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RR Lyrae Stars in M32: Signatures of an Ancient Population
Mateo, Mario; Alonso-García, Javier; Worthey, Guy
We report the discovery of variable stars in the dwarf elliptical galaxy M32 using a series of images obtained with the Wide Field Planetary Camera 2 on the Hubble Space Telescope. The colors, luminosities, and approximate periods of the majority of these stars indicate that they are RR Lyrae stars. Comparisons with the number of such stars identi…
Visible and infrared spectroscopy of minerals and mixtures with the OMEGA/MARS-EXPRESS instrument
Gendrin, Aline; Bibring, Jean-Pierre; Langevin, Yves +4 more
We present the reflectance measurements made with OMEGA during ground calibration on a selection of minerals and mixtures considered as candidates for constituents of the Mars surface. OMEGA is the visible and infrared mapping spectrometer designed to fly on-board the ESA/MARS-EXPRESS probe. These measurements allow to evaluate the instrument perf…
First detection of cold dust in the northern shell of NGC 5128 (Centaurus A)
Schiminovich, D.; Carilli, C. L.; van der Hulst, J. M. +2 more
Deep far-infrared (FIR) imaging data obtained with ISOPHOT at 90 µm, 150 µm, and 200 µm detected the thermal emission from cold dust in the northern shell region of NGC 5128 (Centaurus A), where previously neutral hydrogen and molecular gas has been found. A somewhat extended FIR emission region is present in both the 150 µ…
Variable Stars in the Archival HST Data of Globular Clusters M13, M30 and NGC 6712
Pietrukowicz, P.; Kaluzny, J.
We have analyzed archival HST/WFPC2 time-series data of the central parts of globular clusters M13, M30 and NGC 6712 in search for variable objects. Among a total of 21 identified variables there are 15 new discoveries. The sample includes nine RR Lyr stars, two SX Phe stars and seven W UMa-type contact binaries. One object is preliminarily classi…
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…