Transcript Diapositiva 1

SN Ia
Margutti Raffaella,2005
1. Observational methods
High-z SN experience
(High-z Supernova Team)
2.SN types and Progenitors
SNe II:
1. We can find them only in spiral galaxies
(extreme I population).
2. Type II SNe mark the end of the nuclear energy
production in massive stars (>8 solar masses),
and the start of a ‘new’ life as a neutron star.
3. They are believed to originate from CORE
COLLAPSE of a massive progenitor star with
plenty of H. To be more precise it’s important to
say that for SN IIb most (NOT all) H is removed
during evolution by tidal stripping.
Type II Supernovae Parameters
Mej/Msun
E51
R0/1012
(cm)
M(56Ni)/
Msun
Galaxy
1987A
15
1969L
17
1980K
2.2
1993J
3.26
1.7
3
1.7
15
1.0
22
1.7
0.7
0.075
0.075
0.075
0.075
LMC
NGC
1058
10.8
NGC
6946
5.7
M81
D(Mpc) 0.050
From : “Supernovae and Nucleosynthesis”,Arnett,1996.
3.6
SNe I:
Ia
1. In all Hubble type galaxies (Pop II or disk).
2. They are believed to originate from thermonuclear
disruptions of accreting WDs in close binary systems.
3. The issue of how the WDs grow to the Chandrasekhar
mass is still an open question. We have different
possibilities. Among them:
 Mergers of double degenerates resulting in the
formation of a M>MCH and carbon ignition.
 Accretion of H from a main sequence or evolved
companion.
 Sub-Chandra explosions.
What energies are available from
thermonuclear events?
Fuel
Ashes
Erg/g
1051erg/Msun
4He
56Ni
1.57
3.007
4He
28Si+32S
1.40
2.677
4He
12C+16O
7.28
1.446
12C
24Mg
5.60
1.113
12C+16O
56Co
8.22
1.645
12C+16O
56Ni
7.86
1.561
12C+16O
28Si+32S
6.20
1.231
From : “Supernovae and Nucleosynthesis”,Arnett,1996.
Type Ia Supernovae Parameters
1991T
1989B
1992A
1991bg
Mej/Msun 1.33
1.1
1.1
1.1
E51
1.27
1.7
1.7
1.7
R0/1012
(cm)
M(56Ni)/
Msun
Galaxy
0.001
0.001
0.001
0.001
0.692
0.2
0.15
0.075
NGC
4527
NGC
3627
NGC
1380
NGC
4374
From : “Supernovae and Nucleosynthesis”,Arnett,1996.
I b-c
1. We can find them only in spiral galaxies
(extreme pop I).
2. They are believed to be the result of an iron
core collapse, and hence to be physically
related to type II SNe.
From an observational point of view we are able
to recognize SN types from their
 Spectra.
 Light curve.
See next slides for more…
3. Spectra
4.Light-curves
SN II
(From Arnett,1996.)
SN Ia
 The rate of the decline of the light curve correlates with the
absolute magnitude at maximum (Phillips relation,2003)
 The peak is proportional to the mass of 56Ni synthesized during the
explosion.
 The light curve is powered by a “late time “ source: that is the
radioactive decay:
56Co 
56Fe)
(56Ni 
 The light curves peaks at 10-15 days after core collapse and then
declines because of the increasing transparency of the ejecta and
because of the decreasing number of radioactive elements.
 Galaxies having a younger stellar population appear to host the
most luminous SNeI-a.
 See Arnett,1996,Appendix D, for a complete derivation of
supernovae light curve shapes.
Cappellaro et al. 1997
5.Properties of a perfect standard
candle:
1. It would be extremely bright.
2. It would always have exactly the same
ABSOLUTE magnitude. (in particular this
means that it wouldn’t suffer of EVOLUTION).
3. If the absolute magnitude depends on the
environment (e.g. Hubble type) it should be
well known.
4. Small corrections should be applied (fore/back
ground absorption).
5. Easy to calibrate.
Standard Candles
A population of unevolving
sources, having a fixed intrinsic
luminosity at
ALL redshifts
6.SNe Ia as distance indicators
1.
2.
3.
4.
5.
They are exceedingly luminous , with peak MB
averaging
-19 mag
if
H0= 72 (Kms-1Mpc-1).(Filippenko,2004)
“Normal” SNe Ia have small dispersion around their
peak absolute magnitudes  σ ≤ 0.3
mag.(Filippenko,2004).
Our understanding of the progenitors and explosion
mechanism of SNe Ia is on a reasonably firm physical
basis.
Little cosmic evolution is expected in the peak
luminosity, and it can be modeled.
It’s possible to perform local tests of various possible
complications and evolutionary effect by comparing
nearby SNe in different environments.
7.Possible evolution of SNe Ia
EVOLUTION ( linked with changes in metallicity, mass and
C/O ratio of the progenitor,) could lead to:
1.Lower peak luminosity of SNe at high redshift;
 Overestimated distances
2.More powerful explosions;
Underestimated distances
Problem: it’s difficult to obtain an accurate, independent
measure of the peak luminosity  it’s difficult to directly
test for LUMINOSITY EVOLUTION.
Solution: we can easily determine if whether other
observable properties of high-z and low-z SNe Ia differ.
(If they are all the same is probable that the peak
luminosity is constant a well !!!!)
Observational results about evolution:
1. SNe Ia & host galaxy morphology: the SCP
(Supernova Cosmology Project) found no clear
differences between the cosmological results
obtained with SNe Ia in late-type and earlytype galaxies. (Sullivan et al.,2003)
2. SNe Ia & rise time (from explosion to
maximum brightness): no significant difference
between high-z and low-z SNe Ia (even if at
high red-shift we have usually shorter rises
times). (Filippenko,2004).
3. Number of progenitors: higher in high-z SNe.
Although there is NO clear signs that cosmic
evolution of SNe Ia seriously comprises our
results, it is wise to remain vigilant for possible
problems.
8.Possible effects of extinction:
Luminosity distances have to corrected for interstellar
absorption occurring in the host galaxy and in the Milky
Way. From an observational point of view:
1. Extinction corrections based on the relation between
SN Ia colors and luminosity improve distance
precision for a sample of nearby SNe Ia which
include objects with substantial extinction (Riees et
al.,1996).
2. The consistency of the measured Hubble flow from
SNe Ia with late-type and early-type host galaxies
shows that the extinction corrections applied to dusty
SNe Ia at low red-shift don’t alter the expansion rate
from its value measured from SNe Ia in low dust
environments
3. The scatter in the Hubble diagram is much reduced.
(See next slide).
Hubble diagram for SNe Ia
(The ordinate shows the
distance modulus)
TOP: The objects are assumed
to be standard candles and
there is no correction for
extinction; the result is
σ=0.42 mag.
BOTTOM: the same objects
after corrections for
extinction and intrinsic
differences in luminosity.
The result is σ=0.15 mag.
(From Filippenko, 2004).
Gray dust:
THE PROBLEM:
Large dust grains ( GRAY DUST) ,would not imprint the
reddening signature of typical interstellar extinction upon
which our corrections necessarily rely.
Could a evolution in dust-grain size cause us to
underestimate the extinction?
THE SOLUTION:
Viewing SNe through such gray interstellar grains would
also induce a dispersion in the derived distances. With
a mean gray extinction σ ≈ 0.25 mag (the value
required to explain the measured distances without a
cosmological constant), the expected dispersion would
be σ ≈ 0.40 mag. This is significantly larger than the 0.21
mag dispersion observed.
 The observational results favor the NO-Dust hypothesis
(Riess et al.,2000).
9.Cosmological results
(1999)
• From SNe Ia
• From CBR studies
WMAP (2003):
ΩM = 0.27±0.04
ΩΛ = 0.73±0.04
Ωtot = 1.02±0. 02
SN Ia (2004):
Ωtot = 0.94±0.26
10.References
• Arnett,1996: “Supernovae and Nucleosynthesis”,
Princeton University Press.
• Filippenko,2004: The accelerating universe and
dark energy: evidence from type Ia
supernovae,Lect.Notes Phys,646, 191-221.
• Riees et al.,1996:Astroph. J.,473,88.
• Riees et al.,2000:Astroph. J.,536,62.
• Sullivan et al.,2003:astro-ph/0211444.