Re: GSC 748-1618 color

[Michael Koppelman <lolife@bitstream.net>]

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