1,695 research outputs found
Binary companions of evolved stars in APOGEE DR14: Orbital circularization
Short-period binary star systems dissipate orbital energy through tidal
interactions that lead to tighter, more circular orbits. When at least one star
in a binary has evolved off of the main sequence, orbital circularization
occurs for longer-period (~100 day) systems. Past work by (Verbunt & Phinney
1995) has shown that the orbital parameters and the circularization periods of
a small sample of binary stars with evolved-star members can be understood
within the context of standard tidal circularization theory. Using a sample of
binaries with subgiant, giant, and red clump star members that is nearly an
order of magnitude larger, we reexamine predictions for tidal circularization
of binary stars with evolved members. We confirm that systems predicted by
equilibrium-tide theory to have circular orbits generally have negligible
measured eccentricities. The circularization period is correlated with the
surface gravity (i.e. size) of the evolved member, indicating that the
circularization timescale must be shorter than the evolutionary timescale along
the giant branch. A few exceptions to the conclusions above are mentioned in
the discussion: Some of these exceptions are likely systems in which the
spectrum of the secondary biases the radial velocity measurements, but four
appear to be genuine, short-period, moderate-eccentricity systems.Comment: 13 pages, 6 figures; comments welcom
What bandwidth do I need for my image?
Computer representations of real numbers are necessarily discrete, with some
finite resolution, discreteness, quantization, or minimum representable
difference. We perform astrometric and photometric measurements on stars and
co-add multiple observations of faint sources to demonstrate that essentially
all of the scientific information in an optical astronomical image can be
preserved or transmitted when the minimum representable difference is a factor
of two finer than the root-variance of the per-pixel noise. Adopting a
representation this coarse reduces bandwidth for data acquisition,
transmission, or storage, or permits better use of the system dynamic range,
without sacrificing any information for down-stream data analysis, including
information on sources fainter than the minimum representable difference
itself.Comment: submitted to PAS
Continuous-flow laboratory simulation of stream water quality changes downstream of an untreated wastewater discharge.
In regions of the world with poor provision of wastewater treatment, raw sewage
is often discharged directly into surface waters. This paper describes an
experimental evaluation of the fate of two organic chemicals under these
conditions using an artificial channel cascade fed with a mix of settled sewage
and river water at its upstream end and operated under continuous steady-state
conditions. The experiments underpin an environmental risk assessment
methodology based on the idea of an “impact zone” (IZ) – the zone downstream of
wastewater emission in which water quality is severely impaired by high
concentrations of unionised ammonia, nitrite and biochemical oxygen demand
(BOD). Radiolabelled dodecane-6-benzene sulphonate (DOBS) and aniline
hydrochloride were used as the model chemical and reference compound
respectively. Rapid changes in 14C counts were observed with flow-time for both
these materials. These changes were most likely to be due to complete
mineralisation. A dissipation half-life of approximately 7.1 h was observed for
the 14C label with DOBS. The end of the IZ was defined as the point at which the
concentration of both unionised ammonia and nitrite fell below their respective
predicted no-effect concentrations for salmonids. At these points in the
cascade, approximately 83 and 90% of the initial concentration of 14C had been
removed from the water column, respectively. A simple model of mineral nitrogen
transformations based on Michaelis–Menten kinetics was fitted to observed
concentrations of NH4, NO2 and NO3. The cascade is intended to provide a
confirmatory methodology for assessing the ecological risks of chemicals under
direct discharge co
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