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Journal articles on the topic 'Orion Nebula Cluster'

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Author: Grafiati

Published: 10 December 2022

Last updated: 28 January 2023

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1

de Albuquerque, R. M. G., J. F. Gameiro, S. H. P. Alencar, J. J. G. Lima, C. Sauty, and C. Melo. "Accretion in low-mass members of the Orion Nebula Cluster with young transition disks." Astronomy & Astrophysics 636 (April 2020): A86. http://dx.doi.org/10.1051/0004-6361/201936694.

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Context. Although the Orion Nebula Cluster is one of the most studied clusters in the solar neighborhood, the evolution of the very low-mass members (M* < 0.25 M⊙) has not been fully addressed due to their faintness. Aims. Our goal is to verify if some young and very low-mass objects in the Orion Nebula Cluster show evidence of ongoing accretion using broadband VLT/X-shooter spectra. Methods. For each target, we determined the corresponding stellar parameters, veiling, observed Balmer jump, and accretion rates. Additionally, we searched for the existence of circumstellar disks through available on-line photometry. Results. We detected accretion activity in three young stellar objects in the Orion Nebula Cluster, two of them being in the very low-mass range. We also detected the presence of young transition disks with ages between 1 and 3.5 Myr.

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2

Fujii, Michiko S., Long Wang, Takayuki R. Saitoh, Yutaka Hirai, and Yoshito Shimajiri. "Formation process of the Orion Nebula Cluster." Proceedings of the International Astronomical Union 16, S362 (June 2020): 258–61. http://dx.doi.org/10.1017/s1743921322001508.

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AbstractThe Orion Nebula Cluster (ONC) is one of the nearest open clusters, which we can directly compare to numerical simulations. We performed a simulation of star cluster formation similar to the ONC using our new N-body/smoothed particle hydrodynamics code, ASURA+BRIDGE. We found that the hierarchical formation of star clusters via clump mergers can explain the observed three peaks in the stellar age distribution as well as the dynamically anisotropic structures of the ONC.

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3

Herbst, W., K. L. Rhode, L. A. Hillenbrand, and G. Curran. "Rotation in the Orion Nebula Cluster." Astronomical Journal 119, no. 1 (January 2000): 261–80. http://dx.doi.org/10.1086/301175.

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4

Garay, Guido. "The Trapezium Radio Cluster of the Orion Nebula." International Astronomical Union Colloquium 120 (1989): 333–38. http://dx.doi.org/10.1017/s0252921100024040.

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Abstract.We review the characteristics and discuss the nature of a dense group of compact radio sources found projected toward the Trapezium cluster of the Orion nebula. There are twenty-six radio sources, with flux densities greater than 2 mJy, clustered within a region of 35” radius around θ1C Orionis, the most luminous star of the Trapezium. The density of radio objects, of 1.4×104 pc-3, is extraordinarily high, about a thousand times greater than the density of stars in typical galactic clusters.

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5

Cunha, Katia, and Verne V. Smith. "Fluorine Abundances in the Orion Nebula Cluster." Astrophysical Journal 626, no. 1 (June 10, 2005): 425–30. http://dx.doi.org/10.1086/429861.

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6

Maggio, A., E. Flaccomio, F. Favata, G. Micela, S. Sciortino, E. D. Feigelson, and K. V. Getman. "Coronal Abundances in Orion Nebula Cluster Stars." Astrophysical Journal 660, no. 2 (May 10, 2007): 1462–79. http://dx.doi.org/10.1086/513088.

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7

Hillenbrand, Lynne A., Stephen E. Strom, Nuria Calvet, K. Michael Merrill, Ian Gatley, Russell B. Makidon, Michael R. Meyer, and Michael F. Skrutskie. "Circumstellar Disks in the Orion Nebula Cluster." Astronomical Journal 116, no. 4 (October 1998): 1816–41. http://dx.doi.org/10.1086/300536.

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8

Scally, A., C. Clarke, and M. J. McCaughrean. "Wide binaries in the Orion nebula cluster." Monthly Notices of the Royal Astronomical Society 306, no. 1 (June 11, 1999): 253–56. http://dx.doi.org/10.1046/j.1365-8711.1999.02513.x.

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9

Reipurth, Bo, Marcelo M. Guimarães, Michael S. Connelley, and John Bally. "Visual Binaries in the Orion Nebula Cluster." Astronomical Journal 134, no. 6 (October 25, 2007): 2272–85. http://dx.doi.org/10.1086/523596.

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10

Köhler, R., M. G. Petr-Gotzens, M. J. McCaughrean, J. Bouvier, G. Duchêne, A. Quirrenbach, and H. Zinnecker. "Binary stars in the Orion Nebula Cluster." Astronomy & Astrophysics 458, no. 2 (September 12, 2006): 461–76. http://dx.doi.org/10.1051/0004-6361:20054561.

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11

Scally, Aylwyn, and Cathie Clarke. "Primordial substructure in the Orion Nebula Cluster." Monthly Notices of the Royal Astronomical Society 334, no. 1 (July 2002): 156–66. http://dx.doi.org/10.1046/j.1365-8711.2002.05503.x.

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12

Palla, Francesco, and Steven W. Stahler. "Star Formation in the Orion Nebula Cluster." Astrophysical Journal 525, no. 2 (November 10, 1999): 772–83. http://dx.doi.org/10.1086/307928.

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13

Köhler, Rainer, Monika G. Petr-Gotzens, Mark J. McCaughrean, Jerome Bouvier, Gaspard Duchêne, Andreas Quirrenbach, and Hans Zinnecker. "Binary Stars in the Orion Nebula Cluster." Proceedings of the International Astronomical Union 2, S240 (August 2006): 114–16. http://dx.doi.org/10.1017/s1743921307003912.

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AbstractWe report on a high-spatial-resolution survey for binary stars in the periphery of the Orion Nebula Cluster, at 5–15 arcmin (0.65 – 2 pc) from the cluster center. We observed 228 stars with adaptive optics systems, in order to find companions at separations of 0.13 – 1.12 arcsec (60 – 500 AU), and detected 13 new binaries. Combined with the results of Petr (1998), we have a sample of 275 objects, about half of which have masses from the literature and high probabilities to be cluster members. We used an improved method to derive the completeness limits of the observations, which takes into account the elongated point spread function of stars at relatively large distances from the adaptive optics guide star. The multiplicity of stars with masses >2 M⊙ is found to be significantly larger than that of low-mass stars. The companion star frequency of low-mass stars is comparable to that of main-sequence M-dwarfs, less than half that of solar-type main-sequence stars, and 3.5 to 5 times lower than in the Taurus-Auriga and Scorpius-Centaurus star-forming regions. We find the binary frequency of low-mass stars in the periphery of the cluster to be the same or only slightly higher than for stars in the cluster core (< 3′ from θ1C Ori). This is in contrast to the prediction of the theory that the low binary frequency in the cluster is caused by the disruption of binaries due to dynamical interactions. There are two ways out of this dilemma: Either the initial binary frequency in the Orion Nebula Cluster was lower than in Taurus-Auriga, or the Orion Nebula Cluster was originally much denser and dynamically more active. A detailed report of this work has been published in Astronomy & Astrophysics (Köhler et al. 2006).

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14

Scally, A., C. Clarke, and M. J. McCaughrean. "Dynamical evolution of the Orion nebula cluster." Monthly Notices of the Royal Astronomical Society 358, no. 3 (April 11, 2005): 742–54. http://dx.doi.org/10.1111/j.1365-2966.2004.08617.x.

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15

Abt, Helmut A., Ruyou Wang, and Octavio Cardona. "Spectroscopic binaries in the Orion Nebula cluster." Astrophysical Journal 367 (January 1991): 155. http://dx.doi.org/10.1086/169611.

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16

Herbig, G. H., and D. M. Terndrup. "The Trapezium cluster of the Orion nebula." Astrophysical Journal 307 (August 1986): 609. http://dx.doi.org/10.1086/164447.

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17

Jeffries, R. D. "The distance to the Orion Nebula cluster." Monthly Notices of the Royal Astronomical Society 376, no. 3 (March 16, 2007): 1109–19. http://dx.doi.org/10.1111/j.1365-2966.2007.11471.x.

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18

Preibisch, Thomas, Gerd Weigelt, and Hans Zinnecker. "Multiplicity of Massive Stars." Symposium - International Astronomical Union 200 (2001): 69–78. http://dx.doi.org/10.1017/s0074180900225072.

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We discuss the observed multiplicity of massive stars and implications on theories of massive star formation. After a short summary of the literature on massive star multiplicity, we focus on the O-and B-type stars in the Orion Nebula Cluster, which constitute a homogenous sample of very young massive stars. 13 of these stars have recently been the targets of a bispectrum speckle interferometry survey for companions. Considering the visual and also the known spectroscopic companions of these stars, the total number of companions is at least 14. Extrapolation with correction for the unresolved systems suggests that there are at least 1.5 and perhaps as much as 4 companions per primary star on average. This number is clearly higher than the mean number of ∼ 0.5 companions per primary star found for the low-mass stars in the general field population and also in the Orion Nebula cluster. This suggests that a different mechanism is at work in the formation of high-mass multiple systems in the dense Orion Nebula cluster than for low-mass stars.

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19

Kim, Dongwon, Jessica R. Lu, Quinn Konopacky, Laurie Chu, Elizabeth Toller, Jay Anderson, Christopher A. Theissen, and Mark R. Morris. "Stellar Proper Motions in the Orion Nebula Cluster." Astronomical Journal 157, no. 3 (February 11, 2019): 109. http://dx.doi.org/10.3847/1538-3881/aafb09.

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20

Farias, Juan P., Jonathan C. Tan, and Laurent Eyer. "Hunting for Runaways from the Orion Nebula Cluster." Astrophysical Journal 900, no. 1 (August 27, 2020): 14. http://dx.doi.org/10.3847/1538-4357/aba699.

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21

van Altena, W. F., J. T. Lee, J. F. Lee, P. K. Lu, and A. R. Upgren. "The velocity dispersion of the Orion Nebula cluster." Astronomical Journal 95 (June 1988): 1744. http://dx.doi.org/10.1086/114772.

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22

Rice, Thomas S., Bo Reipurth, Scott J. Wolk, Luiz Paulo Vaz, and N. J. G. Cross. "NEAR-INFRARED VARIABILITY IN THE ORION NEBULA CLUSTER." Astronomical Journal 150, no. 4 (October 6, 2015): 132. http://dx.doi.org/10.1088/0004-6256/150/4/132.

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23

Köhler, R. "What Causes the Low Binary Frequency in the Orion Nebula Cluster?" International Astronomical Union Colloquium 191 (August 2004): 104–8. http://dx.doi.org/10.1017/s0252921100008575.

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AbstractWe report on the results of a binary survey in the outer parts of the Orion Nebula Cluster, 0.7 to 2 pc from the cluster center. The results should help to decide if the binary formation rate was lower in Orion than in Taurus-Auriga, or if many binaries formed initially, but were destroyed in close stellar encounters. We find that the binary frequency of low-mass stars does not depend on the distance to the cluster center. The companion star frequency of intermediate- to high-mass stars shows a trend to decrease with cluster radius, but the statistical significance of this trend is rather weak.

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24

O'Dell, C. R. "Herbig-Haro Objects in the Orion Nebula Region." Symposium - International Astronomical Union 182 (1997): 39–46. http://dx.doi.org/10.1017/s0074180900061520.

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The Orion Nebula Region has two different systems of objects classified as HH objects. The North System is associated with the H2 fingers seen in the infrared and is probably the result of Rayleigh-Taylor instabilities in shocked material moving into the near side of the giant molecular cloud OMC-1. The South System is associated with source(s) within the Trapezium cluster, with the shocked HH objects occuring where jets from pre-main sequence stars impinge on the neutral lid of material that lies across the front of the Orion Nebula. Such jets are different from those driving other HH objects in that these are passing through photoionized material and two of the Orion jets may have been detected.

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25

McCaughrean, Mark J. "Direct Imaging of Circumstellar Disks in the Orion Nebula." International Astronomical Union Colloquium 163 (1997): 546–48. http://dx.doi.org/10.1017/s0252921100043177.

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AbstractWe present observations of the Orion Nebula made with the Hubble Space Telescope in which a number of stars are seen surrounded by dark silhouettes seen projected against the bright background HII region. We find a variety of morphologies, all consistent with thin circumstellar disks spanning a range of diameters (50 to 1000 AU) and inclination angles (0 to > 80 degrees). The silhouette intensity profiles cannot be fit by standard disk models in which the surface density follows a radial power law with an exponent in the range −0.75 to −1.5. Rather, the data are best fit by opaque inner disks with exponential edges, and we discuss possible physical origins of this apparent truncation. Masses in the range 6 × l026−4 × 1030 g (i.e., up to 0.002 M⊙) are determined for the disks by assuming that the faint light measured from them is background light transmitted through the disk. However, these are strict lower limits on the true disk masses, as most of this light can be accounted for by PSF blurring and scattering in the HST optical train; the present observations are in fact consistent with completely opaque disks. Central stars are seen directly in five of the silhouettes, while the presence of a star is inferred in the sixth, where small reflection nebulae are seen above and below the plane of the near edge-on disk. Optical and near-infrared stellar photometry is consistent with young (~ 1 Myr) low-mass (0.3−1.5 M⊙) stars, with several showing evidence for excess near-infrared emission from the disk inner edge. These direct imaging observations are discussed in the wider context of circumstellar disks in the Orion Nebula and Trapezium Cluster, additionally revealed as compact ionized nebulae (so-called “proplyds”) in the vicinity of the central OB stars, and via infrared (>2µm) excesses in stellar photometry. Overall, disks are found to be common in the cluster (>50% of all stars), implying that they can survive the rigours of life near massive stars.

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26

Herbst, W., C. A. L. Bailer-Jones, R. Mundt, K. Meisenheimer, and R. Wackermann. "Stellar Rotation and Disks in the Orion Nebula Cluster." Symposium - International Astronomical Union 202 (2004): 341–43. http://dx.doi.org/10.1017/s0074180900218196.

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The new Wide Field Imager attached to the MPG/ESO 2.2 m telescope on La Silla, Chile, has been used to monitor ∽2000 stars in the Orion Nebula Cluster (ONC) at 815 nm on 45 nights between 25 Dec 1998 and 28 Feb 1999. Over 400 periodic variables have been found, most or all of which are rotating, spotted T Tauri stars (TTS), more than doubling the number of known rotation periods for cluster members. Masses and ages are available for 335 of these from the literature. We confirm the existence of a bimodal period distribution for stars with M > 0.25 M⊙. A surprising new result is that stars of lower mass tend to rotate faster than higher mass stars, perhaps indicating that their disks have dissipated more rapidly in the harsh cluster environment. In the mass range 0.1 − 1 M⊙ between 40% and 80% of the stars have the variability characteristics of weak-line TTS (WTTS), suggesting that the half-life for accretion disks is ∽1 Myr in this cluster and probably even smaller for the lower mass stars.

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27

Hillenbrand, Lynne A., Aaron S. Hoffer, and Gregory J. Herczeg. "AN ENHANCED SPECTROSCOPIC CENSUS OF THE ORION NEBULA CLUSTER." Astronomical Journal 146, no. 4 (September 5, 2013): 85. http://dx.doi.org/10.1088/0004-6256/146/4/85.

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28

Scally, A., and C. Clarke. "Destruction of protoplanetary discs in the Orion Nebula Cluster." Monthly Notices of the Royal Astronomical Society 325, no. 2 (August 1, 2001): 449–56. http://dx.doi.org/10.1046/j.1365-8711.2001.04274.x.

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29

Herbst, W., C. A. L. Bailer-Jones, R. Mundt, K. Meisenheimer, and R. Wackermann. "Stellar rotation and variability in the Orion Nebula Cluster." Astronomy & Astrophysics 396, no. 2 (December 2002): 513–32. http://dx.doi.org/10.1051/0004-6361:20021362.

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30

Zinnecker, Hans. "On the Origin of the Orion Trapezium System." Proceedings of the International Astronomical Union 3, S246 (September 2007): 75–76. http://dx.doi.org/10.1017/s1743921308015354.

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AbstractNumerical SPH simulations of supersonic gravo-turbulent fragmentation of a protocluster cloud (1000 M⊙) suggest that the cloud develops a few subclusters (star+gas systems) which subsequently merge into a single cluster entity. Each subcluster carries one most massive star (likely multiple), thus the merging of subclusters results in a central Trapezium-type system, as observed in the core of the Orion Nebula cluster.

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31

Vicente, Sílvia, João Alves, Isamu Matsuyama, Hervé Bouy, Loredana Spezzi, Joana Ascenso, Filipe D. Santos, and Timo Prusti. "VLT/NACO detection of a proplyd/jet candidate in the core of Trumpler 14." Proceedings of the International Astronomical Union 6, S275 (September 2010): 412–13. http://dx.doi.org/10.1017/s1743921310016534.

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AbstractThis paper reports the discovery and presents the results of a first analysis of the observed morphology of a candidate external irradiated circumstellar disk/jet system found in the deep core of Trumpler 14, a cluster an order of magnitude more massive than the only cluster where bona-fide proplyds have been found, the Trapezium cluster in the Orion Nebula.

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32

Morel, T. "Abundance study of two magnetic B-type stars in the Orion Nebula Cluster." Proceedings of the International Astronomical Union 9, S307 (June 2014): 451–52. http://dx.doi.org/10.1017/s1743921314007364.

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AbstractWe present the results of an abundance analysis of two magnetic B-type stars in the Orion Nebula Cluster that support the lack of a direct relationship between the existence of a magnetic field and a nitrogen excess in the photosphere.

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33

O’Dell, C. R., G. J. Ferland, and J. E. Méndez-Delgado. "Backscattering and Line Broadening in Orion." Astronomical Journal 165, no. 1 (December 19, 2022): 21. http://dx.doi.org/10.3847/1538-3881/ac9f44.

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Abstract Examination of emission lines in high-velocity-resolution optical spectra of the Orion Nebula confirms that the velocity component on the red wing of the main ionization front emission line is due to backscattering in the Photon Dominated Region. This scattered light component has a weak wavelength dependence that is consistent with either general interstellar medium particles or particles in the foreground of the Orion Nebula Cluster. An anomalous line-broadening component that has been known for 60+ years is characterized in unprecedented detail. Although this extra broadening may be due to turbulence along the line of sight of our spectra, we explore the possibility that it is due to Alfvén waves in conditions where the ratio of magnetic and thermal energies are about equal and constant throughout the ionized gas.

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34

Rebull, L. M., S. C. Wolff, S. E. Strom, and R. B. Makidon. "On the Relationship Between Stellar Rotation and Radius in Young Clusters." Symposium - International Astronomical Union 215 (2004): 123–24. http://dx.doi.org/10.1017/s0074180900195397.

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We have compiled data from the literature on rotational velocities and/or periods for > 1000 K & M stars in 10 young clusters ranging in age from Orion to the IC 1391/2602. These data show that most PMS stars < 3 Myr do not appear to spin up in response to contraction, but there is a suggestion of slight spinup by ~8 Myr. These results extend and reinforce our earlier study (Rebull et al. 2002), based on observations of ~300 stars in the Orion Flanking Fields, NGC 2264, and the Orion Nebula Cluster (ONC), which showed that the majority of PMS stars in these three groups apparently do not conserve stellar angular momentum as they contract, but instead evolve at nearly constant angular velocity. This result applies both to stars with and without near-IR I – K excesses indicative of disks.

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35

Olczak, C., S. Pfalzner, and R. Spurzem. "Encounter‐triggered Disk Mass Loss in the Orion Nebula Cluster." Astrophysical Journal 642, no. 2 (May 10, 2006): 1140–51. http://dx.doi.org/10.1086/501044.

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36

Kounkel, Marina, Lee Hartmann, John J. Tobin, Mario Mateo, John I. Bailey, and Meghin Spencer. "SPECTROSCOPIC BINARIES IN THE ORION NEBULA CLUSTER AND NGC 2264." Astrophysical Journal 821, no. 1 (April 1, 2016): 8. http://dx.doi.org/10.3847/0004-637x/821/1/8.

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37

Huff, E. M., and Steven W. Stahler. "Star Formation in Space and Time: The Orion Nebula Cluster." Astrophysical Journal 644, no. 1 (June 10, 2006): 355–63. http://dx.doi.org/10.1086/503357.

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38

Fűrész, Gábor, Lee W. Hartmann, S. Thomas Megeath, Andrew H. Szentgyorgyi, and Erika T. Hamden. "Kinematic Structure of the Orion Nebula Cluster and Its Surroundings1." Astrophysical Journal 676, no. 2 (April 2008): 1109–22. http://dx.doi.org/10.1086/525844.

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39

Tinker, Jeremy, Marc Pinsonneault, and Donald Terndrup. "Angular Momentum Evolution of Stars in the Orion Nebula Cluster." Astrophysical Journal 564, no. 2 (January 10, 2002): 877–86. http://dx.doi.org/10.1086/324153.

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40

Preibisch, Thomas, Yuri Balega, Karl-Heinz Hofmann, Gerd Weigelt, and Hans Zinnecker. "Multiplicity of the massive stars in the Orion Nebula cluster." New Astronomy 4, no. 7 (December 1999): 531–42. http://dx.doi.org/10.1016/s1384-1076(99)00042-1.

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41

Kroupa, Pavel. "Constraints on stellar-dynamical models of the Orion Nebula Cluster." New Astronomy 4, no. 8 (January 2000): 615–24. http://dx.doi.org/10.1016/s1384-1076(99)00048-2.

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42

Hasenberger, Birgit, Jan Forbrich, João Alves, Scott J. Wolk, Stefan Meingast, Konstantin V. Getman, and Ignazio Pillitteri. "Gas absorption and dust extinction towards the Orion Nebula Cluster." Astronomy & Astrophysics 593 (August 29, 2016): A7. http://dx.doi.org/10.1051/0004-6361/201628517.

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43

De Furio, Matthew, Michael R. Meyer, Megan Reiter, John Monnier, Adam Kraus, and Trent Dupuy. "Binary Formation in the Orion Nebula Cluster: Exploring the Substellar Limit." Astrophysical Journal 925, no. 2 (January 31, 2022): 112. http://dx.doi.org/10.3847/1538-4357/ac36d4.

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Abstract We present results constraining the multiplicity of the very low mass stars and substellar objects in the Orion Nebula Cluster (ONC). Our sample covers primary masses 0.012–0.1 M ⊙ using archival Hubble Space Telescope data obtained with the Advanced Camera for Surveys using multiple filters. Studying the binary populations of clusters provides valuable constraints of how the birth environment affects binary formation and evolution. Prior surveys have shown that the binary populations of high-mass, high-density star clusters like the ONC may substantially differ from those in low-mass associations. Very low mass stellar and substellar binaries at wide separations, >20 au, are statistically rare in the Galactic field and have been identified in stellar associations like Taurus-Auriga and Ophiuchus. They also may be susceptible to dynamical interactions, and their formation may be suppressed by feedback from ongoing star formation. We implement a double point-spread function (PSF) fitting algorithm using empirical, position-dependent PSF models to search for binary companions at projected separations >10 au (0.″025). With this technique, we identify seven very low mass binaries, five of which are new detections, resulting in a binary frequency of 12 − 3.2 + 6 % over mass ratios of 0.5–1.0 and projected separations of 20–200 au. We find an excess of very low mass binaries in the ONC compared to the Galactic field, with a probability of 10−6 that the populations are statistically consistent. The substellar population of the ONC may require further dynamical processing of the lowest binding energy binaries to resemble the field population.

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44

Flaccomio, E., G. Micela, N. Pizzolato, S. Sciortino, and P. Ventura. "Activity, Rotation and Convection in Orion: Are the Data Inconsistent with the Ms Activity-Rossby Number Relation?" Symposium - International Astronomical Union 215 (2004): 429–30. http://dx.doi.org/10.1017/s0074180900195981.

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A relation between activity and rotation in young ~ 1Myr PMS in often not observed, suggesting that the mechanism responsible for the X-ray emission may differ from the α - ω dynamo. We re-investigate the matter utilizing recent X-ray and rotational data on the Orion Nebula Cluster (ONC).

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45

Getman, K. V., E. D. Feigelson, M. A. Kuhn, and G. P. Garmire. "Gaia stellar kinematics in the head of the Orion A cloud: runaway stellar groups and gravitational infall." Monthly Notices of the Royal Astronomical Society 487, no. 3 (May 27, 2019): 2977–3000. http://dx.doi.org/10.1093/mnras/stz1457.

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ABSTRACT This work extends previous kinematic studies of young stars in the head of the Orion A cloud (OMC-1/2/3/4/5). It is based on large samples of infrared, optical, and X-ray selected pre-main-sequence stars with reliable radial velocities and Gaia-derived parallaxes and proper motions. Stellar kinematic groups are identified assuming they mimic the motion of their parental gas. Several groups are found to have peculiar kinematics: the NGC 1977 cluster and two stellar groups in the extended Orion nebula (EON) cavity are caught in the act of departing their birthplaces. The abnormal motion of NGC 1977 may have been caused by a global hierarchical cloud collapse, feedback by massive Ori OB1ab stars, supersonic turbulence, cloud–cloud collision, and/or slingshot effect; the former two models are favoured by us. EON groups might have inherited anomalous motions of their parental cloudlets due to small-scale ‘rocket effects’ from nearby OB stars. We also identify sparse stellar groups to the east and west of Orion A that are drifting from the central region, possibly a slowly expanding halo of the Orion nebula cluster. We confirm previously reported findings of varying line-of-sight distances to different parts of the cloud’s Head with associated differences in gas velocity. 3D movies of star kinematics show contraction of the groups of stars in OMC-1 and global contraction of OMC-123 stars. Overall, the head of Orion A region exhibits complex motions consistent with theoretical models involving hierarchical gravitational collapse in (possibly turbulent) clouds with OB stellar feedback.

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Román-Zúñiga, Carlos G., Emilio Alfaro, Aina Palau, Birgit Hasenberger, João F. Alves, Marco Lombardi, and G. Paloma S. Sánchez. "Not so different after all: properties and spatial structure of column density peaks in the pipe and Orion A clouds." Monthly Notices of the Royal Astronomical Society 489, no. 3 (August 23, 2019): 4429–43. http://dx.doi.org/10.1093/mnras/stz2355.

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ABSTRACT We present a comparative study of the physical properties and the spatial distribution of column density peaks in two giant molecular clouds (GMCs), the Pipe Nebula and Orion A, which exemplify opposite cases of star cluster formation stages. The density peaks were extracted from dust extinction maps constructed from Herschel/SPIRE far-infrared images. We compare the distribution functions for dust temperature, mass, equivalent radius, and mean volume density of peaks in both clouds, and made a more fair comparison by isolating the less active Tail region in Orion A and by convolving the Pipe Nebula map to simulate placing it at a distance similar to that of the Orion Complex. The peak mass distributions for Orion A, the Tail, and the convolved Pipe have similar ranges, sharing a maximum near 5 M⊙ and a similar power-law drop above 10 M⊙. Despite the clearly distinct evolutive stage of the clouds, there are very important similarities in the physical and spatial distribution properties of the column density peaks, pointing to a scenario where they form as a result of uniform fragmentation of filamentary structures across the various scales of the cloud, with density being the parameter leading the fragmentation, and with clustering being a direct result of thermal fragmentation at different spatial scales. Our work strongly supports the idea that the formation of clusters in GMC could be the result of the primordial organization of pre-stellar material.

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Schmeja, S., M. S. N. Kumar, D. Froebrich, and R. S. Klessen. "Changing Structures in Galactic Star Clusters." Proceedings of the International Astronomical Union 3, S246 (September 2007): 50–54. http://dx.doi.org/10.1017/s1743921308015263.

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AbstractWe investigate the structures of embedded and open clusters using statistical methods, in particular the combined parameter $\Q$, which permits to quantify the cluster structure. Star clusters build up from several subclusters evolving from a structured to a more centrally concentrated stage. The evolution is not only a function of time, but also of the mass of the objects. Massive stars are usually centrally concentrated, while lower-mass stars are more widespread, reflecting the effect of mass segregation. Using this method we find that in IC 348 and the Orion Nebula Cluster the spatial distribution of brown dwarfs does not follow the central clustering of stars, giving important clues to their formation mechanism by supporting the ejected embryo scenario.

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Schulz, Norbert S. "X-ray Emission from Massive Stars at the Core of Very Young Clusters." Proceedings of the International Astronomical Union 12, S329 (November 2016): 362–65. http://dx.doi.org/10.1017/s1743921317003532.

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AbstractMost cores of very young stellar clusters contain one or more massive stars at various evolutionary stages. Observations of the Orion Nebula Cluster, Trumpler 37, NGC 2362, RCW38, NGC 3603 and many others provide the most comprehensive database to study stellar wind properties of these massive cluster stars in X-rays. In this presentation we review some of these observations and results and discuss them in the context of stellar winds and possible evolutionary implications. We argue that in very young clusters such as RCW38 and M17, shock heated remnants of a natal shell could serve as an alternate explanation to the colliding wind paradigm for the hot plasma components in the X-ray spectra.

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Karl, Martina, Oliver Pfuhl, Frank Eisenhauer, Reinhard Genzel, Rebekka Grellmann, Maryam Habibi, Roberto Abuter, et al. "Multiple star systems in the Orion nebula." Astronomy & Astrophysics 620 (December 2018): A116. http://dx.doi.org/10.1051/0004-6361/201833575.

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This work presents an interferometric study of the massive-binary fraction in the Orion Trapezium cluster with the recently comissioned GRAVITY instrument. We observed a total of 16 stars of mainly OB spectral type. We find three previously unknown companions for θ1 Ori B, θ2 Ori B, and θ2 Ori C. We determined a separation for the previously suspected companion of NU Ori. We confirm four companions for θ1 Ori A, θ1 Ori C, θ1 Ori D, and θ2 Ori A, all with substantially improved astrometry and photometric mass estimates. We refined the orbit of the eccentric high-mass binary θ1 Ori C and we are able to derive a new orbit for θ1 Ori D. We find a system mass of 21.7 M⊙ and a period of 53 days. Together with other previously detected companions seen in spectroscopy or direct imaging, eleven of the 16 high-mass stars are multiple systems. We obtain a total number of 22 companions with separations up to 600 AU. The companion fraction of the early B and O stars in our sample is about two, significantly higher than in earlier studies of mostly OB associations. The separation distribution hints toward a bimodality. Such a bimodality has been previously found in A stars, but rarely in OB binaries, which up to this point have been assumed to be mostly compact with a tail of wider companions. We also do not find a substantial population of equal-mass binaries. The observed distribution of mass ratios declines steeply with mass, and like the direct star counts, indicates that our companions follow a standard power law initial mass function. Again, this is in contrast to earlier findings of flat mass ratio distributions in OB associations. We excluded collision as a dominant formation mechanism but find no clear preference for core accretion or competitive accretion.

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Landin, Natália R., Paolo Ventura, Francesca D'Antona, Luiz T. S. Mendes, and Luiz P. R. Vaz. "Rotational properties of the Orion nebular cluster revised." Proceedings of the International Astronomical Union 2, S239 (August 2006): 311–13. http://dx.doi.org/10.1017/s1743921307000634.

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AbstractThe observational data of the Orion Nebula Cluster (ONC) is reanalyzed by means of new sets of pre-main sequence (PMS) evolutionary tracks including rotation, non-gray boundary conditions (BC's) and either low (LCE) or high convection efficiency (HCE), aiming better understanding of the appropriate physical constraints for the rotational evolution of the stars within the ONC. The role played by convection is a key aspect of our analysis, since there are conflicting results from theory and observations. We derived stellar masses and ages for the ONC by using both LCE and HCE and considered was the role of non-gray atmospheres. Our results show that the resulting mass distribution for the bulk of the ONC population is in the range 0.2-0.4M⊙ for our non-gray models, and in the range 0.1-0.3M⊙ for gray models. In agreement with previous works, we found that a large percentage (∼70%) of low-mass stars (M≤Mtr, where Mtr is a transition mass) in the ONC appears to be fast rotators (P<4days). Mtr depends on the model choosen, being Mtr=0.5 for LCE, Mtr=0.35 for HCE and, as found in previous works, Mtr=0.25 for gray models. Finally, our analysis indicates that a second parameter is needed for a proper description of convection in the PMS phase.

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