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Hydrogen-Deficient Stars:some statistics
Simon Jeffery
Armagh Observatory
Hydrogen-Deficient Stars
Discovery
Classification
Surveys
Distribution
Frequency
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Hydrogen-Deficient Stars
Williamina Fleming 1857-1911
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Sgr
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Stars without hydrogen? Fleming 1891
Ludendorff 1906
Joy & Humason 1923
Plaskett 1927
Payne 1925
Berman 1935 Struve &
Sherman 1940 Greenstein 1940
“The spectrum of Sgr is remarkable since the hydrogen lines are very faint and of the same intensity as the additional dark lines”
H completely absent in R CrB
Hydrogen lines were “greatly weakened by partial emission” in the spectrum of RCrB
the simultaneous appearance of helium and metallic lines might be “due to a supernormal abundance of helium or to the star being an exaggerated form of pseudo-cepheid or giant”
“The uniformity of composition of stellar atmospheres appears to be an established fact”
R CrB
Sgr
Sgr
reluctance
irrefutable evidence
...somehow, a very substantial amount of hydrogen had been lost
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Discovery of helium 1868: A bright yellow line at 587.49nm in the spectrum
of the chromosphere of the Sun 1868: A yellow line in the solar spectrum, labelled D3,,
concluded it was caused by an element unknown on
earth and labeled it: λιος (helios).
1895: Isolated helium by treating cleveite with mineral acids. Actually looking for argon, but after removing N and O noticed a bright-yellow line that matched the D3 line seen in the Sun. Cleveite is an impure variety of uraninite. It has the
composition UO2 with about 10% of the uranium
substituted by rare earth elements. Helium is created by the alpha radiation of the uranium which is trapped (occluded) within the mineral
1907: Identifies alpha particle with He++ nucleus
Sir Joseph Norman Lockyer: 1836-1920
Sir William Ramsay: 1852-1916
cleveite
Pierre Jules Janssen: 1824-1907
Lord Rutherford: 1871-1937
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Helium Stars? Wolf & Rayet
1857 Popper 1940’s Hofmeister 1940 Herbig 1968 Greenstein &
Matthews Bidelman Warner 1967
Greenstein & Sargent 1974
Schmidt, Green & Leibert 1986
EC, HS, SDSS1990 - 2006
Stars with broad emission lines HD124448
FG Sge
AM CVn
“hydrogen-deficient carbon stars” -- a “portmanteau” expression for the lot
Faint blue stars: sdO,sdB
PG1159, sdOC, sdOD
He-sdB, He-sdO
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faint blue stars in the Galactic halo
Greenstein and Sargent 1974, ApJS 28, 157
Jesse Greenstein Wallace Sargent
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The Palomar-Green catalog of uv-excess stellar objects
Green, Schmidt and Liebert 1986, ApJS 61, 305
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Hydrogen-Deficient Stars in the Galaxy recent history high mass low mass degenerates and rejuvenants
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1985: Mysore
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1991:
Tutukov 1991, IAU Symp 145, 351
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Population I and massive helium stars
Helium-rich B stars Wolf-Rayet Stars SN Ib [ Algols ] Ups Sgr variables
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Normal stellar evolution
Iben 1967, Ann Rev A&A 12, 215
Evolution of a 5M star
Iben 1967, Ann Rev A&A 12, 215
He-core burning
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Helium-rich B orIntermediate He stars
CP MS B stars 24 in catalogue of
Drilling & Hill 1986 Helium-variable:
P~1-10d Ori E
dipole magnetic field ~104 G inclined ~90
metal-poor magnetic caps
He-rich patches due to elemental segregation
corotating clouds?
He-richFe-poor
clouds
Groote & Hunger 1997, AA 331, 250
Bond & Levato 1976, PASP 88, 95
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Wolf-Rayet stars 1867: Charles Wolf and George Rayet at
the Observatoire de Paris Early-type stars with bright broad emission
lines Disagreement whether they were H-
deficient up the the early 80’s Found solely in spiral arms, associations
and young clusters N-rich and C-rich sequences
WN and WC H detected in about half About 230 Wolf-Rayets in the Galaxy
(227: van der Hucht 2001) 159 WRs <15m
100 in the LMC, 12 in the SMC
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Type Ib Supernovae similar to SN I
no H lines no Si II at maximum
near star formation sites strong He features
SN IaSN IbSN II-pSN II
Wheeler 1997, Sci.Am.
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SN Ib rates Cappellaro et al. (1993)
Ia: 0.39 +/- 0.19 SnuIb/c: 0.27 +/- 0.18 Snu II: 1.48 +/- 0.65 SNu.
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Sgr
Spectrum~Ap Campbell 1899, Cannon 1912
composite variable strong helium on metallic
spectrum H, H in emission
Plaskett 1928, Morgan 1935, Merrill 1939, Greenstein 1940 et seq.
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Sgr variables Sgr
Mp=3.0±0.3M
Rp~60R
Lp~105 L
nHe/nH~104
Sgr P=138 d
KS Per P=360d
LSS 1922 P~55d
LSS 4300 P~?
? BI Lyn P~?
velocities close to circular orbits about galactic center
less than 200 pc from galactic plane Pop I helium stars with M>MChandrasekhar
SN Ib progenitors ?
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The stellar atmosphere opacity problem
compare late B stars with Sgr similar Teff
similar gravity same resolution
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Low-mass helium stars
R CrB stars Extreme helium stars He-sdB stars He-sdO stars H-def PN central stars O(He) stars PG1159 stars
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1992: St Andrews
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R Coronae Borealis variables ~ 35 known in galaxy,
17 in the LMC (Clayton’s web page)
Irregular light fades (5m) Low-amplitude pulsations Hydrogen-deficient spectrum Infrared excess
R CrBR CrB
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Extreme Helium stars Approx. 20 known in
galaxy Spectrum: A- and B-
Strong HeI Narrow lines: supergiant No Balmer lines Strong N and C
Origin? - clues from distribution chemical composition low-amplitude pulsations
Comparison of spectrum of an extreme helium star with a helium-rich B star.
Jaschek & Jaschek, 1987, The classification of stars, Cambridge
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Distribution and kinematics concentrated towards
gal. center do not share galactic
rotation Galactic bulge
hence range of Z
Jeffery, Drilling & Heber 1987, MNRAS 226, 317
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Helium-rich subdwarfs
PG survey: sdO sdOB sdOC - He-sdO sdOD - He-sdB
~ 50 He-rich subdwarfs in 1996 catalogue: did not discriminate sdB/sdO
SDSS DR4 He-sdB 5 He-sdB: 11
He-sdO/sdB easily confused - need better classifications (cf Drilling et al. )
PG definition (NGP) of sdOD same as for EHe stars found by Drilling in survey of OB+ stars (in plane)
HesdB: Prototype PG1544+488
- is a close binary! Others JL87, LB1766, …
- quite heterogeneous
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Hdef planetary nebulae central stars
Spectral-type [WC] H-poor, C very strong ~50 in 1996 list
Hamann 1996, ASPC 96, 127
NGC6369 - HST/PC
Hamann 1996, ASPC 96, 127
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O(He) stars
He II absorption CIV, NV, OVI
emission 1996: 3 1998: 4 (=3+2-1) GJJC1 = He-sdO PN / no PN ~ 1 “Same domain as
PG1159 stars but considerably less metal rich”
Rauch et al. 1998, A&A
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PG1159 stars
Spectroscopically unusual in the PG survey
Very short-period mulit-periodic variables
Spectra - HeII, highly ionized C, N, in abs and emission
No PN
PG1716
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Degenerates and Rejuvenants
H-def white dwarfs
AM CVn binaries
Born-again stars
Image: Keck Observatory
BPM 37093 (actually a DA, but it’s a neat picture!)
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H-deficient white dwarfs H-dominated 4367
DA 4008 H lines, no HeI or metal DAx 236 H lines, other weak lines DA+bin 123 DA+ms star
He-dominated 1009 DB 332 HeI lines, no H or metal DBx 65 DO 32 He II, plus He I or H DOx 15 DQ 91 Carbon lines DQx 21 DZ 61 Metal lines, no H or He I DC 358 Continuous spectrum DZx 22 Dx 12 (DD,DF,DG,DH,DK,DX)
Total 5376
Similar numbers (0.3dex) in SDSS DR4 catalogue (Eisenstein et al. 2006), but DB gap remains a real phenomenon.
http://www.astronomy.villanova.edu/WDCatalog/index.html
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AM CVn stars “HZ 29 is a peculiar, hydrogen
deficient white dwarf with broad, apparently double absorption lines of He I” (Greenstein and Matthews 1957,1958)
Interacting binary white dwarfs: P~17 - 46 min
Accretion disk seen in high (optically thick) and low (thin) states, cf. CVs
15 systems known (cf. 6 in 1996!) (0) 1x10-6 -1 pc-3 (Roelofs et al. 2007)
Merger progenitors? Probable GWR sources for LISA Reviews: Warner 1995, Nelemans 2005
Warner & Robinson 1972
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Born-again stars 3 in 100 years
Rare? 3x107 / Gyr / Galaxy
Not so rare?
How does this compare with birth-rate of white dwarfs?
What fraction of p-AGB stars experience a late or very late thermal pulse?
FG SgeV605 AqlV4334 Sgr
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Problems to solve Astronomy
statistics distribution
Evolution masses origin and fate links between classes
Physics atmospheres pulsations mass loss convection nucleosynthesis