Outline Introduction The disks of B[e] supergiants Formation mechanism(s) of B[e] supergiant stars’ disks Conclusions
Probing the structure and dynamics of B[e] supergiant stars’ disks
Michaela Kraus
Tartu Observatory
March 16, 2016
M. Kraus Probing the structure and dynamics of B[e] supergiant stars’ disks Outline Introduction The disks of B[e] supergiants Formation mechanism(s) of B[e] supergiant stars’ disks Conclusions
1 Introduction
2 The disks of B[e] supergiants
3 Formation mechanism(s) of B[e] supergiant stars’ disks
4 Conclusions
M. Kraus Probing the structure and dynamics of B[e] supergiant stars’ disks Follow-up infrared surveys (Allen & Swings 1972; Allen 1973, 1974; Allen & Glass 1974, 1975) reveal two distinct populations of emission-line stars emission-line stars with normal stellar IR colors emission-line stars with IR excess emission due to hot dust Conti (1976) suggested to call these peculiar B-type emission-line stars with forbidden lines and dust as B[e] stars Identification of more and more stars with similar properties Definition of general criteria is needed.
Outline Introduction The disks of B[e] supergiants Formation mechanism(s) of B[e] supergiant stars’ disks Conclusions Introduction - B[e] Stars
Discovery of B[e] Stars Geisel (1970) found infrared (IR) excess emission in a sample of emission-line stars of spectral type B with low-excitation emission lines (especially Fe II and [Fe III]).
M. Kraus Probing the structure and dynamics of B[e] supergiant stars’ disks Conti (1976) suggested to call these peculiar B-type emission-line stars with forbidden lines and dust as B[e] stars Identification of more and more stars with similar properties Definition of general criteria is needed.
Outline Introduction The disks of B[e] supergiants Formation mechanism(s) of B[e] supergiant stars’ disks Conclusions Introduction - B[e] Stars
Discovery of B[e] Stars Geisel (1970) found infrared (IR) excess emission in a sample of emission-line stars of spectral type B with low-excitation emission lines (especially Fe II and [Fe III]). Follow-up infrared surveys (Allen & Swings 1972; Allen 1973, 1974; Allen & Glass 1974, 1975) reveal two distinct populations of emission-line stars emission-line stars with normal stellar IR colors emission-line stars with IR excess emission due to hot dust
M. Kraus Probing the structure and dynamics of B[e] supergiant stars’ disks Identification of more and more stars with similar properties Definition of general criteria is needed.
Outline Introduction The disks of B[e] supergiants Formation mechanism(s) of B[e] supergiant stars’ disks Conclusions Introduction - B[e] Stars
Discovery of B[e] Stars Geisel (1970) found infrared (IR) excess emission in a sample of emission-line stars of spectral type B with low-excitation emission lines (especially Fe II and [Fe III]). Follow-up infrared surveys (Allen & Swings 1972; Allen 1973, 1974; Allen & Glass 1974, 1975) reveal two distinct populations of emission-line stars emission-line stars with normal stellar IR colors emission-line stars with IR excess emission due to hot dust Conti (1976) suggested to call these peculiar B-type emission-line stars with forbidden lines and dust as B[e] stars
M. Kraus Probing the structure and dynamics of B[e] supergiant stars’ disks Definition of general criteria is needed.
Outline Introduction The disks of B[e] supergiants Formation mechanism(s) of B[e] supergiant stars’ disks Conclusions Introduction - B[e] Stars
Discovery of B[e] Stars Geisel (1970) found infrared (IR) excess emission in a sample of emission-line stars of spectral type B with low-excitation emission lines (especially Fe II and [Fe III]). Follow-up infrared surveys (Allen & Swings 1972; Allen 1973, 1974; Allen & Glass 1974, 1975) reveal two distinct populations of emission-line stars emission-line stars with normal stellar IR colors emission-line stars with IR excess emission due to hot dust Conti (1976) suggested to call these peculiar B-type emission-line stars with forbidden lines and dust as B[e] stars Identification of more and more stars with similar properties
M. Kraus Probing the structure and dynamics of B[e] supergiant stars’ disks Outline Introduction The disks of B[e] supergiants Formation mechanism(s) of B[e] supergiant stars’ disks Conclusions Introduction - B[e] Stars
Discovery of B[e] Stars Geisel (1970) found infrared (IR) excess emission in a sample of emission-line stars of spectral type B with low-excitation emission lines (especially Fe II and [Fe III]). Follow-up infrared surveys (Allen & Swings 1972; Allen 1973, 1974; Allen & Glass 1974, 1975) reveal two distinct populations of emission-line stars emission-line stars with normal stellar IR colors emission-line stars with IR excess emission due to hot dust Conti (1976) suggested to call these peculiar B-type emission-line stars with forbidden lines and dust as B[e] stars Identification of more and more stars with similar properties Definition of general criteria is needed.
M. Kraus Probing the structure and dynamics of B[e] supergiant stars’ disks Outline Introduction The disks of B[e] supergiants Formation mechanism(s) of B[e] supergiant stars’ disks Conclusions Introduction - B[e] Stars
Defining criteria for B[e] stars strong Balmer emission lines low-excitation permitted emission lines, predominantly of singly ionized metals, in particular of Fe II;
forbidden emission lines of [O I] and [Fe II]; a strong near/mid IR excess due to hot (T 1000 K) circumstellar dust. '
M. Kraus Probing the structure and dynamics of B[e] supergiant stars’ disks ⇓ Characteristics can be found in stars in various evolutionary stages! Classification of the stars with the B[e] phenomenon by Lamers et al. (1998)
⇓ ⇓ ⇓ ⇓ pre-MS stars: post-MS stars: post-MS stars: interacting binaries: Herbig B[e] compact PNe B[e] B[e] supergiants symbiotic stars
The remaining 50% could not be classified and are kept as a separate group of unclassified∼ B[e] stars.
Outline Introduction The disks of B[e] supergiants Formation mechanism(s) of B[e] supergiant stars’ disks Conclusions Introduction - B[e] Stars
Criteria are mainly based on emission features seen in optical spectra These features represent specific physical conditions within the circumstellar material, but contain no information on the star itself !
M. Kraus Probing the structure and dynamics of B[e] supergiant stars’ disks ⇓ ⇓ ⇓ ⇓ pre-MS stars: post-MS stars: post-MS stars: interacting binaries: Herbig B[e] compact PNe B[e] B[e] supergiants symbiotic stars
The remaining 50% could not be classified and are kept as a separate group of unclassified∼ B[e] stars.
Outline Introduction The disks of B[e] supergiants Formation mechanism(s) of B[e] supergiant stars’ disks Conclusions Introduction - B[e] Stars
Criteria are mainly based on emission features seen in optical spectra These features represent specific physical conditions within the circumstellar material, but contain no information on the star itself !
⇓ Characteristics can be found in stars in various evolutionary stages! Classification of the stars with the B[e] phenomenon by Lamers et al. (1998)
M. Kraus Probing the structure and dynamics of B[e] supergiant stars’ disks Outline Introduction The disks of B[e] supergiants Formation mechanism(s) of B[e] supergiant stars’ disks Conclusions Introduction - B[e] Stars
Criteria are mainly based on emission features seen in optical spectra These features represent specific physical conditions within the circumstellar material, but contain no information on the star itself !
⇓ Characteristics can be found in stars in various evolutionary stages! Classification of the stars with the B[e] phenomenon by Lamers et al. (1998)
⇓ ⇓ ⇓ ⇓ pre-MS stars: post-MS stars: post-MS stars: interacting binaries: Herbig B[e] compact PNe B[e] B[e] supergiants symbiotic stars
The remaining 50% could not be classified and are kept as a separate group of unclassified∼ B[e] stars.
M. Kraus Probing the structure and dynamics of B[e] supergiant stars’ disks Outline Introduction The disks of B[e] supergiants Formation mechanism(s) of B[e] supergiant stars’ disks Conclusions Introduction - B[e] Stars
Herbig B[e] cPNe B[e] B[e] supergiant symbiotic B[e] B-type B-type obscured O-type B-type obscured hot spectrum PMS star white dwarf supergiant compact obj. forbidden reflection PN nebula high-density associated emission nebula non-spherical nebula lines wind dust and PMS high-density high-density accretion Balmer accretion dusty disk (outflowing ?) disk lines disk disk
(d)
V921 Sco-A Hen 2-90 Artist’s view Ant nebula Herbig B[e] cPNe supergiant symbiotic
M. Kraus Probing the structure and dynamics of B[e] supergiant stars’ disks Outline Introduction The disks of B[e] supergiants Formation mechanism(s) of B[e] supergiant stars’ disks Conclusions Introduction - B[e] Supergiants
Additional characteristics of B[e] supergiants: Stars are supergiants, i.e. log L /L 4.0 ∗ ≥ Chemically processed materiel indicating an evolved evolutionary phase Hybrid spectra, i.e. simultaneously narrow low-excitation emission lines and broad absorption features of higher-excitation lines Density contrast between equatorial and polar wind of 100 – 1000
LMC B[e] supergiant R 126 (IUE spectrum) Si IV Si IV
1 Hot stellar wind with v 1800 km s− (Zickgraf et al.∞ 1985)' 1 Lines with FWHM of 20 – 30 km s−
M. Kraus Probing the structure and dynamics of B[e] supergiant stars’ disks Outline Introduction The disks of B[e] supergiants Formation mechanism(s) of B[e] supergiant stars’ disks Conclusions Introduction - B[e] Supergiants
Hybrid wind model suggested by Zickgraf et al. (1985).
M. Kraus Probing the structure and dynamics of B[e] supergiant stars’ disks Outline Introduction The disks of B[e] supergiants Formation mechanism(s) of B[e] supergiant stars’ disks Conclusions The disks of B[e] supergiants
Observational evidence for the disk 1. strong infrared excess emission due to hot dust
(from Bonanos et al. 2009)
M. Kraus Probing the structure and dynamics of B[e] supergiant stars’ disks Outline Introduction The disks of B[e] supergiants Formation mechanism(s) of B[e] supergiant stars’ disks Conclusions The disks of B[e] supergiants
Observational evidence for the disk 2. high intrinsic polarization due to electron scattering in a wind with density contrast of 1000 between equatorial and polar wind.
τ 0 0.2 0.4 0.6 0.8 64 Cohen et al. 3
a R 66 1. 2. 3. b R 50 h i = 90 O c S 18 d R 126 e S 12 f S 134 g R 82 2 h S 22
i = 60 O 1.Figure No 3. polarization Schematic view of polarization production in various CSE ge- ometries. When the CSE is unresolved, the net polarization observed will be
the co-addition of all polarization produced. Left: A spherical, homogeneous P (%) 2.distribution Perhaps of scatterers polarization will produce zero net polarization. Center: A non- spherical, non-homogeneous, “blobby” distribution of scatterers may produce g i = 45 O a net polarization, but it will depend on the number, spatial distribution, and e relative densities of the blobs. If the blobs are time-variable, the observed 3.polarization Definitely will also be variable.polarization Right: A disk-like distribution of scatterers 1 will produce a net polarization with a position angle perpendicular to the b disk, because there is little or no cancellation due to polar material. d f i = 30 O CSEs are not spatially resolved, the observed signal is the coadded net polar- ization. As a result, the polarization position angle gives a measurement of the S 111 c orientation of the disk on the sky, even when the disk is not resolved. While the electron scattering polarization is wavelength independent, the ob- a served polarization does show a wavelength dependence. This happens because of the pre- and post-scattering attenuation of polarized light by the disk material (measurementsas the photons work their way through the disk from (Wood & Bjorkman 1995; Wood 0 et al. 1996a,b). When the absorption cross sections are larger, less polarized flux 0 2 4 6 will escape from the disk, and so the net polarization measured will be smaller 2 1/2 9 -3 Melgarejoat those wavelengths. This et effect al. means 2001) that the polarization “spectrum” can
Observational evidence for the disk 3. detection of molecular emission fromCO (McGregor et al. 1988a,b; 1989; Morris et al. 1996; Oksala et al. 2013) and possibly TiO (Zickgraf et al. 1989; Torres et al. 2012)
M. Kraus Probing the structure and dynamics of B[e] supergiant stars’ disks
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