Re: GSC 748-1618 color

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

I would not worry about that bump; you have many other areas with
equivalent deviations.  Bumps on RR Lyr curves typically occur
just short of minimum.  A good book is Horace Smith's RR Lyrae Stars.
   I've placed a single-night BVRI calibration of the field at
ftp://ftp.nofs.navy.mil/pub/outgoing/aah/sequence/g0748.dat
in case anyone wants to compare the TASS V,I results for the
field.  Estimated external error for a single-night calibration
is about 0.03mag.
Arne

Michael Koppelman wrote:
> On Wednesday, February 19, 2003, at 03:55 AM, Patrick Wils wrote:
> 
>> For what it's worth: TASS V-I is largest (redder) when the star is at
>> its faintest, and smallest (bluer) when at maximum.  This would agree
>> with the RR Lyr type.
>>
> 
> According to Light Curves of Variable Stars (Sterken et al 1996), "The 
> RRab stars have relatively high light amplitudes (visual amplitudes of 
> about one magnitude are common) and asymmetrical light curves (a steep 
> rising branch). These stars are believed to be pulsating in their 
> fundamental node. The RRc variables have lower light amplitudes (perhaps 
> about 0.5m) and more nearly sinusoidal light curves. They are believed 
> to be pulsating in their first overtone. The periods of RRab variables 
> are mostly in the range of 0.4 to 1.0 day and the RRc in a range from 
> about 0.2 to 0.5 day."
> 
> 
>  From this light curve:
> 
> http://www.lolife.com/astronomy/gsc748-1618/7481618_phase_3.jpg
> 
> I would describe our star as being sort of in the middle. The rising 
> branch is steeper than the descending branch, but not by much (based on 
> visual inspection). The amplitude is ~0.4m. The period is 0.78 days. The 
> shape is similar to CS Eri (an RRc) in the book above and not at all 
> like SW Dra (an RRab). Just based on the above book, I would put this 
> star in the RRc category.
> 
> I wonder about the little bump at phase 0.25. There is an average of 5 
> observations per point in that area. It could be one or two bad points 
> screwing it up, but it seems like bumps are not uncommon on these 
> things. I think that is just one night of data so it is probably not 
> conclusive.
> 
> Cheers,
> Michael Koppelman
> 
> 
> 
>