arXiv subjects

Anna Aret

Publications and source records attributed to Anna Aret.

14 recordsLinked to original sources

arXiv2026

The refractory fraction of phosphorus in planet-forming discs

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 % within 95th percentile of the posterior distribution. Conclusions. Consistent with a previous finding in the HD 100546 system, we conclude most of the P in the inner protoplanetary disc is locked in dust, likely in refractory minerals like schreibersite or apatite. Our result, combined with the low cosmic abundance of P, is also consistent with the lack of infrared and mm-wavelength observations of P-bearing molecules in protoplanetary discs to date.

astro-ph.EP↗

arXiv2026

The Tartu Observatory Fiber-fed Echelle Spectrograph (TOFES) Data Reduction Pipeline

We introduce the data reduction pipeline for the Tartu Observatory Fiber-fed Echelle Spectrograph (TOFES). TOFES is installed in the Coud\'e 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.

astro-ph.IM↗

arXiv2026

Detectability of deuterium in spectra of early-type stars

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 7 500 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 10 000 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.

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arXiv2025

Abundance analysis of stars hosting gas-rich debris disks

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.

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arXiv2021

A rare phosphorus-rich star in an eclipsing binary from TESS

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.

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arXiv2021

Ariel: Enabling planetary science across light-years

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.

astro-ph.IM↗

arXiv2018

A new outburst of the yellow hypergiant star Rho Cas

Yellow hypergiants are evolved massive stars that were suggested to be in post-red supergiant stage. Post-red supergiants that evolve back to the blue, hot side of the Hertzsprung-Russell diagram can intersect a temperature domain in which their atmospheres become unstable against pulsations (the Yellow Void or Yellow Wall), and the stars can experience outbursts with short, but violent mass eruptions. The yellow hypergiant Rho Cas is famous for its historical and recent outbursts, during which the star develops a cool, optically thick wind with a very brief but high mass-loss rate, causing a sudden drop in the light curve. Here we report on a new outburst of Rho Cas which occurred in 2013, accompanied by a temperature decrease of ~3000 K and a brightness drop of 0.6 mag. During the outburst TiO bands appear, together with many low excitation metallic atmospheric lines characteristic for a later spectral type. With this new outburst, it appears that the time interval between individual events decreases, which might indicate that Rho Cas is preparing for a major eruption that could help the star to pass through the Yellow Void. We also analysed the emission features that appear during phases of maximum brightness and find that they vary synchronous with the emission in the prominent [CaII] lines. We conclude that the occasionally detected emission in the spectra of Rho Cas, as well as certain asymmetries seen in the absorption lines of low to medium-excitation potential, are circumstellar in nature, and we discuss the possible origin of this material.

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arXiv2016

The yellow hypergiant - B[e] supergiant connection

B[e] supergiants and yellow hypergiants share a number of common properties regarding their circumstellar environments. Using the forbidden [O I] and [Ca II] lines as disk tracers, we suggest the presence of a Keplerian disk or ring around the yellow hypergiant V509 Cas and confirm the pole-on inner disk around V1302 Aql. These findings indicate a change in mass-loss behavior from spherical in cooler yellow hypergiants to axisymmetric in the hotter ones during the passage through the Yellow Void. The accumulation of material in the equatorial plane reminds of the disks of B[e] supergiants, supporting the suggestion that yellow hypergiants might appear as B[e] supergiants after they reach the blue edge of the yellow instability domain.

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arXiv2016

Similarities in the structure of the circumstellar environments of B[e] supergiants and yellow hypergiants

Yellow Hypergiants (YHGs) and B[e] supergiants (B[e]SGs), though in different phases in their evolution, display many features in common. This is partly due to the fact that both types of objects undergo strong, often asymmetric mass loss, and the ejected material accumulates in shells, rings, or disk-like structures, giving rise to emission from warm molecules and dust. We performed an optical spectroscopic survey of northern Galactic emission-line stars aimed at identifying tracers for the structure and kinematics of circumstellar environments. We identified two sets of lines, [O I] and [Ca II], which originate from the discs of B[e]SGs. The same set of lines is observed in V1302 Aql and V509 Cas, which are both hot YHGs. While V1302 Aql is known to have a disc-like structure, the kinematical broadening of the lines in V509 Cas suggest a Keplerian disk or ring around this star alike their hotter B[e]SG counterparts.

astro-ph.SR↗

arXiv2016

A new outburst of the yellow hypergiant star $ρ$ Cas

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.

astro-ph.SR↗

arXiv2015

Spectroscopic survey of emission-line stars. I. B[e] stars

Emission-line stars are typically surrounded by dense circumstellar material, often in form of rings or disc-like structures. Line emission from forbidden transitions trace a diversity of density and temperature regimes. Of particular interest are the forbidden lines of [O I] λλ6300, 6364 and [Ca II] λλ7291, 7324. They arise in complementary, high-density environments, such as the inner-disc regions around B[e] supergiants. To study physical conditions traced by these lines and to investigate how common they are, we initiated a survey of emission-line stars. Here, we focus on a sample of nine B[e] stars in different evolutionary phases. Emission of the [O I] lines is one of the characteristics of B[e] stars. We find that four of the objects display [Ca II] line emission: for the B[e] supergiants V1478 Cyg and 3 Pup the kinematics obtained from the [O I] and [Ca II] line profiles agrees with a Keplerian rotating disc scenario; the forbidden lines of the compact planetary nebula OY Gem display no kinematical broadening beyond spectral resolution; the LBV candidate V1429 Aql shows no [O I] lines, but the profile of its [Ca II] lines suggests that the emission originates in its hot, ionized circumbinary disc. As none of the B[e] stars of lower mass displays [Ca II] line emission, we conclude that these lines are more likely observable in massive stars with dense discs, supporting and strengthening the suggestion that their appearance requires high-density environments.

astro-ph.SR↗

arXiv2015

Forbidden calcium lines as disc tracers

Forbidden emission lines are particularly valuable disc tracers, because their profiles reflect the kinematics within their formation region. Here we present a short excerpt from the results of a spectroscopic survey of evolved massive stars surrounded by high-density discs.

astro-ph.SR↗

arXiv2013

SMART - a computer program for modelling stellar atmospheres

Program SMART (Spectra and Model Atmospheres by Radiative Transfer) has been composed for modelling atmospheres and spectra of hot stars (O, B and A spectral classes) and studying different physical processes in them (Sapar & Poolamäe 2003, Sapar et al. 2007). Line-blanketed models are computed assuming plane-parallel, static and horizontally homogeneous atmosphere in radiative, hydrostatic and local thermodynamic equilibrium. Main advantages of SMART are its shortness, simplicity, user friendliness and flexibility for study of different physical processes. SMART successfully runs on PC both under Windows and Linux.

astro-ph.SR↗

arXiv2012

Molecular emission from GG Car's circumbinary disk

The appearance of the B[e] phenomenon in evolved massive stars such as B[e] supergiants is still a mystery. While these stars are generally found to have disks that are cool and dense enough for efficient molecule and dust condensation, the origin of the disk material is still unclear. We aim at studying the kinematics and origin of the disk in the eccentric binary system GG Car, whose primary component is proposed to be a B[e] supergiant. Based on medium- and high-resolution near-infrared spectra we analyzed the CO-band emission detected from GG Car. The complete CO-band structure delivers information on the density and temperature of the emitting region, and the detectable 13CO bands allow us to constrain the evolutionary phase. In addition, the kinematics of the CO gas can be extracted from the shape of the first 12CO band head. We find that the CO gas is located in a ring surrounding the eccentric binary system, and its kinematics agrees with Keplerian rotation with a velocity, projected to the line of sight, of (80\pm 1) km/s. The CO ring has a column density of (5\pm 3)x10^21 cm^-2 and a temperature of 3200\pm 500 K. In addition, the material is chemically enriched in 13CO, which agrees with the primary component being slightly evolved off the main sequence. We discuss two possible scenarios for the origin of the circumbinary disk: (i) non-conservative Roche lobe overflow, and (ii) the possibility that the progenitor of the primary component could have been a classical Be star. Neither can be firmly excluded, but for Roche lobe overflow to occur, a combination of stellar and orbital parameter extremawould be required.

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