Adam R. Foster
Harvard University
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Featured researches published by Adam R. Foster.
The Astrophysical Journal | 2012
Adam R. Foster; Li Ji; Randall K. Smith; N. S. Brickhouse
We describe the latest release of AtomDB, version 2.0.2, a database of atomic data and a plasma modeling code with a focus on X-ray astronomy. This release includes several major updates to the fundamental atomic structure and process data held within AtomDB, incorporating new ionization balance data, state-selective recombination data, and updated collisional excitation data for many ions, including the iron L-shell ions from Fe+16 to Fe+23 and all of the hydrogen- and helium-like sequences. We also describe some of the effects that these changes have on calculated emission and diagnostic line ratios, such as changes in the temperature implied by the He-like G-ratios of up to a factor of two.
The Astrophysical Journal | 2015
Hiroya Yamaguchi; Carles Badenes; Adam R. Foster; Eduardo Bravo; Brian J. Williams; Keiichi Maeda; Masayoshi Nobukawa; Kristoffer A. Eriksen; Nancy S. Brickhouse; Robert Petre; Katsuji Koyama
Despite decades of intense efforts, many fundamental aspects of Type Ia supernovae (SNe Ia) remain elusive. One of the major open questions is whether the mass of an exploding white dwarf (WD) is close to the Chandrasekhar limit. Here, we report the detection of strong K-shell emission from stable Fe-peak elements in the Suzaku X-ray spectrum of the Type Ia supernova remnant (SNR) 3C 397. The high Ni/Fe and Mn/Fe mass ratios (0.11–0.24 and 0.018–0.033, respectively) in the hot plasma component that dominates the K-shell emission lines indicate a degree of neutronization in the supernova ejecta that can only be achieved by electron capture in the dense cores of exploding WDs with a near-Chandrasekhar mass. This suggests a single-degenerate origin for 3C 397, since Chandrasekhar mass progenitors are expected naturally if the WD accretes mass slowly from a companion. Together with other results supporting the double-degenerate scenario, our work adds to the mounting evidence that both progenitor channels make a significant contribution to the SN Ia rate in star-forming galaxies.
The Astrophysical Journal | 2013
Hiroya Yamaguchi; Kristoffer A. Eriksen; Carles Badenes; John P. Hughes; Nancy S. Brickhouse; Adam R. Foster; Daniel J. Patnaude; Robert Petre; Patrick O. Slane; Randall K. Smith
Although collisionless shocks are ubiquitous in astrophysics, certain key aspects of them are not well understood. In particular, the process known as collisionless electron heating, whereby electrons are rapidly energized at the shock front, is one of the main open issues in shock physics. Here we present the first clear evidence for efficient collisionless electron heating at the reverse shock of Tycho’s supernova remnant (SNR), revealed by Fe-K diagnostics using high-quality X-ray data obtained by the Suzaku satellite. We detect K� (3p!1s) fluorescence emission from low-ionization Fe ejecta excited by energetic thermal electrons at the reverse shock front, which peaks at a smaller radius than Fe-K� (2p!1s) emission dominated by a relatively highly-ionized component. Comparison with our hydrodynamical simulations implies instantaneous electron heating to a temperature 1000 times higher than expected from Coulomb collisions alone. The unique environment of the reverse shock, which is propagating with a high Mach number into rarefied ejecta with a low magnetic field strength, puts strong constraints on the physical mechanism responsible for this heating, and favors a crossshock potential created by charge deflection at the shock front. Our sensitive observation also reveals that the reverse shock radius of this SNR is about 10% smaller than the previous measurement using
The Astrophysical Journal | 2014
Randall K. Smith; Adam R. Foster; Richard J. Edgar; Nancy S. Brickhouse
The ubiquitous diffuse soft (1/4 keV) X-ray background was one of the earliest discoveries of X-ray astronomy. At least some of the emission may arise from charge exchange between solar wind ions and neutral atoms in the heliosphere, but no detailed models have been fit to the available data. Here, we report on a new model for charge exchange in the solar wind, which, when combined with a diffuse hot plasma component, filling the Local Cavity provides a good fit to the only available high-resolution soft X-ray and extreme ultraviolet spectra using plausible parameters for the solar wind. The implied hot plasma component is in pressure equilibrium with the local cloud that surrounds the solar system, creating for the first time a self-consistent picture of the local interstellar medium.
The Astrophysical Journal | 2011
Adam R. Foster; Paola Testa
New calculations of the energy levels, radiative transition rates, and collisional excitation rates of Fe IX have been carried out using the Flexible Atomic Code, paying close attention to experimentally identified levels and extending existing calculations to higher energy levels. For lower levels, R-matrix collisional excitation rates from earlier work have been used. Significant emission is predicted by these calculations in the 5f-3d transitions, which will impact analysis of Solar Dynamics Observatory Atmospheric Imaging Assembly observations using the 94 A filter.
The Astrophysical Journal | 2012
Anthony Hervé; Grégor Rauw; Yaël Nazé; Adam R. Foster
High-resolution X-ray spectra of O-type stars revealed less wind absorption than expected from smooth winds with conventional mass-loss rates. Various solutions have been proposed, including porous winds, optically thick clumps, or an overall reduction of the mass-loss rates. The latter has a strong impact on the evolution of the star. Our final goal is to analyze high-resolution X-ray spectra of O-type stars with a multi-temperature plasma model in order to determine crucial stellar and wind parameters such as the mass-loss rate, the CNO abundances, and the X-ray temperature plasma distribution in the wind. In this context we are developing a modeling tool to calculate synthetic X-ray spectra. We present here the main ingredients and physics necessary for such a work. Our code uses the most recent version of the AtomDB emissivities to compute the intrinsic emissivity of the hot plasma as well as the CMFGEN model atmosphere code to evaluate the opacity of the cool wind. Following the comparison between two formalisms of stellar wind fragmentation, we introduce, for the first time in X-rays, the effects of a tenuous inter-clump medium. We then explore the quantitative impact of different model parameters on the X-ray spectra such as the position in the wind of the X-ray emitting plasma. For the first time, we also show that the two formalisms of stellar wind fragmentation yield different results, although the differences for individual lines are small and can probably not be tested with the current generation of X-ray telescopes. As an illustration of our method, we compare various synthetic line profiles to the observed O VIII λ18.97 line in the spectrum of ζ Puppis. We illustrate how different combinations of parameters can actually lead to the same morphology of a single line, underlining the need to analyze the whole spectrum in a consistent way when attempting to constrain the parameters of the wind.
The Astrophysical Journal | 2018
N. Cappelluti; E. Bulbul; Adam R. Foster; Priyamvada Natarajan; Megan Urry; Mark W. Bautz; F. Civano; Eric J. Miller; Randall K. Smith
In this paper we report a systematic search for an emission line around 3.5 keV in the spectrum of the Cosmic X-ray Background using a total of
The Astrophysical Journal | 2016
Jeroen Franse; Esra Bulbul; Adam R. Foster; Alexey Boyarsky; Maxim Markevitch; Mark W. Bautz; Dmytro Iakubovskyi; Mike Loewenstein; M. McDonald; Eric J. Miller; Scott W. Randall; Oleg Ruchayskiy; Randall K. Smith
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Astronomy and Astrophysics | 2017
Paul P. Plucinsky; Andrew P. Beardmore; Adam R. Foster; F. Haberl; Eric D. Miller; Andrew Pollock; Steve Sembay
10 Ms Chandra observations towards the COSMOS Legacy and CDFS survey fields. We find a marginal evidence of a feature at an energy of
The Astrophysical Journal | 2016
Esra Bulbul; Maxim Markevitch; Adam R. Foster; Eric J. Miller; Mark W. Bautz; M. Loewenstein; Scott W. Randall; Randall K. Smith
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