Tail Rays Research Articles

A Revised Understanding of the Structure of the Venusian Magnetotail From a High‐Altitude Intercept With a Tail Ray by Parker Solar Probe

AbstractOne of the major discoveries of NASA's 1979–1991 Pioneer Venus Orbiter is that the nightside ionosphere becomes filamentary at high altitude, forming comet‐like tail rays. Pioneer Venus Orbiter could not establish how much farther into the wake of Venus tail rays extend, nor understand how they form. Here we present plasma and fields data from the fourth flyby of Venus by NASA's Parker Solar Probe consistent with an intercept with an ionospheric tail ray. The observations unambiguously demonstrate that Venusian Ionotail Rays can extend to at least 7,800 km in altitude. Using the new Parker observations we are able to identify a tail ray encounter within the Venus Express dataset. We thus present a unified picture of the structure of the magnetotail of Venus based on combined Venus Express, Pioneer Venus Orbiter, and Parker observations, and recent hybrid modeling.

Structural analysis of the comet 45P/Honda based on isophote modeling

The work focuses on using the isophote method to construct a 45P/Honda comet model. At the same time, important problems were solved for modeling the physical surface of a comet and studying the structure of the cometary nucleus. This is due to the fact that, on the basis of modern studies of meteoroids, complex internal processes and dynamic phenomena on their surface have been discovered. The study of comet nuclei is of great importance, since, according to the theory of their formation, they were formed from the matter of the protoplanetary disk. Thus, modeling and analysis of the structure of various comets make it possible to create a more accurate theory of their evolution. This made it possible to evaluate the structural parameters more accurately and reliably. This allowed for the evaluation of the structural parameters more accurately and reliably. Isophotes of the nucleus, coma and tail of comet 45P/Honda were determined. Depending on the point where the comet is located on the trajectory of its orbit, one can see structural changes in the comet’s brightness from the nucleus to the peripheral region. Near the cometary nucleus, the isophotes are circular in shape. If in the center of the model the isophotes have a shape close to narrow rings, then elongations in the direction of the cometary tail and thickening of their structure appear towards the peripheral regions. Large and small tail rays can be distinguished, and the nucleus is well marked. In the future, the author’s method for modeling isophotes, developed in this work, will allow studying the structure of various cometary objects, and, based on the results, determine the degree of comet activity. On the other hand, about the development of the theory of dynamic processes and the evolution of the Solar system, one can use the data on changes in cometary activity in the process of its movement around the Sun.

TOPICAL ANTI-PSORIATIC NANOPARTICULATE DRUG DELIVERY SYSTEM

Objective: Development of effective drug delivery in the treatment of psoriasis is the major challenge for its successful management. To develop and assess the potential of Nanostructured Lipid Carriers (NLCs) enriched with the powdered leaves extracts of Azadirachta indica (AE), Lawsonia inermis (LE) and fruit extract of Mallotus philippensis (ME) in the management of psoriasis.
 Methods: Drug loaded NLCs were prepared via hot homogenization technique by adopting 23 factorial design with factors X1 as the concentration of lipids, X2 concentration of surfactants and X3 being the number of homogenization cycle. The responses Y1 and Y2 were particle size and zeta potential. The optimized batch was obtained from Surface response plot and was evaluated for zeta potential, % entrapment efficiency, % drug loading, Scanning Electron Microscopy(SEM), % in vitro diffusion of drugs from the NLCs, anti-lipid peroxidation and nitric oxide scavenging activities, cytotoxicity on HaCat cell lines, Mouse Tail and Rat ultraviolet ray B photodermatitis models for Psoriasis.
 Results: The optimized batch of NLCs was found within the nanosized range with a relatively low polydispersity index and zeta potential of-20mV. The %EE for an optimized batch of NLCs was found to be 98.97±0.83%, 96.99±0.56% and 99.25±0.55% and the %DL of 21.84±0.15%, 8.55±045%, and 87.91±0.38% respectively for AE, LE and ME.
 The SEM images showed the spherical vesicular structures of drugs loaded NLCs. The in-vitro diffusion of drugs from the NLCs followed initial burst release thereafter sustained release for 24 h. The AE, LE and ME loaded NLCs proved to possess anti-lipid peroxidation and nitric oxide scavenging activities, cytotoxicity on HaCat cell lines, DNA fragmentation on HaCat cell lines which are biomarkers in the pathogenesis of psoriasis. The results of Mouse Tail and Rat ultraviolet ray B photodermatitis models for Psoriasis supported the anti-psoriatic potential of AE, LE and ME loaded NLCs.
 Conclusion: AE, LE and ME loaded NLCs can be used for prolonged topical delivery to the psoriatic skin for an effective treatment.

Photometric study of the C/2014 Q2 (Lovejoy) comet plasma tails

Observations of C/2014 Q2 (Lovejoy) comet were carried out on 7th February, 2015, at the observation station in Mayaki village (No. 583 – Odesa-Mayaki observatory). The integrated-light photometry of the comet was conducted using RC-800 telescope (D = 80 cm; F = 214.0 cm) with FLI MicroLine 9000 CCD camera. The photometric primary reductions included dark-frame subtraction and flat-field correction. The photometric study of the comet plasma tails was performed using an interactive program to construct a series of longitudinal and transverse profiles of individual tail rays. The Shulman diffusion model was applied to interpret the calculated photometric profiles. The comparison of the experimental profiles and those calculated theoretically from the diffusion model enabled us to estimate the following physical parameters of the comet plasma tail: acceleration a = 176 m/sec2 and lifetime of fluorescent ions τ = 2.7⋅103 s; longitudinal and transverse diffusion coefficients, and magnetic flux density B = 97 ± 5.3 nT.

Evaluation of Calcein for Estimating Abundance of Lake Trout Alevins on a Spawning Reef

AbstractReproduction by stocked Lake Trout Salvelinus namaycush is generally estimated as the relative abundance of fry, that is, catch per unit effort in emergent fry traps and in beam trawls, but these estimates have high variance due to spatially heterogeneous distributions of fry. We used calcein, which produces a fluorescent mark in calcified structures, to batch‐mark fry and generate a mark–recapture estimate of fry abundance on a small, shallow spawning reef. Eggs collected from feral Lake Trout in Lake Champlain, Vermont were reared at ambient lake temperatures, and fry were marked 7 d after hatching. Fry were immersed in a salt solution for osmotic induction and then placed for 4 min in a calcein solution. After marking, 18,000 fry were released on a spawning reef, and 2,000 fry were maintained in the hatchery. Wild‐caught fry and hatchery fry were checked for marks every 2–9 d. Mark clarity was highest in the mandible and tail rays. Marks may have faded, but they did not disappear: marks were visible in the mandible in 100% of hatchery fry after 68 d. An average of 37% of wild‐caught fry had marks, yielding a Chapman population estimate (±SD) of 47,486±2,301. The mark–recapture estimate was within the range of fry abundance estimated over 6 years based on egg density data and estimates of hatching success but was substantially higher than estimated for the same year‐class. This work supports prior estimates of fry abundance and provides a potential method for assessing fry abundance on deep reefs and the success of fry stocking.Received June 4, 2013; accepted November 20, 2013

IMF-induced escape of molecular ions from the Martian ionosphere

Abstract. Since Mars does not possess a significant global intrinsic magnetic field, the solar wind interacts directly with the Martian ionosphere and can induce ion escapes from it. Phobos-2 and recent Mars Express (MEX) observations have shown that the escaping ions are O+ as well as molecular O2+ and CO2+. While O+ escape can be understood by the ion pick-up of non-thermal O corona extended around the planet, regarding the heavy molecular O2+ and CO2+, which are buried in the lower ionosphere, a novel escape mechanism needs to considered. Here we attack this problem by global magnetohydrodynamic (MHD) simulations. First, we clarify the global structure of the streamlines that result from the interaction with the solar wind. Then, by focusing on the streamlines that dip into the low-altitude part of the dayside ionosphere, we investigate the escape path of the molecular ions. The effects of the interplanetary magnetic field (IMF) on the molecular ion escape process are investigated by comparing the results with and without IMF. IMF has little effect on O+ escape via ion pick-up mediated by solar wind electron impact ionization of the O corona. O2+ and CO2+ are shoveled from the low-altitude regions of the dayside ionosphere by magnetic tension in the presence of IMF. These ions are pulled by the U-shaped field lines to the north and south poles, and at the terminator, they are concentrated in the noon–midnight meridian plane. These ions remain confined to the noon–midnight plane as they are transported to the nightside to form the tail ray. Then they escape along the streamlines open to the interplanetary space. Under a typical solar wind and IMF condition expected at Mars, O+, O2+ and CO2+ escape fluxes are 8.0 × 1023, 3.5 × 1023 and 5.0 × 1022 ion s−1, respectively, which are in good agreement with the MEX observations.

Thinking Globally, Acting Locally

Semaphorins function in neuronal pathfinding by stimulating the translation of transcripts localized to the growth cone. Targets of semaphorin-induced translation include cofilin and other proteins that promote depolymerization of F-actin and growth cone collapse. New findings from Nukazuka et al . (see commentary by Chisholm) suggest that semaphorin signaling is also required for the proper positioning of epithelial sensory organs called rays in the male C. elegans tail. In animals that carry loss-of-function mutations in both semaphorin-1 ( smp-1) and smp-2 or in the semaphorin receptor plexin-1 ( plx-1 ), the anteriormost ray is mispositioned, and this phenotype can be rescued by mutation of gcn-1 , which encodes a translational repressor. GCN1 activates GCN2, a kinase that represses eukaryotic translation initiation factor 2α (eIF2α). In a series of genetic interaction and overexpression experiments coupled with Western analysis, the authors demonstrated that phosphorylation of eIF2α (P-eIF2α) increased upon semaphorin signaling and decreased in gcn-1 mutants. They also showed that expression of a constitutively active form of eIF2α phenocopied the defects observed in the plx and smp mutants. Because P-eIF2α is a known translational stimulator, they examined expression and translation of the C. elegans cofilin homolog unc-60 in tail ray development. Semaphorin signaling stimulated unc-60 translation through indirect repression of eIF2α activity. Thus, semaphorin-mediated translational regulation is not limited to cells with highly asymmetric shapes such as neurons. Semaphorin signaling may also play a role in positioning epithelial cells, which, although polarized, are not as irregularly shaped as migrating neurons. A. Nukazuka, H. Fujisawa, T. Inada, Y. Oda, S. Takagi, Semaphorin controls epidermal morphogenesis by stimulating mRNA translation via eIF2α in Caenorhabditis elegans . Genes Dev. 22 , 1025-1036 (2008). [Abstract] [Full Text] A. D. Chisholm, Semaphorin signaling in morphogenesis: Found in translation. Genes Dev. 22 , 955-959 (2008). [Abstract] [Full Text]

A global model of cometary tail disconnection events triggered by solar wind magnetic variations

Presented in this paper are the results of a time‐dependent, fully three‐dimensional self‐consistent ideal magneto‐hydrodynamics (MHD) model of disconnection events (DEs) in the cometary plasma tail. Understanding the interaction of cometary plasma with the solar wind is a very important problem in space plasma physics. This study focuses on the detailed MHD processes which occur during DEs based on typical comets with ideal solar wind conditions, as well as different experiences of DEs triggered by different forms of heliospheric current sheet (HCS). The crossing process against a typical HCS, which is interpreted as various tangential discontinuities (TDs), is simulated. Tail rays and/or disconnected tails are formed in such simulations. With our line‐of‐sight integration results, we conclude that observers from different directions relative to the IMF plane will see two different types of DE image series. The magnetic reconnection that occurs in our results confirms previous publications from different models. With additional cases, our study also provides the limitation for such DEs to be triggered: the angle of magnetic field rotation across the TD should be within 90° to 270°. The effects of various intervals of multiple HCS crossings are explored to show that a 2‐h minimum interval is needed for consecutive multiple HCS to trigger a DE. In addition, such DEs caused by multiple HCS crossings have more tail rays and appear closer to observations than those resulted by single HCS crossings. In addition to presenting the first global DE time evolution with a well‐resolved contact‐surface, our results are compared morphologically with observational images. Quasi‐quantitative agreement with observational measurements is found by investigating the recession speed during the DE. Moreover, the importance of having a solar wind condition being able to trigger a frontside magnetic reconnection is found critical for such DEs to originate. The importance of a well‐resolved contact surface to this problem is discussed regarding to the mass loading effect. On the basis of our deductions and simulations, an empirical equation and data table to estimate the minimum upwind boundary distance is derived with respect to the shock distance, which is sensitive to the cometary production rate.

Glypican LON-2 Is a Conserved Negative Regulator of BMP-like Signaling in Caenorhabditis elegans

Bone morphogenetic protein (BMP) pathways are required for a wide variety of developmental and homeostatic decisions, and mutations in signaling components are associated with several diseases. An important aspect of BMP control is the extracellular regulation of these pathways. We show that LON-2 negatively regulates a BMP-like signaling pathway that controls body length in C. elegans. lon-2 acts genetically upstream of the BMP-like gene dbl-1, and loss of lon-2 function results in animals that are longer than normal. LON-2 is a conserved member of the glypican family of heparan sulfate proteoglycans, a family with several members known to regulate growth-factor signaling in many organisms. LON-2 is functionally conserved because the Drosophila glypican gene dally rescues the lon-2(lf) body-size defect. We show that the LON-2 protein binds BMP2 in vitro, and a mutant variation of LON-2 found in lon-2(e2140) animals diminishes this interaction. We propose that LON-2 binding to DBL-1 negatively regulates this pathway in C. elegans by attenuating ligand-receptor interactions. This is the first report of a glypican directly interacting with a growth-factor pathway in C. elegans and provides a mechanistic model for glypican regulation of growth-factor pathways.

Regulation of Growth by Ploidy in Caenorhabditis elegans

Some animals, such as the larvae of Drosophila melanogaster, the larvae of the Appendicularian chordate Oikopleura, and the adults of the nematode Caenorhabditis elegans, are unusual in that they grow largely by increases in cell size. The giant cells of such species are highly polyploid, having undergone repeated rounds of endoreduplication. Since germline polyploid strains tend to have large cells, it is often assumed that endoreduplication drives cell growth, but this remains controversial. We have previously shown that adult growth in C. elegans is associated with the endoreduplication of nuclei in the epidermal syncitium, hyp 7. We show here that this relationship is causal. Manipulation of somatic ploidy both upwards and downwards increases and decreases, respectively, adult body size. We also establish a quantitative relationship between ploidy and body size. Finally, we find that TGF-beta (DBL-1) and cyclin E (CYE-1) regulate body size via endoreduplication. To our knowledge, this is the first experimental evidence establishing a cause-and-effect relationship between somatic polyploidization and body size in a metazoan.

Three‐dimensional hybrid simulation of solar wind interaction with unmagnetized planets

The interaction between the solar wind and unmagnetized planets was investigated using computer simulation and a three‐dimensional hybrid code that treats kinetic ions and massless fluid electrons. In the simulation the planet was treated as an ionized gaseous body with uniform and constant supply of plasma. The results given in this paper showed that the shock size and magnetic barrier intensity are asymmetrical in the direction of the convection electric field because of oxygen ions escaping from the side of the planet to which the electric field was pointing. The calculated asymmetry in the magnetic barrier intensity was consistent with observations, although the direction of the calculated asymmetry in the shock size did not match the asymmetry observed near either Venus or Mars. When the planet size was comparable to the Larmor radius of protons, a multiple‐shock structure was observed in the simulation. It is suggested that this structure is due to dispersion of the magnetosonic waves caused by the finite Larmor radius of protons. The simulation results also showed that ions escaped to the magnetotail through the tail rays and that the tail rays were connected with the plasma sheet.

Acceleration of ionospheric plasma clouds in the Venus ionosheath

A discussion is presented to examine the acceleration and distribution of ionospheric plasma clouds around Venus. It is argued that magnetic forces may not be sufficient to accelerate those features and that their motion should also be influenced by the momentum of the solar wind around the flanks of the ionosheath. Plasma data obtained from selected Pioneer Venus Orbiter (PVO) passes show ionospheric clouds that have been displaced downstream from the planet, with a component directed away from the Venus plasma tail axis. The position and speed of these features suggests that they may not have been only accelerated by magnetic forces, but that most likely were also subject to effects produced by the kinetic energy of the solar wind. This suggestion derives from the observation of plasma tail rays with velocities comparable to the escape speed from the planet and also measurements of superalfvenic solar wind conditions around the flanks of the Venus ionosheath. While plasma clouds can be accelerated by magnetic forces near the subsolar region, where there is a strong accumulation of interplanetary magnetic field fluxes, the available experimental evidence shows that the Venus upper ionospheric plasma is accelerated mostly near the terminator, but not around the subsolar region. These views suggest that the ionospheric plasma clouds could be mostly accelerated around the flanks of the Venus ionosheath.

Regulation of body length and male tail ray pattern formation of Caenorhabditis elegans by a member of TGF-β family

We have identified a new member of the TGF-beta superfamily, CET-1, from Caenorhabditis elegans, which is expressed in the ventral nerve cord and other neurons. cet-1 null mutants have shortened bodies and male tail abnormal phenotype resembling sma mutants, suggesting cet-1, sma-2, sma-3 and sma-4 share a common pathway. Overexpression experiments demonstrated that cet-1 function requires wild-type sma genes. Interestingly, CET-1 appears to affect body length in a dose-dependent manner. Heterozygotes for cet-1 displayed body lengths ranging between null mutant and wild type, and overexpression of CET-1 in wild-type worms elongated body length close to lon mutants. In male sensory ray patterning, lack of cet-1 function results in ray fusions. Epistasis analysis revealed that mab-21 lies downstream and is negatively regulated by the cet-1/sma pathway in the male tail. Our results show that cet-1 controls diverse biological processes during C. elegans development probably through different target genes.

Three‐dimensional MHD simulation of the solar wind interaction with the ionosphere of Venus: Results of two‐component reacting plasma simulation

The large‐scale solar wind interaction with the Venusian ionosphere is numerically simulated in the framework of two‐component, three‐dimensional magnetohydrodynamics (MHD). The finite volume total variation diminishing scheme is used to solve this problem. The impinging solar wind is represented by H+ ions, and the ionosphere is assumed to consist of O+ ions produced by photoionization of atomic oxygen in the Venusian upper atmosphere and by charge exchange of CO2+ ions. The O+ ions are lost by charge exchange with carbon dioxide molecules. The numerical simulations are performed for an interplanetary magnetic field (IMF) perpendicular to the solar wind flow and for the solar wind parameters which correspond to maximum solar activity. Results of the calculation give the formation of the bow shock, the magnetic barrier, and the ionopause in the dayside region as a self‐consistent state of the interaction processes. The dynamical behavior of the dayside ionosphere under the influence of the impinging solar wind and the IMF slipping over the pole results in the formation of wing‐like bulges of the ionosphere and an accompanying poleward flow in the topside ionosphere. The model also reproduces several features of the nightside ionosphere that are predicted by earlier theories and observations, including complex structures such as a flattened ionotail, tail rays, and ionospheric holes, as a continuation of the wing‐like bulge. It is also shown that slow plasma flow in the ionotail and nonideal MHD process play important roles in the formation of the induced magnetotail of the planet.

Venus tail ray observation near Earth

In June, 1996, Venus passed through a very close inferior conjunction with the Sun. At that time the CTOF detector of the CELIAS mass spectrometer experiment on the SOHO spacecraft near Earth's L1 Lagrangian point was measuring heavy ions in the solar wind ∼4.5 × 107 km downstream of Venus. Close to the time predicted by simple geometric arguments for passage of SOHO through the Venus wake, CTOF made three encounters with unusual fluxes of O+ and C+ ions. Their energy distributions resembled those of tail rays originating in the Venus ionosphere or ionopause region rather than of ions produced in the corona of neutral atoms that surrounds the planet. The C+ abundance was ≈ 10% of O+. The observed O+ speed was very close to the simultaneous solar wind speed and the O+ temperature was a cool 5600 K/amu. The flux densities for the three events were (2.4–4.4) × 10³ cm−2s−1.

Cometosheath structures and tail rays: Outcome of bi-ion fluid simulations

Momentum coupling between the solar wind (SW) and the cometary plasma is a crucial element in the plasma dynamics around comets. A bi-ion fluid model is applied instead of one-fluid MHD normally used in 3D global simulations. This new approach accounts for the observational fact of spacecraft measurements at comets that in a region inside the bow shock beginning from about cometary distances, where the mass density of cometary ions and protons becomes comparable, complex interaction processes take place. They are manifested in pronounced plasma structures and additional plasma boundaries. An essential signature of the bi-ion fluid description consists in the occurrence of new (bi-ion) wave modes which may grow to large amplitudes due to a drift of protons relative to the heavies. In this way, a structuring of all plasma parameters results. Additionally, steepening of the underlying bi-ion waves and their phase bunching in multiple “Mach cones” are suggested to be responsible for cometary tail ray formation. Corresponding results of 2D bi-ion fluid simulations are presented.

The interaction of C/1995 O1 Hale-Bopp with the solar wind as recorded in CoCam images: A progress report

The Isaac Newton Group’s CoCam instrument obtained wide-field (10°X 20°) CCD images of the H2O+ tail of Hale-Bopp on March 12–15, 19, 20, 25, 28, 29, 31, April1, 7, 9–13, 21, 23–29 and May 4, 1997. A 6185a filter recorded the distribution of H2O+; 6250a-centered continuum images were also obtained. Initial analysis has revealed the CoCam dataset to be an invaluable record of the large-scale structure of the comet's ion tail. Several images show evidence of upstream parabolic envelopes of ions reminiscent of those reported in C/1908 R1 Morehouse (Eddington A. S., Mon. Not. Roy. Astron. Soc. 70, 442–458, 1910). Studies of these features may help towards a better understanding of the tail ray phenomenon. During most of March and early April, the tail had a largely consistent quiescent appearance, with numerous rays exhibited, but no major disturbances; most probably as a result of being in the stream of fast polar solar wind. A significant kink propagated down the tail around April 9/10. Towards the end of April, as the comet entered more variable solar wind at near-equatorial heliographic latitudes, the tail's morphology became significantly more structured. Striking tail disturbances were recorded in late April and early May, when the comet was in the vicinity of the heliospheric current sheet. Analysis of the dataset continues.

On removing molecular ions from Venus

Acceleration or “pickup” of exospheric atomic oxygen ions by the interplanetary convection electric field is a generally accepted mechanism for the observed removal of O+ from Venus. However, heavier escaping molecular ions (e.g., O2+, CO2+, N2+, CO+, and NO+) in high abundances were also detected in the wake by the Pioneer Venus Orbiter (PVO) neutral mass spectrometer (ONMS) operating in its ion mode. It was recently demonstrated that pickup of O+ at low velocities from the terminator upper ionosphere could explain some characteristics of the Venus ionospheric “tail rays.” Since the PVO ion mass spectrometer data indicate that a significant molecular ion component also contributes to the terminator ionosphere above the collisional region (≥250 to 300 km altitude), we apply the tail ray model to study both the associated low‐altitude O+ flows and the behavior of heavier ions of similar origin. The predicted flow vectors show dawn/dusk asymmetries similar to those in the ONMS observations. Further, the heavier ions achieve higher peak energies, thus improving their chances of detection by the ONMS which has an energy threshold of ∼36 eV in the spacecraft frame. The appeal of this explanation is that no exotic or complicated interpretations are required, and that a broad set of diverse observations fit a common scenario. The same mechanism could in principle be operating at Mars where molecular ions were also detected in the wake on Phobos 2.

MHD vortex mechanism of cometary rays origin

The mechanism of comet ray origin associated with the instability-driven vortices is suggested. According to our scenario, the Kelvin-Helmholtz instability is generated in the magnetic barrier in front of a comet owing to the velocity shear. Nonlinear evolution of this instability was shown in our previous paper to result in a formation of large-scale vortices. An analytical solution of the nonlinear problem of magnetic flux generation (i.e. the magnetic field “twisting”) due to the plasma vorticity is found assuming cylindrical symmetry. The plasma jet formed in the twisted magnetic field and accelerated owing to the pressure gradient is visualized as a cometary ray. Comparison with the results of the Giotto mission to comet Halley shows that rays seem to be generated near the maximum of the magnetic barrier. The characteristic thickness of tail rays of the order of 10 3 km is also explained.

Comparison of the plasma tails of four comets: P/Halley, Okazaki-Levy-Rudenko, Austin, and Levy

view Abstract Citations (9) References (86) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Comparison of the Plasma Tails of Four Comets: P/Halley, Okazaki-Levy-Rudenko, Austin, and Levy Farnham, Tony L. ; Meech, Karen J. Abstract Photographic and charge coupled device (CCD) plasma tail observations are compared for four comets: P/Halley (22 nights in 1985/1986), Okazaki-Levy-Rudenko 1989 XIX (1989 December 2), Austin 1990 V (nine nights in 1990), and Levy 1990 XX (two nights in 1991). We present a discussion of several image-processing techniques used to enhance the visibility of the plasma tail features in order to measure velocities, accelerations, and position angles. The data are used to assess the validity of various physical mechanisms proposed to explain plasma tail phenomena. Seven disconnection events were observed in the comet P/Halley data, two in the Austin data, and none for the other comets. Analysis of these data suggests that while the crossing of the solar neutral sheet (the sector boundary) is a prominent factor in the production of a disconnection event, it is likely that several mechanisms are at work. A sector boundary crossing has been ruled out as the cause of either the 1986 April 26 P/Halley disconnection or the 1990 May 5/6 Austin disconnection. The motions of the disconnection events, knots, and condensations in the tails were seen to increase from 30-60 km/s near the nucleus (within 106 km) to 80-100 km/s at 107 km, consistent with either bulk motion or Alfven waves. Distinguishing between the two cases is not possible with these data. It was found that although the tail ray rotation rate slows as the ray approaches the tail axis, it is not a good indicator of the solar wind speed. Historical plasma tail data are also used to look for clues as to why some comets form well-developed plasma tails and others do not. Publication: The Astrophysical Journal Supplement Series Pub Date: March 1994 DOI: 10.1086/191943 Bibcode: 1994ApJS...91..419F Keywords: Astronomical Models; Austin Comet; Comet Tails; Halley'S Comet; Image Enhancement; Image Processing; Magnetohydrodynamic Waves; Okazaki-Levy-Rudenko Comet; Tables (Data); Astronomical Photography; Charge Coupled Devices; Comet Nuclei; Error Analysis; Giacobini-Zinner Comet; Solar Wind Velocity; Astronomy; COMETS: GENERAL full text sources ADS |