Search Publications
A puzzling periodicity in the pulsating DA white dwarf G 117-B15A
Clemens, J. C.; van Kerkwijk, M. H.; Kotak, R.
We present time-resolved optical spectrophotometry of the pulsating hydrogen atmosphere (DA) white dwarf G 117-B15A. We find three periodicities in the pulsation spectrum (215 s, 272 s, and 304 s) all of which have been found in earlier studies. By comparing the fractional wavelength dependence of the pulsation amplitudes (chromatic amplitudes) wi…
Physical Structure of Planetary Nebulae. II. NGC 7662
Guerrero, Martín A.; Chu, You-Hua; Jaxon, Elizabeth G.
We present a study of the structure and kinematics of the triple-shell planetary nebula NGC 7662 based on long-slit echelle spectroscopic observations and Hubble Space Telescope archival narrowband images. The structure of the main nebula consists of a central cavity surrounded by two concentric shells. The bright inner shell has a nonnegligible t…
Atmospheric photochemistry above possible martian hot spots
Atreya, S. K.; Ignatiev, N. I.; Formisano, V. +2 more
Considering the possibility of outgassing from some localized sources on Mars, we have developed a one-dimensional photochemical model that includes methane (CH4), sulfur dioxide (SO2) and hydrogen sulfide (H2S). Halogens were considered but were found to have no significant impact on the martian atmospheric chemis…
Modeling the Sporadic Meteoroid Background Cloud
Dikarev, V.; Grün, E.; Landgraf, M. +3 more
The orbital distributions of dust particles in interplanetary space are revised in the ESA meteoroid model to incorporate more observational data and to comply with the constraints due to the long-term particle dynamics under the planetary gravity and Poynting–Robertson effect. Infrared observations of the zodiacal cloud by the COBE Earth-bound ob…
Comprehensive modelling of the planetary nebula LMC-SMP 61 and its [WC]-type central star
Hamann, W. -R.; Koesterke, L.; Szczerba, R. +3 more
We present a comprehensive study of the Magellanic Cloud planetary nebula SMP 61 and of its nucleus, a Wolf-Rayet type star classified [WC 5-6]. The observational material consists of HST STIS spectroscopy and imaging, together with optical and UV spectroscopic data collected from the literature and infrared fluxes measured by IRAS. We have perfor…
Gas near active galactic nuclei: A search for the 4.7 µm CO band
Lutz, D.; Genzel, R.; Sturm, E. +2 more
In order to constrain the properties of dense and warm gas around active galactic nuclei, we have searched Infrared Space Observatory spectra of local active galactic nuclei (AGN) for the signature of the 4.7 µm fundamental ro-vibrational band of carbon monoxide. Low resolution spectra of 31 AGN put upper limits on the presence of wide absor…
Properties of a bifurcated current sheet observed on 29 August 2001
Balogh, A.; Klecker, B.; Nakamura, R. +7 more
Available from http://www.copernicus.org/site/EGU/annales/22/7/2535.htm?FrameEngine=false;
Abundances in planetary nebulae: Me 2-1
Pottasch, S. R.; García-Lario, P.; Surendiranath, R.
ISO and IUE spectra of the round planetary nebula
A study of the electrical charging of the Rosetta orbiter: 1. Numerical model
Berthelier, Jean-Jacques; Roussel, Jean-FrançOis
Charging of spacecraft in terrestrial or planetary ionospheres and magnetospheres is a well-known effect which may have detrimental consequences for in-situ plasma measurements. The case of the Rosetta mission is of particular importance because the expected temperatures of cometary ions and electrons in the inner coma of comet Wirtanen are very l…
Astrometric Star Catalogues as Combination of Hipparcos/Tycho Catalogues with Ground-Based Observations
Vondrak, J.
The successful ESA mission Hipparcos provided very precise parallaxes, positions and proper motions of many stars in optical wavelength. Therefore, it is a primary representation of International Celestial Reference System in this wavelength. However, the shortness of the mission (less than four years) causes some problems with proper motions of t…