Photometric and spectral observations of the star EM Cep D. Kjurkchieva & D. Marchev

1. Photometric and spectral observations of the star EM CepD. Kjurkchieva & D. Marchev

2. I. Introduction Disk-like stars The disks form around stars at different evolu-tional stages • T Tau stars • Cataclysmic stars • Symbiotic stars • X-Ray stars • Some semidetached systems

3. The Theaccreation Keplerian disk producetwo-peaked wide emission lines (the inner fast rotating parts produces the wings of their profiles)

4. II. Some preliminary results • The cataclysmic star UX UMa • Our H spectra of (on the left) show • the profile is one-peaked only around the eclipse phase; • the H profilesaretwo-peaked (V and R peak) at the rest phases; • the H line is symmetric at the two quadratutes; The conclusion: two-peaked wide H line of UX UMa is produced from an accretion disk around the white dwarf. This disk is fed by matter from the secondary late compo-nent filling-in its Roche lobe.

5. 2. H spectra of the RS CVn star FK ComKjurkchieva D., Marchev D., 2005, A & A 434, 221, “H observations of the star FK Com” • On the left top – The spectra averaged in phase bins • On the left bottom – The mean spectrum

6. The phase variability of the subtracted spectra gives information about the position of the sources of additional Hemission and absorption Spectra of FK Comaround phases 0,75 and 0,5 Spectra of FK Com around phases 0,25 and 0,5 • It is seen a bulk of emission and a bulk of absorption which position is opposite at the two quadratures.

7. The analysis of the phase variability of the subtracted spectraof FK Com(individual spectra minus the mean spectrum)leads to the conclusionThe two sources of the additional emission and absorptionmoves in anti-phase during the whole cycle.

8. main star - source of the absorption reversalextended half-illuminated disk - source of the emission peaksSAE – source of additional emissionSAA - source of additional absorptionsecondary star – source of the illumination of the disk The modeling of our H spectra leads to a binary configuration ofFK Comconsisting of

9. We noted the similarity of the H profile of FK Com and UX UMain - almost equal intensities of the emission peaks above the continuum- almost equal widths of the absorption reversal, the two emission peaks- presence of additional emission features on the main V and R peak- almost the same position of the emission peaks

10. III. The B-star EM Cep - the exchanging places of the two minima- the standstill at phase 0,83  anindicationof alternation between the two states??? 1. Two types of light curves

11. The irregular times of the minima (O-C=0,01d for a couple of days) confirmation of secular linear decreasing of the period

12. 2. Our H spectra of EM Cep on the left: spectra atBe-state in 2004 - H in emission on the right: spectra at B-state in 2005 - H in absorption

13. Тhe full width and depth of the H profiles of EM Cep at Be and B state are almost the same.

14. on the left: The subtracted H profiles of EM Cep at B state (individual minus spectrum at phase 0.47) have central additional emission (ADEM) and two side additional absorptions (ADABS) bottom: The mirror imageof thesubtracted H profile at phase 0,24 is similar to real H profile at Be state

15. The subtracted spectra of EM Cep at Be state (individual minus spectrum at phase 0.43)show central additional emission (ADEM) around the phases of quadratures

16. The H profiles of EM Cepat phases 0,75 and 0,47coincidence while the positions and the widths of the HeI lines (6677 A) are different. What is the reason? Is there some contribution of secondary star?

17. The radial velocity curves of the two ADABS show the opposite motion of their sources with velocity equal to the star rotational velocity of EM Cep Conclusions from the radial velocity curves: The ADABS compensate ADEM at minima;The sources of ADABS are near the star surface; The angle between the line-of-sight and star rotational axis is small.

18. We noted the similarity of the Hprofile of EM Cep at Be state with that of FK Com in:a) positions and width of the emission peaks; b) whole width of the H line

19. We found also a similarity of the H profile of FK Com and EM Cep with • the shape and phase variability of the H and H lines of the cataclysmic SU UMa-type star HT Cas(Catalan 1995); • the H line of the T Tau-type star AA Tau(Hartmann 1998) .

20. IV.Conclusion • The wide two-peaked H line of EM Cep at Be state means presence of extended disk; • The alternation between the B and Be state may be caused by the change of the optical thickness of the disk; • There are two sources of additional absorption on surface of EM Cepwhich radial velocities are oppositeand their amplitudes are equal to the star rotation velocity; • The phase variability of the brightness and spectra of EM Cepmight be explained by the rotation of some inhomogeneous structure but presence of companion star is not excluded.

21. Why the H emission peaks in the spectra of different types objects (Be stars, FK Com stars, cataclysmic stars, T Tau stars) have the same velocities? Why the full width of the H line in the spectra of these different types objects are the same? Do these facts mean that there is some unifiedmechanism of creating of similar gaseous structure with equal velocities indifferent types of stars?!? V. Open questions