Diffuse Interstellar Bands Research Articles

Electronic spectroscopy of heptacene ions in the search for carriers of diffuse interstellar bands

Context. The absorption bands of the interstellar medium (ISM) in the optical and near-infrared regions called the diffuse interstellar bands (DIBs) have been known for almost a century, yet their origins remain largely unknown. Knowledge of molecular carriers of DIBs would allow for a much better understanding of the chemistry and physics of the ISM. Polycyclic aromatic hydrocarbons (PAHs) and, among them, polyacenes have been suggested as promising candidates for carriers of DIBs. Aims. In this paper, we report on the spectroscopy of heptacene (Hep), the polyacene molecule consisting of seven aromatic rings in a linear arrangement, in its cationic and anionic forms (Hep+/−). The performed spectroscopic studies made it possible to accurately determine the Hep+/− absorption band positions and to conduct a direct comparison of laboratory and observational spectra. Methods. We utilized helium-tagging action spectroscopy to measure the spectra of Hep+/− in a wide spectral range of 3000–13 000 Å. In most cases, the spectra obtained by this method can be directly compared with the observational spectra. By analyzing the spectral shift as a function of the number of attached helium atoms, we obtained precise estimates of the gas-phase band positions. Quantum-chemical computations were used to support and interpret the findings. Matrix isolation spectroscopy provided information on the spectral properties of neutral Hep and extended the spectral range for Hep+. Results. We found several absorption bands characterized by a rather large full width at half maximum in the spectra of Hep+/−. The two most intense bands were found at 4714 ± 5 Å and 12 250 ± 12 Å for Hep+ and at 4673 ± 14 Å and 11326 ± 4 Å for Hep−. We did not find any good match between laboratory and observational spectra. In particular, the intrinsic width of the absorption bands of Hep+/− is much higher than that of most observed DIBs. Conclusions. The non-detection of Hep+/− in the observational spectra excludes the bottom-up formation route for polyacenes in the ISM. Larger polyacene molecules could still be considered as potential carriers of DIBs in the case of an efficient top-down formation route. All currently measured polyacene ions exhibit relatively broad absorption bands. Therefore, additional spectroscopy studies of neutral polyacenes and larger polyacene ions as well as the study of possible top-down formation routes are suggested.

Gas-phase C60Hn+q (n = 0-4, q = 0,1) fullerenes and fulleranes: spectroscopic simulations shed light on cosmic molecular structures.

The discovery of C60, C60+, and C70 in the interstellar medium has ignited a profound interest in the astrochemistry of fullerene and related systems. In particular, the presence of diffuse interstellar bands and their association with C60+ has led to the hypothesis that hydrogenated derivatives, known as fulleranes, may also exist in the interstellar medium and contribute to these bands. In this study, we systematically investigated the structural and spectroscopic properties of C60Hn+q (n = 0-4, q = 0,1) using an automated global minimum search and density functional theory calculations. Our results revealed novel global minimum structures for C60H2 and C60H4, distinct from previous reports. Notably, all hydrogenated fullerenes exhibited lower ionization potentials and higher proton affinities compared to C60. From an astrochemical perspective, our results exposed the challenges in establishing definitive spectroscopic criteria for detecting fulleranes using mid-infrared and UV-Vis spectroscopies. However, we successfully identified distinct electronic transitions in the near-infrared range that serve as distinctive signatures of cationic fulleranes. We strongly advocate for further high-resolution experimental studies to fully explore the potential of these transitions for the interstellar detection of fulleranes.

The Pristine Inner Galaxy Survey (PIGS) – VI. Different vertical distributions between two DIBs at 442.8 nm and 862.1 nm

ABSTRACT Although diffuse interstellar bands (DIBs) were discovered over 100 yr ago, for most of them, their origins are still unknown. Investigation on the correlations between different DIBs is an important way to study the behaviour and distributions of their carriers. Based on stacking thousands of spectra from the Pristine Inner Galaxy Survey, we study the correlations between two DIBs at 442.8 nm (λ442.8) and 862.1 nm (λ862.1), as well as the dust grains, in a range of latitude spanning ∼22° ($4^{\circ }\, {\lt }\, |b|\, {\lt }\, 15^{\circ }$) toward the Galactic Centre ($|\ell |\, {\lt }\, 11^{\circ }$). Tight linear intensity correlations can be found between λ442.8, λ862.1, and dust grains for $|b|\, {\lt }\, 12^{\circ }$ or $E(B\, {-}\, V)\, {\gt }\, 0.3$ mag. For $|b|\, {\gt }\, 12^{\circ }$, λ442.8 and λ862.1 present larger relative strength with respect to the dust grains. A systematic variation of the relative strength between λ442.8 and λ862.1 with |b| and $E(B\, {-}\, V)$ concludes that the two DIBs do not share a common carrier. Furthermore, the carrier of λ862.1 is more abundant at high latitudes than that of λ442.8. This work can be treated as an example showing the significance and potentials to the DIB research covering a large latitude range.

Spectroscopic Confirmation of a Population of Isolated, Intermediate-mass Young Stellar Objects

Wide-field searches for young stellar objects (YSOs) can place useful constraints on the prevalence of clustered versus distributed star formation. The Spitzer/IRAC Candidate YSO (SPICY) catalog is one of the largest compilations of such objects (∼120,000 candidates in the Galactic midplane). Many SPICY candidates are spatially clustered, but, perhaps surprisingly, approximately half the candidates appear spatially distributed. To better characterize this unexpected population and confirm its nature, we obtained Palomar/DBSP spectroscopy for 26 of the optically bright (G < 15 mag) “isolated” YSO candidates. We confirm the YSO classifications of all 26 sources based on their positions on the Hertzsprung–Russell diagram, H and Ca ii line emission from over half the sample, and robust detection of infrared excesses. This implies a contamination rate of <10% for SPICY stars that meet our optical selection criteria. Spectral types range from B4 to K3, with A-type stars being the most common. Spectral energy distributions, diffuse interstellar bands, and Galactic extinction maps indicate moderate-to-high extinction. Stellar masses range from ∼1 to 7 M ⊙, and the estimated accretion rates, ranging from 3 × 10−8 to 3 × 10−7 M ⊙ yr−1, are typical for YSOs in this mass range. The 3D spatial distribution of these stars, based on Gaia astrometry, reveals that the “isolated” YSOs are not evenly distributed in the Solar neighborhood but are concentrated in kiloparsec-scale dusty Galactic structures that also contain the majority of the SPICY YSO clusters. Thus, the processes that produce large Galactic star-forming structures may yield nearly as many distributed as clustered YSOs.

Measuring Optical Extinction toward Young Stellar Objects Using Diffuse Interstellar Bands

Line-of-sight extinction estimates of well-studied young T Tauri and Herbig Ae/Be stars are based on many different measurements and analysis methods. This has resulted in wide scatter among the published A V values for the same star. In this work, we discuss the challenges in measuring extinction to actively accreting and especially outbursting young stellar objects (YSOs). We then explore a method not previously applied to young stars utilizing diffuse interstellar bands (DIBs). In early-type stars, narrow correlations exist between the DIB equivalent widths and the column density of interstellar material, and therefore the line-of-sight extinction. Here, we measure the equivalent widths of the 5780 and 6614 Å DIB features in a sample of actively accreting YSOs, and apply a DIB-reddening calibration to estimate reddening and subsequently extinction. Our calibration is newly derived from a composite of available literature data and fully accounts for the scatter in these measurements. We also compare the DIBs-inferred optical line-of-sight extinction values with previous extinction estimates for our sample stars.

Gas-phase optical absorption spectra of the indene cation (C9H8 +)

The electronic transition spectra of the indene molecular cation (In, ) in the 550–580 nm region has been measured in the gas phase in direct absorption. The spectra were experimentally recorded using sensitive cavity ring-down spectroscopy in a supersonically expanding planar plasma. Two lifetime-broadened vibronic bands are assigned to the - electronic transition system of In. A set of indicative spectroscopic parameters have been obtained from a band contour analysis of the 0 band in combination with supporting ab-initio calculations. The inferred Lorentz line width of indicates an upper state lifetime of . The laboratory data are compared to the diffuse interstellar bands (DIBs), and no matches can be found. Upper limits for In column densities in the diffuse interstellar medium have also been estimated from six sightline spectra.

Optical Spectrum of the Diamantane Radical Cation

Similarities exist between the infrared spectra of diamondoids and unidentified infrared emission bands seen in the spectra of young stars with circumstellar disks. Due to their low ionization energy and absorption in the visible range, the radical cations of these highly stable molecules are also suggested to contribute to the well-known but largely unassigned diffuse interstellar bands. However, thus far only the optical spectrum of the adamantane cation (Ada+) has been measured in the laboratory, which is required for astronomical identification. Herein, we present the optical spectrum of the diamantane radical cation (C14H20 +, Dia+, D 3d) between 400 and 1000 nm in the gas phase. The spectra are obtained by electronic photodissociation (EPD) of mass-selected ions generated by electron ionization and trapping in a cryogenic trap at 5 K. The most intense fragmentation channels are the losses of H and C4H9. The optical spectrum reveals two broad and unresolved bands centered near 760 and 450 nm that are assigned to the D 2(2 E u) ← D 0(2 A 1g) and D 5(2 A 2u) ← D 0(2 A 1g) transitions using density functional theory. Despite a vibrational temperature below 20 K, no vibrational structure is resolved. Franck–Condon simulations of the D 5 ← D 0 transition predict intense vibronic progressions that become indiscernible from the band contour at spectral widths above 350 cm−1. Thus, the lack of resolved spectral features is attributed to lifetime broadening, Franck–Condon congestion arising from geometric changes, and possibly vibronic coupling. In addition to the EPD spectra, we characterize the ground state of Dia+ by analysis of a remeasured photoelectron spectrum and a predicted infrared spectrum.

Fluorescence Excitation and Dispersed Fluorescence Spectra of the 1-Hydronaphthyl Radical (1-C10H9) in Solid para-Hydrogen.

Matrix isolation spectroscopy with para-hydrogen (p-H2) has previously been employed to record IR absorption spectra of hydrogenated and protonated polycyclic aromatic hydrocarbons (PAHs), prospective carriers of unidentified infrared and diffuse interstellar bands. Despite the promising prospects of p-H2 as matrix host, especially the rather weak interaction with the guest molecules and the resulting small matrix shifts, p-H2 matrix isolation spectroscopy has rarely been applied to study electronic transitions of guest molecules. Here, we present the dispersed fluorescence and fluorescence excitation spectrum of the 1-hydronaphthyl radical (1-C10H9) isolated in solid p-H2. We observed a strong 000 band associated with the electronic transition to the first excited electronic state at 18881 cm-1, red-shifted by ∼68 cm-1 relative to a value reported for jet-cooled 1-C10H9. From a comparison of our experimental results to simulated vibrationally resolved electronic absorption and emission spectra computed on the basis of (TD-)DFT geometry optimizations and scaled harmonic vibration calculations using the FCclasses code, we derived assignments for observed vibronic transitions. The dispersed fluorescence spectrum of 1-C10H9 is new; it complements the infrared spectrum and identified many vibrational modes unidentifiable with infrared. The excitation spectrum covers a much wider spectral range than previous reports. We compare the excitation spectrum in solid p-H2 to the reported electronic absorption spectrum of jet-cooled gaseous 1-C10H9 and that of 1-C10H9 isolated in solid Ne to assess the influence of p-H2 as a matrix host on the electronic transition of 1-C10H9 and discuss a potential contribution of 1-C10H9 to the diffuse interstellar bands.

Solid confirmation of the broad DIB around 864.8 nm using stacked Gaia–RVS spectra

Context. Studies of the correlation between different diffuse interstellar bands (DIBs) are important for exploring their origins. However, the Gaia–RVS spectral window between 846 and 870 nm contains few DIBs, the strong DIB at 862 nm being the only convincingly confirmed one. Aims. Here we attempt to confirm the existence of a broad DIB around 864.8 nm and estimate its characteristics using the stacked Gaia–RVS spectra of a large number of stars. We study the correlations between the two DIBs at 862 nm (λ862) and 864.8 nm (λ864.8), as well as the interstellar extinction. Methods. We obtained spectra of the interstellar medium (ISM) absorption by subtracting the stellar components using templates constructed from real spectra at high Galactic latitudes with low extinctions. We then stacked the ISM spectra in Galactic coordinates (ℓ, b) – pixelized by the HEALPix scheme – to measure the DIBs. The stacked spectrum is modeled by the profiles of the two DIBs, Gaussian for λ862 and Lorentzian for λ864.8, and a linear continuum. We report the fitted central depth (CD), central wavelength, equivalent width (EW), and their uncertainties for the two DIBs. Results. We obtain 8458 stacked spectra in total, of which 1103 (13%) have reliable fitting results after applying numerous conservative filters. This work is the first of its kind to fit and measure λ862 and λ864.8 simultaneously in cool-star spectra. Based on these measurements, we find that the EWs and CDs of λ862 and λ864.8 are well correlated with each other, with Pearson coefficients (rp) of 0.78 and 0.87, respectively. The full width at half maximum (FWHM) of λ864.8 is estimated as 1.62 ± 0.33 nm which compares to 0.55 ± 0.06 nm for λ862. We also measure the vacuum rest-frame wavelength of λ864.8 to be λ0 = 864.53 ± 0.14 nm, smaller than previous estimates. Conclusions. We find solid confirmation of the existence of the DIB around 864.8 nm based on an exploration of its correlation with λ862 and estimation of its FWHM. The DIB λ864.8 is very broad and shallow. That at λ862 correlates better with E(BP − RP) than λ864.8. The profiles of the two DIBs could strongly overlap with each other, which contributes to the skew of the λ862 profile.

Guiding astronomical observations by understanding vibronic coupling interactions

Experiments and simulations of ethynyl radical spectra may lead to predictions for larger carbon chains and reveal the molecules responsible for the diffuse interstellar bands.

Survey of Near-infrared Diffuse Interstellar Bands in Y and J Bands. I. Newly Identified Bands

We searched for diffuse interstellar bands (DIBs) in the 0.91 < λ < 1.33 μm region by analyzing the near-infrared (NIR) high-resolution (R = 20,000 and 28,000) spectra of 31 reddened early-type stars (0.04 < E(B − V) < 4.58) and an unreddened reference star. The spectra were collected using the WINERED spectrograph, which was mounted on the 1.3 m Araki telescope at Koyama Astronomical Observatory, Japan, in 2012–2016, and on the 3.58 m New Technology Telescope at La Silla Observatory, Chile, in 2017–2018. We detected 54 DIBs—25 of which are newly detected by this study—and eight DIB candidates. Using this updated list, the DIB distributions over a wide wavelength range, from optical to NIR, are investigated. The FWHM values of the NIR DIBs are found to be narrower than those of the optical DIBs, on average, which suggests that the DIBs at longer wavelengths tend to be caused by larger molecules. Assuming that the larger carriers are responsible for the DIBs at longer wavelengths, and have larger oscillator strengths, we found that the total column densities of the DIB carriers tend to decrease with increasing DIB wavelength. The candidate molecules and ions for the NIR DIBs are also discussed.

Infrared and Laser-Induced Fluorescence Spectra of Sumanene Isolated in Solid para-Hydrogen.

The para-hydrogen (p-H2) matrix-isolation technique has been scarcely used to record electronic absorption and emission spectra. It is expected that its small matrix shifts due to diminished molecular interactions and the softness of the lattice might be advantageous to help identify the carriers of the diffuse interstellar bands. In this article, we present infrared, fluorescence excitation, and dispersed fluorescence spectra of sumanene (C21H12), a bowl-shaped polycyclic aromatic hydrocarbon and a fragment of C60, isolated in solid p-H2. The recorded vibrational wavenumbers from infrared and dispersed fluorescence agree with the scaled harmonic vibrational wavenumbers calculated with the B3PW91/6-311++G(2d,2p) and B3LYP/6-311++G(2d,2p) methods. The recorded fluorescence excitation spectra are consistent with the spectra of jet-cooled gas-phase C21H12 reported previously by Kunishige et al. We found a rather small matrix shift of 55 cm-1 for the S1-S0 electronic transition origin located at 27 888 cm-1. Vibrational wavenumbers associated with the S1 state of C21H12 inferred from the experimental spectrum can be assigned mostly to fundamental normal modes; they are in satisfactory agreement with scaled harmonic vibrational wavenumbers calculated at the TD-B3PW91/6-311++G(2d,2p) level of theory. Significantly more vibrational modes of the S1 state were identified as compared with those in the reported gas-phase work. The potential of p-H2 matrix-isolation spectroscopy to provide electronic excitation spectra suitable for comparison to astronomical observations is discussed by comparing the spectra of C21H12 isolated in solid p-H2 and in solid Ne, a matrix host commonly employed in astrochemistry.

Diffuse Interstellar Bands λ6379, λ6614, and λ6660 in the LAMOST-MRS Spectra

Diffuse interstellar bands (DIBs) have always been a mysterious existence in astronomical research. In this work, we provide more DIB samples to slightly uncover this mystery. With the LAMOST medium-resolution survey (MRS) spectra, we detected three DIBs λ6379, λ6614, and λ6660, obviously superimposed on the spectra of 11,003 stars. These spectra cover spectral types from O to K, which can provide a large number of candidates for further research on DIBs. The sample shows a clear positive correlation between the strength of DIBs and extinction, which agrees with the result in the literature. In addition, there exist two peaks in each of the velocity distribution of these three DIBs, and the velocity differences between two peaks of each pair are consistent. The reason for the two velocity components is due to the Galactic rotation.

Rotationally resolved gas-phase spectrum of the [formula omitted]2Σ+–[formula omitted]2Π3/2 electronic transition for the cyanogen halide radical cation ICN+

A rotationally resolved gas-phase absorption spectrum of the A∼2Σ+–X∼2Π3/2 electronic transition of the cyanogen iodide radical cation ICN+ was observed by cavity ring-down spectroscopy for the first time. This cation was produced in a supersonic planar discharge jet through a mixture of ICN in helium. By the aid of a program for rotational, vibrational and electronic spectra PGOPHER, the rotational constants were determined to be 0.10700(12) and 0.11002(12) cm−1 for the A∼2Σ+ and X∼2Π3/2 electronic states, respectively, and the band origin to be 18262.083(3) cm−1. The rotational constant ratio β {= (B′−B″)/B″} was determined to be −2.8%. The β values for FCN+, ClCN+, BrCN+, and ICN+ were also evaluated theoretically by CAM-B3LYP/CEP-121G using Gaussian 09W. The rotational profile of the absorption band and its temperature dependence for ClCN+, one of the important candidates for Diffuse Interstellar Bands, were simulated, aiding us in the identification of this cation as in interstellar space.

The EDIBLES survey

Context. Several diffuse interstellar bands (DIBs) have profiles with resolved sub-peaks that resemble rotational bands of large molecules. Analysis of these profiles can constrain the sizes and geometries of the DIB carriers, especially if the profiles exhibit clear variations along lines of sight probing different physical conditions. Aims. Using the extensive data set from the ESO Diffuse Interstellar Bands Large Exploration Survey we searched for systematic variations in the peak-to-peak separation of these sub-peaks for three well-known DIBs in lines of sight with a single dominant interstellar cloud. Methods. We used the spectra of twelve single-cloud sight lines to examine the λλ5797, 6379, and 6614 DIB profiles. We measured the peak-to-peak separation in the band profile substructures for these DIBs. We adopted the rotational contour formalism for linear or spherical top molecules to infer the rotational constant for each DIB carrier and the rotational excitation temperature in the sight lines. We compared these to experimentally or theoretically obtained rotational constants for linear and spherical molecules to estimate the DIB carrier sizes. Results. All three DIBs have peak separations that vary systematically between lines of sight, indicating correlated changes in the rotational excitation temperatures. The rotational constant B of the λ6614 DIB was determined independently of the rotational excitation temperature; we derived B6614 = (22.2 ± 8.9) x 10−3 cm−1, consistent with previous estimates. Assuming a similar rotational temperature for the λ6614 DIB carrier and assuming a linear carrier, we found B5797linear = (5.1 ± 2.0) × 10−3 cm−1 and B6379linear = (2.3 ± 0.9) × 10−3 cm−1. If the carriers of those DIBs are spherical species, on the other hand, their rotational constants are half that value, B5797spherical = (2.6 ± 1.0) × 10−3 cm−1 and B6379spherical = (1.1 ± 0.4) × 10−3 cm−1. Conclusions. Systematic variations in the DIB profiles provide the means to constrain the molecular properties. We estimate molecule sizes that range from 7–9 carbon atoms (λ6614 carrier, linear) to 77–114 carbon atoms (λ6379, spherical).

CRIRES high-resolution near-infrared spectroscopy of diffuse interstellar band profiles

Aims. A high spectral resolution investigation of diffuse interstellar bands (DIBs) in the near-infrared (YJ band) is conducted to test new methods, to confirm and improve existing parameters, and to search for new DIBs. Methods. The CRyogenic high-resolution InfraRed Echelle Spectrograph (CRIRES) on the European Southern Observatory's Very Large Telescope was employed to obtain spectra of four reddened background supergiant stars (HD 183143, HD 165784, HD 92207, HD 111613) and an unreddened comparison star (HD 87737) at the highest resolution of R ≈ 100 000 currently achievable at near-infrared wavelengths, more than twice as high as accomplished in previous near-infrared DIB studies. The correction for telluric absorption was performed by a modelling approach. Non-local thermodynamic equilibrium spectral modelling of available optical and the new near-infrared stellar spectra facilitated a comprehensive characterisation of the atmospheric properties of the background stars. As a consequence, a more precise and accurate determination of the reddening and the reddening law along the respective sight lines could be achieved than feasible before by comparison of the observed and model spectral energy distributions. For DIBs that overlap with stellar lines the DIB profile shapes could be recovered. Results. Seventeen known near-infrared DIBs were confirmed, and 12 previously unknown and generally weaker DIBs were identified in the YJ band. Three DIBs that show uniform profiles along all sight lines were identified, possibly connected to transitions from a common lower state of the same carrier. The divergent extinction curve towards the frequently discussed DIB standard star HD 183143 could be reproduced for the first time, requiring extra absorption by ~3.5 mag due to polycyclic aromatic hydrocarbons (PAHs) to match the ultraviolet extinction bump. This extra absorption probably stems from a circumstellar bubble lying in front of the star which is intersected tangentially by the line of sight, making this particular sight line more peculiar than standard.

Absorption Spectra of Electrified Hydrogen Molecules

Molecular hydrogen normally has only weak, quadrupole transitions between its rovibrational states, but in a static electric field it acquires a dipole moment and a set of allowed transitions. Here we use published ab initio calculations of the static electrical response tensors of the H2 molecule to construct the perturbed rovibrational eigensystem and its ground state absorptions. We restrict attention to two simple field configurations that are relevant to condensed hydrogen molecules in the interstellar medium (ISM): a uniform electric field and the field of a pointlike charge. The energy eigenstates are mixtures of vibrational and angular momentum eigenstates so there are many transitions that satisfy the dipole selection rules. We find that mixing is strongest among the states with high vibrational excitation, leading to hundreds of absorption lines across the optical and near-infrared. These spectra are very different from that of the field-free molecule, so if they appeared in astronomical data they would be difficult to assign. Furthermore, in a condensed environment the excited states likely have short lifetimes to internal conversion, giving the absorption lines a diffuse appearance. We therefore suggest electrified H2 as a possible carrier of the diffuse interstellar bands (DIBs). We further argue that in principle it may be possible to account for all of the DIBs with this one carrier. However, despite electrification, the transitions are not very strong and a large column of condensed H2 would be required, making it difficult to reconcile this possibility with our current understanding of the ISM.

Novel Correlations between Diffuse Interstellar Bands and Optical Reddening

The relatively new and expansive Apache Point Observatory Catalog of Optical Diffuse Interstellar Bands was analyzed to identify novel correlations between diffuse interstellar bands (DIBs) and optical reddening E(B − V), with a principal aim being to facilitate future identifications of the host molecular carriers. The following lines exhibit the highest Pearson r correlations in descending order (0.930 ≥ r ≥ 0.885), and are tied to DIBs featuring n ≥ 10 sightlines and possessing equivalent width uncertainties: λ (Å) ≃ 5236.27, 5793.24, 5797.18, 6449.27, 6795.26, 5948.87, 6113.22, 6860.02, 6059.34, 6520.74. Independent observations to confirm the preliminary trends are desirable, and extinction estimates could be subsequently inferred for targets by relying on longer-wavelength (NIR) photometric calibrations linked to a weighted subset of numerous DIBs. Lastly, several DIBs appear unassociated with E(B − V), thereby reaffirming that diverse carriers exist.

Distribution of the diffuse interstellar band λ6614 in the NGC 2264, Rosette Nebula, and S147 regions

ABSTRACT Diffuse interstellar bands (DIBs) are absorption features arising from the interstellar medium, for which the carriers remain unclear. In this work, a total of 3115 stars in the regions of NGC 2264, the Rosette Nebula, and S147 are selected from LAMOST-MRS to study the spatial and velocity distributions of the DIB λ6614 carrier. From the spatial distribution, we find that DIB λ6614 carrier clouds appear to be widely and inhomogeneously distributed in the three target regions. They are either closer or further in distance, or much wider than the three nebulae, and there are gaps within them. The radial velocities of the DIB λ6614 carrier clouds are on average about 13, 20, and 10 km s−1 slower than the radial velocities of the nebulae in the NGC 2264, Rosette Nebula, and S147 regions, respectively. Furthermore, there is probably a high-extinction region from 0.6 to 0.8 kpc in the NGC 2264 direction, where the DIB λ6614 carrier vanishes. In the S147 region, the DIB λ6614 cloud is possibly discontinuous, and the tomographic evidence suggests that there are two DIB λ6614 clouds. The first cloud is at 0.3–0.9 kpc, which is in or near the Local Arm, while the second one emerges at about 1.8 kpc from the Sun and may be associated with S147 and in the Perseus Arm.

Detecting extragalactic diffuse interstellar bands (DIBs) in supernova spectra by using ESO data

Diffuse Interstellar Bands (DIBs) are weak and wide absorption features due to interstellar matter. DIBs are interesting to study because until now their chemical identifications are still unclear. DIBs can be found in reddened spectrum of celestial bodies in our Galaxy and other galaxies. Detecting extragalactic DIBs is challenging, one of the ways is by using an extragalactic supernova spectrum. The supernova acts as a background source to probe interstellar matter in a galaxy. We studied extragalactic DIBs by using the SN 2006X spectrum. The spectrum was observed by using the UVES instrument and the La Silla telescope at the European Southern Observatory (ESO) and was accessed from ESO archives. Detection of DIBs was performed by predicting the central wavelengths of DIBs in the supernova spectrum by taking the galaxy redshift (z) into account and observing DIBs profiles. Small shift variations in the wavelength are allowed. The detection of extragalactic DIBs indicates that DIBs are universal.