The Lomb–Scargle periodogram is a well-known algorithm for detecting and characterizing periodic signals in unevenly sampled data. This paper presents a conceptual introduction to the Lomb–Scargle periodogram and important practical considerations for its use. Rather than a rigorous mathematical treatment, the goal of this paper is to build intuition about what assumptions are implicit in the use of the Lomb–Scargle periodogram and related estimators of periodicity, so as to motivate important practical considerations required in its proper application and interpretation.

We have analyzed high-resolution (FWHM = 0.2 Å) extreme-ultraviolet (EUV, 800–1350 Å) laboratory emission spectra of molecular nitrogen excited by an electron impact at 20 and 100 eV under (mostly) optically thin, single-scattering experimental conditions. A total of 491 emission features were observed from N₂ electronic–vibrational transitions and atomic N i and N ii multiplets and their emission cross sections were measured. Molecular emission was observed at vibrationally excited ground-state levels as high as v'' = 17, from the a ¹Π_g, b ¹Π_u, and b'¹Σ_u⁺ excited valence states and the Rydberg series c'_n+1 ¹Σ_u⁺, c_n ¹Π_u, and o_n ¹Π_u for n between 3 and 9. The frequently blended molecular emission bands were disentangled with the aid of a sophisticated and predictive quantum-mechanical model of excited states that includes the strong coupling between valence and Rydberg electronic states and the effects of predissociation. Improved model parameters describing electronic transition moments were obtained from the experiment and allowed for a reliable prediction of the vibrationally summed electronic emission cross section, including an extrapolation to unobserved emission bands and those that are optically thick in the experimental spectra. Vibrationally dependent electronic excitation functions were inferred from a comparison of emission features following 20 and 100 eV electron-impact collisional excitation. The electron-impact-induced fluorescence measurements are compared with Cassini Ultraviolet Imaging Spectrograph observations of emissions from Titan's upper atmosphere.

This paper documents the seventeenth data release (DR17) from the Sloan Digital Sky Surveys; the fifth and final release from the fourth phase (SDSS-IV). DR17 contains the complete release of the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey, which reached its goal of surveying over 10,000 nearby galaxies. The complete release of the MaNGA Stellar Library accompanies this data, providing observations of almost 30,000 stars through the MaNGA instrument during bright time. DR17 also contains the complete release of the Apache Point Observatory Galactic Evolution Experiment 2 survey that publicly releases infrared spectra of over 650,000 stars. The main sample from the Extended Baryon Oscillation Spectroscopic Survey (eBOSS), as well as the subsurvey Time Domain Spectroscopic Survey data were fully released in DR16. New single-fiber optical spectroscopy released in DR17 is from the SPectroscipic IDentification of ERosita Survey subsurvey and the eBOSS-RM program. Along with the primary data sets, DR17 includes 25 new or updated value-added catalogs. This paper concludes the release of SDSS-IV survey data. SDSS continues into its fifth phase with observations already underway for the Milky Way Mapper, Local Volume Mapper, and Black Hole Mapper surveys.

Stellar physics and evolution calculations enable a broad range of research in astrophysics. Modules for Experiments in Stellar Astrophysics (MESA) is a suite of open source, robust, efficient, thread-safe libraries for a wide range of applications in computational stellar astrophysics. A one-dimensional stellar evolution module, MESAstar, combines many of the numerical and physics modules for simulations of a wide range of stellar evolution scenarios ranging from very low mass to massive stars, including advanced evolutionary phases. MESAstar solves the fully coupled structure and composition equations simultaneously. It uses adaptive mesh refinement and sophisticated timestep controls, and supports shared memory parallelism based on OpenMP. State-of-the-art modules provide equation of state, opacity, nuclear reaction rates, element diffusion data, and atmosphere boundary conditions. Each module is constructed as a separate Fortran 95 library with its own explicitly defined public interface to facilitate independent development. Several detailed examples indicate the extensive verification and testing that is continuously performed and demonstrate the wide range of capabilities that MESA possesses. These examples include evolutionary tracks of very low mass stars, brown dwarfs, and gas giant planets to very old ages; the complete evolutionary track of a 1 M_☉ star from the pre-main sequence (PMS) to a cooling white dwarf; the solar sound speed profile; the evolution of intermediate-mass stars through the He-core burning phase and thermal pulses on the He-shell burning asymptotic giant branch phase; the interior structure of slowly pulsating B Stars and Beta Cepheids; the complete evolutionary tracks of massive stars from the PMS to the onset of core collapse; mass transfer from stars undergoing Roche lobe overflow; and the evolution of helium accretion onto a neutron star. MESA can be downloaded from the project Web site (http://mesa.sourceforge.net/).

The eighteenth data release (DR18) of the Sloan Digital Sky Survey (SDSS) is the first one for SDSS-V, the fifth generation of the survey. SDSS-V comprises three primary scientific programs or "Mappers": the Milky Way Mapper (MWM), the Black Hole Mapper (BHM), and the Local Volume Mapper. This data release contains extensive targeting information for the two multiobject spectroscopy programs (MWM and BHM), including input catalogs and selection functions for their numerous scientific objectives. We describe the production of the targeting databases and their calibration and scientifically focused components. DR18 also includes ∼25,000 new SDSS spectra and supplemental information for X-ray sources identified by eROSITA in its eFEDS field. We present updates to some of the SDSS software pipelines and preview changes anticipated for DR19. We also describe three value-added catalogs (VACs) based on SDSS-IV data that have been published since DR17, and one VAC based on the SDSS-V data in the eFEDS field.

We present a catalog of 536 fast radio bursts (FRBs) detected by the Canadian Hydrogen Intensity Mapping Experiment Fast Radio Burst (CHIME/FRB) Project between 400 and 800 MHz from 2018 July 25 to 2019 July 1, including 62 bursts from 18 previously reported repeating sources. The catalog represents the first large sample, including bursts from repeaters and nonrepeaters, observed in a single survey with uniform selection effects. This facilitates comparative and absolute studies of the FRB population. We show that repeaters and apparent nonrepeaters have sky locations and dispersion measures (DMs) that are consistent with being drawn from the same distribution. However, bursts from repeating sources differ from apparent nonrepeaters in intrinsic temporal width and spectral bandwidth. Through injection of simulated events into our detection pipeline, we perform an absolute calibration of selection effects to account for systematic biases. We find evidence for a population of FRBs—composing a large fraction of the overall population—with a scattering time at 600 MHz in excess of 10 ms, of which only a small fraction are observed by CHIME/FRB. We infer a power-law index for the cumulative fluence distribution of $\alpha =-1.40\pm 0.11({\rm{stat.}}{)}_{-0.09}^{+0.06}({\rm{sys.}})$, consistent with the −3/2 expectation for a nonevolving population in Euclidean space. We find that α is steeper for high-DM events and shallower for low-DM events, which is what would be expected when DM is correlated with distance. We infer a sky rate of $[820\pm 60({\rm{stat.}}{)}_{-200}^{+220}({\rm{sys.}})]/{\rm{sky}}/{\rm{day}}$ above a fluence of 5 Jy ms at 600 MHz, with a scattering time at 600 MHz under 10 ms and DM above 100 pc cm⁻³.

We present identifications and kinematic analysis of 7426 massive (≥8M_⊙) stars in the Small Magellanic Cloud (SMC), using Gaia DR3 data. We used the Gaia (G_BP − G_RP, G) color–magnitude diagram to select the population of massive stars, and parallax to omit foreground objects. The spatial distribution of the 7426 massive star candidates is generally consistent with the spatial distribution of the interstellar medium, such as Hα and H i emission. The identified massive stars show inhomogeneous distributions over the galaxy, showing several superstructures formed by massive stars with a several hundred parsec scale. The stellar superstructures defined by the surface density have opposite mean proper motions in the east and west, moving away from each other. Similarly, the mean line-of-sight velocities of the superstructures are larger to the southeast and smaller to the northwest. The different east–west properties of the superstructures' proper-motion, line-of-sight velocity indicate that the SMC is being stretched by tidal forces and/or ram pressure from the Large Magellanic Cloud to the southeast, thereby rejecting the presence of galactic rotation in the SMC.

We present an overview of best practices for publishing data in astronomy and astrophysics journals. These recommendations are intended as a reference for authors to help prepare and publish data in a way that will better represent and support science results, enable better data sharing, improve reproducibility, and enhance the reusability of data. Observance of these guidelines will also help to streamline the extraction, preservation, integration and cross-linking of valuable data from astrophysics literature into major astronomical databases, and consequently facilitate new modes of science discovery that will better exploit the vast quantities of panchromatic and multidimensional data associated with the literature. We encourage authors, journal editors, referees, and publishers to implement the best practices reviewed here, as well as related recommendations from international astronomical organizations such as the International Astronomical Union for publication of nomenclature, data, and metadata. A convenient Checklist of Recommendations for Publishing Data in the Literature (Appendix A) is included for authors to consult before the submission of the final version of their journal articles and associated data files. We recommend that publishers of journals in astronomy and astrophysics incorporate a link to this document in their Instructions to Authors.

We present the first catalog of very-high-energy and ultra-high-energy gamma-ray sources detected by the Large High Altitude Air Shower Observatory. The catalog was compiled using 508 days of data collected by the Water Cherenkov Detector Array from 2021 March to 2022 September and 933 days of data recorded by the Kilometer Squared Array from 2020 January to 2022 September. This catalog represents the main result from the most sensitive large coverage gamma-ray survey of the sky above 1 TeV, covering decl. from −20° to 80°. In total, the catalog contains 90 sources with an extended size smaller than 2° and a significance of detection at >5σ. Based on our source association criteria, 32 new TeV sources are proposed in this study. Among the 90 sources, 43 sources are detected with ultra-high energy (E > 100 TeV) emission at >4σ significance level. We provide the position, extension, and spectral characteristics of all the sources in this catalog.

We present the final nine-year maps and basic results from the Wilkinson Microwave Anisotropy Probe (WMAP) mission. The full nine-year analysis of the time-ordered data provides updated characterizations and calibrations of the experiment. We also provide new nine-year full sky temperature maps that were processed to reduce the asymmetry of the effective beams. Temperature and polarization sky maps are examined to separate cosmic microwave background (CMB) anisotropy from foreground emission, and both types of signals are analyzed in detail. We provide new point source catalogs as well as new diffuse and point source foreground masks. An updated template-removal process is used for cosmological analysis; new foreground fits are performed, and new foreground-reduced CMB maps are presented. We now implement an optimal C⁻¹ weighting to compute the temperature angular power spectrum. The WMAP mission has resulted in a highly constrained ΛCDM cosmological model with precise and accurate parameters in agreement with a host of other cosmological measurements. When WMAP data are combined with finer scale CMB, baryon acoustic oscillation, and Hubble constant measurements, we find that big bang nucleosynthesis is well supported and there is no compelling evidence for a non-standard number of neutrino species (N_eff = 3.84 ± 0.40). The model fit also implies that the age of the universe is t₀ = 13.772 ± 0.059 Gyr, and the fit Hubble constant is H₀ = 69.32 ± 0.80 km s⁻¹ Mpc⁻¹. Inflation is also supported: the fluctuations are adiabatic, with Gaussian random phases; the detection of a deviation of the scalar spectral index from unity, reported earlier by the WMAP team, now has high statistical significance (n_s = 0.9608 ± 0.0080); and the universe is close to flat/Euclidean ($\Omega _k = -0.0027^{+ 0.0039}_{-0.0038}$). Overall, the WMAP mission has resulted in a reduction of the cosmological parameter volume by a factor of 68,000 for the standard six-parameter ΛCDM model, based on CMB data alone. For a model including tensors, the allowed seven-parameter volume has been reduced by a factor 117,000. Other cosmological observations are in accord with the CMB predictions, and the combined data reduces the cosmological parameter volume even further. With no significant anomalies and an adequate goodness of fit, the inflationary flat ΛCDM model and its precise and accurate parameters rooted in WMAP data stands as the standard model of cosmology.

Time-evolving magnetohydrodynamic (MHD) coronal modeling, driven by a series of time-dependent photospheric magnetograms, represents a new generation of coronal simulations. This approach offers more realistic results than traditional steady coronal models constrained by a static magnetogram. However, its practical application is significantly limited by the low computational efficiency and poor numerical stability in solving low-β issues common in coronal simulations. To address this, we propose an extended magnetic field decomposition strategy and successfully implement it in an implicit MHD coronal model. The traditional decomposition strategies split the magnetic field into a time-invariant potential field and a time-dependent component B₁. This works well for quasi-steady-state coronal simulations where ∣B₁∣ is typically small. However, when the inner-boundary magnetic field evolves, ∣B₁∣ can grow significantly, and its discretization errors often lead to nonphysical negative thermal pressure, ultimately causing the simulation to crash. In the extended magnetic field decomposition strategy, we split the magnetic field into a temporally piecewise-constant field and a time-varying component, B₁. This effectively keeps ∣B₁∣ consistently small throughout the simulations and performs well in solving time-evolving low-β issues, thereby outperforming traditional methods. We incorporate this improved strategy into our implicit MHD coronal model and apply it to simulate the evolution of coronal structures within 0.1 au over two solar-maximum Carrington rotations. The results show that this coronal model effectively captures observational features and performs more than 80 times faster than real-time evolutions using only 192 CPU cores, making it well suited for practical applications in simulating the time-evolving corona.

The second iteration of the Faint Intergalactic-medium Redshifted Emission Balloon (FIREBall-2) is a UV multiobject spectrograph designed to detect emission from the circumgalactic and circumquasar medium at low redshifts (z < 1). The FIREBall-2 instrument uses a zero-pressure suborbital balloon to access a stratospheric transmission window centered around 205 nm. Following the payload's first flight in 2018, several refurbishments and modifications were made to the instrument and telescope to prepare for additional flight opportunities. Here we present an overview of upgrades and improvements made since the previous flight and discuss the 2023 field campaign, which culminated in a flight from Fort Sumner, New Mexico, in 2023 September. The flight was terminated early, prior to science observations; we report here the performance of the instrument in ground calibrations, the flight plan and timeline of events, and the in-flight guidance performance. We also discuss the limitations encountered in 2023 and the future outlook for FIREBall-2.

Classical Cepheids are the archetype of the standard candle, thanks to the period–luminosity relation, which allows us to measure their intrinsic brightness. They are also relatively young and bright, potentially making them excellent tracers of the young stellar population that is responsible for shaping the visible aspect of our Galaxy. However, being observers embedded in the dusty interstellar medium of the Galaxy, deriving reliable photometric distances to classical Cepheids of the Milky Way is a challenge. The typical approach is to use "reddening-free" indices, such as Wesenheit magnitudes, to obviate the need for an extinction correction. However, this approach could lead to unknown systematics—especially toward the inner Galaxy—as its assumption of a universal total-to-selective extinction ratio is not satisfied, particularly in lines of sight where the extinction is high and crosses spiral arms. We instead estimate new distances for 3424 Cepheids based on mid-IR photometry from the Wide-field Infrared Survey Explorer, which suffers minimally from extinction, and by adopting a 3D extinction map to calculate the necessary (albeit small) extinction corrections. We show that our distances are consistent with Gaia's parallaxes for the subset with relative parallax errors smaller than 10%, verifying that our mean distance errors are of the order of 6% and that the mean parallax zero-point for this subsample is 7 μas.

We present the in-lab and on-sky performance for the upgraded 90 GHz focal plane of the Cosmology Large Angular Scale Surveyor, which had four of its seven detector wafers updated during the austral winter of 2022. The update aimed to improve the transition-edge-sensor (TES) stability and bias range and to realize the high optical efficiency of the sensor design. Modifications included revised circuit terminations, electrical contact between the TES superconductor and the normal metal providing the bulk of the bolometer heat capacity, and additional filtering on the TES bias lines. The upgrade was successful: 94% of detectors are stable down to 15% of the normal resistance, providing a wide overlapping range of bias voltages for all TESs on a wafer. The median telescope efficiency improved from $0.4{2}_{-0.22}^{+0.15}$ to $0.6{0}_{-0.32}^{+0.10}$ (68% quantiles). For the four upgraded wafers alone, median telescope efficiency increased to $0.6{5}_{-0.06}^{+0.06}$. Given our efficiency estimate for the receiver optics, this telescope efficiency implies a detector efficiency exceeding 0.90. The overall noise-equivalent temperature of the 90 GHz focal plane improved from $19\,\mu {\rm{K}}\sqrt{{\rm{s}}}$ to $9.7\,\mu {\rm{K}}\sqrt{{\rm{s}}}$.

Numerous solar and space science and operations projects rely heavily on accurate, consistent magnetic field measurements from the solar surface. These projects are hindered by well-known but poorly understood discrepancies between magnetograms obtained with different solar telescopes and instrumentation. Existing efforts to characterize these discrepancies have mostly been limited to direct comparisons between final data products and have been inconclusive regarding the correct measurement. To attack this problem, we model every step of the line-of-sight (LOS) photospheric field measurement all the way to the final magnetogram. Beginning with known MHD simulation data for the magnetic field, the "ground truth," we compute for different viewing angles the radiative transfer for the Stokes spectra using the Rybicky and Hummer (RH) radiative transfer code. We then use the Solar Orbiter Polarimetric and Helioseismic Imager Software Simulator, adapted for the Solar Dynamics Observatory Helioseismic and Magnetic Imager (HMI) instrument, to simulate the instrument response to emergent polarized spectra. We model every significant process undergone by the solar signal during an observation: degradation by instrumental limitations including finite spatial and spectral resolution, Doppler shift variations due to the radial spacecraft orbital velocity, and the effects of Stokes inversion for the LOS magnetic field. Finally, we compare the simulated magnetograms with the MHD field data using the computed line formation information along each LOS and construct a detailed end-to-end magnetogram calibration. Effects of the calibration on real HMI magnetograms are discussed, including open magnetic flux estimates, and are compared with high-resolution data.