uli heber subluminous o stars origin and evolutionary links hydrogen-deficient stars, tübingen...
TRANSCRIPT
Uli Heber
Subluminous O starsOrigin and evolutionary links
Hydrogen-Deficient Stars, Tübingen 20.9.2007
Outline Early results Atmospheric parameters Evolutionary scenarios
- Close binary evolution (RLOF, CEE & WD mergers)
vs
- Delayed core helium flashers
- (non-core helium-burning stars)
Kinematics Summary & Outlook
sdO vs. sdB stars
sdO
sdB
sdB stars: - helium-deficient- „cool“: 20-40kK
sdO stars:- H-deficient- Hot > 40kK- He-sdOs: No hydrogen
sdB stars:He-deficiency from diffusion
Metal abundances HST/STIS UV spectra
- Enrichment of heavy elements (>100 times) except Fe
- Radiative levitation
Fe
PbO´Toole & Heber 2006
CPD-64 461 207 207PB/208PB =solar
Post-EHB vs post-AGB evolution
sdB = Extended Horizontal Branch stars:
- He-burning core & inert H-envelope (<0.01 Msun)
- How to loose the envelope?
- sdO stars=post-EHB?
Post-AGB Objects:-rare-linked to RCrB/EHe stars
sdB sdO
Convective transformation(Wesemael et al. 1982)
Groth et al.(1985):Convection occursin He-rich atmo-spheres only
Convection He/H=1
sdO
sdB
Hot subdwarfs from UVX SurveysLTE- spectroscopic analyses of sdB stars:
- Palomar Green survey: Saffer et al. 1994, Maxted et al. 2000
- Hamburg Quasar Survey: Edelmann et al. 2003
- ESO-Supernova Progenitor Survey (SPY): Lisker et al. 2005
NLTE spectroscopic analyses of sdO-stars:
- SPY (Ströer et al. 2007)
- Sloan Digital Sky Survey (Hirsch et al. 2007)
atmospheric parameters for >200 sdB
atmospheric parameters for 130 sdO
Fits of UVES-spectra (SPY): sdOhigh resolution spectra, UVES@VLT, TMAP NLTE models, H&He only
sdO He sdO
SPY:C & N lines
solar
solar
- C&N strong: diamonds- C strong: triangle- N strong- no C or N: open - All He-rich sdOs
have C and/or N
-None of the He-poor have C/N
The canonical picture
He-ZAMS
Smooth evolutionary time scales:- He-poor scattered in diagram progeny of sdB stars- Clumping of He-rich sdOs can not be explained
SPY&SDSS: sdB, sdO & He-sdO
sdO stars:
He-sdO: clumping at- Teff = 45000K- log g = 5.8
sdB
He-sdOclump
SPY-sds: without error bars
sds in binaries
mostly single-lined: RV curve:mass function
2
33
2 )MM(
)i(sinM
G
PK)M(f
invisvis
vis
SPY: fraction of close binaries: radial velocity variables with P<10dsdBs; :40% (Napiwotzki et al.,2005)
Minimum mass of companion
Napiwotzki et al. 2007
sdOs: 4% RVV (from SPY)
Period distributionNature of companions: white dwarf or low mass m.s. stars
WD
MS
unknown
Morales-Rueda (2006)
Binary Population Synthesis (BPS)
Han et al. (2003)
a: 1. CE ejection
b: 1. stable RLOF
c: 2. CE ejection
d: merger of two
helium white dwarfs
Comparison to Han et al. (HPMM)
sdBs: best match: models with
correlated masses and low CEE efficiency
Poor match: models with 100% CEE efficiency
O-types: He-rich sdOs: stars clump at
45000K, too hot for any HPMM simulation set
He-poor sdO: scattered in (Teff, log g) diagram
Ströer et al. 2007
Non core helium-burning evolution
Castellani, Castellani & Moroni (2006)
M=0.8 Msunη=0.75
Star leaves RGB Before helium ignites in the core (e.g. by mass tranfer to a companion)
Cooling tracks to formhelium white dwarfs
Non-core helium-burning sdB starsHD 188112 (V=10.2) (Heber et al., 2001)
- Hipparcos parallax
- distance = 80 pc
- mass = 0.22 Msun
No helium burning
- companion: M>0.72Msun
Tracks: Driebe et al.
A Hyper-velocity star (HVS) amongst sdO stars from SDSS
HVS
-500 0 +500 km/s
Galactic restframe velocity
SMBH Slingshot
Hills (1988): Disruption of a
binary near a Super-Massive Black Hole
releases companion at up to
1000 km/s or more. Detection of a
single HVS: evidence for a
SMBH
Gualandris et al. (2005)
Summary & Conclusion Origin of sdB/sdO stars? (i) delayed core helium flash (ii) close binary evolution (RLOF & CEE ejection), mergers of He-WDsHe-poor sdOs are the progeny of sdB starsHe-rich sdO stars are hotter than predicted by (i) & (ii) atmospheres: No metal line blanketing metalicity effects evolution (Brown et al. 2007)Post-AGB-evolution & Non-core He-burning evolution: rare due to short evolutionary time scales
Outlook: A pulsating sdO star
Strongest mode: P=119.3 s A=38.6 mmag plus- First Harmonic plus- 8 modes: 62 ... 118s
Woudt et al. (2001)
sdB Asteroseismology
Multi-periodic light variations (few mmag) at periods from 2 to 10min.
Østensen et al. (2001)
Carbon and Nitrogen
SPY: C and/or N linesDetected - in all helium-rich- In none of the helium-poor ones(Ströer et al. 2007)
Challenges Observations: better statistics, better data: the quest for high resolution. metal abundances (see Poster 25) Evolution theory: Prediction of surface abundances for late hot
flasher (Cassisi et al. 2003) & He WD mergers Angular momentum and stellar rotation Stellar atmospheres & envelopes: diffusion (rad. levitation) &
metal line blanketing, see talk by G. Michaud Mass loss and diffusion The role of magnetic fields (O´Toole et al. 2005)
US 708: Keck LRIS spectrum
• Teff = 45500K,
• log g = 5.23,
• mass = 0.5 Mo
• B=19.0 mag
• Distance: 19 kpc
Run-away stars
Ejection scenario:
born in the plane and ejected (Blaauw, 1961)
- binary supernova ejection
- 3 body interaction in an open cluster Calculate path and time of flight:
- radial velocities, distances & proper motion
- orbit integrator: Odenkirchen & Brosche (1992)
- Galactic potential: Allen & Santillan (1991)
BD+75 325 (Lanz et al. 1997)
- Slight enrichment of Fe&Ni
- fully metal line blanketed models:
Teff lower by 6000K than metal free models
Metallicity effects on atmospheric parameters for the sdB SB 707
Solar ([m/H]=0.0):Teff = 33940Klog g= 5.82log He/H=-2.95
10*solar ([m/H]=+1.0) :Teff = 35380Klog g= 5.90log He/H=-2.91
Metal line blanketed LTE models
Summary II
Heavy metals in sdO and sdB stars: Non solar abundances of Fe & Ni in sdO stars Non solar Ni/Fe (>solar) Strong enrichment of many iron group elements in hot
sdB stars (except Fe), about solar in “cool” sdBs (<30000K):
FUV flux suppression UV upturn Teff scale significantly changed by supersolar metal
abundances (line blanketing)
Cosmic accelerator?
Ejection from a cluster by three body interaction?
SN II in a binary release companion at orbital velocity?
Supermassive black hole in the Galactic center?
Better ideas??
Trends of helium abundance
sdB
sdO
He sdO
solar
sdB stars: - 2 sequences
sdO stars: - Spread by 6 orders of magnitude - 1/3 helium- deficient!
sdB and sdO stars from SPYSPY: ESO-VLT+UVES:High-res. Spectra of >1000 Double degenerate
candidates- sdB: 79 (Lisker et al. 2005)
- He-sdO: 30 (Ströer et al. sdO: 28 2007)
- fraction of RV variables (P<10d):
sdB: 39% He-sdO: 4% (1 SB2 binary)
sdB
Combining all studies
Neglecting
selection bias
SDSS sdBs:
To be donesdB
Gap?
SPY-sds: no error bars shown
SDSS-sdOs
Atmospheric models:
- NLTE:
- H+He, no metals
- PRO2 code
(Dreizler &Werner)
- improved He atomic models
- temperature correction scheme (Dreizler, 2003)
sdOHe sdO
NGC 6752: HB &EHB starsMoni-Bidin et al. (2007)
LTE spectral analyses: Teff, logg g match (E)HB prediction
Helium subsolar
EHB Models
Castellani et al. 1994
Helium core mass: 0.47 Msun depen-ding on He and metal abundance(fixed by onset of He core flash)
Horizontal Branch=sequence of envelope mass Menv,
EHB=very low Menv (0.01 Msun), inert H-rich envelope
avoids AGB evolutions
Origin of EHB stars
Castellani & Castellani 1993
M=0.8 Msunη=0.75
EHB-progenitor stars must loosealmost their entire envelope bythe time of the helium core flash strong RGB mass loss;
Low mass stars (Pop. II, globular cluster): Very efficient RGB Reimers windmay be sufficient.
Younger populations, i.e. more massive progenitors (field): ?
Candidate SN Ia ProgenitorKPD 1930+2752:Total mass=1.4 Msun(Chandrasekhar mass)
-Double degenerate-System merges within 2 108 years-SN Ia explosion?(Geier et al. 2007)
More on massive compaions: talk by Stephan Geier
sdB Asteroseismology
Non-radial p-modePulsationa driven by Iron opacity bump:
Predicted instabilityStrip matches Observations
Charpinet et al. (2001)
sdBAsteroseismology
Period matching technique:
Linear theory:Amplitudes can not be predicted
(PG1325+, Charpinet et al. 2006)
sdB Asteroseismology
PG 1605+072: Time resolved spectroscopy (9000 spectra)Radial velocity variations (O´Toole et al. 2005): 20 periods (few km/s)Line profile variations (phase folded, Tillich et al. 2007):
sdB Asteroseismology
Dominant mode:Teff semi-amplitude: 800KLog gsemi-amplitude: 0.08
First harmonic detected
Cleaning for dominant mode:8 weaker modesdetected
sdO stars from SDSS
candidates selected from
all releases according to
colour: u-g<0.2 (0.4)
g-r<0.1 11000 spectra: 40 sdO + 43 He sdO
(Hirsch, Dipl. Thesis)
Fits with NLTE models
He sdO
Early NLTE Analyses : sdO
Classification: He II > He I
He-sdO: no Balmer detectable to the eyeC and/or N strong
sdO: otherwise
Hunger et al. 1980Heber (1987)
Post-EHB
Post-AGB
Evolution of hot subluminous stars: the canonical picture
SdB + sdO stars: Extreme Horizontal Branch stars
EHBHB
sdBsdO
Dorman et al. (1993, ApJ 419, 596)