The Cycles of Alpha Centauri: Double Dipping of AB
In mid-2023, the Sunlike dwarfs of nearby α Centauri (HD 128620 (“A”): G2 V; HD 128621 (“B”): K1 V; hereafter “AB”) coincidentally both entered coronal ( T ≈ 1–3 MK) low states in their long-term X-ray cycles, as captured by the Chandra Observatory and its High Resolution Camera (HRC-I). The assessm...
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| Format: | Article |
| Language: | English |
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IOP Publishing
2023-01-01
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| Series: | The Astronomical Journal |
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| Online Access: | https://doi.org/10.3847/1538-3881/acfef5 |
| _version_ | 1797643217197334528 |
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| author | Thomas Ayres |
| author_facet | Thomas Ayres |
| author_sort | Thomas Ayres |
| collection | DOAJ |
| description | In mid-2023, the Sunlike dwarfs of nearby α Centauri (HD 128620 (“A”): G2 V; HD 128621 (“B”): K1 V; hereafter “AB”) coincidentally both entered coronal ( T ≈ 1–3 MK) low states in their long-term X-ray cycles, as captured by the Chandra Observatory and its High Resolution Camera (HRC-I). The assessment benefited from a sensitivity degradation model for HRC-I based on a “check star,” the F subgiant Procyon ( α Canis Minoris A; HD 61421: F5 IV–V), further validated by Hubble Space Telescope time series of the Fe xii 1241.985 Å and 1349.396 Å coronal forbidden lines ( T ≈ 1.6 MK) of all three stars. The AB starspot-cycle periods noted previously, 19 and 8 yr, appear to be holding. These deviate substantially from the 11 yr solar example, despite only modest differences in the stellar properties. The new cycle-minimum L _X / L _BOL of α Cen A is similar to that of the previous minimum observed by Chandra in 2005–2010, and close to solar-MIN X-ray levels in 2009 and 2019, with implications for the “basal” coronal flux of low-activity early G stars. The recent α Cen B X-ray MIN is similar to that in 2016 but higher than an earlier one in 2007–2009. Significantly, the B X-ray minima (in L _X / L _BOL ) are comparable to the solar Cycle 24 maximum, suggesting plentiful starspots at the B-cycle MIN (contrary to the solar case). Tangentially, the current AB low states favor Doppler-reflex detections of planets, as opposed to the coronal high states, when elevated chromospheric activity can add nuisance signals to radial velocity time series. |
| first_indexed | 2024-03-11T14:12:24Z |
| format | Article |
| id | doaj.art-9ea499fae78c4c839a008d34125b1f82 |
| institution | Directory Open Access Journal |
| issn | 1538-3881 |
| language | English |
| last_indexed | 2024-03-11T14:12:24Z |
| publishDate | 2023-01-01 |
| publisher | IOP Publishing |
| record_format | Article |
| series | The Astronomical Journal |
| spelling | doaj.art-9ea499fae78c4c839a008d34125b1f822023-11-01T19:15:46ZengIOP PublishingThe Astronomical Journal1538-38812023-01-01166521210.3847/1538-3881/acfef5The Cycles of Alpha Centauri: Double Dipping of ABThomas Ayres0https://orcid.org/0000-0002-1242-5124Center for Astrophysics and Space Astronomy, 389 UCB, University of Colorado , Boulder, CO 80309, USA ; Thomas.Ayres@Colorado.eduIn mid-2023, the Sunlike dwarfs of nearby α Centauri (HD 128620 (“A”): G2 V; HD 128621 (“B”): K1 V; hereafter “AB”) coincidentally both entered coronal ( T ≈ 1–3 MK) low states in their long-term X-ray cycles, as captured by the Chandra Observatory and its High Resolution Camera (HRC-I). The assessment benefited from a sensitivity degradation model for HRC-I based on a “check star,” the F subgiant Procyon ( α Canis Minoris A; HD 61421: F5 IV–V), further validated by Hubble Space Telescope time series of the Fe xii 1241.985 Å and 1349.396 Å coronal forbidden lines ( T ≈ 1.6 MK) of all three stars. The AB starspot-cycle periods noted previously, 19 and 8 yr, appear to be holding. These deviate substantially from the 11 yr solar example, despite only modest differences in the stellar properties. The new cycle-minimum L _X / L _BOL of α Cen A is similar to that of the previous minimum observed by Chandra in 2005–2010, and close to solar-MIN X-ray levels in 2009 and 2019, with implications for the “basal” coronal flux of low-activity early G stars. The recent α Cen B X-ray MIN is similar to that in 2016 but higher than an earlier one in 2007–2009. Significantly, the B X-ray minima (in L _X / L _BOL ) are comparable to the solar Cycle 24 maximum, suggesting plentiful starspots at the B-cycle MIN (contrary to the solar case). Tangentially, the current AB low states favor Doppler-reflex detections of planets, as opposed to the coronal high states, when elevated chromospheric activity can add nuisance signals to radial velocity time series.https://doi.org/10.3847/1538-3881/acfef5X-ray telescopesSingle x-ray starsUltraviolet spectroscopyUltraviolet sourcesUltraviolet telescopesStarspots |
| spellingShingle | Thomas Ayres The Cycles of Alpha Centauri: Double Dipping of AB The Astronomical Journal X-ray telescopes Single x-ray stars Ultraviolet spectroscopy Ultraviolet sources Ultraviolet telescopes Starspots |
| title | The Cycles of Alpha Centauri: Double Dipping of AB |
| title_full | The Cycles of Alpha Centauri: Double Dipping of AB |
| title_fullStr | The Cycles of Alpha Centauri: Double Dipping of AB |
| title_full_unstemmed | The Cycles of Alpha Centauri: Double Dipping of AB |
| title_short | The Cycles of Alpha Centauri: Double Dipping of AB |
| title_sort | cycles of alpha centauri double dipping of ab |
| topic | X-ray telescopes Single x-ray stars Ultraviolet spectroscopy Ultraviolet sources Ultraviolet telescopes Starspots |
| url | https://doi.org/10.3847/1538-3881/acfef5 |
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