Hightime domain astrophysics:

1
High-time domain astrophysics SALTICAM and
cataclysmic variables Patrick A. Woudt and Brian
Warner (University of Cape Town)

• Rapid variability in cataclysmic variable stars
• dwarf nova oscillations, quasi-periodic
  oscillations, non-radial pulsations,
• white dwarf rotation periods, (exploration of
  new time domain)
• SALTICAM/SALT
• lessons learned from performance verification
  observations
• High-speed spectroscopy of cataclysmic variable
  stars
• EC2117-54

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Rapid variability in cataclysmic variable
stars a variety of physical phenomena

• Origin of observed rapid variability
• (rapid ? periodicity of few tens of seconds to
  few minutes)
• orbital variation (ES Cet 620 s)
• AM CVn ultracompact binaries
• WDWD binaries
• rotation of the white dwarf (DQ Her 71.07 s)
• related dwarf nova oscillations
• (rotating equatorial belt on WD)
• (VW Hyi 14 40 s)
• pulsations of the white dwarf
• (GW Lib 237 s, 390 s, 650 s)
• non-radial pulsations DA WD instability strip
• DB WD instability strip AM CVn binaries
• radial pulsations?

3
Rapid variability in cataclysmic variable
stars a variety of physical phenomena and their
relevance

• Origin of observed rapid variability
• (rapid ? periodicity of few tens of seconds to
  few minutes)
• orbital variation (ES Cet 620 s) Sources of
  gravitational
• AM CVn ultracompact binaries wave radiation
  (e.g. LISA)
• WDWD binaries Nelemans et al. (2004)
• rotation of the white dwarf (DQ Her 71.07
  s) Physics of accretion onto
• related dwarf nova oscillations compact
  objects (WD and
• (rotating equatorial belt on WD) NS or BH).
• (VW Hyi 14 40 s)
• pulsations of the white dwarf Astroseismology
  of WDs
• non-radial pulsations Mass determination of
• DA/DB WD instability strip WD and accreted
  H-layer.
• Nova/supernova models.
• radial pulsations? Townsley et al. (2004)

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Rapid variability in cataclysmic variable
stars an overview of all our ( UCT) SALTICAM
observations to date
SALTICAM/SALT high-speed photometry of
cataclysmic variables VW Hyi (DN) 09/12/2005 ?
4129 s 80 ms 6x6 (WL) DNOs V 12 - 13
mag 18/12/2006 ? 6810 s 80 ms 6x6
(WL) DNOs SDSS0131 (CV/ZZ) 02/09/2005 ? 100
ms 6x6 (WL) no short V 18.3 mag
(faint) 06/09/2005 ?/? 432 s 100 ms 6x6 (WL)
periodicities GW Lib (DN CV/ZZ)
12/ 13/04/2007 ? on bad column V 9 18
mag 14/04/2007 ? 4000 s 300 ms 2x2
(U) outburst 15/04/2007 ? 2094 s 300 ms 2x2
(U) outburst 25/ 26/05/2007 ? 3151 s
3 s 4x4 (U) faded 27/05/2007 ? 3 s
4x4 (U) faded V368 Ser (CV/ZZ) 13/05/2007 ?
cloudy 3 s 4x4 (B) clear
non-radial a.k.a. SDSS1610 15/05/2007 ? 2 x
2640 s 3 s 4x4 (B) pulsations V 19.1
mag 17/05/2007 ? 5153 s 10 s 4x4 (B) int.
campaign ES Cet (AM CVn) 09/09/2005 ? 1200
s 100 ms 6x6 (WL) cloudy V 16.9
mag 11/09/2005 ? 2377 s 100 ms 6x6 (WL) good
S/N 13/01/2007 ? 3240 s 150 ms 4x4 (WL) good
S/N ? cloudy or poor data ? good data
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Rapid variability in cataclysmic variable stars
VW Hydri dwarf nova oscillation (DNO) /
quasi-periodic oscillation (QPO)
Low Inertia Magnetic-Accretor (LIMA) model of
dwarf nova oscillations magnetically-controlled
accretion onto a rapidly rotating equatorial
belt. (Warner Woudt 2002) Extention to lower
magnetic field strengths of the
intermediate polar model.
DNOs and QPOs in VW Hyi Woudt Warner (2001)
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Rapid variability in cataclysmic variable stars
VW Hydri dwarf nova oscillation (DNO) /
quasi-periodic oscillation (QPO)
V 13.3 mag, Filter white light, Binning
6x6, Texp 80 ms Photometry 2.5 pix aperture
correction (relative)
DNO behaviour in VW Hyi is predictable
(unusual). Excellent ToO target for
SALT
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Rapid variability in cataclysmic variable stars
VW Hydri dwarf nova oscillation (DNO) /
quasi-periodic oscillation (QPO)
V 13.3 mag, Filter white light, Binning
6x6, Texp 80 ms Photometry 2.5 pix aperture
correction (not relative photom.)
Small part of SALTICAM light curve of DNOs in VW
Hyi (P 25.6 s)
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Rapid variability in cataclysmic variable stars
VW Hydri dwarf nova oscillation (DNO) /
quasi-periodic oscillation (QPO)
V 13.3 mag, Filter white light, Binning
6x6, Texp 80 ms Photometry 2.5 pix aperture
correction (relative)
P 25.6 s
P 27.65 s
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Rapid variability in cataclysmic variable stars
ES Ceti ultracompact binary
V 16.9 mag, Filter white light, Binning
6x6, Texp 100 ms Photometry 2.5 pix aperture
aperture correction (IRAF)

• Shortest period binary known
• (Warner Woudt 2002)
• Search for short periodicity
• (pulsation / rotation)
• ? no signal found.

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Rapid variability in cataclysmic variable stars
V368 Serpenti non-radial pulsations part I
Light curve and FT of V368 Ser with SAAO 74-in
UCT CCD (Woudt Warner 2004)

• Around-the-world campaign
• on V368 Ser including
• SALTICAM in May 2007
• Two nights of high-speed
• photometry with SALTICAM
• Hints of signals at short periods,
• confirmation will need to
• come from 24-h round-the-world
• continuous observations.
• Needs large telescopes due to
• faintness of source (V 19 mag)

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Rapid variability in cataclysmic variable stars
V368 Serpenti non-radial pulsations part I
15 May 2007 (3 s)
B 19 mag, Filter B band, Binning 4x4, Texp
3 s Photometry 3.5 pix aperture aperture
correction (IRAF)
17 May 2007 (10 s)
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Rapid variability in cataclysmic variable stars
GW Librae non-radial pulsations part II
First (?) and last (?) image of a 0.6-hr track on
GW Librae during outburst (HJD 2454206.65)
V 9 mag, Filter U band, Binning 2x2 (?
4x4), Texp 300 ms

• First cataclysmic variable in which the white
  dwarf primary resides in the white
• dwarf instability strip (an accreting WD with ZZ
  Ceti pulsations)
• 1983 outburst (erroneously classified as nova),
  second outburst in April 2007
• ? opportunity to study the effects of a DN
  outburst on the pulsation
• frequencies (Warner van Zyl 1998).
• ? change in Teff of WD is likely to
• alter pulsation frequencies
• multi-periodic non-radial pulsations
• at 230 s, 370 s and 650 s
• (unresolved multiplets)
• van Zyl et al. (2004)

GW Librae in outburst (April 2007, AAVSO)
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Rapid variability in cataclysmic variable stars
GW Librae non-radial pulsations part II
First (?) and last (?) image of a 0.6-hr track on
GW Librae during outburst (HJD 2454206.65)
V 9 mag, Filter U band, Binning 2x2 (?
4x4), Texp 300 ms
8 pixel aperture (best S/N) 2.5 pixel
aperture 2.5 pixel aperture aperture correction
Peaks at 680 s and 450 s (pulsations or QPOs ?)
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Rapid variability in cataclysmic variable stars
AM CVn co. non-radial pulsations part III
Roelofs et al. (2005)
Szkody et al. (2002)
DA white dwarf primaries in hydrogen transferring
CVs (?) DB white dwarf primaries in
helium transferring binaries (AM CVn systems)
? Non-radial pulsations in accreting DB white
dwarfs. Higher Teff for instability strip
(22.000-28.000 K vs. 11.300-12.500 K,
respectively). AM CVn with DB approximately in
right Teff regime not yet explored for
non-radial pulsations! However, these objects are
extremely faint (V 21 mag).
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Rapid variability in cataclysmic variable
stars lessons learned from SALTICAM observations
? Scheduling very flexible, excellent for ToO
observations ? Exposure times as low as 80
milliseconds (stable long light curves) ?
45.000 fits images per 1 hr of observations ? No
ultra-short periodicities (subsecond to a few
seconds) in any of our targets ? SALTICAM is
great for high-time resolution studies of
ultracompact binaries ? SALTICAM data
reduction pipeline ? IRAF interface very slow
(better now in pyraf) ? Standard photometry
pipeline highly desirable / necessary (SALT
data product?) ? 1-s SALTICAM clock setting
(hardwired?) leaves strong imprint in FT ? IRAF
conversion of UT to HJD has nasty round-off error
(source of spurious signals in FT)
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High-speed spectroscopy of cataclysmic variables
EC 2117 dwarf nova oscillations

• Photometry with the SAAO 74-in ( UCT CCD)
• V-band photometry
• texp 6 seconds (continuous frame-transfer
  mode)
• online reduction confirmed presence of DNOs,
  lpDNOs and QPOs
• ? trigger SALT observations
• SALT spectroscopy ( RSS)
• windowed and binned (2x2) ? read-out time 5
  seconds
• texp 5 seconds

V-band photometry of EC2117-54 obtained on
17/08/2006
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17 August 2006 (SALTRSS spectroscopy)

• 334 spectra obtained of
• EC 2117-54 over a period of
• 3729 seconds
• EG21 observed as spectro-
• photometric standard
• Used IRAF for extraction,
• wavelength and flux calibration
• Magnitude determined from
• 2nd CCD used to calibrate
• spectra with 74-in data
• photometry.
• (V-band ?c5483 Å, ??831 Å)

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• Some lessons learned (NB data analysis is still
  ongoing!)
• High speed spectroscopy with SALT looks very
  promising!
• Preset gain setting for the FAST/BRIGHT read-out
  mode of RSS results in
• significant discontinuities across 6 read-out
  parts of the 3 CCDs.
• ? solved this by using relative gain settings
  (determined from the EG21
• spectrophotometric standard). Could not use the
  flat fields for this as
• read-out sections 4,5 and 6 were saturated.
• Some programmes benefit enormously from
  simultaneous photometry

Data product of the standard pipeline. For the
improved data product using relative gain
settings see spectrum on page 3
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• Publications of SALT data on related
  observations
• Discovery of first pulsating sdO star
  (spectroscopic confirmation with SALT)
• SDSS J160043.6074802.9 a very rapid sdO
  pulsator
• Woudt, P.A., Kilkenny, D., Zietsman, E., et al.
  2006, MNRAS 371, 1497-1502
• High-speed photometry of VW Hyi (SALTICAM
  high-speed photometry)
• A Cataclysmic Key Program for SALT
• Warner, B. 2006, South African Journal of Science
  102, 120-124
• Student involvement
• Mr. Ewald Zietsman (MSc NASSP)
• works on the SALT/RSS spectra of EC 2117-54