Stellar contents of two young open clusters: NGC 663 and 654
UBVRI CCD photometry in a wide field around two young open clusters, NGC663 and 654, has been carried out. Hα and polarimetricobservations for the cluster NGC 654 have also been obtained. We use thephotometric data to construct colour-colour and colour-magnitudediagrams, from which we can investigate the reddening, age, mass andevolutionary states of the stellar contents of the these clusters. Thereddening across the cluster regions is found to be variable. There isevidence for anomalous reddening law in both clusters; however, moreinfrared and polarimetric data are needed to conclude about thereddening law. Both clusters are situated at about a distance of 2.4kpc. Star formation in both clusters is found to be a continuousprocess. In the case of NGC 663, star formation seems to have takenplace sequentially, in the sense that formation of low-mass starsprecedes the formation of most massive stars. Whereas, in the case ofNGC 654, formation of low-mass stars did not cease after the formationof most massive stars in the cluster.
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The Massive Runaway Stars HD 14633 and HD 15137
We present results from a radial velocity study of two runaway O-typestars, HD 14633 (ON8.5 V) and HD 15137 [O9.5 III(n)]. We find that HD14633 is a single-lined spectroscopic binary with an orbital period of15.4083 days. The second target, HD 15137, is a radial velocity variableand a possible single-lined spectroscopic binary with a period close to1 month. Both binaries have large eccentricity, small semiamplitude, anda small mass function. We show the trajectories of the stars in the skybased on an integration of motion in the Galactic potential, and wesuggest that both stars were ejected from the vicinity of the opencluster NGC 654 in the Perseus spiral arm. The binary orbital parametersand runaway velocities are consistent with the idea that both thesestars were ejected by supernova explosions in binaries and that theyhost neutron star companions. We find that the time of flight sinceejection is longer than the predicted evolutionary timescales for thestars. This discrepancy may indicate that the stars have a lower massthan normally associated with their spectral classifications, that theywere rejuvenated by mass transfer prior to the supernova, or that theirlives have been extended through rapid rotation.Based in part on observations made at the Observatoire de Haute Provence(CNRS), France.
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Merged catalogue of reflection nebulae
Several catalogues of reflection nebulae are merged to create a uniformcatalogue of 913 objects. It contains revised coordinates,cross-identifications of nebulae and stars, as well as identificationswith IRAS point sources.The catalogue is 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/399/141
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Absolute proper motions of open clusters. I. Observational data
Mean proper motions and parallaxes of 205 open clusters were determinedfrom their member stars found in the Hipparcos Catalogue. 360 clusterswere searched for possible members, excluding nearby clusters withdistances D < 200 pc. Members were selected using ground basedinformation (photometry, radial velocity, proper motion, distance fromthe cluster centre) and information provided by Hipparcos (propermotion, parallax). Altogether 630 certain and 100 possible members werefound. A comparison of the Hipparcos parallaxes with photometricdistances of open clusters shows good agreement. The Hipparcos dataconfirm or reject the membership of several Cepheids in the studiedclusters. Tables 1 and 2 are only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
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Spectroscopic observations of young open clusters: IC 1805, NGC 654 and NGC 6823
Spectroscopic observations were made for a sample of 263 stars fromthree young open clusters IC 1805, NGC 654 and NGC 6823 with CCDdetectors in the blue and yellow-red spectral regions. MKK types wereproperly determined for these stars by carefully comparing spectra ofprogram stars with those of a complete grid of MKK standards, which wereobserved with the same instruments as the program stars. For most of theobserved stars precise MKK types were assigned for the first time. A fewof early-type emission-line stars were discovered or confirmed. Thepresence of Be stars in the studied clusters is discussed. Spectra ofthe observed MKK standards also reveal lots of features showingtemperature or luminosity effect in the yellow-red region, which helpedin our stellar spectral classification.
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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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UBV photometry of open clusters in the Cassiopeia region. II - Photoelectric observations of NGC 654
New photoelectric UBV observations of 16 stars in NGC 654 have been usedto restandardize published photoelectric data. The compilation of thebest data is used in conjunction with proper motions for a detailedanalysis of the cluster. The distance-modulus for NGC 654 is (V - M(V))O= 12.00 (d = 2500 pc) and the reddening varies from E(B - V) = 0.74 to1.19. The age, based on new models including the latest opacity tables,is 14.1 x 10 exp 6 yr (log t = 7.15). The F5 Ia supergiant (HD 10494)falls close to the blue end of the blue loop, which is a strong argumentin favor of its membership. The present analysis confirms the tendencyalready observed to find the less reddened stars close to the clustercenter.
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More radial-velocity measurements in young open clusters
Further high resolution radial-velocity measurements are reported in 23young open clusters using the Kitt Peak CCD coude spectrograph on the0.9-m feed telescope. The radial velocities for the cluster stars arederived with the technique of cross correlation. The internal precisionof the velocity measurements is typically 2 km/s for early type stars.From these new data and previously published velocities, the observedstars in two clusters, NGC 663 and NGC 2287, were found to show arelatively small dispersion in the measured mean velocities. Furtherobservations of stars in young clusters will be useful in helping toestablish an early-type-star-velocity standard system.
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The excitation of 12 micron emission from very small particles
The results of IRAS observations of visual reflection nebulaeilluminated by stars with effective temperatures between 3000 and 33,000K are presented. The ratio of the energy radiated in the IRAS 12-micronsband to the total energy radiated at far-infrared wavelengths (60 and100 microns) is about 0.2, with little or no dependence on thetemperature of the illuminating star for stellar temperatures betweenabout 5000 and 33,000 K. This is interpreted as requiring that visualphotons as well as ultraviolet photons are capable of exciting12-microns emission from very small particles.
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Radial-velocity measurements in 20 young open clusters
The further results of a program to determine the radial velocities ofyoung open clusters are presented. Using the KPNO coude spectrographcoupled with the 1-m feed and 2.1-m telescopes, radial velocities havebeen measured for nearly one hundred stars, most of which are ofspectral type B and A, in 20 young clusters. The combination ofinstruments and the use of cross-correlation techniques show that radialvelocities of B and A type stars as faint as 10th magnitude can bedetermined with an internal precision of less than about 2 km/s. Asexpected, the uncertainties in the velocity determination for the youngclusters are dominated by spectroscopic binary stars in these clusters.A third of the stars in the sample are found to be spectroscopicbinaries, but with a large variation in the frequency of binaries fromcluster to cluster. Because the time coverage is still limited, thisshould be considered a lower limit to the binary frequency. Clustervelocities are determined after eliminating binaries and known nonmemberstars. The new velocities are compared with a model galactic rotationcurve, as well as with previous velocity determinations.
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Yellow evolved stars in open clusters
This paper describes a program in which Galactic cluster post-AGBcandidates were first identified and then analyzed for clustermembership via radial velocities, monitored for possible photometricvariations, examined for evidence of mass loss, and classified ascompletely as possible in terms of their basic stellar parameters. Theintrinsically brightest supergiants are found in the youngest clusters.With increasing cluster age, the absolute luminosities attained by thesupergiants decline. It appears that the evolutionary tracks ofluminosity class II stars are more similar to those of class I than ofclass III. Only two superluminous giant star candidates are found inopen clusters.
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Metal abundance and microturbulence in F0-G2 stars and the calibration of the Stromgren m1 index
The strengths of two narrow groups of metal lines are measuredphotoelectrically by means of an echelle spectrometer for 16 F0-G2 giantfield stars and for 12 Hyades main-sequence stars. A model-atmosphereanalysis of these observations and similar observations of main-sequencefield stars observed earlier results in the determination of the metalabundance for 179 stars. In addition, the microturbulence parameter isdetermined for 73 of these stars. The internal accuracy of the resultsis estimated to be plus or minus 0.08 for the logarithmicmetal-to-hydrogen ratio and plus or minus 0.2 km/sec for themicroturbulence parameter. The metal abundances are found to agree verysatisfactorily with values of the logarithmic iron-to-hydrogen ratiodetermined from classical coude spectroscopy regarding both zero pointand scale. It is found that the microturbulence parameter is a functionof the effective temperature and the surface gravity. It increases from1.2 km/sec for solar type stars to approximately 3.0 km/sec for earlyF-type giants.
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A UBV photometric study of the open cluster NGC 654
Photographic UBV magnitudes and colors are presented for 83 stars in theregion of the young open cluster NGC 654, which Stone (1977) determinedto have nonzero membership probabilities. It is noted that one-third ofthese stars lie outside the cluster nuclear region, indicating thepresence of a stellar corona. Further, the coronal stars can be used toinvestigate the known variable reddening in a cluster region much largerthan considered in previous photometric studies. It is found that overthe extended region, the reddening varies from E(B-V) = 0.77 to 1.13magnitudes with several stars having larger reddenings, and avariable-extinction analysis gives an averaged absorption ratio of R =2.9 + or - 0.6 (s.e.) which is in good agreement with an earlier studyby Turner (1976). In addition, attention is given to the cluster H-Rdiagram, a study of the nuclear and coronal cluster regions, and acomparison of the cluster luminosity function with the InitialLuminosity Function of Sandage (1957).
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Molecular clouds associated with reflection nebulae. I - A survey of carbon monoxide emission
The paper presents 2.6 mm wavelength CO and (C-13)O observations of 130molecular clouds associated with reflection nebulae. Enhanced COemission was found in the vicinity of the illuminating star in abouthalf the objects studied. There is a tendency for the CO peak to beslightly displaced from the star. Many examples of peaks that appear toresult from heating of the cloud by the nearby star are found, whileothers appear to be associated with independent concentrations ofmaterial.
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The differential blanketing of the main-sequence and near-main-sequence M67 stars relative to the Hyades and Coma
The blanketing of main-sequence stars in the Hyades, Coma, and M67, andof F subgiants in M67 is compared on the basis of red photometry. Therequired reddening corrections are derived by several techniques thatare insensitive or probably insensitive to blanketing. The meanreddening values obtained are E(B-V) of approximately 0.016 for theHyades, 0.006 for Coma, and 0.053 for M67. These reddening values areshown to imply that there is measurable reddening well inside 100 pc,that Crawford's (1975) A- and F-star relations must be slightly revised,that significant numbers of relatively nearby field A stars are slightlyreddened, that the North Galactic Pole stars of Hilditch et al. (1976)are reddened by 0.01 to 0.03 in B-V, and that Hyades-field F-star b-ycomparisons must be revised. It is found from the reddening-correctedphotometry that: (1) the differential Hyades-M67 blocking is greater inabsolute value for early G late F stars; (2) effects of evolution on theF IV stars in M67 are clearly discernible in the UV and marginally so inB-V; and (3) the F stars on and very near the M67 main sequence haveapproximately the Coma blocking and considerably less than the Hyadesblocking, which indicates that the zero-age metallicity of M67 issolar-normal.
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Membership in the young open cluster NGC 654
Relative proper motions with an average standard error of + or 0.07arcsec/century in each coordinate have been determined for 186 stars inthe region of the young open cluster NGC 654. Of these stars 60 arefound to be probable members, including the A0 Ib supergiant BD +61 deg315. The F5 Ia MK standard HD 10494 tentatively appears to be a probablemember. With an adopted absorption ratio of 3.0, the corrected distancemodulus is 11.9 + or - 0.3 magnitudes or a distance of 2400 pc. Derivedabsolute visual magnitudes and intrinsic (B-V) colors for thesupergiants are given. Three additional bright stars are presented aspossible B-A Ib supergiants. The known variable reddening across thecluster is probably due to foreground dust rather than to dust left overfrom the period of star formation.
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New determinations of R in open clusters
Variable-extinction analyses for 51 galactic clusters, using primarilyzero-age main-sequence-fitted data, are presented and discussed. Forthree of these clusters, spectroscopic data for the brighter stars arepresented. The weighted mean value of R, the ratio of total to selectiveextinction, for all 51 clusters is 3.08 plus or minus 0.03, in very goodagreement with the results of other determinations. Careful examinationof the data for individual clusters suggests that some evidence for adependence of R on intrinsic color and galactic longitude may bepresent.
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Evolved stars in open clusters.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1976ApJS...30..451H&db_key=AST
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The Distribution of Interstellar Matter in NGC 654
The young cluster NGC 654 is studied using UBV photographic photometrywith a view to determining the distribution of interstellar matter in aregion where star formation recently occurred. NGC 654 is found to beenclosed in a shell of interstellar matter of mass 1500Mȯ. The mass of all stars in the cluster is 4000Mȯ.
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Stars in reflection nebulae
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1968AJ.....73..233R&db_key=AST
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A study of reflection nebulae.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1966AJ.....71..990V&db_key=AST
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Distance Moduli of Open Clusters.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1965ApJS...12..215H&db_key=AST
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Galactic structure in Cassiopeia.
Abstract image available at:http://adsabs.harvard.edu/abs/1964AJ.....69..412M
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The Galactic Cluster NGC 654.
Abstract image available at:http://adsabs.harvard.edu/abs/1960ApJ...132..696P
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Dreifarben-Photometrie des offenen Sternhaufens NGC 654 und einer benachbarten Sterngruppe. Mit 5 Textabbildungen
Not Available
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INHABITED SKY
