Larval stages of pentastomids were collected from different organs of small mammals from the Peruvian Amazon. These parasitized mammals included: a western Amazonian oryzomys (Hylaeamys perenensis), an elegant oryzomys (Euryoryzomys nitidus), a lowland paca (Cuniculus paca), two kinkajous (Potos flavus), two silvery woolly monkeys (Lagothrix poeppigii) and a brown-mantled tamarin (Leontocebus fuscicollis). Pentastomids were found in the mesentery and parenchyma of the liver and lungs of these animals. All pentastomids were morphologically identified as nymphs of Porocephalus spp. Only the nymphs collected from select animals (the western Amazonian oryzomys, the elegant oryzomys and the brown-mantled tamarin) were analysed molecularly. Molecular analysis was performed amplifying the mitochondrial cytochrome c oxidase subunit I gene from select nymphs collected from the western Amazonian oryzomys, the elegant oryzomys and the brown-mantled tamarin. The nucleotide sequences exhibited 95.8–97.7% similarity between them. Also, these sequences showed an identity of 95.8–97.9% to Porocephalus crotali (GenBank accession numbers MG559647–MG559655). Molecular analysis indicated the presence of at least two Porocephalus species. These findings represent the first record of Porocephalus in these mammals, thus adding new intermediate hosts for this pentastomid genus. This work represents the first molecular data of Porocephalus in a Neotropical climate.

We have studied structure and electrical properties of Si1−YGeY:H films deposited by low-frequency plasma-enhanced chemical vapor deposition over the entire composition range from Y = 0 to Y = 1. The deposition rate of the films and their structural and electrical properties were measured for various ratios of the germane/silane feed gases and with and without dilution by Ar and by H2. Structure and composition was studied by Auger electron spectroscopy (AES), secondary ion mass spectroscopy (SIMS), and Fourier transform infrared (FTIR) spectroscopy. Surface morphology was characterized by atomic force microscopy (AFM). We found that the deposition rate increased with Y, maximizing at Y = 1 without dilution. The relative rate of Ge and Si incorporation is affected by dilution. Hydrogen preferentially bonds to silicon. Hydrogen content decreases for increasing Y. In addition, optical measurements showed that as Y goes for 0 to 1, the Fermi level moves from mid gap to the conduction band edge; i.e., the films become more n-type. No correlation was found between the pre-exponential and the activation energy of conductivity. The behavior of the conductivity γ-factor suggests a local minimum in the density of states at E ≈ 0.33 eV for the films grown with or without H-dilution and E ≈ 0.25 eV for the films with Ar dilution.

Using an homogeneous sample of $v\sin i$ values for A-type main sequence stars (Royer et al. 2002), the equatorial velocity ($v$) distributions are determined as function of spectral class, from B9 to F2. The chemically peculiar and binary stars are discarded. These distributions of “normal” stars are discussed in terms of stellar formation and evolution, in particular the remaining bimodality observed for the earliest spectral types of the sample. We show that late B and early A-type main-sequence stars have genuine bimodal distributions of true equatorial rotational velocities probably due to the phenomena of angular momentum loss and of redistribution the star underwent before reaching the main sequence. A striking lack of slow rotators is noticed among intermediate and late A-type stars. The bimodal-like shape of their true equatorial rotational velocity distributions could be due to evolutionary effects.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The ESA HIPPARCOS satellite has provided astrometry of unprecedented accuracy, allowing us to reassess, improve and refine the pre-Hipparcos luminosity calibrations. We review the “classical” absolute magnitude calibrations with the Strömgren-Crawford intermediate-band photometric system. A small zero point correction of about 2-4% seems necessary, as well as to refine the dependences on metallicity and projected rotational velocity. The need of a rigorous statistical treatment of the extremely precise Hipparcos data to derive definitive dependences of the luminosity on physical parameters is emphasized.

Frequency doubling a 140 × 110 mm 40 J sub-ps 1054 nm beam for laser matter interaction studies was investigated at the Central Laser Facility, with efficiencies greater than 60% being achieved. The conversion characteristics (efficiency, beam quality, focusability, and pulse length) for two large 157 mm diameter aperture high quality KDP crystals of thickness 2 mm and 4 mm were studied. Using a fundamental drive beam of two times diffraction limited quality, focal spots of four times the diffraction limit in the frequency doubled beam were achieved and beam degradation effects shown to be minimal.

We have analysed the standards of the MK system in the B0-F5 spectral region with the help of Hipparcos parallaxes, using only stars for which the error on the absolute magnitude is ≤ 0.3 mag. The sample stars (about one hundred) were scrutinized for companions and for interstellar extinction. We find that the main sequence is a wide band and that, although in general giants and dwarfs have different absolute magnitudes, the separation between luminosity class V and III is not clear. We conclude that there is no strict relation between luminosity class and absolute magnitude. The relation is only a statistical one and has a large intrinsic dispersion.

We have analysed similarly the system of standards defined by Garrison and Gray (1994) separating low and high rotational velocity standards. We find similar effects as in the original MK system.

An extensive work on the luminosity calibration of the HR diagram has been performed using the LM method based on the Maximum Likelihood estimation (Luri et al. 1996). The method uses all available information: Hipparcos parallax and proper motion data as well as radial velocities and some measured spectroscopic or photometric parameters related to luminosity. On the other hand, the method takes into account the censorship of the sample and the errors of the data. Finally, it is able to identify and separate in a given sample, groups with different luminosity, kinematical or spatial characteristics providing not only the corresponding luminosity calibration relationship, but also improved individual absolute magnitude estimates.

In order to asses how reliable the luminosity calibrations based on the MK spectral classification are, the LM method has been applied to a sample of B to K stars with MK classification selected from the Hipparcos survey. All known binaries, variables and spectroscopically peculiar stars were removed from the sample. The final sample contains 22054 stars. Our results show that the relation between absolute magnitude and luminosity class has a large intrinsic dispersion. As a consequence, the assignation to a star of a mean absolute magnitude given by a MK classification calibration is a rough procedure. It is preferable to use the individual absolute magnitudes estimated using all the available information for each star, like the estimates provided by the LM method (Gómez et al. 1997).

Using Hipparcos parallaxes and proper motions together with radial velocity data and individual ages estimated from isochones, the velocity ellipsoid has been determined as a function of age. On the basis of the available kinematic data two different samples were considered: a first one (7789 stars) for which only tangential velocities were calculated and a second one containing 3104 stars with available U, V and W velocity components and total velocities ≤ 65 km.s-1.

The main conclusions are: -Mixing is not complete at about 0.8-1 Gyr. -The shape of the velocity ellipsoid changes with time getting rounder from σu/σv/σ-w = 1/0.63/0.42 ± 0.04 at about 1 Gyr to1/0.7/0.62 ±0.04 at 4-5 Gyr. -The age-velocity-dispersion relation (from the sample with kinematical selection) rises to a maximum, thereafter remaining roughly constant; there is no dynamically significant evolution of the disk after about 4-5 Gyr. -Among the stars with solar metallicities and log(age) > 9.8 two groups are identified: one has typical thin disk characteristics, the other is older than 10 Gyr and lags the LSR at about 40 km.s-1 . -The variation of the tangential velocity with age(without selection on the tangential velocity) shows a discontinuity at about 10 Gyr, which may be attributed to stars typically of the thick disk populations for ages > 10 Gyr.

As far as the standard picture of galactic evolution and structure is concerned, early-type stars belong to disk populations. However, the existence of a population of early-type stars with nearsolar metallicities and main-sequence surface gravities, together with high velocities and/or standing at large distances away from the plane, is a well known anomaly to this picture.

In order to provide an insight into the different populations of early-type stars, a sample of high-velocity stars has been gathered from the Hipparcos catalogue. We have selected the stars according to B — V < 0.4,and a tangential velocity larger than 80 km/s. The sample is composed of 101 stars.

The high-velocity early-type stars in the solar neighbourhood are a mixture of different stellar populations: blue horizontal halo stars passing near the sun and high-velocity disk stars. We have decomposed into gaussiansthe V and W-distributions of our sample, to isolate the disk from the halo populations. The U-distribution of high-velocity disk stars is clearly asymmetric. The selection bias over the tangential velocities creates a depletion of low U values. Moreover, two thirds of the sample have U < 0 (toward the galactic anticentre, l = 180°). This cannot be explained by the distribution tail of disk stars or stochastic events such as runaway stars, which privilege no direction.

The analysis of stellar kinematics of the local system of young stars from Hipparcos data offers an excellent opportunity to revise models accounting for the origin of the observed deviations from circular motions, and to give new hints on the history of star formation and the dynamical processesinvolved in the evolution of our Galaxy. We have complemented the astrometric Hipparcos data with a careful compilation of available radial velocitiesand Strömgren photometry, information which enables us to obtain reliable space velocities and individual ages for a large number of stars. Thevelocity field has been studied by means of the classical first order approach, interpreting the trends observed in the Oort’s contants in terms of the local expansion of the Gould’s Belt (stars with ages less than 30-50 Myr, at heliocentric distances ρ < 400 — 600 pc). The fundamental geometric parameters of such structure have been determined. Several statistical methods have been applied to identify moving groups in the 4-dimensional space of (U,V,W, age). Our results definitively confirm their existence with mean velocity dispersions of the order of 5-7 km/s. Theobtained results will be published in Astronomy & Astrophysics.

The Hipparcos Input Catalogue -hereafter called HIC– (Turon et al. 1992a, Turon et al. 1994) contains the observing programme of the Hipparcos mission: 118 000 preselected stars, 48 minor planets and three satellites of major planets. These objects were selected on the grounds of more than 200 scientific programmes proposed by the world-wide astronomical community, and dealing with a large variety of astronomical and astrophysical topics. It contains the most up-to-date, comprehensive and homogeneous data and information related to these programme stars, collected during the years 1981-1990 by the INCA Consortium (Hipparcos INput CAtalogue consortium).

The Hertzprung-Russel (HR) diagram luminosity calibration relies basically on three kinds of data: trigonometric parallaxes, kinematical data (proper motions and radial velocities) and cluster distances obtained by the zero-age main sequence fitting procedure. The most fundamental method to calculate the absolute magnitude is the use of trigonometric parallaxes, but up to now, accurate data only exist for stars contained in a small volume around the sun. Individual absolute magnitudes are obtained using trigonometric parallaxes or photometric and spectroscopic calibrations. In these calibrations the accuracy on the absolute magnitude determination ranges from ±0.m2 in the main sequence to ±0m5 in the giant branch. On the other hand, trigonometric parallaxes, kinematical data or cluster distances have been used to make statistical calibrations of the absolute magnitude. The standard error on the mean absolute magnitude calibrations ranges from ±0m3 to ±0m6 on the mean sequence, from ±0m5 to ±0m7 on thegiant branch and is of about 1m for supergiants.

Future improvements in the absolute magnitude determination will depend on the improvement of the basic data from the ground and space. A brief overview of the new available data is presented. In particular, the analysis of the first 30 months data of the Hipparcos mission (H30) (from the 37 months data of the whole mission) allows to perform a statistical evaluation of the improvements expected in the luminosity determination.

Hipparcos, the astrometric satellite of the European Space Agency, launched in August 1989, will provide absolute trigonometric parallaxes for about 100 000 stars brighter than the limiting V-magnitude 12.5. In spite of the difficulties caused by a faulty orbit, the mission is successfully going on. A lifetime of more than 4 years is expected which will allow to reach the original objectives of the mission: 2 milli-arcsec for stars brighter than V-magnitude 9 and 4 to 5 milli-arcsec for fainter stars. The observing programme is based upon a single, uniquely-defined Input Catalogue. Field and open cluster stars of almost all effective temperatures, chemical compositions and gravities are being observed. Most types of binaries and variable stars are well represented, but Hipparcos is discovering new ones. Significant parallaxes (relatives errors smaller than 20%) will be obtained for stars closer than 100 pc (about 36 000 stars). Reliable stellar structure models should fit all the possible observational constraints: the main contribution of Hipparcos parallax data will be the huge improvement in the individual luminosities. The determination of stellar masses from the study of visual binaries will also be improved. The preliminary results of the first-year data reduction are an encouraging indication of the expected quality of the final results. On the basis of a mission duration of 4 years, the final results are foreseen for 1995.

Hipparcos will measure positions, proper motions and parallaxes for about 110 000 stars brighter than B = 13, with an expected mean error of 2.10−3 arcsec in positions and parallaxes and 2.10−3 arcsec/year in proper motions. The contents of the first provisional catalogue with respect to astrophysical problems is described, and the star distribution versus spectral type, magnitude and distance is given. All types of stars are well represented (spectral types, various evolutionary stages, giants, white dwarfs, …). Precise parallaxes for 29 000 stars closer than 100 pc will provide a new base for luminosity calibration, and will allow accurate stellar masses to be determined from double stars with known orbits. Precise proper motions, in conjunction with the improved distances, will substantially improve our knowledge of galactic structure. All types of stars used for the cosmic distance scale calibration are well represented: Cepheids, RR Lyrae, supergiants, open cluster stars.