EDP Sciences

Vol. 607
In section 6. Interstellar and circumstellar matter

Search for hydrogen-helium molecular species in space

by E. Zicler, O. Parisel, F. Pauzat, Y. Ellinger, M-C. Bacchus-Montabonel, and J-P. Maillard A&A 607, A61


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The search for helium in molecular form has been a long standing challenge in astrophysics. Searches for HeH+ have repeatedly come up empty-handed although hydrogenated heavier noble gases have been detected in the interstellar medium. This study proposes an alternative candidate,HeH3+, based on the ubiquitous presence of the H3+ ion in cosmic environments. The authors compute the binding energy, vibrational states, and radiative association rates through two channels. They propose that the HeH+ + H2 dominates by more than four orders of magnitude over the He + H3+ under a wide range of temperatures. Thepaper also provides frequencies to aid in the search for this intriguing molecule whose presence may be important in the context of early universe chemistry.

Vol. 607
In section 6. Interstellar and circumstellar medium

Interferometric view of the circumstellar envelopes of northern FU Orionis-type stars

by O. Fehér, Á. Kóspál, P. Ábrahám, M. R. Hogerheijde, and C. Brinch A&A 607, A39


The FU Ori stage of protostar formation is one of intense photometric and spectroscopic variability, lasting decades, and indicating a phase of enhanced mass transfer onto the forming protostar. The outbursts should also involve enhanced stellar outflows, This paper presents thefirst comprehensive spectrophotometric-interferometric millimeter wavelength study using the IRAM telescopes of the circumstellar environments of these stars including the peripheral regions of their accretion disks and the envelope in superb dynamical and spatial detailin two optically thin isotopes of CO. Outflow was detected in only three stars, but these were all well resolved. Compact structures were seen in 5/8 of the sample stars and the structures produced in channel maps. The combination of star and/or inner disk-like signatures and those of themore extended envelope are consistent with the picture of the FU Ori objects as the transition between completely enshrouded central objectsand the T Tau stage in which the central star dominates the disk.

Vol. 606
In section 6. Interstellar and circumstellar matter

Fibers in the NGC 1333 proto-cluster

by A. Hacar, M. Tafalla, and J. Alves, A&A 606, A123


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The authors carried out a high-sensitivity study of the internal structure, density, temperature, and kinematics of the dense gas content in the Perseus embedded cluster NGC1333 to investigate the initial gas properties in young proto-clusters. They identified 14 velocity-coherent, (tran-)sonic structures within NGC1333, with physical and kinematic properties that are similar to those of quiescent, star-forming fibers previously identified in low-mass star-forming clouds. These fibers are arranged in a complex spatial network, build-up the observed total column density, and contain the dense cores and protostars in this cloud. From a comparison with Taurus, they propose that the observational dichotomy between clustered and non-clustered star-forming regions might be naturally explained by the distinct spatial density of star-forming fibers in these environments.

Vol. 606
In section 5. Galactic structure, stellar clusters and population

Effects of the selection function on metallicity trends in spectroscopic surveys of the Milky Way

by G. Nandakumar, M. Schultheis, M. Hayden, A. Rojas-Arriagada, G. Kordopatis, and M. Haywood, A&A 606, A97


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Large spectroscopic Galactic surveys all undergo a selection process for choosing their targets. This selection function can alter the final form of the metallicity distribution function and the vertical metallicity gradient differently for different surveys. This paper investigates the effects of the selection functions on metallicity trends in the common fields between the APOGEE, LAMOST, RAVE, and Gaia-ESO surveys. The authors use the stellar population synthesis models GALAXIA and TRILEGAL to create mock fields for each survey and apply the selection function in the form of colour and magnitude cuts to replicate the observed sample and investigate the effects of the different selection functions. They find that the selection function has a negligible effect on the metallicity distribution function or the vertical metallicity gradients for the APOGEE, LAMOST, and RAVE surveys. The corrected vertical metallicity gradients between the four surveys are consistent within 1-σ. It is, therefore, possible to combine common fields of these different surveys provided that their metallicities are on the same scale.

Vol. 606
In section 6. Interstellar and circumstellar matter

Three-dimensional mapping of the local interstellar medium with composite data

by L. Capitanio, R. Lallement, J.L. Vergely, M. Elyajouri, and A. Monreal-Ibero, A&A 606, A65


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Obtaining a detailed picture of the 3-D structure of even the local interstellar medium remains a major challenge. The fine structure, averaged out on larger scales, has thus far been the only unambiguous view we have of how the gas and dust are structured on scales of tens of parsecs. The ambitious, successful aim of the present study is to cover lines of sight of up to a few kiloparsecs using stellar parallax and proper motions of background light sources with high accuracy, using the first Gaia data release. The authors do this by combining different measures for the two diffuse components, using a near infrared absorption band (DIB) to obtain extinction (reddening) estimates. They use a novel Bayesian inversion method to reconstruct the fine structure from tens of thousands of DIB measurements of profiles and velocities, with the constraint of maximum extinction in any direction. The structures thus obtained, both clouds and vacancies, can then be compared with multiwavelength data from the UV and XR for further refinement.

Vol. 606
In section 3. Cosmology

Mapping the hot gas temperature in galaxy clusters using X-ray and Sunyaev-Zel'dovich imaging

by R. Adam, M. Arnaud, I. Bartalucci, et al. A&A 606, A64


Temperature is one of the key properties of the hot ionised gas in the intra-cluster medium (ICM) traditionally obtained from X-ray spectroscopic observations. The thermal Sunyaev-Zel'dovich (tSZ) effect can provide an alternative measurement of the ICM temperature if it is combined with X-rays that measure the gas density. In this paper, the authors use this combination to map the temperature distribution of the ICM in the merging cluster MACS J0717.5+3745 taking advantage of deep and resolved tSZ observations from the New IRAM KIDs Array (NIKA) instrument, and from XMM-Newton. The authors demonstrate the capabilities of their approach and find a good morphological agreement between the temperature maps derived from X-ray data only and their map obtained from the tSZ+X-ray combination.