Flexible color adaptation to available ecological niches is vital for the photosynthetic organisms to thrive. Hence, most purple bacteria living in the shade of green plants and algae apply bacteriochlorophyll a pigments to harvest near infra-red light around 850–875 nm. Exceptions are some Ca²⁺-containing species fit to utilize much redder quanta. The physical basis of such anomalous absorbance shift equivalent to ~5.5 kT at ambient temperature remains unsettled so far. Here, by applying several sophisticated spectroscopic techniques, we show that the Ca²⁺ ions bound to the structure of LH1 core light-harvesting pigment–protein complex significantly increase the couplings between the bacteriochlorophyll pigments. We thus establish the Ca-facilitated enhancement of exciton couplings as the main mechanism of the record spectral red-shift. The changes in specific interactions such as pigment–protein hydrogen bonding, although present, turned out to be secondary in this regard. Apart from solving the two-decade-old conundrum, these results complement the list of physical principles applicable for efficient spectral tuning of photo-sensitive molecular nano-systems, native or synthetic.

Photosynthetica covers wide range of photosynthesis research or research including photosynthetic parameters of both experimental and theoretical nature.

In our study, we investigate how early-type stars influence the gases escaping from exoplanet atmospheres into space. We focus on two key aspects: how the star's radiation force and gravity affect the path of these gases, and how fast neutral atoms speed up before changing into ions. By combining theories and models, we aim to understand these processes better. Our research not only deepens our understanding of exoplanets but also sheds light on their relationship with the stars they orbit. Additionally, our models could help predict which chemical elements end up accreting on to the host star. For early-type stars, our predictions might even show up as observable patterns in their spectra, because one of the unique features of early-type stars is that material accreting onto them can easily “pollute” the photosphere.

Context . The characterisation of exoplanetary systems depends on the accurate determination of host star parameters. The Ariel mission will probe the atmospheres of a statistically significant sample of exoplanets, and so requires a precise characterisation of the stellar properties well before its launch in 2031. The homogeneous determination of stellar parameters for Ariel will enable both the optimisation of the final target list and set roots for a reliable interpretation of the formation and evolution of planetary systems. Such a homogeneous characterisation has thus far only been carried out for the cool ( T _eff ≲ 7000 K) host stars among the Ariel target candidates. Aims . We present a uniform determination of fundamental stellar parameters for 18 hot stars ( T _eff ≳ 7000 K) in the Tier 1 candidate list of the Ariel mission candidate sample. Methods . We adopted an iterative spectro-trigonometric approach optimised for high-temperature stars ( T _eff ≳ 7000 K). Highresolution spectra were analysed using the ZEEMAN code with χ ² minimisation, combining model fits to metal and Balmer lines. Surface gravity was refined using photometry-based radii and masses from stellar evolutionary tracks. Results . We derived effective temperatures, surface gravities, projected rotational velocities, microturbulent velocities, overall metal-licities, iron abundances, stellar masses, and radii for our sample of 18 hot stars. Our results were validated against a set of benchmark stars previously presented in the literature, confirming that our methods yield results consistent with previous studies. This ensures an internally consistent parameter scale and maintains continuity across the transition from cool to hot stars within the Ariel sample. Conclusions . The derived parameters provide an internally consistent basis for studying the link between stellar properties and planetary characteristics in intermediate-mass stars (1.5 < M < 2.32 M _⊙ ). Building on our previous work on FGK host stars, we show that correlations between stellar mass, metallicity, and planetary radii also extend to early-type stars, and stellar properties influence the architecture of multi-planet systems.

The direct characterisation of exoplanetary atmospheres remains observationally challenging, especially for close-in gas giants around bright stars. However, recent theoretical work by Jermyn & Kama (2018) suggests an indirect pathway: highly irradiated hot Jupiters with evaporating atmospheres may transfer a fraction of their atmospheric material onto their host stars. This process, known as stellar photospheric contamination, could imprint the chemical composition of the exoplanet's upper atmosphere onto the stellar spectrum, offering a new means of atmospheric characterisation.In this study, we explore the conditions under which such contamination may occur, focusing on star–planet systems involving F and A-type host stars. These stars, with their relatively thin convective zones and high ultraviolet output, are particularly susceptible to detectable enrichment from planetary material. Using a sample of well-characterised hot Jupiters orbiting F-type stars, we model the vertical pressure–temperature (P–T) profiles of their atmospheres, identifying species likely to escape and potentially accumulate on the stellar surface.We then examine how the architecture of each system (e.g. orbital separation, planetary atmosphere evaporation rates) affects the efficiency and detectability of contamination. Our approach combines theoretical atmospheric structure modelling with current and archival spectral data to assess the feasibility of this technique using existing high-resolution spectrographs and to define instrumental requirements for future observations.Our results demonstrate that photospheric contamination is a promising, underutilised method for tracing the chemical fingerprints of exoplanet atmospheres. This work opens new avenues for synergy between stellar spectroscopy and planetary atmospheric studies, offering a complementary tool to direct detection techniques.