195 research outputs found
Recent X-Ray Observations of SN1986J with ASCA and ROSAT
We present ASCA and ROSAT observations of SN 1986J covering the period 1991
August to 1996 January. From observations with the ROSAT HRI and PSPC, we find
that the 0.5-2.5 keV flux decreased proportional to during this
period; the ASCA data are consistent with this result and extend it to the 2-10
keV band. ASCA spectra from 1994 January and 1996 January are consistent with
thermal emission from a solar metallicity plasma at an equilibrium temperature
kT = 5-7.5 keV, somewhat hotter than that observed from other X-ray supernovae.
These spectra also show a clear Fe K emission line at 6.7 keV with FWHM <
20,000 km/s (90% confidence). This limit on the line width is consistent with
the reverse shock model of Chevalier & Fransson (1994), but does not rule out
the clumpy wind model of Chugai (1993).Comment: 20 pages, 9 postscript figures, latex, uses aastex4.0, submitted to
The Astrophysical Journa
Double-Peaked X-Ray Lines from the Oxygen/Neon-Rich Accretion Disk in 4U1626-67
We report on a 39 ks observation of the 7.7-s low-mass X-ray binary pulsar
4U1626-67 with the High Energy Transmission Grating Spectrometer (HETGS) on the
Chandra X-Ray Observatory. This ultracompact system consists of a
disk-accreting magnetic neutron star and a very low mass, hydrogen-depleted
companion in a 42-min binary. We have resolved the previously reported Ne/O
emission line complex near 1 keV into Doppler pairs of broadened (2500 km/s
FWHM) lines from highly ionized Ne and O. In most cases, the blue and red line
components are of comparable strength, with blueshifts of 1550-2610 km/s and
redshifts of 770-1900 km/s. The lines appear to originate in hot (10^6 K),
dense material just below the X-ray-heated skin of the outer Keplerian
accretion disk, or else possibly in a disk wind driven from the pulsar's
magnetopause. The observed photoelectric absorption edges of Ne and O appear
nearly an order of magnitude stronger than expected from interstellar material
and are likely formed in cool, metal-rich material local to the source. Based
on the inferred local abundance ratios, we argue that the mass donor in this
binary is probably the 0.02 M_sun chemically fractionated core of a C-O-Ne or
O-Ne-Mg white dwarf which has previously crystallized.Comment: 9 pages. Accepted for publication in ApJ. Table 2 correcte
Discovery of a Bright Field Methane (T-type) Brown Dwarf by 2MASS
We report the discovery of a bright (J = 13.830.03) methane brown dwarf,
or T dwarf, by the Two Micron All Sky Survey. This object, 2MASSI
J0559191-140448, is the first brown dwarf identified by the newly commissioned
CorMASS instrument mounted on the Palomar 60-inch Telescope. Near-infrared
spectra from 0.9 - 2.35 \micron show characteristic CH bands at 1.1, 1.3,
1.6, and 2.2 \micron, which are significantly shallower than those seen in
other T dwarfs discovered to date. Coupled with the detection of an FeH band at
0.9896 \micron and two sets of K I doublets at J-band, we propose that 2MASS
J0559-14 is a warm T dwarf, close to the transition between L and T spectral
classes. The brightness of this object makes it a good candidate for detailed
investigation over a broad wavelength regime and at higher resolution.Comment: 21 pages, 3 figures, 2 tables, accepted to AJ for publication August
200
Spatially Resolved Chandra HETG Spectroscopy of the NLR Ionization Cone in NGC 1068
We present initial results from a new 440-ks Chandra HETG GTO observation of
the canonical Seyfert 2 galaxy NGC 1068. The proximity of NGC 1068, together
with Chandra's superb spatial and spectral resolution, allow an unprecedented
view of its nucleus and circumnuclear NLR. We perform the first spatially
resolved high-resolution X-ray spectroscopy of the `ionization cone' in any
AGN, and use the sensitive line diagnostics offered by the HETG to measure the
ionization state, density, and temperature at discrete points along the ionized
NLR. We argue that the NLR takes the form of outflowing photoionized gas,
rather than gas that has been collisionally ionized by the small-scale radio
jet in NGC 1068. We investigate evidence for any velocity gradients in the
outflow, and describe our next steps in modeling the spatially resolved spectra
as a function of distance from the nucleus.Comment: 5 pages, 2 figures, 1 video. To appear in refereed Proceedings of
"X-ray Astronomy 2009: Present Status, Multi-Wavelength Approach and Future
Perspectives", Bologna, Italy, September 7-11, 2009, AIP, eds. A. Comastri,
M. Cappi, and L. Angelin
Determining Success or Failure After Foot and Ankle Surgery Using Patient Acceptable Symptom State (PASS) and Patient Reported Outcome Information System (PROMIS)
Background: As the role of generic patient-reported outcomes (PROs) expands, important questions remain about their interpretation. In particular, how the Patient Reported Outcome Measurement Instrumentation System (PROMIS) t score values correlate with the patientsâ perception of success or failure (S/F) of their surgery is unknown. The purposes of this study were to characterize the association of PROMIS t scores, the patientsâ perception of their symptoms (patient acceptable symptom state [PASS]), and determination of S/F after surgery.
Methods: This retrospective cohort study contacted patients after the 4 most common foot and ankle surgeries at a tertiary academic medical center (n = 88). Patient outcome as determined by phone interviews included PASS and patientsâ judgment of whether their surgery was a S/F. Assessment also included PROMIS physical function (PF), pain interference (PI), and depression (D) scales. The association between S/F and PASS outcomes was evaluated by chi-square analysis. A 2-way analysis of variance (ANOVA) evaluated the ability of PROMIS to discriminate PASS and/or S/F outcomes. Receiver operator curve (ROC) analysis was used to evaluate the ability of pre- (n = 63) and postoperative (n = 88) PROMIS scores to predict patient outcomes (S/F and PASS). Finally, the proportion of individuals classified by the identified thresholds were evaluated using chi-square analysis.
Results: There was a strong association between PASS and S/F after surgery (chi-square \u3c0.01). Two-way ANOVA demonstrated that PROMIS t scores discriminate whether patients experienced positive or negative outcome for PASS (P \u3c .001) and S/F (P \u3c .001). The ROC analysis showed significant accuracy (area under the curve \u3e 0.7) for postoperative but not preoperative PROMIS t scores in determining patient outcome for both PASS and S/F. The proportion of patients classified by applying the ROC analysis thresholds using PROMIS varied from 43.0% to 58.8 % for PASS and S/F.
Conclusions: Patients who found their symptoms and activity at a satisfactory level (ie, PASS yes) also considered their surgery a success. However, patients who did not consider their symptoms and activity at a satisfactory level did not consistently consider their surgery a failure. PROMIS t scores for physical function and pain demonstrated the ability to discriminate and accurately predict patient outcome after foot and ankle surgery for 43.0% to 58.8% of participants. These data improve the clinical utility of PROMIS scales by suggesting thresholds for positive and negative patient outcomes independent of other factors.
Level of Evidence: II, prospective comparative series
The effect of national and constituency level expectations on tactical voting in the British general election of 2010
The 2010 elections in the United Kingdom provided voters with numerous and diverse opportunities to reason strategically. The Liberal Democrats (Lib Dems)-traditionally finishing a distant third in terms of seats in Parliament-vied with labour to be the principal competition to the Conservatives, who failed to win a majority of seats, creating a rare case of what the British call a hung parliament. These conditions varied across constituencies at the district level, and we exploit this variation to study the incidence of "tactical" voting. But the national outcome also presented strategic considerations for voters, and the conditions varied to some extent over the course of the campaign, giving voters interviewed at different times different sets of national considerations for tactical voting. This presents us with the opportunity to investigate how both local and national considerations may shape strategic reasoning among voters and relate to each other and to the final choices of voters on Election Day
Spitzer Infrared Spectrograph Observations of M, L, and T Dwarfs
We present the first mid-infrared spectra of brown dwarfs, together with
observations of a low-mass star. Our targets are the M3.5 dwarf GJ 1001A, the
L8 dwarf DENIS-P J0255-4700, and the T1/T6 binary system epsilon Indi Ba/Bb. As
expected, the mid-infrared spectral morphology of these objects changes rapidly
with spectral class due to the changes in atmospheric chemistry resulting from
their differing effective temperatures and atmospheric structures. By taking
advantage of the unprecedented sensitivity of the Infrared Spectrograph on the
Spitzer Space Telescope we have detected the 7.8 micron methane and 10 micron
ammonia bands for the first time in brown dwarf spectra.Comment: 4 pages, 2 figure
Models for Nonthermal Photon Spectra
We describe models of nonthermal photon emission from a homogeneous
distribution of relativistic electrons and protons. Contributions from the
synchrotron, inverse Compton, nonthermal bremsstrahlung and neutral-pion decay
processes are computed separately using a common parameterization of the
underlying distribution of nonthermal particles. The models are intended for
use in fitting spectra from multi-wavelength observations and are designed to
be accurate and efficient. Although our applications have focused on Galactic
supernova remnants, the software is modular, making it straightforward to
customize for different applications. In particular, the shapes of the particle
distribution functions and the shape of the seed photon spectrum used by the
inverse Compton model are defined in separate modules and may be customized for
specific applications. We assess the accuracy of these models by using a
recurrence relation and by comparing them with analytic results and with
previous numerical work by other authors.Comment: 14 pages, 7 figures, Accepted for publication in ApJ Supplemen
The Neon Abundance of Galactic Wolf-Rayet Stars
The fast, dense winds which characterize Wolf-Rayet (WR) stars obscure
their underlying cores, and complicate the verification of evolving
core and nucleosynthesis models. Core evolution can be probed by
measuring abundances of wind-borne nuclear processed elements,
partially overcoming this limitation. Using ground-based mid-infrared
spectroscopy and the 12.81um [NeII] emission line measured in
four Galactic WR stars, we estimate neon abundances and compare to
long-standing predictions from evolved-core models. For the WC star
WR121, this abundance is found to be >~11x the cosmic
value, in good agreement with predictions. For the three less-evolved
WN stars, little neon enhancement above cosmic values is measured, as
expected. We discuss the impact of clumping in WR winds on this
measurement, and the promise of using metal abundance ratios to
eliminate sensitivity to wind density and ionization structure.Comment: Accepted for publication in ApJ; 9 pages, 2 color figures, 4 table
Organic Molecules and Water in the Inner Disks of T Tauri Stars
We report high signal-to-noise Spitzer IRS spectra of a sample of eleven
classical T Tauri stars. Molecular emission from rotational transitions of H2O
and OH and ro-vibrational bands of simple organic molecules (CO2, HCN, C2H2) is
common among the sources in the sample. The gas temperatures (200-800 K) and
emitting areas we derive are consistent with the emission originating in a warm
disk atmosphere in the inner planet formation region at radii < 2 AU. The H2O
emission appears to form under a limited range of excitation conditions, as
shown by the similarity in relative strengths of H2O features from star to star
and the narrow range in derived temperature and column density. Emission from
highly excited rotational levels of OH is present in all stars; the OH emission
flux increases with the stellar accretion rate, and the OH/H2O flux ratio shows
a relatively small scatter. We interpret these results as evidence for OH
production via FUV photo-dissociation of H2O in the disk surface layers. No
obvious explanation is found for the observed range in the relative emission
strengths of different organic molecules or in their strength with respect to
water. We put forward the possibility that these variations reflect a diversity
in organic abundances due to star-to-star differences in the C/O ratio of the
inner disk gas. Stars with the largest HCN/H2O flux ratios in our sample have
the largest disk masses. We speculate that such a trend could result if higher
mass disks are more efficient at planetesimal formation and sequestration of
water in the outer disk, leading to enhanced C/O ratios and abundances of
organic molecules in the inner disk. A comparison of our derived HCN to H2O
column density ratio to comets, hot cores, and outer T Tauri star disks
suggests that the inner disks are chemically active.Comment: Accepted for publication in The Astrophysical Journa
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