Steven Federman

Observation of a new electronic state of CO perturbing WΠ1(v=1)

We observe photoabsorption of the W(1) ← X(0) band in five carbon monoxide isotopologues with a vacuum-ultraviolet Fourier-transform spectrometer and a synchrotron radiation source. We deduce transition energies, integrated cross sections, and natural linewidths of the observed rotational transitions and find a perturbation affecting these. Following a deperturbation analysis of all five isotopologues, the perturbing state is assigned to the v = 0 level of a previously unobserved (1)Π state predicted by ab initio calculations to occur with the correct symmetry and equilibrium internuclear distance. We label this new state E″ (1)Π. Both of the interacting levels W(1) and E″(0) are predissociated, leading to dramatic interference effects in their corresponding linewidths.

High-resolution study of oscillator strengths and predissociation rates for 13C18O - W-X bands and Rydberg complexes between 92.9 and 93.5 nm

We carried out experiments at the SOLEIL synchrotron facility to acquire data for modelling CO photochemistry in the vacuum ultraviolet. We report oscillator strengths and predissociation rates for four vibrational bands associated with transitions from the v = 0 level of the X1 Σ+ ground state to the v = 0–3 vibrational levels of the core excited W1Π Rydberg state, and for three overlapping bands associated with the 4pπ, 5pπ, and 5pσ Rydberg states between 92.9 and 93.4 nm in 13C18O. These results complete those obtained in the same conditions for 12C16O, 13C16O, and 12C18O recently published by us, and extend the development of a comprehensive database of line positions, oscillator strengths, and linewidths of photodissociating transitions for CO isotopologues. Absorption spectra were recorded using the Vacuum UltraViolet Fourier Transform Spectrometer (VUV-FTS) installed on the Dichroisme Et Spectroscopie par Interaction avec le Rayonnement Synchrotron (DESIRS) beamline at SOLEIL. The resolving power of the measurements, R = 300 000 to 400u2009000, allows the analysis of individual line strengths and widths within the bands. Gas column densities in the differentially pumped system were calibrated using the B-X (0–0) band at 115.1 nm in 13C18O.Models of astronomical environments containing CO require accurate molecular data to reproduce and interpret observations. We are conducting experiments at the SOLEIL synchrotron facility to acquire data for modeling CO photochemistry in the vacuum ultraviolet. The improvement in UV spectroscopic instrumentation, both in sensitivity and resolution, provides more accurate laboratory spectroscopic determinations. We report new measurements yielding photoabsorption oscillator strengths and predissociation rates, for 12 C 16 O at 295 K and 77 K, of four bands from X 1 Σ + (v �� = 0) to the v � = 0–3 vibrational levels of the core-excited W 1 Π Rydberg state and for six overlapping bands between 92.97 and 93.35 nm. Absorption spectra were recorded using the vacuum ultraviolet Fourier transform spectrometer installed on the DESIRS beamline at SOLEIL, providing a resolving power R = 350 000. This resolution allows the analysis of individual line strengths and widths in the electronic transitions and the identification of a previously unobserved perturbation in the W(1) level. Gas column densities in the differentially-pumped system were calibrated using the B 1 Σ + – X 1 Σ + (0, 0) band. Absorption bands are analyzed by synthesizing line and band profiles with independently developed codes. These considerably improved results are compared with earlier determinations.

The au-scale structure in diffuse molecular gas towards ζ Persei

Context. Spatial structure in molecular material has a strong impact on its physical and chemical evolution and is still poorly known, especially on very small scales. Aims. To better characterize the small-scale structure in diffuse molecular gas and in particular to investigate the CH production mechanism, we study the spatial distribution of CH, CH, and CN towards the bright star ζ Per on scales in the range 1−20 AU. Methods. We use ζ Per’s proper motion and the implied drift of the line of sight through the foreground gas at a rate of about 2 AU yr−1 to probe absorption line variations between adjacent lines of sight. The good S/N, high or intermediate resolution spectra of ζ Per, obtained in the interval 2003−2011, allow us to search for low column-density and line width variations for CH, CH, and CN. Results. CH and CN lines appear remarkably stable in time, implying an upper limit δN/N ≤ 6% for CH and CN (3σ limit). The weak CHλ4232 line shows a possible increase of 11% during the interval 2004−2007, which appears to be correlated with a comparable increase in the CH velocity dispersion over the same period. Conclusions. The excellent stability of CH and CN lines implies that these species are distributed uniformly to good accuracy within the cloud. The small size implied for the regions associated with the CH excess is consistent with scenarios in which this species is produced in very small (a few AU) localized active regions, possibly weakly magnetized shocks or turbulent vortices.

High-resolution spectroscopy of the A 1 Π(v′=0-10)−X 1 Σ + (v′′=0) bands in 13 C 18 O: term values, ro-vibrational oscillator strengths and Hönl–London corrections

Our knowledge of astronomical environments containing CO depends on accurate molecular data to reproduce and interpret observations. The constant improvement in UV space instrumentation, both in sensitivity and resolution, requires increasingly detailed laboratory data. Following a long-term experimental campaign at the SOLEIL Synchrotron facility, we have acquired complete datasets on the CO isotopologues in the vacuum ultraviolet. Absorption spectra were recorded using the Fourier-transform spectrometer installed on the DESIRS beamline, providing a resolving power R > 106 in the 8–12 eV range. Such resolution allows the analysis of individual line positions and strengths in electronic transitions and the location of perturbations. We continue our previous work on A–X bands of 12C16O and 13C16O, reporting here measurements for the 13C18O isotopologue.

A Multiwavelength Study of the Close Environment of HD 34078

We present 12CO(2–1) emission line observations of the region surrounding HD 34078, together with new optical and FUSE spectra of this runaway star. CO(2–1) emission peaks close to the star position and correlates well with IR thermal dust emission. Our follow‐up of CH and CH+ optical absorption lines confirms the reality of marked time variations while FUSE spectra indicate no such changes for H2. These results are consistent with a picture in which all absorption lines in HD 34078’s spectrum originate from material located close to the star, in a dense inhomogeneous shell formed at the stellar wind/ambient cloud interface where CH and CH+ are overabundant.