(cba:news) new and old stars
jop at astro.columbia.edu
Wed Aug 6 15:54:40 EDT 2003
The dwarf novae have been mercifully quiet in the last coupla weeks. So
we've made some serious progress on other fronts...
Lots of action on V4743 Sgr, one of last year's bright classical novae.
We have a very accurate Porb now (6.69 hrs), and enough data to rule out a
rotational (magnetic) interpretation of the signal near 70 minutes. The
reason is that the signal is obvious in the light curve and basically
invisible in the power spectrum. This is what happens when the signal has
very low coherence. It is also possible that the true underlying signal
is coherent but highly masked by amplitude changes and/or a very complex
internal structure; but that's kind of a remote possibility. Low
coherence doesn't specify the origin of the signal, but it probably
announces what it isn't, namely white dwarf rotation (since the latter is
a fundamental clock which can't really be buffeted on short timescales).
Flickering is some sort of accretion-disk weather, and the learning curve
gets awfully slow in the domain of weather! So it's time to drop V4743
Sgr until late season, when it's worth measuring the orbital amplitude
again (since this is a sort of a bolometer for the hot white dwarf, it's a
very nice number to keep tracking).
The two good (and new) southern targets are:
EC21178-5417 ("Ind" in CV catalogue). This has got some kind of period
around 3.7 hours, exact nature unknown. At 14th mag, it's pretty much red
meat for CBA observation. Go for it!
RZ Gru. A very bright novalike whose orbital period remains totally
unknown for all these years. High time to subdue this elusive target! At
12.7, plenty bright enough to survive the upcoming full moon.
Of the northern targets, I wanted most to stress V1974 Cyg. So far we've
gotten coverage from our military and paramilitary units - Major Tom and
Cap'n Bob. It's an ambitious target at around 16.5, and probably won't
survive the waxing Moon - but see what you can get if yer aperture and sky
quality are up to it.
Then there's V533 Her, still a good target and much brighter at ~14.8.
Finally, SDSS2258-09 for both hemispheres. Still a mystery star. Seems
to jump around in the range 13.5-15, as many of you have noted. There
seems to be a 7.5 hour signal in the data taken so far, origin unknown.
I dunno what will come of it, but this all seems to be worth a closer
look. Keep it up!
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