- ID:
- ivo://CDS.VizieR/J/MNRAS/425/1696
- Title:
- Models of a young star cluster ejecta
- Short Name:
- J/MNRAS/425/1696
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have computed with a fine time grid the evolution of the elemental abundances of He, C, N and O ejected by young (t<20Myr) and massive (M=10^6^M_{sun}_) coeval stellar cluster with a Salpeter initial mass function (IMF) over a wide range of initial abundances. Our computations incorporate the mass loss from massive stars (M>=30M_{sun}_) during their wind phase including the Wolf-Rayet phase and the ejecta from the core-collapse supernovae. We find that during the Wolf-Rayet phase (t<5Myr) the cluster ejecta composition suddenly becomes vastly overabundant in N for all initial abundances and in He, C and O for initial abundances higher than one-fifth of the solar. The C and O abundances in the cluster ejecta can reach over 50 times the solar value with important consequences for the chemical and hydrodynamical evolution of the surrounding interstellar medium.
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- ID:
- ivo://CDS.VizieR/J/A+A/606/A123
- Title:
- Molecular maps of NGC1333
- Short Name:
- J/A+A/606/A123
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Are the initial conditions for clustered star formation the same as for non-clustered star formation? To investigate the initial gas properties in young proto-clusters we carried out a comprehensive and high-sensitivity study of the internal structure, density, temperature, and kinematics of the dense gas content of the NGC1333 region in Perseus, one of the nearest and best studied embedded clusters. The analysis of the gas velocities in the Position-Position-Velocity space reveals an intricate underlying gas organization both in space and velocity. We identified a total of 14 velocity-coherent, (tran-)sonic structures within NGC1333, with similar physical and kinematic properties than those quiescent, star-forming (aka fertile) fibers previously identified in low-mass star-forming clouds. These fibers are arranged in a complex spatial network, build-up the observed total column density, and contain the dense cores and protostars in this cloud. Our results demonstrate that the presence of fibers is not restricted to low-mass clouds but can be extended to regions of increasing mass and complexity. We propose that the observational dichotomy between clustered and non-clustered star-forming regions might be naturally explained by the distinct spatial density of fertile fibers in these environments.
- ID:
- ivo://CDS.VizieR/J/ApJS/94/615
- Title:
- Molecular outflow sources
- Short Name:
- J/ApJS/94/615
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A K'-band imaging survey with a ~8'x3' field of view of all regions associated with CO molecular outflow from the list of Fukui (1989) has been conducted. We present the individual images and describe individual nebulous objects and star clusters. The vast majority of all outflow sources are associated with nebulosity detectable in K', so such nebulae can be used as tracers for very young stars. We find a significant fraction (one-third) of molecular outflow sources to be associated with clusters of young stars. Most of the young embedded clusters show peaks in their K' magnitude histograms that, if interpreted as an evolutionary effect, indicate average ages of the embedded star population of <1x10^6yr.
- ID:
- ivo://CDS.VizieR/J/MNRAS/384/675
- Title:
- Monitoring low-mass stars in NGC 2362
- Short Name:
- J/MNRAS/384/675
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on the results of a time-series photometric survey of NGC 2362, carried out using the CTIO 4-m Blanco telescope and Mosaic-II detector as part of the Monitor project. Rotation periods were derived for 271(*) candidate cluster members over the mass range 0.1~<M/M_{sun}_<~1.2. The rotation period distributions show a clear mass-dependent morphology, qualitatively similar to that in NGC 2264, as would be expected from the age of this cluster. Using models of angular momentum evolution, we show that angular momentum losses over the ~1-5Myr age range appear to be needed in order to reproduce the evolution of the slowest rotators in the sample from the ONC to NGC 2362, as found by many previous studies. By incorporating Spitzer IRAC mid-infrared (mid-IR) measurements, we found that three to four objects showing mid-IR excesses indicative of the presence of circumstellar discs were all slow rotators, as would be expected in the disc regulation paradigm for early pre-main-sequence angular momentum evolution, but this result is not statistically significant at present, given the extremely limited sample size. (*) The abstract indicates 271 clusters, but the actual number is 272.
- ID:
- ivo://CDS.VizieR/J/AJ/147/82
- Title:
- Monitoring of disk-bearing stars in NGC 2264
- Short Name:
- J/AJ/147/82
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the Coordinated Synoptic Investigation of NGC 2264, a continuous 30 day multi-wavelength photometric monitoring campaign on more than 1000 young cluster members using 16 telescopes. The unprecedented combination of multi-wavelength, high-precision, high-cadence, and long-duration data opens a new window into the time domain behavior of young stellar objects. Here we provide an overview of the observations, focusing on results from Spitzer and CoRoT. The highlight of this work is detailed analysis of 162 classical T Tauri stars for which we can probe optical and mid-infrared flux variations to 1% amplitudes and sub-hour timescales. We present a morphological variability census and then use metrics of periodicity, stochasticity, and symmetry to statistically separate the light curves into seven distinct classes, which we suggest represent different physical processes and geometric effects. We provide distributions of the characteristic timescales and amplitudes and assess the fractional representation within each class. The largest category (>20%) are optical "dippers" with discrete fading events lasting ~1-5 days. The degree of correlation between the optical and infrared light curves is positive but weak; notably, the independently assigned optical and infrared morphology classes tend to be different for the same object. Assessment of flux variation behavior with respect to (circum)stellar properties reveals correlations of variability parameters with H{alpha} emission and with effective temperature. Overall, our results point to multiple origins of young star variability, including circumstellar obscuration events, hot spots on the star and/or disk, accretion bursts, and rapid structural changes in the inner disk.
- ID:
- ivo://CDS.VizieR/J/MNRAS/476/3160
- Title:
- Monoceros star-forming region radial velocities
- Short Name:
- J/MNRAS/476/3160
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The principal aim of this work is to study the velocity field in the Monoceros star-forming region using the radial velocity data available in the literature, as well as astrometric data from the Gaia first release. This region is a large star-forming com- plex formed by two associations named Monoceros OB1 and OB2. We have collected radial velocity data for more than 400 stars in the area of 8x12 square degrees and distance for more than 200 objects. We apply a clustering analysis in the subspace of the phase space formed by angular coordinates and radial velocity or distance data using the Spectrum of Kinematic Grouping methodology. We found four and three spatial groupings in radial velocity and distance variables, respectively, corresponding to the Local arm, the central clusters forming the associations and the Perseus arm, respectively.
- ID:
- ivo://CDS.VizieR/J/AJ/151/49
- Title:
- M6 open cluster: star members properties
- Short Name:
- J/AJ/151/49
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present here the first abundance analysis of 44 late B-, A-, and F-type members of the young open cluster M6 (NGC 6405, age about 75 Myr). Low- and medium-resolution spectra, covering the 4500-5840 {AA} wavelength range, were obtained using the FLAMES/GIRAFFE spectrograph attached to the ESO Very Large Telescopes. We determined the atmospheric parameters using calibrations of the Geneva photometry and by adjusting the H_{beta}_ profiles to synthetic ones. The abundances of up to 20 chemical elements, from helium to mercury, were derived for 19 late B, 16 A, and 9 F stars by iteratively adjusting synthetic spectra to the observations. We also derived a mean cluster metallicity of [Fe/H]=0.07+/-0.03 dex from the iron abundances of the F-type stars. We find that for most chemical elements, the normal late B- and A-type stars exhibit larger star-to-star abundance variations than the F-type stars probably because of the faster rotation of the B and A stars. The abundances of C, O, Mg, Si, and Sc appear to be anticorrelated with that of Fe, while the opposite holds for the abundances of Ca, Ti, Cr, Mn, Ni, Y, and Ba as expected if radiative diffusion is efficient in the envelopes of these stars. In the course of this analysis, we discovered five new peculiar stars: one mild Am, one Am, and one Fm star (HD 318091, CD-32 13109, GSC 07380-01211, CP1), one HgMn star (HD 318126, CP3), and one He-weak P-rich (HD 318101, CP4) star. We also discovered a new spectroscopic binary, most likely a SB2. We performed a detailed modeling of HD 318101, the new He-weak P-rich CP star, using the Montreal stellar evolution code XEVOL which self-consistently treats all particle transport processes. Although the overall abundance pattern of this star is properly reproduced, we find that detailed abundances (in particular the high P excess) resisted modeling attempts even when a range of turbulence profiles and mass-loss rates were considered. Solutions are proposed which are still under investigation.
- ID:
- ivo://CDS.VizieR/J/MNRAS/463/696
- Title:
- M67 solar twins chemical compositions
- Short Name:
- J/MNRAS/463/696
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Stars in open clusters are expected to share an identical abundance pattern. Establishing the level of chemical homogeneity in a given open cluster deserves further study as it is the basis of the concept of chemical tagging to unravel the history of the Milky Way. M67 is particularly interesting given its solar metallicity and age as well as being a dense cluster environment. We conducted a strictly line-by-line differential chemical abundance analysis of two solar twins in M67: M67-1194 and M67-1315. Stellar atmospheric parameters and elemental abundances were obtained with high precision using Keck/High Resolution Echelle Spectrometer spectra. M67-1194 is essentially identical to the Sun in terms of its stellar parameters. M67-1315 is warmer than M67-1194 by ~=150K as well as slightly more metal-poor than M67-1194 by ~=0.05dex. M67-1194 is also found to have identical chemical composition to the Sun, confirming its solar-twin nature. The abundance ratios [X/Fe] of M67-1315 are similar to the solar abundances for elements with atomic number Z<=30, while most neutron-capture elements are enriched by ~=0.05dex, which might be attributed to enrichment from a mixture of asymptotic giant branch ejecta and r-process material. The distinct chemical abundances for the neutron-capture elements in M67-1315 and the lower metallicity of this star compared to M67-1194, indicate that the stars in M67 are likely not chemically homogeneous. This poses a challenge for the concept of chemical tagging since it is based on the assumption of stars forming in the same star-forming aggregate.
- ID:
- ivo://CDS.VizieR/J/A+A/603/A85
- Title:
- M67 stars radial velocities
- Short Name:
- J/A+A/603/A85
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a seven-year-long radial velocity survey of a sample of 88 main-sequence and evolved stars to reveal signatures of Jupiter-mass planets in the solar-age and solar-metallicity open cluster M67. We analysed precise radial velocity (RV) measurements obtained with five different instruments. We conducted Monte Carlo simulations to estimate the occurrence rate of giant planets in our radial velocity survey. All the planets previously announced in this RV campaign with their properties are summarised: 3 hot Jupiters around the main-sequence stars YBP1194, YBP1514, and YBP401, and 1 giant planet around the evolved star S364. Two additional planet candidates around the stars YBP778 and S978 are also analysed. We discuss stars that exhibit large RV variability or trends individually. We find an occurrence of giant planets of ~18.0% in a selected period-mass range. This frequency is slightly higher but consistent within the errors with the estimate for the field stars, leading to the general conclusion that open cluster and field statistics agree. However, we find that the rate of hot Jupiters in the cluster (~5.7%) is substantially higher than in the field.
- ID:
- ivo://CDS.VizieR/J/AJ/146/102
- Title:
- Multi-frequency fit of periodic B stars in NGC 884
- Short Name:
- J/AJ/146/102
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Recent progress in the seismic interpretation of field {beta} Cep stars has resulted in improvements of the physical description in the stellar structure and evolution model computations of massive stars. Further asteroseismic constraints can be obtained from studying ensembles of stars in a young open cluster, which all have similar age, distance, and chemical composition. We present an observational asteroseismology study based on the discovery of numerous multi-periodic and mono-periodic B stars in the open cluster NGC 884. We describe a thorough investigation of the pulsational properties of all B-type stars in the cluster. Overall, our detailed frequency analysis resulted in 115 detected frequencies in 65 stars. We found 36 mono-periodic, 16 bi-periodic, 10 tri-periodic, and 2 quadru-periodic stars and one star with nine independent frequencies. We also derived the amplitudes and phases of all detected frequencies in the U, B, V, and I filter, if available. We achieved unambiguous identifications of the mode degree for 12 of the detected frequencies in nine of the pulsators. Imposing the identified degrees and measured frequencies of the radial, dipole, and quadrupole modes of five pulsators led to a seismic cluster age estimate of log(age/yr)=7.12-7.28 from a comparison with stellar models. Our study is a proof-of-concept for and illustrates the current status of ensemble asteroseismology of a young open cluster.