Astronomische Nachrichten最新文献

Type II supernovae (SNe II) have emerged as valuable cosmological probes, serving as alternative and independent tools to Type Ia supernova (SN Ia) cosmology. However, the Hubble diagram dispersion for SNe II is significantly larger than for SNe Ia. In this study, we investigate the SN II luminosity and the host galaxy velocity dispersion with the purpose of improving the scatter in the SN II Hubble diagram. We selected a sample of SNe II discovered by the Dark Energy Survey (DES), and we measured the spectra of their host galaxies using the VLT/FORS2 and Magellan-Baade/MagE spectrographs. From those galaxy spectra, we calculated the stellar velocity dispersion in the central region. Using the effective Sérsic radius from the DES imaging, we standardized the velocity dispersion values to a common aperture. From their i-band light curves, we determined a characteristic plateau brightness for our SNe. For this purpose, we developed an algorithm designed to parameterize the plateau phase. After computing the SN absolute magnitudes using the standard cosmology, we found a modest correlation with the host galaxy velocity dispersion ($��R^2�=�0.57�$). These findings could significantly contribute to SN II cosmology, paving the way for SNe II as more robust cosmological probes.

Color-magnitude diagram of the lower mass end of the Main Sequence of globular cluster NGC 6752, as derived from NIR images of a deep field observed under a HST Large Programme led by L.R.Bedin. Three main stellar populations can be reliably distinguished within this cluster. The three isochrones (blue, green, and red lines) were computed with different chemical compositions, adjusted to match the observed colors of the different generations of stars at an age of 12.63 Gy. In the lower left part of the plot, the corresponding isochrone for the White Dwarfs (at an age of 12.5 Gy) is shown in purple, together with the three WD candidates shown as orange crosses. For each isochrone, specific mass values are marked by labeled filled dots. A detailed analysis of the HST data and a discussion of possible scenarios for the formation of multiple stellar populations within NGC 6752 is presented in the article by Scalco et al., this issue e240018.

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 $��\sim �18�$ years ago reach ultra-deep optical magnitudes ($��V�\sim �31�$) 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 $��\Delta �m_{�F�322�W�2�}�\sim �0.5�$ mag. These infrared excesses require both theoretical and observational follow-ups to confirm their veracity and to ascertain their true nature.

We investigate outflows and the physics of super-Eddington versus sub-Eddington regimes in black hole systems. Our focus is on prospective science using next-generation high-resolution soft x-ray instruments. We highlight the properties of black hole ultraluminous x-ray source (ULX) systems in particular. Owing to scale invariance in accreting black holes, ULX accretion properties, including their outflows, inform our understanding not only of the closely related population of (similar-mass) x-ray binary systems but also of tidal disruption events (TDEs) around supermassive black holes. A subsample of TDEs are likely to transcend super-Eddington to sub-Eddington regimes as they evolve, offering an important unifying analog to ULXs and sub-Eddington x-ray binaries. We demonstrate how next-generation soft x-ray observations with resolving power $��\gtrsim �1000�$ and collecting area $��\gtrsim �1000��{\mathrm{cm}}^2�$ can simultaneously identify ultrafast and more typical wind components, distinguish between different wind mechanisms, and constrain changing wind properties over characteristic variability timescales.

Variability of the Hα emission line profile of the magnetic O-type star HD 54897 over one decade, from 2014 to 2024. In the left panels, each profile is plotted with a different color as is indicated in the legend, showing the corresponding observing date and instrument used: H: HARPS, E: ESPaDOnS, U: UVES, and P: PEPSI. The upper panel shows the profiles based on the spectra observed recently, while the bottom panel shows all available profiles published previously. The right panel shows the same data in a color scale plot. The red color corresponds to the strongest emission, while the blue color shows the Hα line wings appearing in absorption. The observed Hα emission is thought to originatein a disk of increased gas density in the equatorial plane of the magnetic field. For details see the article by Küker et al., this issue, e230169.

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 $��Q_{*}^{\prime }�$ 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 $��Q_{*}^{\prime }�\le �2.33�\times �{10}^7�$.