arXiv subjects

C. Danielski

Publications and source records attributed to C. Danielski.

At least 19 recordsLinked to original sources

arXiv2026

Ariel stellar characterisation IV. Fundamental parameters of 18 hot stars in the Ariel mission candidate sample

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 2029. 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 (\teff\ $\lesssim 7000\,$K) host stars among the Ariel target candidates. We present a uniform determination of fundamental stellar parameters for 18 hot stars in the Tier 1 candidate list of the Ariel mission candidate sample. We adopted an iterative spectro-trigonometric approach optimised for high-temperature stars. High-resolution spectra were analysed using the \textsc{zeeman} code with $\chi^2$ minimisation, combining model fits to metal and Balmer lines. Surface gravity was refined using photometry-based radii and masses from stellar evolutionary tracks. We derived effective temperatures, surface gravities, projected rotational velocities, microturbulent velocities, overall metallicities, 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. The derived parameters provide an internally consistent basis for studying the link between stellar properties and planetary characteristics in intermediate-mass stars. 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.

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arXiv2025

Spectropolarimetric characterisation of exoplanet host stars in preparation of the $Ariel$ mission II. The magnetised wind environment of TOI-1860, DS Tuc A, and HD 63433

We update the status of the spectropolarimetric campaign dedicated to characterise the magnetic field properties of a sample of known exoplanet-hosting stars included in the current target list of the $Ariel$ mission. We analysed spectropolarimetric data collected for 15 G-M type stars with Neo-Narval, HARPSpol, and SPIRou to assess the detectability of the large-scale magnetic field. For three stars we reconstructed the magnetic field topology and its temporal evolution via Zeeman-Doppler imaging (ZDI). Such reconstructions were then used to perform 3D MHD simulations of the stellar wind and environment impinging on the hosted exoplanets. We detected the magnetic field of six stars. Of these, we performed ZDI reconstructions for the first time of TOI-1860 and DS Tuc A, and for the second time of HD 63433, providing temporal information of its large-scale magnetic field. Consistently with previous results on young ($\rm\sim 50-100~Myr$) solar-like stars, the large-scale magnetic field is moderately strong (30-60 G on average) and complex, with a significant fraction of magnetic energy in the toroidal component and high-order poloidal components. We found the orbit of TOI-1860 b to be almost completely sub-Alfv\'enic, the orbits of DS Tuc A b and HD 63433 d to be trans-Alfv\'enic, and the orbits of HD 63433 b and c to be super-Alfv\'enic. We obtained marginal detections of the magnetic field for TOI-836 and TOI-2076, and detections for TOI-1136, but the number of observations is not sufficient for magnetic mapping. A magnetic star-planet connection can occur for most of TOI-1860 b's orbit. This can happen more sporadically for DS Tuc A b and HD 63433 c given the lower fraction of their orbit in the sub-Alfv\'enic regime. The orbit of HD 63433 c is nevertheless more sub-Alfv\'enic than previously simulated owing to the temporal evolution of the stellar magnetic field.

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arXiv2025

A JWST/MIRI view of k Andromedae b: Refining its mass, age, and physical parameters

Context. kAndb is a substellar companion near the planet-brown dwarf boundary, orbiting a B9IV star at 50-100 au. Estimates of its age and mass vary, fueling a decade-long debate. Atmospheric parameters (Teff 1650-2050 K, log(g) 3.5-5.5) remain poorly constrained due to model differences and heterogeneous datasets. Aims. We refine the characterization of kAndb using mid-infrared data to capture its bolometric emission. Combined with NIR measurements, we constrain Teff, log(g), and radius to reduce uncertainties in age and mass. Methods. We obtained JWST/MIRI coronagraphic data (F1065C, F1140C, F1550C) and recalibrated NIR photometry with an updated ATLAS stellar model. MIRI color-magnitude diagrams (CMDs) probe the likelihood of species (CH4, NH3, silicates). We compared H and F1140C colors and magnitudes to isochrones to constrain age and mass. We modeled the spectral energy distribution with atmosphere models to refine Teff, radius, and log(g), and to constrain age and mass using evolutionary models. Results. Cloudy atmosphere models fit best, consistent with the L0/L2 spectral type and position near silicate-atmosphere field objects in the MIRI CMD. We derived an age of 47+-7 Myr and mass of 17.3+-1.8 MJup by weighted-mean model combination. Modeling yielded Teff = 1791+-68 K and radius = 1.42+-0.06 RJup, improving precision by 30%. Log(g) = 4.35+-0.07 dex represents a 70% improvement over the previous best value (4.75+-0.25). Conclusions. The new mass places kAndb just above the deuterium-burning limit. The age is 75% more precise and consistent with the Columba association (42 Myr). The Teff suggests silicate clouds, requiring spectroscopic confirmation. MIRI data were crucial to refining radius and temperature, which led to stronger constraints on age and mass and improving the overall characterization of kAndb.

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arXiv2025

Shaping Galactic Habitability: the impact of stellar migration and gas giants

In exoplanet research, the focus is increasingly on identifying Earth analogs, planets similar in density and habitability potential. As the number of rocky exoplanets grows, parallel discussions have emerged on system architectures and Galactic environments that may support life, drawing comparisons to our own Earth. This has brought renewed attention to the concept of the Galactic Habitable Zone (GHZ) as a broader context for interpreting the diversity of planetary environments. This study is the first to use detailed chemical evolution models to investigate the impact of stellar migration, modeled through a parametric approach, on the GHZ. Our findings reveal that stellar migration significantly enhances the number of stars capable of hosting habitable planets in the outer Galactic regions, with an increase of up to a factor of five at 18 kpc relative to a baseline value of unity at 6 kpc. Furthermore, we explore a novel scenario where the presence of gas giant planets increases the probability for the formation of terrestrial ones. We find that this increased probability is higher in the inner Galactic disc, but is also mitigated by stellar migration. In particular, at the present time, the number of FGK stars hosting terrestrial planets with minimum habitability conditions in the ring centered at 4 kpc is approximately 1.4 times higher than in scenarios where gas giants are assumed to hinder the formation and evolution of Earth-like planets. Without stellar migration, this factor increases to 1.5. Even larger ratios are predicted for terrestrial planets orbiting retired A stars, reaching 2.8 in models with stellar migration and 3.3 in models without it.

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arXiv2025

Ariel stellar characterisation III. Fast rotators and new FGK stars in the Ariel Mission Candidate Sample

The next mission dedicated to the study of planetary atmospheres is the Ariel space mission, planned for launch in 2029, which will observe a variety of planetary systems belonging to different classes around stars with spectral types from M to A. To optimise the scientific outcome of the mission, such stars need to be homogeneously characterised beforehand. In this work, we focus on a methodology based on spectral synthesis for the characterisation of FGK-type stars from the Ariel Tier 1 Mission Candidate Sample (MCS) which exhibit fast rotation. In addition, we analyse slow-rotating FGK-type stars, with either new observations or archival spectra available, consistently as in our previous work using the equivalent width (EW) analysis. To ensure consistency between our methods, we re-analysed a sample of FGK-type stars with the spectral synthesis method and compared it to our previous work. The results of our analysis show excellent agreement with the previous set of derived parameters. We also computed their orbital parameters establishing whether they belong to the Galactic thin or thick discs. With the current set of stellar parameters, we almost double the analysed hosts in the Ariel MCS to 353 stars in total. Using our homogeneous set of stellar parameters, we studied the correlations between stellar and planetary properties for the Ariel MCS analysed so far. We confirmed a close relationship between stellar mass (up to 1.8 solar masses) and giant planet radius, with more inflated planets at lower metallicity. We confirm that giant planets are more frequent around more metal-rich stars that belong to the thin disc, while lower-mass planets are also found in more metal-poor environments, and are more frequent than giant planets in the thick disc as also seen in other works in the literature.

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arXiv2024

Ariel stellar characterisation II. Chemical abundances of carbon, nitrogen, and oxygen for 181 planet-host FGK dwarf stars

One of the ultimate goals of the ESA Ariel space mission is to shed light on the formation pathways and evolution of planetary systems in the Solar neighbourhood. Such an endeavour is only possible by performing a large chemical survey of not only the planets, but also their host stars, inasmuch as stellar elemental abundances are the cipher key to decode the planetary compositional signatures. This work aims at providing homogeneous abundances of C, N, and O of a sample of 181 stars belonging to the Tier 1 of the Ariel Mission Candidate Sample. We applied the spectral synthesis and the equivalent width methods to a variety of atomic and molecular indicators (C I lines at 5052 and 5380.3 A, [O I] forbidden line at 6300.3 A, C_2 bands at 5128 and 5165 A, and CN band at 4215 A) using high-resolution and high S/N spectra collected with several spectrographs. We provide carbon abundances for 180 stars, nitrogen abundances for 105 stars, and oxygen abundances for 89 stars. We analyse the results in the light of the Galactic chemical evolution, and in terms of the planetary companions properties. Our sample basically follows the typical trends with metallicity expected for the [C/Fe], [N/Fe], and [O/Fe] abundance ratios. The fraction between C and O abundances, both yields of primary production, is consistent with a constant ratio as [O/H] increases, whereas the abundance of N tends to increase with the increasing of the O abundance, supporting the theoretical assumption of a secondary production of nitrogen. The [C/N], [C/O], and [N/O] ratios are also correlated with [Fe/H], which might introduce biases in the interpretation of the planetary compositions and formation histories if host stars of different metallicity are compared. We provide relations that can be used to qualitatively estimate whether the atmospheric composition of planets is enriched or not with respect to the host stars.

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arXiv2024

Spectropolarimetric characterisation of exoplanet host stars in preparation of the Ariel mission. Magnetic environment of HD 63433

The accurate characterisation of the stellar magnetism of planetary host stars has been gaining momentum, especially in the context of transmission spectroscopy investigations of exoplanets. Indeed, the magnetic field regulates the amount of energetic radiation and stellar wind impinging on planets, as well as the presence of inhomogeneities on the stellar surface that hinder the precise extraction of the planetary atmospheric absorption signal. We initiated a spectropolarimetric campaign to unveil the magnetic field properties of known exoplanet hosting stars included in the current list of potential Ariel targets. In this work, we focus on HD 63433, a young solar-like star hosting two sub-Neptunes and an Earth-sized planet. These exoplanets orbit within 0.15 au from the host star and have likely experienced different atmospheric evolutionary paths. We analysed optical spectropolarimetric data collected with ESPaDOnS, HARPSpol, and Neo-Narval to compute the magnetic activity indices (log R'_HK , H$α$, and Ca ii infrared triplet), measure the longitudinal magnetic field, and reconstruct the large-scale magnetic topology via Zeeman-Doppler imaging (ZDI). The magnetic field map was then employed to simulate the space environment in which the exoplanets orbit. The reconstructed stellar magnetic field has an average strength of 24 G and it features a complex topology with a dominant toroidal component, in agreement with other stars of a similar spectral type and age. Our simulations of the stellar environment locate 10% of the innermost planetary orbit inside the Alfvén surface and, thus, brief magnetic connections between the planet and the star can occur. The outer planets are outside the Alfvén surface and a bow shock between the stellar wind and the planetary magnetosphere could potentially form.

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arXiv2023

The quest for Magrathea planets I: formation of second generation exoplanets around double white dwarfs

The evolution of binaries that become double white dwarf (DWD) can cause the ejection of high amounts of dust and gas. Such material can give rise to circumbinary discs and become the cradle of new planets, yet no studies so far have focused on the formation of circumbinary planets around DWDs. These binaries will be the main sources of gravitational waves (GWs) detectable by the ESA Laser Interferometer Space Antenna (LISA) mission, opening the possibility to detect circumbinary planets around short-period DWDs everywhere in the Milky Way. We investigate the formation of Magrathea planets by simulating multiple planet formation tracks to explore how seeds growing first by pebble accretion, and then by gas accretion, are affected by the disc environments surrounding DWDs. We present both planetary formation tracks taking place in steady-state discs, and formation tracks taking place in discs evolving with time. The time-dependent tracks account for both the disc accretion rate onto the central binary and the disc photoevaporation rate caused by stellar irradiation. Our results show that planetary formation in circumbinary discs around DWDs can be possible. In particular, the extreme planetary formation environment implies three main significant results: (i) the accretion rate and the metallicity of the disc should be high in order to form sub-stellar objects with masses up to 31 M$_J$, this is achieved only if planet formation starts soon after the onset of the disc and if first generation seeds are present in the disc; (ii) seeds formed within 0.1 Myr, or within 1 Myr, from the onset of the disc can only produce sub-Neptune and Neptunian planets, unless the disc accommodates first generation seeds with mass 10 M$_{\oplus}$; (iii) most of the planets are finally located within 1 au from the disc centre, while they are still undergoing the gas accretion phase.

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arXiv2023

Characterisation of the upper atmospheres of HAT-P-32 b, WASP-69 b, GJ 1214 b, and WASP-76 b through their He I triplet absorption

Characterisation of atmospheres undergoing photo-evaporation is key to understanding the formation, evolution, and diversity of planets. However, only a few upper atmospheres that experience this kind of hydrodynamic escape have been characterised. Our aim is to characterise the upper atmospheres of the hot Jupiters HAT-P-32 b and WASP-69 b, the warm sub-Neptune GJ 1214 b, and the ultra-hot Jupiter WASP-76 b through high-resolution observations of their HeI triplet absorption. In addition, we also reanalyse the warm Neptune GJ 3470 b and the hot Jupiter HD 189733 b. We used a spherically symmetric 1D hydrodynamic model coupled with a non-local thermodynamic equilibrium model. Comparing synthetic absorption spectra with observations, we constrained the main parameters of the upper atmosphere of these planets and classify them according to their hydrodynamic regime. Our results show that HAT-P-32 b photo-evaporates at (130$\pm$70)$\times$10$^{11}$ gs$^{-1}$ with a hot (12 400$\pm$2900 K) upper atmosphere; WASP-69 b loses its atmosphere at (0.9$\pm$0.5)$\times$10$^{11}$ gs$^{-1}$ and 5250$\pm$750 K; and GJ 1214 b, with a relatively cold outflow of 3750$\pm$750 K, photo-evaporates at (1.3$\pm$1.1)$\times$10$^{11}$ gs$^{-1}$. For WASP-76 b, its weak absorption prevents us from constraining its temperature and mass-loss rate significantly; we obtained ranges of 6000-17 000\,K and 23.5$\pm$21.5$\times$10$^{11}$ gs$^{-1}$. Our reanalysis of GJ 3470 b yields colder temperatures, 3400$\pm$350 K, but practically the same mass-loss rate as in our previous results. Our reanalysis of HD 189733 b yields a slightly higher mass-loss rate, (1.4$\pm$0.5)$\times$10$^{11}$ gs$^{-1}$, and temperature, 12 700$\pm$900 K compared to previous estimates. Our results support that photo-evaporated outflows tend to be very light.

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arXiv2022

The CARMENES search for exoplanets around M dwarfs. Variability on long timescales as seen in chromospheric indicators

It is clearly established that the Sun has an 11-year cycle that is caused by its internal magnetic field. This cycle is also observed in a sample of M dwarfs. In the framework of exoplanet detection or atmospheric characterisation of exoplanets, the activity status of the host star plays a crucial role, and inactive states are preferable for such studies. This means that it is important to know the activity cycles of these stars. We study systematic long-term variability in a sample of 211 M dwarfs observed with CARMENES, the high-resolution optical and near-infrared spectrograph at Calar Alto Observatory. In an automatic search using time series of different activity indicators, we identified 26 stars with linear or quadratic trends or with potentially cyclic behaviour. Additionally, we performed an independent search in archival R$^{\prime}_{\rm HK}$ data collected from different instruments whose time baselines were usually much longer. These data are available for a subset of 186 of our sample stars. Our search revealed 22 cycle candidates in the data. We found that the percentage of stars showing long-term variations drops dramatically to the latest M dwarfs. Moreover, we found that the pseudo-equivalent width (pEW) of the H$α$ and Ca ii infrared triplet more often triggers automatic detections of long-term variations than the TiO index, differential line width, chromatic index, or radial velocity. This is in line with our comparison of the median relative amplitudes of the different indicators. For stars that trigger our automatic detection, this leads to the highest amplitude variation in R$^{\prime}_{\rm HK}$, followed by pEW(H$α$), pEW(Ca ii IRT), and the TiO index.

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arXiv2022

Ariel stellar characterisation: I -- homogeneous stellar parameters of 187 FGK planet host stars Description and validation of the method

In 2020 the European Space Agency selected Ariel as the next mission to join the space fleet of observatories to study planets outside our Solar System. Ariel will be devoted to the characterisation of a thousand planetary atmospheres, for understanding what exoplanets are made of, how they formed and how they evolve. To achieve the last two goals all planets need to be studied within the context of their own host stars, which in turn have to be analysed with the same technique, in a uniform way. We present the spectro-photometric method we have developed to infer the atmospheric parameters of the known host stars in the Tier 1 of the Ariel Reference Sample. Our method is based on an iterative approach, which combines spectral analysis, the determination of the surface gravity from {\em Gaia} data, and the determination of stellar masses from isochrone fitting. We validated our approach with the analysis of a control sample, composed by members of three open clusters with well-known ages and metallicities. We measured effective temperature, Teff, surface gravity, logg, and the metallicity, [Fe/H], of 187 F-G-K stars within the Ariel Reference Sample. We presented the general properties of the sample, including their kinematics which allows us to separate them between thin and thick disc populations. A homogeneous determination of the parameters of the host stars is fundamental in the study of the stars themselves and their planetary systems. Our analysis systematically improves agreement with theoretical models and decreases uncertainties in the mass estimate (from 0.21+/-0.30 to 0.10+/-0.02 M_sun), providing useful data for the Ariel consortium and the astronomical community at large.

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arXiv2021

The CARMENES search for exoplanets around M dwarfs. Diagnostic capabilities of strong K I lines for photosphere and chromosphere

There are several strong K I lines found in the spectra of M dwarfs, among them the doublet near 7700 AA and another doublet near 12 500 AA. We study these optical and near-infrared doublets in a sample of 324 M dwarfs, observed with CARMENES, the high-resolution optical and near-infrared spectrograph at Calar Alto, and investigate how well the lines can be used as photospheric and chromospheric diagnostics. Both doublets have a dominant photospheric component in inactive stars and can be used as tracers of effective temperature and gravity. For variability studies using the optical doublet, we concentrate on the red line component because this is less prone to artefacts from telluric correction in individual spectra. The optical doublet lines are sensitive to activity, especially for M dwarfs later than M5.0 V where the lines develop an emission core. For earlier type M dwarfs, the red component of the optical doublet lines is also correlated with H$α$ activity. We usually find positive correlation for stars with H$α$ in emission, while early-type M stars with H$α$ in absorption show anti-correlation. During flares, the optical doublet lines can exhibit strong fill-in or emission cores for our latest spectral types. On the other hand, the near-infrared doublet lines very rarely show correlation or anti-correlation to H$α$ and do not change line shape significantly even during the strongest observed flares. Nevertheless, the near-infrared doublet lines show notable resolved Zeeman splitting for about 20 active stars which allows to estimate the magnetic fields B.

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arXiv2021

A Jovian analogue orbiting a white dwarf star

Studies have shown that remnants of destroyed planets and debris-disk planetesimals can survive the volatile evolution of their host stars into white dwarfs, but detection of intact planetary bodies around white dwarfs are few. Simulations predict that planets in Jupiter-like orbits around stars of $\lt 8 M_\odot$ avoid being destroyed by the strong tidal forces of their stellar host, but as yet there has been no observational confirmation of such a survivor. Here we report on the non-detection of a main-sequence lens star in the microlensing event MOA-2010-BLG-477Lb using near-infrared observations from the Keck Observatory. We determine this system contains a $0.53\pm0.11$ solar mass white dwarf host orbited by a $1.4 \pm 0.3$ Jupiter mass planet with a separation on the plane of the sky of $2.8\pm 0.5$ AU, which implies a semi-major axis larger than this. This system is evidence that planets around white dwarfs can survive the giant and asymptotic giant phases of their host's evolution, and supports the prediction that over half of white dwarfs are predicted to have Jovian planetary companions. Located at approximately 2.0 kpc toward the center of our Galaxy, it likely represents an analog to the end stages of the Sun and Jupiter in our own Solar System.

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arXiv2021

The homogeneous characterisation of Ariel host stars

The Ariel mission will characterise the chemical and thermal properties of the atmospheres of about a thousand exoplanets transiting their host star(s). The observation of such a large sample of planets will allow to deepen our understanding of planetary and atmospheric formation at the early stages, providing a truly representative picture of the chemical nature of exoplanets, and relating this directly to the type and chemical environment of the host star. Hence, the accurate and precise determination of the host star fundamental properties is essential to Ariel for drawing a comprehensive picture of the underlying essence of these planetary systems. We present here a structured approach for the characterisation of Ariel stars that accounts for the concepts of homogeneity and coherence among a large set of stellar parameters. We present here the studies and benchmark analyses we have been performing to determine robust stellar fundamental parameters, elemental abundances, activity indices, and stellar ages. In particular, we present results for the homogeneous estimation of the activity indices S and log(R'HK), and preliminary results for elemental abundances of Na, Al, Mg, Si, C, N. In addition, we analyse the variation of a planetary spectrum, obtained with Ariel, as a function of the uncertainty on the stellar effective temperature. Finally, we present our observational campaign for precisely and homogeneously characterising all Ariel stars in order to perform a meaningful choice of final targets before the mission launch.

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arXiv2021

The Ariel 0.6 - 7.8 $μ$m stellar limb-darkening coefficients

We provide here tables of stellar limb-darkening coefficients (LDCs) for the Ariel ESA M4 space mission. These tables include LDCs corresponding to different wavelength bins and white bands for the NIRSpec, AIRS-Ch0 and AIRS-Ch1 spectrographs, and those corresponding to the VISPhot, FGS1 and FGS2 photometers. The LDCs are calculated with the open-source software ExoTETHyS for three complete grids of stellar atmosphere models obtained with the ATLAS9 and PHOENIX codes. The three model grids are complementary, as the PHOENIX code adopts more modern input physics and spherical geometry, while the models calculated with ATLAS9 cover wider ranges of stellar parameters. The LDCs obtained from corresponding models in the ATLAS9 and PHOENIX grids are compared in the main text. All together the models cover the following ranges in effective temperature ($1\,500 \, K \le T_{\mbox{eff}} \le 50\,000 \, K$), surface gravity (0.0 dex $\le \log{g} \le 6.0$ dex), and metallicity ($-5.0 \le [M/H] \le 1.0$).

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arXiv2021

Determination of stellar parameters for Ariel targets: a comparison analysis between different spectroscopic methods

Ariel has been selected as the next ESA M4 science mission and it is expected to be launched in 2028. During its 4-year mission, Ariel will observe the atmospheres of a large and diversified population of transiting exoplanets. A key factor for the achievement of the scientific goal of Ariel is the selection strategy for the definition of the input target list. A meaningful choice of the targets requires an accurate knowledge of the planet hosting star properties and this is necessary to be obtained well before the launch. In this work, we present the results of a bench-marking analysis between three different spectroscopic techniques used to determine stellar parameters for a selected number of targets belonging to the Ariel reference sample. We aim to consolidate a method that will be used to homogeneously determine the stellar parameters of the complete Ariel reference sample. Homogeneous, accurate and precise derivation of stellar parameters is crucial for characterizing exoplanet-host stars and in turn is a key factor for the accuracy of the planet properties.

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arXiv2018

Atmospheric characterization of directly imaged exoplanets with JWST/MIRI

The Mid-Infrared instrument (MIRI) on board the James Webb Space Telescope will perform the first ever characterization of young giant exoplanets observed by direct imaging in the 5-28 microns spectral range. This wavelength range is key for both determining the bolometric luminosity of the cool known exoplanets and for accessing the strongest ammonia bands. In conjunction with shorter wavelength observations, MIRI will enable a more accurate characterization of the exoplanetary atmospheric properties. Here we consider a subsample of the currently known exoplanets detected by direct imaging and we discuss their detectability with MIRI, either using the coronagraphic or the spectroscopic modes. By using the Exo-REM atmosphere model we calculate the mid-infrared emission spectra of fourteen exoplanets, and we simulate MIRI coronagraphic or spectroscopic observations. Specifically we analyze four coronagraphic observational setups, which depend on (i) the target-star and reference-star offset (0, 3, 14 mas), (ii) the wave-front-error (130, 204 nm rms), (iii) the telescope jitter amplitude (1.6, 7 mas). We then determine the signal-to-noise and integration time values for the coronagraphic targets whose planet-to-star contrasts range from 3.9 to 10.1 mag. We conclude that all the MIRI targets should be observable with different degrees of difficulty, which depends on the final in-flight instrument performances. Furthermore, we test for detection of ammonia in the atmosphere of the coolest targets. Finally, we present the case of HR 8799 b to discuss what MIRI observations can bring to the knowledge of a planetary atmosphere, either alone or in combination with shorter wavelength observations.

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arXiv2018

3D maps of interstellar dust in the Local Arm: using $Gaia$, 2MASS and APOGEE-DR14

Gaia data and stellar surveys open the way to the construction of detailed 3D maps of the Galactic interstellar (IS) dust based on the synthesis of star distances and extinctions. Reliable extinction measurements require very accurate photometric calibrations. We show the first step of an iterative process linking 3D dust maps and photometric calibrations and improving them simultaneously. Our previous 3D map of nearby IS dust was used to select low reddening SDSS/APOGEE-DR14 red giants, and this database served for an empirical effective temperature- and metallicity-dependent photometric calibration in the Gaia G and 2MASS Ks bands. This calibration has been combined with Gaia G-band empirical extinction coefficients recently published, G, J and Ks photometry and APOGEE atmospheric parameters to derive the extinction of a large fraction of the survey targets. Distances were estimated independently using isochrones and the magnitude-independent extinction K(J-Ks). This new dataset has been merged with the one used for the earlier version of dust map. A new Bayesian inversion of distance-extinction pairs has been performed to produce an updated 3D map. We present several properties of the new map. Its comparison with 2D dust emission reveals that all large dust shells seen in emission at mid- and high-latitude are closer than 300pc. The updated distribution constrains the well debated, X-ray bright North Polar Spur to originate beyond 800 pc. We use the Orion region to illustrate additional details and distant clouds. On the large scale the map reveals a complex structure of the Local Arm. 2 to 3 kpc-long chains of clouds appear in planes tilted by 15 deg with respect to the Galactic plane. A series of cavities oriented along a l=60-240deg axis crosses the Arm. (http://stilism.obspm.fr)

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