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Type A star looks like LPV

cappella's picture
cappella
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Joined: 2012-07-22

I am a volunteer at the Planet Hunters' site.
Today I found a lightcurve that looks like an LPV, but when I checked the star's type is was type A.
Here is the star: http://talk.planethunters.org/groups/SPH10023764
Now LPVs are type M and K, mostly, so I don't think this is one.
Maybe someone can have a closer look at it and give his/her opinion.
Thanks,
cappella

HD 185330, a B-type star
Sebastian Otero's picture
Sebastian Otero
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Joined: 2010-09-19

Hi, Abe,

This star is HD 185330 and it is in the Hipparcos catalogue where it shows no variability. Also the GCPD shows V= 6.51. The spread of the available photometry is 0.02 mag. at most.
Its spectral type is B5II-III or B3III in several sources although B5V in 1976A&AS...26..241C. Also B5 He wk in 2009A&A...498..961R.

I don't know why it is mentioned as having a spectral type A in the Planet Hunters site when it has a J-K of -0.14 and a B-V of -0.15.

I can think of several explanations. The first one is that the star is too bright for Kepler at V= 6.5 and that the data are saturated or suffer from some kind of problem.
The fact that the star is completely constant in the data from the first quarter is suspicious. Then we have some apparent inconsistencies in the light curve, like in quarter 2 where the star seems to have awaken slowly but then after a gap in the data we find it fading from a brighter magnitude.

Then it seems to develope a quasi-sinosuidal variation with an amplitude up to 0.003 mag. and a cycle of 40 d. or so. The amplitude is so small that if it is real it couldn't have been detected from the ground.
Being a B-type star it wouldn't surprise if it had switched to the Be state and that spectra would show emission lines. However, Kepler detects variability at such an insignificant level that saying that 0.003 mag. is a sign of Be activity is a risky asumption.

So, no, it is not an LPV. But it is also not an A-type star. So beware of those spectral types not based on actual spectra.

Best wishes,
Sebastian

 

HD 185330, a B-type star
cappella's picture
cappella
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Joined: 2012-07-22

Hi Sebastian,

Nice to meet you here as well :-).

On Planet Hunters there is no Type B qualification, unfortunately, so I look at the temperature to see if a star is Type A or Type B. I use >10000K as a Type B characteristic, but that is not a given.

I have to do some research on the J-K and B-V terminology, as they are new to me.

Thanks for looking into this star and cheers,

Abe

AAVSO 49 Bay State Rd. Cambridge, MA 02138 aavso@aavso.org 617-354-0484