Post date: 22-Apr-2011 00:15:21
Hi;
T Pyx is erupting and is now very bright and easy. The *surprising* (to me at least) eruption of this recurrent novae is critical, as this is playing into the uber-important problem of the Type Ia supernova progenitor problem. Like for the wonderful campaign for U Sco, I am organizing a large campaign for T Pyx, where people the world around will keep fast-photometry of T Pyx nearly full time. I am inviting everyone with a CCD to help solve the mysteries of T Pyx. Some of you have already started, and some of you have already helped with the highly successful U Sco campaign.
T Pyx has always had several unique and mysterious enigmas: The newest mystery is to solve why my prior strong prediction that T Pyx would *not* erupt soon went so obviously wrong. The biggest mystery is whether this unique recurrent nova can ever become a Type Ia supernova. For a long time, the most nagging problem for specialists was to explain how such an interacting binary star with as short an orbital period as T Pyx (1.8 hours) could possibly have such a tremendously high accretion rate so as to drive the recurrent events. Even the critical distance is poorly known and debated from 1000 pc to 3500±1000 pc. [Well, at least the long-standing problem of the weird knots in the nova shell and their slow expansion rate has been solved with my recent HST images {Schaefer, Pagnotta, & Shara 2010, ApJ, 708, 381}.]
The world has already hopped fast to get rapid response programs working for T Pyx. HST has already been looking for the ionization and polarization fronts moving out through the prior nova shell. Swift is already measuring the X-ray and UV brightness and spectra on a daily basis. ESO in Chile have five programs on their 8.2-meter telescopes; for infrared imaging, IR spectroscopy, very-high resolution spectroscopy, medium-resolution spectroscopy from UV to mid-IR, and infrared interferometry. XMM, Suzaku, and Chandra (all X-ray satellites in space) are all soon going to get great spectroscopy and imaging of the shell. In the radio the EVLA and VLBI should be able to watch the shell expanding and maybe even get a parallax. And various observatories in the south are getting classical single-time photometry in many optical and IR bands, as well as optical spectroscopy nightly.
The one task that professionals cannot really do is to monitor T Pyx with fast photometry. From the last eruption (poorly observed) in 1967, we know that T Pyx has a rich array of phenomena, fast hourly variations with a magnitude amplitude, dramatic dropoffs, late plateaus, and perhaps a return to quiescence far brighter than the pre-eruption quiescence. And I honestly expect to find new previously-unsuspected phenomena when we look very closely at T Pyx's optical light curve.
Here are some technical details for use in a fast-photometry program on T Pyx:
An important point is that there are slight changes and additions to the comparison stars for use. The changes come from the usual improvements in the AAVSO comparison star sequences, and the additions are for the R and I colors (although these filters are not preferred).
STAR AAVSO AUID CATALOG RA2000 DEC2000 B V R I
COMP1: "93" 000-BBQ-215 HD77862 09:04:09.4 -32:11:16 9.828 9.324 9.013 8.717
COMP2: "69" 000-BBQ-204 HD77645 09:02:51.8 -32:26:24 6.968 6.933 6.924 6.927
COMP3: "115" 000-BBQ-230 CD-31°6884 09:04:43.8 -32:24:47 12.130 11.537 11.187 10.857
Do not use the star formerly called "84" on the old sequences, as it is a variable star. These are the best three comparison stars, and by preference use COMP1 (=AAVSO "93"), as this will avoid saturation issues for a brighter star and it is fairly close to T Pyx. If you have a large field of view, especially when T Pyx is bright so your integrations must be short, then COMP2 (=AAVSO "69") might be useful, especially because its color is close to that of T Pyx. If you have a small field of view, maybe only COMP3 (=AAVSO "115") might fit on the same image as T Pyx. If you have a small field of view (so only COMP3 fits onto the image) yet have trouble getting adequate SNR on COMP3 while not saturating T Pyx, then I'd recommend perhaps alternating long and short exposures if there are no clouds to change the calibrations between images.
Another issue is the filter to use. (Definitely use a filter. Unfiltered runs will have trouble with crossterms between the airmass and the color, due to T Pyx being bluer than all comparison stars but one and due to T Pyx often being viewed to high airmass.) The preferred filter is the regular 'V' filter. The reason is to standardize to V-band so that all our magnitudes can be plotted together without color questions, and so that we can compare to prior eruptions. So everyone should be running with a V-filter. But some circumstances might make for deviations. If you only have BGR filters, then use the G (green) filter as it is pretty close to V-band and I can correct easy enough. Second choice in filters is B-band, but only if you do not have V-band (or if a neighbor is sure to be getting a V-band light curve simultaneously). If you have an automated filter changer and CCD, then it would be reasonable to have some cadence of V-B-V-B-V-B-V- and so on, or B-V-R-I-B-V-R-I-B-V-R-I- and so on, because T Pyx is bright enough that you can have good time resolution in each color.
T Pyx can be followed to high airmass and in twilight. With differential photometry and bright sources, the photometry will still be good even when you would never expect to get good data. (In years past, I have followed T Pyx to 5 airmass with the comparison stars being differentially constant to high accuracy.) In the upcoming campaign, T Pyx will always be low for northern observers and even southern observers will want to prolong your time-on-target as much as possible (as T Pyx approaches the Sun). So do not be shy about following T Pyx to near the horizon, or in twilight.
T Pyx will be going behind the Sun too soon. It will be closest to the Sun in late August at a distance of 46°. Let me tabulate the distance from the Sun and above the horizon. The altitudes are all taken for the instant of astronomical twilight (when the Sun is 18° below the horizon).
SUN ALTITUDE ALTITUDE
DATE ANGLE (30°S) (30°N)
April 15 114° 83° 27°
May 1 104° 85° 23°
May 15 95° 75° 16°
June 1 83° 63° 3°
June 15 74° 50° -
July 1 65° 36° -
July 15 57° 25° -
Aug 1 50° 11° (evening) -
Aug 15 46° 0° -
Sept 1 46° 22° (morning) -
Sept 15 50° 29° -
Oct 1 55° 38° 7°
Oct15 63° 45° 16°
Nov 1 74° 54° 24°
Nov 15 83° 64° 27°
For southern observers, T Pyx will be largely unobservable from middle July to middle September.
It might also be of some use to place the 1967 eruption light curve onto the current outburst, as that way we can have a reasonable prediction of brightnesses. For this, I have used my derived template from my huge ApJSupp paper (Schaefer 2010, ApJSupp, 187, 275, see Table 16 and Figure 5), with the day of eruption being with respect to the V-band peak. Note that I found all T Pyx eruptions (1890, 1902, 1920, 1944, and 1967) to have essentially identical light curves, so we can reasonably expect that the table below to be pretty accurate (most likely to within one magnitude). We know from the 1967 photometry of Arlo Landolt (Landolt 1970, PASP, 82, 86) that T Pyx shows a lot of intra-night variability, so particular observations will generally deviate from this average template by up to a magnitude or so.
Day JD 2011 date B (mag) V(mag) Comments
-40 2455666 April 14 15.6 15.5 Start of rise
-38 2455668 April 16 10.1 9.9
-35 2455671 April 19 8.4 8.2 Rise slows down
-30 2455676 April 24 8.1 7.8
-10 2455696 May 14 7.4 7.1
0 2455706 May 24 6.7 6.4 Peak
7 2455713 May 31 7.7 7.4
25 2455731 June 18 8.0 8.0
40 2455746 July 3 8.5 8.9
54 2455760 July 17 9.0 9.2 T Pyx lost behind Sun
85 2455791 Aug 17 9.7 10.0 Start of fast decline
105 2455811 Sep 6 11.5 12.0 Start of late plateau, coming out in morning
135 2455841 Oct 6 11.6 12.2 End of late plateau
170 2455876 Nov 10 12.4 12.3
250 2455956 Jan 29(2012) 13.9 13.8 Leveling off?
300 2456006 Mar 19(2012) ... 13.7 Still not at pre-nova quiescence
T Pyx has never been followed to quiescence. With T Pyx being a V1500 Cyg star (Schaefer & Collazzi 2010, AJ, 139, 831), I would expect that the immediate post-eruption light curve will be brighter than the pre-eruption brightness, so maybe the leveling off at day 250 is the return to quiescence, even though this then declined back to 15.5 mag on the timescale of years.
Please help me get fast-photometry around the clock for T Pyx. With our U Sco campaign (the only nova event with more-than-a-little fast photometry), we discovered two new previously-unsuspected types of phenomena. Who knows what we will find from T Pyx!
Cheers,
Brad
Bradley E. Schaefer
Professor, Department of Physics and Astronomy
Louisiana State University
Baton Rouge, Louisiana 70803, USA
225-578-0015