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