As the 7th brightest star and the most luminous star in the solar neighborhood, Rigel (β Orionis) is a very intriguing object. This blue supergiant (B8 Iab; V-mag = +0.05–0.18-mag; B–V = -0.03), at a distance (from Hipparcos) of ~240±35 pc has a 〈MV〉 = -6.7 mag. The following physical properties were determined via spectroscopic, photometric, and interferometric studies: L/L⊙ ≈ 66,000 K; Teff ≈ 12,000 K; M/M⊙ ≈ 17±3; R/R⊙ ≈ 70; τ ≈ 3–10 Myr. Interestingly Rigel has similar physical properties with the 12th mag blue supergiant progenitor of SN 1987A: Sanduleak -69° 202a. Thus Rigel (along with its co-asterism Betelgeuse) are likely to be the nearest progenitors of a Type II supernova. Such a nearby explosion would be V ≈ -11th mag (similar to a quarter moon).

Horizontal branch (HB) stars play a particularly important role in the “age debate,” since they are at the very center of the long-standing “second parameter” problem. In this review, I discuss some recent progress in our understanding of the nature and origin of HB stars.

Optical photometry and radial velocities have been obtained for stars whose near- and mid-infrared colours suggest that they have dusty circumstellar discs; many are RV Tauri variables. A subset of six stars have earlier spectral types and smaller light amplitudes than classical RV Tauri stars. All are spectroscopic binaries, with surprisingly short periods.

The continuum energy distributions of R127 and R110 in the outburst phase are fitted by use of a optically envelope model. Both stars show two peaks in the continuum energy distributions in which one lies in the short-wavelength range (near 1250Å) and the other in the optical band. We suggest that the fluxes in the UV and optical bands may have different origins: the UV flux comes from the central star and the optical flux comes from the expanded optically envelope. We construct such a model for LBVs with the use of two LTE atmosphere models with different temperatures, and find it to be in satisfactory agreement with the observed spectral energy distributions of R127 and R110.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html