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Session 24 - Star Formation in the Galaxy & the LMC.
Display session, Tuesday, June 10
South Main Hall,
As part of a larger study we have obtained high dispersion spectra for a sample of pre-main sequence stars in the Orion Nebula Cluster (ONC) in order to measure v\thinspace sin(i) values. Our sample includes 31 ONC stars brighter than V=18.0 for which accurate rotation periods are known from photometric monitoring. We plan to obtain similar observations for an additional \sim70 stars, which will provide a database of over 100 ONC stars for which both rotation periods and v\thinspace sin(i) are known. The goals of this project are twofold: By combining rotation periods with projected velocities for this large sample of stars, we will be able to apply statistical arguments to arrive at estimates for the mean radii of the stars in several groups segregated by mass and age. Stellar radii and rotational velocities are crucial fundamental parameters which constrain theoretical models describing pre-main sequence (PMS) evolution. However, with the exception of two known PMS eclipsing binaries, we have no direct measurements of the sizes of PMS stars. Our method utilizes a novel approach for the estimation of stellar radii. (2) In addition, v\thinspace sin(i) measurements for stars without photometric periods will allow us to investigate whether our understanding of the initial conditions of rotation in pre-main sequence stars has been biased by the available data derived from spotted stars.
Here we present the results from our initial set of observations. Details of the data analysis will be described, and the derived rotational velocities presented. We will also present simulations showing our planned method for estimating the mean radii of these pre-main sequence stars.
