Palomar Testbed Interferometer Observations of Young Stellar Objects

We present observations of a sample of Herbig AeBe stars, as well as the FU Orionis object V1057 Cygni. Our K-band (2.2μm) observations from the Palomar Testbed Interferometer (PTI) used baselines of 110 m and 85 m, resulting in fringe spacings of ∼4 mas and 5 mas, respectively. Fringes were obtained for the first time on V1057 Cygnias well as V594 Cas. Additional measurements were made of MWC147, while upper limits to visibility-squared are obtained for MWC297, HD190073, and MWC614. These measurements are sensitive to the distribution of warm, circumstellar dust in these sources. If the circumstellar infrared emission comes from warm dust in a disk, the inclination of the disk to the line of sight implies that the observed interferometric visibilities should depend upon hour angle. Surprisingly, the observations of Millan-Gabet, Schloerb and Traub (2001)(hereafter MST) did not show significant variation with hour angle. However, limited sampling of angular frequencies on the sky was possible with the IOTA interferometer, motivating us to study a subset of their objects to further constrain these systems. This revised version was published online in July 2006 with corrections to the Cover Date.     

VLA and MERLIN observations of RZ Cassiopeiae

We present radio interferometric observations of the Algol-type binary system RZ Cassiopeiae made with the VLA and MERLIN arrays at 6 cm over an incomplete orbital cycle of the system (1.195 d). We detected RZ Cas with both instruments. The images were unresolved in both cases, with angular extents comparable to the synthesized beams. The peak flux density in the VLA image was 1.14 mJy beam⁻¹ and in the MERLIN image it was 0.93 mJy beam⁻¹. The derived brightness temperatures are  4.02 × 10⁸  and  4.35 × 10⁸ K  and the effective electron energies are 0.347 and 0.346 MeV for the MERLIN and VLA data respectively. The radio light curve shows an interesting modulation centred close to the primary eclipse which seems to correlate with ASCA SIS observations of the system. The results can be interpreted as an emitting region on the outer hemisphere of the cool component aligned along the centroid axis of the binary system.     

The Hubble relation for a comprehensive sample of QSOs

A correlation between redshifts (z) and apparent magnitudes (V) (Hubble relation) of Quasi Stellar Objects (QSOs) has long been sought. Such a correlation exists for galaxies whose redshifts are of cosmological origin. However, a plot of the two quantities representing the Hubble diagram for QSOs exhibits, in general, a wild scatter. This raises the question whether redshifts of QSOs are cosmological. On the other hand, most luminous QSOs in groups, and subsamples with particular properties, have been reported to show the Hubble relation. In the present paper, we analyse all optically non-variable QSOs in a comprehensive sample. In our analysis we grouped the objects into certain intervals of apparent magnitudes. Correlations obtained between redshifts and magnitudes are all statistically robust. Also, the Hubble relation in the usual formV = 5 logz +C is obeyed very convincingly for QSOs withV < 19.5.     

Bianchi VI0 cosmological model in Saez and Ballester theory

The problem of perfect fluid distribution in spatially homogeneous and anisotropic Bianchi type VI₀ space-time is considered in a scalar tensor theory of gravitation proposed by Saez and Ballester (1985). Exact solutions of the field equations are derived when the metric potentials are functions of cosmic time only. Some physical and geometrical properties of the solutions are also discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Clumpiness in Star Forming Regions

In this article, some aspects of the clumpy nature of molecular clouds are reviewed. In particular the observational evidence for small-scale structures both in low and high mass star forming regions will be discussed. I will review some examples of `clumpiness' such as: i) the molecular clumps ahead of HH objects and how the study of the physical and chemical nature of these clumps is important for the understanding of the clumpiness of the Interstellar Medium; and ii)hot cores and their use as a tool to study the early phases of massive star formation. This revised version was published online in July 2006 with corrections to the Cover Date.     

Colour Properties and Trends in Trans-Neptunian Objects

One of the most puzzling features of the Kuiper Belt, which has been confirmedby numerous surveys, is the optical colour diversity that seems to prevail among the observed TNOs. TNOs and Centaurs have surfaces showing dramaticallydifferent colours and spectral reflectances, from neutral to very red. With therelatively few visible-NIR colour datasets available, the colour diversity seemsalso to extend to the near infrared wavelengths. Relevant statistical analyses havebeen performed and several studies have pointed out strong correlations betweenoptical colours and some orbital parameters (i, e, q) for the Classical KuiperBelt objects. On the other hand, no clear trend is obvious for Plutinos, Scatteredobjects or Centaurs. Another important result is the absence of correlation of colourswith size or heliocentric distance for any of the populations of outer Solar Systemobjects. The strong colour anisotropy found is important because it is a diagnosticof some physical effects processing the surfaces of TNOs and/or some possiblecomposition diversity. In this paper, we will review the current knowledge of thecolour properties of TNOs, describe the observed colour distribution within theEdgeworth–Kuiper belt, and address the problem of their possible origin.     

Two-Parametric Families of Orbits and Multiseparability of Planar Potentials

Combining the results of the inverse problem of dynamics with the theory of multiseparability of planar potentials, we find biparametric families of orbits, whose existence guarantees the multiseparability of the potential. We also study the allowed regions of the plane, where these orbits are traced.     

Geometric Derivation of the Delaunay Variables and Geometric Phases

We derive the classical Delaunay variables by finding a suitable symmetry action of the three torus T³ on the phase space of the Kepler problem, computing its associated momentum map and using the geometry associated with this structure. A central feature in this derivation is the identification of the mean anomaly as the angle variable for a symplectic S ¹ action on the union of the non-degenerate elliptic Kepler orbits. This approach is geometrically more natural than traditional ones such as directly solving Hamilton–Jacobi equations, or employing the Lagrange bracket. As an application of the new derivation, we give a singularity free treatment of the averaged J ₂-dynamics (the effect of the bulge of the Earth) in the Cartesian coordinates by making use of the fact that the averaged J ₂-Hamiltonian is a collective Hamiltonian of the T³ momentum map. We also use this geometric structure to identify the drifts in satellite orbits due to the J ₂ effect as geometric phases.