Query : 2023A&A...671A.162M

2023A&A...671A.162M - Astronomy and Astrophysics, volume 671A, 162 (2023/3-1)

Absolute Ca II H & K and H-alpha flux measurements of low-mass stars: Extending R'HK to M dwarfs.


Abstract (from CDS):

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 , which are only valid for 0.44 ≤ B - V ≤ 0.82. Measurements of calcium emission for cooler dwarfs B - V ≥ 0.82 are difficult because of their intrinsic dimness in the blue end of the visible spectrum.
Aims. We measure the absolute Ca II H & K and Hα flux 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 & K and Ha flux in physical units. We used three different Teff calibrations and investigated their effect on Ca II H & K and Hα 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 χ values for Ca II H & K and Hα in the same manner as for -1.0 ≤ [Fe/H] ≤ + 1.0 in steps of Δ [Fe/H] = 0.5.
Results. We compare different Teff calibrations and find ΔΤeff ∼ several 100 K for mid- to late-M dwarfs. Using these different Teff calibrations, we establish a catalog of log R'HK and ℱ'/ℱbol measurements for 110 HARPS M dwarfs. The difference between our results and the calibrations of is Δ log R'HK = 0.01 dex for a Sun-like star. Our χ values agree well with those of . We confirm 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 confirm that for Ha, the lower boundary of chromospheric flux is in absorption for earlier -M dwarfs and fills into the continuum toward later M dwarfs.
Conclusions. We confirm 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.

Abstract Copyright: © The Authors 2023

Journal keyword(s): stars: activity - stars: low-mass - stars: late-type - stars: chromospheres

Simbad objects: 5

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Number of rows : 5
N Identifier Otype ICRS (J2000)
ICRS (J2000)
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2024
1 G 158-27 PM* 00 06 43.1973190107 -07 32 17.019101068     13.837 13.605 10.15 M5.5V 211 0
2 L 736-30 PM* 04 53 49.9799226169 -17 46 24.309265602 13.598 12.443 10.894 9.876 8.671 M3V 113 0
3 NAME Proxima Centauri b Pl 14 29 42.9461331854 -62 40 46.164680672           ~ 370 0
4 NAME Proxima Centauri Er* 14 29 42.9461331854 -62 40 46.164680672 14.21 12.95 11.13 9.45 7.41 M5.5Ve 1303 0
5 HD 131976 SB* 14 57 26.53330 -21 24 41.5778 10.759 9.559 8.065 7.075 9.02 M1.5V 244 1

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