Evolutionary Processes in Low-Mass Binary Systems

We consider the evolution of certain low-mass binaries, incorporating models of (a) internal evolution, (b) tidal friction, (c) dynamo activity driven by an elementary α,Ω dynamo, (d) stellar wind driven by the activity, and (e) magnetic braking as a consequence of wind and poloidal dynamo-generated magnetic field. In some circumstances the stellar wind is found to remove mass on a nuclear timescale, as is necessary to explain some observed systems. We can hope that various uncertainties in the model may be clarified by a careful comparison of the models with such observed quantities as rotation periods. These are modified by processes (a), (b) and (e). Assuming that stellar evolution is slow, rotation rate should in some circumstances represent a balance between magnetic braking trying to slow the star down and tidal friction trying to spin it up. Preliminary attempts are promising, but indicate that some fine tuning is necessary. When there is a third body present, in an orbit which is inclined but not necessarily of short period, the eccentricity of a close binary can be strongly modified by ‘Kozai cycles’. We show that this may complicate attempts to account for spin rates of stars in close binaries.     

Possible meteoroid streams associated with (69230) Hermes and 2002 SY50

The orbits of (69230) Hermes and 2002 SY₅₀ are similar and the Earth approaches both of them twice: at the end of October the local orbital minimum distances are smaller than 0.007 AU, and at the end of April the distances are smaller than 0.04 AU. This gives us opportunities to observe the meteors associated with these asteroids. Using the geocentric parameters of the orbital close encounters (the theoretical radiants) and our D _N distance function (Valsecchi et al. Mon. Not. R. Astron. Soc. 304 (1999) 743), we searched for meteoroids originated by Hermes and 2002 SY₅₀. A search among 1830 good quality photographic meteors gave negative results: we found no meteor dynamically similar to Hermes or 2002 SY₅₀. In a second search, done in a set of 62150 radio meteors, we applied two methods (M1, M2) and in both cases we found two streams; the streams found with the M1 method had 43 and 30 members, those found with the M2 method had 39 and 14 members. However, these results do not look convincing, due to the small number of common members in the corresponding streams. We therefore conclude that amongst the IAU meteors used in our search there are no compact streams associated with Hermes and 2002 SY₅₀.     

Cygnus A

Cygnus A was the first hyper-active galaxy discovered, and it remains by far the closest of the ultra-luminous radio galaxies. As such, Cygnus A has played a fundamental role in the study of virtually all aspects of extreme activity in galaxies. We present a review of jet theory for powering the double-lobed radio emitting structures in powerful radio galaxies, followed by a review of observations of Cygnus A in the radio, optical, and X-ray relevant to testing various aspects of jet theory. Issues addressed include: jet structure from pc- to kpc-scales, jet stability, confinement, composition, and velocity, the double shock structure for the jet terminus and the origin of multiple radio hotspots, the nature of the filamentary structure in the radio lobes, and the hydrodynamic evolution of the radio lobes within a dense cluster atmosphere, including an analysis of pressure balance between the various gaseous components. Also discussed are relativistic particle acceleration and loss mechanisms in Cygnus A, as well as magnetic field strengths and geometries both within the radio source, and in the intracluster medium. We subsequently review the classification, cluster membership, and the emission components of the Cygnus A galaxy. The origin of the activity is discussed. Concentrating on the nuclear regions of the galaxy, we review the evidence for an obscured QSO, also given the constraints on the orientation of the radio source axis with respect to the sky plane. We present an overview of models of central engines in AGN and observations of Cygnus A which may be relevant to testing such models. We conclude with a brief section concerning the question of whether Cygnus A is representative of powerful high redshift radio galaxies. Received October 10, 1995     

Instrument development to search for biomarkers on mars: Terrestrial acidophile, iron-powered chemolithoautotrophic communities as model systems

Recent findings by the MER rover opportunity confirming the presence of iron minerals that can only be formed in the presence of water emphasize the study of analogous environments to Mars on Earth. The study of chemolithoautotrophic communities living in acidic iron-rich habitats is highly relevant in order to identify Mars analog environment-specific biomarkers. Iron oxidizing bacteria like Leptospirillum ferrooxidans and Acidithiobacillus ferrooxidans have ways of life for which it is feasible to identify a past or present hypothetical niche on Mars. We have developed a strategy for biomarker identification based on: (i) search for biosignatures on acid and metal-rich environments; (ii) development of an immunosensor microarray; and (iii) integration into an instrument for autonomous and remote operation. The instrument that we have built, called Signs Of LIfe Detector (SOLID), is capable of processing a variety of samples for the detection of specific biomarkers. Antibodies against several bacterial strains have been developed and tested in a microarray biosensor on SOLID. Tests with field samples have been successfully performed, allowing the detection of L. ferrooxidans, A. ferrooxidans present in sediment samples.     

Prospects for astrometry with the Hubble Space Telescope

The Hubble Space Telescope (HST), a large optical telescope having an aperture of 2.4 meters and a length of 8.8 meters, is being developed by the National Aeronautics and Space Administration. This telescope will be placed into earth orbit by the space shuttle. Astrometric observations with the HST are made using a Fine Guidance Sensor which is capable of measuring the position of one object relative to another with an accuracy of ±0.002 arcseconds. The astrometric user of HST will be provided with an Astrometric Data Reduction Software package (ADRS). The variety of astrometric problems to be investigated with HST is discussed.     

Physical parameters of near-Earth asteroid 1982 DV

Visual and infrared observations were made of Amor asteroid 1982 DV during its discovery apparition. Broadband visual and near-infrared photometry shows that it is an S-class asteroid. Narrowband spectrophotometry shows an absorption feature due to olivine or pyroxene or both centered at 0.93 μm. Applying a nonrotating thermal model to 10-μm photometry, the geometric albedo is calculated to be approximately 0.27. The geometric albedo for a slowly rotating, rocky surface was calculated for 1 night to be 0.15, consistent with S-class asteroid albedos. Thus, 1982 DV is either one of the most reflective S-class asteroids known, or a significant amount of bare rock is exposed on the asteroid's surface. For the nonrotating model, ellipsoidal dimensions for 1982 DV are 3.5 × 1.4 × 1.4 km.