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Upper Limits on Radio Emission from the K2-18 System
Authors:
Kelvin Wandia,
Chenoa Tremblay,
Michael A. Garrett,
Alex Andersson,
Megan G. Li,
Vishal Gajjar,
Robert J. Beswick,
Jack F. Radcliffe,
David R. DeBoer,
P. B. Demorest,
Daniel Czech,
Wael Farah,
Ian Heywood,
Andrew Siemion
Abstract:
Stellar and planetary magnetic fields play a crucial role in the habitability of a planet and the integrity of its atmosphere. The recently claimed detection of biosignatures, methane, carbon dioxide and dimethyl sulfide/disulfide, in the atmosphere of K2-18 b, a sub-Neptune orbiting an M dwarf star present an intriguing question regarding the stellar magnetic environment and the resistance of the…
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Stellar and planetary magnetic fields play a crucial role in the habitability of a planet and the integrity of its atmosphere. The recently claimed detection of biosignatures, methane, carbon dioxide and dimethyl sulfide/disulfide, in the atmosphere of K2-18 b, a sub-Neptune orbiting an M dwarf star present an intriguing question regarding the stellar magnetic environment and the resistance of the planet's magnetosphere (if it exists) to erosion by magnetic activity from the host. To probe for radio emission from the system, we have conducted observations using the Karl G. Jansky Very Large Array (VLA) at S, C and X-bands (2-4, 4.5-7.5 and 8-10 GHz respectively) to search for coherent and incoherent radio emission. We detect no radio emission associated with incoherent emission mechanisms. We report $3σ$ Stokes I upper limits of $49.8\ μ\rm{Jybeam}^{-1}$ at S-band, $17.7\ μ\rm{Jybeam}^{-1}$at C-band and $18.0\ μ\rm{Jybeam}^{-1}$ at X-band and an upper limit of the ratio of the radio to the total bolometric luminosity of $\log L_\text{R}/\log L_\text{bol}<-8.8$. We have also searched for short duration bursts associated with coherent emission mechanisms at C and X-bands . No signals above a $3σ$ significance threshold are detected. Although no signals are detected our radio observations offer constraints, albeit limited, on the stellar magnetic environment supporting recent X-ray observations indicating K2-18 is a very faint emitter. Our results also contextualise any planetary transmission spectra by providing constraints on the activity level of the host.
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Submitted 7 November, 2025;
originally announced November 2025.
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Developing a Drift Rate Distribution for Technosignature Searches of Exoplanets
Authors:
Megan G. Li,
Sofia Z. Sheikh,
Christian Gilbertson,
Matthias Y. He,
Howard Isaacson,
Steve Croft,
Evan L. Sneed
Abstract:
A stable-frequency transmitter with relative radial acceleration to a receiver will show a change in received frequency over time, known as a "drift rate''. For a transmission from an exoplanet, we must account for multiple components of drift rate: the exoplanet's orbit and rotation, the Earth's orbit and rotation, and other contributions. Understanding the drift rate distribution produced by exo…
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A stable-frequency transmitter with relative radial acceleration to a receiver will show a change in received frequency over time, known as a "drift rate''. For a transmission from an exoplanet, we must account for multiple components of drift rate: the exoplanet's orbit and rotation, the Earth's orbit and rotation, and other contributions. Understanding the drift rate distribution produced by exoplanets relative to Earth, can a) help us constrain the range of drift rates to check in a Search for Extraterrestrial Intelligence (SETI) project to detect radio technosignatures and b) help us decide validity of signals-of-interest, as we can compare drifting signals with expected drift rates from the target star. In this paper, we modeled the drift rate distribution for $\sim$5300 confirmed exoplanets, using parameters from the NASA Exoplanet Archive (NEA). We find that confirmed exoplanets have drift rates such that 99\% of them fall within the $\pm$53 nHz range. This implies a distribution-informed maximum drift rate $\sim$4 times lower than previous work. To mitigate the observational biases inherent in the NEA, we also simulated an exoplanet population built to reduce these biases. The results suggest that, for a Kepler-like target star without known exoplanets, $\pm$0.44 nHz would be sufficient to account for 99\% of signals. This reduction in recommended maximum drift rate is partially due to inclination effects and bias towards short orbital periods in the NEA. These narrowed drift rate maxima will increase the efficiency of searches and save significant computational effort in future radio technosignature searches.
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Submitted 2 November, 2023;
originally announced November 2023.
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A Search for Technosignatures Around 11,680 Stars with the Green Bank Telescope at 1.15-1.73 GHz
Authors:
Jean-Luc Margot,
Megan G. Li,
Pavlo Pinchuk,
Nathan Myhrvold,
Larry Lesyna,
Lea E. Alcantara,
Megan T. Andrakin,
Jeth Arunseangroj,
Damien S. Baclet,
Madison H. Belk,
Zerxes R. Bhadha,
Nicholas W. Brandis,
Robert E. Carey,
Harrison P. Cassar,
Sai S. Chava,
Calvin Chen,
James Chen,
Kellen T. Cheng,
Alessia Cimbri,
Benjamin Cloutier,
Jordan A. Combitsis,
Kelly L. Couvrette,
Brandon P. Coy,
Kyle W. Davis,
Antoine F. Delcayre
, et al. (56 additional authors not shown)
Abstract:
We conducted a search for narrowband radio signals over four observing sessions in 2020-2023 with the L-band receiver (1.15-1.73 GHz) of the 100 m diameter Green Bank Telescope. We pointed the telescope in the directions of 62 TESS Objects of Interest, capturing radio emissions from a total of ~11,680 stars and planetary systems in the ~9 arcminute beam of the telescope. All detections were either…
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We conducted a search for narrowband radio signals over four observing sessions in 2020-2023 with the L-band receiver (1.15-1.73 GHz) of the 100 m diameter Green Bank Telescope. We pointed the telescope in the directions of 62 TESS Objects of Interest, capturing radio emissions from a total of ~11,680 stars and planetary systems in the ~9 arcminute beam of the telescope. All detections were either automatically rejected or visually inspected and confirmed to be of anthropogenic nature. In this work, we also quantified the end-to-end efficiency of radio SETI pipelines with a signal injection and recovery analysis. The UCLA SETI pipeline recovers 94.0% of the injected signals over the usable frequency range of the receiver and 98.7% of the injections when regions of dense RFI are excluded. In another pipeline that uses incoherent sums of 51 consecutive spectra, the recovery rate is ~15 times smaller at ~6%. The pipeline efficiency affects calculations of transmitter prevalence and SETI search volume. Accordingly, we developed an improved Drake Figure of Merit and a formalism to place upper limits on transmitter prevalence that take the pipeline efficiency and transmitter duty cycle into account. Based on our observations, we can state at the 95% confidence level that fewer than 6.6% of stars within 100 pc host a transmitter that is detectable in our search (EIRP > 1e13 W). For stars within 20,000 ly, the fraction of stars with detectable transmitters (EIRP > 5e16 W) is at most 3e-4. Finally, we showed that the UCLA SETI pipeline natively detects the signals detected with AI techniques by Ma et al. (2023).
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Submitted 15 October, 2023; v1 submitted 4 August, 2023;
originally announced August 2023.
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Three years of Sun-as-a-star radial-velocity observations on the approach to solar minimum
Authors:
A. Collier Cameron,
A. Mortier,
D. Phillips,
X. Dumusque,
R. D. Haywood,
N. Langellier,
C. A. Watson,
H. M. Cegla,
J. Costes,
D. Charbonneau,
A. Coffinet,
D. W. Latham,
M. Lopez-Morales,
L. Malavolta,
J. Maldonado,
G. Micela,
T. Milbourne,
E. Molinari,
S. H. Saar,
S. Thompson,
N. Buchschacher,
M. Cecconi,
R. Cosentino,
A. Ghedina,
A. Glenday
, et al. (11 additional authors not shown)
Abstract:
The time-variable velocity fields of solar-type stars limit the precision of radial-velocity determinations of their planets' masses, obstructing detection of Earth twins. Since 2015 July we have been monitoring disc-integrated sunlight in daytime using a purpose-built solar telescope and fibre feed to the HARPS-N stellar radial-velocity spectrometer. We present and analyse the solar radial-veloci…
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The time-variable velocity fields of solar-type stars limit the precision of radial-velocity determinations of their planets' masses, obstructing detection of Earth twins. Since 2015 July we have been monitoring disc-integrated sunlight in daytime using a purpose-built solar telescope and fibre feed to the HARPS-N stellar radial-velocity spectrometer. We present and analyse the solar radial-velocity measurements and cross-correlation function (CCF) parameters obtained in the first 3 years of observation, interpreting them in the context of spatially-resolved solar observations. We describe a Bayesian mixture-model approach to automated data-quality monitoring. We provide dynamical and daily differential-extinction corrections to place the radial velocities in the heliocentric reference frame, and the CCF shape parameters in the sidereal frame. We achieve a photon-noise limited radial-velocity precision better than 0.43 m s$^{-1}$ per 5-minute observation. The day-to-day precision is limited by zero-point calibration uncertainty with an RMS scatter of about 0.4 m s$^{-1}$. We find significant signals from granulation and solar activity. Within a day, granulation noise dominates, with an amplitude of about 0.4 m s$^{-1}$ and an autocorrelation half-life of 15 minutes. On longer timescales, activity dominates. Sunspot groups broaden the CCF as they cross the solar disc. Facular regions temporarily reduce the intrinsic asymmetry of the CCF. The radial-velocity increase that accompanies an active-region passage has a typical amplitude of 5 m s$^{-1}$ and is correlated with the line asymmetry, but leads it by 3 days. Spectral line-shape variability thus shows promise as a proxy for recovering the true radial velocity.
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Submitted 27 April, 2019;
originally announced April 2019.