97 research outputs found
Detection of vibronic bands of C in a translucent cloud towards HD 169454
We report the detection of eight vibronic bands of C, seven of which have
been hitherto unobserved in astrophysical objects, in the translucent cloud
towards HD~169454. Four of these bands are also found towards two additional
objects: HD~73882 and HD~154368. Very high signal-to-noise ratio (1000
and higher) and high resolving power () UVES-VLT spectra (Paranal,
Chile) allow for detecting novel spectral features of C, even revealing
weak perturbed features in the strongest bands. The work presented here
provides the most complete spectroscopic survey of the so far largest carbon
chain detected in translucent interstellar clouds. High-quality laboratory
spectra of C are measured using cavity ring-down absorption spectroscopy in
a supersonically expanding hydrocarbon plasma, to support the analysis of the
identified bands towards HD~169454. A column density of N(C) = cm is inferred and the excitation of the molecule
exhibits two temperature components; K for the low-
states and K for the high- tail. The rotational
excitation of C is reasonably well explained by models involving a
mechanism including inelastic collisions, formation and destruction of the
molecule, and radiative pumping in the far-infrared. These models yield gas
kinetic temperatures comparable to those found for . The assignment of
spectral features in the UV-blue range 3793-4054 \AA\ may be of relevance for
future studies aiming at unravelling spectra to identify interstellar molecules
associated with the diffuse interstellar bands (DIBs).Comment: 15 pages, 13 figures, submitted to MNRA
Diffuse band shifts: a possible explanation
Wetensch. publicatieFaculteit der Wiskunde en Natuurwetenschappe
The relation between column densities of interstellar OH and CH molecules
We present a new, close relation between column densities of OH and CH
molecules based on 16 translucent sightlines (six of them new) and confirm the
theoretical oscillator strengths of the OH A--X transitions at 3078 and 3082
\AA (0.00105, 0.000648) and CH B--X transitions at 3886 and 3890 \AA, (0.00320,
0.00210), respectively. We also report no difference between observed and
previously modelled abundances of the OH molecule.Comment: 4 pages, 0 figures, accepted for publication in MNRA
Dark Dust III: The high-quality single-cloud reddening curve sample. Scrutinizing extinction curves in the Milky Way
The nature of dust in the diffuse interstellar medium can be best
investigated by means of reddening curves where only a single interstellar
cloud lies between the observer and the background source. Published reddening
curves often suffer from various systematic uncertainties. We merge a sample of
895 reddening curves of stars for which both FORS2 polarisation spectra and
UVES high-resolution spectra are available. The resulting 111 sightlines toward
OB-type stars have 175 reddening curves. For these stars, we derive their
spectral type from the UVES high-resolution spectroscopy. To obtain
high-quality reddening curves we exclude stars with composite spectra in the
IUE/FUSE data due to multiple stellar systems. Likewise, we omit stars that
have uncertain spectral type designations or stars with photometric
variability. We neglect stars that show inconsistent parallaxes when comparing
DR2 and DR3 from GAIA. Finally, we identify stars that show differences in the
space and ground-based derived reddening curves between m and the
-band or in . In total, we find 53 stars with one or more reddening
curves passing the rejection criteria. This provides the highest quality Milky
Way reddening curve sample available today. Averaging the curves from our
high-quality sample, we find , confirming previous
estimates. A future paper in this series will use the current sample of precise
reddening curves and combine them with polarisation data to study the
properties of Dark Dust.Comment: Recommended to acceptance by A&
- …