Altair ( α Aql) is one of the nearest stars to the Sun at 5.13 pc and its age has recently been revised to 88 ± 10 Myr, making it one of the youngest stars in the solar neighborhood. This makes Altair a compelling target for high-contrast direct imaging searches for giant planets. We present two epochs of simultaneous F444W and F200W MASK430R JWST/NIRCam coronagraphic imaging observations. After postprocessing, these data achieve F444W contrast levels of 2 × 10 ^−6 at 1″ (5.1 au), 1.5 × 10 ^−7 at 2″ (10.3 au), and a few ×10 ^−8 beyond 4″(20 au). Using the Sonora Flame Skimmer models, this corresponds to sub-Jupiter mass sensitivity beyond 5 au and sub-Saturn mass sensitivity beyond 10 au. We identified several candidate point sources in the field in the first epoch data. Second epoch observations confirmed that none of the candidates were co-moving with Altair and their colors are consistent with background stars. Altair has no known companions, no detected debris disk, and is not associated with any stellar association. Despite this, its youth and proximity ensure it will remain a high-priority target for future high-contrast imaging observations. We additionally discuss Altair as a potential reference star for future observations, presenting measurements of background sources in the field and showing that Altair will remain at least a few arcsec from background stars over the next 10–20 yr, making it a reliable reference target for upcoming imaging campaigns including the Roman Space Telescope Coronagraph Instrument.
Stars born in the high-α disk can later acquire low angular momentum through dynamical scattering during early merger events. Their age–metallicity distribution thus provides a fossil record of the history of both star formation and dynamical perturbations in the early Milky Way disk. Here we identify a sample of 2,078 such stars from more than two million Gaia DR3 subgiants with robust determinations of ages, kinematics, and abundances. From this sample we reconstruct their intrinsic age–metallicity distribution with a forward modeling approach. Our results confirm that these scattered stars are older and more metal-poor than the bulk of the high-α disk on average. In particular, the joint age–metallicity distribution reveals a robust two-component feature: a broad, dominant component with a peak age of ∼11.5 Gyr and [Fe/H]≃-0.59, and an older and more metal-poor component with a peak age of ∼12.5 Gyr and [Fe/H]≃-0.86. The presence of this two-component structure suggests that the high-α disk experienced episodic phases of star formation and chemical enrichment. The age distribution of the younger Splash component, compared with that of the high-α disk, provides evidence for a substantial dynamical perturbation at a lookback time of 10.8–11.5 Gyr, possibly associated with an early passage of Gaia–Sausage–Enceladus (GSE). The older Splash component, with a peak age of ∼12.5 Gyr, may preserve signatures of an earlier interaction, possibly associated with the proposed Low-energy–Kraken–Heracles (LKH) event.
Near-Earth asteroid 2024 XA1 was discovered on 2024 December 3 at 05:55 UT by the 2.3 m Bok Telescope of the University of Arizona. At 07:50 UT on the same day, subsequent orbit refinement confirmed a 100% impact probability, with atmospheric entry predicted at approximately 16:15 UT over eastern Siberia. We obtained observations of 2024 XA1 with the Lijiang 2.4 m telescope in the final ∼1 hr prior to its atmospheric entry. Due to the fact that sidereal tracking was used, the asteroid appears as a long bright trail in each exposure. We developed a method to extract light curves from asteroid trails in such trailed images and evaluate the reconstruction quality by comparing the observed trail image with the model image generated from the recovered light curve. Applying this approach to 2024 XA1 we successfully extracted its light curve. We found that the light curves of 2024 XA1 exhibit a double-peaked structure with two maxima and two minima per cycle. We derived a double-peaked rotation period of ${P}_{{\rm{rot}}}=1.6{3}_{-0.04}^{+0.06}\,{\rm{s}}$ and a peak-to-peak relative flux amplitude of about 46%. This period would make 2024 XA1 the fastest-rotating near-Earth object currently known.
We report the bow shock disappearing (BSD) events at Mercury under quiet solar wind conditions. Using data from the MESSENGER spacecraft, we identified eight BSD events. Assuming a representative solar wind velocity of 400 km s ^−1 , we calculated the critical solar wind densities required for the Alfvén Mach number to equal unity, at which point a bow shock cannot form. In all eight events, these critical densities were substantially lower than the typical solar wind densities at Mercury’s heliocentric distance. The resulting extremely low densities produced high Alfvén speeds, driving the solar wind Alfvén Mach number below unity and causing the bow shock to disappear. BSD events are rare and occur in markedly different space environments at Mercury, warranting detailed further investigation through multipoint observations by the BepiColombo mission.
We present Data Release 5 (DR5) of the Continuum Halos in Nearby Galaxies—an EVLA Survey (CHANG-ES), including select data products. These data were observed with the Karl G. Jansky Very Large Array (VLA) in C configuration, in the L band (1.575 GHz) and C band (6.0 GHz) for all 35 edge-on galaxies in the CHANG-ES sample. We combine the new C-configuration L-band images with our previously released D-configuration C-band data, together with H α and Wide-field Infrared Survey Explorer 22 μ m infrared maps, to separate the thermal and nonthermal radio continuum emission across all 34 galaxies for which H α data are available. This yields spatially resolved maps of the thermal fraction, total and nonthermal band-to-band spectral index, and star formation rate at 15″ resolution. Together with total intensity images at two weightings, these data products are included in an atlas presented here and made publicly available at http://projects.canfar.net/changes . We find that nonthermal spectral indices flatten in star-forming regions and also that radio power increases with star formation rate.
