Astrophysics of Galaxies
Electron irradiation and temperature-programmed desorption of layered ethanolamine-water-methanol ices
Tara L. Stoib, Alejandro Guerrero-Caicedo, Duncan V. Mifsud et al. (+12 more)
Ethanolamine (EtA) is a recently detected interstellar complex organic molecule and a potential precursor to more functionalised N-bearing species. We investigate the electron-driven chemistry of layered EtA–H$_2$O–CH$_3$OH ices deposited at 20~K, combining 2~keV electron irradiation with subsequent temperature-programmed desorption (TPD) while monitoring the solid phase by mid-infrared spectroscopy. These controlled irradiation conditions represent a simplified laboratory analogue of the structural and energetic conditions within interstellar grain mantles. Volatile products released during warming were followed by quadrupole mass spectrometry, and the final residue was analysed by ex situ electrospray ionisation mass spectrometry (ESI-MS). Irradiation produces abundant radiolysis products typical of processed methanol- and water-rich ices, including CO, CO$_2$, H$_2$CO, H$_2$O$_2$, NH$_3$, and OCN$^{-}$. Bands consistent with formic acid and polyoxymethylene-like material are also observed, indicating that carbonyl chemistry and formaldehyde-driven oligomerisation can occur alongside fragmentation in the layered system. Comparison with a choline chloride–H$_2$O reference reveals the emergence of features compatible with methylated EtA derivatives and/or choline-like species, while ESI-MS shows higher-$m/z$ mass families in the residue that are not reproduced in the substrate/background blank. However, spectral congestion and
matrix effects preclude an unambiguous assignment of choline. Our results show that energetic processing of EtA-containing ices can generate a diverse inventory of O- and N-bearing products, providing laboratory constraints on radiation chemistry in cold, irradiated grain mantles under idealised conditions.
Read the full abstract ▾
All authors Tara L. Stoib, Alejandro Guerrero-Caicedo, Duncan V. Mifsud, Péter Herczku, Gergő Lakatos, Zuzana Kaňuchová, Zoltán Juhász, Béla Sulik, Nigel J. Mason, Sergio Ioppolo, Paola Caselli, Barbara Michela Giuliano, Karl E. Duderstadt, Felipe Fantuzzi, Heidy M. Quitián-Lara
Instrumentation and Methods for Astrophysics
The SHARPEx space-to-space VLBI experiment
Freek Roelofs, Christiaan Brinkerink, Albert Catalan Artigas et al. (+16 more)
Space is the next frontier for ultra-high resolution imaging of astrophysical sources with very long baseline interferometry (VLBI). The limited size of the Earth and atmospheric absorption and
turbulence at high frequencies prevent order-of-magnitude resolution improvements from current black hole imaging with the ground-based Event Horizon
Telescope. A two or three-element submm space-based array like SHARP would image the thin black hole
photon ring and measure the black hole
spin and spacetime. Here, we present the SHARP Experiment (SHARPEx) mission concept. SHARPEx will demonstrate key enabling technologies for space-to-space VLBI, including clock syntonization between two satellites, on-board correlation, and sub-wavelength relative orbit determination. SHARPEx will consist of two CubeSat or SmallSat platforms carrying small (~1 m diameter)
antennas, observing at cm wavelengths. While SHARPEx will be a technical demonstrator, a SHARPEx-type follow-up mission with enhanced intersatellite link properties (range and bandwidth) may produce images of bright AGN with unprecedented resolution and fidelity.
Read the full abstract ▾
All authors Freek Roelofs, Christiaan Brinkerink, Albert Catalan Artigas, Heino Falcke, Jaime Fernández, Christian M. Fromm, Felix Glaser, Marc Klein Wolt, Yuri Kovalev, Volodymyr Kudriashov, María Manzano, Rasmus Maråk, Manuel Martin-Neira, Jacobo Pastor Fernández-Posse López, Montserrat Puertolas Turell, Alberto Rodríguez Pérez-Silva, René Rüddenklau, Efthalia Traianou, Roger Vilaseca Miro
Astrophysics of Galaxies
Physical properties of star-forming clumps in nearby galaxies from CLAUDS and HSC-SSP
Jürgen J. Popp, Hugh Dickinson, Stephen Serjeant et al. (+2 more)
Giant
Star-forming Clumps (GSFCs) are kpc-scale regions of enhanced
star-formation with stellar masses of $10^6$ to $10^{10}\,M_\odot$ that are commonly observed in high-
redshift ($z \gtrsim 1$)
galaxies but their formation and role in
galaxy evolution remain unclear. We applied a Faster R-CNN object detection framework (FRCNN) to identify
star-forming clumps in astrophysical imaging data from a mass-complete sample of $\sim$210,000 low-
redshift galaxies ($z\lesssim0.32$), located in the HSC-SSP Wide and Deep fields observed by the Hyper Suprime-Cam Subaru Strategic Survey (HSC-SSP) and CFHT Large Area U-band Deep Survey (CLAUDS). We present a population of $\sim$710,000 detected clumps for which we measured the (u)grizy-photometry and derived the physical properties (stellar mass, age, dust extinction and
star-formation rate) for each clump by fitting the photometric data to stellar population models. We estimate that the clump Stellar Mass Function (cSMF) for young clumps ($<100\,\mathrm{Myr}$) follows a power law with an exponent of $\alpha=1.98\pm0.02$ down to a completeness limit of $\sim10^{8}\,M_\odot$ which is consistent with an in situ formation through violent disk instabilities (VDI). The clumps show elevated
star-formation rates and negative gradients in their ages and stellar masses as a function of galactocentric distance. These gradients are steeper than those measured for the intra-clump regions of the host
galaxies and are robust against uncertainties introduced by different modelling assumptions. For nearby
galaxies we argue that the observed low-
redshift clumps are likely analogues of high-
redshift GSFCs and that the inward migration of
star-forming clumps directly contributes to the central bulge formation of the host
galaxy.
Read the full abstract ▾
All authors Jürgen J. Popp, Hugh Dickinson, Stephen Serjeant, Lucy F. Fortson, Vihang Mehta
High Energy Astrophysical Phenomena
The 2025.6 X-ray Minimum of Eta Carinae
Amit Kashi and Noam Soker
We present observations of the recent 2025.6 X-ray minimum and recovery of $\eta$~Carinae, obtained with NICER/XTI, Swift/XRT, XRISM/Xtend, and Chandra/HRC-I. We construct light curves in the soft (0.5–2 keV) and hard (2–10 keV) bands and derive hardness ratios. The X-ray emission reached its minimum about 10 days earlier than in the previous five cycles. As in previous events, the spectrum softened during the decline, while the X-ray luminosity varied on short timescales. These findings strengthen the conclusion that enhanced line-of-sight absorption, such as that expected during an eclipse, does not have a significant role in producing the spectroscopic event. Instead, they indicate that the X-ray decline is caused by
stochastic variations and instabilities in the two stellar winds and their interaction, destruction of the colliding winds region, and
accretion of primary wind onto the secondary. The main process behind the deep X-ray minimum near periastron is the
accretion of mass lost by the primary
star onto the secondary
star.
Accretion at periastron passages in $\eta$ Carinae implies that
accretion occurred at much higher rates during the nineteenth-century Great and Lesser Eruptions, when the primary
star lost mass at much higher rates. Such
accretion likely launches jets. The broader implication is that
accretion events in binary systems, possibly with jet launching, power other luminous blue variable giant eruptions and intermediate-luminosity optical transients.
Read the full abstract ▾
Astrophysics of Galaxies
Rapid Dark Growth of Seed Black Holes in Self-Interacting Dark Matter
Yu Rong, Shuang-Nan Zhang, Jian-Min Wang et al. (+1 more)
The rapid emergence of massive black holes in the early Universe, possibly related to Little Red Dots, challenges conventional growth from light seeds. Dark-matter
accretion offers a distinct route, and self-interacting dark matter (SIDM) makes it possible by behaving as a collisional fluid. We show that gas inflow can drive strong local contraction of an SIDM
halo, assembling a dense reservoir around a pre-existing black-hole seed. The seed then enters a rapid dark-growth phase and can gain several orders of magnitude in mass within less than $1$ Myr before transitioning to slower
accretion. We self-consistently follow this process by solving the spherical Euler equations with SIDM self-
gravity, collisional heat transport, and an absorbing black-hole sink, rather than imposing an
accretion history. The growth depends most strongly on
halo mass, with weaker sensitivity to inflowing gas fraction, nuclear size, and seed mass. Gas-inflow-driven SIDM
accretion therefore provides an efficient pathway for producing massive black holes in the early Universe.
Read the full abstract ▾
All authors Yu Rong, Shuang-Nan Zhang, Jian-Min Wang, Junxian Wang
Astrophysics of Galaxies
Little Red Dots as a Transient Phase of Self-Interacting Dark Matter Assisted Black Hole Growth
Yu Rong, Shuang-Nan Zhang, Jian-Min Wang et al. (+2 more)
The discovery of Little Red Dots (LRDs) with JWST has revealed a population of compact, red
galaxies hosting rapidly growing black holes at early
cosmic times. Their compact morphologies, broad emission lines, weak X-ray emission, and distinctive V-shaped spectral energy distributions indicate a short-lived phase of black-hole growth within a dense nuclear environment. Here we propose that LRDs arise from a transient episode of self-interacting dark matter (SIDM)-assisted black-hole growth during
galaxy assembly. In this scenario, gas inflows first establish a compact nuclear thick disk, which modifies the central SIDM distribution and provides the obscuring structure around the accreting black hole. Once the SIDM density near the seed black hole becomes sufficiently enhanced, rapid SIDM
accretion drives a major increase in black-hole mass, initiating the transient LRD phase. The resulting obscured growth phase naturally suppresses direct short-wavelength emission and redistributes the radiation field, producing the red continuum and V-shaped spectral signatures of LRDs. This framework links gas inflow, SIDM dynamics, and early black-hole assembly, predicting that LRDs preferentially occur in
galaxies undergoing strong nuclear inflow and evolve into ordinary AGN after this transient phase. Unlike models that require globally rare
halo histories, long super-Eddington gas growth, or purely phenomenological obscuration, our model ties the overmassive black hole, X-ray weakness, spectral shape, and finite duty cycle to one local gas-triggered SIDM event.
Read the full abstract ▾
All authors Yu Rong, Shuang-Nan Zhang, Jian-Min Wang, Junxian Wang, Zhicheng He
Astrophysics of Galaxies
Ten years since the NGC 6334I-MM1 accretion outburst: the impact on its environment
G. C. MacLeod, A. Caratti o Garatti, W. A. Baan et al. (+11 more)
Ten years on, flaring continues in masers associated with NGC 6334I-MM1. Methanol and hydroxyl masers are nearing quiescent values, but water features remain elevated. Several more 1.665 GHz hydroxyl masers, notably, that flared during the
accretion event in NGC 6334I-MM1, are identified and presented. Some hydroxyl masers appear to have been active prior to the 2015 event. Possible explanations are discussed. The radial infrared expansion speed during the
accretion event is estimated to be ~1.8 AU/d. However, the expansion speed along the North-South outflow is about ten times faster (~18 AU/d). The maser flaring activity illuminated clumpy structure in NGC 6334I-MM1. Quasi-periodicity is reported after the 2015
accretion event in the total integrated 12.2 GHz methanol emission, predominantly in $v_{12.2}=[-12.0,-9.9]$ \kms, after the
accretion event in NGC 6334I-MM1. It is not certain if the periodic masers are located in NGC 6334I-MM1, -MM2, or -MM3. The
magnetic field, measured from the Zeeman splitting of two ground state hydroxyl lines, undergoes changes before and after the
flare.
Read the full abstract ▾
All authors G. C. MacLeod, A. Caratti o Garatti, W. A. Baan, D. P. Smits, T. R. Hunter, C. L. Brogan, J. O. Chibueze, R. A. Burns, B. Stecklum, V. Wolf, J. M. Vorster, A. Jengis, J. Esimbek, J. Quick
Astrophysics of Galaxies
Topological Signatures of AGN Feedback in the Simba Simulations
Ryusei R. Kano, Romeel Davé, Tsutomu T. Takeuchi et al. (+1 more)
Active galactic
nuclei (AGN) feedback can alter the abundance and spatial distribution of
galaxies within large-scale structure. We apply topological data analysis (TDA) to Simba hydrodynamical simulations with varying AGN feedback at $z=0$ to determine which
galaxy populations, environments, and spatial scales are most affected. The
galaxy two-point correlation function is most sensitive to feedback at $r<1 h^{-1} Mpc$. We then use Betti curves, persistence diagrams, and the 2-Wasserstein distance to quantify feedback-dependent changes in
topology. Persistence diagrams show clearer differences than Betti curves, particularly for satellite
galaxies. For satellites, loop-like features show significant differences at $\alpha=0.1$–$0.4 h^{-1} Mpc$ for all feedback channels, together with a weaker cumulative difference at $\alpha=1$–$3 h^{-1} Mpc$. The differences are strongest for satellites in quenched
halos with $M_h\gtrsim10^{12} M_\odot$. Optimal matching shows that they are driven mainly by shifts in the birth and death scales of loop-like features rather than by their appearance or disappearance. These results indicate that persistent homology can provide complementary constraints on AGN feedback and environmental quenching in
galaxy surveys.
Read the full abstract ▾
All authors Ryusei R. Kano, Romeel Davé, Tsutomu T. Takeuchi, Hayato Shimabukuro
High Energy Astrophysical Phenomena
A 32-day Quasi-periodic Modulation in the Post-peak Light Curve of the Superluminous Supernova SN 2018bsz
Aiswarya Sankar.K, Ting-Wan Chen, Seán J. Brennan et al. (+8 more)
Recurrent structure in
supernova (SN) light curves may reveal physical clocks associated with central-engine dynamics, binary orbital motion, or interaction with structured circumstellar material (CSM). We present a multiband photometric reanalysis of the nearby hydrogen-poor superluminous SN (SLSN-I) 2018bsz (z=0.0267), using Swift/UVOT and GROND observations spanning approximately 110 rest-frame days after maximum light. After independently modelling and subtracting the smooth decline in each band, Generalized Lomb-Scargle periodograms reveal recurrent residual variations at broadly consistent phases across ten bands from u to Ks. The strongest individual-band detections, in the g, r, i, z, and J bands, yield periods of 31.5-31.8 days, while the joint multiband analysis gives a rest-frame period of P=31.61 (+/-0.03) days. The modulation is traced over approximately three cycles and is therefore described as quasi-periodic. The signal is robust to the adopted detrending procedure, while comparison-
star and lunar-cycle tests disfavour an observational systematic. The modulation is broadly phase-coherent from the optical to the near-infrared, but its amplitude increases towards shorter wavelengths; lower-significance bands also show possible wavelength-dependent shifts in the best-fitting period. The present observations do not uniquely determine the physical origin. Lense-Thirring precession, interaction with CSM structured before the explosion, and post-SN interaction with a surviving companion remain possible. SN 2018bsz provides one of the clearest examples of coherent, month-scale photometric modulation in an SLSN-I.
Read the full abstract ▾
All authors Aiswarya Sankar.K, Ting-Wan Chen, Seán J. Brennan, Morgan Fraser, Keiichi Maeda, Thomas Moore, Sheng Yang, Amar Aryan, Dietrich Baade, Ping Chen, Chow-Choong Ngeow
Astrophysics of Galaxies
Polarization Observations of a sample of Excited OH masers
Derck P. Smits and Paul Fallon
Spectra of 4.7 and 6.0 GHz excited OH masers from 21 pointings towards known
star-forming regions are reported. The C-band observations, using the Green Bank
Telescope in full Stokes mode, have measured how polarization properties vary across the maser profiles in each spectrum and vary between different epochs of observation. Seven sources had no detections of masers at any of the OH transitions. Nine sources were observed to have 4.766 GHz masers, which include two new detections in G188.946+0.886 and G196.454-1.677. No new linear or circular polarization was found in any of these masers. Seven and two sources had 6.035 and 6.031 GHz masers, respectively. All 6.035 GHz masers had some level of circular polarization, and three also had linear polarization. Both linear and circular polarization were found in the 6.031 GHz masers in G133.947+1.064, and weak, 100% LCP in G141.918+1.902.
Magnetic fields have been calculated from measured Zeeman splittings. The strength and orientation of the fields agree with most previous measurements, although there are some indications that the
magnetic fields could be changing. Thermal emission or absorption is seen in several of the 4.7 and 6.0 GHz transitions, many of which have not been reported before.
Read the full abstract ▾
Instrumentation and Methods for Astrophysics
Semi-automated single-mode fiber coupling for AO-fed spectrographs
Aaron J. Crepp, Brian L. Sands and Justin R. Crepp
Conventional astronomical spectrographs are seeing-limited and commonly use multimode fibers to inject starlight into downstream optics. Forthcoming Doppler radial-velocity (RV) instruments are expected to make increasing use of adaptive optics and smaller single-mode fibers (SMF), enabling higher spectral resolution and improved stabilization of the spectrograph point-spread function. However, coupling starlight into SMFs with characteristic diameters of only 5-10 microns at near-infrared wavelengths is technically demanding, requiring
alignment procedures that are both efficient and stable throughout the duration of an observation. In this paper, we describe a semi-automated SMF coupling control program being developed for diffraction-limited RV spectrographs. Representative simulations demonstrate that the controller reduces the
star-fiber separation from approximately 3.9 mode field diameters (MFD) to 0.11 MFD while increasing a normalized coupling metric from zero to values near 0.6-0.8 after acquisition. Application to closely-separated binary
stars is also studied.
Read the full abstract ▾
Solar and Stellar Astrophysics
Meerkat measurement of the radio emission from massive stars in the Galactic plane I. Wolf-Rayet stars
Mathilde Tasseroul, Michaël De Becker, Paula Benaglia et al. (+1 more)
Massive
stars, including Wolf-Rayet
stars, are predominantly found in binary systems. These systems are known to emit both thermal emission from stellar winds and, occasionally, non-thermal emission produced by relativistic electrons accelerated in the wind-wind interaction region. We intend to provide the most complete census of
radio emission from WR
stars in the Galactic plane, using the SARAO MeerKAT Galactic Plane Survey (SMGPS) complemented by the MeerKAT Galactic Center Survey. Our main motivation is to identify hints of synchrotron
radio emission indicative of particle-accelerating colliding-wind binaries (PACWBs). We compiled an input catalogue of 428 WR
stars positionally covered by the SMGPS and the MGCS. Using the survey data, we measured the
radio emission at 1.3 GHz for detected WR
stars. We also measured the upper limits for objects located in sufficiently low
radio background regions. For detected objects, we searched for a
radio excess by comparing the measured fluxes to two different evaluators of the thermal emission from massive
star winds. We detected 23 targets and determined the upper limits for 279 WR
stars. Among the detected objects, 15 display a (significant or potential)
radio excess that cannot be explained by unresolved circumstellar emission of any kind. After removing already known PACWBs, we report the identification of 12 potential new PACWB candidates. Our study has led to the compilation of the most extensive catalogue of Galactic WR
radio emission to date, based on a homogeneous
dataset covering the Galactic plane. The low detection rate indicates either a low occurrence rate of synchrotron emission or substantial attenuation by turnover processes that are clearly dominated by free-free absorption from the WR wind material. Our results open the door to dedicated follow-up observations aimed at ascertaining the nature of the identified
radio excesses.
Read the full abstract ▾
All authors Mathilde Tasseroul, Michaël De Becker, Paula Benaglia, Anandmayee Tej
Earth and Planetary Astrophysics
Reliability of Zodiacal Background Models at Small Solar Elongations
Csaba Kiss, Thomas G. Müller, Javier Licandro et al. (+6 more)
Present models of the zodiacal light (scattered sunlight from interplanetary dust in the visible) and zodiacal emission (thermal emission in the mid-infrared) are primarily constrained by surface-brightness measurements obtained at relatively large solar elongations (e >~ 60 deg). As a result, their predictive accuracy at smaller elongations remains uncertain. This is particularly relevant for solar elongations of e ~ 30-60 deg, where next-generation near-Earth-object discovery missions such as NEO Surveyor and NEOMIR are designed to operate. To evaluate the reliability of these models at small solar elongations, we compile and reanalyze the available small-elongation zodiacal-light and zodiacal-emission measurements and provide the first systematic validation of modern zodiacal-light models in a regime where they have never been independently tested. We compare two models derived from the COBE/DIRBE survey: one constrained primarily by the spatial and temporal variation of the monochromatic sky brightness, and another that additionally uses interband color information and fixes the absolute normalization by requiring the minimum high-latitude residual at 25um to vanish. We find that the former reproduces the observations significantly better. At wavelengths most relevant to infrared near-Earth-object surveys (8-10 um), it typically agrees with measurements to within ~10% at e ~ 40-60 deg. Although it also performs better at e ~ 30 deg, significant discrepancies remain. These results show that zodiacal emission at small solar elongations is still only weakly constrained and that its absolute brightness remains uncertain. New mid-infrared observations are required to improve background estimates for future infrared survey missions.
Read the full abstract ▾
All authors Csaba Kiss, Thomas G. Müller, Javier Licandro, Luca Conversi, Marco Delbo, Karri Muinonen, Marcel Popescu, Paolo Tanga, Róbert Szakáts
High Energy Astrophysical Phenomena
Investigating the influence of the full-kinematics treatment for charged-current processes in binary neutron star mergers
Ramon Jaeger, Henrique Gieg and Tim Dietrich
Weak interactions are fundamental in the merger of binary
neutron stars (BNS). They provide cooling, change the composition of matter outflows, and can lead to significant secular outflows through
neutrino-driven winds. Hence, the inclusion of
neutrino transport has become standard in numerical-relativity simulations of mergers involving
neutron stars. In more detail, the interactions of
neutrinos with matter in a truncated two-moments scheme (M1) are described through interaction rates, calculated from a set of standard interactions. Among those are charged-current reactions, for which the elastic approximation is commonly assumed. More sophisticated alternatives are provided by, e.g., the publicly available NuLib library, or rates computed within a full kinematics approach. In this work, we compare merger simulations of a BNS systems employing each of these three prescriptions for the computation of charged-current weak rates, included in the M1 equations with an implicit-explicit time integrator. We find that the elastic approximation slightly overestimates the dynamical ejecta mass, while underestimating the amount of high electron fraction material therein. Additionally, it overestimates the
neutrino luminosities at early times. The effects of full kinematics in comparison to the NuLib rates appear negligible within the uncertainties of the simulation data. Similarly, the post-merger gravitational-wave spectra for the three prescriptions were found to be indistinguishable within the numerical uncertainties. Nucleosynthetic yields, computed with a nuclear network, are broadly consistent, except in the atomic mass range $A\in[90,125]$ where the elastic approximation shows larger abundances. Finally, the different interaction rates seem to affect the remnant disk properties, hinting at the importance of more accurate interaction rates for simulations spanning secular timescales.
Read the full abstract ▾
High Energy Astrophysical Phenomena
The rise and decline of a transient obscuration event in a moderately distant type-I quasar
A. Akylas, A. Georgakakis, E. Pouliasis et al. (+5 more)
Outflows of ionised material, often dubbed warm absorbers (WAs), are common in nearby Seyferts but sparse in distant and more energetic
quasars (QSOs). We present multi-epoch X-ray and optical observations of the serendipitously identified type-I QSO 2MASS J14302580+4159572 at a
redshift of $z=0.35$, revealing the rare rise and decline of a transient ionised absorber over a 22-year timescale. The discovery observations were obtained with XMM-Newton between 2002 and 2005. The first two observations show unremarkable X-ray spectra typical of unobscured type-I QSOs, whereas the 2005 observation reveals a pronounced suppression of the spectrum below $\sim3\,\mathrm{keV}$. Spectral analysis shows that this event is produced by a moderately ionised absorber with column density $N_{\rm H}\simeq5\times10^{22}\,\mathrm{cm^{-2}}$ and ionisation parameter $\log\xi\simeq1.4$. Joint analysis of XMM-Newton, NuSTAR, and Swift/XRT observations spanning 22 years indicates that the absorber remained stable for nearly 18 years before weakening in the 2023–2024 Swift/XRT data. Throughout this period, the intrinsic 3–10 keV continuum remained remarkably stable, indicating that the observed variability is driven by changes in line-of-sight ionised absorption rather than intrinsic luminosity fluctuations. We interpret the event as a thermally driven ionised outflow located outside the broad-line region (BLR), at sub-parsec to parsec scales, with a density of order $10^{6}\,\mathrm{cm^{-3}}$. Supporting this scenario, the high-ionisation [O\,III] $\lambda4363$ emission line varies in tandem with the X-ray absorption, suggesting that the outflow progressively modifies the ionisation state of the inner narrow-line region (NLR) on decadal timescales. These observations provide a rare view of the long-term
evolution of a
quasar warm absorber and its impact on the circumnuclear environment.
Read the full abstract ▾
All authors A. Akylas, A. Georgakakis, E. Pouliasis, I. Georgantopoulos, C. Ricci, M. Chira, A. Ruiz, E. M. Xilouris
Solar and Stellar Astrophysics
Highly bipolar planetary nebula Hen 2-57 and its possible symbiotic core
J. Merc, J. Mikołajewska, K. Iłkiewicz et al. (+1 more)
We present a multi-wavelength analysis of the highly bipolar object Hen 2-57 based on new optical spectroscopy from the Southern African Large
Telescope (SALT), complemented by archival imaging, and long-term time-series photometry from OGLE and NEOWISE. The nebula exhibits a pronounced hourglass morphology with a
symmetry axis at a position angle of $110\pm5^{\circ}$ and an average lobe opening angle of $\sim$$53^{\circ}$. We also identify pronounced north–south brightness asymmetry, with the southern parts of lobes consistently brighter. The spectral energy distribution shows a strong mid-infrared excess that cannot be reproduced by a single-temperature blackbody, indicating the presence of a dense circumstellar dust structure, likely in the form of a disk or
torus, analogous to that observed in M 2-9. Optical spectroscopy reveals a complex kinematic structure in which the central core is redshifted relative to both the eastern ($55\pm4\ \mathrm{km\,s^{-1}}$) and western ($46\pm3\ \mathrm{km\,s^{-1}}$) lobes. While standard diagnostic diagrams place the extended lobes in the planetary nebula regime, emission-line diagnostics of the central core are consistent with those of symbiotic
stars. The same region also exhibits a steep Balmer decrement, indicative of significant internal dust extinction. Long-term OGLE photometry shows no evidence for coherent stellar pulsations, whereas NEOWISE photometry reveals a gradual mid-infrared fading of $\sim$0.25 mag between 2010 and 2024. Together, these properties support a scenario in which Hen 2-57 hosts a dust-enshrouded D-type symbiotic central engine actively shaping the surrounding bipolar nebula, making it a close analogue of M 2-9.
Read the full abstract ▾
All authors J. Merc, J. Mikołajewska, K. Iłkiewicz, A. Udalski
Solar and Stellar Astrophysics
On the Constancy of Binary Star Fractions in Local Star Clusters
Priya Hasan and Mohammed Saifuddin
We investigate the unresolved binary-
star fraction in a complete sample of 376 open clusters located within 1 kpc of the Sun using Gaia DR3 and ASteCA based synthetic colour magnitude diagram modelling. The binary fraction is a global photometric quantity, sensitive primarily to unresolved binaries that produce measurable broadening above the single-
star main sequence. We find that the median binary fraction of the sample is nearly constant, $0.29\pm 0.03$, with no clear dependence on cluster age, core radius, limiting radius or median mass. This apparent constancy suggests that the global binary content of nearby open clusters is regulated by competing dynamical processes, including disruption of soft binaries, survival and hardening of close binaries, mass segregation, evaporation of single
stars, and long-term cluster dissolution. The result is consistent with theoretical expectations and previous observational studies indicating that cluster binary populations can evolve internally while maintaining a relatively stable global binary fraction. Our findings provide an observational constraint for models of open-cluster formation and dynamical
evolution and highlight the need for future work combining photometric, astrometric, spectroscopic, and N-body approaches to distinguish between primordial and dynamically formed binary populations.
Read the full abstract ▾
Earth and Planetary Astrophysics
Widespread plasma jets in the Martian magnetosheath revealed by dual-spacecraft observations
Abigail Tadlock, Chuanfei Dong, Chi Zhang et al. (+4 more)
Plasma jets in planetary magnetosheaths are transient, high dynamic pressure structures capable of strongly perturbing downstream magnetospheres and modulating solar wind energy transfer. Although recently identified at Mars, their formation mechanisms and global occurrence remain poorly constrained. Using dual-spacecraft observations from Mars Atmosphere and Volatile
EvolutioN (MAVEN) and Tianwen-1, we show that magnetosheath jets occur throughout the Martian magnetosheath, in striking contrast to Earth where jet occurrence is strongly controlled by interplanetary
magnetic field orientation and largely confined to quasi-parallel shock regions. We propose that this widespread distribution is linked to Mars' extended hydrogen corona, which generates pickup ions that drive
proton-cyclotron waves upstream of the bow shock. Because this mechanism is generic to any body with an extended corona (or exosphere) embedded in a stellar wind, this finding bears on solar-wind interactions at comets and other small bodies, and on the space environments of unmagnetized terrestrial
exoplanets. These results indicate that magnetosheath jet formation can be governed not only by external solar wind forcing but also by intrinsic planetary properties, pointing to a previously unrecognized pathway for solar wind-
planet coupling at unmagnetized worlds.
Read the full abstract ▾
All authors Abigail Tadlock, Chuanfei Dong, Chi Zhang, Savvas Raptis, Hongyang Zhou, Xinmin Li, Jiawei Gao
Cosmology and Nongalactic Astrophysics
Constraints on the Pop III Sky Surface Brightness from High-Redshift Caustic Transients in MACS0416
Jakob P. Perivolotis, Pietro Bergamini, Rogier A. Windhorst et al. (+18 more)
Population III (Pop III)
stars are hypothetical zero-
metallicity stellar structures formed from primordial hydrogen and helium. They are theorized to span a wide mass range, extending to several 100 solar masses, and may have played important roles in nucleosynthesis and reionization. Their expected fluxes are far below JWST NIRCam detection limits, making direct observation unlikely. However, extreme magnification near the caustics of massive foreground
galaxy clusters may enable their detection. We search for overlooked high-
redshift (7 <= z <= 17) caustic transits in the
lensing cluster MACS J0416.1-2403. Using three observations spanning 126 days, we create difference images to identify potential candidates. Critical curves for sources at 7 <= z <= 17, derived from a strong-
lensing model, guided visual inspection of three difference-images. No additional transits were found. The longer caustics in our model sweep a larger source-plane area, increasing the probability of detecting an event. Combining this increased statistical sensitivity with deeper imaging, we establish a fainter limit for the unresolved stellar population at z >= 7. From this null result, we constrain the 100 solar mass 2 micron Pop III sky surface brightness to >= 32.8 +/- 0.6 mag arcsec^-2. Modeling the non-detection as a Poisson process gives a posterior mean caustic-transit rate of 0.29 cluster^-1 yr^-1 and a 95 percent upper credible limit of lambda_95 = 0.86 cluster^-1 yr^-1. The inferred rate remains consistent with the adopted fiducial Pop III caustic-transit model and provides an empirical
benchmark for future multi-epoch monitoring campaigns. This search exploits the fact that individual
stars projected close to source-plane caustics can be briefly magnified far beyond their unlensed fluxes. These constraints provide a direct test of the abundance of luminous Pop III
stars at early
cosmic times.
Read the full abstract ▾
All authors Jakob P. Perivolotis, Pietro Bergamini, Rogier A. Windhorst, Erik Zackrisson, Timothy Carleton, Seth H. Cohen, Jordan C. J. D'Silva, Rachel Honor, Rolf A. Jansen, Anton M. Koekemoer, Rafael Ortiz III, Jake Summers, Dan Coe, Christopher J. Conselice, Jose M. Diego, Brenda Frye, Massimo Ricotti, Gibson B. Bowling, Brent Smith, Christopher N. A. Willmer, Haojing Yan
High Energy Astrophysical Phenomena
Polarization of Synchrotron Emission from Rotation Powered Pulsars
Seima Saeki, Shota Kisaka and Jumpei Takata
With the launch of the Imaging X-ray Polarimeter Explorer in 2021, recent observations have provided X-ray polarization data for several rotation-powered
pulsars. To fully exploit these data, it is important to better understand the relationship between polarization properties and the magnetospheric structure. In this paper, we investigate polarization properties in the outer gap model, incorporating both outward emission and inward emission toward the rotation axis, which has not been considered previously. We find that the polarization position angle varies at the intensity peaks, typically accompanied by a high polarization degree, as is in the case for outward emission. Moreover, the variation in the polarization position angle tends to exceed 50 degrees when the intensity peaks of outward and inward emissions overlap, compared to cases with only outward emission. We compare the polarization model including inward emission with IXPE observations. For example, for PSR B1509-58 where inward emission is proposed to be dominant in the outer gap model, we find that observed PA swing prefers a line of sight from the southern hemisphere rather than the northern hemisphere.
Read the full abstract ▾
Astrophysics of Galaxies
Kinematics of the System of Young Open Clusters based on Gaia DR3 Data
A.K.Dambis and A.S.Rastorguev
We use a kinematical model including circular rotation of the Milky-Way disk incorporating effects produced by a spiral density wave with constant radial and vertical components of the velocity dispersion tensor and adopted solar Galactocentric distance R_0=8.277kpc (inferred by
GRAVITY collaboration in 2022) to derive the velocity field parameters for a sample of 2384 open clusters from the Hunt and Reffert (2024) catalog having ages no greater than 100 Myr almost all of which reside at Galactoaxial distances between 5 and 14 kpc. We estimate the velocity-field parameters using maximum-likelyhood method and the affine-invariant variant of the Markov chain Monte-Carlo method proposed by Goodman and Weare (2010) with both methods yieilding almost identical parameter values. The inferred rotation curve, on the whole, is consistent with the results based on our kinematical analysis of a sample of Galactic masers. We find the linear rotation velocity at the solar distance to be V=242.3+/-1.1~km/s; it reaches its maximum V~244 km/s at Galactoaxial distance of about R_g~7 kpc followed by a slow and smooth decline with V~227 km/s at R_g=14 kpc. The inferred radial and vertical components of the velocity dispersion tensor are (sigma U_0, sigma W_0)~(10.63+/-0.15, 4.56+/-0.15) km/s. We find the pitch angle and the phase of the Sun for a four-armed spiral pattern to be i~-11.7+/-0.3 degrees and chi_0~138+/-5 degrees, respectively, and the amplitudes of radial and tangential perturbations, f_R=-3.0+/-0.4 and f_{theta}=-3.1+/-0.4 km/s, respectively.
Read the full abstract ▾
Earth and Planetary Astrophysics
Delayed Methane Detection in 3I/ATLAS: GCR-Driven Subsurface Stratification and Interstellar Exposure Age Constraints
Akshat Rawat and Kinsuk Acharyya
Interstellar comet 3I/ATLAS shows unusual volatile activity, including strong H$_2$O, CO, and CO$_2$ production and a delayed post-perihelion detection of CH$_4$. In this work, we investigate the delayed CH$_4$ detection in an H$_2$O, CO$_2$, and CO ice
matrix using a shape model coupled with a thermophysical
nucleus model that incorporates interstellar processing by Galactic
Cosmic Rays. We track the sublimation, trapping, depletion, and release of these volatiles as a function of heliocentric distance and explore the relevant parameter space through 12000 model runs to identify viable combinations of primordial volatile inventory and effective GCR exposure age that reproduce the observed production rates of these volatiles. The viable models favour a volatile-rich primordial inventory consistent with formation in an ultra-cold ($T < 20$ K) region beyond the CO snowline, followed by an effective GCR processing exposure of 0.87–3.1 Gyr during interstellar passage. GCR processing produces a continuous compositional gradient and converts part of the CO reservoir into secondary CO$_2$ and depletes near-surface CH$_4$ through radiolytic conversion. The delayed CH$_4$ detection can be explained by the survival of CH$_4$ trapped within the deeper H$_2$O
matrix and its subsequent release as subsurface heating progresses after perihelion. The timing of CH$_4$ sublimation can be used to estimate the effective GCR processing age of 3I/ATLAS. The posterior distributions also reveal a degeneracy between primordial dust content and GCR exposure, where dust-rich, weakly processed and ice-rich, strongly irradiated evolutionary pathways produce processed subsurface layers with similar thermophysical properties.
Read the full abstract ▾
Cosmology and Nongalactic Astrophysics
Probing submillimeter number counts below the confusion limit: extreme-value statistics of the P(D) distribution and its modulation by gravitational lensing
Kaustuv Basu, Andrea Guerrero and Frank Bertoldi
The shape of the submillimeter
galaxy number counts below the confusion limit is a key record of
cosmic star formation but is accessible only statistically, through the one-point distribution of map surface brightness, $P(D)$. Classical $P(D)$ analysis compresses the counts into flux-integrated constraints and requires a full instrument forward model. We introduce an extreme-value-theory analysis of the confusion $P(D)$ tail: the peaks-over-threshold formalism, in which exceedances above a threshold $u$ follow a generalized Pareto distribution (GPD). The GPD shape parameter $\xi(u)$ is a flux-resolved, normalization-free readout of the local logarithmic slope of the counts, and its gravitational-
lensing modulation $\Delta\xi(u)$ probes their local
curvature. We derive analytic relations for both, validate them with end-to-end simulations, and apply the method to Planck 857 GHz maps and the Herschel/SPIRE 350 $\mu$m map of GAMA-09. At Planck's 5' resolution the tail reflects the bright, clustered sky rather than the faint counts, though the background alone excludes the single power-law count model. At SPIRE resolution $\xi$ rises markedly with threshold, consistent with the strongly lensed bright population (a first detection of
lensing in a $P(D)$ tail), and the bright-masked map favors the Schechter model. Behind
galaxy clusters we set the first calibrated upper limits on $\Delta\xi(u)$. CCAT/FYST should separate the count models directly, but a cluster-
lensing detection needs more $10^{15}\,M_\odot$ clusters than the sky contains. The GPD tail statistic thus discriminates the functional form of the counts at fluxes of order the threshold, below the detection limit, invariant to map mean, gain and count normalization, and robust to clustering;
lensing supplies a calibrated ruler for count features, whose detection awaits deep, high-resolution surveys of massive clusters.
Read the full abstract ▾
Astrophysics of Galaxies
Early steps in the hierarchical assembly of a Milky Way-mass galaxy 1 Gyr after the Big Bang
Yoshihisa Asada, Marcin Sawicki, Guillaume Desprez et al. (+14 more)
We report JWST observations of a $z_{\rm spec}=5.196$ compact group of three strongly lensed low-mass
galaxies ($M_\star \sim 10^{6-7} M_\odot$ each) whose small line-of-sight velocity offsets (from $-120\pm100$ to $+160\pm110$ km s$^{-1}$) and projected separations ($\sim2$ kpc) suggest that they are undergoing merging. On the basis of abundance-matching arguments, the trio appear to be destined to evolve into a Milky Way-mass
galaxy by the present day. Our spectrophotometric analysis suggests that the stellar mass growth of this system is not simply just due to the merging of its components; rather, it is being dramatically enhanced by intense bursts of
star formation. Presumably initiated by tidally-induced gas inflows, these
star-forming bursts boost the mass growth $2.6\pm0.5$ times that expected in straightforward merging of the existing stellar masses. These spectroscopic observations thus not only demonstrate that hierarchical assembly remains a viable formation channel in the early assembly phases of present-day massive
galaxy, but also that interaction-induced bursts of
star formation are a major accelerator of this assembly process.
Read the full abstract ▾
All authors Yoshihisa Asada, Marcin Sawicki, Guillaume Desprez, Jon Judez, Marusa Bradac, Kartheik Iyer, Nicholas S. Martis, Adam Muzzin, Gael Noirot, Ghassan T. E. Sarrouh, Chris J. Willott, Jacqueline Antwi-Danso, Seiji Fujimoto, Danilo Marchesini, Vladan Markov, Luke Robbins, Visal Sok
Astrophysics of Galaxies
On the Probability Distribution and Null-hypothesis Testing of Cross-correlation for Light Curves in Active Galactic Nuclei
Yan-Rong Li and Jian-Min Wang
Cross-correlation is crucial in studies of multiwavelength flux variability in active galactic
nuclei (AGNs), especially for reverberation mapping analysis, where interpolated cross-correlation function is widely used to measure time lags between light curves. While time-lag uncertainties can be estimated via the flux randomization and random subset selection method, an appropriate framework for assessing cross-correlation significance remains lacking in the literature. Here we attempt to fill this gap by leveraging the well-established property from
stochastic time series theory, namely that the probability distribution of cross-correlation coefficients for independent
stochastic light curves asymptotically approaches a normal distribution. Its variance can be analytically estimated using the auto-correlation functions of the light curves. We employ Monte Carlo simulations to validate this property for irregularly sampled, red-noise AGN light curves, and then propose a fast procedure to perform null-hypothesis testing for the cross-correlation of AGN light curves. We also present exemplary applications to AGN reverberation mapping data. This procedure requires prior determination of the auto-correlation functions of light curves, which can be obtained via model fitting. The long-standing issue regarding unbiasedly recovering the auto-correlation function remains unresolved when light-curve duration is comparable to the typical variation timescale, warranting further future investigation.
Read the full abstract ▾
Solar and Stellar Astrophysics
The Contribution of Starspots to the Lithium Spread in NGC 2264
Yan Luo, Gregory J. Herczeg, Min Fang et al. (+2 more)
Star clusters with ages of a few Myr have a previously unexplained dispersion in the lithium equivalent widths. In this work, we show that much of the lithium spread of the young cluster NGC 2264 can be attributed to the observational presence of starspots. We demonstrate that the equivalent width of Li I 6708 Angstrom changes with observed spot coverage, using a sample of 15 Weak-Lined T Tauri
Stars (WTTSs) with multi-epoch high-resolution ESPaDOnS spectra and photometry. To quantify the contribution of starspots, we construct an empirical two-component starspot model. When differences in visible spot coverage are taken into account, 68% of the WTTSs fall within the model-predicted EW(Li) dispersion for a range from 0-90% visible spot coverage. We find no correlation between the age spread or
gravity and Li I equivalent width in NGC 2264. Our results suggest that invoking starspots can explain much of the apparent lithium spread in NGC 2264 and reduces but does not fully eliminate the need to invoke rotation-driven lithium depletion or other non-standard explanations at such young ages. Future simultaneous measurements of lithium and beryllium in young
stars may provide an independent test of this scenario.
Read the full abstract ▾
All authors Yan Luo, Gregory J. Herczeg, Min Fang, Qinghui Sun, Xiaoting Fu
Instrumentation and Methods for Astrophysics
Investigation of magnetic-field effects on photomultiplier tubes for the first Large-Sized Telescope of the Cherenkov Telescope Array Observatory
Yukiho Kobayashi, Dai Tateishi, Yuji Sunada et al. (+28 more)
Photomultiplier tubes (PMTs) are widely used in imaging atmospheric Cherenkov
telescopes. Their response can depend on the
telescope pointing direction through changes in their orientation relative to the geomagnetic field. Such a dependence was indicated during the calibration campaign of the CTAO LST-1. In this work, the LST-1 calibration data are analyzed to quantify the gain dependence in terms of the geomagnetic field, and dedicated laboratory measurements are performed to test the hypothesis that the observed dependence originates from
magnetic-field effects. Both the on-site and laboratory measurements show a consistent dependence of the PMT gain on the
magnetic field, while the laboratory measurements further separate the effects on the gain and the excess noise factor. These results provide a clearer understanding of the gain variation observed in LST-1 in terms of
magnetic-field effects.
Read the full abstract ▾
All authors Yukiho Kobayashi, Dai Tateishi, Yuji Sunada, Takuto Kiyomoto, Nobuaki Sasaki, Kazuki Abe, Franca Cassol, Shuichi Gunji, Daniela Hadasch, Dirk Hoffmann, Julien Houles, Yusuke Inome, Hideaki Katagiri, Hidetoshi Kubo, Junko Kushida, Daniel Mazin, Masaya Mizote, Tsutomu Nagayoshi, Takeshi Nakamori, Kyoshi Nishijima, Seiya Nozaki, Hideyuki Ohoka, Akira Okumura, Reiko Orito, Takayuki Saito, Shunsuke Sakurai, Mitsunari Takahashi, Yukikatsu Terada, Masahiro Teshima, Tokonatsu Yamamoto, Tatsuo Yoshida
Cosmology and Nongalactic Astrophysics
Distinguishing Coupled Dark Matter Dark Energy from Kinematic Phantom Crossing
Samit Ganguly, Koushik Dutta and Goutam Manna
Recent measurements of
cosmic expansion have renewed interest in dark-energy scenarios in which the effective equation of state exhibits phantom-like
evolution and may cross $w=-1$. Such behavior, however, does not require a fundamental phantom field: in coupled dark-energy-dark-matter~(CDEDM) models, energy exchange between a canonical scalar field and cold dark matter, happens Lagrangian labels, can reproduce the same effective equation of state
evolution as that of phenomenological $w_0w_a$CDM model. We show that this microscopic interaction leaves distinctive, testable signatures in structure growth by forming a two-fluid system in which only cold dark matter feels the scalar-mediated fifth force (and an associated drag term), while baryons remain uncoupled. When combined with
neutrino-free streaming, this setup generates a characteristic coupling,
neutrino-mass degeneracy, whose leading scaling $\sum m_\nu \propto f_c^2 \alpha^2$ follows analytically from the two-fluid growth equations. Using DESI DR2 BAO, CMB distance information, ACT DR6
lensing,
redshift-space distortions, and three
supernova compilations, we find that this scaling is recovered for both exponential and inverse-power-law potentials. We further show that the dominant contribution to the growth response arises from the coupling-induced modification of the background
evolution, with the fifth force enhancing growth and the drag partially counteracting it. Finally, the interaction induces a running dark-matter mass, changing it at recombination by $4.3\%$–$5.5\%$, so CMB distance calculations must account for the evolving dark-matter density. These correlated growth and recombination effects provide a route to distinguish interaction-driven phantom crossing from purely kinematic dark-energy parametrizations.
Read the full abstract ▾
Solar and Stellar Astrophysics
Multi-thermal Structure of Solar Jets based on Combined EUV and Ha Observations
Lei Huang, Yang Guo, Zining Ren et al. (+1 more)
This study investigates the multi-thermal structure of solar jets by combining extreme ultra-violet (EUV) and Ha observations, addressing whether cool and hot components originate from the same jet, their morphological similarities and differences, and the role of mini-filaments. We analyze 70 jet events simultaneously observed by Atmospheric Imaging Assembly (AIA) and Chinese Ha Solar Explorer (CHASE) from 2023 May 25 to 2026 January 15. The events are classified into four types based on whether or not there are significant differences between the two wavebands in terms of length and width; nonlinear force-free field extrapolations are applied to examine
magnetic fields. We find that the cool and hot components correspond to different temperature parts of a unified jet, showing spatiotemporal coincidence and kinematic synchronization. Morphologically, 30% show no significant difference in length/width, 37% differ in one dimension, and 33% differ in both. About 80% involve mini-filament eruptions; jets with filaments more often exhibit morphological differences (filament non-expansion, hot shell thickness, insufficient kinetic energy, or material rarefaction). In contrast, jets without filaments tend to show consistent morphologies; when discrepancies occur, they are mainly linked to small
magnetic field
curvature, which reduces
magnetic tension and leads to less acceleration of cool material. These results highlight the complex interaction between thermal, dynamic, and
magnetic factors in shaping jet morphology.
Read the full abstract ▾
All authors Lei Huang, Yang Guo, Zining Ren, Mingde Ding