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1.
The near infrared spectral reflectance of pure CH4, CO2, H2O, H2S, NH3 and NH4SH frosts has been measured. Comparison with recent Galilean satellite spectra indicates that H2O at approximately 150°K and with about 0.01 cm grain size is the major component on the surface of JII (Europa) and JIII (Ganymede); upper limits for the remaining frosts range from 5 to 28%. Materials other than these frosts must be present on the surface of JI (Io) and JIV (Callisto).  相似文献   

2.
We generated an event catalog with an automated detection algorithm based on the entire EUVI image database observed with the two Solar Terrestrial Relations Observatory (STEREO)-A and -B spacecraft over the first six years of the mission (2006?–?2012). The event catalog includes the heliographic positions of some 20?000 EUV events, transformed from spacecraft coordinates to Earth-based coordinates, and information on associated GOES flare events (down to the level of GOES A5-class flares). The 304 Å wavelength turns out to be the most efficient channel for flare detection (79?% of all EUVI event detections), while the 171 Å (4?%), 195 Å (10?%), and the 284 Å channel (7?%) retrieve substantially fewer flare events, partially due to the suppressing effect of EUV dimming, and partially due to the lower cadence in the later years of the mission. Due to the Sun-circling orbits of STEREO-A and -B, a large number of flares have been detected on the farside of the Sun, invisible from Earth, or seen as partially occulted events. The statistical size distributions of EUV peak fluxes (with a power-law slope of α P =2.5±0.2) and event durations (with a power-law slope of α T =2.4±0.3) are found to be consistent with the fractal-diffusive self-organized criticality model. The EUVI event catalog is available on-line at secchi.lmsal.com/EUVI/euvi_autodetection/euvi_events.txt and may serve as a comprehensive tool to identify stereoscopically observed flare events for 3D reconstruction and to study occulted flare events.  相似文献   

3.
Geomagnetic field variations during five major Solar Energetic Particle (SEP) events of solar cycle 23 have been investigated in the present study. The SEP events of 1 October 2001, 4 November 2001, 22 November 2001, 21 April 2002 and 14 May 2005 have been selected to study the geomagnetic field variations at two high-latitude stations, Thule (77.5° N, 69.2° W) and Resolute Bay (74.4° E, 94.5° W) of the northern polar cap. We have used the GOES proton flux in seven different energy channels (0.8–4 MeV, 4–9 MeV, 9–15 MeV, 15–40 MeV, 40–80 MeV, 80–165 MeV, 165–500 MeV). All the proton events were associated with geoeffective or Earth directed CMEs that caused intense geomagnetic storms in response to geospace. We have taken high-latitude indices, AE and PC, under consideration and found fairly good correlation of these with the ground magnetic field records during the five proton events. The departures of the H component during the events were calculated from the quietest day of the month for each event and have been represented as ΔH THL and ΔH RES for Thule and Resolute Bay, respectively. The correspondence of spectral index, inferred from event integrated spectra, with ground magnetic signatures ΔH THL and ΔH RES along with Dst and PC indices have been brought out. From the correlation analysis we found a very strong correlation to exist between the geomagnetic field variation (ΔHs) and high-latitude indices AE and PC. To find the association of geomagnetic storm intensity with proton flux characteristics we derived the correspondence between the spectral indices and geomagnetic field variations (ΔHs) along with the Dst and AE index. We found a strong correlation (0.88) to exist between the spectral indices and ΔHs and also between spectral indices and AE and PC.  相似文献   

4.
We analyze the occurrence-frequency distributions of peak fluxes [P], total fluxes [E], and durations [T] of solar flares over the last three solar cycles (during 1980??C?2010) from SMM/HXRBS, CGRO/BATSE, and RHESSI hard X-ray data. From the synthesized data we find powerlaw slopes with mean values of ?? P =1.73±0.07 for the peak flux, ?? E =1.62±0.12 for the total flux, and ?? T =1.99±0.35 for flare durations. We find a tendency of an anti-correlation of the powerlaw slope of peak fluxes with the flare rate or sunspot number as a function of the solar cycle. The occurrence powerlaw slope is always steeper by ??????0.1 during a solar-cycle minimum compared with the previous solar-cycle maximum, but the relative amplitude varies for each cycle or instrument. Since each solar cycle has been observed with a different instrument, part of the variation could be attributed to instrumental characteristics and different event selection criteria used in generating the event catalogs. The relatively flatter powerlaw slopes during solar maxima could indicate more energetic flares with harder electron-energy spectra, probably due to a higher magnetic complexity of the solar corona. This would imply a non-stationarity (or solar-cycle dependence) of the coronal state of self-organized criticality.  相似文献   

5.
《Planetary and Space Science》1999,47(3-4):327-330
The asteroid 85 Io has been observed using CCD and photoelectric photometry on 18 nights during its 1995–96 and 1997 apparitions. We present the observed lightcurves, determined colour indices and modelling of the asteroid spin vector and shape. The colour indices (U-B = 0.35±0.02, B-V = 0.66±0.02, V-R = 0.34±0.02, R-I = 0.36±0.02) are as expected for a C-type asteroid. The allowed spin vector solutions have the pole co-ordinates λ0 = 285±4°, β0 = −52±9° or λ0 = 108±10°, β0 = −46±10° and λ0 = 290±10°, β0 = −16±10° with a retrograde sense of rotation and a sidereal period Psid = 0d.286463±0d.000001. During the 1995–96 apparition the International Occultation Time Association (IOTA) observed an occultation event by 85 Io. The observations and modelling presented here were analysed together with the occultation data to develop improved constraints on the size of the asteroid. The derived value of 164 km is about 5% larger than the IRAS diameter. © 1999 Elsevier Science Ltd. All rights reserved.  相似文献   

6.
Baolin Tan 《Solar physics》2008,253(1-2):117-131
From the observations with the Chinese Solar Broadband Radiospectrometer (SBRS/Huairou) in the frequency range of 1.10?–?2.06 GHz and 2.60?–?3.80 GHz during 2004?–?2006, we select 14 flare events which were associated with numerous fast microwave subsecond pulsating structures (period: P<0.5 s). In order to describe these subsecond pulsating structures comprehensively, we defined a set of observable parameters including emission frequency (f 0), bandwidth (b w), polarization degree (r), period (P), duration (D), modulation depth (M), quality factor (Q), single pulse frequency drifting rate (R spfd), global frequency drifting rate (R gfd), and symmetrical factor of the pulse profile (S). Then based on a detailed analysis of the spectrograms of the fast pulsations which occurred in one of these flares (an X3.4 flare/CME event occurred on 13 Dec. 2006), we discuss the possible relations among these observable parameters and their physical implications for the dynamical processes of solar eruptive events, and applied them to interpret the nature of the pulsations in the flare/CME event. Such study of microwave periodic pulsations provides us with a useful tool to probe the details of the flare kernels, and understand the physical mechanism of solar eruptive processes.  相似文献   

7.
The cosmic event of Venus transit across the solar disk occurred on 8 June, 2004. The previous such event was witnessed about 122 years ago on 6 December, 1882. We observed this rare transit in H α 6563 Å line-center from Udaipur Solar Observatory (USO) using both the full-disk and small field-of-view solar telescopes. In the earlier historical transits, a “black-drop” effect was observed in white light images, during the contact phases. The transit of 8 June, 2004 provided a unique opportunity to observe this effect, for the first time, in H α. We report that the “black-drop” effect is present in H α also, as in the white light observations made by the ground-based Global Oscillation Network Group (GONG) instrument and the space-borne Transition Region and Coronal Explorer (TRACE) satellite. We did not observe any noticeable “aureole” (atmospheric glow) around Venus during the ingress or egress phases. We have compared the H α images with the multi-wavelength data obtained from the TRACE satellite.  相似文献   

8.
A statistical analysis of the contemporary (1954-1975) solar flare particle events has been made for the parametersF (integrated, proton fluence in cm-2 in an event with kinetic energy above 10 MeV) andR 0 (the characteristic rigidity). These data are compared with the long-term averaged values determined from stable- and radio-nuclide measurements of lunar samples. The analysis shows that the ancient solar flare proton spectrum was harder (higher R0 values) compared to that observed in contemporary flares. A similar analysis can not be made for the mean long-term averaged flux (ˉJ, cm-2 S-1), since the contemporary averages suffer from an uncertainty due to the statistics of a single event. However, the average flux estimates for time durations 〈T〉 exceeding 103 yr, are free from such uncertainties. The long-term averaged ˉJ values obtained over different time scales (104 - 106 yr) suggest a possible periodic variation in solar flare activity, with enhanced flux level during the last 105 yr. The available data rule out the occurrence of giant flares, with proton fluence exceeding 1015 cm-2 during the last million years.  相似文献   

9.
During the recent apparition of Comet Halley in 1985-86 a transient ionic event in the form of a blob of H2 O+ emission was recorded in thecoma at ～ 0h UT on 1986 March 13. Observations were carried out using a special IHW filter for H2 O+ emission at 7000 å/175 å, a 35 cm telescope, a Fabry-Perot interferometer and an image intensifier camera from Gurushikhar, Mt Abu. (24?39’N,72? 47’E). A Fabry-Perot inter-ferogram in Ha taken a few minutes later at the same location reveals strong hydrogen emission (Hα) associated with the blob. The velocity field in the blob is structured with relative velocities upto ～ 35km s?1. The event is interpreted as arising due to the sector boundary crossing of the interplanetary magnetic field by the comet  相似文献   

10.
We study the interplanetary features and concomitant geomagnetic activity of the two high-speed streams (HSSs) selected by the Whole Heliosphere Interval (WHI) campaign participants: 20 March to 16 April 2008 in Carrington rotation (CR) 2068. This interval was chosen to perform a comprehensive study of HSSs and their geoeffectiveness during this ??deep?? solar minimum. The two HSSs within the interval were characterized by fast solar-wind speeds (peak values >?600 km?s?1) containing large-amplitude Alfvénic fluctuations, as is typical of HSSs during normal solar minima. However, the interplanetary magnetic field (IMF) magnitude [B o] was exceptionally low (??3??C?5 nT) during these HSSs, leading to lower than usual IMF B z values. The first HSS (HSS1) had favorable IMF polarity for geomagnetic activity (negative during northern Spring). The average AE and Dst for the HSS1 proper (HSS1P) were +?258 nT and ??21 nT, respectively. The second HSS (HSS2) had a positive sector IMF polarity, one that is less favorable for geomagnetic activity. The AE and Dst index averages were +?188 nT and ??7 nT, both lower than corresponding numbers for the first event, as expected. The HSS1P geomagnetic activity is comparable to, and the HSS2P geomagnetic activity lower than, corresponding observations for the previous minimum (1996). Both events?? geomagnetic activities are lower than HSS events previously studied in the declining phase (in 2003). In general, V sw was faster for the HSSs in 2008 compared to 1996. The southward IMF B z was lower in the former. The product of these two parameters [V sw and IMF B z ] comprises the solar-wind electric field, which is most directly associated with the energy input into the magnetosphere during the HSS intervals. Thus the combined effects led to the solar wind energy input in 2008 being slightly less than that in 1996. A detailed analysis of magnetic-field variances and Alfvénicity is performed to explore the characteristics of Alfvén waves (a central element in the geoeffectiveness of HSSs) during the WHI. The B z variances in the proto-CIR (PCIR) were ???30 nT2 and <?10 nT2 in the high speed streams proper.  相似文献   

11.
The Utrecht solar hard X-ray spectrometer S-100 on board the ESRO TD-1A satellite covers the energy range above 25 keV with 12 logarithmically spaced channels. Continuous sun-pointing is combined with high time resolution: 1.2 s for the four low energy channels (25–90 keV) and 4.8 s for the others. It is emphasized that the instrument design and calibration yield data virtually free of pile-up and other instrumental defects. A complete set of observations is presented for all well-observed flares during the period March 12, 1972 to October 1, 1973, including four from the highly active period August 1–8, 1972. Photon spectra are computed every 1.2 s for each event by deconvolution through the instrument response, rather than by fitting techniques. Using these actual photon spectra, the index γ for the best fitting single power law and the minimum (thick target) injection rate of electrons above 25 keV, F 25, are calculated. Results for γ and F 25 at 1.2 s intervals are presented for each event. Examination of all these results tentatively suggests a real distinction between events of a purely impulsive nature and prolonged events. Techniques of time series analysis are applied to the burst time profiles. Specifically:
  1. The fluctuations present in the series are shown to be compatible with Poisson noise in the count rate.
  2. It is emphasized that, without spatial resolution, the X-ray source must be characterized by the e-folding time scale τ of the total count rate; examination of individual τ's through the event shows very few statistically real τ's as short as 1.2 s, confirming (1).
  3. For all events, the series are Fourier analysed; no small events showed statistically significant periodicities, but the large event of August 4, 1972 exhibited real periods of 30, 60 and 120 s in both the flux and the spectral index.
  4. Statistically real, small timing differences (～0.2 s) are shown to exist between spike peaks at different photon energies.
A search is made for correlations between instantaneous values of inferred parameters (e.g. F 25, γ and the time scales). Most results are negative, but in the August 4 and 7, 1972 events a very well defined path was followed through the (F 25, γ)-plane, giving insight into the electron acceleration process. Finally some general conclusions are drawn concerning the implications of our analysis for the physics of particle acceleration, including the possibility of two classes of event. Specifically, the severe problems posed by the large electron fluxes (equivalent current ～1017 A) demanded by the data are discussed in relation to flare theories. Some possibilities for getting around these problems, such as by reacceleration in a confinement region, are briefly considered.  相似文献   

12.
We study the 17 January 2010 flare–CME–wave event by using STEREO/SECCHI-EUVI and -COR1 data. The observational study is combined with an analytic model that simulates the evolution of the coronal wave phenomenon associated with the event. From EUV observations, the wave signature appears to be dome shaped having a component propagating on the solar surface ( $\overline{v}\approx280~\mathrm{km}\,\mathrm{s}^{-1}$ ) as well as one off-disk ( $\overline{v}\approx 600~\mathrm{km}\,\mathrm{s}^{-1}$ ) away from the Sun. The off-disk dome of the wave consists of two enhancements in intensity, which conjointly develop and can be followed up to white-light coronagraph images. Applying an analytic model, we derive that these intensity variations belong to a wave–driver system with a weakly shocked wave, initially driven by expanding loops, which are indicative of the early evolution phase of the accompanying CME. We obtain the shock standoff distance between wave and driver from observations as well as from model results. The shock standoff distance close to the Sun (<?0.3 R ⊙ above the solar surface) is found to rapidly increase with values of ≈?0.03?–?0.09 R ⊙, which gives evidence of an initial lateral (over)expansion of the CME. The kinematical evolution of the on-disk wave could be modeled using input parameters that require a more impulsive driver (duration t=90 s, acceleration a=1.7 km?s?2) compared to the off-disk component (duration t=340 s, acceleration a=1.5 km?s?2).  相似文献   

13.
Concurrent interplanetary magnetic field and 0.7–7.6 MeV proton cosmic-ray anisotropy data obtained from instrumentation on Explorers 34 and 41 are examined for five cosmic-ray events in which we observe a persistent eastern-anisotropy phase late in the event (t ? 4 days). The direction of the anisotropy at such times shows remarkable invariance with respect to the direction of the magnetic field (which generally varies throughout the event) and it is also independent of particle species (electrons and protons) and particle speed over the range 0.06 ? β ? 0.56. The anisotropy is from the direction 38.3° ± 2.4° E of the solar radius vector, and is inferred to be orthogonal to the long term, mean interplanetary field direction. Both the amplitude of the anisotropy and the decay time constant show a strong dependence on the magnetic field azimuth. Detailed comparison of the anisotropy and the magnetic field data shows that the simple model of convection plus diffusion parallel to the magnetic field is applicable for this phase of the flare effect. It is demonstrated that contemporary theories do not predict the invariance of the direction as observed, even when the magnetic field is steady; these theories need extension to take into account the magnetic field direction ψ varying from its mean direction ψ o. It is shown that the late phase anisotropy vector is not expected to be everywhere perpendicular to the mean magnetic field. The suggestion that we are observing kinks in the magnetic field moving radially outwards from the Sun leads to the conclusion that the parallel diffusion coefficient varies as 1/cos2 (ψ ? ψ o). Density gradients in the late decay phase are estimated to be ≈ 700%∣AU for 0.7–7.6 MeV protons. A simple theory reproduces the dependence of the decay time constant on anisotropy; it also leads to a radial density gradient of about 1000%∣AU and diffusion coefficient of 1.3 × 1020 cm2 s?1.  相似文献   

14.
The statistical parallax technique is applied to a sample of 262 RRab Lyrae variables with published photoelectric photometry, metallicities, and radial velocities and with measured absolute proper motions. Hipparcos, PPM, NPM, and the Four-Million Star Catalog (Volchkov et al. 1992) were used as the sources of proper motions; the proper motions from the last three catalogs were reduced to the Hipparcos system. We determine parameters of the velocity distribution for halo [(U 0, V 0, W 0) = (?9±12, ?214 ±10, ? 10, ?16±7) km s ?1 and (σ U , σ V , σ W ) = (164±11, 105±7, 95±7) km s ?1] and thick-disk [(U 0, V 0, W 0) = (?16±8, ?41±7, ?18±5) km s ?1], and [(σ U , σ V , σ W ) = (53±9, 42±8, 26±5) km s ?1] RR Lyrae, as well as the intensity-averaged absolute magnitude for RR Lyrae of these populations: 〈M V 〉 = 0.77 ± 0.10 and 〈M V 〉 = +1.11 ± 0.25 for the halo and thickdisk objects, respectively. The metallicity dependence of the absolute magnitude of RR Lyrae is analyzed (〈M V 〉 = (0.76 ± 0.12) + (0.26 ± 0.26) · ([Fe/H]+1.6)=1.17+0.26 · [Fe/H]). Our results are in satisfactory agreement with the ?M V ?(RR)?[Fe/H]relation from Carney et al. (1992) (〈M V 〉(RR)=1.01+0.15·[Fe/H]) obtained by Baade-Wesselink's method. They provide evidence for a short distance scale: the LMC distance modulus and the distance to the Galactic center are 18.22±0.11 and 7.4±0.5 kpc, respectively. The zero point of the distance scale and the kinematic parameters of the RR Lyrae populations are shown to be virtually independent of the source of absolute proper motions used and of whether they are reduced to the Hipparcos system or not.  相似文献   

15.
R. P. Kane 《Solar physics》2014,289(7):2669-2675
When a Coronal Mass Ejection (CME) is ejected by the Sun, it reaches the Earth orbit in a modified state and is called an ICME (Interplanetary CME). When an ICME blob engulfs the Earth, short-scale cosmic-ray (CR) storms (Forbush decreases, FDs) occur, sometimes accompanied by geomagnetic Dst storms, if the B z component in the blob is negative. Generally, this is a sudden process that causes abrupt changes. However, sometimes before this abrupt change (FD) due to strong ICME blobs, there are slow, small changes in interplanetary parameters such as steady increases in solar wind speed V, which are small, but can last for several hours. In the present communication, CR changes in such an event are illustrated in the period 1?–?3 October 2013, when V increased steadily from ～?200 km?s?1 to ～?400 km?s?1 during 24 hours on 1 October 2013. The CR intensities decreased by 1?–?2 % during some hours of this 24-hour interval, indicating that CR intensities do respond to these weak but long-lasting increases in interplanetary solar wind speed.  相似文献   

16.
Soft X-ray data from the XRP experiment on SMM are used to generate the temperature and density in the flaring region of the 1980, June 29 (18∶21 UT) solar flare. The temporal data (T max ～- 20 × 106 K and n max ～- 4 × 1011 cm?3), together with an assumed velocity, are used to simulate mass injection as the input pulse for the MHD model of Wu et al. (1982a, 1983a). The spatial and temporal coronal response is compared with the ground-based, Mark III K-coronameter observations of the subsequent coronal transient. The simulation produces a spatially-wide, large amplitude, temporarily-steepened MHD wave for either of the two ‘canonical’ magnetic topologies (closed and open), but no shock wave. This result appears to be confirmed by the fact that a type II radio event was observed late in the event for only a few minutes, thereby indicating that a steepening wave with temporary, marginal shock formation, was indeed present. The density enhancements produced by the simulation move away from the Sun at the same velocity observed by the K-coronameter. However, the observation of the coronal transient included a rarefaction that does not appear in the simulation. A probable explanation for this discrepancy is the likelihood that the magnitude and temporal profile of the density of the soft X-ray emitting plasma should not have been used as part of the mass injection pulse. We believe that the temperature profile alone, as suggested by earlier simulations, might have been a necessary and sufficient condition to produce both the compression and rarefaction of the ambient corona as indicated by the K-coronameter data. Hence, the dense plasma observed by XRP was probably confined, for the most part, close to the Sun during the ～ 17 min duration of the observations.  相似文献   

17.
Thirteen high-dispersion spectrographs of the eclipsing binary star SZ Cam have been studied with a view of determining more accurate information on: (i) the spectral type and luminosity classifications, (ii) absolute parameters for the component stars, (iii) the stellar environment of SZ Cam. The main results in these categories are as follows: (i) O9.5 Vnk, (ii)m g=19±2M ⊙,m s=6.5±1M ⊙;r g=9.7±3.6R ⊙,r s=4.8±1.7R ⊙;T e～30000 K,T e～23000 K; (iii) there is a local concentration of absorbing material which may reach a density of 2M ⊙ pc?3, and the distance of the star is found to be 600±150 pc. The determined overluminosity of the secondary star and the local concentration of absorbing material are two topics which provide the basis for a discussion section.  相似文献   

18.
《Icarus》1986,65(1):122-128
The Amplitude-Magnitude (AM) method is used for the pole determination of the asteroid 511 Davida, using observations from six oppositions. The possible North poles are found to be λ1 = 92° ± 7°; β1 = 33° ± 6°, and λ2 = 303° ± 4°; β2 = 34° ± 5°, when scattering effect is not taken into account. When scattering is accounted for, solutions not significantly different from (λ1, β1) and (λ2, β2) are obtained. The moderately eccentric and inclined orbit of 511 Davida does not allow us to distinguish between the two pole solutions. A comparison with other methods is necessary in order to make a definitive choice.  相似文献   

19.
The records of the pulsations of Ez(air) and magnetic components during a pc 1 event are discussed.  相似文献   

20.
By means of new photoelectric observations made in 1974 an attempt to determine the poles of asteroids 9 and 44 was made. Following a method based upon the magnitude-aspect and amplitude-aspect relations, the coordinates of the poles for 9 and 44 were found to be, respectively, λ0 = 191° ± 5°, β0 = 56° ± 6° and λ0 = 100° ± 10°, β0 = 50° ± 10°. The previously published pole for asteroid 22, λ0 = 215° ± 10°, β0 = 45° ± 15°, was confirmed. From its phase relation we determined the phase coefficient of 44 Nysa, a very high albedo object (pv = 0.377). The very low phase coefficient obtained (βv = 0.018 mag/deg) agrees very well with an inverse relation between geometrical albedo and phase coefficient. The results are summarized in a table.  相似文献   

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