A Full-Sun Magnetic Index from Helioseismology Inferences

Solar magnetic indices are used to model the solar irradiance and ultimately to forecast it. However, the observation of such indices is generally limited to the Earth-facing hemisphere of the Sun. Seismic maps of the far side of the Sun have proven their capability to locate and track medium–large active regions at the non-visible hemisphere. We present here the possibility of using the average signal from these seismic far-side maps, combined with similarly calculated near-side maps, as a proxy to the full-Sun magnetic activity.     

The effect of a dense atmosphere on the tidally induced potential of Titan

The effect of the dense atmosphere of Titan on the tidal variations of the external gravitational potential of degree two is quantified. The atmospheric tides perturb the external gravitational potential of Titan in two ways. First, the atmosphere itself contributes directly to the external gravitational potential with a period of 15.945 days. Second, the variable loading of the atmosphere induces mass redistribution within Titan, which also changes the external gravitational potential. It is shown that the relative atmospheric contributions to the tides are most likely less than 2% and vanish almost completely for the most plausible models with a subsurface ocean. This suggest that atmospheric tidal perturbations will contribute only negligibly to Cassini measurements of Titan's gravitational field so that the tidal Love numbers derived from these observations can be directly interpreted in terms of the satellite's interior.     

Numerical continuation of families of frozen orbits in the zonal problem of artificial satellite theory

In the zonal problem of a satellite around the Earth, we continue numerically natural families of periodic orbits with the polar component of the angular momentum as the parameter. We found three families; two of them are made of orbits with linear stability while the third one is made of unstable orbits. Except in a neighborhood of the critical inclination, the stable periodic (or frozen) orbits have very small eccentricities even for large inclinations.     

Measurements of Atmospheric Extinction at a Ground Level Observatory

In order to determine the atmospheric extinction at Physics Department Astronomical Observatory of the University of Extremadura, located at Badajoz (Spain), several stars were observed during some clear nights of atmospheric stability in the period 1998–2000, at optical wavelengths corresponding to the filters of the Kron-Cousins and Strömgren photometric systems. The determination of the extinction coefficients was made by assuming the Bouguer's law, which was shown to be a good approximation for this study. The results exhibited temporal variations and can be considered to be associated with clean atmospheres at locations of low altitude.     

Perturbed Gylden Systems and Time-Dependent Delaunay-Like Transformations

We study the possibilities and limitations of the application of generalized Delaunay-like transformations (in the 6-dimensional phase space) and TR-like mappings (in the 8-dimensional, extended phase space) to perturbed two-body problems with a time-varying Keplerian parameter μ(t), that is, to Gylden-type systems. For the sake of theoretical completeness, both negative- and positive-energy motion (with nonstationary coupling parameter) are, in principle, considered. Our developments are intended to introduce canonical variables parallelling the classical ones of Delaunay and the Delaunay-Similar variables of Scheifele. This revised version was published online in August 2006 with corrections to the Cover Date.     

Classical T Tauri Stars and Substellar Analogs

We propose a spectroscopic criterion based on Hα equivalent width and spectral type to classify classical T Tauri stars and substellar analogs. We argue that accreting objects can be identified from low-resolution optical spectroscopy, when their Hα flux is stronger than the saturation limit at Log {Lum(Hα)/Lum(bol)} = ?3.3. Additional criteria, such as the relation between HeI5876 or HeI6678 and Hα, or the ratios between the components of the CaII infrared triplet, are also discussed. We have tested the reliability of these criteria by applying them to several objects with masses in the range 0.11–0.025 M_⊙, which belong to nearby star forming regions and the TW Hya association.     

Instruments, Detectors and the Future of Astronomy with Large Ground Based Telescopes

Results of a survey of instrumentation and detector systems, either currently deployed or planned for use at telescopes larger than 3.5 m, in ground based observatories world-wide, are presented. This survey revealed a number of instrumentation design trends at optical, near, and mid-infrared wavelengths. Some of the most prominent trends include the development of vastly larger optical detector systems (> 10⁹ pixels) than anything built to date, and the frequent use of mosaics of near-infrared detectors – something that was quite rare only a decade ago in astronomy. Some future science applications for detectors are then explored, in an attempt to build a bridge between current detectors and what will be needed to support the research ambitions of astronomers in the future.     

Binary Evolution Compared to Observed Algols

We present a grid of evolutionary tracks of 240 binaries with a B-type primary at birth and initial mass ratios: 0.4, 0.6 and 0.9. Conservative calculations are done for cases A and A/B RLOF. For pure RLOF B, conservative and liberal evolutionary sequences have both been computed. In order to compare statistically our computations with the observed distributions of orbital periods and mass ratios of Algols, we enlightened the Algol appearance in every evolutionary sequence. Conservative RLOF reproduces the observed distribution of orbital periods well, but it underestimates the observed mass ratios in the range q ε [0.4–1].