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Transcript
Title: Near-IR Spectra of Herbig Ae/Be Companions Authors: Bernadette Rodgers, Greg Doppmann, Nicole van der Bliek, Sandrine Thomas and Claudia Araya Abstract: How do stars form as a function of stellar mass? What are the effects of the immediate circumstellar environment? These are 2 fundamental questions that our study of companions to intermediate-mass pre-main sequence stars seeks to address. Herbig Ae/Be stars span the mass range from roughly 1.5 to 10 solar masses, and luminosities from a few to tens of thousands solar luminosities. If there is a break between low and high mass star formation, it occurs within this vast (but relatively sparsely populated) class of objects. Herbig Ae/Be stars have a high multiplicity frequency, and our near-infrared AO imaging survey has greatly expanded the sample of likely companions known. Here we present follow-up spectra that probe the physical conditions and evolutionary state of 25 likely companions. With medium resolution (R~5500) GNIRS and NIFS data we estimate effective temperatures, surface gravities and veiling from the relative and absolute depths of photospheric lines. High resolution (R~18,000) spectra of a few late-type stars better constrain temperature, gravity and veiling, and provide a measure of vsini rotation and radial velocity, by comparison to spectral synthesis models. Brackett-gamma emission (when present) and K-band veiling provide measures of the accretion rate and inner disk strength, respectively. We find high-mass primaries (> 4 M_sun) usually have high-mass companions, but with very different observed luminosities. Late-type companions (Spectral types K and M) are generally associated with lower mass Ae primary stars, but there are exceptions. Many companions in both groups do not show emission, suggesting a lack of accretion activity. We discuss these results in the context of the two questions posed.