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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.
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.

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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.
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.

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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.
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.

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Title: Observational characteristics of the white-light flare of
    August 9, 2011
Authors: Babin, A. N.; Koval', A. N.
2014BCrAO.110..105B    Altcode:
  We analyzed the monochromatic H<SUB>α</SUB> 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 H<SUB>α</SUB> 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 × 10<SUP>10</SUP> ergs cm<SUP>-2</SUP> s<SUP>-1</SUP>, 1.5 ×
  10<SUP>27</SUP> ergs/s, and 5 × 10<SUP>29</SUP> ergs, respectively. The
  H<SUB>α</SUB> 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 H<SUB>α</SUB>
  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.

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Title: Analysis of observations of linear polarization for H
    <SUB>α</SUB> emission of flares and moustaches
Authors: Babin, A. N.; Koval, A. N.
2011BCrAO.107...36B    Altcode:
  In this paper we summarize and analyze the results of observation of
  linear polarization of H <SUB>α</SUB> 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 <SUB>α</SUB> emission in flares and moustaches.

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Title: The fine structure of the velocity field in a 2B/M2.3
    importance flare
Authors: Babin, A. N.; Koval', A. N.
2010KPCB...26..130B    Altcode:
  No abstract at ADS

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Title: Dynamical processes in the June 26, 1999 flare
Authors: Babin, A. N.; Koval, A. N.
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 H<SUB>α</SUB> profiles. The possibility of
  reconciling the results of observations with the theory of chromospheric
  evaporation is considered. The spectroscopic H<SUB>α</SUB> 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 H<SUB>α</SUB> 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 H<SUB>α</SUB> 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 H<SUB>α</SUB> 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.

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Title: The June 15, 1991 and June 26, 1999 white-light flares
Authors: Babin, A. N.; Koval, A. N.
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, H<SUB>α</SUB> 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 × 10<SUP>7</SUP> and 1.1. × 10<SUP>7</SUP> erg cm<SUP>−2</SUP>
  s<SUP>−1</SUP> nm<SUP>−1</SUP>. 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.

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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.
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.

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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.
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<SUP>−1</SUP>.

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Title: Vertical and horizontal magnetic field structure in δ-spot
Authors: Babin, A. N.; Koval, A. N.
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 10<SUP>5</SUP>A/km<SUP>2</SUP> 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.

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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.
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.

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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.
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.

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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.
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 2.7×10<SUP>24</SUP>J. 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 &gt; 1) and
  the second with a temperature of about 6700 K in the upper photosphere.

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Title: Flares above sunspots and magnetic fields (abstract)
Authors: Babin, A. N.; Koval, A. N.
1998PAICz..88...89B    Altcode:
  No abstract at ADS

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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.
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.

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Title: Spectroscopic and monochromatic studies of a white flare of
    15 June 1991
Authors: Babin, A. N.; Koval, A. N.; Ogir, M. B.
1995BCrAO..92...22B    Altcode:
  No abstract at ADS

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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.
1994AstL...20..508B    Altcode: 1994PAZh...20..599B
  No abstract at ADS

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Title: Investigation of the white flare of June 15, 1991
Authors: Babin, A. N.; Koval, A. N.
1993BCrAO..88...51B    Altcode:
  No abstract at ADS

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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.
1992SvAL...18..446N    Altcode: 1992PAZh...18.1088N
  According to the data of radio and optical measurements, magnetic
  fields with unusually high strengths B &gt; 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.

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Title: Spectral observations of the white-light solar flare of June
    15, 1991
Authors: Babin, A. N.; Koval, A. N.
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.

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Title: Above-sunspot flares and magnetic fields. II
Authors: Babin, A. N.; Koval, A. N.
1992BCrAO..84..133B    Altcode:
  No abstract at ADS

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Title: Flares above sunspots and magnetic fields. I.
Authors: Babin, A. N.; Koval', A. N.
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, D<SUB>1</SUB> and D<SUB>2</SUB> lines of sodium, and
  D<SUB>3</SUB> 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.

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Title: Magnetic "flags"
Authors: Babin, A. N.; Koval, A. N.
1992BCrAO..86..143B    Altcode:
  No abstract at ADS

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Title: Flares on a spot and magnetic fields. III
Authors: Babin, A. N.; Koval, A. N.
1992BCrAO..86..136B    Altcode:
  No abstract at ADS

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Title: Flares above sunspots and magnetic fields. Part 1
Authors: Babin, A. N.; Koval, A. N.
1990BCrAO..82..119B    Altcode:
  No abstract at ADS

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Title: Flare above sunspots and magnetic fields. I.
Authors: Babin, A. N.; Koval', A. N.
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, D<SUB>1</SUB>
  and D<SUB>2</SUB> Na I and D<SUB>3</SUB> 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.

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Title: Determination of moustache's linear polarization parameters
    from monochromatic observations.
Authors: Babin, A. N.; Koval', A. N.
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.

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Title: Determination of the linear polarization parameters of whiskers
    from monochromatic observations
Authors: Babin, A. N.; Koval, A. N.
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.

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Title: An investigation of the linear polarization of whiskers
Authors: Babin, A. N.; Koval, A. N.
1987BCrAO..77....8B    Altcode: 1989BCrAO..77....8B
  No abstract at ADS

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Title: Investigation of linear polarization of moustaches.
Authors: Babin, A. N.; Koval', A. N.
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.

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Title: Examining whisker polarization with a H<SUB>α</SUB> filter
Authors: Babin, A. N.; Koval, A. N.
1986BCrAO..75...48B    Altcode: 1986BuCri..75...48B; 1987BCrAO..75...48B
  No abstract at ADS

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Title: On the investigation of polarization of moustaches with a
    Hα filter.
Authors: Babin, A. N.; Koval, A. N.
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 - 3<SUP>m</SUP>)
  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.
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.
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.
1985BCrAO..70....1B    Altcode: 1987BCrAO..70....1B
  No abstract at ADS

---------------------------------------------------------
Title: H<SUB>α</SUB> line shape and linear polarization during the
    pulse phases of two solar flares
Authors: Babin, A. N.; Koval, A. N.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
1982IGAFS..62..249K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Continuous emission from flares
Authors: Baranovskii, E. A.; Koval, A. N.
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
  (tau<SUB>0.5)</SUB> 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.
1982cis..conf..176K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: The continuous emission of flares
Authors: Baranovskii, E. A.; Koval, A. N.
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.
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.
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.
1980IzKry..61...20K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Continuous-spectrum energy distribution of flares, moustaches,
    and emission grains
Authors: Koval, A. N.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
1972BSolD1972...88B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Quantitative analysis of the hydrogen lines in moustaches.
Authors: Koval, A. N.
1972IzKry..44...94K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: On the Asymmetry of Moustaches
Authors: Koval, A. N.; Severny, A. B.
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.
1970IzKry..41..194K    Altcode:
  No abstract at ADS