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Mitaka-shi, Japan

Astrobiology Center

Mitaka-shi, Japan

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Kwon J.,University of Tokyo | Kwon J.,Japan National Astronomical Observatory | Kwon J.,Japan Aerospace Exploration Agency | Tamura M.,University of Tokyo | And 6 more authors.
Astronomical Journal | Year: 2016

We have conducted simultaneous JHKs-band imaging circular and linear polarimetry of the Monoceros R2 (Mon R2) cluster. We present results from deep and wide near-infrared linear polarimetry of the Mon R2 region. Prominent and extended polarized nebulosities over the Mon R2 field are revisited, and an infrared reflection nebula associated with the Mon R2 cluster and two local reflection nebulae, vdB 67 and vdB 69, is detected. We also present results from deep imaging circular polarimetry in the same region. For the first time, the observations show relatively high degrees of circular polarization (CP) in Mon R2, with as much as approximately 10% in the Ks band. The maximum CP extent of a ring-like nebula around the Mon R2 cluster is approximately 0.60 pc, while that of a western nebula, around vdB 67, is approximately 0.24 pc. The extended size of the CP is larger than those seen in the Orion region around IRc2, while the maximum degree of CP of ∼10% is smaller than those of ∼17% seen in the Orion region. Nonetheless, both the CP size and degree of this region are among the largest in our infrared CP survey of star-forming regions. We have also investigated the time variability of the degree of the polarization of several infrared sources and found possible variations in three sources. © 2016. The American Astronomical Society. All rights reserved.


Ryu T.,Graduate University for Advanced Studies | Ryu T.,Japan National Astronomical Observatory | Sato B.,Tokyo Institute of Technology | Kuzuhara M.,Tokyo Institute of Technology | And 75 more authors.
Astrophysical Journal | Year: 2016

A radial velocity (RV) survey for intermediate-mass giants has been in operation for over a decade at Okayama Astrophysical Observatory (OAO). The OAO survey has revealed that some giants show long-term linear RV accelerations (RV trends), indicating the presence of outer companions. Direct-imaging observations can help clarify what objects generate these RV trends. We present the results of high-contrast imaging observations of six intermediate-mass giants with long-term RV trends using the Subaru Telescope and HiCIAO camera. We detected co-moving companions to γ Hya B (0.61-0.14 +0.12M⊙), HD 5608 B (0.10 ± 0.01M⊙), and HD 109272 B (0.28 ± 0.06 M⊙). For the remaining targets (ι Dra, 18 Del, and HD 14067), we exclude companions more massive than 30-60 M Jup at projected separations of 1″-7″. We examine whether these directly imaged companions or unidentified long-period companions can account for the RV trends observed around the six giants. We find that the Kozai mechanism can explain the high eccentricity of the inner planets ι Dra b, HD 5608 b, and HD 14067 b. © 2016. The American Astronomical Society. All rights reserved.


News Article | November 28, 2016
Site: www.eurekalert.org

A group of researchers from the National Astronomical Observatory of Japan (NAOJ), the University of Tokyo, and the Astrobiology Center among others has observed the transit of a potentially Earth-like extrasolar planet known as K2-3d using the MuSCAT instrument on the Okayama Astrophysical Observatory 188-cm telescope. A transit is a phenomenon in which a planet passes in front of its parent star, blocking a small amount of light from the star, like a shadow of the planet. While transits have previously been observed for thousands of other extrasolar planets, K2-3d is important because there is a possibility that it might harbor extraterrestrial life. By observing its transit precisely using the next generation of telescopes, such as TMT, scientists expect to be able to search the atmosphere of the planet for molecules related to life, such as oxygen. With only the previous space telescope observations, however, researchers can't calculate the orbital period of the planet precisely, which makes predicting the exact times of future transits more difficult. This research group has succeeded in measuring the orbital period of the planet with a high precision of about 18 seconds. This greatly improved the forecast accuracy for future transit times. So now researchers will know exactly when to watch for the transits using the next generation of telescopes. This research result is an important step towards the search for extraterrestrial life in the future. K2-3d is an extrasolar planet about 150 light-years away that was discovered by the NASA K2 mission (the Kepler telescope's "second light") (Note 1). K2-3d's size is 1.5 times the size of the Earth. The planet orbits its host star, which is half the size of the Sun, with a period of about 45 days. Compared to the Earth, the planet orbits close to its host star (about 1/5 of the Earth-Sun distance). But, because the temperature of the host star is lower than that of the Sun, calculations show that this is the right distance for the planet to have a relatively warm climate like the Earth's. There is a possibility that liquid water could exist on the surface of the planet, raising the tantalizing possibility of extraterrestrial life. K2-3d's orbit is aligned so that as seen from Earth, it transits (passes in front of) its host star. This causes, short, periodic decreases in the star's brightness, as the planet blocks some of the star's light. This alignment enables researchers to probe the atmospheric composition of these planets by precise measurement of the amount of blocked starlight at different wavelengths. About 30 potentially habitable planets that also have transiting orbits were discovered by the NASA Kepler mission, but most of these planets orbit fainter, more distant stars. Because it is closer to Earth and its host star is brighter, K2-3d is a more interesting candidate for detailed follow-up studies (See Figure 2). The brightness decrease of the host star caused by the transit of K2-3d is small, only 0.07%. However, it is expected that the next generation of large telescopes (Note 2) will be able to measure how this brightness decrease varies with wavelength, enabling investigations of the composition of the planet's atmosphere. If extraterrestrial life exists on K2-3d, scientists hope to be able to detect molecules related to it, such as oxygen, in the atmosphere. The orbital period of K2-3d is about 45 days. Since the K2 mission's survey period is only 80 days for each area of sky, researchers could only measure two transits in the K2 data. This isn't sufficient to measure the planet's orbital period precisely, so when researchers attempt to predict the times of future transits, creating something called a "transit ephemeris," there are uncertainties in the predicted times. These uncertainties grow larger as they try to predict farther into the future. Therefore, early additional transit observations and adjustments to the ephemeris were required before researchers lost track of the transit. Because of the importance of K2-3d, the Spitzer Space Telescope observed two transits soon after the planet's discovery, bringing the total to four transit measurements. However, the addition of even a single transit measurement farther in the future can help to yield a significantly improved ephemeris. Using the Okayama 188-cm Reflector Telescope and the latest observational instrument MuSCAT, the team observed a transit of K2-3d for the first time with a ground based telescope. Though a 0.07% brightness decrease is near the limit of what can be observed with ground based telescopes, MuSCAT's ability to observe three wavelength bands simultaneously enhanced its ability to detect the transit. By reanalyzing the data from K2 and Spitzer in combination with this new observation, researchers have greatly improved the precision of the ephemeris, determining the orbital period of the planet to within about 18 seconds (1/30 of the original uncertainty). This improved transit ephemeris (Figure 3) ensures that when the next generation of large telescopes come online, they will know exactly when to watch for transits. Thus these research results help pave the way for future extraterrestrial life surveys. The NASA K2 mission will continue until at least February 2018, and is expected to discover more potentially habitable planets like K2-3d. Furthermore, K2's successor, the Transiting Exoplanet Survey Satellite (TESS), will be launched in December 2017. TESS will survey the whole sky for two years, and is expected to detect hundreds of small planets like K2-3d near our Solar System. To characterize a 'Second Earth' using the next generation of large telescopes, it will be important to measure the ephemerides and characteristics of planets with additional transit observations using medium sized ground-based telescopes. The team will continue using MuSCAT for research related to the future search for extraterrestrial life. 1. The discovery of K2-3d was reported by a research team led by Ian Crossfield (University of California, Santa Cruz) in 2015. 2. The next generation of large telescopes includes the James Webb Space Telescope (JWST), which NASA will launch in 2018, and the Thirty Meter Telescope (TMT), which is being pursued through international collaboration including Japan.


News Article | November 29, 2016
Site: astrobiology.com

A group of researchers from the National Astronomical Observatory of Japan (NAOJ), the University of Tokyo, and the Astrobiology Center among others has observed the transit of a potentially Earth-like extrasolar planet known as K2-3d using the MuSCAT instrument on the Okayama Astrophysical Observatory 188-cm telescope. A transit is a phenomenon in which a planet passes in front of its parent star, blocking a small amount of light from the star, like a shadow of the planet. While transits have previously been observed for thousands of other extrasolar planets, K2-3d is important because there is a possibility that it might harbor extraterrestrial life. By observing its transit precisely using the next generation of telescopes, such as TMT, scientists expect to be able to search the atmosphere of the planet for molecules related to life, such as oxygen. With only the previous space telescope observations, however, researchers can't calculate the orbital period of the planet precisely, which makes predicting the exact times of future transits more difficult. This research group has succeeded in measuring the orbital period of the planet with a high precision of about 18 seconds. This greatly improved the forecast accuracy for future transit times. So now researchers will know exactly when to watch for the transits using the next generation of telescopes. This research result is an important step towards the search for extraterrestrial life in the future. K2-3d is an extrasolar planet about 150 light-years away that was discovered by the NASA K2 mission (the Kepler telescope's "second light") (Note 1). K2-3d's size is 1.5 times the size of the Earth. The planet orbits its host star, which is half the size of the Sun, with a period of about 45 days. Compared to the Earth, the planet orbits close to its host star (about 1/5 of the Earth-Sun distance). But, because the temperature of the host star is lower than that of the Sun, calculations show that this is the right distance for the planet to have a relatively warm climate like the Earth's. There is a possibility that liquid water could exist on the surface of the planet, raising the tantalizing possibility of extraterrestrial life. K2-3d's orbit is aligned so that as seen from Earth, it transits (passes in front of) its host star. This causes, short, periodic decreases in the star's brightness, as the planet blocks some of the star's light. This alignment enables researchers to probe the atmospheric composition of these planets by precise measurement of the amount of blocked starlight at different wavelengths. About 30 potentially habitable planets that also have transiting orbits were discovered by the NASA Kepler mission, but most of these planets orbit fainter, more distant stars. Because it is closer to Earth and its host star is brighter, K2-3d is a more interesting candidate for detailed follow-up studies (See Figure 2). The brightness decrease of the host star caused by the transit of K2-3d is small, only 0.07%. However, it is expected that the next generation of large telescopes (Note 2) will be able to measure how this brightness decrease varies with wavelength, enabling investigations of the composition of the planet's atmosphere. If extraterrestrial life exists on K2-3d, scientists hope to be able to detect molecules related to it, such as oxygen, in the atmosphere. Transiting planets located in the habitable zone (the orbital region where a planet could hold liquid water on the surface), plotted in terms of planet radius vs. host star magnitude (brightness). Black circles represent confirmed planets discovered by the Kepler mission and white circles represent unconfirmed planet candidates. The orange triangles represent the Earth sized planets TRAPPIST-1c and TRAPPIST-1d observed 40 light-years away by a ground based telescope. TRAPPIST-1c and TRAPPIST-1d are thought to be just outside the habitable zone, but they are plotted for reference. The host star of K2-3d (red star) is the brightest in this figure. The orbital period of K2-3d is about 45 days. Since the K2 mission's survey period is only 80 days for each area of sky, researchers could only measure two transits in the K2 data. This isn't sufficient to measure the planet's orbital period precisely, so when researchers attempt to predict the times of future transits, creating something called a "transit ephemeris," there are uncertainties in the predicted times. These uncertainties grow larger as they try to predict farther into the future. Therefore, early additional transit observations and adjustments to the ephemeris were required before researchers lost track of the transit. Because of the importance of K2-3d, the Spitzer Space Telescope observed two transits soon after the planet's discovery, bringing the total to four transit measurements. However, the addition of even a single transit measurement farther in the future can help to yield a significantly improved ephemeris. Using the Okayama 188-cm Reflector Telescope and the latest observational instrument MuSCAT, the team observed a transit of K2-3d for the first time with a ground based telescope. Though a 0.07% brightness decrease is near the limit of what can be observed with ground based telescopes, MuSCAT's ability to observe three wavelength bands simultaneously enhanced its ability to detect the transit. By reanalyzing the data from K2 and Spitzer in combination with this new observation, researchers have greatly improved the precision of the ephemeris, determining the orbital period of the planet to within about 18 seconds (1/30 of the original uncertainty). This improved transit ephemeris (Figure 3) ensures that when the next generation of large telescopes come online, they will know exactly when to watch for transits. Thus these research results help pave the way for future extraterrestrial life surveys. Predicted transit time deviation from the improved K2-3d transit ephemeris based on this research. The solid red line indicates the predicted times based on this research, the shaded area shows the uncertainty range. Squares, triangles, and circles are respectively the transit time data from the Kepler Telescope, Spitzer Space Telescope, and the latest observing instrument MuSCAT on the Okayama 188-cm Reflector Telescope. Gray marks show the values calculated in previous research and black marks represent the values re-calculated in this research. Purple and orange dotted lines are the transit ephemerides calculated in previous research using the K2 and the K2+Spitzer data, respectively. This research succeeded in correcting the predictions for the 2018 transit times by more than an hour. The NASA K2 mission will continue until at least February 2018, and is expected to discover more potentially habitable planets like K2-3d. Furthermore, K2's successor, the Transiting Exoplanet Survey Satellite (TESS), will be launched in December 2017. TESS will survey the whole sky for two years, and is expected to detect hundreds of small planets like K2-3d near our Solar System. To characterize a 'Second Earth' using the next generation of large telescopes, it will be important to measure the ephemerides and characteristics of planets with additional transit observations using medium sized ground-based telescopes. The team will continue using MuSCAT for research related to the future search for extraterrestrial life. 1. The discovery of K2-3d was reported by a research team led by Ian Crossfield (University of California, Santa Cruz) in 2015. 2. The next generation of large telescopes includes the James Webb Space Telescope (JWST), which NASA will launch in 2018, and the Thirty Meter Telescope (TMT), which is being pursued through international collaboration including Japan.


Narita N.,Astrobiology Center | Narita N.,Japan National Astronomical Observatory | Narita N.,Graduate University for Advanced Studies | Hirano T.,Tokyo Institute of Technology | And 24 more authors.
Astrophysical Journal | Year: 2015

K2-19 (EPIC201505350) is an interesting planetary system in which two transiting planets with radii ∼7 R⊕ (inner planet b) and ∼4 R⊕ (outer planet c) have orbits that are nearly in a 3:2 mean-motion resonance. Here, we present results of ground-based follow-up observations for the K2-19 planetary system. We have performed high-dispersion spectroscopy and high-contrast adaptive-optics imaging of the host star with the HDS and HiCIAO on the Subaru 8.2 m telescope. We find that the host star is a relatively old (≥8 Gyr) late G-type star (Teff ∼ 5350 K, Ms ∼ 0.9 Mo, and Rs ∼ 0.9 Ro). We do not find any contaminating faint objects near the host star that could be responsible for (or dilute) the transit signals. We have also conducted transit follow-up photometry for the inner planet with KeplerCam on the FLWO 1.2 m telescope, TRAPPISTCAM on the TRAPPIST 0.6 m telescope, and Muscat on the OAO 1.88 m telescope. We confirm the presence of transit timing variations (TTVs), as previously reported by Armstrong and coworkers. We model the observed TTVs of the inner planet using the synodic chopping formulae given by Deck & Agol. We find two statistically indistinguishable solutions for which the period ratios (Pc/Pb) are located slightly above and below the exact 3:2 commensurability. Despite the degeneracy, we derive the orbital period of the inner planet Pb ∼ 7.921 days and the mass of the outer planet Mc ∼ 20 M⊕. Additional transit photometry (especially for the outer planet) as well as precise radial-velocity measurements would be helpful to break the degeneracy and to determine the mass of the inner planet. © 2015. The American Astronomical Society. All rights reserved..


Fukui A.,Japan National Astronomical Observatory | Narita N.,Astrobiology Center | Narita N.,Japan National Astronomical Observatory | Narita N.,Graduate University for Advanced Studies | And 11 more authors.
Astrophysical Journal | Year: 2016

The Multicolor Simultaneous Camera for studying Atmospheres of Transiting exoplanets (MuSCAT) is an optical three-band (g2'-, r2'- and zs,2-band) imager that was recently developed for the 188 cm telescope at Okayama Astrophysical Observatory with the aim of validating and characterizing transiting planets. In a pilot observation with MuSCAT we observed a primary transit of HAT-P-14b, a high-surface gravity (gp = 38 ms-2) hot Jupiter around a bright (V=10) F-type star. From a 2.9 hr observation we achieved the five-minute binned photometric precisions of 0.028%, 0.022%, and 0.024% in the g2', r2', and zs,2 bands, respectively, which provided the highestquality photometric data for this planet. Combining these results with those of previous observations, we search for variations of transit timing and duration over five years as well as variations of planet-star radius ratio (Rp Rs) with wavelengths, but can find no considerable variation in any parameters. On the other hand, using the transitsubtracted light curves we simulate the achievable measurement error of Rp Rs with MuSCAT for various planetary sizes, assuming three types of host stars: HAT-P-14, the nearby K-dwarf HAT-P-11, and the nearby M-dwarf GJ1214. Comparing our results with the expected atmospheric scale heights, we find that MuSCAT is capable of probing the atmospheres of planets as small as a sub-Jupiter (Rp ∼ 6Roplus;) around HAT-P-14 in all bands, a Neptune (∼4R⊕) around HAT-P-11 in all bands, and a super-Earth (∼2.5R⊕) around GJ1214 in r2' and zs,2 bands. These results promise that MuSCAT will produce fruitful scientific outcomes in the K2 and TESS era. © 2016. The American Astronomical Society. All rights reserved.


Nakajima T.,Astrobiology Center | Nakajima T.,Japan National Astronomical Observatory | Sorahana S.,University of Tokyo
Astrophysical Journal | Year: 2016

It has been suggested that high C/O ratios (>0.8) in circumstellar disks lead to the formation of carbon-dominated planets. Based on the expectation that elemental abundances in the stellar photospheres give the initial abundances in the circumstellar disks, the frequency distributions of C/O ratios of solar-type stars have been obtained by several groups. The results of these investigations are mixed. Some find C/O > 0.8 in more than 20% of stars, and C/O > 1.0 in more than 6%. Others find C/O > 0.8 in none of the sample stars. These works on solar-type stars are all differential abundance analyses with respect to the Sun and depend on the adopted C/O ratio in the Sun. Recently, a method of molecular line spectroscopy of M dwarfs, in which carbon and oxygen abundances are derived respectively from CO and H2O lines in the K band, has been developed. The resolution of the K-band spectrum is 20,000. Carbon and oxygen abundances of 46 M dwarfs have been obtained by this nondifferential abundance analysis. Carbon-to-oxygen ratios in M dwarfs derived by this method are more robust than those in solar-type stars derived from neutral carbon and oxygen lines in the visible spectra because of the difficulty in the treatment of oxygen lines. We have compared the frequency distribution of C/O distributions in M dwarfs with those of solar-type stars and have found that the low frequency of high-C/O ratios is preferred. © 2016. The American Astronomical Society. All rights reserved.


Sanchez Contreras C.,Astrobiology Center | Velilla Prieto L.,Astrobiology Center | Velilla Prieto L.,CSIC - Institute of Materials Science | Agundez M.,CSIC - Institute of Materials Science | And 9 more authors.
Astronomy and Astrophysics | Year: 2015

OH 231.8+4.2, a bipolar outflow around a Mira-type variable star, displays a unique molecular richness amongst circumstellar envelopes (CSEs) around O-rich AGB and post-AGB stars. We report line observations of the HCO+ and H13CO+ molecular ions and the first detection of SO+, N2H+, and (tentatively) H3O+ in this source. SO+ and H3O+ have not been detected before in CSEs around evolved stars. These data have been obtained as part of a full mm-wave and far-IR spectral line survey carried out with the IRAM 30 m radio telescope and with Herschel/HIFI. Except for H3O+, all the molecular ions detected in this work display emission lines with broad profiles (FWHM ~ 50-90 km s-1), which indicates that these ions are abundant in the fast bipolar outflow of OH 231.8. The narrow profile (FWHM ~ 14 km s-1) and high critical densities (>106cm-3) of the H3O+ transitions observed are consistent with this ion arising from denser, inner (and presumably warmer) layers of the fossil remnant of the slow AGB CSE at the core of the nebula. From rotational diagram analysis, we deduce excitation temperatures of Tex~ 10-20 K for all ions except for H3O+, which is most consistent with Tex 100 K. Although uncertain, the higher excitation temperature suspected for H3O+ is similar to that recently found for H2O and a few other molecules, which selectively trace a previously unidentified, warm nebular component. The column densities of the molecular ions reported here are in the range Ntot≈ [1-8] × 1013 cm-2, leading to beam-averaged fractional abundances relative to H2 of X(HCO+) ≈ 10-8, X(H13CO+) ≈2 × 10-9, X(SO+) ≈4 × 10-9, X(N2H+) ≈ 2 × 10-9, and X(H3O+) ≈ 7 × 10-9 cm-2. We have performed chemical kinetics models to investigate the formation of these ions in OH 231.8 as the result of standard gas phase reactions initiated by cosmic-ray and UV-photon ionization. The model predicts that HCO+, SO+, and H3O+ can form with abundances comparable to the observed average values in the external layers of the slow central core (at ~[3-8] × 1016 cm); H3O+ would also form quite abundantly in regions closer to the center (X(H3O+) ~ 10-9 at ~1016cm). For N2H+, the model abundance is lower than the observed value by more than two orders of magnitude. The model fails to reproduce the abundance enrichment of HCO+, SO+, and N2H+ in the lobes, which is directly inferred from the broad emission profiles of these ions. Also, in disagreement with the narrow H3O+ spectra, the model predicts that this ion should form in relatively large, detectable amounts (≈ 10-9) in the external layers of the slow central core and in the high-velocity lobes. Some of the model-data discrepancies are reduced, but not suppressed, by lowering the water content and enhancing the elemental nitrogen abundance in the envelope. The remarkable chemistry of OH 231.8 probably reflects the molecular regeneration process within its envelope after the passage of fast shocks that accelerated and dissociated molecules in the AGB wind ~800 yr ago. © 2015 ESO.

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