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rodluger / planetplanet

A general photodynamical code for exoplanet light curves
https://rodluger.github.io/planetplanet
GNU General Public License v3.0
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(Even more) arbitrary surface maps #63

Open rodluger opened 7 years ago

rodluger commented 7 years ago

I think my integration method is more general than I had realized. Currently, because I'm restricting my calculations to ellipses, I need the radiance map to be radially symmetric about the hotspot, but I think that we can relax this assumption. The integration step would also work if our curves of constant radiance were any other convex shape. The only bit that would change is the intersection-finding routine, but this can easily be done numerically (as I pointed out here). We'd also need to compute the integral of the shape, but that's quite easy.

I'm thinking that in v2 the user could specify the functional form of the curves of constant radiance, say, as two polynomials: the upper part of the curve and the lower part of the curve, provided they intersect to form a closed shape. We could then easily compute their integrals, and we could still use the GSL root-finder to determine the points of intersection with the occultor.

The tricky bit will be to rotate the shape depending on the viewing angle, but I think this is a simple stretching transformation that can be generalized.

The reason this may be super useful is that the radiance map of a planet could have different longitudinal and latitudinal length scales because of rotation/winds: i.e., the hotspot may be elongated along the equator (currently we're effectively assuming it's a circle).

It will be a bit of work to code this up, but the code should be just as fast!

@ericagol, @jlustigy: what do you think?

rodluger commented 7 years ago

Perhaps an even simpler approach: I can relax the assumption of a circular hotspot and allow the user to specify the aspect ratio of an elliptic hotspot. I'd have to change very little of the code for this.

ericagol commented 7 years ago

This could be a cool extension of the code!

Sometimes, though, the iso-intensity contours can be non-convex, such as the chevron shapes or latitudinally-symmetric spots, such as seen here.

rodluger commented 7 years ago

I think in principle non-convex shapes could work as well (as long as they're easily integrable), but they can have many more intersection points with the occultor, which could be hard to find. I don't know how to handle the fact that the nightside contours are different shapes than the dayside contours, though. We could try to capture the nightside bimodality with some sort of superposition of two eyeballs, which we talked about a bit before.

On Tue, Aug 29, 2017 at 5:22 AM Eric Agol notifications@github.com wrote:

This could be a cool extension of the code!

Sometimes, though, the iso-intensity contours can be non-convex, such as the chevron shapes or latitudinally symmetric spots, such as seen here: http://www.exoclimes.com/wp-content/uploads/2012/02/showman-600x353.png http://url

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