Title: HydrogenDeficient Stars
1Hydrogen-Deficient Stars
Williamina Fleming 1857-1911
2Hydrogen-Deficient Stars
- Simon Jeffery
- Armagh Observatory
Hydrogen-Deficient Stars Discovery Classification
Surveys Distribution Frequency
3? Sgr
4Stars without hydrogen?
- 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
- Fleming 1891
- Ludendorff 1906
- Joy Humason 1923
- Plaskett 1927
- Payne 1925
- Berman 1935
- Struve Sherman 1940
- Greenstein 1940
reluctance
irrefutable evidence
...somehow, a very substantial amount of hydrogen
had been lost
5Discovery of helium
Pierre Jules Janssen 1824-1907
- 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 ?????
(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
Lord Rutherford 1871-1937
6Helium Stars?
- 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
- Wolf Rayet1857
- Popper 1940s
- Hofmeister 1940
- Herbig 1968
- Greenstein Matthews
- Bidelman
- Warner 1967
- Greenstein Sargent 1974
- Schmidt, Green Leibert 1986
- EC, HS, SDSS1990 - 2006
7faint blue stars in the Galactic halo
Jesse Greenstein
Aneila Sargent
Greenstein and Sargent 1974, ApJS 28, 157
8The Palomar-Green catalog of uv-excess stellar
objects
Green, Schmidt and Liebert 1986, ApJS 61, 305
9Hydrogen-Deficient Stars in the Galaxy
- recent history
- high mass
- low mass
- degenerates and rejuvenants
101985 Mysore
111991
Tutukov 1991, IAU Symp 145, 351
12Population I and massive helium stars
- Helium-rich B stars
- Wolf-Rayet Stars
- SN Ib
- Algols
- Ups Sgr variables
13Normal stellar evolution
He-core burning
Evolution of a 5M star Iben 1967, Ann Rev AA 12,
215
Iben 1967, Ann Rev AA 12, 215
14Helium-rich B orIntermediate He stars
- CP MS B stars
- 24 in catalogue of Drilling Hill 1986
- Helium-variable P1-10d
- ? Ori E
- dipole magnetic field 104 G inclined 90?
- metal-poor magnetic caps
- He-rich patches due to elemental segregation
- corotating clouds?
Bond Levato 1976, PASP 88, 95
Fe-poor
He-rich
clouds
Groote Hunger 1997, AA 331, 250
15Wolf-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 80s - 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 lt15m
- 100 in the LMC, 12 in the SMC
16Wolf-Rayet abundances
- WC sequence - ionzn of C
- WCE early
- WCL late
- WN sequence - ionzn of N
- WNL late
- WNE-s early strong em
- WNE-w early weak em
- Hydrogen
- detected - solid symbols
- none - open symbols
Hamann 1996, ASPC 96, 127
17WR star evolution
- Massive stars ?gtgt 40 M?
- Convective core plus overshooting
- Radiatively driven mass loss
- Processed material to surface
WNL
WNE
WC
Maeder 1991, IAUS 145, 221
18Type Ib Supernovae
- similar to SN I
- no H lines
- no Si II at maximum
- near star formation sites
- strong He features
Wheeler 1997, Sci.Am.
19SN Ib rates
- Cappellaro et al. (1993) Ia 0.39 /- 0.19
SnuIb/c 0.27 /- 0.18 Snu II 1.48 /- 0.65
SNu.
20- SN Ib equivalent to SN II in a massive star with
helium envelope
SN II
SN Ib
Wheeler 1988, Sci.Am.
SN II
SN Ib
21?? Sgr
- SpectrumAp
- 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.
22?? Sgr variables
- ? Sgr
- Mp3.00.3M?
- Rp60R?
- Lp105 L?
- nHe/nH104
- ? Sgr
- P138 d
- KS Per
- P360d
- LSS 1922
- P55d
- 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 MgtMChandrasekhar
- SN Ib progenitors ?
23The stellar atmosphere opacity problem
- compare late B stars with ? Sgr
- similar Teff
- similar gravity
- same resolution
24Low-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
251992 St Andrews
26R Coronae Borealis variables
- 35 known in galaxy,17 in the LMC (Claytons
web page) - Irregular light fades (5m)
- Low-amplitude pulsations
- Hydrogen-deficient spectrum
- Infrared excess
R CrB
R CrB
27Extreme 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
28Distribution 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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30Helium-rich subdwarfs
- 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 PG1544488- is a close binary!
- Others JL87, LB1766, - quite heterogeneous
- 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
31Hdef planetary nebulae central stars
- Spectral-type WC
- H-poor, C very strong
- 50 in 1996 list
NGC6369 - HST/PC
Hamann 1996, ASPC 96, 127
Hamann 1996, ASPC 96, 127
32O(He) stars
- He II absorption
- CIV, NV, OVI emission
- 1996 3
- 1998 4 (32-1)
- GJJC1 He-sdO
- PN / no PN 1
- Same domain as PG1159 stars but considerably
less metal rich
Rauch et al. 1998, AA
33PG1159 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
34Degenerates and Rejuvenants
- H-def white dwarfs
- AM CVn binaries
- Born-again stars
BPM 37093 (actually a DA, but its a neat
picture!)
Image Keck Observatory
35H-deficient white dwarfs
- H-dominated 4367
- DA 4008 H lines, no HeI or metal
- DAx 236 H lines, other weak lines
- DAbin 123 DAms 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
36AM 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 P17 - 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
37Born-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 Sge
- V605 Aql
- V4334 Sgr
38The story so far photometry
- 1944 Hoffmeister identifies a new variable in
Sagittae (AN 274, 176)10th magnitude,
irregular, not reddish - Star continues to brighten, and to become redder.
-
- Patrol plates provide history back to 1900
- 1995 van Genderen Gautschy use historical
brightness and colour gt L,Teff (AA 294, 453)
39FG Sge some puzzles
?
high
low
40late thermal pulses
41The very late thermal pulse
- Nuclear helium-burning re-ignited at surface of
e--deg CO core after the H-shell has become
inactive. - Energy released forces outer layers to expand in
1 - 10 years. - H-rich, He-rich and C-rich material mixed by
convective overshoot from the helium-shell flash,
and penetrates through to surface before the star
cools to develop deep opacity-driven convection
zone. - The corollary is that hydrogen is ingested at the
same time as He, C and s-process elements are
manifest at the surface. - (Schönberner 1979, Herwig et al. 1999)
42Hydrogen-Deficient Stars
Williamina Fleming 1857-1911
summary
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46Problems to solve
- Astronomy
- statistics
- distribution
- Evolution
- masses
- origin and fate
- links between classes
- Physics
- atmospheres
- pulsations
- mass loss
- convection
- nucleosynthesis