Observations of magnetic fields on late-type stars

Magnetic-field observations were carried out for 29 G and K main-sequence stars. The area covering-factors of magnetic regions tends to be greater in the K darfs than in the G dwarfs. However, no spectral-type dependence is found for the field strengths, contrary to predictions that pressure equilibrium with the ambient photospheric gas pressure would determine the surface field strengths. Coronal soft X-ray fluxes from the G and K dwarfs correlate well with the fraction of the stellar surface covered by magnetic regions. The dependence of coronal soft X-ray fluxes on photospheric field strengths is consistent with Stein's predicted generation-rates for Alfven waves. These dependences are inconsistent with the one dynamo model for which a specific prediction is offered. Finally, time variability of magnetic fields is seen on the two active stars that have been extensively monitored. Significant changes in magnetic fields are seen to occur on timescales as short as one day. Previously announced in STAR as N83-24435

[1]  W. Unno.  Line Formation of a Normal Zeeman Triplet , 1956 .

[2]  N. Sheeley,et al.  The photospheric network , 1968 .

[3]  G. Preston.  The Mean Surface Fields of Magnetic Stars , 1971 .

[4]  A. Skumanich,et al.  TIME SCALES FOR Ca II EMISSION DECAY, ROTATIONAL BRAKING, AND LITHIUM DEPLETION. , 1971 .

[5]  L. B. Robinson,et al.  THE LICK OBSERVATORY IMAGE-DISSECTOR SCANNER , 1972 .

[6]  R. Giacconi,et al.  X-ray observations of characteristic structures and time variations from the solar corona: preliminary results from Skylab , 1973 .

[7]  J. Stenflo.  Magnetic-field structure of the photospheric network , 1973 .

[8]  A. Boesgaard.  Measurements of magnetic fields in young main-sequence stars , 1974 .

[9]  G. Preston,et al.  MAGNETIC FIELD MEASUREMENTS IN XI BOOTIS A. , 1975 .

[10]  J. Stenflo.  A model of the supergranulation network and of active-region plages , 1975 .

[11]  A. Title,et al.  Measurements of solar magnetic fields by Fourier transform techniques , 1976 .

[12]  A. Renzini,et al.  Theoretical chromospheres of late type stars. I. Acoustic energy generation. , 1977 .

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

[14]  C. Zwaan.  On the appearance of magnetic flux in the solar photosphere , 1978 .

[15]  Myron A. Smith.  ROTATIONAL STUDIES OF LOWER MAIN-SEQUENCE STARS. , 1979 .

[16]  S. P. Worden,et al.  Stellar model chromospheres. IX - Chromospheric activity in dwarf stars , 1979 .

[17]  S. P. Worden,et al.  Stellar model chromospheres. X. High-resolution, absolute flux profiles of the Ca II H and K lines in stars of spectral types F0 - M2. , 1979 .

[18]  J. Linsky,et al.  Outer atmospheres of cool stars. II - MG II flux profiles and chromospheric radiative loss rates , 1979 .

[19]  S. P. Worden,et al.  Observations of magnetic fields on two late-type dwarf stars , 1980 .

[20]  L. Hartmann,et al.  Momentum and energy deposition in late-type stellar atmospheres and winds , 1980 .

[21]  Jr. Robinson.  Magnetic field measurements on stellar sources - A new method , 1980 .

[22]  J. Linsky,et al.  Outer atmospheres of cool stars. V - IUE observations of Capella - The rotation-activity connection , 1980 .

[23]  S. Vogt.  A magnetic study of spotted UV Ceti flare stars and related late-type dwarfs , 1980 .

[24]  B. Pettersen,et al.  Search for linear polarization in solar neighborhood flare stars and spotted stars , 1981 .

[25]  Leon Golub,et al.  Relations among stellar X-ray emission observed from Einstein, stellar rotation and bolometric luminosity , 1981 .

[26]  D. Duncan.  Lithium abundances, K line emission and ages of nearby solar type stars , 1981 .

[27]  S. Baliunas,et al.  Stellar rotation in lower main-sequence stars measured from time variations in H and K emission-line fluxes. I - Initial results , 1981 .

[28]  F. R. Harnden,et al.  Results from an extensive Einstein stellar survey. , 1981 .

[29]  S. Vogt.  A method for unambiguous determination of starspot temperatures and areas - Application to II Pegasi, BY Draconis, and HD 209813 , 1981 .

[30]  G. Marcy.  The magnetic field on the late-type dwarf XI Bootis A , 1981 .

[31]  N. Weiss,et al.  Convection and magnetic fields in stars , 1981 .

[32]  H. M. Johnson.  An X-ray sampling of nearby stars , 1981 .

[33]  R. Robinson,et al.  On an estimate of the dynamo-generated magnetic fields in late-type stars , 1981 .

[34]  P. Ulmschneider,et al.  Comments on the acoustic heating of stellar coronae , 1981 .

[35]  J. Landstreet,et al.  A search for weak longitudinal magnetic fields on late-type stars , 1981 .

[36]  R. Stein.  Stellar chromospheric and coronal heating by magnetohydrodynamic waves , 1981 .

[37]  J. G. Timothy,et al.  Detection of Magnetic Fields in Late-Type Stars with the KPNO McMath Telescope and MAMA Detector System , 1981 .

[38]  J. Tinbergen,et al.  Magnetic structure in cool stars. II - Observational evidence for transverse magnetic fields , 1981 .

[39]  Peter G. Martin,et al.  On the intrinsic polarization of red dwarfs , 1981 .

[40]  R. Rosner,et al.  The cool half of the H-R diagram in soft X-rays , 1981 .

[41]  M. Giampapa,et al.  Stellar model chromospheres. XIII. M dwarf stars. , 1982 .

[42]  F. Walter.  On the coronae of rapidly rotating stars. III - An improved coronal rotation-activity relation in late type dwarfs , 1982 .

[43]  R. Stein,et al.  Heating of stellar chromospheres when magnetic fields are present. , 1982 .