bluuebunny/crossref_metadata_2025_split huggingface dataset:
Exoplanet atmospheres with GIANO
Authors: Guilluy G. , Sozzetti A. , Brogi M. , Bonomo A. S. , Giacobbe P. , Claudi R. , Benatti S. 
Published: April 2019

Context. The study of exoplanetary atmospheres is key to understanding the differences between their physical, chemical, and dynamical processes. Until now, the bulk of atmospheric characterization analyses have been conducted on transiting planets. On a number of sufficiently bright targets, high-resolution spectroscopy (HRS) has also been successfully tested for nontransiting planets mainly by using spectrographs mounted on 8 and 10 m class ground-based telescopes.
Aims. The aim of this analysis is to study the dayside of the nontransiting planet HD 102195b using the GIANO spectrograph mounted at the Telescopio Nazionale Galileo (TNG), and thereby demonstrate the feasibility of atmospheric characterization measurements. In particular, we wish to demonstrate the possibility of molecular detection with the HRS technique for nontransiting planets using 4 m class telescopes.
Methods. Our data-analysis technique exploits the fact that the Doppler-shifted planetary signal changes on the order of many kilometers per second during the observations, in contrast with the telluric absorption which is stationary in wavelength. This allows us to effectively remove the contamination from telluric lines in the GIANO spectra while preserving the features of the planetary spectrum. The emission signal from the atmosphere of HD 102195b is then extracted by cross-correlating the residual GIANO spectra with models of the planetary atmosphere.
Results. We detect molecular absorption from water vapor at the 4.4σ level of statistical significance. We also find convincing evidence for the presence of methane, which is detected at the 4.1σ level. This is the first detection of methane obtained with the HRS technique. The two molecules are detected with a combined significance of 5.3σ, at a semi-amplitude of the planet radial velocity KP = 128 ± 6 km s−1. We estimate a true planet mass of MP = 0.46 ± 0.03 MJ and constrain the orbital inclination in the range 72.5° < i < 84.79° (1σ). Our analysis indicates a noninverted atmosphere for HD 102195b. This is expected given the relatively low temperature of the planet, inefficient to keep TiO/VO in gas phase. Moreover, a comparison with theoretical model expectations corroborates our detection of methane, and a cursory confrontation with chemical model predictions published in the literature suggests that the detected methane and water signatures could be consistent with a low C/O ratio for HD 102195b. Finally, as HD 102195 is one to three magnitudes fainter in the K-band than the nontransiting systems studied until now with 8 m telescopes, our study opens up the possibility for atmospheric characterization of a larger sample of exoplanets.
Average motion of emerging solar active region polarities
Authors: Schunker H. , Birch A. C. , Cameron R. H. , Braun D. C. , Gizon L. , Burston R. B. 
Published: April 2019

Aims. Our goal is to constrain models of active region formation by tracking the average motion of active region polarity pairs as they emerge onto the surface.
Methods. We measured the motion of the two main opposite polarities in 153 emerging active regions using line-of-sight magnetic field observations from the Solar Dynamics Observatory Helioseismic Emerging Active Region (SDO/HEAR) survey. We first measured the position of each of the polarities eight hours after emergence, when they could be clearly identified, using a feature recognition method. We then tracked their location forwards and backwards in time.
Results. We find that, on average, the polarities emerge with an east-west orientation and the separation speed between the polarities increases. At about 0.1 days after emergence, the average separation speed reaches a peak value of 229 ± 11 ms−1, and then starts to decrease. About 2.5 days after emergence the polarities stop separating. We also find that the separation and the separation speed in the east-west direction are systematically larger for active regions that have higher flux. The scatter in the location of the polarities increases from about 5 Mm at the time of emergence to about 15 Mm at two days after emergence.
Conclusions. Our results reveal two phases of the emergence process defined by the rate of change of the separation speed as the polarities move apart. Phase 1 begins when the opposite polarity pairs first appear at the surface, with an east-west alignment and an increasing separation speed. We define Phase 2 to begin when the separation speed starts to decrease, and ends when the polarities have stopped separating. This is consistent with a previous study: the peak of a flux tube breaks through the surface during Phase 1. During Phase 2 the magnetic field lines are straightened by magnetic tension, so that the polarities continue to move apart, until they eventually lie directly above their anchored subsurface footpoints. The scatter in the location of the polarities is consistent with the length and timescales of supergranulation, supporting the idea that convection buffets the polarities as they separate.
High resolution observations with Artemis–JLS
Authors: Bouratzis C. , Hillaris A. , Alissandrakis C. E. , Preka-Papadema P. , Moussas X. , Caroubalos C. , Tsitsipis P. , Kontogeorgos A. 
Published: April 2019

Aims. We examined the characteristics of isolated intermediate drift bursts and their morphologies on dynamic spectra, in particular the positioning of emission and absorption ridges. Furthermore we studied the repetition rate of fiber groups. These were compared with a model in order to determine the conditions under which the intermediate drift bursts appear and exhibit the above characteristics.
Methods. We analyzed sixteen metric type IV events with embedded intermediate drift bursts, observed with the Artemis–JLS radio spectrograph from July 1999 to July 2005 plus an event on 1st August 2010. The events were recorded with the SAO high resolution (10 ms cadence) receiver in the 270–450 MHz range with a frequency resolution of 1.4 MHz. We developed cross- and autocorrelation techniques to measure the duration, spectral width, and frequency drift of fiber bursts in 47 intermediate drift bursts (IMD) groups embedded within the continuum of the sixteen events mentioned above. We also developed a semi-automatic algorithm to track fibers on dynamic spectra.
Results. The mean duration of individual fiber bursts at fixed frequency was δt ≈ 300 ms, while the instantaneous relative bandwidth was fw/f ≈ 0.90% and the total frequency extent was Δftot ≈ 35 MHz. The recorded intermediate drift bursts had frequency drift, positive or negative, with average values of df/fdt equal to −0.027 and 0.024 s−1 respectively. Quite often the fibers appeared in groups; the burst repetition rate within groups was, on average, ∼0.98 s. We distinguish six morphological groups of fibers, based on the relative position of the emission and absorption ridges. These included fibers with emission or absorption ridges only, fibers with the absorption ridge at lower or higher frequency than the emission, or with two absorption ridges above and below the emission. There were also some fibers for which two emission ridges were separated by an absorption ridge. Some additional complex groups within our data set were not easy to classify. A number of borderline cases of fibers with very high drift rate (∼0.30 s−1) or very narrow total bandwidth (∼8 MHz) were recorded; among them there was a group of rope-like fibers characterized by fast repetition rate and relatively narrow total frequency extent. We found that the whistler hypothesis leads to reasonable magnetic field values (∼4.6 G), while the Alfven-wave hypothesis requires much higher field. From the variation of the drift rate with time we estimated the ratio of the whistler to the cyclotron frequency, x, to be in the range of 0.3−0.6, varying by ∼0.05−0.1 in individual fibers; the same analysis gives an average value of the frequency scale along the loop of ∼220 Mm. Finally, we present empirical relations between fiber burst parameters and discuss their possible origin.
Far-infrared continuum absorption of forsterite and enstatite at low temperatures
Authors: Mutschke Harald , Mohr Pierre 
Published: April 2019

Context. The far-infrared continuum opacity of cold dust is an important quantity for the study of debris disks in planetary systems and of protoplanetary disks. Forsterite and enstatite are considered to be the most abundant crystalline dust species in such environments.
Aims. The optical constants of these minerals at wavelengths above 80 μm, which govern the opacity, and their temperature dependence are poorly known. Our aim is to fill in this lack of information with new laboratory data.
Methods. We present spectroscopic transmission measurements on forsterite and enstatite single crystals of up to 10 mm thickness at wavelengths between 45 and 500 μm and for temperatures down to 10 K. We compare our results to literature data originating from powder transmission and from reflection spectroscopy.
Results. The imaginary parts of the refractive indices calculated from the measurements show very strong temperature dependences, which to that extent are not seen in reflection-based data or in powder measurement data. The temperature dependences can be described by a simple theoretical model taking the contributions of single-phonon absorption and phonon difference processes into account. We also observe, for the first time, enstatite absorption bands at 87.5 μm and 116.6 μm wavelengths.
Conclusions. The single-crystal optical constants of forsterite and enstatite predict an extremely small submillimeter opacity of crystalline silicate dust at low temperatures, which would make these particles almost invisible in the thermal radiation of cold dust. Thus, it is important to understand why absorption measurements with mineral powders resulted in much higher opacity values.
Investigation of the WR 11 field at decimeter wavelengths
Authors: Benaglia P. , del Palacio S. , Ishwara-Chandra C. H. , De Becker M. , Isequilla N. L. , Saponara J. 
Published: April 2019

The massive binary system WR 11 (γ2-Velorum) has recently been proposed as the counterpart of a Fermi source. If this association is correct, this system would be the second colliding wind binary detected in GeV γ-rays. However, the reported flux measurements from 1.4 to 8.64 GHz fail to establish the presence of nonthermal (synchrotron) emission from this source. Moreover, WR 11 is not the only radio source within the Fermi detection box. Other possible counterparts have been identified in archival data, some of which present strong nonthermal radio emission. We conducted arcsec-resolution observations toward WR 11 at very low frequencies (150–1400 MHz) where the nonthermal emission – if existent and not absorbed – is expected to dominate. We present a catalog of more than 400 radio emitters, among which a significant portion are detected at more than one frequency, including limited spectral index information. Twenty-one of these radio emitters are located within the Fermi significant emission. A search for counterparts for this last group pointed at MOST 0808–471; this source is 2′ away from WR 11 and is a promising candidate for high-energy emission, having a resolved structure along 325–1390 MHz. For this source, we reprocessed archive interferometric data up to 22.3 GHz and obtained a nonthermal radio spectral index of − 0.97 ± 0.09. However, multiwavelength observations of this source are required to establish its nature and to assess whether it can produce (part of) the observed γ-rays. WR 11 spectrum follows a spectral index of 0.74 ± 0.03 from 150 to 230 GHz, consistent with thermal emission. We interpret that any putative synchrotron radiation from the colliding-wind region of this relatively short-period system is absorbed in the photospheres of the individual components. Notwithstanding, the new radio data allowed us to derive a mass-loss rate of 2.5 × 10−5 M⊙ yr−1, which, according to the latest models for γ-ray emission in WR 11, would suffice to provide the required kinetic power to feed nonthermal radiation processes.
Isocyanogen formation in the cold interstellar medium
Authors: Vastel C. , Loison J. C. , Wakelam V. , Lefloch B. 
Published: April 2019

Context. Cyanogen (NCCN) is the simplest member of the dicyanopolyynes group, and has been proposed as a major source of the CN radical observed in cometary atmospheres. Although not detected through its rotational spectrum in the cold interstellar medium, this very stable species is supposed to be very abundant.
Aims. The chemistry of cyanogen in the cold interstellar medium can be investigated through its metastable isomer, CNCN (isocyanogen). Its formation may provide a clue on the widely abundant CN radical observed in cometary atmospheres.
Methods. We performed an unbiased spectral survey of the L1544 proto-typical prestellar core, using the IRAM-30 m and have analysed, for this paper, the nitrogen chemistry that leads to the formation of isocyanogen. We report on the first detection of CNCN, NCCNH+, C3N, CH3CN, C2H3CN, and H2CN in L1544. We built a detailed chemical network for NCCN/CNCN/HC2N2+ involving all the nitrogen bearing species detected (CN, HCN, HNC, C3N, CNCN, CH3CN, CH2CN, HCCNC, HC3N, HNC3, H2CN, C2H3CN, HCNH+, HC3NH+) and the upper limits on C4N, C2N. The main cyanogen production pathways considered in the network are the CN + HNC and N + C3N reactions.
Results. The comparison between the observations of the nitrogen bearing species and the predictions from the chemical modelling shows a very good agreement, taking into account the new chemical network. The expected cyanogen abundance is greater than the isocyanogen abundance by a factor of 100. Although cyanogen cannot be detected through its rotational spectrum, the chemical modelling predicts that it should be abundant in the gas phase and hence might be traced through the detection of isocyanogen. It is however expected to have a very low abundance on the grain surfaces compared to HCN.
Obscured AGN at 1.5 <z< 3.0 from the zCOSMOS-deep Survey
Authors: Mignoli M. , Feltre A. , Bongiorno A. , Calura F. , Gilli R. , Vignali C. , Zamorani G. , Lilly S. J. , Le Fèvre O. , Bardelli S. , Bolzonella M. , Bordoloi R. , Le Brun V. , Caputi K. I. , Cimatti A. , Diener C. , Garilli B. , Koekemoer A. M. , Maier C. , Mainieri V. , Peng Y. , Pérez Montero E. , Silverman J. D. , Zucca E. 
Published: April 2019

Context. The physics and demographics of high-redshift obscured active galactic nuclei (AGN) is still scarcely investigated. New samples of such objects, selected with different techniques, can provide useful insights into their physical properties.Aims. With the goal to determine the properties of the gas in the emitting region of type 2 AGN, in particular, the gas metal content, we exploit predictions from photoionization models, including new parameterizations for the distance of gas distribution from the central source and internal microturbulence in the emitting clouds, to interpret rest-frame UV spectral data.Methods. We selected a sample of 90 obscured (type 2) AGN with 1.45 ≤z≤ 3.05 from the zCOSMOS-deep galaxy sample by 5σdetection of the high-ionization C IVλ1549 narrow emission line. This feature in a galaxy spectrum is often associated with nuclear activity, and the selection effectiveness has also been confirmed by diagnostic diagrams based on utraviolet (UV) emission-line ratios. We applied the same selection technique and collected a sample of 102 unobscured (type 1) AGN. Taking advantage of the large amount of multiband data available in the COSMOS field, we investigated the properties of the C IV-selected type 2 AGN, focusing on their host galaxies, X-ray emission, and UV emission lines. Finally, we investigated the physical properties of the ionized gas in the narrow-line region (NLR) of this type 2 AGN sample by combining the analysis of strong UV emission lines with predictions from photoionization models.Results. We find that in order to successfully reproduce the relative intensity of UV emission lines of the selected high-ztype 2 AGN, two new ingredients in the photoionization models are fundamental: small inner radii of the NLR (≈90 pc forLAGN = 1045erg s−1), and the internal dissipative microturbulence of the gas-emitting clouds (withvmicr≈ 100 km s−1). With these modified models, we compute the gas-phase metallicity of the NLR, and our measurements indicate a statistically significant evolution of the metal content with redshift. Finally, we do not observe a strong relationship between the NLR gas metallicity and the stellar mass of the host galaxy in our C IV-selected type 2 AGN sample.
Inclination effects on the X-ray emission of Galactic black-hole binaries
Authors: Reig Pablo , Kylafis Nikolaos D. 
Published: April 2019

Context. Galactic black-hole X-ray binaries (BHBs) emit a compact, optically thick, mildly relativistic radio jet when they are in hard and hard-intermediate states. In these states, BHBs exhibit a correlation between the time lag of hard with respect to softer photons and the photon index of the power law component that characterizes the X-ray spectral continuum above ∼10 keV. The correlation, however, shows large scatter. In recent years, several works have brought to light the importance of taking into account the inclination of the systems to understand the X-ray and radio phenomenology of BHBs.
Aims. Our objective is to investigate the role that the inclination plays on the correlation between the time lag and photon index.
Methods. We obtained RXTE energy spectra and light curves of a sample of BHBs with different inclination angles. We computed the photon index and the time lag between hard and soft photons and performed a correlation and linear regression analysis of the two variables. We also computed energy spectra and light curves of BHBs using the Monte Carlo technique that reproduces the process of Comptonization in the jet. We account for the inclination effects by recording the photons that escape from the jet at different angles. From the simulated light curves and spectra we obtained model-dependent photon index and time lags, which we compared with those obtained from the real data.
Results. We find that the correlation between the time lag and photon index is tight in low-inclination systems and becomes weaker in high-inclination systems. The amplitude of the lags is also larger at low- and intermediate-inclination angles than at high inclination. We also find that the photon index and time lag, obtained from the simulated spectra and light curves, also follow different relationships for different inclination angle ranges. Our jet model reproduces the observations remarkably well. The same set of models that reproduces the correlation for the low-inclination systems, also accounts for the correlation for intermediate- and high-inclination systems fairly well.
Conclusions. The large dispersion observed in the time lag – photon index correlation in BHBs can naturally be explained as an inclination effect. Comptonization in the jet explains the steeper dependence of the lags on the photon index in low- and intermediate-inclination systems than in high-inclination systems.
Elemental composition in quiescent prominences
Authors: Parenti S. , Del Zanna G. , Vial J.-C. 
Published: April 2019

Context. The first ionization potential (FIP) bias is currently used to trace the propagation of solar features ejected by the wind and solar eruptions (coronal mass ejections). The FIP bias also helps us to understand the formation of prominences, as it is a tracer for the solar origin of prominence plasma.Aims. This work aims to provide elemental composition and FIP bias in quiescent solar prominences. This is key information to link these features to remnants of solar eruptions measured in-situ within the heliosphere and to constrain the coronal or photospheric origin of prominence plasma.Methods. We used the differential emission measure technique to derive the FIP bias of two prominences. Quiet Sun chromospheric and transition region data were used to test the atomic data and lines formation processes. We used lines from low stage of ionization of Si, S, Fe, C, N, O, Ni, Mg, and Ne, constraining the FIP bias in the range 4.2 ≤ log T ≤ 5.8. We adopted a density-dependent ionization equilibrium.Results. We showed that the two prominences have photospheric composition. We confirmed a photospheric composition in the quiet Sun. We also identified opacity and/or radiative excitation contributions to the line formation of a few lines regularly observed in prominences.Conclusions. With our results we thus provide important elements for correctly interpreting the upcoming Solar Orbiter/SPICE spectroscopic data and to constrain prominence formation.
Observational evidence of third dredge-up occurrence in S-type stars with initial masses around 1 M⊙
Authors: Shetye S. , Goriely S. , Siess L. , Van Eck S. , Jorissen A. , Van Winckel H. 
Published: April 2019

Context. S stars are late-type giants with spectra showing characteristic molecular bands of ZrO in addition to the TiO bands typical of M stars. Their overabundance pattern shows the signature of s-process nucleosynthesis. Intrinsic, technetium (Tc)-rich S stars are the first objects on the asymptotic giant branch (AGB) to undergo third dredge-up (TDU) events. Exquisite Gaia parallaxes now allow for these stars to be precisely located in the Hertzsprung–Russell (HR) diagram. Here we report on a population of low-mass, Tc-rich S stars previously unaccounted for by stellar evolution models.
Aims. Our aim is to derive parameters for a sample of low-mass, Tc-rich S stars and then, by comparing their location in the HR diagram with stellar evolution tracks, to derive their masses and to compare their measured s-process abundance profiles with recently derived STAREVOL nucleosynthetic predictions for low-mass AGB stars.
Methods. Stellar parameters were obtained using a combination of HERMES high-resolution spectra, accurate Gaia Data Release 2 (Gaia-DR2) parallaxes, stellar-evolution models, and newly designed MARCS model atmospheres for S-type stars.
Results. We report on six Tc-rich S stars lying close to the 1 M⊙ (initial mass) tracks of AGB stars of the corresponding metallicity and above the predicted onset of TDU, as expected. This provides direct evidence for TDUs occurring in AGB stars with initial masses as low as ∼1 M⊙ and at low luminosity, that is, at the start of the thermally pulsing AGB. We present AGB models producing TDU in those stars with [Fe/H] in the range −0.25 to −0.5. There is reasonable agreement between the measured and predicted s-process abundance profiles. For two objects however, CD −29°5912 and BD +34°1698, the predicted C/O ratio and s-process enhancements do not simultaneously match the measured ones.