Search for: All records

Abstract We study the formation of stars with varying amounts of heavy elements synthesized by the rapid neutron-capture process (r-process) based on our detailed cosmological zoom-in simulation of a Milky Way–like galaxy with anN-body/smoothed particle hydrodynamics code,asura. Most stars with no overabundance inr-process elements, as well as the stronglyr-process-enhanced (RPE)r-II stars ([Eu/Fe] > +0.7), are formed in dwarf galaxies accreted by the Milky Way within the 6 Gyr after the Big Bang. In contrast, over half of the moderately enhancedr-I stars (+0.3 < [Eu/Fe] ≤ +0.7) are formed in the main in situ disk after 6 Gyr. Our results suggest that the fraction ofr-I andr-II stars formed in disrupted dwarf galaxies is larger the higher their [Eu/Fe] is. Accordingly, the most strongly enhancedr-III stars ([Eu/Fe] > +2.0) are formed in accreted components. These results suggest that non-r-process-enhanced stars andr-II stars are mainly formed in low-mass dwarf galaxies that hosted either none or a single neutron star merger, while ther-I stars tend to form in the well-mixed in situ disk. We compare our findings with high-resolution spectroscopic observations of RPE metal-poor stars in the halo and dwarf galaxies, including those collected by theR-Process Alliance. We conclude that observed [Eu/Fe] and [Eu/Mg] ratios can be employed in chemical tagging of the Milky Way’s accretion history. 

ABSTRACT We compile a catalogue of 578 highly probable and 62 likely red supergiants (RSGs) of the Milky Way, which represents the largest list of Galactic RSG candidates designed for continuous follow-up efforts to date. We match distances measured by Gaia DR3, 2MASS photometry, and a 3D Galactic dust map to obtain luminous bright late-type stars. Determining the stars’ bolometric luminosities and effective temperatures, we compare to Geneva stellar evolution tracks to determine likely RSG candidates, and quantify contamination using a catalogue of Galactic AGB in the same luminosity-temperature space. We add details for common or interesting characteristics of RSG, such as multistar system membership, variability, and classification as a runaway. As potential future core-collapse supernova progenitors, we study the ability of the catalogue to inform the Supernova Early Warning System (SNEWS) coincidence network made to automate pointing, and show that for 3D position estimates made possible by neutrinos, the number of progenitor candidates can be significantly reduced, improving our ability to observe the progenitor pre-explosion and the early phases of core-collapse supernovae. 

Abstract Transient sources such as supernovae (SNe) and tidal disruption events are candidates of high-energy neutrino sources. However, SNe commonly occur in the universe and a chance coincidence of their detection with a neutrino signal cannot be avoided, which may lead to a challenge of claiming their association with neutrino emission. In order to overcome this difficulty, we propose a search for ∼10–100 TeV multiple neutrino events within a timescale of ∼30 days coming from the same direction, called neutrino multiplets. We show that demanding multiplet detection by a ∼1 km 3 neutrino telescope limits the distances of detectable neutrino sources, which enables us to identify source counterparts by multiwavelength observations owing to the substantially reduced rate of the chance coincidence detection of transients. We apply our results by constructing a feasible strategy for optical follow-up observations and demonstrate that wide-field optical telescopes with a ≳4 m dish should be capable of identifying a transient associated with a neutrino multiplet. We also present the resultant sensitivity of multiplet neutrino detection as a function of the released energy of neutrinos and burst rate density. A model of neutrino transient sources with an emission energy greater than a few × 10 51 erg and a burst rate rarer than a few ×10 −8 Mpc −3 yr −1 is constrained by the null detection of multiplets by a ∼1 km 3 scale neutrino telescope. This already disfavors the canonical high-luminosity gamma-ray bursts and jetted tidal disruption events as major sources in the TeV-energy neutrino sky.