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Публикации по объекту
Statistical Constraints for Astrometric Binaries with Nonlinear Motion
Useful constraints on the orbits and mass ratios of astrometric binariesin the Hipparcos catalog are derived from the measured proper motiondifferences of Hipparcos and Tycho-2 (Δμ), accelerations ofproper motions (μ˙), and second derivatives of proper motions(μ̈). It is shown how, in some cases, statistical bounds can beestimated for the masses of the secondary components. Two catalogs ofastrometric binaries are generated, one of binaries with significantproper motion differences and the other of binaries with significantaccelerations of their proper motions. Mathematical relations betweenthe astrometric observables Δμ, μ˙, and μ̈ andthe orbital elements are derived in the appendices. We find a remarkabledifference between the distribution of spectral types of stars withlarge accelerations but small proper motion differences and that ofstars with large proper motion differences but insignificantaccelerations. The spectral type distribution for the former sample ofbinaries is the same as the general distribution of all stars in theHipparcos catalog, whereas the latter sample is clearly dominated bysolar-type stars, with an obvious dearth of blue stars. We point outthat the latter set includes mostly binaries with long periods (longerthan about 6 yr).
| Interstellar NaI and CaII absorption observed towards the Cygnus Loop SNR
We present high resolution spectra (R ~ 5 km s-1) of theinterstellar NaI and CaII absorption lines observed towards 9 early-typestars with distances ranging from 250 to 2300 pc in the line-of-sighttowards the Cygnus Loop Supernova Remnant (SNR). All but one of theseabsorption profiles can be fit using a combination of one or more ofthree absorption components with average best-fit (lsr) velocities ofV1 = + 0.8 km s-1, V2 = +9.0 kms-1 and V3 = +19.7 km s-1. Anadditional velocity component at V4 = +29.7 km s-1is required in order to fit the NaI profile recorded towards the star HD198946, whose distance of 794 pc places it well in excess of the nominal440 pc distance to the SNR. The NaI/CaII column density ratios for thethree higher velocity components are typically <1.0, which aresimilar to values found for high-velocity gas components detectedtowards other evolved SNRs. Even though we have detected the threehigher velocity components solely along the sight-lines towards starswith distance estimates greater than that of the Cygnus Loop, we areunable to definitely associate these components with an interactionbetween the expansion of the SN shock wave and the ambient interstellarmedium. We suggest a more likely origin for these absorption componentsis that of an old pre-cursor SN neutral gas shell, within whoseinterstellar cavity the Cygnus Loop supernova explosion occured some 20000 years ago.
| Far Ultraviolet Spectroscopic Explorer and Hopkins Ultraviolet Telescope Observations of Radiative Shocks in the Cygnus Loop
We report a combination of high and low spectral resolutionfar-ultraviolet spectral data for several groupings of bright radiativeshock filaments in the Cygnus Loop supernova remnant. Thehigh-resolution spectra were obtained with the Far UltravioletSpectroscopic Explorer (FUSE) satellite and cover the 905-1187 Åspectral region at 0.1-0.3 Å resolution, depending on observingaperture. The low-resolution data were obtained with the HopkinsUltraviolet Telescope (HUT) and cover the 850-1850 Å spectralregion at ~3 Å resolution. These data sets complement each other,with the HUT data providing the broader context of a wider range ofemission lines and the FUSE data resolving line profiles from nearbyairglow emissions and allowing detailed line profiles to be studied.Relative line intensities and line profiles change on a wide variety ofspatial scales. O VI λλ1032, 1038 emission is much moregenerally distributed than the optical filaments. The FUSE data providedirect insight into the effects and variability of self-absorption inthe strong resonance lines of O VI and C III λ977. Variability ofthe central reversals in O VI with position indicate a patchy O VIdistribution, with self-absorption occurring locally within the remnant.Self-absorption in C III could be due to the interstellar medium, thelocal regions of the remnant, or a combination. We also find evidencefor overlying molecular hydrogen absorption effects on some lines andsuggest an interstellar (foreground) origin. It is likely that theseeffects have had significant impacts on many previous investigationsthat based their results on the interpretation of low-resolutionspectral data where these effects could not be seen. Based onobservations made with the NASA-CNES-CSA Far Ultraviolet SpectroscopicExplorer. FUSE is operated for NASA by the Johns Hopkins Universityunder NASA contract NAS5-32985.
| An Einstein Observatory SAO-based catalog of B-type stars
About 4000 X-ray images obtained with the Einstein Observatory are usedto measure the 0.16-4.0 keV emission from 1545 B-type SAO stars fallingin the about 10 percent of the sky surveyed with the IPC. Seventy-fourdetected X-ray sources with B-type stars are identified, and it isestimated that no more than 15 can be misidentified. Upper limits to theX-ray emission of the remaining stars are presented. In addition tosummarizing the X-ray measurements and giving other relevant opticaldata, the present extensive catalog discusses the reduction process andanalyzes selection effects associated with both SAO catalog completenessand IPC target selection procedures. It is concluded that X-rayemission, at the level of Lx not less than 10 exp 30 ergs/s, is quitecommon in B stars of early spectral types (B0-B3), regardless ofluminosity class, but that emission, at the same level, becomes lesscommon, or nonexistent, in later B-type stars.
| A kinematic and proper-motion survey of the Cygnus Loop
H-alpha radial velocities, line widths, and line intensities based on 71Fabry-Perot interferometer scans of 61 fields in the Cygnus Loopsupernova remnant SNR are reported. Also, measurements of proper motionsat 39 locations within the Cygnus Loop are summarized. These resultsshow that the remnant is expanding asymmetrically into the ambientinterstellar medium, with rest-frame velocities as high as 380 km/s inthe near half and 150 km/s in the far half. This can plausibly beinterpreted as the result of the progenitor's evolution near a densitydiscontinuity, the consequent formation of a cavity and partial shell,and the SN's interaction with that shell. The remnant's opticallyobserved filamentary structure results from line-of-sight effects asshock waves advance into the irregular inner surface of the shell. Inthis context, the derived expansion velocities and proper motions give aformal distance to the Cygnus Loop of roughly 600 pc, with 1-sigmalimits of 300 and 1200 pc.
| The S201 far-ultraviolet imaging survey. II - A field in Cygnus
Far-ultraviolet imagery of a region in Cygnus, a 20 deg diameter fieldcentered near (1950) R. A. 21 h 31.2 m decl. +37 deg 25 arcmin, wasobtained by the S201 far-ultraviolet camera during the Apollo 16mission. In a 10 minute exposure covering the 1250-1600 A wavelengthrange (effective wavelength 1400 A), 730 star images can be detected,corresponding to a limiting ultraviolet magnitude of about m (1400) =10. Assuming nominal interstellar extinction values in this region nearthe galactic plane, this result corresponds to the detection of A0 Vstars to a distance of 300 pc and of B0 V stars to 1500 pc.Uncertainties in spectral classification and interstellar extinction forindividual objects are probably more significant than calibration ormeasurement errors. Most of the objects detected are identified withstars in the Smithsonian Astrophysical Observatory Star Catalog (1966),or the Catalog of Stellar Identifications (1979) or both, but 87 objectsremain unidentified (or are identified with late-type stars).
| Meridian observations made in Brorfelde (Copenhagen University Observatory) 1975-76.
This catalogue presents positions for selected faint stars mainly fromAGK3 observed with the 7" transit circle at Brorfelde. The stars aredistributed in 43 selected areas around radio sources and are suitableas reference stars for measuring the optical counterparts to the radiosources. The obscr 'itioi cre carried out from 1975.16 to 1976.04, andevery star was observed at least two times giving a m.s.e. of "13 forthe catalogue positions given in the FK4 system. These positions usedtogether with AGK3 proper motions will in the period 1975 to 1980 have am.s.e. at the epoch ranging from `:13 to `:15, which is less than halfof what is expected when using AGK3 positions. Key words: transit circle- catalogue of positions
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Группы:
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Наблюдательные данные и астрометрия
| Созвездие: | Лебедь |
| Прямое восхождение: | 20h53m32.71s |
| Склонение: | +30°57'04.8" |
| Видимая звёздная величина: | 7.91 |
| Расстояние: | 10000000 парсек |
| Собственное движение RA: | 5.5 |
| Собственное движение Dec: | -3 |
| B-T magnitude: | 7.832 |
| V-T magnitude: | 7.904 |
Каталоги и обозначения:
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