Light variations in the candidate for protoplanetary objects HD 179821=V1427 Aql in 1899–1999     

V. P. Arkhipova  N. P. Ikonnikova  R. I. Noskova  G. V. Sokol  S. Yu. Shugarov 《Astronomy Letters》2001,27(3):156-162

We present photoelectric and photographic observations of the supergiant HD 179821 with a large infrared excess, a candidate for protoplanetary objects. Over, ten years of our UBV observations, the star exhibited semiregular light variations with amplitudes $\Delta V = 0\mathop .\limits^m 10$ , $\Delta B = 0\mathop .\limits^m 15$ , and $\Delta U = 0\mathop .\limits^m 25$ , as well as systematic color and light variations. From 1990 until 1996, the yearly mean U-B and B-V color indices decreased by 0.25 and 0.15, respectively. After 1996, the motion of the star in the two-color (B-V)-(U-B) diagram upward and to the left slowed down. The color excess that we derived from our observations, by assuming that the star’s spectral type was F3 I in the 1990s, is E(B-V)=1.0. The photographic observations of HD 179821 from 1899 until 1989 show that its brightness m _pg generally increased while significantly fluctuating. An analysis of the observational data suggests that HD 179821 is most likely a post-AGB star of intermediate or low mass.  相似文献   

Photometric variability and spectrum of the post-AGB candidate IRAS 19200+3457     

V. P. Arkhipova  N. P. Ikonnikova  R. I. Noskova  G. V. Komissarova  V. F. Esipov 《Astronomy Letters》2004,30(11):779-784

We present our photoelectric and spectroscopic observations of the early B supergiant with an IR excess IRAS 19200+3457, a poorly known post-AGB candidate. The star has been found to be photometrically variable. We observed rapid irregular brightness variations with amplitudes up to \(\Delta V = 0\mathop .\limits^m 4, \Delta B = 0\mathop .\limits^m 4\), and \(\Delta U = 0\mathop .\limits^m 5\). IRAS 19200+3457 and three other hot post-AGB stars—V886 Her, V1853 Cyg, and LSIV—12°111—exhibit a similar variability pattern. Our low-resolution spectroscopic observations in the period 2001–2003 show that the spectrum of IRAS 19200+3457 represents an early B star with hydrogen emission lines originating from a circumstellar gaseous envelope. The HeI λ5876 Å, λ6678 Å, λ7065 Å, and OI λ7774 Å lines are in absorption. The hydrogen and, probably, HeI lines proved to be variable. Our observations confirm the conclusion that IRAS 19200+3457 belongs to the class of intermediate-mass protoplanetary objects.  相似文献   

Study of the optical variability of T Tau in the period 1962–2003     

S. Yu. Mel’nikov  K. N. Grankin 《Astronomy Letters》2005,31(2):109-116

We present the results of our long-term U BV R observations of the star T Tauri performed at Mt. Maidanak Observatory from 1986 until 2003. These data, together with previous photoelectric observations of other authors, suggest that the long-term variations of the light curve are not periodic, but have a cycle with a time scale of 6–9 yr. The light curve also exhibits slower variations with time scales of ～30–40 yr. We confirm the existence of periodic brightness variations with a period of \(P = 2\mathop .\limits^d 798\) over many years; this process is peculiar in that the phase and shape of the phase curve change from season to season. We analyze the color behavior of the star. We found evidence of a strong flare occurred on October 5, 1999, when the brightness of the star reached \(9\mathop .\limits^m 22\). This is the strongest flare recorded during its photoelectric observations.  相似文献   

Photometric variability of the protoplanetary nebula LSIV-12°111     

V. P. Arkhipova  N. P. Ikonnikova  R. I. Noskova  G. V. Komissarova 《Astronomy Letters》2002,28(4):257-260

We present our photometric observations of an early B supergiant with an infrared excess, the protoplanetary object LSIV-12°111, and the previously suspected variable star NSV 24971. We confirm its photometric variability. During two observing seasons (2000–2001), the star exhibited rapid irregular light variations with amplitudes $\Delta V \sim 0\mathop .\limits^m 3$ , $\Delta B \sim 0\mathop .\limits^m 3$ , and $\Delta U \sim 0\mathop .\limits^m 4$ and a time scale of ～1^d. There is no correlation between the colors and magnitudes of the star. The variability patterns of LSIV-12°111 and two other hot post-AGB stars, V886 Her and V1853 Cyg, are shown to be similar.  相似文献   

Nova Monocerotis 2002 (V838 Mon) at early outburst stages     

V. P. Goranskii  A. V. Kusakin  N. V. Metlova  S. Yu. Shugarov  E. A. Barsukova  N. V. Borisov 《Astronomy Letters》2002,28(10):691-700

We obtained U BV R photometric and spectroscopic observations during the outburst of V838 Mon. Before its outburst, the B brightness of the star had been stable ( $\tilde15.^m 85$ ) for 45 years. This was a blue star with the color index $(B - V)_0 = - 0\mathop .\limits^m 03 \pm 0\mathop .\limits^m 1$ and may have been a cataclysmic variable. In the middle of March 2002, the outburst amplitude reached $8\mathop .\limits^m 1$ in B. The star has the counterpart V 1006/7 in M 31 in luminosity at maximum and in spectrum. The unusual spectrum at the premaximum stage originated in the expanding photosphere of a cool K-type giant. The expansion velocity of the photosphere was 150 km s^?1; the maximum velocity in the expanding stellar envelope reached 500 km s^?1. The absorption components of neutral metal lines were enhanced by a factor of 3 or 4 compared to a normal K-type star. No overabundance of s-process elements was found. One day before the brightness peak, an intense Hα emission line with broad wings, FWZI=3100 km s^?1, and numerous lines of ionized metals appeared in V838 Mon, which is characteristic of normal classical novae. We show light, color, and spectral variations of the object.  相似文献   

Photometric variability and spectral features of the protoplanetary nebula LSII + 34° 26 = V1853 Cyg     

V. P. Arkhipova  N. P. Ikonnikova  R. I. Noskova  G. V. Komissarova  V. G. Klochkova  V. F. Esipov 《Astronomy Letters》2001,27(11):719-727

We present photoelectric and spectroscopic observations of the protoplanetary object V 1853 Cyg, a B supergiant with an IR excess. Over two years of its observations, the star exhibited rapid irregular light variations with amplitudes $\Delta V = 0\mathop .\limits^m 3$ , $\Delta B = 0\mathop .\limits^m 3$ , $\Delta U = 0\mathop .\limits^m 4$ and no correlation between color and magnitude. Its mean magnitude has not changed since the first UBV observations in 1973 (Drilling 1975). Low-resolution spectroscopic observations show that the spectrum of V 1853 Cyg in 2000 corresponded to that of a B1–B2 star with T _eff ～ 20000 K. High-resolution spectroscopic observations confirm the conclusion that the profiles of absorption and emission lines are variable. We identified the star’s spectral lines and measured the equivalent widths of more than 40 lines. The star’s radial velocity is 〈V _r 〉= ?49 × 5 km s^?1, as measured from absorption lines, and ranges from–50 to–85 km s^–1 for different lines, as measured from shell emission lines. The velocity of the dust clouds on the line of sight determined from diffuse interstellar bands (DIBs) and from interstellar Na I lines is 〈V _r 〉= ?16 × 5 km s^?1. The P Cyg profiles of the He I λ5876 Å and λ6678 Å lines suggest an ongoing mass loss by the star. An analysis of the observational data confirms the conclusion that the star belongs to the class of intermediatemass protoplanetary objects.  相似文献   

Further photometric observations of the X-ray binary A0535+26/V725 Tau: A new activity cycle     

G. V. Zaitseva 《Astronomy Letters》2005,31(2):103-108

We performed new photoelectric U BV observations of the X-ray binary A0535+26 at the Crimean Station of the Sternberg Astronomical Institute in 1998–2003. After the brightness stabilized at a minimum of about 500 days in duration, a new brightness rise steeper than that observed previously began: the brightness increased over two seasons of observations by a total amplitude of \(0\mathop .\limits^m 5\). The physical parameters (T _e , n _e ) of the additional emission that caused this brightening match, within the error limits, were obtained from the averaged over 15 years, data, that include both the ascending and descending branches of the light curve. We found a delay of the variations in the Hα line relative to the continuum, which is no more than one year.  相似文献   

Disk precession and quasi-periodic brightness oscillations of V603 Aql in 2001–2002     

V. Suleimanov  I. Bikmaev  K. Belyakov  N. Sakhibullin  G. Zhukov  Z. Aslan  U. Kiziloglu  I. Khamitov 《Astronomy Letters》2004,30(9):615-629

We present the photometric observations of the old nova V603 Aql with the RTT 150 Russian-Turkish telescope during eleven nights of 2001–2002. We show that the star at this time was in a state with positive superhumps and its photometric period of \(0\mathop .\limits^d 144 - 0\mathop .\limits^d 145\) was longer than the orbital period. We found night-to-night variations in the mean brightness of the system that are consistent with disk precession periods of \(3\mathop .\limits^d 3\) and \(3\mathop .\limits^d 0\) in 2001 and 2002, respectively. Analysis of the results and their comparison with the results of other authors using current theoretical models for disk precession lead us to suggest that the change in the disk precession period was caused by a change in the accretion rate in the system. V603 Aql in a state with negative superhumps was found to be brighter than it is in a state with positive superhumps by \(0\mathop .\limits^m 2 - 0\mathop .\limits^m 3\). We hypothesize that the transition between these states could also be caused by a change in the accretion rate. Quasi-periodic oscillations (QPOs) of the brightness with typical time scales of 9–70 min were detected on each observing night. These time scales were found to change from night to night. The detection of QPOs with a period of about 0.05 of the orbital period and its multiples on certain nights provides evidence for the model of QPO generation through accretion-rate modulation by ionization-front oscillations on the surface of the donor star near the inner Lagrangian point.  相似文献   

Spectroscopic components in the multiple systems ADS 10683 and ADS 11791     

M. G. Smekhov 《Astronomy Letters》2002,28(6):393-396

We presents the results of our study of new spectroscopic components in the visual binaries ADS 10683 (HD 160 239=BD?154 635=HIP 86412; G6/G8V; \(V = 9\mathop .\limits^m 08\); \(B - V = 0\mathop .\limits^m 76\); 2000: 17^h39^m24^s, ?15°46′) and ADS 11791 (HD 175039=BD?054 798=HIP 92726; G5; \(V = 8\mathop .\limits^m 78\); \(B - V = 0\mathop .\limits^m 72\); 2000: 18^h53^m42^s, ?05°33′). ADS 10683B and ADS 11791A are single-lined spectroscopic binaries; their orbital periods are \(6\mathop .\limits^d 9171 \pm 0\mathop .\limits^d 0002\) and \(50\mathop .\limits^d 514 \pm 0\mathop .\limits^d 004\), respectively. We constructed their radial velocity curves and computed their spectroscopic orbital elements.  相似文献   

Continuum spectrum of the star Θ1 Ori C     

E. A. Vitrichenko 《Astronomy Letters》2000,26(4):244-249

Published photoelectric measurements over a wide wavelength range (0.36–18 µm) are used to study the continuum spectrum of the star Θ¹ Ori C. The model that assumes the following three radiation sources is consistent with observations: (1) a zero-age main-sequence O7 star (object 1) of mass M ₁=20M _⊙, radius R ₁=7.4R _⊙, effective temperature T ₂=37 000 K, and absolute bolometric magnitude $M\mathop {bol}\limits^1 = - 7\mathop .\limits^m 7$ ; (2) object 2 with M ₂=15M _⊙, R ₂=16.2R _⊙, T ₂=4000 K, and $M\mathop {bol}\limits^2 = - 5\mathop .\limits^m 1$ ; and (3) object 3 with R ₃10 700 R _⊙, T ₃=190 K, and $M\mathop {bol}\limits^3 = - 0\mathop .\limits^m 6$ . The visual absorption toward the system is $A_V = 0\mathop .\limits^m 95$ and obeys a normal law. The nature of objects 2 and 3 has not been elucidated. It can only be assumed that object 2 is a companion of the primary star, its spectral type is K7, and it is in the stage of gravitational contraction. Object 3 can be a cocoon star and a member of the system, but can also be a dust envelope surrounding the system as a whole.  相似文献   

Occultations of stars brighter than 15<Superscript>m</Superscript> by the largest trans-Neptunian objects in 2004–2014     

D. V. Denissenko 《Astronomy Letters》2004,30(9):630-633

We computed the occultations of stars brighter than 15^m by the largest trans-Neptunian objects (TNOs) for the next ten years. In our search, we used the following catalogs: Hipparcos; Tycho2 with the coordinates of 2838666 stars taken from UCAC2 (Herald 2003); and UCAC2 (Zacharias et al. 2003) with 16356096 stars between \(12\mathop .\limits^m 00\) and \(14\mathop .\limits^m 99\) north of ?45° declination. We predicted the occultations of stars by the seventeen largest numbered TNOs, the recently discovered 2004 DW, and four known binary Kuiper Belt objects. We selected 64 events at solar elongations of no less than 30°, including the extremely rare occultation of a \(6\mathop .\limits^m 5\) star by the double asteroid (66652) 1999 RZ₂₅₃ on October 4, 2007. Observations of these events by all available means are extremely important, since they can provide unique information about the sizes of TNOs and improve our knowledge of their orbits dramatically.  相似文献   

Estimation of errors in the distances to intrinsically reddened stars     

R. M. Raznik  O. V. Agafonova 《Astronomy Letters》2001,27(11):728-731

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A photometric study of the star V1016 Ori     

N. I. Bondar’  É. A. Vitrichenko  M. M. Zakirov 《Astronomy Letters》2000,26(7):452-459

New photoelectric UBVRI observations of the eclipsing variable V 1016 Ori have been obtained with the AZT-11 telescope at Crimean Astrophysical Observatory and with the Zeiss-600 telescope at Mount Maidanak Observatory. Light curves are constructed from the new observations and from published and archival data. We use a total of 340, 348, 386, 185, and 62 magnitude estimates in the bands from U to I, respectively. An analysis of these data has yielded the following results. The photometric elements were refined; their new values are $Min I = JDH 2441966.820 + 65\mathop .\limits^d 4331E$ . The UBVRI magnitudes outside eclipse were found to be $5\mathop .\limits^m 95$ , $6\mathop .\limits^m 77$ , $6\mathop .\limits^m 75$ , $6\mathop .\limits^m 68$ , and $6\mathop .\limits^m 16$ , respectively. No phase effect was detected. We obtained two light-curve solutions: (1) assuming that the giant star was in front of the small one during eclipse, we determined the stellar radii, r _s=0.0141 and r _g=0.0228 (in fractions of the semimajor axis of the orbit); and (2) assuming that the small star was in front of the giant one, we derived r _g=0.0186 and r _s=0.0180 for the V band. The brightness of the primary star in the bands from U to I is L ₁=0.96, 0.92, 0.90, 0.89, and 0.88, the orbital inclination is $i = 87^\circ .1$ , and the maximum eclipse phase is α₀= 0.66. In both cases, we accepted the U hypothesis, assumed the orbit to be elliptical, and took into account the flux from the star Θ¹ Ori E that fell within the photometer aperture. The first solution leads to a discrepancy between the primary radius determined by solving the light curve and the radial-velocity curve and its value estimated from the luminosity and temperature. This discrepancy is eliminated in the second solution, and it turns out that, by all parameters, the primary corresponds to a normal zero-age main-sequence star.  相似文献   

Variability of hot supergiant IRAS 19336-0400 in the early phase of planetary nebula ionization     

V. P. Arkhipova  M. A. Burlak  V. F. Esipov  N. P. Ikonnikova  G. V. Komissarova 《Astronomy Letters》2012,38(3):157-166

We present photoelectric and spectral observations of a hot candidate proto-planetary nebula—early B-type supergiant with emission lines in spectrum—IRAS 19336-0400. The light and color curves display fast irregular brightness variations with maximum amplitudes \(\Delta V = 0_ \cdot ^m 30\), \(\Delta B = 0_ \cdot ^m 35\), \(\Delta U = 0_ \cdot ^m 40\) and color-brightness correlations. By the variability characteristics IRAS 19336-0400 appears similar to other hot proto-planetary nebulae. Based on low-resolution spectra in the range λ4000–7500 Å we have derived absolute intensities of the emission lines Hα, Hβ, Hγ, [S II], [N II], physical conditions in gaseous nebula: n _e = 10⁴ cm^?3, T _e = 7000 ± 1000 K. The emission line Hα, Hβ equivalent widths are found to be considerably variable and related to light changes. By UBV-photometry and spectroscopy the color excess has been estimated: E _B-V = 0.50–0.54. Joint photometric and spectral data analysis allows us to assume that the star variability is caused by stellar wind variations.  相似文献   

Nuclear activity of NGC 5548 from UBVRI observations during 1990–2000     

V. T. Doroshenko  V. M. Lyuty  N. G. Bochkarev  N. I. Merkulova  S. G. Sergeev  V. V. Vlasyuk  V. P. Mikhailov  O. I. Spiridonova  O. V. Ezhkova  K. N. Grankin  S. Yu. Mel’nikov 《Astronomy Letters》2001,27(11):691-702

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Infrared observations of the star R Cas     

A. É. Nadzhip  A. M. Tatarnikov  V. I. Shenavrin  G. Weigelt  B. F. Yudin 《Astronomy Letters》2001,27(5):324-327

We present our JHKLM photometry for R Cas performed during 1988–2000. The pulsation period of R Cas is $P \approx 429\mathop .\limits^d 6$ , with the maximum IR brightness lagging behind the maximum visual brightness by ～0.2 P. The amplitude of light variations appreciably decreases with increasing wavelength at λ≤3 μm. At λ>3 μm, this decrease virtually ceases. There is a step on the ascending branch of IR JHK brightness. The K-L color index increases linearly with K magnitude: $K - L = 0.304K + 1\mathop .\limits^m 20$ . The color temperature dependence, T _K-L =f(K), is also linear: T _K?L = ?622K + 1100 K. In going from minimum to maximum, the K flux (as well as the bolometric flux) from the star and its color temperature T _K-L increase by a factor of ～2.2 and ～1.3, respectively.  相似文献   

Photometric and spectrophotometric observations of the classical symbiotic star YY Her during its return to quiescence     

A. A. Tatarnikova  V. F. Esipov  E. A. Kolotilov  J. Mikolajewska  U. Munari  S. Yu. Shugarov 《Astronomy Letters》2001,27(11):703-711

We present new photometric UBVRI and spectroscopic observations of the symbiotic star YY Her during its return to quiescence after a strong outburst in 1993. High-resolution spectra of YY Her at similar phases at outburst maximum ?=0.48) and in quiescence ?=0.37) are presented for the first time. The ephemeris of YY Her has been refined P=586^d). The last two observed minima (in 1999 and 2000) differed radically in shape from the 1997 minimum described previously. Both were sharp and deep $(\Delta U \sim 1\mathop .\limits^m 6, \Delta V \sim 0\mathop .\limits^m 9)$ . To explain this shape of the V light curve, which is only slightly affected by nebular emission, it should be assumed that the cool component of YY Her fills much of its Roche lobe and has a hot spot on the hemisphere facing the hot component. The emission spectrum rich in Fe II lines, which is characteristic of symbiotic stars, was observed during the outburst, but high-ionization lines (He II λ4686) were also observed. The He I λλ5876, 7065 lines exhibit distinct P Cyg profiles; the centers of the absorption components are shifted from the emission ones by V _r≈100 km s^?1, suggesting moderate outflow velocities.  相似文献   

A photometric and spectroscopic study of the Herbig Ae/Be star XY Per     

S. Yu. Melnikov  O. V. Ezhkova 《Astronomy Letters》2000,26(4):233-243

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AI canis minoris,a pulsating low-mass supergiant at an early transition phase from the AGB to the post-AGB stage of evolution     

V.?P.?Arkhipova  N.?P.?IkonnikovaEmail author  V.?F.?Esipov  G.?V.?Komissarova 《Astronomy Letters》2017,43(6):416-428

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Optical monitoring of the central region of the globular cluster M 15 = NGC 7078: New variable stars     

A. P. Zheleznyak  V. V. Kravtsov 《Astronomy Letters》2003,29(9):599-611

We obtained a series of more than two hundred R-band CCD images for the crowded central (115″×77″) region of the metal-poor globular cluster M 15 with an angular resolution of \(0\mathop .\limits^{''} 5 - 0\mathop .\limits^{''} 9\) in most images. Optimal image subtraction was used to identify variable stars. Brightness variations were found in 83 stars, 55 of which were identified with known cluster variables and the remaining 28 are candidates for new variables. Two of them are most likely SX Phe variables. The variability type of two more stars is uncertain. The remaining stars were tentatively classified as RR Lyrae variables. A preliminary analysis of published data and our results shows that the characteristics of RR Lyrae variables in the densest part (r<35″) of the cluster probably change. More specifically, the maximum of the period distribution of first-and second-overtone (RR1, RR2) pulsating stars shifts toward shorter periods; i.e., there is an increase in the fraction of stars pulsating with periods \( < 0\mathop .\limits^d 3\) and a deficiency of stars with \(0\mathop .\limits^d 35 - 0\mathop .\limits^d 40\). The ratio of the number of these short-period RR Lyrae variables to the number of fundamental-tone (RR0) pulsating variables changes appreciably. We found and corrected the error of transforming the coordinates of variables V128–155 in M 15 into the coordinate system used in the catalog of variable stars in globular clusters.  相似文献