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1.
We have studied the relationships between the brightness, color, and emission-line profiles for the classical T Tauri star RW Aur, which displays an intense emission spectrum and signs of accretion and outflow. Spectral and photometric observations carried out from 1995 to 1999 have been analyzed in the framework of magnetospheric accretion concept, where the brightness of the star depends on the level of the non-photospheric continuum (veiling), which, in turn, depends on the accretion rate. We found that (1) the equivalent widths and profiles of broad emission lines vary independently of the brightness of the star, the brightness and color variations are due primarily to absorption in dust clouds formed by the disk wind; (2) at times when the accretion in the line of sight becomes stronger, all broad emission lines are weakened substantially due to the asymmetry of the magnetosphere and screening of the radiating region; (3) the periodic variations of the U-B and B-V color indices are due to the variable contribution of broad emission lines in the photometric bands; (4) the veiling of the photospheric spectrum is not correlated with either the brightness of the star or the intensity of the accretion components. 相似文献
2.
Results of spectral observations of the isolated Ae Herbig star CQ Tau obtained in 1995–1998 in the Hα line and near the sodium resonance doublet are presented, together with simultaneous photometric monitoring of the star. CQ Tau is a member of the family of young UX Ori stars with nonperiodic Algol-like brightness decreases. The star is surrounded by an accretion disk, in which its emission-line spectrum and part of its absorption-line spectrum are formed. The strong variability of the Hα, D NaI, and HeI 5876 Å lines testifies that the gaseous disk is appreciably inhomogeneous in both the radial and azimuthal directions. This inhomogeneity probably results from uneven feeding by the circumstellar material from the peripheral regions of the circumstellar disk. Over the four years of observations, we observed the star in deep minima three times (ΔV～2). On these nights, an increase in the Hα equivalent width followed the decrease in radiation flux. In the two deepest minima, the normally two-component line profile had only a single component with a nearly symmetrical profile. This behavior of the Hα line is in good agreement with the results of numerical modeling of Algol-like minima and can be used to estimate the parameters of the dust clouds eclipsing the star and inner accretion disk. These estimates suggest that the circumstellar dust clouds can approach very close to the star and be sublimated there. 相似文献
3.
High resolution observations in the region of the Hα, HeII λ 4686, and Hγ lines in the spectrum of the symbiotic binary Z
And were performed during a small-amplitude flare at the end of 2002. The profiles of the hydrogen lines were double-peaked,
and suggest that the lines may be emitted mainly by an optically thin accretion disk. Since the Hα line is strongly contaminated
by emission from the envelope, the Hγ line is used to investigate the properties of the accretion disk. The Hα line has broad
wings, believed to be determined mostly by radiation damping, although the high-velocity stellar wind from the compact object
in the system may also contribute. The Hγ line has a broad emission component, assumed to be emitted mainly from the inner
part of the accretion disk. The HeIIλ 4686 line also has a broad emission component, but is believed to arise in a region
of high-velocity stellar wind. The outer radius of the accretion disk can be calculated from the shift between the peaks.
Assuming that the orbital inclination can range from 47° to 76°, we estimate the outer radius to be 20–50 R⨀. The behavior of the observed lines can be interpreted in the model proposed for the line spectrum during the first large
2000–2002 flare of this binary. 相似文献
4.
We have developed an axisymmetric model for the dust envelope of the carbon star RW LMi with a density distribution typical for the superwind stage using JHKLM photometric data obtained in 1997–2003, supplemented by flux data at optical, mid-IR, and far-IR wavelengths. In contrast to earlier spherically-symmetric models, the model is able to reproduce the observed fluxes in all observed wavelength ranges, and provides a good agreement with the observational data. The estimated mass-loss rate is \(\dot M = 1.2 \times 10^{ - 5} M_ \odot /yr\). The computed brightness distribution of the envelope in the near-IR is in satisfactory agreement with high-resolution observations, while the optical size is considerably larger than is observed. 相似文献
5.
The results of long-term photometric observations of R CrB in the UBV JHKLM bands are presented. The temporal and color characteristics of the emission of the star itself and of its extended dust envelope are analyzed in detail. No stable harmonic has been found in the semiregular variations of the optical brightness of R CrB. Two harmonics with periods P≈3.3 and 11.3 yrs have been detected in the brightness variations of the dust envelope; the minima of these variations coincided in 1999, resulting in a record decrease in the LM brightness of the envelope. This by chance coincided in time with a deep minimum of the visual brightness of the star, resulting in a unique decrease in the total brightness of the star and dust envelope. This enabled estimation of the bolometric flux of the hot dust clouds, which made up only a few per cent of the bolometric flux of the dust envelope. The brightness variations of the dust envelope are not accompanied by appreciable color changes and are associated with variations of its optical depth τ(V) in the range 0.2–0.4. The dust envelope forms at a large and fairly constant distance from the star $(r_{in} \approx 110R_* ,T_{gr} \approx 860 K)$ , from material in its stellar wind, whose intensity $(\dot M_{gas} \approx 2.1 \times 10^{ - 7} M_ \odot /year)$ obeys a Reimers law. No variations synchronous with those of the optical depth of the dust envelope, in particular, with the period P≈3.3 yrs, have been found in the optical emission of R CrB, suggesting that the stellar wind is not spherically symmetric. The dust envelope consists of small grains (a gr≤0.01 µm), while the clouds screening the star from the observer are made up of large grains (a gr≈0.1 µm). The activity of R CrB, whose nature is unclear, is reflected in variations of the stellar-wind intensity and the appearance of dust clouds in the line of sight: these variations are repeated by corresponding changes in the optical depth of the dust envelope with a delay of ～4 years (the time for a particle moving at V env≈45 km/s to move from the star to the boundary of the dust envelope). 相似文献
6.
W. H. Elsanhoury 《Astronomy Reports》2020,64(1):94-106
The work on the kinematical parameters and spatial shape structure have been performed with Gaia DR2 astrometry data of the new recently southern discovered open clusters UFMG 1, UFMG 2, and UFMG 3 in the vicinity (∼1.3 degrees radius) of the rarely studied NGC 5999. The apexes positions with AD‑diagram method are computed for about 107, 168, 98, and 154 members of these star clusters, respectively. Our calculated values of apex coordinates are (Ao, Do) = (102$$_{.}^{^\circ }$$40 ± 1.02 and ‒4$$_{.}^{^\circ }$$60 ± 0.47; NGC 5999), (96$$_{.}^{^\circ }$$69 ± 1.10 and ‒0$$_{.}^{^\circ }$$58 ± 0.045; UFMG 1), (97$$_{.}^{^\circ }$$47 ± 1.09 and 1$$_{.}^{^\circ }$$56 ± 0.051; UFMG 2), and (98$$_{.}^{^\circ }$$65 ± 1.12 and ‒0$$_{.}^{^\circ }$$26 ± 0.060; UFMG 3). Velocity Ellipsoid Parameters (VEPs) for those clusters are also computed, i.e., space velocities $$\left( {\bar {U},\bar {V},\bar {U}} \right)$$ due to Galactic coordinates, dispersion velocities (σ1, σ2, σ3) due to matrix elements μij, projected distances (X, Y, Z) on the disk plane, and the Solar elements (S⊙, lA, bA). According to an approximation of spatial and kinematical shape, UFMGs and NGC 5999 seem to have a spatial difference in their spatial locations, but they appear to have formed in the same region of the Galactic disk. The total cumulative mass MC; including the total number of main-sequence NMS and non-main-sequence Nnon-MS stars of these clusters also evaluated here with a second-order polynomial of mass-luminosity relation in order to get clusters tidal radii (pc). Finally, we concluded that NGC 5999, UFMG 1, and UFMG 2 are dynamically relaxed (i.e., τ ≫ 1), and the fourth one in non-relaxed. 相似文献
7.
An exact solution is found for the interaction of a rotating magnetic field that is frozen into a star with a thin, highly conducting accretion disk. The disk pushes the magnetic-field lines towards the star, compressing the stellar dipole magnetic field. At the corotation radius, where the Keplerian and stellar rotational frequencies are equal, a current loop appears. Electric currents flow in the magnetosphere only along two particular magnetic surfaces, which connect the corotation region and the inner edge of the disk with the stellar surface. It is shown that a closed current surface encloses the magnetosphere. The disk rotation is stopped at some distance from the stellar surface, equal to 0.55 of the corotation radius. The accretion from the disk spins up the stellar rotation. The angular momentum transferred to the star is determined. 相似文献
8.
We present the results of synchronous photometric and polarimetric U BV RI observations of the irregular variable star RZ Psc, acquired at the Crimean Astrophysical Observatory in 1989–2002. The star’s photometric behavior is characterized by short, sporadic Algol-like dimmings. We observed only one deep minimum, with a V amplitude of about 1.5m, during the entire observation time. During this minimum, the star’s linear polarization reached 3.5%. Comparisons with polarization observations of RZ Psc during another deep minimum in 1989 show that the two minima can be described by the same polarization-brightness relation, testifying to an eclipsing nature for the minima. This provides evidence that the optical characteristics of the flattened circumstellar dust envelope that gives rise to the star’s intrinsic polarization have remained virtually unchanged over the last 13 years. We argue that the origin of this stability is the presence of a large dust-free cavity in the central region of the circumstellar dust disk of RZ Psc. The cavity could be associated with binarity of the star or the formation of a planetary system, with most of the dust in the central region of the disk being transformed into large bodies—planetesimals and planets. 相似文献
9.
T. S. Khruzina 《Astronomy Reports》2011,55(5):425-436
We present a “combined” model taking into account visual manifestations of the interaction between the gas flow and the accretion
disk in a close binary system in the form of a “hot line” and a “hot spot.” The binary consists of a red dwarf that fills
its Roche lobe and a compact spherical star (a white dwarf or neutron star) surrounded with a thick ellipsoidal accretion
disk of a complex shape. The disk thickness is not large near the compact star but increases according to a parabolic law
towards its outer edge. The oblique collision of the gaseous flow with matter of the cool, rotating disk, whose outer edge
has a temperature <10 000 K, creates an extended region of enhanced energy release. In the combined model, this region is
represented with a hot line that coincides with the optically opaque part of the flow and is located outside the disk, together
with a hot spot at the outer surface of the disk, on the leeward side of the flow. The synthetic light curves for the combinedmodel
and a hot-line model demonstrate that both models are able to fairly accurately reproduce the shapes of both classical and
atypical light curves of cataclysmic variables in quiescence. Our determination of the parameters of the cataclysmic variable
OY Car from an analysis of its light curves using the two models shows that the basic characteristics of the close binary,
such as the component mass ratio q = M
1/M
2, orbital inclination i, effective temperatures of the red dwarf (T
2) and white dwarf (T
1), and orientation of the disk α
e
, remain the same within the errors. The parameters describing the size of the slightly elliptical disk and the radiation
flux from the disk differ by several percent (∼ 2–8%). A more significant difference is detected in the parameters of the
hot line, due to the different shape and alignment of the flow and the presence of an additional radiation source—the hot
spot—on the disk. 相似文献
10.
11.
A. I. Bogomazov 《Astronomy Reports》2005,49(9):709-713
Observations of eclipses of the radio pulsar B1259-63 by the disk of its Be-star companion SS 2883 provide an excellent opportunity to study the winds of stars of this type. The eclipses lead to variations in the radio flux (due to variations in the free-free absorption), dispersion measure, rotation measure, and linear polarization of the pulsar. We have carried out numerical modeling of the parameters of the Be-star wind and compared the results with observations. The analysis assumes that the Be-star wind has two components: a disk wind in the equatorial plane of the Be star with a power-law fall-off in the electron density n e with distance from the center of the star \(\rho (n_e \sim \rho ^{ - \beta _o } )\), and a spherical wind above the poles. The parameters for a disk model of the wind are estimated. The disk is thin (opening angle 7.5°) and dense (electron density at the stellar surface n0e ～ 1012 cm?3, β0 = 2.55). The spherical wind is weak (n0e ? 109 cm?3, β0 = 2). This is the first comparison of calculated and observed fluxes of the pulsating radio emission. 相似文献
12.
A. N. Rostopchina V. P. Grinin D. N. Shakhovskoi A. A. Lomach N. Kh. Minikulov 《Astronomy Reports》2007,51(1):55-66
We present the results of simultaneous UBVRI photometry and polarimetry of the classical T Tauri star CO Ori carried out at the Crimean Astrophysical Observatory during the 18 years between 1986 and 2004. We show that the variations of linear polarization accompanying the star’s brightness variations follow the law characteristic of UX Ori stars. This suggests that the brightness variations of the star are mainly due to changes of the circumstellar extinction due to non-uniform structure of the circumstellar environment, and to an “optimal” orientation of the circumstellar gas and dust disk relative to the observer, whose line of sight crosses the gas and dust atmosphere of the disk. We determine the star’s intrinsic polarization due to scattering of light in the circumstellar disk. The polarization position angle indicates the orientation of the disk’s symmetry axis in the plane of the sky. Our analysis of an archival light curve for CO Ori confirms the existence of a many-year cycle of photometric activity, suspected by us earlier. The refined period of this cycle is 12.4 years. The existence of such activity cycles of UX Ori stars testifies to considerable deviations of their circumstellar disks from axial symmetry, a reflection of either stellar binarity or the commencement of the process of planetary formation. 相似文献
13.
We consider the role of the disk wind in the formation of hydrogen emission spectra of young intermediate-mass Herbig Ae stars.
The assumed parameters for the kinematic characteristics of the wind region are typical of the theory of magnetocentrifugal
disk winds. Our computations of the excitation and ionization states for atoms in the emitting region are based on the Sobolev
approximation for a medium with a large velocity gradient. The calculations show that hydrogen-line emission profiles can
have a complex structure that depends on the disk-wind parameters, as well as on the system’s orientation relative to the
line of sight. The model proposed is able to explain most types of Hα profiles observed for Herbig Ae stars. 相似文献
14.
Current views of the origin and evolution of single and binary stars suggest that the planets can form aroundmain-sequence
single and binary stars, degenerate dwarfs, neutron stars, and stellarmass black holes according to several scenarios. Planets
can arise during the formation of a star mainly due to excess angular momentum leading to the formation of an accretion-decretion
disk of gas and dust around a single star or the components of a binary. It is the evolution of such disks that gives rise
to planetary systems. A disk can arise around a star during its evolution due to the accretion of matter from dense interstellar
clouds of gas and dust onto the star, the accretion of mass froma companion in a binary system, and the loss of matter during
the contraction of a rapidly rotating star, in particular, if the star rotates as a rigid body and the rotation accelerates
with its evolution along the main sequence. The fraction of stars with planetary systems is theoretically estimated as 30–40%,
which is close to the current observational estimate of ∼34%. 相似文献
15.
V. P. Grinin O. Yu. Barsunova S. G. Sergeev A. A. Arkharov S. Yu. Shugarov A. O. Semenov N. V. Efimova 《Astronomy Reports》2018,62(10):677-688
The results of many-year photometric observations of the weak-line T Tauri star V715 Per in the optical (V RI) and infrared (JHK) photometric bands are presented. The period of the star’s lowamplitude brightness variations in the V RI bands detected earlier, 5.23d, is confirmed. This period persists during the entire 14-year time interval of the observations, but its amplitude varies with time. The same period was found in the variations of JHK infrared fluxes, with the brightness variations in the two ranges being almost synchronous. The most probable origin of these variations is periodic eclipses of the star by its own disk, perturbed by its interaction with the magnetosphere (AA Tau-type variations). In addition to the periodic brightness variations, the star also displayed sporadic Algol-like minima characteristic of UX Ori stars during several years (2005–2011). The amplitude of these variations increasedmonotonically, reaching approximately 1m in the V band by the end of 2010, after which the deep fadings ended. During this entire time interval, the amplitude of the periodic variations was observed to decrease. After 2011, the periodic component began to become stronger again. These changes of the photometric activity of V715 Per can be explained by an increasing rate of gas accretion onto the star, decreasing the radius of warped regions of the disk and leading to accompanying Algol-like fadings. This model assumes a low inclination of the circumstellar disk in V715 Per to the line of sight. 相似文献
16.
17.
Long-term (1984–2008) JHKLM photometry for 254 objects is presented. The observations were carried out in the standard JHKLM photometric system using an original method and a modern IR photometer designed and built at the Sternberg Astronomical Institute.
Our program of studies included searches for and studies of relatively hot circumstellar dust envelopes. The most important
results obtained using these observations include the following. We have detected relatively hot dust envelopes in a number
of objects for the first time, including the RCB star UV Cas, RX Cas, several classical symbiotic stars, etc. A model has
been calculated for the dust envelope of FG Sge, which formed around the star as a result of several successive cycles of
dust condensation beginning in Autumn 1992. Several dust-condensation episodes have been traced in the envelopes of symbiotic
systems (CH Cyg, V1016 Cyg, HM Sge, etc.), as well as the role of the hot component in the formation of the dust envelopes.
We have established from variations of the IR emission that the cool components in the symbiotic novae V1016 Cyg and HM Sge,
and possibly CH Cyg, are Miras. The binarity of V1016 Cyg and HM Sge has also been firmly established. The variability of
a whole series of object has been studied, including the stellar components of close binary systems and several dozen Mira
and semi-regular variables. The ellipsoidality of the components in the RX Cas system (a prototype W Ser star) and the cool
component in the symbiotic systems CI Cyg and BF Cyg has been firmly established. We have obtained the first IR light curve
for the eclipsing system V444 Cyg (WN5+O6), and determined the wavelength dependence of the obtained parameters of the WN5
star. Analysis of the IR light curves of several novae indicate the condensation of dust envelopes in the transition periods
of Cygnus 1992, Aquila 1993, and Aquila 1995. The IR light curve of R CrB has been obtained over a long period and analyzed.
IR observations of the nova-like variable V4334 Sgr have been carried out over four years, over which the star passed through
four stages during its motion along its post-AGB evolutionary track; the star’s bolometric flux and optical depth of its dust
envelope have been estimated, and the structure and mass of the dust layer determined. We have analyzed the IR variability
of the symbiotic star V407 Cyg over 14 years, and found its cool component to be a Mira with a period of 745 days. The observed
pulsations and trend are associated with the luminosity and temperature variations of the Mira, as well as the optical depth
of the dust envelope. The size of the dust grains and mass-loss rate of the Mira have been determined. We have obtained JHKL light curves for the Seyfert galaxy NGC 4151 over 23 years. The IR brightness of the galaxy grew from 1985 through 1996 (by
∼0.9
m
at 1.25 μm, ∼1
m
at 1.65 μm, ∼1.1
m
at 2.2 μm, and ∼1.3
m
at 3.5 μm), while the galaxy simultaneously reddened. The “cool” variable source in NGC 4151 was still in the active state
in 1998, although its luminosity had decreased by approximately 15%–20%. If the “cool” component of the variable source in
this galaxy is a dust envelope heated by the central “hot” source, it should be optically thin to the radiation of this source:
its mean optical depth is in the range 0.05–0.15. Emission from dust particles heated to temperatures of 600–800 K was observed
in the near IR at a distance of several parsecs from the nucleus during the period of activity in 1995–1998; the inferred
mass of emitting dust was 5–20 M
⊙. In 1994–2003, we observed a tendency for NGC 4151 to become bluer at 1.25–1.65 μm while simultaneously reddening at 2.2–3.5
μm. Beginning in Autumn 2000, the galaxy began to emerge from a minimum, which lasted from March 2000 through April 2001 in
the IR; a flare of the galactic nucleus was observed and followed in detail in the IR in this same period. We confirm the
IR variability of the nucleus of the Seyfert galaxy NGC 1068, which can be located in various stages of activity. The variability
of NGC 1068 is associated with a complex source. A periodic component has been detected in the J brightness variations of the oxygen Mira V2108 Oph; we have shown that this star is immersed in a fairly dense dust envelope,
and have calculated amodel for this envelope. We have calculated an (axially symmetrical) dust-envelope model for the carbon
semi-regular variable RWLMi with a density distribution characteristic for the “superwind” stage. This envelope model is able
to reproduce the observed fluxes over the entire observable spectrum, and displays a good agreement with the observational
data. The three hot supergiants V482 Cas, QZ Sge, and HD 338926 may be variable in the IR. Long-term photometry of eight planetary
nebulae in the near IR (1.25–5 μm) has enabled us to firmly establish the IR brightness and color variability of these nebulae
on time scales from several tens of days to six-to-eight years. We have analyzed long-term JK photometry of the X-ray binary Cyg X-1 (V1357 Cyg). Periodicity with a characteristic time scale of ∼11.5 years is visible
in the JK brightness variations of Cyg X-1 in 1984–2007, possibly due to periodic variations of the temperature, radius and luminosity
of the optical component of the binary with P ∼11.5 yr. Fourteen-year IR light curves of five RV Tau stars (R Sge, RV Tau, AC Her, V Vul, and R Sct) and the yellow supergiant
and protoplanetary-nebula candidate V1027 Cyg have been analyzed. A spherically symmetrical dust-envelope model has been calculated
for V1027 Cyg. 相似文献
18.
The accretion of neutral gas (hydrogen and helium) onto a neutron star is studied. The gas is gravitationally captured into the magnetosphere of the star, where it is ionized by thermal radiation from the stellar surface and accelerated by the electric field at the light cylinder and in a tube of open magnetic lines. Particles accelerated at light cylinder generate gamma-ray, some particles move to the star and heat its polar regions, resulting in the emission of X-rays. Our calculations of the model parameters of the X-ray and gamma-ray radiation indicate that the radiation intensities should be sufficient to be observed. 相似文献
19.
T. G. Sitnik 《Astronomy Reports》2011,55(7):616-621
The structure and kinematics of the ISM in an extended vicinity of the star WR 139 is analyzed using the results of original
Hα interferometric observations together with radio and infrared data. A CO cavity with a size of up to 40′ has been detected
around the star at velocities of V
LSR ∼ 2.5–10 km/s; the cavity is bounded to the North by a shell radiating in the optical. Ionized hydrogen emits at the systematic
velocities V
LSR ∼ 6–14 km/s toward the CO cavity, and at V
LSR ≃ 4–11 km/s toward the shell. High-velocity motions of ionized hydrogen inside the cavity testify to the probable expansion
of gas that has been swept out by the stellar wind of WR 139 at velocities of up to 60–80 km/s. 相似文献
20.
We present the first high accuracy UBVRI(RI)c CCD light curves of the newly discovered eclipsing system PS UMa = GSC 4375 1733 ($$P = 9_{·}^{d}27$$, $$V = 12_{·}^{m}42$$). The photometric solutions are found, the physical parameters of the components are derived. The eccentricity of the orbit was found to be negligible e = 0.074, which made it difficult to measure the rate of the apsidal rotation. High accuracy of our observations allowed us to find the reliable parameters of the system. Components (Sp = F7 + G1) have advanced significantly in their evolution, the age of the system is 2.4 billion years. The mass and the radius of G1 component is larger and it is ahead of the F7 component in its evolution. The model of the system best suits the theory in the absence of the overshooting in the core. Obtained from our observations photometrical parallax π = 0$$_{.}^{\prime\prime }$$00102(2) coincides with GAIA DR2 value $$\pi =0_{·}^{\prime\prime }00106(3)$$ within their errors. The new EW type variable with period $$ \approx {\kern 1pt} 0_{·}^{d}40$$ was found in the field of PS UMa. 相似文献