共查询到20条相似文献，搜索用时 31 毫秒
1.
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
2.
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
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.
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
5.
E. H. Semkov 《Astronomische Nachrichten》2006,327(4):328-334
We present recent results from optical photometric and spectroscopic observations of the pre‐main sequence star V1184 Tau (CB 34V). The star is associated with the Bok globule CB 34 and was considered as a FUOR candidate in previous studies. Our photometric data obtained from October 2000 to April 2003 show that the stellar brightness varies with an amplitude of about 0.m 5 (I ), but from August 2003 the photometric behavior of the star has changed dramatically. Three deep brightness minima (ΔI ∼ 4m.2) were observed during the past two years. The analysis of available photometric data suggests that V1184 Tau shows two types of variability produced (1) by rotation of large cool spotted surface and (2) by occultation from circumstellar clouds of dust or from features of a circumstellar disk. The behavior of the V – I index indicates that the star becomes redder towards minimum light, but from a certain turning point (V ∼ 18m.2) it gets bluer and is fading further. Five medium dispersion optical spectra of V1184 Tau were obtained in the period 2001–2004. Signi.cant changes in the profile and strength of the emission lines in the spectrum of V1184 Tau were found. During minimum light the equivalent width of the Hα emission line increases from 4 Å to 9 Å. The [O I] lines (λλ 6003, 6363 Å) are also seen in emission while the sodium doublet keeps its absorption strength and equivalent width. The possibility to reconstruct the historical light curve of V1184 Tau using photographical plate archives is brie.y discussed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
6.
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
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.
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
9.
V. P. Grinin O. Yu. Barsunova S. G. Sergeev N. Ya. Sotnikova T. V. Demidova 《Astronomy Letters》2006,32(12):827-831
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
10.
The photometric activity of the star BF Ori, which belongs to the family of UX Ori-type stars, is studied. New data obtained
with the ASAS robotic telescope confirm the existence of a cyclical component in the light curve for this star with a duration
of roughly 11-12 years. The form of the photometric cycle resembles the theoretical light curves for a young binary system
with a low-mass secondary component, and which is accreting matter from a surrounding common disk. Alternative mechanisms
for the cyclical variability of UX Ori stars are also discussed. 相似文献
11.
Results from optical photometric observations of the PMS star V 1735 Cyg are reported. The star is located in the IC 5146
dark cloud complex—a region of active star formation. On the basis of observed outburst and spectral properties, V 1735 Cyg
was classified as a FUor object. We present data from BVRI CCD photometric observations of the star, collected from March 2003 to January 2009. Plates from the Rozhen Schmidt telescope
archive were scanned for a brightness estimation of the star. A sequence of sixteen comparison stars in the field of V 1735
Cyg was calibrated in BVRI bands. The data from photographic observations made from 1986 to 1992 show a strong light variability (ΔV=1⋅m2). In contrast, the recent photometric data obtained from 2003 to 2009 show only small amplitude variations (ΔI=0⋅m3). The analysis of existing photometric data shows a very slow decrease in star brightness—1⋅m8 (R) for a 44 year period. The possibilities for future photometric investigations of V 1735 Cyg using the photographical
plate archives is discussed briefly. 相似文献
12.
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
13.
We present and discuss the results of our long-term JHKLM photometry for two RV Tau stars (R Sge and RV Tau) and the yellow supergiant V1027 Cyg, a candidate for protoplanetary nebulae. The amplitude of the infrared brightness variations in R Sge and RV Tau over fourteen years of observations was 0 . m 9?1 m ; the infrared brightness variations in V1027 Cyg over eighteen years did not exceed 0 . m 25. The infrared brightness and color of R Sge fluctuated about their gradually changing mean values; the infrared brightness variations agree with a period of 70.77 days. The periodic J brightness and J-H color variations in R Sge can be explained by temperature pulsations with ΔT ≤ 200 K and radial pulsations with [ΔR/R] ≤ 0.2. From 1995 to 2008, the mean J brightness of RV Tau increased, while its mean J-H color index decreased; the variations in the mean J brightness can be associated mainly with stellar temperature variations; a periodic component with P = 78.73 days is observed in the infrared brightness and color fluctuations. The variations in the mean J brightness and J-H color index of the supergiant V1027 Cyg over eighteen years of observations did not exceed a few hundredths of a magnitude; both temperature and radial pulsations may be present in the observed J brightness variations. The most probable period of the infrared brightness fluctuations in V1027 Cyg is 237 ± 2 days. The dust shell of R Sge may consist of two layers with grain temperatures of ～1000 and ～700 K; the optical depth at 1.25 µm is ～0.02 and ～0.24, respectively. The grain temperatures in the circumstellar dust shells of the supergiants RV Tau and V1027 Cyg are ～600 K (RV Tau) and ～700 K (V1027 Cyg). Their optical depths at 1.25 µm are ～0.24 (RV Tau) and ～0.008 (V1027 Cyg). 相似文献
14.
V. P. Arkhipova V. F. Esipov N. P. Ikonnikova G. V. Komissarova S. Yu. Shugarov 《Astronomy Letters》2009,35(8):534-546
New photometric observations of the variable star FG Sge, a rapidly evolving planetary nebula nucleus, were performed in 2003–2008. On 230 nights, we obtained 86 UBV and 155 BV RI (or R c , I c ) magnitude estimates. The maximum amplitude of the V-band light variations was >8 m . Six deep minima and four high maxima were observed. Analysis of the light curve has shown that the pulsation period of the star remained constant since 1991 and was P = 115 days. We have studied the wavelength dependence of the extinction at various phases of the light curve. The blueing of the B-V color at deep minima is interpreted as the result of light scattering in the circumstellar dust shell of the star formed by preceding dust ejections since 1992. Our spectroscopic observations performed on nine nights in 2003–2007 with the 125-cm telescope at the Crimean Station of the Sternberg Institute have confirmed the previously detected intensity variations of the Swan bands and the sodium doublet with brightness. It is noted that the Swan bands originate in the upper atmosphere, the star’s extended envelope, while the sodium doublet originates mainly in the circumstellar shell of FG Sge. We suggest that the star is currently located in the temperature-luminosity diagram at the turning point of the horizontal track of cooling in the direction of hot stars—evolution caused by the last helium shell flash at the planetary nebula stage. 相似文献
15.
We consider a model of cyclic brightness variations in a young star with a low-mass (q = M
2/M
1 ≤ 0.1) companion that accretes matter from the remnants of a protostellar cloud (circumbinary disk). We assume that the orbit
of the companion is circular and that its plane does not coincide with the disk plane. We have computed grids of hydrodynamic
models for such a binary by the SPH method based on which we have investigated the circumstellar extinction variations produced
by the streams of matter and density waves excited in the circumbinary disk by the orbital motion of the companion. We show
that, depending on the inclination and orientation of the binary’s line of nodes relative to the observer, the brightness
of the primary component can undergo various (in shape and depth) oscillations with a period equal to the orbital one. In
contrast to the models with coplanar circular orbits, the accretion rate onto the components of a binary with a noncoplanar
orbit depends on the orbital phase. The results of our computations can be used to study the cyclic activity of UX Ori stars
and young eclipsing binaries with anomalously long eclipses. 相似文献
16.
The systematic UBV observations of six variable post-AGB supergiants in 1991–1999 are presented. Their variability is analyzed. The coolest stars V1027 Cyg and V354 Lac exhibit bimodal pulsations with variable amplitudes. Apart from pulsations, the hotter stars V887 Her and IRAS 19386+0155 show light variations associated with a stellar wind. A variable stellar wind appears to be mainly responsible for the photometric variations in the still hotter stars SAO 163075 and IRAS 20572+4919. Distinct trends in the yearly mean brightness have been found in three of the six supergiants studied, with the trend amplitude being independent of the spectral range. They are interpreted as the result of dust envelopes composed of large grains with R=A V /E(B?V)≥7 becoming optically thin. 相似文献
17.
In the UV spectra of BP Tau, GW Ori, T Tau, and RY Tau obtained with the Hubble Space Telescope, we detected an inflection near 2000 Å in the F λ c (λ) curve that describes the continuum energy distribution. The inflection probably stems from the fact that the UV continuum in these stars consists of two components: the emission from an optically thick gas with T<8000 K and the emission from a gas with a much higher temperature. The total luminosity of the hot component is much lower than that of the cool component, but the hot-gas radiation dominates at λ<1800 Å. Previously, other authors have drawn a similar conclusion for several young stars from low-resolution IUE spectra. However, we show that the short-wavelength continuum is determined from these spectra with large errors. We also show that, for three of the stars studied (BP Tau, GW Ori, and T Tau), the accretion-shock radiation cannot account for the observed dependence F λ c (λ) in the ultraviolet. We argue that more than 90% of the emission continuum in BP Tau at λ>2000 Å originates not in the accretion shock but in the inner accretion disk. Previously, a similar conclusion was reached for six more classical T Tau stars. Therefore, we believe that the high-temperature continuum can be associated with the radiation from the disk chromosphere. However, it may well be that the stellar chromosphere is its source. 相似文献
18.
We analyzed the spectra of eight T Tauri stars (T Tau, RY Tau, CO Ori, EZ Ori, GW Ori, GX Ori, V1044 Ori, and SU Aur) in the wavelength range from 1200 to 3100 Å taken with the STIS spectrograph from the Hubble Space Telescope. For each star, we found an upper limit on the interstellar extinction A v , which proved to be lower than the values obtained by different authors from optical observations. For T Tau and RY Tau, we found the upper limits on their luminosities, masses, and radii as well as the bolometric luminosity of the excess emission continuum. The latter is most likely associated with mass accretion from a protoplanetary disk. We show that the bulk of the emission continuum is radiated in the infrared. For these stars, we determined the ratio of the flux in the C IV 1550 doublet lines to the excess-continuum flux. This ratio proved to be two orders of magnitude lower than its values predicted by the accretion-shock (AS ) models developed by Lamzin (1998) and Calvet and Gullbring (1998). This result leads us to believe that for T Tau and RY Tau, the emission continuum originates in the accretion disk and/or in the boundary layer rather than in the AS, as has been assumed previously. This implies that in these stars, only a small fraction of the accreted matter passes through the AS, while the bulk of this matter settles in the equatorial plane of the star, passing through the boundary layer. 相似文献
19.
Two flares with an amplitude of more than 0m.3 each in B and V colours and another four with less amplitude in U band were detected during photometric and polarimetric
monitoring of the nearby visual binary COU14. Irregular long term brightness and colour variations were registered while no
significant polarization signal was detected. The variability is attributed to the secondary component whose photometric properties
are similar to those of T Tau type stars. For the first time a T Tau type star has been found to be a member of a nearby binary
system with well determined orbital parameters.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
20.
《New Astronomy》2016
The known FU Ori-type young eruptive stars are exceedingly rare (a dozen or so confirmed objects) and 2MASS J06593158-0405277, with its 2014 outburst, is likely the latest addition to the family. All members have displayed just one such eruption in their recorded history, an event lasting for decades. To test the FU Ori nature of 2MASS J06593158-0405277, we have reconstructed its photometric history by measuring its brightness on Harvard photographic plates spanning the time interval 1899–1989. No previous large amplitude eruption similar to that initiated in 2014 has been found, as in bona fide FU Ori-type objects. The median value of the brightness in quiescence of 2MASS J06593158-0405277 is B = 15.5, with the time interval 1935–1950 characterized by a large variability ( ∼ 1 mag amplitude) that contrasts with the remarkable photometric stability displayed at later epochs. The variability during 1935–1950 can either be ascribed to some T Tau like activity of 2MASS J06593158-0405277 itself or to the also young and fainter star 2MASS J06593168-0405224 that lies 5 arcsec to the North and forms an unresolved pair at the astrometric scale of Harvard photographic plates. 相似文献