A Spitzer Survey of Novae in M31

We report the results of the first infrared survey of novae in the nearby spiral galaxy, M31. Both photometric and spectroscopic observations of a sample of 10 novae (M31N 2006-09c, 2006-10a, 2006-10b, 2006-11a, 2007-07f, 2007-08a, 2007-08d, 2007-10a, 2007-11d, and 2007-11e) were obtained with the Spitzer Space Telescope. Eight of the novae were observed with the IRAC (all but M31N 2007-11d and 2007-11e) and eight with the IRS (all but 2007-07f and 2007-08a), resulting in six in common between the two instruments. The observations, which were obtained between ~3 and ~7 months after discovery, revealed evidence for dust formation in two of the novae: M31N 2006-10a and (possibly) 2007-07f, and [Ne II] 12.8 micron line emission in a third (2007-11e). The Spitzer observations were supplemented with ground-based optical photometric and spectroscopic data that were used to determine the speed classes and spectroscopic types of the novae in our survey. After including data for dust-forming Galactic novae, we show that dust formation timescales are correlated with nova speed class in that dust typically forms earlier in faster novae. We conclude that our failure to detect the signature of dust formation in most of our M31 sample is likely a result of the relatively long delay between nova eruption and our Spitzer observations. Indeed, the two novae for which we found evidence of dust formation were the two "slowest" novae in our sample. Finally, as expected, we found that the majority of the novae in our sample belong to the Fe II spectroscopic class, with only one clear example of the He/N class (M31N 2006-10b). Typical of an He/N system, M31N 2006-10b was the fastest nova in our sample, not detected with the IRS, and just barely detected in three of the IRAC bands when it was observed ~4 months after eruption.Comment: 37 pages, 12 figures, accepted for publication in the Astrophysical Journa

Swift observations of the 2006 outburst of the recurrent nova RS Ophiuchi: III. X-ray spectral modelling

Following the Swift X-ray observations of the 2006 outburst of the recurrent nova RS Ophiuchi, we developed hydrodynamical models of mass ejection from which the forward shock velocities were used to estimate the ejecta mass and velocity. In order to further constrain our model parameters, here we present synthetic X-ray spectra from our hydrodynamical calculations which we compare to the Swift data. An extensive set of simulations was carried out to find a model which best fits the spectra up to 100 days after outburst. We find a good fit at high energies but require additional absorption to match the low energy emission. We estimate the ejecta mass to be in the range (2-5) x 10^{-7} solar masses and the ejection velocity to be greater than 6000 km/s (and probably closer to 10,000 km/s). We also find that estimates of shock velocity derived from gas temperatures via standard model fits to the X-ray spectra are much lower than the true shock velocities.Comment: 13 pages, 5 figures, Accepted for publication in Ap

First experiences with HMC for dynamical overlap fermions

We describe an HMC algorithm for dynamical overlap fermions which makes use of their good chiral properties. We test the algorithm in the Schwinger model. Topological sectors are readily changed even in the massless case.Comment: 4 pages with 1 ps figure; crckapb.sty included; to appear in the proceedings of the workshop "Lattice Fermions and Structure of the Vacuum", Oct 5-9, Dubna, Russi

The Morphology of the Expanding Ejecta of V2491 Cygni (2008 N.2)

Determining the evolution of the ejecta morphology of novae provides valuable information on the shaping mechanisms in operation at early stages of the nova outburst. Understanding such mechanisms has implications for studies of shaping for example in proto-Planetary Nebulae. Here we perform morpho-kinematical studies of V2491 Cyg using spectral data to determine the likely structure of the ejecta and its relationship to the central system and shaping mechanisms. We use Shape to model different morphologies and retrieve their spectra. These synthetic spectra are compared with observed spectra to determine the most likely morphology giving rise to them, including system inclination and expansion velocity of the nova ejecta. We find the best fit remnant morphology to be that of polar blobs and an equatorial ring with an implied inclination of 80$^{+3}_{-12}$ degrees and an maximum expansion velocity of the polar blobs of 3100$^{+200}_{-100}$ km/s and for the equatorial ring 2700$^{+200}_{-100}$ km/s. This inclination would suggest that we should observe eclipses which will enable us to determine more precisely important parameters of the central binary. We also note that the amplitude of the outburst is more akin to the found in recurrent nova systems.Comment: 9 pages, 7 figures, accepted for publication in MNRA