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We have studied optical properties of interstellar dust around the Orion A molecular cloud to investigate the size distribution and the composition of dust grains. Orion A is one of the most studied molecular clouds in the solar vicinity (d ≃ 400 pc). In this paper, we used optical and near-infrared photometric data. The optical data were obtained by BVRI bands imaging observations. The near-infrared data consisting of JHKS bands were taken from 2MASS point source catalog. We produced some color excess maps around Orion A and measured their ratios such as E(R − I)/E(B − V). In order to investigate dust properties, we compared the observed ratios with results of simulation performed by Naoi et al. who calculated the extinction in the optical to near-infrared wavelengths based on a standard dust model. They assumed a power-law grain-size distribution with an upper cutoff radius and assumed graphite and silicate as dominant components. As a result, we found that the upper cutoff radius around Orion A is ≃0.3 μm, and silicate predominates compared with graphite (with the fraction of silicate grater than 93%). In addition, we further derived the total-to-selective extinction ratio RV from the observed extinction of AV and the color excess E(B − V), and compared it with the model calculations. Dust properties (i.e., the upper cutoff radius and the ratio of graphite/silicate) derived from RV are almost consistent with those derived from the color excess ratios. [ABSTRACT FROM AUTHOR]

We have carried out observations of CCH (N = 1 − 0), CH3CN (J = 5 − 4), and three 13C isotopologues of HC3N (J = 10 − 9) toward three massive young stellar objects (MYSOs), G12.89+0.49, G16.86−2.16, and G28.28−0.36, with the Nobeyama 45 m radio telescope. Combined with previous results on HC5N, the column density ratios of N(CCH)/N(HC5N), hereafter the CCH/HC5N ratios, in the MYSOs are derived to be ∼15. This value is lower than that in a low-mass warm carbon chain chemistry (WCCC) source by more than one order of magnitude. We compare the observed CCH/HC5N ratios with hot-core model calculations. The observed ratios in the MYSOs can be best reproduced by models when the gas temperature is ∼85 K, which is higher than in L1527, a low-mass WCCC source (∼35 K). These results suggest that carbon-chain molecules detected around the MYSOs exist at least partially in higher temperature regions than those in low-mass WCCC sources. There is no significant difference in column density among the three 13C isotopologues of HC3N in G12.89+0.49 and G16.86-2.16, while HCC13CN is more abundant than the others in G28.28–0.36. We discuss carbon-chain chemistry around the three MYSOs based on the CCH/HC5N ratio and the 13C isotopic fractionation of HC3N. [ABSTRACT FROM AUTHOR]

We present maps in several molecular emission lines of a 1 square degree region covering the W40 and Serpens South molecular clouds belonging to the Aquila Rift complex. The observations were made with the 45 m telescope at the Nobeyama Radio Observatory. We found that the 12CO and 13CO emission lines consist of several velocity components with different spatial distributions. The component that forms the main cloud of W40 and Serpens South, which we call the "main component," has a velocity of VLSR ≃ 7 km s−1. There is another significant component at VLSR ≃ 40 km s−1, which we call the "40 km s−1 component." The latter component is mainly distributed around two young clusters: W40 and Serpens South. Moreover, the two components look spatially anticorrelated. Such spatial configuration suggests that the star formation in W40 and Serpens South was induced by the collision of the two components. We also discuss a possibility that the 40 km s−1 component consists of gas swept up by superbubbles created by SNRs and stellar winds from the Scorpius–Centaurus association. [ABSTRACT FROM AUTHOR]

In this paper, we present results of millimeter-wave observations with various molecular lines made toward MCLD 123.5+24.9 in the Polaris cirrus using the 45 m telescope at Nobeyama Radio Observatory. MCLD 123.5+24.9 is one of the rare dense cores forming in diffuse cirrus clouds where star formation may rarely take place. In order to investigate the structure, dynamics, the evolutionary stage of MCLD 123.5+24.9, we observed this core in 17 emission lines from 13 different molecular species. Emission lines of CS, CCS, and HC3N are strongly detected all over the core, while those of SO and N2H+ are weak or remain undetected, indicating that MCLD 123.5+24.9 is in an early stage of core evolution in terms of chemical composition. Based on comparison of the fractional abundances of CCS and HC3N, which are considered indicators of chemical age, with those of other cores with and without star formation as well as with model calculations in the literature, we suggest that MCLD 123.5+24.9 is in a phase prior to star formation. From the C18O data obtained, we derived the total molecular mass of MCLD 123.5+24.9 to be ~3 Mʘ at an assumed distance of 150 pc. There are three subcores in MCLD 123.5+24.9, called CS-A, CS-B, and CS-C. We derived their masses to be 0.2-0.6 Mʘ. We also investigated the dynamical stability of MCLD 123.5+24.9 and the subcores by applying the virial theorem to find that MCLD 123.5+24.9 is not gravitationally bound as a whole, while the individual subcores are in the virial equilibrium and can collapse with a small increase of external pressure imposed on their surfaces. [ABSTRACT FROM AUTHOR]

Using self-gravitational hydrodynamical numerical simulations, we investigated the evolution of high-density turbulent molecular clouds swept by a colliding flow. The interaction of shock waves due to turbulence produces networks of thin filamentary clouds with a sub-parsec width. The colliding flow accumulates the filamentary clouds into a sheet cloud and promotes active star formation for initially high-density clouds. Clouds with a colliding flow exhibit a finer filamentary network than clouds without a colliding flow. The probability distribution functions (PDFs) for the density and column density can be fitted by lognormal functions for clouds without colliding flow. When the initial turbulence is weak, the column density PDF has a power-law wing at high column densities. The colliding flow considerably deforms the PDF, such that the PDF exhibits a double peak. The stellar mass distributions reproduced here are consistent with the classical initial mass function with a power-law index of –1.35 when the initial clouds have a high density. The distribution of stellar velocities agrees with the gas velocity distribution, which can be fitted by Gaussian functions for clouds without colliding flow. For clouds with colliding flow, the velocity dispersion of gas tends to be larger than the stellar velocity dispersion. The signatures of colliding flows and turbulence appear in channel maps reconstructed from the simulation data. Clouds without colliding flow exhibit a cloud-scale velocity shear due to the turbulence. In contrast, clouds with colliding flow show a prominent anti-correlated distribution of thin filaments between the different velocity channels, suggesting collisions between the filamentary clouds. [ABSTRACT FROM AUTHOR]

We report the results of molecular line observations carried out toward a massive dense core in the Cyg OB 7 molecular cloud. The core has an extraordinarily large mass (∼1.1 × 104M☼) and size (∼2 × 5 pc2), but there is no massive young star forming therein. We observed this core in various molecular lines such as C18O(J = 1-0) using the 45 m telescope at Nobeyama Radio Observatory. We find that the core has an elongated morphology consisting of several filaments and core-like structures. The filaments are massive (102-103M☼), and they are apparently colliding with one another. Some candidates for young stellar objects are distributed around their intersection, suggesting that the collisions of the filaments may have influenced their formation. To understand the formation and evolution of such colliding filaments, we performed numerical simulations using the adaptive mesh refinement technique, adopting the observed core parameters (the mass and size) as the initial conditions. The results indicate that the filaments are formed as seen in other earlier simulations for small cores in the literature, but we could not reproduce the collisions of the filaments simply by assuming a large initial mass and size. We find that collisions of the filaments occur only when there is a large velocity gradient in the initial core, in a sense compressing it. We suggest that the observed core was actually compressed by an external effect, e.g., shocks from nearby supernova remnants, including HB 21 which has been suggested to be interacting with the Cyg OB 7 molecular cloud. [ABSTRACT FROM AUTHOR]