EXOA1
Hence, in this session, we aim to bring together recent results and studies performed by observers, modelers, and experimentalists, and a combination of them to open discussions about the pathways that the community needs to follow to understand the exoplanetary variety fully and promote and inspire the collaboration between teams with different expertise. In particular, this session welcomes any abstract related to the following topics:
(1) groundbreaking discoveries of planets and systems of special interest (due to peculiar physical properties/orbital architectures, amenable targets for atmospheric investigations, etc.);
(2) cutting-edge measurements of exoplanet properties (tidal distortions, spin rates, and angles) and first tentative detections of satellites or rings;
(3) contributions to the general picture of exoplanets (precise measurements of radii, masses and internal planetary compositions, observed/theoretical populations, occurrences, etc.);
(4) demographics studies out of detection surveys from the ground- and/or space-based observatories;
(5) synergies between different techniques for comprehensive exoplanet characterization (photometry, low and high-resolution spectroscopy, radial velocities, transit timing variations, radio observations, etc.);
(6) new tools and software developments for exoplanet searches and characterization (Artificial Intelligence tools, new methodologies and computational architectures, open-source initiatives, etc.)
We report the discovery and validation of three temperate Earth-sized exoplanets, TOI-2267.03 and .01, likely orbiting the primary and TOI-2267.02 likely orbiting the secondary in a binary system of cool stars (primary: M5V, 3030 K; secondary: M6V, 2890 K, separated by 0.4''). The exoplanet pair likely hosted by the primary star orbits close to a 3:2 mean motion resonance, with periods of 2.28 and 3.49 days. These findings are supported by multi-band ground-based photometry that allowed us to confirm the planetary nature of TOI-2267.01 and .03. However, TOI-2267.02 with a period of 2.03 days remains a candidate due to its shallower transit.
The configuration with the three planets orbiting the same stellar component suggests a highly dynamically unstable system, implying the possibility of planets orbiting both stars. To date, only one other system is hypothesized to harbor planets orbiting the two stellar components of a binary: three super-Earths orbiting the two stars of K2-132, two F stars separated by 1''. However, the extremely shallow transits of these candidates orbiting K2-132 prevent any confirmation, maintaining the actual architecture of the system unknown. Hence, TOI-2267 stands out as the only system today where the existence of this unique configuration can be confirmed.
We present the results of our global analysis, the validation of the planet candidates, the planet formation scenario, and the evidence supporting the most likely architecture of the system. We discuss future plans to verify the transit of the TOI-2267.02 candidate, disentangle the host star for each planet, and confirm this odd double planetary system. These results could open a new venue to search for and characterize planetary systems in binaries of low-mass stars, profoundly impacting our understanding of how protoplanetary disks evolve to form such double planetary systems, where TOI-2267 will be a benchmark system.
How to cite: Zúñiga-Fernández, S. and Pozuelos, F. J. and the SPECULOOS Team: The Curious Case of TOI-2267: Three Earth-sized Exoplanets in a Cool Star Binary System, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-1097, https://doi.org/10.5194/epsc2024-1097, 2024.
ESPRESSO is the VLT ultra-stable high-resolution spectrograph, developed by institutions from Switzerland, Italy, Portugal, Spain, and ESO, located in the combined Coudé Lab of the VLT at ESO, and is able to operate either using one 8.2m-VLT UT or simultaneously with the four VLT UTs. ESPRESSO started routine operations in October 2018 at ESO, and is designed to achieve a radial velocity precision of 10 cm/s, thus opening the possibility to explore new frontiers in science such as the search for rocky planets (Pepe et al. 2021).
ESPRESSO has demonstrated unprecedented capabilities, being so far very successful in detecting and characterizing low-mass Earth-like and sub-Earth-like planets. ESPRESSO has exploited its sub-m/s capabilities to break the Earth-mass barrier, thus providing a unique ground-based facility with great synergy with exoplanet dedicated satellites, such as Kepler (e.g. Toledo Padrón et al. 2020; Mortier et al. 2020), TESS (e.g. Demangeon et al. 2021; Barros et al. 2022; Lavie et al. 2023) and CHEOPS (e.g. Leleu et al. 2021).
ESPRESSO has confirmed the Earth-mass planet Proxima b and discovered the sub-Earth mass planet Proxima d with 0.26 Earth masses, just about twice the Mars mass, from the measurement of a tiny RV semiamplitude velocity of 39 cm/s together with a simultaneous precise characterization of the activity of the star (Suárez Mascareño et al. 2020; Faria et al. 2022). We have recently reported the discovery of two Earth-mass planets in the habitable zone for the nearby relatively faint M dwarf star GJ1002 (Suárez Mascareño et al. 2023). All these results further stimulate the search for Earth and sub-Earth mass planets in the nearest stars of the solar neighbourhood, and encourage new detail studies with current and future facilities such as ANDES@ELT (Marconi et al. 2022; Pallé et al. 2023).
The Barnard's star (GJ 699) is the second closest stellar system to the Sun, after the alpha Centauri stellar system, at a distance of about 1.8 parsecs. The isolated star GJ 699 is a low-magnetic activity M4V star that offers a unique opportunity to search for Earth like planets within its habitable zone. The Barnard's star is considered a primary target within the ESPRESSO Guaranteed Time Observations (GTO) due to its proximity to our Sun. Here we present ESPRESSO GTO observations of the Barnard's star focusing on revealing and discussing planet candidates.
How to cite: González Hernández, J. I.: Planet candidates orbiting the Barnard's star seen with ESPRESSO, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-117, https://doi.org/10.5194/epsc2024-117, 2024.
Planetary systems in mean motion resonances hold a special place among the planetary population. They allow us to study planet formation in great detail as dissipative processes are thought to have played an important role in their existence. Additionally, planetary masses in bright resonant systems may be independently measured both by radial velocities (RVs) and transit timing variations (TTVs). In principle, they also allow us to quickly determine the inclination of all planets in the system, as for the system to be stable, they are likely all in coplanar orbits. To describe the full dynamical state of the system, we also need the stellar obliquity that provides the orbital alignment of a planet with respect to the spin of their host star and can be measured thanks to the Rossiter-McLaughlin effect. It was recently discovered that HD 110067 harbours a system of six sub-Neptunes in resonant chain orbits. We will show ESPRESSO high-resolution spectroscopic time series of HD 110067 during the transit of planet c. We find the orbit of HD 110067c to be well aligned. This result is indicative that the current architecture of the system has been reached through convergent migration without any major disruptive events. Finally, we will report transit-timing variation in this system as we find a significant offset of 19 ± 4 minutes in the center of the transit compared to the published ephemeris.
How to cite: Zak, J. and Bocchieri, A. and the collaborators: Rossiter-McLaughlin effect of a sub-Neptune in a resonant chain system, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-47, https://doi.org/10.5194/epsc2024-47, 2024.
There is much still to learn about giant planets, in particular those at relatively long orbital period. Present (TESS, CHEOPS) and future planetary missions (PLATO, Ariel) will make a significant contribution to our understanding of these systems.
One unsolved problem is the origins of warm Jupiters (WJs). If WJs formed beyond the snow line, far from their host stars, then migration is required to bring them to their current orbits. There are several hypotheses explaining the migration history and we are exploring observational tests for these hypotheses. In particular, obliquity (the angle between the stellar rotation and planetary orbital axes) is a key tracer of migration history. Dynamically violent, high-eccentricity migration leads to planets in significantly misaligned orbits with large obliquities, whereas disc-driven migration should result in orbits coplanar with the stellar equator. In contrast to the hot Jupiters, the imprint of dynamical migration in WJs should not be erased through tidal interactions with the convective zone of their stars, because they are tidally detached.
Only around 60 transiting warm Jupiters are currently known, only 16 of which have a measured obliquity. We have a VLT/ESPRESSO programme to measure the obliquities of an unbiased sample of eleven WJs, which will greatly increase the size of the measured sample. Our first observations were made earlier this year, and here we present those data, and our preliminary interpretation.
How to cite: Smith, A., Cabrera, J., Harre, J.-V., and Csizmadia, S.: Studying the origins of warm Jupiters, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-932, https://doi.org/10.5194/epsc2024-932, 2024.
The large number and diversity of exoplanets found in the last decades has raised fundamental questions about their formation and evolution mechanisms.
Many of these are giant planets orbiting very close to their host star, hence their name Hot Jupiters, despite the low occurrence rate of such population (Stevenson 1982; Mayor et al. 2011, Fressin et al. 2013, Santerne et al. 2016). This is mainly driven by the inherent observational bias in their detection, given their small periods, which results in a dominant population of Hot Jupiters which is about 75% of the detected exoplanets. Most of such discoveries arose from wide-field ground-based observatories (Bakos et al. 2006, Mandushev et al. 2005, Udalski et al. 2002), from the Kepler and K2 space missions (Borucki 2017, Howell et al. 2014) and, more recently, from the Transiting Exoplanet Survey Satellite mission (TESS, Ricker et al. 2015).
Giant planets are thought to form via two different mechanisms: either by accreting its mass from the proto-planetary disk (Pollack et al. 1996), or by gravitational instabilities, in which the proto-planetary disk fragments into bound clumps to form a planet (Cameron 1978). Both mechanisms predict low formation rate at close-in orbits. Close to the star gas conditions could prevent the formation of bound clumps (Rafikov 2005), while at the same time such conditions may prevent the formation of sufficient large cores to accrete gas from the proto-planetary disk (Schlichting 2014).
Therefore, the observed population of Hot Jupiters strongly suggests that they might have formed further out, in regions where the conditions for core accretion and gravitational instabilities are more favorable, and migrated inwards into their currently close-in circular orbits.
Possible migration mechanisms consider interactions with the disc (e.g. Walsh et al. 2011) and tidal migration produced by changes in the orbit, which can be induced by planet-planet scattering (Rasio & Ford 1996) or cyclic and/or chaotic secular interactions (Kozai 1962, Lidov 1962, Wu & Lithwick 2011).
Therefore, the observed population of Hot Jupiters strongly suggests that they might have formed further out, in regions where the conditions for core accretion and gravitational instabilities are more favorable, and migrated inwards into their currently close-in circular orbits.
Both mechanisms predict different orbital parameters for the planet population. While disc migration predict mainly circular orbits aligned with the stellar spin, high eccentricity migration predict a wide distribution of eccentriticies and obliquities (Chatterjee et al. 2008).
In this context, the estimation of the bulk structures and atmospheric parameters of such population of exoplanets could provide crucial information about their formation locations in the disc and possible migration paths (Madhusudhan et al. 2014, Mollière et al. 2022).
However, the characterization of the formation history of Hot Jupiters, widely defined as planets with periods smaller than 10 days, can be problematic, as their proximity to their host star may induce radiative and tidal interactions which can affect the interpretation of the origins of the observed population (e.g. Albrecht et al. 2012).
Therefore, giant planets within the snow-line, but at farther distances from their host star, represent a unique opportunity to study possible formation and migration mechanisms in giant planets, as they may not be affected by their proximity to their host star, allowing a more direct comparison of their orbital properties with formation and migration models.
Warm giants, planets broadly defined as planets orbiting their host star with periods longer than 10 days, remained elusive to ground-based transit searches, mainly due to the constrains imposed by the daily cycle. While some detections were possible with the Kepler+K2 missions (i.e. Huang et al. 2016), only with TESS it has been possible to systematically characterize them, either through the detection of periodic transiting signals or single transiters (i.e. Brahm et al. 2019, Gill et al. 2020).
By complementing transit observations with radial velocity (RV) measurements, it is possible to provide a detailed characterization of the dynamical properties of the planetary system.
The Warm gIaNts with TESS (WINE) collaboration is a dedicated survey to identify, confirm and characterize warm giants using TESS data and ground-based photometric and spectroscopic follow-up facilities, with the main goal of building a giant planets database to constrain theories of planetary formation and evolution. We have detected more than 20 Warm giants (Kossakowski et al. 2019, Jordán et al. 2020, Brahm et al. 2020, Schleker et al. 2020, Hobson et al. 2021, Trifonov et al. 2021 and 2023, Brahm, et al. 2023, Hobson et al. 2023, Jones et al. 2024) and we have been following-up dozens of exoplanet candidates. Among our discoveries we highlight the detection of several high eccentricity exoplanets, which are ideal candidates to measure their obliquity using the Rossiter-Maclaughlin effect, and determine the 3D exoplanetary orbits and properly constrain planetary migration theories. The figures show the orbital period-eccentricity diagram, the orbital period-planet radius diagram and the planetary mass-radius diagram where we highlight the discoveries made by our collaboration.
How to cite: Tala Pinto, M., Brahm, R., Jones, M., and Jordán, A.: The WINE collaboration: a Warm Giants planets survey, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-578, https://doi.org/10.5194/epsc2024-578, 2024.
JWST has opened a completely new spectral range in the mid IR for the study of exoplanetary systems which promise to offer unprecedented results both in terms of characterization but also discovery space.
Two observing modes in MIRI are of particular interest : 1) the coronagraphic mode installed in the imager made of four independent coronagraphic masks paired with dedicated filters covering the ~10 to ~20 microns window, and 2) the Medium Resolution Spectrograph which has a much wider spectral range from 5 to 28 microns but without coronagraphic capacity.
We will first describe these two modes and their respective performances, based on actual observations or from simulations. Then we will present the first results from the exoplanet Guaranteed Time Observations team of the MIRI consortium, focusing for instance on the multiplanet system HR8799 (see figure 1 and 2), and highlight some results obtained from General Observers programs. Finally we will discuss the broad interest of MIRI for science cases like cold planets at large orbital separations as well as protoplanets.
Figure 1 : Raw coronagraphic and reference star subtracted images of the multiple planet systems HR8799 obtained with MIRI in 4 different filters at mid IR wavelenghts.
Figure 2: spectral energy distribution of planet HR8799 b compared to 2 atmospheric models fitted on near IR and mid IR photometric data points.
How to cite: Boccaletti, A., Mâlin, M., Rouan, D., Perrot, C., Lagage, P.-O., Lagrange, A.-M., Charnay, B., and Pierre, B.: Direct imaging of exoplanets with JWST/MIRI, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-1187, https://doi.org/10.5194/epsc2024-1187, 2024.
We present a population study of 20 transiting exoplanets, currently the largest sample of exoplanet atmospheres observed to date in the spectral range near-UV to near-IR. Archive data obtained with Hubble STIS and WFC3 instruments are uniformly analysed using the Iraclis pipeline and a suite of spectral retrieval plugins integrated in TauREx 3.1, including the stellar activity plugin ASteRA and the cloud microphysics plugin YunMa. Most exoplanets included in the sample were observed multiple times with the STIS G430L and/or G750L gratings (Fig. 1), allowing for the study of temporal variability caused by changes in the exoplanet atmosphere, due to e.g. cloud/haze variability and/or stellar magnetic activity.
Fig. 1: The spectral data resulting from our data analysis, colour-coded based on the observation timestamps of each STIS visit. The dashed lines centred at 0.59 μm and 0.77 μm indicate where we expect the peaks of the absorption features of sodium and potassium to appear respectively.
Our analysis reveals significant differences among the observations obtained with STIS at various epochs for about half of the planets included in the sample. These data show amplitudes and patterns that are suggestive of time-varying stellar surface heterogeneities that cause contamination in the exoplanetary spectra. At a population level, our analysis reveals that for planets on which stellar activity exerts the most significant influence on their spectrum, even employing the simplest stellar contamination model is sufficient to align water abundance values to the average of the whole sample.
To statistically assess the preference for an active model over a quiet star model, we compute the Bayes Factor resulting from the difference in Bayesian evidence between two retrieval models: one model representing a primary atmosphere with water vapour as the sole opacity source, assuming a uniform stellar photosphere, and the other incorporating the same atmospheric model but considering the star to have a heterogeneous surface. Despite the active star model being statistically penalised for its increased complexity compared to the simpler model, it remains significantly favoured across many spectral cases. This result emphasises the critical nature of accounting for the potential presence of unocculted stellar spots and faculae when performing spectral retrievals in the optical regime. Among the total number of targets investigated, nearly half of them exhibit a strong preference towards the model incorporating an active star, while only one planet strongly favours a quiet star.
Furthermore, we establish new, complementary metrics to assess the extent of stellar activity contamination; the Stellar Activity Distance metric (SAD) and the Stellar Activity Temporal metric (SAT). The SAD, by corroborating the findings of the Bayes Factor analysis, indicates that an active star model better describes the optical observations in approximately half of the planetary spectra. Similarly, the SAT results reveal a bimodal distribution, indicating that spectral variations in the visible regime within this limited planet sample are either minimal or moderately significant.
We analyse in more detail three case studies: WASP-6 b, WASP-39 b and HAT-P-11 b. Our findings align with previous literature results for the first two planets, for which we find an active stellar environment and a quiet star respectively. However, HAT-P-11, expected to be active, is found to show no significant signs of stellar contamination. Across the population, stellar activity contaminates up to half of the studied exoplanet atmospheres albeit at varying extents (Table 1).
Table 1: For each planet, we report the preference (✓) or rejection (×) for stellar contamination based on the metrics outlined in our investigation. The 15 planets with consistent sets of observations are ordered based on their ranking within the sample over all of the metrics from most likely to be contaminated (WASP-6 b) to least likely (WASP-39 b). Colour coding reflects the consensus among metrics: green signifies unanimous or nearly unanimous indications of significant activity; yellow denotes uncertain outcomes, with some metrics leaning towards stellar activity and others against it; red indicates a preference for an inactive star. The 5 planets that do not have consistent data sets are reported separately below the main table. They are not included in the ranking but are colour coded in the same way. For an explanation of the data sets considered in each Case, see Table 2.
Table 2: Data sets utilised to define each Case number. Each STIS visit indicated here is colour-coded in Fig. 1.
Overall, our findings demonstrate the significant role that stellar contamination may have in all exoplanet spectra observations: therefore, comprehending, modelling, and correcting for the impact of stellar activity is important for a complete characterisation of exoplanet atmospheres. This issue becomes particularly relevant with the ongoing JWST observations of small planets, statistically more likely to orbit active stars. Additionally, addressing stellar activity becomes even more pertinent in anticipation of the extensive chemical surveys to be conducted by next-generation space telescopes in the coming decade. For these reasons, targeted campaigns aimed at investigating the activity of exoplanets' stellar hosts through time would significantly contribute to the success of the exoplanet field.
How to cite: Saba, A., Thompson, A., Yip, K. H. (., Ma, S., Tsiaras, A., Al-Refaie, A., and Tinetti, G.: A Population Analysis of 20 Exoplanets Observed from the Optical to the Near-infrared Wavelengths with HST: Evidence for Widespread Stellar Contamination, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-171, https://doi.org/10.5194/epsc2024-171, 2024.
The fidelity of data reduction pipelines significantly influences the interpretation of exoplanetary data. As we approach the operational phases of the James Webb Space Telescope (JWST) and the ARIEL space mission, addressing pipeline-induced variances is imperative due to its profound implications on our understanding of exoplanets. Our study is pioneering in its comparative analysis of pipeline results at a catalogue level, employing a robust framework to statistically evaluate outcomes from the Hubble Space Telescope’s Wide Field Camera 3 across three independent pipelines: Iraclis, EXCALIBUR, and CASCADe.
Despite utilising identical data, substantial differences in extracted spectra and planetary parameters were observed. Notably, variations in detected atmospheric compositions, particularly in water and methane content, and radius and temperature estimation, exemplify significant pipeline-induced biases. These discrepancies manifest most starkly in compositional trends across the exoplanet catalogues, potentially skewing class-wide analyses and misleading interpretations of atmospheric conditions.
This study highlights the urgent need for the exoplanetary science community to standardise data reduction techniques to harness the full potential of future observations. The outcome of our work is vital not only for the academic community but also for upcoming space missions, ensuring that interpretations of exoplanetary atmospheres are based on the most accurate data possible.
How to cite: Mugnai, L. V.: Comparing transit spectroscopy pipelines at the catalogue level: evidence for systematic differences, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-179, https://doi.org/10.5194/epsc2024-179, 2024.
1. Introduction
Between 25% and 50% of discovered white dwarfs have been found to contain heavy elements in their atmospheres (Koester et al, 2014). The sinking timescale of these heavy elements is relatively short, ranging from several days (for hydrogen-dominated white dwarfs) to millions of years (for helium-dominated white dwarfs). Therefore, these heavy elements are believed to originate from external sources other than the white dwarf core, due to the rapid sedimentation of heavy elements in white dwarfs. It is widely believed that the pollution results from the accretion of planetary material, with supportive evidence from observed dusty disks and transiting planets around white dwarfs. Therefore, the composition of pollutants in white dwarfs' atmospheres provides valuable information about the history of exoplanetary systems.
Interestingly, the dominant elements found in accreted material on white dwarfs are rock-forming elements such as Mg, Ca, and Fe, with only a few white dwarfs being polluted by icy materials. This is inconsistent with the abundance of icy objects in exo-Kuiper belt or exo-Oort Cloud objects. Several mechanisms have been proposed to account for the scarcity of volatiles, including the primordially dry nature of the pollutants and observational bias due to asynchronous accretion. However, recent research shows that volatile vapor is necessary to the accretion disk to offer a drag to the debris, thereby facilitating the high accretion rates deduced from observation (Okuya et al, 2023). This implies that volatiles could exist with refractory elements in the disk, but be prevented from accretion onto the white dwarf by some unknown physical process.
White dwarfs have been observed to have atmospheres polluted by heavy elements, which are thought to be accreted from planetary objects. Refractory pollution, such as silicate and iron elements, is more commonly observed than volatile pollution, which includes carbon, nitrogen, oxygen, and sulfur. It is currently unclear whether this scarcity of volatile pollution is due to the prevalence of dry pollutants, such as asteroids and rocky planets, or some unknown mechanism that shields the volatiles. In this work, We propose a mechanism to explain the lack of volatile pollution, which involves the shielding of volatiles by the magnetic field in the scenario of comet accretion.
2. Results
We find that the volatile content in the tidal fragments of comets can effectively sublimate during the process of orbital circularization. Following sublimation, the resulting volatile vapor may be shielded by the magnetosphere of white dwarfs, provided that the magnetosphere radius is greater than the corotation radius. The effectiveness of this volatile-shielded mechanism is determined by the extent of sublimation occurring outside the corotation radius. The main processes in this scenario are the following:
(1) Tidal fragmentation and orbital circularization of comets. Comets are tidally disrupted within the tidal disruption radius. The generated fragments with a maximum size of ~ 200m migrate inward due to the Alfvén wing drag and/or dust drag. In this work, we incorporate the Alfvén wing drag to model the behavior of exo-Oort Cloud objects.
(2) Volatile sublimation. After crossing the ice line, the interior of fragments gets heated up to the sublimation temperature of volatile materials, resulting in gas release from the surface. We adopt the physical properties of Solar System comets to study the thermal evolution and vapor evolution.
(3) Given that the corotation radius is smaller than the magnetosphere radius, the photoionized vapor is shielded from the corotation radius.
Our findings reveal that objects with a size smaller than 500 m can experience complete volatile loss within 1 Myr. The effectiveness of the volatile-shielded mechanism hinges on whether the orbital circularization timescale is shorter or longer than the dry-out timescale. If it is longer, all the volatile content can be shielded from the corotation radius of the white dwarf. However, for a shorter circularization timescale, smaller icy objects can be completely dried out while larger objects retain some volatile content, leading to partial dryness and the presence of volatile material within the corotation radius. Consequently, the volatile-shielded mechanism cannot provide effective protection in such cases. A surface magnetic field weaker than 100~T could allow a sufficiently long circularization timescale for the volatile-shielded mechanism to work. As we mentioned, the prerequisite of this mechanism is that the magnetosphere radius is larger than the corotation radius. For example, for a white dwarf with a rotational period of two days, the magnetic field must be larger than 1~T.
By introducing the magnetic shielding of volatile, we extrapolated a correlation between a white dwarf's magnetic field, spin period, and the composition of the pollutants. We applied our model to nine white dwarfs with known magnetic fields, rotational periods, and atmosphere compositions, and observed that the polluted white dwarf G29-38 (WD2326+049) is volatile shielded in our model, potentially explaining the excess of volatile elements such as C and S in the disk relative to the white dwarf atmosphere. The other eight white dwarfs under investigation {{exhibit receptivity to volatiles.}} This is consistent with the presence of hydrogen in the four investigated DBA white dwarfs.
However, the lack of hydrogen in the four examined DB white dwarfs cannot be explained by our shielding mechanism and may be attributed to the absence of planetary systems or other unknown mechanisms. We suggest that future observations of white dwarfs with different magnetic fields and rotational periods will provide more insights into the efficiency of the volatile-shielded mechanism. Additionally, our model is highly sensitive to the orbital evolution and material properties of exocomets, and a comparison between observations and our model may lead to valuable constraints on the properties and origins of pollutants.
References
Koester, D., Gänsicke, B. T., & Farihi, J. (2014). The frequency of planetary debris around young white dwarfs. Astronomy & Astrophysics, 566, A34.
Okuya, A., Ida, S., Hyodo, R., & Okuzumi, S. (2023). Modelling the evolution of silicate/volatile accretion discs around white dwarfs. Monthly Notices of the Royal Astronomical Society, 519(2), 1657-1676.
How to cite: Zhou, W.-H.: White dwarf magnetospheres: Shielding volatile content of icy objects and implications for volatile pollution scarcity, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-159, https://doi.org/10.5194/epsc2024-159, 2024.
Introduction
The detection and confirmation of long-period transiting planets present significant challenges due to the infrequency of their transits. Such planets are crucial for enhancing our understanding of exoplanet formation and evolutionary dynamics. TOI-4409 b, initially identified by TESS, represents a prototypical case for studying these phenomena.
This study aims to confirm and further characterise TOI-4409 b, a long-period planetary candidate. Utilising a combination of photometric and radial velocity (RV) data, the research focuses on verifying the planet's existence and describing its orbital and physical properties.
Method
The comprehensive analysis incorporated photometric data from TESS, ASTEP, CHAT, and OMES lightcurves, along with RV measurements from HARPS, FEROS, and PFS. In total, the study analysed eight lightcurves from TESS, four from ASTEP, one from CHAT, and three from OMES. RV data spanned from 2018 to 2023, as shown in Figure 1, offering a longitudinal perspective essential for detecting and confirming the planetary signals of TOI-4409 b.
The TESS spacecraft provided the initial detection of TOI-4409 b through its wide-field, high-precision photometry, which is particularly adept at identifying transiting exoplanets. Subsequent observations by the ASTEP telescope, strategically located in Antarctica, leveraged the prolonged periods of darkness and stable atmospheric conditions to observe additional transits. This was critical for capturing the infrequent transits of TOI-4409 b. Lightcurves from CHAT and OMES telescopes further supplemented these observations, enhancing the data's robustness through additional transit captures and minimising gaps in the observational data.
Radial velocity data were obtained using three high-precision spectrometers: HARPS, FEROS, and PFS. These instruments are renowned for their sensitivity in detecting the subtle stellar wobbles induced by orbiting planets, which are crucial for confirming the planetary nature of transit signals. The combined RV dataset enabled a comprehensive analysis of the star's motion, aiding in the verification of TOI-4409 b and suggesting the presence of additional planetary bodies through observed anomalies in the RV signals.
Results
The integrated analysis confirmed TOI-4409 b as an exoplanet with a planetary radius of 7.28±0.20 Earth radii, orbiting a low-mass main sequence star with an effective temperature of approximately 4945±10 K and a stellar radius of 0.720±0.018 solar radii. The orbital period of TOI-4409 b was determined to be 92.4±0.8 days. Two of the processed light curves are shown in Figure 2.
Consistent transit signals across multiple datasets, combined with observed Transit Timing Variations (TTVs), reinforced the candidate’s robustness. These TTVs (showcased in Figure 3), in conjunction with the radial velocity data, suggested the gravitational influence of a second planet in a 20-day orbit around the same star.
The integration of diverse observational methods and data from multiple instruments was pivotal in confirming the planetary status of TOI-4409 b. This approach not only facilitated a thorough characterisation of the planet but also underscored the potential complexities of its orbital dynamics, hinted at by the TTV and RV analyses.
The evidence for a second planet, suggested by anomalies in TTV measurements, points to a potentially rich multi-planetary system, warranting further investigation. This discovery highlights the importance of multi-modal and multi-instrumental data analysis in the field of exoplanet research, where single-method approaches may not suffice due to the complex nature of planetary systems and the limitations of individual observational techniques.
Conclusion
The successful confirmation of TOI-4409 b as a long-period exoplanet and the indication of a secondary nearby planet demonstrates the critical role of global cooperation and technological integration in exoplanetary science. The unique capabilities of the Antarctica-based ASTEP telescope, combined with the extensive data provided by TESS, CHAT, OMES, HARPS, FEROS, and PFS, exemplify how diverse observational assets can come together to enhance our understanding of the universe.
Continued monitoring and future investigations into the TOI-4409 system are essential. They will not only confirm the characteristics and existence of the second suggested planet but will also provide deeper insights into the dynamics and potential habitability of planets in long-period orbits. This study sets a precedent for future research into similar exoplanetary systems, using refined methods and international collaboration to further our understanding of planetary formation and evolution.
Figure 1: All unique photometric observation midtimes, spanning the years 2018 to 2023. This distribution of dates enabled a robust TTV analysis.
Figure 2: TESS (left) lightcurve and ASTEP (right) model fit result, showcasing the transiting nature and the TTV of the signals analysed. All 16 light curves were fitted using the same method.
Figure 3: All the unique transit midtimes of our observations (in BJD - 2458000), alongside their calculated Transit Timing Variations.
How to cite: Reller, P. and the UCL / ESA / Université Côte d’Azur / Max-Planck-Institut für Astronomie / Millennium Institute for Astrophysics & other groups: Confirmation of the long-period Exoplanet TOI-4409 b, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-908, https://doi.org/10.5194/epsc2024-908, 2024.
Giant planets (Mp > 0.3 Mjup) with orbital periods between ~10-200 days (a.k.a warm-Jupiters), are excellent targets to measure their bulk composition, to characterize their atmospheric abundances and to study their formation and evolution mechanisms. In particular, they are less affected by the strong stellar irradiation and tidal interactions with the host star, that their innermost siblings, the so-called hot-Jupiters, suffer.
In this talk I will first describe our MESA (Paxton et al. 2011) based interior/evolutionary models
of gas giants, which include a rocky-icy core, sorrounded by a H/He gaseous envelope, and with metals homogeneously mixed in the envelope. In addition, our models include the effect of the stellar irradiation in the cooling evolution of the planet. For this, we also include the host star evolution in our models, which translates into an increasing insolation level since the zero age main-sequence to present. This is particularly important for planet orbiting stars that are close to the terminal age main-sequence, whose luminosity have significantly increased since their formation. A few examples of our models are presented in Figures 1.
Then, I will present different models of a sample of selected systems, which were validated, and homogeneously characterized (both the stellar and planetary properties) in the context of the Warm gIaNts with TESS collaboration (WINE; Brahm et al. 2019).
Finally, I will compare their internal composition and metallicity with the planet mass and host star properties, and I will discuss these results in the context of planet formation scenarios for gas giants.
Figure 1: Position of TOI-2529 b in the age-radius diagram (black dot). Planet evolutionary models with different envelope composition and insolation level are overplotted. For comparison, a simple model of Jupiter is also shown. Figure from Jones et al. (2024).
How to cite: Jones, M., Brahm, R., and Tala, M.: Modeling the internal composition and evolution of warm Jupiters with MESA, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-579, https://doi.org/10.5194/epsc2024-579, 2024.
Introduction
Rocky airless bodies in the solar system, e.g., Mercury, the Moon, and many asteroids, host a rough silicate regolith layer. The roughness of the surfaces influences the reflectance and emission phase curves of these bodies. At small phase angles, the “opposition effect” increases the reflected radiation and “thermal beaming” leads to higher emitted radiation compared to smooth surfaces (see Figure 1). At higher phase angles, surface roughness leads to “shadowing”, the measured thermal emission is smaller than predicted by the equilibrium model for a smooth surface. The rocky exoplanets LHS 3844 b [1], GJ 1252 b [2], TRAPPIST-1 b [3], and TRAPPIST-1 c [4] are roughly Earth-sized (see Figure 2), likely have no atmospheres, and their surfaces largely remain mysterious. We previously developed and validated a thermal roughness model for airless solar system bodies (the Moon and Mercury) [5]. In this work, we adapt our model to airless exoplanets and analyze how surface roughness and albedo affect the infrared phase curves. The resulting model can then impose constraints on the surface structure of the exoplanets. We will use this approach to analyze upcoming phase curve measurements of LHS 3844 b in the James Webb Space Telescope (JWST) General Observer Program, cycle 2, ID 4008 [6].
Figure 1. The Moon's emission phase curve demonstrates the thermal beaming effect. Adopted from [6].
Figure 2. Radii, temperatures, and stellar distances of the exoplanets studied in this work compared to Mercury, Earth, and the Moon. The radii are not to scale to the distances. The color denotes the dayside surface temperature.
Figure 3. Comparison of the different host star radii and surface temperatures.
Methods
We model the reflectance component of the radiation with the Hapke model [7] and fix all parameters except for the spectral single-scattering albedo. We derive two sets of albedo values from lunar satellite and returned sample data. The “mare” set models a darker surface and represents a more basaltic composition. The “highland” set resembles a comparatively brighter surface and more feldspathic composition. We use the thermal roughness model from [5] for the emission component, which is mainly controlled by the albedo and the roughness parameter (average roughness angle). We simulate disk-resolved radiances of the planets for different phase angles and integrate them over the disk to retrieve the phase curves. We focus on the wavelength region of the JWST NIRSpec G395H/F290LP disperser/filter combination (2.7 μm-5.2 μm).
Results
Figure 4 shows the reflectance and emission phase curves for LHS 3844 b for different roughness angles and albedos. The reflected component is smaller than the emitted component in the infrared wavelength region but not negligible. The thermal beaming and shadowing effects are clearly visible. The opposition effect is most likely not detectable due to the occultation of the planet during the secondary eclipse. The simulations of all four exoplanets show that the albedo influences the amplitude of the phase curve, and the surface roughness alters the shape of the phase curve. Figure 5 shows that the two parameters appear interchangeable at small phase angles (close to the secondary eclipse). However, considering the entire phase curve allows albedo and surface roughness to be separated. Figure 6 shows the combined phase curves for the other three exoplanets. The phase curve of GJ 1252 b is like that of LHS 3844 b and the parameter influences can likely be separated. TRAPPIST-1 b and TRAPPIST-1 c have much lower relative flux densities, which makes parameter retrieval difficult.
Figure 4. Reflectance and emission phase curves for LHS 3844 b. The upper row corresponds to the shorter wavelength region of NIRSpec, and the lower row corresponds to the longer wavelength region. The columns represent the two albedo sets.
Figure 5. Combined reflectance and emission phase curves for LHS 3844 b for different surface roughness angles and albedos.
Figure 6. Combined phase curves for GJ 1252, TRAPPIST-1 b and TRAPPIST-1 c.
Conclusion
The surface roughness and albedo effects are detectable and most likely separable for LHS 3844 b and GJ 1252 b with NIRSpec on JWST. This would allow the retrieval of one or both parameters from phase curve measurements, which can provide information about the nature of extrasolar planetary surfaces. Additional albedo constraints can further improve the retrieval scheme. Due to extensive space weathering, the closely orbiting exoplanets likely have a low albedo, similar to Mercury or the maria of the Moon. The two planets of the TRAPPIST-1 system are less suited for characterization with NIRSpec. Still, MIRI measurements might enable the parameter retrieval.
References
[1] Kreidberg, L., Koll, D.D.B., Morley, C. et al. Nature 573, 87–90 (2019).
[2] Ian J. M. Crossfield et al 2022 ApJL 937 L17
[3] Greene, T.P., Bell, T.J., Ducrot, E. et al. Nature 618, 39–42 (2023).
[4] Zieba, S., Kreidberg, L., Ducrot, E. et al. Nature 620, 746–749 (2023).
[5] Wohlfarth, K., Wöhler, C., Hiesinger, H., Helbert, J. A&A 674 A69 (2023)
[6] S. Zieba, L. Kreidberg, R. Hu, C. Morley, K. Wohlfarth, M. Tenthoff, and C. Wöhler. JWST Proposal 4008. https://www.stsci.edu/jwst/science-execution/program-information?id=4008. (2023)
[7] Bruce Hapke. Journal of Geophysical Research: Solid Earth, 86(B4):3039–3054, (1981)
How to cite: Tenthoff, M., Wohlfarth, K., Wöhler, C., Zieba, S., and Kreidberg, L.: Reflectance and Emission Modelling of Airless Exoplanets, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-649, https://doi.org/10.5194/epsc2024-649, 2024.
