Transcript Type Ia Supernovae as distance indicators

Photometry of Type Ia
Supernovae: Search for the
Second Parameter
Date: May 15, 2009
Author: Kevin Perot
Advisor: Dr. Baron
Outline
•Motivation
–Distance indicators
•Background
–Supernova types
–Type Ia supernovae
• Why they’re cool
• Why they blow up
• How they blow up
• How we use them
•My research
–What I’ve been doing
–My results
Remnant of Tycho’s Nova, a type Ia supernova
observed by Tycho Brahe in 1572.
Distance Indicators
•Measuring distances in astronomy
requires some creativity
•Cosmic distance ladder:
galaxy clusters
nearby galaxies
Milky Way
type Ia
supernovae
radar
parallax
•Why do we care?
–Cosmological parameters
–Composition of early galaxies
main-sequence
cepheids
fitting
Tully-Fisher
relation
Hubble’s Law
nearby stars
solar system
Supernova Types
•Classified based on
spectral lines
–Type II: Strong H
–Type Ia: Strong Si
H
He
S
Si
Fe
Type
Ia
• Essentially no H
–Type Ib: Strong He
• Essentially no H or Si
–Type Ic: Essentially no
H, Si, or He
Type
Ic
Type
Ib
Type
II
Type Ia Supernovae: Distance Indicators I
•What makes type Ia supernovae
good distance indicators?
–Very common
• Average-mass progenitor
–Very bright
• Absolute magnitude: -19.3
• Outshines host galaxy
–Very consistent
• Peak magnitude variation: ~0.3
• Much of this can be corrected for
SN 1994D, discovered in the galaxy
NGC 4526. This galaxy is in the Virgo
cluster, about 60 million light years away.
Type Ia Supernovae: What Causes Them?
•Accretion model
–Two stars are in a binary system
–First, the larger one evolves to a white
dwarf
–Then, the smaller one evolves to a red
giant
–Matter spills from red giant to white dwarf
–When the dwarf reaches the
Chandrasekhar limit (about 1.4 solar
masses), it explodes
White dwarf accreting matter from
giant companion
•Collision model
–Two white dwarfs merge
–Less likely
–May explain anomalously massive
Supernovae
Merging white dwarfs
emitting gravitational waves
Type Ia Supernovae: Explosion Mechanism
•Fusion reignites as mass
approaches Chandrasekhar limit
•Deflagration
–Leaves some material unburned
•Detonation
–Not enough intermediate-mass material
produced
•Delayed Detonation
–Begins as a subsonic deflagration,
allowing the star to pre-expand
–Deflagration turns into a detonation,
burning the remaining material
–Most of the C and O burned to 56Ni,
with some S and Si
Model of a type Ia supernova. The
blue surface shows deflagration; the
white surface shows detonation.
Type Ia Supernovae: Energetics
•All energy released during burning
goes into kinetic energy
White Dwarf
–Unbinds the star
Kinetic Energy
–Depends primarily on C/O ratio
•The light we see comes from
decay of 56Ni
–Primary product of burning
Star
Unbound
–Amount of 56Ni primarily depends on
central density
–Decay heats up supernova remnant
56Ni
Decay
γ
–Remnant initially opaque, but becomes
transparent after a few days
γ
γ
Light Emission
γ
Type Ia Supernovae: Distance Indicators II
•Brightness varies slightly
–Different amounts of 56Ni
•Brightness related to decline
rate
–Brighter supernovae decline more
slowly
–Brighter supernovae are hotter, and
thus more opaque
•Stretch method
•May be more variations we can
account for
My Project
•Learn to use IDL
•Analyze supernova data to
look for more parameters
Light curves in blue and visible bands
–Data from Carnegie Supernova
Project (CSP)
–Very similar observing
parameters
Brightness
–Light curves from 17
supernovae
Time (days)
Theoretical Model
•Model by Peter Höflich
–Variations in progenitor
mass cause variations
along the light curve
–Specifically looking for the
pattern of a high-mass
progenitor
• Most identifiable pattern
High-mass progenitor
Results
•Several light curves fit this
pattern
–Evidence of a range of
progenitor masses between 5
and 7 solar masses
–Decline rate related to
progenitor mass
Questions?
Artist’s conception of type Ia supernova before the explosion and 20 days after
Image sources
–Outline
–http://upload.wikimedia.org/wikipedia/c
ommons/a/ac/Main_tycho_remnant_ful
l.jpg
–Supernova Types
–http://panisse.lbl.gov/~dnkasen/tutorial
/graphics/sn_types.jpg
–Distance Indicators
–http://www.daviddarling.info/images/di
stance_ladder.jpg
–Type Ia Supernovae: Distance
Indicators I
–http://www.cfa.harvard.edu/supernova/
/HighZ.html
–Type Ia Supernovae: What
Causes Them?
–http://www.nscl.msu.edu/files/images/1
301_800.preview.png
–http://images.astronet.ru/pubd/2005/06
/02/0001206140/wd_cxc_c33.jpg
–Slideshow
–http://www.pha.jhu.edu/~bfalck/Iaprog
enitor.jpg
–Type Ia Supernovae: Explosion
Mechanism
–http://images.iop.org/objects/physicsw
eb/world/21/12/35/PWfea6_12-08.jpg
–Type Ia Supernovae: Distance
Indicators II
–http://www.lbl.gov/ScienceArticles/Archive/sabl/2005/October/str
etch_correction.jpg
–Questions?
–http://www.sciencedaily.com/images/2
007/07/070713234636-large.jpg