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1.
V. S. Tamazian N. D. Melikian A. A. Karapetian R. Sh. Natsvlishvili 《Astrophysics》2005,48(3):279-290
Results are presented from a study of 27 spectra of the flare star HU Del obtained during 2000–2002 on the 2.6 meter telescope at the Byurakan Observatory. Two flares were detected, along with a weak correlation between the equivalent widths of the Hα and Hβ emission lines. At the time of the photometric maximum of a flare the equivalent widths of both these lines are minimal and reach their maximum only significantly afterward. A strong increase in the Hβ line intensity is observed which appears to be the consequence of a photometrically undetected, short-duration flare. A possible relationship between the binary (multiple) character and the physical activity of this star is examined briefly in terms of current theoretical models.__________Translated from Astrofizika, Vol. 48, No. 3, pp. 335–348 (August 2005). 相似文献
2.
N. D. Melikian V. S. Tamazian J. A. Docobo A. A. Karapetian G. R. Kostandian R. Iglesias 《Astrophysics》2008,51(3):372-386
Results from a spectral study of one of the brightest cataclysmic variables, the star TT Ari, are presented. They are generally
in good agreement with previous observations, but there are some differences. The luminosity of the star, as well as the equivalent
widths of emission lines, reveal variations that are probably periodic in character. Emission from the star in the CIV 5801Å
and 5812 Å lines is observed for the first time. The observed variations in the symmetry of the broad absorption Balmer series
(beginning with Hβ) may be a consequence of the appearance of a P Cyg line profile. The Hα line manifests a P Cyg profile
consisting of two components corresponding to 600 and 1900 km/s. The average of the ratio EWHα/EWHβ indicates that the formation
of these lines may be explained, at least partially, in terms of a simple photoionization-recombination model.
__________
Translated from Astrofizika, Vol. 51, No. 3, pp. 445–460 (August 2008). 相似文献
3.
Magnetic field structures of Hα flares associated with meter-wave type III bursts during periods of low solar activity in
1975 – 1977 and 1985 – 1987 were investigated. In a statistical analysis it was confirmed that the association rate depends
less on flare importance than on brightness. For subflares (95% of the sample), the location of the Hα flare in the bipolar
pattern turned out to be crucial for the association rate. It is almost one order of magnitude larger for flares occurring
at the border of the active regions, compared to flares located inside the general bipolar pattern. For selected typical examples
of flares, extrapolations of the measured magnetic fields were performed. By matching Hα filtergrams and calculated 3-D structures
it was found that the positions at the border where the flares associated with type III bursts occurred were close to open
field lines extending into the corona. In most investigated cases intrusions of parasitic polarity were found in the vicinity
of the flare locations. The extrapolations showed that subflares located inside the bipolar pattern but have not been associated
with type III bursts were covered by dense arcades of magnetic loops. 相似文献
4.
This is a study of optical emission lines of the nucleus of the Seyfert galaxy NGC 3227. This work is based on 53 spectrograms
obtained with the 6-m telescope at the brightness maximum of this galactic nucleus on January 12–15, 1977. A set of profiles
of the hydrogen Hα, and Hβ lines and the equivalent widths (EWλ) of six emission lines and blends averaged over series of observations are presented. Broadening of the hydrogen line profiles
was observed over the three days. At a level of 0.50 times the peak brightness the hydrogen line profiles were broadened by
12%, 35%, and 44%, respectively. The broadening of the Hβ line was accompanied by a reduction in its equivalent width (EW
;
). It is suggested that a flare was observed in the nucleus of the galaxy on a time scale of 3 days, possibly caused to a
shock wave in long-lived flows from the galaxy nucleus.
__________
Translated from Astrofizika, Vol. 49, No. 4, pp. 499–510 (November 2006). 相似文献
5.
Results from a spectrophotometric study of the galaxy Kaz 701 are presented. Spectra of this galaxy were obtained on the 2.6-m
telescope at the Byurakan Observatory with the SCORPIO spectral camera. In the spectra of Kaz 701, strong Hα, [OIII] λλ5007,
4959, and Hβ emission were observed, and the [SII]λλ6731, 6717 lines were observed with moderate intensities, while the [NII]λ6584
line was scarcely noticeable in the spectra obtained in 2004, but was much more intense in the spectra of 2009. The lines
observed in the spectrum of this galaxy are typical of type Sy2 galaxies. A component was observed in the red wings of both
the Hα and Hβ lines in the data of 2004, but, although these lines were stronger, these components were absent in the spectra
taken in 2009. The relative intensities, equivalent widths, and half widths of these lines are given. These data, obtained
in different observation periods (2004 and 2009), differ greatly; that is, the emission is variable. 相似文献
6.
We present our results of high temporal resolution spectroscopic observation and study in Hα, Ca II, and He I lines for the 2B/M1.9 confined disk flare on September 9, 2001, combining with GOES soft X-ray (SXR) and Yohkoh hard X-ray (HXR) observations. Apparent redshifted and red-asymmetric profiles were observed in the initial phase. The redshift
lasted until the late phase. The derived velocity depends on both the spectral line and the used method. The redshift velocities
computed from the line centers of the observed emission profiles (υ0) are of the order of 10 km s−1 both inside and outside the streak area. However, the velocities determined from the excess profiles by the bisector method
(υ) are larger in the streak (18–50 km s−1). Both υ and the red full widths (RFWs) derived from the excess profiles show temporal variations similar to the HXR light-curve
in the streak area. Moreover, the Hα line wings of nonthermal characteristics, the redshift velocities, and the lifetime of
impulsive broadening suggest that the streak is related to nonthermal electron bombardment. Spectral simulations reveal that
we cannot reproduce the observed profiles in the three lines simultaneously with a set of parameters, indicating that the
flare atmosphere was not homogeneous along the line-of-sight. Most of the observed Hα profiles showed a ‘flat-top’ structure,
implying the flare plasma was optically thick for this line. The electron temperatures (Te) deduced from the line-center intensity of the three lines are similar and estimated to be higher than 7200 K. The obvious
central reversal of the Hα profiles due to absorption of materials in the impulsive phase lasted more than 2 min. However,
the far blue wings of the Ca II profiles in the impulsive phase showed low-intensity emission, which is suggestive of the
existence of large turbulence or macroscopic motion (> 50 km s−1), which is inconsistent with the current flare model. 相似文献
7.
The results of the high-resolution long-term spectral monitoring of the Herbig Ae star HD 31648 in the regions of emission
Hα line, Na I D resonance lines and OI 7774 lines are presented.
We confirmed the conclusion, made in previous papers, that the spectral variability of the star in the region of Hα line have
a cyclic character. It is manifested itself as the changing of the equivalent width and intensity of Hα line of the time scale
of about 1200d.
It is shown, that the stellar wind is non-homogeneous and consists of several components, which are differed each other by
their velocities. They are observed as in the H line as in Na I D resonance lines. The component’s parameters are changed
during the cycle of stellar activity (in the maximum of activity the velocity and density of the wind are taken the largest
values and then they are gradually decreased).
The investigation of rapid variability of the He I 5876 line on the time scale of a few hours allows find the correlation
between the variability of the blue and the red wings of the line. It points at the connection between the accretion and the
outflows. Such connection, in particularly, is predicted by the modeling of the wind from young stars made in the frame of
the magneto-centrifugal model, the accordance of which for the HD 31648 was shown in the previous papers. In the present work
we confirmed this conclusion on the basis of the new data.
We found the weak variability of the stellar brightness (about 0.2m), which is agree with the spectral variability (the brightness
of the star becomes lower in the maximum of the activity). These changes are well explained by the process of the dust transfer
from CS disk by the stellar wind. This process is likely to be more effective in the maximum of activity.
An analysis of the variability of other spectral lines shows the agreement between the changing of the Hα line, the Na I D
resonance doublet lines and KI 7698 line. The weak connection between the He I 5876 and the Na I D lines is also found. Since
the formation regions of He I 5876 and Na I D lines are essentially different, we can conclude that the phenomena, responsible
for the observed cyclic variability, take place in a spacious region of the CS envelope.
We believe that the most plausible reason of found cyclic variability is the reconstruction of the inner structure of the
CS gas envelope, caused by the presence around the star a low mass companion or planet.
__________
Translated from Astrofizika, Vol. 50, No. 4, pp. 565–588 (November 2007). 相似文献
8.
GianLuca Israel 《Astrophysics and Space Science》2007,308(1-4):25-31
On 27th December 2004 SGR 1806–20, one of the most active Soft γ-ray Repeaters (SGRs), displayed an extremely rare event, also known as giant flare, during which up to 1047 ergs were released in the ∼1–1000 keV range in less than 1 s. Before and after the giant flare we carried out IR observations
by using adaptive optics (NAOS-CONICA) mounted on VLT which provided images of unprecedented quality (FWHM better than 0.1″).
We discovered the likely IR counterpart to SGR 1806–20 based on positional coincidence with the VLA uncertainty region and
flux variability of a factor of about 2 correlated with that at higher energies.
Moreover, by analysing the Rossi-XTE/PCA data we have discovered rapid Quasi-Periodic Oscillations (QPOs) in the pulsating
tail of the 27th December 2004 giant flare of SGR 1806–20. QPOs at ∼92.5 Hz are detected in a 50 s interval starting 170 s
after the onset of the giant flare. These QPOs appear to be associated with increased emission by a relatively hard unpulsed
component and are seen only over phases of the 7.56 s spin period pulsations away from the main peak. QPOs at ∼18 and ∼30 Hz
are also detected ∼200–300 s after the onset of the giant flare. This is the first time that QPOs are unambiguously detected
in the flux of a Soft Gamma-ray Repeater, or any other isolated neutron star. We interpret the highest QPOs in terms of the
coupling of toroidal seismic modes with Alfvén waves propagating along magnetospheric field lines. The lowest frequency QPO
might instead provide indirect evidence on the strength of the internal magnetic field of the neutron star.
相似文献
9.
Donald C. Norquist 《Solar physics》2011,269(1):111-127
Designing a statistical solar flare forecasting technique can benefit greatly from knowledge of the flare frequency of occurrence
with respect to sunspot groups. This study analyzed sunspot groups and Hα and X-ray flares reported for the period 1997 – 2007.
Annual catalogs were constructed, listing the days that numbered sunspot groups were observed (designated sunspot group-days,
SSG-Ds) and for each day a record for each associated Hα flare of importance category one or greater and normal or bright
brightness and for each X-ray flare of intensity C 5 or higher. The catalogs were then analyzed to produce frequency distributions
of SSG-Ds by year, sunspot group class, likelihood of producing at least one flare overall and by sunspot group class, and
frequency of occurrence of numbers of flares per day and flare intensity category. Only 3% of SSG-Ds produced a substantial
Hα flare and 7% had a significant X-ray flare. We found that mature, complex sunspot groups were more likely than simple sunspot
groups to produce a flare, but the latter were more prevalent than the former. More than half of the SSG-Ds with flares had
a maximum intensity flare greater than the lowest category (C-class of intensity five and higher). The fact that certain sunspot
group classes had flaring probabilities significantly higher than the combined probabilities of the intensity categories when
all SSG-Ds were considered suggest that it might be best to first predict the flaring probability. For sunspot groups found
likely to flare, a separate diagnosis of maximum flare intensity category appears feasible. 相似文献
10.
N. D. Melikian V. S. Tamazian J. A. Docobo A. A. Karapetian G. R. Kostandian A. L. Samsonian 《Astrophysics》2010,53(2):202-211
Spectral observations of the eclipsing binary RY Sct during 2005 and 2009 on the 2.6-m telescope at the Byurakan Observatory
are reported. Although RY Sct requires further, more detailed study, the present limited observations reveal a number of important
aspects of this star. The maxima of the equivalent widths are observed close to the primary minimum, while their minima are
detected at the brightness maximum, where the spectral lines have very narrow profiles. Emission in the HeI λ6678? line was
seen throughout the observation period, but transforms into weak absorption halfway between the secondary minimum and the
maximum. The observed P-Cyg type changes in the profile of some lines indicates a variable outflow of mass from the star.
Estimates of the average velocity based on the blue components of the absorption lines yield roughly 400 km/s. The main observational
characteristics of RY Sct are closely related to its orbital period. In all likelihood, its complicated spectrum and features
are at least partially caused by intense, variable outflows of matter. 相似文献
11.
High dispersion CCD spectra are used to study the profiles of the Hα and Hβ lines of 48 stars in early spectral classes in
the young diffuse binary cluster h/χ Per. In addition, moderate resolution spectra of 15 B and Be stars were taken over the
interval 4400–4960 Å. One or, possibly, two new Be stars are discovered. The major parameters of the Hα line are measured
for the observed B and Be stars. The spectra over 4400–4960 Å are used to estimate Teff, logg, and υsin i. No traces of emission are detected in the Hα line profiles for 28 of the stars and emission is observed in the Hα line
for 20. During our observations an absorption profile of the Hα line was observed for some of the stars, such as Oo146, Oo566,
Oo922, and Oo1268, although they have previously been identified as Be stars. A significant long-term variability of the Hα
line is discovered for the Be stars Oo1161 and Oo2242. Oo2371 manifests a variability in its faint emission spectrum which
is typical of close binary systems that include a Be star.
__________
Translated from Astrofizika, Vol. 51, No. 2, pp. 305–319 (May 2008). 相似文献
12.
We present broad bandR and narrow band Hα emission line images of a sample of optically selected starburst galaxies from the Markarian lists. The
emission line morphology is studied and global properties like luminosities, equivalent widths and star formation rates are
derived. The radial distribution of Ha flux and the EW are determined using concentric aperture photometry on the emission
line and the continuum images. Ha flux is generally found to peak in the nuclear region and fall off outwards. The EW is found
to peak off-center in most of the cases implying that though the intensity of emission is maximum at the nucleus, the star
formation activity relative to the underlying continuum often peaks away from the center in Markarian starburst galaxies. 相似文献
13.
Based on optical–NIR spectra, we discuss the nebular properties and stellar populations of starburst nuclei. Starbursts are
found to have higher electron densities and higher excitations than HII nuclei. The emission lines have been used to estimate
the nebular oxygen abundances, ionization parameter and radiation softness parameter. From a study of the Hα emission-line equivalent widths and the CaII triplet absorption line equivalent widths, we infer the ages and stellar content
of the starburst regions. Most of the nuclei show evidence for a composite population – a young, ionizing population co-existing
with evolved, non-ionizing stars of about 5–7 Myr, which are evolving towards the peak of RSG distribution.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
14.
“Elementary bursts” refer to fine time structures on scales of tens of milli-second to a few seconds in flare radiations.
In this paper, we investigate temporal and spatial properties of elementary bursts by exploiting high-cadence Hα (100 ms)
and hard X-ray (125 – 500 ms) observations of an impulsive flare on March 16, 2000. We find that the time scale of 2 – 3 s
is likely an upper limit of the elementary bursts in this event, at which hard X-ray emissions observed by different instruments
correlate, low energy (≤30 keV) hard X-rays and Hα flux correlate, and Hα emissions at conjugate flare kernels correlate.
From our methods, and also largely limited by instrument resolutions, there is a weak indication of existence of sub-second
structures. With the high-resolution Hα data, we also attempt to explore the spatial structure of “elementary bursts” by determining
the average spatial displacement of Hα peak emission between successive “elementary bursts” defined from hard X-ray light
curves. We find that, at the time scale of 3 s, the smallest spatial scale, as limited by the imaging resolution, is about
0.4″. We discuss these results with respect to mechanisms of fragmented magnetic energy release. 相似文献
15.
R. Sh. Natsvlishvili 《Astrophysics》1999,42(1):117-118
Flare periodicity has been found in the flare star Pleiades No. 484. The period of its flare activity is determined from an
analysis of the flares’time distribution.
Translated from Astrofizika, Vol. 42, No. 1, pp. 159–160, January–March, 1999. 相似文献
16.
B. E. Zhilyaev A. V. Sergeev M. V. Andreev V. G. Godunova V. N. Reshetnik V. K. Taradii 《Kinematics and Physics of Celestial Bodies》2013,29(3):120-130
A slitless UBVR spectrograph has been built for use on small telescopes. Test observations on the Zeiss-600 telescope at the Terskol peak demonstrated that the spectrograph is an efficient instrument for studying high-speed processes in variable stars with a high temporal resolution. The spectrograph resolving power R ≈ 100 in the vicinity of λ = 480 nm and the error in the determination of the wavelength is approximately 3 nm. The spectrograph provides a moderate signal-to-noise ratio for stars up to 16 m . It permits one to measure equivalent widths of unblended lines down to 0.1 nm. The developed special software based on the theory of quantum statistics makes it possible to detect relative variations in the spectrum of approximately 10?5–10?6 of the bolometric flux of the star. Observations with the spectrograph made it possible to detect variations of emissions in Balmer lines and Ca II H, K lines in the EV Lac flare star in the subsecond range. The spectroscopic monitoring permits one to study stellar flares with small amplitude, to carry out a comprehensive colorimetric analysis of flare plasma, and to determine temperatures and sizes of flares in the light intensity maximum. Observations of the transit of the HAT-P-1 B exoplanet demonstrate that the chromospheric activity power of the parent star does not vary during the transit. The slitless spectrograph with a low resolving capacity opens new prospects in studying active processes occurring on stars’ surfaces. 相似文献
17.
In searchs for flare stars in the vicinity of the Pleiades cluster, three flares were detected in 1970,1972, and 1977 in a
star with the coordinates α
1950
= 3
h
48
m
·9, δ
l950
= 25‡15’.8. The star’s brightness at a minimum is >21
m
·5. The star was tentatively assigned to the U Gem type. To confirm this assumption, we examined photographic plates for the
period of 1947–1987. As a result, we found 12 more flares. The average recurrence time based on the 1963–1977 observations
is about 330 days, and the maximum flare amplitude is >6
m
.Narrow superflares and steady-state flares lasting over 40 days have been observed in the star. The results show that this
is a dwarf nova of the UGSU subtype.
Translated from Astrofizika, Vol. 42, No. 1, pp. 47–52, January–March, 1999. 相似文献
18.
B. Viswanathan R. Shanmugavel S. P. Bagare N. Rajamanickam P. Sriramachandran 《Solar physics》2009,257(2):261-269
High-resolution Fourier transform spectrometer sunspot umbral spectra obtained at the National Solar Observatory/Kitt Peak
were used to identify molecular rotational lines arising from the infrared band systems of CrH and CrD molecules. Measurement
of the equivalent width used the Gaussian-profile approximation method, which is suitable especially for faint lines. Equivalent
widths are measured for an adequate number of best lines of the A – X (0,0) band of CrH and the A – X (0,0;1,0) bands of CrD
and, thereby, the effective rotational temperatures are estimated. 相似文献
19.
A model is constructed for the magnetic field of the He-weak CP star HD 21699. This star has the field structure of a dipole
displaced by 0.4 radii from the center perpendicular to its axis. The magnetic poles appear to be close to one another on
the surface; they are separated by 55°, not by 180° as in the case of a central dipole. The phase dependences of the equivalent
widths of He and Si lines have extrema at the phases corresponding to passage through the visible meridian of zero magnetic
field between the magnetic poles. At the magnetic poles, the intensity of the helium lines is maximal and of the silicon lines,
minimal. The silicon abundance is maximal in the regions where the magnetic field is predominantly tangential to the star’s
surface. Because of averaging over the visible hemisphere and owing to the closeness of the magnetic poles, only one wave
of variation in the intensity of the spectral lines of these chemical elements, one wave of photometric variability, and an
average surface magnetic field Bs are observed.
__________
Translated from Astrofizika, Vol. 50, No. 3, pp. 441–451 (August 2007). 相似文献
20.
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