Cosmology and Nongalactic Astrophysics
CMB Acoustic Power Spectra in STVG-MOG
John W. Moffat
We present a cosmological realization of Scalar–Tensor–Vector
Gravity (STVG–MOG) in which the pre-recombination scalar perturbation dynamics become degenerate with those of $\Lambda$CDM without invoking particle dark matter. In the early universe, nonrelativistic excitations of the massive STVG vector field $\phi_\mu$ behave as a collisionless, pressureless component with vanishing sound speed and background density $\rho_\phi \propto a^{-3}$. On the
Fourier scales relevant for the acoustic peaks, the effective gravitational coupling satisfies $G_{\rm eff}(k,a)\simeq G_N$, so that the metric potentials governing
baryon–
photon oscillations evolve in the same way as in the standard cosmological model. The gravitational wells remain sufficiently deep at horizon entry to preserve the observed height of the third acoustic peak, the most sensitive indicator of a clustering pressureless component prior to recombination. Since Thomson scattering, recombination,
baryon loading, and
photon diffusion are unchanged, the temperature and polarization spectra can coincide with the standard $\Lambda$CDM predictions once the vector sector supplies the effective
dust component. In this framework, the dynamical role usually attributed to cold dark matter is carried instead by a degree of freedom belonging to the gravitational sector itself. We explain why this vector-sector
dust, although dynamically degenerate with cold dark matter in the early universe, is not equivalent to a particle dark matter fluid. The Boltzmann code CLASS is used to obtain a MOG fit to the acoustical power spectrum data.
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Cosmology and Nongalactic Astrophysics
Cosmological perturbations with $f(R)$ gravity scalarons : Galaxy power spectra and the scalaron mass
Abhijit Talukdar, Sanjeev Kalita and Shadab Alam
In this paper we study cosmological perturbations with $f(R)$
gravity scalaron. We consider epoch of transition from early general relativity (GR) phase to late time non-GR phase of cosmogenic history for a viable $f(R)$
gravity Lagrangian close to the $\Lambda$CDM theory at early
cosmic history. We study deviation in matter power spectra from $\Lambda$CDM scenario.
Galaxy power spectra multipoles are generated using
galaxy bias, velocity dispersion and modified
gravity parameters. While monopole and quadrupole matter power in $f(R)$ theory increase towards larger $k$ (small scales), quadrupole power spectrum remains elevated relative to $\Lambda$CDM for smaller $k$ (large scales), upto $k\approx 0.02$. These power spectra provide observables for testing
gravity through the current and future
galaxy survey missions such as DESI, EUCLID, 4MOST and PFS. We report appropriate GR limit of scalaron mass in
galactic and massive black hole scales.
Evolution of the scalaron mass and its general relativistic limit for various
cosmic structures are reported. Deviation from GR in cosmogenic
evolution is attributed to decrease in scalaron mass with
cosmic time.
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Instrumentation and Methods for Astrophysics · Cross-listed from physics.ins-det
High-Frequency Thermal Noise in Michelson Interferometers
Daniel Grass, Sander M. Vermeulen, Ian A. O. MacMillan et al. (+1 more)
Thermal noise in optics constrains the precision of optical experiments, including Michelson interferometers, optical clocks, and optomechanical sensors. While high-power optical experiments such as gravitational-wave detectors are currently limited mainly by
quantum noise, new experiments incorporating recent insights from
quantum metrology are being developed that evade the
quantum shot noise background. In particular, Michelson interferometers that use
photon-counting readout will look for weak, high-frequency signals. Since shot noise is no longer the dominant noise source with these readout schemes, it is important to accurately model thermal noise to characterize signals and design more sensitive experiments. However, previous modeling uses approximations that are no longer valid in these frequency regimes. In the MHz band, the quasistatic approximation does not apply. We therefore develop more general models of substrate and coating mechanical (Brownian) noise, substrate and coating thermoelastic noise, and coating thermorefractive noise. We validate the models with comparisons to previous low-frequency modeling and high-frequency spectra from an experiment that has already taken data, the Holometer. We then apply the new models to GQuEST, an experiment under construction.
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All authors Daniel Grass, Sander M. Vermeulen, Ian A. O. MacMillan, Lee McCuller
High Energy Astrophysical Phenomena
Multiwavelength Probes of Cosmic Ray Transport in Molecular Cloud Structures
Hayden P. H. Ng, Ellis R. Owen, Naomi Tsuji et al. (+1 more)
We investigate how
cosmic ray (CR) transport in molecular clouds and their substructures can be probed using multi-wavelength observations. The detailed microphysics regulating the penetration and coupling of CRs in dense molecular structures is unsettled. Self-generated
turbulence can produce scattering and diffusive transport, while ion-neutral damping in cold, dense gas promotes ballistic CR propagation. We construct a self-consistent framework for CR transport and interactions in magnetized molecular clouds, considering three limiting propagation scenarios: ballistic transport,
diffusion, and a hybrid configuration with a diffusive envelope and quasi-ballistic core. By forward-modeling pion-decay $\gamma$-ray emissivities, CR-driven ionization-rate profiles, and electron synchrotron emission in the hard X-ray band, we connect GeV attenuation and propagation signatures to independent diagnostics of secondary production and CR penetration. As an illustrative example, we apply our framework to the Taurus molecular cloud complex and selected embedded clumps. We show that CR scattering may be substantially enhanced on clump scales, with inferred CR
diffusion coefficients suppressed relative to canonical interstellar medium (ISM) values at GeV energies. In this interpretation, CRs are more closely coupled with dense gas in the ISM, and a diffusive envelope boosts the effective gas column density encountered by the CRs. This increases the hadronic interaction rate in the cloud. In turn, the secondary CR electron injection is also increased, and CR ionization rates are elevated at higher densities. We show that a hard X-ray synchrotron emission component is also generated, which may be detectable with near-future facilities. Finally, we discuss how future $\gamma$-ray, X-ray, and ionization constraints will provide firm tests of CR propagation theories in molecular cloud environments.
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All authors Hayden P. H. Ng, Ellis R. Owen, Naomi Tsuji, Szu-Ting Chen
Earth and Planetary Astrophysics
The First Remotely Detected Biosignature May Not Be the Most Common: Implications for JWST and HWO
Ravi Kopparapu
The first detected member of a new astronomical class is often not representative of the underlying population, but instead reflects the selection effects of the observing technique that found it. We apply this idea to the first remote detection of biosignatures with two leading near future strategies: JWST transmission spectroscopy and HWO reflected light direct imaging. Using the known signal scalings of the two methods together with a simple detectability model, we show how a rare but observationally favored
planet class can dominate early detections even when it is intrinsically uncommon. For JWST, an early biosignature detection is most likely to arise from a detectability favored outlier, such as a sub-Neptune or other atmosphere rich
planet around a nearby M
dwarf, rather than from a true Earth analog. For HWO, the situation is subtler. Among accessible habitable-zone targets around FGK-type
stars, differences in maximum observable distance and hence in effective survey volume may be smaller than in the JWST case, weakening the volume bias. At the same time,
stellar-type-dependent photochemistry can alter biosignature abundances, so the first HWO biosignature may emerge from a balance between photochemical enhancement and
geometric accessibility. Nevertheless, within the accessible sample,
planets with stronger biosignature features and higher reflected light contrast may still be favored in early detections. A first HWO biosignature could be a selection favored outlier and should not be assumed to represent inhabited rocky
planets in general. Crucially, the longest lived biosphere on a
planet is not necessarily its most spectrally detectable one. If the first detection turns out to be an outlier, that may still suggest that a more broader range of habitable environments awaits discovery.
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High Energy Astrophysical Phenomena
The Torques Acting on Accreting Millisecond X-Ray Pulsars in the Outburst and Quiescent States, and During the Long-Term Evolution
Fatmanur Ertugrul, Ali Arda Gencali, Unal Ertan et al. (+1 more)
Accreting millisecond X-ray
pulsars (AMXPs) are transient X-ray sources likely to be in the final evolutionary phases of low-mass X-ray binaries (LMXBs). In this work, we have investigated the torque and X-ray luminosity variations of five AMXPs during outburst and quiescence, using a model previously employed to explain some typical behaviours of LMXBs. Most of these systems
spin up in the outburst state and
spin down in quiescence, while they slow down on the long term. We have obtained reasonable results with the model in agreement with these observations. We have found that the torques produced by the disc-magnetosphere interaction, the
magnetic dipole radiation, and the mass
accretion are compatible with the X-ray luminosity and rotational properties of the sources in their outburst and quiescent states, and during the resultant long-term
evolution. Nevertheless, our results are not sufficient to rule out the
spin-down contribution of the gravitational radiation torques due to significant timing noise and uncertainties about the bolometric corrections for X-ray luminosity during the outbursts of some sources.
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All authors Fatmanur Ertugrul, Ali Arda Gencali, Unal Ertan, Ndiogou Niang
Solar and Stellar Astrophysics
The bound origin of low-mass stellar binaries
A. Generozov, S.S.R. Offner, K.M. Kratter et al. (+3 more)
Most main sequence
stars, unlike our Sun, belong to multiple systems with two or more
stars. How and when these multiples come together and become bound is uncertain, since the earliest stages of
star formation are difficult to resolve. We analyze simulations of
star cluster formation in Milky Way-like conditions, including all key physics and
stellar feedback mechanisms, to understand how multiple systems form. We show that $\approx 70-80\%$ of binaries are gravitationally bound from the moment the second
star forms. Binaries evolve and accrete together, which will affect their planetary systems and chemical
evolution. Half of the binaries are disrupted by the end of the
star-formation epoch, such that $\approx40\%$ of the final single
stars belonged to a multiple at some point, with implications for the
stellar initial mass function. Formation in multiples is the dominant mode of
star formation, accounting for at least 57% of
stars.
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All authors A. Generozov, S.S.R. Offner, K.M. Kratter, H.B. Perets, D. Guszejnov, M.Y. Grudić
Instrumentation and Methods for Astrophysics
The EDGES Analysis Pipeline: Description and Validation
Steven G. Murray, Nivedita Mahesh, Akshatha K. Vydula et al. (+7 more)
The sky-averaged redshifted 21-cm signal from
Cosmic Dawn is expected to provide a unique view of the first compact objects. However, its measurement remains daunting. Difficulties are driven by the large dynamic contrast between the intervening foregrounds and the signal-of-interest, which places extremely high demands on instrumental calibration and data quality measures. The ongoing debate within the field concerning the evidence of a potential first detection by the EDGES experiment highlights the need for a more robust set of analysis methods and tools that are reliable and accessible. In this paper, we detail for the first time the precise calibration and analysis methodology adopted in previous EDGES data releases. These methods are presented in the context of a new open-source end-to-end analysis and simulation package for 21-cm global signal experiments that both formalizes these methods and provides general tools for the broader community. Finally, we describe the raw data used in previous EDGES papers and release these data publicly for extended scrutiny.
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All authors Steven G. Murray, Nivedita Mahesh, Akshatha K. Vydula, Peter Sims, Judd Bowman, Raul A. Monsalve, Alan E. E. Rogers, Rigel C. Capallo, John P. Barrett, Colin J. Lonsdale
High Energy Astrophysical Phenomena
Probing the Mass-loss Histories of Type IIn and II-L Supernovae with Late-time Radio Observations
Charles D. Kilpatrick, Lindsay DeMarchi, Wen-fai Fong et al. (+3 more)
We present VLA observations of 16 Type IIn and Type II-L
supernovae (SNe IIn and SNe II-L) at ~1000–7000 days after explosion, probing circumstellar matter (CSM) at distances >10^16 cm from the progenitor corresponding to mass-loss over hundreds to thousands of years before core collapse. We detect
radio emission from four SNe (1998S, 2005ip, 2008fq, and PTF11iqb) with the remaining 12 yielding upper limits of nu L_nu < 10^35–10^36 erg s^-1 at 3–11 GHz. The detected sources span approximately two orders of magnitude in
radio luminosity, reflecting a wide range of CSM densities and pre-explosion mass-loss histories. All detected sources exhibit steep spectral indices (~<-0.4) consistent with optically-thin synchrotron emission, and the spectral
evolution supports internal free-free absorption as the dominant absorption mechanism at these late epochs. We infer progenitor mass-loss rates of \dot{M}/v_w ~< 10^-5–10^-3 Msun yr^-1/(1000 km s^-1), with the most
radio-luminous objects requiring sustained mass-loss over hundreds to thousands of years. The detection of the intermediate SN IIn/SN II-L object PTF11iqb at luminosities between classical SNe IIn and SNe II-L supports a continuum between these subtypes in terms of CSM interaction strength. Our limits further suggest that SNe IIn and SNe II-L are not separated by long-term mass-loss rate at the radii probed here, but chiefly by the presence and strength of dense circumstellar material immediately before explosion. At epochs >5000 days, some SNe (e.g., 1979C and 1986J) maintain nearly constant
radio luminosity while others decline rapidly, suggesting that the most
radio-luminous SNe IIn arise from progenitors with sustained mass-loss extending >10^4 yr before explosion.
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All authors Charles D. Kilpatrick, Lindsay DeMarchi, Wen-fai Fong, Jennifer E. Andrews, Ori D. Fox, Nathan Smith
Solar and Stellar Astrophysics
SN 2023fyq: direct detection of a Type Ibn supernova progenitor and its multi-wavelength environmental constraints
Xinyi Hong, Ning-Chen Sun, Yali Shao et al. (+9 more)
Context. Type Ibn
supernovae (SNe) are characterized by narrow helium emission lines arising from ejecta-circumstellar medium interaction, yet their progenitors remain debated, with both massive Wolf-Rayet
stars and low-mass helium
stars in binaries proposed. Aims. We aim to directly identify the progenitor of the Type Ibn SN 2023fyq and to characterize its environment in order to constrain the progenitor's nature and evolutionary channel. Methods. We search for the SN progenitor based on pre-explosion and late-time HST and JWST images and derive its properties by fitting the spectral energy distribution. We investigate the SN environment by probing the
stars,
dust, ionized gas and molecular gas with a multi-wavelength
dataset including HST and JWST imaging, VLT/MUSE integral-field-unit spectroscopy and ALMA CO (2–1)
radio interferometry. Results. We discover a pre-explosion source at the SN position, which is consistent with a hot ($T>$15000 K) and luminous (log($L$/$L_\odot$) $\gtrsim$ 5.5) SN progenitor and a possible host
star cluster. The progenitor is confirmed to have disappeared after explosion. Analysis of the SN environment implies that the progenitor likely has an age of log($t$/yr) = 7.1–7.2. These phenomena disfavor a very massive single-
star progenitor and instead support a binary scenario involving a low-mass helium
star and a compact object; the observed progenitor emission likely arises from binary interaction that began at least $\sim$12 yr before the explosion. Conclusions. SN 2023fyq is the first Type Ibn SN with a directly detected progenitor and a possible host
star cluster. It adds to the diversity of Type Ibn SNe in terms of their progenitor channels and mass-loss mechanisms.
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All authors Xinyi Hong, Ning-Chen Sun, Yali Shao, Ke Wang, Junjie Wu, Qiang Xi, Yi-Han Zhao, Justyn Maund, Xiaohan Chen, Anyu Wang, Linxi Zhang, Jifeng Liu
Cosmology and Nongalactic Astrophysics
Modeling the probability distribution for cosmological analysis with photometrically classified samples
Marcos P. Freaza and Ribamar R. R. Reis
In this work we investigated methods for the accurate and efficient incorporation of photometrically classified
supernovae into cosmological analyses, and to assess the impact of the additional uncertainty associated with this procedure on the ability of Type Ia
supernovae (SNeIa) tests to place constraints on cosmological models. We proposed a simplified likelihood, in which the contamination is described as a
redshift dependent change in the mean of the usually assumed Gaussian distribution, and we tested this hypothesis against the usual two-component approach, based on the BEAMS framework. Using the latest version of the DES
supernova sample, dubbed DES-Dovekie, we compared the results when using type probabilities from different classifiers, such as SNIRF and SCONE, and applying different cuts on these probabilities. We show that the new model is strongly favored by the Bayes factor, when compared with the current one, for all configurations, allowing an improvement on the constraining power of photometric
supernova data.
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Instrumentation and Methods for Astrophysics · Cross-listed from gr-qc
Bidirectional Internal Squeezing for Gravitational-Wave Detectors
Sander M. Vermeulen, Umran Serra Koca and Lee McCuller
We present a bidirectional internal squeezing scheme for gravitational-wave detectors and show that it saturates the lowest known lower bounds on
quantum noise from internal optical dissipation. The scheme uses two optical parametric amplification stages inside the signal-extraction cavity that act on intra-cavity fields propagating in opposite directions. Thereby, most
vacuum fields entering the interferometer are squeezed, while the signal and internal
vacuum fields are amplified so that loss in the readout path adds no further noise. We show that the resulting signal-referred
quantum noise spectral density is independent of the arm-cavity input and signal-extraction transmissivities at high frequencies, opening design freedom to mitigate technical constraints and radiation-pressure noise. We derive these results analytically, compare them with other internal squeezing and amplification schemes, and validate the full
quantum-noise spectrum through numerical simulations. We also assess realistic implementations, including dissipation mechanisms and transverse mode mismatch introduced by the scheme, and find that 'mode healing' in the signal-extraction cavity can suppress mismatch losses. These results identify bidirectional internal squeezing as a possible upgrade path for gravitational-wave observatories such as LIGO, and the scheme may also benefit future observatories and other interferometry experiments.
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High Energy Astrophysical Phenomena
Is the Binary Black Hole Population Inference from Gravitational-Wave Data Robust?
Upasana Das and Suvodip Mukherjee
Gravitational-wave observations are playing an instrumental role in understanding the population of binary compact objects in the Universe. These observations have begun to hint at the mass distribution of binary black holes (BBHs), with tentative evidence for features in the mass distribution beyond a simple power-law. Such features, hence, can be connected with different formation scenarios of BBHs and lead to important astrophysical conclusions. However, it is crucial to understand whether these features are truly astrophysical or connected with any unknown systematics. We show in this work that waveform modelling uncertainties can significantly distort inferred features in the BBH mass distribution, which can be more pronounced than the statistical uncertainty, even with the current generation detectors, which can peak close to the lower edge of the pair instability
supernovae (PISN) mass gap, and also can impact the slope of the power-law distribution. So, in order to have a confirmed detection of astrophysical features in the BBH mass distribution and connecting them with BBH formation channels, it is important to consider waveform systematics in the astrophysical population analysis. We show the typical scaling of the systematic error and discuss a few avenues to mitigate this effect for robust measurements in the future.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Rapidly Rotating Neutron Star Collapse in Massive Scalar-Tensor Theories
José Carlos Olvera M., Daniela D. Doneva, Pablo Cerdá-Durán et al. (+2 more)
We present a full 3D numerical
evolution code to study
neutron stars in massive-scalar-tensor theories. The code is embedded in the Einstein Toolkit framework and its implementation constitutes a modified version of the Baumgarte-Shapiro-Shibata-Nakamura formalism with an additional nonminimally coupled scalar field. The approach we follow preserves the standard hydrodynamic
evolution for matter fields, allowing eventually for a straightforward inclusion of more microphysical effects and better flexibility. Using this code, we examine the gravitational collapse of rapidly rotating, scalarized
neutron stars to a black hole by exploring the influence of the scalar field on the dynamical features of the process and on the gravitational-wave emission. We find that for the configurations studied in this work, there is an observational degeneracy in the tensorial gravitational-wave emission between collapsing scalarized
stars and their counterparts in general relativity. However, this degeneracy can be broken through the emission of scalar radiation, which carries an energy of ~10^-3 M_sun c^2. This is orders of magnitude higher than the quadrupolar emission (~10^-7 M_sun c^2) and might be used as an observational probe of modified
gravity. We also find that rapid rotation can enhance this signal, since fast rotating
stars can sustain larger scalar field amplitudes.
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All authors José Carlos Olvera M., Daniela D. Doneva, Pablo Cerdá-Durán, José A. Font, Stoytcho S. Yazadjiev
Astrophysics of Galaxies
Feedback driven interactions between dark and luminous matter to explain tight galaxy scaling relations
Leen Alrawas, Andrea V. Macciò and Carlo Cannarozzo
The tight empirical correlation linking the
stellar disk scale length $R_d$ to the dark matter scale radius $r_0$ has been proposed as possible evidence for a fundamental coupling between
baryons and dark matter beyond
gravity. We re-examine the physical origin of this relation using a sample of 31
galaxies from the NIHAO cosmological hydrodynamical simulations, which include no dark matter-
baryon interactions beyond
gravity and baryonic feedback processes. NIHAO naturally reproduces both the normalization and the small scatter of the observed $R_d-r_0$ relation at $z=0$, while yielding a slightly shallower slope. By tracking
galaxies from $z=2$ to $z=0$, we identify three distinct evolutionary classes: systems undergoing disk expansion, contraction, and quasi-static
evolution. Using a
Bayesian hierarchical framework, we provide the first characterization of the
cosmic evolution of the $R_d-r_0$ relation, tracing the
evolution of its normalization, slope, and intrinsic scatter from $z=2$ to the present day. We find a mild decrease in normalization ($\sim0.07$ dex), a flattening of the slope from $\alpha \simeq 1.05$ to $\alpha \simeq 0.95$, and a weak decline in the intrinsic scatter toward lower
redshift, suggesting that
galaxies evolve preferentially along the relation while jointly re-balancing their
stellar and dark matter scales. By comparing hydrodynamical simulations with their dark-matter-only counterparts, we isolate the impact of
baryons and baryonic feedback on
halo structure. Our results show that
stellar feedback alone can reshape the central potential and naturally establish the observed coupling between luminous and dark matter, without requiring modifications to the dark sector.
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High Energy Astrophysical Phenomena
Neutrino Flavor Conversion Shapes the Rate of Failed Core-collapse Supernovae
Mariam Gogilashvili and Irene Tamborra
The relative rate of
neutron stars and black holes produced by the collapse of massive
stars is highly uncertain. We simulate the
stellar collapse of $195$ progenitors with masses between $9\, M_\odot$ and $120\, M_\odot$, incorporating a schematic treatment of
neutrino flavor conversion. We find that
flavor transformation reshapes the explodability of massive
stars-especially in the $16$-$30\, M_\odot$ mass range-and modifies the compact remnant mass distribution. Our findings identify
neutrino flavor conversion as a fundamental ingredient in predicting
neutron star and black hole populations, while naturally easing the red-supergiant and the
supernova-rate problems, as well as reconciling theoretical expectations with the low-mass tail of the observed
neutron star mass distribution.
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Astrophysics of Galaxies
Co-evolution of Supermassive Black Holes and their Host L* galaxies: implications for Milky Way and M31
Salvador E. Grimozzi, Maria Emilia De Rossi and Andreea S. Font
We investigate the origin of the scatter in supermassive black hole (BH) masses among L*
galaxies, using the ARTEMIS and EAGLE simulations. We classify
galaxies by their central BH-to-
stellar mass ratios and track systems with the lowest and highest ratios (LBH and HBH, respectively). Although these populations have similar properties at z~ 2, they diverge significantly towards lower
redshifts. LBH
galaxies maintain higher gas fractions and sustain
star formation, while HBHs form
stars earlier, experience faster BH growth, more efficient feedback, and subsequent quenching. The simulations broadly match the observed scatter in the BH masses and
galaxy morphologies in the L* regime, linking it to differences in merger histories.
Galaxies with more active merger histories host more massive BHs at present and are predominantly elliptical, whereas those with quieter histories host lower-mass BHs and tend to be disc-like. Mergers induce BH growth through enhanced gas
accretion and direct BH-BH coalescences. However, these channels operate differently: in HBH
galaxies, BHs grow primarily (~90%) through gas
accretion, whereas in LBHs they grow through both gas
accretion and BH–BH mergers, in comparable fractions. These results suggest that the contrasting BH masses in the Milky Way and M31 may arise from differences in their merger histories. We also investigate the role of feedback from
supernovae (SN) versus active
galactic nuclei (AGN) on these scales. AGN feedback appears to be the primary mechanism responsible for quenching MW-mass systems, although SN feedback remains the dominant regulator of their overall
evolution.
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Earth and Planetary Astrophysics
A Revised Mass and Period for the Habitable Zone super-Earth GJ 3378b: A Planet Straddling the Cosmic Shoreline
Paul Robertson, Michael Endl, William D. Cochran et al. (+18 more)
The nearby ($d = 7.7$ pc) M4V
star GJ~3378 is a target of our radial velocity (RV)
exoplanet survey of fully convective
stars in the
Solar neighborhood with the near-infrared spectrograph HPF on the Hobby-Eberly
Telescope (HET) at McDonald Observatory. Recently, Moutou et al.~(2024) announced the discovery of an $m\sin i = 5.26^{+0.94}_{-0.97} M_\oplus$
planet, GJ 3378b, with an orbital period of $24.73 \pm 0.06$ days, based on SPIRou RV data. Here, we present our HPF RVs for GJ 3378, as well as additional Doppler spectroscopy from the extreme precision NEID Spectrometer on the WIYN
telescope at Kitt Peak National Observatory. We have analyzed the HPF+NEID RVs jointly with the published RVs from the CARMENES and SPIRou spectrometers. We present an orbital model for GJ 3378b that differs significantly from the Moutou et al.~solution. The joint RV model reduces the orbital period to $P = 21.45 \pm 0.01$d and the minimum mass to $m \sin i = 2.3 \pm 0.4 M_\oplus$. The shortened orbital distance remains within the conservative circumstellar
liquid-water habitable zone (HZ), while the reduced mass increases the likelihood that the
planet has a terrestrial composition. The revised
planet properties place it near the “
cosmic shoreline," where
planets in the HZs of M
dwarfs may lose their atmospheres due to radiative stripping.
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All authors Paul Robertson, Michael Endl, William D. Cochran, Gudmundur Stefánsson, Suvrath Mahadevan, Caleb I. Cañas, Gogod James, Roan Arendtsz, Ryan C. Terrien, Chad F. Bender, Scott A. Diddams, Mark R. Giovinazzi, Arvind F. Gupta, Samuel Halverson, Shubham Kanodia, Daniel M. Krolikowski, Sarah E. Logsdon, Joe P. Ninan, Claire J. Rogers, Arpita Roy, Christian Schwab
Solar and Stellar Astrophysics
Searching for the Third Wheel: High-Contrast Imaging Constraints on Tertiaries to Black Hole and Neutron Star Binaries
Pranav Nagarajan, Kareem El-Badry and Aniket Sanghi
Black holes (BHs) and
neutron stars (NSs) with low-mass
stellar companions challenge traditional isolated binary
evolution models, motivating hierarchical triple
evolution as a promising alternative. To search for tertiaries, we perform deep, adaptive optics-assisted, near-infrared imaging of five quiescent BH low-mass X-ray binaries (LMXBs),
Gaia BH1, and twelve
Gaia NSs. We detect several faint
stars previously unresolved in survey imaging, but none are close enough to robustly rule out a chance
alignment. To achieve high contrast sensitivity at close separations, we use the reference
star differential imaging strategy with the Karhunen-Loéve Image Processing
algorithm to model and subtract the point-spread function of each target. We identify tertiary candidates in the speckle-dominated regime, but injection-recovery tests suggest most 5$\sigma$ detections are likely artifacts. We derive $5\sigma$ contrast curves and convert these to limits on the mass of main sequence (MS) tertiaries and the effective temperature of white
dwarf (WD) tertiaries consistent with a non-detection. We rule out plausible MS tertiaries and young, hot WD tertiaries at projected separations $\gtrsim 500$ au for the
Gaia compact object binaries and $\gtrsim 2000$ au for the more distant BH LMXBs. While the recent discovery of a $1.2\,M_{\odot}$ tertiary to V404 Cygni supports triple formation scenarios for BH LMXBs, our results suggest such companions are relatively rare. Our observations remain consistent with intermediate-mass tertiaries that have since evolved into cool WDs, detectable with deeper JWST imaging. Follow-up observations are required to measure proper motions and confirm or rule out physical association of tertiary candidates.
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Solar and Stellar Astrophysics
Stellar encounters in the solar neighbourhood and the special case of GJ~710
Eloi Fernandez-Puig, Juan Carlos Morales, Ignasi Ribas et al. (+2 more)
We present a comprehensive characterisation of close
stellar encounters in the
solar vicinity, with a particular focus on placing the predicted fly-by of GJ~710 in context. This
star will come extremely close ($0.0621$\,pc or $\sim10^4$\,AU) to the
Solar System in approximately 1.3\,Myr. Using a linear motion approximation, we identified past and future close
stellar encounters within 1\,pc of the
Solar System, using a complete sample of nearby
stars. We assessed the completeness of our
dataset and applied corrections to the radial velocities, accounting for gravitational
redshift and convective blueshift. Such effects can bias the measured velocities and affect the derived encounter parameters. Furthermore, we computed close encounters for all the
stars in the
Solar System vicinity to build a statistically significant sample of such events. We accounted for binary systems and common proper motion pairs, applying corrections to account for incompleteness at the edges of our time window. We derived reliable statistics for close
stellar encounters of
stars within 25\,pc of the Sun. We report a rate of encounters within 1\,pc and within 0.47\,Myr of $10.6 \pm 4.5$ per Myr and
star, implying an average of one encounter every $95^{+71}_{-28}$\,kyr. Additionally, from the resulting distribution, we can evaluate the relative frequency of the upcoming GJ~710 fly-by, which is found to be quite rare, at a rate of one per $\sim50$\,Myr. This work provides new insights into the dynamic environment of the
solar neighbourhood by quantifying the rates and distributions of close
stellar encounter events.
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All authors Eloi Fernandez-Puig, Juan Carlos Morales, Ignasi Ribas, Júlia Laguna-Miralles, Pol Guijosa
High Energy Astrophysical Phenomena
A 14-year-old Mystery: The Peculiar Case of the Engine-driven SN 2012ap
Itai Sfaradi, Raffaella Margutti, Ryan Chornock et al. (+29 more)
We present late-time ($\delta t > 3000$ d) optical (Keck), X-ray (Chandra and NuSTAR), and
radio (VLA, ALMA, and the uGMRT) observations of the Type Ic-BL SN 2012ap. Previous studies of this SN suggested that it stands out as a key example of a weak engine-driven explosion due to the lack of gamma-ray burst detection and a mildly relativistic ejecta. Recently,
radio sky surveys revealed the rebrightening of the
radio emission from this SN, highlighting the possibilities of a density enhancement at large radii or the existence of an off-axis relativistic jet. While the late-time optical spectra does not exhibit the broad emission lines seen in other interacting SNe, our analysis of the broadband
radio and X-ray emission implies that both scenarios are plausible. If a density enhancement is responsible for the
radio rebrightening, it has to result from a change in the mass-loss rate and/or wind velocity, possibly due to the transition of the progenitor from a red supergiant to a Wolf-Rayet
star. If the late-time
radio component is a result of an off-axis relativistic jet, we find that an energetic narrow jet viewed at $\theta_{\rm obs} \geq 80^{\circ}$ is needed. In this scenario, SN 2012ap is not a result of a weak engine-driven explosion, and, instead, it is similar to other GRBs. However,
radio rebrightenings of Type Ic-BL SNe are not enough on their own to determine the existence of off-axis jets and our planned VLBA observation will help reveal the true nature of this SN.
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All authors Itai Sfaradi, Raffaella Margutti, Ryan Chornock, A. J. Nayana, Eli Wiston, Fabio De Colle, Tracy E. Clarke, Wendy M. Peters, Paz Beniamini, Wenbin Lu, Rodolfo Barniol Duran, Michael Bietenholz, Collin T. Christy, Deanne L. Coppejans, Maria R. Drout, Dina Ibrahimzade, Michal J. Michalowski, Dan Milisavljevic, Conor M. B. Omand, Yihan Wang, Kate D. Alexander, Carles Badenes, Joe Bright, Jonathan Granot, Erica Hammerstein, Wynn V. Jacobson-Galan, Natalie LeBaron, Kohta Murase, Gitika Rameshan, Huei Sears, Michael Stroh, Giacomo Terreran
Solar and Stellar Astrophysics
Hot DQs, magnetic and metal-polluted white dwarfs: spectroscopic insights from a Gaia machine-learning-selected 500 pc sample
Enrique Miguel García Zamora, Santiago Torres Gil, Alberto Rebassa Mansergas et al. (+1 more)
The latest
Gaia data release provides low-resolution spectra for approximately 100 000 white
dwarfs. Though useful for pre-classification, they lack the resolution required for accurate spectral type and parameter determination, motivating spectroscopic follow-up campaigns. In this work, we assess the reliability of machine-learning spectral classifications derived from
Gaia spectra through comparison with medium-resolution spectroscopy, determine the nature of objects classified as "massive helium-rich (DB)" by automated methods, and characterise the properties of warm and hot DQ (carbon-dominated) white
dwarfs,
magnetic and metal-polluted objects. To do this, we observed 255 white
dwarfs with the Gran Telescopio Canarias equipped with the OSIRIS instrument (R ~ 1000). Spectral types were assigned through visual inspection and compared with machine-learning classifications applied to
Gaia spectra.
Magnetic objects were identified via Zeeman splitting, and
magnetic field strengths were estimated. We find machine-learning classifications are highly accurate (> 90% for spectral types in their training sets), despite the low resolution of
Gaia spectra. We show "massive DBs" to be mostly
magnetic white
dwarfs and warm DQs, with only 5 of 112 observed (4.46%) confirmed as genuine DBs. Warm DQs are found along the
Gaia Q branch and exhibit unusually high tangential speeds. We provide spectral classifications for 255 white
dwarfs, demonstrate that Random Forest
algorithms reliably classify low-resolution
Gaia spectra into main spectral types, determine the nature of "massive DBs", and identify a large population of
magnetic white
dwarfs and carbon-rich objects. Several rare subtypes are identified, including 1 DAQ, 1 DQZA, 4 hot, 29 warm DQ
stars, and 63
magnetic white
dwarfs. The properties of warm DQs are consistent with previous studies, supporting their proposed origin as merger remnants.
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All authors Enrique Miguel García Zamora, Santiago Torres Gil, Alberto Rebassa Mansergas, Aina Ferrer i Burjachs
Earth and Planetary Astrophysics
Spinning out of focus: The challenge of rotational line broadening in exoplanet reflection spectroscopy
T. O. Winterhalder, K. Molaverdikhani, D. Cont et al. (+17 more)
Detecting light reflected off the dayside of an
exoplanet in high-resolution spectroscopic data has proved to be a notoriously difficult endeavour. Despite several attempts, the faint signal has yet to be detected. We present a new effort at finding reflection signatures and show how a strong rotational broadening of the reflected spectrum can complicate this objective. We introduce a new figure of merit that quantifies the favourability of different systems for a reflection study, the reflection spectroscopy metric. Applying this metric, we identify the KELT-9 system, which features a highly misaligned, rapidly rotating host
star, as the target for a case study based on a spectroscopic time series obtained by CARMENES. We also perform an injection-recovery test to determine the detectability of the signal in our data and demonstrate its sensitivity to rotational line broadening. The search for a genuine reflection signal in our data resulted in a non-detection. The injection-recovery test puts this finding into context by revealing the critical importance of taking rotational broadening into account when dealing with systems featuring rapidly rotating
stars and large
spin-orbit misalignments. The case study presented here underscores the need to incorporate
stellar rotation and
spin-orbit misalignment into assessments of a given
planet's favourability to reflection studies.
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All authors T. O. Winterhalder, K. Molaverdikhani, D. Cont, F. Yan, E. Nagel, A. Kaminski, L. Nortmann, P. J. Amado, V. J. S. Béjar, G. Bergond, J. A. Caballero, S. Czesla, Th. Henning, G. Morello, D. Montes, E. Palle, A. Quirrenbach, A. Reiners, I. Ribas, A. Schweitzer
High Energy Astrophysical Phenomena
The interaction phase of engine-driven explosions and high-energy winds
Benjamin Amend, Christopher Lagomarsino, Eric R. Coughlin et al. (+1 more)
Wide-angle
outflows, or winds, are associated with a broad range of astrophysical systems, including protostars, massive
stars, X-ray binaries,
tidal disruption events (TDEs), luminous fast blue optical transients (LFBOTs), and starburst
galaxies. When these winds first “turn on," they inflate a “bubble" into their surroundings, bounded by two shocks and a contact discontinuity, and evolve through distinct adiabatic phases prior to the onset of significant radiative cooling. For sufficiently overdense ejecta, the flow quickly relaxes into an interaction-dominated similarity state at early times and later enters an energy-conserving regime. We present a systematic study of these phases for adiabatic winds expanding into power-law density profiles $\rho \propto r^{-n}$ with $0 \leq n \leq 2$. Using analytic scalings together with one-dimensional shock-capturing hydrodynamic simulations, we quantify both the relaxation timescales and the accuracy with which the corresponding similarity solutions reproduce the fluid velocity, density, and pressure throughout the shocked bubble. We show that the interaction solutions are attained within only a few dynamical times and remain valid until the reverse-shocked shell is no longer thin relative to the forward-shocked shell, corresponding in practice to an instantaneous overdensity of order unity. For $n < 2$, the flow subsequently converges to the generalized energy-conserving scaling $R_s \propto t^{3/(5-n)}$, while the special case $n=2$ exhibits a single persistent similarity state. We discuss the durations and implications of these phases for
stellar and
galactic outflows, TDEs, and LFBOTs.
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All authors Benjamin Amend, Christopher Lagomarsino, Eric R. Coughlin, Jonathan Zrake
Cosmology and Nongalactic Astrophysics
Thermostats, Not Engines: A New Picture of Halo Gas Regulation
Hiranya V. Peiris, Andrew Pontzen, Madalina N. Tudorache et al. (+5 more)
We propose that black hole feedback regulates gas in massive
halos by establishing an
entropy ceiling; the resulting buoyant gas migrates to the virial radius with no additional energy input required. The FLAMINGO simulations support this picture: at the virial radius,
outflow entropy is mass-independent for isotropic thermal feedback but depends on the solid angle of directly heated gas for jet feedback. Above a critical
halo mass $M_\rm{crit} \approx 10^{13.5\text{--}14}\, M_\odot$, virial shocks overwhelm the ceiling, predicting rejuvenation of
star formation in the most massive
galaxies, supported by new low-
redshift evidence from
star formation rates and morphologies.
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All authors Hiranya V. Peiris, Andrew Pontzen, Madalina N. Tudorache, Anik Halder, Stephen Thorp, Sinan Deger, Joop Schaye, Matthieu Schaller