* Astronomy

Title: Sequential clustering of star formation in IC 1396
Authors: Ya Fang Huang, Jin Zeng Li

We present in this paper a comprehensive study of the H II region IC 1396 and its star formation activity, in which multi-wavelength data ranging from the optical to the near- and far-infrared were employed. The surface density distribution of all the 2MASS sources with certain detection toward IC 1396 indicates the existence of a compact cluster spatially consistent with the position of the exciting source of the H II region, HD 206267. The spatial distribution of the infrared excessive emission sources selected based on archived 2MASS data reveals the existence of four sub-clusters in this region. One is in association with the open cluster Trumpler 37. The other three are found to be spatially coincident with the bright rims of the H II region. All the excessive emission sources in the near infrared are cross-identified with the AKARI IRC data, an analysis of the spectral energy distributions (SEDs) of the resultant sample leads to the identification of 8 CLASS I, 15 CLASS II and 15 CLASS III sources in IC 1396. Optical identification of the sample sources with R magnitudes brighter than 17 mag corroborates the results from the SED analysis. Based on the spatial distribution of the infrared young stellar objects at different evolutionary stages, the surrounding sub-clusters located in the bright rims are believed to be younger than the central one. This is consistent with a scenario of sequential star formation in this region. Imaging data of a dark patch in IC 1396 by Herschel SPIRE, on the other hand, indicate the presence of two far-infrared cores in LDN 1111, which are likely new generation protostellar objects in formation. So we infer that the star formation process in this H II region was not continuous but episodic.

Read more (2328kb, PDF)

Title: Close encounters of the protostellar kind in IC 1396N
Authors: M.T. Beltran (1), F. Massi (1), F. Fontani (1), C. Codella (1), R. Lopez (2) ((1) INAF-Osservatorio Astrofisico di Arcetri (2) Universitat de Barcelona)

We have mapped in the 2.7 mm continuum and 12CO with the PdBI the IR-dark "tail" that crosses the IC 1396N globule from south to north, and is the most extincted part of this cloud. These observations have allowed us to distinguish all possible associations of molecular hydrogen emission features by revealing the presence of two well-collimated low-mass protostellar outflows at the northern part of the globule. The outflows are located almost in the plane of the sky and are colliding with each other towards the position of a strong 2.12 microns H2 line emission feature.

Read more (782kb, PDF)

Title: Dynamics and PDR properties in IC1396A
Authors: Yoko Okada (1), Rolf Güsten (2), Miguel Angel Requena-Torres (2), Markus Röllig (1), Paul Hartogh (3), Heinz-Wilhelm Hübers (4,5), Thomas Klein (2), Oliver Ricken (1), Robert Simon (1), Jürgen Stutzki (1) ((1) Universität zu Köln, (2) MPIfR, (3) MPS (4) DLR (5) Technische Universität Berlin)

We investigate the gas dynamics and the physical properties of photodissociation regions (PDRs) in IC1396A, which is an illuminated bright-rimmed globule with internal structures created by young stellar objects. Our mapping observations of the [CII] emission in IC1396A with GREAT onboard SOFIA revealed the detailed velocity structure of this region. We combined them with observations of the [CI] 3P_1 - 3P_0 and CO(4-3) emissions to study the dynamics of the different tracers and physical properties of the PDRs. The [CII] emission generally matches the IRAC 8 micron, which traces the polycyclic aromatic hydrocarbon (PAH) emissions. The CO(4-3) emission peaks inside the globule, and the [CI] emission is strong in outer regions, following the 8 micron emission to some degree, but its peak is different from that of [CII]. The [CII] emitting gas shows a clear velocity gradient within the globule, which is not significant in the [CI] and CO(4-3) emission. Some clumps that are prominent in [CII] emission appear to be blown away from the rim of the globule. The observed ratios of [CII]/[CI] and [CII]/CO(4-3) are compared to the KOSMA-tau PDR model, which indicates a density of 10^4-10^5 cm-3.

Read more (421kb, PDF)

Title: The embedded cluster or association Trumpler 37 in IC1396: a search for evolutionary constraints
Authors: T.A. Saurin, E. Bica, C. Bonatto

It is currently widely accepted that open star clusters and stellar associations result from the evolution of embedded star clusters. Parameters such star formation efficiency, time-scale of gas removal and velocity dispersion can be determinants for their future as bound or unbound systems. Finding objects at an intermediate evolution state can provide constraints to model the embedded cluster evolution. Trumpler 37 in the HII region IC1396 is an extended young cluster that presents characteristics of an association. We employed 2MASS photometry to analyse its structure, stellar content and determine its astrophysical parameters. We also analyse 11 bright-rimmed clouds in IC1396 in order to search for young infrared star clusters, and the background open star cluster Teutsch 74, to verify whether it has any contribution to the observed stellar density profile of Trumpler 37. The derived parameters and comparison with template objects from other studies lead us to conclude that Trumpler 37, rather than as a star cluster, will probably emerge from its molecular cloud as an OB association.

Read more (5239kb, PDF)