- ID:
- ivo://CDS.VizieR/J/A+A/635/A187
- Title:
- Massive binaries in Westerlund 1. VII.
- Short Name:
- J/A+A/635/A187
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Context. The formation, properties, and evolution of massive stars remain subject to considerable theoretical and observational uncertainty. This impacts on fields as diverse as galactic feedback, the production of cosmic rays, and the nature of the progenitors of both electromagnetic and gravitational wave transients. Aims. The young massive clusters many such stars reside within provide a unique laboratory for addressing these issues. In this work we provide a comprehensive stellar census of Westerlund 1 in order to to underpin such efforts. Methods. We employed optical spectroscopy of a large sample of early-type stars to determine cluster membership for photometrically-identified candidates, characterise their spectral type, and identify new candidate spectroscopic binaries. Results. Sixty nine new members of Westerlund 1 are identified via I-band spectroscopy. Together with previous observations, they illustrate a smooth and continuous morphological sequence from late-O giant through to OB supergiant. Subsequently, the progression bifurcates, with one branch yielding mid-B to late-F hypergiants, and cool supergiants, and the other massive blue stragglers prior to a diverse population of H-depleted WRs. We identify a substantial population of O-type stars with very broad Paschen series lines, a morphology that is directly comparable to known binaries in the cluster. In a few cases additional low-resolution R-band spectroscopy is available, revealing double-lined He I profiles and confirming binarity for these objects; suggesting a correspondingly high binary fraction amongst relatively unevolved cluster members.Conclusions. Our current census remains incomplete, but indicates that Westerlund 1 contains at least 166 stars with initial masses estimated to lie between ~25M_{sun}_ and ~50M_{sun}_, with more massive stars already lost to supernova. Our data is consistent with the cluster being co-eval, although binary interaction is clearly required to yield the observed stellar population, which is characterised by a uniquely rich cohort of hypergiants ranging from spectral type O to F, with both mass-stripped primaries and rejuvenated secondaries or merger products present. Future observations of Wd1 and similar stellar aggregates hold out the prospect of characterising both single- and binary- evolutionary channels for massive stars and determining their relative contributions. This in turn will permit the physical properties of such objects at the point of core-collapse to be predicted, which is of direct relevance for understanding the formation of relativistic remnants such as the magnetars associated with Wd1 and other young massive clusters.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/668/906
- Title:
- Massive clumps in NGC 6334
- Short Name:
- J/ApJ/668/906
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report observations of dust continuum emission at 1.2mm toward the star-forming region NGC 6334 made with the SEST SIMBA bolometer array. The observations cover an area of ~2deg^2^ with approximately uniform noise. We detected 181 clumps spanning almost 3 orders of magnitude in mass (3-6x10^3^M_{sun}_) and with sizes in the range 0.1-1.0pc.
- ID:
- ivo://CDS.VizieR/J/MNRAS/473/849
- Title:
- Mass segregation in Galactic stellar clusters
- Short Name:
- J/MNRAS/473/849
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We quantify the structure of a very large number of Galactic open clusters and look for evidence of mass segregation for the most massive stars in the clusters. We characterize the structure and mass segregation ratios of 1276 clusters in the Milky Way Stellar Cluster (MWSC) catalogue containing each at least 40 stars and that are located at a distance of up to ~2kpc from the Sun. We use an approach based on the calculation of the minimum spanning tree of the clusters, and for each one of them, we calculate the structure parameter Q and the mass segregation ratio {LAMBDA}_MSR_. Our findings indicate that most clusters possess a Q parameter that falls in the range 0.7-0.8 and are thus neither strongly concentrated nor do they show significant substructure. Only 27 per cent can be considered centrally concentrated with Q values >0.8. Of the 1276 clusters, only 14 per cent show indication of significant mass segregation ({LAMBDA}_MSR_>1.5). Furthermore, no correlation is found between the structure of the clusters or the degree of mass segregation with their position in the Galaxy. A comparison of the measured Q values for the young open clusters in the MWSC to N-body numerical simulations that follow the evolution of the Q parameter over the first 10Myr of the clusters life suggests that the young clusters found in the MWSC catalogue initially possessed local mean volume densities of {rho}*~=10-100M_{sun}_/pc^3^.
- ID:
- ivo://CDS.VizieR/J/A+A/333/897
- Title:
- Mass segregation in open clusters
- Short Name:
- J/A+A/333/897
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- On the basis of the best available member list and duplicity information, we have studied the radial structure of Praesepe and of the very young open cluster NGC 6231. We have found mass segregation among the cluster members and between binaries and single stars, which is explained by the greater average mass of the multiple systems. However, the degree of mass segregation for stars between 1.5 and 2.3M_{sun}_ is less pronounced in Praesepe than in the Pleiades. Furthermore, mass segregation is already present in the very young open cluster NGC 6231 although this cluster is likely still not dynamically relaxed. We discuss the implications of these results and propose a qualitative scenario for the evolution of mass segregation in open clusters. In Praesepe the mass function of single stars and primaries appears to be significantly different, like in the Pleiades. We observe an absence of ellipticity of the outer part of Praesepe.
555. M67 CCD photometry
- ID:
- ivo://CDS.VizieR/J/BaltA/7/369
- Title:
- M67 CCD photometry
- Short Name:
- J/BaltA/7/369
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Seven-color CCD photometry in the Vilnius photometric system of 279 stars down to V=15mag in the open cluster M 67 area is obtained. 13 standard stars in the cluster are measured photoelectrically. Photometric spectral types have been determined for all the stars. The reddening of the cluster is found to be E(B-V)=0.045, the true distance modulus is 9.38mag and the age is 4x10^9^ years. For a description of the Vilnius photometric system, see e.g. <GCPD/21>
- ID:
- ivo://CDS.VizieR/J/BaltA/13/1
- Title:
- M67 CCD Vilnius photometry
- Short Name:
- J/BaltA/13/1
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Seven color CCD photometry in the Vilnius system, supplemented by the Cousins I passband, has been obtained for 412 stars down to V=16mag in the M67 open cluster area. A special method of flat-fielding, giving high accuracy photometry, was used. Photometric spectral types and interstellar reddenings of all stars were determined. The mean mean reddening of the cluster stars is E(B-V)=0.04mag and the distance is 770pc.
- ID:
- ivo://CDS.VizieR/J/AN/328/889
- Title:
- Mean Radial Velocities of open clusters
- Short Name:
- J/AN/328/889
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have used the 2nd version of the Catalogue of Radial Velocities with Astrometric Data (CRVAD-2, Cat. <III/254>) for a new determination of mean RVs of 363 open clusters and stellar associations considering their defined members from proper motions and photometry in the All-Sky Compiled Catalogue of 2.5 Million Stars (ASCC-2.5, Cat. <I/280>). For 330 clusters and associations we compiled previously published RVs from the literature, critically reviewed and partly revised them. The resulting Catalogue of Radial Velocities of Open Clusters and Associations (CRVOCA) provides RVs for 516 open clusters and stellar associations in the Solar neighbourhood. Objects in the catalogue are sorted in the order of increasing right ascension J2000.
- ID:
- ivo://CDS.VizieR/J/MNRAS/434/966
- Title:
- Measurements of Li in T-Tauri stars
- Short Name:
- J/MNRAS/434/966
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have used medium-resolution spectra to search for evidence that proto-stellar objects accrete at high rates during their early 'assembly phase'. Models predict that depleted lithium and reduced luminosity in T-Tauri stars are key signatures of 'cold' high-rate accretion occurring early in a star's evolution. We found no evidence in 168 stars in NGC 2264 and the Orion nebula cluster for strong lithium depletion through analysis of veiling-corrected 6708{AA} lithium spectral line strengths. This suggests that 'cold' accretion at high rates (dM/dt>=5x10^-4^M_{sun}_/yr) occurs in the assembly phase of fewer than 0.5 percent of 0.3<=M*<=1.9M_{sun}_ stars. We also find that the dispersion in the strength of the 6708{AA} lithium line might imply an age spread that is similar in magnitude to the apparent age spread implied by the luminosity dispersion seen in colour-magnitude diagrams. Evidence for weak lithium depletion (<10% in equivalent width) that is correlated with luminosity is also apparent, but we are unable to determine whether age spreads or accretion at rates less than 5x10^-4^M_{sun}_/yr are responsible.
- ID:
- ivo://CDS.VizieR/J/PASP/106/486
- Title:
- Mel 66 CCD photometry
- Short Name:
- J/PASP/106/486
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A CCD study of the peculiar open cluster, Melotte 66, on the vbyHbeta system is presented. The V,(b-y) color-magnitude diagram of this metal-deficient, old disk cluster confirms the anomalous features found in photographic BV studies and extends the main sequence to V=20. The main sequence exhibits a (b-y) color range significantly larger than expected from photometric errors alone; the (b-y) colors are correlated with Hbeta implying that the dispersion is real and is not the result of variable reddening across the cluster. The m1 indices for the turnoff stars imply a spread in [Fe/H] too small to explain the color range. Though the subgiant region is poorly defined, the region above the turnoff in the Hertzsprung gap is richly populated by a group of "yellow stragglers" whose membership is confirmed by radial star counts and radial velocities. The giant branch is richly populated but shows a smaller spread in color at a given V than one would expect from the turnoff region. More important, the giants exhibit a large scatter in m1, in contradiction with the turnoff observations. Various explanations for these observations are discussed, including CN variations among the giants triggered by either binary evolution or rapid rotation among the main-sequence stars.
560. Melotte 66
- ID:
- ivo://CDS.VizieR/J/MNRAS/174/471
- Title:
- Melotte 66
- Short Name:
- J/MNRAS/174/471
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Photoelectric and photographic photometry of the open cluster Melotte 66 is presented. The CM diagram shows most of the characteristics of an old cluster. The giant branch is broad with its blue edge populated preferentially by stars from the outer parts of the cluster. There is no detectable horizontal subgiant sequence. The main sequence turn-off colour, two-colour diagram and the colour difference between the turn-off and the subgiants are used to estimate the age and composition. Melotte 66 appears to have reddening E(B-V)=0.17mag and ultraviolet excess d(U-B)~0.1mag corresponding to [Fe/H]=-0.3. The cluster is probably between 6 and 7x10^9^yr old. A distance modulus (m-M)o=12.4mag is derived, which implies that the cluster lies about 750pc from the galactic plane.