arXiv subjects

Nicole Karnath

Publications and source records attributed to Nicole Karnath.

At least 19 recordsLinked to original sources

arXiv2026

Magneto-Gravitational Regulated Streamer Accretion onto a Class 0 Protostellar System

How do magnetic fields shape the way young stars gather gas from their birth clouds? Using high-resolution Atacama Large Millimeter/submillimeter Array observations of a young triple protostellar system HOPS-182, we identify an elongated stream of gas, or accretion streamer, that extends over several thousand astronomical units (1 astronomical unit is the Earth-Sun distance) and carries a substantial flow of material toward the system. The gas speeds along this filament increase toward the star in a way consistent with gravitational free-fall, while the streamer's shape closely follows the magnetic field threading the region. By comparing the strengths of gravity and magnetic tension and measuring how the gas rotates compared with the local magnetic field, we show that the field is strong enough to help confine and guide the infalling gas and efficiently remove angular momentum. These results suggest that a substantial fraction of the material falling onto young protostellar systems can be funneled through elongated, magnetically structured accretion streamers.

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arXiv2026

Protostellar Outflows Shed Light on the Dominant Close Companion Star Formation Pathways

Understanding the formation pathway for close-companion protostars is central to unraveling the processes that govern stellar multiplicity and very early star formation. We analyze a large sample of 51 Class 0/I close-companion protostellar systems, of which 38 show detectable outflows, yielding 42 measured outflows used in our analysis. We use ALMA observations of 11 systems in Perseus and 40 systems in Orion. These companions formed either directly at these small scales ($\lesssim 500$ au separations) via disk fragmentation or at larger scales ($> 1000$ au separations) via turbulent fragmentation followed by inward migration. Because of differences in formation mechanism, the former is expected to have preferentially aligned disks and outflows, whereas the latter is expected to show no preferred alignment. The relative prevalence of these formation pathways remains uncertain, yet it is critical to forming a comprehensive picture of star formation. We examine the distribution of position angles of companion protostars relative to the position angles of their molecular outflows. The outflow, as traced by $^{12}$CO ($J=2\rightarrow1$), is a useful proxy for the angular momentum of the system, expected to be orthogonal to the binary orbital plane. We use a simple model to account for random sampling of inclination and orbital phase in each system, finding that the observations are consistent with a distribution in which the outflows are preferentially orthogonal to the companions. Based on this analysis, we suggest disk fragmentation is the dominant formation pathway for close-companion protostellar systems.

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arXiv2026

Surveying the Giant HII Regions of the Milky Way with SOFIA: VIII. W43 Main

In this eighth paper of the SOFIA-FORCAST series on Milky Way GHII regions, we present an analysis of the massive star-forming complex W43 Main. We compared our 11 - 37 micron maps with multi-wavelength observations from the near-infrared to radio, and investigated the physical nature of compact sources and dust substructures. We applied SED fitting to constrain properties of the compact infrared objects, and examined the evolutionary states of the extended subregions. We identified 20 compact infrared objects, 16 (80%) of which we classify as massive young stellar objects (MYSOs) or candidate MYSOs. W43 Main resides at the junction of the Scutum spiral arm and the Galactic Bar, a location where enhanced turbulence is anticipated and has been proposed as a potential influence on star-formation activity. Nevertheless, our analysis shows that its Lyman continuum photon production rate, the mass of its most massive MYSO, and its MYSO density are all consistent with the survey-wide median values. We therefore conclude that, despite W43 Main's unique Galactic environment, its present star formation activity appears broadly consistent with that of an average Galactic GHII region.

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arXiv2026

Investigating the Nested Structure of the Outflow from the Low Luminosity Protostar IRAS 16253-2429 using JWST and ALMA

Understanding the earliest stage of star and planet formation requires detailed observations to address the connection and interplay between the accretion, outflow and disk evolution. We present results from the observations of the low luminosity ($L_\mathrm{bol}\sim~0.2~L_\odot$) and mass (M$_*\sim$\,0.15~M$_\odot$) Class~0 protostar IRAS 16253$-$2429, conducted as part of the \textit{eDisk} ALMA large program and the JWST cycle-1 GO program \textit{IPA}. Observations reveal a wide hourglass-shaped continuum cavity traced in scattered light (at $\leq$~5~$\mu$m), with a brighter, extended northern side. We detect 15 pure rotational H$_2$ transitions (E$_\mathrm{up}$:~1015--21411~K), revealing a wide-angle molecular outflow. {The outflow width (as traced in H$_2$~0-0~S(11)) at the protostellar location measures $\leq$35 au, slightly larger than the dust and Keplerian disk diameters ($\sim$30 au) but wider than the 20--23~au jet width in [Fe II].} {The opening angle narrows from 40--35\arcdeg{} for the low-J H$_2$ lines (up to S(5)) and the cold gas component (ALMA $^{12}$CO) to $\sim$28--19\arcdeg{} for the high-J H$_2$ lines (S(7)--S(11)).} Position-velocity diagrams of H$_2$ reveal higher velocities for higher E$_{up}$, ranging from ~12.5 km~s$^{-1}$ for H$_2$~0-0~S(1) and S(2) to ~28.5 km~s$^{-1}$ for H$_2$~0-0~S(5)~and~S(7) with respect to the mean flow velocity. The nested excitation and velocity structure of the collimated jet and wide angle wind suggest a magnetohydrodynamic wind as a likely launching mechanism, similar to the findings in other protostars and Class II sources. The lower velocity mm CO may be gas from the infalling envelope accelerated outwards by the wide angle wind along the cavity walls.

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arXiv2025

IPA. Accretion rate of a low-mass Class 0 protostar, measured via mid-infrared fluorescent OH emission

The earliest stages of star formation are highlighted by complex interactions between accretion, outflow, and radiative processes, which shape the chemical and physical environment of the emerging protostar. James Webb Space Telescope observations of the low-mass, low-luminosity Class 0 protostar IRAS 16253-2429 reveal a central compact source. This object exhibits a rich mid-infrared emission spectrum of OH pure rotational lines and $\rm CO_2$ ro-vibrational lines. Unusually for a young stellar object, it has no mid-infrared line emission from $\rm H_2O$ to match the other molecules. We demonstrate that the emitting OH molecules arise from UV photodissociation of $\rm H_2O$ in its second absorption band at $\lambda = 114-145$ nm, and that the OH emission is a fluorescent cascade starting with highest-excitation rotational states. This situation offers the opportunity of using the infrared OH spectrum to measure the UV flux from the central protostar. Thereby we determine the disk-star accretion rate to be $3 \times 10^{-10} \ M_\sun \ {\rm year^{-1}}$, and demonstrate that the system luminosity arises mostly from the protostar's photosphere rather than from accretion luminosity. The result is in accord with the measured outflow rate of IRAS 16253-2429 and lies within the outflow/accretion-flow rate trend often inferred for protostars; and with episodic accretion as the dominant mechanism by which this protostar has grown.

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arXiv2025

Magnetic Fields in the Bones of the Milky Way

Stars primarily form in galactic spiral arms within dense, filamentary molecular clouds. The largest and most elongated of these molecular clouds are referred to as ``bones," which are massive, velocity-coherent filaments (lengths ~20 to >100 pc, widths ~1-2 pc) that run approximately parallel and in close proximity to the Galactic plane. While these bones have been generally well characterized, the importance and structure of their magnetic fields (B-fields) remain largely unconstrained. Through the SOFIA Legacy program FIELDMAPS, we mapped the B-fields of 10 bones in the Milky Way. We found that their B-fields are varied, with no single preferred alignment along the entire spine of the bones. At higher column densities, the spines of the bones are more likely to align perpendicularly to the B-fields, although this is not ubiquitous, and the alignment shows no strong correlation with the locations of identified young stellar objects. We estimated the B-field strengths across the bones and found them to be ~30-150 $\mu$G at pc scales. Despite the generally low virial parameters, the B-fields are strong compared to the local gravity, suggesting that B-fields play a significant role in resisting global collapse. Moreover, the B-fields may slow and guide gas flow during dissipation. Recent star formation within the bones may be due to high-density pockets at smaller scales, which could have formed before or simultaneously with the bones.

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arXiv2025

FIELDMAPS Data Release: Far-Infrared Polarization in the "Bones" of the Milky Way

Polarization observations of the Milky Way and many other spiral galaxies have found a close correspondence between the orientation of spiral arms and magnetic field lines on scales of hundreds of parsecs. This paper presents polarization measurements at 214 $\mu$m toward ten filamentary candidate ``bones" in the Milky Way using the High-resolution Airborne Wide-band Camera (HAWC+) on the Stratospheric Observatory for Infrared Astronomy (SOFIA). These data were taken as part of the Filaments Extremely Long and Dark: A Magnetic Polarization Survey (FIELDMAPS) and represent the first study to resolve the magnetic field in spiral arms at parsec scales. We describe the complex yet well-defined polarization structure of all ten candidate bones, and we find a mean difference and standard deviation of $-74^{\circ} \pm 32^{\circ}$ between their filament axis and the plane-of-sky magnetic field, closer to a field perpendicular to their length rather than parallel. By contrast, the 850 $\mu$m polarization data from \textit{Planck} on scales greater than 10 pc show a nearly parallel mean difference of $3^{\circ} \pm 21^{\circ}$. These findings provide further evidence that magnetic fields can change orientation at the scale of dense molecular clouds, even along spiral arms. Finally, we use a power law to fit the dust polarization fraction as a function of total intensity on a cloud-by-cloud basis and find indices between $-0.6$ and $-0.9$, with a mean and standard deviation of $-0.7 \pm 0.1$. The polarization, dust temperature, and column density data presented in this work are publicly available online.

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arXiv2025

Gravitational Binding and Star Formation in Molecular Clouds of the Milky Way

The gravitational binding and star-forming properties of molecular clouds (MCs) in the Milky Way (MW) are estimated from CO cloud observations and from a model of pressure-bounded virial equilibrium (PVE). Two CO surveys are analyzed with the standard CO conversion factor. The main results are: (1) For each survey the cloud virial parameter $\alpha_{vir}$ increases by a factor ~2 from galactocentric radius $R_{gal}$ = 4 kpc to 15 kpc. (2) PVE models match these trends only if the surface densities of survey clouds and nearby stars are comparable. This evidence of environmental influence resembles that seen in other disk galaxies. (3) Many survey clouds form stars even though their virial parameter exceeds the critical value $\alpha_{vir}\approx2$. In PVE such clouds with constant velocity dispersion have stable equilibrium and cannot form stars by simple global collapse. (4) However, simulations show that $\alpha_{vir}\approx2$ clouds with dissipating turbulence may form filaments, cores and protostars with little global contraction. Such clouds can match the MW star formation rate if their protostellar cores have mass fraction ~10$^{-3}$. A simple model predicts that the star-forming age of a cloud is proportional to the ratio of its YSOs to its mass. (5) Clouds within ~500 pc of the Sun are predicted to have star-forming ages 1-10 Myr and average YSO age ~2 Myr, matching evolutionary models. The Orion A cloud is predicted to have ~60 Class 0 protostars, ~2900 YSOs and efficiency $SFE\approx0.02$, in good agreement with observed estimates.

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arXiv2025

Characterizing Magnetic Properties of Young Protostars in Orion

The {\em B}-field Orion Protostellar Survey (BOPS) recently obtained polarimetric observations at 870 ${\rm \mu m}$ towards 61 protostars in the Orion molecular clouds with $\sim 1^{\prime\prime}$ spatial resolution using the Atacama Large Millimeter/submillimeter Array. From the BOPS sample, we selected the 26 protostars with extended polarized emission within a radius of $\sim 6^{\prime\prime}$ (2400~au) around the protostar. This allows to have sufficient statistical polarization data to infer the magnetic field strength. The magnetic field strength is derived using the Davis-Chandrasekhar-Fermi method. The underlying magnetic field strengths are approximately 2.0~mG for protostars with a standard hourglass magnetic field morphology, which is higher than the values derived for protostars with rotated hourglass, spiral, and complex magnetic field configurations ($\lesssim1.0$~mG). This suggests that the magnetic field plays a more significant role in envelopes exhibiting a standard hourglass field morphology, and a value of $\gtrsim2.0$ mG would be required to maintain such a structure at these scales. Furthermore, most protostars in the sample are slightly supercritical, with mass-to-flux ratios $\lesssim3.0$. In particular, the mass-to-flux ratios for all protostars with a standard hourglass magnetic field morphology are lower than 3.0. However, these ratios do not account for the contribution of the protostellar mass, which means they are likely significantly underestimated.

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arXiv2025

Surveying the Giant HII Regions of the Milky Way with SOFIA: VII. Galactic Center Regions Sgr B1, Sgr B2, and Sgr C

This study examines the mid-infrared properties of Giant HII (GHII) regions in the Milky Way's Central Molecular Zone (CMZ) -- Sgr B1, Sgr B2, and Sgr C -- using SOFIA-FORCAST imaging at 25 and 37 microns. It compares these mid-infrared data with previous multi-wavelength observations to explore their present star formation activity and global properties. The study identifies 77 massive young stellar object (MYSO) candidates in and around the three regions. Sgr B2 appears to host the youngest MYSOs and have much higher extinction than the other regions, containing several radio sources not detected in the mid-infrared even at 37 microns. Meanwhile, cm radio continuum regions of Sgr B1 shows remarkable correspondence to its mid-infrared emission. Sgr C has fewer confirmed MYSOs, and seems to have a higher fraction of low-mass young stellar objects and contamination from more evolved interloper/foreground stars. Derived MYSO densities are consistent with GHII regions elsewhere in the Galactic plane, though the CMZ GHII regions appear to have less prolific present star formation overall. Unlike Sgr B2, the cm continuum emission in Sgr B1 and Sgr C GHII regions appears to be absent cold dust and molecular gas, suggesting environmental differences, possibly driven by turbulence and rapid dynamical changes near the Galactic Center. Furthermore, unlike typical GHII regions, Sgr B1 and Sgr C are significantly ionized by evolved interloper stars, which likely did not form within these regions. In these ways, Sgr B1 and Sgr C deviate from classical GHII region behavior, thus potentially representing a new category of GHII region or challenging their classification as GHII regions.

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arXiv2024

JWST-IPA: Chemical Inventory and Spatial Mapping of Ices in the Protostar HOPS370 -- Evidence for an Opacity Hole and Thermal Processing of Ices

The composition of protoplanetary disks, and hence the initial conditions of planet formation, may be strongly influenced by the infall and thermal processing of material during the protostellar phase. Composition of dust and ice in protostellar envelopes, shaped by energetic processes driven by the protostar, serves as the fundamental building material for planets and complex organic molecules. As part of the JWST GO program, "Investigating Protostellar Accretion" (IPA), we observed an intermediate-mass protostar HOPS 370 (OMC2-FIR3) using NIRSpec/IFU and MIRI/MRS. This study presents the gas and ice phase chemical inventory revealed with the JWST in the spectral range of $\sim$2.9 to 28 $\mu$m and explores the spatial variation of volatile ice species in the protostellar envelope. We find evidence for thermal processing of ice species throughout the inner envelope. We present the first high-spatial resolution ($\sim 80$ au) maps of key volatile ice species H$_{2}$O, CO$_{2}$, $^{13}$CO$_2$, CO, and OCN$^-$, which reveal a highly structured and inhomogeneous density distribution of the protostellar envelope, with a deficiency of ice column density that coincides with the jet/outflow shocked knots. Further, we observe high relative crystallinity of H$_{2}$O ice around the shocked knot seen in the H$_2$ and OH wind/outflow, which can be explained by a lack of outer colder material in the envelope along the line of sight due to the irregular structure of the envelope. These observations show clear evidence of thermal processing of the ices in the inner envelope, close to the outflow cavity walls, heated by the luminous protostar.

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arXiv2024

The long-period spectroscopic orbit and dust creation in the Wolf-Rayet binary system WR 125

Several long-period binaries with a carbon-rich Wolf-Rayet star and an O star produce dust in their wind collisions. In eccentric binaries, this is seen most strongly near periastron passage. The exact conditions leading to dust creation require orbital properties to be determined, which is difficult owing to their long periods. Recently, the binary system WR 125 (WC7+O9III) began a dust creation episode seen through an infrared outburst first detected by NEOWISE-R, which was the first outburst detected since 1991. We present new near- and mid-infrared photometry, which we use to show consistency between the two outbursts and derive an orbital period of 28.12$^{+0.10}_{-0.05}$ yr. We use a long time-series of optical spectra to place the first constraints on its orbital elements, on the assumption that this system will produce dust near periastron. The orbit has a mild eccentricity of 0.29$\pm$0.12 and is only derived for the Wolf-Rayet component, as the O star's radial velocities have noise that is likely larger than the expected semi-amplitude of the orbit. We also present SOFIA/FORCAST grism spectroscopy to examine the infrared spectral energy distribution (SED) of the dust during this outburst, comparing its properties to other WCd binaries, deriving a dust temperature of 580 K in 2021. This collection of observations will allow us to plan future observations of this system and place the system in the context of dust-creating Wolf-Rayet binaries.

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arXiv2024

On the magnetic field properties of protostellar envelopes in Orion

We present 870 um polarimetric observations toward 61 protostars in the Orion molecular clouds, with ~400 au (1") resolution using the Atacama Large Millimeter/submillimeter Array. We successfully detect dust polarization and outflow emission in 56 protostars, in 16 of them the polarization is likely produced by self-scattering. Self-scattering signatures are seen in several Class 0 sources, suggesting that grain growth appears to be significant in disks at earlier protostellar phases. For the rest of the protostars, the dust polarization traces the magnetic field, whose morphology can be approximately classified into three categories: standard-hourglass, rotated-hourglass (with its axis perpendicular to outflow), and spiral-like morphology. 40.0% (+-3.0%) of the protostars exhibit a mean magnetic field direction approximately perpendicular to the outflow on several 100--1000 au scales. However, in the remaining sample, this relative orientation appears to be random, probably due to the complex set of morphologies observed. Furthermore, we classify the protostars into three types based on the C17O (3--2) velocity envelope's gradient: perpendicular to outflow, non-perpendicular to outflow, and unresolved gradient (<1.0~km/s/arcsec). In protostars with a velocity gradient perpendicular to outflow, the magnetic field lines are preferentially perpendicular to outflow, most of them exhibit a rotated hourglass morphology, suggesting that the magnetic field has been overwhelmed by gravity and angular momentum. Spiral-like magnetic fields are associated with envelopes having large velocity gradients, indicating that the rotation motions are strong enough to twist the field lines. All of the protostars with a standard-hourglass field morphology show no significant velocity gradient due to the strong magnetic braking.

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arXiv2024

Investigating Protostellar Accretion-Driven Outflows Across the Mass Spectrum: JWST NIRSpec IFU 3-5~$μ$m Spectral Mapping of Five Young Protostars

Investigating Protostellar Accretion is a Cycle 1 JWST program using the NIRSpec+MIRI integral field units to obtain 2.9--28 $μ$m spectral cubes of five young protostars with luminosities of 0.2-10,000 L$_{\odot}$ in their primary accretion phase. This paper introduces the NIRSpec 2.9--5.3 $μ$m data of the inner 840-9000 au with spatial resolutions from 28-300 au. The spectra show rising continuum emission; deep ice absorption; emission from H$_{2}$, H~I, and [Fe~II]; and the CO fundamental series in emission and absorption. Maps of the continuum emission show scattered light cavities for all five protostars. In the cavities, collimated jets are detected in [Fe~II] for the four $< 320$~L$_{\odot}$ protostars, two of which are additionally traced in Br-$α$. Knots of [Fe~II] emission are detected toward the most luminous protostar, and knots of [FeII] emission with dynamical times of $< 30$~yrs are found in the jets of the others. While only one jet is traced in H$_2$, knots of H$_2$ and CO are detected in the jets of four protostars. H$_2$ is seen extending through the cavities, showing that they are filled by warm molecular gas. Bright H$_2$ emission is seen along the walls of a single cavity, while in three cavities narrow shells of H$_2$ emission are found, one of which has an [Fe~II] knot at its apex. These data show cavities containing collimated jets traced in atomic/ionic gas surrounded by warm molecular gas in a wide-angle wind and/or gas accelerated by bow shocks in the jets.

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arXiv2024

JWST observations of $^{13}$CO$_{2}$ ice: Tracing the chemical environment and thermal history of ices in protostellar envelopes

The structure and composition of simple ices can be modified during stellar evolution by protostellar heating. Key to understanding the involved processes are thermal and chemical tracers that can diagnose the history and environment of the ice. The 15.2 $μ$m bending mode of $^{12}$CO$_2$ has proven to be a valuable tracer of ice heating events but suffers from grain shape and size effects. A viable alternative tracer is the weaker $^{13}$CO$_2$ isotopologue band at 4.39 $μ$m which has now become accessible at high S/N with the $\textit{James Webb}$ Space Telescope (JWST). We present JWST NIRSpec observations of $^{13}$CO$_2$ ice in five deeply embedded Class 0 sources spanning a wide range in luminosities (0.2 - 10$^4$ L$_{\odot}$ ) taken as part of the Investigating Protostellar Accretion Across the Mass Spectrum (IPA) program. The band profiles vary significantly, with the most luminous sources showing a distinct narrow peak at 4.38 $μ$m. We first apply a phenomenological approach and show that a minimum of 3-4 Gaussian profiles are needed to fit the $^{13}$CO$_2$ absorption feature. We then combine these findings with laboratory data and show that a 15.2 $μ$m $^{12}$CO$_2$ band inspired five-component decomposition can be applied for the isotopologue band where each component is representative of CO$_2$ ice in a specific molecular environment. The final solution consists of cold mixtures of CO$_2$ with CH$_3$OH, H$_2$O and CO as well as segregated heated pure CO$_2$ ice. Our results are in agreement with previous studies of the $^{12}$CO$_2$ ice band, further confirming that $^{13}$CO$_{2}$ is a useful alternative tracer of protostellar heating events. We also propose an alternative solution consisting only of heated CO$_2$:CH$_3$OH and CO$_2$:H$_2$O ices and warm pure CO$_2$ ice for decomposing the ice profiles of the two most luminous sources in our sample.

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arXiv2024

A MultiWavelength Study of the Symbiotic Mira HM Sge with SOFIA and HST

We have targeted the dusty symbiotic mira system HM Sge with four instruments from the IR to the UV. We have used these observations along with archival observations to study how the system has been evolving after its 1975 nova-like outburst. We have detected ro-vibrational water emission in a symbiotic system for the first time using new EXES high spectral resolution infrared spectroscopy. The features, detected in emission, have velocities consistent with the systemic velocity but do not show any clear evidence of high velocity outflows. Mid-infrared photometry and grism spectroscopy show that the oxygen-rich Asymptotic Giant Branch (AGB) dust and dust output has shown little to no change over the past 39 years. In the optical/UV, we detect three main [NII] nebular features that were detected 22 years ago. Two of these features show a small amount of movement corresponding to average outflows speeds of 38 kms and 78 kms since they were previously observed; some previously detected [NII] features are no longer visible. New UV spectroscopy has shown that the nebular environment continues to steadily relax after the system's 1975 outburst. The data suggest however, that the hot component has increased in temperature from 200,000 K in 1989 to now greater than 250,000 K. Our new and archival observations suggest that the evolution of the system after its outburst is swift with little to no major changes after a period of a couple years.

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arXiv2024

Discovery of a collimated jet from the low luminosity protostar IRAS 16253$-$2429 in a quiescent accretion phase with the JWST

Investigating Protostellar Accretion (IPA) is a JWST Cycle~1 GO program that uses NIRSpec IFU and MIRI MRS to obtain 2.9--28~$μ$m spectral cubes of young, deeply embedded protostars with luminosities of 0.2 to 10,000~L$_{\odot}$ and central masses of 0.15 to 12~M$_{\odot}$. In this Letter, we report the discovery of a highly collimated atomic jet from the Class~0 protostar IRAS~16253$-$2429, the lowest luminosity source ($L_\mathrm{bol}$ = 0.2 $L_\odot$) in the IPA program. The collimated jet is detected in multiple [Fe~II] lines, [Ne~II], [Ni~II], and H~I lines, but not in molecular emission. The atomic jet has a velocity of about 169~$\pm$~15~km\,s$^{-1}$, after correcting for inclination. The width of the jet increases with distance from the central protostar from 23 to~60 au, corresponding to an opening angle of 2.6~$\pm$~0.5\arcdeg. By comparing the measured flux ratios of various fine structure lines to those predicted by simple shock models, we derive a shock {speed} of 54~km\,s$^{-1}$ and a preshock density of 2.0$\times10^{3}$~cm$^{-3}$ at the base of the jet. {From these quantities and using a suite of jet models and extinction laws we compute a mass loss rate between $0.4 -1.1\times10^{-10}~M_{\odot}$~yr~$^{-1}$.} The low mass loss rate is consistent with simultaneous measurements of low mass accretion rate ($2.4~\pm~0.8~\times~10^{-9}~M_{\odot}$~yr$^{-1}$) for IRAS~16253$-$2429 from JWST observations (Watson et al. in prep), indicating that the protostar is in a quiescent accretion phase. Our results demonstrate that very low-mass protostars can drive highly collimated, atomic jets, even during the quiescent phase.

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arXiv2024

Surveying the Giant HII Regions of the Milky Way with SOFIA: VI. NGC 3603

We present our sixth set of results from our mid-infrared imaging survey of Milky Way Giant HII regions with our detailed analysis of NGC 3603, the most luminous GHII region in the Galaxy. We used imaging data from the FORCAST instrument on the Stratospheric Observatory For Infrared Astronomy (SOFIA) at 20 and 37 microns which mapped the central ~8.5'x8.5' infrared-emitting area of NGC 3603 at a spatial resolution of <~3". Utilizing these SOFIA data in conjunction with multi-wavelength observations from the near-infrared to radio, including Spitzer-IRAC and Herschel-PACS archival data, we investigate the physical nature of individual infrared sources and sub-components within NGC 3603. For individual compact sources we used the multi-wavelength photometry data to construct spectral energy distributions (SEDs) and fit them with massive young stellar object (MYSO) SED models, and find 14 sources that are likely to be MYSOs. We also detect dust emission from the 3 massive proplyd candidates, as well as from the disk and outflow of the evolved blue supergiant, Sher 25. Utilizing multi-wavelength data, we derived luminosity-to-mass ratio and virial parameters for the star-forming clumps within NGC 3603, estimating their relative ages and finding that NGC 3603 is an older GHII region overall, compared to our previously studied GHII regions. We discuss how NGC 3603, which we categorize as a 'cavity-type' GHII region, exhibits a more modest number of MYSOs and molecular clumps when compared to the 'distributed-type' GHII regions that share similar Lyman continuum photon rates.

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