POSTER PAPER 5.13

Activity-rotation Relationship: Interpretation of an X-ray Derived Rossby Number
N. Pizzolato, A. Maggio, G. Micela, S. Sciortino, P. Ventura

Institute: Dipartimento di Scienze Fisiche ed Astronomiche, Universita di Palermo, Sezione di Astronomia
Institute: Osservatorio Astronomico di Palermo "G. S. Vaiana"
Institute: Osservatorio Astronomico di Roma
Contact Email: nicola@oapa.astropa.unipa.it

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 238 dwarfs in the B-V range 0.5--1.6, including 102 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 7 selected color ranges. We have then determined a color-dependent function, Taue(B-V), which allows us to derive a single "optimized" relation between Lx/Lbol and an empirical X-ray-derived Rossby number Roemp=Prot/Taue .

We show that Taue scales with B-V as Lbol-0.5 and for B-V > 1.3 it is significantly lower than the theoretical convective turnover time. Our result demonstrates that for non-saturated coronae the Lx--Prot relation is equivalent to the Lx/Lbol vs. Roemp relation.

Activity-rotation Relationship: Interpretation of an X-ray Derived Rossby Number [PDF - Type 1 fonts]

Activity-rotation Relationship: Interpretation of an X-ray Derived Rossby Number [PS]

Index Keywords: Activity

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Manuscript submitted: 2001-Sep-05
"The Future of Cool-Star Astrophysics", 2003, Eds. A. Brown, G. M. Harper, & T. R. Ayres. Proceedings of 12th Cambridge Workshop on Cool Stars, Stellar Systems, & The Sun,
© 2003 University of Colorado.