From jop at astro.columbia.edu Tue Jul 9 06:50:03 2013 From: jop at astro.columbia.edu (Joe Patterson) Date: Tue, 09 Jul 2013 06:50:03 -0400 Subject: (cba:news) July stars Message-ID: <51DBEADB.8000801@astro.columbia.edu> Dear CBAers, New stars for the new season. It's time to end the HS1813+61 coverage. The star has wandered between a high-ish and a low-ish luminosity state, and the periodic content has been complicated by that feature. Definitely for analysis in the cold light of winter... and time to end 2013 coverage. And time to replace this "Dra" star by a new kid in Draco: ASASSN-13ax, discovered in a supernova search (and therefore using the supernova lingo as an identifier). In our familiar language, which Taichi Kato likes/promotes and which is well suited to our objects, it would be OTJ180005.78+525635.3. Sitting up there in Draco, perfectly positioned for summer coverage. Enrique has been observing it for a few days, and last night it grew the strong superhumps which are the always-good-for-admission ticket to our club. In particular, it's very likely a WZ Sge star, erupting from mag 21 to 13.5, with some unknown but probably long recurrence period. It's still at mag 14 and will probably flash great superhumps for a couple more weeks. Probably. Anyway, it's a superb target for long runs. We're getting ready to publish our decade-long (but somewhat sporadic) coverage of V1974 Cyg and V1432 Aql, and both stars need a final fix of 2013 data. These two require pretty long coverage, in order to parse among the (known or putative) signals closely spaced in frequency. One month of dense data would bring these campaigns to an end. And the big star in the June CBA world has been PNV1915+07, which has been getting great coverage by practically all of our usual suspects - especially Enrique, Jim Jones, and Greg Bolt. This WZ Sge star, now faded to 16.3, continues to delight with its big periodic wave. Since the 2013 outburst is the first-ever-recorded, and indeed the first time the star publicly announced its existence, we don't know what the future will bring. Let's make sure our telescopes are there to find out! The DQ Her stars (intermediate polars) can take a rest in mid-summer, i.e. now. The two exceptions are V1223 Sgr and IGR1654-19 (Scaringi et al. 2011, A&A 530, A6); each needs a few nights to tie down the long-term cycle count. Finally, don't forget NR TrA and V617 Sgr! These stars have great light curves and need your help. The first is the known remnant of Nova TrA 2008, while the second is a suspected (OK, only by me... but still) remnant of a recent but unnoticed nova event. We're very likely to have a AAVSO+CBA meeting in mid-June 2014, and I especially hope that some of our seldom-seen members can attend. It'll be at Big Bear, or possibly some other southwestern USA location. More info when the details harden up. joe From jop at astro.columbia.edu Sun Jul 14 10:37:01 2013 From: jop at astro.columbia.edu (Joe Patterson) Date: Sun, 14 Jul 2013 10:37:01 -0400 Subject: (cba:news) new stars for mid-July In-Reply-To: <51E2B624.1070208@astro.columbia.edu> References: <51E2B624.1070208@astro.columbia.edu> Message-ID: <51E2B78D.3030001@astro.columbia.edu> Dear CBAers, We're finished now with V617 Sgr. I completed the analysis, and it really seems to be a virtual twin of T Pyx, with an identical light curve and a similarly frantic rate of Porb increase. The one thing it lacks is nova eruptions... which means, in my opinion, keep sunglasses handy. Great to have some company in this truly tiny class of variable stars. We're also leaving HS1813+61. I mentioned that before, but just to stress it. We can back off temporarily on V1432 Aql. The main remaining issue is counting cycles from year to year, and observations in mid-season (like now) have relatively little leverage in proving that cycle count. We'll pick it back up in mid-September. For PNV1915+07, the light curves continue to be fascinating, even as it has declined to V~16.5. So - keep on keepin' on. ASASSN-13ax, the new dwarf nova in Draco, is still at 15th mag and an excellent target. I'm torn about choosing between these targets - but so far, ASASSN-13ax has been relatively neglected... so bear that in mind. But there are three new stars in the midnight sky which should be promoted to major-campaign status now. 1. V1101 Aql. We've studied it just once, in 2004, when it showed a rich power spectrum including a negative superhump. It's around 14th mag, so not a difficult target. There's a neighbor star, but it's very faint, so probably you're best off doing aperture photometry with a large aperture (unless you're very adept with psf fitting). We definitely want LONG time series on this guy, because the expected periods are somewhat long - and that means we really want a great spread in longitude: I was hoping for Europe-Americas-AU/NZ. With a dec of +15, it's probably somewhat out of the Australites' comfort zone; but try - a little bit of off-longitude data can really clobber those daily aliases! 2. V1315 Aql. Very similar comments. Also 14th mag, also likely negative superhumper, and with eclipses too. Whichever of these you choose, I recommend you stick with it, and stick with one comparison star too; there's extra value when the data are repeatedly from the same observer, because it minimizes the problem of inter-telescope calibration. 3. An entirely new star, a 12th-mag guy which is a variable hard X-ray source with a spectrum and Galactic latitude (30 degrees) which are weird - and might be a bright CV in drag. The J2000 position is 21h 24m 12.44s +5d 2m 43.6s. In Equuleus, where practically nothing lives. This is probably not a known variable star, so it might be wise to use a V filter and pay attention to calibration. See what you can learn about it! Can I be so bold as to attach a wish list too? Here are some seasonally-appropriate stars which I would love to study, but I dunno if they are now magnitude-appropriate for the CBA. (Remember, I live in New York, where we strain to see Albireo on the best of nights.) Here they be: V4743 Sgr, V3890 Sgr, V4633 Sgr, V1494 Aql, V1500 Cyg, IM Nor. How bright are these guys? Each of them contains some fascinating physics, if they're bright enough for us to study. Snapshots are fine! Finally, it's just getting to be BW Scl season again - and we want to see how the star has healed itself, or maybe not, from its recent superoutburst. In particular, we'd like to see whether the pulsations have changed in frequency, amplitude, and coherence. So this will be a good southern target for the next couple of months. joe p From jop at astro.columbia.edu Mon Jul 15 08:30:27 2013 From: jop at astro.columbia.edu (Joe Patterson) Date: Mon, 15 Jul 2013 08:30:27 -0400 Subject: (cba:news) V893 Sco In-Reply-To: <20130714222000.GB25057@milkyway.gsfc.nasa.gov> References: <20130714222000.GB25057@milkyway.gsfc.nasa.gov> Message-ID: <51E3EB63.7020308@astro.columbia.edu> Hi CBAers, Koji Mukai has reminded me of our pathetic knowledge of a very important dwarf nova, V893 Sco. It's bright, nearby, quite X-ray-luminous, and has a very short Porb. Plus it has outbursts, doubled emission lines, and probable eclipses. It oughta be royalty among the SU UMas. But actually, despite these shiny credentials, it has never really even acquired citizenship in that realm. Why not? Because neither superoutbursts nor superhumps have ever been reported. Probably those of us interested in such things, e.g. me, have shied away from studying this star. But now that the SU UMa phenomenon has become decidedly the norm, we ought to be interested in the well-documented exceptions, if indeed they are well-documented. V893 Sco is still moderately in season for southerners. I think it would be a great target for long-term CBA coverage, starting now. joe p p.s. Koji also sent me this advertisement for my favorite TV program of my youth. Growing up in Yokohama, it taught me that you can outwit even superpower-equipped villains, if you have a pure heart, a Honda 50, and a dog. http://www.youtube.com/watch?v=HlPco-SUyRk From jop at astro.columbia.edu Thu Jul 18 18:00:47 2013 From: jop at astro.columbia.edu (Joe Patterson) Date: Thu, 18 Jul 2013 18:00:47 -0400 Subject: (cba:news) scratch another star from Aquila In-Reply-To: <20130528142328.D32D413000DA@sedna.astro.columbia.edu> References: <20130528142328.D32D413000DA@sedna.astro.columbia.edu> Message-ID: <51E8658F.9000507@astro.columbia.edu> A quick look at the V1315 Aql data suggests that its superhump is dormant this year (well, this week). So let's take it off the menu for the rest of the year. However, the variable X-ray source is definitely variable at visual wavelengths - and is it ever! It varies by about 2 magnitudes, on many timescales, and the spectrum looks like some kind of very high-excitation mass transfer binary, probably a CV or LMXB. A great, great target for intensive followup with long time series! That's Swift J2124.6+0500, in Equuleus, the Little Horse. joe From jop at astro.columbia.edu Fri Jul 26 07:09:57 2013 From: jop at astro.columbia.edu (Joe Patterson) Date: Fri, 26 Jul 2013 07:09:57 -0400 Subject: (cba:news) UZ Boo, V1101 Aql, mainly Message-ID: <51F25905.5010602@astro.columbia.edu> Hi CBAers, UZ Boo is in outburst again, about 10 years after the last. We've only seen two previous outbursts, both very sparsely observed. This is a dwarf nova with our favorite credentials: nearby (~150 pc), WZ Sge class, relatively long period. Beautiful! Despite the inconvenience of Bootes in late July, this is still an extremely desirable target. With decent weather and a Europe-eastern Americas-western Americas handoff, we stand a pretty good chance of deciphering the period structure. What's happening in Aquila these days? Well, for us, anyway. First, we're finished with V1315 Aql. Nice eclipses, but a weak superhump this year, and we're done with it. The V1432 Aql campaign is going well, but only needs occasional coverage - once a week is just fine. The star I strongly recommend for intensive coverage is V1101 Aquilae, which is busy flashing a beautiful smile full of negative superhumps. Technically I suppose it's "the first Z Cam star to show superhumps" - though that's a somewhat weak statement, since Z Cam is really not a well-defined moniker, and they're hardly ever studied in long nightly time series. Anyway, there are a host of unanswered questions: how long will they last? how stable are they? are there also positive superhumps? is there also a superorbital ("nodal precession") frequency present? At 14.4, everyone can do this star, and I hope some AU-NZ observers will take a crack at it too, since we usually lack observations from Australasia. And be sure to specify comparison star; studies for the superorbital period (supposedly around 4 days) will require a close calibration between observing stations. The two main southern stars I'm promoting now are GW Lib and BW Scl. Both recent erupters which have shown WD pulsations, as well as some mysterious long-period signals - origin still unknown. Decently placed in the sky, and bright enough for average, roughly clear nights (~16.5). I'll repeat a wish list, though: V4743 Sgr, V1494 Aql, IM Nor, V4633 Sgr, V3890 Sgr (in order of increasing faintness and/or difficulty). Faintness or crowded fields guard these stars' secrets quite well, but there are suspicions that those secrets are worth knowing! The X-ray variable in Equuleus. Enrique, Josch, and Jim Jones are covering this guy pretty well, and it's variable on MANY timescales. But so far, no period. Disappointing. Yet the spectrum and extreme variability definitely suggest some kind of high-Mdot CV. At 12th magnitude, good target for small scopes. Let's keep going another 1-2 weeks at least. It might be a good idea to try for a very fast cycle time (10 s?) - so far we haven't investigated that regime. joe