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The Orion Nebula Cluster
as a Paradigm of Star Formation
Poster Presentations

Listing of Poster Abstracts

Cep OB3b: An Older Orion Analogue
Mr.  Thomas Allen (University of Toledo)
We present results from an extensive multi-wavelength survey of Cep OB3b, one of the largest young clusters within 1 kpc of the Sun. By combining Spitzer, Chandra and visible light observations of the cluster, we estimate that Cep OB3b has a membership of approximately 3000 young stars in a region of 10 x 7 pc (Allen et al. 2012). Similar in membership and overall size to the ONC, Cep OB3b is older and more evolved, with most of the young stars located in a cavity with a V-band extinction of less than 2.5 magnitudes. Star formation is still occurring in the molecular clouds that border the cavity. Literature age estimates for this region give a range between 3-6 Myr (Mayne et al. 2007, Littlefair et al. 2010, Bell et al. 2013). To construct an accurate HR diagram, we derive an extinction law for this region between 500 nm and 2.2 um and find it intermediate between that of dense clouds (R~5) and that of the diffuse ISM (R~3). We then use hetospec MMT spectroscopy of 800 members to construct the HR diagram. Compared to the isochrones of Baraffe (1998), these data give an isochronal age of 3 Myr using the VLBA parallax distance for the nearby Cep A region of 700 pc. We find that certain cluster properties, such as the disk fraction and rotation period distribution, vary spatially across the cluster. We analyze whether these variations are due to environmental differences or a mixture of ages in the cluster. In the case of the disks, we conclude that the variations are due to a mixture of ages.
Diffracto-Astrometry of the Orion Trapezium Stars Derived from HST Archive Images
Rafael  Costero  (Universidad Nacional Autonoma de Mexico )
The Diffracto–Astrometry technique was used on 44 Hubble Space Telescope Wide Field Planetary Camera 2 images of the Orion Trapezium (OT), taken over a span of 12 years (1995–2007). We measure the relative positions of the six brighter OT components (A to F), and supplement these with measurements taken from the literature, thus extending our analysis time base to ∼ 200 years. For every pair of components we find the relative rate of separation, which enable us to determine the relative kinematics of the system. Component E shows a velocity larger that the OT’s escape velocity, thus confirming that it is escaping from the gravitational pull of this system. Component F is probably a foreground star. Component C is not a runaway star escaping from the BN-KL star formation region, as previously suggested.
Core-Halo Age Gradients in the NGC2024 and ONC Clusters
Konstantin V.  Getman  (Pennsylvania State University )
The MYStIX (Massive Young Star-Forming Complex Study in Infrared and X-ray; Feigelson et al. 2013) project seeks to characterize 20 OB-dominated young star forming regions (SFRs) at distances <4 kpc using photometric catalogs from the Chandra X-ray Observatory, Spitzer Space Telescope, UKIRT and 2MASS surveys. As part of the MYStIX project, we developed a new stellar chronometer that employs near-infrared and X-ray photometry data, AgeJX. Computing AgeJX averaged over MYStIX (sub)clusters reveals previously unknown age gradients across most of the MYStIX regions as well as within some individual rich clusters. Noticeable intra-cluster gradients are seen in the NGC 2024 (Flame Nebula) star cluster and the Orion Nebula Cluster (ONC). In NGC 2024, the age monotonically increases from the core (t~0.1 Myr within R~0.1 pc) towards the inner halo (t~0.9 Myr at R=0.2-0.5 pc) and further towards the periphery of the cluster (t~1.5 Myr at R~1 pc). In the ONC, the age abruptly increases from the core (t~1.2 Myr within R~0.1pc) towards the periphery (t~1.9 Myr at 0.15<R<1 pc). This is based on AgeJX estimates for 0.3-1.2 Mo stars, and is independent of any consideration of OB stars. Possible astrophysical explanations for the core-halo cluster gradients are discussed.
The Structure and Dynamical State of the Orion Nebula Cluster and Other Young Stellar Clusters
Mr.  Michael Kuhn (The Pennsylvania State University)
MYStIX (Massive Young Star-Forming Complex Study in Infrared and X-ray; Feigelson et al. 2013) is a comparative analysis of 20 nearby young stellar clusters -- including the Orion Nebula Cluster (ONC) -- based on X-ray and infrared excess identification of young stellar members. Analysis of the Orion region is based on the Chandra Orion Ultradeep Project (COUP; Getman et al. 2005) and a Spitzer survey of Orion (Megeath et al. 2013). Clusters of young stars in each region are identified using finite mixture models – the sums of isothermal ellipsoids used to model individual (sub)clusters. Maximum likelihood estimation is used to estimate the model parameters and the Akaike Information Criterion is used to determine the number of subclusters. In the MYStIX star-forming regions, ~150 subclusters are found (1 to >10 per region). The distribution of cluster core radii is log-normal, peaked at 0.18 pc (similar to the ONC) with a standard deviation of 0.4 dex. The ONC lies along an inverse relation between the cluster central density and core radius (power law index slightly shallower than -3). In Orion, a layered structure is revealed, including the small, dense BN-KL cluster projected behind the ONC and star formation in filaments to the north of the ONC. We find that the ONC is best fit by a core-halo structure -- two concentric ellipsoids, one representing a dense core and the other representing a halo. Other MYStIX regions with core-halo structures include, RCW 36, RCW 38, and Tr 14. Some MYStIX regions are well fit by a single isothermal ellipsoid, while others show complex clumpiness or linear structures. We are investigating mass segregation, embeddedness, and fractal structure in these different morphological categories.
The Dispersed Population of Dusty Young Stellar Objects in the Orion OB1 association
Brian Mazur (University of Toledo)
We examine the distribution and properties of the population of young stellar objects outside of the molecular gas in the Orion/OB1 association complex. We present an extended map, covering some ∼ 4◦ 5◦, of Spitzer-identified infrared-excess sources in the area of the OB1 association ‘b’ and ‘c’ sub-groups. Observations were taken with Spitzer during the ‘warm mission’ having only two IRAC channels, namely 3.6μm and 4.5μm. These data complements the cryo-mission IRAC four-band observations taken along the molecular gas covering the Orion A and B clouds, from the Lynds 1647 cloud in the south to NGC 2071 in the north (Megeath et al. 2012) and several fields in the OB1c and OB1b associations (Hernandez et al. 2007a, 2007b). Calibrations were standardised to the cryo-mission, and a catalogue of the entire region was assembled, augmented with available 2MASS, MIPS 24 μm and WISE photometry. We use this data to identify dusty young stellar objects with infrared excesses. After investigating the biases induced by only having 2MASS plus two- channel IRAC photometry in the warm mission survey, we present the spatial distribution of the infrared-excesses through the combined on-cloud and off-cloud region. We use this map to examine the spatial relationship between the current episode of star formation in the clouds and the fossil regions of recent star formation in the off-cloud region.
The Curious Morphology and Orientation of Orion Proplyd HST10
Dr.  Ralph Shuping (Space Science Inst.)
HST10 is one of the largest proplyds in the Orion Nebula and is located approximately 1' SE of the Trapezium stars. Unlike other proplyds in Orion, however, the long-axis of HST10 does not align with theta1 Ori C, but is instead aligned with the rotational axis of the HST10 disk. This cannot be easily explained using current photo-evaporation models. In this poster, we present high spatial resolution ground-based near-infrared images of the Orion proplyd HST-10 using Keck/NIRC2 with the Laser Guide Star Adaptive Optics system along with a multi-epoch analysis of HH objects near HST10 using Hubble Space Telescope WFPC2 and ACS cameras. Our narrow-band near-IR images resolve the proplyd ionization front (IF) and circumstellar disk down to 23 AU at the distance to Orion in Br_gamma, He I, H_2, and PAH emission (3.3 micron). Br_gamma and He I emission primarily trace the ionization front (with the disk showing prominently in silhouette), while the H_2 and PAH emission trace the surface of the disk itself. PAH emission also traces small dust grains within the proplyd envelope which is asymmetric and does not coincide with the IF. Multi-epoch HST images of the HST10 field show proper motion of 3 knots associated with HH 517, clearly indicating that HST10 has a jet and/or outflow. We postulate that the orientation of HST10 is driven by this jet/outflow. Furthermore, we postulate that the curious morphology of the PAH emission may be due to the UV-heating of both sides: one side by theta1 Ori C, and the other by theta2 Ori A.
Using CARMA for Large-Area, High-Angular Resolution Mapping of Dense Gas in Nearby Molecular Clouds
Shaye Storm (University of Maryland)
The CARMA Large Area Star formation Survey (CLASSy) is mapping molecular emission across large areas of the nearby Perseus and Serpens Molecular Clouds. With an angular resolution of 7 arcsec, CLASSy probes dense gas on scales from a few thousand AU to parsecs with CARMA-23 and single-dish observations. The resulting maps of N2H+, HCN, and HCO+ J=1-0 trace the kinematics and structure of the high-density gas in regions covering a wide range of intrinsic star formation activity. This poster presents an overview of three completed CLASSy fields, NGC 1333, Barnard 1, and Serpens Main, and then focuses on the dendrogram analysis that CLASSy is using to characterize the emission structure. We have chosen a dendrogram analysis over traditional clump finding because dendrograms better encode the hierarchical nature of cloud structure and better facilitate analysis of cloud properties across the range of size scales probed by CLASSy. We present a new dendrogram methodology that allows for non-binary mergers of kernels, which results in a gas hierarchy that is more true to limitations of the S/N in the data. The resulting trees from Barnard 1 and NGC 1333 are used to derive physical parameters of the identified gas structures, and to probe the kinematic relationship between gas structures at different spatial scales and evolutionary stages. We derive a flat relation between mean internal turbulence and structure size for the dense gas in both regions, but find a difference between the magnitude of the internal turbulence in regions with and without protostars; the dense gas in the B1 main core and NGC 1333 are characterized by mostly transonic to supersonic N2H+ turbulence, while the B1 filaments and clumps southwest of the main core have mostly subsonic N2H+ turbulence. These initial results, along with upcoming work analyzing the completed CLASSy observations, will be used to test current theories for star formation in turbulent molecular clouds.