Detection of a Proto-planetary Clump in the Habitable Zone of GM Cephei

GM Cephei is an active T Tauri star in the young open cluster Trumpler 37, showing abrupt UX Orionis type of photometric variability. Its light curves exhibit frequent, sporadic brightening events, each of <0.5 mag and lasting for days, which must have been originated from unsteady circumstellar accretion. In addition, the star undergoes a brightness drop up to ~1 mag lasting for about a month, during which the star became bluer when fainter. Moreover, the brightness drops seem to have a recurrence timescale of about 300 days. It is proposed that the brightness drop arises from obscuration of the central star by an orbiting dust concentration, exemplifying disk inhomogeneity in transition between grain coagulation and planetesimal formation in a young circumstellar disk. GM Cep was found to show a few percent polarization in the optical wavelengths, and an enhanced level of polarization during the occultation phase.

Cometary Polarimetry

Comets are known to have a high (2-10 percent) polarization, caused mainly due to dust scattering and resonance fluorescence emission. Since near earth comets are generally bright (integrated visual magnitudes of 10 or even brighter) and as they show high polarization near earth-sun location, one can try to perform imaging polarimetry of such objects with small (40 cm or even smaller) telescopes. By using a dichroic polaroid sheet either in front of the telescope tube or before the imaging detector at the Cassegrain plane, one can record cometary images with a good signal to noise ratio. By rotating the dichroic sheet in three discrete steps and then reducing the corresponding three comet images to a single image, one can determine the linear polarization value at each pixel location on the image. The error in polarization will typically be the inverse of the ‘signal to noise ratio’. Such polarization images of a comet help us to determine its dust properties and also to look for possible dust jet activities. This type of work is possible with small telescopes and minor instruments.

Variation of linear polarization in R Aquarii system

R Aquarii is a very interesting symbiotic system. There is an emission nebulosity close to the star which extends in North-South direction and a “jet” feature of about 6″ with a position angle of 29° has also been observed (Sopka et al. 1982; Mauron et al. 1985; Kafatos et al. 1983). Polarization measurements are important to understand the peculiar geometry of the circumstellar material around the central objects. Wavelength and time dependence of polarization can be used to put constraints on the geometry of the object and to identify the mechanism(s) responsible for polarization. In view of this linear polarization measurements of R Aquarii were carried out by us in UBVRI bands. Observations were made during November-December 1984 on 1 meter telescope of Indian Institute of Astrophysics, Bangalore, with a dual channel photo polarimeter discussed elsewhere (Deshpande et al. 1985). Measured values of percent polarization and position angle at different phases alongwith the earlier observations of Serkowski (1974) and Ladbeck (1985) are plotted in Figure 1.

Flow system fluorescence polarization measurements on fluorescein diacetate-stained EL4 cells.

We have adapted a multiparameter cell sorter to measure the distribution of fluorescence polarization in cell populations. Measurements carried out on EL4 cells show that the percent polarization of fluorescein fluorescence decreases with increasing fluorescence intensity. This inverse relationship between polarization and intensity is shown both within the cell population and by the average values of the two quantities during both the increase and decrease of fluorescence intensity. The quantitative relation between intensity and polarization is different in hypertonic than in isotonic media. These results suggest that polarization measurements carried out at a fixed time after incubation of cells with fluorescein diacetate, which is converted to fluorescein within the cells, may depend in part on the rate of fluorescein accumulation, and that agents that have been reported to change the polarization of fluorescein in living cells may do so by changing the kinetics of fluorescein accumulation.