Return to Home Page
From John Greaves: === Hi Tom >From time to time I'm trying to find the more exotic types of variables in you new candidates' lists, using a touch of the astrophysicals. This is one. ---- GSC 4024 1501 is a variable Herbig Ae/Be (a young stellar object) ionising a nearby HII region. GSC 4024 1501 has a large J-Ks excess, +2.0, B-V is 0.84, it is Halpha emission source HBH 4-9 estimated at spectral type B, is visible in IRAS and MSX5C, the latter seeing it at bands A, C, D and E, with the last showing variability. It's probably the ionising source of the HII region Sharpless 182. POSS plates show this nebula to be quite faint on red plates, so the effect the nebula has on the background component (ie that is going to be brighter than the standard sky background) may offset V and Ic values a bit from truth on a CCD frame, but it is not going to be much at V, and is irrelevant to relative variation. Doesn't appear to be a multiple star, nor does the nebula appear to be a Stromgren Sphere, suggesting there aren't any other B and especially O type comes involved. No known Herbig Haro objects either, so it's not clear whether S 182 is natal or just adjacent. I'm not certain which, if any, nearby Cassiopeia OB Association it belongs to, as there are several around this bit of sky, but it does lie quite close on the sky to star forming region [R2003] 169, which lies at roughly 1.4 kpc (kinematic) distance. At such a distance, the average apparent V and B-V of this star fits well with a late B type star when extinction is allowed for (though there's probably a local component as well to be taken into account), confirming the suggested spectroscopic classification. Rough estimation is Mv ~ -3.5, if E(B-V) is assumed to be around 0.9, for example. The amplitude of variation appears to be on the edge of the acceptable range for the usual visual observer, but it is always possible that the irregular and widely spaced dips such stars are liable undergo to may occur for this star too, even if none are seen in TASS as yet, and visual observers would manage to pick those up easily. They certainly won't be seen without monitoring. I can't remember who exactly is interested in YSOs, but I know someone out there has a preference for them. Tested first by going through all the catalogues after noting it being the reddest object on your September candidates list, then subsuently noting that it had J-Ks excess relative to B-V. Patrick Wils kindly assessed the observational data and light curve and confirmed actual variation. Miniscule plot of V observations enclosed. Cheers John
Return to the Powerful Daisaku Nogami
vsnet-adm@kusastro.kyoto-u.ac.jp
