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24681. 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.
24682. 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.
24683. 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.
24684. 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.
24685. Young star groups in NGC 300
ID:
ivo://CDS.VizieR/J/A+A/594/A34
Title:
Young star groups in NGC 300
Short Name:
J/A+A/594/A34
Date:
21 Oct 2021
Publisher:
CDS
Description:
The purpose of this work is to understand the global characteristics of the stellar populations in NGC 300. In particular, we focused our attention on searching young star groups and study their hierarchical organization. The proximity and orientation of this Sculptor Group galaxy make it an ideal candidate for this study. The research was conducted using archival point spread function (PSF) fitting photometry measured from images in multiple bands obtained with the Advanced Camera for Surveys of the Hubble Space Telescope (ACS/HST). Using the path linkage criterion (PLC), we cataloged young star groups and analyzed them from the observation of individual stars in the galaxy NGC 300. We also built stellar density maps from the bluest stars and applied the SExtractor code to identify overdensities. This method provided an additional tool for the detection of young stellar structures. By plotting isocontours over the density maps and comparing the two methods, we could infer and delineate the hierarchical structure of the blue population in the galaxy. For each region of a detected young star group, we estimated the size and derived the radial surface density profiles for stellar populations of different color (blue and red). A statistical decontamination of field stars was performed for each region. In this way it was possible to build the color-magnitude diagrams (CMD) and compare them with theoretical evolutionary models. We also constrained the present-day mass function (PDMF) per group by estimating a value for its slope. The blue population distribution in NGC 300 clearly follows the spiral arms of the galaxy, showing a hierarchical behavior in which the larger and loosely distributed structures split into more compact and denser ones over several density levels. We created a catalog of 1147 young star groups in six fields of the galaxy NGC 300, in which we present their fundamental characteristics. The mean and the mode radius values obtained from the size distribution are both 25pc, in agreement with the value for the Local Group and nearby galaxies. Additionally, we found an average PDMF slope that is compatible with the Salpeter value.
24686. Young stars and brown dwarfs in Ori OB1b
ID:
ivo://CDS.VizieR/J/A+A/485/931
Title:
Young stars and brown dwarfs in Ori OB1b
Short Name:
J/A+A/485/931
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present here exhaustive lists of known young stars and new candidate members around Alnilam and Mintaka in the Ori OB1b association as well as of fore- and background sources. A total of 133 stars display features of extreme youth, including early spectral types, lithium in absorption, or mid-infrared flux excess. Other two young brown dwarf and 289 star candidates have been identified from an optical/near-infrared colour-magnitude diagram. We list additional 74 known objects that might belong to the association. This compilation of tables can serve as an input for characterisation of the stellar and high-mass substellar populations in the Orion Belt.
24687. Young stars in Cepheus OB3b
ID:
ivo://CDS.VizieR/J/MNRAS/403/545
Title:
Young stars in Cepheus OB3b
Short Name:
J/MNRAS/403/545
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a photometric study of I-band variability in the young association Cepheus OB3b. The study is sensitive to periodic variability on time-scales of less than a day, to more than 20d. After rejection of contaminating objects using V, I, R and narrow-band H{alpha} photometry, we find 475 objects with measured rotation periods, which are very likely pre-main-sequence members of the Cep OB3b star-forming region.
24688. Young stars in Trumpler 37 and NGC 7160
ID:
ivo://CDS.VizieR/J/AJ/130/188
Title:
Young stars in Trumpler 37 and NGC 7160
Short Name:
J/AJ/130/188
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the results of MMT observations of young stars for our study of protoplanetary disks at ages 1-10Myr in two young clusters located in the Cepheus OB2 region: Trumpler 37 (embedded in the HII region IC 1396) and NGC 7160. Using low-resolution optical spectra from the Hectospec multifiber spectrograph, we have tripled the number of known low-mass cluster members, identifying 130 new members in Tr 37 and 30 in NGC 7160. We use indicators of youth (Li absorption at 6707{AA}) and accretion/chromospheric activity (H{alpha} emission) to identify and classify the low-mass cluster members. We derive spectral types for all the low-mass candidates and calculate the individual extinctions and the average over the clusters.
24689. Young stars near CG30 in the Gum Nebula
ID:
ivo://CDS.VizieR/J/ApJ/889/50
Title:
Young stars near CG30 in the Gum Nebula
Short Name:
J/ApJ/889/50
Date:
10 Nov 2021 13:50:07
Publisher:
CDS
Description:
We have conducted a high-dispersion (R~34000) optical spectroscopic study of 10 young stars near the cometary globule CG 30 in the Gum Nebula, a diffuse HII region home to at least 32 cometary globules. All 10 spectroscopically observed stars at the nebula's northern edge are of low mass (spectral types M4.5-K5), have broad H{alpha} emission, and show spectral veiling. Eight of the 10 are classical T Tauri stars. We spectroscopically measure the photospheric properties of CG 30 IRS 4 inside CG 30. Though embedded, CG 30 IRS 4 is T Tauri-like, with relatively slow projected rotation and moderate veiling. Undepleted Li absorptions, strong H{alpha} emissions, and positions well above the main sequence on an H-R diagram suggest that the 10 stars are <~1Myr old. Using our measurements, previous spectroscopy, and previous photometry of 11 other young stars in the area, we determine stellar, kinematic, and accretion properties of a total of 21 young stars. Shared radial velocities, proper motions, distances, and ages suggest that 14 of the young stars (including CG 30 IRS 4) are kinematically related to CG 30. From Gaia DR2 distances to six of these stars, we derive a distance of 358.1+/-2.2pc to the cometary globule complex CG 30/31/38. The CG 30 association has an accretor fraction of 29%+/-14%, low for quiescent clusters of similar age but consistent with other irradiated clusters. The Gum Nebula's moderate radiation environment (G_0_=6.6_-2.7_^+3.2^ at CG 30) may be strong enough to shorten disk lifetimes.
24690. Young stars near the Sun
ID:
ivo://CDS.VizieR/J/other/ARA+A/42.685
Title:
Young stars near the Sun
Short Name:
J/other/ARA+A/42
Date:
21 Oct 2021
Publisher:
CDS
Description:
Until the late 1990s the rich Hyades and the sparse UMa clusters were the only coeval, comoving concentrations of stars known within 60 pc of Earth. Both are hundreds of millions of years old. Then beginning in the late 1990s the TW Hydrae Association, the Tucana/Horologium Association, the beta Pictoris Moving Group, and the AB Doradus Moving Group were identified within ~60pc of Earth, and the eta Chamaeleontis cluster was found at 97pc. These young groups (ages 8-50Myr), along with other nearby, young stars, will enable imaging and spectroscopic studies of the origin and early evolution of planetary systems.

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