The distribution of ionized, molecular, and atomic hydrogen in the disk and especially along the spiral arms of the Whirlpool galaxy, M51, is investigated by combining recently published maps of the H-alpha, H2, and H I surface densities, and a twofold result is reported. The existence is established of a symmetric pattern of peaks and dips in the

Since the beginning of 1990, a sodium based resonance scattering spectrometer belonging to the IRIS Network has operated at Observatorio del Teide side by side with the MkI instrument (a resonance scattering spectrometer based on potassium) from the University of Birmingham and operated since 1975. A 3 month series of simultaneous data obtained in

We present the results of infrared observations of the BL Lacertae object Markarian 501 obtained with the Telescopio Carlos Sanchez of El Observatorio del Teide, Tenerife, Spain. We report the detection of rapid infrared variations. On two nights the K (2.2 micron) magnitude shows variations which a Chi-Squared test establishes have a probability

We describe an experiment aimed at diffraction-limited imaging of astronomical sources in the 2-5/micron range. It is based on a rotation shearing interferometer that extracts the complex degree of coherence of the wavefront directly in the pupil plane. Interference fringes are produced by a Michelson interferometer in the image of the telescope

For a curve C, viewed as a cycle in its Jacobian, we study its image n_*C under multiplication by n on JC. We prove that the subgroup generated by these cycles, in the Chow group modulo algebraic equivalence, has rank at most d-1, where d is the gonality of C. We also discuss some general facts on the action of n_* on the Chow groups.

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