Context.
Molecular outflows are believed to be a key ingredient in the process of star formation. The molecular outflow associated with DR21 Main in Cygnus-X is one of the most extreme molecular ...outflows in the Milky Way in terms of mass and size. The outflow is suggested to belong to a rare class of explosive outflows formed by the disintegration of protostellar systems.
Aims.
We aim to explore the morphology, kinematics, and energetics of the DR21 Main outflow, and to compare those properties to confirmed explosive outflows in order to unravel the underlying driving mechanism behind DR21.
Methods.
We studied line and continuum emission at a wavelength of 3.6 mm with IRAM 30 m and NOEMA telescopes as part of the Cygnus Allscale Survey of Chemistry and Dynamical Environments (CASCADE) program. The spectra include (
J
= 1−0) transitions of HCO
+
, HCN, HNC, N
2
H
+
, H
2
CO, and CCH, which trace different temperature and density regimes of the outflowing gas at high velocity resolution (~0.8 km s
−1
). The map encompasses the entire DR21 Main outflow and covers all spatial scales down to a resolution of 3″ (~0.02 pc).
Results.
Integrated intensity maps of the HCO
+
emission reveal a strongly collimated bipolar outflow with significant overlap of the blueshifted and redshifted emission. The opening angles of both outflow lobes decrease with velocity, from ~80 to 20° for the velocity range from 5 to 45 km s
−1
relative to the source velocity. No evidence is found for the presence of elongated, “filament-like” structures expected in explosive outflows. N
2
H
+
emission near the western outflow lobe reveals the presence of a dense molecular structure, which appears to be interacting with the DR21 Main outflow.
Conclusions.
The overall morphology as well as the detailed kinematics of the DR21 Main outflow are more consistent with a typical bipolar outflow than with an explosive counterpart.
We have observed the massive protostar AFGL 2136 IRS 1 in multiple wavelength windows in the near- to mid-infrared at high (∼3 km s−1) spectral resolution using VLT+CRIRES, SOFIA+EXES, and Gemini ...North+TEXES. There is an abundance of H2O absorption lines from the 1 and 3 vibrational bands at 2.7 m, from the 2 vibrational band at 6.1 m, and from pure rotational transitions near 10-13 m. Analysis of state-specific column densities derived from the resolved absorption features reveals that an isothermal absorbing slab model is incapable of explaining the relative depths of different absorption features. In particular, the strongest absorption features are much weaker than expected, indicating optical depth effects resulting from the absorbing gas being well mixed with the warm dust that serves as the "background" continuum source at all observed wavelengths. The velocity at which the strongest H2O absorption occurs coincides with the velocity centroid along the minor axis of the compact disk in Keplerian rotation recently observed in H2O emission with ALMA. We postulate that the warm regions of this dust disk dominate the continuum emission at near- to mid-infrared wavelengths, and that H2O and several other molecules observed in absorption are probing this disk. Absorption line profiles are not symmetric, possibly indicating that the warm dust in the disk that produces the infrared continuum has a nonuniform distribution similar to the substructure observed in 1.3 mm continuum emission.
Abstract
We have observed the massive protostar AFGL 2136 IRS 1 in multiple wavelength windows in the near- to mid-infrared at high (∼3 km s
−1
) spectral resolution using VLT+CRIRES, SOFIA+EXES, and ...Gemini North+TEXES. There is an abundance of H
2
O absorption lines from the
ν
1
and
ν
3
vibrational bands at 2.7
μ
m, from the
ν
2
vibrational band at 6.1
μ
m, and from pure rotational transitions near 10–13
μ
m. Analysis of state-specific column densities derived from the resolved absorption features reveals that an isothermal absorbing slab model is incapable of explaining the relative depths of different absorption features. In particular, the strongest absorption features are much weaker than expected, indicating optical depth effects resulting from the absorbing gas being well mixed with the warm dust that serves as the “background” continuum source at all observed wavelengths. The velocity at which the strongest H
2
O absorption occurs coincides with the velocity centroid along the minor axis of the compact disk in Keplerian rotation recently observed in H
2
O emission with ALMA. We postulate that the warm regions of this dust disk dominate the continuum emission at near- to mid-infrared wavelengths, and that H
2
O and several other molecules observed in absorption are probing this disk. Absorption line profiles are not symmetric, possibly indicating that the warm dust in the disk that produces the infrared continuum has a nonuniform distribution similar to the substructure observed in 1.3 mm continuum emission.
Context. Outflows are an important part of the star formation process as both the result of ongoing active accretion and one of the main sources of mechanical feedback on small scales. Water is the ...ideal tracer of these effects because it is present in high abundance for the conditions expected in various parts of the protostar, particularly the outflow. Aims. We constrain and quantify the physical conditions probed by water in the outflow-jet system for Class 0 and I sources. Methods. We present velocity-resolved Herschel HIFI spectra of multiple water-transitions observed towards 29 nearby Class 0/I protostars as part of the WISH guaranteed time key programme. The lines are decomposed into different Gaussian components, with each component related to one of three parts of the protostellar system; quiescent envelope, cavity shock and spot shocks in the jet and at the base of the outflow. We then use non-LTE radex models to constrain the excitation conditions present in the two outflow-related components. Results. Water emission at the source position is optically thick but effectively thin, with line ratios that do not vary with velocity, in contrast to CO. The physical conditions of the cavity and spot shocks are similar, with post-shock H2 densities of order 105 − 108 cm-3 and H2O column densities of order 1016 − 1018 cm-2. H2O emission originates in compact emitting regions: for the spot shocks these correspond to point sources with radii of order 10−200 AU, while for the cavity shocks these come from a thin layer along the outflow cavity wall with thickness of order 1−30 AU. Conclusions. Water emission at the source position traces two distinct kinematic components in the outflow; J shocks at the base of the outflow or in the jet, and C shocks in a thin layer in the cavity wall. The similarity of the physical conditions is in contrast to off-source determinations which show similar densities but lower column densities and larger filling factors. We propose that this is due to the differences in shock properties and geometry between these positions. Class I sources have similar excitation conditions to Class 0 sources, but generally smaller line-widths and emitting region sizes. We suggest that it is the velocity of the wind driving the outflow, rather than the decrease in envelope density or mass, that is the cause of the decrease in H2O intensity between Class 0 and I sources.
Water In Star-forming regions with Herschel (WISH) is a key program on the Herschel Space Observatory designed to probe the physical and chemical structures of young stellar objects using water and ...related molecules and to follow the water abundance from collapsing clouds to planet-forming disks. About 80 sources are targeted, covering a wide range of luminosities-from low (< 1) to high (>10)-and a wide range of evolutionary stages-from cold prestellar cores to warm protostellar envelopes and outflows to disks around young stars. Both the HIFI and PACS instruments are used to observe a variety of lines of HO , HO and chemically related species at the source position and in small maps around the protostars and selected outflow positions. In addition, high-frequency lines of CO, CO , and CO are obtained with Herschel and are complemented by ground-based observations of dust continuum, HDO, CO and its isotopologs, and other molecules to ensure a self-consistent data set for analysis. An overview of the scientific motivation and observational strategy of the program is given, together with the modeling approach and analysis tools that have been developed. Initial science results are presented. These include a lack of water in cold gas at abundances that are lower than most predictions, strong water emission from shocks in protostellar environments, the importance of UV radiation in heating the gas along outflow walls across the full range of luminosities, and surprisingly widespread detection of the chemically related hydrides OH and HO in outflows and foreground gas. Quantitative estimates of the energy budget indicate that HO is generally not the dominant coolant in the warm dense gas associated with protostars. Very deep limits on the cold gaseous water reservoir in the outer regions of protoplanetary disks are obtained that have profound implications for our understanding of grain growth and mixing in disks.
Context. Intermediate-mass young stellar objects (YSOs) provide a link to understanding how feedback from shocks and UV radiation scales from low- to high-mass star forming regions. Aims. Our aim is ...to analyze excitation of CO and H2O in deeply embedded intermediate-mass YSOs and compare it with similar studies on low-mass and high-mass YSOs. Methods. Herschel/PACS spectral maps are analyzed for six YSOs with bolometric luminosities of Lbol ~ 102−103L⊙. The maps cover spatial scales of ~104 AU in several CO and H2O lines located in the ~55–210 μm range. Results. Rotational diagrams of CO show two temperature components at Trot ~ 320 K and Trot ~ 700–800 K, comparable to low- and high-mass protostars probed at similar spatial scales. The diagrams for H2O show a single component at Trot ~ 130 K, as seen in low-mass protostars, and about 100 K lower than in high-mass protostars. Since the uncertainties in Trot are on the same order as the difference between the intermediate and high-mass protostars, we cannot conclude whether the change in rotational temperature occurs at a specific luminosity or whether the change is more gradual from low- to high-mass YSOs. Conclusions. Molecular excitation in intermediate-mass protostars is comparable to the central 103 AU of low-mass protostars and consistent within the uncertainties with the high-mass protostars probed at 3 × 103 AU scales, suggesting similar shock conditions in all those sources.
Context. Through spectrally unresolved observations of high-J CO transitions, Herschel Photodetector Array Camera and Spectrometer (PACS) has revealed large reservoirs of warm (300 K) and hot (700 K) ...molecular gas around low-mass protostars. The excitation and physical origin of this gas is still not understood. Aims: We aim to shed light on the excitation and origin of the CO ladder observed toward protostars, and on the water abundance in different physical components within protostellar systems using spectrally resolved Herschel-HIFI data. Methods: Observations are presented of the highly excited CO line J = 16-15 (Eup/kB = 750 K) with the Herschel Heterodyne Instrument for the Far Infrared (HIFI) toward a sample of 24 low-mass protostellar objects. The sources were selected from the Herschel "Water in Star-forming regions with Herschel" (WISH) and "Dust, Ice, and Gas in Time" (DIGIT) key programs. Results: The spectrally resolved line profiles typically show two distinct velocity components: a broad Gaussian component with an average FWHM of 20 km s-1 containing the bulk of the flux, and a narrower Gaussian component with a FWHM of 5 km s-1 that is often offset from the source velocity. Some sources show other velocity components such as extremely-high-velocity features or "bullets". All these velocity components were first detected in H2O line profiles. The average rotational temperature over the entire profile, as measured from comparison between CO J = 16-15 and 10-9 emission, is 300 K. A radiative-transfer analysis shows that the average H2O/CO column-density ratio is 0.02, suggesting a total H2O abundance of 2 × 10-6, independent of velocity. Conclusions: Two distinct velocity profiles observed in the HIFI line profiles suggest that the high-J CO ladder observed with PACS consists of two excitation components. The warm PACS component (300 K) is associated with the broad HIFI component, and the hot PACS component (700 K) is associated with the offset HIFI component. The former originates in either outflow cavity shocks or the disk wind, and the latter in irradiated shocks. The low water abundance can be explained by photodissociation. The ubiquity of the warm and hot CO components suggest that fundamental mechanisms govern the excitation of these components; we hypothesize that the warm component arises when H2 stops being the dominant coolant. In this scenario, the hot component arises in cooling molecular H2-poor gas just prior to the onset of H2 formation. High spectral resolution observations of highly excited CO transitions uniquely shed light on the origin of warm and hot gas in low-mass protostellar objects.
Context. Intermediate-mass young stellar objects (YSOs) provide a link to understanding how feedback from shocks and UV radiation scales from low- to high-mass star forming regions. Aims. Our aim is ...to analyze excitation of CO and H sub(2)O in deeply embedded intermediate-mass YSOs and compare it with similar studies on low-mass and high-mass YSOs. Methods. Herschel/PACS spectral maps are analyzed for six YSOs with bolometric luminosities of L sub(bol) ~ 10 super(2)-10 super(3)L sub(middot in circle). The maps cover spatial scales of ~10 super(4) AU in several CO and H sub(2)O lines located in the ~55-210 mum range. Results. Rotational diagrams of CO show two temperature components at T sub(rot) ~ 320 K and T sub(rot) ~ 700-800 K, comparable to low-and high-mass protostars probed at similar spatial scales. The diagrams for H sub(2)O show a single component at T sub(rot) ~ 130 K, as seen in low-mass protostars, and about 100 K lower than in high-mass protostars. Since the uncertainties in T sub(rot) are on the same order as the difference between the intermediate and high-mass protostars, we cannot conclude whether the change in rotational temperature occurs at a specific luminosity or whether the change is more gradual from low- to high-mass YSOs. Conclusions. Molecular excitation in intermediate-mass protostars is comparable to the central 10 super(3) AU of low-mass protostars and consistent within the uncertainties with the high-mass protostars probed at 3 x 10 super(3) AU scales, suggesting similar shock conditions in all those sources.
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