From jop at astro.columbia.edu Sat Apr 4 21:40:45 2015 From: jop at astro.columbia.edu (Joe Patterson) Date: Sat, 04 Apr 2015 21:40:45 -0400 Subject: (cba:news) shout-out to UX UMa Message-ID: <5520929D.40209@astro.columbia.edu> Hi CBAers, Permit me a short exultation about UX UMa. I dunno exactly why I put this guy on the program. Bright star, well-formed eclipses, a vast previous literature on the star (so that whatever we find, it has extra potential for probative value by comparing with other results). There were no grounds for suspecting superhumps: it was neither a dwarf nova nor a SW Sex star, the period was too long, and besides, how could the previous ~80 papers on UX UMa have missed them? And yet UX UMa is showing up with *great* superhumps, plus the "nodal" signal at nu = 0.27 c/d that is often a concomitant of negative superhumps. If our physical picture of these things is correct, then it means the accretion-disk wobbles retrograde with a period of 3.7 days. (Precisely why is unknown, for this and all the other ~30 negative-superhumpers.) But UX UMa, whose basic properties are pretty well known, flunks all the supposed rules for having superhumps. If it superhumps, then maybe all the other rule-flunking stars also do, and have just concealed them because no one bothered to look with an appropriate research tool. Could it be that disk wobble occurs in *all* CVs who linger in a high-accretion state for at least a few hundred orbits? That appropriate tool is time-series photometry over a range of longitudes. We'll try now to target other bright novalikes of even longer orbital period. This will be trickier, because with our observing/analysis methods, we run some risk of seeing waves in the light curve arising purely from differential extinction. A V filter may well be a superior choice for the brighter stars. However, unfiltered has worked well for UX UMa; its far-northern declination enables observers to get long runs with no great change in airmass, and the increased signal-to-noise will help in the analysis of the eclipses. Anyway, UX UMa will remain a great target for another 10 days at least. Keep up the great work. Every new UX UMa run popping up in my inbox quickens the pulse! joe p ____________________________________________________________ Center for Backyard Astrophysics (CBA) mailing lists https://cbastro.org/communications/mailing-lists/ From jop at astro.columbia.edu Sun Apr 19 11:59:50 2015 From: jop at astro.columbia.edu (Joe Patterson) Date: Sun, 19 Apr 2015 11:59:50 -0400 Subject: (cba:news) stars for April and May, 2015 Message-ID: <5533D0F6.9010600@astro.columbia.edu> In the attached pdf -------------- next part -------------- A non-text attachment was scrubbed... Name: cba41915.pdf Type: application/pdf Size: 76773 bytes Desc: not available URL: -------------- next part -------------- ____________________________________________________________ Center for Backyard Astrophysics (CBA) mailing lists https://cbastro.org/communications/mailing-lists/ From jop at astro.columbia.edu Tue Apr 21 00:27:44 2015 From: jop at astro.columbia.edu (Joe Patterson) Date: Tue, 21 Apr 2015 00:27:44 -0400 Subject: (cba:news) Fwd: [vsnet-alert 18564] ASASSN-15hn: very bright, high amplitude CV candidate In-Reply-To: References: Message-ID: <5535D1C0.9010702@astro.columbia.edu> Gracious, an amplitude of 8.7 mag. Getting awfully impressive. Could be an awfully nice target! joe -------- Forwarded Message -------- Return-Path: Received: from sedna ([unix soc SASSN-15hn 9:7:5.35 -10:42:45.2 2015-04-18.09 13.2 very bright, high amplitude CV candidate, matches to j=21.9 faint source, V>17.0 on 2015-04-14.12, V=12.9 on 2015-04-17.05, V=13.2 on 2015-04-18.09 http://www.astronomy.ohio-state.edu/~assassin/transients.html ____________________________________________________________ Center for Backyard Astrophysics (CBA) mailing lists https://cbastro.org/communications/mailing-lists/ From jop at astro.columbia.edu Tue Apr 21 01:48:08 2015 From: jop at astro.columbia.edu (Joe Patterson) Date: Tue, 21 Apr 2015 01:48:08 -0400 Subject: (cba:news) high-amplitude dwarf novae Message-ID: <5535E498.2010000@astro.columbia.edu> Hi CBAers, Amid all the dwarf novae - and *new* dwarf novae - popping off up there, which are the ones of special interest? No one knows for sure (that would require advance knowledge of the stars, not available on this planet) - but a good bet is the high-outburst-amplitude guys. Why? Well, dwarf novae in full outburst are pretty much a standard candle, depending weakly on orbital period, but basically Mv = +4.5 for the most common dwarf novae, the short-period guys. That's at maximum light. What about minimum light? You have the secondary star (usually negligible for the short-period guys, where the secondaries are all M6 or cooler)... and the white dwarf... and the accretion disk. The last is hard to calculate, but let's take the extreme case of imagining that the disk contributes ZERO light. So the limiting case is that at minimum, the light is purely the WHITE DWARF. That's a useful assumption, because cool white dwarfs with masses typical of those in CVs have an absolute magnitude = +12. So that means the maximum amplitude (between max and min) should be about 7.5 magnitudes. Even WZ Sge, deservedly considered the most extreme of that class, has an amplitude of just 7.3 mag. So the high-amplitude guys (anything over 6.5-7 mag) are particularly interesting, because they represent the most intrinsically faint of the dwarf novae - and probably the oldest, because plenty of evidence shows that stars get fainter as they get older. We really want to study the oldest stars, because we have no idea how CVs end their lives. Theory suggests that CVs should be 5-10x more abundant in the sky than they actually are - and therefore theory is probably wrong as regards the very late stages of evolution. So when the outburst amplitude even exceeds that of WZ Sge, the star is likely to be important. And the brightest dwarf novae are the nearest, since the DN is roughly a standard candle. So "bright and high amplitude" is a strong reason to observe that particular star. This new guy, with an amplitude of 8.5 mag, is definitely in that category. But you guys are getting the light curves, not me. It's also true that the light curves themselves often tell you what's worth pursuing. If it looks interesting, then it is! joe p ____________________________________________________________ Center for Backyard Astrophysics (CBA) mailing lists https://cbastro.org/communications/mailing-lists/