[vsnet-newvar 1740] re De-Reddening of MisV1147 V-I Photometry

[jg@jgws.freeisp.co.uk]

These values are nice.

The spectral class is reaffirmed, quite succinctly too.

The ratio for Av is pretty much ~3 everywhere, except in very localised
places with intense extinction.

Note that the second observation is during a time of 'eclipse'.

From general viewpoint, but primarily the lack of clean eclipses and/or
any true periodicity, the consensus is that this object is undergoing
obscuration events via circumstellar matter as opposed to being eclipsed
by a companion star.  Some other bits of evidence, such as 'Blueing
Effect' and general lightcurve morphology support this.

YSOs often have some sort of infrared excess due to circumstellar
matter.

I see no reason why this shouldn't also be true to some extent in the
far red, ie Ic.

It would be better to search now for references that may allow you to
determine the nature of the obscuration material by taking observation 1
as the 'true' star and base point, and, assuming the difference between
it and observation 2 as being entirely due to the obscuring material (in
the first instance).

The relative amounts of 'extra' reddening at B-V (virtually none), V-Rc
and R-Ic (or V-Ic) during observation 2 may allow some assessment as to
whether the material is primarily gas, primarily dust, and/or both, and
if both, in what sort of ratio.

I am not sure on the details of this matter however, and am further
uncertain as to whether this can be assessed without data from IR
passbands such as J, K and L, which are not readily available.

Possibly Allen's 'Atoms, Stars and Nebulae' would be useful as an
introduction to such topics.


(Has _anyone_ out there got access to a polarimetry filter!?)


Cheers

John Greaves

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