Astronomy and Astrophysics, volume 397, 147-157 (2003/1-1)
The stellar activity-rotation relationship revisited: Dependence of saturated and non-saturated X-ray emission regimes on stellar mass for late-type dwarfs.
PIZZOLATO N., MAGGIO A., MICELA G., SCIORTINO S. and VENTURA P.
Abstract (from CDS):
We present the results of a new study on the relationship between coronal X-ray emission and stellar rotation in late-type main-sequence stars. We have selected a sample of 259 dwarfs in the B-V range 0.5-2.0, including 110 field stars and 149 members of the Pleiades, Hyades, α Persei, IC 2602 and IC 2391 open clusters. All the stars have been observed with ROSAT, and most of them have photometrically-measured rotation periods available. Our results confirm that two emission regimes exist, one in which the rotation period is a good predictor of the total X-ray luminosity, and the other in which a constant saturated X-ray to bolometric luminosity ratio is attained; we present a quantitative estimate of the critical rotation periods below which stars of different masses (or spectral types) enter the saturated regime. In this work we have also empirically derived a characteristic time scale, τe, which we have used to investigate the relationship between the X-ray emission level and an X-ray-based Rossby number Re=Prot/τe: we show that our empirical time scale τe resembles the theoretical convective turnover time for 0.4≲M/M☉≲1.2, but it also has the same functional dependence on B-V as Lbol–1/2 in the color range 0.5≲B-V≲1.5. Our results imply that - for non-saturated coronae - the Lx-Prot relation is equivalent to the Lx/Lbol vs. Re relation.
stars: activity - stars: late-type - X-rays: stars
VizieR on-line data:
<Available at CDS (J/A+A/397/147): stars.dat table1.dat table2.dat refs.dat>
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