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Papers by Yumiko Oasa

Astronomy & Astrophysics, 2021

Context.The discovery of an extrasolar planet with an ocean has crucial importance in the search ... more Context.The discovery of an extrasolar planet with an ocean has crucial importance in the search for life beyond Earth. The polarimetric detection of specularly reflected light from a smooth liquid surface is anticipated theoretically, though the polarimetric signature of Earth’s oceans has not yet been conclusively detected in disk-integrated planetary light.Aims.We aim to detect and measure the polarimetric signature of the Earth’s oceans.Methods.We conducted near-infrared polarimetry for lunar Earthshine and collected data on 32 nights with a variety of ocean fractions in the Earthshine-contributing region.Results.A clear positive correlation was revealed between the polarization degree and ocean fraction. We found hourly variations in polarization in accordance with rotational transition of the ocean fraction. The ratios of the variation to the typical polarization degree were as large as ~0.2–1.4.Conclusions.Our observations provide plausible evidence of the polarimetric signat...

We describe a near-infrared coronagraphic camera built for use with the Subaru 8.2m telescope and... more We describe a near-infrared coronagraphic camera built for use with the Subaru 8.2m telescope and its adaptive optics system. This instrument, CIAO, aims to obtain high-resolution (0.06 arcsec at 2 micron) images of faint objects in close vicinity of bright objects at near-infrared wavelengths. The coronagraphic optics are all cooled. Occulting masks whose diameter ranges from 0.1 to 3 arcsec

Symposium - International Astronomical Union, 2003

We are currently conducting three kinds of IR surveys of star forming regions (SFRs) in order to ... more We are currently conducting three kinds of IR surveys of star forming regions (SFRs) in order to seek for very low-mass young stellar populations. First is a deep JHKs-bands (simultaneous) survey with the SIRIUS camera on the IRSF 1.4m or the UH 2.2m telescopes. Second is a very deep JHKs survey with the CISCO IR camera on the Subaru 8.2m telescope. Third is a high resolution companion search around nearby YSOs with the CIAO adaptive optics coronagraph IR camera on the Subaru. In this contribution, we describe our SIRIUS camera and present preliminary results of the ongoing surveys with this new instrument.

The Astrophysical Journal, 2016

Publications of the Astronomical Society of Japan, 2017

The Astrophysical Journal, 2015

The authors have carried out extensive studies of nearby star-forming regions. The near-infrared ... more The authors have carried out extensive studies of nearby star-forming regions. The near-infrared observations, such as deep survey and spectroscopy, have revealed a significant number of very low-luminosity young stellar objects. Their faintness implies that they could be young brown dwarfs.

We have conducted a deep ISOPHOT survey searching for the precursors of low-luminosity or cold Cl... more We have conducted a deep ISOPHOT survey searching for the precursors of low-luminosity or cold Class 0/I objects, and investigating the nature of the dense cores at 50, 105 and 180 μm. Our observations cover all the dense cores in the ρ Ophiuchi star forming region except for the dense cores associated with IRAS point sources. These dense cores are identified by our previous observations of C18O (J=1-->0) and H13CO+ (J=1-->0) emission lines covering the entire L1688 cloud with the Nobeyama Radio Observatory 45-m telescope. Comparing the ISOPHOT observations with the previous IRAS data, there is a reasonable agreement between ISOPHOT and IRAS fluxes. The rms noise level in the ISOPHOT survey indicates that the sensitivity is about one order of higher than that of IRAS survey. These sensitive observations enable us to detect new sources that were not identified by IRAS survey. In this survey, roughly 20 % of these dense cores are identified in all the three bands of ISOPHOT and ...

Publications of the Astronomical Society of Japan, 2014

ESO Astrophysics Symposia

The goal of our study is to discuss how planet-hosting stars (PHSs) are born by analyzing the che... more The goal of our study is to discuss how planet-hosting stars (PHSs) are born by analyzing the chemical homogeneity in open clusters. We obtained the spectra of 18 A,F,G stars in the Pleiades by the high-resolution spectroscopic observations in last January. Out of the 18 stars, the metallcities of 10 stars were derived, and their mean metallicity was obtained to be [Fe/H]mean = +0.02±0.14dex. This high dispersion may imply the chemical diversity in Pleiades. We report the results of our analysis.