6,648 research outputs found
Spectroscopy Made Easy: A New Tool for Fitting Observations with Synthetic Spectra
We describe a new software package that may be used to determine stellar and atomic parameters by matching observed spectra with synthetic spectra generated from parameterized atmospheres. A nonlinear least squares algorithm is used to solve for any subset of allowed parameters, which include atomic data (log gf and van der Waals damping constants), model atmosphere specifications (T(sub eff, log g), elemental abundances, and radial, turbulent, and rotational velocities. LTE synthesis software handles discontiguous spectral intervals and complex atomic blends. As a demonstration, we fit 26 Fe I lines in the NSO Solar Atlas (Kurucz et al.), determining various solar and atomic parameters
The Far-Ultraviolet Spectra of TW Hya. II. Models of H2 Fluorescence in a Disk
We measure the temperature of warm gas at planet-forming radii in the disk
around the classical T Tauri star (CTTS) TW Hya by modelling the H2
fluorescence observed in HST/STIS and FUSE spectra. Strong Ly-alpha emission
irradiates a warm disk surface within 2 AU of the central star and pumps
certain excited levels of H2. We simulate a 1D plane-parallel atmosphere to
estimate fluxes for the 140 observed H2 emission lines and to reconstruct the
Ly-alpha emission profile incident upon the warm H2. The excitation of H2 can
be determined from relative line strengths by measuring self-absorption in
lines with low-energy lower levels, or by reconstructing the Ly-alpha profile
incident upon the warm H2 using the total flux from a single upper level and
the opacity in the pumping transition. Based on those diagnostics, we estimate
that the warm disk surface has a column density of log
N(H2)=18.5^{+1.2}_{-0.8}, a temperature T=2500^{+700}_{-500} K, and a filling
factor of H2, as seen by the source of Ly-alpha emission, of 0.25\pm0.08 (all
2-sigma error bars). TW Hya produces approximately 10^{-3} L_\odot in the FUV,
about 85% of which is in the Ly-alpha emission line. From the H I absorption
observed in the Ly-alpha emission, we infer that dust extinction in our line of
sight to TW Hya is negligible.Comment: Accepted by ApJ. 26 pages, 17 figures, 6 table
Reinforcing the link between the double red clump and the X-shaped bulge of the Milky Way
The finding of a double red clump in the luminosity function of the Milky Way bulge has been interpreted as evidence for an X-shaped structure. Recently, an alternative explanation has been suggested, where the double red clump is an effect of multiple stellar populations in a classical spheroid. In this Letter we provide an observational assessment of this scenario and show that it is not consistent with the behaviour of the red clump across different lines of sight, particularly at high distances from the Galactic plane. Instead, we confirm that the shape of the red clump magnitude distribution closely follows the distance distribution expected for an X-shaped bulge at critical Galactic latitudes. We also emphasize some key observational properties of the bulge red clump that should not be neglected in the search for alternative scenarios
Stellar density profile and mass of the Milky Way Bulge from VVV data
We present the first stellar density profile of the Milky Way bulge reaching
latitude . It is derived by counting red clump stars within the
colour\--magnitude diagram constructed with the new PSF-fitting photometry from
VISTA Variables in the V\'\i a L\'actea (VVV) survey data. The new stellar
density map covers the area between and
with unprecedented accuracy, allowing to establish a direct link between the
stellar kinematics from the Giraffe Inner Bulge Spectroscopic Survey (GIBS) and
the stellar mass density distribution. In particular, the location of the
central velocity dispersion peak from GIBS matches a high overdensity in the
VVV star count map. By scaling the total luminosity function (LF) obtained from
all VVV fields to the LF from Zoccali et al.(2003), we obtain the first fully
empirical estimate of the mass in stars and remnants of the Galactic bulge.
The Milky Way bulge stellar mass within (, ) is
.Comment: 4 pages, 5 figures, accepted for publication on A&
CT scan evaluation of glenoid component fixation: a prospective study of 27 minimally cemented shoulder arthroplasties
BACKGROUND: Glenoid component failure is the most common complication of total shoulder arthroplasty. It can be correlated with failure of the component itself to resist wear and deformation, failure of fixation or failure of the glenoid bone. Anchor Peg Glenoid component (Depuy(®)) seems to have a higher bone fixation in biomechanical canine model: it is a all-polyethylene, concave component with one circumferentially fluted, central, interference-fit peg and three small cemented peripheral pegs. MATERIALS AND METHODS: We realized a prospective study of Anchor Peg total shoulder arthroplasty, included 27 patients suffering from primary arthrosis or arthritis, without rotator cuff tear. A clinical and radiographic evaluation was performed at 3 months, 1 and 2 years; a CT scan was made in postoperative and analyzed central peg’s bone integration 1 year later. RESULTS: Improvement of postoperative Constant score and radiographic good results were correlated with satisfactory subjective results reported by patients. We observed radiolucent lines under glenoid component in 3 cases. Twenty-six CT scans were available at 1 year: it showed complete bone integration around the central peg in 21 cases and partial peripheral bone integration in four cases. Only one patient had any tissue integration around the peg, probably because of his implantation near cortical bone of scapular spine. DISCUSSION/CONCLUSION: Long-term result of arthroplasty is correlated with glenoid durable fixation to underlying bone: this study shows higher fixation of glenoid component with bone integration of central peg. However, these results will have to be confirmed in a later revision
The WFC3 Galactic Bulge Treasury Program: Metallicity Estimates for the Stellar Population and Exoplanet Hosts
We present new UV-to-IR stellar photometry of four low-extinction windows in
the Galactic bulge, obtained with the Wide Field Camera 3 on the Hubble Space
Telescope (HST). Using our five bandpasses, we have defined reddening-free
photometric indices sensitive to stellar effective temperature and metallicity.
We find that the bulge populations resemble those formed via classical
dissipative collapse: each field is dominated by an old (~10 Gyr) population
exhibiting a wide metallicity range (-1.5 < [Fe/H] < 0.5). We detect a
metallicity gradient in the bulge population, with the fraction of stars at
super-solar metallicities dropping from 41% to 35% over distances from the
Galactic center ranging from 0.3 to 1.2 kpc. One field includes candidate
exoplanet hosts discovered in the SWEEPS HST transit survey. Our measurements
for 11 of these hosts demonstrate that exoplanets in the distinct bulge
environment are preferentially found around high-metallicity stars, as in the
solar neighborhood, supporting the view that planets form more readily in
metal-rich environments.Comment: Accepted for publication in The Astrophysical Journal Letters. Latex,
5 pages, ApJ forma
Time-Varying Potassium in High-Resolution Spectra of the Type Ia Supernova 2014J
We present a time series of the highest resolution spectra yet published for
the nearby Type Ia supernova (SN) 2014J in M82. They were obtained at 11 epochs
over 33 days around peak brightness with the Levy Spectrograph (resolution
R~110,000) on the 2.4m Automated Planet Finder telescope at Lick Observatory.
We identify multiple Na I D and K I absorption features, as well as absorption
by Ca I H & K and several of the more common diffuse interstellar bands (DIBs).
We see no evolution in any component of Na I D, Ca I, or in the DIBs, but do
establish the dissipation/weakening of the two most blueshifted components of K
I. We present several potential physical explanations, finding the most
plausible to be photoionization of circumstellar material, and discuss the
implications of our results with respect to the progenitor scenario of SN
2014J.Comment: 11 pages, 8 figures, 3 tables, submitted to Ap
Impact of the implantable cardioverter-defibrillator on rehospitalizations
Patients who survive out-of-hospital ventricular tachycardia or ventricular fibrillation are at risk of sudden cardiac death and often return to hospital after initial discharge. The frequency and duration of readmittance to hospital are not well known. Thus, the purpose of this study was to evaluate the impact of the implantable cardioverter defibrillator on frequency and duration of hospitalizations. Methods Between 1989 and 1993, 38 consecutive patients who had drug-refractory ventricular tachyarrhythmias were selected for the study. A total of 38 patients were implanted with the implantable cardioverter-defibrillator in accordance with the guidelines of the European Society of Cardiology. This analysis includes 35 of the 38 patients (92%). All hospitalizations which occurred one year before and one year after were studied. Clinical information for all patients was obtained by consulting medical records and by interviewing personal general practitioners. Results The annual number of hospitalizations before and after implantation of the implantable cardioverter defibrillator was, respectively, 3·28 ± 2 hospitalizations/patient/year and 0·88 ± 1·23 hospitalizations/patient/year (P<0·05). Before implantation of the implantable cardioverter-defibrillator, patients were hospitalized a mean of 32·94 plusmn; 24·18 days/patient/year and after, 9·31 ± 32·14 days/patient/year (P<0·05). The number of hospitalizations for cardiac reasons decreased by 90%. Before implantation, the most frequent cause was ventricular tachyarrhythmia (47 hospitalizations for ventricular tachycardia and eight for ventricular fibrillation), while after implantation, it was as a result of the shock from the implantable cardioverter defibrillator (II hospitalizations). The number of hospitalizations for non-cardiac reasons were similar in the two time periods. Of the 35 patients, 26 (74%) had at least one appropriate successful ventricular tachycardia interrupted by the implantable cardioverter-defibrillator, while 17 patients (49%) had their ventricular fibrillation terminated. There is a significant difference in the rate of hospitalizations to intensive care units (ICU) between the two periods. Before implantation, 30% of hospital days were spent in the ICU, with 3% after. Conclusions This study documents that the implantable cardioverter-defibrillator not only reduces the frequency and duration of hospital stays, but reduces admissions to the more expensive units in hospital. Taking into account the reduction in hospitalizations, the payback period for the implantation of an implantable cardioverter-defibrillator is 19 months. (Eur Heart J 1996; 17: 1565-1571
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