Contents
Images
Upload your image
DSS Images Other Images
Related articles
A HST study of the environment of the Herbig Ae/Be star LkHα 233 and its bipolar jet
Context: LkHα 233 is a Herbig Ae/Be star with a collimated bipolarjet. As such, it may be a high-mass analogue to the classical T Tauristars and their outflows. Aims: We investigate optical forbidden linesalong the LkHα 233 jet to determine physical parameters of thisjet (electron density ne, hydrogen ionisation fractionxe, electron temperature T_e). The knowledge of theseparameters allows us a direct comparison of a jet from a Herbig starwith those from T Tauri stars. Methods: We present the results ofHST/STIS and WFPC2 observations of LkHα 233 andits environment. These are the first observations of this object with aspatial resolution of ≤0.1 arcsec at optical wavelengths. Our STISdata provide spectroscopic maps that allow us to reconstruct highangular resolution images of the bipolar jet from LkHα 233covering the first ≈2000 AU from the star in the blueshifted outflowlobe and ≈4000 AU in the redshifted lobe. These maps are analysedwith a diagnostic code that yields ne, xe, T_e,and mass density nH within the jet. Results: The WFPC2images in broad-band filters clearly show a dark lane caused either by acircumstellar disk or a dust torus. The circumstellar environment ofLkHα 233 can be interpreted as a conical cavity that was clearedby a bipolar jet. In this interpretation, the maximum of the optical andnear-infrared brightness distribution does not coincide with the staritself which is, in fact, deeply extincted. In the blueshifted lobe,ne is close to or above the critical density for [SII] lines(2.5 × 10^4 cm-3) in the first arcsecond and decreaseswith distance from the source. The ionisation xe ≈0.2{-}0.6 gently rises for the first 500 AU of the flow and shows twore-ionisation events further away from the origin. The electrontemperature Te varies along the flow between 10^4 K and 3× 10^4 K. The nH is between 3 × 103and 10^5 cm-3, and the mass flux dot{M}≈10-8{-}10-7 {M}ȯ yr-1.The (radial) outflow velocities are ≈80{-}160 km s-1, andthey appear to increase with distance from the source. In the redshiftedlobe, the excitation conditions are quite different: Te,ne, xe, and nH are all lower than inthe blueshifted lobe, but have the same order of magnitude. Conclusions: All these derived parameters are just beyond or at theupper limits of those observed for classical T Tauri star jets. This mayindicate that the flows from the higher mass Herbig stars are indeedscaled-up examples of the same phenomenon as in T Tauri stars.Based on observations made with the NASA/ESA Hubble Space Telescope,obtained at the Space Telescope Science Institute, which is operated bythe Association of Universities for Research in Astronomy, Inc., underNASA contract NAS5-26555.
| Laser Guide Star Adaptive Optics Integral Field Spectroscopy of a Tightly Collimated Bipolar Jet from the Herbig Ae Star LkHα 233
We have used the integral field spectrograph OSIRIS and laser guide staradaptive optics at Keck Observatory to obtain high angular resolution(0.06"), moderate spectral resolution (R~=3800) images of the bipolarjet from the Herbig Ae star LkHα 233, seen in near-IR [Fe II]emission at 1.600 and 1.644 μm. This jet is narrow and tightlycollimated, with an opening angle of only 9°, and has an averageradial velocity of ~100 km s-1. The jet and counterjet areasymmetric, with the redshifted jet much clumpier than its counterpartat the angular resolution of our observations. The observed propertiesare in general similar to jets seen around T Tauri stars, although ithas a relatively large mass flux of 1.2+/-0.3×10-7Msolar yr-1, near the high end of the observedmass flux range around T Tauri stars. We also spatially resolve aninclined circumstellar disk around LkHα 233, which obscures thestar from direct view. By comparison with numerical radiative transferdisk models, we estimate the disk midplane to be inclinedi=65deg+/-5deg relative to the plane of the sky.Since the star is seen only in scattered light at near-infraredwavelengths, we detect only a small fraction of its intrinsic flux.Because previous estimates of its stellar properties did not account forthis, either LkHa 233 must be located closer than previously believed,or its true luminosity must be greater than previously supposed,consistent with its being a ~4 Msolar star near the stellarbirth line.Some of the data presented herein were obtained at the W. M. KeckObservatory, which is operated as a scientific partnership among theCalifornia Institute of Technology, the University of California, andthe National Aeronautics and Space Administration. The Observatory wasmade possible by the generous financial support of the W. M. KeckFoundation.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| Herbig Ae/Be Stars in nearby OB Associations
We have carried out a study of the early-type stars in nearby OBassociations spanning an age range of ~3-16 Myr, with the aim ofdetermining the fraction of stars that belong to the Herbig Ae/Be class.We studied the B, A, and F stars in the nearby (<=500 pc) OBassociations Upper Scorpius, Perseus OB2, Lacerta OB1, and Orion OB1,with membership determined from Hipparcos data. We also included in ourstudy the early-type stars in the Trumpler 37 cluster, part of the CepOB2 association. We obtained spectra for 440 Hipparcos stars in theseassociations, from which we determined accurate spectral types, visualextinctions, effective temperatures, luminosities and masses, usingHipparcos photometry. Using colors corrected for reddening, we find thatthe Herbig Ae/Be stars and the classical Be (CBe) stars occupy clearlydifferent regions in the JHK diagram. Thus, we use the location on theJHK diagram, as well as the presence of emission lines and of strong 12μm flux relative to the visual, to identify the Herbig Ae/Be stars inthe associations. We find that the Herbig Ae/Be stars constitute a smallfraction of the early-type stellar population even in the youngerassociations. Comparing the data from associations with different agesand assuming that the near-infrared excess in the Herbig Ae/Be starsarises from optically thick dusty inner disks, we determined theevolution of the inner disk frequency with age. We find that the innerdisk frequency in the age range 3-10 Myr in intermediate-mass stars islower than that in the low-mass stars (<1 Msolar) inparticular, it is a factor of ~10 lower at ~3 Myr. This indicates thatthe timescales for disk evolution are much shorter in theintermediate-mass stars, which could be a consequence of more efficientmechanisms of inner disk dispersal (viscous evolution, dust growth, andsettling toward the midplane).
| New periodic variables from the Hipparcos epoch photometry
Two selection statistics are used to extract new candidate periodicvariables from the epoch photometry of the Hipparcos catalogue. Theprimary selection criterion is a signal-to-noise ratio. The dependenceof this statistic on the number of observations is calibrated usingabout 30000 randomly permuted Hipparcos data sets. A significance levelof 0.1 per cent is used to extract a first batch of candidate variables.The second criterion requires that the optimal frequency be unaffectedif the data are de-trended by low-order polynomials. We find 2675 newcandidate periodic variables, of which the majority (2082) are from theHipparcos`unsolved' variables. Potential problems with theinterpretation of the data (e.g. aliasing) are discussed.
| CCD measurements of visual double stars made with the 74 cm and 50 cm refractors of the Nice Observatory (2nd series)
We present 619 measurements of 606 visual double stars made by CCDimaging from 1996 to 1999 with the 74 cm and 50 cm refractors of theNice observatory. Angular separation, position angle and magnitudedifference are given. Magnitude differences estimated from CCD imagesare compared with magnitude differences given in the Hipparcos catalog.The residuals in angular separation and position angle are computed forbinaries with known orbit. Table 2 is only available in electronic format the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) orvia http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/378/954
| A HIPPARCOS Census of the Nearby OB Associations
A comprehensive census of the stellar content of the OB associationswithin 1 kpc from the Sun is presented, based on Hipparcos positions,proper motions, and parallaxes. It is a key part of a long-term projectto study the formation, structure, and evolution of nearby young stellargroups and related star-forming regions. OB associations are unbound``moving groups,'' which can be detected kinematically because of theirsmall internal velocity dispersion. The nearby associations have a largeextent on the sky, which traditionally has limited astrometricmembership determination to bright stars (V<~6 mag), with spectraltypes earlier than ~B5. The Hipparcos measurements allow a majorimprovement in this situation. Moving groups are identified in theHipparcos Catalog by combining de Bruijne's refurbished convergent pointmethod with the ``Spaghetti method'' of Hoogerwerf & Aguilar.Astrometric members are listed for 12 young stellar groups, out to adistance of ~650 pc. These are the three subgroups Upper Scorpius, UpperCentaurus Lupus, and Lower Centaurus Crux of Sco OB2, as well as VelOB2, Tr 10, Col 121, Per OB2, alpha Persei (Per OB3), Cas-Tau, Lac OB1,Cep OB2, and a new group in Cepheus, designated as Cep OB6. Theselection procedure corrects the list of previously known astrometricand photometric B- and A-type members in these groups and identifiesmany new members, including a significant number of F stars, as well asevolved stars, e.g., the Wolf-Rayet stars gamma^2 Vel (WR 11) in Vel OB2and EZ CMa (WR 6) in Col 121, and the classical Cepheid delta Cep in CepOB6. Membership probabilities are given for all selected stars. MonteCarlo simulations are used to estimate the expected number of interloperfield stars. In the nearest associations, notably in Sco OB2, thelater-type members include T Tauri objects and other stars in the finalpre-main-sequence phase. This provides a firm link between the classicalhigh-mass stellar content and ongoing low-mass star formation. Detailedstudies of these 12 groups, and their relation to the surroundinginterstellar medium, will be presented elsewhere. Astrometric evidencefor moving groups in the fields of R CrA, CMa OB1, Mon OB1, Ori OB1, CamOB1, Cep OB3, Cep OB4, Cyg OB4, Cyg OB7, and Sct OB2, is inconclusive.OB associations do exist in many of these regions, but they are eitherat distances beyond ~500 pc where the Hipparcos parallaxes are oflimited use, or they have unfavorable kinematics, so that the groupproper motion does not distinguish it from the field stars in theGalactic disk. The mean distances of the well-established groups aresystematically smaller than the pre-Hipparcos photometric estimates.While part of this may be caused by the improved membership lists, arecalibration of the upper main sequence in the Hertzsprung-Russelldiagram may be called for. The mean motions display a systematicpattern, which is discussed in relation to the Gould Belt. Six of the 12detected moving groups do not appear in the classical list of nearby OBassociations. This is sometimes caused by the absence of O stars, but inother cases a previously known open cluster turns out to be (part of) anextended OB association. The number of unbound young stellar groups inthe solar neighborhood may be significantly larger than thoughtpreviously.
| Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
| Molecular line observations of a comet-shaped cloud (LBN 437) in the Lacerta OB1 association
Two prominent nuclei of a large, comet-like (10 pc in length) dust andgas complex, located in the Lacerta Constellation (l~96deg, b~-15deg),have been observed in molecular lines of CO, NH_3_ and H_2_CO. We willrefer to the whole system as the LBN 437 complex. It lies at the edge ofthe youngest subgroup of the Lac OB1 association and is associated withthis young group of stars. The cometary head, condensation A, containsreflection nebulae and a group of faint LkHα stars, among themLkHα 233. H_2_CO(1_11_-1_10_) ^13^CO(1-0) and (2-1) line maps showan elongated configuration of size ~2x0.5pc and a mass of150-300Msun_xNH_3_(1,1) and (2,2) inversion line observationsof Condensation A reveal the existence of a cold (10K) and dense(3x10^4^cm^-3^) core of elliptical shape. The mass and linear dimensionsof this NH_3_ clump are 15Msun_, ~0.16pc (semi-major axis)and ~0.10pc (semi-minor axis). From IRAS 60-100μm images and^12^CO(1-0) line data, we infer dust and gas temperatures of ~37K forthe surrounding low-column density, far-IR emitting material. It isconcluded that Condensation A consists of a cold dense core, from whichnewly formed Hα emission line stars have formed. This issurrounded by a lower density envelope whose warm surface is heatedexternally by a nearby B star (HD 213976). Condensation B, lying nearthe end of the cometary "tail", was mapped in H_2_CO absorption,although NH_3_ emission lines were not detected.
| Intrinsic colour indices of O- and B- type stars in the Vilnius photometric system.
Not Available
| Galactic OB associations in the northern Milky Way Galaxy. I - Longitudes 55 deg to 150 deg
The literature on all OB associations was reviewed, and their IRAS pointsource content was studied, between galactic longitude 55 and 150 deg.Only one third of the 24 associations listed by Ruprecht et al. (1981)have been the subject of individual studies designed to identify thebrightest stars. Distances to all of these were recomputed using themethod of cluster fitting of the B main sequence stars, which makes itpoossible to reexamine the absolute magnitude calibration of the Ostars, as well as for the red supergiant candidate stars. Also examinedwas the composite HR diagram for these associations. Associations withthe best defined main sequences, which also tend to contain very youngclusters, referred to here as OB clusters, have extremely few evolved Band A or red supergiants. Associations with poorly defined mainsequences and few OB clusters have many more evolved stars. They alsoshow an effect in the upper HR diagram referred to as a ledge byFitzpatrick and Garmany (1990) in similar data for the Large MagellanicCloud. It is suggested that the differences in the associations are notjust observational selection effects but represent real differences inage and formation history.
| Photoelectric photometry of OB stars in the Vilnius system
Not Available
| Absolute magnitudes of B emission line stars - Correlation between the luminosity excess and the effective temperature
A new determination of the visual absolute magnitude of Be stars iscarried out. For this, a new calibration of visual absolute magnitudesof B stars of luminosity classes, V, IV, and III is first obtained froma sample of 215 stars. The absolute luminosity excess in the visual isdetermined for a sample of 49 Be stars. It is found that this excess iscorrelated with the effective temperature of the underlying stars. Awell defined correlation between this excess and the emission in thefirst two Balmer lines is established. From these results, using asimple model of circumstellar envelope, it is inferred that the zones ofthe circumstellar envelope contributing to the emission in the continuumand in the lines have to be rather small. It is also deduced that theemission measure of the envelope is correlated with the temperature ofthe central star and that the irregular photometric variations of Bestars are an envelope-opacity phenomenon.
| Luminosities, masses, and ages of B-type stars
Measurements of H-gamma lines and photometry of the Balmer discontinuityare combined with models of stellar atmospheres and interiors to derivevalues of T(eff) log g, mass, and M(bol) for main-sequence B-type starsin the Alpha Per and the Pleiades clusters and in the Orion, Sco-Gen,and I Lac associations. The masses as a function of T(eff) agree withthe analyses of eclipsing binary orbits. The luminosities yielddistances for the observed clusters and associations that are in goodagreement with independent determinations. The observed main sequence isbroader than predicted by standard models and suggests that mixing mayplay a role in extending the main-sequence lifetime. Stars within eachcluster and association show a range of ages, a result that suggeststhat star formation occurred over a period of at least 1-3 x 10 to the7th yr.
| The Herbig Ae-Star LKH-ALPHA:233 and a Related Compact Region of Star Formation
Not Available
| Radial velocity measurements. II - Ground-based observations of the program stars for the HIPPARCOS satellite
New radial velocities for 446 stars of magnitude 9.0 or brighter in 1616-sq-deg fields of the Northern Hemisphere are determined by automaticPDS measurement of 80-A/mm-dispersion spectra obtained at theObservatoire de Haute Provence using a 17-cm-diameter objective prism.The fields were selected to provide data for the input catalog of theESA Hipparcos astrometric satellite. The measurement techniques andprecision are discussed, and the results are presented in extensivetables and graphs.
| Catalog of O-B stars observed with Tokyo Meridian Circle
A catalog of the O-B stars, selected from 'Blaauw-Parenago' list andRubin's catalog, has been compiled on the FK4 system by the observationsmade with Gautier 8-inch Meridian Circle at the Tokyo AstronomicalObservatory during the period, 1971 to 1979. It contains 1059 stars andwas compiled for the future establishment of high precision propermotions of O-B stars.
| The determination of the helium abundance in main-sequence B stars
It is pointed out that the abundances of deuterium, helium, and lithiumprovide fundamental constraints on cosmological models. The centralquestion is related to the compatibility of the observed abundances withbig bang models of primordial nucleosynthesis, taking into account amodification by subsequent nuclear processing in stars or a modificationof standard models. The present paper has the objective to assesscritically the feasibility of deriving accurate helium abundances frommeasurements of the photospheric lines in main-sequence B-type stars. Amethod is established for assigning atmospheric parameters tomain-sequence stars with spectral types in the range (approximately)B1-B5. It is found that an analysis of stars in distant anticenter H IIregions and clusters offer an alternative method which seems capable ofdetermining relative abundances with more than the requisite accuracy.
| New Double Stars Discovered at Nice - Part Sixteen
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1981A&AS...43...79C&db_key=AST
| The fundamental physical parameters of main-sequence and near main-sequence B type stars as derived from uvby,beta photometry
From spectrophotometric measurements of hydrogen line intensities, uvbyphotometry and photoelectrically determined H-beta and H-gamma indicesof 75 B2-B6 main-sequence stars, effective temperature and surfacegravity are derived by using the model atmospheres computed by Kurucz(1974). Comparisons between the g values and the MK luminosityclassification show good agreement for the MK standard stars but ratherserious disagreement for the average stars in such a way that most ofthe stars classified in luminosity class V really belong to class IV.Using the evolutionary model sequences calculated by Hejlesen et al.(1972) the stellar mass, age and luminosity are determined from the uvbyand beta data through effective temperature and surface gravity. Thetheoretically derived luminosities are in excellent agreement with theluminosities derived by calibrations.
| Spectral classification from the ultraviolet line features of S2/68 spectra. V - Supplement series
The paper presents the ultraviolet classification of more than 450 B-Aand F spectra obtained with the sky survey telescope mounted on the TD1satellite. Concerning abnormal objects, attention is given to the Bestars, the binary stars, the helium weak stars, and the lambda Booobjects. With regard to Be stars, it is concluded that the 1930 Awavelength feature is linked to the existence of either shell structuresor Fe II emission lines in the visual spectral range. In addition, it issuggested that stellar spectra at wavelengths of 1410, 1610-20 and 2400A are equivalent to the He-weak group in the classical range.
| Four-color photometry for the association Lac OB1.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1976PASP...88..930C&db_key=AST
| Spectral classification of stars in Lac OB1
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1976AJ.....81.1120G&db_key=AST
| Evidence of helium abundance differences between young groups of stars
Seven groups of B-type stars - Sco-Cen, NGC 6231, LacOBI,OriOBIb, h + chi Per, CepOBIII, and field stars - wereinvestigated photoelectrically to determine whether helium abundance isuniform in the solar neighborhood and in a region of the spiral arm ofthe Galaxy. Observations were performed using an echelle spectrometer inthe narrow band index of the I (4026) of the He I-4026 line. Amodel-atmosphere analysis of I (4026) and the beta index of the H betaline shows that in the spectral range B O-B 2, the relation between I(4026) and beta is insensitive to differences in the surface gravity butsensitive to differences in the helium to hydrogen ratio. It is foundthat stars in the two groups most distant from the sun - h + chi Per andCepOBIII - have a lower helium abundance than stars in the solarneighborhood.
| Spectral types in the Lac OB1 association.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1976PASP...88..141L&db_key=AST
| Internal motions in the associations II Per and I Lac.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1969AJ.....74..891L&db_key=AST
| Photoelectric distances of 461 Northern OB-stars and galactic structure from Hγ- luminosities Author: Beer, A.
Abstract image available at:http://adsabs.harvard.edu/abs/1964MNRAS.128..261B
| Stellar Rotation in Galactic Clusters.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1962ApJ...136..381A&db_key=AST
| Hβ Photometry for the Association i Lacertae.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1961ApJ...133..860C&db_key=AST
| Coordonnées moyennes de 86 étoiles 0 et B déterminées à l'Observatoire de Paris et réduites sans mouvements proper à l'équinoxe 1950,0
Not Available
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
| Constellation: | Lézard |
| Right ascension: | 22h34m30.19s |
| Declination: | +40°46'29.6" |
| Apparent magnitude: | 7.013 |
| Distance: | 289.855 parsecs |
| Proper motion RA: | -0.3 |
| Proper motion Dec: | -2.4 |
| B-T magnitude: | 6.85 |
| V-T magnitude: | 7 |
Catalogs and designations:
|
