Author name code: dodson
ADS astronomy entries on 2022-09-14
author:"Dodson, Helen W."
------------------------------------------------------------------------
Title: Dependence of radio emission in large Hα flares 1967 1970
upon the orientation of the local solar magnetic field
Authors: Roelof, E. C.; Dodson, H. W.; Hedeman, E. R.
Bibcode: 1983SoPh...85..339R
Altcode:
During 1967-1970, the greatness of ∼ 90 large flares (Hα importance
≳ 2) was influenced by the orientation of the large-scale (∼ 100 000
km) magnetic field structure over the flare site. Although the average
X-ray and optical emissions are only slightly larger for flares with
their overlying fields directed southward, as opposed to northward,
the meter-wave-length prompt flux maxima are, on average, an order
of magnitude greater for the flares with southward oriented magnetic
fields. There is a comparable, but possibly smaller difference in
the 10 cm-λ fluxes. We therefore conclude that, during this period,
the orientation of the overlying magnetic field affects the amount
of electromagnetic flare energy radiated promptly in the corona
(10 cm-λ and m-λ), relative to that radiated in the chromosphere
(X-ray and optical). We demonstrate that this statistical effect shows
some variability in degree during the period, although the trend is
consistent throughout.
Title: Large scale solar magnetic fields at the site of Flares,
the greatness of flares, and solar-terrestrial disturbances
Authors: Dodson, H. W.; Hedeman, E. R.; Roelof, E. C.
Bibcode: 1982GeoRL...9..199D
Altcode:
Major solar flares during 1967-1970 are significantly more likely to
occur in active regions whose inferred overlying large-scale (∼100,000
km) magnetic flux is oriented preferentially north-to-south than for
south-to-north or indeterminant orientations. This purely solar effect
may be the dominant cause of previously reported correlations between
southward solar active region magnetic fields and enhancements in
geomagnetic disturbances, solar wind velocities and (newly reported
here) solar flare proton fluxes. If this effect may be generalized to
other portions of the solar cycle, it could offer a fundamental clue
to the flare mechanism which should also prove useful in the prediction
of solar-terrestrial disturbances.
Title: Evolutionary charts of solar activity (calcium plages) as
functions of heliographic longitude and time
Authors: Hedeman, E. R.; Dodson, H. W.; Roelof, E. C.
Bibcode: 1981jhu..rept.....H
Altcode:
The richness and diversity of data relating to solar activity present
a challenge from the point of view of organization and evaluation. For
phenomena such as plages and centers of activity that tend to last
for more than one solar rotation, a sequence of evolutionary charts
based on heliographic longitude for successive solar rotations are
discussed. Such a diagrammatic representation of calcium plages
as a function of longitude and time, coupled with considerations of
heliographic latitude, permits relatively easy and confident recognition
of successively returning centers of activity.
Title: Experimental comprehensive solar flare indices for major and
certain lesser flares, 1975-1979
Authors: Dodson, H. W.; Hedeman, E. R.
Bibcode: 1981STIN...8217042D
Altcode:
Data for solar cycle 20 and information for the ascending branch of
cycle 21 are presented. Five components comprise the 'profile' of
the flare. The sum of the five gives the comprehensive flare index
(CF). Values of the CFI are derived for flares that are considered
to have been well above average in either ionizing, H alpha, or radio
frequency radiation.
Title: Evolutionary charts of solar activity (calcium plages) as
functions of heliographic longitude and time, 1964-1979
Authors: Hedeman, E. Ruth; Dodson, Helen Walter; Roelof, E. C.
Bibcode: 1981ecsa.book.....H
Altcode:
No abstract at ADS
Title: Commens on filament disintegration and its relation to other
aspects of solar activity
Authors: Dodson, H. W.; Hedeman, R.; Rovira, M.
Bibcode: 1980BAAA...18...51D
Altcode:
Los estudios de desapariciones bruscas en los ciclos
solares 19 y 20 (hasta 1969) indican que estos eventos suceden
frecuentemente. Aproximadamente el 30 % de todos los filamentos mayores
en estos ciclos se desintegraron en el curso de su trayecto a través
del disco solar.
Title: Examples of problem flares or situations in past
solar-terrestrial observations
Authors: Dodson, H. W.; Hedeman, E. R.; Mohler, O. C.
Bibcode: 1979stp.....1..385D
Altcode:
Instances of solar activity are discussed in terms of their relative
interference with making solar terrestrial observations. Unexpected
flares of significance are reported and the geophysical effects of
these flares are noted.
Title: Some comments on flares after many years of observation.
Authors: Dodson, H. W.; Hedeman, E. R.
Bibcode: 1976SoPh...47..267D
Altcode:
Ground based observations of flares are reviewed to seek implications
for a flare build-up on either a long or a short time scale. Plots
of flare frequency and importance for certain individual centers of
activity suggest a possible crescendo in flare occurrence days and
hours before the development of large and significant flares. The
X-ray records follow the same pattern of apparent build-up. A possible
dependence between successive major flares, as phases one and two of
a single complex flare event, suggests that the time scale in which
the total flare event takes place may show extreme variation.
Title: Distribution of proton producing flares around the sun.
Authors: Smart, D. F.; Shea, M. A.; Dodson, H. W.; Hedeman, E. R.
Bibcode: 1976spre.conf..797S
Altcode: 1976spre.proc..797S
The catalog of solar particle events for the period 1955-1969 is used as
the basic data source for the identification of the solar proton events
and the association of each event with a specific solar flare. Among
the proton events examined, 154 events were confidently associated
with solar flares and 171 events with polar cap absorption. It is
shown that the distribution of solar proton flares on the visible
hemisphere of the sun can be represented by a Gaussian function with
maximum between 30 and 40 deg W heliographic longitude. In particular,
69-86% of the polar cap absorption events detected at the earth are
associated with a solar flare on the visible hemisphere of the sun. Of
the 14-31% proton cap absorption and proton events that occur on the
invisible hemisphere, the largest number of these should be from a
flare behind the western limb of the sun.
Title: Large-Scale Organization of Solar Activity in Time and Space
Authors: Dodson, H. W.; Hedeman, E. R.
Bibcode: 1976saop.book...19D
Altcode:
No abstract at ADS
Title: Large-scale structure of solar activity and its time and
spatial variations.
Authors: Dodson, H. W.; Hedeman, E. R.
Bibcode: 1976npsa.conf....9D
Altcode:
No abstract at ADS
Title: Experimental comprehensive solar flare indices for certain
flares, 1970-1974
Authors: Dodson, H. W.; Hedeman, E. R.
Bibcode: 1975STIN...7627156D
Altcode:
Comprehensive indices for major flares are given for 1970-74. The
values of the Comprehensive Flare Index were derived for a group of
flares that are considered to have been well above average in either
ionizing, H or radio frequency radiation.
Title: Comments on the course of solar activity during the declining
phase of solar cycle 20 (1970 74)
Authors: Dodson, H. W.; Hedeman, E. R.
Bibcode: 1975SoPh...42..121D
Altcode:
In the declining phase of solar cycle 20 (1970-74) three pulses of
activity occurred and resulted in two well defined `stillstands'
in the smoothed means of sunspot, 2800 MHz, and calcium plage
data. Marked diminutions in spot and 2800 MHz flux took place in
1970 and 1971, respectively, and were accompanied by concomitant
decreases in flare-occurrence. Studies of the latitude distribution
of spots and flares show the extent of the dominance of the northern
hemisphere in cycle 20 and the marked phase shift between northern
and southern hemispheres. In the years studied, the longitudes of
centers of activity clustered in identifiable zones or hemispheres for
relatively long intervals of time. From mid-1973 to mid-1974 the Sun
had a relatively inactive hemisphere centered on ∼0° longitude. The
relationship of certain well defined `coronal holes' to this inactive
hemisphere of the chromosphere is noted. The first two spot groups of
the new cycle formed in November 1974 and January 1975 in the longitude
zone associated with relatively high levels of old cycle activity,
a repetition of the pattern observed in 1963-64.
Title: Course of Solar Activity during the Declining Phase of Solar
Cycle 20
Authors: Dodson, H. W.; Hedeman, E. R.
Bibcode: 1975BAAS....7R.364D
Altcode:
No abstract at ADS
Title: Catalog of solar particles events, 1955 - 1969.
Authors: Dodson, H. W.; Hedeman, E. R.; Kreplin, R. W.; Martres,
M. -J.; Obridko, V. N.; Shea, M. A.; Smart, D.; Tanaka, H.; Svestka,
Z.; Simon, P.; Fritzová-Svestková, L.; Guitart, A.
Bibcode: 1975cspe.book.....D
Altcode: 1975QB505.C37......
No abstract at ADS
Title: Comparison of activity in solar cycles 18, 19, and 20.
Authors: Dodson, H. W.; Hedeman, E. R.; Mohler, O. C.
Bibcode: 1974RvGSP..12..329D
Altcode: 1974RvGeo..12..329D
No abstract at ADS
Title: A small subflare in CINOF program, 1972 June 14, 1936 UT
Authors: Dodson, H. W.; Hedeman, E. R.
Bibcode: 1974stp.....1...63D
Altcode:
According to H-alpha and/or K3 records of McMath Plage 11926, the
flare event on 1972 June 14 at 1936 UT was one of a series of four
subflares that occurred in this plage between 1600 and 2030 UT. These
chromospheric brightenings apparently were associated with a moderately
active system of narrow filaments just beyond the southern boundary of
the calcium plage. Comparison with magnetographic data shows that in
general these subflares occurred in the neighborhood of a secondary
neutral line near the southern boundary of the plage. The brightest
H-alpha component of the 1936 UT event, however, developed over the
penumbra of the large following spot of Mt. Wilson group 18859, near
the eastern end of the filament system, and cut nearly perpendicularly
across the closely packed cluster of magnetic contours surrounding
the spot.
Title: International Cooperative Survey of Energetic Solar Particle
Events - A Progress Report
Authors: Dodson, H. W.; Hedeman, E. R.
Bibcode: 1972BAAS....4R.380D
Altcode:
No abstract at ADS
Title: Reevaluation of Relationships between Solar Flares and Sporadic
Geomagnetic Storms.
Authors: Dodson, H. W.; Hedeman, E. R.
Bibcode: 1972BAAS....4R.309D
Altcode:
No abstract at ADS
Title: Comments on Filament-Disintegration and Its Relation to Other
Aspects of Solar Activity
Authors: Dodson, Helen W.; Hedeman, E. Ruth; De Miceli, Marta Rovira
Bibcode: 1972SoPh...23..360D
Altcode:
Studies of `disparitions brusques' in solar cycles 19 and 20 (to 1969)
indicate that such events occur frequently. Approximately 30% of all
large filaments in these cycles disintegrated in the course of their
transit across the solar disk. `Major' flares occurred with above
average frequency on the last day on which 141 large disappearing
filaments were observed (1958-60; 1966-69). Relationships between a
disintegrating filament on July 10-11, 1959, a prior major flare,
a newly formed spot, and concomitant growth of Hα plage are
presented. Observation of prior descending prominence material
apparently directed towards the location of the flare of 1959 July
15d19h23m is reported. The development
of the filament-associated flare of February 13, 1967 is described.
Title: Large-Scale Organization of Solar Activity in Time and Space
Authors: Dodson, Helen W.; Hedeman, E. Ruth
Bibcode: 1972PrAA...30...19D
Altcode:
No abstract at ADS
Title: Time Variations in Solar Activity
Authors: Dodson, H. W.; Hedeman, E. R.
Bibcode: 1972ASSL...29..151D
Altcode: 1972sun..conf..151D
No abstract at ADS
Title: Time variations in solar activity.
Authors: Dodson, H. W.; Hedeman, E. R.
Bibcode: 1972sstp.conf..151D
Altcode:
No abstract at ADS
Title: Circumstances at times of major flares in regions with small
or no spots.
Authors: Dodson, H. W.; Hedeman, E. R.
Bibcode: 1971BAAS....3R.260D
Altcode:
No abstract at ADS
Title: An experimental, comprehensive flare index and its derivation
for "major" flares, 1955-1969
Authors: Dodson, Helen Walter; Hedeman, E. Ruth
Bibcode: 1971ecfi.book.....D
Altcode:
No abstract at ADS
Title: Major Hα Flares in Centers of Activity with very Small or
no Spots
Authors: Dodson, Helen W.; Hedeman, E. Ruth
Bibcode: 1970SoPh...13..401D
Altcode:
Major Hα flares (importance ≥ 2) in plages with only small
or no spots constitute a rare but well observed aspect of solar
activity. Information relating to 83 such flares has been assembled and
studied. In the years 1956-1968 these flares represented ∼ 7% of all
confirmed flares of importance ≥ 2. In general, the flares were of
unusually long duration and rose to maximum intensity slowly. A flash
phase was often absent or poorly defined. In a number of cases, the
flare emission included two bright filaments more or less parallel. The
flares usually occurred during the late, flare-poor phase of a center of
activity, and their outbreak did not presage a resurgence of activity
in subsequent rotations. The flares were frequently associated with
the position of dark filaments.
Title: IQSY data review: Solar activity.
Authors: Michard, R.; Dodson, H. W.; Hedeman, E. R.
Bibcode: 1970AIQSY...6..187M
Altcode:
No abstract at ADS
Title: Solar Circumstances at the Time of the Cosmic Ray Increase
on January 28, 1967
Authors: Dodson, Helen W.; Hedeman, E. Ruth
Bibcode: 1969SoPh....9..278D
Altcode:
Solar circumstances have been evaluated for January 28, 1967, the
date of an observed ground level enhancement of cosmic rays which
was not preceded by observation of a suitably great Hα flare. On the
visible solar hemisphere, a bright subflare at S23° E19° occurred
in appropriate time association with the cosmic ray event, and was
accompanied by weak X-ray enhancement and radio frequency emission. If
this flare, alone, or in combination with other minor flares observed
on the visible hemisphere on January 28 was the source of the energetic
cosmic rays recorded on that date, then current thinking regarding
the characteristics of cosmic ray flares must be modified.
Title: Solar Circumstances at the Time of the Cosmic-Ray Increase
on 28 January 1967
Authors: Dodson, Helen W.; Hedeman, E. Ruth
Bibcode: 1969BAAS....1..275D
Altcode:
No abstract at ADS
Title: The solar particle event of July 16 19, 1966 and its possible
association with a flare on the invisible solar hemisphere
Authors: Dodson, Helen W.; Hedeman, E. Ruth; Kahler, Stephen W.; Lin,
Robert P.
Bibcode: 1969SoPh....6..294D
Altcode:
An energetic solar proton and electron event was observed by particle
detectors aboard Explorer 33 (AIMP-1) and OGO-3 during the period
July 16-19, 1966. Optical and radio observations of the sun suggest
that these particles were produced by a flare which may have occurred
on July 16 near the central meridian of the invisible hemisphere. The
active region to which the flare is assigned is known to have produced
the energetic particle events of July 7 and 28, 1966. The propagation
of the particles in the July 16-19 event over the ∼180° extent
of solar longitude from the flare to the earth is discussed, and it
is concluded that there must exist a means of rapidly distributing
energetic particles over a large area of the sun. Several possible
mechanisms are suggested.
Title: Later development of the center of activity of the proton
flare, 7 July 1966: Optical observations.
Authors: Dodson, H. W.; Hedeman, E. R.
Bibcode: 1969AIQSY...3..215D
Altcode:
No abstract at ADS
Title: The history and morphology of solar activity, 1964 - 1965.
Authors: Dodson, H. W.; Hedeman, E. R.
Bibcode: 1969AIQSY...4....3D
Altcode:
No abstract at ADS
Title: The behavior of the active region prior to the proton flare
7 July 1966, based on lambda -sweep records.
Authors: Dodson, H. W.
Bibcode: 1969AIQSY...3..154D
Altcode:
No abstract at ADS
Title: McMath-Hulbert Observatory of the University of Michigan
Authors: Mohler, Orren C.; Dodson, Helen W.
Bibcode: 1968SoPh....5..417M
Altcode:
No abstract at ADS
Title: The Proton Flare of August 28, 1966
Authors: Dodson, Helen W.; Hedeman, E. Ruth
Bibcode: 1968SoPh....4..229D
Altcode:
The proton flare of August 28, 1966 began on Hα records at
15h21m35s UT. It presented an unusually
complex development with flare emission occurring in two distinct
plages. The brightest part of the flare attained maximum intensity,
152 % of the continuum, between 15h30m and
15h32m UT. Photometric measurements show that
a long-enduring part of the flare continued to decline in intensity
until at least 21h20m UT.
Title: Increasing optical evidence for mass motions in solar flares,
1937-1967
Authors: Dodson, H. W.; Hedeman, E. R.
Bibcode: 1968mmsf.conf...37D
Altcode:
No abstract at ADS
Title: Some Patterns in the Development of Centers of Solar Activity,
1962-66
Authors: Dodson, H. W.; Hedeman, E. R.
Bibcode: 1968IAUS...35...56D
Altcode:
No abstract at ADS
Title: The Proton Flare of 28 August 1966
Authors: Dodson, Helen W.; Dedeman, E. Ruth
Bibcode: 1968AJS....73Q..59D
Altcode:
No abstract at ADS
Title: Related Flares
Authors: Dodson, Helen W.; Hedeman, E. Ruth
Bibcode: 1966ApJ...145..224D
Altcode:
Observations of four major flare events between 12b45 and 21b0@ U.T. on
September 18, 1957, in a great center of activity at N. 20 E. OS
provide additional evidence that certain solar events called "flares"
may not be independent phenomena. The events can be interpreted as four
flares or as two flares, each with two phases and two maxima. The first
interpretation implies that at least two families of homologous flares
occurred within the same center of activity. The second organization
of the data means that the late phase of each flare is considered to
be in some sense a consequence or development of phenomena initiated
during the early phase of the complex event. Either interpretation of
the observations indicates that major homologous flares can repeat in
less than 5 hours. High-magnification spectroheliograms of these flares
made with radiation from the centers of Ha and the K-line of ionized
calcium show detailed correspondence in the location of the flare
emission at these two wavelengths. The radio frequency, ionospheric,
and geomagnetic phenomena associated with the flares are considered.
Title: Solar Activity during the First 14 Months of the International
Years of the Quiet Sun
Authors: Dodson, Helen W.; Hedeman, E. Ruth; Stewart, Frederic L.
Bibcode: 1965Sci...148.1328D
Altcode:
No abstract at ADS
Title: Comments on Related Flares.
Authors: Dodson, Helen W.; Hedeman, E. Ruth
Bibcode: 1965AJ.....70S.673D
Altcode:
On 18 September 1957 between 12h45rn and 21h00rn UT there took
place on the solar disk near N 200 B 050 four major chromospheric
brightenings that were reported by the various observers as either
two, three, or four major flares. Examination of both hydrogen and
calcium spectroheliograms showed that events 1 and 3 were in apparently
identical locations within the plage, and that events 2 and 4 formed
another set of homologous flares, to use the term currently applied to
flares that repeat in the same region. The events can be interpreted
either as four separate flares or, as two flares each with two phases
and two maxima. If the first interpretation is correct, the events
indicate that at least two families of homologous flares occurred within
the same center of activity. Questions regarding possible physical
differences between such families of flares immediately arise. The
concomitant radio frequency emission and the detailed development of
the flares seem to favor the second interpretation, and the events
appear in our Working List of IGY Flares as two flares, each with two
maxima. Imp or- F Beginning End Maximum tance Position <1303 >1425
1325 3 N23 E10 <1425 >1600 1530 N20 E04 <1722 >1818 1740 N
23 E08 1818 2110 1840 3+ N20 E03 This latter organization of the events
means that the second phase of each flare is considered to be in some
sense a consequence or development of phenomena initiated during the
first phase. The observations thus suggest that events reported as
major flares in the same center of activity with maxima separated by
as much as two or more hours may refer, in some cases, to two phases
of a complex solar event rather than to independent phenomena. Either
interpretation of the four events on 1957 September 18 indicates that
major homologous flares can repeat in less than 5 h and suggests that
more information on recurrent flares is desirable.
Title: An Unexpected Effect in Solar Cosmic Ray Data Related to
29.5 Days
Authors: Dodson, Helen W.; Hedeman, E. Ruth
Bibcode: 1964JGR....69.3965D
Altcode:
Data relating to the detection of solar protons in the neighborhood
of the earth (1952-1963) and to neutron counts (1958-1963) have been
distributed on the basis of the mean synodic solar rotation period,
27.3 days, and the approximate synodic month, 29.5 days. In the latter,
apparent departures from random distribution are especially marked. At
the present time it is not clear whether the 29.5-day `effect' is
related to the sun or the moon or is only a statistical accident.
Title: Solar Activity During the First Six Months of the International
Years of the Quiet Sun
Authors: Dodson, Helen W.; Hedeman, E. Ruth; Stewart, Frederic L.
Bibcode: 1964Sci...145.1050D
Altcode:
No abstract at ADS
Title: An Observation of the Longitudinal Magnetic Field in a
Sunspot Group.
Authors: Teske, Richard G.; Dodson, Helen W.; Hedeman, E. Ruth
Bibcode: 1964ApJ...139.1336T
Altcode:
An isogauss contour map of the longitudinal magnetic field in the
active spot group of September, 1963, was constructed from photographic
observations using the inverse Zeeman effect. Possible effects of the
observed steep field gradients on results which might be obtained with
a scanning magnetograph are discussed.
Title: Problems of differentiation of flares with respect to
geophysical effects
Authors: Dodson, Helen W.; Hedeman, E. Ruth
Bibcode: 1964P&SS...12..393D
Altcode:
No abstract at ADS
Title: Moving Material Accompanying the Flare of 1959 July
16d21h14m UT
Authors: Dodson, H. W.; Hedeman, E. R.
Bibcode: 1964NASSP..50...15D
Altcode: 1964psf..conf...15D
No abstract at ADS
Title: Solar Minimum and the International Years of the Quiet Sun
Authors: Dodson, Helen W.; Hedeman, E. Ruth
Bibcode: 1964Sci...143..237D
Altcode:
No abstract at ADS
Title: Selected High-Resolution Strip Scans of the 10.7-CM Sun.
Authors: Covington, Arthur E.; Harvey, Gladys A.; Dodson, Helen W.
Bibcode: 1962ApJ...135..531C
Altcode:
Strip scans of the solar disk at a frequency of 2800 Mc have been made
with a fan-shaped beam 1 2 east-west by 2 north-south, and certain of
these records have been selected for comparison with associated optical
features. A radio profile only 12 per cent broader than the theoretical
antenna pattern has been associated with a narrow optical region near
the solar limb and indicates that the theoretical pattern has probably
been achieved. Two different types of radio-emissive regions have been
studied in some detail. These are the centrally located region of July
4,1959, which shows two peaks, and that of February 14,1960, which is
of comparable extent but has a relatively flat-topped single peak. The
associated optical features show structure similar to that of the radio
regions An example is shown of the daily east-west displacements from
the center of the solar disk of a radio-emissive region, in which
systematic differences from calculated displacements are related to
changes in the emissive region. Some evidence is presented to suggest
that the radio-emissive region over a sunspot region is a flat disk
rather than a spherical cap. It appears from the various investigations
that the narrow 1 2 beam is the largest that can be used satisfactorily
for measuring the flux from individual radio-emissive regions, as well
as providing some indication of their gross structure.
Title: Observation of Loop-Type Prominences in Projection against
the Disk at the Time of Certain Solar Flares
Authors: Dodson, Helen W.
Bibcode: 1961PNAS...47..901D
Altcode:
No abstract at ADS
Title: Solar Features Associated with Ellerman's "Solar Hydrogen
Bombs"
Authors: McMath, Robert R.; Mohler, Orren C.; Dodson, Helen W.
Bibcode: 1960PNAS...46..165M
Altcode:
No abstract at ADS
Title: Survey of Number of Solar Flares Observed during the
International Geophysical Year
Authors: Dodson, Helen W.; Hedeman, E. Ruth
Bibcode: 1960JGR....65..123D
Altcode:
According to the McMath-Hulbert Observatory working list of world-wide
flares there were more than 6700 solar events during the IGY for which
at least one observer estimated the importance to be >¯1. According
to reports to World Data Centers the flare patrol was gratifyingly
complete and uniform. However, examination of the starting times of the
reported flares reveals evidence for a serious lack of homogeneity in
the IGY flare data. Approximately twice as many flares, >¯1, were
reported per hour from 05h to 16h UT as during
the remainder of the Universal Day. This strong dependence on UT exists
in the flare data for each month of the IGY. Examination of the patrol
hours and flare reports for May and July 1958 for each of the 19 Hα
cinematographic patrol stations shows that the principal photographic
patrol stations fail to confirm the very high rate of flare occurrence
for 05h to 16h UT that appears in the total IGY
data. Visual observations between 05h and 16h
UT, apparently constitute the principal source of inhomogeneity in the
flare data. For the hours 17 to 04 in the Universal Day the IGY flare
reports are based primarily on the cinematographic patrol. Comparison
of the number of flares and subflares indicates that in the IGY data
for the hours 05 to 16 UT many flare events are listed as flares that
probably would have been classified as subflares by the principal
cinematographic observers.
Title: Survey of Number of Flares Observed during the IGY.
Authors: Dodson, H. W.; Hedeman, H. R.
Bibcode: 1960AJ.....65S..51D
Altcode:
In the McMath-Hulbert Observatory working list of world-wide flares
there are more than 6700 solar events during the IGY for which at
least one observer estimated the importance to be > 1. According
to reports to World Data Centers the flare patrol was gratifyingly
complete and uniform. However, examination of the starting times of the
reported flares reveals evidence for a serious lack of homogeneity in
the IGY flare data. Approximately twice as many flares, > 1, were
reported per hour from ~5 h to 16 h UT as during the remainder of the
Universal Day. This strong dependence on UT exists in the flare data
for each month of the IGY. Examination of the patrol hours and flare
reports for May and July 1958 for each of the 19 Ha cinematographic
patrol stations shows that the principal photographic patrol stations
fail to confirm the very high rate of flare occurrence for ~5 h to l6h
UT that appears in the total IGY data. Furthermore, for the hours 17
to 04 in the Universal Day the IGY flare reports are based primarily
on the cinematographic patrol. Comparison of the number of flares and
subflares indicates that in the IGY data for the hours OS to 16 UT
many flare events are listed as flares that probably would have been
classified as subflares by the principal cinematographic observers.
Title: Flares of July 16, 1959.
Authors: Dodson, H. W.; Hedeman, H. R.
Bibcode: 1960AJ.....65R..51D
Altcode:
Two flares of importance 3 and 3+, respectively, occurred on July 16,
1959 in the north central part of the solar disk. They were separated
in time by about five hours. The two flares differed greatly in their
radio frequency emission. The earlier flare was accompanied primarily by
a type II or slow-drift burst. The second was one of the relatively few
flares known to be associated in time with great emission at centimeter
wavelengths, with great con- tinuum radiation at radio frequencies,
and with enhancement of high energy particles in the neighborhood of
the earth. For these two flares, the time intervals between start and
maximum were similar, being 23 and 21 minutes, respectively. Although
these values are longer than average for flares in general, they are not
abnormally long for flares of importance 3. During the second of the two
flares, spectroheliograms were made by systematic changes of wavelength
throughout 6A of the spectrum centered on Ha. These spectroheliograms
revealed numerous hydrogen absorption features, some with ascending
and some with descending motions. In the late stages of the flare,
spectroheliograms taken to the redward of Ha, showed an extensive
system of curved dark features which may be loop-type prominences
in projection against the disk. Comparison revealed a conspicuous
difference in the locations of the two flares. Portions of the flare
with the great centimeter and continuum radiation occurred directly
over the umbrae of large spots. No portion of the earlier flare, which
did not have this type of radio-frequency emission, appeared over the
umbra of a large spot. Similar comparisons have been made for a small
number of other flares. The association between very great centimeter
wavelength radio emission and close proximity of Ha flare and large
spot umbra is sufficiently good to warrant further investigation.
Title: Crochet-Associated Flares.
Authors: Dodson, Helen W.; Hedeman, E. Ruth
Bibcode: 1958ApJ...128..636D
Altcode:
Flares associated with geomagnetic crochets in the interval 1949-1954
were of high average importance but exhibited an atypical distribution
on the solar disk, with reduced frequency near the center. The
crochet-flares in this interval were not identical with flares
associated with "major" sudden ionospheric disturbances There was a
close relationship between crochet-flares and flares with wide Ha at
maximum Average geomagnetic indices rose to a high maximum on day 2
following crochet-flares with "major early bursts" at radio frequency
<200 Mc/s but not after crochet-flares in general.
Title: Geomagnetic Disturbances Associated with Solar Flares with
Major Premaximum Bursts at Radio Frequencies ???? 200 Mc/s
Authors: Dodson, Helen W.; Hedeman, E. Ruth
Bibcode: 1958JGR....63...77D
Altcode:
Study of world-wide solar and geomagnetic data has shown a
close association between flares with "major early bursts" at
radio frequencies 200 Mc/s and sudden-commencement geomagnetic
storms. Intercomparison of Hα and radio-frequency solar data for
January 1949 to April 1956 has given positive evidence for such "major
early bursts" with 115 of the approximately 3,000 flares observed
during the 7-1/3 year interval. This type of radio-frequency event is,
therefore, relatively rare. Geomagnetic storms were reported by at least
one observatory within less than five days after the occurrence of 92
per cent of the 115 flares with "major early bursts." The average time
interval between the flare and the start of the subsequent geomagnetic
storm was slightly less than 2½ days. Average superposed values of
Kp and Ap were high on days 2, 3, and 4 after flares of importance 3
with "major early bursts," but this was not the case after flares of
importance 3 when emission at frequencies 200 Mc/s was not present or
occurred only in the post maximum phase of the flare. The possibility
of a "central meridian effect" has been investigated. The average,
superposed values of Kp for the disk passage of the 77 regions
concerned is very similar to that "predicted" for disk passage of
active regions with storm-producing flares in random positions, and
with double frequency and/or effectiveness for the five days nearest
central meridian passage. The latter assumptions are in accordance
with observations. The geomagnetic effectiveness of each of the 115
flares with "major early bursts" was re-evaluated on the basis of
all available world-wide solar data. Sixty-eight of the 115 flares
were considered to be the most probable single solar cause of 68
geomagnetic storms. Study of these 68 cases of well-associated flares
and geomagnetic storms indicated that storm-producing flares occurred
at all meridian distances and in all importance categories. However,
centrality of position and high flare importance favored greater
severity in the subsequent storm. Again, the average time interval
between flare and start of storm was 56 hours.
Title: Observation of solar "points".
Authors: Mohler, Orren C.; Dodson, Helen W.
Bibcode: 1958AJ.....63R.309M
Altcode:
There is a type of object on the sun visible through a Lyot Ha filter
and photographed on hydrogen and calcium spectroheliograms that is the
source of the spectroscopic feature called "hydrogen bombs" by Ellerman
(1917) and "moustaches" by Severny (1956). These objects were observed
through the filter by Lyot (I 944) and called by him "points." We
shall adopt his nomenclature because it indicates the small size and
usually circular shape of the phenomenon. Points are identified by their
characteristic spectrum, viz., brilliant emission streaks extending
several angstroms on either or both sides of Ha but not crossing
it. Emission on the violet side is generally more intense than that on
the red. At the McMath-Hulbert Observatory points are observed by two
methods. (I) They are seen visually in a Lyot-Ha filter and then placed
on the slit of the vacuum spectrograph for definitive identification
and spectrographic study. (2) The points are recorded on series of 15
spectroheliograms made at different wave lengths, systematically spaced
within 3A on either side of the center of Ha or the K-line. Points are
photographed with especial ease on K spectroheliograms. Our observations
show that points occur generally on the outer edge of the penumbra of
spots. They are very small, only fractions of seconds of arc. They are
numerous three or four per spot. Average life times are of the order of
nine minutes, but may be as short as two. They are recurrent. Points
frequently have been observed to be at the base of small active dark
flocculi. Our observations to date indicate little or no positional
relationship between points and major flares, even though the latter
have broken out in the field during well controlled observations of
points. The generality of points in the neighborhood of inactive as
well as active spots suggests that they should be considered as part
of normal spot development. Ellerman, F. 1917, Ap. J. 46, 298. Lyot,
B. 1944, Ann. Astroph. 7, 31. Severny, A. B. 1956, Observatory, 76,
241. McMath-Hulbert Observatory, University of Michigan, Pontiac, Mich.
Title: Studies at the McMath-Hulbert Observatory of Radio Frequency
Radiation at the Time of Solar Flares
Authors: Dodson, H. W.
Bibcode: 1958PIRE...46..149D
Altcode:
The complex flare phenomenon is described in terms of its photographic
aspect on Hα spectroheliograms, associated prominence activity,
terrestrial effects, and the general pattern of radio frequency
emission. Flare-associated events at 2800 and 200 mc are reviewed,
and the association between flares and the onset of 200-mc noise storms
is discussed. Records of 2800 and 200-mc radiation at the time of 277
flares are compared. Flare-events at frequencies less than 200 mc are
considered, and a study of 496 flares at 80 mc is summarized.
Title: Crochet-associated flares.
Authors: Dodson, Helen W.; Hedeman, Ruth E.
Bibcode: 1958AJ.....63R.304D
Altcode:
The crochet is a relatively minor disturbance of the earth's magnetic
field which occurs concomitantly with certain flares. lATME Bulletins
for 1949-54 list 185 crochets. Solar or ionospheric data confirm 148. Ha
flares were observed in 109 cases. The 109 crochet-flares occurred in
52 different centers of activity and constituted 10 per cent of the
flares in those regions. Even though short-wave fades were reported
with 87 per cent of the crochet flares, the crochet phenomenon does
not satisfactorily delineate flares with the greatest ionospheric
disturbances. Crochet flares exhibit an atypical distribution on the
solar disk. Instead of the usual concentration near the center, crochet
flares show highest frequency about 500 on either side of the central
meridian. This double-humped distribution is not duplicated in the disk
positions of 217 flares with "major" ionospheric disturbances. It is,
however, very similar to the distribution of flares with wide Ha, and
for crochet flares, the average width of Ha is large. The scarcity
of crochet flares near the central meridian is not a simple result
of masking of crochets by more severe geomagnetic disturbances since
averaged geomagnetic indices were high during the western transit
of the crochet regions but not during central meridian passage. The
crochet does not assist in identifying flares that are followed
by geomagnetic disturbances. However, averaged geomagnetic indices
following crochet-flares with "major early bursts" at 200 Mc/s rise to
a high maximum on day 2 even though crochet-flares are relatively far
from the central meridian. The study indicates that crochet-flares
do not form a random sample of important flares and that there are
systematic differences between flares with crochets and those with
"major" ionospheric disturbances. McMath-Hulbert Observatory, University
of Michigan, Pontiac, Mich.
Title: RÉSUMÉ of Visually and Photographically Observed Solar
Activity at the Time of 200 Mc/S Noise Storms Near the 1954 Solar
Minimum.
Authors: Dodson, Helen W.; Hedeman, E. Ruth
Bibcode: 1957ApJ...125..827D
Altcode:
No abstract at ADS
Title: Flares with major early bursts at frequencies <200 Mc/s
and subsequent geomagnetic disturbances.
Authors: Dodson, Helen W.; Hedeman, E. Ruth
Bibcode: 1957AJ.....62Q.140D
Altcode:
Intercomparison of world-wide optical and radio-frequency solar data
has shown that during the 713 year interval between January 1949 and
April 1956 only 113 of the approximately 3000 observed flares are known
to have had major bursts at frequencies <200 Mc/s during the pre-
maximum phase of the Ha flare. Even though the records are unavoidably
incomplete, the major early burst appears to be a relatively rare
solar event. During the time interval studied, such bursts occurred in
conjunction with flares in all importance categories and at all central
meridian distances. World-wide geomagnetic reports show that 92 per
cent of the above 113 flares were followed by onsets of geomagnetic
storms in less than five days. The average time interval between the
occurrence of flares with major early bursts and the start of storms
was 2~2' days. Superposed values of the geomagnetic indices (Kp and A ~)
show large increases starting two days after the flare, with maximum on
the third day. Special studies of all flares of importance 3 and 3 +
in the same period showed that the above relationship was maintained
when these flares had early major bursts but was not maintained when
emission at frequencies <200 Mc/sec was not present or when such
emission occurred only in the post maximum phase of the flare. The
113 flares with major early bursts were associated with 79 separate
geomagnetic storms. For 64 of the storms at least one station
reported the sudden commencement phenomenon, and for 41 a majority
of the stations classified the storm as sudden commencement. Only 3
of the 79 storms were members of well established 27-day recurrent
series. Studies are now in progress to evaluate the roles of flare
importance and position, and phase of solar cycle. More abundant radio
data giving polarization and dynamic spectra should further improve the
relationships here indicated. McMath-Hulbert Observatory, University
of Michigan, Pontiac, Mich.
Title: Relation between optical solar features and solar radio
emission
Authors: Dodson, H. W.
Bibcode: 1957IAUS....4..327D
Altcode:
No abstract at ADS
Title: Photometry of Solar Flares.
Authors: Dodson, Helen W.; Hedeman, E. Ruth; McMath, Robert R.
Bibcode: 1956ApJS....2..241D
Altcode:
On the basis of photometric light-curves for 194 flares and subflares,
the following data have been derived. 1.Ha intensity often varies
differently in different parts of the same flare. 2.The change of Ha
intensity with time in a flare can be well represented by the series
of curves given by the equation iog =(iog Ii ax) t a(t-trnax), where
t is measured in minutes and a is positive for the ascending branch,
negative for the descending branch, and takes values between 0.40 and
0.00313. For the descending branch of the light-curve, a is always
smaller than for the ascending branch. The most usual value of a for
the ascending branch is 0.10; for the descending branch a is -<0.025
for 87 per cent of the cases. 3.Ha flare intensities have been measured
in units of both the local and the centra] continuum at x 6590. In the
former, average Ha intensity at flare maximum ranged from 0.66 for
subflares and 0.88 for flares of importance 1 to intensity 1.17 and
1.28 for flares of importance 2 and 3, respectively. In units of the
central continuum the average values are about 0.1 lower. The brightest
measured maximum was 1.9 times the local continuum for a flare at CMD 72
. 4.No convincing relationship has been found between rate of increase
of intensity and maximum intensity attained by the flare. However,
the slowest rate of increase apparently diminishes the chances of
attaining a maximum as bright as the contmuous spectrum. 5.There is
evidence for center-to4imb variation in numerous characteristics of
the Ha flares in this study. The slowest rates of rise and decline
were observed only for flares ithin 55 of the central meridian, and
the fastest rates of decline only for flares within 40 of the solar
limb. Average intensity in units of the local continuum increased
with increasing central meridian distance of the flares. In units of
the central continuum, the average intensity diminished from center
to limb. "Limb-darkening" equations for the flares and subflares are
as follows: Flares: lc=O.63+O.34COS 0, Subilares: lc=O.36+O.26CC)S
0. For flares of the same importance, average duration diminished with
increasing distance from the center of the disk. Near the center of
the disk, the Ha flare usua]ly lasted as long as, or longer than,
the associated ionospheric disturbance, but for flares near the
limb the reverse was true. 6.For the flares in this study, area and
intensity increase together, but the correlation coefficient of these
two measures is only 0.58 + 0.03 p.e. 7.Flare duration was associated
more closely with flare area than with maximum intensity. The duration
of flares as measured by photometric light-curves is much longer than
the average duration of flares reported in the Quarterly Bulletin of
Solar Activity. 8.The reported starting times of SID's usually fall
during the period of increasing intensity in the flare. Except in
unusual cases, SID's were not reported unless the flare intensity was
at least 0.8 of the local continuum and the area was of the order of
200 millionths of the solar disk. Near the limb the SID often lasts
longer than the Ha flare. 9.There is apparently less diminution from
center to limb in the ionizing radiation from flares than in Ha. 10. The
ionospheric disturbances were unusually small for certain large and
relatively bright flares associated with the onsets of 200-Mc/s noise
storms. 11. Examination of ionospheric records for the times of the
flares and subflares in this study has provided evidence for a new
type of flare-associated ionospheric effect, a gradual ionospheric
disturbance, in contradistinction to the sudden SID or Dellinger
effect. The 45 reported SID's have been augmented by 19 additional,
well-confirmed ionospheric disturbances and by 23 less certain
events. 12. There is no evidence to indicate that subflares are not
just smaller, fainter examples of the flare phenomenon. Flares and
subflares in this study have similar disk distributions and rates of
increase and decrease of intensity. Ionospheric disturbances accompanied
at least four of the brightenings here classified as subflares.
Title: Development of an active solar region August 20-26, 1954.
Authors: Dodson, Helen W.
Bibcode: 1956AJ.....61....2D
Altcode:
It is possible to study the development of active solar regions under
circumstances of unusual simplicity during the time when the sun
is just emerging from minimum in the eleven-year cycle. The week of
August 20-26, 1954 provided exactly this opportunity. Between 15h00m
and 15h10m UT on August 20, a small calcium plage formed very close
to the central meridian at about 300 south latitude. By 18h00m a spot
was visible. In the week following its formation, the calcium plage
grew to at least 3000 millionths of the solar hemisphere and became
2.4 times as bright as the dark portions of the mottled background of
the K232 spectroheliograms. Isophotometric studies of the calcium plage
as photographed at the McMathHulbert Observatory provide quantitative
data for comparison with spot, magnetic, radio flux, and coronal
data most kindly made available by astronomers in all parts of the
world. At least four flares were observed in the region before it
traversed the west limb. No other active regions were observed on the
solar disk between August 20 and 25. To the best of our information,
ionospheric disturbances did not accompany the observed flares. It
is tempting to associate the recrudescence of geomagnetic activity
in early September with the resurgence of observed solar activity
in August, though the time relationships here indicated are far from
those generally considered acceptable in such matters. The difficulties
encountered in this study of a very simple case of solar activity give
some indication of the problems that will be inherent in efforts to
disentangle the complex solar data during the International Geophysical
Year in 1957-58 when the sun will have advanced toward maximum in the
eleven-year cycle of activity. AIcMath-Hulbert Observatory, University
of Michigan, Ann Arbor, Mich.
Title: Detailed study of the development of an active solar region,
1954 August 20-27
Authors: Dodson, Helen W.; Hedeman, E. Ruth
Bibcode: 1956MNRAS.116..428D
Altcode:
The week of 1954 August provided an opportunity to study the development
of an active solar region under circumstances of unusual simplicity. The
calcium plage formed near the central meridian of the solar disk between
and 15h10m U.T. on August 20. In the week following its formation, the
calcium plage grew to at least 3500 millionths of the solar hemisphere
and became 2 4 times as bright as the dark portions of the mottled
background of the K282 spectroheliograms. Isophotometric studies of the
calcium plage provide quantitative data for comparison with sunspot,
magnetic, geomagnetic, radio flux, and coronal data made available by
astronomers in all parts of the world. At least five flares or subflares
were observed in the region before it traversed the west limb. The
study presents a comprehensive and partially quantitative account 9f
of the formation, growth and decline of an isolated centre of solar
activity. The problems encountered are illustrative of those that will
be met on a grander scale in the solar studies of the International
Geophysical Year.
Title: Center-to-limb effects in solar flare observations.
Authors: Dodson, Helen W.
Bibcode: 1955AJ.....60R.158D
Altcode:
The study of photometric light-curves for 194 flares and subflares
indicates certain center-to- limb variations in the Ha observations
of solar flares. First, the position of the flare on the apparent disk
apparently influences the observed rates of change of Ha intensity. The
slowest rates of both rise and decline were observed only for flares
in the central part of the solar disk. The fastest rates of decline
occurred only with flares near the limb of the sun. The average
intensity of flares at maximum varied with central meridian distance,
showing definite limb darkening in units of the central continuous
spectrum. Limb darkening in the center of Ha is apparently less for
flares than for the undisturbed parts of the solar disk. It is also less
than for the continuous spectrum near Ha. Linear equations expressing
limb darkening for flares andflares are: Flares: Ic = 0.63
0.34 cos (), Subflares:Ic = 0.36 0.26 cos 0, where 6 is the angular
distance of the flare from the center of the solar disk. In units of
the local continuum the average intensity at maximum increased from
center to limb, for both flares and subflares. For flares within 400
of the central meridian, the average value of the central intensity
was less than the local continuum. For flares with central meridian
distance greater than 400, the average intensity was greater than the
local continuous spectrum. The average width of Ha at maximum also
increases from center to limb. For flares of the same importance in
the photometric study, the average duration diminished with increasing
distance of the flares from the central meridian. Furthermore, Ha
flares near the center of the disk usually lasted longer than the
reported associated SID. For flares far from the center, the reported
ionospheric disturbances tended to last longer than the Ha phenomena. Mc
Ma th-Hulbert Observatory, University of Michigan, Ann Arbor, Mich.
Title: The Width of Hα in Solar Flares.
Authors: Goldberg, Leo; Dodson, Helen W.; Müller, Edith A.
Bibcode: 1954ApJ...120...83G
Altcode:
It is shown that the observed large widening, at or near maximum,
of the Ha emission line in certain solar flares can be explained as a
consequence of radiation damping and the high abundance of two- quantum
H atoms in the line of sight. When the effective width `of the Ha line
is calculated according to the theory of self-absorption, the assumption
of radiation damping leads to agreement with the observed lines widths
when the number of two-quantum H atoms lies in the approximate range per
cm2 in the line of sight. If it is assumed that the lateral extension
of a flare is large compared with its thick- ness, the theory predicts
that the effective width of Ha should be proportional to the square
root of sec 0, where 0 is the angular distance from the center of the
solar disk. Study of the Ha line widths of 610 flares reported in the
Quarterly Bulletin of the I.A.U. for the period January, 1949, through
June, 1952, reveals that the average line width increases steadily
with increasing central meridian distance of the flares. Furthermore,
flares with exceptionally wide lines ( 4.0 A) are observed most often
in flares 45 or more from the central meridian. The relation between
effective line width and central intensity found by Ellison is explained
as primarily a consequence of self-absorption. Finally, the existing
observational evidence in favor of the Stark effect as an important
cause of the line broadening is examined and found unconvincing.
Title: Solar Flares and Associated 2800 Mc/sec (10.7 Cm) Radiation.
Authors: Dodson, Helen W.; Hedeman, E. Ruth; Covington, A. E.
Bibcode: 1954ApJ...119..541D
Altcode:
Study of 2800 Mc/sec solar radiation at the time of 213 flares and 173
subflares has shown distinctive radio events associated with 57 per cent
of the flares and 19 per cent of the subflares. The flare-associated
distinctive events at 2800 Mc/sec can be described by essentially
the same types and categories already used to report outstanding
disturbances at this radio frequency: single bursts; single-simple
bursts with and without a postburst increase; single-complex bursts
with and without a postburst increase; gradual rises and falls of
flux. In addition, there is the designation "null," or no distinctive
event. There is strong evidence that there is an outstanding event
or disturbance in 2800 Mc/sec solar radiation only when a flare or
subflare is in progress. Time relationships between Ha flares and 2800
Mc/sec events suggest that two quite different types of phenomena may
be represented in the flare-associated 2800 Mc/sec radiation. One is
a sudden burst- type feature which occurs during the rise to maximum
of the Ha flare. The other is the more gradual rise and fall of ffux
and "postburst increase," which lasts as long as, or longer than,
the flare itself. Both types of phenomena appear to start with the Ha
flare. Flares associated with large "postburst increases" or "gradual
rises and falls" show a high concentration toward the central part
of the solar disk. This is not the case for the strictly "burst-type"
disturbances. The importance of the flare, the position of the flare on
the solar disk, and accompanying ionospheric disturbances are considered
with respect to the form and energy excess of the associated events
at 2800 Mc/sec.
Title: Intensity Measures of Calcium Plages for Comparison with
10.3-CENTIMETER Solar Radiation, October 16, 1951.
Authors: Dodson, Helen W.
Bibcode: 1954ApJ...119..564D
Altcode:
Photometric studies of K232 spectroheliograms for October 16, 1951,
are compared with Covington's records of the positions of 10.3-cm
(2800 Mc/sec) emissive regions on the sun for the same date. There
were three emissive regions at 10.3 cm, and there were three maxima
in the east-west distribution of calcium plage intensity on the solar
disk. Sunspots were observed in only two of the three regions.
Title: High Latitude Sunspot, August 13, 1953
Authors: Dodson, Helen W.
Bibcode: 1953PASP...65..256D
Altcode:
No abstract at ADS
Title: Absorption of 10.7-centimetre Solar Radiation during Flare
of May 19, 1951
Authors: Covington, A. E.; Dodson, Helen W.
Bibcode: 1953JRASC..47..207C
Altcode:
No abstract at ADS
Title: Solar Flares and Associated 200 Mc/sec Radiation.
Authors: Dodson, Helen W.; Hedeman, E. Ruth; Owren, Leif
Bibcode: 1953ApJ...118..169D
Altcode:
Study of 200 Mc/sec solar radiation for the times of 194 flares
indicates distinctive radio events associated with 78 per cent of the
flares. The flare-associated distinctive events can be divided into ten
descriptive types or categories: major burst, major burst with second
part, minor burst, minor burst with econd part, micro burst, group of
bursts, series of bursts, noise storm in progress, onset of noise storm,
and rise in base level. In addition, there is the designation "null,"
or no distinctive event. Consideration of the time relationships between
flares and 200 Mc/sec events suggests that two quite different types
of phenomena may be represented in the flare-associated 200 Mc/sec
radiation. The first or "early" phenomenon includes very sudden,
relatively isolated, burstlike features which occur close to the time
of start of the . The second or "late" phenomenon includes the more
gradual rises in base level and onsets of noise storms. These usually
start at or after the time of flare maximum. The "early" and "late"
phenomena can occur in conjunction with each other, or either of the
two can occur separately. The importance of the flare, position on the
solar disk, and accompanying ionospheric disturbances are considered
with respect to the form and energy excess of the flare-associated 200
Mc/sec events. The various aspects of the complex flare phenomenon, as
observed photographically and visually, are discussed. An association is
suggested between the high-velocity ejections observed at the onset of
certain flares and the occurrence of a major burst at 200 Mc/sec. From
the point of view of the parameters considered in this paper, the
flares for which there were no distinctive events on the 200 Mc/sec
records constitute a random sample from the entire set of 194 flares.
Title: Spectroheliographic observations, 1952 February 25
Authors: Dodson, H. W.; Mohler, O. C.
Bibcode: 1953Obs....73..116D
Altcode:
No abstract at ADS
Title: Ejection of Hydrogen and Ionized Calcium Atoms with High
Velocity at the Time of Solar Flares.
Authors: Dodson, Helen W.; Hedeman, E. Ruth; Chamberlain, Joseph
Bibcode: 1953ApJ...117...66D
Altcode:
High-velocity ejections of both hydrogen and ionized calcium atoms at
the time of onset of five flares near the solar limb are described. For
four of the five cases, reports of solar radiation at radio frequencies
are available and indicate bursts or "outbursts" at the start of the
flare and ejection. Consideration of time relationships and of the
frequency of occurrence of 200 Mc/sec bursts with flares leads to the
suggestion that the burst at radio frequencies is to be associated
with the high-velocity ejection rather than with the Ha brightening.
Title: Solar flares and associated 2800 Mc/sec radiation.
Authors: Dodson, H. W.; Hedeman, E. Ruth; Covington, A. E.
Bibcode: 1953AJ.....58R.213D
Altcode:
A study of solar radiation at 2800 Mc/sec, 10.7 cm, at the time of 387
flares and subflares shows that the percentage of Ha brightenings with
associated events at this radio frequency increases with the importance
of the flare. Only 20 per cent of the subflares were associated with
2800 Mc/sec events, but for 87 per cent of the flares of importance
2 and 3 there were concomitant events on the radio recqrds. The
flare-associated distinctive events at 2800 Mc/sec can be described by
essentially the same types and categories already used in the published
reports of outstanding disturbances at this radio frequency. They
range from small single bursts to larger simple or complex bursts
which may or may not be followed by a post-burst increase. The type
"gradual rise and fall" which had appeared only once in the published
list of disturbances was augmented when the records were examined for
the times of flares. Comparison of the times for flares and bursts
shows that the flares and bursts start together. The 2800 Mc/sec burst
reaches its maximum before maximum intensity has been attained by the
Ha flare. The times of ending of the bursts cluster closely around the
time of Ha maximum. Although the event called gradual rise and fall
appears to start with the flare, it does not reach its maximum until Ha
maximum has been attained, or later. Time relationships as well as the
appearance of the records suggest that the flare-associated events at
2800 Mc/sec may include two quite different types of phenomena. One is
the sudden burst-type feature which occurs during the rise to maximum
of the flare. The other is the more gradual rise and fall. The two can
occur separately or in conjunction with each other. In the latter case,
the gradual rise and fall is designated as a post-burst increase. The
energy excesses of the flare-associated disturbances vary by a factor
as great as 50 000 On the average, the energy excess increases with
flare importance. Closeness of the flare to the central meridian of
the sun apparently favors the occurrence of a gradual rise and fall
or post-burst increase that is of intrinsically great magnitude,
or that is large in comparison to the associated burst. The purely
burst-type phenomena do not seem to be influenced by position of the
flare on the disk. Examination of solar records for the times of all
reported disturbances at 2800 Mc/sec from 1947 to 1952 provides strong
evidence that there is an outstanding disturbance at 2800 Mc/sec only
when a flare or subflare is in progress. McAIath-Hulbert Observatory,
University of Michigan, Ann Arbor, Mich., and National Research
Council,* Ottawa, Canada.
Title: Solar Flares: Photometry and 200 Mc/Sec Radiation
Authors: Dodson, H. W.
Bibcode: 1953sun..book..692D
Altcode:
No abstract at ADS
Title: Observation of active regions on the sun by radio
interferometer and spectroheliograph.
Authors: Dodson, Helen W.; Owren, Leif
Bibcode: 1952AJ.....57...10D
Altcode:
On a number of days the solar radio frequency radiation contains a
variable component in addition to the basic thermal radiation of the
quiet sun. At meter wave lengths the low resolving power of current
radio telescopes makes it necessary to use interferometers if one wants
to establish whether this enhanced radiation originates in small,
localized areas or comes from the entire radio disk. The Cornell
200 Mc$sec radio interferometer consists of two identical broadside
antennas placed 51 wave lengths apart on an East-West line. Two coaxial
cables of equal electrical length connect the antennas with a common
superheterodyne receiver. The half-power beam widths of the individual
lobes in the composite antenna polar diagram are comparable to the
sun's angular diameter. The pointing accuracy of the interferometer is
3 to 5 minutes of arc. The antennas are set to the sun's upper transit
altitude and the interference pattern recorded as the sun drifts through
the polar diagram around local noon. By comparison between the burst
amplitudes recorded simultaneously with a 200 Mc7sec radio telescope
and the interferometer, the burst interference pattern can be separated
out and its time relationship to the interference pattern of the quiet
sun established. The source of the bursts can thus be confined to a
strip 175 to 173 solar diameter broad and parallel to the celestial
meridian. The 1950-51 observations with the radio interferometer include
two determinations of the positions of outbursts associated with solar
flares and 14 determinations of the locations of the burst sources, the
latter falling within six well-separated time intervals. Comparisons
are made between the positions of the sources of enhanced radio
emission and the locations of solar features observed optically at
the McMath-Hulbert Observatory. The regions where such features occur
are designated as active or inactive from considerations of the size
and magnetic field strength of sun spots, extent and intensity of the
bright calciu ii plages surrounding them, the number and importance
of flares and active dark flocculi occurring in these plage regions,
as well as prominence or coronal activity during passage over the
limbs, or the absence of such transient phenomena. *On leave from
the Institute of Theoretical Astrophysics, University of Oslo. It
is found that on all days investigated at Cornell the enhanced 200
Mc7sec emission comes from one or two localized areas on the sun. The
burst sources are found to be associated with those regions on the
sun which must be designated as active from the optical point of
view. The coincidence in position as well as in time between the two
radio outbursts and the two optical flares provides strong evidence
for the association of the two phenomena. McMath-Hulbert Observatory,
University of Michigan, Pontiac, Mich., and the School of Electrical
Engineersug, Cornell University, Ithaca, N. Y.
Title: Solar flares and associated 1.5 meter radiation.
Authors: Dodson, Helen W.; Hedeman, E. Ruth; Owren, Leif
Bibcode: 1952AJ.....57R...9D
Altcode:
The McMath-Hulbert Observatory of the University of Michigan and
the School of Electrical Engineering of Cornell University have for
the last year and three-quarters conducted a cooperative program in
which the goal has been the detailed comparison, hour by hour, of
the solar radio radiations at 1.5 meters with solar activity observed
photographically and visually. Different solar phenomena apparently
influence the 1.5 meter records, but it is for solar flares that the
relationships are most clear cut. This study is based principally on
those flares for which complete photographic records are available at
the McMath-Hulbert Observatory, but it has been extended to include data
reported by the International Astronomical Union and the Central Radio
Propagation Laboratory of the National Bureau of Standards. Between the
start of the Cornell Radio records on July 18, 1948 and December 31,
1950, there are 141 flares for which the optical and radio data permit
definitive comparison. It should be emphasized that a solar flare is
a * On leave of absence from Institute of Theoretical Astrophysics,
University of Oslo. complex phenomenon and that the aspect of the
flare that is related to the response at 1.5 meters is not certain. The
complexity of the flare phenomenon becomes clear when it is realized
that in addition to the usually observed sudden brightening in Ha
there may or may not be (I) an ultraviolet component of sufficient
intensity to cause a sudden ionospheric disturbance on the earth,
(2) a spreading of a low grade brightening to relatively distant
parts of the plage in the later stages of the flare, (3) active dark
flocculi or surges in projection on the disk, (4) the actual ejection
of material particles. The 200 Mc$sec response to flares shows a wide
range in both magnitude and kind. These responses can be divided into
seven descriptive categories or types. I) Major bursts (including the
group known as outbursts); (22 cases). 2) Minor bursts; (22 cases). 3)
Micro bursts; (6 cases). 4) Series of bursts; (32 cases). 5) Small
rise in base level; (4 cases). 6) Noise storms; (26 cases). 7) Nulls;
(29 cases). Eighty per cent of the flares produced some form of energy
excess on the 1.5 meter records. For 25 of the 29 flares for which
there was no distinctive radio response the associated solar phenomena
were relatively unimportauf. For at least 4 cases, however, the flares
were of importance 2 or more. The energy excess represented by the flare
response at 1.5 meters has been measured for 20 flares. For these cases
there appears to be a direct relationship between the importance of the
flare and the energy excess associated with it. Comparisons of the times
of onset of the optical flare and the radio response indicate that the
major, minor, and micro-bursts tend to occur at the very commencement
of the optical rise. The series of bursts begin before the observer
detects the start of the flare in Ha radiation. On the other hand,
many of the noise storms and rises in base level have their onset at
or near flare maximum. These delayed responses increase in intensity
as the flare fades and often attain their greatest intensity just as
the optical flare has faded completely. McMath-Hulbert Observatory,
University of Michigan, Pontiac, Mich., and School of Electrical
Engsneersng, Cornell University, Ithaca, N. Y.
Title: A Solar Flare and Associated Dark Flocculi of may 19, 1951.
Authors: Dodson, Helen W.
Bibcode: 1952ApJ...115..320D
Altcode:
The dark absorbing material that accompanied the flare of May 19,
1951, 19h57 , extended at least 125,000 km from the apparent region of
ejection and displayed radial velocities that ranged from -182 to +225
km/sec. The motions indicated are consistent with the interpretation
of the dark flocculus as a giant surge seen in projection on the
disk. This absorbing material modified the form and intensity of the
associated flare.
Title: A solar prominence bright in projection on the disk
Authors: Dodson, H. W.; Hedeman, E. R.
Bibcode: 1952Obs....72...30D
Altcode:
No abstract at ADS
Title: The Limb Flare of may 8, 1951.
Authors: Dodson, Helen W.; McMath, Robert R.
Bibcode: 1952ApJ...115...78D
Altcode:
Published data indicate that flares have been observed at the limb
of the sun with elevations above the chromosphere of 8000-80,000
km. Continuous records of the solar limb and disk secured on Ha
spectroheliograms at the McMath-Hulbert Observatory show the outbreak
and development of a number of these flarelike prominences. They
range in form from relatively small cap-type prominences to the
great flare prominence of May 8, 1951. This latter object rose to a
height of 50,000 km in less than 90 seconds. During this interval the
Ha lines of the spectrum were 8-10 A wide and showed large Doppler
displacements. Throughout the remainder of the flare the change in
height was negligible, and the Ha spectrum lines were 5-6 A wide and
symmetrical. This flare prominence was four times as bright as the
undisturbed Ha disk, was accompanied by an increase in 200-Mc/sec
radiation from the sun, and was associated with a sudden disturbance
of the earth's ionosphere.
Title: The limb flare of May 8, 1951.
Authors: Dodson, Helen W.
Bibcode: 1951AJ.....56..124D
Altcode:
interesting because many investigators consider flares to be essentially
low-level phenomena. Hot spectroheliograms and spectra taken at
the McMath-Hulbert Observatory on May 8, 1951 show the development
of an extraordinarily bright limb object whose occurrence coincided
with the onset and duration of a sudden ionospheric disturbance. The
flare-like prominence reached a maximum intensity of four times that
of the undisturbed Hot disk, an intensity which is comparable to
that of some of the most important disk flares. Cornell records show
200 MC solar noise disturbances at the times of onset and maximum of
this flare-like prominence. During the first minute of the activity
the brilliant prominence rose with a velocity of the order of 700
km/sec and reached a height of 6o,ooo km. Hot spectra taken during
this period show Doppler shifts indicating motion tangential to the
sun's surface greater than 300 km/sec. Hot was 8A to IoA wide. It is
believed that this flare-like prominence was associated with the very
large spot group still behind the east limb. The lowest levels of the
solar region associated with the flare were in all probability occulted
by the sun itself. McMath-Hulbert Observatory, University of Michigan,
Pontiac, Mich.
Title: The Eruptive Prominence of August 7, 1950.
Authors: Dodson, Helen W.; Donselman, Robert W.
Bibcode: 1951ApJ...113..519D
Altcode:
The eruptive prominence of August 7, 1950, is shown to be associated
with an active sunspot group and plage area. Spectra of the prominence
indicate that the large opening in the prominence prior to and during
the eruption was due to the absence of Ha radiation and was not a
result of wave-length displacement caused by high radial velocity. The
velocities of the measured features varied in a similar way with time
and ranged from 10 km/sec to an average maximum of 155 km/sec. A burst
of 200 Mc solar radio noise occurred when the ascending prominence
reached a height of 285,000 km.
Title: Photometric studies of solar flares.
Authors: Dodson, Helen W.; McMath, Robert R.; Hedeman, E. Ruth
Bibcode: 1951AJ.....56...37D
Altcode:
The development, at the McMath-Hulbert Observatory during 1950, of
a new and improved densitometer for the measurement of intensities
of features photographed on 35 mm motion picture film has permitted
an extension of the study of the "light curves" of solar flares. The
intensity of the flare is expressed in terms of the intensity of the
adjacent undisturbed disk as recorded on Ha spectroheliograms taken
with slits 0.4A wide. The study to date has included twenty-one flares
photographed in 1949, eight of importance I, nine of importance 2,
and four of importance 3. The intensities at maximum range from 1.6 to
5 times the intensity of the undisturbed Hot background. All flares
in this study for which the intensity of the flare was greater than
3 times that of the background were accompanied by sudden ionospheric
disturbances regardless of the location of the flare on the solar disk
or the area of the disturbance. Sudden ionospheric disturbances were
not restricted to association with only the largest and most intense
flares. On August 22, 1949 a flare of importance I, ~~O from the center
of the sun, was accompanied by a sudden ionospheric disturbance even
though it covered only 51 millionths of the solar hemisphere and reached
an intensity of only 2.4 at maximum. This flare occurred directly over
two spots. Two flares that took place on November I, 1949 in the same
plage area, about 400 from the center of the sun, present an interesting
anomaly. The first flare began at 1637 U.T., reached intensity 2.4 at
maximum and extended over 130 millionths of the solar hemisphere. It
was accompanied by a sudden ionospheric disturbance. The second flare
broke out in the same plage area at 1954 U.T. This flare was more
intense (2.75), larger (376 millionths) and lasted for a longer time
(66 minutes) but there is no report of a sudden ionospheric disturbance
for the period of its occurrence. Although both flares took place in
the same plage area and between the same two large spots, the detailed
regions involved in the two flares did not coincide or overlap in any
way. The light curves of the flares make possible not only a study
of the role of the maximum intensity in flare effects, but they also
permit an investigation of the time relationships between the first
indications of flare activity on the sun, the attainment of maximum
intensity, the onset of the sudden ionospheric disturbance, and the
relative durations of the solar and ionospheric phenomena. Although the
work to date includes only a portion of the flares recorded in 1949, it
is hoped that the photometric measures can be extended to include much
of the large body of observational material secured during the recent
solar maximum. MeMath-Hulbert Observatory, Lake A ngelus. Pontiac. Mich
Title: A study of the eruptive prominence of 1948 September 27
Authors: Dodson, Helen W.; Weston, Edwin B.
Bibcode: 1950MNRAS.110..199D
Altcode:
Motions in an eruptive prominence are discussed. The radial
velocities of the prominence gases are found to be consistent with the
cross-motions shown by the spectroheliograms. This agreement is strong
evidence in favour of the hypothesis of moving material. Motions of
descending nodules and of an unusual ascending spike are included in
the study.
Title: Position and Development of the Solar Flares of may 8 and
10, 1949.
Authors: Dodson, Helen W.
Bibcode: 1949ApJ...110..382D
Altcode:
This paper describes in detail the position and development of the
solar flare of May 10, 1949. The underlying spots strongly influenced
the pattern of flare material. Intensity-curves show that for most
regions the increase in brightness was very sudden; the decline was
slower and at such a rate as to suggest an exponential law. At maximum
the brightest regions had four times the intensity of the undisturbed
Ha disk. There was close correlation in the times of commencement and
maximum of the flare and the accompanying radio-noise bursts on 480
Mc and 160 Mc. The flare of May 10 is compared to another flare that
occurred in the same sunspot group on May 8
Title: The Frequency and Positions of Flares Within Three Active
Sunspot Areas.
Authors: Dodson, Helen W.; Hedeman, E. Ruth
Bibcode: 1949ApJ...110..242D
Altcode:
Continuous spectroheliographic records of three active sunspot groups
secured during 105 hours of observation include 83 flares for which
the intensity was at least four times the intensity of the undis-
turbed disk of the spectroheiograms. Composite maps of these flares
indicate that they occurred repeat- edly in the same location and with
a certain continuity or chainlike nature in position. Although they
appeared most often in the region between spots, or close to and over
the penumbrae of spots, upon occa- sion, they seemed to occur exactly
over the umbrae of the spots. Many flares appeared to follow, in part,
channels already established by dark filaments (prominences seen in
projection on the disk); the filaments persisted even though they were
adjacent to, or apparently over, the bright flares. Spectroheliograms
of spot group II carry the record of a hitherto unreported, postflare
phenomenon. Flare 1 of July 29, 1947, and flares 2, 3, and 4 of July 31,
1947, occurred in the same position and were followed by the ejection
of a long bright streamer. In each case the streamer was at first
brighter than the undisturbed disk of the hydrogen spectroheliogram
and then became dark or bordered by a region of dark absorption
Title: Positions of solar flares within a SPOT group.
Authors: Dodson, Helen W.; Hedeman, Ruth
Bibcode: 1949AJ.....54..125D
Altcode:
The 5o-foot tower telescope and Stone spectroheliograph of the
McMath-Hulbert Observatory were used during the recent sun spot maxlmum
to secure continuous photographic records of active areas during the
sunlit hours of their transit across the solar disk. The records for
three of these areas, viz. Mount Wilson No. 8129, 8745, and the complex
region comprising the three spots 8767-8769 have been examined for data
regarding the detailed position of flares. The results of the analysis
can be summarized as follows: (I) Some flares appear as long bright
ropes or filaments; others as small bright dots. The composite plot
or locus of flare positions, however, suggests a certain underlying
continuity for both types; flares seem to lie along axes or chains,
some of which are curved. (2) Flares occur repeatedly in the same
location. (3) Although flares occur most often in the region between
spots, or close to and over the penumbrae of spots, they do, upon
occasion, seem to occur exactly over the umbrae of spots. (4) Many
flares seem to follow, in part, channels already established by the dark
filaments (prominences seen in projection). The relationships are not
clear: some flares apparently lie along the sides of filaments; in other
cases, they seem to form limiting boundaries; at still other times,
the phenomena appear to be independent. (5) Although some filaments have
been observed to disappear shortly after the outbreak of a great flare,
the spectroheliograms here studied indicate that certain filaments
can persist even though they are adjacent to, or even apparently over,
a bright flare. Observatory, Univers?ty of Michigan, Ann Arbor, M?ch.
Title: Position and development of the great solar flare of May
10, 1949.
Authors: Dodson, Helen W.
Bibcode: 1949AJ.....54R.183D
Altcode:
On May 10, 1949 a large bright flare occurred in a spot group, 170S,
120E, between 20h03m and 22h20m U.T. Observations made at Central
Radio Propagation Laboratory indicate that it was accompanied by
a great burst of solar noise and followed by a severe magnetic
storm. Ha spectroheliograms show that about 15 minutes before the
principal outburst the region began to brighten in two widely separated
points. The location and extent of the flare was strongly influenced
by the underlying spots. Furthermore, the most intense portion of
the flare lay directly over one of the principal spot components. The
spectroheliograms of the flare were made with a band pass of 0.36 A
centered on Ha. Intensity measures indicate that at maximum the flare
had four times the intensity of the undisturbed Ha disk. The rate of
decline suggests an exponential law. Spectroheliograms of the spot
group taken before and after this great flare are remarkably similar. A
curved, dark filament was a conspicuous feature of the region before
the flare. Its trace was clearly marked across the flare, and the
filament itself was still strong and well defined on May I I. However,
on this date a large neighboring filament had disappeared, and the
spot associated with the most intense portion of the flare had become
visible on the Ha spectroheliograms. On May 8 an earlier flare had been
observed in the same spot group. Comparison of the two photographic
records indicates that the pattern and location of the two outbreaks
were very similar. On May 8th, a portion of the flare apparently moved
directly towards a sun spot and both outbreaks showed a slow limbward
drift of the flare position with time. MeMath-Hulbert Observatory,
University of Michigan, Ann Arbor, Michigan.
Title: Solar Filament of September 7, 1948
Authors: Dodson, Helen W.; McMath, Robert R.
Bibcode: 1948PASP...60..366D
Altcode:
No abstract at ADS
Title: A geometrical aid in the determination of the disk positions
of solar limb phenomena.
Authors: Dodson, Helen W.; Hedeman, E. Ruth
Bibcode: 1948AJ.....53..111D
Altcode:
An understanding of the significance of prominence activity may
perhaps be acquired more readily if limb phenomena can be correlated
more closely with associated features on the solar disk. The disk
position corresponding to a limb feature is usually quite uncertain
since prominences of great heights can be obseryed very far from the
solar limb. The methods suggested in this paper have proved successful
in determining the heliographic coordinates of certain prominence
features recorded in the motion pictures taken at the McMath-Hulbert
Observatory. Apparent height and heliographic latitude of stable solar
prominences change with time because of solar rotation. If the poles
of the axis of rotation are assumed to be on the limb, a prominence of
height, h/R, of true heliographic latitude, B, and meridian distance,
6, will appear of height, H/i?, where H h R ~ ~~r1 - cos2Ocos2B - I, R
being the solar radius. The difference between true and apparent height
A/i? is given by AD (i +h)(1 - V1 - cos2Ocos2B). Furthermore tan B = sin
0 tan P where p is the observed heliographic latitude. For prominences
within 300 of the limb, B differs from p by less than ~0, and in
practical cases heliographic latitude can be considered as determined
to this degree of accuracy by using the observed latitude p. The great
uncertainty of disk position corresponding to limb observation lies in
meridian distance and hence in heliographic longitude. For example,
a prominence observed to be .o~i? in height, at latitude 400, may
be located anywhere within a range of 600 of heliographic longitude
depending on whether its true height is .o5i? or as much as .15i?. The
rate of change of H/i? with 6, and hence with time, is different for
different values of h/i?, 6, and B, and this variation can be used
to determine the true height and heliographic longitude of stable
features of prominences provided the observations cover an adequate
time interval. In practice it is possible to use the set of curves of
A/i? versus 6 for h/i? = .10 for all prominences for which h/i? ~ .15,
provided 6 > 600 and an error in height of not more than 2000 km is
permitted. In particular, this method has been applied successfully to
prominences photographed on August 22-24, 1946, September 18-21, 1946,
and July 1-3, 1947, with the tower telescope of the McMath-Hulbert
Observatory. In each case it has been possible to identify the several
features of a semi-active prominence with corresponding portions of a
filament and to study the relationship of active and stable portions of
the prominence to spots and faculous regions on the disk. McMath-Hulbert
Observatory, University of Michigan, Lake Angelus, Pontiac, Mich.
Title: Studies of variable stars in M15
Authors: Dodson, Helen W.; Cornwall, Elizabeth R.; Thorndike, Samuel L.
Bibcode: 1946PAAS...10R..48D
Altcode:
No abstract at ADS
Title: Spectra of bright chromospheric eruptions
Authors: Dodson, Helen W.; van Dijke, Suzanne
Bibcode: 1946PAAS...10..122D
Altcode:
No abstract at ADS
Title: Annual Meeting
Authors: Dodson, Helen W.
Bibcode: 1945MMAAR..43....8D
Altcode:
No abstract at ADS
Title: Recent Progress in Astrophysics Observations of the Planets
by Lyot, Gentili and Camichel from the PIC du Midi in 1941 and 1942
Authors: Dodson, Helen W.
Bibcode: 1943ApJ....97...75D
Altcode:
No abstract at ADS
Title: Recent Solar Observations in Hydrogen and Helium Light.
Authors: Dodson, Helen W.; van Dijke, Suzanne E. A.
Bibcode: 1942ApJ....95..325D
Altcode:
Prominences as seen in X 5876 of helium are sometimes higher
or more abundant at the higher levels than the same prominences
seen in Ha. Suggestions are made for more detailed studies of
chromospheric eruptions. The greatly widened hydrogen emission lines
and the appearance of helium emission and absorption in the spectra of
eruptions are discussed. Certain very bright, low-lying, relatively
inactive prominences are identified as the limb counterparts of the
bright eruptions on the disk
Title: Annual Meeting
Authors: Dodson, Helen W.
Bibcode: 1942MMAAR..40....8D
Altcode:
No abstract at ADS
Title: Note: Use of the Hale Spectrohelioscope for the Observation
of Spectra of Chromospheric Eruptions.
Authors: Dodson, Helen W.
Bibcode: 1941ApJ....93..208D
Altcode:
No abstract at ADS
Title: Solar Phenomena Preceding the Ionospheric Storm of March
1, 1941
Authors: Dodson, Helen W.; van Dijke, Suzanne E. A.
Bibcode: 1941TeMAE..46..360D
Altcode: 1941JGR....46..360D
At the Whitin Observatory at Wellesley College a 60-mm Zeiss refractor
has been used in conjunction with the Hale spectrohelioscope to
study the visual spectra (λ4800-λ7000) of bright chromospheric
eruptions. The spectra of 20 eruptions were examined between November,
1940, and June, 1941. In general, they showed the hydrogen lines in
bright emission, the helium line, λ5876, in absorption, and no change
in the intensity of the continuous background of the spectrum. There
were two conspicuous exceptions to this pattern.
Title: The Spectrum of 25 Orionis, 1933-1939.
Authors: Dodson, Helen W.
Bibcode: 1940ApJ....91..126D
Altcode:
During 1933-1938 the hydxogen lines showed equal emission components
and no variations in velocity. Throughout this interval the emission
lines steadily increased in width. In 1938-1939 the violet component
became stronger than the red, velocities increased, and emission
widths diminished
Title: Annual Meeting
Authors: Dodson, Helen W.
Bibcode: 1939MMAAR..37...14D
Altcode:
No abstract at ADS
Title: Bright chromospheric eruptions studied at the Whitin
Observatory in 1939
Authors: Dodson, Helen W.; Cornwall, Elizabeth R.
Bibcode: 1939PAAS....9..258D
Altcode:
No abstract at ADS
Title: A Study of the Spectrum of 25 Orionis
Authors: Dodson, Helen W.
Bibcode: 1936ApJ....84..180D
Altcode:
A study of 147 spectrograms of 25 Orionis, covering the interval
1915-1933, has shown simultaneous variations of the velocities of the
central absorptions and the emission lines of hydrogen. These changes
are nearly synchronous with changes of the ratio V/R of the components
of the emission lines. The period shows a consistent decrease from i8i
7 days to 1025 days, and the velocity amplitude of the central absorp-
tions was subject to a conspicuous decrease followed by an increase,
with extreme values of 40 and 120 km/sec. The central absorption
velocities of H/3, H-y, and Ho are in phase; but the amplitude increases
in the order named. This is true also of the emission velocities. The
changes in the emission velocities anticipate those in the central
absorptions by about 100 days. The emission ratio V/R shows a marked
difference of phase from line to line, H~ antici- pating Hy by about 200
days, and H-y anticipating H$. The emission lines vary conspicuously in
width and show two maxima of width in each velocity cycle. These maxima
occur at times of maximum and minimum velocity. The helium lines and the
broad hydrogen absorption which underlies the emission show systematic
variations of velocity and changes of contour which are definitely
related to the velocities of the hydrogen central absorption, but are
conspicuously out of phase with the latter. With the exception of the
phenomena of the helium and broad hydrogen absorption, the variations
observed find a satisfactory interpretation in terms of the rotating-
pulsating nebulous atmosphere suggested by McLaughlin
Title: Spectrum of Be star 25 Orionis
Authors: Dodson, Helen W.
Bibcode: 1936PAAS....8..109D
Altcode:
No abstract at ADS
Title: A study of the spectrum of 25 Orions ...
Authors: Dodson, Helen Walter
Bibcode: 1936sstf.book.....D
Altcode: 1936QB883.D6.......
No abstract at ADS
Title: Radial velocities from microphotometer tracings
Authors: Dodson, Helen W.
Bibcode: 1936PAAS....8Q...7D
Altcode:
No abstract at ADS
Title: A Study of the Spectrum of 25 Orionis.
Authors: Dodson, Helen W.
Bibcode: 1934PhDT.........1D
Altcode:
No abstract at ADS
Title: A note on helium lines in three Be spectra
Authors: Mohler, Orren; Dodson, Helen W.
Bibcode: 1933PAAS....7..182M
Altcode:
No abstract at ADS