|Two new evolved bipolar planetary nebulae in the solar neighbourhood|
We present AAO/UKST Hα+[N II] narrow-band imagery and low- andmedium-resolution optical spectroscopy of RCW24 and RCW69. These nebulaewere previously classified as HII regions, but we now show them to betwo of the largest and nearest bipolar Type I PNe yet discovered.Distances were estimated using extinction-distance and kinematicmethods, and via a new Hα surface brightness-radius relation. Theadopted distances are 1.0 +/- 0.3kpc for RCW24 and 1.3 +/- 0.2kpc forRCW69. Both objects have enhanced nitrogen abundances, withlogN/O~=+0.44 for RCW24, and logN/O=+0.33 for RCW 69. Systemicvelocities and |z| distances are VLSR = +5 km s-1and |z| ~ 23pc for RCW 24, and VLSR = -33 km s-1and only |z| ~ 7pc for RCW 69. Both PNe originated from massiveprogenitors (>2.0-2.5Msolar), as deduced from theirchemical abundances, large ionized masses, small |z| distances, lowpeculiar velocities and relatively hot central stars. These two objectsform an important addition to the small sample of evolved bipolar PNe inthe solar neighbourhood.
|The Remarkable Be Star HD 110432 (BZ Crucis)|
HD 110432 (B1e) has gained considerable recent attention because it is ahard, variable X-ray source with local absorption and also because itsoptical spectrum is affected by an extensive Be disk. From time-serialechelle data obtained over 2 weeks during 2005 January and February, wehave discovered several remarkable characteristics in the star's opticalspectrum. The line profiles show rapid variations on some nights, whichcan most likely be attributed to irregularly occurring and short-livedmigrating subfeatures. Such features have been found in spectra ofγ Cas and AB Dor, two stars for which it is believed magneticfields force circumstellar clouds to corotate over the star's surface.The star's optical spectrum also exhibits a number of mainly Fe II andHe I emission features with double-lobed profiles typical of anoptically thin circumstellar disk viewed nearly edge-on. Using spectralsynthesis techniques for the January data, we find that its temperatureand column density are close to 9800 K and roughly3×1022 cm-2, respectively. Its projecteddisk size covers remarkably large 100 stellar areas, and the emittingvolume resides at a surprisingly large distance of 1 AU from the star.Surprisingly, we also find that the absorption wings of the strongestoptical and UV lines in the spectrum extend to at least +/-1000 kms-1, even though the rotational velocity is 300-400 kms-1. We are unable to find a satisfactory explanation forthese extreme line broadenings. Otherwise, HD 110432 and γ Casshare similarly peculiar X-ray and optical characteristics. Theseinclude a high X-ray temperature, erratic X-ray variability ontimescales of a few hours, optical metallic emission lines, andsubmigrating features in optical line profiles. Because of thesesimilarities, we suggest that HD 110432 is a member of a select newclass of ``γ Cas analogs.''
|Proper motion determination of open clusters based on the UCAC2 catalogue|
We present the kinematics of hundreds of open clusters, based on theUCAC2 Catalogue positions and proper motions. Membership probabilitieswere obtained for the stars in the cluster fields by applying astatistical method uses stellar proper motions. All open clusters withknown distance were investigated, and for 75 clusters this is the firstdetermination of the mean proper motion. The results, including the DSSimages of the cluster's fields with the kinematic members marked, areincorporated in the Open Clusters Catalogue supported on line by ourgroup.
|Astrophysical parameters of Galactic open clusters|
We present a catalogue of astrophysical data for 520 Galactic openclusters. These are the clusters for which at least three most probablemembers (18 on average) could be identified in the ASCC-2.5, a catalogueof stars based on the Tycho-2 observations from the Hipparcos mission.We applied homogeneous methods and algorithms to determine angular sizesof cluster cores and coronae, heliocentric distances, mean propermotions, mean radial velocities, and ages. For the first time we derivedistances for 200 clusters, radial velocities for 94 clusters, and agesof 196 clusters. This homogeneous new parameter set is compared withearlier determinations, where we find, in particular, that the angularsizes were systematically underestimated in the literature.
|On the determination of age and mass functions of stars in young open star clusters from the analysis of their luminosity functions|
We construct the observed luminosity functions of the remote young openclusters NGC 2383, 2384, 4103, 4755, 7510 and Hogg 15 from CCDobservations of them. The observed LFs are corrected for field starcontamination determined with the help of a Galactic star count model.In the case of Hogg 15 and NGC 2383 we also consider the additionalcontamination from neighbouring clusters NGC 4609 and 2384,respectively. These corrections provide a realistic pattern of clusterLF in the vicinity of the main-sequence (MS) turn-on point and atfainter magnitudes reveal the so-called H-feature arising as a result ofthe transition of the pre-MS phase to the MS, which is dependent on thecluster age. The theoretical LFs are constructed representing a clusterpopulation model with continuous star formation for a short time-scaleand a power-law initial mass function (IMF), and these are fitted to theobserved LF. As a result, we are able to determine for each cluster aset of parameters describing the cluster population (the age, durationof star formation, IMF slope and percentage of field starcontamination). It is found that in spite of the non-monotonic behaviourof observed LFs, cluster IMFs can be described as power-law functionswith slopes similar to Salpeter's value. The present main-sequenceturn-on cluster ages are several times lower than those derived from thefitting of theoretical isochrones to the turn-off region of the uppermain sequences.
|Proper Motions of Open Star Clusters and the Rotation Rate of the Galaxy|
The mean proper motions of 167 Galactic open clusters withradial-velocity measurements are computed from the data of the Tycho-2catalog using kinematic and photometric cluster membership criteria. Theresulting catalog is compared to the results of other studies. The newproper motions are used to infer the Galactic rotation rate at the solarcircle, which is found to be ω0=+24.6±0.8 km s-1 kpc-1.Analysis of the dependence of the dispersion of ω0 estimates onheliocentric velocity showed that even the proper motions of clusterswith distances r>3 kpc contain enough useful information to be usedin kinematic studies demonstrating that the determination of propermotions is quite justified even for very distant clusters.
|A Catalog of Star-Forming Regions in the Galaxy|
This Catalog of Star-Forming Regions in the Galaxy contains coordinatesand fluxes of young objects in the radio and infrared, as well as dataon the radial velocities of recombination and molecular lines, for morethan three thousand star-forming regions. In addition to photometric andkinematic data, we present information on diffuse and reflectingnebulae, dark and molecular clouds, and other objects related to youngstars. The catalog consists of two parts. The main catalog listsstar-forming regions in order of Galactic longitude and is supplementedby analogous information for star-forming regions in complexes of darkclouds with large angular sizes that are closest to the Sun. The maincatalog is located at http://www.strasbg.-u.fr/pub/cats. In ourpreliminary study of the catalog data using a formal classification ofthe star-forming regions, we subdivided these objects into severalclasses and characterized them as being populated primarily by massiveor low-mass stars at early or late stages of the star-formation process.We also distinguish between relatively nearby and distant complexes.
|On the stellar content of the open clusters Melotte 105, Hogg 15, Pismis 21 and Ruprecht 140|
CCD observations in the B, V and I passbands have been used to generatecolour-magnitude diagrams reaching down to V ~ 19 mag for two slightlycharacterized (Melotte 105 and Hogg 15) and two almost unstudied (Pismis21 and Ruprecht 140) open clusters. The sample consists of about 1300stars observed in fields of about 4arcmin x4arcmin . Our analysis showsthat neither Pismis 21 nor Ruprecht 140 are genuine open clusters sinceno clear main sequences or other meaningful features can be seen intheir colour-magnitude diagrams. Melotte 105 and Hogg 15 are openclusters affected by E(B-V) = 0.42 +/- 0.03 and 0.95 +/- 0.05,respectively. Their distances to the Sun have been estimated as 2.2 +/-0.3 and 2.6 +/- 0.08 kpc, respectively, while the corresponding agesestimated from empirical isochrones fitted to the Main Sequence clustermembers are ~ 350 Myr and 300 Myr, respectively. The present data arenot consistent with the membership of the WN6 star HDE 311884 to Hogg15. Tables 2 to 5 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.793.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/370/931
|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 (22.214.171.124) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
|Massive young stellar objects with molecular outflows|
We studied three members of the sample of 31 cold and luminous southernIRAS sources, which was compiled by Osterloh et al. (1997). These youngstellar objects are characterized by extremely red IRAS colours[Snu (100 mu m) > Snu (60 mu m) > Snu(25 mu m) > 20xSnu (12 mu m)]. Based on their strongCO line wings found in previous observations, the three objects IRAS12091-6129, IRAS 12405-6238, and IRAS 16019-4903 were selected in orderto investigate their nature and the outflow structure in more detail.The mapping in the CO J = 2->1 line as well as the lambda 1.3 mmcontinuum dust emission show that all three sources are deeply embeddedin dense cloud cores. Strong CO line wings and their mapping indicatethe presence of bipolar gas outflows in all three cases. N- and Q-bandimaging resolve some substructures inside the lambda 1.3 mm maps andgive evidence for deeply embedded young stellar objects which seem todrive the observed outflows. The comparison of the FIR imaging with theresults in K imply that most of the K-band nebulosities are reprocessedradiation escaping through inhomogeneities in a dense cloud. We derivedphysical parameters such as H_2 column densities and cloud core massesfrom the CO and the bolometer measurements, and we compared theproperties of the outflows and of the surrounding clouds with thosefound for well-known high-, intermediate- and low-mass objects. Thiscomparison showed that the newly detected outflow systems belong to themost energetic outflows in our galaxy observed so far. Based onobservations collected at the European Southern Observatory, La Silla,Chile
|Absolute proper motions of 181 young open clusters.|
|Chemical Evolution of the Galactic Disk: Evidence for a Gradient Perpendicular to the Galactic Plane|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995AJ....110.2813P&db_key=AST
|Briefly noted: Irish astronomy (poem)|
|Catalogue of blue stragglers in open clusters.|
An extensive survey of blue straggler candidates in galactic openclusters of both hemispheres is presented. The blue stragglers wereselected considering their positions in the cluster colour-magnitudediagrams.They were categorized according to the accuracy of thephotometric measurements and membership probabilities. An amount of 959blue straggler candidates in 390 open clusters of all ages wereidentified and classified. A set of basic data is given for everycluster and blue straggler. The information is arranged in the form of acatalogue. Blue stragglers are found in clusters of all ages. Thepercentage of clusters with blue stragglers generally grows with age andrichness of the clusters. The mean ratio of the number of bluestragglers to the number of cluster main sequence stars is approximatelyconstant up to a cluster age of about 10^8.6^ yr and rises for olderclusters. In general, the blue stragglers show a remarkable degree ofcentral concentration.
|Formation and evolutionary properties of the Galactic open cluster system|
Results are reported from a statistical analysis of observational dataon 100 open clusters within 2 kpc of the sun, selected from the catalogof Lynga (1987). The selection criteria and the completeness of thesample are discussed; the data are compiled in a table; and the analysisresults are presented in a series of graphs and characterized in detail.A cluster formation rate of 0.45 clusters/kpc Myr is found,significantly lower than the rates determined previously (using clusterswithin 1 kpc of the sun) and corresponding to a cluster star-formationefficiency of 0.0063. The low average cluster lifetime (about 10 Myr)suggests that clusters are formed as unstable systems.
|Observations of interstellar lines towards HD 110432|
|Photometric metal abundances of high-luminosity red stars in young and intermediate-age open clusters|
UBV, DDO, and Washinton photometry has been obtained for G and K starslocated in or near 22 young and intermediate-age open clusters. Nearly65 percent of the observed stars are found to have a high probability ofbeing cluster members, while the remaining 35 percent are likely to bered field stars. Five clusters (NGC 2383, NGC 3033, Ruprecht 20, NGC5168, and NGC 6249) probably do not contain any red giants. Sixteenclusters are found to be nearly solar in composition; three are slightlymetal-poor or metal-rich; one (Ruprecht 20) is moderately metal-poor(Fe/H = -0.3); and another (NGC 5617) is moderately metal-rich (Fe/H =0.3). None of the clusters with derived Washington abundances appear tobe enriched in elements of the CNO group.
|The Sagittarius-Carina Arm Structure and Parameters of Spiral Pattern|
|Young stellar-gas complexes in the Galaxy|
It is found that about 90 percent of OB-associations and o-b2 clusterssituated within 3 kpc of the sun can be united into complexes withdiameters of 150-700 pc. Almost all of these clusters contain giantmolecular clouds with a mass greater than about 100,000 solar masses. Anumber of complexes are associated with giant H I clouds; a few of thesmall complexes are situated in the HI caverns. The concentration ofOB-associations and young clusters in star complexes attests to theircommon origin in the supergiant gaseous clouds.
|A cluster analysis of open clusters|
The Galactic distribution of 361 open clusters is studied using acluster analysis method. It is shown that more than half of the clustersenter groups with characteristic dimensions of several hundred parsecs.To distinguish physical clusters from random condensations, criteriabased on age similarity, the color of the main-sequence blue end, andthe integrated color and radial velocity of the clusters are used. Theproximity of these values suggests a physical unity and common origin ofclusters in a group.
|A cluster analysis of young open clusters|
Cluster analysis methods are used to consider the galactic distributionof 224 open clusters with an age up to 10 to the 8th yrs. Most of theseclusters enter condensations with characteristic dimensions of a fewhundred parsecs. Some condensations are so similar in terms of the age,integrated color, and radial velocity of their components, that thiscannot be considered a coincidence. This suggests that each condensationis a physical entity consisting of clusters apparently linked by acommon origin.
|Mass-losing red giants in open clusters|
Mass-losing stars in open clusters with main-sequence turn-offs atintermediate mass have been searched for by using the IRAS data base.The absence of many strong 60 micron sources in open clusters impliesthat intermediate-mass stars lose much of their mass during an intensewind phase of rather short duration. For stars of about seven solarmasses, this phase, if it exists at all, lasts for not much more than100,000 yr. For stars of about four solar masses, the intense wind phaseappears to last considerably less than 10 million yr; it may well lastfor less than a million yr.
|Catalogue of UBV Photometry and MK Spectral Types in Open Clusters (Third Edition)|
|Integrated Photometric Parameters of Open and Globular Clusters|
|Open clusters and galactic structure|
A total of 610 references to 434 clusters are employed in thecompilation of a catalog of open clusters with color-magnitude diagramson the UBV or RGU systems. Estimates of reddening, distance modulus, ageand number of cluster members are included. Although the sample isconsidered representative of the discoverable clusters in the galaxy,the observed distribution is nonuniform because of interstellarobscuration. Cluster distribution in the galactic plane is found to bedominated by the locations of dust clouds rather than by spiralstructure. The distributions of clusters as a function of age andrichness class show that the lifetimes of poor clusters are much shorterthan rich ones, and that clusters in the outer disk survive longer thanthose in the inner disk. An outer disk age which is only about 50% theage of the globular clusters is indicated by cluster statistics. Thethickening of the galactic disk with increasing galactocentric distancemay be due to either a younger dynamical age or a lower gravitationalpotential in the outer regions.
|Comparative Studies of Young Open Clusters - Part Two - an Atlas of Composite Colour-Magnitude Diagrams|
Abstract image available at:http://adsabs.harvard.edu/abs/1981A&AS...44..467M
|A catalogue of galactic clusters observed in three colours|
This catalogue contains photometric data for 190 galactic clusters, allobserved in UBV or RGU. The distances of the young clusters (with spless than b3) have been calculated or recalculated according to method Aof Becker (1963). The galactic distribution of these clusters confirmstheir role of being good spiral tracers.
|Uniform survey of clusters in the southern Milky Way.|
Abstract image available at:http://adsabs.harvard.edu/abs/1975AJ.....80...11V
|The open cluster NGC 4609 behind the Coalsack|
Abstract image available at:http://adsabs.harvard.edu/abs/1971PASP...83..218F