SHAO Astrophysics Colloquium

Title - Exoplanets from the radial velocities of nearby stars

Speaker: Hugh Jones (University of Hertfordshire)

Time: 3 pm, July 11 (Thursday)

Location: Lecture hall, 3rd floor

Abstract - For most of human history extrasolar planets had a lot in common with dragons. Many people believed in them, but there were no confirmed cases. In 1995 some people's view of both changed with the potential discoveries such as 51 Peg b and Nine Dragon Pillar. In 2000 with the discovery of the transits event in the star HD209458, exoplanets became widely accepted and have since been discovered in large numbers. Though still we are only barely sensitive to Solar System's like our own. Our knowledge about the exoplanets around the dominant population of stars, the low-mass stars or M dwarfs is even more cursory. Hence the discovery of terrestrial-like exoplanets around Proxima, Trappist-1 and Barnard's star is providing interesting insights into their prevalence and diversity. This talk will be focussed on efforts to constrain Solar System analogues around cool stars and Solar type stars despite their faintness and sustained activity and will emphasise (i) the combination of data from different experiments, (ii) the wavelength sensitivity of signals and (iii) new instrumentation.

Special Colloquium

Title:  Einstein’s Microscope: Caustic Transiting Stars in Lensing Clusters as Probes of Dark Matter Granular Structure

Speaker: Liang Dai (IAS)

Time: 10:00 am, July 10 (Wednesday)

Location: Lecture Hall, 3rd floor

Abstract:Despite the triumph of the Cold Dark Matter (CDM) paradigm on large scales, empirical evidence for the DM structure on sub-galactic scales is scarce. As has recently been uncovered by the Hubble Space Telescope (HST), massive galaxy clusters, Nature’s most powerful gravitational magnifiers, can lens individual luminous stars at z~ 1–2 that lie fortuitously near the lensing caustic in a caustic straddling lensed galaxy, by extreme magnification factors ~ 10^2–10^3. I will discuss several important aspects about this remarkable phenomenon. First, these highly magnified stars have dramatically enhanced observability because they are inevitably subject to intermittent microlensing due to intracluster stars, and they are sensitive to stellar-mass compact DM objects inside the cluster halo. Second, their image positions in the critical curve vicinity can be perturbed by intervening low-mass DM subhalos inside the cluster halo, making them powerful targets for testing a key prediction of the CDM model. In addition, at the culmination of microlensing events with a magnification factor ~ 10^3 – 10^4, the star’s flux becomes susceptible to minuscule fluctuations in the lens surface density, which allows to probe mini-halos if the DM is made of the QCD axion.