2,237 research outputs found
Thermal control system corrosion study
During the development of an expert system for autonomous control of the Space Station Thermal Control System (TCS), the thermal performance of the Brassboard TCS began to gradually degrade. This degradation was due to filter clogging by metallic residue. A study was initiated to determine the source of the residue and the basic cause of the corrosion. The investigation focused on the TCS design, materials compatibility, Ames operating and maintenance procedures, and chemical analysis of the residue and of the anhydrous ammonia used as the principal refrigerant. It was concluded that the corrosion mechanisms involved two processes: the reaction of water alone with large, untreated aluminum parts in a high pH environment and the presence of chlorides and chloride salts. These salts will attack the aluminum oxide layer and may enable galvanic corrosion between the aluminum and the more noble stainless steel and other metallic elements present. Recommendations are made for modifications to the system design, the materials used, and the operating and maintenance procedures, which should largely prevent the recurrence of these corrosion mechanisms
Alien Registration- Folsom, Millicent A. (Bangor, Penobscot County)
https://digitalmaine.com/alien_docs/15850/thumbnail.jp
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
The magnetic field of the double-lined spectroscopic binary system HD 5550
(Abridged) In the framework of the BinaMicS project, we have begun a study of
the magnetic properties of a sample of intermediate-mass and massive
short-period binary systems, as a function of binarity properties. We report in
this paper the characterisation of the magnetic field of HD 5550, a
double-lined spectroscopic binary system of intermediate-mass, using
high-resolution spectropolarimetric Narval observations of HD 5550. We first
fit the intensity spectra using Zeeman/ATLAS9 LTE synthetic spectra to estimate
the effective temperatures, microturbulent velocities, and the abundances of
some elements of both components, as well as the light-ratio of the system. We
then fit the least-square deconvolved profiles to determine the radial and
projected rotational velocities of both stars. We then analysed the shape and
evolution of the LSD profiles using the oblique rotator model to
characterise the magnetic fields of both stars.
We confirm the Ap nature of the primary, previously reported in the
literature, and find that the secondary displays spectral characteristics
typical of an Am star. While a magnetic field is clearly detected in the lines
of the primary, no magnetic field is detected in the secondary, in any of our
observation. If a dipolar field were present at the surface of the Am star, its
polar strength must be below 40 G. The faint variability observed in the Stokes
profiles of the Ap star allowed us to propose a rotation period of
d, close to the orbital period (6.82 d),
suggesting that the star is synchronised with its orbit. By fitting the
variability of the profiles, we propose that the Ap component hosts a
dipolar field inclined with the rotation axis at an angle
and a polar strength G. The field strength is
the weakest known for an Ap star.Comment: 13 pages, 12 figures, accepted for publication in Astronomy &
Astrophysic
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