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The outer atmosphere of Tau - I. A new chromospheric model
McMurry, A. D.
A new model of the chromosphere of α Tau (K5 III) has been developed. The lower part of the model is based on an earlier one designed mainly to fit the Ca ii H and K lines. The new model extends through the upper chromosphere, to account for lines of C i, C ii, Si ii and Mg ii, and into the transition region up to 105 K to account for e…
Evidence for Langmuir envelope solitons in solar type III burst source regions
MacDowall, R. J.; Goldstein, M. L.; Stone, R. G. +2 more
We present observational evidence for the generation of Langmuir envelope solitons in the source regions of solar type III radio bursts. The solitons appear to be formed by electron beams which excite either the modulational instability or oscillating two-stream instability (OTSI). Millisecond data from the Ulysses Unified Radio and Plasma Wave Ex…
Characteristic Scales of Photospheric Flows and Their Magnetic and Temperature Markers
Lawrence, J. K.; Cadavid, A. C.; Ruzmaikin, A. A.
We study the characteristic scales of quiet-Sun photospheric velocity fields along with their temperature and magnetic markers in Doppler images from the Michelson Doppler Imager aboard the SOHO satellite (SOHO/MDI) in simultaneous, Doppler, magnetic, and intensity images from the San Fernando Observatory and in full-disk magnetograms and an inten…
Infrared Photometry of Red Supergiants in Young Clusters in the Magellanic Clouds
Keller, Stefan C.
We present broadband infrared photometry for 52 late-type supergiants in the young Magellanic Cloud clusters NGC 330, 1818, 2004, and 2100. Standard models are seen to differ in the temperature they predict for the red supergiant population by on the order of 300 K. It appears that these differences are most probably due to the calibration of the …
Six intermediate-mass stars with far-infrared excess: a search for evolutionary connections
Wisniewski, John P.; Bjorkman, Karen S.; Miroshnichenko, Anatoly S. +3 more
We present the results of high-resolution spectroscopic, low-resolution spectrophotometric and spectropolarimetric and broad-band multicolour observations of four B-type stars (HD 4881, 5839, 224648 and 179218) and two A-type stars (HD 32509 and 184761) with strong far-infrared (IR) excesses. The excess in HD 184761, which is located at a distance…
Anomalous Line Shifts From Local Intensity Gradients on the Soho/cds NIS Detector
Haugan, S. V. H.
Line shifts for some emission lines on the SOHO/CDS NIS detector appear to be strongly correlated with local intensity gradients along the slit in a way that seems impossible to explain with a physical solar model. Line widths also show a correlation with local intensity gradients. The most plausible instrumental explanation seems to be an ellipti…
The Fe/O elemental abundance ratio in the solar wind as observed with SOHO CELIAS CTOF
Wurz, P.; Bochsler, P.; Ipavich, F. M. +4 more
Using data of the Charge Time-of-Flight (CTOF) mass spectrometer of the Charge, Element, and Isotope Analysis System (CELIAS) on board the Solar and Heliospheric Observatory (SOHO) from ~80 days of observation around solar minimum we derive a value for the Fe/O abundance ratio for the inecliptic solar wind of 0.11+/-0.03. Since Fe has a low first …
Evidence for non-potential magnetic fields in the quiet Sun
Chae, Jongchul; Woodard, M. F.
A comparison of BBSO Hα centerline filtergrams and videomagnetograms was made to investigate the existence of non- potential magnetic fields in the quiet Sun near magnetic network. We use the fibril structure in the Hα images as a proxy for the horizontal chromospheric magnetic field which we compare with the horizontal field obtained by potential…
Understanding A-type supergiants. I. Ultraviolet and visible spectral atlas
Talavera, A.; Verdugo, E.; Gómez de Castro, A. I.
This paper is the first of a series whose aim is to perform a systematic study of A-type supergiant atmospheres and winds. Here we present a spectral atlas of 41 A-supergiants observed by us in high and medium resolution in the visible and ultraviolet. The atlas consists of profiles of the Hα , Hβ , Hγ , Hdelta , Hepsilon , Ca II (H and K), Na I (…
Theoretical Modeling of ISO Results on Planetary Nebula NGC 7027
Bjorkman, J. E.; Federman, S. R.; Yan, M. +1 more
We present a thermal and chemical model of the neutral envelope of planetary nebula NGC 7027. In our model, the neutral envelope is composed of a thin dense shell of constant density and an outer stellar wind region with the usual inverse-square law density profile. The thermal and chemical structure is calculated with the assumption that the inci…