bluuebunny/crossref_metadata_2025 huggingface dataset:
Collisional evolution of asteroids
Authors: Farinella P. , Davis D.R. , Marzari F. , Vokrouhlický D.
Published: July 2016

We review the evidence for, and the modelling work devoted to, the substantial collisional evolution which has generated the current asteroid population and continually injects asteroid fragments into dynamicalroutesthrough which they can reach near-Earth space and sometimes hit our planet. The main obstacles to further progress in this research field are theoretical (mainly related to the physics of high-velocity impacts), but better observational data (in particular on the small-size end of the asteroid population) would help. However, in the last decade new insights have been obtained on specific important issues, such as the total mass of the asteroids at the time when the accretion process was stopped (only moderately larger than the current one), the “demography” of asteroid families (how many/how old they are and how they evolve) and the way meteorites and near-Earth asteroids are delivered/transported by a complex mixture of collisional and dynamical mechanisms.
Chemical and physical aging of comets
Authors: Meech K.J.
Published: July 2016

Aging effects for comet nuclei encompass both chemical and physical changes to the nucleus which may be manifested as a change in the level of and type of activity that the nucleus experiences. Recent observations have shown the importance of the amorphous to crystalline water ice phase transition in comet nuclei for controlling activity at large distances, and for altering the porosity and volatile distribution in the interior of comets. Evidence for secular changes in activity levels or differences between dynamical classes of comets which have spent different amounts of time in the inner solar system must be decoupled from expected primordial differences between comets. Long-term observational programs by several groups have demonstrated that the effects of aging are detectable. This paper will discuss the expected primordial comet differences, the expected physical and chemical effects of aging, the techniques for observing differences in activity levels, and will present summaries of results of several observing programs.
The possibility of capture of short-period comets on retrograde satellite orbits
Authors: Pittich E.M. , Solovaya N.A.
Published: July 2016

The possibility to capture a small body moving on a heliocentric stable orbit by Jupiter has been investigated. Initial conditions were taken from the 8th retrograde satellite of Jupiter where we changed the orbital velocity so that the fictitious body was now in a heliocentric stable orbit. Using the numerical integrate techniques, we found conditions at which the small body can be captured by Jupiter on a retrograde orbit. To change the stable heliocentric orbit of the body to a transfer orbit to Jupiter, we used the techniques of small orbital velocity variations.
A study of cometary eruptions through OH radio-lines
Authors: Silva A.M. , Miró R.D.
Published: July 2016

We have developed a model for theH2OandOHevolution in a comet outburst, assuming that together with the gas, a distribution of icy grains is ejected. With an initial mass of icy grains of 108kg released, theH2OandOHproductions are increased up to a factor two, and the growth curves change drastically in the first two days. The model is applied to eruptions detected in theOHradio monitorings and fits well with the slow variations in the flux. On the other hand, several events of short duration appear, consisting of a sudden rise ofOHflux, followed by a sudden decay on the second day. These apparent short bursts are frequently found as precursors of a more durable eruption. We suggest that both of them are part of a unique eruption, and that the sudden decay is due to collisions that de-excite theOHmaser, when it reaches the Cometopause region located at 1.35 × 105kmfrom the nucleus.
Motion of the near-nucleus shells of comet Hale-Bopp and rotation of its nucleus
Authors: Churyumov K.I. , Evtushevsky O.M. , Kravtsov F.I.
Published: July 2016

270 images of the near-nucleus region of comet HB were obtained both in integral light (without filters) and using the narrow band interference IHW filters CO+C3C2, RC (red continuum). Prom the measurements of the expanding shells (arcs) the following result was obtained: the period of rotation of the comet nucleus is equal to 11.41±0.05 h; expansion velocities of the shells (arcs)vare in the limits of 0.61-1.99 kms−1, and accelerations of the shellsgin the limits from −18.3 × 10−3ms−2to 4.0 × 10−3ms−2.
Dust shells in the coma of C/1995 O1 (Hale-Bopp)
Authors: Paulech T.
Published: July 2016

The comet Hale-Bopp was continuously observed from September 1996 to April 1997. We used altogether 316 images of Hale-Bopp to analyse the evolution of dust shells system close to the nucleus. We performed measurements of relative distance of envelopes and velocity of its expansion. Evolution of the spiral arm revealed spin of the nucleus. We estimated the period of rotation to be 11.42 hours. With purpose to confront the real CCD images of dust éjecta and the measured ejection velocities a computer model of formation and expansion of the dust shells has been developed.
Distribution of long-period comets in perihelion distance
Authors: Klačka J.
Published: July 2016

Distribution of long-period comets in perihelion distance is investigated. The relationN( > q)=C qαseems to be a good approximation to the reality −N(>q)is the number of long-period comets with perihelion distance greater than the valueq( in AU). The complete group of long-period comets is characterized by the valueα =4/3, however, also subsets are important.
Resonances and chaos in the asteroid belt
Authors: Šidlichovský M.
Published: July 2016

The present paper reviews the evolution of our understanding of the effect of resonances on the distribution of asteroids in the asteroid belt. The history of this problem goes back to the Kirkwood's discovery (1867) of the Kirkwood gaps located at resonances with Jupiter. We started to understand the mechanism of their origin only in last decades. It seems that only gravitational effects are sufficient for the depletion. It is now clear that the overlap of secular resonances inside the orbital resonance is the most effective mechanism leading to large chaos and variation of orbital elements. This results in the final removal of asteroids from the gaps by collisions with the inner planets. Chaos, however, does not always mean fast removal of the body. The question of the so called stable chaos will be discussed together with the offered explanations (the high order resonances and the so called three-body resonances). Recently it was shown that chaotic diffusion can play an important role for the 2/1 resonance where the aforementioned explanation for other gaps fails. Basic facts will be reviewed but we will not go into this problem as the importance of chaotic diffusion in dynamics of asteroids (and comets) will be the subject of invited lecture at this conference given by Morbidelli and Nesvorný.
Symmetric Multistep Methods Revisited: II. Numerical Experiments
Authors: Fukushima T.
Published: July 2016

By using the stability condition and general formulas developed by Fukushima (1998 = Paper I) we discovered that, just as in the case of the explicit symmetric multistep methods (Quinlan and Tremaine, 1990), when integrating orbital motions of celestial bodies, the implicit symmetric multistep methods used in the predictor-corrector manner lead to integration errors in position which grow linearly with the integration time if the stepsizes adopted are sufficiently small and if the number of corrections is sufficiently large, say two or three. We confirmed also that the symmetric methods (explicit or implicit) would produce the stepsize-dependent instabilities/resonances, which was discovered by A. Toomre in 1991 and confirmed by G.D. Quinlan for some high order explicit methods. Although the implicit methods require twice or more computational time for the same stepsize than the explicit symmetric ones do, they seem to be preferable since they reduce these undesirable features significantly.
Models of comets with strongly variable nongravitational effects
Authors: Królikowska M. , Sitarski G. , Szutowicz S.
Published: July 2016

The nongravitational motion of five “erratic” short-period comets is studied on the basis of published astrometric observations. We present the precession models which successfully link all the observed apparitions of the comets: 21P/Giacobini-Zinner, 31P/Schwassmann-Wachmann 2, 32P/Comas Solá, 37P/Forbes, and 43P/Wolf-Harrington. We used the Sekanina's forced precession model of the rotating cometary nucleus to include the nongravitational terms into equations of the comet's motion. Values of six basic parameters (four connected with the rotating comet nucleus and two describing the precession of spin-axis of the nucleus) have been determined along the orbital elements from positional observations of the comets. The solutions were derived with additional assumptions which introduce instantaneous changes of modulus of reactive force,Aand of maximum of cometary activity with respect to perihelion time. The present precession models impose some contraints on sizes and rotational periods of cometary nuclei. According to our solutions the nucleus of 21P/Giacobini-Zinner with oblateness along the spin-axis of about 0.32 (equatorial to polar radius of 1.46) is the most oblate among five investigated comets.
An Overview of Solar and Stellar Flare Research
Authors: Haisch Bernhard M.
Published: July 2016

An overview of the many topics discussed atIAUColloquium No.104is presented as an introduction to the Proceedings. Suggested areas for future research emerging from the conference are summarized.
Solar and Stellar Flares: Questions and Problems
Authors: Mullan D. J.
Published: July 2016

Although progress has been made in understanding certain aspects of the physics of solar and stellar flares, there are a number of topics which, in the author's opinion, still pose a problem. We summarize these topics here.
Magnetic Equilibria and Instabilities
Authors: Sakurai Takashi
Published: July 2016

Solar flares are understood as a process of explosive liberation of magnetic energy, coming after a slow phase of energy build-up. The slow evolution of magnetic equilibria may end up with (a) the termination of an equilibrium sequence, or (b) an instability. The distinction between the two can be made by drawing schematic potential curves. Case (a) has been extensively studied in two-dimensional models. The appearance of multiple solutions, or disappearance of a solution takes place as the system evolves away from the current-free configuration. Case (b) can be discussed in terms of ideal MHD or resistive MHD instabilities. A possible route to explosive energy release is suggested by combining these two cases.
Application of Image Dissector Photomultipliers
Authors: Hoag A. A. , Ball W. F. , Trumbo D. E.
Published: July 2016

We describe an image dissector photoelectric system that is used for acquisition, guiding, focussing, and photometric monitoring in telescope control. A similar system is used for area scanning and spectrophotometry.
Advances in Densitometry
Authors: Hambleton J.
Published: July 2016

Firstly I should like to apologise for Mr. Loebl’s inability to come here today. Because of illness, he has been asked to rest and since he and I are working together on the same problems, he has asked me to present this paper.

It must be obvious to all concerned in the evaluation of photographic images, that microdensitometry has rapidly changed with the advance in technology. Improvements have taken place over the years in the use and refinement of double beam recording instruments. Present trends indicate that little further can be done regarding optical resolution and diffraction limited systems can now be built. The quantitative evaluation of images based on a line integral has not changed in principle for many years. A scanning spot of the requisite size is passed across, for example, a spectral line, and the densitometric profile line gives the information required, either by its height or its area.
Automated Spectrophotometry
Authors: Thompson G. I.
Published: July 2016

Starting from a digitized and calibrated stellar spectrum—what can we most usefully do with it?

Traditionally a spectrum consists of two parts, a continuum and some lines. These have been variously defined in the past, so perhaps another definition may be allowed. Over large ranges the two components can be distinguished quite sharply in the spatial frequency plane. The continuum contains only low frequencies, whereas in the line the information is contained in the high frequencies. In the word “continuum” is included the instrumental absorption functions, emulsion sensitivity, wide interstellar and atmospheric bands, and even the wide wings of very strong lines. From the word “lines”, on the other hand, the strongest lines are excluded; these may contain intermediate spatial frequencies in their core regions. They are relatively infrequent and so may be treated as special cases.
Intelligent Terminals: The Distributed Computer System at McDonald Observatory
Authors: Nather R. Edward
Published: July 2016

A special matching facilities grant obtained from the National Science Foundation, in connection with the construction of the 107-inch reflector at McDonald Observatory, included the cost of an IBM 1800 process control computer. This computer was delivered in December, 1967, and has been in routine operation at the Observatory for slightly more than one year. The original system plan was presented as a paper at the meeting of the A.S.P. in June, 1968 and is shown in symbolic form in Figure 1. The essential features of the design were that it be advisory in nature and operate on a time-shared basis to provide assistance to the 107-inch, 82-inch and 36-inch telescopes. Facilities for automatic data acquisition were deferred until this initial plan was completed.
Polarization of Infrared Objects
Authors: Kruszewski A. , Smak J.
Published: July 2016

We know several infrared objects showing large intrinsic polarization (FORBES 1967, APPENZELLER and O’DELL 1967, KRUSZEWSKI 1968, SERKOWSKI 1969, SHAWL 1969, SHAWL and ZELLNER 1970, KRUSZEWSKI 1971, DYCK, FORBES and SHAWL 1971).

In the following discussion I shall speak about the broad category of infrared stars which consists of reddest and coolest giants (M8 or later) and supergiants (M5 or later). This restriction is made because the yellow supergiants seem to have different polarization properties and these properties most likely extend to supergiants as late as M 2 or even M 4. Also it is not clear if normal red variables can be treated together with infrared objects.
To the Explanation of the Polarization of the Radiation of Mu Cephei
Authors: Friedemann CH.
Published: July 2016

Assuming a stellar magnetic dipole-field which aligns particles in the stellar atmosphere the observed polarization of the light of µ Cephei can be explained. The spatial orientation of the rotational axis, the angle between the magnetic axis and the rotational axis and the period of rotation were derived from the observational values. The period of rotation amounts to about 1650d ± 100d. In case aligned graphite flakes are present in the outer layers of the stellar atmosphere the calculated degree of polarization amounts to about 1.5 %. According to the chemical composition of the atmosphere it is more probably that siliciumcarbide particles cause the polarization. In this case the degree of polarization amounts to approximately 0.75%. The portion of polarization originating in interstellar space was estimated to Pi ≈0.8% and the position angle is about Θi ≈45°.
Microwave Emission from Stars
Authors: Schwartz PH. R.
Published: July 2016

During the past several years, the radio astronomical detection of a large number of complex organic and inorganic molecules has led to an entirely new concept of the chemical composition, kinematics and excitation of the interstellar medium. The microwave molecular transitions detected thus far fall into two natural categories: 1. „normal“ (i.e. nearly LTE) emission and absorption lines, and 2. anomalous or „masered“ emission lines. The first category includes molecules found in both high and low excitation regions whose intensity, linewidth and other characteristics may be described in terms of a physically realistic excitation temperature. Nearly all of the known microwave lines fall into this category. Typically, molecular lines of this type are found in HII regions, dark nebulae and, occasionally, extended circum-stellar shells. Only two molecules populate the second category: OH and H20. Emission from OH lambda doublet transitions in several rotational states and from the 618—523 rotational transition of H20 exhibits many strange characteristics: tremendous intensity, narrow line-width, non LTE distribution of hyperfine intensities, linear and circular polarization, and rapid variability. OH and H20 emission originates from extremely localized regions, often as small as a few A.U. in diameter, in or near some HII regions and some cool, late type stars. The behavior of OH and H20 emission lines is best explained by assuming that the microwave radiation is amplified by some narrow band non-linear process in the sources.
Red Variables with and without OH Radio Emission
Authors: Strohmeier W.
Published: July 2016

Radio astronomers detected in 1963 hydroxyl molecules (first in absorption), in form of microwave lines at the frequencies 1612, 1665, 1667, and 1720 MHz (1612.231 + 1720.533 (=) 1665.401 + 1667.358), corresponding to a wavelength near 18 cm. Since 1968, some infrared stars have been known to be observable with radio telescopes as sources of such microwave lines, in emission with line widths of 2 kHz or less. In addition to the ground state, a Π state with Λ = 1, the OH molecule has three known electronic excited states, Σ states with Λ = 0, at about 30 000, 60 000, and 90 000 cm−1 above the ground state. These electric-dipole transitions are about 104 times stronger than the magnetic-dipole transitions which produce hydrogen or deuterium lines; the energy of the 2II3/2 state is less than that of the 2II1/2 state what indicates that the observed OH radio emission is subject to far infrared stellar radiation.
A Photometric Search for Circumstellar Shell Variability and Pre-Main Sequence Delta Scuti Variables
Authors: Breger M. , Hardorp J.
Published: July 2016

A light variability study in NGC 2264 shows that about 25 % of the pre-main sequence A and F stars show irregular short-period variability and/or brightness changes since 1953. There exists a good correlation between this variability and (other) shell indicators. The scatter in the pre-main sequence band in the color-magnitude diagram can be partially explained by shells and an age spread between 1 and 3 × 106 years is indicated. W 90, a star below the main sequence, has brightened by half a magnitude to V = 12.5 since 1953. The corresponding color variation suggests a ratio of total to selective extinction of about 9.
Time Scales of Stars during the Crossing of the Cepheid Strip
Authors: Lauterborn D. , Refsdal S. , Roth M. L.
Published: July 2016

In a recent paper (LAUTERBORN, REFSDAL, WEIGERT, 1971) the central He burning phase of 5 M⊙ stars was investigated. It was shown that the structure of such stars is very sensitive to the chemical profile in and above the hydrogen burning shell. The loops in the H-R diagram which such stars often make were for instance found to be very sensitive to changes in this profile. It was also shown that an assumed mass loss of about 10% in the red giant region will suppress a loop completely.
UBV Observations of the Ultrashort Period Variable HZ 29
Authors: Krzemiński W.
Published: July 2016

The periodic light variability of HZ 29 (= AM CVn) discovered in 1962 by SMAK (1967) was subsequently studied in detail by OSTRIKER and HESSER (1968; hereinafter referenced as OH). The observations of SMAK were confirmed to the blue and ultraviolet light and those of OSTRIKER and HESSER to the integrated light; these revealed light variations in the form of a slightly distorted double sinusoid. This distortion manifests itself that the alternate maxima are broader and, consequently, the alternate minima occur near phase 0.54 P (when phases are counted from minima preceding broader maxima). The over-all amplitude of light oscillations is between 0.02 and 0.05 mag., the period, as determined by OH, is 1051.118 ±0.015 sec.
RW Arietis; an RR Lyrae Variable Star in an Eclipsing System
Authors: Wisniewski W. Z.
Published: July 2016

RW Arietis was observed photoelectrically in the UBV-system during fall and winter 1966 with the 70 cm telescope at the Lunar and Planetary Laboratory Catalina station, University of Arizona, Tucson, on 19 nights. Peculiar variations of the usually stable RRc light curve observed on three nights can be interpreted as a superposition of the RR Lyrae type variation and an eclipsing type variation.
Search for Contracting Close Binaries
Authors: Koch R. H.
Published: July 2016

The selection of close binaries which compose the usual tabulations of solutions has informed us in detail on main sequence stellar atmospheric and interior parameters, and on the theories of the tidal and radiative interactions, and has permitted the creation of the theory of binary evolution. As we have seen, the eruptive doubles are beginning to yield to modern instrumentation. Adding more pairs to those already „understood“ will bring continuity into our appreciations of these processes and undoubtedly change them sowewhat. The origins of close pairs, however, remain obscure and one can only say that the theories which describe fission of a proto-star after its core de-couples from the envelope seem promising. The latest presentation of this idea by BODENHEIMER and OSTRIKER (1970) can be viewed as the successor to the indicative theories of ROXBURGH (1966) and CAMERON (1969). In this way of looking at binary origins it is simply a question of when fission occurred in the proto-stellar interval. Observationally, candidate stars are anything but numerous and it is for this reason that we have begun the program described here.
New Variable Stars in the Globular Cluster NGC 6401
Authors: Terzan A. , Rutily B.
Published: July 2016

115 new variable stars have been detected in a one square degree field centered on the globular cluster NGC 6401. Two of them (No. 157 and 164) seem to belong to the cluster.
On the Changes of Periods of RR Lyrae Variables in the Globular Clusters M5, M53 and NGC 5053
Authors: Goranskij V. P. , Kukarkin B. V. , Samus’ N. N.
Published: July 2016

The period of a variable star is very sensitive to extremely minor changes in luminosity, mass, radius, surface temperature, etc. of the star. With new theoretical calculations of the interior structure of stars in the late stages of evolution now available, the investigation of instabilities in the periods of the RR Lyrae variables in globular clusters becomes urgent.
Mean Magnitudes and Colours of Six Cepheids in Three Red Globular Clusters of the Large Magellanic Cloud
Authors: Demers Serge
Published: July 2016

Photographic B and V light curves are determined for six variables, with periods longer than one day, in and near NGC 1751, NGC 1953, and NGC 2121. New photoelectric sequences are used to calibrate the plates. The mean magnitudes and colours of these variables are similar to the magnitudes and colours of Classical Cepheids of the same period. The photometric properties of these variables are unlike Population II Cepheids in the Galaxy but are comparable to field Cepheids of the Large Magellanic Cloud.
On the Two Oosterhoff Groups of Globular Clusters
Authors: Van Albada T. S. , Baker Norman
Published: July 2016

The observational evidence leading to the classification, following Oosterhoff, of globular clusters containing RR Lyrae stars into two distinct groups, is summarized and discussed in the light of results of stellar evolution theory and pulsation theory. The dichotomy is caused, at least in part, by a dichotomy in the ‘transition period’ between the type-ab and type-c stars which reflects a difference in effective temperature at the transition point. When this difference is accounted for, there remains a smaller average difference between the groups, though no longer a clear dichotomy, that is probably a mass and luminosity effect. If this remaining difference is interpreted as a luminosity effect the average difference in luminosity between the two Oosterhoff groups is at most 0.1 mag. It is suggested that Christy’s theoretical relationship between transition period and luminosity cannot be valid, at least not for clusters of different Oosterhoff groups. It is conjectured that the transition-temperature dichotomy may be a reflection of different predominant directions of evolution along the horizontal branch, accompanied by a hysteresis effect in the pulsations.
The Helium Abundance in the Envelopes of the Bluest RR Lyrae Stars in Globular Clusters and Dependence of Globular Cluster Variable Star Properties on Chemical Composition
Authors: Mironov A. V.
Published: July 2016

The helium abundance Y in the envelopes of RR Lyrae stars in globular clusters has been estimated. The values of Y range from 0.07 to 0.59. The properties of variable stars in globular clusters of two types distinguished by a type of dependence of the horizontal branch form on the chemical composition are compared. The clusters of type I are shown to be on the average poorer in RR Lyrae stars than those of type II. The RR Lyrae stars in type I clusters are on the average brighter by 0.1 mag. It is found that as Y increases, the cluster richness in W Virginis variables decreases.
The program of minor planets observations at the Crimea Observatory
Authors: Chernykh N. S. , Chernykh L. I.
Published: July 2016

Systematic photographic observations of minor planets were undertaken at the Crimean Astrophysical Observatory by one of authors (N. S. Chernykh) in the autumn of 1963. This program was initiated at the request of the Institute for Theoretical Astronomy (Leningrad). By the end of 1964 a group for the program in the Crimea was organized by the Institute and since that time the Crimean program of photographic asteroid observations is jointly carried out by the Crimean Astrophysical Observatory and the Institute for Theoretical Astronomy. The group of observers of minor planets now consists of L. I. Chernykh, T. M. Smirnova, B. A. Burnasheva (I.T.A.) and N. S. Chernykh (Cr.A.O.) and two laboratory assistants: G. Ya. Smirnova and N. S. Pecherskih (I.T.A.).
On following up newly-discovered earth-approaching minor planets
Authors: Marsden B. G.
Published: July 2016

Recent experience suggests that it is not necessary to introduce a 24-hour information service for following up discoveries of fast-moving objects. Success can be achieved by intelligent action and only a moderate degree of urgency. There is some interest in making deliberate searches for new Apollo objects and hence a great need for follow-up observations.
On the generalized restricted problem of three bodies
Authors: Duboshin G. N.
Published: July 2016

The particular case of the complete generalized three-body problem where one of the body-points does not exert influence on the other two is analysed. These active material points act on the passive point and also on each other with forces (attraction or repulsion), proportional to the product of masses of both points and a certain function of the time, their mutual distances and their first and second derivatives. Furthermore it is not supposed that generally the th ird axiom of mechanics (action = reaction) takes place.

One determines the conditions for some particular solutions which exist, when the three points form the equilateral triangle or remain always on a straight line.

Finally, some conclusions on the Liapunov stability in the simplest cases are drawn.
Structure and evolution of the asteroid belt
Authors: Chebotarev G. A. , Shmakova M. Ya.
Published: July 2016

Investigations concerning the structure of the asteroid belt make it possible to distinguish four main stages in its evolution. The first stage. The formation of a certain number of protoplanets (ten-hundred) between the orbits of Mars and Jupiter, simultaneously with major planets. The protoplanets had the dimensions of the presently largest asteroids. The peculiarity of their orbits consisted of a predominance of large inclinations. The second stage. The unstable “primary” asteroid belt which came into existence as a result of mutual collisions of the protoplanets and occupied the zone with daily mean motion between 300 and 990″. Numerous close encounters of asteroids with Jupiter. The formation of planets having unusual orbits (Hidalgo, the Trojans and others). The formation of a wide gap (300–540″) which separated the stable asteroid belt from Jupiter’s orbit. The third stage. The stable asteroid belt in the zone 540–990″. The predominance of planets of “the spherical” subsystem. The formation of gaps corresponding to “acute” commensurabilities in mean motions with Jupiter. The fourth stage. The present asteroid belt occupying the zone 450–1110″. The asteroid belt gradually expanded in the direction towards the Sun. The bulk of young planets concentrating in the ecliptic plane. The total mass of the asteroid belt during the time of its existence has decreased to a fraction of its former value.
On the motion of comet P/d’Arrest
Authors: Klepczynski W. J.
Published: July 2016

The differences between numerically approximated partial derivatives and partial derivatives obtained by integrating the variational equations are computed for Comet P/d’Arrest. The effect of errors in the IAU adopted system of masses, normally used in the integration of the equations of motion of comets of this type, is investigated. It is concluded that the resulting effects are negligible when compared with the observed discrepancies in the motion of this comet.
The past orbit of Halley’s comet
Authors: Kiang T.
Published: July 2016

I have re-examined the records in the Chinese“Standard Histories”on this famous object, including one set of relatively precise observations made in the year 837 A.D., which has only recently become available in an English translation (Ho 1962). This set, when properly interpreted, consists of the comet’s right ascension on 10 specified dates, given to the nearest half of a Chinese degree (1 Chinese degree = 360°/365.25). While the records of the other returns are not so precise, they can nevertheless be used with great advantage to determine the time of perihelion passage. These records provide an almost complete coverage back to the year 240 B.C.
the effects of resonance with Jupiter in the system of short-period comets
Authors: Kresák L̆ubor
Published: July 2016

Structural effects of the resonance with the mean motion of Jupiter on the system of short-period comets are discussed. The distribution of mean motions, determined from sets of consecutive perihelion passages of all known periodic comets, reveals a number of gaps associated with low-order resonance; most pronounced are those corresponding to the simplest commensurabilities of 5/2, 2/1, 5/3, 3/2, 1/1 and 1/2. The formation of the gaps is explained by a compound effect of five possible types of behaviour of the comets set into an approximate resonance, ranging from quick passages through the gap to temporary librations avoiding closer approaches to Jupiter. In addition to the comets of almost asteroidal appearance, librating with small amplitudes around the lower resonance ratios (Marsden, 1970b), there is an interesting group of faint diffuse comets librating in characteristic periods of about 200 years, with large amplitudes of about±8% in μ and almost±180° in σ, around the 2/1 resonance gap. This transient type of motion appears to be nearly as frequent as a circulating motion with period of revolution of less than one half that of Jupiter. The temporary members of this group are characteristic not only by their appearance but also by rather peculiar discovery conditions.
Origin and evolution of comets
Authors: Everhart Edgar
Published: July 2016

A Monte Carlo study is described that leads to an understanding of the evolution of comets, particularly how the short-period comets can arise. Some results have appeared in the March 1972 issue of Astrophysical Letters, Vol. 10, pages 131–135 (Paper I), but further results are presented here for the first time.

This is a report of a particular study and is not a general review of the subject. References to many other papers are given in the above article. Here it suffices to mention that the author has read and profited by the excellent papers by Belyayev, Callandreau, Chebotarev, Delsemme, Dobrovolskij, Havnes, Kazimirchak-Polonskaya, Kresak, Levin, Lyttleton, Marsden, H. A. Newton, Oort, Öpik, Porter, Roemer, Russell, Sekanina, Shteins, Sitarski, Strömgren, Tisserand, Vsekhsvyatskij, and Whipple, as well as many others. Many of the ideas here are not new, but they are implemented for the first time on a really high speed computer.

A fundamental assumption whose consequences are to be developed is that all comets initially approach the solar system on near parabolic orbits.
On possible mechanisxms for dust ejection from comets
Authors: Dobrovolsky O. V.
Published: July 2016

There are three different mechanisms for dust generation in comets described in the literature on comets.

First case. Simple ejection of primordial dust particles from the nucleus by outflowing gas.

Second case. Creation of dust particles on the surface of the nucleus as a mineral crust is formed and destructed by mini-explosions. The crust may originate either as a result of accumulation of primordial particles or directly bear on the surface during sublimation of appropriate substances even when there are no mineral particles in the nucleus at all. Periodical mini-explosions create a quasi-continuous outflow of particles.

Third case. Dust particles originate in the gas phase in the vicinity of the nucleus like soot particles in a flame as a result of condensation of carbon moleculae vapor (Dolginov’s mechanism).
The structure of meteor streams associated with Comet Halley: Eta Aquarids and Orionids
Authors: Hajduk Anton
Published: July 2016

The association of Comet Halley with the Orionid and Eta Aquarid meteor streams is not commonly accepted at present. Southworth (1961) has determined the differences in the orbital elements of the Orionid stream and Comet Halley on the basis of 19 photographic meteors and found them to be rather large.

Extensive observational material obtained since the beginning of this century, including a homogeneous series of the radar observations, carried out at the Springhill Meteor Observatory during the periods of the Orionid meteor shower activity in 1957–1967 has been used by the author (Hajduk 1971) to study the stream structure and its association with Comet Halley from a statistical point of view.

The present analysis is an extension of the paper mentioned, based mainly on the radar observations of the Eta Aquarid meteor shower carried out at the Springhill Observatory during the period 1958–67. The total number of 240,000 radar meteor echoes observed in 670 hours between May 1 and May 10 during each of the years previously cited was used in this investigation. The observed variations in the hourly rates of echoes of different duration enable us to study the density distribution and size distribution of meteoric particles along and across the stream.
High-Resolution Dynamic Spectrum of a Spectacular Radio Burst from AD Leonis
Authors: Abada-Simon Meil , Lecacheux Alain , Aubier Monique , Bookbinder Jay A.
Published: July 2016

AD Leonis is a very active, single dMe flare star. The similarities between this type of star and the Sun has led to study their radio radiation, which originates from their corona. The high brightness temperatures and other characteristics of most dMe radio bursts can be attributed to a non-thermal, coherent mechanism: plasma radiation or a cyclotron maser instability (CMI) are both plausible explanations. Even for the strongest burst of AD Leo which reached 940 mJy
at 21 cm, it was not possible to discriminate between these two mechanisms (Bastian et al. 1990).

Here we present an intense burst from AD Leo, exhibiting strong spikes for which the CMI seems to be the only reasonable explanation. In Sect. 2 we describe the observations, and in Sect. 3 we give an interpretation for this event.
Coherent Radio Bursts from RS CVn Binareis
Authors: Franciosini Elena , White Stephen M.
Published: July 2016

We present VLA observations of RS CVn binaries which indicate that the low-frequency polarization inversion usually ascribed to the quiescent radio emission of these systems is in fact due to the presence, much of the time, of a coherent burst emission. Fig. 1 shows two examples of this coherent emission in the behaviour of the light curves of HR1099 in left and right circular polarization at 1.4 GHz. The emission is highly circularly polarized, with one polarized component steady or slowly varying in a way similar to the higher frequency emission (Fig. 1a), while the other shows rapid fluctuations on timescales of ∼10s and a slower modulation on longer timescales. The similarity of the time profiles in two 50 MHz-wide sidebands 30 MHz apart indicates that the fluctuating component is broadband; moreover, the sense of polarization at 1.4 GHz is opposite to that of the quiescent emission at higher frequencies (attributed to gyrosynchrotron emission), which is exactly the behaviour attributed to the 1.4GHz quiescent emission of these systems by Mutel etal. (1987).

The rapid fluctuations and high polarization are characteristic of a coherent emission process. We argue that a combination of two sources of emission is generally present at 1.4 GHz: a very highly (possibly 100%) polarized coherent component, and a weakly-polarized, steady gyrosynchrotron component. Since the polarization at higher frequencies should be the x-mode of (optically thin) gyrosynchrotron emission, we infer that the low frequency polarization probably represents the o-mode. The observed characteristics of the emission then suggest that the most likely mechanism for the highly-polarized component is plasma emission at the fundamental of the plasma frequency. Such plasma emission is relatively rare on the Sun at 1.4 GHz, but could occur in the hotter coronae of RS CVn systems because the higher temperature reduces the free-free opacity which is thought to absorb 1.4 GHz plasma emission on the Sun.
A Large Amplitude Flaring dMe Star in the 1978 October 6B γ-ray Burst Error Box
Authors: Greiner J. , Motch C.
Published: July 2016

During a search for flaring optical counterparts to γ-ray burst sources (GRBs) on archival patrol plates, an optical outburst image was found in the 3200 arcmin2 error box of the GRB which occurred on 1978 October 6 (GB 781006B = GBS 0008+13; Greiner et al. 1991) and was named S 10933 according to the convention of new Sonneberg variables. This outburst image appears on three simultaneously exposed plates taken on 1966 August 14/15 from 23.33 to 0.13 UT. The brightness estimates yielded mpg = 13m.3 ± 0m.1 and mv = 13m.8 ± 0m.2 with a high negative colour index of C = −0m.5 ± 0m.3.
A Major Optical Flare on the Recently Discovered X-ray Active dMe Star G102-21
Authors: Pagano I. , Ventura R. , Rodonò M. , Peres G. , Micela G.
Published: July 2016

During UBV photoelectric measurements of G102-21 - a dM3 star recently discovered as a remarkably active X-ray source by Micela et al. (1995) - we have observed the flare shown in Fig. 1 (left panel). The observed flux increase at flare maximum and the energy output (cf. Table 1) make this event one of the largest amplitude and most energetic flares ever detected on UV Cet-type stars.

The ratios EU/EB (=8.9) and EU/EV (=3.9) are more than 7 and 2 times larger, respectively, than the mean values found for typical dMe flares by Lacy et al. (1976). Moreover, assuming the empirical relation between the absolute magnitude MV and the mean energy dissipation during a flare (Gurzadyan 1980), the energy released in the U band exceeds the predicted one by a factor of ∼ 3 · 103. Clearly, we observed a rather peculiar and rare event that does not appear to be a typical flare on red-dwarf stars.
Flare in Late-type Stars: UV
Authors: Brendan Byrne P.
Published: July 2016

Early studies of stellar flares were made entirely in the optical regime. It was recognised that flares arose from the generation of hot plasma within the stellar chromosphere at whose temperature (indicated, for instance, by the presence of a strong, blue optical continuum) a substantial emission in the ultraviolet would be expected. It was not until the advent of space-borne instruments of adequate sensitivity, however, that direct confirmation of this prediction was forthcoming. In this review I examine some results of more than a decade of observation of stellar flares in the UV.

The major source of ultraviolet data on stellar flares has been the International Ultraviolet Explorer (IUE) satellite (Boggess et al. 1979). In order to understand the limitations of our current understanding in this area it is important to appreciate some of the characteristics of its instrumentation. IUE’s telescope is of 40 cm aperture and it is equipped with a spectrograph which can operate at two resolutions, i.e. Δλ/λ ∼350 (LORES) and ∼17000 (HIRES). Its detectors are optimised for operation in two wavebands, i.e. ∼1150-1950Å (SW) and ∼1950-3200 Å (LW). IUE’s small apert ure results in a limited sensitivity, a consequence of which is a modest time resolution when studying stellar flares (a long exposure time is needed to gain adequate signal-to-noise). IUE’s elliptical 24-hour quasi-geosynchronous orbit and its resulting interactive mode of operation make continuous monitoring feasible, a feature suiting flare star work.
Flares in Late-type Stars: X-Ray
Authors: Pallavicini Roberto
Published: July 2016

Flare-like brightenings, similar to those observed on the Sun but on a larger energy scale, are observed in a variety of late-type stars, including classical M dwarf flare stars, RS CVn-type binaries and pre-main sequence (PMS) objects. These events, which are observable over the whole electromagnetic spectrum, are interpreted as due to rapid release of magnetic energy at the star surface. Comprehensive reviews of stellar flares have been presented by Haisch &: Rodonò (1989), Pettersen (1991), Haisch et al. (1991), Pallavicini (1992a), as well as in contributions at this conference. Here I will discuss X-ray emission, with emphasis on flares on M dwarfs and RS CVn binaries.

X-ray observations are important because they provide information on the high-temperature coronal portion of the flare and, at least in principle, could give clues as to the primary energy release and particle acceleration. In the stellar case there are severe limitations of the diagnostic capabilities of X-ray observations, in comparison to the solar case. In fact, stellar flares have up to now been observed only at soft X-ray energies (≤ 10 keV) where thermal processes greatly dominate over non-thermal ones (optical continuum observations have to be used in this case as a proxy for hard X-rays). Moreover, stellar X-ray observations are spatially unresolved and so far of poor spectral resolution. Thus, the observational data that are readily accessible are only light curves, average temperatures T and volume integrated emission measures EM = ∫ n2dV, but there is no direct information on parameters such as density, volume and detailed geometry.
Short-Duration X-ray Transients Observed With WATCH on Granat: Are Some of Them Related to Stellar Flares?
Authors: Castro-Tirado Alberto J. , Brandt Søren , Lund Niels , Lapshov Igor , Sunyaev Rashid
Published: July 2016

During 1990-92, the WATCH all-sky X-ray monitor on GRANAT has discovered 6 short-duration X-ray transients. We discuss their possible relationship to peculiar stars. Only one source, GRS 1100-77 seems to be related to a T Tauri star.
ROSAT Observation of a Giant X-ray Flare on the Active Binary Algol
Authors: Ottmann R.
Published: July 2016

ROSAT/PSPC observations of a long-duration, giant X-ray flare on the eclipsing binary Algol are presented. With a total thermally radiated energy of 7 Ŀ 1036 erg, this flare is one of the largest events ever observed. The flare decay is modeled by means of the quasi-static cooling method, which yields a height of the flare loop arcade of ≃ 1RK, and a plasma density of 1011 cm−3.
ASCA X-ray Spectra of Quiescent and Flaring Emission from AB Doradus
Authors: White S.M. , Pallavicini R. , Lim J.
Published: July 2016

The Japanese satellite ASCA carries X-ray detectors which combine excellent sensitivity and high spectral resolution. We observed the young, rapidly-rotating K dwarf AB Doradus with ASCA in November 1993. The star’s X-ray flux was essentially steady for the first half of the observation, and then a series of flares occurred during the second half. The flares showed rise times of 30 minutes and decay times of several hours. The quiescent X-ray luminosity was 2 × 1030 ergs s−1 (0.5-10 keV). At the flare peaks, LX(> 0.5 keV)/Lbol = .002.

AB Dor has a relatively high count rate in the ASCA data and we can obtain high-quality spectra for different periods of the light curve. In Fig. 1 we present spectra corresponding to the period of quiescence, the rising phase and peak of each of the three flares combined, and the decay periods of each of the flares combined. The rise/peak curve (upper) has been multiplied by 2 for purposes of display. We have subtracted the quiescent spectrum from the flare spectra (i.e., used it as a background spectrum) for this display and subsequent analysis.

The detailed differences between these spectra display the importance of the high spectral resolution provided by ASCA. One important difference, not readily evident in this figure, is the Fe K line complex at 6.4-6.7 keV. This line, a diagnostic of hot plasma, is strong in the rise/peak spectrum, moderate in the decay spectrum and weak in the quiescent spectrum. A time profile of the counts in this energy range shows little significant emission during the quiescent periods but strong emission at the flare peaks.