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A Millimeter Continuum Survey for Massive Protoclusters in the Outer Galaxy
Our search for the earliest stages of massive star formation turned up12 massive pre-protocluster candidates plus a few protoclusters. Forthis search, we selected 47 FIR-bright IRAS sources in the outer Galaxy.We mapped regions of several square arcminutes around the IRAS source inthe millimeter continuum in order to find massive cold cloud corespossibly being in a very early stage of massive star formation. Massesand densities are derived for the 128 molecular cloud cores found in theobtained maps. We present these maps together with near-infrared,mid-infrared, and radio data collected from the 2MASS, MSX, and NVSScatalogs. Further data from the literature on detections of high-densitytracers, outflows, and masers are added. The multiwavelength data setsare used to characterize each observed region. The massive cloud cores(M>100 Msolar) are placed in a tentative evolutionarysequence depending on their emission at the investigated wavelengths.Candidates for the youngest stages of massive star formation areidentified by the lack of detections in the above-mentionednear-infrared, mid-infrared, and radio surveys. Twelve massive coresprominent in the millimeter continuum fulfill this requirement. Sinceneither FIR nor radio emission have been detected from these cloudcores, massive protostars must be very deeply embedded in these cores.Some of these objects may actually be pre-protocluster cores: an up tonow rare object class, where the initial conditions of massive starformation can be studied.
| Near-Infrared Imaging of the Star Formation Region AFGL 5142
Near-infrared JHK' and H2 v=1-0 S(1) imaging observations ofthe star-forming region AFGL 5142 are presented. A cluster of youngstars is confirmed to be embedded in the dense molecular cloud core.Many point sources are newly detected. The cluster's K'-magnitudedistribution and [H-K'] color peak have brighter and reddermagnitudes than those outside the cluster. Many of the cluster sourcesexhibit infrared excesses typical of T Tauri stars, Herbig Ae/Be stars,and protostars. The observations also reveal new H2 lineemission around the cluster, exhibiting several jets, filaments, and afaint elliptical structure. The jets are associated with the CO outflowsin the region. The powering sources of the jets, the CO outflows, andthe small faint elliptical structure are identified and analyzedindividually. The strong H2 jets and faint diffuse emissionfurther confirm that the cluster is in an early stage of evolution.
| 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.
| Far-infrared loops in the 2nd Galactic Quadrant
We present the results of an investigation of the large-scale structureof the diffuse interstellar medium in the 2nd Galactic Quadrant(90°≤l≤180°). 145 loops were identified on IRAS-basedfar-infrared maps. Our catalogue lists their basic physical properties.The distribution clearly suggests that there is an efficient processthat can generate loop-like features at high Galactic latitudes.Distances are provided for 30 loops. We also give an observationalestimate of the volume filling factor of the hot gas in the Local Arm,4.6%≤f2nd<6.4%.Appendices A-C 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/418/131
| Metallicity distribution on the galactic disk
Depending mainly on UBVCCD data, the metallicities of 91 open starclusters nearby the galactic disk have been estimated using Cameron's[A&A 147 (1985b) 39] method. The metallicity radial gradient alongthe galactic plane is found to be -0.09 dex/kpc; which is in a very goodagreement with Panagia and Tosi [A&A 96 (1981) 306] and Carraro etal. [MNRAS 296 (1998) 1045]. Vertically on the galactic disk, withinabout 800 pc, the metallicity gradient is found to be so trivial. Anaverage age-metallicity relation has been examined, which confirms theprevious suggestion that the metallicity of a cluster depending mainlyon its position on the galactic disk more than its age.
| Stellar tracers of the Cygnus Arm. I. Spectroscopic study of bright photometric candidates
We present medium-resolution spectroscopy of a sample of stars in thesecond Galactic quadrant selected from the literature because theircolours suggest that they are moderately-reddened early-type stars atvery large distances. From the derived spectral types and observedcolours, we calculate distances to all these objects. For a sizablefraction of our sample, we find distances well in excess of what isexpected for Perseus Arm objects, even allowing for rather generouserrors. In the interval l=150degr -180degr , there is a large number ofobjects with distances in excess of 4 kpc, which are likely tracing theOuter or Cygnus Arm. In particular, we find that the association Cam OB3is placed on this Arm. Based on our results, the extent and definitionof the associations Cas OB4 and Aur OB2 need to be reevaluated.Based on observations made at Observatoire de Haute Provence (CNRS),France.
| Determination of temperature of the ionizing stars of H II regions
The determination of temperature (T_eff) of the ionizing stars of H Iiregions was considered. In this work we used photoionization models forH Ii regions ionized by a single star to show that the index R=log ([OIi]lambda lambda 3726+3729/[O Iii]lambda 5007) can be used to estimateT_eff. The relation R vs. T_eff proved to be rather independent of thechemical abundances, but strongly dependent on the ionization parameterof the nebula. In order to check the reliability of using R fortemperature determination, we compared the values of T_eff obtained viathe index R for a sample of H Ii regions with data available in theliterature with independent estimations.
| 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.
| Morphological analysis of open clusters' propertiesII. Relationships projected onto the galactic plane
A morphological analysis study of open clusters' properties has beenachieved for a sample of 160 UBVCCD open star clusters of approximately128,000 stars near the galactic plane. The data was obtained and reducedfrom using the same reduction procedures, which makes this catalogue thelargest homogeneous source of open clusters' parameters.
| Integrated photometric characteristics of galactic open star clusters
Integrated UBVRI photometric parameters of 140 galactic open clustershave been computed. Integrated I(V-R)0 and I(V-I)0colours as well as integrated parameters for 71 star clusters have beenobtained for the first time. These, in combination with published data,altogether 352 objects, are used to study the integrated photometriccharacteristics of the galactic open clusters. The I(MV)values range from -9.0 to -1.0 mag corresponding to a range in totalmass of the star clusters from ~ 25 to 4*E4 Msun.The integrated colours have a relatively narrow range, e.g., I(B-V){_0}varies from -0.4 to 1.2 mag. The scatter in integrated colours at agiven integrated magnitude can be understood in terms of differences infraction of red giants/supergiants in the clusters. The observedintegrated magnitudes and colours agree with the synthetic ones, exceptthe dependences of I(V-R)0 and I(V-I)0 colours forclusters younger than ~ 100 Myrs and also of the integrated magnitudesof oldest clusters. The large sample provides the most accurate agedependence of integrated magnitudes and colours determined so far. Theluminosity function of the I(MV) has a peak around -3.5 magand its slope indicates that only ~ 1% of the open clusters in thegalactic disc are brighter than I(MV)=-11 mag. No variationhas been found of integrated magnitude with galactocentric distance andmetallicity.
| Morphological analysis of open clusters' propertiesI. Properties' estimations
A sample of 160 UBVCCD observations of open star clusters near thegalactic plane has been studied, and a catalogue of their propertiesobtained. The main photometrical properties have been re-estimated selfconsistently and the results have been compared with those of Lynga[Lynga, G., 1987. Catalog of Open Cluster Data, 5th Edition, StellarData Centers, Observatoire de Strasbourg, France].
| An Empirical Test and Calibration of H II Region Diagnostics
We present spectrophotometry in the 3600-9700 Å region for asample of 39 H II regions in the Galaxy and Magellanic Clouds, for whichindependent information is available on the spectral types and effectivetemperatures of the ionizing stars. The spectra have been used toevaluate nebular diagnostics of stellar temperature, metal abundance,and ionization parameter, and to compare the observed behavior of theline indices with predictions of nebular photoionization models. Weobserve a strong degeneracy between forbidden-line sequences produced bychanges in stellar Teff and metal abundance, which severelycomplicates the application of many forbidden-line diagnostics toextragalactic H II regions. Our data confirm however that the Edmunds& Pagel [O II]+[O III] abundance index and the Vílchez &Pagel η' index provide more robust diagnostics of metalabundance and stellar effective temperature, respectively. A comparisonof the fractional helium ionization of the H II regions with stellartemperature confirms the reliability of the spectral type versusTeff calibration for the relevant temperature rangeTeff<=38,000 K. We use empirical relations between thenebular hardness indices and Teff to reinvestigate the casefor systematic variations in the stellar effective temperatures and theupper initial mass functions of massive stars in extragalactic H IIregions. The data are consistent with a significant softening of theionizing spectra (consistent with cooler stellar temperatures) withincreasing metal abundance, especially for Z<=Zsolar.However, unresolved degeneracies between Z and Teff stillcomplicate the interpretation of this result.
| Calibration of Nebular Emission-Line Diagnostics. I. Stellar Effective Temperatures
We present a detailed comparison of optical H II region spectra tophotoionization models based on modern stellar atmosphere models. Weexamine both spatially resolved and integrated emission-line spectra ofthe H II regions DEM L323, DEM L243, DEM L199, and DEM L301 in the LargeMagellanic Cloud. The published spectral classifications of the dominantstars range from O7 to WN3, and morphologies range from Strömgrensphere to shell structure. Two of the objects include SNR contamination.The overall agreement with the predictions is generally within 0.2 dexfor major diagnostic line ratios. An apparent pattern in the remainingdiscrepancies is that the predicted electron temperature is ~1000 Khotter than observed. [Ne III] intensities are also slightlyoverpredicted, which may or may not be related. We model the shockemission for the SNR-contaminated objects and find excellent agreementwith the observations for composite shock and photoionized spectra. DEML301's emission apparently results from both shocks and density-boundedphotoionization. The existence of contaminating shocks can be difficultto ascertain in the spatially integrated spectra. Our analysis of thecomplex DEM L199 allows a nebular emission-line test of unprecedenteddetail for WR atmospheres. Surprisingly, we find no nebular He IIλ4686 emission, despite the fact that both of the dominant WN3stars should be hot enough to fully ionize He I in their atmospheres.The nebular diagnostics are again in excellent agreement with the data,for stellar models not producing He+-ionizing photons. Theoptical diagnostics are furthermore quite insensitive to the ionizingenergy distribution for these early WR stars. We confirm that the η'emission-line parameter is not as useful as hoped for determining theionizing stellar effective temperature, T*. Both empiricallyand theoretically, we find that it is insensitive forT*>~40 kK and that it also varies spatially. Theshock-contaminated objects show that η' will also yield a spuriouslyhigh T* in the presence of shocks. It is furthermoresensitive to shell morphology. We suggest [Ne III]/Hβ as anadditional probe of T*. Although it is abundance dependent,[Ne III]/Hβ has higher sensitivity to T*, is independentof morphology, and is insensitive to shocks in our objects. Theseobservations should be useful data points for a first empiricalcalibration of nebular diagnostics of T*, which we attemptfor LMC metallicity.
| A survey of the 6.7 GHz methanol maser emission from IRAS sources. I. Data
We report the first results of a search for 6.7 GHz methanol masers inthe direction of 1399 IRAS objects north of declination-20deg with the flux densities greater than 100 Jy at 60 mu mand the flux density ratio F60/F25>1.Observations were made with the sensitivity of 1.7 Jy and the velocityresolution of 0.04 km s-1 using the 32-m Toruń radiotelescope. Maser emission was found in 182 sources, including 70 newdetections. 32 new sources were identified with objects of radioemission associated with star-forming regions. Comparison of the presentdata set with other observations suggests that about 65% of methanolmasers exhibit moderate or strong variations on time-scales of about 4and 8 years. Table 2 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/Abstract.html
| J=1-0 HCN toward bright far-infrared sources in the outer Galaxy
Results of the J=1-0 HCN observations toward 34 bright far-infraredsources selected from the IRAS Point Source Catalog are reported.Together with 17 sources observed in this line earlier (Pirogov et al.,1996) they form a complete sample of the sources with flux densitiesS(100 mu m)>500 Jy and delta > 0degr in the outer Galaxy. The HCNdata are compared with the HCO(+) , NH_3, CS and CO data taken fromliterature. Prominent correlations with nearly similar slopes of ~ 1 arerevealed between line integrated intensities of the molecules known tobe high density tracers (HCN, HCO(+) , NH_3 and CS). The correlationsbecome higher after adding the data for dark clouds, small globules andcirrus cores implying similar excitation and formation mechanisms of theconsidered molecules. Collisional excitation in regions with differentdensities as well as different molecular abundances and velocitydispersions in different types of cores seem to be important inproducing these correlations. The following relations hold on theaverage over ~ 3 orders of magnitude of integrated intensities:I(HCN)>~ I(HCO(+) ~ ) I(CS) > I(NH_3) where ammonia integratedintensities are several times lower than HCN ones. Correlations are alsofound between HCN and CO integrated intensities for the sample sourcesas well as between HCN line widths and those of other species. The HCNlines have the same widths as the HCO(+) ones and are larger than CS andespecially NH_3 line widths. Weak correlations are found between HCNline widths and luminosities of IRAS sources as well as between HCNintegrated intensities, IRAS flux densities at 100mu m and luminositiesof IRAS sources divided by distance squared. The sources with mostintense HCN lines have associated water masers and molecular outflowswhile the lack of associated maser and outflow implies weak or no HCNemission. In order to reproduce the anomalies of the J=1-0 HCN hyperfinestructure (R12 < 0.6) detected in several sources togetherwith suprathermal line widths the model calculations are performed. Twomodels have been considered: a microturbulent one with a smooth densitydistribution and a clumpy model. It is found that in the parameter spaceexplored a clumpy model is preferable in comparison with amicroturbulent one due to the absence of self-reversals on calculatedprofiles and the possibility of reproducing HCN profile anomalies andsuprathermal line widths. Detailed clumpy model simulations have beenperformed to fit the observed HCN and H(13) CN spectra toward S140 IRS1.The best fit model parameters are calculated, including radialdependencies of clump density and volume filling factor.
| The Medicina survey of methanol masers at 6.7 GHz
A survey of Class II methanol masers at 6.7 GHz was made in the Northernhemisphere with the 32-m Medicina radio telescope. 42 objects weredetected, 20 of them are new detections at 6.7 GHz. Our results showthat the detection rate of 6.7 GHz masers toward the inner part of theGalaxy is higher than in other directions. It is confirmed that most ofthe methanol masers are associated with faint compact HII regions. The6.7 GHz methanol masers show large velocity dispersion and largevelocity offset from the velocity of parent molecular clouds. Table 2 isonly available in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| A 13CO Survey of Molecular Clouds in Gemini and Auriga
A large-scale survey for molecular clouds in 13CO(J = 1-0) was performedtoward the Gemini and Auriga regions (170 deg < l <= 196 deg and-10 deg <= b < 10 deg) with velocity coverages of -30 < VLSR< +30 km s-1 and -20 < VLSR < +40 km s-1 for 170 deg < l<= 188 deg and 188 deg < l <= 196 deg, respectively, by usingthe two 4 m millimeter-wave telescopes at Nagoya University. An area of520 deg2 was covered at an 8' grid spacing with a 2.'7 beam, and 29,250positions were observed. Significant 13CO emission (>=1.2 K km s-1 =3 sigma ) is detected at 1032 positions, and 139 distinct 13CO cloudsare identified. Physical properties such as molecular column density,size, and mass are derived for each cloud. Comparison with known H IIregions and other associated visible objects indicates that 98 of the139 clouds are located at ~2 kpc, while the rest lie at <~ 1 kpc. Thecandidates for protostars are selected from IRAS point sources and 141sources are identified as protostellar candidates associated with the13CO clouds. A statistical study of the 13CO clouds and of thecandidates for protostars shows the following results: 1. The massspectra of the 13CO clouds are well represented by a power law,Ncloud(>=Mcloud) = 1.4 x 104(Mcloud/Mȯ)-0.83 - 1.4 for theclouds at ~2 kpc and Ncloud(>=Mcloud) = 3.5 x102(Mcloud/Mȯ)-0.64 - 2.4 for the rest. 2. The line width, DeltaVcomp, and the size, R, of the 13CO clouds show a power-law relationwith an index 0.24 +/- 0.06, where the dispersion in the fitting isfairly large. 3. A virial analysis made for the 13CO clouds indicatesthat the relation between the virial mass, Mvir, and the mass measuredin 13CO, Mcloud, is aproximated well by (Mvir/Mȯ) = 2.0 x101(Mcloud/Mȯ)0.72, which suggests that smaller clouds tend to bemore weakly bound gravitationally than larger clouds or are dispersingif the external pressure is negligible. This is probably the cuase of asmall index value of the line width-size relation. 4. The luminosityfunction of the IRAS point sources associated with 13CO clouds are wellrepresented by a power law withN_⋆(>=L_⋆)=4.0x102L^{-0.29}_⋆-1.9x10 forthose at ~2 kpc and N_⋆(>=L_⋆)=2.3x10L^{-0.27}_⋆-3.2for the rest. 5. The luminosity of the most luminous IRAS point sourcein a given molecular cloud increases systematically with the mass of theassociated cloud. 6. The 13CO clouds associated with IRAS point sources,which are regarded as ongoing star-forming clouds, tend to be moremassive and larger in size and to have higher column densities thanthose without any sign of star formation. These relations are found tobe consistent with those derived in Cygnus by Dobashi, Bernard, &Fukui and in Cepheus-Cassiopeia by Yonekura et al. In order to study thestar formation activities, we studied the ratio of virial mass and themass measured in 13CO, Mvir/Mcloud, and its relation with starformation. It is clearly seen that the star-forming 13CO clouds have lowMvir/Mcloud, and all the clouds with high Mvir/Mcloud exhibit no sign ofstar formation. This suggests that star formation rarely occurs inclouds with overall kinetic energy higher than the gravitational energy.
| New detections of H_2O maser sources on the 13.7 M radio telescope of Purple Mountain Observatory
Observations of H_2O maser sources on the 13.7 m radio telescope ofPurple Mountain Observatory from 1990 Aug. to 1994 Jan. are summarized.For searching new water masers, the total number of search candidates isabout 360, with 110 objects detected. Among them are 96 new detections.A list of the new detections and their spectra are presented. Table 1and Fig. 1 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html
| A report on the studies of star clusters with the UPSO 104-cm Sampurnanand telescope during last 25 years
Not Available
| Infrared emission and H-R diagram of bright far-infrared sources during star formation
Young stellar objects (YSOs) were studied using a set of bright FIRsources selected from IRAS-PSC and associated with high-mass YSOs. Amodified blackbody photospheric model, double-shell dust emission model,and a detailed radiation transfer model were used to fit the observedinfrared fluxes, and some physical parameters, such as the photospherictemperature of the central star, the circumstellar extinction, andthermal structure of dust shell were derived. Using the derivedphotospheric temperatures and corresponding stellar luminosities, wehave determined the positions on an extended H-R diagram and theevolution properties of the investigated bright FIR sources. We havefound that there is a trend of continuous increase of the infraredspectral slope S (12-60) from 12 to 60 microns along the direction tomain sequence stars at the same mass line of H-R diagram. For the YSOs,which are evolving at the same time, there is also a trend of increaseof S (12-60) with mass. We analyzed the nature of the bright FIRsources. It seems that the extended H-R diagram presented here is a goodmeans to study this kind of objects, which are deeply embedded inmolecular clouds and dust envelopes.
| 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.
| High-Velocity Molecular Gas from High-Mass Star Formation Regions
Abstract image available at:http://adsabs.harvard.edu/abs/1996ApJ...457..267S
| 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.
| A study of the relation between 22 GHz H2O masers and CO outflows in intense far-infrared sources on the stages of star formation.
Not Available
| IRAS LRS Spectra of the Sharpless H II Regions
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJS..100..389C&db_key=AST
| IRAS sources beyond the solar circle. VI. Analysis of the FIR, H_2_O, and CO emission.
For a sample of 1357 IRAS sources with FIR colours of young stellarobjects we have compared the occurrence and properties of H_2_O maser-and ^12^CO(1-0) emission with the observed and derived IRAS parameters.We find that the distribution of differences between the CO and H_2_Ovelocities is a Gaussian with a FWHM of about 11km/s. The mean velocitydifference is nearly zero. The velocity of the peak H_2_O emission isnot at a preferred location within the velocity interval where emissionis detected. The H_2_O maser detection rate increases with both the FIRluminosity and the ^12^CO(1-0) line width: belowlog(L_FIR_/Lsun_)=3.5, less than 10% of the sources showmaser emission, whereas H_2_O is detected towards almost all of thesources above log(L_FIR_/Lsun_)=4.5. For the sources withH_2_O maser emission, the average CO line width (FWHM about 5.0km/s) isapproximately twice as large as for those without detected H_2_Oemission, an effect which is independent of the sources' FIR luminosity.However a significant fraction of sources with no detected H_2_Oemission still have line widths larger than 1.9km/s, the median valuefor the quiescent gas not associated with the IRAS sources. The maximumH_2_O maser luminosity at each FIR luminosity is proportional to L_FIR_:L_H_2_O_/Lsun_=10^-7.4^(L_FIR_/Lsun_). In IRAScolour-colour plots, sources can be distinguished in maser-like andnon-maser-like sources according to their CO line widths and FIRluminosity. At a given L_FIR_ the maximum T^*^_A_ found for ^12^CO(1-0)decreases with distance from the Sun, likely due to beam fillingeffects. Few sources with maser emission have T^*^_A_ below 7.5K, whenobserved with the IRAM 30-m telescope. There is no difference in themaximum T^*^_A_ of sources with maser-like and non-maser-like IRAScolours. We have derived the intrinsic luminosity- and mass distributionof sources with (non)-maser-like IRAS colours, correcting forincompleteness effects at lower luminosities. The slope of the IMF forsources with maser-like colours and mass larger than 10Msun_is found to be -2.8+/-0.3.
| New detections of 5_1_-6_0_A^+^-methanol masers towards IRAS sources.
We present the results of our second search for 6.7-GHz methanol maserstowards colour-selected IRAS sources. Five hundred and twenty IRASsources that meet the far-infrared colour criteria set by Wood &Churchwell for ultra-compact HII regions were searched for 6.7-GHzmethanol maser emission, to a sensitivity limit of 5Jy. Thirty one newmaser sources were detected. We also compare the FIR colours of thenewly detected maser sources with those detected by Schutte et al.(1993) and the IRAS counterparts of sources that have both methanol andhydroxyl maser emission. It was found that the average flux distributionof the newly detected sources differs significantly from that of allother known 6.7-GHz methanol maser sources. It is argued that thedifferences may be due either to intrinsic differences between the threegroups of sources or to interstellar extinction. An analysis of therelation between the 6.7-GHz maser and IRAS flux densities shows thatthe maser flux density is always less than the 100 μm flux densitywhile only three sources have a maser flux density greater than the 60μm flux density. Far-infrared pumping of the 6.7-GHz methanol masersis therefore in principle viable although it was found that the apparentmaser efficiency will exceed 10 per cent for a significant number ofsources in the case of FIR pumping by photons between 50 and 100μm.The overall detection rates on the IRAS [25-12] vs [60-12] two-colourdiagram are also presented. Possible new search strategies for masers incolour-selected IRAS sources are discussed.
| 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.
| CCD photometry of galactic open star clusters IV. NGC 366
Not Available
| CCD photometry of galactic open star clusters-III. NGC 1931
Not Available
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