EDP Sciences

Vol. 615
In section 1. Letters to the Editor

Time-dependent molecular emission in IRC+10216

by J.R. Pardo, J. Cernicharo, L. Velilla Prieto, et al. A&A 615, L4


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This paper presents the first results from an almost three-year long monitoring of the molecular emission from the Mira variable star IRC+10216. Several rotational lines from species such as HC3N, HC5N, CCH, C4H, C5H, and CN present evidence of periodical variability, with periods consistent with the stellar IR variability. The different phase lags in the light curves suggest that the variability of the molecular lines results from radiative transfer and pumping effects, and not from chemical changes in the envelope composition.

Vol. 614
In section 14. Catalogs and data

The stellar content of the XMM-Newton slew survey

by S. Freund, J. Robrade, C. Schneider, and J.H.M.M. Schmitt, A&A 614, A125


Wide-field optical telescopes survey the sky every night. This is especially difficult in the X-ray band, for which we rely only on the ROSAT all-sky survey performed in 1990-1991. In recent years the time spent by the XMM-Newton satellite to slew from one target to the other has been scientifically exploited. This has given us the XMM-Newton Slew Survey (XMMSL), which covers 84% of the sky and counting. In this work Freund and collaborators have used the XMMSL source catalog and correlated it with the Gaia optical catalog to pinpoint X-ray emitting stars. They identified 6815 stars of all spectral types with a majority of late-type stars, providing the largest census so far.

Vol. 614
In section 6. Interstellar and circumstellar matter

Interstellar bromine abundance is consistent with cometary ices from Rosetta

by N.F.W. Ligterink and M. Kama, A&A 614, A112


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This paper presents a unique, intriguing study of the abundance of a rare halogen, bromine, in the gas phase by the Rosetta mission in comet 67P/Churyumov-Gerasimenko. Obtaining the abundance of rare heavy elements has been a challenge for interstellar medium studies for decades and untill now, it has not been possible to measure this element in the diffuse gas phase. For comet 67P, the detection of HBr and the measured elemental ratio Br/O = (1 − 7) × 10^−6 is consistent with the ratios found for its cousin Cl (for which the Br/Cl ratio is consistent with terrestrial values), and consistent with all of the Br being sequestered in cometary ice mantles. The derived abundances are compared with upper limits for HBr and HBr^+ from infrared spectra of several star forming regions and employ chemical network modeling to understand the molecular abundances. This study represents the first direct measurement of the bromine abundance in a cosmic environment other than meteorites.

Vol. 614
In section 4. Extragalactic astronomy

Constraints on submicrojansky radio number counts based on evolving VLA-COSMOS luminosity functions

by M. Novak, V. Smolcic, E. Schinnerer, G. Zamorani, I. Delvecchio, M. Bondi, and J. Delhaize A&A 614, A47


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Radio emission in galaxies at frequencies below 30 GHz is mostly synchrotron radiation from cosmic electrons gyrating in magnetic fields. The electrons are accelerated by supernovae in star forming (SF) galaxies, and by an accreting supermassive black hole (SMBH) in active galactic nuclei (AGN). Comparison with other wavelengths, such as optical, IR, or X-ray, is necessary to disentangle the two possibilities. This paper presents the results of the Large Program COSMOS-3GHz with the VLA. The total radio luminosity function (LF) since z~5.7 has been derived for the radio selected sample of 7826 galaxies with robust optical/near-infrared (NIR) counterparts. The populations of SF galaxies and AGN are separated on the basis of presence or absence of a radio excess with respect to the star-formation rates (SFRs) derived from the infrared (IR) emission. The redshift dependent pure luminosity evolution (PLE) model fitted to the data with an MCMC algorithm is in very good agreement with the previously published VLA-COSMOS LFs. Different models of evolving LFs are able to reproduce the observed radio sky brightness, despite relying on extrapolations toward the faint end. The results imply that no new radio emitting galaxy population is present below 1 microJy. Selecting galaxies with radio flux densities between 0.1 and 10 microJy will yield a starforming galaxy in 90-95% of the cases with a large percentage of these galaxies existing around a redshift of z ~ 2, thus providing useful constraints for planned surveys with the Square Kilometer Array (SKA) and its precursors.

Vol. 614
In section 4. Extragalactic astronomy

ALMA observations of AGN fuelling. The case of PKS B1718–649

by F. M. Maccagni, R. Morganti, T. A. Oosterloo, J. B. R. Oonk, and B. H. C. Emonts A&A 614, A42


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Active galaxy nuclei (AGN) are fueled by cold gas falling into the center, and the energy released by their activity can produce some feedback to eject gas, and moderate accretion and growth of the black hole. These complex processes can be traced through observations of the cold gas, under the atomic (HI) or molecular form of either the warm through near-infrared H2 lines or cold through the millimetric CO lines. The authors present ALMA observations of the CO (2–1) line in the spiral galaxy NGC 6328, which hosts a radio AGN, PKSB1718–649. The CO line gas in the disk of the galaxy (15kpc) is warped, a possible sign of interaction. While the outer parts follow the north-south orientation of the galaxy major axis, in the inner parts the gas abruptly changes orientation and forms a circumnuclear disk of radius 700pc, whose major axis is perpendicular to that of the outer disk. This structure is characteristic of a kinematically decoupled core (KDC). Together with the centered CO emission, ALMA reveals a CO absorption in front of the continuum source, at red-shifted velocities by 365km/s with respect to the systemic velocity. This absorbing CO gas could trace molecular clouds falling onto the central super-massive black hole. The physical conditions of molecular clouds in the a circumnuclear disk are in good agreement with the predictions for the conditions of the gas when cold chaotic accretion triggers an active galactic nucleus.

Vol. 613
In section 10. Planets and planetary systems

The nature of the TRAPPIST-1 exoplanets

by S. Grimm, B.-O. Demory, M. Gillon, et al. A&A 613, A68


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Using time-transit variations and a genetic algorithm, Grimm et al. improve the uncertainties on the internal densities of the TRAPPIST planets by a factor of between five and eight. These results will help shed light on the compositions of these planets and eventually on the formation of this system.