A SALT Spectropolarimetric Survey of Supernovae (fiS fl)€¦ · A SALT Spectropolarimetric...

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Oct 30, 2003 SN Survey - SSII 1 A SALT Spectropolarimetric Survey of Supernovae (S 4 ) K. Nordsieck Univ of Wisconsin Supernova taxonomy Polarization of Supernovae Survey Structure Why SALT? Astrophysical questions SNIa Core Collapse SNe 1993J (IIb) Oct 30, 2003 SN Survey - SSII 2 Supernova Importance Need to understand explosion process to model return of heavy elements to ISM energetic input to ISM Need to clarify progenitors to couple to star formation/ galaxy models Both I and IIs used for cosmological distance indicators- are they really standard candles? Some really fun gas dynamics problems Non spherical explosions a hot theoretical topic- needs observational input! Possible relation to γ ray bursts

Transcript of A SALT Spectropolarimetric Survey of Supernovae (fiS fl)€¦ · A SALT Spectropolarimetric...

Page 1: A SALT Spectropolarimetric Survey of Supernovae (fiS fl)€¦ · A SALT Spectropolarimetric Survey of Supernovae (fiS4fl) K. Nordsieck Univ of Wisconsin Ł Supernova taxonomy

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Oct 30, 2003 SN Survey - SSII 1

A SALT Spectropolarimetric Survey

of Supernovae (�S4�)K. Nordsieck

Univ of Wisconsin

� Supernova taxonomy� Polarization of Supernovae� Survey Structure� Why SALT?� Astrophysical questions

� SNIa� Core Collapse SNe 1993J (IIb)

Oct 30, 2003 SN Survey - SSII 2

Supernova Importance

� Need to understand explosion process to model� return of heavy elements to ISM� energetic input to ISM

� Need to clarify progenitors to couple to star formation/ galaxy models

� Both I and II�s used for cosmological distance indicators-are they really standard candles?

� Some really fun gas dynamics problems� Non spherical explosions a hot theoretical topic- needs

observational input!� Possible relation to γ ray bursts

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Oct 30, 2003 SN Survey - SSII 3

Classification� Currently classified by 2 criteria

� Spectra (I, II; a,b,c..)� Light Curves (P = plateau , L = linear)

HHNarrow HH, II->Ib

No HNo H,He

Si, no H,HeCriterion

HH, CaIIIIP

H, [CaII] H, CaIIIIL

H, He ?IIn

[OI], [CaII]H, CaIIIIb

MgI], [OI]HeI Ib

[OI], CaIIOI, FeII, CaII, NaIIc

FeII (P-Cyg)SiII, CaII (abs)IaLate (em)Early (P-Cyg)Class

H, He stripped; γ bursts?

Much HSome HCircumstellar HTiny H envelope

H stripped

Massive core collapseWD at C LimitProgenitor?

Oct 30, 2003 SN Survey - SSII 4

Past Polarization of Supernovae

Bright, or 8m class telescopes

Line pol => modelingMultiple PA�s; jets?Time dependence:I decreases; II increases

71987 �2003

Med S/N Spectro-Polarimetry

Usually peak only

Ia: < 0.3%Ib-II: all pol, up to 4%; decr w/ H mass

10?1983 �1999

Low S/N Spectro-Polarimetry

Unknown interstellar pol (ISP)

Some II�s polarized131968 �1995

Broadband

CommentResult# SNPeriodType

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Oct 30, 2003 SN Survey - SSII 5

What Causes Polarization?� Two possibilities

� Scattering of SN light off ambient dust � No, time dependence is wrong

� Electron scattering in ejecta � Yes� Electron scattering pseudo-photosphere is asymmetric ~ 10

� 40% ! 0.5 � 2% pol� Explosion is homologous (Hubble flow). As it expands,

see deeper into ejecta, to lower velocities and asymmetry of inner layers

� Eventually, becomes optically thin, polarization vanishes� Line polarization

� competition of line opacity with e-scat in photosphere !polarization reduction

� P-Cygni lines above photosphere => polarization inverse P-Cygni

Oct 30, 2003 SN Survey - SSII 6

Good Spectropolarimetry

0.5%, axisymMacDonald-113.1Ia pec (lo lum)

1999by

2%? Uncertain ISP

Lick, Keck-10 � 4012IIn1998S

2%, 3 PA�sVLT, Suburu-6 � 312.5Ic pec2002ap

0.7% Ca jet?VLT512.7Ia2001el

0.7%, axisymLick, Keck7 - 16313.5II-P1999em

Incr to 1%, diff PA lines & cont

PBO, Steward, Lick

-1 � 4010.8IIb1993J

Incr to 1%, axisym

AAT et al-84 � 1762.9II-P pec1987A

CommentGroupEpochsPk VTypeSN

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Oct 30, 2003 SN Survey - SSII 7

Survey

� We need more than one example in each bin!� Adding asymmetry to spectra and light curve may

clarify classification (eg Seyfert I-II unification)� Need

� time coverage (3 -4 epochs) for classification and ISP estimation

� to get on as early as possible (I highest pol, II unpol)� low resolution (R < 1000), very high S/N� can be done in poor seeing and bright/ grey moon

Oct 30, 2003 SN Survey - SSII 8

Why SALT?

� Spectroscopic survey distributed over sky � the best kind for SALT/ HET telescopes

� Spectropolarimeter ~2x more sensitive than Keck LRS, VLT FORS1

� Polarimeter always available� 100% queue mode- can get on quickly, schedule

epochs optimally

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Oct 30, 2003 SN Survey - SSII 9

Time estimation

� Want to go down ~ 3 mag from peak

� Use 900 l/mm VPH (R ~ 1000), binning to lower polarimetric resolution as required

� => Faintest peak mag < 16� Using discovery rate/yr for last

12 yrs, will see 10 � 20/year� Run for 3 years to get statistics� 20/ year x 4 epochs = 80 tracks

= 8 nights = 3% of SALT� Soliciting SALT collaborators!

RPol errMag

10000.02%Brightest peak

12

6500.1%Faintest peak

16

400.1%Faintest useful

19

<16<15Type

10.15.7Ia

18.39.6Tot

6.32.8II

2.01.2Ib,c

Oct 30, 2003 SN Survey - SSII 10

Astrophysical questions - Ia

� Ia�s claimed to be a one-parameter family: pk luminosity vs decline rate

� Theoretical explanation: as time of deflagration ! detonation gets earlier, get incomplete combustion, less Ni, lower lum, faster decline

� But there must be a variety of progenitors, from accretion disk to WD mergers: how do these lead to one-parameter family

� Clue from asymmetry: mergers should give more

� The one low-lum Ia is more polarized than the one hi-lum one!

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Oct 30, 2003 SN Survey - SSII 11

Astrophysical Questions � Core Collapse

� There are a variety of ways to induce asymmetry:� asymmetric explosion (axisymmetric? jet?)� ejecta running into asymmetrical environment

(axisymmetric)� burning nonuniformities that make Ni clumps (non-

axisymmetric)

� Do II�s with different H envelope masses and environments all have the same asymmetry source?

� Some are axisymmetric and some are not!

Oct 30, 2003 SN Survey - SSII 12

SN 1993J (IIb)

Tran et al 1997 PASP 109, 489

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Oct 30, 2003 SN Survey - SSII 13

SN 2001el (Ia)

Continuum axis

Ca jet axis

Model

Kasen et al 2003 ApJ 593, 788

Flux

% Pol

Vector

Oct 30, 2003 SN Survey - SSII 14

SN 1999em (II-P)

Leonard et al 2001 ApJ 553, 861

Spectral symmetry

Time variability

Flux