Update from the DC Planet Search
Winter continues to trudge toward conclusion at the Naval Observatory in the heart of Washington DC. Despite the odd blizzard, the weather – and the equipment in USNO’s 24-inch dome – has cooperated fairly well so far in 2006. We’ve also been fortunate to add a new observer to our team. Zach Dugan is a Junior astronomy major at Yale (and a DC resident during school breaks). At the moment, Zach is taking a semester Down Under, at the University of Melbourne, but he will rejoin us in a few months. The Naval Academy also finalized an indefinite loan of a liquid nitrogen-cooled ccd camera to USNO, making the search for exoplanet transits a much-improved operation, and certainly less of a headache for observer and USNA Senior John Pepin. We have endured two camera failures, light pollution challenges, and pointing difficulties (owing to 1970â€™s vintage â€“ read slipping — analog sidereal time dials) in his quest to detect transits. Nevertheless, he got a chance to present initial results with a poster at the January AAS Meeting.
Our recent transit searches have focused on two interesting planetary systems. The first, HD 80606, has been an elusive, and long-running target for the transitsearch.org collaboration. The parent star, HD 80606A is a relatively ordinary metal-rich solar-type star in a wide binary. It harbors a planet with an absolutely crazy orbit: P=111.4 days, e=0.935. (Have a go at fitting it with the Systemic Console.) In the figure below, we plot its position at daily intervals, with the orbits of Earth, Venus, and Mercury shown for comparison:
HD 80606 b likely has some of the worst weather in the Galaxy, and hence we would learn an extraordinary amount from follow-up observations if it were found to transit. Although the planet regularly whips down within 6 stellar radii of the stellar surface, the orientation of the orbit is not particularly well suited for possible occultations, and the a-priori transit probability is a slim 1.7%.
The most recent transit detection opportunity occurred in a 3-sigma window that covered about a day to either side of Jan. 26th. We met the window at the ready with the USNO 24-inch, but the weather was largely uncooperative, and we were clouded out on both the 25th and 26th. We were, however, able to obtain observations throughout the evening of the 27th. No transit was observed. The non-detection rules out some of the allowed parameter space, and thus makes our task slightly easier during the next transit opportunity on May 17th. Mark your calendars!
In the meantime, we’ve shifted focus to HD 102195, an interesting system that harbors a planet with a much shorter 4.115 day period. The discovery of HD 102195 “b” was announced by Jian Ge at the January 2006 AAS meeting, and it’s the first planet to come out of the new University of Florida Exoplanet Tracker system. So far, only a short abstract about the planet has been published, but from the information reported in the abstract, it appears that a full photometric transit check may not yet have been obtained.
The a-priori odds that HD 102195 b can be observed in transit are quite high, around 10%. The chances don’t get much better than that, and so this planet represents an exciting opportunity. It’s not an easy target, though. The primary is a very young 600 million year-old K0V star with a ~12 day rotational period, an the stellar surface is riddled with star-spots.
For this search, we are collaborating with transit photometry veteran Ron Bissinger, who’s based out in Pleasanton, California. The transit windows for this system are fairly wide, but the 4.11-day period has meant that a program to repeatedly check for transits is readily doable. HD 102195 is visible now (it is close to Zavijava in Virgo), so both Ron and us have been observing.
Thus far, no transits have been detected. Ron, in fact, has recently moved to another candidate; we may follow suit shortly. But if we do have the good fortune to make a detection, weâ€™ll have to be very careful to separate the transit dip from flux variations arising from the starspots. Look for a final report in the near future.
Meanwhile, we here at USNO are working on an ABSCICON poster paper that reports our recent millimeter observations with VLA and ATCA that searched for a dust-ring orbiting GJ 876. Knowledge of the presence (or absence) of a dust ring can provide us with a better understanding of both the system orbital plane, and its population of icy and asteroidal bodies. But weâ€™ll save those details for the poster. And also, look for Ryan Montgomery’s paper at ABSCICON. Rumor on the street is that his simulations have cooked up some fresh-baked Earths orbiting 0.1 solar mass stars…