Yoshizo Okamoto

Discovery of Small-scale Spiral Structures in the Disk of SAO 206462 (HD 135344B): Implications for the Physical State of the Disk from Spiral Density Wave Theory

We present high-resolution, H-band imaging observations, collected with Subaru/HiCIAO, of the scattered light from the transitional disk around SAO 206462 (HDxa0135344B). Although previous sub-mm imagery suggested the existence of a dust-depleted cavity at r ≤ 46 AU, our observations reveal the presence of scattered light components as close as 02 (~ 28 AU) from the star. Moreover, we have discovered two small-scale spiral structures lying within 05 (~ 70 AU). We present models for the spiral structures using the spiral density wave theory, and derive a disk aspect ratio of h ~ 0.1, which is consistent with previous sub-mm observations. This model can potentially give estimates of the temperature and rotation profiles of the disk based on dynamical processes, independently from sub-mm observations. It also predicts the evolution of the spiral structures, which can be observable on timescales of 10-20 years, providing conclusive tests of the model. While we cannot uniquely identify the origin of these spirals, planets embedded in the disk may be capable of exciting the observed morphology. Assuming that this is the case, we can make predictions on the locations and, possibly, the masses of the unseen planets. Such planets may be detected by future multi-wavelength observations.

MID-INFRARED IMAGING OF THE TRANSITIONAL DISK OF HD 169142: MEASURING THE SIZE OF THE GAP*

The disk around the Herbig Ae star HDxa0169142 was imaged and resolved at 18.8 and 24.5 μm using Subaru/COMICS. We interpret the observations using a two-dimensional radiative transfer model and find evidence for the presence of a large gap. The mid-infrared images trace dust that is emitted at the onset of a strong rise in the spectral energy distribution (SED) at 20 μm, and are therefore very sensitive to the location and characteristics of the inner wall of the outer disk and its dust. We determine the location of the wall to be 23+3 – 5xa0AU from the star. An extra component of hot dust must exist close to the star. We find that a hydrostatic optically thick inner disk does not produce enough flux in the near-infrared, and an optically thin, geometrically thick component is our solution to fit the SED. Considering the recent findings of gaps and holes in a number of Herbig Ae/Be group I disks, we suggest that such disk structures may be common in group I sources. Classification as group I should be considered a strong case for classification as a transitional disk, though improved imaging surveys are needed to support this speculation.

Surface temperature measurement near ambient conditions using infrared radiometers with different detection wavelength bands by applying a grey-body approximation: estimation of radiative properties for non-metal surfaces

The visualization technique using an infrared radiometer has been widely used to estimate the two-dimensional temperature distribution on a surface. Infrared radiometry is a nondestructive remote sensing technique and is applicable to various engineering problems such as invisible flaw detection, heat transfer measurement and so on. It is important to analyse its fundamental characteristics to establish a practical technique of measuring temperature. We therefore discuss them experimentally using infrared radiometers with three detection wavelength bands. The radiative properties near ambient conditions are proposed for various non-metal surfaces, where the grey-body approximation may be applied.

End effect in a coaxial cylindrical viscometer

The end effect in a coaxial cylindrical viscometer was determined as an effective length of an inner cylinder (bob) using the multiple bob method. In this viscometer, the data are for a rotating bob and not for a rotating cup. The end correction appears to increase over the Reynolds number 10, even in low viscosity and Newtonian liquids. It is shown that a conical end of the bob and a wide gap between the bob and cup give a larger end correction. The visualization of the liquid flow at the bottom of the bob makes it clear that the stream lines enter into the annular gap even in Couette flow, which is supposed to disturb the flow in the gap. With the increment of the Reynolds number, these entrances become larger, although the flow is not Couette but Taylor and turbulent flows.

High-resolution 25 μm Imaging of the Disks around Herbig Ae/Be Stars

We imaged circumstellar disks around 22 Herbig Ae/Be stars at 25 μm using Subaru/COMICS and Gemini/T-ReCS. Our sample consists of an equal number of objects from each of the two categories defined by Meeus et al.; 11 group I (flaring disk) and II (flat disk) sources. We find that group I sources tend to show more extended emission than group II sources. Previous studies have shown that the continuous disk is difficult to resolve with 8 m class telescopes in the Q band due to the strong emission from the unresolved innermost region of the disk. This indicates that the resolved Q-band sources require a hole or gap in the disk material distribution to suppress the contribution from the innermost region of the disk. As many group I sources are resolved at 25 μm, we suggest that many, but not all, group I Herbig Ae/Be disks have a hole or gap and are (pre-)transitional disks. On the other hand, the unresolved nature of many group II sources at 25 μm supports the idea that group II disks have a continuous flat disk geometry. It has been inferred that group I disks may evolve into group II through the settling of dust grains into the mid-plane of the protoplanetary disk. However, considering the growing evidence for the presence of a hole or gap in the disk of group I sources, such an evolutionary scenario is unlikely. The difference between groups I and II may reflect different evolutionary pathways of protoplanetary disks.

Measurement of turbulent heat transfer using infrared thermography near ambient conditions and its quantitative error estimation

Infrared thermography was applied to measurement of turbulent heat transfer in order to investigate its applicability under near-ambient conditions. Natural convection along a vertical smooth flat plate and forced convection along a smooth flat plate were realized in a large darkroom, where individual heat transfer coefficients were quantitatively measured using infrared thermography in the laminar, transition, and turbulent regions. The measurement error was then estimated using ANSI/ASME PTC 19.1-1985 measurement uncertainty to confirm the accuracy. It is obvious from a series of application experiments and error analyses that the present technique is useful for estimating turbulent heat transfer quantitatively and dynamically. Infrared thermography is an appropriate measurement procedure for engineering applications because it can be applied to diagnose a two-dimensional and dynamical temperature field instantaneously and nondestructively

Key science drivers for MICHI: a mid-IR instrument concept for the TMT

A mid-infrared (MIR) imager and spectrometer is being investigated for possible construction in the early operation of the Thirty Meter Telescope (TMT). Combined with the MIR adaptive optics (AO) system (MIRAO), the instrument will afford ~15 times higher sensitivity and ~4 times better spatial resolution (0.07”) at 10μm compared to 8m-class telescopes. Additionally, through exploiting the large collection area of the TMT, the high-dispersion spectroscopy mode will be unrivaled by other ground- and space-based facilities. These combined capabilities offer the possibility for breakthrough science, as well as ‘workhorse’ observing modes of imaging and low/moderate spectral resolution. In this paper we summarize the primary science drivers that are guiding the instrument design.

Uncertainty analysis of surface temperature measurement using infrared radiometer

In general, measurement error, including a precision error and a bias error, is defined as the difference between the true and measured values. Moreover, measurement error is also necessarily included in the temperature measurement using IR radiometer; however error estimation for IR radiometer has not been investigated yet. In the present study we discussed several primary factors on a measurement error and estimate a qualitative error pertaining to IR radiometer using the uncertainty analysis method based on ANSI/ASME PTC 19.1 - 1985. Detailed clarification of measurement error is important to develop a practical temperature measurement using IR radiometer. It was newly revealed from the uncertainty analysis utilized here that the measurement using IR radiometer is available in obtaining several radiative quantities. In addition, from a series of thermal visualization using IR radiometer, the relation between friction energy and a surface temperature is clarified to tribology behavior of the surface.

Study on heat transfer and temperature field of rotating friction interface

An experimental study was conducted to visualize and analyze heat mass transfer and temperature fields of a rotating dry-friction interface. The friction temperature distribution of selflubricated plastic materials was observed by means of the infrared radiometer. In a combination of POM-POM, and POM-PPS materials, the transient temperature distribution along the axis is expressed in the error function and the temperature rise of the friction interface AT was correlated to the friction value μFV/A, which means the heat flux by friction heat generation. Finally, it was clear from a series of experiments that the surface temperature rise, heat flux of the friction and rubbing time played a significant role in our experiment.

Thermal image study of detecting near-underground structures by means of infrared radiometer

An infrared radiometer is used to detect several flaws of industrial structural elements, as one remote sensing device. The thermal image method (TIM) was carried out to analyze location and dimension of the internal flaws of mechanical components, like piping, vessel, slab and pile. Internal flaws were detected by visualizing abnormal behavior of radiation temperature distribution of the tested surface by solar and artificial heat injection. The induced nonuniform temperature shows the existence of the internal flaws imaged on the CRT display of the infrared radiometer. As one application subject, the TIM method was extensively applied to near-underground buried materials of ancient remains; such as corner stone, stone settlement, shell mound, and tomb. The paper represents basic experimental and analytical results of preliminary and demonstration model tests of the buried materials in the soil and rock by solar, direct, and indirect combustion heaters. After continuous irradiation heating, we measured and recorded transient radiation temperature distribution of the tested ground surface which inserts the model near-underground tests plates of stylene, concrete, stone and gravel, changing width and depth of the test plates. Nonuniform and discontinuous temperature distribution of the tested surface above the inserted plates shows the existence of near- underground buried materials. Furthermore, transient temperature and heat flow behavior was numerically analyzed by solving a transient two-dimensional heat-balance equation. Calculation results were quite useful to analyze the experimental heat flow behavior around the buried object.