Nonthermal Motions and Atmospheric Heating of Cool Stars
The magnetic processes associated with the nonthermal broadening of optically thin emission lines appear to carry enough energy to heat the corona and accelerate the solar wind. We investigate whether nonthermal motions in cool stars exhibit the same behavior as on the Sun by analyzing archival stel...
| 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 |
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| Online Access: | https://doi.org/10.3847/1538-4357/acca14 |
| _version_ | 1797699295757991936 |
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| author | S. Boro Saikia T. Lueftinger V. S. Airapetian T. Ayres M. Bartel M. Guedel M. Jin K. G. Kislyakova P. Testa |
| author_facet | S. Boro Saikia T. Lueftinger V. S. Airapetian T. Ayres M. Bartel M. Guedel M. Jin K. G. Kislyakova P. Testa |
| author_sort | S. Boro Saikia |
| collection | DOAJ |
| description | The magnetic processes associated with the nonthermal broadening of optically thin emission lines appear to carry enough energy to heat the corona and accelerate the solar wind. We investigate whether nonthermal motions in cool stars exhibit the same behavior as on the Sun by analyzing archival stellar spectra taken by the Hubble Space Telescope, and full-disk Solar spectra taken by the Interface Region Imaging Spectrograph. We determined the nonthermal velocities by measuring the excess broadening in optically thin emission lines formed in the stellar atmosphere; the chromosphere, the transition region, and the corona. Assuming the nonthermal broadening is caused by the presence of Alfvén waves, we also determined the associated wave energy densities. Our results show that with a nonthermal velocity of ∼23 km s ^−1 the Sun-as-a-star results are in very good agreement with values obtained from spatially resolved solar observations. The nonthermal broadening in our sample shows a correlation to stellar rotation, with the strength of the nonthermal velocity decreasing with decreasing rotation rate. Finally, the nonthermal velocity in cool Sun-like stars varies with atmospheric height or temperature of the emission lines, and peaks at transition region temperatures. This points toward a solar-like Alfvén wave-driven heating in stellar atmospheres. However, the peak is at a lower temperature in some cool stars suggesting that other magnetic processes such as flaring events could also dominate. |
| first_indexed | 2024-03-12T04:05:49Z |
| format | Article |
| id | doaj.art-9c94aaf02c164335813c61df34abda05 |
| institution | Directory Open Access Journal |
| issn | 1538-4357 |
| language | English |
| last_indexed | 2024-03-12T04:05:49Z |
| publishDate | 2023-01-01 |
| publisher | IOP Publishing |
| record_format | Article |
| series | The Astrophysical Journal |
| spelling | doaj.art-9c94aaf02c164335813c61df34abda052023-09-03T11:18:50ZengIOP PublishingThe Astrophysical Journal1538-43572023-01-01950212410.3847/1538-4357/acca14Nonthermal Motions and Atmospheric Heating of Cool StarsS. Boro Saikia0https://orcid.org/0000-0002-3673-3746T. Lueftinger1V. S. Airapetian2https://orcid.org/0000-0003-4452-0588T. Ayres3https://orcid.org/0000-0002-1242-5124M. Bartel4M. Guedel5https://orcid.org/0000-0001-9818-0588M. Jin6https://orcid.org/0000-0002-9672-3873K. G. Kislyakova7https://orcid.org/0000-0003-4680-6774P. Testa8https://orcid.org/0000-0002-0405-0668University of Vienna , Department of Astrophysics, Türkenschanzstrasse 17, A-1180 Vienna, Austria ; sudeshna.boro.saikia@univie.ac.atEuropean Space Agency, European Space Research and Technology Centre , Keplerlaan 1, 2201-AZ Noordwijk, The NetherlandsNASA Goddard Space Flight Center , Greenbelt, MD USA; American University , Washington, DC, USACenter for Astrophysics and Space Astronomy, 389 UCB, University of Colorado , Boulder, CO 80309, USAUniversity of Vienna , Department of Astrophysics, Türkenschanzstrasse 17, A-1180 Vienna, Austria ; sudeshna.boro.saikia@univie.ac.atUniversity of Vienna , Department of Astrophysics, Türkenschanzstrasse 17, A-1180 Vienna, Austria ; sudeshna.boro.saikia@univie.ac.atLockheed Martin Solar and Astrophysics Lab (LMSAL) , Palo Alto, CA 94304, USAUniversity of Vienna , Department of Astrophysics, Türkenschanzstrasse 17, A-1180 Vienna, Austria ; sudeshna.boro.saikia@univie.ac.atHarvard-Smithsonian Center for Astrophysics , 60 Garden St, Cambridge, MA 02193, USAThe magnetic processes associated with the nonthermal broadening of optically thin emission lines appear to carry enough energy to heat the corona and accelerate the solar wind. We investigate whether nonthermal motions in cool stars exhibit the same behavior as on the Sun by analyzing archival stellar spectra taken by the Hubble Space Telescope, and full-disk Solar spectra taken by the Interface Region Imaging Spectrograph. We determined the nonthermal velocities by measuring the excess broadening in optically thin emission lines formed in the stellar atmosphere; the chromosphere, the transition region, and the corona. Assuming the nonthermal broadening is caused by the presence of Alfvén waves, we also determined the associated wave energy densities. Our results show that with a nonthermal velocity of ∼23 km s ^−1 the Sun-as-a-star results are in very good agreement with values obtained from spatially resolved solar observations. The nonthermal broadening in our sample shows a correlation to stellar rotation, with the strength of the nonthermal velocity decreasing with decreasing rotation rate. Finally, the nonthermal velocity in cool Sun-like stars varies with atmospheric height or temperature of the emission lines, and peaks at transition region temperatures. This points toward a solar-like Alfvén wave-driven heating in stellar atmospheres. However, the peak is at a lower temperature in some cool stars suggesting that other magnetic processes such as flaring events could also dominate.https://doi.org/10.3847/1538-4357/acca14Stellar atmospheresStellar winds |
| spellingShingle | S. Boro Saikia T. Lueftinger V. S. Airapetian T. Ayres M. Bartel M. Guedel M. Jin K. G. Kislyakova P. Testa Nonthermal Motions and Atmospheric Heating of Cool Stars The Astrophysical Journal Stellar atmospheres Stellar winds |
| title | Nonthermal Motions and Atmospheric Heating of Cool Stars |
| title_full | Nonthermal Motions and Atmospheric Heating of Cool Stars |
| title_fullStr | Nonthermal Motions and Atmospheric Heating of Cool Stars |
| title_full_unstemmed | Nonthermal Motions and Atmospheric Heating of Cool Stars |
| title_short | Nonthermal Motions and Atmospheric Heating of Cool Stars |
| title_sort | nonthermal motions and atmospheric heating of cool stars |
| topic | Stellar atmospheres Stellar winds |
| url | https://doi.org/10.3847/1538-4357/acca14 |
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