arXiv subjects

S. A. Lamzin

Publications and source records attributed to S. A. Lamzin.

22 records · Page 2Linked to original sources

arXiv2008

The model of dynamo with small number of modes and magnetic activity of T Tauri stars

The model that describes operation of dynamo in fully convective stars is presented. It is based on representation of stellar magnetic field as a superposition of finite number of poloidal and toroidal free damping modes. In the frame of adopted low of stellar differential rotation we estimated minimal value of dynamo number D, starting from which generation of cyclic magnetic field in stars without radiative core is possible. We also derived expression for period of the cycle. It was found that dynamo cycles of fully convective stars and stars with thin convective envelopes differ in a qualitative way: 1) distribution of spots over latitude during the cycle is different in these stars; 2) the model predicts that spot formation in fully convective stars should be strongly suppressed at some phases of the cycle. We have analyzed historical lightcurve of WTTS star V410 Tau and found that long term activity of the star is not periodic process. Rather one can speak about quasi cyclic activity with characteristic time of $\sim 4$ yr and chaotic component over imposed. We concluded also that redistribution of cool spots over longitude is the reason of long term variations of V410 Tau brightness. It means that one can not compare directly results of photometric observations with predictions of our axially symmetric (for simplicity) model which allows to investigate time evolution of spot's distribution over latitude. We then discuss what kind of observations and in which way could be used to check predictions of the dynamo theory.

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arXiv2007

On the origin of continuum and line emission in CTTSs

We calculated profiles of CIV 1550, Si IV 1400, NV 1240 and OVI 1035 doublet lines using results of 3D MHD simulations of disc accretion onto young stars with dipole magnetic field. It appeared that our calculations can not reproduce profiles of these lines observed (HST/GHRS-STIS and FUSE) in CTTSs's spectra. We also found that the theory predicts much larger C IV 1550 line flux than observed (up to two orders of magnitude in some cases) and argue that the main portion of accretion energy in CTTSs is liberated outside accretion shock. We conclude that the reason of disagreement between the theory and observation is strongly non-dipole character of CTTS's magnetic field near its surface.

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arXiv2005

The analysis of magnetic field measurements of T Tau

It is shown that the existence of hot accretion spots at the surface of T Tau practically has no effect on the accuracy of estimation of its magnetic field strength at photospheric level. We also found that one can interpret results of T Tau's photospheric magnetic field strength measurements carried out via different methods in the frame of the following alternative: 1) if T Tau's inclination angle $i\le 10^\circ,$ then magnetic field of the star may be dipolar with the angle between rotational and magnetic axes is near $85^\circ;$ 2) if it will be found (e.g. from interferometric observations) that $i>10^\circ,$ then magnetic field of T Tau is essentially non-dipolar or/and non-stationary.

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arXiv2003

Possible detection of a magnetic field in T Tauri

Medium-resolution $(R\simeq 15000)$ circular spectropolarimetry of T Tauri is presented. The star was observed twice: on November 11, 1996 and January 22, 2002. Weak circular polarization has been found in photospheric absorption lines, indicating a mean surface longitudinal magnetic field $B_{\|}$ of $160\pm 40$ G and $140\pm 50$ G at the epoch of the first and second observations respectively. While these values are near the detection limit of our apparatus, we belive that they are real. In any case one can conclude from our data that $B_{\|}$ of T Tau does not significantly exceed 200 G, which is much less than surface magnetic field strength of the star ($>2.3$ kG) found by Guenther et al. (1999) and Johns-Krull et al. (2000). We discuss possible reasons of this difference.

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