Astronomische Nachrichten最新文献

Simulated differential transmission spectra of various “superhabitable” planet scenarios. For comparison, the predicted spectra of Kepler-62e (a terrestrial planet in the habitable zone of a K dwarf) and the modern Earth around the Sun are shown as well. Spectral features are displayed in ppm relative to each planet's baseline transit depth, revealing individual molecular signatures, including O₂, O₃, CH₄, H₂O, N₂O, CO₂, CH₃Cl, and CO. Solid gray lines represent planets receiving an incident stellar flux of 0.8 solar constants (S0 = 1366 W/m²), positioned between the inner edge and center of their respective host star's habitable zone, while dashed lines represent the same planets at 0.6 S0, aligned with the center of the habitable zone. The prospects of observing possible biosignatures in the atmospheres of transiting “superhabitable” exoplanets with the James Webb Space Telescope are discussed in the related paper by I. Vilović et al. published in this issue e20240081.

Hunting for white dwarfs in eROSITA surveys 1-4 with special processing. The Gaia color-magnitude diagram shows all white dwarf candidates from the Gaia white dwarf catalogue (Gentile Fusillo et al. 2021), colour-coded with the probability of being a white dwarf. Black circles mark sources in the ROSAT white dwarf catalogue (Fleming et al. 1996) that match entries in the Gaia white dwarf catalogue (light blue crosses indicate those in the German half of the eROSITA sky). Orange crosses mark eROSITA sources with a hardness ratio of ≤ −0.94 and with counterparts in the Gaia white dwarf catalogue. Those highlighted with a dark green circle have a probability larger than 90 % of being a white dwarf in that catalogue. The cooling tracks of white dwarfs with masses between 0.4 and 1.2 solar masses are shown as gray lines in steps of 0.1 solar masses (top to bottom). For more details see the related paper by S. Friedrich et al. published in this issue e240139.

We combine infrared (IR) observations collected by the James Webb Space Telescope with optical deep images by the Hubble Space Telescope taken ~20 years earlier to compute proper-motion membership for the globular cluster (GC) M4 (NGC 6121) along its entire white dwarf (WD) cooling sequence (CS). These new IR observations allow us, for only the second time in a GC, to compare WD models with observations over a wide range of wavelengths, constraining fundamental astrophysical properties of WDs. Furthermore, we investigate the presence of WDs with IR excess along the WD CS of M4, similar to the recent study conducted on the GC NGC 6397. We also determine the age difference between M4 and NGC 6397 by comparing the absolute F150W2 magnitudes of the luminosity function peak at the bottom of the observed WD CS and find that M4 is slightly younger, by 0.8 ± 0.5 Gyr.

Pulsating Ultraluminous X-ray Sources (PULXs) are a class of extragalactic sources with high X-ray luminosity, in excess of $��{10}^{39}�$ erg $��s^{�-�1�}�$, and showing pulsations that associate them with neutron stars accreting at a super-Eddington rate. A simplified model is presented, which describes the thermal emission from an accreting, highly magnetized neutron star and includes the contributions from an accretion disk and an accretion envelope surrounding the star magnetosphere. Through numerical calculations, we determine the flux, pulsed fractions, polarization degree, and polarization angle considering various viewing geometries. The model is confronted with the XMM-Newton spectra of M51 ULX-7, and the best fitting viewing geometries are estimated. A measurement of the polarization observables, which will be available with future facilities, along with spectroscopic data obtained with XMM-Newton, will provide considerable additional information on these sources.

In our search for life beyond the Solar System, certain planetary bodies may be more conducive to life than Earth. However, the observability of these “superhabitable” (SH) planets in the habitable zones around K dwarf stars has not been fully modeled. This study addresses this gap by modeling the atmospheres of SH exoplanets. We employed the 1D model Atmos to define the SH parameter space, POSEIDON to calculate synthetic transmission spectra, and PandExo to simulate JWST observations. Our results indicate that planets orbiting mid-type K dwarfs, receiving 80% of Earth's solar flux, are optimal for life. These planets sustain temperate surfaces with moderate CO₂ levels, unlike those receiving 60% flux, where necessarily higher CO₂ levels could hinder biosphere development. Moreover, they are easier to observe, requiring significantly fewer transits for biosignature detection compared with Earth-like planets around Sun-like stars. For instance, detecting biosignature pairs like oxygen and methane from 30 pc would require 150 transits (43 years) for a SH planet, versus over 1700 transits (~1700 years) for Earth-like planets. While such observation times lie outside of JWST mission timescales, our study underscores the necessity of next-generation telescopes and provides valuable targets for future observations with, for example, the ELT.

Stellar masses are found from the orbital elements of binary systems which are, in turn, computed from weighted astrometric measures. Astrometric measures of double stars (their position angle and separation) rarely include uncertainties, and published binary star orbits rarely include the weighting systems used in the determination of the orbital elements. Here we propose a simple method for estimating uncertainties of ground-based measures of visual double stars based on precision space-based astrometry of optical (not binary) double stars, which can be used as unbiased weights for all double star measures. The precision of ground-based measures is examined as (i) a function of the date of observation, (ii) the telescope aperture, and (iii) the instrumentation (technique) used at the telescope. We also note in the Appendix, 19 pairs that are incorrectly described in Lin2 and six rectilinear pairs that may display curved motion.