| 1. |
- Hennemann, M., et al.
(författare)
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Herschel observations of embedded protostellar clusters in the Rosette molecular cloud
- 2010
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 518, s. L84-
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Tidskriftsartikel (refereegranskat)abstract
- The Herschel OB young stellar objects survey (HOBYS) has observed the Rosette molecular cloud, providing an unprecedented view of its star formation activity. These new far-infrared data reveal a population of compact young stellar objects whose physical properties we aim to characterise. We compiled a sample of protostars and their spectral energy distributions that covers the near-infrared to submillimetre wavelength range. These were used to constrain key properties in the protostellar evolution, bolometric luminosity, and envelope mass and to build an evolutionary diagram. Several clusters are distinguished including the cloud centre, the embedded clusters in the vicinity of luminous infrared sources, and the interaction region. The analysed protostellar population in Rosette ranges from 0.1 to about 15 M-circle dot with luminosities between 1 and 150 L-circle dot, which extends the evolutionary diagram from low-mass protostars into the high-mass regime. Some sources lack counterparts at near-to mid-infrared wavelengths, indicating extreme youth. The central cluster and the Phelps & Lada 7 cluster appear less evolved than the remainder of the analysed protostellar population. For the central cluster, we find indications that about 25% of the protostars classified as Class I from near-to mid-infrared data are actually candidate Class 0 objects. As a showcase for protostellar evolution, we analysed four protostars of low-to intermediate-mass in a single dense core, and they represent different evolutionary stages from Class 0 to Class I. Their mid-to far-infrared spectral slopes flatten towards the Class I stage, and the 160 to 70 mu m flux ratio is greatest for the presumed Class 0 source. This shows that the Herschel observations characterise the earliest stages of protostellar evolution in detail.
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| 2. |
- Men'shchikov, A., et al.
(författare)
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Filamentary structures and compact objects in the Aquila and Polaris clouds observed by Herschel
- 2010
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 518, s. L103-
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Tidskriftsartikel (refereegranskat)abstract
- Our PACS and SPIRE images of the Aquila Rift and part of the Polaris Flare regions, taken during the science demonstration phase of Herschel discovered fascinating, omnipresent filamentary structures that appear to be physically related to compact cores. We briefly describe a new multi-scale, multi-wavelength source extraction method used to detect objects and measure their parameters in our Herschel images. All of the extracted starless cores (541 in Aquila and 302 in Polaris) appear to form in the long and very narrow filaments. With its combination of the far-IR resolution and sensitivity, Herschel directly reveals the filaments in which the dense cores are embedded; the filaments are resolved and have deconvolved widths of similar to 35 '' in Aquila and similar to 59 '' in Polaris (similar to 9000 AU in both regions). Our first results of observations with Herschel enable us to suggest that in general dense cores may originate in a process of fragmentation of complex networks of long, thin filaments, likely formed as a result of an interplay between gravity, interstellar turbulence, and magnetic fields. To unravel the roles of the processes, one has to obtain additional kinematic and polarization information; these follow-up observations are planned.
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| 3. |
- Motte, F., et al.
(författare)
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Initial highlights of the HOBYS key program, the Herschel imaging survey of OB young stellar objects
- 2010
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 518, s. L77-
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Tidskriftsartikel (refereegranskat)abstract
- We present the initial highlights of the HOBYS key program, which are based on Herschel images of the Rosette molecular complex and maps of the RCW120 H II region. Using both SPIRE at 250/350/500 mu m and PACS at 70/160 mu m or 100/160 mu m, the HOBYS survey provides an unbiased and complete census of intermediate-to high-mass young stellar objects, some of which are not detected by Spitzer. Key core properties, such as bolometric luminosity and mass (as derived from spectral energy distributions), are used to constrain their evolutionary stages. We identify a handful of high-mass prestellar cores and show that their lifetimes could be shorter in the Rosette molecular complex than in nearby low-mass star-forming regions. We also quantify the impact of expanding H II regions on the star formation process acting in both Rosette and RCW 120.
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| 4. |
- Schneider, N., et al.
(författare)
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The Herschel view of star formation in the Rosette molecular cloud under the influence of NGC 2244
- 2010
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 518, s. L83-
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Tidskriftsartikel (refereegranskat)abstract
- Context. The Rosette molecular cloud is promoted as the archetype of a triggered star-formation site. This is mainly due to its morphology, because the central OB cluster NGC 2244 has blown a circular-shaped cavity into the cloud and the expanding H II-region now interacts with the cloud. Aims. Studying the spatial distribution of the different evolutionary states of all star-forming sites in Rosette and investigating possible gradients of the dust temperature will help to test the "triggered star-formation" scenario in Rosette. Methods. We use continuum data obtained with the PACS (70 and 160 mu m) and SPIRE instruments (250, 350, 500 mu m) of the Herschel telescope during the science demonstration phase of HOBYS. Results. Three-color images of Rosette impressively show how the molecular gas is heated by the radiative impact of the NGC 2244 cluster. A clear negative temperature gradient and a positive density gradient (running from the H II-region/molecular cloud interface into the cloud) are detected. Studying the spatial distribution of the most massive dense cores (size scale 0.05 to 0.3 pc), we find an age-sequence (from more evolved to younger) with increasing distance to the cluster NGC 2244. No clear gradient is found for the clump (size-scale up to 1 pc) distribution. Conclusions. The existence of temperature and density gradients and the observed age-sequence imply that star formation in Rosette may indeed be influenced by the radiative impact of the central NGC 2244 cluster. A more complete overview of the prestellar and protostellar population in Rosette is required to obtain a firmer result.
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| 5. |
- Ward-Thompson, D., et al.
(författare)
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A Herschel study of the properties of starless cores in the Polaris Flare dark cloud region using PACS and SPIRE
- 2010
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 518, s. L92-
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Tidskriftsartikel (refereegranskat)abstract
- The Polaris Flare cloud region contains a great deal of extended emission. It is at high declination and high Galactic latitude. It was previously seen strongly in IRAS Cirrus emission at 100 microns. We have detected it with both PACS and SPIRE on Herschel. We see filamentary and low-level structure. We identify the five densest cores within this structure. We present the results of a temperature, mass and density analysis of these cores. We compare their observed masses to their virial masses, and see that in all cases the observed masses lie close to the lower end of the range of estimated virial masses. Therefore, we cannot say whether they are gravitationally bound prestellar cores. Nevertheless, these are the best candidates to be potential prestellar cores in the Polaris cloud region.
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| 6. |
- Larsson, B., et al.
(författare)
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The ISO-LWS map of the Serpens cloud core. I. The SEDs of the IR/SMM sources
- 2000
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Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 363, s. 253-268
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Tidskriftsartikel (refereegranskat)abstract
- Iso-Lws mapping observations of the Serpens molecular cloud core are presented. The spectral range is 50 - 200 μ m and the map size is 8',x 8'. These observations suffer from severe source confusion at Fir wavelengths and we employ a Maximum Likelihood Method for the spectro-spatial deconvolution. The strong and fairly isolated source SMM 1/FIRS 1 presented a test case, whose modelled spectral energy distribution (SED), within observational errors, is identical to the observed one. The model results for the other infrared and submillimetre sources are therefore likely to represent their correct SEDs. Simulations demonstrating the reliability and potential of the developed method support this view. It is found that some sources do not exhibit significant Fir emission and others are most likely not pointlike at long wavelengths. In contrast, the SEDs of a number of SMMs are well fit by modified single-temperature blackbodies over the entire accessible spectral range. For the majority of sources the peak of the SEDs is found within the spectral range of the Lws and derived temperatures are generally higher (>= 30 K) than have been found by earlier deconvolution attempts using Iras data. SMM sizes are found to be only a few arcsec in diameter. In addition, the SMMs are generally optically thick even at Lws wavelengths, i.e. estimated lambda (TAu=1) are in the range 160-270 μ m. The Rayleigh-Jeans tails are less steep than expected for optically thin dust emission. This indicates that the SMMs are optically thick out to longer wavelengths than previously assumed, an assertion confirmed by self-consistent radiative transfer calculations. Models were calculated for five sources, for which sufficient data were available, viz. SMM 1, 2, 3, 4 and 9. These models are optically thick out to millimetre wavelengths (wavelength of unit optical depth 900 to 1 400 μ m). Envelope masses for these SMMs are in the range 2-6 Msun, which is of course considerably more massive than estimates based on the optically thin assumption. The luminosities are in the range 10-70 Lsun, suggesting the formation of low-mass to intermediate mass stars, so that the existence of such massive envelopes argues for extreme youth of the SMMs in the Serpens cloud core. Finally, we present, for the first time, the full infrared SEDs for the outburst source DEOS, both at high and low intensity states. Based on observations with Iso, an Esa project with instruments funded by Esa Member States (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) and with the participation of Isas and Nasa.
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| 7. |
- Larsson, B., et al.
(författare)
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The ISO-LWS map of the Serpens cloud core. II. The line spectra
- 2002
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 386, s. 1055-1073
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Tidskriftsartikel (refereegranskat)abstract
- We present spectrophotometric ISO imaging with the LWS and the CAM-CVF of the Serpens molecular cloud core. The LWS map is centred on the far infrared and submillimetre source FIRS 1/SMM 1 and its size is 8',x 8'. The fine structure line emission in [O I] 63 mu m and [C II] 157 mu m is extended on the arcminute scale and can be successfully modelled to originate in a PDR with G0 = 15 +/- 10 and n(H2) in the range of (104-105) cm-3. Extended emission might also be observed in the rotational line emission of H2O and high-J CO. However, lack of sufficient angular resolution prevents us from excluding the possibility that the emssion regions of these lines are point like, which could be linked to the embedded objects SMM 9/S 68 and SMM 4. Toward the Class 0 source SMM 1, the LWS observations reveal, in addition to fine structure line emission, a rich spectrum of molecular lines, superposed onto a strong, optically thick dust continuum (Larsson et al. \cite{Lar00}). The sub-thermally excited and optically thick CO, H2O and OH lines are tracing an about 103 AU source with temperatures higher than 300 K and densities above 106 cm-3 (M=0.01 Msun). The molecular abundances, X=N(mol)/N(H2), are X=(1, 0.1, 0.02, ge 0.025) x 10-4 for CO, H2O, OH and 13CO, respectively. Our data are consistent with an ortho-to-para ratio of 3 for H2O. OH appears highly overabundant, which we tentatively ascribe to an enhanced (X-ray) ionisation rate in the Serpens cloud core (zeta >> 10-18 s-1). We show that geometry is of concern for the correct interpretation of the data and based on 2D-radiative transfer modelling of the disk/torus around SMM 1, which successfully reproduces the entire observed SED and the observed line profiles of low-to-mid-J CO isotopomers, we can exclude the disk to be the source of the LWS-molecular line emission. The same conclusion applies to models of dynamical collapse (``inside-out'' infall). The 6{' '} pixel resolution of the CAM-CVF permits us to see that the region of rotational H2 emission is offset from SMM 1 by 30{' '}, at position angle 340deg, which is along the known jet flow from the Class 0 object. This H2 gas is extinguished by AV = 4.5 mag and at a temperature of 10310 K, which suggests that the heating of the gas is achieved through relatively slow shocks. Although we are not able to establish any firm conclusion regarding the detailed nature of the shock waves, our observations of the molecular line emission from SMM 1 are to a limited extent explainable in terms of an admixture of J-shocks and of C-shocks, the latter with speeds of about (15-20) km s-1, whereas dynamical infall is not directly revealed by our data. Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, The Netherlands and the UK) and with the participation of ISAS and NASA.
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