## Sunday, December 4, 2011

### Finding Exoplanets

As a third lab, I played around with the tools on portal.lcogt.net.
First, I started off by analyzing an image of CoRoT2b. The program asked me to pick a target star (to see if it has an exoplanet), a piece of dark sky for reference, and three calibration stars. Then, using the program, I could "analyze" the image. The measurements of the light curves of the stars I picked was saved to the combined light curve. Then I repeated the first few steps with 13 different images of the same piece of the night sky.
The second step was to classify the calibrator lightcurves as being flat, having a dip, having a blip, being periodic, or just odd. I classified two of the calibrators as seeming to have dips. These curves are then contributed to the final lightcurve for further analysis.
I couldn't figure out a way to save an image of the final lightcurve, but I can just describe it. The light curve (a plot of relative brightness as a function of time) had a drop in brightness of  5.94% and a transit time of 2.306 hours.

Using the following equations, and the above measurements, we can calculate several important features of the exoplanet.

$t_{trans}=\frac{PR_*}{\pi a}$

In this case, the mass of the star was inferred to be 0.97 solar masses. The radius of the planet was found to be 2.48 Rjupiter at a distance of 0.028AU with an orbital period of 1.743 days. This seems unrealistic to me. Even just visually speaking, the light curve was pretty shallow dip. Also, .028AU is 5.6 solar Radii, which isn't a plausible distance for the orbital distance.
Although, I could have very well measured something wrong or measured the wrong star altogether. It could also be a result of poor alignment of my tags or the small sample of pictures.

The next star I looked at was HAT-P-25b. The process for this was just like that for CoRoT2b, only this time with 109 pictures instead of 13. In this case, I thought one calibrator star had no dip, one had a dip, and one had a periodic pattern. The light curve dipped 3.82% with a transit time of 2.769 hours. The size of the star is about 1.01 solar masses. Using these quantities, the planet radius is inferred to be 1.89 times that of Jupiter with an orbital radius of .047AU and an orbital period of 3.653 days.
This still feels a little strange to me, but I'm not sure where my mistake lies :/ (also, it could be that I don't have a good sense yet of the plausible properties of a transiting planet).

Overall, this lab was pretty awesome! While I was labeling all of the pictures, my room-mate walked by and asked "Are you really looking at pictures of stars again?" :)

#### 1 comment:

1. Hahaha I love looking at pictures of stars!

I'm not a planets person, but to me the parameters for your planets don't sound that unrealistic. Planets that are close to the stars are generally easiest to detect. Let's do a little calculating to check if this is reasonable:

Your planets are roughly a Jupiter mass, so they have roughly the same radius as Jupiter, or a tenth of the radius of the Sun. So they should block roughly 1% (=0.1^2) of the Sun's light. This agrees with your measurements to order of magnitude.

What other reasoning can you use to check if your results are reasonable?