From jop at astro.columbia.edu Thu Jul 1 17:10:17 2004 From: jop at astro.columbia.edu (Joe Patterson) Date: Thu, 1 Jul 2004 17:10:17 -0400 (EDT) Subject: (cba:news) Var Her 04, mostly Message-ID: Dear CBAers, Well, Mister Var Her 04 is showing, at this early stage, some grounds for the conjectured resemblance to WZ Sge. The main outburst seems to have ended a day ago; "echo" outbursts, if any, will support this resemblance - but only time will tell re them. However, the power spectrum of the superhumps (i.e. collection of frequencies in the light curve) is very much like that of WZ Sagittae. Most dwarf novae show only a simple power spectrum, containing the fundamental and a few harmonics (exact integer multiples of wsh). WZ Sge showed a much richer spectrum, with each "harmonic" containing substructure (separated by integer multiples of W, the putative precession frequency. The rule of thumb for these things is that each orbital orbital harmonic (at nw) is actually a multiplet containing n+1 components, with frequencies nw-mW, where m=0,1,..., n. The m=n component is almost always dominant, which gives superhumps their characteristic and repeatable shape. Appreciable amplitude in other components yields noncommensurate frequencies, and this causes recurring structure to come and go in the lightcurve on a timescale of a few days. CBA lightcurves are chock full of the documentary record of this structure in superhumps, and we have dutifully reported it in a couple dozen papers. But to this day, not a single referee has ever commented on it; not a single reader has ever asked about it; not a single paper has ever referenced it. Unfortunately, no one (certainly including us!) knows what this fine-structure means. So we just report it, and hope that the day is not far off when someone will come up with some worthy idea about what it means. In the meantime, it's useful for one thing; assuming that the parsing of frequencies is as described above, it can be used for deciding what the orbital frequency is, even when the outburst light is strong. In particular, Var Her 04 shows a very rich power spectrum seemingly following this rule, with w=17.64(1) c/d and W=0.30(2) c/d. Among the many components noncommensurate with wsh=w-W, the 3w component is particularly strong. Components are seen out to the 5th harmonic, All of this comes from the diligence of CBA photometrists: Lew Cook, Tonny, Dave Messier, Michael Richmond, Russ Durkee, Brian Martin, Mike Koppelman, Donn Starkey. Several others are preparing data sets for submission, so this supply should significantly increase. Also, the star will likely be up to more hijinks in the coming weeks, so keep a close watch on this wonderful star! Var Her is stealing all the thunder in the northern sky. BZ Cir is staging a superoutburst in the southern sky, also for the first time recorded. Data on that star would be awfully nice! We're coming up on a very bright Moon period, and some observers may want to start up the V603 Aql campaign. I hope. At V=11.7 and a dec of 0 degrees, I hope and trust it'll be popular with everyone! joe From jop at astro.columbia.edu Thu Jul 1 17:53:57 2004 From: jop at astro.columbia.edu (Joe Patterson) Date: Thu, 1 Jul 2004 17:53:57 -0400 (EDT) Subject: (cba:news) observing techniques Message-ID: By the way, I wanted to stress again the advisability of what has become our standard observing technique: white-light photometry with good time resolution (better than ~60 s). Unless you have a 20-inch or better, you just can't afford to lose the factor of 8 in counts that a filter will exact. With rare and quite subtle exceptions, the waveforms of CVs very closely resemble each other in all passbands relevant to ground-based photometry. So with filters you degrade the signal and get little back in return. The best reason to use filters is not that you'll see new phenomena (because you won't - or worse, you will because your data is now of much lower quality)... but because it minimizes differential extinction, which is a hazard of our enterprise. With the 1.3 m telescope on Kitt Peak, we usually use a V filter, but only to reduce differential extinction - and only because we have enough photons to reject 90% of them. Occasionally for a special purpose we'll spin filters and get BVRI time series. But only in specialized cases. For faint stars the penalty is really huge - a factor of 8 in counts, and about a factor of 6 in time resolution. At 10th magnitude you might be able to afford that... but generally your data will be of much greater usefulness if you observe unfiltered (and fairly fast). Nothing new there; just a reminder. joe From jop at astro.columbia.edu Fri Jul 2 14:56:01 2004 From: jop at astro.columbia.edu (Joe Patterson) Date: Fri, 2 Jul 2004 14:56:01 -0400 (EDT) Subject: (cba:news) Re: observing techniques In-Reply-To: <066FA66E-CBB7-11D8-A91C-000A95C4DF7E@bitstream.net> Message-ID: > Joe, I get it but would wonder -- I thought it would be much easier to > combine observations if they were made filtered. I know you've combined > tens of zillions of observations so this must not be the case? > > As a side note, I usually observe filtered because I don't have a clear > filter and don't want to refocus. (read: lazy). > Yes, that's a point. If everyone used the same filter and the same comparison star, it would be quite a significant point; the splicing of light curves from various observers would be very easy, and that might even be enough to justify the factor of 8 loss in photons. But we're a ragtag army, with every soldier possessing different weapons - and fighting the war really on their own terms. So I've been used to studying data obtained with different cameras, different filters, no filters, different comparison stars. By being that omnivorous, we usually manage to get a LOT of data. So how do you splice it? Well, from many hundreds of nights of photometry simultaneous between multiple observers, a simple answer emerges: SIMPLE ADDITIVE CONSTANTS (in delta magnitude). You can reduce the systematic observer-to-observer difference to about 0.03 mag that way. You can't do much better; differences of 0.01-0.02 mag exist from night to night even when nothing (perceptible) changes, and there are during-the-night drifts of 0.02-0.03 mag (presumably due to differential extinction). These annoying little effects can be measured and partially removed, but by then you're spending a lot of time on calibration - time that is better spent observing our fascinating stars! Often it happens that there is little or no observer overlap, in which case there's nothing to splice. In that case I just subtract the mean delta mag, and trend if there is one. That is THE most powerful way to prepare a time series for period search (as long as you remember that you have blinded yourself to the lowest frequencies by this subtraction!). In practice the scientific usefulness of the time series is mostly set by the QUANTITY and STATISTICAL QUALITY (not calibration quality) of the delta magnitudes. I imagine some observers are worried about what Saint Peter is going to say about all this when you meet him at the Pearly Gates. On the off chance that he happens to be a photometrist, I grant you that he's more likely to be a classical than a high-speed photometrist. In which case you may well be in trouble, because the classical art thrives on calibration. I'm sorry, you'll just have to do some quick talking. (Personally I am not worried, since I'll be rejected on numerous other grounds.) BY THE WAY... Jonathan tells me that we now have a "cba-chat" exploder enabled. Send messages to cba-chat at cbastro.org whenever the item is more like chat than like news. We'll see if it works. Thank you, Michael (Richmond), for prodding us to actually implement this idea. joe From jop at astro.columbia.edu Sat Jul 3 19:19:31 2004 From: jop at astro.columbia.edu (Joe Patterson) Date: Sat, 3 Jul 2004 19:19:31 -0400 (EDT) Subject: (cba:news) V803 Cen bright and probably humping (at last) (fwd) Message-ID: Well, we were waiting for this! About 5 days of time series, and we'll have CONTINUOUS coverage of the whole 90-day cycle. joe Hi all, V803 Cen is very active at the moment at magnitude 12.6. This must be the expected superoutburst and I am measuring the humping period at CBA Pretoria. It looks that the overall cycle duration of V803 Cen is a bit longer than was accepted, not so? Since we had thunderstorms (so unseasonal here) last night, I have no knowledge on thee exact starting time of the present outburst. Regards, Berto Monard Bronberg Observatory / CBA Pretoria From jop at astro.columbia.edu Wed Jul 7 09:23:33 2004 From: jop at astro.columbia.edu (Joe Patterson) Date: Wed, 7 Jul 2004 09:23:33 -0400 (EDT) Subject: (cba:news) [vsnet-alert 8230] Rapid brightening, eclipse and humps of Nova Sco 2004 = ASAS 171251-3056.6 (fwd) Message-ID: Dear CBAers, Well, it is not yet clear what kind of a star (presumably a nova of some variety) this thing is, but Pojmanski's light curve shows a pow'f'l interesting drop! Well-placed, bright (magnitude 10-11), and even briefly accessible for the lower northern observatories. Let's scope this star out a bit! joe BTW the V803 Cen coverage has been good - let's extend it just a few more days! ---------- Forwarded message ---------- Date: Wed, 7 Jul 2004 09:37:37 +0200 From: Grzegorz Pojmanski To: vsnet-alert at kusastro.kyoto-u.ac.jp Subject: [vsnet-alert 8230] Rapid brightening, eclipse and humps of Nova Sco 2004 = ASAS 171251-3056.6 Rapid brightening, eclipse and humps of Nova Sco 2004 = ASAS 171251-3056.6 After halt at V=10.64 (for ~ 0.15 d) Nova Sco 2004 = ASAS 171251-3056.6 entered rapid brightening phase on UT 07.144 (HJD 2453193.651) gaining 0.07 in less than 2 hours (0.9 mag/day) during which apparent eclipse was caught on UT 07.225 (delta mag 0.3, delta t < 15 minutes) Fluctuations with amplitude > 0.04 and period of ~ 0.058 d are now clearly visible. Its current brightness (UT 07.27) is V=10.56 See: Light curve and images can be found on http://www.astrouw.edu.pl/cgi-asas/asas_disc/171251-3056.6,3193.6 Nearest neighbour: http://www.astrouw.edu.pl/cgi-asas/asas_disc/171258-3055.8,3193.6 Grzegorz Pojmanski, ASAS From jop at astro.columbia.edu Sat Jul 10 10:16:17 2004 From: jop at astro.columbia.edu (Joe Patterson) Date: Sat, 10 Jul 2004 10:16:17 -0400 (EDT) Subject: (cba:news) Stars for mid-July Message-ID: Dear CBAers, Getting ready here to leave for a CV conference in Strasbourg. Time to clean up some loose ends... Var Her 04 remains faint... but much more seriously, it is now too heavily contaminated by its very close neighbor to study in unfiltered (or any non-blue) light. Unless it echoes, back into the shadows for mister Var Her. Very, very nice display of superhump signals though - wonderfully intricate! If it re-erupts ("echoes"), then vault it back onto the northern list. Berto tells me that V803 Cen has drooped down from its early July supermax. That's good enough for me - let's suspend for the year. Quite impressive coverage, despite a somewhat poor sky position - from Berto, Paul Warhurst (in Argentina), Bob Rea, Greg Bolt, Peter Nelson. Full 95 day coverage - from one supermax to the next! It's a good time to start campaigns on V603 Aql and V1315 Aql - both well-placed and available to both hemispheres. Those are my top recommendations. It looks like we can put V1494 Aql to bed for the year (very well covered by Bob Rea), and also RX1643+34 (kind of orphaned by all the dwarf novae). I remain very interested by V825 Her - but so far have had trouble selling that one! I hope, and expect, to write from France. Better hustle now... joe From jop at astro.columbia.edu Tue Jul 20 06:02:18 2004 From: jop at astro.columbia.edu (Joe Patterson) Date: Tue, 20 Jul 2004 06:02:18 -0400 (EDT) Subject: (cba:news) AX Cap and V825 Her Message-ID: Dear CBAers, Just back from the Strasbourg CV conference. Went a lot better than my last overseas conference adventure! And returning gave me a chance to dig into the week's CBA data - with very interesting results. Lew Cook and Dave Messier (and Tom Krajci before moving back to the USA) have been observing V825 Her, a decently bright (14) and little-studied novalike. The published radial-velocity period is 4.9 hours - but the light curve shows a large-amplitude modulation at 8.6 hours. Quite an oddity! And very well suited to the CBA, since with a distribution over terrestrial longitude we can get very long nightly observing runs. Rod Stubbings found an eruption of AX Cap, and Berto's time-series photometry revealed large-amplitude waves at 2.8 hours. Thus it is a new SU UMa star, and at this Porb it really merits quite a bit of interest. The superhumps just started, and AX Cap is well positioned for all but our most northerly observers. So there's a big shakeup of target stars this month. We'll postpone the V1315 Aql campaign, and cease the campaigns on V1186 Sco, Var Her 2004, V4633 Sgr, V4743 Sgr, V4744 Sgr, V4745 Sgr. V603 Aql is definitely worth continuing, and now, but takes a back seat to AX Cap. AX Cap and V825 Her are the stars for the next few weeks! AX Cap is 15-16 so may present some problems on poor nights. Those would then be suitable for V603 Aql (at 11.7). V825 Her is bright enough, but this period can be awkwardly long. Above about 1.8 airmasses, differential extinction can be pretty important... and you will need somewhat long runs to help define this 8-9 hour modulation. A V filter will reduce or eliminate differential extinction (since it keeps the effective wavelengths of variable and comparison stars equal to within 200 A or so)... but this assumes you have enough photons to pay the price. There's no conventional understanding of stable periods much longer than Porb, and it's nearly always the case that Pspec=Porb. So at this point V825 Her is a mystery - let's try to dispel it! joe From jop at astro.columbia.edu Tue Jul 20 11:21:14 2004 From: jop at astro.columbia.edu (Joe Patterson) Date: Tue, 20 Jul 2004 11:21:14 -0400 (EDT) Subject: (cba:news) Comp star for V825 Herculis Message-ID: Since the period in V825 Her is long, my usual practice (in analyzing data) of normalizing to mean light is not feasible - because some runs will be mostly near the max, others mostly near the min, of the signal. Therefore it will pay to use a common comparison star, for which I recommend GSC 3081-61 (about V=13.1, and 3.7 arcmin W/ 0.5 arcmin S from the variable). We can cope with other comparison stars, but that's the prime choice. The CV itself is said to vary in the range 14.1-14.4, and that's consistent with the magnitudes we find. joe From jop at astro.columbia.edu Thu Jul 29 18:57:38 2004 From: jop at astro.columbia.edu (Joe Patterson) Date: Thu, 29 Jul 2004 17:57:38 -0500 (EST) Subject: (cba:news) stars to retire! Message-ID: Well, the dwarf novae are fading and Olde Whiteface is getting mighty bright. Time to make an adjustment. AX Cap is really too faint to do any more. I dunno about V2527 Oph - I imagine it has some life left in it, as soon as the Moon gets out of the way. V825 Her is done for the year. More detail tomorrow about these observing campaigns. A good time to resume coverage of V603 Aql and V1315 Aql! joe