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 ($G_{\mathrm{RVS}}$ < 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.
Dolev Bashi; Vasily A Belokurov; S. T. Hodgkin
arXiv (Cornell University) · DOI
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. Utilising data from Gaia DR3, we analysed the radial velocity (RV) uncertainty $σ_{\mathrm{RV}}$ distribution of a sample of main-sequence stars. We used a novel Bayesian framework to model the dependence in $σ_{\mathrm{RV}}$ of single and binary systems allowing us to estimate binary fractions $F$ in a sample of bright ($G_{\mathrm{RVS}}$ < 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 vs 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.
Oliver Müller; Francine R. Marleau; Nick Heesters; Pierre–Alain Duc; Marcel S. Pawlowski; Mélina Poulain; Rebecca A. Habas; Elisabeth Sola; M Urbano; Rory Smith; Patrick R. Durrell; Éric Emsellem; Rubén Sánchez-Janssen; Sungsoon Lim; Sanjaya Paudel
Astronomy and Astrophysics · DOI
A recent study of the distribution of dwarf galaxies in the MATLAS sample in galaxy groups revealed an excess of flattened satellite structures, reminiscent of the co-rotating planes of dwarf galaxies discovered in the local Universe. If confirmed, this lends credence to the plane-of-satellite problem and further challenges the standard model of hierarchical structure formation. However, with only photometric data and no confirmation of the satellite membership, the study could not address the plane-of-satellite problem in full detail. Here we present spectroscopic follow-up observations of one of the most promising planes-of-satellite candidates in the MATLAS survey, the satellite system of NGC 474. Employing MUSE at the VLT and full spectrum fitting, we studied 13 dwarf galaxy candidates and confirmed nine to be members of the field around NGC 474. Measuring the stellar populations of all observed galaxies, we find that the MATLAS dwarfs have lower metallicities than the Local Group dwarfs at a given luminosity. Two dwarf galaxies may form a pair of satellites based on their close projection and common velocity. Within the virial radius, we do not find a significant plane-of-satellites, however, there is a sub-population of six dwarf galaxies which seem to be anti-correlated in phase-space. Due to the low number of dwarf galaxies, this signal may arise by chance. With over 2000 dwarf galaxy candidates found in the MATLAS survey, this remains an intriguing data set to study the plane-of-satellites problem in a statistical fashion once more follow-up observations have been conducted.
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; P. Saracco; Diana Scognamiglio
arXiv (Cornell University) · DOI
The INSPIRE project has built the largest sample of ultra-compact massive galaxies (UCMGs) at 0.12, 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 low-mass end 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 low-mass end of 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 dwarf-richer IMF than that of low-DoR counterparts. This might indicate that the cosmic epoch and formation mechanisms influence the fragmentation of the star formation cloud and hence might be the explanation for IMF variations detected in massive ETGs.
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
arXiv (Cornell University) · DOI
Radio Frequency Interference (RFI) is emitted from various sources, terrestrial or orbital, and create a nuisance for ground-based 21cm experiments. In particular, single-dish 21cm intensity mapping experiments will be highly susceptible to contamination from these sources due to its wide primary beam and sensitivity. This work aims to simulate the contamination effects emitted from orbital sources in the Radio Navigational Satellite System within the 1100-1350 MHz frequency. This simulation can be split into two parts: (I) satellite positioning, emission power, and beam response on the telescope and (II) fitting of the satellite signal to data in order to improve the original model. We use previously observed single dish MeerKAT L-band data which needs to be specially calibrated to include data contaminated by satellite-based RFI. We find that due to non-linearity effects, it becomes non-trivial to fit the satellite power. However, when masking regions where this non-linearity is problematic, we can recreate the satellite contamination with high accuracy around its peak frequencies. The simulation can predict satellite movements and signal for past and future observations, which can help in RFI avoidance and testing novel cleaning methods. The predicted signal from simulations sits below the noise in the target cosmology window for the L-band (970 - 1015 MHz) making it difficult to confirm any out-of-band emission from satellites. However, a power spectrum analysis shows that such signal can still contaminate the 21cm power spectrum at these frequencies. In our simulations, this contamination overwhelms the auto-power spectrum but still allows for a clean detection of the signal in cross-correlations with mild foreground cleaning. Whether such contamination does exist one will require further characterization of the satellite signals far away from their peak frequencies.
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; Amy Bonsor; Siyi Xu; Alastair Mitchell Buchan; P. Dufour; B. L. Klein; S. T. Hodgkin; Markus Kissler Patig; Carl Melis; Walton, C.; Alycia J. Weinberger
arXiv (Cornell University) · DOI
This second paper presents an in-depth analysis of the composition of the planetary material that has been accreted onto seven white dwarfs with circumstellar dust and gas emission discs with abundances reported in Paper I. The white dwarfs are accreting planetary bodies with a wide range of oxygen, carbon, and sulfur volatile contents, including one white dwarf that shows the most enhanced sulfur abundance seen to date. Three white dwarfs show tentative evidence (2-3$σ$) 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 one percent 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.
Laura K. Rogers; Christopher J. Manser; Amy Bonsor; Erik Dennihy; S. T. Hodgkin; Markus Kissler Patig; Samuel Lai; Carl Melis; Siyi Xu; N. P. Gentile Fusillo; Boris T. Gänsicke; Andrew R. H. Swan; Odette Toloza; Dimitri Veras
arXiv (Cornell University) · DOI
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 broadband 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 timescales of weeks, while the oxygen and iron lines remain relatively stable. Near-infrared JHKs photometry reveals dust emission changes of up to 0.2 magnitudes in the Ks band over similar timescales, marking the shortest variability timescales observed to date. The two epochs with the strongest emission were correlated between the dust (Ks 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; Amaury H. M. J. Triaud; Matteo Brogi; Thomas A Baycroft; Matthew R. Standing; Pierre F L Maxted; David V. Martin; S. Lalitha; Martin Bo Nielsen
arXiv (Cornell University) · DOI
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 ($\rm M_{*} < 0.35\,M_{\rm sun}$) 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 11-$σ$ 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 (1-$σ$) 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.
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 &lt; [Fe/H] &lt; −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 &gt; 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 &gt; 0.95, and close to the Galactic plane, | Z max |&lt; 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] &lt; −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 &lt; [Fe/H] &lt; −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.