Disentangling Stellar and Airglow Emission Lines from Hubble Space Telescope (HST) Cosmic Origins Spectrograph (COS) Spectra
H i Ly α (1215.67 Å) and the O i triplet (1302.17, 1304.86, and 1306.03 Å) are bright far-ultraviolet (FUV) emission lines that trace the stellar chromosphere. Observations of stellar Ly α and O i using the Hubble Space Telescope's (HST) most sensitive FUV spectrograph, the Cosmic Origins Spect...
| 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/acad7d |
| _version_ | 1827826766247362560 |
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| author | Fernando Cruz Aguirre Allison Youngblood Kevin France Vincent Bourrier |
| author_facet | Fernando Cruz Aguirre Allison Youngblood Kevin France Vincent Bourrier |
| author_sort | Fernando Cruz Aguirre |
| collection | DOAJ |
| description | H i Ly α (1215.67 Å) and the O i triplet (1302.17, 1304.86, and 1306.03 Å) are bright far-ultraviolet (FUV) emission lines that trace the stellar chromosphere. Observations of stellar Ly α and O i using the Hubble Space Telescope's (HST) most sensitive FUV spectrograph, the Cosmic Origins Spectrograph (COS), are contaminated with geocoronal emission, or airglow. This study demonstrates that airglow emission profiles as observed by COS are sufficiently stable to create airglow templates that can be reliably subtracted from the data, recovering the underlying stellar flux. We developed a graphical user interface to implement the airglow subtraction on a sample of 171 main-sequence F-, G-, K-, and M-type dwarfs from the COS data archive. Correlations between recovered stellar emission and measures of stellar activity were investigated. Several power-law relationships are presented for predicting the stellar Ly α and O i emission. The apparent brightness of the stellar emission relative to the airglow is a critical factor in the success or failure of an airglow subtraction. We developed a predictor for the success of an airglow subtraction using the signal-to-noise ratio of the nearby chromospheric emission line Si iii (1206.51 Å). The minimum attenuated Ly α flux that was successfully recovered is 1.39 × 10 ^−14 erg cm ^−2 s ^−1 , and we recommend this as a minimum flux for COS Ly α recoveries. |
| first_indexed | 2024-03-12T03:17:03Z |
| format | Article |
| id | doaj.art-7a6be17c60574f6299653002e18aa581 |
| institution | Directory Open Access Journal |
| issn | 1538-4357 |
| language | English |
| last_indexed | 2024-03-12T03:17:03Z |
| publishDate | 2023-01-01 |
| publisher | IOP Publishing |
| record_format | Article |
| series | The Astrophysical Journal |
| spelling | doaj.art-7a6be17c60574f6299653002e18aa5812023-09-03T14:08:26ZengIOP PublishingThe Astrophysical Journal1538-43572023-01-0194629810.3847/1538-4357/acad7dDisentangling Stellar and Airglow Emission Lines from Hubble Space Telescope (HST) Cosmic Origins Spectrograph (COS) SpectraFernando Cruz Aguirre0https://orcid.org/0000-0003-4628-8524Allison Youngblood1https://orcid.org/0000-0002-1176-3391Kevin France2https://orcid.org/0000-0002-1002-3674Vincent Bourrier3https://orcid.org/0000-0002-9148-034XLaboratory for Atmospheric and Space Physics, University of Colorado, 600 UCB , Boulder, CO 80309, USA ; edcr4756@colorado.eduNASA Goddard Space Flight Center, Greenbelt , MD 20771, USALaboratory for Atmospheric and Space Physics, University of Colorado, 600 UCB , Boulder, CO 80309, USA ; edcr4756@colorado.eduGeneva Observatory Versoix , SwitzerlandH i Ly α (1215.67 Å) and the O i triplet (1302.17, 1304.86, and 1306.03 Å) are bright far-ultraviolet (FUV) emission lines that trace the stellar chromosphere. Observations of stellar Ly α and O i using the Hubble Space Telescope's (HST) most sensitive FUV spectrograph, the Cosmic Origins Spectrograph (COS), are contaminated with geocoronal emission, or airglow. This study demonstrates that airglow emission profiles as observed by COS are sufficiently stable to create airglow templates that can be reliably subtracted from the data, recovering the underlying stellar flux. We developed a graphical user interface to implement the airglow subtraction on a sample of 171 main-sequence F-, G-, K-, and M-type dwarfs from the COS data archive. Correlations between recovered stellar emission and measures of stellar activity were investigated. Several power-law relationships are presented for predicting the stellar Ly α and O i emission. The apparent brightness of the stellar emission relative to the airglow is a critical factor in the success or failure of an airglow subtraction. We developed a predictor for the success of an airglow subtraction using the signal-to-noise ratio of the nearby chromospheric emission line Si iii (1206.51 Å). The minimum attenuated Ly α flux that was successfully recovered is 1.39 × 10 ^−14 erg cm ^−2 s ^−1 , and we recommend this as a minimum flux for COS Ly α recoveries.https://doi.org/10.3847/1538-4357/acad7dDwarf starsMain sequence starsHubble Space TelescopeUltraviolet spectroscopyStellar activity |
| spellingShingle | Fernando Cruz Aguirre Allison Youngblood Kevin France Vincent Bourrier Disentangling Stellar and Airglow Emission Lines from Hubble Space Telescope (HST) Cosmic Origins Spectrograph (COS) Spectra The Astrophysical Journal Dwarf stars Main sequence stars Hubble Space Telescope Ultraviolet spectroscopy Stellar activity |
| title | Disentangling Stellar and Airglow Emission Lines from Hubble Space Telescope (HST) Cosmic Origins Spectrograph (COS) Spectra |
| title_full | Disentangling Stellar and Airglow Emission Lines from Hubble Space Telescope (HST) Cosmic Origins Spectrograph (COS) Spectra |
| title_fullStr | Disentangling Stellar and Airglow Emission Lines from Hubble Space Telescope (HST) Cosmic Origins Spectrograph (COS) Spectra |
| title_full_unstemmed | Disentangling Stellar and Airglow Emission Lines from Hubble Space Telescope (HST) Cosmic Origins Spectrograph (COS) Spectra |
| title_short | Disentangling Stellar and Airglow Emission Lines from Hubble Space Telescope (HST) Cosmic Origins Spectrograph (COS) Spectra |
| title_sort | disentangling stellar and airglow emission lines from hubble space telescope hst cosmic origins spectrograph cos spectra |
| topic | Dwarf stars Main sequence stars Hubble Space Telescope Ultraviolet spectroscopy Stellar activity |
| url | https://doi.org/10.3847/1538-4357/acad7d |
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