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The optical transient of the faint gamma-ray burst GRB 990308 was detected by the QUEST camera on the Venezuelan 1 m Schmidt telescope starting 3.28 hr after the burst. Our photometry gives V=18.32+/-0.07, R=18.14+/-0.06, B=18.65+/-0.23, and R=18.22+/-0.05 for times ranging from 3.28 to 3.47 hr after the burst. The colors correspond to a spectral

We derive a bound on the magnetic dipole moment of the top quark in the context of the effective Lagrangian approach by using the ratios Rb=Γb/Γh, Rl=Γh/Γl and the Z width. We take into account the vertex and oblique corrections. We obtain the allowed region for the magnetic dipole moment of top quark as -2.94

This thesis presents observational kinematic results for a significant sample of disk galaxies. Spectra of both the gaseous and stellar components are available for almost the whole sample. The first aim was to make a comparative study of the gas and the stellar kinematics to see whether there was any correlation between the kinematic behavior and

IAUC 7273 available at Central Bureau for Astronomical Telegrams.

We present near-infrared photometry (J band) and low-resolution optical spectroscopy (600-1000 nm) for one of the faintest substellar member candidates in the young σ Orionis cluster, S Ori 47 (I=20.53; Béjar, Zapatero Osorio, & Rebolo). Its very red (I-J) = 3.3+/-0.1 color and its optical spectrum allow us to classify S Ori 47 as an L1.5-type