Stellar light curves from edge-on double white dwarf (DWD) systems have periodic lensing/eclipsing signals at times of alignment between the two components as seen by the observer. Here, we study the characterization and detection of these signals. In common DWDs, the Einstein radii have similar orders of magnitude to the radii of the white dwarfs (WDs), and the projected source and lens radii normalized to the Einstein radius (ρ⋆ and ρl) are ∼1. Both of them are reduced with the orbital period and the lens mass. If ρl ≃ 1 the lensing-induced minor image is always blocked by the lens, which results in lower magnification factors. If ρl ≲ 1, and in transit events, the finite-lens effects decrease the light curves' width. When ρl ≳ 1 (which happens for close DWDs consisting of a low-mass WD and a massive one) deep or complete eclipses dominate over lensing effects. The self-lensing signals are maximal for massive DWDs in wide orbits. We study the detectability of lensing/eclipsing signals in edge-on DWDs in observations by NASA's Transiting Exoplanet Survey Satellite (TESS), the Vera Rubin Observatory Large Synoptic Survey Telescope (LSST), and the Nancy Grace Roman Space Telescope. We simulate stellar light curves due to edge-on DWDs and generate synthetic data points based on their observing strategies. Detection efficiency is maximal for extremely low-mass WDs in close orbits, and the numbers of DWDs within 100 pc and an observing cone with detectable lensing/eclipsing signals in one observing window of 27.4 days for TESS and 62 days for Roman are ∼1 and <1, respectively. Detecting these signals by LSST is barely possible because of its long cadence.
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The Astronomical Journal is an open access journal publishing original astronomical research, with an emphasis on significant scientific results derived from observations. Publications in AJ include descriptions of data capture, surveys, analysis techniques, astronomical interpretation, instrumentation, and software and computing.
Remembering former AJ editor, Paul W. Hodge (1934–2019)
GOLD OPEN ACCESS FROM 1 JANUARY 2022
Sedighe Sajadian 2025 AJ 169 164
Loïc Albert et al 2025 AJ 169 163
Brown dwarfs lack nuclear fusion and cool with time; the coldest known have an effective temperature below 500 K, and are known as Y dwarfs. We present a James Webb Space Telescope (JWST) photometric data set of Y dwarfs: 23 were imaged in wide-field mode, 20 using NIRCam with the F150W and F480M filters, and three using NIRISS with the F480M filter. We present an F480M versus F150W – F480M color–magnitude diagram for our sample, and other brown dwarfs with F150W and F480M colors synthesized from JWST spectra by S. A. Beiler et al. For one target, WISEA J083011.95+283716.0, its detection in the near-infrared confirms it as one of the reddest Y dwarfs known, with F150W – F480M = 9.62 mag. We provide its updated parallax and proper motion. One of the Beiler et al. Y dwarfs, CWISEP J104756.81+545741.6, is unusually blue, consistent with strong CO absorption seen in its spectrum, which the F480M filter is particularly sensitive to. The strong CO and the kinematics of the object suggest it may be very low mass and young. We update the resolved photometry for the close binary system WISE J033605.05–014350.4 AB, and find that the secondary is almost as cold as WISE 085510.83–071442.5, with Teff ≲ 300 K, however the F150W – F480M color is significantly bluer, possibly suggesting the presence of water clouds. Astrometry is measured at the JWST epoch for the sample which is consistent with parallax and proper motion values reported by J. D. Kirkpatrick et al. and F. Marocco et al.
Muhammad Yarahmadi and Amin Salehi 2025 AJ 169 161
In this study, we explore the characteristics of bulk flow across various redshift ranges within the frameworks of f(R) gravity, perturbed f(R) gravity, and perturbed f(R) gravity coupled with neutrinos. Our investigation reveals profound insights into large-scale cosmic flows and their interactions with major cosmic structures, such as the Sloan Great Wall (SGW) and the King Ghidorah Supercluster (KGSc). We find that incorporating neutrinos into the perturbed f(R) gravity model results in a substantial increase in bulk flow velocities across all redshifts, with notable enhancements in the higher redshift ranges, where velocities can exceed 3000 km s−1 in the 0.8 < z < 1.4 range. Moreover, the direction of the bulk flow in this model closely aligns with the dark energy dipole, especially at redshifts z > 0.4, showing near-perfect congruence with cosmic superclusters. This suggests a significant interaction between neutrinos and cosmic structures, influencing cosmic acceleration. At lower redshifts, such as 0.1 < z < 0.2, the bulk flow aligns with the SGW, while in the 0.4 < z < 0.6 range it aligns with the KGSc. In the low redshift range 0.001 < z < 0.016, although velocities are lower, neutrinos still subtly increase the bulk flow velocity and maintain alignment with nearby cosmic structures, such as the Local Supercluster. Our results underscore the critical role of neutrinos in shaping cosmic flows and offer new insights into the interplay between dark energy, neutrinos, and modified gravity models. Future research should delve deeper into these interactions to elucidate the mechanisms influencing large-scale cosmic structures.
Tracy L. Beck 2025 AJ 169 160
The optical star in the T Tauri triple system is the prototype of young Sun-like stars in our galaxy. This complex and dynamic system has evidence for misaligned disks and outflows, and molecular material in a circumbinary ring that obscures the southern infrared binary, T Tau South. Observations by members of the American Association of Variable Star Observers show that T Tau North, the optical star, has dimmed by up to ∼2 mag in the visual over the course of the past decade. The dimming across the B, V, R, and I bands has a color character typical of changes in interstellar medium extinction, suggesting an increase in obscuration along the line of sight to T Tau North. Material associated with the circumbinary ring around T Tau South has been predicted to occult the optical star via wide-scale orbital motion of the system. Through analysis of the geometrical configuration and motion of dust structures in the system, it seems that a great dimming of T Tau North by line-of-sight material associated with the T Tau South binary has, in fact, begun. Based on the extent and motion of the circumbinary ring material associated with the southern binary, T Tau North will likely experience dimming events for decades to come and may disappear entirely from the optical sky as the densest midplane region of the ring traverses our line of sight.
Javier Viaña et al 2025 AJ 169 159
Traditional microlensing event vetting methods require highly trained human experts, and the process is both complex and time consuming. This reliance on manual inspection often leads to inefficiencies and constrains the ability to scale for widespread exoplanet detection, ultimately hindering discovery rates. To address the limits of traditional microlensing event vetting, we have developed LensNet, a machine learning pipeline specifically designed to distinguish legitimate microlensing events from false positives caused by instrumental artifacts, such as pixel bleed trails and diffraction spikes. Our system operates in conjunction with a preliminary algorithm that detects increasing trends in flux. These flagged instances are then passed to LensNet for further classification, allowing for timely alerts and follow-up observations. Tailored for the multiobservatory setup of the Korea Microlensing Telescope Network and trained on a rich data set of manually classified events, LensNet is optimized for early detection and warning of microlensing occurrences, enabling astronomers to organize follow-up observations promptly. The internal model of the pipeline employs a multibranch Recurrent Neural Network architecture that evaluates time-series flux data with contextual information, including sky background, the full width at half-maximum of the target star, flux errors, point-spread function quality flags, and air mass for each observation. We demonstrate a classification accuracy above 87.5% and anticipate further improvements as we expand our training set and continue to refine the algorithm.
Sedighe Sajadian 2025 AJ 169 164
Stellar light curves from edge-on double white dwarf (DWD) systems have periodic lensing/eclipsing signals at times of alignment between the two components as seen by the observer. Here, we study the characterization and detection of these signals. In common DWDs, the Einstein radii have similar orders of magnitude to the radii of the white dwarfs (WDs), and the projected source and lens radii normalized to the Einstein radius (ρ⋆ and ρl) are ∼1. Both of them are reduced with the orbital period and the lens mass. If ρl ≃ 1 the lensing-induced minor image is always blocked by the lens, which results in lower magnification factors. If ρl ≲ 1, and in transit events, the finite-lens effects decrease the light curves' width. When ρl ≳ 1 (which happens for close DWDs consisting of a low-mass WD and a massive one) deep or complete eclipses dominate over lensing effects. The self-lensing signals are maximal for massive DWDs in wide orbits. We study the detectability of lensing/eclipsing signals in edge-on DWDs in observations by NASA's Transiting Exoplanet Survey Satellite (TESS), the Vera Rubin Observatory Large Synoptic Survey Telescope (LSST), and the Nancy Grace Roman Space Telescope. We simulate stellar light curves due to edge-on DWDs and generate synthetic data points based on their observing strategies. Detection efficiency is maximal for extremely low-mass WDs in close orbits, and the numbers of DWDs within 100 pc and an observing cone with detectable lensing/eclipsing signals in one observing window of 27.4 days for TESS and 62 days for Roman are ∼1 and <1, respectively. Detecting these signals by LSST is barely possible because of its long cadence.
Loïc Albert et al 2025 AJ 169 163
Brown dwarfs lack nuclear fusion and cool with time; the coldest known have an effective temperature below 500 K, and are known as Y dwarfs. We present a James Webb Space Telescope (JWST) photometric data set of Y dwarfs: 23 were imaged in wide-field mode, 20 using NIRCam with the F150W and F480M filters, and three using NIRISS with the F480M filter. We present an F480M versus F150W – F480M color–magnitude diagram for our sample, and other brown dwarfs with F150W and F480M colors synthesized from JWST spectra by S. A. Beiler et al. For one target, WISEA J083011.95+283716.0, its detection in the near-infrared confirms it as one of the reddest Y dwarfs known, with F150W – F480M = 9.62 mag. We provide its updated parallax and proper motion. One of the Beiler et al. Y dwarfs, CWISEP J104756.81+545741.6, is unusually blue, consistent with strong CO absorption seen in its spectrum, which the F480M filter is particularly sensitive to. The strong CO and the kinematics of the object suggest it may be very low mass and young. We update the resolved photometry for the close binary system WISE J033605.05–014350.4 AB, and find that the secondary is almost as cold as WISE 085510.83–071442.5, with Teff ≲ 300 K, however the F150W – F480M color is significantly bluer, possibly suggesting the presence of water clouds. Astrometry is measured at the JWST epoch for the sample which is consistent with parallax and proper motion values reported by J. D. Kirkpatrick et al. and F. Marocco et al.
Muhammad Yarahmadi and Amin Salehi 2025 AJ 169 161
In this study, we explore the characteristics of bulk flow across various redshift ranges within the frameworks of f(R) gravity, perturbed f(R) gravity, and perturbed f(R) gravity coupled with neutrinos. Our investigation reveals profound insights into large-scale cosmic flows and their interactions with major cosmic structures, such as the Sloan Great Wall (SGW) and the King Ghidorah Supercluster (KGSc). We find that incorporating neutrinos into the perturbed f(R) gravity model results in a substantial increase in bulk flow velocities across all redshifts, with notable enhancements in the higher redshift ranges, where velocities can exceed 3000 km s−1 in the 0.8 < z < 1.4 range. Moreover, the direction of the bulk flow in this model closely aligns with the dark energy dipole, especially at redshifts z > 0.4, showing near-perfect congruence with cosmic superclusters. This suggests a significant interaction between neutrinos and cosmic structures, influencing cosmic acceleration. At lower redshifts, such as 0.1 < z < 0.2, the bulk flow aligns with the SGW, while in the 0.4 < z < 0.6 range it aligns with the KGSc. In the low redshift range 0.001 < z < 0.016, although velocities are lower, neutrinos still subtly increase the bulk flow velocity and maintain alignment with nearby cosmic structures, such as the Local Supercluster. Our results underscore the critical role of neutrinos in shaping cosmic flows and offer new insights into the interplay between dark energy, neutrinos, and modified gravity models. Future research should delve deeper into these interactions to elucidate the mechanisms influencing large-scale cosmic structures.
Tracy L. Beck 2025 AJ 169 160
The optical star in the T Tauri triple system is the prototype of young Sun-like stars in our galaxy. This complex and dynamic system has evidence for misaligned disks and outflows, and molecular material in a circumbinary ring that obscures the southern infrared binary, T Tau South. Observations by members of the American Association of Variable Star Observers show that T Tau North, the optical star, has dimmed by up to ∼2 mag in the visual over the course of the past decade. The dimming across the B, V, R, and I bands has a color character typical of changes in interstellar medium extinction, suggesting an increase in obscuration along the line of sight to T Tau North. Material associated with the circumbinary ring around T Tau South has been predicted to occult the optical star via wide-scale orbital motion of the system. Through analysis of the geometrical configuration and motion of dust structures in the system, it seems that a great dimming of T Tau North by line-of-sight material associated with the T Tau South binary has, in fact, begun. Based on the extent and motion of the circumbinary ring material associated with the southern binary, T Tau North will likely experience dimming events for decades to come and may disappear entirely from the optical sky as the densest midplane region of the ring traverses our line of sight.
Javier Viaña et al 2025 AJ 169 159
Traditional microlensing event vetting methods require highly trained human experts, and the process is both complex and time consuming. This reliance on manual inspection often leads to inefficiencies and constrains the ability to scale for widespread exoplanet detection, ultimately hindering discovery rates. To address the limits of traditional microlensing event vetting, we have developed LensNet, a machine learning pipeline specifically designed to distinguish legitimate microlensing events from false positives caused by instrumental artifacts, such as pixel bleed trails and diffraction spikes. Our system operates in conjunction with a preliminary algorithm that detects increasing trends in flux. These flagged instances are then passed to LensNet for further classification, allowing for timely alerts and follow-up observations. Tailored for the multiobservatory setup of the Korea Microlensing Telescope Network and trained on a rich data set of manually classified events, LensNet is optimized for early detection and warning of microlensing occurrences, enabling astronomers to organize follow-up observations promptly. The internal model of the pipeline employs a multibranch Recurrent Neural Network architecture that evaluates time-series flux data with contextual information, including sky background, the full width at half-maximum of the target star, flux errors, point-spread function quality flags, and air mass for each observation. We demonstrate a classification accuracy above 87.5% and anticipate further improvements as we expand our training set and continue to refine the algorithm.
Xunzhou Chen et al 2025 AJ 169 158
The Five-hundred-meter Aperture Spherical radio Telescope (FAST) has been fully operational since 2020 January 11. We present a comprehensive analysis of the beam structure for each of the 19 feed horns on FAST's L-band receiver across the Stokes I, Q, U, and V parameters. Using an on-the-fly mapping pattern, we conducted simultaneous sky mapping using all 19 beams directed toward polarization calibrators J1407+2827 and J0854+2006 from 2020 to 2022. Electromagnetic simulations were also performed to model the telescope's beam patterns in all Stokes parameters. Our findings reveal a symmetrical Gaussian pattern in the Stokes I parameter of the central beam without strong sidelobes, while the off-center beams exhibit significant asymmetrical shapes that can be fitted using a combination of log-normal and Gaussian distributions. The inner beams have higher relative beam efficiencies and smaller beam sizes compared to those of the outer beams. The sidelobes of the inner beams contribute approximately 2% of the total flux in the main lobe, increasing to 5% for outer beams, with a peak at 6.8%. In Stokes U, a distinct four-lobed cloverleaf beam squash structure is observed, with similar intensity levels in both inner and outer beams. In Stokes V, a two-lobed beam squint structure is observed in the central beam, along with a secondary eight-lobed structure. The highest squint peak in Stokes V is about 0.3% of the Stokes I in the outer beams. These results align closely with the simulations, providing valuable insights for the design of radio multibeam observations.
S. Juneau et al 2025 AJ 169 157
The Dark Energy Spectroscopic Instrument (DESI) cosmology survey includes a Bright Galaxy Survey (BGS), which will yield spectra for over 10 million bright galaxies (r < 20.2 AB mag). The resulting sample will be valuable for both cosmological and astrophysical studies. However, the star/galaxy separation criterion implemented in the nominal BGS target selection algorithm excludes quasar host galaxies in addition to bona fide stars. While this excluded population is comparatively rare (∼3–4 per square degrees), it may hold interesting clues regarding galaxy and quasar physics. Therefore, we present a target selection strategy that was implemented to recover these missing active galactic nuclei (AGN) from the BGS sample. The design of the selection criteria was both motivated and confirmed using spectroscopy. The resulting BGS-AGN sample is uniformly distributed over the entire DESI footprint. According to DESI survey validation data, the sample comprises 93% quasi-stellar objects (QSOs), 3% narrow-line AGN or blazars with a galaxy contamination rate of 2%, and a stellar contamination rate of 2%. Peaking around redshift z = 0.5, the BGS-AGN sample is intermediary between quasars from the rest of the BGS and those from the DESI QSO sample in terms of redshifts and AGN luminosities. The stacked spectrum is nearly identical to that of the DESI QSO targets, confirming that the sample is dominated by quasars. We highlight interesting small populations reaching z > 2, which are either faint quasars with nearby projected companions or very bright quasars with strong absorption features including the Lyα forest, metal absorbers, and/or broad absorption lines.
Chow-Choong Ngeow and Anupam Bhardwaj 2025 AJ 169 156
We report the search of RR Lyrae in the vicinity of a newly discovered ultrafaint dwarf galaxy, Aquarius III. Based on the known RR Lyrae catalogs and gri-band light curves retrieved from public archives, we identified a RR Lyrae with distance, metallicity, and proper motion consistent with Aquarius III. Therefore, this RR Lyrae is the first variable star identified to be associated with Aquarius III, despite its projected distance is more than 15 times the half-light radius of Aquarius III. On the other hand, a dedicated time-series monitoring of the central part of Aquarius III, out to a projected radius of approximately four half-light radius, revealed there is no RR Lyrae in this region. We ran a set of synthetic color–magnitude diagrams with properties similar to Aquarius III, and found a nonnegligible probability that Aquarius III could have (at least one) RR Lyrae. We have also identified a RR Lyrae candidate but most likely it is a background halo star.
Lauren Halstead Willett et al 2025 AJ 169 155
The mass accretion rates of young stellar objects (YSOs) are key to understanding how stars form, how their circumstellar disks evolve, and even how planets form. We develop a Bayesian framework to determine the accretion rates of a sample of 15 YSOs using archival data from the VIRUS spectrograph (R ∼ 800, 3500–5500 Å) on the Hobby–Eberly Telescope. We are publicly releasing our developed tool, dubbed nuts-for-ysos, as a Python package, which can also be applied to other spectroscopic data sets (https://github.com/laurenwillett/nuts-for-ysos). The nuts-for-ysos code fits a simple accretion model to the near-UV and optical continuum of each VIRUS spectrum. Our Bayesian approach aims to identify correlations between model parameters using the No U-Turn Sampler (NUTS). Moreover, this approach self-consistently incorporates all parameter uncertainties, allowing for a thorough estimation of the probability distribution for accretion rate not accomplished in previous works. Using nuts-for-ysos, we derive accretion rates of each YSO. We then verify the reliability of our method by comparing to results separately derived from only the spectral emission lines, and to results from earlier studies of the Lupus, Chamaeleon I, and NGC 1333 regions. Finally, we discuss what qualitative trends, covariances, and degeneracies were found among model parameters. The technique developed in this paper is a useful improvement that can be applied in the future to larger samples of YSOs observed by VIRUS or other spectrographs.
Ata Sarajedini 2025 AJ 169 154
We present the deepest color–magnitude diagram (CMD) for NGC 205 in the F606W (≈V) and F814W (≈I) filters. Our archival Hubble Space Telescope/Advanced Camera for Surveys field is centered ∼38 northwest of the galaxy's center. The CMD shows the canonical features of a predominantly intermediate-to-old age stellar population. Among other features, the CMD reveals a prominent red clump as well as a blue horizontal branch. Notably absent is any significant signature of a young main sequence typically produced by a stellar population with an age less than a few Gyr. From the magnitude of the red-giant-branch tip, we derive a distance modulus of (m − M)o = 24.66 ± 0.05. When compared with α-enhanced theoretical isochrones, the color distribution of the red giant branch stars yields a peak metallicity value of [Fe/H] = −0.51 ± 0.10. Our photometry also reveals a sample of 479 RR Lyrae variable stars (443 ab-type and 36 c-type). Utilizing equations that relate the periods and amplitudes to the metallicities of these stars, we find a mean 〈[Fe/H]〉 = −1.45 ± 0.02 on the Zinn & West scale for the purely old stellar population in NGC 205. The quoted uncertainty represents the standard error of the mean abundance value is consistent with that of the six genuine old globular clusters in NGC 205.