記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

出版者・発行元：Oxford University Press (OUP)  

<jats:title>Abstract</jats:title>
<jats:p>AP Lyn and V837 Her are long-period Mira variable stars in the Milky Way. We performed VLBI Exploration of Radio Astrometry (VERA) phase-referenced observations towards H2O masers associated with AP Lyn and V837 Her. The annual parallaxes of AP Lyn and V837 Her were obtained to be 2.008 ± 0.038 mas and 1.090 ± 0.014 mas, corresponding to distances of 498 ± 10 pc and 917 ± 12 pc, respectively. From our multi-epoch infrared observations using the Kagoshima University 1 m telescope, we derived the mean J-, H-, and K′-band magnitudes of AP Lyn, V837 Her, and an additional long-period Mira variable BX Cam, whose parallax is known. We derived their pulsation periods to be 433 ± 1 d, 520 ± 1 d, and 458 ± 1 d, respectively, using the K′-band light curves. The MK–log P relation of long-period Mira variables seem to be violated by Mira variable stars with larger-than-expected MK values (like OZ Gem) in the Milky Way because of circumstellar extinction leading to an observed dimming effect. AP Lyn, V837 Her, and BX Cam (like OZ Gem) are dimming from the trend to O-rich stars in the Large Magellanic Cloud. This implies that the high metallicity of the Milky Way galaxy increases the opacity of the Mira-type variable stars and strengthens mass loss.</jats:p>

DOI： 10.1093/pasj/psaa056

出版者・発行元：Oxford University Press (OUP)  

<jats:title>Abstract</jats:title>
<jats:p>OZ Geminorum (OZ Gem) is a galactic Mira variable in the Milky Way (MW). We measured its annual parallax with VLBI Exploration of Radio Astrometry to be π = 0.806 ± 0.039 mas, corresponding to a distance of D = 1.24 ± 0.06 kpc. Based on multi-epoch infrared observations with the Kagoshima University 1 m telescope, we also derived the mean J-, H-, and K′-band magnitudes of OZ Gem to be 5.75 ± 0.47 mag, 4.00 ± 0.16 mag, and 2.65 ± 0.16 mag, respectively. We derived a pulsation period of OZ Gem as 592 ± 1 d from the K′-band lightcurve. From the period–luminosity (P–L) relation and two-color diagram of the Large Magellanic Cloud (LMC), the property of OZ Gem suggests that OZ Gem is assigned among the carbon-rich Mira variables. However, our optical spectroscopic observational results (with the 1.5 m Kanata telescope) confirmed OZ Gem to be an oxygen-rich Mira star with the detection of multiple titanium oxide transition absorption lines. We suggest that OZ Gem is a low-mass star evolving to an OH/IR star with large mass loss and dust formation. It is predicted that the lower limit to the initial mass of AGB stars for developing the C-rich surface chemistry is larger in the MW than in the LMC because of larger metallicity, and OZ Gem is likely to be the first example to prove this. Our results highlight the necessity of deriving the PL relation of the Milky Way with high accuracy.</jats:p>

DOI： 10.1093/pasj/psaa024

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

出版者・発行元：Oxford University Press (OUP)  

<jats:title>Abstract</jats:title><jats:p>We conducted near-infrared ($\mathit {JHK}_{\rm s}$) imaging polarimetry toward the infrared dark cloud (IRDC) M 17 SWex, including almost all of the IRDC filaments as well as its outskirts, with the polarimeter SIRPOL on the IRSF 1.4 m telescope. We revealed the magnetic fields of M 17 SWex with our polarization-detected sources that were selected by some criteria based on their near-IR colors and the column densities toward them, which were derived from the Herschel data. The selected sources indicate not only that the ordered magnetic field is perpendicular to the cloud elongation as a whole, but also that at both ends of the elongated cloud the magnetic field appears to be bent toward its central part, i.e., a large-scale hourglass-shaped magnetic field perpendicular to the cloud elongation. In addition to this general trend, the elongations of the filamentary subregions within the dense parts of the cloud appear to be mostly perpendicular to their local magnetic fields, while the magnetic fields of the outskirts appear to follow the thin filaments that protrude from the dense parts. The magnetic strengths were estimated to be ∼70–$300\, \mu$G in the subregions, of which the lengths and average number densities are ∼3–9 pc and ∼2–7 × 103 cm−3, respectively, by the Davis–Chandrasekhar–Fermi method with the angular dispersion of our polarization data and the velocity dispersion derived from the C18O (J = 1–0) data obtained by the Nobeyama 45 m telescope. These field configurations and our magnetic stability analysis of the subregions imply that the magnetic field has controlled the formation/evolution of the M 17 SWex cloud.</jats:p>

DOI： 10.1093/pasj/psz072

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

出版者・発行元：Oxford University Press (OUP)  

<jats:title>Abstract</jats:title>
<jats:p>We present monitoring campaign observations at optical and near-infrared (NIR) wavelengths for a radio-loud active galactic nucleus (AGN) at z = 0.840, SDSS J110006.07+442144.3 (hereafter, J1100+4421), which was identified during a flare phase in late 2014 February. The campaigns consist of three intensive observing runs from the discovery to 2015 March, mostly within the scheme of the OISTER collaboration. Optical–NIR light curves and simultaneous spectral energy distributions (SEDs) are obtained. Our measurements show the strongest brightening in 2015 March. We found that the optical–NIR SEDs of J1100+4421 show an almost steady shape despite the large and rapid intranight variability. This constant SED shape is confirmed to extend to ∼5 μm in the observed frame using the archival WISE data. Given the lack of absorption lines and the steep power-law spectrum of αν ∼ −1.4, where $f_{\nu }\propto \nu ^{\alpha _{\nu }}$, synchrotron radiation by a relativistic jet with no or small contributions from the host galaxy and the accretion disk seems most plausible as an optical–NIR emission mechanism. The steep optical–NIR spectral shape and the large amplitude of variability are consistent with this object being a low νpeak jet-dominated AGN. In addition, sub-arcsecond resolution optical imaging data taken with Subaru Hyper Suprime-Cam does not show a clear extended component and the spatial scales are significantly smaller than the large extensions detected at radio wavelengths. The optical spectrum of a possible faint companion galaxy does not show any emission lines at the same redshift, and hence a merging hypothesis for this AGN-related activity is not supported by our observations.</jats:p>

DOI： 10.1093/pasj/psx075

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

出版者・発行元：Oxford University Press (OUP)  

<jats:title>Abstract</jats:title><jats:p>We present our optical follow-up observations to search for an electromagnetic counterpart of the first gravitational wave source GW150914 in the framework of the Japanese collaboration for Gravitational wave ElectroMagnetic follow-up (J-GEM), which is an observing group utilizing optical and radio telescopes in Japan, as well as in New Zealand, China, South Africa, Chile, and Hawaii. We carried out a wide-field imaging survey with the Kiso Wide Field Camera (KWFC) on the 1.05 m Kiso Schmidt telescope in Japan and a galaxy-targeted survey with Tripole5 on the B&C 61 cm telescope in New Zealand. Approximately 24 deg2 regions in total were surveyed in i-band with KWFC and 18 nearby galaxies were observed with Tripole5 in g-, r-, and i-bands 4–12 days after the gravitational wave detection. Median 5 σ depths are i ∼ 18.9 mag for the KWFC data and g ∼ 18.9 mag, r ∼ 18.7 mag, and i ∼ 18.3 mag for the Tripole5 data. The probability for a counterpart to be in the observed area is 1.2% in the initial skymap and 0.1% in the final skymap. We do not find any transient source associated to an external galaxy with spatial offset from its center, which is consistent with the local supernova rate.</jats:p>

DOI： 10.1093/pasj/psw061

出版者・発行元：Oxford University Press (OUP)  

<jats:title>Abstract</jats:title>
<jats:p>We present extensively dense observations of the super-Chandrasekhar supernova (SC SN) candidate SN 2012dn from −11 to +140 d after the date of its B-band maximum in the optical and near-infrared (NIR) wavelengths conducted through the OISTER ToO (Optical and Infrared Synergetic Telescopes for Education and Research Target of Opportunity) program. The NIR light curves and color evolutions up to 35 days after the B-band maximum provided an excellent match with those of another SC SN 2009dc, providing further support to the nature of SN 2012dn as an SC SN. We found that SN 2012dn exhibited strong excesses in the NIR wavelengths from 30 d after the B-band maximum. The H- and Ks-band light curves exhibited much later maximum dates at 40 and 70 d after the B-band maximum, respectively, compared with those of normal SNe Ia. The H- and Ks-band light curves subtracted by those of SN 2009dc displayed plateaued evolutions, indicating an NIR echo from the surrounding dust. The distance to the inner boundary of the dust shell is limited to 4.8–6.4 × 10−2 pc. No emission lines were found in its early phase spectra, suggesting that the ejecta–circumstellar material interaction could not occur. On the other hand, we found no signature that strongly supports the scenario of dust formation. The mass-loss rate of the pre-explosion system is estimated to be 10−6–10−5 M⊙ yr−1, assuming that the wind velocity of the system is 10–100 km s−1, which suggests that the progenitor of SN 2012dn could be a recurrent nova system. We conclude that the progenitor of this SC SN could be explained by the single-degenerate scenario.</jats:p>

DOI： 10.1093/pasj/psw047

出版者・発行元：Oxford University Press (OUP)  

<jats:p>Monitor of All sky X-ray Image (MAXI) discovered a new outburst of an X-ray transient source named MAXI  J1421−613. Because of the detection of three X-ray bursts from the source, it was identified as a neutron star low-mass X-ray binary. The results of data analyses of the MAXI GSC (Gas Slit Camera) and the Swift XRT (X-Ray Telescope) follow-up observations suggest that the spectral hardness remained unchanged during the first two weeks of the outburst. All the XRT spectra in the 0.5–10 keV band can be well explained by thermal Comptonization of multi-color disk blackbody emission. The photon index of the Comptonized component is ≈ 2, which is typical of low-mass X-ray binaries in the low/hard state. Since X-ray bursts have a maximum peak luminosity, it is possible to estimate the (maximum) distance from its observed peak flux. The peak flux of the second X-ray burst, which was observed by the GSC, is about 5 photons cm−2 s−1. By assuming a blackbody spectrum of 2.5 keV, the maximum distance to the source is estimated as 7 kpc. The position of this source is contained by the large error regions of two bright X-ray sources detected with Orbiting Solar Observatory-7 (OSO-7) in the 1970s. Besides this, no past activities at the XRT position are reported in the literature. If MAXI  J1421−613 is the same source as (one of) these, the outburst observed with MAXI may have occurred after a quiescence of 30–40 years.</jats:p>

DOI： 10.1093/pasj/psv003

出版者・発行元：Oxford University Press (OUP)  

<jats:title>Abstract</jats:title>
<jats:p>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.</jats:p>

DOI： 10.1093/pasj/psu095

出版者・発行元：Oxford University Press (OUP)  

<jats:p>We have carried out near-infrared imaging observations of the Orion Nebula with Wide Field Cryogenic Telescope-II. The observations covered a 1$^{\circ}$$\times$ 1$^{\circ}$ area with a resolution of 12$''$ through two narrow-band filters at 3.3 $\mu $ m, tuned to the C–H band and 3.7 $\mu $ m off-the-band emissions of PAHs. We detected diffuse emissions extending larger than 10$'$ from the Trapezium cluster in both filters. We extracted the fluxes of the 3.3 $\mu $ m band emission (${F}_{\rm band}$ ) and of the 3.7 $\mu $ m continuum emission (${F}_{\rm cont}$ ) from the 3.3 $\mu $ m and 3.7 $\mu $ m filter data, respectively. The ${F}_{\rm band}$ and ${F}_{\rm cont}$ maps have similar extension over a 10$'$$\times$ 10$'$ area centered on the Trapezium cluster. Although an overall morphological resemblance can be seen between the ${F}_{\rm band}$ and ${F}_{\rm cont}$ maps, the ratio ${F}_{\rm band}/{F}_{\rm cont}$ varies from region to region in the area. The variation of ${F}_{\rm band}/{F}_{\rm cont}$ is attributed to differences of the PAH ionization degree. Adopting emissivities of neutral and ionized PAHs, we calculated the PAH ionization degrees, and constructed a PAH ionization map in the Orion Nebula. The ionization degree varies significantly from region to region in the Orion Nebula, being $\sim$ 50% at the photo-dissociation regions of the Orion Bar, and less ionized at both sides. This partial ionization revealed based on near-infrared observations is consistent with the ionization states estimated from recent mid-infrared observations.</jats:p>

DOI： 10.1093/pasj/64.6.127

出版者・発行元：Oxford University Press (OUP)  

<jats:title>Abstract</jats:title>
<jats:p>We conducted wide-field ($ \sim$ 8$ '$$ \times$ 8$ '$ ) $ \textit{JHK}_{\rm s}$ imaging polarimetric observations toward the massive star-formation region M 17. The southern H II bar is identified as large-scale infrared reflection nebula (IRN) illuminated by OB stars in the cluster center, while the northern bar shows polarization originating from dichroic extinction. Three small-scale bipolar IRN with centro-symmetric polarization patterns were identified, and their illuminating sources, embedded young stellar objects (YSOs), are most likely the driving sources of bipolar outflows. $ \textit{JHK}_{\rm s}$ polarizations of point sources in M 17 show a wavelength dependence of the polarization of dichroic extinction in the general interstellar medium, indicating $ \alpha$$ \sim$ 1.8 for the empirical relation $ P$$ \propto$$ \lambda^{-\alpha}$ of interstellar polarization. The distribution of the polarization angle shows two peaks at 170$ ^{\circ}$ and 110$ ^{\circ}$ , indicating a non-uniform magnetic field structure in M 17. The direction of the magnetic field in the cluster region is south-north. However, the magnetic field in the H II region is roughly between 100$ ^{\circ}$ –140$ ^{\circ}$ , roughly perpendicular to the Galactic disk. Such a configuration indicates that the magnetic field in the cluster region is twisted from the primordial orientation in the cluster formation. The magnetic field in the southern bar has a total strength of $ \sim$ 230$ \ \mu$ G, and is 40$ ^{\circ}$ inclined to the plane of the sky. The outflows driven by YSOs in M 17 show a poor relation with the surrounding magnetic fields. This fact implies that the magnetic field in M 17 does not dominate the orientations of protostars formed inside.</jats:p>

DOI： 10.1093/pasj/64.5.110

出版者・発行元：Oxford University Press (OUP)  

<jats:title>Abstract</jats:title>
<jats:p>XSS J12270 $-$ 4859 (J12270) is an enigmatic source of unknown nature. Previous studies revealed that the source has unusual X-ray temporal characteristics, including repetitive short-term flares, followed by spectral hardening, non-periodic dips, and dichotomy in activity; i.e., intervals filled with flares and those without. Together with a power-law X-ray spectrum, it is suggested to be a low-mass X-ray binary. In order to better understand the object, we present the results of our near-infrared (NIR) photometry and linear polarimetry observations as well as X-ray spectroscopy observations, which overlap with each other partially in time, taken respectively with the InfraRed Survey Facility (IRSF) and the Rossi X-ray Timing Explorer (RXTE). We detected several simultaneous NIR and X-ray flares for the first time. No significant NIR polarization was obtained. We assembled data taken with IRSF, RXTE, Suzaku, Swift, and other missions in the literature and compared the flare profile and the spectral energy distribution (SED) with some representative high-energy sources. Based on some similarities of the repetitive NIR and X-ray flaring characteristics and the broad SED, we argue that J12270 is reminiscent of microquasars with a synchrotron jet, which is at a very low-luminosity state of $\approx$ 10 $^{-4}$ Eddington luminosity for a stellar mass black hole or neutron star at a reference distance of 1 kpc.</jats:p>

DOI： 10.1093/pasj/63.sp3.s759

出版者・発行元：Oxford University Press (OUP)  

<jats:p>X-ray and near-infrared ( $J$ – $H$ – $K_{\rm s}$ ) observations of the galactic black-hole binary GX 339 $-$ 4 in the low/hard state were performed with Suzaku and IRSF in 2009 March. The spectrum in the 0.5–300 keV band is dominated by thermal Comptonization of multicolor disk photons, with a small contribution from a direct disk component, indicating that the inner disk is almost fully covered by hot corona with an electron temperature of $\approx$ 175 keV. The Comptonizing corona has at least two optical depths, $\tau$$\approx$ 1, 0.4. Analysis of the iron-K line profile yields an inner-disk radius of (13.3 $^{+6.4}_{-6.0}$ ) $\ R_{\rm g}$ ( $\ R_{\rm g}$ represents the gravitational radius $GM/c^2$ ), with the best-fit inclination angle of $\approx$ 50 $^\circ$ . This radius is consistent with that estimated from the continuum fit by assuming the conservation of photon numbers in Comptonization. Our results suggest that the standard disk of GX 339 $-$ 4 is likely truncated before reaching the innermost stable circular orbit (for a non-rotating black hole) in the low/hard states at $\sim\ $ 1% of the Eddington luminosity. The one-day averaged near-infrared light curves are found to be correlated with hard X-ray flux with $F_{\rm Ks}$$\propto$$F_{\rm X}^{0.45}$ . The flatter near-infrared $\nu F_{\nu}$ spectrum than the radio one suggests that the optically thin synchrotron radiation from the compact jets dominates the near-infrared flux. Based on a simple analysis, we estimate the magnetic field and size of the jet base to be 5 $\times$ 10 $^{4}\ $ G and 6 $\times$ 10 $^{8}\ $ cm, respectively. The synchrotron self Compton component is estimated to be approximately 0.4% of the total X-ray flux.</jats:p>

DOI： 10.1093/pasj/63.sp3.s785

出版者・発行元：Oxford University Press (OUP)  

<jats:title>Abstract</jats:title>
<jats:p>We have carried out the first near-infrared (NIR) polarimetric imaging observations of the central part (7$\rlap{.}^{\prime}$7 $\times$ 7$\rlap{.}^{\prime}$7 $\sim 110 {\rm\; pc} \times 110 {\rm\; pc}$) of 30 Doradus. The totals of 106, 131, and 34 sources have significant polarization degrees at $J, H$, and $K_{\rm s}$, respectively. The $E$-vectors toward 30 Dor were mapped with unprecedentedly high resolutions. As previously noticed by optical observations, there is an overall tendency for the $E$-vectors to be roughly aligned in the east-west direction. In addition, our observations reveal a more complex structure of their alignment. The position angles of the $E$-vectors are not uniform, but show a gradual spatial variation. It is plausible to assume that they trace the magnetic field toward 30 Dor. One of the expanding shells toward 30 Dor, Shell 5, is clearly enveloped by $E$-vectors. The expanding shell has probably swept the magnetic field together into the rim, while creating the curved structure. We obtained the ratios of polarization degree among the NIR wavelengths: $P_H / P_J = 0.76\pm0.02$ and $P_{K_{\rm s}} / P_H = 0.87\pm0.06$. These fit a power-law dependence of $P \propto \lambda^{-0.9}$.</jats:p>

DOI： 10.1093/pasj/59.3.519

出版者・発行元：Oxford University Press (OUP)  

<jats:title>Abstract</jats:title>
<jats:p>We present a near-infrared ($JHK_{\rm s}$) photometric catalog, including 14811185 point sources for a 40 deg$^2$ area of the Large Magellanic Cloud, 2769682 sources for an 11 deg$^2$ area of the Small Magellanic Cloud, and 434145 sources for a 4 deg$^2$ area of the Magellanic Bridge. The 10$\sigma$ limiting magnitudes are 18.8, 17.8, and 16.6 mag at $J, H$, and $K_{\rm s}$, respectively. The photometric and astrometric accuracies for bright sources are 0.03–0.04 mag and 0$\rlap {.}{^{\prime\prime}}$1, respectively. Based on the catalog, we also present (1) spatial distributions, (2) luminosity functions, (3) color–color diagrams, and (4) color–magnitude diagrams for point sources toward the Magellanic Clouds.</jats:p>

DOI： 10.1093/pasj/59.3.615

出版者・発行元：Oxford University Press (OUP)  

<jats:title>Abstract</jats:title>
<jats:p>We carried out deep and wide ($\sim$8$^{\prime}\times ^{\prime}$8) $JHK_{\rm s}$ imaging polarimetry in the southern region of the Eagle Nebula (M 16). The polarization intensity map reveals that two YSOs with near-IR reflection nebulae are located at the tips of two famous molecular pillars (Pillars 1 and 2) facing toward the exciting stars of M 16. The centrosymmetric polarization pattern are consistent with those around Class I objects having circumstellar envelopes, confirming that star formation is now taking place at the two tips of the pillars under the influence of UV radiation from the exciting stars. Polarization measurements of point sources show that magnetic fields are aligned along some of the pillars, but in a direction that is quite different to the global structure in M 16.</jats:p>

DOI： 10.1093/pasj/59.3.507

出版者・発行元：Oxford University Press (OUP)  

<jats:title>Abstract</jats:title>
<jats:p>We conducted wide-field $JHK_{\rm s}$ imaging polarimetry toward NGC 2024, which is a massive star-forming region in the Orion B cloud. We found a prominent and extended polarized nebula over NGC 2024, and constrained the location of the illuminating source of the nebula through an analysis of polarization vectors. A massive star, IRS 2b with a spectral type of O8-B2, is located in the center of the symmetric vector pattern. Five small polarized nebulae associated with YSOs were discovered on our polarization images. These nebulae are responsible for the structures of circumstellar matter (i.e., disk/envelope systems) that produce strongly polarized light through dust scattering. For the point-like sources, we performed software aperture polarimetry in order to measure integrated polarizations, with which we detected candidate sources associated with circumstellar material. We found five young brown dwarfs with highly polarized integrated emission. These sources serve as direct evidence for the existence of a disk/envelope system around brown dwarfs. We investigated the fraction of highly polarized sources against the intrinsic luminosity of stars ($\propto$ mass), and found that the source detection rate remains constant from low luminosity (brown dwarfs) to higher luminosity (solar-type) stars. This result indicates that the relative disk scale-hight is rather independent of the stellar mass. We investigated the magnetic field structure of NGC 2024 through measurements of dichroic polarization. The average position angle of projected magnetic fields across the region is found to be 110${}^{\circ}$. We found a good consistency in magnetic field structures obtained using near-infrared dichroic polarization and sub-mm/far-infrared dust emission polarization, indicating that the dichroic polarizations at near-infrared wavelengths trace magnetic field structures inside dense ($A_{V} \lesssim 50$ mag) molecular clouds.</jats:p>

DOI： 10.1093/pasj/59.3.487

出版者・発行元：Oxford University Press (OUP)  

<jats:title>Abstract</jats:title>
<jats:p>We conducted deep JHK$_{\rm s}$ imaging polarimetry of a $\sim$ 8$' \times$ 8$'$ area of the NGC 2071 star-forming region. Our polarization data revealed various infrared reflection nebulae (IRNe) associated with the central IR young star cluster NGC 2071IR and identified their illuminating sources. There are at least 4 IRNe in NGC 2071IR, and several additional IRNe were identified around nearby young stars in the same field-of-view. Each illuminating source coincides with a known near-IR source, except for IRS 3, which is only a part of IRN 2 and is illuminated by the radio source 1c. Aperture polarimetry of each cluster source was used to detect unresolved circumstellar disk/outflow systems. Aperture polarimetry of the other point-like sources within the field was conducted in this region for the first time. The magnetic field structures (from $\sim$ 1 pc down to $\sim$ 0.1 pc) were derived using both aperture polarimetry of the point-like sources and imaging polarimetry of the shocked H$_2$ emission that is seen as the dominant knotty nebulae in the $K_{\rm s}$ band image; both are of dichroic origin and the derived field directions are consistent with each other. The magnetic field direction projected on the sky is also consistent with that inferred from the 850$\mu$m thermal continuum emission polarimetry of the central 0.2 pc region, but is running roughly perpendicular ($\sim$ 75$^{\circ}$) to the direction of the large-scale outflow. We argue that the field strength is too weak to align the outflow in the large-scale field direction via magnetic braking.</jats:p>

DOI： 10.1093/pasj/59.3.467

出版者・発行元：Oxford University Press (OUP)  

<jats:title>Abstract</jats:title>
<jats:p>We present a study of the newly discovered McNeil’s nebula in Orion using simultaneous observations of the $JHK_{\mathrm{s}}$-bands with the near-infrared (NIR) camera SIRIUS on the IRSF 1.4m telescope. The cometary infrared nebula is clearly seen extending toward both north and south from the NIR source (V1647 Orionis), which illuminates McNeil’s nebula. The compact nebula has an apparent diameter of about $70 {}^{\prime \prime }$. The nebula is blue (bright in $J$) and has a cavity structure with two rims extending toward the north-east and the north-west. The north-east rim is brighter and sharp, while the north-west rim is diffuse. The north-east rim can be traced out to $\sim 40 {{}^{\prime \prime }}$ from the location of the NIR source. In contrast, no cavity structure can be seen toward the south, although the diffuse nebula is extended out to $\sim 20 {{}^{\prime \prime }}$. New NIR photometric data show a significant variation in the magnitudes ($\gt 0.15 \,\mathrm{mag} &gt; 0.15 \,\mathrm{mag}$) of the source of McNeil’s nebula within a period of one week, which is possibly under the phase of eruptive variables, like FUors or EXors.</jats:p>

DOI： 10.1093/pasj/57.1.203