Search

In this study, we revisit 32 planetary systems around evolved stars observed within the framework of the Okayama Planet Search Program (OPSP) and its collaborative framework of the East Asian Planet Search Network to search for additional companions and investigate the properties of stars and giant planets in multiple-planet systems. With our latest radial velocities obtained from Okayama Astrophysical Observatory, we confirm an additional giant planet in the wide orbit of the 75 Cet system (⁠|$P_{\rm {c}} = 2051.62_{-40.47}^{+45.98}\ \rm {d}$|⁠ , |$M_{\rm {c}}\sin i=0.912_{-0.090}^{+0.088}\,\,M_{\rm {J}}$|⁠ , and |$a_{\rm {c}}=3.929_{-0.058}^{+0.052}\ \rm {au}$|⁠), along with five stars exhibiting long-term radial velocity accelerations, which indicates massive companions in the wide orbits. We also find that the radial velocity variations of several planet-harboring stars may indicate additional planet candidates, stellar activities, or other understudied sources. These stars include ϵ Tau, 11 Com, 24 Boo, 41 Lyn, 14 And, HD 32518, and ω Ser. We further constrain the orbital configuration of the HD 5608, HD 14067, HD 120084, and HD 175679 systems by combining radial velocities with astrometry, as their host central stars exhibit significant astrometric accelerations. For other systems, we simply refine their orbital parameters. Moreover, our study indicates that the OPSP planet-harboring stars are more metal poor compared to the currently known planet-harboring stars, and this is likely due to the B − V color upper limit at 1.0 for star selection in the beginning of the survey. Finally, by investigating the less massive giant planets (<5  M J) around currently known planet-harboring evolved stars, we find that metallicity positively correlates with the multiplicity and total planet mass of the system, which can be evidence for the core-accretion planet formation model. [ABSTRACT FROM AUTHOR]

We report the detection of a giant planet orbiting the G-type giant star HD 167768 from radial velocity measurements using the High Dispersion Echelle Spectrograph (HIDES) at Okayama Astrophysical Observatory (OAO). HD 167768 has a mass of |$1.08_{-0.12}^{+0.14}\, M_{\odot }$|⁠ , a radius of |$9.70_{-0.25}^{+0.25}\, R_{\odot }$|⁠ , a metallicity of |$[\mbox{Fe}/\mbox{H}]=-0.67_{-0.08}^{+0.09}$|⁠ , and a surface gravity of |$\log g = 2.50_{-0.06}^{+0.06}$|⁠. The planet orbiting the star is a warm Jupiter, having a period of |$20.6532_{-0.0032}^{+0.0032}\:\mbox{d}$|⁠ , a minimum mass of |$0.85_{-0.11}^{+0.12}\, M_{\rm {J}}$|⁠ , and an orbital semimajor axis of |$0.1512_{-0.0063}^{+0.0058}\:\mbox{au}$|⁠. The planet has one of the shortest orbital periods among those ever found around deeply evolved stars (log  g < 3.5) using radial velocity methods. The equilibrium temperature of the planet is 1874 K, as high as a hot Jupiter. The radial velocities show two additional regular variations at 41 d and 95 d, suggesting the possibility of outer companions in the system. Follow-up monitoring will enable validation of the periodicity. We also calculated the orbital evolution of HD 167768 b and found that the planet will be engulfed within 0.15 Gyr. [ABSTRACT FROM AUTHOR]

We present ionized gas properties of nine local ultra/luminous infrared galaxies (U/LIRGs) at z < 0.04 through Integral Field Unit (IFU) observations with KOOLS-IFU on the Seimei Telescope. The observed targets are drawn from the Great Observatories All-sky LIRG Survey (GOALS), covering a wide range of merger stages. We successfully detect emission lines such as Hβ, [O  iii ]λ5007, Hα, [N  ii ]λλ6549, 6583, and [S  ii ]λλ6717, 6731 with a spectral resolution of R = 1500–2000, which provides (i) a spatially resolved (∼200–700 pc) moment map of ionized gas and (ii) diagnostics for an active galactic nucleus (AGN) within the central ∼3–11 kpc in diameter for our sample. We find that the [O  iii ] outflow that is expected to be driven by an AGN tends to be stronger (i) towards the galactic center and (ii) as a sequence of the merger stage. In particular, the outflow strength in the late-stage (stage D) mergers is about 1.5 times stronger than that in the early-state (stage B) mergers, which indicates that galaxy mergers could induce AGN-driven outflow and play an important role in the co-evolution of galaxies and supermassive black holes. [ABSTRACT FROM AUTHOR]

We report the discovery of a triple-giant-planet system around an evolved star HD 184010 (HR 7421, HIP 96016). This discovery is based on observations from Okayama Planet Search Program, a precise radial velocity survey, undertaken at Okayama Astrophysical Observatory between 2004 April and 2021 June. The star is K0 type and located at the beginning of the red giant branch. It has a mass of |$1.35_{-0.21}^{+0.19}\, M_{\odot }$|⁠ , a radius of |$4.86_{-0.49}^{+0.55} R_{\odot }$|⁠ , and a surface gravity log  g of |$3.18_{-0.07}^{+0.08}$|⁠. The planetary system is composed of three giant planets in a compact configuration: the planets have minimum masses of |$M_{\rm {b}}\sin i = 0.31_{-0.04}^{+0.03}\, M_{\rm {J}}$|⁠ , |$M_{\rm {c}}\sin i = 0.30_{-0.05}^{+0.04}\, M_{\rm {J}}$|⁠ , and |$M_{\rm {d}}\sin i = 0.45_{-0.06}^{+0.04}\, M_{\rm {J}}$|⁠ , and orbital periods of |$P_{\rm {b}}=286.6_{-0.7}^{+2.4}\:$| d, |$P_{\rm {c}}=484.3_{-3.5}^{+5.5}\:$| d, and |$P_{\rm {d}}=836.4_{-8.4}^{+8.4}\:$| d, respectively, which are derived from a triple Keplerian orbital fit to three sets of radial velocity data. The ratio of orbital periods are close to P d :  P c :  P b ∼ 21 : 12 : 7, which means the period ratios between neighboring planets are both lower than 2 : 1. The dynamical stability analysis reveals that the planets should have near-circular orbits. The system could remain stable over 1 Gyr, initialized from co-planar orbits, low eccentricities (e = 0.05), and planet masses equal to the minimum mass derived from the best-fitting circular orbit fitting. Besides, the planets are not likely in mean motion resonance. The HD 184010 system is unique: it is the first system discovered to have a highly evolved star (log  g < 3.5 cgs) and more than two giant planets all with intermediate orbital periods (102 < P < 103 d). [ABSTRACT FROM AUTHOR]

A near-infrared telescope with an effective aperture diameter of 30 mm has been developed. The primary objective of the development is to observe northern bright stars in the J , H , and K s bands and provide accurate photometric data on those stars. The second objective is to observe a belt-like region along the northern Galactic plane (| b | ≤ 5° and δ ≥ −30°) repeatedly, to monitor bright variable stars there. The telescope has been in use since 2016 December. The purpose of this paper is to describe the design and operational performances of the telescope, the photometric calibration methods, and our scientific goals. We show that the telescope has the ability to provide photometry with an uncertainty of less than |$5\%$| for stars brighter than 7, 6.5, and 6 mag in the J , H , and K s bands, respectively. The repeatability of the photometric measurements for the same star is better than |$1\%$| for bright stars. Our observations will provide accurate photometry on bright stars that are lacking in the Two Micron Sky Survey and the Two Micron All-Sky Survey. Repeated observations at a good cadence will also reveal their nature in terms of variability in the near-infrared. [ABSTRACT FROM AUTHOR]

We report the detection of radial velocity (RV) variations in nine evolved G- and K-type giant stars. The observations were conducted at Okayama Astrophysical Observatory. Planets or planet candidates can best explain these regular variations. However, a coincidence of near 280 d variability among five of them prevents us from fully ruling out stellar origins for some of the variations, since all nine stars behave similarly in stellar properties. In the planet hypotheses for the RV variations, the planets (including one candidate) may survive close to the boundary of the so-called "planet desert" around evolved stars, having orbital periods between 255 and 555 d. Besides, they are the least-massive giant planets detected around G- and K-type giant stars, with minimum masses between 0.45  M J and 1.34  M J. We further investigated other hypotheses for our detection, yet none of them can better explain regular RV variation. With our detection, we can be convinced that year-long regular variation with amplitude down to 15 m s−1 for G- and K-type giant stars is detectable. Moreover, we performed simulations to further confirm the detectability of planets around these stars. Finally, we explored giant planets around intermediate-mass stars, and likewise found a four-Jupiter-mass gap (e.g. Santos et al. 2017, A&A, 603, A30), which is probably a boundary of the giant planet population. [ABSTRACT FROM AUTHOR]

There are about a dozen symbiotic stars known to produce high-velocity jets during outbursts. MWC 560 (V694 Mon) is a symbiotic star that seems to show a permanent jet. After showing an unexpected brightening in 2018 November, it has continued to brighten until 2021 and is currently in the brightest state ever. We have been conducting long-term high-dispersion spectroscopic monitoring of this object since 2016 March. An emission wing with v FWHM ≈ 700 km s−1 in the hydrogen Balmer line at an unexpected brightening event in 2018 was reported by Ando et al. (2021 , PASJ, 73, L1). In subsequent continuous observations, this emission wing was no longer seen on 2019 February 6. The absorption lines seen in the hydrogen Balmer lines are gradually deepening and spreading to the slower side of the velocity, and the outflow velocity is becoming slower. The expanding component generated by the outburst was initially observed in the emission wing just after the 2018 outburst, got gradually cooler, and was observed in the absorption line after 2019. [ABSTRACT FROM AUTHOR]

MWC 560 (V694 Mon) is classified as a symbiotic binary consisting of a white dwarf and an M5III red giant. In this object, a very- high-speed component, thought to be a jet, has been reported in the hydrogen Balmer line. We have been conducting long-term spectroscopic monitoring since the brightening in 2016 February. An irregular rebrightening was reported by Goranskij et al. (2018 , Astronomer's Telegram, 12227), who also showed that the high-velocity absorption component was not seen on 2018 November 16. Our low-resolution spectroscopic observations showed no high-velocity absorption component on 2018 November 14, and wide emission lines in Balmer line region (Hα, Hβ). However, high-resolution spectroscopy revealed the presence of slow, weak absorbing components and an emission wing on 2018 December 25. MWC 560 began to brighten in 2018 November, and it is gradually brightening as of 2020 April 14. For the absorption component, we propose a shell expansion of a classical symbiotic nova that occurred in 2016. During the 2018 brightening a new emission wing with v FWHM ≈ 700 km s−1 was confirmed, which could be triggered by disk instability like a dwarf nova. This paper summarizes the results of long-term monitoring observations and the recent changes in MWC 560. [ABSTRACT FROM AUTHOR]

Nonvariable OH/IR stars are thought to have just left the asymptotic giant branch (AGB) phase. In this conventional picture, they must still show strong circumstellar extinction caused by the dust ejected during the AGB phase, and the extinction is expected to decrease over time because of the dispersal of the circumstellar dust after the cessation of stellar mass loss. The reduction of extinction makes the stars become apparently brighter and bluer with time, especially in the near-infrared (NIR) range. We look for such long-term brightening of nonvariable OH/IR stars by using 2MASS, UKIDSS, and OAOWFC survey data. As such, we obtain multiepoch NIR data taken over a 20 yr period (1997–2017) for 6 of 16 nonvariable OH/IR stars, and all 6 objects are found to be brightening. The K-band brightening rate of five objects ranges from 0.010 to 0.130 mag yr−1, which is reasonably explained with the conventional picture. However, one OH/IR star, OH 31.0−0.2, shows a rapid brightening, which cannot be explained only by the dispersal of the dust shell. Multicolor (J-, H-, and K-band) data are obtained for three objects, OH 25.1−0.3, OH 53.6−0.2, and OH 77.9+0.2. Surprisingly, none of them appears to have become bluer, and OH 53.6−0.2 is found to have reddened at a rate of 0.013 mag yr−1 in (J – K). Our findings suggest other mechanisms such as rapid changes in stellar properties (temperature or luminosity) or a generation of a new batch of dust grains. [ABSTRACT FROM AUTHOR]

An overview of the Seimei telescope, a 3.8 m optical infrared telescope located on Mt. Chikurinji in the Okayama prefecture of Japan, is presented. Seimei is a segmented-mirror telescope whose primary mirror consists of 18 petal-shaped segments. The telescope tube supporting the thin segmented mirrors is structurally incorporated within large arc-rails providing the elevation axis. The tube has a light-weight homologous structure designed with a genetic algorithm. The total weight of the telescope tube, including 1.4-ton optics, is only 8 tons. By virtue of its light weight, the telescope is able to point at an object anywhere in the observable sky within one minute. The telescope is operated by Kyoto University in collaboration with the National Astronomical Observatory of Japan (NAOJ). Half of the telescope time is used by Kyoto University. The remaining time is open to the Japanese astronomical community. NAOJ is responsible for the management of the open-use time, including handling of the observation proposals. The telescope is now regularly performing scientific observations on the basis of a variety of proposals. [ABSTRACT FROM AUTHOR]

We performed a far-IR imaging survey of the circumstellar dust shells of 144 evolved stars as a mission program of the AKARI infrared astronomical satellite using the Far-Infrared Surveyor (FIS) instrument. With this survey, we deliver far-IR surface brightness distributions of roughly 10′ × 40′ or 10′ × 20′ areas of the sky around the target evolved stars in the four FIS bands at 65, 90, 140, and 160 μm. Our objectives are to characterize the far-IR surface brightness distributions of the cold dust component in the circumstellar dust shells, from which we derive the amount of cold dust grains as low as 20 K and empirically establish the early mass loss history. In this first installment of the series, we introduce the project and its aims, describe the observations, data reduction, and surface brightness correction process, and present the entire data set along with the results of integrated photometry measurements (i.e. the central source and circumstellar dust shell together). We find that: (1) far-IR emission is detected from all but one object at the spatial resolution about 30′–50′ in the corresponding bands; (2) roughly 60%–70% of the target sources show some extension; (3) previously unresolved nearby objects in the far IR are now resolved around 28 target sources; (4) the results of photometry measurements are reasonable with respect to the entries in the AKARI/FIS Bright Source Catalogue, despite the fact that the targets were assumed to be point sources when catalogue flux densities were computed; and (5) an IR two-color diagram would place the target sources in a roughly linear distribution that may correlate with the age of the circumstellar dust shell and can potentially be used to identify which targets are more extended than others. [ABSTRACT FROM AUTHOR]

We present optical (g', Rc, and Ic) to near-infrared (J) simultaneous photometric observations for a primary transit of GJ3470b, a Uranus-mass transiting planet around a nearby M dwarf, by using the 50 cm MITSuME telescope and the 188 cm telescope, both at the Okayama Astrophysical Observatory. From these data, we derive the planetary mass, radius, and density as 14.1±1.3 M⊙, 4.32-0.10+0.21 R⊕, and 0.94±0.12 g cm-3, respectively, thus confirming the low density that was reported by Demory et al. based on the Spitzer/IRAC 4.5 μm photometry (0.72-0.12+0.13 g cm-3). Although the planetary radius is about 10% smaller than that reported by Demory et al., this difference does not alter their conclusion that the planet possesses a hydrogen-rich envelope whose mass is approximately 10% of the planetary total mass. On the other hand, we find that the planet-to-star radius ratio (Rp/Rs ) in the J band (0.07577-0.00075+0.00072) is smaller than that in the Ic (0.0802±0.0013) and 4.5 μm (0.07806+0.00052 -0.00054) bands by 5.8%±2.0% and 2.9%±1.1%, respectively. A plausible explanation for the differences is that the planetary atmospheric opacity varies withwavelength due to absorption and/or scattering by atmospheric molecules.Although the significance of the observed Rp/Rs variations is low, if confirmed, this fact would suggest that GJ3470b does not have a thick cloud layer in the atmosphere. This property would offer a wealth of opportunity for future transmission-spectroscopic observations of this planet to search for certain molecular features, such as H2O, CH4, and CO, without being prevented by clouds. [ABSTRACT FROM AUTHOR]

We report on the development of a wide-field near-infrared (0.9–2.5 |$\, \mu$| m) camera built as a renewal of the existing classical Cassegrain 0.91 m telescope at Okayama Astrophysical Observatory. The optics system was replaced with fast hybrid optics (f/2.5) composed of forward Cassegrain optics and quasi-Schmidt optics, which results in an effective image circle of 52 mm diameter on the focal plane. The new camera, called the Okayama Astrophysical Observatory Wide-Field Camera (OAOWFC), has imaging capabilities in the |$Y$|⁠ , |$J$|⁠ , |$H$|⁠ , and |$K_{\rm s}$| bands over a field of view of |$0.^{\!\!\!\circ }47 \times 0.^{\!\!\!\circ }47$| with a HAWAII-1 HgCdTe PACE focal plane array. The primary purpose of OAOWFC is to search for variability in the Galactic plane in the |$K_{\rm s}$| band and to promptly follow up transients. We have demonstrated a photometric repeatability of 2% in the densest field in the northern Galactic plane and successfully discovered previously unreported variable stars. The observations of OAOWFC are fully autonomous, and we started scientific operations in 2015 April. [ABSTRACT FROM AUTHOR]

Observations of transient objects, such as short gamma-ray bursts and electromagnetic counterparts of gravitational wave sources, require prompt spectroscopy. To carry out prompt spectroscopy, we have developed an optical-fiber integral field unit (IFU) and connected it with an existing optical spectrograph, KOOLS. KOOLS–IFU was mounted on the Okayama Astrophysical Observatory 188 cm telescope. The fiber core and cladding diameters of the fiber bundle are 100 μm and 125 μm, respectively, and 127 fibers are hexagonally close-packed in the sleeve of the two-dimensional fiber array. We conducted test observations to measure the KOOLS–IFU performance and obtained the following conclusions: (1) the spatial sampling is |${2{^{\prime\prime}_{.}}34}$| |$\, \pm \,$| |${0{^{\prime\prime}_{.}}05}$| per fiber, and the total field of view is |${30{^{\prime\prime}_{.}}4}$| |$\, \pm \,$| |${0{^{\prime\prime}_{.}}65}$| with 127 fibers; (2) the observable wavelength and the spectral resolving power of the grisms of KOOLS are 4030–7310 Å and 400–600, 5020–8830 Å and 600–900, 4160–6000 Å and 1000–1200, and 6150–7930 Å and 1800–2400, respectively; and (3) the estimated limiting magnitude is 18.2–18.7 AB mag during 30 min exposure under optimal conditions. [ABSTRACT FROM AUTHOR]

We report the detection of planets around two evolved giant stars from radial velocity measurements at Okayama Astrophysical observatory. 24 Boo (G3 IV) has a mass of $$0.99\,M_{\odot }$$, a radius of $$10.64\,R_{\odot }$$, and a metallicity of [Fe/H] = −0.77. The star hosts one planet with a minimum mass of 0.91  M Jup and an orbital period of 30.35 d. The planet has one of the shortest orbital periods among those ever found around evolved stars using radial-velocity methods. The stellar radial velocities show additional periodicity with 150 d, which can probably be attributed to stellar activity. The star is one of the lowest-metallicity stars orbited by planets currently known. γ Lib (K0 III) is also a metal-poor giant with a mass of $$1.47\,M_{\odot }$$, a radius of $$11.1\,R_{\odot }$$, and [Fe/H] = −0.30. The star hosts two planets with minimum masses of 1.02  M Jup and 4.58  M Jup, and periods of 415 d and 964 d, respectively. The star has the second-lowest metallicity among the giant stars hosting more than two planets. Dynamical stability analysis for the γ Lib system sets the minimum orbital inclination angle to be about 70° and suggests that the planets are in 7:3 mean-motion resonance, though the current best-fitting orbits for the radial-velocity data are not totally regular. [ABSTRACT FROM AUTHOR]

Examines the spin temperature of ammonia in comet C/1999S4 (LINEAR). Importance of ammonia in comets; Calculation of ortho-to-para ratio of ammonia; Suggestion of a formation region of the cometary ammonia ice between the orbit of Saturn and Uranus in the solar nebula.

We present results of optical polarimetric and multi-band photometric observations for γ-ray loud, narrow-line Seyfert 1 galaxy 1H 0323+342. This object has been monitored by the 1.5-m Kanata telescope since 2012 September, but following a γ-ray flux enhancement detected by Fermi Large Area Telescope (Fermi-LAT) on MJD 56483 (2013 July 10), dense follow-up was performed by 10 0.5–2.0-m telescopes in Japan over one week. The 2-yr RC-band light curve showed clear brightening corresponding to the γ-ray flux increase, and then decayed gradually. The high state as a whole lasted for ∼ 20 d, during which we clearly detected optical polarization from this object. The polarization degree (PD) of the source increased from 0%–1% in quiescence to ∼ 3% at maximum and then declined to the quiescent level, with the duration of the enhancement being less than 10 d. The moderate PD around the peak allowed us to precisely measure the daily polarization angle (PA). As a result, we found that the daily PAs were almost constant and aligned to the jet axis, suggesting that the magnetic field direction at the emission region is transverse to the jet. This implies either a presence of helical/toroidal magnetic field or transverse magnetic field compressed by shock(s). We also found small-amplitude intra-night variability during the 2-hr continuous exposure on a single night. We discuss these findings based on the turbulent multi-zone model recently advocated by Marscher (2014, ApJ, 780, 87). Optical to ultraviolet (UV) spectrum showed a rising shape in the higher frequency and the UV magnitude measured by Swift/UVOT (UV and Optical Telescope) was steady even during the flaring state, suggesting that thermal emission from accretion disk is dominant in that band. [ABSTRACT FROM AUTHOR]