The Spectrum and Light Curve of CH Cygni during its Recent Broad Minimum

摘要

During 2006 CH Cyg declined steadily from V 7: 3 to 9.4, which is close to the faintest recorded minimum of 11.0 achieved after its outburst in the 1980s. We present light and color curves as well as low-resolution spectra that demonstrate that the decline was largely due to an increase in circumstellar absorption. In addition to the main 95 day pulsation period, a long secondary period of 1410 days, which is twice the spectroscopic period noted by Hinkle et al., modulates the pulsation light curve of the M7 III cool giant. The presence of two pulsation periodicities with such a large ratio is typical of AGB semiregular stars. Spectra of resolution 35,000 show the usual absorption lines of the M6 giant and various emission lines, especially Fe II and [Fe II], with radial velocities showing gas on the near sDEe of CH Cyg to be expanding at 10 km s(-1). Sharp resonance lines of Na I and K I in absorption show expansions of 20 and 40 km s(-1).