An Early Investigation Of The Striated Tail Of Comet Hale-Bopp (C/1995 O1)     

Pittichovâ  J.  Sekenina  Z.  Birkle  K.  Boehnhardt  J.  Engels  D.  Keller  P. 《Earth, Moon, and Planets》1997,78(1-3):329-338

The Sekanina-Farrell particle fragmentation model for the striated tails of dust comets is successfully applied to two images of comet Hale-Bopp to study the motions of 12 striae in a time span of March 12–15, 1997. There is evidence for recurring outbursts with a periodicity of 11^h21^m, consistent with results based on analysis of dust jets. The ejecta in all the striae appear to have been released from one source on the nucleus between the end of January and the second half of February 1997, some 60 to 40 days before perihelion. The parent particles were subjected to a radiation pressure acceleration of β_p ≃ 0.55 and their fragmentation lifetimes in 11 of the 12 striae were practically constant and equal to 13–15 days, when normalized to 1 AU from the Sun. Brief analysis of Watanabe et al.'s measurements of striae on their images from March 5–9, 1997 shows even shorter fragmentation lifetimes for the parent particles, mostly about 7–11 days at1 AU. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Evidence for the nucleus rotation in streamer patterns of Comet Halley's dust tail     

K. Beisser  H. Boehnhardt 《Astrophysics and Space Science》1987,139(1):5-12

A generalized Finson-Probstein formalism was used to analyse the streamer patterns in the dust tail of Comet Halley as observed between 22 February and 11 March, 1986. A periodic appearance of a pattern of double streamers was found in the dust tail, indicating a time interval in the emission of this structures of about 6.5 days, if interpreted as synchrones. The time interval between the emission of the two components of each double streamer is about 2.5 days. The results are discussed with respect to the rotation of Halley's nucleus.This work is based on observations made at the European Southern Observatory by ESO staff personal and by observers of the Astronomical Institute of the Ruhr-University, Bochum. We, furthermore, used an exposure made at the U.K. Schmidt telescope at Siding Spring, Australia, operated by the Royal Observatory Edinburgh, and published by Sekanina and Larson (1986).  相似文献   

Pre-Impact Mid-IR and Optical Observations of Comet 9P/Tempel 1     

H.-U. Kaeufl  T. Bonev  H. Boehnhardt  Y. R. Fernandez  C. Lisse 《Earth, Moon, and Planets》2005,97(3-4):331-339

Comet 9P/Tempel 1, the target of the Deep Impact mission, has been intensively observed for a long time period before the encounter. Pre-impact ground based monitoring of the comet was an important prerequisite for the success of the first space experiment in which a comet is treated by an artificial impact. It provided the background data needed to disentangle the features caused by the impact from variations caused by the natural activity of the comet. In this paper we present results from the ESO-monitoring of the comet, conducted in the thermal infrared and optical spectral ranges during several months before the Deep Impact encounter with the comet.  相似文献   

Preface and Dedication     

A'Hearn  Michael F.  Boehnhardt  Hermann  Kidger  Mark  West  Richard M. 《Earth, Moon, and Planets》1997,78(1-3):3-3

Earth, Moon, and Planets -  相似文献   

Results from the Eso Large Program on Transneptunian Objects and Centaurs     

Boehnhardt  Hermann  Barucci  Antonella  Delsanti  Audrey  De Bergh  Catherine  Doressoundiram  Alain  Romon  Jennifer  Dotto  Elisabetta  Tozzi  Gianpaolo  Lazzarin  Monica  Fornasier  Sonia  Peixinho  Nuno  Hainaut  Olivier  Davies  John  Rousselot  Philippe  Barrera  Luis  Birkle  Kurt  Meech  Karen  Ortiz  JoseLuis  Sekiguchi  Tomohiko  Watanabe  Jun-ichi  Thomas  Nick  West  Richard 《Earth, Moon, and Planets》2003,92(1-4):145-156

BVRI photometry of 107 TNOs and Centaurs establishes the range of spectral gradients to be between –5 to 55%/100 nm (with one exception). A cluster of very red Cubewanos is firmly identified in orbits of low inclination and eccentricity beyond 40 AU from the Sun. Further correlations between surface colours and dynamical parameters (inclination and perihelion distance) are suggested for Cubewanos and scattered disk objects, but lack complete confidence for their reality. Plutinos and Centaurs do not show any clear correlation between surface colours and orbital parameters. We present in this paper 12 spectra obtained in the visible region and nine of them for which we obtained also near infrared spectra up to 2.4 microns. A few other objects have been observed, but the data are still under reduction and analysis. The principal reported results obtained are: (i) a wide range of visible slopes; (ii) evidence for surface variations on 2001 PT₁₃; and (iii) possible detection of few percent of water ice (1999 TC_36}, 2000 EB₁₇₃, 1999 DE₉, 2001 PT₁₃, 2000 QC₂₄₃, 1998 SG₃₅).  相似文献   

Nucleus and tail studies of comet P/Swift-tuttle     

H. Boehnhardt  K. Birkle  M. Osterloh 《Earth, Moon, and Planets》1996,73(1):51-70

CCD images of comet P/Swift-Tuttle, obtained in April 1994 with the 2.2m telescope at ESO La Silla/Chile, showed a comaless stellar nucleus. From absolute photometry we estimated the equivalent radius of the cometary nucleus to be about 11 km (assuming an albedo of 0.04 as for P/Halley) for two rotation phase angles which differ by about 75 deg. From that we conclude that the nucleus is either of rather spherical shape or that the viewing geometry was almost pole-on during our observations.An analysis of the plasma tail and inner coma of the comet by means of photographic plates and CCD images through IHW and BVR filters, obtained with the 80cm Schmidt camera and the 1.2m telescope at Calar Alto/Spain in November 1992, revealed several tail rays, head streamers and substructures in brightness excess areas in the coma. While some of the tail rays extended to several million km nuclear distance, most of them can be traced to starting points which lie in a region just 20000–35000 km projected distance tailward from the nucleus.  相似文献   

Stardust-NExT,Deep Impact,and the accelerating spin of 9P/Tempel 1     

Michael J.S. Belton  Karen J. Meech  Steven Chesley  Jana Pittichová  Brian Carcich  Michal Drahus  Alan Harris  Stephen Gillam  Joseph Veverka  Nicholas Mastrodemos  William Owen  Michael F. A’Hearn  S. Bagnulo  J. Bai  L. Barrera  Fabienne Bastien  James M. Bauer  J. Bedient  B.C. Bhatt  Hermann Boehnhardt  H. Zhao 《Icarus》2011,213(1):345-368

The evolution of the spin rate of Comet 9P/Tempel 1 through two perihelion passages (in 2000 and 2005) is determined from 1922 Earth-based observations taken over a period of 13 year as part of a World-Wide observing campaign and from 2888 observations taken over a period of 50 days from the Deep Impact spacecraft. We determine the following sidereal spin rates (periods): 209.023 ± 0.025°/dy (41.335 ± 0.005 h) prior to the 2000 perihelion passage, 210.448 ± 0.016°/dy (41.055 ± 0.003 h) for the interval between the 2000 and 2005 perihelion passages, 211.856 ± 0.030°/dy (40.783 ± 0.006 h) from Deep Impact photometry just prior to the 2005 perihelion passage, and 211.625 ± 0.012°/dy (40.827 ± 0.002 h) in the interval 2006–2010 following the 2005 perihelion passage. The period decreased by 16.8 ± 0.3 min during the 2000 passage and by 13.7 ± 0.2 min during the 2005 passage suggesting a secular decrease in the net torque. The change in spin rate is asymmetric with respect to perihelion with the maximum net torque being applied on approach to perihelion. The Deep Impact data alone show that the spin rate was increasing at a rate of 0.024 ± 0.003°/dy/dy at JD2453530.60510 (i.e., 25.134 dy before impact), which provides independent confirmation of the change seen in the Earth-based observations.The rotational phase of the nucleus at times before and after each perihelion and at the Deep Impact encounter is estimated based on the Thomas et al. (Thomas et al. [2007]. Icarus 187, 4–15) pole and longitude system. The possibility of a 180° error in the rotational phase is assessed and found to be significant. Analytical and physical modeling of the behavior of the spin rate through of each perihelion is presented and used as a basis to predict the rotational state of the nucleus at the time of the nominal (i.e., prior to February 2010) Stardust-NExT encounter on 2011 February 14 at 20:42.We find that a net torque in the range of 0.3–2.5 × 10⁷ kg m² s^?2 acts on the nucleus during perihelion passage. The spin rate initially slows down on approach to perihelion and then passes through a minimum. It then accelerates rapidly as it passes through perihelion eventually reaching a maximum post-perihelion. It then decreases to a stable value as the nucleus moves away from the Sun. We find that the pole direction is unlikely to precess by more than ～1° per perihelion passage. The trend of the period with time and the fact that the modeled peak torque occurs before perihelion are in agreement with published accounts of trends in water production rate and suggests that widespread H₂O out-gassing from the surface is largely responsible for the observed spin-up.  相似文献   

Split Comet C/2001 A2 (LINEAR)     

Jehin  Emmanuel  Boehnhardt  Hermann  Sekanina  Zdenek  Bonfils  Xavier  Schütz  Oliver  Beuzit  Jean-Luc  Billeres  Malvina  Garradd  Gordon J.  Leisy  Pierre  Marchis  Franck  Más  Antonio  Origlia  Livia  Scarpa  Daniel  Thomas  Daniel  Tozzi  Gian Paolo 《Earth, Moon, and Planets》2002,90(1-4):147-151

Comet C/2001 A2 experienced several splitting events duringits 2001 perihelion passage. The first break-upevent was observed in March 2001 (IAUC 7616).In this paper we report the first results of ourextensive imaging and spectroscopic monitoring campaignwith ESO telescopes over several weeks before andafter the perihelion passage on May 25 2001.  相似文献   

The acceleration and the deceleration of the tumbling period of Rocket Intercosmos 11 during the first two years after launch     

H. Boehnhardt  H. Koehnhke  A. Seidel 《Astrophysics and Space Science》1989,162(2):297-313

We have analysed the development of the tumbling period of Rocket Intercosmos 11 (1974-34-B) during the first 2 years after launch. We interpret the period increase, observed from August 1974 to June 1976, as being caused by torque moments due to eddy currents induced in the hollow cylinder by the magnetic field of the Earth. The spin-decay time of 1974-34-B was 1.13 yr. This compares well to results derived by Williams and Meadows in 1978 for other Soviet rocket bodies.The tumbling acceleration of 1974-34-B, observed in June 1974, is interpeted as outgassing effect of rest propellant which remained inside the rocket after burn-off. A model of the outgassing acceleration is developed and compared to the period measurements of 1974-34-B. A reasonable good agreement between observed and predicted periods can be derived by using a nonlinear regression fit. An initial mass ratio of the rest propellant and the empty rocket cylinder is estimated.  相似文献   

Comet Splitting – Observations and Model Scenarios     

Boehnhardt  Hermann 《Earth, Moon, and Planets》2000,89(1-4):91-115

Splitting events affect cometary nuclei to a different level of severity ranging from complete disruption of the nucleus (e.g., C/1999 S4 LINEAR) to separation of major fragments (e.g., 73P/Schwassmann-Wachmann 3) and spill-offs of smaller boulders (e.g., C/2001 A2 LINEAR).Fragmentation of comets produces secondary products over a wide range of sizes (from cometesimals to sub-micron dust). It is detectable through the presence of fragments (with own comae and tails) in the coma of the parent nucleus, through outbursts in its activity and through arc-lets (“coma wings”)associated with fragments. The secondaries have different life times and show different non-gravitational forces. Nucleus splitting is also considered to generate whole families of comets (Kreutz group) or — if gravitational bound — multiple nuclei (e.g., C/1995 O1 Hale-Bopp). It may explain the striae phenomena seen in dust tails of bright comets (C/1995 O1 Hale-Bopp) and the detection of chains of impact craters onother bodies in the solar system. As process of significant mass loss it is relevant for the scenario of nucleus extinction, at the same time it also plays a role for the number statistics of existing (observable) comets and for the size distribution of comet nuclei. Various model scenarios for nucleus splitting are proposed: tidal disruption, rotational splitting, break-up due to internal gas pressure, fragmentation due to collision with other bodies. Only in one case, Comet D/1993 F1Shoemaker-Levy 9, the physical process of fragmentation could be undoubtedly identified. In any case, comet splitting provides important insights inthe internal structure, surface layering and chemistry of comet nuclei.  相似文献