共查询到20条相似文献,搜索用时 15 毫秒
1.
G.A. Gurzadyan 《Astrophysics and Space Science》2003,286(3-4):515-528
The problem of ionization for magnesium and radiation field in k and h MgII doublet in common envelopes – roundchroms – formed
around the RS CVn type systems is examined. It is shown that: a) The roundchroms are completely opaque in the lines of k and
h MgII doublet; b) F, G or K type cool stars as secondary in such binaries ensure the complete ionization of magnesium atoms
within the whole volume of roundchrom; c) The density of k and h MgII doublet radiation field in the main volume of roundchrom
is extremely high, on four-five orders of magnitude, than is derived for its outer boundary. These results have direct relation
to the observed saddle-like and very broad shapes of k and h MgII emission lines in the spectrum of RS CVn type close binaries.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
2.
G.A. Gurzadyan 《Astrophysics and Space Science》2000,274(4):785-798
An unexpected empirical fact, a dependence of the observed luminosities inhigh excitation emission lines – 1240 NV, 1400 SiIV, 1550 CIV, 1640 HeII– on the intercomponent distance a of RS CVn type close binary systems,is revealed. It is assumed that those high excitation emission lines aregenerated most probably in a cone-like region between the Lagrangian pointL
1 and the surface of the primary component of the system. Thebehavior of high excitation emission lines at various phases of theeclipse in the case of two binary systems, SX Cas and 22 Vul, indicatesthe possibility of existence of such a `Lagrangian cone' in the structureof common chromospheres – roundchroms – of close binary systems as amain source of generation of high excitation emission lines. 相似文献
3.
G. A. Gurzadyan 《Astrophysics and Space Science》1996,241(2):211-225
Roundchrom is a common chromosphere enveloping both components of close binary system. In present article, the problem of the construction of outward boundary of the roundchrom is examined, particularly, identifying this boundary with zero-velocity equipotential Lagrangian surface corresponding to a definite value of Jacoby constantC. The roundchroms for seven RS CVn type close binary systems as well for an interacting binary HD 207739 are constructed. The main parameters of these roundchroms are obtained, particularly, the electron concentrations are of the order of 1010 cm–3. 相似文献
4.
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
5.
Natalya Raguzova 《Astrophysics and Space Science》2002,281(3):641-649
Using the numerical code (`Scenario Machine') we study of number and physical properties of binary Be stars. Evolutionary
tracks leading to a formation of the observational binary systems are presented. We conclude that synchronization must be
taken into account when calculating binary Be star evolution and calculate the minimal orbital period for Be/evolved companion
binary. The obtained distributions over orbital parameters are in good agreement with the observational lack of short-period
Be/X-ray binaries. According to our calculations 70% of all Be stars must have a white dwarf. The white dwarfs in these systems
should be hot enough with the surface temperature distribution peaking at 10000–20000 K. Their detection is possible during
the period of the lack of Be star envelope by the detection of white dwarf extremely UV and soft X-ray emission. This method
of registration appears to be particularly promising for `single' early-type Be stars because in these systems the white dwarfs
must have a very high surface temperature. However, the loss of the Be disc-like envelope does not often occur and it is a
rather rare event for many Be stars. The best possibility of white dwarf detection is given by the study of helium spectral
lines found in emission from several Be stars. The ultraviolet continuum energy of these Be stars is found to be not enough
to produce the observed helium emission. Besides, we also discuss the orbital properties of binary Be star systems with other
evolved companions such as helium stars and neutron stars and give a possible explanation for the lack of Be/black hole binaries.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
6.
The rare-earth ions cerium ii, lanthanum ii, dysprosium ii, and additionally zirconium ii and iron ii, are seen as weak emission features in the wings of the solar Ca ii H and K lines. The strength of these emission lines increases on the disk toward the limb. We provide recent high-resolution
observations at disk center and at the limb. The identity of the weak lines is re-worked. We point out the unique role of
eclipse spectra in distinguishing between the photospheric and chromospheric origins of emission lines. It is then demonstrated
from our full disk (Sun-as-a-Star) and center disk archives, 1974 – 2010, that no activity cycle related signal is evident
(save for the H and K lines themselves). 相似文献
7.
We present simple analytic models which predict the peak X-ray emission measure and temperature attained in flares in which
the chromospheric evaporation process takes place either in a single ‘monolithic’ loop or in a loop consisting of several
filaments that are created successively as the energy release process proceeds in time. As possible mechanisms driving chromospheric
evaporation we consider both classical heat conduction from the loop top and non-thermal electron beams. The model predictions
are tested for a set of 18 well studied RHESSI microflares. The results suggest beam driven evaporation in filamented loops
as being capable of accounting for the observed emission measures and temperatures though there are issues with the very high
beam densities needed. On the other hand, estimates of the emission measures achieved by conductive evaporation which are
derived by using the Rosner – Tucker – Vaiana (RTV) scaling law are much larger than the observed ones. Possible reasons for
this discrepancy are discussed. 相似文献
8.
G. Trottet J.-P. Raulin G. Giménez de Castro T. Lüthi A. Caspi C. H. Mandrini M. L. Luoni P. Kaufmann 《Solar physics》2011,273(2):339-361
Solar flares observed in the 200 – 400 GHz radio domain may exhibit a slowly varying and time-extended component which follows
a short (few minutes) impulsive phase and can last for a few tens of minutes to more than one hour. The few examples discussed
in the literature indicate that such long-lasting submillimeter emission is most likely thermal bremsstrahlung. We present
a detailed analysis of the time-extended phase of the 27 October 2003 (M6.7) flare, combining 1 – 345 GHz total-flux radio
measurements with X-ray, EUV, and Hα observations. We find that the time-extended radio emission is, as expected, radiated
by thermal bremsstrahlung. Up to 230 GHz, it is entirely produced in the corona by hot and cool materials at 7 – 16 MK and
1 – 3 MK, respectively. At 345 GHz, there is an additional contribution from chromospheric material at a few 104 K. These results, which may also apply to other millimeter–submillimeter radio events, are not consistent with the expectations
from standard semiempirical models of the chromosphere and transition region during flares, which predict observable radio
emission from the chromosphere at all frequencies where the corona is transparent. 相似文献
9.
Berger T.E. De Pontieu B. Fletcher L. Schrijver C.J. Tarbell T.D. Title A.M. 《Solar physics》1999,190(1-2):409-418
TRACE observations of active regions show a peculiar extreme ultraviolet (EUV) emission over certain plage areas. Termed `moss'
for its spongy, low-lying, appearance, observations and modeling imply that the phenomenon is caused by thermal conduction
from 3–5 MKcoronal loops overlying the plage: moss is the upper transition region emission of hot coronal loops. The spongy
appearance is due to the presence of chromospheric jets or `spicules' interspersed with the EUV emission elements. High cadence
TRACE observations show that the moss EUV elements interact with the chromospheric jets on 10 s time scales. The location
of EUV emission in the moss does not correlate well to the locations of underlying magnetic elements in the chromosphere and
photosphere, implying a complex magnetic topology for coronal loop footpoint regions. We summarize here the key observations
leading to these conclusions and discuss new implications for understanding the structuring of the outer solar atmosphere.
Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1005286503963 相似文献
10.
O. N. Sholukhova S. N. Fabrika A. V. Zharova A. F. Valeev V. P. Goranskij 《Astrophysical Bulletin》2011,66(2):123-143
We present the results of studying the spectral and photometric variability of the luminous blue variable star V532 in M33.
The photometric variations are traced from 1960 to 2010, spectral variations—from 1992 to 2009. The star has revealed an absolute
maximum of visual brightness (1992–1994, high/cold state) and an absolute minimum (2007–2008, low/hot state) with a brightness
difference of ΔB ≈ 2.3
m
. The temperature estimates in the absolute maximum and absolute minimum were found to be T ∼ 22000 K and T ∼ 42000 K, respectively. The variability of the spectrum of V532 is fully consistent with the temperature variations in its
photosphere, while both permitted and forbidden lines are formed in an extended stellar atmosphere. Broad components of the
brightest lines were found, the broadening of these components is due to electron scattering in the wind parts closest to
the photosphere. We measured the wind velocity as a difference between the emission and absorption peaks in the PCyg type
profiles. The wind velocity clearly depends on the size of the stellar photosphere or on the visual brightness, when brightness
declines, the wind velocity increases. In the absolute minimum a kinematic profile of the V532 atmosphere was detected. The
wind velocity increases and its temperature declines with distance from the star. In the low/hot state, the spectral type
of the star corresponds to WN8.5h, in the high/cold state—to WN11. We studied the evolution of V532 along with the evolution
of AGCar and the massive WR binary HD5980 in SMC. During their visual minima, all the three stars perfectly fit with the WNL
star sequence by Crowther and Smith (1997). However, when visual brightness increases, all the three stars form a separate
sequence. It is possible that this reflects a new property of LBV stars, namely, in the high/cold states they do not pertain
to the bona fide WNL stars. 相似文献
11.
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
12.
We analyse data from Hinode spacecraft taken over two 54-minute periods during the emergence of AR 11024. We focus on small-scale portions within the
observed solar active region and discover the appearance of very distinctive small-scale and short-lived dark features in
Ca ii H chromospheric filtergrams and Stokes I images. The features appear in regions with close-to-zero longitudinal magnetic field, and are observed to increase in length
before they eventually disappear. Energy release in the low chromospheric line is detected while the dark features are fading.
Three complete series of these events are detected with remarkably similar properties, i.e. lifetime of ≈ 12 min, maximum length and area of 2 – 4 Mm and 1.6 – 4 Mm2, respectively, and all with associated brightenings. In time series of magnetograms a diverging bipolar configuration is
observed accompanying the appearance of the dark features and the brightenings. The observed phenomena are explained as evidencing
elementary flux emergence in the solar atmosphere, i.e. small-scale arch filament systems rising up from the photosphere to the lower chromosphere with a length scale of a few solar
granules. Brightenings are explained as being the signatures of chromospheric heating triggered by reconnection of the rising
loops (once they have reached chromospheric heights) with pre-existing magnetic fields, as well as being due to reconnection/cancellation
events in U-loop segments of emerging serpentine fields. The characteristic length scale, area and lifetime of these elementary
flux emergence events agree well with those of the serpentine field observed in emerging active regions. We study the temporal
evolution and dynamics of the events and compare them with the emergence of magnetic loops detected in quiet Sun regions and
serpentine flux emergence signatures in active regions. The physical processes of the emergence of granular-scale magnetic
loops seem to be the same in the quiet Sun and active regions. The difference is the reduced chromospheric emission in the
quiet Sun attributed to the fact that loops are emerging in a region of lower ambient magnetic field density, making interactions
and reconnection less likely to occur. Incorporating the novel features of granular-scale flux emergence presented in this
study, we advance the scenario for serpentine flux emergence. 相似文献
13.
Graeme H. Smith 《Astrophysics and Space Science》1997,253(1):119-138
In the spectra of red giants the chromospheric emission feature found in the core of the Ca II K line often exhibits an asymmetric
profile. This asymmetry can be documented by a parameter V/R which is classified as > 1, 1, or < 1 if the violet wing of the
emission profile is of greater, equal, or lower intensity than the redward wing. A literature search has been conducted to
compile a V/R dataset which builds on the large survey of bright field giants made by Wilson (1976). Among stars of luminosity
classes II–III–IV the majority of those with V/R > 1 are found to be bluer than B-V =1.3, while those with V/R < 1 are mostly
redder than this colour. Stars with nearly symmetric profiles, V/R≈ 1, are found throughout the colour range 0.8 < B-V < 1.5.
There is no sharp transition line separating stars of V/R > 1 and < 1 in the colour-magnitude diagram, but rather a ‘transition
zone’ centered at B-V ≈ 1.3. The center of this zone coincides closely with a ‘coronal dividing line’ identified by Haish,
Schmitt and Rosso (1991) as the red envelope in the H–R diagram of giants detected in soft x-ray emission by ROSAT. It is
suggested that both the transition to a Ca II K emission asymmetry of V/R < 1 and the drop in soft x-ray activity across the
coronal dividing line are related to changes in the dynamical state of the chromospheres of red giants. By contrast, the onset
of photometric variability due to pulsation occurs among stars of early-M spectral type, that are redward of the mid-point
of the Ca II V/R ‘transition zone’, suggesting that the chromospheric motions which produce an asymmetry of V/R < 1 are established
prior to the onset of pulsation.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
14.
Reversed-polarity structures of chromospheric magnetic fields are magnetic gulfs and islands of opposite polarity relative
to the underlying photospheric fields. In this paper data measured with the Solar Magnetic Field Telescope of the Huairou
Solar Observing Station in Beijing were analyzed. From more than 300 pairs of photospheric magnetograms (in FeI λ5324.19 Å) and relevant chromospheric magnetograms (Hβ λ4861.34 Å), the reality of the reversed-polarity structures is demonstrated. According to an analysis of the fine structure
of the magnetic field in the two layers of active regions, we found that there are probably four different types as follows:
Type A: magnetic islands of opposite polarity corresponding to photospheric fields appear in the chromospheric magnetogram.
Type B: magnetic gulfs of opposite polarity corresponding to photospheric fields appear in the chromospheric magnetogram.
Type C is the reverse of type B. That is, a magnetic gulf of opposite polarity corresponding to the chromospheric field appears
in the photospheric magnetogram.
Type D is the reverse of type A. 相似文献
15.
Shanti Priya Devarapalli Rukmini Jagirdar M. Parthasarathy D. K. Sahu Vijay Mohan B. C. Bhatt Vineet S. Thomas 《Astrophysics and Space Science》2018,363(4):69
The analysis of spectroscopic data for 30 Algol-type binaries is presented. All these systems are short period Algols having primaries with spectral types B and A. Dominant spectral lines were identified for the spectra collected and their equivalent widths were calculated. All the spectra were examined to understand presence of mass transfer, a disk or circumstellar matter and chromospheric emission. We also present first spectroscopic and period study for few Algols and conclude that high resolution spectra within and outside the primary minimum are needed for better understanding of these Algol type close binaries. 相似文献
16.
Spectral recordings in the region near 2800 Å are examined from the IUE archives for the twenty most active radio stars, which are also close binary systems. In all of these spectra, the doublet k and h Mg II is seen in strong emission. We find that the observed fluxes of the magnesium doublet emission are directly proportional to the mean fluxes of the observed radio emission at the frequency of 8.4 GHz. The same correlation is found between the absolute luminosities of the radio emission and magnesium doublet emissions. It is argued that the source of both emissions, radio and magnesium doublet, is related to a high temperature stratified cloud located between the components of the binary system. The fluxes of the magnesium doublet emission of these sources are much larger, by one or two orders of magnitude, compared with the usual chromospheric magnesium emission seen in single stars. 相似文献
17.
Maria A. Loukitcheva Sami K. Solanki Stephen White 《Astrophysics and Space Science》2008,313(1-3):197-200
The very nature of the solar chromosphere, its structuring and dynamics, remains far from being properly understood, in spite
of intensive research. Here we point out the potential of chromospheric observations at millimeter wavelengths to resolve
this long-standing problem. Computations carried out with a sophisticated dynamic model of the solar chromosphere due to Carlsson
and Stein demonstrate that millimeter emission is extremely sensitive to dynamic processes in the chromosphere and the appropriate
wavelengths to look for dynamic signatures are in the range 0.8–5.0 mm. The model also suggests that high resolution observations
at mm wavelengths, as will be provided by ALMA, will have the unique property of reacting to both the hot and the cool gas,
and thus will have the potential of distinguishing between rival models of the solar atmosphere. Thus, initial results obtained
from the observations of the quiet Sun at 3.5 mm with the BIMA array (resolution of 12″) reveal significant oscillations with
amplitudes of 50–150 K and frequencies of 1.5–8 mHz with a tendency toward short-period oscillations in internetwork and longer
periods in network regions. However higher spatial resolution, such as that provided by ALMA, is required for a clean separation
between the features within the solar atmosphere and for an adequate comparison with the output of the comprehensive dynamic
simulations. 相似文献
18.
G.A. Gurzadyan 《Astrophysics and Space Science》2003,288(4):429-444
It is shown that the formation of a roundchrom, i.e. a common chromosphere,in W UMa type contact binaries is inevitable. The
geometrical forms of roundchroms for ten contact binaries are obtained. For contact binaries the round-chroms of open type
are predicted along with a possibility of outflow of round-chrom's gaseous matter from the outer Lagrangian point L2. The main parameters of roundchroms, the electron concentration n
e, efficient emission volume V, power of emission in magnesium doublet 2800 MgII etc. are obtained for the ten contact binaries. The decrease of the mean
electron concentration in roundchrom n
e with the increase of the intercomponent distance a is discovered: n
e
∼ a
-1.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
19.
The CCD echelle spectra of the chromospherically active binary HR 5553 are obtained using the 2.16 m telescope with Coudé
echelle spectrograph of Beijing Observatory in April 1996. The features of Ca II H & K, Hα, He I D3 and Ca II IRT2 (λ 8542
AA) & IRT3 (λ 8662 AA) are presented. The absolute fluxes of these lines which provide the useful information to study the
chromospheric activity of HR 5553 are given. The fundamental parameters of the cool dwarf component of HR 5553 are determined
using the analysis of the observed spectra with a resolution of R ≃ 60000 and signal-to-noise ratio S/N = 100 ∼ 300. A detailed
spectroscopic analysis has yielded the following fundamental parameters: Effective temperature: Teff = 4881 K Surface gravity:
log(g) = 3.65 Logarithmic iron abundance: [Fe/H] = –0.30 as well as that of other 12 metal elements (relative to the Sun)
are listed in the Table II and Table III. Microturbulence: ζ = 1.20 km s-1. Magnetic field measurements of the cool dwarf
component of HR 5553 have been made using the Stenflo-Lindegren statistical analysis and the profile-addition technique. The
magnetic field strength and filling factor are obtained.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
20.
Zongjun Ning 《Solar physics》2011,273(1):81-92
We explore the speed distributions of X-ray source motions after the start of chromospheric evaporation in two Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) flares. First, we make CLEAN images at 15 energy bands with a 12 second integration window; then, we outline a flaring
loop geometry to cover the looptop and footpoint sources as much as possible. Consistent with the previous steps, we find
converging motion of the double footpoint sources along the flaring loop in these two events. This motion is dependent on
the energy band and time and is typically seen at 3 – 25 keV, indicating a chromospheric evaporation origin. The speed distributions
at various energy bands are measured for the 10 September 2002 flare, which exhibits a separation-to-mergence motion pattern
well correlated with the rising-to-decay phases at 50 – 100 keV. 相似文献