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Register a new userDeuterated methanol in Orion BN/KL
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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.
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We present a comprehensive study of the deuterated molecules detected in the fullband HIFI survey of the Orion KL region. Ammonia, formaldehyde, and methanol and their singly deuterated isotopologues are each detected through numerous transitions in this survey with a wide range in optical depths and excitation conditions. In conjunction with a recent study of the abundance of HDO and H$_2$O in Orion KL, this study yields the best constraints on deuterium fractionation in an interstellar molecular cloud to date. As previous studies have found, both the Hot Core and Compact Ridge regions within Orion KL contain significant abundances of deuterated molecules, suggesting an origin in cold grain mantles. In the Hot Core, we find that ammonia is roughly a factor of 2 more fractionated than water. In the Compact Ridge, meanwhile, we find similar deuterium fractionation in water, formaldehyde, and methanol, with D/H ratios of (2---8) $times$ $10^{-3}$. The [CH$_2$DOH]/[CH$_3$OD] ratio in the Compact Ridge is found to be $1.2 pm 0.3$. The Hot Core generally has lower deuterium fractionation than the Compact Ridge, suggesting a slightly warmer origin, or a greater contribution from warm gas phase chemistry.
We report the first high angular resolution imaging (3.4arcsec $times$ 3.0arcsec) of deuterated formaldehyde (HDCO) toward Orion--KL, carried out with the Submillimeter Array (SMA). We find that the spatial distribution of the formaldehyde emission systematically differs from that of methanol: while methanol is found towards the inner part of the region, HDCO is found in colder gas that wraps around the methanol emission on four sides. The HDCO/H$_2$CO ratios are determined to be 0.003--0.009 within the region, up to an order of magnitude higher than the D/H measured for methanol. These findings strengthen the previously suggested hypothesis that there are differences in the chemical pathways leading to HDCO (via deuterated gas phase chemistry) and deuterated methanol (through conversion of formaldehyde into methanol on the surface of icy grain mantles).
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.
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.
As one of the prime targets of interstellar chemistry study, Orion BN/KL clearly shows different molecular distributions between large nitrogen- (e.g., C2H5CN) and oxygen-bearing (e.g., HCOOCH3) molecules. However, acetone (CH3)2CO, a special complex O-bearing molecule, has been shown to have a very different distribution from other typical O-bearing molecules in the BN/KL region. We searched for acetone within our IRAM Plateau de Bure Interferometer 3 mm and 1.3 mm data sets. Twenty-two acetone lines were searched within these data sets. The angular resolution ranged from 1.8 X 0.8 to 6.0 X 2.3 arcsec^2, and the spectral resolution ranged from 0.4 to 1.9 km s-1. Nine of the acetone lines appear free of contamination. Three main acetone peaks (Ace-1, 2, and 3) are identified in Orion BN/KL. The new acetone source Ace-3 and the extended emission in the north of the hot core region have been found for the first time. An excitation temperature of about 150 K is determined toward Ace-1 and Ace-2, and the acetone column density is estimated to be 2-4 X 10^16 cm-2 with a relative abundance of 1-6 X 10^-8 toward these two peaks. Acetone is a few times less abundant toward the hot core and Ace-3 compared with Ace-1 and Ace-2. We find that the overall distribution of acetone in BN/KL is similar to that of N-bearing molecules, e.g., NH3 and C2H5CN, and very different from those of large O-bearing molecules, e.g., HCOOCH3 and (CH3)2O. Our findings show the acetone distribution is more extended than in previous studies and does not originate only in those areas where both N-bearing and O-bearing species are present. Moreover, because the N-bearing molecules may be associated with shocked gas in Orion BN/KL, this suggests that the formation and/or destruction of acetone may involve ammonia or large N-bearing molecules in a shocked-gas environment.
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