Absolute Ca II H and K and H-alpha flux measurements of low-mass stars
- Autor(en)
- C.~J. Marvin, A. Reiners, G. Anglada-Escudé, S.~V. Jeffers, S. Boro Saikia
- Abstrakt
Context. With the recent surge of planetary surveys focusing on detecting Earth-mass planets around M dwarfs, it is becoming more important to understand chromospheric activity in M dwarfs. Stellar chromospheric calcium emission is typically measured using the R' HK calibrations of Noyes et al. (1984), which are only valid for 0.44 ≤ B - V ≤ 0.82. Measurements of calcium emission for cooler dwarfs B - V = 0.82 are diffcult because of their intrinsic dimness in the blue end of the visible spectrum. Aims. We measure the absolute Ca II H and K and Ha Rflux of a sample of 110 HARPS M dwarfs and also extend the calibration of R' HK to the M dwarf regime using PHOENIX stellar atmosphere models. Methods. We normalized a template spectrum with a high signal-to-noise ratio that was obtained by coadding multiple spectra of the same star to a PHOENIX stellar atmosphere model to measure the chromospheric Ca II H and K and Hα flux in physical units. We used three different Teff calibrations and investigated their effect on Ca II H and K and Ha activity measurements. We performed conversions of the Mount Wilson S index to R' HK as a function of effective temperature for the range 2300 K = Teff = 7200 K. Last, we calculated continuum luminosity x values for Ca II H & K and Ha in the same manner as West & Hawley (2008) for -1.0 = [Fe/H] = +1.0 in steps of [Fe/H] = 0.5. Results. We compare different Teff calibrations and find Teff ∼ several 100 K for mid- to late-M dwarfs. Using these different Teff calibrations, we establish a catalog of log R' HK and FH'a/Fbol measurements for 110 HARPS M dwarfs. The difference between our results and the calibrations of Noyes et al. (1984) is δ log R' HK = 0.01 dex for a Sun-like star. Our values agree well with those of West and Hawley (2008). We confrm that the lower boundary of chromospheric Ca II H and K activity does not increase toward later-M dwarfs: it either stays constant or decreases, depending on the Teff calibration used. We also confrm that for Ha, the lower boundary of chromospheric ?ux is in absorption for earlier -M dwarfs and flls into the continuum toward later M dwarfs. Conclusions. We confrm that we can effectively measure R' HK in M dwarfs using template spectra with a high signal-to-noise ratio. We also conclude that our calibrations are a reliable extension of previous R' HK calibrations, and effective temperature calibration is the main source of error in our activity measurements.
- Organisation(en)
- Institut für Astrophysik
- Externe Organisation(en)
- Georg-August-Universität Göttingen, Max-Planck-Institut für Sonnensystemforschung
- Journal
- Astronomy & Astrophysics
- Band
- 671
- Anzahl der Seiten
- 26
- ISSN
- 0004-6361
- DOI
- https://doi.org/10.1051/0004-6361/201937306
- Publikationsdatum
- 03-2023
- Peer-reviewed
- Ja
- ÖFOS 2012
- 103004 Astrophysik, 103003 Astronomie
- Schlagwörter
- ASJC Scopus Sachgebiete
- Astronomy and Astrophysics, Space and Planetary Science
- Link zum Portal
- https://ucrisportal.univie.ac.at/de/publications/c0f9fd62-125f-4096-89f7-a1e35117aac5