bluuebunny/crossref_metadata_2025 huggingface dataset:
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.
Thermal emission from bow shocks
Authors: Green Samuel , Mackey Jonathan , Haworth Thomas J. , Gvaramadze Vasilii V. , Duffy Peter
Published: April 2019

The Bubble Nebula (or NGC 7635) is a parsec-scale seemingly spherical wind-blown bubble around the relatively unevolved O star BD+60°2522. The young dynamical age of the nebula and significant space velocity of the star suggest that the Bubble Nebula might be a bow shock. We ran 2D hydrodynamic simulations to model the interaction of the wind of the central star with the interstellar medium (ISM). The models cover a range of possible ISM number densities of n = 50−200 cm−3 and stellar velocities of v* = 20−40 km s−1. Synthetic Hα and 24 μm emission maps predict the same apparent spherical bubble shape with quantitative properties similar to observations. The synthetic maps also predict a maximum brightness similar to that from the observations and agree that the maximum brightness is at the apex of the bow shock. The best-matching simulation had v* ≈ 20 km s−1 into an ISM with n ∼ 100 cm−3, at an angle of 60° with respect to the line of sight. Synthetic maps of soft (0.3−2 keV) and hard (2−10 keV) X-ray emission show that the brightest region is in the wake behind the star and not at the bow shock itself. The unabsorbed soft X-rays have a luminosity of ∼1032−1033 erg s−1. The hard X-rays are fainter: ∼1030−1031 erg s−1, and may be too faint for current X-ray instruments to successfully observe. Our results imply that the O star creates a bow shock as it moves through the ISM and in turn creates an asymmetric bubble visible at optical and infrared wavelengths and predicted to be visible in X-rays. The Bubble Nebula does not appear to be unique; it could simply be a favourably oriented, very dense bow shock. The dense ISM surrounding BD+60°2522 and its strong wind suggest that it could be a good candidate for detecting non-thermal emission.
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.
Evidence of two spectral breaks in the prompt emission of gamma-ray bursts
Authors: Ravasio M. E. , Ghirlanda G. , Nava L. , Ghisellini G.
Published: April 2019

The long-lasting tension between the observed spectra of gamma-ray bursts (GRBs) and the predicted synchrotron emission spectrum might be solved if electrons do not completely cool. Evidence of incomplete cooling was recently found in Swift GRBs with prompt observations down to 0.1 keV, and in one bright Fermi burst, GRB 160625B. Here we systematically search for evidence of incomplete cooling in the spectra of the ten brightest short and long GRBs observed by Fermi. We find that in eight out of ten long GRBs there is compelling evidence of a low-energy break (below the peak energy) and good agreement with the photon indices of the synchrotron spectrum (respectively −2/3 and −3/2 below the break and between the break and the peak energy). Interestingly, none of the ten short GRBs analysed shows a break, but the low-energy spectral slope is consistent with −2/3. In a standard scenario, these results imply a very low magnetic field in the emission region (B′∼10 G in the comoving frame), at odd with expectations.
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.
Constraining mixing in massive stars in the Small Magellanic Cloud
Authors: Schootemeijer A. , Langer N. , Grin N. J. , Wang C.
Published: April 2019

Context. The evolution of massive stars is strongly influenced by internal mixing processes such as semiconvection, convective core overshooting, and rotationally induced mixing. None of these processes are currently well constrained.

Aims. We investigate models for massive stars in the Small Magellanic Cloud (SMC), for which stellar-wind mass loss is less important than for their metal-rich counterparts. We aim to constrain the various mixing efficiencies by comparing model results to observations.

Methods. For this purpose, we use the stellar-evolution code MESA to compute more than 60 grids of detailed evolutionary models for stars with initial masses of 9…100 M⊙, assuming different combinations of mixing efficiencies of the various processes in each grid. Our models evolve through core hydrogen and helium burning, such that they can be compared with the massive main sequence and supergiant population of the SMC.

Results. We find that for most of the combinations of the mixing efficiencies, models in a wide mass range spend core-helium burning either only as blue supergiants, or only as red supergiants. The latter case corresponds to models that maintain a shallow slope of the hydrogen/helium (H/He) gradient separating the core and the envelope of the models. Only a small part of the mixing parameter space leads to models that produce a significant number of blue and red supergiants, which are both in abundance in the SMC. Some of our grids also predict a cut-off in the number of red supergiants above log L/L⊙ = 5…5.5. Interestingly, these models contain steep H/He gradients, as is required to understand the hot, hydrogen-rich Wolf-Rayet stars in the SMC. We find that unless it is very fast, rotation has a limited effect on the H/He profiles in our models.

Conclusions. While we use specific implementations of the considered mixing processes, they comprehensively probe the two first-order structural parameters, the core mass and the H/He gradient in the core-envelope interface. Our results imply that in massive stars, mixing during the main-sequence evolution leads to a moderate increase in the helium core masses, and also that the H/He gradients above the helium cores become very steep. Our model grids can be used to further refine the various mixing efficiencies with the help of future observational surveys of the massive stars in the SMC, and thereby help to considerably reduce the uncertainties in models of massive star evolution.
Young stellar populations in early-type dwarf galaxies
Authors: Hamraz E. , Peletier R. F. , Khosroshahi H. G. , Valentijn E. A. , den Brok M. , Venhola A.
Published: April 2019

Aims. To understand the stellar population content of early-type dwarf galaxies (dEs) and their environmental dependence, we compare the slopes and intrinsic scatter of color–magnitude relations (CMRs) for three nearby clusters, Fornax, Virgo, and Coma. Additionally, we present and compare internal color profiles of these galaxies to identify central blue regions with younger stars.

Methods. We use the imaging of the HST/ACS Fornax cluster in the magnitude range of −18.7 ≤ Mg′ ≤ −16.0 to derive magnitudes, colors, and color profiles, which we compare with literature measurements from the HST/ACS Virgo and Coma Cluster Survey. We take advantage of HST accuracy to investigate and parameterize the (g′−z′) color profiles of these dEs.

Results. Based on analysis of the color profiles, we report on a large number of dEs with young stellar populations at their center in all three clusters. While for Virgo and Coma the number of blue-cored dEs is found to be 85%±2% and 53%±3%, respectively, for Fornax, we find that all galaxies have a blue core. We show that bluer cores reside in fainter dEs, similar to the trend seen in nucleated dEs. We find no correlation between the luminosity of the galaxy and the size of its blue core. Moreover, a comparison of the CMRs of the three clusters shows that the scatter in the CMR of Virgo is considerably larger than in the Fornax and Coma clusters. Presenting adaptive smoothing we show that the galaxies on the blue side of the CMR often show evidence for dust extinction, which strengthens the interpretation that the bluer colors are due to young stellar populations. We also find that outliers on the red side of the CMR are more compact than what is expected for their luminosity. We find several of these red outliers in Virgo, often close to more massive galaxies. No red outlying compact early-types are found in Fornax and Coma in this magnitude range while we find three in the Virgo cluster. We show that the CMR of the Fornax and Virgo clusters are slightly bluer than that of Coma. We suggest that the large number of outliers and larger scatter found for Virgo CMR are a result of the alternative assembly history of this cluster.
Thermal properties of slowly rotating asteroids: results from a targeted survey
Authors: Marciniak A. , Alí-Lagoa V. , Müller T. G. , Szakáts R. , Molnár L. , Pál A. , Podlewska-Gaca E. , Parley N. , Antonini P. , Barbotin E. , Behrend R. , Bernasconi L. , Butkiewicz-Bąk M. , Crippa R. , Duffard R. , Ditteon R. , Feuerbach M. , Fauvaud S. , Garlitz J. , Geier S. , Goncalves R. , Grice J. , Grześkowiak I. , Hirsch R. , Horbowicz J. , Kamiński K. , Kamińska M. K. , Kim D.-H. , Kim M.-J. , Konstanciak I. , Kudak V. , Kulczak P. , Maestre J. L. , Manzini F. , Marks S. , Monteiro F. , Ogłoza W. , Oszkiewicz D. , Pilcher F. , Perig V. , Polakis T. , Polińska M. , Roy R. , Sanabria J. J. , Santana-Ros T. , Skiff B. , Skrzypek J. , Sobkowiak K. , Sonbas E. , Thizy O. , Trela P. , Urakawa S. , Żejmo M. , Żukowski K.
Published: April 2019

Context.Earlier work suggests that slowly rotating asteroids should have higher thermal inertias than faster rotators because the heat wave penetrates deeper into the subsurface. However, thermal inertias have been determined mainly for fast rotators due to selection effects in the available photometry used to obtain shape models required for thermophysical modelling (TPM).

Aims.Our aims are to mitigate these selection effects by producing shape models of slow rotators, to scale them and compute their thermal inertia with TPM, and to verify whether thermal inertia increases with the rotation period.

Methods.To decrease the bias against slow rotators, we conducted a photometric observing campaign of main-belt asteroids with periods longer than 12 h, from multiple stations worldwide, adding in some cases data from WISE andKeplerspace telescopes. For spin and shape reconstruction we used the lightcurve inversion method, and to derive thermal inertias we applied a thermophysical model to fit available infrared data from IRAS, AKARI, and WISE.

Results.We present new models of 11 slow rotators that provide a good fit to the thermal data. In two cases, the TPM analysis showed a clear preference for one of the two possible mirror solutions. We derived the diameters and albedos of our targets in addition to their thermal inertias, which ranged between 3−3+33and 45−30+60J m−2s−1∕2K−1.

Conclusions.Together with our previous work, we have analysed 16 slow rotators from our dense survey with sizes between 30 and 150 km. The current sample thermal inertias vary widely, which does not confirm the earlier suggestion that slower rotators have higher thermal inertias.
The Fornax 3D project: Thick disks in a cluster environment
Authors: Pinna F. , Falcón-Barroso J. , Martig M. , Coccato L. , Corsini E. M. , de Zeeuw P. T. , Gadotti D. A. , Iodice E. , Leaman R. , Lyubenova M. , Martín-Navarro I. , Morelli L. , Sarzi M. , van de Ven G. , Viaene S. , McDermid R. M.
Published: April 2019

We have used deep MUSE observations to perform a stellar-kinematic and population analysis of FCC 153 and FCC 177, two edge-on S0 galaxies in the Fornax cluster. The geometrical definition of the different structural components of these two galaxies allows us to describe the nature of their thick disks. These are both old, relatively metal poor and [Mg/Fe]-enhanced, and their star formation history (SFH) reveals a minor younger component whose chemical properties suggest its later accretion. Moreover, the outer regions of these geometrically defined thick disks show higher values of metallicity and lower values of [Mg/Fe]. These stars probably formed in the thin-disk region and they were dynamically heated to form the flares present in these two galaxies. We propose different formation scenarios for the three populations of these thick disks: in-situ formation, accretion and disk heating. A clear distinction in age is found between the metal poor and [Mg/Fe]-enhanced thick disks (old, ∼12 − 13 Gyr), and the metal rich and less [Mg/Fe]-enhanced thin disks (young, ∼4 − 5 Gyr). These two galaxies show signs of relatively recent star formation in their thin disks and nuclear regions. While the thin disks show more continuous SFHs, the nuclei display a rather bursty SFH. These two galaxies are located outside of the densest region of the Fornax cluster where FCC 170 resides. This other edge-on S0 galaxy has recently been studied, and we have compared and discussed our results with this previous study. The differences between these three galaxies, at different distances from the cluster center, suggest that the environment can have a strong effect on the galaxy evolutionary path.
A diversity of starburst-triggering mechanisms in interacting galaxies and their signatures in CO emission
Authors: Renaud F. , Bournaud F. , Agertz O. , Kraljic K. , Schinnerer E. , Bolatto A. , Daddi E. , Hughes A.
Published: April 2019

The physical origin of enhanced star formation activity in interacting galaxies remains an open question. Knowing whether starbursts are triggered by an increase in the quantity of dense gas or an increase in the star formation efficiency therein would improve our understanding of galaxy evolution and make it possible to transfer the results obtained in the local Universe to high-redshift galaxies. In this paper, we analyze a parsec-resolution simulation of a model of interacting galaxies similar to the Antennae Galaxies. We find that the interplay of physical processes such as tides, shear, and turbulence shows complex and important variations in time and space, but that different combinations of these processes can produce similar signatures in observable quantities such as the depletion time and CO emission. Some clouds within the interacting galaxies exhibit an excess of dense gas (> 104 cm−3), while others only attain similarly high densities in the tail of their density distribution. The clouds with an excess of dense gas are found across all regions of the galaxies, but their number density varies between regions due to different cloud assembly mechanisms. This translates into variations in the scale dependence of quantities related to cloud properties and star formation. The super-linearity of the relationship between the star formation rate and gas density implies that the dense gas excess corresponds to a decrease in the depletion time, and thus leads to a deviation from the classical star formation regime that is visible up to galactic scales. We find that the αCO conversion factor between the CO luminosity and molecular gas mass exhibits stronger spatial than temporal variations in a system like the Antennae. Our results raise several caveats for the interpretation of observations of unresolved star-forming regions, but also predict that the diversity of environments for star formation will be better captured by the future generations of instruments.
Can the long-term hemispheric asymmetry of solar activity result from fluctuations in dynamo parameters?
Authors: Nepomnyashchikh Alexander , Mandal Sudip , Banerjee Dipankar , Kitchatinov Leonid
Published: April 2019

Context. The hemispheric asymmetry of sunspot activity observed possesses a regular component varying on a timescale of several solar cycles whose origin and properties are currently debated.

AimsThis paper addresses the question of whether the long-term hemispheric asymmetry can result from random variations of solar dynamo parameters in time and latitude.

Methods. Scatter in the observed tilt angles of sunspot groups was estimated to infer constraints on fluctuations in the dynamo mechanism for poloidal field regeneration. A dynamo model with fluctuations in the Babcock-Leighton typeα-effect was designed in accordance with these constraints and then used to compute a large number of magnetic cycles for statistical analyses of their hemispheric asymmetry.

ResultsHemispheric asymmetry in the simulated dynamo results from the presence of an equator-symmetric part in the oscillating magnetic field. The sub-dominant quadrupolar oscillations are stochastically forced by dominant dipolar oscillations via the equator-symmetric part of the fluctuatingα-effect. The amplitude and sense of the asymmetry of individual cycles varies on a timescale of the order of four dynamo-cycle periods. The variations are irregular and not periodic. The model suggests that asymmetry in the polar magnetic fields in the solar minima can be used as a precursor for asymmetry of sunspot activity in the following solar cycle.
High-precision analysis of binary stars with planets
Authors: Saffe C. , Jofré E. , Miquelarena P. , Jaque Arancibia M. , Flores M. , López F. M. , Collado A.
Published: April 2019

Aims. We explore for the first time the probable chemical signature of planet formation in the remarkable binary system HD 106515. Star A hosts a massive long-period planet with ~9 MJup detected by radial velocity, while there is no planet detected at the B star. We also refine stellar and planetary parameters by using non-solar-scaled opacities when modelling the stars.

Methods. We carried out a simultaneous determination of stellar parameters and abundances by applying for the first time non-solar-scaled opacities in this binary system, in order to reach the highest possible precision. We used a line-by-line strictly differential approach, using the Sun and then the A star as reference. Stellar parameters were determined by imposing an ionization and excitation balance of Fe lines, with an updated version of the FUNDPAR program, ATLAS12 model atmospheres, and the MOOG code. Opacities for an arbitrary composition were calculated through the opacity sampling method. The chemical patterns were compared with solar-twins condensation temperature Tc trends from the literature and also mutually between both stars. We take the opportunity to compare and discuss the results of the classical solar-scaled method and the high-precision procedure applied here.

Results. Stars A and B in the binary system HD 106515 do not seem to be depleted in refractory elements, which is different when comparing the Sun with solar twins. The terrestrial planet formation would have been less efficient in the stars of this binary system. Together with HD 80606/7, this is the second binary system that does not seem to present a (terrestrial) signature of planet formation, when both systems host an eccentric giant planet. This is in agreement with numerical simulations, where the early dynamical evolution of eccentric giant planets clears out most of the possible terrestrial planets in the inner zone. We refined the stellar mass, radius, and age for both stars and found a notable difference of ~78% in R⋆ compared to previous works. We also refined the planet mass to mp sini = 9.08 ± 0.20 MJup, which differs by ~6% compared with the literature. In addition, we showed that the non-solar-scaled solution is not compatible with the classical solar-scaled method, and some abundance differences are comparable to non-local thermodynamic equilibrium (NLTE) or galactic chemical evolution (GCE) effects especially when using the Sun as reference. Therefore, we encourage the use of non-solar-scaled opacities in high-precision studies such as the detection of Tc trends.
Ellerman bombs and UV bursts: transient events in chromospheric current sheets
Authors: Hansteen V. , Ortiz A. , Archontis V. , Carlsson M. , Pereira T. M. D. , Bjørgen J. P.
Published: April 2019

Context. Ellerman bombs (EBs), observed in the photospheric wings of the Hα line, and UV bursts, observed in the transition region Si IV line, are both brightenings related to flux emergence regions and specifically to magnetic flux of opposite polarity that meet in the photosphere. These two reconnection-related phenomena, nominally formed far apart, occasionally occur in the same location and at the same time, thus challenging our understanding of reconnection and heating of the lower solar atmosphere.

Aims. We consider the formation of an active region, including long fibrils and hot and dense coronal plasma. The emergence of a untwisted magnetic flux sheet, injected 2.5 Mm below the photosphere, is studied as it pierces the photosphere and interacts with the preexisting ambient field. Specifically, we aim to study whether EBs and UV bursts are generated as a result of such flux emergence and examine their physical relationship.

Methods. The Bifrost radiative magnetohydrodynamics code was used to model flux emerging into a model atmosphere that contained a fairly strong ambient field, constraining the emerging field to a limited volume wherein multiple reconnection events occur as the field breaks through the photosphere and expands into the outer atmosphere. Synthetic spectra of the different reconnection events were computed using the 1.5D RH code and the fully 3D MULTI3D code.

Results. The formation of UV bursts and EBs at intensities and with line profiles that are highly reminiscent of observed spectra are understood to be a result of the reconnection of emerging flux with itself in a long-lasting current sheet that extends over several scale heights through the chromosphere. Synthetic spectra in the Hα and Si IV 139.376 nm lines both show characteristics that are typical of the observations. These synthetic diagnostics suggest that there are no compelling reasons to assume that UV bursts occur in the photosphere. Instead, EBs and UV bursts are occasionally formed at opposite ends of a long current sheet that resides in an extended bubble of cool gas.
Barium and related stars, and their white-dwarf companions
Authors: Escorza A. , Karinkuzhi D. , Jorissen A. , Siess L. , Van Winckel H. , Pourbaix D. , Johnston C. , Miszalski B. , Oomen G.-M. , Abdul-Masih M. , Boffin H. M. J. , North P. , Manick R. , Shetye S. , Mikołajewska J.
Published: April 2019

Barium (Ba) dwarfs and CH subgiants are the less evolved analogues of Ba and CH giants. They are F- to G-type main-sequence stars polluted with heavy elements by their binary companions when the companion was on the asymptotic giant branch (AGB). This companion is now a white dwarf that in most cases cannot be directly detected. We present a large systematic study of 60 objects classified as Ba dwarfs or CH subgiants. Combining radial-velocity measurements from HERMES and SALT high-resolution spectra with radial-velocity data from CORAVEL and CORALIE, we determine the orbital parameters of 27 systems. We also derive their masses by comparing their location in the Hertzsprung–Russell diagram with evolutionary models. We confirm that Ba dwarfs and CH subgiants are not at different evolutionary stages, and that they have similar metallicities, despite their different names. Additionally, Ba giants appear significantly more massive than their main-sequence analogues. This is likely due to observational biases against the detection of hotter main-sequence post-mass-transfer objects. Combining our spectroscopic orbits with the HIPPARCOS astrometric data, we derive the orbital inclination and the mass of the WD companion for four systems. Since this cannot be done for all systems in our sample yet (but should be possible with upcoming Gaia data releases), we also analyse the mass-function distribution of our binaries. We can model this distribution with very narrow mass distributions for the two components and random orbital orientations on the sky. Finally, based on BINSTAR evolutionary models, we suggest that the orbital evolution of low-mass Ba systems can be affected by a second phase of interactions along the red giant branch of the Ba star, which impact the eccentricities and periods of the giants.
MUSE unravels the ionisation and origin of metal-enriched absorbers in the gas halo of a z = 2.92 radio galaxy
Authors: Kolwa S. , Vernet J. , De Breuck C. , Villar-Martín M. , Humphrey A. , Arrigoni-Battaia F. , Gullberg B. , Falkendal T. , Drouart G. , Lehnert M. D. , Wylezalek D. , Man A.
Published: April 2019

We have used the Multi-Unit Spectroscopic Explorer (MUSE) to study the circumgalactic medium (CGM) of a z = 2.92 radio galaxy, MRC 0943−242 by parametrising its emitting and absorbing gas. In both Lyα λ1216 and He II λ1640 lines, we observe emission with velocity shifts of Δv ≃ −1000 km s−1 from the systemic redshift of the galaxy. These blueshifted components represent kinematically perturbed gas that is aligned with the radio axis, and is therefore a signature of jet-driven outflows. Three of the four known Lyα absorbers in this source are detected at the same velocities as C IV λλ1548, 1551 and N V λλ1239, 1243 absorbers, proving that the gas is metal-enriched more so than previously thought. At the velocity of a strong Lyα absorber which has an H I column of NH I/cm−2 = 1019.2 and velocity shift of Δv ≃ −400 km s−1, we also detect Si II λ1260 and Si II λ1527 absorption, which suggests that the absorbing gas is ionisation bounded. With the added sensitivity of this MUSE observation, we are more capable of adding constraints to absorber column densities and consequently determining what powers their ionisation. To do this, we obtain photoionisation grid models in CLOUDY which show that AGN radiation is capable of ionising the gas and producing the observed column densities in a gas of metallicity of Z/Z⊙ ≃ 0.01 with a nitrogen abundance a factor of 10 greater than that of hydrogen. This metal-enriched absorbing gas, which is also spatially extended over a projected distance of r ≳ 60 kpc, is likely to have undergone chemical enrichment through stellar winds that have swept up metals from the interstellar-medium and deposited them in the outer regions of the galaxy’s halo.
Parton Distribution Functions and Lattice QCD
Authors: Lin Huey-Wen
Published: April 2019

Recently, there have been rapid developments in lattice-QCD calculations of proton structure, especially in the parton distribution functions (PDFs). We overcame a longstanding obstacle and for the first time in lattice-QCD are able to directly calculate the Bjorken-x dependence of the quark, helicity and transversity distributions. The PDFs are obtained using the large-momentum eﬀective field theory (LaMET) framework where the full Bjorken-x dependence of finite-momentum PDFs, called “quasi-PDFs”, can be calculated on the lattice. The quasi-PDF nucleon matrix elements are renormalized non-perturbatively in RI/MOM-scheme. Following a nonperturbative renormalization of the parton quasi-distribution in a regularization-independent momentum-subtraction scheme, we establish its matching to the
$ \overline {{\rm{MS}}} $
PDF and calculate the non-singlet matching coeﬃcient at next-to-leading order in perturbation theory. In this proceeding, I will show the progress that has been made in recent years, highlighting the latest state-of-the art PDF calculations at the physical pion mass. Future impacts on the large-x global PDF fits are also discussed.
QCD strings and the U(1) problem
Authors: Xiong Chi
Published: April 2019

We promote the usual QCD θ-parameter to a field and interpret it as the phase of the quark condensate, which becomes nontrivial when topological defects, vortices in our formulation, are induced in the quark condensate by the QCD strings (chromoelectric flux tubes). The QCD topological term emerges naturally as a derivative coupling between the Chern-Simons current and a supercurrent in the quark condensate. This new formulation can address theUA(1) problem and leads to the chiral magnetic eﬀects. It is possible that in this formulation the strong CP problem can be avoided without the axion particle.
Collective phenomena in hadron and nuclear interactions at high multiplicity
Authors: Dunin V. , Gribowsky A. , Kokoulina E. , Kutov A. , Nikitin V. , Riadovikov V. , Shulyakovsky R. , Volkov V. , Vorobiev A.
Published: April 2019

Multiparticle production is described in the language of quarks and gluons. In the experiment the real hadrons are registered. For transfer from quarks and gluons to observed hadrons, various phenomenological models are used. In order to describe the high multiplicity region, we have developed a gluon dominance model. It represents a convolution of two stages. First stage is described by QCD. For second one (hadronisation), the phenomenological model is used. The description of topological cross sections inp$ \bar p $ collisions within of our model testifies that in hadron collisions the mechanism of hadronisation is being replaced by the recombination one. At that point, gluons play an active role in the multiparticle production process, and valence quarks are passive. They stay in the leading particles, and only the gluon splitting is responsible for the region of high multiplicity. The model with inclusion of intermediate quark charged topologies describes topological cross sections in annihilation. We observe the significant growth of a scaled variance of number of neutral pions with increasing of the total multiplicity at U-70 accelerator at IHEP (Protvino). The following experiment with 3.5 A GeV deuteron, lithium and carbon beams of the Nuclotron (JINR, Dubna) falling at a carbon target is carried out at the NIS-GIBS setup. The noticeable excess yield of soft photons(pT< 50 MeV/c) is observed. The existing models based on Monte Carlo simulation and theoretical estimations predict a lower yield. Our Collaboration plans to study excess of soft photon yield and other phenomena at the SPD (Spin Physics Detector) setup at JINR, Dubna with polarised beams of proton and light nuclei up to 25 GeV.
Intriguing feature of multiplicity distributions
Authors: Rybczyński Maciej , Wilk Grzegorz , Włodarczyk Zbigniew
Published: April 2019

Multiplicity distributions, P(N), provide valuable information on the mechanism of the production process. We argue that the observed P(N) contain more information (located in the small N region) than expected and used so far. We demonstrate that it can be retrieved by analysing specific combinations of the experimentally measured values of P(N) which we call modified combinants, Cj, and which show distinct oscillatory behavior, not observed in the usual phenomenological forms of the P(N) used to fit data. We discuss the possible sources of these oscillations and their impact on our understanding of the multiparticle production mechanism.
Interpreting BEC in e+ e- annihilation
Authors: Metzger W.J. , Csörgő T. , Novák T. , Lökös S.
Published: April 2019

The usual interpretation of Bose-Einstein correlations (BEC) of identical boson pairs relates the width of the peak in the correlation function at small relative four-momentum to the spatial extent of the source of the bosons. However, in the τ-model, which successfully describes BEC in hadronic Z decay, the width of the peak is related to the temporal extent of boson emission. Some new checks on the validity of both the τ-model and the usual descriptions are presented.
Testing nonextensive statistics in relativistic heavy-ion collisions
Authors: Wolschin Georg
Published: April 2019

Numerical solutions of the nonlinear Fokker-Planck equation (FPE) which has been associated with nonextensive q-statistics show that the available data on rapidity distributions for stopping in relativistic heavy-ion collisions cannot be reproduced with any permitted value of the nonextensivity parameter (1 < q < 1.5). This casts doubt on the nonextensivity concept that is widely used in relativistic heavy-ion physics.
Jet tomography in high-energy nuclear collisions
Authors: Zhang Ben-Wei , Ma Guo-Yang , Dai Wei , Wang Sa , Zhang Shan-Liang
Published: April 2019

When an energetic parton traversing the QCD medium, it may suffer multiple scatterings and lose energy. This jet quenching phenomenon may lead to the suppression of leading hadron productions as well as medium modifications of full jet observables in heavy-ion collisions. In this talk we discuss the nuclear modificationfactors and yield ratios of identified meson such as η, ρ0, φ, ω, and
$ K_{\rm{S}}^0 $
as well as π meson at large pT in A+A collisions at the next to-leading order (NLO) with high-twist approach of parton energy loss. Then we discuss a newly developed formalism of combing NLO matrix elements and parton shower (PS) for initial hard production with parton energy loss in the QGP, and its application in investigating massivegauge boson(Z0/W±)tagged jet productions and b
$ \bar {b} $
dijet correlations in Pb+Pb at the LHC.
Recent NA48/2 results on rare kaon decays
Authors: Madigozhin Dmitry
Published: April 2019

NA48/2 results contributing to ChPT testing are presented. A sample of 1663 events of the rare decay $ K^ \pm \to \mu ^ \pm ve^ + e^ - $ has been selected with a minimume+e−eﬀective mass of 140 MeV. The measured model independent decay rate is in agreement with ChPT predictions. The branching ratio of the $ K^ \pm \to \mu ^ \pm ve^ + e^ - $ decay, never observed so far, has been obtained from a sample of about 5000 candidates with less than 6% background, also in agreement with ChPT predictions. In addition, a most precise measurement of the charged kaon semileptonic formfactors has been obtained from 4.4 millionKe3and 2.3 millionKµ3events collected in 2004.