共查询到20条相似文献，搜索用时 15 毫秒
1.
2.
Flavio Scappini Cesare Cecchi-Pestellini Claudio Codella Alexander Dalgarno 《Monthly notices of the Royal Astronomical Society》2000,317(1):L6-L10
HCO+ has been detected for the first time towards the star Cygnus OB2 No. 12 through emission of the 1–0 rotational transition at 89 GHz. The CO( J =2−1) transition has also been observed. The observations are consistent with a model of dense regions embedded in a low-density clump gas. If actually present, the dense component would have an aggregate size L 1300 au, in agreement with estimates of small-scale density fluctuations observed along diffuse lines of sight. 相似文献
3.
Michael De Becker Gregor Rauw Jean-Pierre Swings 《Astrophysics and Space Science》2005,297(1-4):291-298
We present the results of an intensive spectroscopic campaign in the optical waveband revealing that Cyg OB2 #8A is an O6+O5.5
binary system with a period of about 21.9 days. Cyg OB2 #8A is a bright X-ray source, as well as a non-thermal radio emitter.
We discuss the binarity of this star in the framework of a campaign devoted to the study of non-thermal emitters, from the
radio waveband to γ-rays. In this context, we attribute the non-thermal radio emission from this star to a population of relativistic
electrons, accelerated by the shock of the wind-wind collision. These relativistic electrons could also be responsible for
a putative γ-ray emission through inverse Compton scattering of photospheric UV photons, thus contributing to the yet unidentified
EGRET source 3EG J2033+4118.
Based partly on data Obtained at the Observatoire de Haute-Provence, France. 相似文献
4.
K. L. Page J. P. Osborne P. A. Evans G. A. Wynn A. P. Beardmore R. L. C. Starling M. F. Bode A. Ibarra E. Kuulkers J.-U. Ness G.J. Schwarz 《Monthly notices of the Royal Astronomical Society》2010,401(1):121-130
We present extensive, high-density Swift observations of V2491 Cyg (Nova Cyg 2008 No. 2). Observing the X-ray emission from only one day after the nova discovery, the source is followed through the initial brightening, the super-soft source phase and back to the pre-outburst flux level. The evolution of the spectrum throughout the outburst is demonstrated. The UV and X-ray light curves follow very different paths, although changes occur in them around the same times, indicating a link between the bands. Flickering in the late-time X-ray data indicates the resumption of accretion. We show that if the white dwarf (WD) is magnetic, it would be among the most magnetic known; the lack of a periodic signal in our later data argues against a magnetic WD, however. We also discuss the possibility that V2491 Cyg is a recurrent nova, providing recurrence time-scale estimates. 相似文献
5.
Saul J. Adelman 《Monthly notices of the Royal Astronomical Society》1999,310(1):146-156
Elemental abundances of the moderately rotating B9–A3 stars λ UMa, 59 Her, 14 Cyg and 29 Cyg have been derived in a consistent manner with previous studies of this series from spectrograms obtained with Reticon and CCD detectors. The derived elemental abundances show that λ UMa is a mild Am star, while 59 Her is slightly metal-rich. Although 14 Cyg has values closer to solar than these stars, its subsolar Ca and Sc abundances indicate that it might be the hottest known hot-Am star. 29 Cyg is a metal-poor λ Boo star. 相似文献
6.
E. Gallo R. P. Fender R. I. Hynes 《Monthly notices of the Royal Astronomical Society》2005,356(3):1017-1021
Observations of V404 Cyg performed using the Westerbork Synthesis Radio Telescope at four frequencies, over the interval 1.4–8.4 GHz, have provided us with the first broad-band radio spectrum of a 'quiescent' stellar mass black hole. The measured mean flux density is of 0.35 mJy, with a spectral index α=+0.09 ± 0.19 (such that S ν ∝να ). Synchrotron emission from an inhomogeneous partially self-absorbed outflow of plasma accounts for the flat/inverted radio spectrum, in analogy with hard-state black hole X-ray binaries, indicating that a steady jet is being produced between a few 10−6 and a few per cent of the Eddington X-ray luminosity. 相似文献
7.
8.
Richard G. McMahon Robert S. Priddey Alain Omont Ignas Snellen Stafford Withington 《Monthly notices of the Royal Astronomical Society》1999,309(1):L1-L5
We present polarization observations of the gravitational lens system B1422+231 made at 8.4 GHz using the VLBA and the 100-m telescope at Effelsberg. All four images of the quasar show structure on the milliarcsec scale. The three bright images show tangential stretching as expected from lens models. Some basic properties of gravitational lensing are exhibited by this system. The surface brightness of images A and B are the same and the parity reversal expected in image B is revealed, for the first time, by polarization observations. There is a large differential Faraday rotation between images A and B. 相似文献
9.
10.
C. Clarke G. Lodato S. Y. Melnikov M. A. Ibrahimov 《Monthly notices of the Royal Astronomical Society》2005,361(3):942-954
We present the results of a photometric monitoring campaign of three well-studied FU Orionis systems (FU Orionis, V1057 Cygni and V1515 Cygni) undertaken at Maidanak Observatory between 1981 and 2003. When combined with photometric data in the literature, this data base provides a valuable resource for searching for short time-scale variability – both periodic and aperiodic – as well as for studying the secular evolution of these systems. In the case of V1057 Cyg (which is the system exhibiting the largest changes in brightness since it went into outburst) we compare the photometric data with time-dependent models. We show that prior to the end of the 'plateau' stage in 1996, the evolution of V1057 Cyg in the V –( B − V ) colour–magnitude diagram is well represented by disc instability models in which the outburst is triggered by some agent – such as an orbiting planet – in the inner disc. Following the end of the plateau phase in 1996, the dimming and irregular variations are consistent with occultation of the source by a variable dust screen, which has previously been interpreted in terms of dust condensation events in the observed disc wind. Here we instead suggest that this effect results from the interaction between the wind and an infalling dusty envelope, the existence of this envelope having been previously invoked in order to explain the mid-infrared emission of FU Orionis systems. We discuss how this model may explain some of the photometric and spectroscopic characteristics of FU Orionis systems in general. 相似文献
11.
12.
J. C. A. Miller-Jones † E. Gallo ‡ M. P. Rupen A. J. Mioduszewski W. Brisken R. P. Fender P. G. Jonker T. J. Maccarone 《Monthly notices of the Royal Astronomical Society》2008,388(4):1751-1758
Observations of the black hole X-ray binary V404 Cyg with the very long baseline interferometer the High Sensitivity Array (HSA) have detected the source at a frequency of 8.4 GHz, providing a source position accurate to 0.3 mas relative to the calibrator source. The observations put an upper limit of 1.3 mas on the source size (5.2 au at 4 kpc) and a lower limit of 7 × 106 K on its brightness temperature during the normal quiescent state, implying that the radio emission must be non-thermal, most probably synchrotron radiation, possibly from a jet. The radio light curves show a short flare, with a rise time of ∼30 min, confirming that the source remains active in the quiescent state. 相似文献
13.
14.
15.
Sz. Csizmadia Zs. Nagy T. Borkovits T. Hegedüs I.B. Bír Z.T. Kiss 《Astronomische Nachrichten》2008,329(1):39-43
EM Cygni is a Z Cam‐subtype eclipsing dwarf nova. Its orbital period variations were reported in the past but the results were in conflict to each other while other studies allowed the possibility of no period variation. In this study we report accurate new times of minima of this eclipsing binary and update itsO –C diagram.We also estimate the mass transfer rate in EM Cygni system and conclude that the mass transfer is far from the critical value. The mass transfer rate determined from the eclipse timings is in agreement with the spectroscopically determined value. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
16.
The extinction curves of single clouds, seen towards the stars HD 147165, 179406 and 202904, have been modelled using various mixtures containing both the bare and inhomogeneous (composite and/or multilayer) grains. It has been shown that the models composed of the bare graphite and silicate grains together with the multilayer grains containing silicates, organic refractory and water ice, are more useful in explaining extinction under the reduced cosmic abundances. The models based on Mathis' composite grains or on Greenberg & Li's core-mantle grains can also provide quite good fits of the extinction and the measured scattering parameters, but still require an excessive amount of carbon which results in too large a C/O ratio. The inhomogeneous grains essentially contribute to the extinction in practically the whole wavelength range of our extinction curves. As a rule, such grains have quite wide size distributions, centred at around 100 nm, although graphite grains are mainly of small sizes. 相似文献
17.
Spectral and photographic observations of an 11′×11′ region in the center of the known association Cyg OB7 are presented.
The observations were made on the 2.6-m telescope of the Byurakan Astrophysical Observatory in 2004. The spectral camera SCORPIO,
a multiregime focal reducer for the primary focus, was used. One new HH node and three new emission stars were discovered
in the region under study. One of the previously known emission stars is found to have spectral class M0Ve and to lie at a
distance of 200 pc. Some variability is detected in the brightness of a known infrared nebula and the cometary nebula CN2.
__________
Translated from Astrofizika, Vol. 49, No. 3, pp.375–390 (August 2006). 相似文献
18.
Janet E. Drew R. Greimel M. J. Irwin S. E. Sale 《Monthly notices of the Royal Astronomical Society》2008,386(4):1761-1773
Stellar photometry derived from the INT/WFC Photometric Hα Survey (IPHAS) of the Northern Galactic plane can be used to identify large, reliable samples of A0–A5 stars. For every A-type star, so identified, it is also possible to derive individual reddening and distance estimates, under the assumption that most selected objects are on or near the main sequence, at a mean absolute r ' magnitude of 1.5–1.6. This study presents the method for obtaining such samples and shows that the known reddenings and distances to the open clusters NGC 7510 and NGC 7790 are successfully recovered. A sample of over 1000 A-type stars is then obtained from IPHAS data in the magnitude range 13.5 < r ' < 20 from the region of sky including the massive northern OB association Cyg OB2. An analysis of these data reveals a concentration of ∼200 A stars over an area about a degree across, offset mainly to the south of the known 1–3 Myr old OB stars in Cyg OB2: their dereddened r ' magnitudes fall in the range 11.8–12.5. These are consistent with a ∼7 Myr old stellar population at distance modulus DM = 10.8, or with an age of ∼5 Myr at DM = 11.2. The number of A-type stars found in this clustering alone is consistent with a lower limit to the cluster mass of ∼104 M⊙ . 相似文献
19.
We have searched our previously published radio surveys of the Cygnus X region for faint radio point sources that may be associated with luminous stars of the Cyg OB2 association. Five positional coincidences have been found between stars and 1420 MHz radio sources. A particularly interesting example is the Wolf-Rayet star VCLS 146, which has shown a rapid change in 1420 MHz flux density. In addition, sensitive upper limits have been derived for the emission from 14 early-type stars, which help establish the time history of their non-thermal radio emission. Two radio features have been detected which have the properties of cometary HII regions, except that they are several arcminutes in size. Their detection provides evidence of recent star formation in Cyg OB2. 相似文献
20.
Young Woon Kang Ho-il Kim Woo-Baik Lee Kyu-Dong Oh 《Monthly notices of the Royal Astronomical Society》2001,325(2):707-714
We present BVR full-light curves of V388 Cyg to provide a complete photometric solution for the first time. The light curves show a high degree of asymmetry (O'Connell effect). The maxima at 0.25 phase (Max I) are 0.023, 0.018 and 0.012 mag higher than those at 0.75 phase (Max II) in B , V and R , respectively. Three possible spot models are applied to fit the asymmetric light curves of V388 Cyg, in order to explain the O'Connell effect. We conclude that the model of the cool spot on the cooler star is the most reasonable model for V388 Cyg. The continuous period variation is confirmed by recently collected times of minima, including one minimum that is determined in this paper. The period decrease rate is estimated as d p /d t =−2.055×10−7 d yr−1 . 相似文献