Astronomy & Astrophysics

https://www.aanda.org/

List of Papers (Total 11,556)

Gaia Data Release 2 - First stellar parameters from Apsis

The second Gaia data release (Gaia DR2) contains, beyond the astrometry, three-band photometry for 1.38 billion sources. One band is the G band, the other two were obtained by integrating the Gaia prism spectra (BP and RP). We have used these three broad photometric bands to infer stellar effective temperatures, Teff, for all sources brighter than G = 17 mag with Teff in the...

Determining the mass loss limit for close-in exoplanets: what can we learn from transit observations?

Aims. We study the possible atmospheric mass loss from 57 known transiting exoplanets around F, G, K, and M-type stars over evolutionary timescales. For stellar wind induced mass loss studies, we estimate the position of the pressure balance boundary between Coronal Mass Ejection (CME) and stellar wind ram pressures and the planetary ionosphere pressure for non- or weakly...

Abundance analysis of barium and mild barium stars

Aims.We compare and discuss abundances and trends in normal giants, mild barium, and barium stars, searching for differences and similarities between barium and mild barium stars that could help shed some light on the origin of these similar objects. Also, we search for nucleosynthetic effects possibly related to the s-process that were observed in the literature for elements...

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...

On Lyman-line asymmetries in quiescent prominences

Aims. We study the asymmetries of the synthetic hydrogen Lyman lines and the process responsible for their formation.Methods. To obtain the synthetic Lyman line profiles, we use a multi-thread prominence fine-structure model consisting of identical 2D threads. The 2D thread models are in MHS equilibrium, include an empirical prominence-corona transition region, and solve...

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...

Multi-wavelength observations of a nearby multi-phase interstellar cloud

Aims. High-resolution spectroscopic observations (UV HST/STIS and optical) are used to characterize the physical state and velocity structure of the multiphase interstellar medium seen towards the nearby (170 pc) star HD 102065. The star is located behind the tail of a cometary-shaped, infrared cirrus-cloud, in the area of interaction between the Sco-Cen OB association and 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...

Ground-based CCD astrometry with wide field imagers - I. Observations just a few years apart allow decontamination of field objects from members in two globular clusters

This paper is the first of a series of papers in which we will apply the methods we have developed for high-precision astrometry (and photometry) with the Hubble Space Telescope (HST) to the case of wide-field ground-based images. In particular, we adapt the software originally developed for WFPC2 to ground-based, wide field images from the WFI at the ESO 2.2 m telescope. In this...

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

Radiative and magnetic properties of solar active regions - II. Spatially resolved analysis of O V 62.97 nm transition region emission

Context. Global relationships between the photospheric magnetic flux and the extreme ultraviolet emission integrated over active region area have been studied in a previous paper by Fludra & Ireland (, A&A, 483, 609). Spatially integrated EUV line intensities are tightly correlated with the total unsigned magnetic flux, and yet these global power laws have been shown to be...

The P Cygni supergiant [OMN2000] LS1 – implications for the star formation history of W51

Aims. We investigate the nature of the massive star [OMN2000] LS1 and use these results to constrain the history of star formation within the host complex W51.Methods. We utilised a combination of near-IR spectroscopy and non-LTE model atmosphere analysis to derive the physical properties of [OMN2000] LS1, and a combination of theoretical evolutionary calculations and Monte Carlo...

Atmospheric image blur with finite outer scale or partial adaptive correction

Context. Seeing-limited resolution in large telescopes operating over wide wavelength ranges depends substantially on the turbulence outer scale and cannot be adequately described by one seeing value.Aims. This study attempts to clarify frequent confusions between seeing and the full-width at half-maximum of long-exposure images in large telescopes, also often called delivered...

Dielectronic recombination of argon-like ions

Context. We present a theoretical investigation of dielectronic recombination (DR) of Ar-like ions that sheds new light on the behavior of the rate coefficient at low-temperatures where these ions form in photoionized plasmas. Aims. We provide results for the total and partial Maxwellian-averaged DR rate coefficients from the initial ground level of K ii–Zn xiii ions. It is...

TANGO I: Interstellar medium in nearby radio galaxies - Molecular gas

Context. Powerful radio-AGN are hosted by massive elliptical galaxies that are usually very poor in molecular gas. Nevertheless, gas is needed at their very center to feed the nuclear activity.Aims. We study the molecular gas properties (i.e., mass, kinematics, distribution, origin) of these objects, and compare them with results for other known samples.Methods. At the IRAM-30m...

Radiation from rapidly rotating oblate neutron stars

A theoretical framework for emission originating from rapidly rotating oblate compact objects is described in detail. Using a Hamilton-Jacobi formalism, we show that special relativistic rotational effects such as aberration of angles, Doppler boosting, and time dilatation naturally emerge from the general relativistic treatment of rotating compact objects. We use the Butterworth...

Nature of the energy source powering solar coronal loops driven by nanoflares

Context. Magnetic energy is required to heat the corona, the outer atmosphere of the Sun, to millions of degrees.Aims. We study the nature of the magnetic energy source that is probably responsible for the brightening of coronal loops driven by nanoflares in the cores of solar active regions.Methods. We consider observations of two active regions (ARs), 11890 and 12234, in which...

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...