Search Publications
Large-Scale Evolution of the Active Region NOAA 7978, 7981, 7986 Observed by Goes, Soho, and Yohkoh
van Driel-Gesztelyi, L.; Foing, B.; Fludra, A. +3 more
We took part in a joint project aimed to study the large-scale evolution of an active region from its emergence throughout its decay for several solar rotations. Our interest focuses on the understanding of how energy is generated, released, deposited, and transformed in active regions. To this end, we determined physical parameters like intensity…
The Fe II excitation mechanism in KQ Puppis
Johansson, S. G.; Redfors, A.
We discuss different excitation processes behind the Fe II emission lines in the IUE spectrum of KQ Puppis (Boss 1985), a VV Cephei type of spectroscopic binary. Several papers have been published on the subject suggesting a number of processes behind the strong Fe II emission lines. We propose that there are two processes operating: selective pho…
71 Tauri: Hyades Enigma Resolved?
Ayres, Thomas R.; Simon, Theodore
71 Tauri (HD 28052; F0 IV-V) is an enigmatic object for two reasons: (1) it is the second brightest X-ray source in the Hyades, yet early F stars as a rule are not strong coronal emitters; and (2) it lies a magnitude above the cluster main sequence, but radial velocity studies and speckle imaging suggest that it is single. Recently, long-slit ultr…
ISO far-infrared observations of rich galaxy clusters. III. Abell 2029, Abell 2052, Abell 2142
Nørgaard-Nielsen, H. U.; Pedersen, K.; Hansen, L. +3 more
A sample of five rich galaxy clusters has been mapped by ISO at 60 mu m, 100 mu m, 135 mu m, and 200 mu m using the PHT-C camera. In previous papers Abell 2670 and Sérsic 159-03 were discussed. Here we present the results for Abell 2029, Abell 2052, and Abell 2142. The conclusion of the survey is that the relatively small fields (~60 square arc mi…
On the Correlation between CO Absorption and Far-Ultraviolet Nonlinear Extinction toward Galactic OB Stars
Feldman, Paul D.; Andersson, B. -G.; Burgh, Eric B. +1 more
A sample of 59 sight lines to reddened Galactic OB stars was examined for correlations of the strength of the CO Fourth Positive (A1Π-X1Σ+) absorption band system with the ultraviolet interstellar extinction curve parameters. We used archival high-dispersion NEWSIPS IUE spectra to measure the CO absorption for comp…
Mode Identification in Pulsating White Dwarfs Using the HST
Kepler, S. O.; Clemens, J. C.; Jiang, X. J. +3 more
We obtained time-resolved ultraviolet spectroscopy for the pulsating DA stars G 226-29 and G 185-32 and for the pulsating DBV star PG 1351+489 with the Hubble Space Telescope Faint Object Spectrograph, to compare the ultraviolet to the optical pulsation amplitudes. We find that for essentially all observed pulsation modes the amplitude rises to th…
The spectral variations of the O-type runaway supergiant HD 188209
Galeev, A.; Herrero, A.; Kaufer, A. +4 more
We report spectral time series of the late O-type runaway supergiant HD 188209. Radial velocity variations of photospheric absorption lines with a possible quasi-period of ~6.4d have been detected in high-resolution echelle spectra. Night-to-night variations in the position and strength of the central emission reversal of the Hα profile occurring …
Emission lines of O bt III in the optical and ultraviolet spectra { } of planetary nebulae
Feibelman, W. A.; Keenan, F. P.; Aller, L. H. +3 more
Recent R-matrix calculations of electron impact excitation rates in O Iii are used to calculate electron temperature and density-dependent emission line ratios R1 = I(4363 Å) / I(4960 Å+ 5007 Å), R2 = I(1661 Å+ 1667 Å) / I(4960 Å+ 5007 Å) and R3 = I(2322 Å) / I(1661 Å+ 1667 Å), for a range of electron temperatures …
Chemical enrichment by massive stars
Thuan, T. X.; Izotov, Y. I.
Heavy element abundances derived from high-quality ground-based and Hubble Space Telescope (HST) spectroscopic observations of low-metallicity blue compact galaxies (BCGs) with oxygen abundances 12+log O/H between 7.1 and 8.3 are discussed. None of the heavy element-to-oxygen abundance ratios studied here (C/O, N/O, Ne/O, Si/O, S/O, Ar/O, Fe/O) de…
Far-infrared [C Ii]/continuum ratio toward the central kiloparsecs of M31. Comparison with that of our Galaxy
Mochizuki, K.
We observed the nearby spiral galaxy M31 with the Long-Wavelength Spectrometer on board the Infrared Space Observatory. Far-infrared line-to-continuum ratios of [C II] / 100 µ m =~ 6 x 10-3 were obtained for the central kiloparsec region along the major axis of the galaxy. These ratios are 2-3 times higher than those in the Galact…