[vsnet-newvar 1736] re De-reddening of V-I Photometry for MisV1147

[jg@jgws.freeisp.co.uk]

Doug West wrote :

> I have ran into a snag in my effort to de-redden Arne Henden's V-I
> photometry for MisV1147.  If you remember, I was trying to calculate the
> spectral class of the object.  To de-redden the photometry on of the
> quantities I need to know is E(V-I). To calculate E(V-I) I need to know
> the approximate distance.  This area of the sky has a high interstellar
> extinction, that is, 2.6<Av<3.3 mag at 1 kpc according to Neckel and
> Klare, 1980, Aston. Astrophys. Suppl. Ser. 42:215-281.  Doing a quick
> literature search in ADS didn't reveal a typical absolute magnitude for
> YSO's.  I have found wide variation in the estimated luminosity values for
> the objects.  Does anyone have a qualified guess as to what distance I
> should use in my de-reddening calculations?

Hi Doug

As noted in an earlier post, this object lies in the direction of the OB
Association Cepheus OB1.

Although not necessarily a member of said (then again, it is an early
YSO, and this a star forming region for early type stars), it is more
liable to be in the Galactic spiral arm that Cepheus OB1 is situated in,
and which passes through Cepheus here, than a random field star born
outside any spiral arm or molecular cloud complex or the like.  It is
not likely for a young star to have moved much from its birthplace as of
yet.

So, that gives you a distance you can reasonbly assume, at least for a
first look.

The distance to CEP OB1 is 3.4 kpc, ie 3400 parsecs.


Indeed, if using these values for V-Ic gives agreement with the B-V
results, then the assumption will be somewhat confirmed and membership
of this Association, or at least close proximity thereto, likely.


It is a shame that the absolute magnitude of these objects is not well
constrained.  Possibly they're inherently scattered.


Cheers

John Greaves

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