We mapped the (1,1), (2,2), and (3,3) lines of NH 3 toward the molecular cloud associated with the Monkey Head Nebula (MHN) with a 1. 6 angular resolution using a Kashima 34 m telescope operated by the National Institute of Information and Communications Technology (NICT). The kinetic temperature of the molecular gas is 15-30 K in the eastern part and 30-50 K in the western part. The warmer gas is confined to a small region close to the compact H ii region S252A. The cooler gas is extended over the cloud even near the extended H ii region, the MHN. We made radio continuum observations at 8.4 GHz using the Yamaguchi 32 m radio telescope. The resultant map shows no significant extension from the Hα image. This means that the molecular cloud is less affected by the MHN, suggesting that the molecular cloud did not form by the expanding shock of the MHN. Although the spatial distribution of the Wide-field Infrared Survey Explorer and Two Micron All Sky Survey point sources suggests that triggered low-and intermediate-mass star formation took place locally around S252A, but the exciting star associated with it should be formed spontaneously in the molecular cloud.
We report the results of very long baseline interferometry (VLBI) observations of H2O masers in the IRAS 20143+3634 star-forming region (SFR) using VERA (VLBI Exploration of Radio Astrometry). By tracking masers for a period of over two years we measured a trigonometric parallax of π = 0.367 ± 0.037 mas, corresponding to a source distance of $D = 2.72 ^{+0.31}_{-0.25}$ kpc and placing it in the Local spiral arm. Our trigonometric distance is just 60% of the previous estimation based on radial velocity, significantly impacting the astrophysics of the source. We measured proper motions of −2.99 ± 0.16 mas yr−1 and −4.37 ± 0.43 mas yr−1 in RA and Dec, respectively, which were used to estimate the peculiar motion of the source as (Us, Vs, Ws) = (−0.9 ± 2.9, −8.5 ± 1.6, +8.0 ± 4.3) km s−1 for R0 = 8 kpc and Θ0 = 221 km s−1, and (Us, Vs, Ws) = (−1.0 ± 2.9, −9.3 ± 1.5, +8.0 ± 4.3) km s−1 for R0 = 8.5 kpc and Θ0 = 235 km s−1. IRAS 20143+3634 was found to be located near the tangent point in the Cygnus direction. Using our observations we derived the angular velocity of Galactic rotation of the local standard of rest (LSR), Ω0 = 27.3 ± 1.6 km s−1 kpc−1, which is consistent with previous values derived using VLBI astrometry of SFRs at the tangent points and Solar circle. It is higher than the value recommended by the International Astronomical Union of Ω0 = 25.9 km s−1 kpc−1 which was calculated using the Galactocentric distance of the Sun and circular velocity of the LSR.
We have measured the annual parallax of the water maser source associated with star forming region NGC2264 from observations with VLBI Exploration of Radio Astrometry (VERA). We detected masers at V L SR = 7.2 km s −1 . We discussed its driving sources of detected maser spots. One of the maser spots was associated with a centimeter continuum source observed with VLA. Neither optical, infrared nor X-ray sources is catalogued near the spot. The other maser spot is located close to an X-ray source, although there is no optical or infrared counterpart. The proper motion of the former spot was (μ α , μ δ ) = (23. 91 ± 4.29, −29.81 ± 4.27) and the proper motion of latter spot was (μα , μ δ ) = (−0.96 ± 0.58, −6.05 ± 3.06). For the latter spot, the peculiar motion is ∼ 150 km s −1 and it has the high velocity and this may be a jet or an outflow from a young star. The observed parallax is 1.365 ± 0.098 mas, corresponding to the distance of 738 + 57 −50 pc. This value is constant with the photometric distance of NGC2264 previously measured. The fitting result of the parallax is shown in figure 1. We also observed in NH3 (1,1), (2,2), (3,3) lines of NGC2264 with the Kashima 34m telescope. We estimated the star formation efficiency (SFE) of NGC2264 from the dense molecular mass of NH3 and the stellar mass calculated by Teixeira et al.(2012). The SFE is 9 -12 % which is consistent with previous results.
Abstract.We mapped the NH3 (1,1), (2,2), and (3,3) lines of the molecular cloud associated with the Monkey Head Nebula (MHN) with 1 .6 angular resolution using Kashima 34 m telescope. Its kinetic temperature distribution was contrary to what is expected for a molecular cloud at the edge of an expanding H II region and suggested that the massive star associated with S252A compact HII region formed spontaneously rather than through a sequential process.
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