Enabling planetary science across light-years. Ariel Definition Study Report

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

Elavhõbeda isotoopide lahknemiskulg keemiliselt pekuliaarsete tähtede atmosfäärides

Chemically peculiar (CP) stars are hot main-sequence stars with distinctly abnormal abundances of several elements. In addition to the element abundance anomalies, peculiar isotopic mixtures of several elements (e.g. He, Li, Hg, Pt) have been observed in many CP stars. According to the general opinion the anomalous abundances form in atmospheres of the stars, while the bulk composition of the entire star is normal. Mechanism responsible for generation of these peculiarities is radiative-driven atomic diffusion. The diffusion theory provides reliable explanation for observed abundance inhomogeneities in CP stars, but isotopic anomalies cannot be explained by radiative-driven diffusion alone. Radiation pressure is almost the same for all isotopes of an element and thus cannot cause isotope separation. However, additional effect called light-induced drift (LID) appears when radiation is absorbed in the spectral line. Magnitude and direction of LID depend on the asymmetry of the spectral line profile. This effect was discovered about 30 years ago in laser experiments and noted to be effective for isotope separation in laboratory conditions. The main objective of the present thesis is to evaluate phenomenon of light-induced drift as possible mechanism of diffusive separation of isotopes in atmospheres of CP stars. Analytical formulae, describing LID in quiescent stellar atmospheres have been derived. Software has been composed for computation of evolutionary scenarios of isotope separation due to gravity, radiative pressure and LID. Atomic and spectral data for model computations have been collected and capacious model computations have been carried out. Obtained results confirm important role of the LID in triggering and generating diffusional separation of mercury isotopes in the quiescent atmospheres of chemically peculiar stars.Keemiliselt pekuliaarsed (CP) tähed on kuumad peajada tähed paljude keemiliste elementide ebatavalise sisaldusega. Esineb nii mitmesuguste keemiliste elementide defitsiiti kui ka liiasust võrreldes Päikese koostisega. Lisaks sisalduse anomaaliatele on vaatlustest leitud ka mitmete elementide (nt He, Li, Hg, Pt) isotoopkoostise anomaaliad. Üldlevinud arvamuse kohaselt tekivad anomaalsed sisaldused täheatmosfääris, samas kui kogu tähe keemiline koostis jääb tavaliseks. Tekkemehhanismiks on atomaarne difusioon, mille kulgu määrab atmosfääri läbiva kiirguse ja gravitatsiooni koosmõju. Üldiselt pakub difusiooniteooria rahuldavat seletust mitmekesistele keemiliste elementide sisalduse anomaaliatele, kuid olulisi raskusi tekib isotoopkoostise anomaaliate seletamisega. Kiirgusrõhk mõjub keemilise elemendi erinevatele isotoopidele peaaegu ühtemoodi ja seega ei saa põhjustada isotoopide lahknemist. Kuid kiirguse neeldumisel spektrijoones tekib lisaks tavalisele kiirgusrõhule ka valgusindutseeritud triiv (LID), mille suund ja suurus sõltub spektrijoone profiili asümmeetriast. See efekt avastati umbes 30 aastat tagasi laserieksperimentides ja juba siis täheldati, et LID on eriti efektiivne isotoopide eraldamiseks. Valgusindutseeritud triivi rolli selgitamine elavhõbeda isotoopide difusioonilisel lahknemisel CP tähtede atmosfäärides ongi käesoleva väitekirja peaeesmärk. Selleks on tuletatud analüütilised valemid, mis kirjeldavad valgusindutseeritud triivi CP tähtede atmosfääridele vastavates füüsikalistes tingimustes; on koostatud tarkvara, mis võimaldavab modelleerida isotoopide lahknemiskulgu raskusjõu, kiirgusrõhu ja LIDi koosmõjul; on kogutud arvutusteks vajalikud atomaar- ja spektraalandmed ning läbi viidud ulatuslikud mudelarvutused. Töö tulemusena on kindlaks tehtud valgusindutseeritud triivi oluline roll elavhõbeda isotoopide separeerumisel CP tähtede atmosfäärides

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 the 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: Enabling planetary science across light-years

Ariel Definition Study ReportAriel Definition Study Report, 147 pages. Reviewed by ESA Science Advisory Structure in November 2020. Original document available at: https://www.cosmos.esa.int/documents/1783156/3267291/Ariel_RedBook_Nov2020.pdf/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

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