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�����Ի���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.

Ilaria Carleo; Amadeo Castro-González; Enric Pallé; Felipe Murgas; Grzegorz Nowak; Gaia Lacedelli; Thomas Masseron; Emily W. Wong; Patrick Eggenberger; Vincent Bourrier; Dawid Jankowski; Krzysztof Goździewski; Douglas R. Alves; James S. Jenkins; Sergio Messina; Keivan G. Stassun; Jose I. Vines; Matteo Brogi; David R. Ciardi; Catherine A. Clark; William Cochran; Karen A. Collins; Hans J. Deeg; Elise Furlan; Davide Gandolfi; Samuel Geraldía González; Artie P. Hatzes; Coel Hellier; Steve B. Howell; Judith Korth; Jorge Lillo-Box; John H. Livingston; Jaume Orell-Miquel; Carina M. Persson; Seth Redfield; Boris Safonov; David Baker; Rafael Delfin Barrena Delgado; Allyson Bieryla; Andrew Boyle; Pau Bosch-Cabot; Núria Casasayas Barris; Stavros Chairetas; Jerome P. De Leon; Izuru Fukuda; Akihiko Fukui; Pere Guerra; Kai Ikuta; Kiyoe Kawauchi; Emil Knudstrup; Florence Libotte; Michael B. Lund; Rafael Luque; Eduardo Lorenzo Martín Guerrero De Escalante; Bob Massey; Edward J. Michaels; Giuseppe Morello; Norio Narita; Hannu Parvianien; Richard P. Schwarz; Avi Shporer; Monika Stangret; Noriharu Watanabe; Cristilyn N. Watkins (2026).��.��Astronomy & Astrophysics, 707, A4.��

As scientists discover more types of exoplanets (planets outside our solar system), they are rethinking what conditions might allow a planet to be habitable. Traditionally, the “habitable zone” is defined as the range of distances from a star where liquid water could exist on a planet’s surface. In this study, the authors propose a broader concept called the��“temperate zone,”��defined by the amount of stellar energy a planet receives (instellation), specifically between 0.1 and 5 times the amount Earth gets from the Sun. This wider range includes more planets that might potentially support life under different conditions.

The researchers also introduce the TEMPOS survey, which focuses on measuring the sizes of planets orbiting very cool, small stars known as M dwarfs. As part of this effort, they discovered and confirmed two planets: TOI-6716 b and TOI-7384 b. TOI-6716 b is about the same size as Earth, while TOI-7384 b is larger (closer to a “mini-Neptune”). Both orbit relatively cool M dwarf stars and complete an orbit in just a few days. The team used multiple methods—including ground-based observations, high-resolution imaging, and statistical validation—to confirm these planets and precisely measure their sizes.

Both planets receive relatively high levels of stellar energy, placing them near the hotter inner edge of the proposed temperate zone. This means they may be too warm for Earth-like conditions, but they are still valuable for studying planetary environments. Notably, TOI-6716 b could be a promising target for the James Webb Space Telescope, especially for��transmission spectroscopy��(a technique that analyzes starlight passing through a planet’s atmosphere to detect its composition), if it has retained an atmosphere. Overall, this work expands the range of planets considered potentially interesting for habitability studies and contributes new targets for future observation.

Figure 1.

��

Astronomers have observed that planets similar in size to Neptune are rarely found orbiting Sun-like stars with very short orbital periods of about four days or less. This region is known as the Neptune desert. Because such planets are uncommon, each new discovery provides important clues about how these planets form and evolve.

We report the discovery of TOI-333b, a planet located in the Neptune desert. It has a mass of about 20 times that of Earth (20.1 ± 2.4 Earth masses), a radius about 4.3 times Earth’s, and a bulk density of 1.42 g/cm³. The planet orbits an F7V-type star every 3.78 days. Its host star is slightly more massive and hotter than the Sun, with a mass of 1.2 solar masses and an effective temperature of about 6240 K. The system is likely younger than 1 billion years, based on the strength of the lithium absorption line near 6708 angstroms, which is commonly used as an age indicator in stars.

Models suggest that TOI-333b likely has a relatively small hydrogen and helium (H/He) gas envelope, making up only about 8 to 19 percent of its total mass. Other models, such as those for irradiated ocean worlds, suggest it could instead contain a significant amount of water, with about 20 percent of its mass in H2O and a rocky core making up roughly one third of the planet. Overall, the planet is likely dominated either by a mostly rocky interior with very little gas or by a rocky world with a large water component.

Compared with other known planets in the Neptune desert, TOI-333b is more massive than about 77 percent of them and larger than about 82 percent. Its host star is also among the hottest known for planets in this region. Because of these properties, the TOI-333 system provides a valuable opportunity to study how Neptune-sized planets evolve in close orbits around hot stars.

Fig 1: Left��: TESS-detrended light curve phase-folded to the best-fitting period listed in����and zoomed to show the transit event. The blue and white circles correspond to modelled photometric data and binned data with the associated photon noise error. The blue line and shaded region show the median transit model and its 1σ confidence interval.��Centre��: same as the left panel for the LCOGT-SAAO telescope.��Right��: same as the left panel for the NGTS mission.��Bottom��: Residuals of the best-fit model.

Extreme ultraviolet (EUV; 100–912 angstroms) radiation from stars plays a major role in shaping planets. EUV photons can ionize hydrogen and other atoms, which affects how planetary atmospheres form, change, and sometimes erode over time. However, for most stars that host exoplanets, their EUV radiation is difficult to measure directly and is therefore not well known.

In this study, we used a modeling method called the differential emission measure (DEM) technique to estimate the EUV spectra of eight nearby stars. These stars were previously observed with high-quality data by the Extreme Ultraviolet Explorer (EUVE) satellite between 1992 and 2002. The sample includes stars of different spectral types, from cooler M-type stars to hotter F-type stars, such as AD Leo, ε Eridani, κ¹ Ceti, Procyon, α Centauri A and B, and ξ Boötis A and B.

Our DEM-based model spectra closely match the original EUVE measurements. For most individual data points, the modeled values are within a factor of three of the observed flux densities, and for the total energy emitted between 100 and 300 angstroms, the agreement is within 30 percent. We provide the atomic data, X-ray, EUV, and far-ultraviolet observations used as inputs, along with the DEM models and the predicted EUV spectra. These predicted spectra extend beyond the original EUVE wavelength range of 90–510 angstroms.

We also found that different layers of a star’s outer atmosphere contribute differently to its EUV emission. The transition region and the corona both produce EUV radiation, but their relative contributions vary from star to star. The corona, in particular, is strongly affected by stellar flares, which cause temporary and unpredictable increases in EUV radiation at certain wavelengths. The amount and pattern of this variability depend on the star’s temperature structure, flare activity, and magnetic activity cycle.

These findings are important because many studies of planetary atmospheric evolution rely on estimates of stellar EUV radiation. Understanding how EUV emission varies over time helps improve models of how exoplanet atmospheres respond to their host stars.

Figure 1.��Demonstration of the DEM technique applied to SIRS (T. N. Woods et al.��). The top-left panel shows the median DEM value across 10⁵��draws from the posterior distribution (solid green line) with shading spanning the interval between the 16th–84th percentile of the DEM draw values and the horizontal bars are the flux constraints discussed in Section��. The bars labeled with ion species correspond to measured integrated line fluxes from that species while the unlabeled bars correspond to spectral bins where the contribution function is a sum from unresolved blends of lines and continuum processes. The top-right panel and its associated color bar show the��Gλ(T) contribution function matrix calculated using atomic data, with the position of dark patches along a single wavelength column corresponding to the plasma temperature that contributes more observed emission at that wavelength (assuming an equal distribution of plasma at all temperatures). The bottom panel compares the model-generated DEM spectrum (green) to the original data (black) with the shaded interval representing the model uncertainty determined by sampling from the posterior distribution of DEM shapes and systematic uncertainty inflation��s-factors.