Hydrogen-Deficient Stars:some statistics

Simon Jeffery

Armagh Observatory

Hydrogen-Deficient Stars

Discovery

Classification

Surveys

Distribution

Frequency

Hydrogen-Deficient Stars

Williamina Fleming 1857-1911

Sgr

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

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

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

faint blue stars in the Galactic halo

Greenstein and Sargent 1974, ApJS 28, 157

Jesse Greenstein Wallace Sargent

The Palomar-Green catalog of uv-excess stellar objects

Green, Schmidt and Liebert 1986, ApJS 61, 305

Hydrogen-Deficient Stars in the Galaxy recent history high mass low mass degenerates and rejuvenants

1985: Mysore

1991:

Tutukov 1991, IAU Symp 145, 351

Population I and massive helium stars

Helium-rich B stars Wolf-Rayet Stars SN Ib [ Algols ] Ups Sgr variables

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

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

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

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.

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.

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.

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 ?

The stellar atmosphere opacity problem

compare late B stars with Sgr similar Teff

similar gravity same resolution

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

1992: St Andrews

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

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

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

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

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

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

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

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!)

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

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

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

Problems to solve Astronomy

statistics distribution

Evolution masses origin and fate links between classes

Physics atmospheres pulsations mass loss convection nucleosynthesis