Rodrigo Ibata; Khyati Malhan; Wassim Tenachi; Anke Arentsen; M. Bellazzini; Paolo Bianchini; P. Bonifacio; E. Caffau; Foivos I. Diakogiannis; Raphaël Errani; Benoît Famaey; Salvatore Ferrone; Nicolas F. Martin; P. Di Matteo; G. Monari; Florent Renaud; Else Starkenburg; Guillaume F. Thomas; Akshara Viswanathan; Zhen Yuan
The Astrophysical Journal · DOI ↗
Abstract We present an atlas and follow-up spectroscopic observations of 87 thin stream-like structures detected with the STREAMFINDER algorithm in Gaia DR3, of which 28 are new discoveries. Here, we focus on using these streams to refine mass models of the Galaxy. Fits with a double-power-law halo with the outer power-law slope set to − β h = −3 yield an inner power-law slope of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML&quot; overflow="scroll"> <mml:mo>−</mml:mo> <mml:msub> <mml:mi>γ</mml:mi> <mml:mi>h</mml:mi> </mml:msub> <mml:mo>=</mml:mo> <mml:mo>-</mml:mo> <mml:mo stretchy="false">(</mml:mo> <mml:msubsup> <mml:mn>0.97</mml:mn> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.21</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.17</mml:mn> </mml:mrow> </mml:msubsup> <mml:mspace width="0.25em"/> <mml:mo stretchy="false">)</mml:mo> </mml:math> , a scale radius of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML&quot; overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>r</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>0</mml:mn> <mml:mo>,</mml:mo> <mml:mi>h</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>14.7</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1.0</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>4.7</mml:mn> </mml:mrow> </mml:msubsup> <mml:mspace width="0.25em"/> <mml:mi>kpc</mml:mi> </mml:math> , a halo density flattening q m , h = 0.75 ± 0.03, and a local dark matter density of ρ h ,⊙ = 0.0114 ± 0.0007 M ⊙ pc −3 . Freeing β yields <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML&quot; overflow="scroll"> <mml:mi>β</mml:mi> <mml:mo>=</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>2.53</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.16</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.42</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> , but this value is heavily influenced by our chosen virial mass limit. The stellar disks are found to have a combined mass of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML&quot; overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>4.20</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.53</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.44</mml:mn> </mml:mrow> </mml:msubsup> <mml:mo>×</mml:mo> <mml:msup> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> </mml:msup> <mml:mspace width="0.25em"/> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>⊙</mml:mo> </mml:mrow> </mml:msub> </mml:math> , with the thick disk contributing 12.4% ± 0.7% to the local stellar surface density. The scale lengths of the thin and thick disks are <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML&quot; overflow="scroll"> <mml:msubsup> <mml:mn>2.17</mml:mn> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.08</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.18</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML&quot; overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>1.62</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.13</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.72</mml:mn> </mml:mrow> </mml:msubsup> <mml:mspace width="0.25em"/> <mml:mi>kpc</mml:mi> </mml:math> , respectively, while their scale heights are <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML&quot; overflow="scroll"> <mml:msubsup> <mml:mn>0.347</mml:mn> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.010</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.007</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML&quot; overflow="scroll"> <mml:msubsup>
L. Venuti; Ann Marie Cody; G. Beccari; L. M. Rebull; M. J. Irwin; Apoorva Thanvantri; Sowmya Thanvantri; S. H. P. Alencar; Clara O. Leal; Geert Barentsen; J. E. Drew; Steve B. Howell
The Astronomical Journal · DOI ↗
Abstract Pre-main-sequence disk accretion is pivotal for determining the final stellar properties and the early conditions for close-in planets. We aim to establish the impact of internal (stellar mass) and external (radiation field) parameters on the disk evolution in the Lagoon Nebula massive star-forming region. We employ simultaneous u , g , r , i , H α time-series photometry, archival infrared data, and high-precision K2 light curves to derive the stellar, disk, and accretion properties for 1012 Lagoon Nebula members. We estimate that of all young stars in the Lagoon Nebula, 34%–37% have inner disks traceable down to ∼12 μ m, while 38%–41% are actively accreting. We detect disks ∼1.5 times more frequently around G, K, and M stars than around higher-mass stars, which appear to deplete their inner disks on shorter timescales. We find tentative evidence for a faster disk evolution in the central regions of the Lagoon Nebula, where the bulk of the O/B population is located. Conversely, disks appear to last longer at the nebula outskirts, where the measured fraction of disk-bearing stars tends to exceed that of accreting and disk-free stars. The derived mass accretion rates show a nonuniform dependence on stellar mass between ∼0.2 and 5 M ⊙ . In addition, the typical accretion rates appear to differ across the Lagoon Nebula extension, with values twice lower in the core region than at its periphery. Finally, we detect tentative radial density gradients in the surface accretion shocks, leading to lags in the appearance of light curve brightness features as a function of wavelength that can amount to ∼7%–30% of the rotation period.
Dolev Bashi; Vasily Belokurov; S. T. Hodgkin
Monthly Notices of the Royal Astronomical Society · DOI ↗
ABSTRACT The study of binary stars in the Galactic halo provides crucial insights into the dynamical history and formation processes of the Milky Way. In this work, we aim to investigate the binary fraction in a sample of accreted and in situ halo stars, focusing on short-period binaries. Utilizing data from Gaia Data Release 3 (DR3), we analysed the radial velocity uncertainty $\sigma _{\mathrm{RV}}$ distribution of a sample of main-sequence stars. We used a novel Bayesian framework to model the dependence in $\sigma _{\mathrm{RV}}$ of single and binary systems allowing us to estimate binary fractions F in a sample of bright ($G_{\mathrm{RVS}}$ &amp;lt; 12) Gaia sources. We selected the samples of in situ and accreted halo stars based on estimating the 6D phase space information and affiliating the stars to the different samples on an action angle versus energy ($L_{\mathrm{z}}{\!-\!}E$) diagram. Our results indicate a higher, though not significant, binary fraction in accreted stars compared to the in situ halo sample. We further explore binary fractions using cuts in E and $L_z$, and find a higher binary fraction in both high-energy and prograde orbits that might be explained by differences in metallicity. By cross-matching our Gaia sample with APOGEE DR17 catalogue, we confirm the results of previous studies on higher binary fractions in metal-poor stars and find the fractions of accreted and in situ halo stars consistent with this trend. Our finding provides new insights into binary stars’ formation processes and dynamical evolution in the primordial Milky Way Galaxy and its accreted dwarf Galaxies.
Zhen Yuan; Chengdong Li; Nicolas F. Martin; G. Monari; Benoît Famaey; A. Siebert; Rimpei Chiba; Anke Arentsen; Federico Sestito; Guillaume F. Thomas; V. Hill; Rodrigo Ibata; G. Kordopatis; Else Starkenburg; Akshara Viswanathan
Astronomy and Astrophysics · DOI ↗
The most metal-poor stars (e.g., [Fe/H] ≤ –2.5) are the ancient fossils from the early assembly epoch of our Galaxy. They very likely formed before the the thick disk. Recent studies have shown that a non-negligible fraction of them have prograde planar orbits, which means that their origin is a puzzle. It has been suggested that a later-formed rotating bar could have driven these old stars from the inner Galaxy outward and transformed their orbits so that they became more dominated by rotation. However, it is unclear whether this mechanism can explain these stars as observed in the solar neighborhood. We explore whether this scenario is feasible by tracing these stars backward in an axisymmetric Milky Way potential with a bar as perturber. We integrated their orbits backward for 6 Gyr under two bar models: one model with a constant pattern speed, and the other with a decelerating speed. Our experiments show that for the constantly rotating bar model, the stars of interest are little affected by the bar and cannot have been driven from a spheroidal inner Milky Way to their current orbits. In the extreme case of a decelerating bar, some of the very metal-poor stars on planar and prograde orbits can be brought from the inner Milky Way, but ∼90% of them were nevertheless already dominated by rotation ( J ϕ ≥ 1000 km s −1 kpc) 6 Gyr ago. The chance that these stars started with spheroid-like orbits with low rotation ( J ϕ ≲ 600 km s −1 kpc) is very low (&lt; 3%). We therefore conclude that within the solar neighborhood, the bar is unlikely to have shepherded a significant fraction of spheroid stars in the inner Galaxy to produce the overdensity of stars on prograde planar orbits that is observed today.
Hanyuan Zhang; Vasily Belokurov; N. W. Evans; Zhao‐Yu Li; Jason L. Sanders; Anke Arentsen
Monthly Notices of the Royal Astronomical Society · DOI ↗
ABSTRACT We present a novel method to constrain the formation time of the Milky Way disc using the chrono-kinematic signatures of the inner Galaxy. We construct an O-rich Mira variable sample from the Gaia long-period variable catalogue to study the kinematic behaviour of stars with different ages in the inner Galaxy. From the Auriga suite of cosmological zoom-in simulations, we find that the age of the oldest stellar population with imprints of the bar in density and kinematics matches the disc spin-up epoch. This is because stars born before the spin-up show insufficient rotation and are not kinematically cold enough to be efficiently trapped by the bar. We find that the bar kinematic signature disappears for Mira variables with a period shorter than 190 d. Using the period–age relation of Mira variables, we constrain the spin-up epoch of the Milky Way to be younger than $\sim 11{-}12$ Gyr (redshift $\sim 3$). We also discuss and compare our method and result to other evidence of the Milky Way spin-up epoch under the context of a realistic age uncertainty. Age uncertainty leads to an overestimation of the disc formation time when performing backward modelling. Our constrain of the spin-up epoch is independent from previous studies because it relies on the kinematics of the inner Galaxy instead of the solar vicinity.
Federico Sestito; Christian R. Hayes; Kim A. Venn; Jaclyn Jensen; Alan W. McConnachie; John Pazder; Fletcher Waller; Anke Arentsen; P. Jablonka; Nicolas F. Martin; Tadafumi Matsuno; Julio F. Navarro; Else Starkenburg; Sara Vitali; John Bassett; Trystyn A. M. Berg; Rubén Díaz; Michael L. Edgar; V. Firpo; Manuel Gómez-Jiménez; V. M. Kalari; Sam Lambert; Jon Lawrence; Gordon L. Robertson; Roque Ruiz-Carmona; R. Salinas; Kim M. Sebo; Sudharshan Venkatesan
Monthly Notices of the Royal Astronomical Society · DOI ↗
ABSTRACT This study focuses on Pristine$\_180956.78$−294759.8 (hereafter P180956, [Fe/H] = −1.95 ± 0.02), a star selected from the Pristine Inner Galaxy Survey (PIGS), and followed-up with the recently commissioned Gemini High-resolution Optical SpecTrograph (GHOST) at the Gemini South telescope. The GHOST spectrograph’s high efficiency in the blue spectral region (3700−4800 Å) enables the detection of elemental tracers of early supernovae (e.g. Al, Mn, Sr, and Eu). The star exhibits chemical signatures resembling those found in ultrafaint dwarf (UFD) systems, characterized by very low abundances of neutron-capture elements (Sr, Ba, and Eu), which are uncommon among stars in the Milky Way halo. Our analysis suggests that P180956 bears the chemical imprints of a small number (2 or 4) of low-mass hypernovae ($\sim 10{-}15{\rm \, M_\odot }$), which are needed to mostly reproduce the abundance pattern of the light-elements (e.g. [Si, Ti/Mg, Ca] ∼0.6), and one fast-rotating intermediate-mass supernova ($\sim 300{\rm \, km \ s^{-1}}$, $\sim 80{-}120{\rm \, M_\odot }$), which is the main channel contributing to the high [Sr/Ba] (∼+1.2). The small pericentric ($\sim 0.7{\rm \, kpc}$) and apocentric ($\sim 13{\rm \, kpc}$) distances and its orbit confined to the plane ($\lesssim 2{\rm \, kpc}$) indicate that this star was likely accreted during the early Galactic assembly phase. Its chemo-dynamical properties suggest that P180956 formed in a system similar to a UFD galaxy accreted either alone, as one of the low-mass building blocks of the proto-Galaxy, or as a satellite of Gaia–Sausage–Enceladus. The combination of Gemini’s large aperture with GHOST’s high efficiency and broad spectral coverage makes this new spectrograph one of the leading instruments for near-field cosmology investigations.
Michalina Maksymowicz-Maciata; Chiara Spiniello; Ignacio Martín-Navarro; Anna Ferré-Mateu; Davide Bevacqua; Michele Cappellari; G. D’Ago; C. Tortora; M. Arnaboldi; Johanna Hartke; N. R. Napolitano; P. Saracco; Diana Scognamiglio
Monthly Notices of the Royal Astronomical Society · DOI ↗
ABSTRACT The INSPIRE project has built the largest sample of ultra-compact massive galaxies (UCMGs) at 0.1 &amp;lt; z &amp;lt; 0.4 and obtained their star formation histories (SFHs). Due to their preserved very old stellar populations, relics are the perfect systems to constrain the earliest epochs of mass assembly in the Universe and the formation of massive early-type galaxies. The goal of this work is to investigate whether a correlation exists between the degree of relicness (DoR), quantifying the fraction of stellar mass formed at z &amp;gt; 2, and the other stellar population parameters. We use the Full-Index-Fitting method to fit the INSPIRE spectra to single stellar population (SSP) models. This allows us to measure, for the first time, the slope of the IMF, as well as stellar metallicity [M/H], [Mg/Fe], [Ti/Fe], and [Na/Fe] ratios, and study correlations between them and the DoR. Similarly to normal-sized galaxies, UCMGs with larger stellar masses have overall higher metallicities. We found a correlation between the IMF slope and the DoR, that, however, breaks down for systems with a more extended SFH. An even stronger dependency is found between the IMF and the fraction of mass formed at high-z. At equal velocity dispersion and metallicity, galaxies with a higher DoR have a larger dwarf-to-giant ratio, i.e. a bottom heavy IMF, than that of low-DoR counterparts. This might indicate that the cosmic epoch and therefore different formation scenarios influence the fragmentation of the star formation cloud and hence might be the explanation for IMF variations detected in massive ETGs.
M. Bellazzini; D. Massari; E. Ceccarelli; A. Mucciarelli; A. Bragaglia; M. Riello; F. De Angeli; P. Montegriffo
Astronomy and Astrophysics · DOI ↗
We used photometric metallicity estimates for about 700 000 stars in the surroundings of the Sun, with very accurate distances and 3D motions measures from Gaia DR3, to explore the properties of the metal-poor (−2.0 &lt; [Fe/H] ≤ −1.5; MP) and very metal-poor ([Fe/H] ≤ −2.0; VMP) stars with disc kinematics in the sample. We confirm the presence of a significant fraction of MP and VMP stars with disc-like orbits and that prograde orbits are prevalent among them, with a prograde-to-retrograde ratio of P / R ∼ 3. We highlight a statistically significant difference in the distribution of the Z component of the angular momentum ( L Z ) and orbital eccentricity between prograde and retrograde disc-like MP stars for the first time. The same kind of difference is found in the VMP sub-sample, albeit at a much lower level of statistical significance, likely due to the small sample size. We show that prograde disc-like MP and VMP stars display an additional component of the | L Z | distribution with respect to their retrograde counterpart. This component is at higher | L Z | with respect to the main peak of the distribution, possibly hinting at the presence of a pristine prograde disc in the Milky Way. This hypothesis is supported by the results of the analysis of a large sub-sample dominated by stars born in situ. In this case, the prevalence of prograde stars is also clearly detected at [Fe/H] ≤ −1.5, and their | L Z | distribution is more skewed toward high | L Z | values than their retrograde counterpart. This suggests that the seed of what will eventually evolve into the main disc components of the Milky Way may have already been in place in the earliest phases of the Galaxy assembly.
Hanyuan Zhang; Anke Arentsen; Vasily Belokurov
Monthly Notices of the Royal Astronomical Society · DOI ↗
ABSTRACT The question of whether the Milky Way’s disc extends to low metallicity has been the subject of debate for many years. We aim to address the question by employing a large sample of giant stars with radial velocities and homogeneous metallicities based on the Gaia Data Release 3 BP/RP(XP) spectra. We study the 3D velocity distribution of stars in various metallicity ranges, including the very metal-poor (VMP) regime ($\mathrm{[M/H]} &amp;lt; -2.0$). We find that a clear, stand-alone disc population, i.e. that with a ratio of rotational velocity to velocity dispersion $v/\sigma &amp;gt; 1$, starts to emerge only around $\mathrm{[M/H]} \sim -1.3$, and is not visible for $\mathrm{[M/H]} &amp;lt; -1.6$. Using Gaussian mixture modelling, we show that there are two halo populations in the VMP regime: one stationary and one with a net prograde rotation of $\sim\!\! 80\ \mathrm{km\, s}^{-1}$. In this low-metallicity range, we are able to place constraints on the contribution of a rotation-supported thick disc sub-population to a maximum of $\sim\!\! 3$ per cent in our sample. We compare our results to previous claims of discy VMP stars in both observations and simulations and find that having a prograde halo component could explain most of these.
Brandon Engelbrecht; Mário G. Santos; José Fonseca; Yichao Li; Jingying Wang; Melis O Irfan; Stuart Harper; Keith Grainge; Philip Bull; Isabella P. Carucci; Steven Cunnington; Alkistis Pourtsidou; Marta Spinelli; Laura Wolz
Monthly Notices of the Royal Astronomical Society · DOI ↗
ABSTRACT Radio frequency interference (RFI) is emitted from various sources, terrestrial or orbital, and creates a nuisance for ground-based 21-cm experiments. In particular, single-dish observations will be highly susceptible to RFI due to their wide primary beam and sensitivity. This work aimed to simulate the contamination effects from the Radio Navigational Satellite System (RNSS) within the 1100–1350 (MHz) frequency band. The simulation can be divided into two parts: (i) satellite positioning, emission power, and the beam response on the telescope, and (ii) calibration of the satellite signals to data to improve the original model. We utilize previously observed single-dish L-band data from the Meer-Karoo Array Telescope (MeerKAT), which requires special calibration to account for regions contaminated by satellite-based RFI. We find that we can recreate the satellite contamination with high accuracy around its peak frequencies provided the satellite is not too close to the telescope’s pointing direction. The simulation can predict satellite movements and signals for past and future observations, aiding in RFI avoidance and testing novel cleaning methods. The predicted signal sits below the noise in the target cosmology window in the L band (970–1015 MHz) making it difficult to confirm any out-of-band emission from satellites. However, in our simulations, this contamination still overwhelmed the 21-cm auto-power spectrum. Nevertheless, it is possible to detect the signal in cross-correlations after mild foreground cleaning. Whether such out of band contamination does exist will require further characterization of the satellite signals far away from their peak frequencies.
Laura K. Rogers; Amy Bonsor; Siyi Xu; Andrew M. Buchan; P. Dufour; B. Klein; S. T. Hodgkin; M. Kissler‐Patig; Carl Melis; C. Walton; Alycia J. Weinberger
Monthly Notices of the Royal Astronomical Society · DOI ↗
ABSTRACT This second paper presents an in-depth analysis of the composition of the planetary material that has been accreted on to seven white dwarfs with circumstellar dust and gas emission discs with abundances reported in Rogers et al. The white dwarfs are accreting planetary bodies with a wide range of oxygen, carbon, and sulphur volatile contents, including one white dwarf that shows the most enhanced sulphur abundance seen to date. Three white dwarfs show tentative evidence (2–3$\sigma$) of accreting oxygen-rich material, potentially from water-rich bodies, whilst two others are accreting dry, rocky material. One white dwarf is accreting a mantle-rich fragment of a larger differentiated body, whilst two white dwarfs show an enhancement in their iron abundance and could be accreting core-rich fragments. Whilst most planetary material accreted by white dwarfs display chondritic or bulk Earth-like compositions, these observations demonstrate that core-mantle differentiation, disruptive collisions, and the accretion of core-mantle differentiated material are important. Less than 1 per cent of polluted white dwarfs host both observable circumstellar gas and dust. It is unknown whether these systems are experiencing an early phase in the disruption and accretion of planetary bodies, or alternatively if they are accreting larger planetary bodies. From this work there is no substantial evidence for significant differences in the accreted refractory abundance ratios for those white dwarfs with or without circumstellar gas, but there is tentative evidence for those with circumstellar gas discs to be accreting more water rich material which may suggest that volatiles accrete earlier in a gas-rich phase.
Laura K. Rogers; Christopher J. Manser; Amy Bonsor; Erik Dennihy; S. T. Hodgkin; M. Kissler‐Patig; Samuel Lai; Carl Melis; Siyi Xu; N. P. Gentile Fusillo; Boris Gänsicke; Andrew Swan; Odette Toloza; Dimitri Veras
Monthly Notices of the Royal Astronomical Society Letters · DOI ↗
ABSTRACT There is increasing evidence for the presence and variability of circumstellar dust and gas around white dwarfs that are polluted with exoplanetary material, although the origin of this dust and gas remains debated. This paper presents the first near-simultaneous observations of both circumstellar dust (via broad-band emission) and gas (via emission lines) around a polluted white dwarf. From the optical spectra the gaseous emission lines, notably the calcium infrared triplet and magnesium lines, show significant increases and decreases in their strength over time-scales of weeks, while the oxygen and iron lines remain relatively stable. Near-infrared JHK$_{\rm s}$ photometry reveals dust emission changes of up to 0.2 magnitudes in the K$_{\rm s}$ band over similar time-scales, marking the shortest variability time-scales observed to date. The two epochs with the strongest emission were correlated between the dust (K$_{\rm s}$-band brightening) and gas (strengthened calcium and magnesium lines), showing for the first time that the dust and gas must be produced near-simultaneously with a common origin, likely in collisions.
Daniel Sebastian; A. H. M. J. Triaud; Matteo Brogi; Thomas A Baycroft; Matthew R. Standing; P. F. L. Maxted; David V. Martin; S. Lalitha; M. B. Nielsen
Monthly Notices of the Royal Astronomical Society · DOI ↗
ABSTRACT High-contrast eclipsing binaries with low mass M-dwarf secondaries are precise benchmark stars to build empirical mass–radius relationships for fully convective low-mass ($\rm M_{\star } \lt 0.35\, M_{\odot }$) dwarf stars. The contributed light of the M-dwarf in such binaries is usually much less than one per cent at optical wavelengths. This enables the detection of circumbinary planets from precise radial velocity measurements. High-resolution cross-correlation techniques are typically used to detect exoplanet atmospheres. One key aspect of these techniques is the post-processing, which includes the removal of telluric and spectral lines of the host star. We introduce the application of such techniques to optical high-resolution spectra of the circumbinary planet-host TOI-1338/BEBOP-1, turning it effectively into a double-lined eclipsing binary. By using simulations, we further explore the impact of post-processing techniques for high-contrast systems. We detect the M-dwarf secondary with a significance of 11σ and measure absolute dynamical masses for both components. Compared to previous model-dependent mass measurements, we obtain a four times better precision. We further find that the post-processing results in negligible systematic impact on the radial velocity precision for TOI-1338/BEBOP-1 with more than $96.6\,$ per cent (1σ) of the M-dwarf’s signal being conserved. We show that these methods can be used to robustly measure dynamical masses of high-contrast single-lined binaries providing important benchmark stars for stellar evolution particularly near the bottom of the main sequence. We also demonstrate how to retrieve the phase curve of an exoplanet with high-resolution spectroscopy using our data.
Sarah G. Kane; Vasily Belokurov; Miles Cranmer; Stephanie Monty; Hanyuan Zhang; Anke Arentsen
Monthly Notices of the Royal Astronomical Society · DOI ↗
ABSTRACT Globular clusters (GCs) are sites of extremely efficient star formation, and recent studies suggest they significantly contributed to the early Milky Way’s stellar mass build-up. Although their role has since diminished, GCs’ impact on the Galaxy’s initial evolution can be traced today by identifying their most chemically unique stars – those with anomalous nitrogen and aluminum overabundances and oxygen depletion. While they are a perfect tracer of clusters, be it intact or fully dissolved, these high-[N/O], high-[Al/Fe] GC-origin stars are extremely rare within the current Galaxy. To address the scarcity of these unusual, precious former GC members, we train a neural network (NN) to identify high-[N/O], high-[Al/Fe] stars using low-resolution Gaia Blue Photometer/Red Photometer spectra. Our NN achieves a classification accuracy of approximately $\approx 99~{{\ \rm per\ cent}}$ and a false positive rate of around $\approx 7~{{\ \rm per\ cent}}$, identifying 878 new candidates in the Galactic field. We validate our results with several physically motivated sanity checks, showing, for example, that the incidence of selected stars in Galactic GCs is significantly higher than in the field. Moreover, we find that most of our GC-origin candidates reside in the inner Galaxy, having likely formed in the proto-Milky Way, consistent with previous research. The fraction of GC candidates in the field drops at a metallicity of [Fe/H]$\approx -1$, approximately coinciding with the completion of spin-up, i.e. the formation of the Galactic stellar disc.
Federico Sestito; Anke Arentsen; Sara Vitali; Martin Montelius; Romain Lucchesi; Kim A. Venn; Nicolas F. Martin; Julio F. Navarro; Else Starkenburg
Astronomy and Astrophysics · DOI ↗
We aim to constrain the chemo-dynamical properties of the Sagittarius (Sgr) dwarf galaxy using carbon abundances. At low metal- licities in particular, these properties reveal the early chemical evolution of a system, tracing the contributing supernovae (SNe) and how much of their ejecta eventually made it into the next stellar generation. Our sample from the Pristine Inner Galaxy Survey (PIGS) includes ~350 metal-poor ([Fe/H] &lt; −1.5) stars in the main body of Sgr with good quality spectroscopic observations. Our metal-poor Sgr population has a larger velocity dispersion than metal-rich Sgr from the literature, which could be explained by outside-in star formation, extreme Galactic tidal perturbations, and/or the presence of a metal-rich disc and bar + metal-poor halo. The average carbon abundance [C/Fe] in Sgr is similar to that of other classical dwarf galaxies (DGs) and consistently lower than in the Milky Way by ~0.2–0.3 dex at low metallicities. The interstellar medium in DGs, including Sgr, may have retained yields from more energetic Population III and II supernovae (SNe), thereby reducing the average [C/Fe]. Additionally, SNe Ia producing more Fe than C would start to contribute at lower metallicity in DGs/Sgr than in the Galaxy. The presence of a [C/Fe] gradient for Sgr stars with [Fe/H] ≳ −2.0 (~6.8 × 10 −4 dex arcmin −1 ) suggests that SNe la contributed to the system at those metallicities, especially in its inner regions. There is a low frequency of carbon-enhanced metal-poor (CEMP) stars in our Sgr sample. At higher metallicities and carbon abundances (i.e. mostly CEMPs), this may be due to photometric selection effects, but those are less likely to affect non-CEMP stars. Given the lower average [C/Fe] in DGs, we propose using the same CEMP definition ([C/Fe] &gt; +0.7) as that applied to the Galaxy at large ends up underpredicting the number of CEMP stars in DGs. Burthermore, for Sgr, a cut at [C/Fe] ∽ +0.35 may be more appropriate, which brings the frequency of CEMP stars in agreement with that of the whole Galaxy.
Federico Sestito; Sara Vitali; P. Jofré; Kim A. Venn; David S. Aguado; Claudia Aguilera-Gómez; Anke Arentsen; Danielle de Brito Silva; R. G. Carlberg; Camilla J. L. Eldridge; F. Gran; V. Hill; P. Jablonka; G. Kordopatis; Nicolas F. Martin; Tadafumi Matsuno; Samuel Rusterucci; Else Starkenburg; Akshara Viswanathan
Astronomy and Astrophysics · DOI ↗
The most metal-poor stars provide valuable insights into the early chemical enrichment history of a system, carrying the chemical imprints of the first generations of supernovae. The most metal-poor region of the Sagittarius dwarf galaxy remains inadequately observed and characterised. To date, only ∼4 stars with [Fe/H] &lt; −2.0 have been chemically analysed with high-resolution spectroscopy. In this study, we present the most extensive chemical abundance analysis of 12 low-metallicity stars with metallicities down to [Fe/H] = −3.26 and located in the main body of Sagittarius. These targets, selected from the Pristine Inner Galaxy Survey, were observed using the MIKE high-resolution spectrograph at the Magellan-Clay telescope, which allowed us to measure up to 17 chemical species. The chemical composition of these stars reflects the imprint of a variety of type II supernovae (SNe II). A combination of low- to intermediate-mass high-energy SNe and hypernovae (∼10 − 70 M ⊙ ) is required to account for the abundance patterns of the lighter elements up to the Fe-peak. The trend of the heavy elements suggests the involvement of compact binary merger events and fast-rotating (up to ∼300 km s −1 ) intermediate-mass to massive metal-poor stars (∼25 − 120 M ⊙ ) that are the sources of rapid and slow processes, respectively. Additionally, asymptotic giant branch stars contribute to a wide dispersion of [Ba/Mg] and [Ba/Eu]. The absence of an α −knee in our data indicates that type Ia supernovae did not contribute in the very metal-poor region ([Fe/H] ≤ −2.0). However, they might have started to pollute the interstellar medium at [Fe/H] &gt; −2.0, given the relatively low [Co/Fe] in this metallicity region.
Anke Arentsen; G. Monari; A. B. A. Queiroz; Else Starkenburg; Nicolas F. Martin; C. Chiappini; David S. Aguado; Vasily Belokurov; R. G. Carlberg; Stephanie Monty; GyuChul Myeong; M. Schultheis; Federico Sestito; Kim A. Venn; Sara Vitali; Zhen Yuan; Hanyuan Zhang; Sven Buder; Geraint F. Lewis; William H. Oliver; Zhen Wan; D. B. Zucker
Monthly Notices of the Royal Astronomical Society · DOI ↗
ABSTRACT The oldest stars in the Milky Way (born in the first few billion years) are expected to have a high density in the inner few kpc, spatially overlapping with the Galactic bulge. We use spectroscopic data from the Pristine Inner Galaxy Survey (PIGS) to study the dynamical properties of ancient, metal-poor inner Galaxy stars. We compute distances using starhorse, and orbital properties in a barred Galactic potential. With this paper, we release the spectroscopic AAT/PIGS catalogue (13 235 stars). We find that most PIGS stars have orbits typical for a pressure-supported population. The fraction of stars confined to the inner Galaxy decreases with decreasing metallicity, but many very metal-poor stars (VMP; [Fe/H] &amp;lt;−2.0) stay confined ($\sim 60~{{\ \rm per \, cent}}$ stay within 5 kpc). The azimuthal velocity vϕ also decreases between [Fe/H] = −1.0 and −2.0, but is constant for VMP stars (at ∼+40 km s−1). The carbon-enhanced metal-poor (CEMP) stars in PIGS appear to have similar orbital properties compared to normal VMP stars. Our results suggest a possible transition between two spheroidal components – a more metal-rich, more concentrated, faster rotating component, and a more metal-poor, more extended and slower/non-rotating component. We propose that the former may be connected to pre-disc in-situ stars (or those born in large building blocks), whereas the latter may be dominated by contributions from smaller galaxies. This is an exciting era where large metal-poor samples, such as in this work (as well as upcoming surveys, e.g. 4MOST), shed light on the earliest evolution of our Galaxy.
Nicolas F. Martin; Else Starkenburg; Zhen Yuan; M. Fouesneau; Anke Arentsen; F. De Angeli; F. Gran; Martin Montelius; Samuel Rusterucci; R. Andrae; M. Bellazzini; P. Montegriffo; Anna F. Esselink; Hanyuan Zhang; Kim A. Venn; Akshara Viswanathan; David S. Aguado; G. Battaglia; Manuel Bayer; P. Bonifacio; E. Caffau; Patrick Côté; R. G. Carlberg; S. Fabbro; Emma Fernández-Alvar; J. I. Gónzalez Hernández; Isaure González Rivera de La Vernhe; V. Hill; Rodrigo Ibata; P. Jablonka; G. Kordopatis; C. Lardo; Alan W. McConnachie; Camila Navarrete; Julio F. Navarro; A. Recio–Blanco; Rubén Sánchez-Janssen; Federico Sestito; Guillaume F. Thomas; Sara Vitali; Kristopher Youakim
Astronomy and Astrophysics · DOI ↗
We used the spectro-photometric information of ∼219 million stars from Gaia ’s Data Release 3 (DR3) to calculate synthetic, narrowband, metallicity-sensitive CaHK magnitudes that mimic the observations of the Pristine survey, a survey of photometric metallicities of Milky Way stars that has been mapping more than 6500 deg 2 of the northern sky with the Canada–France–Hawaii Telescope since 2015. These synthetic magnitudes were used for an absolute recalibration of the deeper Pristine photometry and, combined with broadband Gaia information, synthetic and Pristine CaHK magnitudes were used to estimate photometric metallicities over the whole sky. The resulting metallicity catalogue is accurate down to [Fe/H]∼−3.5 and is particularly suited for the exploration of the metalpoor Milky Way ([Fe/H] &lt; −1.0). We make available here the catalogue of synthetic CaHK syn magnitudes for all stars with BP/RP information in Gaia DR3, as well as an associated catalogue of more than ∼30 million photometric metallicities for high signal-to-noise FGK stars. This paper further provides the first public data release of the Pristine catalogue in the form of higher quality recalibrated Pristine CaHK magnitudes and photometric metallicities for all stars in common with the BP/RP spectro-photometric information in Gaia DR3. We demonstrate that, when available, the much deeper Pristine data greatly enhance the quality of the derived metallicities, in particular at the faint end of the catalogue ( G BP ≳ 16). Combined, both photometric metallicity catalogues include more than two million metal-poor star candidates ([Fe/H] phot &lt; −1.0) as well as more than 200 000 and ∼8000 very and extremely metal-poor candidates ([Fe/H] phot &lt; −2.0 and &lt; −3.0, respectively). Finally, we show that these metallicity catalogues can be used efficiently, among other applications, for Galactic archaeology, to hunt for the most metal-poor stars, and to study how the structure of the Milky Way varies with metallicity, from the flat distribution of disk stars to the spheroid-shaped metal-poor halo.
Isaure González Rivera de La Vernhe; V. Hill; G. Kordopatis; F. Gran; Emma Fernández-Alvar; Anke Arentsen; Guillaume F. Thomas; Federico Sestito; Camila Navarrete; Nicolas F. Martin; Else Starkenburg; Akshara Viswanathan; G. Battaglia; Kim A. Venn; Sara Vitali
Astronomy and Astrophysics · DOI ↗
Context. Metal-poor stars hold key information on the early Milky Way. Through the identification and characterisation of substructures, one can understand internal mechanisms (including merger and accretion events), which are indispensable to reconstruct the formation history of the Galaxy. Aims. To allow an investigation of a population of very metal-poor stars ([Fe/H] &lt; –1.7) with disc-like orbits (planar and prograde), high angular momenta ( L z / J tot &gt; 0.5) and rotational velocities ( V ϕ &gt; 180 km.s −1 ) proposed in the literature, we used a sample of ∼3 M giant stars with Gaia DR3 BP/RP information and Pristine-Gaia metallicities down to –4.0 dex that we aimed to decontaminate. To achieve this, we constructed a sample as free as possible from spurious photometric estimates, an issue commonly encountered for high V ϕ metal-poor stars. Methods. We created a statistically robust sample of ∼36 000 Pristine-Gaia very metal-poor ([Fe/H] &lt; –1.7) giant stars, using APOGEE and LAMOST data (adding GALAH and GSP-spec for verification) to estimate and remove contamination. We investigated the spatial and kinematic properties of the decontaminated sample, making use of V ϕ as well as the action space, which are both powerful tools to disentangle stellar populations. Results. The global distribution of very metal-poor stars in our sample shows the typical kinematics, orbital properties, and spatial distributions of a halo; however, as in previous works, we found a pronounced asymmetry in the L z and V ϕ distributions, in favour of prograde stars. We showed that this excess is predominantly due to prograde-planar stars (10% of the very metal-poor population), which can be detected down to [Fe/H] = –2.9 at a 2 σ confidence level. This prograde-planar population contains stars with V ϕ &gt; 180 km.s −1 and Z max &lt; 1.5 kpc. While the overall orbital configurations ( Z max − R max or action space distributions) of our sample match that of a halo, the highly prograde and planar subset (2% of the very metal-poor population) also bears characteristics classically associated with a thick disc: (i) a spatial distribution compatible with a short-scaled thick disc, (ii) a Z max − R max distribution similar to the one expected from the thick disc prediction of the Gaia Universe Model Snapshot, and (iii) a challenge to erase its signature assuming a stationary or prograde halo with V ¯ ϕ ∼30−40 km.s −1 . Altogether, these results seem to rule out that these highly prograde and planar stars are part of a thin disc population and, instead, support a contribution from a metal-weak thick disc. Higher resolution spectra are needed to fully disentangle the origin(s) of the population.
Stephanie Monty; Vasily Belokurov; Jason L. Sanders; Terese T. Hansen; Charli M. Sakari; Madeleine McKenzie; GyuChul Myeong; Elliot Y Davies; Anke Arentsen; D. Massari
Monthly Notices of the Royal Astronomical Society · DOI ↗
ABSTRACT We combine stellar orbits with the abundances of the heavy, r-process element europium and the light, $\alpha$-element, silicon to separate in situ and accreted populations in the Milky Way (MW) across all metallicities. At high orbital energy, the accretion-dominated halo shows elevated values of [Eu/Si], while at lower energies, where many of the stars were born in situ, the levels of [Eu/Si] are lower. These systematically different levels of [Eu/Si] in the MW and the accreted halo imply that the scatter in [Eu/$\alpha$] within a single galaxy is smaller than previously thought. At the lowest metallicities, we find that both accreted and in situ populations trend down in [Eu/Si], consistent with enrichment via neutron star mergers. Through compiling a large data set of abundances for 54 globular clusters (GCs), we show that differences in [Eu/Si] extend to populations of in situ/accreted GCs. We interpret this consistency as evidence that in r-process elements GCs trace the star formation history of their hosts, motivating their use as sub-Gyr timers of galactic evolution. Furthermore, fitting the trends in [Eu/Si] using a simple galactic chemical evolution model, we find that differences in [Eu/Si] between accreted and in situ MW field stars cannot be explained through star formation efficiency alone. Finally, we show that the use of [Eu/Si] as a chemical tag between GCs and their host galaxies extends beyond the Local Group, to the halo of M31 – potentially offering the opportunity to do Galactic Archaeology in an external galaxy.