Erik M. Leitch — Page 2

arXiv1999

An Absolute Flux Density Measurement of the Supernova Remnant Casseopia A at 32 GHz

We report 32 GHz absolute flux density measurements of the supernova remnant Cas A, with an accuracy of 2.5%. The measurements were made with the 1.5-meter telescope at the Owens Valley Radio Observatory. The antenna gain had been measured by NIST in May 1990 to be $0.505 \pm 0.007 \frac{\rm mK}{\rm Jy}$. Our observations of Cas A in May 1998 yield $S_{cas,1998} = 194 \pm 5 {\rm Jy}$. We also report absolute flux density measurements of 3C48, 3C147, 3C286, Jupiter, Saturn and Mars.

astro-ph↗

arXiv1998

Mass Extinctions and The Sun's Encounters with Spiral Arms

The terrestrial fossil record shows that the exponential rise in biodiversity since the Precambrian period has been punctuated by large extinctions, at intervals of 40 to 140 Myr. These mass extinctions represent extremes over a background of smaller events and the natural process of species extinction. We point out that the non-terrestrial phenomena proposed to explain these events, such as boloidal impacts (a candidate for the end-Cretaceous extinction), and nearby supernovae, are collectively far more effective during the solar system's traversal of spiral arms. Using the best available data on the location and kinematics of the Galactic spiral structure (including distance scale and kinematic uncertainties), we present evidence that arm crossings provide a viable explanation for the timing of the large extinctions.

astro-ph↗