The early outburst light curve of the 2011 eruption of the Recurrent Nova T Pyxidis from Solar Mass Ejection Imager (SMEI) observations
ATel #3373; R. Hounsell (Liverpool JMU), M. J. Darnley (Liverpool JMU), D. J. Harman (Liverpool JMU), M. F. Bode (Liverpool JMU), J. M. Clover (UCSD/CASS), P. P. Hick (UCSD/CASS), A. Buffington (UCSD/CASS), B. V. Jackson (UCSD/CASS), J. Osborne (University of Leicester), A. W. Shafter (SDSU)
on 23 May 2011; 13:00 UT
Credential Certification: Rebekah Hounsell (rah@astro.livjm.ac.uk)
We report white light observations of the 2011 outburst of Recurrent Nova T Pyxidis obtained using the USAF/NASA Solar Mass Ejection Imager (SMEI) on board the Coriolis satellite (see Hounsell et al., 2010 for details, all magnitudes quoted here are native to the SMEI photometric system). The instrument has a peak quantum efficiency at approximately 700 nm with a FWHM ~ 300 nm. T Pyx was discovered by M. Linnolt (Hawaii, United States) at a visual magnitude of 13.0 on 2011 April 14.29 UT (2455665.79; which we take as t = 0 days; AAVSO#436, CBET#2700, IAUC# 9205 ). This is the first outburst of T Pyx since December 7th 1966, with previous outbursts in 1890, 1902, 1920, and 1944.
The first reliable detection of the nova outburst by SMEI occurred at the end of the rapid rise seen in AAVSO data, at m = 8.70 ± 0.10 on 2011 April 15.70 UT (2455667.20 JD; t = 1.4 days). Since then SMEI has observed T Pyx approximately every 102 minutes.
Following the initial SMEI detection, the light curve rose very slowly over the following 12 days, reaching an average magnitude of approximately 8.03 on 2011 April 27th (2455678.84 JD; t= 13.1 days). During this almost "plateau" phase quasi-periodic variations were observed, with peak to peak times varying between one and two days. The amplitudes of these variations ranged between 0.35 and 0.50 mags.
Following this plateau phase there was a gap in the SMEI data (due to instrumental problems) lasting ~ 1.4 days, after which the light curve was seen to rise more steeply to m = 6.91 ± 0.04 on 2011 May 5.17 UT (2455686.67 JD; t = 20.9 days). It subsequently declined to m = 7.51 ± 0.05 on 2011 May 8.06 UT (2455689.56 JD; t = 23.8 days) and then rose again to m = 6.81 ± 0.04 on 2011 May 10.46 UT (2455691.96 JD; t = 26.2 days). The amplitude of these variations ranged between 0.6 and 0.7 magnitudes. A further rise occurred after the latter peak where the nova reached m = 6.39 ± 0.03 on 2011 May 12.79 (2455694.29 JD; t = 28.5 days). When comparing the SMEI data to the nova light curve template provided in Schaefer 2010 we believe this to be the optical peak of the nova outburst. The nova is now seen to be on its decline.
The variations seen in the SMEI light curve during its rise are similar to those found by Schaefer 2010, who reported "rapid" oscillations in the 1966 outburst light curve (Landolt 1970) with amplitudes of approximately 0.5 to 1.0 magnitudes, on the timescale of about a day.
The most recent detection recorded by SMEI was at m = 7.40 ± 0.05 on 2011 May 20.90 UT (2455702.40 JD; t = 36.6 days). SMEI observations are continuing.
The USAF/NASA SMEI is a joint project of the University of California San Diego, Boston College, the University of Birmingham (UK), and the Air Force Research Laboratory. R. Hounsell acknowledges support from an STFC postgraduate studentship.
