共查询到20条相似文献，搜索用时 31 毫秒
1.
Results of observations of the long-period variable Y Ori are presented. The photoelectric observations in UBVR were made at the 60-cm telescope of the high-altitude Maydanak station of the Tashkent Astronomical Institute during the autumn of 1989. The UBVR lightcurves as well as the variations in the color indices U-B, B-V, and V-R are presented. The photographic observations were made at the 40 Schmidt telescope of the Byurakan Observatory and at the 70-cm Maksutov telescope of the Abastumani Observatory. A nebulosity was discovered around Y Ori in red light near the brightness maximum. Such a formation is observed for the first time, not only for Y Ori but also for long-period variables in general. The obtained results are discussed in this work.Translated fromAstrofizika, Vol. 38, No. 1, pp. 5–15, January–March, 1995. 相似文献
2.
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
3.
I. N. Chkhikvadze 《Astrophysics》2004,47(1):1-10
Studies of the Herbig Ae/Be star V586 Ori based on photoelectric observations in the Strömgren system are reported. It is found that as the brightness decreases, the Balmer discontinuity index initially increases and then begins to drop. As the star fades, the index decreases. We have previously found similar variations in the indices and C for UX Ori, RR Tau, and V351 Ori. It is shown that V586 Ori has the characteristics of a shell-star. 相似文献
4.
We give the results of photographic, photoelectric, and spectral observations of the flare star PP Ori. The 109 photographic observations used, which were obtained on the 40 Schmidt telescope of the Byurakan Observatory over a period of about 20 years, and four spectra obtained on the same telescope with a4° objective prism show no variation in brightness. Photoelectric observations in the UBVR bands using the 50cm and 60cm telescopes of the high-altitude Maidanak station of the Tashkent Astronomical Institute in 1987 and 1989 give grounds for suspecting a variation in brightness much larger than observational errors. Spectral observations of the star PP Ori made on the 2.6m telescope of the Byurakan Observatory show weak H emission. The results of all these observations show that PP Ori is an Orion variable of spectral class K7-M0 with absolute visual magnitude7
m
5–8
m
5.Translated fromAstrofizika, Vol. 38, No. 2, 1995. 相似文献
5.
An historical light curve for the UX Ori star CQ Tau is constructed for the period from 1939 through 2003. The star’s photometric behavior includes a cyclical component with a period of about 21 years. An analysis of the periodogram reveals a shorter cycle with a duration of about 1020 days after this cycle is subtracted. Since the photometric activity of UX Ori type stars is caused by variations in the circumstellar extinction, both of these cycles indicate the existence of large-scale deviations from axial symmetry in the distribution of matter in the circumstellar disk of CQ Tau. The orbiting of these inhomogeneities about the star also causes oscillatory variations in its brightness. An analysis of the color-magnitude diagrams reveals differences in the optical parameters of the circumstellar dust along the line of sight in various phases of the 21-year cycle: absorption by larger particles predominates near the brightness maximum of CQ Tau. This means that the reduced circumstellar extinction in this part of the circumstellar disk is the result of a smaller contribution from small particles; this may be evidence of the onset of a process of coagulation of the dust particles and their conversion into large-scale bodies and planetesimals.__________Translated from Astrofizika, Vol. 48, No. 2, pp. 165–174 (May 2005). 相似文献
6.
R. A. Kandalyan 《Astrophysics》2005,48(2):237-243
The properties of OH megamaser galaxies in the radio continuum are discussed. Many radio sources in OH megamaser galaxies exhibit relatively flat (α ≥ −0.5) radio spectra between frequencies of 1.49 and 8.44 GHz along with high brightness temperatures (Tb ≥ 104 K). In these galaxies the line and radio continuum fluxes are not correlated. The continuum radio emission of OH megamasers is predominantly nonthermal and is associated either with an active nucleus or with compact star formation. The thermal component of the radio emission from these galaxies can be neglected. The observed flat radio spectra and high brightness temperatures imply the existence of an active galactic nucleus, although some megamasers may be associated with compact star formation.__________Translated from Astrofizika, Vol. 48, No. 2, pp. 281–290 (May 2005). 相似文献
7.
V. P. Grinin A. A. Arkharov O. Yu. Barsunova S. G. Sergeev L. V. Tambovtseva 《Astronomy Letters》2009,35(2):114-120
We present the results of our infrared JHK photometry for the unusual UX Ori star V1184 Tau. Comparison with previous observations performed before the catastrophic decline in its optical brightness in 2004 (when the star faded approximately by a factor of 100) has shown the following: the star faded approximately by 2 m and 1 m in the J and H bands, respectively, while its K brightness remained almost constant. This pattern of infrared variability seems incompatible with the mechanism of variable circumstellar extinction responsible for the dramatic decline in the star’s optical brightness. However, if this mechanism is considered in the context of an accretion disk model with a puffed-up inner rim in the dust sublimation zone and with a disk wind producing an expanding gas-dust atmosphere above the disk surface, then the paradox can be resolved. In this model, the photometric activity of V1184 Tau in both visible and near-infrared spectral ranges, including the sharp brightness decline in 2004, can be explained by an increase in the geometric thickness of the disk in the dust sublimation zone caused by enhanced accretion of circumstellar matter onto the star. There is reason to believe that such events occur periodically and result from the presence of a companion to V1184 Tau moving in a highly eccentric orbit. The offered interpretation of the photometric activity of V1184 Tau allows this object to be classified as an UX Ori star based on the observed photometric effect and, at the same time, as a FU Ori star based on the pattern of the physical process that produced this effect. 相似文献
8.
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
9.
Data are presented from a spectral and photometric study of the long-period variable star Y Ori, which we have classified
as a type M7IIIe near its brightness minimum. In the blue part of the spectrum, features from a star of an earlier spectral
class are superimposed on the spectrum of a cool giant, so that a variable excess emission is observed at wavelengths of 4000–4200
Å. As opposed to the monotonically decreasing intensity of the Balmer lines (EWHα > EWHβ > EWHγ > EWHδ) in normal stars belonging to the earlier spectral classes, a reverse relationship, with EWHγ < EWHδ is detected in Y Ori.
Translated from Astrofizika, Vol. 51, No. 4, pp. 567–575 (November 2008). 相似文献
10.
Paul A. Boley rey M. Sobolev Vadim V. Krushinsky Roy van Boekel Thomas Henning Aleksei V. Moiseev Maksim V. Yushkin 《Monthly notices of the Royal Astronomical Society》2009,399(2):778-782
The intent of this study is to determine the nature of the star and associated nebulosity S 235 B, which are located in a region of active star formation still heavily obscured by the parent molecular cloud. Low-resolution ( R = 400) long-slit spectra of the star and nebulosity, and medium- ( R = 1800) and high-resolution ( R = 60 000) spectra of the central star are presented along with the results of Fabry–Perot interferometric imaging of the entire region. Based on the long-slit and Fabry–Perot observations, the nebulosity appears to be entirely reflective in nature, with the stellar component S 235 B★ providing most of the illuminating flux. The stellar source itself is classified here as a B1V star, with emission-line profiles indicative of an accretion disc. S 235 B★ thus belongs to the relatively rare class of early-type Hebrig Be stars. Based on the intensity of the reflected component, it is concluded that the accretion disc must be viewed nearly edge-on. Estimates of the accretion rate of S 235 B★ from the width of the Hα profile at 10 per cent of maximum intensity, a method which has been used lately for T Tauri stars and Brown Dwarfs, appear to be inconsistent with the mass outflow rate and accretion rate implied from previous infrared observations by Felli et al., suggesting this empirical law does not extend to higher masses. 相似文献
11.
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
12.
J. E. Dyson 《Astrophysics and Space Science》1977,51(1):197-204
The galactic nebula S206 contains a half shell of high excitation nebulosity which is centred on the associated exciting star. The suggestion has been made that this structure is caused by the interaction of stellar mass loss from the star with nebular gas. A steady state model of such an interaction is investigated quantitatively. The required mass loss rate from the star is about 10–7
M
yr–1 which is compatible with the observationally derived mass-loss rates from early-type stars. 相似文献
13.
We present our 2-year-long photometric (V, R c, I c) observations of the T Tauri star V1184 Tau. They show that the relatively quiet “photometric life” of this object, which ended in 2004 with a sharp brightness decline by four magnitudes, was succeeded by a qualitatively new (in nature) period of activity characterized by high-amplitude irregular photometric variability. Judging by its color variations, the object belongs to the class of UX Ori stars and, hence, variable circumstellar extinction is responsible for its brightness variations. Moreover, the (V?I c)/V color-magnitude diagram for the object is identical to that for UX Ori itself, suggesting that the optical properties of dust grains in the circumstellar space of these stars are similar. At the same time, V1184 Tau is quite dissimilar to UX Ori stars in its light curve, variability amplitude (reaching 4.5 magnitudes in the V band), and some other parameters. 相似文献
14.
We have made high resolution observations of HCN (1-0) emission from the carbon star Y Canum Venaticorum using the Nobeyama Millimeter Array. We find that the emission region is not well resolved by the synthesized beam of 3.7 × 4.6 over the entire velocity range (VLSR =10 to 35 km s–1). We find that the true brightness temperature probably exceeds 200 K at many velocity channels as well as at the 26 km s–1 maser spike. The broad emission component may be the result of superimposed maser spikes. The high brightness requires an unreasonably high HCN fractional abundance if LTE is assumed. It is likely that the HCN abundance previously reported for the star is considerably affected by the maser action. A new maser spike has been found at VLSR = 29 km s–1 相似文献
15.
The spectra of the star V1118 Ori obtained during the fuor-like outburst in 1989 are typical of classical T Tau stars. The Balmer emission lines of hydrogen and Call are the most prominent lines in the spectrum. A short-wavelength absorption component of the H line shifted –500 km/sec from the H peak was observed in the spectrum of December 19, 1989, which indicates an strong outflow of material from the star. The rate of fuor-like outbursts for V1118 Ori during its active period has been once every three years on the average. There is some similarity between slow out bursts and the outbursts of EXors (subfuors).Translated fromAstrofizika, Vol. 39, No. 3, pp. 365–374, July–September, 1996. 相似文献
16.
H. Hüseyin Menteşe 《Astrophysics and Space Science》1994,220(2):279-287
We have investigated the star Ori with IUE high resolution SWP spectrum in order to derive curve of growth and column densities of Al II, Si II, S II, Fe II, Ni II and Zn II. It has been possible to fit these ions on one empirical curve of growth with a velocity parameterb = 11 km s–1 for the star studied.Based on observations made by the International Ultraviolet Explorer (IUE), and collected at the Villafranca Satellite Tracking Station of the European Space Agency. 相似文献
17.
Photoelectric UBVR observations of the young irregular variable star V586 Ori are presented and discussed. 相似文献
18.
We have obtained H emission line profiles from R Aquarii, a Mira variable surrounded by a complex nebulosity, using a very high-resolution Fabry-Pérot spectrometer. A new feature that was seen in our observations is the fact that the line profile shows a splitting which we interpret as due to two expanding shells surrounding the star with velocities of 5 km s–1 and 15 km s–1. The expansion velocities show an acceleration outwards due perhaps to the radiation pressure caused momentum transfer. Possible periodic variation of radial velocity derived from observations is discussed. 相似文献
19.
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
20.