An Alternative to Spinning Dust for the Microwave Emission of LPH 201.663+1.643: an Ultracompact HII Region

The microwave spectral energy distribution of the dusty, diffuse H II region LPH 201.663+1.643 has been interpreted by others as tentative evidence for microwave emission from spinning dust grains. We present an alternative interpretation for that particular object; specifically, that an ultracompact H II region embedded within the dust cloud would explain the available observations as well or better than spinning dust. Parameters for the size, surface brightness, and flux density of the putative ultracompact HII region, derived from the microwave observations, are within known ranges. A possible candidate for such an ultracompact H II region is IRAS 06337+1051, based upon its infrared colors. However, IRAS 06337+1051's infrared flux appears to be too small to be consistent with the microwave flux required for this alternative model to explain the observations.Comment: 11 pages, 3 figures, accepted to ApJ Letter

Detecting Life-bearing Extra-solar Planets with Space Telescopes

One of the promising methods to search for life on extra-solar planets (exoplanets) is to detect life's signatures in their atmospheres. Spectra of exoplanet atmospheres at the modest resolution needed to search for oxygen, carbon dioxide, water, and methane will demand large collecting areas and large diameters to capture and isolate the light from planets in the habitable zones around the stars. For telescopes using coronagraphs to isolate the light from the planet, each doubling of telescope diameter will increase the available sample of stars by an order of magnitude, indicating a high scientific return if the technical difficulties of constructing very large space telescopes can be overcome. For telescopes detecting atmospheric signatures of transiting planets, the sample size increases only linearly with diameter, and the available samples are probably too small to guarantee detection of life-bearing planets. Using samples of nearby stars suitable for exoplanet searches, this paper shows that the demands of searching for life with either technique will require large telescopes, with diameters of order 10m or larger in space.Comment: 15 pages, 6 figures, submitted to Ap.

Near-surface ocean current sensors : problems and performance

When current meters are used to measure mean horizontal currents in surface gravity waves, immunity to the vertical component of flow is important, even though the net vertical flow averages to zero and is normal to the desired horizontal components. A technique is presented for estimating the magnitude of the errors introduced by imperfect rejection of the off-axis flows (cross-talk) from laboratory measurements of the current meter "vertical-cosine-response." The predicted dynamic response is shown to compare favorably with laboratory measurements. The measured steady state vertical-cosine-response functions for several practical current sensors are summarized and used to estimate the magnitude of wave-induced errors in horizontal mean current measurements. A new dye technique for evaluating near-surface current meter performance in waves is shown.Prepared for the Working Con6enence on CURRENT MEASUREMENTS sponsored by the NOAA 0ffice of Ocean Engineering with the Delaware Sea Grant College Program