Cataclysmic Variables and Symbiotic Stars – Challenging Targets forSmall Telescopes

Laurits LeedjärvTartu Observatory, Estonialaurits.leedjarv@to.ee

Observing Techniques, Instrumentation and Sciencefor Metre-Class Telescopes September 23–26, 2013 Tatranská Lomnica

• Brief overview of CVs and SSs

• Some examples of light curves – what others have done

• Some examples of spectroscopic variations of SSs – own work

• What can be studied with small telescopes, what do not we know?

• Small optical telescopes are important, but …

Cataclysmic Variables (CV)

Close binary systems containing an accreting white dwarf (WD) primary andRoche-lobe-filling secondary (main sequence staror brown dwarf)

Orbital periods of CVs mostly between ~70 minutesand 7–8 hours, with a gap between 2–3 hours

Catalogue of Cataclysmic Binaries, Low-Mass X-Ray Binaries and Related Objects Ritter & Kolb 2003, A&A, 404, 301; update RKcat7.20, 1 July 2013contains 1094 CVs, 104 LMXBs, and 483 related objects.

Downes et al. 2001 (PASP, 113, 764), edition 2006 lists1600 CVs.

Recent sky surveys have revealed new CVs,for example:

SDSS – about 290 CVs (Szkody et al. 2011, AJ, 142: 181 and references therein; http://www.astro.washington.edu/users/szkody/cvs/index.html)

CRTS (Catalina Real-Time Transient Survey) – > 1000 CVs (including those discovered by SDSS)(Drake et al. 2009, ApJ, 696, 780; http://crts.caltech.edu)

CVs are classified into different types according to their variability and outburst characteristics:

Non-magnetic CVs

- classical novae

- recurrent novae (with a dwarf or giant secondary)

- dwarf novae (U Gem, Z Cam, SU UMa, SS Cyg type)

- nova-like CVs VY Scl stars AM CVn stars SW Sex stars

Magnetic CVs

- polars (AM Her stars)

- intermediate polars (DQ Her stars)

Symbiotic Stars (SS)

Interacting binary systems containing a white dwarf(usually accreting from stellar wind, sometimes via disk)and a red giant, in general not filling its Roche lobe.

Both stars are embedded into gaseous nebula, partlyionized by the hot component.

≥230 symbiotic stars knownA Catalogue of Symbiotic Stars Belczyński et al. 2000,A&ASS, 146, 407Corradi et al. 2010, A&A, 509, A41Miszalski et al. 2013, MNRAS, 432, 3186

Classification to S and D types

S (Stellar): normal M giant, orbital periods 200–2000(5700) days

D (Dusty): Mira type cool component, orbital periodsin tens of years

Yellow (S – without dust, and D’ – dusty): F, G or K type giant, orbital periods like in S-typeCarbon

Classification of SS based on the nature and variabilityof the hot component:

Classical (Z And type) SS - about 2–3 mag eruptions at irregular intervals (a few years)

Symbiotic novae - one about 6–10 mag outburst recorded

Symbiotic recurrent novae - repeating outbursts (~2–10 mag) at ~10–100 years intervals

Quiescent SS - no outburst related brightness variations

Some examples of CV light curves

Flickering of the peculiar VY Scl type CV MV Lyr

The eclipsing polar HU Aqr – CV with two planets!?

Examples of SS light curves

The prototype Z And

AG Dra

The peculiar SS CH Cyg

The eclipsing SS AR Pav

The symbiotic nova V1016 Cyg

Parimucha et al. 2002, A&A, 391, 999

Some examples of monitoring symbiotic stars atTartu Observatory

1.5-metre telescope, Cassegrain spectrograph

CH Cyg – non-typical symbiotic starBurmeister & Leedjärv 2009, A&A, 504, 171

Yellow symbiotic star AG Dra Leedjärv et al. 2004, A&A, 415, 273; Leedjärv & Burmeister 2012, Baltic Astr, 21, 131; Leedjärv et al. in preparation

Hβ and He II λ4686

AG Dra – relations between the U magnitude and strength ofthe emission lines

Z And – discovery of bipolar jets from the optical spectraSkopal & Pribulla 2006, ATel, 930; Skopal, Pribulla, Budaj et al. 2009, ApJ, 690, 1222; Burmeister & Leedjärv 2007, A&A, 461, L5

Disappearance of high-excitationemission lines during theoutburst of Z And in 2006

Astrophysical phenomena to be studied in CVs and SSs:

- Accretion disks (viscosity, angular momentum loss, disk instability, …)

- Physics of boundary layer

- Accretion from stellar wind

- Role of magnetic fields (accretion streams, columns etc)

- Thermonuclear burning on WD surface (thermonuclear runaways, nova and recurrent nova outbursts, “flashes” of symbiotic stars, …)

- Forming and accelerating bipolar jets

- Raman scattering on HI atoms

- Accretion induced collapse of WD → SN Ia

… … …

Different time scales involved:

Seconds to (tens of) minutes – flickering in CVs and (only a few) SSs: accretion disk ↔ boundary layer

Tens of minutes to hours – orbital motion in CVs,superhumps

Days to (tens of) years – recurrence of dwarf nova outbursts, superoutbursts, magnetic phenomena inmagnetic CVs; spectral variations of SSs

Hundreds of days to years – orbital motion in S-type SSs

Years to decades – outbursts of classical SSs

Decades – recurrent nova outbursts; orbital motions in D-type SSs

Hundreds to thousands of years (?) – symbiotic novaoutbursts

Thousands to tens of thousands of years – recurrence of classical nova outbursts

The brightest SSs have V ~ 7 mag, CVs ~10 mag

Variability on “human” time scales

⇓Ideal targets for metre-class telescopes,for long-term monitoring as well as for case studies(e.g. Doppler tomography, eclipse mapping)

Small telescopes can contribute into solving someopen questions related to CVs and SSs:

• Where are the “period bouncers” – CVs after reaching the period minimum at ~70 minutes, presumably evolving back to longer periods?

• Interplay of magnetic braking and gravitational radiation, causing the period gap?

• What is the physics of viscosity in accretion disks?

• What causes the low states of polars as well as novalike systems with orbital periods between 3 and 4 hours?

• What is the actual number density and distribution of CVs in the Galaxy?

• What is the nature and mechanism of ~2 – 3 mag outbursts of classical symbiotic stars?

• What is the role of RLOF and ellipsoidal variations in the mass transfer mechanism of symbiotic stars?

• Which symbiotic stars and under which conditions do emit collimated bipolar jets?

• Are symbiotic stars precursors of SN Ia?

• What is the total number of symbiotic stars in the Galaxy?

Some examples of organizations and campaigns contributing to CV and SS research with small telescopes

AAVSOAmerican Association of Variable Star Observerswww.aavso.org

WET

www.wholeearthtelescope.org

VSNET Variable Star Network

www.kusastro.kyoto-u.ac.jp/vsnet (in hibernation?)

ANS CollaborationAsiago Novae and Symbiotic Stars Collaborationwww.ans-collaboration.org

ANS Collaboration

Novae(?) Boundary layerHot spot and accretion columnsColliding winds in SSs

Accretion diskH burning WD Red giant in SSs

MS star or browndwarf in CVs

Gaseous envelopesof SSsRadio jets in SSsand CVs

Summary

Cataclysmic Variables and Symbiotic Stars deservecontinuous monitoring.Telescopes of 1–2 metre size with proper instrumentation are big enough for many purposes.

However, nature and behaviour of CVs and SSs can befully understood only if information across the wholeelectromagnetic spectrum is taken into account.

Thank you for attention!