Abstract
We report measurements and analysis of high-velocity (> 20,000 km/s) and photospheric absorption features in a series of spectra of the Type Ia supernova (SN) 2009ig obtained between -14d and +13d with respect to the time of maximum B-band luminosity. We identify lines of Si II, Si III, S II, Ca II and Fe II that produce both high-velocity (HVF) and photospheric-velocity (PVF) absorption features. SN 2009ig is unusual for the large number of lines with detectable HVF in the spectra, but the light-curve parameters correspond to a slightly overluminous but unexceptional SN Ia (M_B = -19.46 mag and Delta_m15 (B) = 0.90 mag). Similarly, the Si II lambda_6355 velocity at the time of B-max is greater than "normal" for a SN Ia, but it is not extreme (v_Si = 13,400 km/s). The -14d and -13d spectra clearly resolve HVF from Si II lambda_6355 as separate absorptions from a detached line forming region. At these very early phases, detached HVF are prevalent in all lines. From -12d to -6d, HVF and PVF are detected simultaneously, and the two line forming regions maintain a constant separation of about 8,000 km/s. After -6d all absorption features are PVF. The observations of SN 2009ig provide a complete picture of the transition from HVF to PVF. Most SN Ia show evidence for HVF from multiple lines in spectra obtained before -10d, and we compare the spectra of SN 2009ig to observations of other SN. We show that each of the unusual line profiles for Si II lambda_6355 found in early-time spectra of SN Ia correlate to a specific phase in a common development sequence from HVF to PVF.
Highlights
Research on Type Ia supernovae (SNe Ia) has been guided for many years by the general agreement that the progenitors are carbon–oxygen (C/O) white dwarf (WD) stars as first predicted by Hoyle & Fowler (1960)
If the Mg ii λ4481 line produced a HVF at −14 days, it would have a velocity of about 24,000 km s−1, and it would appear at about 29,000 km s−1 in the velocity space of Si iii λ4560
The correlation of line profiles from pre-maximum spectra of other SNe Ia to the spectral sequence of SN 2009ig confirms a suggestion made by Stanishev et al (2007) that the “peculiar” profiles of Si ii λ6355 in early-time spectra of SN Ia can be explained as part of a common evolutionary sequence that includes separate HVF and PVF components
Summary
Research on Type Ia supernovae (SNe Ia) has been guided for many years by the general agreement that the progenitors are carbon–oxygen (C/O) white dwarf (WD) stars as first predicted by Hoyle & Fowler (1960). High-velocity (HVF) absorption features from Ca ii lines are frequently identified in spectra of SNe Ia obtained a week or more before B-max, but reliable identifications of HVF from other elements are rare. Foley et al (2012) use the same pre-maximum data of SN 2009ig as we do to identify and discuss differences in line profiles of Ca ii H&K, Ca ii IR3, and Si ii λ6355 They reveal the two-component nature of early Si ii λ6355 features and propose that HVF may be ubiquitous in SN Ia. Here we focus on the location and composition of HVF line forming regions. We directly compare the development of Si ii λ6355 features in the spectra of SN 2009ig to sequences of early-time spectra of five other SN Ia. Velocity measurements show that the HVF and PVF line forming regions remain separated by about 8000 km s−1 in SN 2009ig.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
