explanation      blue bibcodes open ADS page with paths to full text
Author name code: zakharov
ADS astronomy entries on 2022-09-14
=author:"Zakharov, V.V." 

---------------------------------------------------------
Title: Comets beyond 4 au: How pristine are Oort nuclei?
Authors: Fulle, Marco; Lazzarin, M.; La Forgia, F.; Zakharov, V. V.;
   Bertini, I.; Mazzotta Epifani, E.; Ammannito, E.; Buzzoni, A.; Capria,
   M. T.; Carbognani, A.; Da Deppo, V.; Della Corte, V.; Fiscale, S.;
   Frattin, E.; Inno, L.; Migliorini, A.; Pernechele, C.; Rotundi, A.;
   Sindoni, G.; Tubiana, C.; Milani, G.; Aletti, A.; Bacci, P.; Baj, G.;
   Bellini, F.; Bryssinck, E.; Di Grazia, M.; Facchini, M.; Feraco, M.;
   Guido, E.; Ligustri, R.; Kugel, F.; Maestripieri, M.; Tirelli, D.;
   Valvasori, A.; Snodgrass, C.; Jones, G. H.
2022MNRAS.513.5377F    Altcode:
  The ESA mission Comet Interceptor will target an Oort or interstellar
  comet during its first approach to the Sun. Meanwhile, the Vera
  Rubin LSST Survey will observe hundreds of active comets per month
  beyond 4 au from the Sun, where water vapour pressure is expected
  to be too low to eject dust. We discuss observations of dust tails
  at heliocentric distances larger than 4 au in order to retrieve the
  physical parameters driving cometary activity beyond Jupiter by means
  of a probabilistic tail model, which is consistent with the activity
  model defining the gas coma parameters due to the sublimation of carbon
  monoxide, molecular oxygen, methane, ethane, and carbon dioxide since
  the activity onset at 85 au from the Sun. We find that: (i) All the
  observed dust tails are consistent with the adopted activity model;
  (ii) The tail fits depend on three free parameters only, all correlated
  to the nucleus size; (iii) Tail fits are always improved by anisotropic
  dust ejection, suggesting activity of Oort nuclei dominated by seasons;
  (iv) Inbound seasons suggest cometary activity before the ejection of
  protocomets into the Oort cloud, as predicted by the activity model;
  (v) Oort nuclei larger than 1 km may be characterized by a fallout
  up to ≍100 m thick deposited during ≍60 yr inbound; (vi) On the
  other side, Oort nuclei smaller than 1 km may appear more pristine
  than Jupiter Family Comets when observed at 1 au from the Sun.

---------------------------------------------------------
Title: On the similarity of dust flows in the inner coma of comets
Authors: Zakharov, V. V.; Rotundi, A.; Della Corte, V.; Fulle, M.;
   Ivanovski, S. L.; Rodionov, A. V.; Bykov, N. Y.
2021Icar..36414476Z    Altcode:
  The atmosphere of a comet is formed by the sublimation, due to solar
  illumination, of its volatile component and the dust particles ejected
  from its nucleus and entrained by the gas flow. Contemporary dusty-gas
  coma models take into account numerous physical processes occurring in
  the coma and a complex geometry of the nucleus. For the description
  of the dusty-gas flow in the coma, such models introduce a large
  number of governing parameters characterizing physical properties
  and processes. The relative role of these processes is not easy
  to ascribe therefore a relevant inter-comparison of model results
  becomes difficult. <P />The present work introduces a set of universal,
  dimensionless parameters, which characterize the dust motion in the
  inner cometary coma. This approach allows one to: (i) reduce the number
  of parameters for analysis; (ii) reveal dust flows similarities; (iii)
  rescale the available numerical solutions. The present work demonstrates
  application of this approach to a realistic coma model. <P />Description
  of dust motion with dimensionless parameters allows us to make a
  parametric study for a broad range of conditions and to find simple
  analytic approximations (via a polynomial function) of the numerical
  results suitable for rough estimations of dust density in the coma.

---------------------------------------------------------
Title: Observational constraints to the dynamics of dust particles
    in the coma of comet 67P/Churyumov-Gerasimenko
Authors: Frattin, E.; Bertini, I.; Ivanovski, S. L.; Marzari, F.;
   Fulle, M.; Zakharov, V. V.; Moreno, F.; Naletto, G.; Lazzarin, M.;
   Cambianica, P.; Cremonese, G.; Ferrari, S.; Ferri, F.; Güttler, C.;
   La Forgia, F.; Lucchetti, A.; Pajola, M.; Penasa, L.; Rotundi, A.;
   Sierks, H.; Tubiana, C.
2021MNRAS.504.4687F    Altcode: 2021arXiv210410950F; 2021MNRAS.tmp.1157F
  In this work, we aim to characterize the dust motion in the inner
  coma of comet 67P/Churyumov-Gerasimenko to provide constraints for
  theoretical 3D coma models. The OSIRIS camera on-board the Rosetta
  mission was able for the first time to acquire images of single dust
  particles from inside the cometary coma, very close to the nucleus. We
  analyse a large number of particles, performing a significant
  statistic of their behaviour during the post-perihelion period, when
  the spacecraft covered distances from the nucleus ranging between
  80 and 400 km. We describe the particle trajectories, investigating
  their orientation and finding highly radial motion with respect to
  the nucleus. Then, from the particle brightness profiles, we derive a
  particle rotational frequency of ν &lt; 3.6 Hz, revealing that they
  are slow rotators and do not undergo fragmentation. We use scattering
  models to compare the observed spectral radiance of the particles with
  the simulated ones in order to estimate their size, finding values that
  range from millimetres up to centimetres. The statistics performed in
  this paper provide useful parameters to constrain the cometary coma
  dynamical models.

---------------------------------------------------------
Title: Practical relations for assessments of the gas coma parameters
Authors: Zakharov, V. V.; Rodionov, A. V.; Fulle, M.; Ivanovski,
   S. L.; Bykov, N. Y.; Della Corte, V.; Rotundi, A.
2021Icar..35414091Z    Altcode:
  To ensure the safety of a spacecraft and efficiency of the instrument
  operations it is indispensable to have simple (i.e. with minimal
  number of parameters and which does not require long time simulations)
  models for the assessments of the dusty-gas coma. A dusty-gas flow
  from cometary nucleus preserves common general structure regardless
  the features of a particular comet. Therefore, elementary models which
  account only for the main factors affecting the dusty-gas motion could
  be used for rough estimations of such characteristics and asymptotic
  behavior of dusty-gas motion. <P />In a wide range of conditions a
  presence of dust in the coma does not affect the gas motion. Therefore,
  it is possible to study the dynamics of a gas environment separately,
  without taking into account the dust. The present work is devoted
  to the gas environment of the comet. The main goal of the work is to
  develop a simplified model of gas environment which allows to estimate
  spatial distribution of gas parameters in the coma in the range of
  nucleus-centric distances from ten to thousand radius of the nucleus.

---------------------------------------------------------
Title: Experimental Phase Function and Degree of Linear Polarization
    Curves of Millimeter-sized Cosmic Dust Analogs
Authors: Muñoz, O.; Moreno, F.; Gómez-Martín, J. C.; Vargas-Martín,
   F.; Guirado, D.; Ramos, J. L.; Bustamante, I.; Bertini, I.; Frattin,
   E.; Markannen, J.; Tubiana, C.; Fulle, M.; Güttler, C.; Sierks,
   H.; Rotundi, A.; Della Corte, V.; Ivanovski, S.; Zakharov, V. V.;
   Bockelée-Morvan, D.; Blum, J.; Merouane, S.; Levasseur-Regourd,
   A. C.; Kolokolova, L.; Jardiel, T.; Caballero, A. C.
2020ApJS..247...19M    Altcode:
  We present laboratory measurements of the phase functions and degree of
  linear polarization (DLP) curves of a selection of millimeter-sized
  cosmic dust analog particles. The set includes particles with
  similar sizes but diverse internal structure (compact and porous) and
  absorbing properties. The measured phase functions are found to be in
  all cases very different from those of micron-sized particles. They
  show a monotonic decrease with increasing phase angle from the back-
  to the side-scattering region, reaching a minimum at large phase
  angles before a steep increase of the forward peak. This is in stark
  contrast to the phase functions of micron-sized particles, which are
  rather flat at low and intermediate phase angles. The maximum of the
  DLP for millimeter-sized compact particles is shifted toward larger
  phase angles (∼130°) compared to that of micron-sized particles
  (∼90°). Porosity plays an important role in the measured DLP
  curves: the maximum significantly decreases for increasing porosity
  as a result of multiple scattering within the particle. Large porous
  particles with highly absorbing inclusions can reproduce both the
  OSIRIS/Rosetta phase functions and ground-based DLP observations of
  comet 67P/Churyumov-Gerasimenko.

---------------------------------------------------------
Title: Models of Rosetta/OSIRIS 67P Dust Coma Phase Function
Authors: Moreno, F.; Guirado, D.; Muñoz, O.; Bertini, I.; Tubiana,
   C.; Güttler, C.; Fulle, M.; Rotundi, A.; Della Corte, V.; Ivanovski,
   S. L.; Rinaldi, G.; Bockelée-Morvan, D.; Zakharov, V. V.; Agarwal,
   J.; Mottola, S.; Toth, I.; Frattin, E.; Lara, L. M.; Gutiérrez,
   P. J.; Lin, Z. Y.; Kolokolova, L.; Sierks, H.; Naletto, G.; Lamy,
   P. L.; Rodrigo, R.; Koschny, D.; Davidsson, B.; Barucci, M. A.;
   Bertaux, J. -L.; Bodewits, D.; Cremonese, G.; Da Deppo, V.; Debei,
   S.; De Cecco, M.; Deller, J.; Fornasier, S.; Ip, W. -H.; Keller,
   H. U.; Lazzarin, M.; López-Moreno, J. J.; Marzari, F.; Shi, X.
2018AJ....156..237M    Altcode: 2018arXiv180910424M
  The phase function of the dust coma of comet 67P has been determined
  from Rosetta/OSIRIS images. This function shows a deep minimum at phase
  angles near 100°, and a strong backscattering enhancement. These
  two properties cannot be reproduced by regular models of cometary
  dust, most of them based on wavelength-sized and randomly oriented
  aggregate particles. We show, however, that an ensemble of oriented
  elongated particles of a wide variety of aspect ratios, with radii
  r ≳ 10 μm, and whose long axes are perpendicular to the direction
  of the solar radiation, are capable of reproducing the observed phase
  function. These particles must be absorbing, with an imaginary part
  of the refractive index of about 0.1 to match the expected geometric
  albedo, and with porosity in the 60%-70% range.

---------------------------------------------------------
Title: The near-nucleus gas coma of comet 67P/Churyumov-Gerasimenko
    prior to the descent of the surface lander PHILAE
Authors: Zakharov, V. V.; Crifo, J. -F.; Rodionov, A. V.; Rubin, M.;
   Altwegg, K.
2018A&A...618A..71Z    Altcode:
  Context. The European Space Agency (ESA) Rosetta mission was the
  most comprehensive study of a comet ever performed. In particular,
  the Rosetta orbiter, which carried many instruments for monitoring the
  evolution of the dusty gas emitted by the cometary nucleus, returned
  an enormous volume of observational data collected from the close
  vicinity of the nucleus of comet 67P/Churyumov-Gerasimenko. <BR />
  Aims: Such data are expected to yield unique information on the physical
  processes of gas and dust emission, using current physical model fits
  to the data. We present such a model (the RZC model) and our procedure
  of adjustment of this model to the data. <BR /> Methods: The RZC
  model consists of two components: (1) a numerical three-dimensional
  time-dependent code solving the Eulerian/Navier-Stokes equations
  governing the gas outflow, and a direct simulation Monte Carlo (DSMC)
  gaskinetic code with the same objective; and (2) an iterative procedure
  to adjust the assumed model parameters to best-fit the observational
  data at all times. <BR /> Results: We demonstrate that our model is
  able to reproduce the overall features of the local neutral number
  density and composition measurements of Rosetta Orbiter Spectrometer
  for Ion and Neutral Analysis (ROSINA) Comet Pressure Sensor (COPS)
  and Double Focusing Mass Spectrometer (DFMS) instruments in the period
  August 1-November 30, 2014. The results of numerical simulations
  show that illumination conditions on the nucleus are the main driver
  for the gas activity of the comet. We present the distribution of
  surface inhomogeneity best-fitted to the ROSINA COPS and DFMS in
  situ measurements.

---------------------------------------------------------
Title: Asymptotics for spherical particle motion in a spherically
    expanding flow
Authors: Zakharov, V. V.; Ivanovski, S. L.; Crifo, J. -F.; Della Corte,
   V.; Rotundi, A.; Fulle, M.
2018Icar..312..121Z    Altcode:
  In the context of an increasing number of complex multiparametric
  dust coma models it was found convenient to construct an elementary
  model with a minimum number of parameters selected to represent the
  key processes acting on the dust. The models outputs can be used
  as a reference evaluation of these processes with rough estimates
  of the resulting dust properties e.g. velocity. <P />The present
  work introduces three, universal, dimensionless parameters which
  characterize the dust motion in an expanding flow, and computes as
  a function of these parameters the dust terminal velocity, the time
  it takes to acquire it, and the distance at which it is acquired. <P
  />The motion of dust grains is presented as a system of dimensionless
  ordinary differential equations the solution of which depends upon the
  above mentioned three parameters. The numerical integration of this
  system was performed over a wide range of parameter space covering the
  whole range of physically possible conditions. <P />Precomputed results
  of dust terminal velocity, time and distance where it is reached are
  presented in dimensionless form. To obtain dimensional values for a
  particular case it is sufficient to perform algebraic operations.

---------------------------------------------------------
Title: The Near-Nucleus Dusty Gas Coma of Comet 67P Prior to the
    Descent of PHILAE
Authors: Zakharov, V. V.; Marzari, F.; Crifo, J. -F.; Bertini, I.;
   Rodionov, A. V.; Fulle, M.
2017EPSC...11..683Z    Altcode:
  We here describe the RZC model developed to predict the gas environment
  of the comet 67P (it was used for estimation of the aerodynamic forces
  on the Rosetta lander in November 2014) and the results of adjustment
  of this model to the observational data obtained by the Rosetta probe
  before landing. We outline the physical approach adopted to overcome the
  difficulties resulting from (1) the extreme complexity of the nucleus
  surface, (2) the absence of direct measurements of the gas flux at
  the surface itself, (3) the time-dependence of the gas production
  induced by the fast nucleus rotation. Also, we present the results
  of our attempts to fit the dust coma images obtained by the Optical,
  Spectroscopic, and Infrared Remote Imaging System (OSIRIS).

---------------------------------------------------------
Title: Dynamics of aspherical dust grains in a cometary atmosphere:
    I. axially symmetric grains in a spherically symmetric atmosphere
Authors: Ivanovski, S. L.; Zakharov, V. V.; Della Corte, V.; Crifo,
   J. -F.; Rotundi, A.; Fulle, M.
2017Icar..282..333I    Altcode:
  In-situ measurements of individual dust grain parameters in the
  immediate vicinity of a cometary nucleus are being carried by the
  Rosetta spacecraft at comet 67P/Churyumov-Gerasimenko. For the
  interpretations of these observational data, a model of dust grain
  motion as realistic as possible is requested. In particular, the results
  of the Stardust mission and analysis of samples of interplanetary dust
  have shown that these particles are highly aspherical, which should
  be taken into account in any credible model. The aim of the present
  work is to study the dynamics of ellipsoidal shape particles with
  various aspect ratios introduced in a spherically symmetric expanding
  gas flow and to reveal the possible differences in dynamics between
  spherical and aspherical particles. Their translational and rotational
  motion under influence of the gravity and of the aerodynamic force and
  torque is numerically integrated in a wide range of physical parameters
  values including those of comet 67P/Churyumov-Gerasimenko. The main
  distinctions of the dynamics of spherical and ellipsoidal particles
  are discussed. The aerodynamic characteristics of the ellipsoidal
  particles, and examples of their translational and rotational motion
  in the postulated gas flow are presented.

---------------------------------------------------------
Title: The 2016 Feb 19 outburst of comet 67P/CG: an ESA Rosetta
    multi-instrument study
Authors: Grün, E.; Agarwal, J.; Altobelli, N.; Altwegg, K.;
   Bentley, M. S.; Biver, N.; Della Corte, V.; Edberg, N.; Feldman,
   P. D.; Galand, M.; Geiger, B.; Götz, C.; Grieger, B.; Güttler, C.;
   Henri, P.; Hofstadter, M.; Horanyi, M.; Jehin, E.; Krüger, H.; Lee,
   S.; Mannel, T.; Morales, E.; Mousis, O.; Müller, M.; Opitom, C.;
   Rotundi, A.; Schmied, R.; Schmidt, F.; Sierks, H.; Snodgrass, C.;
   Soja, R. H.; Sommer, M.; Srama, R.; Tzou, C. -Y.; Vincent, J. -B.;
   Yanamandra-Fisher, P.; A'Hearn, M. F.; Erikson, A. I.; Barbieri, C.;
   Barucci, M. A.; Bertaux, J. -L.; Bertini, I.; Burch, J.; Colangeli,
   L.; Cremonese, G.; Da Deppo, V.; Davidsson, B.; Debei, S.; De Cecco,
   M.; Deller, J.; Feaga, L. M.; Ferrari, M.; Fornasier, S.; Fulle,
   M.; Gicquel, A.; Gillon, M.; Green, S. F.; Groussin, O.; Gutiérrez,
   P. J.; Hofmann, M.; Hviid, S. F.; Ip, W. -H.; Ivanovski, S.; Jorda,
   L.; Keller, H. U.; Knight, M. M.; Knollenberg, J.; Koschny, D.; Kramm,
   J. -R.; Kührt, E.; Küppers, M.; Lamy, P. L.; Lara, L. M.; Lazzarin,
   M.; Lòpez-Moreno, J. J.; Manfroid, J.; Epifani, E. Mazzotta; Marzari,
   F.; Naletto, G.; Oklay, N.; Palumbo, P.; Parker, J. Wm.; Rickman,
   H.; Rodrigo, R.; Rodrìguez, J.; Schindhelm, R.; Shi, X.; Sordini,
   R.; Steffl, A. J.; Stern, S. A.; Thomas, N.; Tubiana, C.; Weaver,
   H. A.; Weissman, P.; Zakharov, V. V.; Taylor, M. G. G. T.
2016MNRAS.462S.220G    Altcode: 2016MNRAS.tmp.1212G
  On 2016 Feb 19, nine Rosetta instruments serendipitously
  observed an outburst of gas and dust from the nucleus of comet
  67P/Churyumov-Gerasimenko. Among these instruments were cameras and
  spectrometers ranging from UV over visible to microwave wavelengths,
  in situ gas, dust and plasma instruments, and one dust collector. At
  09:40 a dust cloud developed at the edge of an image in the shadowed
  region of the nucleus. Over the next two hours the instruments
  recorded a signature of the outburst that significantly exceeded the
  background. The enhancement ranged from 50 per cent of the neutral gas
  density at Rosetta to factors &gt;100 of the brightness of the coma
  near the nucleus. Dust related phenomena (dust counts or brightness
  due to illuminated dust) showed the strongest enhancements (factors
  &gt;10). However, even the electron density at Rosetta increased by
  a factor 3 and consequently the spacecraft potential changed from
  ∼-16 V to -20 V during the outburst. A clear sequence of events
  was observed at the distance of Rosetta (34 km from the nucleus):
  within 15 min the Star Tracker camera detected fast particles (∼25
  m s<SUP>-1</SUP>) while 100 μm radius particles were detected by the
  GIADA dust instrument ∼1 h later at a speed of 6 m s<SUP>-1</SUP>. The
  slowest were individual mm to cm sized grains observed by the OSIRIS
  cameras. Although the outburst originated just outside the FOV of the
  instruments, the source region and the magnitude of the outburst could
  be determined.

---------------------------------------------------------
Title: 3D numerical simulations of radiative transfer in the
    cometary coma
Authors: Zakharov, V. V.; Crifo, J. -F.; Bockelée-Morvan, D.;
   Biver, N.
2013EPSC....8..719Z    Altcode:
  We report about the resent advances in the development of our 3D model
  of water excitation in cometary atmosphere in which radiation transfer
  is treated on the base of the accelerated Monte Carlo method.

---------------------------------------------------------
Title: 3D+t Mathematical Simulation of the Dusty-Gas Cometary
    Atmosphere (Application to the Comet 103P/ Hartley 2)
Authors: Zakharov, V. V.; Crifo, J. -F.; Rodionov, A. V.
2012epsc.conf..678Z    Altcode: 2012espc.conf..678Z
  We report the results of application of our 3D+t dustgas coma model to a
  model nucleus which shape and dimensions close to those of 103P/Hartley
  2 nucleus and conditions at the moment of closest approach i.e. at
  13:59:47.31 UTC on 4 November 2010 (1.064 AU from the Sun). We assume
  various cases of gas and dust production of the nucleus taking into
  account available observational data.

---------------------------------------------------------
Title: Dynamics of aspherical dust for the GIADA experiment in the
coma of 67P/Churyumov- Gerasimenko: I. Comparison with the spherical
    approximation
Authors: Ivanovski, S. L.; Zakharov, V. V.; Crifo, J. -F.; Della Corte,
   V.; Fulle, M.; Rotundi, A.
2012epsc.conf..592I    Altcode: 2012espc.conf..592I
  We report the recent advances in developing of the model of aspherical
  dust grain dynamics [1] in the cometary atmosphere of 67P/Churyumov-
  Gerasimenko. The present model is aimed to support the scientific
  objectives of GIADA in-situ experiment [2] on board of the ESA ROSETTA
  probe and will provide predictions on the real dust cometary grains. The
  currently used 3D+t models [3, 4] assume sphericity of the grains but
  the dynamics of aspherical grains can be very different from spherical
  [5].At this stage we study grains moving under the influence of two
  forces: aerodynamic and gravitational and discuss the distinctions
  between the aspherical and the spherical approximations.

---------------------------------------------------------
Title: Investigation of dust and water ice in comet 9P/Tempel 1 from
    Spitzer observations of the Deep Impact event
Authors: Gicquel, A.; Bockelée-Morvan, D.; Zakharov, V. V.; Kelley,
   M. S.; Woodward, C. E.; Wooden, D. H.
2012A&A...542A.119G    Altcode:
  Context. The Spitzer spacecraft monitored the Deep Impact event on
  2005 July 4 providing unique infrared spectrophotometric data that
  enabled exploration of comet 9P/Tempel 1's activity and coma properties
  prior to and after the collision of the impactor. <BR /> Aims: The
  time series of spectra take with the Spitzer Infrared Spectrograph
  (IRS) show fluorescence emission of the H<SUB>2</SUB>O ν<SUB>2</SUB>
  band at 6.4 μm superimposed on the dust thermal continuum. These
  data provide constraints on the properties of the dust ejecta cloud
  (dust size distribution, velocity, and mass), as well as on the water
  component (origin and mass). Our goal is to determine the dust-to-ice
  ratio of the material ejected from the impact site. <BR /> Methods: The
  temporal evolution of the continuum was analyzed using a dust thermal
  model which considers amorphous carbon and intimate silicate-carbon
  mixtures. The water emission was extracted from the spectra and the
  water columns within the Spitzer extraction aperture were inferred
  using a fluorescence excitation model. Time-dependent models simulating
  the development of the ejecta cloud and the sublimation of icy grains
  were developed to interpret the temporal evolution of both dust and
  water emissions within the field of view. <BR /> Results: Both the
  color temperature of the grains in the ejecta cloud (375 ± 5 K)
  and their size distribution show that a large quantity of submicron
  grains were ejected by the impact. The velocity of the smallest grains
  is 230 m s<SUP>-1</SUP>, with a power index for the size dependence
  of 0.3-0.5, in agreement with gas loading. The total mass of dust is
  (0.7-1.2) × 10<SUP>5</SUP> kg for grain sizes 0.1-1 μm and (0.5-2.1)
  × 10<SUP>6</SUP> kg for sizes 0.1-100 μm. A sustained production
  of water is observed, which can be explained by the sublimation of
  pure ice grains with sizes less than 1 μm and comprising a mass
  of ice of (0.8-1.8) × 10<SUP>7</SUP> kg. The contribution of dirty
  ice grains to the ice budget is negligible. Assuming that water was
  essentially produced by icy grains present in the ejecta cloud, our
  measurements suggest a very high ice-to-dust ratio of about 10 in the
  excavated material, which greatly exceeds the gas-to-dust production
  rate ratio of ~0.5 measured for the background coma. Alternately, if
  a large amount of material felt back to the surface and sublimated,
  ice-to-dust ratios of 1-3 are not excluded. A better understanding of
  the cratering event on 9P/Tempel 1 is required to disentangle between
  the two hypotheses. Evidence for grain fragmentation in the ejecta
  cloud is found in the data. The pre-impact water production rate is
  measured to be (4.7 ± 0.7) × 10<SUP>27</SUP> mol s<SUP>-1</SUP>.

---------------------------------------------------------
Title: Model of Aspherical Dust Dynamics for GIADA Experiment in the
Coma of 67P/Churyumov-Gerasimenko: I. Comparison with the Spherical
    Approximation
Authors: Ivanovski, S. L.; Zakharov, V. V.; Crifo, J. F.; Della Corte,
   V.; Rotundi, A.; Fulle, M.
2012LPICo1667.6444I    Altcode:
  We report the recent advances in developing of the model of aspherical
  dust grain dynamics in the cometary atmosphere for GIADA experiment
  on a board of ROSETTA orbiter. We discuss its distinctions from the
  spherical grain model.

---------------------------------------------------------
Title: Mathematical Simulation of the 3D+t Dusty-Gas Cometary
    Atmosphere of Comet 103P/ Hartley 2
Authors: Zakharov, V. V.; Crifo, J. -F.; Rodionov, A. V.
2012LPICo1667.6401Z    Altcode:
  We report the results of application of our 3D+t dust-gas coma
  model to a model nucleus which shape and dimensions close to those of
  103P/Hartley 2 nucleus and conditions at the moment of closest approach
  in EPOXI mission.

---------------------------------------------------------
Title: Pure ice grains in the coma of 9P/Tempel 1 after Deep Impact
Authors: Gicquel, A.; Bockelée-Morvan, D.; Zakharov, V. V.; Kelley,
   M. S.; Woodward, C. E.; Wooden, D. H.
2011epsc.conf..233G    Altcode: 2011DPS....43..233G
  The Deep Impact (DI) spacecraft encountered comet 9P/Tempel 1 on July
  4th, 2005. The spacecraft released an impactor that collided with the
  comet nucleus and excavated (possibly unprocessed) cometary material
  in a prominent ejecta plume. We report on the temporal evolution
  of water molecules observed with the IRS instrument on the Spitzer
  Space telescope after impact. We show that it can only be explained
  by the presence of subliming pure ice grains. The mass of water ice
  in subliming 0.1 - 1 μm grains is close to 2 x 106 kg.

---------------------------------------------------------
Title: A numerical study of the dusty-gas atmosphere of comet
    67P/Churyumov-Gerasimenko
Authors: Zakharov, V. V.; Rodionov, A. V.; Crifo, J. -F.; Fulle, M.
2011epsc.conf..126Z    Altcode: 2011DPS....43..126Z
  We apply out 3D+t model to study the influence of H2O and CO production
  and its nonuniformity on the gas and dust dynamics in the vicinity of
  a rotating three-dimensional nucleus. The parameters of simulations
  correspond to the conditions of the rendezvous of the Rosetta probe
  with the comet 67P/Churyumov-Gerasimenko. We assume various models of
  gas and dust production of the nucleus taking into account available
  VLT observations. We present also the estimations of aerodynamic forces
  and dust contamination of the Rosetta orbiter and the lander.

---------------------------------------------------------
Title: Monte-Carlo and multifluid modelling of the circumnuclear dust
    coma II. Aspherical-homogeneous, and spherical-inhomogeneous nuclei
Authors: Zakharov, V. V.; Rodionov, A. V.; Lukianov, G. A.; Crifo,
   J. F.
2009Icar..201..358Z    Altcode:
  We use our newly developed Dust Monte-Carlo (DMC) simulation technique
  [Crifo, J.F., Lukianov, G.A., Rodionov, A.V., Zakharov, V.V.,
  2005. Icarus 176, 192-219] to study the dynamics of dust grains in
  the vicinity of some of the benchmark aspherical, homogeneous cometary
  nuclei and of the benchmark spherical, inhomogeneous nuclei studied by
  us precedingly. We use the interim unrealistic simplifying assumptions
  of grain sphericity, negligible nucleus rotation rate, and negligible
  tidal force, but take accurately into account the nucleus gravitational
  force, gas coma aerodynamic force, and solar radiation pressure force,
  and consider the full mass range of ejectable spherical grains. The
  resulting complicated grain motions are described in detail, as well
  as the resulting complicated and often counter-intuitive dust coma
  structure. The results are used to answer several important questions:
  (1) When computing coma dust distributions, (a) is it acceptable to
  take into consideration only one or two of the above mentioned forces
  (as currently done)? (b) to which accuracy must these forces be known,
  in particular is it acceptable to represent the gravity of an aspherical
  nucleus by a spherically symmetric gravity? (c) how do the more
  efficient but less general Dust Multi-Fluid (DMF) computations compare
  with the DMC results? (2) Are there simple structural relationships
  between the dust coma of a nucleus at small heliocentric distance r, and
  that of the same nucleus at large r? (3) Are there similarities between
  the gas coma structures and the associated dust coma structures? (4)
  Are there dust coma signatures revealing non-ambiguously a spherical
  nucleus inhomogeneity or an homogeneous nucleus asphericity? (5)
  What are the implications of the apparently quite general process of
  grain fall-backs for the evolution of the nucleus surface, and for
  the survival of a landed probe?

---------------------------------------------------------
Title: Navier Stokes and direct Monte-Carlo simulations of the
    circumnuclear gas coma. III. Spherical, inhomogeneous sources
Authors: Zakharov, V. V.; Rodionov, A. V.; Lukyanov, G. A.; Crifo,
   J. F.
2008Icar..194..327Z    Altcode:
  We pursue our program of comparative simulations of the cometary
  gas coma by the two most advanced techniques available: (1) numerical
  solution of Navier-Stokes equations coupled to the Boltzman equation in
  the surface boundary layer, and (2) direct Monte-Carlo simulation. Here,
  we consider two different spherical but compositionally inhomogeneous
  nuclei, at three very different levels of gas production. The results
  show the same excellent agreement between the two methods in a domain
  adjacent to the surface as found precedingly, practically down to
  free-molecular conditions. A wealth of coma density patterns with
  non-intuitive structure is obtained. Some of these structures appear
  even under free-molecular effusion from the surface. The physical origin
  of all structures is discussed, and their evolution with changing
  gas production is studied. The computed comae are compared to those
  computed by various authors precedingly. Intercomparison of the present
  results demonstrates that differing inhomogeneity patterns may lead to
  similar structures in the gas coma. Comparison between these structures
  and those created by homogeneous, aspherical surfaces shows that it
  is not possible to guess from empirical rules which one of the two
  processes is responsible for the creation of a given structure. The
  implications for the interpretation of future high resolution images,
  or of future in situ mass spectrometric samplings of the near-nucleus
  gas coma are discussed.

---------------------------------------------------------
Title: Monte-Carlo Modelling of the Circumnuclear Dust Coma: Benchmark
    Aspherical-Homogeneous and Spherical-Inhomogeneous Nuclei
Authors: Zakharov, V. V.; Crifo, J. F.; Lukianov, G. A.; Rodionov,
   A. V.
2008LPICo1405.8148Z    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Numerical Simulations of Water Spectra Obtained with the
    Microwave Instrument for the Rosetta Orbiter (MIRO) from Comet
    67P/Churyumov-Gerasimenko
Authors: Zakharov, V. V.; Bockelée-Morvan, D.; Biver, N.; Crovisier,
   J.; Crifo, J. F.; Gulkis, S.; Rodionov, A. V.
2008LPICo1405.8144Z    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: High-resolution CN spectroscopy of small-scale solar magnetic
    features
Authors: Zakharov, V. V.; Gandorfer, A.; Solanki, S. K.
2007msfa.conf..161Z    Altcode:
  High-resolution spectroscopic observations of small-scale magnetic
  elements in the solar photosphere were carried out in the spectral
  region 387.5388.4 nm with the 1-m Swedish Solar Telescope (SST). This
  part of the spectrum covers not only the violet CN band-head, but also
  contains some lines of the CH molecule. The analysis of the line-core
  intensity contrasts of the CN and CH lines in bright points (BPs)
  yielded that on average the BPs appear brighter, thus providing a higher
  rms contrast, in the CN than in the CH lines in the same spectral band.

---------------------------------------------------------
Title: High-Resolution CN Spectroscopy of Small-Scale Solar Magnetic
    Features
Authors: Zakharov, V. V.; Gandorfer, A.; Solanki, S. K.
2006IAUJD...3E..87Z    Altcode:
  High-resolution spectroscopic observations of the Sun have been
  carried out with the TRIPPEL spectrograph installed at the new 1-m
  Swedish Solar Telescope (SST) using realtime AO correction. A detailed
  spectroscopic analysis of individual photospheric bright points (BP)
  and faculae-like structures simultaneously in two spectral domains,
  i.e 387.588&lt;λ&lt;388.473 nm (violet CN band) and in a blue spectral
  band at 436.1&lt;λ&lt;436.9 nm, containing absorption lines of CH,
  obtained at the disc center and near the limb is presented. The
  estimated spatial resolution of the obtained spectra is around
  0.25 arcsec while the spectral resolving power is around 130.000
  in the first domain, and 76.000 in the second spectral region,
  respectivlely. The first spectral band covers absorption lines of
  both, CH and CN molecules, as well as many atomic lines. This enabled
  us to make a quantitative comparison of their absorption and Doppler
  shifts in the different photospheric features. The absorption lines
  of the CN molecule and many atoms are depressed in a BP's interior
  with respect to those in the quiet Sun. Our quantitative comparison
  of the relative line depression of CH lines with respect to CN lines
  showed that the latter have weaker absorption by a factor of 1.28 at
  the disc centre and 1.32 near the limb. The CN line-core intensity,
  at the disc centre, has higher BP contrast than the contrast in the
  CH line-core by a factor of 1.9, and the ratio of these contrasts
  is decreasing with increasing continuum intensity of the BPs. This
  trend is similar to that obtained from previous simultaneous G-band
  and violet CN-band imaging observations. Measurements of contrasts and
  rms contrasts of line-core, integrated and local continuum intensities
  are provided. Analysis of Doppler shifts and line broadening of an
  Fe I line at 387.777 nm revealed an increase of the FWHM in the BP's
  interior and in dark intergranular lanes and a decrease with increasing
  intensity of the granules. The first results of a direct comparison
  of observed CN spectra with those simulated in MHD models in different
  photospheric features is presented.

---------------------------------------------------------
Title: A new approach for modeling the dust dynamics in the
    near-nucleus coma
Authors: Lukyanov, G. A.; Crifo, J. F.; Zakharov, V. V.; Rodionov,
   A. V.
2006AdSpR..38.1976L    Altcode:
  We describe the first step of development of a most general code for
  the investigation of the dust dynamics inside the gas-dust interaction
  region surrounding an active cometary nucleus. The code is based on a
  Monte Carlo approach, which allows (a) consideration of realistic, i.e.,
  extremely complicated assumptions with respect to the dust and nucleus
  size, shape and composition, (b) the derivation of the dust velocity
  distribution at each point, an information needed for the analysis of
  future in situ dust samplings, and (c) allowance for all the forces
  acting on the grains, i.e., aerodynamical, gravitational, radiative
  and inertial. In the present first step, the trivial (unrealistic)
  assumptions of nucleus and dust grain homogeneity and sphericity are
  still made, and only the nucleus gravity, the aerodynamic force and
  the radiation pressure force are considered. The code was tested
  assuming a Halley-like grain mass distribution extending from 10
  <SUP>-18</SUP> to 10 <SUP>-2</SUP> g, and nucleus H <SUB>2</SUB>O
  sublimation rates from 3 × 10 <SUP>26</SUP> to 3 × 10 <SUP>28</SUP>
  molecule/s. The results demonstrate that (1) even in this simple case,
  none of the preceding forces can be a priori neglected; (2) due to
  the combined action of these forces, a wealth of currently overlooked
  complex grain trajectories exist. These results are compared to the
  previously developed dust multi-fluid (DMF) method, thus evidencing
  the relative capabilities of the two methods.

---------------------------------------------------------
Title: Direct Monte Carlo and multifluid modeling of the circumnuclear
    dust coma. Spherical grain dynamics revisited
Authors: Crifo, J. -F.; Loukianov, G. A.; Rodionov, A. V.; Zakharov,
   V. V.
2005Icar..176..192C    Altcode:
  This paper describes the first computations of dust distributions in
  the vicinity of an active cometary nucleus, using a multidimensional
  Direct Simulation Monte Carlo Method (DSMC). The physical model is
  simplistic: spherical grains of a broad range of sizes are liberated
  by H <SUB>2</SUB>O sublimation from a selection of nonrotating sunlit
  spherical nuclei, and submitted to the nucleus gravity, the gas drag,
  and the solar radiation pressure. The results are compared to those
  obtained by the previously described Dust Multi-Fluid Method (DMF)
  and demonstrate an excellent agreement in the regions where the DMF
  is usable. Most importantly, the DSMC allows the discovery of hitherto
  unsuspected dust coma properties in those cases which cannot be treated
  by the DMF. This leads to a thorough reconsideration of the properties
  of the near-nucleus dust dynamics. In particular, the results show that
  (1) none of the three forces considered here can be neglected a priori,
  in particular not the radiation pressure; (2) hitherto unsuspected
  new families of grain trajectories exist, for instance trajectories
  leading from the nightside surface to the dayside coma; (3) a wealth
  of balistic-like trajectories leading from one point of the surface
  to another point exist; on the dayside, such trajectories lead to
  the formation of "mini-volcanoes." The present model and results
  are discussed carefully. It is shown that (1) the neglected forces
  (inertia associated with a nucleus rotation, solar tidal force) are,
  in general, not negligible everywhere, and (2) when allowing for these
  additional forces, a time-dependent model will, in general, have to
  be used. The future steps of development of the model are outlined.

---------------------------------------------------------
Title: Comparison between Navier-Stokes and DSMC Simulations of the
    Rarefied Gas Flow from Model Cometary Nuclei
Authors: Lukyanov, G. A.; Zakharov, V. V.; Rodionov, A. V.; Crifo,
   J. F.
2005AIPC..762..331L    Altcode:
  We compare two fundamental ways of modeling the steady gas flows in
  the near-nuclear atmosphere (coma) of comets. Several heliocentric
  distances and several homogeneous non-rotating model nuclei - spherical
  and aspherical - were considered, in order to cover a wide range of
  boundary conditions at the surface of the nucleus and of gas flow
  rarefaction in the coma. Two methods were used for simulations: (1)
  the Direct Monte-Carlo Simulation (DSMC), (2) the so-called “BE-NSE”
  method, which self-consistently solves the Boltzmann equation (BE)
  in the immediate nonequilibrium vicinity of the nucleus surface,
  and the Navier-Stokes equations (NSE) in the downstream region. For
  the BE solution, a locally plane-parallel approximation is made,
  using Cercignani's (1981) algorithms. The two methods were found to
  agree over an unexpectedly large parameter range. To maximize the
  modeling efficiency, a hybrid approach combining the BE-NSE approach
  in the denser regions, with DSMC in the more rarefied regions is
  also described.

---------------------------------------------------------
Title: Physical Model of the coma of Comet 67P/Churyumov-Gerasimenko
Authors: Crifo, J. F.; Lukyanov, G. A.; Zakharov, V. V.; Rodionov,
   A. V.
2004ASSL..311..119C    Altcode: 2004nrt..conf..119C
  No abstract at ADS

---------------------------------------------------------
Title: Physical Model of the Coma of Comet 67P/Churyumov-Gerasimenko
Authors: Crifo, J. -F.; Rodionov, A. V.; Bockelée-Morvan, D.;
   Lukyanov, G. A.; Zakharov, V. V.
2004cosp...35.1046C    Altcode: 2004cosp.meet.1046C
  Several Rosetta mission instruments will perform totally new
  observations which require an extremely realistic physical modelling
  of the coma -- not just approximate orders of magnitude: for instance,
  the high resolution mm wave sounder MIRO, and the in-situ dust velocity
  analyzer GIADA. In addition, the deposition of the lander will require
  an accurate and predictive model of the gas distribution. We describe
  the design specifications and the present state of an ongoing program
  of three-dimensional, time-dependent, physically realistic simulation
  of the gas and dust coma of the comet. The model excludes unphysical
  simplifications: the nucleus can have any external shape, and assume any
  realistic rotation state. The gas is assumed to be produced either by
  surface sublimation, or by diffusion from the interior, or by both
  processes, and the dust is assumed to be detached from it by the
  aerodynamic force. Realistic dust shapes can be handled. To compute
  the gas and dust distribution, the model uses Fluid Equations and/or
  Direct Monte-Carlo Simulations. For want of space, we cannot show here
  time-dependent simulations (see paper by A.V. Rodionov et al. in session
  B1.2), but only present a few recent steady-state results illustrating
  the present capabilities of the model: (1) an example of DSMC simulation
  of the gas coma near 3 AU, revealing the extent of the fluid region;
  (2) the computed structure of the near-nucleus gas and dust coma if the
  nucleus has a shape similar to that considered possible by Lamy et al
  (2003); (3) an example of DSMC simulation of the dynamics of heavy
  grains (near to the lift-off limit), showing complex trajectories as
  well as fall-backs onto the surface.

---------------------------------------------------------
Title: Navier-Stokes and direct Monte Carlo simulations of the
    circumnuclear coma II. Homogeneous, aspherical sources
Authors: Crifo, J. F.; Loukianov, G. A.; Rodionov, A. V.; Zakharov,
   V. V.
2003Icar..163..479C    Altcode:
  The dayside near-nucleus comae formed by solar-driven sublimation
  from two different aspherical nuclei made of an homogeneous mixture
  of ice and dust are computed by (1) solving Navier-Stokes equations
  and (2) direct Monte Carlo simulations, for different nucleus sizes,
  heliocentric distances, and dust-to-ice mixing ratios. Excellent
  agreement between the two methods is found down to surprisingly
  low production rates; it is found that the limit of validity of
  the first method is not simply related to the coma rarefaction: a
  new dimensionless number is tentatively offered to characterize this
  limit. The present solutions show that the weak shocks always present
  in the fluid coma persist practically down to truly free-molecular
  conditions, excluding the observational discovery of a structureless
  coma. They also show that rarefied flow in the near-nucleus coma can
  have a quite complicated structure, in particular inside topographic
  depressions. As an example, coma recondensation on the sunlit
  flanks of a cavity was found to be possible. We compute, for the
  first time, a true collisionless coma and show that structures are
  still present in it but are confined to the immediate vicinity of the
  surface. Finally, we describe in detail the kinetic conditions in a
  rarefied water coma, i.e., the velocity distribution asymmetry and
  the rotational-translational nonequilibrium. The significance of the
  results for future missions to comets is outlined.

---------------------------------------------------------
Title: Comparison between Navier-Stokes and Direct Monte-Carlo
    Simulations of the Circumnuclear Coma. I. Homogeneous, Spherical
    Source
Authors: Crifo, J. F.; Lukianov, G. A.; Rodionov, A. V.; Khanlarov,
   G. O.; Zakharov, V. V.
2002Icar..156..249C    Altcode:
  The structure of the near-nucleus H <SUB>2</SUB>O atmosphere formed by
  sublimation under solar heating of a hypothetical large dusty ice sphere
  is computed (1) by the direct simulation Monte-Carlo method (DSMC) and
  (2) by solving Navier-Stokes equations (NSE) combined with a locally
  plane-parallel solution of the collisional Boltzmann equation for the
  nonequilibrium near-surface Knudsen layer. For Hale-Bopp-like comets,
  perfect agreement is obtained between the two methods on the day and
  night sides. This excellent agreement is maintained on the near-nucleus
  dayside for less productive comets, even down to production rates as
  low as those expected for Comet P/Wirtanen near 3 AU. It provides a
  direct validation of the gasdynamic simulations performed in support
  of the ESA Rosetta mission lander descent optimization studies (Crifo
  et al. 2001) and also confirms the similarity between the dayside coma
  and underexpanded axially symmetric free jets pointed out in Crifo
  (1986). On the nightside, moderate to high discrepancies appear between
  the two solutions as the production rate decreases, revealing the limits
  of the NSE method. The limits of the present study are delineated,
  and directions for future investigations are indicated.