J/A+A/619/A73 Solar Twins age-chromospheric activity   (Lorenzo-Oliveira+, 2018)

The Solar Twin Planet Search. VI. The age-chromospheric activity relation. Lorenzo-Oliveira D., Freitas F., Melendez J., Bedell M., Ramirez I., Bean J., Asplund M., Spina L., Dreizler S., Alves-Brito A., Casagrande L. <Astron. Astrophys. 619, A73 (2018)> =2018A&A...619A..73L 2018A&A...619A..73L (SIMBAD/NED BibCode)
ADC_Keywords: Stars, G-type ; Magnetic fields ; Effective temperatures ; Abundances, [Fe/H]; Stars, ages Keywords: stars: solar-type - stars: evolution - stars: fundamental parameters - magnetic fields Abstract: It is well known that the magnetic activity of solar-type stars decreases with age, but it is widely debated in the literature whether there is a smooth decline or if there is an early sharp drop until 1-2Gyr that is followed by a relatively inactive constant phase. We revisited the activity-age relation using time-series observations of a large sample of solar twins whose precise isochronal ages and other important physical parameters have been determined. We measured the CaII H and K activity indices using 9000 HARPS spectra of 82 solar twins. In addition, the average solar activity was calculated through asteroids and Moon reflection spectra using the same instrumentation. Thus, we transformed our activity indices into the S Mount Wilson scale (SMW), recalibrated the Mount Wilson absolute flux and photospheric correction equations as a function of Te, and then computed an improved bolometric flux normalized activity index logR'HK(Teff) for the entire sample. New relations between activity and the age of solar twins were derived by assessing the chromospheric age-dating limits using logR'HK(Teff). We measured an average solar activity of SMW=0.1712±0.0017 during solar magnetic cycles 23-24 covered by HARPS observations, and we also inferred an average of SMW=0.1694±0.0025 for cycles 10-24, anchored on a sunspot number correlation of S index versus. We also found a simple relation between the average and the dispersion of the activity levels of solar twins. This enabled us to predict the stellar variability effects on the age-activity diagram, and consequently, to estimate the chromospheric age uncertainties that are due to the same phenomena. The age-activity relation is still statistically significant up to ages around 6-7Gyr, in agreement with previous works using open clusters and field stars with precise ages. Our research confirms that CaII H& K lines remain a useful chromospheric evolution tracer until stars reach ages of at least 6-7Gyr. We found evidence that for the most homogenous set of old stars, the chromospheric activity indices seem to continue to decrease after the solar age toward the end of the main sequence. Our results indicate that a significant part of the scatter observed in the age-activity relation of solar twins can be attributed to stellar cycle modulations eects. The Sun seems to have a normal activity level and variability for its age. Description: Our sample was selected from the 88 solar twins presented in Ramirez et al. (2014A&A...572A..48R 2014A&A...572A..48R). From this sample, we obtained data for 70 stars with the HARPS instrument (Mayor et al., 2003Msngr.114...20M 2003Msngr.114...20M) at the 3.6 m telescope at the La Silla observatory, to search for planets around solar twins (program 188.C-0265, Bedell et al., 2015A&A...581A..34B 2015A&A...581A..34B; Melendez et al., 2015Msngr.161...28M 2015Msngr.161...28M, 2017A&A...597A..34M 2017A&A...597A..34M). Additional data for 12 stars were found in the ESO archive. File Summary: -------------------------------------------------------------------------------- FileName Lrecl Records Explanations -------------------------------------------------------------------------------- ReadMe 80 . This file table1.dat 136 82 All the solar twins observed by HARPS, their respective programs and S values compiled from the literature table2.dat 111 82 Parameters of all sample solar twins -------------------------------------------------------------------------------- See also: III/159 : Ca II H and K Measurements Made at MWO (Duncan+ 1991) J/AJ/111/439 : Chromospheric emission in late-type stars. (Henry+ 1996) J/ApJS/152/261 : Chromospheric Ca II emission in nearby stars (Wright+, 2004) J/MNRAS/372/163 : Activity indices for southern stars (Jenkins+, 2006) J/A+A/531/A8 : Activity indices & velocities for 890 stars (Jenkins+, 2011) Byte-by-byte Description of file: table1.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 6 I6 --- HIP HIP number 7 A1 --- n_HIP [*] Note on HIP (G1) 9-114 A106 --- ESO ESO programs 116-120 F5.3 --- S ? CaII H and K activity S-index 122-126 F5.3 --- e_S ? rms uncertainty on S 128-136 A9 --- r_S Reference for S value (1) -------------------------------------------------------------------------------- Note (1): References as follows: 1 = Ramirez et al. (2014A&A...572A..48R 2014A&A...572A..48R) 2 = Jenkins et al. (2011, Cat. J/A+A/531/A8) 3 = Jenkins et al. (2006, Cat. J/MNRAS/372/163) 4 = Wright et al. (2004, Cat. J/ApJS/152/261) 5 = Henry et al. (1996, Cat. J/AJ/111/439) 6 = Duncan et al. (1991ApJS...76..383D 1991ApJS...76..383D, Cat. III/159) 7 = Melendez et al. (2009ApJ...704L..66M 2009ApJ...704L..66M) -------------------------------------------------------------------------------- Byte-by-byte Description of file: table2.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 6 I6 --- HIP HIP number 7 A1 --- n_HIP [*] Note on HIP (G1) 9- 13 F5.3 mag Vmag V magnitude 15- 19 F5.3 mag e_Vmag ? rms uncertainty on Vmag 21- 25 F5.3 mag B-V ? B-V colour index 27- 31 F5.3 mag e_B-V ? rms uncertainty on B-V 33- 36 I4 K Teff Effective temperature 38- 39 I2 K e_Teff ? rms uncertainty on Teff 41- 45 F5.3 [cm/s2] logg ? Surface gravity 47- 51 F5.3 [cm/s2] e_logg ? rms uncertainty on logg 53- 58 F6.3 [-] [Fe/H] ? Metallicity 60- 64 F5.3 [-] e_[Fe/H] ? rms uncertainty on [Fe/H] 66- 70 F5.3 --- SMW Mount Wildson CaII H and K activity S-index, SMW 72- 76 F5.3 --- e_SMW rms uncertainty on SMW 78- 83 F6.3 --- logR'HK(Teff) logR'HK activity index (from Teff) 85- 89 F5.3 --- e_logR'HK(Teff) rms uncertainty on logR'HK(Teff) 91- 93 F3.1 Gyr Age ? Age 95- 97 F3.1 Gyr E_Age ? Error on Age (upper limit) 99-101 F3.1 Gyr e_Age ? Error on Age (lower limit) 103-106 I4 --- NObs Number of observations 108-111 F4.1 yr Time Time-span -------------------------------------------------------------------------------- Global notes: Note (G1): *: Spectroscopic binary -------------------------------------------------------------------------------- History: From electronic version of the journal References: Ramirez et al., Paper I 2014A&A...572A..48R 2014A&A...572A..48R Bedell et al., Paper II 2015A&A...581A..34B 2015A&A...581A..34B Tucci Maia et al., Paper III 2016A&A...590A..32T 2016A&A...590A..32T dos Santos et al., Paper IV 2016A&A...592A.156D 2016A&A...592A.156D Melendez et al., Paper V 2017A&A...597A..34M 2017A&A...597A..34M
(End) Patricia Vannier [CDS] 06-Nov-2018
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