A New Interpretation of the Bipolar HII Region S106 from HCN J = 3 - 2 Mapping Observations

The first mapping observations of the bipolar HII region S106 in HCN J = 3 - 2 line were made by KOSMA submillimeter telescope in April, 2004. The results show that there is a bipolar outflow centered on the high-mass star S106 IRS4 and that the flat structure of molecular cloud core is perpendicular to the axis of the outflow. This image roughly corresponds to the optical image where a dark lane bisects the bipolar HII region. Together with the optical, infrared and radio data, we conclude that the central UC HII region and molecular outflow formed before the     

A study of the ultra-compact H-II region NGC 7538-IRS

From an analysis of VLBI observations of H₂CO and OH maser emission in the direction of the ultra-conpact HII region NGC 7538-IRS 1, the following model is proposed: The HII region is surrounded by a thick dusty shell which breaks open at the two poles and there is a bipolar outflow. Around it is a rotating gas/dust ring and matter falls from the ring onto the surface of the HII region. The whole system, HII region and the ring, moves with a sight line velocity of −61.0 km/s inside a large cloud which moves with a sight line velocity of −57 km/s. The H₂CO and OH masers occur near the poles of the HII region and within 0.2 R_HII of the surface. The positions of the H₂O maser and other line sources are discussed in term of this model.     

ASTE observations of the massive-star forming region Sgr B2: a giant impact scenario

We report mapping observations of a 35 pc × 35 pc region covering the Sgr B2 molecular cloud complex in the ¹³CO (3-2) and the CS (7-6) lines using the ASTE 10 m telescope with high angular resolution. The central region was mapped also in the C¹⁸O (3-2) line. The images not only reproduce the characteristic structures noted in the preceding millimeter observations, but also highlight the interface of the molecular clouds with a large velocity jump of a few tens of km s⁻¹. These new results further support the scenario that a cloud–cloud collision has triggered the formation of massive cloud cores, which form massive stars of Sgr B2. Prospects of exciting science enabled by ALMA are discussed in relation to these observations.     

Morphological and kinematic signatures of a binary central star in the planetary nebula Hu 2-1

We present H α , [N  ii ] and [O  iii ] ground-based and HST archive images, VLA–A 3.6-cm continuum and H92 α emission-line data and high-resolution long-slit [N  ii ] spectra of the planetary nebula Hu 2-1. A large number of structural components are identified in the nebula: an outer bipolar and an inner shell, two pairs of collimated bipolar structures at different directions, monopolar bow-shock-like structures, and an extended equatorial structure within a halo. The formation of Hu 2-1 appears to be dominated by anisotropic mass ejection during the late-AGB stage of the progenitor and by variable, 'precessing' collimated bipolar outflows during the protoplanetary nebula and/or early planetary nebula phases. Different observational results strongly support the existence of a binary central star in Hu 2-1, among them (1) the observed point-symmetry of the bipolar lobes and inner shell, and the departures from axial symmetry of the bipolar lobes, (2) the off-centre position of the central star, (3) the detection of mass ejection towards the equatorial plane, and (4) the presence of 'precessing' collimated outflows. In addition, (5) an analysis of the kinematics shows that the systemic velocity of the bipolar outflows does not coincide with the systemic velocity of the bipolar shell. We propose that this velocity difference is a direct evidence of orbital motion of the ejection source in a binary system. From a deduced orbital velocity of ∼10 km s⁻¹, a semimajor axis of ∼ 9–27 au and period of ∼ 25–80 yr are obtained, assuming a reasonable range of masses. These parameters are used to analyse the formation of Hu 2-1 within current scenarios of planetary nebulae with binary central stars.     

A Kinematical Study of the NGC 7538 IRS 1 Region

We present high angular resolution images of both NH3(1,1)and (2,2) lines toward NGC 7538 IRS 1.The density and velocity-position plots have been used to study the interaction among the outflows,winds and their environment.For the first time we have found an expanding half-shell of molecular gas around the HⅡ region associated with IRS 1,which may be produced by the interaction of the bipolar outflows and the winds originating in IRS 1-3,and optical HⅡ region NGC 7538 with ambient molecular gas.     

On the distance to the Ophiuchus star‐forming region

The Ophiuchus molecular cloud complex has produced in Lynds 1688 the richest known embedded cluster within ∼300 pc of the Sun. Unfortunately, distance estimates to the Oph complex vary by nearly ∼40% (∼120–165 pc). Here I calculate a new independent distance estimate of 135±8 pc to this benchmark star‐forming region based on Hipparcos trigonometric parallaxes to stars illuminating reflection nebulosity in close proximity to Lynds 1688. Combining this value with recent distance estimates from reddening studies suggests a consensus distance of 139±6 pc (4% error), situating it within ∼11 pc of the centroid of the ∼5 Myr old Upper Sco OB subgroup of Sco OB2 (145 pc). The velocity vectors for Oph and Upper Sco are statistically indistinguishable within ∼1 km s^–1 in each vector component. Both Oph and Upper Sco have negligible motion (<1 km s^–1) in the Galactic vertical direction with respect to the Local Standard of Rest, which is inconsistent with the young stellar groups having formed via the high velocity cloud impact scenario. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Investigation of star formation toward the Sharpless 155 H II region

We present a comprehensive study of star formation toward the H II region Sharpless 155(S155).Star-formation activities therein were investigated based on multi-wavelength data from optical to the far-infrared.The surface density distribution of selected 2MASS sources toward S155 indicates the existence of a compact cluster,which is spatially consistent with the position of the exciting source of the H II region,HD 217086.A sample of more than 200 sources with excessive emission in the infrared were selected based on their 2MASS color indices.The spatial distribution of the sample sources reveals the existence of three young subclusters in this region,among which subcluster A is spatially coincident with the bright rim of the H II region.In addition,photometric data from the WISE survey were used to identify and classify young stellar objects(YSOs).To further explore the evolutionary stages of the candidate YSOs,we fit the spectral energy distributions of 44 sources,which led to the identification of 14 Class I,27 Class II and 3 Class HI YSOs.The spatial distribution of the classified YSOs at different evolutionary stages presents a spatiotemporal gradient,which is consistent with a scenario of sequential star formation.On the other hand,Herschel PACS observations toward the interface between S155 and the ambient molecular cloud disclose an arc-shaped dust layer,the origin of which could be attributed to the UV dissipation from early type stars,e.g.HD 217061,in S155.Four dusty cores were revealed by the Herschel data,which hints at new generations of star formation.     

Chemical abundances for Hf 2-2, a planetary nebula with the strongest-known heavy-element recombination lines

We present high-quality optical spectroscopic observations of the planetary nebula (PN) Hf 2-2. The spectrum exhibits many prominent optical recombination lines (ORLs) from heavy-element ions. Analysis of the H  i and He  i recombination spectrum yields an electron temperature of ∼900 K, a factor of 10 lower than given by the collisionally excited [O  iii ] forbidden lines. The ionic abundances of heavy elements relative to hydrogen derived from ORLs are about a factor of 70 higher than those deduced from collisionally excited lines (CELs) from the same ions, the largest abundance discrepancy factor (adf) ever measured for a PN. By comparing the observed O  ii λ4089/λ4649 ORL ratio to theoretical value as a function of electron temperature, we show that the O  ii ORLs arise from ionized regions with an electron temperature of only ∼630 K. The current observations thus provide the strongest evidence that the nebula contains another previously unknown component of cold, high-metallicity gas, which is too cool to excite any significant optical or ultraviolet CELs and is thus invisible via such lines. The existence of such a plasma component in PNe provides a natural solution to the long-standing dichotomy between nebular plasma diagnostics and abundance determinations using CELs on the one hand and ORLs on the other.     

A SCUBA survey of Orion – the low-mass end of the core mass function

We have re-analysed all of the Submillimetre Common User Bolometer Array (SCUBA) archive data of the Orion star-forming regions. We have put together all of the data taken at different times by different groups. Consequently, we have constructed the deepest submillimetre maps of these regions ever made. There are four regions that have been mapped: Orion A North and South, and Orion B North and South. We find that two of the regions, Orion A North and Orion B North, have deeper sensitivity and completeness limits, and contain a larger number of sources, so we concentrate on these two. We compare the data with archive data from the Spitzer Space Telescope to determine whether or not a core detected in the submillimetre is pre-stellar in nature. We extract all of the pre-stellar cores from the data and make a histogram of the core masses. This can be compared to the stellar initial mass function (IMF). We find the high-mass core mass function (CMF) follows a roughly Salpeter-like slope, just like the IMF, as seen in previous work. Our deeper maps allow us to see that the CMF turns over at,  ∼1.3 M_⊙  about a factor of 4 higher than our completeness limit. This turnover has never previously been observed, and is only visible here due to our much deeper maps. It mimics the turnover seen in the stellar IMF at  ∼0.1 M_⊙  . The low-mass side of the CMF is a power law with an exponent of, 0.35 ± 0.2 which is consistent with the low-mass slope of the young cluster IMF of 0.3 ± 0.1. This shows that the CMF continues to mimic the shape of the IMF all the way down to the lower completeness limit of these data at  ∼0.3 M_⊙  .     

Long-slit spectroscopy of the compact planetary nebula Hu 2-1

Long-slit spectra of high spectral and spatial resolution of the compact planetary nebula Hu 2-1, are presented. The analysis of the [NII] 6583 emission line detected in the spectra allows us to identify the kinematical components present in the nebula and to deduce their basic geometry. We use position-velocity maps of the [NII] 6583/H line intensity ratio in order to identify nebular regions in which shock-excitation and/or overabundace of N exist.     

Morphology, kinematics and modelling of the elliptical planetary nebula Sa 2-21

The little studied PN, Sa 2-21 has been observed using the Manchester echelle spectrometer at the Anglo-Australian telescope. Narrow band, long-slit spectra were obtained at six positions over two perpendicular position angles in both the [N ii ]λ6584  Å and [O iii ]λ5007  Å emission lines. An [O iii ] halo has been detected for the first time. A morphological modelling program was used to help determine the geometry, structure and kinematics of this ellipsoidal PN. It is proposed that the structure includes a pair of mid-latitude rings of [N ii ] emission, not previously seen in elliptical PNe. Radial spokes of [O iii ] emission have been detected in the main nebular shell indicating the presence of dynamical instabilities.     

A turbulent MHD model for molecular clouds and a new method of accretion on to star-forming cores

We describe the results of a sequence of simulations of gravitational collapse in a turbulent magnetized region. The parameters are chosen to be representative of molecular cloud material. We find that several protostellar cores and filamentary structures of higher than average density form. The filaments inter connect the high-density cores. Furthermore, the magnetic field strengths are found to correlate positively with the density, in agreement with recent observations. We make synthetic channel maps of the simulations, and show that material accreting on to the cores is channelled along the magnetized filamentary structures. This is compared with recent observations of S106, and shown to be consistent with these data. We postulate that this mechanism of accretion along filaments may provide a means for molecular cloud cores to grow to the point where they become gravitationally unstable and collapse to form stars.     

Integral spectroscopy of the nebula GM 1-29 and the star PV Cep

Integral spectroscopy data for the nebula GM 1-29 and the source star PV Cep obtained on the 2.6-m telescope at the Byurakan Observatory are presented. The structure and kinematics of a collimated emission outflow directed along the axis of the nebula are studied. Changes in the radial velocity and intensity of the absorption component of the nebular Hα line are observed and studied; these are interpreted as a result of an anisotropy in the stellar wind at distances on the order of several stellar radii, where this absorption is formed. __________ Translated from Astrofizika, Vol. 51, No. 3, pp. 461–468 (August 2008).