共查询到20条相似文献,搜索用时 15 毫秒
1.
N. D. Melikian V. S. Tamazian J. A. Docobo A. A. Karapetian R. Sh. Natsvlishvili 《Astrophysics》2006,49(4):488-496
Spectral observations of the flare star EV Lac made on the 2.6-m telescope at the Byurakan Observatory in 2000–2002 are reported.
A powerful flare was detected and it was possible to follow the variation in the equivalent widths of the Hα and Hβ lines,
both during the flare and during the quiescent phase of the star. It is shown that the profiles and equivalent widths of the
lines underwent substantial changes. The equivalent widths of these emission lines reached a maximum roughly 40 min after
the flare maximum.
__________
Translated from Astrofizika, Vol. 49, No. 4, pp. 573–583 (November 2006). 相似文献
2.
A. A. Akopian 《Astrophysics》1998,41(1):47-52
New estimates are proposed for the number of flare stars. They are compared with Ambartsumian’s well-known estimate. Using
the new estimates, it is found that flare stars of the same luminosity in the Orion association have the same average flare
frequency.
Translated from Astrofizika, Vol. 41, No. 1, pp. 73–80, January-March. 1998. 相似文献
3.
Horizontal motion has been studied of the matter along the active region at different heights of the photosphere (115–580
km) in the initial phase of the two-ribbon solar flare on September 4, 1990, near the solar limb, accompanied by the ejection.
Photospheric velocities varied in the range −3.5 ... 2.5 km/s. The direction of motion in the photosphere and the chromosphere
was mainly toward the observer. Kinematic elements have been discovered in the structure of the horizontal velocity field.
Their size reduced as they approached the maximum of the flare from 7–12 to 4–5 Mm, and the velocity amplitude decreased.
Throughout the whole investigated active region, vortex motions were observed in the photosphere and chromosphere. Temporal
changes in the horizontal velocity field in node areas and in their vicinity were oscillatory in nature and occurred almost
simultaneously along the entire height of the photosphere. 相似文献
4.
A. A. Akopian 《Astrophysics》2008,51(1):48-57
The frequency of flares is one of the basic characteristics of the activity of flare stars. Long-term variations in the flaring
frequency are determined by comparing the distribution functions of the flaring frequency for systems of flare stars with
different ages.
__________
Translated from Astrofizika, Vol. 51, No. 1, pp. 63–74 (February 2008). 相似文献
5.
Observations of the Pleiades cluster by the method of stellar tracks, carried out on the 40-inch Schmidt telescope of Byurakan
Astrophysical Observatory, have resulted in the detection of 49 flares from 38 stars, 17 of which were not previously known
to be flare stars. It is shown that for bright stars (U ≤ 16.0) the detection of flares in observations by the method of stellar
tracks is at least three times more efficient than for observations by the method of stellar chains. Another advantage of
the first method is that one can detect brief flares that last less than 6 min. The visual stellar magnitude at the minimum
for the brightest of the flare stars that we found is 11.92. This raised the upper luminosity limit of known flare stars in
the Pleiades by 0.21 magnitude. A comparison of the expected number of bright flare stars in the Pleiades with the number
of all bright members of the cluster (falling in the range from V ≈ 12.0 toV ≈16.0) suggested that all these stars evidently
must be flare stars.
Translated from Astrofizika, Vol. 42, No. 3, pp. 351–358, July–September, 1999. 相似文献
6.
C. Debi Prasad Ashok Ambastha Nandita Srivastava Sushanta C. Tripathy Mona J. Hagyard 《Journal of Astrophysics and Astronomy》1997,18(1):39-55
Super-active region NOAA 6555 was highly flare productive during the period March 21st–27th, 1991 of its disk passage. We
have st udied its chromospheric activity using high spatial resolution Hα filtergrams taken at Udaipur along with MSFC vector
magnetograms. A possible relationship of flare productivity and the variation in shear has been explored. Flares were generally
seen in those subareas of the active region which possessed closed magnetic field configuration, whereas only minor flares
and/or surges occurred in subareas showing open magnetic field configuration. Physical mechanisms responsible for the observed
surges are also discussed. 相似文献
7.
An investigation of the two-dimensional distribution of flare stars in the Pleiades led to the discovery of a dip in their
surface density at a distance of 3.2 pc from the center of the cluster. The same feature is found in the three-dimensional
distribution of these stars.
Translated from Astrofizika, Vol. 42, No. 4, pp. 537–540, October–December, 1999. 相似文献
8.
The evolutionary and spatial characteristics of the motions in the flaring chromosphere of a 2B/M2.3 flare are investigated
by analyzing the asymmetry in the Hα profiles. The possibility of reconciling the results of observations with the theory of chromospheric evaporation is considered.
The spectroscopic Hα observations of the flare performed with the KG-2 CrAO coronagraph with a temporal resolution of 5–10 s and a spatial resolution
as high as 1 arcsec cover all stages of flare development. The following results have been obtained: (1) The Hα profile asymmetry is a general characteristic of the flare emission irrespective of its intensity and its belonging to different
structural features and phases of flare development. (2) Most of the Hα emission profiles in flare regions exhibit a red asymmetry. However, a blue asymmetry was observed in small local regions
at all stages of flare development. (3) A red asymmetry that appeared before the onset of the impulsive phase and persisted
after its end was observed at the sites of main energy release, i.e., the energy source responsible for the dynamical processes
in the flare came into operation earlier and existed longer than the HXR emission. (4) The asymmetry pattern changed with
flare phase: the red wing intensity dominated in the pre-impulsive phase and at the onset of the impulsive and gradual phases
(while the line core was unshifted or slightly shifted). At the maximum of the impulsive phase, the nearly symmetric profiles
with extended wings were redshifted as a whole, i.e., the entire emitting volume moved down with a velocity of several tens
of km/s. This type of asymmetry cannot be explained by the dynamical model of chromospheric condensation (Canfield and Gayley
1987). (5) The Hα profiles show no evidence of chromospheric heating by a beam of nonthermal electrons during the impulsive phase (Canfield
et al. 1984). (6) The lifetime of the downflows and the change in their velocities with time are inconsistent with the dynamical
model of chromospheric condensation (Fisher 1989). (7) The morphological features of the velocity field are also inconsistent
with the theory of chromospheric evaporation, because the highest differently directed velocities were detected at the flare
loop tops, not at the sites of main energy release. We conclude that the investigated flare shows spectral features that are
inconsistent with the standard chromospheric evaporation model. 相似文献
9.
L. G. Kocharov G. A. Kovaltsov G. E. Kocharov E. I. Chuikin I. G. Usoskin M. A. Shea D. F. Smart V. F. Melnikov T. S. Podstrigach T. P. Armstrong H. Zirin 《Solar physics》1994,150(1-2):267-283
Data on X-,γ-ray, optical and radio emission from the 1991 June 15 solar flare are considered. We have calculated the spectrum of protons
that producesγ-rays during the gradual phase of the flare. The primary proton spectrum can be described as a Bessel-function-type up to
0.8 GeV and a power law with the spectral index ≈3 from 0.8 up to 10 GeV or above. We have also analyzed data on energetic
particles near the Earth. Their spectrum differed from that of primary protons producingγ-ray line emission. In the gradual phase of the flare additional pulses of energy release occurred and the time profiles of
cm-radio emission andγ-rays in the 0.8–10 MeV energy band and above 50 MeV coincided. A continuous and simultaneous stochastic acceleration of the
protons and relativistic electrons at the gradual phase of the flare is considered as a natural explanation of the data. 相似文献
10.
Results are presented from a study of solar radius measurements taken with the solar astrolabe at the TUBITAK National Observatory
(TUG) over seven years, 2001–2007. The data series with standard deviation of 0.35 arcsec shows the long-term variational
trend with 0.04 arcsec/year. On the other hand, the data series of solar radius are compared with the data of sunspot activity
and H-α flare index for the same period. Over the seven year trend, we have found significant linear anti-correlations between the
solar radius and other indicators such as sunspot numbers, sunspot areas, and H-α flare index. While the solar radius displays the strongest anti-correlation (−0.7676) with sunspot numbers, it shows a significant
anti-correlation of −0.6365 with sunspot areas. But, the anti-correlation between the solar radius and H-α flare index is found to be −0.4975, slightly lower than others. In addition, we computed Hurst exponent of the data sets
ranging between 0.7214 and 0.7996, exhibiting the persistent behavior for the long term trend. In the light of the strong
correlations with high significance, we may suggest that there are a causal relationship between the solar radius and solar
time series such as sunspot activity and H-α flare index. 相似文献
11.
The flare plasma temperature calculated from GOES-11 (1.5–12.4 and 3.1–24.8 keV) data is compared with the solar nonthermal
fluxes in various energy ranges in the December 6, 2006 event. Particle acceleration and plasma heating episodes took place
in the pre-flare and impulsive phases; a hard (ACS SPI > 150 keV) X-ray emission was observed 5 min before the onset of the GOES X-ray flare and was not accompanied by a temperature
rise. A close correlation has been found between the flare plasma temperature and the hard X-ray intensity. The temperature
delayed by 0.4 min turned out to be directly proportional to the logarithm of the ACS SPI count rate within the first 3 min
of the impulsive phase. This shows that the accelerated electrons responsible for the X-ray emission were the main plasma
heating source in the pre-flare and impulsive phases. The correlation between the temperature and the hard X-ray intensity
disappears after the observation of a resonance peak at a frequency of 245 MHz. Significant electron fluxes may no longer
be able to effectively heat the expanding plasma when its density in the interaction region reaches ∼109 cm−3. The observations of the July 23, 2002 and December 5, 2006 events confirm the trends found. 相似文献
12.
We have taken the case of a circular Hα filament observed on May 9,1979 erupting into a double-ribbon flare associated with
a non-spot region. The plage motions are responsible for the filament reorientation and, here as a special case, wherein the
filament attains a clear circular shape before the onset of a flare. We conclude that the change in the orientation of the
Hα filament marks the instability giving rise to the flare. 相似文献
13.
Wahab Uddin Ramesh Chandra Syed Salman Ali 《Journal of Astrophysics and Astronomy》2006,27(2-3):267-276
We observed 4B/X17.2 flare in Hα from super-active region NOAA 10486 at ARIES, Nainital. This is one of the largest flares
of current solar cycle 23, which occurred near the Sun’s center and produced extremely energetic emission almost at all wavelengths
from γ-ray to radio-waves. The flare is associated with a bright/fast full-halo earth directed CME, strong type II, type III
and type IV radio bursts, an intense proton event and GLE. This flare is well observed by SOHO, RHESSI and TRACE. Our Hα observations
show the stretching/de-twisting and eruption of helically twisted S shaped (sigmoid) filament in the south-west direction
of the active region with bright shock front followed by rapid increase in intensity and area of the gigantic flare. The flare
shows almost similar evolution in Hα, EUV and UV. We measure the speed of Hα ribbon separation and the mean value is ∼ 70
km s-1. This is used together with photospheric magnetic field to infer a magnetic reconnection rate at three HXR sources at the
flare maximum. In this paper, we also discuss the energetics of active region filament, flare and associated CME. 相似文献
14.
Time series of daily numbers of solar Hα flares from 1955 to 1997 are studied by means of wavelet power spectra with regard
to predominant periods in the range of ∼ 24 days (synodic). A 24-day period was first reported by Bai (1987) for the occurrence
rate of hard X-ray flares during 1980–1985. Considering the northern and southern hemisphere separately, we find that the
24-day period is not an isolated phenomenon but occurs in each of the four solar cycles investigated (No. 19–22). The 24-day
period can be established also in the occurrence rate of subflares but occurs more prominently in major flares (importance
classes ≥ 1). A comparative analysis of magnetically classified active regions subdivided into magnetically complex (i.e.,
including a γ and/or δ configuration) and non-complex (α, β) reveals a significant relation between the appearance of the
24-day period in Hα flares and magnetically complex sunspot groups, whereas it cannot be established for non-complex groups.
It is suggested that the 24-day period in solar flare occurrence is related to a periodic emergence of new magnetic flux rather
than to the surface rotation of sunspots. 相似文献
15.
Based on the methods of coronal seismology, we have investigated the ten-second quasi-periodic pulsations of the optical flare
emission from the active red dwarf EQ Peg B detected with the William Herschel Telescope on La Palma. We propose and analyze
a model in which they could be produced by sausage oscillations of a coronal flare loop. The amplitude and phase relations
between the displacement components of the radial oscillations and the conditions for their excitation in loops with footpoints
frozen into the photosphere are considered. The temperature (≈6 × 107 K), plasma density (≈2.7 × 1011 cm−3), and magnetic field strength (≈540 G) in the region of energy release have been determined. Our estimate of the flare loop
length (≈0.4R
⋆) provides evidence for the existence of extended coronae on red dwarf stars. 相似文献
16.
We present results of a study of photospheric horizontal motions at the initial and main phases of the solar flare which happened
on September 4, 1990, near the solar limb. The flare was accompanied by matter ejection. Spectra of the flare were obtained
using the AZU-26 horizontal solar telescope at the MAO NAS (Terskol observatory). We found variations of the matter motion
velocity’s value and direction at different stages of the photosphere during the flare development. The velocity changed in
a range from −4 to 2 km/s. Comparisons of the obtained data with variations of the chromospheric radial velocities showed
that the horizontal matter motions in the photosphere and chromosphere are mostly directed toward the observer but at particular
time moments their direction changed. At two different knots, the time shift of the photospheric velocities is different.
The highest velocities were observed at the main phase of the flare. At the initial phase of the flare, in the matter ejection
region, we note a velocity increase compared with its preflare value and at the flare knots. 相似文献
17.
V. V. Hambaryan L. V. Mirzoyan R. Wichmann J. Krautter R. Neuhäuser 《Astrophysics》1997,40(4):354-362
The X-ray data of a sample of 104 flare stars (FSs) in the Pleiades cluster region obtained by Stauffer et al. [1] on the
basis of deep ROSAT PSPC observations are analyzed. If we divide the X-ray emission detected in late-type stars of the Pleiades
cluster into FSs and non-FSs, we find that X-ray luminosities of stars of both groups can be considered as coming from the
same parent population. Moreover, in order to classify stars in a sample of 23 late-type Pleiades stars of unknown nature
discriminant analysis in a four-dimensional parameter space (log (Lx, log (Lx/Lbol), and ROSAT hardness ratios HR1 and HR2) has been used. It can be shown that the majority of these stars (16) are very likely
FSs rather than non-FSs.
Published in Astrofizika, Vol. 40, No. 4, pp. 545–557, October-December, 1997. 相似文献
18.
We investigate the radiative and conductive cooling in the solar flare observed by RHESSI on 2005 September 13. The radiative
and conductive loss energies are estimated from the observations after the flare onset. Consistent with previous findings,
the cooling is increased with time, especially the radiation becomes remarkable on the later phase of flare. According our
method, about half of thermal energy is traced by RHESSI soft X-rays, while the other half is lost by the radiative (∼38%)
and conductive (∼9%) cooling at end of the hard X-rays in this event. The nonthermal energy input of P
nth (inferred from RHESSI hard X-ray spectrum) is not well correlated with the derivative of thermal energy of
\fracdEthdt\frac{\mathrm{d}E_{\mathrm{th}}}{\mathrm{d}t} (required to radiate the RHESSI soft X-ray flux and spectrum) alone. However, after consideration the radiation and conduction,
a high correlation is obtained between the derivative of total thermal energy (
\fracdEth+Erad+Econddt\frac{\mathrm{d}E_{\mathrm{th}}+E_{\mathrm{rad}}+E_{\mathrm{cond}}}{\mathrm{d}t}) and nonthermal energy input (P
nth) from the flare start to end, indicating the relative importance of conductive and direct radiative losses during the solar
flare development. Ignoring the uncertainties to estimate the energy from the observations, we find that about ∼12% fraction
of the known energy is transferred into the thermal energy for the 2005 September 13 flare. 相似文献
19.
We present the analysis of a compact flare that occurred on 26 February 2002 at 10:26 UT, seen by both RHESSI and TRACE. The
size of the nearly circular hard X-ray source is determined to be 5.6 (±0.8)′′, using different methods. The power-law distribution
of non-thermal photons is observed to extend down to 10 keV without flattening, and to soften with increasing distance from
the flare kernel. The former indicates that the energy of the precipitating flare electron population is larger than previously
estimated: it amounts to 2.6 (±0.8)×1030 erg above 10 keV, assuming thick-target emission. The thermal energy content of the soft X-ray source (isothermal temperature
of 20.8 (±0.9) MK) and its radiated power were derived from the thermal emission at low energies. TRACE has observed a low-temperature
ejection in the form of a constricted bubble, which is interpreted as a reconnection jet. Its initial energy of motion is
estimated. Using data from both satellites, an energy budget for this flare is derived. The kinetic energy of the jet bulk
motion and the thermal and radiated energies of the flare kernel were more than an order of magnitude smaller than the derived
electron beam energy. A movie is available on the CD-ROM accompanying this volume.
Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1022478300679 相似文献
20.
S. W. Kahler 《Solar physics》1978,59(1):87-104
Solar X-ray flare images from Skylab and data from full Sun detectors were used in a statistical analysis to determine the relationship between flare volumes and flare energetics. Data from the rise phases of 45 flares were used in the analysis. For each event the diameter D, length L, and volume V of the flare loops were determined and then compared to the thermal energy, rate of increase of thermal energy, and rise time of the soft X-ray flux. The latter three quantities were all found to be positively correlated with D, L, and V. However, the thermal energy per unit volume and rate of increase of thermal energy per unit volume decrease with increasing volume. No correlation was found between emission measure Y and volume V, indicating that the electron density tends to be smaller for larger flare volumes. We find a larger dynamic range for V than for Y, hence knowledge of V is more critical than that of Y for calculating the thermal energy of the X-ray emitting structure, which is proportional to Y
0.5
V
0.5. Using certain assumptions, the results were compared to several flare models. The classical neutral sheet model, the sheared loop model of Spicer and even models using the magnetic field in a passive role for the energy release were all found to be consistent with the results. 相似文献