Common Properties of Some Be Stars Optical Polarization Parameters

Arsenijević, J.; Marković-Kršljanin, S.; Kubičela, A.; Jankov, S.

doi:10.1007/978-94-011-1030-3_61

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“…The maximum brightness in the long-term cycle precedes the maximum of the emission strength for a few years . The maximum of the emission strength coincides with the maximum of continuum polarization (Arsenijević et al 1994). These facts seem to indicate that the brightening of the object is related to a temporarily extended photosphere which can be satisfactorily modelled by rotating model photospheres (Hirata 1995).…”

Section: Introductionmentioning

confidence: 57%

“…1 shows, they also found a clear correlation between continuum polarization and W Hα . This correlation was later confirmed by a large series of observations published by Arsenijević et al (1994). Juza et al (1994) summarized the history of the investigation of κ Dra up to 1993.…”

Section: Character Of Long-term Variationsmentioning

confidence: 76%

“…This was followed by a steep decrease to its minimum value of 53 km s −1 on HJD 52 684.5418 (in 2003). Note that Arsenijević et al (1994) reported the maximum value of the peak separation of 206 km s −1 (in the years 1961−1962 and 1985−1986) and the minimum of 69 km s −1 in 1980. Figure 4e displays the longterm behaviour of Hα peak separation based on the new and compiled data.…”

Section: Peak Separation (∆ν P )mentioning

confidence: 96%

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Properties and nature of Be stars

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A&A

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Abstract.We present an analysis of new spectroscopic observations of the bright Be star κ Dra obtained at the Ondřejov observatory during 1992−2003 and UBV photometric observations secured at several observatories. General characteristics and a line identification of the spectrum of κ Dra are obtained in the regions 3730−5650 Å and 5850−7800 Å by a comparison with the theoretical spectrum. The fundamental stellar parameters have been obtained from a comparison with a grid of NLTE model atmospheres. The best fit was found for T eff = 14 000 K, log g = 3.5, and v sin i = 170 km s −1 . These values together with a Hipparcos parallax lead to a stellar mass M = 4.8 ± 0.8 M and radius R = 6.4 ± 0.5 R . It is encouraging to see that these values agree well with the expected evolutionary mass and radius for the effective temperature we derived. Long-term variations of κ Dra were analysed using measurements of equivalent widths, central intensities, peak intensities of emission lines and emission peak velocity differences for Hα, Hβ, Hγ, Hδ, and some helium, silicon, and iron lines. The previously reported period of 23 years in the variation of the emission strength is probably a cyclic, not a strictly periodic phenomenon. An attempt to find out a period from all available records of the Hβ emission strength led to a value of (8044 ± 167) days (22.0 years) but the phase plots show that each cycle has a different shape and length. The maximum strength of the emission lags behind the brightness maximum. This is a behaviour usually observed for long-term changes of Be stars with a positive correlation between the brightness and emission strength. Since there are obviously no published speckle observations of the star, we suggest these should be carried out. They could help to deny or confirm the possibility that the emission episodes are triggered by a periastron passage of a putative binary companion moving in an eccentric orbit with a 8044-d period, as it seems to be the case for some Be binaries. For the moment, the nature and origin of the disk around κ Dra remains unknown. From the comparison of the electronic spectra obtained at different phases of the long-term cycle and synthetic spectra it appears that there are no detectable changes in the photospheric part of the Balmer lines related to variations in the Balmer emission strength which could be attributed to an extended photosphere corresponding to inner parts of the disk, optically thick in continuum.