(cba:news) T Pyx 2020-1

[Joe Patterson]

Hi CBAers,
As many of you know, we have a paper on IM Nor/T Pyx about to go out the 
door (early version on astro-ph a few weeks ago).  Although IM Nor is 
nominally the subject, the crux of the relevant physics lies with T Pyx, 
because that star's historical record is vast... and also because the 
analysis of IM Nor itself is greatly hampered by interstellar extinction.

So even though we wrote a long paper in 2017 on T Pyx alone, it's time 
for another - because our audacious claims re the T Pyx/IM Nor 
phenomenon (runaway mass transfer, resulting in the binary's death) 
could use more scrutiny with new data.  There are two important issues 
which our new observations could address:
(1) Is the rate of orbital-period increase now the same as it was 
pre-outburst, or measurably less?
(2) Has the star's brightness, averaged over many orbits, changed from 
the pre-outburst average?

Sunce we observe it a LOT, we don't need a great deal of new data to 
address these questions. A few weeks of coverage will do it.  Ideally 
the runs should be >2.5 hours long, and it would be best if you obtained 
some through a V filter, and some through your usual setup (probably 
unfiltered or some sort of minus-blue filter).  The reason for the V 
filter is calibration, of course.  The reason for some unfiltered 
coverage is to compare it with what you have done in past years.

This sort of approach has  a good chance to distinguish between the two 
leading interpretations:
(a) T Pyx is doomed.
(b) T Pyx is just having a bad coughing fit, lasting a few centuries. 
This interpretation has been advanced by Brad Schaefer, with some pretty 
decent evidence to back it up.

Pyxis is usually reserved for southern observers.  But at -32 degrees, 
this star is also fine for southern-USA observers, if you plan your 
observations around meridian passage, when the star is moving 
horizontally.  Of course we always dislike airmass - but most of all, we 
dislike CHANGES in airmass. (And thanks to those of you who include 
airmass in their observing reports.)

joe
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