Context. Young early-type HAeBe stars are still embedded in the molecular clouds in which they formed. They illuminate reflection nebulae, which shape the surrounding molecular cloud and may trigger ...star formation. They are therefore ideal places to search for ongoing star formation activity. Aims. NGC 2023 is illuminated by the Herbig Be star HD 37903. It is the most massive member of a small young cluster with about 30 PMS stars, several of which are Class I objects that still heavily accrete. It might therefore be expected that they might drive molecular outflows. We examined the whole region for outflows. Methods. We analyzed previously published APEX data to search for and characterize the outflows in the NGC 2023 region. This is the first systematic search for molecular outflows in this region. Since the outflows were mapped in several CO transitions, we can determine their properties quite well. Results. We have discovered four molecular outflows in the vicinity of NGC 2023, three of which are associated with Class I objects. MIR-63, a bright mid-infrared and submillimeter Class I source, is a binary with a separation of 2″.4 and drives two bipolar outflows orthogonal to each other. The large southeast–northwest outflow excites the Herbig-Haro flow HH 247. MIR-73, a Class I object, which is also a far-infrared source, drives a pole-on outflow. MIR-62 is a Class II object with strong infrared excess and a luminosity of 7 L ⊙ . It is not detected in the far-infrared. The Class I sources have bolometric luminosities of about 20 L ⊙ or lower, that is, they are all low-mass stars. One other far-infrared source, MIR-75, may have powered an outflow in the past because it now illuminates an egg-shaped cavity. Conclusions. The four outflows are all powered by young stars and are located in the immediate vicinity of NGC 2023. They are at a similar evolutionary stage, which suggests that their formation may have been triggered by the expanding C II region.
Opening the Treasure Chest in Carina Mookerjea, B.; Sandell, G.; Güsten, R. ...
Astronomy and astrophysics (Berlin),
06/2019, Volume:
626
Journal Article
Peer reviewed
Open access
Pillars and globules are the best examples of the impact of the radiation and wind from massive stars on the surrounding interstellar medium. We mapped the G287.84-0.82 cometary globule (with the ...Treasure Chest cluster embedded in it) in the South Pillars region of Carina (i) in C II, 63 μm O I, and CO(11–10) using the heterodyne receiver array upGREAT on SOFIA and (ii) in J = 2–1 transitions of CO, 13CO, C18O, and J = 3–2 transitions of H2CO using the APEX telescope in Chile. We used these data to probe the morphology, kinematics, and physical conditions of the molecular gas and the photon-dominated regions (PDRs) in G287.84-0.82. The velocity-resolved observations of C II and O I suggest that the overall structure of the pillar (with red-shifted photoevaporating tails) is consistent with the effect of FUV radiation and winds from η Car and O stars in Trumpler 16. The gas in the head of the pillar is strongly influenced by the embedded cluster, whose brightest member is an O9.5 V star, CPD −59°2661. The emission of the C II and O I lines peak at a position close to the embedded star, while all the other tracers peak at another position lying to the northeast consistent with gas being compressed by the expanding PDR created by the embedded cluster. The molecular gas inside the globule was probed with the J = 2–1 transitions of CO and isotopologs as well as H2CO, and analyzed using a non-local thermodynamic equilibrium model (escape-probability approach), while we used PDR models to derive the physical conditions of the PDR. We identify at least two PDR gas components; the diffuse part (~ 104 cm−3) is traced by C II, while the dense (n ~ 2–8 × 105 cm−3) part is traced by C II, O I, and CO(11–10). Using the F = 2–1 transition of 13C II detected at 50 positions in the region, we derived optical depths (0.9–5), excitation temperatures (80–255 K) of C II, and N(C+) of 0.3–1 × 1019 cm−2. The total mass of the globule is ~1000 M⊙, about half of which is traced by C II. The dense PDR gas has a thermal pressure of 107–108 K cm−3, which is similar to the values observed in other regions.
FEEDBACK from the NGC 7538 H II region Beuther, H.; Schneider, N.; Simon, R. ...
Astronomy and astrophysics (Berlin),
3/2022, Volume:
659
Journal Article
Peer reviewed
Open access
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.
Herbig Ae/Be objects are pre-main sequence stars surrounded by gas- and dust-rich circumstellar discs. These objects are in the throes of star and planet formation, and their characterisation informs ...us of the processes and outcomes of planet formation processes around intermediate mass stars. Here we analyse the spectral energy distributions of disc host stars observed by the Herschel open time key programme “Gas in Protoplanetary Systems”. We present Herschel/PACS far-infrared imaging observations of 22 Herbig Ae/Bes and 5 debris discs, combined with ancillary photometry spanning ultraviolet to sub-millimetre wavelengths. From these measurements we determine the diagnostics of disc evolution, along with the total excess, in three regimes spanning near-, mid-, and far-infrared wavelengths. Using appropriate statistical tests, these diagnostics are examined for correlations. We find that the far-infrared flux, where the disc becomes optically thin, is correlated with the millimetre flux, which provides a measure of the total dust mass. The ratio of far-infrared to sub-millimetre flux is found to be greater for targets with discs that are brighter at millimetre wavelengths and that have steeper sub-millimetre slopes. Furthermore, discs with flared geometry have, on average, larger excesses than flat geometry discs. Finally, we estimate the extents of these discs (or provide upper limits) from the observations.
We analyze a C II 158 μm map obtained with the L2 GREAT receiver on SOFIA of the reflection nebula illuminated by the early B star S 1 in the ρ Oph A cloud core. This data set has been complemented ...with maps of CO(3–2), 13CO(3–2), and C18O(3–2), observed as a part of the James Clerk Maxwell Telescope (JCMT) Gould Belt Survey, with archival HCO+(4–3) JCMT data, as well as with O I 63 and 145 μm imaging with Herschel/PACS. The C II emission is completely dominated by the strong emission from the photon dominated region (PDR) in the nebula surrounding S 1 expanding into the dense Oph A molecular cloud west and south of S 1. The C II emission is significantly blueshifted relative to the CO spectra and also relative to the systemic velocity, particularly in the northwestern part of the nebula. The C II lines are broader toward the center of the S 1 nebula and narrower toward the PDR shell. The C II lines are strongly self-absorbed over an extended region in the S 1 PDR. Based on the strength of the 13C II F = 2–1 hyperfine component, C II is significantly optically thick over most of the nebula. CO and 13CO(3–2) spectra are strongly self-absorbed, while C18O(3–2) is single peaked and centered in the middle of the self-absorption. We have used a simple two-layer LTE model to characterize the background and foreground cloud contributing to the C II emission. From this analysis we estimated the extinction due to the foreground cloud to be ~9.9 mag, which is slightly less than the reddening estimated toward S 1. Since some of the hot gas in the PDR is not traced by low-J CO emission, this result appears quite plausible. Using a plane parallel PDR model with the observed O I(145)/C II brightness ratio and an estimated FUV intensity of 3100–5000 G0 suggests that the density of the C II emitting gas is ~3–4 × 103 cm−3.
We observed a sample of 20 representative Herbig Ae/Be stars and 5 A-type debris discs with PACS onboard Herschel, as part of the GAS in Protoplanetary Systems (GASPS) project. The observations were ...done in spectroscopic mode, and cover the far-infrared lines of O i, C ii, CO, CH+, H2O, and OH. We have a O i 63 μm detection rate of 100% for the Herbig Ae/Be and 0% for the debris discs. The O i 145 μm line is only detected in 25% and CO J = 18-17 in 45% (and fewer cases for higher J transitions) of the Herbig Ae/Be stars, while for C ii 157 μm, we often find spatially variable background contamination. We show the first detection of water in a Herbig Ae disc, HD 163296, which has a settled disc. Hydroxyl is detected as well in this disc. First seen in HD 100546, CH+ emission is now detected for the second time in a Herbig Ae star, HD 97048. We report fluxes for each line and use the observations as line diagnostics of the gas properties. Furthermore, we look for correlations between the strength of the emission lines and either the stellar or disc parameters, such as stellar luminosity, ultraviolet and X-ray flux, accretion rate, polycyclic aromatic hydrocarbon (PAH) band strength, and flaring. We find that the stellar ultraviolet flux is the dominant excitation mechanism of O i 63 μm, with the highest line fluxes being found in objects with a large amount of flaring and among the largest PAH strengths. Neither the amount of accretion nor the X-ray luminosity has an influence on the line strength. We find correlations between the line flux of O i 63 μm and O i 145 μm, CO J = 18-17 and O i 6300 Å, and between the continuum flux at 63 μm and at 1.3 mm, while we find weak correlations between the line flux of O i 63 μm and the PAH luminosity, the line flux of CO J = 3-2, the continuum flux at 63 μm, the stellar effective temperature, and the Brγ luminosity. Finally, we use a combination of theO i 63 μm and 12CO J = 2-1 line fluxes to obtain order of magnitude estimates of the disc gas masses, in agreement with the values that we find from detailed modelling of two Herbig Ae/Be stars, HD 163296 and HD 169142. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.
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. The warm ionized medium (WIM) occupies a significant fraction of the Galactic disk. Determining the WIM properties at the leading edge of spiral arms is important for understanding its ...dynamics and cloud formation. Aims. We derive the properties of the WIM at the inner edge of the Scutum arm tangency, which is a unique location in which to disentangle the WIM from other components, using the ionized gas tracers C+ and N+. Methods. We use high spectral resolution C ii 158 μm and N ii 205 μm fine structure line observations taken with the upGREAT and GREAT instruments, respectively, on SOFIA, along with auxiliary H i and 13CO observations. The observations consist of samples in and out of the Galactic plane along 18 lines of sight (LOS) between longitude 30° and 32°. Results. We detect strong N ii emission throughout the Scutum tangency. At VLSR = 110 to 125 km s-1 where there is little, if any, 13CO, we are able to disentangle the N ii and C ii emission that arises from the WIM at the arm’s inner edge. We find an average electron density ~0.9 cm-3 in the plane, and ~0.4 cm-3 just above the plane. The N ii emission decreases exponentially with latitude with a scale height ~55 pc. For VLSR< 110 km s-1 there is N ii emission tracing highly ionized gas throughout the arm’s molecular layer. This ionized gas has a high density, n(e)~ 30 cm-3, and a few percent filling factor. We also find evidence for C ii absorption by foreground gas. Conclusions. N ii and C ii observations at the Scutum arm tangency reveal a highly ionized gas with average electron density about 10 to 20 times those of the interarm WIM, and is best explained by a model in which the interarm WIM is compressed as it falls into the potential well of the arm. The widespread distribution of N ii in the molecular layers shows that high density ionized gas is distributed throughout the Scutum arm. The electron densities derived from N ii for these molecular cloud regions are ~30 cm-3, and probably arise in the ionized boundary layers of clouds. The N ii detected in the molecular portion of the spiral arm arises from several cloud components with a combined total depth ~8 pc. This N ii emission most likely arises from ionized boundary layers, probably the result of the shock compression of the WIM as it impacts the arm’s neutral gas, as well as from extended H ii regions.
Water is key in the evolution of protoplanetary disks and the formation of comets and icy/water planets. While high-excitation water lines originating in the hot inner disk have been detected in ...several T Tauri stars (TTSs), water vapor from the outer disk, where most water ice reservoirs are stored, was only reported in the nearby TTS TW Hya. We present spectrally resolved Herschel/HIFI observations of the young TTS DG Tau in the ortho- and para-water ground-state transitions at 557 and 1113 GHz. The lines show a narrow double-peaked profile, consistent with an origin in the outer disk, and are ~19-26 times brighter than in TW Hya. In contrast, CO and CII lines are dominated by emission from the envelope/outflow, which makes H sub(2)O lines a unique tracer of the disk of DG Tau. Disk modeling with the thermo-chemical code ProDiMo indicates that the strong UV field, due to the young age and strong accretion of DG Tau, irradiates a disk upper layer at 10-90 AU from the star, heating it up to temperatures of 600 K and producing the observed bright water lines. The models suggest a disk mass of 0.015-0.1 M sub(middot in circle), consistent with the estimated minimum mass of the solar nebula before planet formation, and a water reservoir of ~10 super(2)-10 super(3) Earth oceans in vapor and ~100 times larger in the form of ice. Hence, this detection supports the scenario of ocean delivery on terrestrial planets by the impact of icy bodies forming in the outer disk.
We present wide-field near-infrared (IR) images of the DR21/W75 high-mass star-forming region, obtained with the Wide Field Camera (WFCAM) on the United Kingdom Infrared Telescope. Broad-band JHK and ...narrow-band H2 1-0S(1) images are compared to archival mid-IR images from the Spitzer Space Telescope, and 850-μm dust-continuum maps obtained with the Submillimeter Common User Bolometer Array (SCUBA). Together these data give a complete picture of dynamic star formation across this extensive region, which includes at least four separate star-forming sites in various stages of evolution. The H2 data reveal knots and bow shocks associated with more than 50 individual flows. Most are well collimated, and at least five qualify as parsec-scale flows. Most appear to be driven by embedded, low-mass protostars. The orientations of the outflows, particularly from the few higher mass sources in the region (DR21, DR21(OH), W75N and ERO 1), show some degree of order, being preferentially orientated roughly orthogonal to the chain of dusty cores that runs north-south through DR21. Clustering may inhibit disc accretion and therefore the production of outflows; we certainly do not see enhanced outflow activity from clusters of protostars. Finally, although the low-mass protostellar outflows are abundant and widely distributed, the current generation does not provide sufficient momentum and kinetic energy to account for the observed turbulent motions in the DR21/W75 giant molecular clouds. Rather, multiple epochs of outflow activity are required over the million-year time-scale for turbulent decay.
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