Pizzolato, Nicola

Contact Email: nicola@oapa.astropa.unipa.it
Institute: Dipartimento di Scienze Fisiche ed
Astronomiche, Sez. di Astronomia, Università di Palermo, Italy
First Coauthor: A. Maggio
Institute: Osservatorio Astronomico di Palermo G. S. Vaiana, Piazza del Parlamento 1, I-90134 Palermo, Italy
Second Coauthor: G. Micela
Institute: Osservatorio Astronomico di Palermo G. S. Vaiana, Piazza del Parlamento 1, I-90134 Palermo, Italy
Presenting Thesis: Yes
Subject Area: Stellar Evolution
Waveband: X-rays
Technique: Computational Astrophysics
Presentation: Poster Display
Title: Activity-rotation relationship: interpretation of the X-ray derived Rossby number
Abstract: In this work we present results of a new study on the relationship between X-ray emission and an empirical Rossby number. Using an extended sample of 251 dwarfs in the B-V range 0.5 - 2.0, including 115 field stars and 136 members of clusters, we have first established power-law correlation functions between the X-ray to bolometric luminosity ratio and the rotation period for stars in 8 selected color ranges. We have then determined a color-dependent function, $\tau_e(B-V)$, which allows us derive a single "optimized" relation between $L_{\rm x}/L_{\rm bol}$ and the empirical Rossby number $R_e=P_{\rm rot}/\tau_e$. We show that $\tau_e$ scales with B-V as $L_{\rm bol}^{-0.5}$ and for B-V>1.3 it is significantly lower than the theoretical convective turnover time. This result demonstrates that for non-saturated coronae the $L_{\rm x}$ -  $P_{\rm rot}$ relation is equivalent to the $L_{\rm x}/L_{\rm bol}$ vs. R_e relation. [3rd co-author name: P. Ventura 3rd co-author inst.: Osservatorio Astronomico di Roma, Via Frascati 33, I-00040 Monteporzio, Italy 4th co-author name: S. Sciortino 4th co-author inst.: Osservatorio Astronomico di Palermo G. S. Vaiana, Piazza del Parlamento 1, I-90134 Palermo, Italy]