arXiv subjects

John Southworth

Publications and source records attributed to John Southworth.

At least 19 recordsLinked to original sources

arXiv2026

NGTS clusters survey - VII. An Enigmatic Short-Period Circumsecondary Disk Candidate in Orion

Young stellar systems provide key insights into the processes governing star/planet formation, often exhibiting complex and evolving photometric variability. In this paper, we present an analysis of the object around NOI 105872, observed by the Next Generation Transit Survey (NGTS) to eclipse a young ($4.1\pm0.4$ Myr) M-type star in the Orion Nebula Cluster. The system displays deep, asymmetric eclipses with a period of $\sim0.69$ days, alongside variability in morphology. We combine photometric observations spanning approximately a decade from multiple ground- and space-based facilities to investigate the nature of this system. We explore a range of physical scenarios to reproduce the eclipse profiles and their evolution. After analysis, our preferred explanation is a circumsecondary disk surrounding a companion in orbit around the M-type primary. We adopt a six-parameter disk model and fit the eclipse profiles independently to each dataset. The best-fitting solution yields a disk radius of $\sim 0.005 \mathrm{au}$ or $0.98 R_{*}$, with broadly consistent orientations across epochs, but with variations that may be attributed to disk precession or intrinsic stellar variability. Constraints from the Hill radius imply a companion mass consistent with a very low-mass stellar companion. These results establish NOI 105872 as a candidate for a circumsecondary disk system in a young stellar environment. Continued photometric monitoring and spectroscopic follow-up will be essential to confirm this interpretation. If confirmed, systems such as NOI 105872 provide valuable benchmarks for understanding disk dynamics, companion formation, and the origin of complex eclipse phenomena in young stars.

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arXiv2026

Multiplicity of Cool Stars and their Evolution

Making up a sizeable portion of the galactic census, stellar multiples are experiencing a renaissance. Enabling the study of multiple strands of the study of cool stars, stellar multiples have been found and characterised in great numbers by the missions of the last decade, allowing the exploration of stellar parameters and populations, observation of stellar interactions, studies into stellar formation and evolution, and characterisation of circumbinary systems. This exciting explosion of science is only set to continue, with future missions set to offer even further insights into the topic. Within these proceedings we will summarise the presentations and discussions on cool stellar multiplicity within our splinter sessions at the 23rd Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun, as we examine the present state of the field and look to what the future may bring.

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arXiv2026

Rediscussion of eclipsing binaries. Paper 32. The eccentric F-type system EY Cephei

EY Cep is a detached eclipsing binary containing two F0 V stars in an orbit with a period of 7.97 d and an eccentricity of 0.440. We determine the physical properties of the system using light-curves from the Transiting Exoplanet Survey Satellite and published spectroscopic measurements. We find masses of 1.523 +/- 0.008 Msun and 1.494 +/- 0.014 Msun, radii of 1.491 +/- 0.004 Rsun and 1.446 +/- 0.004 Rsun, and temperatures of 7070 +/- 170 K and 6990 +/- 150 K. We calculate the system's distance to be 300.3 +/- 3.8 pc, in excellent agreement with the Gaia DR3 parallax, and estimate its age to be 220 Myr. We find no evidence for pulsations, but there are hints of variation in the eclipse times potentially attributable to a third body on a longer-period eccentric orbit.

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arXiv2026

Rediscussion of eclipsing binaries. Paper 31. The slowly-pulsating B-star system CV Velorum in the PLATO southern field

CV Vel is a detached eclipsing binary containing two B2.5 V stars in a circular orbit of period 6.889 d. Both stars show line-profile variations arising from g-mode oscillations, characteristic of slowly-pulsating B-stars, and rotational axes misaligned with the orbital axis. We present the first photometric analysis of the system based on light curves from a space telescope. By combining our results with published spectroscopic observations we determine the stars' masses to be 6.065 +/- 0.015 Msun and 5.950 +/- 0.012 Msun, and their radii to be 4.094 +/- 0.056 Rsun and 3.978 +/- 0.049 Rsun. The precision of the radius measurements is limited by the pulsations in the light curves. We identify two confirmed (0.4886 c/d and 0.3695 c/d) and two candidate (0.7468 c/d and 0.7048 c/d) pulsation frequencies but cannot reliably identify further frequencies due to the short duration of the available light curves (approximately 50 d). CV Vel is in the first field to be observed by the PLATO satellite so in future may become the first EB containing an SPB star for which we have a light curve with a high photometric precision and a duration of over one year.

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arXiv2026

The PLATO Science Calibration and Validation Plan: Targets for the First Long-pointing Field

In order to meet the science goals of the PLATO space mission, an extensive science calibration and validation plan has been designed. This paper describes this plan, as well as the methodology adopted to select the science calibration and validation stars that have entered its input catalogue. This is the so-called {\tt scvPIC}, which is part of the general PLATO Input Catalogue (PIC) for the first selected long pointing field in the Southern Hemisphere known as LOPS2. While many of PLATO's science requirements needed dedicated stars as calibrators as discussed here, its most stringent requirement is the delivery of the age of the host stars of exoplanetary systems with an accuracy better than 10\% for a G0V star of {\it V} = 10 mag, i.e. a nearby Sun-like star. This is presently not within reach for large populations of dwarfs and subgiants in the Milky Way as it requires the models of their stellar interiors to be improved. We discuss how this ambitious age requirement led to the selection of tens of thousands of red giants, and of thousands of main-sequence early F-type gravity-mode pulsators in order to deduce their internal rotation profile across stellar evolution. This asteroseismic observable will then be imported as key information into improved models of dwarfs and subgiants in the Milky Way as optimal modelling tools for ever better age-dating of the exoplanet hosts as the PLATO mission moves along. Additional calibrators and validators included in the {\tt scvPIC} are a few thousands of binaries, a few hundreds of legacy and benchmark stars, a few hundred photometrically stable stars, and six transiting brown dwarfs.

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arXiv2026

Rediscussion of eclipsing binaries. Paper XXIX. The F-type twin system BS Draconis

We present an analysis of BS Dra, a detached eclipsing binary containing two almost-identical F3 V stars in a 3.36-d circular orbit, based on 40 sectors of observations from the Transiting Exoplanet Survey Satellite (TESS) and published spectroscopic results. We measure masses of 1.305 +/- 0.015 Msun and 1.284 +/- 0.017 Msun, and radii of 1.409 +/- 0.006 Rsun and 1.400 +/- 0.006 Rsun, for the two components. The high quality of the TESS data allow -- for the first time -- a definitive identification of the primary eclipse, which is 0.007 mag deeper than the secondary. The primary star is the hotter, larger and more massive of the two: the ratios of the radii and surface brightnesses are both slightly but significantly below unity. We find a distance concordant with the Gaia DR3 parallax and, by comparison to theoretical models, an age of 1600 +/- 300 Myr and a slightly sub-solar chemical composition. Our mean times of primary eclipse, each representing all eclipses in one sector, have a scatter of only 0.37 s around a linear ephemeris: BS Dra may be useful as a celestial clock.

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arXiv2026

TEPCat: The Transiting Extrasolar Planet Catalogue

Transiting extrasolar planets are extraordinarily valuable for understanding the characteristics and formation of planets, because they are the only exoplanets whose physical and orbital properties can be measured to high precision. Thousands are now known, and it is important to maintain a database of them for use by the scientific community. TEPCat performs this task: it is a critical compilation of the physical and observable properties of the known transiting planetary systems. This work introduces the motivation for TEPCat, its scope, contents, and implementation. Example plots of interesting quantities are constructed. The classification of planets and of the eclipse features in their light curves is discussed. TEPCat is maintained and freely available online at https://www.astro.keele.ac.uk/jkt/tepcat/

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arXiv2026

Rediscussion of eclipsing binaries. Paper XXVIII. The metallic-lined system DV Bootes

DV Boo is a detached eclipsing binary containing a metallic-lined A-star and a chemically normal late-F star, in an orbit with a period of 3.783 d and a possible slight eccentricity. We use a light curve from the Transiting Exoplanet Survey Satellite (TESS) and published spectroscopic results to determine the physical properties of the system to high precision. We find masses of 1.617 +/- 0.003 Msun and 1.207 +/- 0.004 Msun, and radii of 1.948 +/- 0.008 Rsun and 1.195 +/- 0.022 Rsun. The precision of the radius measurements is limited by the shallow partial eclipses and the unavailability of a spectroscopic light ratio due to the chemical peculiarity of the primary star. We measure a distance to the system of 125.0 +/- 1.5 pc, in good agreement with the Gaia DR3 parallax, and an age of 1.3 Gyr. A comparison with theoretical models suggests the system has a modestly sub-solar metallicity, in conflict with the slightly super-solar photospheric abundances of the secondary star.

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arXiv2026

Detached eclipsing binary star science in the 2040s

Detached eclipsing binary stars (DEBS) are currently the best source of accurate and precise fundamental stellar parameters. This makes DEBS crucial targets for constraining the impact of various physical processes on stellar structure and evolution. Long-period binaries are particularly interesting because their separation minimises interactions between the components. This makes long-period binaries more comparable to single stars. However, the current sample of DEBS with high precision stellar parameters are dominated by short-period systems (e.g. ~90% of the Gaia DR3 eclipsing binaries have periods < 5 days). Facilities capable of performing detailed studies of long-period DEBS will be essential to further improve our understanding of stellar structure and evolution. Such facilities would need to be able to obtain spectroscopic observations of more distant objects at high resolution and cadence. 2-8m class telescopes with echelle spectrographs and an ability to monitor a large sample of stars would be required.

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arXiv2025

Transformational astrophysics and exoplanet science with Habitable Worlds Observatory's High Resolution Imager

Habitable Worlds Observatory (HWO) will be NASA's flagship space telescope of the 2040s, designed to search for life on other planets and to transform broad areas of astrophysics. NASA are seeking international partners, and the UK is well-placed to lead the design and construction of its imaging camera - which is likely to produce the mission's most visible public impact. Early participation in the mission would return investment to UK industry, and bring generational leadership for the UK in space science, space technology, and astrophysics.

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arXiv2025

Doomed Worlds II: Reassessing Suggestions of Orbital Decay for TrES-5 b

TrES-5b is one of only three ultra-hot Jupiters (UHJs) with suggestions of a possibly decreasing orbital period that have persisted through multiple independent analyses (G. Maciejewski et al. 2021; S. R. Hagey et al. 2022; E. S. Ivshina & J. N. Winn 2022; W. Wang et al. 2024; L. C. Yeh et al. 2024). While WASP-12 b's decreasing period is well-explained by tidally induced orbital decay (K. C. Patra et al. 2017), and stellar acceleration has been proposed for WASP-4 b (L. G. Bouma et al. 2020), the cause of the apparent trend for TrES-5 b has not been satisfactorily explained. This work extends the previous observations with 14 new ground-based transits from 2016-2024 and two newly-published midtimes for data from 2007 and 2009. Four TESS sectors (75, 77, 82, and 84) have also been included for the first time. With the new data, the case for a decreasing orbital period is much weaker than before. The revised rate of period change, dP/dt=-5.3 +/- 2.2 ms yr^-1, is less than half that was found in previous work and the preference for a quadratic over a linear model, as measured through Delta BIC_LQ, has been falling since 2020, with a current value of 11. Furthermore, these results are not robust to outliers; removing a single early transit midtime causes the effect to vanish (Delta BIC_LQ = -1). Additionally, no significant periodic signals in the transit timing data are identified. The current data are well explained by a linear ephemeris.

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arXiv2025

Using Stellar Spectral Energy Distributions to Measure Exoplanet Parameters

The ability to make accurate determinations of planetary parameters is inextricably linked to measuring physical parameters of the host star, in particular the stellar radius. In this paper we fit the stellar spectral energy distributions of exoplanet hosts to measure their radii, making use of only archival photometry, the $Gaia$ parallaxes and $Gaia$ extinction maps. Using the extinction maps frees us of the degeneracy between temperature and extinction which has plagued this method in the past. The resulting radii have typical random uncertainties of about 2 per cent. We perform a quantitative study of systematic uncertainties affecting the methodology and find they are similar to, or smaller than, the random ones. We discuss how the stellar parameters can be used to derive the properties of both transiting exoplanets, and those where only a radial-velocity curve is available. We then explore in detail the improvements the method makes possible for the parameters of the PanCET sample of transiting planets. For this sample we find the best literature measurements of the planetary radii have mean uncertainties about 40 per cent larger than those presented here, with the new measurements achieving precisions of 2 per cent in radius and 10 per cent in mass. In contrast to much recent work, these transiting exoplanets parameters are derived without using theoretical models of stellar interiors, freeing them of the assumptions those models contain, and any priors for stellar age. As the data used are available for the whole sky, the method can be used for self-consistent measurements of the planetary parameters of a very large fraction of known exoplanets.

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arXiv2025

Rediscussion of eclipsing binaries. Paper XXVII. The totally-eclipsing system UZ Draconis

UZ Dra is a detached and totally-eclipsing binary containing two late-F stars in a circular orbit of period 3.261 d. It has been observed by the Transiting Exoplanet Survey Satellite in 41 sectors, yielding a total of 664,809 high-quality flux measurements. We model these data and published radial velocities to determine the physical properties of the system to high precision. The masses of the stars are 1.291 +/- 0.012 Msun and 1.193 +/- 0.009 Msun, and their radii are 1.278 +/- 0.004 Rsun and 1.122 +/- 0.003 Rsun. The high precision of the radius measurements is made possible by the (previously unrecorded) total eclipses and the extraordinary amount of data available. The light curves show spot modulation at the orbital period, and both stars rotate synchronously. Our determination of the distance to the system, 185.7 +/- 2.4 pc, agrees very well with the parallax distance of 185.39 +/- 0.39 pc from Gaia DR3. The properties of the system are consistent with theoretical predictions for an age of 600 +/- 200 Myr and a slightly super-solar metallicity.

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arXiv2025

EBOP MAVEN: A machine learning model to estimate the input parameters for analytic fitting of detached eclipsing binary light curves

Detached eclipsing binary stars (dEBs) are a key source of data on fundamental stellar parameters. Within the light curve databases of survey missions such as Kepler and TESS are a wealth of new systems awaiting characterisation. We aim to improve the scalability of efforts to process these data by developing a Convolutional Neural Network (CNN) machine learning model to assist in the automation of their analysis. From a phase-folded and binned dEB light curve the model predicts system parameters relating to stellar fractional radii, orbital inclination and eccentricity, and the stellar brightness ratio, for use as input values in subsequent formal analysis with the established JKTEBOP analytic code. We find the model able to predict these parameters for a previously unseen test dataset of 20000 synthetic dEB systems with a mean error of 14.1% when compared with the label values, improving to 8.6% against a subset representative of real systems. When tested with the TESS light curves of a set of real well-characterised systems, the model's predictions yield a mean error of $8.7\pm0.7\%$ when compared with label values derived from existing published analyses. Subsequent fitting of the TESS light curves with the JKTEBOP analytic code while using the model predictions as input values finds 27 of the 28 systems achieving a good fit. On the strength of these results, we plan to build a new characterisation pipeline based on the machine learning model and JKTEBOP code with the intention of producing a target catalogue of dEB systems for potential observation with the forthcoming PLATO mission.

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arXiv2025

Pulsations in Binary Star Systems

High-precision and long-duration light curves from space telescopes have revolutionized the fields of asteroseismology and binary star systems. In particular, the number of pulsating systems in eclipsing binaries has drastically increased thanks to space-based observations covering almost the entire sky. When combined with multi-epoch spectroscopy, this allows us not only to measure model-independent dynamical masses and radii for thousands of eclipsing binary systems, but also facilitates the powerful synergy of binarity and asteroseismology. Moreover, asteroseismology of pre- and post-interaction binary stars allows the physics of binary evolution to be constrained, including tides, mass transfer, and even mergers. We conclude that: (1) eclipsing binaries are among the best laboratories for testing stellar structure and evolution theory because we are able to measure their masses and radii independently of models; (2) combining binary and asteroseismic modeling yields precise constraints on the physical processes at work within stellar interiors, such as rotation and mixing; (3) pulsating binaries are challenging to study given the plethora of different techniques and physical processes that need to be considered depending on their orbital and physical properties; and (4) the impact of tides on the pulsational, stellar structure, and orbital properties of a binary system can be tested through tidal asteroseismology.

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arXiv2025

Absolute Parameters of Young Stars: NO Puppis

The southern early-type, young, eccentric-orbit eclipsing binary NO Puppis forms the A component of the multiple star Gaia DR3 552\-8147999779517568. The B component is an astrometric binary now at a separation of about 8.1 arcsec. There may be other fainter stars in this interesting but complex stellar system. We have combined several lines of evidence, including TESS data from 4 sectors, new ground-based BVR photometry, HARPS (ESO) and HERCULES (UCMJO) high-resolution spectra and astrometry of NO Pup. We derive a revised set of absolute parameters with increased precision. Alternative optimal curve-fitting programs were used in the analysis, allowing a wider view of modelling and parameter uncertainties. The main parameters are as follows: $M_{Aa} = 3.58 \pm 0.11$, $M_{Ab} = 1.68 \pm 0.09$ (M$_\odot$); $R_{Aa} = 2.17 \pm 0.03$, $R_{Ab} = 1.51 \pm 0.06$ (R$_\odot$), and $T_{\rm e Aa} = 13300 \pm 500$, $T_{\rm e Ab} = 7400 \pm 500$ (K). We estimate approximate masses of the wide companions, Ba and Bb, as $M_{Ba} = 2.0$ and $M_{Bb} = 1.8$ (M$_\odot$). The close binary's orbital separation is $a= 8.51 \pm 0.05$ (R$_\odot$); its age is approximately $20$ Myr and distance $172 \pm 1$ pc. The close binary's secondary (Ab) appears to be the source of low amplitude $ δ$ Scuti-type oscillations, although the form of these oscillations is irregular and unrepetitive. Analysis of the $ λ$ 6678 He I profile of the primary show synchronism of the mean bodily and orbital rotations. The retention of significant orbital eccentricity, in view of the closeness of the A-system components, is unexpected and poses challenges for the explanation that we discuss.

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arXiv2025

Rediscussion of eclipsing binaries. Paper XXVI. The F-type long-period system HP Draconis

HP Dra is a well-detached eclipsing binary containing two late-F stars on an orbit with a relatively large period of 10.76 d and a small eccentricity of 0.036. It has been observed in 14 sectors using the Transiting Exoplanet Survey Satellite (TESS). We use these data plus literature spectroscopic measurements to establish the properties of the component stars to high precision, finding masses of 1.135 +/- 0.002 Msun and 1.098 +/- 0.002 Msun and radii of 1.247 +/- 0.005 Rsun and 1.150 +/- 0.005 Rsun. We find a much smaller third light than previous analyses, resulting in significant changes to the measured radii. These properties match theoretical predictions for an age of 3.5 Gyr and a solar metallicity. We present a spectrum of the Ca H and K lines in which chromospheric activity is visible from both components. The distance we find to the system, 77.9 +/- 1.2 pc, matches the Gaia DR3 parallax value of 79.2 +/- 0.3 pc.

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arXiv2025

Rediscussion of eclipsing binaries. Paper XXV. The chemically-peculiar system AR Aurigae

AR Aur is a detached eclipsing binary containing two late-B stars which are chemically peculiar, on a circular orbit of period 4.135 d. The primary is a HgMn star which shows temporal changes in its chemical abundances and spectral line profiles, whilst the secondary is a likely weak Am star. Published analyses of the system have used spectroscopic light ratios to constrain the eclipse models and found that the secondary star is larger than the primary. This unexpected outcome has been taken as an indication that the system is young and the secondary has yet to reach the main sequence. In this work we present the first analysis of the light curve of the system obtained by the Transiting Exoplanet Survey Satellite (TESS), whose quality allows us to avoid using a spectroscopic light ratio to constrain the solution. When combined with literature spectroscopic results we obtain highly precise masses of 2.544 +/- 0.009 Msun and 2.358 +/- 0.009 Msun, and radii of 1.843 +/- 0.002 Rsun and 1.766 +/- 0.003 Rsun. The light ratio is inconsistent with spectroscopic determinations, confirming the suggestion of Takeda (2025) that spectroscopic light ratios of the system are unreliable due the chemical peculiarity of the stars. The properties of the system are matched by theoretical predictions for a slightly super-solar metallicity and an age of 33 +/- 3 Myr: both components are young main-sequence stars.

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