Understanding high-mass star formation is one of the top-priority issues in astrophysics. Recent observational studies have revealed that cloud-cloud collisions may play a role in high-mass star ...formation in several places in the Milky Way and the Large Magellanic Cloud. The Trifid Nebula M20 is a well-known Galactic H ii region ionized by a single O7.5 star. In 2011, based on the CO observations with NANTEN2, we reported that the O star was formed by the collision between two molecular clouds ∼0.3 Myr ago. Those observations identified two molecular clouds toward M20, traveling at a relative velocity of . This velocity separation implies that the clouds cannot be gravitationally bound to M20, but since the clouds show signs of heating by the stars there they must be spatially coincident with it. A collision is therefore highly possible. In this paper we present the new CO J = 1-0 and J = 3-2 observations of the colliding clouds in M20 performed with the Mopra and ASTE telescopes. The high-resolution observations revealed that the two molecular clouds have peculiar spatial and velocity structures, i.e., a spatially complementary distribution between the two clouds and a bridge feature that connects the two clouds in velocity space. Based on a new comparison with numerical models, we find that this complementary distribution is an expected outcome of cloud-cloud collisions, and that the bridge feature can be interpreted as the turbulent gas excited at the interface of the collision. Our results reinforce the cloud-cloud collision scenario in M20.
The second survey of the molecular clouds in the Large Magellanic Cloud in super(12)CO was carried out by NANTEN. The sensitivity of this survey is twice as high as that of the previous NANTEN ...survey, leading to a detection of molecular clouds with image M sub(image). We identified 272 molecular clouds, 230 of which are detected at three or more observed positions. We derived the physical properties, such as size, line width, and virial mass, of the 164 GMCs that have an extent more than the beam size of NANTEN in both the major and minor axes. The CO luminosity and virial mass of the clouds show a good correlation of image, with a Spearman rank correlation of 0.8, suggesting that the clouds are in nearly virial equilibrium. Assuming the clouds are in virial equilibrium, we derived an X sub(CO)-factor of image cm super(-2) (K km s super(-1)) super(-1). The mass spectrum of the clouds is fitted well by a power law of image above the completeness limit of image M sub(image). The slope of the mass spectrum becomes steeper if we fit only the massive clouds, e.g., image for image M sub(image).
Electrostatic precipitation Mizuno, A.
IEEE transactions on dielectrics and electrical insulation,
10/2000, Volume:
7, Issue:
5
Journal Article
Peer reviewed
Electrostatic precipitators have been used widely in industry, and play an important role in environmental protection. An electrostatic precipitator (ESP) can be operated with a high collection ...efficiency and a low pressure drop. Recently, an ESP also has been used for cleaning indoor air. In this review, principles of electrostatic precipitation, such as particle charging, migration velocity of charged particles and collection efficiency, are described. The performance of the ESP deteriorates by abnormal phenomena, including back corona for treating high resistivity dust, abnormal re-entrainment for low resistivity dust, and corona quenching for fine dusts. To cope with these phenomena, new technologies have been developed. Pulsed energization is a technique which copes with high resistivity dusts, and this results in lower power consumption. Using pulsed energization, non-thermal plasma can be generated and chemical reactions can be promoted for treating gaseous pollutants such as NO and volatile organic compounds. Wet ESP can also remove dusts and gaseous pollutants simultaneously. These new advancements will widen the field of application of electrostatic precipitation. Some novel applications of ESP, such as removal of dioxin from incinerators, are also included in this review.
ABSTRACT RCW 120 is a Galactic H ii region that has a beautiful ring shape that is bright in the infrared. Our new CO J = 1-0 and J = 3-2 observations performed with the NANTEN2, Mopra, and ASTE ...telescopes have revealed that two molecular clouds with a velocity separation of 20 km s−1 are both physically associated with RCW 120. The cloud at −8 km s−1 apparently traces the infrared ring, while the other cloud at −28 km s−1 is distributed just outside the opening of the infrared ring, interacting with the H ii region as suggested by the high kinetic temperature of the molecular gas and by the complementary distribution with the ionized gas. A spherically expanding shell driven by the H ii region is usually considered to be the origin of the observed ring structure in RCW 120. Our observations, however, indicate no evidence of the expanding motion in the velocity space, which is inconsistent with the expanding shell model. We postulate an alternative that, by applying the model introduced by Habe & Ohta, the exciting O star in RCW 120 was formed by a collision between the present two clouds at a collision velocity of ∼30 km s−1. In the model, the observed infrared ring can be interpreted as the cavity created in the larger cloud by the collision, whose inner surface is illuminated by the strong ultraviolet radiation after the birth of the O star. We discuss that the present cloud-cloud collision scenario explains the observed signatures of RCW 120, i.e., its ring morphology, coexistence of the two clouds and their large velocity separation, and absence of the expanding motion.
ABSTRACT We present distributions of two molecular clouds having velocities of 2 and 14 km s−1 toward RCW 38, the youngest super star cluster in the Milky Way, in the 12CO J = 1-0 and 3-2 and 13CO J ...= 1-0 transitions. The two clouds are likely physically associated with the cluster as verified by the high intensity ratio of the J = 3-2 emission to the J = 1-0 emission, the bridging feature connecting the two clouds in velocity, and their morphological correspondence with the infrared dust emission. The velocity difference is too large for the clouds to be gravitationally bound. We frame a hypothesis that the two clouds are colliding with each other by chance to trigger formation of the ∼20 O stars that are localized within ∼0.5 pc of the cluster center in the 2 km s−1 cloud. We suggest that the collision is currently continuing toward part of the 2 km s−1 cloud where the bridging feature is localized. This is the third super star cluster alongside Westerlund 2 and NGC 3603 where cloud-cloud collision has triggered the cluster formation. RCW 38 is the youngest super star cluster in the Milky Way, holding a possible sign of on-going O star formation, and is a promising site where we may be able to witness the moment of O star formation.
We present new large field observations of molecular clouds with NANTEN2 toward the super star cluster NGC 3603 in the transitions super(12)CO(J = 2-1, J = 1-0) and super(13)CO(J = 2-1, J = 1-0). We ...suggest that two molecular clouds at 13 km s super(-1) and 28 km s super(-1) are associated with NGC 3603 as evidenced by higher temperatures toward the H II region, as well as morphological correspondence. The mass of the clouds is too small to gravitationally bind them, given their relative motion of ~20 km s super(-1). We suggest that the two clouds collided with each other 1 Myr ago to trigger the formation of the super star cluster. This scenario is able to explain the origin of the highest mass stellar population in the cluster, which is as young as 1 Myr and is segregated within the central sub-pc of the cluster. This is the second super star cluster along with Westerlund 2 where formation may have been triggered by a cloud-cloud collision.
A large-scale study of the molecular clouds toward the Trifid Nebula, M20, has been made in the J = 2-1 and J = 1-0 transitions of 12CO and 13CO. M20 is ionized predominantly by an O7.5 star ...HD164492. The study has revealed that there are two molecular components at separate velocities peaked toward the center of M20 and that their temperatures--30-50 K as derived by a large velocity gradient analysis--are significantly higher than the 10 K of their surroundings. We identify the two clouds as the parent clouds of the first generation stars in M20. The mass of each cloud is estimated to be ~103 M and their separation velocity is ~8 km s--1 over ~1-2 pc. We find that the total mass of stars and molecular gas in M20 is less than ~3.2 X 103 M , which is too small by an order of magnitude to gravitationally bind the system. We argue that the formation of the first generation stars, including the main ionizing O7.5 star, was triggered by the collision between the two clouds in a short timescale of ~1 Myr, a second example alongside Westerlund 2, where a super-star cluster may have been formed due to cloud-cloud collision triggering.
RX J1713.7-3946 is the most remarkable TeV gamma -ray supernova remnant (SNR) that emits gamma -rays in the highest energy range. We have made a new combined analysis of CO and H I in the SNR and ...derived the total protons in the interstellar medium (ISM). We have found that the inclusion of the H I gas provides a significantly better spatial match between the TeV gamma -rays and ISM protons than the H sub(2) gas alone. In particular, the southeastern rim of the gamma -ray shell has a counterpart only in the H I. The finding shows that the ISM proton distribution is consistent with the hadronic scenario that cosmic-ray (CR) protons react with ISM protons to produce the gamma -rays. This provides another step forward for the hadronic origin of the gamma -rays by offering one of the necessary conditions missing in the previous hadronic interpretations. We argue that the highly inhomogeneous distribution of the ISM protons is crucial in the origin of the gamma -rays. Most of the neutral gas was likely swept up by the stellar wind of an OB star prior to the supernova (SN) explosion to form a low-density cavity and a swept-up dense wall. The cavity explains the low-density site where the diffusive shock acceleration of charged particles takes place with suppressed thermal X-rays, whereas the CR protons can reach the target protons in the wall to produce the gamma -rays. The present finding allows us to estimate the total CR proton energy to be ~10 super(48) erg, 0.1% of the total energy of the SN explosion.
The high temperature superconductor (HTS) dual-band bandpass filter (DB-BPF) has been developed for microwave intermediate frequency (IF) signals (8-12 GHz) of a multi-frequency millimeter-wave ...atmospheric spectrometer. The HTS DB-BPF consists of 6-pole and 12-pole BPFs with an 8.348 GHz center frequency and 0.27 GHz band width and an 11.156 GHz center frequency and 1.46 GHz band width, respectively. The HTS DB-BPF was fabricated using YBa 2 Cu 3 O y thin films on R-Al 2 O 3 substrate. Fabricated DB-BPF is evaluated by experiment and simulation with good agreement. We started the long-term monitoring of atmospheric molecular species using DB-BPF at Syowa station in Antarctica.
We present a new analysis of the interstellar protons toward the TeV γ-ray SNR RX J0852.0−4622 (G266.2−1.2, Vela Jr.). We used the NANTEN2 12CO(J = 1-0) and Australia Telescope Compact Array and ...Parkes H i data sets in order to derive the molecular and atomic gas associated with the TeV γ-ray shell of the SNR. We find that atomic gas over a velocity range from VLSR = −4 to 50 km s−1 or 60 km s−1 is associated with the entire SNR, while molecular gas is associated with a limited portion of the SNR. The large velocity dispersion of the H i is ascribed to the expanding motion of a few H i shells overlapping toward the SNR but is not due to the Galactic rotation. The total masses of the associated H i and molecular gases are estimated to be M and ∼103 M , respectively. A comparison with the High Energy Stereoscopic System TeV γ-rays indicates that the interstellar protons have an average density around 100 cm−3 and shows a good spatial correspondence with the TeV γ-rays. The total cosmic-ray proton energy is estimated to be ∼1048 erg for the hadronic γ-ray production, which may still be an underestimate by a factor of a few due to a small filling factor of the SNR volume by the interstellar protons. This result presents a third case, after RX J1713.7−3946 and HESS J1731−347, of the good spatial correspondence between the TeV γ-rays and the interstellar protons, lending further support for a hadronic component in the γ-rays from young TeV γ-ray SNRs.
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