Vol. 631
In section 14. Catalogs and data

GALACTICNUCLEUS: A high-angular-resolution JHKs imaging survey of the Galactic centre. II

by F. Nogueras-Lara, R. Schödel, A. T. Gallego-Calvente, et al., 2019, A&A, 631, A20 alt

The Galactic center (GC) is the galactic nucleus closest to us and the most complicated place of the Milky Way to study. It is a main target in astrophysics, but the extreme stellar densities (∼ 10^{5−7} pc−3) and the very high extinction are serious obstacles to the study of the structure and the stellar population of the GC. It requires an angular resolution of ~ 0.2” to characterize the GC stellar population, however, previous studies are limited in angular resolution to >0.6”. The authors had many nights of observations with HAWK-I at the ESO-VLT, and present an exquisite dataset, the GALACTICNUCLEUS catalog. The catalog is a near-infrared JHKs high-angular resolution (0.2”) survey of the nuclear bulge of the Milky Way.

Vol. 630
In section 10. Planets and planetary systems

Oxygen isotopic ratios in Martian water vapour observed by ACS MIR on board the ExoMars Trace Gas Orbiter

by J. Alday et al., 2019, A&A, 630, A91 alt

Isotopic ratios of several elements (H, N, O, and noble gases) in the martian atmosphere can depart from their terrestrial counterparts, providing diagnostics of evolution processes such as atmospheric loss or interaction with the surface, as well as possible fractionation effects within the present-day martian atmosphere. While the martian D/H ratio, enhanced by a typical factor of approximately six over the Earth value, is well-documented, much less is known about the oxygen isotope ratios (18O/16O and 17O/16O) in water vapor. Furthermore, published measurements are thus far limited to a value of 18O/16O in the near-surface atmosphere obtained by the Curiosity Rover. Using early solar occultation infrared measurements of H216O, H218O, and H217O with the ACS (Atmospheric Chemistry Suite) instrument onboard the Trace Gas Orbiter mission, Alday et al. report vertically resolved profiles of 18O/16O and 17O/16O in H2O for the first time. They find these two ratios to be only mildly enhanced, by 200+/-80 per mil for 18O/16O and 230+/-110 per mil for 17O/16O, over the telluric standard values. This result likely stems from the combination of a low oxygen escape and a large oxygen reservoir. Within measurement errors, no vertical variability of the isotopic ratios can be distinguished from these early data. Accumulating measurements over varying seasonal and spatial conditions will allow for the search of fractionation effects, such as at water condensation, within the atmosphere.

Vol. 629
In section 3. Cosmology

Baryon acoustic oscillations at z = 2.34 from the correlations of Ly alpha absorption in eBOSS DR14

by V. de Sainte Agathe et al., 2019, A&A, 629, A85

The imprint of primordial baryon acoustic oscillations (BAO) in the correlation function of Ly absorption in quasar provides an independent way of determining cosmological parameters that is based only on low-redshift measurements. The authors of this paper use Ly alpha and Ly beta spectral regions from the BOSS and eBOSS DR14 QSO data sample to study BAO. The model they have built for the Lyalpha autocorrelation function incorporates the effects of redshift space distortions, non-linear growth of matter, contamination by metals, and modeling of high-column density systems along lines of sight to quasars. The cosmological measurements obtained are in agreement with the predictions of the flat cold dark matter model favored by the measurement of cosmic microwave background anisotropies by Planck. The authors also combine the measurements of this analysis with the ones obtained from the cross-correlation of Ly alpha presented in a companion paper (Blomqvist et al. 2019), which alone would favor a value of the DH=rd ratio of 3% higher than the one favored by the Lyalpha auto-correlation. Combining the two methods, the ensemble of BAO measurements is in good agreement with the the latest Planck model, within only a 1.7 sigma difference at z=2.34.

Vol. 629
In section 6. Interstellar and circumstellar matter

HR 10: a main-sequence binary with circumstellar envelopes around both components

by B. Montesinos, C. Eiroa, J. Lillo-Box, et al., 2019, A&A, 629, A19 alt

The authors carry out a detailed study of HR 10 in order to explain the observed variability.They find that the photospheric Ca II K lines can be decomposed into a few components tracing the radial velocity of the individual stars, and show that HR 10 is a binary. This also indicates that other stars exhibiting variability attributed to falling evaporating body (FEB) model phenomena might actually be binaries and behave in a way that is qualitatively similar to HR 10.

Vol. 629
In section 6. Interstellar and circumstellar matter

The Gaia-ESO survey: Calibrating a relationship between age and the [C/N] abundance ratio with open clusters

by G. Casali, et al., 2019, A&A, 629, A62 alt

Present-day, large high-resolution spectroscopic surveys provide high quality abundance measurements of chemical elements that belong to the different nucleosynthesis channels, and thus also provide constraints on stellar age. The abundance ratio [C/N] is known to be an excellent indicator of stellar age, and in this work the authors calibrate the empirical relationship between the stellar age and [C/N] using giant stars in the large sample of Galactic open star clusters observed by the Gaia-ESO and APOGEE surveys. The relationship found for these star clusters, with well determined ages, were then applied to the Galactic giant field stars in the surveys where C and N abundances were measured. This analysis of the field stars shows an age separation between thin and thick disk stars and age trends within their populations, where age increases as metallicity decreases.

Vol. 629
In section 14. Catalogs and data

Mapping the stellar age of the Milky Way bulge with the VVV. II. Deep JKs catalog release based on PSF photometry

by F. Surot, E. Valenti, S L. Hidalgo, et al., 2019, A&A, 629, A1 alt

The Galactic bulge is an old and massive component of the Milky Way that can be resolved into individual stars and so presents a uniquely detailed opportunity to understand how the bulk of the stars in our Galaxy formed and evolved. This provides crucial insight into the formation of all bulges. This paper presents a detailed and comprehensive catalog of the Milky Way bulge stellar population from deep and accurate point spread function fitting photometry of multi-epoch J and K_s images coming from the VISTA Variables in the Via Lactea (VVV) survey of the inner ~300 deg^2 of the Galaxy. The resulting photometric database contains nearly 600 million stars, typically extending down to stars ~1–2 mag below the oldest main sequence turnoff, except along the plane where extinction makes the limit brighter. Examples of possible applications are provided to demonstrate the tremendous potential inherent to this new dataset, including (i) star count studies through the dataset completeness map, (ii) surface brightness map, and (iii) cross-correlation with Gaia Data Release 2. This database is an invaluable collection for the whole community. All the photometric catalogs, including completeness information, are publicly available through the ESO Science Archive as part of the MW-BULGE-PSPHOT release.

Vol. 629
In section 1. Letters to the Editor

Close-in giant-planet formation via in-situ gas accretion and their natal disk properties

by Y. Hasegawa, T. Y. M. Yu, and B. M. S. Hansen 2019, A&A, 629, L1 alt

The origin of Jupiter-like planets at close orbital distances from their star remains uncertain. Many models assume that their formation occurs beyond the snow line via core accretion, and that once formed, planets migrate inwards, either by planet-disk interaction or by planet-planet interaction coupled with stellar tides. Another class of models calls for in-situ formation instead. In this latter case, the distribution of exoplanets with distance must correlate with the formation efficiency, that is, by the ability of giant planetary cores to accrete local disk gas. Under this hypothesis, Hasegawa et al. use the observed occurrence rate of close-in Jupiters to infer the properties of the planet-forming disks, meaning the radial profile of disk temperature, surface density, and efficiency of angular momentum transport. Remarkably, the resulting density profile shows a general increase with distance, very different from the r^{-3/2} dependence in the standard Hayashi minimum-mass solar nebula (MMSN) model. Based on their disk model, the authors also infer the radial dependence of the magnetic field, and find that it switches from a regime of stellar dipole fields (r^-3) in the star vicinity to one of large-scale fields (r^-2) in the inner disk, with a transition near ~0.1 au that may correspond to the valley in the period distribution of giant exoplanets.

Vol. 628
In section 7. Stellar structure and evolution

A luminous stellar outburst during a long-lasting eruptive phase first, and then SN IIn 2018cnf

by A. Pastorello, A. Reguitti, A. Morales-Garoffolo, et al. 2019, A&A, 628, A93

It is always difficult to shed light on the latest stages of a dying star that blows off like a supernova. Nowadays, we have wide-field optical surveys that monitor the sky every night and collect those data for the ages. When a supernova explodes, one can inspect these archival images by looking for past signs of activity. Very few cases of this pre-explosion activity are currently known. In this paper, the authors reveal an eruptive phase from SN2018cnf, which occured approximately three years before the explosion. This event appears to have formed the circumstellar ambient into which the supernova exploded. Indeed, spectral signatures for the interaction of the supernova ejecta with this medium were observed in the supernova spectra. This indicates that the progenitor is probably a massive hypergiant star.

Vol. 628
In section 3. Cosmology

An ALMA+ACA measurement of the shock in the Bullet Cluster

by L. Di Mascolo, T. Mroczkowski, E. Churazov, et al. 2019, A&A, 628, A100

With the advent of the ALMA+ACA array, the thermal Sunyaev-Zeldovich (SZ) effect is becoming one of the most efficient tools for characterizing galaxy cluster merger shocks, in addition to the more traditionally used X-ray observations. The well-known Bullet Cluter, with its spectacular wester shock front, represents the ideal test case for such studies. The authors of this paper characterize the shock properties of the cluster, using deep, high-resolution interferometric SZ effect observations in combination with X-ray analysis. They thus demonstrate that the two sets are highly complementary. In practice, the application of the interferometric modeling technique – using X-ray-motivated priors – allows the authors to place constraints on the electron pressure discontinuity across the shock. The pressure jump implies a Mach number of M = 2.08+- 0.12, which is significantly lower than the one derived from Chandra data alone. The assumption of purely adiabatic electron temperature change across the shock leads to M = 2.5, which is in better agreement with the X-ray estimate. The authors extensively test their modeling choices by varying the geometry, in pre- and post-shock pressure slopes, and by underlying pressure distribution. They conclude that the main limitations are due to the complex morphology observed in the X-ray surface brightness and the uncertainties on the three-dimensional morphology of the cluster. Only a full joint-likelihood analysis of interferometric SZ and X-ray observations, as well as single-dish SZ measurement, would eventually allow us to overcome these limitations.