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1. The Sydney Radio Star Catalogue: Properties of radio stars at megahertz to gigahertz frequencies

   https://doi.org/10.1017/pasa.2024.72  

   Driessen, Laura Nicole; Pritchard, Joshua; Murphy, Tara; Heald, George; Robrade, Jan; Das, Barnali; Duchesne, Stefan William; Kaplan, David L; Lenc, Emil; Lynch, Christene R; et al (January 2024, Publications of the Astronomical Society of Australia)

   Abstract We present the Sydney Radio Star Catalogue, a new catalogue of stars detected at megahertz to gigahertz radio frequencies. It consists of 839 unique stars with 3 405 radio detections, more than doubling the previously known number of radio stars. We have included stars from large area searches for radio stars found using circular polarisation searches, cross-matching, variability searches, and proper motion searches as well as presenting hundreds of newly detected stars from our search of Australian SKA Pathfinder observations. The focus of this first version of the catalogue is on objects detected in surveys using SKA precursor and pathfinder instruments; however, we will expand this scope in future versions. The 839 objects in the Sydney Radio Star Catalogue are distributed across the whole sky and range from ultracool dwarfs to Wolf-Rayet stars. We demonstrate that the radio luminosities of cool dwarfs are lower than the radio luminosities of more evolved sub-giant and giant stars. We use X-ray detections of 530 radio stars by the eROSITA soft X-ray instrument onboard the Spectrum Roentgen Gamma spacecraft to show that almost all of the radio stars in the catalogue are over-luminous in the radio, indicating that the majority of stars at these radio frequencies are coherent radio emitters. The Sydney Radio Star Catalogue can be found in Vizier or athttps://radiostars.org. 

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2. An Image-based Search for Pulsar Candidates in the MeerKAT Bulge Survey

   https://doi.org/10.3847/1538-4357/ad74fd  

   Frail, Dale A; Polisensky, Emil; Hyman, Scott D; Cotton, William D; Kassim, Namir E; Silverstein, Michele L; Sengar, Rahul; Kaplan, David L; Calore, Francesca; Berteaud, Joanna; et al (October 2024, The Astrophysical Journal)

   Abstract We report on the results of an image-based search for pulsar candidates toward the Galactic bulge. We used mosaic images from the MeerKAT radio telescope that were taken as part of a 173 deg²survey of the bulge and Galactic center of our Galaxy atLband (856–1712 MHz) in all four StokesI,Q,U, andV. The image rms noise levels of 12–17μJy ba⁻¹represent a significant increase in sensitivity over past image-based pulsar searches. Our primary search criterion was circular polarization, but we used other criteria, including linear polarization, in-band spectral index, compactness, variability, and multiwavelength counterparts to select pulsar candidates. We first demonstrate the efficacy of this technique by searching for polarized emission from known pulsars and comparing our results with measurements from the literature. Our search resulted in a sample of 75 polarized sources. Bright stars or young stellar objects were associated with 28 of these sources, including a small sample of highly polarized dwarf stars with pulsar-like steep spectra. Comparing the properties of this sample with the known pulsars, we identified 30 compelling candidates for pulsation follow-up, including two sources with both strong circular and linear polarization. The remaining 17 sources are either pulsars or stars, but we cannot rule out an extragalactic origin or image artifacts among the brighter, flat-spectrum objects. 

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3. A circular polarization survey for radio stars with the Australian SKA Pathfinder

   https://doi.org/10.1093/mnras/stab299  

   Pritchard, Joshua; Murphy, Tara; Zic, Andrew; Lynch, Christene; Heald, George; Kaplan, David L; Anderson, Craig; Banfield, Julie; Hale, Catherine; Hotan, Aidan; et al (March 2021, Monthly Notices of the Royal Astronomical Society)

   null (Ed.)

   ABSTRACT We present results from a circular polarization survey for radio stars in the Rapid ASKAP Continuum Survey (RACS). RACS is a survey of the entire sky south of δ = +41○ being conducted with the Australian Square Kilometre Array Pathfinder telescope (ASKAP) over a 288 MHz wide band centred on 887.5 MHz. The data we analyse include Stokes I and V polarization products to an RMS sensitivity of 250 μJy PSF−1. We searched RACS for sources with fractional circular polarization above 6 per cent, and after excluding imaging artefacts, polarization leakage, and known pulsars we identified radio emission coincident with 33 known stars. These range from M-dwarfs through to magnetic, chemically peculiar A- and B-type stars. Some of these are well-known radio stars such as YZ CMi and CU Vir, but 23 have no previous radio detections. We report the flux density and derived brightness temperature of these detections and discuss the nature of the radio emission. We also discuss the implications of our results for the population statistics of radio stars in the context of future ASKAP and Square Kilometre Array surveys. 

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4. A Volume-limited Radio Search for Magnetic Activity in 140 Exoplanets with the Very Large Array

   https://doi.org/10.3847/1538-3881/ad58be  

   Ortiz_Ceballos, Kevin_N; Cendes, Yvette; Berger, Edo; Williams, Peter_K_G (August 2024, The Astronomical Journal)

   Abstract We present results from a search for radio emission in 77 stellar systems hosting 140 exoplanets, predominantly within 17.5 pc using the Very Large Array (VLA) at 4–8 GHz. This is the largest and most sensitive search to date for radio emission in exoplanetary systems in the GHz frequency range. We obtained new observations of 58 systems and analyzed archival observations of an additional 19 systems. Our choice of frequency and volume limit is motivated by radio detections of ultracool dwarfs (UCDs), including T dwarfs with masses at the exoplanet threshold of ∼13M_J. Our surveyed exoplanets span a mass range of ≈10⁻³–10M_Jand semimajor axes of ≈10⁻²–10 au. We detect a single target—GJ 3323 (M4) hosting two exoplanets with minimum masses of 2 and 2.3M_⊕—with a circular polarization fraction of ≈40%; the radio luminosity agrees with its known X-ray luminosity and the Güdel–Benz relation for stellar activity suggesting a likely stellar origin, but the high circular polarization fraction may also be indicative of star–planet interaction. For the remaining sources our 3σupper limits are generallyL_ν≲ 10^12.5erg s⁻¹Hz⁻¹, comparable to the lowest radio luminosities in UCDs. Our results are consistent with previous targeted searches of individual systems at GHz frequencies while greatly expanding the sample size. Our sensitivity is comparable to predicted fluxes for some systems considered candidates for detectable star–planet interaction. Observations with future instruments such as the Square Kilometre Array and Next-Generation VLA will be necessary to further constrain emission mechanisms from exoplanet systems at GHz frequencies. 

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5. Multi-epoch sampling of the radio star population with the Australian SKA Pathfinder

   https://doi.org/10.1093/mnras/stae127  

   Pritchard, Joshua; Murphy, Tara; Heald, George; Wheatland, Michael S.; Kaplan, David L.; Lenc, Emil; O’Brien, Andrew; Wang, Ziteng (January 2024, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT The population of radio-loud stars has to date been studied primarily through either targeted observations of a small number of highly active stars or wide-field, single-epoch surveys that cannot easily distinguish stellar emission from background extragalactic sources. As a result it has been difficult to constrain population statistics such as the surface density and fraction of the population producing radio emission in a particular variable or spectral class. In this paper, we present a sample of 36 radio stars detected in a circular polarization search of the multi-epoch Variables and Slow Transients (VAST) pilot survey with ASKAP at 887.5 MHz. Through repeat sampling of the VAST pilot survey footprint we find an upper limit to the duty cycle of M-dwarf radio bursts of $$8.5 \,\rm {per\,cent}$$, and that at least 10 ± 3 $$\rm {per\,cent}$$ of the population should produce radio bursts more luminous than $$10^{15} \,\rm {erg}\mathrm{s}^{-1} \,\mathrm{Hz}^{-1}$$. We infer a lower limit on the long-term surface density of such bursts in a shallow $$1.25 \,\mathrm{m}\rm {Jy}\rm\ {PSF}^{-1}$$ sensitivity survey of $${9}^{\, +{11}}_{-{7}}\times 10^{-3}$$  $$\,\deg ^{-2}$$ and an instantaneous radio star surface density of 1.7 ± 0.2 × 10−3  $$\,\deg ^{-2}$$ on 12 min time-scales. Based on these rates we anticipate ∼200 ± 50 new radio star detections per year over the full VAST survey and $${41\, 000}^{\, +{10\, 000}}_{-{9\, 000}}$$ in next-generation all-sky surveys with the Square Kilometre Array. 

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