Physical Sciences and Mathematics Commons^™

Parallaxes And Distance Estimates For 14 Cataclysmic Variable Stars, John R. Thorstensen

Dartmouth Scholarship

I used the 2.4 m Hiltner Telescope at MDM Observatory in an attempt to measure trigonometric parallaxes for 14 cataclysmic variable stars. Techniques are described in detail. In the best cases the parallax uncertainties are below 1 mas, and significant parallaxes are found for most of the program stars. A Bayesian method that combines the parallaxes together with proper motions and absolute magnitude constraints is developed and used to derive distance estimates and confidence intervals. The most precise distance derive here is for WZ Sge, for which I find 43: 3.1:6 1:5 pc. Six Luyten Half-Second stars with previous precise …

Stellar Pollution And [Fe/H] In The Hyades, Aaron Dotter, Brian Chaboyer

Dartmouth Scholarship

The Hyades open cluster presents a unique laboratory for planet formation and stellar pollution studies because all of the stars have essentially the same age and were born from the same cloud of gas. Furthermore, with an age of ~650 Myr, most of the intermediate- and low-mass stars are on the main sequence. Given these assumptions, the accretion of metal-rich material onto the surface of a star during and shortly after the formation of planetary systems should be evident via the enhanced metallicity of the star. Building on previous work, stellar evolution models that include the effects of stellar pollution …

Constraints From Infrared Space Observatory Data On The Velocity Law And Clumpiness Of Wr 136., R. Ignace, M. F. Quigley, J. P. Cassinelli

Richard Ignace

Observations with the Infrared Space Observatory (ISO) SWS spectrometer are used to constrain the velocity law and wind clumping of the well-studied Wolf-Rayet (WR) star WR 136 (HD 192163) (WN6). Because the free-free continuum opacity in WR winds increases steadily with wavelength in the IR, each point in the continuous spectrum may be regarded as forming in a pseudo-photosphere of larger radius for longer wavelength. Using this idea in combination with an analysis of the Doppler-broadened widths of several \ion{He}{2} recombination lines, we can derive information about the velocity law and clumpiness of the stellar wind of WR 136. Adopting …

Using Optical And Near-Infrared Photometry To Test Macho Lens Candidates, Ted Von Hippel, Et Al.

Publications

We obtained new VLT/ISAAC H-band observations for five MACHO LMC source stars and adjacent LMC field regions. After combining our near-IR photometry with Hubble Space Telescope/PC BVRI optical photometry, we compared the MACHO objects to the adjacent field stars in a variety of color-magnitude and color-color diagrams. These diagnostic diagrams were chosen to be sensitive to our hypothesis that at least some of the MACHO lenses were foreground Galactic disk or thick-disk M dwarfs. For the five lensed objects we studied, our hypothesis could be ruled out for main-sequence lens masses ≥0.1 M☉ for distances out to …

Constraining The Evolution Of Zz Ceti, Anjum S. Mukadam, S. O. Kepler, D. E. Nather, M. Kilic, F. Mullally, T. Von Hippel, S. J. Kleinman, A. Nitta, J. A. Guzik, P. A. Bradley, J. Matthews, K. Sekiguchi, D. J. Sullivan, T. Sullivan, R. R. Shobbrook, P. Birch, X. J. Jiang, D. W. Xu, S. Joshi, B. N. Ashoka, P. Ibbetson, E. Leibowitz, E. O. Ofek, E. G. Meištas, R. Janulis, R. D. Ališauskas, R. Kalytis, G. Handler, D. Kilkenny, D. O'Donoghue, D. W. Kurtz, M. Müller, P. Moskalik, W. Ogloza, S. Zola, J. Krzesiński, F. Johnannessen, J. M. Gonzalez-Perez, J. E. Solheim, R. Silvotti, S. Bernabei, G. Vauclair, N. Dolez, J. N. Fu, M. Chevreton, M. Manteiga, O. Suárez, A. Ulla, M. S. Cunha, T. S. Metcalfe, A. Kanaan, L. Fraga, A. F. M. Costa, O. Giovannini, G. Fontaine, P. Bergeron, M. S. O'Brien, D. Sanwal, M. A. Wood, T. J. Ahrens, N. Silvestri, E. W. Klumpe, S. D. Kawaler, R. Riddle, M. D. Reed, T. K. Watson

Publications

We report our analysis of the stability of pulsation periods in the DAV star (pulsating hydrogen atmosphere white dwarf) ZZ Ceti, also called R548. On the basis of observations that span 31 years, we conclude that the period 213.13 s observed in ZZ Ceti drifts at a rate dP/dt ≤ (5:5 ± 1:9) x 10^-15 s s^-1, after correcting for proper motion. Our results are consistent with previous Ṗ values for this mode and an improvement over them because of the larger time base. The characteristic stability timescale implied for the pulsation period is …

0937+2931_Opt_Lris, Adam J. Burgasser

Publications and Research

No abstract provided.

The Galactic Center Nonthermal Filaments: Recent Observations And Theory, Ted La Rosa, Michael E. Nord, T. Joseph W. Lazio, Steven N. Shore, Namir E. Kassim

Faculty and Research Publications

The large-scale topology and strength of the Galactic Center magnetic field have been inferred from radio imaging of the nonthermal filaments (NTFs). These objects, which seem to be unique to the Galactic center, are defined by extreme aspect ratios and a high degree of polarization. Recent high resolution, wide-field VLA imaging of the GC at 90 cm has revealed new candidate NTFs with a wide range of orientations relative to the Galactic plane. We present follow up 6 cm polarization observations of 6 of these candidates and confirm 4 as new NTFs. Together the new 90 and 6 cm results …

0415-0935_Opt_Lris, Adam J. Burgasser

Publications and Research

No abstract provided.

Book Review: Observer's Guide To Stellar Evolution: The Birth, Life, And Death Of Stars, T. D. Oswalt

Publications

This document is Dr. Oswalt’s review of Observer's Guide to Stellar Evolution : the Birth, Life, and Death of Stars by Mike Inglis. Springer, 2003 236p, 1-85233-465-7 $44.95

Xmm-Newton Observations Of The Nitrogen-Rich Wolf-Rayet Star Wr 1., R. Ignace, L. M. Oskinova, J. C. Brown

Richard Ignace

We present XMM-Newton results for the X-ray spectrum from the N-richWolf-Rayet (WR) star WR1. The EPIC instrument was used to obtain a medium-resolution spectrum. The following features characterize this spectrum: ( a) significant emission "bumps" appear that are coincident with the wavelengths of typical strong lines, such as MgXI, SiXIII, and SXV; (b) little emission is detected above 4 keV, in contrast to recent reports of a hard component in the stars WR 6 and WR 110 which are of similar subtype; and ( c) evidence for sulfur K-edge absorption at about 2.6 keV, which could only arise from absorption …

A Model Of Zebra Emission In Solar Type Iv Radio Bursts, J. Labelle, R. A. Treumann, P. H. Yoon, M. Karlicky

Dartmouth Scholarship

Solar type IV radio bursts present a theoretical challenge because they are composed of both continuum emission and fine structures. The latter include "zebra bursts," which appear as harmonically spaced multiplets that shift in frequency with time. Similarities between these features and terrestrial auroral emissions suggest a new model to explain zebra-structured type IV emissions. In this model, the basic generation mechanism is identical with that proposed by Winglee and Dulk: mode conversion of Z-mode waves generated by the cyclotron maser mechanism under the condition fuh = Nfce, with N an integer; however, we propose a twist …

Mechanisms For The Origin Of Turbulence In Non-Star-Forming Clouds: The Translucent Cloud Mbm 40, Steven N. Shore, Loris Magnani, Ted La Rosa, Meredith N. Mccarthy

Faculty and Research Publications

We present a multiline, high spatial and velocity resolution CO, H I, and IRAS 100 μm study of the high-latitude, low-mass, non-star-forming, translucent molecular cloud MBM 40. The cloud mass is distributed into two ridges, or filaments, that form a hairpin structure. Velocity channel maps indicate a highly ordered flow in the molecular gas, with the northeastern part of the filament moving away from and the southwestern filament moving toward the observer relative to the mean cloud radial velocity. Significant changes in emissivity occur over 0.03 pc, indicating large transverse density gradients along the ridges. However, the velocity field appears …

Early Quintessence In Light Of Thewilkinson Microwave Anisotropy Probe, Robert R. Caldwell, Michael Doran, Christian M. Mller, Gregor Schfer, Christof Wetterich

Dartmouth Scholarship

We examine the cosmic microwave background (CMB) anisotropy for signatures of early quintessence dark energy—a nonnegligible quintessence energy density during the recombination and structure formation eras. Only very recently does the quintessence overtake the dark matter and push the expansion into overdrive. Because the presence of early quintessence exerts an influence on the clustering of dark matter and the baryon-photon fluid, we may expect to find trace signals in the CMB and the mass fluctuation power spectrum. In detail, we demonstrate that suppressed clustering power on small length scales, as suggested by the combined Wilkinson Microwave Anisotropy Probe/CMB/large-scale structure …

Rotational Velocities Of B, A, And Early‐F Narrow‐Lined Stars, Francis C. Fekel

Information Systems and Engineering Management Research Publications

Projected rotational velocities for 58 B, A, and early‐F stars have been determined from high‐resolution spectroscopic observations made at Kitt Peak National Observatory with the coudé feed telescope. All the stars are slowly rotating with vsin i<60 km s−1. Because of their low rotational velocities, 15 of the stars have been observed as prospective, early‐type, radial velocity standards.

Multisite Observations Of The Pms Δ Delta Scuti Star V351 Ori, V. Ripepi, Terry D. Oswalt, M. Marconi, S. Bernabei, Et Al.

Publications

We present the results of multisite observations spanning two years on the pre–main-sequence (PMS) star V351 Ori. A total of around 180 hours of observations over 29 nights have been collected, allowing us to measure five different periodicities, most likely related to the Scuti variability of V351 Ori. Comparison with the predictions of linear nonadiabatic radial pulsation models put stringent constraints on the stellar parameters and indicate that the distance to V351 Ori is intermediate between the lower limit measured by Hipparcos (210 pc) and that of the Orion Nebula (450 pc). However, radial pulsation models are unable to reproduce …

Optical Photometry And X-Ray Monitoring Of The "Cool Algol" Bd+05˚706: Determination Of The Physical Properties, Guillermo Torres, Jeff A. Mader, Laurence A. Marschall, Ralph Neuhauser, Alaine S. Duffy

Physics and Astronomy Faculty Publications

We present new photometric observations in the BVRI bands of the double-lined eclipsing binary BD +05706 conducted over three observing seasons, as well as new X-ray observations obtained with ROSAT covering a full orbital cycle (P = 18.9 days). A detailed light-curve analysis of the optical data shows the system to be semidetached, confirming indications from an earlier analysis by Torres et al. (published in 1998), with the less massive and cooler star filling its Roche lobe. The system is a member of the rare class of cool Algol systems, which are different from the ‘‘ classical ’’ Algol systems …

Fluorescence In Ultraviolet Active Binaries: The Case Of Ff Aquarii, Todd R. Vaccaro, R. E. Wilson

Physics and Astronomy Faculty Publications

The eclipsing binary FF Aquarii (FF Aqr) consists of a small hot star of uncertain type and a red giant. An Hα feature varies from absorption during eclipse to maximum emission during hot star transit. We have obtained simultaneous differential photometry in BVRI bands and Hα spectroscopy in 1998 that covered an entire orbit with some overlap. A binary star model was used with our light-curve, radial velocity and Hα data to refine stellar and orbital parameters. A new ephemeris indicates that the period has increased or is longer than previously thought. A physically simple algorithm is developed that generates …

Spatially Resolved Spectroscopy Of Coma Cluster Early-Type Galaxies - Iii. The Stellar Population Gradients, D. Mehlert, D. Thomas, R. P. Saglia, R. Bender, G Wegner

Dartmouth Scholarship

Based on Paper I of this series (Mehlert et al. 2000), we derive central values and logarithmic gradients for the Hβ, Mg and Fe indices of 35 early-type galaxies in the Coma cluster. We find that pure elliptical galaxies have on average slightly higher velocity dispersions, lower Hβ, and higher metallic line-strengths than galaxies with disks (S0). The latter form two families, one comparable to the ellipticals and a second one with significantly higher Hβ, and weaker metallic lines. Our measured logarithmic gradients within the effective radius are ⟨△Mg b⟩ ≈ −0.037, ⟨△⟨Fe⟩⟩ ≈ −0.029, ⟨△Hβ⟩ ≈ +0.017 and ⟨△σ⟩ …

Redshift-Distance Survey Of Early-Type Galaxies: Circular-Aperture Photometry, M. V. Alonso, M. Bernardi, L. N. Da Costa, G. Wegner

Dartmouth Scholarship

We present R -band CCD photometry for 1332 early-type galaxies, observed as part of the ENEAR survey of peculiar motions using early-type galaxies in the nearby universe. Circular apertures are used to trace the surface brightness profiles, which are then fitted by a two-component bulge-disk model. From the fits, we obtain the structural parameters required to estimate galaxy distances using the Dn - and fundamental plane relations. We find that about 12% of the galaxies are well represented by a pure r1/4 law, while 87% are best fitted by a two-component model. There are 356 repeated observations of 257 galaxies …

The Zeeman Effect In The Sobolev Approximation: Applications To Spherical Stellar Winds., R. Ignace, K. G. Gayley

Richard Ignace

Modern spectropolarimeters are capable of detecting subkilogauss field strengths using the Zeeman effect in line profiles from the static photosphere, but supersonic Doppler broadening makes it more difficult to detect the Zeeman effect in the wind lines of hot stars. Nevertheless, the recent advances in observational capability motivate an assessment of the potential for detecting the magnetic fields threading such winds. We incorporate the weak-field longitudinal Zeeman effect in the Sobolev approximation to yield integral expressions for the flux of circularly polarized emission. To illustrate the results, two specific wind flows are considered: (i) spherical constant expansion with v(r) = …

The Conspicuous Absence Of X-Ray Emission From Carbon-Enriched Wolf-Rayet Stars., L. M. Oskinova, R. Ignace, W.-R. Hamann, A. M. T. Pollock, J. C. Brown

Richard Ignace

The carbon-rich WC5 star WR 114 was not detected during a 15.9 ksec XMM-Newton observation, implying an upper limit to the X-ray luminosity of L-X less than or similar to 2.5 x 10(30) erg s(-1) and to the X-ray to bolometric luminosity ratio of L-X/L(bo)l less than or similar to 4 x 10(-9). This confirms indications from earlier less sensitive measurements that there has been no convincing X-ray detection of any single WC star. This lack of detections is reinforced by XMM-Newton and Chandra observations of WC stars. Thus the conclusion has to be drawn that the stars with radiatively-driven …

Bv Photometry Of Ux Ari In The Period 1987–2002, Vidar Aarum Ulvås, Gregory W. Henry

Information Systems and Engineering Management Research Publications

We present 14.3 years of previously unpublished photometric observations of UX Ari. The observations were obtained between 1987.9 and 2002.2 using the T3 0.4-metre Automatic Photoelectric Telescope at Fairborn Observatory and consist of 1228 B band and 1213 V band measurements. The comparison star was 62 Ari. We have analyzed the new data together with previously published photometric observations. The V magnitude shows variations with dominant periods of about 12 and 25 years, where the longest period seems to correspond to an activity cycle. The previously reported anticorrelation between the colour and V magnitude variations is confirmed.

The Orbit And Pulsation Periods Of The Γ Doradus Variable Hr 6844 (V2502 Ophiuchi), Francis C. Fekel, Gregory W. Henry

Information Systems and Engineering Management Research Publications

We obtained spectroscopic and photometric observations of the γ Doradus variable HR 6844 (=V2502 Ophiuchi). Radial velocities show that this star is a single-lined binary with a period of 4.4852 days. The primary is an F1 V star, while the secondary is likely an M dwarf. Velocity residuals to a circular orbit have a period of 1.3071 days and an amplitude of ∼3 km s-1. Three periods of light variation were detected, 1.30702, 1.4350, and 0.62286 days. The first period is essentially identical to that found in the radial velocities and has the largest amplitude, a peak-to-peak value of 0.067 …

Spectroscopy Of Early F Stars: Γ Doradus Candidates And Possible Metallic Shell Stars, Francis C. Fekel, Phillip B. Warner, Anthony B. Kaye

Information Systems and Engineering Management Research Publications

We obtained high-resolution spectroscopic observations of 34 γ Doradus candidates. From the red-wavelength spectra, we determined spectral classes, radial velocities, and projected rotational velocities. The spectra of seven late A or early F stars show metallic lines that have composite profiles consisting of a narrow component near the center of a broad line, indicating that they may be shell stars or binaries. Several stars, including HD 152896, HD 173977, HD 175337, and HD 195068/9, show large line profile asymmetries. Two stars, HD 11443 (=α Trianguli) and HD 149420, are ellipsoidal variables and not γ Doradus stars. The percentage of binary …

Microlensing Of Circumstellar Envelopes Ii. Emission Lines From Radial And Azimuthal Flow During Fold Caustic Crossings., H. M. Bryce, R. Ignace, M. A. Hendry

Richard Ignace

This paper examines the line profile evolution due to bulk motion in circumstellar envelopes during microlensing fold caustic crossing events. These events have recently been shown to be a sensitive probe of stellar surface brightness profiles, thus providing a means - through both photometric and spectroscopic observations - to constrain and test stellar atmosphere models. Here it is demonstrated, through the examination of simplified line profiles, that spectroscopic studies of fold caustic crossings could also prove to be a powerful diagnostic of bulk motion in circumstellar envelopes.

Observational Constraints On General Relativistic Energy Conditions, Cosmic Matter Density And Dark Energy From X-Ray Clusters Of Galaxies And Type-La Supernovae, P. Schuecker, R. R. Caldwell, H. Böhringer, C. A. Collins

Dartmouth Scholarship

New observational constraints on the cosmic matter density Ωm and an effectively redshift-independent equation

of state parameter wx of the dark energy are obtained while simultaneously testing the strong and null energy conditions of

general relativity on macroscopic scales. The combination of REFLEX X-ray cluster and type-Ia supernova data shows that

for a flat Universe the strong energy condition might presently be violated whereas the null energy condition seems to be

fulfilled. This provides another observational argument for the present accelerated cosmic expansion and the absence of exotic

physical phenomena related to a broken null energy condition. The marginalization of …

Radial Velocity Survey Of Members And Candidate Members Of The Tw Hydrae Association, Guillermo Torres, Eike W. Guenther, Laurence A. Marschall, Ralph Neuhauser, David W. Latham, Robert P. Stefanik

Physics and Astronomy Faculty Publications

We report spectroscopic observations of stars belonging to the young nearby group known as the TW Hydrae association, as well as of a number of potential members of the association identified in kinematic and X-ray surveys. Multiple radial velocity measurements were obtained for each object, several of which turn out to be multiple systems. Orbital solutions are presented for three double-lined binaries, one singlelined binary, and a double-lined triple system, all with short periods. Effective temperatures and projected rotational velocities are presented for each visible object. None of the candidate members of the association in our sample are confirmed as …

Multiperiodicity In Five Small‐Amplitude Pulsating Red Giants, John R. Percy, Gurtina Besla, Vince Velocci, Gregory W. Henry

Information Systems and Engineering Management Research Publications

We report multiperiodicity in five small‐amplitude pulsating red giants: RZ Ari, V523 Mon, BC CMi, UX Lyn, and FS Com. For each of these stars, two or three periods recur in each season of our 5000 day database of V observations. The periods and their ratios are consistent with low‐order radial pulsation modes. The amplitudes of the modes change significantly on timescales of 1–5 yr; specifically, the amplitudes of the dominant periods vary on timescales of 2000–3500 days. Most often, the amplitudes of the modes in a given star rise and fall in unison.

A Dozen New Γ Doradus Stars, Gregory W. Henry, Francis C. Fekel

Information Systems and Engineering Management Research Publications

We use new high-dispersion spectroscopic and precise photometric observations to identify 12 new γ Doradus stars. Two of the 12 systems are double-lined binaries that show obvious velocity variability. Five other stars have metallic lines with composite profiles characterized by a narrow feature near the center of each broad component. Spectrograms of the Hα line indicate that all five stars are binaries rather than shell stars. The remaining five stars in our sample are probably single. All 12 stars are photometrically variable with amplitudes between 6 and 87 mmag in Johnson B and periods between 0.3 and 1.2 days. Four …

Intergalactic Globular Clusters, Michael J. West, Ted Von Hippel, Patrick Cote, Henry C. Ferguson, Michael D. Gregg, Andres Jordan, Ronald O. Marzke, Nial R. Tanvir

Publications

We confirm and extend our previous detection of a popula- tion of intergalactic globular clusters in Abell 1185, and report the first discovery of an intergalactic globular cluster in the nearby Virgo cluster of galaxies. The numbers, colors and luminosities of these objects can place constraints on their origin, which in turn may yield new insights to the evolution of galaxies in dense environments.