Re: GSC 748-1618

[Tass Mailing List <tass@mail.alembic.net>]

Date: Wed, 21 Feb 2007 17:35:43 -0600
From: Michael Koppelman <lolife@bitstream.net>
To: Tass Mailing List <tass@mail.alembic.net>
Subject: Re: GSC 748-1618

Good point, Adam. Doug is convinced that it is a Cepheid but I'm
curious how one would tell? It does seem a bit too symmetric for an
RRab...

M.


On Feb 21, 2007, at 1:21 PM, Tass Mailing List wrote:

>
> Date: Wed, 21 Feb 2007 01:39:59 -0800 (PST)
> From: Adam Kraus <alk@phobos.caltech.edu>
> To: Tass Mailing List <tass@mail.alembic.net>
> Subject: Re: GSC 748-1618
>
>
> Hi Michael,
>
> It actually may not be too red for an RRab. If I have the right
> coordinates (SIMBAD is not responding at the moment), GSC 748-1618
> sits at
> a very low galactic latitude (b=4 deg). This means you're probably
> picking
> up a nontrivial amount of extinction. If the intrinsic colors are near
> zero, then adding 2.1 magnitudes of visual extinction would supply
> just
> about the right amount of reddening: E(B-V)=0.7 and E(V-I)=0.85.
> This is
> also roughly consistent with its NIR colors from 2MASS: J-K=0.43,
> H-K=0.12. Both colors can be reproduced for an A-F star with 2-2.5
> mags
> of visual extinction.
>
> Its brightness (K=9.5) suggests that if it's an RRab, it's sitting
> out at
> ~1 kpc, so ~2 magnitudes of visual extinction may be a reasonable
> number.
> It's a little suspicious that it's so close to the plane, so alternate
> explanations that involve disk stars are certainly plausible, but
> there
> are going to be some halo stars there too. (This probably explains the
> ASAS classification - if I recall, they divide pulsators by galactic
> latitude and call everything near the plane a short-period cepheid.)
>
> I can't comment one way or the other about the light curve
> morphology. I
> mostly chase after low-mass detached eclipsing binaries, so
> anything I see
> that's sinusoidal gets refiled in my "someday" stack.
>
> Adam
>
> On Wed, 21 Feb 2007, Tass Mailing List wrote:
>
>>
>> Date: Tue, 20 Feb 2007 22:55:32 -0600
>> From: Michael Koppelman <lolife@bitstream.net>
>> To: tass@tass-survey.org
>> Subject: GSC 748-1618
>>
>> You guys remember this discussion?
>>
>>> On Sat, 1 Mar 2003, Patrick Wils wrote:
>>>
>>>>
>>>> --- Doug Welch <welch@physics.mcmaster.ca> wrote:
>>>>> I am a little curious why people have decided to ignore
>>>>> my suggestion that this is a short-period, overtone
>>>>> Cepheid. Perhaps it wouldn't seem so strange then!
>>>>
>>>> Yes, I agree now (I was quite sure it was an RR Lyrae star
>>> before, but
>>>> it doesn't fit in either of the RRab or RRc class, so it can't be).
>>>> Aren't these overtone Cepheids always double mode pulsators ?  In
>>> that
>>>> case a frequency analysis should reveal a second period of about
>>> 0.63
>>>> days.
>>>>
>>>> Patrick
>>>>
>>
>> Take a look at the attached PNG file. ASAS has since called this a
>> "DCEP-FO". Does that make sense? I'm not even sure what that means.
>> We've been thinking this was an RRab but it is too red at B-V~0.7 and
>> V-I~0.8
>>
>> Cheers,
>>
>> M.
>>
>