each element to model predictions to learn about the nature of one of the first stars.

Their work is the first to use COS on the Hubble Space Telescope to study the elements in ancient stars. These never-before-seen products of one of the first stars reveal that the particular star that introduced these atoms into space was likely massive, probably more than 20 times more massive than our own Sun, and exploded as a relatively faint supernova. ...

Detection of Phosphorus, Sulphur, and Zinc in the Carbon-Enhanced Metal-Poor Star BD+44 493

• Ian U. Roederer, Vinicius M. Placco, Timothy C. Beers
  Astrophysical Journal Letters 824(2):L19 (2016 June 20) DOI: 10.3847/2041-8205/824/2/L19
  arXiv.org > astro-ph > arXiv:1605.03968 > 12 May 2016

[neufer]

• Star light, star bright,
  The First Star I see tonight;
  I wish I may, I wish I might,
  Have the wish I wish tonight.

[Ann]

Amazing. This star, also known as SAO 38029, appears to be slightly bluer than the Sun, with a color index of around 0.55. It is moderately nearby, some 700 light-years away or so, and it is zipping by us fast. That makes sense if it is a halo star, as SAO 38029 is likely to be. Who knows, this star may even be an escapee from a globular cluster.

SAO 38029 is about 8 times brighter than the Sun, and Simbad Astronomical Database calls it a red giant. Forget it! There is nothing red about it. On the other hand, my software calls it a B2 star, and there is nothing B about it, either.

What a survivor this star is from the childhood of the universe!

Ann

[Chris Peterson]

SAO 38029 is about 8 times brighter than the Sun, and Simbad Astronomical Database calls it a red giant. Forget it! There is nothing red about it. On the other hand, my software calls it a B2 star, and there is nothing B about it, either.

Note that this star is not identified as a red giant, but rather, as lying on the red giant branch. That's very different. Certainly, the foot of the red giant branch includes B-type stars.

[Ann]

SAO 38029 is about 8 times brighter than the Sun, and Simbad Astronomical Database calls it a red giant. Forget it! There is nothing red about it. On the other hand, my software calls it a B2 star, and there is nothing B about it, either.

Note that this star is not identified as a red giant, but rather, as lying on the red giant branch. That's very different.

Good point.

Certainly, the foot of the red giant branch includes B-type stars.

Click to view full size image

The Pleiades. Photo: The Digitized Sky Survey/ NASA/ESA/AURA/Caltech

For young clusters, that is true. I'm sure it can be argued that Alcyone, brightest star of the Pleiades, is technically located at the foot of the red giant branch, because Alcyone is still a B-type star even though it is beginning to evolve off the main sequence.

But as for SAO 38029, it is definitely not a B-type star. Its color is far too red for the star to belong to spectral class B. The star can be seen in the direction of the Andromeda constellation, not too far from the band of the Milky Way across the sky, and its position implies that it might be reddened by dust in our galaxy. But in fact it is too nearby to be significantly reddened by dust between itself and the Earth.

Ann

[bystander]

Relics of the Milky Way's First Generation of Stars
University of Michigan | 2016 June 21