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

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

The accreation Keplerian disk produce two-peaked wide emission lines (the inner fast rotating parts produces the wings of their profiles)

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 profiles are two-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.

2. H spectra of the RS CVn star FK Com Kjurkchieva D. , Marchev D 2. H spectra of the RS CVn star FK Com Kjurkchieva 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

Spectra of FK Com around phases 0,25 and 0,5 The phase variability of the subtracted spectra gives information about the position of the sources of additional H emission and absorption Spectra of FK Com around 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.

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

binary configuration of FK Com consisting of The modeling of our H spectra leads to a binary configuration of FK Com consisting of main star - source of the absorption reversal extended half-illuminated disk - source of the emission peaks SAE – source of additional emission SAA - source of additional absorption secondary star – source of the illumination of the disk

We noted the similarity of the H profile of FK Com and UX UMa in - 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

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

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

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

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

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 image of the subtracted H profile at phase 0,24 is similar to real H profile at Be state

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

Is there some contribution of secondary star? The H profiles of EM Cep at phases 0,75 and 0,47 coincidence 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?

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.

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

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) .

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 Cep which radial velocities are opposite and their amplitudes are equal to the star rotation velocity; The phase variability of the brightness and spectra of EM Cep might be explained by the rotation of some inhomogeneous structure but presence of companion star is not excluded.

V. Open questions 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 unified mechanism of creating of similar gaseous structure with equal velocities in different types of stars?!?