Author name code: hart ADS astronomy entries on 2022-09-14 =author:"Hart, A.B." ------------------------------------------------------------------------ Title: Moon Dust and Coal Ash Authors: Hart, A. B.; Raask, E. Bibcode: 1969Natur.223..762H Altcode: No abstract at ADS Title: Evershed-type lines of the solar limb Authors: Hart, A. B. Bibcode: 1962MNRAS.124..239H Altcode: From spectra of the extreme limb of the Sun 13 faint emission lines have been detected, in the H and K region, which do not appear in Mitchell's list of chromospheric lines. Four of these lines have previously been observed by Jewell and Evershed and have been ascribed by Thackeray, following Menzel's "c-line" identifications, to rare-earth elements. These identifications are found to be due to chance coincidences of wavelength and it is shown from intensity measurements that with one exception the 13 lines do not extend into the chromosphere. It is concluded that these "emission lines" are probably narrow gaps between the numerous faint absorption lines which fill this region of the spectum. Title: Problems in the determination of contours of solar lines near the extreme limb Authors: Hart, A. B. Bibcode: 1960MNRAS.120..106H Altcode: in the first part of the paper the distorting effects of the Earth's atmosphere on the distribution of light at the extreme linib of the Sun are considered. An analytical expression is found which describes the resultant redistribution of light in the focal plane of the telescope; the effects of "seeing" are represented by a Gaussian term, particle scartering and non-specular reflection by the telescope optics are included in a -law term. This redistribution function forms the kernel of the integral equation relating the true and observed intensities at any point. A geometrical idealization reduces the two-dimensional equation to an equation in one dimension. of solving this equation which do not presuppose an analytical form of the true distribution are investigated and it is shown that the solutions must be regarded as discontinuous. in order to apply these methods, observations of the K line of Ca II were made at points within + 10" arc of the limb, on two days. The relevant parameters in the redistribution function were determined from the observations. A numerical application of the solution of the integral equation then gave the true line profiles. The accuracy attainable in the solution is shown to depend rather strongly on the width of the kernel and hence on the atmospheric conditions. Title: The Period of BD+36°3991. Authors: Hart, A. B. Bibcode: 1957ApJ...126..463H Altcode: No abstract at ADS Title: VII. Vertical distribution of the equatorial velocity field Authors: Hart, A. B. Bibcode: 1956MNRAS.116..489H Altcode: In an attempt to determine the vertical distribution of the velocity field from its centre-limb variation, 274 line-of-sight velocities obtained in an earlier paper (from Fe line Doppler displacements) are analysed. They are divided into 3 groups, whose successive positions are separated by I 1 0 of heliographic longitude, and a relation is sought between the velocity dispersion displayed by a group and its position on the disk. No definitive result is obtained. A positive result is, however, derived from a comparison of velocity measurements on strong (the two Na D) lines and on weak (one Ni and one Ti) lines having, respectively, average Rowland intensities 25 and . The Doppler shifts are found from microphotometer tracings at 40 positions on each of 4 of the spectra earlier used for the Fe line measurements. At each of the 40 positions the four measurements are combined, thereby reducing the error in the velocity at any point to + (8)I (7) km sec-3 for the Ni-Ti sequence and to + (o) l (8) km for the Na sequence. After correction for effects of measurement error, the mean velocity amplitude is l (z) km for the Ni-Ti sequence, compared with t (0) km sec-1 for the Na. A statistical discussion shows that the velocity sequences are similar, but that the difference in mean amplitude is significant. From a simple model of line formation and taking account of redistribution of light by the apparatus function of the spectroscope, the weak and strong line velocities are shown to refer to approximate optical depths and , respectively, as measured in the continuum. The amplitude of the velocity field, therefore, diminishes extremely rapidly with increasing height in the photosphere. Title: Motions in the Sun at the photospheric level. VI. Large-scale motions in the equatorial region Authors: Hart, A. B. Bibcode: 1956MNRAS.116...38H Altcode: A series of line-of-sight velocity measurements, made on spectra of the Sun obtained at Oxford in 1953 May, is described. Spectra some `5 mm in height, taken with a solar image of 8 mm diameter, covered an arc of length 4 x Io km in the surface extending inwards from the limb. Measurement was made of two plates, taken an hour apart at the East equatorial limb, each carrying four exposures obtained in rapid succession. Each of the eight spectra was measured at 140 pomts mm apart, corresponding to an average spatial resolution of 4 X I0 km on the solar surface. The error to be attributed to a velocity measurement is carefully considered ; with the fine- grain plates used in the present investigation, a value t 009(0)10 02(8) km is found for the error of measurement of a single velocity. An investigation of the equatorial velocity field is based on the 1120 measurements of velocity. Measurements from the four exposures on a plate were combined to give the best values of the velocity, thereby reducing the uncertainty of the velocity at any point on the surface to 1 (5) 1 (4) km sec-1. The residual velocities remaining after the limb effect and the component of solar rotation have been removed show a dispersion of + o 6( ) km sec-1. This dispersion exceeds the error of the velocity at a point on the surface by some eight times the uncertainty of the latter, thus providing conclusive proof of the existence of a velocity field. An irregular distribution of the velocity residuals over the solar surface is found ; correlographic analysis gives 26 X I0 km as the average linear extent of a velocity fluctuation. The stability of the field is established from the similarity in the velocity distribution at the beginning and end of the period of observation. Finally, a suggestion is put forward for the possible origin of the field. Title: Motions in the Sun at the photospheric level. IV. The equatorial rotation and possible velocity fields in the photosphere Authors: Hart, A. B. Bibcode: 1954MNRAS.114...17H Altcode: From spectra of the equatorial photosphere taken near the limb of the Sun between 1950 October and 1952 June, 480 determinations of line-of-sight velocity are made. A careful investigation shows, contrary to an earlier suggestion, that the effect on velocities, of light scattered in the Earth's atmosphere and in the telescope, is negligible. In order that each day on which observations are made should carry equal weight in the final solution, only 334 of the determinations are used to find the mean equatorial velocity. After the elimination of limb effect, the velocity due to solar rotation is found to be I 9I km sec-1 for the mean epoch 1951.5. The individual determinations have a large dispersion about this mean and a statistical discussion shows that the chance is less than one in a thousand that the dispersion is due to errors of measurement. It is therefore highly probable that the velocity varies from point to point in the photosphere. The extreme range in measured velocity is approximately o 3 km sec-1 and successive maxima or minima of velocity appear to be separated by a distance of the order of 75 ooo km. Some evidence is found for bands of co11stant velocity 0c9urring perpendicular to the solar equator, but this is less certain. The existence of such velocity changes may account for the discrepant rates of rotation found by earlier observers. Title: Spectroscopic determination of solar rotation Authors: Hart, A. B. Bibcode: 1954PhDT........54H Altcode: No abstract at ADS Title: Thermal Decomposition of Hydrogen Peroxide in the Vapour Phase Authors: Hart, A. B. Bibcode: 1949Natur.163..876H Altcode: Baker and Ouellet1 reported that when they boiled 98 per cent hydrogen peroxide solution at 100° C. and passed the vapour at pressures varying between 3 and 18 cm. of mercury through a wide `Pyrex' tube heated to 335° C., they got no explosion even when they passed an electric discharge along the tube or caused a piece of cotton to burn in the gas. We find that, in a 3-cm. diameter `Pyrex' tube at 100° C., thermal decomposition flames and explosions are very readily initiated by a hot wire or a spark when the pressure is about 2 cm. of mercury or higher. At atmospheric pressure the explosion is very violent and is initiated by catalytic spots on imperfectly cleaned glass. The minimum temperature to which a wire must be heated to cause immediate ignition of the gas at atmospheric pressure has been roughly determined to be about 600° C. Thus, hydrogen peroxide seems similar in its behaviour in the vapour phase to the di-alkyl peroxides with which Harris2 obtained thermal explosions. These compounds, unlike hydrogen peroxide, decompose entirely homogeneously below 170° C., the temperature around which the explosions occur. The results of the latest workers with hydrogen peroxide are not in complete agreement on this point. Giguére3 reports no slow thermal decomposition at temperatures as high as 420° C.; but Mackenzie and Ritchie4 are of the opinion that their results may indicate an appreciable gas-phase reaction in the upper part of their temperature range (namely, 82-137° C.).