|NGC 1624 (OCl 403, Cr 53) A very young open cluster|
We present the first CCD photometric UBVRI observations of thenot-so-well-studied open cluster NGC 1624 (OCl 403, Cr 53;α2000 = 04 h 40 m 36 s; δ2000 = +50˚ 27′ 42″ Trumpler class = I 2p N). This cluster was observed on 01 February 2004 with the 2 mHimalayan Chandra Telescope at Hanle using a LN2 cooled 2k × 2kCCD. The cluster presents differential reddening with E(B-V) valuesranging from 0.70 to 0.90 mag, which could be attributed to the presenceof the HII region wherein the cluster is embedded. It is found to be ata distance of 6.025 ± 0.5 kpc and the age of this cluster isestimated to be ˜3.98 × 106 years. In view ofthese parameters, it can be considered as a young enough cluster locatedin the direction of the Perseus constellation with the galacticcoordinates of l = 155˚.35 and b = + 02˚.58. Thus it could also be used as a suitable candidatefor tracing the Outer Perseus spiral arm of our Galaxy. The initial massfunction slope is derived as 1.65 ± 0.25 by applying thecorrections for field star contamination and data incompleteness. Thisis in good agreement with the Salpeter value within the limits oferrors.
|Study of young open cluster NGC 1624 (OCl 403, Cr 53)|
|Collaborative Research of Open Star Clusters|
Preliminary results on observations of open clusters are pre-sented. Theproject has been initiated in the framework of the Uzbek-Taiwan andTaiwan-Baltic collaboration, mainly to upgrade and make use offacilities at Maidanak Observatory. We present detailed,multi-wavelength studies of the young cluster NGC 6823 and theassociated complex nebulosity, to diagnose the young stellar populationand star formation history in the region. In addition, 7 compact openclusters have been monitored for stellar variability. We show howobservations like these could feasibly be used to look for exoplanettransit events. We also expect to join the Whole-Earth Telescope effortin future campaigns for asteroseismology.
|Distances to Cepheid open clusters via optical and K-band imaging|
We investigate the reddening and main-sequence-fitted distances to 11young, Galactic open clusters that contain Cepheids. Each clustercontains or is associated with at least one Cepheid variable star.Reddening to the clusters is estimated using the U-B:B-V colours of theOB stars and the distance modulus to the cluster is estimated via B-V:Vand V-K:V colour-magnitude diagrams. Our main-sequence fitting assumesthat the solar-metallicity zero-age main sequence of Allen appliesuniversally to all the open clusters, although this point iscontroversial at present. In this way we proceed to calibrate theCepheid period-luminosity (PL) relation and find MV=-2.87× logP- 1.243 +/- 0.09, MK=-3.44 × logP- 2.21 +/-0.10 and absolute distance moduli to the Large Magellanic Cloud (LMC) of18.54 +/- 0.10 from the V-band and 18.48 +/- 0.10 from the K-band givingan overall distance modulus to the LMC of μ0= 18.51 +/-0.10. This is in good agreement with the previous Cepheid PL-K result ofLaney & Stobie at μ0= 18.51 +/- 0.09 and with theHipparcos parallax-calibrated Cepheid PL-K estimate of Feast &Catchpole at μ0= 18.66 +/- 0.10 when no account is takenof the LMC metallicity.We also find that the two-colour U-B:B-V diagrams of two importantclusters are not well fitted by the standard main-sequence line. In onecase, NGC 7790, we find that the F stars show a UV excess and in thesecond case, NGC 6664, they are too red in U-B. Previous spectroscopicestimates of the metallicity of the Cepheids in these clusters appear tosuggest that the effects are not due to metallicity variations. Otherpossible explanations for these anomalies are positional variations inthe dust reddening law and contamination by foreground or backgroundstars.
|Stellar tracers of the Cygnus Arm. I. Spectroscopic study of bright photometric candidates|
We present medium-resolution spectroscopy of a sample of stars in thesecond Galactic quadrant selected from the literature because theircolours suggest that they are moderately-reddened early-type stars atvery large distances. From the derived spectral types and observedcolours, we calculate distances to all these objects. For a sizablefraction of our sample, we find distances well in excess of what isexpected for Perseus Arm objects, even allowing for rather generouserrors. In the interval l=150degr -180degr , there is a large number ofobjects with distances in excess of 4 kpc, which are likely tracing theOuter or Cygnus Arm. In particular, we find that the association Cam OB3is placed on this Arm. Based on our results, the extent and definitionof the associations Cas OB4 and Aur OB2 need to be reevaluated.Based on observations made at Observatoire de Haute Provence (CNRS),France.
|Spectroscopic Binaries in Young Open Clusters|
We have analysed the binarity and multiplicity characteristics of 120O-type stars in 22 very young open clusters and found marked differencesbetween the "rich" (N >= 6 O-type stars and primaries) and "poor" (N= 1) clusters. In the rich clusters, the binary frequencies vary between14% (1 SB among 7 stars) and 80% (8 SBs among 10 stars). Multiplesystems seem not to be frequent and stars are spread all over thecluster area. In poor clusters, the binary frequency of the O-typeobjects is nearly 100%, with orbital periods around 3 days. Severalbinaries are also eclipsing. Additional companions are always present.They form either hierarchical multiple stars or trapezium systems. Thesemassive multiple systems are generally found close to the clustercenter, although there are exceptions.
|HII regions as cavities.|
Abstract image available at:http://adsabs.harvard.edu/abs/1994RMxAA..29...88D
|What happens when the massive stars form?|
Observations show that O stars rapidly disrupt their parental molecularclouds and thus prevent more stars from forming in a cluster. The cloudsare eroded by stellar radiation and accelerated by stellar wind actingin concert with the Oort/Spitzer rocket effect. Once the visually opaquemolecular material is removed from the neighborhood of an OB cluster,the stars contribute significantly to the diffuse interstellar radiationfield and ionize a vast volume of space.
|A CO survey of regions around 34 open clusters. II - Physical properties of cataloged molecular clouds|
The physical properties of the 148 molecular clouds found in a CO surveyof regions around 34 young open clusters have been examined. Expressionsare given for the cloud size spectrum and the mass spectrum. Themass-radius relation implies that clouds of all size larger than a fewpc have about the same mean volume density. Power laws with slopes of0.6 and 3 describe, respectively, the relations of CO linewidth andcloud mass to cloud size. The clouds are distinctly nonspherical andappear to be randomly oriented with respect to the Galactic plane. Theobservations can be explained by a model for molecular clouds in whichclouds are ensembles of dense clumps of gas. Based on such a model, itis shown that molecular clouds are perturbed on a time scale shortcompared to the time required for them to reestablish virialequilibrium.
|The abundance of sulfur in extragalactic H II regions|
A long-slit CCD survey of forbidden S III 9069, 9532 A radiation in 13extragalactic H II regions is presented, and the data are used to studythe variation of S/O as a function of O/H. The data are consistent withthe idea that S/O remains constant as O/H varies. There is no evidencethat S/O is larger at low O/H. Photoionization models confirm thatobservations of O(+)/O(2+) and S(+)/S(2+) can be used to estimate theeffective temperature of the ionizing stars in an H II region. Thisprovides a potentially powerful new tool for studying the ionizing starsof H II regions in external galaxies. However, the models fail toreproduce the S(+)/S(2+) ratio in nebulae with large O(2+) fractions forreasonable values of T(eff). Simple chemical evolution models arecalculated to compare observations with expectations from stellarneucleosynthesis calculations.
|A CO survey of regions around 34 open clusters|
Results are presented from a systematic search for CO emission fromregions around 34 young open clusters in the outer Galaxy. The clustershave well-determined distances ranging from about 1 to 5 kpc and agesnot greater than about 100 Myr. It was found that some moderately youngclusters have no associated CO emission. All the surveyed clustersyounger than about 5 Myr have associated with them at least onemolecular cloud more massive than 10,000 solar mass, while the molecularclouds associated with clusters older than about 10 Myr are not moremassive than a few thousands solar masses. It was also found thatmolecular clouds are receding from young clusters at a rate of about 10km/sec, and that they seem to be destroyed by their interaction with thestars. Sites of ongoing star formation were identified in a number ofclouds associated with young clusters.
|A Star-Hop from Capella|
|On the redistribution of OB star luminosity and the warming of nearby molecular clouds|
IRAS observations of the neighborhoods of six H II regions in the outerGalaxy are correlated with CO maps of the same regions. It is found thatmore than half of the far-IR luminosity from within about 25 to 75 pc ofthe ionizing stars is contributed by dust associated with molecularclouds. It is shown that a major and increasing fraction of the OBcluster starlight is not absorbed locally. The observations suggest thatthe H II regions are not radiation-bounded and have ion densities ofabout 1/cu cm. A model describing the interstellar environment of OBstar clusters as a function of time is presented.
|Catalog of open clusters and associated interstellar matter.|
|Exciting stars and the distances of the diffuse nebulae|
|The brighter 94 micron sources observed by the far-infrared sky survey experiment|
Approximately 9000 sq deg were surveyed in four IR bands with arocket-borne Far-Infrared Sky Survey Experiment (FIRSSE). The surveycovered the galactic plane between 120 deg and 255 deg longitude andincluded the Orion and Taurus molecular clouds. A list of confirmedsources brighter than 1000 Jy at 94 microns plus other objects ofinterest is presented along with their measured fluxes at 20, 27, and 40microns. The sources are associated with galactic H II regions,molecular clouds, and cool stars. Their average extended sourcetemperatures range between about 35 and 70 K, and their IR luminositiesrange between about 100 - 100,000 solar luminosities.
|Studies of bright diffuse galactic nebulae with special regard to their spatial distribution.|
|TThe source of luminosity in galactic nebulae.|
|A general study of diffuse galactic nebulae.|