J/A+A/605/A102 Stellar models. 0.85<M<6, Z=0.0001-0.014 (Charbonnel+, 2017)
The magnetic strip(s) in the advanced phases of stellar evolution.
Theoretical convective turnover timescale and Rossby number for low- and
intermediate-mass stars up to the AGB at various metallicities.
Charbonnel C., Decressin T., Lagarde N., Gallet F., Palacios A.,
Auriere M., Konstantinova-Antova R., Mathis S., Anderson R.I., Dintrans B.
<Astron. Astrophys., 605, A102 (2017)>
=2017A&A...605A.102C 2017A&A...605A.102C (SIMBAD/NED BibCode)
ADC_Keywords: Models, evolutionary
Keywords: stars: activity - stars: interiors - stars: magnetic field -
stars: rotation - dynamo
Abstract:
Recent spectropolarimetric observations of otherwise ordinary (in
terms e.g. of surface rotation and chemical properties) G, K, and M
giants have revealed localized magnetic strips in the
Hertzsprung-Russell diagram coincident with the regions where the
first dredge-up and core helium burning occur.
We seek to understand the origin of magnetic fields in such
late-type giant stars, which is currently unexplained. In analogy with
late-type dwarf stars, we focus primarily on parameters known to
influence the generation of magnetic fields in the outer convective
envelope.
We compute the classical dynamo parameters along the evolutionary
tracks of low- and intermediate-mass stars at various metallicities
using stellar models that have been extensively tested by
spectroscopic and asteroseismic observations. Specifically, these
include convective turnover timescales and convective Rossby numbers,
computed from the pre-main sequence (PMS) to the tip of the red giant
branch (RGB) or the early asymptotic giant branch (AGB) phase. To
investigate the effects of the very extended outer convective
envelope, we compute these parameters both for the entire convective
envelope and locally, that is, at different depths within the
envelope. We also compute the turnover timescales and corresponding
Rossby numbers for the convective cores of intermediate-mass stars on
the main sequence.
Our models show that the Rossby number of the convective envelope
becomes lower than unity in the well-delimited locations of the
Hertzsprung-Russell diagram where magnetic fields have indeed been
detected.
We show that α-Ω dynamo processes might not be
continuously operating, but that they are favored in the stellar
convective envelope at two specific moments along the evolution
tracks, that is, during the first dredge-up at the base of the RGB and
during central helium burning in the helium-burning phase and
early-AGB. This general behavior can explain the so-called magnetic
strips recently discovered by dedicated spectropolarimetric surveys of
evolved stars.
Description:
Grid of stellar models and convective turnover timescale for four
metallicities (Z= 0.0001, 0.002, 0.004, and 0.014) in the mass range
from 0.85 to 6.0M☉. The models are computed either with standard
prescriptions or including both thermohaline convection and
rotation-induced mixing. For the whole grid, we provide the usual
stellar parameters (luminosity, effective temperature, lifetimes,
...), together with the turnover timescale estimated a different
heights in the convective envelope and their corresponding Rossby
number.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
z0001.dat 900 7252 Grid of stellar models for Z=0.0001
z002.dat 900 7227 Grid of stellar models for Z=0.002
z004.dat 900 5811 Grid of stellar models for Z=0.004
z014.dat 900 6339 Grid of stellar models for Z=0.014
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See also:
J/A+AS/101/415 : Grids of stellar models III. (Charbonnel+ 1993)
J/A+AS/102/339 : Grids of stellar models IV (Schaerer+, 1993)
J/A+AS/103/97 : Grids of stellar models V. (Meynet+ 1994)
J/A+AS/115/339 : Stellar models VI. (Charbonnel+, 1996)
J/A+AS/128/471 : Grids of stellar models. VII. (Mowlavi+ 1998)
J/A+AS/135/405 : Grids of stellar models. VIII. (Charbonnel+ 1999)
J/A+A/543/A108 : Grid of stellar models, asteroseismology (Lagarde+, 2012)
J/A+A/537/A146 : Stellar models with rotation. 0.8<M<120, Z=0.014
(Ekstrom+, 20102)
J/A+A/541/A41 : Basic tracks at Zinit=0.006 (Mowlavi+, 2012)
J/A+A/558/A103 : Stellar models with rotation. 0.8<M<120, Z=0.002
(Georgy+, 2013)
Byte-by-byte Description of file: z0001.dat z002.dat z004.dat z014.dat
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Bytes Format Units Label Explanations
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1- 6 F6.4 --- Z Initial Z abundance
8 A1 --- T [rs] s: standard prescriptions or
r: th+rot prescriptions
10- 13 F4.2 Msun Mass [0.85/6] Initial mass
(0.85, 1.0, 1.5, 2.0, 2.5, 3.0, 4.0, 6.0)
15- 17 I3 --- Mod Model number
19- 26 F8.2 Lsun L Surface luminosity
28- 33 F6.2 Rsun Reff Photospheric radius
35- 39 I5 K Teff Effective temperature
41- 49 E9.3 g/cm3 rhoeff Photospheric density
51- 59 E9.3 [cm/s2] log(g) Photospheric gravity
61- 70 E10.4 Msun/yr Mloss Mass-loss rate
72- 81 F10.8 Msun M Stellar mass
83- 98 E16.4 yr t Age
100-109 E10.4 d tchp/2 Convective turnover timescale calculated at
half of the pressure scale height
111-120 E10.4 d tchp Convective turnover timescale calculated at
the pressure scale height
122-131 E10.4 d tcrconv/2 Convective turnover timescale calculated at
half of the radius of the convective envelope
133-142 E10.4 d tcmconv/2 Convective turnover timescale calculated at
half of the mass of the convective envelope
144-153 E10.4 d tcmax Maximum convective turnover timescale
155-164 E10.4 d tg Global convective turnover timescale
166-175 E10.4 Rsun rhp/2 Radius at which tc_hp/2 was estimated
177-186 E10.4 Rsun rhp Radius at which tc_hp was estimated
188-197 E10.4 Rsun rrconv/2 Radius at which tc_rconv/2 was estimated
199-208 E10.4 Rsun rmconv/2 Radius at which tc_mconv/2 was estimated
210-219 E10.4 Rsun rmax Radius at which tc_max was estimated
221-230 E10.4 --- Rohp/2 Rossby number associated to tc_hp/2
232-241 E10.4 --- Rohp Rossby number associated to tc_hp
243-252 E10.4 --- Rorconv/2 Rossby number associated to tc_rconv/2
254-263 E10.4 --- Romconv/2 Rossby number associated to tc_mconv/2
265-274 E10.4 --- Romax Rossby number associated to tc_max
276-285 E10.4 --- Rog Rossby number associated to tg
287-296 E10.4 K Tc Central temperature
298-306 E9.3 K Tmax Maximum of temperature
308-316 E9.3 Msun MrTmax Mass coordinate of Tmax
318-329 D12.6 g/cm3 rhoc Central density
331-339 E9.3 g/cm3 rhomax Density at the location of Tmax
341-349 E9.3 dPa Pc Central pressure (cgs)
351-359 E9.3 Msun Mbenv Mass at the base of convective envelope
361-372 D12.6 --- XHc Central abundance of H (mass fraction)
374-383 E10.4 --- XHe3c Central abundance of 3He (mass fraction)
385-394 E10.4 --- XHe4c Central abundance of 4He (mass fraction)
396-405 E10.4 --- XC12c Central abundance of 12C (mass fraction)
407-416 E10.4 --- XC13c Central abundance of 13C (mass fraction)
418-427 E10.4 --- XC14c Central abundance of 14C (mass fraction)
429-438 E10.4 --- XN14c Central abundance of 14N (mass fraction)
440-449 E10.4 --- XO16c Central abundance of 16O (mass fraction)
451-460 E10.4 --- XO17c Central abundance of 17O (mass fraction)
462-471 E10.4 --- XO18c Central abundance of 18O (mass fraction)
473-482 E10.4 --- XF19c Central abundance of 19F (mass fraction)
484-493 E10.4 --- XNe20c Central abundance of 20Ne (mass fraction)
495-504 E10.4 --- XNe21c Central abundance of 21Ne (mass fraction)
506-515 E10.4 --- XNe22c Central abundance of 22Ne (mass fraction)
517-526 E10.4 --- XNa23c Central abundance of 23Na (mass fraction)
528-537 E10.4 --- XMg24c Central abundance of 24Mg (mass fraction)
539-548 E10.4 --- XMg25c Central abundance of 25Mg (mass fraction)
550-559 E10.4 --- XMg26c Central abundance of 26Mg (mass fraction)
561-570 E10.4 --- XAl26c Central abundance of 26Al (mass fraction)
572-581 E10.4 --- XAl27c Central abundance of 27Al (mass fraction)
583-592 E10.4 --- XSi28c Central abundance of 28Si (mass fraction)
594-603 E10.4 --- XHs Surface abundance of H (mass fraction)
605-614 E10.4 --- XH2s Surface abundance of 2H (mass fraction)
616-625 E10.4 --- XHe3s Surface abundance of 3He (mass fraction)
627-636 E10.4 --- XHe4s Surface abundance of 4He (mass fraction)
638-647 E10.4 --- XLi6s Surface abundance of 6Li (mass fraction)
649-658 E10.4 --- XLi7s Surface abundance of 7Li (mass fraction)
660-669 E10.4 --- XBe7s Surface abundance of 7Be (mass fraction)
671-680 E10.4 --- XBe9s Surface abundance of 9Be (mass fraction)
682-691 E10.4 --- XB10s Surface abundance of 10B (mass fraction)
693-702 E10.4 --- XB11s Surface abundance of 11B (mass fraction)
704-713 E10.4 --- XC12s Surface abundance of 12C (mass fraction)
715-724 E10.4 --- XC13s Surface abundance of 13C (mass fraction)
726-735 E10.4 --- XC14s Surface abundance of 14C (mass fraction)
737-746 E10.4 --- XN14s Surface abundance of 14N (mass fraction)
748-757 E10.4 --- XO16s Surface abundance of 16O (mass fraction)
759-768 E10.4 --- XO17s Surface abundance of 17O (mass fraction)
770-779 E10.4 --- XO18s Surface abundance of 18O (mass fraction)
781-790 E10.4 --- XF19s Surface abundance of 19F (mass fraction)
792-801 E10.4 --- XNe20s Surface abundance of 20Ne (mass fraction)
803-812 E10.4 --- XNe21s Surface abundance of 21Ne (mass fraction)
814-823 E10.4 --- XNe22s Surface abundance of 22Ne (mass fraction)
825-834 E10.4 --- XNa23s Surface abundance of 23Na (mass fraction)
836-845 E10.4 --- XMg24s Surface abundance of 24Mg (mass fraction)
847-856 E10.4 --- XMg25s Surface abundance of 25Mg (mass fraction)
858-867 E10.4 --- XMg26s Surface abundance of 26Mg (mass fraction)
869-878 E10.4 --- XAl26s Surface abundance of 26Al (mass fraction)
880-889 E10.4 --- XAl27s Surface abundance of 27Al (mass fraction)
891-900 E10.4 --- XSi28s Surface abundance of 28Si (mass fraction)
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Acknowledgements:
Corinne Charbonnel, Corinne.Charbonnel(at)unige.ch
(End) Patricia Vannier [CDS] 06-Feb-2018