Search

We report the detection of radio recombination line (RRL) H40α towards 75 sources, with data obtained from ACA (Atacama Compact 7 m Array) observations in the ATOMS (ALMA Three-millimeter Observations of Massive Star-forming regions) survey of 146 active Galactic star-forming regions. We calculated ionized gas mass and star formation rate (SFR) with H40α line emission. The mass of ionized gas is significantly smaller than molecular gas mass, indicating that ionized gas is negligible in the star-forming clumps of the ATOMS sample. The SFR estimated with RRL H40α agrees well with that calculated with the total bolometric luminosity (Lbol) when SFR ≥ 5 M⊙ Myr−1, suggesting that millimetre RRLs could well sample the upper part of the initial mass function and thus be good tracers of SFR. We also study the relationships between Lbol and the molecular line luminosities (L$^{^{\prime }}_{\rm mol}$) of CS J = 2–1 and HC3N J = 11–10 for all the 146 ATOMS sources. The $L_{\rm bol} \!-\! L^{\prime }_{\rm mol}$ correlations of both the CS J = 2–1 and HC3N J = 11–10 lines appear approximately linear and these transitions have success in predicting Lbol similar to that of more commonly used transitions. The Lbol-to-$L^{\prime }_{\rm mol}$ ratios or SFR-to-mass ratios (star formation efficiency) do not change with galactocentric distances (RGC). Sources with H40α emission (or H ii regions) show higher Lbol-to-$L^{\prime }_{\rm mol}$ ratios than those without H40α emission, which may be an evolutionary effect.

The nature of the gas in CO-rich debris discs remains poorly understood, as it could either be a remnant from the earlier Class II phase or of secondary origin, driven by the destruction of icy planetesimals. The aim of this paper was to elucidate the origin of the gas content in the debris discs via various simple molecules that are often detected in the less-evolved Class II discs. We present millimetre molecular line observations of nine circumstellar discs around A-type stars: four CO-rich debris discs (HD 21997, HD 121617, HD 131488, HD 131835) and five old Herbig Ae protoplanetary discs (HD 139614, HD 141569, HD 142666, HD 145718, HD 100453). The sources were observed with the Atacama Large Millimeter/submillimeter Array (ALMA) in Bands 5 and 6 with 1-2'' resolution. The Herbig Ae discs are detected in the CO isotopologues, CN, HCN, HCO$^+$, C2H, and CS lines. In contrast, only CO isotopologues are detected in the debris discs, showing a similar amount of CO to that found in the Herbig Ae protoplanetary discs. Using chemical and radiative transfer modelling, we show that the abundances of molecules other than CO in debris discs are expected to be very low. We consider multiple sets of initial elemental abundances with various degrees of H2 depletion. We find that the HCO+ lines should be the second brightest after the CO lines and that their intensities strongly depend on the overall CO/H$_2$ ratio of the gas. However, even in the ISM-like scenario, the simulated HCO+ emission remains weak as required by our non-detections., 15 pages, 9 figures, 7 tables Accepted for publication in MNRAS

We have performed a molecular line search towards the flaring 6.7-GHz masers G 24.33+0.13, and G 359.6−0.24 using the Australia Telescope Compact Array. We present spectra of the 6.7-GHz class II methanol and 22.2-GHz water masers towards these sources and provide a comparison with other recent flaring events these sources have experienced. We also detect the fourth example of a 23.4-GHz class I methanol maser and the 11th example of a 4.8-GHz formaldehyde maser towards G 24.33+0.13. Alongside these results, we also observe the previously detected ammonia (3,3) emission and report upper limits on the presence of various other cm-wavelength methanol, ammonia, and OH transitions. Our results are consistent with the flaring of G 24.33+0.13 being driven by a variable accretion rate in the host high mass young stellar object.

We present ALMA 3 mm molecular line and continuum observations with a resolution of ~3.5" towards five first hydrostatic core (FHSC) candidates (L1451-mm, Per-bolo 58, Per-bolo 45, L1448-IRS2E and Cha-MMS1). Our goal is to characterize their envelopes and identify the most promising sources that could be bona fide FHSCs. We identify two candidates which are consistent with an extremely young evolutionary state (L1451-mm and Cha-MMS1), with L1451-mm being the most promising FHSC candidate. Although our envelope observations cannot rule out Cha-MMS1 as a FHSC yet, the properties of its CO outflow and SED published in recent studies are in better agreement with the predictions for a young protostar. For the remaining three sources, our observations favor a prestellar nature for Per-bolo 45 and rule out the rest as FHSC candidates. Per-bolo 58 is fully consistent with being a Class 0, while L1448 IRS2E shows no emission of high-density tracers (NH2D and N2H+) at the location of the previously identified compact continuum source, which is also undetected in our observations. Thus we argue that there is no embedded source at the presumptive location of the FHSC candidate L1448 IRS2E. We propose instead, that what was thought to be emission from the presumed L1448 IRS2E outflow corresponds to outflow emission from a nearby Class 0 system, deflected by the dense ambient material. We compare the properties of the FHSC candidates studied in this work and the literature, which shows that L1451-mm appears as possibly the youngest source with a confirmed outflow., 26 pages, 14 figures. Accepted for publication in MNRAS

A new line list for hydronium (H316O+) is computed. The line list is based on a new ab initio dipole moment surface (CCSD(T)/aug-cc-pVQZ) and a new empirical potential energy surface (PES). The empirical PES of H3O+ was obtained by refining an ab initio surface through a global fit to the experimentally determined rovibrational energies collected from the literature covering the ground, $\nu _1^{\pm }$, $\nu _2^{\pm }$, $2\nu _2^{\pm }$, $\nu _3^{\pm }$, and $\nu _4^{\pm }$ vibrational states. The line list covers the wavenumber range up to 10 000 cm−1 (wavelengths $\gt 1 \, \mu$m) and should be complete for temperatures up to T = 1500 K. This is the first comprehensive line list for H3O+ with extensive wavenumber coverage and accurate transitional probabilities. Prospects of detection of hydronium in spectra of Solar system giant planets as well as exoplanets are discussed. The eXeL line list is publicly available from the ExoMol and CDS data bases.

The GYT line list covering rotational, rovibrational and rovibronic transitions of the mercapto radical SH is presented. This work extends and replaces the SNaSH line list [Yurchenko et al., 2018, MNRAS, 478, 270] which covers the ground (electronic) $X$ $^{2}\Pi$ state only. This extension is prompted by the tentative identification of the ultra-violet features of SH as being of importance in the transmission spectrum of the ultra-hot Jupiter exoplanet WASP-121b [Evans et al., 2018, AJ., 156, 283]. This GYT line list model is generated by fitting empirical potential energy, spin-orbit and electronic angular momenta functions to experimentally measured wavelengths within the $X$ $^{2}\Pi$ and $A$ $^{2}\Sigma^{+}$ states and to the $A$ $^{2}\Sigma^{+}$ - $X$ $^{2}\Pi$ band system using ab initio curves as a starting reference point. The fits are compatible with the quoted uncertainty of the experimental data used of $\sim$ 0.03 - 0.3 cm$^{-1}$. The GYT line list covers wavelengths longer than 0.256 $\mu$m and includes 7686 rovibronic states and 572 145 transitions for $^{32}$SH. Line lists for the $^{33}$SH, $^{34}$SH, $^{36}$SH and $^{32}$SD isotopologues are generated including a consideration of non-Born-Oppenheimer effects for SD. The line lists are available from the CDS (http://cdsarc.u-strasbg.fr) and ExoMol (www.exomol.com) data bases.

We present a polarimetric investigation of the protoplanetary nebula Frosty Leo performed with the Submillimeter Array. We were able to detect, in the low continuum level (peak at 14.4 mJy beam$^{-1}$), a marginal polarization at $\sim2.6\sigma$. The molecular line investigation based on the CO $J=3\rightarrow2$ emission shows a peak emission of 68.1 Jy beam$^{-1}$ km s$^{-1}$ and the polarization detection in this CO line is also marginal, with a peak at $\sim3.8\sigma$. In both cases, it was therefore not possible to use the electric vector maps (B-field) to accurately trace the magnetic field (B-field) within the PPN. The spatio-kinematic modelling realised with the different velocity channel maps indicates three main structures: a distorted torus accompanied by a bipolar outflow or jet aligned with its axis and a flattened spherical "cap". The comparison of the CO polarization segments with our model suggests that the polarized emission probably arises in the first two components., Comment: 8 pages, Accepted for publication in Monthly Notices of the Royal Astronomical Society

Using the Mopra telescope, we have targeted 61 regions in the Carina Nebula, covering an area of 1.5 square degrees, of bright and compact 870 $\mu$m dust continuum emission for molecular line emission from a host of 16 spectral lines at 3mm, including several dense gas tracers. We found that the clumps detected in Carina in general have in average higher temperatures (27 K compared to 21 K), and lower masses (214 M$_\odot$ compared to 508 M$_\odot$) than clumps located at a similar distance to us in the Galactic Plane. We compare the properties of the molecular line emission of these clumps with the MALT90 survey, finding that the detection rates of the molecular lines are similar to MALT90 clumps that are classified as PDRs. However, most of the clumps located within 10' of $\eta$ Carina have little molecular line emission detected in our observations. Given the lack of maser detection in the Carina region, we also compared the properties the clumps in Carina to those of Galactic clumps associated with 6.7-GHz methanol masers. We found that the clumps in Carina are warmer, less massive, and show less emission from the four most commonly detected molecules, HCO$^+$, N$_2$H$^+$, HCN, and HNC, compared to clumps associated with masers in the Galactic Plane. Overall our results are consistent with the scenario in which the high radiation field of $\eta$ Carina is dramatically affecting its local environment, and therefore the chemical composition of the dense clumps., Comment: 16 Pages, 16 Figures, 4 Tables

Observations of prestellar cores in star-forming filaments show two distinct morphologies. While molecular line measurements often show broad cores, submillimeter continuum observations predominantly display pinched cores compared to the bulk of the filament gas. In order to explain how different morphologies arise, we use the gravitational instability model where prestellar cores form by growing density perturbations. The radial extent at each position is set by the local line-mass. We show that the ratio of core radius to filament radius is determined by the initial line-mass of the filament. Additionally, the core morphology is independent of perturbation length scale and inclination, which makes it an ideal diagnostic for observations. Filaments with a line-mass of less than half its critical value should form broad cores, whereas filaments with more than half its critical line-mass value should form pinched cores. For filaments embedded in a constant background pressure, the dominant perturbation growth times significantly differ for low and high line-mass filaments. Therefore, we predict that only one population of cores is present if all filaments within a region begin with similar initial perturbations.

International audience; The era of interferometric observations leads to the need of a more and more precise description of physical structures and dynamics of star-forming regions, from pre-stellar cores to protoplanetary discs. The molecular emission can be traced in multiple physical components such as infalling envelopes, outflows and protoplanetary discs. To compare with the observations, a precise and complex radiative transfer modelling of these regions is needed. We present gass (Generator of Astrophysical Sources Structure), a code that allows us to generate the three-dimensional (3D) physical structure model of astrophysical sources. From the gass graphical interface, the user easily creates different components such as spherical envelopes, outflows and discs. The physical properties of these components are modelled thanks to dedicated graphical interfaces that display various figures in order to help the user and facilitate the modelling task. For each component, the code randomly generates points in a 3D grid with a sample probability weighted by the molecular density. The created models can be used as the physical structure input for 3D radiative transfer codes to predict the molecular line or continuum emission. An analysis of the output hyper-spectral cube given by such radiative transfer code can be made directly in gass using the various post-treatment options implemented, such as calculation of moments or convolution with a beam. This makes gass well suited to model and analyse both interferometric and single-dish data. This paper is focused on the results given by the association of gass and lime, a 3D radiative transfer code, and we show that the complex geometry observed in star-forming regions can be adequately handled by gass+lime.

Comprehensive vibration-rotation line lists for eight isotopologues of carbon monosulphide (CS) ($^{12}$C$^{32}$S, $^{12}$C$^{33}$S, $^{12}$C$^{34}$S, $^{12}$C$^{36}$S, $^{13}$C$^{32}$S, $^{13}$C$^{33}$S, $^{13}$C$^{34}$S, $^{13}$C$^{36}$S) in their ground electronic states are calculated. These line lists are suitable for temperatures up to 3000 K. A spectroscopically-determined potential energy curve (PEC) and dipole moment curve (DMC) are taken from literature. This PEC is adapted to suit our method prior to the computation of ro-vibrational energies. The calculated energies are then substituted by experimental energies, where available, to improve the accuracy of the line lists. The {\it ab initio} DMC is used without refinement to generate Einstein A coefficients. Full line lists of vibration-rotation transitions and partition functions are made available in an electronic form as supporting information to this paper and at \url{this http URL}.

In this paper we selected a sample of massive star forming regions from the Red MSX Source (RMS) survey, to study star formation activities (mainly outflow and inflow signatures).

Recent dust continuum surveys have shown that filamentary structures are ubiquitous along the Galactic plane. While the study of their global properties has gained momentum recently, we are still far from fully understanding their origin and stability. Theories invoking magnetic field have been formulated to help explain the stability of filaments; however, observations are needed to test their predictions. In this paper, we investigate the structure and radial equilibrium of five filamentary molecular clouds with the aim of determining the role that magnetic field may play. To do this, we use continuum and molecular line observations to obtain their physical properties (e.g. mass, temperature and pressure). We find that the filaments have lower lineal masses compared to their lineal virial masses. Their virial parameters and shape of their dust continuum emission suggests that these filaments may be confined by a toroidal dominated magnetic field.

We investigate observational signatures of triggered star formation in bright rimmed clouds (BRCs) by using molecular line transfer calculations based on radiation-hydrodynamic radiatively-driven-implosion models. We find that for BRCs the separation in velocity between the line profile peak of an optically thick and an optically thin line is determined by both the observer viewing angle and the density of the shell driving into the cloud. In agreement with observations, we find that most BRC line profiles are symmetric and that asymmetries can be either red or blue, in contrast to the blue-dominance expected for a collapsing cloud. Asymmetries in the line profiles arise when an optically thick line is dominated by the shell and an optically thin line is dominated by the cloud interior to the shell. The asymmetries are red or blue depending on whether the shell is moving towards or away from the observer respectively. Using the known motions of the molecular gas in our models we rule out the envelope expansion with core collapse mechanism as the cause of the lack of blue-asymmetry in our simulated observations. We show that the absence of a strong photon dominated region (PDR) around a BRC may not rule out the presence of triggered star formation: if the BRC line profile has a strong blue component then the shell is expected to be driving towards the observer, suggesting that the cloud is being viewed from behind and the PDR is obstructed. This could explain why BRCs such as SFO 80, 81 and 86 have a blue secondary peak and only a weak PDR inferred at 8 microns. Finally we also test the use of 12CO, 13CO and C18O as diagnostics of cloud mass, temperature and column density. We find that the inferred conditions are in reasonable agreement with those from the models., 17 pages, Accepted for publication in MNRAS, revision following editor proof

High-angular resolution observations of dense molecular cores show that these cores can be clumpier at smaller scales, and that some of these clumps can also be unbound or transient. The use of chemical models of the evolution of the molecular gas provides a way to probe the physical properties of the clouds. We study the properties of the clump and inter-clump medium in the starless CS core in LDN 673 by carrying out a molecular line survey with the IRAM 30-m telescope toward two clumps and two inter-clump positions. We also observed the 1.2-mm continuum with the MAMBO-II bolometer at IRAM. The dust continuum map shows four condensations, three of them centrally peaked, coinciding with previously identified sub-millimetre sources. We confirm that the denser clump of the region, $n\sim3.6 \times10^5$\cmt, is also the more chemically evolved, and it could still undergo further fragmentation. The inter-clump medium positions are denser than previously expected, likely $n\sim1\times10^3$--1$\times10^4$\cmt\ due to contamination, and are chemically young, similar to the gas in the lower density clump position. We argue that the density contrast between these positions and their general young chemical age would support the existence of transient clumps in the lower density material of the core. We were also able to find reasonable fits of the observationally derived chemical abundances to models of the chemistry of transient clumps.

The discovery of extrasolar planets is one of the major scientific advances of the last two decades. Hundreds of planets have now been detected and astronomers are beginning to characterise their composition and physical characteristics. To do this requires a huge quantity of spectroscopic data most of which is not available from laboratory studies. The ExoMol project will offer a comprehensive solution to this problem by providing spectroscopic data on all the molecular transitions of importance in the atmospheres of exoplanets. These data will be widely applicable to other problems and will be used for studies on cool stars, brown dwarfs and circumstellar environments. This paper lays out the scientific foundations of this project and reviews previous work in this area. A mixture of first principles and empirically-tuned quantum mechanical methods will be used to compute comprehensive and very large rotation-vibration and rotation-vibration-electronic (rovibronic) line lists. Methodologies will be developed for treating larger molecules such as methane and nitric acid. ExoMol will rely on these developments and the use of state-of-the-art computing.

Molecular line observations may serve as diagnostics of the degree to which the number density of cosmic ray protons, having energies of 10s to 100s of MeVs each, is enhanced in starburst galaxies and galaxies with active nuclei. Results, obtained with the UCL\_PDR code, for the fractional abundances of molecules as functions of the cosmic-ray induced ionisation rate, $\zeta$, are presented. The aim is not to model any particular external galaxies. Rather, it is to identify characteristics of the dependencies of molecular abundances on $\zeta$, in part to enable the development of suitable observational programmes for cosmic ray dominated regions (CRDRs) which will then stimulate detailed modelling. For a number density of hydrogen nuclei of of $10^4$ cm$^{-3}$, and high visual extinction, the fractional abundances of some species increase as $\zeta$ increases to $10^{-14}$ s$^{-1}$, but for much higher values of $\zeta$ the fractional abundances of all molecular species are significantly below their peak values. We show in particular that OH, H$_{2}$O, H$_{3}^{+}$, H$_{3}$O$^{+}$ and OH$^{+}$ attain large fractional abundances ($\geqslant 10^{-8}$) for $\zeta$ as large as $10^{-12}$ s$^{-1}$. HCO$^{+}$ is a poor tracer of CRDRs when $\zeta > 10^{-13}$ s$^{-1}$. Sulphur-bearing species may be useful tracers of CRDRs gas in which $\zeta \sim 10^{-16}$ s$^{-1}$. Ammonia has a large fractional abundance for $\zeta \leqslant 10^{-16}$ s$^{-1}$ and nitrogen appears in CN-bearing species at significant levels as $\zeta$ increases, even up to $\sim 10^{-14}$ s$^{-1}$. In this paper, we also discuss our model predictions, comparing them to recent detections in both galactic and extragalactic sources. We show that they agree well, to a first approximation, with the observational constraints.

Results of molecular line observations toward the Sagittarius B1 complex are reported. Maps of the HCN, HCO + and SiO J = 1–0 emissions were taken with the NRO 45-m telescope. With these data, combined with the ASTE CO J = 3–2 survey data, we have investigated the spatial structure, kinematics and physical conditions of two peculiar molecular features: CO0.55+0.07 and SiO0.56� 0.01. The CO arc, CO0.55+0.07, shows clear expanding motion with sizes of 8.5 � 6.8 pc 2 and an expansion velocity of 40 km s � 1 . The SiO shell, SiO0.56� 0.01, has a size of 3.0 � 3.4 pc 2 , and surrounds an X-ray Fe line source, G0.570� 0.018. The mass and the kinetic energy of CO0.55+0.07 +

In the present work we compare in detail some of the major theoretical libraries with observations, aiming at detecting weaknesses and strengths from the stellar population modelling point of view. We compared model predictions and observations for broad- band colours and for high resolution spectral features. Concerning the broad-band colours, we measured the stellar colour given by three recent sets of model atmospheres and flux distributions(Castelli & Kurucz 2003; Gustafsson et al. 2003; Brott & Hauschildt 2005), and compared them with a recent UBVRIJHK calibration (Worthey & Lee 2007). We found that the models can reproduce with reasonable accuracy the stellar colours for a fair interval in effective temperatures and gravities. The exceptions are: 1) the U-B colour, where the models are typically redder than the observations, and; 2) the very cool stars in general (V-K > ~3).Concerning the high resolution features, we measured 35 spectral indices defined in the literature on three high resolution synthetic libraries (Coelho et al. 2005; Martins et al. 2005; Munari et al. 2005), and compared them with the observed measurements given by three empirical libraries (Valdes et al.2004; Sanchez-Blazquez et al. 2006; Prugniel & Soubiran 2001). We found that the direct comparison between models and observations is not a simple task, given the uncertainties in parameter determinations of empirical libraries. Taking that aside, we found that in general the three libraries present similar behaviours and systematic deviations. For stars with Teff < 7000K, the library by Coelho et al. (2005) is the one with best average performance. We detect that lists of atomic and molecular line opacities still need improvement, specially in the blue region of thespectrum, and for the cool stars (Teff < ~4500K)., 18 pages, 16 figures - accepted for publication in MNRAS. Complete paper (which includes online appendix) available at http://www.astro.iag.usp.br/~lucimara/martins_coelho_rev2.ps

We demonstrate how the observed H2O ice column densities toward three dense globules in the Southern Coalsack could be used to constrain the ages of these sources. We derive ages of ~10^5 yr, in agreement with dynamical studies of these objects. We have modelled the chemical evolution of the globules, and show how the molecular abundances are controlled by both the gas density and the initial chemical conditions as the globules formed. Based on our derived ages, we predict the column densities of several species of interest. These predictions should be straightforward to test by performing molecular line observations, Comment: 10 pages, 4 figures, in press at MNRAS

The ubiquity of filamentary structure at various scales through out the Galaxy has triggered a renewed interest in their formation, evolution, and role in star formation. The largest filaments can reach up to Galactic scale as part of the spiral arm structure. However, such large scale filaments are hard to identify systematically due to limitations in identifying methodology (i.e., as extinction features). We present a new approach to directly search for the largest, coldest, and densest filaments in the Galaxy, making use of sensitive Herschel Hi-GAL data complemented by spectral line cubes. We present a sample of the 9 most prominent Herschel filaments, including 6 identified from a pilot search field plus 3 from outside the field. These filaments measure 37-99 pc long and 0.6-3.0 pc wide with masses (0.5-8.3)$\times10^4 \, M_\odot$, and beam-averaged ($28"$, or 0.4-0.7 pc) peak H$_2$ column densities of (1.7-9.3)$\times 10^{22} \, \rm{cm^{-2}}$. The bulk of the filaments are relatively cold (17-21 K), while some local clumps have a dust temperature up to 25-47 K. All the filaments are located within, Comment: Published 2015MNRAS.450.4043W; this version contains minor proof corrections. FT-based background removal code at https://github.com/esoPanda/FTbg SED fitting code at http://hi-gal-sed-fitter.readthedocs.org 3D interactive visualization at http://www.eso.org/~kwang

Results are presented from a model of molecular line formation in collapsing star-forming cores. The study includes, for the first time, a self-consistent chemical and dynamical model which is then directly coupled to an appropriate radiative transfer model. The assumptions of chemical uniformity or simple monotonic variations within such cores are shown to be unacceptable. The results show that the abundance variations and the line profiles are highly sensitive to the assumed values of the free parameters in the chemical model. Extreme caution is therefore advised in the quantitative analysis of emission-line profiles from infall sources. The implied degeneracy can be overcome by multiple line-of-sight observations of many species and transitions.

We evaluate the intrinsic three dimensional shapes of molecular cores, by analysing their projected shapes. We use the recent catalogue of molecular line observations of Jijina et al. and model the data by the method originally devised for elliptical galaxies. Our analysis broadly supports the conclusion of Jones et al. that molecular cores are better represented by triaxial intrinsic shapes (ellipsoids) than biaxial intrinsic shapes (spheroids). However, we find that the best fit to all of the data is obtained with more extreme axial ratios ($1:0.8:0.4$) than those derived by Jones et al. More surprisingly, we find that starless cores have more extreme axial ratios than protostellar cores -- starless cores appear more `flattened'. This is the opposite of what would be expected from modeling the freefall collapse of triaxial ellipsoids. The collapse of starless cores would be expected to proceed most swiftly along the shortest axis - as has been predicted by every modeller since Zel'dovich - which should produce more flattened cores around protostars, the opposite of what is seen., Comment: 7 pages, 3 figures

Molecular line observations of the giant molecular cloud associated with the northern Orion complex of the I Ori OB association are presented. An area of 1½ deg2 including the reflection nebulae NGC 2068 and NGC 2071, the Herbig-Haro complex M-78 HH and parts of the extended dust clouds L 1627 and L 1630 was surveyed in the CO and 13CO J = 1-0 lines at millimeter wavelengths. At least 12 molecular clouds are observed within the extended cloud, with CO intensity well correlated with regions of optical absorption. Intense molecular clouds are also observed close to NGC 2068 and NGC 2071, while the region surrounding the Herbig-Haro complex appears as a 5-K temperature enhancement. A velocity gradient of approximately 0.43 km s-1 pc-1 is observed across the cloud complex, indicating rotation about an axis lying along the minor axis of the northern Orion complex and at an angle of ~ 75° to the gradient plane.

Des cartes de l'emission CO J=2→1 et HCO + J=3→2 sont presentees pour la source d'ecoulement moleculaire Orion B. L'ecoulement apparait unipolaire et montre une acceleration du gaz moleculaire jusqu'a 0,6 pc de l'etoile excitatrice. L'emission HCO + provient du noyau du nuage ou la temperature d'excitation est environ 25 K. Les estimations de la masse sont compatibles avec un modele dans lequel le noyau possede une temperature cinetique de 30-50 K, sans depletion moleculaire sur des grains