We report sub-parsec-scale observations of the 321 GHz H2O emission line in the radio galaxy NGC 1052. The H2O line emitter size is constrained in <0.6 mas distributed on the continuum core component. The brightness temperature exceeding 106 K and the intensity variation indicate certain evidence for maser emission. The maser spectrum consists of redshifted and blueshifted...
We performed a correlation analysis between the brightness temperature of the CO line and number density of H ii regions in the longitude–velocity diagram (LVD) of the Milky Way in order to investigate the volumetric star-formation law. We determined the index α of the Kennicut–Schmidt law for the molecular gas defined by |$\rho _{\rm SFR}\propto \rho _{\rm H_2}^\alpha$|, where...
We report on the results of a survey we conducted on the Japanese public’s attitudes toward astronomy. This survey was conducted via an online questionnaire, with 2000 responses received. Based on these data, we present what kind of interest the general public in Japan has in astronomy. We also conducted a questionnaire survey of those involved in communicating astronomy to the...
It has been argued that SDSS J1430+2303 possesses a supermassive black hole binary that has been predicted to merge within a few months or three years from 2022 January. We have conducted follow-up optical spectroscopic observations of SDSS J1430+2303 with the KOOLS-IFU on the Seimei Telescope in 2022 May, June, and July, and 2023 April. The observed spectrum around Hα shows a...
We study the long-term evolution of the Milky Way (MW) over cosmic time by modeling the star formation, cosmic rays, metallicity, stellar dynamics, outflows, and inflows of the galactic system to obtain various insights into the galactic evolution. The mass accretion is modeled by the results of cosmological N-body simulations for the cold dark matter. We find that the star...
We present the HINOTORI (Star Formation History Investigation To Find Rejuvenation) project to reveal the nature of rejuvenation galaxies (RGs), which are galaxies that restarted their star formation after being quiescent. As the first step of HINOTORI, we construct the largest RG sample with 1071 sources. We select these RGs from 8857 MaNGA (Mapping Nearby Galaxies at APO...
The effect of the surrounding environment of supernova remnant shocks on nonthermal X-rays from accelerated electrons, with or without interacting dense material, is an open issue. We conduct spatially resolved X-ray spectroscopy of the shock–cloud interacting region of RCW 86 with XMM–Newton. It is found that bright soft X-ray filaments surround the dense cloud, observed with...
A planet embedded in a protoplanetary disk produces a gap by disk–planet interaction. It also generates velocity perturbation of gas, which can also be observed as deviations from the Keplerian rotation in the channel map of molecular line emission, called kinematic planetary features. These observed signatures provide clues to determine the mass of the planet. We investigated...
Large solar flares occasionally trigger significant space-weather disturbances that affect the technological infrastructures of modern civilization, and therefore require further investigation. Although these solar flares have been monitored by satellite observations since the 1970s, large solar flares occur only infrequently and restrict systematic statistical research owing to...
We report on the determination of the mass of TOI-519 b, a transiting substellar object around a mid-M dwarf. We carried out radial velocity measurements using Subaru/InfraRed Doppler (IRD), revealing that TOI-519 b is a planet with a mass of |$0.463^{+0.082}_{-0.088}\, M_{\rm Jup}$|. We also found that the host star is metal rich ([Fe/H] = 0.27 ± 0.09 dex) and has the lowest...
Chromospherically active binaries are important in the understanding of the origins of optical flares. Since studies of flares in binaries are important, we perform a detailed analysis of 11 flares emitted by the RS CVn binary source CF Tucanae using the Transiting Exoplanet Survey Satellite (TESS). We assume a 10000 K blackbody spectrum to determine the flare energies, which...
In this study, we reported the results of high-resolution (|${0{^{\prime \prime}_{.}}14}$|) Atacama Large Millimeter/submillimeter Array (ALMA) observations of the 225 GHz dust continuum and CO molecular emission lines from the transitional disk around SY Cha. Our high-resolution observations clearly revealed the inner cavity and the central point source for the first time. The...
Hadronic γ-ray sources associated with supernova remnants (SNRs) can serve as stopwatches for the escape of cosmic rays from SNRs, which gradually develops from highest-energy particles to lowest-energy particles with time. In this work, we analyze the 13.7 yr Fermi-LAT data to investigate the γ-ray feature in/around the SNR G298.6−0.0 region. With γ-ray spatial analyses, we...
V* PX Vir is a nearby single-lined spectroscopic binary with the primary being a variable of a BY Dra-type star. It has a period of ∼216 d and the components of the system are two low-mass pre-main-sequence stars. By a simultaneous least-squares fit to the radial velocities, the relative positions, and the revised Hipparcos intermediate astrometric data, the complete orbital...
Studying massive binaries in different evolution stages or environments may help us to solve the problem of the evolution of massive binaries. The metallicity in the Small Magellanic Cloud (SMC) is much lower than that in our Milky Way, and binaries in the SMC are rarely studied. OGLE-SMC-ECL-2063 is a short-period early-type binary with a period of |${0{_{.}^{\circ}}6317643...
Microquasar SS 433 located at the geometric center of radio nebula W 50 is a suitable source for investigating the physical process of how galactic jets affect the surrounding interstellar medium (ISM). Previous studies have searched for evidence of the interaction between the SS 433 jet and ISM, such as neutral hydrogen gas and molecular clouds; however, it is still unclear...
The Atacama Large Millimeter/submillimeter Array (ALMA) serendipitously detected H2O |$J_{K_{\rm a}, K_{\rm c}} = 10_{2,9}$|–93, 6 emission at 321 GHz in NGC 1052. This is the first submillimeter maser detection in a radio galaxy and the most luminous 321 GHz H2O maser known to-date with the isotropic luminosity of |$1090\, L_{\odot }$|. The line profile consists of a broad...
A disformal Kerr black hole solution is a rotating black hole solution in a modified gravity theory which breaks the circular condition of spacetime differently from the case of the Kerr spacetime. In this paper, assuming that Sagittarius A* (Sgr A*) is a disformal Kerr black hole, we examine the potential to test the spacetime geometry with a hypothetical pulsar whose orbital...
Studies of the three-dimensional structures of galactic magnetic fields are now entering a new era, with broad-band, highly sensitive radio observations and new analysis methods. To reveal the magnetic field configuration from the observed intensities integrated along the line of sight, it is necessary to derive an appropriate model involving various combinations of parameters...
Faraday tomography is a new method of the study of cosmic magnetic fields enabled by broad-band low-frequency radio observations. Using Faraday tomography it is possible to obtain the Faraday dispersion function, which contains information on the line-of-sight distributions of magnetic fields, thermal electron density, and cosmic ray electron density by measuring the polarization...
The dark age of the Universe, when no luminous object existed, ended with the birth of the first stars, galaxies, and black holes. This epoch is called cosmic dawn. Cosmic reionization is the major transition of the intergalactic medium in the Universe driven by ionizing photons emitted from luminous objects. Although the epoch through the dark ages to reionization is a milestone...
In the first days of WZ Sge-type dwarf nova (DN) outbursts, the 2 : 1 resonance induces a spiral arm structure in the accretion disk, which is observed as early superhumps in optical light curves. We reports on our optical observations of an eclipsing WZ Sge-type DN PNV J00444033+4113068 during its 2021 superoutburst using the 3.8 m Seimei telescope and through the Variable Star...
Solar eclipses have been recorded throughout history and across various ethnic groups. Their records have benefitted scientific discussions on multiple topics. These astronomical spectacles have also been recorded in the Japanese archipelago, but little has been known of the historical observations in the northern end: Hokkaido Island (known as Ezo Island until 1869). Here, we...
We observed H2O (616→523) maser emission associated with the high-mass star-forming region IRAS 23139+5959 using the KaVA, a combination of very long baseline interferometry (VLBI) arrays between the Korean VLBI Network and the VLBI Exploration of Radio Astrometry (Japan). Through multi-epoch KaVA observations, we detected three groups of maser features, two of which coincide...