Context. The fine-structure line of atomic oxygen at 63 μm (OI63μm) is an important diagnostic tool in different fields of astrophysics: it is for example predicted to be the main coolant in several ...environments of star-forming regions (SFRs). However, our knowledge of this line relies on observations with low spectral resolution, and the real contribution of each component (photon-dominated region, jet) in the complex environment of SFRs to its total flux is poorly understood. Aims. We investigate the contribution of jet and photon-dominated region emission, and of absorption to the OI63μm line towards the hot gas around the ultra-compact Hii region G5.89–0.39 and study the far-IR line luminosity of the source in different velocity regimes through spectroscopically resolved spectra of atomic oxygen, CII, CO, OH, and H2O. Methods. We mapped G5.89–0.39 in OI63μm and in CO(16–15) with the GREAT receiver onboard SOFIA. We also observed the central position of the source in the ground-state OH 2Π3/2 J = 5/2 → J = 3/2 triplet and in the excited OH 2Π1/2 J = 3/2 → J = 1/2 triplets with SOFIA. These data were complemented with APEX CO(6–5) and CO(7–6) maps and with Herschel/HIFI maps and single-pointing observations in lines of CII, H2O, and HF. Results. The OI spectra in G5.89–0.39 are severely contaminated by absorptions from the source envelope and from different clouds along the line of sight. Emission is detected only at high velocities, and it is clearly associated with the compact north-south outflows traced by extremely high-velocity emission in low-J CO lines. The mass-loss rate and the energetics of the jet system derived from the OI63μm line agree well with previous estimates from CO, thus suggesting that the molecular outflows in G5.89–0.39 are driven by the jet system seen in OI. The far-IR line luminosity of G5.89–0.39 is dominated by OI at high-velocities; the second coolant in this velocity regime is CO, while CII, OH and H2O are minor contributors to the total cooling in the outflowing gas. Finally, we derive abundances of different molecules in the outflow: water has low abundances relative to H2 of 10-8−10-6, and OH of 10-8. Interestingly, we find an abundance of HF to H2 of 10-8, comparable with measurements in diffuse gas. Conclusions. Our study shows the importance of spectroscopically resolved observations of the OI63μm line for using this transition as diagnostic of star-forming regions. While this was not possible until now, the GREAT receiver onboard SOFIA has recently opened the possibility of detailed studies of the OI63μm line to investigate the potential of the transition for probing different environments.
Abstract
We unveil the stellar wind–driven shell of the luminous massive star-forming region of RCW 49 using SOFIA FEEDBACK observations of the C
ii
158
μ
m line. The complementary data set of the
...12
CO and
13
CO
J
= 3 → 2 transitions is observed by the APEX telescope and probes the dense gas toward RCW 49. Using the spatial and spectral resolution provided by the SOFIA and APEX telescopes, we disentangle the shell from a complex set of individual components of gas centered around RCW 49. We find that the shell of radius ∼6 pc is expanding at a velocity of 13 km s
−1
toward the observer. Comparing our observed data with the ancillary data at X-ray, infrared, submillimeter, and radio wavelengths, we investigate the morphology of the region. The shell has a well-defined eastern arc, while the western side is blown open and venting plasma further into the west. Though the stellar cluster, which is ∼2 Myr old, gave rise to the shell, it only gained momentum relatively recently, as we calculate the shell’s expansion lifetime of ∼0.27 Myr, making the Wolf–Rayet star WR 20a a likely candidate responsible for the shell’s reacceleration.
FEEDBACK from the NGC 7538 H II region Beuther, H.; Schneider, N.; Simon, R. ...
Astronomy and astrophysics (Berlin),
3/2022, Letnik:
659
Journal Article
Recenzirano
Odprti dostop
Context.
The interaction of expanding H
II
regions with their environmental clouds is one of the central questions driving the Stratospheric Observatory for Infrared Astronomy (SOFIA) legacy program ...FEEDBACK.
Aims.
We want to understand the interaction of the prototypical NGC 7538 H
II
region with the neighboring molecular cloud hosting several active star-forming regions.
Methods.
Using the SOFIA, we mapped an area of ~210′
2
(~125 pc
2
) around NGC 7538 in the velocity-resolved ionized carbon fine-structure line CII at 1.9 THz (158 μm). Complementary observed atomic carbon CI at 492 GHz and high-J CO(8–7) data, as well as archival near- and far-infrared, cm continuum, CO(3–2), and HI data are folded into the analysis.
Results.
The ionized carbon CII data reveal rich morphological and kinematic structures. While the overall morphology follows the general ionized gas that is also visible in the radio continuum emission, the channel maps show multiple bubble-like structures with sizes on the order of ~80–100″ (~1.0–1.28 pc). While at least one of them may be an individual feedback bubble driven by the main exciting sources of the NGC 7538 H
II
region (the O3 and O9 stars IRS6 and IRS5), the other bubble-like morphologies may also be due to the intrinsically porous structure of the H
II
region. An analysis of the expansion velocities around 10 km s
−1
indicates that thermal expansion is not sufficient but that wind-driving from the central O-stars is required. The region exhibits a general velocity gradient across, but we also identify several individual velocity components. The most blue-shifted CII component has barely any molecular or atomic counterparts. At the interface to the molecular cloud, we find a typical photon-dominated region (PDR) with a bar-shape. Ionized C
+
, atomic C
0
and molecular carbon CO show a layered structure in this PDR. The carbon in the PDR is dominated by its ionized C
+
form with atomic C
0
and molecular CO masses of ~0.45 ± 0.1
M
⊙
and ~1.2 ± 0.1
M
⊙
, respectively, compared to the ionized carbon C
+
in the range of 3.6−9.7
M
⊙
. This bar-shaped PDR exhibits a velocity-gradient across, indicating motions along the line of sight toward the observer.
Conclusions.
Even if it is shown to be dominated by two nearby exciting sources (IRS6 and IRS5), the NGC 7538 H
II
region exhibits a diverse set of substructures that interact with each other as well as with the adjacent cloud. Compared to other recent CII observations of H
II
regions (e.g., Orion Veil, RCW120, RCW49), the bubble-shape morphologies revealed in CII emission that are indicative of expanding shells are recurring structures of PDRs.
FEEDBACK is a SOFIA (Stratospheric Observatory for Infrared Astronomy) legacy program dedicated to study the interaction of massive stars with their environment. It performs a survey of 11 galactic ...high mass star-forming regions in the 158 m (1.9 THz) line of C ii and the 63 m (4.7 THz) line of O i. We employ the 14 pixel Low Frequency Array and 7 pixel High Frequency Array upGREAT heterodyne instrument to spectrally resolve (0.24 MHz) these far-infrared fine structure lines. With a total observing time of 96h, we will cover ∼6700 arcmin2 at 14 1) angular resolution for the C ii line and 6 3 for the O i line. The observations started in spring 2019 (Cycle 7). Our aim is to understand the dynamics in regions dominated by different feedback processes from massive stars such as stellar winds, thermal expansion, and radiation pressure, and to quantify the mechanical energy injection and radiative heating efficiency. This is an important science topic because feedback of massive stars on their environment regulates the physical conditions and sets the emission characteristics in the interstellar medium (ISM), influences the star formation activity through molecular cloud dissolution and compression processes, and drives the evolution of the ISM in galaxies. The C ii line provides the kinematics of the gas and is one of the dominant cooling lines of gas for low to moderate densities and UV fields. The O i line traces warm and high-density gas, excited in photodissociations regions with a strong UV field or by shocks. The source sample spans a broad range in stellar characteristics from single OB stars, to small groups of O stars, to rich young stellar clusters, to ministarburst complexes. It contains well-known targets such as Aquila, the Cygnus X region, M16, M17, NGC7538, NGC6334, Vela, and W43 as well as a selection of H ii region bubbles, namely RCW49, RCW79, and RCW120. These C ii maps, together with the less explored O i 63 m line, provide an outstanding database for the community. They will be made publically available and will trigger further studies and follow-up observations.
Context. During the formation of a star, material is ejected along powerful jets that impact the ambient material. This outflow regulates star formation by e.g. inducing turbulence and heating the ...surrounding gas. Understanding the associated shocks is therefore essential to the study of star formation. Aims. We present comparisons of shock models with CO, H2, and SiO observations in a “pure” shock position in the BHR71 bipolar outflow. These comparisons provide an insight into the shock and pre-shock characteristics, and allow us to understand the energetic and chemical feedback of star formation on Galactic scales. Methods. New CO (Jup = 16, 11, 7, 6, 4, 3) observations from the shocked regions with the SOFIA and APEX telescopes are presented and combined with earlier H2 and SiO data (from the Spitzer and APEX telescopes). The integrated intensities are compared to a grid of models that were obtained from a magneto-hydrodynamical shock code, which calculates the dynamical and chemical structure of these regions combined with a radiative transfer module based on the “large velocity gradient” approximation. Results. The CO emission leads us to update the conclusions of our previous shock analysis: pre-shock densities of 104 cm-3 and shock velocities around 20−25 km s-1 are still constrained, but older ages are inferred (~4000 years). Conclusions. We evaluate the contribution of shocks to the excitation of CO around forming stars. The SiO observations are compatible with a scenario where less than 4% of the pre-shock SiO belongs to the grain mantles. We infer outflow parameters: a mass of 1.8 × 10-2 M⊙ was measured in our beam, in which a momentum of 0.4 M⊙ km s-1 is dissipated, corresponding to an energy of 4.2 × 1043 erg. We analyse the energetics of the outflow species by species. Comparing our results with previous studies highlights their dependence on the method: H2 observations only are not sufficient to evaluate the mass of outflows.
We demonstrate for the first time the closure of an electronic phase lock loop for a continuous-wave quantum cascade laser (QCL) at 1.5 THz. The QCL is operated in a closed cycle cryo cooler. We ...achieved a frequency stability of better than 100 Hz, limited by the resolution bandwidth of the spectrum analyser. The PLL electronics make use of the intermediate frequency (IF) obtained from a hot electron bolometer (HEB) which is downconverted to a PLL IF of 125 MHz. The coarse selection of the longitudinal mode and the fine tuning is achieved via the bias voltage of the QCL. Within a QCL cavity mode, the free-running QCL shows frequency fluctuations of about 5 MHz, which the PLL circuit is able to control via the Stark-shift of the QCL gain material. Temperature dependent tuning is shown to be nonlinear, and of the order of -16 MHz/K. Additionally we have used the QCL as local oscillator (LO) to pump an HEB and perform, again for the first time at 1.5 THz, a heterodyne experiment, and obtain a receiver noise temperature of 1741 K.
We present the performance of the upGREAT heterodyne array receivers on the SOFIA telescope after several years of operations. This instrument is a multi-pixel high resolution (
R
≳
1
0
7
) ...spectrometer for the Stratospheric Observatory for Far-Infrared Astronomy (SOFIA). The receivers use 7-pixel subarrays configured in a hexagonal layout around a central pixel. The low frequency array receiver (LFA) has
2
×
7
pixels (dual polarization), and presently covers the 1.83–2.07
THz frequency range, which allows to observe the CII and OI lines at 158
μ
m and 145
μ
m wavelengths. The high frequency array (HFA) covers the OI line at 63
μ
m and is equipped with one polarization at the moment (7 pixels, which can be upgraded in the near future with a second polarization array). The 4.7
THz array has successfully flown using two separate quantum-cascade laser local oscillators from two different groups. NASA completed the development, integration and testing of a dual-channel closed-cycle cryocooler system, with two independently operable He compressors, aboard SOFIA in early 2017 and since then, both arrays can be operated in parallel using a frequency separating dichroic mirror. This configuration is now the prime GREAT configuration and has been added to SOFIA’s instrument suite since observing cycle 6.
Aims. We investigate the gas dynamics and the physical properties of photodissociation regions (PDRs) in IC 1396A, which is an illuminated bright-rimmed globule with internal structures created by ...young stellar objects. Methods. Our mapping observations of the C ii emission in IC 1396A with GREAT onboard SOFIA revealed the detailed velocity structure of this region. We combined them with observations of the C i 3P1−3P0 and CO(4–3) emissions to study the dynamics of the different tracers and physical properties of the PDRs. Results. The C ii emission generally matches the IRAC 8 μm, which traces the polycyclic aromatic hydrocarbon (PAH) emissions. The CO(4–3) emission peaks inside the globule, and the C i emission is strong in outer regions, following the 8 μm emission to some degree, but its peak is different from that of C ii. The C ii emitting gas shows a clear velocity gradient within the globule, which is not significant in the C i and CO(4–3) emission. Some clumps that are prominent in C ii emission appear to be blown away from the rim of the globule. The observed ratios of C ii/C i and C ii/CO(4–3) are compared to the KOSMA-τ PDR model, which indicates a density of 104–105 cm-3.
We demonstrate two different sources at 1.3 THz based on multiplier chains (72nd harmonic generation), which exhibit linewidths at the level of 2×10
−12
in relative units. The multiplication ...processes are shown not to contribute significantly to this linewidth. The phase noise of one of the sources and the fractional power in the carrier (76%) were determined. The application of these sources as references for quantum cascade THz lasers and for spectroscopy of ultracold molecules is suggested. Thus, rotational spectroscopy with few Hz resolution at 1.3 THz is possible with the present easy-to-use sources. An approach for reducing the linewidth by a factor on the order of 10
3
to the 1×10
−15
level using optical technology is proposed.
We present a new multi-pixel high resolution (R ≳ 107) spectrometer for the Stratospheric Observatory for Far-Infrared Astronomy (SOFIA). The receiver uses 2 × 7-pixel subarrays in orthogonal ...polarization, each in an hexagonal array around a central pixel. We present the first results for this new instrument after commissioning campaigns in May and December 2015 and after science observations performed in May 2016. The receiver is designed to ultimately cover the full 1.8−2.5 THz frequency range but in its first implementation, the observing range was limited to observations of the CII line at 1.9 THz in 2015 and extended to 1.83−2.07 THz in 2016. The instrument sensitivities are state-of-the-art and the first scientific observations performed shortly after the commissioning confirm that the time efficiency for large scale imaging is improved by more than an order of magnitude as compared to single pixel receivers. An example of large scale mapping around the Horsehead Nebula is presented here illustrating this improvement. The array has been added to SOFIA’s instrument suite already for ongoing observing cycle 4.
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