design of coronagraphs, radio exoplanets

I had lunch today with my PhD co-advisor Judy Cohen (Caltech) (who co-advised me with Roger Blandford—my official advisor—and Gerry Neugebauer). We had a wide-ranging conversation, about NSF and NASA funding situations, next-generation space projects, stellar abundance measurements, and even high-contrast imaging. That last subject got Judy to introduce me to Dimitri Mawet (Caltech), who builds coronagraphs. The conversation with Mawet made me seriously regret that I didn't talk about coronagraphs in my seminar yesterday on noise modeling! Mawet and I discussed the design space of coronagraphs that I learned about a few weeks ago from Remi Soummer (STScI). Here are a few random notes from our discussion:

For real coronagraphs, fresnel-style computations of the field in the camera are not good enough; you really need to simulate the full electromagnetic vector field. That's music to my applied-math ears! Fresnel-style calculations might be good enough for star-shade design. It seems to me like the highly non-convex optimization that is being done to design coronograph internals are fairly limited, in the sense that the full space has not been searched in any sense (and it is hard to see how it could be); there might be low-hanging fruit here. Phase-vortex plates might be a good component for new coronographs, possibly combined with the other kinds of masks and stops. There is no good technology for adaptively managing stops or phase plates in real time, actively. Flexible, actuated mirrors are such good technology, we should use that as much as we can first. There are various codes out there to do the electromagnetic calculations, but none of them (it sounds to me) are using everything they could be from an applied-math perspective. I might be wrong on that last point!

At the end of the day, there was a planetary science colloquium by Alex Wolszczan (PSU) about possible use of radio astronomy to find planets (something I discussed with Dave Spiegel many moons ago). He is looking at low-mass stars, some of which actually pulse (like pulsars!) in the radio. I didn't understand the physics of this, but there are possibilities that magnetized Jupiters might pulse in the radio, and also might respond to stellar coronal mass ejections and so forth.

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