From jop at astro.columbia.edu Wed Aug 1 11:49:18 2018 From: jop at astro.columbia.edu (Joe Patterson) Date: Wed, 1 Aug 2018 11:49:18 -0400 Subject: (cba:news) POLARS... intermediate and full-fledged Message-ID: <5d0e3c01-ce4b-15cd-e5be-868dfbef39a6@astro.columbia.edu> Hi CBAers, Something new! We are preparing a proposal to observe a bunch of polars (AM Her stars) in hard X-rays (10-60 keV). These energies are comparable to the free-fall energy onto a white dwarf. And since the conventional model for polars invokes accreting gas falling directly to the surface, this observation can reveal the white-dwarf masses (more massive WDs are much smaller, and thus should produce much higher infall energies). This experiment has been done successfully for a few of the celebrity polars. We'd like to try it for some of the rank and file. Here are the stars: VV Pup, UZ For, EP Dra, V834 Cen, V2301 Oph, HU Aqr, ST LMi. All these stars are known or at least likely to have high and low states, and it's important to know how bright they are now. Probably the X-ray observation will only succeed if the star is in a high state. So at a minimum, is the star *currently* in a high state? 1. This will probably require a 2-hour observation, since the stars vary strongly over an orbital cycle (generally 1.5-2.2 hours). 2. Someone will need to estimate how long the star is likely to stay bright. JUst a guess, of course... and I suppose that's my job (by consulting literature), but if anyone feels like doing that search of previous papers, I'd be grateful. 3. Most of these stars are around 16-17 mag, and for that we always recommend unfiltered light. But consider also a V filter. Time resolution is of no great importance here, and unfiltered brings some problem, since these stars typically have very crazy colors (because of cyclotron radiation. This is mitigated by V, which has a much narrower poassband and is the reference standard of most previously published studies. Try to get as many as you can. Not much need to do a *second* 2-hour light curve of a particular star. Being faint and rapid large-amplitude flickerers, these stars tend to persuade the rookie observer that the data are no good. But on a good night, it's likely the data are quite good. We hope to submit this proposal, or part of it, soon... so see what you can do with this! Re the intermediate polars, and the Star of the Year ASASSN-18ey, I'll write tomorrow. joe p ____________________________________________________________ Center for Backyard Astrophysics (CBA) mailing lists https://cbastro.org/communications/mailing-lists/ From jp42 at columbia.edu Wed Aug 1 17:03:25 2018 From: jp42 at columbia.edu (Joe Patterson) Date: Wed, 1 Aug 2018 17:03:25 -0400 Subject: (cba:news) (cba:chat) POLARS... intermediate and full-fledged In-Reply-To: <308C46CC-47C9-4B56-8DFE-2F02B0599A94@gmail.com> References: <5d0e3c01-ce4b-15cd-e5be-868dfbef39a6@astro.columbia.edu> <308C46CC-47C9-4B56-8DFE-2F02B0599A94@gmail.com> Message-ID: <8e616595-fadf-d35f-1463-ec498ac0924d@columbia.edu> Aha, the critical question. ASASSN-18ey is one of the two great success stories of the CBA (the other being WZ Sge in 2001). I watch greedily for each new message and salivate when it comes.? The present data will tell an eloquent story about black-hole superhumps. But there's a statistical rule to consider.? If you have 10 nights of data, then to have a really *significant* increase in data, you need 20 nights.? We have ~110 nights, so to learn a lot more, we need 110 more. We can't get that - the Sun will start killing us in another month (remember, the period is 17 hours).? So the moral is that we can back off the intensive coverage now.? Nevertheless, if you've been getting long nightly runs and can still do it, they will be very helpful for another month. Botttom line: a good time to start thinking about (and observing) other targets.? I'll send a few more suggestions tonight. joe p On 8/1/2018 12:33 PM, David Cejudo wrote: > Hello! > Should i stop pointing ti ASASSN-18ey? > I have a few nights? worth of data to upload yet and the telescope is programmed to point to it again tonight. > > David Cejudo. > >> El 1 ago 2018, a las 17:49, Joe Patterson escribi?: >> >> Hi CBAers, >> >> Something new! >> >> We are preparing a proposal to observe a bunch of polars (AM Her stars) in hard X-rays (10-60 keV). These energies are comparable to the free-fall energy onto a white dwarf. And since the conventional model for polars invokes accreting gas falling directly to the surface, this observation can reveal the white-dwarf masses (more massive WDs are much smaller, and thus should produce much higher infall energies). >> >> This experiment has been done successfully for a few of the celebrity polars. We'd like to try it for some of the rank and file. Here are the stars: VV Pup, UZ For, EP Dra, V834 Cen, V2301 Oph, HU Aqr, ST LMi. All these stars are known or at least likely to have high and low states, and it's important to know how bright they are now. Probably the X-ray observation will only succeed if the star is in a high state. So at a minimum, is the star *currently* in a high state? >> >> 1. This will probably require a 2-hour observation, since the stars vary strongly over an orbital cycle (generally 1.5-2.2 hours). >> >> 2. Someone will need to estimate how long the star is likely to stay bright. JUst a guess, of course... and I suppose that's my job (by consulting literature), but if anyone feels like doing that search of previous papers, I'd be grateful. >> >> 3. Most of these stars are around 16-17 mag, and for that we always recommend unfiltered light. But consider also a V filter. Time resolution is of no great importance here, and unfiltered brings some problem, since these stars typically have very crazy colors (because of cyclotron radiation. This is mitigated by V, which has a much narrower poassband and is the reference standard of most previously published studies. >> >> Try to get as many as you can. Not much need to do a *second* 2-hour light curve of a particular star. >> >> Being faint and rapid large-amplitude flickerers, these stars tend to persuade the rookie observer that the data are no good. But on a good night, it's likely the data are quite good. >> >> We hope to submit this proposal, or part of it, soon... so see what you can do with this! >> >> Re the intermediate polars, and the Star of the Year ASASSN-18ey, I'll write tomorrow. >> >> joe p >> >> >> ____________________________________________________________ >> Center for Backyard Astrophysics (CBA) mailing lists >> https://cbastro.org/communications/mailing-lists/ > ____________________________________________________________ > Center for Backyard Astrophysics (CBA) mailing lists > https://cbastro.org/communications/mailing-lists/ ____________________________________________________________ Center for Backyard Astrophysics (CBA) mailing lists https://cbastro.org/communications/mailing-lists/ From jop at astro.columbia.edu Fri Aug 3 07:42:36 2018 From: jop at astro.columbia.edu (Joe Patterson) Date: Fri, 3 Aug 2018 07:42:36 -0400 Subject: (cba:news) ASASSN-18ey = MAXI J1820+070 Message-ID: <0027bdf7-6bb6-ac26-6d86-edc0d90b2d1d@astro.columbia.edu> Hi CBAers, More on the Great Star of 2018. Despite what I wrote last time, it appears now that the X-ray transient has entered a new phase. The superhump (amplitude) has either faded rapidly, or is accompanied now by some other signal of comparable size. If the latter, it will likely be a challenge to figure out, because its period would be *close* to the 0.69 day period of the superhump. So this is NOT a time to decrease vigilance. In particular, the nightly light curves over the last week have been largely missing contributions from the Americas - so I hope we can improve on that! Another comment of lower weight. Over the ~100 day campaign so far, about half the observers have used V filters, and half unfiltered. Until recently, it has been straightforward to convert between these scales with additive constants (constant for a given observer, reflecting mainly the passband of the unfiltered or lightly-filtered CCD). But the conversions of a few weeks/months ago don't seem to apply now. Possibly because the star's color has changed a lot, or the instrumentation? Hard to say when the coverage is getting more sketchy. It also seems that a strong UV/blue component may have turned on, because the time-series at airmasses beyond 2.0 are pretty corrupted by the extra extinction. So I advise cutting off the time series around 2 airmasses. These issues can be greatly minimized by using a V (or Sloan g) filter, and it doesn't really matter whose V filter you use - it merely nudges the magnitude a few hundredths, which is easy for me to measure (and apply that measured constant). Since the star is still 13th magnitude and likely to stay near that level for another month or more, you might consider switching to a V filter. (For the rest of the year; switching back and forth is not a good idea.) On the other hand, don't abandon the star! With enough coverage I can still measure these additive constants - even if they're slowly changing. Sorry to be so much "in the weeds" on this issue. It's an exciting star! Maybe I'll go have a cup of herbal tea now.... joe p ____________________________________________________________ Center for Backyard Astrophysics (CBA) mailing lists https://cbastro.org/communications/mailing-lists/ From jop at astro.columbia.edu Wed Aug 8 07:12:35 2018 From: jop at astro.columbia.edu (Joe Patterson) Date: Wed, 8 Aug 2018 07:12:35 -0400 Subject: (cba:news) HU Aquarii, a new campaign target Message-ID: Hi CBAers, We're likely to have a hard X-ray (NUSTAR) observation of this star on August 17, and may have some Swift coverage before then also. Now's a good time to start time -series observations. The star is around 16.0, with very deep eclipses. Hence probably an unfiltered target for most of us. Someone, though, should try V (Gordon?), since these AM Her stars have very weird colors. Meaning: inferring V from "unfiltered" magnitudes is pretty uncertain. In fact, come to think of it, everyone should consider taking some time to establish that relationship for their system.* In Aquarius, thus an equal-opportunity target, plus transiting around midnight. Let's get the program going in the next few nights - it'll also give us good baseline, plus some fallback insurance if August 17 weather goes bad. Recent interest in this star has been spurred by the relatively large variations in mid-eclipse timing - you know, planets, etc. So I guess that's another reason to observe this guy. But even if the planetary hypothesis goes pfffft (most do), there's still some pretty big wiggles in O-C, to be explained by some other astrophysical tool. Maybe something related to the physics of CVs? Hey, just a suggestion! But... don't forget Maxie either... or VW Hyi (campaign still going for another ~2 days)! joe p *Don't go crazy with this, though. It's just to get some idea. Since comparison stars don't have "unfiltered" magnitudes, it's in principle impossible! ____________________________________________________________ Center for Backyard Astrophysics (CBA) mailing lists https://cbastro.org/communications/mailing-lists/ From jop at astro.columbia.edu Fri Aug 17 18:26:02 2018 From: jop at astro.columbia.edu (Joe Patterson) Date: Fri, 17 Aug 2018 18:26:02 -0400 Subject: (cba:news) HU Aquarii - a job well done! Message-ID: <2cbd6222-9931-0cb5-1058-81eb6e58684d@astro.columbia.edu> Hi CBAers, The hard X-ray observation took place, and now we have a pretty well-covered optical light curve from 2 days before to 2 days after. Bravo! That specifies the timing of the binary very well, and now we just have to wait for the analysis of the X-ray data - to reveal the shock temperature and therefore the mass of the white dwarf. So that wraps up the 2018 campaign on HU Aqr. I was very pleasantly surprised by the data quality on such a faint star. joe p ____________________________________________________________ Center for Backyard Astrophysics (CBA) mailing lists https://cbastro.org/communications/mailing-lists/ From jop at astro.columbia.edu Wed Aug 22 10:51:55 2018 From: jop at astro.columbia.edu (Joe Patterson) Date: Wed, 22 Aug 2018 10:51:55 -0400 Subject: (cba:news) Maxie and other things Message-ID: <932e3bfd-89e4-7494-487d-59fb1f8afc8a@astro.columbia.edu> Hi CBAers, Thanks to Lew and Doug for airing the threats to the continued life of WWV/WWVH. The WWV broadcasts are more or less what started me in astronomy. I had seen an aurora, and wanted to know how I could see more. I was told that you had to listen to WWV for "geophysical alerts"... and since it (and all the stations in its vicinity) broadcast only in Morse code, I decided to learn Morse code. Then decided I might as well become a ham, got a license, etc. Sign the petition! Plus I always liked to listen for the leap second on December 31. Then got curious about leap seconds... leading on to the rest of life. On to stars du jour. The campaigns on VW Hyi and the various polars are over. I'll write later about what came out - mainly from the hard X-ray observation. But we have active campaigns on various seasonally appropriate *intermediate* polars, and it's time to ramp those up, as Maxie (ASASSN-18ey) has been sucking up all the oxygen. See below. But Maxie is still a viable target, and will be for ~6 more weeks. People are still getting great-quality V-band photometry at 13.4 mag, but unfortunately not as *many* people. So it's getting hard to extract maxima/minima from its 17-hour wave. That wave was a superhump, but could now possibly be an orbital signal, depending on its stability and waveform. We need more intense coverage to answer that question, which is an important one! V-band is best, don't fret time resolution as the 17-hour wave is *leisurely*! Do fret length of run, though; at 17 hours, short runs are hard to work with. 3 hours or more is a good rule of thumb. IPs (DQ Her stars) can tolerate short observation, but all CBA targets greatly profit from length of run. This is because all CVs are subject to erratic flickering on all time scales - so short runs are *easily* bedevilled by flickering. Anyway, here's the current CBA MOST WANTED list for IPs: AO Psc V1223 Sgr V2306 Cyg V2069 Cyg FO Aqr V1033 Cas joe p MU Cam ____________________________________________________________ Center for Backyard Astrophysics (CBA) mailing lists https://cbastro.org/communications/mailing-lists/