X-ray emission from nearby M-dwarfs: the super-saturation phenomenon

A rotation rate and X-ray luminosity analysis is presented for rapidly rotating single and binary M-dwarf systems. X-ray luminosities for the majority of both single and binary M-dwarf systems with periods below ≃5–6 d (equatorial velocities, Veq≳6 km s−1) are consistent with the current rotation-activity paradigm, and appear to saturate at about 10−3 of the stellar bolometric luminosity. The single M-dwarf data show tentative evidence for the super-saturation phenomenon observed in some ultra-fast rotating (≳100 km s−1) G- and K-dwarfs in the IC 2391, IC 2602 and Alpha Persei clusters. The IC 2391 M star VXR60b is the least X-ray active and most rapidly rotating of the short period (Prot≲2 d) stars considered herein, with a period of 0.212 d and an X-ray activity level of about 1.5 sigma below the mean X-ray emission level for most of the single M-dwarf sample. For this star, and possibly one other, we cautiously believe that we have identified the first evidence of super-saturation in M-dwarfs. If we are wrong, we demonstrate that only M-dwarfs rotating close to their break-up velocities are likely to exhibit the super-saturation effect at X-ray wavelengths. The M-dwarf X-ray data also show that there is no evidence for any difference in the X-ray behaviour between the single and binary systems, because for the single stars, the mean log LxLbol=−3.21±0.04 (0.2≲Prot≲10.1 d), whereas for the binary stars, the mean log LxLbol=−3.19±0.10 (0.8≲Prot≲10.4 d). Furthermore, we show that extremely X-ray active M-dwarfs exhibit a blue excess of about 0.1 magnitudes in U–B compared with less active field M-dwarfs. Such an excess level is comparable to that observed for extremely chromospherically active M-dwarfs. Moreover, as is the case for M-dwarf Ca ii H and K activity levels, there is an exclusion zone of X-ray activity between the extremely active M-dwarfs and the less active ones.

[1]  E. J. Totten,et al.  Stellar Clusters and Associations: Convection, Rotation, and Dynamos , 2000 .

[2]  G. Cutispoto.  Long-term monitoring of active stars - VII. photometry collected in March 1991 , 1998 .

[3]  T. Simon,et al.  A Deep X‐Ray Image of IC 2391 , 1998 .

[4]  G. Cutispoto.  Long-term monitoring of active stars - VII. photometry collected in March 1991 , 1998 .

[5]  D. James,et al.  Rotation, activity and lithium in NGC 6475 , 1997 .

[6]  M. Giampapa,et al.  Rotational Velocities and Chromospheric/Coronal Activity of Low-Mass Stars in the Young Open Clusters IC 2391 and IC 2602 , 1997 .

[7]  J. Linsky,et al.  The ROSAT All-Sky Survey of Active Binary Coronae. III. Quiescent Coronal Properties for the BY Draconis-Type Binaries , 1997 .

[8]  E. Weis.  Photometry of Stars with Large Proper Motion , 1996 .

[9]  J. Schmitt,et al.  ROSAT Pointed Observations of the Alpha Persei Cluster , 1996 .

[10]  B. Patten,et al.  The Evolution of Rotation and Activity in Young Open Clusters: IC 2391 , 1996 .

[11]  S. Sofia,et al.  Rotation Periods of Late-Type Stars in the Young Open Cluster IC 2602 , 1995, astro-ph/9812168.

[12]  M. Giampapa,et al.  Correlations of Coronal X-Ray Emission with Activity, Mass, and Age of the Nearby K and M Dwarfs , 1995 .

[13]  J. Stauffer,et al.  Spectral and Temporal Characteristics of X-Ray-Bright Stars in the Pleiades , 1995 .

[14]  M. Giampapa,et al.  The X-Ray View of the Low-Mass Stars in the Solar Neighborhood , 1995 .

[15]  R. Schwartz,et al.  BVRI PHOTOMETRY OF CANDIDATE EUV ROSAT SOURCES , 1995 .

[16]  J. Schmitt,et al.  ROSAT All-Sky Survey Observations of the Hyades , 1995 .

[17]  John R. Stauffer,et al.  A deep imaging survey of the Pleiades with ROSAT , 1994 .

[18]  RE 0618 + 75: a very short-period, binary dMe system , 1993 .

[19]  B. Patten,et al.  THE EVOLUTION OF STELLAR CORONAE: INITIAL RESULTS FROM A ROSAT PSPC OBSERVATION OF IC 2391 , 1993 .

[20]  D. Soderblom,et al.  Rotation and chromospheric emission among F, G, and K dwarfs of the Pleiades , 1993 .

[21]  R. Schild,et al.  PHOTOMETRIC LIGHT CURVES FOR TEN RAPIDLY ROTATING STARS IN ALPHA PERSEI, THE PLEIADES, AND THE FIELD , 1993 .

[22]  G. Bromage,et al.  Gliese 841A: an EUV-selected chromospherically active binary system⋆ , 1993 .

[23]  P. Charbonneau,et al.  Angular momentum transport in magnetized stellar radiative zones. I: Numerical solutions to the core spin-up model problem , 1992 .

[24]  David G. Monet,et al.  U.S. Naval Observatory CCD parallaxes of faint stars. I - Program description and first results , 1992 .

[25]  C. Jordan,et al.  The dependence of coronal temperatures on Rossby numbers , 1991 .

[26]  J. Booth,et al.  PHOTOMETRY OF DWARF K AND M STARS , 1988 .

[27]  O. Vilhu,et al.  Chromospheric-coronal activity at saturated levels , 1987 .

[28]  L. Mundy,et al.  Models of molecular cloud cores. III. A mulitransition study of H2CO , 1987 .

[29]  M. Bessell,et al.  THE COUSINS AND KRON VRI SYSTEMS. , 1987 .

[30]  R. Hellings,et al.  Inhomogeneous cosmology. III - Primordial gravitational waves and dust , 1987 .

[31]  G. Ghisellini.  Pair production in synchrotron self-Compton models: the case of one generation of pairs , 1987 .

[32]  S. Baliunas,et al.  Rotation, convection, and magnetic activity in lower main-sequence stars , 1984 .

[33]  M. Zombeck.  Handbook of Space Astronomy and Astrophysics , 1982 .

[34]  Michael S. Bessell,et al.  UBVRI PHOTOMETRY II: THE COUSINS VRI SYSTEM, ITS TEMPERATURE AND ABSOLUTE FLUX CALIBRATION, AND RELEVANCE FOR TWO-DIMENSIONAL PHOTOMETRY. , 1979 .

[35]  Thomas G. Barnes,et al.  Stellar angular diameters and visual surface brightness – III. An improved definition of the relationship , 1978 .

[36]  R. Rosner,et al.  Dynamics of the quiescent solar corona , 1978 .

[37]  Leon Golub,et al.  Heating of coronal plasma by anomalous current dissipation. [induced by solar magnetic flux , 1977 .

[38]  M. Schwarzschild.  On Noise Arising from the Solar Granulation. , 1948 .

[39]  V. Ferraro.  The non-uniform rotation of the Sun and its magnetic field , 1937 .