Basics of Cataclysmic Variables

iPTF Summer School August 28, 2014

Paula Szkody U of Washington

A Cataclysmic Variable :

• is a close binary system

• has a white dwarf primary

• has a cool low mass secondary

• actively transfers mass

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]

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

Disk System Polar

Intermediate Polar

LARP

CV Types

Steve HowellSteve Howell

common envelope

Possible evolution paths

phase

Angular momentum losses

Pre-CV

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?

CVs mostly blue but color range too wide to find objects -- need color + variability + spectra to find true populations

SDSS showedSDSS showed::

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:

Summary of Variability and timescales for Interacting Binaries

Science from DN Outbursts

• Long term heating of WD

• Mass accreted

• Irradiation of secondary

• Disk heating and cooling

AAVSO

outbursts of SS Cygni

Dwarf novaeRepeated disk instabilityRepeated disk instability

.

Z Cam system

standstills

July 23

Short Porb, Low M Short Porb, Low M outburst ~ 1/20 yrsoutburst ~ 1/20 yrs

..

AAVSO data plotted by Matt Templeton

Apr12 07

GW Lib 2007outburst: amp ~ 9 mag

27 days

Return to quiescence at V=17 > 4 yrs

V1159 Ori

ER UMA Type Supercycles

Superhumps at SOB

ApJ, 1984, 282, 236

MRO MRO

NOFS

Tramposch et al. 2005, PASP 117, 262

P= 1.9 hr

Positive SH

Negative SH

quiescence

outburst

rise

Novalike systems with periods of 3-4 hrs

Honeycutt & Kafka, 2004, AJ, 128, 1279

Low states

Honeycutt, Turner

& Adams 2003

Roboscope

Totally Unknown: Long term variability

2 like this now known

SDSS1238:Phot P:40.25 min

Spect P:80.5 min

Long P: 8-12 hrs

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)

NOFS P=3.96hr

Eclipsing systems- WD goes behind M star

P=2.4hr

Hot spot

USNO

Eclipse of accretion column by M star Polar

SDSS1344+20 KPNO 2.1m 2011

PTF candidate magnetics (Margon, Levitan,Prince, Hallinan 2013 ASPCS)

Wickramasinghe & Ferrario 2000, PASP

B=30 MG

Theta= 90 deg

higher opt depth

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

Typical LARP B=60 MG, Mdot = 10-14 solar mass/yrApJ, 683, 967, 2008

Cyclotron harmonics result in strange colors

Finding LARPs is not easy -

Low Accretion Rate Polars as a function of magnetic field

Schmidt et al. 2005, ApJ, 630, 1037

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

• 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

Light curves & DFTs of accreting pulsator SDSS0745+45

SDSS finds 9/16 accreting pulsators

Mukadam et al. 2007 AJ

SH

pulse

FO Aqr Patterson et al. 1998 PASP Pspin= 21 min

Spin from Intermediate Polar

Science from Flickering

• Signature of active accretion (blobs?)

• Timescales of sec (Polars)

• Timescales of min (disk)

• Origin from spot, column or inner disk

Novalike LS PegNovalike LS Peg

Recurrent nova Recurrent nova (Dobratka et al. 2010)(Dobratka et al. 2010)

Flickering Examples

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

Examples from CSS

~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

unpredictability of CVs!Observe and enjoy the

szkody@astro.washington.edu