Astronomy and Astrophysics – Astrophysics – Solar and Stellar Astrophysics
Scientific paper
2010-05-04
Astronomy and Astrophysics
Astrophysics
Solar and Stellar Astrophysics
Abstract shortened. 15 pages, 7 figures, 5 tables. Accepted for the publication in Astronomy and Astrophysics
Scientific paper
We present the results of contemporaneous spectroscopic and photometric monitoring of the young solar-type star HD171488 (Prot~1.337 d) aimed at studying surface inhomogeneities at photospheric/chromospheric levels. Echelle FOCES spectra (R~40000) and Johnson photometry have been performed in 2006. Spectral type, rotational velocity, metallicity, and gravity were determined using a code developed by us. The metallicity was measured from the analysis of iron lines. The spectral subtraction technique was applied to the most relevant chromospheric diagnostics included in the FOCES spectral range (CaII IRT, Halpha, HeI-D3, Hbeta, CaII H&K). A model with two large high-latitude spots is sufficient to reproduce the B/V light curves and the radial velocity modulation, if a temperature difference between photosphere and spots of 1500 K is used. A Doppler imaging analysis of photospheric lines confirms a similar spot distribution. With the help of an analogous geometric two-spot model, we are able to reproduce the modulations in the residual chromospheric emissions adopting different values of ratios between the flux of plages and quiet chromosphere (5 for Halpha and 3 for CaII). Facular regions of solar type appear to be the main responsible for the modulations of chromospheric diagnostics. Both the spot/plage model and the cross-correlation between the light curve and the chromospheric line fluxes display a lead effect of plages with respect to spots (20-40 deg in longitude). The active regions of the rapidly rotating star HD171488 are similar to the solar ones in some respect, because the spot temperature is close to that of sunspot umbrae and the plage flux-contrast is consistent with the average solar values. The main differences with respect to the Sun are larger sizes and higher latitudes.
Biazzo Katia
Cakirli Omur
Frasca Antonio
Kővári Zs.
Marilli Ettore
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