Rotationally Driven Ultraviolet Emission of Red Giant Stars. II. Metallicity, Activity, Binarity, and Subsubgiants
Red-giant-branch (RGB) stars are overwhelmingly observed to rotate very slowly compared to main-sequence stars, but a few percent of them show rapid rotation and high activity, often as a result of tidal synchonization or other angular momentum transfer events. In this paper we build upon previous w...
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2025-01-01
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| Series: | The Astronomical Journal |
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| Online Access: | https://doi.org/10.3847/1538-3881/adc92a |
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| author | Don Dixon Keivan G. Stassun Robert D. Mathieu Jamie Tayar Lyra Cao |
| author_facet | Don Dixon Keivan G. Stassun Robert D. Mathieu Jamie Tayar Lyra Cao |
| author_sort | Don Dixon |
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| description | Red-giant-branch (RGB) stars are overwhelmingly observed to rotate very slowly compared to main-sequence stars, but a few percent of them show rapid rotation and high activity, often as a result of tidal synchonization or other angular momentum transfer events. In this paper we build upon previous work using a sample of 7286 RGB stars from APOGEE DR17 with measurable rotation. We derive an updated NUV excess versus $v\sin i$ rotation–activity relation that is consistent with our previous published version, but reduces uncertainty through the inclusion of a linear [M/H] correction term. We find that both single stars and binary stars generally follow our rotation–activity relation, but single stars seemingly saturate at P _rot / $\sin i$ ∼ 10 days while binary stars show no sign of saturation, suggesting they are able to carry substantially stronger magnetic fields. Our analysis reveals subsubgiant stars (SSGs) to be the most active giant binaries, with rotation synchronized to orbits with periods ≲20 days. Given their unusually high level of activity compared to other short-period synchronized giants, we suspect the SSGs are most commonly overactive RS CVn stars. Using estimates of critical rotation we identify a handful giants rotating near breakup and determine tidal spin up to this level of rotation is highly unlikely and instead suggest planetary engulfment or stellar mergers in a fashion generally proposed for FK Comae stars. |
| format | Article |
| id | doaj-art-89c24fbd4f2a41fe8b3d9a05fa96328c |
| institution | Kabale University |
| issn | 1538-3881 |
| language | English |
| publishDate | 2025-01-01 |
| publisher | IOP Publishing |
| record_format | Article |
| series | The Astronomical Journal |
| spelling | doaj-art-89c24fbd4f2a41fe8b3d9a05fa96328c2025-08-20T03:49:45ZengIOP PublishingThe Astronomical Journal1538-38812025-01-01169630910.3847/1538-3881/adc92aRotationally Driven Ultraviolet Emission of Red Giant Stars. II. Metallicity, Activity, Binarity, and SubsubgiantsDon Dixon0https://orcid.org/0000-0001-6977-9495Keivan G. Stassun1https://orcid.org/0000-0002-3481-9052Robert D. Mathieu2https://orcid.org/0000-0002-7130-2757Jamie Tayar3https://orcid.org/0000-0002-4818-7885Lyra Cao4https://orcid.org/0000-0002-8849-9816Department of Physics and Astronomy, Vanderbilt University , Nashville, TN 37235, USA; Department of Physics, Fisk University , Nashville, TN 37208, USADepartment of Physics and Astronomy, Vanderbilt University , Nashville, TN 37235, USA; Department of Physics, Fisk University , Nashville, TN 37208, USADepartment of Astronomy, University of Wisconsin-Madison , Madison, WI 53706, USADepartment of Astronomy, University of Florida , Gainesville, FL 32611, USADepartment of Physics and Astronomy, Vanderbilt University , Nashville, TN 37235, USARed-giant-branch (RGB) stars are overwhelmingly observed to rotate very slowly compared to main-sequence stars, but a few percent of them show rapid rotation and high activity, often as a result of tidal synchonization or other angular momentum transfer events. In this paper we build upon previous work using a sample of 7286 RGB stars from APOGEE DR17 with measurable rotation. We derive an updated NUV excess versus $v\sin i$ rotation–activity relation that is consistent with our previous published version, but reduces uncertainty through the inclusion of a linear [M/H] correction term. We find that both single stars and binary stars generally follow our rotation–activity relation, but single stars seemingly saturate at P _rot / $\sin i$ ∼ 10 days while binary stars show no sign of saturation, suggesting they are able to carry substantially stronger magnetic fields. Our analysis reveals subsubgiant stars (SSGs) to be the most active giant binaries, with rotation synchronized to orbits with periods ≲20 days. Given their unusually high level of activity compared to other short-period synchronized giants, we suspect the SSGs are most commonly overactive RS CVn stars. Using estimates of critical rotation we identify a handful giants rotating near breakup and determine tidal spin up to this level of rotation is highly unlikely and instead suggest planetary engulfment or stellar mergers in a fashion generally proposed for FK Comae stars.https://doi.org/10.3847/1538-3881/adc92aGiant starsStellar rotationStellar activityBinary stars |
| spellingShingle | Don Dixon Keivan G. Stassun Robert D. Mathieu Jamie Tayar Lyra Cao Rotationally Driven Ultraviolet Emission of Red Giant Stars. II. Metallicity, Activity, Binarity, and Subsubgiants The Astronomical Journal Giant stars Stellar rotation Stellar activity Binary stars |
| title | Rotationally Driven Ultraviolet Emission of Red Giant Stars. II. Metallicity, Activity, Binarity, and Subsubgiants |
| title_full | Rotationally Driven Ultraviolet Emission of Red Giant Stars. II. Metallicity, Activity, Binarity, and Subsubgiants |
| title_fullStr | Rotationally Driven Ultraviolet Emission of Red Giant Stars. II. Metallicity, Activity, Binarity, and Subsubgiants |
| title_full_unstemmed | Rotationally Driven Ultraviolet Emission of Red Giant Stars. II. Metallicity, Activity, Binarity, and Subsubgiants |
| title_short | Rotationally Driven Ultraviolet Emission of Red Giant Stars. II. Metallicity, Activity, Binarity, and Subsubgiants |
| title_sort | rotationally driven ultraviolet emission of red giant stars ii metallicity activity binarity and subsubgiants |
| topic | Giant stars Stellar rotation Stellar activity Binary stars |
| url | https://doi.org/10.3847/1538-3881/adc92a |
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