Re: more GSC 748-1618

[Arne Henden <aah@nofs.navy.mil>]

Michael,
   Don't trust the B and V values listed in Simbad for a
variable star; they are not necessarily taken at the same
phase in the variation, nor even by the same observer.  They
are just representative of the star.  In reality, RR Lyr has colors
that are very typical for the variable type.
   Any RR Lyr or cepheid is brighter than the main sequence at
the same temperature, and tend to be quite distant (for example,
only RR Lyr itself has a crude parallax; the rest of the RR Lyrs
are too distant).  This almost always means the stars are reddened.
So typical measured colors are not typical intrinsic colors.
   Pre-maximum bumps are common in pulsating stars, especially
the metal-poor ones.  You should read Smith's book to see what
the possible explanations for such bumps might be.  It is good
that you are reading up on such pulsators.  Doug is the real
expert here, having looked at thousands of pulsator light curves
in the course of the Macho project.
Arne


Michael Koppelman wrote:
> I have an astronomy textbook and it has an idealized light curve of RR 
> Lyr and it has a similar bump prior to the maximum. I went a-lookin' for 
> more detailed light curves of RR Lyr and found one in a paper entitled 
> "The Blazhko Effect of RR Lyrae in 1996" by Smith et al 
> (2003PASP..115...43S). The light curve rises a little then dips down 
> before it rises to maximum. Another curve of RR Lyr is in "Light Curves 
> of Variable Stars" (Sterken & Jaschek) on page 84.
> 
> For GSC 748-1618, Arne got B-V (at minimum) of 0.72. V-I at max is 
> around 0.75 and at min is at 0.87. This seems to imply a G-type star.
> 
> RR Lyr, on the other hand, is described by SIMBAD as having B-V=-0.59 
> and type F5. Their B-V seems completely wrong to me. According to 
> SCHOENEICH et al (1979IBVS.1557....1S) B-V is more like 0.178 at 
> maximum. I don't know how RR Lyr could be as blue as B-V=-0.59 and yet 
> be described as an F5 -- isn't that way too blue for F5? VizieR catalogs 
> generally have B-V ~ 0.4 or so for RR Lyr.
> 
> So what I'm pondering is: this star is much redder than RR Lyr. It has a 
> similar shape to RR Lyr, but the "bump" shape is much more evident in I 
> than V. It seems to me that this star has a "red" overtone.
> 
> This star is situated in the Orion arm of the Milky Way so I suppose it 
> is possible there is a lot of reddening?
> 
> Cheers,
> Michael Koppelman
> 
> 
> 
>