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A study of the neglected Galactic H ii region NGC 2579 and its companion ESO 370-9
Context: The Galactic H ii region NGC 2579 has stayed undeservedlyunexplored due to identification problems which persisted untilrecently. Both NGC 2579 and its companion ESO 370-9 have beenmisclassified as planetary or reflection nebula, confused with eachother and with other objects. Due to its high surface brightness, highexcitation, angular size of few arcminutes and relatively lowinterstellar extinction, NGC 2579 is an ideal object for investigationsin the optical range. Located in the outer Galaxy, NGC 2579 is anexcellent object for studying the Galactic chemical abundance gradients. Aims: To present the first comprehensive observational study on thenebular and stellar properties of NGC 2579 and ESO 370-9, including thedetermination of electron temperature, density structure, chemicalcomposition, kinematics, distance, and the identification and spectralclassification of the ionizing stars, and to discuss the nature of ESO370-9. Methods: Long slit spectrophotometric data in the optical rangewere used to derive the nebular electron temperature, density andchemical abundances and for the spectral classification of the ionizingstar candidates. Hα and UBV CCD photometry was carried out toderive stellar distances from spectroscopic parallax and to measure theionizing photon flux. Results: The chemical abundances of He, N, O, Ne,S, Cl, and Ar were obtained. Maps of electron density and radialvelocity with a spatial resolution of 5" × 5" were composed fromlong slit spectra taken at different declinations. Three O starsclassified as O5 V, O6.5 V, and O8 V were found responsible for theionization of NGC 2579, while ESO 370-9 is ionized by a single O8.5 Vstar. The estimated mass of ionized gas of ≈25 M_ȯ indicatesthat ESO 370-9 is not a planetary nebula, but a small H ii region. Aphotometric distance of 7.6 ± 0.9 kpc and a kinematic distance of7.4 ± 1.4 kpc were obtained for both objects. At thegalactocentric distance of 12.8 ± 0.7 kpc, NGC 2579 is one of themost distant Galactic H ii regions for which direct abundancedeterminations have been accomplished.
| New catalogue of blue stragglers in open clusters
We present a catalogue of blue-straggler candidates in galactic openclusters. It is based on the inspection of the colour-magnitude diagramsof the clusters, and it updates and supersedesthe first version(Ahumada & Lapasset 1995). A new bibliographical search was made foreach cluster, and the resulting information is organised into twotables. Some methodological aspects have been revised, in particularthose concerning the delimitation of the area in the diagrams where thestragglers are selected.A total of 1887 blue-straggler candidates have been found in 427 openclusters of all ages, doubling the original number. The catalogued starsare classified into two categories mainly according to membershipinformation.The whole catalogue (Tables 8, 9, notes, and references) is 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/463/789
| 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.
| 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%.
| Star-forming complexes and the spiral structure of our Galaxy
We have carried out a multiwavelength study of the plane of our Galaxyin order to establish a star-forming-complex catalogue which is ascomplete as possible. Features observed include Hα , H109alpha ,CO, the radio continuum and absorption lines. For each complex we havedetermined the position, the systemic velocity, the kinematic distanceand, when possible, the stellar distance and the correspondinguncertainties. All of these parameters were determined as homogeneouslyas possible, in particular all the stellar distances have been(re)calculated with the same calibration and the kinematic distanceswith the same mean Galactic rotation curve. Through the complexes withstellar distance determination, a rotation curve has been fitted. It isin good agreement with the one of Brand & Blitz (1993). We alsoinvestigated the residual velocities relative to the circular rotationmodel. We find that departures exist over large areas of the arms, withdifferent values from one arm to another. From our data and in goodagreement with previous studies, the Galactic warp is observed. It doesnot seem correlated with the departures from circular rotation. Finally,as segment-like features are noted from the complexes' distribution, wetried to find if they are indicative of a larger underlying structure.Then, we attempted to interpret the complexes' distribution in terms ofspiral structure by fitting models with two, three and four logarithmicspiral arms. The four-arm model seems more appropriate to represent thegrand design of our Galaxy. In this model the Norma arm and the externalarm appear as being the two extremities of a single arm called theNorma-Cygnus arm. The new data and fitted model confirm the four-segmentmodel of Georgelin & Georgelin (1976), clarifying the arms' designand extension and doubling their known length. Based on observationscollected at the European Southern Observatory. Tables 1 and 3(table1.ps and table3.txt) 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/397/133
| Internal Variation of Electron Density in Galactic and Extragalactic HII Regions
Not Available
| Optical Coordinates of Southern Planetary Nebulae
A homogeneous set of new measurements of nearly all (995 out of 1007)objects from the Strasbourg-ESO Catalogue of Galactic Planetary Nebulaeor in the first supplement of this catalogue in the area covered by theDENIS survey (δ < +2 degrees) is given here. A list of 24 newand 27 wrong crossidentifications with sources in the IRAS PSC catalogueand some confusion in the literature is listed as well.
| Proper motions of open clusters within 1 kpc based on the TYCHO2 Catalogue
We present mean absolute proper motions of 112 open clusters, determinedusing the data from the Tycho2 Catalogue. For 28 clusters, this is thefirst determination of proper motion. The measurements made use of alarge number of stars (usually several tens) for each cluster. The totalnumber of stars studied in the fields of the 164 open clusters is 5016,of which 4006 were considered members. The mean proper motions of theclusters and membership probability of individual stars were obtainedfrom the proper motion data by applying the statistical method proposedby Sanders (\cite{Sanders71}). Based on observations of the ESAHipparcos satellite. Tables 1, 2 and 5 to 117 are only available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/376/441
| Integrated photometry of galactic H Ii regions
Integrated photoelectric measurements of the equivalent width W_Hβ, the [O Iii]/Hβ ratio and the Hβ emission line flux arepresented for 31 southern hemisphere galactic H Ii regions. The Lymancontinuum photon fluxes are obtained for some of these objects. Theintegrated [O Iii]/Hβ ratios have not shown any statisticallysignificant deviation from non-integrated measurements found in theliterature.
| 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
| Internal variation of electron density in galactic Hbt II regions
A study on the internal variation of the electron density in galactic HIi regions has been conducted on a sample of 15 objects of differentsizes and evolutionary stages. The [S Ii] lambda 6716/lambda 6731 lineratio was adopted as electron density indicator. Long slitspectrophotometry of high signal-to-noise ratio with spectral dispersionof 0.75 Ä,pxl-1 and spatial scale of 0\farcs90pxl-1 were obtained at different slit positions andorientations. No systematic spatial variation of electron density wasdetected in nearly half of the objects studied (S255, S 257, S 271,S 285, S 301, S305, NGC 3372 and IC1275). They are in general the most diffuse and probablyevolved objects with low mean densities in the range Ne ~20-140 cm-3. The remaining objects (S 288,S 307, NGC 2579, NGC3503, Gum 62, Gum 64aand M 20) with mean densities Ne ~ 80-360cm-3, have shown a statistically significant electron densitydependence on position. In most of these cases, the spatial variation ofdensity may be interpreted as a radial gradient with the densitydecreasing from the centre to the edges. M 20 shows asystematic non-radial variation of electron density with maximum valuesoccurring at its prominent dark lanes. A mean filling factor of theorder of phi = 0.1 was found compatible with the data. Based on theirdensity profiles, NGC 2579, Gum62, Gum 64a and possibly NGC3503 were indicated as candidates of showing a `champagneflow'.
| The dust content of planetary nebulae: a reappraisal
We have performed a statistical analysis using broad band IRAS data onabout 500 planetary nebulae with the aim of characterizing their dustcontent. Our approach is different from previous studies in that it usesan extensive grid of photoionization models to test the methods forderiving the dust temperature, the dust-to-gas mass ratio and theaverage grain size. In addition, we use only distance independentdiagrams. With our models, we show the effect of contamination by atomiclines in the broad band IRAS fluxes during planetary nebula evolution.We find that planetary nebulae with very different dust-to-gas massratios exist, so that the dust content is a primordial parameter for theinterpretation of far infrared data of planetary nebulae. In contrastwith previous studies, we find no evidence for a decrease in thedust-to-gas mass ratio as the planetary nebulae evolve. We also showthat the decrease in grain size advocated by Natta & Panagia(\cite{NattaPanagia}) and Lenzuni et al. (\cite{Lenzuni}) is an artefactof their method of analysis. Our results suggest that the timescale fordestruction of dust grains in planetary nebulae is larger than theirlifetime. Table~1 is only accessible in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Studies of ultracompact HII regions - II. High-resolution radio continuum and methanol maser survey
High spatial resolution radio continuum and 6.67-GHz methanol spectralline data are presented for methanol masers previously detected by Walshet al. (1997). Methanol maser and/or radio continuum emission is foundin 364 cases towards IRAS-selected regions. For those sources withmethanol maser emission, relative positions have been obtained to anaccuracy of typically 0.05 arcsec, with absolute positions accurate toaround 1 arcsec. Maps of selected sources are provided. The intensity ofthe maser emission does not seem to depend on the presence of acontinuum source. The coincidence of water and methanol maser positionsin some regions suggests there is overlap in the requirements formethanol and water maser emission to be observable. However, there is astriking difference between the general proximity of methanol and watermasers to both cometary and irregularly shaped ultracompact (UC) Hiiregions, indicating that, in other cases, there must be differingenvironments conducive to stimulating their emission. We show that themethanol maser is most likely present before an observable UC Hii regionis formed around a massive star and is quickly destroyed as the UC Hiiregion evolves. There are 36 out of 97 maser sites that are linearlyextended. The hypothesis that the maser emission is found in acircumstellar disc is not inconsistent with these 36 maser sites, but isunlikely. It cannot, however, account for all other maser sites. Analternative model which uses shocks to create the masing spots can morereadily reproduce the maser spot distributions.
| Planetary Nebulae in the NRAO VLA Sky Survey
The 1.4 GHz NRAO VLA Sky Survey (NVSS) images and source catalog wereused to detect radio emission from the 885 planetary nebulae north ofJ2000 declination delta = -40 deg in the Strasbourg-ESO Catalogue ofGalactic Planetary Nebulae. We identified 680 radio sources brighterthan about S = 2.5 mJy beam-1 (equivalent to T ~ 0.8 K in the 45" FWHMNVSS beam) with planetary nebulae by coincidence with accurate opticalpositions measured from Digitized Sky Survey (DSS) images. Totalextinction coefficients c at lambda = 4861 Angstroms were calculated forthe 429 planetary nebulae with available H beta fluxes and low free-freeoptical depths at 1.4 GHz. The variation of c with Galactic latitude andlongitude is consistent with the extinction being primarily interstellarand not intrinsic.
| The Puppis OB III association: polarization measurements
Optical linear polarization measurements of association members andfield stars in the region of the Puppis OB III association arepresented. The association members are found to have larger values ofpolarization than the field stars.In the direction of the associationthere are two regions of polarizing interstellar medium with magneticfields that are nearly at right angles to each other. The observed ratioof polarization to reddening for stars in this direction is about afactor of 3 smaller than the mean interstellar value indicating either avery poor efficiency of dust grain alignment, or a magnetic fieldconfiguration that is predominantly longitudinal.
| Studies of ultracompact HII regions - I. Methanol maser survey of IRAS-selected sources
A survey of ultracompact (UC) Hii regions has been carried out bysearching for 6.669-GHz methanol maser emission from a sample of 535IRAS-selected candidates. A total of 201 candidates exhibit methanolemission. These sources have been used, in conjunction with previouslyidentified UC Hii regions, to provide a base for further studies of suchregions. Estimates of distances have indicated that the identified UCHii regions tend to have some Galactic structure but it is not clearwhether they lie in or between the spiral arms of the Galaxy. Theregions are tightly constrained to the plane of the Galaxy. Comparisonof identified regions and IRAS sources selected by Wood & Churchwellindicates that there there is some degree of contamination, which couldbe due to an older phase in the life on an UC Hii region where methanolmaser emission is not apparent. Luminosities and spectral types havebeen derived for many of the regions. The maximum number of maser spotsobserved seems to increase with increasing peak maser luminosity, whichindicates that the maser emission is more dependent on the abundance ofmethanol than the availability of far-infrared radiation.
| Classification and Identification of IRAS Sources with Low-Resolution Spectra
IRAS low-resolution spectra were extracted for 11,224 IRAS sources.These spectra were classified into astrophysical classes, based on thepresence of emission and absorption features and on the shape of thecontinuum. Counterparts of these IRAS sources in existing optical andinfrared catalogs are identified, and their optical spectral types arelisted if they are known. The correlations between thephotospheric/optical and circumstellar/infrared classification arediscussed.
| Properties That Cannot Be Explained by the Progenitors of Planetary Nebulae
I classify a large number of planetary nebulae (458) according to theprocess that caused their progenitors to blow axisymmetrical winds. Theclassification is based primarily on the morphologies of the differentplanetary nebulae, assuming that binary companions, stellar orsubstellar, are necessary in order to have axisymmetrical mass loss onthe asymptotic giant branch. I propose four evolutionary classes,according to the binary-model hypothesis: (1) Progenitors of planetarynebula that did not interact with any companion. These amount to ~10% ofall planetary nebulae. (2) Progenitors that interact with stellarcompanions that avoided a common envelope, 11^{+2}_{-3}% of all nebulae.(3) Progenitors that interact with stellar companions via a commonenvelope phase, 23^{+11}_{-5}% of all nebulae. (4) Progenitors thatinteract with substellar (i.e., planets and brown dwarfs) companions viaa common envelope phase, 56^{+5}_{-8}% of all nebulae. In order todefine and build the different classes, I start with clarifying somerelevant terms and processes related to binary evolution. I then discusskinematical and morphological properties of planetary nebulae thatappear to require the interaction of the planetary nebula progenitorsand/or their winds with companions, stellar or substellar.
| All-Sky 4.85 GHz Flux Measurements of H II Regions
We present an all-sky flux catalog of 760 H II regions with angularsizes ranging up to 10' at 4.85 GHz. The data were compiled in aself-consistent manner from existing images of the Green Bank andParkes-MIT-NRAO 4.85 GHz radio continuum surveys. Nearly 35% of these HII regions have fluxes measured from these surveys for the first time.We compared our results to the previously published source catalogs thatfit the same data. The new flux measurements agree within 5%--7% ofthese values and fall well within the formal errors. The diameters fallwithin 16% of the previously published fits to the same data, which iswithin the formal uncertainties of these values.
| A search for OH maser emission from post-asymptotic giant branch stars.
We present a survey for OH maser emission at 18cm in the direction of196 IRAS point sources. The primary aim of the survey was to detect OHmaser emission from post-asymptotic giant branch (post-AGB) stars. OHemission and/or absorption was detected in the direction of 77 sourcesof which 57 OH detections were previously unknown, giving an overalldetection rate of 39 per cent. Fourteen maser sources associated withevolved stars or planetary nebulae were found, corresponding to 7 percent of the total observed. These included three planetary nebulae (twonew OH detections), nine post-AGB stars (three new OH detections) andtwo cold OH/IR stars (both previously known). Two sources were ofuncertain identification (both new OH detections). The remainder of theOH sources were identified with young stellar objects and with HIIregions. The survey included the detection of OH maser emission from HD101584, an early-type supergiant at high Galactic latitude. For severalof the post-AGB stars, changes have occurred in the OH spectral profilesover a period of several years. This is interpreted as evidence forrapid changes in the stellar winds, due either to interactions withstellar companions, novae-like events or rapid stellar evolution.
| A catalogue of massive young stellar objects.
A catalogue of massive young stellar objects which contains about 250objects is presented. This catalogue is an updated version of thecatalogue of Henning et al. (1984). It provides comprehensiveinformation on infrared and radio flux densities, molecular line data,association with maser sources, and outflow phenomena.
| A CS(2-1) survey of IRAS point sources with color characteristics of ultra-compact HII regions.
We have made a complete survey of the CS(2-1) emission toward IRAS pointsources in the galactic plane. The sources observed were selectedaccording to their far infrared (FIR) colors, which are characteristicof UC HII regions. They have 25μm/12μm flux ratios larger than 3.7and 60μm/12μm flux ratios larger than 19.3. The survey covered aregion from b=-2deg to b=2deg from l=300deg to l=0deg and from l=0deg tol=60deg, and from b=-4deg to b=4deg elsewhere. We detected 843 sourcesout of 1427 sources observed. The distributions of detected andundetected sources in a FIR color-color diagram show some differences,suggesting that more than one type of object is present in our observedsample.
| The 11 Micron Emissions of Carbon Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJ...449..246G&db_key=AST
| 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.
| Detection of Thirty-Five New 5/1-6/0A+- Methanol Masers Towards IRAS Sources
Abstract image available at:http://adsabs.harvard.edu/abs/1993MNRAS.261..783S
| A catalogue of narrow band images of planetary nebulae
The paper presents a catalog of narrow-band images of 255 planetarynebulae (PNe) taken with the 3.5 m ESO NTT, using EFOSC2, the faintobject camera, and spectrograph. The results include properties ofseveral PNe which were previously listed as unresolved, show extendedstellar objects, list several new bipolar proto-PNe, and describe a fewpreviously unknown faint haloes. A new list is presented of sizes inH-alpha and forbidden OIII images, including information on all peculiarobjects and features which have not been seen previously.
| Star formation in the VELA molecular clouds. I - The IRAS-bright Class I sources
Combining near-IR, IRAS, and millimeter molecular line data, thebrightest members of the Class I population in the Vela molecular cloudswere identified. The median luminosity is about 600 solar luminosities,corresponding to intermediate-mass Class I objects, which willeventually settle on the stellar main sequence as B stars. It issuggested that the theory of low-mass star formation is also applicableto the formation of higher-mass stars. It is proposed that the giantmolecular clouds in Vela, being stretched out along the galactic plane,provide a close-up view of typical, initially relatively quiescentgalactic star formation.
| The extinction constants for galactic planetary nebulae
The extinction constants are determined from Balmer decrementmeasurements for over 900 planetary nebulae. Comparison with publishedextinction constants shows that the results from ESO are fairlyreliable. An analysis of the extinction constants derived from theBalmer decrement and from the radio/Hβ flux ratio indicates thatthe latter tends to be systematically smaller than the former forincreasing extinction. We suggest that the radio measurements ofPottasch's group probably underestimate the radio fluxes, at least forsome (faintest) objects.
| A VLA search for young galactic supernova remnants
The VLA in its 36-cm configuration was used to observe 290 known compactgalactic plane radio sources at 20 cm in order to identify very youngSNRs. Supernova were detected with diameters between 5 and 20 arcsec.Compact structure was detected in 168 of the 290 sources; 73 sourceswere unresolved or slightly resolved point sources, 21 were single-wellresolved, 56 were double, and 18 were triple or complex. The large-scalestructure was completely resolved for 122 of the sources. Additionalobservations at 6 cm with the VLA in the 11-km configuration were madeof 14 sources with apparent shell structures that might have beencharacteristic of young SNRs. Low-resolution observations were made at20 cm of 62 fields where the source was completely resolved in thehigh-resolution images. One source, G25.5 + 0.2, is a possible veryyoung SNR. New H66-alpha recombination line observations place severeconstraints on any thermal interpretation for this object.
| A quantitative study of the 7.7 and 11.3 micron emission bands based on IRAS/LRS spectra
A quantitative analysis of the emission bands at 7.7 and 11.3 microns inthe mid-IR spectra of HII regions, reflection nebulae, planetarynebulae, and galaxies is presented. The investigation is based on asample of 113 sources whose spectra have been extracted from theIRAS/LRS data base. Relations of the intensity of the emission bandswith physical conditions such as the excitation, and the relativecontributions of emission bands and continuum around 10 microns to themid-IR and FIR fluxes are presented and analyzed. A strong linearcorrelation is found between 7.7 and 11.3 micron band luminosities. Thegood correlation and the small dispersion (30 percent, compatible withthe measurement errors) confirm, on a sample of sources, that thecarriers of the 7.7 and 11.3 micron emission features belong to the samefamily, most likely aromatic molecular species such as PAH molecules.
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