共查询到20条相似文献,搜索用时 62 毫秒
1.
Nelson L. Reginald Joseph M. Davila O. C. St. Cyr Douglas M. Rabin Madhulika Guhathakurta Donald M. Hassler Hadi Gashut 《Solar physics》2011,270(1):235-251
An experiment was conducted in conjunction with the total solar eclipse on 29 March 2006 in Libya to measure both the electron
temperature and its flow speed simultaneously at multiple locations in the low solar corona by measuring the visible K-coronal
spectrum. Coronal model spectra incorporating the effects of electron temperature and its flow speed were matched with the
measured K-coronal spectra to interpret the observations. Results show electron temperatures of (1.10±0.05) MK, (0.70±0.08) MK,
and (0.98±0.12) MK, at 1.1 R
⊙ from Sun center in the solar north, east and west, respectively, and (0.93±0.12) MK, at 1.2 R
⊙ from Sun center in the solar west. The corresponding outflow speeds obtained from the spectral fit are (103±92) km s−1, (0+10) km s−1, (0+10) km s−1, and (0+10) km s−1. Since the observations were taken only at 1.1 R
⊙ and 1.2 R
⊙ from Sun center, these speeds, consistent with zero outflow, are in agreement with expectations and provide additional confirmation
that the spectral fitting method is working. The electron temperature at 1.1 R
⊙ from Sun center is larger at the north (polar region) than the east and west (equatorial region). 相似文献
2.
C. O. Lee J. G. Luhmann J. T. Hoeksema X. Sun C. N. Arge I. de Pater 《Solar physics》2011,269(2):367-388
The solar cycle 23 minimum period has been characterized by a weaker solar and interplanetary magnetic field. This provides
an ideal time to study how the strength of the photospheric field affects the interplanetary magnetic flux and, in particular,
how much the observed interplanetary fields of different cycle minima can be understood simply from differences in the areas
of the coronal holes, as opposed to differences in the surface fields within them. In this study, we invoke smaller source
surface radii in the potential-field source-surface (PFSS) model to construct a consistent picture of the observed coronal
holes and the near-Earth interplanetary field strength as well as polarity measurements for the cycles 23 and 22 minimum periods.
Although the source surface value of 2.5 R
⊙ is typically used in PFSS applications, earlier studies have shown that using smaller source surface heights generates results
that better match observations during low solar activity periods. We use photospheric field synoptic maps from Mount Wilson
Observatory (MWO) and find that the values of ≈ 1.9 R
⊙ and ≈ 1.8 R
⊙ for the cycles 22 and 23 minimum periods, respectively, produce the best results. The larger coronal holes obtained for the
smaller source surface radius of cycle 23 somewhat offsets the interplanetary consequences of the lower magnetic field at
their photospheric footpoints. For comparison, we also use observations from the Michelson Doppler Imager (MDI) and find that
the source surface radius of ≈ 1.5 R
⊙ produces better results for cycle 23, rather than ≈ 1.8 R
⊙ as suggested from MWO observations. Despite this difference, our results obtained from MWO and MDI observations show a qualitative
consistency regarding the origins of the interplanetary field and suggest that users of PFSS models may want to consider using
these smaller values for their source surface heights as long as the solar activity is low. 相似文献
3.
We present multi-colour CCD observations of the low-temperature contact binaries, V453 Mon and V523 Cas. Their light curves
are modelled to determine a new set of stellar and orbital parameters. Analysis of mid-eclipse times yields a new linear ephemeris
for both systems. A period decrease (dP/dt=2.3×10−7 days/yr) in V453 Mon is discovered. V523 Cas, however, is detected to show a period increase (dP/dt=9.8×10−8 days/yr) because of the mass transfer of a rate of 1.1×10−7 M⊙ yr−1, from a less massive donor. Using these findings we can determine the physical parameters of the components of V523 Cas to
be M
1=0.76 (3)M
⊙, M
2=0.39 (2)M
⊙, R
1=0.74 (2)R
⊙, R
2=0.55 (2)R
⊙, L
1=0.19 (3)L
⊙, L
2=0.14 (3)L
⊙, and the distance of system as 46(9) pc. 相似文献
4.
We show that within distances from the Sun's surface less than the height of a streamer helmet, each of two neighboring rays of the streamer belt, as they approach the solar surface, bends around the helmet on either side of it. Also, a minimum angular diameter of the rays of d2°–3° remains virtually constant within R=1.2–6.0 R
. A density inhomogeneity (`blob') can be produced above the helmet top visible to at least R6 R
. In this case the initial velocity of the `blob' increases with solar distance from where it is generated to something like the velocity of the bulk solar wind with which the `blob' is carried away. 相似文献
5.
Experiments on the violation of equivalence principle (EP) and solar system give a number of constraints in which any modified
gravity model must satisfy them. We study these constraints on a kind of f(R) gravity as f(R) = R(1±eln([(R)/(Rc)]))f(R) = R(1\pm\epsilon\ln({R \over R_{c}})). For this investigation we use of chameleon mechanism and show that a spherically body has thin-shell in this model. So that
we obtain an effective coupling of the fifth force which is suppressed through a chameleon mechanism. Also, we obtain γ
PPN
=1±1.13×10−5 which is agreement with experiment results. At last, we show that for R
c
≈ρ
c
this model is consistent with EP, thin shell condition and fifth force of chameleon mechanism for ε⋍10−14. 相似文献
6.
A. I. Yatsenko 《Astrophysics and Space Science》1988,142(1-2):85-88
Summary In this paper the results of the research of the stars proper motions Trapezium components are reported. They are: the galactic
coordinates of the solar aprx and the Sun velocity (L
⊙=43±18°,B
⊙=+28±13°,V
⊙=13±4 km s−1), the dispersion of peculiar velocities in the direction of the galactic coordinates for the above mentioned stars (σ
l
=±11 km s−1, σ
b
=±7 km s−1).The attained accuracy of the proper motions (±0.005″ yr−1) is shown to be insufficient to the study of internal space motions in these systems. At present the work to increase the
relative proper motions accuracy for multiple system components and to improve reductions from the relative to absolute proper
motions, is being carried out in the Main Astronomical Observatory (Academy of Sciences of the Ukrainian SSR). The new catalogue
of the AGK3 stars is composed now in the vicinity of the galactic equator in order to improve reductions from the relative
to absolute proper motions. The r.m.s. errors of the proper motions, obtained in the AGK3 system, are ±0.005″ yr−1. 相似文献
7.
Kenneth H. Schatten 《Solar physics》1970,12(3):484-491
The Faraday rotation of a radio source (Pioneer 6) occulted by the solar corona has been measured by Levy et al. (1969).
During the course of these measurements, three large-scale transient phenomena were observed. These events were preceded by
subflares and class 1 flares. These transient events are interpreted as evidence for a coronal magnetic bottle at 10 R
⊙. The velocity of propagation for the disturbance is set at 200 km/sec; the dimension of the region, 10 R
⊙; field strength at 10 R
⊙, 0.02 G; particle density, 2.0 × 104/cm3; Alfvén speed, 320 km/sec. From the nature of the observations and the lack of related effects from similar flares on the
interplanetary sector pattern observed at 1 AU, it is suggested that such coronal magnetic bottles expand to perhaps 10–30
R
⊙ and then contract to a few solar radii. Such a phenomena is evidence for an expansion of the corona with a sub-Alfvénic velocity.
It is further suggested that such magnetic bottles may be important in the storage and diffusion of solar generated cosmic
ray particles.
NAS-NRC Postdoctoral Resident Research Associate. 相似文献
8.
We compare the shape and position of some plasma formations visible in the polar corona with the cyclic evolution of the global
magnetic field. The first type of object is polar crown prominences. A two-fold decrease of the height of polar crown prominences
was found during their poleward migration from the middle latitudes to the poles before a polar magnetic field reversal. The
effect could be assigned to a decrease of the magnetic field scale. The second type of object is the polar plumes, ray like
structures that follow magnetic field lines. Tangents to polar ray structures are usually crossed near some point, “a magnetic
focus,” below the surface. The distance q between the focus and the center of the solar disk changes from the maximum value about 0.65 R
⊙ at solar minimum activity to the minimum value about 0.45 R
⊙ at solar maximum. At first glance this behaviour seems to be contrary to the dynamics of spherical harmonics of the global
magnetic field throughout a cycle. We believe that the problem could be resolved if one takes into account not only scale
changes in the global magnetic field but also the phase difference in the cyclic variations of large-scale and small-scale
components of the global field. 相似文献
9.
Digitized synoptic charts of photospheric magnetic fields were analyzed for the past 4 incomplete solar activity cycles (1969–2000).
The zonal structure and cyclic evolution of large-scale solar magnetic fields were investigated using the calculated values
of the radial B
r, |B
r|, meridional B
θ, |B
θ|, and azimuthal B
φ, |B
φ| components of the solar magnetic field averaged over a Carrington rotation (CR). The time–latitude diagrams of all 6 parameters
and their correlation analysis clearly reveal a zonal structure and two types of the meridional poleward drift of magnetic
fields with the characteristic times of travel from the equator to the poles equal to ∼16–18 and ∼2–3 years. A conclusion
is made that we observe two different processes of reorganization of magnetic fields in the Sun that are related to generation
of magnetic fields and their subsequent redistribution in the process of emergence from the field generation region to the
solar surface. Redistribution is supposed to be caused by some external forces (presumably, by sub-surface plasma flows in
the convection zone). 相似文献
10.
P. K. Manoharan 《Solar physics》2006,235(1-2):345-368
Knowledge of the radial evolution of the coronal mass ejection (CME) is important for the understanding of its arrival at
the near-Earth space and of its interaction with the disturbed/ambient solar wind in the course of its travel to 1 AU and
further. In this paper, the radial evolution of 30 large CMEs (angular width > 150∘, i.e., halo and partial halo CMEs) has been investigated between the Sun and the Earth using (i) the white-light images of
the near-Sun region from the Large Angle Spectroscopic Coronagraph (LASCO) onboard SOHO mission and (ii) the interplanetary scintillation (IPS) images of the inner heliosphere obtained from the Ooty Radio Telescope (ORT). In the LASCO field of view at heliocentric
distances R≤30 solar radii (R⊙), these CMEs cover an order of magnitude range of initial speeds, VCME≈260–2600 km s−1. Following results have been obtained from the speed evolution of these CMEs in the Sun–Earth distance range: (1) the speed
profile of the CME shows dependence on its initial speed; (2) the propagation of the CME goes through continuous changes,
which depend on the interaction of the CME with the surrounding solar wind encountered on the way; (3) the radial-speed profiles
obtained by combining the LASCO and IPS images yield the factual view of the propagation of CMEs in the inner heliosphere
and transit times and speeds at 1 AU computed from these profiles are in good agreement with the actual measurements; (4)
the mean travel time curve for different initial speeds and the shape of the radial-speed profiles suggest that up to a distance
of ∼80 R⊙, the internal energy of the CME (or the expansion of the CME) dominates and however, at larger distances, the CME's interaction
with the solar wind controls the propagation; (5) most of the CMEs tend to attain the speed of the ambient flow at 1 AU or
further out of the Earth's orbit. The results of this study are useful to quantify the drag force imposed on a CME by the
interaction with the ambient solar wind and it is essential in modeling the CME propagation. This study also has a great importance
in understanding the prediction of CME-associated space weather at the near-Earth environment. 相似文献
11.
Four series of coronal images have been obtained by the expedition of Abastumani Astrophysical Observatory during the August
11, 1999 total solar eclipse with the help of a photographic mirror–lens polarimeter (D = 100 mm, F = 1000 mm). Each series include three images corresponding to three positions of the polarization analyzer. The position
of the solar disk center relative to the Moon's center has been determined beforehand. In addition, the background skylight
polarization and intensity are calculated. All measurements are absolute given in units of the Sun's average surface brightness.
A new technique for separation of the F- and K-coronae is used. It was found that in the equatorial regions the model of hydrostatic distribution of the density with T = constant is not quite accurate for the August 11, 1999 corona and there is a temperature gradient in this region. For r1 = 1.3R⊙ and r2 = 1.8R⊙ we derived T1 = 1.25×106 K and T2 = 1.07×106 K, respectively. The average polarization degree in the equatorial regions changes from 10 to 40%, while in the polar regions
the maximum value reaches only 10%. The values of electron densities Ne(r) vary from 1.32×108 cm−3 (r = 1.1R⊙) to 2.0×106 cm−3 (r = 2.0R⊙). Our data are compared with previous measurements. 相似文献
12.
A comprehensive case and statistical study of CME onsets has been conducted on the solar limb using the CDS, LASCO and EIT
instruments aboard the SOHO spacecraft. This is the first dedicated campaign to establish firmly the EUV signatures of CME
onsets and is based on a series of low-corona observing campaigns made in 2002. The event database consisted of 36 multiple
emission line sequences observed with CDS and the study builds, in particular, on studies of EUV coronal dimming which have
been associated with CME onsets. We witness a range of dimming events in EUV coronal emission line data. Shorter events, commonly
of duration < 4 hours, we find are indirectly associated with CME onsets whereas longer-duration dimmings (> 4 hours) appear
to be either due to coronal evolution or rotational effects. However, for some CME onsets, where the CDS pointing was appropriate,
no dimming was observed. Dimming observed in EIT typically occurred immediately after the launch of a loop or prominence,
and in 5 out of 9 events there is evidence of a matter buildup within the loop before launch. A total of 10 events occurred
where CDS was used to directly observe the CME footprint, but no relationship between these events was found. The results
suggest that the response of the corona to a CME launch differs between the low (1.0 R
⊙≤R≤1.2 R
⊙) and middle (1.2 R
⊙<R≤2.0 R
⊙) corona regions, hence implying a difference between dimming observations conducted with different instruments. 相似文献
13.
K. R. Anantharamaiah Pradeep Gothoskar T. J. Cornwell 《Journal of Astrophysics and Astronomy》1994,15(4):387-414
We present Very Large Array observations at wavelengths of 2, 3.5, 6, and 20 cm, of angular broadening of radio sources due
to the solar wind in the region 2–16 solar radii. Angular broadening is anisotropic with axial ratios in the range 2–16. Larger
axial ratios are observed preferentially at smaller solar distances. Assuming that anisotropy is due to scattering blobs elongated
along magnetic field lines, the distribution of position angles of the elliptically broadened images indicates that the field
lines are non-radial even at the largest heliocentric distances observed here. At 5R⊙, the major axis scattering angle is
∼ 0.7" atλ= 6 cm and it varies with heliocentric distance asR
-1.6. The level of turbulence, characterized by the wave structure function at a scale of 10 km along the major axis, normalized
toλ = 20 cm, has a value 20 ± 7 at 5R⊙and varies with heliocentric distance asR
-3. Comparison with earlier resu lts suggest that the level of turbulence is higher during solar maximum. Assuming a power-law
spectrum of electron density fluctuations, the fitted spectral exponents have values in the range 2.8–3.4 for scale sizes
between 2–35 km. The data suggests temporal fluctuations (of up to 10%) in the spectral exponent on a time scale of a few
tens of minutes. The observed structure functions at different solar distances do not show any evidence for an inner scale;
the upper limits are l k m at 2R⊙ and 4 km at 13R⊙. These upper limits are in conflict with earlier determinations and may suggest a reduced inner scale during solar maximum. 相似文献
14.
F. Sánchez-Bajo E. García-Melendo J. M. Gómez-Forrellad 《Astrophysics and Space Science》2007,312(3-4):151-159
New ephemeris and the absolute parameters—masses, radii and luminosities—of the contact systems VW LMi and BX Dra have been
obtained, by means of the analysis of the minima data available in the literature (for the determination of the ephemeris)
and combining the previously published spectroscopic information and the results of the Wilson-Devinney method using photometric
data (for the determination of the absolute parameters). The VW LMi O−C analysis confirms the multiplicity of the system detected previously from the spectroscopic data. Masses of the VW LMi contact
system primary and secondary components are 1.67 ± 0.02M
⊙ and 0.70 ± 0.02M
⊙, respectively. The corresponding radii are 1.709 ± 0.007R
⊙ and 1.208 ± 0.006R
⊙, respectively. For the BX Dra contact system the masses are 2.19 ± 0.13M
⊙ and 0.63 ± 0.06M
⊙, and the radii, 2.13 ± 0.04R
⊙ and 1.26 ± 0.03R
⊙, for the primary and secondary, respectively. In both cases, the estimated luminosities seem to be slightly greater that
the values derived from the Hipparcos distances. 相似文献
15.
We report quantitative analysis of the radial gradient of solar angular velocity at depths down to about 15 Mm below the solar surface for latitudes up to 75° using the Michelson Doppler Imager (MDI) observations of surface gravity waves (fmodes) from the Solar and Heliospheric Observatory (SOHO). A negative outward gradient of around –400 nHz/R
, equivalent to a logarithmic gradient of the rotation frequency with respect to radius which is very close to –1, is found to be remarkably constant between the equator and 30° latitude. Above 30° it decreases in absolute magnitude to a very small value at around 50°. At higher latitudes the gradient may reverse its sign: if so, this reversal takes place in a thin layer extending only 5 Mm beneath the visible surface, as evidenced by the most superficial modes (with degrees l>250). The signature of the torsional oscillations is seen in this layer, but no other significant temporal variations of the gradient and value of the rotation rate there are found. 相似文献
16.
Charles H. Nelson Douglas S. Hall Francis C. Fekel Robert E. Fried Richard E. Lines Helen C. Lines 《Astrophysics and Space Science》1991,182(1):1-17
Photometry of HD 155638=V792 Her has been analyzed to determine the elements of this totally eclipsing RS CVn binary. The light variation outside eclipse was found to have a period of 27d.07±0d.07, which is slightly different from the 27d.5384±0d.0045 orbital period. Analysis of the eclipses was achieved by a modification of the Russell-Merrill technique. With the aid of radial velocity measures, absolute elements were obtained for the hot and cool stars, respectively;R
h=2.58R
,R
c=12.28R
,M
h=1.40M
,M
c=1.46M
,i=80o.61 and velocity semi-amplitudesK
c=48.36 km s–1±0.79 km s–1, andK
h=50.50 km s–1±0.33 km s–1. The apparent magnitudes areV
h=9
m
.73 andV
c=8
m
.48. The distance to HD 155638 was estimated to be 310 parsecs. 相似文献
17.
S. Chandrasekhar 《Journal of Astrophysics and Astronomy》1994,15(2):105-109
The density of the white dwarf stars is reconsidered from the point of view of the theory of the poly tropic gas spheres,
and gives for themean density of a white dwarf (under ideal conditions) the formula ρ=2.162 × 106 × (M/⊙)2.
The above formula is derived on considerations which are a much nearer approximation to the conditionsactually existent in a white dwarf than the previous calculations of Stoner based on uniform density distribution in the star and which gave
for the limiting density the formula ρ=3.977 × 106 × (M/⊙)2. 相似文献
18.
The Naval Research Laboratory (NRL) Solwind coronagraph recorded the outer corona at elongations 2_5 R to 10 R during the 6 1/2-year interval from March 1979, before solar maximum, to the beginning of solar minimum in September 1985. During the minimum period, when the solar magnetic field was dipole-like, the observed corona consisted of the equatorial streamer belt that is characteristic of solar minimum, and that is interpreted as an edgewise view of a nearly flat current sheet or coronal disk lying near the plane of the heliographic equator. The observed disk was a radial projection from the magnetic neutral line that was computed for the 2.5 R source surface surrounding the Sun. At earlier times, shortly after solar maximum, the observed corona often consisted of a single coronal disk similar to that at solar minimum, but strongly tilted to the heliographic equator. Again this disk projected from a tilted magnetic neutral line that was computed for the 2.5 R source surface. Solar rotation allowed this coronal disk to be viewed in all aspects. In the edgewise view it appeared as a tilted streamer belt. In the broadside view the more flower-like pattern of solar maximum was observed. The latter view was interpreted as a non-uniform distribution of coronal material in the thin coronal disk. There were many intervals during the declining phase of the solar cycle when the computed magnetic neutral line at 2.5 R remained relatively simple but was not the source of an observable coronal disk. This latter result was probably because of the limitations of plane-of-sky observations, combined with short-term changes in the corona. Altogether, a single coronal disk, either flat or somewhat convoluted, was recognizable during only one third of the year lifetime of the coronagraph. 相似文献
19.
L. V. Glazunova 《Astronomy Letters》2011,37(6):414-419
Based on two high-dispersion spectra of the close binary BW Boo, we have detected lines of the secondary component whose contribution
to the combined spectrum does not exceed 2%. We have determined the rotation velocities of the components and spectroscopic
orbital elements. Numerous lines of neutral and ionized iron have been used to determine the effective temperature and surface
gravity for the primary component. The photometric light curves for this binary have been solved for the first time. Its primary
component is an A2Vm star with a mass of 2 ± 0.1M
⊙ and a radius of 1.9 ± 0.4R
⊙. Its rotation velocity is 2 km s−1, which is a factor of 18 lower than the pseudo-synchronous velocity for this component. The G6 secondary component, a T Tau
star, has a rotation velocity of 17 km s−1, amass of 1.1M
⊙, and a radius of 1 R
⊙. The age of the binary has been estimated to be 107 yr. 相似文献
20.
Michael Schulz 《Astrophysics and Space Science》1973,24(2):371-383
The magnetohydrodynamics of solar-wind flow lead logically to the formation of one warped annular neutral surface that apparently
extends from ≈ 2r
⊙ (solar radii) to the boundary of the heliosphere. The most likely asymptotic configuration for this neutral sheet intersects
the heliomagnetic equatorial plane along four corotating arcs. The observer sees a reversal of magnetic polarity on each crossing
of the neutral surface, and so interprets each reversal as the crossing of a sector boundary. 相似文献