From jop at astro.columbia.edu Thu Apr 13 05:35:13 2006 From: jop at astro.columbia.edu (Joe Patterson) Date: Thu, 13 Apr 2006 05:35:13 -0400 (EDT) Subject: (cba:news) spring 06 stars Message-ID: <200604130935.k3D9ZDc25812@fidelio.phys.columbia.edu> Dear CBAers, The flowers and leaves are emerging from the long freeze... and it's time for the new season of stars to emerge, too. Quite a few need to retire for the season, mainly because solar glare is getting just too bothersome. These are: Swif0732-16, WX Cen, DW Cnc, UMa 6, BG CMi, and V405 Aur. We had good campaigns on the first four, and will be writing up the results later this year. The latter two were somewhat sparsely observed - probably enough to maintain cycle count and thereby improve knowledge of their periods, but we'll see for sure when we do the complete study of the year's data (always in the summer!). It's also too late for WX Pyx. This is an unpopular target among CBAers, to my chagrin. Definitely a touch faint, but with quite a big periodic signal. Anyway, I think it's gone... so I'll cheerlead for it next year. I still like RX1039-05 = Sex. This star is 18th mag, but the periodic signal is huge (>1 mag) and especially big in the infrared. Several CBAers have gotten good data, especially Bob Rea; a few more nights of coverage would finish up a good season and - I think - clinch a long-term ephemeris with certainty. Alas for me, the same is not true for RX1050-14 = Hya. This star is of huge interest as a candidate period-bouncer - the most ancient of the CVs (assuming they exist at all). Two years ago we had a decent indication of a photometric signal at a period close to the period suggested by spectroscopy. The latter was not firm, and certainly not accurate; we could have done much better with photometry. But as the poet sayeth, coulda woulda shoulda. Tom Krajci's diligent coverage showed that at our level of sensitivity (0.03 mag), there's no significant periodic signal. That generally gets you demoted from CBA lists. Soooo... here come the spring stars. I'm gonna take a pass on IY UMa, which some of you are observing now. It did jump into supermax, and this eclipsing dwarf nova has truly great supermaxima. But we published a very extensive study back in 2000 (I think)... and there's a good chance that our conclusion now would be "yep, it's pretty much the same." Of course we can't know this without looking, but it's pattern among dwarf novae. Light curves obtained so far do help tighten the ephemeris... but I don't think it warrants a big effort now. April is the big month for the AM CVn stars. The brightest of these are AM CVn (V=14.2 at 1237+38) and HP Lib (V=13.6 at 1535-14). Both have very intricate superhumps and a detectable signal at Porb - and very low flickering, which is a delight since it allows much greater sensitivity to periodic signals. They're also prime targets for the gravitational- wave experiments of the next decade. Since we seem to be the only people who can measure these periods with any precision, it's incumbent on us to establish long-term ephemerides (for Porb, that is). The stars are bright enough to overcome moonlight, so I strongly recommend that these be prime targets for the next couple of weeks. In the south, I also recommend EX Hya in the next week or two. The ephemeris is getting a bit rusty - time to tune it up! It takes a couple of weeks, because there are TWO periods that have to be adequately decoupled: the 98 min orbital period and the 67 minute spin period. That's a pow'f'l short list. But that gives us a better chance for very concentrated coverage... and I think it's proper till dark skies give us access to the fainter among our stars. For those of you planning to come to Big Bear, let me remind you about dates. The conference proper is Wednesday and Thursday, May 24 and 25. Information about logistics is on the "socastrosci" website. It's preceded by a day of workshops on May 23. Since Tonny and Jerry are presenting workshops, I imagine that some/most of the CBAers will be present on the 23rd as well. A few of us will be driving in from Tucson on the night of the 22nd - but most people are making their own travel arrangements. You need to register on the SAS website, but there's no CBA registration or anything of that ilk. Since we're all likely to be in the Northwoods resort, it should be a simple matter to arrange to meet together and discuss items of mutual interest. Any questions, please write. Happy observing! joe From jop at astro.columbia.edu Wed Apr 19 08:12:51 2006 From: jop at astro.columbia.edu (Joe Patterson) Date: Wed, 19 Apr 2006 08:12:51 -0400 (EDT) Subject: (cba:news) meet SDSS1238-03 Message-ID: Hi CBAers, Olde Whiteface has moved mostly outa the way, and I'm feeling lucky... For the past 2 days we have been monitoring SDSS1238-03 from Kitt Peak. The light curve is very remarkable. There's a signal near 38 c/day which probably signifies the orbit (=2 nu-orb, perhaps). There's also another signal near that frequency, which must have a different origin (unknown). But then there's a very large amplitude signal (~0.4 mag) with a period of about 10 hours. It's too early to tell whether the latter is really stable, or for that matter whether any of these signals are. But the power spectrum is certainly tantalizing. Because of its location on the celestial equator, no one can get long runs on this star from any fixed location. It's really a prime target for CBA coverage, except for its faintness (V~17.3). But the amplitude of the low-frequency signal, and maybe even ALL the signals, is pretty high... and the Moon no longer interferes in that part of the sky. So my guess is that many of you can get a decent light curve on this star if the sky conditions are good. It's really NECESSARY to have multi-longitude coverage, if we're ever going to understand that low-frequency signal. Can you give it a try? Our Kitt Peak run continues for a while... so we're vitally interested in any help we can recruit, especially from exotic longitudes, on this star. It's labelled "Vir" in the Downess catalogue, and I think goes by the full name SDSS J123813-033933. Good luck with this fascinating star. joe From jop at astro.columbia.edu Wed Apr 19 13:58:56 2006 From: jop at astro.columbia.edu (Joe Patterson) Date: Wed, 19 Apr 2006 13:58:56 -0400 (EDT) Subject: (cba:news) other comments on faint CBA stars In-Reply-To: Message-ID: Hi Michael et al., Yes, time resolution is not so critical since the periods of interest are ~35 min and longer. But here's the more general point... For SDSS1238-03, and for faint CVs generally, don't be distracted by the common rules of thumb for "good photometry". Some people say "1% accuracy" as the rule of thumb - in which case, you need >10000 counts, plus an accurate calibration (standards to <1%). This is feasible for practically no CV in the sky... and it is largely useless even where it is feasible, because CVs show intrinsic erratic variability ("flickering") which is >>1%. Someday we will understand that flickering, and whoever has very extensive and accurate data on it has some chance of making that breakthrough. But it's an unsolved problem, and unless you hope to be the person who finally makes that breakthrough, you're better off considering the flickering to be THE BASIC BACKGROUND AGAINST WHICH YOU HAVE TO DETECT PERIODIC SIGNALS. The latter - the periodic signals - are very different in that they have (more or less) straightforward physical interpretations, so that's what I always consider to be the reasonable goal of these observing campaigns. The bottom line in all of this is that you can usually consider "5% statistics" to be a satisfactory statistical accuracy, and you can almost settle for 3%. In unfiltered light, my guess is that CBAers can reach this in about 120 s - for a star as bright as sdss1238-03. The light curves won't be pretty enough to send home to Mom, or even to frame in your observing shack. But they're likely to be an effective tool for sniffing out the periodic structure in the star - especially when combined with the homely light curves of other observers in a global network. Sorry for being long-winded! But I'd like to encourage experiemnts on fainter stars - and to steer people away from very long exposures, since the latter have only a SLIGHT advantage in signal-to-noise, and they are much more prone to serious systemtaic error (drive errors, cosmic ray hits, wind gusts, etc.) joe From jop at astro.columbia.edu Mon Apr 24 17:01:49 2006 From: jop at astro.columbia.edu (Joe Patterson) Date: Mon, 24 Apr 2006 17:01:49 -0400 (EDT) Subject: (cba:news) victory over AM CVn, now for sdss1238... Message-ID: Dear CBAers, We've finished 45 nights of AM CVn coverage, and today I caught up with all the analysis and derived new ephemerides. The orbital (1028 s) variation is always hard to spot, and this year all the more, because the negative superhump (1011 s) was strong. But with enough coverage, which we got, one can still extract the weaker signals in the presence of strong ones. So we emerged with three timings of minimum light, all agreeing within 0.02 cycles (20 s). Comparing with the long term ephemeris, it's now clear that the period is slowly decreasing over the available 28 year baseline. So we can retire AM CVn for the year. But I'm still lusting after SDSS1238-03! This is 17th magnitude and I realize not a real fun object for CBAers... but is a terribly important star and shows a strong maximum about every 7 hours. Under good conditions this should be accessible to apertures of 25 cm and above - and with its nice equatorial position, we ought to be able to get worldwide coverage. I'll write later on brighter stars! joe From jop at astro.columbia.edu Fri Apr 28 06:59:27 2006 From: jop at astro.columbia.edu (Joe Patterson) Date: Fri, 28 Apr 2006 06:59:27 -0400 (EDT) Subject: (cba:news) (cba:chat) SDSSJ1238-03, Nearby Variable Star (fwd) Message-ID: fyi, just in case there are non-chatters out there... joe ---------- Forwarded message ---------- Date: Fri, 28 Apr 2006 03:58:38 +0000 From: Bob Koff To: CBA Chat Subject: (cba:chat) SDSSJ1238-03, Nearby Variable Star For those of you working SDSSJ1238-03, I've come across a variable star close to the target that you'll want to avoid using as a comp star. The location of the star is at RA 12 37 56.95, Dec -03 38 08.2 . The unfiltered magnitude is about 15.8. It looks like an RR Lyrae, and I've got a preliminary period of about 10 hours. You can see the lightcurve at http://www.antelopehillsobservatory.org/lightcurves/V1238-03.png As you can see, it would make a really poor comp star :-) I have not found any reference to this star in Simbad, GCVS or ROTSE. Regards, Bob Koff ____________________________________________________________ Center for Backyard Astrophysics (CBA) mailing lists https://cbastro.org/communications/mailing-lists/