Wavelength dependence of angular diameters of M giants: an observational perspective

We discuss the wavelength dependence of angular diameters of M giants from an observational perspective. Observers cannot directly measure an optical-depth radius for a star, despite this being a common theoretical definition. Instead, they can use an interferometer to measure the square of the fringe visibility. We present new plots of the wavelength-dependent centre-to-limb variation (CLV) of intensity of the stellar disk as well as visibility for Mira and non-Mira M giant models. We use the terms ``CLV spectra'' and ``visibility spectra'' for these plots. We discuss a model-predicted extreme limb-darkening effect (also called the narrow-bright-core effect) in very strong TiO bands which can lead to a misinterpretation of the size of a star in these bands. We find no evidence as yet that this effect occurs in real stars. Our CLV spectra can explain the similarity in visibilities of R Dor (M8IIIe) that have been observed recently despite the use of two different passbands. We compare several observations with models and find the models generally under-estimate the observed variation in visibility with wavelength. We present CLV and visibility spectra for a model that is applicable to the M supergiant alpha Ori.Comment: 16 pages with figures. Accepted by MNRA

Microwave-assisted protocol for squalene isolation and conversion from oil-deodoriser distillates

Aiming to design a green and efficient protocol for squalane production from low-cost biomasses, a practical and scalable procedure for squalene extraction and hydrogenation to squalane is presented herein. The oil-deodoriser distillates that are produced by the vegetal-oil production chain are a renewable and cheap source of squalene. We were able to isolate an enriched fraction containing 89.0% of pure squalene (yield 55.4%) from a matrix containing about 2% squalene. Efficient microwave- assisted esterification under heterogeneous catalysis enabled the separation of fatty-acid methyl esters (FAME) via vacuum distillation. The residue was purified by flash-chromatography on a C-18 silica column using MeOH/H2O/2-propanol as the mobile phase. Finally, squalene was hydrogenated to the more stable squalane in a pressure-resistant microwave reactor. The reaction was performed over a Pd/C catalyst in EtOH, and even in solvent-free conditions, and was optimised using commercial squalene (5 bar of H2 at 100°C for 1 h)

Correcting for Activity Effects on the Temperatures, Radii, and Estimated Masses of Low-Mass Stars and Brown Dwarfs

We present empirical relations for determining the amount by which the effective temperatures and radii---and therefore the estimated masses---of low-mass stars and brown dwarfs are altered due to chromospheric activity. Accurate estimates of stellar radii are especially important in the context of searches for transiting exoplanets, which rely upon the assumed stellar radius/density to infer the planet radius/density. Our relations are based on a large set of well studied low-mass stars in the field and on a set of benchmark low-mass eclipsing binaries. The relations link the amount by which an active object's temperature is suppressed, and its radius inflated, to the strength of its Halpha emission. These relations are found to approximately preserve bolometric luminosity. We apply these relations to the peculiar brown-dwarf eclipsing binary 2M0535-05, in which the active, higher-mass brown dwarf has a cooler temperature than its inactive, lower-mass companion. The relations correctly reproduce the observed temperatures and radii of 2M0535-05 after accounting for the Halpha emission; 2M0535-05 would be in precise agreement with theoretical isochrones were it inactive. The relations that we present are applicable to brown dwarfs and low-mass stars with masses below 0.8 Msun and for which the activity, as measured by Halpha, is in the range -4.6 < log Lha/Lbol < -3.3. We expect these relations to be most useful for correcting radius and mass estimates of low-mass stars and brown dwarfs over their active lifetimes (few Gyr). We also discuss the implications of this work for determinations of young cluster IMFs.Comment: To appear in Cool Stars 17 proceeding

The Effects of Tax-Based Saving Incentives On Saving and Wealth

This paper evaluates research examining the effects of tax-based saving incentives on private and national saving. Several" factors make this an unusually difficult problem. First, households that participate in, or are eligible for, saving incentive plans have systematically stronger tastes for saving than other households. Second, the data indicate that households with saving incentives have taken on more debt than other households. Third, significant changes in the 1980s in financial markets, pensions, social security, and nonfinancial assets interacted with the expansion of saving incentives. Fourth, saving incentive accounts represent pre-tax balances, whereas conventional taxable accounts represent post-tax balances. Fifth, the fact that employer contributions to saving incentive plans are a part of total employee compensation is typically ignored. A major theme of this paper is that analyses that ignore these issues overstate the impact of saving incentives on saving. We show that accounting for these factors largely or completely eliminates the estimated positive impact of saving incentives on saving found in the literature. Thus, we conclude that little if any of the overall contributions to existing saving incentives have raised private or national saving. *Portions of this article were published in the JEP, 1996, under title of "The Illusory Effects of Saving Incentives on Saving."