arXiv subjects

Kevin N. Ortiz Ceballos

Publications and source records attributed to Kevin N. Ortiz Ceballos.

9 recordsLinked to original sources

arXiv2026

Discovery of a Nearby Ultra-fast Magnetic White Dwarf Propeller: Common Pathways to Magnetic Cataclysmic Variables

The fastest spinning white dwarfs (WDs), which approach break-up speeds, are found in close binary systems. In the two known magnetic WD ``propellers'', AE~Aqr and LAMOST J0240+1952, the magnetic WD spins so rapidly that it ejects the material transferred by its Roche-lobe-filling companion rather than accreting it. We report the discovery of the third such system, 1eRASS J042633.5$-$250226 (1eRASS J0426/Valeria), at only 265 pc, identified by combining SRG/eROSITA and \textit{Gaia} data via the ``X-ray Main Sequence''. TESS photometry shows AE~Aqr-like flaring and orbital modulation with $P_{\mathrm{orb}} \approx 6.62$ hr, and ZTF shows month-long high/low state changes. Phase-resolved Palomar/DBSP spectroscopy confirms the orbital period and yields a donor radial velocity of $K_2 = 202\pm7$ km s$^{-1}$. High-speed Palomar/CHIMERA photometry detects optical pulsations on three nights with the strongest detection at $P_\textrm{spin} = 26.8$ sec, though further observations are needed to confirm this as the WD spin. Spectral fitting of the donor in the low state reveals a late K-type star with $T_{\mathrm{donor}} = 4100\pm150$ K. Zeeman splitting in the optical spectrum yields a candidate field strength of $B_{\mathrm{WD}} = 26 \pm 3$ MG, meaning the system will evolve into a polar. Like other WD propellers, the system is X-ray faint ($L_X \approx 7\times 10^{30}$ erg s$^{-1}$), but is not detected in the radio, and a spin period is not detected in X-rays by SRG/eROSITA. The proximity of this system and evolutionary model constraints on the timeframe of the propeller phase yield a birth rate density of $\sim8\times10^{-16} \textrm{pc}^{-3} \textrm{yr}^{-1}$, which agrees with that of magnetic CVs, suggesting that a substantial fraction of magnetic CVs pass through a propeller phase.

astro-ph.HE↗

arXiv2026

Discovery of radio emission from the exoplanet $β$ Pictoris b

Planetary magnetic fields shape atmospheric escape, mediate interactions with stellar winds, and encode information about planetary interiors, yet they have not been directly measured for planets beyond the Solar System. A direct observable signature is auroral radio emission produced by the electron cyclotron maser instability, whose highest emitted frequency is set by the magnetic field strength at its source. Although auroral radio bursts are observed in Solar System planets and in some ultracool dwarfs, no radio detection has previously been unambiguously localized to an extrasolar planet rather than its host star. Here, we report the first direct detection of auroral radio emission from an exoplanet, the giant planet $β$ Pictoris b, with the MeerKAT array. We detect rapid, recurring, and highly circularly polarized bursts, as well as persistent emission, at frequencies of 0.85 to 3.5 GHz. We identify the emission as electron cyclotron maser radiation, which implies a magnetic field of $\gtrsim 1.25$ kG at the planet, the first such direct field strength measurement for an exoplanet.

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arXiv2026

WASP-12b Exhibits Persistent In-Transit H$α$ Absorption

High-resolution H$α$ and He 10830 Å transit spectroscopy can trace the extended upper atmospheres of exoplanets, typically revealing excess in-transit absorption that occurs in the planet's rest frame. However, hydrodynamical simulations predict that absorption should not strictly follow the planet's orbital motion if gas quickly escapes the planetary Roche lobe and shears into tidal tails. The ultra-hot Jupiter WASP-12b fills an exceptionally large fraction of its Roche lobe ($R_p/R_\mathrm{Roche} = 0.55$), and in this paper we present evidence for tidally-modulated outflow kinematics on this unique planet. We observed a transit of WASP-12b with MMT/Hectochelle and found an excess H$α$ absorption of $3.29^{+0.35}_{-0.36}\%$ (9.3$σ$) during the transit and extending at least 30~min post-egress. The signal does not follow the planet's orbital motion and instead appears largely in the stellar rest frame, similar to the extended helium outflows in HAT-P-32b and HAT-P-67b, and is slightly redshifted ($+5.4_{-1.7}^{+1.5}$ km s$^{-1}$). We demonstrate that a similar signal appears across previous high-sensitivity observations dating back to 2012 once the atypical signal kinematics and baseline self-subtraction are taken into account. Finally, we present a three-dimensional Athena++ model of WASP-12b's outflowing atmosphere that simultaneously exhibits the observed extended morphology and lack of planet-aligned velocity gradient. Our study highlights the necessity of three-dimensional simulations for interpreting absorption lines formed in strong outflows, where gas may not simply follow the planet's Doppler signature.

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arXiv2026

High Tide or Riptide on the Cosmic Shoreline? A Water-Rich Atmosphere or Stellar Contamination for the Warm Super-Earth GJ~486b from JWST Observations

Planets orbiting M-dwarf stars are prime targets in the search for rocky exoplanet atmospheres. The small size of M dwarfs renders their planets exceptional targets for transmission spectroscopy, facilitating atmospheric characterization. However, it remains unknown whether their host stars' highly variable extreme-UV radiation environments allow atmospheres to persist. With JWST, we have begun to determine whether or not the most favorable rocky worlds orbiting M dwarfs have detectable atmospheres. Here, we present a 2.8-5.2 micron JWST NIRSpec/G395H transmission spectrum of the warm (700 K, 40.3x Earth's insolation) super-Earth GJ 486b (1.3 R$_{\oplus}$ and 3.0 M$_{\oplus}$). The measured spectrum from our two transits of GJ 486b deviates from a flat line at 2.2 - 3.3 $σ$, based on three independent reductions. Through a combination of forward and retrieval models, we determine that GJ 486b either has a water-rich atmosphere (with the most stringent constraint on the retrieved water abundance of H2O > 10% to 2$σ$) or the transmission spectrum is contaminated by water present in cool unocculted starspots. We also find that the measured stellar spectrum is best fit by a stellar model with cool starspots and hot faculae. While both retrieval scenarios provide equal quality fits ($χ^2_ν$ = 1.0) to our NIRSpec/G395H observations, shorter wavelength observations can break this degeneracy and reveal if GJ 486b sustains a water-rich atmosphere.

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arXiv2025

A Radio Search for Star-Planet Interaction in TOI-540 and SPECULOOS-3

We present the first targeted centimeter-band radio observations of two recently-discovered exoplanet systems that are prime candidates for magnetic star-planet interaction (SPI): TOI-540 and SPECULOOS-3. The targets were selected due to the small orbital separation of their known planets, as well as for indications of stellar magnetic activity, given that for SPI radio emission may be strongest when a sufficiently magnetized star hosts a close-in planet. The deep, multi-epoch Very Large Array (SPECULOOS-3) and MeerKAT (TOI-540) observations yield non-detections, with $3σ$ limits of $\lesssim 7.5$ $μ$Jy ($4-8$ GHz) and $\lesssim 30-80$ $μ$Jy ($0.8-1.7$ GHz), respectively. For SPECULOOS-3 b we rule out observable SPI for most of its orbit, while for TOI-540 b we sample a narrower range, around planetary transit. We model possible planetary magnetic field strength constraints for both systems, and conclude that our observations are sensitive enough to sample SPI emission in these systems if present and directed at us, even for a planetary field of only $\sim 1$ G.

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arXiv2025

Arecibo Wow! II: Revised Properties of the Wow! Signal from Archival Ohio SETI Data

The Wow! Signal, detected in 1977 by the Ohio State University SETI project, remains one of the most intriguing unexplained radio transients. The most recent significant revision of its properties took place in the late 1990s; however, further advances were limited by readily available data from this event. Here we retrieved and analyzed decades of previously unpublished Ohio SETI observations, enabling the most comprehensive re-evaluation of the properties of the Wow! Signal to date with modern methods. Our results reveal significant revisions to its parameters that may help explain why its source has been so difficult to identify. We refine its potential origin to two adjacent fields centered on the right ascension $α=19^{\mathrm h}25^{\mathrm m}02^{\mathrm s} \pm 3^{\mathrm s}$ or $19^{\mathrm h}27^{\mathrm m}55^{\mathrm s} \pm 3^{\mathrm s}$, and the declination $δ=-26^°57' \pm 20'$ (J2000), a location both narrower and slightly displaced from earlier estimates. We measure a higher peak flux density exceeding 250 Jy and a frequency of $1420.726 \pm 0.005$ MHz, implying a galactic source with a substantially higher radial velocity than previously assumed. Our analysis provides additional support for the hypothesis that the Wow! Signal most likely had an astrophysical origin rather than being attributed to radio interference. In particular, we confirm that small, cold HI clouds can produce narrowband signals similar to its detection, which might suggest a common origin. These findings provide the most precise constraints to date on the location, intensity, and frequency of the Wow! Signal and offer a new path to identify its origin.

astro-ph.HE↗

arXiv2024

A Volume-Limited Radio Search for Magnetic Activity in 140 Exoplanets with the Very Large Array

We present results from a search for radio emission in 77 stellar systems hosting 140 exoplanets, predominantly within 17.5 pc using the Very Large Array (VLA) at $4-8$ GHz. This is the largest and most sensitive search to date for radio emission in exoplanetary systems in the GHz frequency range. We obtained new observations of 58 systems, and analyzed archival observations of an additional 19 systems. Our choice of frequency and volume limit are motivated by radio detections of ultracool dwarfs (UCDs), including T dwarfs with masses at the exoplanet threshold of $\sim\!13\,M_J$. Our surveyed exoplanets span a mass range of $\approx\,10^{-3}-10\,M_J$ and semi-major axes of $\approx\,10^{-2}-10\,$AU. We detect a single target - GJ 3323 (M4) hosting two exoplanets with minimum masses of 2 and 2.3$\,M_\oplus$ - with a circular polarization fraction of $\approx\,40\%$; the radio luminosity agrees with its known X-ray luminosity and the Güdel-Benz relation for stellar activity suggesting a likely stellar origin, but the high circular polarization fraction may also be indicative of star-planet interaction. For the remaining sources our $3σ$ upper limits are generally $L_ν\lesssim\,10^{12.5}\,\mathrm{erg}\,\mathrm{s}^{-1}\,\mathrm{Hz}^{-1}$, comparable to the lowest radio luminosities in UCDs. Our results are consistent with previous targeted searches of individual systems at GHz frequencies while greatly expanding the sample size. Our sensitivity is comparable to predicted fluxes for some systems considered candidates for detectable star-planet interaction. Observations with future instruments such as the Square Kilometer Array and Next Generation Very Large Array will be necessary to further constrain emission mechanisms from exoplanet systems at GHz frequencies.

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arXiv2024

A High-Resolution Non-Detection of Escaping Helium In The Ultra-Hot Neptune LTT 9779b: Evidence for Weakened Evaporation

The recent discovery of ``ultra-hot'' ($P < 1$ day) Neptunes has come as a surprise: some of these planets have managed to retain gaseous envelopes despite being close enough to their host stars to trigger strong photoevaporation and/or Roche lobe overflow. Here, we investigate atmospheric escape in LTT 9779b, an ultra-hot Neptune with a volatile-rich envelope. We observed two transits of this planet using the newly-commissioned WINERED spectrograph ($R\sim68,000$) on the 6.5 m Clay/Magellan II Telescope, aiming to detect an extended upper atmosphere in the He 10830 A triplet. We found no detectable planetary absorption: in a 0.75 A passband centered on the triplet, we set a 2$σ$ upper limit of 0.12% ($δR_p/H < 14$) and a 3$σ$ upper limit of 0.20% ($δR_p/H < 22$). Using a H/He isothermal Parker wind model, we found corresponding 95% and 99.7% upper limits on the planetary mass-loss rate of $\dot{M} < 10^{10.03}$ g s$^{-1}$ and $\dot{M} < 10^{11.11}$ g s$^{-1}$ respectively, smaller than predicted by outflow models even considering the weak stellar XUV emission. The low evaporation rate is plausibly explained by a metal-rich envelope, which would decrease the atmospheric scale height and increase the cooling rate of the outflow. This hypothesis is imminently testable: if metals commonly weaken planetary outflows, then we expect that \textit{JWST} will find high atmospheric metallicities for small planets that have evaded detection in He 10830 A.

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arXiv2021

Habitability Models for Astrobiology

Habitability has been generally defined as the capability of an environment to support life. Ecologists have been using Habitat Suitability Models (HSMs) for more than four decades to study the habitability of Earth from local to global scales. Astrobiologists have been proposing different habitability models for some time, with little integration and consistency among them, being different in function to those used by ecologists. Habitability models are not only used to determine if environments are habitable or not, but they also are used to characterize what key factors are responsible for the gradual transition from low to high habitability states. Here we review and compare some of the different models used by ecologists and astrobiologists and suggest how they could be integrated into new habitability standards. Such standards will help to improve the comparison and characterization of potentially habitable environments, prioritize target selections, and study correlations between habitability and biosignatures. Habitability models are the foundation of planetary habitability science and the synergy between ecologists and astrobiologists is necessary to expand our understanding of the habitability of Earth, the Solar System, and extrasolar planets.

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