Document Type

Honors Project On-Campus Access Only

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Advisor: Dr. Barton Pritzl

Abstract

Herbig AeBe (HAeBe) binary systems are good environments for the study of pre-main sequence stellar evolution in companion stars whose mass may be significantly lower than that of the primary star. Measurements of the spectral type and surface gravity of the companion star in the system allow it to be placed on the H-R diagram, where theoretical evolutionary model tracks can then constrain its mass and age, and comparisons can be made between these low mass stars and those formed without the presence of a high mass star. We present two different ways to measure effective temperature (Teff) and estimate surface gravity (log g) from the spectra of late type stars, depending on the spectral resolution (R=18000, R=6000 or 1700). At high resolution, detailed model fits to the shapes of Na lines at 2.21 microns and the (2-0) 12CO bandhead at 2.29 microns provide an accurate way to measure effective temperature (sigma = 190 K) and surface gravity (sigma = 0.82 cm s-2), in addition to allowing for values of vsini, veiling, and radial velocity to be estimated. At medium resolution, the equivalent widths of 10 of the strongest absorption lines present in the NIR spectrum were measured to determine Teff at a lower accuracy. Preliminary results show that these techniques are useful for characterizing late-type companions. Analysis of two stars is discussed, more data is needed to address statistical questions about the nature of HAeBe companions and better calibrate classification techniques.

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