bluuebunny/crossref_metadata_2025_split huggingface dataset:
Reaction of NH+, NH2+, and NH3+ ions with H2 at low temperatures
Authors: Rednyk S. , Roučka Š. , Kovalenko A. , Tran T. D. , Dohnal P. , Plašil R. , Glosík J. 
Published: April 2019

Aims. We present an experimental investigation of the exothermic reactions of NH+, NH2+, and NH3+ ions with H2 at temperatures relevant for interstellar clouds.
Methods. The reactions were studied using a variable-temperature 22-pole radio frequency ion trap instrument.
Results. The temperature dependences of rate coefficients of these reactions have been obtained at temperatures from 15 up to 300 K. The reaction of NH+ with H2 has two channels, which lead to NH2+ ( ∼ 97%) and H+3 ( ∼ 3%) with nearly constant reaction rate coefficients (kaNH+(17 K) = 1.0 × 10−9 cm3 s−1 and kbNH+(17 K) = 4.0 × 10−11 cm3 s−1, respectively). The reaction of NH2+ with H2 produces only NH3+ ions. The measured rate coefficient monotonically decreases with increasing temperature from kNH2+(17 K) = 6 × 10−10 cm3 s−1 to kNH2+(300 K) = 2 × 10−10 cm3 s−1. The measured rate coefficient of the reaction of NH3+ with H2, producing NH+4, increases with decreasing temperature from 80 K down to 15 K, confirming that the reaction proceeds by tunnelling through a potential barrier.
Uncertainties in gas kinematics arising from stellar continuum modeling in integral field spectroscopy data: the case of NGC 2906 observed with VLT/MUSE
Authors: Bellocchi E. , Ascasibar Y. , Galbany L. , Sánchez S. F. , Ibarra–Medel H. , Gavilán M. , Díaz Á. 
Published: April 2019

Context. Integral field spectroscopy (IFS) provides detailed information about galaxy kinematics at high spatial and spectral resolution, and the disentanglement of the gaseous and stellar components is a key step in the analysis of the data.
Aims. We study how the use of several stellar-subtraction methods and line fitting approaches can affect the derivation of the main kinematic parameters (velocity and velocity dispersion fields) of the ionized gas component.
Methods. The target of this work is the nearby galaxy NGC 2906, observed with the MUSE instrument at the Very Large Telescope (VLT). A sample of twelve spectra is selected from the inner (nucleus) and outer (spiral arms) regions, characterized by different ionization mechanisms. We compare three different methods to subtract the stellar continuum (FIT3D, STARLIGHT and pPXF), combined with one of the following stellar libraries: MILES, STELIB and GRANADA+MILES.
Results. The choice of the stellar-subtraction method is the most important ingredient affecting the derivation of the gas kinematics, followed by the choice of the stellar library and by the line-fitting approach. In our data, typical uncertainties in the observed wavelength and width of the Hα and [NII] lines are of the order of ⟨δλ⟩rms ∼ 0.1 Å and ⟨δσ⟩rms ∼ 0.2 Å (i.e., ∼5 and 10 km s−1, respectively). The results obtained from the [NII] line seem to be slightly more robust, as it is less affected by stellar absorption than Hα. All methods considered yield statistically consistent measurements once a mean systemic contribution Δλ¯ = Δσ¯ = 0.2 ΔMUSE is added in quadrature to the line-fitting errors, where ΔMUSE = 1.1 Å ∼50 km s−1, which denotes the instrumental resolution of the MUSE spectra.
Conclusions. Although the subtraction of the stellar continuum is critical in order to recover line fluxes, any method (including none) can be used to measure the gas kinematics, as long as an additional component, Δλ¯ = Δσ¯ = 0.2 ΔMUSE, is added to the error budget.
Stellar cusp and warm dust at the heart of NGC 1068
Authors: Rouan D. , Grosset L. , Gratadour D. 
Published: April 2019

Aims. Establishing precisely how stars and interstellar medium distribute within the central 100 pc area around an AGN, down to the pc scale, is key to understanding the late stages of transfer of matter onto the accretion disc.
Methods. Using adaptive optics-assisted (SPHERE-VLT) near-IR images in the H band, Ks band, and several narrow bands of the Seyfert 2 galaxy NGC 1068, we analysed the radial distribution of brightness in the central r <  100 pc area down to the pc scale. The median-averaged radial profiles are fitted by a cusp (power law) plus a central point source. A simple radiative transfer model is also used to interpret the data.
Results. We find that the fit of radial brightness profiles beyond 10 pc is done quite precisely at Ks band by a cusp of exponent −2.0 plus a central point source and by a cusp of exponent −1.2 at H. The difference of exponents between H band and Ks band can be explained by differential extinction, provided that the distribution of dust is itself cuspy, with an exponent −1.0. However, the derived stellar density is found to follow a r−4 cusp, which is much steeper than any other cusp, either theoretically predicted around a massive black hole, or observed in the centre of early- and late-type galaxies or in mergers. Introducing a segregation in the stellar population with a central excess of giant stars leads to a somewhat less steep exponent; however, the de-reddened luminosity of the stellar cusp, as well as the mass of dust and gas all appear much too high to be realistic. An alternative scenario, where the Ks-band profile is well fitted by a combination of radiation from a stellar cusp identical to the H-band profile and thermal emission of warm/hot dust heated by the central engine appears much more satisfactory. NGC 1068 is shown to satisfy a relationship between half-light radius, cusp luminosity, and exponent that we established using a sample of luminous infrared galaxies (LIRGs) and ultraluminous infrared galaxies ULIRGs. This suggests that the cusp is the remnant of a recent starburst. We identify the central point-like source with the very hot dust at the internal wall of the putative torus and derive an intrinsic luminosity that requires a central extinction AK ≈ 8, a value consistent with predictions by several torus models.
Conclusions. The overall picture revealed by this study is closely consistent with the scheme of a central rather steep stellar cusp, embedded in a diluted medium of warm dust, while a compact and dense structure identified with the putative torus is required to interpret a highly reddened point-like central source of very hot dust.
Radial abundance gradients in the outer Galactic disk as traced by main-sequence OB stars
Authors: Bragança G. A. , Daflon S. , Lanz T. , Cunha K. , Bensby T. , McMillan P. J. , Garmany C. D. , Glaspey J. W. , Borges Fernandes M. , Oey M. S. , Hubeny I. 
Published: April 2019

Context. Elemental abundance gradients in galactic disks are important constraints for models of how spiral galaxies form and evolve. However, the abundance structure of the outer disk region of the Milky Way is poorly known, which hampers our understanding of the spiral galaxy that is closest to us and that can be studied in greatest detail. Young OB stars are good tracers of the present-day chemical abundance distribution of a stellar population and because of their high luminosities they can easily be observed at large distances, making them suitable to explore and map the abundance structure and gradients in the outer regions of the Galactic disk.
Aims. Using a sample of 31 main-sequence OB stars located between galactocentric distances 8.4−15.6 kpc, we aim to probe the present-day radial abundance gradients of the Galactic disk.
Methods. The analysis is based on high-resolution spectra obtained with the MIKE spectrograph on the Magellan Clay 6.5-m telescope on Las Campanas. We used a non-NLTE analysis in a self-consistent semi-automatic routine based on TLUSTY and SYNSPEC to determine atmospheric parameters and chemical abundances.
Results. Stellar parameters (effective temperature, surface gravity, projected rotational velocity, microturbulence, and macroturbulence) and silicon and oxygen abundances are presented for 28 stars located beyond 9 kpc from the Galactic center plus three stars in the solar neighborhood. The stars of our sample are mostly on the main-sequence, with effective temperatures between 20 800−31 300 K, and surface gravities between 3.23−4.45 dex. The radial oxygen and silicon abundance gradients are negative and have slopes of −0.07 dex kpc−1 and −0.09 dex kpc−1, respectively, in the region 8.4 ≤ RG ≤ 15.6 kpc.
Conclusions. The obtained gradients are compatible with the present-day oxygen and silicon abundances measured in the solar neighborhood and are consistent with radial metallicity gradients predicted by chemodynamical models of Galaxy Evolution for a subsample of young stars located close to the Galactic plane.
Gaia Data Release 2
Authors: Rimoldini L. , Holl B. , Audard M. , Mowlavi N. , Nienartowicz K. , Evans D. W. , Guy L. P. , Lecoeur-Taïbi I. , Jevardat de Fombelle G. , Marchal O. , Roelens M. , De Ridder J. , Sarro L. M. , Regibo S. , Lopez M. , Clementini G. , Ripepi V. , Molinaro R. , Garofalo A. , Molnár L. , Plachy E. , Juhász Á. , Szabados L. , Lebzelter T. , Teyssier D. , Eyer L. 
Published: April 2019

Context. More than half a million of the 1.69 billion sources in Gaia Data Release 2 (DR2) are published with photometric time series that exhibit light variations during the 22 months of observation.
Aims. An all-sky classification of common high-amplitude pulsators (Cepheids, long-period variables, δ Scuti/SX Phoenicis, and RR Lyrae stars) is provided for stars with brightness variations greater than 0.1 mag in G band.
Methods. A semi-supervised classification approach was employed, firstly training multi-stage random forest classifiers with sources of known types in the literature, followed by a preliminary classification of the Gaia data and a second training phase that included a selection of the first classification results to improve the representation of some classes, before the improved classifiers were applied to the Gaia data. Dedicated validation classifiers were used to reduce the level of contamination in the published results. A relevant fraction of objects were not yet sufficiently sampled for reliable Fourier series decomposition, consequently classifiers were based on features derived from statistics of photometric time series in the G, GBP, and GRP bands, as well as from some astrometric parameters.
Results. The published classification results include 195 780 RR Lyrae stars, 150 757 long-period variables, 8550 Cepheids, and 8882 δ Scuti/SX Phoenicis stars. All of these results represent candidates whose completeness and contamination are described as a function of variability type and classification reliability. Results are expressed in terms of class labels and classification scores, which are available in the vari_classifier_result table of the Gaia archive.
Effect of radiative heat transfer in porous comet nuclei: case study of 67P/Churyumov-Gerasimenko
Authors: Hu Xuanyu , Gundlach Bastian , von Borstel Ingo , Blum Jürgen , Shi Xian 
Published: April 2019

Context.Radiative heat transfer occurs in a porous medium, such as regolith on planetary bodies. Radiation enhances the efficiency of heat transport through the subsurface, effecting a strong temperature dependence of thermal conductivity. However, this effect has been omitted in many studies of comet 67P/Churyumov-Gerasimenko (67P).Aims.We concisely review the method for characterizing radiative heat transfer and present a generic treatment in thermal modeling. In particular, we study the impact of radiative heat transfer on 67P subject to both diurnal and seasonal variations of insolation.Methods.We adapted a numerical model based on the Crank–Nicolson scheme to estimate the subsurface temperatures and water production rate of 67P, where conductivity may vary with depth.Results.Radiative heat transfer is efficient during the day near the surface but it dicreases at night, which means that more energy is deposited underneath the diurnal thermal skin. The effect increases with pore size and accordingly, with the size of the constituent aggregates of the nucleus. It also intensifies with decreasing heliocentric distance. Close to perihelion, within 2 au, for example, radiation may raise the temperature by more than 20 K at a depth of 5 cm, compared with a purely conductive nucleus. If the nucleus is desiccated and composed of centimeter-sized aggregates, the subsurface at 0.5 m may be warmed to above 180 K.Conclusions.Radiative heat transfer is not negligible if the nucleus of 67P consists of aggregates that measure millimeters or larger. To distinguish its role and ascertain the pore size of the subsurface, measurements of temperatures from a depth of ~1 cm down to several decimeters are most diagnostic. The water production rate of the nucleus, on the other hand, does not provide a useful constraint.
Magnetic wind-driven accretion in dwarf novae
Authors: Scepi Nicolas , Dubus Guillaume , Lesur Geoffroy 
Published: April 2019

Context. Dwarf novae (DNe) and X-ray binaries exhibit outbursts thought to be due to a thermal-viscous instability in the accretion disk. The disk instability model (DIM) assumes that accretion is driven by turbulent transport, customarily attributed to the magneto-rotational instability (MRI). However, recent results point out that MRI turbulence alone fails to reproduce the light curves of DNe.
Aims. Our aim is to study the impact of wind-driven accretion on the light curves of DNe. Local and global simulations show that magneto-hydrodynamic winds are present when a magnetic field threads the disk, even for relatively high ratios of thermal pressure to magnetic pressure (β ≈ 105). These winds are very efficient in removing angular momentum but do not heat the disk, thus they do not behave as MRI-driven turbulence.
Methods. We add the effect of wind-driven magnetic braking in the angular momentum equation of the DIM but neglect the mass loss due to the wind. We assume a fixed magnetic configuration: dipolar or constant with radius. We use prescriptions for the wind torque and the turbulent torque derived from shearing box simulations.
Results. The wind torque enhances the accretion of matter, resulting in light curves that look like DNe outbursts when assuming a dipolar field with a moment μ ≈ 1030 G cm3. In the region where the wind torque dominates the disk is cold and optically thin, and the accretion speed is super-sonic. The inner disk behaves as if truncated, leading to higher quiescent X-ray luminosities from the white dwarf boundary layer than expected with the standard DIM. The disk is stabilized if the wind-dominated region is large enough, potentially leading to “dark” disks that emitting little radiation.
Conclusion. Wind-driven accretion can play a key role in shaping the light curves of DNe and X-ray binaries. Future studies will need to include the time evolution of the magnetic field threading the disk to fully assess its impact on the dynamics of the accretion flow.
Single metal-poor ultra compact dwarf galaxy at one kiloparsec distance from the low-mass elliptical galaxy FCC 47
Authors: Fahrion Katja , Georgiev Iskren , Hilker Michael , Lyubenova Mariya , van de Ven Glenn , Alfaro-Cuello Mayte , Corsini Enrico M. , Sarzi Marc , McDermid Richard M. , de Zeeuw Tim 
Published: April 2019

Context. Photometric surveys of galaxy clusters have revealed a large number of ultra compact dwarfs (UCDs) around predominantly massive elliptical galaxies. Their origin is still debated as some UCDs are considered to be the remnant nuclei of stripped dwarf galaxies while others seem to mark the high-mass end of the star cluster population.Aims. We aim to characterize the properties of a UCD found at very close projected distance (rwproj= 1.1 kpc) from the centre of the low-mass (M ∼ 1010 M⊙) early-type galaxy FCC 47. This is a serendipitous discovery from MUSE adaptive optics science verification data. We explore the potential origin of this UCD as either a massive cluster or the remnant nucleus of a dissolved galaxy.Methods. We used archivalHubbleSpace Telescope data to study the photometric and structural properties of FCC 47-UCD1. In the MUSE data, the UCD is unresolved, but we used its spectrum to determine the radial velocity and metallicity.Results. The surface brightness of FCC 47-UCD1 is best described by a single King profile with low concentrationC = Rt/Rc ∼ 10 and large effective radius (reff = 24 pc). Its integrated magnitude and blue colour (Mg = −10.55 mag, (g − z) = 1.46 mag) combined with a metallicity of [M/H] = −1.12 ± 0.10 dex and an age > 8 Gyr obtained from the full fitting of the MUSE spectrum suggests a stellar population mass ofM* = 4.87 × 106 M⊙. The low S/N of the MUSE spectrum prevents detailed stellar population analysis. Due to the limited spectral resolution of MUSE, we can only give an upper limit on the velocity dispersion (σ <  17 km s−1), and consequently on its dynamical mass (Mdyn <  1.3 × 107 M⊙).Conclusions. The origin of the UCD cannot be constrained with certainty. The low metallicity, old age, and magnitude are consistent with a star cluster origin, whereas the extended size is consistent with an origin as the stripped nucleus of a dwarf galaxy with a initial stellar mass of a few 108 M⊙.
The CARMENES search for exoplanets around M dwarfs
Authors: Schweitzer A. , Passegger V. M. , Cifuentes C. , Béjar V. J. S. , Cortés-Contreras M. , Caballero J. A. , del Burgo C. , Czesla S. , Kürster M. , Montes D. , Zapatero Osorio M. R. , Ribas I. , Reiners A. , Quirrenbach A. , Amado P. J. , Aceituno J. , Anglada-Escudé G. , Bauer F. F. , Dreizler S. , Jeffers S. V. , Guenther E. W. , Henning T. , Kaminski A. , Lafarga M. , Marfil E. , Morales J. C. , Schmitt J. H. M. M. , Seifert W. , Solano E. , Tabernero H. M. , Zechmeister M. 
Published: April 2019

Aims. We determine the radii and masses of 293 nearby, bright M dwarfs of the CARMENES survey. This is the first time that such a large and homogeneous high-resolution (R >  80 000) spectroscopic survey has been used to derive these fundamental stellar parameters.
Methods. We derived the radii using Stefan–Boltzmann’s law. We obtained the required effective temperatures Teff from a spectral analysis and we obtained the required luminosities L from integrated broadband photometry together with the Gaia DR2 parallaxes. The mass was then determined using a mass-radius relation that we derived from eclipsing binaries known in the literature. We compared this method with three other methods: (1) We calculated the mass from the radius and the surface gravity log g, which was obtained from the same spectral analysis as Teff. (2) We used a widely used infrared mass-magnitude relation. (3) We used a Bayesian approach to infer stellar parameters from the comparison of the absolute magnitudes and colors of our targets with evolutionary models.
Results. Between spectral types M0 V and M7 V our radii cover the range 0.1 R⊙ <  R <  0.6 R⊙ with an error of 2–3% and our masses cover 0.09 ℳ⊙ < ℳ< 0.6ℳ⊙ with an error of 3–5%. We find good agreement between the masses determined with these different methods for most of our targets. Only the masses of very young objects show discrepancies. This can be well explained with the assumptions that we used for our methods.
The HADES RV programme with HARPS-N at TNG
Authors: Pinamonti M. , Sozzetti A. , Giacobbe P. , Damasso M. , Scandariato G. , Perger M. , González Hernández J. I. , Lanza A. F. , Maldonado J. , Micela G. , Suárez Mascareño A. , Toledo-Padrón B. , Affer L. , Benatti S. , Bignamini A. , Bonomo A. S. , Claudi R. , Cosentino R. , Desidera S. , Maggio A. , Martinez Fiorenzano A. , Pagano I. , Piotto G. , Rainer M. , Rebolo R. , Ribas I. 
Published: April 2019

Context.Small rocky planets seem to be very abundant around low-mass M-type stars. Their actual planetary population is however not yet precisely understood. Currently, several surveys aim to expand the statistics with intensive detection campaigns, both photometric and spectroscopic.Aims.The HADES program aims to improve the current statistics through the in-depth analysis of accurate radial-velocity (RV) monitoring in a narrow range of spectral sub-types, with the precision needed to detect small planets with a few Earth masses.Methods.We analyse 106 spectroscopic HARPS-N observations of the active M0-type star GJ 685 taken over the past five years. We combine these data with photometric measurements from different observatories to accurately model the stellar rotation and disentangle its signals from genuine Doppler planetary signals in the RV data. We run an MCMC analysis on the RV and activity index time series to model the planetary and stellar signals present in the data, applying Gaussian Process regression technique to deal with the stellar activity signals.Results.We identify three periodic signals in the RV time series, with periods of 9, 24, and 18 d. Combining the analyses of the photometry of the star with the activity indexes derived from the HARPS-N spectra, we identify the 18 d and 9 d signals as activity-related, corresponding to the stellar rotation period and its first harmonic, respectively. The 24 d signal shows no relation to any activity proxy, and therefore we identify it as a genuine planetary signal. We find the best-fit model describing the Doppler signal of the newly found planet, GJ 685 b, corresponding to an orbital periodPb= 24.160−0.047+0.061d and a minimum massMPsini= 9.0−1.8+1.7M⊕. We also study a sample of 70 RV-detected M-dwarf planets, and present new statistical evidence of a difference in mass distribution between the populations of single- and multi-planet systems, which can shed new light on the formation mechanisms of low-mass planets around late-type stars.
Highly structured disk around the planet host PDS 70 revealed by high-angular resolution observations with ALMA
Authors: Keppler M. , Teague R. , Bae J. , Benisty M. , Henning T. , van Boekel R. , Chapillon E. , Pinilla P. , Williams J. P. , Bertrang G. H.-M. , Facchini S. , Flock M. , Ginski Ch. , Juhasz A. , Klahr H. , Liu Y. , Müller A. , Pérez L. M. , Pohl A. , Rosotti G. , Samland M. , Semenov D. 
Published: April 2019

Context. Imaged in the gap of a transition disk and found at a separation of about 195 mas (~22 au) from its host star at a position angle of about 155°, PDS 70 b is the most robustly detected young planet to date. This system is therefore a unique laboratory for characterizing the properties of young planetary systems at the stage of their formation.
Aims. We aim to trace direct and indirect imprints of PDS 70 b on the gas and dust emission of the circumstellar disk in order to study the properties of this ~5 Myr young planetary system.
Methods. We obtained ALMA band 7 observations of PDS 70 in dust continuum and 12CO (3–2) and combined them with archival data. This resulted in an unprecedented angular resolution of about 70 mas (~8 au).
Results. We derive an upper limit on circumplanetary material at the location of PDS 70 b of ~0.01 M⊕ and find a highly structured circumstellar disk in both dust and gas. The outer dust ring peaks at 0.65′′ (74 au) and reveals a possible second unresolved peak at about 0.53′′ (60 au). The integrated intensity of CO also shows evidence of a depletion of emission at ~0.2′′ (23 au) with a width of ~0.1′′ (11 au). The gas kinematics show evidence of a deviation from Keplerian rotation inside ≲0.8′′ (91 au). This implies a pressure gradient that can account for the location of the dust ring well beyond the location of PDS 70 b. Farther in, we detect an inner disk that appears to be connected to the outer disk by a possible bridge feature in the northwest region in both gas and dust. We compare the observations to hydrodynamical simulations that include a planet with different masses that cover the estimated mass range that was previously derived from near-infrared photometry (~5–9 MJup). We find that even a planet with a mass of 10 MJup may not be sufficient to explain the extent of the wide gap, and an additional low-mass companion may be needed to account for the observed disk morphology.