Alastair B. Claringbold
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Alastair B. Claringbold has a total of 243 co-authors. Here are the top co-authors by number of shared publications:
- Peter J. Wheatley
Department of Physics, University of Warwick
16 shared publications - Eva-Maria Ahrer
Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg, Germany
11 shared publications - James Kirk
Astrophysics Group, Department of Physics, Imperial College London , Prince Consort Rd, London SW7 2AZ
11 shared publications - James McCormac
Department of Physics, University of Warwick
10 shared publications - Duncan A. Christie
Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg, Germany
9 shared publications - Maria Zamyatina
Department of Physics and Astronomy, Faculty of Environment, Science and Economy, University of Exeter , Exeter EX4 4QL
9 shared publications
Latest Publications
- Open Access
- 23 October 2026
- Published by Oxford University Press (OUP) in Monthly Notices of the Royal Astronomical Society
- Vol. 553 (1)
Correction to: TIC-65910228 b / NGTS-38 b, a 180 d transiting warm super-Jupiter
- 23 October 2026
- Published by Oxford University Press (OUP) in Monthly Notices of the Royal Astronomical Society
- Vol. 553 (1)
Open AccessCorrection to: TIC-65910228 b / NGTS-38 b, a 180 d transiting warm super-Jupiter
- Open Access
- 3 July 2026
- Published by Oxford University Press (OUP) in Monthly Notices of the Royal Astronomical Society
- Vol. 550 (2)
NGTS-39 b: a 58 d transiting warm Jupiter in an eccentric orbit
We report the discovery and characterization of NGTS-39 b (TIC 453147896 b), a warm Jupiter transiting a Sun-like star on a 58.2 d, eccentric (e = $0.386\pm 0.019$) orbit. NGTS-39 b was first identified from a Transiting Exoplanet Survey Satellite single transit event, and subsequently confirmed with NGTS photometry and radial velocity measurements from CORALIE and HARPS. The host star is a bright ($T_{\mathrm{mag}}$ = 11.02) F9 dwarf with effective temperature of Teff = $6053_{-30}^{+67}$ K. NGTS-39 b is a Jupiter-sized gas giant with a radius of $1.088\pm 0.012$ RJ and a mass of $1.467\pm 0.081$ MJ. Its equilibrium temperature is $519_{-5}^{+6}$ K, placing it between short-period hot Jupiters and cold, Jupiter-like giants. The high orbital eccentricity and intermediate equilibrium temperature of NGTS-39 b make it a valuable test case for formation and migration models, particularly in the poorly sampled regime of long-period gas giants. The RV data show a linear trend of $\dot{\gamma } = -17.75$ m s$^{-1}$ yr$^{-1}$, which indicates the presence of an outer companion. The discovery of NGTS-39 b contributes to the small but growing population of transiting warm Jupiters with P> 50 d orbiting bright stars.- 3 July 2026
- Published by Oxford University Press (OUP) in Monthly Notices of the Royal Astronomical Society
- Vol. 550 (2)
Open AccessNGTS-39 b: a 58 d transiting warm Jupiter in an eccentric orbit
We report the discovery and characterization of NGTS-39 b (TIC 453147896 b), a warm Jupiter transiting a Sun-like star on a 58.2 d, eccentric (e = $0.386\pm 0.019$) orbit. NGTS-39 b was first identified from a Transiting Exoplanet Survey Satellite single transit event, and subsequently confirmed with NGTS photometry and radial velocity measurements from CORALIE and HARPS. The host star is a bright ($T_{\mathrm{mag}}$ = 11.02) F9 dwarf with effective temperature of Teff = $6053_{-30}^{+67}$ K. NGTS-39 b is a Jupiter-sized gas giant with a radius of $1.088\pm 0.012$ RJ and a mass of $1.467\pm 0.081$ MJ. Its equilibrium temperature is $519_{-5}^{+6}$ K, placing it between short-period hot Jupiters and cold, Jupiter-like giants. The high orbital eccentricity and intermediate equilibrium temperature of NGTS-39 b make it a valuable test case for formation and migration models, particularly in the poorly sampled regime of long-period gas giants. The RV data show a linear trend of $\dot{\gamma } = -17.75$ m s$^{-1}$ yr$^{-1}$, which indicates the presence of an outer companion. The discovery of NGTS-39 b contributes to the small but growing population of transiting warm Jupiters with P> 50 d orbiting bright stars. - Open Access
- 5 June 2026
- Published by Oxford University Press (OUP) in Monthly Notices of the Royal Astronomical Society
- Vol. 549 (4)
TIC-65910228 b / NGTS-38 b, a 180 d transiting warm super-Jupiter
We present the discovery of TIC-65910228 b / NGTS-38 b, a giant exoplanet with a radius of $1.081\pm 0.047$ RJ and a mass of $4.77_{-0.37}^{+0.39}$ MJ on a long-period ($180.52797\pm 0.00036$ d), moderately eccentric (e = $0.3086\pm 0.010$) orbit transiting a bright (V=$10.230\pm 0.020$ mag) metal rich ([Fe/H]=$0.33\pm 0.09$ ‘dex’) F6V–F7V type host star. The planet was initially detected from a single transit in TESS Sector 33. A photometric monitoring campaign of 228 nights with NGTS detected a transit egress of the planet, which together with spectroscopic radial velocity monitoring with CORALIE and HARPS identified an orbital period of 180.5 d. These radial velocity measurements also showed the mass of the companion to be planetary. Additional transit observations coordinated by the TESS follow-up observing program allowed further confirmation and refinement of this period. With its relatively cool equilibrium temperature of $457\pm 11$ K, NGTS-38 b joins a small but growing population of well characterized transiting warm-Jupiters and has one of the longest periods of any discovered to date. The target is situated in the LOPS2 field of the upcoming PLATO mission which will allow for greater refinement of the system parameters and potential for the discovery of additional companions too small and/or too long-period to be seen by TESS or NGTS. NGTS-38 b’s bright host star and wide orbital separation make it an attractive target for further study, including potential measurement of its spin-orbit alignment or targeted exomoon/ring searches.- 5 June 2026
- Published by Oxford University Press (OUP) in Monthly Notices of the Royal Astronomical Society
- Vol. 549 (4)
Open AccessTIC-65910228 b / NGTS-38 b, a 180 d transiting warm super-Jupiter
We present the discovery of TIC-65910228 b / NGTS-38 b, a giant exoplanet with a radius of $1.081\pm 0.047$ RJ and a mass of $4.77_{-0.37}^{+0.39}$ MJ on a long-period ($180.52797\pm 0.00036$ d), moderately eccentric (e = $0.3086\pm 0.010$) orbit transiting a bright (V=$10.230\pm 0.020$ mag) metal rich ([Fe/H]=$0.33\pm 0.09$ ‘dex’) F6V–F7V type host star. The planet was initially detected from a single transit in TESS Sector 33. A photometric monitoring campaign of 228 nights with NGTS detected a transit egress of the planet, which together with spectroscopic radial velocity monitoring with CORALIE and HARPS identified an orbital period of 180.5 d. These radial velocity measurements also showed the mass of the companion to be planetary. Additional transit observations coordinated by the TESS follow-up observing program allowed further confirmation and refinement of this period. With its relatively cool equilibrium temperature of $457\pm 11$ K, NGTS-38 b joins a small but growing population of well characterized transiting warm-Jupiters and has one of the longest periods of any discovered to date. The target is situated in the LOPS2 field of the upcoming PLATO mission which will allow for greater refinement of the system parameters and potential for the discovery of additional companions too small and/or too long-period to be seen by TESS or NGTS. NGTS-38 b’s bright host star and wide orbital separation make it an attractive target for further study, including potential measurement of its spin-orbit alignment or targeted exomoon/ring searches. - Open Access
- 29 May 2026
- Published by EDP Sciences in Astronomy & Astrophysics
- Vol. 711, A86
High five from ASTEP. Three validated planets and two eclipsing binaries in a diverse set of long-period candidates
We present the analysis of five long-period TESS Objects of Interest (TOIs), , with orbital periods exceeding one month. Initially identified by the Transiting Exoplanet Survey Satellite (TESS), we extensively monitored these targets with the Antarctic Search for Transiting Exoplanets (ASTEP), supported by other facilities in the TESS Follow-up Observing Program (TFOP) network. all orbiting Sun-like stars These targets occupy a relatively underexplored region of the period-radius parameter space, offering valuable primordial probes for planetary formation and migration as warm planets better maintain their evolutionary fingerprints. To characterise these systems, we leveraged high-resolution speckle imaging to search for nearby stellar companions, and refine stellar parameters using both reconnaissance spectroscopy and spectral energy distribution (SED) fitting. We combined TESS photometry with high-precision ground-based observations from ASTEP, and when available, included additional photometry and radial velocity data. We applied statistical validation to assess the planetary nature of each candidate and used to jointly model the photometric and spectroscopic datasets. We validate the planetary nature of three TOIs, including the two warm Saturns TOI-4507,b (8.2, 104,d) and TOI-3457,b (10.0, 32.6,d), as well as the warm sub-Neptune TOI-707,b (2.4, eclipsing binaries, namely TOI-2404 and TOI-4404. 52.8,d). The remaining two candidates are most consistent with These results help populate the sparse regime of warm planets, which serve as key tracers of planetary evolution, and demonstrate ASTEP’s effectiveness as a ground-based follow-up instrument for long-period systems.
- 29 May 2026
- Published by EDP Sciences in Astronomy & Astrophysics
- Vol. 711, A86
Open AccessHigh five from ASTEP. Three validated planets and two eclipsing binaries in a diverse set of long-period candidates
We present the analysis of five long-period TESS Objects of Interest (TOIs), , with orbital periods exceeding one month. Initially identified by the Transiting Exoplanet Survey Satellite (TESS), we extensively monitored these targets with the Antarctic Search for Transiting Exoplanets (ASTEP), supported by other facilities in the TESS Follow-up Observing Program (TFOP) network. all orbiting Sun-like stars These targets occupy a relatively underexplored region of the period-radius parameter space, offering valuable primordial probes for planetary formation and migration as warm planets better maintain their evolutionary fingerprints. To characterise these systems, we leveraged high-resolution speckle imaging to search for nearby stellar companions, and refine stellar parameters using both reconnaissance spectroscopy and spectral energy distribution (SED) fitting. We combined TESS photometry with high-precision ground-based observations from ASTEP, and when available, included additional photometry and radial velocity data. We applied statistical validation to assess the planetary nature of each candidate and used to jointly model the photometric and spectroscopic datasets. We validate the planetary nature of three TOIs, including the two warm Saturns TOI-4507,b (8.2, 104,d) and TOI-3457,b (10.0, 32.6,d), as well as the warm sub-Neptune TOI-707,b (2.4, eclipsing binaries, namely TOI-2404 and TOI-4404. 52.8,d). The remaining two candidates are most consistent with These results help populate the sparse regime of warm planets, which serve as key tracers of planetary evolution, and demonstrate ASTEP’s effectiveness as a ground-based follow-up instrument for long-period systems.
- Open Access
- 18 March 2026
- Published by Oxford University Press (OUP) in Monthly Notices of the Royal Astronomical Society
- Vol. 548 (4)
BOWIE-ALIGN: exploring degeneracies in the muted transmission spectrum of the aligned hot Jupiter NGTS-2b with NIRSpec/G395H
We present the first atmospheric observation and characterisation of the aligned, 1468 K hot Jupiter, NGTS-2b, with one JWST NIRSpec/G395H transit. These observations complete the GO 3838 observing campaign of the BOWIE-ALIGN program, which aims to investigate the link between hot Jupiter atmospheric composition and formation history through the atmospheric analysis of planets orbiting F stars that are aligned and misaligned with the host stellar spin axis. The 2.84–5.18 μm spectrum shows weak absorption features attributed to H2O and CO2 absorption, which our free chemistry retrievals fit with posteriors that converge on high mean molecular weight solutions attained through significant H2O mixing ratios. By comparing our results to interior modelling, we show that some of these solutions exceed the 43.5 × solar upper limit we obtained from our interior structure models. Such solutions are likely due to cloud-metallicity degeneracies and insufficient wavelength coverage to resolve them. We show that, in the case of our observations, the likelihood distribution of H2O abundances is flat and uninformative, such that our retrievals are biased by the prior. Additionally, our statistically favoured atmospheric solution contains absorption from SO. The chemical abundances retrieved with this model are likely not astrophysically feasible and we demonstrate that the presence of SO is driven by only two data points. Our equilibrium chemistry retrievals hint at a subsolar C/O ratio and supersolar metallicity; however, we find wide posterior distributions that extend to solar values.
- 18 March 2026
- Published by Oxford University Press (OUP) in Monthly Notices of the Royal Astronomical Society
- Vol. 548 (4)
Open AccessBOWIE-ALIGN: exploring degeneracies in the muted transmission spectrum of the aligned hot Jupiter NGTS-2b with NIRSpec/G395H
We present the first atmospheric observation and characterisation of the aligned, 1468 K hot Jupiter, NGTS-2b, with one JWST NIRSpec/G395H transit. These observations complete the GO 3838 observing campaign of the BOWIE-ALIGN program, which aims to investigate the link between hot Jupiter atmospheric composition and formation history through the atmospheric analysis of planets orbiting F stars that are aligned and misaligned with the host stellar spin axis. The 2.84–5.18 μm spectrum shows weak absorption features attributed to H2O and CO2 absorption, which our free chemistry retrievals fit with posteriors that converge on high mean molecular weight solutions attained through significant H2O mixing ratios. By comparing our results to interior modelling, we show that some of these solutions exceed the 43.5 × solar upper limit we obtained from our interior structure models. Such solutions are likely due to cloud-metallicity degeneracies and insufficient wavelength coverage to resolve them. We show that, in the case of our observations, the likelihood distribution of H2O abundances is flat and uninformative, such that our retrievals are biased by the prior. Additionally, our statistically favoured atmospheric solution contains absorption from SO. The chemical abundances retrieved with this model are likely not astrophysically feasible and we demonstrate that the presence of SO is driven by only two data points. Our equilibrium chemistry retrievals hint at a subsolar C/O ratio and supersolar metallicity; however, we find wide posterior distributions that extend to solar values.
- Open Access
- 25 February 2026
- Published by Oxford University Press (OUP) in Monthly Notices of the Royal Astronomical Society
- Vol. 547 (3)
LRG-BEASTS: detection of sodium and evidence for water absorption in the hot Saturn HAT-P-44b
We present the low-resolution optical transmission spectrum of the inflated hot Saturn HAT-P-44b. The planet is a close sibling in radius (1.24 $\mathrm{R_{Jup}}$), temperature (1100 K), and mass (0.35 $\mathrm{M_{Jup}}$) to the exceedingly well-characterized WASP-39b. Using the ACAM instrument on the William Herschel Telescope, we obtain a transmission spectrum with sub-scale height precision of 246 ppm, with a wavelength range of 495–874 nm and a 20 nm resolution, despite a relatively faint host star ($V\mathrm{_{mag} = 13.2}$). We detect absorption due to sodium with 3.9$\sigma$ confidence. Atmospheric retrieval of the transmission spectrum also reveals evidence for H$_2$O absorption and Rayleigh scattering from H$_2$ gas consistent with a cool 800 K atmosphere and a supersolar metallicity of 7$^{+16}_{-5}$ $\times$ solar. Comparison of retrieval models disfavour the inclusion of a super-Rayleigh scattering slope or high-altitude clouds (at ${\lt} 1$ mbar) while being agnostic towards the presence of mid-altitude clouds. Our transmission spectrum of HAT-P-44b shows strong similarity to that of its sibling WASP-39b. This is the tenth planet in the Low-Resolution Ground-Based Exoplanet Atmosphere Survey using Transmission Spectroscopy survey.- 25 February 2026
- Published by Oxford University Press (OUP) in Monthly Notices of the Royal Astronomical Society
- Vol. 547 (3)
Open AccessLRG-BEASTS: detection of sodium and evidence for water absorption in the hot Saturn HAT-P-44b
We present the low-resolution optical transmission spectrum of the inflated hot Saturn HAT-P-44b. The planet is a close sibling in radius (1.24 $\mathrm{R_{Jup}}$), temperature (1100 K), and mass (0.35 $\mathrm{M_{Jup}}$) to the exceedingly well-characterized WASP-39b. Using the ACAM instrument on the William Herschel Telescope, we obtain a transmission spectrum with sub-scale height precision of 246 ppm, with a wavelength range of 495–874 nm and a 20 nm resolution, despite a relatively faint host star ($V\mathrm{_{mag} = 13.2}$). We detect absorption due to sodium with 3.9$\sigma$ confidence. Atmospheric retrieval of the transmission spectrum also reveals evidence for H$_2$O absorption and Rayleigh scattering from H$_2$ gas consistent with a cool 800 K atmosphere and a supersolar metallicity of 7$^{+16}_{-5}$ $\times$ solar. Comparison of retrieval models disfavour the inclusion of a super-Rayleigh scattering slope or high-altitude clouds (at ${\lt} 1$ mbar) while being agnostic towards the presence of mid-altitude clouds. Our transmission spectrum of HAT-P-44b shows strong similarity to that of its sibling WASP-39b. This is the tenth planet in the Low-Resolution Ground-Based Exoplanet Atmosphere Survey using Transmission Spectroscopy survey. - Open Access
LRG-BEASTS: Detection of sodium and evidence for water absorption in the hot Saturn HAT-P-44b
We present the low-resolution optical transmission spectrum of the inflated hot Saturn HAT-P-44b. The planet is a close sibling in radius (1.24 $\mathrm{R_{Jup}}$), temperature (1100 K), and mass (0.35 $\mathrm{M_{Jup}}$) to the exceedingly well-characterized WASP-39b. Using the ACAM instrument on the William Herschel Telescope (WHT), we obtain a transmission spectrum with sub-scale height precision of 246 ppm, with a wavelength range of 495 -- 874 nm and a 20 nm resolution, despite a relatively faint host star ($V\mathrm{_{mag} = 13.2}$). We detect absorption due to sodium with 3.9$σ$ confidence. Atmospheric retrieval of the transmission spectrum also reveals evidence for \ch{H2O} absorption and Rayleigh scattering from \ch{H2} gas consistent with a cool 800 K atmosphere and a super-solar metallicity of 7$\substack{+16 \\ -5}$$\times$solar. Comparison of retrieval models disfavour the inclusion of a super-Rayleigh scattering slope or high-altitude clouds (at $<1$ mbar) while being agnostic towards the presence of mid-altitude clouds. Our transmission spectrum of HAT-P-44b shows strong similarity to that of its sibling WASP-39b.} This is the tenth planet in the LRG-BEASTS (Low-Resolution Ground-Based Exoplanet Atmosphere Survey using Transmission Spectroscopy) survey.Open AccessLRG-BEASTS: Detection of sodium and evidence for water absorption in the hot Saturn HAT-P-44b
We present the low-resolution optical transmission spectrum of the inflated hot Saturn HAT-P-44b. The planet is a close sibling in radius (1.24 $\mathrm{R_{Jup}}$), temperature (1100 K), and mass (0.35 $\mathrm{M_{Jup}}$) to the exceedingly well-characterized WASP-39b. Using the ACAM instrument on the William Herschel Telescope (WHT), we obtain a transmission spectrum with sub-scale height precision of 246 ppm, with a wavelength range of 495 -- 874 nm and a 20 nm resolution, despite a relatively faint host star ($V\mathrm{_{mag} = 13.2}$). We detect absorption due to sodium with 3.9$σ$ confidence. Atmospheric retrieval of the transmission spectrum also reveals evidence for \ch{H2O} absorption and Rayleigh scattering from \ch{H2} gas consistent with a cool 800 K atmosphere and a super-solar metallicity of 7$\substack{+16 \\ -5}$$\times$solar. Comparison of retrieval models disfavour the inclusion of a super-Rayleigh scattering slope or high-altitude clouds (at $<1$ mbar) while being agnostic towards the presence of mid-altitude clouds. Our transmission spectrum of HAT-P-44b shows strong similarity to that of its sibling WASP-39b.} This is the tenth planet in the LRG-BEASTS (Low-Resolution Ground-Based Exoplanet Atmosphere Survey using Transmission Spectroscopy) survey. - Open Access
- 21 January 2026
- Published by Oxford University Press (OUP) in Monthly Notices of the Royal Astronomical Society
- Vol. 546 (4)
BOWIE-ALIGN: Sub-solar C/O ratio and metallicity atmosphere of the misaligned hot Jupiter HAT-P-30 b
We present the JWST NIRSpec/G395H transmission spectrum of the misaligned hot Jupiter HAT-P-30b from 2.8–5.2 $\mu$m as part of the BOWIE-ALIGN survey, a comparative survey designed to probe the link between planet formation and atmospheric composition in samples of misaligned and aligned hot Jupiters orbiting F-type stars. Through independent data reductions and retrieval analyses, we find evidence for absorption features of $\mathrm{H_{2}O}$ and $\mathrm{CO_{2}}$ in the atmosphere of HAT-P-30 b. Our retrieved abundances are consistent with equilibrium chemistry, from which we infer a sub-solar C/O ratio (0.16–0.45), and sub-solar and sub-stellar metallicity (0.2–0.8$\times$solar, compared to a stellar metallicity of 1.1–1.6$\times$solar), with muted spectral features. This composition challenges formation models of continuous migration and accretion within a steady disc of stellar metallicity, and could be the result of low C/O ratio gas accretion within the water ice line, low metallicity accretion due to the trapping of volatiles further out in the disc, or the combined accretion of low metallicity gas and carbon-poor solids.- 21 January 2026
- Published by Oxford University Press (OUP) in Monthly Notices of the Royal Astronomical Society
- Vol. 546 (4)
Open AccessBOWIE-ALIGN: Sub-solar C/O ratio and metallicity atmosphere of the misaligned hot Jupiter HAT-P-30 b
We present the JWST NIRSpec/G395H transmission spectrum of the misaligned hot Jupiter HAT-P-30b from 2.8–5.2 $\mu$m as part of the BOWIE-ALIGN survey, a comparative survey designed to probe the link between planet formation and atmospheric composition in samples of misaligned and aligned hot Jupiters orbiting F-type stars. Through independent data reductions and retrieval analyses, we find evidence for absorption features of $\mathrm{H_{2}O}$ and $\mathrm{CO_{2}}$ in the atmosphere of HAT-P-30 b. Our retrieved abundances are consistent with equilibrium chemistry, from which we infer a sub-solar C/O ratio (0.16–0.45), and sub-solar and sub-stellar metallicity (0.2–0.8$\times$solar, compared to a stellar metallicity of 1.1–1.6$\times$solar), with muted spectral features. This composition challenges formation models of continuous migration and accretion within a steady disc of stellar metallicity, and could be the result of low C/O ratio gas accretion within the water ice line, low metallicity accretion due to the trapping of volatiles further out in the disc, or the combined accretion of low metallicity gas and carbon-poor solids. - Open Access
BOWIE-ALIGN: Sub-solar C/O ratio and metallicity atmosphere of the misaligned hot Jupiter HAT-P-30b
We present the JWST NIRSpec/G395H transmission spectrum of the misaligned hot Jupiter HAT-P-30b from 2.8--5.2 $μ$m as part of the BOWIE-ALIGN survey, a comparative survey designed to probe the link between planet formation and atmospheric composition in samples of misaligned and aligned hot Jupiters orbiting F-type stars. Through independent data reductions and retrieval analyses, we find evidence for absorption features of H$_2$O and CO$_2$ in the atmosphere of HAT-P-30b. Our retrieved abundances are consistent with equilibrium chemistry, from which we infer a sub-solar C/O ratio (0.16--0.45), and sub-solar and sub-stellar metallicity (0.2--0.8$\times$solar, compared to a stellar metallicity of 1.1--1.6$\times$solar), with muted spectral features. This composition challenges formation models of continuous migration and accretion within a steady disc of stellar metallicity, and could be the result of low C/O ratio gas accretion within the water ice line, low metallicity accretion due to the trapping of volatiles further out in the disc, or the combined accretion of low metallicity gas and carbon-poor solids.Open AccessBOWIE-ALIGN: Sub-solar C/O ratio and metallicity atmosphere of the misaligned hot Jupiter HAT-P-30b
We present the JWST NIRSpec/G395H transmission spectrum of the misaligned hot Jupiter HAT-P-30b from 2.8--5.2 $μ$m as part of the BOWIE-ALIGN survey, a comparative survey designed to probe the link between planet formation and atmospheric composition in samples of misaligned and aligned hot Jupiters orbiting F-type stars. Through independent data reductions and retrieval analyses, we find evidence for absorption features of H$_2$O and CO$_2$ in the atmosphere of HAT-P-30b. Our retrieved abundances are consistent with equilibrium chemistry, from which we infer a sub-solar C/O ratio (0.16--0.45), and sub-solar and sub-stellar metallicity (0.2--0.8$\times$solar, compared to a stellar metallicity of 1.1--1.6$\times$solar), with muted spectral features. This composition challenges formation models of continuous migration and accretion within a steady disc of stellar metallicity, and could be the result of low C/O ratio gas accretion within the water ice line, low metallicity accretion due to the trapping of volatiles further out in the disc, or the combined accretion of low metallicity gas and carbon-poor solids. - Open Access
- 12 December 2025
- Published by Oxford University Press (OUP) in Monthly Notices of the Royal Astronomical Society
- Vol. 547 (2)
A 43 d transiting Neptune and two 25 d Saturns from TESS , NGTS, and ASTEP
Beyond orbital periods of 10 d, there is a dearth of known transiting gas giants. On longer orbits, planets are less affected by their host star, and become ideal probes of planet formation, migration, and evolution. We report the discovery of a long-period Neptune and two Saturns, each initially identified as single transits in the TESS (Transiting Exoplanet Survey Satellite) photometry, and solved through additional transits from ground-based follow-up photometric observations by NGTS (Next Generation Transit Survey) and ASTEP (Antarctic Search for Transiting ExoPlanets). High-resolution radial velocity mass measurements using CORALIE and HARPS (High Accuracy Radial Velocity Planet Searcher) confirm their planetary nature. From joint modelling of the photometric and spectroscopic data, we determine an orbital period of $43.12655_{-0.00017}^{+0.00012}~$ d, radius of $3.65\pm 0.22~\mathrm{R_{\hbox{$\oplus $}}}$, and mass of $19.1_{-4.5}^{+4.9}~\mathrm{M_{\hbox{$\oplus $}}}$ for NGTS-34 b, making it one of the longest period well-characterized transiting Neptunes. Orbiting a late F-type star, bright in the K band (Kmag$~\simeq 7.9$), it is amenable for cool atmosphere studies using James Webb Space Telescope or Ariel (Atmospheric Remote-sensing Infrared Exoplanet Large). TOI-4940 b is a small Saturn on a $25.867811_{-0.000056}^{+0.000058}~$ d orbit with a radius of $6.61\pm 0.37~\mathrm{R_{\hbox{$\oplus $}}}$ and an upper mass limit $< 89~\mathrm{M_{\hbox{$\oplus $}}}$. NGTS-35 b(=TOI-6669 b) is a larger Saturn on a $25.241192\pm 0.000022~$ d, moderately eccentric orbit ($e = 0.192_{-0.033}^{+0.037}$), with a radius of $10.90\pm 0.65~\mathrm{R_{\hbox{$\oplus $}}}$ and a mass of $152_{-19}^{+22}~\mathrm{M_{\hbox{$\oplus $}}}$. With an assumed albedo $A=0.3$, each of these planets has an equilibrium temperature below 700 K, with NGTS-35 b especially cold at $450~$ K. These three giants add to the small but growing population of long-period planets that can further our understanding of planet formation mechanisms.- 12 December 2025
- Published by Oxford University Press (OUP) in Monthly Notices of the Royal Astronomical Society
- Vol. 547 (2)
Open AccessA 43 d transiting Neptune and two 25 d Saturns from TESS , NGTS, and ASTEP
Beyond orbital periods of 10 d, there is a dearth of known transiting gas giants. On longer orbits, planets are less affected by their host star, and become ideal probes of planet formation, migration, and evolution. We report the discovery of a long-period Neptune and two Saturns, each initially identified as single transits in the TESS (Transiting Exoplanet Survey Satellite) photometry, and solved through additional transits from ground-based follow-up photometric observations by NGTS (Next Generation Transit Survey) and ASTEP (Antarctic Search for Transiting ExoPlanets). High-resolution radial velocity mass measurements using CORALIE and HARPS (High Accuracy Radial Velocity Planet Searcher) confirm their planetary nature. From joint modelling of the photometric and spectroscopic data, we determine an orbital period of $43.12655_{-0.00017}^{+0.00012}~$ d, radius of $3.65\pm 0.22~\mathrm{R_{\hbox{$\oplus $}}}$, and mass of $19.1_{-4.5}^{+4.9}~\mathrm{M_{\hbox{$\oplus $}}}$ for NGTS-34 b, making it one of the longest period well-characterized transiting Neptunes. Orbiting a late F-type star, bright in the K band (Kmag$~\simeq 7.9$), it is amenable for cool atmosphere studies using James Webb Space Telescope or Ariel (Atmospheric Remote-sensing Infrared Exoplanet Large). TOI-4940 b is a small Saturn on a $25.867811_{-0.000056}^{+0.000058}~$ d orbit with a radius of $6.61\pm 0.37~\mathrm{R_{\hbox{$\oplus $}}}$ and an upper mass limit $< 89~\mathrm{M_{\hbox{$\oplus $}}}$. NGTS-35 b(=TOI-6669 b) is a larger Saturn on a $25.241192\pm 0.000022~$ d, moderately eccentric orbit ($e = 0.192_{-0.033}^{+0.037}$), with a radius of $10.90\pm 0.65~\mathrm{R_{\hbox{$\oplus $}}}$ and a mass of $152_{-19}^{+22}~\mathrm{M_{\hbox{$\oplus $}}}$. With an assumed albedo $A=0.3$, each of these planets has an equilibrium temperature below 700 K, with NGTS-35 b especially cold at $450~$ K. These three giants add to the small but growing population of long-period planets that can further our understanding of planet formation mechanisms.