clumpy streams from a clumpy halo, CVs

I went up to Columbia today to see Kathryn Johnston and David Schiminovich. I took the local train, so that I would have plenty of time to read and comment on the latest draft of Joo Yoon's paper (with Johnston and me) on tidal streams. In the paper we use scaling relations—dimensional analysis and order-of-magnitude arguments—to describe the dynamical effects of halo substructure on cold stellar streams; then we compare with numerical simulations and observations. The result (against my wishes) is that the rattiness of the Pal-5 and GD-1 streams is consistent, at least roughly, with what is expected in a CDM halo. Argh! But Yoon has done a great job.

At Columbia's Pizza Lunch, Christian Knigge (Southampton) gave a nice explanation of CVs, which are accreting WDs in close binaries with red dwarfs. Because they are Roche-lobe-filling, they have orbital evolution (mass-transfer) times equal to the thermal (Kelvin-Helmholz) times in the dwarf stars. So the non-main-sequence-ness of the dwarf star gives a semi-direct measure of the instantaneous mass-transfer rate. Nice! He also argued that at some periods, there should be many non-CV binaries; Schiminovich and I might be able to detect those in our time-domain GALEX stuff.

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