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1.
On the basis of the published times of minima and our own observations, we analysed the period change of the Algol-type eclipsing binary CU Pegasi. Over almost seventy years of observations, the parabolic period change has been clearly seen as dP/dt = 1.38 × 10−6 d/year. The estimated mass transfer in the system is about 1 × 10−7 MM⊙/year. 相似文献
2.
The results of spectroscopic observations on the 6-m telescope in 1978–1994 are given for V350 Cep, a T Tauri star with an
unusual light curve, located in the star-forming region NGC 7129. A general characterization of the spectrum is given, with
the relative intensities and radial velocities of the main lines, and manifestations of spectral variability are described.
Strong fluorescence in Fe I lines is observed. A pronounced strengthening and shift of H and Ca II emission in 1982 indicate
the ejection of an additional shell. At the same time, no evolutionary changes typical offuors are found in the spectrum of
V350 Cep. The star may be an EX Lupi object (an exor).
Translated from Astrofizika, Vol. 42, No. 2, pp. 165–178, April–June, 1999 相似文献
3.
In January 2005 spectral observations of the radio source Z0254+43 were made on the BTA at the Special Astrophysical Observatory
(SAO) of the Russian Academy of Sciences (RAN) and its red shift was found to be z=4.057. The BVRI magnitudes were found to
be 22.68, 21.19, 19.94, and 19.23, respectively. Photometric observations in December 2005 on the Zeiss-1000 at the SAO revealed
no significant variation in the optical emission from this object over that year. We can discuss its variability on an hourly
time scale with some caution. The variability of the flux from Z0254+43 was observed from 1990–2005 on the RATAN-600 over
a wide range of frequencies. It turns out that the amplitude of the variability is minimal at a frequency of ∼8 GHz. A model
for the variability has been constructed which yields an estimate of ∼28° for the orientation of the jet of Z0254+43 to the
line of sight. The luminosity of Z0254+43 in the optical range is ∼2·1026 W/Hz and in the radio frequency range, ∼2·1027 W/Hz.
__________
Translated from Astrofizika, Vol. 49, No. 2, pp. 209–220 (May 2006). 相似文献
4.
Multicolor photometric and polarimetric observations of the eclipsing binary EK Cep at the Crimean Astrophysical Observatory
in 1995 and 2006–2007 are reported. Polarimetric observations were made of stars in the neighborhood of EK Cep. It is shown
that the observed linear polarization of EK Cep is determined by a variable circumstellar constituent, as well as by the interstellar
component. Various possible mechanisms for formation of the intrinsic polarization of binary stars are discussed.
Translated from Astrofizika, Vol. 52, No. 1, pp. 117–126 (February 2009). 相似文献
5.
L. Hric V. Breus N. A. Katysheva S. Yu. Shugarov P. Dubovský 《Astronomische Nachrichten》2014,335(4):362-366
We present the results of 10 years of photometric CCD observations of the intermediate polar V709 Cas obtained by using different instruments during 2003–2013. We detected a new variability with a period of Pnew = 0.d016449979(5) which seems to be real. The spin variability is not clearly seen in all our data, so we are unable to study any evolution of the white dwarf rotation. From the best night (in 2010) we obtained a spin period of Pspin = 311.s8(5). We analyzed the orbital variability using (O – C) analysis. We found no variations of the orbital period on a timescale of 10 years, but the linear fit to the (O – C) diagram shows that the value of the orbital period is Porb = 0.d2222123(6), which is close to the earlier published values. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
6.
At present, long-term (over 30 years) multicolor photometric observations give the possibility to determine general properties
of spotted areas on late-type stars. Star-spot modeling from broadband photometric data has been carried out by Alekseev and
Gershberg since 1996 under the assumption that spots are situated in two latitudinal zones. Here we propose a new analysis
of their results for several G and K dwarf stars with high irregular activity. On these stars, EK Dra, VY Ari, V775 Her, and
V833 Tau, two spot belts exist separately and do not merge into a single equatorial active region, as occurs on cooler red-dwarf
stars. The zonal spottedness models allow us to fit simultaneously both rotational modulation and long-term variability of
stellar brightness. These models give evidence for an equatorward drift of the lower latitude boundary of the spotted region,
φ0, during the rising phase of activity, beyond any possible errors concerned with our methodology. In order to evaluate the
drift rate we introduce the concept of `effective' spot belt, whose width is independent of longitude. This permits us to
construct butterfly diagrams for stellar spots. The equatorward drift rates of the lower boundary of the spotted region D=dφlow/dt are (− 1)–(− 2) deg year−1 in the years of increasing spottedness. These values are less than the analogous solar one D≈−4 deg year−1 for the rising phase of the cycle. Thus, cyclic activity can be revealed from butterfly diagrams and derived drifts of starspots
prior to a possible detection from the spectral analysis of photometric variability. Finally, we briefly discuss a possible
explanation of high-latitude activity and surface drifts of starspots in the framework of the current state of dynamo theory. 相似文献
7.
The Total Irradiance Monitor (TIM): Science Results 总被引：2，自引：0，他引：2
The solar observations from the Total Irradiance Monitor (TIM) are discussed since the SOlar Radiation and Climate Experiment
(SORCE) launch in January 2003. The TIM measurements clearly show the background disk-integrated solar oscillations of generally
less than 50 parts per million (ppm) amplitude over the ∼2 ppm instrument noise level. The total solar irradiance (TSI) from
the TIM is about 1361 W/m2, or 4–5 W/m2 lower than that measured by other current TSI instruments. This difference is not considered an instrument or calibration
error. Comparisons with other instruments show excellent agreement of solar variability on a relative scale. The TIM observed
the Sun during the extreme activity period extending from late October to early November 2003. During this period, the instrument
recorded both the largest short-term decrease in the 25-year TSI record and also the first definitive detection of a solar
flare in TSI, from which an integrated energy of roughly (6± 3)×1032 ergs from the 28 October 2003 X17 flare is estimated. The TIM has also recorded two planets transiting the Sun, although
only the Venus transit on 8 June 2004 was definitive. 相似文献
8.
We present the results of our study of the H2O maser emission from the source W75N, which is associated with a star-forming region, between November 1994 and March 1999. The observations were carried out with the RT-22 radio telescope of the Pushchino Radio Astronomy Observatory (Lebedev Physical Institute). The maser emission in 1994–1999 can be represented as a superposition of flares of separate components with a duration from two to six months, which occurred mainly in the radial-velocity range 8–17.5 km s?1. We detected a regular drift of the velocity centroid from 13 to 9 km s?1 and an abrupt change in its velocity from 9 to 5 km s?1, which took place at the initial stage of maser activity. Based on the variability of the total H2O flux in all years of our observations of W75N (from December 1979 through March 1999), we conclude that the long-period variability of the water-vapor maser emission has a period of ～11.5 years. We give arguments that this variability is mainly associated with the most compact group of maser spots, whose positions coincide with the position of the continuum source VLA 2. 相似文献
9.
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
10.
Slow magnetohydrodynamic (MHD) standing wave oscillations in hot coronal loops for both strong (i.e. τd/P∼ 1) and weak (i.e. τd/P≥ 2) damping are investigated taking account of viscosity, thermal conductivity and optically thin radiation. The individual
effect of the dissipative terms is not sufficient to explain the observed damping. However, the combined effect of these dissipative
terms is sufficient to explain the observed strong damping, as well as weak damping seen by SUMER. We find that, the ratio
of decay time (τd) and period (P) of wave, i.e., τd/P (which defines the modes of damping, whether it is strong or weak) is density dependent. By varying density from 108 to 1010 cm−3 at a fixed temperature in the temperature range 6 – 10 MK, observed by SUMER, we get two sets of damping: one for which τ
d/P∼ 1 corresponds to strong damping that occurs at lower density and another that occurs at higher density for which τd/P ≥ 2 corresponds to weak damping. Contrary to strong-damped oscillations, the effect of optically thin radiation provides
some additional dissipation apart from thermal conductivity and viscosity in weak-damped oscillations. We have, therefore,
derived a resultant dispersion relation including the effect of optically thin radiation. Solutions of this dispersion relation
illustrate how damping time varies with physical parameters of loops in both strong and weak damping cases. 相似文献
11.
Several new precise times of minima, based on CCD observations, have been secured for the relatively seldom studied eclipsing
binary V865 Cyg (P=0d.365 days). Its O–C diagram was analysed and new light elements are given. We showed that there is probably no parabolic period increase in V865 Cyg.
Instead, a single abrupt period increase can be distinguished in the O–C diagram. 相似文献
12.
Yuangui Yang 《Astrophysics and Space Science》2008,314(1-3):151-162
This paper presents charge-couple device (CCD) photometric observations for the eclipsing binary AW UMa. The V-band light
curve in 2007 was analyzed using the 2003 version of the Wilson–Devinney code. It is confirmed that AW UMa is a total eclipsing
binary with a higher degree of contact f=80.2% and a lower mass ratio of q=0.076. From the (O−C) curve, the orbital period shows a continuous period decrease at a rate of dP/dt=−2.05×10−7 d yr−1. The long-term period decrease suggested that AW UMa is undergoing the mass transfer from the primary component to the secondary
one, accompanied by angular momentum loss due to mass outflow L
2. Weak evidence indicates that there exists a cyclic variation with a period of 17.6 yr and a small amplitude of A=0.
d
0019, which may be attributed to the light-time effect via the third body. If the existence of an additional body is true,
it may remove a great amount of angular momentum from the central system. For this kind of contact binary, as the orbital
period decreases, the shrinking of the inner and outer critical Roche lobes will cause the contact degree f to increase. Finally, this kind of binary will merge into a single rapid-rotation star. 相似文献
13.
Results from optical photometric observations of the pre-main sequence star GM Cep are reported in the paper. The star is
located in the field of the young open cluster Trumpler 37—a region of active star formation. GM Cep shows a large amplitude
rapid variability interpreted as a possible outburst from EXor type in previous studies. Our data from BVRI CCD photometric observations of the star are collected from June 2008 to February 2011 in Rozhen observatory (Bulgaria) and
Skinakas observatory (Crete, Greece). A sequence of sixteen comparison stars in the field of GM Cep was calibrated in the
BVRI bands. Our photometric data for a 2.5 years period show a high amplitude variations ($\Delta V \sim2\mbox{$\Delta V \sim2\mbox{) and two deep minimums in brightness are observed. The analysis of collected multicolor photometric data shows the typical
of UX Ori variables a color reversal during the minimums in brightness. On the other hand, high amplitude rapid variations
in brightness typical for the Classical T Tauri stars also present on the light curve of GM Cep. Comparing our results with
results published in the literature, we conclude that changes in brightness are caused by superposition of both: (1) magnetically
channeled accretion from the circumstellar disk, and (2) occultation from circumstellar clouds of dust or from features of
a circumstellar disk. 相似文献
14.
V. P. Arkhipova V. F. Esipov N. P. Ikonnikova G. V. Komissarova A. M. Tatarnikov B. F. Yudin 《Astronomy Letters》2009,35(11):764-779
We present new results of our UBV photometry for HD 179821=V1427 Aql, an F supergiant with an infrared excess, from 2000 to 2008. The semiregular low-amplitude
(ΔV = 0.
m
05−0.
m
20) photometric variability of the star with a cycle period from 130 to 200 days is caused by pulsations, along with the instability
of a variable stellar wind. V1427 Aql also exhibits a long-term trend in the brightness and colors that is probably attributable
to a change in the stellar temperature as a result of mass loss episodes, which cause variations in the continuum formation
level. We present the results of our JHKLM photometry for V1427 Aql in 1992–2008. We trace the trend in the near-infrared brightness, which agrees with the long-term
variability in the V band. Based on broadband photometry, we have determined the color excess for V1427 Aql: E(B−V) = 0.7. Based on low-resolution spectroscopy, we have estimated the stellar temperature and revealed variability of the Hα line caused by a change in the contribution from the emission component. The hypotheses of whether the star belongs to post-AGB
objects or to massive yellow hypergiants are discussed. 相似文献
15.
Based on our spectroscopic observations of the variable planetary nebula IC 4997 in 2003–2009, we have obtained the relative
fluxes in optical emission lines. The interstellar extinction c = 0.35 has been found from the Balmer decrement by taking into account the effect of self-absorption in hydrogen lines in
dense nebular regions. The variations in the Balmer decrement point to variability of the self-absorption and circumstellar
extinction. We have investigated the variations in the relative intensities of some spectral lines and their ratios with time.
The drop in the ratios F(λ4363)/F(Hγ) and F(λ363)/F(λ4959) that began back in 1990–1995 has continued, suggesting a decrease in the electron density and temperature in the central
nebular region. The ratio F(λ6731)/F(λ6717) has remained constant. It gives an estimate for the electron density in the outer regions of IC 4997, N
e
∼ 104 cm−3. 相似文献
16.
A. A. Arkharov E. V. Ruban V. V. Novikov L. I. Yagudin T. Yu. Puzakova R. Zalles 《Astronomy Letters》2006,32(8):566-568
We present the results of our spectrophotometric observations of 64 southern stars in the wavelength range 320–730 nm. These
results are extra-atmospheric quasi-monochromatic fluxes from the stars expressed in absolute energy units (W m−2 m−1) at spectral intervals of 2.5 nm.
Published in Russian in Pis’ma v Astronomicheskiĭ Zhurnal, 2006, Vol. 32, No. 8, pp. 628–630.
The article was translated by the authors. 相似文献
17.
We present the observations of the Irr galaxy IC 10 at the 6-m SAO telescope with the panoramic Multi-Pupil Fiber Spectrograph
(MPFS). Based on the results of these observations and our long-slit spectroscopy performed previously, we have investigated
the ionized-gas emission spectrum in the region of intense star formation and refined the gas metallicity estimates. We show
that the “diagnostic diagrams” constructed from our observations agree best with the new improved ionization models by Martin-Manjon
et al. Using these models, we have determined the electron density and gas ionization parameter and ionizing-cluster characteristics,
the age and mass, from the spectra of the investigated HII regions. The cluster ages and masses are shown to be within the
ranges 2.5–5 Myr and (0.2–1) × 105
M
⊗, respectively. 相似文献
18.
A. I. Belova V. F. Suleimanov I. F. Bikmaev I. M. Khamitov G. V. Zhukov D. S. Senio I. Yu. Belov N. A. Sakhibullin 《Astronomy Letters》2013,39(2):111-125
We present the results of photometric observations of a bright cataclysmic variable TT Ari with an orbital period of 0.13755 days. CCD observations were carried out with the Russian-Turkish RTT 150 telescope in 2001 and 2004 (13 nights). Multi-color photoelectric observations of the system were obtained with the Zeiss 600 telescope of SAO RAS in 1994–1995 (6 nights). In 1994–1995, the photometric period of the system was smaller than the orbital one (0 . d 132 and 0 . d 134), whereas it exceeded the latter (0 . d 150 and 0 . d 148) in 2001, 2004. An additional period exceeding the orbital one (0 . d 144) is detected in 1995 modulations. We interpret it as indicating the elliptic disc precession in the direction of the orbital motion. In 1994, the variability in colors shows periods close to the orbital one (0 . d 136, b-v), as well as to the period indicating the elliptic disk precession (0 . d 146, w-b). We confirm that during the epochs characterized by photometric periods shorter than the orbital one, the quasi-periodic variability of TT Ari at time scales about 20 min is stronger than during epochs with long photometric periods. In general, the variability of the system can be described as a “red” noise with increased amplitudes of modulations at characteristic time scales of 10–40 min. 相似文献
19.
K. S. Dwarakanath Siddharth Malu Ruta Kale 《Journal of Astrophysics and Astronomy》2011,32(4):529-532
We have discovered a giant radio halo in the massive merging cluster MACSJ0417.5-1154. This cluster, at a redshift of 0.443,
is one of the most X-ray luminous galaxy cluster in the MAssive Cluster Survey (MACS) with an X-ray luminosity in the 0.1–2.4
keV band of 2.9×1045 erg s − 1. Recent observations from GMRT at 230 and 610 MHz have revealed a radio halo of ∼ 1.2 × 0.3 Mpc2 in extent. This halo is elongated along the North-West, similar to the morphology of the X-ray emission from Chandra. The
1400 MHz radio luminosity (L
r) of the halo is ∼2 × 1025 W Hz − 1, in good agreement with the value expected from the L
x − L
r correlation for cluster halos. 相似文献
20.
We present the results of our photometric (V RI) and spectroscopic observations of the young variable star V730 Cep (MisV1147) classified by Uemura et al. (2004) as a Herbig Be star. Our photometry confirms the conclusion of the above authors that this star has a complex pattern of variability including periodic or quasi-periodic brightness variations with a period of about 14 days and deep Algol-like minima typical for UX Ori stars. Our spectroscopy shows that the classification of V730 Cep as a Herbig Be star is wrong. Actually, this star has a much lower temperature and belongs to the family of T Tauri stars. This allows us to explain the nature of the unusual photometric activity of V730 Cep based on a combination of two well-known models of variable circumstellar extinction applied to young stars: AA Tau- and UX Oritype variability. It follows from our observations that the color tracks on the V ?(V ?I) color–magnitude diagram for these models slightly differ: the AA Tau-type variability of circumstellar extinction is caused by larger grains than the UX Ori-type variability. Such a difference can be due to an increase in the characteristic sizes of circumstellar dust as the star is approached and has a simple explanation: small dust grains evaporate faster than large ones. 相似文献