Transient torus A unified after-AGB binary scenario?

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Transient torusA unified after-AGB binary
scenario?

1. Frankowski

Institut dAstronomie et dAstrophysique, ULB,
Brussels, Belgium
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SUMMARY

• The family of after AGB binaries
• The binary evolution channels
• Dynamical RLOF versus wind accretion
• no period gap a 20-yrs old problem!
• eccentric orbits at short periods
• New observational hints
• rapid rotation of the accreting companions
• circumbinary disks
• Quest for a binary channel avoiding the period gap

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1. The family of after AGB binary systems

binary evolution scheme
...all binaries in which at least one
component has gone through the AGB
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1. The family of after AGB binary systems

...includes several classes of
s-process-rich stars resulting from mass transfer
from a former AGB companion (now a white dwarf)
after AGB ? post-AGB!
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1. The family of after-AGB binary systems

is not confined to s-process-rich objects!
1. Post-AGB stars (some s-process-rich, not all!)
Dominik et al. AA 397, 595-609 (2003)
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1. The family of after-AGB binary systems

is not confined to s-process-rich objects!
1. Post-AGB stars (some s-process-rich, not all!)
2. Binary CSPNe
ionising UV
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1. The family of after-AGB binary systems

is not confined to s-process-rich objects!
1. Post-AGB stars (some s-process-rich, not all!)
2. Binary CSPNe
3. Red symbiotics with massive WD companions
(Mh gt 0.5Msun)
Tomov, 1995, MNRAS, 272, 189
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1. The family of after-AGB binary systems

is not confined to s-process-rich objects!
1. Post-AGB stars (some s-process-rich, not all!)
2. Binary CSPNe
3. Red symbiotics with massive WD companions
(Mh gt 0.5Msun)
4. Cataclysmic variables (some after AGB, not
all!)
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1. The family of after-AGB binary systems

is not confined to s-process-rich objects!
1. Post-AGB stars (some s-process-rich, not all!)
2. Binary CSPNe
3. Red symbiotics with massive WD companions
(Mh gt 0.5Msun)
4. Cataclysmic variables (some after AGB, not
all!)
Why some after AGB stars show peculiar
abundances while others do not?

• Partially solved, with the exception of
• why not all post-AGB are s-process-rich?
• why red symbiotics are not S stars?

Frankowski Jorissen 2007, BaltAstr 16, 104
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1. The family of after-AGB binary systems

is not confined to s-process-rich objects!
1. Post-AGB stars (some s-process-rich, not all!)
2. Binary CSPNe
3. Red symbiotics with massive WD companions
(Mh gt 0.5Msun)
4. Cataclysmic variables (some after AGB, not
all!)
Do we understand their orbital characteristics?
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2. Binary evolution channels
Catastrophic outcome generally associated with
mass transfer through RLOF from the more massive
AGB star with a deep convective envelope
After O. Pols, 2005
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3. Hard reality (or dynamical RLOF versus
wind accretion)
Post-AGB
S
S (large fM)
Ba
Ba (triple)
Frankowski, Ph.D. thesis, 2004
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Solutions proposed thus far

• How to avoid drastic CE orbit shrinkage
• CRAP (Companion-Reinforced Attrition Process)
• Tout Eggleton 1988, MNRAS 231, 823
• inhibits s-process pollution
• Diminished binding energy of the envelope
• Han et al. 1995, MNRAS 277, 1442
• Dewi Tauris 2000, AA 360, 1043
• is ionisation energy recyclable?
• Inclusion of tidal forces
• Karakas et al. 2000, MNRAS, 316, 689
• Pols et al. 2003, in Symbiotic stars probing
  stellar evolution, ASP Conf. Ser. 303, p. 293
• did not help
• Angular-momentum-balance-based CE instead of
  energy-based
• Nelemans et al. 2000, AA 360, 1011
• Nelemans Tout 2005, MNRAS 356, 753

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Solutions proposed thus far
How to stay eccentric

• Eccentricity pumping by a circumbinary disk
• Waelkens et al. 1996, AA 314, L17
• Artymowicz et al. 1991, ApJ 370, L35

• Periastron mass loss
• Soker, 2000, AA 357, 557

Dwarf Ba Post-AGB Ba
but only for detached systems!
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4. Observational hints
4.1 RS CVn and Ba (seemingly conflicting)
properties in the same object

• X-rays, Halpha emission typical of RS
  CVn
• fast rotation

- long orbital periods typical of Ba/symbio

• 56 Peg Frankowski Jorissen 2006, Observatory
  126, 25
• HD 165141 Jorissen et al. 1996, AA 306, 467
• d symbiotics Jorissen et al. 2005, AA 441,
  1135
• WIRRing stars Jeffries Stevens 1996, MNRAS
  279, 180
• Abell-35 CSPNe Thevenin Jasniewicz 1997, AA
  320, 91

Evidence for fast rotation, due to spin
accretion from wind Theuns et al. 1996,
MNRAS 280, 1264
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4. Observational hints
4.2 Circumbinary disks/waists/toruses,
bipolar outflows

• Bipolar PNe (also some ellipticals) the reason we
  are here
• V Hya (S) Knapp et al. 1999, AA 351, 97
• Gru (S) Sahai 1992, AA 253, L33
• Post-AGBs Van Winckel 2003, ARAA 41, 391

Dominik et al. AA 397, 595-609 (2003)
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4. Observational hints
4.3 New results on binarity of early M
giants from CORAVEL/ELODIE campaign
to monitor RV of Hipparcos survey stars

• binarity rate of 15
• e-log P diagram!
• Early M giant binaries share
• the tidal envelope of
• post-AGBs... do they just stay
• in place!?

Jorissen et al. 2007, in preparation
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4. Observational hints(stressed by
theoreticians!)
4.3 Pulsation, dust formation and
radiation-driven wind

• Reshaping of the Roche equipotentials
• Reduction of the effective gravity of the
  mass-losing star
• Jorissen 2003, AGB Stars, Springer, 461
• Schuerman 1972, ApSS 19, 351

Frankowski Tylenda 2001, AA 367, 513
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4. Theoretical hints

• 4.4 Role of a non-catastrophic RLOF mass transfer
• despite a deep convective envelope
• when the companion is massive enough (depleting
  the
• convective envelope eases the condition
  somewhat)
• Hjellming Webbink 1987, ApJ 318, 794
• possibility of L2/L3 outflows
• e.g. Podsiadlowski, Joss Hsu 1992, ApJ 391, 246

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5. The transient torus scenario - avoiding the
period gap

• Wind accretion
• an accretion disc is formed
• the companion is spun-up efficiently

• (Near) RLOF with
• substantial L2/L3 dusty outflows
• importance of wind acceleration zone

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5. The transient torus scenario - avoiding the
period gap

• Formation of a
• circumbinary torus
• radiation pressure acts
• on dust
• matter escapes through
• the vicinity of the outer
• Lagrangian point
• Fallback due to
• shadowing?

• Formation of
• a Keplerian disk from
• torus' leftovers
• pumping up the
• eccentricity

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5. The transient torus scenario - tidal effects
of the circumbinary disk
The most simplistic approach to the binary-disk
tidal interaction slowing down the stars at
apastron. Phase lag required for tidal
operation, so
vapgtVdisk This leads to a limiting eccentricity
of about 0.5-0.6. Disk mass 10-2 M? enough
for getting high eccentricities.
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5. The 'transient torus' -the effect on the
e-log P diagram
Placing the simple e limit on the e-log P
diagrams of after-AGB systems looks very
promising! Closer check assume that this disk
evolution follows the L2 outflow stage and
proceeds until the disk is pushed to a certain
distance.
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5. The transient torus scenario - at work
Post-AGB
S
S (large fM)
Ba
Ba (triple)
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5. The transient torus scenario - at work
1. Finally something that resembles the observed
e-log P diagram for post-AGB, Ba and related
stars! 2. s-process enriched and non-enriched
post-AGBs are naturally mixed, depending on
the TT timing and mass of the companion 3.
Smaller eccentricities of Ba stars possibly due
to a combination of primary's evolutionary
stage at TT, mass of the secondary and tidal
effects at secondary's ascent to RGB
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Summary

1. Attempt to understand the after-AGB binaries
   together, as sharing defining moments in life.
2. Various observational and theoretical hints led
   us to formulation of the 'transient
   torus' scenario.
3. Promising first results for the e-log P
   diagram of post-AGB, Ba and S stars!