First Star Survivors as Metal-Rich Halo Stars that Experienced Supernova Explosions in Binary Systems

The search for the first stars formed from metal-free gas in the universe is one of the key issues in astronomy because it relates to many fields, such as the formation of stars and galaxies, the evolution of the universe, and the origin of elements. It is not still clear if metal-free first stars can be found in the present universe. These first stars are thought to exist among extremely metal-poor stars in the halo of our Galaxy. Here we propose a new scenario for the formation of low-mass first stars that have survived until today and observational counterparts in our Galaxy. The first stars in binary systems, consisting of massive- and low-mass stars, are examined using stellar evolution models, simulations of supernova ejecta colliding with low-mass companions, and comparisons with observed data. These first star survivors will be observed as metal-rich halo stars in our Galaxy. We may have identified a candidate star in the observational database where elemental abundances and kinematic data are available. Our models also account for the existence of several solar-metallicity stars in the literature having space velocities equivalent to the halo population. The proposed scenario demands a new channel of star formation in the early universe and is a supplementary scenario for the origin of the known metal-poor stars.Comment: 41 pages, 14 figures, accepted for publication in PASJ (to be published in open access

First star survivors as metal-rich halo stars that experienced supernova explosions in binary systems

The search for the first stars formed from metal-free gas in the universe is one of the key issues in astronomy because it relates to many fields, such as the formation of stars and galaxies, the evolution of the universe, and the origin of elements. It is not still clear if metal-free first stars can be found in the present universe. These first stars are thought to exist among extremely metal-poor stars in the halo of our Galaxy. Here we propose a new scenario for the formation of low-mass first stars that have survived until today and observational counterparts in our Galaxy. The first stars in binary systems, consisting of massive- and low-mass stars, are examined using stellar evolution models, simulations of supernova ejecta colliding with low-mass companions, and comparisons with observed data. These first star survivors will be observed as metal-rich halo stars in our Galaxy. We may have identified a candidate star in the observational database where elemental abundances and kinematic data are available. Our models also account for the existence in the literature of several solar-metallicity stars that have space velocities equivalent to the halo population. The proposed scenario demands a new channel of star formation in the early universe and is a supplementary scenario for the origin of the known metal-poor stars

Two-Layer Pop-Up Origami Deployable Membrance Reflectarray Antenna Stowed in 1U CubeSat

The present paper shows the innovative deployable reflectarray antenna concept that enables to stow a 1m-by-1m square antenna into 1U CubeSat volume. The antenna is composed of two-layer membranes to obtain an air gap. A one-layer deployable membrane structure was demonstrated by the 3U CubeSat OrigamiSat-1 in 2019. The authors are currently developing two technologies to realize the reflectarray antenna. First, the deployable two-layer membrane structure is to be achieved by using pop-up picture book’s mechanism. Second, reflection elements for the reflectarray antenna that do not cross folding lines are proposed to avoid gain degradation