- ID:
- ivo://CDS.VizieR/J/A+A/508/833
- Title:
- SACY III. Li abundances
- Short Name:
- J/A+A/508/833
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Our study is a follow-up of the SACY project, an extended high spectral resolution survey of more than two thousand optical counterparts to X-ray sources in the southern hemisphere targeted to search for young nearby association. Nine associations have either been newly identified, or have had their member list revised. Groups belonging to the Sco-Cen-Oph complex are not considered in the present study. These nine associations, with ages of between about 6Myr and 70Myr, form an excellent sample to study the Li depletion in the pre-main sequence (PMS) evolution. In the present paper, we investigate the use of Li abundances as an independent clock to constrain the PMS evolution. Using our measurements of the equivalent widths of the Li resonance line and assuming fixed metallicities and microturbulence, we calculated the LTE Li abundances for 376 members of various young associations. In addition, we considered the effects of their projected stellar rotation.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/872/58
- Title:
- Sagittarius stream stars with APOGEE obs.
- Short Name:
- J/ApJ/872/58
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The SDSS-IV Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey provides precise chemical abundances of 18 chemical elements for ~176000 red giant stars distributed over much of the Milky Way Galaxy (MW), and includes observations of the core of the Sagittarius dwarf spheroidal galaxy (Sgr). The APOGEE chemical abundance patterns of Sgr have revealed that it is chemically distinct from the MW in most chemical elements. We employ a k-means clustering algorithm to six-dimensional chemical space defined by [(C+N)/Fe], [O/Fe], [Mg/Fe], [Al/Fe], [Mn/Fe], and [Ni/Fe] to identify 62 MW stars in the APOGEE sample that have Sgr-like chemical abundances. Of the 62 stars, 35 have Gaia kinematics and positions consistent with those predicted by N-body simulations of the Sgr stream, and are likely stars that have been stripped from Sgr during the last two pericenter passages (<2Gyr ago). Another 20 of the 62 stars exhibit chemical abundances indistinguishable from the Sgr stream stars, but are on highly eccentric orbits with median rapo ~25kpc. These stars are likely the "accreted" halo population thought to be the result of a separate merger with the MW 8-11 Gyr ago. We also find one hypervelocity star candidate. We conclude that Sgr was enriched to [Fe/H]~-0.2 before its most recent pericenter passage. If the "accreted halo" population is from one major accretion event, then this progenitor galaxy was enriched to at least [Fe/H]~-0.6, and had a similar star formation history to Sgr before merging.
- ID:
- ivo://CDS.VizieR/J/ApJ/756/133
- Title:
- ScoCen debris disks around B- and A-type stars
- Short Name:
- J/ApJ/756/133
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have obtained Spitzer Space Telescope Multiband Imaging Photometer for Spitzer (MIPS) 24 micron and 70 micron observations of 215 nearby, Hipparcos B- and A-type common proper-motion single and binary systems in the nearest OB association, Scorpius-Centaurus. Combining our MIPS observations with those of other ScoCen stars in the literature, we estimate 24 micron B+A-type disk fractions of 17/67 (25^+6^_-5_%), 36/131 (27^+4^_-5_%), and 23/95 (24^+5^_-4_%) for Upper Scorpius (~11Myr), Upper Centaurus Lupus (~15Myr), and Lower Centaurus Crux (~17Myr), respectively, somewhat smaller disk fractions than previously obtained for F- and G-type members. We confirm previous IRAS excess detections and present new discoveries of 51 protoplanetary and debris disk systems, with fractional infrared luminosities ranging from LIR/L*=10^-6^ to 10^-2^ and grain temperatures ranging from Tgr=40 to 300K. In addition, we confirm that the 24 micron and 70 micron excesses (or fractional infrared luminosities) around B+A-type stars are smaller than those measured toward F+G-type stars and hypothesize that the observed disk property dependence on stellar mass may be the result of a higher stellar companion fraction around B- and A-type stars at 10-200AU. Finally, we note that the majority of the ScoCen 24 micron excess sources also possess 12 micron excess, indicating that Earth-like planets may be forming via collisions in the terrestrial planet zone at ~10-100Myr.
- ID:
- ivo://CDS.VizieR/J/ApJ/738/122
- Title:
- ScoCen debris disks Around F- and G-type stars
- Short Name:
- J/ApJ/738/122
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We obtained Spitzer Space Telescope Multiband Imaging Photometer for Spitzer (MIPS) 24 micron and 70 micron observations of 182 nearby, Hipparcos F- and G-type common proper motion single and binary systems in the nearest OB association, Scorpius-Centaurus. We also obtained Magellan/MIKE R~50,000 visual spectra at 3500-10500{AA} for 181 candidate ScoCen stars in single and binary systems. Combining our MIPS observations with those of other ScoCen stars in the literature, we estimate 24 micron F+G-type disk fractions of 9/27 (33%+/-11%), 21/67 (31%+/-7%), and 25/71 (35%+/-7%) for Upper Scorpius (~10Myr), Upper Centaurus Lupus (~15Myr), and Lower Centaurus Crux (~17Myr), respectively. We confirm previous IRAS and MIPS excess detections and present new discoveries of 41 protoplanetary and debris disk systems, with fractional infrared luminosities ranging from L_IR/L_*=10^-5^ to 1.0^-2^ and grain temperatures ranging from T_gr_=40-300K. We searched for an increase in 24 micron excess at an age of 15-20Myr, consistent with the onset of debris production predicted by coagulation N-body simulations of outer planetary systems. We found such an increase around 1.5M_{sun}_ stars but discovered a decrease in the 24 micron excess around 1.0M_{sun}_ stars. We additionally discovered that the 24 micron excess around 1.0M_{sun}_ stars is larger than predicted by self-stirred models. Finally, we found a weak anti-correlation between fractional infrared luminosity (L_IR/L_*) and chromospheric activity (R'_HK), that may be the result of differences in stellar HK properties, such as mass, luminosity, and/or winds. We obtained Spitzer Space Telescope Multiband Imaging Photometer for Spitzer (MIPS) 24 micron and 70 micron observations of 182 nearby, Hipparcos F- and G-type common proper motion single and binary systems in the nearest OB association, Scorpius-Centaurus. We also obtained Magellan/MIKE R~50,000 visual spectra at 3500-10500{AA} for 181 candidate ScoCen stars in single and binary systems. Combining our MIPS observations with those of other ScoCen stars in the literature, we estimate 24 micron F+G-type disk fractions of 9/27 (33%+/-11%), 21/67 (31%+/-7%), and 25/71 (35%+/-7%) for Upper Scorpius (~10Myr), Upper Centaurus Lupus (~15Myr), and Lower Centaurus Crux (~17Myr), respectively. We confirm previous IRAS and MIPS excess detections and present new discoveries of 41 protoplanetary and debris disk systems, with fractional infrared luminosities ranging from L_IR/L_* = 10^-5^ to 10^-2^ and grain temperatures ranging from T_gr_=40-300K. We searched for an increase in 24 micron excess at an age of 15-20Myr, consistent with the onset of debris production predicted by coagulation N-body simulations of outer planetary systems. We found such an increase around 1.5M_{sun}_ stars but discovered a decrease in the 24 micron excess around 1.0M_{sun}_ stars. We additionally discovered that the 24 micron excess around 1.0M_{sun}_ stars is larger than predicted by self-stirred models.
- ID:
- ivo://CDS.VizieR/J/MNRAS/461/794
- Title:
- Scorpius-Centaurus K-Type Stars
- Short Name:
- J/MNRAS/461/794
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results of a spectroscopic survey for new K- and M-type members of Scorpius-Centaurus (Sco-Cen), the nearest OB Association (~100-200pc). Using an X-ray, proper motion and color-magnitude selected sample, we obtained spectra for 361 stars, for which we report spectral classifications and Li and Ha equivalent widths. We identified 156 new members of Sco-Cen, and recovered 51 previously published members. We have combined these with previously known members to form a sample of 493 solar-mass (~0.7-1.3M_[sun}_) members of Sco-Cen.We investigated the star-formation history of this sample, and re-assessed the ages of the massive main-sequence turn-off and the G-type members in all three subgroups. We performed a census for circumstellar disks in our sample using WISE infrared data and find a protoplanetary disk fraction for K-type stars of 4.4^+1.6^_-0.9_% for Upper Centaurus-Lupus and Lower Centaurus-Crux at ~16Myr and 9.0^+0.4^_-2.2_% for Upper Scorpius at~10Myr.
- ID:
- ivo://CDS.VizieR/J/MNRAS/435/1671
- Title:
- SCUBA-2 850um survey in {sigma} Ori cluster
- Short Name:
- J/MNRAS/435/1671
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results from a large 850um survey of the {sigma} Orionis cluster using the SCUBA-2 camera on the James Clerk Maxwell Telescope. The 0.5 diameter circular region we surveyed contains 297 young stellar objects with an age estimated at about 3Myr. We detect nine of these objects, eight of which have infrared excesses from an inner disc. We also serendipitously detect three non-stellar sources at >5{sigma} that are likely background submillimetre galaxies. The nine detected stars have inferred disc masses ranging from 5 to about 17M_Jup_, assuming similar dust properties as Taurus discs and an interstellar medium gas-to-dust ratio of 100. There is a net positive signal towards the positions of the individually undetected infrared excess sources indicating a mean disc mass of 0.5M_Jup_. Stacking the emission towards those stars without infrared excesses constrains their mean disc mass to less than 0.3M_Jup_, or an equivalent Earth mass in dust. The submillimetre luminosity distribution is significantly different from that in the younger Taurus region, indicating disc mass evolution as star-forming regions age and the infrared excess fraction decreases. Submillimetre Array observations reveal CO emission towards four sources demonstrating that some, but probably not much, molecular gas remains in these relatively evolved discs. These observations provide new constraints on the dust and gas mass of protoplanetary discs during the giant planet building phase and provide a reference level for future studies of disc evolution.
- ID:
- ivo://CDS.VizieR/J/MNRAS/430/2358
- Title:
- SDSS photometry of LMC cluster SL 529
- Short Name:
- J/MNRAS/430/2358
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results on the age and metallicity estimates of the poorly studied Large Magellanic Cloud (LMC) cluster SL 529, from CCD SDSS gr photometry obtained at the Gemini South telescope with the GMOS attached. The cluster main-sequence turnoffs (MSTO) region possesses an extended structure, with an age spread (~0.5Gyr) bigger than the mean age width of known extended MSTO (EMSTO) LMC clusters. We report for the first time a mean cluster age of 2.25Gyr and a mean cluster metallicity of Z=0.004, which place it as the most metal-poor and oldest cluster in the EMSTO LMC cluster group. In addition, the cluster red clump appears to be formed by two concentrations of stars - although it is not clear whether this feature can be caused, in part, by binary interactions and mergers - whereas the cluster core radius of 4.2pc is in excellent agreement with those determined for the previously 12 known EMSTO LMC clusters.
- ID:
- ivo://CDS.VizieR/J/A+A/481/345
- Title:
- SED evolution in massive young stellar objects
- Short Name:
- J/A+A/481/345
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The mechanism of formation of massive stars is still a matter of debate. It is not yet clear if it can be considered to be a scaled-up analogue of the low-mass star regime, or if there are additional agents like merging of lower-mass forming objects or accretion from initially unbound material. Most of the uncertainties come from the lack of diagnostic tools to evolutionarily classify large samples of candidate massive protostellar objects that can then be studied in more detail. We want to verify whether diagnostic tools like the SED shape and the relationship between envelope mass and bolometric luminosity can be extended to the study of high-mass star formation. The 8-1200um SED of YSOs in 42 regions of massive star formation has been reconstructed using MSX, IRAS, and submm data partly available from previous works. Apart from IRAS catalogue fluxes, the fluxes in the Mid-IR and sub-mm/mm were derived directly from the images. The SEDs were fitted to an extensive grid of envelope models with embedded ZAMS stars, available from the literature. Sources that could not be fitted with a single model were then fitted with a two-component model composed of an embedded ZAMS for the mid-IR part and a single-temperature optically thin greybody for the longer wavelength emitting component. Sources were classified as "IR" if they were fitted with an embedded ZAMS envelope, and "MM" if they could only be fitted with a greybody with a peak at high {lambda} further subclassification was based on being the most massive object in the field ("P", for primary) or not ("S", for secondary).
- ID:
- ivo://CDS.VizieR/J/A+A/581/A124
- Title:
- SFR IRAS 05137+3919 star and jet multiplicity
- Short Name:
- J/A+A/581/A124
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a study of the complex high-mass star forming region IRAS05137+3919 (also known as Mol8), where multiple jets and a rich stellar cluster have been described in previous works. Our goal is to determine the number of jets and shed light on their origin, and thus determine the nature of the young stars powering these jets. We also wish to analyse the stellar clusters by resolving the brightest group of stars. The star forming region was observed in various tracers and the results were complemented with ancillary archival data. The new data represent a substantial improvement over previous studies both in resolution and frequency coverage. In particular, adaptive optics provides us with an angular resolution of 80mas in the near IR, while new mid- and far-IR data allow us to sample the peak of the spectral energy distribution and thus reliably estimate the bolometric luminosity. Thanks to the near-IR continuum and millimetre line data we can determine the structure and velocity field of the bipolar jets and outflows in this star forming region. We also find that the stars are grouped into three clusters and the jets originate in the richest of these, whose luminosity is ~2.4x10^4^L_{sun}_. Interestingly, our high-resolution near-IR images allow us to resolve one of the two brightest stars (A and B) of the cluster into a double source (A1+A2). We confirm that there are two jets and establish that they are powered by B-type stars belonging to cluster C1. On this basis and on morphological and kinematical arguments, we conclude that the less extended jet is almost perpendicular to the line of sight and that it originates in the brightest star of the cluster, while the more extended one appears to be associated with the more extincted, double source A1+A2. We propose that this is not a binary system, but a small bipolar reflection nebula at the root of the large-scale jet, outlining a still undetected circumstellar disk. The gas kinematics on a scale of ~0.2pc seems to support our hypothesis, because it appears to trace rotation about the axis of the associated jet.
- ID:
- ivo://CDS.VizieR/J/PASJ/62/391
- Title:
- SiO and H2O masers in Stephenson 2 cluster
- Short Name:
- J/PASJ/62/391
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of radio observations of red supergiants in a star cluster, Stephenson (1990AJ.....99.1867S)'s #2 (Cl Stephenson 2), and of candidates for red supergiants in three star clusters, Mercer et al. (2005ApJ...635..560M)'s #4, #8, and #13 ([MCM2005b] 4, [MCM2005b] 8 and [MCM2005b] 13), in the SiO and H_2_O maser lines. The Stephenson's #2 cluster and nearby aggregation at the southwest contain more than 15 red supergiants.
