A SALT Spectropolarimetric Survey of Supernovae (fiS fl)€¦ · A SALT Spectropolarimetric...
Transcript of A SALT Spectropolarimetric Survey of Supernovae (fiS fl)€¦ · A SALT Spectropolarimetric...
1
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
2
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
3
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
4
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
5
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!
6
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
7
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