127 research outputs found
X-ray Spectroscopy of the Radiation-Driven Winds of Massive Stars: Line Profile and Line Ratio Diagnostics
Massive stars drive powerful, supersonic winds via the radiative momentum
associated with the thermal UV emission from their photospheres. Shock
phenomena are ubiquitous in these winds, heating them to millions, and
sometimes tens of millions, of degrees. The emission line spectra from the
shock-heated plasma provide powerful diagnostics of the winds' physical
conditions, which in turn provide constraints on models of wind shock heating.
Here I show how x-ray line transfer is affected by photoelectric absorption in
the partially ionized component of the wind and how it can be modeled to
determine the astrophysically important mass-loss rates of these stellar winds.
I also discuss how photoexcitation out of metastable excited levels of
helium-like ions can provide critical information about the location of the hot
plasma in magnetically channeled massive star winds.Comment: Invited talk presented at the 16th International Conference on Atomic
Processes in Plasmas, Monterey, CA, March 2009; will appear in an
AIP-published conference proceedings. 10 pages, 4 figures (2 color, but color
not crucial
Fe L-Shell Density Diagnostics in Theory and Practice
We provide a discussion of the density and photoexcitation sensitivity of the
X-ray spectra of Fe L-shell ions (Fe XVII-Fe XXIV) calculated with the
Livermore X-ray Spectral Synthesizer, a suite of IDL codes that calculates
spectral models of highly charged ions based primarily on HULLAC atomic data.
These models are applicable to collisionally ionized laboratory or cosmic
plasmas with electron temperatures T_e ~ 2-45 MK (0.2-4 keV) and electron
densities n_e > 1E11 cm^{-3}. Potentially useful density diagnostics are
identified for Fe XVII and Fe XIX-Fe XXIII, with the most straightforward being
the Fe XVII I(17.10 A)/I(17.05 A) line ratio and the Fe XXII I(11.92 A)/I(11.77
A) line ratio. Applying these models to the Chandra X-ray Observatory High
Energy Transmission Grating spectrum of the intermediate polar EX Hya, we find
that the strength of all the Fe L-shell lines are consistent with electron
densities n_e > 1E14 cm^{-3}. Specifically, from the observed Fe XVII I(17.10
A)/I(17.05 A) line ratio, we infer an electron density n_e > 2E14 cm^{-3} at
the 3 sigma level, while from the observed Fe XXII I(11.92 A)/I(11.77 A) line
ratio, we infer n_e = 1.0^{+2.0}_{-0.5}E14 cm^{-3} at the 1 sigma level and n_e
> 2E13 cm^{-3} at the 3 sigma level.Comment: 11 pages including 9 encapsulated postscript figures; LaTeX format,
uses aipproc.cls, aip-6d.clo, and aipxfm.sty; to appear in the proceedings of
X-ray Diagnostics for Astrophysical Plasmas: Theory, Experiment, and
Observation, ed. R. K. Smith (Melville: AIP
The Fe XXII I(11.92 A)/I(11.77 A) Density Diagnostic Applied to the Chandra High Energy Transmission Grating Spectrum of EX Hydrae
Using the Livermore X-ray Spectral Synthesizer, which calculates spectral
models of highly charged ions based primarily on HULLAC atomic data, we
investigate the temperature, density, and photoexcitation dependence of the
I(11.92 A)/I(11.77 A) line ratio of Fe XXII. We find that this line ratio has a
critical density n_c \approx 5x10^13 cm^-3, is approximately 0.3 at low
densities and 1.5 at high densities, and is very insensitive to temperature and
photoexcitation, so is a useful density diagnostic for sources like magnetic
cataclysmic variables in which the plasma densities are high and the efficacy
of the He-like ion density diagnostic is compromised by the presence of a
bright ultraviolet continuum. Applying this diagnostic to the Chandra High
Energy Transmission Grating spectrum of the intermediate polar EX Hya, we find
that the electron density of its T_e \approx 12 MK plasma is n_e =
1.0^{+2.0}_{-0.5} x 10^14 cm^-3, orders of magnitude greater than that
typically observed in the Sun or other late-type stars.Comment: 11 pages including 3 encapsulated postscript figures; LaTeX format,
uses aastex.cls; accepted on 2003 April 3 for publication in The
Astrophysical Journa
Effect of NLTE Emissivity Models on NIF Ignition Hohlraum Power Requirements
Abstract not provide
First Application of the Fe XVII I(17.10 A)/I(17.05 A) Line Ratio to Constrain the Plasma Density of a Cosmic X-ray Source
We show that the Fe XVII I(17.10 A)/I(17.05 A) line ratio observed in the
Chandra HETG spectrum of the intermediate polar EX Hydrae is significantly
smaller than that observed in the Sun or other late-type stars. Using the
Livermore X-ray Spectral Synthesizer, which calculates spectral models of
highly charged ions based on HULLAC atomic data, we find that the observed
I(17.10 A)/I(17.05 A) line ratio can be explained if the plasma density n_e >
3x10^{14} cm^{-3}. However, if photoexcitation is included in the level
population kinetics, the line ratio can be explained for any density if the
photoexcitation temperature T_bb > 55 kK. For photoexcitation to dominate the
Fe XVII level population kinetics, the relative size of the hotspot on the
white dwarf surface must be f < 2%. This constraint and the observed X-ray flux
requires a density n > 2x10^{14} cm^{-3} for the post-shock flow. Either way,
then, the Chandra HETG spectrum of EX Hya requires a plasma density which is
orders of magnitude greater than that observed in the Sun or other late-type
stars.Comment: 13 pages including 1 table and 4 encapsulated postscript figures;
LaTeX format, uses aastex.cls; accepted on 2001 June 27 for publication in
The Astrophysical Journa
Search for gravitational waves associated with the InterPlanetary Network short gamma ray bursts
We outline the scientific motivation behind a search for gravitational waves
associated with short gamma ray bursts detected by the InterPlanetary Network
(IPN) during LIGO's fifth science run and Virgo's first science run. The IPN
localisation of short gamma ray bursts is limited to extended error boxes of
different shapes and sizes and a search on these error boxes poses a series of
challenges for data analysis. We will discuss these challenges and outline the
methods to optimise the search over these error boxes.Comment: Methods paper; Proceedings for Eduardo Amaldi 9 Conference on
Gravitational Waves, July 2011, Cardiff, U
Awesome SOSS: Transmission Spectroscopy of WASP-96b with NIRISS/SOSS
The future is now - after its long-awaited launch in December 2021, JWST
began science operations in July 2022 and is already revolutionizing exoplanet
astronomy. The Early Release Observations (ERO) program was designed to provide
the first images and spectra from JWST, covering a multitude of science cases
and using multiple modes of each on-board instrument. Here, we present
transmission spectroscopy observations of the hot-Saturn WASP-96b with the
Single Object Slitless Spectroscopy (SOSS) mode of the Near Infrared Imager and
Slitless Spectrograph, observed as part of the ERO program. As the SOSS mode
presents some unique data reduction challenges, we provide an in-depth
walk-through of the major steps necessary for the reduction of SOSS data:
including background subtraction, correction of 1/f noise, and treatment of the
trace order overlap. We furthermore offer potential routes to correct for field
star contamination, which can occur due to the SOSS mode's slitless nature. By
comparing our extracted transmission spectrum with grids of atmosphere models,
we find an atmosphere metallicity between 1x and 5x solar, and a solar
carbon-to-oxygen ratio. Moreover, our models indicate that no grey cloud deck
is required to fit WASP-96b's transmission spectrum, but find evidence for a
slope shortward of 0.9m, which could either be caused by enhanced Rayleigh
scattering or the red wing of a pressure-broadened Na feature. Our work
demonstrates the unique capabilities of the SOSS mode for exoplanet
transmission spectroscopy and presents a step-by-step reduction guide for this
new and exciting instrument.Comment: MNRAS, in press. Updated to reflect published versio
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