(cba:news) V339 Del and the supersofts

Joe Patterson jop at astro.columbia.edu
Tue Oct 15 05:47:13 EDT 2013


Hi CBAers,

When novae erupt, they eject a large, thick shell of gas, which is what 
we see when we look at it from afar.  In fact, a nova at maximum light 
looks pretty much like a normal A-type supergiant (not the big emission 
lines which make the class famous).  Then, as a few weeks or months 
pass, the shell thins out as it continues to expand.  Emission lines 
appear... and eventually a soft X-ray source signalling a very hot white 
dwarf, when we can finally see down to the central object.

Now soft X-ray telescopes cost about 500 million bucks, which none of us 
(well, hardly any of us) have.  But if we can see down to the white 
dwarf, then probably the secondary star can also, since it's so much 
closer.  So you might expect a strong "reflection effect" from the 
heating of one side of the secondary; and as this surface wheels about 
in its binary motion, a strictly periodic signal at Porb in the optical 
emission may occur.  Properly interpreted and calibrated, the amplitude 
of this signal in energy units can serve as a *bolometer* for the white 
dwarf.

It's a great experiment to do on every sufficiently bright nova, and if 
we could do it, we would save about 499.995 million bucks (figuring 
$5000 for the total cost of all your equipment).  It fails when the nova 
is near max, because the line of sight is so cluttered with absorbing 
gas... and fails decades later, because the white dwarf has cooled.  But 
for a few years after max, it's sometimes possible to measure this.

Kim Page just announced, in ATel 5470, the discovery of the soft 
("supersoft" in the current lingo) X-rays in V339 Del, using the Swift 
X-ray telescope.  And I recall in the last couple of days that Arto 
(Oksanen) announced a *possible* 3-hourish wiggle appearing in the 
optical light curve.  That sets the stage: it's now time to make a 
strong effort to detect that periodic signal!  (Oh yeah, and it's our job.)

The star is still very bright at V~8.8, so you'll have to employ some 
tricks to avoid saturation.  Obviously filtering (V or R recommended), 
and short exposure, and maybe also de-focusing if you've had some 
experience with that technique and are confident that it won't 
contaminate your results.  Since I'm sitting here in a reclining chair, 
far from the battlefield, your own practical solutions probably have 
more value than my advice.

See if you can find that signal, and show the US Congress how a proper 
job is done.

joe
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