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.

The star K2-19 is known to host two Neptune-sized planets that orbit very close to each other in a precise gravitational pattern called a 3:2 resonance, meaning their orbital periods are tightly linked. Because of this interaction, the planets do not pass in front of their star at perfectly regular intervals, producing strong variations in transit timing that carry information about their masses and orbits. Earlier studies, based on about 3 years of data, estimated relatively large planetary masses and unexpectedly high orbital eccentricities, or deviations from circular orbits. These high eccentricities were difficult to explain with standard models of planet formation, which motivated a new analysis using a much longer observational record.

In this study, we analyzed 10 years of transit observations using a detailed photodynamical model that accounts for the planets’ mutual gravitational effects. The longer data set confirms the earlier mass estimates for both planets, but significantly revises their orbital shapes. Instead of highly elongated orbits, the planets are now found to have much lower eccentricities, which are more in line with what is expected from conventional planet formation theories, although the orbits are still not perfectly circular. We show that the previously reported high eccentricities were driven by a single problematic transit observation taken during twilight, where observational effects caused the start of the transit to be misidentified, leading to a timing error of about 12 minutes.

Using data that span multiple long-term interaction cycles between the planets, we also applied a simpler analytical approach based on Fourier analysis of the transit-timing variations. This method reproduced the planet mass estimates to within about 2% of the full photodynamical results and did so without being sensitive to the exact eccentricities. In addition, we report evidence for a possible third planet located farther out in the system. Finally, updated modeling of the internal structure of the inner planet, K2-19 b, suggests a metal content consistent with formation through core accretion, the standard process thought to build most planets.

Fig. 1

Detection of the candidate planet e.��Left: gray data points represent the K2 data without the transits of planets b, c, and d. The orange data points show the mean GP model. The black light curve indicates the four transits we found.��Center: periodogram of the nuance algorithm.��Right: phased light curve without the noise model (gray points), binned (dark gray), and transit model (black line).

]]> /valiant/2025/12/19/calibration-of-binary-population-synthesis-models-using-white-dwarf-binaries-from-apogee-galex-and-gaia/ Fri, 19 Dec 2025 16:46:02 +0000 /valiant/?p=5560 Rubio, A. C., Breivik, K., Badenes, C., El-Badry, K., Anguiano, B., Linck, E., Majewski, S. R., & Stassun, K. G. (2025).��.��Astronomy and Astrophysics,��704, A6.��

This study looks at how pairs of stars (binary systems) exchange mass over time and how this process shapes their final outcomes. In many binary systems, material can flow from one star to the other, but this mass transfer can be either stable or unstable, and in some cases the two stars briefly share a common envelope of gas. These processes are complex, so astronomers often use fast computer models called binary population synthesis codes, which simplify the physics by using adjustable parameters to describe how stable mass transfer is, how efficiently mass is accreted, and how effectively a common envelope is ejected. The goal of this work is to better determine realistic values for these uncertain parameters by comparing model predictions with real astronomical observations.

Binary systems made up of a white dwarf and a main-sequence star are especially useful for this purpose because they can form through different evolutionary paths: stable mass transfer, unstable mass transfer with a common-envelope phase, or even with little interaction at all. These different histories leave clear signatures in today’s systems, such as their orbital periods and stellar masses. The authors use the APOGEE–GALEX–Gaia Catalog (AGGC), which contains over 500 such binaries with well-measured radial velocities, as a benchmark. They compare the observed distribution of the maximum change in radial velocity (ΔRVₘₐₓ) with simulated populations generated using COSMIC, a publicly available binary population synthesis code. In the simulations, they vary how stable mass transfer is at different giant-star stages, how efficiently stars eject their envelopes during common-envelope phases, and how much mass is retained during stable transfer.

The comparison shows that the observed data favor models in which a larger fraction of systems undergo stable mass transfer when the donor star is on the first ascent of the giant branch, as well as models where common-envelope ejection is very efficient. For the smaller number of systems where white dwarf masses can be estimated, the results slightly favor nonconservative stable mass transfer, meaning some mass is lost from the system rather than fully accreted. Because COSMIC and similar models link envelope ejection efficiency and envelope binding energy together, the finding of high ejection efficiency may imply either that extra energy sources, such as recombination energy in the envelope, help expel it, or that the envelope is less tightly bound than previously assumed. The authors note that future datasets, including upcoming Gaia releases and observations from the LISA mission, will allow even stronger tests of these models across a wider range of binary systems.

Fig 1.

Overview of the WD binaries in the APOGEE-Gaia-Galex catalog (AGGC). The left panel shows the full APOGEE dataset in blue and the companions of WDs in orange. The right panel shows the ΔRV_max��distribution for different cuts in the data: MS+MS binaries from the full APOGEE dataset in blue, all WD binaries in the AGGC in green, and WD+MS binaries in black. The full APOGEE dataset contains 455796 targets; the MS binaries in that sample number 151266. The full AGGC has 1157 candidate WD binaries, while the WD+MS systems number 588.

]]> /valiant/2025/11/23/two-warm-earth-sized-exoplanets-and-an-earth-sized-candidate-in-the-m5v-m6v-binary-system-toi-2267/ Sun, 23 Nov 2025 16:58:22 +0000 /valiant/?p=5456 Zúniga-Fernández, Sebastian., Pozuelos, Francisco J., Devora-Pajares, Martín., Cuello, Nicolas., Greklek-McKeon, Michael., Stassun, Keivan Guadalupe., van Grootel, Valérie., Rojas-Ayala, Bárbara., Korth, Judith., Günther, Maximilian N., Burgasser, Adam J., Hsu, Chihchun., Rackham, Benjamin V., Barkaoui, Khalid., Timmermans, Mathilde., Cadieux, Charles., Alonso, Roi., Strakhov, Ivan A., Howell, Steve B., Littlefield, Colin., Furlan, Elise., Amado, Pedro J., Jenkins, Jon M., Twicken, Joseph D., Sucerquia, Mario., Davis, Yasmin T., Schanche, Nicole E., Collins, Karen A., Burdanov, Artem Yu., Davoudi, Fatemeh., Demory, Brice Olivier., Delrez, Laetitia., Dransfield, Georgina., Ducrot, Elsa., García, Lionel J., Gillon, Michaël., Gómez Maqueo Chew, Y. Gómez Maqueo., Janó-Muñoz, Clàudia., Jehin, Emmanuël., Murray, Catriona Anne., Niraula, Prajwal., Pedersen, Peter Pihlmann., Queloz, Didier., Rebolo-Lopez, Rafael., Scott, Madison G., Sebastian, Daniel., Hooton, Matthew J., Thompson, Samantha J., Triaud, Amaury H.M.J., de Wit, Julien., Ghachoui, Mourad., Benkhaldoun, Z., Doyon, René Crossed Dsign©., Lafrenière, David., Casanova, Víctor M., Sota, Alfredo., Plauchu-Frayn, Ilse., Khandelwal, Akanksha., Zong Lang, Francis., Schroffenegger, Urs., Wampfler, Susanne F., Lendl, Monika A., Schwarz, Richard P., Murgas, Felipe., Palle´, Enric B., & Parviainen, Hannu. (2025).��.��Astronomy and Astrophysics,��702, A85.��

We report the discovery of two “warm” exoplanets orbiting a very tight pair of small, cool stars called TOI-2267. This binary system consists of an M5 star (TOI-2267A) and an M6 star (TOI-2267B) that appear extremely close together in the sky—only 0.384 arcseconds apart—which corresponds to a physical separation of about 8 astronomical units. The system is located just 22 parsecs from our Solar System. To confirm that the signals we detected were truly planets, we combined data from NASA’s Transiting Exoplanet Survey Satellite (TESS) with ground-based observations, high-resolution imaging, archival measurements, and statistical validation techniques.

Based on the available data, we cannot yet tell for certain which of the two stars the planets actually orbit. If the planets orbit TOI-2267A, they are close to Earth-sized, with radii of 1.00±0.11 and 1.14±0.13 Earth radii for TOI-2267 b (which orbits every 2.28 days) and TOI-2267 c (which orbits every 3.49 days). If they instead orbit TOI-2267B, their radii would be slightly larger due to the star’s dimmer brightness, at 1.22±0.29 and 1.36±0.33 Earth radii.

TESS data also show a third, strong periodic signal at 2.03 days, labeled TOI-2267.02. Statistical analysis suggests this signal is also likely caused by a planet, but follow-up observations from the ground did not detect it, so it remains a “planetary candidate.” Its radius would be roughly Earth-sized—0.95±0.12 or 1.13±0.30 Earth radii—depending on whether it orbits star A or B.

If the candidate is confirmed, orbital dynamics show that all three planets cannot orbit the same star without becoming unstable. The most likely arrangements are that planets b and c orbit one star while .02 orbits the other, or that .02 and c orbit the same star while b orbits the other. A configuration where .02 and b orbit the same star appears unstable. The fact that planets b and c lie close to a 3:2 mean-motion resonance (meaning their orbital periods are in a nearly perfect 3:2 ratio) also suggests they orbit the same star, with .02 around the other.

If this scenario is correct, TOI-2267 would be the most compact binary system known to host planets around��both��stars. This makes it a rare and valuable system for understanding how planets form and evolve in environments where two stars orbit extremely close together.

Fig. 1

Spectral energy distribution of TOI-2267. Red symbols represent the observed photometric measurements, where the horizontal bars represent the effective width of the passband. Blue symbols are the model fluxes from the best-fit NextGen stellar atmosphere model for the two stellar components (hot component in blue, cool component in red, combined light in black).

Within the Camelopardalis OB1 (Cam OB1) region—a part of the Galaxy rich in young stars and gas—astronomers previously identified a single subgroup of stars. Recent Gaia data, however, reveal three distinct star clusters in roughly the same area of the sky (galactic longitude 137°–145°, latitude −2°–5°) and at a similar distance of about 1,000 parsecs (∼3,260 light-years).

This study identifies these three clusters, refines their membership lists, and estimates their ages, while examining their 3D structures, motions, and origins. Using Gaia measurements of positions and velocities, supplemented by radial velocities from the Sloan Digital Sky Survey, the clusters are found to be approximately 10, 15.8, and 20 million years old, containing about 140, 469, and 184 stars, respectively. Although the clusters currently overlap in space, tracing their motions backward shows that each formed in a distinct location, with no influence on the others’ formation.

Two clusters originated within the Cam OB1 region, while the oldest cluster formed near the edge of the Perseus Spiral Arm, in the direction of the Perseus OB1 or Cassiopeia OB6 associations. This work demonstrates how stellar groups from different parts of the Galaxy can pass through each other as they move through space.

Figure 1.��IR (ALLWISE) color image in the direction of Cam OB1: red (W4), green (W2), and blue (W1). The four rectangles limit the areas of the associations Cassiopeia (Cas) OB6 and Perseus OB1 (Per OB1), located in the Perseus Arm, and the generic subgroups of Cam OB1 (including NGC 1502) as listed in literature. Overplotted are the three Cam OB1 cluster members as identified by this work.

MML 48 is a newly discovered eclipsing binary star system—two stars that orbit each other and periodically pass in front of one another, causing dips in their combined brightness as seen from Earth. It is located in the Upper Centaurus Lupus region, part of the larger Scorpius–Centaurus association, and is estimated to be ~16 million years old. The system contains two young, low-mass stars with very different sizes and masses.

Using both space-based and ground-based telescopes, astronomers studied the system through time-series photometry (tracking changes in brightness) and spectroscopy (analyzing starlight to measure motion and composition). Because one star is much more massive and brighter than the other—with a mass ratio of ~0.21—the system was modeled as a��single-lined spectroscopic��and��eclipsing binary, meaning only the brighter star’s spectrum can be clearly observed.

The stars orbit each other every ~2.017 days, measured with extremely high precision. The primary (larger) star has a mass of ~1.2 times that of the Sun, while the secondary (smaller) star has a mass of ~0.25 solar masses. Both stars are still contracting toward the main sequence and therefore have larger radii than mature stars of similar mass—~1.57 and ~0.59 times the Sun’s radius, respectively.

MML 48 is one of only five known eclipsing binary systems with low-mass, pre–main-sequence stars of intermediate age (~15–25 million years). It also has the most extreme mass ratio among them. Notably, the primary star is currently undergoing a “fusion bump,” a temporary increase in core energy due to the buildup of helium-3 (^3He) before it reaches equilibrium in the proton-proton (p–p) I fusion chain. This makes MML 48 A the first young star in an eclipsing system observed during this evolutionary stage.

Because of its age, well-measured properties, and unique evolutionary phase, MML 48 provides an important benchmark for understanding how low-mass stars develop, helping refine models of stellar evolution during periods of rapid change.

WASP time-series photometry of primary eclipses of MML 48 obtained in 2006–2014. The secondary eclipse is too shallow to see in this photometry, indicating the secondary is a very low-mass companion. These data were not used to derive the EB parameters since the light curves are contaminated by a nearby background star 15″ to the west (2MASS 14413595−4700280).

]]> /valiant/2025/10/23/fumes-iv-optical-and-far-ultraviolet-spectra-of-a-flare-on-the-m-dwarf-gj-4334/ Thu, 23 Oct 2025 19:09:38 +0000 /valiant/?p=5257 Duvvuri, Girish M.; Pineda, John Sebastian; Garciá Soto, Aylin; Berta-Thompson, Zachory K.; Youngblood, Allison A.; France, Kevin C.; Newton, Elisabeth R.; Stassun, Keivan Guadalupe. (2025). FUMES. IV. Astronomical Journal, 170(4), 249.

On September 20, 2017, astronomers observed the star GJ 4334, a small, cool M5V dwarf star that rotates once every ~23.5 days. The observations were part of a larger survey of moderately active M dwarfs and were conducted simultaneously using the Hubble Space Telescope’s Space Telescope Imaging Spectrograph (covering far-ultraviolet light from 1160–1710 Å) and the Dual Imaging Spectrograph on the 3.5-meter telescope at Apache Point Observatory (covering optical light from 3750–5050 Å and 5800–6950 Å).

During the observation, GJ 4334 produced a flare—a sudden, intense burst of energy. The flare began with an increase in optical chromospheric emission lines (light emitted from the star’s lower atmosphere), followed by a rapid rise and decay of multiple far-ultraviolet emission lines formed in the transition region (the layer between the star’s chromosphere and corona). Afterward, the optical lines decayed more slowly. The flare caused noticeable broadening and asymmetry in the optical lines, likely due to bulk motions of plasma on the star’s surface, and elevated fluxes (brightness) persisted after the flare in both optical and far-ultraviolet light. Higher-order Balmer lines (specific hydrogen emission lines) were found to rise earlier and decay faster than lower-order lines.

The flare’s equivalent durations in individual emission lines ranged from ~800 to 30,000 seconds, corresponding to energies of ~10²⁸–3×10²⁹ ergs per line. Comparing GJ 4334’s flare behavior with TESS observations of EV Lacertae, a similar-mass but faster-rotating M dwarf, revealed that GJ 4334 produces relatively more large flares than expected from the power-law trend of smaller flares.

This dataset provides a rare opportunity to study flares near a key stage in the evolution of stellar magnetic activity, helping astronomers understand how magnetic energy is released in low-mass stars.

Figure 1.��The quiescent APO optical spectrum is plotted in dark blue while the spectrum at flare peak is plotted in orange, with separate panels for the two arms of DIS. The flare only seems to brighten lines relative to the continuum level, leaving the majority of the continuum unchanged. The exception is the continuum below 4500 Å, which appears slightly enhanced. A subset of the optical lines analyzed in this work have been highlighted with ion labels above the line peak.