Highlights - Volume 495-3 (March I 2009)

In section 1. Letters

“Pluto's lower atmosphere structure and methane abundance from high-resolution spectroscopy and stellar occultations”, by E. Lellouch, B. Sicardy, C. de Bergh, H.-U. Kaufl, S. Kassi, and A. Campargue, A&A 495, p. L17

Although it has been demoted from the planet rank recently, Pluto is definitely an interesting object, one with an atmosphere that has been shown to vary in mass by a factor two as a result of seasonal variations. In this issue, E. Lellouch et al. determine precisely for the first time the present abundance of methane in its atmosphere with both high-resolution spectroscopic observations and occultation light-curves. Surprisingly, methane which condenses in the low-temperature atmosphere appears to be very significantly supersaturated, a sign that the atmosphere is very clean and devoid of condensation nuclei. The observations are useful to understand the seasonal evolution of Pluto's atmosphere.

In section 13. Astronomical instrumentation

“Maximum-likelihood detection of sources among Poissonian noise”, by I.M. Stewart, A&A 495, p. 989

Present X-ray observatories operate in a relatively low-exposure regime and exhibit Poissonian noise at background flux levels. The author examines a maximum likelihood (ML) technique for detecting compact sources in such datasets, and uses Monte Carlo simulations to show that ML compares favorably with a variety of source detection methods and that it also has several practical advantages. This paper provides a common and optimal framework for the data analysis community, in a presentation style that balances mathematical rigor with common sense.