We present a theoretical calculation of the influence of ultraviolet radiative pumping on the excitation of the rotational levels of the ground vibrational state for HD molecules under conditions of the cold diffuse interstellar medium (ISM). Two main excitation mechanisms have been taken into account in our analysis: (i) collisions with atoms and molecules and (ii) radiative pumping by the interstellar ultraviolet (UV) radiation field. The calculation of the radiative pumping rate coefficients $Γ_{\rm ij}$ corresponding to Drane's model of the field of interstellar UV radiation, taking into account the self-shielding of HD molecules, is performed. We found that the population of the first HD rotational level ($J = 1$) is determined mainly by radiative pumping rather than by collisions if the thermal gas pressure $p_{\rm th}\le10^4\left(\frac{I_{\rm{UV}}}{1}\right)\,\mbox{K\,cm}^{-3}$ and the column density of HD is lower than $\log N({\rm{HD}})<15$. Under this constraint the populations of rotational levels of HD turns out to be as well a more sensitive indicator of the UV radiation intensity than the fine-structure levels of atomic carbon. We suggest that taking into account radiative pumping of HD rotational levels may be important for the problem of the cooling of primordial gas at high redshift: ultraviolet radiation from first stars can increase the rate of HD cooling of the primordial gas in the early Universe.
This paper considers a very special set of a few interstellar features --- broad diffuse interstellar bands (DIBs) at 4430, 4882, 5450, 5779 and 6175 ÅÅ. The set is small, and measurements of equivalent widths of these DIBs are challenging because of severe stellar, interstellar, and sometimes, also telluric contaminations inside their broad profiles. Nevertheless, we demonstrate that they do correlate pretty tightly (DIBs 4882 and 5450 to a lesser extent though) with other narrower diffuse bands, as well as with the color excess E(B$-$V). The studied broad DIBs correlate well with both inters…
Emission of fullerenes in their infrared vibrational bands has been detected in space near hot stars. The proposed attribution of the diffuse interstellar bands at 9577 and 9632 Å to electronic transitions of the buckminsterfullerene cation (i.e. C$_{60}^+$ ) was recently supported by new laboratory data, confirming the presence of this species in the diffuse interstellar medium (ISM). In this letter, we present the detection, also in the diffuse ISM, of the 17.4 and 18.9 $μ$m emission bands commonly attributed to vibrational bands of neutral C$_{60}$. According to classical models that comput…
A previous article argued that the antagonism between sight-lines with and without a bump at 2200 Å disappears, and that the observed properties of interstellar extinction can be globally understood, if it is accepted that scattered starlight contaminates the observed spectrum of reddened stars. The present paper develops this new paradigm by providing a better understanding of the characteristics of this scattered light. It further examines the consequences of this revision of interstellar extinction theory for interpreting the 2200 Å bump and the diffuse interstellar bands (DIBs). Two implic…
We present the first mid-IR detection of the linear polarization toward the star CygOB2-12, a luminous blue hypergiant that, with Av of ~10 mag of foreground extinction, is a benchmark in the study of the properties of dust in the diffuse interstellar medium. The 8-13 micrometer spectropolarimetry, obtained with the CanariCam multi-mode camera at the Gran Telescopio Canarias (GTC), shows clear trends with wavelength characteristic of silicate grains aligned in the interstellar magnetic field. The maximum polarization, detected with 7.8 statistical significance near 10.2 micrometers, is (1.24 +…
Recently, the presence of fullerenes in the interstellar medium (ISM) has been confirmed especially with the first confirmed identification of two strong diffuse interstellar bands (DIBs) with C60+. This justifies reassesing the importance of interstellar fullerenes of various sizes with endohedral or exohedral inclusions and heterofullerenes (EEHFs). The phenomenology of fullerenes is complex. In addition to fullerene formation in shock shattering, fully dehydrogenated PAHs in diffuse interstellar (IS) clouds could perhaps efficiently transform into fullerenes including EEHFs. But it is extre…
Context. Insight into the conditions that drive the physics and chemistry in interstellar clouds is gained from determining the abundance and charge state of their components. Aims. We propose an evaluation of the C60:C60+ ratio in diffuse and translucent interstellar clouds that exploits electronic absorption bands so as not to rely on ambiguous IR emission measurements. Methods. The ratio is determined by analyzing archival spectra and literature data. Information on the cation population is obtained from published characteristics of the main diffuse interstellar bands attributed to C60+ and…
We study, for the first time, the relations of two strong diffuse bands (DIBs) at 9633 and 9577~Å, commonly attributed to C$_{60}^+$, to other interstellar features seen in optical and UV spectra including H{\sc i}, Ca{\sc i}, Fe{\sc ii}, Na{\sc i}, Ti{\sc ii}, CN, CH, CH$^+$, and C$_2$ and DIBs 5780, 5797, 6196, 6269, 6284, and 6614. We analyzed 62 lines of sight where the stellar contamination by Mg{\sc ii} was corrected or found negligible for DIB 9633. Equivalent widths of DIB 9577 were measured in 62 lines of sight. Poor mutual correlation between the strengths of the above features and t…
Inverse Raman scattering and the diffuse interstellar bands: an exploration of the systemic interconnections between spontaneous and inverse Raman scattering and extended red emission, Red Rectangle bands, and diffuse interstellar bands
We present a general parameter study, in which the abundance of interstellar argonium (ArH$^+$) is predicted using a model for the physics and chemistry of diffuse interstellar gas clouds. Results have been obtained as a function of UV radiation field, cosmic-ray ionization rate, and cloud extinction. No single set of cloud parameters provides an acceptable fit to the typical ArH$^+$, OH$^+$ and $\rm H_2O^+$ abundances observed in diffuse clouds within the Galactic disk. Instead, the observed abundances suggest that ArH$^+$ resides primarily in a separate population of small clouds of total vi…
The paper describes profile broadening and peak wavelength variation of diffuse interstellar bands (DIBs) measured for 46 lines of sight, probably caused by physical properties of intervening clouds. Full width at half maximum of four studied diffuse bands (5780, 5797, 6196 and 6614 Å) demonstrate strong variability sometimes doubling the features' width. Despite the high magnitude of the effect, our current analysis is restricted to the strongest diffuse bands because the weaker ones require a much higher S/N ratio. The profile broadening in the studied DIBs moves the profile's centers toward…
Diffuse interstellar bands in Upper Scorpius: Probing variations in the DIB spectrum due to changing environmental conditions
我们研究了局部环境条件对Sco OB 2星协上天蝎座亚群内弥漫星际带（DIB）载流子的影响。我们用FEROS获得了光谱，并测量了五个DIB（在5780，5797，6196，6379和6613埃）以及双原子分子（CH，CH+，CN）和原子（KI，CaI）对89个目标在上天蝎座方向的吸收线的等效宽度。我们建立了一个简单的辐射转移和化学网络模型的扩散星际介质（ISM）片在UppSco前面的有效辐射场推断。在探测UppScoISM的55条视线范围内，得到了星际辐射场强度I_UV和分子氢分数f_H2。讨论了DIB强度、CH和CH+线强度、E（B-V）、I_UV和f_H_2之间的关系。5780和5797个DIB之间的比率揭示了在云密度和暴露于星际辐射场方面对当地环境的（空间）依赖性，反映了这些DIB载体的分子性质。
In the second paper of the series, we have modeled low frequency carbon radio recombination lines (CRRL) from the interstellar medium. Anticipating the LOw Frequency ARray (LOFAR) survey of Galactic CRRLs, we focus our study on the physical conditions of the diffuse cold neutral medium (CNM). We have used the improved departure coefficients computed in the first paper of the series to calculate line-to-continuum ratios. The results show that the line width and integrated optical depths of CRRL are sensitive probes of the electron density, gas temperature, and the emission measure of the cloud.…
The content of interstellar clouds, in particular the inventory of diffuse molecular gas, remains uncertain. We identified a sample of isolated clouds, approximately 100 solar masses in size, and used the dust content to estimate the total amount of gas. In Paper 1, the total inferred gas content was found significantly larger than that seen in 21-cm emission measurements of atomic hydrogen. In this paper we test the hypothesis that the apparent excess 'dark' gas is cold atomic hydrogen, which would be evident in absorption but not in emission due to line saturation. The results show there is …
The chemistry of the diffuse interstellar medium is driven by the combined influences of cosmic rays, ultraviolet (UV) radiation, and turbulence. Previously detected at the outer edges of photodissociation regions (PDRs) and formed from the reaction of C+ and OH, CO+ is the main chemical precursor of HCO+ and CO in a thermal, cosmic-ray, and UV-driven chemistry. Our aim was to test whether the thermal cosmic-ray and UV-driven chemistry is producing CO in diffuse interstellar molecular gas through the intermediate formation of CO+ We searched for CO+ absorption with the Atacama Large Millimeter…
With the use of the data from archives, we studied the correlations between the equivalent widths of four diffuse interstellar bands (4430$Å$, 5780$Å$, 5797$Å$, 6284$Å$) and properties of the target stars (colour excess values, distances and Galactic coordinates). Many different plots of the diffuse interstellar bands and their maps were produced and further analysed. There appears to be a structure in the plot of equivalent widths of 5780$Å$ DIB (and 6284$Å$ DIB) against the Galactic $x$-coordinate. The structure is well defined below $\sim150$ m$Å$ and within $|x|<250$ pc, peaking around $x=…
Magnetism is one of the most important forces on the interstellar medium (ISM), anisotropically regulating the structure and star formation that drive galactic evolution. Recent high dynamic range observations of diffuse gas and molecular clouds have revealed new links between interstellar structures and the ambient magnetic field. ISM morphology encodes rich physical information, but deciphering it requires high-resolution measurements of the magnetic field: linear polarization of starlight and dust emission, and Zeeman splitting. These measure different components of the magnetic field, and …
Whether ice in cold cosmic environments is physically separated from the silicate dust or mixed with individual silicate moieties is not known. However, different grain models give very different compositions and temperatures of grains. The aim of the present study is a comparison of the mid-IR spectra of laboratory silicate-grains/water-ice mixtures with astronomical observations to evaluate the presence of dust/ice mixtures in interstellar and circumstellar environments. The laboratory data can explain the observations assuming reasonable mass-averaged temperatures for the protostellar envel…
The advent of more precise measurements of distance estimates for some objects (bayesian estimates for filaments, trigonometric estimates for masers) permits a better comparison of their relative locations, and a comparison with a most recent spiral arm model fitted to the diffuse CO 1-0 gas. Our results support the idea that some bone-like filaments, greater than 10 pc (labeled elsewhere as bones, mst, herschel) and smaller than 100 pc, are observed near the potential minimum of the Scutum spiral arm (bone-like filaments are offset outward from masers by about 200 pc).
The origin of the diffuse interstellar bands is one of the longest-standing mysteries of the interstellar medium is explored within the framework of The Heterogeneous dust Evolution Model at the IaS (THEMIS). The likely nature of the diffuse interstellar band carriers and their evolution is here explored within the framework of the structures and sub-structures inherent to doped hydrogenated amorphous carbon grains in the interstellar medium. Based on the natural aromatic-rich moieties (ashphaltenes) recovered from coal and oil the likely structure of their interstellar analogues is investigat…
The Abundance of Boron in Diffuse Interstellar Clouds
我们提出了一个全面的调查硼丰度在弥漫的星际云的观测与空间望远镜成像光谱仪（STIS）的哈勃太空望远镜。我们的56条银河系视线的样本是对B II 1362共振线的存档STIS数据进行完整搜索的结果，每个检测都被O I 1355，Cu II 1358和Ga II 1414（可用时）以相同速度吸收的存在所证实。五个以前的测量星际B II戈达德高分辨率摄谱仪观测纳入我们的分析，产生一个合并的样本，超过四倍的视线与显着的硼检测。我们的调查也构成了第一个广泛的分析星际镓从STIS光谱和扩大以前发表的结果氧和铜。观测探测了高密度和低密度的扩散环境，使星际消耗的密度依赖效应能够在每个元素的气相丰度数据中清楚地识别出来。在硼的情况下，增加的相对贫化线的视线密度相当于0.8德克斯之间的丰度差的暖相和冷相的弥漫星际介质。在温暖的低密度气体中，硼的丰度为B/H =（2.4+/-0.6）*10^-10，这意味着相对于陨石硼的丰度，硼的丰度减少了60%。除了耗尽的影响，我们的调查揭示了具有增强的硼丰度的视线，这些硼丰度可能追踪最近产生的11 B，其产生于涉及宇宙射线或中微子的spiritual反应。未来的观测将有助于解开11B合成的两个spectrum通道的相对贡献。
We report cosmic ray ionization rates towards ten reddened stars studied within the framework of the EDIBLES (ESO Diffuse Interstellar Bands Large Exploration Survey) program, using the VLT-UVES. For each sightline, between 2 and 10 individual rotational lines of OH$^+$ have been detected in its (0,0) and (1,0) $A^3Π-X^3Σ^-$ electronic band system. This allows constraining of OH$^+$ column densities towards different objects. Results are also presented for 28 additional sightlines for which only one or rather weak signals are found. An analysis of these data makes it possible to derive the pri…
Grain growth by accretion of gas-phase metals is a common assumption in models of dust evolution, but in dense gas, where the timescale is short enough for accretion to be effective, material is accreted in the form of ice mantles rather than adding to the refractory grain mass. It has been suggested that negatively-charged small grains in the diffuse interstellar medium (ISM) can accrete efficiently due to the Coulomb attraction of positively-charged ions, avoiding this issue. We show that this inevitably results in the growth of the small-grain radii until they become positively charged, at …
Understanding the effects of dust extinction is important to properly interpret observations. The optical total-to-selective extinction ratio, Rv = Av/E(B-V), is widely used to describe extinction variations in ultraviolet and optical bands. Since the Rv=3.1 extinction curve adequately represents the average extinction law of diffuse regions in the Milky Way, it is commonly used to correct observational measurements along sightlines toward diffuse regions in the interstellar medium. However, the Rv value may vary even along different diffuse interstellar medium sightlines. In this paper, we in…
The carriers of the still (mostly) unidentified diffuse interstellar bands (DIBs) have been a long-standing mystery ever since their first discovery exactly 100 years ago. In recent years, the ubiquitous detection of a large number of DIBs in a wide range of Galactic and extragalactic environments has led to renewed interest in connecting the occurrence and properties of DIBs to the physical and chemical conditions of the interstellar clouds, with particular attention paid to whether the DIB strength is related to the shape of the interstellar extinction curve. To shed light on the nature and …
We confirm, using spectra from seven observatories, that the diffuse bands 6196 and 6614 are very tightly correlated. However, their strength ratio is not constant as well as profile shapes. Apparently the two interstellar features do not react in unison to the varying physical conditions of different interstellar clouds.
We have revisited the chemistry of chlorine-bearing species in the diffuse interstellar medium with new observations of the HCl$^+$ molecular ion and new astrochemical models. Using the GREAT instrument on board SOFIA, we observed the $^2Π_{3/2}\, J = 5/2 - 3/2$ transition of HCl$^+$ near 1444 GHz toward the bright THz continuum source W49N. We detected absorption by diffuse foreground gas unassociated with the background source, and were able to thereby measure the distribution of HCl$^+$ along the sight-line. We interpreted the observational data using an updated version of an astrochemical …
