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Type Ia Supernovae: Homogeneity and Diversity
Stockholm University, Faculty of Science, Department of Physics.
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The use of type Ia supernovae as distance estimators has shown that about 75% of the energy content of the universe has a negative equation of state parameter and thus, drives the acceleration of the universe. Constraining the exact nature of this energy is one of the main goals in cosmology. As the statistics of observed high-redshift supernovae increases, systematic effects become the limiting factor to pursue such investigations, thus deeper understanding of the physical properties of SNe is of great importance.

In this thesis we investigate spectral homogeneity and diversity of local and high redshift supernovae. Special emphasis has been given to the analysis of optical spectra of local peculiar supernovae 1999aa and 1999ac. The study of the spectra of SN 1999aa pointed out that this SN could be a link between the extreme peculiar SN 1991T and normal SNe. Moreover, the identification of a high velocity component of Ca II and possibly of a low velocity component of C III suggests some degree of asphericity in the ejecta of this supernova. Evidence for a deflagration of a C+O white dwarf was found in the early spectra of SN 1999ac.

The spectral proprieties of a vast sample of local SNe are also studied by means of newly introduced spectral indicators. These were used to possibly improve the intrinsic spread of SN peak magnitudes to 0.15 mag, independently of light curve parameters.

The first quantitative comparison between local and high redshift supernova is carried out. No evidence for extreme peculiar sub-luminous SNe was found in our data set including 13 SNe with redshift range z=0.279-0.912. Furthermore, SN2002fd (z=0.279) was found to show spectral characteristics similar to SN 1991T/SN 1999aa-like supernovae.

We also present a feasibility study of the Hubble diagram in rest frame I-band up to z~0.5, and show the possibility to probe the presence of intergalactic dust, which could possibly mimic the effect of dark energy in the Hubble diagram.

Place, publisher, year, edition, pages
Stockholm: Fysikum , 2004. , 101 p.
Keyword [en]
Physics
Identifiers
URN: urn:nbn:se:su:diva-58OAI: oai:DiVA.org:su-58DiVA: diva2:195691
Public defence
2004-03-19, sal FB53, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 10:00
Opponent
Supervisors
Available from: 2004-02-26 Created: 2004-02-26Bibliographically approved
List of papers
1. Spectroscopic Observations and Analysis of the Peculiar SN 1999aa
Open this publication in new window or tab >>Spectroscopic Observations and Analysis of the Peculiar SN 1999aa
2004 (English)In: Astronomical Journal, ISSN 0004-6256, E-ISSN 1538-3881, Vol. 128, no 1, 387-404 p.Article in journal (Refereed) Published
Abstract [en]

We present an extensive new time series of spectroscopic data of the peculiar SN 1999aa in NGC 2595. Our data set includes 25 optical spectra between -11 and +58 days with respect to B-band maximum light, providing an unusually complete time history. The early spectra resemble those of an SN 1991T-like object but with a relatively strong Ca H and K absorption feature. The first clear sign of Si II lambda6355, characteristic of Type Ia supernovae, is found at day - 7, and its velocity remains constant up to at least the first month after B-band maximum light. The transition to normal-looking spectra is found to occur earlier than in SN 1991T, suggesting SN 1999aa as a possible link between SN 1991T - like and Branch-normal supernovae. Comparing the observations with synthetic spectra, doubly ionized Fe, Si, and Ni are identified at early epochs. These are characteristic of SN 1991T - like objects. Furthermore, in the day - 11 spectrum, evidence is found for an absorption feature that could be identified as high velocity C II lambda6580 or Halpha. At the same epoch C III lambda4648.8 at photospheric velocity is probably responsible for the absorption feature at 4500 Angstrom. High-velocity Ca is found around maximum light together with Si II and Fe II confined in a narrow velocity window. Implied constraints on supernovae progenitor systems and explosion hydrodynamic models are briefly discussed.

Keyword
supernovae : general; supernovae : individual (SN 1999aa)
Identifiers
urn:nbn:se:su:diva-23927 (URN)
Note
Part of urn:nbn:se:su:diva-58Available from: 2004-02-26 Created: 2004-02-26 Last updated: 2017-12-13Bibliographically approved
2. SN 1999ac: On the presence of high velocity carbon
Open this publication in new window or tab >>SN 1999ac: On the presence of high velocity carbon
Manuscript (Other academic)
Identifiers
urn:nbn:se:su:diva-23928 (URN)
Note
Part of urn:nbn:se:su:diva-58Available from: 2004-02-26 Created: 2004-02-26 Last updated: 2010-01-13Bibliographically approved
3. Search for spectral evolution in high-redshift Type Ia supernovae: evidence for SN 1991T/SN 1999aa-like object at z=0.279
Open this publication in new window or tab >>Search for spectral evolution in high-redshift Type Ia supernovae: evidence for SN 1991T/SN 1999aa-like object at z=0.279
Manuscript (Other academic)
Identifiers
urn:nbn:se:su:diva-23929 (URN)
Note
Part of urn:nbn:se:su:diva-58Available from: 2004-02-26 Created: 2004-02-26 Last updated: 2010-01-13Bibliographically approved
4. A new set of spectral quantities characterizing type Ia supernovae: and their correlation with peak luminosity
Open this publication in new window or tab >>A new set of spectral quantities characterizing type Ia supernovae: and their correlation with peak luminosity
Manuscript (Other academic)
Identifiers
urn:nbn:se:su:diva-23930 (URN)
Note
Part of urn:nbn:se:su:diva-58Available from: 2004-02-26 Created: 2004-02-26 Last updated: 2010-01-13Bibliographically approved
5. Rest frame I band Hubble diagram for type Ia supernovae up to z~0.5
Open this publication in new window or tab >>Rest frame I band Hubble diagram for type Ia supernovae up to z~0.5
Manuscript (Other academic)
Identifiers
urn:nbn:se:su:diva-23931 (URN)
Note
Part of urn:nbn:se:su:diva-58Available from: 2004-02-26 Created: 2004-02-26 Last updated: 2010-01-13Bibliographically approved

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