From jop at astro.columbia.edu Mon Nov 11 17:50:26 2002 From: jop at astro.columbia.edu (Joe Patterson) Date: Mon, 11 Nov 2002 17:50:26 -0500 (EST) Subject: (cba:news) stars for mid-november Message-ID: Dear CBAers, Time to report on the main two campaign stars of the moment, VY Scl and V592 Cas. Both have been covered very well. V592 Cas has basically lost its superhumps. The humps we found in 98 were fairly lame to begin with, and now they've dropped below detection limits. Impressively bashful. It does have the side benefit that without this signal, the detection of higher-frequency signals ("QPOs") becomes clearer. And in particular, we have a very high-quality power spectrum (averaged over 30 nights) showing a broad signal near 95 cycles/day. But it's reason to quit. Away with it! VY Scl is weirder. It's very well covered by Berto, Jonathan, Bob Rea, Neil Butterworth, and Greg Bolt... pretty much round-the-world coverage. There are signals near 1 c/d, but they have lousy stability... and with poor stability and an unfortunate choice of frequency, the matter becomes very difficult to prove. We have a good orbital ephemeris, QPOs at 50 c/day, and some suspicions of negative superhumps. But as the data set gets better, the results don't get clearer... not a happy circumstance. Since we can't do better than global coverage, I think we should retire VY Scl for the season (unless it dives into a low state!) The southern star of the night should be EC05287-5857. Very nice collection of periodic signals in this fella, and they appear at first glance to be stable. Let's try for that horizon to horizon! The best northern campaign star is Tau 2 (KUV 0358+0614), and I hope I can convince some southerners to observe it also. I believe it will be a great winner also, available to all hemispheres and practically all night long! Finally, for small northern scopes and moonlit skies, a campaign on BZ Cam is right around the corner. Be the first on your block to get the new season's light curve. joe From jop at astro.columbia.edu Thu Nov 21 13:39:56 2002 From: jop at astro.columbia.edu (Joe Patterson) Date: Thu, 21 Nov 2002 13:39:56 -0500 (EST) Subject: (cba:news) successes and entreaties Message-ID: Dear CBAers, Just one more class until a school break, when I can get back to some good variable star work. In the meantime... The campaign on EC0528-5857 has been entirely successful. We have round-the-world fully calibrated coverage, and 45 days worth - it don't get no better than that! The main signals present are at 6.701(4) and 6.126(6) c/d. The high stability of the former strongly favors its identification as nu-orb - implying an apsidal superhump with a period excess of 9.4%. Quite an excellent match to AO Psc in that regard - yet no evidence for magnetism as is so obvious in AO Psc (from coherent 14 minute pulses). It's surprising to see that a disk phenomenon like superhumps should be so indifferent as to whether a strong magnetic field is present! I think that result ain't gonna get no better - let's give EC0528 a golden handshake and move on. The first ten days of the Tau2 campaign have been really fascinating. This is definitely a multiperiodic star. The signals are strong and rich in harmonic content. So far all of the coverage is from North America, so there are still some aliasing issues (even with 7 hour runs). We urgently need some European/African/Oceanic artillery trained on this star! At 0400+06, it's well positioned for everyone, crossing the meridian at local midnight the world over. I'll send a recommended comp star in the next message. But as usual the comp star recommendation is weak; you can choose one convenient for you, and the chef can probably calibrate it out in the CBA kitchen (using time overlaps). I think the Moon has just now cleared out of the way, so I'm really psyched for 3 solid weeks of coverage. >From time to time I mention FY Per and FS Aur. These are strange stars which flash photometric periods evidently unrelated to their orbital periods (though slow - 1.5 and 3.4 hrs). They're reasonably bright and northern - excellent targets for northern small scopes. In the south, on a really still night, you can hear a novalike variable crying out for coverage. This is EC04224-2014, probably a UX UMa star with a period near 4 hrs. It's about 12th magnitude, which is probably why you can hear it. The star is called simply "Eri" (along with others of that name) in the Living CV Catalogue. Coords 04 24 41.06 -20 07 11.5. So that's the Thanksgiving menu. Let's hope it includes no turkeys. joe From jop at astro.columbia.edu Thu Nov 21 15:53:03 2002 From: jop at astro.columbia.edu (Joe Patterson) Date: Thu, 21 Nov 2002 15:53:03 -0500 (EST) Subject: (cba:news) Tau 2 comp star Message-ID: The observations to date are mostly by Jerry Foote and Bob Fried, who evidently used the same comparison star. But I don't know for sure which star that is. Jerry and Bob, are you at liberty to reveal this? Anyway, I'm guessing it's the star 2.5 arcmin directly south from Tau 2, known as GSC 79-1192. joe From jop at astro.columbia.edu Thu Nov 21 16:36:21 2002 From: jop at astro.columbia.edu (Joe Patterson) Date: Thu, 21 Nov 2002 16:36:21 -0500 (EST) Subject: (cba:news) Re: Tau 2 comp star (fwd) Message-ID: > Jerry and Bob, are you at liberty to reveal this? Anyway, > I'm guessing it's the star 2.5 arcmin directly south from Tau 2, known as > GSC 79-1192. Bingo! Give that man a Milky Way....Burp. Bob That appears to be an affirmatory. Good comp star. Oh, and following a suggestion by Lew Cook, let's start to name comp stars as a matter of routine from now on. Specification of location is good enough (for me), but the star's catalogue name would of course be better for archive purposes. And the best way to do it is in the header or the text file itself (rather than a separate message) - again because of the archive. If that entails some awkwardness, then don't sweat it - but do let me know which is your comp star. Thanks! joe From jk at cbastro.org Sun Nov 24 01:59:48 2002 From: jk at cbastro.org (Jonathan Kemp) Date: Sat, 23 Nov 2002 20:59:48 -1000 (HST) Subject: (cba:news) comp stars, software, and such Message-ID: Hi CBAers, Regarding the selection of comp stars and the general process of becoming acquainted with a field, I highly recommend use of the Aladin Interactive Sky Atlas which is produced by the CDS in Strasbourg, France. A Java-based application that can be run via the web or downloaded and run in a stand-alone manner on an internet-connected machine, Aladin allows you to overlay digitized sky images from various surveys with names and data for objects from a wide variety of catalogs. For example, you can plot a DSS image of a CV field with all the GSC and Tycho stars and get their IDs, calculate the distance on an image from one's variable to one's comparison star, or overlay nearby USNO stars to get a very rough color from red and blue magnitudes from the A2.0 catalog. There are seemingly infinite uses for and possibilities with this software tool, and I often use it to find and check comparison stars when I observe CVs. More info on Aladin can be found at http://aladin.u-strasbg.fr/ . Also, a while back there was some discussion about keeping accurate time when operating a telescope and collecting data. While I generally collect CV data in the Unix/Linux world, there are several tools for the Windows platform that allow automatic and periodic synchronization of your PC clock, many of which are free. Once upon a time David Harvey recommended using a program called SocketWatch which is shareware, can be registered for a small fee, and is produced by a company called RoboMagic. I've had good luck with this and a slew of other tools produced by the same company that produces SocketWatch, including WetSock, DayToday, and MoonPhase. They are small and simple programs that can synchronize your PC clock, show weather info in your system tray, show the day and date in your system tray (especially useful if your system is on UT to avoid confusion), and show the age and phases of the moon in your system tray, respectively. There are many companies that produce tools like each of these, but I've found this one single small outfit produces several useful tools that I have registered and frequently use myself on the Windows partition of my PC. More info can be found at http://www.robomagic.com/ . Cheers, Jonathan CBA Hilo From jop at astro.columbia.edu Sun Nov 24 11:42:48 2002 From: jop at astro.columbia.edu (Joe Patterson) Date: Sun, 24 Nov 2002 11:42:48 -0500 (EST) Subject: (cba:news) Re: comp stars, software, and such In-Reply-To: Message-ID: > > Concerning identifying the comp. stars used in future data submissions. The > different GSC catalogs use different numbering schemes, so would you prefer > some sort of comp. star ID such as: > GSC 2.2 N3320100520 so that you have a non-ambiguous identification? Or is > there a better (standard?) way to ID comp stars? Thanks, Tom, for bringing this up. Well for a long time I was totally happy with "star 1.6' SSW of RU Loopy". Then the GSC came along and eventually it became routine to use it. So many of our published papers give the GSC name of our main comp. Now we have GSC 2.2 with a bigger name. I don't object to this at all, but I see that observers are sending data with the old numbering scheme. So I don't want to plunge into any new system until it's obvious that the average CBA observer can routinely use it. I just don't know that much about what kind of information resources you have available at your desktop. In fact I don't know that much about what's available at *my* desktop, for that matter. Anyway, I do want to stress that standardization of comparison stars is not ultimately of much importance for our programs. Why? Because the first thing I do to a long-night time series is to SUBTRACT THE MEAN AND TREND. This *greatly* improves the sensitivity to periodic signals in the 4-40 c/day range, usually our range of maximum interest. Only for the lowest frequencies does calibration matter. And even for those, the best calibration is achieved from simultaneous observation, even if the two telescopes use different comparison stars. I've noticed from experience that the additive constants needed to splice data between telescopes vary by 0.02-0.03 mag from night to night, and that this error is about the same regardless of which comp star you use. (The exact origin of it is probably complex, but I suspect that the dominant element comes from the very wide bandpass of unfiltered data - the price we pay to *have* a powerful research program on CVs with small telescopes). So the main message is just to *report* the comp star. Since Jonathan is archiving all data and we plan to make the time series themselves retrievable, this is just good housekeeping. The secondary message is to try to use a common comp star, since that provides a crude calibration even when no simultaneity is achieved (it's by no means always achieved). You can definitely use a different comp if you like, with no significant loss in the science - but then stick to it. As for the naming scheme, I still like the GSC 1 or even the buried-treasure direction... but I'll make it my business to figure out whatever newfangled name you've supplied. There are some comp-star recommendations on the CBA website for many stars. At the bottom of the "charts" page, there's a clickable "Earlier CBA charts". They're not complete, but we thought at some point (on grounds of color and brightness) these stars might make good comps. But of course you know your equipment (and saturation limits, and night quality) best, and your judgment is probably the most reliable guide. joe