All posts for the month March, 2016

Among other fun things I did this week during spring break, I practiced using one of the Physics Dept.’s new telescopes. It’s a lovely little 127-mm Maksutov-Cassegrain with a robotic mount. I also used a NexImage 5 camera. While the telescope is a joy to use, the camera is a pain, and I can’t convince it to return color images.

In any case, I took advantage of the clear night on Friday and imaged Jupiter from the middle school baseball field across the street from my house. In spite of the fact that neither the seeing nor tracking were great, some post-processing with Registax returned a nice little image.

Jupiter, from my backyard.

Jupiter, from my backyard.

Next steps: I need to do a better job with the tracking (probably need some new gear to improve the telescope alignment). A new camera might also be in order.





UPDATE (2016 Mar 24): The paper is now available for free on astro-ph.

The Astrophysical Journal published today a paper by my colleagues and myself investigating in detail a way to look for moons around transiting exoplanets.

The discoveries of thousands of planets and planetary candidates over the last few decades has motivated a parallel effort to find exomoons. In addition to providing a base of operations for the Empire, exomoons might actually be a better place to find extrasolar life than exoplanets in some ways.

This technique for finding exomoons, called the Orbital Sampling Effect, was developed by René Heller and involves looking for the subtle signature of a moon’s shadow alongside the shadow of its transiting planet host, as depicted in the image below.

At epoch (1), a satellite’s transits just before the planet. At epoch (2), the planet's transit begins, inducing a large dip the measured stellar brightness. At epoch (3), the satellite modifies the planet's transit light curve slightly but measurably.

The dark cloud shown around the planet represents the exomoon’s shadow, averaged over several orbits. At epoch (1), a satellite transits just before the planet. At epoch (2), the planet’s transit begins, inducing a large dip in the measured stellar brightness. At epoch (3), the satellite modifies the planet’s transit light curve slightly but measurably.

This simple technique has advantages over alternative exomoon searches in that it doesn’t require significant computational resources to implement. It can also use data already available from the Kepler and K2 missions. However, on its own, the technique can’t provide a moon’s mass, only its size, and it requires many transits of the host planet to find the moon’s quite subtle transit signature.

No exomoon has been found yet in spite of tremendous efforts to find them, so the search continues.


Artist's conception of cloudy GJ 1214 b. From

Artist’s conception of cloudy GJ 1214 b. From

At journal club this week, we discussed the recent discovery using data from the K2 mission of the sub-Neptune planet K2-28.

This planet, roughly twice the size of Earth, circles a very small M-dwarf star so closely that it only takes two days to complete one orbit. Even though the planet is very close to its star, the star is so cool (3000 K) and so small (30% the size of our Sun) that the planet’s temperature is only 600 K. (A planet in a similar orbit around our Sun would be 1200 K.)

The authors of the discovery paper point out that this planet is similar in many ways to another famous planet, GJ 1214 b. Like GJ 1214 b, K2-28 b is member of this puzzling but ubiquitous class of sub-Neptune planets — planets that fall somewhere between the Earth and Neptune in size and composition and do not exist in our solar system*. Both planets also orbit relatively nearby M-dwarfs, which means, like GJ 1214 b, K2-28 b might be amenable to follow-up observations.

Previous follow-up observations of GJ 1214 b indicated that planet’s atmosphere is very cloudy or hazy. So K2-28 b could provide another very important toehold along the road toward understanding this strange class of hybrid planet.

*unless Planet Nine turns out to be real