Barbara A. Whitney

Probing the early evolution of dust grains through detailed YSO models

Understanding the evolution of young stellar objects (YSOs) from a protostar to a main-sequence star is key to understanding the origins and evolution of planetary systems. Highresolution polarimetric observations from the Hubble Space Telescope Near Infrared Camera and Multi-Object Spectrometer (NICMOS) of objects known to span the earliest stellar evolutionary phases are combined with (1) 3-D radiative transfer codes, and (2) a grid of dust grain models, to gain insight into the initial phases of dust grain growth and evolution away from an interstellar medium (ISM) distribution. Fractional polarization is a strong function of wavelength; therefore by developing detailed models of polarimetric images in the infrared, we can begin to sensitively constrain not only the geometry and optical depth of the scattering medium, but also the grain size distribution. We are studying four YSOs known to span the earliest stellar evolutionary phases (IRAS04302+2247 (Class I), IRAS04016+2610 (Class I), CoKu Tau/1 (Cla...

Insights into star cluster formation from λ 1μm

We would like to know how molecular clouds turn into stellar clusters, and with what efficiency massive stars form in those clusters, since massive stars are the main agents responsible for evolution of the interstellar medium of galaxies, and their subsequent star-formation history. The imprint of ‘precluster’ molecular cloud conditions can be observed, but only in the least evolved, most embedded clusters, necessarily at wavelengths that can penetrate more than 10 visual magnitudes of extinction. Mid-infrared photometric imaging, most recently and extensively from Spitzer , can be used to select young stellar objects in clustered star-formation environments in our Galaxy and nearby galaxies. Relatively sophisticated methods have been developed, but the fundamental principle remains the selection of sources that have excess infrared emission from circumstellar dust. By fitting radiative-transfer models to a sources spectral-energy distribution between ~1 and ~100μm, we constrain the circumstellar dust distribution and evolutionary state. We can explore many things with this protostellar distribution in mass/luminosity and time/evolutionary state. For example we do not see strong evidence for primordial mass segregation in initial studies. We find evidence of primordial hierarchical substructure, greater clustering at the youngest stages, and even imprints of the pre-stellar Jeans scale. We see correlation of the youngest sources with dense molecular clumps and constrain the timescales for chemical processing and dispersal of those clumps. We have only begun to mine the wealth of existing Spitzer , emerging Herschel and soon ALMA data.

Measuring the lifecycle of baryonic matter in the Large Magellanic Cloud with the Spitzer SAGE-LMC survey

The recycling of matter between the interstellar medium (ISM) and stars are key evolutionary drivers of a galaxys baryonic matter. The Spitzer wavelengths provide a sensitive probe of circumstellar and interstellar dust and hence, allow us to study the physical processes of the ISM, the formation of new stars and the injection of mass by evolved stars and their relationships on the galaxy-wide scale of the LMC. Due to its proximity, favorable viewing angle, multi-wavelength information, and measured tidal interactions with the Small Magellanic Cloud (SMC), the LMC is uniquely suited for surveying the agents of a galaxys evolution (SAGE), the ISM and stars. The SAGE-LMC project is measuring these key transition points in the life cycle of baryonic matter in the LMC. Here we present a connective view of the preliminary quantities estimated from SAGE-LMC for the total mass of the ISM, the galaxy wide star formation rate and the current stellar mass loss return. For context, we compare these numbers to the LMCs stellar mass.