We present the IXPE observation of GRB 221009A, which includes upper limits on the linear polarization degree of both prompt and afterglow emission in the soft X-ray energy band. GRB 221009A is an exceptionally bright gamma-ray burst (GRB) that reached Earth on 2022 October 9 after traveling through the dust of the Milky Way. The Imaging X-ray Polarimetry Explorer (IXPE) pointed at GRB 221009A on October 11 to observe, for the first time, the 2–8 keV X-ray polarization of a GRB afterglow. We set an upper limit to the polarization degree of the afterglow emission of 13.8% at a 99% confidence level. This result provides constraints on the jet opening angle and the viewing angle of the GRB, or alternatively, other properties of the emission region. Additionally, IXPE captured halo-rings of dust-scattered photons that are echoes of the GRB prompt emission. The 99% confidence level upper limit to the prompt polarization degree depends on the background model assumption, and it ranges between ∼55% and ∼82%. This single IXPE pointing provides both the first assessment of X-ray polarization of a GRB afterglow and the first GRB study with polarization observations of both the prompt and afterglow phases.

We report on the first polarimetric study of (3200) Phaethon, the target of JAXA’s DESTINY⁺ mission, in the negative branch to ensure its anhydrous nature and to derive an accurate geometric albedo. We conducted observations at low phase angles (Sun-target-observer angle, α = 8.8–32.4°) from 2021 October to 2022 January and found that Phaethon has a minimum polarization degree P_min = −1.3 ± 0.1 per cent, a polarimetric slope h = 0.22 ± 0.02 per cent deg⁻¹, and an inversion angle α₀ = 19.9 ± 0.3°. The derived geometric albedo is p_V = 0.11 (in the range of 0.08–0.13). These polarimetric properties are consistent with anhydrous chondrites, contradict hydrous chondrites, and typical cometary nuclei.

Context. The yellow hypergiant star V509 Cas is currently undergoing an extreme phase of evolution. Having experienced eruptive mass-loss outbursts in the 20th century, the star’s effective temperature reached record high values in the early 2000s. However, since then, the star’s behaviour has displayed an unprecedented level of stability. In spite of that, the star could be traversing through the ‘yellow void’ instability region. Aims. To describe the current evolutionary state of V509 Cas, we analysed its variability using photometric and spectroscopic data collected over recent years. By comparing our findings with historical records, we aim to determine whether the star’s surface shows signs of stabilisation. Additionally, we investigate the variability of emission components in the wings of certain spectral lines to highlight the contribution of the circumstellar gaseous disc to this phenomenon. Methods. Our spectroscopic monitoring observations were carried out at Tartu Observatory over the course of seven years, supplemented by echelle spectra obtained at the Nordic Optical Telescope, as well as publicly available photometric data from Gaia, AAVSO, and AAVSO’s Bright Star Monitor programme. We estimated the variability of effective temperature and radial velocity from the spectral time series and correlated it with the brightness variability of V509 Cas. Results. The results indicate that the star’s average brightness level has remained stable throughout the observed period, with an amplitude of variability ∼0.1 mag. While the amplitude of short-term temperature fluctuations has decreased compared to the early 2000s, the variability of the radial velocity remains similar to historical values from the early 20th century. Moreover, we show how the variable radial velocity affects the emission components in some absorption lines (e.g. Sc II) and how that follows the hypothesis of a disc surrounding the star.

The Earth close approach of near-Earth asteroid 2005 LW3 on 2022 November 23 represented a good opportunity for a second observing campaign to test the timing accuracy of astrometric observation. With 82 participating stations, the International Asteroid Warning Network collected 1046 observations of 2005 LW3 around the time of the close approach. Compared to the previous timing campaign targeting 2019 XS, some individual observers were able to significantly improve the accuracy of their reported observation times. In particular, U.S. surveys achieved good timing performance. However, no broad, systematic improvement was achieved compared to the previous campaign, with an overall negative bias persisting among the different observers. The calibration of observing times and the mitigation of timing errors should be important future considerations for observers and orbit computers, respectively.

Context . The distances to evolved massive stars in the Milky Way are poorly constrained by Gaia parallaxes because these stars are bright and variable. This makes it difficult to determine their fundamental stellar parameters, such as radius or luminosity, and infer their evolutionary states. Aims . We aim to improve the distance estimates of yellow hypergiants (YHGs) and yellow supergiants (YSGs) by identifying possible cluster and association memberships. Using these distances, we derived updated luminosities and revised their positions in the Hertzsprung-Russell diagram. Methods . We compiled a sample of 35 luminous yellow massive stars (YHGs and the most luminous YSGs) from the literature. We used Gaia DR3 astrometry to identify possible membership in clusters and OB associations. We derived distances by combining the parallaxes of nearby co-moving stars. We independently validated these distances by comparing the stellar radial velocities to the Galactic H I kinematic map. We combined angular diameters and effective temperature values from the literature with the new distances to estimate the luminosities. Results . We improved the distance estimates for 28 of the 35 stars through association with co-moving stellar groups. For an additional 6 stars, we provided distance estimates based on the H I kinematic map. For one star, the distance remains unclear. Most YSGs are members of young stellar populations, while the environments of the YHGs are more diverse, and the origin populations for some of them remain unclear. We derived updated luminosities for a subset of 20 stars. Most YHGs have luminosities above log L / L _⊙ = 5.4, while YSGs occupy a wider range of luminosities, and the luminosities of the most luminous YSGs are similar to those of YHGs.

Context. The hypergiant RW Cep is one of the largest stars in the Galaxy. The evolution and mass loss of such stars have profound effects on their surrounding regions and their galaxy as a whole. Between 2020 and 2024, RW Cep experienced a historic mass-loss event known as the Great Dimming. Aims. This study provides a spectroscopic analysis of RW Cep during the Great Dimming. We examine its atmospheric dynamics and place it in the context of the star’s variability behaviour since the early 2000s. Methods. We conducted high-cadence spectroscopic observations of RW Cep during the dimming event using the Tartu Observatory 1.5-meter telescope and the Nordic Optical Telescope. We analysed the atmospheric dynamics by measuring the radial velocities and line depths of Fe I and other spectral lines. Results. The radial velocities of the Fe I lines reveal a vertical velocity gradient of 10–20 km s⁻¹ in the atmosphere, correlating with the strength of the spectral lines. Stronger lines, formed in higher atmospheric layers, have higher radial velocities. We measured the systemic velocity at −50.3 km s⁻¹. During the dimming, radial velocities were affected by additional emission from the ejected gas, which was blue-shifted relative to the absorption lines. Post-dimming, we observed large-scale atmospheric motions with an amplitude of ~25 km s⁻¹. Strong resonance lines of Ba II, K I, Na I, and Ca I showed stable central emission components at −56 km s⁻¹, which are likely of circumstellar origin.