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Articles 391 - 420 of 494

Full-Text Articles in Astrophysics and Astronomy

The Clock Paradox In A Static Homogeneous Gravitational Field, Preston Jones, Lucas F. Wanex Feb 2006

The Clock Paradox In A Static Homogeneous Gravitational Field, Preston Jones, Lucas F. Wanex

Publications

The gedanken experiment of the clock paradox is solved exactly using the general relativistic equations for a static homogeneous gravitational field. We demonstrate that the general and special relativistic clock paradox solutions are identical and in particular that they are identical for finite acceleration. Practical expressions are obtained for proper time and coordinate time by using the destination distance as the key observable parameter. This solution provides a formal demonstration of the identity between the special and general relativistic clock paradox with finite acceleration and where proper time is assumed to be the same in both formalisms. By solving the …

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Cool White Dwarfs In The Sloan Digital Sky Survey, Mukremin Kilic, Jeffrey A. Munn, Hugh C. Harris, James W. Liebert, Ted Von Hippel, Kurtis A. Williams, Travis S. Metcalfe, D. E. Winget, Stephen E. Levine Jan 2006

Cool White Dwarfs In The Sloan Digital Sky Survey, Mukremin Kilic, Jeffrey A. Munn, Hugh C. Harris, James W. Liebert, Ted Von Hippel, Kurtis A. Williams, Travis S. Metcalfe, D. E. Winget, Stephen E. Levine

Publications

A reduced proper motion diagram utilizing Sloan Digital Sky Survey (SDSS) photometry and astrometry and USNO-B plate astrometry is used to separate cool white dwarf candidates from metal-weak, high-velocity, mainsequence Population II stars (subdwarfs) in the SDSS Data Release 2 imaging area. Follow-up spectroscopy using the Hobby-Eberly Telescope, the MMT, and the McDonald 2.7 m telescope is used to demonstrate that the white dwarf and subdwarf loci separate cleanly in the reduced proper motion diagram and that the contamination by subdwarfs is small near the cool white dwarf locus. This enables large, statistically complete samples of white dwarfs, particularly the …

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The White Dwarf Luminosity Function From Sloan Digital Sky Survey Imaging Data, Hugh C. Harris, Jeffrey A. Munn, Mukremin Kilic, James W. Liebert, Kurtis A. Williams, Ted Von Hippel, Stephen E. Levine, David G. Monet, Daniel J. Eisenstein, S. J. Kleinman, T. S. Metcalfe, Atsuko Nikka, D. E. Winget, J. Brinkmann, Masataka Fukugita, G. R. Knapp, Robert H. Lupton, J. Allyn Smith, Donald P. Schneider Jan 2006

The White Dwarf Luminosity Function From Sloan Digital Sky Survey Imaging Data, Hugh C. Harris, Jeffrey A. Munn, Mukremin Kilic, James W. Liebert, Kurtis A. Williams, Ted Von Hippel, Stephen E. Levine, David G. Monet, Daniel J. Eisenstein, S. J. Kleinman, T. S. Metcalfe, Atsuko Nikka, D. E. Winget, J. Brinkmann, Masataka Fukugita, G. R. Knapp, Robert H. Lupton, J. Allyn Smith, Donald P. Schneider

Publications

A sample of white dwarfs is selected from the Sloan Digital Sky Survey (SDSS) Data Release 3 using their reduced proper motions, based on improved proper motions from combined SDSS and USNO-B data. Numerous SDSS and follow-up spectra (Kilic and coworkers) are used to quantify completeness and contamination of the sample; kinematicsmodels are used to understand and correct for velocity-dependent selection biases.A luminosity function is constructed covering the range 7 < Mbol < 16, and its sensitivity to various assumptions and selection limits is discussed. The white dwarf luminosity function based on 6000 stars is remarkably smooth and rises nearly monotonically to Mbol=15.3. It then drops abruptly, although the small number of low-luminosity stars in the sample and their unknown atmospheric composition prevent quantitative conclusions about this decline. Stars …

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Book Review: The Amateur Astronomer's Introduction To The Celestial Sphere, T. D. Oswalt Jan 2006

Book Review: The Amateur Astronomer's Introduction To The Celestial Sphere, T. D. Oswalt

Publications

This document is Dr. Oswalt’s review of The Amateur Astronomer's Introduction to the Celestial Sphere by William Millar. Cambridge, 2006 299p, 052167123X $40.00, 9780521671231 $40.00.

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Observations Of Triboelectric Charging Effects On Langmuir-Type Probes In Dusty Plasma, Aroh Barjatya, Charles M. Swenson Jan 2006

Observations Of Triboelectric Charging Effects On Langmuir-Type Probes In Dusty Plasma, Aroh Barjatya, Charles M. Swenson

Publications

Investigation of Earth’s mesosphere using sounding rockets equipped with a myriad of instruments has been a highly active field in the last 2 decades. This paper presents data from three separate instruments: an RF impedance probe, a DC fixed bias Langmuir probe, and an electric field probe, that were flown on a mesospheric sounding rocket flight investigating the presence of charged dust within and/or around a sporadic metal layer. The combined data set indicates a case of payload surface charging, the causes of which are investigated within this paper. A generic circuit model is developed to analyze payload charging and …

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The Dust Cloud Around The White Dwarf G29-38, William T. Reach, Ted Von Hippel, Et Al. Dec 2005

The Dust Cloud Around The White Dwarf G29-38, William T. Reach, Ted Von Hippel, Et Al.

Publications

We present new observations of the white dwarf G29-38 with the camera (4.5 and 8 μm), photometer (24 μm), and spectrograph (5.5-14 μm) of the Spitzer Space Telescope. This star has an exceptionally large infrared excess, amounting to 3% of the bolometric luminosity. The spectral energy distribution (SED) has a continuum peak around 4.5 μm and a 9-11 μm emission feature 1.25 times brighter than the continuum. A mixture of amorphous olivine and a small amount of forsterite in an emitting region 1-5 R☉ from the star can reproduce the shape of the 9-11 μm feature. The SED …

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A Multisite Photometric Campaign On The Pre-Main-Sequence ₰ Delta Scuti Pulsator Ip Per, V. Ripepi, T. D. Oswalt, S. Bernabei, M. Marconi, Et Al. Dec 2005

A Multisite Photometric Campaign On The Pre-Main-Sequence ₰ Delta Scuti Pulsator Ip Per, V. Ripepi, T. D. Oswalt, S. Bernabei, M. Marconi, Et Al.

Publications

We present the results of a photometric multisite campaign on the δ Scuti Pre-Main-Sequence star IP Per. Nine telescopes have been involved in the observations, with a total of about 190 h of observations over 38 nights. Present data confirms the multiperiodic nature of this star and leads to the identification of at least nine pulsational frequencies. Comparison with the predictions of linear non-adiabatic radial pulsation models allowed us to identify only five of the nine observed frequencies, and to constrain the position of IP Per in the HR diagram. The latter is in good agreement with the empirical determination …

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Measuring The Evolution Of The Most Stable Optical Clock G 117-B15a, S. O. Kepler, Ted Von Hippel, Et Al. Dec 2005

Measuring The Evolution Of The Most Stable Optical Clock G 117-B15a, S. O. Kepler, Ted Von Hippel, Et Al.

Publications

We report our measurement of the rate of change of period with time () for the 215 s periodicity in the pulsating white dwarf G 117-B15A, the most stable optical clock known. After 31 years of observations, we have finally obtained a 4 σ measurement observed = (4.27 ± 0.80) × 10-15 s s-1. Taking into account the proper-motion effect of proper = (7.0 ± 2.0) × 10-16s s-1, we obtain a rate of change of period with time of = (3.57 ± 0.82) × 10-15 s s-1. This value is consistent with the cooling rate in our white dwarf …

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Book Review: Stargazer: The Life And Times Of The Telescope, T. D. Oswalt Dec 2005

Book Review: Stargazer: The Life And Times Of The Telescope, T. D. Oswalt

Publications

This document is Dr. Oswalt’s review of Stargazer : the Life and Times of the Telescope by Fred Watson. Da Capo, 2004 342p, 0306814323 $24.95

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Faint Blue Objects In The Hubble Deep Field–South Revealed: White Dwarfs, Subdwarfs, And Quasars, Mukremin Kilic, Ted Von Hippel, Et Al. Nov 2005

Faint Blue Objects In The Hubble Deep Field–South Revealed: White Dwarfs, Subdwarfs, And Quasars, Mukremin Kilic, Ted Von Hippel, Et Al.

Publications

We explore the nature of the faint blue objects in the Hubble Deep Field–South. We have derived proper motions for the point sources in the Hubble Deep Field–South using a 3 yr baseline. Combining our proper-motion measurements with spectral energy distribution fitting enabled us to identify four quasars and 42 stars, including three white dwarf candidates. Two of these white dwarf candidates, HDF-S 1444 and 895, are found to display significant proper motion, 21:1±7:9 and 34:9 ± 8:0 mas yr -1, and are consistent with being thick-disk or halo white dwarfs located at ̴2 kpc. The other faint …

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Book Review: The Scientific Legacy Of Fred Hoyle, T. D. Oswalt Nov 2005

Book Review: The Scientific Legacy Of Fred Hoyle, T. D. Oswalt

Publications

This document is Dr. Oswalt’s review of The Scientific Legacy of Fred Hoyle ed. by Douglas Gough Cambridge, 2004 249p, 0521824486 $75.00.

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Coordinated Cluster/Double Star Observations Of Dayside Reconnection Signatures, M. W. Dunlop, M. G. G. T. Taylor, J. A. Davies, C. J. Owen, F. Pitout, A. N. Fazakerley, K. Nykyri, Et Al. Nov 2005

Coordinated Cluster/Double Star Observations Of Dayside Reconnection Signatures, M. W. Dunlop, M. G. G. T. Taylor, J. A. Davies, C. J. Owen, F. Pitout, A. N. Fazakerley, K. Nykyri, Et Al.

Publications

The recent launch of the equatorial spacecraft of the Double Star mission, TC-1, has provided an unprecedented opportunity to monitor the southern hemisphere dayside magnetopause boundary layer in conjunction with northern hemisphere observations by the quartet of Cluster spacecraft. We present first results of one such situation where, on 6 April 2004, both Cluster and the Double Star TC-1 spacecraft were on outbound transits through the dawnside magnetosphere. The observations are consistent with ongoing reconnection on the dayside magnetopause, resulting in a series of flux transfer events (FTEs) seen both at Cluster and TC-1, which appear to lie north and …

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Excess Infrared Radiation From The Massive Daz White Dwarf Gd 362: A Debris Disk?, Mukremin Kilic, Ted Von Hippel, Et Al. Oct 2005

Excess Infrared Radiation From The Massive Daz White Dwarf Gd 362: A Debris Disk?, Mukremin Kilic, Ted Von Hippel, Et Al.

Publications

We report the discovery of excess K-band radiation from the massive DAZ white dwarf star GD 362. Combining infrared photometric and spectroscopic observations, we show that the excess radiation cannot be explained by a stellar or substellar companion, and is likely to be caused by a debris disk. This would be only the second such system known, discovered 18 years after G29-38, the only single white dwarf currently known to be orbited by circumstellar dust. Both of these systems favor a model with accretion from a surrounding debris disk to explain the metal abundances observed in DAZ white dwarfs. …

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Deep Photometry Of The Globular Cluster M5: Distance Estimates From White Dwarf And Main-Sequence Stars, Andrew C. Layden, Ted Von Hippel, Et Al. Oct 2005

Deep Photometry Of The Globular Cluster M5: Distance Estimates From White Dwarf And Main-Sequence Stars, Andrew C. Layden, Ted Von Hippel, Et Al.

Publications

We present deep VI photometry of stars in the globular cluster M5 (NGC 5904) based on images taken with the Hubble Space Telescope. The resulting color-magnitude diagram reaches below V ≈27 mag, revealing the upper 2–3 mag of the white dwarf cooling sequence and main-sequence stars 8 mag and more below the turnoff. We fit the main sequence to subdwarfs of known parallax to obtain a true distance modulus of (m ̶ M )0 = 14:45 ± 0:11 mag. A second distance estimate based on fitting the cluster white dwarf sequence to field white dwarfs with known parallax …

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Galactic Open Clusters, Ted Von Hippel Sep 2005

Galactic Open Clusters, Ted Von Hippel

Publications

The study of open clusters has a classic feel to it since the subject predates anyone alive today. Despite the age of this topic, I show via an ADS search that its relevance and importance in astronomy has grown faster in the last few decades than astronomy in general. This is surely due to both technical reasons and the interconnection of the field of stellar evolution to many branches of astronomy. In this review, I outline what we know today about open clusters and what they have taught us about a range of topics from stellar evolution to Galactic structure …

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Book Review: Observing Variable Stars, Novae, And Supernovae, T. D. Oswalt Sep 2005

Book Review: Observing Variable Stars, Novae, And Supernovae, T. D. Oswalt

Publications

This document is Dr. Oswalt’s review of Observing Variable Stars, Novae, and Supernovae by Gerald North with Nick James Cambridge, 2004 230p, 0521820472 $45.00.

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Where Are The Magnetic White Dwarfs With Detached, Nondegenerate Companions?, James W. Liebert, Dayal T. Wickramsinghe, Gary D. Schmidt, Nicole M. Silvestri, T. D. Oswalt, Et Al. May 2005

Where Are The Magnetic White Dwarfs With Detached, Nondegenerate Companions?, James W. Liebert, Dayal T. Wickramsinghe, Gary D. Schmidt, Nicole M. Silvestri, T. D. Oswalt, Et Al.

Publications

The Sloan Digital Sky Survey has already more than doubled the sample of white dwarfs with spectral classifications, the subset with detached M dwarf companions, and the subset of magnetic white dwarfs. In the course of assessing these new discoveries, we have noticed a curious, unexpected property of the total lists of magnetic white dwarfs and of white dwarf plus main-sequence binaries: there appears to be virtually zero overlap between the two samples! No confirmed magnetic white dwarf has yet been found in such a pairing with a main-sequence star. The same statement can be made for the samples of …

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Antiphase Oh And Oi Airglow Emissions Induced By A Short-Period Ducted Gravity Wave, Jonathan B. Snively, Victor P. Pasko Apr 2005

Antiphase Oh And Oi Airglow Emissions Induced By A Short-Period Ducted Gravity Wave, Jonathan B. Snively, Victor P. Pasko

Publications

"Numerical simulation of a ducted gravity wave event suggests that OH (8,3) and O(1S) 557.7 nm airglow emissions layers may exhibit opposite-phase intensities when perturbed by a short-period wave undergoing vertical reflection. This effect arises due to the time and temperature dependance of the OH excitation reaction, coupled with the linear polarization properties of vertically-standing waves."

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A Measure Of The Hurst Exponent Variability On Ground Based Magnetometer Data For Quiet And Active Magnetospheric Periods, Dario O. Cersosimo Apr 2005

A Measure Of The Hurst Exponent Variability On Ground Based Magnetometer Data For Quiet And Active Magnetospheric Periods, Dario O. Cersosimo

Master's Theses - Daytona Beach

Ground-based magnetometer data were analyzed for the period of 1991-2001. The data were classified into periods of quiet and active magnetospheric activity. Those periods classified as quiet required that Kp < 1 for not less than 48 consecutive hours and active periods required a Kp > 4 for not less than 24 consecutive hours. Detrended fluctuation analysis was employed to analyze 40 events. A monofractal approach was used to identify differences in the Hurst exponent of quiet and active events. No statistical differences were found using this approach since both types of events displayed quasirandom walk behavior. A second approach determined the temporal variations in the Hurst exponent for each event. The Hurst exponent is temporally …

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Planetary Wave Activity Observed In Polar Mesospheric Clouds, David A. Mackler Apr 2005

Planetary Wave Activity Observed In Polar Mesospheric Clouds, David A. Mackler

Master's Theses - Daytona Beach

In this paper, the Solar Backscatter UV spectrometer (SBUV) Polar Mesospheric Cloud (PMC) dataset was investigated for planetary wave activity following the earlier study by Merkel [2002]. To counter the sparse nature of the data, four separate methods of analysis are used in determining if planetary waves are present and how they effect PMC formation. The four methods are histograms (both in frequency of occurrence and mean albedo), periodograms using the Lomb-Scargle method, frequency-wavenumber analysis using a 2D Lomb-Scargle method from Wu et. al [1995], and a temporal (yearly) analysis of the 5, 6.5, and 10 day wave amplitudes. The …

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From Young And Hot To Old And Cold: Comparing White Dwarf Cooling Theory To Main-Sequence Stellar Evolution In Open Clusters, Ted Von Hippel Mar 2005

From Young And Hot To Old And Cold: Comparing White Dwarf Cooling Theory To Main-Sequence Stellar Evolution In Open Clusters, Ted Von Hippel

Publications

I explore the current ability of both white dwarf cooling theory and main-sequence stellar evolution theory to accurately determine stellar population ages by comparing ages derived using both techniques for open clusters ranging from 0.1 to 4 Gyr. I find good agreement between white dwarf and main-sequence evolutionary ages over the entire age range currently available for study. I also find that directly comparing main-sequence turnoff ages to white dwarf ages is only weakly sensitive to realistic levels of errors in cluster distance, metallicity, and reddening. Additional detailed comparisons between white dwarf and main-sequence ages have tremendous potential to refine …

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Book Review: The New Amateur Astronomer, T. D. Oswalt Mar 2005

Book Review: The New Amateur Astronomer, T. D. Oswalt

Publications

This document is Dr. Oswalt’s review of The New Amateur Astronomer by Martin Mobberley. Springer, 2004 229p, 1852336633 $34.95

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The Chromospheric Activity And Ages Of M Dwarf Stars In Wide Binary Systems, Nicole M. Silvesteri, T. D. Oswalt, Suzanne L. Hawley Feb 2005

The Chromospheric Activity And Ages Of M Dwarf Stars In Wide Binary Systems, Nicole M. Silvesteri, T. D. Oswalt, Suzanne L. Hawley

Publications

We investigate the relationship between age and chromospheric activity for 139 M dwarf stars in wide binary systems with white dwarf companions. The age of each system is determined from the cooling age of its white dwarf component. The current limit for activity-age relations found for M dwarfs in open clusters is 4 Gyr. Our unique approach to finding ages for M stars allows for the exploration of this relationship at ages older than 4 Gyr. The general trend of stars remaining active for a longer time at later spectral type is confirmed. However, our larger sample and greater age …

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The Initial-Final Mass Relationship: Spectroscopy Of White Dwarfs In Ngc 2099 (M37), Jasonjot Singh Kalirai, Ted Von Hippel, Et Al. Dec 2004

The Initial-Final Mass Relationship: Spectroscopy Of White Dwarfs In Ngc 2099 (M37), Jasonjot Singh Kalirai, Ted Von Hippel, Et Al.

Publications

We present new observations of very faint white dwarfs (WDs) in the rich open star cluster NGC 2099 (M37). Following deep, wide-field imaging of the cluster using the Canada-France-Hawaii Telescope, we have now obtained spectroscopic observations of candidate WDs using both the Gemini Multi-Object Spectrograph on Gemini North and the Low-Resolution Imaging Spectrometer on Keck. Of our 24 WD candidates (all fainter than V = 22.4), 21 are spectroscopically confirmed to be bona fide WDs, four or five of which are most likely field objects. Fitting 18 of the 21 WD spectra with model atmospheres, we find that most WDs …

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Coordinate Conditions For A Uniformly Accelerated Or Static Plane Symmetric Metric, Preston Jones, Lucas Wanex Dec 2004

Coordinate Conditions For A Uniformly Accelerated Or Static Plane Symmetric Metric, Preston Jones, Lucas Wanex

Publications

The coordinate conditions for three exact solutions for the metric components of a coordinate system with constant acceleration or of a static plane symmetric gravitational field are presented. First, the coordinate condition that the acceleration of light is constant is applied to the field equations to derive the metric of a coordinate system of constant acceleration. Second, the coordinate conditions required to produce the metrics of Rindler and Lass are applied to the field equations to calculate the components of these two metrics and the coordinate velocities and coordinate accelerations for light of these two metrics are compared to the …

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Geocoronal Hydrogen Studies Using Fabry-Perot Interferometers, S. M. Nossal, E. J. Mierkiewicz, F. L. Roesler, J. Bishop, R. J. Reynolds Nov 2004

Geocoronal Hydrogen Studies Using Fabry-Perot Interferometers, S. M. Nossal, E. J. Mierkiewicz, F. L. Roesler, J. Bishop, R. J. Reynolds

Publications

Ground based Fabry-Perot observations of solar excited geocoronal hydrogen fluorescence emissions are one of the primary means of studying the neutral upper atmosphere [Atreya et al., 1975; Meriwether et al., 1980; Yelle and Roesler, 1985; Shih et al., 1985; Kerr et al., 2001a,b; He et al., 1993; Nossal et al., 1993, 1998, 2004; Bishop et al., 2001; Mierkiewicz, 2002; and references therein]. Excellent reviews of early ground-based geocoronal Balmer α observations are found in: Krassovsky et al. [1966], Krassovsky [1971], Donahue [1964, 1966], Tinsley [1974], Fahr and Shizgal [1983] and Kerr et al. [2001a]. Instruments onboard satellites and rockets also …

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The White Dwarf Luminosity Function: The Shape Of Things To Come, Ted Von Hippel, M. Kilie, J. Munn, K. Williams, J. Libert, D. E. Winget, T. S. Metcalfe, Et Al. Oct 2004

The White Dwarf Luminosity Function: The Shape Of Things To Come, Ted Von Hippel, M. Kilie, J. Munn, K. Williams, J. Libert, D. E. Winget, T. S. Metcalfe, Et Al.

Publications

We describe a new survey for cool white dwarfs that supplements Sloan Digital Sky Survey photometry with USNO proper motions and followup spectroscopy. To date we have discovered and spectroscopically confirmed 80 new moderate temperature and cool white dwarfs. We have also found a handful of high-velocity white dwarfs and we expect a sizable fraction of these to be thick disk or possibly halo objects. Our survey is designed to find 104 new white dwarfs, although only 60 will be among the faintest white dwarfs (MV 16), where most of the age-sensitivity resides. We discuss an extension of our survey …

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Photometric Identification Of Cool White Dwarfs, M. Kilic, D. E. Winget, Ted Von Hippel, C. F. Claver Oct 2004

Photometric Identification Of Cool White Dwarfs, M. Kilic, D. E. Winget, Ted Von Hippel, C. F. Claver

Publications

We investigate the use of a narrowband DDO51 filter for photometric identification of cool white dwarfs. We report photometric observations of 30 known cool white dwarfs with temperatures ranging from 10,000 K down to very cool temperatures (3500 K). Follow-up spectroscopic observations of a sample of objects selected using this filter and our photometric observations show that DDO51 filter photometry can help select cool white dwarf candidates for follow-up multiobject spectroscopy by rejecting 65% of main-sequence stars with the same broadband colors as the cool white dwarfs. This technique is not selective enough to efficiently feed single-object spectrographs. We present …

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Redefining The Empirical Zz Ceti Instability Strip, Anjum S. Mukadam, Ted Von Hippel, Et Al. Sep 2004

Redefining The Empirical Zz Ceti Instability Strip, Anjum S. Mukadam, Ted Von Hippel, Et Al.

Publications

We use the new ZZ Ceti stars (hydrogen-atmosphere white dwarf variables; DAVs) discovered within the Sloan Digital Sky Survey (Mukadam et al. 2004) to redefine the empirical ZZ Ceti instability strip. This is the first time since the discovery of white dwarf variables in 1968 that we have a homogeneous set of spectra acquired using the same instrument on the same telescope, and with consistent data reductions, for a statistically significant sample of ZZ Ceti stars. The homogeneity of the spectra reduces the scatter in the spectroscopic temperatures, and we find a narrow instability strip of width ~950 K, from …

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Book Review: Sky Vistas: Astronomy For Binoculars And Richestfield Telescopes, T. D. Oswalt Sep 2004

Book Review: Sky Vistas: Astronomy For Binoculars And Richestfield Telescopes, T. D. Oswalt

Publications

This document is Dr. Oswalt’s review of Sky Vistas : Astronomy for Binoculars and Richestfield Telescopes by Craig Crossen and Gerald Rhemann Springer, 2004 279p, 3211008519 $69.95

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