[vsnet-chat 7567] A somewhat extreme amplitude object in the TW Hya Association

[substellar at Safe-mail.net]

Whilst we're thinking Southern regions, TWA 30.  It sounds a bit like an airline flight from times past, but it is instead a T Tauri star in the TW Hya Association which is an increasingly the flavour of the month region in satellite studies amongst other, as it is probably one of the nearest and youngest stellar assocations to us, especially for low mass stars.

The Catalina Real Time Survey picked this up as variable a few days ago from the Siding Spring Survey part ( http://nesssi.cacr.caltech.edu/SSS/Allns.html )

here's their information :-

summary :- http://nesssi.cacr.caltech.edu/SSS/20100715/1007150310754130644.html

lightcurve :- http://nesssi.cacr.caltech.edu/SSS/20100715/1007150310754130644p.html

identification :- http://nesssi.cacr.caltech.edu/SSS/Circulars/1007150310754130644.html

It's in SIMBAD under two different object identifiers :-

http://simbad.u-strasbg.fr/simbad/sim-coo?Coord=11+32+18.314-30+19+51.85&CooFrame=ICRS&CooEqui=2000.0&CooEpoch=J2000&Radius.unit=arcmin&submit=query+around&Radius=1

This looks to be an extreme CTTS (Classical T Tauri Star) variation of about three and a half magnitudes.

As CRTS notes, there is a recent paper on the star http://arxiv.org/abs/1003.3447 (Looper et al 2010ApJ...714...45L)

But the CRTS data are also showing about three and a half magnitudes quasiregular variation.  This might be the most extremely varying object in the whole of TW Hya, and it's a bit extreme for any T Tau star in regular terms.  But with the sparse data so far, whether or not there's any cyclicity, or quasicyclicity (or even "timescale") to these events is not certain.  If it is due to accretion disc obscuration or something exotic like that, say in a KH15 D sort of way, more monitoring would be needed.  BVIc should allow things to be attempted to be sorted out, for instance.  If the variation was photospheric the change in colour indices would follow one pattern in terms of B-V and V-Ic due to blackbody and Wien's Law reasons, if the fades are due to disc or obscuration by other attenuating material then B is extincted more than V which is extincted more than Ic, so the colours B-V and V-Ic should show themselves to be affected relatively differently than they are in the blackbody/photospheric case.  It probably does go a bit faint for amateurs to be able to follow fully though.  The above Looper paper notes large variation in Av (absorption) 1.5 to 9.0 which is ~~ 0.5 to 3 in E(B-V) terms.  Rc is not recommended as there also appears to be variable Halpha emission, which could complicate matters if Rc was used.

Anyway, the paper's there, the stars active enough, and the paper suggests it's an important object to follow for low mass stellar formation studies.  This'd probably be epoch photometry stuff, two or three contiguous observations per night (for backup/confirmation of observations) spread over time, whenever convenient, to fill in the history of changes, rather than time series stuff.

Certainly the number of in depth papers on the object Looper et al suggest it might be an analogue to, AA Tau, is large.

Just something a little different to the norm that isn't a well known or well monitored object.  Probably a bit late in the season for this year, but a long term project anyway.

Cheers

John

PS Southern observers will note that this Sidings Spring addition to CRTS, using the images taken by Rob McNaught and Gordon Garrard for the Southern CSS NEO work, has come on stream.  A recent outburst of TY PsA was caught by it for instance, although it doesn't replace visual observers as it isn't all sky and isn't all time.  But every now and again it might catch something bright that is missed elsewhere, and has some Celestial Equator overlap for the Northerners too.