group meetings awesome

My goodness Wednesdays are good research days! As per usual, I spent the day at the CCA, where the research activity was dominated by my two group meetings. Here are some notes I took at each:

Sarah Pearson (Columbia) introduced herself at the stars group meeting; she talked about stellar streams and using them to constrain the shape of the MW dark-matter halo. With Pal 5 stream morphology alone, she can show that the Law & Majewski potential (used to explain Sagittarius) must be wrong, because it would create very strong stream fanning (which happens in chaotic potentials). Pearson is also thinking about finding thin streams in external galaxies, because morphology alone is so potentially constraining.

After Pearson, I asked about the projects from the Gaia Sprint, and their statuses. Leistedt (NYU) said things about modeling the color-magnitude diagram. He complained about the difficulty of fitting mixtures of Gaussians, especially because of initialization-dependence. Morton (Princeton) talked about his code to fit stellar properties given photometry and parallaxes. He complained about working with extinction in the broad G bandpass; this required a structural change to his code. (He mentioned also a high-resolution spectroscopic survey of transiting planet hosts, that could be relevant to us). Morton also brought up the interesting and fun issue that if you have a sample of transiting planet hosts, it is hard to get a control sample, because in no sense does “no transiting planet” mean &ldquo:has no planet”. This is worth more discussion! Angus (Columbia) talked about her work on rotation for stars with parallaxes; she is computing rotational ages. She has looked at the age–dispersion relation and also the ages of stellar pairs, to test age estimators and check that the wide pairs have small ages. In this discussion, the idea came up to compare photometric rotation periods with spectroscopic v sini measurements. Starkenburg (CCA) talked about RAVE+Gaia data on known stellar cluster members, to observe the kinematic escape of stars. We discussed a possible self-consistent model, accounting for the observed stellar mass. Anderson (CCA) spoke about photometric twins. These should be spectroscopic twins, asteroseismic twins, and (as Angus pointed out) even photometric light-curve twins! Leigh (AMNH) talked about numerical scattering experiments he is doing to look at the hypervelocity stars coming from the Galactic Center. He is comparing competing models for the scattering mechanism at the SMBH. Hawkins (Columbia) spoke about his hierarchical model of the population of red clump stars. He can show that they are standard candles to 0.08-ish mag, depending on which sample he chooses. His hierarchical model de-noises the parallaxes and makes very strong predictions for future Gaia data releases!

In the cosmology group meeting, Francisco Villaescusa-Navarro (CCA) spoke about HI gas and intensity mapping, in the context of large-scale structure with the SKA. There are strong trade-offs between resolution for angular and line-of-sight measures of the BAO. We discussed how to suppress the noise and foregrounds in practice for future measurements. He gets percent-level expectations for the Hubble Law at redshifts 0.5<z<2.5, which is promising, but will it satisfy our demands? That might be beat by Euclid! But he is considering only radial modes, not transverse modes. The discussion included lots of talk about beams, foregrounds, estimators, deconvolution, calibration, ancillary data, and self-calibration, with heavy participation by Kris Sigurdson (UBC).

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