[vsnet-chat 4015] Re: QX Pup

[aah@nofs.navy.mil]

I wrote, and Kato-san replied twice, as following:
>>>To be strictly accurate (and less confusing!), QX Pup
>>>is the embedded, invisible Mira inside of the
>>>bipolar nebula OH 231.8+4.2.
>>    If the starlight were not entirely visible, how come the spectral
>> classification of M6I or M9III was obtained ??  Are we observing the
>> scattered light from the Mira star?
>   For example, A&A 355, 1103 (2000), clearly shows the M-type spectrum
>in the optical, indicating the presence of significant amount of scattered
>starlight contributing to the optical light.

Yes, Sanchez Contreras et al. show the reflected light of the Mira off
of the nebula; in this manner and also from the IR spectra, we know
that the star is M6-M9.  However, you cannot see the Mira directly; it
is too deeply embedded in its dust cocoon.  I quote from their paper:

"The emission in the R image arises from two inner, relatively narrow
nebulosities located at both sides of the central star and aligned
with the nebular axis, the southern being intrinsically brighter than
the northern one.  The size of the south nebulosity in R is about
4"x4" at half maximum."

Later, they also state:
"Since the source illuminating the nebula is a Mira variable star (Sect. 1),
the brightness of these nebulosities is expected to change with time."

The amateur images I've seen posted would show such a small nebulosity
as star-like.  With a period of 708 days, and a maximum around JD2444396
(Kastner, et al. 1997, ApJ 398, 552), the Mira would currently be at
phase 0.63 from Kastner's K-band light curve.  However, my recollection is
that K-band and V-band variations are not phase-locked, and in addition,
the composite light curve Kastner et al. show is not convincing to me
regarding the JD of maximum, so how bright the inner nebulosity would
be at the current epoch is uncertain.  They state one possible reason
for the phasing discrepancies is light travel time to the lobes,
giving a phase lag on the observed reflected light (since their
30arcsec measuring aperture included the inner nebulosities as well
as the Mira), and actually use this value to obtain a distance -- neat idea,
but one that also highlights the difficulty in working with embedded sources.
  It would be an interesting project for amateurs to follow the
brightness variation of the southern lobe and
see if they can get a better period for the Mira.

Arne

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