Johanna Coronado | Pontificia Universidad Catolica de Chile (original) (raw)
Papers by Johanna Coronado
VizieR Online Data Catalog, 2019
The Astrophysical Journal, 2020
We present 15, 000 metal-rich ([Fe/H] > −0.2 dex) A and F stars whose surface abundances deviate ... more We present 15, 000 metal-rich ([Fe/H] > −0.2 dex) A and F stars whose surface abundances deviate strongly from Solar abundance ratios and cannot plausibly reflect their birth material composition. These stars are identified by their high [Ba/Fe] abundance ratios ([Ba/Fe] > 1.0 dex) in the LAMOST DR5 spectra analyzed by Xiang et al. (2019). They are almost exclusively main sequence and subgiant stars with T eff 6300 K. Their distribution in the Kiel diagram (T eff-log g) traces a sharp border at low temperatures along a roughly fixed-mass trajectory (around 1.4 M) that corresponds to an upper limit in convective envelope mass fraction of around 10 −4. Most of these stars exhibit distinctly enhanced abundances of iron-peak elements (Cr, Mn, Fe, Ni) but depleted abundances of Mg and Ca. Rotational velocity measurements from GALAH DR2 show that the majority of these stars rotate slower than typical stars in an equivalent temperature range. These characteristics suggest that they are related to the so-called Am/Fm stars. Their abundance patterns are qualitatively consistent with the predictions of stellar evolution models that incorporate radiative acceleration, suggesting they are a consequence of stellar internal evolution particularly involving the competition between gravitational settling and radiative acceleration. These peculiar stars constitute 40% of the whole population of stars with mass above 1.5 M , affirming that "peculiar" photospheric abundances due to stellar evolution effects are a ubiquitous phenomenon for these intermediate-mass stars. This large sample of Ba-enhanced chemically peculiar A/F stars with individual element abundances provides the statistics to test more stringently the mechanisms that alter the surface abundances in stars with radiative envelopes.
Monthly Notices of the Royal Astronomical Society, 2018
Samples of reliably identified halo wide binaries are scarce. If reasonably free from selection e... more Samples of reliably identified halo wide binaries are scarce. If reasonably free from selection effects and with a small degree of contamination by chance alignments, these wide binaries become a powerful dynamical tool, having provided one of the very few experiments capable of constraining the nature of dark matter in the Milky Way halo. Currently, however, the best available sample of halo wide binaries is confined to the solar neighbourhood, and is plagued by small number statistics at the widest separations. We present the results of a programme aimed to probe the wide binary population of the Galactic halo at significantly larger distances, and which informs future searches that could improve the statistics by orders of magnitude. Halo stars were taken from the Sloan Digital Sky Survey after analysing the Galactic orbits of stars in the reduced proper motion diagram. We then select candidate binaries by searching for pairs with small differences in proper motion and small projected separation on the sky. Using medium-resolution spectroscopy, a subsample of candidates is validated via radial velocities, finding that about 68 per cent of candidate pairs up to 20 arcsec separation can be considered genuine halo wide binaries, to the limits of the available data. Precise parallaxes from Gaia confirm that most of our selected pairs have their components at the same distances, independently confirming the robustness of our selection method. These results should prove valuable to guide the optimal assembly of larger catalogues of halo wide binaries from upcoming large databases, e.g. Gaia and LSST.
Monthly Notices of the Royal Astronomical Society, 2018
Spectrophotometric distances to stars observed by large spectroscopic surveys offer a crucial com... more Spectrophotometric distances to stars observed by large spectroscopic surveys offer a crucial complement to parallax distances that remain very important also after the future Gaia data releases. Here, we present a probabilistic approach to modelling spectroscopic information for a subset of 4000 main sequence stars with good parallaxes (σ / < 0.1) from the LAMOST × TGAS × 2MASS cross-match, yielding a precise spectroscopic distance estimator with uncertainties of ∼6 per cent for single stars. Unlike previous approaches to this problem, we explicitly account for the individual parallax uncertainties in the model building and fully incorporate the fraction of near-equal binaries of main sequence stars, which would lead to biased distance estimates if neglected. Using this model, we estimate the distance for all (150 000) main sequence stars from LAMOST Data Release 5, without parallax information. As an application, we compute their orbital actions, where our more precise distances result in 5 times smaller action uncertainties. This illustrates how future studies of the Milky Way's orbital structure can benefit from using our model. For the fainter and more distant stars of most current spectroscopic surveys, an approach such as the one presented in this work will deliver better distances than Gaia Data Release 2.
Monthly Notices of the Royal Astronomical Society, 2019
The Astrophysical Journal, 2019
We present results from an observing campaign to identify low-metallicity stars in the Best & Bri... more We present results from an observing campaign to identify low-metallicity stars in the Best & Brightest Survey. From medium-resolution (R∼1200-2000) spectroscopy of 857 candidates, we estimate the stellar atmospheric parameters (T eff , g log , and Fe H [ ]), as well as carbon and α-element abundances. We find that 69% of the observed stars have Fe H [ ]−1.0, 39% have Fe H [ ]−2.0, and 2% have Fe H [ ]−3.0. There are also 133 carbon-enhanced metal-poor (CEMP) stars in this sample, with 97 CEMP GroupI and 36 CEMP GroupII stars identified in the A(C) versus [Fe/H] diagram. A subset of the confirmed low-metallicity stars were followed-up with high-resolution spectroscopy, as part of the R-process Alliance, with the goal of identifying new highly and moderately r-process-enhanced stars. Comparison between the stellar atmospheric parameters estimated in this work and from high-resolution spectroscopy exhibit good agreement, confirming our expectation that medium-resolution observing campaigns are an effective way of selecting interesting stars for further, more targeted, efforts.
Monthly Notices of the Royal Astronomical Society, 2019
We compare the distribution in position and velocity of nearby stars from the Gaia DR2 radial vel... more We compare the distribution in position and velocity of nearby stars from the Gaia DR2 radial velocity sample with predictions of current theories for spirals in disc galaxies. Although the rich substructure in velocity space contains the same information, we find it more revealing to reproject the data into action-angle variables, and we describe why resonant scattering would be more readily identifiable in these variables. We compute the predicted changes to the phase-space density, in multiple different projections, that would be caused by a simplified isolated spiral pattern, finding widely differing predictions from each theory. We conclude that the phase-space structure present in the Gaia data shares many of the qualitative features expected in the transient spiral mode model. We argue that the popular picture of apparently swing-amplified spirals results from the superposition of a few underlying spiral modes.
The Astronomical Journal, 2018
We present results from a medium-resolution (R∼2000) spectroscopic follow-up campaign of 1694 b... more We present results from a medium-resolution (R∼2000) spectroscopic follow-up campaign of 1694 bright (V<13.5), very metal-poor star candidates from the RAdial Velocity Experiment (RAVE). Initial selection of the low-metallicity targets was based on the stellar parameters published in RAVE Data Releases 4 and 5. Follow up was accomplished with the Gemini-N and Gemini-S, the ESO/NTT, the KPNO/Mayall, and the SOAR telescopes. The wavelength coverage for most of the observed spectra allows for the determination of carbon and α-element abundances, which are crucial for considering the nature and frequency of the carbon-enhanced metalpoor (CEMP) stars in this sample. We find that 88% of the observed stars have Fe H [ ]−1.0, 61% have Fe H [ ]−2.0, and 3% have Fe H [ ]−3.0 (with four stars at Fe H [ ]−3.5). There are 306 CEMP star candidates in this sample, and we identify 169 CEMP GroupI, 131 CEMP GroupII, and 6 CEMP GroupIII stars from the A(C) versus [Fe/H] diagram. Inspection of the C a [ ] abundance ratios reveals that five of the CEMP GroupII stars can be classified as "mono-enriched second-generation" stars. Gaia DR1 matches were found for 734 stars, and we show that transverse velocities can be used as a confirmatory selection criteria for low-metallicity candidates. Selected stars from our validated list are being followed-up with high-resolution spectroscopy to reveal their full chemical-abundance patterns for further studies.
Astronomy & Astrophysics, 2010
Aims. We present the results of our detailed spectroscopic and photometric analysis of two previo... more Aims. We present the results of our detailed spectroscopic and photometric analysis of two previously unknown <1 M detached eclipsing binaries: ASAS J045304-0700.4 and ASAS J082552-1622.8. Methods. With the HIgh Resolution Echelle Spectrometer (HIRES) on the Keck-I telescope, we obtained spectra of both objects covering large fractions of orbits of the systems. We also obtained V and I band photometry with the 1.0-m Elizabeth telescope of the South African Astronomical Observatory (SAAO). The orbital and physical parameters of the systems were derived with the PHOEBE and JKTEBOP codes. We investigated the evolutionary status of both binaries with several sets of widely-used isochrones. Results. Our modelling indicates that (1) ASAS J045304-0700.4 is an old, metal-poor, active system with component masses of M 1 = 0.8338 ± 0.0036 M , M 2 = 0.8280 ± 0.0040 M and radii of R 1 = 0.848 ± 0.005 R and R 2 = 0.833 ± 0.005 R , which places it at the end of the Main Sequence evolution-a stage rarely observed for this type of stars. (2) ASAS J082552-1622.8 is a metal-rich, active binary with component masses of M 1 = 0.7029 ± 0.0045 M , M 2 = 0.6872 ± 0.0049 M and radii of R 1 = 0.694 +0.007 −0.011 R and R 2 = 0.699 +0.011 −0.014 R. Both systems show significant out-of-eclipse variations, probably owing to large, cold spots. We also investigated the influence of a third light in the second system.
Monthly Notices of the Royal Astronomical Society, 2020
Stars born at the same time in the same place should have formed from gas of the same element com... more Stars born at the same time in the same place should have formed from gas of the same element composition. But most stars subsequently disperse from their birth siblings, in orbit and orbital phase, becoming ‘field stars’. Here, we explore and provide direct observational evidence for this process in the Milky Way disc, by quantifying the probability that orbit-similarity among stars implies indistinguishable metallicity. We define the orbit similarity among stars through their distance in action-angle space, Δ(J, θ), and their abundance similarity simply by Δ[Fe/H]. Analysing a sample of main-sequence stars from Gaia DR2 and LAMOST, we find an excess of pairs with the same metallicity (Δ[Fe/H] < 0.1) that extends to remarkably large separations in Δ(J, θ) that correspond to nearly 1 kpc distances. We assess the significance of this effect through a mock sample, drawn from a smooth and phase-mixed orbit distribution. Through grouping such star pairs into associations with a frien...
The Astrophysical Journal, 2022
Stars originate from the dense interstellar medium, which exhibits filamentary structure to scale... more Stars originate from the dense interstellar medium, which exhibits filamentary structure to scales of ∼1 kpc in galaxies like our Milky Way. We explore quantitatively how much resulting large-scale correlation there is among different stellar clusters and associations in orbit-phase space, characterized here by actions and angles. As a starting point, we identified 55 prominent stellar overdensities in the 6D space of orbit (actions) and orbit-phase (angles) among the ∼2.8 million stars with radial velocities from Gaia EDR3 and with d ≤ 800 pc. We then explored the orbit-phase distribution of all sample stars in the same orbit patch as any one of these 55 overdensities. We find that very commonly numerous other distinct orbit-phase overdensities exist along these same orbits, like pearls on a string. These “pearls” range from known stellar clusters to loose, unrecognized associations. Among orbit patches defined by one initial orbit-phase overdensity, 50% contain at least 8 addition...
We present the orbital and physical parameters of the detached eclipsing binary V1200 Centauri (A... more We present the orbital and physical parameters of the detached eclipsing binary V1200 Centauri (ASAS J135218-3837.3) from the analysis of spectroscopic observations and light curves from the All Sky Automated Survey (ASAS) and SuperWASP database. The radial velocities were computed from the high-resolution spectra obtained with the OUC 50-cm telescope and PUCHEROS spectrograph and with 1.2m Euler telescope and CORALIE spectrograph using the cross-correlation technique TODCOR. We found that the absolute parameters of the system are M 1 = 1.394 ± 0.030 M ⊙ , M 2 = 0.866 ± 0.015 M ⊙ , R 1 = 1.39 ± 0.15 R ⊙ , R 2 = 1.10 ± 0.25 R ⊙ . We investigated the evolutionary status and kinematics of the binary and our results indicate that V1200 Centauri is likely a member of the Hyades moving group, but the largely inflated secondary's radius may suggest that the system may be even younger, around 30 Myr. We also found that the eclipsing pair is orbited by another, stellar-mass object on a 351-day orbit, which is unusually short for hierarchical triples. This makes V1200 Cen a potentially interesting target for testing the formation models of multiple stars.
VizieR Online Data Catalog, 2019
The Astrophysical Journal, 2020
We present 15, 000 metal-rich ([Fe/H] > −0.2 dex) A and F stars whose surface abundances deviate ... more We present 15, 000 metal-rich ([Fe/H] > −0.2 dex) A and F stars whose surface abundances deviate strongly from Solar abundance ratios and cannot plausibly reflect their birth material composition. These stars are identified by their high [Ba/Fe] abundance ratios ([Ba/Fe] > 1.0 dex) in the LAMOST DR5 spectra analyzed by Xiang et al. (2019). They are almost exclusively main sequence and subgiant stars with T eff 6300 K. Their distribution in the Kiel diagram (T eff-log g) traces a sharp border at low temperatures along a roughly fixed-mass trajectory (around 1.4 M) that corresponds to an upper limit in convective envelope mass fraction of around 10 −4. Most of these stars exhibit distinctly enhanced abundances of iron-peak elements (Cr, Mn, Fe, Ni) but depleted abundances of Mg and Ca. Rotational velocity measurements from GALAH DR2 show that the majority of these stars rotate slower than typical stars in an equivalent temperature range. These characteristics suggest that they are related to the so-called Am/Fm stars. Their abundance patterns are qualitatively consistent with the predictions of stellar evolution models that incorporate radiative acceleration, suggesting they are a consequence of stellar internal evolution particularly involving the competition between gravitational settling and radiative acceleration. These peculiar stars constitute 40% of the whole population of stars with mass above 1.5 M , affirming that "peculiar" photospheric abundances due to stellar evolution effects are a ubiquitous phenomenon for these intermediate-mass stars. This large sample of Ba-enhanced chemically peculiar A/F stars with individual element abundances provides the statistics to test more stringently the mechanisms that alter the surface abundances in stars with radiative envelopes.
Monthly Notices of the Royal Astronomical Society, 2018
Samples of reliably identified halo wide binaries are scarce. If reasonably free from selection e... more Samples of reliably identified halo wide binaries are scarce. If reasonably free from selection effects and with a small degree of contamination by chance alignments, these wide binaries become a powerful dynamical tool, having provided one of the very few experiments capable of constraining the nature of dark matter in the Milky Way halo. Currently, however, the best available sample of halo wide binaries is confined to the solar neighbourhood, and is plagued by small number statistics at the widest separations. We present the results of a programme aimed to probe the wide binary population of the Galactic halo at significantly larger distances, and which informs future searches that could improve the statistics by orders of magnitude. Halo stars were taken from the Sloan Digital Sky Survey after analysing the Galactic orbits of stars in the reduced proper motion diagram. We then select candidate binaries by searching for pairs with small differences in proper motion and small projected separation on the sky. Using medium-resolution spectroscopy, a subsample of candidates is validated via radial velocities, finding that about 68 per cent of candidate pairs up to 20 arcsec separation can be considered genuine halo wide binaries, to the limits of the available data. Precise parallaxes from Gaia confirm that most of our selected pairs have their components at the same distances, independently confirming the robustness of our selection method. These results should prove valuable to guide the optimal assembly of larger catalogues of halo wide binaries from upcoming large databases, e.g. Gaia and LSST.
Monthly Notices of the Royal Astronomical Society, 2018
Spectrophotometric distances to stars observed by large spectroscopic surveys offer a crucial com... more Spectrophotometric distances to stars observed by large spectroscopic surveys offer a crucial complement to parallax distances that remain very important also after the future Gaia data releases. Here, we present a probabilistic approach to modelling spectroscopic information for a subset of 4000 main sequence stars with good parallaxes (σ / < 0.1) from the LAMOST × TGAS × 2MASS cross-match, yielding a precise spectroscopic distance estimator with uncertainties of ∼6 per cent for single stars. Unlike previous approaches to this problem, we explicitly account for the individual parallax uncertainties in the model building and fully incorporate the fraction of near-equal binaries of main sequence stars, which would lead to biased distance estimates if neglected. Using this model, we estimate the distance for all (150 000) main sequence stars from LAMOST Data Release 5, without parallax information. As an application, we compute their orbital actions, where our more precise distances result in 5 times smaller action uncertainties. This illustrates how future studies of the Milky Way's orbital structure can benefit from using our model. For the fainter and more distant stars of most current spectroscopic surveys, an approach such as the one presented in this work will deliver better distances than Gaia Data Release 2.
Monthly Notices of the Royal Astronomical Society, 2019
The Astrophysical Journal, 2019
We present results from an observing campaign to identify low-metallicity stars in the Best & Bri... more We present results from an observing campaign to identify low-metallicity stars in the Best & Brightest Survey. From medium-resolution (R∼1200-2000) spectroscopy of 857 candidates, we estimate the stellar atmospheric parameters (T eff , g log , and Fe H [ ]), as well as carbon and α-element abundances. We find that 69% of the observed stars have Fe H [ ]−1.0, 39% have Fe H [ ]−2.0, and 2% have Fe H [ ]−3.0. There are also 133 carbon-enhanced metal-poor (CEMP) stars in this sample, with 97 CEMP GroupI and 36 CEMP GroupII stars identified in the A(C) versus [Fe/H] diagram. A subset of the confirmed low-metallicity stars were followed-up with high-resolution spectroscopy, as part of the R-process Alliance, with the goal of identifying new highly and moderately r-process-enhanced stars. Comparison between the stellar atmospheric parameters estimated in this work and from high-resolution spectroscopy exhibit good agreement, confirming our expectation that medium-resolution observing campaigns are an effective way of selecting interesting stars for further, more targeted, efforts.
Monthly Notices of the Royal Astronomical Society, 2019
We compare the distribution in position and velocity of nearby stars from the Gaia DR2 radial vel... more We compare the distribution in position and velocity of nearby stars from the Gaia DR2 radial velocity sample with predictions of current theories for spirals in disc galaxies. Although the rich substructure in velocity space contains the same information, we find it more revealing to reproject the data into action-angle variables, and we describe why resonant scattering would be more readily identifiable in these variables. We compute the predicted changes to the phase-space density, in multiple different projections, that would be caused by a simplified isolated spiral pattern, finding widely differing predictions from each theory. We conclude that the phase-space structure present in the Gaia data shares many of the qualitative features expected in the transient spiral mode model. We argue that the popular picture of apparently swing-amplified spirals results from the superposition of a few underlying spiral modes.
The Astronomical Journal, 2018
We present results from a medium-resolution (R∼2000) spectroscopic follow-up campaign of 1694 b... more We present results from a medium-resolution (R∼2000) spectroscopic follow-up campaign of 1694 bright (V<13.5), very metal-poor star candidates from the RAdial Velocity Experiment (RAVE). Initial selection of the low-metallicity targets was based on the stellar parameters published in RAVE Data Releases 4 and 5. Follow up was accomplished with the Gemini-N and Gemini-S, the ESO/NTT, the KPNO/Mayall, and the SOAR telescopes. The wavelength coverage for most of the observed spectra allows for the determination of carbon and α-element abundances, which are crucial for considering the nature and frequency of the carbon-enhanced metalpoor (CEMP) stars in this sample. We find that 88% of the observed stars have Fe H [ ]−1.0, 61% have Fe H [ ]−2.0, and 3% have Fe H [ ]−3.0 (with four stars at Fe H [ ]−3.5). There are 306 CEMP star candidates in this sample, and we identify 169 CEMP GroupI, 131 CEMP GroupII, and 6 CEMP GroupIII stars from the A(C) versus [Fe/H] diagram. Inspection of the C a [ ] abundance ratios reveals that five of the CEMP GroupII stars can be classified as "mono-enriched second-generation" stars. Gaia DR1 matches were found for 734 stars, and we show that transverse velocities can be used as a confirmatory selection criteria for low-metallicity candidates. Selected stars from our validated list are being followed-up with high-resolution spectroscopy to reveal their full chemical-abundance patterns for further studies.
Astronomy & Astrophysics, 2010
Aims. We present the results of our detailed spectroscopic and photometric analysis of two previo... more Aims. We present the results of our detailed spectroscopic and photometric analysis of two previously unknown <1 M detached eclipsing binaries: ASAS J045304-0700.4 and ASAS J082552-1622.8. Methods. With the HIgh Resolution Echelle Spectrometer (HIRES) on the Keck-I telescope, we obtained spectra of both objects covering large fractions of orbits of the systems. We also obtained V and I band photometry with the 1.0-m Elizabeth telescope of the South African Astronomical Observatory (SAAO). The orbital and physical parameters of the systems were derived with the PHOEBE and JKTEBOP codes. We investigated the evolutionary status of both binaries with several sets of widely-used isochrones. Results. Our modelling indicates that (1) ASAS J045304-0700.4 is an old, metal-poor, active system with component masses of M 1 = 0.8338 ± 0.0036 M , M 2 = 0.8280 ± 0.0040 M and radii of R 1 = 0.848 ± 0.005 R and R 2 = 0.833 ± 0.005 R , which places it at the end of the Main Sequence evolution-a stage rarely observed for this type of stars. (2) ASAS J082552-1622.8 is a metal-rich, active binary with component masses of M 1 = 0.7029 ± 0.0045 M , M 2 = 0.6872 ± 0.0049 M and radii of R 1 = 0.694 +0.007 −0.011 R and R 2 = 0.699 +0.011 −0.014 R. Both systems show significant out-of-eclipse variations, probably owing to large, cold spots. We also investigated the influence of a third light in the second system.
Monthly Notices of the Royal Astronomical Society, 2020
Stars born at the same time in the same place should have formed from gas of the same element com... more Stars born at the same time in the same place should have formed from gas of the same element composition. But most stars subsequently disperse from their birth siblings, in orbit and orbital phase, becoming ‘field stars’. Here, we explore and provide direct observational evidence for this process in the Milky Way disc, by quantifying the probability that orbit-similarity among stars implies indistinguishable metallicity. We define the orbit similarity among stars through their distance in action-angle space, Δ(J, θ), and their abundance similarity simply by Δ[Fe/H]. Analysing a sample of main-sequence stars from Gaia DR2 and LAMOST, we find an excess of pairs with the same metallicity (Δ[Fe/H] < 0.1) that extends to remarkably large separations in Δ(J, θ) that correspond to nearly 1 kpc distances. We assess the significance of this effect through a mock sample, drawn from a smooth and phase-mixed orbit distribution. Through grouping such star pairs into associations with a frien...
The Astrophysical Journal, 2022
Stars originate from the dense interstellar medium, which exhibits filamentary structure to scale... more Stars originate from the dense interstellar medium, which exhibits filamentary structure to scales of ∼1 kpc in galaxies like our Milky Way. We explore quantitatively how much resulting large-scale correlation there is among different stellar clusters and associations in orbit-phase space, characterized here by actions and angles. As a starting point, we identified 55 prominent stellar overdensities in the 6D space of orbit (actions) and orbit-phase (angles) among the ∼2.8 million stars with radial velocities from Gaia EDR3 and with d ≤ 800 pc. We then explored the orbit-phase distribution of all sample stars in the same orbit patch as any one of these 55 overdensities. We find that very commonly numerous other distinct orbit-phase overdensities exist along these same orbits, like pearls on a string. These “pearls” range from known stellar clusters to loose, unrecognized associations. Among orbit patches defined by one initial orbit-phase overdensity, 50% contain at least 8 addition...
We present the orbital and physical parameters of the detached eclipsing binary V1200 Centauri (A... more We present the orbital and physical parameters of the detached eclipsing binary V1200 Centauri (ASAS J135218-3837.3) from the analysis of spectroscopic observations and light curves from the All Sky Automated Survey (ASAS) and SuperWASP database. The radial velocities were computed from the high-resolution spectra obtained with the OUC 50-cm telescope and PUCHEROS spectrograph and with 1.2m Euler telescope and CORALIE spectrograph using the cross-correlation technique TODCOR. We found that the absolute parameters of the system are M 1 = 1.394 ± 0.030 M ⊙ , M 2 = 0.866 ± 0.015 M ⊙ , R 1 = 1.39 ± 0.15 R ⊙ , R 2 = 1.10 ± 0.25 R ⊙ . We investigated the evolutionary status and kinematics of the binary and our results indicate that V1200 Centauri is likely a member of the Hyades moving group, but the largely inflated secondary's radius may suggest that the system may be even younger, around 30 Myr. We also found that the eclipsing pair is orbited by another, stellar-mass object on a 351-day orbit, which is unusually short for hierarchical triples. This makes V1200 Cen a potentially interesting target for testing the formation models of multiple stars.