Search Publications
A Cepheid Distance to NGC 4603 in Centaurus
Zepf, Stephen E.; Davis, Marc; Madore, Barry F. +5 more
In an attempt to use Cepheid variables to determine the distance to the Centaurus cluster, we have obtained images of NGC 4603 with the Hubble Space Telescope for 9 epochs (totalling 24 orbits) over 14 months in the F555W filter and 2 epochs (totalling six orbits) in the F814W filter. This galaxy has been suggested to lie within the ``Cen 30'' por…
Far-Infrared and Submillimeter Observations and Physical Models of the Reflection Nebula Cederblad 201
van Dishoeck, Ewine F.; Hogerheijde, Michiel R.; Tielens, Alexander G. G. M. +3 more
Infrared Space Observatory (ISO) [C II] 158 µm, [O I] 63 µm, and H2 9 and 17 µm observations are presented of the reflection nebula Ced 201, which is a photon-dominated region (PDR) illuminated by a B9.5 star with a color temperature of 10,000 K (a cool PDR). In combination with ground-based [C I] 609 µm, CO,
Oscillations of the upper chromosphere
Vial, J. -C.; Bocchialini, K.; Lemaire, P. +2 more
Variations of intensity and wavelength in several UV lines have been observed with the SUMER spectroheliometer onboard SOHO, and they have been analysed to obtain oscillation spectra and phase differences between lines of different ions. Lines intensities of neutral or singly ionized atoms (with temperature of formation ≤ 30 000 K) exhibit an incr…
H2O from R Cas: ISO LWS-SWS observations and detailed modelling
Justtanont, K.; Barlow, M. J.; Tielens, A. G. G. M. +7 more
We present 29-197 mu m spectra of the oxygen-rich Mira variable star, R Cas, obtained with the Long- and Short- Wavelength Spectrometers (LWS and SWS) on board the Infrared Space Observatory (ISO). The LWS grating observations were made during two pulsational stellar phases, phi { ~ } 0.5 and 0.2 in August 1996 and June 1997 when the stellar lumin…
New Identifications of Si VIII and S X Lines in the Solar Coronal Spectrum Measured by SOHO/SUMER
Feldman, U.; Kink, I.; Engström, L.
This paper reports the identification of 14 lines in the solar coronal spectrum as high-excitation 2s22p23s-2s22p23p and 2s22p23p-2s22p23d transitions in Si VIII and S X (N I isoelectronic sequence). The analysis combines solar spectra, recorded by the SUMER (S…
Can Kelvin-Helmholtz instabilities of jet-like structures and plumes cause solar wind fluctuations at 1 AU?
Suess, S. T.; Parhi, S.; Sulkanen, M.
The long high-latitude sampling of Ulysses provides the opportunity to study fine structures. At latitudes poleward of ~-60° the solar wind had fluctuations in velocity gradients which were attributed to ``microstreams.'' The data also suggested fluctuations characterized by magnetic plus thermal pressure balance structures ('PBS'). At higher freq…
Reference Frames in Astronomy
Johnston, K. J.; de Vegt, Chr.
Advances in wide-angle astrometric measurements of three to four orders of magnitude in the last thirty years have resulted in a redefinition of the fundamental astronomical reference frame. This new frame, the International Celestial Reference Frame (ICRF), is based on the radio positions of 212 compact extragalactic radio sources. The ICRF defin…
NICMOS Observations of Interaction-triggered Star Formation in the Luminous Infrared Galaxy NGC 6090
Rieke, Marcia; Evans, Aaron S.; Scoville, Nick Z. +2 more
High-resolution 1.1, 1.6, and 2.2 µm imaging of the luminous infrared galaxy NGC 6090 obtained with NICMOS on the Hubble Space Telescope is presented. These new observations are centered on the two nuclei of the merger and reveal the spiral structure of the eastern galaxy and the amorphous nature of the western galaxy. The nuclear separation…
Toward an Understanding of the Mid-Infrared Surface Brightness of Normal Galaxies
Dale, Daniel A.; Rubin, Robert H.; Malhotra, Sangeeta +3 more
We report a mid-infrared color and surface brightness analysis of IC 10, NGC 1313, and NGC 6946, three of the nearby galaxies studied under the Infrared Space Observatory Key Project on Normal Galaxies. Images with less than 9" (170 pc) resolution of these nearly face-on, late-type galaxies were obtained using the LW2 (6.75 µm) and LW3 (15 &…
Observations of heliospheric planar and offset-planar magnetic structures
Balogh, A.; Jones, G. H.; Horbury, T. S.
Planar magnetic structures are regions of solar wind plasma where the magnetic field orientation is constrained within a fixed plane for durations of several hours. Within these structures, magnetic field discontinuities are seen, with the discontinuity surfaces being almost co-planar. The results of a survey of planar magnetic strutures detected …