Synthesis and Spectroscopy of Buckminsterfullerene Cation C60+ in a Cryogenic Ion Trapping Instrument

The assignment of several diffuse interstellar bands in the near-infrared to C60+ ions present at high abundance in space has renewed interest in the astrochemical importance of fullerenes and analogues. Many of the latter have not been produced in macroscopic quantities, and their spectroscopic properties are not available for comparison with astronomical observations. An apparatus has been constructed that combines laser vaporisation synthesis with spectroscopic characterisation at low temperature in a cryogenic trap. This instrument is used here to record the electronic absorptions of C60+ produced by laser vaporisation of graphite. These are detected by (helium tagged) messenger spectroscopy in a cryogenic trap. By comparison with spectra obtained using a sublimed sample of Buckminsterfullerene, the observed data show that this isomer is the dominant C60+ structure tagged with helium at m/z=724, indicating that the adopted approach can be used to access the spectra of other fullerenes and derivatives of astrochemical interest.

Establishing new diffuse interstellar band correlations to identify common carriers

ABSTRACT Observations from the Apache Point Observatory Catalog of Optical Diffuse Interstellar Bands (DIBs) were analysed to establish highly correlated pairs in terms of their equivalent widths (EWs) (r > 0.95), which importantly facilitate the identification of common carriers. A total of 154 846 possible DIB pairs were originally examined, yet only those with a sufficient number of sightlines (n > 9) that included EW uncertainties were subsequently investigated. The highest correlations for the resulting 56 893 DIB pairs are 6284.05–6203.58 Å (r = 0.990 ± 0.001), 6203.58–5780.64 Å (r = 0.986 ± 0.001), 6993.12–6269.89 Å (r = 0.984 ± 0.001), 6843.76–6792.51 Å (r = 0.984 ± 0.005), 6203.58–5487.64 Å (r = 0.983 ± 0.002), and 5061.50–4969.12 Å (r = 0.983 ± 0.009). The bands 5363.77, 5780.64, 6203.58, and 6284.05 Å appear most frequently. Novel relations linked to those DIBs and others warrant further research, in particular those pairs that involve one or both DIBs with low EWs (e.g. 5609.82, 6269.89, 6993.12, and 7224.16 Å). Numerous DIBs correlated with the prominent 4429.33 Å band were also discovered. The intriguing proposal of anionic hydrogen clusters as possible DIB carriers is also discussed.

A Comparison of the Simulations and Observations for a Nearby Spiral Arm

The analysis is focused on the ability of galactic open clusters to trace the spiral arms, based on the recent data releases from Gaia. For this, a simple 1D description of the motion of spiral arms and clusters is introduced. As next step, results are verified using a widely accepted kinematic model of the motion in spiral galaxies. As expected, both approaches show that open clusters older than about 100 Myr are bad tracers of spiral arms. The younger clusters (ideally < 30 Myr) should be used instead. This agrees with the most recent observational evidence. The latest maps of the diffuse interstellar bands are compared with the spiral structure of the Milky Way and the Antennae Galaxies. The idea of these bands being useful for studying a galactic structure cannot be supported based on the current data.

Galactic extinction laws: II. Hidden in plain sight, a new interstellar absorption band at 7700 Å broader than any known DIB

We have detected a broad interstellar absorption band centred close to 7700 Å and with a FWHM of 176.6±3.9 Å. This is the first such absorption band detected in the optical range and is significantly wider than the numerous diffuse interstellar bands (DIBs). It remained undiscovered until now because it is partially hidden behind the A telluric band produced by O2. The band was discovered using STIS@HST spectra and later detected in a large sample of stars of diverse type (OB stars, BA supergiants, red giants) using further STIS and ground-based spectroscopy. The EW of the band is measured and compared with our extinction and K i λλ7667.021,7701.093 measurements for the same sample. The carrier is ubiquitous in the diffuse and translucent Galactic ISM but is depleted in the environment around OB stars. In particular, it appears to be absent or nearly so in sightlines rich in molecular carbon. This behaviour is similar to that of the σ-type DIBs, which originate in the low/intermediate-density UV-exposed ISM but are depleted in the high-density UV-shielded molecular clouds. We also present an update on our previous work on the relationship between E(4405 − 5495) and R5495 and incorporate our results into a general model of the ISM.

An optical spectroscopic and polarimetric study of the microquasar binary system SS 433

Aims. Our aim is to study the mass transfer, accretion environment, and wind outflows in the SS 433 system, concentrating on the so-called stationary lines. Methods. We used archival high-resolution (X-shooter) and low-resolution (EMMI) optical spectra, new optical multi-filter polarimetry, and low-resolution optical spectra (Liverpool Telescope), spanning an interval of a decade and a broad range of precessional and orbital phases, to derive the dynamical properties of the system. Results. Using optical interstellar absorption lines and H I 21 cm profiles, we derive E(B − V) = 0.86 ± 0.10, with an upper limit of E(B − V) = 1.8 ± 0.1 based on optical Diffuse Interstellar Bands. We obtain revised values for the ultraviolet and U band polarizations and polarization angles (PA), based on a new calibrator star at nearly the same distance as SS 433 that corrects the published measurement and yields the same PA as the optical. The polarization wavelength dependence is consistent with optical-dominating electron scattering with a Rayleigh component in U and the UV filters. No significant phase modulation was found for PA while there is significant variability in the polarization level. We fortuitously caught a flare event; no polarization changes were observed but we confirm the previously reported associated emission line variations. Studying profile modulation of multiple lines of H I, He I, O I, Na I, Si II, Ca II, Fe II with precessional and orbital phase, we derive properties for the accretion disk and present evidence for a strong disk wind, extending published results. Using transition-dependent systemic velocities, we probe the velocity gradient of the wind, and demonstrate that it is also variable on timescales unrelated to the orbit. Using the rotational velocity, around 140 ± 20 km s−1, a redetermined mass ratio q = 0.37 ± 0.04, and masses MX = 4.2 ± 0.4 M⊙, MA = 11.3 ± 0.6 M⊙, the radius of the A star fills – or slightly overfills – its Roche surface. We devote particular attention to the O I 7772 Å and 8446 Å lines, finding that they show different but related orbital and precessional modulation and there is no evidence for a circumbinary component. The spectral line profile variability can, in general, be understood with an ionization stratified outflow predicted by thermal wind modeling, modulated by different lines of sight through the disk produced by its precession. The wind can also account for an extended equatorial structure detected at long wavelength.