Astronomy & Astrophysics

https://www.aanda.org/

List of Papers (Total 6,401)

Ground-based CCD astrometry with wide-field imagers - II. A star catalog for M 67: WFI@2.2 m MPG/ESO astrometry, FLAMES@VLT radial velocities

Context. The solar-age open cluster M 67 (C0847+120, NGC 2682) is a touchstone in studies of the old Galactic disk. Despite its outstanding role, the census of cluster membership for M 67 at fainter magnitudes and their properties are not well-established.Aims. Using proprietary and archival ESO data, we have obtained astrometric, photometric, and radial velocities of stars in a...

The candidate filament close to the 3C 295 galaxy cluster: optical and X-ray spectroscopy

We present a detailed analysis of the overdensity of X-ray sources close to the 3C 295 galaxy cluster () to assess whether it is associated with a filament of the large-scale structure of the Universe. We obtained optical spectra of the optical counterparts of eleven sources associated with the filament, finding that one is at . This is a type 1 AGN at 1.5 arcmin from the cluster...

X-rays from jet-driving protostars and T Tauri stars

Aims.We study jet-driving protostars and T Tau stars to characterize their X-ray emission. We seek soft spectral components that may be due to shock emission, and search for soft, shock-induced emission displaced from the stellar position. Methods.We study two stellar samples, the first consisting of lightly absorbed T Tau stars with strong jets, the other containing protostars...

SiO line emission from C-type shock waves: interstellar jets and outflows

We study the production of SiO in the gas phase of molecular outflows, through the sputtering of Si-bearing material in refractory grain cores, which are taken to be olivine. We calculate also the rotational line spectrum of the SiO. The sputtering is driven by neutral particle impact on charged grains, in steady-state C-type shock waves, at the speed of ambipolar diffusion. The...

High-resolution spectroscopy for Cepheids distance determination - III. A relation between γ-velocities and γ-asymmetries

Context. Galactic Cepheids in the vicinity of the Sun have a residual line-of-sight velocity, or γ-velocity, which shows a systematic blueshift of about 2 km s-1 compared to an axisymmetric rotation model of the Milky Way. This term is either related to the space motion of the star and, consequently, to the kinematic structure of our Galaxy, or it is the result of the dynamical...

Variations of the solar granulation motions with height using the GOLF/SoHO experiment

Context. Below 1 mHz, the power spectrum of helioseismic velocity measurements is dominated by the spectrum of convective motions (granulation and supergranulation) and it is difficult to detect the low-order acoustic modes and gravity modes.Aims. We attempt to understand more clearly the behavior of solar granulation as a function of observing height in the solar atmosphere and...

Soft X-ray spectral variability of AM Herculis

Context. Polars (AM Herculis binaries) are a prominent class of bright soft X-ray sources, many of which were discovered with ROSAT.Aims. We present a homogenous analysis of all the pointed ROSAT PSPC observations of polars subdivided into two papers that discuss the prototype polar AM Her in detail and summarize the class properties of all other polars.Methods. We derive the...

The photometric evolution of star clusters and the preferential loss of low-mass bodies – with an application to globular clusters

Context. To obtain an accurate description of broad-band photometric star cluster evolution, certain effects should be accounted for. Energy equipartition leads to mass segregation and the preferential loss of low-mass stars, while stellar remnants severely influence cluster mass-to-light ratios. Moreover, the stellar initial mass function and cluster metallicity affect...

Vertical structure of debris discs

Context. The vertical thickness of debris discs is often used as a measure of these systems

Evolution of the magnetic field of Betelgeuse from 2009–2017

Context. Betelgeuse is an M-type supergiant that presents a circularly polarized (Stokes V) signal in its line profiles, interpreted in terms of a surface magnetic field.Aims. The weak circular polarization signal has been monitored over 7.5 years in order to follow its evolution on different timescales, and eventually to determine its physical origin. Linear polarization...

Ongoing astrometric microlensing events of two nearby stars

Context. Astrometric microlensing is an excellent tool to determine the mass of stellar objects. By measuring the astrometric shift of a background source star in combination with precise predictions of its unlensed position and of the lens position, gravitational lensing allows to one determine the mass of the lensing star with a precision of 1%, independently of any prior...

Eyes on K2-3: A system of three likely sub-Neptunes characterized with HARPS-N and HARPS

Context. M-dwarf stars are promising targets for identifying and characterizing potentially habitable planets. K2-3 is a nearby (45 pc), early-type M dwarf hosting three small transiting planets, the outermost of which orbits close to the inner edge of the stellar (optimistic) habitable zone. The K2-3 system is well suited for follow-up characterization studies aimed at...

Accreting, highly magnetized neutron stars at the Eddington limit: a study of the 2016 outburst of SMC X-3

Aims. We study the temporal and spectral characteristics of SMC X-3 during its recent (2016) outburst to probe accretion onto highly magnetized neutron stars (NSs) at the Eddington limit.Methods. We obtained XMM-Newton observations of SMC X-3 and combined them with long-term observations by Swift. We performed a detailed analysis of the temporal and spectral behavior of the...

The empirical Gaia G-band extinction coefficient

Context. The first Gaia data release unlocked the access to photometric information for 1.1 billion sources in the G-band. Yet, given the high level of degeneracy between extinction and spectral energy distribution for large passbands such as the Gaia G-band, a correction for the interstellar reddening is needed in order to exploit Gaia data.Aims. The purpose of this manuscript...

A Virgo Environmental Survey Tracing Ionised Gas Emission (VESTIGE) - I. Introduction to the survey

The Virgo Environmental Survey Tracing Ionised Gas Emission (VESTIGE) is a blind narrow-band (NB) Hα+[NII] imaging survey carried out with MegaCam at the Canada–France–Hawaii Telescope. The survey covers the whole Virgo cluster region from its core to one virial radius (104 deg2). The sensitivity of the survey is of f(Hα) ~ 4 × 10−17 erg s−1 cm−2 (5σ detection limit) for point...

Radio jets and gamma-ray emission in radio-silent narrow-line Seyfert 1 galaxies

We have detected six narrow-line Seyfert 1 (NLS1) galaxies at 37 GHz that were previously classified as radio silent and two that were classified as radio quiet. These detections reveal the presumption that NLS1 galaxies labelled radio quiet or radio silent and hosted by spiral galaxies are unable to launch jets to be incorrect. The detections are a plausible indicator of the...

Deep millimeter spectroscopy observations toward NGC 1068

Aims. We aim for a better understanding of gas properties in the circum-nuclear disk (CND) region of the nearby gas-rich Seyfert 2 galaxy NGC 1068. We focus on line identification and the basic physical parameters estimation of molecular gas in the CND region.Methods. We used the IRAM 30 m telescope to conduct deep millimeter spectroscopy observations toward the center of NGC...

Infrared outbursts as potential tracers of common-envelope events in high-mass X-ray binary formation

Context. Classic massive binary evolutionary scenarios predict that a transitional common-envelope (CE) phase could be preceded as well as succeeded by the evolutionary stage when a binary consists of a compact object and a massive star, that is, a high-mass X-ray binary (HMXB). The observational manifestations of common envelope are poorly constrained. We speculate that its...

Herschel-PACS photometry of faint stars for sensitivity performance assessment and establishment of faint FIR primary photometric standards,

Aims. Our aims are to determine flux densities and their photometric accuracy for a set of seventeen stars that range in flux from intermediately bright (≲2.5 Jy) to faint (≳5 mJy) in the far-infrared (FIR). We also aim to derive signal-to-noise dependence with flux and time, and compare the results with predictions from the Herschel exposure-time calculation tool.Methods. We...

The nature of the TRAPPIST-1 exoplanets

Context. The TRAPPIST-1 system hosts seven Earth-sized, temperate exoplanets orbiting an ultra-cool dwarf star. As such, it represents a remarkable setting to study the formation and evolution of terrestrial planets that formed in the same protoplanetary disk. While the sizes of the TRAPPIST-1 planets are all known to better than 5% precision, their densities have significant...

VLTI-GRAVITY measurements of cool evolved stars - I. Variable photosphere and extended atmosphere of the Mira star R Peg

Context. Dynamic model atmospheres of Mira stars predict variabilities in the photospheric radius and in atmospheric molecular layers which are not yet strongly constrained by observations.Aims. Here we measure the variability of the oxygen-rich Mira star R Peg in near-continuum and molecular bands.Methods. We used near-infrared K-band spectro-interferometry with a spectral...

Searching for Hα emitting sources around MWC 758 - SPHERE/ZIMPOL high-contrast imaging,

Context. MWC 758 is a young star surrounded by a transitional disk. The disk shows an inner cavity and spiral arms that could be caused by the presence of protoplanets. Recently, a protoplanet candidate has been detected around MWC 758 through high-resolution L′-band observations. The candidate is located inside the disk cavity at a separation of ~111 mas from the central star...

On the formation of runaway stars BN and x in the Orion Nebula Cluster

We explore scenarios for the dynamical ejection of stars BN and x from source I in the Kleinmann-Low nebula of the Orion Nebula Cluster (ONC), which is important because it is the closest region of massive star formation. This ejection would cause source I to become a close binary or a merger product of two stars. We thus consider binary-binary encounters as the mechanism to...

Detection of CI line emission towards the oxygen-rich AGB star omi Ceti

We present the detection of neutral atomic carbon CI(3P1–3P0) line emission towards omi Cet. This is the first time that CI is detected in the envelope around an oxygen-rich M-type asymptotic giant branch (AGB) star. We also confirm the previously tentative CI detection around V Hya, a carbon-rich AGB star. As one of the main photodissociation products of parent species in the...

More about solar g modes

Context. The detection of asymptotic solar g-mode parameters was the main goal of the GOLF instrument onboard the SOHO space observatory. This detection has recently been reported and has identified a rapid mean rotation of the solar core, with a one-week period, nearly four times faster than all the rest of the solar body, from the surface to the bottom of the radiative zone.Aim...