A new evolutionary scenario of intermediate-mass star-formation revealed by multi-wavelength observations of OMC-2/3

We have performed millimeter- and submilli- meter-wave survey observations using the Nobeyama millimeter array (NMA) and the Atacama Submillimeter Telescope Experiment (ASTE) in one of the nearest intermediate-mass (IM) star-forming regions: Orion Molecular Cloud-2/3 (OMC-2/3). Using the high-resolution capabilities offered by the NMA (∼several arcsec), we observed dust continuum and H¹³CO⁺(1–0) emission in 12 pre- and proto-stellar candidates identified previously in single-dish millimeter observations. We unveiled the evolutionary changes with variations of the morphology and velocity structure of the dense envelopes traced by the H¹³CO⁺(1–0) emission. Furthermore, using the high-sensitivity capabilities offered by the ASTE, we searched for large-scale molecular outflows associated with these pre- and proto-stellar candidates observed with the NMA. As a result of the CO(3–2) observations, we detected six molecular outflows associated with the dense gas envelopes traced by H¹³CO⁺(1–0) and 3.3 mm continuum emission. The estimated CO outflow momentum increases with the evolutionary sequence from early to late type of the protostellar cores. We also found that the 24 μm flux increases as the dense gas evolutionary sequence. We propose that the enhancement of the 24 μm flux is caused by the growth of the cavity (i.e. the CO outflow destroys the envelope) as the evolutionary sequence. Our results show that the dissipation of the dense gas envelope plays an essential role in the evolution of the IM protostars. The extremely high-sensitivity and high-angular resolution offered by ALMA will reveal unprecedented details of the inner ∼50 AU of these protostars, which will provide us a break through in the classic scenario of IM star/disk formation.     

Scientific role of ACA for low-mass star-formation study

We discuss the scientific role of the Atacama Compact Array (ACA), the Japanese contribution to the ALMA project, for low-mass star-formation study. Our recent observations of several low-mass protostellar envelopes in the submillimeter CS (J=7–6) and HCN (J=4–3) lines with the SMA and ASTE have revealed that these submillimeter emissions are more extended than ∼2000 AU and show different velocity structures from those traced by millimeter lines. These results suggest the importance of taking short-spacing informations the ACA can offer. Our comprehensive imaging simulations of these protostellar envelopes, as well as prestellar cores and debris disks, unprecedentedly demonstrate the scientific importance of ACA.     

APPLICATION OF MEM SPECTRAL ESTIMATION TO MU RADAR OBSERVATION

Preliminary results of the wind velocity estimation using the Maximum Entropy Method (MEM) to MUradar observation data sets are presented. The comparison of the results from the periodogram method and theMEM shows that the MEM estimation is reliable, and has higher accuracy, resolution and detectability than theestimation from periodogram method. The high accuracy power spectrum obtained by the MEM is veryuseful to studying the atmospheric turbulence structure. However. the MEM needs the longer computingtime for obtaining the high accuracy spectrum. Particularly, the estimation of MEM will bring serious devia-tion at lower signal-to-noise ratio.     

Low temperature mud-explosion of Mt. Yaké, Prefs. Nagano-Gifu,Central Japan,on 17th June 1962 as an example of endogenous katamorphism of volcanic rock at the destructive stage of the volcano

Mt. Yaké or Yaké-daké is a dissected dome-shaped volcano mainly composed of the biotite bearing augite-hypersthene-hornblende andesite lavas extruded on the high mountain ridge consisting of the granite and hard Palaeozoic rocks between two prefectures Nagano and Gifu in the central part of Japan. It had been almost in dormant state only with weak fumarole activity on and around its summit dome since the former active period from 1907 to 1932. Incandescent lava emission has never been recorded in the historic age. On 17th June 1962 at about 21 h 55 m, a sudden explosion took place on the northern side of the dome. After successive explosions a fissure, about 700 m in length, was formed. On 19th from the northeast end of the fissure, milky hot water suspending muddy material flowed out. The mud flow ran down on the slope along the dry gully and poured into the Lake Taisyo-iké, about 2.5 km east of the vent. The lake was formed in 1915-eruption when a tremendous mud flow dammed up Azusagawa, the river running through the valley east of the volcano. Ejected blocks were deposited on the area within 1 km from the vent. Ash was deposited about 1 cm in thickness on the area about 4 km east of the volcano. Several mud flows poured into the Lake Taisyo-iké and the River Azusagawa. But no red-hot ejecta was observed during the present eruption, and temperature near the vent was lower than 100°C. Thus the present eruption is said to be low temperature phreatic explosions. In suspensoids of the hot water and in clayey matter deposited around the new vent are contained the montmorillonites, which hove never been found in the rocks exposed on the volcano in spite of the detailed investigation of the writers over 10 years. On the other hand, the mineral is not expected to be formed in the altered rocks under oxydized state on the surface. It was fine, at least no rain, before and during the explosions and the mud flow ran down along the dry gully. So the hot water was purely derived from the inner part of the volcano and the mud flow was not brought about by rain fall after deposition of ejecta on the volcano. The mud flow must have been formed endogenously under the volcano where the katamorphism of the rocks forming the volcano had advanced owing to chemical action of volcanic gas in the long period before the eruption.     

Validation of HRDI MLT winds with meteor radars

A validation study of the mesospheric and lower-thermospheric (MLT) wind velocities measured by the High-Resolution Doppler Imager (HRDI) on board the Upper-Atmosphere Research Satellite (UARS) has been carried out, comparing with observations by meteor radars located at Shigaraki, Japan and Jakarta, Indonesia. The accuracy of the HRDI winds relative to the meteor radars is obtained by a series of simultaneous wind measurements at the time of UARS overpasses. Statistical tests on the difference in the wind vectors observed by HRDI and the meteor radars are applied to determine whether the wind speed has been overestimated by HRDI (or underestimated by the MF radars) as previously noticed in HRDI vs. MF radar comparisons. The techniques employed are the conventional t-test applied to the mean values of the paired wind vector components as well as wind speeds, and two nonparametric tests suitable for testing the paired wind speed. The square-root transformation has been applied before the Mests of the wind speed in order to fit the wind-speed distribution function to the normal distribution. The overall results show little evidence of overestimation by HRDI (underestimation by meteor radars) of wind velocities in the MLT region. Some exceptions are noticed, however, at the altitudes around 88 km, where statistical differences occasionally reach a level of significance of 0.01. The validation is extended to estimate the precision of the wind velocities by both HRDI and meteor radars. In the procedure, the structure function defined by the mean square difference of the observed anomalies is applied in the vertical direction for the profile data. This method assumes the isotropy and the homogeneity of variance for the physical quantity and the homogeneity of variance for the observational errors. The estimated precision is about 6m s^– for the Shigaraki meteor radar, 15 m s^–1 for the Jakarta meteor radar, and 20 m s^–1 for HRDI at 90-km altitude. These values can be used ot confirm the statistical significance of the wind field obtained by averaging the observed winds.     

An intercomparison between the GSWM, UARS, and ground based radar observations: a case-study in January 1993

The Global-Scale Wave Model (GSWM) is a steady-state two-dimensional linearized model capable of simulating the solar tides and planetary waves. In an effort to understand the capabilities and limitations of the GSWM throughout the upper mesosphere and thermosphere a comparative analysis with observational data is presented. A majority of the observational data used in this study was collected during the World Day campaign which ran from 20 January to 30 January 1993. During this campaign data from 18 ground-based observational sites across the globe and two instruments located on the UARS spacecraft were analyzed. Comparisons of these data with the simulations from the GSWM indicate that the GSWM results are in reasonable agreement with the observations. However, there are a number of cases where the agreement is not particularly good. One such instance is for the semidiurnal tide in the northern hemisphere, where the GSWM estimates may exceed observations by 50%. Through a number of numerical simulations, it appears that this discrepancy may be due to the eddy diffusivity profiles used by the GSWM. Other differences relating to the diurnal tide and the quasi-two-day wave are presented and discussed. Additionally, a discussion on the biases and aliasing difficulties which may arise in the observational data is alos presented.     

Full-correlation analysis of turbulent scattering layers in the mesosphere observed by the MU radar

We have applied a full-correlation analysis technique to the echo power fluctuations observed by the MU radar (35°N, 136°E), and analyzed the horizontal structure of the scattering pattern in the mesosphere as well as their horizontal motions. The velocity of the scattering pattern did not agree with the background wind velocity, but was associated with the horizontal propagating direction of a saturated inertia gravity wave identified in the wind field. The length of the long axis of the characteristic ellipse of the scattering pattern was approximately 50 km, and the direction was almost perpendicular to the propagating direction of the wave. The correlation time of the scattering pattern was approximately 700 s, which is much longer than the lifetime of the isolated turbulence itself. This implies that the observed scattering pattern is associated with a region where the saturated inertia gravity wave generates turbulence.     

Diurnal variations of the planetary boundary layer observed with anL-band clear-air doppler radar

Based on continuous observations of the planetary boundary layer (PBL) with anL-band (1357.5 MHz) boundary-layer radar (BLR) at a hilly location in Japan, we have discovered that on clear days, a thin enhanced echo layer corresponding to the top of the PBL (or mixed layer) appeared at about 500 m height in the morning and ascended to about 1500 m in the afternoon. Strong upward velocities were observed below the echo layer (or inside the PBL), reaching 1500 m in the afternoon.     

Geochemistry and Fluid Inclusions Analysis of Vein Quartz in the Multiple Hydrothermal Systems of Mankayan Mineral District,Philippines

Several high‐sulfidation epithermal gold orebodies in the Mankayan Mineral District were formed in an environment that has been already affected by earlier porphyry‐type mineralization. This study reports the geologic and geochemical characteristics of the Carmen and Florence epithermal orebodies, which are located in the south of the Lepanto main enargite–gold orebody. The gold‐bearing epithermal quartz veins in the Carmen and Florence areas are of two types: (i) the enargite‐rich veins and (ii) the quartz–pyrite–gold (QPG) veins. The two types of veins are mainly hosted by the Cretaceous Lepanto Metavolcanics basement rocks, with minor veins cutting the Pleistocene Imbanguila Dacite Pyroclastics. The mineral assemblages and homogenization temperatures of fluid inclusions indicate that the Carmen and Florence orebodies were deposited by fluids varying from high to very high sulfidation state. The enargite and QPG epithermal veins of Carmen and Florence cut porphyry‐type quartz veinlet stockworks and veins that host polyphase hypersaline fluid inclusions that did not homogenize at or below 400°C. These high‐temperature quartz exhibits distinctly different mineral chemistry from the quartz of the QPG and enargite‐rich epithermal veins. In particular, the Ti content of quartz of the porphyry‐type veinlet stockwork is elevated (>100 ppm), whereas the Ti concentration of the epithermal vein quartz crystals are below detection limits. The Fe concentration of quartz is high in epithermal vein quartz (>300 ppm), whereas nearly undetected in the porphyry‐type stockwork veinlet quartz. Multiple generations of quartz with different mineral chemistry, fluid inclusions morphology, temperature, salinity and bulk gas compositions, and stable isotopic ratios indicate the variable hydrothermal conditions throughout the mineralization history of the Mankayan District. The temperature, pH, sulfidation state, oxidation state, and fluid composition vary among the orebodies in Carmen and Florence areas. Furthermore, the characteristics of earlier alteration affected the apparent characteristics of subsequent mineralization.     

Latitudinal and Vertical Distributions of Phytoplankton Absorption Spectra in the Central North Pacific during Spring 1994

Vertical changes of phytoplankton absorption spectra along 175°E from 48°N to 15°S were examined during spring 1994. The absorption spectra were analyzed using three different approaches; averaging the spectra within same oceanic areas, EOF analysis, and multiple regression analysis. Average spectra showed differences in five oceanic areas; subarctic, Kuroshio, subtropical surface, equatorial surface, and subtropical and equatorial subsurface areas. The distributions of the EOF mode of the variance of absorption spectra and of the pigments estimated by the multiple regression analysis indicated consistent differences of the spectra between those areas. Kuroshio water contains highest chlorophyll a concentrations and low chlorophyll-a-specific absorption spectra, and this may be caused by the package effect with large phytoplankton cell and by low concentrations of photo-protected carotenoids. Subtropical and equatorial subsurface water showed high absorption at 480 nm and indicated the effects of chlorophyll b. Absorption of the subsurface phytoplankton also showed a shift of the blue peak, possibly caused by the presence of divinyl-chlorophyll a. The consistency of the three different analytical methods indicates that the phytoplankton absorption includes significant information on pigment composition along a north-south vertical section of the central North Pacific.