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Author name code: plaskett
ADS astronomy entries on 2022-09-14
=author:"Plaskett, H.H."
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Title: Solar wavelengths and the limb effect.
Authors: Plaskett, H. H.
1977MNRAS.179..339P Altcode:
The possibility is considered that some effect of photospheric velocity
is contained within the wavelength of the center of gravity of an
asymmetric solar line measured with a micrometer microscope from a
grating spectrum of some specified point on the solar disk and within
the interferometrically known wavelength of the same line at the center
of the disk. An attempt is made to show that apparent anomalies in
solar wavelengths are due to a radial current with vertical velocity
and that the limb effect is probably a consequence of this current. A
vertical velocity of about 0.39 km/s is obtained from analysis of
the limb effect, and both photospheric and chromospheric origins of
the radial current are investigated. It is concluded that there is
insufficient information to determine whether this current occurs in
the photosphere or the chromosphere.
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Title: Herman Zanstra.
Authors: Plaskett, H. H.
1974QJRAS..15...57P Altcode:
No abstract at ADS
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Title: Equatorial currents in the photosphere
Authors: Plaskett, H. H.
1973MNRAS.163..183P Altcode:
From spectra photographed at Oxford in 1966 and 1968 sight-line
velocities of the equatorial zone of the Sun are tabulated. After
correction of these for limb effect an axisymmetric solution gives
the zonal and meridional components of photospheric velocity. In the
Northern and Southern Hemispheres of an equatorial zone of constant
angular velocity there occurs at a latitude of some 10 a dominantly
meridional current. The properties of the current are described, a
possible origin of its meridional part proposed and some suggestions
are made on why the current has hitherto escaped detection.
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Title: Limb darkening and solar rotation-II
Authors: Plaskett, H. H.
1970MNRAS.148..149P Altcode:
Spectrophotometric measures of surface brightness at A for diametrically
opposite limbs of the Sun confirm that the poles are at least five
per cent brighter than the equatorial limb. Solutions by Radau
integration for the source function and computation of photospheric
models give temperature as a function of linear height for a
number of latitudes. The currents due to the resulting meridional
temperature-gradient occur in a photospheric Ekmanlayer and are of
the same order of magnitude as those found from velocities measured
at Oxford in 1953 and 1960. These thermal currents are stable and are
maintained against viscous loss by heat absorbed in the photosphere. To
these currents is probably due the observed decrease of angular velocity
towards the poles of the Sun. The origin of polar heating is however
as yet unknown.
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Title: The polar rotation of the Sun
Authors: Plaskett, H. H.
1966MNRAS.131..407P Altcode:
Spectroscopic measures of the rotation of the Sun are given for 190
photo- spheric positions in the latitude range 45750 (section 1). After
a correction for limb effect, made from the measures themselves (section
2), these velocities show meridional currents directed towards the
equator and a difference of rotation in the northern and southern
hemispheres (section 3. i). Interpreting these velocities as the
result of a balanced motion between a posttilated meridional pressure
gradient and an inertial Coriolis force, the polar retardation of the
Sun's rotation appears to be due to zonal currents moving towards the
apparent east in an otherwise uniformly rotating photo- sphere (section
3.2). A re-discussion of unconfirmed measures of limb darkening in shows
differences of polar and equatorial temperature which may be the origin
of the meridional pressure gradient and which quantitatively describe
the observed velocities (section 3.3). Moreover from an analysis of
the meridional components of velocity some evidence is found of Rossby
waves, a phenomenon characteristic of well-established zonal winds in
the Earth's atmosphere (section 4). From these zonal currents which
tend to brake the rotation of the photo sphere and from the suspected
polar heating, it is speculatively inferred that beneath the hydrogen
convection zone the Sun may complete a rotation in some I hours
(section 5).
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Title: The physics of the Sun
Authors: Plaskett, H. H.
1965Obs....85..178P Altcode:
No abstract at ADS
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Title: Heat flow in stars
Authors: Plaskett, H. H.
1963Obs....83..236P Altcode:
No abstract at ADS
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Title: Limb darkening and solar rotation
Authors: Plaskett, H. H.
1962MNRAS.123..541P Altcode:
In finding the darkening to the limb the determination of , the
position on the disk, must be no less accurate than that of 1(o, it)
the surface brightness. Both requirements are met by photographic
spectrophotometry and with this method new measures are made of limb
darkeriing along east-west and northsouth radii (Table V). From these
measures photo- spheric models are computed for heliographic latitudes
o0 and 750 (Table IX). The horizontal temperature-gradient between
these latitudes produces a heliostrophic wind blowing from apparent
west to east. A comparison with measures of photospheric velocity
(Table X) suggests that the hydrogen convection zone is in uniform
rotation and that the polar retardation of the Sun's rotation is due
to a purely photospheric circulation driven by polar heating.
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Title: Motions in the Sun at the photospheric level, VIII. Solar
rotation and photospheric circulation
Authors: Plaskett, H. H.
1959MNRAS.119..197P Altcode:
From spectra exposed 1953 April zI-Z3, sight-line velocities have been
measured at 33z points over the visible surface of the Sun. For any
point the sight-line velocity can be expressed as a linear function of
velocity components directed to the west and the nofth. Least-squares
solutions of such observation equations for various latitudes reveal
an asymmetry of rotational velocities in the equatorial zone and the
presence of meridional currents. These motions suggest the existence
of a circulation in the photosphere similar to that shown in the upper
atmosphere of the Earth. This hypothesis is examined in the light of an
investigation by M. J. Lighthill, and an observational test is proposed.
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Title: Excitation of chromospheric emission
Authors: Plaskett, H. H.
1956MNRAS.116..419P Altcode:
The presence of the Lyman-alpha line in emission across the whole
disk of the Sun suggests that the chromosphere is excited by a
mechanism additional to that g}ven by the absorption of photospheric
radiation. To find some of the properties of this additional excitation
the observed intensity of a chromospheric line, as observed at
the limb of the Sun outside an eclipse, is derived as an integral
containing the source function. A numerical method of solving this
integral equation is outlined, and from the solution the excitation
temperature and the density can be found as functions of radial height
in the chromosphere. Other applications of the integral equation are
briefly discussed.
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Title: The Oxford 35 m solar telescope
Authors: Plaskett, H. H.
1955MNRAS.115..542P Altcode:
A new telescope for solar work with an equivalent focal length of
35 2 m is described. It is an ordinary Cassegrain reflector used at
the coud focus. The optical requirements for satisfactory performance
are listed and some of the mechanical features briefly described. The
performance is assessed from a Hartmann test.
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Title: Interpretation of Fraunhofer-line profiles
Authors: Plaskett, H. H.
1955MNRAS.115..256P Altcode:
From the experimentally determined cross-sections of the Na atom for
collisions of the second kind it is shown that the hypothesis of true
absorption is probably not applicable to the formation of Fraunhofer
lines in the solar photosphere. Using atomic transition probabilities
for radiative excitation and ionization, values of the source functions
and the ratio of the line to the continuous absorption coefficients are
derived in terms of kinetic, excitation and ionization temperatures. The
functional dependence of these quantities on the optical depth is such
as to permit a numerical integration of the exact equation of transfer,
and the method of effecting this integration is outlined
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Title: Physical conditions in the solar photosphere
Authors: Plaskett, H. H.
1955VA......1..637P Altcode:
From the source-function, recently derived by SYKES, the temperature
is found as a function of optical depth in the solar photosphere. The
temperature distribution leads in turn to the gas pressure. To find
these and other physical parameters it is necessary to assume that the
photosphere is in local thermodynamic equilibrium. The uncertainty
produced in these quantities by this and other assumptions, as well
as by observational error, is briefly discussed. The deep layers of
the photosphere, where ( d ln T/ d ln p) > 0·4, are unstable;
the steep temperature gradient may arise from boundary cooling. It is
shown that solar granulation probably originates in the zone of observed
instability rather than in the deeper-lying hydrogen-convection zone.
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Title: Motions in the Sun at the photospheric level. V. Velocities
of granules and of other localized regions
Authors: Plaskett, H. H.
1954MNRAS.114..251P Altcode:
Velocities and surface brightness in three Oxford spectra, showing
granulation, have been measured. The results are in good agreement
with those earlier found by Richardson and Schwarzschild in a Mount
Wilson spectrum. In two of the three Oxford spectra a significant
correlation coefficient of r= - has been found between the surface
brightness and the sight-lin component of the velocity, showing that
the bright granular matter is moving vertically upwards. Assuming that
the top of the granulation zone occurs at an optical depth of unity,
km sec-' is a lower limit to the velocity of ascent of the bright
granular matter. The smallness, or in one spectrum the absence, of any
correlation between surface brightness and velocity suggests that the
granular velocities are being partially or completely maske by some
other perturbation of velocity. Removing from the observed velocities
that part due to granulation, the perturbing velocities are found to
originate in an oscillatory velocity field with an average period of
5 of arc and an amplitude of the order of 0.5 km sec-'.
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Title: The Oxford solar spectroscope
Authors: Plaskett, H. H.
1952MNRAS.112..177P Altcode:
The prismatic spectroscope, used with the Oxford solar telescope,
has a clear aperture of 15 2 cin and a focal length of 8 96 m. The
linear dispersion varies from min A-' at A4ooo to min A-' at A . The
horizontal apparatus function, determined from the Kr.line A , has a
half-width of A with a marked asynirnetry to the red. The practical
resolving power at this wave4ength is 93 900, less than one-third of
that predicted by diffraction theory. Because of the asymmetry in the
apparatus function the centres of intensity of solar absorption lines
are displaced to the red by amounts which vary as their equivalent
widths; precautions must therefore be adopted in the measurement of
Doppler displacements. The yertical apparatus function (up and down
the slit) has a half-width of mm. This tends to wash out the spectra of
fine details on the solar surface, but theory and practical experience
show that spectra of solar' granules can be obtained. For unanalysed
white light, incident on a slit with a height of 19 mm, the general
scattered light in the focal plane is i 6 per cent.
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Title: Motions in the Sun at the photospheric level. I. Methods
Authors: Plaskett, H. H.
1952MNRAS.112..414P Altcode:
for determining sight-line velocities at specified points on the
solar photosphere are described. The portion of the solar image, the
spectrufl of which is to be pho\ographed, is observed with an angular
magnification of 390 times. The image may be guided, independently
of the telescopic controls, and the photograph taken at the instant
of best seeing. The spectra are measured against a centre spectrum by
Evershed's positive-on-negative method on a self-recording micrometer;
possible line displacements due to the asymmetry of the horizontal
apparatus function of the spectroscope are thus elminated. An equation
of condition between the three rectangular velocity components of motion
in the photosphere and the measured sight-line velocity is derived.
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Title: Astronomical Spectroscopy (Presidential Address, 1947)
Authors: Plaskett, H. H.
1947MNRAS.107..117P Altcode:
No abstract at ADS
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Title: Astronomical telescopes (Presidential Address, 1946)
Authors: Plaskett, H. H.
1946MNRAS.106...80P Altcode:
No abstract at ADS
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Title: (Presidential Address) on presenting the Gold Medal to
Professor J. H. Oort
Authors: Plaskett, H. H.
1946MNRAS.106..242P Altcode:
No abstract at ADS
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Title: The observational determination of the line absorption
coefficient and its variation with depth in the solar atmosphere
Authors: Plaskett, H. H.
1941MNRAS.101....3P Altcode:
No abstract at ADS
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Title: The Oxford solar telescope and Hartmann tests of its
performance
Authors: Plaskett, H. H.
1939MNRAS..99..219P Altcode:
No abstract at ADS
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Title: Solar granulation
Authors: Plaskett, H. H.
1936MNRAS..96..402P Altcode:
No abstract at ADS
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Title: A Moll-type microphotometer and its performance
Authors: Plaskett, H. H.
1934MNRAS..95..160P Altcode:
No abstract at ADS
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Title: Book Reviews: The Place of Observation in Astronomy
Authors: Plaskett, H. H.
1934PA.....42..173P Altcode:
No abstract at ADS
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Title: The formation of the magnesium b lines in the solar atmosphere
Authors: Plaskett, H. H.
1931MNRAS..91..870P Altcode: 1931HarRe..70....1P
No abstract at ADS
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Title: Hydrogen emission lines in nebulae
Authors: Plaskett, H. H.
1931Obs....54...49P Altcode:
No abstract at ADS
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Title: Line Intensities in Nebular Spectra
Authors: Plaskett, H. H.
1931PDAO....4..188P Altcode:
No abstract at ADS
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Title: Line intensities in nebular spectra (abstract)
Authors: Plaskett, H. H.
1931PAAS....6R.149P Altcode:
No abstract at ADS
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Title: The composite stellar and nebular spectrum of Z Andromedae
Authors: Plaskett, H. H.
1931PDAO....4..119P Altcode:
No abstract at ADS
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Title: Line intensities in nebular spectra (abstract)
Authors: Plaskett, H. H.
1929PA.....37R...9P Altcode:
No abstract at ADS
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Title: Line Intensities in Nebular Spectra.
Authors: Plaskett, H. H.
1928HarCi.335....1P Altcode:
Includes: Line Intensities in N.G.C. 1976 and 7027 - Line Intensities
in Six Planetary Nebulae - Physical Interpretation of Line Intensities.
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Title: Scientific Books: The Internal Constitution of the Stars
Authors: Plaskett, H. H.
1927Sci....66...81P Altcode: 1927Sci....66...81E
No abstract at ADS
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Title: A possible origin of the nebular lines (abstract)
Authors: Plaskett, H. H.
1927PAAS....5R..77P Altcode:
No abstract at ADS
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Title: The wedge method and its application to astronomical
spectrophotometry (abstract)
Authors: Plaskett, H. H.
1927PAAS....5Q..78P Altcode:
No abstract at ADS
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Title: Corrections to a List of Spectroscopic Binaries
Authors: Plaskett, H. H.
1924JRASC..18..367P Altcode:
No abstract at ADS
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Title: The Nature of Science
Authors: Plaskett, H. H.
1924JRASC..18..294P Altcode:
No abstract at ADS
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Title: The spectra of nebulae (abstract)
Authors: Plaskett, H. H.
1924PA.....32..462P Altcode:
No abstract at ADS
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Title: A Possible Origin of the Nebular Lines
Authors: Plaskett, H. H.
1923Natur.112..392P Altcode:
THE hypothesis that the lines of unknown origin in the spectra of
nebulæ are due to the atom of some hitherto undiscovered element (“
nebulium ”) is not the only one that may be advanced. The recently
developed quantum theory of band spectra makes it at least possible that
these lines could have their origin in a molecule with small moment of
inertia composed of atoms of those elements which are known to exist
in nebulæ. It is proposed in this letter to show that the existing
astronomical evidence is not in contradiction to this alternative
hypothesis, and also to indulge in some speculation as to the nature
of such a molecule.
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Title: Spectra of three O-type stars (abstract)
Authors: Plaskett, H. H.
1923PA.....31R..19P Altcode:
No abstract at ADS
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Title: The wedge method and its application to astronomical
spectrophotometry (abstract)
Authors: Plaskett, H. H.
1923PA.....31Q.659P Altcode:
No abstract at ADS
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Title: A possible origin of the nebular lines (abstract)
Authors: Plaskett, H. H.
1923PA.....31R.658P Altcode:
No abstract at ADS
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Title: The Pickering Series and Bohr's Atom
Authors: Plaskett, H. H.
1922JRASC..16..137P Altcode:
No abstract at ADS
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Title: The Intensity Distribution in Typical Stellar Spectra
Authors: Plaskett, H. H.
1922PAAS....4..226P Altcode:
No abstract at ADS
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Title: The Radial Velocities of 594 Stars
Authors: Plaskett, J. S.; Harper, W. E.; Young, R. K.; Plaskett, H. H.
1922PAAS....4..277P Altcode:
No abstract at ADS
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Title: The Spectra of Three O-Type Stars
Authors: Plaskett, H. H.
1922PAAS....4R.380P Altcode:
No abstract at ADS
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Title: The Spectroscopic Orbit of Z Vulpeculae
Authors: Plaskett, H. H.
1922PAAS....4..227P Altcode:
No abstract at ADS
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Title: The Pickering Series in O Type Stars.
Authors: Plaskett, H. H.
1921Natur.108..209P Altcode:
IF the Pickering series, consisting of the lines 5411, 4542, 4200,
etc., in stellar spectra, is due to ionised helium, it is known
from the investigations of Fowler and from Bohr's theory that there
must be additional lines which appear as violet components of the
Balmer series of hydrogen. As these components have an average
separation of 2 Å. they should be readily seen in the spectra of O
type stars. Unfortunately, there are two unfavourable circumstances:
first, the O type stars are all faint, and, secondly, the lines of
both the Balmer and the Pickering series are in general so diffuse as
to be hopelessly blended.
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Title: The Radial Velocities of 600 Stars (Abstract)
Authors: Plaskett, J. S.; Harper, W. E.; Young, R. K.; Plaskett, H. H.
1921PASP...33R.212P Altcode:
No abstract at ADS
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Title: Radiation from the Carbon Arc
Authors: Plaskett, H. H.
1921Natur.107..648P Altcode:
AN application of Merton and Nicholson's form of the wedge method
has been made to the study of the intensity distribution in typical
stellar spectra. In the late type spectra (including the sun), which
are sufficiently bright at the red end, the energy curves give a marked
depression from 0.50-0.67µ-a result not obtained by other observers. As
the spectrum of the carbon arc, assumed to radiate as a black body
at a temperature of 3750° Abs., is used to remove the colour curve
of the plate, a possible cause of this depression, which is common to
all stellar spectra that have been observed in the red, would lie in
an intensity distribution in the carbon arc differing from that assumed.
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Title: The radial velocities of 594 stars.
Authors: Plaskett, J. S.; Harper, W. E.; Young, R. K.; Plaskett, H. H.
1921PDAO....2....1P Altcode:
No abstract at ADS
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Title: Eighty-eight spectroscopic binaries.
Authors: Plaskett, J. S.; Harper, W. E.; Young, R. K.; Plaskett, H. H.
1921PDAO....1..287P Altcode:
No abstract at ADS
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Title: The spectra of three O-type stars.
Authors: Plaskett, H. H.
1921PDAO....1..325P Altcode:
No abstract at ADS
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Title: The Origin of Spectra (concluded)
Authors: Plaskett, H. H.
1920JRASC..14..269P Altcode:
No abstract at ADS
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Title: The Origin of Spectra
Authors: Plaskett, H. H.
1920JRASC..14..221P Altcode:
No abstract at ADS
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Title: Spectroscopy, Astronomical, The intensity distribution in
the continuous spectrum and the intensity of the hydrogen lines in
γ Cassiopei&aelig
Authors: Plaskett, H. H.
1920MNRAS..80..771P Altcode:
No abstract at ADS
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Title: One hundred spectroscopic binaries.
Authors: Plaskett, J. S.; Harper, W. E.; Young, R. K.; Plaskett, H. H.
1920PDAO....1..163P Altcode:
No abstract at ADS
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Title: Atmospheric Haze and a Suspected Variation in Solar Rotation
in 1915
Authors: Plaskett, H. H.
1919JRASC..13..391P Altcode:
No abstract at ADS
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Title: The solar rotation in 1913
Authors: Plaskett, H. H.
1918PAAS....3Q..89P Altcode:
No abstract at ADS
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Title: A Variation in Solar Rotation
Authors: Plaskett, H. H.
1917ApJ....45..144P Altcode:
No abstract at ADS
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Title: The Psychology of Differential Measurements
Authors: Plaskett, H. H.
1916JRASC..10..220P Altcode:
No abstract at ADS
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Title: A Variation in the Solar Rotation
Authors: Plaskett, H. H.
1916ApJ....43..145P Altcode:
No abstract at ADS
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Title: The Solar Rotation in 1913
Authors: Plaskett, H. H.
1914JRASC...8..307P Altcode:
No abstract at ADS
