Physical Sciences and Mathematics Commons^™

The June 2008 Flare Of Markarian 421 From Optical To Tev Energies, P. T. Reynolds, Et Al

Physical Sciences Publications

We present optical, X-ray, high-energy (30 GeV) and very high energy (100 GeV; VHE) observations of the high-frequency peaked blazar Mrk 421 taken between 2008 May 24 and June 23. A high-energy γ-ray signal was detected by AGILE with between June 9 and 15, with F(E>100 MeV) = 42+14 –12 × 10–8 photons cm–2 s–1. This flaring state is brighter than the average flux observed by EGRET by a factor of ~3, but still consistent with the highest EGRET flux. In hard X-rays (20-60 keV) SuperAGILE resolved a five-day flare (June 9-15) peaking at ~55 mCrab. SuperAGILE, …

Discovery Of Very High-Energy Gamma-Ray Radiation From The Bl Lac 1es 0806+524, P. T. Reynolds, Et Al

Physical Sciences Publications

The high-frequency-peaked BL Lacertae object 1ES 0806+524, at redshift z = 0.138, was observed in the very high energy (VHE) gamma-ray regime by VERITAS between 2006 November and 2008 April. These data encompass the two- and three-telescope commissioning phases, as well as observations with the full four-telescope array. 1ES 0806+524 is detected with a statistical significance of 6.3 standard deviations from 245 excess events. Little or no measurable variability on monthly timescales is found. The photon spectrum for the period 2007 November to 2008 April can be characterized by a power law with photon index 3.6 ± 1.0stat ± 0.3sys …

Direct Distance Measurement To The Dusty White Dwarf Gd 362, Mukremin Kilic, John R. Thorstensen, D. Koester

Dartmouth Scholarship

We present trigonometric parallax observations of GD 362 obtained over seven epochs using the MDM 2.4m Hiltner Telescope. The existence of a dust disk around this possibly massive white dwarf makes it an interesting target for parallax observations. The measured parallax for GD 362 places it at a distance of 50.6 pc, which implies that its radius and mass are ~ 0.0106 Rsun and 0.71 Msun, respectively. GD 362 is not as massive as initially thought (1.2Msun). Our results are entirely consistent with the distance and mass estimates (52.2 pc and 0.73 Msun) by Zuckerman et al., who demonstrated that …

Planetary Systems Around Close Binary Stars: The Case Of The Very Dusty, Sun-Like, Spectroscopic Binary Bd+20 307, Benjamin Zuckerman, Francis C. Fekel, Michael H. Williamson, Gregory W. Henry, Michael P. Muno

Information Systems and Engineering Management Research Publications

Field star BD+20 307 is the dustiest known main-sequence star, based on the fraction of its bolometric luminosity, ~4%, that is emitted at infrared wavelengths. The particles that carry this large infrared luminosity are unusually warm, comparable to the temperature of the zodiacal dust in the solar system, and their existence is likely to be a consequence of a fairly recent collision of large objects such as planets or planetary embryos. Thus, the age of BD+20 307 is potentially of interest in constraining the era of terrestrial planet formation. The present project was initiated with an attempt to derive this …

Multiwavelength Constraints On The Day–Night Circulation Patterns Of Hd 189733b, Heather Knutson, David Charbonneau, Nicolas B. Cowan, Jonathan J. Fortney, Adam P. Showman, Eric Agol, Gregory W. Henry, Mark E. Everett, Lori E. Allen

Information Systems and Engineering Management Research Publications

We present new Spitzer observations of the phase variation of the hot Jupiter HD 189733b in the MIPS 24 μm bandpass, spanning the same part of the planet's orbit as our previous observations in the IRAC 8 μm bandpass (Knutson et al. 2007). We find that the minimum hemisphere-averaged flux from the planet in this bandpass is 76% ± 3% of the maximum flux; this corresponds to minimum and maximum hemisphere-averaged brightness temperatures of 984 ± 48 K and 1220 ±  47 K, respectively. The planet reaches its maximum flux at an orbital phase of 0.396 ± 0.022, corresponding to …

Cooling Of The Crust In The Neutron Star Low-Mass X-Ray Binary Mxb 1659-29, Edward M. Cackett, Rudy Wijnands, Jon M. Miller, Edward F. Brown, Nathalie Degenaar

Physics and Astronomy Faculty Research Publications

In quasi-persistent neutron star transients, long outbursts cause the neutron star crust to be heated out of thermal equilibrium with the rest of the star. During quiescence, the crust then cools back down. Such crustal cooling has been observed in two quasi-persistent sources: KS 1731-260 and MXB 1659-29. Here we present an additional Chandra observation of MXB 1659-29 in quiescence, which extends the baseline of monitoring to 6.6 yr after the end of the outburst. This new observation strongly suggests that the crust has thermally relaxed, with the temperature remaining consistent over 1000 days. Fitting the temperature cooling curve with …

A Catalog Of Outer Ejecta Knots In The Cassiopeia A Supernova Remnant, Molly C. Hammell, Robert A. Fesen

Dartmouth Scholarship

Hubble Space Telescope images of the core-collapse supernova remnant Cassiopeia A are used to identify high-velocity knots of ejecta located outside the remnant's main emission shell of expanding debris. These ejecta fragments are found near or ahead of the remnant's forward shock front and mostly lie from 120^'' to 300^'' in radial distance from the remnant's center of expansion. Filter flux ratios when correlated with published spectra show that these knots can be divided into three emission classes: (1) knots dominated by [N II] λλ6548, 6583 emissions, (2) knots dominated by [O II] λλ7319, 7330 emissions, and (3) …

Magnetic Field Measurements Of O Stars With Fors 1 At The Vlt., S. Hubrig, M. Schöller, R. Schnerr, J. González, Richard Ignace, H. Henrichs

ETSU Faculty Works

Context.The presence of magnetic fields in O-type stars has been suspected for a long time. The discovery of these fields would explain a wide range of well documented enigmatic phenomena in massive stars, in particular cyclical wind variability, Hα emission variations, chemical peculiarity, narrow X-ray emission lines, and non-thermal radio/X-ray emission. Aims.To investigate the incidence of magnetic fields in O stars, we acquired 38 new spectropolarimetric observations with FORS 1 (FOcal Reducer low dispersion Spectrograph) mounted on the 8-m Kueyen telescope of the VLT. Methods.Spectropolarimetric observations were obtained at different phases for a sample of 13 O …

Magnetic Field Measurements Of O Stars With Fors 1 At The Vlt., S. Hubrig, M. Schöller, R. S. Schnerr, J. F. González, R. Ignace, H. F. Henrichs

Richard Ignace

Context.The presence of magnetic fields in O-type stars has been suspected for a long time. The discovery of these fields would explain a wide range of well documented enigmatic phenomena in massive stars, in particular cyclical wind variability, Hα emission variations, chemical peculiarity, narrow X-ray emission lines, and non-thermal radio/X-ray emission.
Aims.To investigate the incidence of magnetic fields in O stars, we acquired 38 new spectropolarimetric observations with FORS 1 (FOcal Reducer low dispersion Spectrograph) mounted on the 8-m Kueyen telescope of the VLT.
Methods.Spectropolarimetric observations were obtained at different phases for a sample of 13 O …

Parallax And Distance Estimates For Twelve Cataclysmic Variable Stars, John R. Thorstensen, Sébastien Lépine, Michael Shara

Dartmouth Scholarship

We report parallax and distance estimates for 12 more cataclysmic binaries and related objects observed with the 2.4 m Hiltner telescope at MDM Observatory. The final parallax accuracy is typically ~1 mas. Notable results include distances for V396 Hya (CE 315), a helium double degenerate with a relatively long orbital period, and for MQ Dra (SDSSJ155331+551615), a magnetic system with a very low accretion rate. We find that the Z Cam star KT Persei is physically paired with a K main-sequence star lying 15 arcsec away. Several of the targets have distance estimates in the literature that are based on …

Chemical Analysis Of Five Red Giants In The Globular Cluster M10 (Ngc 6254), Sharina Haynes, Geoffrey Burks, Christian I. Johnson, Catherine A. Pilachowski

Information Systems and Engineering Management Research Publications

We have determined Al, α, Fe-peak, and neutron capture elemental abundances for five red-giant branch (RGB) stars in the Galactic globular cluster M10. Abundances were determined using equivalent width analyses of moderate-resolution (R ∼ 15,000) spectra obtained with the Hydra multifiber positioner and bench spectrograph on the WIYN telescope. The data sample the upper RGB from the luminosity level near the horizontal branch to about 0.5 mag below the RGB tip. We find, in agreement with previous studies, that M10 is moderately metal-poor with [Fe/H] = -1.45 (σ = 0.04). All stars appear enhanced in Al with 〈[Al/Fe]〉 = +0.33 …

The Evolution Of Late‐Time Optical Emission From Sn 1986j, Dan Milisavljevic, Robert A. Fesen, Bruno Leibundgut, Robert P. Kirshner

Dartmouth Scholarship

We present late-time optical images and spectra of the Type IIn supernova SN 1986J. HST ACS/WFC images obtained in 2003 February show it to be still relatively bright, with m_F606W = 21.4 and m_F814W = 20.0 mag. Compared to 1994 December HST WFPC2 images, SN 1986J shows a decline of only <1 mag in brightness over 8 years. Ground-based spectra taken in 1989, 1991, and 2007 show a 50% decline in Hα emission between 1989 and 1991, and an order of magnitude drop between 1991 and 2007, along with the disappearance of He I line emissions during the period 1991-2007. The object's [O I] λλ6300, 6364, [O II] λλ7319, 7330 and [O III] λλ4959, 5007 emission lines show two prominent peaks near –1000 and –3500 km s⁻¹, with the more blueshifted component declining significantly in strength between 1991 and 2007. The observed spectral evolution suggests two different origins for SN 1986J's late-time optical emission: dense, shock-heated circumstellar material, which gave rise to the initially bright Hα, He I, and [N II] λ5755 …

The Dartmouth Stellar Evolution Database, Aaron Dotter, Brian Chaboyer, Darko Jevremović, Veselin Kostov

Dartmouth Scholarship

The ever-expanding depth and quality of photometric and spectroscopic observations of stellar populations increase the need for theoretical models in regions of age-composition parameter space that are largely unexplored at present. Stellar evolution models that employ the most advanced physics and cover a wide range of compositions are needed to extract the most information from current observations of both resolved and unresolved stellar populations. The Dartmouth Stellar Evolution Database is a collection of stellar evolution tracks and isochrones that spans a range of [Fe/H] from –2.5 to +0.5, [α/Fe] from –0.2 to +0.8 (for [Fe/H] ≤ 0) or +0.2 (for …

Veritas Discovery Of > 200 Gev Gamma-Ray Emission From The Intermediate-Frequency-Peaked Bl Lacertae Object W Comae, P. T. Reynolds, Et Al

Physical Sciences Publications

We report the detection of very high energy γ-ray emission from the intermediate-frequency-peaked BL Lacertae object W Comae (z = 0.102) by VERITAS. The source was observed between 2008 January and April. A strong outburst of γ-ray emission was measured in the middle of March, lasting for only 4 days. The energy spectrum measured during the two highest flare nights is fit by a power law and is found to be very steep, with a differential photon spectral index of Γ = 3.81 ± 0.35stat± 0.34syst. The integral photon flux above 200 GeV during those two nights corresponds to …

Constraining The Surface Inhomogeneity And Settling Times Of Metals On Accreting White Dwarfs, Michael H. Montgomery, S.E. Thompson, Ted Von Hippel

Publications

Due to the short settling times of metals in DA white dwarf atmospheres, any white dwarfs with photospheric metals must be actively accreting. It is therefore natural to expect that the metals may not be deposited uniformly on the surface of the star. We present calculations showing how the temperature variations associated with white dwarf pulsations lead to an observable diagnostic of the surface metal distribution, and we show what constraints current data sets are able to provide. We also investigate the effect that time-variable accretion has on the metal abundances of different species, and we show how this can …

The Effects Of Clumps In Explaining X-Ray Emission Lines From Hot Stars., J. Cassinelli, Richard Ignace, W. Waldron, J. Cho, N. Murphy, A. Lazarian

ETSU Faculty Works

It is now well established that stellar winds of hot stars are fragmentary and that the X-ray emission from stellar winds has a strong contribution from shocks in winds. Chandra high spectral resolution observations of line profiles of O and B stars have shown numerous properties that had not been expected. Here we suggest explanations by considering the X-rays as arising from bow shocks that occur where the stellar wind impacts on spherical clumps in the winds. We use an accurate and stable numerical hydrodynamic code to obtain steady state physical conditions for the temperature and density structure in a …

The Effects Of Clumps In Explaining X-Ray Emission Lines From Hot Stars., J. P. Cassinelli, R. Ignace, W. L. Waldron, J. Cho, N. A. Murphy, A. Lazarian

Richard Ignace

It is now well established that stellar winds of hot stars are fragmentary and that the X-ray emission from stellar winds has a strong contribution from shocks in winds. Chandra high spectral resolution observations of line profiles of O and B stars have shown numerous properties that had not been expected. Here we suggest explanations by considering the X-rays as arising from bow shocks that occur where the stellar wind impacts on spherical clumps in the winds. We use an accurate and stable numerical hydrodynamic code to obtain steady state physical conditions for the temperature and density structure in a …

A Multiwavelength Analysis Of The Halo Planetary Nebula Dddm‐1, R. B. C. Henry, K. B. Kwitter, R. J. Dufour, J. N. Skinner

Dartmouth Scholarship

We present new HST optical imagery as well as new UV and IR spectroscopic data obtained with the Hubble Space Telescope and Spitzer Space Telescope, respectively, of the halo planetary nebula DdDm-1. For the first time we present a resolved image of this object, which indicates that the morphology of DdDm-1 can be described as two orthogonal elliptical components in the central part surrounded by an extended halo. The extent of the emission is somewhat larger than was previously reported in the literature. We combine the spectral data with our own previously published optical measurements to derive nebular abundances …

Infrared Spectroscopy Of Symbiotic Stars. Vi. Combined Orbits For Two S-Type Systems: V455 Scorpii And Ss 73-90, Francis C. Fekel, Kenneth H. Hinkle, Richard R. Joyce, Peter R. Wood, Ian D. Howarth

Information Systems and Engineering Management Research Publications

We have combined new infrared radial velocities and previously obtained spectropolarimetric observations to compute orbits of the M6 giants in two southern S-type symbiotic systems. The spectropolarimetric data enable the orbital inclinations of the systems to be determined, placing greater constraints on the properties of the components. V455 Sco has a circular orbit with a period of 1398 ± 6 days and an inclination of 94° ± 1°. The orbit of SS 73-90 has a period of 898 ± 5 days, a modest eccentricity of 0.16, and an inclination of 97° ± 7°. The center of mass velocity of each …

Initial Measurements Of Black Hole Spin In Gx 339-4 From Suzaku Spectroscopy, J. M. Miller, C. S. Reynolds, A. C. Fabian, E. M. Cackett, G. Miniutti, J. Raymond, D. Steeghs, R. Reis, J. Homan

Physics and Astronomy Faculty Research Publications

We report on a deep Suzaku observation of the stellar-mass black hole GX 339-4 in outburst. A clear, strong, relativistically shaped iron emission line from the inner accretion disk is observed. The broadband disk reflection spectrum revealed is one of the most sensitive yet obtained from an accreting black hole. We fit the Suzaku spectra with a physically motivated disk reflection model, blurred by a new relativistic line function in which the black hole spin parameter is a variable. This procedure yielded a black hole spin parameter of a=0.89+/-0.04. Joint modeling of these Suzaku spectra and prior XMM-Newton spectra obtained …

Orbits And Pulsations Of The Classical Ζ Aurigae Binaries, Joel A. Eaton, Gregory W. Henry, Andrew P. Odell

Information Systems and Engineering Management Research Publications

We have derived new orbits for ζ Aur, 32 Cyg, and 31 Cyg with observations from the Tennessee State University (TSU) Automatic Spectroscopic Telescope, and used them to identify nonorbital velocities of the cool supergiant components of these systems. We measure periods in those deviations, identify unexpected long-period changes in the radial velocities, and place upper limits on the rotation of these stars. These radial-velocity variations are not obviously consistent with radial pulsation theory, given what we know about the masses and sizes of the components. Our concurrent photometry detected the nonradial pulsations driven by tides (ellipsoidal variation) in both …

Book Review: Guide To Observing Deep-Sky Objects: A Complete Global Resource For Astronomers, T. D. Oswalt

Publications

This document is Dr. Oswalt’s review of Guide to Observing Deep-Sky Objects : a Complete Global Resource for Astronomers by Jeff A. Farinacci. Springer, 2007 189p, 9780387728506 $29.95

The First Mid-Infrared Spectra Of Cool White Dwarfs, Mukremin Kilic, Ted Von Hippel, Et Al.

Publications

We present the first mid-infrared spectra of two cool white dwarfs obtained with the Spitzer Space Telescope. We also present 3.5–8 μ m photometry for 19 cool white dwarfs with 5000 K ≤T_eff ≤ 9000 K. We perform a detailed model atmosphere analysis of these white dwarfs by fitting their UBVRIJHK and Spitzer photometry with state-of-the-art model atmospheres, and demonstrate that the optical and infrared spectral energy distributions of cool white dwarfs are well reproduced by our grid of models. Our mid-infrared photometry and 7.5-14.5 μm spectrum of WD 0018–267 are consistent with a T_eff = 5720 …

Deep Advanced Camera For Surveys Imaging In The Globular Cluster Ngc 6397: The Cluster Color-Magnitude Diagram And Luminosity Function, Harvey B. Richer, Aaron Dotter, Jarrod Hurley, Jay Anderson

Dartmouth Scholarship

We present the color-magnitude diagram (CMD) from deep Hubble Space Telescope imaging in the globular cluster NGC 6397. The Advanced Camera for Surveys (ACS) was used for 126 orbits to image a single field in two colors (F814W, F606W) 5' SE of the cluster center. The field observed overlaps that of archival WFPC2 data from 1994 and 1997 which were used to proper motion (PM) clean the data. Applying the PM corrections produces a remarkably clean CMD which reveals a number of features never seen before in a globular cluster CMD. In our field, the main-sequence stars appeared to terminate …

The Chromospherically Active, Triple, Ellipsoidal, And Eclipsing Binary Hd 6286 = Be Piscium: A Laboratory For Binary Evolution, Klaus G. Strassmeier, János Bartus, Francis C. Fekel, Gregory W. Henry

Information Systems and Engineering Management Research Publications

Aims. We present a detailed analysis of the star HD 6286 = BE Psc from 16 years of spectroscopic observations and 18 seasons of photometric ones. The star is an evolved, chromospherically active, eclipsing binary, consisting of a K1 giant plus an F6 dwarf/subgiant in a circular orbit with a period of 35.671 days. A faint, close visual companion of spectral type ≈G0 makes the system triple. The orbital inclination of the eclipsing pair is 818.

Methods. We have obtained simultaneous solutions with our extensive set of radial velocities and light curves that include the star spot variability of …

The Extremely Rapid Rotational Braking Of The Magnetic Helium-Strong Star Hd 37776, Zdeněk Mikulášek, Jiří Krtička, Gregory W. Henry, Juraj Zverko, Jozef Žižňovský, David A. Bohlender, Iosif I. Romanyuk, Jan Janík, Hrvoje Božić, D. Korčáková, Miloslav Zejda, Ivan Kh. Iliev, Petr Škoda, Miroslav Šlechta, Tomáš Gráf, Martin Netolický, Michal Ceniga

Information Systems and Engineering Management Research Publications

Context. Light and spectrum variations of the magnetic chemically peculiar (mCP) stars are explained by the oblique rigid rotator model with a rotation period usually assumed to be stable on a long time scale. A few exceptions, such as CU Vir or 56 Ari, have been reported as displaying an increase in their rotation period. A possible increase in the period of light and spectrum variations has also been suggested from observations of the helium-strong mCP star HD 37776 (V901 Ori).

Aims. In this paper we attempt to confirm the possible period change of HD 37776 and discuss a possible …

The Nature Of The Ultraluminous Oxygen‐Rich Supernova Remnant In Ngc 4449, Dan Milisavljevic, Robert A. Fesen

Dartmouth Scholarship

Optical images and spectra, both ground based and taken by Hubble Space Telescope (HST), of the young, luminous O-rich supernova remnant in the irregular galaxy NGC 4449 are presented. HST images of the remnant and its local region were obtained with the ACS/WFC using filters F435W, F555W, F814W (B, V, and I, respectively), F502N ([O III]), F658N (Hα + [N II]), F660N ([N II]), and F550M (line-free continuum). These images show an unresolved remnant (FWHM < 0.05'') located within a rich cluster of OB stars which itself is enclosed by a nearly complete interstellar shell seen best in Hα + [N II] emission approximately 8'' × 6'' (150 pc × 110 pc ) in size. The remnant and its associated OB cluster are isolated …

Investigating The Nature Of Absorption Lines In The Chandra X-Ray Spectra Of The Neutron Star Binary 4u 1820-30, E. M. Cackett, J. M. Miller, J. Raymond, J. Homan, M. Van Der Klis, M. Méndez, D. Steeghs, R. Wijnands

Physics and Astronomy Faculty Research Publications

We use four Chandra gratings spectra of the neutron star low-mass X-ray binary 4U 1820-30 to better understand the nature of certain X-ray absorption lines in X-ray binaries, including the Ne II, Ne III, Ne IX, O VII, and O VIII lines. The equivalent widths of the lines are generally consistent between the observations, as expected if these lines originate in the hot interstellar medium. No evidence was found that the lines were blueshifted, again supporting the interstellar medium origin, although this may be due to poor statistics. There is apparent variability in the O VIII Lyα line equivalent width …

Comparing Various Multi-Component Global Heliosphere Models, H.-R. Müller, V. Florinski, J. Heerikhuisen, V. V. Izmodenov

Dartmouth Scholarship

Modeling of the global heliosphere seeks to investigate the interaction of the solar wind with the partially ionized local interstellar medium. Models that treat neutr al hydrogen self-consistently and in great detail, together with the plasma, but that neglect magnetic fields, constitute a sub-category within global heliospheric models. There are several different modeling strategies used for this sub-category in the literature. Differences and commonalities in the modeling results from different strategies are pointed out.

A New Look At The Local White Dwarf Population, J. B. Holberg, E. M. Sion, Terry D. Oswalt, G. P. Mccook, S. Foran, John P. Subasavage

Publications

We have conducted a detailed new survey of the local population of white dwarfs lying within 20 pc of the Sun. A new revised catalog of local white dwarfs containing 122 entries (126 individual degenerate stars) is presented. This list contains 27 white dwarfs not included in a previous list from 2002, as well as new and recently published trigonometric parallaxes. In several cases new members of the local white dwarf population have come to light through accurate photometric distance estimates. In addition, a suspected new double degenerate system (WD 0423+120) has been identified. The 20 pc sample is currently …