Contenidos
Imágenes
Subir su imagen
DSS Images Other Images
Artículos relacionados
Times of Minima for Neglected Eclipsing Binaries in 2004
Times of minima obtained during 2004 for a number of neglected eclipsingbinaries are presented.
| A Medium Resolution Near-Infrared Spectral Atlas of O and Early-B Stars
We present intermediate-resolution (R~8000-12,000) high signal-to-noise(S/N) H- and K-band spectroscopy of a sample of 37 optically visiblestars, ranging in spectral type from O3 to B3 and representing mostluminosity classes. Spectra of this quality can be used to constrain thetemperature, luminosity, and general wind properties of OB stars, whenused in conjunction with sophisticated atmospheric model codes. Mostimportant is the need for moderately high resolutions (R>=5000) andvery high signal-to-noise (S/N>=150) spectra for a meaningful profileanalysis. When using near-infrared spectra for a classification system,moderately high signal-to-noise (S/N~100) is still required, though theresolution can be relaxed to just a thousand or two. In the Appendix weprovide a set of very high-quality near-infrared spectra of Brackettlines in six early-A dwarfs. These can be used to aid in the modelingand removal of such lines when early-A dwarfs are used for telluricspectroscopic standards.
| 3D mapping of the dense interstellar gas around the Local Bubble
We present intermediate results from a long-term program of mapping theneutral absorption characteristics of the local interstellar medium,motivated by the availability of accurate and consistent parallaxes fromthe Hipparcos satellite. Equivalent widths of the interstellar NaID-line doublet at 5890 Å are presented for the lines-of-sighttowards some 311 new target stars lying within ~ 350 pc of the Sun.Using these data, together with NaI absorption measurements towards afurther ~ 240 nearby targets published in the literature (for many ofthem, in the directions of molecular clouds), and the ~ 450lines-of-sight already presented by (Sfeir et al. \cite{sfeir99}), weshow 3D absorption maps of the local distribution of neutral gas towards1005 sight-lines with Hipparcos distances as viewed from a variety ofdifferent galactic projections.The data are synthesized by means of two complementary methods, (i) bymapping of iso-equivalent width contours, and (ii) by densitydistribution calculation from the inversion of column-densities, amethod devised by Vergely et al. (\cite{vergely01}). Our present dataconfirms the view that the local cavity is deficient in cold and neutralinterstellar gas. The closest dense and cold gas ``wall'', in the firstquadrant, is at ~ 55-60 pc. There are a few isolated clouds at closerdistance, if the detected absorption is not produced by circumstellarmaterial.The maps reveal narrow or wide ``interstellar tunnels'' which connectthe Local Bubble to surrounding cavities, as predicted by the model ofCox & Smith (1974). In particular, one of these tunnels, defined bystars at 300 to 600 pc from the Sun showing negligible sodiumabsorption, connects the well known CMa void (Gry et al. \cite{gry85}),which is part of the Local Bubble, with the supershell GSH 238+00+09(Heiles \cite{heiles98}). High latitude lines-of-sight with the smallestabsorption are found in two ``chimneys'', whose directions areperpendicular to the Gould belt plane. The maps show that the LocalBubble is ``squeezed'' by surrounding shells in a complicated patternand suggest that its pressure is smaller than in those expandingregions.We discuss the locations of several HI and molecular clouds. Usingcomparisons between NaI and HI or CO velocities, in some cases we areable to improve the constraints on their distances. According to thevelocity criteria, MBM 33-37, MBM 16-18, UT 3-7, and MBM 54-55 arecloser than ~ 100 pc, and MBM 40 is closer than 80 pc. Dense HI cloudsare seen at less than 90 pc and 85 pc in the directions of the MBM 12and MBM 41-43 clouds respectively, but the molecular clouds themselvesmay be far beyond. The above closest molecular clouds are located at theneutral boundary of the Bubble. Only one translucent cloud, G192-67, isclearly embedded within the LB and well isolated.These maps of the distribution of local neutral interstellar NaI gas arealso briefly compared with the distribution of both interstellar dustand neutral HI gas within 300 pc.Tables 1 and 2 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp:cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/411/447
| Two new bright Ae stars
Two newly identified Ae stars, nu Cyg and kappa UMa, were discoveredin the course of the Magnetic Survey of Bright main sequence stars(Monin et al. 2002). We present their Hα profiles along withmeasurements of their equivalent width and parameters of emissionfeatures. Emission in the Hα line of nu Cyg is variable on atime scale of 3 years. kappa UMa exhibits weak emission which is ratherstable. The emission is thought to arise from a circumstellar disk, andwe have estimated the size of that disk.Both new emission stars are IRASsources. Their IR color excesses are consistent with those of classicalAe stars. Thus, nu Cyg and kappa UMa appear not to belong to the classof Herbig Ae/Be stars. We argue that the frequency of Ae stars may beunderestimated due to the difficulty of detection of weak emission insome A stars.Based on observations collected at the 1 m telescope of the SpecialAstrophysical Observatory (Nizhnij Arkhyz, Russia).
| Catalogue of averaged stellar effective magnetic fields. I. Chemically peculiar A and B type stars
This paper presents the catalogue and the method of determination ofaveraged quadratic effective magnetic fields < B_e > for 596 mainsequence and giant stars. The catalogue is based on measurements of thestellar effective (or mean longitudinal) magnetic field strengths B_e,which were compiled from the existing literature.We analysed the properties of 352 chemically peculiar A and B stars inthe catalogue, including Am, ApSi, He-weak, He-rich, HgMn, ApSrCrEu, andall ApSr type stars. We have found that the number distribution of allchemically peculiar (CP) stars vs. averaged magnetic field strength isdescribed by a decreasing exponential function. Relations of this typehold also for stars of all the analysed subclasses of chemicalpeculiarity. The exponential form of the above distribution function canbreak down below about 100 G, the latter value representingapproximately the resolution of our analysis for A type stars.Table A.1 and its references are only available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/407/631 and Tables 3 to 9are only available in electronic form at http://www.edpsciences.org
| Stellar and circumstellar activity of the Be star omega CMa. I. Line and continuum emission in 1996-2002
Echelle spectroscopy and mostly unaided-eye photometry of the southernBe star omega CMa were obtained in the period1996-2003. The monitoring is bracketed by two brightenings by 0.4m-0.5m.The results of a literature search suggest that such phases occur aboutonce a decade and have various commonalities. Along with thesephotometric events goes enhanced line emission. This is due to anincreased total mass of the disk as well as to a change in its densityprofile. The models by Poeckert & Marlborough(\cite{1978ApJS...38..229P}, \cite{1979ApJ...233..259P}) imply that theenhanced continuum flux originates from the inner disk. Higher-orderBalmer line emission is correlated with brightness. The increase inHα is retarded by some months, possibly indicating a time delayin filling up and ionizing the outer disk. In the (U-B) vs. (B-V) colourdiagram and the D54 vs. D34 Balmer decrementdiagram the path from the ground to the bright state is distinct fromthe return path. This could result from the bulk of the disk matterbeing in the outer (inner) disk during the photometric ground (high)state, while the two transitions between the two states are both due tochanges progressing radially outward. Some mu Cen-like outbursts(Rivinius et al. \cite{1998A&A...333..125R}) seem to occur in allphases. It is conceivable that the build-up of the inner disk is causedby more frequent or more effective outbursts. During the photometricbright state various other phenomena gain in prominence and suggest thisto be a phase of increased activity. Of particular interest, butpossibly only apparently related to this phase, are absorptioncomponents at redshifts well beyond the range covered by the combinationof rotation and nonradial pulsation.Based on observations collected at the European Southern Observatory atLa Silla, Chile, ESO (proposal nos. 55.D-0502, 56.D-0381, 58.D-0697,62.H-0319, 64.H-0548).
| Autocorrelation Analysis of Hipparcos Photometry of Short-Period Be Stars
We have used Hipparcos epoch photometry and a form of autocorrelationanalysis to investigate the amplitude and timescale of the short-periodvariability of 82 Be stars, including 46 Be stars that were analyzed byHubert & Floquet using Fourier and CLEAN analysis and 36 other Bestars that were suspected of short-period variability. Our method hasgiven useful information for about 84% of these stars; for the rest, thetime distribution of the Hipparcos epoch photometry limits thecapability of our technique.
| High-Resolution Mid-Infrared Morphology of Cygnus A
We present subarcsecond-resolution mid-infrared images at 10.8 and 18.2μm of Cyg A. These images were obtained with the University ofFlorida mid-IR camera/spectrometer OSCIR at the Keck II 10 m telescope.Our data show extended mid-IR emission primarily to the east of thenucleus with a possible western extension detected after imagedeconvolution. This extended emission is closely aligned with thebiconical structure observed at optical and near-IR wavelengths by theHubble Space Telescope. This emission is consistent with dust heatedfrom the central engine of Cyg A. We also marginally detect large-scalelow-level emission extending more than 1.5 kpc from the nucleus, whichmay be caused by in situ star formation, line emission, and/orpolycyclic aromatic hydrocarbon contamination within the bandpass of ourwide N-band filter.
| Magnetic survey of bright northern main sequence stars
The first results of a systematic search for magnetic fields in thebrightest upper main sequence (MS) stars are presented. The main goal isto survey the stars with about the same detection limit and to improveexisting statistics of their magnetism. The target list contains 57upper MS stars and represents well B0.5-F9 stars. High-resolution Zeemanspectra were obtained for 30 stars of the list. The accuracy of themagnetic field measurements ranges from 20 to 300 G depending mainly onspectral class. In the majority of studied stars we did not detectmagnetic fields. In some stars we suspect the presence of a weakmagnetic field. These are the best candidates for more extensivestudies. A particular case is the star chi Dra where we probablydetected the global magnetic field. The longitudinal field strength isB_l= -54+/-12 G. Further observations of this star are needed to confirmthe detection and to ascertain if the magnetic field is variable withthe period of rotation. Based on observations collected at the 1 mtelescope of the Special Astrophysical Observatory (Nizhnij Arkhyz,Russia).
| Rotational velocities of A-type stars in the northern hemisphere. II. Measurement of v sin i
This work is the second part of the set of measurements of v sin i forA-type stars, begun by Royer et al. (\cite{Ror_02a}). Spectra of 249 B8to F2-type stars brighter than V=7 have been collected at Observatoirede Haute-Provence (OHP). Fourier transforms of several line profiles inthe range 4200-4600 Å are used to derive v sin i from thefrequency of the first zero. Statistical analysis of the sampleindicates that measurement error mainly depends on v sin i and thisrelative error of the rotational velocity is found to be about 5% onaverage. The systematic shift with respect to standard values fromSlettebak et al. (\cite{Slk_75}), previously found in the first paper,is here confirmed. Comparisons with data from the literature agree withour findings: v sin i values from Slettebak et al. are underestimatedand the relation between both scales follows a linear law ensuremath vsin inew = 1.03 v sin iold+7.7. Finally, thesedata are combined with those from the previous paper (Royer et al.\cite{Ror_02a}), together with the catalogue of Abt & Morrell(\cite{AbtMol95}). The resulting sample includes some 2150 stars withhomogenized rotational velocities. Based on observations made atObservatoire de Haute Provence (CNRS), France. Tables \ref{results} and\ref{merging} are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.125.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/393/897
| CO 1st overtone spectra of cool evolved stars: Diagnostics for hydrodynamic atmosphere models
We present spectra covering the wavelength range 2.28 to 2.36 mu m at aresolution of Delta lambda = 0.0007 mu m (or R = 3500) for a sample of24 cool evolved stars. The sample comprises 8 M supergiants, 5 M giants,3 S stars, 6 carbon stars, and 2 RV Tauri variables. The wavelengthscovered include the main parts of the 12C16O v =2-0 and 3-1 overtone bands, as well as the v = 4-2 and 13CO v= 2-0 bandhead regions. CO lines dominate the spectrum for all the starsobserved, and at this resolution most of the observed features can beidentified with individual CO R- or P-branch lines or blends. Theobserved transitions arise from a wide range of energy levels extendingfrom the ground state to E/k > 20 000 K. We looked for correlationsbetween the intensities of various CO absorption line features and otherstellar properties, including IR colors and mass loss rates. Two usefulCO line features are the v = 2-0 R14 line, and the CO v = 2-0 bandhead.The intensity of the 2-0 bandhead shows a trend with K-[12] color suchthat the reddest stars (K-[12] > 3 mag) exhibit a wide range in 2-0bandhead depth, while the least reddened have the deepest 2-0 bandheads,with a small range of variation from star to star. Gas mass loss ratesfor both the AGB stars and the red supergiants in our sample correlatewith the K-[12] color, consistent with other studies. The data implythat stars with dot M_gas < 5x 10-7 Msuny-1 exhibit a much narrower range in the relative strengthsof CO 2-0 band features than stars with higher mass loss rates. Therange in observed spectral properties implies that there are significantdifferences in atmospheric structure among the stars in this sample.Figures 4-9, 11-14, 16, 17, 19-21, 23, 24 are only avalaible inelectronic form at http://www.edpsciences.org
| Detection and Significance of [Zn IV] 3.625 Microns in Planetary Nebulae
We have identified a line at 3.625 μm in the planetary nebulae (PNs)NGC 7027 and IC 5117 as the2D3/2-2D5/2 fine-structuretransition of the 3d9 ion Zn+3. Zinc (N=30) isbelieved to be made primarily by explosive nucleosynthesis and r-processneutron capture reactions, and because Zn/H closely tracks Fe/H inmetal-poor stars and is relatively undepleted into dust in the ISM, Zn/Hhas been used as a surrogate for Fe/H in the high-redshift universe.However, some isotopes of Zn are also produced as part of the s-processin asymptotic giant branch stars, the progenitors of PNs. Although thereis currently no published calculation of the collision strength for [ZnIV] 3.625 μm, for plausible values the observed line fluxes do notrequire Zn/H greater than solar, suggesting that these two PNs, whichhave elevated abundances of other s-process elements and C, are notsignificantly self-enriched in Zn. Consequently, Zn/H determined fromemission lines should be a good indicator of elemental Fe/H in PNs,where gas-phase Fe/H values cannot be used directly because of depletioneffects, enabling comparisons between nebular and stellar Fe/Habundances. We also report an upper limit on the strength of the 1-0P(2) line of HeH+ at 3.608 μm in NGC 7027.
| Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics
The Catalogue, available at the Centre de Données Stellaires deStrasbourg, consists of 13 573 records concerning the results obtainedfrom different methods for 7778 stars, reported in the literature. Thefollowing data are listed for each star: identifications, apparentmagnitude, spectral type, apparent diameter in arcsec, absolute radiusin solar units, method of determination, reference, remarks. Commentsand statistics obtained from CADARS are given. The Catalogue isavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcar?J/A+A/367/521
| The proper motions of fundamental stars. I. 1535 stars from the Basic FK5
A direct combination of the positions given in the HIPPARCOS cataloguewith astrometric ground-based catalogues having epochs later than 1939allows us to obtain new proper motions for the 1535 stars of the BasicFK5. The results are presented as the catalogue Proper Motions ofFundamental Stars (PMFS), Part I. The median precision of the propermotions is 0.5 mas/year for mu alpha cos delta and 0.7mas/year for mu delta . The non-linear motions of thephotocentres of a few hundred astrometric binaries are separated intotheir linear and elliptic motions. Since the PMFS proper motions do notinclude the information given by the proper motions from othercatalogues (HIPPARCOS, FK5, FK6, etc.) this catalogue can be used as anindependent source of the proper motions of the fundamental stars.Catalogue (Table 3) is only available at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strastg.fr/cgi-bin/qcat?J/A+A/365/222
| Speckle Observations of Double Stars with PISCO at Pic du Midi: Measurements in 1998
We present astrometric measurements of binary stars based on speckleobservations of 164 independent sequences of observations(~104 frames each) made with the PISCO speckle camera at Picdu Midi. These measurements concern 147 objects, of which 134 were foundto be double with a separation in the range 0.1"-1.0". These objectswere mainly selected among grade 3 orbits to improve the accuracy oftheir orbits and to constrain their masses. We discovered the binarityof 59 Aql with an angular separation of 0.09"+/-0.01".
| Emerging trends of optical interferometry in astronomy
The current status of the high spatial resolution imaging interferometryin optical astronomy is reviewed in the light of theoreticalexplanation, as well as of experimental constraints that exist in thepresent day technology. The basic mathematical interlude pertinent tothe interferometric technique and its applications in astronomicalobservations are presented in detail. An elaborate account of the randomrefractive index fluctuations of the atmosphere producing randomaberrations in the telescope pupil, elucidating the trade offs betweenlong-exposure and short-exposure imaging is given. Further, the othermethods viz., (i) speckle spectroscopy, (ii) speckle polarimetry, (iii)phase closure, (iv) aperture synthesis, (v) pupil plane interferometry,(vi) differential speckle interferometry etc., using single moderate orlarge telescopes are described as well. The salient features of variousdetectors that are used for recording short-exposure images aresummarized. The mathematical intricacies of the data processingtechniques for both Fourier modulus and Fourier phase are analyzed; thevarious schemes of image restoration techniques are examined as wellwith emphasis set on their comparisons. The recent technologicalinnovation to compensate the deleterious effects of the atmosphere onthe telescope image in real-time is enumerated. The experimentaldescriptions of several working long baseline interferometers in thevisible band are summarized. The astrophysical results obtained tilldate are highlighted.
| Stellar Angular Diameters of Late-Type Giants and Supergiants Measured with the Navy Prototype Optical Interferometer
We have measured the angular diameters of 50 F, G, K, and M giant andsupergiant stars using the Navy Prototype Optical Interferometer atwavelengths between 649 and 850 nm and using three baselines withlengths up to 37.5 m. Uniform-disk diameters, obtained from fits to thevisibility amplitude, were transformed to limb-darkened diametersthrough the use of limb-darkening coefficients for plane-parallelstellar atmosphere models. These limb-darkened diameters are comparedwith those measured with the Mark III optical interferometer and withthose computed by the infrared flux method. Sources of random andsystematic error in the observations are discussed.
| Speckle Interferometry of New and Problem HIPPARCOS Binaries
The ESA Hipparcos satellite made measurements of over 12,000 doublestars and discovered 3406 new systems. In addition to these, 4706entries in the Hipparcos Catalogue correspond to double star solutionsthat did not provide the classical parameters of separation and positionangle (rho,theta) but were the so-called problem stars, flagged ``G,''``O,'' ``V,'' or ``X'' (field H59 of the main catalog). An additionalsubset of 6981 entries were treated as single objects but classified byHipparcos as ``suspected nonsingle'' (flag ``S'' in field H61), thusyielding a total of 11,687 ``problem stars.'' Of the many ground-basedtechniques for the study of double stars, probably the one with thegreatest potential for exploration of these new and problem Hipparcosbinaries is speckle interferometry. Results are presented from aninspection of 848 new and problem Hipparcos binaries, using botharchival and new speckle observations obtained with the USNO and CHARAspeckle cameras.
| On the normal energy distribution in stellar spectra: O5-O8 stars
The spectral energy curves for a number of O4-O8 stars are analyzedusing measurements taken from six sources of spectrophotometric data.Based on the normal UBV color indices for O stars, these stars aredivided into three groups (O5, O6-O7, and O8), for each of which thenormal energy distribution is derived and presented. Comparison of thesedistributions indicates clear differences between the O5 and O8subclasses at UV wavelengths. A single normal distribution curve is,therefore, insufficient to characterize the O spectral class as a whole.
| Integrated Ultraviolet Spectra and Line Indices of M31 Globular Clusters and the Cores of Elliptical Galaxies
We present observations of the integrated light of four M31 globularclusters (MIV, MII, K280, and K58) and of the cores of six ellipticalgalaxies (NGC 3605, 3608, 5018, 5831, 6127, and 7619) made with theFaint Object Spectrograph on the Hubble Space Telescope. The spectracover the range 2200-4800 Å at a resolution of 8 Å withsignal-to-noise ratio of more than 20 and flux accuracy of ~5%. To thesedata we add from the literature IUE observations of the dwarf ellipticalgalaxy M32, Galactic globular clusters, and Galactic stars. The stellarpopulations in these systems are analyzed with the aid of mid-UV andnear-UV colors and absorption line strengths. Included in the measuredindices is the key NH feature at 3360 Å. We compare these lineindex measures with the 2600 - 3000 colors of these stars and stellarpopulations. We find that the M31 globular clusters, Galactic globularclusters/Galactic stars, and elliptical galaxies represent threedistinct stellar populations, based on their behavior in color-linestrength correlations involving Mg II, NH, CN, and several UV metallicblends. In particular, the M31 globular cluster MIV, as metal-poor asthe Galactic globular M92, shows a strong NH 3360 Å feature. Otherline indices, including the 3096 Å blend that is dominated bylines of Mg I and Al I, show intrinsic differences as well. We also findthat the broadband line indices often employed to measure stellarpopulation differences in faint objects, such as the 4000 Å andthe Mg 2800 breaks, are disappointingly insensitive to these stellarpopulation differences. We find that the hot (T > 20,000 K) stellarcomponent responsible for the ``UV upturn'' at shorter wavelengths canhave an important influence on the mid-UV spectral range (2400-3200Å) as well. The hot component can contribute over 50% of the fluxat 2600 Å in some cases and affects both continuum colors and linestrengths. Mid-UV spectra of galaxies must be corrected for this effectbefore they can be used as age and abundance diagnostics. Of the threestellar populations studied here, M31 globular clusters and ellipticalgalaxies are more similar to each other than either is to the Galacticstellar populations defined by globular clusters and nearby stars.Similarities between the abundance-pattern differences currentlyidentified among these stellar populations and those among globularcluster stars (N, Al enhancements) present a curious coincidence thatdeserves future investigation. Based on observations with the NASA/ESAHubble Space Telescope, obtained at the Space Telescope ScienceInstitute, which is operated by the Association of Universities forResearch in Astronomy, Inc., under NASA contract NAS 5-26555.
| The ROSAT all-sky survey catalogue of optically bright main-sequence stars and subgiant stars
We present X-ray data for all main-sequence and subgiant stars ofspectral types A, F, G, and K and luminosity classes IV and V listed inthe Bright Star Catalogue that have been detected as X-ray sources inthe ROSAT all-sky survey; several stars without luminosity class arealso included. The catalogue contains 980 entries yielding an averagedetection rate of 32 percent. In addition to count rates, sourcedetection parameters, hardness ratios, and X-ray fluxes we also listX-ray luminosities derived from Hipparcos parallaxes. The catalogue isalso available in electronic form via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| The Tokyo PMC catalog 90-93: Catalog of positions of 6649 stars observed in 1990 through 1993 with Tokyo photoelectric meridian circle
The sixth annual catalog of the Tokyo Photoelectric Meridian Circle(PMC) is presented for 6649 stars which were observed at least two timesin January 1990 through March 1993. The mean positions of the starsobserved are given in the catalog at the corresponding mean epochs ofobservations of individual stars. The coordinates of the catalog arebased on the FK5 system, and referred to the equinox and equator ofJ2000.0. The mean local deviations of the observed positions from theFK5 catalog positions are constructed for the basic FK5 stars to comparewith those of the Tokyo PMC Catalog 89 and preliminary Hipparcos resultsof H30.
| Identifications for Baade's Variables in Sagitta and Cygnus
Not Available
| The Pulkovo spectrophotometric catalog of bright stars in the range from 320 to 1080 NM - A supplement
The Pulkovo spectrophotometric catalog was published in Baltic AstronomyVol. 5, No. 4 (1996). Here we present a supplement of the catalogcontaining the flux distribution data for 77 stars in the wavelengthrange from 320 to 735 nm. Actually, this is a direct continuation ofTable 6 of the catalog.
| Circumstellar Gas in the Wide Binary HD 188037
We report radio, optical, and ultraviolet studies of the wide binary HD188037 (=IRC +20439). We detect the CO (2--1) and (1--0) rotationallines from the circumstellar envelope in this system, which consists ofa luminous (~7000 Lȯ) mass-losing M-type star and, at a separationof 0."75, a main-sequence A-type star. The strong (2--1) line has a veryunusual skewed shape with a width at zero intensity of about 30 km s-1,which we explain with a model wherein the gas ejected by the M-type staris preferentially photodissociated on one side of the outflow byultraviolet light from the A-type companion. We infer that the wind fromthe M giant expands at 15 km s-1 and, for an estimated distance of 300pc, carries ~3 x 10-7 Mȯ yr-1. Our simplified model for CO in awind being photodissociated by ultraviolet from a companion explains whyCO can be detected around Mira yet not around alpha Sco.
| Systematic Errors in the FK5 Catalog as Derived from CCD Observations in the Extragalactic Reference Frame.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....114..850S&db_key=AST
| Short-term variability in comet C/1995 O1 Hale-Bopp.
Simultaneous uvby Stroemgren photometric observations of the cometHale-Bopp have been collected during nearly three weeks. The Fouriertransform method has been used to analyse the periodicities inluminosity present in this comet. Two different periodicities have beenfound: a long period of 7.19 days and a shorter one of 5.5 hours. The5.5-hour periodicity may correspond to a full rotation of 11 hourswhereas the 7.19-day periodicity could be related with the precessionperiod. Other possibilities are discussed.
| The Pulkovo Spectrophotometric Catalog of Bright Stars in the Range from 320 TO 1080 NM
A spectrophotometric catalog is presented, combining results of numerousobservations made by Pulkovo astronomers at different observing sites.The catalog consists of three parts: the first contains the data for 602stars in the spectral range of 320--735 nm with a resolution of 5 nm,the second one contains 285 stars in the spectral range of 500--1080 nmwith a resolution of 10 nm and the third one contains 278 stars combinedfrom the preceding catalogs in the spectral range of 320--1080 nm with aresolution of 10 nm. The data are presented in absolute energy unitsW/m(2) m, with a step of 2.5 nm and with an accuracy not lower than1.5--2.0%.
| A High-Resolution Survey of Interstellar Ca II Absorption
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJS..106..533W&db_key=AST
| The Wolf-Rayet counterpart of Cygnus X-3.
We present orbital-phase resolved I and K-band spectroscopy of CygnusX-3. All spectra show emission lines characteristic of Wolf-Rayet starsof the WN subclass. On time scales longer than about one day, the linestrengths show large changes, both in flux and in equivalent width. Inaddition, the line ratios change, corresponding to a variation inspectral subtype of WN6/7 to WN4/5. We confirm the finding that at timeswhen the emission lines are weak, they shift in wavelength as a functionof orbital phase, with maximum blueshift coinciding with infrared andX-ray minimum, and maximum redshift half an orbit later. Furthermore, weconfirm the prediction - made on the basis of previous observations -that at times when the emission lines are strong, no clear wavelengthshifts are observed. We describe a simplified, but detailed model forthe system, in which the companion of the X-ray source is a Wolf-Rayetstar whose wind is at times ionised by the X-ray source, except for thepart in the star's shadow. With this model, the observed spectralvariations can be reproduced with only a small number of freeparameters. We discuss and verify the ramifications of this model, andfind that, in general, the observed properties can be understood. Weconclude that Cyg X-3 is a Wolf-Rayet/X-ray binary.
|
Enviar un nuevo artículo
Enlaces relacionados
- - No se han encontrado enlaces -
En viar un nuevo enlace
Miembro de los siguientes grupos:
|
Datos observacionales y astrométricos
| Constelación: | Cisne |
| Ascensión Recta: | 20h57m10.40s |
| Declinación: | +41°10'02.0" |
| Magnitud Aparente: | 3.94 |
| Distancia: | 109.051 parsecs |
| Movimiento Propio en Ascensión Recta: | 11.6 |
| Movimiento Propio en Declinación: | -14 |
| B-T magnitude: | 3.95 |
| V-T magnitude: | 3.932 |
Catálogos y designaciones:
|
