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25371. 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.
25372. 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.
25373. 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.
25374. 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.
25375. Young stellar clusters in the Rosette
ID:
ivo://CDS.VizieR/J/A+A/557/A29
Title:
Young stellar clusters in the Rosette
Short Name:
J/A+A/557/A29
Date:
21 Oct 2021
Publisher:
CDS
Description:
The Rosette complex is a well studied region of the galactic plane which presents the apparent characteristics of a triggered star forming region. This is however still debated as no strong evidence corroborates this statement. We focused on characterizing the young stellar population in the Rosette to improve our understanding of the processes that regulate the star formation in this region. We propose an original method relying on the joint analysis of the star color and density in the near-infrared. It yielded the identification of 13 clusters, 2 of them being new discoveries. Based on their spectral index from UKIDSS K-band to WISE W3-band, we identified 535 YSO candidates within these cluster boundaries.
25376. 2403 young stellar groups
ID:
ivo://CDS.VizieR/J/A+A/644/A101
Title:
2403 young stellar groups
Short Name:
J/A+A/644/A101
Date:
21 Oct 2021
Publisher:
CDS
Description:
The purpose of this work is to study the properties of the spatial distribution of the young population in three nearby galaxies in order to better understand the first stages of star formation. We used ACS/HST photometry and the "path-linkage criterion" in order to obtain a catalog of young stellar groups (YSGs) in the galaxy NGC 2403. We studied the internal distribution of stars in these YSGs using the Q parameter. We extended these analyses to the YSGs detected in in NGC 300 and NGC 253 our previous works. We built the young stars' density maps for these three galaxies. Through these maps, we were able to identify and study young stellar structures on larger scales. We found 573 YSGs in the galaxy NGC 2403, for which we derived their individual sizes, densities, luminosity function, and other fundamental characteristics. We find that the vast majority of the YSGs in NGC 2403, NGC 300 and NGC 253 present inner clumpings, following the same hierarchical behavior that we observed in the young stellar structures on larger scales in these galaxies. We derived values of the fractal dimension for these structures between ~1.5 and 1.6. These values are very similar to those obtained in other star forming galaxies and in the interstellar medium, suggesting that the star formation process is regulated by supersonic turbulence.
25377. Young stellar groups and their most massive stars
ID:
ivo://CDS.VizieR/J/ApJ/727/64
Title:
Young stellar groups and their most massive stars
Short Name:
J/ApJ/727/64
Date:
21 Oct 2021
Publisher:
CDS
Description:
We analyze the masses and spatial distributions of 14 young stellar groups in Taurus, Lupus3, ChaI, and IC348. These nearby groups, which typically contain 20-40 members, have membership catalogs complete to ~0.02M_{sun}_, and are sufficiently young that their locations should be similar to where they formed. These groups show five properties seen in clusters having many more stars and much greater surface density of stars: (1) a broad range of masses, (2) a concentration of the most massive star toward the center of the group, (3) an association of the most massive star with a high surface density of lower mass stars, (4) a correlation of the mass of the most massive star with the total mass of the group, and (5) the distribution of a large fraction of the mass in a small fraction of the stars.
25378. Young stellar kinematic group candidate members
ID:
ivo://CDS.VizieR/J/ApJ/762/88
Title:
Young stellar kinematic group candidate members
Short Name:
J/ApJ/762/88
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a new method based on a Bayesian analysis to identify new members of nearby young kinematic groups. The analysis minimally takes into account the position, proper motion, magnitude, and color of a star, but other observables can be readily added (e.g., radial velocity, distance). We use this method to find new young low-mass stars in the {beta} Pictoris and AB Doradus moving groups and in the TW Hydrae, Tucana-Horologium, Columba, Carina, and Argus associations. Starting from a sample of 758 mid-K to mid-M (K5V-M5V) stars showing youth indicators such as H{alpha} and X-ray emission, our analysis yields 214 new highly probable low-mass members of the kinematic groups analyzed. One is in TW Hydrae, 37 in {beta} Pictoris, 17 in Tucana-Horologium, 20 in Columba, 6 in Carina, 50 in Argus, 32 in AB Doradus, and the remaining 51 candidates are likely young but have an ambiguous membership to more than one association. The false alarm rate for new candidates is estimated to be 5% for {beta} Pictoris and TW Hydrae, 10% for Tucana-Horologium, Columba, Carina, and Argus, and 14% for AB Doradus. Our analysis confirms the membership of 58 stars proposed in the literature. Firm membership confirmation of our new candidates will require measurement of their radial velocity (predicted by our analysis), parallax, and lithium 6708{AA} equivalent width. We have initiated these follow-up observations for a number of candidates, and we have identified two stars (2MASSJ01112542+1526214, 2MASSJ05241914-1601153) as very strong candidate members of the {beta} Pictoris moving group and one strong candidate member (2MASSJ05332558-5117131) of the Tucana-Horologium association; these three stars have radial velocity measurements confirming their membership and lithium detections consistent with young age.
25379. Young stellar object candidates toward Orion
ID:
ivo://CDS.VizieR/J/A+A/572/A89
Title:
Young stellar object candidates toward Orion
Short Name:
J/A+A/572/A89
Date:
21 Oct 2021
Publisher:
CDS
Description:
We analyze 359 ultraviolet tiles from the All Sky Imaging Survey of the space mission GALEX covering roughly 400 square degrees toward the Orion star-forming region. There are a total of 1555174 ultraviolet sources that were cross-matched with other catalogs (2MASS, UCAC4, SDSS, DENIS, CMC15, and WISE) to produce a list of 290717 reliable sources with a wide range of photometric information. Using different color selection criteria, we identify 111 young stellar object candidates showing both ultraviolet and infrared excesses, of which 81 are new identifications. We discuss the spatial distribution, the spectral energy distributions, and other physical properties of these stars. Their properties are, in general, compatible with those expected for T Tauri stars. This population of TTS candidates is widely dispersed around the Orion molecular cloud.
25380. Young stellar objects in Lupus star-forming region
ID:
ivo://CDS.VizieR/J/AJ/159/200
Title:
Young stellar objects in Lupus star-forming region
Short Name:
J/AJ/159/200
Date:
21 Oct 2021
Publisher:
CDS
Description:
The identification and characterization of stellar members within a star-forming region are critical to many aspects of star formation, including formalization of the initial mass function, circumstellar disk evolution, and star formation history. Previous surveys of the Lupus star-forming region have identified members through infrared excess and accretion signatures. We use machine learning to identify new candidate members of Lupus based on surveys from two space-based observatories: ESA's Gaia and NASA's Spitzer. Astrometric measurements from Gaia's Data Release 2 and astrometric and photometric data from the Infrared Array Camera on the Spitzer Space Telescope, as well as from other surveys, are compiled into a catalog for the random forest (RF) classifier. The RF classifiers are tested to find the best features, membership list, non-membership identification scheme, imputation method, training set class weighting, and method of dealing with class imbalance within the data. We list 27 candidate members of the Lupus star-forming region for spectroscopic follow-up. Most of the candidates lie in Clouds V and VI, where only one confirmed member of Lupus was previously known. These clouds likely represent a slightly older population of star formation.

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