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.

radar parallax main-sequence fitting cepheids Tully-Fisher relation type Ia supernovae solar system nearby stars Milky Way nearby galaxies galaxy clusters Hubble’s Law 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 H He S Si Fe 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: Outshines host galaxy –Very consistent Peak magnitude variation: ~0.3 Much of this can be corrected for SN 1994D, discovered in the galaxy NGC 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 56 Ni, 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 56 Ni –Primary product of burning –Amount of 56 Ni 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 56 Ni Decay Light Emission γ γ γ γ

Type Ia Supernovae: Distance Indicators II Brightness varies slightly –Different amounts of 56 Ni 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 Brightness 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 – ommons/a/ac/Main_tycho_remnant_ful l.jpg –Supernova Types – /graphics/sn_types.jpg –Distance Indicators – stance_ladder.jpg –Type Ia Supernovae: Distance Indicators I – /HighZ.html –Type Ia Supernovae: What Causes Them? – 1301_800.preview.png – /02/ /wd_cxc_c33.jpghttp://images.astronet.ru/pubd/2005/06 /02/ /wd_cxc_c33.jpg –Slideshow – enitor.jpghttp:// enitor.jpg –Type Ia Supernovae: Explosion Mechanism – eb/world/21/12/35/PWfea6_12-08.jpg –Type Ia Supernovae: Distance Indicators II – Articles/Archive/sabl/2005/October/str etch_correction.jpghttp:// Articles/Archive/sabl/2005/October/str etch_correction.jpg –Questions? – 007/07/ large.jpghttp:// 007/07/ large.jpg