44,170 research outputs found
The Spectroscopic Orbits of Three Double-lined Eclipsing Binaries: I. BG Ind, IM Mon, RS Sgr
We present the spectroscopic orbit solutions of three double-lines eclipsing
binaries, BG Ind, IM Mon and RS Sgr. The first precise radial velocities (RVs)
of the components were determined using high resolution echelle spectra
obtained at Mt. John University Observatory in New Zealand. The RVs of the
components of BG Ind and RS Sgr were measured using Gaussian fittings to the
selected spectral lines, whereas two-dimensional cross-correlation technique
was preferred to determine the RVs of IM Mon since it has relatively short
orbital period among the other targets and so blending of the lines is more
effective. For all systems, the Keplerian orbital solution was used during the
analysis and also circular orbit was adopted because the eccentricities for all
targets were found to be negligible. The first precise orbit analysis of these
systems gives the mass ratios of the systems as 0.894, 0.606 and 0.325,
respectively for BG Ind, IM Mon and RS Sgr. Comparison of the mass ratio
values, orbital sizes and minimum masses of the components of the systems
indicates that all systems should have different physical, dynamical and
probable evolutionary status.Comment: 17 pages, 6 figures and 4 tables, accepted for publication in New
Astronom
Absolute dimensions of eclipsing binaries. XXIV, The Be star system DW Carinae, a member of the open cluster Collinder 228
Context. The study of detached eclipsing binaries which are members of stellar clusters is is a powerful way of determining the properties of the cluster and of constraining the physical ingredients of theoretical stellar evolutionary models.
Aims. DWCarinae is a close but detached early B-type eclipsing binary in the young open cluster Collinder 228. We have measured accurate physical properties of the components of DWCar (masses and radii to 1%, effective temperatures to 0.02 dex) and used these to derive the age, metallicity and distance of Collinder 228.
Methods. The rotational velocities of both components of DWCar are high, so we have investigated the performance of double-Gaussian fitting, one- and two-dimensional cross-correlation and spectral disentangling for deriving spectroscopic radial velocites in the presence of strong line blending. Gaussian and cross-correlation analyses require substantial corrections for the effects of line
blending, which are only partially successful for cross-correlation. Spectral disentangling is to be preferred because it does not assume anything about the shapes of spectral lines, and is not significantly affected by blending. However, it suffers from a proliferation
of local minima in the least-squares fit. We show that the most reliable radial velocities are obtained using spectral disentangling constrained by the results of Gaussian fitting. Complete Strömgren uvby light curves have been obtained and accurate radii have been measured from them by modelling the light curves using the Wilson-Devinney program. This procedure also suffers from the
presence of many local minima in parameter space, so we have constrained the solution using an accurate spectroscopic light ratio. The effective temperatures and reddening of the system have been found from Strömgren photometric calibrations.
Results. The mass and radius of DWCarA are MA = 11.34 ± 0.12 M and RA = 4.558 ± 0.045 R. The values for DWCar B are MB =10.63 ± 0.14 M and RB = 4.297 ± 0.055 R. Strömgren photometric calibrations give effective temperatures of TeffA = 27 900 ±1000 K and TeffB = 26 500 ± 1000 K, and a reddening of Eb−y = 0.18 ± 0.02, where the quoted uncertainties include a contribution from the intrinsic uncertainty of the calibrations. The membership of DWCar in Cr 228 allows us to measure the distance, age and chemical composition of the cluster. We have used empirical bolometric corrections to calculate a distance modulus of 12.24 ±0.12 mag for DWCar, which is in agreement with, and more accurate than, literature values. A comparison between the properties of DWCar and the predictions of recent theoretical evolutionary models is undertaken in the mass-radius and mass-Teff diagrams. The
model predictions match the measured properties of DWCar for an age of about 6 Myr and a fractional metal abundance of Z ≈ 0.01
Analytical and experimental FWHM of a gamma camera: theoretical and practical issues
It is well known that resolution on a gamma camera varies as a
function of distance, scatter and the camera\u2019s characteristics (collimator type,
crystal thickness, intrinsic resolution etc). Manufacturers frequently provide only
a few pre-calculated resolution values (using a line source in air, 10\u201315 cm from
the collimator surface and without scattering). However, these are typically not
obtained in situations resembling a clinical setting. From a diagnostic point of view,
it is useful to know the expected resolution of a gamma camera at a given distance
from the collimator surface for a particular setting in order to decide whether it is
worth scanning patients with \u201csmall lesion\u201d or not. When dealing with absolute
quantification it is also mandatory to know precisely the expected resolution and its
uncertainty in order to make appropriate corrections.
Aim. Our aims are: to test a novel mathematical approach, the cubic spline interpolation,
for the extraction of the full width at half maximum (FWHM) from the
acquisition of a line source (experimental resolution) also considering measurement
uncertainty; to compare it with the usually adopted methods such as the gaussian
approach; to compare it with the theoretical resolution (analytical resolution) of a
gamma camera at different distances; to create a web-based educational program
with which to test these theories.
Methods. Three mathematical methods (direct calculation, global interpolation using
gaussian and local interpolation using splines) for calculatingFWHMfroma line
source (planar scintigraphy) were tested and compared. A NEMA Triple Line Source
Phantom was used to obtain static images both in air and with different scattering
levels. An advanced, open-source software (MATLAB/Octave and PHP based) was
created \u201cad hoc\u201d to obtain and compareFWHMvalues and relative uncertainty.
Results and Conclusion. Local interpolation using splines proved faster and more
reliable than the usually-adopted Gaussian interpolation. The proposed freely available
software proved effective in assessing bothFWHMand its uncertainty
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