Eclipsing binaries are pairs of stars that pass in front of each other from our point of view, and they are one of the best ways to measure basic stellar properties such as mass and radius. The challenge is that working out these properties has usually taken a lot of time and computing power, so only a small number of systems have been fully analyzed. To speed this up, the authors created a neural network, a type of artificial intelligence that learns patterns from data, which can use light curves from many common filters, radial velocity measurements for both stars, and information about the stars’ brightness across the spectrum to estimate the stars’ and orbit’s properties. The model was designed to handle messy real-world data, including extra light from nearby stars, starspots, and missing measurements, and it can also report uncertainty in each prediction. After training on simulated data, the researchers tested it on about 200 eclipsing binaries that had already been studied in detail. The model could estimate masses and radii to within about 20% and surface temperature to within about 500 K, and it did so much faster than traditional methods. Although it is not as precise as a detailed star-by-star analysis, it is well suited to the huge surveys now producing thousands of eclipsing binaries, helping researchers quickly find the most interesting systems for deeper study.

Figure 1.��Distribution of the parameter space covered by the synthetic EBs.

This study looks at how aging stars generate magnetic fields and how that affects the way they lose rotation over time. Previous observations suggested that when stars rotate very slowly, their large-scale magnetic fields can become disorganized, which weakens magnetic braking, the process by which a star slows down as it loses angular momentum through its magnetic wind. Computer simulations also predict that at slow enough rotation rates, a star’s surface can switch from “solar-like” differential rotation, where the equator spins faster than the poles, to “antisolar” differential rotation, where the poles spin faster than the equator. These conditions usually are not reached on the main sequence, the long stable part of a star’s life, because magnetic braking prevents stars from slowing that much. But when a star evolves into a subgiant and expands, its rotation can slow further and possibly cross that threshold. To test these ideas, the researchers combined asteroseismology, which uses tiny oscillations inside a star to probe its structure, from NASA’s TESS mission with spectropolarimetry, a technique that measures magnetic fields using polarized light, from the Large Binocular Telescope, focusing on the old metal-rich subgiant 31 Aql. They found that the star has a strong large-scale magnetic field and that 50 years of chromospheric emission data show it does not cycle the way the Sun does, matching the predicted behavior. The star also shows different rotation periods at different times, consistent with differential rotation, although the data do not reveal whether the pattern is solar-like or antisolar. By combining the TESS data with rotational modeling, the team estimated the current wind-braking torque and found evidence that magnetic braking has become active again in this evolved star. They also used the results to place an initial estimate on the Rossby number, a quantity that relates rotation to convection, for the transition to antisolar differential rotation.

��

Figure 1.��Top: power spectral density (PSD) in the frequency range of the fitted modes. In gray is the raw spectrum and in black a smoothed PSD. The blue line represents the fitted spectrum. The vertical red, yellow, and magenta bars indicate the central frequencies of the��ℓ��=��0, 1, and 2 modes, respectively. Bottom: échelle diagram with Δν��=��88.40μHz. The fitted modes and their associated uncertainties are shown as circles, diamonds, and triangles with the same color-coding as in the top panel.

To better understand��protoplanetary disks—the disks of gas and dust around young stars where planets form—scientists need models that can explain both their��spectra��(how they emit light at different wavelengths) and their physical structure. In earlier work, the authors developed a combined approach called the��EaRTH Disk Model, which links observational data from infrared spectra with��radiative transfer models��(simulations of how light moves through and interacts with matter).

In this study, they improve one part of that model: how temperature is distributed across the disk. Instead of using a more complex method that requires breaking the disk into many small pieces for calculation, they introduce a simpler mathematical description that still captures how temperature varies with location. This new approach uses an empirical (data-driven) relationship between spatial properties of the disk, making it easier for models to fit real observations while staying physically realistic.

They tested the updated model using infrared data from the��Spitzer Space Telescope, focusing on��transition disks��(disks with gaps or holes that may indicate planet formation). The results provide insights into the disks’ composition (mineralogy) and structure, including evidence for��grain growth and processing—key steps in the early stages of planet formation.

Figure 1.��Model fit plots of TZTD empirical mineralogical analysis of Spitzer/IRS spectra of targets indicated in Table��. Red: cool-disk component constituents; blue: warm-disk component constituents; see Figure Set��in the����for legend of dust components.

]]> /valiant/2026/04/29/mapping-the-distant-and-metal-poor-milky-way-with-sdss-v/ Wed, 29 Apr 2026 04:16:39 +0000 /valiant/?p=6591 Chandra, Vedant; Cargile, Phillip A.; Ji, Alexander P.; Conroy, Charlie; Rix, Hans-Walter; Cunningham, Emily; Dias, Bruno; Laporte, Chervin; Cerny, William; Limberg, Guilherme; Bandyopadhyay, Avrajit; Bonaca, Ana; Casey, Andrew R.; Donor, John; Fernández-Trincado, José G.; Frinchaboy, Peter M.; Gupta, Pramod; Hawkins, Keith; Johnson, Jennifer A.; Kollmeier, Juna A.; Lucey, Madeline; Medan, Ilija; Mészáros, Szabolcs; Morrison, Sean; Sánchez-Gallego, José; Saydjari, Andrew K.; Sayres, Conor; Schlaufman, Kevin C.; Stassun, Keivan G.; Tayar, Jamie; Way, Zachary (2026).��.��Astrophysical Journal, 1000(2), 283.��

The Sloan Digital Sky Survey V (SDSS-V) is carrying out the first full-sky survey of stars in the Milky Way’s��stellar halo(the extended, sparse region surrounding the galaxy) using low-resolution��spectroscopy��(analyzing starlight to learn about stars’ properties). This study describes the data-processing system used for this survey, which combines multiple types of observations—stellar spectra, brightness measurements (photometry), and distance information from��parallax—to estimate key properties such as a star’s temperature, chemical composition (metallicity), abundance of certain elements (like��alpha elements, which trace stellar history), and distance.

The resulting dataset, called the��BOSS-MINESweeper catalog, was carefully tested by comparing its results with well-studied star clusters and more precise, high-resolution surveys. The catalog proves powerful for several types of research: it can identify unusual stars with rare chemical signatures, reveal previously unknown structures in the distant halo, and map how stars move across the galaxy on very large scales.

Overall, this work provides a major new resource for studying the formation and evolution of the Milky Way. The catalog is publicly available and will continue to grow with future data releases.

Figure 1.��Top: distribution of SDSS-V halo stars observed up through 2024, in Galactic coordinates. This figure includes data observed from both APO and LCO, although only APO data are released in DR19. Bottom: stellar distribution in Gaia color–magnitude space, colored by median SNR (in the 4750−5500 Å region) of the co-added BOSS spectrum. Contours of target density are overlaid. The displayed color range corresponds to stellar temperatures from ≈3800 to 6500 K.

This study reports the discovery and confirmation of a small, Earth-sized��exoplanet��(a planet outside our solar system) called��TOI-1080 b, which orbits its star every ~4 days. The host star is a nearby, relatively quiet��M dwarf��(a small, cool type of star) located about 25.6 parsecs (~83 light-years) away. The planet was first detected by the TESS space telescope using the��transit method��(observing dips in starlight as the planet passes in front of the star) and confirmed with additional space- and ground-based observations.

TOI-1080 b has a radius about 1.2 times that of Earth and a moderate��equilibrium temperature��of around 368 K (about 95°C), placing it in a “temperate” range compared to many hotter close-in planets. Measurements of the star’s motion (radial velocity) suggest the planet’s mass is less than about 10.7 times Earth’s mass. The researchers also ruled out the presence of other nearby planets of similar size in short orbits around the same star.

Because it is relatively small, nearby, and orbits a quiet star, TOI-1080 b is an excellent candidate for further study—especially for examining its possible��atmosphere��using powerful telescopes like the James Webb Space Telescope (JWST). It is considered a high-priority target for ongoing programs focused on detailed studies of rocky, Earth-like worlds.

Figure 1.

FIRE spectrum of TOI-1080. The target spectrum (red) is shown alongside that of the��SPEX��SXD spectrum of the M3.5 V standard Luyten’s Star (GJ 273; grey). The higher spectral resolution of the FIRE spectrum gives it a more jagged appearance. Strong M-dwarf spectral features and spectral regions with strong tellurics are indicated. The figure shows the normalized flux of the planet host TOI-1080 as a function of wavelength, between 0.9 to 2.35 microns.

Brown dwarfs (BDs)��are objects with masses between planets and stars, making them useful for understanding how properties change across this range. In this study, researchers report the discovery of two such objects—TOI-4776 b��and��TOI-5422 b—identified using data from the TESS space telescope. Both are��transiting systems, meaning the brown dwarf passes in front of its host star, causing a small, measurable dip in brightness that reveals its size and orbit. Although the two objects have similar masses, they differ in age and physical properties.

TOI-4776 b is younger and larger, orbiting its star every ~10 days, and appears��“i�Դڱ����ٱ��”—its radius is bigger than expected based on standard models of how brown dwarfs evolve. In contrast, TOI-5422 b is older, smaller, and orbits more quickly (about every 5 days). It appears slightly����вԻ������ܳ����Դdzܲ�,”��meaning it emits less light than models predict, which is unusual for objects like this.

The study also found that the star hosting TOI-5422 b shows brightness variations linked to its rotation, suggesting the brown dwarf may be influencing the star’s spin. The alignment between the star’s rotation and the brown dwarf’s orbit indicates a close dynamical relationship. Overall, these two systems provide valuable examples for testing and refining models of how brown dwarfs form and evolve over time.

Figure 1.��Detrended TESS light curve of TOI-5422 shown as dark blue points. The star was observed at 10 minute cadence in TESS Sectors 43, 44, and 45, and 2 minute cadence in Sectors 71 and 72. Removed TESS data in Sectors 43–45 are shown as gray points. The binning shown here as yellow points uses bin sizes of 90 minutes. This star also exhibits photometric variations likely due to stellar rotation; these effects have been removed for the transit analysis. The red line is the fitted model from��EXOFASTv2.

]]> /valiant/2026/04/29/the-importance-of-standardizing-spectra-in-the-era-of-large-spectroscopic-surveys-a-case-study-of-m-dwarfs-in-sdss-v/ Wed, 29 Apr 2026 03:23:42 +0000 /valiant/?p=6557 Medan, Ilija; Way, Zachary; Rojas-Ayala, Bárbara; Stringfellow, Guy S.; Sayres, Conor; Stassun, Keivan G.; Casey, Andrew R.; Lépine, Sébastien; Galligan, Emma; Souto, Diogo; Saydjari, Andrew K. (2025).��.��Astronomical Journal, 170(6), 302.��

The Sloan Digital Sky Survey V (SDSS-V) will collect a large number of spectra—detailed “fingerprints” of light—from��M dwarfs, which are small, cool stars that are very common in our galaxy. However, analyzing these stars is challenging because their atmospheres produce complex spectra filled with many overlapping��molecular absorption features��(dark bands where molecules absorb light), making it hard to determine key properties like temperature or composition using traditional models. To get around this, researchers often use��machine learning, training algorithms to estimate stellar properties by learning from higher-quality data. But these methods can introduce errors, partly because of how the spectra are��normalized—a process that adjusts the data to make comparisons easier.

In most stars, normalization involves identifying a smooth baseline (the��continuum) and measuring how much light is absorbed relative to it. For M dwarfs, this is difficult because their spectra are so dominated by absorption features that a clear baseline is hard to define. To solve this, the authors developed a new method that estimates a��‼�����ܻ�dz��DzԳپ��Գܳܳ�”—an approximate baseline—by identifying the least absorbed parts of the spectrum and fitting a smooth curve through them. They tested and refined this approach using simulated data designed to mimic real observations, including effects from instruments and noise.

The results show that this new method produces more consistent spectra for stars with similar properties and better distinguishes between different types of M dwarfs compared to existing techniques. This improvement is important for making more accurate measurements of stellar properties in large surveys like SDSS-V, especially when using advanced modeling approaches such as machine learning.

Figure 1.��H-R diagram of the number of spectra observed with BOSS for the Milky Way Mapper (MWM) during SDSS-V until MJD = 60715 (2025 February 9). The top and right histograms show the cumulative distributions of in��G –��RP and��MG, respectively. For the��MG��distribution, the location of main-sequence spectral types as a function of��MG��from M. J. Pecaut & E. E. Mamajek () are shown for reference. From the��MG��cumulative distribution on the right, an impressive ∼one-third of BOSS MWM spectra are of M dwarfs.

]]> /valiant/2026/04/29/spyglass-vii-a-the-demographics-and-ages-of-small-nearby-young-associations/ Wed, 29 Apr 2026 03:22:18 +0000 /valiant/?p=6554 Kerr, Ronan; Paolino, Facundo Pérez; Tan, Jonathan C.; Speagle, Joshua S.; Kraus, Adam L.; Fernández-Trincado, José G.; Stassun, Keivan G.; Chanamé, Julio (2025).��.��Astrophysical Journal, 995(2), 217.��

Recent surveys using data from the��Gaia space telescope��have uncovered many small, faint groups of young stars that were previously too sparse to detect. These groups, called��stellar associations��(loose collections of stars that formed together), are still poorly understood, especially because their isolated locations may preserve clues about how they formed without being heavily disturbed by gravity from nearby objects. In this study, researchers examined 15 of these newly identified associations for the first time by combining Gaia data—which provides precise measurements of star positions and brightness—with additional��spectroscopy��(analysis of starlight to determine motion and composition).

They confirmed which stars belong to each group, looked for internal structure, estimated their total mass, and determined their ages. Some of these associations are extremely small, containing less than 20 times the mass of the Sun, making them the smallest known groups of this kind. In a few cases, the researchers found smaller subgroups within the larger associations, including a newly identified one that appears to have a different origin than its neighbors. Using models of how stars evolve over time (called��isochrones) and other age indicators like��lithium depletion��(a method based on how stars burn lithium as they age), they estimated ages ranging from about 7 million to 43 million years.

Overall, this work provides the first detailed look at a previously overlooked population of young star groups. Studying these small and relatively undisturbed systems could help scientists better understand how stars form and evolve in our region of the galaxy.

Figure 1.��Fits to the background contamination for all 15 associations included in this paper, which provide false-positive rates, or the rate at which field stars are incorrectly assigned to the association. For populations where a Gaussian fit was used to fit the background, the fit is shown in dark blue, while the RV histogram of all stars is shown in light blue. The shaded region is masked, as that is the RV range occupied by the association. For populations with features that make a fit difficult, we take the mean and standard deviation of a set of probable nonmembers, which are indicated by the red bins. A curve representing the field model in these cases is shown in dark red. In TOR1, we show��P_fp��results separately for the two components discussed in Section��.

]]> /valiant/2026/04/29/giant-outer-transiting-exoplanet-mass-gota-em-survey-vii-toi-6041-a-multi-planet-system-including-a-warm-neptune-exhibiting-strong-transit-timing-variations/ Wed, 29 Apr 2026 02:44:21 +0000 /valiant/?p=6531 Heidari, Neda; Alnajjarine, Ahmad; Osborn, Hugh P.; Dragomir, Diana; Dalba, Paul; Benz, Willy; Hébrard, Guillaume; Laskar, Jacques; Billot, Nicolas; Günther, Maximilian N.; Wilson, Thomas G.; Alibert, Yann; Bonfanti, Andrea; Bieryla, Allyson; Broeg, Christopher; Correia, Alexandre C. M.; Egger, Jan A.; Essack, Ziyaad; Furlan, Elsa; Gandolfi, Davide; Grieves, Neil; Howell, Steve; Lacourse, David; Pezzotti, Carlo; Pritchard, Tom; Sousa, Sérgio G.; Ulmer-Moll, Stéphanie; Villanueva, Sergio; Alonso, Roi; Asquier, Julien; Bárczy, Tamás; Barrado, David; Barros, Susana C. C.; Baumjohann, Wolfgang; Borsato, Luca; Brandeker, Alexis; Buder, Sven; Collier Cameron, Andrew; Csizmadia, Szilárd; Cubillos, Patricio E.; Davies, Melvyn B.; Deleuil, Magali; Delfosse, Xavier; Deline, Alexandre; Demangeon, Olivier D. S.; Demory, Brice; Derekas, Attila; Edwards, Billy; Ehrenreich, David; Erikson, Anders; Fortier, Andrea; Fossati, Luca; Fridlund, Malcolm; Gazeas, Konstantinos; Gillon, Michaël; Güdel, Manuel; Hasiba, Jozef; Heitzmann, Alexandre; Helling, Christiane; Jenkins, Jon M.; Keller, Tobias; Kane, Stephen R.; Stassun, Keivan G.; Kiss, László L.; Korth, Judith; Lam, Kwok-Wai F.; Latham, David W.; Lecavelier des Etangs, Alain; Leleu, Adrien; Lendl, Monika; Maxted, Pierre F. L.; McDermott, Sean; Merín, Bruno; Mordasini, Christoph; Nascimbeni, Valerio; Nowak, Grzegorz; Olofsson, Göran; Pagano, Ignasi; Pallé, Enric; Piotto, Giampaolo; Pollacco, Don; Queloz, Didier; Ragazzoni, Roberto; Rauer, Heike; Ribas, Ignasi; Ricker, George; Santos, Nuno C.; Scandariato, Gaetano; Seager, Sara; Ségransan, Damien; Simon, Alexandre E.; Smith, Alexis M. S.; Stalport, Marie; Striegel, Sebastian; Sulis, Stefano; Szabó, Gyula M.; Udry, Stéphane; Van Grootel, Valérie; Vanderspek, Roland; Venturini, Julien; Villaver, Eva; Viotto, Valerio; Walton, Nicholas A.; Winn, Joshua N.; Wolf, Sebastian (2026).��.��Astronomy and Astrophysics, 707, A134.��

This study describes a newly analyzed planetary system called��TOI-6041, centered around a relatively bright, Sun-like star. Researchers identified at least two planets orbiting this star. The inner planet,��TOI-6041 b, is a “warm Neptune,” meaning it is similar in size to Neptune but orbits closer to its star, giving it a higher temperature. It was first noticed as a single dip in brightness (a��transit, when a planet passes in front of its star) in data from the TESS space telescope. Follow-up observations with TESS and another space telescope, CHEOPS, detected more transits, allowing scientists to determine that the planet orbits its star roughly every 26 days. Interestingly, the timing of these transits is not perfectly regular—there are noticeable shifts of up to about an hour, known as��transit-timing variations (TTVs), which often संकेतthe gravitational influence of other planets in the system.

Additional measurements using the��radial velocity (RV)��method—which detects tiny wobbles in a star caused by orbiting planets—revealed a second planet,��TOI-6041 c, with a much longer orbit of about 88 days and a mass at least a quarter that of Jupiter. The researchers suggest that the gravitational pull of this outer planet could explain the unusual timing variations of the inner planet, but only if planet c has a somewhat elongated (eccentric) orbit. Their calculations show that such an arrangement could remain stable over time. However, another possibility is that there is a third, smaller planet in the system that has not yet been directly detected, which could also be causing the timing irregularities—especially if it is in a special orbital relationship called a��resonance��(where orbital periods are in simple ratios).

Because the current data are not yet precise enough to fully resolve these possibilities, the authors emphasize the need for more observations. Better measurements would help determine the exact masses of the planets and clarify how they interact, ultimately improving our understanding of the system’s structure and long-term stability.

Fig 1: Spectral energy distribution of TOI-6041. Red symbols represent the observed photometric measurements, where the horizontal bars represent the effective width of the pass band. Blue symbols show the model fluxes from the best-fit PHOENIX atmosphere model (black). The absolute flux-calibrated��Gaia��spectrum is shown as a gray swathe in the inset figure.

The Sloan Digital Sky Survey V (SDSS-V) is an ambitious project designed to map the entire sky by analyzing light from stars, galaxies, and other cosmic objects in unprecedented detail. It uses a technique called��spectroscopy, which breaks light into its component colors (like a rainbow) to reveal information about an object’s composition, motion, and physical properties. What makes SDSS-V unique is its “panoptic spectroscopy,” meaning it repeatedly observes the whole sky across a wide range of wavelengths—from visible (optical) light to infrared—allowing scientists to track how objects change over time.

To do this efficiently, SDSS-V uses��multiobject spectroscopy (MOS), where hundreds of optical fibers (thin light-guiding cables) are precisely positioned by robots to collect light from many objects at once. These fibers feed the light into instruments called��spectrographs, which measure the detailed spectrum. The survey operates from telescopes in both the northern and southern hemispheres, ensuring full-sky coverage. It also introduces a newer method called��integral field spectroscopy (IFS), which captures spectral information across large patches of sky simultaneously, rather than just from individual points. This is achieved using an array of small lenses and fibers that together create a detailed, spatially resolved map of light over a wide area.

SDSS-V is organized into three main science programs. The��Milky Way Mapper��studies the chemical composition and motion of stars to reconstruct the formation history of our galaxy (often called its “chemodynamical” evolution). The��Black Hole Mapper��focuses on understanding how supermassive black holes grow and influence their surroundings. The��Local Volume Mapper��examines nearby galaxies to learn how energy and elements are distributed and recycled within them. By combining advanced instruments with a long-term observing strategy, SDSS-V is set to greatly expand our understanding of the universe, while also complementing data from major space missions. It builds on the legacy of earlier SDSS projects, continuing their tradition of large-scale collaboration and high-impact astronomical data.

Figure 1.��A schematic representation of SDSS-V: an all-sky, multiepoch spectroscopic facility and its science programs. Dual-hemisphere survey operations are undertaken at APO and LCO. Multiobject fiber spectroscopy is being carried out with two 2.5 m telescopes, each feeding a near-IR APOGEE spectrograph (300 fibers,��R��∼��22,000) and an optical BOSS spectrograph (500 fibers,��R��∼��2000). This enables a sky survey rate of ≳ 25 deg²��hr⁻¹. Ultra–wide-field integral field spectroscopy is being carried out by the LVM-I at LCO using a smaller 0.16 m telescope, with a ∼2000-fiber IFU feeding three optical��R��∼��4000 spectrographs. This schematic also outlines the three primary science programs: the MWM (red), drawing on both APOGEE (red) and BOSS (yellow) spectra; the BHM (orange), taking BOSS spectra of fainter targets; and the LVM (green), performing IFU mapping of the ionized ISM in the MW and nearby galaxies (image credit: M. Seibert).