explanation blue bibcodes open ADS page with paths to full text
Author name code: hart
ADS astronomy entries on 2022-09-14
=author:"Hart, A.B."
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Title: Moon Dust and Coal Ash
Authors: Hart, A. B.; Raask, E.
1969Natur.223..762H Altcode:
No abstract at ADS
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Title: Evershed-type lines of the solar limb
Authors: Hart, A. B.
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.
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Title: Problems in the determination of contours of solar lines near
the extreme limb
Authors: Hart, A. B.
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.
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Title: The Period of BD+36°3991.
Authors: Hart, A. B.
1957ApJ...126..463H Altcode:
No abstract at ADS
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Title: VII. Vertical distribution of the equatorial velocity field
Authors: Hart, A. B.
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.
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Title: Motions in the Sun at the photospheric level. VI. Large-scale
motions in the equatorial region
Authors: Hart, A. B.
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.
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Title: Motions in the Sun at the photospheric level. IV. The
equatorial rotation and possible velocity fields in the photosphere
Authors: Hart, A. B.
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.
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Title: Spectroscopic determination of solar rotation
Authors: Hart, A. B.
1954PhDT........54H Altcode:
No abstract at ADS
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Title: Thermal Decomposition of Hydrogen Peroxide in the Vapour Phase
Authors: Hart, A. B.
1949Natur.163..876H Altcode:
Baker and Ouellet<SUP>1</SUP> 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 Harris<SUP>2</SUP> 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. Giguére<SUP>3</SUP> reports no slow thermal
decomposition at temperatures as high as 420° C.; but Mackenzie and
Ritchie<SUP>4</SUP> 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.).
