arXiv subjects
Publications and source records attributed to C. Moutou.
We searched for spectral signatures from the exosphere of HD209458 in the UV and the near-IR with UVES and ISAAC at the VLT. We looked in particular for the helium absorption feature at 10 830 Åpredicted to be among the strongest ones. The upper limit of the He I line derived is 0.5% at 3 $σ$ for a 3 Åbandwith. Planet-induced chromospheric activity search on HD209458 was also performed.
We obtained Halpha diffraction limited data of the LBV star P Cyg using the ONERA Adaptive Optics (AO) facility BOA at the OHP 1.52m telescope on October 1997. Taking P Cyg and the reference star 59 Cyg AO long exposures we find that P Cyg clearly exhibits a large and diffuse intensity distribution compared to the 59 Cyg's point-like source. A deconvolution of P Cyg using 59 Cyg as the Point Spread Function was performed by means of the Richardson-Lucy algorithm. P Cyg clearly appears as an unresolved star surrounded by a clumped envelope. The reconstructed image of P Cyg is compared to similar spatial resolution maps obtained from radio aperture synthesis imaging. We put independent constraints on the physics of P Cyg which agree well with radio results. We discuss future possibilities to constrain the wind structure of P Cyg by using multi-resolution imaging, coronagraphy and long baseline interferometry to trace back its evolutionary status.
Diluted arrays of many optical apertures will be able to provide h igh-resolution snapshot images if the beams are combined according to the densified-pupil scheme. We show that the same principle can also provide coronagraphic images, for detecting faint sources near a bright unresolved one. Recent refinements of coronagraphic techniques, i.e. the use of a phase mask, active apodization and dark-speckle analysis, are also applicable for enhanced contrast. Implemented in the form of a proposed 50-500m Exo-Earth Discoverer array in space, the principle can serve to detect Earth-like exo-planets in the infra-red. It can also provide images of faint nebulosity near stars, active galactic nuclei and quasars. Calculations indicate that exo-planets are detectable amidst the zodiacal and exo-zodiacal emission faster than with a Bracewell array of equivalent area, a consequence of the spatial selectivity in the image.
The detection of a new 16.4 micron emission feature in the ISO-SWS spectra of NGC 7023, M17, and the Orion Bar is reported. Previous laboratory experiments measured a mode near this wavelength in spectra of PAHs (Polycyclic Aromatic Hydrocarbons), and so we suggest the new interstellar 16.4 micron feature could be assigned to low-frequency vibrations of PAHs. The best carrier candidates seem to be PAH molecules containing pentagonal rings.
One way to better apprehend the problem of diffuse interstellar bands (DIBs) is to search for correlations between the bands in a large sample of spectra towards various lines of sight: a strict correlation may imply that a common carrier is at the origin of the bands, whereas a non-correlation means that different species are involved. We propose this observational test for 10 DIBs collected in up to 62 Galactic lines of sight. Strong DIBs do not strictly correlate, and sometimes the correlation is very poor. Only one example of a strict correlation has been found in our sample between the DIBs at 6614 and 6196 A, that could significate a single carrier for those two bands. The general absence of strict correlations is discussed in the context of molecular carriers for the DIBs.
We present here the 7.0-8.7 micron spectrum of the bright reflection nebula NGC 7023. Our observations are made with the Short Wavelength Spectrometer (SWS) on the European satellite Infrared Space Observatory (ISO). The vibrational bands of the ionized fullerene C60+ are expected at 7.11 and 7.51 microns, while those of the neutral fullerene C60 are expected at 7.0 and 8.45 microns. We estimate an upper limit in NGC 7023 for the C60+ abundance of <0.26% of the interstellar abundance of carbon, while C60 contains <0.27% of interstellar carbon.