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(cba:news) V339 Del and the supersofts (Joe Patterson) [2013-10-15T09:47:25Z]


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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