Cored Apple Bipolarity : A Global Instability to Convection in Radial Accretion?

We propose that the prevalence of bipolarity in Young Stellar Objects is due to the fine tuning that is required for spherical accretion of an ambient medium onto a central node.It is shown that there are two steady modes that are more likely than radial accretion, each of which is associated with a hyperbolic central point in the meridional stream lines, and consequently with either an equatorial inflow and an axial ejection or vice versa. In each case the stream lines pass through a thick accretion torus, which is better thought of as a standing pressure wave rather than as a relatively inert Keplerian structure.We base our arguments on a simple analytic example,which is topologi cally generic,wherein each bipolarmode is created by the rebound of accreting matter under the action of the thermal,magnetic,turbulent and centrifugal pressures created in the flow. In both bipolar modes the presence of non-zero angular momentum implies axial regions wherein the pressure is first reduced below the value at infinity and then becomes negative, where the solution fails because rotating material can not enter this region without suction.The model thus has empty stems where the activity of the central source must dominate.So the basic engine of the bipolar flow discussed here is simply the rebound of freely falling material from a thick pressure disc into an axial low pressure region.The low mass,high velocity outflow must be produced in this region by an additional mechanism. This is reminiscent of the cored apple structure observed recently in the very young bipolar source VLA 1623.Comment: PostScript, 10 page

New constraints on a triaxial model of the Galaxy

We determine the values of parameters of an N-body model for the Galaxy developed by Fux via comparison with an unbiased, homogeneous sample of OH/IR stars. Via Monte-Carlo simulation, we find the plausibilities of the best-fitting models, as well as their errors. The parameters that are constrained best by these projected data are the total mass of the model and the viewing angle of the central Bar, although the distribution of the latter has multiple maxima. The best model has a viewing angle of 44 degrees, semi-major axis of 2.5 kpc, a bar mass of 1.7E10 solar masses and a tangential velocity of the local standard of rest of 171 km/s . We argue that the lower values that are commonly found from stellar data for the viewing angle (around 25 degrees) arise when too few coordinates are available, when the longitude range is too narrow or when low latitudes are excluded from the fit. The new constraints on the viewing angle of the galactic Bar from stellar line-of-sight velocities decrease further the ability of the Bar's distribution to account for the observed micro-lensing optical depth toward Baade's window : our model reproduces only half the observed value. The signal of triaxiality diminishes quickly with increasing latitude, fading within approximately one scaleheight. This suggests that Baade's window is not a very appropriate region to sample Bar properties.Comment: 10 pages, 8 figures, TeX, accepted for publication in MNRA

El reconocimiento del matrimonio canónico ante el Derecho del Estado.

Material incluido en el volumen especial de la revista del Instituto Martín de Azpilcueta, Universidad de Navarra : Ius Canonicum (1999), en honor de Javier Hervada

Discovery of a high-redshift Einstein ring

We report the discovery of a partial Einstein ring of radius 1.48arcsec produced by a massive (and seemingly isolated) elliptical galaxy. The spectroscopic follow-up at the VLT reveals a 2L* galaxy at z=0.986, which is lensing a post-starburst galaxy at z=3.773. This unique configuration yields a very precise measure of the mass of the lens within the Einstein radius, (8.3e11 +- 0.4)/h70 Msolar. The fundamental plane relation indicates an evolution rate of d [log (M/L)B] / dz = -0.57+-0.04, similar to other massive ellipticals at this redshift. The source galaxy shows strong interstellar absorption lines indicative of large gas-phase metallicities, with fading stellar populations after a burst. Higher resolution spectra and imaging will allow the detailed study of an unbiased representative of the galaxy population when the universe was just 12% of its current age.Comment: 5 pages, 3 figures, accepted in A&A Le