J.-D. T. Smith

SCORE 1+: enhancing a unique mid-infrared spectrograph

SCORE is a cross-dispersed echelle spectrograph, built as a prototype for the Short-High module of SIRTFs IRS instrument. It operates over the 7.5-15 micrometers N-band atmospheric window, and has ben used on Palomars Hale telescope several times since November, 1996. Since the initial run, a number of improvements have ben undertaken or are in the process being undertaken which enhance SCOREs performance and simplify its operation. One such addition, now completed, is a second detector array which serves as a slit-viewer with 12 inch diameter field of view around the slit. This viewer allows easy acquisition and guidance for sources with dim or absent optical counterparts, and accurately registers the position of the slit on the source with the recorded spectrum. Software written in the IDL environment optimizes the extraction of spectra form SCOREs mid-IR crossed-echelle data. The echelle, while providing the advantage of increased pixel utilization, introduces several difficulties, including curved orders, order cross- talk, and differentially slanted lines. These and other instrumental artifacts must be removed to achieve the highest spectral signal-to-noise. The pixel efficiency will be further increased by the use of a grism predisperser. The grism will provide approximately even spacing between orders of the echelle, in contrast with the decreasing spacing towards shorter wavelength orders generated by the current grating. SCORE is already one of the most powerful short- slit spectrographs operating in this wavelength band, and, with the implementation of these improvements, will deliver even greater capability.

The Wolf-Rayet Phenomenon in the Infrared: Massive Stars Probing Stellar Formation

A technique for identifying star formation that uses unambiguously stellar radiation has led to a class of objects known as Wolf-Rayet galaxies, so named because of their measured contingent of Wolf-Rayet (WR) stars, a class of peculiar emission-line objects characterized by extreme mass-loss rates of . The mass loss is driven in 4 1 10 M ∼ 10 M yr p 10 M , , fast ( km s ), dense stellar winds, in 1 365 km s ≤ v ≤ 5000 which broad emission lines are formed. Although detecting the unusual emission features that signal the presence of WR stars in the integrated spectra of galaxies is challenging, this direct diagnostic provides incontrovertible evidence of massive star formation and provides powerful constraints on the formation timescale. Although the WR direct detection technique is powerful, it has so far been applied using only a handful of strong optical wind lines, which cannot probe environments in which star formation is embedded in dust. Though intrinsically weaker, the possibility of extending this diagnostic to use infrared WR wind emission lines to pierce the veil of extinction that may cloak a substantial fraction of star formation in the local and distant universe is what motivated this thesis. To form an accurate template of their IR spectra, we undertook a mid-IR spectral survey of WR stars selected to cover a broad distribution of subtypes. We present 8–13 mm spectra at resolution of 29 northern Galactic WR stars, including R ∼ 600 14 WC, 13 WN, 1 WN/WC, and an additional reclassified WN star. Most constitute the first ever reported mid-IR spectrum. Lines of He i and He ii, accompanied in some stars by [Ne ii] and [S iv], are strongly present in 22 of the sources observed, while six of the sources exhibit the powerful emission of heated circumstellar carbon dust. Correspondence with optically determined subtypes is found to be incomplete, with significant deviations for the later types seen in both WN and WC. For a single WC star, WR 121, neon abundance in the wind is estimated