Author name code: oranje ADS astronomy entries on 2022-09-14 =author:"Oranje, B.J." ------------------------------------------------------------------------ Title: Magnetic structure in cool stars. IX. Ultraviolet emission lines from chromospheres and transition regions. Authors: Oranje, B. J. Bibcode: 1986A&A...154..185O Altcode: A compilation of ultraviolet fluxes from 132 stars in the IUE catalog is analyzed in order to study the power-law relations for chromospheric and transition region lines. Flux-flux plots covering 5 decades for transition-region lines and 3.5 decades for chromospheric lines indicate tight power-law relations in the case of single stars, particularly FK Comae stars and most binary stars. The relations are found to be independent of spectral type or luminosity class. Departures from the obtained flux-flux relations are found in the case of emission line dwarfs, and F-type and G-type contact binaries, respectively. The tightness of the relations between the emission fluxes from different temperature regimes suggests that the overall structure and heating of the outer atmospheres of cool stars are determined by a single parameter. A summary of the measured IUE images is given. Title: Magnetic structure in cool stars. VIII. The MG II H and K surface fluxes in relation to the MT Wilson photometric CA II H and K measurements. Authors: Oranje, B. J.; Zwaan, C. Bibcode: 1985A&A...147..265O Altcode: Data from IUE observations of 14 F, G, and K stars of luminosity II-V in the Mg II h + k lines are presented in tables and compared with published Mt. Wilson photometry of the Ca II H + K lines, and empirical relations are derived to facilitate the use of Ca II H + K data in investigating the chromospheric structure of cool stars. The results are presented in graphs, and consideration is given to the Vaughan-Preston gap for main-sequence stars; the (B-V)-dependent flux minima for main-sequence (LC V) stars, LC IV subgiants, and LC III giants (consistent with a dynamo model with magnetic braking and tidal synchronization); the very large fluxes of FK Com stars; and the positions of the LC II bright giants and LC I supergiants on the chromospheric-flux/color diagram. Title: The Ca II K emission from the sun as a star. II. The plage emission profile. Authors: Oranje, B. J. Bibcode: 1983A&A...124...43O Altcode: Ca II K line spectrograms of the full solar disk obtained in the Utrecht solar monitoring program from October, 1979 through mid-1982 are interpreted, and the results are extrapolated to stars of solar type. A mean plage emission profile (PEP) averaged over the solar disk and over time, a differential function independent of spectral resolution to the first order, is plotted for the wavelength range from 393.2800 to 393.4754 nm. The PEP is shown to remain essentially constant in shape, varying only in amplitude with solar activity, and hence to be a more adequate indicator of the plage contribution to the Ca II K line profile than the conventional line-core spectrum. The PEP is used to calculate line-core profiles for main-sequence stars of solar effective temperature: less active stars have simple absorption profiles without K2 peaks, while the surface of more active stars is covered up to 65 percent by plages. The Wilson-Bappu width is shown to be the most accurate indicator of luminosity, since it is least sensitive to stellar activity. Title: The CA II K emission from the sun as a star. I - Observational parameters Authors: Oranje, B. J. Bibcode: 1983A&A...122...88O Altcode: Solar full disk Ca II K line spectrograms obtained during the maximum activity of cycle 21 have yielded observational parameters characterizing the line core emission from the sun as a star, together with numerical relations between these parameters. The Ca II K line-core emission is found to vary during the activity maximum by almost as much as the mean difference between solar maximum and solar minimum values, and the distance between the K1 minima increases markedly with increasing core emission. In addition, the violet/red asymmetry in the emission core decreases with increasing emission, and the inner line wings brighten. Title: Magnetic structure in cool stars. V. Chronospheric and transition-region emission from giants. Authors: Oranje, B. J.; Zwaan, C.; Middelkoop, F. Bibcode: 1982A&A...110...30O Altcode: The outer atmospheres of giants at larger heights than the low chromosphere, where the Ca II H and K lines are formed, are studied. In particular, the coupling between the upper chromosphere and the transition region is investigated. G and early K-type giants of different Ca II H and K line-core flux were selected for observations with the IUE. The transition-region flux, defined as the sum of fluxes in the lines of Si IV, C IV, and N V are plotted against the chromospheric flux, defined as the sum of the fluxes in lines of O I and Si II. A surprisingly tight relation is found between transition-region and chromospheric flux which extends over two orders of magnitude in the chromospheric flux and three orders in the transition-region flux. This relation holds for all stars in the sample, including giants, main-sequence stars, and close binaries. The results are discussed in terms of discrete solar-like magnetic structure. Title: A selective solar irradiance spectrometer Authors: Oranje, B. J. Bibcode: 1982A&A...109...32O Altcode: An optical device is described for the averaging of intensity over solid angle. This integrator serves to obtain irradiance spectra from the entire solar disk, or from smaller areas of arbitrary size and shape. The integrator consists of optical elements inserted between a conventional telescope and spectrometer. The loss in signal in comparison with intensity spectrometry is only about 50%, and there is no loss of spectral resolution. Illustrative results are shown from the Utrecht 'the-sun-as-a-star' monitoring program of the disk-averaged Ca II H and K line cores.