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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 (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:
FileName Lrecl Records Explanations
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
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
Bytes Format Units Label Explanations
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)
Acknowledgements: Corinne Charbonnel, Corinne.Charbonnel(at)unige.ch
(End) Patricia Vannier [CDS] 06-Feb-2018
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