Solar and Stellar Astrophysics · Cross-listed from hep-ph
Axions and the RR Lyrae Period-Luminosity Relation
Jeremy Sakstein and Djuna Croon
We investigate the impact of
axions on the period-luminosity relation (PLR) of RR Lyrae
stars. During the red giant branch phase, emission through the electron coupling cools the core, increasing its mass at ignition. The larger core produces more luminous horizontal-branch
stars, systematically shifting the zero point of the RR Lyrae PLR toward brighter magnitudes. We model the RR Lyrae population of the globular cluster M3 using stellar
evolution and pulsation calculations tailored to its age and composition, and compare the resulting synthetic $K_s$-band PLR with observations. For $\alpha_{26}\equiv 10^{26}g_{ae}^2/4\pi=0.5$, the
axion-induced shift in the predicted PLR is comparable to the current uncertainty in the absolute M3 zero-point calibration.
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Solar and Stellar Astrophysics · Cross-listed from cs.CV
Super-Resolution of Solar Magnetograms via Adaptive Stratified Ensemble Learning with Uncertainty Estimation
Sina Norouzi Kandalan, Haodi Jiang, Jason T. L. Wang et al. (+1 more)
Single-image super-resolution of Sun's photospheric magnetograms enables consistent analysis across heterogeneous space-based instruments and supports long-term studies of solar
magnetic field
evolution. We address the super-resolution task from SOHO/MDI (low-resolution) to SDO/HMI (high-resolution) line-of-sight (LOS) magnetograms using a modified RRDBNet architecture initialized by ESRGAN pretrained weights. Through systematic per-image diagnostic analysis, we identify image complexity as the dominant predictor of reconstruction errors. To exploit this finding, we introduce an adaptive stratified specialist ensemble (SSE) of three specialist networks with uncertainty estimation, where each specialist network is trained by images from three different complexity strata using a weighted random sampling strategy. During inference, a lightweight router based on input image statistics assigns each test image to the appropriate specialist network. Our experimental results demonstrate the good performance of the proposed ensemble and its superiority over closely related methods.
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All authors Sina Norouzi Kandalan, Haodi Jiang, Jason T. L. Wang, Qin Li
Solar and Stellar Astrophysics · Cross-listed from astro-ph.GA
Sequential Star-Formation and the Near-Infrared Stellar Populations within N159
Nolan Habel, E. Sabbi, Peter Zeidler et al. (+19 more)
We present the first results from a JWST/NIRCam study of the
star-forming region N159, one of the richest H II complexes in the Large Magellanic Cloud. This region stretches over $\sim$130 pc, and exemplifies large-scale sequential
star formation. We present photometric results of $>$300,000 point sources combining data from ten near-infrared JWST filters spanning 1-4.7 microns. We detect sources as faint as $\sim$27 magnitudes at F115W, corresponding to stellar masses reaching below $\sim$0.1 $M_{\odot}$. By constructing several color-magnitude and color-color diagrams, we separate young
stars from main-sequence and older
stars within N159, finding evidence for stellar populations younger than 0.5 Myr. Of the young population, we identify accreting, pre-main sequence
stars from their Paschen-$\alpha$ (Pa$\alpha$) excess and a population of sources bearing strong infrared (IR) excess, representing candidate young stellar objects (YSOs). Within this population, we identify a subpopulation of sources with H$_2$O ice absorption. The IR-excess-bearing YSO candidates correlate spatially with dust filaments and molecular gas demonstrating their embedded state. The distribution of stellar and candidate YSO populations across N159 reveal more evolved
star-forming populations in the N159E region and newer
star formation in the N159W region, supporting the sequential
star formation scenario for this region.
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All authors Nolan Habel, E. Sabbi, Peter Zeidler, Tuila Ziliotto, Laurie Chu Margaret Meixner, Guido De Marchi, O. C. Jones, Alec S. Hirschauer, Beena Meena, Jeroen Jaspers, Laura Lenkic, Remy Indebetouw, Karl D. Gordon, Burcu Gunay, Suzanne Madden, James Muzerolle Page, Omnarayani Nayak, Antonella Nota, Theo Oneill, Massimo Robberto, Tony Wong, Petia Yanchulova Mercia-Jones
Solar and Stellar Astrophysics · Cross-listed from astro-ph.GA
New Optical and Mid-Infrared RR Lyrae Period-Luminosity-Metallicity Relations for Precision Distances and Metallicity Distributions in the Magellanic Clouds
Clara E. Martínez-Vázquez, Joseph P. Mullen, Massimo Marengo et al. (+11 more)
RR Lyrae (RRL)
stars, thanks to the existence of their period-luminosity relations, have been widely used as primary standard candles within the Milky Way and the Local Group of
galaxies. We present in this work the latest empirical RRL period-luminosity-
metallicity (PLZ) and period-Wesenheit-
metallicity (PWZ) relations combining optical ($V, I$) and mid-infrared data ($W1$) using OGLE and WISE photometry, anchored to Gaia DR3 parallaxes. We calibrate these relations with the largest, most complete, and homogeneous catalog of Galactic
halo field RRL spectroscopic
metallicities. These new PLZ/PWZ relations provide distance measurements in remarkable agreement with those derived from eclipsing binaries in the Large and Small Magellanic Clouds (MC): $(m-M)_{0, LMC} = 18.47 \pm 0.07 (stat) \pm 0.05 (sys)$ mag and $(m-M)_{0, SMC} = 18.87 \pm 0.09 (stat) \pm 0.06 (sys)$ mag (within 1% and 10% of eclipsing binary distances, respectively). We have also re-calibrated photometric
metallicity relations to derive individual [Fe/H] abundances of LMC and SMC RRL
stars. This allowed us to investigate the
metallicity gradient of the MCs and discover two distinct populations of fundamental mode RRL
stars in the LMC (only one is instead found in the SMC). Our newly derived mid-infrared period-luminosity relations are poised to become an essential tool to derive precise distances of older stellar populations in the Local Group of
galaxies, and can easily be adapted to observations obtained in JWST NIRCam photometric bands.
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All authors Clara E. Martínez-Vázquez, Joseph P. Mullen, Massimo Marengo, Giuseppe Bono, Vittorio F. Braga, Santi Cassisi, Brian Chaboyer, Massimo Dall'Ora, Valentina D'Orazi, Michele Fabrizio, Giuliana Fiorentino, Matteo Monelli, Peter B. Stetson, Frédéric Thévenin
Solar and Stellar Astrophysics
A Multiband Catalog of Infrared-Excess Sources in the Vela-Carina Region: VVVX, DECaPS, and GLIMPSE
R. M. Torres, R. K. Saito, V. Fermiano et al. (+4 more)
Multiwavelength surveys of the Galactic midplane enable the identification of infrared-excess sources, signatures of circumstellar material, though high extinction and crowding hinder detection. We construct a homogeneous catalog of infrared-excess candidates in a $\sim$7.0 deg$^2$ field of the Vela-Carina region, characterizing their excess emission via spectral energy distribution (SED) analysis. We combine optical photometry from DECaPS, near-infrared photometry from VVVX, and mid-infrared photometry from Spitzer/GLIMPSE using hierarchical positional cross-matching. Candidates are selected via photometric quality and MIR color diagnostics, and their SEDs are analyzed with VOSA using theoretical atmosphere model grids. Photogeometric distances are adopted, while Gaia DR3 and NEOWISE variability provide complementary diagnostics. From the matched 249,719-source VVVX-GLIMPSE-DECaPS catalog, we identify 1,512 MIR-excess objects, of which 191 have complete 12-band photometry with S/N > 10, enabling detailed SED analysis. Photogeometric distances are statistically consistent with
geometric distances for nearly the entire sample. SED analysis independently supports the MIR-excess nature of most sources, indicating emission beyond stellar photospheres. About 15% of sources are flagged variable by Gaia, while NEOWISE light curves reveal MIR variability of a few tenths of a magnitude. Comparisons with published YSO and variability-selected catalogs show limited overlap, particularly with variability-selected samples, indicating that MIR-excess selection complements other approaches to identifying candidate YSOs in the Vela-Carina region. The resulting catalog provides a well-defined MIR-excess sample with homogeneous multiband photometry, SED characterization, distances, and variability diagnostics, forming a foundation for future spectroscopic and time-domain studies.
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All authors R. M. Torres, R. K. Saito, V. Fermiano, P. Esteves, B. W. Borges, D. Quispe, D. Minniti
Solar and Stellar Astrophysics
Light-curve analysis of the classical nova YZ Ret: revisit with fully self-consistent nova outburst models
Izumi Hachisu and Mariko Kato
YZ Ret is a well observed nova from the first detection of an X-ray flash phase in classical novae until the end of a supersoft X-ray source phase. We have reanalyzed multiwavelength light curves of YZ Ret over the total duration of the outburst. Our fully self-consistent nova outburst model, a 1.25 $M_\odot$ white dwarf (WD) and a mass
accretion rate of $1\times 10^{-9} ~M_\odot$ yr$^{-1}$ on to the WD, reasonably reproduced $V$/$g$ light curves as well as the very early X-ray flash and late supersoft X-ray light curves. This model explains the emergence epoch of the GeV gamma-ray emission because a shock naturally arises far outside the nova (WD) photosphere just after the optical maximum. In our model, before optical maximum, later ejected matter has a smaller velocity than that of earlier ejecta and therefore the ejecta expands while, after optical maximum, later ejected matter has a larger velocity than that of earlier ejecta and collision with the earlier ejecta makes a shock.
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Solar and Stellar Astrophysics · Cross-listed from astro-ph.EP
M Dwarf Singles and Multis Have Dissimilar Metallicities Indicating Different Origins
Aida Behmard, Sheila Sagear, Yuxi Lu et al. (+3 more)
It is unclear if host
star metallicities differ between systems with one detected transiting
planet ("singles") or multiple detected transiting
planets ("multis") around FGK dwarfs. Here, we find strong evidence that they do for M dwarfs. We use a homogeneous sample of FGK and M dwarf chemical abundances to demonstrate that M dwarf multis are significantly more metal-poor than singles ($p$ = 0.00079), even when we only consider small (<4 $R_{\oplus}$)
planets ($p$ = 0.0013). This result emerges at the late-K to M dwarf transition. We observe that M dwarf multis become more metal-poor as a function of increasing
planet multiplicity. Additionally,
planets in singles have significantly higher eccentricities and shorter orbital periods compared to
planets in multis. We interpret these findings as evidence that M dwarf singles lead relatively active dynamical lives, and the different planetary architectures of singles and multis arise from distinct dynamics influenced by
metallicity. This may not occur in FGK systems because their more massive protoplanetary disks may supply enough
planet-forming material to instigate dynamics that lead to only one transiting
planet, even when the host
star metallicity is low. Another possibility is that multis are less compact around FGK dwarfs because they form from larger disks, which may often cause them to be observed as singles in transit data.
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All authors Aida Behmard, Sheila Sagear, Yuxi Lu, Romy Rodríguez Martínez, Adrian M. Price-Whelan, Soichiro Hattori
Solar and Stellar Astrophysics · Cross-listed from astro-ph.GA
N/O-enhanced chemical enrichment by massive stars: the interplay of optically-thick winds and rotation
Boyuan Liu, Michela Mapelli, Lumen Boco et al. (+1 more)
Recent JWST observations have revealed a sample of high-$z$
galaxies with highly enhanced N/O abundance ratios, $\log\rm (N/O)\gtrsim -1.1$. Strong optically-thick winds of rotating massive
stars going through the Wolf-Rayet (WR) phase provide a viable explanation for such N/O enhancements, supported by the direct spectroscopic WR signatures discovered in a few
galaxies. Such strong winds are also needed to reproduce the single WR
stars in the Small Magellanic Cloud (SMC). Here, we compute the metal yields of massive ($\sim 20-100\ \rm M_\odot$), metal-poor
stars using two sets of MESA single stellar
evolution models with and without optically-thick winds in a dense grid of
metallicities ($Z_\star\sim 0.001-0.0045$) and initial
spins ($\omega\equiv\Omega/\Omega_{\rm crit}\sim 0-0.7$). Considering an initial
spin distribution based on observations of O-type
stars in the SMC, we find that both sets produce strong N/O enhancements up to $\rm \log(N/O)\sim 0.1$ within a few Myr after a starburst. The models with optically-thick winds undergo a rapid transition from high N/O to the `normal' state of $\rm \log(N/O)\sim -1.5$ at $t\sim 3-4$ Myr driven by C/O-rich winds, while the transition is slower and weaker without optically-thick winds. The optically-thick-wind scenario can reproduce the nebular C, N, O, and He abundance patterns of three representative high-$z$
galaxies showing direct WR signatures: RXCJ2248-ID, Sunburst Arc, and MARTA 4327, with stellar
metallicities and ages similar to those inferred from SED-fitting. This can be interpreted as a coherent
evolution sequence captured before ($t\lesssim 3$ Myr), during ($t\sim 3-4$ Myr), and after ($t\gtrsim 5$ Myr) the transition. In contrast, the optically-thin-wind-only scenario ejects much less C and O via winds and cannot reproduce Sunburst Arc and MARTA 4327. The yields are available at https://zenodo.org/records/22897057.
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All authors Boyuan Liu, Michela Mapelli, Lumen Boco, Xihan Ji
Solar and Stellar Astrophysics · Cross-listed from astro-ph.HE
SN2025aico: An Interesting Case Of $^{56}$Ni Mixing, Ejecta Asymmetries, and Dust Formation in a Type IIb Supernova
Grace Davis, Kyle Medler, Chris Ashall et al. (+8 more)
Stripped-envelope
supernovae provide a window into how massive
stars lose their layers, mix radioactive material, produce dust, and explode asymmetrically. We present optical, near-infrared (NIR), and mid-infrared (MIR) observations of SN~2025aico, a Type~IIb
supernova in LEDA~35384. Our spectroscopic sequence, spanning $+1$ to $+167$ d after explosion, follows its
evolution from a photospheric phase exhibiting both hydrogen and helium features to prominent helium emission and, ultimately, nebular-phase ejecta. Using He I $1.083$ and $2.0581\,\mu$m transitions, we investigated the kinematics and geometry of the helium-rich material. Both transitions exhibit a three-phase, non-monotonic velocity
evolution: an initial rapid decline, a subsequent increase, and an eventual plateau. We interpret this behavior as evidence for limited outward mixing of $^{56}$Ni, such that radioactive energy deposition reaches the outer helium-rich ejecta progressively as the ejecta expand, producing the non-thermal electrons responsible for helium excitation. After $\sim100$ d, both NIR He I transitions develop double-peaked emission profiles. Similar structure in the oxygen emission indicates ejecta asymmetry. Comparison with other
supernovae suggests a tentative connection between this structure and explosion energy, potentially linked to the delay between core collapse and explosion. Serendipitous JWST observations at $+124.4$d reveal an infrared excess. Modeling favors warm ($\sim800$–$1500$K) carbon dust newly formed in the ejecta, together with cooler carbon or silicate dust likely associated with pre-existing circumstellar material. SN~2025aico demonstrates how continuous optical-to-MIR observations can connect progenitor
evolution, explosion physics, ejecta geometry, and dust production.
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All authors Grace Davis, Kyle Medler, Chris Ashall, Willem B. Hoogendam, Cameron Pfeffer, David O. Jones, Shunsaku Horiuchi, Tyco Mera, Benjamin Shappee, Charlotte Ward, Grace Showerman
Solar and Stellar Astrophysics
Spectroscopic Study of the Circularly Polarised Radio Source TYC 2834-1385-1: An Active Binary
Tamara A. S. Bleeker, Alexander Hoogerbrug, Elise Koo et al. (+2 more)
Close binaries with active chromospheres have recently been shown to emit circularly polarised
radio emission at low frequencies, motivating detailed studies of their orbital properties. We present high-resolution ($R=85,000$) optical spectroscopy of TYC 2834-1385-1, a previously unclassified
radio source, obtained with the HERMES spectrograph on the Mercator
Telescope. We identify the source as a double-lined spectroscopic binary and measure radial velocities from both metallic absorption and Ca II emission lines. We find an orbital period of $P=3.601\pm0.002$ days and nearly equal radial-velocity semi-amplitudes for the two components. The system exhibits strong Ca II H and K emission, which is consistent with a BY Dra-type binary containing two similar late-G/early-K main-sequence
stars, with a preliminary classification of K0V. This represents one of the first spectroscopic confirmations of a chromospherically active binary following its identification in a low-frequency
radio survey.
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All authors Tamara A. S. Bleeker, Alexander Hoogerbrug, Elise Koo, Rudy Wijnands, Joseph R. Callingham
Solar and Stellar Astrophysics · Cross-listed from physics.space-ph
First Observation of a Polar Coronal Hole-like Fast Solar Wind Stream in the Sub-Alfvénic Solar Corona: an Analysis of Turbulence Properties
Riddhi Bandyopadhyay, Sujan Prasad Gautam, William H. Matthaeus et al. (+2 more)
Parker Solar Probe, near its 23rd perihelion in March 2025, sampled an extended interval of sub-Alfvénic solar wind likely originating from a large equatorial coronal hole. At heliocentric distances of approximately 10 solar radii, with speed mostly above 400 km/s, this interval is a first example of “polar coronal hole-like (PCH-l) fast" solar wind observed in the sub-Alfvénic solar corona. We characterize the
turbulence properties of this unique interval using Parker Solar Probe measurements. Despite being sampled well inside the nominal Alfvén surface, the
turbulence appears to be already well developed while remaining strongly transverse and highly imbalanced, exhibiting a large cross helicity. These observations provide new constraints on the development and
evolution of solar wind
turbulence within the lower corona.
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All authors Riddhi Bandyopadhyay, Sujan Prasad Gautam, William H. Matthaeus, Yeimy J. Rivera, Samuel T. Badman
Solar and Stellar Astrophysics
PROSWIN: Probabilistic Solar Wind Speed Forecasting Using Deep Distributional Regression From Solar Images
Daniel Collin, Yuri Shprits, Luca Chiarabini et al. (+3 more)
Accurately predicting fast solar wind conditions is challenging, as uncertainties are large and unquantified by traditional single-value prediction models. In particular, the risks of high-speed solar wind streams (HSSs), which can cause damage to technological infrastructure, cannot be reliably assessed without probabilistic forecasts. We present PROSWIN, a probabilistic machine learning model that forecasts the hourly solar wind speed (SWS) at Earth with a four-day lead time. The approach combines solar images and magnetograms using a deep neural network coupled to a distributional regression
algorithm. Because standard error metrics underweight the relevance of HSS peaks, we further introduce the prediction score, a model-selection metric that jointly rewards timeline and HSS peak accuracy. On 14 years of data, our forecast achieves very well-calibrated uncertainties (<1% average deviation). Using the continuous ranked probability score (CRPS), a metric that assesses distributional accuracy, we obtain a timeline CRPS of 41.0 km/s, an HSS peak CRPS of 45.3 km/s, and a prediction score of 42.3 km/s. We find that the 171 Å channel is an important complement to the typically used 193 Å and 211 Å channels and that the prediction score for model selection improves the applicability of the model. Compared to selected models from the literature, ours is the only one that is accurate for both timeline and HSS peak values, rather than trading one off against the other. These results support the advantages of probabilistic over single-value solar wind models. The introduced methods are also transferable to other forecasting problems.
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All authors Daniel Collin, Yuri Shprits, Luca Chiarabini, Stefan J. Hofmeister, Nadja Klein, Guillermo Gallego
Solar and Stellar Astrophysics · Cross-listed from astro-ph.GA
Globular cluster candidates uncovered by VVVX and MUSE
P. Rodríguez Cuevas, B. Dias, D. Minniti et al. (+1 more)
The Milky Way has about 220 cataloged globular clusters. This number is far smaller than what is found in a similar
galaxy such as Andromeda, which has about 600 globular clusters. Two possible reasons for this large difference might be observational bias and cluster dissolution. The infrared photometric survey VISTA Variables in the Via Lactea Extended has discovered many globular cluster candidates toward the Galactic bulge that need confirmation. We confirm the globular cluster nature of four candidates from the Galactic bulge based on radial velocities from MUSE data. Following our previous experience and method, we searched for a peak in the radial velocity distribution by deconvolving the radial velocity distribution into its bulge, disk, and potential cluster components. For Minni 23, we confirm the previously found parameters: this is an old and metal-rich bulge globular cluster. Additionally, we found a radial velocity peak associated with the candidate globular cluster Minni 07, with $\mu_{RV,cl}=80^{+26}_{-22}$ ${\rm km\ s}^{-1}$, $\sigma_{RV,cl}=48^{+15}_{-15}$ ${\rm km\ s}^{-1}$. We also derived $A_V=1.5$ and [Fe/H]$\approx-0.27$ for Minni 07. On the other hand, we were unable to reliably confirm the globular cluster nature for the candidates Minni 10 and Minni 19 with the currently available data. The devised strategy has proven to be efficient for the proposed goals, and it is worth repeating it for the larger sample of candidate globular clusters.
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All authors P. Rodríguez Cuevas, B. Dias, D. Minniti, E. Garro
Solar and Stellar Astrophysics
Catalogue of Solar Radio Bursts Detected by the LOFAR LV614 Station at the Irbene Observatory during Solar Cycle 25
Jānis Šteinbergs, Dmitrii Kolotkov, Valery M. Nakariakov et al. (+3 more)
A catalogue (https://doi.org/10.5281/zenodo.20157853) of solar
radio bursts detected with the LV614 LOFAR station at the Irbene Observatory, Latvia, in the stand-alone mode from June 2022 to August 2025 in the 29-60 MHz frequency range is presented. Observations were conducted with the weekly cadence, one-second time resolution, and 0.195 MHz spectral resolution. The cumulative duration of the observation was 1125.2 h. For all analysed observations, bandpass calibration was applied using Cassiopeia A as a reference source. In total, the catalogue includes 335 solar
radio bursts.
Radio bursts of all five main types, I-V, were detected. Specifically, the catalogue contains parameters of 23, 8, 293, 6, and 5 bursts of Type I, II, III, IV, and V, respectively. The detected burst peak flux ranges from 0.3 SFU to 234 SFU. The catalogue provides information about the peak flux and frequency, and the estimated height of the source above the solar surface. For Type II and III bursts, we also give the estimations of the frequency drifts, with mean values $ 0.043 ~\mathrm{MHz\,s^{-1}}$ and $4.383 ~\mathrm{MHz\,s^{-1}}$, respectively. We also estimated the fit $df/dt = Af^a$, with the best fit parameters $A=0.78$ and $a=0.43$. The numbers of Type I and III events are found to decrease with the peak flux, with the power law indices about $-0.9$ and $-1.25$, respectively. For Type III, we estimated electron beam speed ranging from 0.005 to 0.477 of the speed of light for the fundamental frequency, and 0.008 to 0.794 of the speed of light for its second harmonic.
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All authors Jānis Šteinbergs, Dmitrii Kolotkov, Valery M. Nakariakov, Vladislavs Bezrukovs, Pietro Zucca, Jānis Kaminskis
Solar and Stellar Astrophysics
V844 Herculis: An Exceptional Intermediate Polar Hiding in an Ordinary Dwarf Nova
Anousha Greiveldinger, Peter Garnavich, Colin Littlefield et al. (+16 more)
We present time-series spectroscopy of the SU UMa-type dwarf nova V844 Her during quiescence. We discover high-velocity Balmer and He I emission features modulated at a period of 29.3$\pm$0.1 minutes. The spectroscopic periodicity is identical to the photometric period detected only during superoutbursts. Interpreting this as the result of
magnetic accretion onto the white dwarf, we identify V844 Her as an intermediate polar (IP). The
spin period of the white dwarf is most likely to be 29.3 minutes. In a few IP systems, optical modulation is seen at twice the
spin frequency, so we can not rule out that the
spin period is 58.6 minutes. The orbital period of V844 Her is only 1.31 hr, meaning that the system has the shortest binary period and one of the smallest orbit-to-
spin ratios of the confirmed IPs. We present extensive optical, ultraviolet, and X-ray observations of V844 Her during the 2023 superoutburst. Compared with quiescence, the XRT count rate decreases during superoutburst. While the enhanced mass transfer during the superoutburst likely increases X-ray production, we propose that the drop in the count rate comes from the loss of soft X-rays due to an additional column from the outbursting disk.
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All authors Anousha Greiveldinger, Peter Garnavich, Colin Littlefield, Mark R. Kennedy, Paula Szkody, Jordan Tweddale, Mark Whittle, Teófilo Arranz, Donald Collins, James DeYoung, Sjoerd Dufoer, Charles Galdies, Jean-Francois Gout, Franz-Josef Hambsch, Emmanuel Kardasis, David Messier, Arto Oksanen, Gary Poyner, Richard Sabo
Solar and Stellar Astrophysics
A VLBA survey of radio stars in the Orion Nebula Cluster: III. Inter-epoch variability analysis
E. T. O'Kelly, J. Forbrich, S. A. Dzib et al. (+1 more)
We present a multi-epoch Very Long Baseline Array (VLBA) survey of
radio sources in the Orion Nebula Cluster (ONC), updating the detection statistics and investigating inter-epoch variability. The
dataset comprises eight C-band (4-8 GHz) epochs targeting 575
radio sources previously identified in deep Very Large Array surveys. VLBA observations result in resolutions of milliarcseconds and are only sensitive to high brightness temperatures meaning only non-thermal emission is observed. We detect 226 unique
radio sources corresponding to a detection fraction of 39 per cent. The majority of sources (~83 per cent) are detected only once indicating that non-thermal emission associated with Young Stellar Objects (YSOs) is highly intermittent. To quantify variability, we use per-epoch peak flux densities and the variability factor (VF) defined as the ratio between the maximum and minimum fluxes. We identify 21 sources (~9 per cent of detected sources) that exhibit high variability defined as a change of flux density by at least a factor of five. We crossmatch with the COUP Chandra survey to identify sources as YSOs. We identify COUP counterparts for ~56 per cent of the detected sources. The remaining population cannot be explained solely by variability or background contamination, suggesting a population of
radio detected YSOs without X-ray counterparts. We find a clear correlation between
radio and X-ray luminosities consistent with the Güdel-Benz relation, the empirical relation between non-thermal
radio and thermal X-ray emission for magnetically active
stars.
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All authors E. T. O'Kelly, J. Forbrich, S. A. Dzib, J. Vargas-González
Solar and Stellar Astrophysics · Cross-listed from astro-ph.EP
NGTS clusters survey - VII. An Enigmatic Short-Period Circumsecondary Disk Candidate in Orion
Niamh Mallaghan, Ernst J. W. de Mooij, Christopher A. Watson et al. (+31 more)
Young stellar systems provide key insights into the processes governing
star/
planet formation, often exhibiting complex and evolving photometric variability. In this paper, we present an analysis of the object around NOI 105872, observed by the Next Generation Transit Survey (NGTS) to eclipse a young ($4.1\pm0.4$ Myr) M-type
star in the Orion Nebula Cluster. The system displays deep, asymmetric eclipses with a period of $\sim0.69$ days, alongside variability in morphology. We combine photometric observations spanning approximately a decade from multiple ground- and space-based facilities to investigate the nature of this system. We explore a range of physical scenarios to reproduce the eclipse profiles and their
evolution. After analysis, our preferred explanation is a circumsecondary disk surrounding a companion in orbit around the M-type primary. We adopt a six-parameter disk model and fit the eclipse profiles independently to each
dataset. The best-fitting solution yields a disk radius of $\sim 0.005 \mathrm{au}$ or $0.98 R_{*}$, with broadly consistent orientations across epochs, but with variations that may be attributed to disk precession or intrinsic stellar variability. Constraints from the Hill radius imply a companion mass consistent with a very low-mass stellar companion. These results establish NOI 105872 as a candidate for a circumsecondary disk system in a young stellar environment. Continued photometric monitoring and spectroscopic follow-up will be essential to confirm this interpretation. If confirmed, systems such as NOI 105872 provide valuable
benchmarks for understanding disk dynamics, companion formation, and the origin of complex eclipse phenomena in young
stars.
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All authors Niamh Mallaghan, Ernst J. W. de Mooij, Christopher A. Watson, Edward Gillen, Matthew Kenworthy, Louise D. Nielsen, David R. Anderson, Matthew P. Battley, Edward M. Bryant, Matthew R. Burleigh, Benjamin M. J. Cadell, Sarah L. Casewell, Alexander Chaushev, V. S. Dhillon, Elsa Ducrot, Jorge Fernandez Fernandez, Samuel Gill, Michael Gillon, Michael R. Goad, Faith Hawthorn, Katlyn L. Hobbs, James McCormac, Maximiliano Moyano, Catriona A. Murray, Toby Rodel, Suman Saha, Ramotholo R. Sefako, John Southworth, Mathilde Timmermans, Amaury H. M. J. Triaud, Jose Vines, Richard G. West, Peter J. Wheatley, Tafadzwa Zivave
Solar and Stellar Astrophysics
Are there really some eccentric eclipsing binaries having orbital periods below 1 d?
P. Zasche and M. Wolf
The stellar binary systems are classical tools for studying dynamics, and tidal circularization is one of the processes taking place in these. During the last few years, several dozen systems have been published supposedly having orbital periods shorter than 1 d, and have also been published as having eccentric orbits. Such a configuration is due to their spatial closeness, and the tides very improbable. Therefore, we performed a thorough analysis of all these eclipsing binaries (>140), showing that the vast majority of the published systems (> 98%) are in fact circular. Especially, the eclipsing binaries identified and published from the Gaia DR3 catalogue suffer from a lack of data, and about 50 per cent had incorrectly derived periods. This mostly incorrect identification of the eccentric orbits is due to automatic pipelines and routines running without human checking/validating, and also due to the large number of systems with (evolving) spots on the surfaces of either of the
stars. Only two eccentric orbits were found below the 1-d period limit, while the
star TIC 1190662 with an orbital period of about 0.888 d has a surprisingly large value of eccentricity about 0.21.
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Solar and Stellar Astrophysics
CME Kinematics with Optical Flow: Multi-Coronagraph Insights into Internal Velocity Dispersion
Pritam Das, Vaibhav Pant and Neeraj Rathore
Coronal mass ejections (CMEs) exhibit poorly understood internal velocity distributions. In this work, we introduce an optical flow-based method, DOFCAT (Dense Optical Flow CME Analysis Tool), applied to high-resolution data from ASPIICS/Proba-3 and METIS/Solar Orbiter to examine the internal velocity dispersion of different substructures within CMEs in the Middle Corona. We also introduce a Gaussian-tapered
Fourier (GTF) filter that suppresses brightness artifacts in running-difference images from the ASPIICS wideband channel. We then apply DOFCAT to four CME events observed across ASPIICS and METIS, extracting their internal velocity information. Our results show that the velocity profiles of both the CME front and core change with position angle and are non-uniform. For impulsive CMEs, the height offset between the front and core begins to increase following the impulsive acceleration phase, while CMEs without a clear impulsive phase show a more gradual
evolution of the height offset. We find that this increase in height difference occurs rapidly between 2.3–3.0\,R$_\odot$. Furthermore, the front shows a higher velocity spread than the core, with impulsiveness evident in the CME leading half. We further compute the radial self-similarity coefficient separately for the front and the core, finding that the front expands non-self-similarly initially and tends toward self-similarity at larger heights, while the core remains relatively self-similar. These findings confirm that CMEs contain complex internal flows and layered substructures within the traditional three-part morphology. Our results demonstrate the utility of DOFCAT on high-resolution coronagraphs for probing CME dynamics and provide new insights into CME initiation and
evolution.
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Solar and Stellar Astrophysics
Evidence for the emergence of stellar magnetic fields during rapid mass transfer
Gregg A. Wade, Tomer Shenar, Pablo Marchant et al. (+6 more)
Binary interaction fundamentally alters the
evolution of massive
stars, yet the physical consequences of mass transfer remain poorly constrained. Here we present high-resolution spectroscopic observations of Plaskett's
Star (HD 47129) that reveal small radial-velocity variations of its
magnetic secondary, coherent with the system's 14.4 d orbital period. These measurements support an evolved, post-mass-transfer configuration in which the narrow-lined primary is a partially Roche-lobe-filling stripped
star with a mass of $5.9^{+1.8}_{-1.4},M_\odot$, while the secondary is a $40.8^{+9.3}_{-6.7},M_\odot$, rapidly rotating
magnetic accretor. The system provides a rare opportunity to observe the immediate aftermath of mass transfer in a massive binary and offers compelling new evidence linking binary interaction to the emergence of strong stellar magnetism. Because
magnetic fields regulate angular-momentum loss and transport, their formation through mass transfer could alter the subsequent
evolution of massive binaries, with consequences for stellar populations,
supernova progenitors and yields, and the formation of gravitational-wave sources.
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All authors Gregg A. Wade, Tomer Shenar, Pablo Marchant, Michael Abdul-Masih, Matteo Cantiello, Jason Grunhut, Oleg Kochukhov, Hugues Sana, Selma E. de Mink