Solar Neighborhood Research Articles

The stellar ‘Snake’ – II. The mass function

ABSTRACT We present a comprehensive investigation on the mass function (MF) of a snake-like stellar structure in the solar neighbourhood, building on our previous discovery. To ensure the reliability of the data, we reselect the member stars of the Stellar ‘Snake’ in the latest Gaia Data Release 3 using the same approach as the initial series of articles. We also precisely measure the physical parameters of the clusters within the Stellar Snake. In light of the high completeness of the member stars in the cluster regions, we develop a simulated model colour–magnitude diagram-based inference method to derive the mass function, binary fraction, and mass-ratio distribution of the clusters in the Stellar Snake. Notably, despite their similar ages and metallicity, we discover systematic variations in the MFs along the elongation direction of the Snake in the mass range of 0.5 to 2.0 M⊙. The ‘head’ of the Snake conforms to a canonical initial mass function with a power-law slope of α ∼ −2.3. Extending towards the ‘tail’, the MF becomes more top-light, indicating a deficiency of massive stars within these clusters. This result provides evidence for the delayed formation of massive stars in the clusters. Such clues give support to the hypothesis that the Stellar Snake constitutes as a hierarchically primordial structure.

Molecular Structure Engineering of Isomeric Additives for Long Lifetime Zn Anodes.

Modulating the solvation structure of hydrated zinc ions using organic additives stands as a pragmatic approach to suppress dendrite formation and corrosion on zinc metal anodes (ZMAs), thereby enhancing the rechargeability of aqueous Zn-ion batteries. However, fundamental screening principles for organic additives with diverse molecular structures remain elusive, especially for isomers with the same molecular formula. This study delves into the impact of three isomeric hexagonal alcohols (mannitol, sorbitol, and galactitol) as additives in adjusting Zn2+ solvation structural behaviors within ZnSO4 baseline electrolytes. Electrical measurements and molecular simulations reveal the specific molecular structure of mannitol, which features interweaving electron clouds between adjacent hydroxyl groups, achieving a high local electron cloud density. This phenomenon significantly enhances desolvation abilities, thus establishing a more stable anode/electrolyte interface chemistry. Even at 5mA cm-2 for 2.5 mAh cm-2 capacity, Zn||Zn symmetric cells with mannitol-regulated electrolyte display an impressive 1170 h lifespan, far exceeding those with other isomer additives and is nearly tenfold longer than that with a pure ZnSO4 electrolyte (120 h). Rather than strictly adhering to focusing on chemical composition, this study with emphasison optimizing molecular structure offers a promising untapped dimension to screen more efficient additives to enhance the reversibility of ZMAs.

Impacts of the Local arm on the local circular velocity inferred from the Gaia DR3 young stars in the Milky Way

ABSTRACT A simple one-dimensional axisymmetric disc model is applied to the kinematics of O type and B type stars (OB stars) near the Sun obtained from Gaia Data Release 3 catalogue. The model determines the ‘local centrifugal speed’ Vc(R0) – defined as the circular velocity in the Galactocentric rest frame, where the star would move in a near-circular orbit if the potential is axisymmetric with the local potential of the Galaxy. We find that the Vc(R0) values and their gradient vary across the selected region of stars within the solar neighbourhood. By comparing with an N-body/hydrodynamic simulation of a Milky Way-like galaxy, we find that the kinematics of the young stars in the solar neighbourhood is affected by the Local arm, which makes it difficult to measure Vc(R0). However, from the resemblance between the observational data and the simulation, we suggest that the known rotational velocity gap between the Coma Bernices and Hyades-Pleiades moving groups could be driven by the co-rotation resonance of the Local arm, which can be used to infer the azimuthally averaged circular velocity. We find that Vc(R) obtained from the D < 2 kpc sample is well matched with this gap at the position of the Local arm. Hence, we argue that our results from the D < 2 kpc sample, Vc(R0) = 234 ± 2 km s−1, are close to the azimuthally averaged circular velocity rather than the local centrifugal speed, which is influenced by the presence of the Local arm.

Structure, kinematics, and time evolution of the Galactic warp from Classical Cepheids

ABSTRACT The warp is a well-known undulation of the Milky Way disc. Its structure has been widely studied, but only since Gaia DR2 has it been possible to reveal its kinematic signature beyond the solar neighbourhood. In this work, we present an analysis of the warp traced by Classical Cepheids by means of a Fourier decomposition of their height (Z) and, for the first time, of their vertical velocity (Vz). We find a clear but complex signal that in both variables reveals an asymmetrical warp. In Z, we find the warp to be almost symmetric in amplitude at the disc’s outskirts, with the two extremes never being diametrically opposed at any radius and the line of nodes presenting a twist in the direction of stellar rotation for R > 11 kpc. For Vz, in addition to the usual m = 1 mode, an m = 2 mode is needed to represent the kinematic signal of the warp, reflecting its azimuthal asymmetry. The line of maximum vertical velocity is similarly twisted as the line of nodes and trails behind by ≈25°. We develop a new formalism to derive the pattern speed and change in amplitude with time $\dot{A}$ of each Fourier mode at each radius, via a joint analysis of the Fourier decomposition in Z and Vz. By applying it to the Cepheids we find, for the m = 1 mode, a constant pattern speed in the direction of stellar rotation of 9.2 ± 3.1 km s−1 kpc−1, a negligible $\dot{A}$ up to R ≈ 14 kpc and a slight increase at larger radii, in agreement with previous works.

A Parsec-scale Catalog of Molecular Clouds in the Solar Neighborhood Based on 3D Dust Mapping: Implications for the Mass–Size Relation

We dendrogram the Leike et al. 3D dust map, leveraging its ∼1 pc spatial resolution to produce a uniform catalog of molecular clouds in the solar neighborhood. Using accurate distances, we measure the properties of 65 clouds in true 3D space, eliminating much of the uncertainty in mass, size, and density. Clouds in the catalog contain a total of 1.1 × 105 M ☉, span distances of 116−440 pc, and include a dozen well-studied clouds in the literature. In addition to deriving cloud properties in 3D volume density space, we create 2D dust extinction maps from the 3D data by projecting the 3D clouds onto a 2D “Sky” view. We measure the properties of the 2D clouds separately from the 3D clouds. We compare the scaling relation between the masses and sizes of clouds following Larson. We find that our 2D projected mass–size relation, M ∝ r 2.1, agrees with Larson's Third Relation, but our 3D derived properties lead to a scaling relation of about one order larger: M ∝ r 2.9. Validating predictions from theory and numerical simulations, our results indicate that the mass–size relation is sensitive to whether column or volume density is used to define clouds, since mass scales with area in 2D (M ∝ r 2) and with volume in 3D (M ∝ r 3). Our results imply a roughly constant column and volume density in 2D and 3D, respectively, for molecular clouds, as would be expected for clouds where the lower density, larger volume-filling gas dominates the cloud mass budget.

Evaluating global vegetation products for application in heterogeneous forest-savanna landscapes

ABSTRACT While satellite-derived global vegetation structure products are powerful and easy to use, their utility for studying spatial patterns within heterogeneous landscapes such as forest-savanna mosaics has not been extensively evaluated. We explored the application of global vegetation structure products in heterogeneous landscapes by comparing them with Airborne Laser Scanning. Specifically, we assessed the accuracy and bias of two fractional cover products, MODIS Vegetation Continuous Fields (VCF) and Hansen Global Forest Change (GFC), and one global canopy height model, Global Forest Canopy Height Model (CHM), in comparison with the same variables derived from local ALS point clouds. We found that there were limitations to all three products. MODIS VCF was less accurate than its reported accuracy by at least 3%, and GFC was 10% less accurate than MODIS VCF. While Global CHM had a similar magnitude of error to its reported product accuracy, product agreement was much lower (R2 0.19 vs. R2 0.61). We also found that the context of the analysis is important when choosing whether to use one fractional product over the other. Global products should be applied with caution in heterogeneous landscapes. Increased training and validation from these landscapes could improve the performance of these products and their utility for landscape-scale ecological research.

Fusion-competition framework of local topology and global texture for head pose estimation

RGB image and point cloud involve texture and geometric structure, which are widely used for head pose estimation. However, images lack of spatial information, and the quality of point cloud is easily affected by sensor noise. In this paper, a novel fusion-competition framework (FCF) is proposed to overcome the limitations of a single modality. The global texture information is extracted from image and the local topology information is extracted from point cloud to project heterogeneous data into a common feature subspace. The projected texture feature weighted by the channel attention mechanism is embedded into each local point cloud region with different topological features for fusion. The scoring mechanism creates competition among the regions involving local-global fused features to predict final pose with the highest score. According to the evaluation results on the public and our constructed datasets, the FCF improves the estimation accuracy and stability by an average of 13.6 % and 12.7 %, which is compared to nine state-of-the-art methods.

PPSurf: Combining Patches and Point Convolutions for Detailed Surface Reconstruction

Abstract3D surface reconstruction from point clouds is a key step in areas such as content creation, archaeology, digital cultural heritage and engineering. Current approaches either try to optimize a non‐data‐driven surface representation to fit the points, or learn a data‐driven prior over the distribution of commonly occurring surfaces and how they correlate with potentially noisy point clouds. Data‐driven methods enable robust handling of noise and typically either focus on a global or a local prior, which trade‐off between robustness to noise on the global end and surface detail preservation on the local end. We propose PPSurf as a method that combines a global prior based on point convolutions and a local prior based on processing local point cloud patches. We show that this approach is robust to noise while recovering surface details more accurately than the current state‐of‐the‐art. Our source code, pre‐trained model and dataset are available at https://github.com/cg‐tuwien/ppsurf.

Uniting and APOGEE to unveil the cosmic chemistry of the Milky Way disc

The spatial distribution of Galactic stars with different chemical abundances encodes information on the processes that drove the formation and evolution of the Milky Way. Survey selection functions are indispensable for analysing astronomical catalogues produced by large-scale surveys. The use of these selection functions in data modelling is more complex when data from different surveys are to be modelled simultaneously. We introduce a procedure for constructing the selection function of a sample of red clump stars that have parallaxes and elemental abundances from the mission. We separately constructed the selection function of the APOGEE DR17 red clump stars, which depends on very different observables and has a very different spatial coverage. We combined the two surveys and accounted for their joint selection function to provide strong constraints on the radial and vertical density distribution of mono-abundance populations, with offering a dense coverage of the solar neighbourhood, while APOGEE reaches larger distances near the Galactic plane. We confirm that the radial density profile steepens with increasing metallicity. The combined sample also indicates a metallicity-dependent flaring of the alpha -poor disc. We provide the code for constructing the selection function we used in this study through the GaiaUnlimited Python package.

Kinematic structure of the stellar population of the solar neighborhood by Gaia DR3

The data of modern catalogs allow us to consider in detail the issue of the spatial velocity distribution. The stars in the solar vicinity make it possible to avoid errors and draw detailed conclusions about their kinematics. For a corrected study, we took a sample of stars from the Gaia DR3 within 300 pc. This area contains a number of star clusters and streams. It was found that in the circumscribed vicinity the direction of the stars is divided into several vast concentrations, the apex of motion of which lies in the direction of the motion of the Sun and in the direction of motion of the Ursa Major group, which in turn is divided into two separate groups in direction in space. In addition, a group of stars is considered, which, according to their kinematic characteristics, most likely belong to a halo or bulge. High-velocity stars are also considered under the assumption of their nature.

The Age Distribution of Stellar Orbit Space Clumps

The orbit distribution of young stars in the Galactic disk is highly structured, from well-defined clusters to streams of stars that may be widely dispersed across the sky, but are compact in orbital action-angle space. The age distribution of such groups can constrain the timescales over which conatal groups of stars disperse into the “field.” Gaia data have proven powerful in identifying such groups in action-angle space, but the resulting member samples are often too small and have too narrow a color–magnitude diagram (CMD) coverage to allow robust age determinations. Here, we develop and illustrate a new approach that can estimate robust stellar population ages for such groups of stars. This first entails projecting the predetermined action-angle distribution into the 5D space of positions, parallaxes, and proper motions, where much larger samples of likely members can be identified over a much wider range of the CMD. It then entails isochrone fitting that accounts for: (a) widely varying distances and reddenings; (b) outliers and binaries; (c) sparsely populated main-sequence turnoffs, by incorporating the age information of the low-mass main sequence; and (d) the possible presence of an intrinsic age spread in the stellar population. When we apply this approach to 92 nearby stellar groups identified in 6D orbit space, we find that they are predominantly young (≲1 Gyr), mono-age populations. Many groups are established (known) localized clusters with possible tidal tails, while others tend to be widely dispersed and manifestly unbound. This new age-dating tool offers a stringent approach to understanding on which orbits stars form in the solar neighborhood and how quickly they disperse into the field.

Insights from super-metal-rich stars: Is the Milky Way bar young?

Context. Bar formation and merger events can contribute to the rearrangement of stars within the Galaxy in addition to triggering star formation (SF) epochs. Super-metal-rich (SMR) stars found in the solar neighbourhood (SNd) can be used as tracers of such events as they are expected to originate only in the inner Galaxy and to have definitely migrated. Aims. We study a homogeneous and large sample of SMR stars in the SNd to provide tighter constraints on the epoch of the bar formation and its impact on the Milky Way (MW) disc stellar populations. Methods. We investigated a sample of 169 701 main sequence turnoff (MSTO) and subgiant branch (SGB) stars with 6D phase space information and high-quality stellar parameters coming from the hybrid-CNN analysis of the Gaia-DR3 RVS stars. We computed distances and ages using the StarHorse code with a mean precision of 1% and 11%, respectively. Of these stars, 11 848 have metallicity ([Fe/H]) above 0.15 dex. Results. We report a metallicity dependence of spatial distribution of stellar orbits shown by the bimodal distribution in the guiding radius (Rg) at 6.9 and 7.9 kpc, first appearing at [Fe/H] ~ 0.1 dex, becoming very pronounced at higher [Fe/H]. In addition, we observe a trend where the most metal-rich stars, with [Fe/H] ~ 0.4 dex, are predominantly old (9–12 Gyr), but show a gradual decline in [Fe/H] with age, reaching approximately 0.25 dex about 4 Gyr ago, followed by a sharp drop around 3 Gyr ago. Furthermore, our full dataset reveals a clear peak in the age–metallicity relationship during the same period, indicating a SF burst around 3–4 Gyr ago with slightly sub-solar [Fe/H] and enhanced [α/Fe]. Conclusions. We show that the SMR stars are good tracers of bar activity.We interpret the steep decrease in the number of SMR stars at around 3 Gyr as the end of the bar formation epoch. In this scenario the peak of bar activity also coincides with a peak in the SF activity in the disc. Although the SF burst around 3 Gyr ago has been reported previously, its origin was unclear. Here we suggest that the SF burst was triggered by the high bar activity, 3–4 Gyr ago. According to these results and interpretation, the MW bar could be young.

Measuring the Milky Way Vertical Potential with the Phase Snail in a Model-independent Way

The vertical phase-space spiral (snail) is a direct sign of disequilibrium of the Milky Way’s disk. Nevertheless, the wrapping of the phase snail contains information on the vertical potential. We propose a novel method to measure the vertical potential utilizing the intersections between the snail and z/V z axes, for which we know the maximum vertical heights (Z max) or velocities ( Vz,max ). Using a refined linear interpolation method, we directly obtain (Zmax,12Vz,max2) for these snail intersections to constrain the vertical potential profile empirically. Our method is model-independent, since no assumptions about the snail shape or the vertical potential have been made. Although the snail binned by the guiding center radius (R g ) is more prominent, it traces a vertical potential shallower than that of the snail binned by the same galactocentric radius (R). We apply an empirical method to correct this difference. We measure the snail intersections in several R g bins within 7.5 < R g < 11.0 kpc for Gaia DR3 and apply the interpolation method to deduce the potential values at several vertical heights. The potential at the snail intersections, as well as the following mass modeling, is consistent with the popular Milky Way potentials in the literature. For the R g -binned phase snail in the solar neighborhood, the mass modeling indicates a local dark matter density of ρ dm = 0.0150 ± 0.0031 M ⊙ pc−3, consistent with previous works. Our method could be applied to larger radial ranges in future works to provide independent and stronger constraints on the Milky Way’s potential.

Protostellar Cores in Sagittarius B2 N and M

We present 500 and 700 au resolution 1 and 3 mm Atacama Large Millimeter/submillimeter Array observations, respectively, of protostellar cores in protoclusters Sagittarius B2 (Sgr B2) North (N) and Main (M), parts of the most actively star-forming cloud in our Galaxy. Previous lower-resolution (5000 au) 3 mm observations of this region detected ∼150 sources inferred to be young stellar objects (YSOs) with M > 8 M ⊙. With a 10-fold increase in resolution, we detect 371 sources at 3 mm and 218 sources in the smaller field of view at 1 mm. The sources seen at low resolution are observed to fragment into an average of two objects. About one-third of the observed sources fragment. Most of the sources we report are marginally resolved and are at least partially optically thick. We determine that the observed sources are most consistent with Stage 0/I YSOs, i.e., rotationally supported disks with an active protostar and an envelope, that are warmer than those observed in the solar neighborhood. We report source-counting-based inferred stellar mass and the star formation rate of the cloud: 2800 M ⊙ and 0.0038 M ⊙ yr−1 for Sgr B2 N and 6900 M ⊙ and 0.0093 M ⊙ yr−1 for Sgr B2 M, respectively.

Life Origin in the Milky Way Galaxy: III. Spatial Distribution of Overheated Stars in the Solar Neighborhood

Life Origin in the Milky Way Galaxy: III. Spatial Distribution of Overheated Stars in the Solar Neighborhood

HESS J1809-193: Gamma-Ray Emission by Cosmic Rays from a Past Explosion

The very-high-energy γ-ray source HESS J1809-193 has been detected by the LHAASO and HAWC observatory beyond 100 TeV energy. It is an interesting candidate for exploring the underlying mechanisms of γ-ray production due to the presence of supernova remnants, pulsars, and molecular clouds close to it. We have considered the injection of the energetic cosmic rays from a past explosion, whose reminiscent may be SNR G011.0-00.0, which is located within the extended γ-ray source HESS J1809-193. We explain the multiwavelength data from the region of HESS J1809-193 with synchrotron, inverse Compton, and bremsstrahlung emission of cosmic-ray electrons and secondary γ-ray production in interactions of cosmic-ray protons with the cold protons in the local molecular clouds within a time-dependent framework including the diffusion loss of cosmic rays. The observational data have been modeled with the secondary photons produced by the time-evolved cosmic-ray spectrum assuming the age of the explosion is 4500 yr.

Curvature estimation for point cloud 2-manifolds based on the heat kernel

&lt;p&gt;The geometry processing of a point cloud 2-manifold (or point cloud surface) heavily depends on the discretization of differential geometry properties such as Gaussian curvature, mean curvature, principal curvature, and principal directions. Most of the existing algorithms indirectly compute these differential geometry properties by seeking a local approximation surface or fitting point clouds with certain polynomial functions and then applying the curvature formulas in classical differential geometry. This paper initially proposed a new discretized Laplace-Beltrami operator by applying an inherent distance parameter, which acts as the foundation for precisely estimating the mean curvature. Subsequently, the estimated mean curvature was taken as a strong constraint condition for estimating the Gaussian curvatures, principal curvatures, and principal directions by determining an optimal ellipse. The proposed methods are mainly based on the heat kernel function and do not require local surface reconstruction, thus belonging to truly mesh-free methods. We demonstrated the correctness of the estimated curvatures in both analytic and non-analytic models. Various experiments indicated that the proposed methods have high accuracy. As an exemplary application, we utilized the mean curvature for detecting features of point clouds.&lt;/p&gt;

RR Lyrae from binary evolution: abundant, young, and metal-rich

ABSTRACT RR Lyrae are a well-known class of pulsating horizontal branch stars widely used as tracers of old, metal-poor stellar populations. However, mounting observational evidence shows that a significant fraction of these stars may be young and metal-rich. Here, through detailed binary stellar evolution modelling, we show that all such metal-rich RR Lyrae can be naturally produced through binary interactions. Binary companions of these RR Lyrae stars formed through binary interactions partly strip their progenitor’s envelopes during a preceding red giant phase. As a result, stripped horizontal branch stars become bluer than their isolated stellar evolution counterparts and thus end up in the instability strip. In contrast, in the single evolution scenario, the stars can attain such colours only at large age and low metallicity. While binary-made RR Lyrae can possess any ages and metallicities, their Galactic population is relatively young (1 – $9\, {\rm Gyr}$) and dominated by the thin disc and the bulge. We show that Galactic RR Lyrae from binary evolution are produced at rates compatible with the observed metal-rich population and have consistent G-band magnitudes, Galactic kinematics, and pulsation properties. Furthermore, these systems dominate the RR Lyrae population in the solar neighbourhood. We predict that all metal-rich RR Lyrae have an A, F, G, or K-type companion with a long orbital period ($P \gtrsim 1000\, {\rm d}$). Observationally characterizing the orbital periods and masses of such stellar companions will provide valuable new constraints on mass and angular momentum-loss efficiency for Sun-like accretors and the nature of RR Lyrae populations.

Stellar rotations and the disentanglement of the Galactic thin and thick discs

ABSTRACT The kinematics, mean α-elements, and ages of the stars reveal two distinct disc populations observed in the Solar neighbourhood. Although several studies have been carried out to characterize abundances of chemical elements and kinematic identifications in these populations, there are few studies that dealt with the analysis of stellar rotation and characteristics of populations focused on low-mass stars of the F and G types. In this work, we propose a new approach to classify stellar populations from the thin and thick disc for F and G dwarf stars by relating chemical abundance and rotation (v sin i) of these stars in the rotational–chemical–plane (v sin i–[α/Fe]–[Fe/H] plot). Our results show that the two rotational-chemical sequences disentangled, high- and low-[α/Fe] components, present properties (α-enhanced, ages, kinematics, space velocity gradients, local density ratio) closely linked to the stars of the chemically and kinematically defined as thin and thick disc components. This study has an impact on calibrations that relate ages to rotation (gyro-chronology) as well as age to chemical abundances (chemochronology), as well as sheds light on the understanding of the processes of Galactic disc formation.

Radial phase spirals in the Solar neighbourhood

ABSTRACT The second data release of ESA’s Gaia mission revealed numerous signatures of disequilibrium in the Milky Way’s disc. These signatures are seen in the planar kinematics of stars, which manifest as ridges and ripples in R–vϕ, and in vertical kinematics, where a prominent spiral is seen in the z–vz phase space. In this work, we show an equivalent ΔR–vR phase spiral forms following a perturbation to the disc. We demonstrate the behaviour of the ΔR–vR phase spirals in both a toy model and a high-resolution N-body simulation of a satellite interaction. We then confront these models with the data, where we find partial ΔR–vR phase spirals in the Solar neighbourhood using the most recent data from Gaia DR3. This structure indicates ongoing radial phase mixing in the Galactic disc, suggesting a history of recent perturbations, either through internal or external (e.g. satellite) processes. Future work modelling the z–vz and ΔR–vR phase spirals in tandem may help break degeneracy’s between possible origins of the perturbation.