Dr. Sergio Dieterich is awarded an NSF Astronomy and Astrophysics Postdoctoral Fellowship to carry out a program of research and education at the Department of Terrestrial Magnetism of the Carnegie Institution of Washington. Brown dwarfs are objects that never acquired enough mass during their formation to attain the internal temperature and pressure necessary to ignite the sustained nuclear fusion of hydrogen, which is the hallmark of a stellar object. Understanding the boundary between very low mass stars and brown dwarfs has deep implications for the search for life in the Universe. It is likely that life may evolve on planets orbiting stars but it is more difficult for life to evolve on brown dwarf systems due to their constantly changing temperature. Dr. Dieterich studies trends in temperature, radius, and luminosity of objects near the stellar/substellar boundary. His thesis work identified a stellar and a substellar population based on these trends. This work will now be extended to a larger sample of stars, and will explore how chemical compositions for different stars change this boundary. Dr. Dieterich will use his experience as a former middle and high school physical science teacher to facilitate the integration of astronomy in the high school physics curriculum. He will compile an activity book that will serve as a resource for physics teachers who wish to enrich their classes by illustrating physical concepts with examples from astronomy.
Dr. Dieterich will address the following three scientific questions during his fellowship: (1) What is the luminosity function at the stellar/substellar boundary? (2) How does metallicity affect the properties of objects with masses close to the hydrogen burning minimum mass? and (3) How can we use objects with known dynamical masses to create a more robust and detailed Mass-Luminosity Relation at the stellar/substellar boundary? The unique resources of Carnegie's Las Campanas Observatory in Chile are key to answering these questions. Because an accurate distance measurement is essential for establishing luminosity and radius, Dr. Dieterich and collaborators will use the Carnegie Astrometric Planet Search Camera (CAPSCam) on the du Pont 2.5 meter telescope to determine precise trigonometric parallaxes so as to make the study sample volume-complete. Several Las Campanas telescopes will also be used to obtain optical photometry for these very faint objects, which is necessary for calculating bolometric fluxes. Metallicities for the sample will be established through spectroscopic observations done with the Magellan 6.5 meter telescopes. The MagAO adaptive optics system on the Magellan II telescope is one of the only ground based systems capable of obtaining diffraction-limited images in optical wavelengths. This unique capability will be used for the photometric characterization of stars in close binary systems for which dynamical masses are known. The resolved optical photometry will then be used to determine luminosity and effective temperature for these stars, therefore populating the mass-luminosity relation.
