EXOA9
Session assets
Orals: Fri, 23 Sep | Room Albéniz+Machuca
Super-Neptunes straddle between ice and gas giants, with masses between that of Neptune and Saturn, and their study can contribute to a better understanding of exoplanetary systems' formation and evolution. Here we present a new transiting super-Neptune discovered by the WASP-South [1] transit survey, WASP-193b (K. Barkaoui et al. Submitted in Nature Astronomy). Photometric follow-up was performed by the TRAPPIST-South [2] and SPECULOOS-South telescopes [3] (right panel in Fig. 1) and spectroscopic measurements were collected by the HARPS [4] and CORALIE [5] spectrographs (bottom left in Fig. 1). We performed a joint analysis of the light curves and radial velocity time series using the MCMC [6] algorithm to constrain the system's physical properties. WASP-193b completes an orbit around its F9V-type host star every 6.25d. Its mass is 0.14 ± 0.03MJupiter (i.e. 2.6 MNeptune) and its radius is 1.46 ± 0.06 RJupiter, which translates into an ultra-low density of 0.060 ± 0.014 g cm-3 (Fig. 2).
Its huge radius cannot be reproduced by standard models of irradiated gas giants [7], even when assuming a coreless structure. A mechanism of energy deposit into its interior (e.g. Ohmic dissipation or tidal heating) has to be advocated to explain its bloated state. Its high equilibrium temperature (Teq = 1254 ± 31 K), combined with its super-low density and the infrared brightness (Jmagnitude = 10.95) of its host star, make WASP-193b an exquisite target for a thorough atmospheric characterization with HST and JWST. The measurement of its orbital obliquity could also inform us of its dynamical history [9], shedding light on its energy budget evolution.
Fig. 1: Top left panel: Detrended discovery light-curve of WASP-193 obtained with WASP-South (gray points: unbinned and black points: bin width = 30min), period-folded using the orbital period deduced from our data analysis. Right panel: Follow-up transit photometry of WASP-193b. Four transits observed by TRAPPIST-South and one by SPECULOOS-South, period-folded using the best-fitting transit ephemeris deduced from our global MCMC analysis. Each individual transit light curve has been corrected by the baseline model. The coloured points are data binned to 7.2min and the best-fitting model is superimposed in red. Right panels: Residuals from the fits for each transit light curve. Bottom left panel: RVs obtained with the CORALIE (blue) and HARPS (red) spectrographs for WASP-193 period-folded using the best-fitting orbital model is superimposed as a solid line (in m s-1).
| Parameter | Value | Unit |
| Stellar paramaters for WASP-193 | ||
| Mean density ρ* | 0.557 ± 0.049 | Solar density |
| Stellar mass M* | 1.059 ± 0.077 | Solar mass |
| Stellar radius R* | 1.239 ± 0.028 | Solar radius |
| Planetary paramters for WASP-193b | ||
| Planet/star area ratio (Rp/R*)2 | 1.411 ± 0.085 | % |
| Orbital period | 6.2463345 ± 0.0000003 | days |
| Scaled semi-major axis a/R* | 11.74 ± 0.35 | Solar radius |
| Orbital semi-major axis a | 0.0676 ± 0.0015 | AU |
| Orbital inclination ip | 88.49 ± 0.65 | deg |
| Eccentricity e | 0.056 ± 0.055 | |
| Planetary density ρp | 0.0587 ± 0.0140 | g cm-3 |
| Surface gravity log gp | 2.22 ± 0.10 | cgs |
| Planetary mass Mp | 0.139 ± 0.029 | Jupiter mass |
| Planetary radius Rp | 1.464 ± 0.058 | Jupiter radius |
| Equilibrium temperature Teq | 1254 ± 31 | K |
| Irradiation | (5.62 ± 0.54)x105 | W m-2 |
Table. 1: The WASP-193 system parameters derived from our global MCMC analysis (medians and 1σ limits of the marginalized posterior probability distributions).
Fig. 2: Mass--density diagram of known transiting exoplanets from NASA Archive of Exoplanets. The size of the points scales with the planetary radius. The points are coloured according to their Transmission Spectroscopy Metric (TSM, [9]). WASP-193b is shown with its corresponding error bars. We highlighted also least dense planets known to date are labelled: Kepler-51b, Kepler-51c, Kepler-51d [10] and HAT-P-67b [11]. Giant planets of the Solar System are also shown.
References
[1] Pollacco, D. L., et al. 2006, PASP, 118, 1407
[2] Gillon, M., et al. 2011, EPJ Web of Conferences, 11, 06002
[3] Jehin, E., et al. 2018, The Messenger, 174, 2
[4] Francesco, P., et al. 2000, Proc. SPIE Vol. 4008, p. 582-592
[5] Queloz, D., et al. 2000, Springer-Verlag, p. 548
[6] Gillon, M., et al. 2012, , 542, A4
[7] Fortney, J. J., et al. 2007, , 659, 1661
[8] Triaud, A. H. M. J., et al. 2010, , 524, A25
[9] Kempton, E. M. R., et al. 2018, PASP, 130, 114401
[10] Masuda, K. 2014, , 783, 53
[11] Zhou, G., et al. 2017, , 153, 211
How to cite: Barkaoui, K., Pozuelos, F. J., Gillon, M., Coel, H., and teams, W. T. S. H. A. C.: WASP-193b: An extremely low-density super-Neptune, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-709, https://doi.org/10.5194/epsc2022-709, 2022.
With the swift advance in exoplanet sciences it is now possible to characterize not only the fundamental parameters (mass and radius) of planets but also their interior structure and bulk composition. The former is known to influence on the habitability conditions of terrestrial planets, and the latter in itself is a key aspect to understand planet formation processes and the origin of their diversity.
In order to accurately assess planetary internal composition, the derivation of the chemical abundances of the host stars is of extreme importance. In particualr, stellar abundances of Fe, Si, Mg are proposed as principal constraints to reduce degeneracy in exoplanet interior structure models under assumption of identical composition of these elements in the rocky planets and their host stars.
This regularly used assumption is based on our knowledge that stars and planets form from the same primordial gas and dust cloud. It is also supported by our Solar System observations for which we know that the composition of major rock forming elements (such as Mg, Si, and Fe) in the meteorites and telluric planets (with the exception of Mercury) is similar to that of the Sun. However, direct observational evidence for the aforementioned assumption for exoplanets is absent.
By using the largest possible sample of precisely characterized low-mass planets and their host stars, we show that the composition of the planet building blocks indeed correlates with the properties of the rocky planets (see Fig. 1). We also find that on average the iron-mass fraction of planets is higher than that of the primordial values, owing to the disk-chemistry and planet formation processes. Additionally, we show that super-Earths and super-Mercuries appear to be distinct populations with differing compositions, implying differences in their formation processes. We suggest that giant impact alone is not responsible for the high-densities of super-Mercuries.
I propose an oral contribution to speak about these very recent results published in Scinece.
Fig. 1 The iron-mass fraction of the planets inferred from the planets' mass and radius as a function of the iron-mass fraction of the protoplanetary disk, estimated from the host star abundances. Super-Mercuries (in brown) and super-Earths (in blue) appear as two distinct groups.
How to cite: Adibekyan, V., Dorn, C., Sousa, S., Santos, N., Bitsch, B., Israelian, G., Mordasini, C., Barros, S., Delgado Mena, E., Demangeon, O., Faria, J., Figueira, P., Hakobyan, A., Osagh, M., Soares, B., Kunitomo, M., Takeda, Y., Jofré, E., Petrucc, R., and Martioli, E.: Diversity of terrestrial planets: a link to the chemical makeup of their host stars, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-74, https://doi.org/10.5194/epsc2022-74, 2022.
Even though our understanding of giant planet formation and evolution mechanisms has significantly improved over the past twenty years, the impact of the host star’s properties (mass, temperature, age, and metallicity) on the giant planet distribution remains to be thoroughly studied. The timescales and occurrences of the different planet formation scenarios have to be assessed, quantified, and compared. To that extent, detecting hot Jupiters and brown dwarfs orbiting hot stars is essential if we want to constrain giant planet and brown dwarf formation models across various stellar types and the impact of stellar mass (e.g., core-accretion models predict an increase in gas giant frequency with stellar mass). However, obtaining mass measurements of planets orbiting stars hotter than the Kraft break (6200 K) is inherently more difficult than for Solar-type stars. These stars have thin convective envelopes and do not efficiently generate magnetic winds. As a result, they remain rapidly rotating and due to their high temperature they exhibit fewer spectral lines. Their high rotation velocities lead to a substantial broadening of their observed spectral lines, making RV measurements of hot stars difficult. In addition, stellar activity and pulsations can induce RV variations that can mask or even mimic the RV signature of orbiting exoplanets. In particular, only 20% (99 exoplanets) of transiting exoplanets with precise densities have been detected to orbit AF-type stars with Teff > 6200 K (< F8V). Figure 1 summarizes the scarcity of planets detected around host stars with different stellar types. The vertical line at 6200 K indicates the Kraft break where stars retain their high rotational velocities.
We began a radial velocity follow-up survey in January 2021 with the CORALIE spectrograph to obtain mass measurements (and thus densities) of TESS (Transiting Exoplanet Survey Satellite) Objects of Interest (TOIs). The sample consists of 350 TESS giant planet candidates (R > 7 R⊕) brighter than V = 12 mag. We obtain precise radial velocities with the cross-correlation function (CCF) technique using updated binary masks specifically for hot stars. In this sample we find ~40% are false positives (including stellar binaries), ~20% are planets, and ~4% are brown dwarfs with the remainder yet to be characterised (Figure 2). I will present the statistical findings of our survey and our new detections including three brown dwarf companions, TOI-629b, TOI-1982b, and TOI-2543b, and one massive planet, TOI-1107b (Psaridi et al. 2022, Figure 3). Both TOI-1107b and TOI-1982b present an anomalously inflated radius with respect to the age of these systems. TOI-629 is among the hottest stars with a known transiting brown dwarf. TOI-629b and TOI-1982b are among the most eccentric brown dwarfs. The massive planet and the three brown dwarfs add to the growing population of well-characterized giant planets and brown dwarfs transiting AF-type stars and they reduce the apparent paucity.
Furthermore, we acquired 10 nights on the HARPS spectrograph during P108 to further characterise planet candidates in the Saturn regime transiting fast rotating stars with Teff > 6550 that require higher precision and efficiency. This program ended in the discovery of several planetary discoveries including TOI-615b, TOI-622b and TOI-2641b (Psaridi et al. in prep), three Saturn-mass planets orbiting stars above the Kraft break (Figure 4).
Figure 1: Number of known exoplanets with precise mass and radius measurements (σM/M ≤ 25% and σR/R ≤ 8%) as a function of stellar effective temperature. The black vertical line at 6200 K indicates the Kraft break.
Figure 2: Companion radius over stellar effective temperature Teff diagram for our TESS sample. The red circles display the confirmed false positives (including SB1, SB2, blends etc), the blue circles display the confirmed planets and the black circles diplay the confirmed brown dwarfs. The grey circles display TOIs that have not yet been solved. The size scales inversely with the period of the companion.
Figure 3: Companion mass over stellar effective temperature Teff diagram for massive planets (MP > 3 MJup) and transiting brown dwarfs shown in blue. The four new companions are shown in yellow. The red circles display confirmed companions detected by TESS. The size scales inversely with the period of the companion. The red, vertical line corresponds to the Kraft break (6200 K) while the horizontal lines correspond to the approximate boundaries of the brown dwarf regime (13 MJup) and the transition to high-mass brown dwarfs (42.5 MJup). Figure from Psaridi et al. 2022.
Figure 4: RVs from CORALIE (black) and HARPS (orange) with Keplerian model showing the detection of three Saturn-mass planets transiting F-type stars. The errobar in blue displays the photon noise and in red the photon noise plus the stellar jitter.
How to cite: Psaridi, A., Bouchy, F., Lendl, M., and Grieves, N.: Exploring the densities of planets and brown dwarfs transiting hot stars above the Kraft break, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-643, https://doi.org/10.5194/epsc2022-643, 2022.
Our Galaxy is composed of different stellar populations which are characterized by different chemical abundances. They are thought to imprint the composition of small bodies formed together with planets : planet building blocks (PBB), asteroids and interstellar objects.
We investigated the expected PBB composition in different Galactic regions using the ground-based spectroscopic surveys GALAH and APOGEE ; and the stoichiometric condensation model from Bitsch & Battistini (2020). This study has revealed the potential link between the PBB composition and the stellar populations across the Galaxy (Cabral et al, submitted).
Interestingly, the PBB compositions determined from large observational surveys reveal common trends determined previously with synthetic models. We confirm the PBB composition valley separating the thin disk stars from the thick disk stars (i.e. a bimodal distribution of compositions) already highlighted in our previous study (Cabral et al. 2019) using the Besançon stellar population synthesis model of the Milky Way.
Moreover, we find that metal-poor stars both in the thin and thick disks should host water-rich PBB. Given the importance of water abundance in planet formation simulations (Morbidelli et al. 2015, Ros et al. 2013, 2019), we discuss in a galactic context the potential impact for the early phases of planet formation.
Overall we find that the chemical abundances of host stars should impact the composition of exoplanets, as well as small body populations found around these stars. Our results imply that thick disk stars (which are rather alpha-rich, metal-poor stars) are suitable hosts for ice-rich small bodies (cf. Figure). Whether thick disk stars are suitable for water worlds or/and hycean planets (Madhusudhan et al. 2021) remains matter of debate.
How to cite: Cabral, N., Guilbert-Lepoutre, A., Bitsch, B., and Lagarde, N.: How does the origin of stars in the Milky Way affects the composition of planet building blocks?, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-894, https://doi.org/10.5194/epsc2022-894, 2022.
Posters: Thu, 22 Sep, 18:45–20:15 | Poster area Level 2
Evolved stars are excellent targets for precision radial velocity studies for three main reasons: i) they are cooler and rotate slower than their former main-sequence progenitor, which allows us to achieve a radial velocity precision at the m/s level for intermediate-mass stars, ii) we can study the dynamical evolution of planetary orbits due to the interaction with the expanding stellar envelope, and iii) they are significantly brighter than main sequence stars at a similar distance, allowing high SNRs to be acquired in an efficient manner.
Since 2009, we have been conducting a radial velocity survey called EXPRESS (EXoPlanets aRound Evolved StarS) aimed at detecting giant planets and studying the correlation between their orbital parameters and the host star properties (mass, metallicity, age) and to investigate whether planets can survive the stellar evolution after the main-sequence. For this, we have obtained thousands of individual radial velocities epochs over the course of 13 years, for a sample of 166 bright giant stars, resulting in the detection of ~30 planetary systems, including multi-planet systems, brown dwarfs in the desert, a gas giant in a compact binary system, among others. Figure 1 shows the orbital period versus host star mass, for planets detected among the EXPRESS sample. In addition, we have detected more than 20 stellar binary companions, resolved with RVs, astrometry and high-contrast direct imaging observations. Moreover, we have recently combined our data with those obtained by the PPPS and the Lick Surveys. Among our results we highlight:
1) Giant planets are more frequent around metal-rich giant stars.
2) The fraction of giant planets increases with the stellar mass, up to a maximum at ~1.7 Msun. Beyond ~3.0 Msun, no planets are found.
3) A surprisingly high fraction of giant planets around low-luminosity RGB stars of 39.4 +/- 8.0%.
4) An overall higher fraction of giant planet around RGB stars (f~14%) compared to post-RGB Horizontal-branch stars (f ~ 7%).
In this talk I will describe our project, including observations, data reduction, planet detections and the results in collaboration with the PPPS and the Lick Survey.
Finally, I will discuss our findings in the context of planetary formation and evolution, particularly after the main-sequence.
Figure 1: Orbital period versus stellar mass for EXPRESS planets. The symbol size is proportional to the minimum planet mass (Mp sini). Planets in multiple systems are connected by a dashed line. The red and blue dots correspond to RGB and HB host stars, respectively.
How to cite: Jones, M. and Jenkins, J.: Giants around giants: 13 year observations of the EXPRESS RV program, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-63, https://doi.org/10.5194/epsc2022-63, 2022.
With a sample of 5000 objects at hand, exoplanet demographics is beginning to grasp key aspects of the physical mechanisms lurking beneath the multifaceted hues of the observed exoplanetary architectures. Ascertaining the dependence of planetary properties on stellar mass, and whether their very formation is possible even within the short-lived protoplanetary disks surrounding massive stars, compulsorily requires a complete and unbiased census of the exoplanet population. However, most exoplanet surveys have so far focused on stars not larger than the Sun, and 90% of known exoplanets are closer to their star than the Earth is to the Sun. This strong observational bias, connected to the preference of transits and radial velocities for close-in planets and low-mass stars, has recently started being alleviated by direct imaging, a technique that is instead preferentially sensitive to young giant planets in wide orbits. Radial velocity studies have found that the occurrence of giant planets is higher around more massive stars up to about 2 M_sun; an abrupt turnover is then observed, with the occurrence eventually falling to zero at M>3 M_sun. To clarify if this trend is real, or if a wide-orbit population of giant planets is escaping detection, we have started the B-star exoplanet abundance study (BEAST), a direct-imaging study based on the high-contrast capabilities of SPHERE@VLT. BEAST is looking for exoplanets around 85 B stars belonging to the young (5-30 Myr) Scorpius-Centaurus association. While the survey is still in progress, its early results -that I will show here- are already intriguing: even binary systems such as b Centauri (Janson et al. 2021), or stars doomed to explode as supernovae such as μ2 Scorpii (Squicciarini et al. 2022), can possess their planetary systems, challenging the predictions of conventional formation models.
How to cite: Squicciarini, V.: The B-star exoplanet abundance study (BEAST): at the frontier of planet formation, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-158, https://doi.org/10.5194/epsc2022-158, 2022.
A central question in exoplanetary research is the characterisation of the composition and internal structure of exoplanets. However, the observable parameters of an exoplanet are scarce and generally limited to the planet’s mass and radius and the properties of its host star. This means that it is not possible to fully constrain the internal structure parameters of an exoplanet, such as the iron core mass fraction, the presence of a water layer or the amount of gas, from these observations: The problem is intrinsically degenerate [1,2].
To overcome this difficulty, a Bayesian inference scheme is used, which is an inverse method based on Bayes’ theorem. It updates the previously assumed probability of the internal structure parameters (the prior) based on the probability of the observation given the same parameters (the likelihood), returning the posterior distribution of these parameters.
In our case, the likelihood is determined based on an internal structure model, which calculates the radius of a planet with a given mass and composition based on the planetary structure equations as described in [6]. This calculated radius and the transit depth it implies are then compared to the observed transit depth of the real planet. For the internal structure model, we use the BICEPS code as described in [4] and based on [2,3] to model the core, mantle and water layers of the planet; the atmosphere is modelled separately according to [5]. For the composition, we assume that the planetary composition matches the one of the star exactly [7].
We developed a full grid approach that has multiple advantages over the traditionally used scheme based on Markov chain Monte Carlo methods. To compensate for the higher number of sampling points that such a brute force approach requires, we trained a deep neural network to replace the internal structure model, which significantly reduces the computation time of the model. Additionally, we take into account that the measured masses and radii of the planets in the same system are correlated, since they were measured relative to the same star. This allows for an increase in computation time that is only linear when adding an additional planet. The full approach including the internal structure model is described in more detail in [8].
This method has already been used to characterise the internal structure of various exoplanets observed by the CHEOPS mission, e.g. [8] and [9] (and more submitted). As an example, Figures 1 – 4 show the internal structure of TOI-561 b, c, d and e, calculated using the planetary and stellar parameters published in [9]. Note that the corresponding figures in [9] showing the posteriors of the internal structure parameters unfortunately do not use the published stellar parameters, see [10] for more details.
Figure 1. Posterior distribution of the most important internal structure parameters of TOI-561 b using the planetary and stellar parameters published in [9]. The shown parameters are the core and water mass fractions of the solid planet, the molar fractions of Si and Mg in the mantle and Fe in the core and the gas mass of the planet in Earth masses in a logarithmic scale. The dashed lines show the 5 and 95% quantiles, while in the titles the median and the 5 and 95% quantiles are shown.
Figure 2. Same as Figure 1 but for planet TOI-561 c.