We present the first X-ray spectropolarimetric results for Cygnus X-1 in its soft state from a campaign of five IXPE observations conducted during 2023 May–June. Companion multiwavelength data during the campaign are likewise shown. The 2–8 keV X-rays exhibit a net polarization degree PD = 1.99% ± 0.13% (68% confidence). The polarization signal is found to increase with energy across the Imaging X-ray Polarimetry Explorer’s (IXPE) 2–8 keV bandpass. The polarized X-rays exhibit an energy-independent polarization angle of PA = −25.°7 ± 1.°8 east of north (68% confidence). This is consistent with being aligned to Cyg X-1’s au-scale compact radio jet and its parsec-scale radio lobes. In comparison to earlier hard-state observations, the soft state exhibits a factor of 2 lower polarization degree but a similar trend with energy and a similar (also energy-independent) position angle. When scaling by the natural unit of the disk temperature, we find the appearance of a consistent trend line in the polarization degree between the soft and hard states. Our favored polarimetric model indicates that Cyg X-1’s spin is likely high (a _* ≳ 0.96). The substantial X-ray polarization in Cyg X-1's soft state is most readily explained as resulting from a large portion of X-rays emitted from the disk returning and reflecting off the disk surface, generating a high polarization degree and a polarization direction parallel to the black hole spin axis and radio jet. In IXPE’s bandpass, the polarization signal is dominated by the returning reflection emission. This constitutes polarimetric evidence for strong gravitational lensing of X-rays close to the black hole.

To explain the nature of the high reddening (A_V ≃ 10 mag) towards one of the most luminous stars in the Galaxy – Cyg OB2 #12 (B5 Ia-0), also known as MT304, we carried out spectrophotometric observations of 24 stars located in its vicinity. We included five new B-stars among the members of Cygnus OB2, and for five more photometrically selected stars we spectroscopically confirmed their membership. We constructed the map of interstellar extinction within 2.5 arcmin radius and found that interstellar extinction increases towards MT304. According to our results the most reddened OB-stars in the association after MT304 are J203240.35+411420.1 and J203239.90+411436.2, located about 15 arcsec away from it. Interstellar extinction towards these stars is about 9 mag. The increase of reddening towards MT304 suggests that the reddening excess may be caused by the circumstellar shell ejected by the star during its evolution. This shell absorbs 1 mag, but its chemical composition and temperature are unclear. We also report the detection of a second component of MT304, and discovery of an even fainter third component, based on data of speckle interferometric observations taken with the Russian 6-m telescope.

We report the results of optical spectroscopy of the blue supergiant Sk−69° 279 and its circular shell in the Large Megellanic Cloud (LMC) with the Southern African Large Telescope (SALT). We classify Sk−69° 279 as an O9.2 Iaf star and analyse its spectrum by using the stellar atmosphere code cmfgen, obtaining a stellar temperature of ≈30 kK, a luminosity of $$\log (L_*/\rm \, L_\odot )=5.54$$, a mass-loss rate of $$\log (\dot{M}/\rm \, M_\odot \, {\rm yr}^{-1}$$)=−5.26, and a wind velocity of 800 km s⁻¹. We found also that Sk−69° 279 possesses an extended atmosphere with an effective temperature of ≈24 kK and that its surface helium and nitrogen abundances are enhanced, respectively, by factors of ≈2 and 20–30. This suggests that either Sk−69° 279 was initially a (single) fast-rotating ($$\gtrsim 400 \, {\rm \, km\, s^{-1}}$$) star, which only recently evolved off the main sequence, or that it is a product of close binary evolution. The long-slit spectroscopy of the shell around Sk−69° 279 revealed that its nitrogen abundance is enhanced by the same factor as the stellar atmosphere, which implies that the shell is composed mostly of the CNO processed material lost by the star. Our findings support previous propositions that some massive stars can produce compact circumstellar shells and, presumably, appear as luminous blue variables while they are still on the main sequence or have only recently left it.

We consider the luminous blue variable (LBV) star V532 in M33, also known as Romano’s star, in two different spectral states: in the optical minimum

We report the identification of the unusual emission-line stellar-like object in the nearby low-metallicity ($Z \sim 0.1 \, \mathrm{Z_{\odot }}$) dwarf galaxy NGC 4068. Our observations performed with long-slit spectrograph and Fabry–Perot interferometer demonstrate high velocity dispersion in H α line, presence of He ii λ4686Å line and peculiarly low [S ii]/[N ii] fluxes ratio for this object. From observational data, we derived that the object represents a single star of high bolometric luminosity (L* ∼ 1.5 × 106 L⊙) surrounded by an expanding nebula with kinematical age of t ∼ 0.5 Myr. The nebula exhibits significant nitrogen overabundance [log (N/O) ∼ −0.05, that is by ∼1.4 dex higher than expected for low-metallicity galaxies]. We suggested that this is a massive blue supergiant (BSG) or Wolf–Rayet (WR) star surrounded by its ejecta interacting with the interstellar medium. We calculated the models of the nebula using cloudy photoionization code, applying cmfgen-modelled BSG and WR stars as ionization sources. We found a best agreement between the modelled and observed spectra for the model assuming ionization by low-metallicity WR star of mass $M_*\approx 80\, \rm M_\odot$, ionizing the nebula through the strong wind and enriching the interstellar medium with nitrogen.