Rubidium Abundances in Cool Giants from High-resolution H-band Spectra: A New Diagnostic for Galactic Chemical Evolution
The Galactic center and inner disk of the Milky Way contain complex stellar populations obscured by heavy dust extinction. To study their chemical composition, high-resolution near-infrared (near-IR) spectroscopy is necessary. Expanding the set of elements measurable in the near-IR, especially neutr...
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2025-01-01
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| Online Access: | https://doi.org/10.3847/1538-4357/ade87a |
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| author | Nils Ryde Jess Kocher Govind Nandakumar Henrik Hartman Marta Molero Henrik Jönsson Gregory Mace Erica Sawczynec Kyle F. Kaplan |
| author_facet | Nils Ryde Jess Kocher Govind Nandakumar Henrik Hartman Marta Molero Henrik Jönsson Gregory Mace Erica Sawczynec Kyle F. Kaplan |
| author_sort | Nils Ryde |
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| description | The Galactic center and inner disk of the Milky Way contain complex stellar populations obscured by heavy dust extinction. To study their chemical composition, high-resolution near-infrared (near-IR) spectroscopy is necessary. Expanding the set of elements measurable in the near-IR, especially neutron-capture elements, improves our ability to trace nucleosynthesis and Galactic chemical evolution. This work aims to identify and characterize a spectral line suitable for determining rubidium (Rb) abundances. Rubidium is produced in roughly equal parts by the r - and s -processes. We analyze high-resolution ( R = 45,000) Immersion GRating INfrared Spectrograph (or IGRINS) near-IR spectra of 40 M giants in the solar neighborhood, most observed with Gemini South. We perform spectral synthesis of the Rb i line at 15289.48 Å, using new ${\mathrm{log}}\,gf$ values and including an astrophysical calibration of the blending Fe i lines. The resulting [Rb/Fe] ratios are compared to other neutron-capture elements and interpreted with chemical evolution models. We demonstrate that the used Rb line is a reliable abundance indicator in M giants and the coolest K giants, but becomes too weak at higher temperatures. [Rb/Fe] shows a decreasing trend with metallicity, mirroring that of ytterbium (Yb), another mixed r -/ s -process element. Our results agree with optical studies, validating the use of this near-IR line. Comparisons with chemical evolution models confirm that both s - and r -process sources are needed to explain the Rb trend. This work adds Rb to the list of elements measurable in high-resolution H - and K -band spectra, enabling studies of one more neutron-capture element in dust-obscured regions like the Galactic center and inner disk. |
| format | Article |
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| institution | DOAJ |
| issn | 1538-4357 |
| language | English |
| publishDate | 2025-01-01 |
| publisher | IOP Publishing |
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| spelling | doaj-art-dc2c3280c00c42f09ebc96be78e4358d2025-08-20T03:09:19ZengIOP PublishingThe Astrophysical Journal1538-43572025-01-01988223510.3847/1538-4357/ade87aRubidium Abundances in Cool Giants from High-resolution H-band Spectra: A New Diagnostic for Galactic Chemical EvolutionNils Ryde0https://orcid.org/0000-0001-6294-3790Jess Kocher1https://orcid.org/0009-0005-2049-3847Govind Nandakumar2https://orcid.org/0000-0002-6077-2059Henrik Hartman3https://orcid.org/0000-0001-9853-2555Marta Molero4Henrik Jönsson5https://orcid.org/0000-0002-4912-8609Gregory Mace6https://orcid.org/0000-0001-7875-6391Erica Sawczynec7https://orcid.org/0000-0002-8378-1062Kyle F. Kaplan8https://orcid.org/0000-0001-6909-3856Division of Astrophysics, Department of Physics, Lund University , Box 118, SE-22100 Lund, Sweden ; nils.ryde@fysik.lu.seDivision of Astrophysics, Department of Physics, Lund University , Box 118, SE-22100 Lund, Sweden ; nils.ryde@fysik.lu.seAryabhatta Research Institute of Observational Sciences , Manora Peak, Nainital 263002, IndiaMaterials Science and Applied Mathematics, Malmö University , SE-205 06 Malmö, SwedenInstitut für Kernphysik, Technische Universität Darmstadt , Schlossgartenstr. 2, Darmstadt D-64289, Germany; INAF, Osservatorio Astronomico di Trieste , Via Tiepolo 11, I-34131 Trieste, ItalyMaterials Science and Applied Mathematics, Malmö University , SE-205 06 Malmö, SwedenDepartment of Astronomy and McDonald Observatory, University of Texas at Austin , 2515 Speedway, Stop C1400, Austin, TX 78712-1205, USADepartment of Astronomy, University of Texas at Austin , 2515 Speedway, Stop C1400, Austin, TX 78712-1205, USADepartment of Astronomy, University of Texas at Austin , 2515 Speedway, Stop C1400, Austin, TX 78712-1205, USAThe Galactic center and inner disk of the Milky Way contain complex stellar populations obscured by heavy dust extinction. To study their chemical composition, high-resolution near-infrared (near-IR) spectroscopy is necessary. Expanding the set of elements measurable in the near-IR, especially neutron-capture elements, improves our ability to trace nucleosynthesis and Galactic chemical evolution. This work aims to identify and characterize a spectral line suitable for determining rubidium (Rb) abundances. Rubidium is produced in roughly equal parts by the r - and s -processes. We analyze high-resolution ( R = 45,000) Immersion GRating INfrared Spectrograph (or IGRINS) near-IR spectra of 40 M giants in the solar neighborhood, most observed with Gemini South. We perform spectral synthesis of the Rb i line at 15289.48 Å, using new ${\mathrm{log}}\,gf$ values and including an astrophysical calibration of the blending Fe i lines. The resulting [Rb/Fe] ratios are compared to other neutron-capture elements and interpreted with chemical evolution models. We demonstrate that the used Rb line is a reliable abundance indicator in M giants and the coolest K giants, but becomes too weak at higher temperatures. [Rb/Fe] shows a decreasing trend with metallicity, mirroring that of ytterbium (Yb), another mixed r -/ s -process element. Our results agree with optical studies, validating the use of this near-IR line. Comparisons with chemical evolution models confirm that both s - and r -process sources are needed to explain the Rb trend. This work adds Rb to the list of elements measurable in high-resolution H - and K -band spectra, enabling studies of one more neutron-capture element in dust-obscured regions like the Galactic center and inner disk.https://doi.org/10.3847/1538-4357/ade87aM giant starsInfrared spectroscopyGalaxy chemical evolutionChemical abundances |
| spellingShingle | Nils Ryde Jess Kocher Govind Nandakumar Henrik Hartman Marta Molero Henrik Jönsson Gregory Mace Erica Sawczynec Kyle F. Kaplan Rubidium Abundances in Cool Giants from High-resolution H-band Spectra: A New Diagnostic for Galactic Chemical Evolution The Astrophysical Journal M giant stars Infrared spectroscopy Galaxy chemical evolution Chemical abundances |
| title | Rubidium Abundances in Cool Giants from High-resolution H-band Spectra: A New Diagnostic for Galactic Chemical Evolution |
| title_full | Rubidium Abundances in Cool Giants from High-resolution H-band Spectra: A New Diagnostic for Galactic Chemical Evolution |
| title_fullStr | Rubidium Abundances in Cool Giants from High-resolution H-band Spectra: A New Diagnostic for Galactic Chemical Evolution |
| title_full_unstemmed | Rubidium Abundances in Cool Giants from High-resolution H-band Spectra: A New Diagnostic for Galactic Chemical Evolution |
| title_short | Rubidium Abundances in Cool Giants from High-resolution H-band Spectra: A New Diagnostic for Galactic Chemical Evolution |
| title_sort | rubidium abundances in cool giants from high resolution h band spectra a new diagnostic for galactic chemical evolution |
| topic | M giant stars Infrared spectroscopy Galaxy chemical evolution Chemical abundances |
| url | https://doi.org/10.3847/1538-4357/ade87a |
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