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Articles 1 - 26 of 26
Full-Text Articles in Astrophysics and Astronomy
An Observational Test Of The Spherical Model Atmospheres For The M Class Giants: The Case Of Δ2 Lyrae, Jeffrey J. Sudol, J. A. Benson, H. M. Dyck, M. Scholz
An Observational Test Of The Spherical Model Atmospheres For The M Class Giants: The Case Of Δ2 Lyrae, Jeffrey J. Sudol, J. A. Benson, H. M. Dyck, M. Scholz
Physics & Engineering Faculty Publications
No abstract provided.
Polarization From Microlensing Of Spherical Circumstellar Envelopes By A Point Lens., J. F. L. Simmons, J. E. Bjorkman, R. Ignace, I. J. Coleman
Polarization From Microlensing Of Spherical Circumstellar Envelopes By A Point Lens., J. F. L. Simmons, J. E. Bjorkman, R. Ignace, I. J. Coleman
Richard Ignace
We discuss the flux and polarization signals obtained from the microlensing of stars with extended circumstellar envelopes by a single point-mass lens. A previous paper considered the case of main-sequence stars, and showed that microlensing of the stellar photosphere could produce a small net polarization (up to 0.1 per cent). In this paper, we show that stars with extensive envelopes will show a much higher level of variable polarization (up to 10 per cent), even if they are spherically symmetric. Since the stellar envelopes most likely to be lensed are produced by red giant winds, we also investigate the effects …
An Isolated, Recently Shocked Ism Cloud In The Cygnus Loop Supernova Remnant, D. J. Patnaude, R. A. Fesen, J. C. Raymond, N. A. Levenson
An Isolated, Recently Shocked Ism Cloud In The Cygnus Loop Supernova Remnant, D. J. Patnaude, R. A. Fesen, J. C. Raymond, N. A. Levenson
Dartmouth Scholarship
Spatially resolved ROSAT X-ray and ground-based optical data for the southwestern region of the Cygnus Loop supernova remnant (SNR) reveal in unprecedented detail the very early stages of a blast-wave interaction with an isolated interstellar cloud. Numerous internal cloud shock fronts near the upstream flow and along the cloud edges are visible optically as sharp filaments of enhanced H emission. Faint X-ray emission is seen along a line of Balmer-dominated shock filaments north and south of the cloud with an estimated X-ray gas temperature of 1.2 106 K (0.11 keV), corresponding to a shock velocity of 290 km s1 . …
Identification Of Cool White Dwarfs In The Noao Deep Wide-Field Survey, M. Kilic, Don E. Winget, T. Von Hippel, C.F. Claver
Identification Of Cool White Dwarfs In The Noao Deep Wide-Field Survey, M. Kilic, Don E. Winget, T. Von Hippel, C.F. Claver
Publications
The chronology of star formation is recorded in the white dwarf luminosity function (WDLF). White dwarf (WD) structure implies a relatively simple connection between WD luminosity and age. First attempts to exploit WDs as chronometers [3,4,6] showed that the WDLF was a map of the history of star formation in the disk, and a significant shortfall of low-luminosity degenerates–the inevitable consequence of the finite age of the disk. The shortfall near log(L/L⊙)≈−4.5 implies a disk age of 6.5–9.5 Gyr [2]. The WDLF from wide common proper motion binaries [5] does not show the shortfall seen by Liebert et al. (1988). …
Search For Oxygen In Cool Dq White Dwarf Atmospheres, M. Kilic, Ted Von Hippel, D. E. Winget, D. F. Lester, D. Saumon
Search For Oxygen In Cool Dq White Dwarf Atmospheres, M. Kilic, Ted Von Hippel, D. E. Winget, D. F. Lester, D. Saumon
Publications
The existence of carbon in cool He white dwarf (WD) atmospheres has been known for a relatively long time[5]. The presence of carbon in these atmospheres is explained by convective dredge up of interior carbon [6]. Pelletier et al. (1986) presented the first detailed calculations of this process and showed that carbon diffuses upwards from the core into the base of the He-rich envelope where it can be dredged up by a surface convection zone. As the temperature of the star decreases, more carbon diffuses upward, and the base of convection zone moves deeper into the star, further enriching the …
Spatially Resolved Spectroscopy Of Coma Cluster Early-Type Galaxies - Ii. The Minor Axis Dataset, G. Wegner, E. M. Corsini, R. P. Saglia, R. Bender
Spatially Resolved Spectroscopy Of Coma Cluster Early-Type Galaxies - Ii. The Minor Axis Dataset, G. Wegner, E. M. Corsini, R. P. Saglia, R. Bender
Dartmouth Scholarship
We present minor axis, offset major axis and one diagonal long slit spectra for 10 E and S0 galaxies of the Coma cluster drawn from a magnitude-limited sample studied before. We derive rotation curves, velocity dispersion profiles and the H3 and H4 coefficients of the Hermite decomposition of the line of sight velocity distribution. Moreover, we derive the line index profiles of Mg, Fe and Hβ line indices and assess their errors. The data will be used to construct dynamical models of the galaxies and study their stellar populations.
Six New Γ Doradus Stars, Gregory W. Henry, Francis C. Fekel
Six New Γ Doradus Stars, Gregory W. Henry, Francis C. Fekel
Information Systems and Engineering Management Research Publications
We present high‐resolution spectroscopy and precision photometry of six new γ Doradus stars, one of which was independently discovered by another group. This brings the total number of confirmed γ Doradus variables to 30. All six of these variables fall in the spectral class range F0–F2; all but one are subgiants. The six stars have between one and five photometric periods in the range 0.3–1.2 days. We find no evidence for higher frequency δ Scuti pulsations in any of these six stars. Our spectroscopic observations reveal HD 108100 to be the first confirmed γ Doradus variable with composite broad and …
Wiyn Open Cluster Study. Xi. Wiyn 3.5 Meter Deep Photometry Of M35 (Ngc 2168), Ted Von Hippel, Aaron Steinhauer, Ata Sarajedini, Constantine P. Deliyannis
Wiyn Open Cluster Study. Xi. Wiyn 3.5 Meter Deep Photometry Of M35 (Ngc 2168), Ted Von Hippel, Aaron Steinhauer, Ata Sarajedini, Constantine P. Deliyannis
Publications
We present deep BVI observations of the core of M35 and a nearby comparison field obtained at the WIYN 3.5 m telescope under excellent seeing conditions. These observations probe to V > 26 and display the lower main sequence in BV and VI CMDs down to V = 23.3 and 24.6, respectively. At these faint magnitudes the background Galactic field stars are far more numerous than the cluster stars, yet by using a smoothing technique and CMD density distribution subtraction we are able to recover the cluster fiducial main sequence and luminosity function to V = 24.6. We find the location …
Extraordinary Late‐Time Infrared Emission Of Type Iin Supernovae, Christopher L. Gerardy, Robert A. Fesen, Ken-Ichi Nomoto, Peter M. Garnavich
Extraordinary Late‐Time Infrared Emission Of Type Iin Supernovae, Christopher L. Gerardy, Robert A. Fesen, Ken-Ichi Nomoto, Peter M. Garnavich
Dartmouth Scholarship
Near-infrared observations are presented for five Type IIn supernovae (SN 1995N, SN 1997ab, SN 1998S, SN 1999Z, and SN 1999el) that exhibit strong infrared excesses at late times (t > 100 days). H- and K-band emission from these objects is dominated by a continuum that rises toward longer wavelengths. The data are interpreted as thermal emission from dust, probably situated in a preexisting circumstellar nebula. The IR luminosities implied by single-temperature blackbody fits are quite large, >1041-1042 ergs s-1, and the emission evolves slowly, lasting for years after maximum light. For SN 1995N, the integrated energy release via …
X-Ray And Optical Variations In The Classical Be Star Γ Cassiopeia: The Discovery Of A Possible Magnetic Dynamo, Richard D. Robinson, Myron A. Smith, Gregory W. Henry
X-Ray And Optical Variations In The Classical Be Star Γ Cassiopeia: The Discovery Of A Possible Magnetic Dynamo, Richard D. Robinson, Myron A. Smith, Gregory W. Henry
Information Systems and Engineering Management Research Publications
The classical B0.5e star γ Cassiopeia is known to be a unique X-ray source by virtue of its moderate LX (1033 ergs s-1), hard X-ray spectrum, and light curve punctuated by ubiquitous flares and slow undulations. The peculiarities of this star have led to a controversy concerning the origin of these emissions: whether they are from wind infall onto a putative degenerate companion, as in the case of normal Be/X-ray binaries, or from the Be star itself. Recently, much progress has been made to resolve this question: (1) the discovery that γ Cas is a moderately eccentric binary system (P …
Automated Stellar Spectral Classification And Parameterization For The Masses, Ted Von Hippel, Carlos Allende Prieto, Chris Sneden
Automated Stellar Spectral Classification And Parameterization For The Masses, Ted Von Hippel, Carlos Allende Prieto, Chris Sneden
Publications
Stellar spectroscopic classification has been successfully automated by a number of groups. Automated classification and parameterization work best when applied to a homogeneous data set, and thus these techniques primarily have been developed for and applied to large surveys. While most ongoing large spectroscopic surveys target extragalactic objects, many stellar spectra have been and will be obtained. We briefly summarize past work on automated classification and parameterization, with emphasis on the work done in our group. Accurate automated classification in the spectral type domain and parameterization in the temperature domain have been relatively easy. Automated parameterization in the metallicity domain, …
Chromospherically Active Stars. Xxi. The Giant, Single-Lined Binaries Hd 89546 And Hd 113816, Francis C. Fekel, Gregory W. Henry, Joel A. Eaton, Julius Sperauskas, Douglas S. Hall
Chromospherically Active Stars. Xxi. The Giant, Single-Lined Binaries Hd 89546 And Hd 113816, Francis C. Fekel, Gregory W. Henry, Joel A. Eaton, Julius Sperauskas, Douglas S. Hall
Information Systems and Engineering Management Research Publications
We have obtained spectroscopy and photometry of the chromospherically active, single-lined spectroscopic binaries HD 89546 and HD 113816. HD 89546 has a circular orbit with a period of 21.3596 days. Its primary has a spectral type of G9 III and is somewhat metal-poor with [Fe/H]~-0.5. HD 113816 has an orbit with a period of 23.6546 and a low eccentricity of 0.022. Its mass function is extremely small, 0.0007 Msolar, consistent with a very low inclination. The primary is a slightly metal-poor K2 III. A decade or more of photometric monitoring with an automatic telescope demonstrates that both systems display brightness …
Metal Abundances And Kinematics Of Bright Metal-Poor Giants Selected From The Lse Survey: Implications For The Metal-Weak Thick Disk, Timothy C. Beers, John S. Drilling, Silvia Rossi, Masashi Chiba, Jaehyon Rhee, Birgit Fṻhrmeister, John E. Norris, Ted Von Hippel
Metal Abundances And Kinematics Of Bright Metal-Poor Giants Selected From The Lse Survey: Implications For The Metal-Weak Thick Disk, Timothy C. Beers, John S. Drilling, Silvia Rossi, Masashi Chiba, Jaehyon Rhee, Birgit Fṻhrmeister, John E. Norris, Ted Von Hippel
Publications
We report medium-resolution (1–2A ˚ ) spectroscopy and broadband (UBV) photometry for a sample of 39 bright stars (the majority of which are likely to be giants) selected as metal-deficient candidates from an objective-prism survey concentrating on Galactic latitudes below |b| = 30, the Luminous Stars Extension (LSE) survey of Drilling & Bergeron. Although the primary purpose of the LSE survey was to select OB stars (hence the concentration on low latitudes), the small number of bright metal-deficient giant candidates noted during this survey provide interesting information on the metal-weak thick disk (MWTD) population. Metal abundance estimates are obtained from …
Redshift-Distance Survey Of Early-Type Galaxies. I. The Enearc Cluster Sample*, M. Bernardi, M. V. Alonso, L. N. Da Costa, C. N. A. Willmer, A. Wegner
Redshift-Distance Survey Of Early-Type Galaxies. I. The Enearc Cluster Sample*, M. Bernardi, M. V. Alonso, L. N. Da Costa, C. N. A. Willmer, A. Wegner
Dartmouth Scholarship
This paper presents data on the ENEARc subsample of the larger ENEAR survey of nearby early-type galaxies. The ENEARc galaxies belong to clusters and were specifically chosen to be used for the construction of a D-n-sigma template. The ENEARc sample includes new measurements of spectroscopic and photometric parameters (redshift, velocity dispersion, line index Mg-2, and the angular diameter d(n)), as well as data from the literature. New spectroscopic data are given for 229 cluster early-type galaxies in 28 clusters. Objective criteria, based on catalogs of groups of galaxies derived from complete redshift surveys of the nearby universe, are used to …
Infrared Spectra Of The Subluminous Type Ia Supernova Sn 1999by, Peter Hoflich, Christopher L. Gerardy, Robert A. Fesen, Shoko Sakai
Infrared Spectra Of The Subluminous Type Ia Supernova Sn 1999by, Peter Hoflich, Christopher L. Gerardy, Robert A. Fesen, Shoko Sakai
Dartmouth Scholarship
Near-infrared (NIR) spectra of the subluminous Type Ia supernova SN 1999by are presented that cover the time evolution from about 4 days before to 2 weeks after maximum light. Analysis of these data was accomplished through the construction of an extended set of delayed detonation (DD) models covering the entire range of normal to subluminous SNe Ia. The explosion, light curves, and time evolution of the synthetic spectra were calculated self-consistently for each model, with the only free parameters being the initial structure of the white dwarf and the description of the nuclear burning front during the explosion. From these, …
Profile Shapes For Optically Thick X-Ray Emission Lines From Stellar Winds., R. Ignace, K. G. Gayley
Profile Shapes For Optically Thick X-Ray Emission Lines From Stellar Winds., R. Ignace, K. G. Gayley
Richard Ignace
We consider the consequences of appreciable line optical depth for the profile shape of X-ray emission lines formed in stellar winds. The hot gas is thought to arise in distributed wind shocks, and the line formation is predominantly via collisional excitation followed by radiative decay. Such lines are often modelled as optically thin, but the theory has difficulty matching resolved X-ray line profiles. We suggest that for strong lines of abundant metals, newly created photons may undergo resonance scattering, modifying the emergent profile. Using Sobolev theory in a spherically symmetric wind, we show that thick-line resonance scattering leads to emission …
Theoretical Uncertainties In The Subgiant--Mass Age Relation And The Absolute Age Of Omega Cen, Brian Chaboyer, Lawrence M. Krauss
Theoretical Uncertainties In The Subgiant--Mass Age Relation And The Absolute Age Of Omega Cen, Brian Chaboyer, Lawrence M. Krauss
Dartmouth Scholarship
The theoretical uncertainties in the calibration of the relationship between the subgiant mass and age in metal-poor stars are investigated using a Monte Carlo approach. Assuming that the mass and iron abundance of a subgiant star are known exactly, uncertainties in the input physics used to construct stellar evolution models and isochrones lead to a Gaussian 1 σ uncertainty of ±2.9% in the derived ages. The theoretical error budget is dominated by the uncertainties in the calculated opacities. Observations by Kałużny et al. of detached double-lined eclipsing binary OGLEGC 17 in the globular cluster ω Centauri have found that the …
The Quadruple System Μ Orionis: Three-Dimensional Orbit And Physical Parameters, Francis C. Fekel, Colin D. Scarfe, David J. Barlow, William I. Hartkopf, Brian D. Mason, Harold Mcalister
The Quadruple System Μ Orionis: Three-Dimensional Orbit And Physical Parameters, Francis C. Fekel, Colin D. Scarfe, David J. Barlow, William I. Hartkopf, Brian D. Mason, Harold Mcalister
Information Systems and Engineering Management Research Publications
The star μ Orionis is a spectroscopic visual quadruple system in which each visual component is a short-period spectroscopic binary. The visual orbit has a period of 18.644 yr, a high eccentricity of 0.7426, and a high inclination of 962. The visual primary consists of an Am star and probably a G or early K dwarf that orbit each other in a nearly circular orbit with a period of 4.4475858 days. The visual secondary consists of a pair of F5: V stars in a circular orbit with a period of 4.7835361 days. While the masses of the two stars are …
Modeling The Galactic Center Nonthermal Filaments As Magnetized Wakes, Russell B. Dahlburg, Giorgio Einaudi, Ted N. La Rosa, Steven N. Shore
Modeling The Galactic Center Nonthermal Filaments As Magnetized Wakes, Russell B. Dahlburg, Giorgio Einaudi, Ted N. La Rosa, Steven N. Shore
Faculty and Research Publications
We simulate the Galactic center nonthermal laments as magnetized wakes formed dynamically from amplification of a weak ( tens of l G) global magnetic field through the interaction of molecular clouds with a Galactic center wind. One of the key issues in this cometary model is the stability of the lament against dynamical disruption. Here we show two-dimensional MHD simulations for interstellar conditions that are appropriate for the Galactic center. The structures eventually disrupt through a shear-driven nonlinear instability but maintain coherence for lengths up to 100 times their width as observed. The final instability, which destroys the lament through …
Time Series Analysis Of V511 Lyrae Photometry, J. Lyytinen, Peter Johansson, Lauri Jetsu, Eero Esko, Thomas Hackman, Douglas S. Hall, Gregory W. Henry, S. Kontinen, P. Könönen, S. Maisala, A. Palviainen, Kyösti Ryynänen
Time Series Analysis Of V511 Lyrae Photometry, J. Lyytinen, Peter Johansson, Lauri Jetsu, Eero Esko, Thomas Hackman, Douglas S. Hall, Gregory W. Henry, S. Kontinen, P. Könönen, S. Maisala, A. Palviainen, Kyösti Ryynänen
Information Systems and Engineering Management Research Publications
Our time series analysis of sixteen BV light curves of the chromospherically active binary V511 Lyr confirmed the rotation period uniquely. The seasonal periodicity changes of 3.8% indicated the presence of detectable surface differential rotation. The significant periodicity in the light curve minimum epochs suggested that the strongest starspot formation in V511 Lyr was concentrated on one stable active longitude.
Are Stars With Planets Polluted?, N. Murray, B. Chaboyer
Are Stars With Planets Polluted?, N. Murray, B. Chaboyer
Dartmouth Scholarship
We compare the metallicities of stars with radial velocity planets to the metallicity of a sample of field dwarfs. We confirm recent work indicating that the stars-with-planets sample as a whole is iron-rich. However, the lowest mass stars tend to be iron-poor, with several having [Fe/H] < -0.2, demonstrating that high metallicity is not required for the formation of short-period Jupiter-mass planets. We show that the average [Fe/H] increases with increasing stellar mass (for masses below 1.2 M☉) in both samples, but that the increase is much more rapid in the stars-with-planets sample. The variation of metallicity with stellar age also differs between the two samples. We examine possible selection effects related to variations in the sensitivity of radial velocity surveys with stellar mass, apparent magnitude, and stellar metallicity, and …
Velocity Observations Of Multiple-Mode Asymptotic Giant Branch Variable Stars, Kenneth H. Hinkle, Thomas Lebzelter, Richard R. Joyce, Francis C. Fekel
Velocity Observations Of Multiple-Mode Asymptotic Giant Branch Variable Stars, Kenneth H. Hinkle, Thomas Lebzelter, Richard R. Joyce, Francis C. Fekel
Information Systems and Engineering Management Research Publications
Numerous infrared spectroscopic observations were obtained of nine asymptotic giant branch (AGB) field M giants that have multiple periods of light variability. Each star has a short period of several months, which is typical of low amplitude pulsation for stars on the AGB, as well as a long period of 1–3 yr, which is significantly longer than the predicted fundamental-mode pulsations for these stars. The location of these stars in the AGB period-luminosity relation is discussed. For six of the nine giants we found radial-velocity periods that confirm the long-period light variability. Although we considered the possibility that the velocity …
Five New Δ Scuti Stars, Gregory W. Henry, Francis C. Fekel
Five New Δ Scuti Stars, Gregory W. Henry, Francis C. Fekel
Information Systems and Engineering Management Research Publications
We present high‐resolution spectroscopy and precision photometry of five new, relatively bright δ Scuti stars. They were originally chosen as photometric comparison stars in our program of automated, high‐precision photometry of solar‐type stars and subsequently recognized as new variable stars. We conducted follow‐up spectroscopic and photometric observations to determine the properties of the stars and their types of variability. All five of the stars presented here belong to the most common subgroup of low‐amplitude, Population I δ Scuti variables. One of the stars, HD 10502, is the third example of a δ Scuti variable with composite broad and narrow spectroscopic …
Fluorescence And Chromospheric Activity Of V471 Tau, Todd R. Vaccaro, Robert E. Wilson
Fluorescence And Chromospheric Activity Of V471 Tau, Todd R. Vaccaro, Robert E. Wilson
Physics and Astronomy Faculty Publications
The red dwarf + white dwarf eclipsing binary V471 Tau shows a variable Hα feature that varies from absorption during eclipse to maximum emission during white dwarf transit. In 1998 we obtained simultaneous BVRI photometry and Hα spectroscopy, with thorough phase coverage of the 12.5 hour orbital period. A binary star model was used with our light curve, radial velocity, and Hα data to refine stellar and orbital parameters. Combined absorption-emission profiles were generated by the model and fit to the observations, yielding a red star radius of 0.94⊙. Orbital inclination 78° is required with this size and other known …
Wiyn Open Cluster Study Xi: Wiyn1 3.5m Deep Photometry Of M35 (Ngc 2168), Ted Von Hippel, Aaron Steinhauer, Ata Sarajedini, Constantine P. Deliyannis
Wiyn Open Cluster Study Xi: Wiyn1 3.5m Deep Photometry Of M35 (Ngc 2168), Ted Von Hippel, Aaron Steinhauer, Ata Sarajedini, Constantine P. Deliyannis
Publications
We present deep BV I observations of the core of M35 and a nearby comparison field obtained at the WIYN 3.5m telescope under excellent seeing conditions. These observations probe to V > 26, and display the lower main sequence in BV and V I CMDs down to V = 23.3 and 24.6, respectively. At these faint magnitudes the background Galactic field stars are far more numerous than the cluster stars, yet by using a smoothing technique and CMD density distribution subtraction we are able to recover the cluster fiducial main sequence and luminosity function to V = 24.6. We find the …
Book Review: Flash!: The Hunt For The Biggest Explosions In The Universe, T. D. Oswalt
Book Review: Flash!: The Hunt For The Biggest Explosions In The Universe, T. D. Oswalt
Publications
This document is Dr. Oswalt’s review of Flash! : the hunt for the biggest explosions in the universe by Govert Schilling. tr. by Naomi Greenberg-Slovin Cambridge, 2002 291p, 0-521-80053-6 $28.00