From jop at astro.columbia.edu Wed Aug 1 17:36:27 2001 From: jop at astro.columbia.edu (Joe Patterson) Date: Wed, 1 Aug 2001 17:36:27 -0400 (EDT) Subject: (cba:news) KL Dra and WZ Sge Message-ID: Dear CBAers, I'm sure you saw Matt Wood's announcement a few hours ago - a large periodic signal in KL Dra, an obscure star once mistaken for a supernova. We know only a little about KL Dra - that the spectrum is dominated by helium when bright, that it rises only to about mag 16.7, that its quiescent magnitude is >20. Many times I've wondered how we were ever going to learn more. And this is how! It would be great to follow it for a few days now, to take advantage of this bright state (which is probably short-lived). Send the data to Matt, and also to the archive. Very tough star to do, with its brightness and the Moon getting kind of annoying. But I thought there might be some show-offs out there! 19 24 38.0 +59 41 46 (2000) Chart in the Downes catalog, living edition. http://icarus.stsci.edu/~downes/cvcat The main event is still WZ Sge. We've gotten excellent data sets lately from Tim Hager, Michael Richmond, Dan Kaiser, and Rudolf Novak, in addition to the regulars. Plus Gianluca Masi of course! Keep up the pressure on ol' WZ. joe From jop at astro.columbia.edu Thu Aug 9 02:53:40 2001 From: jop at astro.columbia.edu (Joe Patterson) Date: Thu, 9 Aug 2001 02:53:40 -0400 (EDT) Subject: (cba:news) WZ Sge Message-ID: DEar CBAers, Still in Germany here. The CV meeting is all abuzz over WZ Sge, and I hope you'll maintain the vigil. USA coverage is now a bit weaker - Michael Richmond and Brian Martin are workin' hard, but in not the best climates. How about some longitudinal pride? Back Tuesday I think. V1223 Sgr is probably the best alternate target in the south (Bob, methinks it`s time to switch to that from V442 Oph). The German keyboard presents a challenge. joe From jop at astro.columbia.edu Fri Aug 17 07:29:56 2001 From: jop at astro.columbia.edu (Joe Patterson) Date: Fri, 17 Aug 2001 07:29:56 -0400 (EDT) Subject: (cba:news) stars for August... but mainly WZ Sge Message-ID: Dear CBAers, 8/17/01 Just back from Germany, spending many pleasant hours analyzing the treasure trove of WZ Sge data. So far, the star has been flashing all the main features seen in the 1978 outburst. Namely: * very rapid rise to peak brightness at 8.0 * quick fall to 8.5, then slow decline at dwarf novae's official rate of ~0.13 mag/d * large photometric humps at or nearly at Porb, dominating light curve for ~12 days * large superhumps growing suddenly around day 12, with a period ~1% longer than Porb, decaying on a timescale of a couple of weeks * a few dips suggestive of eclipse features. Of course, the observational material is ~10 times richer now, thanks to the felicitous timing of the outburst (Sagitta in July, not December!). Thus some of these features are provable now, not merely suggested, and in general we can greatly sharpen the detail of our measurements. As the brightest and probably nearest of all dwarf novae, WZ Sge in 2001 will likely teach us lessons we'll still be meditating on 20 years from now. Of course every imaginable space-borne telescope will be watching WZ Sge in the days ahead, and most already have. In the hard UV/soft X-ray, the star shows a forest of high-excitation emission lines. Some less imaginable telescopes may be heard from, too. The star is now down to 10.6, and for most of you this requires a change in observing strategy. That 8th mag star you've been using - I believe GSC 1621-1830 - is now too bright, since it will saturate if you expose WZ Sge itself adequately. I recommend changing comparison stars; Bob Rea has switched to 1621-1939, so consider that one and use 10-20 s exposure times, which might give good signal-to-noise. Since the bright-spot eclipse seems to have returned in some guise, producing narrow notches in the light curve, it might seem a good idea to keep the time resolution short so as to define those notches properly. For small telescopes, though, you really can't get enough signal in a few seconds - so the data needs averaging and the nominal time resolution is lost. In the bargain, all this ugly dead time creeps in. So in general I'd recommend for telescopes under 0.6 m that you concentrate on getting the WZ Sge images properly exposed, and accept whatever exposure time that entails (under 35 s I hope - if you need to go longer, well, relax your criterion for "properly exposed"). The bigger scopes can do the faster stuff. A related question is filters. Professional astronomers love filters, since they don't have to pay for them, and have plenty of aperture which allows tham to reject 90% of the light without penalty. (Oh yeah, because they sometimes bring useful astrophysical info too.) But three circumstances make filter use nearly always inappropriate for us. 1. We are usually starving for light, and can't bear to reject 90% of it. 2. We often want high time resolution, which makes problem 1 even more severe. 3. The luminous parts of CVs are nearly always (and absolutely always in the case of bright erupting CVs) hot sources of continuous radiation, and the periodic signals are broad-band phenomena depending only weakly on wavelength. Is any such dependence (there probably is some) of interest? Yes, perhaps. But in the process you will have paid a heavy price in the quality of your light curves. Professional astronomers who have not used amateur equipment often fail to realize these points, because really the *opposite* is true when you have a big enough telescope. With the 52-inch we nearly always use filters, because photons are abundant, and filters enable both calibration and much better treatment of extinction effects. Starting about now we'll get a WZ Sge page on the website, though many of you have your own WZ Sge features now (Masi, Martin, Richmond, as well as the usual excellent job by VSNET). Feel free to advertise your own site in this space (and I'll do so next message, when I'll collect the addresses). Now... on to STARS. There's still a lotta life left in WZ Sge, so that's the prime object for the north. Gianluca Masi, Brian Martin, and Michael Richmond have been accumulating great riches of data, with contributions also from Tonny, Rudolf, Donn Starkey, Lew Cook, Dave Skillman, and some intrepid New Zealanders (mainly Bob Rea and Bill Allen). The NZ contribution has been really helpful since we still have no northern coverage from San Francisco Bay westward to the Black Sea. The other objects I wanted to promote are KL Dra (big northern scopes only), V1223 Sgr (south only), and the equatorial DQ Her stars AO Psc and FO Aqr [we *always* love these stars, but they're to be visited just once in while, with attention to accurate timing, not in big campaigns]. Enough for now. Happy observing! joe From jop at astro.columbia.edu Sat Aug 18 19:13:05 2001 From: jop at astro.columbia.edu (Joe Patterson) Date: Sat, 18 Aug 2001 19:13:05 -0400 (EDT) Subject: (cba:news) WZ Sge tonight Message-ID: Dear CBAers, HST is set to observe WZ Sge tonight, 559-1148 UT, very convenient for USA/Canada. Skip dessert and get thee to a telescope. joe From jk at cbastro.org Tue Aug 21 16:23:34 2001 From: jk at cbastro.org (Jonathan Kemp) Date: Tue, 21 Aug 2001 10:23:34 -1000 (HST) Subject: (cba:news) new at the cba web site Message-ID: Dear CBAers, I just wanted to let you know about some new features that we've recently introduced at the CBA web site. First, after introducing an approximately real-time display of recently submitted data sets, we have now introduced a similar automated sorting of data sets by station (for full-fledged, frequently-contributing members) and by object! The latter is still a bit under development with a few objects yet to be added, but please feel free to take a look. If you wish to resubmit past data to the archive, please contact me (Joe and I have dug out our much of our old CV photometry dating back to late 1997 and have entered it into the archive). Second, we have inaugurated a product review section that features articles by CBA members on those products which might be of greatest interest to our members. The first feature in this section is a piece by Tonny Vanmunster (CBA Belgium) on the wonderful new AIP4WIN software which may be an appropriate answer for future CBA data reduction needs. We also eagerly solicit additional contributions to this section on other products which might be of interest to other CBA members (Meade/Celestron telescopes, SBIG/Apogee CCDs, The Sky, CCDOPS, MaxIm DL, MuniPack, EZPhot, Hellier's book, etc.). Third, we have included a preprint for the recently submitted article on HP Librae (abstract below). Please pay us a visit and let us know what you think! Cheers, Jonathan CBA Hilo -- Superhumps in Cataclysmic Binaries. XXI. HP Librae (= EC 15330-1403) J. Patterson, R. Fried, R. Rea, J. Kemp, C. Espaillat, D. Skillman, D. Harvey, D. O'Donoghue, J. McCormick, F. Velthuis, S. Walker, A. Retter, Y. Lipkin, N. Butterworth, P. McGee, & L. Cook Publications of the Astronomical Society of the Pacific submitted, August 2001 We report photometry of the helium-dominated cataclysmic variable HP Librae during 1995-2001. The main photometric signal varies between 1118.89 and 1119.14 seconds, on a timescale of a few years, and displays a waveform characteristic of "superhumps". After subtracting the main signal, we found a weak residual signal at 1102.70+-0.05 s, which we interpret as the underlying orbital period of the binary. The full amplitude of this putative orbital variation is just 0.005 mag, the weakest orbital signal yet found in a CV. The 1119 s signal of HP Lib is a superb match to the well-studied 1051 s superhump of AM CVn, the "mother of all helium CVs". The superhump shows no change in amplitude or waveform on any timescale, and no essential change in period on timescales shorter than ~3000 cycles. Such great stability makes the star a promising test case for detailed studies of the underlying spiral structure in the disk, the likely cause of superhumps. Comparison of orbital and superhump periods for the family of AM CVn stars supplies evidence that these stars are evolving towards longer orbital period. From jop at astro.columbia.edu Thu Aug 23 07:40:23 2001 From: jop at astro.columbia.edu (Joe Patterson) Date: Thu, 23 Aug 2001 07:40:23 -0400 (EDT) Subject: (cba:news) Nemesis to WZ Sge... Message-ID: Dear CBAers, No, not the weather. That too, maybe. But now that WZ is fading a bit, it's time to worry more about the nefarious little companion star. All previous studies have had to do something about the companion, and we do too. If feasible, you could just exclude it from your aperture or psf photometry. In our photoelectric photometry from the 1970s, that's what usually did. The enclosed discussion by Arne Henden gives the relevant numbers which indicate how to do this, and are also a measure of the severity of the problem. *************************************************** WZ Sge 20:07:36.53 +17:42:15.2 J2000 companion 20:07:35.77 +17:42:17.1 J2000 with typical errors of 100mas. This gives a separation of 10.9 arcsec. Magnitudes of the companion alone: V B-V U-B V-R R-I 13.884 1.526 1.592 0.776 0.692 (0.03mag total errors except for U-B which has 0.07mag error). You should not have problems with contamination as long as your aperture is 12 arcsec in diameter or smaller. I'd suggest either using a small aperture or else one large enough to encompass both stars; the inbetween ranges will have some weird results. Remember, however, that the contamination is highly dependent on your passband, worse at red wavelengths or with unfiltered photometry. *************************************** Most of us observe unfiltered, which approximates an R passband, implying that full contamination means an extra unwanted R=13.11 star. Looking at the data you've sent, it's pretty easy for me to tell which observers have cleanly excluded or included this star. But in-between cases are hard to identify, and will inevitably give noisy data since the amount of contamination will depend drastically on the instantaneous seeing. Don't mess with Mister Inbetween (Sinatra 1942). Unless your telescope drive and/or seeing are really bad, I recommend excluding the companion. This is because background from sky and companion will start to overwhelm you beyond about magnitude 13.5 - and the light curves will suffer greatly. We're interested in the detailed light curves on the approach to quiescence. A too-small aperture hurts light curves too, but you'll be able to study those problems, gain experience, and maybe even fix them... whereas a too-large aperture just swamps everything in the ocean of Poisson noise. In any case, send me a note describing how you've extracted your delta-magnitudes so far, and whether you can do OK with a box that excludes the companion. Our emphasis is time-series, so this is not the most critical issue for us... but now's the time to report the details, and find the right strategy for WZ Sge's fainter days ahead. Thanks, Arne, for your measurements, and for improving our attention to this issue! joe