Galactic Velocity Research Articles

A spectroscopic and kinematic survey of fast hot subdwarfs

Hot subdwarfs (sdO/B) are the stripped helium cores of red giants formed via binary interactions. Close hot subdwarf binaries with massive white dwarf companions have been proposed as possible progenitors of thermonuclear supernovae type Ia (SN Ia). If the supernova is triggered by stable mass transfer from the helium star, the companion should survive the explosion and should be accelerated to high velocities. The hypervelocity star US 708 is regarded as the prototype for such an ejected companion. To find more of those objects we conducted an extensive spectroscopic survey. Candidates for such fast stars have been selected from the spectroscopic database of the Sloan Digital Sky Survey (SDSS) and several ground-based proper-motion surveys. Follow-up spectroscopy has been obtained with several 4m- to 10m-class telescopes. Combining the results from quantitative spectroscopic analyses with space-based astrometry from Gaia Early Data Release 3 (EDR3) we determined the atmospheric and kinematic parameters of 53 fast hot subdwarf stars. None of these stars is unbound to the Galaxy, although some have Galactic restframe velocities close to the Galactic escape velocity. 21 stars are apparently single objects, that crossed the Galactic disc within their lifetimes in the sdO/B stage and could be regarded as potential candidates for the SN Ia ejection scenario. However, the properties of the full sample are more consistent with a pure old Galactic halo population. We therefore conclude that the fast sdO/B stars we found are likely to be extreme halo stars.

Resonant and Ultra-short-period Planet Systems Are at Opposite Ends of the Exoplanet Age Distribution

Exoplanet systems are thought to evolve on secular timescales over billions of years. This evolution is impossible to directly observe on human timescales in most individual systems. While the availability of accurate and precise age inferences for individual exoplanet host stars with ages τ in the interval 1 Gyr ≲ τ ≲ 10 Gyr would constrain this evolution, accurate and precise age inferences are difficult to obtain for isolated field dwarfs like the host stars of most exoplanets. The Galactic velocity dispersion of a thin-disk stellar population monotonically grows with time, and the relationship between age and velocity dispersion in a given Galactic location can be calibrated by a stellar population for which accurate and precise age inferences are possible. Using a sample of subgiants with precise age inferences, we calibrate the age–velocity dispersion relation in the Kepler field. Applying this relation to the Kepler field’s planet populations, we find that Kepler-discovered systems plausibly in second-order mean-motion resonances have 1 Gyr ≲ τ ≲ 2 Gyr. The same is true for systems plausibly in first-order mean-motion resonances, but only for systems likely affected by tidal dissipation inside their innermost planets. These observations suggest that many planetary systems diffuse away from initially resonant configurations on secular timescales. Our calibrated relation also indicates that ultra-short-period (USP) planet systems have typical ages in the interval 5 Gyr ≲ τ ≲ 6 Gyr. We propose that USP planets tidally migrated from initial periods in the range 1 day ≲ P ≲ 2 days to their observed locations at P < 1 day over billions of years and trillions of cycles of secular eccentricity excitation and inside-planet damping.

The Lockman–SpReSO project

Context. The Lockman–SpReSO project is an optical spectroscopic survey of 956 far-infrared (FIR) objects within the Lockman Hole field limited by magnitude RC(AB) &lt; 24.5. Fe II and Mg II absorption lines have been detected in 21 out of 456 objects with a determined spectroscopic redshift in the catalogue. The redshifts of these objects are in the range 0.5 ≲ z ≲ 1.44. Aims. The aim of this study is to investigate material ejection from star-forming regions and material infall into galaxies by analysing the Fe II and Mg II absorption lines. Additionally, we explore whether the correlations found in previous studies between these galactic wind velocities, line equivalent widths (EWs), and galaxy properties such as stellar mass (M*), star formation rate (SFR), and specific star formation rate (sSFR) are valid for a sample with FIR-selected objects. The objects analysed span an M* range of 9.89 &lt; log(M*/M⊙) &lt; 11.50 and an SFR range of 1.01 &lt; log(SFR) &lt; 2.70. Methods. We performed measurements of the Mg IIλλ2796, 2803, Mg Iλ2852, Fe IIλλ2374, 82, Fe IIλλ2586, 2600, and Fe IIλ2344 spectral lines present in the spectra of the selected sample to determine the EW and velocity of the flows observed in the star-forming galaxies. Subsequently, we conducted 107 bootstrap simulations using the Spearman’s rank correlation coefficient (ρs) to explore correlations with galaxy properties. Furthermore, we calculated the covering factor, gas density, and optical depth for the measured Fe II doublets. Results. Our analysis reveals strong correlations between the EW of Mg II lines and both M* (ρs = 0.43, 4.5σ) and SFR (ρs = 0.42, 4.4σ). For the Fe II lines, we observed strong correlations between the EW and SFR (ρs ∼ 0.65, &gt; 3.9σ), with a weaker correlation for M* (ρs ∼ 0.35, &gt; 1.9σ). No notable correlations were found between velocity measurements of the Mg II line and M*, SFR, or sSFR of the objects (ρs ∼ 0.1). However, a strong negative correlation was found between the velocity of the Fe II lines and the SFR of the galaxies (ρs ∼ −0.45, ∼3σ). Our results align with those of previous studies, although only FIR-selected objects are investigated here. Finally, we detect a candidate ‘loitering outflow’, a recently discovered subtype of the iron low-ionisation broad absorption line (FeLoBAL) quasars, at a redshift of z = 1.4399, exhibiting emission in C III] and low line velocities (|v|≲200 km s−1).

He-rich Hot Subdwarf Stars Observed in Gaia DR3 and LAMOST DR7: Carbon and Nitrogen Abundances and Kinematics

We conducted an analysis of the abundances of He, C, and N in 210 He-rich hot subdwarfs observed within both the Gaia Data Release 3 (DR3) and LAMOST DR7 data sets. This analysis involved fitting the LAMOST spectra with Tlusty/Synspec non-LTE synthetic spectra. By examining the Galactic spatial positions, velocity vectors, and orbital parameters of these stars, we determined their Galactic population memberships utilizing LAMOST radial velocities and Gaia DR3 parallaxes along with proper motions. Our investigation revealed two positive correlations of C and one positive correlation of N with respect to the He abundance. We found a clear C abundance dichotomy where approximately 82% of the stars show N enrichment above the solar value. Moreover, we observed a bimodal distribution of C abundances, prominently evident in both the Galactic thin and thick disks but absent in the halo population. Furthermore, we found that the scenario of the merger channel of double helium white dwarfs is inadequate to explain the formation of C-deficient He-rich hot subdwarfs.

Kepler-discovered Multiple-planet Systems near Period Ratios Suggestive of Mean-motion Resonances Are Young

Before the launch of the Kepler Space Telescope, models of low-mass planet formation predicted that convergent type I migration would often produce systems of low-mass planets in low-order mean-motion resonances. Instead, Kepler discovered that systems of small planets frequently have period ratios larger than those associated with mean-motion resonances and rarely have period ratios smaller than those associated with mean-motion resonances. Both short-timescale processes related to the formation or early evolution of planetary systems and long-timescale secular processes have been proposed as explanations for these observations. Using a thin disk stellar population’s Galactic velocity dispersion as a relative age proxy, we find that Kepler-discovered multiple-planet systems with at least one planet pair near a period ratio suggestive of a second-order mean-motion resonance have a colder Galactic velocity dispersion and are therefore younger than both single-transiting and multiple-planet systems that lack planet pairs consistent with mean-motion resonances. We argue that a nontidal secular process with a characteristic timescale no less than a few hundred Myr is responsible for moving systems of low-mass planets away from second-order mean-motion resonances. Among systems with at least one planet pair near a period ratio suggestive of a first-order mean-motion resonance, only the population of systems likely affected by tidal dissipation inside their innermost planets has a small Galactic velocity dispersion and is therefore young. We predict that period ratios suggestive of mean-motion resonances are more common in young systems with 10 Myr ≲ τ ≲ 100 Myr and become less common as planetary systems age.

Galactic runaway O and Be stars found usingGaiaDR3

Context.A relevant fraction of massive stars are runaway stars. These stars move with a significant peculiar velocity with respect to their environment.Aims.We aim to discover and characterize the population of massive and early-type runaway stars in the GOSC and BeSS catalogs usingGaiaDR3 astrometric data.Methods.We present a two-dimensional method in the velocity space to discover runaway stars as those that deviate significantly from the velocity distribution of field stars. Field stars are considered to follow the Galactic rotation curve.Results.We found 106 O runaway stars, 42 of which were not previously identified as runaways. We found 69 Be runaway stars, 47 of which were not previously identified as runaways. The dispersion of runaway stars is a few times higher inZandbthan that of field stars. This is explained by the ejections they underwent when they became runaways. The percentage of runaways is 25.4% for O-type stars, and it is 5.2% for Be-type stars. In addition, we conducted simulations in three dimensions for our catalogs. They revealed that these percentages could increase to ∼30% and ∼6.7%, respectively. Our runaway stars include seven X-ray binaries and one gamma-ray binary. Moreover, we obtain velocity dispersions of ∼5 km s−1perpendicular to the Galactic plane for O- and Be-type field stars. These values increase in the Galactic plane to ∼7 km s−1for O-type stars due to uncertainties and to ∼9 km s−1for Be-type stars due to Galactic velocity diffusion.Conclusions.The excellentGaiaDR3 astrometric data have allowed us to identify a significant number of O-type and Be-type runaways in the GOSC and BeSS catalogs. The higher percentages and higher velocities found for O-type compared to Be-type runaways underline that the dynamical ejection scenario is more likely than the binary supernova scenario. Our results open the door to identifying new high-energy systems among our runaways by conducting detailed studies.

Age Distribution of Exoplanet Host Stars: Chemical and Kinematic Age Proxies from GAIA DR3

The GAIA space mission is impacting astronomy in many significant ways by providing a uniform, homogeneous, and precise data set for over 1 billion stars and other celestial objects in the Milky Way and beyond. Exoplanet science has greatly benefited from the unprecedented accuracy of the stellar parameters obtained from GAIA. In this study, we combine photometric, astrometric, and spectroscopic data from the most recent Gaia DR3 to examine the kinematic and chemical age proxies for a large sample of 2611 exoplanets hosting stars whose parameters have been determined uniformly. Using spectroscopic data from the Radial Velocity Spectrometer on board GAIA, we show that stars hosting massive planets are metal-rich and α-poor in comparison to stars hosting small planets. The kinematic analysis of the sample reveals that stellar systems with small planets and those with giant planets differ in key aspects of galactic space velocity and orbital parameters, which are indicative of age. We find that the galactic orbital parameters have a statistically significant difference of 0.06 kpc for Z max and 0.03 for eccentricity, respectively. Furthermore, we estimated the stellar ages of the sample using the MIST-MESA isochrone models. The ages and their proxies for the planet-hosting stars indicate that the hosts of giant planetary systems are younger when compared to the population of stars harboring small planets. These age trends are also consistent with the chemical evolution of the galaxy and the formation of giant planets from the core-accretion process.

Constraints on the Galactic centre environment from Gaia hypervelocity stars III: insights on a possible companion to Sgr A*

ABSTRACT We consider a scenario in which Sgr A* is in a massive black hole binary (MBHB) with an as-of-yet undetected supermassive or intermediate-mass black hole companion. Dynamical encounters between this MBHB and single stars in its immediate vicinity would eject hypervelocity stars (HVSs) with velocities beyond the Galactic escape velocity of the Galaxy. In this work, we use existing HVS observations to constrain for the first time the existence of a companion to Sgr A*. We simulate the ejection of HVSs via the ‘MBHB slingshot’ scenario and show that the population of HVSs detectable today depends strongly on the companion mass and the separation of the MBHB. We demonstrate that the lack of uncontroversial HVS candidates in Gaia Data Release 3 places a firm upper limit on the mass of a possible Sgr A* companion. Within one milliparsec of Sgr A*, our results exclude a companion more massive than $2000 \, \mathrm{M_\odot }$. If Sgr A* recently merged with a companion black hole, our findings indicate that unless this companion was less massive than $500 \, \mathrm{M_\odot }$, this merger must have occurred at least 10 Myr ago. These results complement and improve upon existing independent constraints on a companion to Sgr A* and show that large regions of its parameter space can now be ruled out.

Spin-dependent sub-GeV inelastic dark matter-electron scattering and Migdal effect. Part I. Velocity independent operator

The ionization signal provide an important avenue of detecting light dark matter. In this work, we consider the sub-GeV inelastic dark matter and use the non-relativistic effective field theory (NR-EFT) to derive the constraints on the spin-dependent DM-electron scattering and DM-nucleus Migdal scattering. Since the recoil electron spectrum of sub-GeV DM is sensitive to tails of galactic DM velocity distributions, we also compare the bounds on corresponding scattering cross sections in Tsallis, Empirical and standard halo models. With the XENON1T data, we find that the exclusion limits of the DM-proton/neutron and DM-electron scattering cross sections for exothermic inelastic DM are much stronger that those for the endothermic inelastic DM. Each limits of the endothermic inelastic DM can differ by an order of magnitude at most in three considered DM velocity distributions.

Measuring the Quantum State of Dark Matter

AbstractIt is shown how the time series obtained from searches for ultralight bosonic dark matter (DM), such as the axion, can be used to determine whether it is in a coherent or incoherent quantum state. The example is essentially trivial, but it is hoped that explicitly addressing it will provoke experimental exploration. In the standard coherent state, oscillations in the number density occur over the coherence time, , where m is the particle mass and v is the galactic virial velocity, leading to a reduction in the constraining power of experiments operating on timescales , due to the unknown global phase. On the other hand, if the DM is incoherent then no such strong number oscillations occur since the ensemble average over particles in different streams gives an effective phase average. If an experiment detects a signal then the coherent or incoherent nature of DM can be determined by time series analysis over the coherence time. This finding is observationally relevant for DM masses, (corresponding to coherence times between a year and 100 s).

VLBI astrometry on the white dwarf pulsar AR Scorpii

ABSTRACT AR Scorpii (AR Sco), the only-known radio-pulsing white dwarf binary, shows unusual pulsating emission at the radio, infrared, optical, and ultraviolet bands. To determine its astrometric parameters at the radio band independently, we conducted multi-epoch Very Long Baseline Interferometry (VLBI) phase-referencing observations with the European VLBI Network at 5 GHz and the Chinese VLBI Network plus the Warkworth 30-m telescope (New Zealand) at 8.6 GHz. By using the differential VLBI astrometry, we provide high-precision astrometric measurements on the parallax ($\pi =8.52_{-0.07}^{+0.04}$ mas) and proper motion ($\mu _{\alpha }=9.48_{-0.07}^{+0.04}$ mas yr−1, $\mu _{\delta }=-51.32_{-0.38}^{+0.22}$ mas yr−1). The new VLBI results agree with the optical Gaia astrometry. Our kinematic analysis reveals that the Galactic space velocities of AR Sco are quite consistent with that of both intermediate polars and polars. Combined with the previous tightest VLBI constraint on the size, our parallax distance suggests that the radio emission of AR Sco should be located within the light cylinder of its white dwarf.

Evidence for Population-dependent Vertical Motions and the Long-lived Nonsteady Lopsided Milky Way Warp

We present a Galactic disk vertical velocity analysis using OB type stars (OB stars), red clump (RC) stars, and main-sequence turnoff (MSTO) stars with different average age populations crossmatched with LAMOST DR5 and Gaia DR3. We show that the vertical velocities of the three populations clearly vary with the Galactocentric distance (R) and the younger stellar population has a stronger increasing trend in general. The bending and breathing modes indicated by the vertical motions are dependent on the populations and vary with spatial locations. These vertical motions may be due to the Galactic warp, or minor mergers, or nonequilibrium of the disk. Assuming the warp is the dominant component, we find that the amplitude of the warp (γ, Z ω ) of OB stars (younger population) is larger than that of RC stars (medium population) and the latter is also larger than that for MSTO stars (older population), which is in agreement with other independent analyses of stellar density distribution, and supports that the warp is a long-lived, nonsteady structure and is time evolving. This conclusion is robust whether the line of nodes ϕ w is fixed or is a free parameter (with ϕ w being around 3°−8.°5 as the best fit). Furthermore, we find that the warp is lopsided with asymmetries along the azimuthal angle (ϕ).

Limits on the nuclearite flux using the ANTARES neutrino telescope

In this work, a search for nuclearites of strange quark matter by using nine years of ANTARES data taken in the period 2009–2017 is presented. The passage through matter of these particles is simulated taking into account a detailed description of the detector response to nuclearites and of the data acquisition conditions. A down-going flux of cosmic nuclearites with Galactic velocities (β = 10-3) was considered for this study. The mass threshold for detecting these particles at the detector level is 4 × 1013 GeV/c 2. Upper limits on the nuclearite flux for masses up to 1017 GeV/c 2 at the level of ∼ 5 × 10-17 cm-2 s-1 sr-1 are obtained. These are the first upper limits on nuclearites established with a neutrino telescope and the most stringent ever set for Galactic velocities.

Establishing the accuracy of asteroseismic mass and radius estimates of giant stars

Context. Eclipsing binary stars with an oscillating giant component allow accurate stellar parameters to be derived and asteroseismic methods to be tested and calibrated. To this aim, suitable systems need to be firstly identified and secondly measured precisely and accurately. KIC 4054905 is one such system, which has been identified, but with measurements of a relatively low precision and with some confusion regarding its parameters and evolutionary state. Aims. Our aim is to provide a detailed and precise characterisation of the system and to test asteroseismic scaling relations. Methods. Dynamical and asteroseismic parameters of KIC 4054905 were determined from Kepler time-series photometry and multi-epoch high-resolution spectra from FIES at the Nordic Optical Telescope. Results. KIC 4054905 was found to belong to the thick disk and consist of two lower red giant branch (RGB) components with nearly identical masses of 0.95 M⊙ and an age of 9.9 ± 0.6 Gyr. The most evolved star with R ≃ 8.4 R⊙ displays solar-like oscillations. These oscillations suggest that the star belongs to the RGB, supported also by the radius, which is significantly smaller than the red clump phase for this mass and metallicity. Masses and radii from corrected asteroseismic scaling relations can be brought into full agreement with the dynamical values if the RGB phase is assumed, but a best scaling method could not be identified. Conclusions. The dynamical masses and radii were measured with a precision better than 1.0%. We firmly establish the evolutionary nature of the system to be that of two early RGB stars with an age close to 10 Gyr, unlike previous findings. The metallicity and Galactic velocity suggest that the system belongs to the thick disk of the Milky Way. We investigate the agreement between dynamical and asteroseismic parameters for KIC 4054905 measured in various ways. This suggests that consistent solutions exist, but the need to analyse more of these systems continues in order to establish the accuracy of asteroseismic methods.

LAMOST meets Gaia: The Galactic open clusters

Open clusters (OCs) are born and evolve along the Milky Way (MW) plane. On them is imprinted the history of the Galactic disc, including its chemical and dynamical evolution. Chemical and dynamical properties of OCs can be derived from photometric, spectroscopic, and astrometric data of their member stars. Based on the photometric and astrometric data from the Gaia mission, the membership of stars in more than two thousand Galactic clusters has been identified in the literature. The chemical properties (e.g. metallicity) and kinematical properties (e.g. radial velocity), however, are still poorly known for many of these clusters. In synergy with the large spectroscopic survey LAMOST (data release 8) and Gaia (data release 2), we report a new comprehensive catalogue of 386 OCs. This catalogue has homogeneous parameter determinations of radial velocity, metallicity, and dynamical properties, such as orbit, eccentricity, angular momenta, total energy, and 3D Galactic velocity. These parameters enable the first radial velocity determination for 44 clusters, and the first spectroscopic [Fe/H] determination for 137 clusters. The metallicity distributions of the majority of clusters show falling trends in the parameter space of the Galactocentric radius, the total energy, and the Z component of angular momentum, except for two old groups that show flat tails in their own parameter planes. Cluster populations of ages younger and older than 500 Myr distribute diversely on the disc. The latter have a spatial consistency with the Galactic disc flare. The 3D spatial comparison between very young clusters (&lt; 100 Myr) and nearby molecular clouds revealed a wide range of metallicity distribution along the Radcliffe gas cloud wave, indicating a possible inhomogeneous mixing or fast star formation along the wave. This catalogue will serve the community as a useful tool to trace the chemical and dynamical evolution of the MW.

Analysis of the Distance Scales by Cepheids from the Gaia EDR3 Catalogue Data

We study the kinematics of a sample of classical Cepheids younger than 120 Myr. For these stars, the estimates of distances taken from Skowron et al., which are based on the period–luminosity relation, and the line-of-sight velocities and the proper motions from the Gaia catalog are available. There are also distance estimates derived from the trigonometric parallaxes contained in the Gaia ERD3 catalog. A method, which relies on comparison of the first-order derivative of the Galactic rotation angular velocity, showed the need to lengthen the distance scales determined by Skowron et al. by about 10%. This conclusion was confirmed by direct comparison to the distances predicted on using the trigonometric parallaxes. With taking into account this result, we obtained new estimates of the Galactic rotation parameters and the parameters of a spiral density wave.

Evidence for the Late Arrival of Hot Jupiters in Systems with High Host-star Obliquities

It has been shown that hot Jupiters systems with massive, hot stellar primaries exhibit a wide range of stellar obliquities. On the other hand, hot Jupiter systems with low-mass, cool primaries often have stellar obliquities close to zero. Efficient tidal interactions between hot Jupiters and the convective envelopes present in lower-mass main-sequence stars have been a popular explanation for these observations. If this explanation is accurate, then aligned systems should be older than misaligned systems. Likewise, the convective envelope mass of a hot Jupiter’s host star should be an effective predictor of its obliquity. We derive homogeneous stellar parameters—including convective envelope masses—for hot Jupiter host stars with high-quality sky-projected obliquity inferences. Using a thin-disk stellar population’s Galactic velocity dispersion as a relative age proxy, we find that hot Jupiter host stars with larger-than-median obliquities are older than hot Jupiter host stars with smaller-than-median obliquities. The relative age difference between the two populations is larger for hot Jupiter host stars with smaller-than-median fractional convective envelope masses and is significant at the 3.6σ level. We identify stellar mass, not convective envelope mass, as the best predictor of stellar obliquity in hot Jupiter systems. The best explanation for these observations is that many hot Jupiters in misaligned systems arrived in the close proximity of their host stars long after their parent protoplanetary disks dissipated. The dependence of observed age offset on convective envelope mass suggests that tidal realignment contributes to the population of aligned hot Jupiters orbiting stars with convective envelopes.

Interacting planetary nebulae III: verification and galactic population based on the measurements of Gaia EDR3

The phenomenon of interaction between planetary nebulae (PNe) and the interstellar medium (ISM) is one of the significant issues in the field of astrophysics. The main objective of this paper is to verify the interaction process for objects that have been known as interacting PNe (IPNe) in the literature. This study is based on parallax and proper motion observations facilitated recently by the early third data release of the Gaia space mission. Based on the proper nebular central star (CS) motion towards the region of interaction between the PN and ISM, we were able to verify the interaction process for a group of 68 PNe and disprove the interaction process for a group of 33 PNe. The members of both groups were confirmed as genuine PN-ISM interacting objects in the literature. The members belonging to the 33 PNe group are false PN-ISM interacting objects that mimic the structure of IPNe. Moreover, we calculated the physical and kinematic properties of the verified group and analyzed their galactic population classification using reliable and precise measurements of the proper motion and parallax of the CS. We find that 41% and 41% of this group are associated with galactic thin and thick disks, respectively, while 18% are members of thin or thick disks. The kinematical results show that the galactic thin-disk members have smaller vertical galactic heights, space velocities, and peculiar velocities than those belonging to the galactic thick disk.

Evaporation of dark matter from celestial bodies

Scatterings of galactic dark matter (DM) particles with the constituents of celestial bodies could result in their accumulation within these objects. Nevertheless, the finite temperature of the medium sets a minimum mass, the evaporation mass, that DM particles must have in order to remain trapped. DM particles below this mass are very likely to scatter to speeds higher than the escape velocity, so they would be kicked out of the capturing object and escape. Here, we compute the DM evaporation mass for all spherical celestial bodies in hydrostatic equilibrium, spanning the mass range [10-10 - 102] M⊙, for constant scattering cross sections and s-wave annihilations. We illustrate the critical importance of the exponential tail of the evaporation rate, which has not always been appreciated in recent literature, and obtain a robust result: for the geometric value of the scattering cross section and for interactions with nucleons, at the local galactic position, the DM evaporation mass for all spherical celestial bodies in hydrostatic equilibrium is approximately given by Ec/Tχ ∼ 30, where Ec is the escape energy of DM particles at the core of the object and Tχ is their temperature. In that case, the minimum value of the DM evaporation mass is obtained for super-Jupiters and brown dwarfs, m evap ≃ 0.7 GeV. For other values of the scattering cross section, the DM evaporation mass only varies by a factor smaller than three within the range 10-41 cm2 ≤ σp ≤ 10-31 cm2, where σp is the spin-independent DM-nucleon scattering cross section. Its dependence on parameters such as the galactic DM density and velocity, or the scattering and annihilation cross sections is only logarithmic, and details on the density and temperature profiles of celestial bodies have also a small impact.

Chemical Properties of the Local Disk and Halo. II. Abundances of 3745 M Dwarfs and Subdwarfs from Improved Model Fitting of Low-resolution Spectra

Abstract We present a model-fit pipeline to determine the stellar parameters of M-type dwarfs, which is an improvement on our previous work described in Hejazi et al. We apply this pipeline to analyze the low-resolution (R ∼ 2000) spectra of 3745 M dwarfs/subdwarfs, collected at the MDM Observatory, Lick Observatory, Kitt Peak National Observatory, and Cerro Tololo Inter-American Observatory. We examine the variation of the inferred parameter values in the H-R diagram constructed from their Gaia Early Data Release 3 (EDR3) parallaxes and optical magnitudes. We also study the distribution of our stars in the abundance diagram of [α/Fe] versus [M/H] and inspect the variation of their metallicity class, effective temperature, and surface gravity, as well as their Galactic velocity components U, V, and W, in this diagram. In addition, the analyses of the stars’ projected motions in the two-dimensional UV, VW, and UW planes, the variation of their chemical parameters in these planes, and their distribution in the abundance−velocity diagrams are important parts of this study. The precision of our model-fit pipeline is confirmed by the clear stratification of effective temperature and chemical parameters in the H-R diagram; the similarity of the stars’ distribution in the [α/Fe] versus [M/H] diagram and in the metallicity−velocity planes to those from other studies; the revealing of substructure in the abundance−velocity diagrams; and chemical homogeneity between the components of a set of binary systems.