(cba:news) Post-outburst orbital light curves of novae
jp42 at columbia.edu
Mon Mar 25 10:50:25 EDT 2019
More on this short- and long-term project of studying the orbital light
curves of recent novae...
This is truly a project which will have long-term significance. If we
only knew the just-after- eruption orbital light curves of the famous
novae - DQ Her, V603 Aql, GK Per, RR Pic, CP Pup... what a bonanza that
would be! The reason is that in early post-eruption, there's a big ol'
luminous white dwarf, which illuminates the accretion disk. After the
WD temperature drops below about 300000 K, it's no longer observable in
X-ray telescopes. But "absence of evidence is not evidence of
absence"... and there's a critical and open question: on what timescale
does the binary transition from illuminating-WD-dominated to
accretion-dominated? The orbital light curve (and eclipse shapes, for
the binaries of higher inclination) is a good probe of this. We pretty
much know the story 50-100 years after outburst, but we'd like to know 3-10!
The novae which reached V>10 in outburst are generally not worth
pursuing. Same for the galactic center guys. It's the bright ones
which are worth the effort. Koji's links will tell you a lot of info
about these. You'd be surprised how little is known about the
post-novae: a flurry of ATels, maybe 2 published papers... and then:
hey, it's on to the next nova. Claus Tappert and Linda Schmidtobreick
are exceptions; they pay close attention to the old novae on all
relevant timescales, and have some big glass available (both based in
Chile). Otherwise, it's somewhat of an orphaned subject.
(Spectroscopically, Fred Walter - the source of the "SMARTS" links - is
the world's authority on the subject.)
That's some background. Most old novae have *nothing at all* known
about their behavior 5-20 years after outburst. Even if you have just
an upper limit on magnitude - the minimal quantum of information - it
could be useful. Collect 'em and send!
On 3/25/2019 8:20 AM, Joe Patterson wrote:
> Among those stars:
> T Pyx done for the season. We have enough to nail down the ephemeris
> - and hopefully the physics!
> HP Lib and CR Boo: It's important to start the HP Lib season, which
> would be about now (late March). But about a week of coverage would
> nail down the early-season phase of the periodic signal(s??). After
> that, CR Boo wins. Because it has outbursts, unlike AM CVn and HP
> Lib, it's hard to say in advance what the priority-setting standard is
> (are outbursts more or less informative than quiescence?) Except for
> one thing: its transitions to 17th magnitude, which used to be rare
> and probably still are, are of VERY high interest, A few weeks of
> coverage will make these priority decisions easier.
> There are some other southern stars asking for coverage.
> 1. IM Nor. Got a paper almost ready to roll. A few 2019 eclipse
> timings will fortify the long-term ephemeris. It's far-southern and
> normally mag 18 out of eclipse, so likely only in Gordon's territory.
> 2. WX Cen. Another "V Sge" star, like IM Nor and T Pyx, with very
> rapid change in Porb. A bright star, friendly for all scopes... but
> very desirous of long runs, since Porb is long and the eclipses
> somewhat shallow (~0.5 mag).
> 3. NR TrA. We've been tracing out the orbital light curve since its
> 2008 outburst. Let's get a high-quality result for 2019!
> 4. V407 Lup. Time to start the season on this fascinating and
> possibly unique star, a 2016 nova. Paper in an advanced state on this
> guy, but needing another season.
> We've gotten great results from our surveys of the post-eruption
> orbital light curves, in general. Koji Mukai's list of recent novae
> is an excellent source of material to study:
> The great majority of these targets are desirous of LONG
> observations... but the AM CVn stars are less finicky than the others.
> joe p
> On 3/24/2019 11:54 PM, Gordon Myers wrote:
>> Joe, what's priority among CR Boo, HP Lib and T Pyx?
>> -----Original Message-----
>> From: cba-chat <cba-chat-bounces at cbastro.org> On Behalf Of Joe Patterson
>> Sent: Sunday, March 24, 2019 8:05 AM
>> To: cba-news at cbastro.org; cba-chat at cbastro.org
>> Subject: (cba:chat) the "ultracompact" project: AM CVn, HP Lib, CR Boo
>> Hi CBAers,
>> I wanted to write in some detail about the AM CVn project underway.
>> In our Skillman et al. 1999, we spelled out the star's basic period
>> structure in full detail: an orbital period of 1028.7322 s, a
>> positive superhump at 525.6 s (actually its "subharmonic" at 1051.2),
>> and a negative superhump at 1011.4 s. That paper also listed many
>> other sum and difference frequencies present at lower amplitude; but
>> these are the basics.
>> Many theoretical and observational papers on superhumping CVs have
>> ascertained the origin of positive superhumps: an eccentric
>> instability at the 3:1 orbital resonance in the disk. Because it's
>> seated in the disk, it doesn't have high stability, but wanders in
>> phase on a timescale of days to weeks. The orbital signal is weaker
>> (just 0.008 mag full amplitude), which is why we're the only people
>> (so far; TESS will see it easily) who have ever detected it.
>> Nevertheless, we've obtained timings over 27 years (at least) and
>> found the orbital period slowly decreasing, on a timescale of 60
>> million years. This arises from a combination of mass transfer
>> (which increases the period) and gravitational radiation (which
>> decreases the period). AM CVn is expected to be one of the brightest
>> steady Galactic sources in the next generation of space-based
>> gravitational-wave detectors.
>> Thanks in no small measure to David Cejudo's relentless coverage from
>> Madrid, the 2019 coverage has confirmed the Porb change - our main goal.
>> Great! But now we're within reach of another goal, not yet
>> achieved for any star. Do the positive and negative superhumps
>> change their
>> periods in phase, in anti-phase, or uncorrelated? If the *negative*
>> superhump arises also at the 3:1 resonance (not known!), then it's
>> reasonable to expect that the signals will be in anti-phase. Any
>> other result... well, we'll have to think that one through!
>> I doubt that any other star will enable such a test, because AM CVn's
>> constancy in brightness is unparalleled (basically within 0.02-0.03
>> mag). So let's KEEP IT GOING - at least another month.
>> BTW the preferred term nowadays is "ultracompacts", rather than AM
>> CVns, because there is also a collection of similar binaries (Porb<50
>> min) which have neutron-star or black-hole accretors. Much less is
>> known about them, but the physics is likely identical (except very,
>> very close to the accretor).
>> Two other AM CVns (oops, ultracompacts) are candidates, and bright
>> enough for a similar, but less detailed, test. These are HP Lib and
>> CR Boo. Negative superhumps haven't even been *discovered* in these
>> stars (yet), so we have a way to go. Nor is the orbital period known
>> for sure. But we can find these things, if they're present at
>> anything exceeding ~0.003 mag. Behold the power of time series!
>> They're also seasonally appropriate, and with friendly coordinates -
>> accessible to everyone. Let's get going on these stars!
>> joe p
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