Transcript Helium Stars in the Galaxy - uni

Hydrogen-Deficient Stars:
some statistics
Simon Jeffery
Armagh Observatory
Hydrogen-Deficient Stars
Discovery
Classification
Surveys
Distribution
Frequency
Williamina Fleming
1857-1911
HydrogenDeficient Stars
 Sgr
Stars without hydrogen?
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Fleming 1891
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Ludendorff 1906
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“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
reluctance
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Joy & Humason
1923
Plaskett 1927
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Payne 1925
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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”
irrefutable evidence
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Berman 1935
Struve &
Sherman 1940
Greenstein 1940
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R CrB
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 Sgr
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 Sgr
...somehow, a very substantial
amount of hydrogen had been
lost
Pierre Jules
Janssen:
1824-1907
Discovery of helium
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Sir Joseph
Norman Lockyer:
1836-1920
Sir William
Ramsay:
1852-1916
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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
cleveite
Lord Rutherford: 
1871-1937
1907: Identifies alpha particle with He++ nucleus
Helium Stars?
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Wolf & Rayet
1857
Popper 1940’s
Hofmeister 1940
Herbig 1968
Greenstein &
Matthews
Bidelman
Warner 1967
Greenstein & Sargent
1974
Schmidt, Green &
Leibert 1986
EC, HS, SDSS
1990 - 2006
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Stars with broad emission lines
HD124448
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FG Sge
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AM CVn
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“hydrogen-deficient carbon stars”
-- a “portmanteau” expression for the lot
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Faint blue stars: sdO,sdB
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PG1159, sdOC, sdOD
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He-sdB, He-sdO
Jesse Greenstein
Wallace Sargent
faint blue stars
in the Galactic halo
Greenstein and Sargent 1974,
ApJS 28, 157
The Palomar-Green catalog
of uv-excess stellar objects
Green, Schmidt and Liebert
1986, ApJS 61, 305
Hydrogen-Deficient
Stars in the Galaxy
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recent history
high mass
low mass
degenerates and rejuvenants
1985: Mysore
1991:
Tutukov 1991, IAU Symp 145, 351
Population I
and massive
helium stars
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Helium-rich B stars
Wolf-Rayet Stars
SN Ib
[ Algols ]
Ups Sgr variables
Normal stellar evolution
He-core
burning
Evolution of a 5M star
Iben 1967, Ann Rev A&A 12, 215
Iben 1967, Ann Rev A&A 12, 215
Helium-rich B or
Intermediate He stars
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Bond & Levato 1976, PASP 88, 95
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Fe-poor
He-rich
clouds
Groote & Hunger 1997, AA 331, 250
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?
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Wolf-Rayet stars
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1867: Charles Wolf and George Rayet at
the Observatoire de Paris
Early-type stars with bright broad emission
lines
Disagreement whether they were Hdeficient 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
SN Ia
SN Ib
SN II-p
SN II
Type Ib Supernovae
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similar to SN I
no H lines
 no Si II at maximum
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Wheeler 1997, Sci.Am.
near star formation sites
strong He features
SN Ib rates
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Cappellaro et al. (1993)
Ia: 0.39 +/- 0.19 Snu
Ib/c: 0.27 +/- 0.18 Snu
II: 1.48 +/- 0.65 SNu.
 Sgr
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Spectrum~Ap
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Campbell 1899, Cannon 1912
composite variable
strong helium on metallic
spectrum
H, H in emission
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Plaskett 1928, Morgan 1935, Merrill
1939, Greenstein 1940 et seq.
 Sgr variables
 Sgr
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Mp=3.0±0.3M
Rp~60R
Lp~105 L
nHe/nH~104
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 Sgr
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KS Per
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P~?
? BI Lyn
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P~55d
LSS 4300
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P=360d
LSS 1922
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P=138 d
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 ?
The stellar
atmosphere
opacity
problem
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compare late B
stars with  Sgr
 similar
Teff
 similar gravity
 same resolution
Low-mass helium stars
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R CrB stars
Extreme helium stars
He-sdB stars
He-sdO stars
H-def PN central stars
O(He) stars
PG1159 stars
1992: St Andrews
R Coronae Borealis
variables
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R CrB
~ 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 CrB
Extreme Helium stars
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Approx. 20 known in
galaxy
Spectrum: A- and BStrong HeI
 Narrow lines: supergiant
 No Balmer lines
 Strong N and C
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Comparison of spectrum of an extreme
helium star with a helium-rich B star.
Jaschek & Jaschek, 1987, The classification
of stars, Cambridge
Origin? - clues from
distribution
 chemical composition
 low-amplitude pulsations
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Distribution
and
kinematics
concentrated towards
gal. center
 do not share galactic
rotation
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Galactic bulge
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Jeffery, Drilling & Heber 1987, MNRAS 226, 317
hence range of Z
Helium-rich subdwarfs
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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
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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
Hdef planetary
nebulae central stars
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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
O(He) stars
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Rauch et al. 1998, A&A
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”
PG1159 stars
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PG17
16
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Spectroscopically
unusual in the PG
survey
Very short-period
mulit-periodic
variables
Spectra - HeII,
highly ionized C, N,
in abs and emission
No PN
Degenerates and
Rejuvenants
BPM 37093 (actually a DA,
but it’s a neat picture!)
Image: Keck Observatory
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H-def white dwarfs
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AM CVn binaries
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Born-again stars
H-deficient white dwarfs
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DA
DAx
DA+bin
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http://www.astronomy
.villanova.edu/WDCat
alog/index.html
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H-dominated
He-dominated
DB
DBx
DO
DOx
DQ
DQx
DZ
DC
DZx
Dx
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4008
236
123
Total
332
65
32
15
91
21
61
358
22
12
4367
H lines, no HeI or metal
H lines, other weak lines
DA+ms star
1009
HeI lines, no H or metal
He II, plus He I or H
Carbon lines
Metal lines, no H or He I
Continuous spectrum
(DD,DF,DG,DH,DK,DX)
5376
Similar numbers (0.3dex) in SDSS DR4 catalogue
(Eisenstein et al. 2006), but DB gap remains a real
phenomenon.
AM CVn stars
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Warner & Robinson 1972
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“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
Born-again stars
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3 in 100 years
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3x107 / Gyr / Galaxy
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FG Sge
V605 Aql
V4334 Sgr
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Rare?
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?
Problems to solve
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Astronomy
statistics
 distribution
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Evolution
masses
 origin and fate
 links between classes
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Physics
atmospheres
 pulsations
 mass loss
 convection
 nucleosynthesis
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