Measuring expansion velocities in Type II-P supernovae

作者：Takats K^*; Vinko J

来源：Monthly Notices of the Royal Astronomical Society, 2012, 419(4): 2783-2796.

DOI：10.1111/j.1365-2966.2011.19921.x

• supernovae: general
• supernovae: individual: SN 1999em
• supernovae: individual: SN 2004dj
• supernovae: individual: SN 2004et
• supernovae: individual: SN 2005cs
• supernovae: individual: SN 2006bp

We estimate photospheric velocities of Type II-P supernovae (SNe) using model spectra created with SYNOW, and compare the results with those obtained either by more conventional techniques, such as cross-correlation, or by measuring the absorption minimum of P Cygni features. Based on a sample of 81 observed spectra of five SNe, we show that SYNOW provides velocities that are similar to those obtained by more sophisticated non-local thermodynamic equilibrium modelling codes, but they can be derived in a less computation-intensive way. The estimated photospheric velocities (v(model)) are compared to those measured from Doppler shifts of the absorption minima of the H beta and the Fe II lambda 5169 features. %26lt;br%26gt;Our results confirm that Fe II velocities (v(Fe)) have a tighter and more homogeneous correlation with the estimated photospheric velocities than those measured from H beta, but both suffer from phase-dependent systematic deviations. The same is true for a comparison with the cross-correlation velocities. We verify and improve the relations between v(Fe), vH beta and vmodel in order to provide useful formulae for interpolating/extrapolating the velocity curves of Type II-P SNe to phases not covered by observations. We also discuss implications of our results for the distance measurements of Type II-P SNe and show that the application of the model velocities is preferred in the expanding photosphere method.

• 出版日期2012-2