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Synthetic spectra and light curves of type Ia supernovae [Elektronische Ressource] / Markus Kromer

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¨ ¨TECHNISCHE UNIVERSITAT MUNCHENMax-Planck-Institut fur Astrophysik¨Synthetic spectra and light curvesof Type Ia supernovaeMarkus KromerVollst¨andigerAbdruckdervonderFakult¨atfur¨ PhysikderTechnischenUniversita¨tMunchen zur Erlangung des akademischen Grades eines¨Doktors der Naturwissenschaften (Dr. rer. nat.)genehmigten Dissertation.Vorsitzender: Univ.-Prof. Dr. L. OberauerPruf¨ er der Dissertation:1. Hon.-Prof. Dr. W. Hillebrandt2. Univ.-Prof. Dr. W. WeiseDie Dissertation wurde am 23.09.2009 bei der Technischen Universit¨at Munc¨ heneingereicht und durch die Fakulta¨t fur¨ Physik am 27.11.2009 angenommen.iiiContents1 Introduction 11.1 Supernova classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.2 Astrophysical impact . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61.3 Objective of this thesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 Thermonuclear supernovae 132.1 Observational characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132.1.1 Spectra . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132.1.2 Light curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152.1.3 Spectropolarimetry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182.1.4 Light echoes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182.1.5 Rates . . . . . . . . . .

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¨ ¨TECHNISCHE UNIVERSITAT MUNCHEN
Max-Planck-Institut fur Astrophysik¨
Synthetic spectra and light curves
of Type Ia supernovae
Markus Kromer
Vollst¨andigerAbdruckdervonderFakult¨atfur¨ PhysikderTechnischenUniversita¨t
Munchen zur Erlangung des akademischen Grades eines¨
Doktors der Naturwissenschaften (Dr. rer. nat.)
genehmigten Dissertation.
Vorsitzender: Univ.-Prof. Dr. L. Oberauer
Pruf¨ er der Dissertation:
1. Hon.-Prof. Dr. W. Hillebrandt
2. Univ.-Prof. Dr. W. Weise
Die Dissertation wurde am 23.09.2009 bei der Technischen Universit¨at Munc¨ hen
eingereicht und durch die Fakult¨at fur¨ Physik am 27.11.2009 angenommen.iii
Contents
1 Introduction 1
1.1 Supernova classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.2 Astrophysical impact . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.3 Objective of this thesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2 Thermonuclear supernovae 13
2.1 Observational characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.1.1 Spectra . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.1.2 Light curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.1.3 Spectropolarimetry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.1.4 Light echoes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.1.5 Rates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
2.2 Basic model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
2.3 Progenitor scenarios . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
2.4 Explosion mechanism. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
3 Basics of radiative transfer 29
3.1 Description of the radiation field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
3.2 Radiation in thermodynamic equilibrium . . . . . . . . . . . . . . . . . . . . . . . . . 30
3.3 Interaction of radiation and matter . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
3.3.1 Local thermodynamic equilibrium . . . . . . . . . . . . . . . . . . . . . . . . 33
3.3.2 Bound-bound opacity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
3.3.3 Continuum opacities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
3.3.4 Interaction of γ-photons and matter . . . . . . . . . . . . . . . . . . . . . . . 37
3.4 Statistical equilibrium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
3.4.1 Rate equations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
3.4.2 Radiative rates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
3.4.3 Collisional rates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
3.5 Transfer equation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
4 Implementation 45
4.1 Monte Carlo radiative transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
4.2 Homologous expansion, Sobolev approximation . . . . . . . . . . . . . . . . . . . . . 47
4.3 Outline of the code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
4.3.1 Setting up the computational domain . . . . . . . . . . . . . . . . . . . . . . 51
4.3.2 Energy deposition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
4.3.3 Propagation of γ-packets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52iv Contents
4.3.4 Treatment of thermal kinetic energy . . . . . . . . . . . . . . . . . . . . . . . 54
4.3.5 Treatment of atomic internal energy . . . . . . . . . . . . . . . . . . . . . . . 55
4.3.6 Propagation of UVOIR radiation . . . . . . . . . . . . . . . . . . . . . . . . . 58
4.3.7 Extraction of spectra and light curves . . . . . . . . . . . . . . . . . . . . . . 61
4.4 Plasma conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
4.4.1 Radiation field models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
4.4.2 Excitation and ionization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
4.4.3 Thermal balance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
4.5 Parallelization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
4.6 Atomic data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
5 Two simple test cases 73
5.1 The parameterized 1D deflagration model W7 . . . . . . . . . . . . . . . . . . . . . . 73
5.1.1 Simple versus detailed ionization treatment . . . . . . . . . . . . . . . . . . . 74
5.1.2 Influence of atomic data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
5.1.3 Comparison with other codes . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
5.2 An ellipsoidal toy model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
5.2.1 The model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
5.2.2 Spectral evolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
5.2.3 Broad-band light curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
5.2.4 Secondary maximum in the NIR bands . . . . . . . . . . . . . . . . . . . . . 88
6 Application to hydrodynamic explosion models 91
6.1 Comparing a deflagration to the faint end of delayed detonations . . . . . . . . . . . 91
6.1.1 Spectral evolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
6.1.2 Broad-band light curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
6.1.3 Comparison to observations . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
6.2 SN 2005bl and the class of 1991bg like objects . . . . . . . . . . . . . . . . . . . . . . 105
6.2.1 Broad-band light curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
6.2.2 Spectral evolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
6.2.3 Ejecta asymmetries. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
6.3 Sub-Chandrasekhar-mass models – an alternative route to 1991bg-like objects? . . . 119
6.3.1 Broad-band light curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
6.3.2 Spectral evolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
6.3.3 Understanding the asymmetry effects . . . . . . . . . . . . . . . . . . . . . . 125
7 Conclusions 131v
List of Figures
1.1 SN 2002bo in NGC 3190 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Supernova classification scheme . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.3 Characteristic spectra for the different supernova types at various epochs . . . . . . 3
1.4 Formation of a P-Cygni line profile . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.5 Light curve width-luminosity relation of Type Ia supernovae . . . . . . . . . . . . . . 7
1.6 Hubble diagram of Type Ia supernovae . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.1 Spectral evolution of a normal SN Ia . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
2.2 Spectroscopic diversity of SNe Ia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
2.3 Broad-band light curves of Type Ia supernovae . . . . . . . . . . . . . . . . . . . . . 17
2.4 Peak B-band magnitude vs. light curve decline parameter Δm (B) for a sample of15
SNe Ia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2.5 “Zorro”-diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
2.6 Parameter space for progenitor systems in the single degenerate scenario . . . . . . . 23
2.7 Structure of a 3D deflagration model . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
4.1 Flow chart outlining the mode of operation of the code . . . . . . . . . . . . . . . . . 50
4.2 Schematic illustration of the macro-atom formalism . . . . . . . . . . . . . . . . . . . 56
4.3 Illustration of the selection of the next photon absorption from a randomly sampled
optical depth τ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60r
4.4 Influence of the initial grey approximation . . . . . . . . . . . . . . . . . . . . . . . . 61
4.5 Renormalization factors for the photoionization rate coefficients . . . . . . . . . . . . 65
4.6 Schematic view of the thermal balance calculation . . . . . . . . . . . . . . . . . . . 68
4.7 Scaling behaviour of our code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
5.1 Spectral evolution of the parameterized 1D explosion model W7. . . . . . . . . . . . 74
5.2 RadialionizationstructureoftheW7model,illustratingtheinfluenceofthedifferent
ionization treatments of the code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
−15.3 Temperature evolution of the W7 model at a radial velocity of 9590kms . . . . . 76
5.4 Radial temperature distribution of the W7 model at 31 days after the explosion . . . 77
5.5 W7 spectra illustrating the influence of different ionization treatments and atomic
data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
5.6 Broad-band light curves for the W7 model . . . . . . . . . . . . . . . . . . . . . . . . 79
5.7 Flux redistribution by line fluorescence in the W7 model at 20 days after the explosion 80
5.8 Flux redistribution by line fluorescence in the W7 model at 35 days after the explosion 81
5.9 Spectral evolution of the ellipsoidal toy model . . . . . . . . . . . . . . . . . . . . . . 85
5.10 Broad-band light curves for the ellipsoidal toy model . . . . . . . . . . . . . . . . . . 86vi List of Figures
5.11 Region of last emission for the ellipsoidal toy model . . . . . . . . . . . . . . . . . . 87
5.12 Ionization structure of iron in the ellipsoidal toy model . . . . . . . . . . . . . . . . . 89
6.1 Comparison of the composition structure of a delayed detonation and a pure defla-
gration model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
6.2 Angle-averaged spectral evolution of a delayed detonation model . . . . . . . . . . . 96
6.3 Angle-averaged spectral evolution of a deflagration model . . . . . . . . . . . . . . . 97
6.4 Broad-band light curves for the delayed detonation and deflagration models . . . . . 98
6.5 Ionization structure and J-band regions of last emission for the delayed detonation
model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
6.6 Ionization structure and J-band regions of last emission for the deflagration model . 101
6.7 Comparingtheangle-averagedlightcurvesofthedeflagrationanddelayeddetonation
model to a sample of different SNe Ia. . . . . . . . . . . . . . . . . . . . . . . . . . . 102
6.8 Comparing spectra of the delayed detonation and deflagration model with SN 2005hk104
6.9 Comparing spectra of the delayed detonation and deflagration model with SN 1986G 105
6.10 Radial abundance stratification of SN 2005bl compared to a merger model . . . . . . 106
6.11 Final composition structure of the merger model . . . . . . . . . . . . . . . . . . . . 107
6.12 Synthetic light curves for the merger model compared to a sample of 1991bg-like
objects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
6.13 Histograms showing the distribution of peak magnitudes of the merger model over
the different lines-of-sight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
6.14 Diversity of the B-band light curve of the merger model due to geometry effects . . 111
6.15 Angle-averaged spectral evolution of the merger model compared to SN 2005bl . . . 113
6.16 Spectral evolution of the merger model compared to SN 2005bl . . . . . . . . . . . . 116
6.17 Line velocities in the merger model compared to SN 2005bl . . . . . . . . . . . . . . 117
6.18 Regions of last emission in the merger model . . . . . . . . . . . . . . . . . . . . . . 118
6.19 Final composition structure of the sub-Chandrasekhar-mass model . . . . . . . . . . 120
6.20 Synthetic light curves for the sub-Chandrasekhar-mass model compared to a sample
of 1991bg-like objects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122
6.21 Spectral evolution of the sub-Chandrasekhar-mass model compared to SN 2005bl . . 124
6.22 Composition structure of the helium-stripped sub-Chandrasekhar-mass model . . . . 125
6.23 Synthetic light curves for the sub-Chandrasekhar-mass model after artificially strip-
ping the helium shell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127
6.24 Comparing maximum light spectra of the sub-Chandrasekhar-mass model and a toy
model for which the material from the helium shell was removed . . . . . . . . . . . 128vii
List of Tables
4.1 Atomic data sets used in the calculations . . . . . . . . . . . . . . . . . . . . . . . . 71
5.1 ΔM =M −M for selected bands in the ellipsoidal model at different timesminor major
after explosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
5.2 Peak times and Δm for selected bands in the ellipsoidal model . . . . . . . . . . . 8815
6.1 Nucleosynthesis yields of the delayed detonation and deflagration model . . . . . . . 94
6.2 Probing the distribution of monochromatic peak magnitudes of our merger model
against a normal distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
6.3 Nucleosynthesis yields of selected species for the sub-Chandrasekhar-mass model . . 120viii List of Tables1
1 Introduction
Ever since the dawn of mankind people have been fascinated by the myriads of stars twinkling on a
clearnightsky,askingquestionssuchas“Whatarethoseobjectsandhowdotheywork?”. Although
these questions were mainly of spiritual nature in ancient times, even then people followed closely
the movements of the Sun and the Moon to calculate the calendar. This was of great importance
not only for religious celebrations but also to determine the sowing dates [see e.g. the recently
discovered sky disc of Nebra (Meller 2003, Schlosser 2003), which dates back to 1600 B.C.].
Inmakingtheseobservationsourancestorsrealizedquiteearlythatthenightskyisnotimmutable.
They observed the planets on their periodical orbits on the sky and learned to predict their move-
ments. Besides these regular moving objects they also discovered “guest stars” which appeared
suddenly and faded away after some time: these objects – some of them so bright that they have
been visible at daytime – were named novae as a shorthand note for the Latin stellae novae (i.e.
new stars).
Ittookuntilthe20thcenturytorealize,thatthesenovaearenotauniqueclassofobjects. Basedon
theobservationof(super)novaSAndromedaeintheAndromedagalaxyin1885(seedeVaucouleurs
& Corwin 1985 for a historical review on this event), which appeared much brighter than earlier
novae which had been observed in the Andromeda galaxy, Lundmark (1925) proposed two different
classes of novae: an “upper” and a “lower” class different by about four orders of magnitude in
brightness. Baade & Zwicky (1934) eventually introduced the name supernova to distinguish these
bright events from the classical novae.
Figure 1.1: SN 2002bo in NGC 3190 (European Supernova Collaboration & Benetti et al. 2004).
Supernovae are characterized by a rapid rise (typically ∼ 20days) in brightness and tremendous
42 43 −1peakluminositiesof10 ...10 ergs ,comparabletotheluminosityofanentiregalaxy(seeFigure
1.1). After maximum light they fade away over several years leaving behind a gaseous object, the2 1. Introduction
51 53supernova remnant. The total energy release in a supernova amounts to 10 ...10 erg. This
enormous energy represents a significant fraction of the energy bound in a star, which led to
the idea that supernovae are associated with the death of stars (Baade & Zwicky 1934, Hoyle &
Fowler 1960). The final fate of a star depends crucially on its initial mass M. For M . 8Mi i ⊙
33(M = 1.989?10 g denotes a solar mass, Unsold & Baschek 2002) fusion processes in the stellar¨⊙
interior end with the burning of helium to carbon and instabilities during the final burning phases
lead to a large mass loss. Thus the total mass of those stars falls below the Chandrasekhar limit
and the degenerate-electron pressure can stabilize their cores against gravity such that they end as
White Dwarfs (Chandrasekhar 1931). For M & 8M fusion goes all the way up to silicon burningi ⊙
which produces iron. Since iron has the largest binding energy of all elements, fusion cannot
provide any further energy. Thus, those stars collapse under the influence of their gravitational
forces, resultingineitheraneutronstarorablackhole. Duetothestrongtemperaturedependence
of the nuclear fusion reactions, more massive stars consume their fuel faster and thus live shorter
lives (for a detailed discussion of stellar evolution see e.g. Kippenhahn & Weigert 1990).
In contrast, the less luminous classical novae are associated with phenomena due to mass transfer
in close binary systems, the so-called cataclysmic variable stars (see Warner 1995 for a detailed
discussion).
1.1 Supernova classification
Originating from the work of Minkowski (1941), the supernova classification scheme is still purely
empirical and based on the optical spectra at maximum light [an up-to-date version according
to Turatto (2003) is shown in Figure 1.2]. Minkowski (1941) separated the supernovae into two
distinct classes – Type II and Type I – depending on whether they show or do not show hydrogen
lines in their maximum light spectra, respectively.
thermonuclear core collapse
no yesHI II
IIP
SiII no IILIIb
yes
yes HeI
no Ib strong
Ia ejecta−CSMIc interaction
IInIb/c pec
hypernovae
Figure 1.2: Supernova classification scheme according to Turatto (2003).
shapelight curve