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Adaptive Optics Photometry and Astrometry of Binary Stars. III. a Faint Companion Search of O-Star Systems
We present the results of an adaptive optics survey for faint companionsamong Galactic O-type star systems (with V lsim 8) using the AdvancedElectro-Optical System (AEOS) 3.6 m telescope on Haleakala. We surveyedthese O-star systems in the I-band, typically being able to detect acompanion with a magnitude difference of utrimI lsim 6 in theprojected separation range 0farcs5 < ρ < 1farcs0, andutrimI lsim 9.5 in the range 1farcs0 < ρ < 5farcs0.In the course of the survey, we discovered 40 new companions among 31 ofthe 116 objects examined and made astrometric and differential magnitudemeasurements of 24 additional known pairs, several of them beingconfirmation detections. We present new astrometric orbits for twobinaries, BU 1032AB (WDS 05387–0236 σ Ori AB) and SEE 322(WDS 17158–3344 HD 155889AB). We lack magnitude differences forother filter bands, so it is difficult to determine physical fromline-of-sight companions, but we present empirical arguments for thelimiting magnitude difference where field contamination is significant.Based on observations made at the Maui Space Surveillance Systemoperated by Detachment 15 of the US Air Force Research Laboratory'sDirected Energy Directorate.
| A Spectrophotometric Study of the Coma of Comet C/2001 A2 (LINEAR)
Low-resolution spectrographic observations of comet C/2001 A2 (LINEAR)were carried out between 2001 July 5 and 9 at Beijing AstronomicalObservatory using its 2.16 m telescope. From the spatial distributionsof the brightness profiles of C2, C3, CN,NH2, and the dust continuum, we are able to trace the sourceregions of these cometary radicals and their parent molecules. The CNemission displayed a remarkable asymmetry, with its intensity peakshifted to the tailward side by as much as 1000 km away from the centerof the dust continuum. There is thus a strong indication that the CN hasa distributed source not necessarily associated with the centralnucleus. A probable release mechanism is associated with a CN jetstructure detected in imaging photometric measurements.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| Subarcsecond Structure and Velocity Field of Optical Line-emitting Gas in NGC 1052
We have obtained integral field spectra of the low-ionizationemission-line region in the galaxy NGC 1052 by using the KyotoTridimensional Spectrograph II mounted on the Subaru Telescope. Our highsignal-to-noise ratio data with precise template subtraction haverevealed weaker features at the nucleus, including the [Fe III] and HeII emission lines, as well as a broad component of the Hβ emission.The broad Hβ component suggests the existence of a broad-lineregion. The spatial structure and velocity field derived from the datacube suggest the existence of three main components: a high-velocitybipolar outflow, low-velocity disk rotation, and a spatially unresolvednuclear component. The outflow axis does not coincide with the diskrotation axis. The opening angle of the outflow decreases with velocityshift from the systemic velocity both in bluer and redder velocitychannels. This is explained only if the outflow has intrinsically highervelocity components inside, i.e., in regions closer to the outflow axis.At both sides of the bipolar outflow, we find that the highest velocitycomponents are detached from the nucleus. This gap can be explained byan acceleration of at least a part of the flow or the surroundingmatter, or by bow shocks that may be produced by even higher velocityoutflow components that are not yet detected. Along the edges of theoutflow and extending east-northeast and west-southwest, there existstrong [O III] emission ridges. These are closely related to the radiojet-counterjet structure. The abrupt change in the velocity field of theionized gas and a large [OIII]/Hβ line flux ratio in this regionsuggest a strong interaction of the jets, and possibly also of someridge components of the line-emitting gas, with the interstellar matter.
| X-Ray Counterparts of Runaway Stars
An X-ray search for possible compact companions of runaway OB stars hasbeen conducted using pointed ROSAT observations. Of a list of 71 runawaystars, ROSAT exposures were available for 24, of which 13 are detected.These numbers are nearly 3 times larger than for a previously studiedEinstein sample, and spectral information is exploited as well.Luminosities, hardness ratios, and long-term variability are as fornormal OB stars and do not suggest the presence of collapsed companions.A result like this is often interpreted as support for dynamicalejection from a dense group rather than a supernova event in a binary asa production process for runaway stars. There are, however, severalcircumstances that may adversely affect the observability of a compactcompanion, or after a supernova explosion systems may be disruptedbecause of the large natal kick velocity imparted to the neutron star asa result of asymmetries in the explosions. It is noted that there isactually evidence for both of these production routes and that they maybe expected to occur sequentially in the evolution of OB associations.
| On the Hipparcos parallaxes of O stars
We compare the absolute visual magnitude of the majority of bright Ostars in the sky as predicted from their spectral type with the absolutemagnitude calculated from their apparent magnitude and the Hipparcosparallax. We find that many stars appear to be much fainter thanexpected, up to five magnitudes. We find no evidence for a correlationbetween magnitude differences and the stellar rotational velocity assuggested for OB stars by Lamers et al. (1997, A&A, 325, L25), whosesmall sample of stars is partly included in ours. Instead, by means of asimulation we show how these differences arise naturally from the largedistances at which O stars are located, and the level of precision ofthe parallax measurements achieved by Hipparcos. Straightforwardlyderiving a distance from the Hipparcos parallax yields reliable resultsfor one or two O stars only. We discuss several types of bias reportedin the literature in connection with parallax samples (Lutz-Kelker,Malmquist) and investigate how they affect the O star sample. Inaddition, we test three absolute magnitude calibrations from theliterature (Schmidt-Kaler et al. 1982, Landolt-Börnstein; Howarth& Prinja 1989, ApJS, 69, 527; Vacca et al. 1996, ApJ, 460, 914) andfind that they are consistent with the Hipparcos measurements. AlthoughO stars conform nicely to the simulation, we notice that some B stars inthe sample of \citeauthor{La97} have a magnitude difference larger thanexpected.
| Line profile variability in the spectra of Oef stars. II. HD 192281, HD 14442 and HD 14434
We present the very first analysis of the spectroscopic variability ofthe three rapidly rotating Oef stars HD 192281 (O5(ef)), HD 14442(O5.5ef) and HD 14434 (O6.5(ef)). Radial velocities of the He IIλ 4541 line reveal no evidence of binarity on time scales of afew days, or from one year to the next, for any of the targets. The HeII λ 4686 double-peaked emission and, to some extent, the Hβabsorption line display significant profile variability in the spectraof all three stars. Data gathered during different observing runs spreadover six years reveal a rather stable time scale for HD 192281 and HD14442, whereas the variability pattern changes significantly from oneyear to the other. The case of HD 14434 is less clear as no obvious timescale emerges from our analysis. In a tentative way to interpret thisvariability, stellar rotation remains a possible clock for HD 192281 andHD 14442. However, currently available models addressing stellarrotation fail to explain some crucial aspects of the observedvariability behaviour, which appear to be even more complex in the caseof HD 14434.Based on observations collected at the Observatoire de Haute-Provence,France.
| Low-Ionization Emission-Line Regions around the Nucleus of the Seyfert Galaxy NGC 1068
We present the results of tridimensional spectrophotometric observationsof the central region of the Seyfert galaxy NGC 1068 obtained by usingKyoto tridimensional spectrograph I. A brief description of theinstrument is presented. We have found the existence of low-ionized gasextending out of the ionization cone. It is characterized by higher ([SII ] λ6716+λ6731) / Hα than within the cone. Theratio peaks at 5'' ‑ 6'' east and west of the nucleus and reachesto 0.5-0.6. The ionization of the gas outside the cone by the scatterednuclear continuum is examined. We argue that a substantial fraction ofthe gases outside the cone could be ionized by the scattered nuclearcontinuum, including the diffuse arc structure seen in an HST image. Inaddition, we also attempt discussions according to the kinematic andspectroscopic properties of two possible gaseous components derived bythe line decomposition: a narrow component that seems to follow thegalactic rotation, and a broad one that may be deviated from it.
| Raman-Scattered He II at 4851 Å in the Symbiotic Stars HM Sagittae and V1016 Cygni
We report the detection of a weak emission feature at around 4851Å in the spectra of the symbiotic stars HM Sge and V1016 Cyg andidentify these as Raman-scattered He II features. This feature arisesfrom the inelastic scattering of He II (2-8) photons on the ground stateof neutral hydrogen. Raman-scattered He II at 4851 Å was firstidentified by van Groningen in the symbiotic star RR Tel and later inthe young planetary nebula NGC 7027. V1016 Cyg is one of many stars thatis known to exhibit strong, broad Raman-scattered O VI features in itsspectrum. These data represent the first detection of Raman-scattered HeII in the symbiotic star HM Sge. A brief discussion on the implicationsof this identification is presented.
| New Runaway O-stars Based on Data from HIPPARCOS
12 new runaway O-stars are identified using an analysis of their propermotions based on data from HIPPARCOS. The peculiar tangential and totaltransverse velocities of these stars are determined. A list of theobserved runaway stars is given.
| A Galactic O Star Catalog
We have produced a catalog of 378 Galactic O stars with accuratespectral classifications that is complete for V<8 but includes manyfainter stars. The catalog provides cross-identifications with othersources; coordinates (obtained in most cases from Tycho-2 data);astrometric distances for 24 of the nearest stars; optical (Tycho-2,Johnson, and Strömgren) and NIR photometry; group membership,runaway character, and multiplicity information; and a Web-based versionwith links to on-line services.
| A study of RV in Galactic O stars from the 2MASS catalogue
We present new measurements of the interstellar reddening parameterRV=AV/E(B-V) towards 185 O stars, using J, H,Ks photometry from the 2MASS project. The results arecombined with data from the literature of 95 stars where RVhas been derived with the same technique, 22 of which in common with ourpresent sample from the 2MASS project catalogue. The averageRV from these 258 O stars is of 3.19 +/- 0.50. All objectswhose RV departs from this value by more than 2 sigma havebeen recognized. Ten objects have RV higher than this valueand two lower. It is found that anomalous RV can scarcely beassociated with anomalies in the general interstellar medium, e.g. withdifferent behaviour in different spiral arms. They are clearly linked tolocal cloud effect. In the Cygnus region RV values follow thebehaviour of the general interstellar medium, while in the Carina arm,in spite of the relatively larger distance, local cloud effects prevail.An explanation for this is suggested. The relatively few stars of oursample whose Hipparcos parallaxes are reliable, are found to havedistances systematically smaller than the distances derived by thespectroscopic parallaxes. We argue that this effect is consistent withthe recently claimed discovery of grey extinction towards OB stars.This publication makes use of data products from the Two Micron All SkySurvey (2MASS), which is a joint project of the University ofMassachusetts and the Infrared Processing and Analysis Center/CaliforniaInstitute of Technology, funded by the National Aeronautics and SpaceAdministration and the National Science Foundation.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/410/905
| Integral field spectroscopy of SN 2002er with PMAS
We present observations of the Type Ia supernova SN2002er during the brightening phase. The observations wereperformed with the Potsdam Multi Aperture Spectrophotometer (PMAS)integral field instrument. Due to the 8arcsecx8 arcsec field of view ofthe spectrograph an accurate background subtraction was possible.Results from analyses of the evolution of absorption features incomparisons with other SNe show that SN 2002er is a fairly bright TypeIa supernova with a peak brightness of MB=-19.6+/-0.1.
| Line profile variability in the spectra of Oef stars. I. BD + 60deg 2522
We report the analysis of a long term observing campaign designed tomonitor the spectroscopic variability of the Oef star BD+60deg 2522. We find that the double-peaked He {II} lambda4686 emission line undergoes strong profile variability on time scalesof 2-3 day. However, the time scale as well as the pattern of thesevariations turn out to be epoch dependent and the phenomenon is thusmost likely not ruled by a single stable clock. On the other hand, theabsorption lines in the spectrum of BD +60deg 2522 displayline profile variability on time scales of a few hours that might berelated to non-radial pulsations. We tentatively propose that thebeating of several non-radial pulsation modes triggers transientlarge-scale density perturbations in a confined stellar wind thatproduce the 2-3 day time scale variability.Based on observations collected at the Observatoire de Haute Provence,France.
| HD 192281 and HD 10125: A Study of their Local ISM using Radio and Infrared Data
Massive stars like HD 192281 (O5 V n((f))p) and HD 10125 (O9 5 Ib orO9.7 II) have a substantial impact on their surrounding interstellarmedium (ISM) via their high Lyman continuum flux and their strongstellar winds.
| Radio observations of interstellar bubbles surrounding massive stars}
We show radio continuum observations of the WR ring nebulae around WR101 and WR 113 obtained using the VLA and HI 21 cm line data of theinterstellar bubble around the O type stars BD +24 deg 3866 and BD+25deg 3952 obtained with the DRAO Synthesis Telescope. We review previousradio continuum and HI line results toward WR and O-type stars.
| Spectroscopic study of blue compact galaxies. I. The spectra
Blue compact galaxies are compact objects that are dominated by intensestar formation. Most of them have dramatically different propertiescompared to the Milky Way and many other nearby galaxies. Using theIRAS, H I data, and optical spectra, we wanted to measure the currentstar formation rates, stellar components, metallicities, and starformation histories and evolution of a large blue compact galaxy sample.We anticipate that our study will be useful as a benchmark for studiesof emission line galaxies at high redshift. In the first paper of thisseries, we describe the selection, spectroscopic observation, datareduction and calibration, and spectrophotometric accuracy of a sampleof 97 luminous blue compact galaxies. We present a spectrophotometricatlas of rest-frame spectra, as well as tables of the recessionvelocities and the signal-to-noise ratios. The recession velocities ofthese galaxies are measured with an accuracy of delta V< 67 kms-1. The average signal-to-noise ratio of sample spectra is ~51. The spectral line strengths, equivalent widths and continuum fluxesare also measured for the same galaxies and will be analyzed in the nextpaper of this series. The atlas and tables of measurements will be madeavailable electronically. Table 3 and Fig. 4 are only available inelectronic form at the 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/389/845
| Unveiling the structure of the planetary nebula M 2-48:. Kinematics and physical conditions
The kinematics and physical conditions of the bipolar planetary nebula M2-48 are analysed from high and low dispersion long-slit spectra.Previous CCD narrow-band optical observations have suggested that thisnebula is mainly formed by a pair of symmetric bow-shocks, an off-centersemi-circular shell, and an internal bipolar structure. The bipolaroutflow has a complex structure, characterised by a series of shockedregions located between the bright core and the polar tips. There is anapparent kinematic discontinuity between the bright bipolar core and theouter regions. The fragmented ring around the bright bipolar regionpresents a low expansion velocity and could be associated with ejectionin the AGB-PN transition phase, although its nature remains unclear. Thechemical abundances of the central region are derived, showing that M2-48 is a type I planetary nebula (PN).
| Evidence for Asphericity in a Subluminous Type Ia Supernova: Spectropolarimetry of SN 1999by
We present polarization spectra near maximum light for the stronglysubluminous Type Ia supernova SN 1999by that show that the supernova isintrinsically polarized. SN 1999by has an observed, overall level ofpolarization of ~0.3%-0.8%, a rise of the polarization P redward of 6500Å, and a change in polarization across the Si II λ6150feature of about 0.4%. The presentation of the polarization at differentwavelengths in the Q-U plane is shown to be a powerful tool to determinethe overall geometry and the interstellar component. The distribution ofpoints with wavelength using this empirical Q-U plane method revealsthat SN 1999by has a well-defined axis of symmetry and suggests aninterstellar polarization (ISP) vector with PISP=0.3% andposition angle Θ=150deg with an error circle in the Q-Uplane of radius about 0.1%. Synthetic non-LTE spectra for axisymmetricconfigurations based on delayed-detonation models have been computedassuming ellipsoidal geometry. The input ejecta structure andcomposition are based on a Chandrasekhar mass delayed-detonation model.The parameters of the explosion are chosen to reproduce the timeevolution of IR spectra of SN 1999by without further adjustments.Spherical models are then mapped onto ellipsoidal geometries and theaxis ratio, viewing angle, and ISP adjusted to provide the bestagreement with the polarization spectra. Both flux and polarizationspectra can be reasonably well reproduced by models with an asphericityof ~20% observed equator-on. The general properties of the polarizationcan be understood as a consequence of the structure of subluminousmodels. Best fits are obtained for the theoretical models withPISP=0.25% and Θ=140deg, consistent with theempirical method. We discuss our results for this subluminous Type Ia inthe context of ``normally bright'' Type Ia supernovae. For normallybright Type Ia, the photosphere is near the inner iron-rich layers atmaximum light and the ubiquitous iron lines give a rapid variation tothe model polarization spectra. In subluminous models, the photospherenear maximum is in the silicon layers with fewer lines and a smootheroverall polarization spectrum, as observed for SN 1999by. Though dataare sparse, the low upper limits for polarization determined for manynormal events in contrast to the high polarization in SN 1999by maysuggest a relation between the asymmetry we observed and the mechanismthat produces a subluminous Type Ia. Among various mechanisms, rapidrotation of the progenitor white dwarf and/or an explosion during abinary white dwarf merger process are likely candidates to explain theasphericity in SN 1999by.
| Balmer-dominated Spectra of Nonradiative Shocks in the Cygnus Loop, RCW 86, and Tycho Supernova Remnants
We present an observational and theoretical study of the opticalemission from nonradiative shocks in three supernova remnants: theCygnus Loop, RCW 86, and Tycho. The spectra of these shocks aredominated by collisionally excited hydrogen Balmer lines, which haveboth a broad component caused by proton-neutral charge exchange and anarrow component caused by excitation of cold neutrals entering theshock. In each remnant, we have obtained the broad-to-narrow flux ratiosof the Hα and Hβ lines and measured the Hα broadcomponent width. A new numerical shock code computes the broad andnarrow Balmer line emission from nonradiative shocks in partiallyneutral gas. The Balmer line fluxes are sensitive to Lyman line trappingand the degree of electron-proton temperature equilibration. The codecalculates the density, temperature, and size of the postshockionization layer and uses a Monte Carlo simulation to compute narrowBalmer line enhancement from Lyman line trapping. The initial fractionof the shock energy allocated to the electrons and protons (theequilibration) is a free parameter. Our models show that variations inelectron-proton temperature equilibration and Lyman line trapping canreproduce the observed range of broad-to-narrow ratios. The results give80%-100% equilibration in nonradiative portions of the northeast CygnusLoop (vS~300 km s-1), 40%-50% equilibration innonradiative portions of RCW 86 (vS~600 km s-1),and <~20% equilibration in Tycho (vS~2000 kms-1). Our results suggest an inverse correlation betweenmagnetosonic Mach number and equilibration in the observed remnants.
| 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
| On the origin of the O and B-type stars with high velocities. II. Runaway stars and pulsars ejected from the nearby young stellar groups
We use milli-arcsecond accuracy astrometry (proper motions andparallaxes) from Hipparcos and from radio observations to retrace theorbits of 56 runaway stars and nine compact objects with distances lessthan 700 pc, to identify the parent stellar group. It is possible todeduce the specific formation scenario with near certainty for twocases. (i) We find that the runaway star zeta Ophiuchi and the pulsarPSR J1932+1059 originated about 1 Myr ago in a supernova explosion in abinary in the Upper Scorpius subgroup of the Sco OB2 association. Thepulsar received a kick velocity of ~ 350 km s-1 in thisevent, which dissociated the binary, and gave zeta Oph its large spacevelocity. (ii) Blaauw & Morgan and Gies & Bolton alreadypostulated a common origin for the runaway-pair AE Aur and mu Col,possibly involving the massive highly-eccentric binary iota Ori, basedon their equal and opposite velocities. We demonstrate that these threeobjects indeed occupied a very small volume ~ 2.5 Myr ago, and show thatthey were ejected from the nascent Trapezium cluster. We identify theparent group for two more pulsars: both likely originate in the ~ 50 Myrold association Per OB3, which contains the open cluster alpha Persei.At least 21 of the 56 runaway stars in our sample can be linked to thenearby associations and young open clusters. These include the classicalrunaways 53 Arietis (Ori OB1), xi Persei (Per OB2), and lambda Cephei(Cep OB3), and fifteen new identifications, amongst which a pair ofstars running away in opposite directions from the region containing thelambda Ori cluster. Other currently nearby runaways and pulsarsoriginated beyond 700 pc, where our knowledge of the parent groups isvery incomplete.
| On the Correlation between CO Absorption and Far-Ultraviolet Nonlinear Extinction toward Galactic OB Stars
A sample of 59 sight lines to reddened Galactic OB stars was examinedfor correlations of the strength of the CO Fourth Positive(A1Π-X1Σ+) absorption bandsystem with the ultraviolet interstellar extinction curve parameters. Weused archival high-dispersion NEWSIPS IUE spectra to measure the COabsorption for comparison with parametric fits of the extinction curvesfrom the literature. A strong correlation with the nonlinear far-UVcurvature term was found with greater absorption, normalized to E(B-V),being associated with more curvature. A weaker trend with the linearextinction term was also found. Mechanisms for enhancing CO in dustenvironments exhibiting high nonlinear curvature are discussed.
| Starbursts in barred spiral galaxies. IV. On young bars and the formation of abundance gradients
The oxygen (O/H) and N/O abundance ratios along the bar of 16 barredspiral starburst galaxies are determined using long-slit spectroscopy.The abundance gradients and the spatial distribution of the ionized gasalong the bar are used to understand the role of bars in starburstgalaxies. The oxygen abundance gradients are steeper than in normalbarred galaxies, with a mean of -0.15 dex/kpc, while the intersects arelow. This excludes the possibility that starburst galaxies in thissample are chemically evolved galaxies rejuvenated by the effect of abar. The nitrogen-to-oxygen abundance gradients are flatter than theoxygen ones with a mean of -0.05 dex/kpc. But N/O intersects are high,which rules out the possibility that a large quantity of gas wasrecently funneled by a bar toward the center of a young galaxy. There isno correlation between the abundance gradients and the bar properties,which suggests that bars did not influence the chemical evolution ofthese galaxies. Therefore, bars cannot be at the origin of the bursts inthe nuclei of our sample galaxies. The oxygen and N/O abundancegradients are generally stronger in the bar than in the disk and arelinked together by a linear relation consistent with a primary +secondary origin for the production of nitrogen. This can be fullyexplained in terms of star formation history in these galaxies. Thegradients build up from the inside out, becoming stronger as the oxygenand N/O abundances increase in the bulge while staying low in the disk.This behavior is consistent with a simple Schmidt law relating thedensity of star formation to that of gas. In many of the samplegalaxies, star formation occurs at one or both ends of the bar. The lowlevel of chemical enrichment in these regions suggests that theyrecently experienced bar-triggered star formation: this is the onlyvisible effect of bars. Our analysis shows that bars probably appearedvery recently (a few 107 years) in the starburst galaxies,which are relatively ``young'' galaxies still in the process offormation. Based on observations obtained at the 193cm telescope ofObservatoire de Haute--Provence, operated by INSU (CNRS)
| Optical Spectroscopy of the Central Regions of Bright Barred Spiral Galaxies
Optical red spectra of a set of 18 bright barred spiral galaxies arepresented. The study is aimed at determining the local kinematics, andthe physical conditions of ionized gas in the compact nucleus (inside adiameter of 5") and in the circumnuclear regions (inside a diameter of20"). Only 8 galaxies showed bright emission from their east and westside of the nucleus. The spectrum of each region was analizedseparately. In other 10 galaxies the line emission was so weak that wewere only able to obtain an average spectrum of the central emission. Noemission was detected in the remaining 8 galaxies. An estimate of thedynamical mass is presented based on the observed velocities in thecircumnuclear regions. In NGC 4314 and NGC 6951, that show H_alphaemission distributed in circumnuclear ring structures, we determine the[NII]/H_alpha and [SII]/H_alpha ratios for the eastern and westernregions of the rings. The velocity difference for the two sides is usedto derive the rotation velocity of the gas around the compact nucleus.The ratio [NII]6583/H_alpha is a factor of 2 larger in the compactnucleus of NGC 6951 than in its western side. The electron gas densitieshave been estimated from the [SII] lines ratio.
| Radial Velocity Study of the Dwarf Novae KT Per and TZ Per
Not Available
| Mapping the gas kinematics and ionization structure of four ultraluminous IRAS galaxies
We present a study of the morphology, kinematics and ionizationstructure of the extended emission-line regions in fourintermediate-redshift (0.1181000kms-1 within 1arcsec of the nucleus, suggesting thatany merger is well-advanced. Emission-line intensity ratios point toactive galactic nucleus (AGN) photoionization for the excitation of thisgas at the systemic velocity. An isolated blob ~8kpc from the nucleuswith a much smaller velocity dispersion may lie in a structure similarto the photoionization cones seen in lower-luminosity objects. A second,spatially unresolved, narrow-line component is also present on nucleus,blueshifted by ~=990kms-1 from the systemic and plausiblypowered by photoionizing shocks. IRAS F23060+0505 has more orderedkinematics, with a region of increased FWHM coincident with the bluehalf of a dipolar velocity field. The systemic velocity rotation curveis asymmetric in appearance, as a result either of the on-going mergeror of nuclear dust obscuration. From a higher-resolution ISIS spectrum,we attribute the blue asymmetry in the narrow-line profiles to aspatially resolved nuclear outflow. Emission-line intensity ratiossuggest shock+precursor ionization for the systemic component,consistent with the X-ray view of a heavily obscured AGN. Thelower-luminosity objects IRAS F01217+0122 and F01003-2238 complete thesample. The former has a featureless velocity field with a high FWHM, ahigh-ionization AGN spectrum and a ~1Gyr old starburst continuum. IRASF01003-2238 has a dipolar velocity field and an Hii region emission-linespectrum with a strong blue continuum. After correction for intrinsicextinction, the latter can be reproduced with ~107 O5 stars,sufficient to power the bolometric luminosity of the entire galaxy. Weaccommodate this diversity within the merger-induced evolutionaryscenario for ultraluminous infrared galaxies: the merger status isassessed from the kinematics in a way which is consistent withmorphological and colour information on the galaxies, or with theinferred ages of the young stellar populations and the dominance of theAGN.
| 1-m spectroscopy of normal OB stars
We have obtained spectra of 70 normal OB stars in the near-IR I(1-μm) band. The strongest features are those due to lines of thehydrogen Paschen series and neutral and ionized helium, which are, forthe most part, in absorption. The information content in this spectralrange is sufficient for only a rough classification of hot stars into`early O', `late O' and `B' types. Curiously, the leading He i tripletline, He i λ1.0830 μm, is usually not detectable, although ina few stars it is in emission; its behaviour generally correlates withthe leading helium singlet line, He i λ 2.058 μ m. These twofeatures appear to be present in emission only in stars with extremes ofmass loss or wind extension.
| Catalogue of H-alpha emission stars in the Northern Milky Way
The ``Catalogue of Stars in the Northern Milky Way Having H-alpha inEmission" appears in Abhandlungen aus der Hamburger Sternwarte, Band XIin the year 1997. It contains 4174 stars, range {32degr <= l() II< 214degr , -10degr < b() II < +10degr } having the Hαline in emission. HBH stars and stars of further 99 lists taken from theliterature till the end of 1994 were included in the catalogue. We givethe cross-identification of stars from all lists used. The catalogue isalso available in the Centre de Données, Strasbourg ftp130.79.128.5 or http://cdsweb.u-strasbg.fr and at the HamburgObservatory via internet.
| Eclipsing phenomena of the symbiotic star CH Cygni
Eclipsing phenomena of the inner binary with a period of 756 d in thetriple symbiotic system CH Cyg may have been detected in detailedspectrophotometric observations. The eclipse of the hot component by thered giant started on 1994 October 11 and finished between 1995 January 8and 18. The ingress duration was less than one day. The radius of thered giant is estimated to be 288+/-15Rsolar from the duration of theeclipse. Assuming the bolometric correction of the red giant (M7 III) as4, the distance to this object is estimated to be 307+/-32 pc, whichagrees well with that obtained in the observations by Hipparcos. Theinterstellar extinction in the direction of this object may be muchlower than that in the nearby areas. It has been suggested that theouter binary system with an orbital period of about 15 yr is aneclipsing one. It seems unlikely, however, that the variation of theactivity of this object with a time-scale of more than 10 yr was aresult of eclipses.
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Observation and Astrometry data
| Constellation: | Schwan |
| Right ascension: | 20h12m33.12s |
| Declination: | +40°16'05.4" |
| Apparent magnitude: | 7.561 |
| Distance: | 540.541 parsecs |
| Proper motion RA: | -7.9 |
| Proper motion Dec: | -1.8 |
| B-T magnitude: | 7.908 |
| V-T magnitude: | 7.59 |
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INHABITED SKY
