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Posts: 131433
Date:
Trumpler 37
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Title: The stellar content of the young open cluster Trumpler 37
Authors: R. Errmann, R. Neuhäuser, L. Marschall, G. Torres, M. Mugrauer, W.P. Chen, S.C.-L. H, C. Briceno, R. Chini, . Bukowiecki, D.P. Dimitrov, D. Kjurkchieva, E.L.N. Jensen, D.H. Cohen, Z.-Y. Wu, T. Pribulla, M. Vako, V. Krushevska, J. Budaj, Y. Oasa, A.K. Pandey, M. Fernandez, A. Kellerer, C. Marka

With an apparent cluster diameter of 1.5° and an age of ~4 Myr, Trumpler 37 is an ideal target for photometric monitoring of young stars as well as for the search of planetary transits, eclipsing binaries and other sources of variability. The YETI consortium has monitored Trumpler 37 throughout 2010 and 2011 to obtain a comprehensive view of variable phenomena in this region. In this first paper we present the cluster properties and membership determination as derived from an extensive investigation of the literature. We also compared the coordinate list to some YETI images. For 1872 stars we found literature data. Among them 774 have high probability of being member and 125 a medium probability. Based on infrared data we re-calculate a cluster extinction of 0.9-1.2 mag. We can confirm the age and distance to be 3-5 Myr and ~870 pc. Stellar masses are determined from theoretical models and the mass function is fitted with a power-law index of alpha=1.90 (0.1-0.4 solar masses) and alpha=1.12 (1-10 solar masses).

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Posts: 131433
Date:
IC1396A
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A New View of the Elephant's Trunk Nebula

IC1396_full_s.jpg

The Elephant's Trunk nebula, formally known as IC1396A, is a cloud of gas and dust located 2400 light years from Earth in the constellation Cepheus. The Elephant Trunk is part of a larger region of ionised gas illuminated by a nearby massive O-type star (located outside the image to the left). Radiation and winds from this hot star compress and ionise the edges of cloud, resulting in the bright "ionisation fronts" seen in this image.
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Posts: 131433
Date:
RE: IC1396
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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.

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Posts: 131433
Date:
Elephant Trunk Nebula
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Title: The Elephant Trunk Nebula and the Trumpler 37 cluster: Contribution of triggered star formation to the total population of an HII region
Authors: Konstantin V. Getman (1), Eric D. Feigelson (1,2), Aurora Sicilia-Aguilar (3), Patrick S. Broos (1), Michael A. Kuhn (1), Gordon P. Garmire (1) ((1) Penn State University, (2) Center for Exoplanets and Habitable Worlds at PSU, (3) Universidad Aut noma de Madrid)

Rich young stellar clusters produce HII regions whose expansion into the nearby molecular cloud is thought to trigger the formation of new stars. However, the importance of this mode of star formation is uncertain. This investigation seeks to quantify triggered star formation (TSF) in IC 1396A (a.k.a., the Elephant Trunk Nebula), a bright rimmed cloud (BRC) on the periphery of the nearby giant HII region IC 1396 produced by the Trumpler 37 cluster. X-ray selection of young stars from Chandra X-ray Observatory data is combined with existing optical and infrared surveys to give a more complete census of the TSF population. Over 250 young stars in and around IC 1396A are identified; this doubles the previously known population. A spatio-temporal gradient of stars from the IC 1396A cloud toward the primary ionising star HD 206267 is found. We argue that the TSF mechanism in IC 1396A is the radiation-driven implosion process persisting over several million years. Analysis of the X-ray luminosity and initial mass functions indicates that >140 stars down to 0.1 solar masses were formed by TSF. Considering other BRCs in the IC 1396 HII region, we estimate the TSF contribution for the entire HII region exceeds 14-25% today, and may be higher over the lifetime of the HII region. Such triggering on the periphery of HII regions may be a significant mode of star formation in the Galaxy.

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Posts: 131433
Date:
RE: IC1396
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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.

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Posts: 131433
Date:
IC 1396 Nebula
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IC1396, also called the Elephant's Trunk Nebula, is one of the largest emission nebulae in the Northern Sky with a diameter of 3 degrees. It is a giant cloud of gas and dust at a distance of 2400 light years from Earth. It is illuminated by the massive O-type star HD 206267 in the centre. Radiation and winds from this hot star are thought to compress parts of the cloud and trigger star formation.
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Posts: 131433
Date:
RE: IC1396
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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.

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Posts: 131433
Date:
IC 1396
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Title: Wide-Field Survey of Emission-line Stars in IC 1396
Authors: M. Nakano, K. Sugitani, M. Watanabe, N. Fukuda, D. Ishihara, M. Ueno

We have made an extensive survey of emission-line stars in the IC 1396 HII region to investigate the low-mass population of pre-main sequence (PMS) stars. A total of 639 H-alpha emission-line stars were detected in an area of 4.2 deg² and their i'-photometry was measured. Their spatial distribution exhibits several aggregates near the elephant trunk globule (Rim A) and bright-rimmed clouds at the edge of the HII region (Rim B and SFO 37, 38, 39, 41), and near HD 206267, which is the main exciting star of the HII region. Based on the extinction estimated from the near-infrared (NIR) colour-colour diagram, we have selected pre-main sequence star candidates associated with IC 1396. The age and mass were derived from the extinction corrected colour-magnitude diagram and theoretical pre-main sequence tracks. Most of our PMS candidates have ages of < 3 Myr and masses of 0.2-0.6 Mo. Although it appears that only a few stars were formed in the last 1 Myr in the east region of the exciting star, the age difference among subregions in our surveyed area is not clear from the statistical test. Our results may suggest that massive stars were born after the continuous formation of low-mass stars for 10 Myr. The birth of the exciting star could be the late stage of slow but contiguous star formation in the natal molecular cloud. It may have triggered to form many low-mass stars at the dense inhomogeneity in and around the HII region by a radiation-driven implosion.

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Posts: 131433
Date:
Trumpler 37
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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.

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Posts: 131433
Date:
RE: IC1396
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Title: Sequential star formation in a cometary globule (BRC37) of IC1396
Authors: Hisashi Ikeda, Koji Sugitani, Makoto Watanabe, Naoya Fukuda, Motohide Tamura, Yasushi Nakajima, Andrew J. Pickles, Chie Nagashima, Takahiro Nagayama, Hidehiko Nakaya, Makoto Nakano, Tetsuya Nagata

We have carried out near-IR/optical observations to examine star formation toward a bright-rimmed cometary globule (BRC37) facing the exciting star(s) of an HII region (IC1396) containing an IRAS source, which is considered to be an intermediate-mass protostar. With slit-less spectroscopy we detected ten H_alpha emission stars around the globule, six of which are near the tip of the globule and are aligned along the direction to the exciting stars. There is evidence that this alignment was originally towards an O9.5 star, but has evolved to align towards a younger O6 star when that formed. Near-IR and optical photometry suggests that four of these six stars are low-mass young stellar objects (YSOs) with masses of ~0.4 M_sun. Their estimated ages of ~1 Myr indicate that they were formed at the tip in advance of the formation of the IRAS source. Therefore, it is likely that sequential star formation has been taking place along the direction from the exciting stars towards the IRAS source, due to the UV impact of the exciting star(s). Interestingly, one faint, H_alpha emission star, which is the closest to the exciting star(s), seems to be a young brown dwarf that was formed by the UV impact in advance of the formation of other YSOs at the tip.

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