Following Shin et al. (2023b), which is a part of the "Systematic KMTNet Planetary Anomaly Search" series (i.e., a search for planets in the 2016 KMTNet prime fields), we conduct a systematic search of the 2016 KMTNet subprime fields using a semi-machine-based algorithm to identify hidden anomalous events missed by the conventional by-eye search. We find four new planets and seven planet candidates that were buried in the KMTNet archive. The new planets are OGLE-2016-BLG-1598Lb, OGLE-2016-BLG-1800Lb, MOA-2016-BLG-526Lb, and KMT-2016-BLG-2321Lb, which show typical properties of microlensing planets, i.e., giant planets orbit M-dwarf host stars beyond their snow lines. For the planet candidates, we find planet/binary or 2L1S/1L2S degeneracies, which are an obstacle to firmly claiming planet detections. By combining the results of Shin et al. (2023b) and this work, we find a total of nine hidden planets, which is about half the number of planets discovered by eye in 2016. With this work, we have met the goal of the systematic search series for 2016, which is to build a complete microlensing planet sample. We also show that our systematic searches significantly contribute to completing the planet sample, especially for planet/host mass ratios smaller than 10−3, which were incomplete in previous by-eye searches of the KMTNet archive.
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)
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In-Gu Shin et al 2024 AJ 167 269
Christopher Sneden and George W. Preston 2024 AJ 167 268
We have investigated the absorption shapes of atomic lines and Hα in RR Lyrae stars. We used the database of high-resolution spectra gathered with the Las Campanas Observatory du Pont Telescope, analyzing a set of about 2700 short exposure spectra of 17 RRab and 5 RRc variables. To increase the signal-to-noise ratio of the spectra for each star, we first coadded spectra in small photometric phase bins, and then coadded metallic line profiles in velocity space. The resulting line absorption shapes vary with photometric phase in a consistent manner for all RRab stars, while exhibiting no obvious phase-related variations for the RRc stars. We interpret these line profile variations in terms of velocity gradients in the photospheric layers that produce absorption line profiles. The Hα profiles are much broader, indicative of shock temperatures of order 100,000 K.
Parisa Sangtarash and Sedighe Sajadian 2024 AJ 167 266
One of the most important applications of microlensing observations is the detection of free-floating planets (FFPs). The timescale of microlensing due to FFPs (tE) is short (a few days). Discerning the annual parallax effect in observations of these short-duration events due to FFPs by one observer is barely possible, though their parallax amplitude is larger than that in common events. In microlensing events due to FFPs, the lens–source relative trajectory alters because of the observer's motion by δu. This deviation is a straight line as long as tE ≪ P⊕, and its size is δu ∝ πrel (P⊕ is the observer's orbital period). So, most observed microlensing events due to close FFPs have simple Paczyńsky light curves with indiscernible but important parallax. To evaluate the destructive effects of invisible parallax in such events, we simulate ∼9650 microlensing events due to FFPs with tE < 10 days that are observed only by the Nancy Grace Roman Space Telescope (Roman). We conclude that in half of these microlensing events the missing parallax alters the real light curves, changing their shape and derived properties (by Δχ2 ≳ 100). By fitting Paczyński light curves to these affected events we evaluate the relative and dimensionless deviations in the lensing parameters from their real values (δtE, δρ⋆, ...). We conclude that around 46 FFPs that are discovered by Roman have light curves highly affected by invisible parallax with δtE > 0.1 and δρ⋆ > 0.1. Our study reveals the importance of simultaneous and dense observations of the same microlensing events viewed by Roman by other observers circling the Sun in different orbits.
Randa Asa'd et al 2024 AJ 167 265
We present the first application of the novel approach based on data-driven machine learning methods applied to Multi-Unit Spectroscopic Explorer (MUSE) field data to derive stellar abundances of star clusters. MUSE has been used to target more than 10,000 fields, and it is unique in its ability to study dense stellar fields such as stellar clusters providing spectra for each individual star. We use MUSE data of the extragalactic young stellar cluster NGC 1856, located in the Large Magellanic Cloud (LMC). We present the individual stellar [Fe/H] abundance of 327 cluster members in addition to [Mg/Fe], [Si/Fe], [Ti/Fe], [C/Fe], [Ni/Fe], and [Cr/Fe] abundances of subsample sets. Our results match the LMC abundances obtained in the literature for [Mg/Fe], [Ti/Fe], [Ni/Fe], and [Cr/Fe]. This study is the first to derive [Si/Fe] and [C/Fe] abundances for this cluster. The revolutionary combination of integral-field spectroscopy and data-driven modeling will allow us to understand the chemical enrichment of star clusters and their host galaxies in greater detail expanding our understanding of galaxy evolution.
Xu Li et al 2024 AJ 167 264
Strong gravitational lensing is a powerful tool for investigating dark matter and dark energy properties. With the advent of large-scale sky surveys, we can discover strong-lensing systems on an unprecedented scale, which requires efficient tools to extract them from billions of astronomical objects. The existing mainstream lens-finding tools are based on machine-learning algorithms and applied to cutout-centered galaxies. However, according to the design and survey strategy of optical surveys by the China Space Station Telescope (CSST), preparing cutouts with multiple bands requires considerable efforts. To overcome these challenges, we have developed a framework based on a hierarchical visual transformer with a sliding window technique to search for strong-lensing systems within entire images. Moreover, given that multicolor images of strong-lensing systems can provide insights into their physical characteristics, our framework is specifically crafted to identify strong-lensing systems in images with any number of channels. As evaluated using CSST mock data based on a semianalytic model named CosmoDC2, our framework achieves precision and recall rates of 0.98 and 0.90, respectively. To evaluate the effectiveness of our method in real observations, we have applied it to a subset of images from the DESI Legacy Imaging Surveys and media images from Euclid Early Release Observations. A total of 61 new strong-lensing system candidates are discovered by our method. However, we also identified false positives arising primarily from the simplified galaxy morphology assumptions within the simulation. This underscores the practical limitations of our approach while simultaneously highlighting potential avenues for future improvements.
Open all abstracts, in this tab
In-Gu Shin et al 2024 AJ 167 269
Following Shin et al. (2023b), which is a part of the "Systematic KMTNet Planetary Anomaly Search" series (i.e., a search for planets in the 2016 KMTNet prime fields), we conduct a systematic search of the 2016 KMTNet subprime fields using a semi-machine-based algorithm to identify hidden anomalous events missed by the conventional by-eye search. We find four new planets and seven planet candidates that were buried in the KMTNet archive. The new planets are OGLE-2016-BLG-1598Lb, OGLE-2016-BLG-1800Lb, MOA-2016-BLG-526Lb, and KMT-2016-BLG-2321Lb, which show typical properties of microlensing planets, i.e., giant planets orbit M-dwarf host stars beyond their snow lines. For the planet candidates, we find planet/binary or 2L1S/1L2S degeneracies, which are an obstacle to firmly claiming planet detections. By combining the results of Shin et al. (2023b) and this work, we find a total of nine hidden planets, which is about half the number of planets discovered by eye in 2016. With this work, we have met the goal of the systematic search series for 2016, which is to build a complete microlensing planet sample. We also show that our systematic searches significantly contribute to completing the planet sample, especially for planet/host mass ratios smaller than 10−3, which were incomplete in previous by-eye searches of the KMTNet archive.
Christopher Sneden and George W. Preston 2024 AJ 167 268
We have investigated the absorption shapes of atomic lines and Hα in RR Lyrae stars. We used the database of high-resolution spectra gathered with the Las Campanas Observatory du Pont Telescope, analyzing a set of about 2700 short exposure spectra of 17 RRab and 5 RRc variables. To increase the signal-to-noise ratio of the spectra for each star, we first coadded spectra in small photometric phase bins, and then coadded metallic line profiles in velocity space. The resulting line absorption shapes vary with photometric phase in a consistent manner for all RRab stars, while exhibiting no obvious phase-related variations for the RRc stars. We interpret these line profile variations in terms of velocity gradients in the photospheric layers that produce absorption line profiles. The Hα profiles are much broader, indicative of shock temperatures of order 100,000 K.
Parisa Sangtarash and Sedighe Sajadian 2024 AJ 167 266
One of the most important applications of microlensing observations is the detection of free-floating planets (FFPs). The timescale of microlensing due to FFPs (tE) is short (a few days). Discerning the annual parallax effect in observations of these short-duration events due to FFPs by one observer is barely possible, though their parallax amplitude is larger than that in common events. In microlensing events due to FFPs, the lens–source relative trajectory alters because of the observer's motion by δu. This deviation is a straight line as long as tE ≪ P⊕, and its size is δu ∝ πrel (P⊕ is the observer's orbital period). So, most observed microlensing events due to close FFPs have simple Paczyńsky light curves with indiscernible but important parallax. To evaluate the destructive effects of invisible parallax in such events, we simulate ∼9650 microlensing events due to FFPs with tE < 10 days that are observed only by the Nancy Grace Roman Space Telescope (Roman). We conclude that in half of these microlensing events the missing parallax alters the real light curves, changing their shape and derived properties (by Δχ2 ≳ 100). By fitting Paczyński light curves to these affected events we evaluate the relative and dimensionless deviations in the lensing parameters from their real values (δtE, δρ⋆, ...). We conclude that around 46 FFPs that are discovered by Roman have light curves highly affected by invisible parallax with δtE > 0.1 and δρ⋆ > 0.1. Our study reveals the importance of simultaneous and dense observations of the same microlensing events viewed by Roman by other observers circling the Sun in different orbits.
Randa Asa'd et al 2024 AJ 167 265
We present the first application of the novel approach based on data-driven machine learning methods applied to Multi-Unit Spectroscopic Explorer (MUSE) field data to derive stellar abundances of star clusters. MUSE has been used to target more than 10,000 fields, and it is unique in its ability to study dense stellar fields such as stellar clusters providing spectra for each individual star. We use MUSE data of the extragalactic young stellar cluster NGC 1856, located in the Large Magellanic Cloud (LMC). We present the individual stellar [Fe/H] abundance of 327 cluster members in addition to [Mg/Fe], [Si/Fe], [Ti/Fe], [C/Fe], [Ni/Fe], and [Cr/Fe] abundances of subsample sets. Our results match the LMC abundances obtained in the literature for [Mg/Fe], [Ti/Fe], [Ni/Fe], and [Cr/Fe]. This study is the first to derive [Si/Fe] and [C/Fe] abundances for this cluster. The revolutionary combination of integral-field spectroscopy and data-driven modeling will allow us to understand the chemical enrichment of star clusters and their host galaxies in greater detail expanding our understanding of galaxy evolution.
Xu Li et al 2024 AJ 167 264
Strong gravitational lensing is a powerful tool for investigating dark matter and dark energy properties. With the advent of large-scale sky surveys, we can discover strong-lensing systems on an unprecedented scale, which requires efficient tools to extract them from billions of astronomical objects. The existing mainstream lens-finding tools are based on machine-learning algorithms and applied to cutout-centered galaxies. However, according to the design and survey strategy of optical surveys by the China Space Station Telescope (CSST), preparing cutouts with multiple bands requires considerable efforts. To overcome these challenges, we have developed a framework based on a hierarchical visual transformer with a sliding window technique to search for strong-lensing systems within entire images. Moreover, given that multicolor images of strong-lensing systems can provide insights into their physical characteristics, our framework is specifically crafted to identify strong-lensing systems in images with any number of channels. As evaluated using CSST mock data based on a semianalytic model named CosmoDC2, our framework achieves precision and recall rates of 0.98 and 0.90, respectively. To evaluate the effectiveness of our method in real observations, we have applied it to a subset of images from the DESI Legacy Imaging Surveys and media images from Euclid Early Release Observations. A total of 61 new strong-lensing system candidates are discovered by our method. However, we also identified false positives arising primarily from the simplified galaxy morphology assumptions within the simulation. This underscores the practical limitations of our approach while simultaneously highlighting potential avenues for future improvements.
Clayton Robertson et al 2024 AJ 167 263
The Balmer decrement (Hα/Hβ) provides a constraint on attenuation, the cumulative effects of dust grains in the ISM. The ratio is a reliable spectroscopic tool for deriving the dust properties of galaxies that determine many different quantities such as star formation rate, metallicity, and SED models. Here, we measure independently both the attenuation and Hα/Hβ of an occulting galaxy pair: VV 191. Attenuation measurements in the visible spectrum (AV,stars) from dust maps derived from the F606W filter of HST and the F090W filter of JWST are matched with spaxel-by-spaxel Hα/Hβ observations from the George and Cynthia Mitchell Spectrograph of the McDonald Observatory. The 0.5–0.7 μm bandpass covers the Balmer lines for VV 191. The dust maps of JWST and HST provide the high sensitivity necessary for comparisons and tracking trends of the geometrically favorable galaxy. We present maps and plots of the Balmer lines for the VV 191 galaxy pair and for a specific region highlighting dust lanes for VV 191b in the overlap region. We compute AV,H II from Hα/Hβ and plot both quantities against AV,stars. Our results show that regions with higher dust content, residing closer to the spiral center, dominate ionized gas attenuation, leading to an overestimation of AV,H II by a factor of 2. Further out in the spiral arms, the lower dust content leads to more agreement between the attenuations, indicating a lower star formation rate and larger contribution from older stars to the stellar continuum outside the Petrosian radius.
Valentina La Torre et al 2024 AJ 167 261
The current and upcoming large data volume galaxy surveys require the use of machine-learning techniques to maximize their scientific return. This study explores the use of Self-Organizing Maps (SOMs) to estimate galaxy parameters with a focus on handling cases of missing data and providing realistic probability distribution functions for the parameters. We train an SOM with a simulated mass-limited lightcone assuming a ugrizYJHKs+IRAC data set, mimicking the Hyper Suprime-Cam Deep joint data set. For parameter estimation, we derive SOM likelihood surfaces considering photometric errors to derive total (statistical and systematic) uncertainties. We explore the effects of missing data, including which bands are particularly critical to the accuracy of the derived parameters. We demonstrate that the parameter recovery is significantly better when the missing bands are "filled in" rather than if they are completely omitted. We propose a practical method for such recovery of missing data.
Meghan Speckert et al 2024 AJ 167 262
We observed the Galactic open cluster Berkeley 50 in order to determine its stellar content, distance, and age. We obtained UBV photometry of 1145 stars in a 123 × 123 field, and used Gaia proper motions and parallaxes to identify 64 members, of which we obtained spectra of the 17 brightest members. The majority of the observed population we classified as B dwarfs, with the exception of a newly identified red supergiant star, which our spectroscopy shows has a B-type companion. Our study establishes the distance as 3.8 kpc, with an average color-excess E(B − V) = 0.9. Comparison of the physical properties of the cluster with the Geneva evolutionary tracks places the age of the cluster as 50–60 Myr, with its most massive members being ∼7M⊙
Jingjing Wu et al 2024 AJ 167 260
The automated and efficient classification of astronomical spectra is an important research issue in the era of large sky surveys. Most current studies on automatic spectral classification primarily focus on specific data sets and demonstrate outstanding performance. However, the diversity in spectra poses formidable challenges for these classification models, as they exhibit limited capability to generalize across more comprehensive data sets. In response to these challenges, we pioneer a method called the multiscale partial convolution net (MSPC-Net), which amalgamates partial, large kernel, and grouped convolution to facilitate multilabel spectral classification. By harnessing the capabilities of partial convolution, MSPC-Net can effectively reduce the number of model parameters, accelerate the training process, and mitigate the overfitting issue. Integrating large kernel and grouped convolution empowers the model to capture local and global features simultaneously, enhancing its overall classification efficacy. To rigorously evaluate the model's performance, we generate ten different data sets sourced from the Sloan Digital Sky Survey and Large Sky Area Multi-Object Spectroscopic Telescope. These data sets encompass stellar class, stellar subclass, and full classification, providing a comprehensive assessment across various application scenarios. The experimental results reveal that MSPC-Net consistently outperforms the other models across different data sets, especially demonstrating superior performance in the last two data sets with full classification. Consequently, MSPC-Net is poised to find extensive applications in the detailed classification for large-scale sky survey projects. This work not only addresses the challenges of generalization in spectral classification but also contributes significantly to the advancement of robust models for astronomical research.
Zhaotong Xie et al 2024 AJ 167 259
The Square Kilometre Array (SKA) radio telescope will achieve unparalleled sensitivity and angular resolution, substantially progressing our research into the formation and development of the early universe. Sensitivity is one of the most critical telescope metrics, often used to determine the observing mode and observing time of a radio source. It is also used to determine imaging parameters to balance imaging sensitivity and spatial resolution during data processing. In this paper, to meet the needs of continuum imaging pipeline data processing for the SKA1-LOW telescope, we derive equations for point-source-sensitivity (PSS) calculations under multichannel, multipolarization, discrete frequency sampling, discrete time sampling, and different weighting schemes. After validating the correctness of the equation, we improved and refined the sensitivity calculation application in the Radio Astronomy Simulation, Calibration, and Imaging Library, and further calculated the variation of the PSS versus angular resolution for the full-scale SKA1-LOW with different weighting schemes, and provided SKA1-LOW broadband image performance as functions of angular scale for four frequencies. These results can provide not only a theoretical basis for the construction and commissioning of the SKA1-LOW telescope but also guidance for imaging processing in future scientific data processing.