- ID:
- ivo://CDS.VizieR/J/A+A/590/A13
- Title:
- New candidate members in young associations
- Short Name:
- J/A+A/590/A13
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The young associations offer us one of the best opportunities to study the properties of young stellar and sub-stellar objects and directly image planets thanks to their proximity (<200pc) and age (5-150Myr). However, many previous works have been limited to identifying the brighter, more active members (1Msun) due to photometric survey sensitivities limiting the detections of lower-mass objects. We search the field of view of 542 previously identified members of the young associations to identify wide / extremely wide (1000-100,000au in physical separation) companions. Methods. We have combined 2MASS near-infrared photometry (J, H, K) with proper motion values (from UCAC4, PPMXL, NOMAD) to identify companions in the field of view of known members. We collated further photometry and spectroscopy from the literature and conducted our own high-resolution spectroscopic observations for a sub-sample of candidate members. This complementary information allowed us to assess the efficiency of our method. We identified 84 targets (45:0.2-1.3M_{sun}_, 17:0.08-0.2M_{sun}_, 22:<0.08M_{sun}_) in our analysis, 10 of which have been identified from spectroscopic analysis in previous young association works. For 33 of these 84 we were able to further assess their membership using a variety of properties (X-ray emission, UV excess, H{alpha}, lithium and KI equivalent widths, radial velocities, and CaH indices). We derive a success rate of 76-88% for this technique based on the consistency of these properties. Once confirmed, the targets identified in this work would significantly improve our knowledge of the lower-mass end of the young associations. Additionally, these targets would make an ideal new sample for the identification and study of planets around nearby young stars. Given the predicted sub-stellar mass of the majority of these new candidate members and their proximity, high-contrast imaging techniques would facilitate the search for new low-mass planets.
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Search Results
- ID:
- ivo://CDS.VizieR/J/MNRAS/449/1536
- Title:
- New damped Ly{alpha} absorbers
- Short Name:
- J/MNRAS/449/1536
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Quasar damped Ly{alpha} (DLA) absorption-line systems with redshifts z<1.65 are used to trace neutral gas over approximately 70 percent of the most recent history of the Universe. However, such systems fall in the UV and are rarely found in blind UV spectroscopic surveys. Therefore, it has been difficult to compile a moderate-sized sample of UV DLAs in any narrow cosmic time interval. However, DLAs are easy to identify in low-resolution spectra because they have large absorption rest equivalent widths. We have performed an efficient strong-Mg ii-selected survey for UV DLAs at redshifts z=[0.42,0.70] using Hubble Space Telescope's low-resolution ACS-HRC-PR200L prism. This redshift interval covers ~1.8Gyr in cosmic time, i.e. t~[7.2,9.0]Gyr after the big bang. A total of 96 strong MgII absorption-line systems identified in Sloan Digital Sky Survey spectra were successfully observed with the prism at the predicted UV wavelengths of Ly{alpha} absorption. We found that 35 of the 96 systems had a significant probability of being DLAs. One additional observed system could be a very high N_HI_ DLA (N_HI_~2x10^22^atoms/cm^2^ or possibly higher), but since very high N_HI_ systems are extremely rare, it would be unusual for this system to be a DLA given the size of our sample. Here we present information on our prism sample, including our best estimates of N_HI_ and errors for the 36 systems fitted with DLA profiles. This list is valuable for future follow-up studies of low-redshift DLAs in a small redshift interval, although such work would clearly benefit from improved UV spectroscopy to more accurately determine their neutral hydrogen column densities.
- ID:
- ivo://CDS.VizieR/J/MNRAS/448/2737
- Title:
- New PMS K/M Stars in Upper Scorpius
- Short Name:
- J/MNRAS/448/2737
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present 237 new spectroscopically confirmed pre-main-sequence K- and M-type stars in the young Upper Scorpius subgroup of the Sco-Cen association, the nearest region of recent massive star formation. Using the Wide-Field Spectrograph at the Australian National University 2.3 m telescope at Siding Spring, we observed 397 kinematically and photometrically selected candidate members of Upper Scorpius, and identified new members by the presence of lithium absorption. The HR-diagram of the new members shows a spread of ages, ranging from ~3 to 20Myr, which broadly agrees with the current age estimates of ~5-10Myr. We find a significant range of Li 6708 equivalent widths among the members, and a minor dependence of HR-diagram position on the measured equivalent width of the Li 6708{AA} line, with members that appear younger having more lithium. This could indicate the presence of either populations of different age, or a spread of ages in Upper Scorpius. We also use Wide-Field Infrared Survey Explorer data to infer circumstellar disc presence in 25 of the members on the basis of infrared excesses, including two candidate transition discs. We find that 11.2+/-3.4% the M0-M2 spectral type (0.4-0.8M_{sun}_) Upper Sco stars display an excess that indicates the presence of a gaseous disc.
- ID:
- ivo://CDS.VizieR/J/AJ/158/54
- Title:
- New Taurus members from stellar to planetary masses
- Short Name:
- J/AJ/158/54
- Date:
- 06 Dec 2021 11:31:43
- Publisher:
- CDS
- Description:
- We present a large sample of new members of the Taurus star-forming region that extend from stellar to planetary masses. To identify candidate members at substellar masses, we have used color-magnitude diagrams and proper motions measured with several wide-field optical and infrared (IR) surveys. At stellar masses, we have considered the candidate members that were found in a recent analysis of high-precision astrometry from the Gaia mission. Using new and archival spectra, we have measured spectral types and assessed membership for these 161 candidates, 79 of which are classified as new members. Our updated census of Taurus now contains 519 known members. According to Gaia data, this census should be nearly complete for spectral types earlier than M6-M7 at A_J_<1. For a large field encompassing ~72% of the known members, the census should be complete for K<15.7 at A_J_<1.5, which corresponds to ~5-13 M_Jup_ for ages of 1-10 Myr based on theoretical evolutionary models. Our survey has doubled the number of known members at >=M9 and has uncovered the faintest known member in M_K_, which should have a mass of ~3-10 M_Jup_ for ages of 1-10 Myr. We have used mid-IR photometry from the Spitzer Space Telescope and the Wide-field Infrared Survey Explorer to determine whether the new members exhibit excess emission that would indicate the presence of circumstellar disks. The updated disk fraction for Taurus is ~0.7 at =<M3.5 and ~0.4 at >M3.5.
- ID:
- ivo://CDS.VizieR/J/AJ/156/76
- Title:
- New young stars and brown dwarfs in Upper Sco
- Short Name:
- J/AJ/156/76
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- To improve the census of the Upper Sco association (~11 Myr, ~145 pc), we have identified candidate members using parallaxes, proper motions, and color-magnitude diagrams from several wide-field imaging surveys and have obtained optical and infrared spectra of several hundred candidates to measure their spectral types and assess their membership. We also have performed spectroscopy on a smaller sample of previously known or suspected members to refine their spectral types and evidence of membership. We have classified 530 targets as members of Upper Sco, 377 of which lack previous spectroscopy. Our new compilation of all known members of the association contains 1631 objects. Although the census of Upper Sco has expanded significantly over the last decade, there remain hundreds of candidates that lack spectroscopy. The precise parallaxes and proper motions from the second data release of Gaia should extend down to substellar masses in Upper Sco, which will greatly facilitate the identification of the undiscovered members.
- ID:
- ivo://CDS.VizieR/J/AJ/141/58
- Title:
- NGC 2204 and NGC 2243 red giant abundances
- Short Name:
- J/AJ/141/58
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Detailed element abundances have been determined for 10-13 stars each in the open clusters (OCs) NGC 2204 and NGC 2243 based on Hydra multi-object echelle spectra obtained with the CTIO 4m telescope. We have found average cluster metallicities of [Fe/H]=-0.23+/-0.04 and -0.42+/-0.05 for NGC 2204 and NGC 2243, respectively, from an equivalent width analysis.
- ID:
- ivo://CDS.VizieR/J/MNRAS/438/3507
- Title:
- NGC 5824 calcium triplet equivalent widths
- Short Name:
- J/MNRAS/438/3507
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a detailed study of the strengths of the calcium triplet absorption lines in the spectra of a large sample of red giant members of the luminous outer Galactic halo globular cluster NGC 5824. The spectra were obtained with the FORS2 and GMOS-S multi-object spectrographs at the VLT and the Gemini-S telescope, respectively. By comparing the line strengths of the NGC 5824 stars with those for red giants in clusters with well-established abundances, we conclude that there is an intrinsic abundance dispersion in NGC 5824 characterized by an inter-quartile range in [Fe/H] of 0.10dex and a total range of ~0.3dex. As for {omega} Cen and M22, the abundance distribution shows a steep rise on the metal-poor side and a shallower decline on the metal-rich side. There is also some indication that the distribution is not unimodal with perhaps three distinct abundance groupings present. NGC 5824 has a further unusual characteristic: the outer surface density profile shows no signs of a tidal cutoff. Instead, the profile has a power-law distribution with cluster stars detected to a radius exceeding 400pc. We postulate that NGC 5824 may be the remnant nuclear star cluster of a now disrupted dwarf galaxy accreted during the formation of the Galaxy's halo. We further speculate that the presence of an intrinsic [Fe/H] spread is the characteristic that distinguishes former nuclear star clusters from other globular clusters.
- ID:
- ivo://CDS.VizieR/J/A+A/539/A11
- Title:
- NGC 1316/1317 planetary nebula kinematics
- Short Name:
- J/A+A/539/A11
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present positions and velocities for 796 planetary nebulae (PNe) in the Fornax Brightest Cluster Galaxy NGC 1316 (Fornax A). The planetary nebulae and existing kinematics are used to explore the rotation of this merger remnant and constrain dynamical models. Using FORS2 on the VLT, the PN velocities were measured using a counter-dispersed slitless-spectroscopy technique that produced the largest-to-date sample outside of the Local Group. Spherical, non-rotating, constant-anisotropy Jeans models were con- strained by observations of the planetary nebulae and existing integrated light spectra.
- ID:
- ivo://CDS.VizieR/J/A+A/527/A148
- Title:
- NGC6397 red giants chemical composition
- Short Name:
- J/A+A/527/A148
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The chemical compositions of globular clusters provide important information on the star formation that occurred at very early times in the Galaxy. In particular the abundance patterns of elements with atomic number z<=13 may shed light on the properties of stars that early on enriched parts of the star-forming gas with the rest-products of hydrogen-burning at high temperatures. We analyse and discuss the chemical compositions of a large number of elements in 21 red giant branch stars in the metal-poor globular cluster NGC6397. We compare the derived abundance patterns with theoretical predictions in the framework of the "wind of fast rotating massive star"-scenario. High-resolution spectra were obtained with the FLAMES/UVES spectrograph on the VLT. We determined non-LTE abundances of Na, and LTE abundances for the remaining 21 elements, including O (from the [OI] line at 630nm), Mg, Al, alpha, iron-peak, and neutron-capture elements, many of which had not been previously analysed for this cluster. We also considered the influence of possible He enrichment in the analysis of stellar spectra. We find that the Na abundances of evolved, as well as unevolved, stars in NGC6397 show a distinct bimodality, which is indicative of two stellar populations: one primordial stellar generation of composition similar to field stars, and a second generation that is polluted with material processed during hydrogen-burning, i.e., enriched in Na and Al and depleted in O and Mg. The red giant branch exhibits a similar bimodal distribution in the Stroemgren colour index c_y_=c_1_-(b-y), implying that there are also large differences in the N abundance. The two populations have the same composition for all analysed elements heavier than Al, within the measurement uncertainty of the analysis, with the possible exception of [Y/Fe]. Using two stars with almost identical stellar parameters, one from each generation, we estimate the difference in He content, Delta-Y=0.01+/-0.06, given the assumption that the mass fraction of iron is the same for the stars. NGC6397 hosts two stellar populations that have different chemical compositions of N, O, Na, Mg, and probably Al. The cluster is dominated (75%) by the second generation. We show that massive stars of the first generation can be held responsible for the abundance patterns observed in the second generation long-lived stars of NGC6397. We estimate that the initial mass of this globular cluster is at least ten times higher than its present-day value.
530. NGC 330 seen by MUSE
- ID:
- ivo://CDS.VizieR/J/A+A/634/A51
- Title:
- NGC 330 seen by MUSE
- Short Name:
- J/A+A/634/A51
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A majority of massive stars are part of binary systems, a large fraction of which will inevitably interact during their lives. Binary-interaction products (BiPs), i.e. stars affected by such interaction, are expected to be commonly present in stellar populations. BiPs are thus a crucial ingredient in the understanding of stellar evolution. We aim to identify and characterize a statistically significant sample of BiPs by studying clusters of 10-40Myr, an age at which binary population models predict the abundance of BiPs to be highest. One example of such a cluster is NGC 330 in the Small Magellanic Cloud. Using MUSE WFM-AO observations of NGC 330, we resolve the dense cluster core for the first time and are able to extract spectra of its entire massive star population. We develop an automated spectral classification scheme based on the equivalent widths of spectral lines in the red part of the spectrum. We characterize the massive star content of the core of NGC 330 which contains more than 200 B stars, 2 O stars, 6 A-type supergiants and 11 red supergiants. We find a lower limit on the Be star fraction of 32+/-3% in the whole sample. It increases to at least 46+/-10% when only considering stars brighter than V=17mag. We estimate an age of the cluster core between 35 and 40Myr and a total cluster mass of 88^+17^_-18_*10^3M_{sun}_. We find that the population in the cluster core is different than the population in the outskirts: while the stellar content in the core appears to be older than the stars in the outskirts, the Be star fraction and the observed binary fraction are significantly higher. Furthermore, we detect several BiP candidates that will be subject of future studies.
