A southern hemisphere survey of the 5780 and 6284 Å diffuse interstellar bands: correlation with the extinction

Diffuse interstellar bands (DIBs) are a collection of weak interstellar absorptions in the spectra of reddened objects. We have successfully measured three strong DIBs (i.e., λ 5780, 5797, and 6614 Å) on the spectra of 125 Galactic Archaeology with HERMES (GALAH) target stars. The fitting uses a template spectrum in order to extract and measure individual DIB. We applied a correlation study between DIBs and confirmed that DIBs are positively correlated with each other, meaning that their carrier(s) are co-existing in the interstellar medium. Also, DIBs are well-correlated with color excess E(B-V). From this result, which is in a good agreement with earlier studies, conclude that DIBs can be used as a tracer of the interstellar medium.

Interstellar diffuse bands are usually extracted from hot star spectra\nbecause they are characterized by smooth continua. It introduces a strong\nlimitation on the number of available targets, and reduces potential studies of\nthe IS matter and the use of absorptions for cloud mapping. We have developed a\nnew automatic fitting method appropriate to interstellar absorptions in spectra\nof cool stars that possess stellar atmospheric parameters. We applied this\nmethod to the extraction of three DIBs in high resolution VLT FLAMES/GIRAFFE\nspectra of red clump stars from the bulge. By combining all stellar synthetic\nspectra, HITRAN-LBLRTM atmospheric transmission spectra and diffuse band\nempirical absorption profiles, we determine the 6196, 6204, and 6284 A DIB\nstrength toward the 219 target stars and discuss the sources of uncertainties.\nIn order to test the sensitivity of the DIB extraction, we intercompare the\nthree results and compare the DIB equivalent widths with the reddening derived\nfrom an independent extinction map based on OGLE photometric data. Most stellar\nspectra could be well reproduced by the composite stellar, atmospheric and\ninterstellar models. Measurement uncertainties on the EWs are smaller for the\nbroad and strong 6284 A DIB, and are of the order of 10-15%. Uncertainties on\nthe two narrow and weaker DIBs are larger, as expected, and found to be highly\nvariable from one target to the other. They strongly depend on the radial\nvelocity of the star . DIB-DIB correlations among the three bands demonstrate\nthat a meaningful signal is extracted. For the 6284 and 6204 A DIBs, the\nstar-to-star variability of the equivalent width (EW) also reflects features of\nthe OGLE extinction map...\n

We study how diffuse interstellar bands (DIBs) measured toward distance-distributed target stars can be used to locate dense interstellar (IS) clouds in the Galaxy and probe a line-of-sight (LOS) kinematical structure, a potential useful tool when gaseous absorption lines are saturated or not available in the spectral range. Cool target stars are numerous enough for this purpose. We have devised automated DIB fitting methods appropriate to cool star spectra and multiple IS components. The data is fitted with a combination of a synthetic stellar spectrum, a synthetic telluric transmission, and empirical DIB profiles. In parallel, stellar distances and extinctions are estimated self-consistently by means of a 2D Bayesian method, from spectroscopically-derived stellar parameters and photometric data. We have analyzed Gaia-ESO Survey (GES) and previously recorded spectra that probe between $\sim$ 2 and 10 kpc long LOS in five different regions of the Milky Way. Depending on the observed spectral intervals, we extracted one or more of the following DIBs: $\lambda\lambda$ 6283.8, 6613.6 and 8620.4. For each field, we compared the DIB strengths with the Bayesian distances and extinctions, and the DIB Doppler velocities with the HI emission spectra. For all fields, the DIB strength and the target extinction are well correlated. In case of targets widely distributed in distance, marked steps in DIBs and extinction radial distance profiles match with each other and broadly correspond to the expected locations of spiral arms. For all fields, the DIB velocity structure agrees with HI emission spectra and all detected DIBs correspond to strong NaI lines. This illustrates how DIBs can be used to locate the Galactic interstellar gas and to study its kinematics at the kpc scale.

Diffuse Interstellar Bands (DIBs) are set of absorption features, mostly at optical and near infrared wavelengths, that are found in the spectra of reddened stars and other objects. DIBs are actively being investigated to understand the nature of their properties and carriers and also their roles in interstellar matter enrichment. Among of the proposed carriers is large carbonaceous molecules (fullerenes). Interestingly, such as C60 and C70 have been detected in Planetary Nebulae (PN) environment. This detection allows us to study DIBs in fullerene-rich space environment. In this work, we study the presence of DIBs in central star of planetary nebulae (CSPN) by using archival data of optical spectra observed with 8.1-m Gemini South Telescope and Gemini Multi-Object Spectrographs (GMOS, spectral range of 3900 Å - 5900 Å and resolution of R ∼ 2300) and also from 2.5-m Isaac Newton Telescope with IDS spectrograph (R ∼ 2300). We measured the equivalent width of 4430, 5870 and 6283 Å DIB by fitting the detected DIB profile with the empirical template derived from higher resolution data. We investigated 4430, 5870 and 6283 Å DIBs in the spectra of CSPN and their correlation with the colour excess (E(B-V)). The correlation between the DIB strength and E(B-V) has positive value. We found that the 4430 and 5870 Å DIBs are generally more abundant on the PN environment.

Diffuse interstellar bands (DIBs) are weak and broad interstellar absorption features in astronomical spectra that originate from unknown molecules. To measure DIBs in spectra of late-type stars more accurately and more efficiently, we developed a random forest model to isolate the DIB features from the stellar components. We applied this method to 780 thousand spectra collected by the Gaia Radial Velocity Spectrometer (RVS) that were published in the third data release (DR3). After subtracting the stellar components, we modeled the DIB at 8621 Å (λ8621) with a Gaussian function and the DIB around 8648 Å (λ8648) with a Lorentzian function. After quality control, we selected 7619 reliable measurements for DIB λ8621. The equivalent width (EW) of DIB λ8621 presented a moderate linear correlation with dust reddening, which was consistent with our previous measurements in Gaia DR3 and the newly focused product release. The rest-frame wavelength of DIB λ8621 was updated as λ0 = 8623.141 ± 0.030 Å in vacuum, corresponding to 8620.766 Å in air, which was determined by 77 DIB measurements toward the Galactic anticenter. The mean uncertainty of the fit central wave-length of these 77 measurements is 0.256 Å. With the peak-finding method and a coarse analysis, DIB λ8621 was found to correlate better with the neutral hydrogen than with the molecular hydrogen (represented by 12CO J = (1−0) emission). We also obtained 179 reliable measurements of DIB λ8648 in the RVS spectra of individual stars for the first time, further confirming this very broad DIB feature. Its EW and central wavelength presented a linear relation with those of DIB λ8621. A rough estimation of λ0 for DIB λ8648 was 8646.31 Å in vacuum, corresponding to 8643.93 Å in air, assuming that the carriers of λ8621 and λ8648 are comoving. Finally, we confirmed the impact of stellar residuals on the DIB measurements in Gaia DR3, which led to a distortion of the DIB profile and a shift of the center (≲0.5 Å), but the EW was consistent with our new measurements. With our measurements and analyses, we propose that the approach based on machine learning can be widely applied to measure DIBs in numerous spectra from spectroscopic surveys.

Enigmatic problem in astronomical spectroscopy is diffuse interstellar bands (DIBs). DIBs are ∼ 500 weak and broad absorption features seen in the spectra of stars or other astronomical objects located behind interstellar materials. Despite the unknown ions or molecules that caused the absorptions, except for two near infrared DIBs, DIBs can be used as a potential interstellar medium (ISM) tracer to map Galactic structure. Gaia is a mission of the European Space Agency (ESA) which was launched on 2013. It provides precise distances which greatly improve our knowledge of the structure and history of our Galaxy. In this work, we used previously determined DIB equivalent width (EW) measurements by means of DIB fitting that is a combination of a synthetic stellar spectrum, a synthetic telluric transmission, and empirical DIB profile to the Gaia–ESO Large Public Spectroscopic Survey data. From DIB measurements from stellar spectra of distributed target stars and together with Gaia DR2 distances, we investigated the ISM distribution along particular line of sight, i.e., (l,b)∼(213°, -2°) which probes Local and Perseus Arm.

Stellar spectroscopic surveys may bring useful statistical information on the links between Diffuse Interstellar Bands (DIBs) and interstellar environment. DIB databases can also be used as a complementary tool for locating interstellar (IS) clouds. Our goal is to develop fully automated methods of DIB measurements to be applied to extensive data from stellar surveys. We present a method appropriate for early-type nearby stars, its application to high-resolution spectra of 130 targets recorded with ESO FEROS spectrograph, and comparisons with other determinations. Using a DIB average profile deduced from the most reddened stars, we performed an automated fitting of a combination of a smooth stellar continuum, the DIB profile, and, when necessary, a synthetic telluric transmission. Measurements are presented for 16 DIBs in the optical domain that could be extracted automatically: 4726.8, 4762.6, 4963.9, 5780.4, 5797.1, 5849.8, 6089.8, 6196.0, 6203.0-6204.5, 6269.8, 6283.8, 6379.3, 6445.3, 6613.6, 6660.7, and 6699.3 {\AA}.

Diffuse interstellar bands (DIBs) are broad and weak absorption features that appear in spectra recorded towards stars that lie behind interstellar (IS) clouds. They are known as a long-standing challenge in astronomical spectroscopy because of their unknown carriers. However, they are also a potential IS tracers, in particular to probe distant clouds because they are not easily saturated. We devised automated DIB-fitting methods appropriate for cool star spectra and multiple IS components. The data were fitted with a combination of a synthetic stellar spectrum, a synthetic telluric transmission, and empirical DIB profiles. The initial number of DIB components and their radial velocity were guided by HI 21 cm emission spectrum, or, when available in the spectral range, IS neutral sodium (NaI) absorption lines. For NaI, radial velocities of IS NaI lines and DIBs were maintained linked during a global simultaneous fit. Using the tools, we have analyzed Gaia-ESO Survey (GES) spectra of stars that probe between 2-10 kpc long line-of-sight (LOS) in few different regions of the Milky Way (fields). For all fields, the DIB strength and target extinction are well correlated. We show that, toward distance-distributed target stars, DIBs can be used to locate dense clouds in the Galaxy (i.e., Galactic arm) and probe a LOS kinematical structure. In addition, we have devised the DIB-DIB global fit to study the relation between DIBs and can be a potential tool to trace interstellar environmental conditions.

Context. The limited number of high-resolution spectra of hot stars is inadequate for statistical studies of diffuse interstellar bands (DIBs). In contrast, the vast quantity of low-resolution spectroscopic surveys on cool stars holds great potential for investigating the relationship between DIBs and the known interstellar medium (ISM), as well as the spatial distribution of their unidentified carriers. Aims. We attempt to measure the DIBs λ5780, λ5797, and λ6614 in over two million low-resolution spectra of cool stars from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST). Based on these DIB measurements, we reviewed and investigated the correlation between DIBs and extinction; the kinematics of DIBs; and the Galactic distribution of DIBs from a statistical perspective. Methods. We developed a pipeline to measure the DIBs λ5780, λ5797, and λ6614 in the LAMOST low-resolution spectra. Four modules in the pipeline consist of building the target and reference dataset; extracting the ISM residual spectra from the target spectra; measuring the DIBs in the residual spectra; and quality control of the measurements. Results. We obtained DIB measurements of spectra of late-type stars from LAMOST, and selected 176 831, 13 473, and 110 152 high-quality (HQ) measurements of the DIBs λ5780, λ5797, and λ6614, respectively, corresponding to 142074, 11 480, and 85 301 unique sources. Using these HQ measurements, we present Galactic maps of the DIBs λ5780 and λ6614 in the northern sky for the first time. The central wavelengths of the DIBs λ5780, λ5797, and λ6614 in air are determined to be 5780.48 ± 0.01, 5796.94 ± 0.02, and 6613.64 ± 0.01 Å, respectively, based on their kinematics. A statistical fit of the equivalent widths of these three DIBs per unit extinction provides values of 0.565, 0.176, and 0.256 Å mag−1. As a result of this work, three catalogs of the HQ measurements for the DIBs λ5780, λ5797, and λ6614 are provided via https://nadc.china-vo.org/res/r181484/. Conclusions. To the best of our knowledge, this is the largest number of measurements of these three DIBs to date. It is also the first time that Galactic maps of the DIBs λ5780 and λ6614 in the northern hemisphere are presented, and that the central wavelengths of the DIBs λ5780, λ5797, and λ6614 are estimated from kinematics.

A longstanding challenge in astronomical spectroscopy is to uncover the carriers of diffuse interstellar bands (DIBs). They are broad absorption features due to the interstellar matter (ISM). They are seen in stellar spectra of background stars or other astronomical objects. Although we do not know utterly the carriers of the DIBs, they can be a promising tracer of the ISM. One of the interesting properties is their correlations with the interstellar (IS) extinction. For each band, the correlation has considerable dispersion and differences that possibly due to the IS physical conditions. Some DIBs are sensitive to the stellar radiation field, and some are not. To study the effect, we measured the DIB observed in Be/B stars spectra. The stars were observed by using Bosscha Compact Spectrograph at the Bosscha Observatory, Lembang, Indonesia. We performed an automated fitting of a combination of a smooth stellar continuum, the DIB profile, and a synthetic telluric transmission to the spectrum. The DIB measurements were compared to the general DIBs-extinction relationship. The correlation is found to be in good agreement with previous determinations.

Context. The diffuse interstellar bands (DIBs) are a set of hundreds of unidentified absorption features that appear almost ubiquitously throughout the interstellar medium. Most DIBs appear at optical wavelengths, but some are in the near-infrared. Aims. We aim to characterise near-infrared DIBs at high spectral resolving power towards multiple targets. Methods. We observed 76 early-type stars at a resolving power of 50 000 (velocity resolution ~6 km s−1) and signal-to-noise ratios of several hundreds using the CRyogenic high-resolution InfraRed Echelle Spectrograph (CRIRES). These data allow us to investigate the DIBs around 1318.1, 1527.4, 1561.1, 1565.1, 1567.0, 1574.4, and 1624.2 nm. We detected a total of six DIB features and 17 likely stellar features through comparisons with a model spectrum computed with CMFGEN. Additionally, we measured equivalent widths of the DIBs at 1318.1 and 1527.4 nm using observations with X-shooter towards ten very highly reddened (3.2 < E(B–V) < 6.5) Cepheid variable stars and towards four stars observed at low values of precipitable water vapour as well as by using other archive data. Results. We measured correlations (correlation coefficient r ~ 0.73–0.96, depending on the subsample used) between DIB equivalent width and reddening for the DIBs at 1318.1, 1561.1, 1565.1, and 1567.0 nm. Comparing the near-infrared DIBs with 50 of the strongest optical DIBs, we find correlations r > ~0.8 between the 1318, 1527, 1561, 1565, and 1567 nm and the optical DIBs 5705, 5780, 6203, 6283, and 6269 Å. The 5797 Å DIB is less well correlated with the near-infrared DIBs. The DIB at 9632.1 Å, which is likely C60+, is not well correlated with the 1318.1 nm DIB. Partial correlation coefficients using E(B-V) as the covariate were also determined. For stars earlier than B2, the 1318.1 nm DIB is affected by an emission line on its blue wing that is likely stellar in nature, although we cannot rule out an interstellar or circumstellar origin for this line caused by, for example, a DIB in emission. The 1318.1 nm DIB also has an extended red wing. The line is reasonably well fitted by two Gaussian components, although neither the component equivalent width (EW) ratios nor the separation between components are obviously correlated with such indicators as λλ5780/5797 and reddening. The EW at 1318 nm correlates with H I with EW(1318 nm)/E(B – V) decreasing with f(H2). Five pairs of stars within one arcmin of each other show very similar 1318.1 nm DIB profiles. Possible variation in the 1318.1 nm feature is seen between HD 145501 and HD 145502 (separated by 41 arcsec, equivalent to 7200 au) and HD 168607 and HD 168625 (separated by 67 arcsec, equivalent to 0.52 pc on the plane of the sky). Seventeen sightlines have repeat CRIRES observations separated by six to 14 months, and two sightlines have repeat X-shooter observations separated by 9.9 yr. No time variability was detected in the 1318.1 nm DIB in the CRIRES data nor in the 5780.5 Å, 5797.1 Å, 1318.1 nm, and 1527.4 nm DIBs. Tentative time variation is observed in the C60+ DIBs at 9577 and 9632 Å towards HD 183143, although it is very close to the noise level and requires confirmation. Conclusions. The Near Infrared (NIR) DIBs observed occur more in more UV-irradiated regions than the 5797 Å DIB allowing the study of heavily reddened sightlines. Future searches for time variability in DIBs will require either higher quality data, larger intervals between epochs, or both.

We have compared the B-V colour excess, E(B-V), obtained for a sample of five optically visible massive YSOs both from diffuse interstellar bands (DIBs) in their spectra and from their optical continuum slopes. Our targets are HD 200775, BD+40 4124, MWC 1080, MWC 297 and MWC 349A. First, E(B-V) towards each of the targets is derived by dereddening the observed continua to match those of B-type standard stars. A survey of DIBs in the spectra of the massive YSOs, and a control field star, then reveals that the DIBs are significantly weaker in the former than would be expected based on the total E(B-V) values. This result is strengthened by the finding that the DIBs in the control field star, HD 154445, have on average the strength expected from its continuum E(B-V). A rough estimate of the foreground reddening of intervening diffuse interstellar medium shows it to be smaller than the DIB-E(B-V), implying that at least part of the DIB carriers are formed within the parental molecular clouds in which the YSOs are embedded. The formation efficiency of the DIBs varies strongly however from cloud to cloud. The DIB-E(B-V) compares favourably with the total E(B-V) towards BD+40 4124, but is almost negligible in the line of sight towards MWC 297. Despite this general, but not unexpected, deficit we provide evidence that the DIB at 5849 Angstrom is a good tracer of total extinction in these lines of sight.

In a sample of 114 diffuse cloud sightlines spanning a wide range of interstellar environments, we find the equivalent widths of the diffuse interstellar bands (DIBs) λ6196.0 and λ6613.6 to be extremely well correlated, with a correlation coefficient of 0.986. A maximum likelihood functional relationship analysis shows that the observations are consistent with a perfect correlation if the observational errors, which are dominated by continuum placement and other systematics such as interfering lines, have been underestimated by a factor of 2. The quality of this correlation far exceeds other previously studied correlations, such as that between the λ5780.5 DIB and either the color excess or the atomic hydrogen column density. The unusually tight correlation between these two DIBs would seem to suggest that they might represent the first pair of DIBs known to be due to the same molecular carrier. However, further theoretical work will be required to determine whether the different linewidths and band shapes of these two DIBs can be consistent with a common carrier. If the two DIBs do not in fact share the same molecular carrier, their two carriers must be chemically very closely related.

ABSTRACTWe use more than 872 000 mid- to high-resolution (R ∼ 20 000) spectra of stars from the GALactic Archaeology with HERMES (GALAH) survey to discern the spectra of diffuse interstellar bands (DIBs). We use four windows with the wavelength ranges 4718–4903, 5649–5873, 6481–6739, and 7590–7890 Å, giving a total coverage of 967 Å. We produce ∼400 000 spectra of interstellar medium (ISM) absorption features and correct them for radial velocities of the DIB clouds. Ultimately, we combine the 33 115 best ISM spectra into six reddening bins with a range of 0.1 < E(B − V) < 0.7 mag. A total of 183 absorption features in these spectra qualify as DIBs, and their fitted model parameters are summarized in a detailed catalogue. From these, 64 are not reported in the literature, of which 17 are certain, 14 are probable and 33 are possible. We find that the broad DIBs can be fitted with a multitude of narrower DIBs. Finally, we create a synthetic DIB spectrum at unit reddening. This should allow us to narrow down the possible carriers of DIBs, to explore the composition of the ISM, and ultimately to model dust and star formation better as well as to correct Galactic and extragalactic observations. The majority of certain DIBs show a significant excess of equivalent width when compared with reddening. We explain this with observed lines of sight penetrating more uniform DIB clouds compared with clumpy dust clouds.

Context. Three-dimensional maps of the Galactic interstellar medium are general astrophysical tools. Reddening maps may be based on the inversion of color excess measurements for individual target stars or on statistical methods using stellar surveys. Three-dimensional maps based on diffuse interstellar bands (DIBs) have also been produced. All methods benefit from the advent of massive surveys and may benefit from Gaia data. Aims. All of the various methods and databases have their own advantages and limitations. Here we present a first attempt to combine different datasets and methods to improve the local maps. Methods. We first updated our previous local dust maps based on a regularized Bayesian inversion of individual color excess data by replacing Hipparcos or photometric distances with Gaia Data Release 1 values when available. Secondly, we complemented this database with a series of ≃5000 color excess values estimated from the strength of the λ15273 DIB toward stars possessing a Gaia parallax. The DIB strengths were extracted from SDSS/APOGEE spectra. Third, we computed a low-resolution map based on a grid of Pan-STARRS reddening measurements by means of a new hierarchical technique and used this map as the prior distribution during the inversion of the two other datasets. Results. The use of Gaia parallaxes introduces significant changes in some areas and globally increases the compactness of the structures. Additional DIB-based data make it possible to assign distances to clouds located behind closer opaque structures and do not introduce contradictory information for the close structures. A more realistic prior distribution instead of a plane-parallel homogeneous distribution helps better define the structures. We validated the results through comparisons with other maps and with soft X-ray data. Conclusions. Our study demonstrates that the combination of various tracers is a potential tool for more accurate maps. An online tool makes it possible to retrieve maps and reddening estimations.