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VARIABILITY OF CHROMOSPHERIC LINES IN LATE-TYPE DWARF STARS

GIUSEPPE CUTISPOTO and MARK S. GIAMPAPA
Publications of the Astronomical Society of the Pacific
Vol. 100, No. 633 (November 1988), pp. 1452-1460
Stable URL: http://www.jstor.org/stable/40679243
Page Count: 9
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
VARIABILITY OF CHROMOSPHERIC LINES IN LATE-TYPE DWARF STARS
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Abstract

The results of a high-resolution spectroscopie synoptic program of observations of key chromospheric diagnostics in a sample of dwarf stars are reported. Synoptic observations of the Hα absorption line in three M-dwarf (non-dMe) stars, GL 15A (dMl), GL411 (dM2), and GL526 (dM4), disclose the occurrence of low-amplitude variability in the strength of this partially chromospheric feature. Synoptic observations of the Ha emission line in the well-known spotted variable, BY Dra (K7-M0), reveal that this feature is highly variable in strength with no apparent correlation between its variability and the known photometric (spot) phase or the orbital phase of this active binary system. Synoptic observations of the He I D₃ line at 5876 Å in the spectra of three solar-type dwarfs, X¹ Ori (GO), ξ Boo A (G8), and 70 Oph A (K0), also reveal the occurrence of low-level variability in the strength of this purely chromospheric absorption feature in two of the three program objects. The frequency of observation is, in the case of both spectral diagnostics, insufficient to discern if the observed variability is periodic as would be expected from the rotational modulation of spatially extensive and asymmetrically distributed active region complexes. The nature and possible origins of the variability observed in Ha and D₃, respectively, are discussed.

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