共查询到20条相似文献，搜索用时 625 毫秒
1.
Y. P. Varshni 《Astrophysics and Space Science》1988,149(2):197-215
The emission and absorption lines (3716–4290) in the spectrum of the quasar 0237–233 are identified within the framework of the PLS model. The available evidence indicates that it is a helium star. Similarities between the spectral properties of 0237–233 and the star Upsilon Sagittarii are pointed out. Predictions are made for the absorption-line spectrum which falls outside 3716–4290 and also for an expected discontinuity at 2600. 相似文献
2.
We present the results of our long-term U BV R observations of the star T Tauri performed at Mt. Maidanak Observatory from 1986 until 2003. These data, together with previous photoelectric observations of other authors, suggest that the long-term variations of the light curve are not periodic, but have a cycle with a time scale of 6–9 yr. The light curve also exhibits slower variations with time scales of ～30–40 yr. We confirm the existence of periodic brightness variations with a period of \(P = 2\mathop .\limits^d 798\) over many years; this process is peculiar in that the phase and shape of the phase curve change from season to season. We analyze the color behavior of the star. We found evidence of a strong flare occurred on October 5, 1999, when the brightness of the star reached \(9\mathop .\limits^m 22\). This is the strongest flare recorded during its photoelectric observations. 相似文献
3.
J. Zvolánková 《Earth, Moon, and Planets》1995,68(1-3):653-660
The activity of the Leonid shower in the years 1944–1953 was derived from visual records obtained at the Skalnaté Pleso Observatory, using the zenithal exponent = 1.47 in the reduction factor cos
z
R. 相似文献
4.
Our 8-year-long JHKLM photometry of the Seyfert galaxy NGC 1068 has confirmed its IR variability. The amplitudes of the brightness variations in
the J (1.25 μm) and K (2.2 μm) bands are within 0
.
m
15 and 0
.
m
3, respectively, and exceed the observational errors by more than a factor of 5. The nucleus of NGC 1068 is a variable source
and can be at different phases of activity. The brightness of the galaxy in all bands except J decreased from 1998 until 2004. In this period, there was a tendency for the J brightness to increase. The variable source in NGC 1068 is a complex structured object. At least two sources radiate in the
wavelength range 1.25–5 μm: a hot source whose radiation shows up in the range 1.25–1.65 μm and a cold source radiating at
long wavelengths (2.2–5 μm). The color temperature of the hot source increased from 2300 K (the beginning of our observations)
to ∼2700 K (the end of our observations). In contrast, the temperature of the cold source decreased by several tens of degrees
(in the temperature range 800–900 K). The IR brightness and color variations observed in 1998–2004 are attributable to the
dispersal of the dust envelope that formed around the galactic nucleus some 30 years ago and reached its maximum density in
1994–1995. Our analysis of the spectral energy distributions for the galaxy has shown that the observed radiation in the range
1.25–5 μm can be represented as the sum of radiations from two blackbody sources. For the first period of our observations
(JD 2451400), the temperatures of the hot and cold sources are ∼3100 and 760 K, respectively. For the second period (JD 2453230),
they are ∼3200 and 720 K, respectively. The hot source is relatively compact; it is smaller in size than the cold source by
several tens of times. The mean sizes of the hot and cold sources are ∼2.35 × 1016 and ∼7.8 × 1017 cm, respectively. The total mean luminosity of the two sources did not change between the beginning and the end of our observations.
The optical depth of the dust envelope averaged over the spectrum of the hot source is τ ∼ 1.5. In 2004, the state of the dust envelope almost returned to its 1974 level, i.e., the dust envelope formation and dispersal
cycle was ∼11 000 days (∼30 yr).
Original Russian Text ? O.G. Taranova, V.I. Shenavrin, 2006, published in Pis’ma v Astronomicheskiĭ Zhurnal, 2006, Vol. 32,
No. 7, pp. 489–496. 相似文献
5.
Doppler measurements of the photosphere of the entire Sun carried out at the Crimean Astrophysical Observatory (CrAO) in 1974–2007 by the differential technique showed the presence of an enigmatic periodicity of P 1 = 159.967(4) min. The phase of this oscillation was constant over the entire 34-year of surveys and interval. The true nature of this phenomenon is unknown. Pulsation with the former period P 0 = 160.0101(15) min has been reliably detected only in the first nine years, from 1974 to 1982. It is noted that (a) the average amplitude of the P 1 oscillation in the first half of the data was nearly 34% higher than in the second half and (b) the beat period of 400(14) d of these two pulsations is equal within error to the Jovian synodic period (399 d). A hypothesis is discussed relating the P 1 oscillation to the superfast rotation of the inner solar core. 相似文献
6.
In 2008, we observed the spectrum of the planetary nebula He 1–5, which has had no ionization source for more than 50 years.
Comparison with the observations performed in 1972–1976 and 1988 shows that the line intensity ratio I(λ5007[O III])/I(Hβ) decreased by a factor of 2.5, the intensity ratio of the red [N II] doublet to Hα was almost constant, and the [S II]-to-Hα intensity ratio may have slightly increased. The observed changes in the spectrum agree, within the limits of the observational
errors, with the calculations of gas recombination in a medium-excitation nebula performed by Tylenda in 1980, but the nitrogen
line intensities are higher than the calculated ones by 10–15%. This is most likely related to the slightly reduced nitrogen
abundance adopted in the model. The onset of nebular recombination dates from the end of the 19th century and is consistent
with its estimate from the photometric history of the central star. 相似文献
7.
We present the results of our studies of the Hα line in the spectrum of a UX Ori star (WW Vul) based on our spectroscopic observations performed with the 2-m telescope at the Shamakhi Astrophysical Observatory, the National Academy of Sciences of Azerbaijan, in 2006–2010. We have detected variability in all the measured parameters of the Hα profile both during each observing season and from season to season. A comparative analysis of our data and published studies has led to the conclusion that the regime of outflow with a variable power in the star WW Vul, on the whole, is preserved for almost 40 years (1972–2010) and the accretion of gas from the circumstellar disk onto the stellar surface is occasionally observed. Changes in the regime of variability in the behavior of the Hα emission line have been revealed in the 2006–2010 observing seasons. In four cases (for July 8, 2006, August 17, 2008, June 13, 2010, and August 2, 2010), we have detected a second emission component in the blue wing of the Hα emission line. 相似文献
8.
The short-term periodicities of the flare index are investigated in detail using Fourier and wavelet transforms for the full disc and for the northern and the southern hemispheres of the Sun separately over the epoch of almost 4 cycles (1966–2002). The most pronounced power peaks were found by the Fourier transform to be present at 25.6, 27.0, 30.2, and 33.8 days. The wavelet transform results show that the occurrence of periodicities of flare index power is highly intermittent in time. A comparison of the results of the Fourier transform and the time-period wavelet transform of the flare index time series has clarified the importance of different periodicities, whether they are or are not the harmonics of the basic ones, as well as the temporal location of their occurrence. We found that the modulation of the flare index due to the 27-day solar rotation is more pronounced during the declining portion of solar cycle than during the rising portion. 相似文献
9.
The north – south asymmetries (NSA) of three solar activity indices are derived and mutually compared over a period of more
than five solar cycles (1945 – 2001). A catalogue of the hemispheric sunspot numbers, the data set of the coronal green line
brightness developed by us, and the magnetic flux derived from the NSO/KP data (1975 – 2001) are treated separately within
the discrete low- and mid-latitude zones (5° – 30°, 35° – 60°). The calculated autocorrelations, cross-correlations, and regressions
between the long-term NSA data sets reveal regularities in the solar activity phenomenon. Namely, the appearance of a distinct
quasi-biennial oscillation (QBO) is evident in all selected activity indices. Nevertheless, a smooth behavior of QBO is derived
only when sufficient temporal averaging is performed over solar cycles. The variation in the significance and periodicity
of QBO allows us to conclude that the QBO is not persistent over the whole solar cycle. A similarity in the photospheric and
coronal manifestations of the NSA implies that their mutual relation will also show the QBO. A roughly two-year periodicity
is actually obtained, but again only after significant averaging over solar cycles. The derived cross-correlations are in
fact variable in degree of correlation as well as in changing periodicity. A clear and significant temporal shift of 1 – 2
months in the coronal manifestation of the magnetic flux asymmetry relative to the photospheric manifestation is revealed
as a main property of their mutual correlation. This shift can be explained by the delayed large-scale coronal manifestation
in responding to the emergence of the magnetic flux in the photosphere. The reliability of the derived results was confirmed
by numerical tests performed by selecting different numerical values of the used parameters. 相似文献
10.
In the following study our aim is to analyse the magnetic flux-rope topology of some events observed in the interplanetary medium related to ejecta. The magnetic field structures associated with interplanetary coronal mass ejections are globally classified in magnetic clouds and ejecta. One of the main questions regarding these phenomena concerns their flux-rope or non-flux-rope magnetic field line configuration. From the experimental measurements the only way to elucidate such a question is analysing the corresponding data by means of a flux-rope physical model. After selecting the ejecta events observed during the period 1997?–?2006, we have analysed them in light of an analytical model with that topology for the magnetic field components, initially developed for magnetic clouds, and with a non-force-free character; then, incorporating the expansion of the magnetic structure during their evolution in the interplanetary medium. Different parameters obtained from the fitting of the model are related to the orientation of the axis of the magnetic flux-rope structure and, additionally, the closest distance approach of the spacecraft to its axis. One of the main conclusions achieved concerns the fact that the axes of most of those structures are close to the Sun–Earth line, which implies that the passage of the spacecraft through the corresponding ejecta event is by its flank. In general, we show a rough procedure for the analysis and classification of ejecta in terms of their magnetic field topology. 相似文献
11.
N. V. Narizhnaya 《Solar System Research》2016,50(5):344-351
Observational results are presented for Jupiter and its Galilean moons from the Normal Astrograph at Pulkovo Observatory in 2013–2015. The following data are obtained: 154 positions of the Galilean satellites and 47 calculated positions of Jupiter in the system of the UCAC4 (ICRS, J2000.0) catalogue; the differential coordinates of the satellites relative to one another are determined. The mean errors of the satellites’ normal places in right ascension and declination over the entire observational period are, respectively: εα = 0.0065″ and εδ = 0.0068″, and their standard deviations are σα = 0.0804″ and σδ = 0.0845″. The equatorial coordinates are compared with planetary and satellite motion theories. The average (O–C) residuals in the two coordinates relative to the motion theories are 0.05″ or less. The best agreement with the observations is achieved by a combination of the EPM2011m and V. Lainey-V.2.0|V1.1 motion theories; the average (O–C) residuals are 0.03″ or less. The (O–C) residuals for the features of the positions of Io and Ganymede are comparable with measurement errors. Jupiter’s positions calculated from the observations of the satellites and their theoretical jovicentric coordinates are in good agreement with the motion theories. The (О–С) residuals for Jupiter’s coordinates are, on average, 0.027″ and–0.025″ in the two coordinates. 相似文献
12.
The results of the solar radius measurements from February 2001 to November 2003 with the solar astrolabe at the TUBITAK National
Observatory are presented. The mean semi-diameter for the period, corrected for systematic effects such as the Fried parameter
and the zenith distance, is found to be 959.29 ± 0.01 arc sec. A comparison of the monthly averages of the solar radius with
the monthly means of sunspot numbers shows that the semi-diameter of the Sun increases with an amplitude of 0.017 arc sec
per year in opposite phase with solar cycle 23. 相似文献
13.
We investigate the excitation of magnetoacoustic–gravity waves generated from localized pulses in the gas pressure as well as in the vertical component of velocity. These pulses are initially launched at the top of the solar photosphere, which is permeated by a weak magnetic field. We investigate three different configurations of the background magnetic field lines: horizontal, vertical, and oblique to the gravitational force. We numerically model magnetoacoustic–gravity waves by implementing a realistic (VAL-C) model of the solar temperature. We solve the two-dimensional ideal magnetohydrodynamic equations numerically with the use of the FLASH code to simulate the dynamics of the lower solar atmosphere. The initial pulses result in shocks at higher altitudes. Our numerical simulations reveal that a small-amplitude initial pulse can produce magnetoacoustic–gravity waves, which are later reflected from the transition region due to the large-temperature gradient. The cavities in the lower solar atmosphere are found to have the best conditions to act as a resonator for various oscillations, including their trapping and leakage into the higher atmosphere. Our numerical simulations successfully model the excitation of such wave modes, their reflection and trapping, as well as the associated plasma dynamics. 相似文献
14.
D. N. Sob’yanin 《Astronomy Letters》2016,42(11):745-751
The electromagnetic field in a magnetized neutron star and the underlying volume charges and currents are found. A general case of a rigidly rotating neutron star with infinite conductivity, arbitrary distribution of the internal magnetic field, arbitrarily changing angular velocity, and arbitrary surface velocity less than the velocity of light is considered. Quaternions are used to describe rotation and determine the magnetic field. It is shown that the charge density is not equal to and can exceed significantly the common Goldreich–Julian density. Moreover, corrections to the magnetic field due to stellar rotation are zero. For a rotating neutron star, twisting magnetic field lines causes charge accumulation and current flows. This fact shows a possible link between changing internal magnetic field topology and observed activity of neutron stars. 相似文献
15.
The motion of dust structures in the circumnuclear region of comet Hale–Bopp is studied. About 270 envelope images were obtained with the AZT-8 reflector (D = 0.7 m, F = 28 m) and the Filin-3 image intensifier. We carried out our observations at the observational station of the Astronomical Observatory of Shevchenko Kiev State University in the village of Lesniki (near Kiev). The recording from the image-intensifier screen was made on Foto-100 film during 23 nights from March 24 to May 10, 1997. The circumnuclear region was imaged both in white light (without filters) and with IHW CO+ (ef = 426 nm), C3 (ef = 496 nm), C2 (ef = 514 nm), and RC (red continuum, ef = 684 nm) narrow-band interference filters. Based on our measurements of the radial expansion of dust structures, we determined the velocities, 0.61–1.99 km s–1; accelerations, from –18.3 × 10–3 to 4.0 × 10–3 m s–2; and rotation period of the cometary nucleus, 111.41h ± 0.05h. 相似文献
16.
In the present work we study (i) the charged black hole in Einstein–Gauss–Bonnet (EGB) theory, known as the Einstein–Maxwell–Gauss–Bonnet
(EMGB) black hole and (ii) the black hole in EGB gravity with a Yang–Mills field. The thermodynamic geometry of these two
black hole solutions has been investigated, using the modified entropy in Gauss–Bonnet theory. 相似文献
17.
The north – south (N – S) asymmetry of solar activity is investigated by using the data on coronal green-line brightness and
total number and total area of sunspots over the period of 1939 – 2001. Typical time variations of the N – S asymmetry are
found to be consonant in these indices. Quasi-biennial oscillations (QBO) of solar activity are well recognizable in the N – S
asymmetry of the examined indices. Moreover, the QBO are much better manifested in the N – S asymmetry of the individual indices
than in the original (N plus S) indices. The time variations of relative QBO power are synchronous for the N – S asymmetry
of various solar activity indices whereas such a synchronization is weaker for the indices themselves. It is revealed that
the relative QBO power found in the N – S asymmetry of the studied indices has a negative correlation with the value of the
N – S asymmetry itself. The findings indicate that the N – S asymmetry should be regarded as a fundamental phenomenon of solar
activity similarly manifested in different activity indices. These findings should be taken into account when any dynamo theory
of solar activity is constructed. 相似文献
18.
《天文和天体物理学研究(英文版)》2020,(4)
Object J053253.51–695915.1(J053253) in the Large Magellanic Cloud(LMC) is reported as a young stellar object(YSO). Its chemical abundances reflect the initial composition of the gas cloud in which the star formed. However, the discovery that this star shows the enhancement of the neutron(n)-capture elements and the higher ratio of the heavier n-capture elements relative to the lighter n-capture elements is puzzling. Using an abundance decomposed method, we explore the astrophysical origins of the n-capture elements in this star. We find that the abundance characteristic of the higher ratio of the heavier n-capture elements to the lighter n-capture elements can be explained by the pollution of the r-process event and the contamination of the s-process material. 相似文献
19.
Effect of Moon perturbation on the energy curves and equilibrium points in the Sun–Earth–Moon system
《New Astronomy》2021
In this paper, we have considered that the Moon motion around the Earth is a source of a perturbation for the infinitesimal body motion in the Sun–Earth system. The perturbation effect is analyzed by using the Sun–Earth–Moon bi–circular model (BCM). We have determined the effect of this perturbation on the Lagrangian points and zero velocity curves. We have obtained the motion of infinitesimal body in the neighborhood of the equivalent equilibria of the triangular equilibrium points. Moreover, to know the nature of the trajectory, we have estimated the first order Lyapunov characteristic exponents of the trajectory emanating from the vicinity of the triangular equilibrium point in the proposed system. It is noticed that due to the generated perturbation by the Moon motion, the results are affected significantly, and the Jacobian constant is fluctuated periodically as the Moon is moving around the Earth. Finally, we emphasize that this model could be applicable to send either satellite or telescope for deep space exploration. 相似文献
20.
J. Craig Wheeler 《Astrophysics and Space Science》1977,50(1):125-131
The final dynamical collapse of oxygen cores of 103 and 104
M
which undergo the pair formation instability is computed. These cores are found to suffer complete collapse, presumably to form black holes, in contrast to cores of 100M
which have previously been found to explode completely, leaving no remnant. These calculations represent a first attempt to ascertain the outcome of evolution over several decades of mass previously unexplored. The outcome may have some relevance to models of X-ray sources in globular clusters. 相似文献