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Physics Astrophysics

astro-ph Watch Astrophysics

Wednesday 26 August

High Energy Astrophysical Phenomena

Is the mysterious Punctum a primordial black hole?

Man Ho Chan

A recent study has discovered a highly polarized millimeter continuum source called Punctum located at the central region of NGC 4945 which doesn't fit any known category. Apart from the radio detection at $\approx 100$ GHz, there is no identified counterpart to Punctum in other radio, infra-red, optical, and X-ray bands. All available potential models, including magnetar, supernova remnant and microquasar, cannot provide satisfactory explanation for the exceptionally high polarization of $\sim 50$% and large luminosity in mm band $L_{\rm mm} \approx 2\times 10^{35}$ erg/s within a small size $<2$ pc shown in Punctum. In this article, we discuss the possibility that Punctum is indeed a primordial black hole (PBH) with a dark matter density spike. We show that the synchrotron radiation due to the electrons and positrons produced from dark matter annihilation can satisfactorily explain the observed properties of Punctum and we can effectively obtain the annihilation cross section $\langle \sigma v \rangle \sim 10^{-33}$ cm$^3$/s using our developed analytic framework. Furthermore, if the Punctum PBH mass is $\sim 10-100M_{\odot}$, the preferred dark matter mass range is $m_{\rm DM} \sim 10-1000$ MeV.
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Solar and Stellar Astrophysics

Broadband 12-26 GHz Radio Radiation Reveals Evidence for Micro-flares on AU Mic

Isaiah I. Tristan, Rachel A. Osten, Yuta Notsu et al. (+2 more)

We present sequential 12-18 and 18-26 GHz radio-band ($Ku$, $K$) VLA observations of the 22 Myr dM1e star AU Mic. We detect two flares and two marginal events over a total of 3 contiguous hours on source, resulting in a radio flare rate of $\sim$1 flare hour$^{-1}$. While this rate is consistent with previous $Ku$-band observations, both flaring ($<$1 mJy) and quiescent ($\sim$0.4 mJy) flux densities are significantly lower. Furthermore, the quiescent spectral shape here is distinct, allowing for unique constraints on the radio-emitting sources of AU Mic. The time-averaged quiescent spectrum is best described by gyrosynchrotron radiation with a peak around 17 GHz and an optically thin spectral index of $\alpha \approx -0.6$. We estimate that the source regions have magnetic field strengths of $\sim$1 kG and cover a fraction of $<$0.5% of the stellar surface, yet the instantaneous total electron kinetic energies are $\sim$10$^{28}$ erg. The power-law index describing the distribution of electrons with energy derived from the spectral index, $\delta \approx 2$, implies a near-continuous injection of electrons. This could arise from micro-flares that occur over the surface of AU Mic that sustain the radio radiation. One clear flare per band occurs, with decay-to-rise $e$-folding time ratios of $3 - 4$, indicating magnetic trapping of the electrons. The $Ku$-band flare is optically thick during the rise and peak times, indicating a peak frequency above 18 GHz. Together, these quiescent and flaring characteristics suggest that continuous, unresolved micro-flaring and magnetic trapping dominate the non-thermal radio emission of active M-dwarf coronae.
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All authors Isaiah I. Tristan, Rachel A. Osten, Yuta Notsu, Adina D. Feinstein, Adam F. Kowalski

Solar and Stellar Astrophysics

Large fraction of blends from Rowan et al. (2023)

P Zasche

Following the work by Rowan et al., I found that a large fraction of systems presented as triple/quadruple stars are in fact only blends. After careful inspection of 225 candidate systems from Rowan et al., I found that one-third of them are, in fact, only blended signals of two different eclipsing binaries, well separated from each other on the sky. Their typical angular separation is dozens of arcsec, reaching up to more than 100 arcsec for some targets. This is probably due to relatively large TESS pixels and insufficient cross-checking of all available catalogues and photometric data. I present a list of 76 confirmed blends with their correct identification and respective periods. Such a high fraction (33.8 per cent) of reported false-positive systems should be taken into account in future studies, when reporting to new discoveries of doubly eclipsing candidates.
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Astrophysics of Galaxies

Recovering the effective impact parameters in integral-field absorption-line tomography

J. A. Hernández-Guajardo, L. F. Barrientos, C. Ledoux et al. (+3 more)

Integral-field-unit (IFU) spectroscopy of extended background sources, such as gravitational arcs, delivers many closely spaced absorption sightlines through the circumgalactic medium (CGM) of foreground galaxies. However, the source extent and smearing through the point spread function (PSF) cause each spaxel to integrate light from a region larger than itself. The usually adopted geometric spaxel centre is therefore not representative of where the absorbed flux originates. Informed by high-resolution imaging, we introduce a flux-contribution formalism that reconstructs the spatial origin of the flux in each spaxel by defining flux-weighted coordinates and impact parameters. Using a data-driven simulation built on a real gravitational-arc configuration, we show that spaxel centres are displaced from the flux-weighted positions by $|\Delta\mathbf{x}| \propto \theta_{\rm PSF}(1-f)$, with $f$ the spaxel-source overlap fraction, and that the resulting impact-parameter bias scales with the lensing magnification as $\mu^{-1/2}$. These offsets are largest for off-arc spaxels and flatten the radial column-density profiles. They also inject a coherent geometry-driven scatter that mimics intrinsic CGM structure and that is removed neither by a tighter spaxel selection nor by a finer spatial binning. For identical uncertainties, the spaxel-centre coordinates leave residuals of about twice the noise level ($\chi^2_\nu \sim 4$), whereas the flux-weighted coordinates recover the input profile to within the uncertainties ($\chi^2_\nu \sim 1$) and remain robust to a PSF misspecification of $\pm 10\%$. The method we propose provides a better-motivated and readily adoptable framework for tomographic studies, whether as the primary analysis or as a robustness check on spaxel-centre results.
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All authors J. A. Hernández-Guajardo, L. F. Barrientos, C. Ledoux, N. Tejos, E. J. Johnston, P. Anshul

Astrophysics of Galaxies

Laplace surface of eccentric orbits around Kerr black hole and black-hole effects on Lidov-Kozai cycles

Haonan Quan and Xing Wei

We study the Laplace surface of eccentric orbits around a Kerr black hole with a companion star. The two relativistic effects (periapsis apsidal precession and Lense-Thirring precession) balance companion's tidal effect. By solving the secular equations, we find that the two branches of equilibrium solutions exist only in a narrow range of orbital inclinations of test particle, and that the stability exists when companion's obliquity approaches 90 degree. We then study the black-hole effects on Lidov-Kozai cycles. In addition to the black-hole suppression on cycle amplitude, we find that the cycle frequency is non-monotonic about distance from black hole and reaches its minimum in the transition between GR apsidal precession and companions's tidal precession. Finally we use this mechanism to well interpret the nearly isotropic orientation of S-cluster in the Galactic center.
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Astrophysics of Galaxies

A systematic study of AGN feedback in a disk galaxy using MACER. III. High Gas Fractions in AGN Hosts

Yuxuan Zou, Feng Yuan, Suoqing Ji et al. (+4 more)

We use high-resolution hydrodynamic simulations in the MACER framework to explain why low-redshift PG quasar hosts can retain substantial cold-gas reservoirs, with gas fractions and gas-to-stellar mass ratios showing little dependence on instantaneous AGN luminosity. This paper is the third in a series systematically studying AGN feedback in a disk galaxy subject to cosmological gas inflow. The simulations include multiphase gas, star formation, stellar feedback, and self-consistent radiative and mechanical AGN feedback. We reproduce the observed weak connection between host-galaxy gas content and AGN luminosity over L_AGN/L_Edd ~ 10^{-5}-10, while the galaxy nevertheless undergoes pronounced gas depletion and star-formation quenching. During the quenching phase, the cold-gas mass declines by nearly three orders of magnitude, and the evolution of the gas distribution shows that AGN feedback progressively removes both cold and hot gas from the galaxy. The star formation rate is more closely linked to the cold-gas mass than to AGN luminosity. This behavior arises from a timescale mismatch: AGN luminosity varies on ~ 10^5-10^6 yr timescales, whereas repeated AGN-driven outflows cumulatively deplete the galaxy-scale gas reservoir over ~ 1 Gyr. Our simulations therefore provide a physical explanation for the gas-rich PG quasar hosts and show that their observed gas properties are fully consistent with effective, long-term ejective AGN feedback.
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All authors Yuxuan Zou, Feng Yuan, Suoqing Ji, Jinyi Shangguan, Hassen M. Yesuf, Lu Shen, Luis C. Ho

Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Multi-messenger signal from QCD-Axion Ultracompact Minihalos

Dorian W. P. Amaral, Enrico D. Schiappacasse and Karla Tapia-Rebolledo

We explore the multimessenger signatures from ultracompact minihalos (UCMHs) seeded by stellar-mass primordial black holes (PBHs) and composed of QCD-axion dark matter. Using the secondary-infall framework, with relic-abundance and isocurvature conditions from a pre-inflationary Peccei-Quinn scenario, we numerically recover the characteristic halo profile and adopt a conservative constant-density core for the innermost region. We study the gravitational wave and electromagnetic signatures from neutron-star-PBH inspirals inside these dense structures. Dynamical friction produces a gravitational-wave dephasing relative to the vacuum binary, observable with LISA for primordial black holes with masses $\lesssim\! 10M_\odot$. Simultaneously, gravitationally focused axions can resonantly convert into photons in the neutron-star magnetosphere, producing a narrow-band radio signature. For nearby galactic neutron stars, the projected sensitivity of the Green Bank radio telescope GBT captures the QCD-axion band in the $\mu{\rm eV}$ mass range. Gravitational waves therefore probe the presence and structure of the UCMH, while the radio signal probes the particle nature of its dark matter, making their joint observation a distinctive test of a mixed dark sector.
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High Energy Astrophysical Phenomena

Constraining gamma-ray burst viewing angles with Swift/XRT afterglow light curves

Cheng-Jie Sun, Shuang-Xi Yi, Lin Zhou et al. (+6 more)

Gamma-ray bursts (GRBs) are among the most energetic phenomena in the universe, and their afterglow light curves encode information about jet geometry and viewing angle. To constrain GRB viewing angles, we analyzed jet break features in Swift X-Ray Telescope afterglow light curves using two top-hat jet models: a simplified geometric model without high-latitude emission (model 1) and a comprehensive model including it (model 2). Both models were applied to a sample of 20 GRBs in an interstellar medium (ISM) and 20 in a wind medium, selected so that jet breaks are attributed to the edge effect with sufficient data coverage, and fitted with Markov Chain Monte Carlo methods. We examined viewing angles and off-axis ratios q = $\theta_{\rm obs}/\theta_{\rm jet}$ under both density profiles, evaluating the impact of high-latitude emission. Based on reduced chi-squared and Bayesian information criterion comparisons, model 1 fits all GRBs better. Most GRBs have small off-axis ratios (mean q = 0.1851 for model 1), indicating viewing angles generally close to the jet axis; the log-space viewing-angle distribution is approximately Gaussian. A Kolmogorov-Smirnov test shows no significant difference in off-axis ratios between ISM and wind media, nor between bursts with and without an X-ray plateau. While viewing angles decrease significantly with redshift, the off-axis ratio shows no significant evolution, consistent with off-axis alignment being independent of cosmic epoch.
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All authors Cheng-Jie Sun, Shuang-Xi Yi, Lin Zhou, Yuan-Chuan Zou, Yu-Peng Yang, Si-Ji Xin, Yan-Kun Qu, Wen-Long Zhang, Fa-Yin Wang

Earth and Planetary Astrophysics

Centimeter-wave OH observations of comets 12P/Pons-Brooks and C/2023 A3 (Tsuchinshan-ATLAS) with FAST

Long-Fei Chen, Juncen Li, Zhen Wang et al. (+5 more)

We present centimeter-wave spectroscopic observations of the OH 18-cm lines in two bright comets, 12P/Pons-Brooks and C/2023 A3 (Tsuchinshan-ATLAS), conducted with the Five-hundred-meter Aperture Spherical radio Telescope (FAST) during their 2024 apparitions. For the Halley-type comet 12P/Pons-Brooks, five epochs of OH observations were obtained. The main OH lines at 1665 and 1667 MHz were robustly detected in absorption during one pre-perihelion epoch, while upper limits were derived for two post-perihelion epochs. For the dynamically new Oort Cloud comet C/2023 A3 (Tsuchinshan-ATLAS), six epochs of OH observations were obtained. The 1665 and 1667 MHz lines were robustly detected in absorption during two epochs immediately following the comet's closest approach to Earth. We also reported a tentative detection of the 1721 MHz satellite line in one of these two epochs. The low OH detection rates for these two bright comets are primarily attributable to their unfavorable heliocentric radial velocity during the observations, which resulted in the anti-maser negative inversion mode of the OH excitation. We calculated the OH production rates for both comets and found that, after considering the small beam size of FAST and the collisional quenching effect, production rates are consistent with the data from literature. Specifically, this matches the power-law fit of the OH production rates for comet 12P/Pons-Brooks, as well as the production rates at comparable heliocentric distances among comet C/2023 A3 (Tsuchinshan-ATLAS) and four other dynamically new Oort Cloud comets.
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All authors Long-Fei Chen, Juncen Li, Zhen Wang, Jian-Yang Li, Wing-Huen Ip, Zhong-Yi Lin, Bin Yang, Chao-Wei Tsai

Cosmology and Nongalactic Astrophysics

The optimal redshift for dark energy II: application to cosmological data and the evidence for the phantom crossing of the CPL equation of state

Travis Seth Rippentrop, Mustapha Ishak and Kristian Gonzalez

Recent results from DESI and other cosmological datasets have indicated a preference for dynamical dark energy, with a time-evolving equation of state (EOS), $w(z)$. Furthermore, analyses using the CPL parameterization give an EOS with a phantom crossing of the $w(z)=-1$ line. In a companion paper-I, we assumed the CPL parameterization and its generalization, and introduced the formalism of the optimal scale factor (or redshift), a quantity designed to simultaneously maximize the distance from the cosmological constant value of $-1$ and to minimize the uncertainty on the EOS, thereby maximizing the tension with the cosmological constant at that specific redshift for a given dataset combination. In this paper-II, we apply the optimal-redshift formalism to available baryon acoustic oscillation, Cosmic Microwave Background, and supernova dataset combinations, with a particular focus on the phantom-line crossing within CPL. Motivated by the relatively low significance of previous constraints on the EOS in the region below the phantom line, we calculate the optimal redshift for a variety of dataset combinations to identify those that best constrain departures from $w(z)=-1$ before and after the crossing. We find combinations and corresponding optimal redshifts for which $w(z)$ lies below the “$-1$” line with new significance levels reaching $3.01$–$3.22\sigma$ before the crossing point, and $3.30$–$3.55\sigma$ above “$-1$" after the crossing. Our focus in this work is the application of a new framework that maximizes the significance of the phantom-crossing signal within CPL using currently available datasets. Determining whether this crossing is effective or intrinsic, and identifying the underlying microphysical models, constitute separate questions from the aim of the present work and remain important directions for future investigation, further motivated by our findings. Abridged.
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High Energy Astrophysical Phenomena

What is the reason for the lack of cool evolved stars near the center of the Galaxy?

Petr Kurfürst, Michal Zajaček, Norbert Werner et al. (+2 more)

The observed deficit of bright late-type giants in the central parsec of the Milky Way remains an open problem. We investigate whether repeated passages of red giants (RGs) through a past jet from Sgr$~$A$^*$ can modify their envelopes and apparent spectral types. Three-dimensional hydrodynamical simulations follow a $1\,M_\odot$, $100\,R_\odot$ RG through up to ten jet crossings at $10^{-3}\,\text{pc}$, using jet kinetic luminosities of $10^{42}$, $10^{44}$, and $10^{48}\,\text{erg}\,\text{s}^{-1}$. Each passage produces shocks, envelope ablation, and an asymmetric downstream tail. For jet luminosities up to $10^{44}\,\text{erg}\,\text{s}^{-1}$, the cumulative ablated mass evolves approximately as $\Delta M\propto t^{1/2}$ and reaches about $10^{-4}\,M_\odot$ over a $10^5\,\text{yr}$ active phase. Repeated heating also raises the surface temperature from about $3600$ to $8500\,\text{K}$ during the first ten passages, potentially making an M-type giant appear as an A-type source. Jet feedback may therefore contribute to the apparent depletion of cool giants and the excess of hot stars in galactic nuclei (GN).
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All authors Petr Kurfürst, Michal Zajaček, Norbert Werner, Jiří Krtička, Matúš Labaj

Tuesday 25 August

Instrumentation and Methods for Astrophysics

Engineering of titanium transition edge sensor wafers for the BA4-90/150 receiver of BICEP Array

A.Patel, P. A. R. Ade, Z. Ahmed et al. (+83 more)

BA4-90/150, the fourth receiver to be deployed in the BICEP Array (BA) series, is a dichroic 90/150 GHz instrument targeting the frequency space where sensitivity to the CMB polarization is maximized. The receiver will be deployed in the 2026-2027 austral summer, and is set to position BA to achieve exceptionally precise measurements of cosmic microwave background (CMB) polarization and strengthen constraints on inflationary models. Recent measurements in existing BA receivers suggest that unexpectedly high loop gain in the titanium (Ti) transition edge sensors (TESs) produces excess high-frequency noise that is consequently aliased down into the science band through the time-division multiplexed readout. To reduce the loop gain, we fabricated and tested prototype Ti TES wafers containing 16 modified detector architectures designed to broaden the superconducting transition and reduce the transition steepness (alpha). We present detector performance results, which will directly inform the final integrated wafer now being designed for full receiver commissioning.
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All authors A.Patel, P. A. R. Ade, Z. Ahmed, M. Amiri, D. Barkats, R. Basu Thakur, C. A. Bischoff, D. Beck, J. J. Bock, V. Buza, B. Cantrall, J. R. Cheshire IV, J. Connors, J. Cornelison, M. Crumrine, A. J. Cukierman, E. Denison, L. Duband, M. A. Echter, M. Eiben, B. D. Elwood, S. Fatigoni, J. P. Filippini, A. Fortes, M. Gao, C. Giannakopoulos, N. Goeckner-Wald, D. C. Goldfinger, S. Gratton, J. A. Grayson, A. Greathouse, P. K. Grimes, M. Halpern, S. Henderson, T. D. Hoang, J. Hubmayr, H. Hui, K. D. Irwin, M. Izquierdo Poza, J. H. Kang, K. S. Karkare, S. Kefeli, J. M. Kovac, C. Kuo, K. Lasko, K. Lau, M. Lautzenhiser, T. Liu, S. C. Mackey, N. Maher, K. G. Megerian, L. Minutolo, L. Moncelsi, Y. Nakato, H. T. Nguyen, R. O'Brient, S. N. Paine, M. A. Petroff, A. R. Polish, T. Prouve, C. Pryke, C. D. Reintsema, T. Romand, M. Salatino, A. Schillaci, B. Schmitt, B. Singari, A. Soliman, T. St. Germaine, A. Steiger, B. Steinbach, R. Sudiwala, K. L. Thompson, C. Tucker, A. D. Turner, C. Vergès, A. G. Vieregg, A. Wandui, A. C. Weber, J. Willmert, W. L. K. Wu, H. Yang, C. Yu, L. Zeng, C. Zhang, S. Zhang

Cosmology and Nongalactic Astrophysics

The optimal redshift for dark energy I: formalism and interpretation

Mustapha Ishak, Travis Seth Rippentrop and Kristian Gonzalez

We introduce the concept of the optimal redshift for dark energy, a statistically motivated redshift at which departures of the dark-energy equation of state (EOS) from the cosmological-constant value are tested most effectively. Within a generalized CPL parameterization, we derive an analytic expression for the optimal redshift by maximizing the separation of the EOS from $w=-1$ relative to the corresponding uncertainty. We establish the optimal redshift relationship to the phantom-crossing and pivot redshifts. As an illustration, we apply the formalism to the dataset combination of DESI DR2 BAO measurements, the DES Year-6 independent BAO measurement, and the recalibrated DES-Dovekie supernova sample. Adopting the null hypothesis $\mathcal{H}_0:w(a_{\rm opt})=-1$, we find a tension of ~$2.8\sigma$ with the cosmological-constant prediction at the optimal redshift, compared with ~$2.6\sigma$ at the pivot redshift, despite the latter having a smaller EOS uncertainty. This behavior reflects the specific design of the optimal redshift to maximize the statistical significance of a departure of the EOS from the -1 value of the $\Lambda$CDM model. We further provide statistical and geometrical interpretations of the optimum. In the CPL parameter space, the pivot corresponds to the projection that minimizes the variance of the equation of state, whereas the optimum maximizes its squared-distance from the cosmological-constant value over its variance. While the optimum is dataset and parameterization dependent, the underlying optimization principle and definition of the optimal redshift can be extended beyond the CPL framework. Future applications to DESI, Rubin LSST, Euclid, Roman Space Telescope, and other Stage-IV dark-energy surveys appear particularly promising.
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Earth and Planetary Astrophysics

Discovery and Characterization of the TOI-4468 Planetary System: A Transiting Hot Jupiter With a Lone Nearby Outer Companion

Joseph R. Livesey, Benjamin J. Hord, Juliette Becker et al. (+28 more)

We report the discovery of two planets, a hot Jupiter and a nearby outer sub-Neptune, orbiting the star TOI-4468. This system is unique among the current exoplanet census in that it features a close outer companion to a hot Jupiter without an accompanying inner companion. By jointly fitting radial velocity measurements taken with the NEID spectrograph and transit photometry from TESS and several ground-based observatories, we constrain the orbital periods, masses, and radii of these two planets. We confirm the planetary nature of the hot Jupiter TOI-4468 b ($R = 1.01 R_J$, $m = 0.54 M_J$, $P = 2.77$ days). We also validate the outer planet TOI-4468 c ($R = 0.28 R_J$, $P = 7.01$ days) statistically, incorporating constraints from ground-based observations. We also identify, but cannot confirm, an additional radial velocity signal which may be due to an outer giant in this system with an orbital period of 624 days. From the observed geometry of this system, we argue that it must never have encountered an early secular resonance that is thought to excite the mutual inclination of other hot Jupiter/outer companion systems. We discuss the possibility of an undetected inner companion, as well as potential implications for hot Jupiter formation.
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All authors Joseph R. Livesey, Benjamin J. Hord, Juliette Becker, Andrew Vanderburg, Joseph E. Rodriguez, Elise Koo, Chelsea X. Huang, Gudmundur Stefánsson, Karen A. Collins, Ivan A. Strakhov, Zijun He, Maxwell A. Kroft, Robert Aloisi, Khalid Barkaoui, Fabian Rodriguez Frustaglia, Alyssa Jankowski, Kinga Kasprzyk, Judith Korth, Coleman Nelson, Hannu Parviainen, Adam Popowicz, Manfred Raetz, Richard P. Schwarz, Eva Stafne, Keivan G. Stassun, Thomas G. Beatty, Paul Foster, Thomas MacLean, Devansh Mathur, Lizhou Sha, Melinda Soares-Furtado

Instrumentation and Methods for Astrophysics

Spatially Scanned STIS Spectra of the Exoplanet Host Star 55 Cnc

D. E. Welty, J. D. Lothringer, D. K. Sing et al. (+3 more)

We discuss the analysis of two sets of optical/near-IR spectra of the exoplanet host star 55 Cnc, obtained with the Space Telescope Imaging Spectrograph (STIS) and grating G750L in spatial scanning mode, in order to assess the performance of that relatively new observing mode for studies of transiting exoplanets. Standard pipeline reductions of the CCD spectral images were augmented by custom procedures for removing both cosmic rays and the strong fringing seen at wavelengths longer than 7000 A. Both total ("white-light") fluxes and the fluxes for narrower wavelength intervals were extracted from the processed spectral images. Apart from slight ($\sim$400 ppm) orbit-to-orbit offsets between the relative fluxes in each set, the patterns exhibited by the flux values within each orbit are very similar. The systematic differences in the fluxes are somewhat smaller than those seen in STIS spectra of 55 Cnc obtained in "stare mode", where the CCD is deliberately saturated at a fixed pointing. A parameterized detrending method similar to those commonly used to remove instrumental effects from time series observations of exoplanet host stars was then applied to the extracted fluxes. For the total fluxes, the scatter about the detrending models is $\sim$30-40 ppm – comparable to the best precision previously obtained for time series photometry with HST – but is somewhat larger for narrower wavelength bins. The depth of the transit of the super-Earth 55 Cnc e ($\sim$450 ppm for the total flux) is consistent with previous values. Both the scan-mode and the stare-mode observations of 55 Cnc e appear to indicate an unexpected (and variable?) increase in the transit radius Rp/Rs between 0.55 and 1.0 $\mu$m. While these data are somewhat limited, they do suggest that spatial scanning with the STIS CCD can provide high-quality optical/near-IR spectra of the brighter exoplanet hosts. (edited)
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All authors D. E. Welty, J. D. Lothringer, D. K. Sing, A. M. Jones, A. Riley, C. R. Proffitt

Instrumentation and Methods for Astrophysics

Deep Learning-Based Coarse Alignment and Cophasing of a Distributed-Aperture Telescope. Application to the Small ExoLife Finder (SELF)

N. Arteaga-Marrero, J. Iborra-Luis, A. Padrón-Brito et al. (+1 more)

The ExoLife Finder (ELF), a 35–50-meter-class Fizeau interferometric telescope, was designed to detect biosignatures on exoplanets through direct imaging. The Small ExoLife Finder (SELF), a 3.5-meter prototype, serves as a testbed for the innovative technologies required for such a facility. A key challenge is the precise cophasing of its distributed aperture, where the optical path differences between subapertures must remain below a small fraction of the operating wavelength. This work investigates convolutional neural networks (CNNs) to estimate alignment errors directly from focal-plane images, enabling fast, data-driven coarse alignment to the few-micrometer level. A supervised regression framework was developed using a custom CNN to model the nonlinear mapping between subaperture misalignments and focal-plane intensity distributions. Training and validation datasets were generated from high-fidelity optical simulations of the simplified SELF system. Gaussian-noise augmentation was used to assess robustness, and several established CNN architectures were evaluated for comparison. The proposed approach reconstructed piston and tilt misalignments across all mirror pairs, demonstrating that focal-plane interference patterns can be exploited for alignment estimation. The custom CNN provided a favorable balance between estimation performance, robustness, and computational efficiency, with millisecond-scale inference times. A trade-off between performance and noise robustness was identified, with noise augmentation improving reconstruction at low signal-to-noise ratios but reduced performance under near noise-free conditions. These results demonstrate the feasibility of data-driven focal-plane wavefront sensing for distributed-aperture telescopes and provide a basis for autonomous, computationally efficient cophasing strategies for future high-resolution interferometric systems.
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All authors N. Arteaga-Marrero, J. Iborra-Luis, A. Padrón-Brito, J. Kuhn

Solar and Stellar Astrophysics

ABYSS. IV. Identifying signatures of stellar youth in APOGEE spectra

Valentina Bonilla Villalobos, Marina Kounkel, Joseph Mullen et al. (+9 more)

We develop a convolutional neural network classifier that performs spectroscopic identification of stellar youth (<40 Myr) in APOGEE spectra. This classifier is sensitive to several youth-related features, including rotational broadening, which is common in younger stars, and to several discrete lines that appear to be indicative of a very spotted photosphere. The model is successful at identifying youth across a wide range of stars, achieving its strongest performance at discriminating young M and K dwarfs, while maintaining useful discriminatory power for hotter stars as well. This work enables more robust separation of pre-main-sequence stars from more evolved sources in the field even when they have comparable Teff and log(g), providing a reliable means to substantially reduce contamination in photometrically selected YSO candidates. In addition to constructing a classifier for APOGEE spectra, we also perform classification of young stars in optical BOSS spectra.
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All authors Valentina Bonilla Villalobos, Marina Kounkel, Joseph Mullen, Eleonora Zari, Alexandre Roman-Lopes, Keivan Stassun, Ricardo López-Valdivia, Jinyoung S. Kim, Mojgan Aghakhanloo, Facundo Pérez Paolino, Jonathan C. Tan, Jesús Hernández

Instrumentation and Methods for Astrophysics

Capra: Scalable HEALPix-Native Intensity Reconstruction for High-Resolution IMAP Analyses

Nikola Bukowiecka, Daniel B. Reisenfeld and Maciej Bzowski

We present Capra, a HEALPix-native pipeline for reconstructing all-sky energetic neutral atom (ENA) intensity maps from the NASA Interstellar Boundary Explorer (IBEX) and Interstellar Mapping and Acceleration (IMAP) missions' event-counting data. Capra produces two products: (1) a baseline boresight-assigned map, and (2) an optional smoothed map on the HEALPix grid. This produces smooth, physically interpretable maps with consistent resolution changes and reference-frame transformations. The smoothed Capra maps recover the large-scale ENA morphology while reducing sampling-driven mottling and strip-like artifacts. Relative comparison with the Theseus reconstruction shows broadly consistent large-scale structure, with the discrepancies reflecting differences in reconstruction methods, rather than major morphological discrepancies. We verify invariance (preservation) of count numbers, rates, and intensities across tessellations under coordinate transformations, and demonstrate numerical convergence up to HEALPix resolution Nside = 64 for a representative dataset. We show that thread-based parallelism performance exhibits approximately linear strong scaling, with bounded memory usage, enabling efficient high-resolution reconstruction and making Capra well-suited for high-resolution IMAP reconstruction.
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Instrumentation and Methods for Astrophysics

TESSExtractor: A web-based interactive tool for light-curve visualisation and period estimation using TESS full-frame images

Javier Serna, Jesús Hernández, Sean P. Matt et al. (+23 more)

We present a user-friendly web application that allows users to extract, visualise, and interact with TESS light-curves (LCs) from full-frame images. The service works for any star identified in the TIC database or using stellar coordinates. TESSExtractor performs photometry using a circular aperture centred on the object of interest, with a sky annulus for background subtraction. The application also uses cotrending basis vectors provided by TESS to correct photometry for possible systematic effects. The Lomb-Scargle Periodogram is used to obtain periods from the LC. The TESSExtractor's website offers an intuitive interface for scientific and educational purposes and is publicly available at https://www.tessextractor.app. This tool simplifies the analysis of TESS LCs and provides valuable insight for researchers seeking to extract and analyse TESS data for a variety of scientific goals (e.g., stellar rotation, activity, transient detection, asteroseismology, or simply detection of planetary transits or stellar companions, among others). TESS provides insights into our understanding of time-domain astrophysics, and TESSExtractor provides an accessible and intuitive web interface for scientific exploitation of TESS data. We demonstrate that TESSExtractor produces LCs of sufficient quality for both quantitative and morphological time-domain studies.
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All authors Javier Serna, Jesús Hernández, Sean P. Matt, Giovanni Pinzón, Astaroth Elizabethson, Jorge Martínez-Palomera, Carlos G. Román-Zúñiga, Sergio Sánchez-Sanjuán, Jaime Morice, Thanawuth Thanathibodee, Margarita Pereyra, Mauricio Tapia, Alejandro García-Varela, Juan F. Cabrera-García, Marcelo Jaque Arancibia, María Gracia Batista, Ricardo López-Valdivia, Raúl Michel, Ezequiel Manzo-Martínez, Keivan G. Stassun, Cesar Briceño, Sydney Robertson, Tanay Ayiliath, David Fernández, Fabián Ahumada, Alejandro Alfonso

Instrumentation and Methods for Astrophysics

CCAT: The Prime-Cam Instrument for the Fred Young Submillimeter Telescope – Overview and Status

Eve M. Vavagiakis, Yuhan Wang, Lawrence T. Lin et al. (+32 more)

Prime-Cam is a first-generation science instrument for the CCAT Observatory's six-meter aperture Fred Young Submillimeter Telescope (FYST), under construction at an elevation of 5600 m on Cerro Chajnantor in Chile's Atacama Desert. Prime-Cam will deliver over ten times greater mapping speed at submillimeter wavelengths than current facilities for unprecedented broadband and spectroscopic measurements in windows between 1.4 – 0.3 mm (220 – 850 GHz). When fully populated, Prime-Cam will field over 100,000 kinetic inductance detectors across seven independently optimized instrument modules. With Prime-Cam, the CCAT Collaboration will address a suite of science goals, from Big Bang cosmology, to galaxy evolution and star formation over cosmic time. Prime-Cam is scheduled for integration in FYST in late 2026, followed by a year of early science observations with the 280 and 350 GHz instrument modules. We discuss the design and in-lab testing of the 1.8-m diameter Prime-Cam receiver and 280 GHz instrument module, and give an update on deployment status and early science plans.
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All authors Eve M. Vavagiakis, Yuhan Wang, Lawrence T. Lin, Manuel Aravena, Jason E. Austermann, Frank Bertoldi, James Burgoyne, Victoria Butler, Scott Chapman, Steve K. Choi, Dongwoo Chung, Abigail Crites, Ankur Dev, Cody J. Duell, Michel Fich, Laura Fissel, Rodrigo G. Freundt, Eliza Gazda, Anthony I. Huber, Doug Johnstone, Ben Keller, Paul Malachuk, Alicia Middleton, Jenna Moore, Michael D. Niemack, Thomas Nikola, Yoko Okada, Darshan A. Patel, Tilak M. Patel, Dominik A. Riechers, Douglas Scott, Gordon J. Stacey, Benjamin J. Vaughan, Samantha Walker, Ruixuan Xie

Instrumentation and Methods for Astrophysics

A Singular Value Decomposition Framework for Jovian Radio Emissions from Parker Solar Probe

Evan Wille, Zack Li, Marc Pulupa et al. (+3 more)

Jovian decametric and hectometric radio emissions provide critical insights into Jupiter's magnetospheric dynamics and its electrodynamic coupling with Io. Across 21 perihelion encounters since its first light in 2018, the Parker Solar Probe mission has repeatedly recorded high-resolution radio and plasma wave data near closest approach, as a result serving as a long-term distant observer of the Jovian system. However, extracting these relatively faint planetary signals from the continuous solar wind background presents a significant analytical challenge, as the data is routinely saturated by quasi-thermal plasma noise, spacecraft instrumental interference, and solar bursts. To overcome these observational barriers, we present a generalized empirical pipeline that utilizes Singular Value Decomposition coupled with a deterministic, dual-stage noise filtering process. By converting dynamic spectra into a periodic, phase-folded reference frame, this model isolates structured Jovian emissions from the stochastic heliospheric background, demonstrating empirical Signal-to-Noise Ratio improvements of $1.54 \pm 0.11$ dB, reaching up to $3.32$ dB. Additionally, a secondary “Eigenfaces” matrix factorization is applied to identify long-term global morphological trends and serve as a detection method for future Jovian emissions. This automated mathematical framework extracts transient planetary signals without relying on localized spatial constraints, establishing the viability of PSP as a Jovian radio observatory.
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All authors Evan Wille, Zack Li, Marc Pulupa, Leon V.E. Koopmans, Philippe Zarka, Stuart Bale

Astrophysics of Galaxies

Tracing Galaxy Bias Through the Cosmic Web: The Role of Filaments

Constanza A. Soto-Suárez, Antonio D. Montero-Dorta, Daniela Galárraga-Espinosa et al. (+4 more)

The large-scale clustering of galaxies depends not only on their internal properties but also on their location within the cosmic web, which defines the anisotropic environments where galaxies form and evolve. Filaments serve as bridges through which galaxies and dark matter flow from low-density regions toward the highest-density nodes. In this work, we aim to map galaxy bias, which quantifies how these tracers follow the underlying dark matter density field, through the cosmic web, with a special emphasis on filaments. We look for dependencies on filament properties, such as length and density, and characterize the spatial variations of the large-scale bias along the filamentary spine. We applied the DisPerSE algorithm to identify the cosmic web in the TNG300 volume of the IllustrisTNG simulation. To measure large-scale galaxy bias, we utilized an object-by-object estimator, which provides advantages over standard estimators. We find that galaxies in node outskirts exhibit the highest large-scale bias values, reaching up to $\sim4$ times the values expected from theoretical models based on halo mass alone. Low-mass red galaxies in filaments and filament outskirts also display enhanced bias, which is strongly reduced after excluding galaxies close to nodes. Together, these results suggest that proximity to massive nodes plays a central role in shaping environmental secondary bias. Furthermore, galaxy bias decreases with filament length, from mean values of $1.4$ for short filaments to $-0.5$ for longer structures. This relation persists at fixed halo mass and galaxy color, and is not primarily driven by the average local galaxy density of the filament. Finally, short filaments exhibit an approximately uniform longitudinal bias profile, whereas long filaments show an increase in normalized bias from $\sim0.85$ near the saddle point to $\sim1.06$ close to the node.
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All authors Constanza A. Soto-Suárez, Antonio D. Montero-Dorta, Daniela Galárraga-Espinosa, Ignacio G. Alfaro, Andrés Balaguera-Antolínez, Ravi K. Sheth, Pablo López

Instrumentation and Methods for Astrophysics

Study of Vibrations at SOAR

Andrei Tokovinin

The 4.1-m Southern Astrophysics Research (SOAR) telescope in Chile resembles larger optical telescopes by its thin actively controlled primary mirror, built-in tip-tilt correction, lightweight structure, and adaptive optics (AO) turbulence correction. The non-stationary vibration of the SOAR optical axis with a frequency of 50 Hz and an amplitude reaching 20-30 mas has been detected by the AO system, degrading the quality of optical speckle interferometric data. Accelerometers revealed that the 50 Hz tremor, driven by an external source, propagates within telescope structure and is strongly amplified by the response of the fast tip-tilt mirror servo system, producing characteristic elliptical beam path. The AO system also evidenced periodic components at 47 Hz in the defocus (matching the frequency of fans in electronic racks and computers) and at ~65 Hz in the astigmatism. The latter is associated with structural resonances of the SOAR primary mirror support, apparently excited by the wind. Periodic tracking errors with typical frequencies of 0.5-2.5 Hz are mostly caused by periodic errors of the encoders, depending on their alignment, and can be amplified by the mount servo at fast tracking rates. Vibration characterization at SOAR informs similar studies at other telescopes.
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Astrophysics of Galaxies

To be lensed or not to be lensed: on the nature of the alleged high-z lensed quasars J0109-5424 and P170+20

Aurora Mata-Sanchez, Emanuele P. Farina, Anniek J. Gloudemans et al. (+17 more)

We present a detailed multi-wavelength analysis of two gravitationally lensed z>6 quasar candidates: J0109-5424 and P170+20. Using JWST/NIRSpec near-infrared data from the Aether survey, we demonstrate that J0109-5424 is in fact a FeLoBAL quasar at z=2.07, exhibiting strong iron broad absorption lines that mimic the Lyman break. From the Pabeta emission line, we estimate a black hole mass of 3.9 x 10^8 Msun and a bolometric luminosity of Lbol = 7.7 x 10^45 erg/s for this quasar. Follow-up HST/ACS WFC imaging of P170+20 with the F555W filter, probing emission below the Lyman limit of the quasar, reveals a compact source located 0.09+/-0.04 arcsec from the quasar position. PSF modelling and subtraction yield no evidence for extended emission. This is inconsistent with a foreground galaxy acting as a lens. Furthermore, we obtain Gemini-South/Flamingos 2 near-infrared observations to complement the existing optical Gemini-North/GMOS spectrum of P170+20. Our spectral analysis shows that the observed spectral shape of P170+20 is consistent with a composite quasar and M-dwarf spectrum. However, this interpretation remains uncertain, as a chance alignment between an ultracool dwarf and a quasar within 0.1 arcsec would be unlikely. Overall, our findings establish J0109-5424 as an intermediate redshift source and do not favor the lensed nature of P170+20, although this possibility cannot be conclusively ruled out, highlighting the challenges of selecting lensed quasars at high redshift.
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All authors Aurora Mata-Sanchez, Emanuele P. Farina, Anniek J. Gloudemans, Debora Pelliccia, Roberto Decarli, Eduardo Banados, Silvia Belladitta, Manuela Bischetti, Sarah E. Bosman, Xander Byrne, Thomas Connor, Frederick B. Davies, Thales A. Gutcke, Weizhe Liu, Chiara Mazzucchelli, Romain A. Meyer, Silvia Onorato, Fabian Walter, Feige Wang, Jinyi Yang

Earth and Planetary Astrophysics

Tidal Demise: The Evolution and Fate of a Hypothetical Venus Moon

Stephen R. Kane, Franck Selsis, Jeremy Leconte et al. (+1 more)

Venus possesses no natural satellite, raising the question whether a formed moon could have survived. We explore the tidal evolution of a Venus-moon system, coupling Venus's spin to the satellite's orbit under tides from the moon and Sun. We survey spin period ($P_0 = 5$–100~hr), moon mass ($M_m = 0.01$–$10~M_{\rm Moon}$), eccentricity, quality factor, and initial semi-major axis under both constant-$Q$ and constant time lag models. Survival depends on competition between outward migration ($\propto M_m$) and synchronous radius expansion ($\propto M_m^2$): for circular orbits around rapidly spinning Venus ($P_0 \lesssim 12$~hr), a lunar-mass satellite survives the age of the Solar System in both models. For $P_0 \lesssim 10$~hr, eccentricity pumping can destabilize low-mass satellites, while for $P_0 \gtrsim 15$~hr or $M_m \gtrsim 2~M_{\rm Moon}$ the synchronous radius overtakes the orbit and drives Roche destruction within $\sim$0.03–1.7~Gyr in the constant-$Q$ model. The constant time lag model instead permits quasi-synchronous survival for massive moons at fast spin. Explaining Venus's present state requires satisfying two constraints simultaneously: loss of the satellite and despinning of an initially rapid rotator. Both are met only within a restricted region of parameter space, favoring moderate post-impact spin periods and lunar-to-super-lunar masses. Giant impact simulations predict spin periods $\gtrsim$12~hr for Venus's present rotation, placing a lunar-mass satellite at the survival boundary. For last-impact conditions within this region, the present absence of a Venusian satellite arises through tidal evolution alone; a subsequent catastrophic stripping event, while capable of removing a moon, is not required.
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All authors Stephen R. Kane, Franck Selsis, Jeremy Leconte, Sean N. Raymond

Earth and Planetary Astrophysics

Kepler-50: Two Planets in Close Resonance Perturbed by a Non-transiting Planet

Daniel Jontof-Hutter, Jason F. Rowe, Jack J. Lissauer et al. (+1 more)

Kepler-50 has two transiting planets close to the 6:5 commensurability. We analyze transit times measured from Kepler data with dynamical fits. We attribute the residual signal to a near-resonance non-transiting third planet in the system. The parameters of the third planet are degenerate. We identified 55 (15) regions of interest for an exterior (interior) perturber, and characterize system parameters in each region of interest with posterior sampling. We find that removing samples that are not long-term stable provides few additional constraints on posteriors, and that the transit times do not confirm the likely 2-body resonant state of the transiting planets as $\approx$ 68% of posterior samples that are likely stable are also likely in libration. We identify a small fraction of samples that are in 3-body libration. Despite the degeneracies, we recover robust, tightly constrained masses for Kepler-50 b and c ($2.35^{+0.48}_{-0.43}$ $M_{\oplus}$ and $4.43^{+0.45}_{-0.49}$ $M_{\oplus}$, respectively) and strongly detected non-zero relative eccentricity for Kepler-50 b and c with ($e_c\cos\varpi_c$ - $e_b\cos\varpi_b$) = -0.045 $\pm 0.003$, and ($e_c\sin\varpi_c$ - $e_b\sin\varpi_b$) = -0.030 $\pm 0.004$. These close neighbors are in the radius valley and sub-Neptune by size, respectively ($1.750 \pm 0.038$ $R_{\oplus}$ and $2.079 \pm 0.060$ $R_{\oplus}$). With one of the closest planet pairs known and one of the closest to first-order commensurability, the Kepler-50 system is an especially valuable benchmark for planet formation theory.
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All authors Daniel Jontof-Hutter, Jason F. Rowe, Jack J. Lissauer, Daniel C. Fabrycky

Cosmology and Nongalactic Astrophysics

Cosmic topology. Part Va. Information content of the observable Universe

Deyan P. Mihaylov, Mikel Martin Barandiaran, Stefano Anselmi et al. (+14 more)

If the Universe possesses a compact spatial topology with characteristic scale not much larger than the diameter of the observable Universe, then the associated symmetry transformations imprint specific statistical correlations on density perturbations. We derive the covariance between perturbation modes in the full topology volume and compute the induced covariance between modes in the observable subvolume. We then use this covariance to estimate the available information about topology contained in the full set of observable linear perturbations. For two sample Euclidean examples - the cubic three-torus ($E_1$) and a three-torus with a quarter turn ($E_3$) - the three-dimensional density field carries enough information to detect topology on scales up to 25 percent larger than those accessible from the two-dimensional cosmic microwave background anisotropies alone. Future probes of the cosmic density field using deep galaxy surveys or neutral-hydrogen 21-cm intensity mapping, combined with computationally intensive searches over the large parameter space of admissible topologies, thus offer a plausible avenue to extending the range of detectable cosmic topologies.
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All authors Deyan P. Mihaylov, Mikel Martin Barandiaran, Stefano Anselmi, Javier Carron Duque, Glenn D. Starkman, Yashar Akrami, Craig J. Copi, Andrew H. Jaffe, Arthur Kosowsky, James B. Mertens, Anna Negro, George Alestas, Ricardo G. Rodrigues, Thiago S. Pereira, Amirhossein Samandar, Andrius Tamosiunas, Cynthia Trendafilova

Solar and Stellar Astrophysics

A Seismic Technique for Obtaining White Dwarf Fundamental Parameters from Mean Period Spacings and Astrometry

Keaton J. Bell and Agnès Bischoff-Kim

We present a new statistical technique that utilizes the synergy of precision astrometry and time series photometry from modern space missions to obtain reliable physical parameters of pulsating white dwarf stars. We compute a grid of white dwarf structural models that span the helium-atmosphere pulsating white dwarf (DBV) instability strip, showing that mean period spacings between adjacent pulsation modes and absolute magnitudes derived from Gaia astrometry vary monotonically and in opposing directions across parameter space. While most efforts in white dwarf asteroseismology to directly fit individual pulsation periods to stellar models result in degenerate and poorly resolved solutions, the "seismic technique" produces unique and reliable seismic solutions for global parameters of mass and effective temperature when a reliable mean period spacing is detected. Our models sample various physically plausible interior chemical composition profiles based on modern evolutionary models to propagate uncertainty from the precise structures of actual stars. Once the global stellar parameters are tightly constrained, seismically resolving white dwarf interior structures becomes more computationally tractable, and degeneracies can be resolved. This new seismic technique is largely insensitive to the precise absorption line profiles interpreted by the widely used spectroscopic technique, and therefore provides complementary constraints that can be used to test spectroscopic methods. We demonstrate the method for the pulsating helium-atmosphere white dwarf WD 0158-160 observed by TESS, obtaining $T_\mathrm{eff} = 24584\pm 971$ K and $M_\star = 0.608\pm 0.013$ $M_\odot$.
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Astrophysics of Galaxies

The ionizing properties of JWST's compact broad-line emitters

Sara Mascia, Jorryt Matthee, Alberto Torralba et al. (+4 more)

The recent JWST discovery of a numerous population of broad-line emitters (BLEs) at $z>4$ has reopened the question of whether sources other than faint galaxies contributed significantly to cosmic reionization. To assess this contribution, we present a systematic census of compact, blue broad-line emitters at $4\leq z\leq7$ selected from the DJA, designed to isolate sources in which the UV continuum and the broad-line emission originate from the same compact physical region. Starting from a parent sample of 4145 galaxies with NIRSpec/PRISM spectroscopy and NIRCam imaging, we apply criteria on broad Ha emission (FWHM$>2000$km s-1, detected at S/N$\geq5$, complete at $L_{Ha,broad}\geq10^{42.7}$erg s-1), blue continuum slopes ($\beta_{UV}\leq-1.5$, $\beta_{opt}<0.5$), and morphological compactness in both the rest-frame UV and optical, returning a final sample of 20 sources. This constitutes $\sim20%$ of the PRISM-selected broad-line sample, which is dominated by Little Red Dots (LRDs). We find that the compact blue BLEs display hot ionizing continua, high-ionization UV lines (CIV, NIV], HeII), and elevated Lya emitter fractions ($X_{Lya}=50-67%$) relative to star-forming galaxies and LRDs. Beyond their similar lack of X-ray emission, their optical spectra closely resemble those of LRDs. This suggests that compact blue BLEs extend this population towards lower column density envelopes, but with similar engines, rather than representing a physically distinct population. Using Sirocco to model physical configurations that reproduce the observed spectra, we find a high ionizing photon production efficiency (log$\xi_{ion}\sim25.4$Hz erg-1) and a weighted average escape fraction $fesc\sim0.2$ for the bluest sources, and $\sim0.01$ for LRDs. This implies that broad-line sources do not dominate reionization globally, but given their luminosity, their contribution can dominate up to few Mpc scales.
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All authors Sara Mascia, Jorryt Matthee, Alberto Torralba, Jenny E. Greene, Anna-Christina Eilers, Edoardo Iani, Rohan P. Naidu

Solar and Stellar Astrophysics

EncoTESS: Age-Sensitive Encodings from Raw TESS Light Curves

Phil R. Van-Lane, Joshua S. Speagle, Ryan Cloutier et al. (+3 more)

Main sequence stars of spectral types late F through M exhibit systematic variability in photometric light curves, particularly when they are young. Rotational modulation of starspots manifests as quasi-sinusoidal variability, which enables the measurement of rotation periods. Variability can also be stochastic, as in stellar flaring. However, since measurements of stochastic processes depend on the time of observation, they are typically noisier. Considering that different manifestations of variability have unique observational nuances, models that naturally unify these are incredibly useful for stellar characterization. Towards this goal, we have developed EncoTESS: a Time Series Foundation Model (TSFM) trained on a subset of TESS 2-min light curves. EncoTESS is specifically designed to handle the observational noise, heteroskedastic measurements, irregular sampling, and large data gaps common to TESS data. It is also ~1% of the size of a typical literature TSFM, so can be run easily on a modern laptop. EncoTESS encodes light curves into a fixed-size latent parameter space, which can be used to infer physical stellar properties and recovers light curve summary statistics well. EncoTESS outperforms rotation period and variability amplitude as age indicators for stars that have not converged onto the slow rotator sequence yet; broadly these include K and M stars less than ~100 Myr, and M stars less than ~1 Gyr. We focus on age inference as an application of EncoTESS in this work, but other downstream tasks such as stellar classification could also be explored. The architecture of EncoTESS enables its future extension to TESS light curves of all cadences, and additional surveys such as Kepler and the upcoming PLATO mission. The core EncoTESS framework and library of encodings produced for the stars used in this work are publicly available at https://github.com/philvanlane/encotess.
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All authors Phil R. Van-Lane, Joshua S. Speagle, Ryan Cloutier, Christopher A. Theissen, Gwendolyn M. Eadie, Ilay Kamai