Re: GSC 748-1618 period

[Doug Welch <welch@physics.mcmaster.ca>]

Michael,

This looks very much like a first-overtone Cepheid of period 0.77 days.
A very large fraction of the Cepheids in the LMC and SMC with periods
this short are double-mode with the less dominant mode being the second
radial overtone! It would be extremely interesting if TASS/you has/have 
caught a mode selection change (which is possible but has never been 
observed in these stars).

My former grad student Andy Rorabeck wrote a paper which you might be
interested in looking at:

ApJ, 511, 185 (1999) Alcock et al

There are very few first-overtone Cepheids of this short period
known in the Milky Way - mainly because of amplitude selection
effects in old photographic surveys.

Cheers,
Doug

On Fri, 14 Feb 2003, Michael Koppelman wrote:

> So I'm working on GSC 748-1618. I have TASS data and I have my own 
> data. When I use only my more recent data it looks like this:
> 
> http://www.lolife.com/astronomy/gsc748-1618/7481618_phase_1.jpg
> 
> While perhaps not the actual period, it is clearly related to the 
> period.
> 
> When I add all the data, which includes the TASS data and my earliest 
> data, the same period looks like this:
> 
> http://www.lolife.com/astronomy/gsc748-1618/7481618_phase_2.jpg
> 
> It seems like maybe I'm just off by a factor of two or something, but 
> I've tried every probably period between 0.5d and 3d and I can't find 
> anything that makes all the data work.
> 
> The data is here:
> 
> http://www.lolife.com/astronomy/gsc748-1618/data_hjd.txt
> 
> If you are interested.
> 
> Thanks for any insights. It is possible the period is changing on the 
> time scale of a year or so?
> 
> Michael Koppelman
> 
> 

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