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* old and bolonia study programme


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Diversity in extinction laws of Type Ia supernovae measured between 0.2 and 2 μm
Rahman Amanullah, Tanja Petrushevska, 2015, original scientific article

Abstract: We present ultraviolet (UV) observations of six nearby Type Ia supernovae (SNe Ia) obtained with the Hubble Space Telescope, three of which were also observed in the near-IR (NIR) with Wide-Field Camera 3. UV observations with the Swift satellite, as well as ground-based optical and NIR data provide complementary information. The combined data set covers the wavelength range 0.2–2 μm. By also including archival data of SN 2014J, we analyse a sample spanning observed colour excesses up to E(B − V) = 1.4 mag. We study the wavelength-dependent extinction of each individual SN and find a diversity of reddening laws when characterized by the total-to-selective extinction RV. In particular, we note that for the two SNe with E(B − V) ≳ 1 mag, for which the colour excess is dominated by dust extinction, we find RV = 1.4 ± 0.1 and RV = 2.8 ± 0.1. Adding UV photometry reduces the uncertainty of fitted RV by ∼50 per cent allowing us to also measure RV of individual low-extinction objects which point to a similar diversity, currently not accounted for in the analyses when SNe Ia are used for studying the expansion history of the Universe.
Found in: ključnih besedah
Summary of found: ... circumstellar matter, supernovae: general, supernovae: individual: SNe 2012cg,...
Keywords: circumstellar matter, supernovae: general, supernovae: individual: SNe 2012cg, supernovae: individual: 2012cu, dust, extinction
Published: 23.01.2018; Views: 2378; Downloads: 0
.pdf Fulltext (6,52 MB)

Time-varying sodium absorption in the Type Ia supernova 2013gh
Raphael Ferretti, R. Amanullah, Ariel Goobar, Joel Johansson, T. Petrushevska, 2016, original scientific article

Abstract: Context. Temporal variability of narrow absorption lines in high-resolution spectra of Type Ia supernovae (SNe Ia) is studied to search for circumstellar matter. Time series which resolve the profiles of absorption lines such as Na I D or Ca II H&K are expected to reveal variations due to photoionisation and subsequent recombination of the gases. The presence, composition, and geometry of circumstellar matter may hint at the elusive progenitor system of SNe Ia and could also affect the observed reddening law. Aims. To date, there are few known cases of time-varying Na I D absorption in SNe Ia, all of which occurred during relatively late phases of the supernova (SN) evolution. Photoionisation, however, is predicted to occur during the early phases of SNe Ia, when the supernovae peak in the ultraviolet. We attempt, therefore, to observe early-time absorption-line variations by obtaining high-resolution spectra of SNe before maximum light. Methods. We have obtained photometry and high-resolution spectroscopy of SNe Ia 2013gh and iPTF 13dge, to search for absorptionline variations. Furthermore, we study interstellar absorption features in relation to the observed photometric colours of the SNe. Results. Both SNe display deep Na I D and Ca II H&K absorption features. Furthermore, small but significant variations are detected in a feature of the Na I D profile of SN 2013gh. The variations are consistent with either geometric effects of rapidly moving or patchy gas clouds or photoionisation of Na I gas at R ≈ 1019 cm from the explosion. Conclusions. Our analysis indicates that it is necessary to focus on early phases to detect photoionisation effects of gases in the circumstellar medium of SNe Ia. Different absorbers such as Na I and Ca II can be used to probe for matter at different distances from the SNe. The nondetection of variations during early phases makes it possible to put limits on the abundance of the species at those distances.
Found in: ključnih besedah
Summary of found: ...supernovae (SNe Ia) is studied to search for circumstellar matter. Time series which resolve the profiles...
Keywords: supernovae: general – supernovae: individual: SN 2013gh – dust, extinction – circumstellar matter – supernovae: individual: iPTF 13dge
Published: 23.01.2018; Views: 2364; Downloads: 0
.pdf Fulltext (1,84 MB)

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