High precision radial velocity studies over the last decade have demonstrated that nearly 12% of nearby main-sequence stars harbor Jovian-like planets. The unexpected properties of many of these extrasolar planets (e.g. the 'hot Jupiters') have resulted in many proposed revisions to the once well-accepted theory of how planets form. Unfortunately, there are few observational constraints to test these new theories. The most direct way to establish these constraints would be to conduct a sensitive search for planets orbiting low mass stars with ages comparable to the predicted planet formation timescale (less than about 10 million years). Unfortunately, traditional optical spectroscopic techniques are not able to accomplish this because of the relative faintness of young stars at optical wavelengths and, more critically, because of the large star spots associated with young stars that can mask the radial velocity reflex motion caused by a planet.
The study to be carried out here by Dr. White involves a novel technique to overcome both of these observational challenges using high dispersion infrared spectroscopy. First, infrared wavelengths are much closer to the peak in the energy distribution of young low mass stars, so the target stars are effectively brighter than they are at optical wavelengths. Second, at these longer wavelengths, the contrast between the stellar photosphere and cool star spots is diminished significantly, and this translates (almost linearly) into reduced radial velocity 'noise' caused by these spots; predictions suggest a gain of a factor of about 5.
Motivated by this, Dr. White has begun an infrared radial velocity survey of approximately 80 young (age less than 20 million years) stars. With the data in hand, a precision better than about 100 m/s can already be demonstrated, sufficient to find the most massive known extrasolar planets, if present. Conservative estimates show that refining the analysis techniques alone should improve the precision by a factor of 2 or 3. This award will support both the continuation of this first-ever spectroscopic infrared search for young planets, and the further development of this pioneering high precision infrared technique.
It is expected that this work will influence how the next generation of infrared spectrographs is designed and how future planet searches will be conducted; the results so far have already helped guide plans for future high dispersion infrared spectroscopic facilities. A graduate research assistant at the University of Alabama in Hunstville will also be supported and trained in infrared observing through this project.
