No. 382: †
Speaker: 堀内 貴史（東京大学天文学教育研究センター） †
Title: Evaluation of magnitudes of the Starlink satellites by simultaneous multicolor observations †
Abstract: The U.S. company, SpaceX plans to launch 42,000 Starlink satellites by the mid-2020s. However, these satellites orbit at relatively low altitudes (e.g. 550 km), and there are concerns that the light pollution from sunlight reflection likely affects observations. In January 2020, SpaceX launched a test satellite, Darksat with a black coating on its surface to reduce the reflection flux. In order to verify the effect of its black coating, we observed Darksat and unpainted Starlink satellites by simultaneous multicolor observations (g’: green, Rc: red, and Ic: near-infrared) with the 105 cm Murikabushi telescope/MITSuME. While the magnitude of Darksat is about 7, being difficult to see with the naked eyes, this brightness is sufficient to affect any observations. In June 2020, SpaceX launched Visorsat, which is a satellite with a sun visor to reduce the reflected sunlight. At the present stage, there is no sufficient verification on whether the sun visor is effective at various wavelengths. In this study, we are therefore conducting the simultaneous multicolor observations of Visorsat and the ordinary Starlink satellites through the OISTER campaign. The preliminary observations of Visorsat with the Murikabushi telescope have already shown that the apparent magnitude of Visorsat is not fainter than that of Darksat, ranging from 6.5 mag (g' band) to 5.7 mag (Ic band). Since most of the satellites to be launched by SpaceX in the future will be visor satellites, it is very important to investigate the effects of the Starlink satellites as soon as possible to reduce the light pollution in astronomical observations.
No. 381: 10 May 2022 (Tue) 16:15 - 17:15 †
Speaker: 西村優里（東京大学天文学教室） ／ Yuri Nishimura (University of Tokyo, Department of Astronomy) †
Title: Molecular spectroscopy in local and high-redshift galaxies: What do "dense gas tracers" mean? †
Abstract: Thanks to the technical advancement of (sub)millimeter observing facilities, a great number of molecular lines are now routinely observed with high sensitivity and high angular resolution. These molecular lines and line ratios are useful tools for studying physical, kinematic, and chemical properties of extragalactic systems. To fully exploit line diagnostics, it is important to relate different size scale observations: detailed understanding of nearby systems by spatially-resolved observations is essential to better interpretation of more distant objects which cannot be observed at the same physical resolution. In this talk, I will present (1) 10 pc-scale multiline mapping toward a Galactic star-forming region W3(OH); (2) spatially- and spectrally-resolved HCN and HCO+ observations of local (ultra)luminous infrared galaxies from the CONquest sample (for more detail on CONquest, see Falstad+2021); and (3) ALMA Band 3 (rest-frame ~350 GHz) line survey toward the Cloverleaf, a gravitationally-lensed quasar at z=2.56. I will first discuss which molecular emission arises from which part of the molecular cloud, and then focus on how galactic-scale dynamics, such as outflows, can alter line ratios.