Smithsonian Astrophysical Observatory

About: Smithsonian Astrophysical Observatory is a facility organization based out in Cambridge, Massachusetts, United States. It is known for research contribution in the topics: Galaxy & Stars. The organization has 1665 authors who have published 3622 publications receiving 132183 citations. The organization is also known as: SAO.

Tidally Triggered Star Formation in Close Pairs of Galaxies: Major and Minor Interactions

Abstract: We study star formation in a sample of 345 galaxies in 167 pairs and compact groups drawn from the original CfA2 Redshift Survey and from a follow-up search for companions. We construct our sample with attention to including pairs with luminosity contrast ≥ 2. These 57 galaxies with ≥ 2 provide a set of nearby representative cases of minor interactions, a central feature of the hierarchical galaxy formation model. Here we report the redshifts and positions of the 345 galaxies in our sample and of 136 galaxies in apparent pairs that are superpositions. In the pairs sample as a whole, there are strong correlations between the equivalent width of the Hα emission line and the projected spatial and line-of-sight velocity separation of the pair. For pairs of small luminosity contrast, < 2, the member galaxies show a correlation between the equivalent width of Hα and the projected spatial separation of the pair. However, for pairs with large luminosity contrast, ≥ 2, we detect no correlation between the equivalent width of Hα and the projected spatial separation. The relative luminosity of the companion galaxy is more important in a gravitational tidal interaction than the intrinsic luminosity of the galaxy. Central star formation across the entire pairs sample depends strongly on the luminosity ratio, , a reasonable proxy for the mass ratio of the pair; pairs composed of similarly luminous galaxies produce the strongest bursts of star formation. Pairs with ≥ 2 rarely have EW(Hα) 70 A.

Multi-model ensemble simulations of tropospheric NO2 compared with GOME retrievals for the year 2000

Abstract: We present a systematic comparison of tropo- spheric NO2 from 17 global atmospheric chemistry mod- els with three state-of-the-art retrievals from the Global Ozone Monitoring Experiment (GOME) for the year 2000. The models used constant anthropogenic emissions from IIASA/EDGAR3.2 and monthly emissions from biomass burning based on the 1997-2002 average carbon emissions from the Global Fire Emissions Database (GFED). Model output is analyzed at 10:30 local time, close to the overpass time of the ERS-2 satellite, and collocated with the measure- ments to account for sampling biases due to incomplete spa-

The elemental composition of asteroid 433 Eros: Results of the NEAR-Shoemaker X-ray spectrometer

Abstract: We report major element composition ratios for regions of the asteroid 433 Eros imaged during two solar flares and quiet sun conditions during the period of May to July 2000. Low aluminum abundances for all regions argue against global differentiation of Eros. Magnesium/silicon, aluminum/silicon, calcium/silicon, and iron/silicon ratios are best interpreted as a relatively primitive, chondritic composition. Marked depletions in sulfur and possible aluminum and calcium depletions, relative to ordinary chondrites, may represent signatures of limited partial melting or impact volatilization.

A constructive model potential method for atomic interactions

Abstract: A model potential method is presented that can be applied to many electron single centre and two centre systems. The development leads to a Hamiltonian with terms arising from core polarization that depend parametrically upon the positions of the valence electrons. Some of the terms have been introduced empirically in previous studies. Their significance is clarified by an analysis of a similar model in classical electrostatics. The explicit forms of the expectation values of operators at large separations of two atoms given by the model potential method are shown to be equivalent to the exact forms when the assumption is made that the energy level differences of one atom are negligible compared to those of the other.