The Elusive Nature of (early) R-stars

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The Elusive Nature of (early) R-stars
Inma Domínguez
Tangata L. Piersanti O. Straniero (INAF-OACT)
C. Abia O. Zamora (UGR) R. Cabezón D.
García-Senz (UPC)
10th Torino Workshop on AGB
Nucleosynthesis from Rutherford to
Beatrice Hill Tinsley and beyond
January, 25-29, 2010 Chistchurch, New Zealand
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Observed properties

• Low Luminosities LC(N) / 10
• Teff 3800 4600 K
• C(N) ? 3500 K

R-cool
R-hot
Not on the AGB ? Core He-burning ?
NIR
C(N) R-cool

• Not in Binary systems
• McClure 1997

(30 of ? in binaries)
? Previous merger
R-hot
Zamora et al. 2009
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• Chemical properties

M/H 0 ? - 0.77 C/O 0.8 ? 3 12C/13C
5 ? 20 N/Fe 0.1 ? 1 ?(Li) 0.5 ? 1 No
s-elements enhancement No evidence of
O-depletion
R-hot
Li
R-hot
R-cool
R-cool

• He-burning CN cycle

Zamora et al. 2009
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• Chemical properties

Dominy 1984
Zamora et al. 2009

• Peculiar He-flash in a low mass RG ?
• Peculiar mixing

But NOT in the standard He-flash !!
Most ? do not modify their surface composition
at the He-flash
Dearborn et al. 2006 Lattanzio et al. 2006 Mocak
et al. 2008-2009
Confirm by 3D HYDRO
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Carbon D-up
Like 3-Dup / H-shell extinguishes
X neutrinos
ad hoc
0.4 M?
0.4 M?
Angelou Lattanzio 2008
Time
Paczynski Tremaine 1977
Increasing core-cooling by axions
Domínguez et al. 1999 Increasing
core-cooling by neutrinos
But All ? !!
12C/13C ? !!
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Internal rotation in low mass stars
Mengel Gross, 1969
A series of flashes occurring progressively
closer to the center
NO MIXING
Mfl ? w
min
for w 0.16 rad/s NO mixing !!
Merger ? Rotation
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Merger scenario binary synthesis population
Izzard et al. 2007
Number and location in the Galaxy of observed
R-stars
Dominant channel at M/H 0 ? RG
He WD

• Very common in nature
• Not studied in detail before

2 He WDs Iben 1990 (no rotation) Guerrero et
al. 2004 (SPH)

• Merging ? Rotation
• ? Different physical structure !!

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Selecting the models
RG He WD (70 )
MRGcore
77
23
too luminous !! (core mass ?)
Izzard et al. 2007
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Numerical Simulations
Phases in the merging scenario

• Coalescence Common envelope phase
• Merging itself Accretion disk around
  degenerate core
• Accretion Mass deposition onto the He core

• 3D Hydrodynamical simulations - SPH Merging
• FRANEC structures accretion phase
  evolution

MRG 1.4 1.3 1.2 MRGcore
0.19 0.20 0.17 MWD 0.2
0.15 0.38 Mfin 0.76 0.75
0.78 Mcore 0.5 0.36 0.55 A
(R?) 20 20 16
masses in M?
Coalescence (Population Synthesis)
Piersanti et al. 2010 (submitted)
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MWD 0.15 M? MRG_core 0.2 M?
SPH RG 50000 WD 37000 resolve 104 in ?
SPH based on Monaghan 2005
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• High accretion rates 10-6 - 10-4 M?
  /second

• High angular velocities core rigid rotation ?
  0.036 rad/s
• No He-burning

(artificial viscosity ??)
Tmax 1.6 108 K ? 5280 g/cm3
?nuc ??? ?hyd

• in 2 hours Keplerian disk ? evol. time-scales
  long

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• FRANEC accretion phase evolution

Accretion Mass deposition onto the He core
10-5 M? /yr
(Eddington limit)

• Assume inner core expanded envelope decoupled
• (different time-scales, presence of the accretion
  disk)

masses in M?
MRG 1.4 1.3 1.2 MRGcore
0.19 0.20 0.17 MWD 0.2
0.15 0.38 Mfin 0.76 0.75
0.78 Mcore 0.5 0.36 0.55
Piersanti et al. 2010 (submitted)

• Different assumptions
• Angular momentum deposited by the accreted
  matter
• Angular momentum transport efficiency into the
  accreting He-core

No-rotation Rigid-rotation
Differential-rotation
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After accretion
During accretion
10-5 M? /yr
NO He-burning
He-ignition
No rotation
?acc ltlt ?dif
central ignition
Diff. rotation
0. 0.1 0.2 0.3 0.4 0.5 M/M?
0. 0.1 0.2 0.3 0.4 0.5 M/M?
Piersanti et al. 2010
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After accretion ? H-burning active ? No
mixing
Differential rotation
No rotation
Rigid rotation

104
107
109
100
100
0.6
0.5
0.4
0.1
0.1
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• Accretion is the main physical mechanism
  driving the evolution of the ?
• inner core expanded envelope decoupled
• ?acc ltlt ?diff compression ? local T ?
• 
  No He-burning
• After accretion evolutionary time-scales
  longer
• thermal energy diffuses inward ? whole
  core T ?
• 
  (less degenerate)
• 
  re-ignition of H-burning shell
• He-ignition closer to the center
• He-flash less strong
• 
  
• Rotation modulates that behaviour T ? ?
  ? MHe-core ?

vs standard single RGB
No-rot rig-rot dif-rot MHe
0.40 0.41 0.47 Mig 0.12
0.04 0.00 ?Mf 0.24 0.36
0.45
bigger
If MHeWD ? ??
inner
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massive He-WDs ?
RG He WD
MRGcore
Number is OK
77
23
Zamora et al. 2009 40 of the sample wrongly
classified
too luminous !! (core mass ?)
Izzard et al. 2007
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MWD 0.38 M? MRG 1.20 M? (MRGcore 0.17
M?)

• At the end of accretion
• TMAX 1.28 108 K BUT
• 6500 g/cm3
• Mild He-flashes within He-core

Mild flashes
For MWD ? weak He-flashes Isolated by
accretion disk
Piersanti et al. 2010
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• Merging of a RG He-WD in common envelope
• is very common in nature (Izzard et al. 2007)
• We have studied the final outcome
• Physical structure very different from standard
  single RGB (T, ? and rotation)
• physical conditions do not favour external or
  stronger He-flashes
• NO mixing of C-rich material into the envelope
• (early) R-stars progenitors still missing

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C-rich RR Lyrae
Tohunga !!!
Wallerstein et al. 2009
Mixing at the He-flash ??
Wallerstein et al. 2009
Fe/H C/Fe N/Fe O/Fe
C/O KP Cyg 0.18 0.52 0.90
-0.07 1.7 UY CrB - 0.40 0.65
1.26 0.59 0.83 R-hot -0.28
0.53 0.60 (?) 1.6
No s-elements

• 12C from He-burning
• 13C from proton captures over 12C
• 14N from proton captures over 13C

H mixes with 12C (Pop. III) How ??
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The Nature of (early) R-stars ??
Te Araroa (long way)
runanga ka pai (Excellent meeting)
Kia Ora (Good luck/Good health)
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The Nature of R-stars ??still Elusive Te Araroa
(long way)
runanga ka pai (Excellent meeting)
Kia Ora (Good luck/Good health)
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Population III stars

• He-convective zone into H-rich layers
• H-ingestion
• Two convective shells
• Convective envelope into N and C-rich regions

12C/13C C-rich N-rich
Hollowell, Iben, Fugimoto, 1990
Picardi et al. 2004 Cristallo et al.
2007 Schlattl et al. 2002
D-up
H-ingestion
He-ignition close to H/He H-shell less efficient
? Lack of CNO elements
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2 He-WDs of MWD 0.4 M?
The maximum temperature
?
thermonuclear flash
Tmax 2 108 K
Tmax 1.6 108 K
Guerrero, García-Berro, Isern, 2004
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Rotation
Differential
Rigid
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No rotation
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(No Transcript)
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Galactic distribution
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Galactic distribution