Re: GSC 748-1618

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

Date: Wed, 7 Mar 2007 05:24:06 +0100
From: Wolfgang Renz <w_renz@onlinehome.de>
To: Tass Mailing List <tass@mail.alembic.net>
Subject: Re: GSC 748-1618


The color index and the mags of GSC 748-1618 are varying pretty synchronious.
AFAIK that possible for RR Lyr stars but shouldn't for all CEP type stars.
Especially not when comparing B-V to V or bluer band mags.

Right ?

Clear skies
 Wolfgang

-- 
Wolfgang Renz, Karlsruhe, Germany
Rz.BAV = WRe.vsnet = RWG.AAVSO



----- Original Message -----
From: "Tass Mailing List" <tass@mail.alembic.net>
To: <Undisclosed recipients:>
Sent: Thursday, February 22, 2007 3:11 AM
Subject: Re: GSC 748-1618


> 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.