arXiv subjects

Lee Hartmann

Publications and source records attributed to Lee Hartmann.

At least 19 recordsLinked to original sources

arXiv2026

IPA: Morphology and Kinematics of Molecular Hydrogen Winds in Five Young Protostars across the Mass Spectrum Observed with JWST

Molecular winds may play a key role in governing angular momentum transport and accretion during the early evolution of protostars. We present the morphology and kinematic properties of the H$_2$ emission in five young, envelope-dominated, protostars across a broad bolometric luminosity range, from 0.2 to $10^4~L_{\odot}$, observed with the NIRSpec/IFU and MIRI/MRS onboard JWST as part of the Investigating Protostellar Accretion (IPA) program. A rich set of pure rotational lines of H$_2$, up to $v=0-0$ S(18), and a few ro-vibrational lines are detected in the winds, revealing bipolar structures. The H$_2$ lines show a stratified/onion-like structure morphologically and kinematically, where the lines with higher $E_{\rm up}$ show a higher degree of collimation and higher velocities. Additionally, the wind velocity scales with the $L_{\rm bol}$ of the host protostellar system. In 4 out of 5 protostars, H$_2$ emission fills the outflow cavity without showing pronounced limb brightening. We also report a tentative detection of H$_2$ wind rotation in IRAS 16253, which suggests a launch radius of $\sim4$ au and the magnetic lever arm parameter of $\sim5-10$. Taken together, these properties of the H$_2$ winds can be explained by the magnetohydrodynamic disk wind models. We detect a collimated, high-velocity H$_2$ jet toward HOPS 370, which is more evolved than the extremely young source HH 211, but is accreting at a high accretion rate. This suggests that the presence of collimated molecular jets in protostars is more closely connected to accretion rate than system age.

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arXiv2026

Accretion onto the Embedded Protostar L1527 IRS: Insights from JWST NIRSpec and MIRI Observations

Accretion is the primary driver of protostellar evolution, regulating mass assembly and shaping the physical and chemical environments of young stellar objects. Quantifying accretion in the Class 0 protostellar phase is particularly important, yet remains observationally challenging due to high extinction toward the central protostars. In this paper, we present JWST NIRSpec and MIRI/MRS IFU data towards the Class 0 protostar L1527 IRS. We extract one-dimensional spectra and find emission from atomic and molecular hydrogen, water, OH, and several ionic species. The atomic hydrogen lines, Br$\alpha$, Pf$\alpha$, and Pf$\gamma$ are the most critical to this study since they can be used as accretion diagnostics. The existence of these atomic hydrogen lines viewed in scattered light indicates that accretion is likely occurring magnetospherically rather than through a boundary layer. Moment 0 emission maps show that the hydrogen emission is co-spatial with the scattered light continuum with a strong east-west asymmetry which is not due to outflow shocks. We additionally present moment 0 maps of other detected species and discuss their emission morphology. By primarily analyzing the Br$\alpha$ line, the strongest of our detected atomic hydrogen lines, we characterize the accretion onto L1527 IRS by estimating the accretion luminosity to be $0.4~\text{L}_\odot$ and the accretion rate to be around $1\times10^{-7}~ \text{M}_\odot \text{yr}^{-1}$. We lastly discuss the implications of our results with respect to both non-steady and asymmetric accretion possibly occurring in L1527 IRS.

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arXiv2026

The Structure and Kinematics of Three Class 0 Protostellar Jets from JWST

We present observations of jets within 2000 au of three deeply embedded protostars using 2.9-27 micron observations with JWST. These observations show the morphologies and kinematics of the collimated jets from three protostars, the low-mass Class 0 protostars B335 and HOPS 153, and the intermediate-mass protostar HOPS 370. These jets are traced by shock-ionized fine-structure line emission observed with the JWST NIRSpec and MIRI IFUs. We find that [Fe II] emission traces the full extent of the inner 1000 to 2000 au of the jets, depending on distance to the protostar, while other ions mostly trace isolated shocked knots. The jets show evidence of wiggling motion in the plane of the sky as well as asymmetries between blue and red-shifted lobes. The widths of the jets increase non-monotonically with distance from the central protostar, with opening angles ranging from 2.1 degrees to < 10.1 degrees for the three protostars in the sample. The jets have total velocities ranging from 147 to 184 km/s after correcting for disk inclination. For B335, an 8-month gap between NIRSpec and MIRI MRS observations enabled measurement of the tangential velocity of a shocked knot; in combination with the radial velocity, this shows that the jet has a different inclination than the outflow cavity. We find multiple knots before and during a recent outburst in B335, although the knots were more frequent during the burst. The asymmetries between blue- and red-shifted lobes strongly suggest complex interactions between the circumstellar disks and magnetic fields.

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arXiv2025

Observational signatures of outside-in accretion bursts in embedded protostars

Optical and infrared surveys have detected increasing numbers of disc accretion outbursts in young stars. Some models of these FU Ori-type events predict that the outburst should start at near- to mid-infrared wavelengths before an optical rise is detected, and this lag between infrared and optical bursts has been observed in at least two systems. Detecting and characterizing infrared precursors can constrain the outburst trigger region, and thus help identify the mechanism producing the outburst. However, because FU Ori objects are generally young and usually embedded in dusty protostellar envelopes, it is not clear whether or how well such infrared precursors can be detected in the presence of strong envelope extinction. To explore this question, we combine time-dependent outburst models of the inner disc with an outer dusty disc and protostellar envelope, and calculate the resulting spectral energy distributions (SEDs) using the radiative transfer code RADMC3D. We find that, for envelope mass infall rates about 10^{-5} Msun/yr (rc/30 au)^{-1/2}, where rc is a characteristic inner radius for the infalling envelope, the infrared precursor is only apparent in the SED when viewed along the outflow cavity. At other inclinations, the precursor is most easily distinguished at infall rates of 10^{-6} Msun/yr (rc/30 au)^{-1/2}. We also show that far-IR and submm/mm monitoring can enable the indirect detection of precursor evolution long before the optical outburst, emphasizing the potential of long-wavelength monitoring for studying the earliest stages of protostar formation.

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arXiv2025

On the protostellar mass-luminosity relation

We present a preliminary view of the protostellar mass-luminosity relation using current samples of protostars with dynamical mass estimates. To provide a lower limit to the expected luminosities, we adopt an empirical estimate for the intrinsic (without accretion) protostellar luminosity and radius as a function of mass. We find that many of the protostars with current dynamical mass estimates track the empirical mass-luminosity "birthline" reasonably closely, suggesting that their accretion luminosities may be at most comparable to their photospheric radiation. In turn, this implies that mass accretion rates for many objects are well below that required to build up the final stellar mass in typical estimated protostellar lifetimes. A small subset of the protostars have luminosities well above the predicted photospheric values, consistent with evolutionarily-important mass addition. These results hint at a possible bimodal distribution of accretion, but a firm conclusion is not possible given the small size of and likely biases in the current sample.

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arXiv2024

High Mass Inner Regions Found in Five Outbursting Sources

Young stellar objects are thought to commonly undergo sudden accretion events that result in a rise in bolometric luminosity. These outbursts likely coincide with the onset of planet formation, and could impact the formation of planets. The reason behind this dramatic enhancement of accretion is an active area of research, and the mass of the system is a critical parameter. Using Northern Extended Millimeter Array, we survey five outbursting sources (three FU Ori, one EX Or, one 'peculiar' source) with the primary goal of determining the system's mass using an optically thin line of CO. We estimate the mass of a central region for each object that using both continuum emission and C17O J=2-1. The C17O emission likely includes both disk and inner envelope material, thus acts as an upper limit on the disk mass, ranging from 0.33-3.4 Msun for our sources. These derived masses suggest that the inner approx. 1000 au contains enough mass along the line of sight for these sources to be gravitationally unstable.

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arXiv2024

Complex Organics Surrounding the FU Ori-Type Object V1057 Cyg Indicative of Sublimated Ices

FU Ori and EX Lup type objects present natural experiments for understanding a critical stage in the star and planet formation process. These objects offer insight into the diversity of molecules available to forming planetary systems due to a sudden increase in accretion and central luminosity causes the disk and surrounding material to increase in temperature. This allows for volatiles to sublimate off of grains and exist in the gas-phase for tens to hundreds of years post initial outburst. While this dynamic stage may be common for solar-type protostars, observations of the chemical impact of these bursts are rare. In this article, we present observations from the NOrthern Extended Millimeter Array (NOEMA) of five Young Stellar Objects (YSOs) that have undergone outbursts within the past 100 years and catalog the volatile chemistry found within approx 1000 au of the YSO. Only one source clearly shows a line rich spectra with >11 molecules detected including complex organics and water, as is an expected spectra signature for a post-outburst source. This source is V1057 Cyg, and we present it as the northern analog to the well studied and molecule-rich FU Ori source, V883 Ori. Our conclusions on the chemical inventory of the other four sources in our sample are sensitivity limited, as V1057 Cyg contains the highest disk/envelope gas mass.

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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 $\mu$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 $\mu$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 $\mu$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 $\mu$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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arXiv2023

IPA: Class 0 Protostars Viewed in CO Emission Using JWST

We investigate the bright CO fundamental emission in the central regions of five protostars in their primary mass assembly phase using new observations from JWST's Near-Infrared Spectrograph (NIRSpec) and Mid-Infrared Instrument (MIRI). CO line emission images and fluxes are extracted for a forest of $\sim$150 ro-vibrational transitions from two vibrational bands, $v=1-0$ and $v=2-1$. However, ${}^{13}$CO is undetected, indicating that ${}^{12}$CO emission is optically thin. We use H$_2$ emission lines to correct fluxes for extinction and then construct rotation diagrams for the CO lines with the highest spectral resolution and sensitivity to estimate rotational temperatures and numbers of CO molecules. Two distinct rotational temperature components are required for $v=1$ ($\sim600$ to 1000 K and 2000 to $\sim 10^4$ K), while one hotter component is required for $v=2$ ($\gtrsim 3500$ K). ${}^{13}$CO is depleted compared to the abundances found in the ISM, indicating selective UV photodissociation of ${}^{13}$CO; therefore, UV radiative pumping may explain the higher rotational temperatures in $v=2$. The average vibrational temperature is $\sim 1000$ K for our sources and is similar to the lowest rotational temperature components. Using the measured rotational and vibrational temperatures to infer a total number of CO molecules, we find that the total gas masses range from lower limits of $\sim10^{22}$ g for the lowest mass protostars to $\sim 10^{26}$ g for the highest mass protostars. Our gas mass lower limits are compatible with those in more evolved systems, which suggest the lowest rotational temperature component comes from the inner disk, scattered into our line of sight, but we also cannot exclude the contribution to the CO emission from disk winds for higher mass targets.

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arXiv2023

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~$\mu$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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arXiv2023

Investigating Protostellar Accretion-Driven Outflows Across the Mass Spectrum: JWST NIRSpec IFU 3-5~$\mu$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 $\mu$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 $\mu$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-$\alpha$. 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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arXiv2023

Magnetically-activated accretion outbursts of pre-main sequence discs

We investigate whether triggering of the magnetorotational instability (MRI) in protoplanetary discs can account for the wide diversity of observed accretion outbursts. We show that short-lived, relatively low accretion rate events probably result from triggering in the inner disc and can occur at low surface densities, comparable to or smaller than the minimum mass solar nebula, and thus are very unlikely to result from MRI triggering by gravitational instability. We develop time-dependent accretion disc models using an $\alpha$-viscosity approach and calculate light curves to compare with observations. Our modeling indicates that the lag time between infrared and optical bursts seen in Gaia 17bpi can be explained with an outside-in propagation with an $\alpha \sim 0.1$ in the MRI-active region, consistent with other estimates. While outbursts in inner discs can show time delays of a few years between infrared and optical light curves, our models indicate that large, FU Ori-like bursts can exhibit infrared precursors decades before optical bursts. Detecting such precursors could enable analysis of the central star before it is overwhelmed by the rapid accreting material, as well as constraining outburst physics. Our results emphasize the importance of near-infrared monitoring of young stellar objects in addition to optical surveys. In addition, our findings emphasize the need for more sophisticated, three-dimensional, non-ideal magnetohydrodynamic simulations to fully exploit observational results.

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arXiv2023

Constraints on star formation in Orion A from Gaia

We develop statistical methods within a Bayesian framework to infer the star formation history from photometric surveys of pre-main sequence populations. Our procedures include correcting for biases due to extinction in magnitude-limited surveys, and using distributions from subsets of stars with individual extinction measurements. We also make modest corrections for unresolved binaries. We apply our methods to samples of populations with Gaia photometry in the Orion A molecular cloud. Using two well-established sets of evolutionary tracks, we find that, although our sample is incomplete at youngest ages due to extinction, star formation has proceeded in Orion A at a relatively constant rate between ages of about 0.3 and 5 Myr, in contrast to other studies suggesting multiple epochs of star formation. Similar results are obtained for a set of tracks that attempt to take the effects of strong magnetic fields into account. We also find no evidence for a well-constrained "birthline" that would result from low-mass stars appearing first along the deuterium-burning main sequence, especially using the magnetic evolutionary tracks. While our methods have been developed to deal with Gaia data, they may be useful for analyzing other photometric surveys of star-forming regions.

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arXiv2022

300: An ACA 870 $\mu$m Continuum Survey of Orion Protostars and their Evolution

We present an 870 $\mu$m continuum survey of 300 protostars from the Herschel Orion Protostar Survey using the Atacama Compact Array (ACA). These data measure protostellar flux densities on envelope scales $\leq$8000 au (20") and resolve the structure of envelopes with 1600 au (4") resolution, a factor of 3-5 improvement in angular resolution over existing single-dish 870 $\mu$m observations. We compare the ACA observations to Atacama Large Millimeter/submillimeter Array 12 m array observations at 870 $\mu$m with $\sim$0.1 (40 au) resolution. Using the 12 m data to measure the fluxes from disks and the ACA data within 2500 au to measure the combined disk plus envelope fluxes, we calculate the 12 m/ACA 870 $\mu$m flux ratios. Our sample shows a clear evolution in this ratio. Class 0 protostars are mostly envelope-dominated with ratios $<$0.5. In contrast, Flat Spectrum protostars are primarily disk-dominated with ratios near 1, although with a number of face-on protostars dominated by their envelopes. Class I protostars span the range from envelope to disk-dominated. The increase in ratio is accompanied by a decrease in the envelope fluxes and estimated mass infall rates. We estimate that 80$\%$ of the mass is accreted during the envelope-dominated phase. We find that the 12 m/ACA flux ratio is an evolutionary indicator that largely avoids the inclination and foreground extinction dependence of spectral energy distribution-based indicators.

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arXiv2022

Extension of HOPS Out to 500 ParSecs (eHOPS). I. Identification and Modeling of Protostars in the Aquila Molecular Clouds

We present a Spitzer/Herschel focused survey of the Aquila molecular clouds ($d \sim 436$~pc) as part of the eHOPS (extension of HOPS Out to 500 ParSecs) census of nearby protostars. For every source detected in the Herschel/PACS bands, the eHOPS-Aquila catalog contains 1-850~$\mu$m SEDs assembled from 2MASS, Spitzer, Herschel, WISE, and JCMT/SCUBA-2 data. Using a newly developed set of criteria, we classify objects by their SEDs as protostars, pre-ms sequence stars with disks, and galaxies. A total of 172 protostars are found in Aquila, tightly concentrated in the molecular filaments that thread the clouds. Of these, 71 (42\%) are Class 0 protostars, 54 (31\%) are Class I protostars, 43 (25\%) are flat-spectrum protostars, and 4 (2\%) are Class II sources. Ten of the Class 0 protostars are young PACS Bright Red Sources similar to those discovered in Orion. We compare the SEDs to a grid of radiative transfer models to constrain the luminosities, envelope densities, and envelope masses of the protostars. A comparison of the eHOPS-Aquila to the HOPS protostars in Orion finds that the protostellar luminosity functions in the two star-forming regions are statistically indistinguishable, the bolometric temperatures/envelope masses of eHOPS-Aquila protostars are shifted to cooler temperatures/higher masses, and the eHOPS-Aquila protostars do not show the decline in luminosity with evolution found in Orion. We briefly discuss whether these differences are due to biases between the samples, diverging star formation histories, or the influence of environment on protostellar evolution.

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arXiv2022

Gemini-LIGHTS: Herbig Ae/Be and massive T-Tauri protoplanetary disks imaged with Gemini Planet Imager

We present the complete sample of protoplanetary disks from the Gemini- Large Imaging with GPI Herbig/T-tauri Survey (Gemini-LIGHTS) which observed bright Herbig Ae/Be stars and T-Tauri stars in near-infrared polarized light to search for signatures of disk evolution and ongoing planet formation. The 44 targets were chosen based on their near- and mid-infrared colors, with roughly equal numbers of transitional, pre-transitional, and full disks. Our approach explicitly did not favor well-known, "famous" disks or those observed by ALMA, resulting in a less-biased sample suitable to probe the major stages of disk evolution during planet formation. Our optimized data reduction allowed polarized flux as low as 0.002% of the stellar light to be detected, and we report polarized scattered light around 80% of our targets. We detected point-like companions for 47% of the targets, including 3 brown dwarfs (2 confirmed, 1 new), and a new super-Jupiter mass candidate around V1295 Aql. We searched for correlations between the polarized flux and system parameters, finding a few clear trends: presence of a companion drastically reduces the polarized flux levels, far-IR excess correlates with polarized flux for non-binary systems, and systems hosting disks with ring structures have stellar masses $<$ 3 Msun. Our sample also included four hot, dusty "FS CMa" systems and we detected large-scale ($>100$ au) scattered light around each, signs of extreme youth for these enigmatic systems. Science-ready images are publicly available through multiple distribution channels using a new FITS file standard jointly developed with members of the VLT/SPHERE team.

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arXiv2022

Anisotropic Infall and Substructure formation in Embedded Disks

The filamentary nature of accretion streams found around embedded sources suggest that protostellar disks experience heterogenous infall from the star-forming environment, consistent with the accretion behavior onto star-forming cores in top-down star-cluster formation simulations. This may produce disk substructures in the form of rings, gaps, and spirals continuing to be identified by high-resolution imaging surveys in both embedded Class 0/I and later Class II sources. We present a parameter study of anisotropic infall, informed by the properties of accretion flows onto protostellar cores in numerical simulations, and varying the relative specific angular momentum of incoming flows as well as their flow geometry. Our results show that anisotropic infall perturbs the disk and readily launches the Rossby wave instability (RWI). It forms vortices at the inner and outer edge of the infall zone where material is deposited. These vortices drive spiral waves and angular momentum transport, with some models able to drive stresses corresponding to a viscosity parameter on the order of $\alpha \sim 10^{-2}$. The resulting azimuthal shear forms robust pressure bumps that act as barriers to radial drift of dust grains, as demonstrated by post-processing calculations of drift-dominated dust evolution. We discuss how a self-consistent model of anisotropic infall can account for the formation of millimeter rings in the outer disk as well as producing compact dust disks, consistent with observations of embedded sources.

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arXiv2022

The ODYSSEUS Survey. Motivation and First Results: Accretion, Ejection, and Disk Irradiation of CVSO 109

The Hubble UV Legacy Library of Young Stars as Essential Standards (ULLYSES) Director's Discretionary Program of low-mass pre-main-sequence stars, coupled with forthcoming data from ALMA and JWST, will provide the foundation to revolutionize our understanding of the relationship between young stars and their protoplanetary disks. A comprehensive evaluation of the physics of disk evolution and planet formation requires understanding the intricate relationships between mass accretion, mass outflow, and disk structure. Here we describe the Outflows and Disks around Young Stars: Synergies for the Exploration of ULLYSES Spectra (ODYSSEUS) Survey and present initial results of the classical T Tauri Star CVSO 109 in Orion OB1b as a demonstration of the science that will result from the survey. ODYSSEUS will analyze the ULLYSES spectral database, ensuring a uniform and systematic approach in order to (1) measure how the accretion flow depends on the accretion rate and magnetic structures, (2) determine where winds and jets are launched and how mass-loss rates compare with accretion, and (3) establish the influence of FUV radiation on the chemistry of the warm inner regions of planet-forming disks. ODYSSEUS will also acquire and provide contemporaneous observations at X-ray, optical, NIR, and millimeter wavelengths to enhance the impact of the ULLYSES data. Our goal is to provide a consistent framework to accurately measure the level and evolution of mass accretion in protoplanetary disks, the properties and magnitudes of inner-disk mass loss, and the influence of UV radiation fields that determine ionization levels and drive disk chemistry.

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