Photospheric and chromospheric activity on the young solar-type star HD 171488 \n(V889 Herculis)
Makaleler > Tam Makale · 2010
Yazarlar: A. Frasca, K. Biazzo, Zs. Kővári, E. Marilli, Esin SİPAHİ KILIÇ
https://doi.org/10.1051/0004-6361/201014460, Uluslararası, 2010
DOI: 10.1051/0004-6361/201014460/pdf
Özet
\n Aims. We present the results of contemporaneous spectroscopic and photometric monitoring of the young solar-type\nstar HD 171488 (Prot $\\simeq$ 1.337 days) aimed at studying surface inhomogeneities at both \nphotospheric and chromospheric levels.\n Methods. Echelle FOCES spectra (R $\\simeq$ 40 000) and Johnson BV photometry have\nbeen performed in August 2006, with a good coverage of rotational phases. Spectral type, rotational velocity, \nmetalicity, and gravity were determined with a code developed by us (Rotfit) and a library of high-resolution spectra\nof slowly-rotating reference stars. The metalicity was measured from the analysis of iron lines with the Moog code.\nThe spectral subtraction technique was applied to the most relevant chromospheric diagnostics included in the FOCES spectral range,\nnamely $\\ion{Ca}{ii}$ IRT, Hα, $\\ion{He}{i}$ D3, Hβ, and $\\ion{Ca}{ii}$ H&K lines. \n Results. A simple model with two large high-latitude spots is sufficient to reproduce the B and V light curves \nas well as the radial velocity modulation if a temperature difference between photosphere and spots of about 1500 K is used. A Doppler-imaging analysis \nof photospheric lines basically confirms a similar spot distribution. \nWith the help of an analogous geometric two-spot model, we are able to reproduce the observed modulations in the residual \nchromospheric emissions adopting different values of ratios between the flux of plages and the quiet chromosphere (about 5 for Hα and 3 for \n$\\ion{Ca}{ii}$ diagnostics).\nFacular regions of solar type appear to be the main responsible features for the modulations of chromospheric diagnostics. \nBoth the spot/plage model and the cross-correlation between the light curve and the chromospheric line fluxes display a significant lead effect of plages \nwith respect to spots (from 20$\\degr$ to 40$\\degr$ in longitude), as already observed in some active solar-type stars and RS CVn systems.\n Conclusions. The contemporaneous monitoring of photospheric and chromospheric diagnostics in the young and rapidly rotating solar-type star HD 171488\nallowed us to detect active regions which have nearly the same location at both atmospheric layers, with plages slightly\nleading spots in longitudes. These active regions are similar to the solar ones in some respects, because the spot temperature is close to that\nof sunspot umbrae and the plage flux-contrast is consistent with the average solar values. The main differences with respect to the Sun are \nlarger sizes and higher latitudes. \n