16 results match your criteria Astrophysics And Space Science[Journal]

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How deterministic is the Earth ionosphere's response to solar activity?

Adolfo L Mendez

Astrophys Space Sci 2022 27;367(5):52. Epub 2022 May 27.

Math and Natural Science Department, Miami Dade College, Padron Campus, Miami, FL 33135 USA.

This contribution is aimed at an analysis of the dynamics of free-electron density fluctuations in the ionospheric critical plasma frequency f0F2 by using some tools from the theory of nonlinear dynamical systems. The results suggest the existence of low-dimensional attractors that point to a characterization of the free electron density fluctuations in the f0F2 as a deterministic chaotic system. The study carried out focused on the response of the ionosphere to solar activity as a function of the ascending and descending phases of the solar cycle. Read More

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The mystery of unidentified infrared emission bands.

Sun Kwok

Astrophys Space Sci 2022 2;367(2):16. Epub 2022 Feb 2.

Department of Earth, Ocean, and Atmospheric Sciences, University of British Columbia, Vancouver, Canada.

A family of unidentified infrared emission (UIE) bands has been observed throughout the Universe. The current observed spectral properties of the UIE bands are summarized. These properties are discussed in the frameworks of different models of the chemical carriers of these bands. Read More

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February 2022

A study of pulsation & rotation in a sample of A-K type stars in the field.

Astrophys Space Sci 2018 3;363(12):260. Epub 2018 Dec 3.

Department of Physics, CHRIST (Deemed to be University), Hosur Road, Bengaluru, 560029 Karnataka India.

We present the results of time-series photometric analysis of 15106 A-K type stars observed by the space mission. We identified 513 new rotational variables and measured their starspot rotation periods as a function of spectral type and discuss the distribution of their amplitudes. We examined the well-established period-color relationship that applies to stars of spectral types F5-K for all of these rotational variables and, interestingly, found that a similar period-color relationship appears to extend to stars of spectral types A7 to early-F too. Read More

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December 2018

New UV-source catalogs, UV spectral database, UV variables and science tools from the GALEX surveys.

Astrophys Space Sci 2018 28;363(3):56. Epub 2018 Feb 28.

2Space Telescope Science Institute, Baltimore, USA.

We present a new, expanded and improved catalog of Ultraviolet (UV) sources from the GALEX All-Sky Imaging survey: GUVcat_AIS (Bianchi et al. in Astrophys. J. Read More

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February 2018

Structure of the solar photosphere studied from the radiation hydrodynamics code ANTARES.

Astrophys Space Sci 2017;362(9):181. Epub 2017 Aug 31.

Faculty of Mathematics, University of Vienna, Nordbergstrasse 15, 1090 Wien, Austria.

The ANTARES radiation hydrodynamics code is capable of simulating the solar granulation in detail unequaled by direct observation. We introduce a state-of-the-art numerical tool to the solar physics community and demonstrate its applicability to model the solar granulation. The code is based on the weighted essentially non-oscillatory finite volume method and by its implementation of local mesh refinement is also capable of simulating turbulent fluids. Read More

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The hierarchical stability of the seven known large size ratio triple asteroids using the empirical stability parameters.

Astrophys Space Sci 2014;349(2):677-680. Epub 2013 Oct 26.

Carl Sagan Center, SETI Institute, 189 Bernardo Avenue, Mountain View, CA 94043 USA.

In this study, the hierarchical stability of the seven known large size ratio triple asteroids is investigated. The effect of the solar gravity and primary's are considered. The force function is expanded in terms of mass ratios based on the Hill's approximation and the large size ratio property. Read More

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October 2013

Planetary atmosphere evolution: do other habitable planets exist and can we detect them?

J F Kasting

Astrophys Space Sci 1996 ;241(1):3-24

Department of Geosciences, Penn State University, University Park, PA 16802, USA.

The goal of this conference is to consider whether it is possible within the next few decades to detect Earth-like planets around other stars using telescopes or interferometers on the ground or in space. Implicit in the term "Earth-like" is the idea that such planets might be habitable by Earth-like organisms, or that they might actually be inhabited. Here, I shall address two questions from the standpoint of planetary atmosphere evolution. Read More

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November 1999

Ways that our Solar System helps us understand the formation of other planetary systems and ways that it doesn't.

G W Wetherill

Astrophys Space Sci 1996 ;241(1):25-34

Department of Terrestrial Magnetism, Carnegie Institution of Washington, USA.

Models of planetary formation can be tested by comparison of their ability to predict features of our Solar System in a consistent way, and then extrapolated to other hypothetical planetary systems by different choice of parameters. When this is done, it is found that the resulting systems are insensitive to direct effects of the mass of the star, but do strongly depend on the properties of the disk, principally its surface density. Major uncertainty results from lack of an adequate theoretical model that predicts the existence, size, and distribution of analogs of our Solar System, particularly the gas giants Jupiter and Saturn. Read More

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November 1999

Observations of chemical processing in the circumstellar environment.

Astrophys Space Sci 1995 ;224:81-4

Astronomy Department, Univ. of Maryland, USA.

High resolution interferometer and single-dish observations of young, deeply embedded stellar systems reveal a complex chemistry in the circumstellar environments of low to intermediate mass stars. Depletions of gas-phase molecules, grain mantle evaporation, and shock interactions actively drive chemical processes in different regions around young stars. We present results for two systems, IRAS 05338-0624 and NCG 1333 IRAS 4, to illustrate the behavior found and to examine the physical processes at work. Read More

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Chemical evolution of circumstellar matter around young stellar objects.

Astrophys Space Sci 1995 ;224:237-49

Leiden Observatory, The Netherlands.

Recent observational studies of the chemical composition of circumstellar matter around both high- and low-mass young stellar objects are reviewed. The molecular abundances are found to be a strong function of evolutionary state, but not of system mass or luminosity. The data are discussed with reference to recent theoretical models. Read More

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Possible consequences of absence of "Jupiters" in planetary systems.

G W Wetherill

Astrophys Space Sci 1994 ;212:23-32

Dept. of Terrestrial Magnetism, Carnegie Institution of Washington, Washington, DC, USA.

The formation of the gas giant planets Jupiter and Saturn probably required the growth of massive approximately 15 Earth-mass cores on a time scale shorter than the approximately 10(7) time scale for removal of nebular gas. Relatively minor variations in nebular parameters could preclude the growth of full-size gas giants even in systems in which the terrestrial planet region is similar to our own. Systems containing "failed Jupiters," resembling Uranus and Neptune in their failure to capture much nebular gas, would be expected to contain more densely populated cometary source regions. Read More

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The search for other planets: clues from the solar system.

T Owen

Astrophys Space Sci 1994 ;212:1-11

Institute for Astronomy, Honolulu, Hawaii, USA.

Studies of element abundances and values of D/H in the atmospheres of the outer planets and Titan support a two-step model for the formation of these bodies. This model suggests that the dimensions of Uranus provide a good index for the sensitivity required to detect planets around other stars. The high proportion of N2 on the surfaces of Pluto and Triton indicates that this gas was the dominant reservoir of nitrogen in the early solar nebula. Read More

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Astrometry of southern radio sources.

Astrophys Space Sci 1991 ;177:79-83

Division of Radiophysics, CSIRO, Australia.

An overview is presented of a number of astrometry and astrophysics programs based on radio sources from the Parkes 2.7 GHz catalogues. The programs cover the optical identification and spectroscopy of flat-spectrum Parkes sources and the determination of their milliarc-second radio structures and positions. Read More

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Upper limits for the ethyl-cyanide abundances in TMC-1 and L134N: chemical implications.

Y C Minh W M Irvine

Astrophys Space Sci 1991 ;175:165-9

Department of Physics and Astronomy, University of Massachusetts, Amherst, USA.

We have sought interstellar ethyl-cyanide via its 2(02)-1(01) transition towards two cold, dark clouds and report upper limits of the total column densities of 3 x 10(12) cm-2 and 2 x 10(12) cm-2 for TMC-1 and L134N, respectively. We also observed the 2(02)-1(01) transition of vinyl cyanide previously identified in TMC-1 by Matthews and Sears (1983b). The detection of vinyl cyanide and the non-detection of ethyl cyanide in TMC-1 are consistent with gas phase ion-molecule chemical models, and there is thus no necessity of invoking grain surface synthesis for vinyl cyanide in cold clouds. Read More

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December 1995

Photochemical fractionation of 16O in the space medium modeled by resonance excitation of CO by H-Lyman alpha.

Astrophys Space Sci 1988 ;145:303-19

Scripps Institution of Oceanography, La Jolla, California, USA.

Inferences about the formation of primordial matter in our solar system rest on analysis of the earliest preserved materials in meteorites, of the structure of the solar system today, and of matter in evolving stellar systems elsewhere. The isotope distribution in meteorites suggests that molecular excitation processes similar to those observed today in circumstellar regions and dark interstellar clouds were operating in the early solar nebula. Laboratory model experiments together with these observations give evidence on the thermal state of the source medium from which refractory meteoritic dust formed. Read More

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Band structure of the solar system: an objective test of the grouping of planets and satellites.

Astrophys Space Sci 1988 ;144:357-72

Scripps Institution of Oceanography, University of California, San Diego, La Jolla, USA.

Alfvén in his early work on the origin of the solar system (1942-1946) noted a pronounced band structure in the gravitational potential distribution of secondary bodies, and suggested this feature to be directly related to the formation process. When the critical velocity phenomenon was later discovered, a close agreement was found between the planet-satellite bands on one hand, and the critical velocity limits of the major compound elements in the interstellar medium on the other, suggesting a specific emplacement mechanism for the dusty plasma which presumably constituted the solar nebula. Since the originally perceived band structure was outlined in a qualitative fashion, an attempt is made here to analyze the distribution by a statistical technique, testing the significance of clustering of the observational data in the bands. Read More

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