Lunch Colloquium
Dr. Mark Walker	SCHEDULED

Manly Astrophysics, Australia

In astronomy, solid hydrogen has been largely ignored for over 50 years. That was a mistake. It came about because the pure solid was shown to sublimate rapidly under interstellar conditions; but in the ISM solid H2 is expected to become electrically charged, and the electric field suppresses sublimation. I will argue that the spectroscopic properties of interstellar dust make a strong case in support of solid H2 being a major dust component. In turn, that suggests that our Galaxy possesses a substantial reservoir of dark gas clouds - hydrogen "snow clouds". I'll describe a new picture of the physics of interstellar scattering of radio waves, based on the tidal disruption of H2 "snow clouds" by stars. Somewhat surprisingly, that work has also led us to a beautiful new model of the rare, but spectacular, R Coronae Borealis stars.

	Special Colloquium
Prof. Dr. Bhaswati Mookerjea	SCHEDULED

Tata Institute of Fundamental Research (TIFR)

The Space Applications Centre (SAC) of the Indian Space Research Organization (ISRO) has successfully designed and developed the critical components for the first Indian sub-millimeter telescope. The observatory will be located initially at the 4500 m Hanle site of the Indian Astronomical Observatory and will be a partnership of ISRO withe Indian Sub-millimeter-wave Astronomy Alliance, which is a partnership of scientists from leading Indian astronomy, physics and space research institutions. The 6-m telescope in the first phase will be equipped with a dual band receiver at 230--345 GHz and will be used for the studies of the neutral interstellar medium. The observatory by virtue of its longitudinal position has the potential to be a new location for the Event Horizon Telescope (EHT). The Himalayan sites are among a small number locations globally, that have sufficient atmospheric transmission to allow observations in the sub-millimeter wavelength bands, at frequencies of about 200-500 GHz and higher. In this talk, I will present the current status of the Indian sub-millimeter observatory as well as the ongoing and future work on the characterization of the Himalayan sites for sub-millimeter astronomy.

	Main Colloquium
Prof. Thorsten Kleine	SCHEDULED

Max Planck Institute for Solar System Research

TBD

	Special Colloquium
Prof. Dr. Tom Megeath	SCHEDULED

The University of Toledo

TBD

	Main Colloquium
Prof. Dr. Selma de Mink	CANCELED

MPA

+++postponed+++

	Main Colloquium
Dr. Jaques Roland	SCHEDULED

Observatoire de Paris

Variations of the flux density of the nucleus of an extragalactic radio source can be due either to the variations of the synchrotron spectra of the black holes contained in the nucleus, or to the ejection of VLBI components. As a consequence of the variations of the synchrotron spectra of the black holes, there will be periods during which the low frequency and the high frequency observations will be aligned on the same BH, say BH1, and periods during which the low frequency and the high frequency observations will be aligned on different BHs, say BH1 and BH2. We obtained centroid position time series at 15 GHz from MOJAVE modelfitting giving epoch positions of the VLBI components and for each epoch, we calculated the 15~GHz flux barycenter positions using a beam $B = 2$ mas which corresponds to the $8$~GHz beam. The comparison of the $8$~GHz and $15$~GHz time series shows that: a) the time series are generally correlated, but they can be anti-correlated during some periods and b) the absolute position of the ICRF3 survey corresponds to the mean position of the $15$~GHz flux density barycenter within $\leq 0.100$ mas$. The comparison of the $8$ and $15$~GHz has been done for 2201+315 which structure of the nucleus is known and for 0851+202 and 0923+392 which structures of the nucleus are not known.

	Main Colloquium
Prof. Heinz Andernach	SCHEDULED

University of Guanajuato

TBD