Interrogating (In)visibilities

Critical attention to invisible disability raises interesting questions about the social and corporeal (in)visibility of disability. The article conceptualizes invisible disability in relation to the visible body, while maintaining the category’s ties with social visibility. To explore invisible disability, economies of visibility—originally proposed in black feminist media scholarship—is developed as a lens to explore the connections between (in)visible embodiment and social visibility in media texts. The lens is used to examine the representation of characters with invisible disability and visible disability in the case study of the popular Australian soap opera Home and Away. The examination illuminates economies of visibility as a productive way of grappling with how invisible disability vexes the visual binary of disabled/able-bodied.

Comparison of Gaia and Hipparcos parallaxes of close visual binary stars and the impact on determinations of their masses

Precise measurement of the fundamental parameters of stellar systems, including mass and radius, depends critically on how well the stellar distances are known. Astrometry from space provides parallax measurements of unprecented accuracy, from which distances can be derived, initially from the Hipparcos mission, with a further refinement of that analysis provided by van Leeuwen in 2007. The publication of the Gaia DR2 catalogue promises a dramatic improvement in the available data. We have recalculated the dynamical masses of a sample of 1 700 close visual binary stars using Gaia DR2 and compared the results with masses derived from both the original and enhanced Hipparcos data. We show the van Leeuwen analysis yields results close to those of Gaia DR2, but the latter are significantly more accurate. We consider the impact of the Gaia DR2 parallaxes on our understanding of the sample of visual binaries.

VIBES: Visual Binary Exoplanet survey with SPHERE

Context. Recent surveys indicate that planets in binary systems are more abundant than previously thought, which is in agreement with theoretical work on disc dynamics and planet formation in binaries. So far, most observational surveys, however, have focused on short-period planets in binaries, thus little is known about the occurrence rates of planets on longer periods (≥10 au). Aims. In order to measure the abundance and physical characteristics of wide-orbit giant exoplanets in binary systems, we have designed the “VIsual Binary Exoplanet survey with Sphere” (VIBES) to search for planets in visual binaries. It uses the SPHERE instrument at VLT to search for planets in 23 visual binary and four visual triple systems with ages of <145 Myr and distances of <150 pc. Methods. We used the IRDIS dual-band imager on SPHERE to acquire high-contrast images of the sample targets. For each binary, the two components were observed at the same time with a coronagraph masking only the primary star. For the triple star, the tight components were treated as a single star for data reduction. This enabled us to effectively search for companions around 50 individual stars in binaries and four binaries in triples. Results. We derived upper limits of <13.7% for the frequency of sub-stellar companions around primaries in visual binaries, <26.5% for the fraction of sub-stellar companions around secondaries in visual binaries, and an occurrence rate of <9.0% for giant planets and brown dwarfs around either component of visual binaries. We have combined our observations with literature measurements to astrometrically confirm, for the first time, that 20 binaries and two triple systems, which were previously known, are indeed physically bound. Finally, we discovered a third component of the binary HD 121336. Conclusions. The upper limits we derived are compatible with planet formation through the core accretion and the gravitational instability processes in binaries. These limits are also in line with limits found for single star and circumbinary planet search surveys.

Visual binary testing of methanol contained in ethyl alcohol

A method for control of methanol traces in rectified ethyl alcohol and alcoholic drinks based on visual binary testing using one reference sample was proposed. An indicator reaction of formaldehyde interaction (product of methanol oxidation) with chromotropic acid disodium salt was chosen for methanol screening. The conditions of indicator reaction proceeding are analogous as for the spectrophotometric technique of methanol determination: methanol was oxidized to formaldehyde with potassium permanganate in an acidic medium; the formaldehyde then reacts with chromotropic acid in the presence of hot concentrated sulfuric acid and forms a violet product (color of this product is stable for 12 hours). It was established that the absorption spectrum of the reaction product does not change on going from 96% ethanol to aqueous-ethanol solutions with a volume fraction of 40% ethanol. The maximum light absorption of the reaction product corresponded to 570 nm. All further studies were carried out in water-ethanol solutions with a volume fraction of ethanol of 40%. According to regulatory documents the normalized limiting content of methanol (clim) in ethyl alcohol of the “Lux” grade (the most common in the alcoholic industry) and alcoholic beverages is 0.01% by by volume counted upon anhydrous alcohol. The comparison sample (the solution of colored reaction product of indicator reaction) had to be less than the normilized level on the value which providing the risk of false-negative test result not more than 5%. To determination the threshold concentration of methanol in the comparison sample was applied the statistics of observation. For the aim the solution of colored product corresponding to the normalized limiting methanol concentration clim = 0.01% by volume was prepared and comparison samples with lower methanol concentrations were also prepared. The interval of unreliability was discovered with the help of observers. The frequency of detecting of the difference in the color of comparison samples and normalized sample (P(c)) changed from 0 to 1 in this interval. The value of methanol concentration 0.0072% by volume counted upon anhydrous alcohol was taken for the lower boundary of the interval and the value of methanol concentration 0.01% by volume counted upon anhydrous alcohol was chosen the upper border of the interval. This interval was divided on eight concentrations with step Dс = 0.0004% by volume. Three parallel series of solutions were prepared and 48 observations for each concentration were received. The experimental efficiency curve obtained was checked for compliance with the mathematical functions of the known distributions: normal, logistic, lognormal, exponential and Weibull distribution function using the statistical criterions c2 and Kolmogorov-Smirnov λ. The efficiency curve was described by the theoretical functions of the lognormal and Weibull distributions. Calculated at a confidence level of 0.95 estimation of the threshold concentration for the comparison sample was 0.0073% by volume fraction corresponding to anhydrous alcohol. The visual binary testing of methanol trace in alcoholic drinks was carried out. The accuracy of visual binary testing of methanol was confirmed by gas chromatography.

Finding binary star fractions in any distribution

Candidate visual binary systems are often found by identifying two stars that are closer together than would be expected by chance. However, in regions with non-trivial density distributions, the ‘random’ distances between stars varies because of the background distribution, as well as the presence of binaries. We show that when no binaries are present, the distribution of the ratios of the distances to the nearest and tenth nearest neighbours, d1/d10, is always well approximated by a Gaussian with mean 0.2–0.3 and variance 0.16–0.19 for any underlying density distribution. The introduction of binaries causes some (or all) nearest neighbours to become closer than expected by random chance, introducing a component to the distribution where d1/d10 is much lower than expected. We show how a simple single or double Gaussian fit to the distribution of d1/d10 can be used to find the binary fraction in any underlying density distribution quickly and simply.