Recurrent Nova T Pyx is Deviating from 1967 Eruption Light Curve
ATel #3707; B. E. Schaefer (Louisiana State University) and A. Oksanen (Caisey Harlingten Observatory)
on 25 Oct 2011; 16:19 UT
Credential Certification: Bradley E. Schaefer (schaefer@lsu.edu)
Subjects: Optical, Request for Observations, Nova
We report on the light curve of the recurrent nova T Pyx, now in eruption (IAUC # 9205 , ATel #3549, ATel #3647). Our optical observations are made with the 0.5-m telescope at the Caisey Harlingten Observatory near San Pedro de Atacama in Chile. The V-band magnitudes were made as part of time series (with 30-second time resolution) lasting 0.9-3.6 hours on 115 nights since May 12. T Pyx was followed throughout the entire interval of solar conjunction (with T Pyx 46.4° from the Sun on August 25). After August 4, our data from Chile provides the only CCD measures in the AAVSO database to October 20. From the initial hour of the eruption until August 3, the AAVSO data base (http://www.aavso.org/lcg) contains 75,024 magnitudes. The light curves for the 1967 and earlier eruptions are in Schaefer (2010, ApJSupp, 187, 275; see Figures 2-5 and Table 16), while this paper demonstrated that all known eruption light curves for the same recurrent nova are identical to within uncertainties.
| T-T0 (days) | 2011 Date | 2011 V (mag) | 1967 V (mag) | Comments |
| 0 | Apr 13 | 15.5 | 14.6 | Start of fast rise |
| 2 | Apr 15 | 9.9 | 9.9 | End of fast rise |
| 5 | Apr 18 | 8.0 | 8.2 | ... |
| 10 | Apr 23 | 7.6 | 7.8 | ... |
| 29 | May 12 | 6.4 | 7.2 | 2011 peak |
| 40 | May 23 | 7.3 | 6.4 | 1967 peak |
| 47 | May 30 | 8.0 | 7.4 | ... |
| 80 | July 2 | 8.4 | 8.9 | ... |
| 110 | Aug 1 | 10.0 | 9.6 | Supersoft X-ray turnon |
| 125 | Aug 16 | 10.7 | 10.0 | 1967 sharp drop start |
| 140 | Aug 31 | 10.8 | 11.5 | Supersoft X-ray plateau start |
| 145 | Sep 5 | 10.9 | 12.0 | 1967 sharp drop end |
| 194 | Oct 24 | 11.5 | 12.3 | ... |
The T Pyx eruption light curves for 1967 and 2011 are identical, up until around August 20. The one qualifier on this statement is that the bumps in the two light curves are at different times, likely due to the chance timing of randomly placed bumps. At 125 days after the eruption start, the 1967 light curve displays a sharp drop from V=10.0 to 12.0 over 20 days. But the 2011 light curve shows no such drop, even up until 65 days later. This is the first time that a recurrent nova has ever been seen to have a significantly different light curve between eruptions. Nova light curves are only functions of the white dwarf mass, magnetic field, accumulated mass, composition, and accretion rate, with the first four of these being identical between eruptions. However, T Pyx had its average pre-eruption B magnitude change from 14.70±0.04 before 1967 to 15.59±0.01 before 2011 (Schaefer et al. 2011, arXiv:1109.0065), so the accretion rate has changed. We suggest that the change is a result solely of a 2.3X change in accretion rate.
Observers are needed to follow the light curve to quiescence. Observational questions of particular interest are when the photometric oscillations on the orbital period resume (also important for measuring the change of the orbital period across the eruption) and whether the supersoft source will sustain an elevated quiescent level for perhaps years after the eruption is over.
