SIMBAD references

The photometric and polarimetric observations of the isolated TTauri star TW Hya are presented. It is found that a period 2.196 days derived from the present data satisfies all the available photometry. The steep increase in the amplitude towards shorter wavelengths indicates that the light variation is caused by hot spots. Apart from the periodic variations sudden increase in brightness of the order of 0.2mag lasting one or two days was also noticed. A low resolution study of the Hα emission and Li I 6708Å absorption shows that the line strengths do not have any correlation with the rotational phase in TW Hya. Since the synoptic linear polarization measurements obtained during 1990, 1991 and 1992 showed that TW Hya has variable polarization, further measurements were obtained over nine consecutive nights during 1993. The data indicate that the linear polarization in TW Hya has two components, namely, a low amplitude component which is present throughout and a large amplitude short-lived component which occurs randomly.