Faculty of Physics Astronomy and Informatics

We report the detection of the ground-state rotational transition of the methylidyne cation CH + and its isotopologue 13 CH + toward the remote massive star-forming regions W33A, W49N, and W51 with the HIFI instrument onboard the Herschel satellite. Both lines are seen only in absorption against the dust continuum emission of the star-forming regions. The CH + absorption is saturated over almost the entire velocity ranges sampled by the lines-of-sight that include gas associated with the star-forming regions (SFR) and Galactic foreground material. The CH + column densities are inferred from the optically thin components. A lower limit of the isotopic ratio [ 12 CH + ]/[ 13 CH + ] > 35.5 is derived from the absorptions of foreground material toward W49N. The column density ratio, N(CH +)/N(HCO +), is found to vary by at least a factor 10, between 4 and >40, in the Galactic foreground material. Line-of-sight 12 CH + average abundances relative to total hydrogen are estimated. Their average value, N(CH +)/N H > 2.6 × 10 −8 , is higher than that observed in the solar neighborhood and confirms the high abundances of CH + in the Galactic interstellar medium. We compare this result to the predictions of turbulent dissipation regions (TDR) models and find that these high abundances can be reproduced for the inner Galaxy conditions. It is remarkable that the range of predicted N(CH +)/N(HCO +) ratios, from 1 to ∼50, is comparable to that observed.

We report the detection of the ground-state rotational transition of the methylidyne cation CH + and its isotopologue 13 CH + toward the remote massive star-forming regions W33A, W49N, and W51 with the HIFI instrument onboard the Herschel satellite. Both lines are seen only in absorption against the dust continuum emission of the star-forming regions. The CH + absorption is saturated over almost the entire velocity ranges sampled by the lines-of-sight that include gas associated with the star-forming regions (SFR) and Galactic foreground material. The CH + column densities are inferred from the optically thin components. A lower limit of the isotopic ratio [ 12 CH + ]/[ 13 CH + ] > 35.5 is derived from the absorptions of foreground material toward W49N. The column density ratio, N(CH +)/N(HCO +), is found to vary by at least a factor 10, between 4 and >40, in the Galactic foreground material. Line-of-sight 12 CH + average abundances relative to total hydrogen are estimated. Their average value, N(CH +)/N H > 2.6 × 10 −8 , is higher than that observed in the solar neighborhood and confirms the high abundances of CH + in the Galactic interstellar medium. We compare this result to the predictions of turbulent dissipation regions (TDR) models and find that these high abundances can be reproduced for the inner Galaxy conditions. It is remarkable that the range of predicted N(CH +)/N(HCO +) ratios, from 1 to ∼50, is comparable to that observed.

Mutual relations between column densities of H 2 , CH and CO molecules as well as between the latter and strengths of the major 5780 and 5797 diffuse bands are presented and discussed. The CH radical seems to be a good H 2 tracer, possibly better than CO. It is also demonstrated that the molecular fraction of the H 2 molecule is correlated with an intensity ratio of 5797 and 5780 DIBs, suggesting the possible formation of narrow DIB carriers in denser clouds, dominated by molecular hydrogen and reasonably shielded from ionizing UV radiation by small dust grains.

The term “families of diffuse bands” (DIBs) appeared in 1986/87 when my collaborators: Gordon A.H. Walker, Bengt E. Westerlund and I found that the strength ratio of the major DIBs 5780 and 5797 is heavily variable. We proved that at the same E(B-V) the DIB intensities may vary by as much as a factor of three or more. A similar result was published by Karl Josafatsson and Ted Snow soon after. A decade later, we proved (with Chris Sneden) that certain DIB strength ratios seem to be related to intensities of the known features of simple molecular species; this led to the introduction of the so called σ and ζ type interstellar clouds. The former are characterized by very weak molecular features (but broad DIBs – very strong) while the latter by rather strong bands of simple radicals and weak broad DIBs. Currently we face a bunch of questions: are the DIB intensities related to those of certain molecular species, e.g.C2as suggested by Lew Hobbs' and Ted Snow's group? Do the DIB ...

We demonstrate evident Doppler splitting in the profiles of many narrow diffuse interstellar bands (DIBs). Their components are compared with those of atomic and molecular lines of interstellar origin. It is shown that it is likely that the species that shares both wavelength shifts and strength ratios of the Doppler components seen in the DIB profiles is the CH radical. Because of this profile resemblance, it is recommended that CH lines can be used to shift spectra to the rest velocity frame for interstellar features, especially to determine the DIB rest wavelengths on the basis of the CH line at 4300.3132 Å in the spectrum of HD 147889. Our results strongly support a molecular origin of diffuse bands.

This paper presents a new systematic survey of diffuse interstellar bands in the optical wavelength range from 5650 to 6865Å based on echelle spectra of medium-reddened early-type stars acquired at McDonald Observatory. Adding up interstellar spectra of the same type (as it was done by Kre lowski et al. 1997) we reached a very high signal-to-noise ratio. In this spectral range 89 new features have been discovered, 62 of them certain. In the whole spectral range of this survey we have found 240 features, 213 of them certain.

This paper presents a survey of the high-resolution profiles of selected, moderately weak diffuse interstellar bands (DIBs) between 4725 and 6730 Å. In very high signal-to-noise spectra, obtained as a result of averaging several individual exposures of reddened, early-type stars that show Doppler splitting of <2 km s −1 in interstellar gas lines, the profiles seem to have a substructure. This supports the molecular origin hypothesis for DIBs. We studied the profiles of the diffuse interstellar bands at wavelengths of 4726.

The recently published idea that intensities of some weak diffuse interstellar bands (DIBs) are related to the C 2 molecule column density have been examined. We use a set of high quality echelle spectra of heavily reddened stars, acquired at the Bohyunsan Optical Astronomical Observatory (South Korea), with a resolution R = 30 000. The high quality (high S/N ratio) of our spectra is proved by the fact that despite using the most widely used Phillips (2, 0) band of the C 2 molecule (near 8760 Å), we can trace the (3, 0) Phillips band (near 7725 Å) as well. Equivalent widths of four (5176, 5542, 5546 and 5769 Å) out of 16 examined DIBs demonstrate relatively good correlation with C 2 column density. However, a majority of the studied DIBs, already reported as "C 2 " ones, most likely are not related to this simplest carbon molecule. A removal of peculiar objects like HD 34078 from the analyzed sample does not substantially change the level of correlations.

This paper presents a finding of the correlation between the width of a strong diffuse interstellar band at 6196 Å and the excitation temperature of C 2 based on high resolution and high signal-to-noise ratio spectra. The excitation temperature was determined from absorption lines of the Phillips A

We report the detection of the ground-state rotational transition of the methylidyne cation CH + and its isotopologue 13 CH + toward the remote massive star-forming regions W33A, W49N, and W51 with the HIFI instrument onboard the Herschel satellite. Both lines are seen only in absorption against the dust continuum emission of the star-forming regions. The CH + absorption is saturated over almost the entire velocity ranges sampled by the lines-of-sight that include gas associated with the star-forming regions (SFR) and Galactic foreground material. The CH + column densities are inferred from the optically thin components. A lower limit of the isotopic ratio [ 12 CH + ]/[ 13 CH + ] > 35.5 is derived from the absorptions of foreground material toward W49N. The column density ratio, N(CH +)/N(HCO +), is found to vary by at least a factor 10, between 4 and >40, in the Galactic foreground material. Line-of-sight 12 CH + average abundances relative to total hydrogen are estimated. Their average value, N(CH +)/N H > 2.6 × 10 −8 , is higher than that observed in the solar neighborhood and confirms the high abundances of CH + in the Galactic interstellar medium. We compare this result to the predictions of turbulent dissipation regions (TDR) models and find that these high abundances can be reproduced for the inner Galaxy conditions. It is remarkable that the range of predicted N(CH +)/N(HCO +) ratios, from 1 to ∼50, is comparable to that observed.

We report the detection of absorption lines by the reactive ions OH + , H 2 O + and H 3 O + along the line of sight to the submillimeter continuum source G10.6−0.4 (W31C). We used the Herschel HIFI instrument in dual beam switch mode to observe the ground state rotational transitions of OH + at 971 GHz, H 2 O + at 1115 and 607 GHz, and H 3 O + at 984 GHz. The resultant spectra show deep absorption over a broad velocity range that originates in the interstellar matter along the line of sight to G10.6−0.4 as well as in the molecular gas directly associated with that source. The OH + spectrum reaches saturation over most velocities corresponding to the foreground gas, while the opacity of the H 2 O + lines remains lower than 1 in the same velocity range, and the H 3 O + line shows only weak absorption. For LSR velocities between 7 and 50 km s −1 we estimate total column densities of N(OH +) ≥ 2.5 × 10 14 cm −2 , N(H 2 O +) ∼6 × 10 13 cm −2 and N(H 3 O +) ∼4.0 × 10 13 cm −2. These detections confirm the role of O + and OH + in initiating the oxygen chemistry in diffuse molecular gas and strengthen our understanding of the gas phase production of water. The high ratio of the OH + by the H 2 O + column density implies that these species predominantly trace low-density gas with a small fraction of hydrogen in molecular form.

We present a careful analysis of very high resolution (R = 220 000) profiles of two well correlated diffuse interstellar bands (DIBs): 6196 and 6614Å observed along 7 lines of sight free of the Doppler splitting in interstellar atomic lines. The high signal-to-noise ratio (S/N) of the spectra (∼600-1000) allows us to draw definite conclusion that the ratio of equivalent widths of the two DIBs is not always exactly the same, i.e. they do not seem to originate at the same carrier. The DIB profiles vary from object to object but the variations are different for every DIB. The width of 6196 DIB may change by up to 1.5 times lowest value while that of 6614 remains almost constant. The broadening of 6196 is not caused by the Doppler splitting, absent in atomic interstellar lines. Possibly this fact reflects a strong dependence of the carrier excitation pattern on small variations of physical parameters. The variations of substructure strength ratios inside the 6614 DIB profile, evident in our spectra, are apparently caused by a mechanism different from that which broadens DIB 6196.

We present observations of the major diffuse interstellar bands (DIBs) at 5780 and 5797Å as well as literature data and our own observations of the violet lines of CH and CH + , in the lines of sight toward some 70 stars representing various degrees of the interstellar reddening. The correlations are shown and discussed in the context of indicators such as far-UV extinction parameters and neutral molecular abundances. The results show that the DIBs in question (λλ5797 and 5780) both probably form in diffuse cloud interiors, in a related regime where CH and H 2 form. The ratio of the two DIBs correlates with CH abundance, confirming that the λ5797 carrier is favoured in enhanced molecular gas regions over the λ5780 carrier. The ratio of the two DIBs correlates poorly with CH + abundance. Our compilation of observational data also suggests that the DIB ratio may be equally useful as a cloud type indicator as is R V , the ratio of total to selective extinction, and much more readily observed.

We discuss the behaviour of broad and narrow diffuse interstellar bands inside the Orion association. The peculiarities, observed in this region, such as enormous weakness of some features as well as wavelength shifts of others suggest that the diffuse band carriers - most probably some sort of complex molecules - accrete onto grain surfaces. It appears that the processes which occur upon accretion make the narrow DIBs vanish while the broader features are less attenuated but always red-shifted. The observed shapes of interstellar extinction curves suggest that where this happens the small dust grains which are responsible for the FUV extinction are also reduced in numbers which naturally goes along with gas accretion and increased ratio of total to selective extinction.

A new kind of interstellar cloud is proposed. These are rare (just a few examples among ∼300 lines of sight) objects with the Ca I 4227-Å, Fe I 3720-Å and 3860-Å lines stronger than those of K I (near 7699 Å) and Na I (near 3302 Å). We propose the name 'CaFe' for these clouds. Apparently they occupy different volumes from the well-known interstellar H I clouds where the K I and ultraviolet Na I lines are dominant features. In the CaFe clouds we have not found either detectable molecular features (CH, CN) or diffuse interstellar bands which, as commonly believed, are carried by some complex, organic molecules. We have found the CaFe clouds only along sightlines toward hot, luminous (and thus distant) objects with high rates of mass loss. In principle, the observed gas-phase interstellar abundances reflect the combined effects of the nucleosynthetic history of the material, the depletion of heavy elements into dust grains and the ionization state of these elements which may depend on irradiation by neighbouring stars.

Ultra-high-resolution (R ∼ 300 000) profiles of four diffuse interstellar bands (DIBs) are presented. The λλ 5797-, 5850-, 6196-and 6379-Å DIBs were observed towards the reddened supergiant HD 24398, a line of sight free of Doppler splitting; thus the observed profiles can be considered as intrinsic to the DIB carriers. Three of the profiles show substructure which supports the hypothesis of a molecular origin for these DIBs.

We relate the equivalent widths of the major diffuse interstellar bands (DIBs) near 5797 and 5780 Å with different colour excesses, normalized by EðB 2 VÞ, which characterize the growth of interstellar extinction in different wavelength ranges. It is demonstrated that the two DIBs correlate best with different parts of the extinction curve, and the ratio of these diffuse bands is best correlated with the far-ultraviolet (UV) rise. A number of peculiar lines of sight are also found, indicating that the carriers of some DIBs and the far-UV extinction can be separated in certain environments, e.g. towards the Per OB2 association.

The paper analyses the profiles of interstellar features observed towards heavily reddened stars. All the features show spectacular Doppler-splitting but the radial velocities of the single components as well as the number of such components vary from feature to feature in the same spectrum. Implications concerning the wavelengths of unidentified interstellar lines or bands are briefly discussed.

The paper presents a survey of profiles of reasonably strong diffuse interstellar bands (DIBs) based on the extensive set of high-resolution spectra acquired with the aid of echelle spectrographs installed at the 2-m Terskol, 2-m Pic du Midi and 1-m SAO telescopes. The surveyed diffuse interstellar bands cover the spectral ranges of blue and near-infrared, i.e the DIBs not surveyed by Kreøowski & Schmidt. The possible modifications caused by stellar and telluric lines are discussed. The very broad features such as 4430 are not discussed because the shapes of their profiles, extracted from echelle spectra, are very uncertain. The signal-to-noise (S/N) ratios of the spectra are not high enough to enable discussion of the profiles of numerous weak interstellar features discovered recently.