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Author name code: evans
ADS astronomy entries on 2022-09-14
=author:"Evans, John W." OR =author:"Evans, J.W." year:1932-1993 -aff:"United Kingdom" -aff:"Wormley"
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Title: The birefringent filter (Journal of the Optical Society of
America 1949)
Authors: Evans, J. W.
1993inas.book...71E Altcode:
No abstract at ADS
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Title: Hale Prize Lecture - Enjoyment in an Astronomical Occupation
( J. W. EVANS )
Authors: Evans, J. W.
1981BAAS...13..805E Altcode:
No abstract at ADS
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Title: Sacramento Peak Observatory, Sunspot, New Mexico. Observatory
report.
Authors: Evans, J. W.
1977BAAS....9..243E Altcode:
No abstract at ADS
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Title: Introductory Review of Solar Activity
Authors: Evans, J. W.
1976saop.book....3E Altcode:
No abstract at ADS
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Title: Observed Oddities in the Lines H, K, b and H&beta
Authors: Evans, J. W.; Catalano, C. P.
1972SoPh...27..299E Altcode:
We compare microphotometer intensity traces perpendicular to dispersion
in simultaneous spectrograms of good spatial resolution traced at
various Δλ's in each of the lines. Cross correlations between the
different traces show the following: (a) For each Δλ<SUB>K</SUB> there
is a corresponding Δλ<SUB>b</SUB><SUB>1</SUB>at which the coefficient
of correlation, r, is a maximum, usually > 0.8. (b) No such high
correlations are found between H and Hβ. (c) Comparison of traces
in the continuum and at all observed Δλ's in K, H, b<SUB>1</SUB>,
b<SUB>2</SUB> show a range of Δλ's in each line over which r is very
significantly negative, while Hβ shows no such peculiarity.
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Title: Introductory Review of Solar Activity
Authors: Evans, John W.
1972PrAA...30....3E Altcode:
No abstract at ADS
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Title: Solar Instrumentation (Part I)
Authors: Evans, John W.
1971spas.conf...61E Altcode:
No abstract at ADS
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Title: Introduction to Research on the Solar Corona
Authors: Evans, J. W.
1971ASSL...27....1E Altcode: 1971psc..conf....1E
No abstract at ADS
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Title: The Chromospheric Spectrum at the 1962 Eclipse
Authors: Dunn, R. B.; Evans, J. W.; Jefferies, J. T.; Orrall, F. Q.;
White, O. R.; Zirker, J. B.
1968ApJS...15..275D Altcode:
A joint expedition of the High Altitude Observatory, Sacramento Peak
Observatory, and the National Bureau of Standards obtained slitless
spectrograms of the flash spectrum at the February 5,1962, total eclipse
of the Sun. The spectrograms covered the wavelength range of about
3200 to 9100 A with a height resolution of 100 km. The spectrographic
equipment, the observations, the photometric calibration procedures,
and the methods adopted to reduce the large quantity of data are
described. The results are presented in a set of tables that show the
wavelength and identification (where known) of each of the 3500 lines
recorded. A separate set of tables lists the intensity of each line at
each height. The latter tables are ordered according to the element,
ionization stage, and multiplet number associated with the line.
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Title: Color in Solar Granulation
Authors: Evans, John W.
1968SoPh....3..344E Altcode:
Pairs of spectra exposed simultaneously in the yellow and ultraviolet
show exactly the same solar granulation in the two colors. This is
contrary to Vassilyeva's earlier results. The difference is probably
due to her neglect of atmospheric dispersion.
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Title: Summary of Nobel Symposium 9
Authors: Evans, J. W.
1968mmsf.conf..243E Altcode:
No abstract at ADS
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Title: Princeton University Observatory report.
Authors: Evans, J. W.
1967AJ.....72.1128E Altcode:
No abstract at ADS
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Title: Solar Granules in the Ultraviolet and Yellow.
Authors: Evans, John W.
1967AJ.....72S.795E Altcode:
Studies of rms vertical velocities in the solar atmosphere, evidenced
by local Doppler shifts in Fraunhofer lines, show a marked dependence
on both line strength and the wavelength region. The rms velocities
increase towards the ultraviolet, and with increasing line strength
(i.e., with height in the solar atmosphere). This is a report of an
investigation to determine whether the detail of photospheric granular
structure also varies between widely separated wavelength regions. The
observational material consists of four pairs of spectrograms showing
good spatial resolution along the slit. Each pair consists of a short
length of the spectrum centered at N3954 (UV) and another at N5888 (Y)
exposed simultaneously. The spectrograph slit was carefully oriented
perpendicular to the horizon, parallel to the small displacements
caused by differential atmospheric refraction. Each UV frame was traced
perpendicular to dispersion by a digital microdensitometer at five
continuum wavelengths, and each Y frame at three wavelengths. The cross
correlations between the four pairs are 0.85+0.02, and we conclude that
the granular structure at N3954 is very nearly identical with that at
N5888. This result directly contradicts that found by Vassiljeva (Solar
Phys. 1,16,1966) from photoelectric scanning across the solar disk
with a sensitive spot 0 "2 in diameter. She found that the correlation
rapidly decreased with wavelength difference, and had a value of only
about 0.1 for a span of 1900 A. The Sacramento Peak spectrograms showed
a relative displacement along the slit of 2 "1 between the UV and y
images due to atmospheric refractive dispersion. I suggest that the
low correlations between the structures Vassilj eva recorded at widely
different wavelengths are the result of the atmospheric dispersion. This
would cause her 0 "2 sensitive spot to scan along parallel lines in
different colors, the separation of which would increase with wavelength
difference, and inclination to the vertical circle.
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Title: Sacramento Peak Observatory
Authors: Evans, John W.
1967SoPh....1..157E Altcode:
No abstract at ADS
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Title: Motions in the Solar Atmosphere
Authors: Evans, John W.
1966ossg.book...77E Altcode:
No abstract at ADS
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Title: Observational Study of the Dynamics of the Solar Atmosphere
Authors: Evans, John W.
1965ASSL....3...52E Altcode: 1965pss..conf...52E
No abstract at ADS
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Title: Inclined inhomogeneities in the solar photosphere
Authors: Evans, John W.
1964ApNr....9...33E Altcode:
No abstract at ADS
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Title: Inclined Inhomogeneities in the Solar Atmosphere.
Authors: Evans, John W.
1964AJ.....69R.541E Altcode:
Good spectrograms of undisturbed regions on the sun show a pattern
of lengthwise threads representing granulation. I have measured the x
positions (perpendicular to dispersion) of threads as a function of X
distance from the center of the strong line Fe4383.6 from AX=0.2 A to
the continuum, and at the centers of other lines nearby. The standard
deviation of a single measure corresponds to +20 to +40 km on the sun
for sharp or fuzzy threads. Inspection of many spectrograms showed
that many threads are visible curved, as though the positions of the
corresponding granules along the slit varied with A~. The measurements
on one spectrogram covering 135 000 km on the sun showed the following
thread characteristics: (a) The x displacements are symmetrical,
having the same sign and magnitude on the blue and violet sides of
the line. The sign of the displacement is quite random. (b) Of the
58 bright threads visible in the spectrogram, the x displacements of
39 were >~160 km; of 4, >~970 km; and the rms for all was 500
km. (c) The displacements are present in all Fraunhofer lines and are
very strongly correlated with line strength for any single thread. (d)
There is no systematic tendency for threads to become fuzzy in their
curved portions. My interpretation of this behavior is that a curved
thread represents a columnar inhomogeneity which is sharply inclined
to the vertical along the slit direction. At different AX's (or at
the centers of weaker lines) we see cross sections of the column
at a series of different heights, and hence at different apparent x
positions. Allowing a very liberal 500 km for the total height range,
the statistics show that high inclinations of 45o are the normal thing
for bright inhomogeneities. This ignores the uncomfortable fact that
the observed displacements occur between 5 and 20 Doppler widths from
the line core, where we might expect a very small height range, and
little height discrimination.
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Title: Review of Publications- The Solar Corona edited
Authors: Evans, John W.
1963JRASC..57..268E Altcode:
No abstract at ADS
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Title: Vertical Motions at Different Heights in the Solar Atmosphere.
Authors: Evans, John W.
1963AJ.....68R..72E Altcode:
Although the vertical motions in the solar atmosphere responsible for
the "wiggles" in Fraunhofer lines are largely oscillatory (Leighton,
Noyes, and Simon, Astrophys. J. 135, 474,1962; Evans and Michard,
ibid. 136, 493,1962) the instantaneous velocity field is random. The
rms vertical velocity ~v increases systematically with the strength
of the line measured, and hence with geometrical height on the sun
(Evans and Michard, Astrophys. J. 135, 812,1962). We should therefore
expect to find a decrease in ~v as we measure the velocities at
increasing distances AX from the centers of strong high-level lines,
where we see to lower levels in the solar atmosphere. The L)oppler
shifts in the profiles of Hot, H~, D1, and b2 have been measured for
at least 50 points alo~ig each line. The measured velocities show
without exception the expected smooth decrease from a maximum near
the line center to a value ~2' to ~` as great at the largest AX's
~t which velocities could be determined. Less exact measurements
(by the method described by Evans and Michard) in fe 3856.4 and Ca
II 8542 lead to a similar result. This finding tidies up our concept
of the height dependence of ~. We can use ~v with some confidence
as a tool for ordering the Fraunhofer lines according to effective
height of origin, and to relate them to the height of absorption in
the wings of the strong lines. We must remember, however, that the
"effective height" of ~ line is not very clearly defined since the
contribution function extends over a considerable height range, and
differs somewhat from one line to the next. As an index to height,
however, ~v has the merit of being a straightforward observational
quantity depending only on mass motion, which must be the same in a
given element of volume for all atoms regardless of their properties
or the physical state of their envlronment.
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Title: Motions in the Solar Atmosphere
Authors: Evans, John W.
1963S&T....25..321E Altcode:
No abstract at ADS
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Title: Emission-Line Ratios in the Solar Corona.
Authors: Aly, M. K.; Evans, J. W.; Orrall, F. Q.
1963ApJ...137.1313A Altcode:
No abstract at ADS
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Title: Observational study of macroscopic inhomogeneities in the
solar atmosphere. V. Statistical study of the time variations of
the solar inhomogeneities
Authors: Evans, J. W.; Michard, R.; Servajean, R.
1963AnAp...26..368E Altcode:
No abstract at ADS
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Title: The solar corona
Authors: Evans, John W.
1963soco.conf.....E Altcode: 1963QB529.S6.......
No abstract at ADS
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Title: A Photometric Study of the Continuum and Seventeen Emission
Lines in the Inner Solar Corona.
Authors: Aly, M. K.; Evans, J. W.; Orrall, F. Q.
1962ApJ...136..956A Altcode:
Absolute intensities of the continuum and a number of emission lines
between x 3300 and X 6800 have been measured as a function of position
angle on spectrograms of the inner corona obtained by B. Lyot and
M. K. Alyat the total eclipse of February 25,1952, at Khartoum. More
detailed measurements were made in a bright coronal condensation on
the west limb, where the continuum and the following emission lines
were measurable: XX 3328, 3388, 3454, 3534, 3601, 3643, 3801, 3988,
4086, 4232, 4412, 5116, 5303, 5445, 5694, 6374, 6702. On the assumption
that the condensation is axially symmetric, we have found the electron
density and the emission as functions of distance from the axis of
symmetry. The lines of lowest ionization potential show a decrease in
emission at the center of the condensation while the continuum and the
emission of the remaining lines show increasing concentration toward
the center with increasing ionization potential. (An exception is X
3643, which behaves like a line of lower ionization potential than
Ni xui.) X 3534 appears to be much too bright to be due to V x unless
the abundance of vanadium is very much higher than current estimates
for the photosphere.
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Title: Correlations in the Time Variations of Macroscopic
Inhomogeneities in the Solar Atmosphere.
Authors: Evans, J. W.; Main, P.; Michard, R.; Servajean, R.
1962ApJ...136..682E Altcode:
No abstract at ADS
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Title: Observational Study of Macroscopic Inhomogeneities in the
Solar Atmosphere. III. Vertical Oscillatory Motions in the Solar
Photosphere.
Authors: Evans, J. W.; Michard, R.
1962ApJ...136..493E Altcode:
We have studied the Doppler displacements in two time sequences of
spectrograms, one showing Fe I 5171.61, Mgi 5172.70 (b2), and Tii
5173.75 at the center of the solar disk, the other showing Fei 5324.19
at the limb. At the center we find that the velocity field consists
mainly of short-lived oscillations of small elements of the solar
atmosphere. The r.m.s. velocity amplitudes are 0.42 and 0.81 km/sec
at low and high levels, respectively. The periods of the vertical
oscillations cover roughly the range seconds, with a mean value around
242 sec. The periods seem to decrease with height in the atmosphere. An
autocorrelation study shows also that the vertical velocity field is
dominated by periodic oscillations, the time-correlation function having
a strong positive peak at 300 seconds from the origin. The study of the
time lags of oscillations between strong and faint lines suggests that
they are of a type intermediate between progressive sonic waves (for the
shorter periods) and standing waves (for the longer periods). Gradual
transition from the first type to the second seems to occur during the
life of a given oscillation. There is an indication that the individual
oscillations are associated with individual granules. Near the limb,
the observed horizontal motions consist of slowly changing velocities
of the order of 0.5 km/sec in large surface elements, on which are
superposed smaller random velocities of short duration. Oscillations
rapidly disappear away from the center of the disk. The horizontal
and vertical observable motions appear to be physically independent.
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Title: Observational Study of Macroscopic Inhomogeneities in the
Solar Atmosphere. II. Brightness Fluctuations in Fraunhofer Lines
and the Continuum.
Authors: Evans, J. W.; Michard, R.
1962ApJ...136..487E Altcode:
Large brightness fluctuations are observed at the centers of Fraunhofer
lines of average and great strength. Their character is described for
different lines and different parts of line profiles. Root-mean- square
values are given for a number of cases. The scale of these features is
comparable to the size of photospheric granulation. There are no simple
relations between the brightness fluctuations in Fraunhofer lines,
Doppler displacements of the lines, and continuum granulation. The
bearing of these observations on recent inhomogeneous models of the
photosphere is briefly discussed.
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Title: Observational Study of Macroscopic Inhomogeneities in the
Solar Atmosphere. I. Velocity Displacements of Fraunhofer Lines as
a Function of Line Strength and Position on Disk.
Authors: Evans, J. W.; Michard, R.
1962ApJ...135..812E Altcode:
The "random turbulent velocities," , of macroscopic motion in the
solar atmosphere have been directly observed at the center of the
disk as local Doppler displacements in 18 lines, ranging in Rowland
intensity from 0 to 1000 (K3 line of Ca ii) The measurements show a
marked increase of with line strength. On a given spectrogram, the
correlation between the velocity shifts of one line with those of
another line diminishes steadily as the intensity difference between
the two lines increases. There is thus a quantitative and qualitative
variation in the velocity field with height, as indicated by line
strengths. The center-to4imb variations in were determined for four
lines with Rowland intensities from 0 to 20. The strong and faint lines
behave differently. The very pronounced increases of with line strength
observed at the center of the disk disappears toward the limb. Here,
within observational accuracy, is the same for all line strengths
in the observed range. We suggest that the velocity field consists
of a vertical component which increases strongly with height and a
horizontal component independent of height.
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Title: The Solar Granulation
Authors: Evans, J. W.
1962IAUTB..11..196E Altcode:
No abstract at ADS
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Title: Local Doppler Effects in the Photosphere.
Authors: Evans, John W.; Mauter, Horst
1961AJ.....66...42E Altcode:
Highresolution spectrograms taken under conditions of good seeing at
Sacramento Peak show the characteristic Doppler distortions of the
solar Fraunhofer lines due to photospheric turbulence. The studies of
Richardson and Schwarzschild (1950), Plaskett (1954), Goldberg, Mohler,
Unno, and Brown (1960), and others, have fixed the directly resolvable
dimensional characteristics and velocity distribution of the turbulent
elements. This note reports the result of a first effort to determine
the time variations. It is based upon a series of 31 spectrograms of
the Fei line, x5324.2, taken at 20-sec intervals, and a 2-hr motion
picture of the lines of Fei and Cri between A5327.5 and A5329.5, taken
at a rate of 12 frames per minute. Isophotometer tracings of the 31
spectrograms yielded curves of velocity as a function of position in the
solar image along the spectrograph slit. The mean length of a turbulent
element along the slit was 3.1", while the smallest element observed
was 1.2". The rms velocity in this small sample varied between 0.25
and 0.4 km/sec. The distribution of durations of individual velocity
peaks, during which they develop and decay, is still uncertain,
since a number of the larger peaks persisted throughout the 10-minute
interval of observation. Longer observing intervals, with attention to
the rotational motion of the solar surface past a fixed slit, will be
necessary for a definitive result. The present observations, however,
showed a marked positive correlation between the maximum velocity
attained and the duration of a peak. The smallest duration observed
with any confidence (with due regard for the uncertainties of guiding
and seeing variations) was about two minutes, with a peak velocity
of +0.5 km/sec. The motion pictures show the velocity fluctuations
under rather mediocre seeing, and convey the impression of random
velocity changes at any one point along the slit, with characteristic
times of the order of three minutes. There were a few instances
of a rather definite oscillation at one point between positive and
negative velocities, going through as many as three complete cycles,
with periods of about five minutes. Whether or not these are simply
chance occurrences remains to be determined by a statistical study.
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Title: Flare-associated magnetic activity in the sun.
Authors: Evans, John W.
1959AJ.....64R.330E Altcode:
Observations of the longitudinal Zeeman effects in a solar active
center show the variations of magnetic field streng~h during a period
of 144 minutes on 30 April 1958, which included the development
and decay of a flare of importance I ~. The measurements show that
the flare crossed the neutral line of zero longitudinal field, and,
although the extremities lay in regions of steep field gradients,
most of the flare area was a region of low gradient. A small but
pronounced S pole within the flare area developed and faded away in
exact synchronism with the flare intensity. However, the large magnetic
changes affected the whole field of the active center. The integrated
magnetic energy of the region underwent a sharp decrease of about 16
per cent during the 14 minute rising phase of flare intensity, and
an even sharper recoverN to its initial value immediately after flare
maximum. This behavior was shared by the large sunspot fields and the
area outside the sunspots. On the assumption that the field was 5000
km deep, the energy change of the active center amounted to 4 X I0~'
ergs. The Ha radiation of the flare during its life was about 1028
ergs. Thus the changes in magnetic energy prob~bly exceed the total
radiation of the flare in the Balmer and Lyman series by a considerable
factor. Sacramento Peak Observatory Sunspot, New Mexico
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Title: Solar photographs from 80,000 feet.
Authors: Schwarzschild, M.; Rogerson, J. B., Jr.; Evans, J. W.
1958AJ.....63..313S Altcode:
During the summer of 1957 three unmanned balloon flights have been
carried out with the aim of obtaining direct solar photographs with
high definition, undisturbed by atmospheric seeing. The first flight
had the purpose of testing the pointing mechanism and carried only a
dummy telescope. The full telescope, constructed by Perkin-Elmer Co.,
carried on the second and third flights, consisted of a parabolic
mirror of ~~-inch aperture, f/8, an enlarging lens which produced an
effective focal length of 200 feet, and a 35-mm movie camera taking an
exposure each second with exposure time 0~.00I. The focus was scanned
over a range of 10 to 20 times the focus tolerance. In the pointing
control which was constructed by the Research Service Laboratories
of the University of Colorado, photo- diodes were employed to find
the sun and center on it. Motor-driven magnetic clutches were used
to move the telescope with the motion in azimuth being accomplished
by rotating against a heavy flywheel carrying the batteries. In
the execution of the flights, carried out by General Mills, Inc.,
no serious difficulties were encountered in the launching, tracking
and recovering of the equipment. The cost of repairs for launching
damage averaged for each of the three flights about 5 per cent
of the construction cost. *Presented at the 99th A.A.S. meeting,
Indianapolis, Ind., December 27-30, 1957. Several exposures of very
high definition were obtained, both of the center of the solar disk
and of the limb. These exposures show that the solar granulation has
a cellular though highly irregular character. The bright cells appear
separated from each other by dark, often very sharp lines. The sizes
of the elements seem to range from 2" down to 0'.'3. This project was
sponsored by the Office of Naval Research and the Geophysics Research
Directorate of the Air Force. Princeton University Observatory,
Princeton, N. J., and Sacramento Peak Observatory, Sunspot, N. M.
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Title: Instrumentation for Global Observation of the Sun during
the IGY
Authors: Evans, John W.
1958gigy.conf...21E Altcode:
No abstract at ADS
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Title: Observations of the Solar Emission Corona Outside Eclipse
Authors: Evans, John W.
1957PASP...69..421E Altcode:
No abstract at ADS
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Title: The Sacramento Peak Observatory
Authors: Evans, John W.
1956S&T....15..436E Altcode:
No abstract at ADS
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Title: Solar Instrumentation
Authors: Evans, J. W.; Dunn, R. B.
1956SCoA....1....5E Altcode:
No abstract at ADS
