The Physics of Accreting White Dwarfs in Cataclysmic ... · White Dwarf Temperatures in the...

The Physics of Accreting White Dwarfs in Cataclysmic Variables:

Current Challenges

Edward M. SionDepartment of Astrophysics &

Planetary Science Villanova University

6/16/17 LANL Physics of White DwarfsPatrick Godon Paula SzkodyVillanova Univ. Univ.Washington

6/16/17 LANL Physics of White Dwarfs

Introductory Overview of Accreting White Dwarfs in Cataclysmic Variables (CVs)

Far UV Spectral Fitting Results

Observed Properties of CV White Dwarfs

Hydrodynamic Accretion Simulations of Boundary Layer Structure and Mixing into the White Dwarf Envelope

Surface Abundances, Temperatures and Rotational Velocities

---- Chemical Abundance Anomalies

---- Nitrogen to Carbon Ratio

----Heavy Nuclide Overabundances

----Diffusion Phenomena

Large HST Cycle 20 GO program and GAIA

Observed T_eff - < Mdot> / P_orb Distribution

Implications for Angular Momentum Braking Laws

Conclusions and Open Questions

Physical Processes in Isolated White Dwarfs

Thermal Cooling

Gravitational and Thermal Diffusion

Convection and Convective mixing and dredge-up

Radiative Levitation and Weak Winds

Accretion from Debris Disks and the Interstellar Medium

Core Crystallization


Sion,E.1985,ApJ,297,538 6/16/17 LANL Physics of White Dwarfs

Synthetic Spectra

• High Gravity LTE and NLTE Model Atmospheres (TLUSTY200, SYNSPEC98)

• Optically Thick, Steady State, Accretion Disk Models (TLUSDISK200)

• Accretion Belt Models

• Accretion Rings

• Accretion Curtain Models6/16/17 LANL Physics of White Dwarfs

Figure 6

Sion, E. M. et al. (2008), ApJ, 681, 543Teff + 41,000K +/-1000K


Figure 3

Sion, E. M. et al.(2008), ApJ, 681, 543


Teff = 34,000K +/- 1000K

Figure 1

Sion, E.M. et al. (2008), ApJ, 681, 543


Teff = 28,000K, Log g = 8.3

Godon, P. et al. (2008), ApJ, 679,1447SS Aur


U Gem White Dwarf


Non-Magnetic Cataclysmic VariablesTemperatures, Rotation Rates, Chemical Abundancesand Masses (Log g) of the Accreting White Dwarfs?

Rate of Angular Momentum Loss; Which Braking Law?

Origin of the N/C Abundance Anomaly? Formerly MoreMassive “Peeled Down” Donor Star, or the AccretingWhite Dwarf?


Are Non-Magnetic CVs SN Ia Progenitors, i.e. do the WD masses increase or decrease with time?

Magnetic Cataclysmic Variables

Intermediate Polars

Magnetic Field Strengths

White Dwarf Temperatures in the accretion capsand outside the accretion caps

Accretion Rates onto the magnetic white dwarf

Lateral and Radial Diffusion of accreted matter into themagnetic white dwarf

Identity of magnetic CV white dwarf progenitors


Polars


V = 3350 km/s; log g = 6, emitting area and flux contributionVW Hyi 11% and 16%, respectively.

1996, ApJL, 471, L41


Balsara, D., Fisker, J., Godon, P., Sion, E.2009, ApJ, 702, 1536

Hertzfelder,M. \& Kley,W.2017, A\&A,in press (arXiv:1705.07658)

Structure of the 2D BL poorly understoodStructure depends on M_wd, V_rot, MdotThe BL is only ~ 1% of the WD radius

For high Mdot (Mdot > 10^-10 Msun/yr)Steep drop in velocity; Heavy depletion of mass; T = 500,000K; optically thick; Soft and Hard X-ray and UV emission.

The gas spreads rapidly toward the poles or is halted at a certain latitude.The extent of the mixing with the star depends on stellar rotation and viscosity

For low Mdot (< 10^-10 Msun/yr), the BL is optically thin and reaches T= 10^8 K

Balsara, D., Fisker, J., Godon,P., Sion,E. 2009,ApJ, 702, 1536


6/16/17 LANL Physics of White DwarfsHertzfelder, M.\& Kley,W.2017, A\&A, in press

IP Peg DN 1.16 ± 0.02 E

GY Cnc DN 0.99 ± 0.12 E

U Gem DN 1.14 ± 0.07 S

AM Her Polar 0.88 S

SDSS1035+05 DN 0.94 E

SDSS1006+23 DN 0.78 ± 0.12 E

SDSS1702+32 DN 0.94 E

SDSS0926+36 AMCVn 0.84 E

MR Ser Polar 0.71 S

QQ Vul Polar 0.70 S

OY Car DN 0.69 E

HT Cas NL 0.61 E 6/16/17 LANL Physics of White Dwarfs

Z Cha DN 0.54 E

OU Vir DN 0.89 E

DQ Her Nova 0.60 ± 0.07 E

WZ Sge DN 0.85 S

EX Dra DN 0.75 ± 0.02 E

V347 Pup DN 0.63 ± 0.04 E

EM Cyg DN 1.13 ± 0.08 E

AC Cnc NL 0.76 ± 0.03 E

V363 Aur NL 0.90 ± 0.06 E

QS Vir DN 0.78 S

ST LMi Polar 0.76 S

Southworth, J. et al.2009, A\&A, ; Sion,E., \& Szkody, P.2011, White Dwarfs, in press 6/16/17 LANL Physics of White Dwarfs

Object Type Porb Abundance

GW Lib DN 76.8 Z ~ 0.1

BW Scl DN 78.2 Al 3.0±0.8, rest 0.5±0.2

LL And DN 79.2 Z ≤ ~1

WZ Sge DN 81.6 C 0.5, Fe 0.1, S 0.1, Si 0.005

AL Com DN 81.6 Z ~ 0.3

SW UMa DN 81.8 Al 1.7±0.5, rest 0.2±0.1

H V Vir DN 83.5 Z ~ 0.3

WX Cet DN 83.9 Z ~ 0.1

EG Cnc DN 86.4 Z ~ 0.3

BC UMa DN 90.2 Al 2.0±0.5, rest 0.3±0.1

VY Aqr DN 90.8 Si 0.05, C 1.0

EK Tra DN 91.6 Z < 1


Object Type Porb Abundance

VW Hyi DN 106.9 Si 0.3, C 0.3, N3, O 3, Al 2, P 20, Mn 50

EF Peg DN 123 Z ~ 0.1-0.3

MV Lyr NL 191.0 C0.5, N 0.5, Si 0.2

DW UMa NL 198.0 Z ~ 0.47

WW Ceti DN 253 C 0.1. N 2, Si 0.3

U Gem DN 254.7 C 0.3 - 0.35, N 35 - 41, Si 1.4 - 4, 6.6 – 10

SS Aur DN 263.2 C 0.1, Si 0.1, N 2.0

RX And DN 302.2 C 0.05, Si 0.1

RU Peg DN 539.4 C 0.1, Si 0.1, N ~ 8

BV Cen DN 878.6


Object Type Porb Vsini

EF Peg DN 123 < 300

MV Lyr NL 191.0 200

DW UMa NL 198.0 370

VW Ceti DN 253 600

U Gem DN 254.7 150

SS Aur DN 263.2 400

RX And DN 302.2 500

Z Cam DN 417.4 330

RU Peg DN 539.4 100


The suprasolar abundances of metals with A > 20 must originate in the white dwarf but either the large N/C in the mass transferring donor originates from peeling down to the CNO processed core of aformerly more massive secondary or the large N/C as well as the Al and P are the result of contamination of the secondary by the products of explosive CNO burning during the "common envelope" stage of a nova outburst.

The S-type symbiotic RW Hya contains a hot WD with Teff = 160,000K burning H in a steady state with the rate of accretion. This is the first confirmation, using brute force NLTE model atmospheres, of the high temperatures derived for the hot components of symbiotics by modified Zanstra methods.

Conclusions



Numerical evaluation of energy equation below, term by term, reveals that theenergy in consequence of shear mixing competes with the photon luminosity during long-term accretion leading to a nova.

Hydrodynamic simulations must be carried out to assess how the accretedmaterial mixes with the stellar envelope and affects the onset of a thermonuclearRunaway. Is there mixing by shear turbulence? (e.g.Sparks and Kutter 1987, ApJ


WZ Sagittae, P_orb = 81 min.


Sion, E.M.et al.1995, ApJ, 439, HST FOS spectra

The WD in WZ Sge has Teff = 14,900K, Log g = 8All other metals between 0.1 and 0.001 solarDiffusion timescales for 0.6 Msun and 1.0 Msun are 2.7 days and 0.7 days, respectively

(Paquette et al.1986, ApJS, 61, 167)

Cheng et al.1997, ApJL, 484, L149HST GHRS spectraV_rot sin i = 1200 km/s +300/-400 km/s

Steeghs, D. et al.2007, ApJ, 667, 442 HST STISEinstein Redshift0.85 +/- 0.04 Msun


Diffusion timescale for C in a H-rich WDPaquette et al.1986, ApJS, 61, 1972.7d & 0.7d for 0.6 and 1.0Msun, resp.

The NV emission is typically very strong and the CIV emission is very weak or absent.

Enhancement of nitrogen and depletion of carbon is the hallmark of CNO processing.

~10% of the cataclysmic variables (CVs) reveal large abundanceratios of nitrogen to carbon, most commonly from the ratio of intensities of NV (1238, 1242) to CIV (1548, 1550) resonance doublet emission lines in the far ultraviolet (G¨ansicke et al. 2003).

The emission lines almost certainly arise from theaccretion disk (or boundary layer) that forms when the Roche-lobe filling donor secondary transfers gas to the white dwarf primary star.

The N/C abundance anomaly has also been seen in magnetic CVs such as AE Aqr (Mouchet et al. 2003), BY Cam (Mouchet et al.2003), V1309 Ori (Szkody & Silber 1996) and MN Hya (Schmidt & Stockman 2001)

The N/C Abundance Inversion in Cataclysmic Variables


Origin of the N/C Abundance Anomaly? A Formerly More Massive “Peeled Down” Donor Star AND/OR the Accreting White Dwarf?

A nova explosion involves the dynamical ejection of the accreted layers and a “common envelope” phase consisting of remaining gas that did not achieve escape and either envelops the entire binary or remains as an extended atmosphere supported by the continued stable H-burning on the plateau branch near L_edd.

Accretion of CNO-processed material by the secondary during the dynamical nova shell ejection is probably minimal. However, during the “common envelope” stage, the accretion of CNO-processed materialmay be appreciable (Sion \& Sparks 2014, ApJL, 796, L10)


Does the large N/C in the mass transferring donor originate from peeling down by mass transfer into the CNO processed core of a formerly more massive secondary?

.

6/16/17 LANL Physics of White Dwarfsara, M., Sion, E. \& Godon, P.2017, ApJ, in preparation


Sion, E.1995, ApJ, 438, 876

(But see Balman, Godon \& Sion.2014, A\&A, 572, 114)

Boris T. Gaensicke Univ.Warwick, Klaus Beuermann Univ. Gottingen, Lars Bildsten Univ.California - Santa Barbara, Domitilla De Martino Osservatorio Astronomico di Capodimonte, Patrick Godon Villanova Univ., Arne A. Henden AAVSO, Ivan Hubeny Univ. Arizona, Christian Knigge University of Southampton, Knox S. Long STScI, Thomas R. Marsh, Univ. Warwick,Joseph Patterson, Columbia Univ., Matthias Schreiber,Univ.Valparaiso,Edward M. Sion Villanova Univ., Paula Szkody Univ.Washington,DeanTownsley Univ.Alabama, Monica Zorotovic, Univ.Valparaiso

HST Cycle 21 Large GO Project: B.Gaensicke, PI

48 Cataclysmic Variables of all sub-classesSeveral Eclipsing CVs => Accurate MassesMany Sub-gap systems (SU UMa’s, poss. Post-bouncers)A Number of CVs above the gap (U Gems, N-L)

6/16/17 LANL Physics of White DwarfsPala, A.et al.2017, MNRAS, 456, 2855

--The surface temperatures, chemical abundances, rotation rates and accretion ratesonto the hot accreting WD components are being secured in a wide variety of interacting binaries spanning the range of orbital periods from hundreds of days (Symbiotics) down to orbital periods of minutes (AM CVn Systems).

--CV White Dwarfs above the period gap are hotter than the ones below the period gap

--Magnetic CV White Dwarfs are cooler than Non-Magnetic CV White Dwarfs at agiven orbital period.

--CV White Dwarfs rotate much faster than single white dwarfs but not as fast as expected from the accreted angular Momentum during the lifetime of the CV.

--CV White Dwarf masses appear to be higher below the period gap than the WD masses above the period gap (Zorotovic et al.2011, ApJ).

~10% or more of CVs reveal the N/C abundance anomaly. For at least some of theCVs the C/N anomaly and suprasolar abundances of A > 20 nuclides (e.g. Al, P) imply their origin from Explosive Thermonuclear Burning, then contamination of the donor starduring the common envelope phase of the nova, followed by re-accretion by the White

Dwarf (Sion and Sparks, 2014, ApJL).

CONCLUSIONS


OPEN QUESTIONS Do CVs really evolve across the period gap or are there two distinct populations of

CVs, one above the period gap and one below the period gap?

Do CV white dwarf masses increase, stay the same, or decrease with time?

Are H-rich CVs with near-Chandrasekhar mass WDs the single degenerate pathwayType Ia supernovae?

2D and 3D radiation hydrodynamic simulations of accreting gas flows INTO the WD envelope are badly needed. Does shear mixing occur?

What is the evolutionary status of the Nova-like Variables?

What is the correct angular momentum braking law for CVs above the period gap?

Are the CNO-processed abundances due to core material from the donor or contamination of the donor star due to TNR burning on the white dwarf?


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