Re: GSC 748-1618

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

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.
>