Day 726

Wednesday.

1408.4211
Signatures of a companion star in Type Ia Supernovae
Maeda, Kutsuna, Shigeyama

While SNe Ia have been used as precise cosmological distance indicators, their progenitor systems remain unresolved.  One of the key questions is if there is a non-degenerate companion star at the time of a thermonuclear explosion of a WD.  Investigate if an interaction between the SN ejecta and the companion star may result in observable footprints around the maximum brightness and thereafter, by performing multidimensional radiation transfer simulations based on hydro sims of the interaction.  Find that such systems result in variations in various observational characteristics due to different viewing directions, while the predicted behaviors (redder and fainter for the companion direction) are opposite to what were suggested by the previous study.  The variations are generally modest and within observed scatters.  However, the model predicts trends between some observables different from observationally derived, thus a large sample of SNe Ia with small calibration errors may be used to constrain the existence of such a companion star.  The variations in different colors in optical band passes can be mimicked by external extinctions, thus such an effect could be a source of a scatter in the peak luminosity and derived distance.  After the peak, hydrogen-rich materials expelled from the companion will manifest themselves in hydrogen lines.  Halpha is however extremely difficult to identify.  Alternatively, find that P_beta in post-maximum NIR spectra can potentially provide powerful diagnostics.

1408.4323
Kepler and the long period variables
Hartig et al

Track photometry of 8 SR AGB stars using 30 minute cadence over a period of 45 months.  Light curves are shown to be smooth at the millimagnitude level over shorter time intervals.  No flares or other rapid events detached on the sub-day time scale.  Shortest AGB period detected is on the order of 100 days.  All SR variables shown to have multiple modes, typically fundamental + first overtone.  A second common characteristic of SR variables is shown to be the simultaneous excitation of multiple closely separated periods for the same overtone mode.  Approximately half the sample had a much longer variation in the light curve, likely a long secondary period.  The light curves were all well represented by a combination of sinusoids.  However, the properties of the sinusoids are time variable with irregular variations present at low level.  No non-radial pulsations were detected. It is argued that the long secondary period variation seen in many SR variables is intrinsic to the star and linked to multiple mode pulsation.