From jop at astro.columbia.edu Sat Sep 1 06:52:33 2012 From: jop at astro.columbia.edu (Joe Patterson) Date: Sat, 01 Sep 2012 06:52:33 -0400 Subject: (cba:news) CC Scl: ready, set, go; and AO Psc: faith restored? Message-ID: <5041E8F1.9090802@astro.columbia.edu> Dear CBAers, I just read a fascinating paper (on astro-ph: arxiv.org/abs/1208.5936) by Patrick Woudt, Brian Warner, et al. (mostly the South Africans) about CC Scl, long known as a respectable dwarf nova. They show clear evidence of a 6.5 minute period, which certainly looks like that of a DQ Her star (intermediate polar). Yet it is seemingly well credentialed as a short-Porb, max-plus-supermax dwarf nova, which superhumps just when dwarf-nova rules require it, and never when those rules forbid it. Who invited that? Maybe we have to change the rules somewhat... and at the very least we need to take a very close look at this star. It's right up our alley, transiting near local midnight and just begging for long time series. Perfect for the australites, and acceptable for some of the borealites too. I think it's generally between 13 and 17.5, hence suitable for most of us. To properly resolve the 6.5 minute signal, a 90-second cycle time will be adequate (as long as it's not *exactly* commensurate with 389.5 seconds!), although faster would be slightly better. This 6.5 minute signal is no barn-burner, though; you might not see it directly in the light curve, though probably will in the power spectrum. More of a barn-burner is the 14 minute signal of AO Psc, which is about 0.05-0.07 mag in a star which generally reports for duty at V=13-14 - and is therefore another alluring target in September-October. Partly because of the following tale. In 1999 we carried out a long campaign on AO Psc. We found periodic signals at 14.3 minutes, 13.4 minutes, and 3.6 hours - standard issue for this star. And we also found a clear signal at 4.0 hours. It certainly looked like a bona fide superhump, and therefore exciting: first superhump found in a DQ Her star! But the signal was very, very close to exactly one-sixth of a sidereal day, and I suspected that it was an artifact of differential extinction. This is a known bugaboo of us white-light enthusiasts, and when I studied it carefully I saw that the ephemeris for maximum light of the new signal positioned it pretty close to culmination in Arizona, where much of the data was taken. Super-suspicious, so I never published it. But over the past twenty years we have observed hundreds of stars with comparable zeal - just as blue as AO Psc, but we never saw anything like this. One, two, and even three cycles/sidereal day - yeah, we're familiar with those, and I just yawn then away. But never six. If you observe enough stars and enough superhumps, eventually some numbers will pop up which look suspicious, but are mere coincidences. Now that we are much more global than in 1999, we could check this with a similarly energetic campaign. So let's do it. Being equatorial, nobody can get long runs on AO Psc. But on the other hand, everyone can see it. So we should be able to patch together a very nice global light curve. The field is practically blank, so there's a comparison-star issue. It would be good to come up with two comparison stars of good quality, and observers could choose the one convenient for them (field of view, brightness, etc.). Some of you guys are awfully good at this (Jim Jones is an ace) - and sitting here in NYC with no telescope, I'm certainly not. White light is OK, and V (or Sloan g. or something close) would be somewhat better if you have lots of photons to spare. Finally, if you have the option to supply the airmass with each point, that would be helpful; I plan to correct the white-light observations for differential extinction (which I normally don't, in the spirit of keeping human hands off the data as much as possible). Oh, and if you can, avoid multiple-comparison-star photometry (i.e., merging several to form a composite V-C). That taxes my diminishing supply of brain cells. Buena suerte! joe p From jop at astro.columbia.edu Wed Sep 12 20:17:36 2012 From: jop at astro.columbia.edu (Joe Patterson) Date: Wed, 12 Sep 2012 20:17:36 -0400 Subject: (cba:news) HST coverage Message-ID: <50512620.7090609@astro.columbia.edu> Dear CBAers, Now for something different. We hope and expect to get some HST spectra this fall, and beyond. But the CVs need to be in quiescence for the observations to proceed, because they're worried that the strong UV flux in outburst will fry the detectors. We need to essentially prove that the stars will be in quiescence - and in particular that they have been in quiescence for at least a month. To do this, we'd like nightly observations of each star. In the next message, I'll forward Boris Gansicke's description of the full list, which has references, links, etc. Here I just want to mention the stars for which we need to observations NOW. This is not a CBA-style campaign, calling for time series. Snapshot observations are fine. V-band magnitudes are ideal, but unfiltered is OK too, if you know how bright the comparison star is. Upper limits are fine too; they'll likely attest to quiescence, but they need to be quantitative. Here's the list: SDSS 0137-09 = GZ Cet HM Leo = NSV 18241 SDSS 1006+2337 = CSS 050301:100658+233724 MR UMa = RX1131+43 SDSS 1538+5123 (also RX) BB Ari SDSS 0407-0644 = LT Eri Actually, the last of these *is* a good CBA target, and in October will be a superb target - beautiful eclipses and superhumps. For now we'll settle for snapshots, though time series would be nice. There are three other stars which will very soon get on our list, so I might as well list 'em now: HS 0218+3229 SDSS 0011-0647 RX 023238.8-371812 These are plenty useful now. I earnestly hope that some of you guys can launch an observing program like this! Different from our usual, and with more overhead with all the target-shifting... but it's the key to getting the HST go-ahead, which will give us our long-sought glimpse of the ultraviolet spectra. joe From jop at astro.columbia.edu Wed Sep 12 20:21:44 2012 From: jop at astro.columbia.edu (Joe Patterson) Date: Wed, 12 Sep 2012 20:21:44 -0400 Subject: (cba:news) links for snapshot program Message-ID: <50512718.5080304@astro.columbia.edu> here it is: http://deneb.astro.warwick.ac.uk/phsdaj Good luck with this ambitious program - these are likely to be faint stars! But if you can't see 'em, that's fine - just figure out what the appropriate limit is. joe From jop at astro.columbia.edu Wed Sep 12 21:23:35 2012 From: jop at astro.columbia.edu (Joe Patterson) Date: Wed, 12 Sep 2012 21:23:35 -0400 Subject: (cba:news) correct page of links In-Reply-To: <50513495.6050401@astro.columbia.edu> References: <50513495.6050401@astro.columbia.edu> Message-ID: <50513597.1080204@astro.columbia.edu> oops, here's the correct page: http://deneb.astro.warwick.ac.uk/phsdaj/public_html/12870/12870_PhaseII.html From jop at astro.columbia.edu Thu Sep 20 11:42:13 2012 From: jop at astro.columbia.edu (Joe Patterson) Date: Thu, 20 Sep 2012 11:42:13 -0400 Subject: (cba:news) Fwd: SDSS1642+1347 - intensify the monitoring In-Reply-To: References: Message-ID: <505B3955.3040901@astro.columbia.edu> Hi CBAers, This from Boris. Not one of our usuals... but now in the correct (for HST) sky position, and on the schedule. Have at it - pronto! joe Hi Arne & Joe, can you ask for more intense observations of SDSS1642+1347, which STScI chose as our first target to be done, beginning of October. Arne, it would also be great if you can check the position / proper motion that I have, RA(2000) Dec(2000) p.m.(RA) pm(Dec) 16 42 48.51 +13 47 51.50 -14.4 mas/yr -2.0 mas/yr Thanks, Boris