arXiv subjects

Pere Guerra

Publications and source records attributed to Pere Guerra.

17 recordsLinked to original sources

arXiv2026

Gas-depleted planet formation occurred in the four-planet system around the red dwarf LHS 1903

Small exoplanet radii show two populations, referred to as super-Earths and sub-Neptunes, separated by a gap known as the radius valley. This may be produced by the removal of atmospheres due to stellar or internal heating, or lack of an initial envelope. We us transit photometry and radial velocity measurements to detect and characterize four planets orbiting LHS 1903, a red dwarf (M-dwarf) star in the Milky Way's thick disk. The planets have orbital periods between 2.2 and 29.3 days, and span the radius valley within a single planetary system. The derived densities indicate that LHS 1903 b is rocky, while LHS 1903 c and LHS 1903 d have extended atmospheres. Although the most distant planet from the host star, LHS 1903 e, has no gaseous envelope, indicating it formed from gas-depleted material.

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arXiv2026

TOI-3862 b: A dense super-Neptune deep in the hot Neptune desert

The structure and evolution of close-in exoplanets are shaped by atmospheric loss and migration processes, which give rise to key population features such as the hot Neptune desert, ridge, and savanna - regions of the period-radius space whose boundaries offer critical insights into planetary formation and survival. As part of the KESPRINT collaboration, we selected the TESS transiting planet candidate TOI-3862.01 for radial velocity follow-up to confirm its planetary nature and characterize its mass and bulk properties. This planet candidate is of particular interest due to its position in the middle of the hot Neptune desert, making it a valuable probe for testing theories of planet migration and atmospheric loss. We confirmed the planetary nature and determined the mass of TOI-3862.01 (hereinafter TOI-3862b) by performing a joint fit with both transit and radial velocity data, precisely characterizing the bulk properties of this planet. TOI-3862b is a super-Neptune on a 1.56-day orbit around a Sun-like star with an effective temperature of 5300$\pm$50K. It has a mass of 53.7$_{-2.9}^{+2.8}$ M$_{\oplus}$ and a radius of 5.53$\pm$0.18 R$_{\oplus}$, corresponding to a density of 1.7$\pm$0.2 g/cm^3. This places it among the rare population of hot and dense super-Neptune desert planets. TOI-3862b, residing deep in the hot Neptune desert, represents a rare occurrence in an otherwise sparsely populated region, offering a valuable opportunity to probe the processes that may allow planets to survive in such environments.

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arXiv2025

Precise mass and radius determination for two new and one known Neptune-sized planets around G Dwarf hosts

As part of the KESPRINT collaboration, we present the discovery and characterization of three exoplanets in the sub-Neptune to super-Neptune regime, spanning key regions of the exo-Neptunian landscape. TOI-1472c and TOI-1648b are newly discovered sub-Neptunes, while TOI-1472b is a previously known super-Neptune for which we provide an improved mass measurement. These planets have orbital periods of 6--15 days and radii of 2.5--4.1 R$_\oplus$, probing regions where planet formation and atmospheric evolution remain poorly understood. We combine TESS transit photometry with ground-based radial velocities to determine precise masses, radii, and orbital properties. TOI-1472b has a mass of $18.0^{+0.84}_{-0.85}$ M$_\oplus$ and a radius of $4.06 \pm 0.10$ R$_\oplus$, TOI-1472c has a mass of $21.1^{+0.96}_{-0.99}$ M$_\oplus$ and a radius of $3.33 \pm 0.08$ R$_\oplus$, and TOI-1648b has a mass of $7.4^{+1.1}_{-1.3}$ M$_\oplus$ and a radius of $2.54^{+0.14}_{-0.12}$ R$_\oplus$. The planets exhibit a range of eccentricities (0.041--0.178), indicating diverse evolutionary histories. TOI-1648b, with a high Transmission Spectroscopy Metric (TSM $\sim$59), is a promising target for atmospheric characterization. Together, these three planets provide precise constraints on the structure, composition, and dynamical evolution of small to intermediate-sized exoplanets, enriching our understanding of the exo-Neptunian landscape.

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arXiv2025

TrES-1 b: A Case Study in Detecting Secular Evolution of Exoplanet Orbits

We present a comprehensive analysis of transit, eclipse, and radial velocity data of the hot Jupiter TrES-1 b and confirm evidence of orbital variations on secular timescales. Apparent variations due to systemic motion and light travel time effects have been ruled out, indicating that the observed changes are dynamical in origin. Joint modeling of the TrES-1 b data favors an apsidal precession model, but the rapid precession rate of $4^\circ$ yr$^{-1}$ cannot be explained without invoking an undetected close-in planetary companion, which remains unseen in the data. While radial velocity measurements reveal a previously undetected companion candidate on a wide, eccentric orbit, it is unlikely to drive the observed evolution of TrES-1 b. However, an orbital decay model provides a plausible alternative if the loss of orbital energy is driven by planetary obliquity tides. We find that the best-fit orbital decay rate of $-7.1^{ +1.5}_{-1.6}$ ms yr$^{-1}$ is aligned with theoretical predictions for modified tidal quality factors of hot Jupiters if TrES-1 b has a planetary obliquity $\varepsilon_p > 30^\circ$. We encourage follow-up observations of this system, particularly of eclipse timing and radial velocities, to further constrain the nature of the observed evolution. This paper provides a practical framework for studying secular variations and aims to accelerate future research on similar systems.

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arXiv2024

OrCAS: Origins, Compositions, and Atmospheres of Sub-neptunes. I. Survey Definition

Sub-Neptunes - volatile-rich exoplanets smaller than Neptune - are intrinsically the most common type of planet known. However, the formation and nature of these objects, as well as the distinctions between sub-classes (if any), remain unclear. Two powerful tools to tease out the secrets of these worlds are measurements of (i) atmospheric composition and structure revealed by transit and/or eclipse spectroscopy, and (ii) mass, radius, and density revealed by transit photometry and Doppler spectroscopy. Here we present OrCAS, a survey to better elucidate the origins, compositions, and atmospheres of sub-Neptunes. This radial velocity survey uses a repeatable, quantifiable metric to select targets suitable for subsequent transmission spectroscopy and address key science themes about the atmospheric & internal compositions and architectures of these systems. Our survey targets 26 systems with transiting sub-Neptune planet candidates, with the overarching goal of increasing the sample of such planets suitable for subsequent atmospheric characterization. This paper lays out our survey's science goals, defines our target prioritization metric, and performs light-curve fits and statistical validation using existing TESS photometry and ground-based follow-up observations. Our survey serves to continue expanding the sample of small exoplanets with well-measured properties orbiting nearby bright stars, ensuring fruitful studies of these systems for many years to come.

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arXiv2023

Identification of the Top TESS Objects of Interest for Atmospheric Characterization of Transiting Exoplanets with JWST

JWST has ushered in an era of unprecedented ability to characterize exoplanetary atmospheres. While there are over 5,000 confirmed planets, more than 4,000 TESS planet candidates are still unconfirmed and many of the best planets for atmospheric characterization may remain to be identified. We present a sample of TESS planets and planet candidates that we identify as "best-in-class" for transmission and emission spectroscopy with JWST. These targets are sorted into bins across equilibrium temperature $T_{\mathrm{eq}}$ and planetary radius $R{_\mathrm{p}}$ and are ranked by transmission and emission spectroscopy metric (TSM and ESM, respectively) within each bin. In forming our target sample, we perform cuts for expected signal size and stellar brightness, to remove sub-optimal targets for JWST. Of the 194 targets in the resulting sample, 103 are unconfirmed TESS planet candidates, also known as TESS Objects of Interest (TOIs). We perform vetting and statistical validation analyses on these 103 targets to determine which are likely planets and which are likely false positives, incorporating ground-based follow-up from the TESS Follow-up Observation Program (TFOP) to aid the vetting and validation process. We statistically validate 23 TOIs, marginally validate 33 TOIs to varying levels of confidence, deem 29 TOIs likely false positives, and leave the dispositions for 4 TOIs as inconclusive. 14 of the 103 TOIs were confirmed independently over the course of our analysis. We provide our final best-in-class sample as a community resource for future JWST proposals and observations. We intend for this work to motivate formal confirmation and mass measurements of each validated planet and encourage more detailed analysis of individual targets by the community.

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arXiv2023

TOI-4010: A System of Three Large Short-Period Planets With a Massive Long-Period Companion

We report the confirmation of three exoplanets transiting TOI-4010 (TIC-352682207), a metal-rich K dwarf observed by TESS in Sectors 24, 25, 52, and 58. We confirm these planets with HARPS-N radial velocity observations and measure their masses with 8 - 12% precision. TOI-4010 b is a sub-Neptune ($P = 1.3$ days, $R_{p} = 3.02_{-0.08}^{+0.08}~R_{\oplus}$, $M_{p} = 11.00_{-1.27}^{+1.29}~M_{\oplus}$) in the hot Neptune desert, and is one of the few such planets with known companions. Meanwhile, TOI-4010 c ($P = 5.4$ days, $R_{p} = 5.93_{-0.12}^{+0.11}~R_{\oplus}$, $M_{p} = 20.31_{-2.11}^{+2.13}~M_{\oplus}$) and TOI-4010 d ($P = 14.7$ days, $R_{p} = 6.18_{-0.14}^{+0.15}~R_{\oplus}$, $M_{p} = 38.15_{-3.22}^{+3.27}~M_{\oplus}$) are similarly-sized sub-Saturns on short-period orbits. Radial velocity observations also reveal a super-Jupiter-mass companion called TOI-4010 e in a long-period, eccentric orbit ($P \sim 762$ days and $e \sim 0.26$ based on available observations). TOI-4010 is one of the few systems with multiple short-period sub-Saturns to be discovered so far.

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arXiv2022

TOI-1136 is a Young, Coplanar, Aligned Planetary System in a Pristine Resonant Chain

Convergent disk migration has long been suspected to be responsible for forming planetary systems with a chain of mean-motion resonances (MMR). Dynamical evolution over time could disrupt the delicate resonant configuration. We present TOI-1136, a 700-Myr-old G star hosting at least 6 transiting planets between $\sim$2 and 5 $R_\oplus$. The orbital period ratios deviate from exact commensurability by only $10^{-4}$, smaller than the $\sim$\,$10^{-2}$ deviations seen in typical Kepler near-resonant systems. A transit-timing analysis measured the masses of the planets (3-8$M_\oplus$) and demonstrated that the planets in TOI-1136 are in true resonances with librating resonant angles. Based on a Rossiter-McLaughlin measurement of planet d, the star's rotation appears to be aligned with the planetary orbital planes. The well-aligned planetary system and the lack of detected binary companion together suggest that TOI-1136's resonant chain formed in an isolated, quiescent disk with no stellar fly-by, disk warp, or significant axial asymmetry. With period ratios near 3:2, 2:1, 3:2, 7:5, and 3:2, TOI-1136 is the first known resonant chain involving a second-order MMR (7:5) between two first-order MMR. The formation of the delicate 7:5 resonance places strong constraints on the system's migration history. Short-scale (starting from $\sim$0.1 AU) Type-I migration with an inner disk edge is most consistent with the formation of TOI-1136. A low disk surface density ($Σ_{\rm 1AU}\lesssim10^3$g~cm$^{-2}$; lower than the minimum-mass solar nebula) and the resultant slower migration rate likely facilitated the formation of the 7:5 second-order MMR. TOI-1136's deep resonance suggests that it has not undergone much resonant repulsion during its 700-Myr lifetime. One can rule out rapid tidal dissipation within a rocky planet b or obliquity tides within the largest planets d and f.

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arXiv2022

The TESS-Keck Survey. XI. Mass Measurements for Four Transiting sub-Neptunes orbiting K dwarf TOI-1246

Multi-planet systems are valuable arenas for investigating exoplanet architectures and comparing planetary siblings. TOI-1246 is one such system, with a moderately bright K dwarf ($\rm{V=11.6,~K=9.9}$) and four transiting sub-Neptunes identified by TESS with orbital periods of $4.31~\rm{d},~5.90~\rm{d},~18.66~\rm{d}$, and $~37.92~\rm{d}$. We collected 130 radial velocity observations with Keck/HIRES and TNG/HARPS-N to measure planet masses. We refit the 14 sectors of TESS photometry to refine planet radii ($\rm{2.97 \pm 0.06~R_\oplus},\rm{2.47 \pm 0.08~R_\oplus}, \rm{3.46 \pm 0.09~R_\oplus}$, $\rm{3.72 \pm 0.16~R_\oplus}$), and confirm the four planets. We find that TOI-1246 e is substantially more massive than the three inner planets ($\rm{8.1 \pm 1.1 M_\oplus}$, $\rm{8.8 \pm 1.2 M_\oplus}$, $\rm{5.3 \pm 1.7 M_\oplus}$, $\rm{14.8 \pm 2.3 M_\oplus}$). The two outer planets, TOI-1246 d and TOI-1246 e, lie near to the 2:1 resonance ($\rm{P_{e}/P_{d}=2.03}$) and exhibit transit timing variations. TOI-1246 is one of the brightest four-planet systems, making it amenable for continued observations. It is one of only six systems with measured masses and radii for all four transiting planets. The planet densities range from $\rm{0.70 \pm 0.24}$ to $3.21 \pm 0.44 \rm{g/cm^3}$, implying a range of bulk and atmospheric compositions. We also report a fifth planet candidate found in the RV data with a minimum mass of 25.6 $\pm$ 3.6 $\rm{M_\oplus}$. This planet candidate is exterior to TOI-1246 e with a candidate period of 93.8 d, and we discuss the implications if it is confirmed to be planetary in nature.

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arXiv2022

Validation of 13 Hot and Potentially Terrestrial TESS Planets

The James Webb Space Telescope (JWST) will be able to probe the atmospheres and surface properties of hot, terrestrial planets via emission spectroscopy. We identify 18 potentially terrestrial planet candidates detected by the Transiting Exoplanet Survey Satellite (TESS) that would make ideal targets for these observations. These planet candidates cover a broad range of planet radii ($R_{\rm p} \sim 0.6 - 2.0 R_\oplus$) and orbit stars of various magnitudes ($K_s = 5.78 - 10.78$, $V = 8.4 - 15.69$) and effective temperatures ($T_{\rm eff }\sim 3000 - 6000$ K). We use ground-based observations collected through the TESS Follow-up Observing Program (TFOP) and two vetting tools -- DAVE and TRICERATOPS -- to assess the reliabilities of these candidates as planets. We validate 13 planets: TOI-206 b, TOI-500 b, TOI-544 b, TOI-833 b, TOI-1075 b, TOI-1411 b, TOI-1442 b, TOI-1693 b, TOI-1860 b, TOI-2260 b, TOI-2411 b, TOI-2427 b, and TOI-2445 b. Seven of these planets (TOI-206 b, TOI-500 b, TOI-1075 b, TOI-1442 b, TOI-2260 b, TOI-2411 b, and TOI-2445 b) are ultra-short-period planets. TOI-1860 is the youngest ($133 \pm 26$ Myr) solar twin with a known planet to date. TOI-2260 is a young ($321 \pm 96$ Myr) G dwarf that is among the most metal-rich ([Fe/H] = $0.22 \pm 0.06$ dex) stars to host an ultra-short-period planet. With an estimated equilibrium temperature of $\sim 2600$ K, TOI-2260 b is also the fourth hottest known planet with $R_{\rm p} < 2 \, R_\oplus$.

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arXiv2022

A transiting, temperate mini-Neptune orbiting the M dwarf TOI-1759 unveiled by TESS

We report the discovery and characterization of TOI-1759~b, a temperate (400 K) sub-Neptune-sized exoplanet orbiting the M~dwarf TOI-1759 (TIC 408636441). TOI-1759 b was observed by TESS to transit on sectors 16, 17 and 24, with only one transit observed per sector, creating an ambiguity on the orbital period of the planet candidate. Ground-based photometric observations, combined with radial-velocity measurements obtained with the CARMENES spectrograph, confirm an actual period of $18.85019 \pm 0.00014$ d. A joint analysis of all available photometry and radial velocities reveal a radius of $3.17 \pm 0.10\,R_\oplus$ and a mass of $10.8 \pm 1.5\,M_\oplus$. Combining this with the stellar properties derived for TOI-1759 ($R_\star = 0.597 \pm 0.015\,R_\odot$; $M_\star = 0.606 \pm 0.020\,M_\odot$; $T_{\textrm{eff}} = 4065 \pm 51$ K), we compute a transmission spectroscopic metric (TSM) value of over 80 for the planet, making it a good target for transmission spectroscopy studies. TOI-1759 b is among the top five temperate, small exoplanets ($T_\textrm{eq} < 500$ K, $R_p < 4 \,R_\oplus$) with the highest TSM discovered to date. Two additional signals with periods of 80 d and $>$ 200 d seem to be present in our radial velocities. While our data suggest both could arise from stellar activity, the later signal's source and periodicity are hard to pinpoint given the $\sim 200$ d baseline of our radial-velocity campaign with CARMENES. Longer baseline radial-velocity campaigns should be performed in order to unveil the true nature of this long period signal.

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arXiv2022

A Possible Alignment Between the Orbits of Planetary Systems and their Visual Binary Companions

Astronomers do not have a complete picture of the effects of wide-binary companions (semimajor axes greater than 100 AU) on the formation and evolution of exoplanets. We investigate these effects using new data from Gaia EDR3 and the TESS mission to characterize wide-binary systems with transiting exoplanets. We identify a sample of 67 systems of transiting exoplanet candidates (with well-determined, edge-on orbital inclinations) that reside in wide visual binary systems. We derive limits on orbital parameters for the wide-binary systems and measure the minimum difference in orbital inclination between the binary and planet orbits. We determine that there is statistically significant difference in the inclination distribution of wide-binary systems with transiting planets compared to a control sample, with the probability that the two distributions are the same being 0.0037. This implies that there is an overabundance of planets in binary systems whose orbits are aligned with those of the binary. The overabundance of aligned systems appears to primarily have semimajor axes less than 700 AU. We investigate some effects that could cause the alignment and conclude that a torque caused by a misaligned binary companion on the protoplanetary disk is the most promising explanation.

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arXiv2021

TIC 172900988: A Transiting Circumbinary Planet Detected in One Sector of TESS Data

We report the first discovery of a transiting circumbinary planet detected from a single sector of TESS data. During Sector 21, the planet TIC 172900988b transited the primary star and then 5 days later it transited the secondary star. The binary is itself eclipsing, with a period of P = 19.7 days and an eccentricity of e = 0.45. Archival data from ASAS-SN, Evryscope, KELT, and SuperWASP reveal a prominent apsidal motion of the binary orbit, caused by the dynamical interactions between the binary and the planet. A comprehensive photodynamical analysis of the TESS, archival and follow-up data yields stellar masses and radii of M1 = 1.2384 +/- 0.0007 MSun and R1 = 1.3827 +/- 0.0016 RSun for the primary and M2 = 1.2019 +/- 0.0007 MSun and R2 = 1.3124 +/- 0.0012 RSun for the secondary. The radius of the planet is R3 = 11.25 +/- 0.44 REarth (1.004 +/- 0.039 RJup). The planet's mass and orbital properties are not uniquely determined - there are six solutions with nearly equal likelihood. Specifically, we find that the planet's mass is in the range of 824 < M3 < 981 MEarth (2.65 < M3 < 3.09 MJup), its orbital period could be 188.8, 190.4, 194.0, 199.0, 200.4, or 204.1 days, and the eccentricity is between 0.02 and 0.09. At a V = 10.141 mag, the system is accessible for high-resolution spectroscopic observations, e.g. Rossiter-McLaughlin effect and transit spectroscopy.

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arXiv2021

TESS discovery of a super-Earth and three sub-Neptunes hosted by the bright, Sun-like star HD 108236

We report the discovery and validation of four extrasolar planets hosted by the nearby, bright, Sun-like (G3V) star HD~108236 using data from the Transiting Exoplanet Survey Satellite (TESS). We present transit photometry, reconnaissance and precise Doppler spectroscopy as well as high-resolution imaging, to validate the planetary nature of the objects transiting HD~108236, also known as the TESS Object of Interest (TOI) 1233. The innermost planet is a possibly-rocky super-Earth with a period of $3.79523_{-0.00044}^{+0.00047}$ days and has a radius of $1.586\pm0.098$ $R_\oplus$. The outer planets are sub-Neptunes, with potential gaseous envelopes, having radii of $2.068_{-0.091}^{+0.10}$ $R_\oplus$, $2.72\pm0.11$ $R_\oplus$, and $3.12_{-0.12}^{+0.13}$ $R_\oplus$ and periods of $6.20370_{-0.00052}^{+0.00064}$ days, $14.17555_{-0.0011}^{+0.00099}$ days, and $19.5917_{-0.0020}^{+0.0022}$ days, respectively. With V and K$_{\rm s}$ magnitudes of 9.2 and 7.6, respectively, the bright host star makes the transiting planets favorable targets for mass measurements and, potentially, for atmospheric characterization via transmission spectroscopy. HD~108236 is the brightest Sun-like star in the visual (V) band known to host four or more transiting exoplanets. The discovered planets span a broad range of planetary radii and equilibrium temperatures, and share a common history of insolation from a Sun-like star ($R_\star = 0.888 \pm 0.017$ R$_\odot$, $T_{\rm eff} = 5730 \pm 50$ K), making HD 108236 an exciting, opportune cosmic laboratory for testing models of planet formation and evolution.

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arXiv2020

ExoClock Project: An open platform for monitoring the ephemerides of Ariel targets with contributions from the public

The Ariel mission will observe spectroscopically around 1000 exoplanets to further characterise their atmospheres. For the mission to be as efficient as possible, a good knowledge of the planets' ephemerides is needed before its launch in 2028. While ephemerides for some planets are being refined on a per-case basis, an organised effort to collectively verify or update them when necessary does not exist. In this study, we introduce the ExoClock project, an open, integrated and interactive platform with the purpose of producing a confirmed list of ephemerides for the planets that will be observed by Ariel. The project has been developed in a manner to make the best use of all available resources: observations reported in the literature, observations from space instruments and, mainly, observations from ground-based telescopes, including both professional and amateur observatories. To facilitate inexperienced observers and at the same time achieve homogeneity in the results, we created data collection and validation protocols, educational material and easy to use interfaces, open to everyone. ExoClock was launched in September 2019 and now counts over 140 participants from more than 15 countries around the world. In this release, we report the results of observations obtained until the 15h of April 2020 for 119 Ariel candidate targets. In total, 632 observations were used to either verify or update the ephemerides of 83 planets. Additionally, we developed the Exoplanet Characterisation Catalogue (ECC), a catalogue built in a consistent way to assist the ephemeris refinement process. So far, the collaborative open framework of the ExoClock project has proven to be highly efficient in coordinating scientific efforts involving diverse audiences. Therefore, we believe that it is a paradigm that can be applied in the future for other research purposes, too.

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arXiv2020

TOI-1235 b: a keystone super-Earth for testing radius valley emergence models around early M dwarfs

Small planets on close-in orbits tend to exhibit envelope mass fractions of either effectively zero or up to a few percent depending on their size and orbital period. Models of thermally-driven atmospheric mass loss and of terrestrial planet formation in a gas-poor environment make distinct predictions regarding the location of this rocky/non-rocky transition in period-radius space. Here we present the confirmation of TOI-1235 b ($P=3.44$ days, $r_p=1.738^{+0.087}_{-0.076}$ R$_{\oplus}$), a planet whose size and period are intermediate between the competing model predictions thus making the system an important test case for emergence models of the rocky/non-rocky transition around early M dwarfs ($R_s=0.630\pm 0.015$ R$_{\odot}$, $M_s=0.640\pm 0.016$ M$_{\odot}$). We confirm the TESS planet discovery using reconnaissance spectroscopy, ground-based photometry, high-resolution imaging, and a set of 38 precise radial-velocities from HARPS-N and HIRES. We measure a planet mass of $6.91^{+0.75}_{-0.85}$ M$_{\oplus}$, which implies an iron core mass fraction of $20^{+15}_{-12}$% in the absence of a gaseous envelope. The bulk composition of TOI-1235 b is therefore consistent with being Earth-like and we constrain a H/He envelope mass fraction to be $<0.5$% at 90% confidence. Our results are consistent with model predictions from thermally-driven atmospheric mass loss but not with gas-poor formation, suggesting that the former class of processes remain efficient at sculpting close-in planets around early M dwarfs. Our RV analysis also reveals a strong periodicity close to the first harmonic of the photometrically-determined stellar rotation period that we treat as stellar activity, despite other lines of evidence favoring a planetary origin ($P=21.8^{+0.9}_{-0.8}$ days, $m_p\sin{i}=13.0^{+3.8}_{-5.3}$ M$_{\oplus}$) that cannot be firmly ruled out by our data.

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arXiv2020

Original Research By Young Twinkle Students (ORBYTS): Ephemeris Refinement of Transiting Exoplanets

We report follow-up observations of transiting exoplanets that have either large uncertainties (>10 minutes) in their transit times or have not been observed for over three years. A fully robotic ground-based telescope network, observations from citizen astronomers and data from TESS have been used to study eight planets, refining their ephemeris and orbital data. Such follow-up observations are key for ensuring accurate transit times for upcoming ground and space-based telescopes which may seek to characterise the atmospheres of these planets. We find deviations from the expected transit time for all planets, with transits occurring outside the 1 sigma uncertainties for seven planets. Using the newly acquired observations, we subsequently refine their periods and reduce the current predicted ephemeris uncertainties to 0.28 - 4.01 minutes. A significant portion of this work has been completed by students at two high schools in London as part of the Original Research By Young Twinkle Students (ORBYTS) programme.

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