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1.
在1996年8月5日——1997年5月15日对Hale-Bopp彗星进行了照相观测,多次观测到Hale-Bopp彗星彗核的小规模分裂,喷流,壳层结构及彗发的膨胀现象。 相似文献
2.
Comet Hale-Bopp was observed with the 80 cm reflector + CCD at the Haute-Provence observatory (OHP) and with the 62 cm reflector
+ CCD at the Saint-Véran observatory (Queyras, France). The morphology of the shells was followed from their first appearence
on 1997 Jan. 30, until their disappearance on May 9. These shells spread from the nucleus region with a velocity in agreement
with a nuclear rotation period of about 11.33 hours. We report also a short and bright dust ejection on May 8. CN images show
a long spiral jet in the tailward side invisible on continuum images. The circumnuclear structures have been followed at Saint-Véran
from Apr. 5 to Apr. 11, 1997 with a high spatial resolution (200 km/pixel). We have followed the emergence of a recurrent
linear polar jet. Measurements of its expansion show a constant acceleration of material with typical expansion velocity of
1 km/s. The CCD frames show the interconnection between spiral jets and the successive shells.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
3.
Mueller Béatrice E.A. Samarasinha Nalin H. Belton Michael J.S. 《Earth, Moon, and Planets》1997,77(3):181-188
Imaging of coma morphology of Comet Hale-Bopp from pre-perihelion through perihelion to post-perihelion is presented. Broad
band images from 1996 and late 1997 show nearly radial jets streaking out from the nucleus. During both 1996 and late 1997,
the brightest jets are approximately in a northern/northeastern direction. The slight curvature present in these radial jets
is consistent with radiation pressure effects. Narrow band images around perihelion show two distinctive pictures of the CN
and the continuum coma morphology. Spirals are clearly seen in the CN images but not in the continuum where structure is confined
to the sunward side. The CN structure is consistent with continuous outgassing of the source of CN from the nucleus during
both day and night.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
4.
Manzini Federico Crippa Roberto Oldani Virgino Guaita Cesare 《Earth, Moon, and Planets》1999,87(2):73-85
Using a CCD camera attached to the 0.335 m and 0.20 m reflectors of S.A.S. Observatory (Novara, Italy), we followed the linear
jets and shells of comet Hale–Bopp between May 1996 and May 1997. In addition to confirming the model of Sekanina and Bohenhardt
(1997), the study of the linear jets provided indications concerning the orientation of the comet's axis of rotation over
time. The study of the shells revealed that the speed at which they move away from the nucleus was not constant. A periodic
variation of the shell expansion velocity may not be excluded : if so, a possible precessional effect on the axis of rotation
of the comet's nucleus could explain this behavior.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
5.
BRAUNSTEIN M. COMSTOCK R. HOFFMAN P. WOMACK M. DEGLMAN F. PINNICK D. AAKER G. GOLDSCHEN M. JACOBSON A. ZILKA J. FAITH D. MOORE S. RICOTTA J. WEIST A. MODI C. 《Earth, Moon, and Planets》1997,78(1-3):219-227
An optical archive of comet Hale-Bopp was obtained over 28 nights from June 1996 to May 1997 covering a range of heliocentric
distances of r = 4.12 − 0.91. The CCD images were obtained with the 0.8-m University of Washington Manastash Ridge Observatory
and the 0.25-m Pennsylvania State University at Eriemobile observatory. The reduced images clearly document the evolution
of features of the coma, which were dominated by radial jetsfrom r = 4.1 − 2.3 AU, curved fan-shaped jets from r = 1.2 − 1.0
AU, and arcs or shells for 0.9 < r < 1.0 AU. We present the images and derive an average dust expansion velocity of Vdust = 0.67 ± 0.07 km s−1 from measurements of the arc features. The images in thearchive will be made available to other researchers for further study.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
6.
We present the coronal index of solar activity (CI) for 1997 and use the 1996 and 1997 data to examine the properties of the solar minimum between cycles 22 and 23. To compute CI, we used only the intensities of the green corona from Lomnický tít and Sacramento Peak coronal stations. Values of CI were low in the first half of 1997 with an increase from September toward the end of 1997. We determined the minimum in the green corona to be May 1996, which is in coincidence with the results from 2800 MHz radio flux, the Mg II index and the Wolf number. 相似文献
7.
William Liller 《Planetary and Space Science》1997,45(12):1505-1513
Systematic CCD photometry of Comet 1995 O1 (Hale-Bopp) began in early August 1995 shortly after its discovery (IAU Circular 6187) and continued until mid-November 1996. The light curve derived from a 34″ square centered on the nucleus shows clearly and objectively how the inner regions of the comet brightened during this 15 month period. Possible connections between sudden brightenings and reported outbursts are investigated. During the interval August–December 1995, the magnitude of the comet showed strong evidence of a periodicity of 20±5 days with a full amplitude of approximately 0.20 mag. It is noteworthy that this result spans both the period of 18 days suggested by Sekanina (1995, 1996) and the “superperiod” of 22±2 days reported by Jorda et al. (1997). However, in 1996 neither this periodicity nor any other could be detected with certainty in the photometric data. 相似文献
8.
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
9.
R. Gil-Merino L.J. Goicoechea M. Serra A. Oscoz E. Mediavilla J. Buitrago 《Astrophysics and Space Science》1998,263(1-4):47-50
From optical data of Q0957+561 for 1995/1996 seasons (in the g band) and 1996/1997 seasons (in the R band) they are derived
upper limits on the amplitude of the rapid microlensing fluctuations of 0.07 mag and 0.05 mag, respectively. The photometry
in the R band (1996/1997 seasons) was taken at Teide Observatory (IAC-80 Telescope), Instituto de Astrofisica de Canarias,
Spain. In this contribution, we also study the microlensing history (from 1981 to 1996) of the Twin QSO, which is a curious
system with two optical images of similar brightness.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
10.
LAFFONT CÉLINE ROUSSELOT P. CLAIREMIDI J. MOREELS G. BOICE D. C. 《Earth, Moon, and Planets》1997,78(1-3):211-217
An observation program for measuring the activity of Comet Hale-Bopp was conducted at the Observatoire de Haute Provence from
August 1996 to April 1997. Narrow band images were obtained from the 120 cm telescope. A set of four filters at 513, 516,
527 and 682 nm was used to measure the C2 emission in the (1,1) and (0,0) band and the intensity of the dust-scattered continuum. The luminosity of the central part
of the coma was measured in the continuum and C2 emissions, as a function of heliocentric distance before perihelion. The activity of the comet considerably increased between
October 1996 and February 1997. The images obtained in August, September and October 1996 show the presence of strong jets.
In February, March and April 1997, series of roughly concentric arcs were observed in the sunward hemisphere of the coma.
The arcs were also detected in the spatial distribution of the I(682 nm)/I(527 nm) red color ratio and the I(513 nm)/I(516
nm) C2 emission ratio. Using the I(513 nm)/I(516 nm) ratio as a parameter to measure the degree of excitation of C2 molecules, we can show that the local production of gas, probably resulting from dust fragmentation, should be taken into
account.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
11.
We have used the daily values of the equatorial rotation rate determined from the Mt. Wilson daily Doppler-velocity measurements
during the period 3 December 1985 – 5 March 2007 to search for periodicities in the solar equatorial rotation rate on time
scales shorter than 11 years. After the daily values have been binned into 61-day intervals, a cosine fit with a period of
one year was applied to the sequence to remove any seasonal trend. The spectral properties of this sequence were then investigated
by using standard Fourier analysis, maximum-entropy methods, and a Morlet-wavelet analysis. From the analysis of the Fourier
power spectrum we detected peaks with periodicities around 7.6, 2.8, and 1.47 years and 245, 182, and 158 days, but none of
them were at a statistically significant level. In the Morlet-wavelet analysis the ≈1.47-year periodicity is detected only
for 1990 (i.e., near the maximum of cycle 22) and near the end of cycle 22 in 1995. From the same wavelet analysis we found some evidence
for the existence of a 2.8-year periodicity and a 245-day periodicity in the equatorial rotation rate around the years 1990
and 1992, respectively. In the data taken during the period 1996 – 2007, when the Mt. Wilson spectrograph instrumentation
was more stable, we were unable to detect any signal from the wavelet analysis. Thus, the detected periodicities during the
period before 1996 could be artifacts of frequent changes in the Mt. Wilson spectrograph instrumentation. However, the temporal
behavior of most of the activity phenomena during cycles 22 (1986 – 1996) and 23 (after 1997) is considerably different. Therefore,
the presence of the aforementioned short-term periodicities during the last cycle and absence of them in the current cycle
may, in principle, be real temporal behavior of the solar rotation during these cycles. 相似文献
12.
W. -H. Ip 《Astrophysics and Space Science》1988,144(1-2):347-352
The electrodynamic model of generation of electric currents in the solar atmosphere, by means of twisting of emerging magnetic flux loops, is investigated with emphasis on the small-scaled EUV/X-ray bright points. It is found that the corresponding power input from such conversion of kinetic energy of the turbulent photospheric plasma into magnetic energy could amount to about 25% of the total energy flux of the solar wind and solar radiation. However, if similar filamentary structures containing colder material are formed in abundance, the total energy budget would be correspondingly larger and the resulting mass injection phenomena may be related to the so-called coronal bullets observed in UV. These energetic features suggest that the coronal dynamics and heating could be dictated by plasma structures with angular sizes <0.1–1. The Solar and Heliospheric Observatory (SOHO) mission will be essential in addressing these issues basic to solar corona and solar wind acceleration.Paper dedicated to Professor Hannes Alfvén on the occasion of his 80th birthday, 30 May 1988. 相似文献
13.
The Siberian Solar Radio Telescope: the current state of the instrument,observations, and data 总被引：2，自引：0，他引：2
Grechnev V.V. Lesovoi S.V. Smolkov G. Ya. Krissinel B.B. Zandanov V.G. Altyntsev A.T. Kardapolova N.N. Sergeev R.Y. Uralov A.M. Maksimov V.P. Lubyshev B.I. 《Solar physics》2003,216(1-2):239-272
The Siberian Solar Radio Telescope (SSRT) is one of the world's largest solar radio heliographs. It commenced operation in
1983, and since then has undergone several upgrades. The operating frequency of the SSRT is 5.7 GHz. Since 1992 the instrument
has had the capability to make one-dimensional scans with a high time resolution of 56 ms and an angular resolution of 15 arc sec.
Making one of these scans now takes 14 ms. In 1996 the capability was added to make full, two-dimensional images of the solar
disk. The SSRT is now capable of obtaining images with an angular resolution of 21 arc sec every 2 min. In this paper we describe
the main features and operation of the instrument, particularly emphasizing issues pertaining to the imaging process and factors
limiting data quality. Some of the data processing and analysis techniques are discussed. We present examples of full-disk
solar images of the quiet Sun, recorded near solar activity minimum, and images of specific structures: plages, coronal bright
points, filaments and prominences, and coronal holes. We also present some observations of dynamic phenomena, such as eruptive
prominences and solar flares, which illustrate the high-time-resolution observations that can be done with this instrument.
We compare SSRT observations at 5.7 GHz, including computed `light curves', both morphologically and quantatively, with observations
made in other spectral domains, such as 17 GHz radio images, Hα filtergrams and magnetograms, extreme-ultraviolet and X-ray
observations, and dynamic radio spectra. 相似文献
14.
Sekiguchi T. Watanabe J. Fukushima H. Yamamoto T. Yamamoto N. 《Earth, Moon, and Planets》1997,78(1-3):143-148
In order to monitor the various phenomena of comets, we continuously made the near-nucleus imaging observations of comets
at National Astronomical Observatory, Mitaka. Here we report on the results of the observations of two spectacular comets.
One is the analysis of photometry of C2 emission images in the coma of comet Hyakutake (C/1996 B2). By comparing the production rates of C2 radicals with C2H2 molecules, we conclude that the most C2 radicals were originated from C2H2, while some of them might be produced from other parents. The second item is the analysis of the morphology of C2 emission images in the coma of comet Hale-Bopp(C/1995 O1). By applying a ring masking technique, we detected asymmetrical
distribution of the C2 molecules. The results of these two comets might suggest that a portion of C2 radicals were formed by the disintegration of the small organic dust grains, like the so-called CHON particles.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
15.
Vasundhara R. Chakraborty Pavan Hänel Andreas Heiser Erwin 《Earth, Moon, and Planets》1997,78(1-3):321-328
Persistent jet and shell structures from comet Hale-Bopp showing gradual changes in the shapes and orientations with aspect
angle and solar illumination geometry indicate long lived active sources. A model to simulate the dust features has been applied
to the series of observations from September 1996 to May 1997. Most of the structures can be explained as arising due to ejections
from persistent active regions at comet-o-centric latitudes near +65°, +55°, −5° to −15°, −35° and −65°. The best fitting
pole positions vary between 255° ±10° and 275° ± 10° in right ascension and −45° ± 10° to −75° ± 10° in declination. Lower
limits on the dust and gas production rates at various epochs are presented.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
16.
Allen Maxwell J. Oluseyi Hakeem M. Walker Arthur B. C. Hoover Richard B. Barbee Troy W. 《Solar physics》1997,174(1-2):367-401
The Multi-Spectral Solar Telescope Array (MSSTA), a rocket-borne solar observatory, was successfully launched from White Sands Missile Range, New Mexico, on May 13, 1991 at 19:05 UT. The telescope systems onboard the MSSTA obtained several full disk solar images in narrow bandpasses centered around strong soft X-ray, EUV, and FUV emission lines. Each telescope was designed to be sensitive to the coronal plasmas at a particular temperature, for seven temperatures ranging from 20000 K to 4000000 K. We report here on the images obtained during the initial flight of the MSSTA, and on the chromospheric and coronal structure of polar plumes observed over both poles of the Sun. We have also co-aligned the MSSTA images with Kitt Peak magnetograms taken on the same day. We are able to positively identify the magnetic structures underlying the polar plumes we analyze as unipolar. We discuss the plume observations and present a radiative energy balance model derived from them. 相似文献
17.
We carry out flux monitoring on a sample of 169 Gigahertz Peaked Spectrum (GPS) radio sources at 5 GHz and find that about one-third of them show considerable Inter-Month Variability (IMV), and these IMV phenomena are likely to be caused by interstellar scintillation (ISS). Furthermore, we find that those showing IMV tend to be point-like or core-jet structures at VLBI scale. 相似文献
18.
Sensitivity Kernels for Time-Distance Inversion 总被引：1，自引：0，他引：1
Jensen Jesper Munk Jacobsen Bo Holm Christensen-Dalsgaard Jørgen 《Solar physics》2000,192(1-2):231-239
Inversion of local-area helioseismic time-distance data has so far only been done in the ray approximation (Kosovichev, 1996). Since this is a high-frequency approximation its applicability can be questioned for the solar case. Bogdan (1997) showed that for a simple solar model the localized wave packets do follow, but are not confined to, the ray path. We use an approximation based on the first Fresnel zone that has been developed in geophysics by Snieder and Lomax (1996) to go beyond the ray approximation in the inversions. We have calculated sensitivity kernels using both approximations. To test them we use a finite-difference forward modeling of the whole wave field in an acoustic medium reminiscent of the Sun. We use the finite-difference modeling to calculate sensitivity kernels for the full wave field and compare this with the other kernels. The results show that the Fresnel-zone-based kernels are in good agreement with the sensitivity obtained from the modeling. Thus these new kernels represent a significant step forward in the inversion of time-distance data. 相似文献
19.
《Planetary and Space Science》1999,47(10-11):1277-1283
A regular extensive CCD imaging of Saturn allowed us to analyze the discrete cloud activity in the Equatorial Zone from 1995 to 1997. The large-scale storm observed in 1994 at +10° (Sanchez-Lavega et al., 1994, Sanchez-Lavega et al., 1996) was rediscovered in 1995, reaching a lifetime >1 year. Its slow motion characterized by a zonal velocity difference of −150 ms−1 relative to background flow is confirmed. Our red and near infrared observations showed a strong increase of white cloud activity in the southern Equatorial Zone (latitude −13.5°) during 1996, declining later on during 1997. Cloud tracking of two prominent plumes and other features allowed us to measure zonal wind velocities and to compare them to the Voyager zonal flow velocity profile. We note that in general the 1995–1997 features have velocities lower than those measured with the Voyagers. Altitude differences in the clouds and hence different zonal velocities, or real changes in the zonal jet as a consequence of Saturn’s insolation cycle and ring-shadowing, can be the reason for such differences. 相似文献
20.
In the following study our aim is to analyse the magnetic flux-rope topology of some events observed in the interplanetary medium related to ejecta. The magnetic field structures associated with interplanetary coronal mass ejections are globally classified in magnetic clouds and ejecta. One of the main questions regarding these phenomena concerns their flux-rope or non-flux-rope magnetic field line configuration. From the experimental measurements the only way to elucidate such a question is analysing the corresponding data by means of a flux-rope physical model. After selecting the ejecta events observed during the period 1997?–?2006, we have analysed them in light of an analytical model with that topology for the magnetic field components, initially developed for magnetic clouds, and with a non-force-free character; then, incorporating the expansion of the magnetic structure during their evolution in the interplanetary medium. Different parameters obtained from the fitting of the model are related to the orientation of the axis of the magnetic flux-rope structure and, additionally, the closest distance approach of the spacecraft to its axis. One of the main conclusions achieved concerns the fact that the axes of most of those structures are close to the Sun–Earth line, which implies that the passage of the spacecraft through the corresponding ejecta event is by its flank. In general, we show a rough procedure for the analysis and classification of ejecta in terms of their magnetic field topology. 相似文献