Abstract We present a method for constructing dynamical models of stellar systems described by distribution functions and constrained by discrete-kinematic data. We implement various improvements compared to earlier applications of this approach, demonstrating with several examples that it can deliver meaningful constraints on the mass distribution even in situations where the density profile of tracers and the selection function of the kinematic catalog are unknown. We then apply this method to the Milky Way nuclear star cluster, using kinematic data (line-of-sight velocities and proper motions) for a few thousand stars within 10 pc from the central black hole, accounting for the contributions of the nuclear stellar disk and the Galactic bar. We measure the mass of the black hole to be 4 × 10 6 M ⊙ with a 10% uncertainty, which agrees with the more precise value obtained by the GRAVITY instrument. The inferred stellar mass profile depends on the choice of kinematic data, but the total mass within 10 pc is well constrained in all models to be (2.0–2.3) × 10 7 M ⊙ . We make our models publicly available as part of the Agama software framework for galactic dynamics.

Abstract Understanding the evolution of pulsar dispersion measures is vital to high-precision timing experiments, as well as astrometric experiments to determine pulsar positions and proper motions. In this work, we present a novel approach to measuring dispersion measure gradients using pulsar scintillometry. This approach makes use of the multipath propagation through the interstellar medium to simultaneously probe dispersion measures along multiple sight lines from a single observation. Using existing data of PSR B0834+06, we are able to measure gradients of 9.7 ± 0.3 × 10 −6 pc cm −3 mas −1 .

Stellar streams are sensitive laboratories for understanding the small-scale structure in our Galaxy’s gravitational field. Here, we analyze the morphology of the 300 S stellar stream, which has an eccentric, retrograde orbit and thus could be an especially powerful probe of both baryonic and dark substructures within the Milky Way. Due to extensive background contamination from the Sagittarius stream (Sgr), we perform an analysis combining Dark Energy Camera Legacy Survey photometry, 𝐺𝑎𝑖𝑎 DR3 proper motions, and spectroscopy from the Southern Stellar Stream Spectroscopic Survey ( 𝑆 5 ). We redetermine the stream coordinate system and distance gradient, then apply two approaches to describe 300 S ’s morphology. In the first, we analyze stars from 𝐺𝑎𝑖𝑎 using proper motions to remove Sgr. In the second, we generate a simultaneous model of 300 S and Sgr based purely on photometric information. Both approaches agree within their respective domains and describe the stream over a region spanning 33 ∘ . Overall, 300 S has three well-defined density peaks and smooth variations in stream width. Furthermore, 300 S has a possible gap of ∼ 4.7 ∘ and a kink. Dynamical modeling of the kink implies that 300 S was dramatically influenced by the Large Magellanic Cloud. This is the first model of 300 S ’s morphology across its entire known footprint, opening the door for deeper analysis to constrain the structures of the Milky Way.

Abstract The 3D structure of the Milky Way’s central molecular zone (CMZ) informs our understanding of star formation cycles, black hole accretion, and the evolution of galactic nuclei. However, a comprehensive 3D model has remained elusive, as no singular data set nor theory contains the requisite information to describe the orbital motion of the gas. We implement a Bayesian framework to flexibly combine data sets across the electromagnetic spectrum for molecular clouds in our CMZ catalog. We develop near/far metrics for each data set, including dust extinction, absorption, stellar densities, X-ray echoes, and proper motions; and report a posterior positional probability density function (PPDF) for each cloud. We then use the posterior PPDF distributions for all CMZ clouds to search for a best-fitting x 2 orbit. We find that no single orbit is a perfect fit, but the structure can overall be represented by nested x 2 orbits, with major axes ranging from about 72 < a < 146 pc. We also present projected line-of-sight distance estimates for all 31 clouds in the catalog. Our results highlight asymmetries along the line of sight, with most clouds lying on the near side of the Galactic center, and agree overall with current near/far assumptions for most CMZ clouds, including those in the Sgr A region, which may be much closer to the center. We conclude that the CMZ can be well-described by x 2 orbital families and that the overall gas distribution is more complex than a single closed or open elliptical orbit.

Recent discoveries show that chemically peculiar (CP) stars also reside in globular clusters (GCs). The channels leading to chemical peculiarity are, however, still under discussion. The main goals of our investigation are to identify the CP stars in GCs and search for systematic relations among different stellar groups commonly observed in GCs and chemical peculiarity. Additionally, we search for possible correlations of the occurrence rate of CP stars with the cluster properties. We obtained BVg2 multicolour photometry for 18 southern GCs with the 1.54m Danish telescope located at La Silla observatory in Chile. The data were reduced and processed with standard tools. To avoid blending, we omitted central parts of the clusters. We determined the membership of the stars to a particular GC based on the proper motion and parallax of the stars from the Gaia DR3 catalogue. Colour-magnitude diagrams were constructed, and only stars on horizontal branch and in the region of blue stragglers were considered for further analysis. Construction of the Δ a diagram allowed us to identify CP candidate stars with high probability. To test the reliability of our approach, we used spectroscopic observations of M53. Iraf Except for four GCs, CP candidates were found in all other GCs with the average fraction of 4.2,%. We found that a significant portion of the candidates are blue stragglers. These constitute a full sample of identified CP candidates in four GCs and represent more than 60,% of the candidates in ten GCs. The a photometry was found as a powerful tool for the identification of CP stars in GCs. We discovered a possible connection between chemical peculiarity and blue straggler stars.

OB runaway stars are massive stars moving through interstellar space with a high velocity (up to 200,km -1 ). They are produced by dynamical ejections in young massive clusters or by supernova explosions in massive binaries. OB runaways can travel several hundred parsec before exploding as supernovae, affecting the dynamical and chemical evolution of the Galaxy. The Vel,OB1 association is one of the largest OB associations, hosting about 20,O-type and more than 50,B-type stars. Our aim is to find OB runaway stars in this region. By quantifying their number and identifying their parent clusters, we seek to better understand their production channels and their impact on the surrounding medium. We used ,DR3 coordinates, parallaxes, and proper motions of massive stars in the field centred on Vel,OB1 to identify OB runaways by measuring their peculiar velocity. Under suitable physical conditions, OB runaways create observable bow shocks in the interstellar medium (ISM). We inspected infrared WISE images to identify wind bow shocks and their associated OB runaways. By reconstructing their path, we tried to locate their parent cluster and estimate their travel times. Gaia We identified six young stellar clusters hosting most of the massive-star population in Vel OB1 (distance 1.6-2.1 kpc; age 1-10 Myr). From the tangential velocity distribution of the members, we derived a threshold velocity of 15 km s -1 to classify a star as a runaway. We identified 25,OB runaways (including the high-mass X-ray binary Vela X-1) and one F-type runaway. We detected 16,arc-like features, four for the first time, and six of the features are associated with OB runaways selected by peculiar velocity. Ten bow shocks are aligned with the proper motion of the runaways. Parent clusters are identified for seven runaways. Most likely, the majority of these runaways are produced by dynamical ejection. The runaway fraction of the young stellar population in Vel,OB1 is about 30 %. Many OB runaways, even some far above the Galactic plane, produce wind bow shocks, which consequently reveal information on local ISM conditions.

Abstract The Sagittarius dwarf spheroidal galaxy (Sgr dSph) provides us with the unique opportunity to study an ongoing Galactic cannibalistic event between our Milky Way (MW) Galaxy and a satellite dwarf galaxy. Understanding this event crucially requires memberships and high-precision metallicities. Here, we present the first major membership star catalog of the Sgr dwarf core (≈140,000 sources) and Messier 54 (M54; ≈2000 sources) with positions, proper motions, and parallaxes from the third Gaia data release (DR3), supplemented with metallicities from the Apache Point Observatory Galactic Evolution Experiment (or APOGEE). We initially isolate the Sgr dwarf core and M54 spatially from prior literature positions. Using evolutionary subsamples separated within a color–magnitude diagram, we analyze the substructures of the Sgr core and infer its positional relationship with M54 within 5D phase space. A sample of MW stars from a similar Galactic latitude were used to identify contaminants and separate member stars from the core of the Sgr dSph and M54 using a Gaussian mixture model. We present the derived proper motions, parallaxes, and metallicities for these evolutionary subsamples and demonstrate the precision of our sample using red clump (RC) standard candles. We find distance moduli for the Sgr core and M54 of ( m − M ) 0 = 16.95 8 − 0.044 + 0.044 mag and ( m − M ) 0 = 16.9 4 − 0.056 + 0.047 mag, corresponding to heliocentric distances of d = 24.63 5 − 0.49 + 0.49 kpc and d = 24.45 2 − 0.602 + 0.537 kpc, respectively. Using RC distance analysis, our results imply that there is no separation between the Sgr core and M54. Finally, we describe the metallicity distributions of the evolved stars within these two systems, finding evidence for the infall scenario.

Abstract We present the confirmation of HD 190360 d, a warm ( P = 88.69 0 − 0.049 + 0.051 days ), low-mass ( m sin i = 10.2 3 − 0.80 + 0.81 M ⊕ ) planet orbiting the nearby ( d = 16.0 pc), Sun-like (G7) star HD 190360. We detect HD 190360 d at high statistical significance even though its radial velocity (RV) semiamplitude is only K = 1.48 ± 0.11 m s −1 . Such low-amplitude signals are often challenging to confirm due to potential confusion with low-amplitude stellar signals. The HD 190360 system previously had two known planets: the 1.7 M J (true mass) HD 190360 b on a 7.9 yr orbit and the 21 M ⊕ (minimum mass) HD 190360 c on a 17.1 days orbit. Here, we present an in-depth analysis of the HD 190360 planetary system that comprises more than 30 yr of RV measurements and absolute astrometry from the Hipparcos and Gaia spacecraft. Our analysis uses more than 1400 RVs, including nearly 100 from NEID. The proper motion anomaly as measured by these two astrometric missions solves for the dynamical mass of HD 190360 b and contributes to our understanding of the overall system architecture, while the long baseline of RVs enables the robust characterization of HD 190360 c and confirms the discovery of HD 190360 d.

Context. Traditionally, high-mass X-ray binaries (HMXBs) are considered atypical products of close binary evolution where the primary component of the progenitor binary has formed a compact object through a supernova explosion, shedding a significant portion of the overall binary mass in the process. This rapid mass loss from the system results in an extra peculiar systemic velocity with respect to the system’s local standard of rest. Moreover, there is also a contribution to the peculiar systemic velocity from a natal velocity kick, which is imparted to the compact object upon formation. Provided that the binary remains bound, both the rapid mass loss and the natal kick cause the system to gain a significant systemic velocity of typically several tens of kilometers per second with respect to its standard of rest. This makes the system rapidly leave the environment where it was born. This classical picture has now been challenged by discoveries of systems with low or negligible peculiar systemic velocities, arising from more exotic supernova types, such as electron-capture or ultrastripped supernovae. These supernovae explode with a low degree of asymmetry and only eject a small amount of mass, yielding low peculiar systemic velocities. Aims. We investigate the occurrence of HMXBs in open clusters and, if they are present, use the cluster parameters to constrain the system properties and the physics of the supernovae that produced them. Methods. We used Gaia astrometry data and derived catalogs to examine whether known HMXBs are physical members of open clusters, using membership criteria based on positions, parallaxes, and proper motions. Results. We identify four HMXB and HMXB candidates that are members of open clusters: IGR J16465-4507 in CWNU 2672, SGR 0755-2933 in HSC 1981, HD 119682 in NGC 5281, and NGC 6649 9 in NGC 6649. Their presence in open clusters implies that they were born without significant systemic kick, which provides important constraints to supernova explosion mechanisms in close binary systems. The residual tangential velocities we derive (0.9 ± 0.4 km/s for SGR 0755-2933 and 2.6 ± 0.5 km/s for IGR J16465-4507) provide direct observational evidence for the ultralow kick mode recently identified in Be X-ray binary populations, demonstrating that such systems can remain gravitationally bound to their parent clusters

Context . The recent discovery of free-floating planets (FFPs) in nearby young stellar associations suggests that these objects might be common in the Galaxy. Our search for FFPs in the young Lower Centaurus-Crux (LCC) association using the VISTA Variables in the Vía Láctea VVV and VVVX surveys revealed several candidates with distances d < 200 pc. Aims . The main goal of the paper is to identify binary FFPs among this sample. The presence of such binaries is useful to contrast two different main formation scenarios: the formation in the circumstellar disk of the parent star with subsequent ejection by dynamical interactions and the in situ formation by gravitational collapse of a protostellar cloud. Methods . We used the Gaia , VVV, VVVX, and DECaPS databases to identify pairs of low-mass objects in the LCC association sharing common proper motions. We examined the optical and near-IR color-magnitude and color-color diagrams, and visually confirmed the detections in the available optical and near-IR images. Results . We find 17 young low-mass binaries in the LCC association, with distances starting from 68 pc and projected separations ranging from 88 to 6742 au. A couple of candidates have additional faint companions that need confirmation to secure them as triple systems. Adopting an age of 17 Myr for the LCC association, we find that 14 of the components are faint enough to have planetary masses. Conclusions . Our results indicate that binaries represent ≳2% of the population of FFPs in the LCC association, and this suggests that their preferred formation mechanism is the gravitational collapse independent of a star. Also, many of the recently discovered FFPs in LCC may be unresolved giant binary planets. The wide range of colors and flux reversals observed suggests that the existence of clouds in their atmospheres is important and points to continuity with the BD populations.

Ultra-faint dwarf galaxies (UFDs) are among the oldest and most metal-poor stellar systems in the Universe. Their metallicity distribution encodes the fossil record of the earliest star formation, feedback, and chemical enrichment, providing crucial tests of models of the first stars, galaxy assembly, and dark matter halos. However, due to their faint luminosities and the limited number of bright giants, spectroscopic studies of UFDs typically probe only small stellar samples. Here, we present an analysis of multi-epoch Hubble Space Telescope and James Webb Space Telescope observations of the UFD Boötes I. Using a deep color–magnitude diagram in the F606W and F322W2 bands, extending from the subgiant branch to the M dwarfs, and stellar proper motions to identify likely members, we obtained an unprecedentedly clean census of the system. The exquisite quality of the diagram, combined with the sensitivity of M-dwarf colors to metallicity, allowed us to constrain the metallicity distribution in a large stellar sample. As a first step, we then exploited the metallicity sensitivity of M-dwarf colors to derive the metallicity distribution function. We find that most of the stars ∼85% have [Fe/H] < −2, and that roughly ∼17% have [Fe/H] < − 3. Then, we derived the binary fraction in Boötes I. This is crucial since binaries can bias kinematic mass estimates, affect stellar population analyzes, and shape the photometric signatures used to infer metallicity. We find that 20 ± 2% of stellar systems in Boötes I are binaries with mass ratios larger than 0.4, corresponding to a total binary fraction of ∼30%. This value is comparable to the binary fractions observed in globular clusters of similar stellar mass, suggesting that the presence of dark matter does not significantly affect the binary properties of Boötes I.

ABSTRACT We report the discovery of 31 new open clusters (OCs) identified in Gaia DR3 data through a systematic search over 220 adjacent $1^\circ \times 1^\circ$ fields towards the Galactic anticentre, in the direction of the Perseus arm gap. Eight of them display low-density structures, possibly indicating open cluster remnants properties. The objects were identified and characterized through a combined analysis of photometric, kinematic, and spatial distributions, a methodology successfully applied in our previous works. Their structural properties, mean proper motions, ages, distances and reddening were derived and their centres cross-matched with the available catalogues. The clusters are low-concentrated systems and are mostly located within $3\lt d\lt 5$ kpc, exhibiting reddening up to $E(B-V)\approx 1.5$, and ages from $\sim$20 Myr to 1 Gyr. The new OCs represent a significant increase in the anticentre cluster census: 31 per cent for $3\lt d\lt 4$ kpc and 12 per cent for $d\gt 4$ kpc. They do not belong to the Perseus arm, but may be associated with the Outer Norma arm. The Gulf of Camelopardalis region appears as an interruption in the Perseus arm, possibly reflecting low star-formation activity, dust obscuration, or that the Milky Way is a flocculent, rather than a grand-design spiral galaxy.

There is now strong evidence that the Milky Way (MW) hosts a nuclear stellar disc (NSD). However, whether the NSD is purely axisymmetric or contains a nuclear bar remains unresolved. Since approximately 50% of barred galaxies with MW-like mass in the local Universe host a nuclear bar, investigating whether the MW hosts one is of interest. We conducted a systematic analysis to identify robust kinematic diagnostics capable of determining whether the MW hosts a nuclear bar. Using N-body simulations, we explored the kinematic signatures indicative of a nuclear bar. Using the phase-space coordinates longitude $( )$, we tested various diagnostics assuming different nuclear bar orientations. We also evaluated how sample size, dust extinction, and bar amplitude influence the efficacy of the diagnostics. We identify two independent kinematic diagnostics capable of revealing a nuclear bar in the MW: (1) the vertex deviation, l_̊m v, of the (v_ and latitude $(b)$, proper motions (μ_ ), and line-of-sight velocity $(v_ and μ_ ̊m b ̊m los -v_ ̊m los ) velocity ellipse and (2) the asymmetry in the μ_ versus ell distribution. While both are impacted by the sample size and extinction, the vertex deviation proves more robust, especially when combining stars from multiple observational fields. We also assessed the correlation between the line-of-sight velocity and the h_3 Gauss-Hermite moment (‘skewness') of the line-of-sight velocity but find no clear distinction between an NSD and a nuclear bar based on this metric. Our results suggest that data from the current KMOS survey may allow a marginal detection of a nuclear bar using the vertex deviation method. A companion paper provides further validation and detailed analysis of this approach. Nonetheless, future surveys will provide the high-quality data necessary to fully exploit the diagnostics outlined in this study.

Quasi-stellar objects (QSOs) are essential for investigating the structure and evolution of the Universe. Historically, their identification has been concentrated in the northern hemisphere, primarily due to the sky coverage of major astronomical surveys. The QUBRICS (QUasars as BRIght beacons for Cosmology in the Southern hemisphere) survey, started in 2019 to address this asymmetry, has identified more than 1300 new bright (i<19.5) high-redshift (2.5<z<6) QSOs in the southern sky. This study aims to quantify, using an independent QSO sample, the completeness and recall of the QUBRICS QSO selection methods, based on extreme gradient boosting (XGB) and probabilistic random forest (PRF) techniques, since completeness is a fundamental metric for ensuring the statistical robustness of QSO-based cosmological investigations. We analyzed a subset of DR3 sources (G<18.25, $|b|>25$ deg, negligible parallax and proper motion) with low-resolution spectra, from which we obtained a sample of 3501 QSOs. To determine how many QSOs were correctly identified as candidates, we crossmatched this independent sample with the datasets used for selection: 894 QSOs with z>2.5 fell within the XGB dataset footprint, of which 152 were unclassified and thus eligible for completeness testing. Similarly, 675 QSOs with z>2.5 were within the PRF dataset footprint, including 69 unclassified objects. Gaia The XGB correctly identified as candidates 136 (89%) of the 152 QSOs with z>2.5 listed in the XGB dataset as unclassified objects. The PRF correctly identified as candidates 46 (66%) of the 69 QSOs with z>2.5 listed in the PRF dataset as unclassified objects. These findings confirm the high efficiency of the QUBRICS selection methods (recall $=89%$) and provide the completeness estimate for spectroscopically confirmed QSOs (82%), which is necessary for cosmological studies that use QUBRICS data. This work also provides reliable redshifts for 1223 new QSOs (median redshift z=2.1 and magnitude G=17.8), which will help improve the performance of future selections.

Abstract Young stellar moving groups offer unique opportunities to investigate the early evolution of stellar and planetary systems. In continuation of an ongoing effort to age-date compelling planetary systems, we provide an in-depth age analysis of KELT-20—a young A-type star that hosts a well-aligned ultrahot Jupiter. This system poses a useful case study to investigate migration mechanisms at early stages of evolution. Using Gaia DR3 data, we identify 77 stars with proper motions consistent with KELT-20, including 19 with measured radial velocities that enable full 3D kinematic confirmation. Using isochronal analyses, gyrochronology, photometric variability, and stellar activity indicators, we converge on an age of 58 ± 5 Myr. This constraint provides critical insights into the dynamical processes shaping hot Jupiter formation.

Abstract We present X-ray proper motion (PM) measurements of 19 pulsars using new and archival data from the Chandra X-ray Observatory, including pulsar wind trails and X-ray filaments. Precise X-ray PMs are often limited by uncertainties in aligning observations to a common reference frame. Our analysis uses unresolved X-ray flux from stars in the Gaia catalog in addition to X-ray bright point sources for alignment, improving uncertainties. We obtain absolute positions referenced to Gaia with typical astrometric precision ∼30 mas and PM statistical uncertainties down to 1.3 mas yr −1 , the most precise X-ray PM achieved to date. With our improved frame alignment, PM accuracies are now limited by the pulsar flux in most cases. These results reveal a new X-ray filament and illuminate the wind nebula structures and origins of several of these pulsars.

ABSTRACT We present predictions for proper motions, infall times and times of first pericentric passage for 39 of M31’s satellite galaxies. We estimate these by sampling satellite orbits from cosmological N-body simulations matched on mass, distance and velocity along the line of sight, in addition to properties of the host system. Our predictions are probabilistic based on repeated sampling from the uncertainty distributions of all quantities involved. We use these constraints on the satellites’ orbital histories in conjunction with their published star formation histories to investigate the dominant environmental mechanisms for quenching satellites of M31-like hosts. Around half of the satellites appear to have quenched before their first pericentric passage around M31. Only the most massive satellites (with stellar masses $\gt 10^8\mathrm{M}_{\odot }$) are able to maintain star formation for up to billions of years after infall. The majority of faint satellites, with $M_\star \lt 10^8\, \mathrm{M}_\odot$, were likely quenched before entering the M31 system. We compare our results for M31 against predictions for the Milky Way’s satellites from the literature; M31’s has a more active recent accretion history with more recently quenched satellites than the Milky Way.

Abstract Observations show that multiple stellar populations (MPs) are ubiquitous in globular clusters. The Hubble Space Telescope (HST) has been a pivotal tool for previous photometric studies of MPs. The Chinese Space Station Survey Telescope (CSST) is a 2 m telescope scheduled for launch. One of its imaging instruments, the Survey Camera (SC), combines ultraviolet sensitivity comparable to that of HST with a significantly larger field of view, making it well-suited for conducting large-scale photometric surveys of MPs within extensive stellar stream structures. In this work, we perform mock observations of the stellar stream Palomar 5 to assess the feasibility of detecting MPs with the CSST/SC. The results indicate that the CSST/SC cannot resolve MPs in stellar streams at distances comparable to Palomar 5 (≳20 kpc) with one or 10 150 s exposures. This fundamental limitation arises from the absence of the precise proper motions required to disentangle stream members. We estimate that successful resolution would require the target stream to be ≲8 kpc under a 150 s exposure. Furthermore, using theoretical color–magnitude diagrams, we find that the CSST/SC g band provides an optimal balance between contamination rate and completeness rate for member identification in the cluster’s core. However, this approach fails in the stream due to severe field star contamination. Therefore, future CSST observations of Palomar 5 and its tidal tails will employ multiple epochs across several bands to obtain the deep photometry and proper motion data for a definitive MP analysis.

Abstract We present a comparative analysis of supernova remnant Cassiopeia A based on two deep, narrow-band images covering the [Fe ii ] 1.644 μ m + [Si i ] 1.645 μ m lines obtained in 2013 and 2020 with the same instruments on the UKIRT 3.8 m telescope. The identical setup and observing procedure allow for direct, accurate measurements of morphological and kinematic changes over a 7 yr baseline. We identified 263 compact knots in the 2020 image and, through comparison with the 2013 catalog of B.-C. Koo et al., classified them into quasi-stationary circumstellar knots and fast-moving knots (FMKs) of supernova ejecta. The FMKs show significant flux fluctuations, and many of those detected in 2013 are absent in the 2020 image. Proper-motion measurements derived from cross-correlation analysis indicate that most FMKs follow nearly ballistic expansion, whereas some, particularly those just beyond the eastern Fe-rich, X-ray-emitting ejecta region, exhibit noticeable deceleration. The proper motions of the main ejecta shell were also measured and modeled as a uniformly expanding shell with a systemic motion, which reproduces the observed geometric and kinematic asymmetries of the remnant.

Abstract Studying the remnants of young core-collapse supernovae (SNe) can yield insight into the chemical composition of their progenitors and the geometry of the explosions. The supernova remnant (SNR) G292.0+1.8 is one of only three known oxygen-rich SNRs in the galaxy—remnants of core collapse of which relatively pure fragments of ejecta can be seen. Several dozen ejecta knots from G292.0+1.8 were the subject of a proper motion analysis, based on [O iii ] 5007 Å images taken over a 22 yr baseline by P. F. Winkler et al. They determined that the transverse velocities of the filaments are linearly proportional to their distances from a common expansion center; thus, the O-rich filaments have been traveling with little deceleration since the initial SN event, ∼3000 yr ago. In this paper, we use optical spectra of G292.0+1.8, all taken from the Cerro Tololo Inter-American Observatory, to measure radial velocities for 93 knots. Assuming undecelerated expansion, as indicated by the proper motions, the radial velocity should be proportional to the distance from the center along the line of sight, just as the proper motions are proportional to the transverse distance. Therefore, we can map the three-dimensional structure and kinematics of the SNR. We find that the knots generally follow a broad biconical distribution, suggesting that the SN explosion produced broad jets of ejecta. This structure is similar to that seen in some other young core-collapse SNRs.