Search

Detection of low-frequency (≤1.4 GHz) radio emission from stellar and planetary systems can lead to new insights into stellar activity, extrasolar space weather, and planetary magnetic fields. In this work, we investigate three large field-of-view surveys at 74 MHz, 150 MHz, and 1.4 GHz, as well as a myriad of multiwavelength ancillary data, to search for radio emission from about 2600 stellar objects, including about 800 exoplanetary systems, 600 nearby low-mass stars, and 1200 young stellar objects located in the Taurus and Upper Scorpius star-forming regions. The selected sample encompasses stellar spectral types from B to L and distances between 5 and 300 pc. We report the redetection of five stars at 1.4 GHz, one of which also shows emission at 150 MHz. Four of these are low- and intermediate-mass young stars, and one is the evolved star α Sco. We also observe radio emission at the position of a young brown dwarf at 1.4 GHz and 150 MHz. However, due to the large astrometric uncertainty of radio observations, a follow-up study at higher angular resolution would be required to confirm whether the observed emission originates from the brown dwarf itself or a background object. Notably, all of the selected radio sources are located in nearby star-forming regions. Furthermore, we use image stacking and statistical methods to derive upper limits on the average quiescent radio luminosity of the families of objects under investigation. These analyses provide observational constraints for large-scale searches for current and ongoing low-frequency radio emissions from stars and planets.

Young stars surrounded by disks with very low mass accretion rates are likely in the final stages of inner disk evolution and therefore particularly interesting to study. We present ultraviolet (UV) observations of the ~5-9 Myr old stars RECX-1 and RECX-11, obtained with the Cosmic Origins Spectrograph and Space Telescope Imaging Spectrograph on the Hubble Space Telescope, as well as optical and near-infrared spectroscopic observations. The two stars have similar levels of near-UV emission, although spectroscopic evidence indicates that RECX-11 is accreting and RECX-1 is not. The line profiles of Hα and He I λ10830 in RECX-11 show both broad and narrow redshifted absorption components that vary with time, revealing the complexity of the accretion flows. We show that accretion indicators commonly used to measure mass accretion rates, e.g., U-band excess luminosity or the Ca II triplet line luminosity, are unreliable for low accretors, at least in the middle K spectral range. Using RECX-1 as a template for the intrinsic level of photospheric and chromospheric emission, we determine an upper limit of 3 × 10^(–10) M_☉ yr–1 for RECX-11. At this low accretion rate, recent photoevaporation models predict that an inner hole should have developed in the disk. However, the spectral energy distribution of RECX-11 shows fluxes comparable to the median of Taurus in the near-infrared, indicating that substantial dust remains. Fluorescent H2 emission lines formed in the innermost disk are observed in RECX-11, showing that gas is present in the inner disk, along with the dust.