1,380 research outputs found
Economic Deposits at Blue Hill
Guidebook for field trips in east-central and north-central Maine: 66th annual meeting October 12 and 13, 1974: Trip B-
A 33 year constancy of the X-ray coronae of AR Lac and eclipse diagnosis of scale height
Extensive X-ray and extreme ultraviolet (EUV) photometric observations of the
eclipsing RS CVn system AR Lac were obtained over the years 1997 to 2013 with
the Chandra X-ray Observatory Extreme Ultraviolet Explorer. During primary
eclipse, HRC count rates decrease by ~40%. A similar minimum is seen during one
primary eclipse observed by EUVE but not in others owing to intrinsic source
variability. Little evidence for secondary eclipses is present in either the
X-ray or EUV data, reminiscent of earlier X-ray and EUV observations. Primary
eclipses allow us to estimate the extent of a spherically symmetric corona on
the primary G star of about 1.3Rsun, or 0.86Rstar, and indicate the G star is
likely brighter than the K component by a factor of 2-5. Brightness changes not
attributable to eclipses appear to be dominated by stochastic variability and
are generally non-repeating. X-ray and EUV light curves cannot therefore be
reliably used to reconstruct the spatial distribution of emission assuming only
eclipses and rotational modulation are at work. Moderate flaring is observed,
where count rates increase by up to a factor of three above quiescence.
Combined with older ASCA, Einstein, EXOSAT, ROSAT and Beppo-SAX observations,
the data show that the level of quiescent coronal emission at X-ray wavelengths
has remained remarkably constant over 33 years, with no sign of variation due
to magnetic cycles. Variations in base level X-ray emission seen by Chandra
over 13 years are only ~10%, while variations back to pioneering Einstein
observations in 1980 amount to a maximum of 45% and more typically about 15%.Comment: To appear in the Astrophysical Journa
The Equivalence Principle as a Stepping Stone from Special to General Relativity: A Socratic Dialog
In this paper we show how the student can be led to an understanding of the
connection between special relativity and general relativity by considering the
time dilation effect of clocks placed on the surface of the Earth. This paper
is written as a Socratic dialog between a lecturer Sam and a student Kim.Comment: 8 pages, 1 figure, uses the revtex4 documentclass. Submitted to the
American Journal of Physics. Minor modification and corrections following
referees' comment
Geometry Diagnostics of a Stellar Flare from Fluorescent X-rays
We present evidence of Fe fluorescent emission in the Chandra HETGS spectrum
of the single G-type giant HR 9024 during a large flare. In analogy to solar
X-ray observations, we interpret the observed Fe K line as being
produced by illumination of the photosphere by ionizing coronal X-rays, in
which case, for a given Fe photospheric abundance, its intensity depends on the
height of the X-ray source. The HETGS observations, together with 3D Monte
Carlo calculations to model the fluorescence emission, are used to obtain a
direct geometric constraint on the scale height of the flaring coronal plasma.
We compute the Fe fluorescent emission induced by the emission of a single
flaring coronal loop which well reproduces the observed X-ray temporal and
spectral properties according to a detailed hydrodynamic modeling. The
predicted Fe fluorescent emission is in good agreement with the observed value
within observational uncertainties, pointing to a scale height \rstar. Comparison of the HR 9024 flare with that recently observed on II
Peg by Swift indicates the latter is consistent with excitation by X-ray
photoionization.Comment: accepted for publication on the Astrophysical Journal Letter
A Home Device for Vestibular Stimulation
The goal of this project, which was presented to the team by Kevin Maher (President of Advanced Therapeutic devices), was to develop a product prototype for safe, vestibular stimulation for children with developmental disabilities. Vestibular stimulation is a form of therapy that increases muscle coordination. It works by stimulating the canals and sacs within the inner ear that detect accelerations. The project targeted children from ages two to seven years old, under 48 inches tall, and less than 100 lbs. The production device also sought to differ from stimulation devices found in hospitals in a few respects: it would cost under 1700 and no more than 500 lb. The design met all of the requirements and had adequate safety for any child’s needs, but the team thought the design needed significant changes before it became a final product
X-ray Flares of EV Lac: Statistics, Spectra, Diagnostics
We study the spectral and temporal behavior of X-ray flares from the active
M-dwarf EV Lac in 200 ks of exposure with the Chandra/HETGS. We derive flare
parameters by fitting an empirical function which characterizes the amplitude,
shape, and scale. The flares range from very short (<1 ks) to long (10 ks)
duration events with a range of shapes and amplitudes for all durations. We
extract spectra for composite flares to study their mean evolution and to
compare flares of different lengths. Evolution of spectral features in the
density-temperature plane shows probable sustained heating. The short flares
are significantly hotter than the longer flares. We determined an upper limit
to the Fe K fluorescent flux, the best fit value being close to what is
expected for compact loops.Comment: 9 pages; 9 figures; latex/emulateapj style; Submitted to The
Astrophysical Journa
3.6 and 4.5 μm Phase Curves and Evidence for Non-equilibrium Chemistry in the Atmosphere of Extrasolar Planet HD 189733b
We present new, full-orbit observations of the infrared phase variations of the canonical hot Jupiter HD 189733b obtained in the 3.6 and 4.5 μm bands using the Spitzer Space Telescope. When combined with previous phase curve observations at 8.0 and 24 μm, these data allow us to characterize the exoplanet's emission spectrum as a function of planetary longitude and to search for local variations in its vertical thermal profile and atmospheric composition. We utilize an improved method for removing the effects of intrapixel sensitivity variations and robustly extracting phase curve signals from these data, and we calculate our best-fit parameters and uncertainties using a wavelet-based Markov Chain Monte Carlo analysis that accounts for the presence of time-correlated noise in our data. We measure a phase curve amplitude of 0.1242% ± 0.0061% in the 3.6 μm band and 0.0982% ± 0.0089% in the 4.5 μm band, corresponding to brightness temperature contrasts of 503 ± 21 K and 264 ± 24 K, respectively. We find that the times of minimum and maximum flux occur several hours earlier than predicted for an atmosphere in radiative equilibrium, consistent with the eastward advection of gas by an equatorial super-rotating jet. The locations of the flux minima in our new data differ from our previous observations at 8 μm, and we present new evidence indicating that the flux minimum observed in the 8 μm is likely caused by an overshooting effect in the 8 μm array. We obtain improved estimates for HD 189733b's dayside planet-star flux ratio of 0.1466% ± 0.0040% in the 3.6 μm band and 0.1787% ± 0.0038% in the 4.5 μm band, corresponding to brightness temperatures of 1328 ± 11 K and 1192 ± 9 K, respectively; these are the most accurate secondary eclipse depths obtained to date for an extrasolar planet. We compare our new dayside and nightside spectra for HD 189733b to the predictions of one-dimensional radiative transfer models from Burrows et al. and conclude that fits to this planet's dayside spectrum provide a reasonably accurate estimate of the amount of energy transported to the night side. Our 3.6 and 4.5 μm phase curves are generally in good agreement with the predictions of general circulation models for this planet from Showman et al., although we require either excess drag or slower rotation rates in order to match the locations of the measured maxima and minima in the 4.5, 8.0, and 24 μm bands. We find that HD 189733b's 4.5 μm nightside flux is 3.3σ smaller than predicted by these models, which assume that the chemistry is in local thermal equilibrium. We conclude that this discrepancy is best explained by vertical mixing, which should lead to an excess of CO and correspondingly enhanced 4.5 μm absorption in this region. This result is consistent with our constraints on the planet's transmission spectrum, which also suggest excess absorption in the 4.5 μm band at the day-night terminator
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