A remarkable recurrent nova in M 31: The 2010 eruption recovered and evidence of a six-month period

The Andromeda Galaxy recurrent nova M31N 2008-12a has been caught in eruption nine times. Six observed eruptions in the seven years from 2008 to 2014 suggested a duty cycle of ~1 year, which makes this the most rapidly recurring system known and the leading single-degenerate Type Ia Supernova progenitor candidate; but no 2010 eruption has been found so far. Here we present evidence supporting the recovery of the 2010 eruption, based on archival images taken at and around the time. We detect the 2010 eruption in a pair of images at 2010 Nov 20.52 UT, with a magnitude of m_R = 17.84 +/- 0.19. The sequence of seven eruptions shows significant indications of a duty cycle slightly shorter than one year, which makes successive eruptions occur progressively earlier in the year. We compared three archival X-ray detections with the well observed multi-wavelength light curve of the 2014 eruption to accurately constrain the time of their optical peaks. The results imply that M31N 2008-12a might have in fact a recurrence period of ~6 months (175 +/- 11 days), making it even more exceptional. If this is the case, then we predict that soon two eruptions per year will be observable. Furthermore, we predict the next eruption will occur around late Sep 2015. We encourage additional observations.Comment: 4 pages, 3 figures, 2 tables; submitted to A&A Letter

A very luminous, highly extinguished, very fast nova - V1721 Aquilae

Fast novae are primarily located within the plane of the Galaxy, slow novae are found within its bulge. Because of high interstellar extinction along the line of sight many novae lying close to the plane are missed and only the brightest seen. One nova lying very close to the Galactic plane is V1721 Aquilae, discovered in outburst on 2008 September 22. Spectra obtained 2.69 days after outburst revealed very high expansion velocities (FWHM ~6450 km/s). In this paper we have used available pre- and post-outburst photometry and post-outburst spectroscopy to conclude that the object is a very fast, luminous, and highly extinguished A_V=11.6+/-0.2) nova system with an average ejection velocity of ~3400 km/s. Pre-outburst near-IR colours from 2MASS indicate that at quiescence the object is similar to many quiescent CNe and appears to have a main sequence/sub-giant secondary rather than a giant. Based on the speed of decline of the nova and its emission line profiles we hypothesise that the axis ratio of the nova ejecta is ~1.4 and that its inclination is such that the central binary accretion disc is face-on to the observer. The accretion disc's blue contribution to the system's near-IR quiescent colours may be significant. Simple models of the nova ejecta have been constructed using the morphological modelling code XS5, and the results support the above hypothesis. Spectral classification of this object has been difficult owing to low S/N levels and high extinction, which has eliminated all evidence of any He/N or FeII emission within the spectra. We suggest two possibilities for the nature of V1721 Aql: that it is a U Sco type RN with a sub-giant secondary or, less likely, that it is a highly energetic bright and fast classical nova with a main sequence secondary. Future monitoring of the object for possible RN episodes may be worthwhile, as would archival searches for previous outbursts.Comment: 9 pages 10 figures, accepted for publication in A&A. Abstract has been slightly shortened from published versio

A DETAILED PHOTOMETRIC AND SPECTROSCOPIC STUDY OF THE 2011 OUTBURST OF THE RECURRENT NOVA T Pyxidis FROM 0.8 TO 250 DAYS AFTER DISCOVERY

We investigated the optical light curve of T Pyx during its 2011 outburst through compiling a database of Solar Mass Ejection Imager (SMEI) and AAVSO observations. The SMEI light curve, providing unprecedented detail covering t=1.5-49 days post-discovery, was divided into four phases based on the idealised nova optical light curve; the initial rise (1.5-3.3 days), the pre-maximum halt (3.3-13.3 days), the final rise (14.7-27.9 days), and the early decline (27.9 days - -). The SMEI light curve contains a strongly detected period of 1.44_0.05 days during the pre-maximum halt phase. These oscillations resemble those found in recent TNR models arising from instabilities in the expanding envelope. No spectral variations that mirror the light curve periodicity were found however. The marked dip at t_22-24 days just before light curve maximum at t=27.9 days may represent the same (shorter duration) phenomenon seen in other novae observed by SMEI and present in some model light curves. The spectra from the 2m Liverpool Telescope and SMARTS 1.5m telescope were obtained from t=0.8-80.7 and 155.1-249.9 days, covering the major phases of development. The nova was observed very early in its rise where a distinct high velocity ejection phase was evident with derived Vej_4000 km

On the progenitors of local group novae. II. the red giant nova rate of M31

In our preceding paper, Liverpool Telescope data of M31 novae in eruption were used to facilitate a search for their progenitor systems within archival Hubble Space Telescope (HST) data, with the aim of detecting systems with red giant secondaries (RG-novae) or luminous accretion disks. From an input catalog of 38 spectroscopically confirmed novae with archival quiescent observations, likely progenitors were recovered for eleven systems. Here we present the results of the subsequent statistical analysis of the original survey, including possible biases associated with the survey and the M31 nova population in general. As part of this analysis we examine the distribution of optical decline times (t(2)) of M31 novae, how the likely bulge and disk nova distributions compare, and how the M31 t(2) distribution compares to that of the Milky Way. Using a detailed Monte Carlo simulation, we determine that 30 (+13/-10) percent of all M31 nova eruptions can be attributed to RG-nova systems, and at the 99 percent confidence level, >10 percent of all M31 novae are RG-novae. This is the first estimate of a RG-nova rate of an entire galaxy. Our results also imply that RG-novae in M31 are more likely to be associated with the M31 disk population than the bulge, indeed the results are consistent with all RG-novae residing in the disk. If this result is confirmed in other galaxies, it suggests any Type Ia supernovae that originate from RG-nova systems are more likely to be associated with younger populations, and may be rare in old stellar populations, such as early-type galaxies