The spectrum of HD 191612 has been found to display large, recurrent variations between two highly reproducible, peculiar states; at least four transformations have occurred since 1950. In one state, the spectral type is O6-O7, with C III λ4650 emission comparable to N III λ4640 (the definition of the Of?p category) and P Cygni profiles at He II

We present measurements of the near-infrared Ca II triplet (CaT, CaT*), Paschen (PaT), and magnesium (Mg I) indices for a well-studied sample of 19 bulges of early to intermediate spiral galaxies. We find that both the CaT* and CaT indices decrease with central velocity dispersion σ with small scatter. This dependence is similar to that recently

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We present ground-based spectra of early-type star candidates in the Local Group galaxies M 33 and NGC 6822 taken at the 4.2 m William Herschel Telescope (La Palma, Spain). Photospheric parameters Teff and log g were derived by LTE modeling of the Balmer lines. When possible, mass-loss rates were calculated from the Halpha profiles computing

We describe the technique that will be used to develop a set of on-orbit calibrators for the Infrared Array Camera (IRAC) and demonstrate the validity of the method for stars with spectral types either K0-M0 III or A0-A5 V. For application to SIRTF, the approach is intended to operate with all available optical, near-infrared (NIR), and mid