Triggered massive-star formation on the borders of Galactic H II regions. III. Star formation at the periphery of Sh2-219
Context: .Massive-star formation triggered by the expansion of H iiregions. Aims: .To understand if sequential star formation istaking place at the periphery of the H ii region Sh2-219. Methods:.We present 12CO J=2→ 1 line observations of thisregion, obtained at the IRAM 30-m telescope (Pico Veleta, Spain).Results: .In the optical, Sh2-219 is spherically symmetric around itsexciting star; furthermore it is surrounded along three quarters of itsperiphery by a ring of atomic hydrogen. This spherical symmetry breaksdown at infrared and millimetre wavelengths. A molecular cloud of about2000 M_ȯ lies at the southwestern border of Sh2-219, in the H igap. Two molecular condensations, elongated along the ionization front,probably result from the interaction between the expanding H ii regionand the molecular cloud. In this region of interaction there lies acluster containing many highly reddened stars, as well as a massive starexciting an ultracompact H ii region. More surprisingly, the brightestparts of the molecular cloud form a "chimney", perpendicular to theionization front. This chimney is closed at its south-west extremity byHα walls, thus forming a cavity. The whole structure is 7.5 pclong. A luminous Hα emission-line star, lying at one end of thechimney near the ionization front, may be responsible for thisstructure. Confrontation of the observations with models of H ii regionevolution shows that Sh2-219 is probably 105 yr old. The ageand origin of the near-IR cluster observed on the border of Sh2-219remain unknown.
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On the binarity of Herbig Ae/Be stars
We present high-resolution spectro-astrometry of a sample of 28 HerbigAe/Be and three F-type pre-main-sequence stars. The spectro-astrometry,which is essentially the study of unresolved features in long-slitspectra, is shown from both empirical and simulated data to be capableof detecting binary companions that are fainter by up to 6mag atseparations larger than ~0.1arcsec. The nine targets that werepreviously known to be binary are all detected. In addition, we reportthe discovery of six new binaries and present five further possiblebinaries. The resulting binary fraction is 68 +/- 11 per cent. Thisoverall binary fraction is the largest reported for any observed sampleof Herbig Ae/Be stars, presumably because of the exquisite sensitivityof spectro-astrometry for detecting binary systems. The data hint thatthe binary frequency of the Herbig Be stars is larger than that of theHerbig Ae stars. The Appendix presents model simulations to assess thecapabilities of spectro-astrometry and reinforces the empiricalfindings. Most spectro-astrometric signatures in this sample of HerbigAe/Be stars can be explained by the presence of a binary system. Twoobjects, HD 87643 and Z CMa, display evidence for asymmetric outflows.Finally, the position angles of the binary systems have been comparedwith available orientations of the circumprimary disc and these appearto be coplanar. The alignment between the circumprimary discs and thebinary systems strongly suggests that the formation of binaries withintermediate-mass primaries is due to fragmentation as the alternative,stellar capture, does not naturally predict aligned discs. The alignmentextends to the most massive B-type stars in our sample. This leads us toconclude that formation mechanisms that do result in massive stars, butpredict random angles between the binaries and the circumprimary discs,such as stellar collisions, are also ruled out for the same reason.
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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.
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UBV beta Database for Case-Hamburg Northern and Southern Luminous Stars
A database of photoelectric UBV beta photometry for stars listed in theCase-Hamburg northern and southern Milky Way luminous stars surveys hasbeen compiled from the original research literature. Consisting of over16,000 observations of some 7300 stars from over 500 sources, thisdatabase constitutes the most complete compilation of such photometryavailable for intrinsically luminous stars around the Galactic plane.Over 5000 stars listed in the Case-Hamburg surveys still lackfundamental photometric data.
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Catalogue of stars in the northern Milky Way having H-alpha in emission
Not Available
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Intrinsic colour indices of O- and B- type stars in the Vilnius photometric system.
Not Available
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Photoelectric photometry of OB stars in the Vilnius system
Not Available
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Empirical temperature calibrations for early-type stars
Three temperature calibrations of suitable photometric quantities havebeen derived for O and B stars. A sample of 120 stars with reliableT(eff.) determinations has been used for establishing each calibration.The different calibrations have been critically discussed and compared.Temperature determinations for 1009 program stars have been obtainedwith an accuracy of the order of 10 percent.
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A new determination from OB stars of the galactic rotation constants and the distance to the galactic centre.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1974MNRAS.167..621B&db_key=AST
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Optical observations and model for Cygnus X-1.
Abstract image available at:http://adsabs.harvard.edu/abs/1973ApJ...182..549H
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Some Spectroscopic Characteristics of the OB Stars: an Investigation of the Space Distribution of Certain OB Stars and the Reference Frame of the Classification
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1971ApJS...23..257W&db_key=AST
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Photoelectric 4430 A observations of 506 O, B and A stars.
Not Available
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Stellar Radial Velocities in the Perseus Arm.
Abstract image available at:http://adsabs.harvard.edu/abs/1963ApJ...138.1002A
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Photoelectric measures of the 4430 A diffuse interstellar band
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1963MNRAS.125..141W&db_key=AST
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Die Lichtkurven-Leuchtkraft-Beziehung Neuer Sterne. Mit 8 Textabbildungen
Not Available
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Studies in Galactic STRUCTURE.II.LUMINOSITY Classification for 1270 Blue Giant Stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1955ApJS....2...41M&db_key=AST
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U Lacertae-A Distant Variable Star with an Unusual Spectrum
Not Available
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Polarization of Stellar Radiation. III. The Polarization of 841 Stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1951ApJ...114..241H&db_key=AST
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A Finding List of O and B Stars of High Luminosity.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1951ApJ...113..141N&db_key=AST
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INHABITED SKY
