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      The pristine nature of SMSS 1605−1443 revealed by ESPRESSO

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          Abstract

          Context. SMSS J160540.18−144323.1 is the carbon-enhanced metal-poor (CEMP) star with the lowest iron abundance ever measured, [Fe/H] = −6.2, which was first reported with the SkyMapper telescope. The carbon abundance is A(C)≈6.1 in the low-C band, as the majority of the stars in this metallicity range. Yet, constraining the isotopic ratio of key species, such as carbon, sheds light on the properties and origin of these elusive stars.

          Aims. We performed high-resolution observations of SMSS 1605−1443 with the ESPRESSO spectrograph to look for variations in the radial velocity ( v rad) with time. These data have been combined with older MIKE and UVES archival observations to enlarge the temporal baseline. The 12C/ 13C isotopic ratio is also studied to explore the possibility of mass transfer from a binary companion.

          Methods. A cross-correlation function against a natural template was applied to detect v rad variability and a spectral synthesis technique was used to derive 12C/ 13C in the stellar atmosphere.

          Results. We confirm previous indications of binarity in SMSS 1605−1443 and measured a lower limit 12C/ 13C > 60 at more than a 3 σ confidence level, proving that this system is chemically unmixed and that no mass transfer from the unseen companion has happened so far. Thus, we confirm the CEMP-no nature of SMSS 1605−1443 and show that the pristine chemical composition of the cloud from which it formed is currently imprinted in its stellar atmosphere free of contamination.

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          The Chemical Composition of the Sun

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            Gaia Early Data Release 3 : Summary of the contents and survey properties

            Context. We present the early installment of the third Gaia data release, Gaia EDR3, consisting of astrometry and photometry for 1.8 billion sources brighter than magnitude 21, complemented with the list of radial velocities from Gaia DR2. Aims. A summary of the contents of Gaia EDR3 is presented, accompanied by a discussion on the differences with respect to Gaia DR2 and an overview of the main limitations which are present in the survey. Recommendations are made on the responsible use of Gaia EDR3 results. Methods. The raw data collected with the Gaia instruments during the first 34 months of the mission have been processed by the Gaia Data Processing and Analysis Consortium and turned into this early third data release, which represents a major advance with respect to Gaia DR2 in terms of astrometric and photometric precision, accuracy, and homogeneity. Results. Gaia EDR3 contains celestial positions and the apparent brightness in G for approximately 1.8 billion sources. For 1.5 billion of those sources, parallaxes, proper motions, and the ( G BP − G RP ) colour are also available. The passbands for G , G BP , and G RP are provided as part of the release. For ease of use, the 7 million radial velocities from Gaia DR2 are included in this release, after the removal of a small number of spurious values. New radial velocities will appear as part of Gaia DR3. Finally, Gaia EDR3 represents an updated materialisation of the celestial reference frame (CRF) in the optical, the Gaia -CRF3, which is based solely on extragalactic sources. The creation of the source list for Gaia EDR3 includes enhancements that make it more robust with respect to high proper motion stars, and the disturbing effects of spurious and partially resolved sources. The source list is largely the same as that for Gaia DR2, but it does feature new sources and there are some notable changes. The source list will not change for Gaia DR3. Conclusions. Gaia EDR3 represents a significant advance over Gaia DR2, with parallax precisions increased by 30 per cent, proper motion precisions increased by a factor of 2, and the systematic errors in the astrometry suppressed by 30–40% for the parallaxes and by a factor ~2.5 for the proper motions. The photometry also features increased precision, but above all much better homogeneity across colour, magnitude, and celestial position. A single passband for G , G BP , and G RP is valid over the entire magnitude and colour range, with no systematics above the 1% level
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              Evolution of Asymptotic Giant Branch Stars

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                Author and article information

                Contributors
                Journal
                Astronomy & Astrophysics
                A&A
                EDP Sciences
                0004-6361
                1432-0746
                January 2023
                January 10 2023
                January 2023
                : 669
                : L4
                Article
                10.1051/0004-6361/202245392
                9a200112-7dde-4625-b11d-ba4fb19d4b51
                © 2023

                https://creativecommons.org/licenses/by/4.0

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