Variable Stars - Rotating
Hills Observatory: 1 January 2013 to 6 May 2018
Variable stars with nonuniform surface brightness and/or ellipsoidal shapes, whose variability is caused by axial rotation with respect to the observer. The nonuniformity of surface brightness distributions may be caused by the presence of spots or by some thermal or chemical inhomogeneity of the atmosphere caused by a magnetic field whose axis is not coincident with the rotation axis. These stars are subdivided into the following types: ACV  Alpha2 Canum Venaticorum variables. These are main-sequence stars with        spectral types B8p-A7p and displaying strong magnetic fields.  Spectra show        abnormally strong lines of Si, Sr, Cr, and rare earths whose intensities vary with        rotation. They exhibit magnetic field and brightness changes (periods of 0.5-160        days or more). The amplitudes of the brightness changes are usually withine        0.01-0.1 mag in V. ACVO  Rapidly oscillating Alpha2 CVn variables. These are nonradially pulsating,        rotating magnetic variables of Ap spectral type (DO Eri). Pulsation periods are in        the range of 6-12 mmag (0.004-0.01 days), while amplitudes of light variation        caused by the pulsation are about 0.01 mag in V. The pulsational variations are        superposed on those caused by rotation. BY   BY Draconis-type variables, which are emission-line dwarfs of dKe-dMe spectral        type showing quasiperiodic light changes with periods from a fraction of a day to        120 days and amplitudes from several hundredths to 0.5 mag in V.  The light        variability is caused by axial rotation of a star with a variable degree of        nonuniformity of the surface brightness (spots) and chromospheric activity.        Some of these stars also show flares similar to those of UV Cet stars, and in        those cases they also belong to the latter type and are simultaneously considered        eruptive variables. ELL  Rotating ellipsoidal variables (b Per, Alpha Vir). These are close binary systems        with ellipsoidal components, which change combined brightnesses with periods        equal to those of orbital motion because of changes in emitting areas toward an        observer, but showing no eclipses. Light amplitudes do not exceed 0.1 mag in V.        FKCOM  FK Comae Berenices-type variables. These are rapidly rotating giants with        nonuniform surface brightnesses, which have G-K spectral types with broad H        and K Ca II emission and sometimes Halpha.  They may also be spectroscopic        binary systems. Periods of light variation (up to several days) are equal to        rotational periods, and amplitudes are several tenths of a magnitude. It is not        excluded that these objects are the product of further evolution of EW (W UMa)        close binary systems (see below). PSR  Optically variable pulsars (CM Tau), which are rapidly rotating neutron stars with        strong magnetic fields, radiating in the radio, optical, and X-ray regions. Pulsars        emit narrow beams of radiation, and periods of their light changes coincide with        rotational periods (from 0.004 to 4 s), while amplitudes of the light pulses reach        0.8 mag. SXARI  SX Arietis-type variables. These are main-sequence B0p-B9p stars with        variable-intensity He I and Si III lines and magnetic fields.  They are sometimes        called helium variables. Periods of light and magnetic field changes (about 1 day)        coincide with rotational periods, while amplitudes are approximately 0.1 mag in V.        These stars are high-temperature analogs of the ACV variables.