The Rotation Of Comet C/1995 O1 Hale–Bopp From Inner Coma Photometry     

Ortiz  J. L.  Rodríguez  E. 《Earth, Moon, and Planets》1997,77(3):207-215

We present a further investigation of the periodogram resulting from the photometric data by Rodríguez et al. (1997) for comet C/1995 O1 Hale–Bopp and interpret that the main period in the data is 11.23 ± 0.01 h, but not 7.19 days. The latter is now attributed to an alias of the 11.23-h period. Assuming that the periodicity observed in the photometry is the solar day, the 11.23-h period is consistent with estimates of the sidereal rotation period by Farnham et al. (1998), and Jorda et al. (1997–1999) provided that the obliquity of the comet‘s equatorial plane to its orbital plane is larger than 75° and 80°, respectively. This result is in agreement with estimates of the obliquity by Sekanina (1997–1999) and Jorda et al. (1998). A weaker periodic signal in the light curve could be 5.48 ± 0.01 h, but we suggest that this is an alias of a 3.25 ± 0.01 h period of unknown origin. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Velocity-Resolved Observations of Hα Emission From Comet C/1995 O1 (Hale–Bopp)     

Morgenthaler  Jeffrey P.  Harris  Walter M.  Scherb  Frank  Doane  Nathaniel E.  Oliversen  Ronald J. 《Earth, Moon, and Planets》2002,90(1-4):89-97

We present hydrogen Balmer-α spectra of comet C/1995 O1(Hale–Bopp) recorded on 5 nights from 1997 February 1 to April 19 by ahigh-resolution (Δ v = 5 km s^-1) Fabry–Pérot spectrometer for a4'.1 (∼2.7 × 10⁵ km) FOV centered 5' sunwardof the nucleus. The Hα line profile is an important diagnostic ofphotolytic heating in cometary atmospheres. Extraction of the spectrafrom the Fabry–Pérot ring images was complicated by obscuration of the telescope FOV due to Hale–Bopp's low elevation, but the measuredH-α line widths of 11–13 km s^-1 (FWHM) are insensitive to the spectral extraction technique. The line widths are consistent withestimates derived from a successful model of Hale–Bopp's hydrogenLyman-α coma assuming the inner coma is opaque to Hα. Wediscuss methods for improving the spectral extraction technique andderiving a precise instrument profile which will allow the detailedshape of the line profile to constrain coma models.  相似文献   

The Rotational Parameters Of Hale–Bopp (C/1995 O1) From Observations Of The Dust Jets At Pic Du Midi Observatory     

Jorda  L.  Rembor  K.  Lecacheux  J.  Colom  P.  Colas  F.  Frappa  E.  Lara  L. M. 《Earth, Moon, and Planets》1997,77(3):167-180

We observed comet Hale-Bopp (C/1995 O1) at Pic du Midi Observatory in 1997 from February 2.24 UT to March 31.89 UT with the 1.05-m telescope equipped with a CCD camera and broad- and narrow-band IHW filters. A total of 30000 images were acquired both during night- and day-time. The images were automatically reduced and all the images obtained within 10 min. were co-added to give a set of ∼1000 images used during the analysis. We can identify two jets on the images. The position angle of the brightest jet from February 2.24 UT to March 5.22 UT is measured using an automatic routine which searches for the averaged position angle of the maximum of brightness at a projected distance of 3200–6100 km from the optocenter. A preliminary model of nucleus rotation is used to fit the data and retrieve the rotational parameters of the nucleus. The best fit is found for a source located at a latitude of 64 ± 3°, a sidereal rotation period of 11.35 ± 0.04 h and a right ascension and declination of the North pole of 275 ± 10° and -57 ± 10°. This preliminary analysis shows no evidence for a precession. Grains with velocities of 450–600 m s⁻¹ and radii <;∼ 1 μm dominate the optical scattering cross section in the jets. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

A Determination of The Nuclear Size of Comet Hale–Bopp (C/1995 O1)     

Sekanina  Z. 《Earth, Moon, and Planets》1997,77(3):147-153

The signal of the nucleus was digitally extracted from six images of the innermost coma of this comet, obtained with the Hubble Space Telescope’s Wide-Field Planetary Camera 2 in the planetary mode between October 23, 1995 and October 17, 1996. Two different anisotropic, power-type laws were used to filter out the contribution from the dust coma: one peaking at the center of the elliptical surface brightness distribution (law A), the other peaking at its focus (law B). The nuclear R magnitudes in the Cousins system, reduced to a zero phase angle and to 1 AU from Earth and the Sun with a phase coefficient of 0.035 mag/deg and an inverse square distance power law, are found to average 9.46 ± 0.07 and 9.48 ± 0.18 when law A and law B are applied, respectively. These results become 9.49 ± 0.07 and 9.51 ± 0.17, when the nucleus signal on the October 1995 image is assumed to consist of a sum of the contributions from two unresolved nuclear components. In either scenario, no systematic variations are apparent in the nuclear brightness with time, which suggests the absence of any significant contamination of the extracted nuclear signal by the coma. Assuming a geometric albedo of 4 percent, the corresponding effective nuclear diameter amounts to 71 ± 4 km (formal error). This result substantially exceeds the size estimates published by Weaver et al., which are based only on the October 1995 observation and which were obtained with the help of a different reduction method. Runs in which a power-type law fitting the contribution from the coma was assumed to hold all the way to a small fraction of a pixel from the nucleus led to distinctly inferior solutions and yielded spurious values ll70 km for the nuclear diameter. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Nitrogen Sulfide In Comets Hyakutake (C/1996 B2) And Hale–Bopp (C/1995 O1)     

Canaves  Marcus V.  De Almeida  Amaury A.  Boice  Daniel C.  Sanzovo  Gilberto C. 《Earth, Moon, and Planets》2002,90(1-4):335-347

The chemistry of both nitrogen and sulfur presents interesting problems in comets.In this paper, we use a model of cometary comae with gas-phase chemical kineticsand gas dynamics to predict molecular abundances in the inner coma region for twoof the brightest comets in the past 20 years, Hyakutake (C/1996 B2) and Hale–Bopp(C/1995 O1). In this progress report we concentrate on the gas-phase chemistry of thenitrogen sulfide (NS) radical at a heliocentric distance of 1 AU to study the abundanceof NS using a detailed photo and chemical reaction network with over 100 species andabout 1000 reactions. The results are compared with recent observations of CometHale–Bopp and reveal that conventional gas-phase reactions schemes do not produceNS in sufficient quantities to explain the observations. We plan to continue therefinement of the model to improve agreement with observational constraints.  相似文献   

Coma Morphology And Constraints On The Rotation Of Comet Hale–Bopp (C/1995 O1)     

Samarasinha  Nalin H.  Mueller  Béatrice E. a.  Belton  Michael J. S. 《Earth, Moon, and Planets》1997,77(3):189-198

We present constraints on the spin state of comet Hale-Bopp based on coma morphology. Three cases of rotational states are compatible with near perihelion observations: (1) principal-axis rotation, (2) complex rotational state with a small precessional angle, or (3) complex rotational state with a large ratio between the component periods. For principal axis rotators, images from 1996 (pre-perihelion) are consistent with a rotational angular momentum vector, M, directed at ecliptic longitude and latitude (250°, -5°) while images from late 1997 (post-perihelion) indicate (310°, -40°). This may suggest a change in M. A complex rotational state with small precessional angle requires only a small or no change in M over the active orbital arc. In this case, M is directed near ecliptic longitude and latitude (270°, -20°). A rotationally excited nucleus with a large ratio between component periods requires the nucleus to be nearly spherical. The transformation of dust coma morphology from near-radial jets to bright arcs and then again to near-radial jets is interpreted as a heliocentric and geocentric distance dependent evolutionary sequence. The spiral structures seen in CN filters near perihelion (in contrast to sunward side arcs seen in continuum) can be explained if the precursor of CN molecules (likely sub-micron grains) are emitted from the nucleus at low levels (≈ 10% of the peak daytime emission) during the nighttime. This may be indicative of a nucleus with a CO-rich active area(s). This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

The Near-Nuclear Study of Comet Hale Bopp     

Tao Jun  Qian Bochen  Gu Mingfeng  Tang Yuan  Song Baojun 《天文研究与技术》1999,(Z1)

ＩｎｔｒｏｄｕｃｔｉｏｎＣｏｍｅｔＨａｌｅ Ｂｏｐｐ(Ｈａｌｅ,1 995 )ｉｓａｎｅｘｔｒｅｍｅｌｙｂｒｉｇｈｔｃｏｍｅｔ.Ｉｔｈａｓｂｅｅｎａｃｔｉｖｅｗｈｅｎｄｉｓｃｏｖ ｅｒｙａｔ 7ＡＵｆｒｏｍｔｈｅＳｕｎ(Ｓｅｋａｎｉｎａ ,1 996 ) .Ｔｈｅｌｏｃａｌｉｚｅｄｅｊｅｃｔｉｏｎｏｆｄｕｓｔａｎｄｇａｓｐｒｏｄｕｃｅｄｃｏｍ ｐｌｅｘｃｏｍａｓｔｒｕｃｔｕｒｅｔｈａｔｃａｎｂｅｕｓｅｄｔｏｓｔｕｄｙｔｈｅｅｊｅｃｔｉｏｎｓｐｅｅｄａｎｄｎｕｃｌｅｕｓｒｏｔａｔｉｏｎｐｅｒｉｏｄ .Ｆｕｒ ｔｈｅｒｍｏｒｅ…  相似文献   

The 1995–2002 Long-Term Monitoring of Comet C/1995 O1 (HALE–BOPP) at Radio Wavelength     

Biver  Nicolas  Bockelée-Morvan  Dominique  Colom  Pierre  Crovisier  Jacques  Henry  Florence  Lellouch  Emmanuel  Winnberg  Anders  Johansson  Lars E.B.  Gunnarsson  Marcus  Rickman  Hans  Rantakyrö  Fredrik  Davies  John K.  Dent  William R.F.  Paubert  Gabriel  Moreno  Raphaël  Wink  Jörn  Despois  Didier  Benford  Dominic J.  Gardner  Matt  Lis  Dariusz C.  Mehringer  David  Phillips  Thomas G.  Rauer  Heike 《Earth, Moon, and Planets》2002,90(1-4):5-14

The bright comet Hale–Bopp provided the first opportunity to follow the outgassing rates of a number of molecular species over a large range of heliocentric distances. We present the results of our observing campaign at radio wavelengths which began in August 1995 and ended in January 2002. The observations were carried out with the telescopes of Nançay, IRAM, JCMT, CSO and, since September 1997, SEST. The lines of nine molecules (OH, CO, HCN, CH₃OH, H₂CO, H₂S, CS, CH₃CN and HNC) were monitored. CS, H₂S, H₂CO, CH₃CN were detected up to r_h= 3–4 AU from the Sun, while HCN and CH₃OH were detected up to 6 AU. CO, which is the main driver of cometary activity at heliocentric distances larger than 3–4 AU, was last detected in August 2001, at r_h= 14 AU. The gas production rates obtained from this programme contain important information on the nature of cometary ices, their thermal properties and sublimation mechanisms.Line shapes allow to measure gas expansion velocities, which, at large heliocentric distances, might be directly connected to the temperature of the nucleus surface. Inferred expansion velocity of the gas varied as r_h ^-0.4 within 7 AU from the Sun, but remained close to 0.4 km s^-1 further away. The CO spectra obtained at large r_hare strongly blueshifted and indicative of an important day-to-night asymmetry in outgassing and expansion velocity. The kinetic temperature of the coma, estimated from the relative intensities of the CH₃OH and CO lines, increased with decreasing r_h, from about 10 K at 7 AU to 110 K around perihelion.  相似文献   

C/1995 O1 Hale–Bopp: Short and Long Distance activity from a Theoretical Model     

Capria  Maria Teresa  Coradini  Angioletta  De Sanctis  Maria Cristina 《Earth, Moon, and Planets》2002,90(1-4):217-225

A theoretical model of the nucleus thermal evolutionand differentiation is used to simulatethe evolution along the orbit of the gasand dust emissions of comet Hale–Bopp. The model was already applied to this comet (Capria et al., 2000b): At that time only the results of the observations obtained shortly after the perihelion were available. Now much more data have been published and we present more refined and complete results about the production rates of gasand dust along the orbit and the internal stratigraphy. The results of our model on long distance activity and its explanation are also presented.  相似文献   

Modelling of Shape Changes of the Nuclei of Comets C/1995 O1 Hale–Bopp and 46P/Wirtanen Caused by Water Ice Sublimation     

Dziak-Jankowska  Beata  Leliwa-Kopystyński  Jacek  Królikowska  Mał Gorzata 《Earth, Moon, and Planets》2002,90(1-4):35-44

The aim of this modelling work is to assess shape changes of cometary nuclei caused by sublimation of ices. The simplest possible model is assumed with the nucleus being initially spherical and its thermal conductivity being neglected. We have calculated the time-dependent sublimation flux versus cometographic latitude. If the rotation axis of the comet is inclined to the orbital plane, then sublimation leads to non-symmetrical changes of the nucleus shape. Calculations were performed for the nuclei of comets Hale–Bopp and Wirtanen.  相似文献