Constraints on Magnetic Braking from the G8 Dwarf Stars 61 UMa and τ Cet
During the first half of their main-sequence lifetimes, stars rapidly lose angular momentum to their magnetized winds, a process known as magnetic braking. Recent observations suggest a substantial decrease in the magnetic braking efficiency when stars reach a critical value of the Rossby number, th...
| Main Authors: | , , , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
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IOP Publishing
2023-01-01
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| Series: | The Astrophysical Journal Letters |
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| Online Access: | https://doi.org/10.3847/2041-8213/acce38 |
| _version_ | 1797696142892335104 |
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| author | Travis S. Metcalfe Klaus G. Strassmeier Ilya V. Ilyin Jennifer L. van Saders Thomas R. Ayres Adam J. Finley Oleg Kochukhov Pascal Petit Victor See Keivan G. Stassun Sandra V. Jeffers Stephen C. Marsden Julien Morin Aline A. Vidotto |
| author_facet | Travis S. Metcalfe Klaus G. Strassmeier Ilya V. Ilyin Jennifer L. van Saders Thomas R. Ayres Adam J. Finley Oleg Kochukhov Pascal Petit Victor See Keivan G. Stassun Sandra V. Jeffers Stephen C. Marsden Julien Morin Aline A. Vidotto |
| author_sort | Travis S. Metcalfe |
| collection | DOAJ |
| description | During the first half of their main-sequence lifetimes, stars rapidly lose angular momentum to their magnetized winds, a process known as magnetic braking. Recent observations suggest a substantial decrease in the magnetic braking efficiency when stars reach a critical value of the Rossby number, the stellar rotation period normalized by the convective overturn timescale. Cooler stars have deeper convection zones with longer overturn times, reaching this critical Rossby number at slower rotation rates. The nature and timing of the transition to weakened magnetic braking have previously been constrained by several solar analogs and two slightly hotter stars. In this Letter, we derive the first direct constraints from stars cooler than the Sun. We present new spectropolarimetry of the old G8 dwarf τ Cet from the Large Binocular Telescope, and we reanalyze a published Zeeman Doppler image of the younger G8 star 61 UMa, yielding the large-scale magnetic field strengths and morphologies. We estimate mass-loss rates using archival X-ray observations and inferences from Ly α measurements, and we adopt other stellar properties from asteroseismology and spectral energy distribution fitting. The resulting calculations of the wind braking torque demonstrate that the rate of angular momentum loss drops by a factor of 300 between the ages of these two stars (1.4–9 Gyr), well above theoretical expectations. We summarize the available data to help constrain the value of the critical Rossby number, and we identify a new signature of the long-period detection edge in recent measurements from the Kepler mission. |
| first_indexed | 2024-03-12T03:22:27Z |
| format | Article |
| id | doaj.art-a3a09f0e714f4e8ebaaae620aaaee3dd |
| institution | Directory Open Access Journal |
| issn | 2041-8205 |
| language | English |
| last_indexed | 2024-03-12T03:22:27Z |
| publishDate | 2023-01-01 |
| publisher | IOP Publishing |
| record_format | Article |
| series | The Astrophysical Journal Letters |
| spelling | doaj.art-a3a09f0e714f4e8ebaaae620aaaee3dd2023-09-03T13:52:03ZengIOP PublishingThe Astrophysical Journal Letters2041-82052023-01-019481L610.3847/2041-8213/acce38Constraints on Magnetic Braking from the G8 Dwarf Stars 61 UMa and τ CetTravis S. Metcalfe0https://orcid.org/0000-0003-4034-0416Klaus G. Strassmeier1https://orcid.org/0000-0002-6192-6494Ilya V. Ilyin2https://orcid.org/0000-0002-0551-046XJennifer L. van Saders3https://orcid.org/0000-0002-4284-8638Thomas R. Ayres4https://orcid.org/0000-0002-1242-5124Adam J. Finley5https://orcid.org/0000-0002-3020-9409Oleg Kochukhov6https://orcid.org/0000-0003-3061-4591Pascal Petit7https://orcid.org/0000-0001-7624-9222Victor See8https://orcid.org/0000-0001-5986-3423Keivan G. Stassun9https://orcid.org/0000-0002-3481-9052Sandra V. Jeffers10https://orcid.org/0000-0003-2490-4779Stephen C. Marsden11https://orcid.org/0000-0001-5522-8887Julien Morin12https://orcid.org/0000-0002-4996-6901Aline A. Vidotto13https://orcid.org/0000-0001-5371-2675White Dwarf Research Corporation , 9020 Brumm Trail, Golden, CO 80403, USA ; travis@wdrc.orgLeibniz-Institut für Astrophysik Potsdam (AIP) , An der Sternwarte 16, D-14482 Potsdam, GermanyLeibniz-Institut für Astrophysik Potsdam (AIP) , An der Sternwarte 16, D-14482 Potsdam, GermanyInstitute for Astronomy, University of Hawaií , 2680 Woodlawn Drive, Honolulu, HI 96822, USACenter for Astrophysics and Space Astronomy, 389 UCB, University of Colorado , Boulder, CO 80309, USADepartment of Astrophysics-AIM, University of Paris-Saclay and University of Paris , CEA, CNRS, Gif-sur-Yvette Cedex F-91191, FranceDepartment of Physics and Astronomy, Uppsala University , Box 516, SE-75120 Uppsala, SwedenUniversité de Toulouse , CNRS, CNES, 14 avenue Edouard Belin, F-31400, Toulouse, FranceEuropean Space Agency (ESA) , European Space Research and Technology Centre (ESTEC), Keplerlaan 1, 2201 AZ Noordwijk, The NetherlandsVanderbilt University , Department of Physics & Astronomy, 6301 Stevenson Center Lane, Nashville, TN 37235, USAMax-Planck-Institut für Sonnensystemforschung , Justus-von-Liebig-weg 3, D-37077, Göttingen, GermanyCentre for Astrophysics, University of Southern Queensland , Toowoomba, Queensland, 4350, AustraliaCentre national de la recherche scientifique (CNRS), Université de Montpellier , Place Eugène Bataillon, F-34095, Montpellier, FranceLeiden Observatory, Leiden University , PO Box 9513, 2300 RA, Leiden, The NetherlandsDuring the first half of their main-sequence lifetimes, stars rapidly lose angular momentum to their magnetized winds, a process known as magnetic braking. Recent observations suggest a substantial decrease in the magnetic braking efficiency when stars reach a critical value of the Rossby number, the stellar rotation period normalized by the convective overturn timescale. Cooler stars have deeper convection zones with longer overturn times, reaching this critical Rossby number at slower rotation rates. The nature and timing of the transition to weakened magnetic braking have previously been constrained by several solar analogs and two slightly hotter stars. In this Letter, we derive the first direct constraints from stars cooler than the Sun. We present new spectropolarimetry of the old G8 dwarf τ Cet from the Large Binocular Telescope, and we reanalyze a published Zeeman Doppler image of the younger G8 star 61 UMa, yielding the large-scale magnetic field strengths and morphologies. We estimate mass-loss rates using archival X-ray observations and inferences from Ly α measurements, and we adopt other stellar properties from asteroseismology and spectral energy distribution fitting. The resulting calculations of the wind braking torque demonstrate that the rate of angular momentum loss drops by a factor of 300 between the ages of these two stars (1.4–9 Gyr), well above theoretical expectations. We summarize the available data to help constrain the value of the critical Rossby number, and we identify a new signature of the long-period detection edge in recent measurements from the Kepler mission.https://doi.org/10.3847/2041-8213/acce38SpectropolarimetryStellar evolutionStellar magnetic fieldsStellar rotationStellar winds |
| spellingShingle | Travis S. Metcalfe Klaus G. Strassmeier Ilya V. Ilyin Jennifer L. van Saders Thomas R. Ayres Adam J. Finley Oleg Kochukhov Pascal Petit Victor See Keivan G. Stassun Sandra V. Jeffers Stephen C. Marsden Julien Morin Aline A. Vidotto Constraints on Magnetic Braking from the G8 Dwarf Stars 61 UMa and τ Cet The Astrophysical Journal Letters Spectropolarimetry Stellar evolution Stellar magnetic fields Stellar rotation Stellar winds |
| title | Constraints on Magnetic Braking from the G8 Dwarf Stars 61 UMa and τ Cet |
| title_full | Constraints on Magnetic Braking from the G8 Dwarf Stars 61 UMa and τ Cet |
| title_fullStr | Constraints on Magnetic Braking from the G8 Dwarf Stars 61 UMa and τ Cet |
| title_full_unstemmed | Constraints on Magnetic Braking from the G8 Dwarf Stars 61 UMa and τ Cet |
| title_short | Constraints on Magnetic Braking from the G8 Dwarf Stars 61 UMa and τ Cet |
| title_sort | constraints on magnetic braking from the g8 dwarf stars 61 uma and τ cet |
| topic | Spectropolarimetry Stellar evolution Stellar magnetic fields Stellar rotation Stellar winds |
| url | https://doi.org/10.3847/2041-8213/acce38 |
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