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[vsnet-gcvs 109] Re: [vsnet-chat 4739] Upsilon Sagittarii status
Dear friends:
I made a HUGE MISTAKE ( :-(( last week when I sent a
message about upsilon Sagittarii.
Don't ask why but it looks like my brain was full of air that night and I
said that upsilon Sagittarii was a yellow semiregular star.
A fact that can be easily proved wrong by takimg a look at the B-V color
index only: 0.1 !!
It's ironic, since I was trying to clarify problems with the classification
(and I was one of those who didn't agree with the classification of most of
the variables as SR's,....!!!) and I ended up with a mess.
Thom Gandet made me realize this. He also commented:
"... Both stars have very early spectral types.
They are approximately B2Vpe and A2Ia(Shell), but the spectra vary
with time and there has been some minor disagreement about the
precise types. However, it is certain that both stars are hot,
blue stars."
"... Therefore, neither star of this system is "yellow" or could be
> classified as SR. (The SR classification is used only for late-type
> ("yellow" or "red") pulsating stars...)"
Actually the semiregular variations detected seem to belong to a special
group made up by most of the hydrogen-deficient stars. Most of the RCB stars
also show that behaviour (well, they are hydrogen-deficient too...).
However, when these stars show semiregular variations and have a redder
color (without showing RCB fading events) they have been classified as SR's:
it is the case of V4152 Sgr for instance.
I think they should compose another group of SR stars.
Gamma Herculis is another star that has been classified as SRd (yellow F to
K variables) when its spectral type is A9III.
But as Thom told me, upsilon Sgr, unlike other pulsating stars is a binary
and this may explain some of the variations observed.
In any case, it may be clear that UPSILON SAGITTARII is NOT a cool yellow
pulsating star !!!!
Sorry for this huge mistake !
Sebastian.
PS: the photometric numbers and the fact that the star is not an eclisping
binary were right.......
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