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Publications

2001

Astrophysics and Astronomy

Articles 1 - 7 of 7

Full-Text Articles in Physical Sciences and Mathematics

Three-Dimensional Spectral Classification Of Low-Metallicity Stars Using Artificial Neural Networks, Shawn Snider, Ted Von Hippel, Et Al. Nov 2001

Three-Dimensional Spectral Classification Of Low-Metallicity Stars Using Artificial Neural Networks, Shawn Snider, Ted Von Hippel, Et Al.

Publications

We explore the application of artificial neural networks (ANNs) for the estimation of atmospheric parameters (Teff, log g, and [Fe/H]) for Galactic F- and G-type stars. The ANNs are fed with medium-resolution (Δλ ~ 1-2 Å) non-flux-calibrated spectroscopic observations. From a sample of 279 stars with previous high-resolution determinations of metallicity and a set of (external) estimates of temperature and surface gravity, our ANNs are able to predict Teff with an accuracy of σ(Teff) = 135-150 K over the range 4250 ≤ Teff ≤ 6500 K, log g with an accuracy …

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Plasma Transport At The Magnetospheric Boundary Due To Reconnection In Kelvin-Helmholtz Vortices, K. Nykyri, A. Otto Sep 2001

Plasma Transport At The Magnetospheric Boundary Due To Reconnection In Kelvin-Helmholtz Vortices, K. Nykyri, A. Otto

Publications

The Kelvin-Helmholtz( KH) mode has long been considered for viscous interaction at the magnetospheric boundary but it is not expected to produce significant mass transport. The presented results indicate that the Kelvin- Helmholtz instability can indeed cause a transfer of mass into the magnetotail during times of northward IMF. The vortex motion of KH waves can generate a strongly twisted magnetic field with multiple current layers. Magnetic reconnection in the strong current layers inside the vortices can detach high density plasma filaments from the magnetosheath. This may explain observed high density and low temperature filaments in the magnetosphere and the …

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Three-Dimensional Spectral Classification Of Low-Metallicity Stars Using Artificial Neural Networks, Shawn Snider, Ted Von Hippel, Carlos Allende Prieto, Timothy C. Beers, Christopher Sneden, Et Al. Jul 2001

Three-Dimensional Spectral Classification Of Low-Metallicity Stars Using Artificial Neural Networks, Shawn Snider, Ted Von Hippel, Carlos Allende Prieto, Timothy C. Beers, Christopher Sneden, Et Al.

Publications

We explore the application of artificial neural networks (ANNs) for the estimation of atmospheric parameters (Teff, log g, and [Fe/H]) for Galactic F- and G-type stars. The ANNs are fed with medium-resolution (Δλ ~ 1-2 Å) non-flux-calibrated spectroscopic observations. From a sample of 279 stars with previous high-resolution determinations of metallicity and a set of (external) estimates of temperature and surface gravity, our ANNs are able to predict Teff with an accuracy of σ(Teff) = 135-150 K over the range 4250 ≤ Teff ≤ 6500 K, log g with an accuracy of σ(log …

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A Determination Of The Local Density Of White Dwarf Stars, J. B. Holberg, Terry D. Oswalt, E. M. Sion Feb 2001

A Determination Of The Local Density Of White Dwarf Stars, J. B. Holberg, Terry D. Oswalt, E. M. Sion

Publications

The most recent version of the Catalog of Spectroscopically Identified White Dwarfs lists 2249 white dwarf stars. Among these stars are 109 white dwarfs that have either reliable trigonometric parallaxes or color-based distance moduli that place them at a distance within 20 pc of the Sun. Most of these nearby white dwarfs are isolated stars, but 28 (25% of the sample) are in binary systems, including such well-known systems as Sirius A/B and Procyon A/B. There are also three double degenerate systems in this sample of the local white dwarf population. The sample of local white dwarfs is largely complete …

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White Dwarfs In Common Proper Motion Binary Systems: Mass Distribution And Kinematics, Nicole M. Silvestri, Terry D. Oswalt, Matt A. Wood, J. Allyn Smith, I. Neill Reid, Edward M. Sion Jan 2001

White Dwarfs In Common Proper Motion Binary Systems: Mass Distribution And Kinematics, Nicole M. Silvestri, Terry D. Oswalt, Matt A. Wood, J. Allyn Smith, I. Neill Reid, Edward M. Sion

Publications

We present the mass distribution, gravitational redshifts, radial velocities, and space motions of white dwarf stars in common proper motion binary systems. The mass distribution we derive for the 41 DA white dwarfs in this study has a mean of 0.68 ± 0.04 MꙨ. This distribution has a slightly higher mean and larger dispersion than most previous white dwarf studies. We hypothesize that this is due to a higher fraction of cool (average Teff ̴ 10,000 K), hence old, white dwarfs in our sample. Our results indicate that samples made up of predominantly cool, old white dwarf stars …

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White Dwarfs In Open Clusters: New Tests Of Stellar Evolution And The Age Of The Galaxy, Ted Von Hippel Jan 2001

White Dwarfs In Open Clusters: New Tests Of Stellar Evolution And The Age Of The Galaxy, Ted Von Hippel

Publications

White dwarf cooling theory and very deep observations in star clusters provide a new tool to test stellar evolution theory and time scales. In particular, white dwarf cooling theory is now testing the degree of enhanced core mixing in stars with turnoff ages of 1 to 2 Gyr. More generally, I show the good overall agreement between white dwarf and modern isochrone ages over the range 0.1 to 4 Gyr.

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Break Out Session: The Future Of White Dwarf Observing, Ted Von Hippel Jan 2001

Break Out Session: The Future Of White Dwarf Observing, Ted Von Hippel

Publications

On Thursday, June 15, 2000 the conference participants joined on of four afternoon break out sessions. Our break out session was charged with addressing the the following questions: Astronomy is changing. Eight to ten meter telescopes looking towards the edge of the Universe will dominate the astronomical landscape. Queue scheduling, large surveys, and the current emphasis towards the red end of the spectrum will also affect us. What consequences do these changes imply for our field? How can we convince telescope assignment committees to grand observing time to proposers from our community?

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