Context. Phosphorus (P) is an essential element for life on Earth and a potential tracer of planet formation history. However, there has been no detection of P-bearing molecules in protoplanetary discs so far. Herbig Ae/Be stars constantly accrete matter from their pro- toplanetary disc, which alters the composition of the stellar photosphere due to their shallow convective, or fully radiative, envelope. The altered surface composition reflects the composition of the accreting matter, and thus that of the inner protoplanetary disc. This accretion contamination of stellar photosphere can persist after accretion has ended in young A and B-type stars (age < 50 Myr). Aims. We aim to quantify the fraction of P locked in dust (the refractory fraction of P) compared to gas in the inner protoplanetary disc around Herbig Ae/Be stars. Methods. We measure the stellar parameters and abundance of 5 Herbig Ae/Be stars using optical and UV spectra, to compare their P and Fe abundances. We also used a 20 Myrs old main sequence B-type star, which has P and Fe abundance estimated from optical spectrum. Fe is assumed to be completely locked in refractory reservoirs in the inner disc. A parameterised relationship between the stellar P and Fe abundance gives the fraction of P locked in refractory reservoirs. Results. We find the refractory fraction of P in the inner protoplanetary disc to be > 96

The interactions between stars and their orbiting planets, driven by forces such as stellar radiation and gravity, play an essential role in shaping exoplanetary atmospheres and gas-rich debris discs. One way to look into the composition of these environments is to observe how they can contaminate the stellar photospheres. For that, we examine how stellar radiation pressure and gravity influence atomic species and analyze their effects across various stellar effective temperatures. Using the radiative-to-gravitational force ratio, we determined the atomic movement direction and assessed the velocity boost imparted to neutral atoms escaping from exoplanet atmospheres or debris discs. Incorporating the solar far ultraviolet/extreme ultraviolet spectrum to address flux discrepancies in the ATLAS9 model, we find that radiation affects atoms differently according to their ionization state, with highly ionized species less affected by stellar radiation. Our results conclude that the stars most suitable for observing stellar contamination are those between 6500 and 8000 K, with neutral noble gases and ionized iron-peak elements as the most likely contaminants.

Context . Deuterium is easily destroyed in stellar interiors through nuclear fusion. It is therefore usually not expected to be present in stellar photospheres. Early-type stars, with radiative envelopes that mix slowly, may provide a favourable environment for the survival of recently accreted deuterium. Aims . In this study, we explore the detectability of deuterium in B-, A-, and F-type stars, which possess radiative envelopes that can delay the mixing and destruction of recently accreted material. Methods . We used synthetic spectra to generate model observations including deuterium, focusing on Balmer line regions, for stars with effective temperatures between 7500 K and 12 500 K and a surface gravity of log g = 4.0. To assess the detectability of deuterium, we employed a Markov chain Monte Carlo framework over a range of signal-to-noise ratios between 100 and 1000. We then applied this method to observed spectra of the A9 star HD 32115 and the B9.5 star 21 Peg. Results . We show how detection limits of deuterium abundance depend on signal-to-noise ratio, effective temperature, and projected rotational velocity. For example, for a 10000 K star, the detection limit decreases from D/H = −4.6 dex to −5.5 dex, as the signal-to-noise ratio increases from 100 to 1000. For HD 32115, we find an upper limit of D/H < −5.5 dex, and for 21 Peg < −4.9 dex. We conclude that the detection of deuterium on early-type stars may be possible in some heavily accretion-contaminated cases, providing a new diagnostic tool for the study of proto- or exo-planetary material.

We introduce the data reduction pipeline for the Tartu Observatory Fiber-fed Echelle Spectrograph (TOFES). TOFES is installed in the Coudé room and will be connected to the 1.5 m Tartu Observatory AZT-12 telescope through a four-channel instrument adapter to be mounted at the Cassegrain focus of the telescope. The spectrograph has an average spectral resolution of 30,000 and covers the 390 to 900 nm wavelength band in a single exposure. The data reduction pipeline, based on the PyReduce package, was tested on spectra of the Sun. We also present the Spectroscopy-Toolbox package, which was developed to provide additional tools for diagnostics and spectral line identification for radial velocity measurements. The spectrograph will address a range of scientific questions, including the stellar characterisation of Herbig AeBe stars to measure accretion contamination from their protoplanetary disks, the stellar characterisation of exoplanet host-stars including the Ariel space mission targets, and radial velocity monitoring of large-scale atmospheric variability in massive stars.

The hypergiant RW Cep is one of the largest stars in our galaxy. The evolution and mass loss of such stars has profound effects on their surrounding regions and the galaxy as a whole. Between 2020 and 2024, RW Cep experienced a historic mass-loss event known as the Great Dimming. 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. 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. The radial velocities of the Fe I lines reveal a vertical velocity gradient of 10-20 km/s 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. 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 amplitude ~25 km/s. Strong resonance lines of Ba II, K I, Na I and Ca I showed stable central emission components at -56 km/s, likely of circumstellar origin.

Accretion from protoplanetary or debris disks can contaminate the stellar photosphere, which is detectable in stars with radiative envelopes due to relatively slower photospheric mixing. The contaminated photosphere reflects ongoing disk processes, detectable through stellar spectroscopy. We investigate the composition of six gas-rich debris disk-hosting A-type stars to understand possible links with their debris disk or earlier accretion stages. We used archival spectra to estimate the stellar parameters and abundances of our sample. We also estimated the stellar photospheric accretion contamination parameter, fph which indicates the fraction of accreting material on the stellar photosphere. The oxygen abundance in intermediate-mass stars decreases with age until the debris disk stage (< 20 Myr). The downward trend could result from H2O ice accumulating in dust traps or the formation of hydrated asteroids in the protoplanetary disk, locking oxygen in solids and reducing its accretion onto the star. All stars have similar volatile abundances (C, O), but HD 110058 and HD 32297 show refractory depleted abundances. The near-zero fph values in the six stars suggest that any currently accreted gas would not overwhelm mixing in the photosphere and would not impact the observed composition. The refractory depleted abundances in HD 110058 and HD 32297 suggest residual, or even chronic, accretion contamination from their earlier protoplanetary stages when the accretion rates were about five orders of magnitude higher. For HD 110058, with the highest refractory depletion, we estimated a lower limit on its earlier protoplanetary accretion rate of 9 x 10^(-8) Msun/yr, similar to other Herbig stars and equal to the Herbig star - HD 100546. This supports our hypothesis that refractory depletion in HD 110058 originates from a prior phase of higher accretion of dust-poor material.

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.

The chemical composition of two binary stars, HD 135344A and HD 135344B, is compared, from which conclusions can be drawn about the protoplanetary disk around the star HD 135344B. Since binary stars are form from the same gas and dust cloud, their chemical composition is thought to be similar. To study the protoplanetary disk around the secondary star we have to characterize the host star and the primary star for a comparative analysis. The HD 135344B disk is one of the least known transition disks, which has asymmetrical properties in scattered light and heat radiation. Photometric images of near-infrared scattered light shows two big spiral arms and an internal dust-free cavity.Spectral observations are used to determine the physical parameters and chemical composition of stars, which are matched to synthetic model spectra. The synthetic or model spectrum is found by the Zeeman spectrum sythesis code, which is written in the programming language Fortran. In our presentation, we will present our conclusions regarding the chemical composition of the HD 135344B disk based on the comparative analysis of the binary system’s chemical composition.

ABSTRACT The viscous decretion disc (VDD) scenario has been used to model the observables of the Be stars. Its capability to predict individual observables has been confirmed for several Be stars. Here, we simultaneously analyse the spectroscopic and $BVI$-band photometric data for the Be star MT91-213 with the Monte Carlo radiative-transfer code hdust to determine the stellar parameters, geometry, and physical conditions for its circumstellar disc. MT91-213 is the primary component of a binary system whose companion is the pulsar PSR J2032+4127. We find that the VDD model can simultaneously reproduce the multiple observables qualitatively, but not quantitatively. We determine the mass of the primary star to be 13.1 ${\rm M}_{\odot }$ which is smaller than reported in the literature. We present a dynamical scenario for the evolving disc density from a diffuse to a dense phase. Also, we determine that the inclination of the disc is about 40$^{\circ }$ which means it is 20$^{\circ }$ tilted from the orbit of the secondary star. Our results indicate that the mass loss rate for MT91-213 is $\sim 10^{-7}$ to $10^{-6} {\rm M}_{\odot }\,\mathrm{yr}^{-1}$ which is in agreement with the suggested values in the literature, required to explain the observed X-ray synchrotron luminosity, $L_\mathrm{x}$, for PSR J2032+4127.

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 similar to 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.

Ariel, the Atmospheric Remote-sensing Infrared Exoplanet Large-survey, was adopted as the fourth medium-class mission in ESA's Cosmic Vision programme to be launched in 2029. During its 4-year mission, Ariel will study what exoplanets are made of, how they formed and how they evolve, by surveying a diverse sample of about 1000 extrasolar planets, simultaneously in visible and infrared wavelengths. It is the first mission dedicated to measuring the chemical composition and thermal structures of hundreds of transiting exoplanets, enabling planetary science far beyond the boundaries of the Solar System. The payload consists of an off-axis Cassegrain telescope (primary mirror 1100 mm x 730 mm ellipse) and two separate instruments (FGS and AIRS) covering simultaneously 0.5-7.8 micron spectral range. The satellite is best placed into an L2 orbit to maximise the thermal stability and the field of regard. The payload module is passively cooled via a series of V-Groove radiators; the detectors for the AIRS are the only items that require active cooling via an active Ne JT cooler. The Ariel payload is developed by a consortium of more than 50 institutes from 16 ESA countries, which include the UK, France, Italy, Belgium, Poland, Spain, Austria, Denmark, Ireland, Portugal, Czech Republic, Hungary, the Netherlands, Sweden, Norway, Estonia, and a NASA contribution.

Tartu Observatory telescopes offer unique guaranteed access to objects in the Northern hemisphere. The observational facilities include a 1.5- m and 0.6-m classic Cassegrain reflectors, and 0.31-m remotely controllable telescope . The 1.5 m telescope is currently equipped with a long-slit Cassegrain spectrograph used for stellar characterisation. Historically, the objects of interest have been massive stars but we are now developing new research direction and expanding the list of targets to exoplanet- and disk-hosting stars. We have started evaluating our capabilities to characterise host stars spectroscopically to determine their parameters and composition. In 2020, we carried out a pilot study of a TESS candidate planet host, which we found to have a rare, strong chemical peculiarity [1]. This also allowed us to prepare our tools, workflow, and end-to-end analysis. We are also contributing to the European Space Agency Ariel space mission by offering stellar activity monitoring. The 0.6-m and 0.31-m telescopes are utilised for photometric measurements and the 0.31-m one in particular has been a workhorse for exoplanet transit monitoring. Since 2020, we have made significant preparations to develop and prove our transit observation capabilities: we have observed more than 70 transit light curves. About half of them have been submitted to ExoClock to contribute to Ariel mission planning. Concerning future upgrades, Tartu Observatory will have new instruments by the middle of 2023. The upgrades include procuring a medium resolution echelle spectrograph (projected bandwidth 390 nm to 750 nm, R= 25 000) and new photometer (Johnson-Cousins BVRI and SDSS filters) for the 1.5-m telescope, which will not only enhance our capabilities in both spectroscopic and photometric data retrieval of host stars. In addition, a new remote control system of the telescope will be installed and improvements on instrumentation for the 0.6-m and 0.31-m photometric telescopes will be made. This presentation will give an overview of our facilities, and of current and future spectroscopic and photometric capabilities. References: * “A rare phosphorus-rich star in an eclipsing binary from TESS”, Colin P. et al., A&A 658 A105 (2022), DOI: 10.1051/0004-6361/202142124

Context: Few exoplanets around hot stars with radiative envelopes have been discovered, although new observations from the TESS mission are improving this. Stars with radiative envelopes have little mixing at their surface, and thus their surface abundances provide a sensitive test case for a variety of processes including potentially star-planet interactions. Atomic diffusion is particularly important in these envelopes, producing chemically peculiar objects such as Am and HgMn stars. Aims: An exoplanet candidate around the B6 star HD 235349 was identified by TESS. Here we determine the nature of this transiting object and identify possible chemical peculiarities in the star. Methods: HD 235349 was observed using the long-slit spectrograph at Tartu Observatory, as well as photometrically by the TESS mission. The spectra were modeled to determine stellar parameters and chemical abundances. The photometric light curve was then analyzed in the context of the stellar parameters to determine properties of the transiting object. Results: We find the transiting object is a low-mass stellar companion, not a planet. However, the primary of this eclipsing binary is a rare type of chemically peculiar star. A strong overabundance of P is found with overabundances of Ne and Nd, and mild overabundances of Ti and Mn, while He is mildly underabundant. There is also clear evidence for vertical stratification of P in the atmosphere of the star. The lack of Hg and weak Mn overabundance suggests that this is not a typical HgMn star. It may be in the class of helium-weak phosphorus-gallium (He-weak PGa) stars, or an intermediate between these two classes. Conclusions: We show that HD 235349 is a rare type of chemically peculiar star (He-weak PGa) in an eclipsing binary system with a low-mass stellar companion. This appears to be the first He-weak PGa star discovered in an eclipsing binary.

Ariel, the Atmospheric Remote-sensing Infrared Exoplanet Large-survey, was adopted as the fourth medium-class mission in ESA's Cosmic Vision programme to be launched in 2029. During its 4-year mission, Ariel will study what exoplanets are made of, how they formed and how they evolve, by surveying a diverse sample of about 1000 extrasolar planets, simultaneously in visible and infrared wavelengths. It is the first mission dedicated to measuring the chemical composition and thermal structures of hundreds of transiting exoplanets, enabling planetary science far beyond the boundaries of the Solar System. The payload consists of an off-axis Cassegrain telescope (primary mirror 1100 mm x 730 mm ellipse) and two separate instruments (FGS and AIRS) covering simultaneously 0.5-7.8 micron spectral range. The satellite is best placed into an L2 orbit to maximise the thermal stability and the field of regard. The payload module is passively cooled via a series of V-Groove radiators; the detectors for the AIRS are the only items that require active cooling via an active Ne JT cooler. The Ariel payload is developed by a consortium of more than 50 institutes from 16 ESA countries, which include the UK, France, Italy, Belgium, Poland, Spain, Austria, Denmark, Ireland, Portugal, Czech Republic, Hungary, the Netherlands, Sweden, Norway, Estonia, and a NASA contribution.

Spectroscopic monitoring of the yellow hypergiant $ρ$ Cas revealed a new outburst in 2013, which is obvious from the development of TiO bands in the spectra. Also many atmospheric lines characteristic for a later spectral type appear. This spectroscopic outburst is in agreement with the photometric light curve, which displays a drop by about 0.6 mag during the same period.

In the present paper we analyze the anomalies in the atmospheres of HgMn stars. The abundance anomalies include both overabundances and underabundances of heavy elements. Recent observations show strongly anomalous isotopic composition of Hg, Pt, Tl and of He. Generation of abundance anomalies in quiescent atmospheres of CP stars is successfully explained by the mechanism of diffusional segregation of elements due to oppositing gravitational and radiative forces, but the formation of isotopic anomalies is not yet well explained. New diffusion mechanism called light-induced drift (LID), added to the one of radiative acceleration, successfully explains the observed isotopic anomalies. We have refined the theory of LID and applied it to CP star atmospheres. The results of computations confirm the important role of LID for diffusive segregation of isotopes.

B[e] Supergiants are a phase in the evolution of some massive stars for which we have observational evidence but no predictions by any stellar evolution model. The mass-loss during this phase creates a complex circumstellar environment with atomic, molecular, and dust regions usually found in rings or disk-like structures. However, the detailed structure and the formation of the circumstellar environment are not well-understood, requiring further investigation. To address that we initiated an observing campaign to obtain a homogeneous set of high-resolution spectra in both the optical and NIR (using MPG-ESO/FEROS, GEMINI/Phoenix and VLT/CRIRES, respectively). We monitor a number of Galactic B[e] Supergiants, for which we examined the [OI] and [CaII] emission lines and the bandheads of the CO and SiO molecules to probe the structure and the kinematics of their formation regions. We find that the emission from each tracer forms either in a single or in multiple equatorial rings.