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1.
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   

2.
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   

3.
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   

4.
Radical readjustments in the photometric activity of young stars owing to sudden changes in the circumstellar extinction are discussed using the light curves of two UX Ori type stars, CQ Tau and V1184 Tau, as examples. Changes of this sort can be caused by large deviations from axial symmetry in the distribution of circumstellar dust, as well as by large variations in the mass accretion rate in circumstellar disks. A large amount of dust may also appear in the vicinity of a young star owing to collisions of planetesimals. __________ Translated from Astrofizika, Vol. 51, No. 1, pp. 5–13 (February 2008).  相似文献   

5.
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   

6.
The rotational velocities of young stars of the UX Ori type and related objects are analyzed. It is shown that there is a weak but statistically significant correlation between υsin i and the amplitudes of photometric variability of these stars. It reflects the fact that the brightness variability of this type of star is determined mainly by variations in the column density of circumstellar dust along the line of sight. The latter depends, in turn, on the orientation of the circumstellar disk and is greatest when the disk is oriented edgeon to the observer or at a small angle to the line of sight. Translated from Astrofizika, Vol. 43, No. 3, pp. 329-337, July– September, 2000.  相似文献   

7.
UBVRI photometric observations and models of spotting are presented for four noneclipsing RS CVn systems: IN Com (G5III/IV), IL Com (F8V+F8V), UX Ari (K01V+G5V), and V711 Tau (K1IV+G5V). A low amplitude variability caused by cold (T=1700K)spots which can occupy up to 19% of the star's surface is confirmed for the little-studied star IL Com. Long-term light curves are constructed and the stellar magnitudes and color indices of the unspotted photospheres are estimated for IN com, UX Ari, and V711 Tau. It is shown that UX Ari becomes bluer with decreasing brightness, so its variability cannot be fully explained in terms of cold spots. Models of spotting on In Com and V711 Tau are constructed from the full set of available photometric observations. The spots on both of these variables lie at middle latitudes and occupy up to 22% (In Com) and 33% (V711 Tau) of the stars' surfaces. Both stars manifest a tendency for the width of the spots to decrease as their area increases. This is a crude analog of the Maunder butterflies. These stars experience cyclical spot activity and have a differential rotation of the type found on the sun.  相似文献   

8.
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   

9.
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   

10.
VV Orionis is a detached eclipsing binary system consisting of stars of spectral types B1 V and B4 V with a period of 1.d4854. There is also a third component whose orbital period about the eclipsing pair is about 120 days. In recent years there have been several new photoelectric and spectroscopic investigations of this system, and the results of these are compared. Both the geometric and photometric orbital elements appear to be well determined. VV Ori A appears to be of normal size and mass for its spectral class, but VV Ori B seems to be somewhat smaller than would be expected for a normal B4 V star. Linear limb-darkening coefficients are derived for VV Ori A, and these are in good agreement with theory. This system is of particular importance, because it is only one of very few earlytype systems for which reliable limb-darkening coefficients can be expected to be obtained. The contribution of the light of the third component to the system has also been determined, and it appears most likely that VV Ori C is a star of spectral type A3 V.Paper presented at the Lembang-Bamberg IAU Colloquium No. 80 on Double Stars: Physical Properties and Generic Relations, held at Bandung, Indonesia, 3–7 June, 1983.  相似文献   

11.
We present our photometric observations of the T Tauri star H 187. They confirm our conclusion that a new extended eclipse has begun in this young object. By the end of 2005, H 187 reached its minimum light following which its brightness began to slowly increase. Comparison with the previous ～3.5-yr-long eclipse observed by Cohen et al. shows that the new eclipse follows the previous eclipse fairly closely and, hence, it was caused by a second passage of the same extended dust or gas-dust cloud around the object. We have estimated the period between these events to be 4.7 yr. The object reddened during the eclipse, suggesting that the extinction was produced by small grains ～0.1μm in size. Possible mechanisms of such unusual eclipses are discussed. We draw an analogy between these eclipses and the cycles of photometric activity observed in UX Ori stars. Light curves similar to those observed for H 187 are shown to be obtained in the model of a young binary system with a low-mass companion accreting matter from the remnants of a protostellar cloud at a rate of ～10?9 M ⊙ yr?1.  相似文献   

12.
Photopolarimetry of the classic Herbig Ae star VV Ser was carried out at the Crimean Astrophysical Observatory as a part of the longterm program of UX Ori type stars monitoring. An exceptionally deep minimum, down to V = 14m8, was observed in 1998. For the first time for this star the blueing effect was detected in U – B and B – V color indexes. Record-high for UX Ori stars linear polarization (12.8 ± 1.4% in B) was observed in this minimum.  相似文献   

13.
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   

14.
We present a photometric study of three chromospherically active stars with long periods (V340 Gem, SAO 62042 and FI Cnc). The observations were made at the ÇOMU Observatory in 2006 and 2007. We have made initial photometric analyses of V340 Gem and SAO 62042, which are newly discovered RS CVn–type SB1 binaries, and established the photometric variations of FI Cnc, which is a single G8III active star. Photometric rotation periods of these stars were obtained by analyzing their light variations. The light variations, observed over three or more consecutive orbital cycles, were investigated by using spot models with the program SPOT. We also discussed the surface differential rotation coefficient for the primary component of the SB1 binary star SAO 62042 in this study, using our own photometric period together with an orbital period taken from the literature.  相似文献   

15.
In the course of photopolarimetric monitoring of the Herbig Ae star WW Vul, an unusual variation of linear polarization upon energence from a deep minimum was recorded, which cannot be explained by the standard mechanism for such objects (UX Ori stars): a variable contribution of radiation scattered by circumstellar dust. An analysis of possible causes of the anomalous behavior of polarization shows that it was most likely due to the presence of aligned, aspherical dust grains in the dust cloud crossing the line of sight at that time.  相似文献   

16.
Photoelectric (UBVR) observations of the eclipsing variable EQ Ori are presented. The ephemerides of primary minima are refined, and the range of the star’s light variations is determined. All light curves are solved by Lavrov’s direct method, and highly accurate photometric orbital elements are obtained for the system. The magnitudes and colors of each component are calculated and analyzed in two-color (U-B)-(B-V) and (U-B)-(V-R) diagrams. The system’s primary component is classified as a metallic-line Am star. The absolute parameters of the components are estimated, and the binary is classified as a detached system with a subgiant: A0 V and K2 IV. EQ Ori has a faint physical companion, which causes the epochs of primary minimum to be systematically displaced with a period of about 30 years. The expected parameters of the distant companion are estimated. The system’s components are at a pre-ZAMS evolutionary stage, with their age being 2×106 years. EQ Ori is thought to be a member of the Ori I association.  相似文献   

17.
Photometric and high resolution spectroscopic data for the Herbig star HD 52721 obtained from October 2009 through October 2010 are presented. We confirm the cyclical character of the photometric variability of HD 52721 discovered previously by others. The variability shows up as minima in the light curve of this star which repeat with a period P = 0d.805 and are typical of eclipsing binary systems. ASAS data covering an observation period from September 2003 through December 2009 show that two neighboring photometric minima differ from one another, and the actual orbital period of the system must be twice as high (P = 1d.610). This is confirmed by the spectroscopic data. These show that the center of gravity of the emission Hα line and the profile of the HeI 6678 line with a distinct, bright circumstellar component have a clear correlation with a period of 1d.610. To all appearances, HD 52721 is a close binary system consisting of two class B2 stars with quite similar parameters. We propose that the observed cyclical variations in the circumstellar parameters may be related to the existence of a global azimuthal inhomogeneity within the shell which rotates synchronously with the orbital motion of the system components.  相似文献   

18.
This study presents an investigation of the orbital period variations of five Algol type binaries, UX Leo, RW Mon, EQ Ori, XZ UMa and AX Vul based on all available minima times. The O–C diagrams of all systems exhibit a periodic variation superimposed on a downward parabolic segment. The mass loss due to magnetic braking effect in the cooler components is assumed to account for the parabolic variation with a downward shape, while it is suggested that the light-time effect (LITE) due to an unseen component around the eclipsing binaries explains the tilted sinusoidal changes in their O–C diagrams. The orbital period decrease rates for the systems are estimated as approximately between about 0.7 and 2.5 s per century. It is clearly seen that mass loss effect is more dominant than the expected mass transfer for classical Algols in this study. The minimum mass of the probable third bodies around the eclipsing pairs was calculated to be ?0.5 M⊙ except for UX Leo, in which it was estimated to be approximately 0.9 M⊙. In order to search for third lights in the light curves of five systems, the V-light curves of the systems were analyzed and their physical and photometric parameters were determined. For UX Leo, a significant third light contribution was determined. We found a very small third light that can be tested using multi-color light curves, for RW Mon, EQ Ori and XZ UMa, while a third light for AX Vul could not be exposed.  相似文献   

19.
The results of photographic and photoelectric observations for the star Y Ori are presented. During these observations a red nebulosity appeared around the star Y Ori near the maximum of brightness. The optical sizes of the nebulosity are comparable with the OH sizes of long period variables and OH/IR stars. A real brightness increase on the decreasing branch of the light curve was detected in U spectral band.Published in Astrofizika, Vol. 38, No. 4, pp. 555–558, October–December, 1995.  相似文献   

20.
Using the GADGET-2 code modified by us, we have computed hydrodynamic models of a protoplanetary disk perturbed by a low-mass companion. We have considered the cases of circular and eccentric orbits coplanar with the disk and inclined relative to its midplane. During our simulations we computed the column density of test particles on the line of sight between the central star and observer. On this basis we computed the column density of circumstellar dust by assuming the dust and gas to be well mixed with a mass ratio of 1: 100. To study the influence of the disk orientation relative to the observer on the interstellar extinction, we performed our computations for four inclinations of the line of sight to the disk plane and eight azimuthal directions. The column densities in the circumstellar disk of the central star and the circumbinary disk were computed separately. Our computations have shown that periodic column density oscillations can arise in both inner and circumbinary disks. The amplitude and shape of these oscillations depend on the system’s parameters (the orbital eccentricity and inclination, the component mass ratio) and its orientation in space. The results of our simulations can be used to explain the cyclic brightness variations of young UX Ori stars.  相似文献   

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