7,385 research outputs found
The Angular Separation of the Components of the Cepheid AW Per
The 6.4 day classical Cepheid AW Per is a spectroscopic binary with a period
of 40 years. Analyzing the centroids of HST/STIS spectra obtained in November
2001, we have determined the angular separation of the binary system. Although
we currently have spatially resolved data for a single epoch in the orbit, the
success of our approach opens the possibility of determining the inclination,
sini, for the system if the measurements are repeated at additional epochs.
Since the system is potentially a double lined spectroscopic binary, the
combination of spectroscopic orbits for both components and the visual orbit
would give the distance to the system and the masses of its components, thereby
providing a direct measurement of a Cepheid mass.Comment: 12 pages, accepted version -- minor change
Mass loss rates from mid-IR excesses in LMC and SMC O stars
We use a combination of BVJHK and Spitzer [3.6], [5.8] and [8.0] photometry
to determine IR excesses for a sample of 58 LMC and 46 SMC O stars. This sample
is ideal for determining IR excesses because the very small line of sight
reddening minimizes uncertainties due to extinction corrections. We use the
core-halo model developed by Lamers & Waters (1984a) to translate the excesses
into mass loss rates and demonstrate that the results of this simple model
agree with the more sophisticated CMFGEN models to within a factor of 2. Taken
at face value, the derived mass loss rates are larger than those predicted by
Vink et al. (2001), and the magnitude of the disagreement increases with
decreasing luminosity. However, the IR excesses need not imply large mass loss
rates. Instead, we argue that they probably indicate that the outer atmospheres
of O stars contain complex structures and that their winds are launched with
much smaller velocity gradients than normally assumed. If this is the case, it
could affect the theoretical and observational interpretations of the "weak
wind" problem, where classical mass loss indicators suggest that the mass loss
rates of lower luminosity O stars are far less than expected.Comment: 15 pages, 10 figures. Accepted for publication in MNRA
The effects of clumping on wind line variability
We review the effects of clumping on the profiles of resonance doublets. By
allowing the ratio of the doublet oscillator strenghts to be a free parameter,
we demonstrate that doublet profiles contain more information than is normally
utilized. In clumped (or porous) winds, this ratio can lies between unity and
the ratio of the f-values, and can change as a function of velocity and time,
depending on the fraction of the stellar disk that is covered by material
moving at a particular velocity at a given moment. Using these insights, we
present the results of SEI modeling of a sample of B supergiants, zeta Pup and
a time series for a star whose terminal velocity is low enough to make the
components of its Si IV 1400 doublet independent. These results are interpreted
within the framework of the Oskinova et al. (2007) model, and demonstrate how
the doublet profiles can be used to extract infromation about wind structure.Comment: 3 pages, to appear in Clumping in Hot Star Winds, W.-R. Hamann, A.
Feldmeier & L. Oskinova, eds., Potsdam: Univ.-Verl., 2007, URN:
http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-1398
Signature of wide-spread clumping in B supergiant winds
We seek to establish additional observational signatures of the effects of
clumping in OB star winds. The action of clumping on strategic wind-formed
spectral lines is tested to steer the development of models for clumped winds
and thus improve the reliability of mass-loss determinations for massive
stars.The SiIV 1400 resonance line doublets of B0 to B5 supergiants are
analysed using empirical line-synthesis models. The focus is on decoding
information on wind clumping from measurements of ratios of the radial optical
depths (tau_(rad)(w)) of the red and blue components of the SiIV doublet. We
exploit in particular the fact that the two doublet components are decoupled
and formed independently for targets with relatively low wind terminal
velocities. Line-synthesis analyses reveal that the mean ratio of tau_(rad)(w)
of the blue to red SiIV components are rarely close to the canonical value of ~
2 (expected from atomic constants), and spread instead over a range of values
between ~1 and 2. These results are interpreted in terms of a photosphere that
is partially obscured by optically thick structures in the outflowing gas.The
spectroscopic signatures established in this study demonstrate the wide-spread
existence of wind clumping in B supergiants. The additional information in
unsaturated doublet profiles provides a means to quantify the porosity of the
winds.Comment: Accepted for publication in A&A Letter
Effectiveness of nutrition diagnosis and intervention
This study is designed to investigate whether the current system of administering fluid to enteral nutrition patients in a mid-sized community hospital is effective based on the enteral feeding order, outcomes recorded by the dietitian in the medical record, or comparison to widely- accepted standards for estimating fluid needs. Data of this retrospective chart review came from 566 medical records that were pulled based on admission date within a one year time span and an order for enteral nutrition (EN) during the patient’s stay. Out of these, 107 records were used due to incomplete chart documentation and inaccessibility of medical records. Results were analyzed using SPSS to compare the amount of EN ordered and the amount given; the amount of EN given and the total fluid intake of the patient; and a comparison of serum electrolyte values as compared to normal standards for the respective hydration levels. The findings show that EN orders are not consistently being followed, and patients tend to be overfed, though their laboratory values do not confirm that they are being overhydrated
Determining the Physical Properties of the B Stars I. Methodology and First Results
We describe a new approach to fitting the UV-to-optical spectra of B stars to
model atmospheres and present initial results. Using a sample of lightly
reddened stars, we demonstrate that the Kurucz model atmospheres can produce
excellent fits to either combined low dispersion IUE and optical photometry or
HST FOS spectrophotometry, as long as the following conditions are fulfilled:
1) an extended grid of Kurucz models is employed,
2) the IUE NEWSIPS data are placed on the FOS absolute flux system using the
Massa & Fitzpatrick (1999) transformation, and
3) all of the model parameters and the effects of interstellar extinction are
solved for simultaneously.
When these steps are taken, the temperatures, gravities, abundances and
microturbulence velocities of lightly reddened B0-A0 V stars are determined to
high precision. We also demonstrate that the same procedure can be used to fit
the energy distributions of stars which are reddened by any UV extinction curve
which can be expressed by the Fitzpatrick & Massa (1990) parameterization
scheme.
We present an initial set of results and verify our approach through
comparisons with angular diameter measurements and the parameters derived for
an eclipsing B star binary. We demonstrate that the metallicity derived from
the ATLAS 9 fits to main sequence B stars is essentially the Fe abundance. We
find that a near zero microturbulence velocity provides the best-fit to all but
the hottest or most luminous stars (where it may become a surrogate for
atmospheric expansion), and that the use of white dwarfs to calibrate UV
spectrophotometry is valid.Comment: 17 pages, including 2 pages of Tables and 6 pages of Figures.
Astrophysical Jounral, in pres
Detection of a Hot Binary Companion of Carinae
We report the detection of a hot companion of Carinae using high
resolution spectra (905 - 1180 \AA) obtained with the Far Ultraviolet
Spectroscopic Explorer (\fuse) satellite. Observations were obtained at two
epochs of the 2024-day orbit: 2003 June during ingress to the 2003.5 X-ray
eclipse and 2004 April several months after egress. These data show that
essentially all the far-UV flux from \etacar shortward of \lya disappeared at
least two days before the start of the X-ray eclipse (2003 June 29), implying
that the hot companion, \etaB, was also eclipsed by the dense wind or extended
atmosphere of \etaA. Analysis of the far-UV spectrum shows that \etaB is a
luminous hot star. The \nii \wll1084-1086 emission feature suggests that it may
be nitrogen-rich. The observed far-UV flux levels and spectral features,
combined with the timing of their disappearance, is consistent with \etacar\
being a massive binary system
Semi-Teleparallel Theories of Gravitation
A class of theories of gravitation that naturally incorporates preferred
frames of reference is presented. The underlying space-time geometry consists
of a partial parallelization of space-time and has properties of Riemann-Cartan
as well as teleparallel geometry. Within this geometry, the kinematic
quantities of preferred frames are associated with torsion fields. Using a
variational method, it is shown in which way action functionals for this
geometry can be constructed. For a special action the field equations are
derived and the coupling to spinor fields is discussed.Comment: 14 pages, LaTe
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