[vsnet-newvar 1710] MisV1147 is probably B5 spectral type

[jg@jgws.freeisp.co.uk]

Doug West's examination of this thing has reappraised a problem I had
with it a while ago.

I was convinced it was a T Tauri star form Arne's photometry, whilst
Taichi Kato favoured an Ae/Be star, now Doug sees an argument for both
an early and a late pair from the same data.

I gave in, and asked Brian Skiff for thoughts.

He introduced me to a reddening parameter called Q, details I cut and
paste below, which are from a calibration table of his that he maintains
(I forget the source ftp url)

Dropping Arne's figures through the simple equation gives around -0.5 to
-0.4 for Q, or B4 - B6 ish.


When it comes to reddening, Q now suggests B5, and Arne's B-V value
suggests a reddening, E(B-V), of about +1.1 if this star is B5, and
using other formulae at the time, I got Av of about 3.3 or so [using Av
= 3.1E(B-V)], whilst if membership of Cep OB1 at 3.5 kpc was assumed,
and taking table absolute magnitude values for B5 stars, in tandem with
the distance modulus for Cep OB1 (12.7), plus this extinction value,
gave an apparent magnitude of around V = 13, which is more or less what
this object is at maximum.  The numbers, though close, didn't fit
perfectly, but spectral type and reddening are not well constrained, and
locally interstellar extinction could be above the usual norm.  There's
a lot of dark clouds around this bit of the sky.

The argument gets a bit circular somewhere along the way in the above,
but an early type star can be made to fit.  The star can readily be an
early type object with strong reddening.  I'm not against anybody double
checking my arithmetic and/or logic stream either!

It's probably an Ae/Be star, but is at an UXOR? (UX Ori subtype).  I
can't decide, as UXORs don't seem to be that well defined/categorized in
the literature I have found on them.


Doug, is it too faint for your Halpha equipment?  The object seems to be
constant at Halpha, even when varying in visible light, according to a
very _small_ amount of data.  The intensity at Halpha is a lot higher
than the continuum.


Cheers

John Greaves


> I.  Q versus spectral type for early-type stars
> 
> Q = (U-B) - 0.72(B-V)  [Johnson & Morgan 1953]
>   = (U-B) - 0.645(B-V)  for B1V-A1V [Heintze 1973, IAU Symp 54]
> 
> 
> type   Q(JM)   Q(H)
> O5    -0.93   -0.93
> O6    -0.93   -0.93
> O8    -0.93   -0.93
> O9    -0.90   -0.89
> B0    -0.90   -0.85
> B0.5  -0.85   -0.81
> B1    -0.78   -0.78
> B2    -0.70   -0.70
> B3    -0.57   -0.62
> B4            -0.55
> B5    -0.44   -0.47
> B6    -0.37   -0.39
> B7    -0.32   -0.32
> B8    -0.27   -0.24
> B9    -0.13   -0.16
> B9.5          -0.12
> A0     0.00

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