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Author name code: oranje
ADS astronomy entries on 2022-09-14
=author:"Oranje, B.J."
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Title: Magnetic structure in cool stars. IX. Ultraviolet emission
lines from chromospheres and transition regions.
Authors: Oranje, B. J.
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.
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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.
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.
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Title: The Ca II K emission from the sun as a star. II. The plage
emission profile.
Authors: Oranje, B. J.
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.
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Title: The CA II K emission from the sun as a star. I - Observational
parameters
Authors: Oranje, B. J.
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.
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Title: Magnetic structure in cool stars. V. Chronospheric and
transition-region emission from giants.
Authors: Oranje, B. J.; Zwaan, C.; Middelkoop, F.
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.
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Title: A selective solar irradiance spectrometer
Authors: Oranje, B. J.
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.
