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تسجيل مستخدم جديدA statistical analysis of circumstellar material in Type Ia supernovae
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A key tracer of the elusive progenitor systems of Type Ia supernovae (SNe Ia) is the detection of narrow blueshifted time-varying Na I D absorption lines, interpreted as evidence of circumstellar material (CSM) surrounding the progenitor system. The origin of this material is controversial, but the simplest explanation is that it results from previous mass loss in a system containing a white dwarf and a non-degenerate companion star. We present new single-epoch intermediate-resolution spectra of 17 low-redshift SNe Ia taken with XShooter on the ESO Very Large Telescope. Combining this sample with events from the literature, we confirm an excess (~20 per cent) of SNe Ia displaying blueshifted narrow Na I D absorption features compared to non-blueshifted Na I D features. The host galaxies of SNe Ia displaying blueshifted absorption profiles are skewed towards later-type galaxies, compared to SNe Ia that show no Na I D absorption, and SNe Ia displaying blueshifted narrow Na I D absorption features have broader light curves. The strength of the Na I D absorption is stronger in SNe Ia displaying blueshifted Na I D absorption features than those without blueshifted features, and the strength of the blueshifted Na I D is correlated with the B-V colour of the SN at maximum light. This strongly suggests the absorbing material is local to the SN. In the context of the progenitor systems of SNe Ia, we discuss the significance of these findings and other recent observational evidence on the nature of SN Ia progenitors. We present a summary that suggests there are at least two distinct populations of normal, cosmologically useful SNe Ia.
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Type Ia supernovae are key tools for measuring distances on a cosmic scale. They are generally thought to be the thermonuclear explosion of an accreting white dwarf in a close binary system. The nature of the mass donor is still uncertain. In the sin
gle-degenerate model it is a main-sequence star or an evolved star, whereas in the double-degenerate model it is another white dwarf. We show that the velocity structure of absorbing material along the line of sight to 35 type Ia supernovae tends to be blueshifted. These structures are likely signatures of gas outflows from the supernova progenitor systems. Thus many type Ia supernovae in nearby spiral galaxies may originate in single-degenerate systems.
Progenitors of Type Ia supernovae (SNe) have been predicted to modify their ambient circumstellar (CSM) and interstellar environments through the action of their powerful winds. While there is X-ray and optical evidence for circumstellar interaction
in several remnants of Type Ia SNe, widespread evidence for such interaction in Type Ia SNe themselves has been lacking. We consider prospects for detection of CSM shells that have been predicted to be common around Type Ia SNe. Such shells are most easily detected in Na I absorption lines. Variable (declining) absorption is expected to occur soon after the explosion, primarily during the SN rise time, for shells located within 1 - 10 pc of a SN. The distance of the shell from the SN can be determined by measuring the time scale for line variability.
This work aims to study different probes of Type Ia supernova progenitors that have been suggested to be linked to the presence of circumstellar material (CSM). In particular, we have investigated, for the first time, the link between narrow blueshif
ted NaID absorption profiles and the presence and strength of the broad high-velocity CaII near infrared triplet absorption features seen in Type Ia supernovae around maximum light. With the probes exploring different distances from the supernova; NaID > 10$^{17}$cm, high-velocity CaII features < 10$^{15}$cm. For this, we have used a new intermediate-resolution X-shooter spectral sample of 15 Type Ia supernovae. We do not identify a link between these two probes, implying either that, one (or both) is not physically related to the presence of CSM or that the occurrence of CSM at the distance explored by one probe is not linked to its presence at the distance probed by the other. However, the previously identified statistical excess in the presence of blueshifted (over redshifted) NaID absorption is confirmed in this sample at high significance and is found to be stronger in Type Ia supernovae hosted by late-type galaxies. This excess is difficult to explain as being from an interstellar-medium origin as has been suggested by some recent modelling, as such an origin is not expected to show a bias for blueshifted absorption. However, a circumstellar origin for these features also appears unsatisfactory based on our new results given the lack of link between the two probes of CSM investigated.
The circumstellar (CS) environment is key to understanding progenitors of type Ia supernovae (SNe Ia), as well as the origin of a peculiar extinction property toward SNe Ia for cosmological application. It has been suggested that multiple scatterings
of SN photons by CS dust may explain the non-standard reddening law. In this paper, we examine the effect of re-emission of SN photons by CS dust in the infrared (IR) wavelength regime. This effect allows the observed IR light curves to be used as a constraint on the position/size and the amount of CS dust. The method was applied to observed near-infrared (NIR) SN Ia samples; meaningful upper limits on the CS dust mass were derived even under conservative assumptions. We thereby clarify a difficulty associated with the CS dust scattering model as a general explanation for the peculiar reddening law, while it may still apply to a sub-sample of highly reddened SNe Ia. For SNe Ia in general, the environment at the interstellar scale appears to be responsible for the non-standard extinction law. Furthermore, deeper limits can be obtained using the standard nature of SN Ia NIR light curves. In this application, an upper limit of Mdot ~10^{-8}-10^{-7} Msun/yr (for the wind velocity of ~10 km/s) is obtained for a mass loss rate from a progenitor up to ~0.01 pc, and Mdot ~10^{-7}-10^{-6} Msun/yr up to ~0.1 pc.
We present 2603 spectra of 462 nearby Type Ia supernovae (SN Ia) obtained during 1993-2008 through the Center for Astrophysics Supernova Program. Most of the spectra were obtained with the FAST spectrograph at the FLWO 1.5m telescope and reduced in a
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