Long-Term Polarization Changes of 88 Her

Arsenijević, J.; Jankov, S.; Djurašević, G.

doi:10.1017/s0252921100116215

Cited by 4 publications

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“…= 61.55 days. Short-term and long-term variations in the linear optical polarization were also reported by Arsenijevic et al (1986). We have tried, with our extensive joint material, to search for correlation between long-term spectroscopic and Polarimetrie variations with the aim of obtaining information on the behaviour of the circumstellar envelope.…”

Section: Introductionmentioning

confidence: 75%

Long-term spectroscopic and polarimetric variations of the Be star κ Dra

Arsenijević

Jankov

Krsljanin

et al. 1994

Symp. - Int. Astron. Union

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The bright Be star κ Dra (HD 109387, B5 III, v.sini=249 km/s) is one of the rare mid B type stars which have presented FeII emission lines during strong emission phases. Spectroscopic variations were previously reported by many authors over different time scales: years, days and hours. Juza et al. (1991) proposed that κ Dra was the primary component of a binary system with Porb. = 61.55 days. Short-term and long-term variations in the linear optical polarization were also reported by Arsenijevic et al. (1986). We have tried, with our extensive joint material, to search for correlation between long-term spectroscopic and polarimetric variations with the aim of obtaining information on the behaviour of the circumstellar envelope.

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Section: Introductionmentioning

confidence: 75%

Long-term spectroscopic and polarimetric variations of the Be star κ Dra

Arsenijević

Jankov

Krsljanin

et al. 1994

Symp. - Int. Astron. Union

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“…The data for star κ Dra are presented in this Proceedings. The part of 7 Cas data are published in the paper of Arsenijevic et al (1990). The BU Tau data are published in the article of Arsenijevic et al (1993).…”

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confidence: 99%

Common properties of some Be stars optical polarization parameters

Arsenijević

Marković-Kršljanin

Kubičela

et al. 1994

Symp. - Int. Astron. Union

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It is generally accepted that the presence of intinsic polarization of Be stars confirms the basic assumption of an extended non-spherically symmetric envelope, as well as the origin of polarization in scattering of non-polarized stellar radiation on free electrons in the envelope.The long-term polarization variations, for years to decades have been examined in a very limited number of stars. The behaviour of polarization parameters during all activity phases (B, Be, shell ...) is not known with certainty.Having in mind the importance of polarization data of Be stars, on one side, and ability to observe in a very long series with the same telescope available at Belgrade Observatory, on the other, a program of sty dying long-term optical polarization changes has been set up in 1974. The aim was to obtain reliable longterm data on polarization changes in V spectral region and examine these changes during different activity phases of Be stars.Polarimetrie observations at Belgrade Observatory were carried out with the 65-cm Zeiss refractor and the stellar Polarimeter (Kubicela et al. 1976 ) which was modified in 1979 to enable one to obtain digital magnetic records suitable for further computer processing. The measurements were done in the V spectral region. Under "one measurement" we understand up to 8 one-minute Polarimetrie sine-wave signals ρ hase-aver aged. The typical standard deviation of one 8 -minute measurement is 0.07% for Stokes parameters. The interstellar components were estimated or used from the literature. For the star ο And the observed polarization is presented.In Fig. 1 the individual measurements of the observed polarization percentage (a) and corresponding position angles (b) of the star ο And are shown. Figure 2a and b displays the intrinsic polarization percentage and position angles of the star 88 Her. The data for star κ Dra are presented in this Proceedings. The part of 7 Cas data are published in the paper of Arsenijevic et al. (1990). The BU Tau data are published in the article of Arsenijevic et al. (1993).From the sample of our Polarimetrie data of five stars and published data of V magnitude and H a emission strength existing in the literature for the same star, one can come to the followinig conclusion:The intrinsic visual polarization percentage for all five observed stars was smaller than 1 percent. The long-term variations of both intrinsic polarization parameters exsist for all five stars.

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Long-term visual spectrophotometric behaviour of Be stars

Moujtahid

Zorec²,

Hubert

et al. 1998

Astron. Astrophys. Suppl. Ser.

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Abstract. The long-term spectrophotometric variations of 49 Be stars are studied using the U and V magnitudes of the UBV system, the total Balmer discontinuity D and the visible gradient Φ rb . BCD spectrophotometric and photometric data in five different photometric systems, obtained in most cases since 1950 and reduced to the BCD system, were used. The (U, D), (V, D), (Φ rb , D) and (Φ rb , V ) correlations obtained differ from star to star and they can be single or double-valued. They differ clearly for Be phases or Be-shell phases. Be stars with small V sin i showing the "spectrophotometric shell behaviour": D > D * , were found. This finding implies either that strongly flattened models of circumstellar envelopes are in doubt for these stars, or that not all Be stars are rapid rotators. Comparison of observed variations with those predicted for model Be stars with spherical circumstellar envelopes of variable densities and dimensions implies that spectrophotometric patterns of Be phases are due to circumstellar envelopes in low opacity regimes, while those of spectrophotometric shell phases are due to circumstellar envelopes in high opacity regimes. In a given star, the envelope regions responsible for the observed variations of D and Φ rb in spectrophotometric shell phases seem to be smaller and denser than those producing the observed variations of these parameters in spectrophotometric Be phases. The high positive RV found in strong shell phases might favor the formation of compact circumstellar layers near the star.

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Long-Term Polarization Changes of 88 Her

Cited by 4 publications

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Long-term spectroscopic and polarimetric variations of the Be star κ Dra

Long-term spectroscopic and polarimetric variations of the Be star κ Dra

Common properties of some Be stars optical polarization parameters

Long-term visual spectrophotometric behaviour of Be stars

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