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1.
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   

2.
This paper reports on the detection of a satellite around the principal nucleus of comet Hale-Bopp. As shown elsewhere, a successful morphological model for the comet's dust coma necessitates the postulation of overlapping jet activity from a comet pair. The satellite has been detected digitally on images taken with the Hubble Space Telescope's Wide Field Planetary Camera 2 in the planetary mode on five days in May–October 1996. An average satellite-to-primary signal ratio is 0.21 ± 0.03, which implies that the satellite is ∼30 km in diameter, assuming the main nucleus is ∼70 km across. To avoid collision, the separation distance must exceed 50–60 km at all times. The satellite's projected distances on the images vary from 160 to 210 km, or 0.06 to 0.10 arcsec. The satellite was not detected in October 1995, presumably because of its subpixel separation from the primary. The radius of the gravitational sphere of action of the principal nucleus 70 km in diameter is 370–540 km at perihelion, increasing linearly with the Sun's distance: the satellite appears to be in a fairly stable orbit. Its orbital period at ∼180 km is expected to be ∼2–3 days, much shorter than the intervals between the HST observations. If the main nucleus should be no more than 42 km across, Weaver et al.'s upper limit, the satellite's orbit could become unstable, with the object drifting away from the main nucleus after perihelion. Potentially relevant ground-based detections of close companions are reported. Efforts to determine the satellite's orbit and the total mass of the system will get under way in the near future. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

3.
The comet Hale-Bopp (C/1995 O1) has been observed in the infrared (1–2.5 μm) with the Nordic Optical Telescope (NOT) equipped with the Arcetri NICMOS3 camera (ARNICA). Two observational campaigns, each one lasting about one week, were made when the comet heliocentric distance was about 3 AU. The first campaign was at the end of August and the second at the end of September 1996. During both runs two major outbursts were observed, the more intense of them started the day before the beginning of the second run. In the images recorded during the first three nights (24.8–26.8 Sept.) of the second run a dust shell expanding in the northern quadrant with a projected velocity of 0.14–0.28 km/s is clearly evident. The dust production rate increased by at least a factor ≈3 at the time of the outburst. Also evident on the first night is a change in the IR color that is well correlated with the dust shell. This is an indication that the material released by the outburst has a different composition and/or size distribution than that in the “quiescent” dust coma. In this paper we present preliminary results about the evolution and the photometric characteristics of the dust shell. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

4.
Lisse  C. M.  Fernández  Y. R.  A'hearn  M. F.  Kostiuk  T.  Livengood  T. A.  Käufl  H. U.  Hoffmann  W. F.  Dayal  A.  Ressler  M. E.  Hanner  M. S.  Fazio  G. G.  Hora  J. L.  Peschke  S. B.  Grün  E.  Deutsch  L. K. 《Earth, Moon, and Planets》1997,78(1-3):251-257
We present infrared imaging and photometry of the bright, giant comet C/1995 O1 (Hale-Bopp). The comet was observed in an extended infrared and optical observing campaign in 1996–1997. The infrared morphology of the comet was observed to change from the 6 to 8 jet “porcupine” structure in 1996 to the “pinwheel” structure seen in 1997; this has implications for the position of the rotational angular momentum vector. Long term light curves taken at 11.3 μm indicate a dust production rate that varies with heliocentric distance as ∶ r−1.4. Short term light curves taken at perihelion indicate a rotational periodicity of 11.3 hours and a projected dust outflow speed of ∶ 0.4 km s−1. The spectral energy distribution of the dust on October 31, 1996 is well modeled by a mixture of 70% silicaceous and 30% carbonaceous non-porous grains, with a small particle dominated size distribution like that seen for comet P/Halley (McDonnell et al., 1991), an overall dust production rate of 2 × 105 kg s−1, a dust-to-gas ratio of ∶5, and an albedo of 39%. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

5.
Broadband imaging of Comet 67P/Churyumov–Gerasimenko has provided more data on the characterisation of the target of the ESA Rosetta Mission. The comet monitoring between r h=2.37 and r h=2.78 AU postperihelion shows a prominent dust coma which extends up to ≈ 25,000 km from the nucleus, and a long dust structure in approximately anti-tail direction, reaching at least 230,000 km, identified as a neck-line structure. The non-isotropic dust emission is detected from the structures in the inner coma, and it is reflected on the slope of linear fits of surface brightness profiles vs. cometocentric projected distance in log–log representation as m ≈ 0.83−0.941. Besides the long dust spike at position angle of 295°, the morphological study of the dust coma confirms the presence of two structures at position angles of 95 and 195° where the overabundance of dust can be as high as 50% at ρ ≤ 30,000 km. The A f ρ parameter derived from our R broadband data is 26.0 and 29.8 cm at r h=2.37 and 2.48 AU postperihelion. The dust reflectivity S′(λ), a measurement of the dust colour, is 0.061±0.019, a rather neutral colour.  相似文献   

6.
Owens  Alan  Oosterbroek  T.  Orr  A.  Parmar  A. N.  Schulz  R.  Tozzi  G.P. 《Earth, Moon, and Planets》1997,77(3):293-298
We report the detection of soft X-rays from comet C/1995 O1 (Hale-Bopp) by the Low Energy Concentrator Spectrometer (LECS) on-board the X-ray satellite, BeppoSAX. The observations took place on 1996 September 10–11 approximately 1 day after a large dust outburst (Schulz et al., 1997–1999). After correcting for the comets motion, a 7σ enhancement was found centered (2.1 ± 1.3) x 105 km from the position of the nucleus, in the general solar direction. The total X-ray luminosity in the 0.1–2.0 keV energy band is 5 x 1016 erg s−1 which is at least a factor of ∼ 3 greater than measured by the Extreme Ultraviolet Explorer (EUVE)4 days later and suggests that the bulk of the emission measured by the LECS is related to the dust outburst. The extracted LECS spectrum is well fit by a thermal bremsstrahlung-like distribution of temperature of 0.29 ± 0.06 keV - consistent with that observed in other comets. We find no evidence for fluorescent carbon or oxygen emission and place 95% confidence limits of 1.0 x 1015 and 7.8 x 1015 erg s−1 to narrow line emission at 0.28 and 0.53 keV, respectively. We calculate that if such lines are present, they constitute at most 18% of the 0.1–2.0 keV continuum luminosity. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

7.
Optical spectroscopic data are presented on nova LW Serpentis 1978, obtained during its decline fromV 9.0 to ≃10.2 (compared to a value of ∼ 8.0 at recorded maximum). The spectrum and its evolution compare well with a typical nova, though the principal absorption (∼ −750 km s−l) was very weak in comparison with the diffuse-enhanced absorption (∼ −1300 km s−1). The principal absorption could be identified only in the lines of O I λλ7774, 8446, and in moderate-resolution observations of Hα. The salient features of spectral evolution follow: The near-infrared triplet of Ca n continuously weakened. O I λ8446 was always brighter than O I λ 7774, indicating continued importance of Lyman Β fluorescence. The lines due to [O I], [N II] and N n brightened considerably near the end of our observations (37 days from maximum). The Hα emission line was asymmetric all through with more emission towards the red. Its emission profile showed considerable structure. Based on the individual peaks in the Hα line profile, a kinematical model is proposed for the shell of LW Ser. The model consists of an equatorial ring, and a polar cone on the side away from the earth. The nearer polar cone did not show significant emission of Hα during our observations. The polar axis of the shell is inclined at a small angle (∼ 15‡) to the line of sight.  相似文献   

8.
McCARTHY  D.  STOLOVY  S.  KERN  S.  SCHNEIDER  G.  FERRO  A.  SPINRAD  H.  BLACK  J.  SMITH  B. 《Earth, Moon, and Planets》1997,78(1-3):243-249
Near-infrared images of comet Hale-Bopp (C/1995 O1) were obtained from NICMOS/HST on UT August 27–28, 1997, when the comet emerged from the 50 degree solar elongation limit at 2.99 AU from Earth. Diffraction-limited images were obtained with camera 2 filters centered at 1.87, 1.90, 2.04 and 2.22 μm with ∼0.2″ resolution (0.076″/pixel; 165 km/pixel). Over the 1.7-hour baseline of observation, a recent (<7 hours) outburst is seen in the form of an expanding spiral arm with a projected expansion velocity of ∼80 m/s. Other asymmetric features include a jet emanating from the nucleus and several static linear features. Comparisons of the flux distribution in the 2.04 and 2.22 μm filters indicate that the region near the nucleus exhibits a slight, ∼3%, water ice absorption. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

9.
At the First International Conference on Comet Hale–Bopp(Canaries, 1998) many astronomers agreed with the value of theperiod of axial rotation of its nucleus, which was obtained byobservers by a comparison of the two sequential patterns of thedust arcs. It was noted that the pattern had been repeated each∼12 hours. The value 11.35h was taken as the periodof axial rotation. However, alternative periods of 4 and 8 days havealso been suggested. The possible reasons for thisdiscrepancy are discussed. It is shown that a short period could be obtained by a misidentification of the same arc on twosequential images and, as a result, an overestimate of theradial velocity of dust in the arcs. To obtain the half day period one must take the projected velocity of the arc ∼ 1.6 km/s,which exceeds the H2O gas expansion velocity. If one takes a lower expansion velocity a longer period would be obtained.  相似文献   

10.
We propose that at least two stars on or near the AGB have long-lived orbiting disks: HD 44179, the central star in the Red Rectangle, and BM Gem, a carbon-rich star with an oxygen-rich circumstellar envelope. The CO emission from both of these disks has a spike with a width near ∼2 km s−1, indicating disk radii of ∼1016 cm. The dust in such disks is therefore quite cold (near T ∼ 50 K for the Red Rectangle) and may emit primarily at submillimeter wavelengths. The disks around stars where there is also substantial mass loss may not be easily observable; there could be many as yet undiscovered disks around AGB stars This revised version was published online in September 2006 with corrections to the Cover Date.  相似文献   

11.
Very-high spectral resolution observations of the neutral Na emission have enabled measurements of the velocity dispersions of the Na atoms within ∼40,000 km of the opto center of Hale-Bopp. Asymmetric Na D line profiles imply both an in situ or core Na source and a secondary Na source at locations within the inner coma. The core velocity distribution had a FWHM of 2 km s-1. The extended source FWHM increased with distance from the nucleus (up to ∼6 km s-1, but appeared smaller in the more dusty regions (∼2.5–3.0 km s-1) of the inner coma. The D2/D1 line strength ratio was consistent with an optically thin inner coma. Within 5,000 km of the opto center the continuum spatial intensity profiles decreased as ∼r-1 while the Na D emission decreased at less than r-1. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

12.
Womack  M.  Homich  A.  Festou  M. C.  Mangum  J.  Uhl  W. T.  Stern  S. A. 《Earth, Moon, and Planets》1997,77(3):259-264
On-the-Fly maps of emission from the HCO+ J = 3-2 transition at 267.6 GHz were obtained of C/1995 O1 (Hale-Bopp) on 1997 Mar 15.6 UT using the NRAO 12-m telescope with high spatial resolution. Unlike the relatively symmetric and centralized maps of the neutral species CO, HCN and H2CO, the spatial extent of HCO+ emission is very diffuse with a complex structure characterized by at least two physically different regions. The bulk of the HCO+ emission peaks in intensity ∼175,000 km anti-sunward from the nuclear position. This peak emission does not fall directly along the anti-sunward direction, but is rotated by ∼10 degrees toward the east from the anti-sunward direction. A substantial void, or decrease, of HCO+ emission is observed within ∼ 55,000 km of the nucleus. The HCO+ emission in this void is roughly half the intensity of the emission observed 100,000 km away. This decrease of HCO+ emission near the nucleus may indicate that production or excitation of HCO+ is inhibited, or perhaps that HCO+ is easily destroyed in the inner coma, especially within ∼50,000 km of the nucleus. This void roughly coincides with the approximate location and size of the so-called “diamagnetic cavity” in the coma and may mark a significant transition region in the inner coma of Hale-Bopp This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

13.
Bellucci  G. 《Earth, Moon, and Planets》1997,78(1-3):305-311
Previous analysis of imaging spectroscopy data in the 0.4–1 μm spectral range of comet Hale-Bopp, have shown the presence of two regions on the sunward and antisunward sides of the nucleus exhibiting different continuum emission (Bellucci, 1998, hereafter paper I). In this work we present the modeling of the continuum emission in terms of size distribution and composition of the dust grains. The spectra are fitted by micron sized olvine grains. A mechanism to explain the spatial gradient is also proposed. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

14.
In this paper, we investigate the relativistic beaming effects in a well-defined sample of core-dominated quasars using the correlation between the relative prominence of the core with respect to the extended emission (defined as the ratio of core-to lobe-flux density measured in the rest frame of the source) and the projected linear size as an indicator of relativistic beaming and source orientation. Based on the orientation-dependent relativistic beaming and unification paradigm for high luminosity sources in which the Fanaroff-Riley class-II radio galaxies form the unbeamed parent population of both the lobe- and core-dominated quasars which are expected to lie at successively smaller angles to the line of sight, we find that the flows in the cores of these core-dominated quasars are highly relativistic, with optimum bulk Lorentz factor,γ opt∼ 6–16, and also highly anisotropic, with an average viewing angle, ∼ 9°–16°. Furthermore, the largest boosting occurs within a critical cone angle of ≈ 4°–10°.  相似文献   

15.
Hanner  M. S.  Gehrz  R. D.  Harker  D. E.  Hayward  T. L.  Lynch  D. K.  Mason  C. C.  Russell  R. W.  Williams  D. M.  Wooden  D. H.  Woodward  C. E. 《Earth, Moon, and Planets》1997,79(1-3):247-264
The dust coma of comet Hale-Bopp was observed in the thermal infrared over a wide range in solar heating (R = 4.9–0.9 AU) and over the full wavelength range from 3 μm to 160 μm. Unusual early activity produced an extensive coma containing small warm refractory grains; already at 4.9 AU, the 10 μm silicate emission feature was strong and the color temperature was 30% above the equilibrium blackbody temperature. Near perihelion the high color temperature, strong silicate feature, and high albedo indicated a smaller mean grain size than in other comets. The 8–13 μm spectra revealed a silicate emission feature similar in shape to that seen in P/Halley and several new and long period comets. Detailed spectral structure in the feature was consistent over time and with different instruments; the main peaks occur at 9.3, 10.0 and 11.2 μm. These peaks can be identified with olivine and pyroxene minerals, linking the comet dust to the anhydrous chondritic aggregate interplanetary dust particles. Spectra at 16–40 μm taken with the ISO SWS displayed pronounced emission peaks due to Mg-rich crystalline olivine, consistent with the 11.2 μm peak. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

16.
    
The concept of simultaneous multifrequency continuum observations, successfully tested on Comet Hyakutake, was applied to Comet Hale-Bopp, using the Heinrich Hertz Submillimeter Telescope (HHT) with the four color bolometer between 250 and 870 GHz, the IRAM 30m telescope at 240 Ghz, the MPIfR 100-m telescope at 32 GHz, and the IRAM interferometer near 90 and 240 GHz. Near-simultaneous measurements were done between February 15 and April 26, 1997, mainly concentrated in mid March shortly before perigee of the comet. The measurements gave the following preliminary results: Interferometer detection of the nuclear thermal emission. If the signal at the longest interferometer spacing of 170 mis due to thermal emission from the nucleus only, its equivalent diameter is ∼49 km. If, however, this signal contains a contribution from a strongly centrally peaked halo distribution(e.g., r−2 density variation) the diameter may be as low as 35 km. The emission found interferometrically was always 5″ north and 0.1 sec east from the position predicted by Yeoman's solution 55.The comparison of the interferometric continuum emission with the simultanously obtained molecular line observations (reported on this conference) shows the origin of the strongest line emission concentrated on the nucleus. The 30-m observations show a radio halo with a gaussian FWHP of ∼11, corresponding to a diameter of 11000 km at geocentric distance of 1.2 a.u. A spectral index of ∼3.0 for the total signal, which may indicate a smaller mean particle size than for Hyakutake. Assuming an average cometary density of 0.5 gcm−3, the mass contained in the nucleus is ∼1$#x2013;3 1019 g and 1012 g in the particle halo. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

17.
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   

18.
Kane  R.P. 《Solar physics》2004,219(2):357-365
Plots of 12-month moving averages of the radio emission values for 1947–2002 indicated that the ratios (maximum/minimum) of the solar cycles 19–23 were low (∼ 1.2) in the upper chromosphere and lower corona (frequencies near 15 000 MHz), rose to maximum levels of ∼ 3.5 in the middle corona (frequencies ∼ 2000±500 MHz), and dropped thereafter to ∼ 2.5. In some cycles, there were two maxima separated by about 2 years. In cycles 20 and 23, mostly the second maximum was larger than the first maximum, but in cycles 21 and 22, some parameters showed the first maximum larger while others showed the second maximum larger. There was no systematic shift from first maximum to second maximum, with frequency or temperature (or altitude).  相似文献   

19.
SANTOS-SANZ  P.  SABALISCK  N.  KIDGER  M. R.  LICANDRO  J.  SERRA-RICART  M.  BELLOT RUBIO  L. R.  CASAS  R.  GOMEZ  A.  SANCHEZ PORTERO  J.  OSIP  D. 《Earth, Moon, and Planets》1997,78(1-3):235-241
We present a comparison between images of comet C/1995 O1 (Hale-Bopp) obtained from 12 March to 9 May 1997, with two telescopes of the Observatorio del Teide (IAC, Tenerife, Spain) in visible (Johnson-V filter) and three near-infrared narrowband filters (Brγ (2.166 μm), CO (2.295 μm), and Kcon (2.260 μm)). No significant differences are observed between the images in the three near-infrared bands suggesting that any CO emission is very weak, or produced by an extended flat source. We do not find evidence for the existence of an additional infrared component due to emission by warm dust, or to dust grains of diverse composition and/or size. Visible and infrared images of the same rotational phase look almost identical, supporting the view that the observed jets and shells are mainly dust structures. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

20.
We present the results of our infrared observations of WR 140 (=V1687 Cyg) in 2001–2010. Analysis of the observations has shown that the J brightness at maximum increased near the periastron by about 0 m .3; the M brightness increased by ∼2 m in less than 50 days. The minimum J brightness and the minimum L and M brightnesses were observed 550–600 and 1300–1400 days after the maximum, respectively. The JHKLM brightness minimum was observed in the range of orbital phases 0.7–0.9. The parameters of the primary O5 component of the binary have been estimated to be the following: R(O5) ≈ 24.7R ⊙, L(O5) ≈ 8 × 105 L ⊙, and M bol(O5) ≈ −10 m . At the infrared brightness minimum, T g ∼ 820–880 K, R g ≈ 2.6 × 105 R ⊙, the optical depth of the shell at 3.5 μm is ∼5.3 × 10−6, and its mass is ≈1.4 × 10−8 M ⊙. At the maximum, the corresponding parameters are ∼1300 K, 8.6 × 104 R ⊙, ∼2 × 10−4, and ∼6 × 10−8 M ⊙; the mean rate of dust inflow (condensation) into the dust structure is ∼3.3 × 10−8 M ⊙ yr−1. The mean escape velocity of the shell from the heating source is ∼103 km s−1 and the mean dispersal rate of the shell is ∼1.1 × 10−8 M ⊙ yr−1.  相似文献   

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