ABSTRACT
Using APEX-1 and APEX-2 observations, we have detected and studied the rotational lines of the HC3N molecule (cyanoacetylene) in the powerful outflow/hot molecular core G331.512−0.103. We ...identified 31 rotational lines at J levels between 24 and 39; 17 of them in the ground vibrational state v = 0 (9 lines corresponding to the main C isotopologue and 8 lines corresponding to the 13C isotopologues), and 14 in the lowest vibrationally excited state v7 = 1. Using local thermodynamic equilibrium (LTE)-based population diagrams for the beam-diluted v = 0 transitions, we determined Texc = 85 ± 4 K and N(HC3N) = (6.9 ± 0.8) × 1014 cm−2, while for the beam-diluted v7 = 1 transitions we obtained Texc = 89 ± 10 K and N(HC3N) = (2 ± 1) × 1015 cm−2. Non-LTE calculations using H2 collision rates indicate that the HC3N emission is in good agreement with LTE-based results. From the non-LTE method, we estimated Tkin ≃90 K, n(H2) ≃ 2 × 107 cm−3 for a central core of 6 arcsec in size. A vibrational temperature in the range from 130 to 145 K was also determined, values which are very likely lower limits. Our results suggest that rotational transitions are thermalized, while infrared radiative pumping processes are probably more efficient than collisions in exciting the molecule to the vibrationally excited state v7 = 1. Abundance ratios derived under LTE conditions for the 13C isotopologues suggest that the main formation pathway of HC3N is C2H2 + CN → HC3N + H.
Molecular clumps towards compact H ii regions Saldaño, Hugo P; Rubio, M; Cappa, C E ...
Monthly notices of the Royal Astronomical Society,
08/2019, Volume:
487, Issue:
2
Journal Article
Aims. We perform a multiwavelength analysis of the bubble Hii region Sh2-39 (N5) and its environs with the aim of studying the physical properties of Galactic IR bubbles and exploring their impact ...in triggering massive star formation. Methods. To analyze the molecular gas, we used CO(3–2) and HCO+(4–3) line data obtained with the on-the-fly technique from the ASTE telescope. To study the distribution and physical characteristics of the dust, we made use of archival data from ATLASGAL, Herschel, and MSX, while the ionized gas was studied making use of an NVSS image. We used public WISE, Spitzer, and MSX point source catalogs to search for infrared candidate young stellar objects (YSOs) in the region. To investigate the stellar cluster BDS20036 we used IR spectroscopic data obtained with the ARCoIRIS spectrograph, mounted on Blanco 4 m Telescope at CTIO, and new available IR Ks band observations from the VVVeXtended ESO Public Survey (VVVX). Results. The new ASTE observations allowed the molecular gas component in the velocity range from 30 km s-1 to 46 km s-1, associated with Sh2-39, to be studied in detail. The morphology of the molecular gas suggests that the ionized gas is expanding against its parental cloud. We identified four molecular clumps, which were likely formed by the expansion of the ionization front, and determined some of their physical and dynamical properties. Clumps with HCO+ and 870 μm counterparts show evidence of gravitational collapse. We identified several candidate YSOs across the molecular component. Their spatial distribution and the fragmentation time derived for the collected layers of the molecular gas suggest that massive star formation might have been triggered by the expansion of the nebula via the collect and collapse mechanism. The spectroscopical distance obtained for the stellar cluster BDS20036, placed over one of the collapsing clumps in the border of the Hii region, reveals that this cluster is physically associated with the nebula and gives more support to the triggered massive star formation scenario. A radio continuum data analysis indicates that the nebula is older and expands at lower velocity than typical IR Galactic bubbles.
Based on a multiwavelength study, the interstellar medium around the H ii region Sh2-173 has been analysed. The ionized region is clearly detected in the optical and the radio continuum images. The ...analysis of the H i data shows a region of low emissivity that has an excellent morphological correlation with the radio continuum emission. The H ii region is partially bordered by a photodissociation region, which, in turn, is encircled by a molecular structure. The H i and CO structures related to Sh2-173 are observed in the velocity ranges from −25 to −31 km s−1 and from −27 to −39 km s−1, respectively. Taking into account the presence of non-circular motions in the Perseus spiral arm, together with previous distance estimates for the region, we adopt a distance of 2.5 ± 0.5 kpc for Sh2-173. Seven hot stars were identified in the field of Sh2-173, being only one O-type star. The amount of energetic photons emitted by this star is enough to keep the region ionized and heat the dust. Given that an expanding H ii region may trigger star formation, a search for young stellar object (YSO) candidates was made using different infrared point source catalogues. A population of 46 YSO candidates was identified, projected on to the molecular clouds. On the other hand, Sh2-173 is located in a dense edge of a large (∼5°) H i shell, GSH 117.8+1.5-35. The possibility of Sh2-173 being part of a hierarchical system of three generations is suggested. In this scenario, the large H i shell, which probably originated due to the action of Cas OB5, would have triggered the formation of Sh2-173, which, in turn, is triggering new stars in its surrounding molecular cloud. To test this hypothesis, the ages of both the H ii region and the large shell were estimated and compared. We concluded that Sh2-173 is a young H ii region of about 0.6–1.0 Myr old. As for the large shell, we obtained a dynamical age of 5 ± 1 Myr. These age estimates, together with the relative location of the different structures, support the hypothesis that Sh2-173 is part of a hierarchical system.
We report the detection of the radio and infrared (IR) counterparts of the ring nebula around the WN3(h) star HD 211564 (WR 152), located to the south-west of the H ii region Sh2 132. Using radio ...continuum data from the Canadian Galactic Plane Survey, we identified the radio counterparts of the two concentric rings, of about 9 and 16 arcmin in radius, related to the star. After applying a filling factor f= 0.05–0.12, electron densities and ionized masses are in the range 10–16 cm−3 and 450–700 M⊙, respectively. The analysis of the H i gas emission distribution allowed the identification of 5900 M⊙ of neutral atomic gas with velocities between −52 and −43 km s−1 probably linked to the nebula. The region of the nebula is almost free of molecular gas. Only four small clumps were detected, with a total molecular mass of 790 M⊙. About 310 M⊙ are related to a small IR shell-like source linked to the inner ring, which is also detected in the MSX band A. An IRAS young stellar object candidate is detected in coincidence with the shell-like IR source. We suggest that the optical nebula and its neutral counterparts originated from the stellar winds from the Wolf–Rayet star and its massive progenitor, and are evolving in the envelope of a slowly expanding shell centred at of about 31 pc in radius. The bubble's energy conversion efficiency is in agreement with recent numerical analysis and with observational results.
Ionized gas, molecules and dust in Sh2-132 Vasquez, J.; Cappa, C. E.; Pineault, S. ...
Monthly Notices of the Royal Astronomical Society,
July 2010, Volume:
405, Issue:
3
Journal Article
Peer reviewed
Open access
We analyse the various interstellar components of the H ii region Sh2-132. The main stellar source is the double binary system that includes the Wolf–Rayet star WR 153ab. We use radio continuum ...images at 408 and 1420 MHz, and H i 21-cm line data taken from the Canadian Galactic Plane Survey, molecular observations of the 12CO(1–0) line at 115 GHz from the Five College Radio Astronomy Observatory, and available mid- and far-infrared observations obtained with the MSX and IRAS satellites, respectively. Sh2-132 is composed of two shells showing radio continuum counterparts at both frequencies. The emission is thermal in nature. The estimated rms electron density and ionized mass of the nebula are ne≃ 20 cm−3 and . The distribution of the CO emission shows molecular gas bordering the ionized nebula and interacting with it. The velocities of the molecular gas is in the range −38 to −53 km s−1, similar to the velocity of the ionized gas. The emission at 8.3 μm reveals a ring-like feature of about 15 arcmin that encircles the bright optical regions. This emission is due to the polycyclic aromatic hydrocarbons and marks the location of photodissociation regions. The gas distribution in the environs of Sh2-132 can be explained in a scenario where the massive stars in the region photodissociated, ionized and swept up the dense molecular material from the parental cloud through their strong stellar winds and intense ultraviolet (UV) photon flux.
The main driver of biodiversity loss and subsequent decreases in ecosystem functionality is undeniably human interference, destruction and encroachment. The creation and establishment of protected ...areas serve as tools for guaranteeing biodiversity conservation. In this study, we examined the diversity of medium- and large-sized mammals and flightless walking birds that are supported by a protected area system, the Ischigualasto-Talampaya system, and its area of influence. We set up 106 camera traps and analysed all data with rank-abundance curves and Hill numbers as a measure of diversity. Species richness was lower in protected areas, unlike in the buffer zone, due to the absence of domestic species. Native species were present all over the area, but with variations in their abundances, showing that the presence of domestic species in low densities would not negatively affect the richness of native species, but would indeed affect their abundance.
ABSTRACT We investigate the distribution of gas (ionized, neutral atomic and molecular) and interstellar dust in the complex star-forming region NGC6357 with the goal of studying the interplay ...between the massive stars in the open cluster Pis24 and the surrounding interstellar matter. Our study of the distribution of the ionized gas is based on narrow-band Hα, Siiand Oiii images obtained with the Curtis-Schmidt Camera at CTIO, Chile, and on radio continuum observations at 1465 MHz taken with the VLA with a synthesized beam of 40arcsec. The distribution of the molecular gas is analysed using 12CO(1-0) data obtained with the NANTEN radiotelescope, Chile (angular resolution = 2.7arcmin). The interstellar dust distribution was studied using mid-infrared data from the GLIMPSE survey and far-infrared observations fromIRAS. NGC6357 consists of a large ionized shell and a number of smaller optical nebulosities. The optical, radio continuum, and near- and mid-IR images delineate the distributions of the ionized gas and interstellar dust in the Hii regions and in previously unknown wind-blown bubbles linked to the massive stars in Pis24 revealing surrounding photodissociation regions. The CO line observations allowed us to identify the molecular counterparts of the ionized structures in the complex and to confirm the presence of photodissociation regions. The action of the WR star HD157504 on the surrounding gas was also investigated. The molecular mass in the complex is estimated to be (4 ± 2) × 105 M. The mean electron densities derived from the radio data suggest electron densities >200 cm-3, indicating that NGC6357 is a complex formed in a region of high ambient density. The known massive stars in Pis24 and a number of newly inferred massive stars are mainly responsible for the excitation and photodissociation of the parental molecular cloud. PUBLICATION ABSTRACT
We present a study of active star-forming regions in the environs of the H ii region Sh2-205. The analysis is based on data obtained from point source catalogues and images extracted from the ...Two-Micron All-Sky Survey (2MASS), Midcourse Space Experiment (MSX) and IRAS surveys. Complementary data are taken from a CO survey. The identification of primary candidates for star-formation activity is made following colour criteria and a correlation with molecular gas emission. A number of star-formation tracer candidates are projected on to two substructures of the H ii region: SH 148.83–0.67 and SH 149.25–0.00. However, the lack of molecular gas related to these structures casts doubt on the nature of the sources. Additional infrared sources may be associated with the H i shell centred at (l, b) = (149°0′, −1°30′). The most striking active area was found in connection with the H ii region LBN 148.11–0.45, where star-formation candidates are projected on to molecular gas. The analytical model of the ‘collect and collapse’ process shows that star-formation activity could have been triggered by the expansion of this H ii region.
An inter-comparison study of instruments designed to measure the microphysical and optical properties of soot particles was completed. The following mass-based instruments were tested: Couette ...Centrifugal Particle Mass Analyzer (CPMA), Time-of-Flight Aerosol Mass Spectrometer-Scanning Mobility Particle Sizer (AMS-SMPS), Single Particle Soot Photometer (SP2), Soot Particle-Aerosol Mass Spectrometer (SP-AMS) and Photoelectric Aerosol Sensor (PAS2000CE). Optical instruments measured absorption (photoacoustic, interferometric, and filter-based), scattering (in situ), and extinction (light attenuation within an optical cavity). The study covered an experimental matrix consisting of 318 runs that systematically tested the performance of instruments across a range of parameters including: fuel equivalence ratio (1.8 ≤
φ
≤ 5), particle shape (mass-mobility exponent (
D
fm
), 2.0
≤
D
fm
≤ 3.0), particle mobility size (30
≤
d
m
≤ 300 nm), black carbon mass (0.07 ≤
m
BC
≤ 4.2 fg) and particle chemical composition. In selected runs, particles were coated with sulfuric acid or dioctyl sebacate (DOS) (0.5 ≤
Δ
r
ve
≤ 201 nm) where
Δ
r
ve
is the change in the volume equivalent radius due to the coating material. The effect of non-absorbing coatings on instrument response was determined. Changes in the morphology of fractal soot particles were monitored during coating and denuding processes and the effect of particle shape on instrument response was determined. The combination of optical and mass based measurements was used to determine the mass specific absorption coefficient for denuded soot particles. The single scattering albedo of the particles was also measured. An overview of the experiments and sample results are presented.
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