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Articles 1 - 12 of 12
Full-Text Articles in Physical Sciences and Mathematics
Correlation Of Inflation-Produced Magnetic Fields With Scalar Fluctuations, Robert R. Caldwell, Leonardo Motta, Marc Kamionkowski
Correlation Of Inflation-Produced Magnetic Fields With Scalar Fluctuations, Robert R. Caldwell, Leonardo Motta, Marc Kamionkowski
Dartmouth Scholarship
If the conformal invariance of electromagnetism is broken during inflation, then primordial magnetic fields may be produced. If this symmetry breaking is generated by the coupling between electromagnetism and a scalar field—e.g. the inflaton, curvaton, or Ricci scalar—then these magnetic fields may be correlated with primordial density perturbations, opening a new window to the study of non-Gaussianity in cosmology. In order to illustrate, we couple electromagnetism to an auxiliary scalar field in a de Sitter background. We calculate the power spectra for scalar-field perturbations and magnetic fields, showing how a scale-free magnetic-field spectrum with rms amplitude of ∼nG at Mpc …
The Sn 393-Snr Rx J1713.7-3946 (G347.3-0.5) Connection, Robert A. Fesen, Richard Kremer, Daniel Patnaude, Dan Milisavljevic
The Sn 393-Snr Rx J1713.7-3946 (G347.3-0.5) Connection, Robert A. Fesen, Richard Kremer, Daniel Patnaude, Dan Milisavljevic
Dartmouth Scholarship
Although the connection of the Chinese "guest" star of 393 AD with the Galactic supernova remnant RX J1713.7-3946 (G347.3-0.5) made by Wang et al. in 1997 is consistent with the remnant's relatively young properties and the guest star's projected position within the "tail" of the constellation Scorpius, there are difficulties with such an association. The brief Chinese texts concerning the 393 AD guest star make no comment about its apparent brightness, stating only that it disappeared after eight months. However, at the remnant's current estimated 1-1.3 kpc distance and A V 3, its supernova (SN) should have been a visually …
The Acs Survey Of Galactic Globular Clusters. Xi. The Three-Dimensional Orientation Of The Sagittarius Dwarf Spheroidal Galaxy And Its Globular Clusters, Michael H. H. Siegel, Steven R. Majewski, David R. Law, Ata Sarajedini, Aaron Dotter, A Marín-Franch, Brian Chaboyer
The Acs Survey Of Galactic Globular Clusters. Xi. The Three-Dimensional Orientation Of The Sagittarius Dwarf Spheroidal Galaxy And Its Globular Clusters, Michael H. H. Siegel, Steven R. Majewski, David R. Law, Ata Sarajedini, Aaron Dotter, A Marín-Franch, Brian Chaboyer
Dartmouth Scholarship
We use observations from the Hubble Space Telescope Advanced Camera for Surveys (HST/ACS) study of Galactic globular clusters to investigate the spatial distribution of the inner regions of the disrupting Sagittarius dwarf spheroidal galaxy (Sgr). We combine previously published analyses of four Sgr member clusters located near or in the Sgr core (M54, Arp 2, Terzan 7, and Terzan 8) with a new analysis of diffuse Sgr material identified in the background of five low-latitude Galactic bulge clusters (NGC 6624, 6637, 6652, 6681, and 6809) observed as part of the ACS survey. By comparing the bulge cluster color-magnitude …
Time Evolution Of The Reverse Shock In Sn 1006, P. Frank Winkler, Andrew J. S. Hamilton, Knox S. Long, Robert A. Fesen
Time Evolution Of The Reverse Shock In Sn 1006, P. Frank Winkler, Andrew J. S. Hamilton, Knox S. Long, Robert A. Fesen
Dartmouth Scholarship
The Schweizer-Middleditch star, located behind the SN 1006 remnant and near its center in projection, provides the opportunity to study cold, expanding ejecta within the SN 1006 shell through UV absorption. Especially notable is an extremely sharp red edge to the Si II 1260 Å feature, which stems from the fastest moving ejecta on the far side of the SN 1006 shell—material that is just encountering the reverse shock. Comparing Hubble Space Telescope far-UV spectra obtained with the Cosmic Origins Spectrograph in 2010 and with the Space Telescope Imaging Spectrograph in 1999, we have measured the change in this feature …
Acurate Low-Mass Stellar Models Of Koi-126, Gregory A. Feiden, Brian Chaboyer, Aaron Dotter
Acurate Low-Mass Stellar Models Of Koi-126, Gregory A. Feiden, Brian Chaboyer, Aaron Dotter
Dartmouth Scholarship
The recent discovery of an eclipsing hierarchical triple system with two low-mass stars in a close orbit (KOI-126) by Carter et al. (2011) appeared to reinforce the evidence that theoretical stellar evolution models are not able to reproduce the observational mass-radius relation for low-mass stars. We present a set of stellar models for the three stars in the KOI-126 system that show excellent agreement with the observed radii. This agreement appears to be due to the equation of state implemented by our code. A significant dispersion in the observed mass-radius relation for fully convective stars is demonstrated; indicative of the …
A Model Of So-Called "Zebra" Emissions In Solar Flare Radio Burst Continua, R. A. Treumann, R. Nakamura, W. Baumjohann
A Model Of So-Called "Zebra" Emissions In Solar Flare Radio Burst Continua, R. A. Treumann, R. Nakamura, W. Baumjohann
Dartmouth Scholarship
A simple mechanism for the generation of elec- tromagnetic “Zebra” pattern emissions is proposed. “Zebra” bursts are regularly spaced narrow-band radio emissions on the otherwise broadband radio continuum emitted by the ac- tive solar corona. The mechanism is based on the generation of an ion-ring distribution in a magnetic mirror geometry in the presence of a properly directed field-aligned electric po- tential field. Such ion-rings or ion-conics are well known from magnetospheric observations. Under coronal condi- tions they may become weakly relativistic. In this case the ion-cyclotron maser generates a number of electromagnetic ion-cyclotron harmonics which modulate the electron maser …
Discovery Of A Bright, Extremely Low Mass White Dwarf In A Close Double Degenerate System, S. Vennes, J. R. Thorstensen, A. Kawka, P. Németh, J. N. Skinner
Discovery Of A Bright, Extremely Low Mass White Dwarf In A Close Double Degenerate System, S. Vennes, J. R. Thorstensen, A. Kawka, P. Németh, J. N. Skinner
Dartmouth Scholarship
We report the discovery of a bright (V ~ 13.7), extremely low-mass white dwarf in a close double degenerate system. We originally selected GALEX J171708.5+675712 for spectroscopic follow-up among a group of white dwarf candidates in an ultraviolet-optical reduced proper-motion diagram. The new white dwarf has a mass of 0.18 M_solar and is the primary component of a close double degenerate system (P=0.246137 d, K_1 = 288 km/s) comprising a fainter white dwarf secondary with M_2 ~ 0.9 M_solar. Light curves phased with the orbital ephemeris show evidence of relativistic beaming and weaker ellipsoidal variations. The light curves also reveal …
Ejecta Knot Flickering, Mass Ablation, And Fragmentation In Cassiopeia A, Robert A. Fesen, Jordan A. Zastrow, Molly C. Hammell, J. Michael Shull, Devin W. Silvia
Ejecta Knot Flickering, Mass Ablation, And Fragmentation In Cassiopeia A, Robert A. Fesen, Jordan A. Zastrow, Molly C. Hammell, J. Michael Shull, Devin W. Silvia
Dartmouth Scholarship
Ejecta knot flickering, ablation tails, and fragmentation are expected signatures associated with the gradual dissolution of high-velocity supernova (SN) ejecta caused by their passage through an inhomogeneous circumstellar medium or interstellar medium (ISM). Such phenomena mark the initial stages of the gradual merger of SN ejecta with and the enrichment of the surrounding ISM. Here we report on an investigation of this process through changes in the optical flux and morphology of several high-velocity ejecta knots located in the outskirts of the young core-collapse SN remnant Cassiopeia A using Hubble Space Telescope images. Examination of WFPC2 F675W and combined ACS …
Polarization Of The Charge-Exchange X-Rays Induced In The Heliosphere, M. Gacesa, H.-R. Müller, R. Côté, V. Kharchenko
Polarization Of The Charge-Exchange X-Rays Induced In The Heliosphere, M. Gacesa, H.-R. Müller, R. Côté, V. Kharchenko
Dartmouth Scholarship
We report results of a theoretical investigation of polarization of the X-ray emissions induced in charge-exchange collisions of fully stripped solar wind ions C6+and O8+ with the heliospheric hydrogen atoms. The polarization of X-ray emissions has been computed for line-of-sight observations within the ecliptic plane as a function of solar wind ion velocities, including a range of velocities corresponding to the slow and fast solar wind, and Coronal Mass Ejections. To determine the variability of polarization of heliospheric X-ray emissions, the polarization has been computed for solar minimum conditions with self-consistent parameters of the solar wind plasma and heliospheric gas …
A Study Of Carbon Features In Type Ia Supernova Spectra, Jerod T. Parrent, R. C. Thomas, Robert A. Fesen, G. H. Marion
A Study Of Carbon Features In Type Ia Supernova Spectra, Jerod T. Parrent, R. C. Thomas, Robert A. Fesen, G. H. Marion
Dartmouth Scholarship
One of the major differences between various explosion scenarios of Type Ia supernovae (SNe Ia) is the remaining amount of unburned (C+O) material and its velocity distribution within the expanding ejecta. While oxygen absorption features are not uncommon in the spectra of SNe Ia before maximum light, the presence of strong carbon absorption has been reported only in a minority of objects, typically during the pre-maximum phase. The reported low frequency of carbon detections may be due to low signal-to-noise data, low abundance of unburned material, line blending between C II 6580 and Si II 6355, ejecta temperature differences, asymmetrical …
Cross-Correlation Of Cosmological Birefringence With Cmb Temperature, Robert R. Caldwell, Vera Gluscevic, Marc Kamionkowski
Cross-Correlation Of Cosmological Birefringence With Cmb Temperature, Robert R. Caldwell, Vera Gluscevic, Marc Kamionkowski
Dartmouth Scholarship
Theories for new particle and early-Universe physics abound with pseudo-Nambu-Goldstone fields that arise when global symmetries are spontaneously broken. The coupling of these fields to the Chern-Simons term of electromagnetism may give rise to cosmological birefringence (CB), a frequency-independent rotation of the linear polarization of photons as they propagate over cosmological distances. Inhomogeneities in the CB-inducing field may yield a rotation angle that varies across the sky. Here we note that such a spatially-varying birefringence may be correlated with the cosmic microwave background (CMB) temperature. We describe quintessence scenarios where this cross-correlation exists and other scenarios where the scalar field …
A Decline In The Nonthermal X-Ray Emission From Cassiopeia A, Daniel J. Patnaude, Jacco Vink, J. Martin Laming, Robert A. Fesen
A Decline In The Nonthermal X-Ray Emission From Cassiopeia A, Daniel J. Patnaude, Jacco Vink, J. Martin Laming, Robert A. Fesen
Dartmouth Scholarship
We present new Chandra ACIS-S3 observations of Cassiopeia A which, when combined with earlier ACIS-S3 observations, show evidence for a steady ~ 1.5-2%/yr decline in the 4.2-6.0 keV X-ray emission between the years 2000 and 2010. The computed flux from exposure corrected images over the entire remnant showed a 17% decline over the entire remnant and a slightly larger (21%) decline from regions along the remnant's western limb. Spectral fits of the 4.2-6.0 keV emission across the entire remnant, forward shock filaments, and interior filaments indicate the remnant's nonthermal spectral powerlaw index has steepened by about 10%, with interior filaments …