Eigenvector Sky Subtraction

We develop a new method for estimating and removing the spectrum of the sky from deep spectroscopic observations; our method does not rely on simultaneous measurement of the sky spectrum with the object spectrum. The technique is based on the iterative subtraction of continuum estimates and Eigenvector sky models derived from Singular Value Decompositions (SVD) of sky spectra, and sky spectra residuals. Using simulated data derived from small telescope observations we demonstrate that the method is effective for faint objects on large telescopes. We discuss simple methods to combine our new technique with the simultaneous measurement of sky to obtain sky subtraction very near the Poisson limit.Comment: Accepted for publication in The Astrophysical Journal (Letters) 2000 March 7. Includes one extra figure which did not fit in a lette

Design Considerations for a Ground-based Transit Search for Habitable Planets Orbiting M dwarfs

By targeting nearby M dwarfs, a transit search using modest equipment is capable of discovering planets as small as 2 Earth radii in the habitable zones of their host stars. The MEarth Project, a future transit search, aims to employ a network of ground-based robotic telescopes to monitor M dwarfs in the northern hemisphere with sufficient precision and cadence to detect such planets. Here we investigate the design requirements for the MEarth Project. We evaluate the optimal bandpass, and the necessary field of view, telescope aperture, and telescope time allocation on a star-by-star basis, as is possible for the well-characterized nearby M dwarfs. Through these considerations, 1,976 late M dwarfs (R < 0.33 Rsun) emerge as favorable targets for transit monitoring. Based on an observational cadence and on total telescope time allocation tailored to recover 90% of transit signals from planets in habitable zone orbits, we find that a network of ten 30 cm telescopes could survey these 1,976 M dwarfs in less than 3 years. A null result from this survey would set an upper limit (at 99% confidence) of 17% for the rate of occurrence of planets larger than 2 Earth radii in the habitable zones of late M dwarfs, and even stronger constraints for planets lying closer than the habitable zone. If the true occurrence rate of habitable planets is 10%, the expected yield would be 2.6 planets.Comment: accepted to PAS

FT-IR Emission Spectra of Chemisorbed Species, with Application to Species Adsorbed on Alumina

The principles of infrared emission spectroscopy are briefly reviewed with emphasis on the aspects of its application to the study of chemisorbed species. The ma in problems of sample preparation, selection of measurement conditions and the most suitable methods of data treatment are discussed. IR emittance spectra of two typical support materials for supported metal catalysts, alumina and silica, are presented. On the example of a rhenium complex, tetrakisttricarbonyl-us-hydroxo- rhenium), formed on alumina support in catalytic amounts (1.5 to 5% Re) it is shown that the four-measurement technique can lead to observation of the adsorbate bands also in the regions of high substrate emission (between 1300 and 400 cm-1)

FT-IR Spectroscopic Studies of Catalysts

The role of FTIR speetroscopy in catalytic studies is briefly discussed and some typical examples are shown. IR spectra of weakly bound hydrogen on PtjSi02 reveal surface heterogeneity; The hydrogen concentration on the surface is described by a Temkin isotherm. Adsorption of unsaturated C6 ring compounds on hydrogen poor Pt/Si02 is essentially a self\u27-hydrogenation process resulting in the formation of cyclohexane and carbon deposit on the metal surface. Chemisorption of n-hexane and benzene on hydrogen-rlch Ni/Si02 surface gives identical spectra under similar conditions. The same phenomenon is established for n-butane and benzene after chemisorption on the hydrogen-poor surface. The infrared and Raman spectra of C.H6 on NijSi02 suggested a symmetry lowering somewhere between C6v and C3v because of the nonplanarity of C6H6and the site symmetry of the surface

A search for stellar occultations by Uranus, Neptune, Pluto, and their satellites: 1990-1999

A search for occultations of stars by Uranus, Neptune, and Pluto between 1990 and 1999 was carried out by combining ephemeris information and star positions using very accurate occultation modeling software. Stars from both the Space Telescope Guide Catalog and photographic plates taken by Arnold Klemola at Lick Observatory were compared with planet positions from the JPL DE-130 ephemeris, with local modifications for Pluto and Charon. Some 666 possible occultations by the Uranian ring, 143 possible occultations by Neptune, and 40 possible occultations by Pluto and/or Charon were found among stars with visual magnitudes as faint as 16. Before the star positions could be obtained, the occultation prediction software was used to aid many observers in observing the occultation of 28 Sagitarii by Saturn in July 1989. As a test on other outer solar system objects, 17 possible occultations were found in a search of the Guide Star Catalog for occultations by 2060 Chiron, and interesting object between Saturn and Uranus which shows both cometary and asteroidal properties

SKYMAP: Exploring the Universe in software

SKYMAP is a computer program which produces maps of arbitrary portions of the sky in a variety of projections and coordinate systems. Over the past ten years it has been used to produce finder charts for occultations by planets, display scan and image data from the Spacelab 2 Infrared Telescope, and make maps of fields for astronomical observations at X-ray, optical, infrared, and radio wavelengths. It can display multiple source catalogs, including the HST Guide Star Catalog, as well as solar system objects with astrometric accuracy using the JPL DE-130 ephemeris or tabulated positions. SKYMAP can be tuned to a specific task using an ASCII parameter file which controls how information is displayed on any Tektronix-compatible graphics display. The program contains a variety of interactive graphic and image processing features and has been ported to a variety of computer systems. A recent project visually demonstrates source density variation in various commonly-used all-sky catalogs