3,356 research outputs found
The effects of different alcoholic drinks on lipids, insulin and haemostatic and inflammatory markers in older men
Light to moderate drinking is associated with lower risk of coronary heart (CHD) than non-drinkers. We have examined the relationships between total alcohol intake and type of alcoholic beverage and several potential biological mechanisms. We carried out the study in 3158 men aged 60-79 years drawn from general practices in 24 British towns with no history of myocardial infarction, stroke or diabetes and who were not on warfarin. Total alcohol consumption showed a significant positive dose-response relationship with high density lipoprotein cholesterol (HDL-C), coagulation factor IX, haematocrit, blood viscosity, and tissue plasminogen (t-PA) antigen, and an inverse dose-response relationship with insulin, fibrinogen, von Wille- brand factor (vWF) and triglycerides after adjustment for possible confounders. Total alcohol consumption showed weak associations with plasma viscosity and fibrin D-dimer, and no association with factors VII,VIII, or C-reactive protein (CRP). Wine was specifically associated with lower CRP, plasma viscosity, factor VIII and triglycerides. The findings are consistent with the suggestion that HDL-C in particular but also insulin and haemostatic factors may contribute to the beneficial effect of light to moderate drinking on risk of CHD. Wine has effects that may confer greater protection than other alcoholic beverages
Terminal velocities of luminous, early-type SMC stars
Ultraviolet spectra from the Space Telescope Imaging Spectrograph (STIS) are
used to determine terminal velocities for 11 O and B-type giants and
supergiants in the Small Magellanic Cloud (SMC) from the Si IV and C IV
resonance lines. Using archival data from observations with the Goddard
High-Resolution Spectrograph and the International Ultraviolet Explorer
telescope, terminal velocities are obtained for a further five B-type
supergiants. We discuss the metallicity dependence of stellar terminal
velocities, finding no evidence for a significant scaling between Galactic and
SMC metallicities for Teff < 30,000 K, consistent with the predictions of
radiation driven wind theory for supergiant stars. A comparison of the
ratio between the SMC and Galactic samples, while
consistent with the above statement, emphasizes that the uncertainties in the
distances to galactic O-stars are a serious obstacle to a detailed comparison
with theory. For the SMC sample there is considerable scatter in this ratio at
a given effective temperature, perhaps indicative of uncertainties in stellar
masses.Comment: 28 pages, 8 figures, accepted by ApJ; minor revisions prior to
acceptanc
Interpretation of UV Absorption Lines in SN1006
We present a theoretical interpretation of the broad silicon and iron UV
absorption features observed with the Hubble Space Telescope in the spectrum of
the Schweizer-Middleditch star behind the remnant of Supernova 1006. These
features are caused by supernova ejecta in SN1006. We propose that the
redshifted SiII2 1260 A feature consists of both unshocked and shocked SiII.
The sharp red edge of the line at 7070 km/s indicates the position of the
reverse shock, while its Gaussian blue edge reveals shocked Si with a mean
velocity of 5050 km/s and a dispersion of 1240 km/s, implying a reverse shock
velocity of 2860 km/s. The measured velocities satisfy the energy jump
condition for a strong shock, provided that all the shock energy goes into
ions, with little or no collisionless heating of electrons. The line profiles
of the SiIII and SiIV absorption features indicate that they arise mostly from
shocked Si. The total mass of shocked and unshocked Si inferred from the SiII,
SiIII and SiIV profiles is M_Si = 0.25 \pm 0.01 Msun on the assumption of
spherical symmetry. Unshocked Si extends upwards from 5600 km/s. Although there
appears to be some Fe mixed with the Si at lower velocities < 7070 km/s, the
absence of FeII absorption with the same profile as the shocked SiII suggests
little Fe mixed with Si at higher (before being shocked) velocities. The column
density of shocked SiII is close to that expected for SiII undergoing steady
state collisional ionization behind the reverse shock, provided that the
electron to SiII ratio is low, from which we infer that most of the shocked Si
is likely to be of a fairly high degree of purity, unmixed with other elements.
We propose that the ambient interstellar density on the far side of SN1006 is
anomalously low compared to the density around the rest of the remnant. ThisComment: 24 pages, with 8 figures included. Accepted for publication in the
Astrophysical Journa
Fluorine abundances in planetary nebulae
We have determined fluorine abundances from the F II 4789 and F IV 4060
nebular emission lines for a sample of planetary nebulae (PNe). Our results
show that fluorine is generally overabundant in PNe, thus providing new
evidence for the synthesis of fluorine in asymptotic giant branch (AGB) stars.
[F/O] is found to be positively correlated with the C/O abundance ratio, in
agreement with the predictions of theoretical models of fluorine production in
thermally pulsing AGB stars. A large enhancement of fluorine is observed in the
Wolf-Rayet PN NGC 40, suggesting that high mass-loss rates probably favor the
survival of fluorine.Comment: 4 pages, 3 figures, accepted for publication in ApJ Letter
Radiation-driven winds of hot stars. XIII. A description of NLTE line blocking and blanketing towards realistic models of expanding atmospheres
We present significant improvements of our approach in constructing detailed
atmospheric models and synthetic spectra for hot luminous stars:
1. A sophisticated and consistent description of line blocking and
blanketing. Our solution concept renders the line blocking influence on the
ionizing fluxes (mainly the EUV and UV are affected) in identical quality as
the synthetic high resolution spectra representing the observable region. Line
blanketing is properly accounted for in the energy balance.
2. A considerably improved and enhanced atomic data archive providing the
basis for a detailed multilevel NLTE treatment of the metal ions (from C to Zn)
and an adequate representation of line blocking and the radiative line
acceleration.
3. A revised inclusion of EUV and X-ray radiation produced by cooling zones
originating from shock heated matter.
This new tool not only provides an easy to use method for O-star diagnostics,
whereby physical constraints on the properties of stellar winds, stellar
parameters, and abundances can be obtained via a comparison of observed and
synthetic spectra, but also allows the astrophysically important information
about the ionizing fluxes of hot stars to be determined automatically. Results
illustrating this are discussed by means of a basic model grid calculated for
O-stars with solar metallicity. To further demonstrate the astrophysical
potential of our new method we provide a first detailed spectral diagnostic
determination of the stellar parameters, the wind parameters, and the
abundances by an exemplary application to the O9.5Ia supergiant alpha Cam.Comment: 42 Pages, 39 Figures. LaTeX documentclass aa, packages graphicx and
times. Submitted to Astronomy and Astrophysic
Differential O and Si Abundances in M33 Early B Supergiants
We present non-LTE analyses of four M33 early B-supergiant stars and five
Galactic counterparts. This is the first time that B supergiants beyond the
Magellanic Clouds are analyzed by means of detailed Non-LTE techniques. Stellar
temperatures, gravities, microturbulences and Si abundances are derived for all
objects using the Si ionization equilibrium and the Balmer line wings. O
abundances are then also derived. Important approximations made during the
calculations are described, and their influence on the results is analyzed. It
is found that these approximations have no significant effect on the results at
any microturbulence. We find that a strict differential analysis is needed to
detect abundance differences. Thus we compare results line by line in M33 and
Galactic stars of stellar parameters as similar as possible. Three of the four
M33 stars turned out to be O deficient as compared to their Galactic
counterparts, and only one, close to the center of M33 (M33 1054) is found to
be moderately O enriched. From these differential analyses we find that our
data are compatible with a radial O gradient in M33 as that derived from HII
region data: we obtain -0.19+/-0.13 or -0.20+/-0.07 dex/kpc, depending on
whether B133 is included or not. Our data are also consistent with other
possibilities such as a steep increase of the O abundance in the inner region
(at projected distances less than 9 arcmin from the center of M33), followed by
a flat O abundance profile towards the outer parts of M33. Si shows the same
pattern, and it is shown that Si and O correlate well, as expected for
alpha-elements, supporting then the high value of the O abundance gradient in
M33 as compared to the Milky Way and other nearby spiral galaxies.Comment: Accepted for ApJ. Tentatively scheduled for Dec. 20, 2000. 44 pages,
9 tables, 18 figure
Boron Abundances in Main Sequence B-type Stars: A Test of Rotational Depletion during Main Sequence Evolution
Boron abundances have been derived for seven main sequence B-type stars from
HST STIS spectra around the B III 2066 A line. In two stars, boron appears to
be undepleted with respect to the presumed initial abundance. In one star,
boron is detectable but it is clearly depleted. In the other four stars, boron
is undetectable implying depletions of 1 to 2 dex. Three of these four stars
are nitrogen enriched, but the fourth shows no enrichment of nitrogen. Only
rotationally induced mixing predicts that boron depletions are unaccompanied by
nitrogen enrichments. The inferred rate of boron depletion from our
observations is in good agreement with these predictions. Other boron-depleted
nitrogen-normal stars are identified from the literature. Also, several
boron-depleted nitrogen-rich stars are identified, and while all fall on the
boron-nitrogen trend predicted by rotationally-induced mixing, a majority have
nitrogen enrichments that are not uniquely explained by rotation.
The spectra have also been used to determine iron-group (Cr, Mn, Fe, and Ni)
abundances. The seven B-type stars have near solar iron-group abundances, as
expected for young stars in the solar neighborhood. We have also analysed the
halo B-type star, PG0832+676. We find [Fe/H] = -0.88 +/- 0.10, and the absence
of the B III line gives the upper limit [B/H]<2.5. These and other published
abundances are used to infer the star's evolutionary status as a post-AGB star.Comment: 31 pages, 14 figures. accepted to Ap
Bubbles and Filaments: Stirring a Cahn-Hilliard Fluid
The advective Cahn-Hilliard equation describes the competing processes of
stirring and separation in a two-phase fluid. Intuition suggests that bubbles
will form on a certain scale, and previous studies of Cahn-Hilliard dynamics
seem to suggest the presence of one dominant length scale. However, the
Cahn-Hilliard phase-separation mechanism contains a hyperdiffusion term and we
show that, by stirring the mixture at a sufficiently large amplitude, we excite
the diffusion and overwhelm the segregation to create a homogeneous liquid. At
intermediate amplitudes we see regions of bubbles coexisting with regions of
hyperdiffusive filaments. Thus, the problem possesses two dominant length
scales, associated with the bubbles and filaments. For simplicity, we use use a
chaotic flow that mimics turbulent stirring at large Prandtl number. We compare
our results with the case of variable mobility, in which growth of bubble size
is dominated by interfacial rather than bulk effects, and find qualitatively
similar results.Comment: 20 pages, 27 figures. RevTeX
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