Low-resolution Spectra Research Articles

Выбор спектральных переменных в многопараметрической калибровке концентраций C, Mn, Si, Cr, Ni и Cu в низколегированных сталях методами лазерно-искровой эмиссионной спектроскопии

Multivariate calibrations of concentrations of C, Mn, Si, Cr, Ni and Cu have been developed by the partial least squares method for 31 to 39 standard samples of low-alloy steels using low-resolution emission spectra (190-440 nm, resolution 0.4 nm, step 0.1 nm). Three methods of spectral variables selection are considered: a method of ranking spectral variables by their correlation coefficient with the value of the calibrated parameter, a successive projection algorithm and an original modification of searching combination moving windows. The partial least squares model with the spectral variables selection by the method of the searching combination moving windows for C is quantitative: the root mean square error is 0.004%, the residual predictive deviation in the test dataset is 23.4 in the concentration range 0.13 to 0.43 %. Calibrations of Mn (0.04% and 5.2 in the range of 0.47–1.15%), Si (0.003% and 20.7 in the range of 0.15–0.33%), Cr (0.04% and 3.1 in the range of 0.09–0.43%) and Ni (0.01% and 4.8 in the range of 0.05–0.25%) are also quantitative. For Cu in the concentration range of 0.06–0.26%, calibration is qualitative (0.04% and 1.4).

Youth analysis of near-infrared spectra of young low-mass stars and brown dwarfs

Context.Studies of the low-mass population statistics in young clusters are the foundation for our understanding of the formation of low-mass stars and brown dwarfs. Robust low-mass populations can be obtained through near-infrared spectroscopy, which provides confirmation of the cool and young nature of member candidates. However, the spectroscopic analysis of these objects is often not performed in a uniform manner, and the assessment of youth generally relies on the visual inspection of youth features whose behavior is not well understood.Aims.We aim at building a method that efficiently identifies young low-mass stars and brown dwarfs from low-resolution near-infrared spectra, by studying gravity-sensitive features and their evolution with age.Methods.We have built a data set composed of all publicly available (∼2800) near-infrared spectra of dwarfs with spectral types between M0 and L3. First, we investigate methods for the derivation of the spectral type and extinction via comparison to spectral templates and various spectral indices. Then, we examine gravity-sensitive spectral indices and apply machine learning methods in order to efficiently separate young (≲10 Myr) objects from the field.Results.Using a set of six spectral indices for spectral typing, including two newly defined ones (TLI-Jand TLI-K), we are able to achieve a precision below one spectral subtype across the entire spectral type range. We define a new gravity-sensitive spectral index (TLI-g) that consistently separates young objects from field objects; it shows a performance superior to other indices from the literature. Even better separation between the two classes can be achieved through machine learning methods that use the entire near-infrared spectra as an input. Moreover, we show that theHandKbands alone are sufficient for this purpose. Finally, we evaluate the relative importance of different spectral regions for gravity classification as returned by the machine learning models. We find that theH-band broadband shape is the most relevant feature, followed by the FeH absorption bands at 1.2 μm and 1.24 μm and the KI doublet at 1.24 μm.

Compact object candidates with K/M-dwarf companions from LAMOST low-resolution survey

Searching for compact objects (black holes, neutron stars, or white dwarfs) in the Milky Way is essential for understanding the stellar evolution history, the physics of compact objects, and the structure of our Galaxy. Compact objects in binaries with a luminous stellar companion are perfect targets for optical observations. Candidate compact objects can be achieved by monitoring the radial velocities of the companion star. However, most of the spectroscopic telescopes usually obtain stellar spectra at a relatively low efficiency, which makes a sky survey for millions of stars practically impossible. The efficiency of a large-scale spectroscopic survey, the Large Sky Area Multi-Object Fiber Spectroscopy Telescope (LAMOST), presents a specific opportunity to search for compact object candidates, i.e., simply from the spectroscopic observations. Late-type K/M stars are the most abundant populations in our Galaxy. Owing to the relatively large Keplerian velocities in the close binaries with a K/M-dwarf companion, a hidden compact object could be discovered and followed-up more easily. In this study, compact object candidates with K/M-dwarf companions are investigated with the LAMOST low-resolution stellar spectra. Based on the LAMOST Data Release 5, we obtained a sample of $56$ binaries, each containing a K/M-dwarf with a large radial velocity variation $\Delta V_{\rm R} > 150~{\rm km~s}^{-1}$. Complemented with the photometric information from the Transiting Exoplanet Survey Satellite, we derived a sample of $35$ compact object candidates, among which, the orbital periods of $16$ sources were revealed by the light curves. Considering two sources as examples, we confirmed that a compact object existed in the two systems by fitting the radial velocity curve. This study demonstrates the principle and the power of searching for compact objects through LAMOST.

The post-common-envelope binary central star of the planetary nebula Ou 5: a doubly eclipsing post-red-giant-branch system

ABSTRACT We present a detailed study of the stellar and orbital parameters of the post-common envelope binary central star of the planetary nebula Ou 5. Low-resolution spectra obtained during the primary eclipse – to our knowledge the first isolated spectra of the companion to a post-common-envelope planetary nebula central star – were compared to catalogue spectra, indicating that the companion star is a late K- or early M-type dwarf. Simultaneous modelling of multiband photometry and time-resolved radial velocity measurements was then used to independently determine the parameters of both stars as well as the orbital period and inclination. The modelling indicates that the companion star is low mass (∼0.25 M⊙) and has a radius significantly larger than would be expected for its mass. Furthermore, the effective temperature and surface gravity of nebular progenitor, as derived by the modelling, do not lie on single-star post-AGB evolutionary tracks, instead being more consistent with a post-RGB evolution. However, an accurate determination of the component masses is challenging. This is principally due to the uncertainty on the locus of the spectral lines generated by the irradiation of the companion’s atmosphere by the hot primary (used to derive companion star’s radial velocities), as well as the lack of radial velocities of the primary.

Alfnoor: Assessing the Information Content of Ariel's Low-resolution Spectra with Planetary Population Studies

Abstract The Ariel Space Telescope will provide a large and diverse sample of exoplanet spectra, performing spectroscopic observations of about 1000 exoplanets in the wavelength range 0.5–7.8 μm. In this paper, we investigate the information content of Ariel’s Reconnaissance Survey low-resolution transmission spectra. Among the goals of the Ariel Reconnaissance Survey is also to identify planets without molecular features in their atmosphere. In this work, (1) we present a strategy that will allow us to select candidate planets to be reobserved in Ariel’s higher-resolution tier, (2) we propose a metric to preliminary classify exoplanets by their atmospheric composition without performing an atmospheric retrieval, and (3) we introduce the possibility to find other methods to better exploit the data scientific content.

Deep Exploration of the Planets HR 8799 b, c, and d with Moderate-resolution Spectroscopy

Abstract The four directly imaged planets orbiting the star HR 8799 are an ideal laboratory to probe atmospheric physics and formation models. We present more than a decade’s worth of Keck/OSIRIS observations of these planets, which represent the most detailed look at their atmospheres to date by its resolution and signal-to-noise ratio. We present the first direct detection of HR 8799 d, the second-closest known planet to the star, at moderate spectral resolution with Keck/OSIRIS (K band; R ≈ 4000). Additionally, we uniformly analyze new and archival OSIRIS data (H and K band) of HR 8799 b, c, and d. First, we show detections of water (H2O) and carbon monoxide (CO) in the three planets and discuss the ambiguous case of methane (CH4) in the atmosphere of HR 8799 b. Then, we report radial-velocity (RV) measurements for each of the three planets. The RV measurement of HR 8799 d is consistent with predictions made assuming coplanarity and orbital stability of the HR 8799 planetary system. Finally, we perform a uniform atmospheric analysis on the OSIRIS data, published photometric points, and low-resolution spectra. We do not infer any significant deviation from the stellar value of the carbon-to-oxygen ratio (C/O) of the three planets, which therefore does not yet yield definitive information about the location or method of formation. However, constraining the C/O for all the HR 8799 planets is a milestone for any multiplanet system, and particularly important for large, widely separated gas giants with uncertain formation processes.

Probing the atmosphere of WASP-69 b with low- and high-resolution transmission spectroscopy

Consideration of both low- and high-resolution transmission spectroscopy is key for obtaining a comprehensive picture of exoplanet atmospheres. In studies of transmission spectra, the continuum information is well established with low-resolution spectra, while the shapes of individual lines are best constrained with high-resolution observations. In this work, we aim to merge high- with low-resolution transmission spectroscopy to place tighter constraints on physical parameters of the atmospheres. We present the analysis of three primary transits of WASP-69 b in the visible (VIS) channel of the CARMENES instrument and perform a combined low- and high-resolution analysis using additional data from HARPS-N, OSIRIS/GTC, and WFC3/HST already available in the literature. We investigate the Na I D1 and D2 doublet, Hα, the Ca II infra-red triplet (IRT), and K I λ7699 Å lines, and we monitor the stellar photometric variability by performing long-term photometric observations with the STELLA telescope. During the first CARMENES observing night, we detected the planet Na I D2 and D1 lines at ~7 and ~3σ significance levels, respectively. We measured a D2/D1 intensity ratio of 2.5 ± 0.7, which is in agreement with previous HARPS-N observations. Our modelling of WFC3 and OSIRIS data suggests strong Rayleigh scattering, solar to super-solar water abundance, and a highly muted Na feature in the atmosphere of this planet, in agreement with previous investigations of this target. We use the continuum information retrieved from the low-resolution spectroscopy as a prior to break the degeneracy between the Na abundance, reference pressure, and thermosphere temperature for the high-resolution spectroscopic analysis. We fit the Na I D1 and D2 lines individually and find that the posterior distributions of the model parameters agree with each other within 1σ. Our results suggest that local thermodynamic equilibrium processes can explain the observed D2 /D1 ratio because the presence of haze opacity mutes the absorption features.

Fuzzy Cluster Analysis: Application to Determining Metallicities for Very Metal-poor Stars

Abstract This work presents a first attempt to apply fuzzy cluster analysis (FCA) to analyzing stellar spectra. FCA is adopted to categorize line indices measured from LAMOST low-resolution spectra, and automatically remove the least metallicity-sensitive indices. The FCA-processed indices are then transferred to the artificial neural network (ANN) to derive metallicities for 147 very metal-poor (VMP) stars that have been analyzed by high-resolution spectroscopy. The FCA-ANN method could derive robust metallicities for VMP stars, with a precision of ∼0.2 dex compared with high-resolution analysis. The recommended FCA threshold value λ for this test is between 0.9965 and 0.9975. After reducing the dimension of the line indices through FCA, the derived metallicities are still robust, with no loss of accuracy, and the FCA-ANN method performs stably for different spectral quality from [Fe/H] ∼ −1.8 down to −3.5. Compared with traditional classification methods, FCA considers ambiguity in groupings and noncontinuity of data, and is thus more suitable for observational data analysis. Though this early test uses FCA to analyze low-resolution spectra, and feeds the input to the ANN method to derive metallicities, FCA should be able to, in the large data era, also analyze slitless spectroscopy and multiband photometry, and prepare the input for methods not limited to ANN, in the field of stellar physics for other studies, e.g., stellar classification, identification of peculiar objects. The literature-collected high-resolution sample can help improve pipelines to derive stellar metallicities, and systematic offsets in metallicities for VMP stars for three published LAMOST catalogs have been discussed.

A case study of ACV variables discovered in the Zwicky Transient Facility survey

Context. Magnetic chemically peculiar (mCP) stars exhibit complex atmospheres that allow the investigation of the interplay of atomic diffusion, magnetic fields, and stellar rotation. A non-uniform surface distribution of chemical elements and the non-alignment of the rotational and magnetic axes result in the variability of several observables. Photometrically variable mCP stars are referred to as α2 Canum Venaticorum (ACV) variables. Aims. The present work presents a case study of known variables from the Zwicky Transient Facility (ZTF) survey, with the aim of investigating the survey’s suitability for the detection and study of new ACV variables. Methods. Using suitable selection criteria based on the known characteristics of ACV variables, candidate ACV stars were selected from the ZTF Catalog of Periodic Variable Stars. All light curves were inspected in detail to select the most promising candidates. Where available, low-resolution spectra from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) were employed to classify the stars on the MK system and confirm their status as mCP stars. Results. We have identified 86 new promising ACV star candidates. Fifteen of these stars have LAMOST spectra available that, in all cases, confirm them as classical mCP stars, which highlights the viability of our approach. We present astrophysical parameters for all sample stars that can be sorted into four subgroups characterized by distinct light curve shapes. Anti-phase variations in different photometric passbands, in particular, are a unique characteristic of a subset of ACV stars readily usable for their identification. The availability of data in three different passbands (g, r, and i) is a major advantage of the ZTF survey. Conclusions. On the basis of our experience with other photometric surveys and the analysis of light curves, we conclude that the ZTF is well suited to the search for, and the analysis of, ACV variables that are not considered in the available ZTF variable star catalogs. Further work will focus on the development and refinement of a search algorithm to correctly identify these stars in ZTF data and, subsequently, in massive photometric time series databases in general.

A Framework for Utilizing High-Resolution Mass Spectrometry and Nontargeted Analysis in Rapid Response and Emergency Situations.

Unknown chemical releases constitute a large portion of the rapid response situations to which the US Environmental Protection Agency is called on to respond. Workflows used to address unknown chemical releases currently involve screening for a large array of known compounds using many different targeted methods. When matches are not found, expert analytical chemistry knowledge is used to propose possible candidates from the available data, which generally includes low-resolution mass spectra and situational clues such as the location of the release, nearby industrial operations, and other field-reported facts. The past decade has witnessed dramatic improvements in capabilities for identifying unknown compounds using high-resolution mass spectrometry (HRMS) and nontargeted analysis (NTA) approaches. Complementary developments in cheminformatics tools have further enabled an increase in NTA throughput and identification confidence. Together with the expanding availability of HRMS instrumentation in monitoring laboratories, these advancements make NTA highly relevant to rapid response scenarios. In this article, we introduce the concept of NTA as it relates to rapid response needs and describe how it can be applied to address unknown chemical releases. We advocate for the consideration of HRMS-based NTA approaches to support future rapid response scenarios. Environ Toxicol Chem 2022;41:1117-1130. Published 2021. This article is a U.S. Government work and is in the public domain in the USA.

The first data release of LAMOST low-resolution single-epoch spectra

LAMOST Data Release 5, covering ∼17 000 deg2 from –10° to 80° in declination, contains 9 million co-added low-resolution spectra of celestial objects, each spectrum combined from repeat exposure of two to tens of times during Oct 2011 to Jun 2017. In this paper, we present the spectra of individual exposures for all the objects in LAMOST Data Release 5. For each spectrum, the equivalent width of 60 lines from 11 different elements are calculated with a new method combining the actual line core and fitted line wings. For stars earlier than F type, the Balmer lines are fitted with both emission and absorption profiles once two components are detected. Radial velocity of each individual exposure is measured by minimizing χ 2 between the spectrum and its best template. The database for equivalent widths of spectral lines and radial velocities of individual spectra are available online. Radial velocity uncertainties with different stellar type and signal-to-noise ratio are quantified by comparing different exposure of the same objects. We notice that the radial velocity uncertainty depends on the time lag between observations. For stars observed in the same day and with signal-to-noise ratio higher than 20, the radial velocity uncertainty is below 5km s−1, and increases to 10 km s−1 for stars observed in different nights.

The IGRINS YSO Survey II: Veiling Spectra of Pre-main-sequence Stars in Taurus-Auriga

Abstract We present measurements of the H- and K-band veiling for 141 young stellar objects (YSOs) in the Taurus-Auriga star-forming region using high-resolution spectra from the Immersion Grating Near-Infrared Spectrometer. In addition to providing measurements of r H and r K , we produce low-resolution spectra of the excess emission across the H and K bands. We fit temperatures to the excess spectra of 46 members of our sample and measure near-infrared excess temperatures ranging from 1200–2200 K, with an average of 1575 ± 225 K. We compare the luminosity of the excess continuum emission in Class II and Class III YSOs and find that a number of Class III sources display a significant amount of excess flux in the near-infrared. We conclude that the mid-infrared SED slope, and therefore young stellar object classification, is a poor predictor of the amount of near-infrared veiling. If the veiling arises in thermal emission from dust, its presence implies a significant amount of remaining inner-disk (<1 au) material in these Class III sources. We also discuss the possibility that the veiling effects could result from massive photospheric spots, unresolved binary companions, or accretion emission. Six low-mass members of our sample contain a prominent feature in their H-band excess spectra that is consistent with veiling from cool photospheric spots.

Energy deposition in Saturn’s equatorial upper atmosphere

We construct Saturn equatorial neutral temperature and density profiles of H, H2, He, and CH4, between 10−12 and 1 bar using measurements from Cassini’s Ion Neutral Mass Spectrometer (INMS) taken during the spacecraft’s final plunge into Saturn’s atmosphere on 15 September 2017, combined with previous deeper atmospheric measurements from the Cassini Composite InfraRed Spectrometer (CIRS) and from the UltraViolet Imaging Spectrograph (UVIS). These neutral profiles are fed into an energy deposition model employing soft X-ray and Extreme UltraViolet (EUV) solar fluxes at a range of spectral resolutions (Δλ=4×10−3nm to 1 nm) assembled from TIMED/SEE, from SOHO/SUMER, and from the Whole Heliosphere Interval (WHI) quiet Sun campaign. Our energy deposition model calculates ion production rate profiles through photo-ionisation and electron-impact ionisation processes, as well as rates of photo-dissociation of CH4. The ion reaction rate profiles we determine are important to obtain accurate ion density profiles, meanwhile methane photo-dissociation is key to initiate complex organic chemical processes. We assess the importance of spectral resolution in the energy deposition model by using a high-resolution H2 photo-absorption cross section, which has the effect of producing additional ionisation peaks near 800 km altitude. We find that these peaks are still formed when using low-resolution (Δλ=1nm) or mid-resolution (Δλ=0.1nm) solar spectra, as long as high-resolution cross sections are included in the model.

LASPM: the LAMOST stellar parameter pipeline for M-type stars and application to the sixth and seventh data release (DR6 and DR7)

The molecular-rich atmospheres of M type stars complicate our understanding to their atmospheric properties. Recently, great progress has been made in atmospheric modeling of M-type stars, and we take advantage of the updated BT-Settl model grid to develop a pipeline LASPM to measure atmospheric parameters (T eff, log g, [M/H]) of M-type stars from low-resolution spectra. The pipeline was applied to the sixth and seventh data release (DR6 & DR7) of Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST), which released atmospheric parameters for 610 419 and 680 185 M-type spectra, respectively. The key algorithm is to find the best-matching for templates in the synthetic spectral library for an observed spectrum, and then minimizing χ 2 through a linear combination of five best-matching templates. The intrinsic precisions of the parameters were estimated by using the multiple epoch observations for the same stars, which are 118 K, 0.20 dex, 0.29 dex for T eff, log g, and [M/H] respectively. The T eff and log g are consistent with the spectral and luminosity classifications by LAMOST 1D pipeline, and the loci of giants and dwarfs both on spectral index and color-magnitude diagrams show the validity. The metallicities of LASPM are also checked with the selected members of four open clusters (NGC 2632, Melotte 22, ASCC_16, and ASCC_19), which are consistent without any bias. Comparing the results between LASPM and the APOGEE Stellar Parameter and Chemical Abundance Pipeline (ASPCAP), there is a scatter of 73 K, 0.22 dex, 0.21 dex for T eff, log g, and [M/H], respectively.

Ultracool Dwarfs Observed with the Spitzer Infrared Spectrograph. I. An Accurate Look at the L-to-T Transition at ∼300 Myr from Optical Through Mid-infrared Spectrophotometry

Abstract We present Spitzer IRS 5–14 μm spectra and 16 μm and 22 μm photometry of the T2.5 companion to the ∼300 Myr old G0V star HN Peg. We incorporate previous 0.8–5 μm observations to obtain the most comprehensive spectral energy distribution (SED) of an intermediate-gravity L/T-transition dwarf that, together with an accurate Gaia EDR3 parallax of the primary, enables us to derive precise fundamental parameters. We find that young (≈0.1–0.3 Gyr) early-T dwarfs on average have ≈140 K lower effective temperatures, ≈20% larger radii, and similar bolometric luminosities compared to ≳1 Gyr old field dwarfs with similar spectral types. Our accurate infrared spectrophotometry offers new detail at wavelengths where the dominant carbon-bearing molecules have their strongest transitions: at 3.4 μm for methane and at 4.6 μm for carbon monoxide. We assess the performance of various widely available photospheric models and find that models with condensates and/or clouds better reproduce the full SED of this moderately young early-T dwarf. However, cloud-free models incorporating a more general convective instability treatment reproduce at least the low-resolution near-infrared spectrum similarly well. Our analysis of R ≈ 2300 J-band spectra shows that the near-infrared potassium absorption lines in HN Peg B have similar strengths to those seen in both younger and older T2–T3 dwarfs. We conclude that while alkali lines are well established as surface gravity indicators for L-type or warmer stars, they are insensitive to surface gravity in early-T dwarfs.

On the Use of Field RR Lyrae As Galactic Probes: IV. New Insights Into and Around the Oosterhoff Dichotomy*

Abstract We discuss the largest and most homogeneous spectroscopic data set of field RR Lyrae variables (RRLs) available to date. We estimated abundances using both high-resolution and low-resolution (ΔS method) spectra for fundamental (RRab) and first overtone (RRc) RRLs. The iron abundances for 7941 RRLs were supplemented with similar estimates that are available in the literature, ending up with 9015 RRLs (6150 RRab, 2865 RRc). The metallicity distribution shows a mean value of 〈[Fe/H]〉 = −1.51 ± 0.01, and σ(standard deviation) = 0.41 dex with a long metal-poor tail approaching [Fe/H] ≃ − 3 and a sharp metal-rich tail approaching solar iron abundance. The RRab variables are more metal-rich (〈[Fe/H]〉ab = −1.48 ± 0.01, σ = 0.41 dex) than RRc variables (〈[Fe/H]〉c = −1.58 ± 0.01, σ = 0.40 dex). The relative fraction of RRab variables in the Bailey diagram (visual amplitude versus period) located along the short-period (more metal-rich) and the long-period (more metal-poor) sequences are 80% and 20%, while RRc variables display an opposite trend, namely 30% and 70%, respectively. We found that the pulsation period of both RRab and RRc variables steadily decreases when moving from the metal-poor to the metal-rich regime. The visual amplitude shows the same trend, but RRc amplitudes are almost two times more sensitive than RRab amplitudes to metallicity. We also investigated the dependence of the population ratio (N c /Ntot) of field RRLs on the metallicity and we found that the distribution is more complex than in globular clusters. The population ratio steadily increases from ∼0.25 to ∼0.36 in the metal-poor regime, it decreases from ∼0.36 to ∼0.18 for −1.8 ≤ [Fe/H] ≤ −0.9 and it increases to a value of ∼0.3 approaching solar iron abundance.

Evidence of Accretion Burst: The Viscously Heated Inner Disk of the Embedded Protostar IRAS 16316-1540

Abstract Outbursts of young stellar objects occur when the mass accretion rate suddenly increases. However, such outbursts are difficult to detect for deeply embedded protostars due to their thick envelope and the rarity of outbursts. The near-IR spectroscopy is a useful tool to identify ongoing outburst candidates by the characteristic absorption features that indicate a disk origin. However, without high-resolution spectroscopy, the spectra of outburst candidates can be confused with the late-type stars since they have similar spectral features. For the protostar IRAS 16316-1540, the near-IR spectrum has line equivalent widths that are consistent with M-dwarf photospheres. However, our high-resolution IGRINS spectra reveal that the absorption lines have boxy and/or double-peaked profiles, as expected from a disk and not the star. The continuum emission source is likely the hot, optically thick disk, heated by viscous accretion. The projected disk rotation velocity of 41 ± 5 km s−1 corresponds to ∼0.1 au. Based on the result, we suggest IRAS 16316-1540 as an ongoing outburst candidate. Viscous heating of disks is usually interpreted as evidence for ongoing bursts, which may be more common than previously estimated from low-resolution near-IR spectra.

Sr and Ba abundances: Comparing machine-learning with star-by-star analyses

Context. A new large sample of 895 s-process-rich candidates out of 454 180 giant stars surveyed by LAMOST at a low spectral resolution (R ~ 1800) has been reported by Norfolk et al. (2019, MNRAS, 490, 2219; hereafter N19). Aims. This study is aimed at confirming the s-process enrichment at the higher resolution (R ~ 86 000) offered by the HERMES-Mercator spectrograph for the 15 brightest targets of the N19 sample, which consists of 13 Sr-only stars and two Ba-only stars (designating stars with only the Sr or only Ba lines strengthened). Methods. Abundances were derived for elements Li, C (including the 12C/13C isotopic ratio), N, O, Na, Mg, Fe, Rb, Sr, Y, Zr, Nb, Ba, La, and Ce, using the TURBOSPECTRUM radiative transfer LTE code with MARCS model atmospheres. Binarity has been tested by comparing the Gaia DR2 radial velocity (epoch 2015.5) with the HERMES velocity obtained 1600–1800 days (about 4.5 yr) later. Results. Among the 15 programme stars, 4 show no s-process overabundances ([X/Fe] < 0.2 dex), 8 show mild s-process overabundances (at least three heavy elements with 0.2 < [X∕Fe] < 0.8), and 3 have strong overabundances (at least three heavy elements with [X/Fe] ≥ 0.8). Among the 13 stars classified as Sr-only by the previous investigation, 4 have no s-process overabundances, 8 are mild barium stars, and 1 is a strong barium star. The two Ba-only stars turn out to be both strong barium stars. Especially noteworthy is the fact that these two are actually dwarf barium stars. Two among the three strong barium stars show clear evidence in support of their binary character, as expected for objects produced through mass-transfer. The results for the no s-process and mild barium stars are more surprising; namely, among the no-s stars, there are two binaries out of four, whereas only one out the eight diagnosed mild barium stars shows a clear signature of radial-velocity variations. Conclusions. Blending effects and saturated lines have to be considered very carefully when using machine-learning techniques, especially when applied to low-resolution spectra. Among the Sr-only stars from the previous study sample, about 60% (8/13) of them can be expected to be true mild barium stars and about 8% to be strong barium stars; this fraction is likely close to 100% for the N19 Ba-only stars (2/2). Therefore, we recommend to limit the sample to N19 Ba-only stars when one needs an unpolluted sample of mass-transfer (i.e., extrinsic) objects.

On the Use of Field RR Lyrae as Galactic Probes. V. Optical and Radial Velocity Curve Templates

Abstract We collected the largest spectroscopic catalog of RR Lyrae (RRLs) including ≈20,000 high-, medium-, and low-resolution spectra for ≈10,000 RRLs. We provide the analytical forms of radial velocity curve (RVC) templates. These were built using 36 RRLs (31 fundamental—split into three period bins—and five first-overtone pulsators) with well-sampled RVCs based on three groups of metallic lines (Fe, Mg, Na) and four Balmer lines (H α , H β , H γ , H δ ). We tackled the long-standing problem of the reference epoch to anchor light-curve and RVC templates. For the V-band, we found that the residuals of the templates anchored to the phase of the mean magnitude along the rising branch are ∼35% to ∼45% smaller than those anchored to the phase of maximum light. For the RVC, we used two independent reference epochs for metallic and Balmer lines and we verified that the residuals of the RVC templates anchored to the phase of mean RV are from 30% (metallic lines) up to 45% (Balmer lines) smaller than those anchored to the phase of minimum RV. We validated our RVC templates by using both the single-point and the three phase point approaches. We found that barycentric velocities based on our RVC templates are two to three times more accurate than those available in the literature. We applied the current RVC templates to Balmer lines RVs of RRLs in the globular NGC 3201 collected with MUSE at VLT. We found the cluster barycentric RV of V γ = 496.89 ± 8.37(error) ± 3.43 (standard deviation) km s−1, which agrees well with literature estimates.

The ultra-hot-Jupiter KELT-16 b: dynamical evolution and atmospheric properties

ABSTRACT We present broad-band photometry of 30 planetary transits of the ultra-hot-Jupiter KELT-16 b, using five medium-class telescopes. The transits were monitored through standard $B,\, V,\, R,\, I$ filters and four were simultaneously observed from different places, for a total of 36 new light curves. We used these new photometric data and those from the TESS space telescope to review the main physical properties of the KELT-16 planetary system. Our results agree with previous measurements but are more precise. We estimated the mid-transit times for each of these transits and combined them with others from the literature to obtain 69 epochs, with a time baseline extending over more than 4 yr, and searched for transit time variations. We found no evidence for a period change, suggesting a lower limit for orbital decay at 8 Myr, with a lower limit on the reduced tidal quality factor of $Q^{\prime }_{\star }\gt (1.9 \pm 0.8) \times 10^5$ with $95{{\rm {per\ cent}}}$ confidence. We built up an observational, low-resolution transmission spectrum of the planet, finding evidence of the presence of optical absorbers, although with a low significance. Using TESS data, we reconstructed the phase curve finding that KELT-16 b has a phase offset of 25.25 ± 14.03 °E, a day- and night-side brightness temperature of 3190 ± 61 K and 2668 ± 56 K, respectively. Finally, we compared the flux ratio of the planet over its star at the TESS and Spitzer wavelengths with theoretical emission spectra, finding evidence of a temperature inversion in the planet’s atmosphere, the chemical composition of which is preferably oxygen-rich rather than carbon-rich.