共查询到20条相似文献，搜索用时 15 毫秒
1.
T. A. Polyakova 《Astrophysics》1998,41(4):367-371
Photoelectric observations of the brightness and polarization of the carbon star UX Dra in 1989–1993 are presented and discussed.
The strong variations in this star’s period and the impossibility of determining it from our observations forced us to use
an extrapolation of Vetešnik’s periodvariation curve. As in Vetesnik’s observations, our determinations of UX Dra’s brightness
are satisfied far better by a period twice as long. The variations in UX Dra’s brightness and polarization parameters resemble
most closely those of an RV Tau star, in our opinion.
Translated from Astrofizika, Vol. 41. No. 4, pp. 561–568, October–December, 1998. 相似文献
2.
We have analyzed our long-term (1995–2008) JHKLM photometry for three variable RV Tau supergiants. It follows from this analysis that: the amplitude of the JHK brightness variations is approximately the same, 0
m
. 9–1
m
, for the three stars; a negative linear trend is noticeable in the variations of the mean J brightness for AC Her; and the mean J brightness of R Sct and V Vul remained constant. The observed J brightness fluctuations in the supergiants are shown to be consistent either only with the temperature pulsations (AC Her
and V Vul) or with the temperature and radial pulsations (R Sct). We have detected long-term pulsations in the J brightness and J-H color variations of the supergiants with the following characteristic time scales: ∼1500 days (AC Her), ∼3500 days (R Sct),
and ∼800 and ∼1500 days (V Vul). Our search for a periodic component in the infrared brightness variations of the three stars
has revealed periods that differ from those obtained from optical observations. We show that relatively hot dust shells (T
d ∼ 700–800 K) exist around the supergiants under study; the densest and most massive shell was observed for V Vul. The ranges
of optical-depth variations for the dust shells were τ(1.25 μm) ≈ 0.04–0.10 (AC Her), ≈0.02–0.12 (R Sct), and ≈0.18–0.32 (V Vul). The spectral types in the infrared varied over
narrower ranges than those that followed from optical observations of these stars. 相似文献
3.
R. Vasundhara 《Journal of Astrophysics and Astronomy》1989,10(1):85-88
Results of a search for occultations of stars in the SAO catalogue by Saturn’s outer magnetosphere during 1989-1990 are presented.
A total of nine events are predicted to occur during this period. The most favourable event will be the occultation of 28
Sgr (SAO 187255) during July 2–3, 1989. Occultations of SAO 187036, SAO 188348 and SAO 188120 occur near opposition and therefore
can be observed over a wide longitude range 相似文献
4.
The comparison of the brightness and area of coronal holes (CH) to the solar wind speed, which was started by Obridko et al. (Solar Phys.
260, 191, 2009a) has been continued. While the previous work was dealing with a relatively short time interval 2000 – 2006, here we have
analyzed the data on coronal holes observed in the Sun throughout activity Cycle 23. A catalog of equatorial coronal holes
has been compiled, and their brightness and area variations during the cycle have been analyzed. It is shown that CH is not
merely an undisturbed zone between the active regions. The corona heating mechanism in CH seems to be essentially the same
as in the regions of higher activity. The reduced brightness is the result of a specific structure with the magnetic field
being quasi-radial at as low an altitude as 1.1R
⊙ or a bit higher. The plasma outflow decreases the measure of emission from CH. With an adequate choice of the photometric
boundaries, the CH area and brightness indices display a fairly high correlation (0.6 – 0.8) with the solar wind velocity
throughout the cycle, except for two years, which deviate dramatically – 2001 and 2007, i.e., the maximum and the minimum of the cycle. The mean brightness of the darkest part of CH, where the field lines are nearly
radial at low altitudes, is of the order of 18 – 20% of the solar brightness, while the brightness of the other parts of the
CH is 30 – 40%. The solar wind streams originate at the base of the coronal hole, which acts as an ejecting nozzle. The solar
wind parameters in CH are determined at the level where the field lines are radial. 相似文献
5.
Ch. V. Sastry 《Solar physics》1994,150(1-2):285-294
We have mapped the continuum emission from the undisturbed Sun at a wavelength of 8.7 m during 1981–1985 using the large decameter-wave
radiotelescope at Gauribidanur, India with a resolution of 26 #x00D7; 38 arc min. During the period August 6–30, 1983, the
Sun was exceptionally quiet at meter and decameter wavelengths, and we were able to make maps on several consecutive days.
On these days the position of the centroid of the radio Sun agreed quite closely with the center of the optical Sun indicating
that there is very little or no contribution from active regions. But the observed peak brightness temperature varied from
100 000 to 700 000 K. The half-power widths of the brightness distribution were in the range of 3 to 4R
⊙. The variations of the brightness temperature and the half-power widths are not correlate. It is therefore suggested that
the variations of the brightness temperature are not caused by uniform density variations or due to scattering by an irregular
corona. 相似文献
6.
Observations of 35 long-period variables have been done mainly at the Byurakan Astrophysical Observatory during the last years.
A polarimetric monitoring of 34 stars has been carried out with simultaneous photometric measurements for some of them. Photometric
data in the UBVR bands have been obtained for the star Y Ori, which is the faintest one. The results show that the degree
of light polarization is correlated with the period and brightness of these stars. This indicates that the degree of light
polarization is connected with the mass loss as well. Finally the photoelectric observations of the stars Y Ori, T Cep, R
Gem, and R Boo show a short-term increase of their brightness in the decreasing branch of their light curves. The measured
(U-B) or (B-V) colors of detected rapid variations are bluer than the colors of the star measured before these events. It
is supposed that the change of polarization with time, the relatively blue colors of miras near their minimum brightness,
and the colors of detected rapid variations may be explained by the influence of a invisible blue companion, as in the case
of the star R Aqr.
Published in Astrofizika, Vol. 42, No. 3, pp. 341–350, July–September, 1999. 相似文献
7.
We present new photometric data and analyze long-term UBV observations of three candidates for protoplanetary nebulae—F supergiants with infrared excesses at high Galactic latitudes—IRAS
18095+2704, IRAS 19386+0155, and IRAS 19500-1709. All these stars exhibit quasi-periodic low-amplitude variations caused by
pulsations against the background of long-term brightness trends. For IRAS 18095+2704=V887 Her, we have found a pulsation
period of 109 days and revealed a linear brightness trend—the star brightens at constant (within the limits of the measurement
errors) yearly mean color indices. The light curve of IRAS 19386+0155=V1648 Aql in 2000–2008 is represented by a wave with
a fundamental period of 102 days whose modulation with a close period of 98 days leads to variations with a variable amplitude.
V1648 Aql also shows a systematic rise in V brightness along with a reddening. IRAS 19500–1709=V5112 Sgr exhibits irregular pulsations with periods of 39 and 47 days.
The long-term variability component of V5112 Sgr may indicate that the star is binary. 相似文献
8.
We report the results of spectropolarimetric observations of the supergiant ζ Ori A made with 6-m BTA telescope of the SAO RAS. We found regular variations of line profiles in the spectrum of the star
with a period of 1–3 hours and point to their possible association with nonradial photospheric pulsations. We also searched
for a possible weak magnetic field in ζ Ori A, but observations did not confirm the existence of such a field in the star considered. 相似文献
9.
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
10.
High-frequency quasi-periodic variations (HF QPOs) in the X-ray light curves of black hole X-ray novae can be understood as
oscillations of the accretion disk in a nonlinear 3:2 resonance. An m = 0 vertical oscillation near a black hole modulates the X-ray emission through gravitational lensing (light-bending) at
the source. Certain oscillations of the accretion disk will also modulate the mass accretion rate, and in neutron-star systems
this would lead to nearly periodic variations in brightness of the luminous boundary layer on the stellar surface – the amplitude
of the neutron-star HF QPOs would be thus increased relative to the black hole systems.
The “kHz QPOs” in black holes are in the hecto-Hz range. 相似文献
11.
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
12.
A. V. Getling 《Solar physics》2006,239(1-2):93-111
Two series of solar-granulation images – the La Palma series of 5 June 1993 and the SOHO MDI series of 17 – 18 January 1997
– are analysed both qualitatively and quantitatively. New evidence is presented for the existence of long-lived, quasi-regular
structures (first reported by Getling and Brandt, Astron. Astrophys. 382, L5 (paper I), 2002), which no longer appear unusual in images averaged over 1 – 2-hour time intervals. Such structures appear
as families of light and dark concentric rings or families of light and dark parallel strips (“ridges” and “trenches” in the
brightness distributions). In some cases, rings are combined with radial “spokes” and can thus form “web” patterns. The characteristic
width of a ridge or trench is somewhat larger than the typical size of granules. Running-average movies constructed from the
series of images are used to seek such structures. An algorithm is developed to obtain, for automatically selected centres,
the radial distributions of the azimuthally averaged intensity, which highlight the concentric-ring patterns. We also present
a time-averaged granulation image processed with a software package intended for the detection of geological structures in
aerospace images. A technique of running-average-based correlations between the brightness variations at various points of
the granular field is developed and indications are found for a dynamical link between the emergence and sinking of hot and
cool parcels of the solar plasma. In particular, such a correlation analysis confirms our suggestion that granules – overheated
blobs – may repeatedly emerge on the solar surface. Based on our study, the critical remarks by Rast (Astron. Astrophys. 392, L13, 2002) on the original paper by Getling and Brandt (paper I) can be dismissed. 相似文献
13.
In the present work we give the results of photometric and polarimetric observations of the star SAO 124414 simultaneously in the BVR ranges of the spectrum. The observations were made over three years at Byurakan Astrophysical Observatory. Strong variations in the degree of light polarization in all three spectral ranges were recorded while the star's brightness was constant during the observations. It is confirmed that the recorded polarization has a stellar character. An analysis of the polarimetric measurements did not reveal periodicity in the variations of the degree of polarization. 相似文献
14.
Multicolor photometric data are presented for the asynchronous polar V1500 Cyg during 2000–2009, i.e., 23–35 years after its
outburst. Some examples of individual light curves of the system are shown. An analysis of these reveals large variations
in its brightness and color with the phase of the orbital period owing to a “reflection effect” caused by reradiation from
the side of the red dwarf facing the hot white dwarf and heated by its hard ultraviolet radiation. The variations in the O-C
residuals and in the maximum intensity with the phase of the synodic period are illustrated. It is found that the amplitude
A of the orbital fluctuations increases in proportion to the intensity I at a rate dA/dI=0.64. This behavior of V1500 Cyg
is most likely caused by periodic shading of the illuminated part of the red dwarf, where the degree of shading depends on
the phase of the synodic cycle. 相似文献
15.
We present a detailed analysis of the soft X-ray (0.1–2.4 keV) emission of the Seyfert 1 galaxy Mrk 926 in order to investigate
its long-term variation. The X-ray data were obtained from the ROSAT-PSPC archives. The light curves show a gradual decrease
of brightness for a time scales of 36months with the exception of a single flare event superimposed on the gradual variation
of brightness. The light variations for three different energy bands and the hardness ratios were investigated to search for
correlations; no correlation was confirmed. In order to compare spectral variations during the flare event with other periods,
the spectral parameters were determined. Results of our analysis are discussed within the framework of the accretion disk
phenomenon.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
16.
V. P. Arkhipova N. P. Ikonnikova G. V. Komissarova V. F. Esipov 《Astronomy Letters》2006,32(9):594-603
We present the results of our photoelectric observations of HD 51585 (OY Gem), a B[e] star with an infrared excess and a candidate for protoplanetary nebulae, obtained with a 60-cm telescope at the Crimean Station of the Sternberg Astronomical Institute in 1992–2005. The star exhibited rapid irregular brightness variations with amplitudes from We present the results of our photoelectric observations of HD 51585 (OY Gem), a B[e] star with an infrared excess and a candidate
for protoplanetary nebulae, obtained with a 60-cm telescope at the Crimean Station of the Sternberg Astronomical Institute
in 1992–2005. The star exhibited rapid irregular brightness variations with amplitudes from
in the V band to
in U band within the observing season as well as slow systematic variations with amplitudes from
in the V band to
in the U band and with a quasi-period of ∼2800 days. The B-V color index varied within
and did not follow the slow systematic brightness variations, while U-B correlated with the U brightness and varied between
at maximum light and
at minimum light. Our low-resolution spectroscopy performed in 1994–2005 has revealed significant variability of the Balmer
and Paschen hydrogen emission lines as well as the He I and O I lines. Equivalent widths are given for the H I, He I, O I,
and Fe II lines; a correlation has been found between the star’s photometric variability and the hydrogen line intensities.
Our joint analysis of the photometric and spectroscopic data suggests that variations in a strong stellar wind are responsible
for the variability of the star.
Original Russian Text ? V.P. Arkhipova, N.P. Ikonnikova, G. V. Komissarova, V. F. Esipo, 2006, published in Pis’ma v Astronomicheskiĭ
Zhurnal, 2006, Vol. 32, No. 9, pp. 662–671. 相似文献
17.
Photoelectric observations of the RS CVn type non-eclipsing binary UX Arietis obtained at Nizamiah Observatory during the
observing seasons of 1975–76, 1981–82 and 1982–83 are presented. The light curve of UX Ari showed a distortion wave with an
amplitude inV varying from 0.02 mag during 1975–76 to 0.15 mag during 1982–83. An analysis of the available data shows that the light maximum
is almost constant. It is also evident that the light-curve minimum decreases as the wave amplitude increases. The constant
light at maximum,V = 6.51 ± 0.03 indicates the unspotted photospheric brightness. It is also suggested that the variation in meanV brightness is mainly due to spot activity and not due to intrinsic variation. 相似文献
18.
E. P. Pavlenko 《Astrophysics》2006,49(1):105-119
Series of photometric CCD observations of the asynchronous polar BY Cam in a low accretion state (R = 14m–16m) were made on the K-380 telescope at the Crimean Astrophysical Observatory (CrAO) over 100 hours in the course of 31 nights
during 2004–2005. A period of P
1 = 0.137120±0.000002 days was found for the variations in the brightness, along with less significant periods of P
2 = 0.139759±0.000003 and P3 = 0.138428±0.000002 days, where P2 and P3 are obviously the orbital and rotation periods, while the dominant period P1 is the sideband period. A modulation in the brightness and an amplitude of 0.137 days in the oscillations at the orbital-rotational
beat period (synodic cycle) of 14.568±0.003 day are found for the first time. The profile of the modulation period is four
humped. This indicates that the magnetic field has a quadrupole component, which shows up well during the low brightness state.
Accretion takes place simultaneously into two or three accretion zones, but at different rates. The times of the times of
maxima for the main accretion zone vary with the phase of the beat period. Three types of variation of this sort are distinguished:
linear, discontinuous, and chaotic, which indicate changes in the accretion regimes. At synodic phases 0.25 and 0.78 the bulk
of the stream switches by 180°, and at phase 0.55, by ∼75°. At phases of 0.25–0.55 and 0.55–0.78, the O-C shift with a period
of 0.1384 days, which can be explained by a retrograde shift of the main accretion zone relative to the magnetic pole and/or
a change in the angle between the field lines and the surface of the white dwarf owing to the asynchronous rotation. For phases
of 0.78–1.25 the motion of the accretion zone is quite chaotic. It is found that synchronization of the components occurs
at a rate of less than dProt/Prot∼10−9 day/day.
__________
Translated from Astrofizika, Vol. 49, No. 1, pp. 121–137 (February 2006). 相似文献
19.
V. V. Shimansky S. A. Pozdnyakova N. V. Borisov I. F. Bikmaev V. V. Vlasyuk O. I. Spiridonova A. I. Galeev S. S. Mel’nikov 《Astrophysical Bulletin》2009,64(4):349-364
We analyze the physical state and the properties of the close binary systems HS 1857+5144 and Abell 65. We took the spectra
of both systems over a wide range of orbital phases with the 6-m telescope of the Special Astrophysical Observatory of the
Russian Academy of Sciences (SAO RAS) and obtained their multicolor light curves with the RTT150 and Zeiss-1000 telescopes
of the SAO RAS. We demonstrate that both Abell 65 and HS 1857+5144 are young precataclysmic variables (PV) with orbital periods
of P
orb
= 1.
d
003729 and P
orb
= 0.
d
26633331, respectively. The observed brightness and spectral variations during the orbital period are due to the radiation
of the cold component, which absorbs the short-wave radiation of the hot component and reemits it in the visual part of the
spectrum. A joint analysis of the brightness and radial velocity curves allowed us to find the possible and optimum sets of
their fundamental parameters. We found the luminosity excesses of the secondary components of HS 1857+5144 and Abell 65 with
respect to the corresponding Main Sequence stars to be typical for such objects. The excess luminosities of the secondary
components of all young PVs are indicative of their faster relaxation rate towards the quiescent state compared to the rates
estimated in earlier studies. 相似文献
20.
We consider a model for the cyclic brightness variations of a young star with a low-mass companion that accretes matter from
the remnants of a protostellar cloud. At small inclinations of the binary orbit to the line of sight, the streams of matter
and the density waves excited in the circumbinary disk can screen the primary component of the binary from the observer. To
study these phenomena, we have computed grids of hydrodynamic models for binary systems by the SPH method based on which we
have calculated the phase light curves for the different orientations of the orbit. The model parameters were varied within
the following ranges: the component mass ratio q = 0.01–0.1 and the eccentricity e = 0–0.5. We adopted optical grain characteristics typical of circumstellar dust. Our computations have shown that the brightness
oscillations with orbital phase can have a complex structure. The amplitudes and shapes of the light curves depend strongly
on the inclination of the binary orbit and its orientation relative to the observer and on the accretion rate. The results
of our computations are used to analyze the cyclic activity of UX Ori stars. 相似文献