Presentation on theme: "Hydrogen-Deficient Stars: some statistics Simon Jeffery Armagh Observatory Hydrogen-Deficient Stars Discovery Classification Surveys Distribution Frequency."— Presentation transcript:
Hydrogen-Deficient Stars: some statistics Simon Jeffery Armagh Observatory Hydrogen-Deficient Stars Discovery Classification Surveys Distribution Frequency
Stars without hydrogen? n Fleming 1891 n Ludendorff 1906 n Joy & Humason 1923 n Plaskett 1927 n Payne 1925 n Berman 1935 n Struve & Sherman 1940 n Greenstein 1940 n “The spectrum of Sgr is remarkable since the hydrogen lines are very faint and of the same intensity as the additional dark lines” n H completely absent in R CrB n Hydrogen lines were “greatly weakened by partial emission” in the spectrum of RCrB n 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” n “The uniformity of composition of stellar atmospheres appears to be an established fact” n R CrB n Sgr reluctance irrefutable evidence...somehow, a very substantial amount of hydrogen had been lost
Discovery of helium n 1868: A bright yellow line at 587.49nm in the spectrum of the chromosphere of the Sun n 1868: A yellow line in the solar spectrum, labelled D 3,, concluded it was caused by an element unknown on earth and labeled it: λιος (helios ). n 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 D 3 line seen in the Sun. u Cleveite is an impure variety of uraninite. It has the composition UO 2 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 n 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? n Wolf & Rayet 1857 n Popper 1940’s n Hofmeister 1940 n Herbig 1968 n Greenstein & Matthews n Bidelman n Warner 1967 n Greenstein & Sargent 1974 n Schmidt, Green & Leibert 1986 n EC, HS, SDSS 1990 - 2006 n Stars with broad emission lines n HD124448 n FG Sge n AM CVn n “hydrogen-deficient carbon stars” -- a “portmanteau” expression for the lot n Faint blue stars: sdO,sdB n PG1159, sdOC, sdOD n He-sdB, He-sdO
faint blue stars in the Galactic halo Greenstein and Sargent 1974, ApJS 28, 157 Jesse GreensteinWallace Sargent
The Palomar-Green catalog of uv-excess stellar objects Green, Schmidt and Liebert 1986, ApJS 61, 305
Hydrogen-Deficient Stars in the Galaxy n recent history n high mass n low mass n degenerates and rejuvenants
Population I and massive helium stars n Helium-rich B stars n Wolf-Rayet Stars n SN Ib n [ Algols ] n 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 or Intermediate He stars n CP MS B stars n 24 in catalogue of Drilling & Hill 1986 n Helium-variable: P~1-10d n Ori E u dipole magnetic field ~10 4 G inclined ~90 u metal-poor magnetic caps u He-rich patches due to elemental segregation u corotating clouds? He-rich Fe-poor clouds Groote & Hunger 1997, AA 331, 250 Bond & Levato 1976, PASP 88, 95
Wolf-Rayet stars n 1867: Charles Wolf and George Rayet at the Observatoire de Paris n Early-type stars with bright broad emission lines n Disagreement whether they were H- deficient up the the early 80’s n Found solely in spiral arms, associations and young clusters n N-rich and C-rich sequences WN and WC n H detected in about half n About 230 Wolf-Rayets in the Galaxy u (227: van der Hucht 2001) u 159 WRs <15 m n 100 in the LMC, 12 in the SMC
Wolf-Rayet abundances n WC sequence - ion zn of C u WCE early u WCL late n WN sequence - ion zn of N u WNL late u WNE-s early + strong em u WNE-w early + weak em n Hydrogen u detected - solid symbols u none - open symbols Hamann 1996, ASPC 96, 127
WR star evolution n Massive stars >> 40 M n Convective core plus overshooting n Radiatively driven mass loss n Processed material to surface Maeder 1991, IAUS 145, 221 WNL WC WNE
Type Ib Supernovae n similar to SN I F no H lines F no Si II at maximum n near star formation sites n strong He features SN IaSN Ib SN II-p SN II Wheeler 1997, Sci.Am.
SN Ib rates n Cappellaro et al. (1993) Ia: 0.39 +/- 0.19 Snu Ib/c: 0.27 +/- 0.18 Snu II: 1.48 +/- 0.65 SNu.
n SN Ib equivalent to SN II in a massive star with helium envelope SN IISN Ib Wheeler 1988, Sci.Am. n where are progenitors ? SN IISN Ib
Sgr n Spectrum~Ap u Campbell 1899, Cannon 1912 n composite variable n strong helium on metallic spectrum n H , H in emission u Plaskett 1928, Morgan 1935, Merrill 1939, Greenstein 1940 et seq.
Sgr variables n Sgr u M p =3.0±0.3M u R p ~60R u L p ~10 5 L u n He /n H ~10 4 n Sgr u P=138 d n KS Per u P=360d n LSS 1922 u P~55d n LSS 4300 u P~? n ? BI Lyn u P~? n velocities close to circular orbits about galactic center n less than 200 pc from galactic plane n Pop I helium stars with M>M Chandrasekhar n SN Ib progenitors ?
The stellar atmosphere opacity problem n compare late B stars with Sgr u similar T eff u similar gravity u same resolution
Low-mass helium stars n R CrB stars n Extreme helium stars n He-sdB stars n He-sdO stars n H-def PN central stars n O(He) stars n PG1159 stars
R Coronae Borealis variables n ~ 35 known in galaxy, 17 in the LMC (Clayton’s web page) n Irregular light fades (5 m ) n Low-amplitude pulsations n Hydrogen-deficient spectrum n Infrared excess R CrB
Extreme Helium stars n Approx. 20 known in galaxy n Spectrum: A- and B- u Strong HeI u Narrow lines: supergiant u No Balmer lines u Strong N and C n Origin? - clues from u distribution u chemical composition u 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 u concentrated towards gal. center u do not share galactic rotation n Galactic bulge u hence range of Z Jeffery, Drilling & Heber 1987, MNRAS 226, 317
Helium-rich subdwarfs n PG survey: n sdO n sdOB n sdOC - He-sdO n sdOD - He-sdB n ~ 50 He-rich subdwarfs in 1996 catalogue: did not discriminate sdB/sdO n SDSS DR4 u He-sdB5 u He-sdB:11 n He-sdO/sdB easily confused - need better classifications (cf Drilling et al. ) n PG definition (NGP) of sdOD same as for EHe stars found by Drilling in survey of OB + stars (in plane) n HesdB: n Prototype PG1544+488 - is a close binary! n Others JL87, LB1766, … - quite heterogeneous
Hdef planetary nebulae central stars n Spectral-type [WC] n H-poor, C very strong n ~50 in 1996 list Hamann 1996, ASPC 96, 127 NGC6369 - HST/PC Hamann 1996, ASPC 96, 127
O(He) stars n He II absorption n CIV, NV, OVI emission n 1996: 3 n 1998: 4 (=3+2-1) n GJJC1 = He-sdO n PN / no PN ~ 1 n “Same domain as PG1159 stars but considerably less metal rich” Rauch et al. 1998, A&A
PG1159 stars n Spectroscopically unusual in the PG survey n Very short-period mulit-periodic variables n Spectra - HeII, highly ionized C, N, in abs and emission n No PN PG17 16
Degenerates and Rejuvenants n H-def white dwarfs n AM CVn binaries n Born-again stars Image: Keck Observatory BPM 37093 (actually a DA, but it’s a neat picture!)
H-deficient white dwarfs u H-dominated4367 n DA4008 H lines, no HeI or metal n DAx236 H lines, other weak lines n DA+bin123 DA+ms star u He-dominated1009 n DB332 HeI lines, no H or metal n DBx65 n DO32 He II, plus He I or H n DOx15 n DQ91 Carbon lines n DQx21 n DZ61 Metal lines, no H or He I n DC358 Continuous spectrum n DZx22 n Dx12(DD,DF,DG,DH,DK,DX) u Total5376 Similar numbers ( 0.3dex) in SDSS DR4 catalogue (Eisenstein et al. 2006), but DB gap remains a real phenomenon. http://www.astronomy.villanova.edu/WDCat alog/index.html
AM CVn stars n “HZ 29 is a peculiar, hydrogen deficient white dwarf with broad, apparently double absorption lines of He I” (Greenstein and Matthews 1957,1958) n Interacting binary white dwarfs: P~17 - 46 min n Accretion disk seen in high (optically thick) and low (thin) states, cf. CVs n 15 systems known (cf. 6 in 1996!) n (0) 1x10 -6 -1 pc -3 (Roelofs et al. 2007) n Merger progenitors? n Probable GWR sources for LISA n Reviews: Warner 1995, Nelemans 2005 Warner & Robinson 1972
Born-again stars n 3 in 100 years u Rare? n 3x10 7 / Gyr / Galaxy u Not so rare? n How does this compare with birth-rate of white dwarfs? n What fraction of p-AGB stars experience a late or very late thermal pulse? n FG Sge n V605 Aql n V4334 Sgr
Problems to solve n Astronomy u statistics u distribution n Evolution u masses u origin and fate u links between classes n Physics u atmospheres u pulsations u mass loss u convection u nucleosynthesis