P. E. Nissen, J. Christensen-Dalsgaard, J. R. Mosumgaard, V. Silva Aguirre, E. Spitoni, K. Verma.
High-precision abundances of elements in solar-type stars. Evidence of two distinct sequences in abundance-age relations
See arXiv version
15 pages, 19 figures. Accepted for publication in A&A
Abstract
HARPS spectra with signal-to-noise ratios S/N > 600 at 6000 A were analysed with MARCS model atmospheres to obtain 1D LTE abundances of C, O, Na, Mg, Al, Si, Ca, Ti, Cr, Fe, Ni, Sr, and Y for 72 nearby solar-type stars with metallicities in the range -0.3 < [Fe/H] < +0.3 and ASTEC stellar models were used to determine stellar ages from effective temperatures, luminosities obtained via Gaia DR2 parallaxes, and heavy element abundances. The resulting age-metallicity distribution appears to consist of two distinct populations: a sequence of old stars with a steep rise of [Fe/H] to about +0.3 dex at an age of ~7 Gyr and a younger sequence with [Fe/H] increasing from -0.3 dex to about +0.2 dex over the last six Gyr. Furthermore, the trends of several abundance ratios, [O/Fe], [Na/Fe], [Ca/Fe], and [Ni/Fe], as a function of stellar age split into two corresponding sequences. The [Y/Mg]-age relation, on the other hand, shows no offset between the two age sequences and has no significant dependence on [Fe/H], but the components of a visual binary star, zeta Reticuli, have a large and puzzling deviation. The split of the age-metallicity distribution into two sequences may be interpreted as evidence of two episodes of accretion of gas onto the Galactic disk with a quenching of star formation in between. Some of the [X/Fe]-age relations support this scenario but other relations are not so easy to explain, which calls for a deeper study of systematic errors in the derived abundances as a function of [Fe/H], in particular 3D non-LTE effects.
amalie@auriga:~/Nextcloud/Uddannelse/UNI/phd/iSIMBA/isimbadk/htmlrequests$ ^C
amalie@auriga:~/Nextcloud/Uddannelse/UNI/phd/iSIMBA/isimbadk/htmlrequests$ python3 arxivposts.py 2006.06013
P. E. Nissen, J. Christensen-Dalsgaard, J. R. Mosumgaard, V. Silva Aguirre, E. Spitoni, K. Verma. (Stellar Astrophysics Centre Department of Physics and Astronomy Aarhus University Denmark.)
High-precision abundances of elements in solar-type stars. Evidence of two distinct sequences in abundance-age relations
See arXiv version
15 pages, 19 figures. Accepted for publication in A&A
Abstract
HARPS spectra with signal-to-noise ratios S/N > 600 at 6000 A were analysed with MARCS model atmospheres to obtain 1D LTE abundances of C, O, Na, Mg, Al, Si, Ca, Ti, Cr, Fe, Ni, Sr, and Y for 72 nearby solar-type stars with metallicities in the range -0.3 < [Fe/H] < +0.3 and ASTEC stellar models were used to determine stellar ages from effective temperatures, luminosities obtained via Gaia DR2 parallaxes, and heavy element abundances. The resulting age-metallicity distribution appears to consist of two distinct populations: a sequence of old stars with a steep rise of [Fe/H] to about +0.3 dex at an age of ~7 Gyr and a younger sequence with [Fe/H] increasing from -0.3 dex to about +0.2 dex over the last six Gyr. Furthermore, the trends of several abundance ratios, [O/Fe], [Na/Fe], [Ca/Fe], and [Ni/Fe], as a function of stellar age split into two corresponding sequences. The [Y/Mg]-age relation, on the other hand, shows no offset between the two age sequences and has no significant dependence on [Fe/H], but the components of a visual binary star, zeta Reticuli, have a large and puzzling deviation. The split of the age-metallicity distribution into two sequences may be interpreted as evidence of two episodes of accretion of gas onto the Galactic disk with a quenching of star formation in between. Some of the [X/Fe]-age relations support this scenario but other relations are not so easy to explain, which calls for a deeper study of systematic errors in the derived abundances as a function of [Fe/H], in particular 3D non-LTE effects.
