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Register a new userExplosive Outflows Powered by the Decay of Non-Hierarchical Multiple Systems of Massive Stars: Orion BN/KL
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The explosive BN/KL outflow emerging from OMC1 behind the Orion Nebula may have been powered by the dynamical decay of a non-hierarchical multiple system $sim$500 years ago that ejected the massive stars I, BN, and source n, with velocities of about 10 to 30 km s$^{-1}$. New proper motion measurements of H$_2$ features show that within the errors of measurement, the outflow originated from the site of stellar ejection. Combined with published data, these measurements indicate an outflow age of $sim$500 years, similar to the time since stellar ejection. The total kinetic energy of the ejected stars and the outflow is about 2 to $6 times 10^{47}$ ergs. It is proposed that the gravitational potential energy released by the formation of a short-period binary, most likely source I, resulted in stellar ejection and powered the outflow. A scenario is presented for the formation of a compact, non-hierarchical multiple star system, its decay into an ejected binary and two high-velocity stars, and launch of the outflow. Three mechanisms may have contributed to the explosion in the gas: (i) Unbinding of the circum-cluster envelope following stellar ejection, (ii) disruption of circumstellar disks and high-speed expulsion of the resulting debris during the final stellar encounter, and (iii) the release of stored magnetic energy. Plausible proto-stellar disk end envelope properties can produce the observed outflow mass, velocity, and kinetic energy distributions. The ejected stars may have acquired new disks by fall-back or Bondi-Hoyle accretion with axes roughly orthogonal to their velocities. The expulsion of gas and stars from OMC1 may have been driven by stellar interactions.
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High spatial resolution low-J 12CO observations have shown that the wide-angle outflow seen in the Orion BN/KL region correlates with the famous H2 fingers. Recently, high-resolution large-scale mappings of mid- and higher-J CO emissions have been reported toward the Orion molecular cloud 1 core region using the APEX telescope. Therefore, it is of interest to investigate this outflow in the higher-J 12CO emission, which is likely excited by shocks. The observations were carried out using the dual-color heterodyne array CHAMP+ on the APEX telescope. The images of the Orion BN/KL region were obtained in the 12CO J=6-5 and J=7-6 transitions with angular resolutions of 8.6 and 7.4 arcsec, respectively. The results show a good agreement between our higher-J 12CO emission and SMA low-J 12CO data, which indicates that this wide-angle outflow in Orion BN/KL is likely the result of an explosive event that is related to the runaway objects from a dynamically decayed multiple system. From our observations, we estimate that the kinetic energy of this explosive outflow is about 1-2x10^47 erg. In addition, a scenario has been proposed where part of the outflow is decelerated and absorbed in the cloud to explain the lack of CO bullets in the southern part of BN/KL, which in turn induces the methanol masers seen in this region.
Deuterated molecules have been detected and studied toward Orion BN/KL in the past decades, mostly with single-dish telescopes. However, high angular resolution data are critical not only for interpreting the spatial distribution of the deuteration ratio but also for understanding this complex region in terms of cloud evolution involving star-forming activities and stellar feedbacks. We present here the first high angular resolution (1.8 arcsec times 0.8 arcsec) images of deuterated methanol CH2DOH in Orion BN/KL observed with the IRAM Plateau de Bure Interferometer from 1999 to 2007 in the 1 to 3 mm range. Six CH2DOH lines were detected around 105.8, 223.5, and 225.9 GHz. In addition, three E-type methanol lines around 101-102 GHz were detected and were used to derive the corresponding CH3OH rotational temperatures and column densities toward different regions across Orion BN/KL. The strongest CH2DOH and CH3OH emissions come from the Hot Core southwest region with an LSR velocity of about 8 km/s. We derive [CH2DOH]/[CH3OH] abundance ratios of 0.8-1.3times10^-3 toward three CH2DOH emission peaks. A new transition of CH3OD was detected at 226.2 GHz for the first time in the interstellar medium. Its distribution is similar to that of CH2DOH. Besides, we find that the [CH2DOH]/[CH3OD] abundance ratios are lower than unity in the central part of BN/KL. Furthermore, the HDO 3(1,2)-2(2,1) line at 225.9 GHz was detected and its emission distribution shows a shift of a few arcseconds with respect to the deuterated methanol emission that likely results from different excitation effects. The deuteration ratios derived along Orion BN/KL are not markedly different from one clump to another. However, various processes such as slow heating due to ongoing star formation, heating by luminous infrared sources, or heating by shocks could be competing to explain some local differences observed for these ratios.
During their infancy, stars are well known to expel matter violently in the form of well-defined, collimated outflows. A fairly unique exception is found in the Orion BN/KL star-forming region where a poorly collimated and somewhat disordered outflow composed of numerous elongated ``finger-like structures was discovered more than 30 years ago. In this letter, we report the discovery in the same region of an even more atypical outflow phenomenon. Using $^{13}$CO(2-1) line observations made with the Submillimeter Array (SMA), we have identified there a 500 to 1,000 years old, expanding, roughly spherically symmetric bubble whose characteristics are entirely different from those of known outflows associated with young stellar objects. The center of the bubble coincides with the initial position of a now defunct massive multiple stellar system suspected to have disintegrated 500 years ago, and with the center of symmetry of the system of molecular fingers surrounding the Kleinmann-Low nebula. We hypothesize that the bubble is made up of gas and dust that used to be part of the circumstellar material associated with the decayed multiple system. The Orion hot core, recently proposed to be the result of the impact of a shock wave onto a massive dense core, is located toward the south-east quadrant of the bubble. The supersonic expansion of the bubble, and/or the impact of some low-velocity filaments provide a natural explanation for its origin.
Complex Organic Molecules (COMs) are believed to form in the ice mantle of dust grains and are released to the gas by thermal sublimation when grain mantles are heated to temperatures of $T_{rm d}gtrsim 100,rm K$. However, some COMs are detected in regions with temperatures below 100 K. Recently, a new mechanism of rotational desorption due to centrifugal stress induced by radiative torques (RATs) is proposed by Hoang & Tram 2020 that can desorb COMs at low temperatures. In this paper, we report observational evidence for rotational desorption of COMs toward the nearest massive star-forming region Orion BN/KL. We compare the abundance of three representative COMs which have very high binding energy computed by the rotational desorption mechanism with observations by ALMA, and demonstrate that the rotational desorption mechanism can explain the existence of such COMs. We also analyze the polarization data from SOFIA/HAWC+ and JCMT/SCUBA-2 and find that the polarization degree at far-infrared/submm decreases with increasing the grain temperature for $T_{rm d}gtrsim 71,rm K$. This is consistent with the theoretical prediction using the Radiative Torque (RAT) alignment theory and Radiative Torque Disruption (RATD) mechanism. Such an anti-correlation between dust polarization and dust temperature supports the rotational disruption as well as rotational desorption mechanism of COMs induced by RATs.
We present observations towards one of the closest regions of high mass star formation, Orion BN/KL, performed at both low resolution mode (grating mode) and high resolution mode (Fabry-Perot) with the Long Wavelength Spectrometer on board the Infrared Space Observatory. We detected the CO rotational lines from Jup = 15 to Jup = 45. While the lines with Jup<= 32 are spectrally unresolved, the higher lying lines show a broadened profile. Finally, we detected two 13CO lines, namely at Jup = 18 and 24, from which we could derive the opacities of the relative 12CO lines. The LVG analysis of the observed line spectrum allows to distinguish three main physical components with different temperatures, densities and column densities: 1) lines with Jup< 20 originate mainly in the diffuse photodissociation region surrounding the source; 2) lines with Jup between 20 and 30 originate in the high velocity outflow (plateau) emanating from IrC2; 3) lines with Jup > 32 originate in the hot and dense gas of the shocked component of the outflow. We discuss how future observations with HIFI, onboard the Far Infrared Space Telescope (FIRST) will allow to spectrally and spatially disentangle the three components, and, consequently, characterise more precisely the Orion BN/KL star forming region.
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