Author name code: koval
ADS astronomy entries on 2022-09-14
=author:"Koval, A.N."
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Title: Peculiarities of the photospheric line-of-sight velocity
field in the active region NOAA 12403 at the time of M2.9 solar flare
Authors: Koval, A. N.; Babin, A. N.
Bibcode: 2019A&AT...31..125K
Altcode:
On the basis of spectral observations we have studied the photospheric
line-of-sight velocity field in the active region during the flare
M2.9. In the small local region in the immediate vicinity of the flare
ribbon we observed strong line-of-sight velocities in the opposite
directions in contiguous fine-structure elements. The velocity
amplitudes reached 3.2 km/s. These velocities increased noticeably
during the period of rapid increase in the brightness of the flare
and decreased with its fading. The pattern of the distribution of
line-of-sight velocity along the slit suggests the spiral motions. The
noticeable restructuring of the magnetic field in the investigated
region occurred for several hours after the flare. The photospheric
velocity phenomena precede the photospheric magnetic field modification.
Title: On a Magnetic Anomaly in the Umbra of the Following Spot of
an NOAA 12192 Active Region
Authors: Babin, A. N.; Koval', A. N.; Tsap, Yu. T.; Borisenko, A. V.
Bibcode: 2018Ge&Ae..58.1149B
Altcode:
This paper examines the evolution and morphology of a magnetic
anomaly: the appearance and disappearance of a longitudinal magnetic
flux with opposite polarity at an area of about 10 arc seconds in
the umbra of the following sunspot of an NOAA 12192 active region,
which was observed from 21 to 26 October 2014 in the SDO/HMI and
SOLIS/VSM magnetograms. Information collected by spacecraft and under
on-ground observations including data from the Sun Service of the
Crimean Astrophysical Observatory of the Russian Academy of Sciences
are analyzed. Based on the methods of observation and determination
of longitudinal magnetic fields in SDO/HMI in line FeI 6173.34 Å
it was revealed, that combinations of contours appearing due to
magnetic force lines inclinations relative to the line-of-sight
and line-of-sight velocities can cause a significant undervalue
of the magnetic field intensity in magnetograms, but polarity
does not reverse. The fine spatial structure, evolution features,
close correlation with ultraviolet loops system in SDO/AIA images,
"moustaches", and no temporal and spatial correlation with flares point
to a connection between the detected anomaly and the new magnetic
flux emergence of opposite polarity in a spot's umbra at an earlier
decay stage. We analyze magnetic force lines reconnection and show
that annigilation of the magnetic fields of opposite polarities can
take place for many hours at small ( 30 km) scales and this fact is
verified by observation results. There are additional facts in favor
of the cluster model of a solar spot by Severny-Parker.
Title: Studies of the atmospheric structure of the solar white-light
flare of August 9, 2011
Authors: Babin, A. N.; Baranovskii, E. A.; Koval', A. N.
Bibcode: 2016ARep...60..768B
Altcode:
Semi-empirical models for three kernels emitting in the continuum
during the pre-impulsive and impulsive phases of the white-light flare
of August 9, 2011 have been calculated, based on observations of the
continuum brightness near 6579 Å, Hα profiles, and photospheric iron
lines. These computations show that, in order to achieve agreement
between the computed and observed profiles and the contrast of the
continuum emission of the impulsive kernels of the white-light flare,
the temperature must be increased in both the lower chromosphere and
the upper photosphere. The most efficient heating is located deeper in
the photosphere in the pre-impulsive than in the impulsive phase, and
chromospheric heating is negligible in the pre-impulsive phase. Spectral
data and the results of model computations indicate that it is difficult
to explain the emission of the white-light flare kernels as the effect
of heating by energy transported from the corona into lower-lying,
deep layers of the atmosphere by canonical transport mechanisms.
Title: Observational characteristics of the white-light flare of
August 9, 2011
Authors: Babin, A. N.; Koval', A. N.
Bibcode: 2014BCrAO.110..105B
Altcode:
We analyzed the monochromatic Hα and spectral (within a
range of 6549-6579 Å) observational data for the 2B/X6.9 flare of
August 9, 2011, that produced emission in the optical continuum. The
morphology and evolution of the Hα flare and the position,
time evolution, spectrum, and energetics of the white-light flare
(WLF) kernels were studied. The following results were obtained:
the flare erupted in the region of collision of a new and rapidly
growing and propagating magnetic flux and a preexisting one. This
collision led to a merger of two active bipolar regions. The
white-light flare had a complex structure: no less than five kernels
of continuum emission were detected prior to and in the course of the
impulsive flare phase. Preimpulsive and impulsive white-light emission
kernels belonged to different types (types II and I, respectively) of
white-light flares. A close temporal agreement between the white-light
emission maxima and the microwave emission peak was observed for the
impulsive white-light emission kernels. The maximum flux, luminosity,
and total energy emitted by the brightest impulsive WLF kernel equaled
1.4 × 1010 ergs cm-2 s-1, 1.5 ×
1027 ergs/s, and 5 × 1029 ergs, respectively. The
Hα profiles within the impulsive WLF kernels had broad wings
(with a total extent of up to 26 Å and a half-width of up to 9 Å)
and self-reversed cores. The profiles were symmetrical, but were shifted
towards the red side of the spectrum. This is indicative of a downward
motion of the entire emitting volume with a radial velocity of several
tens of km/s. The intensity pattern in the wings did not correspond
to the Stark one. The profiles were broadened by nonthermal turbulent
motions with velocities of 150-300 km/s. The observed Hα
profiles were analyzed and compared in their features to the profiles
calculated for an intense heating of the chromosphere by nonthermal
electrons accompanied by the development of a chromospheric condensation
propagating downward. We came to the conclusion that the analyzed flare
exhibited spectral features that may not be readily explained within
the framework of chromosphere heating by a beam of nonthermal electrons.
Title: Analysis of observations of linear polarization for H
α emission of flares and moustaches
Authors: Babin, A. N.; Koval, A. N.
Bibcode: 2011BCrAO.107...36B
Altcode:
In this paper we summarize and analyze the results of observation of
linear polarization of H α emission for solar flares and
moustaches obtained earlier. Basic structural and evolutional properties
of the observed polarization are formulated and presented. A conclusion
is drawn that polarization data obtained from rough time and spatial
averaging of Stokes parameters distort the true picture of polarization
of H α emission in flares and moustaches.
Title: The fine structure of the velocity field in a 2B/M2.3
importance flare
Authors: Babin, A. N.; Koval', A. N.
Bibcode: 2010KPCB...26..130B
Altcode:
No abstract at ADS
Title: Dynamical processes in the June 26, 1999 flare
Authors: Babin, A. N.; Koval, A. N.
Bibcode: 2010BCrAO.106...14B
Altcode:
The evolutionary and spatial characteristics of the motions in the
flaring chromosphere of a 2B/M2.3 flare are investigated by analyzing
the asymmetry in the Hα profiles. The possibility of
reconciling the results of observations with the theory of chromospheric
evaporation is considered. The spectroscopic Hα observations
of the flare performed with the KG-2 CrAO coronagraph with a temporal
resolution of 5-10 s and a spatial resolution as high as 1 arcsec
cover all stages of flare development. The following results have
been obtained: (1) The Hα profile asymmetry is a general
characteristic of the flare emission irrespective of its intensity and
its belonging to different structural features and phases of flare
development. (2) Most of the Hα emission profiles in
flare regions exhibit a red asymmetry. However, a blue asymmetry was
observed in small local regions at all stages of flare development. (3)
A red asymmetry that appeared before the onset of the impulsive phase
and persisted after its end was observed at the sites of main energy
release, i.e., the energy source responsible for the dynamical processes
in the flare came into operation earlier and existed longer than the
HXR emission. (4) The asymmetry pattern changed with flare phase:
the red wing intensity dominated in the pre-impulsive phase and at
the onset of the impulsive and gradual phases (while the line core was
unshifted or slightly shifted). At the maximum of the impulsive phase,
the nearly symmetric profiles with extended wings were redshifted
as a whole, i.e., the entire emitting volume moved down with a
velocity of several tens of km/s. This type of asymmetry cannot
be explained by the dynamical model of chromospheric condensation
(Canfield and Gayley 1987). (5) The Hα profiles show no
evidence of chromospheric heating by a beam of nonthermal electrons
during the impulsive phase (Canfield et al. 1984). (6) The lifetime
of the downflows and the change in their velocities with time are
inconsistent with the dynamical model of chromospheric condensation
(Fisher 1989). (7) The morphological features of the velocity field
are also inconsistent with the theory of chromospheric evaporation,
because the highest differently directed velocities were detected
at the flare loop tops, not at the sites of main energy release. We
conclude that the investigated flare shows spectral features that are
inconsistent with the standard chromospheric evaporation model.
Title: The June 15, 1991 and June 26, 1999 white-light flares
Authors: Babin, A. N.; Koval, A. N.
Bibcode: 2008BCrAO.104....7B
Altcode:
Observational properties of two white-light flares (WLFs), on June
15, 1991, and June 26, 1999, are presented and compared. This is of
particular interest, because the former was one of the most intense
flares of X-ray class X12, while the latter was a compact flare of
class M2.3. Significant differences between some flare parameters
(GOES class, Hα classification, the number of WLF kernels
and their location in the sunspot group, the size and duration of the
WLF emission, and the peak flux density of the microwave emission)
have been found. However, both these events had approximately the same
powers of the emission per unit area in continuum near 658.0 nm: E =
1.5 × 107 and 1.1. × 107 erg cm−2
s−1 nm−1. There is generally a good temporal
coincidence between the microwave and hard X-ray emissions and the WLF
emission during the impulsive phase, but the light curve of the WLF
emission on June 26, 1999, shows a stronger correlation with the X-ray
emission in the energy range 14-23 keV. Both flares can be classified
by their spectral characteristics as type I white-light flares.
Title: Changes of the CaI λ6102.7 Å line profile and the magnetic
field structure during the August 12, 1981 solar flare
Authors: Babin, A. N.; Koval, A. N.
Bibcode: 2008BCrAO.104...11B
Altcode:
We study the changes of the CaI λ6102.7 Å line profile and the
magnetic field structure during the 1B/M2.2 while-light flare of August
12, 1981. The two brightest flare knots located in the penumbra of
a sunspot with a δ configuration are investigated. The 1 ± V line
profiles are analyzed. The reduction and analysis of our observations
have yielded the following results. (1) The line profiles changed
significantly during the flare, especially at the time of optical
continuum emission observed near the flare maximum. In addition to the
significant decrease in the depth, a narrow polarized emission whose
Zeeman splitting corresponded to a longitudinal magnetic field strength
of 3600 Gs was observed. This is much larger than the magnetic field
strength in the underlying sunspot determined from the Zeeman splitting
of absorption lines. (2) The largest changes of the CaI λ6102.7 Å
line profile observed during the flare can lead to an underestimation
of the longitudinal magnetic field strength measured with a video
magnetograph by a factor of 4.5, but they cannot be responsible for
the polarity reversal. (3) A sharp short-term displacement of the
neutral line occurred at a time close to the flare maximum, which
gave rise to a reversed-polarity magnetic field on a small area of the
active region, i.e., a magnetic transient. This can be interpreted as
a change in the inclination of the magnetic field lines to the line
of sight during the flare. The short-term depolarization of the CaI
λ6102.7 Å line emission observed at the other flare knot can also
be the result of a change in the magnetic field structure. (4) These
fast dynamic changes of the magnetic field lines occurred after the
maximum of the impulsive flare phase and were close in time to the
appearance of type II radio emission.
Title: Ni I 6768 Å line profile variations during a solar flare
and their effect on the SOHO/MDI magnetic field measurements
Authors: Babin, A. N.; Koval, A. N.
Bibcode: 2007BCrAO.103...63B
Altcode:
Observational data on the Ni I 6768 Å line profile variations during
the impulsive and post-impulsive phases of the July 18, 2002 while
light flare (WLF) in the kernel of WLF emission and in other flare
kernels are presented. The line profiles at the sites of intense
photospheric motions in active regions are also studied. The effect
of the observed Ni I 6768 Å line profile variations on the SOHO/MDI
magnetic field measurements is estimated. The following conclusions
have been reached. (1) The thermodynamic structure of the photo-spheric
layers changes significantly during the flare. As a result, the Ni
I line profile changes, particularly at the site of WLF emission. At
this time, the line depth decreases significantly, but the line does
not show any emission reversal. Subsequently, a relatively slow return
to the conditions of an undisturbed photosphere is observed. (2) The
technique of SOHO/MDI magnetic field measurements is insensitive to
such line variations. Therefore, the detected variations during the
flare did not result in any noticeable errors in the MDI longitudinal
magnetic field measurements. (3) The line profile is broadened, shifted
as a whole, and asymmetric at the sites of active regions where intense
photospheric motions appear. In the MDI measurements, such changes
in the profile lead to an underestimation of the magnetic field by
approximately 10% if the line-of-sight velocity of the photo-spheric
ejection is about 1.6 km s−1.
Title: Vertical and horizontal magnetic field structure in δ-spot
Authors: Babin, A. N.; Koval, A. N.
Bibcode: 2001IzKry..97...43B
Altcode:
The vertical and horizontal magnetic field structure and vertical
electric current densities in the AR NOAA 6659 have been investigated
from the analysis of the polarized spectral photographic observations
7 and 11 June 1991 in the wavelength interval 610.1-615.2 nm. The
following results were obtained: 1) The regions with different vertical
gradients of the magnetic field coexist simultaneously at the adjacent
parts of the δ-spot. 2) The penumbra of the δ-spot is the region
of strong and complex magnetic fields: at some sites of the penumbra
the strength of the magnetic field is higher by 400-500 Gs than at
adjacent umbra. 3) At the region of the largest flare activity the
magnetic field consists of the structural elements with size from
3 to 15 arcsec in which the transverse magnetic field directions are
distinguished by 90°. 4) Sharp change of the transverse magnetic field
direction with height were detected at some regions of δ-spot. 5)
The vertical electric current densities in the delta spot reach the
values up to 105A/km2 at the period without the
significant flare activity. 6) The rise of the magnetic flux tubes
with strong magnetic fields (3200-4000 Gs) with the line of sight
velocities of about 0.6-1.5 km/s have been detected. It was concluded
that the main peculiarity which determines high flare activity of
delta-spot configuration is the emergence of a new twisted rope with
high magnetic field in the region of strong nonpotential magnetic field.
Title: On the emission from the white light flare of 15 June 1991
in C I, C II, Mg II, and He II lines.
Authors: Babin, A. N.; Koval', A. N.
Bibcode: 1999KFNT...15...51B
Altcode: 1999KNFT...15...51B
The spectra of the brightest kernel in the 1991 June 15 white light
solar flare obtained during the impulsive phase are analysed. The
magnesium and carbon lines represent a range of flare plasma
temperatures from about 8000 K (C I) to 20000 K (C II). The authors
give the central peak intensity wavelength, width at half maximum,
total power radiated in the line obtained from the line emission
analysis for the central part of the white light flare kernel. The
emission lines of C I, Mg II, and He II are symmetrical, unshifted and
have a Gaussian profile. The profiles of C II lines are asymmetrical,
and fitting of two-Gaussian profiles to the C II λ657.8 nm line shows
that there is a redshifted component in addition to the unshifted
one. An upper temperature limit of about 30000 K was obtained for the
He II emission region.
Title: On the emission from the white-light flare of 15 June 1991
in C I, C II, Mg II, and He II lines.
Authors: Babin, A. N.; Koval', A. N.
Bibcode: 1999KPCB...15...36B
Altcode:
Analyzes the spectra of the brightest kernel in the white-light flare
of 15 June 1991 acquired during the impulsive phase. The emission
lines of C I, C II, Mg II, and He II in the region λλ651.7 - 659.8
nm are investigated. The magnesium and carbon lines represent a
range of flare plasma temperatures from about 8000 K (C I) to 20000
K (C II). The authors give the central peak intensity wavelength,
the width at half maximum, and the total power radiated in the lines
for the central part of the flare kernel. The C I, Mg II, and He II
emissions are symmetrical, unshifted, they have a Gaussian profile. The
C II λ657.8 nm profile is asymmetrical, it can be represented by
two Gaussian profiles, one unshifted and the other redshifted, the
latter corresponding to a dynamic plasma moving with a line-of-sight
velocity of about 20 km/s. Nonthermal line broadening increases with
flare plasma temperature from 4 km/s for T = 10000 K to 10 km/s for T
= 20000 K. The observed He II λ656.0 nm line width gives T = 30000
K for the upper temperature limit in the He II emission region. The
intensities of this line are also used to determine the upper level
population and the upper limit of the lower level population in the
corresponding transition (6-4). The population of level 4 was found
to be by a factor of 100 higher than the population determined for
other flares from the intensity of the He II λ468.4 nm (4-3) line
under the assumption of its small optical thickness. The line He II
λ468.6 nm seems not to be optically thin.
Title: The white-light flare of 15 June 1991: observations and
model calculations.
Authors: Babin, A. N.; Baranovskij, Eh. A.; Koval', A. N.; Kalman,
B.; Gerlei, O.
Bibcode: 1998KPCB...14..253B
Altcode:
Observations of the white-light flare (WLF) of 15 June 1991 are
analyzed. Photographic observations at 550 nm were made at the Debrecen
Observatory, and spectra of the brightest knot (λλ651.7 - 659.7 nm)
were acquired at the Crimean Observatory during the impulsive phase. The
flare spectrum was peculiar even for WLFs. The continuum intensity
substantially increased toward shorter wavelengths - it was 120%
of the quiet photosphere brightness at 656 nm and 150% at 550 nm. All
photospheric absorption lines were almost completely filled in the flare
core spectrum. Previously unreported emission lines He II λ656.01 nm,
C I λ658.77 nm, C II λ657.80 and λ658.28 nm, and Mg II λ654.59 nm
were observed. The Hα line had very extensive emission wings (about
4 nm wide) and a central reversal. The total flare energy in the
optical continuum was 2.7×1024J. Based on the continuum
brightness at two wavelengths and eight photospheric line profiles,
the authors calculated a model atmosphere for the brightest knot in
the flare during its impulsive phase. The best fit to the observations
is obtained with a model which has two hot emission layers, one with
a temperature up to 30000 K in the lower photosphere (τ > 1) and
the second with a temperature of about 6700 K in the upper photosphere.
Title: Flares above sunspots and magnetic fields (abstract)
Authors: Babin, A. N.; Koval, A. N.
Bibcode: 1998PAICz..88...89B
Altcode:
No abstract at ADS
Title: An Investigation of the Motion of the Site of the Impact of
Comet Shoemaker-Levy 9 Fragment G on Jupiter
Authors: Babin, A. N.; Koval', A. N.
Bibcode: 1996SoSyR..30..131B
Altcode:
The revolution velocity of the impact site of the comet ShoemakerLevy
9 fragment G is deter- mined on the basis of photographic observations
of Jupiter from July 28 until August 31, 1994. It proved to be smaller
than the velocity of Jovian system III by 0.584 0.017 deg/day. This
difference can imply a proper east- ward motion of the impact site
with a velocity of 6 m/s.
Title: Spectroscopic and monochromatic studies of a white flare of
15 June 1991
Authors: Babin, A. N.; Koval, A. N.; Ogir, M. B.
Bibcode: 1995BCrAO..92...22B
Altcode:
No abstract at ADS
Title: Observations of magnetic fields in the upper chromosphere in
the He I line lambda 10830 Å
Authors: Babin, A. N.; Koval', A. N.; Shcherbakova, Z. A.
Bibcode: 1994AstL...20..508B
Altcode: 1994PAZh...20..599B
No abstract at ADS
Title: Investigation of the white flare of June 15, 1991
Authors: Babin, A. N.; Koval, A. N.
Bibcode: 1993BCrAO..88...51B
Altcode:
No abstract at ADS
Title: Magnetic field in the chromosphere and corona of the spot
group SGD 26825 (1991 June).
Authors: Nesterov, N. S.; Babin, A. N.; Koval', A. N.; Moiseev, I. G.
Bibcode: 1992SvAL...18..446N
Altcode: 1992PAZh...18.1088N
According to the data of radio and optical measurements, magnetic
fields with unusually high strengths B > 2.6 kG and with a complex
structure were detected in the chromosphere and corona of the spot
group SGD 26825; the fields existed during 3 days.
Title: Spectral observations of the white-light solar flare of June
15, 1991
Authors: Babin, A. N.; Koval, A. N.
Bibcode: 1992SvAL...18..294B
Altcode: 1992PAZh...18..727B
Spectra of the white-light flare knot obtained during the pulse
phase of a 3B-importance flare in the 6517-6598-A range are
investigated. Features of the continuum and H-alpha emission are
determined, and energy characteristics of the flare are estimated.
Title: Above-sunspot flares and magnetic fields. II
Authors: Babin, A. N.; Koval, A. N.
Bibcode: 1992BCrAO..84..133B
Altcode:
No abstract at ADS
Title: Flares above sunspots and magnetic fields. I.
Authors: Babin, A. N.; Koval', A. N.
Bibcode: 1992BCrAO..82..119B
Altcode:
Magnetic fields have been examined for two flares of magnitude 2B in the
penumbra of spots with δ-configurations by reference to the emission
lines of iron, D1 and D2 lines of sodium, and
D3 for helium, the magnetic fields of the spots on which
the flares occurred were also determined. The emission from the metals
and helium occurred not more than 3″from the points at which the
fields changed sign in the spots; the field strengths indicated by the
metal emission lines were over 2000 G, while those indicated by helium
were about 1000 G, but with the polarity unaltered. The observations
indicate that there are elements unresolved by the telescope having
magnetic fields opposite in direction. The line-of-sight velocities
have been determined from the emission and absorption lines. Material
in the deeper layers rises and that in the upper layers sinks with
velocities of 1 - 3 km/sec.
Title: Magnetic "flags"
Authors: Babin, A. N.; Koval, A. N.
Bibcode: 1992BCrAO..86..143B
Altcode:
No abstract at ADS
Title: Flares on a spot and magnetic fields. III
Authors: Babin, A. N.; Koval, A. N.
Bibcode: 1992BCrAO..86..136B
Altcode:
No abstract at ADS
Title: Flares above sunspots and magnetic fields. Part 1
Authors: Babin, A. N.; Koval, A. N.
Bibcode: 1990BCrAO..82..119B
Altcode:
No abstract at ADS
Title: Flare above sunspots and magnetic fields. I.
Authors: Babin, A. N.; Koval', A. N.
Bibcode: 1990IzKry..82..129B
Altcode:
The magnetic fields in two importance 2B flares that were located in
the penumbra of sunspots with δ-configuration have been determined
by Zeeman splitting of the emission lines of Fe I, D1
and D2 Na I and D3 He I. The magnetic fields of
the sunspots were estimated, too. The metal and helium emissions are
located not further than 3 arcsec from the place of the sign change
of the sunspot's magnetic field. The strength of the magnetic field
calculated from metal emission lines exceeds 2000 Gs, from helium lines
it is about 1000 Gs, and the polarity reversal is not observed. Within
the same volume of sunspots the observations revealed the coexistence of
subtelescopic elements with magnetic fields of opposite direction. The
line-of-sight velocities in flares are estimated by emission and
absorption lines. The matter is ascending at a deeper level of the
solar atmosphere and descending at a upper level with velocities of 1 -
3 km/s.
Title: Determination of moustache's linear polarization parameters
from monochromatic observations.
Authors: Babin, A. N.; Koval', A. N.
Bibcode: 1988IzKry..80..110B
Altcode:
The time dependence of moustache's contrast, polarization degree and
polarization plane orientation are studied with a time resolution of
≡20 s.
Title: Determination of the linear polarization parameters of whiskers
from monochromatic observations
Authors: Babin, A. N.; Koval, A. N.
Bibcode: 1988BCrAO..80..106B
Altcode: 1990BCrAO..80..106B
Variations of the contrast, degree of polarization, and
polarization-plane azimuths of whiskers with time were studied at a
time resolution of ≡20 sec.
Title: An investigation of the linear polarization of whiskers
Authors: Babin, A. N.; Koval, A. N.
Bibcode: 1987BCrAO..77....8B
Altcode: 1989BCrAO..77....8B
No abstract at ADS
Title: Investigation of linear polarization of moustaches.
Authors: Babin, A. N.; Koval', A. N.
Bibcode: 1987IzKry..77....9B
Altcode:
A technique for the observation of the polarization of solar
emission features in the H-alpha line is described. The technique
makes it possible to obtain, in one exposure, a set of four polarized
spectrograms of the same region of the sun for four positions of the
linear-polarization analyzer axes which are separated by 45 deg. The
proposed method can be used to determine all of the parameters of
the linear polarization of emission. The results of the investigation
of the emission polarization of moustaches in one active region are
presented. The degree of polarization and its distribution along the
H-alpha profile is determined as well as the azimuths of the moustache
polarization plane.
Title: Examining whisker polarization with a Hα filter
Authors: Babin, A. N.; Koval, A. N.
Bibcode: 1986BCrAO..75...48B
Altcode: 1986BuCri..75...48B; 1987BCrAO..75...48B
No abstract at ADS
Title: On the investigation of polarization of moustaches with a
Hα filter.
Authors: Babin, A. N.; Koval, A. N.
Bibcode: 1986IzKry..75...52B
Altcode:
The results of the first investigation of linear polarization of
moustaches' emission with a birefringent Hα filter and a λ/2 plate are
presented. The authors have found a short-living (1 - 3m)
considerable (up to some tens per cent) polarization of moustaches
which may appear some times during their lifetime. For the rest time
it is smaller or absent at all. The orientation of the electric vector
vibration in the considered moustaches is close to the center of the
solar disc direction and approximately parallel to filaments of the
arch system.
Title: On the Fine Structure of Polarized Elements in Solar Flares
and Moustaches
Authors: Babin, A. N.; Koval, A. N.
Bibcode: 1985SoPh...98..159B
Altcode:
Hα spectral observations of flares and moustaches using linear
polarization analyser have been carried out. It is found that some
flare knots and moustaches show strong polarization.
Title: On the polarization of emission of moustaches observed near
the solarlimb.
Authors: Babin, A. N.; Koval, A. N.
Bibcode: 1985IzKry..73....3B
Altcode:
H-alpha spectral observations of moustaches carried out with a
linear polarization analyzer are presented with attention given to
four cases in which the moustaches assume different forms in the
orthogonal polarization spectra: these differences are manifested
either in moustache structure or luminosity. In all cases, the
greatest differences can be seen in the red wing of the H-alpha line;
this finding suggests that there may be asymmetry in the polarization
structure. The degree of polarization of moustache emission is high (up
to 24 percent), exceeding theoretical resonance scattering values. In
close moustache pairs, only the weak component is polarized. It is
suggested that the emission only during the brightening stage. For
polarized for moustaches or of their finely structured elements is
polarized only during the brightening stage. For polarized moustache
emission, electric vector oscillations move predominantly in the
direction perpendicular to the magnetic field.
Title: Fine structure of polarized flare elements
Authors: Babin, A. N.; Koval, A. N.
Bibcode: 1985BCrAO..70....1B
Altcode: 1987BCrAO..70....1B
No abstract at ADS
Title: Hα line shape and linear polarization during the
pulse phases of two solar flares
Authors: Babin, A. N.; Koval, A. N.
Bibcode: 1985BCrAO..72..122B
Altcode: 1987BCrAO..72..122B
No abstract at ADS
Title: Investigation of the linear polarization and H-alpha line
profiles during the pulsed phase of two solar flares
Authors: Babin, A. N.; Koval, A. N.
Bibcode: 1985IzKry..72..142B
Altcode:
Attention is given to the profiles and linear polarization of
the H-alpha line in importance 2B and 1B flares. Three types of
emission line profiles were observed simultaneously: nearly symmetric
profiles with and without absorption in the line center, and asymmetric
profiles. Two components could be discerned in all cases: (1) emission
contributing to the central part of the line, and (2) emission
contributing to the extended wings. For the symmetric profiles, the
velocity of emitting-core motion toward the photosphere is 10-20 km/s;
it ceases at a later stage of the flare. For asymmetric profiles, the
downward radial velocity is 40-60 km/s. Linear polarization is observed
in six of twenty emission details of an importance 2B flare and in one
of five of an importance 1B flare. Polarization is observed either
throughout the profile, or only in the central part of the line. It
is noted that the degree and direction of polarization change upon
transition to neighboring points on the same flare knot.
Title: Fine structure of polarized flare elements
Authors: Babin, A. N.; Koval, A. N.
Bibcode: 1985IzKry..70....3B
Altcode:
The investigation of linear polarization of solar emission features
is being continued. From the spectral observations in the Hα line
obtained with high spatial resolution it was found that in a distance
scale of some arcsecond in some flare knots not only the value but
also the sign of the polarization determined by the authors 1983 is
changed. In the flare region some emission knots like moustaches or
grains of continuous emission show strong polarization.
Title: Solar limb whisker emission polarization
Authors: Babin, A. N.; Koval, A. N.
Bibcode: 1985BCrAO..73....1B
Altcode: 1987BCrAO..73....1B; 1985BuCri..73....1B
No abstract at ADS
Title: Variations in the magnetic fields of sunspots related to
flares.
Authors: Koval', A. N.; Stepanyan, N. N.
Bibcode: 1983PDHO....5..235K
Altcode: 1984PDHO....5..235K
The spectrograms of sunspots obtained at the tower telescope - BST-2
of the Crimean observatory with polarization analyzer have been
examined. The authors have measured the magnetic fields of sunspots
by Zeeman-splitting of eight spectral lines originating at different
depths in the solar atmosphere (from 60 km to 1200 km). A detailed
study of the magnetic field of two sunspot groups during the flares, of
importance 1B and 2N and with time resolution 1 - 7 min, has been made.
Title: Flare-associated changes in sunspot magnetic fields
Authors: Koval, A. N.; Stepanyan, N. N.
Bibcode: 1983BCrAO..68....1K
Altcode: 1985BCrAO..68....1K
No abstract at ADS
Title: A study of the linear polarization of some solar emission
features
Authors: Babin, A. N.; Koval, A. N.
Bibcode: 1983IzKry..66...89B
Altcode:
A study is made of the H-alpha spectrograms of two flares of importance
2 and four flares of importance 1, as well as six emission ejections
on the solar disc recorded by using linear polarization analyzers. The
features studied are characterized by strong emission asymmetry and
high velocities. Of the 27 features examined, nine exhibit noticeable
polarization, which exceeds the rms measurement error by a factor of
3-6. Polarization in the H-alpha line is asymmetrical, being much
more pronounced in the red region than in the blue region. Often,
polarization is observed in the red region only. In other cases, the
polarization of emission details does not differ within the experimental
uncertainty, from that of the instruments.
Title: Some results of a search for low-frequency plasma turbulence
in large chromospheric flares
Authors: Koval, A. N.; Oks, E. A.
Bibcode: 1983IzKry..67...90K
Altcode:
Data on line broadening in a turbulent plasma are reported, and the
possibility of detecting the hypothetic plasma turbulence in solar
flares is discussed. A method is proposed for analyzing the profiles
of the Balmer lines in the flares with allowance for the Fc electric
fields due to the low-frequency waves of plasma charge division. The
method is used to analyze Balmer line profiles in three proton flares,
and low-frequency fields with characteristic intensities of about 5 and
3 CGS are found in the flares of 08/18/59 and 09/26/63, respectively. It
is pointed out that further observations of the spectra of large flares
are needed to arrive at a definite conclusion.
Title: Variations of sunspot magnetic fields in relation to flares
Authors: Koval, A. N.; Stepanian, N. N.
Bibcode: 1983IzKry..68....3K
Altcode:
Spectrograms obtained with a polarization analyzer at the Crimean
Astrophysical Observatory are analyzed in order to determine the
relationship between magnetic field strengths in sunspots and solar
flare activity. Magnetic field strengths were measured by Zeeman
splitting in eight different spectral lines at various levels of
the solar atmosphere. Maximum magnetic field strength was recorded
at a level of 400-600 km. The appearance of solar flares was found
to coincide with increases in magnetic field strength in adjacent
sunspots. The average rates of the variations occurring before, during,
and after the flares were 356 (+ or - 75), -324 (+ or - 64), and -48
(+ or - 23) Gs per hour, respectively. Some possible explanations for
the coincidences are discussed.
Title: Linear polarization of some solar emission features
Authors: Babin, A. N.; Koval, A. N.
Bibcode: 1983BCrAO..66...81B
Altcode: 1985BCrAO..66...81B
No abstract at ADS
Title: Some results on low-frequency plasma turbulence in large
chromospheric flares
Authors: Koval, A. N.; Oks, E. A.
Bibcode: 1983BCrAO..67...78K
Altcode: 1985BCrAO..67...78K
No abstract at ADS
Title: Sunspot Magnetic Fields on 1981JUL28-31
Authors: Koval, A. N.; Stepanyan, N. N.
Bibcode: 1982IGAFS..62..249K
Altcode:
No abstract at ADS
Title: Continuous emission from flares
Authors: Baranovskii, E. A.; Koval, A. N.
Bibcode: 1982IzKry..65...35B
Altcode:
The distribution of the emission in the continuous spectrum and in
the wings of the K Ca II and D2 Na I lines is investigated for three
large flares. The characteristic features of the spectral distribution
are interpreted in terms of the thermal source of the emission. It is
shown that the emission source can only be in the deeper layers of the
atmosphere, that is, in the photosphere. The distribution of temperature
with optical depth is determined for four continuous emission cores. It
is found that the emission in the Balmer continuum observed in one of
the flares is caused by a thin layer in the photosphere at a depth
(tau0.5) of 0.3. The temperature in this layer reaches
8600 K.
Title: Some results of polarization observations of flares in the
visible region of the spectrum.
Authors: Koval', A. N.
Bibcode: 1982cis..conf..176K
Altcode:
No abstract at ADS
Title: The continuous emission of flares
Authors: Baranovskii, E. A.; Koval, A. N.
Bibcode: 1982BCrAO..65...31B
Altcode: 1984BCrAO..65...31B
No abstract at ADS
Title: Determination of the physical conditions in the
continuous-emission grains
Authors: Baranovskii, E. A.; Koval, A. N.
Bibcode: 1981BCrAO..64..119B
Altcode: 1984BCrAO..64..119B
No abstract at ADS
Title: A determination of the physical conditions of
continuous-emission grains
Authors: Baranovskii, E. A.; Koval, A. N.
Bibcode: 1981IzKry..64..127B
Altcode:
For continuous-emission grains, the way in which the amount of emission
depends on the wavelength in the continuous spectrum and in the wings
the K Ca II and D2 Na I lines is determined from observations. The
relation is then compared with a theoretical relation calculated
for various depths of occurrence of the grains. It is found that the
observed characteristics of the grains are well explained by a model
in which the temperature of the photospheric layers is increased by
200-300 K.
Title: The Profiles of the CAII H K in the Continuous Emission Threads
Authors: Koval, A. N.
Bibcode: 1980IzKry..61...20K
Altcode:
No abstract at ADS
Title: Continuous-spectrum energy distribution of flares, moustaches,
and emission grains
Authors: Koval, A. N.
Bibcode: 1979IzKry..59...64K
Altcode:
Data on the continuous spectra of solar flares, moustaches, and grains
are reviewed. The contrast of emission grains increases towards the
violet; the contrast of moustaches is practically independent of
wavelength; the contrast of flares slightly increases towards the
red. Energy distribution curves have a maximum at 4100-4200 A for the
grains and 4400-4500 A for moustaches and flares.
Title: Distribution of energy in the continuous spectrum of flares,
whiskers and emission grains
Authors: Koval, A. N.
Bibcode: 1979BCrAO..59...46K
Altcode:
No abstract at ADS
Title: Measurement of the magnetic fields in prominences and flares
by a photographic method
Authors: Koval, A. N.
Bibcode: 1977BCrAO..57..106K
Altcode:
No abstract at ADS
Title: On the measurement of magnetic fields in prominences and
flares by the photographic method.
Authors: Koval, A. N.
Bibcode: 1977IzKry..57..133K
Altcode:
Polarized H-alpha spectrograms of several active prominences and
flares are studied which were obtained with a quarter-wave plate
and a Wollaston prism attached to a small solar tower telescope. A
magnetic-field strength of 250 to 300 G is determined for two surge
prominences and shown to be within or slightly above the limits of
error. The magnetic-field strength is estimated to be 650 to 1000 G in
two knots of a third prominence. Large differences in line profiles are
observed in spectra of opposite polarization for several flare knots,
and it is found that certain flare knots consist of structural elements
with different polarizations. A significant degree of polarization is
measured in flare and prominence emission.
Title: Some parameters in forecasting of solar active region
development.
Authors: Koval', A. N.; Koval, A. N.; Stepanyan, N. N.
Bibcode: 1976str..book..235K
Altcode:
No abstract at ADS
Title: On the character of the emission lines asymmetry in some
limb flares.
Authors: Koval, A. N.
Bibcode: 1976IzKry..55...42K
Altcode:
A detailed study of H-alpha emission-line asymmetry at different
stages in the development of two limb flares has been carried out. It
is shown that the asymmetrical shape of the flare emission lines is
due to a superposition of weaker extended one-sided emission on the
flare emission.
Title: Some parameters in forecasting of solar active region
development
Authors: Koval, A. N.; Stepanyan, N. N.
Bibcode: 1976CoSka...6..235K
Altcode:
No abstract at ADS
Title: Variations of two-level magnetic fields and Halpha
-observations of the spot group on August 18 - 30, 1971.
Authors: Babin, A. N.; Kartashova, L. G.; Koval, A. N.; Ogir, M. B.;
Stepanian, N. N.
Bibcode: 1974IzKry..52...92B
Altcode:
Results are reported for H-alpha observations of a large sunspot group
and measurements of the magnetic field strengths in the 6302-A Fe I and
6103-A Ca I lines. Analysis of all the observational data shows that
(1) all centers of activity in the group are situated in regions of
contact between fields of opposite polarities; (2) sunspot activity
increases both with the formation of new magnetic hills and spots in
which the magnetic fields have the opposite polarity of the surrounding
field and with separation from the main group of nuclei whose magnetic
fields also have the opposite polarity of the surrounding field;
(3) the upper-level magnetic field (measured in the 6103-A line)
is greater than the lower-level one (measured in the 6302-A line)
prior to flare activity in nearby sunspots; and (4) an increase in the
strength of the upper-level field is also observed in connection with
absorption ejecta and arched filamentary systems.
Title: Some peculiarities of metal emission lines in flares and
moustaches.
Authors: Koval, A. N.
Bibcode: 1974IzKry..52..100K
Altcode:
Metallic emission-line splitting in solar flares is investigated
using data from hundreds of ground-based spectrograms. Emission-line
splitting is found not to be due either to magnetic field polarization
or the effect of Fraunhofer-line umbral translucence. Photometric
analysis of the Fe I lines shows that the line splitting is caused
by self-reversal of the optically thickest lines. The excitation
temperature of the absorption layers in two flares is determined to
be 6000 deg and 6500 deg, respectively. Examination of the nature
of metallic emission lines in moustaches shows that the appearance
of moustache emission is determined by the optical thickness of the
emission layer in a particular line.
Title: A dependence between flare activity of sunspot groups and
the orientation of the line dividing the magnetic field polarities.
Authors: Koval, A. N.
Bibcode: 1974IzKry..51...13K
Altcode:
No abstract at ADS
Title: Change of magnetic fields of spots on two levels in connection
with the development of active regions.
Authors: Koval', A. N.; Stepanyan, N. N.
Bibcode: 1973SZFiz...3..210K
Altcode:
No abstract at ADS
Title: Variations of magnetic fields of sunspots at two levels in
connection with the development of active regions.
Authors: Koval, A. N.; Stepanyan, N. N.; Stepanjan, N. N.
Bibcode: 1972BSolD1972...83K
Altcode:
No abstract at ADS
Title: Some parameters of flocculi characteristics for flare activity.
Authors: Brailovskaya, I. Yu.; Koval, A. N.; Ogir, M. B.; Stepanyan,
N. N.
Bibcode: 1972BSolD1972...88B
Altcode:
No abstract at ADS
Title: Quantitative analysis of the hydrogen lines in moustaches.
Authors: Koval, A. N.
Bibcode: 1972IzKry..44...94K
Altcode:
No abstract at ADS
Title: On the Asymmetry of Moustaches
Authors: Koval, A. N.; Severny, A. B.
Bibcode: 1970SoPh...11..276K
Altcode:
A careful photometry of moustaches is carried out to reveal asymmetry
of their emission in the far wings (Δλ ⩾ 1 Å), if it exists. The
presence of background continuous emission in spectra of moustaches
demands special care with the photometry, and makes the current method
of comparison of rest-intensities inadequate. The other sources
of errors are also discussed. The blue asymmetry, as a systematic
difference of intensities between the blue and the red wing shows itself
in some cases, being 2-3 times larger than the probable errors. In
most moustaches investigated, the accompanying background continuous
emission shows a rapid increase to the violet.
Title: Description and testing of the Horizontal Solar Telescope of
the Crimean Astrophysical Observatory.
Authors: Koval, A. N.; Stepanyan, N. N.
Bibcode: 1970IzKry..41..194K
Altcode:
No abstract at ADS