Time filter

Source Type

Kamirenjaku, 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.. Source

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. Source

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. Source

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. Source

Discover hidden collaborations