A Long-duration Superflare on the K Giant HD 251108
Many giant stars are magnetically active, which causes rotational variability, chromospheric emission lines, and X-ray emission. Large outbursts in these emission features can set limits on the magnetic field strength and thus constrain the mechanism of the underlying dynamo. HD 251108 is a Li-rich...
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2024-01-01
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| Series: | The Astrophysical Journal |
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| Online Access: | https://doi.org/10.3847/1538-4357/ad8b2c |
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| author | Hans Moritz Günther Dheeraj Pasham Alexander Binks Stefan Czesla Teruaki Enoto Michael Fausnaugh Franz-Josef Hambsch Shun Inoue Hiroyuki Maehara Yuta Notsu Jan Robrade J. H. M. M. Schmitt P. C. Schneider |
| author_facet | Hans Moritz Günther Dheeraj Pasham Alexander Binks Stefan Czesla Teruaki Enoto Michael Fausnaugh Franz-Josef Hambsch Shun Inoue Hiroyuki Maehara Yuta Notsu Jan Robrade J. H. M. M. Schmitt P. C. Schneider |
| author_sort | Hans Moritz Günther |
| collection | DOAJ |
| description | Many giant stars are magnetically active, which causes rotational variability, chromospheric emission lines, and X-ray emission. Large outbursts in these emission features can set limits on the magnetic field strength and thus constrain the mechanism of the underlying dynamo. HD 251108 is a Li-rich active K-type giant. We find a rotational period of 21.3 days with color changes and additional long-term photometric variability. Both can be explained with very stable stellar spots. We followed the decay phase of a superflare for 28 days with NICER and from the ground. We track the flare decay in unprecedented detail in several coronal temperature components. With a peak flux around 10 ^34 erg s ^−1 (0.5–4.0 keV) and an exponential decay time of 2.2 days in the early decay phase, this is one of the strongest flares ever observed, yet it follows trends established from samples of smaller flares, for example, for the relations between H α and X-ray flux, indicating that the physical process that powers the flare emission is consistent over a large range of flare energies. We estimate a flare loop length about 2–4 times the stellar radius. No evidence is seen for abundance changes during the flare. |
| format | Article |
| id | doaj-art-4a05090a9bd444a8ae5862fdcb4f0fdb |
| institution | OA Journals |
| issn | 1538-4357 |
| language | English |
| publishDate | 2024-01-01 |
| publisher | IOP Publishing |
| record_format | Article |
| series | The Astrophysical Journal |
| spelling | doaj-art-4a05090a9bd444a8ae5862fdcb4f0fdb2025-08-20T01:54:18ZengIOP PublishingThe Astrophysical Journal1538-43572024-01-019771610.3847/1538-4357/ad8b2cA Long-duration Superflare on the K Giant HD 251108Hans Moritz Günther0https://orcid.org/0000-0003-4243-2840Dheeraj Pasham1https://orcid.org/0000-0003-1386-7861Alexander Binks2https://orcid.org/0000-0001-5976-4644Stefan Czesla3https://orcid.org/0000-0002-4203-4773Teruaki Enoto4https://orcid.org/0000-0003-1244-3100Michael Fausnaugh5https://orcid.org/0000-0002-9113-7162Franz-Josef Hambsch6https://orcid.org/0000-0003-0125-8700Shun Inoue7https://orcid.org/0000-0003-3085-304XHiroyuki Maehara8https://orcid.org/0000-0003-0332-0811Yuta Notsu9https://orcid.org/0000-0002-0412-0849Jan Robrade10https://orcid.org/0000-0002-4939-8940J. H. M. M. Schmitt11https://orcid.org/0000-0003-2554-9916P. C. Schneider12https://orcid.org/0000-0002-5094-2245MIT Kavli Institute for Astrophysics and Space Research , 77 Massachusetts Avenue, Cambridge, MA 02139, USA ; hgunther@mit.eduMIT Kavli Institute for Astrophysics and Space Research , 77 Massachusetts Avenue, Cambridge, MA 02139, USA ; hgunther@mit.eduInstitut für Astronomie und Astrophysik, Eberhard-Karls Universität Tübingen , Sand 1, 72076 Tübingen, GermanyThüringer Landessternwarte Tautenburg , Sternwarte 5, 07778 Tautenburg, GermanyDepartment of Physics, Kyoto University , Sakyo, Kyoto 606-8502, Japan; RIKEN Cluster for Pioneering Research , 2-1 Hirosawa, Wako, Saitama 351-0198, JapanTexas Tech University , Department of Physics & Astronomy, Lubbock, TX 79409, USAVereniging Voor Sterrenkunde (VVS) , Oostmeers 122 C, 8000 Brugge, Belgium; AAVSO , 185 Alewife Brook Parkway, Suite 410, Cambridge, MA 02138, USA; Groupe Européen d’Observations Stellaires (GEOS) , 23 Parc de Levesville, 28300 Bailleau l’Evêque, France; Bundesdeutsche Arbeitsgemeinschaft für Veränderliche Sterne e.V. (BAV) , Munsterdamm 90, 12169 Berlin, GermanyDepartment of Physics, Kyoto University , Sakyo, Kyoto 606-8502, JapanOkayama Branch Office , Subaru Telescope, National Astronomical Observatory of Japan, NINS, Kamogata, Asakuchi, Okayama 719-0232, JapanLaboratory for Atmospheric and Space Physics, University of Colorado Boulder , 3665 Discovery Drive, Boulder, CO 80303, USA; National Solar Observatory , 3665 Discovery Drive, Boulder, CO 80303, USAHamburger Sternwarte, University of Hamburg , Gojenbergsweg 112, 21029 Hamburg, GermanyHamburger Sternwarte, University of Hamburg , Gojenbergsweg 112, 21029 Hamburg, GermanyHamburger Sternwarte, University of Hamburg , Gojenbergsweg 112, 21029 Hamburg, GermanyMany giant stars are magnetically active, which causes rotational variability, chromospheric emission lines, and X-ray emission. Large outbursts in these emission features can set limits on the magnetic field strength and thus constrain the mechanism of the underlying dynamo. HD 251108 is a Li-rich active K-type giant. We find a rotational period of 21.3 days with color changes and additional long-term photometric variability. Both can be explained with very stable stellar spots. We followed the decay phase of a superflare for 28 days with NICER and from the ground. We track the flare decay in unprecedented detail in several coronal temperature components. With a peak flux around 10 ^34 erg s ^−1 (0.5–4.0 keV) and an exponential decay time of 2.2 days in the early decay phase, this is one of the strongest flares ever observed, yet it follows trends established from samples of smaller flares, for example, for the relations between H α and X-ray flux, indicating that the physical process that powers the flare emission is consistent over a large range of flare energies. We estimate a flare loop length about 2–4 times the stellar radius. No evidence is seen for abundance changes during the flare.https://doi.org/10.3847/1538-4357/ad8b2cStellar x-ray flaresK giant starsRed giant clumpStellar flaresStellar coronae |
| spellingShingle | Hans Moritz Günther Dheeraj Pasham Alexander Binks Stefan Czesla Teruaki Enoto Michael Fausnaugh Franz-Josef Hambsch Shun Inoue Hiroyuki Maehara Yuta Notsu Jan Robrade J. H. M. M. Schmitt P. C. Schneider A Long-duration Superflare on the K Giant HD 251108 The Astrophysical Journal Stellar x-ray flares K giant stars Red giant clump Stellar flares Stellar coronae |
| title | A Long-duration Superflare on the K Giant HD 251108 |
| title_full | A Long-duration Superflare on the K Giant HD 251108 |
| title_fullStr | A Long-duration Superflare on the K Giant HD 251108 |
| title_full_unstemmed | A Long-duration Superflare on the K Giant HD 251108 |
| title_short | A Long-duration Superflare on the K Giant HD 251108 |
| title_sort | long duration superflare on the k giant hd 251108 |
| topic | Stellar x-ray flares K giant stars Red giant clump Stellar flares Stellar coronae |
| url | https://doi.org/10.3847/1538-4357/ad8b2c |
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