Palomar/Las Campanas Imaging Atlas of Blue Compact Dwarf Galaxies: II. Surface Photometry and the Properties of the Underlying Stellar Population

We present the results from an analysis of surface photometry of B, R, and Halpha images of a total of 114 nearby galaxies drawn from the Palomar/Las Campanas Imaging Atlas of Blue Compact Dwarf galaxies. Surface brightness and color profiles for the complete sample have been obtained. We determine the exponential and Sersic profiles that best fit the surface brightness distribution of the underlying stellar population detected in these galaxies. We also compute the (B-R) color and total absolute magnitude of the underlying stellar population and compared them to the integrated properties of the galaxies in the sample. Our analysis shows that the (B-R) color of the underlying population is systematically redder than the integrated color, except in those galaxies where the integrated colors are strongly contaminated by line and nebular-continuum emission. We also find that galaxies with relatively red underlying stellar populations (typically (B-R)>~1mag) show structural properties compatible with those of dwarf elliptical galaxies (i.e. a smooth light distribution, fainter extrapolated central surface brightness and larger scale lengths than BCD galaxies with blue underlying stellar populations). At least ~15% of the galaxies in the sample are compatible with being dwarf elliptical (dE) galaxies experiencing a burst of star formation. For the remaining BCD galaxies in the sample we do not find any correlation between the recent star formation activity and their structural differences with respect to other types of dwarf galaxies.Comment: 35 pages, 6 figures, accepted for publication in ApJS. Postscript files of panels f1a-f1o of figure 1 are available online at http://www.ociw.edu/~agpaz/astro-ph/apjs2004

The Curious Case of NGC6908

The object NGC6908 was once thought to be simply a surface-brightness enhancement in the eastern spiral arm of the nearby spiral galaxy NGC6907. Based on an examination of near-infrared imaging, the object is shown in fact to be a lenticular S0(6/7) galaxy hidden in the optical glare of the disk and spiral structure of the larger galaxy. New radial velocities of NGC6908 (3,060+/-16 (emission); 3,113+/-73 km/s (absorption)) have been obtained at the Baade 6.5m and the duPont 2.5m telescopes at Las Campanas, Chile placing NGC6908 at the same expansion-velocity distance as NGC6907 (3,190+/-5 km/s), eliminating the possibility of a purely chance line-of-sight coincidence. The once-enigmatic asymmetries in the disk and outer spiral structure of NGC6907 are now explained as being due to an advanced merger event. Newly discovered tails and debris in the outer reaches of this galaxy further support the merger scenario for this system. This pair of galaxies is a rather striking example of two objects discovered over 100 years ago, whose true nature was lost until modern detectors operating at infrared wavelengths gave us a new (high-contrast) look. Other examples of embedded merger remnants may also reveal themselves in the growing samples of near-infrared imaging of nearby galaxies; and a pilot study does reveal several other promising candidates for follow-up observations.Comment: 17 pages, 8 figures, accepted for publication in A

Mapping the star formation history of Mrk86: I. Data and models

We have obtained optical (BVR, [OIII]5007 and Halpha), near infrared (JHK) imaging and long-slit optical spectroscopy for the Blue Compact Dwarf galaxy Mrk86 (NGC2537). In this paper, the first of two, we present optical-near- infrared colors and emission-line fluxes for the currently star-forming regions, intemediate aged starburst and underlying stellar population. We also describe the evolutionary synthesis models used in Paper II. The R and Halpha luminosity distributions of the galaxy star-forming regions show maxima at M_R=-9.5 and L_Halpha=10^37.3 erg s^-1. The underlying stellar population shows an exponential surface brigthness profile with central value, mu_E,0=21.5 mag arcsec^-2, and scale, alpha=0.88 kpc, both measured in the R-band image. In the galaxy outer regions, dominated by this component, no significant color gradients are observed. Finally, a set of evolutionary synthesis models have been developed, covering a wide range in metallicity and burst strength.Comment: 21 pages, 14 figures, 2 landscape tables, accepted for publication in Astronomy & Astrophysics Supplement Series, for higher resolution images see ftp://cutrex.fis.ucm.es/pub/OUT/gil/PAPERS/aa00_I.ps.g

Alfabetización y educación de adultos en Nicaragua

De febrero a marzo de 1980 se realizo en Nicaragua la Cruzada Nacional de Alfabetización (CNA). Previamente, un censo había puesto de manifiesto la existencia de un 50,4% de analfabetos entre la población mayor de diez años. El proyecto se llevo a cabo con financiación nacional y diversas colaboraciones procedentes de países extranjeros y organismos internacionales. La campaña fue planificada como un proyecto político -sustentado en las organizaciones revolucionarias- entre cuyos objetivos se contaba, además de la erradicación al analfabetismo, la incorporación de las masas al proceso revolucionaria en curso. Al mismo tiempo se pretendía un mejoramiento de las condiciones de vida del campesino, mediante la divulgación de hábitos de higiene, salud y medicina preventiva y la realización de pequeñas obras de construcción. El método de alfabetización utilizado sigue la línea de P. Freire, adaptado a la realidad nicaragiiense y a la existencia de una serie de contenidos política-ideológicos. El desarrollo de la CNA se baso en el aporte de casi ciento ochenta mil jóvenes voluntarios -los brigadistas- que se extendieron por toda la geografía del país, conviviendo con los campesinos en una relación de mutuo aprendizaje. Antes de la campaña los brigadistas habían recibido unos cursillos de capacitación, que se continuaron en sesiones semanales de formación política y técnico-pedagógica mientras duro la alfabetización. La CNA supuso la reducción del índice del analfabetismo al 12%, pero también un mayor conocimiento de la realidad nacional para el brigadista y una incidencia positiva en las condiciones de vida del medio campesino. Al término de la CNA se crea el Viceministerio de Educación de Adultos para poner en marcha el programa de Educación Popular Básica, cuyos objetivos principales son continuar la formación político-ideológica y ofrecer los conocimientos básicos que permitan posteriormente capacitar técnicamente a los alfabetizados.During February and March 1980 a National Literacy Campaign was carried out in Nicaragua. A census had previously revealed that 50,4% of the population over the age of ten was illiterate. The project was financed with national funds and various contributions from foreign countries and international organizations. The campaign was part of a political project -supported by the revolutionary organizations -which, besides putting an end to illiteracy, aimed at incorporating the population to the revolutionary process taking place. It also aimed at improving the living conditions of the peasants, by spreading hygiene and health habits, preventive medicine and housing improvements. The method used in the campaign follows P. Freire's lines adjusted to the Nicaraguan reality and to a series of political-ideological contents. The National Literacy Campaign took place thanks to the collaboration of 180.000 young volunteers -the brigadistas- who where distributed throughout the country amongst the peasants to teach and learn from them. Before the campaign the brigadistas took training courses on political instruction and educational techniques, which they continued on a weekly basis during the campaign. With the National Literacy Campaign the illiteracy index was reduced to 12%, but the brigadistas also gained a wider knowledge of the national reality, influencing positively the living conditions of the peasants A Viceministry of Education for Adults was created when the National Literacy Campaign ended, in order to start a program of Popular Basic Education. Its main aims being to continue providing political-ideological instruction and offer basic knowledge to allow for a further technical training of the new literates

Dipolar atomic spin ensembles in a double-well potential

We experimentally study the spin dynamics of mesoscopic ensembles of ultracold magnetic spin-3 atoms located in two separated wells of an optical dipole trap. We use a radio-frequency sweep to selectively flip the spin of the atoms in one of the wells, which produces two separated spin domains of opposite polarization. We observe that these engineered spin domains are metastable with respect to the long-range magnetic dipolar interactions between the two ensembles. The absence of inter-cloud dipolar spin-exchange processes reveals a classical behavior, in contrast to previous results with atoms loaded in an optical lattice. When we merge the two subsystems, we observe spin-exchange dynamics due to contact interactions which enable the first determination of the s-wave scattering length of 52Cr atoms in the S=0 molecular channel a_0=13.5^{+11}_{-10.5}a_B (where a_B is the Bohr radius).Comment: 9 pages, 7 figure