AO-2: Approved Programmes

Announced on 25 February 2021

The second Announcement of Opportunity (AO-2) for the CHEOPS Guest Observers Programme came out on 4 November 2020, and closed approximately 4 weeks later on 1 December 2020. The CHEOPS Time Allocation Committee (TAC) met on the 2-3 February 2021.

Based on the recommendations made by the TAC, the Director of Science has awarded observing time on CHEOPS to the proposals listed in the table below. 9 programmes have been awarded observing time on CHEOPS, covering a total of 638.1 orbits. The number of orbits that have been awarded is below what had been foreseen to be allocated for this call - details of how it will be possible to apply for the remaining orbits will be announced in coming months.

Targets that are part of these programmes have been added to the Reserved Target List and cannot be included in observing programmes of other scientists until the AO-2 observations have been completed.

Principal Investigators of proposals that have been awarded time will be contacted by email, and are required to complete and submit observation requests at their earliest convenience  Guidelines on how to prepare observation requests can be found in the document at this link.

Abstracts

ID001 — The most precise radius and mass determination of an exo-Earth (PI: Jose Caballero)
Gl 486 b is a transiting rocky planet in a 1.47 d orbital period around a relatively bright M3.5 V low-mass star at only 8.08 pc. Using TESS, CARMENES and MAROON-X, Trifonov et al. (subm. to Science) measured precise planet mass and radius of 2.82 M⊕ and 1.605 R⊕ with relative uncertainties of 4.2% and 5.1%, respectively. We aim to improve the Gl 486 b's mass and radius determination down to 2-3% with additional precise RV data and, crucially, photometric follow-up by CHEOPS. Such a precision in the planet mass and radius would give rise to rocky planet internal composition and structure studies not done before (e.g. constraining the core-to-mantle ratio with an accuracy better than 10%, investigating the planet's oxygen fugacity). Because of its equilibrium temperature, below the molten lava temperature boundary but high enough for having the largest emission and transmission spectroscopic metrics among M-dwarf transiting rocky planets, and the relative brightness and weak activity of its stellar host, Gl 486 b is also ideal for atmospheric investigation. A better mass and, especially, radius determination can constrain theories for how terrestrial planets around M dwarfs form and retain atmospheres. We request observing 10 transits in 10 visits of 2 orbits each (total requested time: 20 orbits).

ID002 — Discriminating between conflicting measurements of WASP-161b: Insights into the planet’s atmosphere (PI: Fan Yang)
We propose observing two primary transit events of WASP-161b, using CHEOPS. WASP-161b is an already identified giant planet (Barkaoui et al. 2019). The TESS transit depth reveals an offset at the 2 σ level compared to the transit depth resulting from joint analysis of other multiwavelength data. The difference in the wavelength-dependent transit depth could either be due to atmospheric features, sampling rate distortions of the light curve, or due to errors in the derived limb darkening parameters. The high sampling rate and precision of the CHEOPS data will result in an accurate determination of these parameters. It will then be used as priors in the re-analysis of the previous light curves for a joint recharacterization of its atmosphere. The preferred observable mid-point times are two of 2022-01-04T, 2022-01-10T, 2021-12-25T, 2021-12-19T.

ID004 — Confirming and characterising a catastrophically disintegrating hot rocky planet orbiting DMPP-1 (PI: Carole Haswell)
The catastrophically disintegrating exoplanets (CDEs) were discovered through the variable transits of their dust clouds. The dust co-exists with, and condenses from, the sublimated metal-rich vapour from the surface of a minor planet heated to ~2100K by proximity to its host star. They offer rich opportunities to probe the compositions of rocky bodies outside our own Solar System. Sadly, however, known CDEs orbit stars too faint for the necessary detailed follow-up observations. The Dispersed Matter Planet Project seeks CDE analogues and progenitors orbiting bright, nearby stars. Our target, DMPP-1, is a bright F dwarf hosting a compact multi-planet system of low mass planets detected by our RV programme. TESS data revealed a transit detected at 5 sigma, i.e. a false alarm probability of 1.6%. The transit does not correspond to any of the RV periodicities, but the mass threshold of the extant RV data is about 1 M⊕. The insolation suffered by this putative transiting planet is an exact match to that of the known Kepler CDEs. This TESS transit could therefore correspond to a CDE, or CDE progenitor orbiting a star brighter than V=8. We propose to verify the transit beyond doubt by obtaining CHEOPS coverage of four transits, and to assess the marginal evidence for variable transit depth, which would indicate a dusty transit. We will also perform a sensitive search for transits of the RV planets and other bodies, and analyse the data for phase-curve signals.

ID005 — CHEOPS transits of a 100 Myr old super-Earth in AB Dor moving group (PI: George Zhou)
Planets around bright, young stars are our best laboratories to sample planet evolution in real time. HIP94235b is a super-Earth sized planet candidate orbiting a Gmag=8.2 Sun-like star in the ~100 Myr old AB Doradus moving group, identified in the recent observations from the Transiting Exoplanet Survey Satellite. The planet lies near the evaporation boundary where there is a paucity of super-Earth sized planets around mature aged stars, and is the perfect planet to study atmospheric evaporation processes in-situ. We will use CHEOPS to observe two transits of HIP94235b. These observations are essential to validating the planet, and to refining its transit ephemeris to enable the future atmospheric observations. With only one sector of TESS observations available, and no future TESS visits planned, CHEOPS is the only facility suitable to observe the shallow transits of this important planetary system, and preserve its transit ephemeris for future studies.

ID007 — Improving the bulk densities for small planets observed with HARPS-N, K2, TESS, and CHEOPS (PI: Annelies Mortier)
Transiting planets offer a unique opportunity to measure the bulk density of an exoplanet. This enables studies of planet interior composition and in turn informs planet formation and evolution so we can get a better understanding of the large diversity of exoplanets in the Universe. Despite thousands of known exoplanets, there is still a lack of well characterised small planets. The HARPS-N Science Team has been leading the effort of characterising these small transiting planets, representing a third of these well-characterised small planets. In this proposal we are requesting two CHEOPS transits for each of twelve HARPS-N targets. These targets are planet candidates from the K2 or TESS mission, and a large chunk of the HARPS-N GTO observing time has been or is being invested in order to measure precise and accurate masses for these planets. Securing CHEOPS transits will serve the double goal of improving the radii and masses of these planets. The precise transit photometry of CHEOPS will allow us improve the radius. Furthermore, obtaining two new transits with CHEOPS will reduce the uncertainties on the period and transit time allowing narrower priors on the RV model and thus enabling a more precise mass measurement. Therefore, by combining precise CHEOPS and HARPS-N data, and archival K2/TESS photometry we will be able to deliver the best possible bulk density measurement for these small planets.

ID008 — Probing the starspots of WASP-85 A (PI: Heather Cegla)
Transiting planets offer a unique opportunity to probe and spatially resolve the surfaces of distant stars. In turn, this can also feedback into improvements for the confirmation and characterisation of exoplanets. Our aim is to use CHEOPS photometry and spectroscopic observations of WASP-85 A b to isolate and analyse the first cross-correlation functions (CCFs) of starspots on a star other than the Sun. This is possible through the reloaded RM technique, which requires a high precision light curve to accurately normalise the ground-based spectra; in doing so, we can directly subtract in- from out-of-transit observations to isolate the starlight behind the planet. CHEOPS light curves will also serve as a critical tool to robustly identify when the planet occults an active region. WASP-85 A is ideal as its hot Jupiter regularly occults starspots, and it can be observed simultaneously by CHEOPS and HARPS-N. WASP-85 A’s relatively high effective temperature, whilst maintaining a convective envelope, means the net convective blueshift and limb-dependent variations should be large and readily detectable. In a starspot, the convective blueshift is suppressed and the shape of the local CCF altered; characterising these differences is critical to validate stellar models. This proposal is timely as current/next-gen spectrographs urgently need improved stellar characterisation to push forward planet confirmation and characterisation.

ID010 — What is the nature of the young planets in the V1298 Tau system? (PI: Jean-Michel Desert)
The newborn planetary system comprising of four gas giants transiting the bright 23 Myr old star V1298 Tau presents an exciting opportunity to probe the properties of planetary systems immediately post formation, and to do so within one system. We propose to observe the transits of the hottest inner three Neptunes and sub-Neptunes planets in the system, V1298 Tau b,c, and d. We will measure their mass dynamically through transit timing variations (TTVs), we will improve the precision on their radii, and we will estimate the eccentricity of planet b, the one with the longest period of the inner three planets. In turns, these measurements will inform us about the nature of this planet: we will unveil whether these planets are Neptune-mass objects, or whether they are at lower density.This is important, because such young system are thoughts to be the progenitors to the population of Super-Earths and Mini-Neptunes that have been detected extensively by exoplanet surveys. Ultimately, the planets of the V1298 Tau system could evolve towards planets that straddle the radius valley.

ID012 — Exploring the Diversity of Small Planet Compositions (PI: Diana Dragomir)
The sizes and masses of planets provide a powerful constraint on their composition. But until recently, the exoplanet community had access to large samples of just radii for small planets. TESS is enabling us to finally also measure the masses of an ensemble of small planets. Complementarily, we propose to use CHEOPS to measure precise radii for seven small TESS planets in order to constrain their interior composition, and explore the period-radius valley. The proposed observations will also serve to significantly refine the ephemerides of these planets, constrain their orbital eccentricity, and provide an anchor point at visible wavelengths for infrared transmission spectroscopy observations.

ID013 — How Cloudy is the Neptune Desert? (PI: James Jenkins)
We aim to continue to use the unique capabilities afforded by CHEOPS to measure optical secondary eclipses from planets around the Neptune Desert. We have selected two new planet-hosting stars that are bright enough to gain the required ~30 ppm precision to detect their expected eclipse depths. With these observations we aim to determine the planetary atmospheric albedos, providing the first benchmark ensemble measurements of the characteristics of any clouds or hazes in hot Neptunes. Indeed, the question if Neptunes are simply scaled-down gas giants can be tested directly by these observations, by helping to determine if they are cloud dominated planets or not. The presence, or lack thereof, of clouds also helps to understand the global abundance mixing ratios of planets. For example, we may expect metal-rich planets to exhibit more dense cloud formation, but on the other hand metal-richness may also mean that there is a lack of dayside clouds due to condensates being sequestered at deeper layers in the atmosphere. The long-term goal of the project is to combine these results with measurements from other optical and near-infrared bands to understand in detail the properties of aerosols and other condensates in these low-mass planets. Finally, we shall include the observations we have already attained with CHEOPS for the ultrahot Neptune LTT 9779b, allowing a robust test of the nature of absorbers in the upper atmospheres of irradiated Neptunes.

This page was last updated on 25 February 2021.