Cake Talk: Sherry Suyu (ASIAA) and Henrik Rhodin (DARK) – University of Copenhagen

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Dark Cosmology Centre > Calendar DARK > DARK Calendar 2015 > Cake Talk: Sherry Suyu...

Cake Talk: Sherry Suyu (ASIAA) and Henrik Rhodin (DARK)

15 min Talk by:

Henrik Rhodin (DARK)

Title: Constructing a NIR thermometer for cool giants


A traditional spectroscopic way to determine the effective temperature is from optical spectra using excitation balance of Fe-lines. With technological advances and the advent of the next generation telescopes there will be an emphasis on the relatively unexplored near-IR (NIR) wavelength region (1-5 microns). A method for determining the effective temperature of stars based on NIR spectra is therefore needed. In a proactive attempt, my master thesis explored the NIR for the potential of such a method. Empirical line-strengths were evaluated, and reference iron-linelists were created and optimized for the K-giant benchmark star Arcturus, used as a testbed for the analysis. With an independently determined surface gravity, my results indicate that the effective temperature can be determined with relatively few lines to within a precision of 50 Kelvin.

30 min Talk by:

Sherry Suyu (ASIAA)

Title: Cosmology with Gravitational Lens Time Delays: Past, Present and Future


Strong gravitational lens systems with measured time delays between the multiple images can be used to determine the "time-delay distance" to the lens, which is primarily sensitive to the Hubble constant.  I will describe the ingredients and newly developed techniques for measuring accurately time-delay distances with a realistic account of systematic uncertainties.  I will present the first results of a program to analyze a sample of five strongly lensed quasars with the goal of measuring the Hubble constant to <4% in precision.  Current and upcoming imaging surveys will contain thousands of new lensed quasars, augmenting the existing sample by at least two orders of magnitude. I will describe practical ways to find and follow up the lens candidates, and the bright prospects of gravitational lens time delays as an independent and competitive cosmological probe.