A review of type Ia supernova spectra

SN 2011fe was the nearest and best-observed type Ia supernova in a generation, and brought previous incomplete datasets into sharp contrast with the detailed new data. In retrospect, documenting spectroscopic behaviors of type Ia supernovae has been more often limited by sparse and incomplete temporal sampling than by consequences of signal-to-noise ratios, telluric features, or small sample sizes. As a result, type Ia supernovae have been primarily studied insofar as parameters discretized by relative epochs and incomplete temporal snapshots near maximum light. Here we discuss a necessary next step toward consistently modeling and directly measuring spectroscopic observables of type Ia supernova spectra. In addition, we analyze current spectroscopic data in the parameter space defined by empirical metrics, which will be relevant even after progenitors are observed and detailed models are refined.Comment: 58 pages, 15 figures, 6 tables, accepted for publication in Ap&SS as an invited revie

Circumstellar dust shells of hot post-AGB stars

Using a radiative transfer code (DUSTY) parameters of the circumstellar dust shells of 15 hot post-AGB stars have been derived. Combining the optical, near and far-infrared (ISO, IRAS) data of the stars, we have reconstructed their spectral energy distributions (SEDs) and estimated the dust temperatures, mass loss rates, angular radii of the inner boundary of the dust envelopes and the distances to these stars. The mass loss rates (10$^{-6}-10^{-5}$M$_{\odot}$yr$^{-1}$) are intermediate between stars at the tip of the AGB and the PN phase. We have also studied the ISO spectra of 7 of these stars. Amorphous and crystalline silicate features were observed in IRAS14331-6435 (Hen3-1013), IRAS18062+2410 (SAO85766) and IRAS22023+5249 (LSIII +5224) indicating oxygen-rich circumstellar dust shells. The presence of unidentified infrared (UIR) band at 7.7$\mu$, SiC emission at 11.5$\mu$ and the "26$\mu$" and "main 30$\mu$" features in the ISO spectrum of IRAS17311-4924 (Hen3-1428) suggest that the central star may be carbon-rich. The ISO spectrum of IRAS17423-1755 (Hen3-1475) shows a broad absorption feature at 3.1$\mu$ due to C$_{2}$H$_{2}$ and/or HCN which is usually detected in the circumstellar shells of carbon-rich stars.Comment: 18 pages, accepted for publication in A&

UV (IUE) spectra of the central stars of high latitude planetary nebulae Hb7 and Sp3

We present an analysis of the UV (IUE) spectra of the central stars of Hb7 and Sp3. Comparison with the IUE spectrum of the standard star HD 93205 leads to a spectral classification of O3V for these stars, with an effective temperature of 50,000 K. From the P-Cygni profiles of CIV (1550 A), we derive stellar wind velocities and mass loss rates of -1317 km/s +/- 300 km/s and 2.9X10^{-8} solar mass yr^{-1} and -1603 km/s +/- 400 km/s and 7X10^{-9} solar mass yr^{-1} for Hb7 and Sp3 respectively. From all the available data, we reconstruct the spectral energy distribution of Hb7 and Sp3.Comment: 4 pages, 3 figures, latex, accepted for publication in Astronomy & Astrophysic

Photometry and low resolution spectroscopy of hot post-AGB candidates

We have obtained Johnson U, B, V and Cousins R, I photometry and low resolution spectra of a small sample of hot post-AGB candidates. Using the present data in combination with JHK data from 2MASS, infrared data from the MSX catalog and the IRAS fluxes, we have studied the spectral energy distribution (SED) of these stars. Using the DUSTY code we have estimated the dust temperatures, the distances to the stars, the mass-loss rates, angular radii of the inner boundary of the dust envelopes and dynamical ages from the tip of the AGB. These candidates have also been imaged through a narrow band H-alpha filter, to search for nebulosity around the central stars. Our H-alpha images revealed the bipolar morphology of the low excitation PN IRAS 17395-0841 with an angular extent of 2.8arcsec. The bipolar lobes of IRAS 17423-1755 in H-alpha were found to have an angular extent of 3.5arcsec (south-east lobe) and 2.2arcsec (north-west lobe). The dust envelope characteristics, low resolution spectrum and IRAS colors suggest that IRAS 18313-1738 is similar to the proto-planetary nebula (PPN) HD 51585. The SED of IRAS 17423-1755, IRAS 18313-1738 and IRAS 19127+1717 show a warm dust component (in addition to the cold dust) which may be due to recent and ongoing mass-loss.Comment: 20 pages, 6 figures, h-alpha figure compressed with XV, paper accepted for publication in Astronomy & Astrophysic