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An X-Ray and Near-Infrared Study of Young Stars in the Carina Nebula
We present a multiwavelength study of the central region of the CarinaNebula, including Trumpler 16 and part of Trumpler 14. Our analysis ofthe Chandra X-Ray Observatory archival data led to the identification of454 X-ray sources. These sources were then cross-identified with opticalphotometric and spectroscopic information available from the literatureand with newly obtained near-infrared (JHKs) imagingobservations. A total of 38 known OB stars are found to be X-rayemitters. All the O stars and early-B stars follow the nominal relationbetween the X-ray and bolometric luminosities,LX~10-7Lbol. A few mid- to late-B starsare found to be associated with X-ray emission, likely attributable to TTauri companions. We discovered 16 OB star candidates that suffer alarge extinction in the optical wave bands. Some 300 sources have theX-ray and infrared characteristics of late-type pre-main-sequence stars.Our sample represents the most comprehensive census of the young stellarpopulation in the Carina Nebula so far and should be useful for thestudy of the star formation history of this massive starburst region. Wealso report the finding of a compact (2'×4')group of 10 relatively bright X-ray sources, all of which are detectedin the near-infrared wavelengths and are highly reddened. The group isspatially coincident with the dark V-shaped dust lane bisecting theCarina Nebula and may be part of an embedded association. Thedistribution of the young stellar groups surrounding the H II regionassociated with Trumpler 16 is consistent with the collect-and-collapsescenario of triggered star formation.
| Cloud Fragmentation and Proplyd-like Features in H II Regions Imaged by the Hubble Space Telescope
We have analyzed Hubble Space Telescope ACS and WFPC2 new and archivalimages of eight H II regions to look for new protoplanetary disks(proplyds) similar to those found in the Orion Nebula. We find a wealthof features similar in size (although many are larger) to the brightcusps around the Orion Nebula proplyds. None of them, however, containsa definitive central star. From this, we deduce that the new cusps maynot be proplyds but instead fragments of molecular cloud material. Outof all the features found in the eight H II regions examined, only one,an apparent edge-on silhouette in M17, may have a central star. Thisfeature might join the small number of bona fide proplyds found outsidethe Orion Nebula, in M8, M20, and possibly M16. In line with the resultsfound recently by Smith et al., the paucity of proplyds outside theOrion Nebula can be explained by their transient nature, as well as bythe specific environmental conditions under which they can be observed.Several fragments are seen as dark silhouettes against a brightbackground. We have reanalyzed those found in IC 2944 by Reipurth et al.and found new, similar ones in M16. None of these fragments contains acentral star, and we exclude the possibility that they are disks.Reipurth et al. concluded that the IC 2944 silhouettes are not starforming. We argue here that their assumption of a constant optical depthfor these fragments is not physical and that it is more likely thatthese fragments are star forming, a condition that is supported,although not proved, by their shapes and distributions. The process ofcloud fragmentation and photoevaporation produces a large number ofsmall fragments, while the size hierarchy expected in a photoevaporativeenvironment would not favor small fragments. The size distributionsobserved will constrain any future theories of cloud fragmentation. Onebright microjet candidate is found in M17, protruding from a large,limb-brightened fragment. A second, larger, jetlike feature, similar inshape and size to a Herbig-Haro jet, is found in Pismis 24. No centralstar appears to be associated with either of these jet candidates.Based on observations made with the NASA/ESA Hubble Space Telescopeobtained at the Space Telescope Science Institute, which is operated bythe Association of Universities for Research in Astronomy (AURA), Inc.,under NASA contract NAS5-26555.
| A census of the Carina Nebula - I. Cumulative energy input from massive stars
The Carina Nebula (NGC 3372) is our richest nearby laboratory in whichto study feedback through ultraviolet radiation and stellar winds fromvery massive stars during the formation of an OB association, at anearly phase in the evolution of the surrounding proto-superbubble beforesupernova explosions have influenced the environment. This feedback istriggering successive generations of new star formation around theperiphery of the nebula, while simultaneously evaporating the gas anddust reservoirs out of which young stars are trying to accrete material.This paper takes inventory of the combined effect from all the knownmassive stars that power the Carina Nebula through their total ionizingflux and integrated mechanical energy from their stellar winds. Carinais close enough and accessible enough that spectral types for individualstars are available, and many close binary and multiple systems haverecently been spatially resolved, so that one can simply add them.Adopting values from the literature for corresponding spectral types,the present-day total ionizing photon luminosity produced by the 65 Ostars and three WNL stars in Carina is QH~=1051s-1, the total bolometric luminosity of allstars earlier than B2 is 2.5 × 107Lsolar,and the total mechanical luminosity of stellar winds is LSW~=105Lsolar. The total QH was about 25per cent higher when η Carinae was on the main sequence, before itand its companion were surrounded by its obscuring dust shell; for thefirst 3Myr, the net ionizing flux of the 70 O stars in Carina was about150 times greater than in the Orion Nebula. About400-500Msolar has been contributed to the HII region bystellar wind mass-loss during the past 3Myr. Values for QHand LSW are also given for the individual clusters Tr14, 15and 16, and Bo10 and 11, which are more relevant on smaller spatialscales than the total values for the whole nebula.
| 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.
| Quantitative spectroscopy of BA-type supergiants
Luminous BA-type supergiants have enormous potential for modernastrophysics. They allow topics ranging from non-LTE physics and theevolution of massive stars to the chemical evolution of galaxies andcosmology to be addressed. A hybrid non-LTE technique for thequantitative spectroscopy of these stars is discussed. Thorough testsand first applications of the spectrum synthesis method are presentedfor the bright Galactic objects η Leo (A0 Ib), HD 111613 (A2 Iabe),HD 92207 (A0 Iae) and β Ori (B8 Iae), based on high-resolution andhigh-S/N Echelle spectra. Stellar parameters are derived fromspectroscopic indicators, consistently from multiple non-LTE ionizationequilibria and Stark-broadened hydrogen line profiles, and they areverified by spectrophotometry. The internal accuracy of the methodallows the 1σ-uncertainties to be reduced to 1-2% in T_effand to 0.05-0.10 dex in log g. Elemental abundances are determined forover 20 chemical species, with many of the astrophysically mostinteresting in non-LTE (H, He, C, N, O, Mg, S, Ti, Fe). The non-LTEcomputations reduce random errors and remove systematic trends in theanalysis. Inappropriate LTE analyses tend to systematicallyunderestimate iron group abundances and overestimate the light andα-process element abundances by up to factors of two to three onthe mean. This is because of the different responses of these species toradiative and collisional processes in the microscopic picture, which isexplained by fundamental differences of their detailed atomic structure,and not taken into account in LTE. Contrary to common assumptions,significant non-LTE abundance corrections of ~0.3 dex can be found evenfor the weakest lines (Wλ 10 mÅ). Non-LTEabundance uncertainties amount to typically 0.05-0.10 dex (random) and~0.10 dex (systematic 1σ-errors). Near-solar abundances arederived for the heavier elements in the sample stars, and patternsindicative of mixing with nuclear-processed matter for the lightelements. These imply a blue-loop scenario for η Leo because offirst dredge-up abundance ratios, while the other three objects appearto have evolved directly from the main sequence. In the most ambitiouscomputations several ten-thousand spectral lines are accounted for inthe spectrum synthesis, permitting the accurate reproduction of theentire observed spectra from the visual to near-IR. This prerequisitefor the quantitative interpretation of intermediate-resolution spectraopens up BA-type supergiants as versatile tools for extragalacticstellar astronomy beyond the Local Group. The technique presented hereis also well suited to improve quantitative analyses of less extremestars of similar spectral types.
| High-Mass Cloud Cores in the η Carinae Giant Molecular Cloud
We carried out an unbiased survey for massive dense cores in the giantmolecular cloud associated with η Carinae with the NANTEN telescopein the 12CO, 13CO, and C18O J=1-0emission lines. We identified 15 C18O cores, whose typicalline width ΔVcomp, radius r, mass M, column densityN(H2), and average number density n(H2) were 3.3km s-1, 2.2 pc, 2.6×103 Msolar,1.3×1022 cm-2, and 1.2×103cm-3, respectively. Two of the 15 cores are associated withIRAS point sources whose luminosities are larger than 104Lsolar, which indicates that massive star formation isoccurring within these cores. Five cores, including the two with IRASsources, are associated with MSX point sources. We detectedH13CO+ (J=1-0) emission toward fourC18O cores, two of which are associated with IRAS and MSXpoint sources; another one is associated only with an MSX point source,and the other is associated with neither IRAS nor MSX point sources. Thecore with neither IRAS nor MSX point sources shows the presence of abipolar molecular outflow in 12CO (J=2-1), which indicatesthat star formation is also occurring in the core, and the other threeof the four H13CO+ detections show winglikeemission. In total, 6 C18O cores out of 15 (=40%) haveexperienced star formation, and at least 2 of 15 (=13%) are massivestar-forming cores in the η Car GMC. We found that massive starformation occurs preferentially in cores with larger N(H2),M, and n(H2) and a smaller ratio of Mvir/M. Wealso found that the cores in the η Car GMC are characterized bylarge ΔV and Mvir/M on average compared to the cores inother GMCs observed with the same telescope. These properties of thecores may account for the fact that as much as 60%-87% of the cores donot show any signs of massive star formation. We investigated the originof a large amount of turbulence in the η Car GMC. We found thatturbulence injection from stellar winds, molecular outflows, andsupernova remnants that originated from stars formed within the GMC arenot enough to explain the existing turbulence. We propose thepossibility that the large turbulence was preexisting when the GMC wasformed and is now dissipating. Mechanisms such as multiple supernovaexplosions in the Carina flare supershell may have contributed to form aGMC with a large amount of turbulence.
| 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.
| The Galactic Constants and Rotation Curve from Molecular-Gas Observations
We obtained the photometric distances and radial velocities for themolecular gas for 270 star-forming regions and estimated the distance tothe Galactic center from ten tangent points to be R 0 = 8.01 ±0.44 kpc. Estimates of R 0 derived over the last decade are summarizedand discussed; the average value is R 0 = 7.80 ± 0.33 kpc. Weanalyze deviations from axial symmetry of the gas motion around theGalactic center in the solar neighborhood. Assuming a flat rotationcurve, we obtain Θ0 ˜ 200 km/s for the circular velocity ofthe Sun from regions beyond the Perseus arm. We used these Galacticconstants to construct the Galactic rotation curve. This rotation curveis flat along virtually its total extent from the central bar to theperiphery. The velocity jump in the corotation region of the central barin the first quadrant is 20 km/s. We present analytical formulas for therotation curves of the Northern and Southern hemispheres of the Galaxyfor R 0 = 8.0 kpc and Θ0 = 200 km/s.
| The star cluster Collinder 232 in the Carina complex and its relation to Trumpler 14/16
In this paper we present and analyze new CCD UBVRI photometry down toV≈21 in the region of the young open cluster Collinder 232, locatedin the Carina spiral arm, and discuss its relationship to Trumpler 14and Trumpler 16, the two most prominent young open clusters located inthe core of NGC 3372 (the Carina Nebula). First of all we study theextinction pattern in the region. We find that the total to selectiveabsorption ratio RV differs from cluster to cluster, being3.48±0.11, 4.16±0.07 and 3.73±0.01 for Trumpler 16,Trumpler 14 and Collinder 232, respectively. Then we derive individualreddenings and intrinsic colours and magnitudes using the method devisedby Romaniello et al. (\cite{Romaniello02}). Ages, age spreads anddistances are then estimated by comparing the Colour Magnitude Diagramsand the Hertzsprung-Russel diagram with post and pre-main sequencetracks and isochrones. We find that Trumpler 14 and Collinder 232 lie atthe same distance from the Sun (about 2.5 kpc), whereas Trumpler 16 liesmuch further out, at about 4 kpc from the Sun. As for the age, we findthat Trumpler 16 is older than both Trumpler 14 and Collinder 232. Forall the clusters we indicate the existence of a significant agedispersion, whose precise value is hampered by our inability to properlydistinguish members from non-members. We finally suggest that Collinder232 is a physical aggregate and provide estimates of its basicparameters.Based on observations taken at ESO La Silla.Tables 1 and 2 are 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/418/525
| New infrared star clusters in the southern Milky Way with 2MASS
We carried out a 2MASS J, H and Ks survey of infrared starclusters in the Milky Way sector 230deg< l <350deg. This zone was the least studied in the literature,previously including only 12 infrared clusters or stellar groups with|b|< 10deg, according to the recent catalogue by Bica etal. (2003). We concentrated efforts on embedded clusters, which arethose expected in the areas of known radio and optical nebulae. Thepresent study provides 179 new infrared clusters and stellar groups,which are interesting targets for detailed future infrared studies. Thesample of catalogued infrared clusters and stellar groups in the Galaxyis now increased by 63%.
| 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
| 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 photometric investigation of the young open cluster Trumpler 15
In this paper we present and analyse new CCD UBVRI photometry down to V~21 in the region of the young open cluster Trumpler 15, located in theCarina spiral feature. The cluster is rather compact and has a coreradius of about 2arcmin, which translates to about 1pc at the distanceof the cluster. We provide the first CCD investigation and update itsfundamental parameters. We identify 90 candidate photometric members onthe base of the position in the colour-colour and colour-magnitudediagrams. This sample allows us to obtain a distance of 2.4+/-0.3kpcfrom the Sun and a reddening E (B -V )=0.52+/-0.07. We confirm that thecluster is young, and fix a upper limit of 6×106 yr toits age. In addition, we draw attention to the lower part of the mainsequence (MS) suggesting that some stars can be in contracting phase andon a gap in the MS, which we show to be a real feature, the B1-B5 gapfound in other young open clusters. We finally study in detail theextinction toward Trumpler 15 concluding that it is normal andsuggesting a value of 2.89+/-0.19 for the ratio of total to selectiveabsorption R V .
| Star clusters in the Carina complex: UBVRI photometry of NGC 3114, Collinder 228 and vdB-Hagen 99
In this paper we present and analyze CCD UBVRI photometry in the regionof the three young open clusters NGC 3114, Collinder 228, and vdB-Hagen99, located in the Carina spiral feature. NGC 3114 lies in the outskirtsof the Carina nebula. We found 7 star members in a severely contaminatedfield, and obtain a distance of 950 pc and an age less than 3 x108 yrs. Collinder 228 is a younger cluster (8x106 yrs), located in front of the Carina nebula complex, forwhich we identify 11 new members and suggest that 30% of the stars areprobably binaries. As for vdB-Hagen 99, we add 4 new members, confirmingthat it is a nearby cluster located at 500 pc from the Sun and projectedtoward the direction of the Carina spiral arm. Based on observationstaken at ESO La Silla. Data are available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/379/136
| Star clusterings in the Carina complex: UBVRI photometry of Bochum 9, 10 and 11
We report on the first UBVRI CCD photometry of three poorly known starclusterings in the region of η Carinae: Bochum 9, 10 and 11. We findthat they are young, rather poor, loose open clusters. We argue thatBochum 9 is probably a small and loose open cluster with about 30probable members having E(B-V)=0.63+/-0.08, located 4.6kpc far from theSun, beyond the Carina spiral arm. Similarly, Bochum 10 is a sparseaggregate with 14 probable members having E(B-V)=0.47+/-0.05 and at adistance of 2.7kpc from the Sun. Finally, Bochum 11 is a less than4×106yr old cluster for which we identify 24 members.It has a reddening E(B-V)=0.58+/-0.05, and lies between Bochum 10 and 9,at 3.5kpc from the Sun. We propose that in the field of the cluster somestars might be pre-main-sequence candidates.
| CO (J=4-->3) and [C I] Observations of the Carina Molecular Cloud Complex
We present large-area, fully sampled maps of the Carina molecular cloudcomplex in the CO (J=4-->3) and neutral carbon [C I]3P1-->3P0 transitions.These data were obtained using the 1.7 m Antarctic SubmillimeterTelescope and Remote Observatory (AST/RO). The maps cover an area ofapproximately 3 deg2 with a uniform 1' spatial sampling.Analysis of these data, in conjunction with CO (J=1-->0) data fromthe Columbia CO survey and the IRAS HIRES continuum maps for the sameregion, suggests that the spiral density wave shock associated with theCarina spiral arm may be playing an important role in the formation anddissociation of the cloud complex, as well as in maintaining theinternal energy balance of the clouds in this region. Massive stars format the densest regions of the molecular cloud complex. The winds andoutflows associated with these stars have a disrupting effect on thecomplex and inject mechanical energy into the parent clouds, while theUV radiation from the young stars also heats the parent clouds. Thepresent set of data suggests, however, that massive stars alone may notaccount for the energetics of the clouds in the Carina region. Thedetails of the data and the correlation among the various data sets hintat the possible role that the spiral density wave shock plays in feedinginterstellar turbulence and heating molecular clouds.
| Star clusterings in the Carina complex: vec {UBVRI} photometry of NGC 3324 and Loden 165
We report on UBVRI photometry of two 5' x 5'fields in the region of the young open cluster NGC 3324. One of ourfields covers the core region, while the other is closer to the tidalradius of the cluster. Our study provides the first CCD photometry ofNGC 3324. We find that the cluster is very young and probably containsseveral pre Main Sequence (MS) stars. 25 members are identified on thebasis of their position in the (U-B) vs. (B-V) diagram. We investigatethe relation of the red super-giant HD 92207 with NGC 3324, suggestingthat it probably does not belong to the cluster. Our second field isclose to Loden 165, a possible cluster of stars that has never beenstudied so far. We show that this object is a probable open cluster,much older than NGC 3324 and much closer to the Sun. Based onobservations carried out at ESO La Silla. All the data are available atWEBDA http://obswww.unige.ch/webda/navigation.html.
| 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.
| 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
| Large-Scale Structure of the Carina Nebula
Observations obtained with the Midcourse Space Experiment (MSX)satellite reveal for the first time the complex mid-infrared morphologyof the entire Carina Nebula (NGC 3372). On the largest size scale of~100 pc, the thermal infrared emission from the giant H II regiondelineates one coherent structure: a (somewhat distorted) bipolar nebulawith the major axis perpendicular to the Galactic plane. The CarinaNebula is usually described as an evolved H II region that is no longeractively forming stars, clearing away the last vestiges of its natalmolecular cloud. However, the MSX observations presented here revealnumerous embedded infrared sources that are good candidates for sites ofcurrent star formation. Several compact infrared sources are located atthe heads of dust pillars or in dark globules behind ionization fronts.Because their morphology suggests a strong interaction with the peculiarcollection of massive stars in the nebula, we speculate that these newinfrared sources may be sites of triggered star formation in NGC 3372.
| Absolute proper motions of 181 young open clusters.
Not Available
| Eta Carinae and Its Environment
Eta Carinae (Eta) is one of the most remarkable of all well-studiedstars and perhaps the most poorly understood. Observations with theHubble Space Telescope and other modern instruments have solved a few ofthe mysteries concerning this object while opening a comparable numberof new ones. In this review we first recount some essential backgroundinformation concerning Eta, then we sketch most of the observationaldevelopments of the past few years, related to the star itself and toits ejecta. Throughout, we propose a series of specific unsolvedobservational and theoretical problems that seem especially interestingor important at this time.
| Open Clusters in the Carina Nebula (Invited Paper)
Not Available
| 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.
| Ubvy-Beta Photometry of 100 Stars in the Region of Eta-Carinae
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1994MNRAS.269..857S&db_key=AST
| The young open clusters in the galaxy.
Abstract image available at:http://adsabs.harvard.edu/abs/1994RMxAA..29..141F
| Distribution of hot stars and interstellar dust in Carina.
Not Available
| Topography of the Galactic disk - Z-structure and large-scale star formation
A 3D morphological description of the Galactic disk defined by the youngstellar population is delineated using a sample of young open clusterswith cataloged distances and treated with Kriging techniques. The valuesof the positional variable Z for the cluster sample are considered asprospectings of the displacement of the Galactic disk in respect to theequator in the plane. The Kriging technique is described with emphasison its application to the automatic cartography problem. A view of theGalactic disk in a region of about 3 kpc around the sun emerges fromthis treatment and shows a trough-peak structure with four maindepressions as the more striking features. The most prominentdepression, named Big Dent, is apparent at about 1.8 kpc in anapproximately 240-deg direction. It has an elliptical shape with axissizes of 1.5 and 3 kpc, reaching a Z value of 200 pc below the formalGalactic plane. Two-dimensional sections across some selected directionsof the topography show profiles in good agreement with previousobservational studies based on different object samples.
| Initial masses of WR stars in open clusters.
Abstract image available at:http://adsabs.harvard.edu/abs/1990RMxAA..21..346V
| Component Analysis of Open Clusters
Not Available
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