At journal club, we discussed the discovery of two new hot Jupiters using data from ESA‘s CoRoT mission, with the names CoRoT-28 b and -29 b. Both systems seem a little off.

The host star CoRoT-28 has an inflated radius, suggesting it is ancient and on its way off the main sequence. But it has a lot more lithium than we’d expect for an old star, and its rotation rate is similar to the Sun’s, much faster than we would expect.

Equally puzzling is the transit light curve for CoRoT-29 b (shown below at left). Most transit curves are u-shaped, but CoRoT-29 b’s is strangely asymmetric. The asymmetry resembles what has been seen for a planet transiting a rapidly rotating star — rapid rotation reduces the gravity at the stellar equator, resulting in a cooler, darker region. Barnes et al. (2013) looked at the transit light curves for such a Kepler system and actually used the light curve to study the planet’s orbital inclination.

(left) CoRoT-29 b transit light curve. (right) Planet transiting star spot.

(left) CoRoT-29 b transit light curve. (right) Planet transiting star spot.

But CoRoT-29 doesn’t appear to be a rapid rotator. So instead Cabrera et al. suggest that perhaps the star has a large, nearly stationary star spot and that the planet transits the spot over and over again. However, this scenario would require a nearly stationary spot with a very long lifetime (~90 days), neither of which is expected.

So a few more astrophysical conundra to add to the growing list of puzzling exoplanet discoveries.

Journal club attendees included Jennifer Briggs, Emily Jensen, and Hari Gopalakrishnan.

Had two nice big crashes today with my Blade 180QX. Fortunately, I caught them both on video. Unfortunately, the second broke two propeller arms, so I’m out of commission till replacements come in.

Broken propeller arms

Broken propeller arms

Here’s video of the first crash.

And here’s the second, more spectacular one.



In prep for an upcoming project (and because it’s ridiculously fun), I bought a Blade 180QX multicopter. It’s very easy to fly for someone like me who has no experience, and it comes with a nice camera (although not with the required micro SD card).

I shot this video this evening from Boise’s North End, taking off from North Junior High. I got a nice shot of the foothills, downtown, and the capital building. Be warned: the propellers are really loud.

Found some beautiful basalt columns around Lucky Peak State Park just east of Boise. A quick google search doesn’t turn up any previous surveys, so these could make a good spot for some follow-on studies to our field work back in 2011.

The radial velocity method to detect exoplanet is based on the detection of variations in the velocity of the central star, due to the changing direction of the gravitational pull from an (unseen) exoplanet as it orbits the star. When the star moves towards us, its spectrum is blueshifted, while it is redshifted when it moves away from us. By regularly looking at the spectrum of a star - and so, measure its velocity - one can see if it moves periodically due to the influence of a companion. From http://en.wikipedia.org/wiki/Doppler_spectroscopy#mediaviewer/File:ESO_-_The_Radial_Velocity_Method_%28by%29.jpg.

The radial velocity method to detect exoplanet is based on the detection of variations in the velocity of the central star, due to the changing direction of the gravitational pull from an (unseen) exoplanet as it orbits the star. From http://en.wikipedia.org/wiki/Doppler_spectroscopy#mediaviewer/File:ESO_-_The_Radial_Velocity_Method_%28by%29.jpg.

Another great day at the AAS meeting. One talk that stuck out for me was the dissertation talk from Ben Nelson (PSU). I was amazed at how much he was able to squeeze into his 15 minutes and still not lose the audience.

Among the things he covered was his new MCMC code, RUNDMC, specially suited to analyze radial velocity (RV) observations of planetary systems and thoroughly but quickly sample the sprawling parameter space associated with these systems. He applied his code to several systems to understand how robustly different planetary configurations could be detected in those systems, including whether the RV data favored additional planets in a system or other kinds of variability.

Lots of amazing presentations today, running the gamut from transmission spectroscopy of hot Neptune-like planets to the detailed and puzzling architectures of multi-planet systems. But two talks really stuck out for me.

belts-plasmapause_1 The first one, by Prof. Dan Baker at U Colorado, covered recent developments in the study of the Van Allen radiation belts (which Van Allen preferred to call “zones” — when asked by a reporter what was the function of Van Allen belts, he said they hold up Van Allen’s pants). As a member of the Radiation Belt Storm Probe mission,  Baker explained what we understand and what remains mysterious about these powerful celestial phenomena suspended above our heads, including a bizarre “glass wall” that keeps charged particles at bay.


The European Space Agency’s Rosetta spacecraft captured these photos of the Philae lander descending toward, and then bouncing off, the surface of Comet 67P/Churyumov–Gerasimenko during its historic touchdown on Nov. 12, 2014. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/ID — http://www.space.com/27788-philae-comet-landing-bounce-photos.html

In the afternoon, Dr. Paul Weissman gave the most recent updates on the Rosetta mission, still in orbit around Comet Churyumov-Gerasimenko (which Weissman called “comet CG”). Following up on the more-exciting-than-expected landing of the Philae spacecraft, Weissman explained that the lander struck a surprisingly hard sub-surface layer (comparable in strength to solid ice), which probably contributed to the lander’s unplanned ballistic trajectory around the comet. Lots of other interesting science, including more evidence about the origin of Earth’s water.

Comparison between raw K2 and corrected photometry. Figure 5 for Vanderburg & Johnson (2014).

Comparison between raw K2 and corrected photometry. Figure 5 for Vanderburg & Johnson (2014).

Read a neat paper from Andrew Vanderburg of John Johnson’s Exoplanets group at Harvard about working with data from the upcoming K2 mission.

Having suffered failures of two of its reaction wheels, required to accurately point the telescope, the Kepler mission has ended its nominal science investigation. However, clever engineering will allow the spacecraft to keep operating and doing exciting astronomy as the K2 mission.

Among other goals, the K2 mission will continue to look for transiting exoplanets, which involves looking for the shadows of planets as the occult their host stars. However, small attitude tweaks needed to keep the K2 spacecraft accurately pointed result in fairly large artificial variations in the measured brightnesses of target stars. Removing the effects of these tweaks from K2’s data can be quite challenging, but Vanderburg & Johnson’s recent paper describes one technique for doing that.

By carefully tracking the centers of target stars as they drift across the K2 CCD camera, their technique allows them to remove quite large and complex artificial variability and to recover the actual brightness variations of target stars.

From the paper, the figure at left shows how well they do: the blue dots at the top show the raw measurements, with the artificial variations from attitude tweaks apparent as discontinuous jumps. By carefully modeling the exact position of the target star and removing the effects of its motion across the CCD, the technique produces a much more accurate measurement of the actual brightness variations of the target star, orange dots at bottom.

Applying these techniques to many target stars monitored during one of the K2 engineering tests, Vanderburg & Johnson showed they can produce data nearly as precise as the original Kepler mission — almost as good as sending an astronaut repair team to fix the Kepler spacecraft, but all it took was some sophisticated numerical modeling and a laptop.

This illustration is an artist's impression of the thin, rocky debris disc  discovered around the two Hyades white dwarfs. Rocky asteroids are  thought to have been perturbed by planets within the system and diverted  inwards towards the star, where they broke up, circled into a debris  ring, and were then dragged onto the star itself. From http://en.wikipedia.org/wiki/File:Artist%E2%80%99s_impression_of_debris_around_a_white_dwarf_star.jpg.

This illustration is an artist’s impression of the thin, rocky debris disc discovered around the two Hyades white dwarfs. From http://en.wikipedia.org/wiki/File:Artist%E2%80%99s_impression_of_debris_around_a_white_dwarf_star.jpg.

Fun talk today from Dr. John Debes from the Space Telescope Science Institute (STScI) about white dwarfs eating planetesimals.

White dwarfs are the ghostly embers of former stars — they originate when a star (that is small enough not to become a black hole instead) dies and leaves behind a dense core of carbon and oxygen, enshrouded in a thin hydrogen atmosphere. That white dwarf core then slowly cools and darkens over billions of years, basically doing nothing else.

However, many white dwarfs show telltale signs in their atmospheric spectra of rocky materials. Debes, along with others, has suggested that material arises from asteroids that are perturbed by distant planets around the white dwarf. Those orbits take the asteroids so close to the white dwarf host that they are ripped apart by the star’s gravity, producing a cloud of dust and gas that then accretes onto the star.

Astronomers can very accurately measure the composition of that dust, which can actually tell us something about the compositions of asteroids in distant planetary systems. So astronomers can learn about what makes up the planets in distant systems by studying the remains in these planetary graveyards.