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Full-Text Articles in Physical Sciences and Mathematics

A Chemical-Dynamical Model Of Wave-Driven Sodium Fluctuations, Michael P. Hickey Ph.D., John M.C. Plane Oct 1995

A Chemical-Dynamical Model Of Wave-Driven Sodium Fluctuations, Michael P. Hickey Ph.D., John M.C. Plane

Publications

A comprehensive chemical-dynamical model is used to investigate the interaction of gravity waves with twenty minor species involved in the atomic sodium chemistry in the mesopause region. We find that chemistry becomes important on the underside of the sodium layer, primarily below 85 km altitude, where the relative importance of chemistry in wave-driven sodium fluctuations increases with increasing wave period and increasing horizontal wavelength. We also find that for altitudes below 80 km an adequate determination of the effects of chemistry in these fluctuations requires the inclusion of several reactions related to ozone chemistry. However, the atomic Na density is ...


New Sources For The Hot Oxygen Geocorona: Solar Cycle, Seasonal, Latitudinal, And Diurnal Variations, Michael P. Hickey Ph.D., P. G. Richards, D. G. Torr Sep 1995

New Sources For The Hot Oxygen Geocorona: Solar Cycle, Seasonal, Latitudinal, And Diurnal Variations, Michael P. Hickey Ph.D., P. G. Richards, D. G. Torr

Publications

This paper demonstrates the variability of thermospheric sources of hot oxygen atoms. Numerical calculations were performed for day and night, high and low solar activity, summer and winter, and low- and middle-latitude conditions. Under most conditions, reactions involving metastable species are more important hot O sources than previously considered dissociative recombination of O2+ and NO+. All the hot O sources are an order of magnitude lower at midnight than at noon. At night, dissociative recombination of O2+and NO+ are the most important sources. Quenching of vibrationally excited N2 (N2*) by O is the most important metastable source at night ...


Experiences Of Wfpc-2 Photometry And Psf Modelling, Nial Tanvir, David Robinson, Ted Von Hippel Mar 1995

Experiences Of Wfpc-2 Photometry And Psf Modelling, Nial Tanvir, David Robinson, Ted Von Hippel

Publications

The wide-field chips in WFPC-2 have ~0.0996 arcsec pixels, which is larger than the FWHM of the point spread function (PSF). This poor sampling of WFPC-2 images, means that simple stellar aperture photometry is competitive with profile fitting for moderately crowded fields. One of the problems which must be addressed with profile fitting photometry is that of allowing for variations of the PSF as a function of position on the image. The equivalent problem for aperture photometry is obtaining aperture corrections as a function of position. The aperture correction must be added to each aperture magnitude in order to ...


An Independent Calibration Of Stellar Ages: Hst Observations Of White Dwarfs At V=25, Ted Von Hippel, Gerard Gilmore, D.H.P. Jones Mar 1995

An Independent Calibration Of Stellar Ages: Hst Observations Of White Dwarfs At V=25, Ted Von Hippel, Gerard Gilmore, D.H.P. Jones

Publications

The white dwarf luminosity function of a stellar cluster will have a sharp trunca- tion at a luminosity which is determined by the time since formation of the first white dwarfs in that cluster. Calculation of the dependence of this limiting luminosity on age requires relatively well-understood physics and is independent of stellar evolutionary models. Thus, measurement of the termination of the white dwarf luminosity func- tion provides an independent method to determine the age of a cluster, and thereby to calibrate stellar evolutionary ages. We have obtained HST WFPC2 data in two open clusters, identified the white dwarf sequence ...