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L-band (3.5 μm) IR-excess in massive star formation. II. RCW 57/NGC 3576
Context: .We present a JHKsL survey of the massive star forming regionRCW 57 (NGC 3576) based on L-band data at 3.5 μm taken with SPIREX(South Pole Infrared Explorer), and 2MASS JHKs data at 1.25-2.2 μm.This is the second of two papers, the first one concerning a similarJHKsL survey of 30 Doradus. Aims: .Colour-colour andcolour-magnitude diagrams are used to detect sources with infraredexcess. This excess emission is interpreted as coming from circumstellardisks, and hence gives the cluster disk fraction (CDF). Based on the CDFand the age of RCW 57, it is possible to draw conclusions on theformation and early evolution of massive stars. Methods: .Theinfrared excess is detected by comparing the locations of sources inJHKsL colour-colour and L vs. (K_s-L) colour-magnitude diagrams to thereddening band due to interstellar extinction. Results: .A totalof 251 sources were detected. More than 50% of the 209 sources includedin the diagrams have an infrared excess. Conclusions: .Comparisonwith other JHKsL surveys, including the results on 30 Doradus from thefirst paper, support a very high initial disk fraction (>80%) evenfor massive stars, although there is an indication of a possible fasterevolution of circumstellar disks around high mass stars. 33 sources onlyfound in the L-band indicate the presence of heavily embedded, massiveClass I protostars. We also report the detection of diffuse PAHsemission throughout the RCW 57 region.
| Near infrared photometry of the young clusters NGC 1960, NGC 2453 and NGC 2384
Infrared observations of young star clusters provide vital clues to thestar formation process and evolution of stars. This brief report on mythesis gives a brief description of the observations and analysis of theyoung star clusters NGC 1960, NGC 2453 and NGC 2384 observed in the nearinfrared bands at the Mt Abu Infrared Observatory, Gurushikhar inFebruary 2000. Estimates of distance and age for these clusters for thefirst time using JHK data have been obtained. The colour-magnitudediagrams of these clusters have been extended to the fainter end as faras possible. The observed data was compared to that obtained by 2MASS. Amore detailed paper will be published elsewhere.
| Near infrared photometry of the young clusters NGC 1960, NGC 2453 and NGC 2384
The present paper gives a brief description of the observations andanalysis of the young star clusters NGC 1960, NGC 2453 and NGC 2384observed in the near infrared bands at the Mt Abu Infrared Observatory,Gurushikhar in February 2000. Estimates of distance and age for theseclusters for the first time using JHK data have been obtained. Thecolour-magnitude diagrams of these clusters have been extended to thefainter end as far as possible. The observed data was found to agreereasonably well with that obtained by 2MASS. A more detailed paper willbe published elsewhere.
| 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.
| L-band (3.5 μm) IR-excess in massive star formation. I. 30 Doradus
L-band data of 30 Doradus at 3.5 μm taken with SPIREX (South PoleInfrared Explorer) is presented. The photometry was combined with 2MASSJHK data at 1.25-2.2 μm. Colour-colour and colour-magnitude diagramsare constructed and used to determine the sources with infrared excess.These are interpreted as circumstellar disks, and enable the fraction ofsources with disks (the cluster disk fraction or CDF) to be determined.We find that ~42% of the sources detected at L-band in 30 Doradus havean IR-excess.
| Variability in the stellar initial mass function at low and high mass: three-component IMF models
Three-component models of the initial mass function (IMF) are made toconsider possible origins for the observed relative variations in thenumbers of brown dwarfs, solar-to-intermediate-mass stars and high-massstars. The differences between the IMFs observed for clusters, field andremote field are also discussed. Three distinct physical processes thatshould dominate the three stellar mass regimes are noted. Thecharacteristic mass for most star formation is identified with thethermal Jeans mass in the molecular cloud core, and this presumablyleads to the middle mass range by the usual collapse and accretionprocesses. Pre-stellar condensations (PSCs) observed in millimetre-wavecontinuum studies presumably form at this mass. Significantly smallerself-gravitating masses require much larger pressures and may arisefollowing dynamical processes inside these PSCs, including discformation, tight-cluster ejection, and photoevaporation as studiedelsewhere, but also gravitational collapse of shocked gas in collidingPSCs. Significantly larger stellar masses form in relatively lowabundance by normal cloud processes, possibly leading to steep IMFs inlow-pressure field regions, but this mass range can be significantlyextended in high-pressure cloud cores by gravitationally focused gasaccretion on to PSCs and by the coalescence of PSCs. These modelssuggest that the observed variations in brown dwarf,solar-to-intermediate-mass and high-mass populations are the result ofdynamical effects that depend on environmental density and velocitydispersion. They accommodate observations ranging from shallow IMFs incluster cores to Salpeter IMFs in average clusters and whole galaxies tosteep and even steeper IMFs in field and remote field regions. They alsosuggest how the top-heavy IMFs in some starburst clusters may originateand they explain bottom-heavy IMFs in low surface brightness galaxies.
| Comparison of the Luminosity Functions of Open Clusters Based on USNO-A1 Data
The luminosity and mass functions of a group of Galactic open clustersare constructed by applying a statistical method to photometric datafrom the USNO-A1 catalog. Despite some limitations, this catalog can beused for statistical analyses in Galactic astronomy. Pairwisecomparisons of the derived cluster luminosity functions are performedfor five age intervals. The differences between the luminosity functionsof the open clusters are not statistically significant in most cases. Itis concluded that the luminosity functions are approximately universalthroughout a large volume in the solar neighborhood. Combined luminosityand mass functions are constructed for six age intervals. The slope ofthe mass spectrum may vary somewhat from cluster to cluster, and themean slope may be somewhat higher than the Salpetervalue.
| Astrophysical supplements to the ASCC-2.5. II. Membership probabilities in 520 Galactic open cluster sky areas
We present a catalogue (CSOCA ) of stars residing in 520 Galactic opencluster sky areas which is the result of the kinematic (proper motion)and photometric member selection of stars listed in the homogeneousAll-sky Compiled Catalogue of 2.5 Million Stars (ASCC-2.5). We describethe structure and contents of the catalogue, the selection procedureapplied, and the proper motion and photometric membership constraintsadopted. In every cluster area the CSOCA contains the complete list ofthe ASCC-2.5 stars regardless of their membership probability. Forevery star the CSOCA includes accurate J2000 equatorial coordinates,proper motions in the Hipparcos system, BV photometric data in theJohnson system, proper motion and photometric membership probabilities,as well as angular distances from the cluster centers for about 166 000ASCC-2.5 stars. If available, trigonometric parallaxes, spectral types,multiplicity and variability flags from the ASCC-2.5, and radialvelocities with their errors from the Catalogue of Radial Velocities ofGalactic Stars with high precision Astrometric Data (CRVAD) are alsogiven.
| Morphology of Galactic Open Clusters
We analyzed the shapes of Galactic open clusters by the star-countingtechnique with the Two Micron All Sky Survey star catalog database.Morphological parameters such as the ellipticity and size have beenderived via stellar density distribution, weighed by clusteringprobability. We find that most star clusters are elongated, even for theyoungest star clusters of a few million years old, which are locatednear the Galactic disk. The shapes of young star clusters must reflectthe conditions in the parental molecular clouds and during the clusterformation process. As an open cluster ages, stellar dynamics cause theinner part of the cluster to circularize, but the overall radius getslarger and the stellar density becomes sparser. We discuss how theinternal relaxation process competes with Galactic external perturbationduring cluster evolution.
| Discovery of a Huge Young Stellar Object Interaction Region in Camelopardalis
During the course of a wide-field VI survey of galaxies in the IC342/Maffei Group, a large nebula, which looks like an inclined disk witha jetlike plume emerging from it, was discovered in Camelopardalis. Theobject is most prominent in I. The predominating disk component is6.8m across, which corresponds to 4.0+/-1.6pc at the estimateddistance of 2.0+/-0.8kpc (the Perseus Arm). The plume extends 3.8m(2.2 pc) outward from the core along a direction that is about 20°from the minor axis of the disk. The disk lies along the edge of afilament of dust and molecular gas in the Milky Way. The plume pointstoward the core of the filament. No large-scale emission is seen atHα, and the nebula is invisible in Two Micron All Sky Survey(2MASS) images. About 30" from the center of the disk is IRAS04261+6339, which is a pair of unresolved Hα sources whose IRAScolors and spectra reveal them to be young stellar objects (YSOs). Thenorthern of the two exhibits a near-infrared tail, which is 15" (0.15pc) long in H and directed 66° away from the plume. Although thestars are exposed, as in Class II YSOs, the spectral energy distributionof the pair rises beyond 2 μm, typical of Class I systems. It appearsthat they are transitional YSOs, with characteristics similar to thoseof Holoea (IRAS 05327+3404). The total brightness of the plume plus diskexceeds that of the stars by 1.6 mag in I, yet the V-I color is bluer byonly 0.50 mag. Thus, the nebula cannot be a consequence of reflection,even allowing for differential extinction. It is tentatively identifiedas a remnant of an outflow from a binary YSO, glowing from thephotoluminescence of silicon nanoparticles.
| The discovery of low-mass pre-main-sequence stars in Cepheus OB3b
We report the discovery of a low-mass pre-main-sequence (PMS) stellarpopulation in the younger subgroup of the Cepheus OB3 association, CepOB3b, using UBVI CCD photometry and follow-up spectroscopy. The opticalsurvey covers approximately 1300 arcmin2 on the sky and givesa global photometric and astrometric catalogue for more than 7000objects. The location of a PMS population is well defined in a V versus(V-I) colour-magnitude diagram.Multifibre spectroscopic results for optically selected PMS candidatesconfirm the T Tauri nature for 10 objects, with equal numbers ofclassical TTS (CTTS) and weak-line TTS (WTTS). There are six otherobjects that we classify as possible PMS stars. The newly discovered TTSstars have masses in the range ~0.9-3.0 Msolar and ages from<1 to nearly 10 Myr, based on the Siess, Dufour & Forestiniisochrones. Their location close to the O and B stars of the association(especially the O7n star) demonstrates that low-mass star formation isindeed possible in such an apparently hostile environment dominated byearly-type stars and that the latter must have been less effective ineroding the circumstellar discs of their lower-mass siblings comparedwith other OB associations (e.g. λ-Ori). We attribute this to thenature of the local environment, speculating that the bulk of molecularmaterial, which shielded low-mass stars from the ionizing radiation oftheir early-type siblings, has only recently been removed.
| 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.
| On the Galactic Disk Metallicity Distribution from Open Clusters. I. New Catalogs and Abundance Gradient
We have compiled two new open cluster catalogs. In the first one, thereare 119 objects with ages, distances, and metallicities available, whilein the second one, 144 objects have both absolute proper motion andradial velocity data, of which 45 clusters also have metallicity dataavailable. Taking advantage of the large number of objects included inour sample, we present an iron radial gradient of about -0.063+/-0.008dex kpc-1 from the first sample, which is quite consistentwith the most recent determination of the oxygen gradient from nebulaeand young stars, about -0.07 dex kpc-1. By dividing clustersinto age groups, we show that the iron gradient was steeper in the past,which is consistent with the recent result from Galactic planetarynebulae data, and also consistent with inside-out galactic diskformation scenarios. Based on the cluster sample, we also discuss themetallicity distribution, cluster kinematics, and space distribution. Adisk age-metallicity relation could be implied by those properties,although we cannot give conclusive result from the age- metallicitydiagram based on the current sample. More observations are needed formetal-poor clusters. From the second catalog, we have calculated thevelocity components in cylindrical coordinates with respect to theGalactic standard of rest for 144 open clusters. The velocitydispersions of the older clusters are larger than those of youngclusters, but they are all much smaller than that of the Galactic thickdisk stars.
| Urban Astronomy: Observing the Messier Objects from the City
Not Available
| Near infrared photometry of the young open cluster NGC 1960.
Not Available
| Proper motions of open clusters based on the TYCHO2 Catalogue. II. Clusters farther than 1 kpc
We determined the mean absolute proper motion of 94 open clusterssituated farther than 1 kpc from the Sun. The results are derived fromthe stellar proper motion data given in the Tycho2 Catalogue. The meanproper motion of the clusters and membership probability of individualstars were obtained from the proper motion data by applying thestatistical method proposed by Sanders (\cite{Sanders1971}). Themeasurements made use of a large number of stars, usually several tens,for each cluster. The total number of stars investigated in the fieldsof the clusters is 4864 of which 2021 were considered members. For 55clusters, this is the first determination of the proper motion. Based onobservations of the ESA Hipparcos satellite. Tables 1 to 95 are onlyavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/388/168
| A study of spatial structure of galactic open star clusters
In order to study the relation between the core and corona in galacticstar clusters, the spatial structure of 38 rich open star clusters hasbeen studied using radial density profiles derived from the photometricdata of the Digital Sky Survey. The shape of the radial density profileindicates that the corona, most probably, is the outer region around thecluster. It can exist from the very beginning of the cluster formationand dynamical evolution is not the reason for its occurrence. The studydoes not find any relation between cluster size and age but indicatesthat the clusters with galacto-centric distances >9.5 kpc have largersizes. Further, we find that the average value of the core radius is1.3+/- 0.7 pc and that of annular width of the corona is 5.6+/- 1.9 pc,while average values of densities of cluster members in the core andcorona are 15.4+/- 9.9 star/pc2 and 1.6+/- 0.99star/pc2 respectively. Average field star contaminations inthe core and corona are ~ 35% and 80% respectively. In spite of smallerdensities in the coronal region, it contains ~ 75% of the clustermembers due to its larger area in comparison to the core region. Thisclearly demonstrates the importance of the coronal region in studiesdealing with the entire stellar contents of open star clusters as wellas their dynamical evolution. In contrast to the cluster cores, thestructure of coronal regions differs significantly from one cluster toother.
| The rise and rise of the deep sky image
Presidential Address to the British Astronomical Association, 2000October 25
| Hipparcos Trigonometric Parallaxes and the Distance Scale for Open Star Clusters
Hipparcos trigonometric parallaxes are used to estimate the distances tothe maximum possible number of open star clusters (OSC); distance moduliare estimated for 45 clusters with maximum heliocentric distances ofabout 1000 pc. The latter value can serve as an estimate of the limit towhich it still makes sense to use Hipparcos trigonometric parallaxes todetermine the distances to small groups composed of 6-10 sufficientlybright stars. A systematic correction to the distance moduli of clustersfrom the homogeneous catalog of OSC parameters (Loktin et al. 1997,2000) is estimated, which turns out to be independent of the clusterage.
| Disk Frequencies and Lifetimes in Young Clusters
We report the results of the first sensitive L-band survey of theintermediate-age (2.5-30 Myr) clusters NGC 2264, NGC 2362, and NGC 1960.We use JHKL colors to obtain a census of the circumstellar diskfractions in each cluster. We find disk fractions of 52%+/-10%,12%+/-4%, and 3%+/-3% for the three clusters, respectively. Togetherwith our previously published JHKL investigations of the younger NGC2024, Trapezium, and IC 348 clusters, we have completed the firstsystematic and homogeneous survey for circumstellar disks in a sample ofyoung clusters that both span a significant range in age (0.3-30 Myr)and contain statistically significant numbers of stars whose masses spannearly the entire stellar mass spectrum. Analysis of the combined surveyindicates that the cluster disk fraction is initially very high(>=80%) and rapidly decreases with increasing cluster age, such thatone-half the stars within the clusters lose their disks in <~3 Myr.Moreover, these observations yield an overall disk lifetime of ~6 Myr inthe surveyed cluster sample. This is the timescale for essentially allthe stars in a cluster to lose their disks. This should set a meaningfulconstraint for the planet-building timescale in stellar clusters. Theimplications of these results for current theories of planet formationare briefly discussed.
| The CFHT Open Star Cluster Survey. I. Cluster Selection and Data Reduction
We present this paper in conjunction with a companion paper as the firstresults in the Canada-France-Hawaii Telescope Open Star Cluster Survey.This survey is a large BVR imaging data set of 19 open star clusters inour Galaxy. This data set was taken with the CFH12K mosaic CCD(42'×28'), and the majority of the clusters were imaged underexcellent photometric, subarcsecond seeing, conditions. The combinationof multiple exposures extending to deep (V~25) magnitudes with short(<=10 s) frames allows for studies ranging from faint white dwarfstars to bright turnoff, variable, and red giant stars. The primary aimof this survey is to catalog the white dwarf stars in these clusters andestablish observational constraints on the initial-final massrelationship for these stars and the upper mass limit to white dwarfproduction. Additionally, we hope to better determine the properties ofthe clusters, such as age and distance, and also test evolution anddynamical theories by analyzing luminosity and mass functions. In orderto more easily incorporate these data in further studies, we haveproduced a catalog of positions, magnitudes, colors, and stellarityconfidence for all stars in each cluster of the survey. This reduction,along with the computed calibration parameters for all three nights ofthe observing run will encourage others to use these data in differentastrophysical studies outside of our goals. Additionally, the data setis reduced using the new TERAPIX photometric reduction package, PSFex,which is found to compare well with other packages. This paper isintended both as a source for the astronomical community to obtaininformation on the clusters in the survey and as a detailed reference ofreduction procedures for further publications of individual clusters. Wediscuss the methods employed to reduce the data and compute thephotometric catalog. We reserve both the scientific results for eachindividual cluster and global results from the study of the entiresurvey for future publications. The first of these further publicationsis devoted to the old rich open star cluster, NGC 6819, and appears as acompanion paper in the same issue of the Journal.
| The IMF of open star clusters with Tycho-2
We studied the fields of nine nearby open star clusters based on theTycho-2 catalogue. We determined membership probabilities for the starsin the cluster fields from the stellar proper motions and used theTycho-2 photometry to compute the initial mass function (IMF) of theclusters from the main sequence turn-off point down to approx. 1 M_sun.We found IMF slopes ranging from Gamma =-0.69 down to Gamma =-2.27 (whenthe Salpeter \cite{salpeter} value would be Gamma =-1.35). We alsostudied the membership of individual stars of special astrophysicalinterest. In some cases previous results had to be revised. As aby-product, we investigated some general properties of the Tycho-2catalogue; we confirmed that the Tycho-2 proper motions show onlymarginal deviations from the Hipparcos catalogue. On the other hand, insome regions the completeness of the catalogue seems to decrease atmagnitudes brighter than claimed by Høg et al. (\cite{tycho2}).Based on observations of the ESA Hipparcos satellite.
| 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
| Photometric and kinematic studies of open star clusters. II. NGC 1960 (M 36) and NGC 2194
We present CCD photometry and proper motion studies of the two open starclusters NGC 1960 (M 36) and NGC 2194. Fitting isochrones to the colourmagnitude diagrams, for NGC 1960 we found an age of t=16 Myr and adistance of roughly d=1300 pc and for NGC 2194 t=550 Myr and d=2900 pc,respectively. We combined membership determination by proper motions andstatistical field star subtraction to derive the initial mass functionof the clusters and found slopes of Gamma =-1.23 +/- 0.17 for NGC 1960and Gamma =-1.33 +/- 0.29 for NGC 2194. Compared to other IMF studies ofthe intermediate mass range, these values indicate shallow massfunctions. Partly based on data observed at the German-SpanishAstronomical Centre, Calar Alto, operated by the Max-Planck-Institutefor Astronomy, Heidelberg, jointly with the Spanish National Commissionfor Astronomy
| Statistical parallaxes and kinematical parameters of classical Cepheids and young star clusters
The statistical-parallax method is applied for the first time to spacevelocities of 270 classical Cepheids with proper motions adopted fromHIPPARCOS (1997) and TRC (Hog et al. 1998) catalogs and distances basedon the period-luminosity relation by Berdnikov et al. (1996). Thedistance scale of short-period Cepheids (with periods less than 9 days)is shown to require an average correction of 15-20%, whereas statisticalparallaxes of Cepheids with periods > 9 days are found to agree wellwith photometric distances. It is shown that the luminosities ofshort-period Cepheids must have been underestimated partly due to thecontamination of this subsample by a substantial (20 to 40%) fraction offirst-overtone pulsators. The statistical-parallax technique is alsoapplied for the first time to 117 open clusters younger than 100 millionyears and with proper motions reduced to the HIPPARCOS reference system.It is concluded that a 0.12-0.15 mag increase of the distance scales ofopen clusters and Cepheids would be sufficient to reconcile thestatistical-parallax results inferred for these two types of objects.Such approach leads to an LMC distance modulus of less than 18.40 mag,which agrees, within the errors, with the short distance scale for RRLyrae variables and is at variance with the conclusions by Feast andCatchpole (1998) and Feast et al. (1998), who argue that the LMCdistance modulus should be increased to 18.70 mag. The distance scalebased on the Cepheid period-luminosity relation by Berdnikov and Efremov(1985) seems to be a good compromise. Extragalactic distances, whichrely on long-period Cepheids, seem to require no substantial correction.In addition to statistical parallaxes, kinematical parameters have beeninferred for the combined sample consisting of Cepheids andopen-clusters: solar-motion components (U0 ,V0,W0) = (9, 12, 7) km/s (+/- 1 km/s); velocity-ellipsoid axes(σU; σV; σW) = (15.0,10.3, 8.5) km/s (+/- 1 km/s); the angular velocity of rotation of thesubsystem, ω0 = 28.7 +/- 1 km/s/kpc, the Oort constantA = 17.4 +/- 1.5 km/s, and the second derivative of angular velocity,⋰ω0= 1.15 +/- 0.2 km/s/kpc3.
| Transitional YSOs: candidates from flat-spectrum IRAS sources
We are searching for Young Stellar Objects (YSOs) near the boundarybetween protostars and pre-main-sequence objects, what we termTransitional YSOs. We have identified a sample of 125 objects ascandidate transitional YSOs on the basis of IRAS colors and the opticalappearance on POSS plates. We have obtained optical and near-IR imagingof 82 objects accessible from the Northern Hemisphere and optical imagesof 62 sources accessible from the South. We also created deconvolved 60mu m IRAS images of all sources. We have classified the objects on thebasis of their morphology in the optical and near-IR images. We findthat the majority of our objects are associated with star-formingregions, confirming our expectation that the bulk of these objects areYSOs. Of the 125 objects, 28 have a variety of characteristics verysimilar to other transitional YSOs, while another 22 show some of thesecharacteristics. Furthermore we have found seven objects to be goodcandidates for members of the Herbig Ae/Be stellar group, of which threeare newly identified as such. We have placed a set of images for each ofthe objects in the archives of the Centre de Données astronomiquede Strasbourg (CDS). Based on observations collected at the EuropeanSouthern Observatory, La Silla, Chile.
| The circumstellar environment of IRAS 05327+3404
We continue our study of the young stellar object associated with IRAS05327+3404. We have determined the spectral type of the central star tobe K2. We show that the star is most likely seen directly, not via areflection, and that the extinction is only A_V ~ 2.3 mag. The spectralenergy distribution shows the presence of large amounts of circumstellarmaterial. Near-IR and optical observations of the reflection nebula alsodemonstrate the presence of circumstellar material, and show thematerial to be arranged in a disk with a relatively wide central hole of~ 33 degr opening angle. The central hole and a CO outflow areco-aligned, and are roughly aligned with the ionized outflow. Severalsurprising aspects remain: Although the system has a strong ionizedoutflow, there is little or no evidence of active accretion in the formof UV excess, veiling, or strong high-Balmer line emission. Also, thespectral energy distribution is very wide, and suggests that theoriginal birth cloud had a large rotational velocity. We propose thatthe relative isolation of the system from other star formation activitymay explain the relatively large circumstellar disk for a system with awell-exposed central star.
| Search for star clustering: methodology and application to the Two Micron Galactic Survey
A new approach to the study of the large-scale stellar clusterdistribution in the Galaxy based on two-point correlation techniques ispresented. The basic formalism for this method is outlined, and itsapplications are then investigated by the use of a simple model ofcluster distribution in the Galaxy. This provides an estimate of thepotentials of the two-point correlation function for indicatingclustering in the measured star positions, which can be related to thepresence of star clusters in the observed field. This technique is thenapplied to several areas of the Two Micron Galactic Survey catalogue,from which information is obtained on the distribution of clustersaccording to position in the Galaxy, as well as about age, density ofstars, etc.
| Absolute proper motions of 181 young open clusters.
Not Available
| A bipolar-outflow object in the field of M 36.
We have discovered an object in the field of the Galactic open cluster[1]36 which exhibits a nebulous tail-like structure and a high velocityoutflow. We first observed the jet morphology in optical images taken atthe Michigan-Dartmouth-MIT (MDM) Observatory at Kitt Peak. This source,located at 05h36min05.9s, 34deg06'12.1" (J2000), is found to becoincident with IRAS 05327+3404. CO(1-0) observations (Wouterloot &Brand 1989) showed this object to be a strong emission-line source. Weperformed CO(2-1) observations at the James-Clerk-Maxwell Telescope atMauna Kea which suggest that the outflow is bipolar in nature. Opticalspectroscopy obtained at the La Palma Isaac-Newton 2.5m Telescope showsstrong emission lines, reminiscent of Herbig-Haro emission andconfirming the outflow. The object is probably not associated with[1]36, and may be a far-flung member of the nearby region of starformation, S235. The optical spectra are quite unusual. We conclude thatthe spectra represent two views of the same jet structure from differentviewing angles, one the result of a reflection off the nebulous tail.The IRAS fluxes, optical morphology, and aspects of the optical spectraare similar to the FU Orionis system L1551 IRS5, and may indicate thatthis object is also an FU Orionis star.
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