Quantifying the Transit Light Source Effect: Measurements of Spot Temperature and Coverage on the Photosphere of AU Microscopii with High-resolution Spectroscopy and Multicolor Photometry
AU Microscopii (AU Mic) is an active 24 ± 3 Myr pre-main-sequence M dwarf in the stellar neighborhood ( d = 9.7 pc) with a rotation period of 4.86 days. The two transiting planets orbiting AU Mic, AU Mic b and c, are warm sub-Neptunes on 8.5 and 18.9 day periods and are targets of interest for atmos...
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| Format: | Article |
| Language: | English |
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IOP Publishing
2024-01-01
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| Series: | The Astrophysical Journal |
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| Online Access: | https://doi.org/10.3847/1538-4357/ad0bed |
| _version_ | 1797319192812191744 |
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| author | William C. Waalkes Zachory K. Berta-Thompson Elisabeth R. Newton Andrew W. Mann Peter Gao Hannah R. Wakeford Lili Alderson Peter Plavchan |
| author_facet | William C. Waalkes Zachory K. Berta-Thompson Elisabeth R. Newton Andrew W. Mann Peter Gao Hannah R. Wakeford Lili Alderson Peter Plavchan |
| author_sort | William C. Waalkes |
| collection | DOAJ |
| description | AU Microscopii (AU Mic) is an active 24 ± 3 Myr pre-main-sequence M dwarf in the stellar neighborhood ( d = 9.7 pc) with a rotation period of 4.86 days. The two transiting planets orbiting AU Mic, AU Mic b and c, are warm sub-Neptunes on 8.5 and 18.9 day periods and are targets of interest for atmospheric observations of young planets. Here we study AU Mic’s unocculted starspots using ground-based photometry and spectra in order to complement current and future transmission spectroscopy of its planets. We gathered multicolor Las Cumbres Observatory (LCO) 0.4 m SBIG photometry to study the star's rotational modulations and LCO Network of Robotic Echelle Spectrographs high-resolution spectra to measure the different spectral components within the integrated spectrum of the star, parameterized by three spectral components and their coverage fractions. We find AU Mic’s surface has at least two spectral components: a T _amb = ${4003}_{-14}^{+15}$ K ambient photosphere and cool spots that have a temperature of T _spot = ${3003}_{-71}^{+63}$ K, covering a globally averaged area of 39% ± 4% which increases and decreases by 5.1% ± 0.3% from the average throughout a rotation. We also detect a third flux component with a filling factor less than 0.5% and a largely uncertain temperature between 8500 and 10,000 K that we attribute to flare flux not entirely omitted when time averaging the spectra. We include measurements of spot characteristics using a two-temperature model, which we find agree strongly with the three-temperature results. Our expanded use of various techniques to study starspots will help us better understand this system and may have applications for interpreting the transmission spectra for exoplanets transiting stars of a wide range of activity levels. |
| first_indexed | 2024-03-08T04:03:18Z |
| format | Article |
| id | doaj.art-1e1c00a1a23c40d59c1c33eafb110dad |
| institution | Directory Open Access Journal |
| issn | 1538-4357 |
| language | English |
| last_indexed | 2024-03-08T04:03:18Z |
| publishDate | 2024-01-01 |
| publisher | IOP Publishing |
| record_format | Article |
| series | The Astrophysical Journal |
| spelling | doaj.art-1e1c00a1a23c40d59c1c33eafb110dad2024-02-09T10:27:12ZengIOP PublishingThe Astrophysical Journal1538-43572024-01-0196219710.3847/1538-4357/ad0bedQuantifying the Transit Light Source Effect: Measurements of Spot Temperature and Coverage on the Photosphere of AU Microscopii with High-resolution Spectroscopy and Multicolor PhotometryWilliam C. Waalkes0https://orcid.org/0000-0002-8961-0352Zachory K. Berta-Thompson1https://orcid.org/0000-0002-3321-4924Elisabeth R. Newton2https://orcid.org/0000-0003-4150-841XAndrew W. Mann3https://orcid.org/0000-0003-3654-1602Peter Gao4https://orcid.org/0000-0002-8518-9601Hannah R. Wakeford5https://orcid.org/0000-0003-4328-3867Lili Alderson6https://orcid.org/0000-0001-8703-7751Peter Plavchan7https://orcid.org/0000-0002-8864-1667Department of Astrophysical & Planetary Sciences, University of Colorado Boulder , 2000 Colorado Ave., Boulder, CO 80309, USA; Department of Physics and Astronomy, Dartmouth College , Hanover, NH 03755, USADepartment of Astrophysical & Planetary Sciences, University of Colorado Boulder , 2000 Colorado Ave., Boulder, CO 80309, USADepartment of Physics and Astronomy, Dartmouth College , Hanover, NH 03755, USADepartment of Physics and Astronomy, The University of North Carolina at Chapel Hill , Chapel Hill, NC 27599-3255, USAEarth and Planets Laboratory, Carnegie Institute of Washington , Washington, DC, USASchool of Physics, University of Bristol , Bristol, UKSchool of Physics, University of Bristol , Bristol, UKDepartment of Physics and Astronomy, George Mason University , Fairfax, VA 22030, USAAU Microscopii (AU Mic) is an active 24 ± 3 Myr pre-main-sequence M dwarf in the stellar neighborhood ( d = 9.7 pc) with a rotation period of 4.86 days. The two transiting planets orbiting AU Mic, AU Mic b and c, are warm sub-Neptunes on 8.5 and 18.9 day periods and are targets of interest for atmospheric observations of young planets. Here we study AU Mic’s unocculted starspots using ground-based photometry and spectra in order to complement current and future transmission spectroscopy of its planets. We gathered multicolor Las Cumbres Observatory (LCO) 0.4 m SBIG photometry to study the star's rotational modulations and LCO Network of Robotic Echelle Spectrographs high-resolution spectra to measure the different spectral components within the integrated spectrum of the star, parameterized by three spectral components and their coverage fractions. We find AU Mic’s surface has at least two spectral components: a T _amb = ${4003}_{-14}^{+15}$ K ambient photosphere and cool spots that have a temperature of T _spot = ${3003}_{-71}^{+63}$ K, covering a globally averaged area of 39% ± 4% which increases and decreases by 5.1% ± 0.3% from the average throughout a rotation. We also detect a third flux component with a filling factor less than 0.5% and a largely uncertain temperature between 8500 and 10,000 K that we attribute to flare flux not entirely omitted when time averaging the spectra. We include measurements of spot characteristics using a two-temperature model, which we find agree strongly with the three-temperature results. Our expanded use of various techniques to study starspots will help us better understand this system and may have applications for interpreting the transmission spectra for exoplanets transiting stars of a wide range of activity levels.https://doi.org/10.3847/1538-4357/ad0bedStarspotsM dwarf starsPre-main sequence starsStellar rotationExoplanet atmospheresTransits |
| spellingShingle | William C. Waalkes Zachory K. Berta-Thompson Elisabeth R. Newton Andrew W. Mann Peter Gao Hannah R. Wakeford Lili Alderson Peter Plavchan Quantifying the Transit Light Source Effect: Measurements of Spot Temperature and Coverage on the Photosphere of AU Microscopii with High-resolution Spectroscopy and Multicolor Photometry The Astrophysical Journal Starspots M dwarf stars Pre-main sequence stars Stellar rotation Exoplanet atmospheres Transits |
| title | Quantifying the Transit Light Source Effect: Measurements of Spot Temperature and Coverage on the Photosphere of AU Microscopii with High-resolution Spectroscopy and Multicolor Photometry |
| title_full | Quantifying the Transit Light Source Effect: Measurements of Spot Temperature and Coverage on the Photosphere of AU Microscopii with High-resolution Spectroscopy and Multicolor Photometry |
| title_fullStr | Quantifying the Transit Light Source Effect: Measurements of Spot Temperature and Coverage on the Photosphere of AU Microscopii with High-resolution Spectroscopy and Multicolor Photometry |
| title_full_unstemmed | Quantifying the Transit Light Source Effect: Measurements of Spot Temperature and Coverage on the Photosphere of AU Microscopii with High-resolution Spectroscopy and Multicolor Photometry |
| title_short | Quantifying the Transit Light Source Effect: Measurements of Spot Temperature and Coverage on the Photosphere of AU Microscopii with High-resolution Spectroscopy and Multicolor Photometry |
| title_sort | quantifying the transit light source effect measurements of spot temperature and coverage on the photosphere of au microscopii with high resolution spectroscopy and multicolor photometry |
| topic | Starspots M dwarf stars Pre-main sequence stars Stellar rotation Exoplanet atmospheres Transits |
| url | https://doi.org/10.3847/1538-4357/ad0bed |
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