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17981. 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.
17982. 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.
17983. 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.
17984. 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.
17985. 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.
17986. 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.
17987. 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.
17988. 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.
17989. Young stars south of Taurus-Auriga
ID:
ivo://CDS.VizieR/J/A+AS/124/449
Title:
Young stars south of Taurus-Auriga
Short Name:
J/A+AS/124/449
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present results of intermediate resolution spectroscopy of 131 optical counterparts to 115 ROSAT All-Sky Survey X-ray sources south of the Taurus-Auriga dark cloud complex. These objects have been selected as candidate young stars from a total of 1084 ROSAT sources in a ~300 square degree area. We identify 30 objects as low-mass PMS stars on the basis of the LiI{lambda}6708{AA} doublet in their spectrum, a signature of their young age. All these stars have a spectral type later than F7 and show spectral characteristics typical of weak-line and post-T Tauri stars. The presence of young objects several parsecs away from the regions of ongoing star formation is discussed in the light of the current models of T Tauri dispersal.
17990. Young star systems observed with SALT
ID:
ivo://CDS.VizieR/J/ApJ/840/87
Title:
Young star systems observed with SALT
Short Name:
J/ApJ/840/87
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a spectroscopic and kinematic analysis of 79 nearby M dwarfs in 77 systems. All of these dwarfs are low-proper-motion southern hemisphere objects and were identified in a nearby star survey with a demonstrated sensitivity to young stars. Using low-resolution optical spectroscopy from the Red Side Spectrograph on the South African Large Telescope, we have determined radial velocities, H-alpha, lithium 6708{AA}, and potassium 7699{AA} equivalent widths linked to age and activity, and spectral types for all of our targets. Combined with astrometric information from literature sources, we identify 44 young stars. Eighteen are previously known members of moving groups within 100pc of the Sun. Twelve are new members, including one member of the TW Hydra moving group, one member of the 32 Orionis moving group, 9 members of Tucana- Horologium, one member of Argus, and two new members of AB Doradus. We also find 14 young star systems that are not members of any known groups. The remaining 33 star systems do not appear to be young. This appears to be evidence of a new population of nearby young stars not related to the known nearby young moving groups.

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