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1.
Kocharov  L.  Torsti  J. 《Solar physics》2002,207(1):149-157
We summarize ERNE/SOHO observations of solar energetic particle events associated with impulsive soft X-ray flares and LASCO coronal mass ejections (CMEs). The new observational data support an idea that the >10 MeV proton acceleration may be initiated at different coronal sources, operating in the flaring active region and on the global coronal scale, in concert with CME development. However, the particle acceleration continues beyond the coronal scales and may culminate at the interplanetary CME well after the flare. We emphasize the importance of CME liftoff/aftermath processes in the solar corona and the possible role of seed particle re-acceleration, which may explain the existence of hybrid solar energetic particle events.  相似文献   

2.
We present a catalogue of galaxies in Abell 3653 from observations made with the 2-degree field (2dF) spectrograph at the Anglo-Australian Telescope. Of the 391 objects observed, we find 111 are bona fide members of Abell 3653. We show that the cluster has a velocity of   cz = 32 214 ± 83  km s−1 ( z = 0.10 738 ± 0.00 027)  , with a velocity dispersion typical of rich, massive clusters of  σ cz = 880+66−54  . We find that the cD galaxy has a peculiar velocity of  683 ± 96  km s−1  in the cluster rest frame – some 7σ away from the mean cluster velocity, making it one of the largest and most significant peculiar velocities found for a cD galaxy to date. We investigate the cluster for signs of substructure, but do not find any significant groupings on any length scale. We consider the implications of our findings on cD formation theories.  相似文献   

3.
We estimate the acceleration on the Local Group (LG) from the 2 Micron All-Sky Redshift Survey (2MRS). The sample used includes about 23 200 galaxies with extinction-corrected magnitudes brighter than   K s= 11.25  and it allows us to calculate the flux-weighted dipole. The near-infrared flux-weighted dipoles are very robust because they closely approximate a mass-weighted dipole, bypassing the effects of redshift distortions and require no preferred reference frame. This is combined with the redshift information to determine the change in dipole with distance. The misalignment angle between the LG and the cosmic microwave background (CMB) dipole drops to  12°± 7°  at around  50  h −1 Mpc  , but then increases at larger distances, reaching  21°± 8°  at around  130  h −1 Mpc  . Exclusion of the galaxies Maffei 1, Maffei 2, Dwingeloo 1, IC342 and M87 brings the resultant flux dipole to  14°± 7°  away from the CMB velocity dipole. In both cases, the dipole seemingly converges by  60  h −1 Mpc  . Assuming convergence, the comparison of the 2MRS flux dipole and the CMB dipole provides a value for the combination of the mass density and luminosity bias parameters  Ω0.6m/ b L= 0.40 ± 0.09  .  相似文献   

4.
In this paper we report on optical spectroscopic observations of the low-mass X-ray binary 2S 0921–630 obtained with the Very Large Telescope. We found sinusoidal radial velocity variations of the companion star with a semi-amplitude of  99.1 ± 3.1 km s−1  modulated on a period of 9.006 ± 0.007 d, consistent with the orbital period found previously for this source, and a systemic velocity of  44.4 ± 2.4 km s−1  . Owing to X-ray irradiation, the centre of light measured by the absorption lines from the companion star is probably shifted with respect to the centre of mass. We try to correct for this using the so-called K -correction. Conservatively applying the maximum correction possible and using the previously measured rotational velocity of the companion star, we find a lower limit to the mass of the compact object in 2S 0921–630 of   MX sin3 i > 1.90 ± 0.25 M⊙  (1σ errors). The inclination in this system is well constrained since partial eclipses have been observed in X-ray and optical bands. For inclinations in the range  60° < i < 90°  we find  1.90 ± 0.25 < MX < 2.9 ± 0.4 M⊙  . However, using this maximum K -correction we find that the ratio between the mass of the companion star and that of the compact object, q , is 1.32 ± 0.37, implying super-Eddington mass-transfer rates; however, evidence for that has not been found in 2S 0921–630. We conclude that the compact object in 2S 0921–630 is either a (massive) neutron star or a low-mass black hole.  相似文献   

5.
Solar coronal heating by magnetohydrodynamic (MHD) waves is investigated. ultraviolet (UV) and X-ray emission lines of the corona show non-thermal broadenings. The wave rms velocities inferred from these observations are of the order of 25–60 km s−1 . Assuming that these values are not negligible, we solved MHD equations in a quasi-linear approximation, by retaining the lowest order non-linear term in rms velocity. Plasma density distribution in the solar corona is assumed to be inhomogeneous. This plasma is also assumed to be permeated by dipole-like magnetic loops. Wave propagation is considered along the magnetic field lines. As dissipative processes, only the viscosity and parallel (to the local magnetic field lines) heat conduction are assumed to be important. Two wave modes emerged from the solution of the dispersion relation. The fast mode magneto-acoustic wave, if originated from the coronal base can propagate upwards into the corona and dissipate its mechanical energy as heat. The damping length-scale of the fast mode is of the order of 500 km. The wave energy flux associated with these waves turned out to be of the order of 2.5×105 ergs cm−2 s−1 which is high enough to replace the energy lost by thermal conduction to the transition region and by optically thin coronal emission. The fast magneto-acoustic waves prove to be a likely candidate to heat the solar corona. The slow mode is absent, in other words cannot propagate in the solar corona.  相似文献   

6.
We investigate the mean velocity dispersion and the velocity dispersion profile of stellar systems in modified Newtonian dynamics (MOND), using the N -body code n-mody , which is a particle-mesh-based code with a numerical MOND potential solver developed by Ciotti, Londrillo & Nipoti. We have calculated mean velocity dispersions for stellar systems following Plummer density distributions with masses in the range of 104 to  109 M⊙  and which are either isolated or immersed in an external field. Our integrations reproduce previous analytic estimates for stellar velocities in systems in the deep MOND regime  ( a i, a e≪ a 0)  , where the motion of stars is either dominated by internal accelerations  ( a i≫ a e)  or constant external accelerations  ( a e≫ a i)  . In addition, we derive for the first time analytic formulae for the line-of-sight velocity dispersion in the intermediate regime  ( a i∼ a e∼ a 0)  . This allows for a much-improved comparison of MOND with observed velocity dispersions of stellar systems. We finally derive the velocity dispersion of the globular cluster Pal 14 as one of the outer Milky Way halo globular clusters that have recently been proposed as a differentiator between Newtonian and MONDian dynamics.  相似文献   

7.
We present radial velocities for 2045 stars in the Small Magellanic Cloud (SMC), obtained from the 2dF survey by Evans et al. The great majority of these stars are of OBA type, tracing the dynamics of the young stellar population. Dividing the sample into ad hoc 'bar' and 'wing' samples (north and south, respectively, of the line:  δ=−77°50'+[4α]'  , where α is the right ascension in minutes of time) we find that the velocities in the SMC bar show a gradient of 26.3 ± 1.6 km s−1 deg−1 at a position angle of 126°± 4°. The derived gradient in the bar is robust to the adopted line of demarcation between the two samples. The largest redshifts are found in the SMC wing, in which the velocity distribution appears distinct from that in the bar, most probably a consequence of the interaction between the Magellanic Clouds that is predicted to have occurred 0.2 Gyr ago. The mean velocity for all stars in the sample is +172.0 ± 0.2 km s−1 (redshifted by ∼20 km s−1 when compared to published results for older populations), with a velocity dispersion of 30 km s−1.  相似文献   

8.
The stability of Trojan type orbits around Neptune is studied. As the first part of our investigation, we present in this paper a global view of the stability of Trojans on inclined orbits. Using the frequency analysis method based on the fast Fourier transform technique, we construct high-resolution dynamical maps on the plane of initial semimajor axis a 0 versus inclination i 0. These maps show three most stable regions, with i 0 in the range of  (0°, 12°), (22°, 36°)  and  (51°, 59°),  respectively, where the Trojans are most probably expected to be found. The similarity between the maps for the leading and trailing triangular Lagrange points L 4 and L 5 confirms the dynamical symmetry between these two points. By computing the power spectrum and the proper frequencies of the Trojan motion, we figure out the mechanisms that trigger chaos in the motion. The Kozai resonance found at high inclination varies the eccentricity and inclination of orbits, while the  ν8  secular resonance around   i 0∼ 44°  pumps up the eccentricity. Both mechanisms lead to eccentric orbits and encounters with Uranus that introduce strong perturbation and drive the objects away from the Trojan like orbits. This explains the clearance of Trojan at high inclination  (>60°)  and an unstable gap around  44°  on the dynamical map. An empirical theory is derived from the numerical results, with which the main secular resonances are located on the initial plane of  ( a 0, i 0)  . The fine structures in the dynamical maps can be explained by these secular resonances.  相似文献   

9.
We determine the most likely values of the free parameters of an N -body model for the Galaxy developed by Fux via a discrete–discrete comparison with the positions on the sky and line-of-sight velocities of an unbiased, homogeneous sample of OH/IR stars. Via Monte Carlo simulation, we find the plausibility of the best-fitting models, as well as the errors on the determined values. The parameters that are constrained best by these projected data are the total mass of the model and the viewing angle of the central bar, although the distribution of the latter has multiple maxima. The other two free parameters, the size of the bar and the (azimuthal) velocity of the Sun, are less well-constrained. The best model has a viewing angle of ∼ 44°, a semimajor axis of 2.5 kpc (corotation radius 4.5 kpc, pattern speed 46 km s−1 kpc−1), a bar mass of 1.7×1010 M⊙ and a tangential velocity of the local standard of rest of 171 km s−1. We argue that the lower values that are commonly found from stellar data for the viewing angle (∼25°) arise when too few coordinates are available, when the longitude range is too narrow or when low latitudes are excluded from the fit. The new constraints on the viewing angle of the Galactic bar from stellar line-of-sight velocities decrease further the ability of the distribution of the bar to account for the observed microlensing optical depth toward Baade's window: our model reproduces only half the observed value. The signal of triaxiality diminishes quickly with increasing latitude, fading within approximately 1 scaleheight (≲3°). This suggests that Baade's window is not a very appropriate region in which to sample bar properties.  相似文献   

10.
We consider the problem of the relative motion both of the substructures of the Local Group of galaxies (revealed via the S-tree method), and of the velocity of the Local Group itself. The existence of statistically significant bulk flow of the Milky Way subsystem is shown via a 3D reconstruction procedure, which uses information on the radial velocities of the galaxies but does not take account of their distances. Once the bulk motion of the substructures is estimated we also consider, in combination with the observed cosmic microwave background (CMB) dipole, the mean velocity of the Local Group itself. Assigning to the Local Group the mean motion of its main substructures, we evaluate its peculiar velocity in Milky Way frame V LG→MW = (−7 ± 303, −15 ± 155, +177 ± 144) or 178 km s−1 toward galactic coordinates l  = 245 and b  = +85. Combined with the CMB dipole V MW→CMB, we obtain a Local Group velocity in CMB frame: V LG→CMB = (−41 ± 303, −497 ± 155, 445 ± 144) or 668 km s−1 towards l  = 265 and b  = 42. This estimation is in good agreement, within the 1 σ level, with the estimation of Yahil et al.  相似文献   

11.
We present the study of 20 solar flares observed by “Solar X-ray Spectrometer (SOXS)” mission during November 2003 to December 2006 and found associated with coronal mass ejections (CMEs) seen by LASCO/SOHO mission. In this investigation, X-ray emission characteristics of solar flares and their relationship with the dynamics of CMEs have been presented. We found that the fast moving CMEs, i.e., positive acceleration are better associated with short rise time (< 150 s) flares. However, the velocity of CMEs increases as a function of duration of the flares in both 4.1–10 and 10–20 keV bands. This indicates that the possibility of association of CMEs with larger speeds exists with long duration flare events. We observed that CMEs decelerate with increasing rise time, decay time and duration of the associated X-ray flares. A total 10 out of 20 CMEs under current investigation showed positive acceleration, and 5 of them whose speed did not exceed 589 km/s were associated with short rise time (< 150 s) and short duration (< 1300 s) flares. The other 5 CMEs were associated with long duration or large rise time flare events. The unusual feature of all these positive accelerating CMEs was their low linear speed ranging between 176 and 775 km/s. We do not find any significant correlation between X-ray peak intensity of the flares with linear speed as well as acceleration of the associated CMEs. Based on the onset time of flares and associated CMEs within the observing cadence of CMEs by LASCO, we found that in 16 cases CME preceded the flare by 23 to 1786 s, while in 4 cases flare occurred before the CME by 47 to 685 s. We argue that both events are closely associated with each other and are integral parts of one energy release system.  相似文献   

12.
The high-mass X-ray binary RX J0146.9+6121, with optical counterpart LS I+61°235 (V831 Cas), is an intriguing system on the outskirts of the open cluster NGC 663. It contains the slowest Be type X-ray pulsar known with a pulse period of around 1400 s and, primarily from the study of variation in the emission line profile of Hα, it is known to have a Be decretion disc with a one-armed density wave period of approximately 1240 d. Here we present the results of an extensive photometric campaign, supplemented with optical spectroscopy, aimed at measuring short time-scale periodicities. We find three significant periodicities in the photometric data at, in order of statistical significance, 0.34, 0.67 and 0.10 d. We give arguments to support the interpretation that the 0.34 and 0.10 d periods could be due to stellar oscillations of the B-type primary star and that the 0.67 d period is the spin period of the Be star with a spin axis inclination of  23+10−8  degrees. We measured a systemic velocity of  −37.0 ± 4.3 km s−1  confirming that LS I+61°235 has a high probability of membership in the young cluster NGC 663 from which the system's age can be estimated as 20–25 Myr. From archival RXTE All Sky Monitor (ASM) data we further find 'super' X-ray outbursts roughly every 450 d. If these super outbursts are caused by the alignment of the compact star with the one-armed decretion disc enhancement, then the orbital period is approximately 330 d.  相似文献   

13.
The series of nine impulsive, highly collimated beams of near-relativistic electrons seen by ACE/EPAM on 26 and 27 June 2004 occurred at a quiet time with respect to solar flare and CME production. However, they were accompanied by decametric type III radio bursts observed by WIND/WAVES, which had progressively higher starting frequencies, suggestive of coronal acceleration. There were no CMEs seen by SOHO/LASCO in association with any of the type III bursts except possibly the first. The energy spectrum of the electrons was soft, typically E−4.5 but extended up to at least ∼200 keV. We suggest that the source region for these events is in the high corona. We discuss this result in the context of solar electron acceleration at other times.  相似文献   

14.
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15.
We construct a new sample of ∼1700 solar neighbourhood halo subdwarfs from the Sloan Digital Sky Survey (SDSS), selected using a reduced proper-motion diagram. Radial velocities come from the SDSS spectra and proper motions from the light-motion curve catalogue of Bramich et al. Using a photometric parallax relation to estimate distances gives us the full phase-space coordinates. Typical velocity errors are in the range  30–50 km s−1  . This halo sample is one of the largest constructed to date and the disc contamination is at a level of ≲1 per cent. This enables us to calculate the halo velocity dispersion to excellent accuracy. We find that the velocity dispersion tensor is aligned in spherical polar coordinates and that  (σ r , σφ, σθ) = (143 ± 2, 82 ± 2, 77 ± 2) km s−1  . The stellar halo exhibits no net rotation, although the distribution of   v φ  shows tentative evidence for asymmetry. The kinematics are consistent with a mildly flattened stellar density falling with distance like   r −3.75  .
Using the full phase-space coordinates, we look for signs of kinematic substructure in the stellar halo. We find evidence for four discrete overdensities localized in angular momentum and suggest that they may be possible accretion remnants. The most prominent is the solar neighbourhood stream previously identified by Helmi et al., but the remaining three are new. One of these overdensities is potentially associated with a group of four globular clusters (NGC 5466, NGC 6934, M2 and M13) and raises the possibility that these could have been accreted as part of a much larger progenitor.  相似文献   

16.
We use proper motions and parallaxes from the new reduction of Hipparcos data and Geneva–Copenhagen radial velocities for a complete sample of  ∼15 000  main-sequence and subgiant stars, and new Padova isochrones to constrain the kinematics and star formation history of the solar neighbourhood. We rederive the solar motion and the structure of the local velocity ellipsoids. When the principal velocity dispersions are assumed to increase with time as   t β  , the index β is larger for  σ W (β W ≈ 0.45  ) than for  σ U (β U ≈ 0.31)  . For the three-dimensional velocity dispersion, we obtain  β= 0.35  . We exclude saturation of disc heating after  ∼3 Gyr  as proposed by Quillen & Garnett. Saturation after  ≳4 Gyr  combined with an abrupt increase in velocity dispersion for the oldest stars cannot be excluded. For all our models, the star formation rate (SFR) is declining, being a factor of 2–7 lower now than it was at the beginning. Models in which the SFR declines exponentially favour very high disc ages between 11.5 and 13 Gyr and exclude ages below  ∼10.5 Gyr  as they yield worse fits to the number density and velocity dispersion of red stars. Models in which the SFR is the sum of two declining exponentials representing the thin and thick discs favour ages between 10.5 and 12 Gyr with a lower limit of  ∼10.0 Gyr  . Although in our models the SFR peaked surprisingly early, the mean formation time of solar-neighbourhood stars is later than in ab initio models of galaxy formation, probably on account of weaknesses in such models.  相似文献   

17.
We have studied the kinematics and spatial distribution of the interstellar gas in the sky region  110°≤ l ≤ 135°, 10°≤ b ≤ 20°  , using the extensive Leiden–Dwingeloo Survey of H  i emission and the Columbia Survey of CO emission. The spectra show two main velocity components, namely feature A that has a mean local standard of rest (LSR) velocity of  ∼0  km s−1  and is due to the Lindblad ring of the Gould belt, and feature C that has a mean LSR velocity of  ∼−11  km s−1  and is associated to the local arm or Orion arm. The H  i and CO distributions of feature A in the region trace a large complex of gas and dust known as the Cepheus Flare, which lies at a distance of 300 pc. The spectral line profiles of feature A, which are rather broad and often double-peaked, reveal that the Cepheus Flare forms part of a big expanding shell of interstellar matter that encloses an old supernova remnant associated with a void inside the Cepheus Flare. On the other hand, by analysing the distribution and velocity structure of feature C, we have detected a second large expanding shell in the region, located at a distance of 800 pc in the local arm. This shell surrounds the stellar association Cepheus OB4 and was probably generated by stellar winds and supernovae of Cepheus OB4. The radii, expansion velocities and H  i masses of the two shells are approximately 50 pc, 4  km s−1 and  1.3 × 104 M⊙  for the Cepheus Flare shell and 100 pc, 4 km s−1 and  9.9 × 104 M⊙  for the Cepheus OB4 shell. Both shells have similar ages of the order of a few 106 yr.  相似文献   

18.
To study the kinematics of O-B5 giant stars (luminosity class III), 290 non-Gould belt stars with proper motions taken from the Hipparcos catalogue are used, of which 107 have radial velocities taken from other sources. Semidefinite programming solves for the kinematical parameters and the coefficients of the velocity ellipsoid. The condition that both solutions must yield the same solar velocity is enforced. The results obtained are reasonable: solar velocity of 13.83 ± 0.17 km s−1; Oort's constants, in units of km s−1 kpc−1, A = 16.08 ± 0.72 and   B =−10.74 ± 0.65,  implying a rotational velocity of 228.0 ± 21.4 km s−1 if we take the distance to the Galactic Centre as 8.5 ± 1.1 kpc; velocity dispersions, in units of km s−1, of  σ x = 32.44 ± 5.04, σ y = 26.16 ± 2.75, σ z = 18.71 ± 2.39  with a vertex deviation of      相似文献   

19.
High-resolution spectroscopic observations around the Hα line of the binary star QX Cas covering the whole orbital period are presented. Our radial velocity solution, the first ever determined, requires an eccentric orbit with the following orbital parameters: eccentricity,   e = 0.22 ± 0.01  ; longitude of periastron,  ω= 45°± 5°  ; semi-amplitudes of the radial velocity curves of the primary and secondary stars,   K 1 sin  i = 125.8 ± 0.9 km s−1  and   K 2 sin  i = 144.8 ± 1.1 km s−1  ; gamma velocity,   V 0= 65.1 ± 0.5 km s−1  ; and mass ratio,   q = 0.869 ± 0.013  . The corresponding lower limits of the masses of the components and their separation are         , and   a sin  i = 31.34 ± 0.48 R⊙  .  相似文献   

20.
Using new and archival radio data, we have measured the proper motion of the black hole X-ray binary V404 Cyg to be  9.2 ± 0.3 mas yr−1  . Combined with the systemic radial velocity from the literature, we derive the full three-dimensional heliocentric space velocity of the system, which we use to calculate a peculiar velocity in the range 47–102 km s−1, with a best-fitting value of 64 km s−1. We consider possible explanations for the observed peculiar velocity and find that the black hole cannot have formed via direct collapse. A natal supernova is required, in which either significant mass  (∼11 M⊙)  was lost, giving rise to a symmetric Blaauw kick of up to ∼65 km s−1, or, more probably, asymmetries in the supernova led to an additional kick out of the orbital plane of the binary system. In the case of a purely symmetric kick, the black hole must have been formed with a mass  ∼9 M⊙  , since when it has accreted  0.5–1.5 M⊙  from its companion.  相似文献   

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