J/MNRAS/519/5304 Rossby numbers of convective stars (Landin+, 2023)
Rossby numbers of fully and partially convective stars.
Landin N.R., Mendes L.T.S., Vaz L.P.R, Alencar S.H.P.
<Mon. Not. R. Astron. Soc. 519, 5304-5314 (2023)>
=2023MNRAS.519.5304L 2023MNRAS.519.5304L (SIMBAD/NED BibCode)
ADC_Keywords: Models, evolutionary ; Stars, pre-main sequence ; Stars, masses
Keywords: convection - stars: rotation - stars: pre-main sequence
Abstract:
We investigate stellar magnetic activity from the theoretical point of
view, by using stellar evolution models to calculate theoretical
convective turnover times (τc) and Rossby numbers (Ro) for
pre-main-sequence and main-sequence stars. The problem is that the
canonical place where τc is usually determined (half a mixing
length above the base of the convective zone) fails for fully
convective stars and there is no agreement on this in the literature.
Our calculations were performed with the ATON stellar evolution code.
We concentrated our analysis on fully and partially convective stars
motivated by recent observations of slowly rotating fully convective
stars, whose X-ray emissions correlate with their Rossby numbers in
the same way as in solar-like stars, suggesting that the presence of a
tachocline is not required for magnetic field generation. We
investigate the behaviour of τc over the stellar radius for stars
of different masses and ages. As Ro depends on τc, which varies
strongly with the stellar radius, we use our theoretical results to
determine a better radial position at which to calculate it for fully
convective stars. Using our alternative locations, we fit a sample of
847 stars in the rotation-activity diagram (LX/Lbol versus Ro) with
a two-part power-law function. Our fit parameters are consistent with
previous work, showing that stars with Ro{less than or equal to}Ro_sat
are distributed around a saturation level in LX/Lbol and, for stars
with Ro>Ro_sat, LX/Lbol clearly decays with Ro with an exponent of
-2.4±0.1.
Description:
These data present new pre-main sequence evolutionary tracks
(including local and global convective turnover times, Rossby numbers
and rotation periods) for masses in the range of 0.1 to 1.5 solar
masses in 0.1 solar masses steps. The tracks were generated with a
modified version of D'Antona & Mazzitelli's code (the ATON code)
described in Ventura et al. (1998A&A...334..953V 1998A&A...334..953V). In this new version
we included non-gray boundary conditions (Landin et al.,
2006A&A...456..269L 2006A&A...456..269L), rotation with local conservation of angular
momentum in the whole star (Mendes et al., 1999A&A...341..174M 1999A&A...341..174M) and
convective turnover times calculations. Local convective turnover
times calculations of partially convective stars were performed at
one-half of a mixing length above the base of the convective zone. For
fully convective stars we used an alternative radial position to
calculate it. All models were computed with solar metallicity
(X=0.7155, Y=0.2703, Z=0.0142, 2009,ARA&A...47..481A) and alpha=2.0
(mixing length theory parameter).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 76 450 Evolutionary tracks and convective times
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 4 F4.2 Msun Mass Mass
7- 13 F7.4 [yr] logAge Age of models
16- 22 F7.4 [Lsun] logL Total luminosity
25- 30 F6.4 [K] logTeff Effective temperature
33- 37 F5.3 [cm/s2] loggeff Effective gravity
40- 46 F7.4 [d] logtauc Local convective turnover time
49- 55 F7.4 [d] logtaug Global convective turnover time
58- 65 F8.4 d Prot Rotation period
68- 76 F9.6 --- Ro Rossby number
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History:
From Natalia Landin, nlandin(at)ufv.br
Acknowledgements:
The authors thank Drs. Francesca D'Antona (INAF-OAR, Italy) and
Italo Mazzitelli (INAF-IASF, Italy) for granting them full access to
the ATON evolutionary code.
(End) Natalia Landin [Univ. Fed. of Vicosa], Patricia Vannier [CDS] 28-Dec-2022