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 < [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 ($\mathrm{[M/H]} < -2.0$). We find that a clear, stand-alone disc population, i.e. that with a ratio of rotational velocity to velocity dispersion $v/\sigma > 1$, starts to emerge only around $\mathrm{[M/H]} \sim -1.3$, and is not visible for $\mathrm{[M/H]} < -1.6$. 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.
Emma Fernández-Alvar; G. Kordopatis; V. Hill; G. Battaglia; Carme Gallart; Isaure González Rivera de La Vernhe; Guillaume F. Thomas; Federico Sestito; Anke Arentsen; Nicolas F. Martin; Akshara Viswanathan; Else Starkenburg
Astronomy and Astrophysics · DOI ↗
Context. The emergence of the disc in our Galaxy and the relation between thick and thin disc formation and evolution is still a matter of debate. The chemo-dynamical characterization of disc stars is key to resolving this question, particularly at parameter regimes, where both disc components overlap, such as the region around [Fe/H] ∼ −0.7 corresponding to the thin disc’s metal-poor end. Aims. In this paper, we re-assess the recent detection of a metal-poor extension of stars moving with thin-disc-like rotational velocities between −2 < [Fe/H] < −0.7, carried out on the basis of metallicity estimates obtained from photometric data and their rotational velocity distributions. Methods. We explored the chemo-dynamical properties of metal-poor stars from the recent Gaia third data release (DR3), which includes the first catalog of metallicity estimates from the Radial Velocity Spectrometer (RVS) experiment. We complemented them with the two largest high-resolution ( λ / dλ > 20 000) spectroscopic surveys available: the GALAH DR3 and the APOGEE DR17. Results. We confirm that there are high-angular-momentum stars moving in thin-disc-like orbits, that is, with a high angular momentum of L z / J tot > 0.95, and close to the Galactic plane, | Z max |< 750 pc, reaching metallicity values down to [Fe/H] ∼ −1.5. We also find tentative evidence for stars moving on such orbits at lower metallicities, down to [Fe/H] ∼ −2.5, albeit in smaller numbers. Based on their chemical trends, thin-disc-like stars with [Fe/H] < −1 would have formed in a medium that is less chemically evolved than the bulk of the thick disc. Stars with chemical abundances typical of the thin disc appear at metallicities between −1 < [Fe/H] < −0.7.
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] < −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] > +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] < −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] > −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] <−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] < −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 < −1.0) as well as more than 200 000 and ∼8000 very and extremely metal-poor candidates ([Fe/H] phot < −2.0 and < −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] < –1.7) with disc-like orbits (planar and prograde), high angular momenta ( L z / J tot > 0.5) and rotational velocities ( V ϕ > 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] < –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 > 180 km.s −1 and Z max < 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.
Sakurako Okamoto; A. M. N. Ferguson; N. Arimoto; Itsuki Ogami; Rokas Žemaitis; Masashi Chiba; M. J. Irwin; In Sung Jang; Jin Koda; Yutaka Komiyama; Myung Gyoon Lee; Jeong Hwan Lee; R. Michael Rich; Masayuki Tanaka; Mikito Tanaka
The Astrophysical Journal Letters · DOI ↗
Abstract We present the discovery of NGC253-SNFC-dw1, a new satellite galaxy in the remote stellar halo of the Sculptor Group spiral, NGC 253. The system was revealed using deep, resolved star photometry obtained as part of the Subaru Near-Field Cosmology Survey that uses the Hyper Suprime-Cam on the Subaru Telescope. Although rather luminous ( M V = −11.7 ± 0.2) and massive ( M * ∼ 1.25 × 10 7 M ⊙ ), the system is one of the most diffuse satellites yet known, with a half-light radius of R h = 3.37 ± 0.36 kpc and an average surface brightness of ∼30.1 mag arcmin −2 within the R h . The color–magnitude diagram shows a dominant, old (∼10 Gyr), and metal-poor ([M/H] = −1.5 ± 0.1 dex) stellar population, as well as several candidate thermally pulsing asymptotic giant branch stars. The distribution of red giant branch stars is asymmetrical and displays two elongated tidal extensions pointing toward NGC 253, suggestive of a highly disrupted system being observed at apocenter. NGC253-SNFC-dw1 has a size comparable to that of the puzzling Local Group dwarfs Andromeda XIX and Antlia 2 but is 2 magnitudes brighter. While unambiguous evidence of tidal disruption in these systems has not yet been demonstrated, the morphology of NGC253-SNFC-dw1 clearly shows that this is a natural path to produce such diffuse and extended galaxies. The surprising discovery of this system in a previously well-searched region of the sky emphasizes the importance of surface-brightness limiting depth in satellite searches.
D. L. Harrison; F. van Leeuwen; P. Osborne; P. W. Burgess; F. De Angeli; D. W. Evans
Astronomy and Astrophysics · DOI ↗
Aims. Our goal is to describe two potential options for the Source Environment Analysis pipeline (SEAPipe) for the Gaia mission. This pipeline will enable the discovery of sources that are new to Gaia , in the sense that they were not found by the on-board detection algorithm. These additional sources (secondaries) are discoverable in the vicinity of those Gaia sources (primaries) that were found by the on-board detection. Methods. The main algorithmic steps required are described: the two dimensional image reconstruction of one dimensional transit data; the analysis of these images to find the additional sources present, and the determination of the mean positions; proper motions, parallaxes, and brightness of these sources. Additionally, the Monte Carlo simulations used to characterise the performance of the pipelines are described. Results. The performance of the two options for SEAPipe, the vanilla and image-subtraction versions, are compared. Their selection functions were computed in terms of the magnitude of the secondary sources and their angular separations from their corresponding primary source. The completeness and purity of the resultant catalogue of secondary sources as found by each of the pipelines, given the expected magnitude distribution of the primary sources and the magnitude and angular separation distributions of the secondary sources, is also presented. The image-subtraction pipeline is shown to outperform the vanilla pipeline.
Emily Pass; Jennifer G. Winters; David Charbonneau; Jonathan Irwin; Amber A. Medina
The Astronomical Journal · DOI ↗
Abstract We present results from the volume-complete spectroscopic survey of 0.1–0.3 M ⊙ M dwarfs within 15 pc. This work discusses the active sample without close binary companions, providing a comprehensive picture of these 123 stars with H α emission stronger than −1 Å. Our analysis includes rotation periods (including 31 new measurements), H α equivalent widths, rotational broadening, inclinations, and radial velocities, determined using high-resolution, multiepoch spectroscopic data from the TRES and CHIRON spectrographs supplemented by photometry from TESS and MEarth. Using this volume-complete sample, we establish that the majority of active, low-mass M dwarfs are very rapid rotators: specifically, 74% ± 4% have rotation periods shorter than 2 days, while 19% ± 4% have intermediate rotation periods of 2–20 days, and the remaining 8% ± 3% have periods longer than 20 days. Among the latter group, we identify a population of stars with very high H α emission, which we suggest is indicative of dramatic spindown as these stars transition from the rapidly rotating mode to the slowly rotating one. We are unable to determine rotation periods for six stars and suggest that some of the stars without measured rotation periods may be viewed pole-on, as such stars are absent from the distribution of inclinations we measure; this lack notwithstanding, we recover the expected isotropic distribution of spin axes. Our spectroscopic and photometric data sets also allow us to investigate activity-induced radial-velocity variability, which we show can be estimated as the product of rotational broadening and the photometric amplitude of spot modulation.
Fernando Tinaut-Ruano; Eri Tatsumi; P. Tanga; J. de León; Marco Delbò; F. De Angeli; David Morate; J. Licandro; L. Galluccio
Astronomy and Astrophysics · DOI ↗
Context. Observational and instrumental difficulties observing small bodies below 0.5 μm make this wavelength range poorly studied compared with the visible and near-infrared. Furthermore, the suitability of many commonly used solar analogues, essential in the computation of asteroid reflectances, is usually assessed only in visible wavelengths, while some of these objects show spectra that are quite different from the spectrum of the Sun at wavelengths below 0.55 μm. Stars HD 28099 (Hyades 64) and HD 186427 (16 Cyg B) are two well-studied solar analogues that instead present spectra that are also very similar to the spectrum of the Sun in the wavelength region between 0.36 and 0.55 μm. Aims. We aim to assess the suitability in the near-ultraviolet (NUV) region of the solar analogues selected by the team responsible for the asteroid reflectance included in Gaia Data Release 3 (DR3) and to suggest a correction (in the form of multiplicative factors) to be applied to the Gaia DR3 asteroid reflectance spectra to account for the differences with respect to the solar analogue Hyades 64. Methods. To compute the multiplicative factors, we calculated the ratio between the solar analogues used by Gaia DR3 and Hyades 64, and then we averaged and binned this ratio in the same way as the asteroid spectra in Gaia DR3. We also compared both the original and corrected Gaia asteroid spectra with observational data from the Eight Color Asteroid Survey (ECAS), one UV spectrum obtained with the Hubble Space Telescope (HST) and a set of blue-visible spectra obtained with the 3.6 m Telescopio Nazionale Galileo (TNG). By means of this comparison, we quantified the goodness of the obtained correction. Results. We find that the solar analogues selected for Gaia DR3 to compute the reflectance spectra of the asteroids of this data release have a systematically redder spectral slope at wavelengths shorter than 0.55 μm than Hyades 64. We find that no correction is needed in the red photometer (RP, between 0.7 and 1 μm), but a correction should be applied at wavelengths below 0.55 μm, that is in the blue photometer (BP). After applying the correction, we find a better agreement between Gaia DR3 spectra, ECAS, HST, and our set of ground-based observations with the TNG. Conclusions. Correcting the near-UV part of the asteroid reflectance spectra is very important for proper comparisons with laboratory spectra (minerals, meteorite samples, etc.) or to analyse quantitatively the UV absorption (which is particularly important to study hydration in primitive asteroids). The spectral behaviour at wavelengths below 0.5 μm of the selected solar analogues should be fully studied and taken into account for Gaia DR4.
José María Arroyo-Polonio; G. Battaglia; Guillaume F. Thomas; M. J. Irwin; Alan W. McConnachie; Eline Tolstoy
Astronomy and Astrophysics · DOI ↗
Aims. We aim to compute the binary fraction of “classical” dwarf spheroidal galaxies (dSphs) that are satellites of the Milky Way (MW). This value can offer insights into the binary fraction in environments that are less dense and more metal-poor than our own galaxy. Additionally, knowledge of the binary fraction in dwarf galaxies is important with respect to avoiding overestimations of their dark matter content, inferred from stellar kinematics. Methods. We refined an existing method from the literature, placing an emphasis on providing robust uncertainties on the value of the binary fraction. We applied this modified method to a VLT/FLAMES dataset for Sculptor, specifically acquired for the purpose of velocity monitoring of individual stars, as well as to literature datasets for other six MW “classical” dSphs. In all cases, the targeted stars were mainly red giant branch stars, with expected masses of around 0.8 M ⊙ . The VLT/FLAMES dataset offers the most precise binary fractions compared to literature datasets, due to its time baseline of 12 yr, along with at least nine repeated observations for each star. Results. We found that the binary fraction of Sculptor is 0.55 −0.19 +0.17 . We find that it is important to take into account the Roche lobe overflow for constraining the period distribution of binary stars. In contrast to what has recently been proposed in the literature, our analysis indicates that there is no evidence to support varying the properties of the binary stellar population or their deviations from those established for the solar neighborhood, based on the sample of MW dSphs analyzed here.
Hiroshige Sano; Tristan Whitmarsh; Linda Skingle; Taketoshi Shimakura; Noriaki Yamamoto; Juliet Compston; Hideaki E. Takahashi; Kenneth Poole
Journal of Bone and Mineral Research · DOI ↗
Romosozumab treatment reduces the rate of hip fractures and increases hip bone density, increasing bone formation by inhibiting sclerostin protein. We studied the normal pattern of bone formation and osteocyte expression in the human proximal femur because it is relevant to both antisclerostin treatment effects and fracture. Having visualized and quantified buds of new bone formation in trabeculae, we hypothesized that they would coincide with areas of (a) higher mechanical stress and (b) low sclerostin expression by osteocytes. In patients with hip fracture, we visualized each bud of active modeling-based formation (forming minimodeling structure [FMiS]) in trabecular cores taken from different parts of the femoral head. Trabecular bone structure was also measured with high-resolution imaging. More buds of new bone formation (by volume) were present in the higher stress superomedial zone (FMiS density, N.FMiS/T.Ar) than lower stress superolateral (p < 0.05), and inferomedial (p < 0.001) regions. There were fewer sclerostin expressing osteocytes close to or within FMiS. FMiS density correlated with greater amount, thickness, number, and connectivity of trabeculae (bone volume BV/TV, r = 0.65, p < 0.0001; bone surface BS/TV, r = 0.47, p < 0.01; trabecular thickness Tb.Th, r = 0.55, p < 0.001; trabecular number Tb.N, r = 0.47, p < 0.01; and connectivity density Conn.D, r = 0.40, p < 0.05) and lower trabecular separation (Tb.Sp, r = -0.56, p < 0.001). These results demonstrate modeling-based bone formation in femoral trabeculae from patients with hip fracture as a potential therapeutic target to enhance bone structure. © 2023 American Society for Bone and Mineral Research (ASBMR).