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The Orion Nebula Cluster
as a Paradigm of Star Formation
Talk Abstracts

Listing of Talk Abstracts

Orion Revisited: The Foreground Population to Orion A
Prof.  Joao Alves (U Vienna)
The existence of a young foreground population to Orion A has been long recognized in the literature, although very little work has been done towards its characterization. We present here the first results of a program designed to bring a better understanding of this foreground population. We used the denser regions the Orion A cloud to block optical background light, effectively isolating the stellar population in front of it. We then used a multi-wavelength observational approach to characterize the cloud’s foreground stellar population. We find that there is a rich stellar population in front of the Orion A cloud, from B-stars to M-stars, with a distinct 1) spatial distribution; 2) luminosity function; and 3) velocity dispersion from the reddened population inside the Orion A cloud. The spatial distribution of this population peaks strongly around NGC 1980 (iota Ori) and is, in all likelihood, the extended stellar content of this poorly studied cluster. We infer an age of ∼4−5 Myr for NGC 1980 and estimate a cluster population, or better, an extended population, of about 2000 stars, which makes it one of the most massive clusters in the entire Orion complex. This newly found population overlaps significantly with what is currently assumed to be the ONC and the L1641N populations, and can make up for more than 10−20% of the ONC population (30−60% if the Trapezium cluster is excluded from consideration). What is currently taken in the literature as the ONC is then a mix of several intrinsically different populations, namely 1) the youngest population, including the Trapezium cluster and ongoing star formation in the dense gas inside the nebula; 2) the foreground population, dominated by the NGC 1980 cluster; and 3) the poorly constrained population of foreground and background Galactic field stars. Conclusions. Our results support a scenario where the ONC and L1641N are not directly associated with NGC 1980, i.e., they are not the same population emerging from its parental cloud, but are instead distinct overlapping populations. The nearest massive star formation region and the template for massive star- and cluster formation models is then substantially contaminated by the foreground stellar population of the massive NGC 1980 cluster, formed about 4–5 Myr ago in a different, but perhaps related, event in the larger Orion star formation complex. This result calls for a revision of most of the observables in the benchmark ONC region (e.g., ages, age spread, cluster size, mass function, disk frequency, etc.).
Simulating and Analyzing Two-Fluid Turbulence in Molecular Clouds
Dinshaw Balsara (University of Notre Dame)
The star-forming plasma in molecular clouds is indeed partially ionized. The low level of ionization in the plasma makes it possible to sustain several interesting phenomena that do not occur in single fluid MHD turbulence. In this talk we first analyze MHD wave propagation in such a partially ionized plasma, showing that only certain waves might propagate on the shorter length scales where ions and neutrals decouple. This length scale, known as the ambipolar diffusion length scale, is also interesting because the formation of molecular cores takes place on those length scales. We then simulate this two fluid turbulence and analyze its properties. Several trends are shown to conform to the theoretical analysis in the previous paragraph. Based on that, we extract observational diagnostics associated with linewidth-size relationships of isophotologues and also density PDFs. The first diagnostic is shown to match up with observed data. The second diagnostic is entirely new, and awaits observational confirmation. Taken together, these two diagnostics might give us a different handle on the direction of the magnetic field in three dimensions. Further theoretical analysis of the turbulence is also presented.
Young Complexes in NGC 6822 - Orion's Next Evolutionary Step at 1000 Times the Distance?
Dr.  Lynn Carlson (Leiden Observatory)
I examine of HII region evolution and Photodissociation Region (PDR) properties in relation to stellar populations in three regions of NGC 6822. This Local Group dwarf galaxy has a metallicity less than half Solar and lies 490kpc away, approximately 1000 times more distant than the Orion Nebula. It is close enough that stellar populations are resolved as are nebular structures of evolving young HII regions; we can see that these regions are being driven by O/B stars. We model the radiation field directly from the stellar content and find that it matches the radiation structure determined from far-infrared (FIR) line ratios from Herschel/PACS spectral maps (in [CII], [OI] 63micron, and [OIII] 88micron) and derived total FIR maps from dust spectral energy distribution fitting. This allows us to constrain the radiation and density structure of the PDR. With imaging from HST and HII region modeling, we characterize the expansion of young HII regions. Finally, with mid-IR [SIII] line ratios, we map the ionized gas density. At this distance, Spitzer images are insufficient to confirm continuing star formation in these regions via the identification of Young Stellar Objects (YSOs), but the evolutionary picture and ISM density distribution indicate that we are likely to find YSOs with the advent of JWST. These regions are similar to Orion in that they are powered by a few O/B stars with their large-scale structure on the order of a few parsecs but at lower metallicities. They are somewhat larger then Orion, though still less than 20pc, with stellar content 2-4Myr older than that of Orion. In these senses, they can be seen as obsrevational models of Orion's next evolutionary step.
YSOVAR: Probing Mid-Infrared Variability in Orion and Beyond
Dr.  Ann Marie Cody (California Institute of Technology)
It has been known for decades that young stellar objects (YSOs) display significant optical variability on timescales from hours to years. Yet it has only recently come to light that YSOs and their disks are also highly variable in the infrared. Much of this knowledge is thanks to YSOVAR-- the first sensitive, wide-area, mid-infrared time series photometric monitoring of star-forming regions on times of hours to years. This campaign covered a dozen young clusters, spending half of the time on the Orion Nebula Cluster. I will describe the different types of variability identified and implications for the physical processes occuring on and around disk-bearing YSOs. YSOVAR has also prompted the discovery of six new eclipsing binaries in the ONC, providing new mass and radius benchmarks for pre-main-sequence stellar evolution models.
The Pre-Main Sequence Population of the ONC:Optical Studies
Dr.  Nicola Da Rio (University of Florida)
Obtaining a complete, accurate census of stellar parameters in the ONC is critical to understand the IMF and the star formation history in the region, and provides a necessary foundation for many complementary studies in the region. I will introduce the long-standing efforts to characterize observationally the ONC population, focusing on our recent developments in this direction, the open problems, and the future improvements. I will analyze the critical issues of understanding completeness and accuracy of stellar parameters in Orion - and their scientific implications - and introduce the current standpoint about IMF and age spread in the cluster.
Superthermal Electrons: The Solution to the Chemical Abundance Discrepancy Problem in HII Regions?
Prof.  Michael Dopita (RSAA, The Australian National University)
Recently, Nicholls et al. (2012), inspired by in situ observations of solar system astrophysical plasmas, suggested that the electrons in HII regions are characterised by a $kappa$-distribution of electron energies rather than by a simple Maxwell- Boltzmann distribution. This provides a high-energy tail in the electron distribution, and we show that - while representing only a mild deviation from equilibrium - this is sufficient to strongly influence the inferred chemical abundances. This resolves the long-standing discrepancy (a factor of two!) between the temperature + Ionisation correction factor method, the strong line method, and the recombination line methods used in the derivation of chemical abundances in HII regions. We suggest likely physical causes for the presence of high-energy electrons in HII regions such as the Orion Nebula.
The Orion Nebula Cluster and the MYStIX Survey
Eric  Feigelson (Pennsylvania State University )
Since its detection as a faint diffuse X-ray source by the UHURU satellite in the 1970s, the Orion Nebula Cluster (ONC) has been the principal template for the study of young stellar populations in the X-ray band. Due to magnetic flaring in lower mass stars and shocked winds from high mass stars, X-ray observations are surprisingly effective at uncovering stellar populations in star forming regions. Here we compare the ONC and its environs with 19 other regions within 4 kpc that constitute the Massive Young Star-Forming Complexes in Infrared and X-ray (MYStIX) project. Archive observations by the Chandra X-ray Observatory, Spitzer Space Telescope and UK Infrared Telescope are combined to produce new rich catalogs of pre-main sequence members. Early MYStIX studies compare the structure of the ONC and other young clusters that may lead to new insights into cluster formation astrophysics. Using a new X-ray/infrared stellar age estimator, age gradients within and between subclusters of star forming complexes are found. Later studies will examine topics such as OB wind feedback as seen in the hot bubble southwest of the ONC.
Radio Variability and the X-Ray-Radio Connection -- a Deep JVLA/Chandra View of the Orion Nebula Cluster
Dr.  Jan Forbrich (University of Vienna/Smithsonian)
High-energy processes in Young Stellar Objects (YSOs) can be observed both in X-rays and in the centimetric radio wavelength range. While the past decade has brought a lot of progress in the field of X-ray observations of YSOs, (proto)stellar centimetric radio astronomy has only recently begun to catch up with the advent of the newly expanded Karl G. Jansky Very Large Array (JVLA). The enhanced sensitivity is fundamentally improving our understanding of YSO radio properties by providing unprecedented spectral as well as temporal resolution. As a result, it is becoming easier to disentangle coronal-type nonthermal radio emission emanating from the immediate vicinity of YSOs from thermal emission on larger spatial scales, for example ionized material at the base of outflows. Of particular interest is the correlation of the by now relatively well-characterized X-ray flaring variability with nonthermal radio variability. We have observed the Orion Nebula Cluster, a benchmark for X-ray and radio studies of YSOs, in about 24 hours of simultaneous observations using Chandra and the JVLA. Our first results provide new insights into the cluster, highlighting the capabilities of the JVLA for radio continuum observations of YSOs in general.
Cinematic Scientific Visualization of the Orion Nebula
Lisa Frattare (STScI)
For the IMAX film "Hubble 3D", our team created a three-dimensional model of the Orion Nebula based on Hubble data. We will present the analysis, image processing, virtual modelling, and visualization pipeline that went into the production of the sequence for the film. In addition, we will showcase new techniques and sequences created not on a supercomputer cluster, but on a desktop workstation.
Dynamics of the Orion Nebula: Stars
Prof.  Lee Hartmann (Univ. of Michigan)
I will suggest an overall picture of the formation and evolution of the ONC, building on our current knowledge of the kinematics and structure of the stellar population, and suggest how future observations may test this picture.
Dynamics of the Orion Nebula
William Henney (CRyA, UNAM)
I review what we know about the dynamics of photoionized regions in general and the Orion Nebula in particular. I will cover the fundamental physical processes that are important in setting ionized gas in motion: thermal pressure gradients, stellar winds, jets and other outflows, radiation pressure, magnetic fields, instabilities, turbulence. I will also describe results from recent numerical simulations and observations of the kinematics of the ionized gas in Orion. Some questions that I will address are: Why does Orion not look like a Strömgren sphere? What is the cause of all of the structure that we see? Does the stellar wind have any effect on the dynamics of the nebula? When is it OK to just ignore the dynamics?
The Orion Nebula Cluster as a Paradigm of Star Formation
Lynne A.  Hillenbrand  (Caltech)
Over one and a quarter centuries of scientific interest in the Orion Nebula -- now including investigations spanning the electromagnetic spectrum -- has led us to our current understanding of physical processes in the region. This "Opening for Orion" talk will review some gems from the past and summarize outstanding questions in star formation to be discussed in more detail by other speakers.
ALMA Cycle 0 Observation of Orion Radio Source I
Dr.  Tomoya Hirota (National Astronomical Observatory of Japan)
We present recent results of high-resolution ALMA Cycle 0 observations of the Orion KL region with a resolution of 0.5". We detect submillimeter H2O lines at ALMA bands 7 (300 GHz) and 9 (600 GHz) toward the Orion Radio Source I. The distributions of the H2O lines show systematic velocity gradients along the northwest-southeast direction, which is perpendicular to the molecular outflow traced by the 22 GHz H2O masers and thermal SiO lines. The velocity gradient is consistent with that of the SiO masers observed with previous VERA and VLBA observations. It is a strong evidence of rotation about the northeast-southwest axis. In addition, we also detect continuum emissions at ALMA bands 6 (200 GHz) and 7 toward Source I. We will discuss about physical and dynamical properties of a circumstellar disk around Source I.
Ages and Age Spreads in the Orion Nebula Cluster
Prof.  Rob Jeffries (Keele University)
I will review what we know and don't know about the ages of stars in the ONC and address the thorny problem of how much of an age spread there is in the ONC population. Alternative age indicators will be compared with isochronal ages. The influence of both measurement and theoretical uncertainties will be discussed. Finally, I will touch on whether contamination by a foreground population influences these considerations.
Star Formation in Massive Young Clusters and the Galactic Center
Jessica Lu (IfA, Hawaii)
I will present our work on understanding how the star formation process changes in extreme environments such as the Galactic center and massive young clusters. We measure the outcome of the star formation process - the initial mass function (IMF) - using high resolution infrared imaging and precise astrometry to kinematically seperate star cluster members and contaminating field stars. We find a top-heavy IMF in Galactic center clusters and compare this with the IMF in Milky Way disk clusters, including Orion. I will also discuss how astrometry can be used on nearby clusters, such as Orion, in order to test theories of star formation that predict different internal kinematics and ejection rates in clusters.
Low-mass Stars and Brown Dwarfs in the Orion Nebula Cluster
Prof.  Kevin  Luhman  (Pennsylvania State University )
I will review recent progress on identifying and characterizing the low-mass stars and brown dwarfs in the Orion Nebula Cluster.
The Orion Nebula Cluster as a Benchmark for the Study of the Accretion Process.
Carlo Felice Manara (European Southern Observatory)
The HST Treasury Program on the Orion Nebula Cluster provided us with the most complete and detailed picture of one of the most interesting nearby stellar nursery. In particular, our understanding of the accretion process, which has always been limited by the scarcity of large and homogeneous samples, has hugely benefit from this large sample. While reporting our main results obtained using this dataset in the understanding of the accretion process, I will also show which are the still open and tantalizing questions related to this topic, and how the ONC can still reveal us some secrets of the star and planet formation mechanism. I will focus in particular on our recent result related to the exploration (and partial solution) of the nature of older disks still active and capable of forming planets, which was addressed on two candidate "old" objects in the ONC.
Zooming Out on the ONC: Spitzer and Herschel Surveys of Dusty YSOs in the Orion Molecular Clouds
Prof.  Tom  Megeath  (University of Toledo)
Zooming Out on the ONC: Spitzer and Herchel Observations of Dusty YSOs in the Orion Molecular Clouds: Infrared Surveys with the Spitzer and Herschel space telescopes have provided an unprecedented census of dusty young stellar objects (YSOs) in the Orion Molecular Clouds. We explore the results of these surveys, starting with a study of the internal structure of the ONC using Spitzer data augmented with the COUP survey; these data show a dense concentration of stars which begins to follow the elongated structure of the parental molecular cloud at radii beyond 0.1 pc. We then examine the bulk properties of the ONC and the other clusters in the Orion clouds to ascertain how the properties of clusters depend on the number of members. This analysis shows that the peak stellar surface density of clusters is correlated with the total number of members. As we continue to zoom out, an examination of the entire Orion cloud complex shows that the ONC is a density peak in a population of embedded low mass stars extending over 80 pc. We use the diverse range of environmental conditions present in the Orion cloud complex, from the dense ONC to relatively isolated star formation in Lynds 1641, to examine the relationship between the column density of the natal gas, the YSO surface density, and the incidence of binaries.
Orion Versus ORION: Comparing Simulations of Star Formation with Observations
Dr.  Stella  Offner  (Yale University )
As the nearest massive star forming region, Orion provides an important laboratory for understanding star formation. However, the details of star formation are difficult to recover due to high-optical depth, confusion, projection effects and limited resolution. Consequently, numerical simulations are essential for investigating the nonlinear, multi-physics process of star formation and exploring unresolved underlying properties. However, hydrodynamical simulations, which have full 3D physical information, require radiative post-processing to produce synthetic data that can be directly compared with observations of molecular spectra and continuum emission. In this talk, I will discuss synthetic observations of ORION simulation data. I will compare these with Orion observations of core structure, protostellar kinematics, and protostellar luminosities and then reflect on remaining modeling challenges.
Low-mass Star Formation in the Local Group
Prof.  Nino Panagia (STScI)
We have undertaken a systematic study of pre-main-sequence (PMS) stars spanning a wide range of masses (0.5-4 M_sun), metallicities (0.1-1 Z_sun) and ages (0.5-30 Myr). We have used the Hubble Space Telescope to identify and characterize a large sample of PMS objects in several star forming regions in the Magellanic Clouds, so far including 30 Doradus, the SN1987A field and NGC 1850 in the LMC and NGC 346 and NGC 602 in the SMC, and have compared them to PMS stars in similar regions in the Milky Way, such as NGC 3603 and Trumpler 14. Thanks to a novel method that we have developed to combine broad-band (V, I) photometry with narrow-band Hα imaging, we have determined the physical parameters (temperature, luminosity, age, mass, and mass accretion rate) of more than 3,000 bona-fide PMS stars still undergoing active mass accretion. This is presently the largest and most homogeneous sample of PMS objects with known physical properties and includes not only very young objects, but also PMS stars older than 10-20 Myr that are approaching the main sequence. We will present and discuss the current results of our study, including the fact that the mass accretion rate appears to scale with the first power of the stellar mass, and to decrease with the square root of the age, and approximately with the third root of the metallicity. Thus, the accretion rates for stars of the same mass and age are systematically higher in the Magellanic Clouds than in the Milky Way. These results are bound to have important implications for, and constraints on our understanding of the star formation processes in the Universe.
Local-Density Driven Clustered Star Formation: Model and Implications
Dr.  Genevieve Parmentier (Heidelberg University)
I present a new semi-analytical model for the early evolution of star clusters. This model associates the observed volume density profile of molecular clumps with a locally-defined -- radially-varying -- free-fall time. In this class of models, molecular clumps are characterised by a radial gradient of the star formation efficiency. The model explains naturally: (1) The relation between the local surface densities of gas and young stellar objects observed in molecular clouds of the solar neighbourhood. (2) The growth sequence of surface-density-limited embedded clusters in the cluster radius-density plane. (3) The range of stellar age spreads in star clusters with different densities. I will also discuss how such a model affects our predictions of star cluster survival after the expulsion of their residual star-forming gas.
Beyond Orion: Bridging the Gap to Massive Young Clusters and OB Associations
Dr.  Mubdi Rahman (Johns Hopkins University)
The Orion star forming region has played a crucial role in our understanding of the formation and evolution of young stellar clusters. From the structure and statistics of the embedded stellar cluster, the dynamics and energetics of its natal material, and the interplay between the stars and the gas, the Orion region has provided a template to how stars form in our Galaxy. However, both theoretical and observational work over the past decade has begun to show just how atypical the compact, relatively low mass region is. Observations are beginning to reveal that massive OB associations dominate the star formation within the Galaxy, rather than the compact, less massive Orion-like clusters. In this talk, I will discuss how we bridge the gap between the view of star formation that arises from the Orion Nebula to the most active regions in the Galaxy.
Binarity in the ONC
Bo Reipurth (University of Hawaii)
Observations at high spatial resolution of the stellar population in the ONC has revealed a binary frequency that is about the same as for the field population. This is in contrast to less densely populated star forming associations, which have many more binaries, and it suggests that the initial multiple population of the ONC has already been significantly altered. The role of diverse environments in dynamically processing an original binary population is discussed, as well as the internal dynamical processes in higher-order multiple systems which also play an important role in shaping the present-day population of hard and soft binaries in the ONC.
High-Amplitude Near-Infrared Variability in the Orion Nebula Cluster
Mr.  Thomas Rice (University of Michigan)
We have carried out deep, comprehensive NIR time-series observations of the Orion Nebula Cluster using WFCAM on UKIRT, in an 0.9 x 0.9 degree J, H, K survey comprising ~100 nights in a ~900 day window. Out of 14728 monitored objects brighter than J~20.5, we find 1202 highly variable stars with a Stetson variability index exceeding 1.0, including 539 periodic sources with periods between 2 and 50 days. We have calculated variability properties separately for Class I, II, and III objects, and find that Classes I and II have statistically larger amplitude variability than Class III stars. Many stars have significantly variable J-H and H-K color terms; most of the Class II color-variables show color changes that are consistent with changes in dust reddening, but a substantial fraction show color changes that indicate changes in accretion rate or accretion structure. We report four previously unknown PMS eclipsing binary candidates, along with a wealth of long-duration and high-amplitude variability not seen before with such detail. The 1202 JHK lightcurves and associated data will be made available electronically and in an ApJ paper shortly.
Hubble Tarantula Treasury Survey: Unraveling Tarantula’s Web
Elena  Sabbi (Space Telescope Science Institute )
The Tarantula Nebula in the Large Magellanic Cloud is often considered as on of the few starbursts in the Local Group and the most promising test bed to investigate the conditions under which star formation occurs in more distant starburst galaxies and/or at high-redshift. The Hubble Tarantula Treasury Program is a panchromatic survey of the Tarantula Nebula from the near UV to the near IR. Observations started nine months ago and will end at the beginning of October. We will present for the first time the color-magnitude diagrams derived from the analysis of all the filters, and will discuss the spatial distribution of the various stellar populations in the context of star cluster formation and evolution.
The Orion Nebula in the IR as Seen by SOFIA and Herschel.
Mr.  Francisco Salgado (Leiden Observatory)
Dust grains are an important constituent of the interstellar medium (ISM), playing a major role in a variety of processes, such as star and planet formation galactic extinction gas heating in cold environments and in the chemistry of gas in cold and dense regions. While the composition and properties of dust are well characterized in the diffuse ISM such properties are expected to change depending on the environment. New telescopes (Herschel and SOFIA) allow us to study the emission of dust grains in the infrared regime with high angular resolution. Here, we present observations towards the Orion nebula and report our analysis of the physical properties of dust in terms of the spatial distribution, temperature and mass. We also discuss the interaction of dust and gas in the Orion Bar, the prototypical photodissociation region.
Empirical Constraints on the Masses and Radii of Pre-Main-Sequence Stars from Eclipsing Binaries in Orion
Prof.  Keivan  Stassun  (Vanderbilt University )
We summarize the state of searches for eclipsing binary stars in the Orion Nebula Cluster, including objects with brown dwarf masses up to massive stars, and we summarize the empirically measured masses and radii for the stars in these systems. We discuss how well the various models of pre-main-sequence stellar evolution compare to the empirical measurements. We also highlight a few exemplar systems that reveal the role of chromospheric activity in modifying the radii and temperatures of young, low-mass stars and brown dwarfs, and that demonstrate the dynamical influence of the tertiary stars that are so commonly found in these systems.
Orion's Guide to Massive Star Formation
Prof.  Jonathan Tan (University of Florida)
The Orion Nebula Cluster is the closest region of massive star formation. I review what we know about how massive stars are forming and how they have formed in this cluster, and what lessons are learned for massive star formation in general.
Characterizing a Herschel-detected Sample of Very Red Protostars in Orion
Dr.  John Tobin (NRAO)
We have detected a sample of the reddest, and potentially youngest, protostars in the Orion molecular clouds using data obtained with the PACS instrument onboard the Herschel Space Observatory as part of the Herschel Orion Protostar Survey (HOPS). A total of 55 new protostar candidates are detected at 70 um and 160 um that are either undetected or too faint in the Spitzer/MIPS 24 um band to be reliably classified as protostars. We find that the 11 reddest new protostar candidates are free from extra-galactic contamination and can thus be reliably explained as protostars. We combine our sample with the previsouly identified Spitzer protostar sample to select the reddest sources in Orion; we find 18 sources (11 of which are new) that have extremely red 70/24 um colors. We name these sources "PACS Bright Red sources", or PBRs. We conclude that the red colors of the PBRS can only be explainded by high envelope densities, the highest Class 0 envelope densities / masses of all the observed protostars in Orion. We have obtained follow-up CARMA 3mm continuum and CO (J=1-0) maps toward some of the reddest sources. We find that many sources have 3 mm luminosities comparable to the brightest known low-mass protostars and for some sources most dust emission is originating from spatial scales less than ~5" (2000 AU) indicating either steep density profiles or dense compact structures. We detect evidence of compact outflows in some cases and non detections in others. We have also obtained follow-up observations toward a sub-sample of the PBRs using the PACS spectrometer onboard Herschel, observing the full spectral range between 55 and 190 microns to characterize the high-J CO and water emission which is indicative of shock-heating in the outflows. We detect CO and water lines in 5 of 9 observed sources; only those with bolometric luminosities greater than 1.7 L_sun show detectable lines. While sample overlap between the CARMA and PACS spectroscopy is not complete, we do not detect outflow activity in the CO (J=1-0) line toward sources that do not have detected lines in the PACS spectra. The compact outflows are consistent with the PBRs being very young sources with recently launched outflows and creating shocks strong enough to produce high-J water and CO lines. Those sources without outflow detections may simply have outflows that are too weak to produce detectable lines in the current data.
Early Stages of Star Formation in NGC 6334
Sarah Willis (Harvard-Smithsonian Center for Astrophysics)
NGC 6334 is a giant molecular cloud complex with high far-infrared luminosity located at a distance of 1.6 kpc. We have used near-infrared and Spitzer IRAC observations of NGC 6334 to isolate the YSO population and to study the rate and efficiency of star formation. Using our source catalog of over 2,000 Young Stellar Objects we have identified multiple new sites of ongoing star formation activity along filamentary structures extending tens of parsecs beyond the central molecular ridge of NGC 6334. I will present some of our ongoing work using Herschel and SMA observations to probe the earliest stages of star formation in this complex.
An X-Ray Survey of the Young Stellar Population of LYNDS 1641, the ONC and Iota Orionis
Dr.  Scott Wolk (Harvard-Smithsonian CfA)
We present an XMM-Newton survey of the part of the Orion A cloud and the Orion Nebula. This survey includes the Lynds 1641 (L1641) dark cloud, a region of the Orion A cloud with very few massive stars and hence a relatively low ambient UV flux, and the region around the O9 III star ι Orionis. In addition to proprietary data, we used archival XMM data of the Orion Nebula Cluster (ONC) to extend our analysis to a major fraction of the Orion A cloud. We have detected 1060 X-ray sources in L1641 and the ι Ori region. About 94% of the sources have Two Micron All Sky Survey and Spitzer counterparts, 204 and 23 being Class II and Class I or protostar objects, respectively. In addition, we have identified 489 X-ray sources as counterparts to Class III candidates, given they are bright in X-rays and appear as normal photospheres at mid-IR wavelengths. The remaining 205 X-ray sources are likely distant active galactic nuclei or other galactic sources not related to Orion A. We find that Class III candidates appear more concentrated in two main clusters in L1641. The first cluster of Class III stars is found toward the northern part of L1641, concentrated around ι Ori. The stars in this cluster are more evolved than those in the Orion Nebula. We estimate a distance of 300-320 pc for this cluster showing that it is in the foreground of the Orion A cloud. Another cluster rich in Class III stars is located in L1641 South and appears to be a slightly older cluster embedded in the Orion A cloud. It appears that the ejection event of Mu Columba and AE Auriga by Iota Ori did not occur in the ONC. This is found to be an older, foreground cluster. Furthermore, other evolved Class III stars are found north of the ONC toward NGC 1977.