Constraints on Type Ib/c and GRB Progenitors

Although there is strong support for the collapsar engine as the power source of long-duration gamma-ray bursts (GRBs), we still do not definitively know the progenitor of these explosions. Here we review the current set of progenitor scenarios for long-duration GRBs and the observational constraints on these scenarios. Examining these, we find that single-star models cannot be the only progenitor for long-duration GRBs. Several binary progenitors can match the solid observational constraints and also have the potential to match the trends we are currently seeing in the observations. Type Ib/c supernovae are also likely to be produced primarily in binaries; we discuss the relationship between the progenitors of these explosions and those of the long-duration GRBs.Comment: 36 pages, 6 figure

Extrapolation of synoptic meteorological data in mountainous terrain and its use for simulating forest evapotranspiration and photosynthesis

A model for calculating daily microclimate conditions in mountainous terrain is presented. Maximum–minimum daily air temperatures, precipitation, and dew point are extrapolated from valley stations to adjacent mountain slopes, after making elevation- and aspect-related corrections. The model (MT-CLIM) produces estimates of daily incoming shortwave radiation, air temperature, humidity and vapor pressure deficit, and precipitation for any mountain study site. MT-CLIM was tested against measured meteorological data on six study sites consisting of three north–south slope pairs in western Montana. Correlations between predicted and observed daily conditions on the six study sites for the period April–November 1983 were air temperature, R2 = 0.88–0.92 with standard errors \u3c0.48 °C; relative humidity R2 = 0.63–0.72 with standard errors \u3c15%; radiation R2 = 0.60–0.78 with standard errors \u3c100 W m−2. To test the utility of the model, data from MT-CLIM were used to run the DAYSTRANS/PSN model of evapotranspiration (ET) and photosynthesis (PSN) for western coniferous forests. Seasonal ET calculated from MT-CLIM data deviated by less than 5% from ET calculated from measured meteorological conditions on the six sites. Estimates of seasonal PSN agreed to within 10% of estimates derived from measured meteorological data on all sites except one. For each of the north–south slope study pairs, the combined MT-CLIMDAYTRANS/PSN simulation predicted that north slopes would have higher (5–31%) seasonal PSN than the comparable south slopes, which agrees with observed patterns of forest productivity in this semiarid region

Overstory removal and residue treatments affect soil surface, air, and soil temperature : implications for seedling survival /

no.37

Native shrubs : suitability for revegetating road cuts in northwestern Montana /

no.33

Optical and Near-Infrared Observations of the Peculiar Type Ia Supernova 1999ac

We present 39 nights of optical photometry, 34 nights of IR photometry, and 4 nights of optical spectroscopy of the Type Ia supernova 1999ac. This supernova was discovered 2 weeks before maximum light, and observations were begun shortly thereafter. At early times its spectra resembled the unusual SN 1999aa and were characterized by very high velocities in the Ca II H and K lines but very low velocities in the Si II λ6355 line. The optical photometry showed a slow rise to peak brightness but, quite peculiarly, was followed by a more rapid decline from maximum. Thus, the B- and V-band light curves cannot be characterized by a single stretch factor. We argue that the best measure of the nature of this object is not the decline rate parameter Δm15(B). The B - V colors were unusual from 30 to 90 days after maximum light in that they evolved to bluer values at a much slower rate than normal Type Ia supernovae. The spectra and bolometric light curve indicate that this event was similar to the spectroscopically peculiar slow decliner SN 1999aa