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 resultsRemnant of Tycho’s Nova, a type Ia supernova observed by Tycho Brahe in 1572.

radarparallax

main-sequence fitting cepheids

Tully-Fisherrelation

type Iasupernovae

solar systemnearby stars

Milky Waynearby galaxies

galaxy clusters

Hub

ble’

s La

w

Distance Indicators•Measuring distances in astronomy requires some creativity

•Cosmic distance ladder:

•Why do we care?–Cosmological parameters

–Composition of early galaxies

Supernova Types

•Classified based on spectral lines–Type II: Strong H

–Type Ia: Strong Si• Essentially no H

–Type Ib: Strong He• Essentially no H or Si

–Type Ic: Essentially no H, Si, or He

HHeSSiFe

Type Ia

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

•Collision model–Two white dwarfs merge

–Less likely

–May explain anomalously massive Supernovae

Merging white dwarfs emitting gravitational waves

White dwarf accreting matter from giant companion

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–Unbinds the star

–Depends primarily on C/O ratio

•The light we see comes from decay of 56Ni–Primary product of burning

–Amount of 56Ni primarily depends on central density

–Decay heats up supernova remnant

–Remnant initially opaque, but becomes transparent after a few days

White Dwarf

Kinetic Energy

Star Unbound

56Ni Decay

Light Emission

γ

γ

γ

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

Light curves in blue and visible bands

Brig

htne

ss

Time (days)

My Project

•Learn to use IDL

•Analyze supernova data to look for more parameters–Data from Carnegie Supernova Project (CSP)

–Light curves from 17 supernovae

–Very similar observing parameters

High-mass progenitor

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

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/commons/a/ac/Main_tycho_remnant_full.jpg

–Supernova Types–http://panisse.lbl.gov/~dnkasen/

tutorial/graphics/sn_types.jpg

–Distance Indicators–http://www.daviddarling.info/images/

distance_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/1301_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/physicsweb/world/21/12/35/PWfea6_12-08.jpg

–Type Ia Supernovae: Distance Indicators II

–http://www.lbl.gov/Science-Articles/Archive/sabl/2005/October/stretch_correction.jpg

–Questions?–http://www.sciencedaily.com/images/2

007/07/070713234636-large.jpg