tantalizing hints from cvs with pulsating wds
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Pulsating WD
Paula Szkody, Anjum Mukadam, Boris Gaensicke, Arne Henden + AAVSO, Atsuko Nitta, Ed Sion, Dean Townsley
Wild Stars March 16, Wild Stars March 16, 20092009
Tantalizing Hints from CVs with Pulsating WDs
Why study WD pulsators ?
Pulsations probe inner stellar structurePulsations probe inner stellar structure
uniform density; pulsations penetrate the inner 99% of white dwarf
Asteroseismology allows determination Asteroseismology allows determination of:of: Mass (total and H layer) Rotation rate Core Composition Cooling rate
Why study accreting WD pulsators ?
Find effects of accretion on Find effects of accretion on pulsationspulsations Heating due to accretion Increase in angular momentum Changing surface composition Changing stellar mass
• White dwarfs show non-radial g-modes on account of their high gravity
Periods of 100s to 1000s
• These modes are characterized by quantum numbers (k,l,m)
similar to atomic orbitals
k is #nodes between surface and center
l is # nodes on surface (borders between hot and cool zones)
m is # on surface that pass through pole of rotation axis
Modes of Pulsation
l = 1
m = 1
m = 0
l = 2
m = 1
m = 0
Stellar Surface
see www.whitedwarf.org
Ideal short term seismology● Find a star with many (~10) pulsation modes
● Identify the quantum numbers for each mode
● Use WD pulsation models to get a unique fit to the observed periods
Model fit Temperature, stellar mass H/He layer masses
Model luminosity Distance to star
Multiplet structure Magnetic field or rotation
Model core composition 12C,16O nuclear reaction rate in RG stage
3 major questions:
1) where is the instability strip for accreting pulsators?
2) what are the affects of accretion and outbursts?
3) is there any hope of pulling out mass, spin, etc?
Instability Strips for Non-Interacting
White Dwarf Pulsators
ZZ Ceti11000-12000K
25000K Our question: where is the instabilty strip for accreting pulsators?
Step 1: Find some Accreting Pulsators
Cataclysmic Variables at quiescence
with very short ~80-90 min orbital periods
so accretion rate at a minimum 10-13 M/yr
90% of the optical light comes from the white dwarf
So it’s possible to detect white dwarf pulsations!
13 known accreting pulsators to date
Need:
It’s a short history (1998-2009):
GW Lib 76 17.0 650,370,230 Warner & van Zyl 1998
SDSSJ1610-01 81 19.0 609,347 I. Woudt & Warner 2004
SDSSJ2205+11 83 20.3 575,475,330 II. Warner & Woudt 2004
SDSSJ0131-09 82 18.5 595,335,260 II. Warner & Woudt 2004
V455 And (HS) 81 16.5 300-360 Araujo-Betancor et al. 2005
PQ And 81 19.5 634,1283 Vanlandingham et al,Patterson et al 2005
REJ1255+266 119 18.0 1344,1236,668 Patterson et al 2005
SDSSJ1514+45 19.7 559 IV. Nilsson et al 2006
SDSSJ1339+48 83 17.6 641 IV. Gansicke et al 2006
SDSSJ0745+45 86 19.1 1010,647 V. Mukadam et al 2007
SDSSJ0919+08 81 18.2 260 IV. Mukadam et al 2007
SDSSJ1507+52 67 18.3 1140,660,500 IV. Patterson et al 2008
SDSS0804+51 85 17.9 756 V. Pavlenko 2008
Porb (min) V (mag) Ppulse (sec) Ref
signature of pulsating, accreting WDs
Step 2: Get UV data
Ly region allows best T determination
Pulse amplitudes 6-17 x larger in UV
UV time-series spectroscopy Space Telescope Imaging Spectrograph (STIS) 1150-1750A with 1A resolution,
time-tag
HST Advanced Camera for Surveys (ACS)Solar Blind Channel (SBC) 1200-1900Å6-40A resolution, 1 min integrations
Co-added Spectrum & Light Curve
HST Programs 2002/2008
UV data on 9 so far
until SM4!
Ground data are necessary:
We need to know the optical state (to make sure object is at quiescence - HST insists)
Simultaneous UV & opt pulsation amplitudes are needed to determine the mode
HST Obs
AAVSO + help
HST picks week months in advance
AAVSO issues alert/web page ~ 2 wks-1 month before HST
AAVSO monitors
HST gives date/time 1 week prior to obs
ground obs 24 hr prior t akes halt off
HST observes with ground support
GW Lib Jan 17, 2002 STIS
V455 And Oct 24, 2002 STIS snap
SDSS0131 Jun 18, 2005 SBC
SDSS2205 May 23, 2005 SBC
SDSS1610 June 30, 2005 SBC
PQ And Sep 13 2007 SBC
SDSS0745 Nov 1, 2007 SBC
SDSS0919 Nov 14, 2007 SBC
SDSS1339 Jan 25, 2008 SBC
Object Date Instrument
fits with 2 component WD: 63% at 13,300K, 37% at 17,100Kfits with 2 component WD: 63% at 13,300K, 37% at 17,100K
STIS on GW Lib
16,500 WD model
Accretion disk
SBC Fit to HST spectrum of SDSSJ0745+45
10,000K WD
12,000K WD
15,000K WD
HST data SDSS0745
16,500KWD
SDSS data
UV + opt with WD models
V455 And = HS 2331+39
10,000K
20,000K
12,000K
11,000K
STIS + Calar Alto data on
1200 1600 18001400
HST data on
PQ And
SBC
SBC+opt+WD models
15000
12000
10000
12,000K
Temperatures from HST UV spectroscopySpectral Fits by Boris Gansicke Uncertainties ~ 1000K
GW Lib Jan17, 2002 STIS 15,400
V455 And Oct 24, 2002 STIS (snap) 10,500
SDSS2205+11 May 23,2005 SBC 15,000
SDSS0131-09 Jun 18, 2005 SBC 14,500
SDSS1610-01 Jun 30, 2005 SBC 14,500
PQ And Sep 13, 2007 SBC 12,000
SDSS0745+45 Nov 1, 2007 SBC 16,500
SDSS0919+08 Nov 14, 2007 SBC 13,500
SDSS1339+48 Jan 25, 2008 SBC 12,500
Object Date Instrument Temp (K)
SDSS1507+52 Littlefair et al 2007 eclipse phot 11,000
Latest ZZ Cet instability strip (Gianninas, Bergeron, Fontaine, 2009)
High mass DA WDs can get up to ~14000K
log g
Teff(K)
Is the T difference a Mass difference?
(Arras, Townsley & Bildsten 2006, ApJ, 643, L119)
Helium Abundance < 0.38 Instability Strip like ZZ Ceti stars @11000-12000K Helium abundance > 0.38
Additional instability strip @ 15000K
Helium Abundance > 0.48Strips merge into a wide strip 11000-16000K
Is the difference based on mass and evolution?
Is it a Composition Difference?
Past HST observations show CVs with WDs T’s that should place them in the instability strip but they don’t show pulsations
Of 7 WZ Sge stars with WD = 12-16000K, no obvious pulsations in EG Cnc, LL And, AL Com, HV Vir, WX Cet, VY Aqr, EF Peg
Is this lack of data or lack of pulsations?
Another part of the enigma:
STIS data on EG Cnc
T=12,300K WD
Szkody, Gansicke, Sion & Howell, 2002, ApJ, 574, 950
Optical data on SDSS 1339+48 - telescope and cadence matter
1.2m, 70s int
3.6m, 20s int
Further Clues come from the pulsation analysis...
The first 4 observations were classic cases:
UV periods same as optical
UV/opt amplitude ~ 6-17 as predicted by theory
GW Lib HST-STIS
Szkody, Gansicke, Howell, Sion 2002, ApJ
Orb 1
Orb 2
Orb 4
Orb 3
Szkody et al. (2007, ApJ, 658,1188)
P=214s
P=608s
P=576s
in 2005
DA model for log g=8
by Atsuko Nitta with
(Szkody et al. ApJ 658, 2007)
Teff = 14,500
Teff = 12,500
UV+optical data allow fit to mode
SDSS1610-01
608s pulsation
T from spectrum = 14,500K
Then it got complicated:
PQ And showed optical but no UV pulse
SDSSJ0745 and others showed no pulse in opt or UV!
1285s2337s
UV/Opt amplitude < 1! l=3?
GW Lib 650,370,230 650,370,230 6-17
SDSS0131 581,213,79 213 6
SDSS1610 608,221 608,221 6
SDSS2205 575,475,330 575 6
PQ And c 1263 none <1
SDSS0745 1166-1290 none
SDSS0919 260 none
SDSS1339 c 642 230,210 ?
V455 And c 419,336,310 No obs
SDSS1514 571 none
REJ1255+26 1344,1236,654,582 none <2
Object Opt Periods (s) UV Periods (s) UV/opt amp
Summary of Pulsations
Optical Data prior to HST on
Long Period Pulsator SDSS0745+4538
Light curves Fourier transforms
But in 2007:
Orb P
SDSS0745+4538
2005-2006 2007
30 Oct
31 Oct
1 Nov
2 Nov
6 peaks/ 7200 sec = pulsation 1.5 peaks/ 7200s = orbital
This accreting pulsator stopped pulsating between 2006 -2007!
No respectable ZZ Ceti stops pulsating! [Anjum]
The Catalina Sky Survey detected an outburst of SDSS0745+45 in Oct 2006 - did this matter?
BUT
Unknown SOB occurred
or
Accreting pulsators have changing temperature, mass, angular momentum & surface composition
???
We need long-term observations for each pulsator!
Possible Reasons for non-detection of pulsations:
GW Lib P = 650, 376, 236s
Long monitoring shows that amplitudes can change (Van Zyl et al 2004, MNRAS)
Patrick Woudt SAAO long term monitoring of pulsator SDSS0131From Szkody et al. ApJ 658, 1188, 2007
HST data June 2005 showed P=214s
214s
600s
335s
3 major questions:
1) where is the instability
strip for accreting
pulsators?
2) what are the affects of
accretion and outbursts?
3) is there any hope of
pulling out mass, spin, etc?
Known Outbursts of Accreting Pulsators:
• PQ And (1938, 1967, 1988)
• GW Lib (1983, 2007)
• V455 And (2007)
• REJ1255+26 (1994)
• SDSS0745+45 (2006)
• SDSS0804+51 (2006)
Pulsation Period: Means of measuring Teff ?
Mukadam et al. 2005
AAVSO data plotted by Matt Templeton
Apr12 07
more GALEX May, June 2008
May,June 07
GALEX
WIYN,APO May29,June 1 (387+/-5s? 19 mma)
ULTRACAM (Copperwheat et al. 2009)
GW Lib outburst
13 months past outburst
A new periodicity is apparent 1 yr after outburst
but not seen in UV ???
Before outburst: P=650, 370, 230s
After outburst: P=1145+/-3 s
Mar-June 2008
Copperwheat et al. 2009 MNRAS:
Mar-Apr 1154+/-10s
June 21 296s
1145s
CTIO 4m spectrum:
Tom Harrison Apr 2008
Boris fit:
Twd= 23,000K,
log g=8.46
Quiescent WD
T=15,000K
V~16.3
V
V455 And 2007-2009
AAVSO data plotted by Matt Templeton
Sept 07
V455 And
Pre SOB
Post SOB
spinpulse?
1 yr past outburst:
2 systems like this now known
Phot P ~ 43 minSpect P = 85 min
Spectra look like pulsators
0804+51
Pre-outburst photometry
Pavlenko Dec 2008 astro-ph
Feb 06
Oct 06
Feb 07
Jan 08 May 08
May 08
Oct 06
Feb 07
Pavelenko astro-ph 2008
Jan 08
Pulse P = 756s
Did this system move INTO the instability strip after outburst?
No pulsations in pre-outburst data
Past HST data
Model
10,500K WD
Maybe we can solve this in the next HST cycle with T, mass measurements
12500K
COS time for GW Lib (high T) and V455 And (low T)
3 major questions:
1) where is the instability strip for accreting pulsators?
2) what are the affects of accretion and outbursts?
3) is there any hope of pulling out mass, spin, etc?
Coordinated Campaign on SDSS1610-01 May 2007
Nice power spectrum but no additional pulsation periods!
If triplet is due to WD rotation :
P=4.8days!
van Zyl et al (2004) found similar result for GW Lib: splitting implied rotation P =7.3d!
other causes of splitting - magnetic field?
3 major questions:
1) where is the instability strip for accreting
pulsators? 11,000 - 16,000K
2) what are the affects of accretion and
outbursts?
pulsations disappear, mode splitting
3) is there any hope of pulling out mass, spin,
etc?
difficult - need many more modes and data
What remains to be done to make progress: Observationally:• find the rest of the pulsators (SDSSVI,VII, lit)• fill in the temperatures of the instability strip• monitor GW Lib and V455 And as WDs return to Tquies
• have more campaigns to look for multiplet structure
Theoretically:• find a way to make pulsations disappear
• explain fine structure in pulse
• include WD spin, composition in models
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