Search Publications
Spectral analysis of hot helium-rich white dwarfs.
Werner, K.; Dreizler, S.
We present a model atmosphere analysis of most known hot helium-rich white dwarfs of spectral type DO. The stars represent the non-DA white dwarf cooling sequence from the hot end (T_eff_=~120000K) down to the DB gap (T_eff_=~45000K). From medium resolution optical spectra, effective temperatures, surface gravities, and element abundances are dete…
A search for interstellar gas-phase CO_2_. Gas: solid state abundance ratios.
de Graauw, T.; van Dishoeck, E. F.; Salama, A. +15 more
We present searches for gas-phase CO_2_ features in the ISO-SWS infrared spectra of four deeply embedded massive young stars, which all show strong solid CO_2_ absorption. The abundance of gas-phase CO_2_ is at most 2x10^-7^ with respect to H_2_, and is less than 5% of that in the solid phase. This is in strong contrast to CO, which is a factor of…
Long-term spectroscopic monitoring of BA-type supergiants. I. Halpha_ line-profile variability.
Stahl, O.; Wolf, B.; Kaufer, A. +5 more
We have obtained time series of spectra in the wavelength range 4000-6800 A over several months with high S/N and high resolution in wavelength (λ/{DELTA}λ=~20000) and time ({DELTA}t=~1d) of the late-type B and early-type A supergiants HD91619 (B7Ia), βOri (B8Ia), HD96919 (B9Ia), HD92207 (A0Ia), HD100262 (A2Ia) and αCyg (A2Ia). Halpha_ …
Spectral analyses of late-type WC central stars of planetary nebulae.
Hamann, W. -R.; Jeffery, C. S.; Leuenhagen, U.
The optical spectra of the seven late-type Wolf-Rayet central stars NGC40 ([WC8]), BD+30 3639 ([WC9]), He2-99 ([WC9]), CPD-56 8032, He2-113, M4-18 and K2-16 (all [WC11]) are analyzed by means of spherically expanding model atmospheres. The NLTE simulations account for the elements helium, carbon and oxygen. As main results effective temperature T_…
Phase-locked photospheric and stellar-wind variations of θ^1^Orionis C.
Stahl, O.; Wolf, B.; Pakull, M. W. +9 more
We have obtained a long series of optical spectra and new IUE spectra of θ^1^Ori C, the brightest star in the Orion Trapezium and the main source of ionization of the Orion nebula (M 42). With these data, we have improved the accuracy of the period of the optical emission-line variations and the UV stellar-wind absorption-line variations. We find …
The rich spectrum of circumstellar PAHs.
Waters, L. B. F. M.; Beintema, D. A.; de Graauw, T. +10 more
We present observations taken with the Short Wavelength Spectrometer (SWS) on board the Infrared Space Observatory (ISO) of three evolved C-rich stars, the post-AGB star HR 4049 and two planetary nebulae, IRAS 21282+5050 and NGC 7027. The spectra are dominated by the well-known infrared emission bands, attributed to Polycyclic Aromatic Hydrocarbon…
ISOCAM observations of the Antennae Galaxies.
Altieri, B.; Cesarsky, C.; Boulanger, F. +10 more
We have mapped the Antennae Galaxies (NGC4038/39) in the 6.7 and 15µm continuum emission using ISOCAM (Cesarsky et al., 1996A&A...315L..32C) with =~5 - 8" resolution. Spectrophotometric observations with the CVF in the spectral range 5.5 to 16.5µm have also been obtained. We compare the distribution of the infrared emission in the …
Solid methane toward deeply embedded protostars.
Prusti, T.; de Graauw, T.; Whittet, D. C. B. +6 more
We report on the detection of an absorption feature near 7.67µ m toward the deeply embedded protostellar objects W 33A and NGC 7538 : IRS9. Comparison with laboratory spectra shows that this feature can be identified as the ν_4_ (`deformation') mode of solid state CH_4_ embedded in polar molecules (i.e., H_2_O and/or CH_3_OH) in icy grain ma…
SWS observations of IR emission features towards compact HII regions.
Heras, A. M.; Kessler, M. F.; de Graauw, T. +17 more
We present ISO Short Wavelength Spectrometer (SWS) grating spectra of six compact HII regions. In addition to strong emission lines from atomic species these spectra display infrared bands attributed to Polycyclic Aromatic Hydrocarbons (PAHs). The continuous spectral coverage of the present observations and the high spectral resolution allow to de…
The heliospheric magnetic field at solar minimum: ULYSSES observations from pole to pole.
Balogh, A.; Horbury, T. S.; Forsyth, R. J. +3 more
The fast transit of the Ulysses spacecraft from the south polar regions of the heliosphere to the north polar regions has allowed us to obtain a unique perspective on the configuration and properties of the heliospheric magnetic field at a time of solar minimum activity. We compare the magnetic field in the northern and southern hemispheres and fi…