48 research outputs found
When an old star smolders: On the detection of hydrocarbon emission from S-type AGB stars
Polycyclic aromatic hydrocarbons (PAHs) produce characteristic infrared
emission bands that have been observed in a wide range of astrophysical
environments, where carbonaceous material is subjected to ultraviolet (UV)
radiation. Although PAHs are expected to form in carbon-rich AGB stars, they
have up to now only been observed in binary systems where a hot companion
provides a hard radiation field. In this letter, we present low-resolution
infrared spectra of four S-type AGB stars, selected from a sample of 90 S-type
AGB stars observed with the infrared spectrograph aboard the Spitzer satellite.
The spectra of these four stars show the typical infrared features of PAH
molecules. We confirm the correlation between the temperature of the central
star and the centroid wavelength of the 7.9 {\mu}m feature, present in a wide
variety of stars spanning a temperature range from 3 000 to 12 000 K. Three of
four sources presented in this paper extend this relation towards lower
temperatures. We argue that the mixture of hydrocarbons we see in these S-stars
has a rich aliphatic component. The fourth star, BZ CMa, deviates from this
correlation. Based on the similarity with the evolved binary TU Tau, we predict
that BZ CMa has a hot companion as well.Comment: 5 pages, 2 figures, 2 table
Gas-phase infrared spectra of cationized nitrogen-substituted polycyclic aromatic hydrocarbons
Gas-phase infrared spectra of several ionized nitrogen substituted polycyclic aromatic hydrocarbons (PANHs) have been recorded in the 600-1600 cm(-1) region via IR multiple-photon dissociation (IRMPD) spectroscopy. The UV photoionized PANH ions are trapped and isolated in a quadrupole ion trap where they are irradiated with an IR free electron laser. The PANHs were studied in their radical cation (PANH(+)) and protonated (H+ PANH) forms, and include quinoline, isoquinoline, phenanthridine, benzo[h] quinoline, acridine, and dibenzo[f,h] quinoline. Experimental IRMPD spectra were interpreted with the aid of density functional theory methods. The PANH(+) IR spectra are found to resemble those of their respective non-nitrogenated PAH cations. The IR spectra of H+ PANHs are significantly different owing to the NH inplane bending vibration, which generally couples very well with the aromatic CH bending and CC stretching modes. Implications of the NPAH (+, H+) laboratory spectra are discussed for the astrophysical IR emissions and, in particular, for the band at 6.2 mu m
Interstellar Grains -- The 75th Anniversary
The year of 2005 marks the 75th anniversary since Trumpler (1930) provided
the first definitive proof of interstellar grains by demonstrating the
existence of general absorption and reddening of starlight in the galactic
plane. This article reviews our progressive understanding of the nature of
interstellar dust.Comment: invited review article for the "Light, Dust and Chemical Evolution"
conference (Gerace, Italy, 26--30 September 2004), edited by F. Borghese and
R. Saija, 2005, in pres
Space as a Tool for Astrobiology: Review and Recommendations for Experimentations in Earth Orbit and Beyond
A new method to test the hazards of insecticide spraying on Megachile rotundata F. : trials in tunnels
International audienc
PHOTOCHEMISTRY OF POLYCYCLIC AROMATIC HYDROCARBONS IN COSMIC WATER ICE: THE ROLE OF PAH IONIZATION AND CONCENTRATION
Contains fulltext :
149624.pdf (publisher's version ) (Open Access
An optimization of the effect of deltamethrin against the grain aphid Sitobion avenae
National audienc
An optimization of the effect of deltamethrin against the grain aphid Sitobion avenae
International audienc
Mise au point d'un modele d'optimisation de la date d'un traitement insecticide contre le puceron des epis, Sitobion avenae, dans une perspective de lutte integree
National audienc
Photochemistry of polycyclic aromatic hydrocarbons in cosmic water ice
Context. Polycyclic aromatic hydrocarbons (PAHs) are known to be abundantly present in photon-dominated regions (PDRs), as evidenced by their ubiquitous mid-IR emission bands. Towards dense clouds, however, their IR emission bands are strongly suppressed. It is here where molecules are known to reside on very cold grains (T ≤ 30 K) in the form of interstellar ices. Therefore, it is likely that non-volatile species, such as PAHs, also freeze out on grains. Such icy grains act as catalytic sites and, upon vacuum ultraviolet (VUV) irradiation, chemical reactions are initiated. In the study presented here, these reactions and the resulting photoproducts are investigated for PAH containing water ices.
Aims. The aim of this work is to monitor vacuum ultraviolet induced chemical reactions of PAHs in cosmic ice through their IRÂ signatures, to characterize the families of species formed in these reactions, and to apply the results to astronomical observations.
Methods. Mid-infrared Fourier transform absorption spectroscopic measurements ranging from 6500 to 450Â cm-1 are performed on freshly deposited and vacuum ultraviolet processed PAH containing cosmic H2O ices at low temperatures.
Results. The mid-IR spectroscopy of anthracene, pyrene and benzo[ghi]perylene containing H2O ice is reported. Band strengths of the neutral PAH modes in H2O ice are derived. Additionally, spectra of vacuum ultraviolet processed PAH containing H2O ices are presented. These spectra are compared to spectra measured in VUV processed PAH:argon matrix isolation studies. It is concluded that the parent PAH species is ionized in H2O ice and that other photoproducts, mainly more complex PAH derivatives, also form. The importance of PAHs and their PAH:H2O photoproducts in astronomical mid-infrared spectroscopic studies, in particular in the 5−8 μm region, is discussed. As a test-case, the VUV photolyzed PAH:H2O laboratory spectra are compared to a high resolution ISO-SWS spectrum of the high-mass embedded protostar W33A and to a Spitzer spectrum of the low-mass Young Stellar Object (YSO) RNO 91. For these objects, an upper limit of 2–3% with respect to H2O ice is derived for the contribution of PAHs and PAH:H2O photoproducts to the absorbance in the 5−8 μm region towards these objects