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We report on the current status of radial velocity surveys for white dwarf binaries (double degenerates DDs) including SPY (ESO Supernovae la progenitor survey) recently carried out at the VLT. A large sample of DD will allow us to put strong constraints on the phases of close binary evolution of the progenitor systems and to perform an observational test of the DD scenario for Supernovae of type Ia.
Optical data in the V-band gathered with the 8.2m ESO Very Large Telescope (VLT) at the radio interferometric position of PSR 1706-44 are presented. The pulsar is close to a bright star in projection and was not detected. The pulsar magnitude limit must be fainter than V=24.5 for a distance of ≤ from the bright star. In the outer gap model for an aligned rotor the optical flux should scale with the gammaray flux. For pulsars which emit pulsed gamma-rays but are not detected in the optical bands, the synchrotron cutoff frequency for the tertiary photons must be well below the optical frequencies and the magnetic and spin axes may be misaligned.
The Supernova Working Group was re-established at the IAU XXV General Assembly in Sydney, 21 July 2003, sponsored by Commissions 28 (Galaxies) and 47 (Cosmology). Here we report on some of its activities since 2005.
We present the V light curve and optical/infrared spectra of the Type Ic SN 1997B. We show that (1) this SN displayed lines of the He I series; (2)the expansion velocities were higher than those of SNe with traces of H or large He masses in their envelopes (like SN 1993J); the light curve of SN 1997B decayed slower than that of SN 1993J. The smaller mass to kinetic energy ratio and shallower light curve of SN 1997B are inconsistent with it being a He stripped version of some of the best studied Type Ib or II-transition SNe. We infer that Type Ib/c and II-transition SN progenitors come, at least, with two different types of inner structure.
A few years ago the presence of He in the atmospheres of Type Ic SNe, the nature of their progenitors, and the relation between Type Ib and Type Ic SNe was subject of debate. On the one hand, empirical evidence and theoretical interpretation supported the view that SNe of Type Ib and Ic are different enough to insure that their progenitors result from different paths of stellar evolution. If so, Type Ic SNe originated in bare C+O cores and were expected not to display He I lines in their spectra. On the other hand, it was stressed that Type Ib and Ic SNe could originate in similar stars evolving as interacting binaries.
Although emerging from a range of progenitor stars and the product of different explosion mechanisms the light curves of the various supernova types are shaped mainly by radioactive power. Core-collapse supernovae have in addition early peaks from shock breakout with a subsequent cooling phase and massive extended stars a recombination (plateau) phase. Variations occur mostly due to differences of the progenitor stars. While there appears to be a fair understanding of the light curves of SNe II, new wrinkles are emerging for SNe Ia. The photometry of SNe Ib and SNe Ic remains unsatisfactory.
The temporal brightness variation of supernovae (SNe) as measured by photometry contains valuable and unique information on the evolution of the progenitor star and the explosion event. Combined with optical spectroscopy broad-band light curves have been the main tools for supernova investigations in the past (e.g. Minkowski 1964, Woosley & Weaver 1986, Wheeler & Harkness 1990, Kirshner 1990). The light curves are shaped by the size and mass of the progenitor star, various processes within the explosion itself, the radioactive ashes, and, in certain cases, the local environment.
Accurate photometry is mandatory to disentangle the physics driving the emission and the colors provide information on the temperature evolution. Telltale deviations from blackbody emission arise from the effects of the rapidly expanding atmosphere. The decline rates at different epochs and for supernovae of different types are indicative of the power sources, the explosion energy, and the envelope mass.
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