Three different types of evidence are presented in favour of the hypothesis that the HII regions in disk galaxies with H-alpha luminosities greater than a critical value of 10^(38.6)^ erg s^(-1)^ are density bounded, and that the escaping Lyman continuum photons from these are the principal ionizing agents for the diffuse ISM in disk galaxies. This

IAUC 6875 available at Central Bureau for Astronomical Telegrams.

We present echelle spectroscopy in the 3500- to 7060-Å range for two positions of the Orion nebula. The data were obtained using the 2.1-m telescope at Observatorio Astrónmico Nacional in San Pedro Mártir, Baja California. We have measured the intensities of about 220 emission lines, in particular 81 permitted lines of C+, N+, N++, 0°, 0+, Ne0, Si+

We present optical and infrared observations of Roque Praesepe 1 (RPr 1), a faint ( I=21.01 ) and very red object ( I-K=4.57 ) discovered in a deep CCD survey, covering an area of 800 arcmin2 of the Praesepe open cluster. A low-resolution spectrum shows that RPr 1 is a very late object, the latest object in Praesepe for which a spectrum has been

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In the paper "Third-Order Perturbative Approach to Gravitational Instability: Evolution of Isolated Structures and Environmental Effects" by L. J. Goicoechea and J. Buitrago (ApJ, 483, 541 [1997]), there is a typographical error in equations (4), (5), (8), and (21). In these equations, the volume integrals must include both numerator and