1. S. Hubrig

3. Multiplicity of CP stars S. Hubrig, N. Ageorges, M. Schöller ESO/Chile

4. S. Hubrig Groups of CP stars Pec. typeSp. typeT eff rangemagnetic He-strongB1-B417000-21000Yes He-weakB4-B813000-17000Yes/No SiB7-A09000-14000Yes HgMnB8-A010000-14000Yes/No SrCrEuA0-F07000-10000Yes AmA0-F07000-10000No?

5. S. Hubrig Chemically 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

6. S. Hubrig Evolutionary status of magnetic Ap stars

7. S. Hubrig B stars in the HR diagram

8. S. Hubrig Magnetic 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.

9. S. Hubrig Mass-radius diagram for the young quadruple system AO Vel

10. S. Hubrig HgMn 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: =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, P orb~ 3-15 d.

11. S. Hubrig Alpha And Adelman et al. 2002

12. S. Hubrig AR 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).

13. S. Hubrig Starspot hypothesis for HgMn stars Anticorrelation between Mn and Hg. Crosses indicate single stars Anticorrelation between Mn and Fe abundances Hubrig et al. 2002

14. S. Hubrig HgMn 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?

15. S. Hubrig HgMn 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.

16. S. Hubrig HgMn star HD 216494

17. S. Hubrig Systematic multiplicity study of 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 (9 th 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.

18. S. Hubrig HD 75333 (H image) Keck II AO system Separation for A-B: 1.351”, for Ba-Bb: 65+/-5 mas Contrast between A-Ba: 4.45 m and A-Bb: 5.00 m

19. S. Hubrig Spectral type of companions is between K5 and M0

20. S. Hubrig HD 53244, HgMn, SB1 HD 53929, HgMn, SB1 HD 72208, HgMn, SB2 HD 73340, B9pSi

21. S. Hubrig HD 216494 HD 59067 HD 28217HD 21933

22. S. Hubrig HD 34880HD 33647 HD 35548

23. S. Hubrig HD 32964 HD221507 X-ray emitters

24. S. Hubrig DiscussionDiscussion 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).

25. S. Hubrig