Instrumentation and Methods for Astrophysics
First Very Long Baseline Interferometry Fringe Detection at 690GHz
Ming-Tang Chen, Geoffrey B. Crew, Dan Bintley et al. (+42 more)
We report the first very long baseline interferometry (VLBI) experiment conducted in the 690 GHz atmospheric window. On 2024 November 21, observations with the Atacama Large Millimeter/submillimeter Array, the Atacama Pathfinder EXperiment (APEX), and the James Clerk Maxwell
Telescope (JCMT) were carried out using ALMA's newly developed Band 9 phasing capability. Fringes were detected on the ALMA-APEX baseline during a scan of the
quasar J0423-0120, with a signal-to-noise ratio of ~12 and useful fringe recovery over solution intervals of order tens of seconds, representing the highest-frequency ground-based VLBI fringe detection reported to date. No fringes were found on the ALMA-JCMT baseline, despite excellent weather conditions, consistent with sensitivity predictions and supporting baseline performance models. The ALMA Phasing System maintained stable phasing at Band 9 for ~1-2 minutes before gradually degrading, indicating limitations under these observing conditions. Our analysis shows that, under excellent weather conditions, 690 GHz VLBI can still support fringe recovery over short solution intervals, despite rapid atmospheric phase fluctuations at these frequencies. This work validated key elements of near-terahertz VLBI operation and establishes a technical foundation for routine observations in the 690 GHz atmospheric window.
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All authors Ming-Tang Chen, Geoffrey B. Crew, Dan Bintley, Alan Roy, Keiichi Asada, Johnson Han, Kuan-Yu Liu, Chin-Shin Chang, Andrea McClöskey, Yiqing Song, Vincent Fish, Michael Lindqvist, Satoki Matsushita, Lynn D. Matthews, Hugo Messias, Jan F. Wagner, Ue-Li Pen, Derek Kubo, Teddy Huang, Philippe Raffin, Chih-Wei L. Huang, Pierre Martin-Cocher, Geoffrey C. Bower, Patrick Koch, Lisa Kewley, Timothy Norton, Nimesh Patel, Paul T. P. Ho, Per Friberg, Izumi Mizuno, Akil Marshall, Andrey M. Baryshev, Heino Falcke, Thomas Greve, Jacques Lepine, Manuel Fernández López, Silvina Cichowolski, Carlos Valotto, Ciriaco Goddi, Guillermo Giménez de Castro, Fátima Salete Correra, Marianne Vestergaard, Jes Kristian Jørgensen, Martin E. Pessah, Roman Gold
Astrophysics of Galaxies
A Theoretical Study of the Stellar Parameters and Surface Nucleosynthesis of the Extremely Metal-Poor RGB Giant BD$-18^{\circ}$5550 - Part I: Effects of $\alpha$-enhancement and Internal Mixing
Mrinmay Medhi, Upakul Mahanta, Swapnajyoti Sarma et al. (+1 more)
We present a detailed stellar
evolution study of BD$-18^{\circ}$5550, an extremely metal-poor red giant
star in the Galactic
halo. Such
stars are among the oldest known objects and preserve chemical signatures of the earliest stages of Galactic history. BD$-18^{\circ}$5550 exhibits $\alpha$-enhancement, $\rm[\alpha/Fe]=+0.4$, typical of Population II
halo stars, with enhanced abundances of oxygen, magnesium, and other $\alpha$-elements relative to iron. Using the MESA stellar
evolution code, we perform the first direct determination of its mass, age, radius, and luminosity by simultaneously fitting eight observed stellar properties and multiple chemical abundance ratios. Our analysis yields a current mass of $\rm M=0.76,M_{\odot}$, radius of $R=38.4,R_{\odot}$, luminosity of $\log L=2.8,L_{\odot}$, and an age of $t=11.87$ Gyr, with a 7-fold improvement in age precision. The model reproduces all observed constraints, supporting our treatment of stellar physics, nuclear reactions, and internal mixing. We further investigate the predicted surface chemical composition up to iron and compare it with observations. The surface abundances of elements up to iron remain essentially unchanged throughout the
evolution, while nitrogen shows gradual enrichment, indicating the onset of mixing processes at intermediate RGB stages. The preservation of the other surface abundances provides a valuable window into the chemical conditions of the early Galactic environment. Our results establish BD$-18^{\circ}$5550 as a
benchmark star for constraining stellar
evolution and early Galactic chemical
evolution. Its derived age places it among the oldest
stars in the Milky Way, providing important constraints on the epoch of early
star formation and the initial assembly and
evolution of our
Galaxy.
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All authors Mrinmay Medhi, Upakul Mahanta, Swapnajyoti Sarma, Apurba Talukdar
Solar and Stellar Astrophysics
Studies of Two Post Common Envelope Binary Stars
Chris Koen and Alexei Kniazev
New time series photometry of the short period ($P<0.2$~d) binary
stars ZTF~J032906.36+070408.3 (ZTF~0329) and ATO~J090.7238+00.5996 (ATL~0602) is presented. The primary (hotter)
stars in both systems are white dwarfs, while the cooler
stars are M dwarfs. Archival photometry and new and archival spectra are used to derive the temperatures of the components in the two binaries. Both are single-lined binaries. Velocity curves are fitted to radial velocity measurements of the red dwarfs and used to place lower limits on the masses of the white dwarfs. New and archival time series photometry show
evolution in the shapes of the light curves of both
stars. Spectra of ZTF~0329 show an excess of radiation in the $R_C$ band which is ascribed to electron cyclotron radiation, suggesting that the
star is a low
accretion rate polar. Satisfactory model fits to the multi-filter light curves of ATL~0602 require the presence of cool spots on the red component of the binary. The latter
star exhibits a variety of velocities associated with Balmer and Ca~II emission lines within individual spectra.
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Instrumentation and Methods for Astrophysics · Cross-listed from physics.ins-det
Operation of a negative ion gas time projection chamber without electronegative fill gases
Lachlan J. McKie, Lindsey J. Bignell, Nicholas Adams et al. (+3 more)
The high fidelity reconstruction of particle tracks in micropatterned gaseous time projection chambers renders this technology ideal for future rare-event searches, including direction-sensitive dark matter experiments. Large drift distances are typically required for such experiments, so that the overall spatial resolution is limited by
diffusion. Negative ion drift exhibits lower
diffusion than electron drift and is thus an attractive option for realising a large-scale detector. The use of electronegative gases to create negative ions introduces technical challenges, most notably a reduction in gain when compared to conventional gas mixtures. In this study, we demonstrate a new method for negative ion generation via dissociative electron attachment using the conventional molecular fill gas CF$_4$. Our optical measurements of negative ion drift indicate electron attachment lengths of $<$1 mm and comparable gain to electron avalanches. The individual negative ion avalanches were also time-resolved, allowing the number of ions reaching the readout to be counted. We measure an improved energy resolution by single ion counting, relative to an integrated electron avalanche signal measured under identical gain conditions.
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All authors Lachlan J. McKie, Lindsey J. Bignell, Nicholas Adams, Victoria U. Bashu, Ferdos Dastgiri, Gregory J. Lane
Solar and Stellar Astrophysics
Validity of the CRD limit for modeling scattering polarization in the photospheric Sr I 4607 Å line
Simone Riva, Gioele Janett, Franziska Zeuner et al. (+3 more)
Context. Scattering polarization in the Sr I 4607 Å line is a key diagnostic for small-scale, unresolved
magnetic fields in the quiet solar photosphere, inaccessible to Zeeman-based techniques. The complete frequency redistribution (CRD) limit is commonly used to model this line, but its validity and impact on
magnetic sensitivity have not been systematically investigated. This is timely given new facilities observing this line with unprecedented accuracy, and future synoptic programs targeting long-term quiet-Sun magnetism. Aims. We assess the CRD limit against the general partial frequency redistribution (PRD) description of scattering for the Sr I 4607 Å polarization, focusing on its
magnetic sensitivity via the Hanle effect. Methods. We solved the non-LTE radiative transfer problem for polarized radiation in a semi-empirical 1D plane-parallel static atmosphere, with CRD and PRD scattering, across
magnetic field configurations relevant for Hanle diagnostics. Results. For small-scale unresolved fields, where the field acts only via Hanle depolarization of Q/I, CRD and PRD emergent profiles and Hanle sensitivity are essentially identical. For deterministic fields, CRD remains accurate when polarization signals exceed about 0.3%; for weaker signals, PRD effects can appreciably affect the emergent profiles. Conclusions. CRD is adequate for modeling Sr I 4607 Å scattering polarization in the vast majority of observationally relevant cases; PRD effects matter only for weak polarization signals.
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All authors Simone Riva, Gioele Janett, Franziska Zeuner, Luca Belluzzi, Fabio Riva, Pietro Benedusi
Instrumentation and Methods for Astrophysics · Cross-listed from gr-qc
Clock-noise propagation and calibration for phase-locking configurations in space-based gravitational-wave detectors
Pan-Pan Wang and Cheng-Gang Shao
In space-based gravitational-wave detectors,
laser phase locking transfers the phase of weak received light to a local
laser and maintains the interspacecraft heterodyne frequencies within the phasemeter bandwidth. Fluctuations of the onboard ultrastable oscillators introduce clock noise into these heterodyne phase measurements, requiring additional calibration in time-delay interferometry (TDI). Existing formulations based on six independently formed one-way measurements do not explicitly describe the common-reference clock structure of a master–slave phase-locking configuration. In this work, we formulate clock-noise propagation and calibration directly for this configuration. Starting from carrier and sideband readouts, we derive the clock-noise couplings and construct an ordered sideband-calibration rule. The rule retains noncommuting delays and applies to two-branch TDI combinations satisfying propagation and clock-coefficient closure. For mutually independent onboard clocks with identical fractional-frequency noise spectra, we compare matched realizations with and without phase locking. In the adopted frozen equal-arm model, 45 second-generation combinations with up to 16 links considered here have smaller clock-noise residuals in the phase-locking realization throughout 0.1–10~mHz, before final clock calibration. Numerical simulations of two representative 16-link combinations reproduce the analytical spectra and verify the predicted reduction and calibration. These results show that the phase-locking realizations reduce the clock-noise contribution before final calibration, while the cancellation of master-
laser phase noise still relies on TDI.
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Earth and Planetary Astrophysics
Hybrid Spin-Orbit Tomography for Earth-like Planets: Simultaneous Mapping of Static Surfaces and Dynamic Clouds from Multicolor Light Curves
Atsuki Kuwata and Hajime Kawahara
Photometric variability of directly imaged
exoplanets encodes information on both persistent surface features and time-variable phenomena such as clouds. We present Hybrid
Spin-Orbit
Tomography, a method that simultaneously retrieves multiple static components and a single dynamic component, together with their reflection spectra, from multiband photometric variability. The method integrates spectral unmixing and dynamic
spin-orbit
tomography by introducing a time-dependent component into the forward model. We employ sparse regularization for static surface distributions, volume regularization for reflection spectra, and a Kronecker-sum kernel regularization for the dynamic component. Applying the method to a toy Earth model, we successfully recover static surface distributions together with a single time-dependent cloud component. Furthermore, we apply the method to DSCOVR/EPIC observations of Earth and retrieve a dynamic component consistent with real cloud distributions, together with components broadly interpretable as oceans, vegetation, and land surfaces. Relative to static
spin-orbit unmixing, the hybrid model substantially reduces the residual scatter of the multiband light curves, demonstrating that explicit treatment of dynamic components improves global mapping from color variability. These results provide a step toward the simultaneous
retrieval of static and dynamic planetary components, while highlighting the need for more physical cloud-surface masking models and uncertainty quantification.
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Solar and Stellar Astrophysics
The changing optical and X-ray emission of the dormant $\gamma$ Cas star HD 45314
G. Rauw, Y. Nazé, E. Bryssinck et al. (+25 more)
$\gamma$ Cas
stars are Oe/Be
stars that exhibit bright and hard X-ray emission. HD45314 belonged to this category, but lost its $\gamma$ Cas characteristics as its circumstellar disc started to fade away. The
star was monitored in optical spectroscopy, optical photometry, and X-ray spectroscopy to follow its variability on timescales of hours to years. Time series of magnitudes, colours, line equivalent widths and violet over red peak intensity ratios were analysed with
Fourier methods to uncover possible periodicities. For five years, HD45314 exhibited oscillations of its magnitude and line strengths on a timescale of 230 d. It then declined towards a nearly disc-free stage and is now slowly rebuilding its disc. During these phases, the violet over red peak intensity ratio exhibited a modulation on a timescale of about 1190 d. Over the whole campaign, prominent short-term photometric variations, notably at a frequency of 3.369 d$^{-1}$, were probably due to $\beta$ Cep-type pulsations. The amplitude of these pulsations was stronger during phases of overall brightness changes. In parallel, the X-ray spectrum switched to a low state at the onset of the oscillation phase and has remained in this low state since then. Some residual hard emission is nonetheless observed. HD45314's long-term optical variations bear resemblance with the predictions of smooth particle hydrodynamics calculations, although a close look does reveal some inconsistencies. Unlike some other $\gamma$ Cas
stars, where the X-ray emission remained nearly constant despite major changes of the circumstellar disc, HD45314's X-ray properties changed dramatically as the disc begun to dissipate. These differences might arise from a wider orbital separation between the Oe
star and its putative white dwarf companion or from the ablation of the disc by the radiation field of the Oe
star.
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All authors G. Rauw, Y. Nazé, E. Bryssinck, W. Vollmann, J. Guarro Fló, X. Dupont, M.A. Smith, C. Motch, G.W. Henry, J. Robrade, A. de Bruin, S. Charbonnel, A. Favaro, P. Fricker, O. Garde, O. Gayrard, S. Güssregen, F. Houpert, M. Larsson, R. Leadbeater, V. Lecocq, P. Le Dû, T. Lester, L. Mulato, T. Petit, R. Pomillo, O. Thizy, F. Weil
Solar and Stellar Astrophysics
Connecting Dynamo Theory with DNS Data: A Computational Analysis of $\alpha$ and $\beta$ effects
Kiwan Park
We investigate the influence of current helicity on the turbulent
magnetic diffusivity $\beta$ using three complementary derivations of the $\alpha$ and $\beta$ coefficients, based on the large-scale
magnetic field $\overline{\mathbf{B}}$, the turbulent velocity $\mathbf{u}$, and the turbulent
magnetic field $\mathbf{b}$. Applying these coefficients to raw DNS data, we reconstruct $\overline{\mathbf{B}}$ and compare the results with the original simulations. In the kinematic regime all models agree well with the DNS data. In the nonlinear regime, however, $\beta_{\mathrm{vv-vw}}$ alone produces unbounded growth of $\overline{\mathbf{B}}$. Including the contribution from turbulent
magnetic fields ($\beta_{\mathrm{bb+jb}}$) suppresses this unphysical growth and restores agreement with the DNS results. We find that kinetic helicity drives $\beta$ more negative, while current helicity shifts it back toward zero. Weighted combinations of the coefficients further show that the $\beta$ effect dominates the
evolution of $\overline{\mathbf{B}}$ throughout, whereas the $\alpha$ effect becomes important mainly for sustaining the field in the nonlinear regime. The corresponding IDL analysis scripts are provided to facilitate practical implementation of the theoretical models.
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Astrophysics of Galaxies
Tracing M22's origins: Spatial and chemical constraints on its formation history
Emanuele Dondoglio, Antonino P. Milone, Randa Asa'd et al. (+9 more)
Globular clusters (GCs) are well known to host stellar populations characterized by light-element variations. A subset of Galactic GCs, beyond such 'canonical' populations, contains an additional group enriched in iron, s-process elements, and total C+N+O abundance (i.e., the anomalous
stars). We combine multi-facility photometry with APOGEE spectroscopy to investigate the spatial distribution, chemical properties, and formation history of the stellar populations in M22, with particular focus on its anomalous component. We trace the canonical and anomalous populations, together with their subpopulations, from the cluster center out to eight half-mass radii. The anomalous population becomes increasingly dominant in the outermost regions, whereas no significant radial gradients are detected among its subpopulations. Our chemical analysis reveals light-element anticorrelations within both the canonical and anomalous components, although the latter are shifted toward higher C, N, and Al abundances. For the first time, we show that the Fe, s-process, and C+N+O enhancements among anomalous
stars are not uniform but correlate with their light-element composition: the most chemically extreme anomalous
stars are also the most Fe-, Ce-rich, and C+N+O-poor. We identify a distinct red overdensity on the horizontal branch, likely populated by the most He-poor
stars, and tentatively associate the extreme horizontal branch with the most chemically enriched anomalous population. These observations are difficult to reconcile with M22 being a merger between two GCs. Instead, they qualitatively favor a self-enrichment scenario regulated by dilution, similar to that recently proposed for $\omega$Centauri, with their close chemical correspondence suggesting that they experienced analogous formation histories.
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All authors Emanuele Dondoglio, Antonino P. Milone, Randa Asa'd, Anna F. Marino, Alessandra Mastrobuono-Battisti, Fabrizio Muratore, Tuila Ziliotto, Emanuele Bortolan, Giacomo Cordoni, Maria Vittoria Legnardi, Edoardo P. Lagioia, Marco Tailo
High Energy Astrophysical Phenomena
1LHAASO J1852+0050u: GeV-100TeV Gamma-ray emission Powered by Star-forming Region?
The LHAASO Collaboration
Star-forming regions (SFRs), including HII regions, have recently attracted significant
attention as potential sites of particle acceleration capable of producing PeV
cosmic rays, i.e. as potential Galactic PeVatrons. Yet, SFRs known as candidate PeVatrons are still very rare. Here we report a highly likely physical association between the UHE gamma-ray source 1LHAASO J1852+0050u and coincident
star-forming regions. Using $\sim$4 years of LHAASO data, the extended source 1LHAASO J1852+0050u (called J1852 in this study) was reanalyzed with a significance of $\sim$13$\sigma$ and 39%-containment radius of 0.35$\deg$. This extended source projectively covers dozens of HII regions and an energetic
pulsar PSR J1853+0056. We reanalyzed $\sim$16 years of Fermi-LAT data and found a GeV source (named SrcAG) coincident with the LHAASO source J1852. The CO-line observation shows a molecular clump which coincides with the gamma-ray sources and is related with the ultra-compact HII region G34.26+0.15 at the distance of $\sim$3.3 kpc. Fitting to the spectral energy distribution indicates that PSR J1853+0056 cannot afford the observed gamma-ray flux either for J1852 or SrcAG. Although the contribution from hidden
pulsars to the gamma-ray emission could not be excluded, it is most likely that the GeV-100TeV gamma-ray emission is dominantly powered by SFR through p-p hadronic interaction between the
protons accelerated in the SFR and MCs: the GeV emission is ascribed to the
protons accelerated by protostars' activities, while the TeV emission ascribed to the
protons accelerated by massive
stars in the SFR.
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Solar and Stellar Astrophysics
Automated Detection of Double-Lined Spectroscopic Binaries in High-Resolution Spectra and a Probabilistic Analysis of Stellar Multiplicity
William B. Salazar, Steven Giacalone and Andrew W. Howard
The characterization of Sun-like
stars, including determining whether those
stars are single or have stellar companions, has become increasingly important for missions seeking
planets beyond the Solar System. With upcoming missions like the Habitable Worlds Observatory (HWO) on the horizon, vetting
stars for binarity and confirming potential targets as viable is essential precursor science. In this paper, we present an automated
algorithm that searches for double-lined spectroscopic binaries (SB2s) in high-resolution spectra. Using MOLUSC, we simulate realistic stellar populations to quantify the capability of
algorithm for detecting stellar companions around nearby
stars, with potential applications to HWO target
stars and Gaia DR4
planet-host candidates. In addition, we explore how the detection rate is influenced by complementary observations like high-resolution adaptive optics imaging and time-series radial velocities. We find that our SB2 detection
algorithm alone can rule out 46.1% of stellar-mass companions. High-resolution adaptive optics alone rules out 79.6% of stellar companions. Radial velocity surveys alone ruled out 98.4% and 98.7% for 5-year and 10-year surveys, respectively. When all three methods are combined, the probability of a typical nearby
star having a stellar companion is <1%. The combination of the methods allows us to better understand and resolve target lists for future surveys.
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Astrophysics of Galaxies
CROCODILE-SIDM: Tidal Formation of Dark Matter-Deficient Galaxies as a Test Case
Kenji Kihara, Kentaro Nagamine, Lissandre Bourrat et al. (+3 more)
We introduce CROCODILE-SIDM, a framework for treating self-interacting dark matter (SIDM) with the $N$-body part of GADGET4-Osaka code, as part of CROCODILE simulation family. As a test case, we investigate the impact of SIDM on the tidal formation of dark matter-deficient
galaxies (DMDGs) with velocity-dependent cross-section models. We demonstrate that our implementation reproduces the analytic scattering rate in isolated
halos. Including dynamical friction self-consistently, we evolve a dwarf satellite with $M_*=2\times10^8\,\mathrm{M}_\odot$ in a $\sim10^{11}\,\mathrm{M}_\odot$
halo on a decaying orbit around a massive host, comparing CDM with four SIDM cross sections for two initial satellite density profiles: a cuspy Navarro–Frenk–White (NFW) profile and a cored Burkert profile. We find that self-interactions primarily regulate the amount of DM retained between pericentric passages, and that the sign of this effect depends on the initial profile: a larger cross section retains more DM for the Burkert initial condition but less DM for the NFW initial condition. We show that this opposing behavior reflects the direction of SIDM heat conduction, which is set by the
halo's evolutionary state at infall. Core formation in the cuspy profile assists DM stripping, whereas tidally accelerated gravothermal contraction in the cored profile suppresses tidal mass loss. Consequently, SIDM can either assist or hinder DMDG formation, depending on the satellite's inner structure, making DMDGs a potential probe of SIDM cross section.
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All authors Kenji Kihara, Kentaro Nagamine, Lissandre Bourrat, Leonard Romano, Yuri Oku, Daisuke Toyouchi
High Energy Astrophysical Phenomena
Aarmed with Data: Bumps, Outflows, and Disk-like Emission in TDE 2025aarm
Aysha Aamer, Kate D. Alexander, Charlotte R. Angus et al. (+43 more)
The origin of the optical emission in tidal disruption events (TDEs) remains one of the major outstanding questions in the field, in part due to the limited number of nearby events with high-cadence monitoring to track their evolving photometric and spectroscopic properties. We present multi-wavelength observations of the nearby ($z=0.01368$) TDE\,2025aarm, including near-daily spectroscopic coverage prior to the optical peak. Its proximity makes it one of the brightest TDEs discovered, reaching a peak magnitude of $m_r\sim15.5$ ($M_r\sim-18$). The light curve deviates from a smooth
evolution, exhibiting multiple rebrightening episodes visible in both the individual filter light curves and the bolometric luminosity. Blackbody modelling reveals that these rebrightenings are associated with an increase in temperature of $> 5,000-10,000$\,K, while the inferred photospheric radius remains approximately constant. Simultaneously, the H$\alpha$ line not only increases in blueshift but also broadens, suggesting a link between the continuum rebrightenings to changes in the kinematics of the line-forming gas. We identify a persistent absorption component at $\sim-3900$\,km\,s$^{-1}$ in multiple Balmer lines, providing further evidence for outflowing material. The H$\alpha$ profile also exhibits excess flux compared to a Gaussian on both sides of the line, inconsistent with simple scattering-dominated outflow models. Disk-profile modelling provides evidence for the emergence of a disk-like component least $\sim20$ days after peak, with substantial changes in the disk properties between $\sim50$ and 60 days. These observations highlight the complexity of TDE emission processes and demonstrate how dense multi-wavelength monitoring can disentangle the roles of
accretion, reprocessing, and outflows in shaping TDE emission.
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All authors Aysha Aamer, Kate D. Alexander, Charlotte R. Angus, Panos Charalampopoulos, Megan Newsome, Iair Arcavi, Giorgos Leloudas, Matt Nicholl, Jennifer Andrews, Katie Auchettl, Thomas de Boer, K. Azalee Bostroem, Y.-Z. Cai, Kenneth C. Chambers, Collin T. Christy, Sara Faris, Noah Franz, Sebastian Gomez, Maider González-Bañuelos, Mariusz Gromadzki, Paul J. Groot, Claudia Gutiérrez, Brian Hsu, Mark Huber, Thomas L. Killestein, Chien-Cheng Lin, Thomas B. Lowe, Peter Lundqvist, Dylan Magill, Seppo Mattila, Francesca Onori, Gregory S. H. Paek, Jeniveve Pearson, Miika Pursiainen, Niko Pyykkinen, Conor Ransome, Sara Romagnoli, Jennifer Shi, Manisha Shrestha, Nathan Smith, Maximilian Stritzinger, Bhagya Subrayan, Richard Wainscoat, Ziyang Y. Wang, Simon de Wet, Hannah Wichern
Solar and Stellar Astrophysics
The FU Ori outburst of PR Ori B
Carlos Contreras Pena, Zsofia Nagy, Gregory Herczeg et al. (+42 more)
We report the discovery of a nearby FU Ori-type outburst (FUor), PR Ori B, in the L1641 cluster of the Orion
star-forming region. The high-amplitude variability was first identified in the NEOWISE (3-5 $\mu$m) photometry of the unresolved PR Ori binary system. Long-term, resolved optical photometric monitoring demonstrates that PR Ori B is the driver of a $\Delta G=5~$mag outburst, while PR Ori A has remained constant over the last 20 years. The near-IR spectrum of PR Ori B changes from a late K-type spectral type during quiescence to a viscously heated disk during outburst, including deep absorption in $^{12}$CO and H$_2$O bands. The optical spectrum also exhibits features that are commonly associated with FUors, including P Cygni profiles in Na I D lines and absorption in the Ca II infrared triplet. The luminosity of the outburst (L$_{acc}\sim$30–40 L$_\odot$) is similar to that commonly observed in FUors. The comparison of Spitzer/IRS and VLT/VISIR spectroscopy shows some evidence of silicate crystallisation during the outburst. PR Ori B is one of the closest and brightest FUors discovered over the last few years, only one magnitude fainter than the archetype of the class FU Ori. The proximity and brightness will allow for future high angular resolution observations to probe the physics of the inner disk and to evaluate changes in the disk due to the increased luminosity.
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All authors Carlos Contreras Pena, Zsofia Nagy, Gregory Herczeg, Jeong-Eun Lee, Agnes Kospal, Peter Abraham, Doug Johnstone, Bo Reipurth, Chul-Hwan Kim, Hyun-Il Sung, Yihan Li, Jiaze Wang, Rui Wu, Foteini Lykou, Mizna Ashraf, John Bally, Fernando Cruz-Saenz de Miera, Min Fang, Eleonora Fiorellino, Christoffer Fremling, Teresa Giannini, Jessy Jose, Mansi Kasliwal, Maria Kun, Ho-Gyu Lee, Michal Siwak, Mate Szilagyi, Sung-Yong Yoon, Zsofia Bora, Borbala Cseh, Agoston Horti-David, Zsoka Horvath, Andras Peter Joo, Csilla Kalup, Klara Lelkes, Andras Pal, Zsolt Regaly, Krisztian Sarneczky, Balint Seli, Adam Sodor, Norton O. Szabo, Zsofia Szabo, Robert Szakats, Nora Takacs, Miguel Vioque
High Energy Astrophysical Phenomena
The Evolution of Thermal and Non-thermal Emission Components in GRB 250920C
Jia-Ming Chen, Ke-Rui Zhu, Shan Chang et al. (+5 more)
We present a temporal and time-resolved spectral analysis of GRB 250920C using Fermi/GBM and Swift/BAT data. The
prompt emission consists of two distinct episodes, EI and EII, separated by a significant quiescent interval. We perform
Bayesian spectral fitting with empirical, thermal, composite, and physical synchrotron models. In EI, the spectra show clear evidence for an additional thermal component. The BB+PL model is preferred in most bright time bins, and joint Fermi/GBM+Swift/BAT fits further support the presence of this component. The blackbody temperature generally decreases with time, the blackbody flux follows the pulse profile, and the thermal flux fraction remains high. Fireball-parameter estimates give a photospheric Lorentz factor of a few hundred and an initial radius of $r_{0}\sim10^{9}$–$10^{10}$ cm, with $1+\sigma_{0}$ of order unity and $\eta\gg1$, supporting a thermally dominated baryonic outflow. In contrast, EII is dominated by non-thermal emission. Its low-energy
photon indices do not significantly exceed the synchrotron line of death, and the spectra are well described by fast-cooling synchrotron radiation in a decaying
magnetic field. The magnetization constraint gives $\sigma_{\min}\sim1.1$–$4.3$. Since these values exceed unity, they suggest that EII may be Poynting-flux dominated. These results therefore suggest a possible transition in GRB 250920C from a fireball-dominated EI phase to a Poynting-flux-dominated EII phase.
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All authors Jia-Ming Chen, Ke-Rui Zhu, Shan Chang, Dan Zhu, Yu-Lu Gong, Zhao-Yang Peng, Yong-Gang Zheng, Li Zhang
Cosmology and Nongalactic Astrophysics
A universal connection between lens density profiles and low-frequency wave optics in gravitational-wave lensing
So Tanaka and Teruaki Suyama
We investigate the low-frequency behavior of the amplification factor in gravitational
lensing and explore how it encodes information about the density profile of the
lensing object. We derive the low-frequency expansion of the amplification factor under the Born approximation for a broad class of projected density profiles. For spherically symmetric profiles that decay faster than any power law at large distances, we derive a systematic expansion of the amplification factor in powers of frequency, with the logarithmic dependence appearing only in the leading term, and show that each expansion coefficient is determined by a finite set of moments of the density profile. We then extend the analysis to profiles with power-law tails and demonstrate that such profiles induce additional non-analytic frequency dependences, including fractional powers and logarithmic terms, which directly reflect the asymptotic behavior of the density distribution. Furthermore, we investigate the effects of non-sphericity and show that contributions from the quadrupole moment appear only as higher-order corrections relative to the spherically symmetric component in the low-frequency regime. Finally, we investigate the validity of the Born approximation in the low-frequency expansion. We derive a criterion for the maximum order of the low-frequency expansion up to which the Born approximation remains dominant over the post-Born corrections.
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High Energy Astrophysical Phenomena
Searching for Type Ia Supernovae in the Dark Energy Spectroscopic Instrument
Xiaoyu Zhuang, Song Ran, Dezheng Meng et al. (+9 more)
With the development of large-scale photometric surveys, an increasing number of
supernova candidates are being discovered, leading to a rapidly growing demand for
supernova spectra. In addition to equipping photometric surveys with follow-up spectroscopic facilities, archival spectra from large multi-object spectroscopic surveys can be mined to provide spectroscopic classifications for candidates and to find
supernovae missed by previous surveys. In this work, we combine Principal Component Analysis (PCA), the Local Outlier Factor (LOF)
algorithm, and the
supernova classification tool SNID to search for Type Ia
supernovae among 1,757,303
galaxy spectra from the Dark Energy Spectroscopic Instrument (DESI) Data Release 1 (DR1). We finally obtain 247 Type Ia
supernovae and 17
supernovae of other types. Among these, 202
supernovae lack classification records in the Transient Name Server (TNS) and represent newly identified SNe. These results demonstrate the potential of multi-object spectroscopic surveys to supplement
supernova samples, particularly for transients missed by traditional photometric surveys.
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All authors Xiaoyu Zhuang, Song Ran, Dezheng Meng, Weiyu Ding, Ranfang Zheng, Yao Yao, Zheyu Lin, Bingxue Fu, Fujia Li, Zelin Xu, Jie Song, Xu Kong
High Energy Astrophysical Phenomena
Pulse Signal Simulation of Pulsars
Jalormi Brahmachari and Mayuresh Surnis
The present thesis is a work in progress on improving the simulation of integrated pulse profiles of
pulsars.
Pulsars, highly magnetized rotating
neutron stars, serve as precise
cosmic clocks useful for studying
gravity and the interstellar medium. Although periodic pulses from many
pulsars are observed and modeled at differ- ent
radio frequencies, a robust realistic simulation of their profiles utilizing their parameters remain underdeveloped. The present study focuses on developing a physically consistent model to reproduce observed pulse shapes across multiple frequencies. This study will be useful in coherently understanding the various as- pects of the
pulsar emission mechanism. These integrated pulse profiles are the time-averaged properties of
pulsar emission and are obtained after averaging indi- vidual pulses over a few thousand rotations. Observed to be highly stable, these are indicative of the global properties of the
pulsar magnetosphere. By refining simulation techniques and incorporating the propagation effects of the interstellar medium, this work will prove to be helpful in generating synthetic, yet realistic models. The results are expected to contribute to the interpretation of observa- tional data and to the development of improved timing and emission models for
pulsars
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Astrophysics of Galaxies
High Resolution Spectroscopic Follow-up Observation Results for 13 EMP Candidates Selected by Narrow-band Photometry
Huiling Chen, Yang Huang, Huawei Zhang et al. (+1 more)
Extremely metal-poor (EMP; [Fe/H] < -3.0)
stars preserve key information about the earliest stages of Galactic chemical
evolution. Based on a training set of spectroscopic
metallicities, we constructed catalogs of more than 120,000 EMP candidates from large-scale narrow-band photometric surveys. To validate this approach, we obtained high-resolution CFHT/ESPaDOnS spectra for 13 candidates selected from the SkyMapper-based catalog. The follow-up observation confirms that the narrow-band photometric selection is effective in identifying very metal-poor
stars and retaining a substantial EMP fraction: four targets are confirmed as EMP
stars, and all targets remain very metal-poor with [Fe/H] < -2.4. The photometric
metallicities are systematically lower than the spectroscopic values by 0.44 dex, with a relatively small scatter of 0.19 dex, indicating a systematic offset in the photometric
metallicity scale that could be reduced through improved calibration. Abundances for more than 20 chemical species are derived, leading to the identification of a new potassium-enhanced r-II
star, J2001-1215. By combining chemical abundances with orbital properties, five
stars are found to be dynamically consistent with known Galactic substructures, including Gaia–Sausage–Enceladus, Thamnos, and Sequoia. These
stars provide high-resolution chemical measurements for the extremely metal-poor regime of these Galactic substructures. These results underscore the role of narrow-band photometry in efficiently selecting EMP candidates for targeted high-resolution spectroscopic follow-up, thereby enabling detailed chemical and dynamical studies of the early Milky Way.
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All authors Huiling Chen, Yang Huang, Huawei Zhang, Zhen Guo
Instrumentation and Methods for Astrophysics
A pilot study on the CSST astrometric capability: Detecting astrometric binaries with Gaia synergy via simulated data
Shangyu Wen, Shilong Liao, Zhaoxiang Qi et al. (+8 more)
Context. The China Space-station Survey
Telescope (CSST) will provide deep, wide-field epoch astrometry during its 10-year mission. Astrometric binary orbits constrain the masses of stellar and compact-object components. Orbital recovery depends on astrometric precision and temporal coverage. Combining CSST and Gaia data extends the baseline and improves binary detection. Aims. We evaluate CSST, Gaia, and joint astrometry for binary-candidate selection and 12-parameter (12p) orbit fitting at faint magnitudes ($g>17.8$). We also test how regular CSST cadences affect the yield of 12p fits satisfying our criteria. Methods. We constructed a mock catalog, simulated CSST and Gaia epoch astrometry, and fitted five-parameter (5p) single-
star models to derive astrometric diagnostics, proper-motion anomaly features, and observational-sampling features. A four-stage histogram-based gradient-boosting classifier used these features to select candidates for 12p orbit fitting and assessment. Results. On the independent test set, the classifier reaches a precision of 0.802 and a recall of 0.181 among eligible true binaries. In the scenario-specific fitted samples, joint astrometry raises the fiducial fraction from 6.76% for Gaia alone to 10.46%; for fitted binaries with $P_{\rm true}>15{\rm yr}$, it rises from 2.37% to 6.78%. The current CSST schedule yields few fiducial fits, while idealized regular cadences increase the yield mainly at $g\lesssim21$. Conclusions. In the simulation, joint CSST and Gaia epoch astrometry yields higher fractions of fitted unresolved binaries satisfying the stated criteria than Gaia-only solution. A practical strategy is to select candidates from 5p diagnostics and astrometric anomalies, obtain more regular CSST follow-up observations, and then fit 12p orbital models and apply the selection criteria.
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All authors Shangyu Wen, Shilong Liao, Zhaoxiang Qi, Zhensen Fu, Xiyan Peng, Ye Ding, Qiqi Wu, Qi Xu, Xun Sun, Keyu Zhu, Yong Yu
Solar and Stellar Astrophysics
Planetary Nebula Central Stars as Tracers of Planetary Nebula-Star Cluster Associations in the Galaxy
Vasiliki Fragkou, Luis Lomelí-Núñez, Dante Minniti et al. (+2 more)
Planetary nebulae (PNe) that are physically associated with
star clusters are rare but crucial for stellar
evolution studies because they allow their initial and final stellar properties to be determined independently, contributing to constraints on the initial-to-final-mass relation (IFMR), which traces stellar mass loss. Although the identification of such pairs is essential, most reported cases have been identified incidentally rather than through systematic searches. Here, we attempt to uncover new such associations in our
Galaxy employing literature PN central
stars (CSs) and
star cluster catalogues. Exploring relevant angular positions on the sky and kinematic Gaia DR3 data, we identify 38 candidate CS-cluster pairs. The components of eight of these pairs present consistent interstellar extinctions, and their CS properties are compatible with stellar
evolution models. Two of these candidate pairs are already reported in the literature as true associations. We evaluate separately the remaining six pairs using literature PN observational data, assessing the likelihood of each pair being a true association. The initial and final masses of our best candidates are mostly consistent with the latest IFMR predictions and confirmed cluster-PNe points. An additional 46 CS-cluster pairs have components with compatible angular positions but lack kinematic CS data and are thus presented separately. More data are needed for a precise estimation of the physical parameters of most of our candidates and to confirm these associations, which will be addressed in future studies.
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All authors Vasiliki Fragkou, Luis Lomelí-Núñez, Dante Minniti, Arianna Cortesi, Denise R. Gonçalves
Astrophysics of Galaxies
Time-Domain Dust Astrophysics. II. TransRAT: Time-Dependent Grain Alignment and Disruption by Cosmic Transients and Their Observational Signatures
Thiem Hoang
We introduce TransRAT, a self-consistent time-domain framework that follows the coupled dynamical response of dust to transient irradiation and predicts its observable signatures. We apply TransRAT to a Type~IIP
supernova illuminating a one-zone molecular cloud. Radiative heating raises the grain temperature, modifying the
magnetic susceptibility and Larmor precession, while the enhanced radiation field accelerates radiative precession and can switch the
alignment axis from the
magnetic field (B-RAT) to the radiation direction (k-RAT). Simultaneously, strong RATs align grains faster than gas randomization, extending fast
alignment to smaller grain sizes, and disrupt large grains through RAT disruption (RAT-D), irreversibly modifying the grain size distribution. As the transient fades, the
alignment axis returns to ${\bf B}$ at a rate controlled by the
magnetic susceptibility, whereas the enhanced aligned-grain population and RAT-D-modified grain size distribution can persist long after the radiation has faded- referred to as physical
memory effects. The time-dependent
evolution of grain
alignment and disruption produces distinctive observational signatures: a
flare in extinction and thermal dust polarization followed by a RAT-D-induced dip; a blueward shift of the polarization peak $\lambda_{\max}$; a polarization-angle rotation equal to the projected ${\bf B}$–${\bf k}$ separation ($45^{\circ}$ for our adopted geometry) when RAT-D removes large high-$J$ aligned grains and leaves low-$J$ grains aligned with kRAT followed by angle reverberation as
alignment returns to ${\bf B}$; and a non-monotonic
evolution of $R_V$. The persistent observational manifestations of the transient irradiation, including enhanced polarization, blueshifted $\lambda_{\max}$, modified $R_V$, and polarization-angle
evolution, constitute fossil imprints of past
cosmic transients.
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