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| 17 | + |
| 18 | +<div id="title"> |
| 19 | + |
| 20 | +# JWST Observations of Young protoStars (JOYS): Overview of program and early results |
| 21 | + |
| 22 | +</div> |
| 23 | +<div id="comments"> |
| 24 | + |
| 25 | +[](https://arxiv.org/abs/2505.08002)<mark>Appeared on: 2025-05-14</mark> - _47 pages, 28 + 7 figures, A&A, in press_ |
| 26 | + |
| 27 | +</div> |
| 28 | +<div id="authors"> |
| 29 | + |
| 30 | +E. v. Dishoeck, et al. -- incl., <mark>H. Beuther</mark>, <mark>C. Gieser</mark>, <mark>G. Perotti</mark>, <mark>T. Henning</mark> |
| 31 | + |
| 32 | +</div> |
| 33 | +<div id="abstract"> |
| 34 | + |
| 35 | +**Abstract:** The embedded phase of star formation is a crucial period in the development of a young star as the system still accretes matter, emerges from its natal cloud assisted by powerful jets and outflows, and forms a disk setting the stage for the birth of a planetary system. Mid-infrared spectral line observations, now possible with unprecedented sensitivity, spectral resolution and sharpness with the $_ James Webb Space Telescope_$ (JWST), are key for probing many of the physical and chemical processes on sub-arcsecond scales that occur in highly extincted regions, providing unique diagnostics and complementing millimeter observations. The JWST Observations of Young protoStars (JOYS) program aims to address a wide variety of questions, ranging from protostellar accretion and the nature of primeval jets, winds and outflows, to the chemistry of gas and ice in hot cores and cold dense protostellar environments, and the characteristics of the embedded disks. We introduce the program and show representative JOYS results. JWST Mid-InfraRed Instrument (MIRI) Medium Resolution Spectrometer (MRS) Integral Field Unit (IFU) 5--28 $\mu$ m maps of 17 low-mass targets (23 if binary components counted individually) and 6 high-mass protostellar sources are taken with resolving powers $R=\lambda/\Delta \lambda=1500-4000$ . Small mosaics ranging from $1\times 1$ to $3\times 3$ MRS tiles cover $\sim 4"$ to $20"$ fields of view, providing spectral imaging on spatial scales down to $\sim$ 30 au (low mass) and $\sim$ 600 au (high mass). For HH 211, the complete $\sim 1'$ blue outflow lobe has been mapped with the MRS. Atomic lines are interpreted with published shock models, whereas molecular lines are analyzed with simple rotation diagrams and LTE slab models. The importance of taking infrared pumping into account is stressed. Inferred abundance ratios are compared with detailed hot core chemical models including X-rays. Ice spectra are fitted through comparison with laboratory spectra. The JWST MIRI-MRS spectra show a wide variety of features, with their spatial distribution providing insight into their physical origin. Atomic line maps differ among refractory (e.g., Fe), semi-refractory (e.g., S) and volatile elements (e.g., Ne), and are linked to their different levels of depletion and local (shock) conditions. Jets are prominently seen in lines of [ Fe II ] and other refractory elements whereas the pure rotational $H_2$ lines probe hot ( $\sim 1000$ K) and warm (few $\times 10^2$ K) gas inside the cavity, associated with jets, outflows and cavity walls, for both low- and high-mass sources. Wide-angle winds are found in low- $J$ $H_2$ lines. Nested, stratified jet structures consisting of an inner ionized core with an outer molecular layer are commonly seen in the youngest sources. [ S I ] follows the jet as seen in [ Fe II ] in the youngest protostars, but is different in more evolved sources where it is concentrated on source. Noble gas lines such as [ Ne II ] 12.8 $\mu$ m reveal a mix of jet shock and photoionized emission. H I recombination lines serve as a measure of protostellar accretion rates, but are also associated with more extended jets. Gaseous molecular emission ($CO_2$ , $C_2$ $H_2$ , HCN, $H_2$ O, $CH_4$ , $SO_2$ , SiO) is seen toward several sources, but is cool compared with what is found in more evolved disks, with excitation temperatures of only 100--250 K, and likely associated with the warm inner envelopes ("hot cores") . $CO_2$ is often extended along the outflow, in contrast with $C_2$ $H_2$ which is usually centered on source. Water emission is commonly detected on source even if relatively weak; off source it is seen only in the highest density shocks such as associated with NGC 1333 IRAS4B. Some sources show gaseous molecular lines in absorption, including $NH_3$ in one case. Deep ice features are seen toward the protostars, revealing not just the major ice components but also ions (as part of salts) and complex organic molecules, with comparable abundances from low- to high-mass sources. Relative abundances of some gas and ice species are similar, consistent with ice sublimation in hot cores. A second detection of HDO ice in a solar-mass source is presented, with an HDO/$H_2$ O ice ratio of $\sim$ 0.4 \% , providing a link with HDO/$H_2$ O in disks and comets. A deep search for solid $O_2$ suggests that it is not a significant oxygen reservoir. Only few embedded Class I disks show the same forest of water lines as Class II disks do, possibly caused by significant dust extinction of the upper layers due to limited growth and settling of dust to the midplane in young disks as well as radial drift bringing in small dust. This paper illustrates the many different science questions that a single MIRI-MRS IFU data set can address, with significant similarities between low- and high-mass sources. Large source samples across evolutionary stages and luminosities are needed to further develop these diagnostics of the physics and chemistry of protostellar systems. |
| 36 | + |
| 37 | +</div> |
| 38 | + |
| 39 | +<div id="div_fig1"> |
| 40 | + |
| 41 | +<img src="tmp_2505.08002/./JOYS_Fig2a.png" alt="Fig29.1" width="50%"/><img src="tmp_2505.08002/./JOYS_Fig2b.png" alt="Fig29.2" width="50%"/> |
| 42 | + |
| 43 | +**Figure 29. -** JWST MIRI-MRS spectrum of the low-mass Class 0 protostars |
| 44 | + B1-c (top) and Serpens SMM3 (bottom) illustrating the different |
| 45 | + molecular gas (red) and ice (blue) features that can be observed and |
| 46 | + analyzed, tracing different components of the protostellar |
| 47 | + system. The inserts in the B1-c spectrum aim to highlight the |
| 48 | + gas-phase molecular lines in this source. Atomic emission lines are |
| 49 | + present but not very strong in this source. In |
| 50 | + contrast, both $H_2$ and atomic emission lines are very prominent |
| 51 | + for Serpens SMM3 (bottom). At the bottom of the silicate feature at |
| 52 | + 10 $\mu$m, close to the noise limit, the spectra have been binned by |
| 53 | + a factor of 4 to enhance the $S/N$. See Fig. B.3 and B.11 of |
| 54 | + \citet{vanGelder24overview} for individual MIRI-MRS sub-bands. (*fig:B1c-overview*) |
| 55 | + |
| 56 | +</div> |
| 57 | +<div id="div_fig2"> |
| 58 | + |
| 59 | +<img src="tmp_2505.08002/./JOYS_Fig1.png" alt="Fig1" width="100%"/> |
| 60 | + |
| 61 | +**Figure 1. -** Cartoon of a protostellar source with the various physical |
| 62 | + components studied in this work indicated. (*fig:protostar-cartoon*) |
| 63 | + |
| 64 | +</div> |
| 65 | +<div id="div_fig3"> |
| 66 | + |
| 67 | +<img src="tmp_2505.08002/./JOYS_Fig10.png" alt="Fig8" width="100%"/> |
| 68 | + |
| 69 | +**Figure 8. -** MIRI-MRS maps of the various $H_2$ lines toward the Class 0 |
| 70 | + protostar Serpens SMM3. The white contours in the top left panel |
| 71 | + indicate the dust disk seen in millimeter continuum. The red and |
| 72 | + blue circles on the S(4) image indicate the positions where the |
| 73 | + $H_2$ spectra and rotational diagrams have been extracted. Note that |
| 74 | + the S(3) image at 9.66 $\mu$m is strongly affected by silicate |
| 75 | + extinction, and the S(5) line at 6.9 $\mu$m by ice extinction, hence |
| 76 | + their maps are more noisy. Beam sizes are indicated in the lower |
| 77 | + left corner of each panel. Each panel is scaled to the maximum |
| 78 | + emission of that species. The maximum and minimum colors are (in Jy |
| 79 | + km s$^{-1}$), from top left to bottom right: S(8) (0.008, 0.003); |
| 80 | + S(7) (0.033, 0.007); S(6) (0.013, 0.003); S(5) (0.026, 0.003); S(4) |
| 81 | + (0.089, 0.009); S(3) (0.035, 0.005); S(2) (0.090, 0.009); S(1) |
| 82 | + (0.084, 0.008). (*fig:SMM3H2*) |
| 83 | + |
| 84 | +</div><div id="qrcode"><img src=https://api.qrserver.com/v1/create-qr-code/?size=100x100&data="https://arxiv.org/abs/2505.08002"></div> |
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