New white dwarf
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by bluemagi
Came across this Objid:1237662640125640716. Ra=250.56948 Dec=21.35475,Class=Star 08/09 (167771). Interesting Spectrum.
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by JeanTate in response to bluemagi's comment.
Nice!
An O8/O9 star is not a white dwarf, but a blue supergiant. These are at the top of the Main Sequence, and are still 'burning' hydrogen. They are very massive, and live very short lives (for stars), possibly as brief as ~10 million years. They go out with a bang ... almost all of them self-destruct as a Type II (core collapse) supernova.
As you noted, the spectrum rises into the blue; if you took a spectrum from space, above the Earth's atmosphere (which absorbs UV, thank goodness), it would continue to rise into the far UV; this is one very, very hot star.
Hope this helps, and happy hunting! 😃
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by Budgieye moderator
The spectrum looks like a white dwarf? Is SDSS identifier wrong?
EDIT: Well, they do look similar.
Spectral cross-correlation templates http://classic.sdss.org/dr5/algorithms/spectemplates/
see no 1 and nos 21 and 22http://skyserver.sdss.org/dr12/en/tools/explore/Summary.aspx?id=1237662640125640716
more info on spectra for those interested
PAGE 3 Spectra guide for SDSS images in Galaxy Zoo Talk http://talk.galaxyzoo.org/#/boards/BGZ0000001/discussions/DGZ0000ulp?page=3&comment_id=53fef2ee3d5a77490c0001b6
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by bluemagi
Did find the white dwarf today its OBJid:1237665567158239336 at RA=247.56045 DEC=12.87059. Its interesting to see the 2 spectrums together.
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by Budgieye moderator
Blue supergiant spectrum vs white dwarf
http://skyserver.sdss.org/dr12/en/tools/explore/Summary.aspx?id=1237662640125640716
http://skyserver.sdss.org/dr12/en/tools/explore/Summary.aspx?id=1237665567158239336
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by bluemagi
Thank you for putting the spectrums together. I can't use a computer like the younger generation.
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by JeanTate
Interesting to see why, even at the resolution in the displayed spectra, one is an O8/9 and the other a white dwarf (WD).
I think, in terms of the physics, it's primarily due to pressure: the surface gravity of an O8 supergiant is really low (one reason why it so easily loses so much mass), while that of the WD is really huge. This produces narrow absorption lines in the former, and really broad ones in the latter ("pressure broadening").
Then there are all those other lines in the supergiant, while the WD has only H-Balmer series ones ...
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