The 10 most-cited articles in Astronomische Nachrichten, 2024

Abstract We present James Webb Space Telescope observations of the globular cluster NGC 6397 and use them to extend to infrared wavelengths the characterization of the cluster's entire white dwarf (WD) cooling sequence (CS). The data allows us to probe fundamental astrophysical WD properties and to search for evidence in their colors for (or against) the existence of ancient planetary systems. The existing archival Hubble Space Telescope imaging data obtained years ago reach ultra‐deep optical magnitudes () and allow us to derive a near‐perfect separation between field and cluster members. We detect an apparent split in the lower part of the WD CS of NGC 6397. The red part of the WD CS, containing about 25% of the total, exhibits significant IR‐excess of up to mag. These infrared excesses require both theoretical and observational follow‐ups to confirm their veracity and to ascertain their true nature.

ABSTRACT We present the radial metallicity gradients within the Galactic thin disc population through main‐sequence stars selected on the chemical plane using GALAH DR3 accompanied with Gaia DR3 astrometric data. The [Fe/H], [/Fe] and [Mg/H] radial gradients are estimated for guiding radius as , , dex kpc and for the traceback early orbital radius as , , dex kpc for 66,545 thin‐disc stars, respectively. Alteration of the chemical structure within the Galactic disc caused by the radial orbital variations complicates results for the radial metallicity gradient. The effect of radial orbital variations on the metallicity gradients as a function on time indicates the following results: (i) The presence of a gradient along the disc throughout the time for which the model provides similar prediction, (ii) the radial orbital variations becomes more pronounced with the age of the stellar population and (iii) the effect of radial orbital variations on the metallicity gradients is minimal. The effect of radial orbital variations is found to be at most 6% which does not statistically affect the…

Abstract We present high‐resolution (0.06 Å px) spectroscopic observations of the recurrent nova T Coronae Borealis obtained during the last 1.5 years (September 2022–January 2024), with the 2.0‐m RCC telescope of the Rozhen National Astronomical Observatory, Bulgaria. Double‐peaked emission is visible in the line after the end of the superactive state. We subtract the red giant contribution and measure the distance between the peaks () of the line. For the period July 2023–January 2024, we find that is in range km s. Assuming that the emission is from the accretion disc around the white dwarf, we find average radius of the accretion disc R, which is approximately equal to the Roche lobe size of the white dwarf. Our results indicate that tidal torque plays an important role but that the disc can extend up to the Roche lobe of the accreting star.

ABSTRACT This study outlines a detailed investigation using CCD UBV and Gaia DR3 data sets of the two open clusters Ruprecht 1 (Rup‐1) and Ruprecht 171 (Rup‐171). Fundamental astrophysical parameters such as color excesses, photometric metallicities, ages, and isochrone distances were based on UBV‐data analyses, whereas membership probability calculations, structural and astrophysical parameters, as well as the kinematic analyses were based on Gaia DR3‐data. We identified 74 and 596 stars as the most probable cluster members with membership probabilities over 50% for Rup‐1 and Rup‐171, respectively. The color excesses were obtained as and mag for Rup‐1 and Rup‐171, respectively. Photometric metallicity analyses were performed by considering F‐G type main‐sequence member stars and found to be and dex for Rup‐1 and Rup‐171, respectively. Ages and distances were based on both UBV and Gaia‐data analyses; according to isochrone‐fitting these values were estimated to be Myr, pc for Rup‐1 and Myr, pc for Rup‐171. The present‐day mass function slope of Rup‐1 was estimated as and Rup‐171 as…

Abstract Located at less than two pc away, Luhman 16 AB (WISE J104915.57‐531906.1) is the closest pair of brown dwarfs and the third closest “stellar” system to Earth. An exoplanet candidate in the Luhman 16 binary system was reported in 2017 based on a weak astrometric signature in the analysis of 12 HST epochs. An additional epoch collected in 2018 and re‐analysis of the data with more advanced methods further increased the significance level of the candidate, consistent with a Neptune‐mass exoplanet orbiting one of the Luhman 16 brown dwarf components. We report the joint analysis of these previous data together with two new astrometric HST epochs we obtained to confirm or disprove this astrometric signature. Our new analysis rules out the presence of a planet orbiting one component of the Luhman 16 AB system for masses 1.5 M♆ (Neptune masses) and periods between 400 and 5000 days. However, the presence of third bodies with masses 3 M♆ and periods between 2 and 400 days (1.1 years) cannot be excluded. Our measurements make significant improvements to the characterization of this…

Abstract In this study, spectral, age, kinematic, and orbital dynamical analyses were conducted on metal‐poor and high proper‐motion (HPM) stars, HD 8724 and HD 195633, selected from the Solar neighborhood. This analysis combines detailed abundance measurements, kinematics, and orbital dynamics to determine their origin. Standard 1D local thermodynamic equilibrium analysis provides a fresh determination of the atmospheric parameters: Teff = 4700 ± 115 K, log g = 1.65 ± 0.32 cgs, [Fe/H] = −1.59 ± 0.04 dex, and a microturbulent velocity 1.58 ± 0.50 km s−1 for HD 8724 and Teff = 6100 ± 205 K, log g = 3.95 ± 0.35 cgs, [Fe/H] = −0.52 ± 0.05 dex, and 1.26 ± 0.50 km s−1 for HD 195633. The ages were estimated using a Bayesian approach (12.25 Gyr for HD 8724 and 8.15 Gyr for HD 195633). The escape scenarios of these stars from 170 candidate globular clusters (GCs) in the Galaxy were also investigated because of their chemical and physical differences (HPM and metal‐poor nature). Accordingly, the calculated probability of encounter (59%) for HD 8724 at a distance of five tidal radius suggests…

ABSTRACT The Imaging X‐ray Polarimetry Explorer, recently awarded by the American Astronomical Society with the Bruno Rossi prize, observed several accreting neutron stars in X‐ray binaries during the first 2 years of its prime mission. Results obtained for weakly magnetized neutron stars allow us to model the geometry and the physical status of the different emitting regions (accretion disk, boundary/spreading layer) in a completely novel way, showing a more intricate scenario with respect to the one initially anticipated based on theoretical models. In particular, polarization measurements have demonstrated variations with energy and time, which are highly intriguing. Here, a summary of the IXPE findings for these sources, in particular 4U 1820–303, and Cir X–1 are reported.

ABSTRACT We reanalyze the data of the BU‐FCRAO Galactic Ring Survey (GRS) to understand the dynamics of the turbulent molecular interstellar medium. We define molecular clouds by their spatial half‐power contours of 13CO‐integrated intensity, independent of a boundary based on thresholding or tiling. We find properties of hydrostatic equilibrium (HE) and virial equilibrium (VE), the former independent and the latter dependent on time and spatial scales. We suggest that HE is a stationary property of the turbulence and that molecular clouds are high‐density regions of a fluctuating component. The gravitational and turbulent kinetic energies within clouds are continuously evolving toward a time‐dependent VE with the fluctuating, external, turbulent pressure energy (PE) that can be treated parametrically owing to the shorter time scale for virialization. The average PE is comparable to the pressure of the multiphase ISM at the Galactic mid‐plane. Larson's scaling relations analyzed by different statistical methods are not significant. The nondimensional variances of size, line width,…

Abstract The dynamical evolution of tight star‐planet systems is influenced by tidal interactions between the star and the planet, as was shown recently. The rate at which spins and orbits in such a system evolve depends on the stellar and planetary tidal dissipation efficiency. Here, we present a method to constrain the modified tidal quality factor of a planet‐hosting star whose rotational evolution has been altered by its planet through angular momentum transfer from the planetary orbital motion to the rotation of the stellar convective zone. The altered rotation is estimated from an observed discrepancy of magnetic activity of the planet‐hosting star and a coeval companion star, that is, this method is applicable to star‐planet systems with wide stellar companions. We give an example of the planet‐hosting wide binary system HD189733 and find that the planet host's modified tidal quality factor is constrained to be .

Abstract There are many rotating spheroids in the universe, and many astronomers and physicists have used theoretical methods to study the characteristics of stellar gravity since Newton's time. This paper derives the solutions of eight scattering states ,, and for the Dirac equation with positive‐energy , and establishes the relationship between the differential scattering cross section and the stellar density . It is found that: (1) For the eight scattering states, their average scattering cross‐sections are proportional to , and depend on the star's radius, and the higher the stellar density , the greater the sensitivity of to the change of ; (2) For the four scattering states , their average scattering amplitudes and depend on the mass of the particles; while for the other four scattering states , , then and are independent of . This study links the gravitational characteristics of stars with the scattering cross section, creating a new method for studying the gravitational characteristics, which helps to reveal the mystery of the gravity of rotating ellipsoidal stars.