- ID:
- ivo://CDS.VizieR/J/ApJ/785/47
- Title:
- Sources around target stars in Upper Scorpius
- Short Name:
- J/ApJ/785/47
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a multiplicity survey of 91 stars spanning masses of ~0.2-10 M_{sun}_ in the Upper Scorpius star-forming region, based on adaptive optics imaging with the Gemini North telescope. Our observations identified 29 binaries, 5 triples, and no higher order multiples. The corresponding raw multiplicity frequency is 0.37+/-0.05. In the regime where our observations are complete - companion separations of 0.1''-5'' (~15-800 AU) with magnitude limits ranging from K <9.3 at 0.1'' to K<15.8 at 5'' - the multiplicity frequency is 0.27_0.04_^+0.05^. For similar separations, the multiplicity frequency in Upper Scorpius is comparable to that in other dispersed star-forming regions, but is a factor of two to three higher than in denser star-forming regions or in the field. Our sample displays a constant multiplicity frequency as a function of stellar mass. Among our sample of binaries, we find that both wider (>100 AU) and higher-mass systems tend to have companions with lower companion-to-primary mass ratios. Three of the companions identified in our survey are unambiguously substellar and have estimated masses below 0.04 M_{sun}_ (two of them are new discoveries from this survey - 1RXS J160929.1-210524b and HIP 78530B - although we have reported them separately in earlier papers). These three companions have projected orbital separations of 300-900 AU. Based on a statistical analysis factoring in sensitivity limits, we calculate an occurrence rate of 5-40 M_Jup_ companions of ~4.0% for orbital separations of 250-1000 AU, compared to <1.8% at smaller separations, suggesting that such companions are more frequent on wider orbits.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/713/871
- Title:
- Sources in star-forming region Cyg-OB2 from X-ray
- Short Name:
- J/ApJ/713/871
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Cygnus OB2 is the nearest example of a massive star-forming region (SFR), containing over 50 O-type stars and hundreds of B-type stars. We have analyzed the properties of young stars in two fields in Cyg OB2 using the recently published deep catalog of Chandra X-ray point sources with complementary optical and near-IR photometry. Our sample is complete to ~1M_{sun}_ (excluding A- and B-type stars that do not emit X-rays), making this the deepest study of the stellar properties and star formation history in Cyg OB2 to date. Combining our stellar mass function (MF) and an estimate of the radial density profile of the association suggests a total mass of Cyg OB2 of ~3x10^4^M_{sun}_, similar to that of many of our Galaxy's most massive SFRs.
- ID:
- ivo://CDS.VizieR/J/MNRAS/402/575
- Title:
- Southern ultracool dwarfs in young moving groups
- Short Name:
- J/MNRAS/402/575
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We associate 132 low-mass ultracool dwarfs in the southern hemisphere as candidate members of five moving groups (MGs) using photometric and astrometric selection techniques. Of these objects, we present high-resolution spectroscopy for seven candidates and combine these with previous measurements from the literature to determine spectral types and radial velocities. We thus constrain distance and space motion spectroscopically, allowing the kinematic membership of the MGs to be assessed. Possible membership of MGs has allowed ages and metallicities to be constrained for these objects and evolutionary models have been used to estimate their mass. We estimate that up to ~75 of our candidate MG members should be genuine, and discuss future work that will confirm and exploit this major new sample.
- ID:
- ivo://CDS.VizieR/J/ApJ/787/107
- Title:
- Spatial structure of young stellar clusters. I.
- Short Name:
- J/ApJ/787/107
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The clusters of young stars in massive star-forming regions show a wide range of sizes, morphologies, and numbers of stars. Their highly subclustered structures are revealed by the MYStIX project's sample of 31754 young stars in nearby sites of star formation (regions at distances <3.6kpc that contain at least one O-type star.) In 17 of the regions surveyed by MYStIX, we identify subclusters of young stars using finite mixture models --collections of isothermal ellipsoids that model individual subclusters. Maximum likelihood estimation is used to estimate the model parameters, and the Akaike Information Criterion is used to determine the number of subclusters. This procedure often successfully finds famous subclusters, such as the BN/KL complex behind the Orion Nebula Cluster and the KW-object complex in M17. A catalog of 142 subclusters is presented, with 1-20 subclusters per region. The subcluster core radius distribution for this sample is peaked at 0.17pc with a standard deviation of 0.43dex, and subcluster core radius is negatively correlated with gas/dust absorption of the stars --a possible age effect. Based on the morphological arrangements of subclusters, we identify four classes of spatial structure: long chains of subclusters, clumpy structures, isolated clusters with a core-halo structure, and isolated clusters well fit by a single isothermal ellipsoid.
- ID:
- ivo://CDS.VizieR/J/ApJ/812/131
- Title:
- Spatial structure of young stellar clusters. III.
- Short Name:
- J/ApJ/812/131
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyze the physical properties of stellar clusters that are detected in massive star-forming regions in the MYStIX project - a comparative, multiwavelength study of young stellar clusters within 3.6 kpc that contain at least one O-type star. Tabulated properties of subclusters in these regions include physical sizes and shapes, intrinsic numbers of stars, absorptions by the molecular clouds, and median subcluster ages. Physical signs of dynamical evolution are present in the relations of these properties, including statistically significant correlations between subcluster size, central density, and age, which are likely the result of cluster expansion after gas removal. We argue that many of the subclusters identified in Paper I (Kuhn et al. 2014, J/ApJ/787/107) are gravitationally bound because their radii are significantly less than what would be expected from freely expanding clumps of stars with a typical initial stellar velocity dispersion of ~3 km/s for star-forming regions. We explore a model for cluster formation in which structurally simpler clusters are built up hierarchically through the mergers of subclusters - subcluster mergers are indicated by an inverse relation between the numbers of stars in a subcluster and their central densities (also seen as a density versus radius relation that is less steep than would be expected from pure expansion). We discuss implications of these effects for the dynamical relaxation of young stellar clusters.
- ID:
- ivo://CDS.VizieR/J/MNRAS/484/1838
- Title:
- Spatial substructure of Cygnus OB2
- Short Name:
- J/MNRAS/484/1838
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- For the first time, we have explored the spatial substructure of the Cygnus OB2 association using parallaxes from the recent second Gaia data release. We find significant line-of-sight substructure within the association, which we quantify using a parametrized model that reproduces the observed parallax distribution. This inference approach is necessary due to the non-linearity of the parallax distance transformation and the asymmetry of the resulting probability distribution. Using a Markov Chain Monte Carlo ensemble sampler and an unbinned maximum likelihood test, we identify two different stellar groups superposed on the association. We find the main Cygnus OB2 group at ~1760pc, further away than recent estimates have envisaged, and a foreground group at ~1350pc. We also calculate individual membership probabilities and identify outliers as possible non-members of the association.
- ID:
- ivo://CDS.VizieR/J/AJ/158/48
- Title:
- Speckle interferometry at SOAR in 2018
- Short Name:
- J/AJ/158/48
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The results of speckle interferometric observations at the 4.1 m Southern Astrophysical Research Telescope (SOAR) in 2018 are given, totaling 3097 measurements of 2427 resolved pairs with separations from 11 mas to 5.9" (median 0.15", magnitude difference up to 7 mag) and nonresolutions of 624 targets. This work continues our long-term speckle program. Its main goal is to monitor orbital motion of close binaries, including members of high-order hierarchies and Hipparcos pairs in the solar neighborhood. Also, pre-main-sequence stars in the Orion OB1 association were surveyed, resolving 26 out of 118 targets. In addition, we report the discovery of 35 new companions among field visual multiples (some of which are likely optical) and first-time resolutions of another 31 pairs. By combining the measurements given here with the published ones, we computed 76 orbits for the first time and updated orbital elements of 34 visual binaries. Their periods range from 0.65 to 1100 yr, and their quality varies from first tentative solutions of grade 5 to accurate elements of grades 1 and 2. Finally, a list of 53 spurious pairs discovered by various techniques and unresolved at SOAR is given.
- ID:
- ivo://CDS.VizieR/J/A+A/440/111
- Title:
- Spectra of SMC star clusters
- Short Name:
- J/A+A/440/111
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present flux-calibrated integrated spectra in the range 360-680nm for 18 concentrated SMC clusters. The objects are part of a systematic spectroscopic survey of SMC star clusters which is being undertaken at Complejo Astronomico El Leoncito (CASLEO) in San Juan (Argentina) and Cerro Tololo Inter-American Observatory (CTIO, Chile).
- ID:
- ivo://CDS.VizieR/J/A+A/589/A16
- Title:
- Spectra of W49 massives young stars
- Short Name:
- J/A+A/589/A16
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Massive stars form on different scales ranging from large, dispersed OB associations to compact, dense starburst clusters. The complex structure of regions of massive star formation, and the involved short timescales provide a challenge for our understanding of their birth and early evolution. As one of the most massive and luminous star- forming region in our Galaxy, W49 is the ideal place to study the formation of the most massive stars. By classifying the massive young stars deeply embedded into the molecular cloud of W49, we aim to investigate and trace the star formation history of this region. We analyse near-infrared K-band spectroscopic observations of W49 from LBT/LUCI combined with JHK images obtained with NTT/SOFI and LBT/LUCI. Based on JHK -band photometry and K-band spectroscopy the massive stars are placed in a Hertzsprung Russell diagram. By comparison with evolutionary models, their age and hence the star formation history of W49 can be investigated.
- ID:
- ivo://CDS.VizieR/J/AJ/140/293
- Title:
- Spectroscopic study of the Wolf 630 moving group
- Short Name:
- J/AJ/140/293
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The concept of kinematic assemblages evolving from dispersed stellar clusters has remained contentious since Eggen's initial formulation of moving groups in the 1960s. With high-quality parallaxes from the Hipparcos space astrometry mission, distance measurements for thousands of nearby, seemingly isolated stars are currently available. With these distances, a high-resolution spectroscopic abundance analysis can be brought to bear on the alleged members of these moving groups. If a structure is a relic of an open cluster, the members can be expected to be monolithic in age and abundance in as much as homogeneity is observed in young open clusters. In this work, we have examined 34 putative members of the proposed Wolf 630 moving group using high-resolution stellar spectroscopy.
