SuperCam, a 64-pixel heterodyne imaging array for the 870 micron atmospheric window

We report on the development of SuperCam, a 64 pixel, superheterodyne camera designed for operation in the astrophysically important 870 micron atmospheric window. SuperCam will be used to answer fundamental questions about the physics and chemistry of molecular clouds in the Galaxy and their direct relation to star and planet formation. The advent of such a system will provide an order of magnitude increase in mapping speed over what is now available and revolutionize how observational astronomy is performed in this important wavelength regime. Unlike the situation with bolometric detectors, heterodyne receiver systems are coherent, retaining information about both the amplitude and phase of the incident photon stream. From this information a high resolution spectrum of the incident light can be obtained without multiplexing. SuperCam will be constructed by stacking eight, 1x8 rows of fixed tuned, SIS mixers. The IF output of each mixer will be connected to a low-noise, broadband MMIC amplifier integrated into the mixer block. The instantaneous IF bandwidth of each pixel will be ~2 GHz, with a center frequency of 5 GHz. A spectrum of the central 500 MHz of each IF band will be provided by the array spectrometer. Local oscillator power is provided by a frequency multiplier whose output is divided between the pixels by using a matrix of waveguide power dividers. The mixer array will be cooled to 4K by a closed-cycle refrigeration system. SuperCam will reside at the Cassegrain focus of the 10m Heinrich Hertz telescope (HHT). A prototype single row of the array will be tested on the HHT in 2006, with the first engineering run of the full array in late 2007. The array is designed and constructed so that it may be readily scaled to higher frequencies.Comment: 12 pages, 14 figures, to be published in the Proceedings of SPIE Vol. 6275, "Astronomical Telescopes and Instrumentation, Millimeter and Submillimeter Detectors and Instrumentation for Astronomy III

Formal Public Health Education and Career Outcomes of Medical School Graduates

Few data are available evaluating the associations of formal public health education with long-term career choice and professional outcomes among medical school graduates. The objective of this study was to determine if formal public health education via completion of a masters of public health (MPH) degree among US medical school graduates was associated with early and long-term career choice, professional satisfaction, or research productivity.We conducted a retrospective cohort study in 1108 physicians (17.1% completed a MPH degree) who had 10–20 years of follow-up post medical school graduation. Multivariable logistic regression analyses were conducted.Compared to their counterparts with no MPH, medical school graduates with a MPH were more likely to have completed a generalist primary care residency only [relative risk (RR) 1.79, 95% confidence interval (CI) 1.35–2.29], obtain employment in an academic institution (RR 1.81; 95% CI 1.33–2.37) or government agency (RR 3.26; 95% CI 1.89–5.38), and practice public health (RR 39.84; 95% CI 12.13–107.38) or primary care (RR 1.59; 95% CI 1.18–2.05). Furthermore, medical school graduates with a MPH were more likely to conduct public health research (RR 8.79; 95% CI: 5.20–13.82), receive NIH or other federal funding (RR 3.11, 95% CI 1.74–5.33), have four or more peer-reviewed publications (RR 2.07; 95% CI 1.56–2.60), and have five or more scientific presentations (RR 2.31, 95% CI 1.70–2.98).Formal public health education via a MPH was associated with career choice and professional outcomes among physicians

A millimeter-wave interferometric study of gas-phase silicon dicarbide in the circumstellar envelope surrounding IRC+10216

We have used the Berkeley-Illinois-Maryland Association (BIMA) Array to map emission from the 4\sb{22}-3\sb{21} and 4\sb{04}-3\sb{03} transitions of SiC\sb2 in the circumstellar envelope (CSE) surrounding IRC+10216. The NRAO 12-m telescope was used to fill in missing flux from large scale structure not detected by the interferometer. The interferometry and 12-m single-element data were combined to make full synthesis maps of emission from SiC\sb2 toward IRC+10216.We find that full synthesis maps of the 4\sb{22}-3\sb{21} and 4\sb{04}-3\sb{03} transitions of SiC\sb2 show a distinctly shell-like structure. The emission is not uniformly distributed. Instead, it shows a clumpy appearance on the plane of the sky. The maps of the 4\sb{22}-3\sb{21} transition show a distinct bipolar structure with lobes oriented along a roughly north-south axis. The maps of the 4\sb{04}-3\sb{03} transition show an asymmetric appearance in which the east side of the CSE is $\sim$2-3 brighter than the west side. Radiative transfer models of the data suggest that most of the observed SiC\sb2 is confined to a shell with inner radius $\sim$2 $\times$ 10\sp{16} cm and outer radius $\sim$6 $\times$ 10\sp{16} cm. The abundance of SiC\sb2 ( (SiC\sb2) / (H\sb2)) within the shell is $\sim$10\sp{-6}. We cannot rule out the possibility that some SiC\sb2 originates in the inner envelope near the photosphere but we can put an upper limit on the abundance of SiC\sb2 in the inner envelope. Our data constrains the fractional abundance of SiC\sb2 in the inner envelope (r \sbsp{\sim}{<} 2 $\times$ 10\sp{16} cm) to be no more than $\sim$3 $\times$ 10\sp{-8}. The distribution and abundance of SiC\sb2 suggest that ion-molecule reactions involving C\sb2H\sb2 may be responsible for producing much of the SiC\sb2.Our data also places important constraints on the excitation mechanisms for SiC\sb2. Kinetic temperatures in the outer CSE (\sbsp{\sim}{<}60 K) where much of the SiC\sb2 resides are not high enough to excite the high excitation temperatures across K-ladders observed by Thaddeus et al. (1984) and Avery et al. (1992). This suggests that radiative excitation through the lowest-lying vibrationally-excited state, the \nu\sb3 = 1 antisymmetric mode, may be responsible for the high excitation temperatures across K-ladders. To test this hypothesis we made a sensitive search for rotational transitions of vibrationally excited SiC\sb2 with the NRAO 12-m. Our data suggests that the column density of vibrationally excited SiC\sb2 is at least two orders of magnitude lower than the column density of the ground vibrational state. The upper limit on the column density of vibrationally excited SiC\sb2 is consistent with radiative excitation through the \nu\sb3 = 1 antisymmetric mode.U of I OnlyETDs are only available to UIUC Users without author permissio

The chemistry of extragalactic carbon stars

Prompted by the ongoing interest in Spitzer Infrared Spectrometer spectra of carbon stars in the Large Magellanic Cloud, we have investigated the circumstellar chemistry of carbon stars in low-metallicity environments. Consistent with observations, our models show that acetylene is particularly abundant in the inner regions of low metallicity carbon-rich asymptotic giant branch stars – more abundant than carbon monoxide. As a consequence, larger hydrocarbons have higher abundances at the metallicities of the Magellanic Clouds than in stars with solar metallicity. We also find that the oxygen and nitrogen chemistry is suppressed at lower metallicity, as expected. Finally, we calculate molecular line emission from carbon stars in the Large and Small Magellanic Cloud and find that several molecules should be readily detectable with the Atacama Large Millimeter Array at Full Science operations