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17971. Young open clusters space-age distribution
ID:
ivo://CDS.VizieR/J/PAZh/25/10
Title:
Young open clusters space-age distribution
Short Name:
J/PAZh/25/10
Date:
21 Oct 2021
Publisher:
CDS
Description:
Based on published photoelectric and CCD photometry and using the empirical ZAMS of Kholopov (1980, AZh, 57, 12) and the evolutionary-deviation curves obtained from the grid of isochrones computed by Maeder and Meynet (1991A&AS...89..451M), we determine the distances, color excesses, and ages for 203 Galactic open clusters with logt<8.2. The validity of the derived distance scale is corroborated by the Hipparcos trigonometric parallaxes of seven clusters. The age distribution of the clusters is distorted by observational selection, which is enhanced with increasing heliocentric distance and which is virtually independent of interstellar extinction. As a result, the youngest (logt<=7.5) clusters are represented almost exclusively at heliocentric distances >2kpc, and the mean age of the cataloged clusters with logt<=100Myr decreases from 50Myr in the solar neighborhood down to 15Myr at heliocentric distances >2.4kpc.
17972. Young population in Vela-Puppis region
ID:
ivo://CDS.VizieR/J/A+A/626/A17
Title:
Young population in Vela-Puppis region
Short Name:
J/A+A/626/A17
Date:
21 Oct 2021
Publisher:
CDS
Description:
The Vela-Puppis region is known to host the Vela OB2 association as well as several young clusters featuring OB and pre-main-sequence stars. Several spatial and kinematic subgroups have been identified in recent years. By grouping stars based on their positions and velocity, we can address the question of the dynamical history of the region and the mechanisms that drove stellar formation. The Gaia DR2 astrometry and photometry enables us to characterise the 3D spatial and 3D kinematic distribution of young stars and to estimate the ages of the identified components. We used an unsupervised classification method to group stars based on their proper motions and parallax. We studied the expansion rates of the different identified groups based on 3D velocities and on corrected tangential velocities. We used theoretical isochrones to estimate ages. The young stars can be separated into seven main groups of different ages and kinematical distribution. All groups are found to be expanding, although the expansion is mostly not isotropic. The size of the region, the age substructure, and the anisotropic expansion rates are compatible with a prolonged period of star formation in a turbulent molecular cloud. The current kinematics of the stars cannot be explained by internal processes alone (such as gas expulsion).
17973. 4 young protostars ALMA and NOEMA spectral cubes
ID:
ivo://CDS.VizieR/J/A+A/636/A26
Title:
4 young protostars ALMA and NOEMA spectral cubes
Short Name:
J/A+A/636/A26
Date:
21 Oct 2021
Publisher:
CDS
Description:
Water is a key volatile that provides insights into the initial stages of planet formation. However, little is known about the water vapor abundance in newly formed planet-forming disks. We present H_2_^18^O line observations with ALMA and NOEMA millimeter interferometers toward five young stellar objects. NOEMA observed the 203GHz line while ALMA targeted the 390GHz line. No emission is detected toward any of our five Class I disks. We report upper limits to the integrated line intensities. The inferred water column densities in Class I disks are <10^15^cm^-2^ on 100au scales which include both disk and envelope. Water vapor is not abundant in warm protostellar envelopes around Class I protostars. Upper limits to the water vapor column densities in Class I disks are at least two orders magnitude lower than values found in Class 0 disk-like structures.
17974. Young (proto)stellar population in L1630
ID:
ivo://CDS.VizieR/J/A+A/507/1485
Title:
Young (proto)stellar population in L1630
Short Name:
J/A+A/507/1485
Date:
21 Oct 2021
Publisher:
CDS
Description:
We investigate the young (proto)stellar population in NGC 2023 and the L 1630 molecular cloud bordering the H II region IC 434, using Spitzer IRAC and MIPS archive data, JCMT SCUBA imaging and spectroscopy as well as targeted BIMA observations of one of the Class 0 protostars, NGC 2023 MM 1. We study the distribution of gas, dust and young stars in this region to see where stars are forming, whether the expansion of the H II region has triggered star formation, and whether dense cold cores have already formed stars. We have performed photometry of all IRAC and MIPS images, and used color-color diagrams to identify and classify all young stars seen within a 22'x26' field along the boundary between IC 434 and L 1630.
17975. Young runaway stars within 3kpc
ID:
ivo://CDS.VizieR/J/MNRAS/410/190
Title:
Young runaway stars within 3kpc
Short Name:
J/MNRAS/410/190
Date:
21 Oct 2021
Publisher:
CDS
Description:
Traditionally runaway stars are O and B type stars with large peculiar velocities. We want to extend this definition to young stars (up to ~50Myr) of any spectral type and identify those present in the Hipparcos catalogue applying different selection criteria such as peculiar space velocities or peculiar one-dimensional velocities. Runaway stars are important to study the evolution of multiple star systems or star clusters as well as to identify origins of neutron stars. We compile distances, proper motions, spectral types, luminosity classes, V magnitudes and B-V colours and utilise evolutionary models from different authors to obtain star ages and study a sample of 7663 young Hipparcos stars within 3kpc from the Sun. Radial velocities are obtained from the literature. We investigate the distributions of the peculiar spatial velocity, the peculiar radial velocity as well as the peculiar tangential velocity and its one-dimensional components and obtain runaway star probabilities for each star in the sample. In addition, we look for stars that are situated outside any OB association or OB cluster and the Galactic plane as well as stars of which the velocity vector points away from the median velocity vector of neighbouring stars or the surrounding local OB association/cluster although the absolute velocity might be small. We find a total of 2547 runaway star candidates (with a contamination of normal Population I stars of 20 per cent at most). Thus, after subtraction of those 20 per cent, the runaway frequency among young stars is about 27 per cent. We compile a catalogue of runaway stars which will be available via VizieR.
17976. Young star cluster candidates in M31
ID:
ivo://CDS.VizieR/J/ApJ/559/851
Title:
Young star cluster candidates in M31
Short Name:
J/ApJ/559/851
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a method for finding clusters of young stars in M31 using broadband WFPC2 data from the HST data archive. Applying our identification method to 13 WFPC2 fields, covering an area of 60arcmin^2^, has revealed 79 new candidate young star clusters in these portions of the M31 disk. Most of these clusters are small (<~5pc), young (~10-200Myr) star groups located within large OB associations. We have estimated the reddening values and the ages of each candidate individually by fitting isochrones to the stellar photometry. We provide a catalog of the candidates including rough approximations of their reddenings and ages. We also look for patterns of cluster formation with galactocentric distance, but our rough estimates are not precise enough to reveal any clear patterns.
17977. Young star clusters in nearby molecular clouds
ID:
ivo://CDS.VizieR/J/MNRAS/477/298
Title:
Young star clusters in nearby molecular clouds
Short Name:
J/MNRAS/477/298
Date:
21 Oct 2021
Publisher:
CDS
Description:
The SFiNCs (Star Formation in Nearby Clouds) project is an X-ray/infrared study of the young stellar populations in 22 star-forming regions with distances <~1kpc designed to extend our earlier MYStIX (Massive Young Star-Forming Complex Study in Infrared and X-ray) survey of more distant clusters. Our central goal is to give empirical constraints on cluster formation mechanisms. Using parametric mixture models applied homogeneously to the catalogue of SFiNCs young stars, we identify 52 SFiNCs clusters and 19 unclustered stellar structures. The procedure gives cluster properties including location, population, morphology, association with molecular clouds, absorption, age (Age_JX_), and infrared spectral energy distribution (SED) slope. Absorption, SED slope, and Age_JX_ are age indicators. SFiNCs clusters are examined individually, and collectively with MYStIX clusters, to give the following results. (1) SFiNCs is dominated by smaller, younger, and more heavily obscured clusters than MYStIX. (2) SFiNCs cloud-associated clusters have the high ellipticities aligned with their host molecular filaments indicating morphology inherited from their parental clouds. (3) The effect of cluster expansion is evident from the radius-age, radius-absorption, and radius-SED correlations. Core radii increase dramatically from ~0.08 to ~0.9pc over the age range 1-3.5Myr. Inferred gas removal time-scales are longer than 1Myr. (4) Rich, spatially distributed stellar populations are present in SFiNCs clouds representing early generations of star formation. An appendix compares the performance of the mixture models and non-parametric minimum spanning tree to identify clusters. This work is a foundation for future SFiNCs/MYStIX studies including disc longevity, age gradients, and dynamical modelling.
17978. Young star clusters in The Antennae
ID:
ivo://CDS.VizieR/J/AJ/109/960
Title:
Young star clusters in The Antennae
Short Name:
J/AJ/109/960
Date:
21 Oct 2021
Publisher:
CDS
Description:
New high-resolution images of the disks of NGC 4038/4039 obtained with the Wide Field Camera of the Hubble Space Telescope (HST) are presented. NGC 4038/4039, nicknamed "The Antennae," is a prototypical example of a pair of colliding galaxies believed to be at an early stage of a merger. Down to the limiting magnitude of V~23mag, the HST images reveal a population of over 700 blue pointlike objects within the disks. The mean absolute magnitude of these objects is M_V_=-11mag, with the brightest objects reaching M_V_~-15. Their mean apparent color indices are U-V=-0.7mag and V-I=0.8mag on the Johnson UVI passband system, while their mean indices corrected for internal reddening are (U-V)_0_=-1.0mag and (V-I)_0_=0.5. Their mean effective radius, determined from slightly resolved images, is 18pc (for H0=50km/s/Mpc). Based on their luminosities and resolution, most of these objects cannot be individual stars, but are likely young compact star clusters. The brighter ones are similar to the objects found in NGC 1275 and NGC 7252, which appear to be young globular clusters formed during recent galaxy mergers. Based on their U-V and V-I colors, the brightest, bluest clusters of NGC 4038/4039 appear to be less than 10Myr old. Most of these bright clusters are relatively tightly clustered themselves, with typically a dozen individual clusters belonging to a complex identified as a giant H II region from ground-based observations. The cluster luminosity function (LF) is approximately a power law, {Phi}(L)dL is proportional to L^(-1.78+/-0.05)^dL, with no hint of a turnover at fainter magnitudes. This power-law shape agrees with the LF of Magellanic Cloud clusters and Galactic open clusters, but differs from the LF of old globular cluster systems that is typically Gaussian with a FWHM of ~3mag. Possible explanations for this apparent difference include: (1) We have not observed faint enough to see the turnover, (2) the initial LF of star clusters is a power law but the fainter objects dissolve with time, (3) conditions at the present epoch favor the formation of a wide range of cluster masses while conditions at earlier epochs favored the formation of massive clusters, and (4) the NGC 4038/4039 clusters may not evolve into normal globular clusters. Besides the blue clusters, we also find about a dozen extremely red objects with V-I>3.0. The highest number density of these red objects is found in the SE quadrant, where star formation appears to be most recent. We propose that these objects may be very young star clusters still embedded in their placental dust cocoons.
17979. Young star cluster Westerlund 2 observed with MUSE
ID:
ivo://CDS.VizieR/J/AJ/158/201
Title:
Young star cluster Westerlund 2 observed with MUSE
Short Name:
J/AJ/158/201
Date:
21 Oct 2021
Publisher:
CDS
Description:
We mapped the Galactic young massive star cluster Westerlund 2 with the integral field spectrograph MUSE (spatial resolution: 0.2 arcsec/px, spectral resolution: {Delta}{lambda}=1.25 {AA}, wavelength range: 4600-9350 {AA}) mounted on the Very Large Telescope. We present the fully reduced data set and introduce our new Python package "MUSEpack", which we developed to measure stellar radial velocities (RVs) with an absolute precision of 1-2 km/s without the necessity of a spectral template library. This novel method uses the two-dimensional spectra and an atomic transition line library to create templates around strong absorption lines for each individual star. Automatic, multi-core processing makes it possible to efficiently determine stellar RVs of a large number of stars with the necessary precision to measure the velocity dispersion of young star clusters. MUSEpack also provides an enhanced method for removing telluric lines in crowded fields without sky exposures, and a Python wrapper for ESO's data reduction pipeline. We observed Westerlund 2 with a total of 11 short and 5 long exposures (survey area: ~11 arcmin^2^ or 15.8 pc^2^) to cover the bright nebular emission and OB stars, as well as the fainter pre-main-sequence stars (>=1 M_{sun}_). We extracted 1725 stellar spectra with a mean signal-to-noise ratio of S/N>5 per pixel. Typical RV uncertainties of 4.78 km/s, 2.92 km/s, and 1.1 km/s are reached for stars with a mean S/N>10, S/N>20, and S/N>50 per pixel, respectively. It is possible to reach RV accuracies of 0.9 km/s, 1.3 km/s, and 2.2 km/s with >=5, 3-4, and 1-2 spectral lines used to measure the RVs, respectively. The combined statistical uncertainty on the RV measurements is 1.10 km/s.
17980. Young star forming region NGC 2264 Spitzer sources
ID:
ivo://CDS.VizieR/J/ApJ/794/124
Title:
Young star forming region NGC 2264 Spitzer sources
Short Name:
J/ApJ/794/124
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present Spitzer 3.6, 4.5, 5.8, 8.0, and 24 {mu}m images of the Mon OB1 East giant molecular cloud, which contains the young star forming region NGC 2264, as well as more extended star formation. With Spitzer data and Two Micron All Sky Survey photometry, we identify and classify young stellar objects (YSOs) with dusty circumstellar disks and/or envelopes in Mon OB1 East by their infrared-excess emission and study their distribution with respect to cloud material. We find a correlation between the local surface density of YSOs and column density of molecular gas as traced by dust extinction that is roughly described as a power law in these quantities. NGC 2264 follows a power-law index of ~2.7, exhibiting a large YSO surface density for a given gas column density. Outside of NGC 2264 where the surface density of YSOs is lower, the power law is shallower and the region exhibits a larger gas column density for a YSO surface density, suggesting the star formation is more recent. In order to measure the fraction of cloud members with circumstellar disks/envelopes, we estimate the number of diskless pre-main-sequence stars by statistical removal of background star detections. We find that the disk fraction of the NGC 2264 region is 45%, while the surrounding, more distributed regions show a disk fraction of 19%. This may be explained by the presence of an older, more dispersed population of stars. In total, the Spitzer observations provide evidence for heterogenous, non-coeval star formation throughout the Mon OB1 cloud.

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