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Articles 1 - 15 of 15
Full-Text Articles in Physical Sciences and Mathematics
The Metallicity Of The Cm Draconis System, Ryan C. Terrien, Scott W. Fleming, Suvrath Mahadevan, Rohit Deshpande, Gregory A. Feiden
The Metallicity Of The Cm Draconis System, Ryan C. Terrien, Scott W. Fleming, Suvrath Mahadevan, Rohit Deshpande, Gregory A. Feiden
Dartmouth Scholarship
The CM Draconis system comprises two eclipsing mid-M dwarfs of nearly equal mass in a 1.27-day orbit. This well-studied eclipsing binary has often been used for benchmark tests of stellar models, since its components are amongst the lowest mass stars with well-measured masses and radii (~ 1% relative precision). However, as with many other low-mass stars, non-magnetic models have been unable to match the observed radii and effective temperatures for CM Dra at the 5-10% level. To date, the uncertain metallicity of the system has complicated comparison of theoretical isochrones with observations. In this Letter, we use data from the …
Trajectories And Distribution Of Interstellar Dust Grains In The Heliosphere, Jonathan D. Slavin, Priscilla C. Frisch, Hans-Reinhard Müller, Jacob Heerikhuisen
Trajectories And Distribution Of Interstellar Dust Grains In The Heliosphere, Jonathan D. Slavin, Priscilla C. Frisch, Hans-Reinhard Müller, Jacob Heerikhuisen
Dartmouth Scholarship
The solar wind carves a bubble in the surrounding interstellar medium (ISM) known as the heliosphere. Charged interstellar dust grains (ISDG) encountering the heliosphere may be diverted around the heliopause or penetrate it depending on their charge-to-mass ratio. We present new calculations of trajectories of ISDG in the heliosphere, and the dust density distributions that result. We include up-to-date grain charging calculations using a realistic UV radiation field and full three-dimensional magnetohydrodynamic fluid + kinetic models for the heliosphere. Models with two different (constant) polarities for the solar wind magnetic field (SWMF) are used, with the grain trajectory calculations done …
Supernova Resonance-Scattering Line Profiles In The Absence Of A Photosphere, Brian Friesen, E. Baron, David Branch, Bin Chen, Jerod T. Parrent, R. C. Thomas
Supernova Resonance-Scattering Line Profiles In The Absence Of A Photosphere, Brian Friesen, E. Baron, David Branch, Bin Chen, Jerod T. Parrent, R. C. Thomas
Dartmouth Scholarship
In supernova (SN) spectroscopy relatively little attention has been given to the properties of optically thick spectral lines in epochs following the photosphere's recession. Most treatments and analyses of post-photospheric optical spectra of SNe assume that forbidden-line emission comprises most if not all spectral features. However, evidence exists that suggests that some spectra exhibit line profiles formed via optically thick resonance-scattering even months or years after the SN explosion. To explore this possibility, we present a geometrical approach to SN spectrum formation based on the "Elementary Supernova" model, wherein we investigate the characteristics of resonance-scattering in optically thick lines while …
Self-Consistent Magnetic Stellar Evolution Models Of The Detached, Solar-Type Eclipsing Binary Ef Aquarii, Gregory A. Feiden, Brian Chaboyer
Self-Consistent Magnetic Stellar Evolution Models Of The Detached, Solar-Type Eclipsing Binary Ef Aquarii, Gregory A. Feiden, Brian Chaboyer
Dartmouth Scholarship
We introduce a new one-dimensional stellar evolution code, based on the existing Dartmouth code, that self-consistently accounts for the presence of a globally pervasive magnetic field. The methods involved in perturbing the equations of stellar structure, the equation of state, and the mixing-length theory of convection are presented and discussed. As a first test of the code's viability, stellar evolution models are computed for the components of a solar-type, detached eclipsing binary (DEB) system, EF Aquarii, shown to exhibit large disagreements with stellar models. The addition of the magnetic perturbation corrects the radius and effective temperature discrepancies observed in EF …
Contribution Of The Accretion Disk, Hot Corona, And Obscuring Torus To The Luminosity Of Seyfert Galaxies: Integral And Spitzer Observations, S. Sazonov, S. P. Willner, A. D. Goulding, R. C. Hickox
Contribution Of The Accretion Disk, Hot Corona, And Obscuring Torus To The Luminosity Of Seyfert Galaxies: Integral And Spitzer Observations, S. Sazonov, S. P. Willner, A. D. Goulding, R. C. Hickox
Dartmouth Scholarship
We estimate the relative contributions of the supermassive black hole (SMBH) accretion disk, corona, and obscuring torus to the bolometric luminosity of Seyfert galaxies, using Spitzer mid-infrared (MIR) observations of a complete sample of 68 nearby active galactic nuclei (AGNs) from the INTEGRAL all-sky hard X-ray (HX) survey. This is the first HX-selected (above 15 keV) sample of AGNs with complementary high angular resolution, high signal-to-noise, MIR data. Correcting for the host galaxy contribution, we find a correlation between HX and MIR luminosities: L 15 μm∝L0.74 ± 0.06 HX. Assuming that the observed MIR emission is radiation …
Reevaluating The Mass-Radius Relation For Low-Mass, Main-Sequence Stars, Gregory A. Feiden, Brian Chaboyer
Reevaluating The Mass-Radius Relation For Low-Mass, Main-Sequence Stars, Gregory A. Feiden, Brian Chaboyer
Dartmouth Scholarship
We examine the agreement between the observed and theoretical low-mass (<0.8 M ☉) stellar main-sequence mass-radius relationship by comparing detached eclipsing binary (DEB) data with a new, large grid of stellar evolution models. The new grid allows for a realistic variation in the age and metallicity of the DEB population, characteristic of the local galactic neighborhood. Overall, our models do a reasonable job of reproducing the observational data. A large majority of the models match the observed stellar radii to within 4%, with a mean absolute error of 2.3%. These results represent a factor of two improvement compared to …
The Chandra X-Ray Point-Source Catalog In The Deep2 Galaxy Redshift Survey Fields, A. D. Goulding, W. R. Forman, R. C. Hickox, C. Jones
The Chandra X-Ray Point-Source Catalog In The Deep2 Galaxy Redshift Survey Fields, A. D. Goulding, W. R. Forman, R. C. Hickox, C. Jones
Dartmouth Scholarship
We present the X-ray point-source catalog produced from the Chandra Advanced CCD Imaging Spectrometer (ACIS-I) observations of the combined \sim3.2 deg2 DEEP2 (XDEEP2) survey fields, which consist of four ~0.7-1.1 deg2 fields. The combined total exposures across all four XDEEP2 fields range from ~10ks-1.1Ms. We detect X-ray point-sources in both the individual ACIS-I observations and the overlapping regions in the merged (stacked) images. We find a total of 2976 unique X-ray sources within the survey area with an expected false-source contamination of ~30 sources (~1%). We present the combined logN-logS distribution of sources detected across the XDEEP2 survey fields and …
High-Velocity Outflows Without Agn Feedback: Eddington-Limited Star Formation In Compact Massive Galaxies, Aleksandar M. Diamond-Stanic, John Moustakas, Christy A. Tremonti, Alison L. Coil, Ryan C. Hickox
High-Velocity Outflows Without Agn Feedback: Eddington-Limited Star Formation In Compact Massive Galaxies, Aleksandar M. Diamond-Stanic, John Moustakas, Christy A. Tremonti, Alison L. Coil, Ryan C. Hickox
Dartmouth Scholarship
We present the discovery of compact, obscured star formation in galaxies at z ~ 0.6 that exhibit 1000 km s–1 outflows. Using optical morphologies from the Hubble Space Telescope and infrared photometry from the Wide-field Infrared Survey Explorer, we estimate star formation rate (SFR) surface densities that approach ΣSFR ≈ 3000 M ☉ yr–1 kpc–2, comparable to the Eddington limit from radiation pressure on dust grains. We argue that feedback associated with a compact starburst in the form of radiation pressure from massive stars and ram pressure from supernovae and stellar winds is sufficient …
Deep Silicate Absorption Features In Compton-Thick Active Galactic Nuclei Predominantly Arise Due To Dust In The Host Galaxy, A. D. Goulding, D. M. Alexander, F. E. Bauer, W. R. Forman, R. C. Hickox
Deep Silicate Absorption Features In Compton-Thick Active Galactic Nuclei Predominantly Arise Due To Dust In The Host Galaxy, A. D. Goulding, D. M. Alexander, F. E. Bauer, W. R. Forman, R. C. Hickox
Dartmouth Scholarship
We explore the origin of mid-infrared (mid-IR) dust extinction in all 20 nearby (z < 0.05) bona fide Compton-thick (N H > 1.5 × 1024 cm–2) active galactic nuclei (AGNs) with hard energy (E > 10 keV) X-ray spectral measurements. We accurately measure the silicate absorption features at λ ~ 9.7 μm in archival low-resolution (R ~ 57-127) Spitzer Infrared Spectrograph spectroscopy, and show that only a minority (≈45%) of nearby Compton-thick AGNs have strong Si-absorption features (S 9.7 = ln (f int/f obs) 0.5) which would indicate significant dust attenuation. The majority (≈60%) are star …
Analysis Of The Early-Time Optical Spectra Of Sn 2011fe In M101, J. T. Parrent, D. A. Howell, B. Friesen, R. C. Thomas
Analysis Of The Early-Time Optical Spectra Of Sn 2011fe In M101, J. T. Parrent, D. A. Howell, B. Friesen, R. C. Thomas
Dartmouth Scholarship
The nearby Type Ia supernova SN 2011fe in M101 (cz=241 km s^-1) provides a unique opportunity to study the early evolution of a "normal" Type Ia supernova, its compositional structure, and its elusive progenitor system. We present 18 high signal-to-noise spectra of SN 2011fe during its first month beginning 1.2 days post-explosion and with an average cadence of 1.8 days. This gives a clear picture of how various line-forming species are distributed within the outer layers of the ejecta, including that of unburned material (C+O). We follow the evolution of C II absorption features until they diminish near maximum light, …
The Hidden “Agn Main Sequence”: Evidence For A Universal Black Hole Accretion To Star Formation Rate Ratio Since Z ∼ 2 Producing An M Bh - M * Relation, J. R. Mullaney, E. Daddi, M. Béthermin, D. Elbaz, S. Juneau, M. Pannella, M. T. Sargent, D. M. Alexander, R. C. Hickox
The Hidden “Agn Main Sequence”: Evidence For A Universal Black Hole Accretion To Star Formation Rate Ratio Since Z ∼ 2 Producing An M Bh - M * Relation, J. R. Mullaney, E. Daddi, M. Béthermin, D. Elbaz, S. Juneau, M. Pannella, M. T. Sargent, D. M. Alexander, R. C. Hickox
Dartmouth Scholarship
Using X-ray stacking analyses we estimate the average amounts of supermassive black hole (SMBH) growth taking place in star-forming galaxies at z ~ 1 and z ~ 2 as a function of galaxy stellar mass (M *). We find that the average SMBH growth rate follows remarkably similar trends with M * and redshift as the average star formation rates (SFRs) of their host galaxies (i.e., \dot{M}_BH vprop M * 0.86 ± 0.39 for the z ~ 1 sample and \dot{M}_BH vprop M * 1.05 ± 0.36 for the z ~ 2 sample). It follows that the ratio of …
Late-Time Optical Emission From Core-Collapse Supernovae, Dan Milisavljevic, Robert A. Fesen, Roger A. Chevalier, Robert P. Kirshner
Late-Time Optical Emission From Core-Collapse Supernovae, Dan Milisavljevic, Robert A. Fesen, Roger A. Chevalier, Robert P. Kirshner
Dartmouth Scholarship
Ground-based optical spectra and Hubble Space Telescope images of 10 core-collapse supernovae (CCSNe) obtained several years to decades after outburst are analyzed with the aim of understanding the general properties of their late-time emissions. New observations of SN 1957D, 1970G, 1980K, and 1993J are included as part of the study. Blueshifted line emissions in oxygen and/or hydrogen with conspicuous line substructure are a common and long-lasting phenomenon in the late-time spectra. Followed through multiple epochs, changes in the relative strengths and velocity widths of the emission lines are consistent with expectations for emissions produced by interaction between SN ejecta and …
Spitzer Imaging And Spectral Mapping Of The Oxygen-Rich Supernova Remnant G292.0+1.8, Parviz Ghavamian, Knox S. Long, William P. Blair, Sangwook Park, Robert Fesen
Spitzer Imaging And Spectral Mapping Of The Oxygen-Rich Supernova Remnant G292.0+1.8, Parviz Ghavamian, Knox S. Long, William P. Blair, Sangwook Park, Robert Fesen
Dartmouth Scholarship
We present mid-infrared continuum and emission line images of the Galactic oxygen-rich supernova remnant (SNR) G292.0+1.8, acquired using the MIPS and IRS instruments on the Spitzer Space Telescope. The MIPS 24 μm and 70 μm images of G292.0+1.8 are dominated by continuum emission from a network of filaments encircling the SNR. The morphology of the SNR, as seen in the mid-infrared, resembles that seen in X-rays with the Chandra X-Ray Observatory. Most of the mid-infrared emission in the MIPS images is produced by circumstellar dust heated in the non-radiative shocks around G292.0+1.8, confirming the results of earlier mid-IR …
Ionized Reflection Spectra From Accretion Disks Illuminated By X-Ray Pulsars, D. R. Ballantyne, J. D. Purvis, R. G. Strausbaugh, R. C. Hickox
Ionized Reflection Spectra From Accretion Disks Illuminated By X-Ray Pulsars, D. R. Ballantyne, J. D. Purvis, R. G. Strausbaugh, R. C. Hickox
Dartmouth Scholarship
X-ray reflection signatures are observed around multiple classes of accreting compact objects. Modelling these features yield important constraints on the physics of accretion disks, motivating the development of X-ray reflection models appropriate for a variety of systems and illumination conditions. Here, constant density ionized X-ray reflection models are presented for a disk irradiated with a very hard power-law X-ray spectrum (\Gamma < 1) and a variable high-energy cutoff. These models are then applied to the Suzaku data of the accreting X-ray pulsar LMC X-4, where very good fits are obtained with a highly ionized reflector responsible for both the broad Fe K line and the soft excess. The ionized reflector shows strong evidence for significant Doppler broadening and is redshifted by ~10^4 km/s. These features indicate that the reflecting material is associated with the complex dynamics occurring at the inner region of the magnetically-truncated accretion disk. Thus, reflection studies of X-ray pulsar spectra may give important insights into the accretion physics at the magnetospheric radius.
A Reverberation Lag For The High-Ionization Component Of The Broad-Line Region In The Narrow-Line Seyfert 1 Mrk 335, C. J. Grier, B. M. Peterson, R. W. Pogge, K. D. Denney, M. C. Bentz, Paul Martini, S. G. Sergeev, S. Kaspi, Y. Zu, C. S. Kochanek, B. J. Shappee, C. Araya Salvo, T G. Beatty, J. C. Bird, D. J. Bord, G. A. Borman, X. Che, C. Chen
A Reverberation Lag For The High-Ionization Component Of The Broad-Line Region In The Narrow-Line Seyfert 1 Mrk 335, C. J. Grier, B. M. Peterson, R. W. Pogge, K. D. Denney, M. C. Bentz, Paul Martini, S. G. Sergeev, S. Kaspi, Y. Zu, C. S. Kochanek, B. J. Shappee, C. Araya Salvo, T G. Beatty, J. C. Bird, D. J. Bord, G. A. Borman, X. Che, C. Chen
Dartmouth Scholarship
We present the first results from a detailed analysis of photometric and spectrophotometric data on the narrow-line Seyfert 1 (NLS1) galaxy Mrk 335, collected over a 120 day span in the fall of 2010. From these data we measure the lag in the He ii λ 4686 broad emission line relative to the optical continuum to be 2.7 °æ 0.6 days and the lag in the Hβλ 4861 broad emission line to be 13.9 °æ 0.9 days. Combined with the line width, the He ii lag yields a black hole mass MBH = (2. 6 °æ 0. 8) °ø 107M …