Phase-folded and phase-binned light curve for KELT- 3, from Zhang+ (2015).
At research group meeting on Thursday, we discussed a recent paper by Zhang and colleagues that investigated the performance of Canon’s EOS 60D and whether it was suitable to use for precision photometry to look for exoplanet transits.
Although the authors found the camera exhibited a few peculiarities (that are apparently not described in any of Canon’s documentation), they showed that it could be used to observe exoplanet transits — a really great result.
It means that astronomers, amateur or professional, who want to do transit observations don’t need to spend $10,000 to buy a high-end CCD camera. Instead, they can spend just a few hundred to produce reasonable quality transit light curves.
One especially tantalizing result from the paper: Zhang and colleagues mention having seen exoplanet transit-like signals for four of the target stars they studied, only one of which is known to host a planet — KELT-3 b.
That means they may not only have recovered known transiting with the Canon EOS 60D; they may also have found three new ones. Presumably, they’re in the process of trying to confirm whether the other three are new planets.
UPDATE: The authors kindly updated me to say that follow-up observations indicated these three candidates are all false positives. But they would have discovered KELT-3 b with their survey, if it hadn’t already been discovered. So a pretty amazing achievement.
Attendees included Jennifer Briggs, Andrew Farrar, Nathan Grigsby, Emily Jensen, and Tyler Wade.
At Friday’s journal club, we discussed on two papers. The first, Webber et al. (2015), investigated the effects of clouds on the phase curves for hot Jupiters. Webber et al. found that planet’s phase curve may depend sensitively on whether clouds are distributed uniformly or heterogenously throughout the atmosphere. They also found that the amount of light reflected by an exoplanet depends on the composition of the clouds — clouds made of rocky minerals like MgSiO3 and MgSi2O4 are much brighter than Fe clouds.
From Ballard & Johnson (2015), this figure compares the number of stars with a certain number of planets detected by Kepler (blue diamonds) to our expectations (in red) if single planet systems actually had more planets hidden from Kepler’s view. The disagreement between the blue and red curves suggests that many of those apparently singleton planets really are only children and single and multi-planet systems are inherently different.
The second paper, Ballard & Johnson (2014), investigated the frequency of exoplanets around M-dwarf stars observed by the Kepler mission. Because the Kepler mission found planets by looking for transits, there’s always a good chance that a system with only one detected planet actually has more that just don’t pass in front of their host star as seen from Earth. But we know exactly how to account for this geometric effect.
By accounting for it, Ballard and Johnson showed that Kelper actually found a lot more systems with only one planet than we would expect if there were just more planets in those systems hidden from Kepler‘s view. So there are two distinct kinds of planetary systems around M-dwarfs: those with only one planet (or possibly several planets with large mutual inclinations) and those with several.
Why the difference? Ballard and Johnson find tantalizing hints that stars hosting only one detected planet are older on average. One simple explanation: given enough time, systems with many planets become unstable, and the lonely planets we see today originally had siblings that were gravitationally cast out of the system, to wander the void between the stars. Or the siblings were accreted by their parent stars, like Saturn eating his children. Along with many others, this study helps show that planetary systems can be much more violent places than astronomers originally thought.
Journal club attendees included Jennifer Briggs, Nathan Grigsby, Jared Hand, Tanier Jaramillo, Emily Jensen, Liz Kandziolka, and Jacob Sabin.
The tightly packed system, named Kepler-444, is home to five small planets in very compact orbits. The planets were detected from the dimming that occurs when they transit the disc of their parent star, as shown in this artist’s conception. From http://www.nasa.gov/ames/kepler/astronomers-discover-ancient-system-with-five-small-planets/.
In journal club on Friday, we discussed a fascinating paper from Campante and colleagues announcing discovery of one of the oldest planetary systems ever discovered — Kepler-444. The system comprises five planets, ranging from roughly Mercury- to Venus-sized with orbital periods from about 3 to 9 days.
Studying the frequencies of oscillations within the K-dwarf host star (an approach known as asteroseismology), Campante et al. estimate the host star, and therefore probably the planets, is about 11 billion years old, almost as old as the Milky Way galaxy itself.
To put that age into perspective, by the time our solar system formed, about 5 billion years ago, the Kepler-444 was already a billion years older than our solar system is now.
The existence of such an old system tells us that rocky planets began forming almost as soon as the Milky Way itself formed, which allows for the exciting possibility of very ancient life in the galaxy.
Present at journal club were Jennifer Briggs, Trent Garrett, Nathan Grisgby, Emily Jensen, Liz Kandziolka, Brenton Peck, and Jacob Sabin.
Mechanical failures interrupted Kepler’s original mission, but the telescope is still hunting exoplanets. From http://www.nature.com/news/three-super-earth-exoplanets-seen-orbiting-nearby-star-1.16740.
Discussed a brilliant paper today in journal club from Ian Crossfield and collaborators, in which they announce the discovery of a three-planet system around a nearby M-dwarf star.
The team found the new system in data from the re-incarnated Kepler mission called K2. This system is only the second discovered by the mission (the first was announced a few months ago).
This new system is especially exciting because, as the authors point out, it is observable by other available facilities, allowing astronomers to characterize the planets and star in detail.
The outermost planet in the system, with an orbital period of 45 days, is very near the inner edge of the system’s habitable zone and has a temperature of about 310 K (100 F), making it plausibly habitable. Combined with the fact that we can probably characterize the planet in detail, there’ll probably be a flurry of exciting studies of the system very soon.
Journal club was attended by Jennifer Briggs, Trent Garrett, Nathan Grigsby, Emily Jensen, Liz Kandziolka, and Brenton Peck.