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Globulettes as Seeds of Brown Dwarfs and Free-Floating Planetary-Mass Objects
Some H II regions surrounding young stellar clusters contain tiny dustyclouds, which on photos look like dark spots or teardrops against abackground of nebular emission. From our collection of Hα imagesof 10 H II regions gathered at the Nordic Optical Telescope, we found173 such clouds, which we call ``globulettes,'' since they are muchsmaller than normal globules and form a distinct class of objects. Manyglobulettes are quite isolated and located far from the molecular shellsand elephant trunks associated with the regions. Others are attached tothe trunks (or shells), suggesting that globulettes may form as aconsequence of erosion of these larger structures. None of our objectsappear to contain stellar objects. The globulettes were measured forposition, dimension, and orientation, and we find that most objects aresmaller than 10 kAU. The Rosette Nebula and IC 1805 are particularlyrich in globulettes, for which the size distributions peak at mean radiiof ~2.5 kAU, similar to what was found by Reipurth and coworkers and DeMarco and coworkers for similar objects in other regions. We estimatetotal mass and density distributions for each object from extinctionmeasures and conclude that a majority contain <13 MJ,corresponding to planetary-mass objects. We then estimate the internalthermal and potential energies and find, when also including the effectsfrom the outer pressure, that a large fraction of the globulettes couldbe unstable and would contract on short timescales, <10 6yr. In addition, the radiation pressure and ram pressure exerted on theside facing the clusters would stimulate contraction. Since theglobulettes are not screened from stellar light by dust clouds fartherin, one would expect photoevaporation to dissolve the objects. However,surprisingly few objects show bright rims or teardrop forms. Wecalculate the expected lifetimes against photoevaporation. Theselifetimes scatter around 4×106 yr, much longer thanestimated in previous studies and also much longer than the free-falltime. We conclude that a large number of our globulettes have time toform central low-mass objects long before the ionization front, drivenby the impinging Lyman photons, has penetrated far into the globulette.Hence, the globulettes may be one source in the formation of browndwarfs and free-floating planetary-mass objects in the galaxy.Based on observations made with the Nordic Optical Telescope, operatedon the island of La Palma jointly by Denmark, Finland, Iceland, Norway,and Sweden in the Spanish Observatorio del Roque de los Muchachos of theInstituto de Astrofísica de Canarias.
| Rotating elephant trunks
Aims.We investigate the structure and velocity of cold molecularpillars, "elephant trunks", in expanding H II regions. Methods:.The trunks are seen in silhouette against the bright background in ourHα images. All trunks are filamentary, and show signs of beingtwisted. Four such trunks in NGC 7822, IC 1805, the Rosette Nebula, andDWB 44 were selected, and then mapped mainly in 12CO and13CO. We determine the mass and density of the trunks. Mostof the mass is concentrated in a head facing the central cluster, and insub-filaments forming the body of the trunk that is connected toV-shaped filaments to the outer expanding shell. Results: .Wediscovered that all four trunks rotate as rigid bodies (to a firstapproximation) about their major axes, and that at least two trunks arestretching along their major axes, meaning that the massive heads arelagging behind in the general expansion of the H II regions. Therotational periods are of the order of a few million years - similar tothe age of the clusters. Rotation, then, is responsible for the twistedappearance of many elephant trunks, since they are rooted in the outershells. The trunks carry surprisingly large amounts of angular momentum,3× 1048{-}2× 1050 kg m2s-1, with corresponding rotational energies of up to 1037 J. However, we estimate the total magnetic energies tobe even larger. The trunks continuously reshape, and the formation oftwined, and in many cases helical, sub-filaments can be understood as aconsequence of electromagnetic and inertia forces inside the trunks. Atheory based on the concept of magnetically twisted trunks is developedfurther, where the initial angular momentum is a consequence of thetwisting of parent filaments containing mass condensations. Our resultsalso suggest a new process of removing angular momentum from parentmolecular clouds.
| Turbulent Gas Flows in the Rosette and G216-2.5 Molecular Clouds: Assessing Turbulent Fragmentation Descriptions of Star Formation
The role of turbulent fragmentation in regulating the efficiency of starformation in interstellar clouds is examined from new wide-field imagingof 12CO and 13CO J=1-0 emission from the Rosetteand G216-2.5 molecular clouds. The Rosette molecular cloud is a typicalstar-forming giant molecular cloud, and G215-2.5 is a massive molecularcloud with no OB stars and very little low-mass star formation. Theproperties of the turbulent gas flow are derived from the set ofeigenvectors and eigenimages generated by principal component analysis(PCA) of the spectroscopic data cubes. While the two clouds representquite divergent states of star formation activity, the velocitystructure functions for both clouds are similar. The sonic scale,λS, defined as the spatial scale at which turbulentvelocity fluctuations are equivalent to the local sound speed, and theturbulent Mach number evaluated at 1 pc, M1pc, are derivedfor an ensemble of clouds including the Rosette and G216-2.5 regionsthat span a large range in star formation activity. We find no evidencefor the positive correlations between these quantities and the starformation efficiency that are predicted by turbulent fragmentationmodels. A correlation does exist between the star formation efficiencyand the sonic scale for a subset of clouds withLFIR/M(H2)>1 that are generating young stellarclusters. Turbulent fragmentation must play a limited and nonexclusiverole in determining the yield of stellar masses within interstellarclouds.
| Confirmation of a Stellar Microjet in the Rosette H II Region (NGC 2244)
A possible microjet from a low-mass but young star, which has alreadyshed its cocoon, could be rendered observable by the Lyman photon fluxin the interior of the Rosette Nebula. Outside this environment it maynot have been observable at optical wavelengths. The kinematics of thisproposed monopolar microjet from an F8 Ve star have been investigated byspatially resolved, long-slit, spectral observations with the ManchesterEchelle Spectrometer on the San Pedro Martir telescope (Mexico). Theflow is shown to be approaching to give a radial velocity differencefrom the host nebula of -56 km s-1. An outflow velocity of,at the most, a few hundreds of km s-1 is therefore indicated.If the flow velocity is taken as 200 km s-1, which is foundin other microjets, then this jet's inclination to the sky is ~16°.The mass in the outflowing ionized gas is estimated from the surfacebrightness of the Hα emission as ~6×1027 g togive an estimated mass-loss rate of 10-8 Msolaryr-1, which, along with the detection of the outflowvelocity, confirms its microjet identification even though an uncertainfilling factor was used in these calculations. The hottest cluster star,which is also in the neighborhood of the microjet, is found alone toemit marginally sufficient Lyman photons to account for the ionizationof the jet, although direct observations of the local electron densityfrom optical line ratios are required to confirm this pointconclusively.
| 10 MK Gas in M17 and the Rosette Nebula: X-Ray Flows in Galactic H II Regions
We present the first high spatial resolution X-ray images of twohigh-mass star forming regions, the Omega Nebula (M17) and the RosetteNebula (NGC 2237-2246), obtained with the Chandra X-Ray ObservatoryAdvanced CCD Imaging Spectrometer instrument. The massive clusterspowering these H II regions are resolved at the arcsecond level intomore than 900 (M17) and 300 (Rosette) stellar sources similar to thoseseen in closer young stellar clusters. However, we also detect softdiffuse X-ray emission on parsec scales that is spatially and spectrallydistinct from the point-source population. The diffuse emission hasluminosity LX~=3.4×1033 ergs s-1in M17 with plasma energy components at kT~=0.13 and ~=0.6 keV (1.5 and7 MK), while in Rosette it has LX~=6×1032ergs s-1 with plasma energy components at kT~=0.06 and ~=0.8keV (0.7 and 9 MK). This extended emission most likely arises from thefast O star winds thermalized either by wind-wind collisions or by atermination shock against the surrounding media. We establish that onlya small portion of the wind energy and mass appears in the observeddiffuse X-ray plasma; in these blister H II regions, we suspect thatmost of it flows without cooling into the low-density interstellarmedium. These data provide compelling observational evidence that strongwind shocks are present in H II regions.
| UBVI and Hα Photometry of the Young Open Cluster NGC 2244
New UBVI and Hα photometry has been performed for the young opencluster NGC 2244. We classified 30 OB stars as being members of thecluster using proper-motion data and spectral types from previousinvestigators, along with photometric diagrams obtained in this study.We measured Hα emission strength of the stars by Hαphotometry and set up a selection criterion to select pre-main-sequence(PMS) stars with Hα emission. Fourteen PMS stars and seven PMScandidates were found using the criterion. In addition, six stars foundnear the positions of ROSAT HRI X-ray sources were assumed to be PMSstars and the optical counterparts of these X-ray sources. We determineda reddening of =0.47+/-0.04 for the cluster and atotal-to-selective extinction ratio of RV=3.1+/-0.2. Thedistance modulus derived was V0-MV=11.1. Bycomparing our photometric results with theoretical evolution models, wederived a main-sequence turnoff age of 1.9 Myr and a PMS age spread ofabout 6 Myr. The slope of the initial mass function, Γ, calculatedin the mass range 0.5<=logm<=2.0 could be flat(Γ=-0.7+/-0.1).
| The Rosette molecular complex. II. [CII] 158 MU M observations
We present an extended map in the [CII] 158 mu m fine structure line ofthe Rosette Molecular Cloud Complex, obtained withthe Far Infrared Fabry-Perot Imaging Spectrometer FIFI onboard the NASAKuiper Airborne Observatory. Very weak but significant C(+) emission wasfound deep in the cloud at a distance of around 25 pc from the centralOB cluster. The observed intensity distribution is consistent with thepicture of a clumpy molecular cloud, exposed to an UV flux of around 200G_deg from the central OB cluster NGC 2244 at thecloud edge. The UV radiation creates Photon Dominated Regions (PDRs) onthe clump surfaces throughout the cloud which give rise to the observedweak [CII] 158 mu m line emission (peak intensity 5x10(-4) erg s(-1)sr(-1) cm(-2) ). In contrast to more luminous PDR regions, the emergentC(+) intensity scales logarithmically with the incident UV field but isin agreement with PDR models for a weak UV illumination. The density ofthe [CII] emitting gas is around 10(4) cm(-3) . The rather high value of1% for the [CII] to FIR flux ratio in Rosette indicates a large grainphotoelectrical heating efficiency which might be due to the lowincident UV field. With an average density of 300 cm(-3) , obtained fromCO observations, we derive a high (30-300) clump to interclump densitycontrast, where the UV radiation can penetrate deep into the cloud andinduces emission from many PDRs along the line of sight.
| The Rosette Molecular Complex. I. CO observations
We present (12) CO,(13) CO and C(18) O J=1->0, and (12) CO and (13)CO 2->1 and 3->2 observations of the Rosette MolecularComplex (RMC), obtained with the KOSMA 3m and IRAM 30mtelescopes. We introduce a method for correcting error beam pick-up ofsingle-dish telescopes in spectral line radio maps by using observationsof a smaller telescope and apply it to correct the IRAM 30m datapresented in this paper by the large scale KOSMA 3m data. Theobservations indicate that the RMC is clumpy on a size scale of down toat least 0.1 pc. The molecular density structure is well correlated withthe optical picture in the H_alpha line emission. From a CO multilineanalysis, incorporating the incident UV field, we derive a density oflower than 10(5) cm(-3) for the emitting gas at a beam filling factor ofunity. In direction to the molecular outflow source AFGL961, we find that the (12) CO lines up to J=3->2 have broadwings. They show, as well as the (13) CO J=2->1 and 1->0 lines,self-absorption features due to colder forground material. A secondoutflow is firstly detected close to the embedded IR sourceIR06314+0427. The KOSMA and IRAM (13) CO J=2->1data were analyzed with the clump finding algorithm 'Gaussclumps'.Appropriate scaling shows that the small scale clump mass distributionoverlaps and continues the low mass end of the large scale distribution.The observed structures are therefore self-similar over a length scalecovering at least 0.1 to a few parsec. The clump mass spectral indexalpha for both individual data sets and the combined distribution equals1.6, in good agreement with typical values for other molecular clouds.The molecular clumps were classified using the 'Initial Cloud ParameterSpace' of Bertoldi & McKee (1989). All clumps belong to the regimeof 'Post Implosion Clouds' and possibly form stars.
| An observational study of cometary globules near the Rosette nebula.
Molecular line observations are reported of two regions containing smallcometary globules at the edge of the Rosette Nebula. Observations of theCO, 3CO and C^18^O J=21,-and CO J=43-molecular lines towards Globule 1,the most prominent of the group, show it has a well-developed head-tailstructure, with a head diameter ~0.4pc, and a tail extending ~1.3pcbehind it. The major axis of the system points about 45 degrees awayfrom the direction to the centre of the Rosette Nebula (which containsthe [presumed] illuminating stars), and 20 degrees out of the plane ofthe sky, along a projected line towards the luminous(924Lsun_) infrared source IRAS 06314+0427. The CO lines havea complex velocity structure; with a pronounced broadening at the frontof the head (as viewed from IRAS 06314+0427); a velocity gradient~1.4km/s along the tail, and material at the front of the head isblue-shifted by ~0.5km/s compared to surrounding gas. The CO J=21-lineintensity peaks towards the front of the head, and along the edges ofthe tail. The 3CO J=21-antenna temperatures in the head are very similarto those of CO, suggesting very high opacities or column densities, orthat there is significant CO self-absorption. There is a narrow rim ofCO J=43-emission around the front of the head over a limited velocityrange, which correlates with the position of a faint optical rim, and anarrow ridge of 2μm H_2_ emission. These data give strong support tothe Radiation Driven Implosion (RDI) model of Lefloch and Lazareff (1994-- hereafter LL94), which was developed to explain the physicalstructure of cometary globules. Using an RDI simulation, a remarkablygood fit to the data has been obtained, allowing the CO, 3CO and C^18^Ospatial structures and velocity field to be modelled. This simulationsuggests that Globule 1 is ~400,000years old, and has a mass~50Msun_. Additional observations towards the region close toIRAS 06314+0427 show that it is associated with an intense molecularconcentration lying at the northern end of a ~5pc long molecular ridge,with a mass ~330Msun_, and lies close to the centre of ashell-like condensation.
| The H II Region Sharpless 269. I. Morphological Study of the Radial Velocity, Velocity Dispersion, and Density Fields
We present [S II] lambda lambda 6716.5, 6730.8 radial velocity, velocitydispersion, and density field maps of the H II region Sharpless 269obtained using a scanning Fabry-Perot interferometer. The radialvelocity field shows a clear bipolar morphology probably related to thedust/molecular lane bisecting the H II region. The mean LSR velocity(VLSR) extracted from the data is 16.45 +/- 0.03 km s-1 (1 sigma = 2.77+/- 0.02 km s-1), blueshifted by 1.3 km s-1 from the associatedmolecular cloud. The mean velocity dispersion given by subtraction ofthe instrumental and thermal Doppler broadenings from the FWHM of theline profiles is 16.43 +/- 0.10 km s-1 (1 sigma = 10.40 +/- 0.07 kms-1). Line width analysis yields an east-west gradient caused by theproximity of molecular material and the outflow from a young stellarobject in the western part of the nebula. The electron density field hasa mainly uniform distribution but for a localized increase positionallyassociated with the young stellar object mentioned above. The meandensity is found to be 290 +/- 2 cm-3, while the maximum of the densitydistribution is centered near 200 cm-3. Overall, the results are in goodagreement with an expansion scenario for the ionized gas except for thedensity field which fails to exhibit the predicted exponential drop fromthe exciting star to the edge of the H II region.
| Primordial giant molecular cloud clumps can be probed - optically
Optical processing of deep IIIaF Schmidt plates of a primordial giantmolecular cloud (GMC) is demonstrated revealing information regardingclump-interclump structure. A combination of photographic masking andimage amplification is employed to compress emulsion middensities anddistribute chemical fog throughout the thickness of the emulsioncoating. A chain of clearly defined clumpy globules is noted outside thestellar-wind-evacuated cavity of the Rosette Nebula (NGC 2237-NGC 2246).The clumpy structure is theorized to be the result of interactionsbetween the CO cloud and OB stars in NGC 2244. The GMC clumps are shownto be primordial based on evidence from the photoionization-etchingscale sizes. The GMC is pervaded by an interclump molecular substrate,and the clumpy globules are of interest because they do not result fromfragmentation of stellar-wind-driven shells.
| The young open clusters NGC 2244 and NGC 2264
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1991RMxAA..22...99P&db_key=AST
| A family of cometary globules around an infrared source near the Rosette nebula
The use of a photographic enhancement technique to reveal a family offour Bok globules with tails, or 'cometary' globules, in the southeastquadrant of the Rosette nebula, NGC 2237 - 2246, is reported. Theglobules are not visible on R-glass copies of the NationalGeographic/Palomar Observatory Sky Survey. The tails of the globules allpoint away from the IRAS source 06314 + 0427, the position of whichcoincides with the peak of CO emission. The far-IR luminosity of 06314 +0427 is estimated to be a factor of at least 880 greater than the sun'sluminosity, with a total energy output enough to drive a stellar windthat could produce the observed globules.
| Searches for the protonated interstellar species HC3NH(+), CH3CNH(+), and HOCS(+) - Implications for ion-molecule chemistry
It is reported here that observed limits for the interstellar abundanceratios HC3NH(+)/HC3N, CH3CNH(+)/CH3CN, and HOCS(+)/OCS are consistentwith current interstellar ion-molecule formation models, although thelow abundance of HC3NH(+) precludes several reaction pathways forforming higher-order cyanopolyynes. It is also reported thatHC3NH(+)/HC3N is at least 10 times smaller than HCNH(+)/CHN, a resultthat is not explainable solely by ion-molecule processes and that maysuggest a non-gas-phase depletion mechanism for HCN such as absorptiononto grains. There is no evidence for high-temperature HOCS(+)/OCSchemistry.
| Étude de la nébuleuse Rosette à 1430 MHz et 2315 MHz
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