Jonathan V. Smoker

We present the first planet mass measurement obtained with CRIRES ⁺ radial velocity (RV) observations using the K -band gas cell. Our target, LHS 3844 b (TOI-136), is a transiting super-Earth with radius R _b = 1.286 _−0.044 ^+0.043 R _⊕ and an orbital period of P _b = 0.462929709 _{−0.000000042} ^+0.000000044 d, placing it in the class of ultra-short-period (USP) planets. The host star LHS 3844 is an old (7.8 ± 1.6 Gyr), slowly rotating ( P _rot = 130.0 _−13.4 ^+16.9 ) M5.0 dwarf with M _⋆ = 0.151 ± 0.014 M _⊙ at a distance of 15 pc ( V = 15.2 mag, K = 9.2 mag). Combining our CRIRES ⁺ RVs with archival ESPRESSO spectra, and confirming the signal in each dataset independently, we detected periodic RV variations with a semi-amplitude K _b = 6.95 _−0.60 ^+0.55 m s ⁻¹ , implying a planetary mass of m _b = 2.37 ± 0.25 M _⊕ and a bulk density of ρ _b = 6.15 _−0.61 ^+0.60 g cm ⁻³ cm ⁻³ , consistent with a predominantly rocky composition. We further found excess RV variability that may be attributed to stellar jitter or to an additional planetary signal, for which we identified a tentative super-Earth candidate with a period of ≈6.88 d. Owing to its proximity to its M-dwarf host, LHS 3844 b experiences intense irradiation and is unlikely to retain a substantial H/He envelope. Interior modeling places an upper limit on the iron-core mass fraction, which is consistent with an Earth-like rocky composition. With an emission spectroscopy metric (ESM) of 28, LHS 3844 b is a prime JWST target for atmospheric and surface characterization and the most promising surface-characterization target known. Phase-curve spectroscopy may reveal its surface mineralogy and enable the first robust detection of exoplanet surface spectral features. Our results demonstrate that near-infrared RVs obtained with CRIRES ⁺ enable robust mass measurements of super-Earths orbiting late M dwarfs.

Context. High-precision radial velocity (RV) measurements with slit spectrographs require the instrument profile (IP) and Earth’s atmospheric spectrum to be known and to be incorporated into the RV calculation. Aims. We developed an RV pipeline, called Velocity and IP EstimatoR (viper), to achieve high-precision RVs in the near-infrared (NIR). The code is able to process observations taken with a gas cell and includes modelling of the IP and telluric lines. Methods. We utilised least-square fitting and telluric forward modelling to account for instrument instabilities and atmospheric absorption lines. As part of this process, we demonstrate the creation of telluric-free stellar spectra. Results. By applying viper to observations obtained with the upgraded CRyogenic high-resolution InfraRed Echelle Spectrograph (CRIRES⁺) and a gas absorption cell in the K band, we are able to reach an RV precision of around 3 m/s over a time span of 2.5 years. For observations using telluric lines for the wavelength reference, an RV precision of 10 m/s is achieved. Conclusions. We demonstrate that despite telluric contamination, a high RV precision is possible at NIR wavelengths, even for a slit spectrograph with varying IP. Furthermore, we show that CRIRES⁺ performs well and is an excellent choice for science studies requiring precise stellar RV measurements in the infrared.

Context. Diffuse interstellar bands (DIBs) are faint absorption features of a generally unknown origin. Observational constraints on their carriers have been provided in the vast majority of the cases thanks to observations in our Galaxy. Detections in other galaxies are scarce, both in the Local Group and beyond. However, they can further constrain the nature of the carriers by sampling different environments. They can put the ubiquity of the molecules creating these features to the test. Aims. We aim to map some of the strongest DIBs in an environment that has not been tested thus far: a system harbouring two active galactic nuclei (AGNs). We explore the relation of these DIBs with other components and properties of the interstellar medium, in particular, the dust traced by the attenuation, the sodium absorption doublet, and previously published maps of the atomic and molecular matter. Methods. We used archival Multi Unit Spectroscopic Explorer (MUSE) data of the luminous infrared galaxy (LIRG) NGC 6240. We spatially binned the data with the Voronoi binning technique and modeled the emission of the underlying stellar population with the pPXF code. We measured the spectral features of interest, both in the emission and absorption, with a self-written algorithm using multiple Gaussians. Results. We mapped the DIBλ5780 over an almost contiguous area of ∼76.96 kpc² in the center of the system. We also traced the DIBλ6284 over two separate areas toward the north and south of the system, with an extent of ∼21.22 kpc² and ∼31.41 kpc² (with a total detected area of ∼59.78 kpc²). This is the first time that the λ6284 DIB has been mapped outside our Galaxy. Both maps were compared with the attenuation on the overall stellar population and the ionized gas. As expected, both DIBs are detected in locations with high attenuation (E(B − V)_Gas ≳ 0.3 and E(B − V)_Stellar ≳ 0.1), supporting the connection between DIB carriers and dust. Moreover, when compared with other galaxies, DIBs are better correlated with the stellar (rather than the ionized gas) attenuation. In particular, the DIBλ6284 presents a stronger correlation with reddening than the λ5780 DIB, as determined by the Pearson correlation coefficient with value ρ_t, λ6284 = 0.82 and ρ_t, λ5780 = 0.77. This better correlation can be attributed to a different nature of the carriers causing these DIBs or a combined effect of a dependence with the metallicity and the different locations where these DIBs have been measured. We argue that the latter effect can have a more substantial impact as both λ5780 and λ6284 DIBs belong to the σ-DIB family; thus, they are expected to have similar properties. In addition, we show that Na I D is strongly correlated with both DIBs. We advocate for the utilization of DIBs as a first-order tracer of specific amounts of material in cases where Na I D reaches saturation. This saturation effect can be an observational complication in systems with a large amount of gas, such as (U)LIRGs. Conclusions. The findings presented here show that DIB carriers can exist and survive in an environment as extreme as a galaxy hosting an AGN. These features enable us to envision the possibilities of integral field spectrographs in studying DIBs well beyond our Galaxy.

The Magellanic Stream is a large tail of neutral and ionized gas originating from tidal and hydrodynamical interactions between the Magellanic Clouds as they orbit the Milky Way (MW). It carries a significant gas reservoir that could impact the future evolution of the MW. Despite its importance, no direct observational constraints on the Stream’s distance have been previously published. In this study, we analyze Very Large Telescope/Ultraviolet and Visual Echelle Spectrograph spectra of five blue horizontal branch stars in the MW halo located at distances ranging from 13 to 56 kpc near two regions of the Stream (near Stream longitudes of –79^∘ and –98^∘), with the aim of detecting Ca ii and Na i absorption. No Ca ii or Na i absorption is detected at Stream velocities in any of the individual spectra or in higher signal-to-noise stacks of the spectra. The resulting limits on the Ca ii absorption are significantly lower than the Ca ii columns measured in the Stream along extragalactic sight lines. These nondetections establish a firm lower distance limit of 42 kpc for one region of the Stream. For the other region, we set a firm lower limit of 20 kpc and a tentative lower limit of 55 kpc from the most distant star, but deeper spectra are needed to confirm this. Our results provide the first observational constraints on the gaseous Stream’s distance.

Context. Numerous studies of diffuse interstellar band (DIB) profiles have detected substructures, which in turn suggests that large molecules are acting as their carriers. However, some of the narrowest DIBs generally do not show such substructures, suggesting the possibility of very small carriers. Aims. Based on the previously found tight correlation of the three narrow DIBs at 6196, 6440, and 6623 Å and the present detection of weaker side DIBs to each of them in the extensive dataset from the ESO Diffuse Interstellar Bands Large Exploration Survey, we investigated whether they may stem from small linear carrier molecules. This approach can lead to concrete DIB carrier suggestions, which can be tested in laboratory measurements in future studies. Methods. We suggest that the DIBs we studied here represent individual rotational transitions of a small molecule. We determined the molecular constants from observations and compared them with data from a large set of quantum-chemical calculations to constrain possible carrier candidates. Furthermore, we determined the rotational temperatures by fitting line ratios using the fitted molecular models. Results. We determined molecular constants for three DIB systems and the corresponding transition types. The fitted rotational temperatures lie within the range of known interstellar diatomic molecules. We identified several DIB carrier candidates, almost all of them molecular ions. Some of them are metastable species, indicating the possibility of collision complexes as DIB carriers. Conclusions. If our hypothesis holds, this would be a major step towards the identification of a carrier molecule of the 6196 Å DIB, the strongest among the narrow DIBs.

Context. There have been many attempts to identify families of diffuse interstellar bands (DIBs) with perfectly correlating band strengths. Although major efforts have been made to classify broadly based DIB families and important insights have been gained, no family has been identified with sufficient accuracy or statistical significance to prove that a series of selected DIBs originates from the same carrier. This can be attributed in part to the exclusive use of equivalent widths to establish DIB families. Aims. In a change of strategy, we search for DIBs that are highly correlated in both band strength and profile shape. This approach increases the chance of correlating DIBs being members of one family and originating from the same carrier molecule. We also search for correlations between DIB profile families and atomic interstellar lines, with the goal of further chemically constraining possible DIB carriers. Methods. We adapted the well-known method of time-series alignment to perform a spectral alignment; that is, DIB alignment. In a second step, we analysed the alignment results using a clustering analysis. This method required a statistically significant data set of DIB sight lines. The ESO Diffuse Interstellar Bands Large Exploration Survey (EDIBLES) data were perfectly suited for this application. Results. We report eight DIB families with correlating strengths and profiles, as well as four previously unreported DIBs in the visual range, found using DIB alignment. All profile family members show Pearson correlation coefficients in band strength higher than 0.9. In particular, we report the 6614–6521 Å DIB pair, in which both DIBs show the same triple-peak substructure and an unprecedented band strength Pearson correlation coefficient of 0.9935. The presented approach opens up new perspectives that can guide the laboratory search for DIB carriers.

Massive stars (those ≥8 solar masses at formation) have radiative envelopes that cannot sustain a dynamo, the mechanism that produces magnetic fields in lower-mass stars. Despite this, approximately 7% of massive stars have observed magnetic fields, the origin of which is debated. We used multi-epoch interferometric and spectroscopic observations to characterize HD 148937, a binary system of two massive stars. We found that only one star is magnetic and that it appears younger than its companion. The system properties and a surrounding bipolar nebula can be reproduced with a model in which two stars merged (in a previous triple system) to produce the magnetic massive star. Our results provide observational evidence that magnetic fields form in at least some massive stars through stellar mergers.

Context. Interstellar absorption observed toward stellar targets changes slowly over long timescales, mainly due to the proper motion of the background target relative to the intervening clouds, such that over time, different parts of the intervening cloud are probed. On longer timescales, the slowly changing physical and chemical conditions in the cloud can also cause variation. Detecting such time variations thus provides an opportunity to study cloud structure. Aims. We searched for systematic variations in the absorption profiles of the diffuse interstellar bands (DIBs) and interstellar atomic and molecular lines by comparing the high-quality data set from the recent ESO diffuse interstellar bands large exploration survey (EDIBLES) to older archival observations, bridging typical timescales of ~10 yr with a maximum timescale of 22 yr. Methods. For 64 EDIBLES targets, we found adequate archival observations. We selected 31 strong DIBs, seven atomic lines, and five molecular lines to focus our search on. We carefully considered various systematic effects and used a robust Bayesian quantitative test to establish which of these absorption features could display significant variations. Results. While systematic effects greatly complicate our search, we find evidence for variations in the profiles of the λλ4727 and 5780 DIBs in a few sightlines. Toward HD 167264, we find a new Ca I cloud component that appears and becomes stronger after 2008. The same sightline furthermore displays marginal, but systematic changes in the column densities of the atomic lines originating from the main cloud component in the sightline. Similar variations are seen toward HD 147933. Conclusions. Our high-quality spectroscopic observations in combination with archival data show that it is possible to probe interstellar time variations on time scales of typically a decade. Despite the fact that systematic uncertainties as well as the generally somewhat lower quality of older data complicate matters, we can conclude that time variations can be made visible, both in atomic lines and DIB profiles for a few targets, but that generally, these features are stable along many lines of sight. We present this study as an archival baseline for future comparisons, bridging longer periods.

The nature of dust in the diffuse interstellar medium can be best investigated by means of reddening curves where only a single interstellar cloud lies between the observer and the background source. Published reddening curves often suffer from various systematic uncertainties. We merged a sample of 820 reddening curves of stars for which both FORS2 polarization spectra and UVES highresolution spectra are available. The resulting 111 sightlines towards OB-type stars have 175 reddening curves. For these stars, we derived their spectral-type from the UVES high-resolution spectroscopy. To obtain high-quality reddening curves, we excluded stars with composite spectra in the IUE/FUSE data due to multiple stellar systems. Likewise, we omitted stars that have uncertain spectral-type designations or stars with photometric variability. We neglected stars that show inconsistent parallaxes when comparing data releases two and three from Gaia. Finally, we identified stars that show differences in the space- and ground-based-derived reddening curves between 0.28 µm and the U band or in R_V. In total, we find 53 stars with one or more reddening curves passing the rejection criteria. This provides the highest-quality Milky Way reddening curve sample available today. Averaging the curves from our high-quality sample, we find R_V = 3.1 ± 0.4, confirming previous estimates. A future paper in this series will use the current sample of precise reddening curves and combine them with polarization data to study the properties of dark dust.