Download - Basics of Cataclysmic Variables iPTF Summer School August 28, 2014 Paula Szkody U of Washington
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Basics of Cataclysmic Variables
iPTF Summer School August 28, 2014
Paula Szkody U of Washington
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A Cataclysmic Variable :
• is a close binary system
• has a white dwarf primary
• has a cool low mass secondary
• actively transfers mass
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Types of cataclysmic variables:
• [Nova]
• Dwarf nova (U Gem, Z Cam, SU UMa, WZ Sge, ER UMa)
• Novalike (UX UMa, SW Sex, V Sge, Polar, IP)
• AM CVn
• [Type Ia SN, Symbiotic star]
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DISK ACCRETION MAGNETIC
High M Low M
. .
X-rays
108 K
9000-4000 K
ACCRETION
BL
For slowly rotating WD:
Ldisk = LBL = 1/2GMMwd/Rwd
.
Hard X-rays
Soft X-rays
Cyclotron
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Disk System Polar
Intermediate Polar
LARP
CV Types
Steve HowellSteve Howell
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common envelope
Possible evolution paths
phase
Angular momentum losses
Pre-CV
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Model of CV PopulationHowell, Nelson, Rappaport 2001, ApJ, 550
Log number of CVs
Population models
PG, Hamburg
SDSS.
Magnetic braking
g radiation
Where are detached magnetic WDs + M stars?
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CVs mostly blue but color range too wide to find objects -- need color + variability + spectra to find true populations
SDSS showedSDSS showed::
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CVs in SDSS
2000-2008
Szkody et al. AJ
2002-2011
Papers I-VIII
Need lots of follow-up spectra for ID and properties!
What we learned from SDSS:
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Summary of Variability and timescales for Interacting Binaries
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Science from DN Outbursts
• Long term heating of WD
• Mass accreted
• Irradiation of secondary
• Disk heating and cooling
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AAVSO
outbursts of SS Cygni
Dwarf novaeRepeated disk instabilityRepeated disk instability
.
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Z Cam system
standstills
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July 23
Short Porb, Low M Short Porb, Low M outburst ~ 1/20 yrsoutburst ~ 1/20 yrs
..
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AAVSO data plotted by Matt Templeton
Apr12 07
GW Lib 2007outburst: amp ~ 9 mag
27 days
Return to quiescence at V=17 > 4 yrs
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V1159 Ori
ER UMA Type Supercycles
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Superhumps at SOB
ApJ, 1984, 282, 236
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MRO MRO
NOFS
Tramposch et al. 2005, PASP 117, 262
P= 1.9 hr
Positive SH
Negative SH
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quiescence
outburst
rise
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Novalike systems with periods of 3-4 hrs
Honeycutt & Kafka, 2004, AJ, 128, 1279
Low states
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Honeycutt, Turner
& Adams 2003
Roboscope
Totally Unknown: Long term variability
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2 like this now known
SDSS1238:Phot P:40.25 min
Spect P:80.5 min
Long P: 8-12 hrs
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Science from Orbital variations• Eclipsing systems enable photometric model
• Can detect eclipse of disk, hot spot, WD
• Can parameterize accretion area in magnetic systems
• Porb (1.2-10 hrs) allows population, evolution study
Requires high time resolution (eclipses <15 min)
~30% of disk systems show orbital variations (spot);
100% of polars (amplitudes of 0.1-4 mags)
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NOFS P=3.96hr
Eclipsing systems- WD goes behind M star
P=2.4hr
Hot spot
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USNO
Eclipse of accretion column by M star Polar
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SDSS1344+20 KPNO 2.1m 2011
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PTF candidate magnetics (Margon, Levitan,Prince, Hallinan 2013 ASPCS)
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Wickramasinghe & Ferrario 2000, PASP
B=30 MG
Theta= 90 deg
higher opt depth
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TiO
cyclotron harmonics
Szkody et al. ApJ, 583, 902, 2003
WD Temp = 5000-8000K
7/9 LARPs found in SDSS
B ~ 60 MG
T < 1keV
M~10-14M /yr
P=4.4 hrs
D=100pc
.
34
MQ Dra
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Typical LARP B=60 MG, Mdot = 10-14 solar mass/yrApJ, 683, 967, 2008
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Cyclotron harmonics result in strange colors
Finding LARPs is not easy -
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Low Accretion Rate Polars as a function of magnetic field
Schmidt et al. 2005, ApJ, 630, 1037
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Science from Pulsations, Spins
• 16 White Dwarfs in Instability Strip• Periods about 2-20 min• Amplitudes < 0.1 mag• Gives info about WD interior
Pulsations
Spins• Magnetic White Dwarfs • Periods 10 - 60 min (IP), hrs (polars)• Amplitudes 0.01-0.5 mag• Gives info on magnetic field
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• 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
Spherical gravitational potential Spherical electrostatic potential
l determines the number of borders between hot and cool zones on the surface m is the number of borders that pass through the pole of the rotation axisk determines the number of times the pulsation wiggles from the center to the surface
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Light curves & DFTs of accreting pulsator SDSS0745+45
SDSS finds 9/16 accreting pulsators
Mukadam et al. 2007 AJ
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SH
pulse
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FO Aqr Patterson et al. 1998 PASP Pspin= 21 min
Spin from Intermediate Polar
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Science from Flickering
• Signature of active accretion (blobs?)
• Timescales of sec (Polars)
• Timescales of min (disk)
• Origin from spot, column or inner disk
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Novalike LS PegNovalike LS Peg
Recurrent nova Recurrent nova (Dobratka et al. 2010)(Dobratka et al. 2010)
Flickering Examples
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What we learn from CV variability : • flickering - info on accreting blobs
• pulsations - info on interior of WD, instability strip for accretors
• spin timescale of WD - info on mag field
• orbital variations - info on WD, spot, evolution
• outbursts - info on long term heating
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Examples from CSS
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~1000 potential CVs in CRTS(Drake et al.; Breedt et al. 2014 MNRAS)
• Only ~200 confirmed by spectra
• Most are short P (low M transfer)
• Most are dwarf novae
• Most in thick disk