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  • Thermal and Optical Characterization of Near-Earth Objects: Science Commissioning of the Recently Upgraded Mid-infrared Camera MIRSI on the NASA Infrared Telescope Facility
    Mid-infrared (mid-IR) observations of near-Earth objects (NEOs) have historically been a valuable tool for understanding their physical properties. However, the current state of mid-IR instruments on ground-based telescopes places several limitations on performing thermal characterization of NEOs. The complexity of maintaining these instruments in operational conditions on telescopes has led to their decommissioning. Here, we present the first science commissioning observations out to 12.5 μm from the upgraded Mid-Infrared Spectrograph and Imager (MIRSI) at the NASA-IRTF. We obtained 42 observations of 31 NEOs and derived their diameters and albedos. Since MIRSI allows for simultaneous optical observations with its MIRSI Optical Camera, we were able to determine the absolute magnitude for most of the targets at the time of the thermal acquisition. We present ejecta characterization for the Didymos system from observations made 11 hr and 9 days after the Double Asteroid Redirection Test impact. We present albedo and size measurements for (98943) Torifune 2001 CC21, the fly-by target of the Japanese Extended Hayabusa2 Mission. We also highlight several applications that the MIRSI system will provide for future airless body characterization, such as constraining thermal inertia from simultaneous optical and thermal lightcurves. This work also demonstrates the importance of having MIRSI as an available rapid-response instrument for planetary defense purposes.

  • Survey of Oxygen-rich AGB Stars Using the KVN 4 Receiving Bands—SMASTES. I.
    Simultaneous observations of 19 H2O and SiO maser and thermal lines were performed toward 155 M-type oxygen-rich (O-rich) AGB stars. We used the upgraded four-band (22/43/86/129 GHz) wide receiving system of the Korean VLBI Network (KVN). The 155 O-rich stars composed of 50 semiregulars (SRs), 55 Miras, and 50 OH/IR stars were selected based on previous KVN H2O/SiO detected sources. Both H2O and SiO masers were detected in 23 stars among 50 SRs, 50 stars among 55 Miras, and 24 stars among 50 OH/IRs, respectively. Out of 50 SRs, H2O-only masers, without corresponding SiO maser detection, were observed in four stars. In contrast, no H2O-only masers were detected in any of the 55 Mira or 50 OH/IR stars, which differs from the pattern seen with SiO-only masers. Interestingly, in the 50 SRs, the SiO v = 1, J = 2–1 maser was detected more than the SiO v = 1, J = 1–0 maser despite requiring a higher excitation energy. The 28SiO v = 0, J = 1–0, 2–1, 3–2 lines were detected more frequently at higher rotational transitions, especially in the SRs and Miras. The HCN and SiS were detected from 11 and 3 stars, respectively. For our observational results, we performed statistical analysis on the intensity ratio variations among H2O and various SiO masers, chemical environments, and wind kinematics. The characteristics of these property variations were investigated in the IRAS two-color diagram in relation to their evolutionary stages.

  • Binary Star Orbits. VI. The Interferometric-spectroscopic Binary 73 Leo
    Discordances in radial-velocity measurements of 73 Leonis, made more than a century ago, gave rise to the first suggestion that this fifth-magnitude star was a binary system, but it was 40 yr before an accurate investigation of the object commenced, and a further 25 yr (close to three orbital cycles) before R. F. Griffin’s new velocities, combined with older ones, yielded a high-quality orbit. However, a few years earlier the system had been resolved astrometrically by speckle interferometry, so a combined solution was attempted that yielded a very precise period (σ ∼ 0.1%P, primarily on the strength of the precision of the radial-velocities), with a less-well determined semimajor axis (σ ∼ 2.4%a″). Nonetheless 73 Leo continued to present a challenge to astrometric and photometric techniques alike, and also to spectroscopic classification and stellar-evolution theory. Now, with the superior resolution capability of the Navy Precision Optical Interferometer and new radial-velocity data from the Dominion Astrophysical Observatory high-resolution spectrograph, those uncertainties have been reduced to 0.02% in P and 0.15% in a″. This paper describes the new data acquired since 1997, and reports our new attempts to parameterize the system (including the spectral type of the secondary) by appealing to very recent photometry. Notwithstanding, direct spectroscopic evidence of the secondary component is little more than suggestive, so a complete SB2 solution yielding an orbital parallax and limits to the masses of the component stars remains elusive.

  • Planetesimal Scattering Efficiency of Cold Giant Planet Architectures
    The discovery of many exoplanets has revealed an incredible diversity of orbital architectures. These orbital configurations are intrinsically linked to the potential for habitable environments within the system, since the gravitational influence of the planets governs the angular momentum distribution within the system. This angular momentum distribution in turn alters the planetary orbits and rotational obliquities. In the case of giant planets, their gravitational influence can also produce significant redistribution of volatiles, particularly those that lie beyond the snow line. Here, we present the results of dynamical simulations that investigate the role of cold giant planets in scattering material to inner terrestrial planets. We highlight 10 exoplanetary systems with two or more known giant planets beyond the snow line, and adopt a solar system analog template that investigates the scattering of material within the range 3–8 au. We show that increasing the eccentricity of a Jupiter analog from its present, near-circular value to a moderate range (0.2–0.3) results in an order of magnitude increase in scattered material to the inner part of the system. The inclusion of a Saturn analog to the dynamical model produces a similar increase, highlighting the importance of multiple giant planets beyond the snow line. However, the addition of analogs to Uranus and Neptune can have a minor negative effect on scattering efficiency through the transfer of angular momentum from the inner giant planets.

  • Acceleration of C iv and Si iv Broad Absorption Lines in Quasar SDSS J140058.79+260619.4
    We report the discovery of a velocity shift signature in the C iv and Si iv broad absorption lines (BALs) of the quasar SDSS J140058.79+260619.4 (zem = 2.351). From its two-epoch spectra, we find two BAL systems (systems A and B) in C iv and/or Si iv ions. Firstly, we find obvious variations of equivalent widths across all BAL troughs, which are most plausibly explained by changes in ionization states. Secondly, system A, characterized by a higher velocity and smoother profile shape (than those of System B), shows significant velocity shifts in C iv and Si iv BALs between two epochs, indicating potential outflow accelerations. Over 1.83 yr in the rest frame, we measure velocity differences of −481 ± 64 km s−1 for C iv and −550 ± 95 km s−1 for Si iv, corresponding to acceleration rates of −0.83 ± 0.11 cm s−2 and −0.95 ± 0.17 cm s−2, respectively. Given the limited observational data, the physical origin of this velocity shift signature remains an open question. We considered several plausible mechanisms, favoring either variations in the gas’s ionization state or actual line-of-sight acceleration driven by radiation pressure from the central source.