Astron. Astrophys. Suppl. Ser. 144, 285-306

Analysis of correlations between polarimetric and photometric characteristics of young stars

A new approach to the problem after eleven years' study

R.V.Yudin

Central Astronomical Observatory of the Russian Academy of Sciences at Pulkovo, 196140 Saint-Petersburg, Russia
e-mail:  ruslan@pulkovo.spb.su

Received March 12, 1999; accepted March 14, 2000

Abstract:

We present the results of the investigation of correlations between the polarimetric and photometric characteristics of a sample (496 objects) of young Herbig Ae/Be (HAEBE) stars and T Tauri (TT) stars. It is shown that, for 85% of the sample stars there is a general relation between the degree of optical polarization and the infrared colour index $(V-L)_{\rm obs}$ and the colour excess E(V-L) due to the contribution of a circumstellar dust shell. Polarimetric data were also compared with the value of $v\sin{i}$to search for a possible correlation between the polarization and an inclination of circumstellar disks. Polarimetric data as well as IR excesses are considered and compared for different subgroups of young stars namely: HAEBE and TT stars with Algol-like minima of brightness (26 objects), Vega-type stars and post HAEBE stars (114 objects) and young solar-type stars (58 objects). For statistical purposes the data for young stars were compared with those collected for different groups of evolved objects such as: classical Be stars ($\approx$300 objects), Mira Ceti stars (39 objects), early-type supergiants from the Serkowski et al. ([1975]) catalogue (120 objects) and main sequence (MS) stars within 50 pc from the Sun from the Leroy ([1993]) catalogue (68 objects). The value of polarization is discussed in context with the stages of evolution of circumstellar shells which were established by comparison of spectral energy distribution in the far IR (using the IRAS data). It is shown that most young stars have statistically larger value of polarization in comparison with the stars which are on a stage of evolution close to MS. We are able to contend that the changes in polarimetric behaviour of young stars are connected with evolution of their circumstellar shells.

Key words: polarization -- circumstellar matter -- stars: evolution -- star: pre-mains sequence