February-2017 Colloquium

Date & Time :2017-02-22 16:00:00
Speaker :Dr. S. Vijayan
Scientist - SD
Area :PRADDN
Venue :K. R. Ramanathan Auditorium,PRL

Abstract

Impact craters are the natural windows to explore the planetary bodies. They are one of the predominant surface features on the planetary bodies that formed from the early stage of planetary evolution and continuing till date (sporadically in very small size and scale). Though billion-year-old Cratering records on the Earth are not well preserved, Mars and other planetary bodies do preserve it. On Mars, the recent to older impact craters are preserved and they vary in sizes from few meters to 100’s of km. Mars hosts unique type of craters called layered ejecta craters, which are formed due to interaction with the subsurface volatiles. Along with craters, the Mars holds ample evidence for fluvial activities. The outflow channels on the Martian surface are the typical representative for surface fluvial flows. However, majority of the Martian fluvial activities ceased during the Noachian epoch (~>3.7 Ga), which is still a quest. This talk will discuss about the Cratering history on Mars, their likely correlation to fluvial activities and their contextual relationship to Mars. The geomorphic and chronological evidence suggests that the Martian fluvial activity not completely ceased during Noachian epoch, but occurred sporadically at localized zones during Amazonian (<~3.4 Ga) and Hesperian (~3.4-3.7 Ga) epochs. Chronologically, this implies that the volatile source was preserved in the Martian subsurface to form fluvial related channels on the surface or by forming layered ejecta craters on the surface of Mars.

Date & Time :2017-02-15 16:00:00
Speaker :Dr. Aveek Sarkar
Reader
Area :PRADDN
Venue :K. R. Ramanathan Auditorium,PRL

Abstract

Sun, like other stars, can have wind in its atmosphere. Existence of such 'solar wind' was first proposed in 1958. A few years later, this proposal was confirmed via spacecraft observation. Since then it has attracted a lot of interests from solar physicists. Solar wind shows complicated turbulent behaviour. It has been suggested based on various observations that at 1 AU, solar wind consists of spaghetti-like magnetic field structures with the magnetic topology of flux tubes. It is also observed that the plasma fluctuation spectra at 1 AU show a plasma beta dependence. Reconciling these two sets of observations together, the present talk will discuss the direct numerical simulation of the full magnetohydrodynamic equations and will show that if the plasma inside the flux tube is driven unstable by spatial inhomogeneities in the background plasma pressure, the observed nature of the fluctuating power-spectra agree reasonably well with observations as well as with analytical predictions.

Date & Time :2017-02-01 16:00:00
Speaker :Dr. Lokesh Kumar Dewangan
Scientist-SD, Astronomy and Astrophysics Division, PRL, Ahmedabad.
Area :PRADDN
Venue :K.R.Ramanathan Auditorium, PRL

Abstract

Massive stars (> 8 Msun) have a significant impact, through their energetics, on the evolution of galaxies and the universe in general. The energetics of massive stars can also affect star formation positively and negatively. However, despite their importance, the understanding of the birth and feedback processes involving massive stars is still under debate. In recent years, space-based infrared observations have revealed many massive star-forming regions which contain infrared dark clouds, mid-infrared shells or bubbles, 6.7 GHz methanol maser emission, HII regions, and young star clusters together. It is indeed obvious that such sites host numerous complex physical processes of star formation. At the same time, these sites are extremely promising to probe important observational evidences concerning the formation of massive stars and their feedback. I will present the results of an analysis of promising massive star-forming regions using a multi-scale and multi-wavelength approach.