S. Hubrig

S. Hubrig

Multiplicity of Multiplicity of CP stars CP stars

S. Hubrig, N. Ageorges, M. SchS. Hubrig, N. Ageorges, M. Schööllerller

Multiplicity of Multiplicity of CP stars CP stars

S. Hubrig, N. Ageorges, M. SchS. Hubrig, N. Ageorges, M. Schööllerller

ESO/Chile

S. Hubrig

Groups of CP starsGroups of CP starsGroups of CP starsGroups of CP stars

Pec. type Sp. type Teff range magnetic

He-strong B1-B4 17000-21000 Yes

He-weak B4-B8 13000-17000 Yes/No

Si B7-A0 9000-14000 Yes

HgMn B8-A0 10000-14000 Yes/No

SrCrEu A0-F0 7000-10000 Yes

Am A0-F0 7000-10000 No?

S. Hubrig

Chemically Peculiar Ap Bp StarsChemically Peculiar Ap Bp StarsChemically Peculiar Ap Bp StarsChemically Peculiar Ap Bp Stars

• Main sequence A and B stars in the spectra of which lines of some elements are abnormally strong or weak (e.g., Si, Sr, Cr, Eu, He…)

• They generally have magnetic fields that can be detected through observation of circular polarization in spectral lines

• All observables (magnitude in various photometric bands, spectral line equivalent widths, magnetic field) vary with the same period

• Abnormal line strengths correspond to non-solar element abundances (by up to 5-6 dex), confined to the stellar outer layers and interpreted as resulting from segregation processes

S. Hubrig

Evolutionary status Evolutionary status of magnetic Ap of magnetic Ap

starsstars

Evolutionary status Evolutionary status of magnetic Ap of magnetic Ap

starsstars

S. Hubrig

B stars in the HR diagramB stars in the HR diagramB stars in the HR diagramB stars in the HR diagram

S. Hubrig

Magnetic Ap, Bp and Am starsMagnetic Ap, Bp and Am starsMagnetic Ap, Bp and Am starsMagnetic Ap, Bp and Am stars

• Among the magnetic Ap stars the rate of binaries is 43% (Carrier et al. 2002), and the number of SB2 systems is very small (3?). 122 stars were studied within the CORAVEL program. No eclipsing binaries were found.

• Orbital parameters do not differ from those of normal stars.

• No oscillating Ap stars were found in SB systems (Hubrig et al. 2000).

• The rate of binaries is much smaller among Bp stars (~20%) and only two double-lined eclipsing binaries are known: HD 123335 (Hensberge et al. 2004) and AO Vel (Gonzales et al. 2005).

• 6 Bp/Ap stars can be found in the MSC of A. Tokovinin.

• Am stars show overabundance of heavy elements and underabundance of Ca and Sc. At least 90% are SB systems. Many triples are known. Orbital periods between 2.5 and 100 days.

S. Hubrig

Mass-radius diagram for the young quadruple system AO Vel

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HgMn starsHgMn starsHgMn starsHgMn stars

• Extreme overabundance of Hg (up to 6 dex) and/or Mn (up to 3 dex). ~150 stars known. Many in young associations (Sco-Cen, Orion OB1).

• Most slowly rotating stars on the upper main sequence – exceptionally stable atmospheres: <v sin i>=29 km/s, extremely sharp-lined spectra. Easy to study isotopic and hyperfine structure.

• Spectrum variability? At least Hg lines (Hubrig & Mathys 1995).

• No strong large-scale organized magnetic fields, but tangled magnetic fields are possible.

• No enhanced strength of REE (1-2 dex), but of heavy elements W, Os, Ir, Pt, Au, Hg, Tl, Pb, Bi.

• Anomalous isotopic abundances of Hg, Pt, Tl, Pb, Ca.• More than 2/3 belong to SB. Many stars in multiple systems.• Binary periods of less than 3d are absent, Porb~3-15 d.

S. Hubrig

Alpha AndAlpha AndAlpha AndAlpha And

Adelman et al. 2002

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AR AurigaeAR AurigaeAR AurigaeAR Aurigae

The observed extent of up to +80 km/s of the red wing of the double-line structure of the Hg λ3984 line at the phase 0.490 cannot be explained by the Doppler shift due to the orbital and/or the rotational motion alone (Takeda et al. 1979).

S. Hubrig

Starspot hypothesis Starspot hypothesis for HgMn starsfor HgMn stars

Starspot hypothesis Starspot hypothesis for HgMn starsfor HgMn stars

Anticorrelation between Mn and Hg.Crosses indicate single stars

Anticorrelation between Mn and Fe abundances

Hubrig et al. 2002

S. Hubrig

HgMn starsHgMn starsHgMn starsHgMn stars

• Batten catalogue: only 6 SB systems of B8-B9 spectral type with normal late B-primaries, but with large vsini values.

• Every third system in the MSC catalogue with a B6-B9 primary involves a HgMn star.

• Out of 30 SB HgMn stars observed by speckle interferometry, 15 have visual companions.

• HgMn stars as X-ray emitters have a low-mass companion.• Interest for the star formation theories: important to compare the

ranges of P, luminosity ratios, orbital eccentricities, hierarchy with those for normal B stars.

• 5 SB systems with subsynchronously rotating companions (Guthrie 1986) - all have more than 2 components . Can the additional component be responsible for the subsynchronous rotation?

• A.Tokovinin.: Fraction of SBs belonging to multiple systems depends on the SB periods?

S. Hubrig

HgMn starsHgMn starsHgMn starsHgMn stars

• Tidal despinning to synchronous rotation proceeds from the outside toward the inside of the star. The tidal torque per unit mass varies with depth and latitude in a star, and therefore it tends to induce differential rotation (Zahn 1984; Goldreich & Nicholson 1989). We can assume that the rotation at the surface of HgMn stars is in binary systems could be a poor indicator of the total angular momentum IΏ stored in these stars and that the angular velocity is decreasing outwards.

• Because of the ubiquity of magnetic fields in the universe, we can presume that a weak poloidal field is present in HgMn stars. Then , the toroidal field is produced from the poloidal field by the non-uniform rotation in a characteristic time of only years. The toroidal fields should be able to diffuse slowly outwards, or they might be raised to the stellar surface by eruption or meridional flows.

• The detection of magnetic fields in a few HgMn stars makes plausible the idea, that (like in Ap and Bp stars) a stellar magnetic field coupling the star with its surrounding can transfer its angular momentum outside the star and so slow down rotation.

S. Hubrig

HgMn star HD 216494

S. Hubrig

Systematic multiplicity study Systematic multiplicity study of HgMn starsof HgMn stars

Systematic multiplicity study Systematic multiplicity study of HgMn starsof HgMn stars

• NACO K-band imaging using S13 camera: 41 HgMn stars with K-magnitudes ranging from 5 to 8 to discover all visual companions down to K=14 in the separation range 0.07-13.0“.

• Detected: 29 companions in 26 systems (3 quadruples, 14 triples).

• 6 systems are X-ray emitting – PMS stars as companions?

• Only 4 SB systems have known orbital elements (9th Cat. of SB orbits).

• The nature of companions – physical? Separations mostly < 1“.

• First observations with Keck of the HgMn star HD 75333 – quadruple!

• Upcoming spectroscopic observations with NACO starting in October.

• A few HgMn stars already observed with ISAAC in May.

S. Hubrig

HD 75333 (H image)HD 75333 (H image)HD 75333 (H image)HD 75333 (H image)

Keck II AO system

Separation for A-B: 1.351”,for Ba-Bb: 65+/-5 mas

Contrast between A-Ba: 4.45m

and A-Bb: 5.00m

S. Hubrig

Spectral type of companions is between K5 and M0

S. Hubrig

HD 53244, HgMn, SB1

HD 53929, HgMn, SB1

HD 72208, HgMn, SB2

HD 73340, B9pSi

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HD 216494 HD 59067

HD 28217 HD 21933

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HD 34880 HD 33647

HD 35548

S. Hubrig

HD 32964

HD221507

X-ray emitters

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DiscussionDiscussionDiscussionDiscussion

• The sample of the chemically peculiar stars studied is not large enough to explore possible differences between their multiple system properties and those of normal A and B stars.

• What is the formation mechanism of HgMn stars and how is it related to the B-type star formation? Does it depend on the binary period?

• Many HgMn stars belong to young clusters and associations, so that it is possible to study the effect of environment.

• Study of individual systems (preferably X-ray emitting), to confirm the PMS nature of their companions and explore the physics of their atmospheres by comparison of observed and synthetic spectra to test the validity of PMS evolutionary models for stars of different age and mass (most stars have accurate Hipparcos parallaxes).

S. Hubrig