High Angular Resolution Mid-Infrared Imaging of Young Stars in Orion BN/KL

Greenhill, L. J.; Gezari, D. Y.; Danchi, W. C.; Najita, J.; Monnier, John D.; Tuthill, P. G.

doi:10.1086/386544

Cited by 59 publications

(123 citation statements)

References 34 publications

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“…A single broad absorption feature extending approximately to −65 km s −1 traces mainly the molecular outflow whereas red-shifted emission likely stems from an inner infalling and accreting envelope/disk. This picture is consistent with disk/outflow proposals for this source deduced from cm and mid-infrared wavelength imaging projects (e.g., Menten & Reid 1995;Greenhill et al 2004;Shuping et al 2004). The clearly resolved doublepeaked 13 CO structure allows to conduct the Boltzmann analysis for both components.…”

Section: Discussionsupporting

confidence: 87%

Disk and outflow signatures in Orion-KL: the power of high-resolution thermal infrared spectroscopy

Beuther¹,

Linz²,

Bik³

et al. 2010

A&A

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Context. The Orion-KL region contains the closest examples of high-mass accretion disk candidates. Studying their properties is an essential step in studying high-mass star formation. Aims. Resolving the molecular line emission at high spatial and spectral resolution in the immediate environment of the exciting sources to infer the physical properties of the associated gas. Methods. We used the CRIRES high-resolution spectrograph mounted on the VLT to study the ro-vibrational 12 CO, 13 CO, the Pfund β, and H 2 emission between 4.59 and 4.72 μm wavelengths toward the BN object, the disk candidate source n, and a proposed dust density enhancement IRC3. Results. We detected CO absorption and emission features toward all three targets. Toward the BN object, the data partly confirm the results obtained more than 25 years ago; however, we also identify several new features. While the blue-shifted absorption is likely caused by outflowing gas, toward the BN object we detect CO in emission extending in diameter to ∼3300 AU with a velocity structure close to the v lsr . Although at the observational spectral resolution limit, the 13 CO line width of that feature increases with energy levels, consistent with a disk origin. If one also attributes the extended CO emission to a disk origin, its extent is consistent with other massive disk candidates in the literature. For source n, we also find the blueshifted CO absorption likely from an outflow. However, it also exhibits a narrower range of redshifted CO absorption and adjacent weak CO emission, consistent with infalling motions. We do not spatially resolve the emission for source n. For both sources we conduct a Boltzmann analysis of the 13 CO absorption features and find temperatures between 100 and 160 K, and H 2 column densities of a few times 10 23 cm −2 . The observational signatures from IRC3 are very different with only weak absorption against a much weaker continuum source. However, the CO emission is extended and shows wedge-like position velocity signatures consistent with jet-entrainment of molecular gas, potentially associated with the Orion-KL outflow system. We also present and discuss the Pfund β and H 2 emission in the region. Conclusions. This analysis toward the closest high-mass disk candidates outlines the power of high spectral and spatial resolution mid-infrared spectroscopy for studying the gas properties close to young massive stars. We will extend qualitatively similar studies to larger samples of high-mass young stellar objects to constrain the physical properties of the dense innermost gas structures in more detail and in a statistical sense.

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Section: Discussionsupporting

confidence: 87%

Disk and outflow signatures in Orion-KL: the power of high-resolution thermal infrared spectroscopy

Beuther¹,

Linz²,

Bik³

et al. 2010

A&A

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“…Close to MF2, very high opacities are advocated to explain not detecting the bright source I (e.g. Greenhill et al 2004). Indeed from our continuum data (Sect.…”

Section: Hcooch 3 and Ir 11 μM Mapmentioning

confidence: 66%

HCOOCH₃as a probe of temperature and structure in Orion-KL

Favre

Despois

Brouillet

et al. 2011

A&A

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Context. The Orion Kleinmann-Low nebula (Orion-KL) is a complex region of star formation. Whereas its proximity allows studies on a scale of a few hundred AU, spectral confusion makes it difficult to identify molecules with low abundances. Aims. We studied an important oxygenated molecule, HCOOCH 3 , to characterize the physical conditions, temperature, and density of the different molecular source components. Methyl formate presents strong close rotational transitions covering a wide range of energy, and its emission in Orion-KL is not contaminated by the emission of N-bearing molecules. This study will help in the future 1) to constrain chemical models for the formation of methyl formate in gas phase or on grain mantles and 2) to search for more complex or prebiotic molecules. Methods. We used high-resolution observations from the IRAM Plateau de Bure Interferometer to reduce spectral confusion and to better isolate the molecular emission regions. We used twelve data sets with a spatial resolution down to 1.8 × 0.8 . Continuum emission was subtracted by selecting apparently line-free channels. Results. We identify 28 methyl formate emission peaks throughout the 50 field of observations. The two strongest peaks, named MF1 and MF2, are in the Compact Ridge and in the southwest of the Hot Core, respectively. From a comparison with single-dish observations, we estimate that we miss less than 15% of the flux and that spectral confusion is still prevailing as half of the expected transitions are blended over the region. Assuming that the transitions are thermalized, we derive the temperature at the five main emission peaks. At the MF1 position in the Compact Ridge we find a temperature of 80 K in a 1.8 × 0.8 beam size and 120 K on a larger scale (3.6 × 2.2 ), suggesting an external source of heating, whereas the temperature is about 130 K at the MF2 position on both scales. Transitions of methyl formate in its first torsionally excited state are detected as well, and the good agreement of the positions on the rotational diagrams between the ground state and the v t = 1 transitions suggests a similar temperature. The LSR velocity of the gas is between 7.5 and 8.0 km s −1 depending on the positions and column density peaks vary from 1.6 × 10 16 to 1.6 × 10 17 cm −2 . A second velocity component is observed around 9−10 km s −1 in a north-south structure stretching from the Compact Ridge up to the BN object, and this component is warmer at the MF1 peak. The two other C 2 H 4 O 2 isomers are not detected, and the derived upper limit for the column density is ≤3 × 10 14 cm −2 for glycolaldehyde and ≤2 × 10 15 cm −2 for acetic acid. From the 223 GHz continuum map, we identify several dust clumps with associated gas masses in the range 0.8 to 5.8 M . Assuming that the methyl formate is spatially distributed as the dust is, we find relative abundances of methyl formate in the range ≤0.1 × 10 −8 to 5.2 × 10 −8 . We suggest a relation between the methyl formate distribution and shocks as traced by 2.12 μm H 2 emission.

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“…The masers seem to arise from a small region around the radio continuum source I (Churchwell et al 1987), a young star with a very high luminosity without any infrared counterpart, 10 5 L (Gezari et al 1998;Greenhill et al 2004). This source is also driving the low velocity outflow observed in SiO (Beuther et al 2005;Plambeck et al 2009) and in other molecular species (Paper I).…”

Section: Introductionmentioning

confidence: 99%

A line-confusion limited millimeter survey of Orion KL

Tercero

Vincent

Cernicharo

et al. 2011

A&A

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Aims. We present a study of the silicon-bearing species detected in a line-confusion limited survey towards Orion KL performed with the IRAM 30-m telescope. The analysis of the line survey is organized by families of molecules. Our aim is to derive physical and chemical conditions for each family taking all observed lines into account from all isotopologs of each species. The large number of transitions in different vibrationally excited states covered by our data, which range from 80 to 280 GHz, let us provide reliable source-average column densities (hence, isotopolog abundances and vibrational temperatures) for the detected molecules. In addition, we provide a wide study of the physical properties of the source based on the different spectral components found in the emission lines. Methods. We modeled the lines of the detected molecules using a radiative transfer code, which permit us to choose between large velocity gradient (LVG) and local thermodynamic equilibrium (LTE) approximations depending on the physical conditions of the gas. We used appropriate collisional rates for the LVG calculations. To qualitatively investigate the origin of the SiS and SiO emissions in Orion KL we ran a grid of chemical models.Results. For the v = 1 state of SiO, we detected the J = 2−1 line and, for the first time in this source, emission in the J = 4−3 transition, both of them showing a strong masering effect. For SiO v = 0, we detected 28 SiO, 29 SiO, and 30 SiO; in addition, we have mapped the J = 5−4 SiO line. For SiS, we have detected the main species, 29 SiS, and SiS v = 1. Unlikely other species detected in Orion KL (IRc2), the emission peak of SiS appears at a velocity of 15.5 km s −1 . A study of the 5−4 SiO line around IRc2 shows this feature as an extended component that probably arises from the interaction of the outflow with the ambient cloud. We derive an SiO/SiS column density ratio of 13 in the plateau component, four times lower than the cosmic O/S ratio 48. In addition, we provide upper limits to the column density of several non-detected silicon-bearing species. The results of our chemical models show that while it is possible to reproduce SiO in the gas phase (as well as on the grains), SiS is a product of surface reactions, most likely involving direct reactions of sulfur with silicon.

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High Angular Resolution Mid-Infrared Imaging of Young Stars in Orion BN/KL

Cited by 59 publications

References 34 publications

Disk and outflow signatures in Orion-KL: the power of high-resolution thermal infrared spectroscopy

Disk and outflow signatures in Orion-KL: the power of high-resolution thermal infrared spectroscopy

HCOOCH₃as a probe of temperature and structure in Orion-KL

A line-confusion limited millimeter survey of Orion KL

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High Angular Resolution Mid-Infrared Imaging of Young Stars in Orion BN/KL

Cited by 59 publications

References 34 publications

Disk and outflow signatures in Orion-KL: the power of high-resolution thermal infrared spectroscopy

Disk and outflow signatures in Orion-KL: the power of high-resolution thermal infrared spectroscopy

HCOOCH3as a probe of temperature and structure in Orion-KL

A line-confusion limited millimeter survey of Orion KL

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HCOOCH₃as a probe of temperature and structure in Orion-KL