Author name code: zirin
ADS astronomy entries on 2022-09-14
author:"Zirin, Harold" OR author:"Zirin, Hal"
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Title: Statistical Correlations between Solar Microwave Bursts and
Coronal Mass Ejections
Authors: Dougherty, Brian L.; Zirin, Harold; Hsu, Kathryn
Bibcode: 2002ApJ...577..457D
Altcode:
We compare listings of coronal mass ejections (CMEs) observed by LASCO
on SOHO and solar microwave bursts (SMBs) recorded by the Radio Solar
Telescope Network (RSTN) operated by the United States Air Force. These
data sets are the product of stable and continuous observations of the
whole Sun and provide suitable bases for robust statistical studies. In
total, 3557 coronal ejections and nearly 1051 bursts above 50 sfu
were observed from 1996 January through 2001 May. Correlated events
are easily distinguished by time proximity. Correlations improve as
CME launch heights are projected to the solar limb, when the rms
scatter in CME-SMB delay was as little as 16 minutes, but because
coronal disturbances are only visible when they emerge from behind
occulting disks, timing associations depend on the assumed source and
acceleration. The probability of correlation rises with burst flux,
duration or temporal complexity, and ejection speed or width. For
the 164 SMBs with intensities over 500 sfu, 70%+/-8% were associated
with CMEs. For the 160 CMEs that were halo-like or have speeds over
1000 km s-1 (characteristics that have been associated with
geoeffective events), 60%+/-8% and 84%+/-10% were associated with SMBs,
respectively.
Title: Quantitative measure of quiet photospheric magnetic fields
Authors: Zirin, H.; Cameron, R.
Bibcode: 2002AAS...200.3903Z
Altcode: 2002BAAS...34..701Z
We have analyzed a set of 110 Stokes V spectra of the quiet Sun taken
with the spectrovideomagnetograph at BBSO June 23, 2000. The 480x512
pixel spectrograms are bundled into 3 pixel (1 arc sec) spectra, giving
160 distinct spectra on each frame, or 16400 spectra overall. An element
of magnetic network was included in each spectrogram, so that actual
splitting measurements could be used to check absolute calibration
of the field measures. In each case we measured the V signal in both
5250 and 5247 and compared the values. If the ratio was 3:2 as given by
the g-factors, the data must represent true measured magnetic fields,
since random noise does not understand g-factors. We find the mean
field on each spectrum to range from 3 to 49 gauss in the different
frames, and the median absolute field, from 13 to 30 G. In all cases the
difference between V(5250) and 1.5xV( 5247) is zero within 1.2 standard
errors. To check the popular ``emperor's new clothes" model in which
the fields measured are due to invisible spots with kilogauss fields,
we calculate the mean value of 1.5xV(5247)/0.78- V(5250), expected to
be zero for that model. Rather than zero, that result is typically 3
standard errors from zero, and invariably negative. That result means
that the V(5250) is not saturated, as would be expected in the kilogauss
model. Thus the emperor, in fact, has no clothes. The fields measured in
network elements run from 250 to 700 gauss, and are typically confirmed
within 20% by the measured splitting. The existence of fields of mixed
polarity and strength >10 gauss everywhere in the photosphere gives
an explanation for the support of the chromosphere, which has a scale
height of 1000 Km instead of the expected hydrostatic scale height
<200 Km, as well as the filtering out of unionized high-FIP elements,
which cannot be supported by the magnetic fields, from the solar wind.
Title: Statistical Correlations Between Solar Microwave Bursts and
Coronal Mass Ejections
Authors: Dougherty, B. L.; Zirin, H.
Bibcode: 2002AAS...200.3711D
Altcode: 2002BAAS...34..696D
We compare listings of coronal mass ejections (CMEs) observed by
LASCO on SOHO and solar microwave bursts (SMBs) recorded by the USAF
Radio Solar Telescope Network (RSTN). These data sets are the product
of stable and continuous observations of the whole Sun, and provide
suitable bases for robust statistical studies. In total, 3557 coronal
ejections, and 1051 bursts above 50 sfu were observed from January 1996
through May 2001. Correlated events are easily distinguished by time
proximity. Correlations improve as CME launch heights are projected
to the solar limb, when the rms scatter in CME-SMB delay was as little
as 16 min, but because coronal disturbances are only visible when they
emerge from behind occulting disks, timing associations depend on the
assumed source and acceleration. The probability of correlation rises
with burst flux, duration or temporal complexity, and with ejection
speed or width. For the 164 SMBs with intensities over 500 sfu, 70%
are associated with CMEs. For the 160 CMEs which are halo-like or have
speeds over 1000 km/sec (characteristics that have been associated with
geoactive events), 60% and 84% are associated with SMBs, respectively.
Title: The true structure of weak solar magnetic fields
Authors: Zirin, H.; Cameron, R.
Bibcode: 2002ocnd.confE..30Z
Altcode:
No abstract at ADS
Title: The Field Strength of the Quiet Sun Magnetic Elements
Authors: Zirin, H.; Cameron, R.
Bibcode: 2001AAS...198.7105Z
Altcode: 2001BAAS...33..893Z
By attaching the videomagnetograph to the Coude spectrograph at BBSO,
we can measure weak fields down to 10-20 gauss, and splittings down
to 200 gauss. Using Stenflo's technique of comparing 5250 and 5247,
we find no saturation; the lines (corrected for g-factor) give equal
results within a few per cent and are truly weak. The V measurements
are calibrated by comparison to Zeeman splitting measures above 200
gauss. The filling factor is unity and there are no hidden strong
fields. We find noevidence for kilogauss fileds in the quiet Sun. While
noise limits the agreement of the two lines below 20 gauss, there is
a detectable V signal almost everywhere on the Sun, both unipolar
and mixed, of the order of 5 gauss. We call the new instrument the
spectrovideo-magnetograph (SPVMG). This work supported by the NSF.
Title: Spectovideomagnetograph results and the Stokes V assymmetry
Authors: Cameron, R.; Zirin, H.
Bibcode: 2001AAS...198.7104C
Altcode: 2001BAAS...33R.893C
The Spectrovideomagnetograph at Big Bear Solar Observatory was used
to obtain several thousand individual spectra of small elements
on the solar surface. These measurements display the well known
Stokes V assymmetry, however because the BBSO SPVMG has a significant
different spatial and temporal resolution than previous measurements,
the assymmetry has different properties. In this poster we present our
measurements of the assymmetry and use them to place constraints on the
mechanism producing the assymmetry. We then discuss how the assymmetry
contaminates other quantities derived from the SPVMG measurements, and
how this contamination can be minimized and controlled in our data set.
Title: The Spectrovideomagnetograph Reveals the True Strength of
Photospheric Magnetic Fields
Authors: Zirin, H.; Cameron, R.
Bibcode: 2001AGUSM..SH32C04Z
Altcode:
We present new observations of weak solar magnetic fields from an
instrument which we term the spectrovideomagnetograph (SPVMG). The
sensing system of the videomagnetograph is attached to the Coude
spectrograph at Big Bear and yields a high sensitivity. Using the
criteria introduced by Stenflo, we measure the Stokes V and I components
for the lines FeI 5250 and 5247 in hundreds of spectra. We find that
from 20 to 350 gauss derived field strengths are strictly proportional
to the g-factor and show no saturation. Hence the widely accepted strong
invisible magnetic elements postulated by Stenflo do not exist. The
filling factor is near unity. We measure the Zeeman splitting directly
down to 200 gauss and find good correspondence with our V measure. We
find that the area (outside of sunspots) of the solar surface occupied
by magnetic field of different strengths follows a power law in the
inverse square of the field strength. This applies to fields down to
200G. This has obvious relevance for turbulent surface dynamo models. We
find that at least 90% of the solar surface is covered by weak fields
above 5 gauss, sometimes unipolar and sometimes mixed.
Title: The Spectrovideomagnetograph Reveals the True Strength of
Quiet Sun Magnetic Fields
Authors: Zirin, H.; Cameron, R.
Bibcode: 2000AAS...197.5107Z
Altcode: 2000BAAS...32.1489Z
We present new observations of weak solar magnetic fields with a
technique, which we term the spectro-videomagnetograph (SPVMG) which
permits direct measurement of splittings as small as 200 gauss. Using
the technique of Stenflo we compared the Stokes V-component for the
5250 and 5247 lines. Contrary to Stenflo's results, we find no evidence
for strong fields with small filling factor; i. e., the field strengths
measured as 200 gaussare really 200 gauss and not some stronger field
partly filling the sample. For the weakest measured fields this cannot
be absolutely established, but the evidence supports the existence
of field elements at least as weak as 200 gauss. Observations of
active regions also yield new results. In many cases of fields near
inversion lines, we find doubled sets of Zeeman components, as well as
`flags,' broad components, usually confined to one side of the line,
extending to displacements corresponding to thousands of gauss, with
no corresponding component on the opposite side of the line. We show
examples of these spectra, along with slit jaw images, but have only
a limited understanding of the field structures they represent. We
also have examples of the V-splitting increasing as we approach the
inversion line. We are struggling to understand these and will at
least show them, with or without explanation. Finally, the regions
involving these anomalous Zeeman patterns seem to flare more frequently,
although statistics are limited. This work has been supported by the
NSF under ATM-9726147.
Title: Oscillations and running waves observed in sunspots: Analysis
of an extended sample of sunspots
Authors: Georgakilas, A. A.; Christopoulou, E. B.; Zirin, H.
Bibcode: 2000AAS...197.5109G
Altcode: 2000BAAS...32Q1489G
Sunspots show oscillatory behavior, identifiable as intensity and
velocity variations in photospheric and chromospheric lines. In
the chromospheric layers 3 min standing oscillations are dominant
in the umbra (umbral oscillations), while 5 min running waves are
dominant in the penumbra and superpenumbra. Penumbral waves (RPW)
were first observed in Hα by Zirin and Stein (1972) and independently
by Giovanelli (1972). Since their discovery a number of authors have
tried to determine the physical properties of umbral oscillations
and running penumbral waves (like the frequency and the propagation
velocity) and to identify their nature, as well as the relation between
them. In order to clarify discrepancies, due to the analysis of limited
number of sunspots, we present comprehensive results from the study of
8 sunspots observed from the Big Bear Solar Observatory (BBSO) during
1999 and 2000. Our results show that RPW are propagating with a mean
velocity of the order of 15 km s-1. The fourier analysis
of 'time slice images' (created taking cross sections of every image
of a time series) indicates that there is not a clear relationship
between umbral oscillations and running penumbral waves. This work
was supported by NSF grant ATM-9726147.
Title: The Dependence of Large Flare Occurrence on the Magnetic
Structure of Sunspots
Authors: Sammis, Ian; Tang, Frances; Zirin, Harold
Bibcode: 2000ApJ...540..583S
Altcode:
We have studied 8 yr of active region observations from the United
States Air Force/Mount Wilson data set, supplied by the NOAA World Data
Center, to confirm the relation between δ spots and large flares. We
found that after correcting some errors we were able to describe
relationships among active region size, peak flare soft X-ray (SXR)
flux (measured by GOES 1-8 Å flux), and magnetic classification. We
found the Solar Optical Observing Network magnetic classification to
be reasonably accurate but its area measures to be inaccurate for many
of the regions. This is due partly to transcription errors and partly
to wrong correction for limb foreshortening. Errors could, however,
be repaired by intercomparison of multiple observations. We confirm
Künzel's original idea that regions classified βγδ produce many
more large flares than other regions of comparable size. Almost all
substantial flares occurred in regions classified βγδ by the Air
Force sites. Each region larger than 1000 μh and classified βγδ had
nearly 40% probability of producing flares classified X1 or greater. Yet
only a half-dozen of those, showing the ``island delta'' configuration,
produced great activity. There is a general trend for large regions to
produce large flares, but it is less significant than the dependence
on magnetic class.
Title: Solar Radio Burst Locator
Authors: Dougherty, B. L.; Freely, W. B.; Zirin, H.; Gary, D. E.;
Hurford, G. J.
Bibcode: 2000ASPC..206..367D
Altcode: 2000hesp.conf..367D
No abstract at ADS
Title: The Magnetic Circumstances of Large Flares
Authors: Zirin, H.; Sammis, I.; Tang, F.
Bibcode: 2000ASPC..206...37Z
Altcode: 2000hesp.conf...37Z
No abstract at ADS
Title: The Solar Radio Burst Locator (SRBL) Program
Authors: Dougherty, B. L.; Hurford, G.; Sammis, I.; Zirin, H.
Bibcode: 1999AAS...194.7705D
Altcode: 1999BAAS...31..960D
The Solar Radio Burst Locator (SRBL) is a new ground-based instrument
used to record the spectra of microwave bursts and to locate their
positions on the solar disk. It was designed at Caltech by Gordon
Hurford and will be deployed at several sites around the world in time
for MAX-2000 as part of the US Air Force's Solar Electro-Optical Network
(SEON). It employs a single, automated, six-foot dish and a broad-band
receiving element typically observing 105 selectable frequencies from
one to 18 GHz every five seconds. Additional data is taken at 245, 410,
and 610 MHz. The antenna points at Sun center, and off-center burst
locations are determined from the amplitude and phase of modulation
of the frequency-scanned signal. For bursts greater than 500 sfu,
we have obtained positions with an accuracy of less than 5 arc min
and hope to improve this. The positional information is to be used in
space-weather forecasting, and the spectral data will be a powerful
resource for analysis of burst evolution, electron energy distribution,
and for comparisons with X-ray and particle observations. Combined
with HESSI results, it should yield information on flare magnetic
fields. The database, with continuous all-weather coverage, will be
available on the Web. We will present data on several events already
observed during prototype testing.
Title: Chromospheric Sources of Coronal Rays
Authors: Zirin, H.; Cameron, R.
Bibcode: 1999AAS...194.7808Z
Altcode: 1999BAAS...31..962Z
TRACE images in the 171A FeIX line show coronal rays or small streamers
from network elements. We obtained chromospheric images in center and
wing of Hα at BBSO to investigate the relation of these to spicule
activity at the base, as well as to brightenings and other changes in
the underlying chromosphere. There is a close match of the brightest
Hα centerline elements to coronal rays; other network elements
are seen. Spicule activity does not appear to play a big role. The
coronal changes are fairly slow. We shall also present new data on
spicule lifetimes.
Title: The delta SPOT and active region cutoff energies
Authors: Sammis, I.; Zirin, H.
Bibcode: 1999AAS...194.5401S
Altcode: 1999BAAS...31..908S
It has been demonstrated observationally (Kucera et al. 1997) that
active regions have a cutoff flare energy (E_c) beyond which their
flare production is sharply restricted. This cutoff energy appears
to vary with active region area. Flare models have been created
which predict this (Lu et al 1993., Litvinenko 1996 for example);
these models predict a form E_c(L), where L is some measure of the
extent of the active region. Using USAF and Mt. Wilson active region
observations for active regions in the years 1989-1997, we see that
great flares tend to be produced by complex delta spots (delta spots
with a Mt. Wilson classification of beta gamma ). This argues for a more
complex functional form E_c(L,... ), where the additional parameters
would describe in some way the magnetic configuration.
Title: The Apparent Reversal of Fields at the Solar Limb
Authors: Zirin, Harold
Bibcode: 1999SoPh..184..249Z
Altcode:
We show how the apparent reversal of longitudinal magnetic fields
near the limb is a projection effect and may be used to estimate the
divergence angle of the magnetic canopy. The limb distance at which
the apparent reversal is not seen is the limiting angle of divergence
of lines of force emerging from the surface. We have surveyed a number
of polar limb magnetograms, where the unipolar field makes this easier,
and found the divergence angle to be about 20° from the vertical.
Title: Synoptic Hα Full-Disk Observations of the Sun from Big
Bear Solar Observatory - I. Instrumentation, Image Processing,
Data Products, and First Results
Authors: Denker, C.; Johannesson, A.; Marquette, W.; Goode, P. R.;
Wang, H.; Zirin, H.
Bibcode: 1999SoPh..184...87D
Altcode:
The Big Bear Solar Observatory (BBSO) has a long tradition of synoptic
full-disk observations. Synoptic observations of contrast enhanced
full-disk images in the Ca ii K-line have been used with great success
to reproduce the H i Lα irradiance variability observed with the
Upper Atmosphere Research Satellite (UARS). Recent improvements in
data calibration procedures and image- processing techniques enable us
now to provide contrast enhanced Hα full-disk images with a spatial
resolution of approximately 2'' and a temporal resolution of up to 3
frames min−1.
Title: Variability of Solar UV Irradiance Related to Bright Magnetic
Features Observed in Call K-Line: Relationship between Lyman alpha
and K-line Report for UARS funding agency
Authors: Zirin, Harold; Cameron, Robert
Bibcode: 1999STIN...9910690Z
Altcode:
In this report we comment on the relationship between the Lyman alpha
and Calcium K-line emission from the Sun. We firstly examine resolved
Lyman alpha images (from TRACE) and resolved K-line images. We find
that the Lyman alpha emission is consistent with a linear dependence
on the K-line emission. As this is in conflict with the analysis
of Johannesson et al.(1995, 1998) we proceed by comparing the disk
integrated Lyman alpha flux as a function of ratio between the disk
integrated Mg II core and wing fluxes (Johannesson et al (1998) having
previously found a linear dependence between this index and the BBSO
K-line index). We find that a reasonably good fit can be obtained,
however note the discrepancies which lead Johannesson et al to consider
the square root relationship. We suggest an alternative interpretation
of the discrepancy.
Title: The evolution of intranetwork magnetic elements
Authors: Zhang, Jun; Lin, Ganghua; Wang, Jingxiu; Wang, Haimin;
Zirin, Harold
Bibcode: 1998A&A...338..322Z
Altcode:
We have studied the evolution of Intranetwork (IN) magnetic elements,
using a particularly good series of very deep magnetograms obtained at
Big Bear Solar Observatory. The magnetograms span an interval 10 hours
long and cover an area of 310x 240 arcsec(2) . We are able to follow
528 intranetwork elements from birth to death. The analysis reveals the
following results: (1). The appearance of IN elements can be classified
into the following categories: half of the total IN elements emerge
as clusters of mixed polarities somewhere within the network cells,
one fifth appear as ephemeral regions (tiny bipoles), one fifth result
from the merging of several elements of a given polarity, and one tenth
appear by fragmentation of larger elements. (2). IN elements disappear
in four ways: one third of total IN elements cancel with elements of
opposite polarity, one third decay into weak fields without apparent
interaction with other elements, one fourth merge with IN or network
elements of the same polarity, and one tenth split into smaller IN
elements below detecting limit. (3). About one ninth (one sixth) of
the IN elements merge (cancel) with network features, consequently,
part of the flux in network features is built up from former IN magnetic
flux, and part is eliminated by IN elements. The net effect of merging
and cancellation is a gradual reduction of the total flux of network
elements in the 10 hours observational interval. It seems that not all
the network magnetic flux is the remnant of active region magnetic flux.
Title: Properties and Motions of Ellerman Bombs
Authors: Nindos, Alexander; Zirin, Harold
Bibcode: 1998SoPh..182..381N
Altcode:
We studied the properties and proper motions of Ellerman bombs (EBs)
around a sunspot in a mature active region using high-resolution
off-band Hα filtergrams together with nearly simultaneous
magnetograms. Sixty-four percent of the EBs (class I) did not
correspond accurately to enhanced magnetic field elements while the
rest corresponded well to such elements (class II), which all were
moving magnetic features (MMFs). We studied the lifetimes, shapes and
dimensions, contrasts and time profiles of the EBs. These properties
were essentially the same for both classes, in agreement with previous
authors. Class I EBs did not move but class II EBs tracked the MMFs
well, with horizontal proper motions up to a maximum of 1.1 km s−1 and
their velocity pattern was similar to the velocity pattern of the MMFs.
Title: The motion patterns of intranetwork magnetic elements
Authors: Zhang, Jun; Wang, Jingxiu; Wang, Haimin; Zirin, Harold
Bibcode: 1998A&A...335..341Z
Altcode:
By tracing individual elements, we have measured horizontal velocity
and studied motion patterns of Intranetwork (IN) magnetic elements for
the first time. The magnetograms obtained at Big Bear Solar Observatory
span an interval of 10-hour and cover an area of 310x 240 arc sec(2)
. In general, IN elements move radially and isotropically outwards from
emergence centers to boundaries of supergranule cells at first. However,
when they reach halfway between cell centers and boundaries, the motion
of IN elements is non-isotropic, there are prior directions. Most
of IN elements move towards the edges of network elements. There are
two components of the velocity fields: radial velocity and circular
velocity. >From the centers to the boundaries of supergranule cells,
the magnitude of the radial velocity decreases gradually; but that of
the circular velocity increases obviously, at halfway between cell
center and boundary, the circular acceleration reachs the maximum,
about 10(-1) m s(-2) . The mean circular velocity near the boundary
is about 0.4 km s(-1) . The horizontal speeds deduced by tracing 768
intranetwork elements range from 0.05 km s(-1) to 0.8 km s(-1) with a
peak distribution at 0.4 km s(-1) . Both within the supergranule cells
and on the boundaries, there are convergence centers, but divergence
centers always exist within supergranule cells.
Title: The Astrophysics of the Sun
Authors: Zirin, H.
Bibcode: 1998assu.book.....Z
Altcode:
This is an entirely new edition of Harold Zirin's classic text on the
solar atmosphere. Combining an introductory course in astrophysics
with a comprehensive treatment of the theoretical and observational
aspects of our present knowledge of the sun, the book has been
completely updated. It includes a large number of spectacular new
photographs, including many of the best solar pictures from the world's
observatories. Professor Zirin is one of the leading scientists in his
field. His lucid writing style, combined with considerable teaching
experience, has resulted in a valuable and important textbook of
astrophysics.
Title: The Relation of CA II K Features to Magnetic Field
Authors: Nindos, Alexander; Zirin, Harold
Bibcode: 1998SoPh..179..253N
Altcode:
We studied quantitatively the relation between the intensity of
Caii K-line bright features and the intensity of the associated
magnetic elements using two data sets obtained at the Big Bear
Solar Observatory. Both network and intranetwork (IN) structures were
considered. Magnetic field changes always affected the K-line emission;
for example, the appearance of new bipoles was always followed by
enhanced K-line emission. There is an almost linear correlation between
the K-line intensity and the magnetic field strength of the stronger
network elements (elements with absolute field strength higher than
11-19.5 G). We identified two classes of intranetwork K-line elements:
magnetic and non-magnetic ones. The number of the magnetic K-line IN
elements above a 1-sigma threshold was only 5%-10% of the number of
the non-magnetic ones. The magnetic K-line IN elements were almost 3
to 4 times brighter compared to the non-magnetic elements. On the other
hand, the non-magnetic elements were moving with typical velocities of
35-40 km s−1 while the velocities of the magnetic K-line
elements were of the order of 1 km s−1.
Title: Curious Magnetic Changes in a Quiet Region
Authors: Zirin, H.; Wilson, P. R.; Li, Y.
Bibcode: 1998SoPh..179..269Z
Altcode:
We describe the evolution of weak magnetic fields in a quiet region
observed at the Big Bear Solar Observatory on 1 October 1996. We
observed puzzling changes in which one polarity changed without
corresponding increases or decreases in the other. In the rest of the
same field, no special changes were observed, and a search of nearby
days revealed no similar changes. We do not wish to call Maxwell's
laws into question, we simply state that there are surprising effects
that we cannot understand with current models.
Title: New Studies of Polar Spicules
Authors: Zirin, H.; Cameron, R.
Bibcode: 1998AAS...192.1506Z
Altcode: 1998BAAS...30..840Z
We have studied several hundred images of solar spicules obtained
on June 18 and 19 and July 15 of 1997. The observations were made at
BBSO with the 65cm telescope feeding a Zeiss 1/4 Angstroms filter and
a 1536x1024 Kodak CCD. Overexposed observations were made above the
limb as well as normal exposures on the limb. The filter was tuned
to Hα -0.65A and a 30sec interval was used. We were limited to a
single wavelength because new software was being installed in a new
control computer. The images obtained were processed by high-pass
digital filtering of the original FITS images and reregistered by an
FFT technique. The image scale is 0.17 arcsec per pixel. The disk was
observed on June 18, 1997 to detect the sources of macrospicules and
the limb was observed by overexposure on June 19 to determine the height
trajectory of the faintest Hα We found that: Many more spicules go up
than come down. There are numerous double and multiple spicules. The
macrospicules come from normal network elements and start with an
"Eiffel tower" shape. There is evidence of magnetic changes underlying
these features. Both long macrospicules and complex eruptions are
important at the pole. There is some evidence for rotation in spicules.
Title: Contrast of Faculae at 1.6 Microns
Authors: Wang, Haimin; Spirock, Thomas; Goode, Philip R.; Lee, Chikyin;
Zirin, Harold; Kosonocky, Walter
Bibcode: 1998ApJ...495..957W
Altcode:
We followed Active Region NOAA 7981 from 1996 July 27 to 1996 August
7 at Big Bear Solar Observatory. During the region's limb-to-limb
passage, images at 1.6 μm, 6103 Å, and CaK, as well as line-of-sight
magnetograms were obtained every day to study the variation of
facular/plage contrast and its relationship to magnetic fields. Our
1.6 μm images were observed by a high-quality 320 × 240 PtSi/Si
detector, which produces extremely uniform images. Our data agree with
the early results of Foukal et al. in several aspects: (1) at 1.6 μm,
some faculae are dark at solar disk center and all become bright when
they are close to the limb; (2) the changeover occurs approximately
at cos θ = 0.5-0.7 (3) the threshold of magnetic flux required to
produce a dark structure at 1.6 μm is about 5 × 1018
Mx. Equally important, our result is different from that of Foukal et
al. on an important issue: among about 150 elements studied near the
disk center, only four of these IR dark faculae show no contrast in
the visible continuum. Other elements show dark contrasts in both 1.6
μm and the visible continuum, if there is sufficient resolution in
the data. However, darkening of weaker (lower flux) elements are more
obvious at IR and most bright points seen at red continuum disappear at
IR. These findings do confirm that 1.6 μm images reveal new aspects
of photospheric magnetic structure. In this paper, we also present a
quantitative relationship between the dark contrast of 1.6 μm faculae
and magnetic field strengths at the disk center, as well as the contrast
variation of IR faculae as a function of the disk position.
Title: Lifetime of Intranetwork Magnetic Elements
Authors: Zhang, Jun; Lin, Ganghua; Wang, Jingxiu; Wang, Haimin;
Zirin, Harold
Bibcode: 1998SoPh..178..245Z
Altcode:
Using a 10-hour time sequence of very deep magnetograms of Big Bear
Solar Observatory, we have studied the lifetime of Intranetwork Magnetic
Elements for the first time. The analysis reveals the following results:
Title: Study of Hα Jets on the Quiet Sun
Authors: Wang, Haimin; Johannesson, Anders; Stage, Mike; Lee, Chikyin;
Zirin, Harold
Bibcode: 1998SoPh..178...55W
Altcode: 1998SoPh..178..493W
High-speed jets of solar quiet regions have been observed at Big Bear
Solar Observatory in Hα−1.0 Ú, and compared with high-resolution
magnetograms. Over the whole Sun, the birthrate of the Hα−1.0 Ú
jets is about 19±3 events s−1, which is much lower than
the birthrate of spicules. The average lifetime of these jets is 2±1
min. Hα−1.0 Ú jets are very different from spicules, in the sense
of birthrate, lifetime, and shape. Jets tend to recur in the same sites,
always located in boundaries of supergranules. Under the best observing
conditions, we found that 80% of the major jet sites are associated
with converging magnetic dipoles - mainly the sites where intranetwork
elements are canceling with opposite polarity network elements. In order
to establish a possible relationship between the disk Hα jets and limb
macrospicules, we have also obtained time sequences of Hα center-line
images at the limb. These images are enhanced by median filtering so
that jet structures over the limb are easily studied. We found that
these limb Hα jets (above the spicule forest) repeatedly occur in
the same sites, which is the property shared by the disk Hα−1.0 Ú
jets. However, their mean lifetime is 10 min, substantially longer than
that of disk jets. Comparison with simultaneous SOHO/EIT Heii 304 Ú
images shows that every Heii 304 Ú jet over the limb coincides with an
Hα jet, although Heii 304 Ú jets extend much farther out. Some Hα
jets do not have associated He jets, probably due to the difference
in image resolutions. Hα spectra of selected jets are analyzed,
and we found that jets are not simply blue-shifted; instead, the
line profiles are broadened with significantly larger broadening on
the blue side. Two-component fitting finds that the velocity of the
blue-shifted component (an optically-thin component) is around 20 to
40 km s−1.
Title: Filament Disappearances During the Period of September 1991
through September 1994
Authors: Wang, Haimin; Komenda, Arkadiusz E.; Tang, Frances; Zirin, Hal
Bibcode: 1998SoPh..178..109W
Altcode: 1998SoPh..178..547W
Continuous full-disk Hα images recorded by the Big Bear Solar
Observatory (BBSO) from 1 September 1991 to 19 September 1994 (the
first three years of Yohkoh mission) were digitized and analyzed. The
data set consists of nearly 10000 Hα images, one every half hour for
the period when the BBSO was observing. Two statistical studies of the
disappearing solar filaments based on this set of data are made: (1)
The disk latitude distribution of all larger disappearing filaments
with a minimum length of 70 arc sec, including the time of their
disappearance. Of the 1095 such filaments, 439 disappeared during our
continuous observations, 314 disappeared during the BBSO night gap,
162 disappeared during data gap (more than 94 hours) and 180 rotated
beyond the west limb. If we plot latitudes as a function of time for
all these disappeared filaments, it shows a uniform distribution in
latitude. However, if we plot the distribution of larger disappeared
filaments (200 arc sec or above), then the butterfly trend appears -
position of filaments tends to drift to lower latitude as solar activity
decreases. (2) The disk distribution of all detectable disappearing
filaments, large and small, for the 9-months period, January 1994 to
September 1994. We find that the size distribution of 351 collected
disappeared filaments follows a power law with a power index of −1.40.
Title: Dynamics of solar spicules
Authors: Zirin, H.
Bibcode: 1998ESASP.421...39Z
Altcode: 1998sjcp.conf...39Z
No abstract at ADS
Title: A 10-Year Set of CA I K-Line Filtergrams
Authors: Johannesson, Anders; Marquette, William H.; Zirin, Harold
Bibcode: 1998sers.conf..265J
Altcode:
No abstract at ADS
Title: A 10-Year Set of CA II K-Line Filtergrams
Authors: Johannesson, Anders; Marquette, William H.; Zirin, Harold
Bibcode: 1998SoPh..177..265J
Altcode:
We have processed a 10-year set of BBSO Caii K-line filtergrams covering
most of solar cycle 22. The excess K-line emission is integrated to
form linear and square-root activity indices that are fitted to UV data
from UARS and SME. Good fits are found both for the Mgii core-wing ratio
(linear) and total Lα irradiance (square root) and the indices are thus
good proxies for UV data. The SME Lα irradiance is systematically lower
by 20% than predicted from our corresponding K-line indices. The 10.7
cm radio data confirms that SME underestimated the flux. The network
is partly responsible for the solar cycle variation of the indices
and is relatively more important in Lα than in Mgii and Caii K. This
is due to the saturation of Lα equivalent width. We also report on
substantial improvements to the equipment and reduction software. The
system is now based on a digital CCD camera which promises more accurate
measurements in the upcoming solar cycle 23.
Title: Comparison of Polar and Equatorial Magnetic Fields Near
Sunspot Minimum
Authors: Zhang, L. D.; Zirin, H.; Marquette, W. H.
Bibcode: 1997SoPh..175...59Z
Altcode:
We investigate the polar magnetic fields near sunspot minimum
using high-resolution videomagnetograph data from Big Bear Solar
Observatory. To avoid the problem of center-to-limb variation of the
projected longitudinal field, we compare polar with equatorial field
strengths for the same limb distance. Polar fields are stronger than
the quiet equatorial field, but no greater than equatorial limb data
containing unipolar regions. The difference is entirely in the stronger
field elements. The polar background fields are of mixed polarity
but show a net weak field opposite in sign to that of the stronger
polar elements. We believe this to be the first evidence of widespread
background field. No dependence of the measured signal on the B-angle
was found, so the high-latitude fields do not change strength near the
pole. Further, there was no significant change in the polar fields in
the 15-month period studied. We tried to derive a high-latitude rotation
rate; our data show motion of high-latitude magnetic elements, but the
diurnal trajectory is not much bigger than random motions and field
changes, so the result is inconclusive. We suggest that the polar
fields represent the accumulation of sunspot remnants, the elements
of which last for years in the absence of other fields.
Title: The relation of CaII K line features to magnetic field
intensity
Authors: Nindos, A.; Zirin, H.
Bibcode: 1997BAAS...29.1119N
Altcode:
No abstract at ADS
Title: Comparison of Two Fitting Methods for Ring Diagram Analysis
of Very High l Solar Oscillations
Authors: Patrón, J.; González Hernández, I.; Chou, Dean-Yi;
Sun, M. -T.; Mu, T. -M.; Loudagh, S.; Bala, B.; Chou, Y. -P.; Lin,
C. -H.; Huang, I. -J.; Jiménez, A.; Rabello-Soares, M. C.; Ai, G.;
Wang, G. -P.; Zirin, H.; Marquette, W.; Nenow, J.; Ehgamberdiev, S.;
Khalikov, S.; TON Team
Bibcode: 1997ApJ...485..869P
Altcode:
A new method of fitting tridimensional power spectra of solar
oscillations is described and compared with a previous one whose
use has been more common. The new method fits the parameters of the
Lorentzian profiles in a bidimensional k - ω diagram constructed
from an azimuthal average of the tridimensional one. The horizontal
velocities are then determined keeping these parameters fixed, greatly
reducing the computation time. Both methods are compared for two radial
orders (n = 3, 4) of a tridimensional power spectrum obtained for a
region of about 15° square around solar disk center. The images used
in this work correspond to a 3 day set of 1080 × 1080 pixel intensity
images obtained at the Observatorio del Teide on 1994 November 8-10
with the Taiwanese Oscillation Network (TON) instrument. The results
of the fitted velocities agree within the estimated errors for the
two methods. The reduction of the computing time obtained with the
new method makes it convenient for the ring diagram analysis.
Title: Imaging the Chromospheric Evaporation of the 1994 June 30
Solar Flare
Authors: Silva, Adriana V. R.; Wang, Haimin; Gary, Dale E.; Nitta,
Nariaki; Zirin, Harold
Bibcode: 1997ApJ...481..978S
Altcode:
We analyze simultaneous Hα images (from the Big Bear Solar
Observatory), soft and hard X-ray images and spectra (from the soft
X-ray telescope [SXT], the Bragg Crystal Spectrometer [BCS], and the
hard X-ray telescope [HXT] on Yohkoh), and radio time profiles (from
the Owens Valley Radio Observatory) during the first 3 minutes of the
1994 June 30 flare. The strong blueshifts observed in the Ca XIX soft
X-ray line are interpreted as evidence of chromospheric evaporation,
with maximum up-flow velocities occurring 2 minutes prior to the hard
X-ray emission peak. In this study, we search for moving sources in
Hα, soft and hard X-ray images that correspond to the blueshifted
component. The chromospheric evaporation in this flare is divided
into two phases: an early phase with up-flow velocities of 350-450
km s-1, and a later phase (during the hard X-ray peak)
characterized by velocities of 100-200 km s-1. During the
first chromospheric evaporation phase, the footpoints of a loop seen
in HXT low-energy maps are seen to move toward the loop-top source. No
source displacement is observed in SXT images at this time. Images
of the later phase of chromospheric evaporation show a change in
the source morphology. The early HXT loop is no longer visible, and
HXT maps during this time display the two footpoints of a new loop
visible in SXT images. Now the HXT sources are stationary, and a SXT
footpoint source is seen to move toward the loop top. We interpret
the observed displacement of footpoint sources in HXT (early phase)
and SXT (later phase) maps to be the images of the evaporating front
projected onto the solar disk, while the up-flow velocities (inferred
from the blueshifts) are due to the movement of the same evaporating
material along the line of sight. By combining the up-flow velocities
with the proper motion of the footpoint sources seen in the maps,
we constructed a three-dimensional view of the magnetic loop for each
chromospheric evaporation phase. The early loop is almost semicircular,
with a height of 1.7 × 109 cm, whereas the later magnetic
loop is more elongated (a height of 3.2 × 109 cm), with
its apex closer to the footpoint where most of the evaporation took
place. The implications of these magnetic configurations and the
distinct evaporation phases are discussed.
Title: Is There a Background Polar Field?
Authors: Zirin, H.
Bibcode: 1997SPD....28.0250Z
Altcode: 1997BAAS...29..902Z
Hale long sought the polar field, and its presence was detected by the
Babcocks and by Howard in the form of a conglomeration of fairly strong
field elements of like polarity. While a NASA panel recently pronounced
that the polar field cannot be measured, it is easily detected and has
been studied by various groups. The "polar field" is a crown of strong
magnetic elements that appears at each minimum coextensive with the
polar coronal holes (indeed, apparently producing them). In between
is an irregular continuous background field of about 0.05 gauss,
which Zhang and Zirin recently found had a net polarity opposite the
dominant field in that hemisphere. This is the first detection of a
continuous field on the Sun, all others being concentrated in small
elements. This field is not seen in equatorial unipolar regions. Despite
its wide extent, the uniform field has less flux than a single unipolar
element. The location of zero is crucial to these measurements. The
above detection depended on the difference of sign between the
two poles. We have carried forward these measurements by regularly
reversing the polarity of the modulator of the Leighton-Smithson
videomagnetograph at BBSO, which fixes the zero. So far the results
are mixed, favoring the presence of the background fields but with some
negative results. The complete results to date will be present. Other
parts of the Sun give zero uniform field down to the 0.05 gauss limit.
Title: High Spatial Resolution Observations of a Sunspot with an
``Orphan Penumbra''
Authors: Denker, C.; Zirin, H.; Wang, H.
Bibcode: 1997SPD....28.0245D
Altcode: 1997BAAS...29..901D
We present a detailed analysis of a high spatial resolution, six
hour time-series of a stable sunspot (NOAA 5612) obtained at the
Big Bear Solar Observatory (BBSO) with the 65 cm vacuum reflector on
August 2nd, 1989 (cf. H. Zirin and H. Wang: 1991, Adv. Space. Res.,
Vol. 11, pp. 225-231). The sunspot shows an ``orphan penumbra''
which exhibits motions similar to normal penumbrae. The time-series
consists of filtergrams taken at Hα , CaK, and the continuum. In
addition, magnetograms and dopplergrams were recorded with the
BBSO Video Magnetograph System. Our investigation aims at a better
understanding of moving magnetic features, penumbral fine-structures,
and characteristics of the Evershed flow. Therefore, we derived and
compared the proper motions visible in the different filtergrams,
dopplergrams, and magnetograms.
Title: Filament Eruptions During the Period of Sept. 1991 through
Sept. 1994
Authors: Komenda, Arkadiusz E.; Wang, Haimin; Tang, Frances; Zirin, Hal
Bibcode: 1997SPD....28.0103K
Altcode: 1997BAAS...29..879K
From Sept. 1, 1991 to Sept 12, 1994, full disk Hα images were recorded
continuously at Big Bear Solar Observatory (BBSO) by super-VHS video
recorder. We digitized one image every half hour for that entire
period when the BBSO data are available. About 10,000 halpha images
are archived online, so anybody in the community can have an access
to such an archive, which are useful in studying the evolution of
solar active regions, flares and filament eruptions. In particular,
we are interested in the statistical properties of solar filaments
based on this set of data. In this paper, we present a complete list of
filament disappearance. In the first table, we list the disk location,
size and the time of disappearance of all significant filaments with
a minimum length of 70.1 arcsec. In the second table, we list above
properties of all the detectable filaments for the period of Jan. 1994
to Sept. 1994. The filaments disappear in four different ways: (1)
erupt during continuous observations, so its disappearance time is
accurate to within half hour. (2) disappear during the BBSO night gap
(12 to 14 hours); (3) disappear during date gap (most likely due to
bad weather) and (4) rotate beyond the West limb.
Title: Impact of Magnetic Environment on the Generation of High-Energy
Neutrons at the Sun
Authors: Kocharov, L. G.; Torsti, J.; Tang, F.; Zirin, H.; Kovaltsov,
G. A.; Usoskin, I. G.
Bibcode: 1997SoPh..172..271K
Altcode: 1997ESPM....8..271K
This paper demonstrates the important interplanetary manifestation
of strongly tilted magnetic fields at the flare site. We start with
analysis of Big Bear Solar Observatory (BBSO) observations of magnetic
structures at sites of two flares responsible for >100 MeV neutron
events. Based on these observations, a model of neutron production is
considered. This model takes into account the observed large tilt of
magnetic field lines at footpoints of flare magnetic loops. Results
of the new calculations are compared with both previous calculations
and observations. The tilt of magnetic field lines at the flare site
is proved to be the most important parameter limiting anisotropy of
high-energy secondary emission in solar flares.
Title: Study of Chromospheric Jets
Authors: Lee, Chik-Yin; Johannesson, Anders; Wang, Haimin; Stage,
Mike; Zirin, Hal
Bibcode: 1997SPD....28.1305L
Altcode: 1997BAAS...29Q.917L
In this paper we present a new fast spectral scan method to study Hα
jets, which are more energetic than regular spicules. The observations
achieved high two-dimensional spatial resolution, temporal resolution
and spectral resolution simultaneously. We used the Coude spectrograph
in the Big Bear Solar Observatory for the Hα data acquisition. The
procedure starts with fast spectral scans across the solar surface
(600" by 300") at the vicinity of the solar disk center. The guiding
system is turned off allowing the Sun to drift smoothly relative to
the spectrograph system. A total number of 600 spectral images at
6563A are recorded per scan on an optical disk recorder at a rate of
30 frames/sec. Tracking re-position the system to point to the same
initial coordinates on the Sun for new scans. The process repeats every
30 seconds until 60 scans are completed. The stored images are digitized
for off-line data analysis. A number of different image processing
techniques are used to improve the image quality. These include off-line
correlation tracking and running average among various constructed
images. From the four-dimensional (x,y,t,wavelength) Hα data arrays,
we can reconstruct spectroheliograms (600 by 240 pixels) at different
wavelengths. We calculate velocities of jets by measuring Doppler
shifts of the Hα absorption line, where we used an optically thin jet
model. Velocities of 30 to 50 km/sec for jets are derived. Velocity
maps are constructed thereafter for the scanned region, and are
compiled as movies. We measure the lifetime and size of the jets
from these movies. Lifetimes of a few minutes are observed. Further
approximations are made to find out temperature and density of jets
by fitting the Hα absorption line profile. The results will enable
us to estimate the total mechanical energy released by the jets.
Title: Power Spectra of Solar Network and Non-Network Fields
Authors: Lee, Jeongwoo; Chae, J. -C.; Yun, H. S.; Zirin, H.
Bibcode: 1997SoPh..171..269L
Altcode: 1997SoPh..171..269J
We report new properties of solar magnetic fields in a quiet region
as found from their magnetic power spectra. The power spectra of
network and intranetwork fields (non-network fields) are separately
calculated from a Big Bear magnetogram obtained with moderately high
spatial resolution of 1.5 arc sec and a high sensitivity reaching 2
Mx cm-2. The effect of seeing on the power spectrum has
been corrected using Fried's (1966) Modulation Transfer Function
with the seeing parameter determined in our previous analysis of
the magnetogram. As a result, it is found that the two-dimensional
power spectra of network and non-network fields appear in a form: Γ(
≲ ≲ 1) ∼ -1 and Γ( ≳ 1)
∼ -3.5. Here 0 ≈ 0.47 Mm-1
for network fields and 0 ≈ 0.69 Mm-1 for
non-network fields, the latter of which corresponds to the size
of mesogranulation; 1 ≈ 3.0 Mm-1 for both,
which is about the size of a large granule. The network field spectrum
below 0 appears nearly flat, whereas that of non-network
fields instead decreases towards lower wave numbers as Γ( ) ∼
1.3. The turnover behavior of magnetic field spectra around
1 coincides with that found for the velocity power spectrum,
which may justify the kinetic approach taken in previous theoretical
studies of the solar magnetic power spectra.
Title: New Data and Models of Running Penumbral Waves in Sunspots
Authors: Brisken, Walter F.; Zirin, Harold
Bibcode: 1997ApJ...478..814B
Altcode:
We present new data on running penumbral waves (RPWs) obtained by
appliction of special filtering techniques to high-resolution CCD
images. We find for the first time that the waves decelerate from an
initial velocity of 25 to around 10 km s-1 at the outer
edge and are azimuthally symmetric. They are more or less circular and
are only seen in symmetric, radial sectors of sunspot penumbrae. We
did not see any outward decrease in amplitude. If present, it is not
large. There appears to be a connection between umbral flashes and
RPWs, but we cannot define it with the present data. We present a
geometric model for the waves, which fits the observed deceleration. In
this model, RPWs are spherical waves expanding from a subsurface
region on the axis of the spot. A good fit is obtained with a depth
of 15,000 km and a vertical velocity of 4.5 km s-1. This
model predicts a lag in the wave arrival at successive heights. For
the single spot for which we had good data in three wavelengths,
we found an appropriate lag between the waves at Hα +/- 0.6 Å and
Hα. Therefore, we propose a spherical wave geometric model for RPWs,
although we have no physical model.
Title: The Effect of Seeing on Solar Magnetic Flux Measurements
Authors: Lee, Jeongwoo; Chae, J. -C.; Yun, H. S.; Zirin, H.
Bibcode: 1997SoPh..171...35L
Altcode: 1997SoPh..171...35J
We investigate the influence of seeing upon measurement of magnetic flux
of photospheric fields. For this purpose we quantify seeing variation
in one day's observation at Big Bear Solar Observatory in terms of
the Fried function, a Modulation Transfer Function for the atmospheric
seeing. The temporal variation of seeing quality is compared with that
of magnetic flux measured in a quiet region with size 5' × 4' near
the solar disk center. A good correlation is found between the seeing
change and apparent evolution of magnetic flux values, implying, as a
possibility, that magnetic flux measurement might have been modulated
by seeing. Based on a simple model of ensembles of Gaussian magnetic
elements we argue that even the net flux as well as the total flux
can change due to seeing variation if the magnetograph has a finite
detection threshold and if the intrinsic fluxes in one and the other
polarities are unbalanced.
Title: Appearance of Chromospheric Magnetic Fields above Sunspots
Authors: Wang, J.; Shi, Z.; Yang, X.; Zirin, H.
Bibcode: 1997ASPC..118..116W
Altcode: 1997fasp.conf..116W
It has been revealed by high resolution BBSO Hα magnetograms that the
chromospheric magnetic fields are highly filamentary in nature. The
superpenumbrae of sunspots, arch filament systems, surges and spicules
are all tracing the chromospheric magnetic fibrils. Instead of an
uniform canopy above a sunspot, there is a `fountain' of magnetic
fibrils. The apparent localized polarity reversal, revealed from Huairou
Hβ magnetograms was also identified in Hα magnetograms, and found to
occur in three categories: footpoints of emerging flux regions, preflare
sites, and sites of discontinuous field azimuth within a mature sunspot.
Title: Reconnection and Helicity in a Solar Flare
Authors: Pevtsov, Alexei A.; Canfield, Richard C.; Zirin, Harold
Bibcode: 1996ApJ...473..533P
Altcode:
Using X-ray images, Hα images, and vector magnetograms, we have
studied the evolution of the coronal structure and magnetic field of
NOAA Active Region 7154 during 1992 May 5-12. A two-ribbon 4B/M7.4
flare associated with an Hα filament eruption was observed on May 8,
15:13-19:16 UT. An interesting feature of the region was a long,
twisted X-ray structure, which formed shortly before the flare
and disappeared after it, being replaced by a system of unsheared
postflare loops. Neither the X-ray nor Hα morphology nor the photo
spheric magnetic field shows any indication of gradual buildup of
nonpotential energy prior to the flare. Rather, the long structure
appears to result from the reconnection of two shorter ones just tens
of minutes before the filament eruption and flare. Using vector
magnetograms and X-ray morphology, we determine the helicity density
of the magnetic field using the force-free field parameter α. The
observations show that the long structure retained the same helicity
density as the two shorter structures, but its greater length implies
a higher coronal twist. The measured length and α value combine to
imply a twist that exceeds the threshold for the MHD kink instability
in a force-free cylindrical flux tube. We conclude that theoretical
studies of such simple models, which have found that the MHD kink
instability does not lead to global dissipation, do not adequately
address the physical processes that govern coronal magnetic fields.
Title: The Mystery of the Chromosphere
Authors: Zirin, Harold
Bibcode: 1996SoPh..169..313Z
Altcode:
We discuss many aspects of the solar chromosphere from an observational
point of view, and show that most existing models are in direct
contradiction to radio and eclipse measurements. We plead for attention
to the actual observed radio temperatures and density gradients, as
well as images of the chromosphere. We find that the chromosphere is
not in hydrostatic equilibrium and suggest that the support is due to
the tangled intranetwork fields.
Title: The Pole-Equator Variation of Solar Chromospheric Height
Authors: Johannesson, Anders; Zirin, Harold
Bibcode: 1996ApJ...471..510J
Altcode:
We measured the height of the solar chromosphere as a function of
position angle on seven circumsolar sets of high spatial resolution
Hα filtergrams obtained during 1994-1995. Typically 40 CCD frames
were needed to cover the solar limb. We also measured the frequency
of visible macrospicules along the limb as a function of position
angle. Two different height measures based on the gradient of
the limb profile are defined in the Paper. They show variation with
a pole-equator difference of about 2", the poles being higher. In
centerline Hα the derived height is typically 4300-4400 km at the
equator and just below 6000 km at the solar poles with a true local
scatter of 500 km (rms). A slight increase in height is also seen above
active regions. We see a similar but smaller height variation in the
wing of Hα. We also measured the height difference between the
chromosphere in centerline and the wing of Hα. The off-band limb is
always lower than the centerline limb by an average value of 500 km
(0".7). Because of the self reversal of the chromospheric Hα line, the
off-band chromosphere is twice as bright as the centerline. As a result,
the gradient of the off-band limb profile is considerably steeper
just above the photo sphere. Thus, the popular misconception that
spicules rise above the chromosphere is incorrect, except insofar as
the macrospicules are concerned. We find the latter much more frequent
above at the pole than at the equator, confirming the result of Bohlin
et al. The number of macrospicules near the pole reaches 20 per 150",
or about three per arcmin2 on the disk, while we only count
a few (sometimes none) near the equator. While we defer a serious study
of the macrospicules to a later work, we can already state that these
features are asymmetric in time, i.e., they are seen to go up but not
come down. Comparison with Yohkoh soft X-ray data shows a high
correlation between the enhanced chromospheric height, the macrospicule
frequency, and the location of the polar coronal holes. This agrees
with earlier measurements obtained in lower resolution and suggests a
magnetic cause of the height difference, namely that the presence of
a vertical magnetic field permits the jets to ascend higher.
Title: The 1990 May 24 solar flare and cosmic ray event
Authors: Kocharov, Leon; Kovaltsov, Gennadi; Torsti, Jarmo; Usoskin,
Ilya; Zirin, Harold; Anttila, Antti; Vainio, Rami
Bibcode: 1996AIPC..374..246K
Altcode: 1996hesp.conf..246K
We have analyzed data on solar protons, neutrons, electrons, gamma-ray,
optical and microwave emissions for the 1990 May 24 solar flare. Taking
into account high energy neutron and gamma-ray observations, we have
suggested two neutron injections occurred during the flare. These two
injections are called f- (first) and s- (second). Two components of
interacting protons correspondingly existed to produce these neutrons
at the Sun. The flare gave also a rise to solar cosmic ray event, which
was detected by the neutron monitor network and GOES satellites. Two
components of protons were observed in the interplanetary medium (p-
(prompt) and d- (delayed) components). A possible spectrum of the
s-component of interacting protons coincided with injection spectrum
of p-component of interplanetary protons. For this reason, s- and p-
components of protons may be considered as different portions of a
single population of accelerated particles in the solar corona. The
net result is that three proton components (f-, p/s-, and d-) were
accelerated during flare process developing from the Sun to the
interplanetary medium.
Title: The Velocities of Intranetwork and Network Magnetic Fields
Authors: Wang, H.; Tang, F.; Zirin, H.; Wang, J.
Bibcode: 1996SoPh..165..223W
Altcode:
We analyzed two sequences of quiet-Sun magnetograms obtained on June
4, 1992 and July 28, 1994. Both were observed during excellent seeing
conditions such that the weak intranetwork (IN) fields are observed
clearly during the entire periods. Using the local correlation
tracking technique, we derived the horizontal velocity fields of
IN and network magnetic fields. They consist of two components: (1)
radial divergence flows which move IN fields from the network interior
to the boundaries, and (2) lateral flows which move along the network
boundaries and converge toward stronger magnetic elements. Furthermore,
we constructed divergence maps based on horizonal velocities, which are
a good representation of the vertical velocities of supergranules. For
the June 4, 1992 data, the enhanced network area in the field of view
has twice the flux density, 10% higher supergranular velocity and 20%
larger cell sizes than the quiet, unenhanced network area. Based on
the number densities and flow velocities of IN fields derived in this
paper and a previous paper (Wang et al., 1995), we estimate that the
lower limit of total energy released from the recycling of IN fields
is 1.2 × 1028 erg s−1, which is comparable
to the energy required for coronal heating.
Title: Imaging the Chromospheric Evaporation of the 1994 June 30
Solar Flare
Authors: Silva, Adriana V. R.; Wang, H.; Gary, D. E.; Zirin, H.;
Nitta, N.
Bibcode: 1996AAS...188.3310S
Altcode: 1996BAAS...28R.869S
We analyze simultaneous H _alpha images (from Big Bear Solar
Observatory), soft and hard X-ray images and spectra (from Yohkoh
during the first three minutes of the 1994 June 30 flare. The strong
blueshifts observed in the Ca XIX soft X-ray line are interpreted as
evidence of chromospheric evaporation, with maximum up--flow velocities
occurring two minutes prior to the hard X-ray emission peak. In this
paper, we search for moving sources in H_alpha , soft and hard X-ray
images that correspond to the blueshifted component. The chromospheric
evaporation in this flare is divided into two phases: an early phase
with up-flow velocities of 300-450 km s(-1) , and a later phase (during
the hard X-ray peak) characterized by velocities of 100-200 km s(-1)
. During the first chromospheric evaporation phase, the footpoints
of a loop seen in HXT maps are seen to move towards the loop top
source. No source displacement is observed in SXT images. The hard
X-ray spectra of individual sources, obtained from HXT maps, display a
very steep slope (gamma ~ 10-12). Thermal fitting of the spectra yield
temperatures of 20-50 MK. Images of the later phase of chromospheric
evaporation show the magnetic configuration to have changed. The early
HXT loop is no longer visible and HXT maps during this time display
the two footpoints of a new loop also visible in SXT images. Now
the HXT sources are stationary and a SXT footpoint source is seen to
move toward the loop top. We interpret the observed displacement of
footpoint sources in HXT (early phase) and SXT (later phase) maps to
be the images of the evaporating front projected onto the solar disk,
while the up--flow velocities (inferred from the blueshifts) are due
to the movement of the same evaporating material along the line of
sight. By combining the up--flow velocities with the proper motion
of the footpoint sources seen in the maps, we constructed a 3-D view
of the magnetic loop for each chromospheric evaporation phase. The
early loop is almost semi--circular with a height of 1.7x 10(9) cm,
whereas the later magnetic loop is more elongated (height of 2.3x 10(9)
cm) and asymmetric with its apex closer to the footpoint where most
of the evaporation took place. The implications of these magnetic
configurations and the distinct evaporation phases are discussed.
Title: Three Classes of Chromospheric Ejecta
Authors: Stage, M.; Zirin, H.; Wang, H.
Bibcode: 1996AAS...188.3618S
Altcode: 1996BAAS...28..876S
We searched for Hα counterparts to the CIV explosive events
observed by NRL with the HRTS rocket (Moses et al., 1994). These
features do not correspond to spicules and macrospicules. At Hα
-1.0 Angstroms, we found a third class of features: "eruptive events"
which are thick, violent, and not elongated by the magnetic field like
the first two. Further, we detected these outflows in the Hα +/-0.65
Angstroms spicule images analysed by Suematsu et al. (1995). Although
these ejecta are situated like spicules at the edges of magnetic
network elements, they are morphologically far different. They
appear either as a fat eruption or as a chain of spicules rising
sequentially. They truly deserve the name "chromospheric eruptions,"
which has unfortunately been applied to solar flares. Lifetimes also
distinguish the eruptions from the spicules. While spicules are visible
in the Hα -1.0 Angstroms images for 2 to 3 minutes, the ejections
are a complex wave of eruption moving along the network element and
repeating several times over 10-12 minutes. The phenomenon may repeat,
usually at the same location. Although these lifetimes are considerably
longer than the 90 second CIV lifetimes found by NRL,
they appear morphologically quite similar, and repetition would not
be seen in the short HRTS observing time. Moses et al. suggest that
the CIV events result from magnetic reconfiguration, and
comparison of the locations of the Hα ejections with videomagnetograms
shows that roughly half correlate with magnetic elements undergoing
reconnection. The complex resultant magnetic field configuration could
explain why these events are not constrained to slender flux tubes
like normal spicules. The combined evidence makes the eruptive events
good candidates for CIV counterparts. Moses, D. et al.,
(1994) ApJ 430, 913. Suematsu, Y. et al, (1995) ApJ 450, 411.
Title: OVRO, BBSO, BATSE, and YOHKOH Observations of a Twin Solar
Flare
Authors: Wang, H.; Gary, D. E.; Zirin, H.; Nitta, N.; Schwartz, R. A.;
Kosugi, T.
Bibcode: 1996ApJ...456..403W
Altcode:
We present the results of studies on two solar flares that occurred
on 1993 February 11: an M1.1 flare at 18:07 UT and an M2.7 flare at
18:31 UT. Our study was based on comprehensive observations by the
following observatories: Owens Valley Radio Observatory, which obtains
1-18 GHz microwave images; Big Bear Solar Observatory, which obtains
magnetograms, Hα and He D3 filtergrams; BATSE on board Compton Gamma
Ray Observatory, which obtains high-resolution hard X-ray spectra;
and the Japanese satellite Yohkoh, which obtains high-resolution soft
and hard X-ray images. We find the following: (1) While the optical
and hard X-ray emissions are confined to a small loop near the leading
spot of the active region for both flares, a large-scale soft X-ray
loop connects from the leading to the following spot 160" away. In
low-frequency micro-waves (<4 GHz), sources appear at each end
of the big loop, and the source near the following spot (away from
the Hα flare site) dominates at frequencies <2.8 GHz. For both
flares, as frequency increases, the source near the leading spot
becomes dominant, and the source near the following spot vanishes
gradually. (2) As frequency increases, the centroid of the leading
microwave source moves progressively downward until it reaches the
footpoint at high frequencies. (3) For the M2.7 event, in the compact
loop near the leading spot, two footpoints are seen in both soft and
hard X-rays. The dominant hard X-ray source has a softer spectrum than
the weaker one, suggesting that the weaker one may become dominant
at the higher energies (>100 keV) responsible for the microwave
emission. The high-frequency microwave emission is better associated
with this latter footpoint. (4) The large soft X-ray loop in the M2.7
flare is the postflare loop of the M1.1 flare. This flare is associated
with a different compact loop which is 40" away from the main flare. (5)
For the M2.7 flare, the microwave brightness temperature spectra in
the sources at the two ends of the big loop require very different
source parameters. The primary source near the leading spot can be
explained by nonthermal gyrosynchrotron emission from electrons with
a power-law energy index (δ) of 5.3. The same group of electrons can
explain the observed BATSE hard X-ray spectra. The low-frequency radio
source near the following spot is due to either a thermal component, or
a nonthermal component with a steep energy index (δ= 9.4). Based on the
available information, we cannot distinguish these two possibilities.
Title: Coordinated OVRO, BATSE, Yohkoh, and BBSO Observations of
the 1992 June 25 M1.4 Flare
Authors: Wang, H.; Gary, D. E.; Zirin, H.; Schwartz, R. A.; Sakao,
T.; Kosugi, T.; Shibata, K.
Bibcode: 1995ApJ...453..505W
Altcode:
We compare 1-14 GHz microwave images observed at the Owens Valley Radio
Observatory (OVRO), 16- and 256-channel hard X-ray spectra obtained by
the Burst and Transient Source Experiment (BATSE) onboard the Compton
Gamma Ray Observatory (CGRO), soft and and hard X-ray images obtained
by Yohkoh, and Hα images and magnetograms observed at the Big Bear
Solar Observatory (BBSO) for the 1992 June 25 M1.4 flare. We find the
following unique properties for this flare: (1) Soft X-ray emissions
connect two foot- points, the primary microwave source is located at
one footpoint, and hard X-ray emissions are concentrated in the other
footpoint The radio footpoint is associated with an umbra and may
have stronger magnetic field. (2) During the period that 256-channel
BATSE data are available, the hard X-ray photon spectrum consists
of two components: a superhot component with a temperature of 8.4
× 107 K and emission measure of 2.5 × 1046
cm-3 and a power-law component with a photon index of
4.2. This is the first time that such a high temperature is reported
for the hard X-ray thermal components. It is even more interesting
that such a superhot component is identified before the peak of the
flare. The microwave brightness temperature spectra during the same
period also demonstrate two components: a thermal component near the
loop top and a nonthermal component at the footpoint of the loop. The
microwave thermal component has the similar temperature as that of
the hard X-ray superhot component. These measurements are consistent
with the theory that the microwaves and hard X-rays are due to the
same group of electrons, despite the fact that they are separated by
35,000 km. (3) The soft X-ray emissions brighten the existing loops and
co-align with Hα emissions throughout the entire duration of the flare.
Title: Erratum: The 1991 March 22 Flare: Possible Anistrophy of
High-Energy Neutral Emission
Authors: Kocharov, L. G.; Lee, Jeongwoo W.; Wang, H.; Zirin, H.;
Kovaltsov, G. A.; Usoskin, I. G.
Bibcode: 1995SoPh..161..407K
Altcode:
No abstract at ADS
Title: Reproduction of the Lyman \alpha Irradiance Variability from
Analysis of Full-Disk Images in the CaII K-Line
Authors: Johannesson, A.; Marquette, W.; Zirin, H.
Bibcode: 1995SoPh..161..201J
Altcode:
We have compared three years of daily CaII K-line images from the Big
Bear Solar Observatory (BBSO) with HI Lymanα irradiance data from the
Upper Atmosphere Research Satellite (UARS). The daily full-disk CaII
K-line images are reduced to a new index of integrated excess emission,
which reproduces both the 27 day rotational modulation and the solar
cycle decrease in Lyα irradiance. Our analysis shows that while plages
reproduce the 27-day variation quite well, the total K-line emission
excess above the quiet background is needed to reproduce the secular
solar cycle trend in the Lyα irradiance. The resulting K-line index
exhibits a high degree of correlation (0.9) with the time series of
measured Lyα flux.
Title: Flux distribution of solar intranetwork magnetic fields
Authors: Wang, Jingxiu; Wang, Haimin; Tang, Frances; Lee, Jeongwoo W.;
Zirin, Harold
Bibcode: 1995SoPh..160..277W
Altcode:
Big Bear deep magnetograms of June 4, 1992 provide unprecedented
observations for direct measurements of solar intranetwork (IN) magnetic
fields. More than 2500 individual IN elements and 500 network elements
are identified and their magnetic flux measured in a quiet region
of 300 × 235 arc sec. The analysis reveals the following results:
IN element flux ranges from 1016 Mx (detection limit)
to 2 × 1018 Mx, with a peak flux distribution of 6 ×
1016 Mx.
Title: High-Resolution Observation of Disk Spicules. I. Evolution
and Kinematics of Spicules in the Enhanced Network
Authors: Suematsu, Yoshinori; Wang, Haimin; Zirin, Harold
Bibcode: 1995ApJ...450..411S
Altcode:
We present measurements of a 75 minute sequence of CCD spicule
observations at Hα -0.65 Å, line center, and +0.65 Å. The
observations were made in a region of enhanced network near disk
center, where most spicules are longer and tilted further from the
vertical than those in truly quiet Sun. Images were reregistered with
a correlation coefficient greater than 0.9. We identify the spicules
as those elongated jets that radiate from elements of the magnetic
network and are the main chromospheric features seen in the wing of
Hα. Doppler images produced by red-blue subtraction show an upward
radial velocity during the extension phase and a downward velocity
during contraction for most spicules. Therefore, the spicules are
truly moving up and down. There were a few plagelike cells filled
with weak Hα emission, weak magnetic fields, and no spicules. We
also found many multiple spicules. The data are presented with
commentary on the accompanying videotape. We analyzed the
data to understand the spicule lifetimes and trajectories. We found
that the entire set of wavelengths and Dopplergrams was required to
separate overlapping spicules. Seventy-six of the 96 spicules studied
appear in complete upward and downward trajectories The evidence on
motions is not conclusive. Some proper motions are well represented
by ballistic trajectories with initial injection velocity about 40 km
s-1 for highly inclined spicules. The small decelerations
would require the spicules to be tilted typically 60°-70° from
the line of sight. Since limb observations favor tilts around 30°,
our observations must favor spicules tilted greatly from the radial,
as one finds in these enhanced field regions. The positive correlation
of lifetimes with projected lengths supports this model. However, the
Dopplergrams show that the entire spicule rises and falls as a whole,
which favors a fountain jet or some acceleration in the flux tube. The
downward trajectory may be slightly offset toward the network center
from the upward path. Bright points often appear at the bases of
spicules at Hα -0.65 Å, but during the peak extension or receding
phase of the spicule rather than the beginning; therefore, the spicule
is not a surgelike phenomenon (surges are usually initiated by Hα
brightening or a subflare, invariably in a bipolar feature). Further,
the magnetic elements, which match the Hα bright points exactly,
show no change associated with the brightening. The geometry creates
a problem for coronal heating models, as the spicule tops are at least
10" displaced from the bright-point bases, but no such offset appears
in the K line, for example. There is some evidence that the spicule
is generated several hundred kilometers above the photosphere.
Title: Taiwan Oscillation Network
Authors: Chou, Dean-Yi; Sun, Ming-Tsung; Huang, Teng-Yi; Lai,
Shih-Ping; Chi, Pi-Jen; Ou, Knight-Tien; Wang, Chang-Chi; Lu,
Jui-Yang; Chu, An-Li; Niu, Chi-Seng; Mu, Tao-Mo; Chen, Kuan-Rong;
Chou, Yung-Ping; Jimenez, Antonio; Rabello-Soares, Maria Cristina;
Chao, Horance; Ai, Guoxiang; Wang, Gwo-Ping; Zirin, Harold; Marquette,
William; Nenow, Jeff
Bibcode: 1995SoPh..160..237C
Altcode:
The Taiwan Oscillation Network (TON) is a ground-based network to
measure solar intensity oscillations to study the internal structure
of the Sun. K-line full-disk images of 1000 pixels diameter are taken
at a rate of one image per minute. Such data would provide information
onp-modes withl as high as 1000. The TON will consist of six identical
telescope systems at proper longitudes around the world. Three telescope
systems have been installed at Teide Observatory (Tenerife), Huairou
Solar Observing Station (near Beijing), and Big Bear Solar Observatory
(California). The telescopes at these three sites have been taking
data simultaneously since October of 1994. Anl - v diagram derived
from 512 images is included to show the quality of the data.
Title: AG Ananth, K Kudela, D Venkatesan On the Comparison of Filter
Magnetographs and the Advanced Stokes Polarimeter
Authors: Zirin, Harold
Bibcode: 1995SoPh..159..203Z
Altcode:
Liteset al. (1994) (hereafter LMS) have recently published a comparison
of the response of their magnetograph (the Advanced Stokes Polarimeter
(ASP)) to that they expect from filter-based magnetographs (FM). Not
surprisingly, they conclude the ASP is better. They claim that only
their instrument is ″quantitative,″ and others are not, and that the
transverse field strength and azimuth measured by filter magnetographs
may be in error by up to 50%. While the calculation is formally correct
it ignores the high sensitivity attained by real FM's accumulating
thousands of difference frames. Further, FM's have been cross-compared
and tested empirically, without any such errors appearing. We point
out that the two instruments have different roles, but the functional
use of the FM is far superior to the ASP for solar research. The ASP
may give accurate results for unresolved unipolar fields; it gives
totally erroneous results when the field rapidly changes direction
within its resolution element, as occurs in delta spots.
Title: The Microwave and H alpha Sources of the 1992 January 13 Flare
Authors: Wang, H.; Gary, D. E.; Zirin, H.; Kosugi, T.; Schwartz,
R. A.; Linford, G.
Bibcode: 1995ApJ...444L.115W
Altcode:
We compare X-ray, microwave and H-alpha observations for the 1992
January 13 limb flare. The soft and hard X-ray images of the flare
have been studied thoroughly by Masuda et al. (1994) with Yohkoh
SXT and HXT images. We find that during the hard X-ray emission peak
there is no H-alpha brightening on the disk nor at the limb, so the
main ribbons of this flare must be beyond the limb. The microwave
source maintains a fixed distance about 10 arcsecs from the optical
limb in the frequency range 2.8-14.0 GHz. We interpret this limit
in source position as due to the presence of a microwave limb that
extends higher than the white-light limb -- to a height of 7300 +/-
1500 km. We believe that the high-frequency microwave emissions are
occulted by this extended limb, while the soft and hard X-ray emissions
are able to pass through largely unaffected. We also believe, however,
that the hard X-ray footpoints are also partially occulted by the
photospheric limb, despite the appearance of 'footpoint sources'
in HXT data shown by Masuda et al. The smooth X-ray and microwave
time profiles, microwave-rich emission relative to hard X-rays, and
progressive hard X-ray spectral hardening through the flare peak are
all characteristics that we interpret as being a direct result of the
occultation of footpoint emission.
Title: Erratum - Observations of Vector Magnetic Fields on Flaring
Active Regions
Authors: Chen, J. M.; Wang, H. M.; Zirin, H.; Ai, G. X.
Bibcode: 1995SoPh..158..205C
Altcode:
No abstract at ADS
Title: The 1991 March 22 Flare: Possible Anisotropy of High-Energy
Neutral Emission
Authors: Kocharov, L. G.; Lee, Jeongwoo W.; Wang, H.; Zirin, H.;
Kovaltsov, G. A.; Usoskin, I. G.
Bibcode: 1995SoPh..158...95K
Altcode:
We made a parameter fit to the Haleakala neutron monitor counting
rate during the 1991 March 22 solar flare (Pyle and Simpson, 1991)
using the time profiles of γ-rays at 0.42-80 MeV obtained with
the GRANAT satellite (Vilmeret al., 1994) and the microwave data
from Owens Valley Radio Observatory. We use a two-component neutron
injection function to find that either an impulsive injection or the
`impulsive-plus-prolonged' neutron injection is possible. In both
cases, the number of > 300 MeV neutrons emitted towards the Earth
is estimated as ≈ 2 × 1027 sr−1, which is
less than that of the 1990 May 24 flare by an order of magnitude.
Title: Properties of Running Penumbral Waves
Authors: Brisken, W. F.; Zirin, H.
Bibcode: 1995SPD....26..501B
Altcode: 1995BAAS...27..956B
No abstract at ADS
Title: A ground-based CaII K-line index as a proxy for the UARS
Lyman α irradiance
Authors: Johanesson, A.; Marquette, W.; Zirin, H.
Bibcode: 1995SPD....26..511J
Altcode: 1995BAAS...27..959J
No abstract at ADS
Title: The Microwave and Hα Sources of the 1992 January 13 Flare
Authors: Wang, H.; Gary, D. E.; Zirin, H.; Kosugi, T.; Schwartz,
R. A.; Linford, G.
Bibcode: 1995SPD....26..805W
Altcode: 1995BAAS...27..972W
No abstract at ADS
Title: Correlative Investigations of the 1990 May 24 Solar Flare
Authors: Kocharov, L. G.; Kovaltsov, G. A.; Torsti, J.; Usoskin,
I. G.; Zirin, H.
Bibcode: 1995ICRC....4..159K
Altcode: 1995ICRC...24d.159K
No abstract at ADS
Title: High Resolution Observations of the Polar Magnetic Fields of
the Sun
Authors: Lin, H.; Varsik, J.; Zirin, H.
Bibcode: 1994SoPh..155..243L
Altcode:
High-resolution magnetograms of the solar polar region were used for
the study of the polar magnetic field. In contrast to low-resolution
magnetograph observations which measure the polar magnetic field
averaged over a large area, we focused our efforts on the properties
of the small magnetic elements in the polar region. Evolution of
the filling factor - the ratio of the area occupied by the magnetic
elements to the total area - of these magnetic elements, as well as
the average magnetic field strength, were studied during the maximum
and declining phase of solar cycle 22, from early 1991 to mid-1993.
Title: Peculiar magnetic field evolution of active region NOAA 7562
in August 1993 - results from campaign observation with Yohkoh
Authors: Sakurai, T.; Suematsu, Y.; Ichimoto, K.; Kurokawa, H.; Kitai,
R.; Akioka, M.; Tohmura, I.; Soltau, D.; Mickey, D. L.; Zhang, H.;
Li, W.; Zirin, H.; Tang, F.
Bibcode: 1994ESASP.373..337S
Altcode: 1994soho....3..337S
No abstract at ADS
Title: Neutron and electromagnetic emissions during the 1990 May 24
solar flare
Authors: Kocharov, L. G.; Lee, Jeongwoo W.; Zirin, H.; Kovaltsov,
G. A.; Usoskin, I. G.; Pyle, K. R.; Shea, M. A.; Smart, D. F.
Bibcode: 1994SoPh..155..149K
Altcode:
In this paper, we are primarily concerned with the solar neutron
emission during the 1990 May 24 flare, utilizing the counting rate
of the Climax neutron monitor and the time profiles of hard X-rays
and γ-rays obtained with the GRANAT satellite (Pelaezet al., 1992;
Talonet al., 1993; Terekhovet al., 1993). We compare the derived
neutron injection function with macroscopic parameters of the flare
region as obtained from theHα and microwave observations made at the
Big Bear Solar Observatory and the Owens Valley Radio Observatory,
respectively. Our results are summarized as follows: (1) to explain the
neutron monitor counting rate and 57.5-110 MeV and 2.2 MeV γ-ray time
profiles, we consider a two-component neutron injection function,Q(E,
t), with the form Q(E,t) = Nfexp[-E/Ef
-t/Tf] + N2 exp[-E/Es -
t/Ts], where Nf(s),Ef(s),
andTf(s) denote number, energy, and decay time of the fast
(slow) injection component, respectively. By comparing the calculated
neutron counting rate with the observations from the Climax neutron
monitor we derive the best-fit parameters asTf ≈ 20
s,Ef ≈ 310 MeV,Ts ≈ 260 s,Es
≈ 80 MeV, andNf(E > 100 MeV)/Ns(E >
100 MeV) ≈ 0.2. (2) From the Hα observations, we find a relatively
small loop of length ≈ 2 × 104 km, which may be regarded
as the source for the fast-decaying component of γ-rays (57.5-110
MeV) and for the fast component of neutron emission. From microwave
visibility and the microwave total power spectrum we postulate the
presence of a rather big loop (≈ 2 × 105 km), which we
regard as being responsible for the slow-decaying component of the
high-energy emission. We show how the neutron and γ-ray emission
data can be explained in terms of the macroscopic parameters derived
from the Hα and microwave observations. (3) The Hα observations
also reveal the presence of a fast mode MHD shock (the Moreton wave)
which precedes the microwave peak by 20-30 s and the peak of γ-ray
intensity by 40-50 s. From this relative timing and the single-pulsed
time profiles of both radiations, we can attribute the whole event
as due to a prompt acceleration of both electrons and protons by the
shock and subsequent deceleration of the trapped particles while they
propagate inside the magnetic loops.
Title: Observations of Vector Magnetic Fields in Flaring Active
Regions
Authors: Chen, Jimin; Wang, Haimin; Zirin, Harold; Ai, Guoxiang
Bibcode: 1994SoPh..154..261C
Altcode:
We present vector magnetograph data of 6 active regions, all of
which produced major flares. Of the 20 M-class (or above) flares,
7 satisfy the flare conditions prescribed by Hagyard (high shear and
strong transverse fields). Strong photospheric shear, however, is not
necessarily a condition for a flare. We find an increase in the shear
for two flares, a 6-deg shear increase along the neutral line after a
X-2 flare and a 13-deg increase after a M-1.9 flare. For other flares,
we did not detect substantial shear changes.
Title: The Roots of Coronal Structure in the Sun's Surface
Authors: Golub, Leon; Zirin, Harold; Wang, Haimin
Bibcode: 1994SoPh..153..179G
Altcode:
We have compared the structures seen on X-ray images obtained by a
flight of the NIXT sounding rocket payload on July 11, 1991 with
near-simultaneous photospheric and chromospheric structures and
magnetic fields observed at Big Bear. The X-ray images reflect
emission of both MgX and FeXVI, formed at 1 × 106 K
and 3 × 106 K, respectively. The brightest Hα sources
correspond to a dying sub-flare and other active region components,
all of which reveal coronal enhancements situated spatially well
above the Hα emission. The largest set of X-ray arches connected
plages of opposite polarity in a large bipolar active region. The
arches appear to lie in a small range of angle in the meridian plane
connecting their footpoints. Sunspots are dark on the surface and in
the corona. For the first time we see an emerging flux region in X-rays
and find the emission extends twice as high as the Hα arches. Many
features which we believe to correspond to `X-ray bright points'
(XBPs) were observed. Whether by resolution or spectral band, the
number detected greatly exceeds that from previous work. All of the
brighter XBPs correspond to bipolar Hα features, while unipolar Hα
bright points are the base of more diffuse comet-like coronal arches,
generally vertical. These diverge from individual features by less than
30°, and give a good measure of what the `canopies' must do. The Hα
data shows that all the Hα features were present the entire day, so
they are not clearly disappearing or reappearing. We find a new class
of XBPs which we call `satellite points', elements of opposite polarity
linked to nearby umbrae by invisible field lines. The satellite points
change rapidly in X-ray brightness during the flight. An M1.9 flare
occurred four hours after the flight; examination of the pre-flare
structures reveals nothing unusual.
Title: Solar Fine-Scale Structures in the Corona, Transition Region,
and Lower Atmosphere
Authors: Moses, Dan; Cook, J. W.; Bartoe, J. -D. F.; Brueckner, G. E.;
Dere, K. P.; Webb, D. F.; Davis, J. M.; Harvey, J. W.; Recely, F.;
Martin, S. F.; Zirin, H.
Bibcode: 1994ApJ...430..913M
Altcode:
The American Science and Engineering Soft X-ray Imaging Payload and the
Naval Research Laboratory High Resolution Telescope and Spectrograph
(HRTS) were launched from White Sands on 1987 December 11 in coordinated
sounding rocket flights. The goal was to investigate the correspondence
of fine-scale structures from different temperature regimes in the
solar atmosphere, and particularly the relationship between X-ray bright
points (XBPs) and transition region explosive events. We present results
of the analysis of co-aligned X-ray images, maps of sites of transition
region explosive events observed in C IV 105, HRTS 1600
A spectroheliograms of the Tmin region, and ground-based
magnetogram and He I 10830 A images. We examined the relationship
of He I 10830 A dark features and evolving magnetic features which
correspond to XBPs. We note a frequent double ribbon pattern of the
He I dark feature counterparts to XBPs. We discuss an analysis of the
relationship of XBPs to evolving magnetic features by Webb et al.,
which shows that converging magnetic features of opposite polarity are
the most significant magnetic field counterparts to XBPs. The magnetic
bipolar features associated with XBPs appear as prominent network
elements in chromospheric and transition region images. The features
in C IV observations corresponding to XBP sites are in general bright,
larger scale (approximately 10 arcsec) regions of complex velocity
fields of order 40 km/s, which is typical of brighter C IV network
elements. These C IV features do not reach the approximately 100 km/s
velocities seen in the C IV explosive events. Also, there are many
similar C IV bright network features without a corresponding XBP in the
X-ray image. The transition region explosive events do not correspond
directly to XBPs. The explosive events appear to be concentrated in
the quiet Sun at the edges of strong network, or within weaker field
strength network regions. We find a greater number of C IV events than
expected from the results of a previous Spacelab 2 HRTS disk survey. We
attribute this at least partly to better spatial resolution with the
newer HRTS data. The full-disk X-ray image shows a pattern of dark
lanes in quiet Sun areas. The number density of C IV events is twice
as large inside as outside a dark lane (4.6 x 10-3 vs. 2.3
x 10-3 explosive events per arcsec 2). The dark
lane corresponds to an old decaying magnetic neutral line. We suggest
that this provides an increased opportunity for small-scale convergence
and reconnection of opposite polarity magnetic field features, in
analogy with the results of Webb et al. for XBPs but at a reduced
scale of reconnection.
Title: Flat Microwave Spectra Seen at X-Class Flares
Authors: Lee, Jeongwoo W.; Gary, Dale E.; Zirin, H.
Bibcode: 1994SoPh..152..409L
Altcode:
We report peculiar spectral activity of four large microwave bursts as
obtained from the Solar Arrays at the Owens Valley Radio Observatory
during observations of X-class flares on 1990 May 24 and 1991 March
7, 8, and 22. Main observational points that we newly uncovered are:
(1) flat flux spectra over 1-18 GHz in large amounts of flux ranging
from 102 to 104 s.f.u. at the maximum phase, (2)
a common evolutionary pattern in which the spectral region of dominant
flux shifts from high frequencies at the initial rise to low frequencies
at the decaying phase, and (3) unusual time profiles that are impulsive
at high frequencies but more extended at lower frequencies.
Title: The Global Oscillation Network Group Site Survey - Part Two
Authors: Hill, Frank; Fischer, George; Forgach, Suzanne; Grier,
Jennifer; Leibacher, John W.; Jones, Harrison P.; Jones, Patricia
B.; Kupke, Renate; Stebbins, Robin T.; Clay, Donald W.; Ingram,
Robert E. L.; Libbrecht, Kenneth G.; Zirin, Harold; Ulrichi, Roger
K.; Websteri, Lawrence; Hieda, Lester S.; Labonte, Barry J.; Lu,
Wayne M. T.; Sousa, Edwin M.; Garcia, Charles J.; Yasukawa, Eric
A.; Kennewell, John A.; Cole, David G.; Zhen, Huang; Su-Min, Xiao;
Bhatnagar, Arvind; Ambastha, Aashok; Al-Khashlan, Abdulrahman Sa'ad;
Abdul-Samad, Muhammad-Saleh; Benkhaldoun, Zouhair; Kadiri, Samir;
Sánchez, Francisco; Pallé, Pere L.; Duhalde, Oscar; Solis, Hernan;
Saá, Oscar; González, Ricardo
Bibcode: 1994SoPh..152..351H
Altcode:
The Global Oscillation Network Group (GONG) Project will place a
network of instruments around the world to observe solar oscillations as
continuously as possible for three years. The Project has now chosen the
six network sites based on analysis of survey data from fifteen sites
around the world. The chosen sites are: Big Bear Solar Observatory,
California; Mauna Loa Solar Observatory, Hawaii; Learmonth Solar
Observatory, Australia; Udaipur Solar Observatory, India; Observatorio
del Teide, Tenerife; and Cerro Tololo Interamerican Observatory, Chile.
Title: Vector Magnetic Field Changes Associated with X-Class Flares
Authors: Wang, Haimin; Ewell, M. W., Jr.; Zirin, H.; Ai, Guoxiang
Bibcode: 1994ApJ...424..436W
Altcode:
We present high-resolution transverse and longitudinal magnetic field
measurements bracketing five X-class solar flares. We show that the
magnetic shear, defined as the angular difference between the measured
field and calculated potential field, actually increases after all
of these flares. In each case, the shear is shown to increase along a
substantial portion of the magnetic neutral line. For two of the cases,
we have excellent time resolution, on the order of several minutes,
and we demonstrate that the shear increase is impulsive. We briefly
discuss the theoretical implications of our results.
Title: Electromagnetic and corpuscular emission from the solar flare
of 1991 June 15: Continuous acceleraton of relativistic particles
Authors: Kocharov, L. G.; Kovaltsov, G. A.; Kocharov, G. E.; Chuikin,
E. I.; Usoskin, I. G.; Shea, M. A.; Smart, D. F.; Melnikov, V. F.;
Podstrigach, T. S.; Armstrong, T. P.; Zirin, H.
Bibcode: 1994SoPh..150..267K
Altcode:
Data on X-,γ-ray, optical and radio emission from the 1991 June
15 solar flare are considered. We have calculated the spectrum of
protons that producesγ-rays during the gradual phase of the flare. The
primary proton spectrum can be described as a Bessel-function-type up
to 0.8 GeV and a power law with the spectral index ≈3 from 0.8 up
to 10 GeV or above. We have also analyzed data on energetic particles
near the Earth. Their spectrum differed from that of primary protons
producingγ-ray line emission. In the gradual phase of the flare
additional pulses of energy release occurred and the time profiles of
cm-radio emission andγ-rays in the 0.8-10 MeV energy band and above 50
MeV coincided. A continuous and simultaneous stochastic acceleration
of the protons and relativistic electrons at the gradual phase of the
flare is considered as a natural explanation of the data.
Title: The evolution of magnetic network elements in the quiet Sun
Authors: Liu, Y.; Zhang, H.; Ai, G.; Wang, H.; Zirin, H.
Bibcode: 1994A&A...283..215L
Altcode:
Using the 155-h coordinated magnetograph data of Huairou and Big
Bear Solar Observatories, we have studied the evolution and lifetime
of magnetic network elements in an enhanced network region. Both
statistical and counting methods give a mean lifetime of network
elements of 50h. The network elements are divided into two categories
according to their evolution: 'breakup' and 'merging'. They have similar
average lifetimes. We also find that the number of the elements that
disappear by merging is about twice that by breakup. This may indicate
that the creation and disappearance of magnetic network elements
are balanced.
Title: 850 MU M Observations of the 11 July 1991 Total Solar Eclipse
Authors: Ewell, M. W., Jr.; Zirin, H.; Jensen, J. B.; Bastian, T. S.
Bibcode: 1994IAUS..154..161E
Altcode:
No abstract at ADS
Title: A Study of Solar Prominences near lambda = 1 Millimeter
Authors: Bastian, T. S.; Ewell, M. W., Jr.; Zirin, H.
Bibcode: 1993ApJ...418..510B
Altcode:
The 10.4 m Leighton telescope at the Caltech Submillimeter Observatory
was used to produce full-disk and partial area raster maps of the Sun
during 1991 July 9-11 in advance of the total eclipse of the Sun on
July 11. Maps were made at a wavelength of 850 microns with an angular
resolution of 20".6 and at 1250 microns with an angular resolution
of 30". We have analyzed the 850 microns brightness associated
with Hα filaments present on the disk and find that (1) they are all
associated with regions possessing a brightness comparable to or below
that of the quiet Sun at the center of the disk; and (2) because of
their lack of contrast with the background brightness distribution,
Hα filaments are optically thin at 850 μm. We have also analyzed
contemporaneous observations of a prominence above the solar limb
at both 850 and 1250 mum. We show that (1) the optical depth of
the prominence is τ ≍ 0.12 at 850 μm, confirming the conclusion
drawn from the analysis of Hα filaments; and (2) the line-of- sight
emission measure is <ne2L> = 1.3-2.0 ×
1029 cm-5, and the electron number density is
ne ∼ 1-3 × 1010 cm-3. We
argue that the reduced 850 microns brightness associated with Hα
filaments and, more generally, magnetic neutral lines is due neither
to the presence of an overlying coronal cavity nor to the presence
of absorbing material, as has been suggested previously. We instead
suggest that the reduced brightness is due to the structure of the
underlying chromosphere where, in the case of filament channels,
the predominantly horizontal magnetic field leads to a reduction of
heating and/or a smaller density scale height.
Title: The Coronal Structure above Sunspots and Pores
Authors: Harmon, R.; Rosner, R.; Zirin, H.; Spiller, E.; Golub, L.
Bibcode: 1993ApJ...417L..83H
Altcode:
No abstract at ADS
Title: Soviet revolutions
Authors: Zirin, Harold
Bibcode: 1993Natur.365..796Z
Altcode: 1993Natur.365..796T
No abstract at ADS
Title: The Center-to-Limb Brightness Variation of the Sun at lambda =
850 Microns
Authors: Bastian, T. S.; Ewell, M. W., Jr.; Zirin, H.
Bibcode: 1993ApJ...415..364B
Altcode:
The 10.4 m submillimeter telescope of the Caltech Submillimeter
Observatory was used to map the full disk of the sun on July 9-10,
1991 at a wavelength 850 microns with an angular resolution of 20.6
arcsec. A maximum entropy-type deconvolution was performed to correct
the map for the broad wings of the telescope beam. The brightness
distribution of the resulting map shows (1) a high degree of correlation
with corresponding images in H-alpha, the Ca II K line, and with the
photospheric magnetogram; (2) a systematic center-to-limb brightening
of the quiet sun (about 12 percent at an offset of 0.94 solar radius)
with no apparent difference in the limb brightening between the EW and
NS quadrants; (3) an average contrast of about 11 percent between active
region plages and the quiet sun near disk center; and (4) a smaller
degree of center-to-limb brightening of active region plages (about 5
percent at an offset of 0.94 solar radius), leading to a decrease in
contrast between active region plages and the quiet sun from the center
to limb. We compare the observed center-to-limb brightness variation of
the quiet sun and plages with that expected for several chromospheric
models, including those which include a 'spicular' component. We find
that although the observed center-to-limb variation of the quiet sun
at 850 microns is broadly consistent with the chromospheric models of
Vernazza et al. (1981), it differs in detail.
Title: Magnetic structures and energy of 1989 March flares
Authors: Wu, S. T.; Weng, F. S.; Wang, H. M.; Zirin, H.; Ai, G. X.
Bibcode: 1993AdSpR..13i.127W
Altcode: 1993AdSpR..13..127W
We use a recently developed non-linear force-free model to analyze
the magnetic structures and energy for 1989 March flares. In this
analysis, we extrapolated the magnetic structure using the vector
magnetograms obtained at Huairou Solar Observatory. In order to validate
our extrapolated magnetic field topology, we compared our computed
magnetic field results with Hα pictures obtained at Big
Bear Solar Observatory. The results are presented for the evolution of
the magnetic field structure (i.e. potential and non-linear force-free
field), magnetic energy, and current distribution. It shows that the
location of the occurrences of the flares are approximately related
to the location of the high intensity of the currents. Further, we
demonstrate that the amount of energy in force-free fields is more
than adequate to power the flares.
Title: Observations of Vector Magnetic Fields in Flaring Active
Regions
Authors: Chen, J.; Wang, H.; Zirin, H.; Ai, G.
Bibcode: 1993BAAS...25R1208C
Altcode:
No abstract at ADS
Title: Transition Region Explosive Events in an X-Ray Dark Lane
Region of the Quiet Sun
Authors: Cook, J. W.; Moses, D.; Brueckner, G. E.; Dere, K. P.;
Bartoe, J. -D. F.; Webb, D.; Davis, J. M.; Harvey, J. W.; Recely,
F.; Martin, S. F.; Zirin, H.
Bibcode: 1993BAAS...25.1181C
Altcode:
No abstract at ADS
Title: Narrow lanes of transverse magnetic field in sunspots
Authors: Zirin, H.; Wang, H.
Bibcode: 1993Natur.363..426Z
Altcode:
SOLAR flares are closely associated with magnetic activity on the
surface of the Sun. They typically occur1 in complex
sunspot groups, where the vertical magnetic fields reverse abruptly,
and the horizontal (transverse) fields connecting the vertical poles
are both sheared and strong. A single field inversion line may be
the site of many flares1. Here we report observations of
a large, active sunspot group which reveal a series of oppositely
directed vertical-field inversions separated by extremely narrow
elongated channels of intense horizontal fields. In a minimum-energy
configuration, lines of force connecting oppositely directed vertical
fields simply arch across the inversion line; but when newly emerged
sunspots move through older magnetic-field configurations, the poles are
pushed together and the field lines turn sharply along the inversion
line to reconnect with the vertical field some distance away. These
multiple channels of horizontal field imply a large curl term (▿×B),
and hence a substantial electric current. Our observations show that
almost all of the larger flares in this region occur in these highly
convoluted fields.
Title: Vector Magnetic Field Changes Associated with X-Class Flares
Authors: Ewell, M. W., Jr.; Wang, H.; Zirin, H.; Ai, G.
Bibcode: 1993BAAS...25.1198E
Altcode:
No abstract at ADS
Title: Properties of Spicules
Authors: Zirin, H.; Wang, H.
Bibcode: 1993BAAS...25.1181Z
Altcode:
No abstract at ADS
Title: A Holographic Narrow-Band Filter for Solar Observing
Authors: Rakuljic, G.; Zirin, H.
Bibcode: 1993BAAS...25.1184R
Altcode:
No abstract at ADS
Title: Strong transverse fields in δ-spots
Authors: Zirin, Harold; Wang, Haimin
Bibcode: 1993SoPh..144...37Z
Altcode:
Spectroscopic measurements of the strength and direction of transverse
magnetic fields in six δ-spots are presented. The field direction is
determined by the relative strength of the π- and σ-components at
different polarizer orientations, and is, with one exception, parallel
to the neutral line and as strong as the umbral field. Field strengths
determined by line splitting are as high as 3980 G.
Title: The magnetic and velocity fields of solar active regions
Authors: Zirin, Harold; Ai, Guoxiang; Wang, Haimin
Bibcode: 1993ASPC...46.....Z
Altcode: 1993mvfs.conf.....Z; 1993IAUCo.141.....Z
Various papers on the magnetic and velocity fields of solar active
regions are reported. The general topics addressed include: structure
of active regions, theory of active region structure, techniques of
magnetic field measurements, the relation of the quiet sun to active
regions, fields in the chromosphere and corona, flares and transients,
magnetic shear and electric currents, structure and role of emerging
flux regions, convections and oscillation in active regions.
Title: Microwave Emission From a Sunspot III. Implications for the
Force Balance in a Static Sunspot
Authors: Lee, J. W.; Gary, D. E.; Hurford, G. J.; Zirin, H.
Bibcode: 1993ASPC...46..287L
Altcode: 1993IAUCo.141..287L; 1993mvfs.conf..287L
No abstract at ADS
Title: Submillimeter Observations of the 1991 July 11 Total Solar
Eclipse
Authors: Ewell, M. W., Jr.; Zirin, H.; Jensen, J. B.; Bastian, T. S.
Bibcode: 1993ApJ...403..426E
Altcode:
We present observations of the 1991 July 11 total solar eclipse at
850 microns made with the Caltech Submillimeter Observatory on Mauna
Kea. We find that the 850-micron limb is 3380 +/- 140 km above the
visible limb. We also find that there is a 10 percent limb brightening
in the outer 7 arcsec of the solar disk, and we measure a central
brightness temperature of 6400 +/- 700 K. These results require that
the upper chromosphere not be in hydrostatic equilibrium, with a higher
electron density than is predicted by the standard (VAL) model. We show
that the dependence of limb height on wavelength is well fitted by a
one-parameter model with an electron density scale height of 1200 km;
there is no need to invoke complex spicule geometry to explain the
observations.
Title: The Interaction of Weak and Strong Magnetic Fields on the Sun
(Invited)
Authors: Zirin, H.
Bibcode: 1993ASPC...46..215Z
Altcode: 1993IAUCo.141..215Z; 1993mvfs.conf..215Z
No abstract at ADS
Title: Joint vector magnetograph observations at BBSO, Huairou
Station and Mees Solar Observatory
Authors: Wang, Haimin; Varsik, John; Zirin, Harold; Canfield, Richard
C.; Leka, K. D.; Wang, Jingxiu
Bibcode: 1992SoPh..142...11W
Altcode:
Joint vector magnetograph observations were carried out at Big Bear
Solar Observatory (BBSO), Huairou Solar Observing Station (Huairou),
and Mees Solar Observatory (MSO) in late September 1989. Comparisons of
vector magnetograms obtained at the three stations show a high degree
of consistency in the morphology of both longitudinal and transverse
fields. Quantitative comparisons show the presence of noise, cross-talk
between longitudinal field and transverse field, Faraday rotation
and signal saturation effects in the magnetograms. We have tried to
establish how the scatter in measurements from different instruments
is apportioned between these sources of error.
Title: Breaking out in spots
Authors: Zirin, Harold
Bibcode: 1992Natur.359..271Z
Altcode:
No abstract at ADS
Title: Evolution of Magnetic Fields and Mass Flow in a Decaying
Active Region
Authors: Zhang, Hongqi; Ai, Guoxiang; Wang, Haimin; Zirin, Harold;
Patterson, Alan
Bibcode: 1992SoPh..140..307Z
Altcode:
Five days of coordinated observation were carried out
from 24-29 September, 1987 at Big Bear and Huairou Solar
Observatories. Longitudinal magnetic fields of an αp sunspot active
region were observed almost continuously by the two observatories. In
addition, vector magnetic fields, photospheric and chromospheric Doppler
velocity fields of the active region were also observed at Huairou
Solar Observatory. We studied the evolution of magnetic fields and
mass motions of the active region and obtained the following results:
(1) There are two kinds of Moving Magnetic Features (MMFs). (a) MMFs
with the same magnetic polarity as the center sunspot. These MMFs
carry net flux from the spot, move through the moat, and accumulate at
the moat's outer boundary. (b) MMFs in pairs of mixed polarity. These
MMFs are not responsible for the decay of the spot since they do not
carry away the net flux. MMFs in category (b) move faster than those
of (a). (2) The speed of the mixed polarity MMFs is larger than the
outflow measured by photospheric Dopplergrams. The uni-polar MMFs
are moving at about the same speed as the Doppler outflow. (3) The
chromospheric velocity is in approximately the opposite direction from
the photospheric velocity. The photospheric Doppler flow is outward;
chromospheric flow is inward. We also found evidence that downward
flow appears in the photospheric umbra; in the chromosphere there is
an upflow.
Title: Flows around Sunspots and Pores
Authors: Wang, Haimin; Zirin, Harold
Bibcode: 1992SoPh..140...41W
Altcode:
We report on three sequences of high-resolution white-light and
magnetogram observations obtained in the summer of 1989. The duration
of sub-arcsecond seeing was three to four hours on each day. Study of
the white-light and magnetogram data yields the following results:
For all but one of the sunspots we have observed, both dark fibrils
and bright grains in the inner part of the penumbra of sunspots move
toward the umbra with a speed of about 0.5 km s-1. In the
outer part of the penumbra, movement is away from the umbra. The one
exception is a newly formed spot, which has inflow only in its penumbra.
Title: Strong (4000g) Transverse Fields in Delta Spots
Authors: Zirin, H.
Bibcode: 1992AAS...180.5105Z
Altcode: 1992BAAS...24..814Z
We have measured transverse fields in the neutral line area between
spots of opposite polarity in several delta spots (spots of opposite
polarity in one penumbra). The measurement was made by scanning the
spectrograph slit across the area and recording the 5250 Angstroms
line and the slit jaw image on videotape. Transverse field was
selected by rotating a linear polarizer. The splitting of the
transverse sigma component, measured with a ruler, was as high as
high as 0.3|AA, corresponding to more than 4000 gauss, stronger than
the longitudinal field in the component spots. This demonstrates the
strong, sheared transverse fields along the neutral lines of these
spot configurations. The splitting can be used to calibrate the vector
magnetograph. We have found strong sheared fields of 3000g or more in
every delta spot measured.
Title: Kinematics and Lifetimes of Solar Spicules
Authors: Suematsu, Y.; Wang, H.; Zirin, H.
Bibcode: 1992AAS...180.0702S
Altcode: 1992BAAS...24..738S
We present the dynamical evolution of spicules seen on the solar disk
and the relationship between the spicule formation and Hα bright point
at its footpoint. We used filtergrams in Hα -0.65 Angstroms, 0.0,
and +0.65 Angstroms, (passband = 0.25 Angstroms) obtained at BBSO on
Sep. 16, 1991, with the OSL CCD camera. The observations were made in
a region of enhanced network for one and half hours. The resolution
was 0.4 arcsec/pixel. The time resolution for the filtergrams of
same wavelength was about 20 sec. These filtergrams were carefully
registered with a cross-correlation technique, in order to follow the
time evolution of fine structures. We investigated both proper motions
and line-of-sight Doppler velocities of spicules; the latter were
obtained from the subtraction of Hα -0.65 from +0.65 filtergrams. About
2/3 of the spicules could be traced through up and down phases. For
most short-lived spicules, both their apparent motions and Doppler
velocities indicate that the motion of a spicule is real and it follows
nearly a ballistic trajectory. For some long-lived spicules, we can
see periodic rising motion. In these cases, we can see the lower part
of the spicule showing downward motion even in the rising phase. The
bright points, which are prominent in Hα blue wing, tend to appear or
reach their maximum intensity at about the maximum phase of spicules,
and to be accompanied with downward motions. It is likely that the
Hα bright point does not initiate the spicule formation but rather
it appears as a by-products of the spicule formation. These results
seem to suggest that the spicules are generated by an impulsive upward
force on the chromosphere such as a shock wave propagating upward,
and its seed perturbation might take place at a layer deeper than the
chromosphere, or might be a kinematic process with less heating if it
occurs in the chromosphere.
Title: Strong (7000g) Transverse Fields in Delta Spots
Authors: Zirin, H.
Bibcode: 1992AAS...180.5104Z
Altcode:
We have measured transverse fields in the neutral line area between
spots of opposite polarity in several delta spots (spots of opposite
polarity in one penumbra). The measurement was made by scanning the
spectrograph slit across the area and recording the 5250 Angstroms
line and the slit jaw image on videotape. Transverse field was
selected by rotating a linear polarizer. The splitting of the
transverse sigma component, measured with a ruler, was as high as
high as 0.3|AA, corresponding to more than 7000 gauss, stronger than
the longitudinal field in the component spots. This demonstrates the
strong, sheared transverse fields along the neutral lines of these
spot configurations. The splitting can be used to calibrate the vector
magnetograph. We have found strong sheared fields of 3000g or more in
every delta spot measured.
Title: An Issue of Neglect for Astronomy?
Authors: Harrison, Shirley W.; Zirin, Harold; Bahcall, John N.
Bibcode: 1992PhT....45b.128H
Altcode:
No abstract at ADS
Title: Detection of ``Invisible Sunspots''
Authors: Zirin, Harold; Wang, Haimin
Bibcode: 1992ApJ...385L..27Z
Altcode:
A new CCD system is used to detect tiny sunspots, which are termed
'micropores', associated with elements of the magnetic network far
from active regions. The smallest micropores detected are less than 1
arcsec in diameter and about half the size of the associated magnetic
feature. It is found that the pore size is systematically smaller
than the size of magnetic element seen in the magnetograms, but the
ratio of pore size versus magnetic element size is independent of pore
size, suggesting that the difference is real. For the smaller elements
there is a good linear relation between the brightness deficit of the
pore and the total flux of the magnetic element. The micropores are
distinguishable from dark lanes in the granulation by their long life,
large brightness deficit, and association with magnetic fields.
Title: The secrets of the solar atmosphere.
Authors: Zirin, H.
Bibcode: 1992atc..book...53Z
Altcode:
Contents: 1. A little history. 2. Whither the chromosphere? 3. The
corona and the solar wind. 4. The problem of coronal heating. 5. The
stars.
Title: Solar Optical Instrumentation
Authors: Zirin, H.
Bibcode: 1992ASIC..373..379Z
Altcode: 1992sla..conf..379Z
No abstract at ADS
Title: Solar Activity
Authors: Zirin, H.
Bibcode: 1992ASIC..373..449Z
Altcode: 1992sla..conf..449Z
No abstract at ADS
Title: The Photospeher
Authors: Zirin, H.
Bibcode: 1992ASIC..373..175Z
Altcode: 1992sla..conf..175Z
The photosphere is the surface of the Sun that we see, and the direct
source of its energy. It is dominated by granulation, supergranulation,
and magnetic fields. We discuss the significance of limb darkening,
the opacity, and model structure. The magnetic fields are dominated
by the network, but the weaker fields are also of great interest. We
discuss the Fraunhofer spectrum, and what it tells us about the surface,
and finally, the newly-discovered emission lines at 12μ.
Title: Motions, Fields, and Flares in the 1989 March Active Region
Authors: Wang, Haimin; Tang, Frances; Zirin, Harold; Ai, Guoxiang
Bibcode: 1991ApJ...380..282W
Altcode:
The results of observations of NOAA AR 5395 are presented. The region
was observed every day from limb to limb for significant periods, and
nine of the ten class-X flares were recorded. The region was found to
be a great Delta group, dominated by spots of following (f) polarity,
which moved rapidly westward, producing large changes in magnetic
structure which increased the shear and led to great flares. Aside
from its great size, the region was unusual in that normally p spots
dominate and move westward. In this case there was a 4:1 flux imbalance;
80 percent of the flux measured was of following polarity. The major
following spot in the region was found to move with a near-constant
acceleration, eventually reaching 0.25 km/s. Rapid spot motion was
discovered in all other superactive regions. Small p and f spots move
out from either side of the large f spot, and curl around it in curved
trajectories. The moving penumbral material coalesces into new umbrae.
Title: Obituary: Katsuo Tanaka, 1943-1990
Authors: Zirin, Harold
Bibcode: 1991BAAS...23.1494Z
Altcode:
No abstract at ADS
Title: The Microwave Brightness Temperature Spectrum of the Quiet Sun
Authors: Zirin, H.; Baumert, B. M.; Hurford, G. J.
Bibcode: 1991ApJ...370..779Z
Altcode:
New measurements of the microwave brightness temperature spectrum
of the center of the quiet sun, acquired at Owens Valley over several
months during the 1986-1987 sunspot minimum, are reported. The resulting
brightness temperature spectra are consistent with previous data, but
exhibit much less frequency-to-frequency scatter. The corona is fitted
well by an optically thin source at temperature of 10 to the 6th k,
scale height H = 5 x 10 to the 9th, and density of 3.2 x 10 to the
8th/cu cm, and the chromosphere, an optically thick source at around
11,000 k.
Title: Distribution and Dynamics of a High Temperature Coronal Plasma
Associated with Chromospheric Activity
Authors: Neupert, W. M.; Zirin, H.
Bibcode: 1991BAAS...23..938N
Altcode:
No abstract at ADS
Title: Evolution of Vector Magnetic Field and the August 27, 1990
X-3 Flare
Authors: Wang, H.; Zirin, H.
Bibcode: 1991BAAS...23Q1030W
Altcode:
No abstract at ADS
Title: Mapping of Three-Dimensional Sunspot Fields by Inversion Line
and Symmetry
Authors: Zirin, H.
Bibcode: 1991BAAS...23.1053Z
Altcode:
No abstract at ADS
Title: Magnetic Flux Transport of Decaying Active Regions and Enhanced
Magnetic Network
Authors: Wang, Haimin; Zirin, Harold; Ai, Guoxiang
Bibcode: 1991SoPh..131...53W
Altcode:
Several series of coordinated observations on decaying active regions
and enhanced magnetic network regions have been carried out jointly at
Big Bear Solar Observatory (BBSO) and Huairou Solar Observing Station of
the Bejing Astronomical Observatory in China. The evolution of magnetic
fields in several regions was followed closely for 3 to 7 days. The
transport of magnetic flux from the remnants of decayed active regions
was studied. Three related topics are included in this paper. (1)
We studied the evolution and lifetime of the magnetic network which
defines the boundaries of supergranules. The results are consistent with
our earlier studies: network cells have an average lifetime of about
70 hours; 68% of new cells appeared by growing from a single network
magnetic element; 50% of decaying cells disappeared by contracting
to a network element. (2) We studied the magnetic flux transport in
an enhanced network region in detail, and found the diffusion rate
to be negative, i.e., there was more flux moving towards the decayed
active region than away from it. We found several other cases where the
magnetic diffusion rate does not agree with Leighton's model. The slow
diffusion rate is likely due to the fact that the average velocity of
larger magnetic elements, which carry most of the magnetic flux, is
less than 0.1 km s−1; their average lifetime is longer
than 100 hours. (3) We briefly described some properties of Moving
Magnetic Features (MMFs) around a sunspot (detailed discussion on
MMFs will be presented in a separate paper). In this particular case,
the MMFs did not carry net flux away from the central spot. Instead,
the polarities of MMFs were essentially mixed so that outflowing
positive and negative fluxes were roughly balanced. During the 3-day
period, there was almost no net flux accumulation to form a moat. The
cancellation of MMFs of opposite polarities at the boundary of the
super-penumbra caused quite a few surges and Hα brightenings.
Title: Progress toward an advanced imaging vector magnetograph.
Authors: Cacciani, A.; Paverani, E.; Smith, E.; Zirin, H.
Bibcode: 1991sopo.work..133C
Altcode:
As part of the development phase of an imaging vector magnetograph
the authors have tested at Big Bear Solar Observatory a simple double
band imaging linear polarimeter based on a magneto-optical filter. An
isolated sunspot was observed and the orientation of the field lines of
the penumbra are displayed. They show an evident cyclonic aspect. If
it was caused by Faraday rotation it would be consistent with the
magnetic polarity of the spot.
Title: Solar flares.
Authors: Zirin, Harold; MacKinnon, Alec; McKenna-Lawlor, Susan M. P.
Bibcode: 1991sia..book..964Z
Altcode:
Solar flares are discussed from three complementary viewpoints. The
first is the radiative aspect which includes optical and radio
observations, in addition to the magnetic circumstances of their
origin. It is seen that flares are produced in regions of magnetic
shear, a condition that arises mainly from sunspot motions. In this
regard recipes for the prediction of flares are given. The second view
point considers that flares produce great streams of energetic particles
which carry away much of the flare energy. Gamma and X-ray studies
of the spectra of these particles provide information on the flare's
transient high-temperature plasma. A third consideration, satellite
samples of flare-particle streams, provide diagnostic information on
acceleration mechanisms pertinent to different kinds of flare event,
while shedding complementary light on solar atmospheric composition
at particular flare sites and on physical processes operating in
the corona.
Title: BEARALERTS: A successful flare prediction system
Authors: Zirin, Harold; Marquette, William
Bibcode: 1991SoPh..131..149Z
Altcode:
We describe our BEARALERT program of predicting solar flares or rapid
development of activity in certain sunspot groups. The purpose of the
program is to test our understanding of the flare process by making
public predictions via electronic mail. Neither the exact timing
of the flare nor the possibility of emergence of new active regions
can be predicted. But high-resolution observations of the magnetic
configuration, Ha brightness and structure and other properties of
a region enabled us to announce the onset of 15 of 23 major active
regions over a two-year period, and 15 of 32 BEARALERTS were followed
by this activity. We used high-resolution real-time data available
at the Big Bear Solar Observatory (BBSO). The criteria for prediction
are given and discussed, along with those for filament eruption.
Title: Five billion vodka bottles to the moon : tales of a Soviet
scientist
Authors: Shklovskii, I. S.; Zirin, Mary Fleming; Zirin, Harold
Bibcode: 1991fbvb.book.....S
Altcode: 1991QB36.S56A3.....
No abstract at ADS
Title: High-resolution sunspot observations
Authors: Zirin, H.; Wang, H.
Bibcode: 1991AdSpR..11e.225Z
Altcode: 1991AdSpR..11..225Z
A high-resolution six-hour sequence for a stable round sunspot 22
deg from disk center reveals the following properties: 1)|The
inflow of penumbral material to the umbra is limited to the inner
half of the penumbra. 2)The outer half of the penumbra shows
the Evershed effect outward flow, extending beyond the penumbra. Both
proper motions and Doppler shifts of these elements are observed. The
Evershed flow peaks in discrete elements, which are clearly associated
with regions of stronger and more horizontal magnetic field in the
outer penumbra. 3)From the apparent reversal of field sign in
the penumbra, we estimate that field lines emerge at angle of at
least 22° to the horizontal throughout the penumbra. 4)The MMF
(moving magnetic features) are generally associated with bright K-line
elements. While some are bipolar and most show the penumbral polarity
associated with horizontal field, there are many exceptions. 5)The
``orphan penumbra'' shows motions similar to the normal penumbra.
Title: In Memoriam - Katsuo Tanaka
Authors: Zirin, Harold; Sakurai, Takashi
Bibcode: 1991LNP...387....5Z
Altcode: 1991fpsa.conf....5Z
No abstract at ADS
Title: The Longer Term Evolution of Magnetic Field and Mass Flow in
a Decaying Active Region
Authors: Zhang, Hongqi; Ai, Guoxiang; Wang, Haimin; Zirin, Harold;
Patterson, Alan
Bibcode: 1991LNP...380..271Z
Altcode: 1991IAUCo.130..271Z; 1991sacs.coll..271Z
No abstract at ADS
Title: The Sources of Solar Flares
Authors: Zirin, Harold
Bibcode: 1991LNP...387....9Z
Altcode: 1991fpsa.conf....9Z
We discuss some of the ideas in Tanaka's last paper. While for a long
time it has been known that most, if not all, major flares are caused
by shear associated with flux eruption and spot motion, the source of
this behavior is unknown. Tanaka tried to explain some of the shear
by the changing photospheric intersection with the three-dimensional
twisted erupting flux loops. In this paper we address the general
problem of the origin of such features, and their possible connection
with the ultimate source deep in the Sun.
Title: Optical Properties of Impulsive Flares
Authors: Zirin, Harold; Tang, Frances
Bibcode: 1990ApJS...73..111Z
Altcode:
The optical and morphological properties of impulsive flares are
examined, showing that all impulsive flares occur close to sunspots and
on magnetic inversion lines with steep gradients. Impulsive flares are
defined and flare brightness variations and the magnetic structure of
flares are discussed. The basic characteristics of impulsive flares are
described and the evolution of a typical impulsive flare is outlined.
Title: Microwave Structure of the Quiet Sun at 8.5 GHz
Authors: Gary, Dale E.; Zirin, Harold; Wang, Haimin
Bibcode: 1990ApJ...355..321G
Altcode:
Multifrequency VLA observations of the quiet sun near 8.5 GHz are
presented. Two regions of the sun were observed, one dominated by an
enhanced network corresponding to a decayed active region, and the
other corresponding to an enhanced network with no active features. The
full-day synthesis maps for both show nearly perfect correspondence
to H-alpha images, and to longitudinal magnetograms. The coronal loops
were observed to appear as regions of radio emission with no underlying
longitudinal magnetic fields, being aligned with H-alpha fibrils in the
photosphere, and connecting regions of opposite magnetic polarity. The
emission can be modeled as optically thin free-free emission from a
coronal loop with a peak axial density of approximately 2.4-2.8 x 10
to the 9th/cu cm, for an assumed coronal temperature of 1-2 x 10 to the
6th K. The quiet chromosphere sources are measured, and the significance
of these measurements for existing chromospheric models is discussed.
Title: The Microwave Brightness Temperature Spectrum of the Quiet Sun
Authors: Hurford, G. J.; Zirin, H.; Baumert, B. M.
Bibcode: 1990BAAS...22..851H
Altcode:
No abstract at ADS
Title: Recent High Resolution Observation at BBSO
Authors: Wang, H.; Zirin, H.
Bibcode: 1990BAAS...22..839W
Altcode:
No abstract at ADS
Title: The Photometric Filtergraph Experiment (PFI) for OSL
Authors: Zirin, H.
Bibcode: 1990BAAS...22R.844Z
Altcode:
No abstract at ADS
Title: The BBSO Program for Max'91
Authors: Zirin, H.
Bibcode: 1990BAAS...22..816Z
Altcode:
No abstract at ADS
Title: Flows, flares, and formation of umbrae and light bridges in
BBSO region No. 1167
Authors: Zirin, Harold; Wang, Haimin
Bibcode: 1990SoPh..125...45Z
Altcode:
We present high-resolution observations of the large active region BBSO
No. 1167 (Boulder No. 5060) which cast new light on the structure
of sunspot regions. We obtained excellent data, highlighted by
videomagnetograms (VMG) obtained with our 65-cm telescope, which give
unprecedented spatial resolution, about 0.5'' for much of two 11-hr
periods. This permitted us to see details of the field evolution and
flows in the AR. The Hα filtergrams and D3 filtergrams permit study
of these magnetic changes compared to spots and chromospheric structure.
Title: Observations of Vector Magnetic Fields with a Magneto-Optic
Filter
Authors: Cacciani, Alessandro; Varsik, John; Zirin, Harold
Bibcode: 1990SoPh..125..173C
Altcode:
We describe the use of the magneto-optic filter (MOF) to observe solar
magnetic fields in the potassium line at 7699 Å. The filter has been
used in the Big Bear video-magnetograph since 23 October. It gives a
high sensitivity and dynamic range for longitudinal magnetic fields
and enables us to measure transverse magnetic fields using the sigma
component. Examples of the observations are presented.
Title: Solar flares
Authors: Zirin, Harold
Bibcode: 1990GMS......Q..33Z
Altcode:
General characteristics of solar flares are discussed. They are
a spectacular energy release arising from development of magnetic
strain and shear, resulting from eruption of new magnetic flux near
old. The release of magnetic energy is channeled into hard electrons
(and possibly nucleons), which produce a series of other effects. The
ultimate source of the magnetic complexity that produces flares is
deep in the sun. A number of examples is given, and the difference
between various types of flares is discussed.
Title: Video image selection studies of granules, pores, and penumbral
flows near a large sunspot
Authors: Zirin, Harold; Wang, Haimin
Bibcode: 1989SoPh..119..245Z
Altcode:
An excellent high-resolution movie in the green continuum was produced
by shift-and-add treatment of two 60-min videotapes obtained at the
Big Bear Solar Observatory. We have studied the digitized images by
direct measurement, cross-correlation techniques, and correlation
tracking. The seeing-limited resolution was about 0.3 arc sec.
Title: Seventy-Five Hours of Coordinated Videomagnetograph
Observations
Authors: Wang, Haimin; Zirin, Harold; Patterson, Alan; Al, Guoxiang;
Zhang, Hongqi
Bibcode: 1989ApJ...343..489W
Altcode:
Videomagnetograph observations obtained between September 24 and 29,
1987 are presented which illustrate the evolution of magnetic flux
surrounding a stable sunspot. It is found that the dominant sunspot
mainly ejects magnetic fields of opposite sign, and that the surrounding
plage fields steadily contract and retreat inward toward the umbra,
resulting in shrinking and weakening of the spot and plage. The extent
of the moat is shown to be reduced by 50 percent in a 75-hour period,
with the principal loss of flux probably due to concellation at the
main neutral line. Five subflares were noted, three occurring prior to
cancellation of the magnetic elements at the inversion line and two
occurring during the development and disappearance of an ephemeral
bipolar region.
Title: Studies of granules, pores, and penumbral flows near a
large sunspot
Authors: Wang, H.; Zirin, H.
Bibcode: 1989hsrs.conf..491W
Altcode:
No abstract at ADS
Title: Correspondence between solar fine-scale structures in the
corona, transition region, and lower atmosphere from collaborative
observations
Authors: Moses, J. Daniel; Cook, J. W.; Bartoe, J. -D. F.; Brueckner,
G. E.; Dere, K. P.; Webb, D. F.; Davis, John M.; Recely, F.; Martin,
S. F.; Zirin, H.
Bibcode: 1989sxsr.reptR....M
Altcode:
The Soft X-Ray Imaging Payload and the High Resolution Telescope and
Spectrograph (HRTS) instrument were launched from White Sands on 11
December 1987 in coordinated sounding rocket flights to investigate the
correspondence of coronal and transition region structures, especially
the relationship between X-ray bright points (XBPs) and transition
region small spatial scale energetic events. The coaligned data from
X-ray images are presented along with maps of sites of transition
region energetic events observed in C IV (100,000 K), HRTS 1600 A
spectroheliograms of the Tmin region and ground based
magnetogram and He I 10830 A images.
Title: Astrophysics of the Sun
Authors: Zirin, Harold; Low, Boon Chye
Bibcode: 1989PhT....42g..74Z
Altcode:
No abstract at ADS
Title: Astrophysics of the Sun
Authors: Zirin, Harold; Pasachoff, Jay M.
Bibcode: 1989AmJPh..57..669Z
Altcode:
No abstract at ADS
Title: Observations of the 12 Micron MG i Lines in Various Solar
Features
Authors: Zirin, Harold; Popp, Bruce
Bibcode: 1989ApJ...340..571Z
Altcode:
Measurements of the solar Mg I line at 812/cm are presented, confirming
the ubiquitous narrow emission from the quiet sun with secant limb
brightening observed by Brault and Noyes (1983). It is found that the
central intensity of 12-micron emission lines is greater in plages
than in the quiet sun, with an equivalent width up to 3 times greater
than for the quiet sun. The magnetic fields measured in plages range
from 300 to 800 Gauss. The secant-like limb brightening, and line
ratios suggest that the lines are optically thin and are formed in
collisional equilibrium with Mg II in a thin layer just above the
temperature minimum.
Title: Magnetograph Networking with China
Authors: Zirin, H.; Wang, H.; Ai, G. -X.
Bibcode: 1989BAAS...21..863Z
Altcode:
No abstract at ADS
Title: BEARALERTS: A New Program of Flare Prediction
Authors: Marquette, W.; Zirin, H.
Bibcode: 1989BAAS...21..836M
Altcode:
No abstract at ADS
Title: The Photometric Filtergraph for OSL
Authors: Zirin, H.
Bibcode: 1989BAAS...21..832Z
Altcode:
No abstract at ADS
Title: Study of Supergranules
Authors: Wang, Haiman; Zirin, Harold
Bibcode: 1989SoPh..120....1W
Altcode:
Results of a detailed study on supergranule lifetime and velocity
fields are presented. We show the correlation between the observed
downdraft velocity and the network magnetic flux elements on the quiet
sun. After excluding areas with magnetic flux density ≥ 25 G, we
find that the upper limit of the supergranule vertical speed is 0.1 km
s−1 for both downdraft and updraft, and the r.m.s. speed
is 0.03 km s−1. By observing the evolution of individual
supergranules, we find that the average lifetime of supergranules might
be ≥ 50 hours. We describe different ways of formation and decay of
supergranular cells. New cells usually form in an area containing no
pre-existing supergranule velocity fields. Cells may disappear in two
ways: fragmentation and fading away.
Title: Details of Large Scale Solar Motions Revealed by Granulation
Test Particles
Authors: Simon, G. W.; November, L. J.; Ferguson, S. H.; Shine, R. A.;
Tarbell, T. D.; Title, A. M.; Topka, K. P.; Zirin, H.
Bibcode: 1989ASIC..263..371S
Altcode: 1989ssg..conf..371S
No abstract at ADS
Title: Magnetoconvection on the solar surface.
Authors: Simon, G. W.; Title, A. M.; Topka, K. P.; Tarbell, T. D.;
Shine, R. A.; Ferguson, S. H.; Zirin, H.
Bibcode: 1989GMS....54...53S
Altcode: 1989sspp.conf...53S
The authors describe and illustrate the first high-resolution
observations of horizontal flows on the solar surface and their relation
to magnetic field structure seen in the Sun's photosphere.
Title: Impulsive phase transport.
Authors: Canfield, R. C.; Bely-Dubau, E.; Brown, J. C.; Dulk, G. A.;
Emslie, A. G.; Enome, S.; Gabriel, A. H.; Kundu, M. R.; Melrose,
D.; Neidig, D. F.; Ohki, K.; Petrosian, V.; Poland, A.; Rieger, E.;
Tanaka, K.; Zirin, H.
Bibcode: 1989epos.conf..225C
Altcode:
The work of this group was concerned with how the energy released
in a solar flare is transported through the solar atmosphere before
escaping in the form of radiant and mechanical energy.
Title: Study of weak solar magnetic fields
Authors: Zirin, Harold
Bibcode: 1989cait.reptQ....Z
Altcode:
There have been two major gains in this period: first, the completion
and analysis of round-the-clock observations in cooperation with
the Huairou Observatory in the People's Republic of China, which
enabled us to obtained the first longterm observations of weak solar
magnetic fields, and the application of the magneto-optic filter to
the measurement of magnetic fields. The observations in collaboration
with China have enabled us to make observations for as long as seven
days of solar magnetic regions, with only short interruptions when the
sun could not be seen from the U.S. and China. The stronger elements
of the chromospheric network are rather long lived, lasting about
70 hours. In fact, it is possible that they last longer, because
although the shape changes, it is often possible to still identify a
magnetic entity. The second important result was that one could find
definite evidence of magnetic field cancellation occurring after solar
flares. The increased time coverage enabled us to check the evolution of
the magnetic fields during this period. The other development, the use
of the magneto-optic filter, is full of promise for the future. This
filter is made by using a glass tube filled with potassium which is
placed in a strong magnetic field.
Title: Book-Review - Astrophysics of the Sun
Authors: Zirin, H.; Wiedemann, E.
Bibcode: 1989AN....310..346Z
Altcode:
No abstract at ADS
Title: Book-Review - Astrophysics of the Sun
Authors: Zirin, H.
Bibcode: 1988Sci...242.1586Z
Altcode:
No abstract at ADS
Title: Coordinated videomagnetograph observations by the Big Bear
and Huairou Observatories
Authors: Wang, Haimin; Patterson, Alan; Zirin, Harold; Ai, Guoxiang;
Zhang, Hongqi
Bibcode: 1988fnsm.work..279W
Altcode:
A videomagnetograph patterned after the BBSO system was installed at
Huairou in 1987, and five days of coordinated observing were carried
out from September 24 to 29, 1987. The data were combined to make
a continuous movie of the fields abound a stable spot. A 57 hour
magnetograph run with two seven hour gaps were achieved from 2330 UT,
September 24 to 0830 UT, September 27. The frames were reregistered and
justified to eliminate the change of scale with meridian distance. The
intensities were corrected for cosine effect. Preliminary examination
of the data shows continuous decrease of the total magnetic field during
this period by more than 50 percent. The principal loss of flux appears
to be due to cancellation at the main neutral line. Some flux disappears
due to fragmentation, which makes the elements fall below the threshold,
while only a tiny loss due to diffusion can be detected. It is planned
to continue this program during Max 1991, including transverse field
measurements as well. Several long runs were already obtained in 1988.
Title: The Vertical Structure of Arch Filament Systems in Solar
Emerging Flux Regions
Authors: Chou, Dean-Yi; Zirin, Harold
Bibcode: 1988ApJ...333..420C
Altcode:
The paper studies the vertical velocity of arch filaments in emerging
flux regions by measuring their proper motion near the limb in
H-alpha filtergrams and their radial velocity near the disk center in
H-alpha spectrograms. Both show that arch filaments rise at a velocity
between 10 and 15 km/s. The possible mechanisms producing this high
velocity are discussed. None of them is satifactory, but it appears
that the unloading of the arches by outflow must play a role. From
the strength of H-alpha emission and D3 absorption, the temperature
of arch filaments is estimated at 6000-15,000 K and the density at 10
to the 11th-12th/cu cm.
Title: Book-Review - Astrophysics of the Sun
Authors: Zirin, H.
Bibcode: 1988JBAA...98..316Z
Altcode:
No abstract at ADS
Title: Heading Toward Solar Maximum
Authors: Zirin, Harold
Bibcode: 1988S&T....76..355Z
Altcode:
No abstract at ADS
Title: The Velocity Pattern of Weak Solar Magnetic Fields
Authors: Wang, H.; Zirin, H.
Bibcode: 1988SoPh..115..205W
Altcode:
We have measured the proper motion of magnetic elements on the quiet
Sun by means of local correlation tracking. The existence of a pattern
in the intranetwork (IN) flow is confirmed. This velocity field
is consistent with the direct Doppler measurement of the horizontal
component of the supergranular velocity field. The IN elements generally
move toward the network boundaries. By tracking test points we confirm
that the magnetic elements converge in areas corresponding to the
magnetic network. But because the IN elements are of random polarity,
they cannot contribute to the growth or maintenance of the magnetic
network.
Title: Microwave Structure of the Quiet Sun
Authors: Gary, Dale E.; Zirin, Harold
Bibcode: 1988ApJ...329..991G
Altcode:
The authors present two-frequency VLA observations of the quiet Sun
obtained on 1985 July 13, when the Sun was particularly quiet. The
4.9 GHz full-day synthesis maps correspond closely to images made
in Hα, Ca II K, and magnetograms, while the correspondence is much
reduced at 1.45 GHz. The 4.9 GHz maps have a meshlike appearance
reminiscent of chromospheric network structure. Simultaneous
magnetograms from Big Bear Solar Observatory are used to compare the
structure of the magnetic field with the radio source structure at
the two frequencies. Magnetograms of each pointing field were taken
at least once every half-hour for monitoring the changing structure
of the longitudinal component of the magnetic fields. The authors
identify changes such as the appearance of an ephemeral region and
the cancellation of opposite-polarity magnetic flux, and discuss
corresponding changes in radio sources.
Title: Filament Eruptions and the Impulsive Phase of Solar Flares
Authors: Kahler, S. W.; Moore, R. L.; Kane, S. R.; Zirin, H.
Bibcode: 1988ApJ...328..824K
Altcode:
Filament motion during the onset of the solar flare impulsive
phase is examined. The impulsive phase onset is established from
profiles of about 30 keV X-ray fluxes and the rapid flare brightenings
characteristic of the H-alpha flash phase. The filament motion begins
several minutes before the impulsive or flash phase of the flare. No
new accleration is observed in the motion of the filament during the
onset of the impulsive phase for at least two of the four flares. The
most common H-alpha brightenings associated with the impulsive phase
lie near the magnetic inversion line roughly centered under the erupting
filament. Filament speeds at the onset of the impulsive or flash phase
lie in the range 30-180 km/s. These characteristics indicate that
the filament eruption is not driven by the flare plasma pressure,
but instead marks an eruption of magnetic field driven by a global
MHD instability of the field configuration in the region of the flare.
Title: On the Relation between Photospheric Flow Fields and the
Magnetic Field Distribution on the Solar Surface
Authors: Simon, George W.; Title, A. M.; Topka, K. P.; Tarbell, T. D.;
Shine, R. A.; Ferguson, S. H.; Zirin, H.; SOUP Team
Bibcode: 1988ApJ...327..964S
Altcode:
Using the technique of local correlation tracking on a 28 minute time
sequence of white-light images of solar granulation, the horizontal
flow field on the solar surface is measured. The time series was
obtained by the Solar Optical Universal Polarimeter (SOUP) on Spacelab 2
(Space Shuttle flight 51-F) and is free from atmospheric blurring and
distortion. The SOUP flow fields have been compared with carefully
aligned magnetograms taken over a nine hour period at the Big Bear
Solar Observatory before, during, and after the SOUP images. The flow
field and the magnetic field agree in considerable detail: vectors which
define the flow of the white-light intensity pattern (granulation) point
toward magnetic field regions, magnetic fields surround flow cells, and
magnetic features move along the flow arrows. The projected locations
of free particles ('corks') in the measured flow field congregate at
the same locations where the magnetic field is observed.
Title: Observations of the 12-Micron Recombination Lines
Authors: Zirin, H.
Bibcode: 1988BAAS...20..689Z
Altcode:
No abstract at ADS
Title: Correlation of Transition Region C IV High-Velocity Events
With Magnetogram and He I 10830 Å Data
Authors: Cook, J. W.; Bartoe, J. -D. F.; Brueckner, G. E.; Dere,
K. P.; Recely, F.; Martin, S.; Zirin, H.
Bibcode: 1988BAAS...20..722C
Altcode:
No abstract at ADS
Title: The Caltech solar site survey, 1965 1967
Authors: Zirin, H.; Mosher, James M.
Bibcode: 1988SoPh..115..183Z
Altcode:
We describe the Caltech solar site survey in 1965-1967 directed
by R. B. Leighton. The solar seeing at 102 locations in 34 sites in
Southern California was evaluated by 6009 visual estimates with portable
telescopes. Cloud cover and other meteorological factors were also
measured, and sunlight recorders were operated at several sites. We
have reanalyzed much of the data to determine its consistency and
learn what else we could about the sites. The visual estimates show
good internal consistency and correlation with photographic data.
Title: The Correspondence Between Small-Scale Coronal Structures
and the Evolving Solar Magnetic Field
Authors: Webb, D. F.; Moses, J. D.; Davis, J. M.; Harvey, J. W.;
Martin, S. F.; Zirin, H.
Bibcode: 1988BAAS...20..722W
Altcode:
No abstract at ADS
Title: Variability of solar mesogranulation
Authors: Simon, G. W.; November, L. J.; Acton, L. W.; Ferguson, S. H.;
Shine, R. A.; Tarbell, T. D.; Title, A. M.; Topka, K. P.; Zirin, H.
Bibcode: 1988AdSpR...8g.169S
Altcode: 1988AdSpR...8..169S
From white-light photographs of solar granulation obtained with the
SOUP instrument on Space Shuttle Flight STS-19 we have measured the
motions of granules using local correlation tracking techniques. The
granules are organized into larger-scale structures (mesogranular and
supergranular) which exhibit outflow from upwellings, convergence into
sinks, as well as significant vorticity. Magnetic fields follow these
same flow patterns. We describe these velocity structures, and suggest
that their effect on magnetic field structures may be important to
the solar flare buildup process.
Title: Variability of Solar Ultraviolet Emission
Authors: Zirin, H.
Bibcode: 1988srov.proc..301Z
Altcode:
No abstract at ADS
Title: Astrophysics of the sun
Authors: Zirin, Harold
Bibcode: 1988assu.book.....Z
Altcode: 1988QB521.Z57......
The physical processes active in the sun are examined in a general
introduction, with an emphasis on observational data rather than
theoretical models. Chapters are devoted to the methodology of
solar observations, plasmas in magnetic fields, the interpretation
of radiation, atomic spectra, the interior and photosphere, the
chromosphere, the solar corona, prominences, solar activity, solar
flares, and unanswered questions. Extensive diagrams, graphs, and
sample images are provided.
Title: The relation between convection flows and magnetic structure
at the solar surface
Authors: Simon, G. W.; November, L. J.; Acton, L. W.; Title, A. M.;
Tarbell, T. D.; Topka, K. P.; Shine, R. A.; Ferguson, S. H.; Weiss,
N. O.; Zirin, H.
Bibcode: 1988AdSpR...8k.133S
Altcode: 1988AdSpR...8..133S
We describe recent results from the comparison of data from the Solar
Optical Universal Polarimeter instrument on Spacelab 2 and magnetograms
from Big Bear Solar Observatory. We show that the Sun's surface velocity
field governs the structure of the observed magnetic field over the
entire solar surface outside sunspots and pores. We attempt to describe
the observed flows by a simple axisymmetric plume model. Finally,
we suggest that these observations may have important implications
for the prediction of solar flares, mass ejections, and coronal heating.
Title: An image processing system for research in solar physics
Authors: Zirin, Harold
Bibcode: 1987cait.reptR....Z
Altcode:
A powerful new image processing system consisting of a MicroVAX 2
and a Megavision image processor was purchased by the Big Bear Solar
Observatory. The system has been immensely successful, and a number
of important research projects have already been carried out with it.
Title: Proton flares of 1980-1986
Authors: Zirin, Harold
Bibcode: 1987cait.reptS....Z
Altcode:
Proton flares from 1980 through May 1986 were studied. The particle
events (having proton flux of 10/sq cm/s/sr with energy greater than
or = 10 MeV) and their associated flares are published by the NOAA
Space Environment Service Center in the Solar Geophysical Data. A
total of 39 proton events occurred during the time interval, of which
34 associated source flares were identified. Aspects of the 34 proton
flares investigated in the study and the results are listed below:
Active Regions in which Proton Flares Occurred; Proton Flares and Flares
Associated with Interplanetary Type II Bursts; Hard X-ray Signatures;
and The Proton Flare Scenario.
Title: Arch Filaments Associated with the Formation of Sunspots by
Umbral Merging
Authors: Zirin, Harold
Bibcode: 1987SoPh..114..239Z
Altcode:
The formation of a sunspot during the emergence of a new group is
described. The spot forms from a cluster of small umbrae that do not
converge. Rather, the individual umbrae enlarge and merge into a spot
covering the same area. The formation of each umbra is accompanied by
an intensification of the arch filament anchored in it. The formation
of the sunspot produces no apparent change in the total field.
Title: High-resolution continuum observations of the Sun.
Authors: Zirin, Harold
Bibcode: 1987NASCP2483...79Z
Altcode: 1987tphr.conf...79Z
The aim of the PFI or photometric filtergraph instrument is to
observe the Sun in the continuum with as high resolution as possible
and utilizing the widest range of wavelengths. Because of financial
and political problems the CCD was eliminated so that the highest
photometric accuracy is only obtainable by comparison with the CFS
images. Presently there is a limitation to wavelengths above 2200 A due
to the lack of sensitivity of untreated film below 2200 A. Therefore
the experiment at present consists of a film camera with 1000 feet of
film and 12 filters. The PFI experiments are outlined using only two
cameras. Some further problems of the experiment are addressed.
Title: The Contrast of Faculae Near the Solar Limb
Authors: Wang, H.; Zirin, H.
Bibcode: 1987SoPh..110..281W
Altcode:
We have measured the contrast of solar faculae near the limb on
direct digital video images made with the 65 cm vacuum reflector at
the Big Bear Solar Observatory. We used six broad band filters with
different wavelengths from red to violet. The range of heliocentric
angle covered in our measurements is 0.05 < μ = cos θ < 0.4
(θ = 87°-66°). About 300 images were measured from observations made
during the summers of 1983 and 1985. Over 20000 faculae were measured.
Title: The appearance and disappearance of magnetic flux on the
quiet sun
Authors: Zirin, Harold; Martin, Sara F.
Bibcode: 1987cait.reptQ....Z
Altcode:
Significant new discoveries and findings were made concerning solar
magnetic fields. The majority of magnetic flux on the sun is observed to
disappear when magnetic fields of one polarity migrate into or develop
in juxtaposition with fields of opposite polarity. The cancellation of
magnetic fields can be interpreted as: (a) submergence (b) reconnection
or (c) dissipation (annihilation). Large-scale filaments are observed
to form in the chromosphere immediately above the boundaries between
areas of network magnetic field of opposite polarity where network
cancellation occurs. Small-scale filaments develop in association with
small-scale cancelling magnetic fields at the rate of hundreds per
day. Magnetic fields associated with large-scale solar convection cells,
known as intranetwork magnetic fields, can be detected everywhere on
the visible disk of the sun by using the videomagnetograph to integrate
successive, 1/15 sec. magnetic field images for intervals of 1 to 10
minutes. The intranetwork field appears to be a few seconds of arc in
diameter, and have field strengths of the order of a few to tens of
Gauss. The intranetwork fields appear to originate at the centers of
supergranules and flow to the boundaries of the cells in approximately
radial patterns.
Title: Supergranule and Weak Magnetic Fields Movie
Authors: Wang, H.; Zirin, H.
Bibcode: 1987BAAS...19R.937W
Altcode:
No abstract at ADS
Title: On the Relation Between Large-Scale Granular Flows and
Supergranules and Mesogranules
Authors: Simon, G.; Ferguson, S.; Tarbell, T.; Title, A.; Topka, K.;
November, L.; Zirin, H.
Bibcode: 1987BAAS...19R.935S
Altcode:
No abstract at ADS
Title: Simultaneous Observations of Emerging Flux from the Big Bear
Solar Observatory and the SOUP Instrument on Spacelab 2
Authors: Topka, K.; Ferguson, S.; Title, A.; Tarbell, T.; Zirin, H.;
Simon, G.; November, L.
Bibcode: 1987BAAS...19R.927T
Altcode:
No abstract at ADS
Title: Simultaneous Sunspot Observations from the SOUP Instrument
on Spacelab 2 and the Big Bear Solar Observatory
Authors: Shine, R. A.; Title, A. M.; Topka, K. P.; Tarbell, T. D.;
Zirin, H.
Bibcode: 1987BAAS...19..927S
Altcode:
No abstract at ADS
Title: High Resolution Studies of Penumbral and Pore Phenomena
Authors: Zirin, Harold; Wang, Haimin
Bibcode: 1987BAAS...19..940Z
Altcode:
No abstract at ADS
Title: Correlation Study on the Weak Magnetic Fields
Authors: Wang, H.; Zirin, H.
Bibcode: 1987BAAS...19..941W
Altcode:
No abstract at ADS
Title: Weak Solar Fields and Their Connection to the Solar Cycle
Authors: Zirin, Harold
Bibcode: 1987SoPh..110..101Z
Altcode:
We discuss the weak solar magnetic fields as studied with the
BBSO videomagnetograph (VMG). By weak fields we mean those outside
active and unipolar regions. These are found everywhere on the Sun,
even where there never have been sunspots. These fields consist of
the network and intranetwork (IN) elements. The former move slowly
and live a day or more; the latter move rapidly (typically 300 m
s−1) and live only hours. To all levels of sensitivity the
flux is concentrated in discrete elements, and the background field
has not been detected. The smallest detectable elements at present
are 1016 Mx. The IN elements emerge in bipolar form but
appear to flow in a random pattern rather than to the network edges;
however, any expanding network element is constrained by geometry to
move toward the edges.
Title: New Ideas About Granulation Based on Data from the Solar
Optical Universal Polarimeter Instrument on Spacelab 2 and Magnetic
Data from Big Bear Solar Observatory
Authors: Title, A. M.; Tarbell, T. D.; Topka, K. P.; Shine, R. A.;
Simon, G. W.; Zirin, H.; SOUP Team
Bibcode: 1987LNP...292..173T
Altcode: 1987ssp..conf..173T
The SOUP flow fields have been compared with carefully aligned
magnetograms taken at the BBSO before, during, and after the SOUP
images. The magnetic field is observed to exist in locations where
either the flow is convergent or on the boundaries of the outflow from
a flow cell center. Streamlines calculated from the flow field agree
very well with the observed motions of the magnetic field in the BBSO
magnetogram movies.
Title: Delta spots and great flares
Authors: Zirin, Harold; Liggett, Margaret A.
Bibcode: 1987SoPh..113..267Z
Altcode: 1982SoPh..113..267Z
Using eighteen years of observations at Big Bear, we summarize the
development of δ spots and the great flares they produce. We find δ
groups to develop in three ways: eruption of a single complex active
region formed below the surface, eruption of large satellite spots near
(particularly in front of) a large older spot, or collision of spots
of opposite polarity from different dipoles. Our sample of twenty-one
δ spots shows that once they lock together, they never separate,
although rarely an umbra is ejected. The δ spots are already disposed
to their final form when they emerge. The driving force for the shear
is spot motion, either flux emergence or the forward motion of p spots
in an inverted magnetic configuration.
Title: The Evidence for Magnetic Reconnection in Flares
Authors: Zirin, H.
Bibcode: 1987sman.work...45Z
Altcode:
The author has tried to illustrate the fact that one can make a case
for reconnection in almost every flare large enough to be resolved
optically and magnetically.
Title: Impulsive Phase Observations and Their Interpretation
Authors: Canfield, R. C.; Bely-Dumau, E.; Brown, J. C.; Dulk, G. A.;
Emslie, A. G.; Enome, S.; Gabriel, A. H.; Kundu, M. R.; Melrose,
D.; Neidig, D. F.; Ohki, K.; Petrosian, V.; Poland, A.; Rieger, E.;
Tanaka, K.; Zirin, H.
Bibcode: 1986epos.conf..3.4C
Altcode: 1986epos.confC...4C
No abstract at ADS
Title: Theoretical Studies of Transport Processes
Authors: Canfield, R. C.; Bely-Dumau, E.; Brown, J. C.; Dulk, G. A.;
Emslie, A. G.; Enome, S.; Gabriel, A. H.; Kundu, M. R.; Melrose,
D.; Neidig, D. F.; Ohki, K.; Petrosian, V.; Poland, A.; Rieger, E.;
Tanaka, K.; Zirin, H.
Bibcode: 1986epos.conf.3.34C
Altcode: 1986epos.confBC.34C
No abstract at ADS
Title: Properties of Intermediate-Degree Solar Oscillation Modes
Authors: Libbrecht, K. G.; Zirin, H.
Bibcode: 1986ApJ...308..413L
Altcode:
During the summer of 1985, 8042 high-resolution full disk Doppler
images of the Sun were obtained at Big Bear Solar Observatory in a 12
day period. These images were analyzed for solar oscillation modes with
spherical harmonic degrees 5 ≤ l ≤ 20. The frequencies, lifetimes,
and amplitudes of these modes are presented.
Title: High-Resolution Solar Movies by Frame Selection. Averaging
and Reregistration
Authors: Zirin, H.; Wang, H.
Bibcode: 1986BAAS...18..935Z
Altcode:
No abstract at ADS
Title: The Dependence of He i lambda 10830 Absorption Strength upon
X-Ray Emission in Late-Type Stars
Authors: Zarro, D. M.; Zirin, H.
Bibcode: 1986ApJ...304..365Z
Altcode:
Measurements of He I 10830 A absorption equivalent widths and fractional
X-ray luminosities L(x)/L(bo) are presented for a large sample of
late-type stars. A correlation of increasing 10830 A strength with
increasing L(x)/L(bo) is evident in dwarfs, giants, and supergiants
later than and including spectral type F7. No equivalent correlation
is apparent in main-sequence stars earlier than dF7 (B-V of about
0.5). The data suggest that coronal X-ray irradiation constitutes an
important source of He I excitation in late-type stars. The fact that
X-ray luminosity depends exponentially on 10830 A equivalent width
is attributed to the production of X-rays in active regions covering
only a fraction of the stellar surface. It is conjectured that the
absence of 10830 A X-ray correlation in early dF stars is due to the
increased importance of electron collisional excitation of He I. This
effect is discussed in light of evidence that the nature of magnetic
activity changes significantly across the color range spanned by dF
stars; a change related directly to the increasing depth of stellar
convection with decreasing effective temperature.
Title: Magnetic Shear. III. Hale Region 17255
Authors: Athay, R. G.; Jones, H. P.; Zirin, H.
Bibcode: 1986ApJ...303..877A
Altcode:
Hale active region 17255, which in many respects was the most vigorous
active region observed during the first operational period of SMM,
appears to lie between two large areas of flow (observed in C IV)
converging toward the major axis of the region. In the 6-day period
from November 6-12, 1980, the major axis of the region rotates by
about 25 deg. Several segments of the magnetic neutral line show C
IV flow velocities of opposite sign on either side of the neutral
line. Those segments whose orientation is favorable for measuring
velocity components parallel to the neutral line show evidence that
such flow is present, which is interpreted as evidence for magnetic
shear. This, together with other evidence, suggests that magnetic
shear is widespread in this region, as in the two previous regions
studied. It is concluded that magnetic shear is often associated with
flaring activity but is not a sufficient condition for flaring to occur.
Title: Magnetic Shear. IV. Hale Regions 16740, 16815, and 16850
Authors: Athay, R. G.; Klimchuk, J. A.; Jones, H. P.; Zirin, H.
Bibcode: 1986ApJ...303..884A
Altcode:
Dopplergrams made in C IV 1548 A are studied for evidence of velocity
shear near H-alpha dark filaments and for large-scale flow convergent on
active regions. The three regions studied support earlier conclusions
that shear is a common property of active regions and that active
regions may be the foci of converging plasma flow. Flow patterns
near filaments show divergence or convergence as well as shear. Also
the sense of the shear can be either cyclonic or anticyclonic. No
preference is noted for convergence or divergence or for a particular
sense of shear, and there appears to be no correlation between the
sense of the shear and the sign of the velocity gradient normal to
the filament. The close association of H-alpha dark filaments with
shear lines leads to the suggestion that the filaments may arise from
a cooling instability induced by the Bernoulli effect.
Title: Filament Eruption Speed at the Onset of the Impulsive Phase
of Solar Flares
Authors: Moore, R. L.; Kahler, S. W.; Kane, S. R.; Zirin, H.
Bibcode: 1986BAAS...18R.708M
Altcode:
No abstract at ADS
Title: Impulsive phase transport.
Authors: Canfield, R. C.; Bely-Dubau, E.; Brown, J. C.; Dulk, G. A.;
Emslie, A. G.; Enome, S.; Gabriel, A. H.; Kundu, M. R.; Melrose,
D.; Neidig, D. F.; Ohki, K.; Petrosian, V.; Poland, A.; Rieger, E.;
Tanaka, K.; Zirin, H.
Bibcode: 1986NASCP2439....3C
Altcode:
Contents: 1. Introduction: motivation for transport studies, historical
perspective, overview of the chapter. 2. Impulsive phase observations
and their interpretation: gamma-ray emission above 10 MeV, hard
X-ray and microwave morphology, combined soft and hard X-ray spectra,
iron Kα emission, ultraviolet and hard X-ray emission, white light
emission, Hα emission. 3. Theoretical studies of transport processes:
electron beams and reverse currents, proton transport, radiative energy
transport by amplified decimetric waves. 4. Summary.
Title: White light flare of 24 - 25 April 1984.
Authors: Hiei, Eijiro; Zirin, Harold; Wang, Jingxiu
Bibcode: 1986lasf.conf..129H
Altcode: 1986lasf.symp..129H
White-light brightenings appeared at 4 min. after the starting time of
the Hα flare. The time correlation between white-light brightenings
and hard X-ray flux is good. The bright patches moved toward the same
direction as the Hα bright strands of the flare.
Title: White light flares and atmospheric modeling (Working Group
report).
Authors: Machado, M. E.; Avrett, E. H.; Falciani, R.; Fang, C.;
Gesztelyi, L.; Henoux, J. -C.; Hiei, E.; Neidig, D. F.; Rust, D. M.;
Sotirovski, P.; Svestka, Z.; Zirin, H.
Bibcode: 1986lasf.conf..483M
Altcode:
The authors give a short summary of their discussions, and a set
of recommendations which may help in the study of white light flare
emission processes.
Title: The Sun, inside and out.
Authors: Zirin, H.
Bibcode: 1986sosy.book...15Z
Altcode:
Contents: 1. Introduction. 2. Energy production and transport in
the Sun. 3. The surface of the Sun - sunspots. 4. Solar magnetic
activity. 5. The corona and the solar wind. 6. Closing thoughts.
Title: Observation of flares in the helium lines.
Authors: Zirin, Harold
Bibcode: 1986lasf.conf...78Z
Altcode: 1986lasf.symp...78Z
The author discusses observations of flares in the visible and UV
lines. Observations in He I 5876 and He II 4686 permit isolation of
footpoints and effects of footpoint heating, as well as valuable insight
into physical conditions in both loops and footpoints. Interpretation
of UV line intensities permits assessment of chromospheric heating in
the flares. In general these observations point to temperatures of 30 -
100 thousand degrees and densities above 1012 in the helium
emitting areas.
Title: The great flare of 1982 June 6
Authors: Tanaka, K.; Zirin, H.
Bibcode: 1985ApJ...299.1036T
Altcode:
The great soft X-ray (SXR) flare (X12) of the past solar maximum was
observed by Hinotori and by Big Bear Solar Observatory (BBSO) on June
6, 1982. Hinotori data consist of hard X-ray (HXR) and SXR images in
the rise and decay of the flare, high-resolution soft X-ray spectra
throughout the flare, and HXR and gamma-ray data. The BBSO data include
films of H-alpha, H-alpha blue wing, D3 and longitudinal magnetic field,
as well as video tapes of continuum. Images in HXR, SXR, H-alpha,
D3 and the continuum are compared and SXR spectra analyzed. The
flare resulted from extended motion of a large spot shearing the
magnetic field. D3 and white-light images exhibit a progression from
fast flashes to two ribbons, while both HXR and SXR are centered on
the optical kernels. The continuum emission shows the same temporal
behavior as the HXR at 160 keV. In its early phases, the Fe XXV line
was double-peaked, and a decreasing blueshifted (up to 400 km/sec)
component was observed, from which the evaporation rate of chromospheric
material was estimated. It is suggested that this upflow is adequate
to supply the coronal cloud. Flare energetics are discussed in detail,
and it is concluded that a significant amount of energy was deposited
in the corona, and that nonthermal electrons are the major energy input.
Title: He II emission from solar flares
Authors: Zirin, H.; Hirayama, T.
Bibcode: 1985ApJ...299..536Z
Altcode:
The authors present the first monochromatic images of a solar flare in
the λ4686 line of He II. The observations were obtained in the intense
(X10) flare 1984 May 20. The emission comes from footpoint kernels with
peak intensity 3.3 times the photosphere. This value is about twice that
recorded by spectroscopic observers and far exceeds most published data
for the intensity of the resonance line λ304 and the Balmer α1640 of
He II. The authors calculate the intensities of the He II lines for a
range of temperature and electron density. Satisfactory agreement for
the line intensities of the various lines is obtained for high densities
of the order of 1012.5 - 1013.0cm-3,
which would imply these emissions originate in the deep chromosphere.
Title: Filament Eruptions in the Impulsive Phase of Solar Flares
Authors: Moore, R. L.; Kahler, S. W.; Kane, S. R.; Zirin, H.
Bibcode: 1985BAAS...17..905M
Altcode:
No abstract at ADS
Title: The Smallest Observable Elements of Magnetic Flux
Authors: Wang, J.; Zirin, H.; Shi, Z.
Bibcode: 1985SoPh...98..241W
Altcode:
We have followed disappearing elements of magnetic flux to determine the
smallest elements detectable with the Big Bear videomagnetograph. All
the elements followed were disappearing through interaction with
elements of opposite polarity. The last remaining visible segment of
magnectic field of such features can be used to infer the total magnetic
flux of these and other small flux elements visible on the magnetograms.
Title: Series merging of hydrogen Balmer lines during a stellar flare.
Authors: Zarro, D. M.; Zirin, H.
Bibcode: 1985A&A...148..240Z
Altcode:
The authors demonstrate that the series merging of Stark broadened
hydrogen Balmer profiles can produce a significant and, possibly,
observable continuum enhancement in the vicinity of the Balmer
jump. They discuss the implications of this result for the enhanced
"blue" continuum that is often observed in solar and stellar flares. The
results are compared with a flare spectrum obtained for the dMe star
YZ CMi.
Title: The Correlation of He I λ10830 with Stellar X-Rays
Authors: Zarro, D. M.; Zirin, H.
Bibcode: 1985BAAS...17..753Z
Altcode:
No abstract at ADS
Title: Emerging Flux in Active Regions
Authors: Liggett, M.; Zirin, H.
Bibcode: 1985SoPh...97...51L
Altcode:
We have compared the rates at which flux emerges in active and quiet
solar regions within the sunspot belts. The emerging flux regions
(EFRs) were identified by the appearance of arch filament structures in
Hα. All EFRs in high-resolution films of active regions made at Big
Bear in 1978 were counted. The comparable rate of flux emergence in
quiet regions was obtained from SGD data and independently from EFRs
detected outside the active region perimeter on the same films. The
rate of flux emergence is 10 times higher in active regions than in
quiet regions. A sample of all active regions in 31 days of 1983 gave
a ratio of 7.5. We discuss possible mechanisms which might funnel new
magnetic flux to regions of strong magnetic field.
Title: Magnetic shear. II - Hale region 17244
Authors: Athay, R. G.; Jones, H. P.; Zirin, H.
Bibcode: 1985ApJ...291..344A
Altcode:
A B-gamma(delta) sunspot group with growing delta-spots of trailing
polarity shows evidence in H-alpha filament structure of a transition
from a state of weak magnetic shear to a state of strong shear. The
shear develops in the chromosphere and transition region to the
corona overlying the photospheric magnetic neutral line separating the
delta-spots from the leading polarity at a time when the delta-spots are
undergoing rapid growth. Several major flares occur along the sheared
portion of the neutral line following the shear development. Other
segments of the neutral line far removed from the delta-spots show
similar evidence of shear in the H-alpha filament structure and in C
IV velocity patterns as well. These 'quiescent' regions of shear are
relatively steady or decaying with time and show very little related
activity.
Title: The rise and fall of sunspot group 18962 - A case of magnetic
submergence
Authors: Zirin, H.
Bibcode: 1985ApJ...291..858Z
Altcode:
Normal sunspot groups emerge from below the surface as a big arch; the
footpoints form a dipole that moves apart and the fields eventually
diffuse and disappear. BBSO 18962 was a small dipole with elements
which, after spreading apart in the first day of existence, drew back
together and disappeared below the surface. It is proposed that the
flux loop was pulled back down by magnetic tension and submerged. The
circumstances suggest that this behavior may not be uncommon. It
implies that some dipoles do not decouple from subsurface fields.
Title: Magnetic shear. I - Hale region 16918
Authors: Athay, R. G.; Jones, H. P.; Zirin, H.
Bibcode: 1985ApJ...288..363A
Altcode:
Material motion observed in spectral lines of C IV, C II, and Ca
II formed in the chromosphere-corona transition region and upper
chromosphere exhibits patterns that are closely identified with magnetic
field structure at photospheric levels. Assuming that the fluid flow
follows magnetic lines of force, the authors use chromospheric and
transition region Dopplergrams to infer the broad features of the
magnetic field geometry in these upper layers. For Hale region 16918
they find an area in the transition region and upper chromosphere,
centered roughly over the photospheric magnetic neutral line, in which
the lines of force show a strong tendency to parallel the photospheric
neutral line. The authors interpret this as evidence for magnetic shear,
which is pronounced in the upper layers of the atmosphere.
Title: Evolution of weak solar magnetic fields
Authors: Zirin, H.
Bibcode: 1985AuJPh..38..961Z
Altcode:
The present evaluation of Big Bear videomagnetograph studies of
the evolution of weak solar magnetic fields notes that the general
weak network fields are the remnants of ephemeral regions which also
play a role in the field diffusion as proposed by Marsh (1978). The
intranetwork elements show a shorter lifetime and much more rapid motion
than the network elements. They are in some cases noted to stream
into existing network elements and may merge to form new elements,
but need also show no preferential motion to the network edges. There
seem to be fewer ephemeral regions in magnetically active areas.
Title: A Frequency Angle Interferometer for Solar Microwave
Spectroscopy
Authors: Hurford, G. J.; Read, R. B.; Zirin, H.
Bibcode: 1984SoPh...94..413H
Altcode:
A high-resolution microwave spectrometer has been developed by
converting the Owens Valley solar interferometer to frequency-agile
operation. The system uses 27 m antennas equipped with phase-locked
receivers which can change their observing frequency in 25 or 50
ms. Microwave spectra between 1 and 18 GHz are obtained in a few
seconds by successive observations at up to 86 discrete frequencies. At
each frequency the data are equivalent to the total power from each
antenna and the interferometric amplitude and phase. All data are
fully calibrated with respect to cosmic sources.
Title: Evidence for magnetic field rearrangement in a solar flare
Authors: Zirin, H.
Bibcode: 1984ApJ...281..884Z
Altcode:
The author presents an example of the change in transverse magnetic
field in the course of a solar flare. A filament consisting of sheared
field lines along an inversion line of longitudinal field is replaced
by a set of much shorter field transition arches across the inversion
line. The eruption itself results from the invasion of the area by
fields associated with a moving sunspot.
Title: New Techniques for Global Activity Monitoring
Authors: Zirin, H.
Bibcode: 1984NASCP2310..301Z
Altcode: 1984siva.work..301Z
No abstract at ADS
Title: Persistent 1.5 s oscillations superimposed to a solar burst
observed at two mm-wavelengths
Authors: Zodi, A. M.; Kaufmann, P.; Zirin, H.
Bibcode: 1984SoPh...92..283Z
Altcode:
Long-enduring quasi-periodic oscilations (1.5s) superimposed upon a
solar burst have for the first time been observed simultaneously at
two different mm-wavelengths (22 GHz and 44 GHz). The oscillations
were present throughout the burst duration (about 10 min), and were
delayed at 44 GHz with respect to 22 GHz by 0.3 s. The relative
amplitude of the oscillation was of about 20% at 44 GHz and of about
5% at 22 GHz. Interferometer measurements at 10.6 GHz indicated the
burst source position stable within 1 arc sec. An He I D3
line flare showed two persistent small spots separated by about 10 arc
sec. The 22/44 GHz burst position corresponds well with the location
of the He I D3 spots. The oscillations display features
which distinguish them from ultrafast time structures found in other
bursts. One possible interpretation is a modulation of the synchrotron
emission of trapped electrons by a variable magnetic field on a double
burst source, optically thin at 44 GHz and with optical thickness ≳
0.3 at 22 GHz.
Title: Rotation in Prominences
Authors: Liggett, M.; Zirin, H.
Bibcode: 1984SoPh...91..259L
Altcode:
We have studied rotation in non-eruptive limb prominences; in most cases
dopplergrams could be used to confirm proper motion measurements. In
some cases part of the prominence rotates; in the others, the entire
body is in rotation. Velocities of 15-75 km s-1 are found. Of
fifty-one prominences studied in 1978, five showed rotation.
Title: Balmer Spectra of Flares on YZ CMi
Authors: Zarro, D. M.; Zirin, H.
Bibcode: 1984BAAS...16..508Z
Altcode:
No abstract at ADS
Title: Does New Magnetic Flux Preferentially Energe in Old Active
Regions?
Authors: Zirin, H.; Liggett, M. A.
Bibcode: 1984BAAS...16..534Z
Altcode:
No abstract at ADS
Title: Ionised Helium Emission in Solar Flares
Authors: Zirin, H.; Hirayama, T.
Bibcode: 1984BAAS...16..545Z
Altcode:
No abstract at ADS
Title: Observation of the impulsive phase of a simple flare.
Authors: Tandberg-Hanssen, E.; Kaufmann, P.; Reichmann, E. J.; Teuber,
D. L.; Moore, R. L.; Orwig, L. E.; Zirin, H.
Bibcode: 1984SoPh...90...41T
Altcode: 1984SoPh...90...41B; 1984SoPh...90...41H
We present a broad range of complementary observations of the onset
and impulsive phase of a fairly large (1B, M1.2) but simple two-ribbon
flare. The observations consist of hard X-ray flux measured by the
SMM HXRBS, high-sensitivity measurements of microwave flux at 22 GHz
from Itapetinga Radio Observatory, sequences of spectroheliograms in
UV emission lines from Ov (T ≈ 2 × 105 K) and FeXXI (T
≈ 1 × 107 K) from the SMM UVSP, Hα and HeI D3
cine-filtergrams from Big Bear Solar Observatory, and a magnetogram of
the flare region from the MSFC Solar Observatory. From these data we
conclude: The overall magnetic field configuration in which the flare
occurred was a fairly simple, closed arch containing nonpotential
substructure.
Title: The 1981 July 26-27 flares - Magnetic developments leading
to and following flares
Authors: Zirin, H.
Bibcode: 1983ApJ...274..900Z
Altcode:
The present investigation is concerned with an approach which makes
it possible to determine the key factors in flare production on the
basis of a broad range of observations. The considered observations
are related to a study of at least 10 flares in Hale region 17760
between 17:00 UT 1981 July 26 and 18:00 UT 1981 July 27. Attention
is given to the optical data and phenomenology of the flares. On the
basis of the presented data, it is concluded that flares recurred
in a number of areas in the region, each of which was marked by flux
emergence. In each area, flaring ceased after flux emergence and spot
motion ceased. Flares occur at points where the magnetic field is
stressed by changes associated with sunspot evolution, normally flux
emergence. Homologous flares in H-alpha reflect the general magnetic
layout of the local area in which they occur.
Title: He D3 as a diagnostic for the hard and soft X-rays from
solar flares
Authors: Feldman, U.; Liggett, M.; Zirin, H.
Bibcode: 1983ApJ...271..832F
Altcode:
The time comparison of He D3 and X-ray emission has been studied
in a number of medium-sized flares. In most cases there is a good
agreement between the time histories of the He D3 emission and the
high-temperature (about 2 keV) thermal source. The most intense He D3
emission comes from two small regions on either side of the neutral
line, which are identified with the footpoints of magnetic structures
in which a hot (2.3 x 10 to the 7th K) thermal plasma is formed. The
impulsive X-ray event is marked by the transient brightening of a
number of (usually weaker) He D3 sources. The two types of sources are
well displaced from each other, which is an indication that they are
produced in two different volumes. In some cases a long-lived third
He D3 source is seen.
Title: SOT - A new look at the sun
Authors: Zirin, H.
Bibcode: 1983AsAer..21...66Z
Altcode:
Design and performance features of the solar optical telescope (SOT)
scheduled for Shuttle launch in 1989-90 are described. the SOT will
be a 1.3 m device, capable of revealing surface features 70 km in
diameter and making observations in the UV to reveal phenomena in the
chromosphere. A final focal ratio of f/25 will result in an image that
is 20 times hotter than the actual solar radiation. The SOT design
includes active alignment, focus, and pointing systems to initiate
adjustments in the primary and secondary mirrors by means of return
signals from diodes and retroreflectors. The Shuttle will carry the
instrument into orbit several times over an 18 mo period. Approximately
50,000 photographs will be taken of the sun during a 7-day mission,
and filter graph spectrography will also be performed.
Title: The Optical Flare
Authors: Zirin, H.
Bibcode: 1983SoPh...86..173Z
Altcode:
Optical observationd now present considerable information on the flare
process. It is always associated with filaments and with simplification
of existing magnetic connections, and it arises from the emergence
and expansion of new flux.
Title: Persistent 1.5s oscillations superimposed at a solar burst
observed at two mm-wavelengths
Authors: Zodi, A. M.; Kaufmann, P.; Zirin, H.
Bibcode: 1983STIN...8327948Z
Altcode:
Long-enduring quasi-periodic oscillations (1.5s) superimposed to a
solar burst were observed simultaneously at two different mm-wavelengths
(22 GHz and 44 GHz). The oscillations were present throughout the burst
duration (about 10 min), and were delayed at 44 GHz with respect to 22
GHz by 0.3s. The relatives amplitude of the oscillation was of about
20 percent at 44 GHz and of about 5 percent at 22 GHz. Interferometer
measurements at 10.6 GHz indicated the burst source stable within 1
arcsec. HeD3 line flare indicated two persistent small spots separated
by about 10 arcsec. The 22/44 GHz burst position has good correspondence
with the HeD3 spots' location. The oscillations displays features
which appear to distinguish them from ultrafast time structures found
in other bursts. One possible interpretation was suggested by assuming
a modulation of the gyrosynchrotron emission of trapped electrons by
a variable magnetic field on a double burst source, optically thin at
44 GHz and with optical thickness or approximately 0.3 at 22 GHz.
Title: Microwave and hard X-ray imaging of a solar flare on 1980
November 5
Authors: Hoyng, P.; Marsh, K. A.; Zirin, H.; Dennis, B. R.
Bibcode: 1983ApJ...268..865H
Altcode:
VLA and SMM hard X ray data on the solar flares of November 5, 1980 are
analyzed and compared with data from other sources. The VLA provided
measurements at 15 GHz at 10 sec intervals, using left and right
circular polarizations with a 0.6 arcsec resolution. The hard X ray
imaging spectrometer on the SMM obtained data in six bands from 3.5-30
keV, with 8 x 8 arcsec resolution and 1.5 sec separation. The data were
examined for a possible nonthermal source for the microwave component
of the emissions detected, the origin of 16-30 keV excess fluxes,
the relation between the X ray and microwave sources, the magnetic
connection between observed loops, and the physical characteristics
of the radiating loop. The data were consistent with a model that
assumes fast electrons are accelerated to a single power-law energy
distribution and freely stream along the magnetic field. The data also
agreed with a thick-target model for solar flare X ray emission.
Title: Naked Sunspots
Authors: Liggett, M.; Zirin, H.
Bibcode: 1983SoPh...84....3L
Altcode:
Naked sunspots are spots seen in Hα to be devoid of associated
plage. In magnetograms and K-line little if any opposite polarity field
is found, and in soft X-ray images a blank appears in the region of the
spot. In almost all cases studied in which naked spots resulted the
spot groups had emerged in unipolar regions of the same polarity as
the naked spot. At least half of the naked spots are associated with
coronal holes. The naked spots are long-lived and show rotation rates
close to the Newton-Nunn curve. Most of the naked spots had bright
rims in Hα, and the one spot observed to disappear left no trace in
the background magnetic field. These spots may be a means by which
separation of p from f magnetic polarity occurs.
Title: Photospheric, Chromospheric and Transition-Region Flows in
AR 2517
Authors: Athay, R. G.; Jones, H. P.; Zirin, H.
Bibcode: 1983BAAS...15Q.719A
Altcode:
No abstract at ADS
Title: The Impulsive Phase of a Simple Flare
Authors: Moore, R. L.; Tandberg-Hanssen, E.; Reichmann, E. J.; Teuber,
D. L.; Kaufmann, P.; Orwig, L. E.; Zirin, H.
Bibcode: 1983BAAS...15..697M
Altcode:
No abstract at ADS
Title: High-Resolution Film Photography From SOT: Science with the
Photometric Filtergraph
Authors: Zirin, H.
Bibcode: 1983BAAS...15..709Z
Altcode:
No abstract at ADS
Title: The June 6, 1982 Flare
Authors: Tanaka, K.; Zirin, H.
Bibcode: 1983BAAS...15..712T
Altcode:
No abstract at ADS
Title: Analysis of flares observed during the solar maximum year
Authors: Zirin, H.; Martin, S. F.; Walton, S. R.
Bibcode: 1982cait.rept.....Z
Altcode:
This report encompasses three major projects: (1) Qualitative
characterization of the H-alpha profiles of the flare of 5 November
1980 at 2233 UT; (2) Construction of a film projector/digitizer for
the purpose of projecting half-frame 35mm images onto a television
camera detector; (3) Images of solar plages near the limb in broadband
continuum, and analysis thereof. These projects are described in the
respective three sections of this report.
Title: Lambda 10830 He I observations of 455 stars.
Authors: Zirin, H.
Bibcode: 1982ApJ...260..655Z
Altcode:
A comparison with K line, X-ray and other data, of 10830 A equivalent
widths (EW) measurements in 890 image tube spectra of 455 stars
shows that for the case of G stars, the EW correlates well with K
line intensity. Good correlation is also found between 10830 A EW and
soft X-ray fluxes, confirming the excitation of the line by coronal
soft X-rays, which can serve as a measure of coronal emission. It
is also found that, in contradiction to published models, 10830
A is weak or absent in O, B and A stars, and is absent in F and M
supergiants. Moderate to high 10830 A EW is frequent in F and M dwarfs,
G and K supergiants, and class K3 III. The 58 stars whose 10830 A EW
was found to be of 300 A or more should be relatively intense X-ray
emitters. Almost all RS CVn stars show strong 10830 A absorption,
and T Tauri stars show both absorption and emission.
Title: Gamma-ray and optical observations of the 1979 November 8
solar flare
Authors: Riegler, G. R.; Ling, J. C.; Mahoney, W. A.; Wheaton, W. A.;
Willett, J. B.; Jacobson, A. S.; Prince, T. A.; Zirin, H.
Bibcode: 1982ApJ...259..392R
Altcode:
The solar flare on 1979 November 8 11h 21m 28s UT was observed by
the Tel Aviv telescope of the Big Bear Solar Observatory and the
High Resolution Gamma-Ray Spectrometer on the High Energy Astronomy
Observatory HEAO 3. Photographs in alpha hydrogen show the development
of the flare and a subsequent Moreton wave. Although the flare was
not detected with the high spectral resolution germanium detectors,
the HEAO C-1 CsI shield detected a statistically significant signal
above 80 keV, from 420 to 585 keV, and above 3.8 MeV. The temporal
structure of microwave, optical, X-ray, and gamma-ray emission is
consistent to within about 1 s with a simultaneous flare response at all
energies. There is no evidence for either second-stage acceleration of
charged particles (Bai and Ramaty, 1979) or a delay between gamma-ray
and X-ray continuum emission due to energy-dependent electron energy
loss times (Bai and Ramaty).
Title: The variable HE 10830 angstrom line of Algol.
Authors: Zirin, H.; Liggett, M. A.
Bibcode: 1982ApJ...259..719Z
Altcode:
Spectra of several eclipses of Algol in the range 10500-11000 A where
the line contribution of Algol B is important, are presented. Strong
unshifted 10830 (2000 mA) absorption peaks at primary minimum but
disappears between phases 0.3 and 0.7. At minimum the line must
primarily arise in Algol B, but the presence of 10830 absorption just
outside eclipse, when the contribution to the total light of Algol
B is small, must be due to excitation of He in the atmosphere of the
primary by X-ray irradiation from Algol B, a known X-ray source. A Si
I line from Algol B is also detected, and the Pa-gamma line sometimes
peaks during eclipse. Even if some of the 10830 absorption comes from
Algol A, Algol B still has the strongest 10830 (3000 mA) yet measured
in any star.
Title: The Hα / H-Beta Ratio in Solar Flares
Authors: Zirin, H.; Liggett, M.; Patterson, A.
Bibcode: 1982SoPh...76..387Z
Altcode:
We have measured the ratio of Hα to Hβ central intensities in the
peak kernels of 14 flares, using simultaneous filtergrams. The ratio
is typically one with some scatter. By contrast, in stellar flares
the ratio is about 0.8.
Title: Interferometric observations of solar flare precursors at
10.6 GHz
Authors: Hurford, G. J.; Zirin, H.
Bibcode: 1982cait.rept.....H
Altcode:
The purpose of this study was to examine a data base of interferometric
solar microwave data in order to identify, evaluate and interpret
preflare microwave signatures, with reference to their possible role
for the short-term prediction of solar flares. The data base used was
acquired by the Owens Valley solar interferometer at 10.6 GHz between
February 19, 1980 and March 31, 1981. Twenty-seven major flares which
occurred between February 19 and August 31, 1980 and for which good
quality interferometric data were available, were selected using
optical, soft X-ray OR microwave flux criteria. These events were
analysed in detail; very similar preflare signatures noted in four
(15%) of the cases. Other unusual preflare behavior was noted in four
additional cases. The most common signature was a step-like increase
in signal amplitude, accompanied by a decrease or reversal in the
degree of polarization. Physically, this precursive signature may be
identified with the onset phase of solar flares, when slow heating in
the metastable magnetic loops destabilize the system, leading to rapid
energy release in the impulsive phase. The reason for the distinctive
polarization signature is not understood at present, but may be related
to the site of the heating within the magnetic loops.
Title: Properties of solar flare electrons, deduced from hard X-ray
and spatially resolved microwave observations
Authors: Marsh, K. A.; Hurford, G. J.; Zirin, H.; Dulk, G. A.; Dennis,
B. R.; Frost, K. J.; Orwig, L. E.
Bibcode: 1981ApJ...251..797M
Altcode:
An important question concerning an understanding of impulsive solar
flares is related to the energetic electrons responsible for the
microwave and the hard X-ray emission. A description is presented of
an investigation in which spatially resolved microwave observations
of an impulsive flare and hard X-ray data from the Solar Maximum
Mission (SMM) are used to test the hypothesis that the two types of
emission come from the same basic electron population. The considered
observations are found to imply that the microwaves and hard X-rays
were not produced by a common population of electrons with either a
Maxwellian or single power-law energy distribution. It is suggested
that the calculations should be repeated when observations of stronger
events become available, for which a better determination of the X-ray
spectrum is possible. The possibility is considered that microwaves
and moderately hard X-rays come from spatially different regions.
Title: Magnetic transients in flares
Authors: Zirin, H.; Tanaka, K.
Bibcode: 1981ApJ...250..791Z
Altcode:
Data are presented on magnetic transients (mgtr's) observed in flares on
July 1 and 5, 1980, with Big Bear videomagnetograph. The event of July
1 was a white light flare in which a strong bipolar mgtr was observed
and a definite change in the sunspots occurred at the time of the
flare. In the flare of July 5, a mgtr was observed in only one polarity,
and although no sunspot changes occurred simultaneous with the flare,
significant spot changes occurred in a period of hours. Suggestions
are made as to what might be occurring in the magnetic field. It is
explained why the mgtr cannot be ascribed to time variation or to
emission in the lambda 5324. Attention is also given to the remarkable
penumbral structure associated with the July 5 flare.
Title: Continuum emission in the 1980 July 1 solar flare
Authors: Zirin, H.; Neidig, D. F.
Bibcode: 1981ApJ...248L..45Z
Altcode:
Comparison of continuum measurements of the July 1, 1980 flare at Big
Bear Solar Observatory and Sacramento Peak Observatory show strong
blue emission kernels with the ratio of Balmer continuum (Bac):3862 A
continuum:continuum above 4275 A to be about 10:5:1. The blue continuum
at 3862 A is too strong to be explained by unresolved lines. The
Bac intensity was 2.5 times the photosphere and the strongest 3826 A
continuum was 2 times the photosphere. The brightest continuum kernel
occurred late in the flare, after the hard X-ray peak and related in
time to an isolated peak in the 2.2 MeV line, suggesting that that
continuum was excited by protons above 20 MeV.
Title: On the relationship between soft X-rays and H-alpha-emitting
structures during a solar flare
Authors: Zirin, H.; Feldman, U.; Doschek, G. A.; Kane, S.
Bibcode: 1981ApJ...246..321Z
Altcode:
Based on data obtained during a solar flare on March 31, 1979, soft
X-ray (SXR) and hard X-ray (HXR) bursts are analyzed and compared with
other available data in order to identify structures in H-alpha that
may correspond to the SXR-emitting site. Measurements taken with the
X-ray telescope and the XUV spectroheliograph flown on Skylab, have
shown that the SXR emission from many flares comes from rather small
structures of about 10-20 arcsec across. These structures appear to
be loops that cross the magnetic neutral line. Understanding of the
morphology of SXR was based on data of the solar flare of June 15, 1973,
observed from Skylab, and the work of Moore et al., (1980). Dense,
highly emissive coronal structures, not suggested to be the X-ray
source, were forming, lost energy rapidly by emission and conduction,
and finally formed the loops. It is concluded that bright H-alpha
loops form rapidly as the SXR emission rises, and the overall decay
(cooling rate) of SXR emission is much slower than the formation time
of individual loops.
Title: Near Infrared Spectra of Algol B
Authors: Zirin, H.
Bibcode: 1981BAAS...13..804Z
Altcode:
No abstract at ADS
Title: Can Magnetic Transients be Explained by Line Emission?
Authors: Patterson, A.; Zirin, H.
Bibcode: 1981BAAS...13..820P
Altcode:
No abstract at ADS
Title: The Relationship Between the Microwave and Hard X-Ray Sources
in a Solar Flare
Authors: Marsh, K. A.; Zirin, H.; Hoyng, P.; Dennis, B. R.
Bibcode: 1981BAAS...13..889M
Altcode:
No abstract at ADS
Title: High Spectral Resolution Observations of Solar Microwave
Emission
Authors: Hurford, G. J.; Marsh, K. A.; Zirin, H.
Bibcode: 1981BAAS...13..553H
Altcode:
No abstract at ADS
Title: Can magnetic transients be explained by line emission?
Authors: Patterson, A.; Zirin, H.
Bibcode: 1981BAAS...13..821P
Altcode:
No abstract at ADS
Title: Microwave Observations of the Solar Atmosphere
Authors: Zirin, H.
Bibcode: 1981BAAS...13..559Z
Altcode:
No abstract at ADS
Title: Solar limb brightening at 1.3 millimeters
Authors: Horne, K.; Hurford, G. J.; Zirin, H.; de Graauw, T.
Bibcode: 1981ApJ...244..340H
Altcode:
Radial scans across the solar disk with the 29 arcsec half-power beam
width of the Owens Valley Radio Observatory 10-m telescope provide
evidence for 10 + or - 5% limb brightening in the mean quiet sun
at 1.3 mm. This result is consistent with a spherically symmetric
chromosphere. The solar radius at 1.3 mm was 8.6 + or - 1 arcsec larger
than the optical radius, which is consistent with the expected effect
of a forest of optically thick spicules viewed at the extreme limb.
Title: Transient magnetic field changes in flares
Authors: Patterson, A.; Zirin, H.
Bibcode: 1981ApJ...243L..99P
Altcode:
Magnetic changes have been detected with the videomagnetograph (VMG)
at Big Bear during two large flares in 1979 November 5. Two kinds of
changes were detected in both flares: a decrease in satellite field
strength near the locus of the flare and the appearance of strong
transient fields during the peak of the flare. We explain why we
believe that the observed effects are real and not instrumental and
discuss their significance for flare studies.
Title: High resolution interferometric observations of the solar
limb at 4.9 and 10.7 GHz during the solar eclipse of October, 1977
Authors: Marsh, K. A.; Hurford, G. J.; Zirin, H.
Bibcode: 1981A&A....94...67M
Altcode:
The radial intensity profile of the quiet solar limb has been measured
at high spatial resolution using the VLA at 4.9 GHz and the Owens
Valley solar interferometer at 10.7 GHz during the partial solar
eclipse of October 12, 1977. The spatial resolution (13.8 arcsec at
4.9 GHz and 7.4 arcsec at 10.7 GHz) was provided primarily by the
lunar limb. Substantial limb brightening at 4.9 GHz was found with
a peak brightness temperature corresponding to an 80% increase over
the disk value, and a possible small limb enhancement at 10.7 GHz. The
results are consistent with a simple model consisting of a uniform disk
(provided by a thoroughly roughened transition zone) overlaid by a
corona in hydrostatic equilibrium with a density of 5 x 10 to the 8th
at its base. The lack of the secant-like variation in the microwave
intensity from center to limb is explained by a corona contained in
loop structures rather than in spherically symmetric layers.
Title: Coronal Loops and Active Region Structure
Authors: Webb, D. F.; Zirin, H.
Bibcode: 1981SoPh...69...99W
Altcode:
We intercompared synoptic Hα, Ca K, magnetograph and Skylab soft
X-ray and EUV data for the purpose of identifying the basic coronal
magnetic structure of loops in a `typical' active region and studying
its evolution. We focussed on a complex of activity in July 1973,
especially McMath 12417. Our principal results are: (1) Most of the
brightest loops connected the bright f plage to either the sunspot
penumbra or to p satellite spots; no non-flaring X-ray loops end in
umbrae; (2) short, bright loops had one or both ends in regions of
emergent flux, strong fields or high field gradients; (3) stable,
strongly sheared loop arcades formed over filaments; (4) EFRs were
always associated with compact X-ray arcades; and (5) loops connecting
to other active regions had their bases in outlying plage of weak
field strength in McM 417 where Hα fibrils marked the direction of
the loops. We conclude that a typical loop brightens in response to
magnetic field activity at its feet, which heats the plasma. This
suggests that the loop acts as a trap for gas convected from its base.
Title: VLA observations of impulsive solar flares at 4.9 GHz
Authors: Marsh, K. A.; Hurford, G. J.; Zirin, H.; Hjellming, R. M.
Bibcode: 1980ApJ...242..352M
Altcode:
A series of snapshot synthesis maps constructed as a function of time
provided a complete mapping of source structure in one dimension and
absolute location in two dimensions of five impulsive solar microwave
bursts observed during July 15-18, 1978. It was found that all five
flares were dominated by a single 12-18 arcsec source located between
the H-alpha kernels, near the magnetic neutral line. Spectral data
from Sagamore Hill (1.4-35 GHz) show that the spectral turnover at low
frequencies results from the absorption by the ambient active region;
these results, together with the observed magnetic configuration,
suggest a model which could explain the evolution in source structure
at 4.9 GHz in terms of magnetic reconnection which starts below the
optical depth of the ambient active region equal to 1.
Title: Microwave Movie of a Solar Flare
Authors: Marsh, K. A.; Hurford, G. J.; Zirin, H.; Dulk, G. A.
Bibcode: 1980BAAS...12..794M
Altcode:
No abstract at ADS
Title: Magnetic Transients in Solar Flares
Authors: Zirin, H.
Bibcode: 1980BAAS...12..907Z
Altcode:
No abstract at ADS
Title: Spectra and Polarization of the Spatial Structure of Impulsive
Solar Microwave Bursts
Authors: Hurford, G. J.; Marsh, K. A.; Zirin, H.; Dulk, G. A.; Dennis,
B. R.; Frost, K. J.; Orwig, L. E.
Bibcode: 1980BAAS...12..892H
Altcode:
No abstract at ADS
Title: Microwave Movie of a Solar Flare
Authors: Marsh, K. A.; Hurford, G. J.; Zirin, H.; Dulk, G. A.
Bibcode: 1980BAAS...12..892M
Altcode:
No abstract at ADS
Title: A Continuum Bright Point at the Penumbral Edge
Authors: Zirin, H.; Moore, R. L.
Bibcode: 1980SoPh...67...79Z
Altcode:
A small continuum bright point, observed at the outer edge of the
penumbra of a small spot in a large complex spot group, is related to
an occurrence beneath the Sun's surface. The characteristics of the
point appear to be unique, and the name `penumbra-periphery bright
point' is proposed.
Title: Multichannel spectrophotometry of stellar flares.
Authors: Mochnacki, S. W.; Zirin, H.
Bibcode: 1980ApJ...239L..27M
Altcode:
Stellar flares have been observed using the 32 channel spectrophotometer
on the 5 m telescope. Net flare fluxes in the region 3200-7000 A
are presented. A simple model of blackbody radiation and hydrogen
recombination emission appears to fit the continuum points well. Owing
to vignetting problems, only the region between 4200 and 7000 A was
used for a detailed fit to the Planck function to obtain apparent
temperatures and effective areas. The rise of each flare was associated
with an increase of the area, while the initial steep decline of
the light was associated with a similar decrease of the blackbody
temperature. The maximum temperatures, coincident with maximum light,
were 7500-9500 K, similar to values for solar flares. The hydrogen
line emission rose simultaneously with the continuum but declined more
slowly. The ratio of Hgamma to Halpha was about
1.5 at the peak, declining to about 1.0 after the peak.
Title: Observations of Transient Magnetic Fields in Two Solar Flares
Authors: Zirin, H.; Patterson, A.
Bibcode: 1980BAAS...12..515Z
Altcode:
No abstract at ADS
Title: Microwave Images of Solar Bursts with Arcsecond Resolution
Authors: Hurford, G. J.; Marsh, K. A.; Zirin, H.
Bibcode: 1980BAAS...12..478H
Altcode:
No abstract at ADS
Title: VLA observations of spatial structure in the quiet sun at 6
centimeters, during the 1977 October eclipse
Authors: Marsh, K. A.; Hurford, G. J.; Zirin, H.
Bibcode: 1980ApJ...236.1017M
Altcode:
Observations of a quiet region on the solar disk were made during
the partial solar eclipse of 1977 October 12, using the VLA at
4.9 GHz. Data from 21 baselines were used to make a series of
one-dimensional synthesis maps as the Moon de-occulted the field
of view. Taking successive differences of the one-dimensional maps
and applying a coordinate transformation yielded a two-dimensional
map in which the basic resolution was 2".5 × 12".7. The map showed
that the small-scale structure of the region was dominated by a small
number of compact sources, whose mean angular size and peak brightness
temperature were in the range 9"-25" and (6-8) × 104 K,
respectively. Although comparison with high-resolution Hα photographs
showed no clear correlation with the chromospheric network, at least
three of six source positions were consistent with the locations of
small bipolar regions. This raises the possibility that the radio
sources are associated with X-ray bright points. Theoretical
considerations based on published EUV data show that the observed
microwave structure cannot be explained by the normal chromospheric
network. The available soft X-ray and EUV data are consistent, however,
with the hypothesis that the microwave sources represent X-ray bright
points.
Title: Multifrequency Observations of a Solar Flare at up to 0.2"
Spatial Resolution
Authors: Marsh, K. A.; Zirin, H.; Hurford, G. J.
Bibcode: 1980BAAS...12..478M
Altcode:
No abstract at ADS
Title: Three flares with blue continuum, one with a D3 preflare shell
Authors: Zirin, H.
Bibcode: 1980ApJ...235..618Z
Altcode:
Three flares with short-lived flashes observed with a 65 A wide filter
centered on 3835 A are discussed. Observations at other wavelengths
indicated it is a 'blue continuum'; the flashes occur in pairs at
the ends of flux loops and result from the precipitation of energetic
particles. A shell of D3 absorption was observed in one of the flares,
considered to be a compressed sheet of dense, hot material that limits
the flare until it breaks out as a surge. It is concluded that the
blue continuum may be the same as that seen in flare stars.
Title: Interferometric Observations of the Extreme Solar Limb at
2.8 and 6 cm during the October 1977 Eclipse
Authors: Hurford, G. J.; Marsh, K. A.; Zirin, H.
Bibcode: 1980IAUS...86...61H
Altcode:
No abstract at ADS
Title: Primary energy release
Authors: Kahler, S.; Spicer, D.; Uchida, Y.; Zirin, H.
Bibcode: 1980sfsl.work...83K
Altcode: 1980sofl.symp...83K
The physical processes by which the magnetic energy of a solar active
region is converted to other forms of energy in the appearance
of a solar flare are discussed. Observations of the secondary
manifestations of flare energy release, such as thermal plasmas and
energetic particle emissions, are presented, with particular attention
given to the temporal variations of flare radiation, the various
forms of energy release, flare energy density, flare locations and
sizes, energy distributions and H alpha, hard X-ray and microwave
burst events. Current models of the primary energy release process
are surveyed, and the models of Spicer (1976, 1977), which explains
rapid flare energy release in terms of multiple tearing modes causing
reconnection in sheared magnetic fields, and Uchida and Sakurai
(1976, 1978), which attributes primary energy release to dynamic
collapse caused by the interchange instability of the neutral sheet,
are examined in detail.
Title: The spatial structure of solar microwave bursts
Authors: Marsh, K. A.; Hurford, G. J.; Zirin, H.
Bibcode: 1980IAUS...86..191M
Altcode:
Observations of five impulsive microwave bursts were made during
July 15-18, 1978 using the VLA at 4.9 GHz with temporal and
spatial resolutions of 10 s and up to 1 s respectively. A series of
2-dimensional snapshot synthesis maps was made as a function of time,
and compared with H alpha photographs and magnetograms. Each flare
was characterized by a single source of constant size, located on the
magnetic neutral line between the H alpha kernels.
Title: Solar Structure at 1.3 mm
Authors: Horne, K.; Hurford, G. J.; Zirin, H.; de Graauw, T.
Bibcode: 1979BAAS...11..710H
Altcode:
No abstract at ADS
Title: Interferometric Observations of Subsecond Spikes in a Solar
Microwave Burst
Authors: Hurford, G. J.; Marsh, K. A.; Zirin, H.; Kaufmann, P.
Bibcode: 1979BAAS...11..678H
Altcode:
No abstract at ADS
Title: 32-Channel Spectrophotometry of Stellar Flares
Authors: Mochnacki, S.; Zirin, H.
Bibcode: 1979BAAS...11..629M
Altcode:
No abstract at ADS
Title: Physical Processes of Active Region Coronal Loops
Authors: Webb, D. F.; Zirin, H.
Bibcode: 1979BAAS...11R.410W
Altcode:
No abstract at ADS
Title: VLA observations of solar flares, interpreted with optical,
X-ray, and other microwave data.
Authors: Marsh, K. A.; Hurford, G. J.; Zirin, H.
Bibcode: 1979ApJ...228..610M
Altcode:
Three small solar flares were observed from the active region McMath
14979 during 1655- 1725 UT on 1977 October 12, using the southwest arm
of the Very Large Array (VLA) at 4.9 0Hz. These observations showed
the presence of two distinct flare components: (1) A dominant broad
component of size 10", with gradual rise-and-fall behavior and circular
polarization, and (2) small impulsive components of size 2"-4", 53 987o
circularly polarized. Simultaneous interferometric observations of the
1703 UT flare with the Owens Valley solar interferometer at 10.7 0Hz,
together with the VLA data, fixed the location of the broad component
in two dimensions. Comparison with Ha photographs and magnetograms
showed that this component was located in the magnetic arch at
whose footpoints the Ha flare occurred. The electron temperature and
emission measure implied by OSO8 soft X-ray observations yielded a
corresponding free-free microwave flux which entirely accounted for
the observed emission at 10.7 0Hz. The microwave spectrum at lower
frequencies (2.7 0Hz and 4.9 0Hz) was then consistent with thermal
gyroresonance radiation in a magnetic field of 300 gauss. The radio,
optical, and X-ray observations thereby suggest that the broad microwave
component was a thermal cloud trapped in a magnetic arch. The impulsive
events probably occurred at the positive-polarity footpoints of this
arch. Subject headings: Sun: flares - Sun: radio radiation - Sun: X-rays
Title: The Ecology of Prominences.
Authors: Zirin, H.
Bibcode: 1979phsp.coll..193Z
Altcode: 1979phsp.conf..193Z; 1979IAUCo..44..193Z
The paper discusses the roles of prominences in the solar
scheme. Attention is given to classifications and the ways in which
prominences exist: hydrostatic support, ballistic support, and magnetic
support. In the case of ballistic support, surges are differentiated
from sprays which involve the ejection of material that is already above
the solar surface. Discussion also covers filimets and fibrils and
the conditions for their appearance. It is proposed that most flares
originate in prominence instabilities. In addition supergranulation
is covered, noting the network is not seen on the boundary of unipolar
regions. It is concluded that prominences play a critical role in flares
and field reconnection, and the evolution of solar magnetic fields.
Title: Binary Stars - Stellar Coronae - Red Giants in Old Disk
Clusters - Lower Main Sequence - Degenerate Stars - Rotating Magnetic
White Dwarf
Authors: Mochnacki, S.; Whelan, J.; Berriman, G.; Zirin, H.; Cottrell,
P.; Da Costa, G.; Ake, T.; Schommer, R.; Greenstein, J.; Green, R.;
Schmidt, M.; Stockman, H. S.; Angel, R. P.; Liebert, J. W.; Thompson,
I.; Landstreet, J. D.; Beaver, E. A.
Bibcode: 1979haob.rept..727M
Altcode:
No abstract at ADS
Title: Physics of the Sun - Synoptic Observations at MT.WILSON
Rotation of the Sun - Large-Scale Velocity Fields - Active Regions
Regions - Solar Axis Elements - Big Bear Solar Observatory -
Instruments - Blue Continuum in Flares - Thermal X-Ray Plasma in
Solar Flares
Authors: Howard, R.; Goeden, R.; Eaton, S.; Labonte, B.; Patterson,
A.; Zirin, H.; Tanaka, H.; Moore, R.
Bibcode: 1979haob.rept..716H
Altcode:
No abstract at ADS
Title: Discussion
Authors: Brueckner, J.; Hirayama, T.; Maltby, P.; Schmahl, E. J.;
Zirin, H.
Bibcode: 1979phsp.coll..121B
Altcode: 1979IAUCo..44..121B
No abstract at ADS
Title: Discussion
Authors: Acton, L. W.; Engvold, O.; Heasley, J. N.; Heyvaerts, J.;
Hirayama, T.; Kundu, M. R.; Leroy, J. L.; Malville, J.; Rust, D. M.;
Zirin, H.
Bibcode: 1979phsp.coll...31A
Altcode: 1979IAUCo..44...31A
No abstract at ADS
Title: Discussion
Authors: Acton, L. W.; Engvold, O.; Milkey, R. W.; Orrall, F. Q.;
Zirin, H.
Bibcode: 1979phsp.coll..354A
Altcode: 1979IAUCo..44..354A
No abstract at ADS
Title: Erratum: "The Lalpha /Halpha ratio in solar flares, quasars,
and the chromosphere" [Astrophys. J., Lett., Vol. 222, p. L105 -
L107 (1978)].
Authors: Zirin, H.
Bibcode: 1979ApJ...227L.111Z
Altcode:
No abstract at ADS
Title: Discussion
Authors: Chiuderi-Drago, F.; Kundu, M. R.; Lantos, P.; Zirin, H.
Bibcode: 1979phsp.coll..134C
Altcode: 1979IAUCo..44..134C
No abstract at ADS
Title: Solar optical telescope (SOT).
Authors: Dunn, R. B.; Fisher, R.; Harvey, J.; Lemaire, P.; Milkey,
R.; Smithson, R.; Beckers, J.; Mehltretter, J. P.; Zirin, H.
Bibcode: 1979MmArc.106..135D
Altcode:
No abstract at ADS
Title: Discussion
Authors: Gaizauskas, V.; Heyvaerts, J.; Hirayama, T.; Pneuman, G. W.;
Spicer, D. S.; Withbroe, G. L.; Zirin, H.
Bibcode: 1979phsp.coll..301G
Altcode: 1979IAUCo..44..301G
No abstract at ADS
Title: Discussion
Authors: Engvold, O.; Gaizauskas, Gaizauskas; Rust, D. M.; Sheeley,
N.; Tandberg-Hanssen, E.; Ohman, Y.; Zirin, H.
Bibcode: 1979phsp.coll..207E
Altcode: 1979IAUCo..44..207E
No abstract at ADS
Title: Science opportunities with the SOT.
Authors: Dunn, R. B.; Fisher, R.; Harvey, J.; Lemaire, P.; Milkey,
R.; Smithson, R.; Beckers, J.; Mehltretter, J. P.; Zirin, H.
Bibcode: 1979MmArc.106..245D
Altcode:
No abstract at ADS
Title: Discussion
Authors: Acton, L. W.; Anzer, U.; Engvold, O.; Martin, S. F.; Pneuman,
G. W.; Rust, D. M.; Tandberg-Hanssen, E.; Zirin, H.
Bibcode: 1979phsp.coll..164A
Altcode: 1979IAUCo..44..164A
No abstract at ADS
Title: Discussion
Authors: Anzer, U.; Engvold, O.; Spicer, D. S.; van Tend, W.; Zirin, H.
Bibcode: 1979phsp.coll..331A
Altcode: 1979IAUCo..44..331A
No abstract at ADS
Title: Discussion
Authors: Heyvaerts, J.; Sheridan, K. V.; Zirin, H.
Bibcode: 1979phsp.coll..320H
Altcode: 1979IAUCo..44..320H
No abstract at ADS
Title: The Spatial Structure of Solar Microwave Bursts at High
Resolution
Authors: Marsh, K. A.; Hurford, G. J.; Zirin, H.; Hjellming, R. M.
Bibcode: 1978BAAS...10..672M
Altcode:
No abstract at ADS
Title: The small-scale sources of quiet-Sun centimeter-wave radio
emission.
Authors: Zirin, H.; Hurford, G. J.; Marsh, K. A.
Bibcode: 1978ApJ...224.1043Z
Altcode:
The three-element Owens Valley solar interferometer has been used to
observe quiet-sun structure at 2.8 cm with angular resolutions of 4.6
to 27 arcsec. Results are compared with previous observations at other
centimeter wavelengths in the context of a model based on a random array
of optically thick radiators. This comparison argues against coronal
sources and rules out the possibility of source distributions such as
X-ray bright points and uniquely sized or compact sources. The data
are consistent with the most likely remaining possibility, elements
of the chromospheric network. The more transient nature of the fringes
observed at high resolution can be explained either by a two-component
model which includes large stable sources and small unstable sources
or in terms of the small-scale motions associated with the network.
Title: Optical observations of the sun from a solar probe
Authors: Zirin, H.
Bibcode: 1978clus.nasa...89Z
Altcode:
The spatial resolution of solar surface structure to ultimate limits
with simple instrumentation. The logic is simple: a 10 cm aperture
telescope at 4 solar radii resolves the equivalent of a five meter
telescope in earth orbit. Given the ease of producing a diffraction
limited 10 cm telescope and the difficulty of fabricating a diffraction
limited 5 meter telescope, the performance of the small telescope
could well be better. The telescope described complements planned
solar orbiting telescopes in earth orbit and would need only a few
arcs seconds of pointing.
Title: Studies of solar flares using optical, X-ray and radio data
Authors: Zirin, H.
Bibcode: 1978SoPh...58...95Z
Altcode:
I have studied a number of flares for which good X-ray and optical
data were available. An average lag of 5.5 s between hard X-ray (HXR)
start and Hα start, and HXR peak and Ha peak was found for 41 flares
for which determination was possible. Allowing for time constants the
time lag is zero. The peak Hα lasts until 5-6 keV soft X-ray (SXR)
peak. The level of Hα intensity is determined by the SXR flux.
Title: The Lalpha /Halpha ratio in solar flares, quasars, and the
chromosphere.
Authors: Zirin, H.
Bibcode: 1978ApJ...222L.105Z
Altcode:
The ratio of L-alpha to H-alpha is around unity in flares, quasars,
and the solar chromosphere and prominences. The weakness of L-alpha
is shown to be essentially due to photon trapping and deexcitation,
but it is argued that the surprising stability of this ratio is due to
the role of these lines in cooling the plasma rather than the accidental
parameters used in various models of these widely different phenomena.
Title: VLA Observations of Solar Flares
Authors: Marsh, K. A.; Zirin, H.; Hurford, G. J.
Bibcode: 1978BAAS...10R.454M
Altcode:
No abstract at ADS
Title: Cooperative studies of solar activity and chromospheric
structure
Authors: Zirin, H.
Bibcode: 1976cait.rept.....Z
Altcode:
Observations were carried out and analyzed on the physics of solar
flares, active phenomena in quiet regions: such as ephemeral active
regions, macrospicules and spicules, and Coronal holes and the
chromosphere under coronal holes.
Title: Production of a short-lived filament by a surge.
Authors: Zirin, H.
Bibcode: 1976SoPh...50..399Z
Altcode:
A large surge was observed on September 17, 1971, part of which, after
travelling 200 000 km through the corona, returned to the surface to
form a filament. The filament lasted about 30 min, then rose up and
returned to the source of the surge. We interpret this as the filling
of a semi-stable magnetic trap.
Title: Further observations of the lambda 10830 helium line in stars
and their significance as a measure of stellar activity.
Authors: Zirin, H.
Bibcode: 1976ApJ...208..414Z
Altcode:
Measurements of the 10830-A He line in 198 stars are given along
with data on other features in that spectral range. Nearly 80 per
cent of all G and K stars show some 10830-A absorption or emission;
of these, half are variable and one-quarter show emission. The results
of Vaughan and Zirin (1968) are confirmed that the 10830-A line is not
found in M stars, is weak in F stars, and is particularly strong in
close binaries. The line is found in emission in extremely late M and
S stars along with P-gamma, but the latter is not in emission in the G
and K stars with 10830-A emissions. Variable He emission along with Ti I
emission is found in the RV Tauri variables R Sct and U Mon. In R Aqr,
the Fe XIII coronal line at 10747 A is found in emission along with
a line at 11012 A, which may be singlet He or La II, as well as the
10830-A and P-gamma lines. There is possibly a five-year period in the
appearance of 10830-A emission in theta Her. The nature of coronae or
hot chromospheres in the various stars is extensively discussed without
definite conclusion, except that the 10830-A intensity must be more or
less proportional to the energy deposited in the chromosphere-corona
by nonthermal processes.
Title: Prospectus for the Solar Maximum Year (Invited report)
Authors: Zirin, H.; Tanaka, K.
Bibcode: 1976SoPh...47..385Z
Altcode:
No abstract at ADS
Title: Proceedings of the workshop: the solar constant and the earth's
atmosphere. held at Big Bear Solar Observatory, North Shore Drive,
Big Bear City, Calif., 19 - 21 May 1975.
Authors: Zirin, H.; Moore, R. L.; Walter, J.
Bibcode: 1976SoPh...46..377Z
Altcode:
The paper summarizes the chief points made at an interdisciplinary
workshop on the solar constant and the earth's climate, at which
the main sessions covered the solar background, the climate record
background, solar constant measurements, the effects of solar constant
variations on the atmosphere, and future observational programs. Some
data and graphs are presented showing the principal features of the
earth's climatic history in the past million years, causal factors in
climatic change during the earth's history, the variance spectrum of
climatic change, potential origins of climatic change as a function of
time scale of the change, direct measurements of the solar constant,
relations between the solar constant, the earth's surface temperature,
and the percentage of ice cover for Seller's global-averaged models,
and experiments proposed for the NASA program of measuring the total
and spectral irradiance of the sun from spacecraft.
Title: Production of a short-lived filament by a surge
Authors: Zirin, H.
Bibcode: 1976STIN...7623136Z
Altcode:
A large surge was observed on September 17, 1971 part of which, after
travelling 200,000 km across the surface, returned to the surface to
form a filament. The filament lasted about 30 minutes, then rose up
and returned to the source of the surge. This was interpreted as the
filling of a semi-stable magnetic trap. Analysis of the microwave
radio burst showed it to have been produced by a source optically
thick at 8,800 MHz, with area 4 (arc min)squared and T approximately
275,000 deg, N squaredeV approximately 7 x 10 to the 48th
power. The soft x-ray burst showed a component at 12 x 1,00.000 deg
with N squaredeV approximately 3 x 10 to the 48th power.
Title: Fe XIII line in R Aquarii
Authors: Zirin, H.
Bibcode: 1976Natur.259..466Z
Altcode:
GREGORY and Seaquist1 have detected radio emission from the
interesting object R Aquarii2. In the course of reducing
plates of this star made in 1970 and 1971 in the course of my He
I, λ = 10,830 Å spectral survey, I found the emission line of
the forbidden coronal transition of Fe XIII at λ = 10,747Å. This
line (3P1-3P0) is often
accompanied by the 3P2-3P1
line at λ = 10,798 Å at high densities (Ne >
109). The emission line λ = 10,747 Å is weak, but clearly
seen on two spectra (Fig. 1), with intensity of ~ 100 mA. The spectrum
also shows strong emission lines of He I at 10,830 Å and Pγ as well as
a line at 11,013 Å which may be He I 31S-61P. I
have examined an old plate made by Merrill in 1948 for traces of the
coronal lines at 5,303 Å and 6,374 Å (Fe XIV and Fe X) and found them
absent. G. Wallerstein (personal communication) has kindly examined his
plates from 1970-71 and finds the 6,374-Å line definitely absent. If
the lines are excited by the 2,400-K radiation field of the star, the
6,374-Å and 5,303-Å lines should be much fainter than the 10,747-Å,
because of their higher excitation energy.
Title: Further observations of the lambda 10830 He line in stars
and their significance as a measure of stellar activity
Authors: Zirin, H.
Bibcode: 1975STIN...7614992Z
Altcode:
Measurements of the lambda 1030 He line in 198 stars are given along
with data on other features in that spectral range. Nearly 80% of all
G and K stars show some lambda 10830; of these, half are variable and
1/4 show emission. It was confirmed that lambda 10830 is not found
in M stars, is weak in F stars, and is particularly strong in close
binaries. The line is found in emission in extremely late M and S stars,
along with P gamma, but P gamma is not in emission in G and K stars
with lambda 10830 emissions. Variable He emission and Ti I emission
are found in the RV Tauri variables R Scuti and U Mon. In R Aqr the
Fe XIII coronal line lambda 10747 and a line at lambda 11012 which
may be singlet He or La II are found, as well as lambda 10830 and P
gamma. The nature of coronas or hot chromospheres in the various stars
is discussed. It was concluded that the lambda 10830 intensity must be
more or less proportional to the energy deposited in the chromosphere
corona by non-thermal processes.
Title: Cooperative studies of chromospheric structure and magnetic
fields
Authors: Zirin, H.; Moore, R. L.
Bibcode: 1975cait.rept.....Z
Altcode:
This report concentrates on chromospheric phenomena and their associated
magnetic fields. The following three areas of research are discussed:
(1) Morphology of active regions, i.e. relations between magnetic field
structure and plages, filaments, and flares; (2) Sunspot phenomena,
especially umbral flashes and running penumbral waves; (3) Structure
and dynamics of quiet regions, e.g. chromospheric network, spicules
and oscillations.
Title: The helium chromosphere, coronal holes, and stellar X-rays.
Authors: Zirin, H.
Bibcode: 1975ApJ...199L..63Z
Altcode:
The solar chromosphere at the limb seen in D3 is an irregular bright
band 1000 km thick with a dark band 1000 km thick beneath. The D3
chromosphere disappears in coronal holes. It is shown that the D3
emission, as well as the other He I and He II lines, can be explained
quantitatively by photoionization by coronal back-radiation. A Chapman
layer with N(He)H = 5 times 10 to the 17th power is formed near tau
= 1 in the He I and He II continua. The chromospheric He emission
or absorption is weak in coronal holes because there is no coronal
back-radiation. Based on this model, the soft X-ray flux from stars
with He 10830-A absorption lines is estimated as proportional to the
10830-A equivalent width and the apparent area.
Title: Results of 10830 Observations in 217 Stars.
Authors: Zirin, H.
Bibcode: 1975BAAS....7..470Z
Altcode:
No abstract at ADS
Title: Proceedings of the Workshop: The Solar Constant and the
Earth's Atmosphere
Authors: Zirin, H.; Walter, J.
Bibcode: 1975STIN...7815983Z
Altcode:
A multidisciplinary workshop on the solar constant was held at Big
Bear Solar Observatory in California 19-21 May 1975. The proceedings
covered the following sessions; (1) Solar Background; (2) Climate
Record Background; (3) Measuring the Solar Constant; (4) what happens
to the atmosphere, (5) Summary, and (6) general discussion of Future
Observational Programs. The consensus was that climatic variations
probably were the consequences of solar variation but that current
measurements of the solar constant only reveal that the solar output
does not vary by more than 0.1 to 0.2%. Variations of less than 0.1%
would still be important in causing climatic variation according to
current models.
Title: Sunspot Motion, Flares and Type III Bursts in McMath 11482
Authors: Zirin, H.; Lazareff, B.
Bibcode: 1975SoPh...41..425Z
Altcode:
We have studied a series of flares in McMath 11482, 1972 August 19-22,
with particular reference to the basis for the flares and comparison
with dekameter radio data. We find that the flares were produced by
rapid (∼ 1000 km h−1) westward motion of a large new p
spot. Many flares occur just in front of the spot, and they cease when
the motion stops. All flares occurring in front of the spot produce
type III bursts, while even strong flares elsewhere in the region
produce little or no type III. The time of type III emission agrees
perfectly with the start of the Hα flare. Thus type III bursts are
only produced in favorable configurations.
Title: The D3 Chromosphere, Coronal Holes, and Stellar X-Rays
Authors: Zirin, Harold
Bibcode: 1975BAAS....7..359Z
Altcode:
No abstract at ADS
Title: Development of Activity in McMath 128 and the 24 January
1971 Flare
Authors: Zirin, H.
Bibcode: 1975BBSOP.112....1Z
Altcode:
The development of McMath 11128 is a fascinating example of the role
of magnetic field reconnection and solar activity. When this active
region came over the limb on January 14, it was an ordinary active
region. The sunspots in the leading part, consisting of two p spots
(p1 and p2) and one f spot (f1) remained almost identical for the
entire period. However on January 19 a new sunspot group developed in
the following part of the region and rapidly spread to overtake the
f spot of the first group. In the subsequent reconnection of fields,
a considerable amount of activity took place, finally leading up to
the great flare of the 24th.
Title: The Solar Constant and the Earth's Atmosphere
Authors: Zirin, H.; Walter, J.
Bibcode: 1975scea.conf.....Z
Altcode:
No abstract at ADS
Title: Studies of K Line Filtergrams
Authors: Zirin, H.
Bibcode: 1974SoPh...38...91Z
Altcode:
High resolution filtergrams made with a 0.3 Å K line filter at Big
Bear are discussed. The dark K3 clouds noted in spectra by Bappu and
Sivaraman (1971) are confirmed; they cover about 1/3 of the inside
of supergranule cells, and oscillate (mainly horizontally) with 3-4
min period. Their vertical extent of about 3000 km produces a sharp
broadening of K3 at the extreme limb and obscuration of bright features.
Title: Cinematographic Observations for ATM and their Comparison
with some ATM Results
Authors: Zirin, H.; Holt, J.; Brueckner, G. E.; Bohlin, J. D.; Purcell,
J. D.; Scherrer, V. E.; Sheeley, N. R.; Tousey, R.
Bibcode: 1974BAAS....6R.298Z
Altcode:
No abstract at ADS
Title: Spicules and Fibrils in Hα and K
Authors: Zirin, H.
Bibcode: 1974BAAS....6Q.298Z
Altcode:
No abstract at ADS
Title: The Magnetic Structure of Plages
Authors: Zirin, H.
Bibcode: 1974IAUS...56..161Z
Altcode:
No abstract at ADS
Title: Solar flares
Authors: Zirin, H.
Bibcode: 1974VA.....16....1Z
Altcode:
A review of the knowledge about solar flares which has been
obtained through observations from the earth and from space by
various methods. High-resolution cinematography is best carried out
at H-alpha wavelengths to reveal the structure, time history, and
location of flares. The classification flares in H alpha according to
either physical or morphological criteria is discussed. The study of
flare morphology, which shows where, when, and how flares occur, is
important for evaluating theories of flares. Consideration is given
to studies of flares by optical spectroscopy, radio emissions, and
at X-ray and XUV wavelengths. Research has shown where and possibly
why flares occur, but the physics of the instability involved, of the
particle acceleration, and of the heating are still not understood.
Title: Spicules are Bright and Dark
Authors: Zirin, H.
Bibcode: 1974IAUS...56...49Z
Altcode:
No abstract at ADS
Title: Stellar spectroscopy at 1.1 µ.
Authors: Zirin, H.
Bibcode: 1974sis..conf..357Z
Altcode:
No abstract at ADS
Title: The Flares of August 1972
Authors: Zirin, Harold; Tanaka, Katsuo
Bibcode: 1973SoPh...32..173Z
Altcode:
We present the analysis of observations of the August flares at
Big Bear and Tel Aviv, involving monochromatic movies, magnetograms
and spectra. In each flare the observations fit a model of particle
acceleration in the chromosphere with emission produced by impact and
by heating by the energetic electrons and protons. The region showed
inverted polarity and high gradients from birth, and flares appear
due to strong magnetic shears and gradients across the neutral line
produced by sunspot motions. Post flare loops show a strong change
from sheared, force-free fields parallel to potential-field-like loops,
perpendicular to the neutral line above the surface.
Title: The Flares of August
Authors: Zirin, H.; Tanaka, K.
Bibcode: 1973BAAS....5R.282Z
Altcode:
No abstract at ADS
Title: Interferometry of Solar Radio Sources at 15,000 Wavelengths
Authors: Lang, K. R.; Zirin, H.
Bibcode: 1973BAAS....5Q.275L
Altcode:
No abstract at ADS
Title: Motions and Heating of the August Flares
Authors: Tanaka, K.; Zirin, H.
Bibcode: 1973BAAS....5R.281T
Altcode:
No abstract at ADS
Title: X-ray Observations from the August 2, 1972 Flare
Authors: Datlowe, D. W.; Peterson, L. E.; Tanaka, K.; Zirin, H.
Bibcode: 1973BAAS....5R.270D
Altcode:
No abstract at ADS
Title: Optical Observations of the August 1972 Flares
Authors: Tanaka, Katsuo; Zirin, Harold
Bibcode: 1973NASSP.342...26T
Altcode: 1973heps.conf...26T
No abstract at ADS
Title: Observations of Running Penumbral Waves
Authors: Zirin, Harold; Stein, Alan
Bibcode: 1972ApJ...178L..85Z
Altcode:
Quiet sunspots with well-developed penumbrae show running intensity
waves with period running around 300 seconds. The waves appear connected
with umbral flashes of exactly half the period. Waves are concentric,
regular, with velocity constant around 10 kIn -1 They are probably sound
waves and show intensity fluctuation in Ha centerline or wing of 1() 20
percent. The energy is tiny compared to the heat deflcit of the umbra.
Title: The Sun's Atmosphere. (Book Reviews: Physics of the Solar
Corona. Proceedings of a NATO Advanced Study Institute, Athens,
Greece, Sept. 1970)
Authors: Zirin, H.
Bibcode: 1972Sci...178.1085Z
Altcode: 1972Sci...178.1085M
No abstract at ADS
Title: The Absence of Flares in λ 3835 and the Heating of the
Chromosphere
Authors: Zirin, Harold
Bibcode: 1972SoPh...26..393Z
Altcode:
Simultaneous observations of flares in Hα and a band 15 Å wide
centered on 3835 Å show no change whatever in 3835 Å at the time
of several flares, although the chromospheric network is easily
visible. Flares are therefore transparent in this wavelength.
Title: Response to Dr Frazier's Comments
Authors: Zirin, Harold
Bibcode: 1972SoPh...26..145Z
Altcode:
No abstract at ADS
Title: Reply to `The relations between chromospheric features and
photospheric magnetic fields' by E. N. Frazier
Authors: Foukal, Peter; Zirin, Harold
Bibcode: 1972SoPh...26..148F
Altcode:
No abstract at ADS
Title: Bright Running Penumbral Waves
Authors: Stein, Alan; Zirin, Harold
Bibcode: 1972BAAS....4T.392S
Altcode:
No abstract at ADS
Title: High resolution solar observations from space.
Authors: Zirin, H.
Bibcode: 1972spre.conf.1751Z
Altcode: 1972spre....2.1751Z
No abstract at ADS
Title: Fine Structure of Solar Magnetic Fields
Authors: Zirin, Harold
Bibcode: 1972SoPh...22...34Z
Altcode:
The deduction of magnetic fields from chromospheric structure is
extended to active regions and transverse fields. Fields independently
predicted by these rules from a high resolution Hα filtergram are
compared with a high resolution magnetogram. The Hα method has the
advantage over conventional magnetograms that it shows transverse fields
and relates the fields to the real Sun. It has the disadvantage that
higher spatial resolution is required and that it is difficult and
time consuming in very complicated regions.
Title: Evidence for Magnetic Field Reconnection in Flares.
Authors: Zirin, H.
Bibcode: 1971BAAS....3..461Z
Altcode:
No abstract at ADS
Title: Magnetic Fields, Bremsstrahlung and Synchrotron Emission in
the Flare of 24 October 1969
Authors: Zirin, H.; Pruss, Gail; Vorpahl, Joan
Bibcode: 1971SoPh...19..463Z
Altcode:
An impulsive flare October 24, 1969 produced two bursts with virtually
identical time profiles of 8800 MHz emission and X-rays above 48
keV. The two spikes of hard X-rays correspond in time to the times of
sharp brightening and expansion in the Hα flare. The first burst was
not observed at frequencies below 3000 MHz. This cut off is ascribed
to plasma cutoff above the low-lying flare.
Title: The Manifold Structure of the Chromosphere and Corona
Authors: Zirin, H.
Bibcode: 1971RSPTA.270...77Z
Altcode:
No abstract at ADS
Title: Observations of Stellar Chromospheres
Authors: Zirin, H.
Bibcode: 1971RSPTA.270..183Z
Altcode:
No abstract at ADS
Title: On K-Line Central Reversals
Authors: Pasachoff, Jay M.; Zirin, Harold
Bibcode: 1971SoPh...18...27P
Altcode:
No abstract at ADS
Title: Magnetic field morphology and the development of active
regions.
Authors: Zirin, H.
Bibcode: 1971BAAS....3..266Z
Altcode:
No abstract at ADS
Title: Application of the Chromospheric Magnetograph to Active Regions
(presented by P. Foukal)
Authors: Zirin, H.
Bibcode: 1971IAUS...43..237Z
Altcode:
No abstract at ADS
Title: Die Fackelfeuer der Sonne.
Authors: Zirin, H.
Bibcode: 1971BiWis...8..883Z
Altcode:
No abstract at ADS
Title: Active Regions. II: Mount Wilson 16997. A Small Spot with
Big Flares
Authors: Zirin, H.
Bibcode: 1970SoPh...14..342Z
Altcode:
We describe the great activity associated with Mount Wilson 16997, a
single αp spot without plage that produced a number of large flares
and developed into a substantial center. The activity was signalled
by the emergence of f polarity and weak plage ahead of the spot on 24
September 1968 (although the region was already seen at the limb at the
22 September 1968 eclipse as a active center). A number of explosive
flares with X-rays on the 25th were climaxed by a large flare a 0036 UT
26 September; the latter was associated with the splitting of the old
spot and the emergence of a new one. The polarity axis rotated around
to a normal configuration by the 29th, but a large flare occurred on
that day, too.
Title: Active Regions. I: The Occurrence of Solar Flares and the
Development of Active Regions
Authors: Zirin, H.
Bibcode: 1970SoPh...14..328Z
Altcode:
A summary of data on the occurrence of flares and the development of
active regions, based on cinematographic data is given. It is shown
that flare frequency is determined by the orientation of the magnetic
axis relative to the direction of solar rotation and the morphology
of the magnetic field as seen in Hα. In particular, flares are most
numerous in simple round spots with reversed polarity nearby, although
they may also be frequent in complex spots with polarity reversal.
Title: The Chromospheric Magnetograph
Authors: Veeder, Glenn J.; Zirin, Harold
Bibcode: 1970SoPh...12..391V
Altcode:
By comparison of photoelectric magnetograms with high resolution
Hα pictures it is possible to formulate a set of rules by which the
magnetic field may be derived directly from the filtergrams. This is
possible because of the regularities of magnetic field configurations
on the sun and because chromospheric morphology is determined by the
magnetic field.
Title: The Big Bear Solar Observatory
Authors: Zirin, Harold
Bibcode: 1970S&T....39..215Z
Altcode:
No abstract at ADS
Title: Coronagraph Observations of the Coronal Condensation of 4
February 1962
Authors: Zirin, H.
Bibcode: 1970SoPh...11..497Z
Altcode:
Climax coronagraph observations of the accessible Fe lines, as well
as the CaXV λ5694 line at the time of the 1962 total eclipse, are
analyzed. The spectra show that the ionization equilibrium of iron is
not substantially changed in an intense coronal condensation, at least
for the stages X through XV. The only exception is FeXV λ7059, for
which density effects are important. The stability of the ionization
distribution is explained by the dynamic nature of the Fe ionization,
with ions entering on the high side (FeXVI and up) due to rapid heating
and then cooling through the visible stages.
Title: Identification of the hard X-ray pulse in the flare of
September 11 12, 1968
Authors: Vorpahl, J.; Zirin, H.
Bibcode: 1970SoPh...11..285V
Altcode:
A hard X-ray pulse in the 11-12 September 1968 flare is identified
with the formation of a brilliant kernel. Each stage in the X-ray
event corresponds to a definite phase in flare development.
Title: The Coarse Structure of the Solar Atmosphere
Authors: Simon, M.; Zirin, H.
Bibcode: 1969SoPh....9..317S
Altcode:
Observations of the quiet sun at wavelengths from 3 Å to 75 cm show
(with two exceptions: the Ovi line at 1032 Å and possibly the continuum
at 1.2 mm) either no limb brightening or less than had been supposed. On
the other hand, the brightness temperature is observed to increase with
wavelength in the millimeter and centimeter range. If this increase
is due to greater visibility of hot overlying material, that material
ought to be evident at the limb at shorter wavelengths, resulting in
limb brightening. The only possible explanation for the absence of limb
brightening at almost all wavelengths is that the emitting surface
is rough at all wavelengths, with a scale of roughness approximately
equal to the scale height at each temperature. Contradictions with
existing models, along with the additional observations required for
an improved model are discussed.
Title: De-Occultation X-Ray Events of 2 December, 1967
Authors: Zirin, Harold; Ingham, William; Hudson, Hugh; McKenzie, David
Bibcode: 1969SoPh....9..269Z
Altcode:
A flare rising from behind the solar limb was recorded simultaneously
by the UCSD X-ray detector on OSO-III (7.7-200 keV) and the Caltech
photoheliograph on Robinson Laboratory roof (Hα). The de-occultation
gives excellent spatial resolution of the X-ray source. Spectra
suggest that the material was already heated to 27 000 000° and that
the increase in flux was due to the de-occultation. The flux rise to
maximum was proportional to the apparent area. The uniformity of this
rise shows that there was no special kernel of emission. Comparison
of the deduced volume with the bremsstrahlung formula gives a density
of about 1010 for the 27 000 000° component of the flare;
this is confirmed by consideration of the maximum possible coulomb
braking. The actual decay is more likely by escape rather than coulomb
braking.
Title: Interpretation of XUV Spectroheliograms
Authors: Zirin, Harold
Bibcode: 1969SoPh....9...77Z
Altcode:
Some parameters of chromospheric structure are drawn from recently
published XUV spectroheliograms. The HeII emission above the limb
arises from the small amount of He+ still existing at
106°. The larger amounts of He+ in the cooler
corona at the poles explain the polar cap absorption in λ 304. The
flat distribution of emission in OIV and OV, with a sharp spike at
the limb, is caused by the rough structure of the chromosphere and
the variable excitation in the emitting spicules. The intensity of
the NeVII lines shows that the transition zone between chromosphere
and corona is very sharp.
Title: The Birth of Active Regions
Authors: Weart, Spencer R.; Zirin, Harold
Bibcode: 1969PASP...81..270W
Altcode:
No abstract at ADS
Title: De-occultation x-Ray Event of 2 December 1967
Authors: Hudson, Hugh; McKenzie, David; Zirin, Harold; Ingham, William
Bibcode: 1969BAAS....1T.280H
Altcode:
No abstract at ADS
Title: The Birth of Active Regions
Authors: Weart, Spencer; Zirin, Harold; Kozlovsky, Ben-Zion
Bibcode: 1969BAAS....1Q.295W
Altcode:
No abstract at ADS
Title: Round-the-Clock Photoheliography
Authors: Zirin, Harold; Bohlin, J. David; Weart, Spencer; Feldman, Uri
Bibcode: 1969BAAS....1..297Z
Altcode:
No abstract at ADS
Title: High-Resolution Flare Observations
Authors: Zirin, Harold
Bibcode: 1969BAAS....1..296Z
Altcode:
No abstract at ADS
Title: Two Prominence Eruptions and the Problem of Emission
Authors: Zirin, Harold
Bibcode: 1969SoPh....7..243Z
Altcode:
Two flare unconnected eruptions on January 15 and 29, 1968, are
discussed. The first is a filament which turns bright and erupts
upward, reappearing an hour later. The second is a large eruptive
arch seen against the disk. The arch is bright at the top of its
trajectory, turns dark, but produces chromospheric emission at the
point of impact. The emission at the top of the arch is ascribed to
the velocity shift of the illuminating chromospheric Ha line. It is
shown that such emission will occur only if the motion is transverse
to the line of sight and the prominence is optically thin.
Title: The solar atmosphere.
Authors: Zirin, H.
Bibcode: 1969soat.book.....Z
Altcode:
No abstract at ADS
Title: The Solar Flares of August 28 and 30, 1966
Authors: Zirin, Harold; Lackner, D. Russo
Bibcode: 1969SoPh....6...86Z
Altcode:
We describe observations of the class 3+ flare of August 28, 1966, made
at the Mount Wilson Observatory. This great proton flare followed the
sequence: (1) Precursor flare; (2) Filament eruption; (3) Beginning
in penumbra of large spot; (4) Rapid elongation in two strands; (5)
Great spray and surface wave; (6) Rapid separation of two strands to
maximum brightness; and (7) Slow spread of brightness and decay.
Title: George Ellery Hale, 1868 1938
Authors: Zirin, Harold
Bibcode: 1968SoPh....5..435Z
Altcode:
No abstract at ADS
Title: Abundance Analyses from Extreme-Ultraviolet Emission Lines
Authors: Zirin, Harold
Bibcode: 1968ApJ...154..799Z
Altcode:
The analyses are criticized on grounds that the chromosphere-corona
transition is in dynamic equi- librium and is insufficiently understood
for quantitative analysis A detailed critique of Pottasch's analysis
is given
Title: The O VI emission from the sun
Authors: Kozlovsky, Ben-Zion; Zirin, Harold
Bibcode: 1968SoPh....5...50K
Altcode:
The ionization equilibrium of oxygen is calculated for various
temperatures. A peculiarity in the dielectronic recombination leads
to a considerable fraction of OVI in the corona. Thus, the OVI lines
may be emitted from the corona rather than the transition region.
Title: He^{3} in Several Magnetic Stars
Authors: Zirin, Harold
Bibcode: 1968ApJ...152L.177Z
Altcode:
The presence of He3 in 3 Cen A, ~ UMa, and ~y1 Vir is indicated by the
shift in wavelength of the line He i X10830. In several other stars no
X10830 is observed. Sargent and Jugaku (1961) found that the neutral
helium lines in 3 Cen A correspond essentially to wavelengths expected
for the isotope He3. Because the isotope shifts in the helium lines are
small in the visual region (only XX4922 and 6878 have substantial z~X/X
shifts), I attempted, at Sargent's suggestion, to measure the shift
in the X10830 line in various magnetic stars. According to Fred et
i1. (1951), the He3 shift in X10830 is 1.15 A, a value about twice as
large as that for the lines in the visual region, although ~X/X is the
same. In any event, X10830, being such a strong line, should be more
easily detectable in A stars than is the X5876 line. As part of our
program of chromospheric studies of the X10830 line (Vaughan and Zirin
1968), I obtained spectrograms of a number of peculiar A stars with
the 72-inch camera of the coudé spectrograph of the Hale telescope,
using a single-stage RCA image converter kindly lent by the Carnegie
image-tube committee. The dispersion is 17 A mm-'; a 1-hour exposure is
required for stars of infrared magnitude, I = 4. In the spectrograms
taken before plate No. 10835, the helium doublet (1 A separation, 8:1
ratio) is barely separated. For plates after No. 10835, a transfer
lens consisting of two Canon f/0.9, 50-mm lenses, face to face, was
used. This made it possible to reach a magnitude of I = 5 in 1 hour;
the resolution then improved to 0.5 A. Uncertainty is caused by the
presence of an atmospheric line at 10832.14 A, the weakness of the
helium line, and the low contrast of image-tube spectra. Of course,
if no He i line is observed, we cannot comment on the existence of
He3. Table 1 lists the magnetic stars observed, the plate numbers,
the measured and cor- rected wavelengths, the line strength on a scale
O-5, and a conclusion. Figure 1 (Plate L7) shows spectra of E UMa and
3 Cen A, along with the X10830.31 comparison line. In 3 Cen A, a broad
line is observed at 10830.8 A; the velocity correction of 0.5 A places
the initial stellar wavelength at 10831.3 A, close to the predicted
He3 position. Aside from the fact that the uncorrected wavelength
does not agree with the atmospheric line, the general weakness of the
other atmospheric lines makes it unlikely that the line seen is only
X10832.14. In a2 CVn, a weak line may be present at the He3 position. In
`y' Vir, a broad complex line reaches from 10830 to 10831 A; hence both
He4 and He3 may be present. This star has a radial-velocity shift of -
1.74 A, so that there is no confusion with the atmospheric line. In
a And (plate No. 8993), radial velocity shifts the He3 line to the
red; a broad feature appears on the blue portion of the atmospheric
line. However, plate No. 10835, taken December 11, 1967, shows no helium
line. In UMa, we find a broad line at 10833.7 A. The radial-velocity
correction listed is +0.7; however, the strongest line observed in this
spectrum, the Si i line at 10750.26 A, would require a correction of -
0.87 A. Adopting this correction, we get a wavelength * This work was
supported in part by NASA grant NGR 05-002-034
Title: The Solar Atmosphere
Authors: Zirin, Harold
Bibcode: 1968ASPL...10..121Z
Altcode: 1968ASPL..466.....Z
No abstract at ADS
Title: The Helium Line λ 10830 Å in Late-Type Stars
Authors: Vaughan, Arthur H., Jr.; Zirin, Harold
Bibcode: 1968ApJ...152..123V
Altcode:
Spectroscopic observations in the region XX10660-10915 A in eighty-six
stars are presented. The observations consist primarily of image-tube
spectrograms, with 8 4 A/mm dispersion, taken with the coudé
spectrograph of the 200-inch telescope Additional measurements were
obtained with a spectrum scanner and with a Fabry-Pérot interferometer
in the coudé spectrograph of the 100-inch telescope. The X10830 line of
neutral helium appears in absorption in a substantial number of "normal"
G and early K stars. In these stars there is a rough statistical
tendency for X10830 absorption to increase in strength with increasing
Ca ii K emission intensity. In contrast to the K-line, there is also
a correlation of X10830 intensity with luminosity The line is usually
broader than normal photospheric lines, and violet shifts are common
in highly luminous stars. The line X10830 is probably not present,
at least with appreciable strength, in either F or M stars. The line
appears in emission (typically accompanied by a violet absorption edge)
in E Gem, 12 Peg, U Her, ~y Dra, and Aur. Temporal changes were observed
in a Aqr and ~ Dra. The presence of X10830 in late-type stars indicates
the existence of hot chromospheres Our data sug- gest that the line
originates in discrete clouds or streams rather than a homogeneous
Jayer. Line identifications and eye estimates of intensities in the
range XX10660-10915 A for six stars of types F8-MO are tabulated in
an Appendix at the end of the paper
Title: The Excitation of Coronal Emission Lines as a Measure of
Electron Density
Authors: Zirin, H.
Bibcode: 1968ApJ...151..383Z
Altcode:
Coronal lines in the visible spectium may be classified by whether
they are excited from the ground state by photospheric radiation and
collisions or by collisions oniy. Since the latter disappear at low
density, the peculiar behavior of several lines is explained and a
density criterion obtained
Title: Mass motions in loops, sprays, surges etc., Introductory
lecture
Authors: Zirin, H.
Bibcode: 1968mmsf.conf..131Z
Altcode:
No abstract at ADS
Title: Observations of stellar chromospheres using the He 10830 line
Authors: Zirin, H.
Bibcode: 1968mmsf.conf..239Z
Altcode:
No abstract at ADS
Title: Book Reviews
Authors: Zirin, Harold; Allen, C. W.
Bibcode: 1967GeoJ...12..539Z
Altcode: 1967GeoJI..12..539Z
No abstract at ADS
Title: Spectrographic Observations of the Flare of July 20, 1961
Authors: Zirin, Harold; Acton, Loren W.
Bibcode: 1967ApJ...148..501Z
Altcode:
Spectroscopic observations of the late stages of a limb flare which
occurred on July 20,1961, are presented. Because these observations
were made with an achromatic coronagraph, accurate line intensity
ratios are possible. The He I and He ii line ratios indicate a
recombination-cascade spectrum. Measurements of cbntinuum densities
give values around 1010 in the post-flare loop region and 1011 or more
in the flare. Ca xv line widths correspond to 4.3 X 100 K. A magnetic
loop structure which guides successive surges is studied.
Title: Interpretation of chromospheric structure in the light limb
and XUV observation
Authors: Zirin, H.
Bibcode: 1967AJ.....72..329Z
Altcode:
No abstract at ADS
Title: Buchbesprechungen über: The Solar
Atmosphere. (Ref. E. A. MÜLLER)
Authors: Zirin, H.
Bibcode: 1967ZA.....67..413Z
Altcode:
No abstract at ADS
Title: Detailed analysis of flares, magnetic fields and activity in
the sunspot group of Sept. 13 26, 1963
Authors: Zirin, Harold; Werner, Susan
Bibcode: 1967SoPh....1...66Z
Altcode:
We analyze large-scale H-alpha movies of the large spot group of
Sept. 13-26, 1963, together with radio, ionospheric and magnetic
field data as well as white light pictures. The evolution of the
group and associated magnetic fields is followed, and the positions
of solar flares relative to the fields are noted, along with
their morphology. Although the magnetic field is deformed in time,
characteristic field structures may be traced through the deformation
as the seat of recurrent homologous flares.
Title: The Solar Atmosphere
Authors: Zirin, Harold
Bibcode: 1967easp.book...25Z
Altcode:
No abstract at ADS
Title: Surveyor 1 Observations of the Solar Corona
Authors: Norton, Robert H.; Gunn, James E.; Livingston, W. C.; Newkirk,
G. A.; Zirin, H.
Bibcode: 1967JGR....72..815N
Altcode:
The solar corona was observed by the Surveyor 1 television camera
on June 14, 1966. These observations and corroborative ground-based
measurements are presented.
Title: The Structure of the Solar Chromosphere. II. Spectroheliograms
in λ 10830 Å and Their Interpretation
Authors: Zirin, Harold; Howard, Robert
Bibcode: 1966ApJ...146..367Z
Altcode:
Spectroheliograms made in the X 10830 A line of He 1 show a network
pattern of absorption which coincides with the Ca and Ha network. The
absorption in 10830 is limited to the edges of the network cells, to
plages and filaments. It is concluded that the edges of the network
cells are the only areas in the chromosphere where temperature and
density are sufficiently high to excite the 223 level.
Title: The Sun. (Book Reviews: Physics of the Solar Corona)
Authors: Zirin, H.
Bibcode: 1966Sci...154..497Z
Altcode: 1966Sci...154..497S
No abstract at ADS
Title: Helium 10830 Absorption in Late-Type Stars.
Authors: Zirin, Harold; Vaughan, Arthur H., Jr.
Bibcode: 1966AJ.....71..188Z
Altcode:
Spectrograms of some 40 selected stars with infrared magnitudes J<~3
have been obtained using an RCA type C70071 image converter tube
(furnished by the Carnegie Image Tube Committee) at the 144-in. coude'
spectrograph camera of the 200-in. telescope. The spectra were
photographed with an f/1 transfer lens. The plates have a dispersion of
8.4 A/mm and cover a range of about were 3 h in good seeing. Photometric
scans obtained with the coud~ spectrograph of the 100-in. telescope
equipped with an interferometer are also discussed. About 30 stellar
absorption lines have been identifled. Broad absorption features
corresponding in wavelength to the He I line at 10830 A and not
identifiable with terrestrial water vapor are clearly seen in at least
nine stars (~ Gem, E Peg, E Eri, A And, a Aur, 12 Peg, p Dra, 61 Cyg
A and B). No feature identifiable with He I was found in three stars
(a Ari, L Aur, a Tan). In some stars an ah- sorption feature has been
noted which may be He I Al 0830 displaced to the violet. The line is in
emission in E Gem. The presence of the 10830 line in late-type stars is
of interest as an indication of fairly hightemperature chromospheres,
and possibly "solar activity." Of a number of stars between B8 and A2
also investigated, only p Orionis was found to show He I Al 0830 with
any certainty.
Title: The solar atmosphere
Authors: Zirin, Harold
Bibcode: 1966soat.book.....Z
Altcode: 1966QB528.Z5.......
No abstract at ADS
Title: The solar magnetograph of the High Altitude Observatory
Authors: Lee, R. H.; Rust, D. M.; Zirin, H.
Bibcode: 1965ApOpt...4.1081L
Altcode:
Available from http://www.opticsInfoBase.org/abstract.cfm?id=13895;
Title: Solar Astronomy Neglected
Authors: Howard, Robert; Leighton, Robert; Zirin, Harold; Whitford,
A. E.
Bibcode: 1965Sci...147.1087H
Altcode:
No abstract at ADS
Title: Introductory report
Authors: Zirin, H.
Bibcode: 1965IAUS...22..339Z
Altcode:
No abstract at ADS
Title: Observations of chromospheric fine structure
Authors: Zirin, H.
Bibcode: 1965IAUS...22..197Z
Altcode:
No abstract at ADS
Title: Solar Flares and Concurrent Phenomena in the Solar Atmosphere
Authors: Zirin, H.
Bibcode: 1965ASSL....3...38Z
Altcode: 1965pss..conf...38Z
No abstract at ADS
Title: The Limb Flare of November 20, 1960: a Coronal Phenomenon.
Authors: Zirin, Harold
Bibcode: 1964ApJ...140.1216Z
Altcode:
Observations of the explosive limb flare of November 20, 1960, which
produced a moderate groundlevel cosmic-ray event, are presented. The
explosive phase is shown to coincide with the beginning of radio and
X-ray emission. The fact that the flare occurred over the limb shows
that such emission comes from above 30000 km in the corona. This
emission is even observed at stages when no Ha is seen. Spectra of
the November 20 flare show it to be a coronal phenomenon, particularly
after the energy release in the explosive phase. The total number of
electrons in the line of sight is measured directly from the continuum
radiation, and an electron density of 1011 per cm3 is inferred from
symmetry. The ratio of the two coronal lines of Ca xv is discussed and
compared with theoretical calculations as another method of density
determination. The mean ratio 5694/5445 is observed to be 1.5. From
the ratio of coronal-line intensity to continuum radiation, it is
possible to deduce approximate abundances, and we find the abundance
of calcium to be considerably less (10 times) than that of iron in
the corona. Study of the ratios of three ionized helium lines shows
that the spectrum of ionized helium is due to pure recombination. The
Lyman-a resonance mechanism is shown to be non-existent or unimportant
since the Lyman radiation could only excite He ii levels with n
even, whereas lines originating on n odd are anomalously strong. By
comparing the helium emission with the distribution of coronal and
continuum radiation, we find that most of the material in the flare
is at coronal temperatures. The kinetic energy still present in the
coronal condensation two hours after the explosion was 1030 erg. It
is conceivable that a substantial fraction of the condensation may be
at temperatures >4000000 K.
Title: Identification of Extreme Ultraviolet Solar Emission Lines.
Authors: Zirin, Harold
Bibcode: 1964ApJ...140.1332Z
Altcode:
No abstract at ADS
Title: Average Recombination Gaunt Factors.
Authors: Glasco, Helen P.; Zirin, Harold
Bibcode: 1964ApJS....9..193G
Altcode:
We tabulate the average hydrogenic Gaunt factor calculated for principal
quantum numbers n = 1 to 15 for all individual I-values for temperatures
from 2500 to 2560000 K.
Title: Spectrographic Observations
Authors: Zirin, H.
Bibcode: 1964NASSP..50...33Z
Altcode: 1964psf..conf...33Z
No abstract at ADS
Title: Identification of the Spurious D3 Helium Emission from the
Solar Corona.
Authors: Zirin, Harold; James, Robert; Watson, D. Keith
Bibcode: 1964AJ.....69Q.565Z
Altcode:
Gnevyshev has discussed observations of emission in the D3 helium
line appearing on spectrograms of the solar corona. We have
found that this emission appears on spectrograms as a result
of chromospheric emission scattered by secondary optics of the
coronagraph. Successive spectrograms were made at Climax with the
sun over- and under-occulted. On the under-occulted spectrograms,
in which chromospheric light could reach the secondary optics, D3 was
invariably observed. In the under-occulted coronagrams it was never
observed. The profile of the spurious D3 line in the underocculted
coronagrams is similar to that in the chromosphere.
Title: The Structure of the Solar Chromosphere. I. a Picture Based
on Extreme Ultraviolet, Millimeter, and λ 10830 Data.
Authors: Zirin, Harold; Dietz, R. D.
Bibcode: 1963ApJ...138..664Z
Altcode:
We consider the stringent limits placed on a chromospheric model by
optical, radio, infrared, and ultraviolet data. These observations
appear to favor a picture in which (1) the chromospheric density falls
off rapidly to coronal values by 150() 2000 km, at which height the
temperature has risen to 7000 , before a very sharp transition to
coronal temperatures takes place, and (2) all the high-excitation
emission, including all the helium lines, arises in spicules. In
between the spicules is the corona. The optical observations of the
flash spectrum show that low-excitation lines fall off very sharply
with height, whereas helium and hydrogen lines show a much lower
gradient. Observations of the 10830 line of He I show that it jumps
from an optical depth around 0.1 just inside the limb to a depth of
about 3 just above the limb. This indicates that the spicules cover
just a fraction of the surface but, above the limb, show their intrinsic
optical depth. The radio data for wavelengths below 3 cm is introduced
to show that the boundary temperature of the chromosphere is about 7000
and that the amount of overlying material at a higher temperature is
very small. The surface must either have a very steep density gradient
or be rough. The limb brightening is due to spicules. The extreme
ultraviolet spectrum is discussed in detail. The Lyman continuum
observations indicate an origin at a temperature of 7000 and again set
a limit on any overlying hot layer. The lines of intermediate ions,
such as C ii-iv and 0 ii-v, are shown to originate in a very small
volume, corresponding to that occupied by spicules. Temperatures are
derived for these ions from line ratios; the temperatures range from
30 to 80 thousand degrees.
Title: Vertical Structures in the Chromosphere.
Authors: Cragg, T.; Howard, R.; Zirin, H.
Bibcode: 1963ApJ...138..303C
Altcode:
No abstract at ADS
Title: Coronal Observations and Rocket Solar Ultraviolet Results
Authors: Zirin, H.
Bibcode: 1963AIAAJ...1.1286Z
Altcode: 1963AIAAJ...1.1286.
No abstract at ADS
Title: Coronal Emission from Solar Flares.
Authors: Zirin, Harold
Bibcode: 1963AJ.....68Q..82Z
Altcode:
The spectra of limb flares almost invariably show intense radiation
of the coronal lines of Caxv, CaxilI and ArxIv, as well as strong
continuum. The electron density in the flare condensation may be
obtained on the assumption that the continuum is due to Thompson
scattering. Calculation of the excitation of Caxv shows that the ratio
of line to continuum emission is also a function of density. The results
of these two determinations are compared for a number of flares. The
effect of filamentation may also be evaluated. Recombination radiation
from Hell in such condensations is also a function of density, and
gives us a third determination. Densities ranging from 5 X 10~ to 2 X
lO~~ electrons per cm3 are found. In general, the line: continum ratio
depends on abundance. Approximate abundances for calcium, argon, iron,
and helium are given.
Title: Analysis of the Solar Emission Spectrum from 1300 to 250 A
as Observed in August 1961
Authors: Zirin, H.; Hall, L. A.; Hinteregger, H. E.
Bibcode: 1963spre.conf..760Z
Altcode:
No abstract at ADS
Title: Relative Populations of Fe in the Corona.
Authors: Firor, John; Zirin, Harold
Bibcode: 1963IAUS...16...27F
Altcode:
No abstract at ADS
Title: Physical Conditions in Limb Flares and Active
Prominences. V. Excitation and Ionization of Helium and Metals.
Authors: Zirin, Harold
Bibcode: 1962ApJ...135..521Z
Altcode:
The purpose of this paper is to summarize some of the results obtained
from the study of prominences discussed in earlier papers of this
series The spectrum of He ii in "hot" prominences is shown to be
due to pure recombination. The Lyman-a resonance mechanism must be
ineffective The ionization equilibrium of Sr ii is studied, and it is
found that the weakness of X 4077 in hot prominences is due either to
a temperature of over 40000 or to the fact that only a small fraction
of the prominence is below this temperature From a consideration of
the ionization equilibrium of Ca ii, it is shown that the observed H
and K lines can arise only at temperatures less than 30000 Further, it
is shown that the relative intensities of a number of very different
metallic lines do not change between "hot" and "cold" prominences,
even though their intensities relative to H and He change sharply. Thus
they too must arise in a limited cool volume The H and K lines remain
bright relative to H and He because they are optically very deep and
thus insensitive to changes in the emitting volume.
Title: Another Model of the Coronal Ionization Equilibrium.
Authors: Zirin, H.
Bibcode: 1962AJ.....67..124Z
Altcode:
Edlen has recently identified resonance lines of Fexv and xvi in the
uv solar spectrum. The fact that these lines are much stronger than the
Fexiv permitted lines at 260 and 340 A indicates that the abundance of
Fexv and Fexvi is substantial, much greater than might be inferred from
the intensity of the Fexv coronal line at 7060 A. Reconsideration of
excitation of the upper level of the latter line shows that it can
be de-excited by radiative transitions not involving the emission
of 7060. Using these data, an attempt is made to reconcile the
discrepancy between the coronal temperature as deduced from the
ionization equilibrium and linewidths.
Title: Observations of Five Ionization Stages of Iron in the Solar
Corona.
Authors: Firor, John; Zirin, Harold
Bibcode: 1962ApJ...135..122F
Altcode:
Measurements of the intensity of coronal emission lines from Fe x, Fe
xi, Fe xiii, Fe xiv, and Fe xv are reported. The observation of this
group of lines with high dispersion and in rapid succession was made
possible by the use of an infrared image converter in conjunction with
the Climax coronagraph. A brief description of the image-tube equipment
is given. The observations show no tendency for iron to be concentrated
in the Fe x and Fe xiv stages, as has been suggested by Shklovsky and
others. The distribution of ions among the various ionization stages
deduced from the observed line intensities is used to place a rough
lower limit on the ionization cross-sections. This lower limit is four
times the SchwartzZirin S-wave cross-sections. The distribution of
Fe xiii ions in the excitation states of the ground configuration is
discussed, and the variation of observable line4ntensity ratios with
coronal electron density is predicted for three possible choices of
exdtation cross-section.
Title: Magnetic Fields in Prominences at the Limb
Authors: Zirin, H.
Bibcode: 1962IAUTB..11..439Z
Altcode:
No abstract at ADS
Title: Measurement of magnetic fields in solar prominences
Authors: Zirin, H.; Severny, A.
Bibcode: 1961Obs....81..155Z
Altcode:
No abstract at ADS
Title: The Balmer: Paschen Ratio in the Chromosphere and the
Equilibrium Populations of Hydrogen Angular-Momentum States.
Authors: House, Lewis L.; Athay, R. Grant; Zirin, Harold
Bibcode: 1961ApJ...133..608H
Altcode:
The work reported in this paper is a test of the hypothesis that the
angular-momentum states of hydrogen are not populated according to
their statistical weights. The anomalous ratio of the hydrogen Balmer to
Paschen lines observed at the 1952 eclipse is investigated in relation
to both observations and theoretical calculations. The Paschen decrement
is used to test for a reduced population of states of higher angular
momentum; such a depopulation of states was previously suggested as
accounting for the anomalous ratio. The decrement does not confirm the
suggestion. A statistical equilibrium analysis of the angular-momentum
states is used to determine departures in the populations from their
LTE values. The results indicate that departures are too small to
give the observed Balmer: Paschen ratio. An calculation shows that it
is reasonable to average together the substates of different angular
momentum in hydrogen chromospheric calculations.
Title: Oscillator Strength for the 3s3p^{2} ^{2}S-3s^{2} 3p^{2}P
Transition in AL I.
Authors: Eddy, John A.; House, Lewis L.; Zirin, Harold
Bibcode: 1961ApJ...133..299E
Altcode:
The oscillator strength for the transition 1s22s22p63s23p2 P2i2, 2S1/2
of Al I has been calculated. A potential was obtained which allowed a
numerical solution of the equation for the ground- and excited-state
wave functions. An f-value of 034 was computed from both the dipole
and the momentum matrix elements, using theoretical energy levels
This is thought to be a more reliable value than that derived from
observed energies.
Title: Interstellar Matter at Large Distances from the Galactic Plane.
Authors: Münch, Guido; Zirin, Harold
Bibcode: 1961ApJ...133...11M
Altcode:
The interstellar gas at large distances z from the galactic plane
is studied by the absorption lines it produces on the spectrum of
distant stars off the Milky Way. From the statistics of multiple lines
in various ranges of z, it is shown that some gas clouds probably
exist at z = 1 kpc. The number of clouds observed in 0 5 <z <
1 kpc has been found to be larger than would be expected from the
known distribution of their velocity components in the galactic
plane. The apparent asymmetry in the distribution of high-velocity
clouds is explained as the result of decreased chances of collisions
in the z-direction and also in terms of an intrinsic anisotropy in the
mechanism accelerating the clouds. The typical time required for the
clouds to reach their actual probable height from z = 0 is evaluated
to be 40 X 106 years From the line intensities and by assuming cosmic
abundance of the elements, a relation between the linear dimensions and
the densities of the clouds is established. Irrespective of whether
the clouds are H I or H ii regions, it is found that their continued
existence for 40 X 106 years requires the operation of a process
preventing them from expanding. The physical conditions prevailing
in a galactic halo or corona exerting pressure on the clouds are
next analyzed. It is shown how the observations rule out a halo with
an electron temperature T, around 10 K. A corona with T = 106 K, as
postulated by Spitzer, on the other hand, is found admissible, provided
that the high-velocity clouds at high z are H ii regions. The large
energy input by conduction from the corona may be balanced by radiative
losses only at about T - 10 K. Next the ionization e uilibrium in the
clouds is briefly discussed, and it is suggested that the anomalous
abundance ratio Na Ca observed in interstellar space is the result of
using an unrealistic mean stellar radiation field in the photoionization
computations. In this context, the results of a calculation of the
ionization equilibrium of aluminum is presented It is shown that the Al
I line at X 3964 should have a strength about one-twentieth that of Ca
I X 4226. In a final section the possible mechanisms by means of which
interstellar clouds may be accelerated are discussed. It is shown how
the operation of the Oort-Spitzer process requires a ratio between the
total amounts of ionized and neutral interstellar matter much larger
than is observed. The relevance of magnetic fields in accelerating
small masses of ionized field4ree material is thereby emphasized.
Title: Corrigenda
Authors: Roberts, W. O.; Zirin, H.
Bibcode: 1961JGR....66..340R
Altcode:
No abstract at ADS
Title: Connection of a Loop Prominence with a Sunspot
Authors: Ramseyer, Helene; Warwick, James W.; Zirin, Harold
Bibcode: 1960PASP...72..509R
Altcode:
No abstract at ADS
Title: Backscatter of Cosmic Rays by the Sun's H II Sphere
Authors: Newkirk, G. A.; Warwick, J. W.; Zirin, H.
Bibcode: 1960JGR....65.2540N
Altcode:
No abstract at ADS
Title: Backscatter of Cosmic Rays by the Sun's HII Sphere.
Authors: Newkirk, G. A.; Warwick, J. W.; Zirin, H.
Bibcode: 1960AJ.....65..351N
Altcode:
The phenomena of the cosmic-ray storm following the flare of February
23,1956, have been explained by Meyer, Parker, and Simpson as due to
a field-free cavity around the sun surrounded by a magnetic barrier
outside the earth's orbit. This cavity was supposed to be produced
by a constant "solar wind" of 500 particles/cm3 moving at 1500
km/sec. Several reasons are given to demonstrate the incompatibility
of the constant "solar wind" with theory and observation. The sun is
surrounded by a sphere of ionized hydrogen at least several astronomical
units in diameter, followed by a transition region of roughly the same
thickness. The HIl region is much hotter than the HI region outside. If
the outer HI region is permeated by a galactic magnetic field, pressure
balance ensures that there is virtually no field in the HIl region and
a magnetic shell at the transition region. This shell would produce
the observed reflection of solar cosmic rays.
Title: Recent Progress in Solar Physics
Authors: Roberts, Walter Orr; Zirin, Harold
Bibcode: 1960JGR....65.1645R
Altcode:
A number of significant recent advances in solar physics are
reviewed. New kinds of observations made during the present sunspot
cycle, which began in 1954, have emphasized still further the
apparent complexity of solar phenomena and the need of nonequilibrium
theoretical treatments. Among the new developments discussed are
solar cosmic rays and high-energy particles, flares and prominences,
coronal condensations, solar magnetic fields, and solar radio noise
emission. Theoretical analyses of the conditions of the solar atmosphere
as a hot plasma, and as a gaseous ensemble exhibiting gross departures
from thermodynamic equilibrium, are discussed. New work on atomic
collisional parameters is also reviewed. The article concludes with
a synopsis of certain major unsolved problems of the solar atmosphere.
Title: Physical Conditions in Limb Flares and Active
Prominences.IV. Compersion of Active and Quiescent Prominences.
Authors: Zirin, Harold; Tandberg-Hanssen, Einar
Bibcode: 1960ApJ...131..717Z
Altcode:
Spectra of active and quiescent prominences appearing simultaneously
at the limb of the sun are analyzed and discussed. The quiescent
prominence shows a spectrum identical with that of the chromosphere
at 1500 km, with strong lines of H, He I, and ionized metals and weak
He ii. The active prominence shows strong He ii and very weak ionized
metal lines The lines in the active prominence are very much broader
The width of lines in either prominence is shown to depend on their
excitation potential. It is proposed, as a result of many observations,
that, except for strong lines such as those of hydrogen and Ca ii,
the spectra of prominences fall into two sharply defined classes,
depending on whether they are "hot" or "cool"
Title: Condensation of Prominences from the Corona. With 1 Figure
in the text
Authors: Lüst, R.; Zirin, H.
Bibcode: 1960ZA.....49....8L
Altcode:
No abstract at ADS
Title: Photography of the Infrared Coronal Lines 10747 and 10798 A
with Image Tubes.
Authors: Firor, John; Zirin, Harold
Bibcode: 1960AJ.....65Q.345F
Altcode:
Z emulsion require at least 30 minutes for proper exposure of the
lines with the Climax coronograph-an impracticable exposure time
if a region of the corona is to be explored for variations of line
intensity ratio. We have used electrostatically focused, single stage
tubes, loaned to us by the Carnegie Image Tube Committee, to speed up
exposure. The image on the output phosphor of the tube was photographed
on 35-mm film using a fast lens at roughly unity magnification. With
a selected tube and a dispersion of about 15 A/mm, a 28-mm diam solar
image and a 50-~ slit width, the exposure time is one minute on Plus-X
film. The coronal lines of Fex, XI, XIV, and XV are also obtained by
normal methods within a few hours of these exposures. Quantitative
measurements of the spectra are now being made.
Title: Collisional Ionization Cross-Section for Fe XIV in the Solar
Corona and the Coronal Electron Temperature.
Authors: Schwartz, Sanford B.; Zirin, Harold
Bibcode: 1959ApJ...130..384S
Altcode:
A new calculation of the ionization cross-section of Fe xiv by electron
collision is given, using a hydrogen-like model where all continuum
wave functions approach coulomb functions at large distances from the
atom. The resulting cross-section is more than a factor of 10 smaller
than the values in current use and, when inserted in the coronal
ionization formula, gives an electron kinetic temperature of about 2
X 106 degrees for a green to-red line-intensity ratio of unity.
Title: Physical Conditions in Limb Flares and Active
Prominences. II. a Remarkable Limb Flare, December 18, 1956.
Authors: Zirin, Harold
Bibcode: 1959ApJ...129..414Z
Altcode:
Spectra of a bright limb flare show many lines of metals, hydrogen,
and helium. The temperature in the flare, as deduced from line
broadening, is in the range . Relative line intensities also indicate
high temperatures. The coronal lines X 4086 (Ca xiii) and N 5694 (Ca xv)
are strongly enhanced during the flare. From the behavior of both lines
it is concluded that N 5694 is surely due to Ca xv. Continuous emission
from a dense coronal cloud was observed just before the flare. This
cloud condenses sharply during the flare and dissipates afterward. The
continuous emission from the flare appears due to electron scattering.
Title: Physical Conditions in Limb Flares and Active
Prominence. I. The Loop Prominence of November 12 and 22, 1956.
Authors: Tandberg-Hanssen, E.; Zirin, H.
Bibcode: 1959ApJ...129..408T
Altcode:
Spectra of two bright, fiarelike loop prominences have been analyzed;
it is found that the emission lines (in particular Hfl, H , He I
4713, and He ii 4686) have profiles closely fitted by a Gaussian
distribution of intensity. The measured line widths, however, show
different temperatures for the different atoms. The neutral helium
lines are more than half as broad as the hydrogen lines, and the
He ii line is much broader than the He I lines. It is necessary to
conclude that the lines originate in intertwined regions of different
temperatures. Relative mass motions of the order of 70 km/sec were
measured between different branches of one of the prominences.
Title: The Calculation of Opacities for Stellar Interiors.
Authors: Zirin, Harold
Bibcode: 1958ApJ...128..342Z
Altcode:
A simplified method for the calculation of opacities is given by means
of a sample case. A table of opacities for various temperatures and
densities is given for four mixtures
Title: Spectra of Quiescent and Loop Prominences
Authors: Zirin, Harold; Watson, Keith; Curtis, G. William
Bibcode: 1958PASP...70..406Z
Altcode:
No abstract at ADS
Title: Rocket Observation of X-Ray Emission in a Solar Flare
Authors: Warwick, J. W.; Zirin, H.
Bibcode: 1957Natur.180..500W
Altcode:
THE report1 of normal Lyman alpha- and enhanced X-ray
emissions from the Sun during a solar flare on July 20, 1956, presents
several problems in connexion with observations of ionospheric
absorption as well as the physics of the solar corona.
Title: On the Enhancement of Certain Helium Lines in the Limb Flare
of June 24,1956.
Authors: Zirin, Harold
Bibcode: 1957ApJ...126..159Z
Altcode:
An unusually well-observed limb flare occurred on June 24,1956. The
lines 4471, 4713, 4922, and 6678 of neutral helium, 4686 of ionized
helium, and Ha and H appear strongly in the spectra. The intensities
of 4471, 4686, 4713, and 4922 are about equal. The temperature of
the flare is deduced by comparing the Doppler half-widths of the
helium and hydrogen lines and, more accurately, from the relative
intensities of 4686 and 4471. Both methods give roughly 30000 . The
anomalous excitation of 4713 and 4922 are studied in terms of the helium
equilibrium. It is found that at high temperature and densities these
lines, as well as certain other helium lines, are strongly excited
relative to 4471 and 5876 by collisions from the liS ground state of
helium. The conditions necessary are T > 30000 and N > 3 X 1012.
Title: On the relative intensities of chromospheric Balnier and
Paschen lines.
Authors: Athay, R. G.; Zirin, Harold
Bibcode: 1957AJ.....62..137A
Altcode:
The flash spectrum of the solar chromosphere includes hydrogen Balmer
and Paschen lines originating in common upper levels. We denote the
intensity of the Balmer line arising from the transition n to 2 by B
and the intensity of the Paschen line arising from the transition n
to 3 by Pn. If all terms of the same n are populated in proportion to
their statistical weights and if self-absorption is small, Bn/Pn 3.3
for n > 9. Self-absorption will tend to reduce the observed ratio of
Bn$Pn. From spectrograms obtained at the 1952 eclipse, we find Bn/Pn 8
for n > 14. The discrepancy between observed and predicted ratios of
Bn/Pn is too large to be accounted for by photometric errors. This may
be illustrated by comparing continuum intensities in the ultraviolet
and infrared and by comparing intensities of the H and K lines with
the intensities of the infrared Caii triplet. The relative continuum
intensities for the corona, derived from the same spectrograms,
follow the photospheric curve. Furthermore, the Caii lines have very
nearly the predicted relative intensities. If we discount photometric
errors, then the observed ratio of Bn/Pn implies that some of the
multiplets normally present in the Paschen lines are suppressed. In
fact, it seems necessary to assume that only the s, and d terms are
populated. In this case, the predicted ratio of Bn/Pn 6, which is in
satisfactory agreement with the observations. The above assumption can
be justified if it can be shown that most of the electrons in the upper
term arrive via excitations from the IS, 25 and 2 terms. Quantitative
estimates of rates of excitations from these low- lying terms and rates
of three-body recombinations from the continuum using the Thompson
collision cross-section indicate that three-body recombinations form
the primary source of electrons for the upper levels. This would
imply that all of the multiplets are populated and Bn7Pn should be
3.3. Thus, the Thompson collision cross-section leads to a contradiction
between predicted and observed ratios of Bn/Pn. Observations of the
Paschen-Balmer ratio in prominences are now in progress at Climax. This
work was carried out under the sponsorship of the Office of Naval
Research and the Geophysics Research Directorate, Air Force Cambridge
Research Center. High Altitude Observatory, Boulder, Colo.
Title: Observations of the calcium coronal lines in the vicinity of
a limb flare.
Authors: Zirin, Harold
Bibcode: 1957AJ.....62..149Z
Altcode:
Since the X4o86 coronal line has been identified as due to CaxIli in
the laboratory, we have attempted to compare it with the yellow line,
X5694, to check its identification as Caxv. These lines were observed
almost simultaneously, in the vicinity of an importance-two limb flare
on December 18, 1956. The time variation of both lines parallels that of
the flare. The Doppler half- widths of X4086 and X5694 are equivalent;
both correspond to a temperature of 10,000,0000, if the broadening is
purely thermal. Unless the line broadening is ascribed completely to
micro- turbulence, the conclusion is inescapable that ~4086 and X5694
are both due to highly ionized states of calcium, and therefore X5694
is probably due to Caxv. Twenty-six emission lines are observed in
the flare spectrum between X3888 and ~4I43. These include lines of H,
He, FeI, CaII, All, MnI, MgI, Till and Srii. Comparison of the HeI and
Till profiles yields a kinetic temperature around 200,0000. This work
was carried out under the sponsorship of Air Force Cambridge Research
Center. High Altitude Observatory, Boulder, Colo.
Title: Comprehensive graded-height spectra of solar prominences.
Authors: Zirin, Harold
Bibcode: 1957AJ.....62...42Z
Altcode:
A program on prominence spectra is being carried out at the Climax
station of High Altitude Observatory by David Dodgen, Richard Hansen and
Keith Watson. Spectra are being obtained showing the following lines:
Hydrogen Ha, Hp, H~, 118, He; He 6678, 5876, 4713, 4686, 4471, 4o26;
Caii H and K; and Mg triplet at 5i8oA; as well as occasional other
lines. At each wave length intensities with absolute standardization
at a series of heights at intervals of 58oo km are obtained. In some
cases the spectra extend up to 200,000 km. A number of spectra have
already been obtained, of both quiescent and active prominences. The
temperature of these has been obtained by several different methods,
viz.: Doppler profiles, the Balmer decrement, the 6678/D3 ratio,
and the 4686/6678 ratio. This work was supported by the Geophysics
Research Directorate, the Air Force Cambridge Research Center. High
A ltitude Observatory, Boulder, Colo.
Title: Notes on the Solar Corona and the Terrestrial Ionosphere
Authors: Chapman, Sydney; Zirin, Harold
Bibcode: 1957SCoA....2....1C
Altcode:
No abstract at ADS
Title: On the Association of Solar Radio Emission and Solar
Prominences
Authors: Wild, J. P.; Zirin, H.
Bibcode: 1956AuJPh...9..315W
Altcode:
No abstract at ADS
Title: The Temperature and Equilibrium of Hydrogen in Solar
Prominences.
Authors: Zirin, Harold
Bibcode: 1956ApJ...124..451Z
Altcode:
The Ha, HP, and D3 emission lines of solar prominences in active
coronal regions have been photographed with the t6-inch coronagraph and
high-dispersion spectrograph of the Upper Air Research Observatory,
Sunspot, New Mexico. The Doppler profiles, after elimination of
turbulent motion, give temperatures ranging from 7000 to 50000 K,
depending on the nature of the prominence involved. The statistical
equilibrium of hydrogen in a solar prominence at temperatures of is
analyzed. Among the most important processes are found to be collisional
excitation from the ground state and photoexcitation from the second
level by photospheric radiation. Hardly any of the models are optically
deep in Ha; the critical question turns out to be the Lyman-a depth; if
this is large, the prominence radiates strongly in Ha, and vice versa.
Title: The Helium Equilibrium in Prominences and the Chromosphere.
Authors: Zirin, Harold
Bibcode: 1956ApJ...123..536Z
Altcode:
The equilibrium of helium in a gas suspended above the photosphere is
analyzed by computing in detail the various atomic processes involved
and writing down the equilibrium equations. These equations are
solved for the occupation numbers of He iii, He ii, and the various
important He I levels, in order to predict the relative intensity
of helium lines. The triplet levels are in equilibrium (referred to
the state) with the photospheric radiation with the proper dilution
factor. This gives good agreement with the 5876/10830 ratio measured
by Severny. Particular attention is paid to the ratio of the lines
6678/5876. This is found to vary with temperature only, and the observed
ratio should be a good measure of the temperature of helium.
Title: High dispersion spectra of prominence and coronal emission
lines.
Authors: Zirin, Harold
Bibcode: 1956AJ.....61...14Z
Altcode:
A number of high dispersion spectra of prominence and coronal emission
lines have been obtained with the new coronagraph of the UARO. The
prominence spectra, showing lines of Ha, H~, and D,, exhibit pure
Gaussian profiles, corresponding to temperatures ranging from 10,0000
to 50,0000, with most of the prominences in moderately active green
coronal regions exhibiting temperatures around 25,0000. This confirms
earlier results obtained by Billings and Zirin (1955) with lower
dispersion. Spectra obtained of the green coronal line X5303 show minor
irregularities which might be attributed to small scale macroscopic
motions. The temperatures obtained by assuming the profile of the
coronal line to be produced by pure Doppler broadening range from I ?~ x
106 for fainter coronal emission to 30 ~ 106 for bright peaks. Billings,
D. E. and Zirin, H. `955, A. J. 6o, 155. High Altitude Observatory,
Boulder, Colo. * This research was spnn,ored in part by the Geophysics
Research Directorate of the Air Force Cambridge Research Center,
Air Research and Development Command, under Contract AF 19 (604)-969.
Title: On the association of solar radio emission and solar
prominences.
Authors: Wild, J. Paul; Zirin, Harold
Bibcode: 1956AJ.....61Q.193W
Altcode:
We have examined prominence cinematograms made at Sacramento Peak and
Climax in the years 1949-1955 and compared them with the solar radio
records at 167 Mc/s. No close connection was found between limb events
and radio events, but some eruptions were found to be associated
with simultaneous radio bursts. Three such cases are discussed in
detail. These appear to produce a series of storm bursts of spectral
type I. The radio emission appears to originate from points in the
corona at the leading edge of the disturbance. The limb passages of
large sunspot groups in 1949-1955 were studied on both cinematograms
and single exposure surveys with the view of finding a criterion
for radio-active spots. It was found that spot groups showing looped
prominences and downward streaming from the corona showed a marked
tendency to produce radio storms. Of 14 spots producing enhanced
radio levels, 12 showed this criterion; 9 out of 10 large spots
(>800 X 10-6 of the disk) with loops and streamers produced
enhanced radio emission. This result is ascribed to the fact that
the seat of such storms must lie in the corona and in the presence
of strong ordered magnetic fields; the existence of such conditions
is indicated by the presence of looped prominences. This work was
supported by the Air Force Cambridge Research Center, Geophysics
Research Directorate, through contract AF 19(604)- 969 with the High
Altitude Observatory. Cosnmonwealth ScThntzfic and Industrial Research
Organization, Sydney, Australia, and High Altitude Observatory,
University of Colorado, Boulder, Colo.
Title: Coronal line at 4412A
Authors: Zirin, H.
Bibcode: 1955Obs....75..221Z
Altcode:
No abstract at ADS
Title: Wave Functions, Spin-Orbit and Spin-Spin Parameters for the
1s^{2}2s^{2}2p^{4} Isoelectronic Sequence.
Authors: Zirin, Harold
Bibcode: 1955ApJ...122...52Z
Altcode:
Variational wave functions are presented for the ls22s22p4 isoelectronic
sequence, for the ions 0 1 through Ca xiii. These wave functions make
possible the computation of the spin-orbit and spin-spin parameters
for the ions noted. The results agree well with empirical values.
Title: Energy Levels in the Ground Terms of the Ions a XIII-Ti XVII.
Authors: Layzer, David; Zirin, Harold
Bibcode: 1955ApJ...121..771L
Altcode:
No abstract at ADS
Title: Spin-Orbit Parameters for the p^{2} Configuration, with
Special Reference to the Yellow Coronal Line.
Authors: Zirin, Harold
Bibcode: 1955ApJ...121..528Z
Altcode:
Parameters of variational wave functions for the 1s22s22p2 confignration
with Z = 15 and 20 are given. These are used to calculate the
spin-orbit parameter , as well as the spin-spin parameter 77, for this
isoelectronic sequence. The theoretical values so obtained are found
to agree closely with empirical values. The theoretical value of for
Ca xv is 24,900 , close to Garstang's extrapolated value.
Title: Energy levels in the ground terms of the ions A XIII - Ti XVII
Authors: Layzer, David; Zirin, Harold
Bibcode: 1955elgt.book.....L
Altcode:
No abstract at ADS
Title: The temperature of prominences in active solar regions.
Authors: Billings, Donald E.; Zirin, Harold
Bibcode: 1955AJ.....60Q.155B
Altcode:
Kinetic temperatures of solar prominences may be computed by analyzing
the profiles of emission lines from atoms of two different atomic
weights. Such temperatures have been computed from the emission lines
of hydrogen and helium of prominences appearing on Climax coronal
spectrograms. The temperatures found are in the range I0,000O~20,000O
for many active prominences, in agreement with the computations
of many observers. Certain very active region prominences, however,
show temperatures equal to and greater than 100,0000. The mechanism by
which hydrogen radiates in Ha at temperatures in excess of 100,0000 is
then discussed. By considering the various radiative and collisional
processes occurring in an active, hot prominence we determine the
equations of statistical equilibrium for the first five hydrogen
levels. Solution of these for the occupation numbers of the levels
shows that at a density of i0~~ atoms per cm' or greater, a prominence
thread 5000 km thick will produce the observed Ha intensity, even
though its kinetic temperature is greater than 100,0000. This work was
supported in part by the Office of Naval Research through a contract
with the University of Colorado and in part by the Air Force Cambridge
Research Center, Geophysics Research Directorate through a contract
with Harvard University. High Altitude Observatory, Boulder Cob.,
and Harvard College Observatory, Cambridge, Mass.
Title: Radiative Opacity of Stellar Matter.
Authors: Zirin, Harold
Bibcode: 1954ApJ...119..371Z
Altcode:
The wave functions of free and bound electrons in the dense, highly
ionized stellar material are calculated by a variational principle
of Hulthen and by the Ritz principle, respectively. It is shown by a
selfconsistent type of calculation that one may regard the potential in
the gas as the central potential of the nucleus, plus the potential of
a uniformly distributed cloud of electrons. The free-free absorption
in this shielded potential is calculated, and the Gaunt factor for
this process is found to be generally less than unity. The Rosseland
mean opacity coefficient is computed for a grid of temperatures and
densities, including the free-free absorption, photoelectric absorption
(using Meyerott's cross-sections), and scattering. The line absorption
is not taken into account. It is found that free-free absorption in
hydrogen and helium overweighs that in the heavy elements, so long
as 1 - X - V is 0.2 or less. It is possible to give a power law only
for the opacity in the limited high-density region where scattering is
unimportant; there the opacity varies as ft , but the density variation
is always irregular.
Title: Radiative opacity of stellar matter.
Authors: Zirin, Harold
Bibcode: 1953AJ.....58...50Z
Altcode:
A detailed calculation has been made of absorption coefficients and
opacities of the hot, dense gas inside a star. The basic assumption
made is that the potential field surrounding a nucleus in the stellar
gas is that due to the nucleus and to a uniform cloud of electrons
surrounding it, up to the boundary of a neutral sphere. Outside this ion
sphere the potential is zero. I have found by a variational technique
the wave functions describing the motion of the electrons in this
potential field, both in bound and free states. If we then assume
that the electrons are distributed in energy according t6 the Fermi
Dirac statistics, we may determine the potential field due to the
electrons moving with these wave functions. The resulting potential
field almost exactly duplicates the assumed potential, especially
in very hot gases, therefore justifying our approximation. We have
in computing the self-consistent potential developed the exchange
potential for a non-degenerate free electron gas along the theory
of Dirac. This turns out to be appreciable even in hot gases. I have
determined the absorption coefficients for free-free and bound-free
transitions in various elements of astrophysical interest, using the
wave function of electrons in the assumed potential corresponding to
a given temperature and density. With these absorption coefficients
it is possible to compute the opacity of any astrophysical mixture,
under a wide variety of temperatures and pressures. The opacity turns
out to be much smaller than computed by Miss Harrison, because of
the effect of pressure ionization. As a result of this, the radiative
temperature gradient at the center of the sun must be much smaller, and
the convective core much larger, than found by some other workers using
Miss Harrison's tables. The Rand Corporation, Santa Monica, Ca 1sf.
Title: The Radiative Opacity of Stellar Matter.
Authors: Zirin, Harold
Bibcode: 1953PhDT.........1Z
Altcode:
No abstract at ADS
Title: On the Polarization of Starlight
Authors: Zirin, Harold
Bibcode: 1952BHarO.921...26Z
Altcode:
No abstract at ADS
Title: The Growth and Evolution of Interstellar Dust
Authors: Zirin, Harold
Bibcode: 1952BHarO.921...19Z
Altcode:
No abstract at ADS
Title: An objective prism study of peculiar A stars.
Authors: Zirin, Harold
Bibcode: 1951AJ.....56..146Z
Altcode:
A number of peculiar and metallic-line A stars were found in a survey
of A stars made with the twelve-inch Metcalf refractor and a 130 prism
(85A/mm). Twenty-one areas, each ~0 ~ 70, centered on Kapteyn's Selected
Areas, were covered down to magnitude 9.5. In all, ~8 peculiar and
metallic-line A stars were found, of which 13 are questionable. The
percentage of peculiar stars in classes B9-A3 was found to be 10 per
cent. In north galactic latitudes the frequency appeared to be only 4
per cent, whereas in southern latitudes it is 15 per cent. The stars BD
+ 1504071, +440341, and +430318 are probably spectrum variables. Harvard
College Observatory, Cambridge, Mass
Title: A List of Peculiar A Stars on Objective Prism Plates
Authors: Zirin, Harold
Bibcode: 1951BHarO.920...38Z
Altcode:
No abstract at ADS
Title: An objective prism study of peculiar A stars.
Authors: Zirin, H.
Bibcode: 1951AJ.....56R.146Z
Altcode:
No abstract at ADS