Nothing in space is ever truly stable. For space telescopes such as Ariel, this leads to a noise source in photometric and spectroscopic measurements caused by the movement of the target star or spectra (also refereed to as jitter) across the detectors inconsistent pixels. In order to minimise this source, continuously guiding the telescope becomes a necessity. 

Ariel will perform both photometric and spectroscopic observations of transiting exoplanets across multiple phases of their orbit in order to study the chemical composition of their atmosphere. Given the long duration of these observations, an unstable pointing of the telescope would add significant noise to the time series of the measurements. Therefore, Ariel is equipped with a dedicated instrument: the Fine Guidance Sensor (FGS). While the FGS is a scientific instrument that provides both low-resolution spectra and photometry in bands specific to atmospheric molecular features, it also doubles as an input for the closed loop guiding of the telescope. For this task, the FGS uses two of its three photometric channels to measure the position of the target star at a rate of 10 Hz. This positional information is then sent to the spacecrafts Attitude and Orbit Control System (AOCS), which applies the necessary corrections using the platforms actuators. In order to obtain the necessary measurements, the FGS will be equipped with dedicated guiding algorithms as part of its Instrument Application Software (IASW), which is developed by the University of Vienna.

In this paper we present the current state of the design of these methods. The algorithms are split into Target Acquisition and Tracking, where the former is used to correctly identify the star on a large field of view. On the other hand, Tracking is used during the scientific observations of the target in order to keep the instruments line of sight as stable as possible. In addition to the design and implementation of these algorithms, we also discuss their performance and our tools for their evaluation and testing. The images we use for performance testing are generated using our own simulators. These simulators are able to properly represent the noise sources we expect in the real instrument such as detector noise, line of sight jitter and smearing. Additionally, the simulators are designed to be as fast as possible to allow their reuse in closed loop testing, both in simulation environments and using real hardware.

How to cite: Mösenlechner, G., Ottensamer, R., and Kerschbaum, F.: Guiding and Target Acquisition for the Ariel Space Mission: Algorithms and Performance, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-1190, https://doi.org/10.5194/epsc2024-1190, 2024.

In designing and developing space instruments, fast and reliable tools are essential for validation and optimisation. Within the Ariel Space Mission framework, we have developed novel, versatile tools to estimate space instrument performance: ExoSim 2 and ArielRad.

ExoSim 2 is a time-domain simulator for exoplanet observations, capable of simulating exoplanetary transit, eclipse, and phase curve observations from both ground and space-based instruments. This simulation captures temporal effects such as correlated noise and systematics on the light curve, producing spectral images akin to actual observations. Developed for the Ariel Space Mission, ExoSim 2 assesses the impact of astronomical and instrumental systematics on astrophysical measurements and prepares the data reduction pipeline against realistic data sets. Its outputs can be utilised by various data reduction methods to determine the best pipeline strategy for removing systematics and to assess the confidence level of retrieved quantities. ExoSim 2 is a refactored version of the original ExoSim, featuring improved usability, customisability, and compatibility with Python 3.7+. It includes an installer, documented examples, and a comprehensive guide, allowing users to incorporate new functionalities through user-defined functions.

ArielRad is the Ariel radiometric model, which accurately predicts telescope performance for observing candidate targets across all mission photometric and spectroscopic channels. The software inputs a target description and a parameterisation of the payload, enabling the investigation of various design performances. ArielRad can simulate entire target lists, predicting the observing time and the resulting Signal-to-Noise Ratio (SNR) versus wavelength. By analysing 1000 candidate targets within a 20-minute timescale, it validates different observational strategies. The software architecture is based on ExoRad 2, which is publicly available and can be adapted for future space missions.

Together, ExoSim 2 and ArielRad provide comprehensive tools for the development, validation, and optimisation of space instruments, particularly within the Ariel Space Mission framework. Their versatility and robust performance make them valuable assets for current and future astronomical projects.

How to cite: Mugnai, L. V., Bocchieri, A., Papageorgiou, A., and Pascale, E.: Performance Simulation Tools for Space Telescopes Applied to the Ariel Space Mission, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-892, https://doi.org/10.5194/epsc2024-892, 2024.

The European Space Agency’s Ariel mission, scheduled for launch in 2029, aims to conduct the first large-scale survey of atmospheric spectra of transiting exo-planets. Jitter in the spacecraft’s line of sight is a source of disturbance when measuring the spectra of exoplanet atmospheres. 

We will describe an improved algorithm for de-jittering Ariel observations simulated in the time domain using ExoSim2, the new Exoplanet Observation Simulator, adapted to Ariel. The jitter is based on representative simulations from Airbus Defence and Space, the Ariel spacecraft’s prime contractor. We investigate the accuracy and biases of the retrieved atmospheric spectra from the jitter-detrended observations. 

Using our algorithm to de-jitter photometric and spectroscopic data, we will demonstrate the possibility of achieving the photon noise limited performance compliant with the mission requirements across the whole Ariel spectrum. This work contributes to the development of the data reduction pipeline for Ariel, aligning with its scientific goals, while potentially benefiting other astronomical telescopes and instrumentation.

How to cite: Bocchieri, A., Mugnai, L. V., Pascale, E., and Syty, A.: Ariel detrending: algorithms to mitigate the jitter disturbance, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-240, https://doi.org/10.5194/epsc2024-240, 2024.

The Ariel space mission requires the simultaneous observation of exoplanet systems in visible and infrared wavelengths through spectroscopic and photometric channels. These wavebands are selected and isolated using dichroic beamsplitters. Dichroic beamsplitters, or dichroics, are filters that rely on the optical interference occurring within thin film layers to ensure the transmission and reflection of selective wavelengths from an incident light beam. They aim to facilitate a predetermined pathway of different wavebands by manipulating the separation of precise ranges of wavelengths and play a role in determining the spectral response of an instrument.

The assumption that the layers of coating that comprise the dichroic are entirely uniform may pose a significant limitation to its physical accuracy. Complex dichroic coatings can exhibit phase effects in both transmission and reflection of light, affecting the WaveFront Error (WFE) and, consequently, the point spread function (PSF) as a function of the wavelength. The deviations in the phase observed across the surface of the dichroic are primarily the result of variations in the thickness of a given coating layer, influenced by the accuracy of the technique and equipment used during the deposition process of the coatings.

Here, we use transmission-line modelling to explore the effect of low-spatial frequency variations in the thicknesses of the layers to assess the subsequent impact on the resulting phase of the outgoing beams of a dichroic. We apply our methodology to a case study of an example dichroic that has been designed to comply with the spectral requirements of Ariel’s extreme broadband dichroic, D1.

We will show that these non-uniformities introduce a wavelength-dependent shift in the observed phases of the outgoing beam, which may subsequently degrade the PSF. We obtain estimates of the expected phase variations when subjected to low-spatial frequency errors in thickness. The physical distribution of these errors in the form of WFE maps are propagated through the optical chain of Ariel using PAOS, an open-source, generic Physical Optics Propagation code developed by Ariel scientists, to assess the consequent impact on the PSF at the focal plane of the FGS-2 photometer.

How to cite: Thurairethinam, V., Bocchieri, A., Savini, G., Mugnai, L. V., and Pascale, E.: Modelling phase errors induced by multilayer optical coating using Monte Carlo transmission line modelling and PAOS for performance sensitivity of the Ariel mission, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-1199, https://doi.org/10.5194/epsc2024-1199, 2024.

Twinkle and Ariel, set to launch in 2025 and 2029 respectively, will conduct the first large-scale homogeneous spectroscopic surveys of hundreds of exoplanet atmospheres. This will fully transition the field to an era of population-level atmospheric characterization. In this pilot study, we explore synergies between the two missions by focusing on a select subset of 'cool' planets well-suited for observation by both telescopes.

Using representative noise levels, we compute the number of visits needed, simulate and retrieve observed transmission spectra assuming gaseous, H2/He-dominated atmospheres. We will show that for all targets, atmospheric parameters are generally retrieved within 1-sigma of input values, with Ariel achieving tighter constraints. 

We will demonstrate exploitable synergies between Twinkle and Ariel for this 'cool' planet sample, with Twinkle potentially providing a vantage point to plan Ariel observations. As the missions' target lists take shape, we encourage further investigation by both consortium communities to fully map the synergy potential as the launch dates approach.

How to cite: Bocchieri, A., Booth, L., and Mugnai, L. V.: Exploring Synergies between Twinkle and Ariel: a Pilot Study, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-272, https://doi.org/10.5194/epsc2024-272, 2024.

How to cite: Ouyang, Q., Liu, J., and Huo, Z.: MEAYIN and its Observational Simulation Grid: Advancing the Search for Habitable Exoplanets and Biosignature Characterization, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-1206, https://doi.org/10.5194/epsc2024-1206, 2024.

Mauve is a satellite equipped with a 13-cm telescope and a UV-Visible spectrometer (with anoperative wavelength range of 200-700 nm) conceived to measure stellar magnetic activity and variability. The science program will be delivered via a multi-year collaborative survey program, with thousands of hours each year available for long baseline observations of hundreds of stars, unlocking a significant time domain astronomy opportunity. Mauve’s mission lifetime is 3 years with the ambition of 5 years, and will cover a broad field of regard (–46.4 to 31.8 degrees in ICRS) during this period.

This facility was conceived to support pilot studies and new ideas in science and is fully dedicated to time-domain astronomy. The main surveys to be executed by Mauve are monitoring of

- Flare stars (flares, depending on their energy and frequency, may change the chemistry of planetary atmospheres, power prebiotic chemistry, produce surface biosignatures, or deprive exoplanets of their atmospheres totally)

- Herbig Ae/Be stars (which host protoplanetary disks and few of them are young exoplanet hosts/candidate exoplanet hosts)

- Confirmed exoplanet hosts,

- Contact binary variables (RS CVn variables, symbiotic stars, Algol-type stars, etc.), with several of them hosting exoplanets, such as AF Lep, the recently discovered benchmark system to be studied for exoplanet atmosphere characterisation for its unique features.

Besides these major science themes, the spectrometer’s data can be utilized to support and complement existing and upcoming facilities as a pathfinder, or conduct simultaneous/follow-up observations.

How to cite: Majidi, F. Z., Bradley, L., Ma, S., Saba, A., Tinetti, G., Stotesbury, I., Edwards, B., Savini, G., Favata, F., Tessenyi, M., and Wilcock, B. J.: Mauve: a UV-Vis satellite dedicated to monitor stellar activity and variability, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-282, https://doi.org/10.5194/epsc2024-282, 2024.

All exoplanet host stars are unique and have the capacity to exhibit stellar activity in the form of spots and faculae to differing extents and in a highly temporally variable way. It is therefore reasonable to expect that we are seeing, and will continue to see widespread stellar contamination of differing degrees throughout both current and future observations of exoplanets in transmission. Furthermore, as this contamination is potentially varying on an epoch-to-epoch basis, using a one-size-fits-all analytical approach is unwise and implausible even for a single exoplanetary system. 

For transmission spectra obtained with both current and future instruments, the majority of the information pertaining to the extent of stellar contamination is contained within the shortest wavelength datapoints in the optical regime. As such, good coverage in both the optical and the infrared is essential for conducting accurate combined star-planet retrieval analyses. Unfortunately from the stellar-perspective, the optical regime is usually less prioritised by instrumentation with respect to the infrared, where the bulk of the planetary information lies. As such the optical region tends to have a lower resolution and the datapoints themselves frequently have larger error bars leading a retrieval to assign a lower priority to them during the fitting process. Conducting retrievals on the optical data alone is also not suggested as they require the planetary information contained within the infrared to act as an anchor point in order to perform optimally. Stellar contamination is capable of introducing significant biases in the retrieved planetary parameters if not corrected for so it is paramount that we fully understand the extent of stellar contamination within our observations. In order to achieve this, we need to leverage the information content of the shortest wavelengths to the fullest extent alongside that of the infrared, both so that we can perform complete star-planet analyses of current observations with JWST and in preparation for future exoplanet-dedicated missions e.g. Twinkle and Ariel that will open up the possibility for population studies on an unprecedented scale. 

With this rationale in mind, we introduce two new, complementary metrics, the Stellar Activity Distance (SAD) metric and the Stellar Activity Temporal (SAT) metric which are designed to indicate the extent of stellar contamination at the time of observation in a highly interpretable way. These metrics are intended to aid in the assessment of different retrieval models, alongside existing model comparison tools e.g. the Bayes Factor and activity indicators e.g. log(R′ HK), the uses of which are already well-cemented within the literature, to give a bigger picture context of the host stars stellar activity level, both during an individual observation and over subsequent visits. 

Briefly, the SAD is a chi-squared inspired, goodness-of-fit metric that focuses solely on wavelengths bluewards of 1µm. At first order the SAD seeks to determine whether any slopes in the optical data can be sufficiently reproduced by a Rayleigh scattering slope from atmospheric hazes alone, or whether or not an additional departure from Rayleigh scattering due to stellar contamination is required. This departure can be either in the form of strengthening the positive bluewards slope as is expected for a spot-dominated activity regime or nullifying/reversing the slope in the case of a faculae-dominated regime. The SAD complements the Bayes Factor as although both tools are founded on a similar ideology, they differ in that the SAD focuses solely on the fit in the optical regime, whereas the Bayes Factor indicates which model is preferred by the entire observed spectrum. In contrast, the SAT is designed to assess the repeatability, or lack thereof, of observations from subsequent visits to the same exoplanetary system. As such the SAT requires that the system has been observed at at least two different epochs with the same instrument. By taking the pairwise differences between each datapoint and computing the average we can quantify the differences between multiple observations both in ppm, or as a percentage difference with respect to the planets weighted average transit depth in the IR allowing for comparability between systems. The use of both of these metrics for WASP-6b, a planet orbiting a well-known active host star, are shown in Fig. 1 below.

Figure 1. Left – The Stellar Activity Distance metric (SAD) calculation for a single dataset combining visits with HST STIS grisms G430L and G750L for WASP-6b. The best fit retrieved spectra for two retrieval instances are plotted with the retrieval model accounting for stellar contamination shown in orange and the retrieval model neglecting this shown in cyan. The SAD is calculated as the average distance of the baseline model from the observation divided by the average distance of the stellar contamination model and here shows a strong preference for the inclusion of stellar activity for these observations of WASP-6b. Right – The Stellar Activity Temporal metric (SAT) calculated for the same planet for two G430L visits taken at different epochs. The two observations, shown in purple and cyan, appear to increasingly diverge as a function of decreasing wavelength. The orange dashed line represents the weighted average transit depth for WASP-6b calculated from the HST WFC3 observation in the IR. Adapted from Saba et al. (2024)

In this presentation I will introduce these metrics and show their application to both current observations with HST STIS (Saba et al. 2024) and future observations with Ariel, where they will enable us to extract as much information about the host star and its activity level from the optical FGS photometers as possible. I hope to demonstrate that, alongside other traditional activity indicators, these metrics may be used to give us a better understanding of which exoplanetary systems require follow-up observations through large, ground-based, stellar-focused surveys in order to adequately characterise the host star before we can accurately include their planets within our studies of comparative exoplanetology

REFERENCES
Saba, A., Thompson, A., Hou Yip, K., et al. 2024, arXiv:2404.15505. doi:10.48550/arXiv.2404.15505

How to cite: Thompson, A., Saba, A., Yip, K. H., Ma, S., Tsiaras, A., Al-Refaie, A., and Tinetti, G.: Designing new Stellar Activity Metrics for use with Exoplanet Transmission Spectra Obtained with both Current and Future Missions, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-1202, https://doi.org/10.5194/epsc2024-1202, 2024.

The diversity of upcoming exoplanetary missions, both space and ground-based, will provide unprecedented view of the extrasolar planet population in the broader Galactic context. Missions like PLATO and ARIEL will build on the work of Kepler and TESS by discovering more planets with bright host stars and characterising the atmospheric compostition of a miriad of planetary systems. This is already presenting a need for systematic and coordinated ground-based follow-up observations to better support these missions. The rapid reaction and flexible, remote scheduling capabilities of robotic facilites makes them powerful tools for scientific explotation of time domain topics in general, and in particular of exoplanets and characterisation of their host stars.

We introduce the Joan Oró telescope (TJO), a fully-robotic 0.8m telescope at the Montsec Observatory dedicated to astrophysical research and Space Surveillance and Tracking activities. We present past and ongoing involment in exoplanetary research, such as photometric follow-up programs of CARMENES, TESS and ARIEL targets, and the potential for transient alert observations and unattended long-term monitoring in support of the next generation of exoplanetary surveys.

How to cite: Domènech Rams, G., Herrero, K., Gil, P., Baroch, D., and Domene, F.: Robotic follow-up in the era of exoplanetary surveys:the TJO telescope at Montsec Observatory, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-1127, https://doi.org/10.5194/epsc2024-1127, 2024.

Tartu Observatory's telescopes offer unique guaranteed access to objects in the Northern Hemisphere, facilitating long-term monitoring of various targets. Our largest 1.5 m instrument, has recently undergone significant upgrades, including the installation of a medium-resolution fibre-fed echelle spectrograph covering a bandwidth from 390 nm to 750 nm. This spectrograph offers flexibility with input options between two different fibre sizes, enabling retrieval of medium-resolution spectra.

Moreover, a custom-designed 4-channel instrument cube has been integrated, allowing for the attachment of two additional instruments to the telescope. Among these additions is a photometer equipped with Johnson-Cousins BVRI and Sloan g’r’i’z’ filters. These upgrades enhance our spectroscopic and photometric capabilities, particularly for studying celestial objects such as transits, exoplanet host stars, asteroids, and transients.

In our presentation, we will provide an update on the status of these projects, detailing the improvements made and the impact on our observational capabilities.

How to cite: Ramler, H. and Eenmäe, T.: New fibre-fed Echelle spectrograph and photometer on 1.5 m telescope at Tartu Observatory, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-386, https://doi.org/10.5194/epsc2024-386, 2024.

We can hope that, in a near future, external occulter systems, called Starshade will allow the detection of exo-Earth type exoplanets, but as unresolved points.  The telescopes used will be of a few meters.To get real multi-pixels images of  exoplanets,  interferometry with diluted apertures separated from each other by several hundred meters will be necessary. Can we combine interferometry and external occulters? This is the problem that we examine in our work.

How to cite: Aime, C., Theys, C., and Prunet, S.: Starshades and interferometry for exoplanet imaging, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-1157, https://doi.org/10.5194/epsc2024-1157, 2024.