During the last 10 days MASTER robotic telescopes have discovered six new cataclysmic variables brighter than 17m, two of which are brighter than 14m. Three of six new CVs are truly remarkable. Two of them are being covered pretty well by the observers, but I would like to draw your attention to the stars which are in the need of more observations right now.
First I will summarize the newly discovered CVs in chronological order omitting the 'MASTER OT' prefix before their J2000.0 coordinates.
J000820.50+773119.1 Sep. 27.888 16.6-21.0 Cep ATel #4441
J042609.34+354144.8 Sep. 30.663 12.6-16.7 Per ATel #4441
J054317.95+093114.8 Sep. 30.785 13.4-21.0 Ori ATel #4446
J194741.84-020348.9 Oct. 04.667 16.8-21.5 Aql ATel #4458
J192739.31+020014.3 Oct. 04.680 15.2-19.5 Aql ATel #4458
J071856.78+601833.3 Oct. 08.088 15.5-<21: Cam ATel #4465
J042609.34+354144.8 in Perseus is the first dwarf nova discovered in the common proper motion pair with another red dwarf 16.6" away. This is a hierarchical triple system with the orbital period about 1.6 hr for the close pair and more than 60,000 yr for the third component. The proper motion (16, -42 mas/yr) is as fast as that of U Gem and only 2.5 times slower than SS Cyg - the brightest (and likely the nearest) Northern dwarf nova. This new CV is related to the bright ROSAT X-ray source 1RXS J042608.9+354151 and also has an UV counterpart GALEX J042609.3+354145 (FUV=17.70, NUV=17.52). Following the detection by MASTER, I have found another outburst on Feb. 1993 plates of Moscow collection and yet another 'prehistoric' one on the 1912 (!!!) plate from the digitized Heidelberg observatory plates. Superhumps with an amplitude more than 0.2m and the period evolving from 0.0676d to 0.06715d were found in this system, confirming it to be a UGSU-type variable.
J054317.95+093114.8 is the other object of special interest which is currently entering the most important phase of its light curve. Thanks to Josch Hambsch, we have a uniform coverage of this star in 7 nights from the same telescope and with the same reference stars. Amazingly, the averaged light curve is nearly copying that of MASTER OT J211258.65+242145.4 - UGWZ-type dwarf nova in Vulpecula discovered on June 25 which has collected more than 11,000 observations in AAVSO database. During first 4 nights J0543+0931 was fading at nearly the constant rate of 0.2 mag/day, after which it has entered a plato at around 15.4m (even the magnitude is the same as for J2112+2421)! Meanwhile the amplitude of variability has grown from 0.1m to more than 0.3m. The similarity of two stars is as striking as the difference in their orbital periods. J2112+2421 had superumps period evolving from 0.0598 to 0.0606d. Despite the outburst amplitude (~8m) typical for the WZ Sge type dwarf novae, J0543+0931 is showing the period closer to 0.10d. But if the analogy with J2112+2421 persists, it should fade to ~18m in 3-4 nights from now, after which it can show multiple rebrightenings to ~16m in the next month. This is why the continued observations of this star in Orion are required.
And the third star from the list that can be very interesting is J071856.78+601833.3 in Camelopardalis. The amplitude of variability is at least 6 magnitudes since nothing is visible on the combination of DSS plates to limiting magnitude fainter than 21.5. No time-resolved photometry has been reported so far. The only thing I can tell for sure is that it's blue, since we have obtained confirmation images from MASTER-Tunka in two tubes with two filters simultaneously, and it is definitely brighter in V than in I. So, this one may be a dwarf nova of UGWZ type, or yet another UGSU. In any case, observations are needed!
Denis in Moscow
Josch Hambsch keeps on producing the incredible 3-week long nightly time series for MASTER OT J054317.95+093114.8 with his remote telescope in Atacama. Amazingly, the variable continues its slow fading at almost constant rate for 20 days by now, while having superhump period of 0.0821d - exactly 3/2 times larger than that of UGWZ-type variables! The only analog among the tremendous outburst amplitude dwarf novae that I managed to find on the web is EF Peg. According to RKCat 7.18, EF Peg has an orbital period of 0.0837d and outbursts from 18.5 to 10.7 magnitude every 1200 days or so. At least three past outbursts are present in AAVSO observations, and the fading rate for the first 20 days is really similar to what J054317.95+093114.8 is currently doing. But the close companion of EF Peg makes its observations rather difficult when the CV becomes fainter than ~13m.
Hence the question: is there a reliable information on the further light curve behavior of EF Peg beyond 20 days after the outburst? I mean, is it dropping abruptly like short period UGWZ stars or fading slowly for another month, and were the rebrightenings observed in EF Peg light curve? Also, are there other similar long-period CVs with 8-mag outburst amplitude other than EF Peg? Or could J0543+0931 have been another classical nova like V1974 Cyg (N Cyg 1992) which has orbital period of 0.08126d and outburst by 12.5m? After all, the maximum of J0543+0931 could have been missed.
I have just found an interesting fact about this new CV while checking the archival plates of Moscow collection. MASTER OT J054317.95+093114.8 is located just 40' NW from the famous variable FU Ori! There are hundreds of observations of this field. Moscow collection alone has 112 plates centered at Lambda Ori, more or less evenly distributed between the decades (11 in 1950ies, 20 in 60ies, 47 in 70ies, 32 in 80ies and 2 in 90ies). I have checked 60 plates so far but haven't found any outbursts.
Meanwhile the variable has finally dropped by ~1.5 magnitudes yesterday after 3 weeks of slow fading at almost constant rate of 0.12 mag/day. The nightly monitoring from different longitudes is now very desirable for the next 5-7 days to see if the variable will show the rebrightenings which are the main distinguishing feature of UGWZ-type dwarf novae. The star will be too faint for most instruments to do the time series, but even a couple of positive detections per night will tell a lot. Rebrightenings can take 1.5 days to grow from ~18m to ~16m, and another 1.5 days to fade back. Please give this star a few visits before it goes below 20th magnitude for another 25 years or more!
Just in time when J054317.95+093114.8 has faded, I have discovered yet another UGWZ candidate with 8-mag amplitude of outburst - MASTER OT J081110.46+660008.5 (see ATel #4506 at http://www.astronomerstelegram.org/?read=4506 for more details). This star has r=22.1 in SDSS, but now it has brightened to 14.1m on two MASTER-Amur images! It is located quite close (5") to the galaxy with SDSS r=18.57, so without the high resolution (0.4"/pixel) Sloan images one could have thought it's a supernova. But it can be as interesting object as the one mentioned above. At least blue SDSS colors indicate a very low mass secondary component, hence likely a very short orbital period. The object is located in the westernmost part of Ursae Majoris, very close (8') to the UMa/Cam border. So formally it culminates before sunrise in late October, but it is actually circumpolar for the high Northern latitudes. Hopefully somebody will be able to obtain the time series and measure the period and its changes, like Josch Hambsch has made for J0543+0931.
And now there's yet another 14th-mag one - J203749.39+552210.3 in Cygnus! I'm just back from the glass library - there are 55 plates of the field centered at ADS 13743, but no previous outbursts of this new variable were detected on them. The star is about 21m at quiescence on DSS plates. More details are given in ATel #4515 at http://www.astronomerstelegram.org/?read=4515 published earlier today.
It's amazing how many new large-amplitude CVs are being recently discovered by MASTER-Amur which is 'only' covering ~1000 sq. degree every clear night! That's less than 1/40th of the entire sky, yet the robotic telescope is avoiding the really dense parts of the Milky Way.