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Abstract:
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Studies of the temporal evolution of young stars and their associated properties rely upon the ability of astronomers to determine ages and masses of objects in different evolutionary states . The best method for determining the age and mass of a young stellar object is to place the object on the Hertzsprung -Russell (HR ) diagram and to compare to theoretical evolutionary tracks . Accurate ages allow the investigation of the temporal evolution of properties associated with stellar youth (accretion rates , X -ray activity , circumstellar excess , etc . . . ) . One property intimately linked with stellar youth is the presence (or absence ) of an optically thick primordial circumstellar disk . Objects in "young" star forming regions are more likely to show evidence for a disk than objects in "older" clusters . Within a single cluster , the picture is not as clear . There exist objects in very young clusters ( ~1 Myr ) which show no evidence for circumstellar disks , and there exist objects in very old clusters ( ~10 Myr ) , which show evidence for robust disks , suggesting a variable other than stellar age is driving the evolution of the disks . To investigate whether these outliers are due to age spreads , initial conditions , or simply appear anomalous due to erroneous age determinations , we must determine better placements in the HR diagram by carefully transforming observable quantities (spectral type and apparent magnitude ) into the quantities necessary for comparison evolutionary models (effective temperature and luminosity ) . In the Ophiuchus star forming region , I investigate whether or not objects with disks are younger than disk -less objects . I find no difference in the ages of the two populations , but the systematic and random uncertainties are large enough to mask all but the largest age differences . In the hope of better determining the physical parameters of young stellar objects , I embark on a spectral synthesis campaign to produce comparison synthetic spectra which account for the effects of magnetic fields . This requires the modification of the MOOG spectral synthesis program to handle the full Stokes vector treatment for polarized radiation through a magnetized medium . I create a grid of synthetic spectra covering ranges in effective temperature , surface gravity , and average magnetic field strength relevant for studies of young stellar objects , and develop a Chi -squared minimization routine to determine the best fit synthetic spectrum for a given observed spectrum at an arbitrary resolving power . This grid of synthetic spectra will be an invaluable complement to future near infrared , large band -pass , high -resolving power spectrographs (i .e . IGRINS ) . In addition to these observational and theoretical attempts to reduce systematic errors , I also helped to develop a suite of silicon and KRS -5 grisms for use in the FORCAST instrument , a mid infrared camera on the SOFIA telescope . These grisms will afford the imaging instrument a mid infrared spectroscopic capability at wavelengths normally inaccessible from the ground . I also report on my work to help write FG Widget , the quick -look reduction software package developed to support grism observations . |