arXiv subjects

Adam T. Stevenson

Publications and source records attributed to Adam T. Stevenson.

4 recordsLinked to original sources

arXiv2026

The Dispersed Matter Planet Project Sample -- Detection limits, Occurrence Rates and New Planets

DMPP is a radial-velocity survey that aims to detect planets around stars exhibiting anomalous activity signatures, consistent with the presence of close-in evaporating planets. Here, we report the discovery of 7 new planetary signals in 5 different systems: DMPP-2c & d, HD67200/DMPP-6b & c, HD118006/DMPP-7b, HD191122/DMPP-8b, and HD200133/DMPP-9b. We update the orbital parameters of the DMPP-1, DMPP-2, and DMPP-3 systems, along with those of the planetary systems orbiting HD181433, HD39194, and HD89839. We derive detection limits for all 24 targets in our sample with adequate observational coverage, and test the DMPP hypothesis by calculating the occurrence rates for planets in this configuration. We find that the occurrence rates of planets in our sample with orbital periods shorter than $50~\mathrm{d}$ and masses in the range $3$-$10$ M$_\oplus$ are $83.0^{+27.1}_{-24.4}\%$, for $10$-$30$ M$_\oplus$ are $27.0^{+15.0}_{-11.2}\%$, and for $30$-$100$ M$_\oplus$ are $13.9^{+11.8}_{-7.5}\%$. This is significantly higher than the occurrence rates reported by other radial velocity surveys, providing strong support for the DMPP hypothesis.

astro-ph.EP↗

arXiv2025

BEBOP VIII. SOPHIE radial velocities reveal an eccentric, circumbinary brown dwarf

Circumbinary configurations offer a test of planet formation in an altered environment, where the inner binary has perturbed a protoplanetary disc. Comparisons of the physical and orbital parameters between the circumbinary planet population and the population of exoplanets orbiting single stars will reveal how these disc perturbations affect the assembly of planets. Circumbinary exoplanets detected thus far typically have masses $< 3 \,\rm M_{jup}$ raising the question of whether high-mass circumbinary planets are possible, and also whether population features such as the brown dwarf desert would appear in circumbinary configurations like for single star systems. Here, we report observations taken with the SOPHIE high-resolution spectrograph. These observations reveal an $m_{\rm b}\,\sin i_{\rm b} = 20.9 \,\rm M_{jup}$ outer companion, on an eccentric ($e = 0.43$), $1800\,\rm d$ orbit, which we call BEBOP-4 (AB) b. Using dynamical arguments we constrain the true mass $m_{\rm b}< 26.3 \,\rm M_{jup}$. The inner binary's two eclipsing stellar components have masses $M_{\rm A} = 1.51\,\rm M_\odot$, and $M_{\rm B} = 0.46\,\rm M_\odot$. Their orbital period is $72\,\rm d$, and their eccentricity is $0.27$. This system contains the longest period binary surveyed by the BEBOP project. BEBOP-4b is expected to be detectable using Gaia DR4 single epoch astrometric measurements. Despite a large period ratio of $\sim 25:1$, the substantial eccentricities of both orbits mean that the outer orbit is on the edge of orbital stability, and located in between two destabilising secular resonances. Should the outer companion survive, the BEBOP-4 system appears like a precursor to several post-common envelope binaries exhibiting eclipse timing variations where very massive circumbinary companions have been proposed.

astro-ph.EP↗

arXiv2023

Combing the Brown Dwarf Desert with Gaia DR3

We have created an up-to-date catalogue of 214 brown dwarfs (BDs) in binaries with $P < 10^4$ d. This allows us to examine the population statistics of the brown dwarf desert. We searched $\textit{Gaia}$ DR3 NSS results for orbital inclinations of BD candidates, deriving 12 new masses. Three remain as desert BDs whereas nine candidates are found to be low-mass stars. We improved the RV solutions for three previously studied BD candidates. A further 19 BD masses with periods less than $\sim$ 1200 d were identified in the DR3 $\texttt{binary_masses}$ database. We confirm a valley in the mass distribution with a minimum around 30-35 M$_{\textrm{jup}}$, and find that periods $<$ 100 d are still under-populated in comparison to longer periods. The updated mass and eccentricity distribution of BDs still shows a marginally statistically significant split into high- and low-mass BD populations. This hints at two different parent distributions, and two potential origins $-$ either akin to planetary formation, or stellar. There are no low eccentricity BDs at periods around 100 d. The mass-metallicity distribution of BDs indicates that core accretion is not the dominant formation mechanism for BDs as they do not follow the same trends that giant exoplanets do with metallicity. We identify a diagonal envelope bounding the Gaia BDs in the mass-period plane due to the detection thresholds of the currently available NSS solutions from 34 months of data.

astro-ph.SR↗

arXiv2023

DMPP-3: confirmation of short-period S-type planet(s) in a compact eccentric binary star system, and warnings about long-period RV planet detections

We present additional HARPS radial velocity observations of the highly eccentric ($e \sim 0.6$) binary system DMPP-3AB, which comprises a K0V primary and a low-mass companion at the hydrogen burning limit. The binary has a $507$ d orbital period and a $1.2$ au semi-major axis. The primary component harbours a known $2.2$ M$_{\oplus}$ planet, DMPP-3A b, with a $6.67$ day orbit. New HARPS measurements constrain periastron passage for the binary orbit and add further integrity to previously derived solutions for both companion and planet orbits. Gaia astrometry independently confirms the binary orbit, and establishes the inclination of the binary is $63.89 \pm 0.78 ^{\circ}$. We performed dynamical simulations which establish that the previously identified $\sim800$ d RV signal cannot be attributed to an orbiting body. The additional observations, a deviation from strict periodicity, and our new analyses of activity indicators suggest the $\sim800$ d signal is caused by stellar activity. We conclude that there may be long period planet 'detections' in other systems which are similar misinterpreted stellar activity artefacts. Without the unusual eccentric binary companion to the planet-hosting star we could have accepted the $\sim800$ d signal as a probable planet. Further monitoring of DMPP-3 will reveal which signatures can be used to most efficiently identify these imposters. We also report a threshold detection (0.2 per cent FAP) of a $\sim2.26$ d periodicity in the RVs, potentially attributed to an Earth-mass S-type planet interior to DMPP-3A b.

astro-ph.EP↗