EXOPLANET SEARCH · Searching for extrasolar planets around the lowest mass stars

Searching for extrasolar planets around the lowest mass stars

The main aim of the research project was to search for planets around nearby stars that are of a hitherto ignored stellar type using newly developed technology and methodology to improve our understanding of planet formation and evolution. The specific focus was on the lowest mass stars. Stars of this type are a crucial sample of potential planet hosts because they can be used to illuminate the correlation between stellar mass and planet formation, are the most numerous kind of stars in the galaxy, and allow lower mass planets to be identified for a given level of observational precision. The technique employed was the radial velocity method, but applied for the first time with high precision to the near-infrared spectral regime in order to sidestep the problems of stellar faintness and activity. The project made use of observing time (33 nights) at the Very Large Telescope (VLT) facility of the European Southern Observatory (ESO). We developed a new kind of calibration unit to enable high-precision radial velocities measurements in the near infrared (NIR) for the first time. The calibration unit was a gas absorption cell that was used in conjunction with an existing VLT instrument (CRIRES). The project succeeded in all its planned goals during the fellowship period. At the beginning, we were able to demonstrate the radial velocity measurement precision that had been predicted and aimed for (5 m/s). This in itself was a long-awaited breakthrough, and it opened the door for the planet search to begin in earnest. A paper describing the new gas cell and presenting tests demonstrating its performance based on the first six months of use at the VLT was published early 2010. Also, at the same time we were able to use data from the first six months to refute the claimed detection of an exoplanet around one of our target stars. The star in question was a rather well-known very low-mass star and the previous planet detection claim (announced in May 2009) was based on astrometry. Our measurements were much more sensitive and were strongly inconsistent with the existence of the proposed planet. A paper presenting these results was also published in early 2010. The first two year search program is nearing its completion. We have already identified some planet candidates based on the data obtained so far. After the program is completed we will carefully sift through the data to collect all candidates and establish detection confidence limits. Based on the results so far, it is foreseen that no short-period planets will be identified, and therefore, no quick planet detections will be possible. All the candidates we have so far seem to be in longer periods (i.e. > 100 days) and will require additional observations to confirm and appropriately characterise prior to announcement. In addition to the VLT planet search, we have recently also begun a similar project at the Subaru telescope. We have built and installed a gas cell for an instrument on Subaru, and have been granted three nights of observing time to begin a long-term planet search project. Using this telescope gives us access to stars in the northern hemisphere, and thus allows us to increase our sample size and obtain better statistics for constraining planet formation theory. Aside from the main planet search program, the researcher has also worked on a complementary project to develop a methodology for investigating the atmospheres of low-mass transiting planets. The work on this project continued after the fellowship period, and was ultimately very successful. The results were no less than the first spectrum of a low-mass exoplanet (the mass of the planet is 6.5 times the mass of the Earth). The result very clearly indicates that either the planet must have a small dense atmosphere, or if it has a hydrogendominated atmosphere, there must be a high layer of clouds or hazes obscuring our view of the bulk of the atmosphere. This result has recently been submitted for publication in Nature.

Текст от CORDIS, на английски · Данни: CORDIS, © Европейски съюз