From jop at astro.columbia.edu Sun Oct 1 07:39:22 2017 From: jop at astro.columbia.edu (Joe Patterson) Date: Sun, 1 Oct 2017 07:39:22 -0400 Subject: (cba:news) QR And, WZ Sge, mostly Message-ID: Dear CBAers, Some great (northern) fall weather this year, and a lotta work keeping up with all the CBA data. Fortunately I have my every-7-years sabbatical this semester, so I can do a better job. Our paper on WZ Sge is about ready for circulation (to the numerous authors - you know who you are out there). It spans many years, but another couple of weeks would really help nail things down for 2017. It's a tough target - 15.5 with a neighbor star ~7 arcsec away - and calls for (somewhat) fast integrations, since eclipse ingress and egress are brief. I recommend a 20-30 s cycle time, but I notice that slower is usually OK too. The bottom line won't change. The eclipse times wander very slightly on a timescale of decades. This prevents a measurement of long-term evolution (systematic orbital-period increase or decrease), but the timings seem to wander on the ~25 year ERUPTION cycle. That would be pretty interesting... although we can't prove it since we only have 55 years of data. I look forward to another 55. Of all CVs, WZ Sge is the nearest, brightest in eruption, most studied, possibly oldest, and a dozen other distinctions. It's the Andromeda Galaxy of CVs. But the fast variations in light mean that only the larger CBA scopes (14 inch and up) can contribute substantially. We can definitely quit on QR And. Some really great data - long and top-quality runs - has been arriving on this 12th mag eclipsing binary. Jim Sergeant, Joe Ulowetz, Stephen Brincat, and James Boardman have been leading the way. I'm just about to do the period-change analysis, but am sure that we have enough for 2017. Some morning-target talk, on BRIGHT stars... FY Per is a total mystery star. A well-determined spectroscopic period of 0.2585 d, but every so often, a 90-minute photometric period pops up -just a few hundredths of a magnitude, but not particularly difficult to study since the star is 12th mag. One of these years, we should figure it out! GK Per has a 351-second signal - an intermediate polar (DQ Her star). But it's *really* difficult to spot in quiescence, which is 95% of the time. So no one has figured out its long-term ephemeris; and this matters a lot, because it has by far the highest accretion rate among all DQs (and thus should spin up fast). The reason for failure is that there's a K subgiant in the binary, overwhelming the light from the white dwarf. This can be subdued with ULTRAVIOLET photometry. If you have an ultraviolet filter (and CCD with decent UV sensitivity), you can be the hero with a long program of UV time series. Calibration is of no importance - you just want to make sure a lot of UV photons, and not many others, reach your CCD. It's just a timing project. Airmass is usually a big problem with UV photometry - but less so here, since the point of interest is a 6-minute *periodic* signal. Don't fall in love with your U filter, though. Accurate UV photometry is famously tricky, for many reasons (extinction, low sensitivity, weirdness of the filter itself, etc.) For nearly all purposes - except maybe this one - it's a tool to AVOID. The AAVSO fall meeting is in Nashville this year (Nov 2-4), and it looks like a pretty good collection of CBAers will be there. So I guess I will, too. joe p ____________________________________________________________ Center for Backyard Astrophysics (CBA) mailing lists http://cbastro.org/communications/mailing-lists/ From jop at astro.columbia.edu Thu Oct 26 18:25:46 2017 From: jop at astro.columbia.edu (Joe Patterson) Date: Thu, 26 Oct 2017 18:25:46 -0400 Subject: (cba:news) FY Per, WZ Sge, IGR1955-00, finis; new stars for Oct-Nov Message-ID: Hi CBAers, We've reached season's end with several stars: 1) WZ Sge and IGR1955-00, because the runs are getting short now. 2) FY Per, because there's a LOT of data, and I want to study it carefully before resuming coverage. It varies on the orbital timescale, and also apparently with some longer period that I haven't yet figured out. What I haven't found yet is the 1.5 hour period that originally motivated our program. To be continued after full analysis of the several hundred hours of data! 3) V339 Del, because its variability is really minuscule. Very surprising for this recent nova... and interesting, but further coverage would probably just improve the no-periodic-signal (and hardly any variability at all) result. here's a menu of juicy Oct-Nov-Dec targets. OY CAR, Z CHA, U GEM. All famous eclipsing dwarf novae. We've had a lot of recent success with tracking eclipsing stars... and, more arguably, with interpreting their orbital-period variations. So let's try that with these guys. U Gem should be an easy target; OY Car and Z Cha are harder (esp. since the critical data occur near mid-eclipse). BT Mon (a 1939 nova). Same comments. Faint in mid-eclipse, BUT the eclipse is long and symmetrical, so mid-eclipse can be timed even with lousy data near the bottom. The orbital period is almost exactly 8 hours, so for some observers, there may be no night-time eclipses for many weeks. V959 Mon, RR Pic, T Pyx. Classical novae which we are studying for their orbital-period signals (and variations). T Pyx is slightly off-season, but plenty suitable since the period is sufficiently stable to make full use of relatively short runs (2-3 hours). BY Cam and "Paloma" (RXJ 0524+42). Apparently "asynchronous polars"... and we're devoted to following their (slowly) wandering periods. DQ Her stars (intermediate polars). V418 Gem, V1033 Cas, V902 Mon, BG CMi, and V598 Peg. Except for the last (of which I'm not sure), these are all pretty straightforward targets - not requiring long runs (thought profiting from length) and not requiring every-night dense observation. The objective is to string together a bunch of timings (say 10-20) each observing season, to derive a long-term ephemeris. Finally, ES Cet. We're about to fire off our paper on this 10-minute binary... but each observing season form now on will have significant impact, because sensitivity to period change increases with the SQUARE of the baseline. So it remains a fine target. It's the first CV to demonstrate the controlling influence of gravitational radiation in evolution - and we didn't even have to smash the stars together to do it! joe p p.s. I've not said much about priority in this long list. I will after seeing some of the data. Also, you can get a pretty good idea from looking at your own data - except for the faintest stars, which usually only yield their secrets after a lot of teamwork. ____________________________________________________________ Center for Backyard Astrophysics (CBA) mailing lists http://cbastro.org/communications/mailing-lists/ From jop at astro.columbia.edu Sun Oct 29 11:47:54 2017 From: jop at astro.columbia.edu (Joe Patterson) Date: Sun, 29 Oct 2017 11:47:54 -0400 Subject: (cba:news) VZ Scl campaign Message-ID: Hi CBAers, Thanks to Berto and Gordon, we are accumulating a great campaign on VZ Scl this year... and it seems to be rewarding our efforts with deep eclipses (as always) and superhumps (that's new). However, there are no actual time overlaps between the two stations (Australia and South Africa). In some years coverage from these stations can bridge the Indian Ocean gap, but it just hasn't happened this year; and of course we can never bridge the Atlantic plus Pacific gap! So we need coverage from the Americas. Josch might be able to help us, but another possibility is North American coverage. It's a challenge at this declination, but some of our southern USA observers might be able to handle it. Shawn or Tut, perhaps? We can calibrate* to within ~0.06 mag even without this help, but simultaneity of coverage reduces that error to ~0.02 mag. That would be good. But don't mess with huge variability in airmass, because that's a systematic error we really can't tame at all. joe *BTW "calibrate" means reduce to a COMMON INSTRUMENTAL MAGNITUDE. That's pretty much what we always seek. The more ambitious goal of arriving at a STANDARD magnitude (Sloan, Johnson, etc.) is usually beyond our scope... and is basically irrelevant to our goal (periodic signal searches). Just for the record, though, our instrumental magnitudes are usually ~0.2 mag fainter than a Johnson V. That's assuming you report so-called "CV" magnitudes, which most of you do. ____________________________________________________________ Center for Backyard Astrophysics (CBA) mailing lists http://cbastro.org/communications/mailing-lists/