8,568 research outputs found
Orbital parameters, chemical composition, and magnetic field of the Ap binary HD 98088
HD 98088 is a synchronised, double-lined spectroscopic binary system with a
magnetic Ap primary component and an Am secondary component. We study this rare
system using high-resolution MuSiCoS spectropolarimetric data, to gain insight
into the effect of binarity on the origin of stellar magnetism and the
formation of chemical peculiarities in A-type stars. Using a new collection of
29 high-resolution Stokes VQU spectra we re-derive the orbital and stellar
physical parameters and conduct the first disentangling of spectroscopic
observations of the system to conduct spectral analysis of the individual
stellar components. From this analysis we determine the projected rotational
velocities of the stars and conduct a detailed chemical abundance analysis of
each component using both the SYNTH3 and ZEEMAN spectrum synthesis codes. The
surface abundances of the primary component are typical of a cool Ap star,
while those of the secondary component are typical of an Am star. We present
the first magnetic analysis of both components using modern data. Using
Least-Squares Deconvolution, we extract the longitudinal magnetic field
strength of the primary component, which is observed to vary between +1170 and
-920 G with a period consistent with the orbital period. There is no field
detected in the secondary component. The magnetic field in the primary is
predominantly dipolar, with the positive pole oriented approximately towards
the secondary.Comment: Accepted for publication by MNRAS, 17 pages, 12 figure
Investigating the origin of cyclical wind variability in hot, massive stars - II. Hydrodynamical simulations of co-rotating interaction regions using realistic spot parameters for the O giant Persei
OB stars exhibit various types of spectral variability historically
associated with wind structures, including the apparently ubiquitous discrete
absorption components (DACs). These features have been proposed to be caused
either by magnetic fields or non-radial pulsations. In this second paper of
this series, we revisit the canonical phenomenological hydrodynamical modelling
used to explain the formation of DACs by taking into account modern
observations and more realistic theoretical predictions. Using constraints on
putative bright spots located on the surface of the O giant Persei
derived from high precision space-based broadband optical photometry obtained
with the Microvariability and Oscillations of STars (MOST) space telescope, we
generate two-dimensional hydrodynamical simulations of co-rotating interaction
regions in its wind. We then compute synthetic ultraviolet (UV) resonance line
profiles using Sobolev Exact Integration and compare them with historical
timeseries obtained by the International Ultraviolet Explorer (IUE) to evaluate
if the observed behaviour of Persei's DACs is reproduced. Testing three
different models of spot size and strength, we find that the classical pattern
of variability can be successfully reproduced for two of them: the model with
the smallest spots yields absorption features that are incompatible with
observations. Furthermore, we test the effect of the radial dependence of
ionization levels on line driving, but cannot conclusively assess the
importance of this factor. In conclusion, this study self-consistently links
optical photometry and UV spectroscopy, paving the way to a better
understanding of cyclical wind variability in massive stars in the context of
the bright spot paradigm.Comment: 16 pages, 10 figures, accepted for publication by MNRA
Factors Regulating the Growth of Algae in Continuous Culture in Diluted Secondary Sewage Treatment Plant Effluent and Subsequent Biodegradability
Heterogeneous algal cultures were grown in laboratory continuous culture in continuous flow, completely mixed chemostats in secondary sewage treatment plant effluent diluted to give an ammonia nitrogen concentration of 10 mg/1. Variables were lighting, pH, carbon dioxide availability, and hydraulic residence time.
Optimum growth occurred under pH 7.0, excess CO2, and continuous lighting conditions. The availability of artificially supplied excess CO2 greatly increased the mass (standing crop) at steady-state over that produced under otherwise identical conditions for all residence times studied. For the case of excess CO2 availability, the nitrogen concentration in the algal cells regulated growth rather than the concentration of nutrients in solution. A mathematical expression was hypothesized to describe this phenomenon and was confirmed by the experimental results.
Under dark-aerobic conditions, the algal cultures exerted a two-stage BOD, the second stage apparently beginning after the death of the algal cells. Longer chemostat residence times during growth produced cultures with lower percentage biodegradability. Carbon dioxide enriched growth conditions produced cultures with lower percentage biodegradability than cultures grown in a carbon dioxide deficient medium
Magnetic field, chemical composition and line profile variability of the peculiar eclipsing binary star AR Aur
AR Aur is the only eclipsing binary known to contain a HgMn star, making it
an ideal case for a detailed study of the HgMn phenomenon. HgMn stars are a
poorly understood class of chemically peculiar stars, which have traditionally
been thought not to possess significant magnetic fields. However, the recent
discovery of line profile variability in some HgMn stars, apparently
attributable to surface abundance patches, has brought this belief into
question. In this paper we investigate the chemical abundances, line profile
variability, and magnetic field of the primary and secondary of the AR Aur
system, using a series of high resolution spectropolarimetric observations. We
find the primary is indeed a HgMn star, and present the most precise abundances
yet determined for this star. We find the secondary is a weak Am star, and is
possibly still on the pre-main sequence. Line profile variability was observed
in a range of lines in the primary, and is attributed to inhomogeneous surface
distributions of some elements. No magnetic field was detected in any
observation of either stars, with an upper limit on the longitudinal magnetic
field in both stars of 100 G. Modeling of the phase-resolve longitudinal field
measurements leads to a 3 sigma upper limit on any dipole surface magnetic
field of about 400 G.Comment: Accepted for publication in MNRAS, 11 pages, 9 figure
- …