We present high-resolution observations of the giant extragalactic H II regions NGC 604, NGC 2363, NGC 5461, and NGC 5471, based on observations taken with the ISIS spectrograph on the William Herschel Telescope. We have detected, for the first time, C II and O II recombination lines in these objects. We find that recombination lines give larger C+

Almost every star in our galaxy will eventually become a white dwarf. Since they are relatively simple compared to main-sequence stars, white dwarfs provide one of the best opportunities for learning about stellar structure and evolution. Studies of pulsating white dwarfs give us the opportunity to learn about their internal composition and

We analyze the old stellar population in the near infrared data around the Galactic plane of the 2MASS survey.

We report here the discovery of very low amplitude oscillations in the Pleiades star HD 23628. The 14-nights high quality light curve designates HD 23628 as a new member of the δ Scuti stars class. Amplitude spectra indicate a multi-periodic pulsation behaviour, and four pulsation frequencies have been detected so far. The frequency distribution

We present simultaneous and continuous observations of H_alpha, H_beta, NaI D_1, D_2 and HeI D_3 lines of the chromospherically active binary HR 1099. We have observed HR 1099 for more than 3 weeks almost continuously and monitored two flares. An increase in H_alpha, CaII H & K, H_beta, HeI D_3 and HeI lambda6678 and a strong filling-in of the NaI

The theoretical understanding of the linear standing or propagating magnetohydrodynamic (MHD) waves in a variety of solar coronal structures is far from complete since analytical solutions to the linearised MHD equations can only be found for very simple magnetic configurations. In this work, a numerical code is used to solve the linear MHD wave