In this project, Dr. Barsony and her collaborators will conduct an observational survey to search for sub-stellar or planetary-mass objects in regions of star formation. These objects, called T-dwarfs, are relatively luminous when young, and can be detected because they exhibit broad absorption features from methane in their spectra. The research team will conduct a wide-area infrared survey to find T-dwarfs by imaging at the wavelength of the methane band and at an adjacent wavelength. Objects that are faint in the methane band are likely to be T-dwarf stars.
The research activity will have a broader educational impact through the involvement of undergraduate students in the research effort. Students will be recruited at San Francisco State University and at Utah Valley State College (now Utah Valley University), and will have the opportunity to visit the other institution in the collaboration. The detection of large numbers of T-dwarfs will help improve theories of star formation, especially in the domain between the least-massive stars and the most-massive planets.
One of the most exciting frontiers of astrophysics research today is the discovery and characterization of sub-stellar objects, ranging from brown-dwarf to planetary masses. Brown dwarfs are objects with masses between approximately 12 - 75 Jupiter masses, while planetary mass objects have masses < 12 Jupiter masses. Planetary mass objects are of particular interest because they hold the clues to the formation of our own Solar system. Nature has found a path from the raw material of the interstellar medium to planets. Claims for the discovery of "free-floating planets" in young star clusters raise the question of: "What is the lowest mass object that can form directly from the present-day interstellar medium?" In this project, we used deep, wide-field, near-infrared methane filter imaging to search for planetary mass object candidates in the youngest (1 - 3 million year old) and nearest (d = 120 - 250 parsecs) star-forming regions to Earth. The cool atmospheres of planetary mass objects are rich in methane, and strong, broad, near-infrared methane absorption lines in the spectra of these objects are their distinguishing feature. Unexpectedly, we found a complete absence of methane absorbing objects among our sample star-forming regions. Historically, methane imaging has been successfully used to identify very low mass/planetary mass objects in the solar neighborhood. However, these objects have unknown ages, so their masses cannot be uniquely determined. Since we know the ages of our sample star-forming regions, we can accurately determine the physical properties (i.e., mass, etc.) of all planetary mass objects identified in this project for the first time. The absence of methane, therefore, was a mystery. Recently, however, other research groups using methane imaging to search for planets around nearby stars have found a complete lack of methane too. It is currently thought that this may be due to atmospheric processes in the planetary mass objects, but more work needs to be done. While the methane imaging observations yielded a negative result, we developed and refined a novel new method of identifying brown dwarfs and planetary mass objects over the course of this project. The accuracy of our method in identifying such objects is > 90%. We have currently identified over 2000 candidate new brown dwarfs/planetary mass objects among our sample star-forming regions. This is a significant increase in the number of such objects in each region. Confirmation of both the nature of these objects, and their membership in their respective star-forming region is ongoing. Over the course of this grant, I have been able to provide research opportunities to undergraduate physics students at Utah Valley University, many of whom are minorities and/or women, who otherwise would never have been able to benefit from such an opportunity. The excitement and motivation for learning provided by involvement with the real scientific research enterprise is unique. Through this grant, I have been able to take students on observing trips, attend national professional astronomy meetings, and assist in publishing our results in professional astronomy journals. All these opportunities were, or will be, assets for my students when they apply to graduate school in astronomy, as admissions committees look favorably on evidence of previous research experience.
