arXiv subjects

Munetake Momose

Publications and source records attributed to Munetake Momose.

68 records · Page 4Linked to original sources

arXiv2014

High abundance ratio of $^{13}$CO to C$^{18}$O toward photon-dominated regions in the Orion-A giant molecular cloud

Aims. We derive physical properties such as the optical depths and the column densities of $^{13}$CO and C$^{18}$O to investigate the relationship between the far ultraviolet (FUV) radiation and the abundance ratios between $^{13}$CO and C$^{18}$O. Method. We have carried out wide-field (0.4 deg$^2$) observations with an angular resolution of 25.8 arcsec ($\sim$ 0.05 pc) in $^{13}$CO ($J$=1--0) and C$^{18}$O ($J$=1--0) toward the Orion-A giant molecular cloud using the Nobeyama 45 m telescope in the on-the-fly mode. Results. Overall distributions and velocity structures of the $^{13}$CO and C$^{18}$O emissions are similar to those of the $^{12}$CO ($J$=1--0) emission. The optical depths of the $^{13}$CO and C18O emission lines are estimated to be 0.05 $<$ $τ_{\rm ^{13}CO}$ $<$ 1.54 and 0.01 $<$ $τ_{\rm C^{18}O}$ $<$ 0.18, respectively. The column densities of the $^{13}$CO and C$^{18}$O emission lines are estimated to be 0.2 $\times$ 10$^{16}$ $<$ $N_{\rm ^{13}CO}$ $<$ 3.7 $\times$ 10$^{17}$ cm$^{-2}$ and 0.4 $\times$ 10$^{15}$ $<$ $N_{\rm C^{18}O}$ $<$ 3.5 $\times$ 10$^{16}$ cm$^{-2}$, respectively. The abundance ratios between $^{13}$CO and C$^{18}$O, $X_{\rm ^{13}CO}$/$X_{\rm C^{18}O}$, are found to be 5.7 - 33.0. The mean value of $X_{\rm ^{13}CO}$/$X_{\rm C^{18}O}$ in the nearly edge-on photon-dominated regions is found to be 16.47 $\pm$ 0.10, which is a third larger than that the solar system value of 5.5. The mean value of $X_{\rm ^{13}CO}$/$X_{\rm C^{18}O}$ in the other regions is found to be 12.29 $\pm$ 0.02. The difference of the abundance ratio is most likely due to the selective FUV photodissociation of C$^{18}$O.

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arXiv2014

High-Resolution Submillimeter and Near-Infrared Studies of the Transition Disk around Sz 91

To reveal the structures of a transition disk around a young stellar object in Lupus, Sz 91, we have performed aperture synthesis 345 GHz continuum and CO(3--2) observations with the Submillimeter Array ($\sim1\arcsec$--3$\arcsec$ resolution), and high-resolution imaging of polarized intensity at the $K_s$-band by using the HiCIAO instrument on the Subaru Telescope ($0\farcs25$ resolution). Our observations successfully resolved the inner and outer radii of the dust disk to be 65 AU and 170 AU, respectively, which indicates that Sz 91 is a transition disk source with one of the largest known inner holes. The model fitting analysis of the spectral energy distribution reveals an H$_2$ mass of $2.4\times10^{-3}$ $M_\sun$ in the cold ($T<$30 K) outer part at $65 3\times10^{-9}$ $M_\sun$) of hot ($T\sim$180 K) dust possibly remains inside the inner hole of the disk. The structure of the hot component could be interpreted as either an unresolved self-luminous companion body (not directly detected in our observations) or a narrow ring inside the inner hole. Significant CO(3--2) emission with a velocity gradient along the major axis of the dust disk is concentrated on the Sz 91 position, suggesting a rotating gas disk with a radius of 420 AU. The Sz 91 disk is possibly a rare disk in an evolutionary stage immediately after the formation of protoplanets because of the large inner hole and the lower disk mass than other transition disks studied thus far.

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arXiv2013

Observations of 6.7 GHz Methanol Masers with EAVN I: VLBI Images of the first Epoch of Observations

Very long baseline interferometry (VLBI) monitoring of the 6.7 GHz methanol maser allows us to measure the internal proper motions of the maser spots and therefore study the gas motion around high-mass young stellar objects. To this end, we have begun monitoring observations with the East-Asian VLBI Network. In this paper we present the results of the first epoch observation for 36 sources, including 35 VLBI images of the methanol maser. Since two independent sources were found in three images, respectively, images of 38 sources were obtained. In 34 sources, more than or equal to 10 spots were detected. The observed spatial scale of the maser distribution was from 9 to 4900 astronomical units, and the following morphological categories were observed: elliptical, arched, linear, paired, and complex. The position of the maser spot was determined to an accuracy of approximately 0.1 mas, sufficiently high to measure the internal proper motion from two years of monitoring observations. The VLBI observation, however, detected only approximately 20% of all maser emission, suggesting that the remaining 80% of the total flux was spread into an undetectable extended distribution. Therefore, in addition to high-resolution observations, it is important to observe the whole structure of the maser emission including extended low-brightness structures, to reveal the associated site of the maser and gas motion.

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arXiv2013

Local Enhancement of Surface Density in the Protoplanetary Ring Surrounding HD 142527

We report ALMA observations of dust continuum, 13CO J=3--2, and C18O J=3--2 line emission toward a gapped protoplanetary disk around HD 142527. The outer horseshoe-shaped disk shows the strong azimuthal asymmetry in dust continuum with the contrast of about 30 at 336 GHz between the northern peak and the southwestern minimum. In addition, the maximum brightness temperature of 24 K at its northern area is exceptionally high at 160 AU from a star. To evaluate the surface density in this region, the grain temperature needs to be constrained and was estimated from the optically thick 13CO J=3--2 emission. The lower limit of the peak surface density was then calculated to be 28 g cm-2 by assuming a canonical gas-to-dust mass ratio of 100. This finding implies that the region is locally too massive to withstand self-gravity since Toomre's Q <~1--2, and thus, it may collapse into a gaseous protoplanet. Another possibility is that the gas mass is low enough to be gravitationally stable and only dust grains are accumulated. In this case, lower gas-to-dust ratio by at least 1 order of magnitude is required, implying possible formation of a rocky planetary core.

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arXiv2013

Extensive [CI] Mapping toward the Orion-A Molecular Cloud

We have carried out wide-field (0.17 degree^2) and high-angular resolution (21.3 arcsec ~ 0.04 pc) observations in [CI] line toward the Orion-A giant molecular cloud with the Atacama Submillimeter Telescope Experiment (ASTE) 10 m telescope in the On-The-Fly (OTF) mode. Overall features of the [CI] emission are similar to those of the CO (1--0) emission in Shimajiri et al. (2011); the total intensity ratio of the [CI] to CO emission ranges from 0.05 to 0.2. The optical depth of the [CI] emission is found to be 0.1 -- 0.75, suggesting optically thin emission. The column density of the [CI] emission is estimated to be (1.0 -- 19) x 10^17 cm^-2. These results are consistent with the results of the previous [CI] observations with a low-angular resolution of 2.2 arcmin (e.g. Ikeda et al. 1999). In the nearly edge-on PDRs and their candidates of the Orion Bar, DLSF, M 43 Shell, and Region D, the distributions of the [CI] emission coincide with those of the CO emission, inconsistent with the prediction by the plane-parallel PDR model (Hollenbach & Tielens 1999). In addition, the [CI] distribution in the Orion A cloud is found to be more similar to those of the ^{13}CO (1--0), C^{18}O (1--0), and H^{13}CO^+ (1--0) lines than that of the CO (1--0) line, suggesting that the [CI] emission is not limited to the cloud surface, but is tracing the dense, inner parts of the cloud.

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arXiv2013

High-Contrast Near-Infrared Imaging Polarimetry of the Protoplanetary Disk around RY Tau

We present near-infrared coronagraphic imaging polarimetry of RY Tau. The scattered light in the circumstellar environment was imaged at H-band at a high resolution (~0".05) for the first time, using Subaru-HiCIAO. The observed polarized intensity (PI) distribution shows a butterfly-like distribution of bright emission with an angular scale similar to the disk observed at millimeter wavelengths. This distribution is offset toward the blueshifted jet, indicating the presence of a geometrically thick disk or a remnant envelope, and therefore the earliest stage of the Class II evolutionary phase. We perform comparisons between the observed PI distribution and disk models with: (1) full radiative transfer code, using the spectral energy distribution (SED) to constrain the disk parameters; and (2) monochromatic simulations of scattered light which explore a wide range of parameters space to constrain the disk and dust parameters. We show that these models cannot consistently explain the observed PI distribution, SED, and the viewing angle inferred by millimeter interferometry. We suggest that the scattered light in the near-infrared is associated with an optically thin and geometrically thick layer above the disk surface, with the surface responsible for the infrared SED. Half of the scattered light and thermal radiation in this layer illuminates the disk surface, and this process may significantly affect the thermal structure of the disk.

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arXiv2012

Thermal Structure of a Protoplanetary Disk around HD163296: A Study of Vertical Temperature Distribution by CO Emission Lines

This paper presents observations of a protoplanetary disk around Herbig Ae star HD 163296 in 12CO (J=1-0), 12CO (J=3-2), 13CO (J=1-0), and 13CO (J=3-2) emission lines. Double-peaked emission profiles originating from the rotating circumstellar disk were detected in all the lines. The disk parameters were estimated from model calculation in which the radial distribution of temperature or surface density inside the disk has a power-law form. The surface density should be sufficiently high so that the disk is optically thick for all the CO lines, as discussed in previous studies based on interferometric observations. The temperature and outer radius of the disk were also confirmed to be consistent with the previous results. Taking advantage of difference in position of the photosphere among the CO lines, we revealed temperature distribution in vertical direction. The temperature of 12CO (J=3-2) emitting region is about twice higher than that of any other CO emitting region; the former is about 59 K while the latter is about 31 K at 100 AU from the central star, suggesting that there are at least two distinct temperature regions. The best fit temperature for 13CO (J=1-0) that should trace the deepest region of the disk is even lower, implying that there is also a different temperature region in deep inside of the disk. Such vertical temperature distribution in a disk was identified both in T Tauri and Herbig Ae stars (e.g., DM Tau, AB Aur, and HD 31648), and this should be a common feature in protoplanetary disks.

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arXiv2011

Evidence For Cloud-Cloud Collision and Parsec-Scale Stellar Feedback Within the L1641-N Region

We present high spatial resolution $^{12}$CO ($J=1-0$) images taken by the Nobeyama 45m telescope toward a $48' \times 48'$ area including the L1641-N cluster. The effective spatial resolution of the maps is $21"$, corresponding to 0.04 pc at a distance of 400 pc. A recent 1.1 mm dust continuum map reveals that the dense gas is concentrated in several thin filaments. We find that a few dust filaments are located at the parts where $^{12}$CO ($J=1-0$) emission drops sharply. Furthermore, the filaments have two-components with different velocities. The velocity difference between the two-components is about 3 km s$^{-1}$, corresponding to a Mach number of 10, significantly larger than the local turbulent velocity in the cloud. These facts imply that the collision of the two components (hereafter, the cloud-cloud collision) possibly contributed to the formation of these filaments. Since the two components appear to overlap toward the filaments on the plane of the sky, the collision may have occurred almost along the line of sight. Star formation in the L1641-N cluster was probably triggered by such a collision. We also find several parsec-scale CO shells whose centers are close to either the L1641-N cluster or V 380 Ori cluster. We propose that these shells were created by multiple winds and/or outflows from cluster YSOs, i.e., "protocluster winds." One exceptional dust filament located at the western cloud edge lies along a shell; it is presumably a part of the expanding shell. Both the cloud-cloud collision and protocluster winds are likely to influence the cloud structure and kinematics in this region.

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arXiv2010

The Millimeter Sky Transparency Imager (MiSTI)

The Millimeter Sky Transparency Imager (MiSTI) is a small millimeter-wave scanning telescope with a 25-cm diameter dish operating at 183 GHz. MiSTI is installed at Atacama, Chile, and it measures emission from atmospheric water vapor and its fluctuations to estimate atmospheric absorption in the millimeter to submillimeter. MiSTI observes the water vapor distribution at a spatial resolution of 0.5 deg, and it is sensitive enough to detect an excess path length of <~ 0.05 mm for an integration time of 1 s. By comparing the MiSTI measurements with those by a 220 GHz tipper, we validate that the 183 GHz measurements of MiSTI are correct, down to the level of any residual systematic errors in the 220 GHz measurements. Since 2008, MiSTI has provided real-time (every 1 hr) monitoring of the all-sky opacity distribution and atmospheric transmission curves in the (sub)millimeter through the internet, allowing to know the (sub)millimeter sky conditions at Atacama.

astro-ph.IM↗

arXiv2010

Detection of Strong Millimeter Emission from the Circumstellar Dust Disk Around V1094 Sco: Cold and Massive Disk around a T Tauri Star in a Quiescent Accretion Phase?

We present the discovery of a cold massive dust disk around the T Tauri star V1094 Sco in the Lupus molecular cloud from the 1.1 millimeter continuum observations with AzTEC on ASTE. A compact ($r\lesssim$320 AU) continuum emission coincides with the stellar position having a flux density of 272 mJy which is largest among T Tauri stars in Lupus. We also present the detection of molecular gas associated with the star in the five-point observations in $^{12}$CO J=3--2 and $^{13}$CO J=3--2. Since our $^{12}$CO and $^{13}$CO observations did not show any signature of a large-scale outflow or a massive envelope, the compact dust emission is likely to come from a disk around the star. The observed SED of V1094 Sco shows no distinct turnover from near infrared to millimeter wavelengths, which can be well described by a flattened disk for the dust component, and no clear dip feature around 10 $\micron$ suggestive of absence of an inner hole in the disk. We fit a simple power-law disk model to the observed SED. The estimated disk mass ranges from 0.03 to $\gtrsim$0.12 $M_\sun$, which is one or two orders of magnitude larger than the median disk mass of T Tauri stars in Taurus.

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arXiv2010

New Panoramic View of $^{12}$CO and 1.1 mm Continuum Emission in the Orion A Molecular Cloud. I. Survey Overview and Possible External Triggers of Star Formation

We present new, wide and deep images in the 1.1 mm continuum and the $^{12}$CO ($J$=1-0) emission toward the northern part of the Orion A Giant Molecular Cloud (Orion-A GMC). The 1.1 mm data were taken with the AzTEC camera mounted on the Atacama Submillimeter Telescope Experiment (ASTE) 10 m telescope in Chile, and the $^{12}$CO ($J$=1-0) data were with the 25 beam receiver (BEARS) on the NRO 45 m telescope in the On-The-Fly (OTF) mode. The present AzTEC observations are the widest $(\timeform{1.D7}$ $\times$ $\timeform{2.D3}$, corresponding to 12 pc $\times$ 17 pc) and the highest-sensitivity ($\sim$9 mJy beam$^{-1}$) 1.1 mm dust-continuum imaging of the Orion-A GMC with an effective spatial resolution of $\sim$ 40$\arcsec$. The $^{12}$CO ($J$=1-0) image was taken over the northern $\timeform{1D.2} \times\timeform{1D.2}$ (corresponding 9 pc $\times$ 9 pc) area with a sensitivity of 0.93 K in $T_{\rm MB}$, a velocity resolution of 1.0 km s$^{-1}$, and an effective spatial resolution of 21$\arcsec$. With these data, together with the MSX 8 $μ$m, Spitzer 24 $μ$m and the 2MASS data, we have investigated the detailed structure and kinematics of molecular gas associated with the Orion-A GMC and have found evidence for interactions between molecular clouds and the external forces that may trigger star formation. Two types of possible triggers were revealed; 1) Collision of the diffuse gas on the cloud surface, particularly at the eastern side of the OMC-2/3 region, and 2) Irradiation of UV on the pre-existing filaments and dense molecular cloud cores. Our wide-field and high-sensitivity imaging have provided the first comprehensive view of the potential sites of triggered star formation in the Orion-A GMC.

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arXiv2010

High Resolution Observations of Dust Continuum Emission at 340 GHz from the Low-mass T Tauri Star FN Tauri

FN Tau is a rare example of very low-mass T Tauri stars that exhibits a spatially resolved nebulosity in near-infrared scattering light. To directly derive the parameters of a circumstellar disk around FN Tau, observations of dust continuum emission at 340 GHz are carried out with the Submillimeter Array (SMA). A point-like dust continuum emission was detected with a synthesized beam of ~ 0.7" in FWHM. From the analysis of the visibility plot, the radius of the emission is estimated to be <= 0.29", corresponding to 41 AU. This is much smaller than the radius of the nebulosity, 1.85" for its brighter part at 1.6 micron. The 340 GHz continuum emission observed with the SMA and the photometric data at lambda <= 70 micron are explained by a power-law disk model whose outer radius and mass are 41 AU and (0.24 - 5.9) x 10^{-3} M_{sun}, respectively, if the exponent of dust mass opacity (beta) is assumed to be 0-2. The disk model cannot fully reproduce the flux density at 230 GHz obtained with the IRAM 30-meter telescope, suggesting that there is another extended "halo" component that is missed in the SMA observations. By requiring the halo not to be detected with the SMA, the lower limit to the size of the halo is evaluated to be between 174 AU and 574 AU, depending on the assumed beta value. The physical nature of the halo is unclear, but it may be the periphery of a flared circumstellar disk that is not described well in terms of a power-law disk model, or a remnant of a protostellar envelope having flattened structure.

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arXiv2006

Kinematics of SiO J=8-7 Emission towards the HH 212 Jet

We present SiO J=8-7 (347.3 GHz) observations towards HH 212 using the ASTE telescope. Our observations with a 22''-diameter beam show that the SiO emission is highly concentrated within 1' of the driving source. We carefully compare the SiO observations with archival H_2 1-0 S(1) images and published H_2 echelle spectra. We find that, although the SiO velocities closely match the radial velocities seen in H_2, the distribution of H_2 and SiO emission differ markedly. We attribute the latter to the different excitation conditions required for H_2 and SiO emission, particularly the higher critical density (n_H2 ~10^8 cm^-3) of the SiO J=8-7 emission. The kinematic similarities imply that the H_2 and SiO are associated with the same internal working surfaces. We conclude that the SiO J=8-7 emission has a potential to probe the jet/wind launching region through interferometric observations in the future, particularly for the youngest, most deeply embedded protostars where IR observations are not possible.

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arXiv2003

Interferometric Observations of Formaldehyde in the Protoplanetary Disk around LkCa15

Emission from the $2_{12}-1_{11}$ line of H$_2$CO has been detected and marginally resolved toward LkCa15 by the Nobeyama Millimeter Array. The column density of H$_2$CO is higher than that observed in DM Tau and than predicted by theoretical models of disk chemistry; also the line-intensity profile is less centrally peaked than that for CO. A similar behavior is observed in other organic gaseous molecules in the LkCa 15 disk.

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