138 results on '"Casey, A R"'
Search Results
2. Cool and data-driven: an exploration of optical cool dwarf chemistry with both data-driven and physical models
- Author
-
Rains, Adam D, primary, Nordlander, Thomas, additional, Monty, Stephanie, additional, Casey, Andrew R, additional, Rojas-Ayala, Bárbara, additional, Žerjal, Maruša, additional, Ireland, Michael J, additional, Casagrande, Luca, additional, and McKenzie, Madeleine, additional
- Published
- 2024
- Full Text
- View/download PDF
3. The GALAH survey: tracing the Milky Way's formation and evolution through RR Lyrae stars.
- Author
-
D'Orazi, Valentina, Storm, Nicholas, Casey, Andrew R, Braga, Vittorio F, Zocchi, Alice, Bono, Giuseppe, Fabrizio, Michele, Sneden, Christopher, Massari, Davide, Giribaldi, Riano E, Bergemann, Maria, Campbell, Simon W, Casagrande, Luca, de Grijs, Richard, De Silva, Gayandhi, Lugaro, Maria, Zucker, Daniel B, Bragaglia, Angela, Feuillet, Diane, and Fiorentino, Giuliana
- Subjects
RR Lyrae stars ,MILKY Way ,STELLAR parallax ,LOW mass stars ,STARS - Abstract
Stellar mergers and accretion events have been crucial in shaping the evolution of the Milky Way (MW). These events have been dynamically identified and chemically characterized using red giants and main-sequence stars. RR Lyrae (RRL) variables can play a crucial role in tracing the early formation of the MW since they are ubiquitous, old (t ≥ 10 Gyr) low-mass stars and accurate distance indicators. We exploited Data Release 3 of the GALAH survey to identify 78 field RRLs suitable for chemical analysis. Using synthetic spectra calculations, we determined atmospheric parameters and abundances of Fe, Mg, Ca, Y, and Ba. Most of our stars exhibit halo-like chemical compositions, with an iron peak around [Fe/H] ≈ −1.40, and enhanced Ca and Mg content. Notably, we discovered a metal-rich tail, with [Fe/H] values ranging from −1 to approximately solar metallicity. This sub-group includes almost 1/4 of the sample, it is characterized by thin disc kinematics and displays sub-solar α-element abundances, marginally consistent with the majority of the MW stars. Surprisingly, they differ distinctly from typical MW disc stars in terms of the s-process elements Y and Ba. We took advantage of similar data available in the literature and built a total sample of 535 field RRLs for which we estimated kinematical and dynamical properties. We found that metal-rich RRLs (1/3 of the sample) likely represent an old component of the MW thin disc. We also detected RRLs with retrograde orbits and provided preliminary associations with the Gaia–Sausage–Enceladus, Helmi, Sequoia, Sagittarius, and Thamnos stellar streams. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
4. Stellar spots cause measurable variations in atmospheric metallicity
- Author
-
Wilson, Tanner A, primary and Casey, Andrew R, additional
- Published
- 2023
- Full Text
- View/download PDF
5. The Gaia-ESO Survey: Empirical estimates of stellar ages from lithium equivalent widths (eagles)
- Author
-
Jeffries, R D, primary, Jackson, R J, additional, Wright, Nicholas J, additional, Weaver, G, additional, Gilmore, G, additional, Randich, S, additional, Bragaglia, A, additional, Korn, A J, additional, Smiljanic, R, additional, Biazzo, K, additional, Casey, A R, additional, Frasca, A, additional, Gonneau, A, additional, Guiglion, G, additional, Morbidelli, L, additional, Prisinzano, L, additional, Sacco, G G, additional, Tautvaišienė, G, additional, Worley, C C, additional, and Zaggia, S, additional
- Published
- 2023
- Full Text
- View/download PDF
6. Constraining the rotation profile in a low-luminosity subgiant with a surface rotation measurement
- Author
-
Wilson, Tanner A, primary, Casey, Andrew R, additional, Mandel, Ilya, additional, Ball, Warrick H, additional, Bellinger, Earl P, additional, and Davies, Guy, additional
- Published
- 2023
- Full Text
- View/download PDF
7. The GALAH survey: chemical clocks
- Author
-
Hayden, Michael R, primary, Sharma, Sanjib, additional, Bland-Hawthorn, Joss, additional, Spina, Lorenzo, additional, Buder, Sven, additional, Ciucă, Ioana, additional, Asplund, Martin, additional, Casey, Andrew R, additional, De Silva, Gayandhi M, additional, D’Orazi, Valentina, additional, Freeman, Ken C, additional, Kos, Janez, additional, Lewis, Geraint F, additional, Lin, Jane, additional, Lind, Karin, additional, Martell, Sarah L, additional, Schlesinger, Katharine J, additional, Simpson, Jeffrey D, additional, Zucker, Daniel B, additional, Zwitter, Tomaž, additional, Chen, Boquan, additional, Čotar, Klemen, additional, Feuillet, Diane, additional, Horner, Jonti, additional, Joyce, Meridith, additional, Nordlander, Thomas, additional, Stello, Dennis, additional, Tepper-Garcia, Thor, additional, Ting, Yuan-sen, additional, Wang, Purmortal, additional, Wittenmyer, Rob, additional, and Wyse, Rosemary, additional
- Published
- 2022
- Full Text
- View/download PDF
8. The GALAH Survey: chemical tagging and chrono-chemodynamics of accreted halo stars with GALAH+ DR3 and Gaia eDR3
- Author
-
Buder, Sven, Lind, Karin, Ness, Melissa K., Feuillet, Diane K., Horta, Danny, Monty, Stephanie, Buck, Tobias, Nordlander, Thomas, Bland-Hawthorn, Joss, Casey, Andrew R., De Silva, Gayandhi M., D'Orazi, Valentina, Freeman, Ken C., Hayden, Michael R., Kos, Janez, Martell, Sarah L., Lewis, Geraint F., Lin, Jane, Schlesinger, Katharine. J., Sharma, Sanjib, Simpson, Jeffrey D., Stello, Dennis, Zucker, Daniel B., Zwitter, Tomaz, Ciuca, Ioana, Horner, Jonathan, Kobayashi, Chiaki, Ting, Yuan-Sen, Wyse, Rosemary F. G., and Collaboration, The GALAH
- Subjects
Astrophysics - Solar and Stellar Astrophysics ,formation [Galaxy] ,Space and Planetary Science ,Astrophysics of Galaxies (astro-ph.GA) ,abundances [Galaxy] ,halo [Galaxy] ,FOS: Physical sciences ,Astronomy and Astrophysics ,kinematics and dynamics [Galaxy] ,Astrophysics - Astrophysics of Galaxies ,Solar and Stellar Astrophysics (astro-ph.SR) - Abstract
Since the advent of $Gaia$ astrometry, it is possible to identify massive accreted systems within the Galaxy through their unique dynamical signatures. One such system, $Gaia$-Sausage-Enceladus (GSE), appears to be an early "building block" given its virial mass $> 10^{10}\,\mathrm{M_\odot}$ at infall ($z\sim1-3$). In order to separate the progenitor population from the background stars, we investigate its chemical properties with up to 30 element abundances from the GALAH+ Survey Data Release 3 (DR3). To inform our choice of elements for purely chemically selecting accreted stars, we analyse 4164 stars with low-$��$ abundances and halo kinematics. These are most different to the Milky Way stars for abundances of Mg, Si, Na, Al, Mn, Fe, Ni, and Cu. Based on the significance of abundance differences and detection rates, we apply Gaussian mixture models to various element abundance combinations. We find the most populated and least contaminated component, which we confirm to represent GSE, contains 1049 stars selected via [Na/Fe] vs. [Mg/Mn] in GALAH+ DR3. We provide tables of our selections and report the chrono-chemodynamical properties (age, chemistry, and dynamics). Through a previously reported clean dynamical selection of GSE stars, including $30 < \sqrt{J_R~/~\mathrm{kpc\,km\,s^{-1}}} < 55$, we can characterise an unprecedented 24 abundances of this structure with GALAH+ DR3. Our chemical selection allows us to prevent circular reasoning and characterise the dynamical properties of the GSE, for example mean $\sqrt{J_R~/~\mathrm{kpc\,km\,s^{-1}}} = 26_{-14}^{+9}$. We find only $(29\pm1)\%$ of the GSE stars within the clean dynamical selection region. Our methodology will improve future studies of accreted structures and their importance for the formation of the Milky Way., 29 pages, 18 figures, 6 tables; publicshed in MNRAS; all code to recreate results (based on public data described in arXiv:2011.02505) and figures available at https://github.com/svenbuder/Accreted-stars-in-GALAH-DR3
- Published
- 2021
9. The GALAH Survey: improving our understanding of confirmed and candidate planetary systems with large stellar surveys
- Author
-
Clark, Jake T, primary, Wright, Duncan J, additional, Wittenmyer, Robert A, additional, Horner, Jonathan, additional, Hinkel, Natalie R, additional, Clerté, Mathieu, additional, Carter, Brad D, additional, Buder, Sven, additional, Hayden, Michael R, additional, Bland-Hawthorn, Joss, additional, Casey, Andrew R, additional, De Silva, Gayandhi M, additional, D’Orazi, Valentina, additional, Freeman, Ken C, additional, Kos, Janez, additional, Lewis, Geraint F, additional, Lin, Jane, additional, Lind, Karin, additional, Martell, Sarah L, additional, Schlesinger, Katharine J, additional, Sharma, Sanjib, additional, Simpson, Jeffrey D, additional, Stello, Dennis, additional, Zucker, Daniel B, additional, Zwitter, Tomaž, additional, Munari, Ulisse, additional, and Nordlander, Thomas, additional
- Published
- 2021
- Full Text
- View/download PDF
10. The impact of metallicity on nova populations
- Author
-
Kemp, Alex J, primary, Karakas, Amanda I, additional, Casey, Andrew R, additional, Kobayashi, Chiaki, additional, and Izzard, Robert G, additional
- Published
- 2021
- Full Text
- View/download PDF
11. GALAH survey: chemical clocks.
- Author
-
Hayden, Michael R, Sharma, Sanjib, Bland-Hawthorn, Joss, Spina, Lorenzo, Buder, Sven, Ciucă, Ioana, Asplund, Martin, Casey, Andrew R, De Silva, Gayandhi M, D'Orazi, Valentina, Freeman, Ken C, Kos, Janez, Lewis, Geraint F, Lin, Jane, Lind, Karin, Martell, Sarah L, Schlesinger, Katharine J, Simpson, Jeffrey D, Zucker, Daniel B, and Zwitter, Tomaž
- Subjects
MACHINE learning ,AGE of stars ,CLOCKS & watches ,GALACTIC evolution ,DISPERSION relations ,MILKY Way - Abstract
We present the first large-scale study that demonstrates how ages can be determined for large samples of stars through Galactic chemical evolution. Previous studies found that the elemental abundances of a star correlate directly with its age and metallicity. Using this knowledge, we derive ages for 214 577 stars in GALAH DR3 using only overall metallicities and chemical abundances. Stellar ages are estimated via the machine learning algorithm XGBoost for stars belonging to the Milky Way disc with metallicities in the range −1 < [Fe/H] < 0.5, using main-sequence turn-off stars as our training set. We find that stellar ages for the bulk of GALAH DR3 are precise to 1–2 Gyr using this method. With these ages, we replicate many recent results on the age-kinematic trends of the nearby disc, including the solar neighbourhood's age–velocity dispersion relationship and the larger global velocity dispersion relations of the disc found using Gaia and GALAH. These results show that chemical abundance variations at a given birth radius are small, and that strong chemical tagging of stars directly to birth clusters may prove difficult with our current elemental abundance precision. Our results highlight the need to measure abundances for as many nucleosynthetic production sites as possible in order to estimate reliable ages from chemistry. Our methods open a new door into studies of the kinematic structure and evolution of the disc, as ages may potentially be estimated to a precision of 1–2 Gyr for a large fraction of stars in existing spectroscopic surveys. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
12. The GALAH+ Survey: A new library of observed stellar spectra improves radial velocities and hints at motions within M67
- Author
-
Zwitter, Tomaž, primary, Kos, Janez, additional, Buder, Sven, additional, Čotar, Klemen, additional, Asplund, Martin, additional, Bland-Hawthorn, Joss, additional, Casey, Andrew R, additional, De Silva, Gayandhi M, additional, D’Orazi, Valentina, additional, Freeman, Ken C, additional, Hayden, Michael R, additional, Lewis, Geraint F, additional, Lin, Jane, additional, Lind, Karin, additional, Martell, Sarah L, additional, Schlesinger, Katharine J, additional, Sharma, Sanjib, additional, Simpson, Jeffrey D, additional, Stello, Dennis, additional, Zucker, Daniel B, additional, Beeson, Kevin L, additional, de Grijs, Richard, additional, Nordlander, Thomas, additional, Ting, Yuan-Sen, additional, Traven, Gregor, additional, Vogrinčič, Rok, additional, Watson, Fred, additional, and Wittenmyer, Rob, additional
- Published
- 2021
- Full Text
- View/download PDF
13. The GALAH survey: effective temperature calibration from the InfraRed Flux Method in the Gaia system
- Author
-
Casagrande, Luca, primary, Lin, Jane, additional, Rains, Adam D, additional, Liu, Fan, additional, Buder, Sven, additional, Horner, Jonathan, additional, Asplund, Martin, additional, Lewis, Geraint F, additional, Martell, Sarah L, additional, Nordlander, Thomas, additional, Stello, Dennis, additional, Ting, Yuan-Sen, additional, Wittenmyer, Robert A, additional, Bland-Hawthorn, Joss, additional, Casey, Andrew R, additional, De Silva, Gayandhi M, additional, D’Orazi, Valentina, additional, Freeman, Ken C, additional, Hayden, Michael R, additional, Kos, Janez, additional, Lind, Karin, additional, Schlesinger, Katharine J, additional, Sharma, Sanjib, additional, Simpson, Jeffrey D, additional, Zucker, Daniel B, additional, and Zwitter, Tomaž, additional
- Published
- 2021
- Full Text
- View/download PDF
14. High-resolution spectroscopic follow-up of the most metal-poor candidates from SkyMapper DR1.1
- Author
-
Yong, D, primary, Da Costa, G S, additional, Bessell, M S, additional, Chiti, A, additional, Frebel, A, additional, Gao, X, additional, Lind, K, additional, Mackey, A D, additional, Marino, A F, additional, Murphy, S J, additional, Nordlander, T, additional, Asplund, M, additional, Casey, A R, additional, Kobayashi, C, additional, Norris, J E, additional, and Schmidt, B P, additional
- Published
- 2021
- Full Text
- View/download PDF
15. Population synthesis of accreting white dwarfs: rates and evolutionary pathways of H and He novae
- Author
-
Kemp, Alex J, primary, Karakas, Amanda I, additional, Casey, Andrew R, additional, Izzard, Robert G, additional, Ruiter, Ashley J, additional, Agrawal, Poojan, additional, Broekgaarden, Floor S, additional, and Temmink, Karel D, additional
- Published
- 2021
- Full Text
- View/download PDF
16. The GALAH survey: tracing the Galactic disc with open clusters
- Author
-
Spina, L, primary, Ting, Y-S, additional, De Silva, G M, additional, Frankel, N, additional, Sharma, S, additional, Cantat-Gaudin, T, additional, Joyce, M, additional, Stello, D, additional, Karakas, A I, additional, Asplund, M B, additional, Nordlander, T, additional, Casagrande, L, additional, D’Orazi, V, additional, Casey, A R, additional, Cottrell, P, additional, Tepper-García, T, additional, Baratella, M, additional, Kos, J, additional, Čotar, K, additional, Bland-Hawthorn, J, additional, Buder, S, additional, Freeman, K C, additional, Hayden, M R, additional, Lewis, G F, additional, Lin, J, additional, Lind, K, additional, Martell, S L, additional, Schlesinger, K J, additional, Simpson, J D, additional, Zucker, D B, additional, and Zwitter, T, additional
- Published
- 2021
- Full Text
- View/download PDF
17. Exploring the Galaxy’s halo and very metal-weak thick disc with SkyMapper and Gaia DR2
- Author
-
Cordoni, G, primary, Da Costa, G S, additional, Yong, D, additional, Mackey, A D, additional, Marino, A F, additional, Monty, S, additional, Nordlander, T, additional, Norris, J E, additional, Asplund, M, additional, Bessell, M S, additional, Casey, A R, additional, Frebel, A, additional, Lind, K, additional, Murphy, S J, additional, Schmidt, B P, additional, Gao, X D, additional, Xylakis-Dornbusch, T, additional, Amarsi, A M, additional, and Milone, A P, additional
- Published
- 2020
- Full Text
- View/download PDF
18. GALAH Survey: chemical tagging and chrono-chemodynamics of accreted halo stars with GALAH+ DR3 and Gaia eDR3.
- Author
-
Buder, Sven, Lind, Karin, Ness, Melissa K, Feuillet, Diane K, Horta, Danny, Monty, Stephanie, Buck, Tobias, Nordlander, Thomas, Bland-Hawthorn, Joss, Casey, Andrew R, De Silva, Gayandhi M, D'Orazi, Valentina, Freeman, Ken C, Hayden, Michael R, Kos, Janez, Martell, Sarah L, Lewis, Geraint F, Lin, Jane, Schlesinger, Katharine J, and Sharma, Sanjib
- Subjects
GAUSSIAN mixture models ,DATA release ,CHEMICAL properties - Abstract
Since the advent of Gaia astrometry, it is possible to identify massive accreted systems within the Galaxy through their unique dynamical signatures. One such system, Gaia -Sausage-Enceladus (GSE), appears to be an early 'building block' given its virial mass |$\gt 10^{10}\, \mathrm{M_\odot }$| at infall (z ∼ 1−3). In order to separate the progenitor population from the background stars, we investigate its chemical properties with up to 30 element abundances from the GALAH+ Survey Data Release 3 (DR3). To inform our choice of elements for purely chemically selecting accreted stars, we analyse 4164 stars with low-α abundances and halo kinematics. These are most different to the Milky Way stars for abundances of Mg, Si, Na, Al, Mn, Fe, Ni, and Cu. Based on the significance of abundance differences and detection rates, we apply Gaussian mixture models to various element abundance combinations. We find the most populated and least contaminated component, which we confirm to represent GSE, contains 1049 stars selected via [Na/Fe] versus [Mg/Mn] in GALAH+ DR3. We provide tables of our selections and report the chrono-chemodynamical properties (age, chemistry, and dynamics). Through a previously reported clean dynamical selection of GSE stars, including |$30 \lt \sqrt{J_R / \, \mathrm{kpc\, km\, s^{-1}}} \lt 55$| , we can characterize an unprecedented 24 abundances of this structure with GALAH+ DR3. With our chemical selection we characterize the dynamical properties of the GSE, for example mean |$\sqrt{J_R / \, \mathrm{kpc\, km\, s^{-1}}} =$| |$26_{-14}^{+9}$|. We find only |$(29\pm 1){{\ \rm per\ cent}}$| of the GSE stars within the clean dynamical selection region. Our methodology will improve future studies of accreted structures and their importance for the formation of the Milky Way. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
19. GALAH Survey: improving our understanding of confirmed and candidate planetary systems with large stellar surveys.
- Author
-
Clark, Jake T, Wright, Duncan J, Wittenmyer, Robert A, Horner, Jonathan, Hinkel, Natalie R, Clerté, Mathieu, Carter, Brad D, Buder, Sven, Hayden, Michael R, Bland-Hawthorn, Joss, Casey, Andrew R, De Silva, Gayandhi M, D'Orazi, Valentina, Freeman, Ken C, Kos, Janez, Lewis, Geraint F, Lin, Jane, Lind, Karin, Martell, Sarah L, and Schlesinger, Katharine J
- Subjects
PLANETARY systems ,BROWN dwarf stars ,TELECOMMUNICATION satellites ,INNER planets ,DATA release ,ASTROMETRY ,EXTRASOLAR planets - Abstract
Pioneering photometric, astrometric, and spectroscopic surveys is helping exoplanetary scientists better constrain the fundamental properties of stars within our galaxy and the planets these stars host. In this study, we use the third data release from the stellar spectroscopic GALAH Survey, coupled with astrometric data of eDR3 from the Gaia satellite, and other data from NASA's Exoplanet Archive, to refine our understanding of 279 confirmed and candidate exoplanet host stars and their exoplanets. This homogenously analysed data set comprises 105 confirmed exoplanets, along with 146 K2 candidates, 95 TESS Objects of Interest (TOIs), and 52 Community TOIs (CTOIs). Our analysis significantly shifts several previously (unknown) planet parameters while decreasing the uncertainties for others. Our radius estimates suggest that 35 planet candidates are more likely brown dwarfs or stellar companions due to their new radius values. We are able to refine the radii and masses of WASP-47 e, K2-106 b, and CoRoT-7 b to their most precise values yet to less than 2.3 per cent and 8.5 per cent, respectively. We also use stellar rotational values from GALAH to show that most planet candidates will have mass measurements that will be tough to obtain with current ground-based spectrographs. With GALAH's chemical abundances, we show through chemo-kinematics that there are five planet hosts that are associated with the galaxy's thick disc, including NGTS-4, K2-183, and K2-337. Finally, we show that there is no statistical difference between the chemical properties of hot Neptune and hot rocky exoplanet hosts, with the possibility that short-period rocky worlds might be the remnant cores of hotter, gaseous worlds. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
20. impact of metallicity on nova populations.
- Author
-
Kemp, Alex J, Karakas, Amanda I, Casey, Andrew R, Kobayashi, Chiaki, and Izzard, Robert G
- Subjects
DWARF novae ,STELLAR evolution ,STAR formation ,SPIRAL galaxies ,BINARY codes ,NOVAE (Astronomy) - Abstract
The metallicity of a star affects its evolution in a variety of ways, changing stellar radii, luminosities, lifetimes, and remnant properties. In this work, we use the population synthesis code binary_c to study how metallicity affects novae in the context of binary stellar evolution. We compute a 16-point grid of metallicities ranging from Z = 10
−4 to 0.03, presenting distributions of nova white dwarf masses, accretion rates, delay-times, and initial system properties at the two extremes of our 16-point metallicity grid. We find a clear anticorrelation between metallicity and the number of novae produced, with the number of novae at Z = 0.03 roughly half that at Z = 10−4 . The white dwarf mass distribution has a strong systematic variation with metallicity, while the shape of the accretion rate distribution is relatively insensitive. We compute a current nova rate of approximately 33 novae per year for the Milky Way, a result consistent with observational estimates relying on extra-Galactic novae but an under-prediction relative to observational estimates relying on Galactic novae. However, the shape of our predicted Galactic white dwarf mass distribution differs significantly to existing observationally derived distributions, likely due to our underlying physical assumptions. In M31, we compute a current nova rate of approximately 36 novae per year, under-predicting the most recent observational estimate of |$65^{+15}_{-16}$|. Finally, we conclude that when making predictions about currently observable nova rates in spiral galaxies, or stellar environments where star formation has ceased in the distant past, metallicity can likely be considered of secondary importance compared to uncertainties in binary stellar evolution. [ABSTRACT FROM AUTHOR]- Published
- 2022
- Full Text
- View/download PDF
21. K2-HERMES II. Planet-candidate properties from K2 Campaigns 1-13
- Author
-
Wittenmyer, Robert A, primary, Clark, Jake T, additional, Sharma, Sanjib, additional, Stello, Dennis, additional, Horner, Jonathan, additional, Kane, Stephen R, additional, Stevens, Catherine P, additional, Wright, Duncan J, additional, Spina, Lorenzo, additional, Čotar, Klemen, additional, Asplund, Martin, additional, Bland-Hawthorn, Joss, additional, Buder, Sven, additional, Casey, Andrew R, additional, De Silva, Gayandhi M, additional, D’Orazi, Valentina, additional, Freeman, Ken, additional, Kos, Janez, additional, Lewis, Geraint, additional, Lin, Jane, additional, Lind, Karin, additional, Martell, Sarah L, additional, Simpson, Jeffrey D, additional, Zucker, Daniel B, additional, and Zwitter, Tomaz, additional
- Published
- 2020
- Full Text
- View/download PDF
22. Weighing in on black hole binaries with bpass: LB-1 does not contain a 70 M⊙ black hole
- Author
-
Eldridge, J J, primary, Stanway, E R, primary, Breivik, K, primary, Casey, A R, primary, Steeghs, D T H, primary, and Stevance, H F, primary
- Published
- 2020
- Full Text
- View/download PDF
23. The GALAH survey: temporal chemical enrichment of the galactic disc
- Author
-
Lin, Jane, primary, Asplund, Martin, additional, Ting, Yuan-Sen, additional, Casagrande, Luca, additional, Buder, Sven, additional, Bland-Hawthorn, Joss, additional, Casey, Andrew R, additional, De Silva, Gayandhi M, additional, D’Orazi, Valentina, additional, Freeman, Ken C, additional, Kos, Janez, additional, Lind, K, additional, Martell, Sarah L, additional, Sharma, Sanjib, additional, Simpson, Jeffrey D, additional, Zwitter, Tomaž, additional, Zucker, Daniel B, additional, Minchev, Ivan, additional, Čotar, Klemen, additional, Hayden, Michael, additional, Horner, Jonti, additional, Lewis, Geraint F, additional, Nordlander, Thomas, additional, Wyse, Rosemary F G, additional, and Žerjal, Maruša, additional
- Published
- 2019
- Full Text
- View/download PDF
24. Discovery of s-process enhanced stars in the LAMOST survey
- Author
-
Norfolk, Brodie J, primary, Casey, Andrew R, additional, Karakas, Amanda I, additional, Miles, Matthew T, additional, Kemp, Alex J, additional, Schlaufman, Kevin C, additional, Ness, Melissa, additional, Ho, Anna Y Q, additional, Lattanzio, John C, additional, and Ji, Alexander P, additional
- Published
- 2019
- Full Text
- View/download PDF
25. GALAH+ survey: a new library of observed stellar spectra improves radial velocities and hints at motions within M67.
- Author
-
Zwitter, Tomaž, Kos, Janez, Buder, Sven, Čotar, Klemen, Asplund, Martin, Bland-Hawthorn, Joss, Casey, Andrew R, De Silva, Gayandhi M, D'Orazi, Valentina, Freeman, Ken C, Hayden, Michael R, Lewis, Geraint F, Lin, Jane, Lind, Karin, Martell, Sarah L, Schlesinger, Katharine J, Sharma, Sanjib, Simpson, Jeffrey D, Stello, Dennis, and Zucker, Daniel B
- Subjects
DATA release ,GIANT stars ,SPECTRAL lines ,OPEN clusters of stars ,VELOCITY ,DWARF stars ,STELLAR spectra - Abstract
GALAH+ is a magnitude-limited survey of high-resolution stellar spectra obtained by the HERMES spectrograph at the Australian Astronomical Observatory. Its third data release provides reduced spectra with new derivations of stellar parameters and abundances of 30 chemical elements for 584 015 dwarfs and giants, 88 per cent of them in the Gaia magnitude range 11 < G < 14. Here, we use these improved values of stellar parameters to build a library of observed spectra which is useful to study variations of individual spectral lines with stellar parameters. This and other improvements are used to derive radial velocities with uncertainties which are generally within 0.1 km s
−1 or ∼25 per cent smaller than in the previous release. Median differences in radial velocities measured here and by the Gaia DR2 or APOGEE DR16 surveys are smaller than 30 m s−1 , a larger offset is present only for Gaia measurements of giant stars. We identify 4483 stars with intrinsically variable velocities and 225 stars for which the velocity stays constant over ≥3 visits spanning more than a year. The combination of radial velocities from GALAH+ with distances and sky plane motions from Gaia enables studies of dynamics within streams and clusters. For example, we estimate that the open cluster M67 has a total mass of ∼3300 M⊙ and its outer parts seem to be expanding, though astrometry with a larger time-span than currently available from Gaia eDR3 is needed to judge if the latter result is real. [ABSTRACT FROM AUTHOR]- Published
- 2021
- Full Text
- View/download PDF
26. The GALAH survey: accreted stars also inhabit the Spite plateau.
- Author
-
Simpson, Jeffrey D, Martell, Sarah L, Buder, Sven, Bland-Hawthorn, Joss, Casey, Andrew R, De Silva, Gayandhi M, D'Orazi, Valentina, Freeman, Ken C, Hayden, Michael, Kos, Janez, Lewis, Geraint F, Lind, Karin, Schlesinger, Katharine J, Sharma, Sanjib, Stello, Dennis, Zucker, Daniel B, Zwitter, Tomaž, Asplund, Martin, Da Costa, Gary, and Čotar, Klemen
- Subjects
GAS reservoirs ,INTERSTELLAR medium ,MILKY Way ,NUCLEOSYNTHESIS - Abstract
The European Space Agency (ESA) Gaia mission has enabled the remarkable discovery that a large fraction of the stars near the solar neighbourhood are debris from a single in-falling system, the so-called Gaia -Sausage-Enceladus (GSE). This discovery provides astronomers for the first time with a large cohort of easily observable, unevolved stars that formed in a single extragalactic environment. Here we use these stars to investigate the 'Spite plateau' – the near-constant lithium abundance observed in unevolved metal-poor stars across a wide range of metallicities (−3 < [Fe/H] < −1). Our aim is to test whether individual galaxies could have different Spite plateaus – e.g. the interstellar medium could be more depleted in lithium in a lower galactic mass system due to it having a smaller reservoir of gas. We identified 93 GSE dwarf stars observed and analysed by the GALactic Archaeology with HERMES (GALAH) survey as part of its Data Release 3 (DR3). Orbital actions were used to select samples of GSE stars, and comparison samples of halo and disc stars. We find that the GSE stars show the same lithium abundance as other likely accreted stars and in situ Milky Way stars. Formation environment leaves no imprint on lithium abundances. This result fits within the growing consensus that the Spite plateau, and more generally the 'cosmological lithium problem' – the observed discrepancy between the amount of lithium in warm, metal-poor dwarf stars in our Galaxy, and the amount of lithium predicted to have been produced by big bang nucleosynthesis – is the result of lithium depletion processes within stars. [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
27. The GALAH+ survey: Third data release.
- Author
-
Buder, Sven, Sharma, Sanjib, Kos, Janez, Amarsi, Anish M, Nordlander, Thomas, Lind, Karin, Martell, Sarah L, Asplund, Martin, Bland-Hawthorn, Joss, Casey, Andrew R, De Silva, Gayandhi M, D'Orazi, Valentina, Freeman, Ken C, Hayden, Michael R, Lewis, Geraint F, Lin, Jane, Schlesinger, Katharine J, Simpson, Jeffrey D, Stello, Dennis, and Zucker, Daniel B
- Subjects
STELLAR dynamics ,SPECTRUM analysis ,STELLAR atmospheres ,MILKY Way ,ATMOSPHERIC models ,CHEMICAL elements - Abstract
The ensemble of chemical element abundance measurements for stars, along with precision distances and orbit properties, provides high-dimensional data to study the evolution of the Milky Way. With this third data release of the Galactic Archaeology with HERMES (GALAH) survey, we publish 678 423 spectra for 588 571 mostly nearby stars (81.2 per cent of stars are within <2 kpc), observed with the HERMES spectrograph at the Anglo-Australian Telescope. This release (hereafter GALAH+ DR3) includes all observations from GALAH Phase 1 (bright, main, and faint survey, 70 per cent), K2-HERMES (17 per cent), TESS-HERMES (5 per cent), and a subset of ancillary observations (8 per cent) including the bulge and >75 stellar clusters. We derive stellar parameters T
eff , log g , [Fe/H], vmic , vbroad , and vrad using our modified version of the spectrum synthesis code Spectroscopy Made Easy (sme) and 1D marcs model atmospheres. We break spectroscopic degeneracies in our spectrum analysis with astrometry from Gaia DR2 and photometry from 2MASS. We report abundance ratios [X/Fe] for 30 different elements (11 of which are based on non-LTE computations) covering five nucleosynthetic pathways. We describe validations for accuracy and precision, flagging of peculiar stars/measurements and recommendations for using our results. Our catalogue comprises 65 per cent dwarfs, 34 per cent giants, and 1 per cent other/unclassified stars. Based on unflagged chemical composition and age, we find 62 per cent young low- |$\alpha$| , 9 per cent young high- |$\alpha$| , 27 per cent old high- |$\alpha$| , and 2 per cent stars with [Fe/H] ≤ −1. Based on kinematics, 4 per cent are halo stars. Several Value-Added-Catalogues, including stellar ages and dynamics, updated after Gaia eDR3, accompany this release and allow chrono-chemodynamic analyses, as we showcase. [ABSTRACT FROM AUTHOR]- Published
- 2021
- Full Text
- View/download PDF
28. Exploring the Galaxy's halo and very metal-weak thick disc with SkyMapper and Gaia DR2.
- Author
-
Cordoni, G, Da Costa, G S, Yong, D, Mackey, A D, Marino, A F, Monty, S, Nordlander, T, Norris, J E, Asplund, M, Bessell, M S, Casey, A R, Frebel, A, Lind, K, Murphy, S J, Schmidt, B P, Gao, X D, Xylakis-Dornbusch, T, Amarsi, A M, and Milone, A P
- Subjects
GRAVITATIONAL interactions ,DWARF galaxies ,GALAXIES ,STELLAR orbits ,GRAVITATIONAL energy ,ASTROMETRY - Abstract
In this work, we combine spectroscopic information from the SkyMapper survey for Extremely Metal-Poor stars and astrometry from Gaia DR2 to investigate the kinematics of a sample of 475 stars with a metallicity range of |$-6.5 \le \rm [Fe/H] \le -2.05$| dex. Exploiting the action map, we identify 16 and 40 stars dynamically consistent with the Gaia Sausage and Gaia Sequoia accretion events, respectively. The most metal poor of these candidates have metallicities of |$\rm [Fe/H]=-3.31\, \mathrm{ and }\, -3.74$| , respectively, helping to define the low-metallicity tail of the progenitors involved in the accretion events. We also find, consistent with other studies, that ∼21 per cent of the sample have orbits that remain confined to within 3 kpc of the Galactic plane, that is, | Z
max | ≤ 3 kpc. Of particular interest is a subsample (∼11 per cent of the total) of low | Zmax | stars with low eccentricities and prograde motions. The lowest metallicity of these stars has [Fe/H] = –4.30 and the subsample is best interpreted as the very low-metallicity tail of the metal-weak thick disc population. The low | Zmax |, low eccentricity stars with retrograde orbits are likely accreted, while the low | Zmax |, high eccentricity pro- and retrograde stars are plausibly associated with the Gaia Sausage system. We find that a small fraction of our sample (∼4 per cent of the total) is likely escaping from the Galaxy, and postulate that these stars have gained energy from gravitational interactions that occur when infalling dwarf galaxies are tidally disrupted. [ABSTRACT FROM AUTHOR]- Published
- 2021
- Full Text
- View/download PDF
29. The SkyMapper DR1.1 search for extremely metal-poor stars
- Author
-
Da Costa, G S, primary, Bessell, M S, additional, Mackey, A D, additional, Nordlander, T, additional, Asplund, M, additional, Casey, A R, additional, Frebel, A, additional, Lind, K, additional, Marino, A F, additional, Murphy, S J, additional, Norris, J E, additional, Schmidt, B P, additional, and Yong, D, additional
- Published
- 2019
- Full Text
- View/download PDF
30. A hyper-runaway white dwarf in Gaia DR2 as a Type Iax supernova primary remnant candidate
- Author
-
Ruffini, Nicholas J, primary and Casey, Andrew R, additional
- Published
- 2019
- Full Text
- View/download PDF
31. Keck HIRES spectroscopy of SkyMapper commissioning survey candidate extremely metal-poor stars
- Author
-
Marino, A F, primary, Da Costa, G S, primary, Casey, A R, primary, Asplund, M, primary, Bessell, M S, primary, Frebel, A, primary, Keller, S C, primary, Lind, K, primary, Mackey, A D, primary, Murphy, S J, primary, Nordlander, T, primary, Norris, J E, primary, Schmidt, B P, primary, and Yong, D, primary
- Published
- 2019
- Full Text
- View/download PDF
32. The GALAH survey: co-orbiting stars and chemical tagging
- Author
-
Simpson, Jeffrey D, primary, Martell, Sarah L, additional, Da Costa, Gary, additional, Casey, Andrew R, additional, Freeman, Ken C, additional, Horner, Jonathan, additional, Ting, Yuan-Sen, additional, Nataf, David M, additional, Lewis, Geraint F, additional, Ness, Melissa K, additional, Zucker, Daniel B, additional, Cottrell, Peter L, additional, Čotar, Klemen, additional, Asplund, Martin, additional, Bland-Hawthorn, Joss, additional, Buder, Sven, additional, D’Orazi, Valentina, additional, De Silva, Gayandhi M, additional, Duong, Ly, additional, Kos, Janez, additional, Lin, Jane, additional, Lind, Karin, additional, Schlesinger, Katharine J, additional, Sharma, Sanjib, additional, Zwitter, Tomaž, additional, Kafle, Prajwal R, additional, and Nordlander, Thomas, additional
- Published
- 2018
- Full Text
- View/download PDF
33. The GALAH survey: temporal chemical enrichment of the galactic disc.
- Author
-
Lin, Jane, Asplund, Martin, Ting, Yuan-Sen, Casagrande, Luca, Buder, Sven, Bland-Hawthorn, Joss, Casey, Andrew R, De Silva, Gayandhi M, D'Orazi, Valentina, Freeman, Ken C, Kos, Janez, Lind, K, Martell, Sarah L, Sharma, Sanjib, Simpson, Jeffrey D, Zwitter, Tomaž, Zucker, Daniel B, Minchev, Ivan, Čotar, Klemen, and Hayden, Michael
- Subjects
MAIN sequence (Astronomy) ,STELLAR atmospheres ,NEUTRON stars ,STELLAR mergers ,STAR formation ,NEIGHBORHOODS - Abstract
We present isochrone ages and initial bulk metallicities (|$\rm [Fe/H]_{bulk}$| , by accounting for diffusion) of 163 722 stars from the GALAH Data Release 2, mainly composed of main-sequence turn-off stars and subgiants (|$7000\, \mathrm{ K}> T_{\mathrm{ eff}}> 4000\, \mathrm{ K}$| and |$\log g>3$| dex). The local age–metallicity relationship (AMR) is nearly flat but with significant scatter at all ages; the scatter is even higher when considering the observed surface abundances. After correcting for selection effects, the AMR appears to have intrinsic structures indicative of two star formation events, which we speculate are connected to the thin and thick discs in the solar neighbourhood. We also present abundance ratio trends for 16 elements as a function of age, across different |$\rm [Fe/H]_{bulk}$| bins. In general, we find the trends in terms of [X/Fe] versus age from our far larger sample to be compatible with studies based on small (∼100 stars) samples of solar twins, but we now extend them to both sub- and supersolar metallicities. The α-elements show differing behaviour: the hydrostatic α-elements O and Mg show a steady decline with time for all metallicities, while the explosive α-elements Si, Ca, and Ti are nearly constant during the thin-disc epoch (ages |$\lesssim \! 12$| Gyr). The s-process elements Y and Ba show increasing [X/Fe] with time while the r-process element Eu has the opposite trend, thus favouring a primary production from sources with a short time delay such as core-collapse supernovae over long-delay events such as neutron star mergers. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
34. The GALAH survey: accurate radial velocities and library of observed stellar template spectra
- Author
-
Zwitter, Tomaž, primary, Kos, Janez, additional, Chiavassa, Andrea, additional, Buder, Sven, additional, Traven, Gregor, additional, Čotar, Klemen, additional, Lin, Jane, additional, Asplund, Martin, additional, Bland-Hawthorn, Joss, additional, Casey, Andrew R, additional, De Silva, Gayandhi, additional, Duong, Ly, additional, Freeman, Kenneth C, additional, Lind, Karin, additional, Martell, Sarah, additional, D’Orazi, Valentina, additional, Schlesinger, Katharine J, additional, Simpson, Jeffrey D, additional, Sharma, Sanjib, additional, Zucker, Daniel B, additional, Anguiano, Borja, additional, Casagrande, Luca, additional, Collet, Remo, additional, Horner, Jonathan, additional, Ireland, Michael J, additional, Kafle, Prajwal R, additional, Lewis, Geraint, additional, Munari, Ulisse, additional, Nataf, David M, additional, Ness, Melissa, additional, Nordlander, Thomas, additional, Stello, Dennis, additional, Ting, Yuan-Sen, additional, Tinney, Chris G, additional, Watson, Fred, additional, Wittenmyer, Rob A, additional, and Žerjal, Maruša, additional
- Published
- 2018
- Full Text
- View/download PDF
35. Holistic spectroscopy: complete reconstruction of a wide-field, multiobject spectroscopic image using a photonic comb
- Author
-
Kos, Janez, primary, Bland-Hawthorn, Joss, additional, Betters, Christopher H, additional, Leon-Saval, Sergio, additional, Asplund, Martin, additional, Buder, Sven, additional, Casey, Andrew R, additional, D’Orazi, Valentina, additional, de Silva, Gayandhi, additional, Freeman, Ken, additional, Lewis, Geraint, additional, Lin, Jane, additional, Martell, Sarah L, additional, Schlesinger, Katharine, additional, Sharma, Sanjib, additional, Simpson, Jeffrey D, additional, Zucker, Daniel, additional, Zwitter, Tomaž, additional, Hayden, Michael, additional, Horner, Jonathan, additional, Nataf, David M, additional, and Ting, Yuan-Sen, additional
- Published
- 2018
- Full Text
- View/download PDF
36. On the discovery of K-enhanced and possibly Mg-depleted stars throughout the Milky Way
- Author
-
Kemp, Alex J, primary, Casey, Andrew R, additional, Miles, Matthew T, additional, Norfolk, Brodie J, additional, Lattanzio, John C, additional, Karakas, Amanda I, additional, Schlaufman, Kevin C, additional, Ho, Anna Y Q, additional, Tout, Christopher A, additional, Ness, Melissa, additional, and Ji, Alexander P, additional
- Published
- 2018
- Full Text
- View/download PDF
37. Snake in the Clouds: a new nearby dwarf galaxy in the Magellanic bridge*
- Author
-
Koposov, Sergey E, primary, Walker, Matthew G, additional, Belokurov, Vasily, additional, Casey, Andrew R, additional, Geringer-Sameth, Alex, additional, Mackey, Dougal, additional, Da Costa, Gary, additional, Erkal, Denis, additional, Jethwa, Prashin, additional, Mateo, Mario, additional, Olszewski, Edward W, additional, and Bailey, John I, additional
- Published
- 2018
- Full Text
- View/download PDF
38. Infrared colours and inferred masses of metal-poor giant stars in the Kepler field
- Author
-
Casey, A R, primary, Kennedy, G M, additional, Hartle, T R, additional, and Schlaufman, Kevin C, additional
- Published
- 2018
- Full Text
- View/download PDF
39. The Gaia-ESO Survey: evidence of atomic diffusion in M67?
- Author
-
Bertelli Motta, C, primary, Pasquali, A, additional, Richer, J, additional, Michaud, G, additional, Salaris, M, additional, Bragaglia, A, additional, Magrini, L, additional, Randich, S, additional, Grebel, E K, additional, Adibekyan, V, additional, Blanco-Cuaresma, S, additional, Drazdauskas, A, additional, Fu, X, additional, Martell, S, additional, Tautvaišienė, G, additional, Gilmore, G, additional, Alfaro, E J, additional, Bensby, T, additional, Flaccomio, E, additional, Koposov, S E, additional, Korn, A J, additional, Lanzafame, A C, additional, Smiljanic, R, additional, Bayo, A, additional, Carraro, G, additional, Casey, A R, additional, Costado, M T, additional, Damiani, F, additional, Franciosini, E, additional, Heiter, U, additional, Hourihane, A, additional, Jofré, P, additional, Lardo, C, additional, Lewis, J, additional, Monaco, L, additional, Morbidelli, L, additional, Sacco, G G, additional, Sousa, S G, additional, Worley, C C, additional, and Zaggia, S, additional
- Published
- 2018
- Full Text
- View/download PDF
40. The TESS–HERMES survey data release 1: high-resolution spectroscopy of the TESS southern continuous viewing zone
- Author
-
Sharma, Sanjib, primary, Stello, Dennis, additional, Buder, Sven, additional, Kos, Janez, additional, Bland-Hawthorn, Joss, additional, Asplund, Martin, additional, Duong, Ly, additional, Lin, Jane, additional, Lind, Karin, additional, Ness, Melissa, additional, Huber, Daniel, additional, Zwitter, Tomaz, additional, Traven, Gregor, additional, Hon, Marc, additional, Kafle, Prajwal R., additional, Khanna, Shourya, additional, Saddon, Hafiz, additional, Anguiano, Borja, additional, Casey, Andrew R., additional, Freeman, Ken, additional, Martell, Sarah, additional, De Silva, Gayandhi M., additional, Simpson, Jeffrey D., additional, Wittenmyer, Rob A., additional, and Zucker, Daniel B., additional
- Published
- 2017
- Full Text
- View/download PDF
41. The Gaia-ESO Survey: matching chemodynamical simulations to observations of the Milky Way
- Author
-
Thompson, B. B., primary, Few, C. G., additional, Bergemann, M., additional, Gibson, B. K., additional, MacFarlane, B. A., additional, Serenelli, A., additional, Gilmore, G., additional, Randich, S., additional, Vallenari, A., additional, Alfaro, E. J., additional, Bensby, T., additional, Francois, P., additional, Korn, A. J., additional, Bayo, A., additional, Carraro, G., additional, Casey, A. R., additional, Costado, M. T., additional, Donati, P., additional, Franciosini, E., additional, Frasca, A., additional, Hourihane, A., additional, Jofré, P., additional, Hill, V., additional, Heiter, U., additional, Koposov, S. E., additional, Lanzafame, A., additional, Lardo, C., additional, de Laverny, P., additional, Lewis, J., additional, Magrini, L., additional, Marconi, G., additional, Masseron, T., additional, Monaco, L., additional, Morbidelli, L., additional, Pancino, E., additional, Prisinzano, L., additional, Recio-Blanco, A., additional, Sacco, G., additional, Sousa, S. G., additional, Tautvaišienė, G., additional, Worley, C. C., additional, and Zaggia, S., additional
- Published
- 2017
- Full Text
- View/download PDF
42. The Gaia–ESO Survey: dynamical models of flattened, rotating globular clusters
- Author
-
Jeffreson, S. M. R., primary, Sanders, J. L., additional, Evans, N. W., additional, Williams, A. A., additional, Gilmore, G. F., additional, Bayo, A., additional, Bragaglia, A., additional, Casey, A. R., additional, Flaccomio, E., additional, Franciosini, E., additional, Hourihane, A., additional, Jackson, R. J., additional, Jeffries, R. D., additional, Jofré, P., additional, Koposov, S., additional, Lardo, C., additional, Lewis, J., additional, Magrini, L., additional, Morbidelli, L., additional, Pancino, E., additional, Randich, S., additional, Sacco, G. G., additional, Worley, C. C., additional, and Zaggia, S., additional
- Published
- 2017
- Full Text
- View/download PDF
43. On the run: mapping the escape speed across the Galaxy with SDSS
- Author
-
Williams, Angus A., primary, Belokurov, Vasily, additional, Casey, Andrew R., additional, and Evans, N. Wyn, additional
- Published
- 2017
- Full Text
- View/download PDF
44. The mass distribution of Population III stars
- Author
-
Fraser, M., primary, Casey, A. R., additional, Gilmore, G., additional, Heger, A., additional, and Chan, C., additional
- Published
- 2017
- Full Text
- View/download PDF
45. Sc and neutron-capture abundances in Galactic low- and high-α field halo stars
- Author
-
Fishlock, C. K., primary, Yong, D., additional, Karakas, A. I., additional, Alves-Brito, A., additional, Meléndez, J., additional, Nissen, P. E., additional, Kobayashi, C., additional, and Casey, A. R., additional
- Published
- 2017
- Full Text
- View/download PDF
46. The GALAH survey: observational overview andGaiaDR1 companion
- Author
-
Martell, S. L., primary, Sharma, S., additional, Buder, S., additional, Duong, L., additional, Schlesinger, K. J., additional, Simpson, J., additional, Lind, K., additional, Ness, M., additional, Marshall, J. P., additional, Asplund, M., additional, Bland-Hawthorn, J., additional, Casey, A. R., additional, De Silva, G., additional, Freeman, K. C., additional, Kos, J., additional, Lin, J., additional, Zucker, D. B., additional, Zwitter, T., additional, Anguiano, B., additional, Bacigalupo, C., additional, Carollo, D., additional, Casagrande, L., additional, Da Costa, G. S., additional, Horner, J., additional, Huber, D., additional, Hyde, E. A., additional, Kafle, P. R., additional, Lewis, G. F., additional, Nataf, D., additional, Navin, C. A., additional, Stello, D., additional, Tinney, C. G., additional, Watson, F. G., additional, and Wittenmyer, R., additional
- Published
- 2016
- Full Text
- View/download PDF
47. GALAH survey and Gaia DR2: dissecting the stellar disc's phase space by age, action, chemistry, and location.
- Author
-
Bland-Hawthorn, Joss, Sharma, Sanjib, Tepper-Garcia, Thor, Binney, James, Freeman, Ken C, Hayden, Michael R, Kos, Janez, De Silva, Gayandhi M, Ellis, Simon, Lewis, Geraint F, Asplund, Martin, Buder, Sven, Casey, Andrew R, D'Orazi, Valentina, Duong, Ly, Khanna, Shourya, Lin, Jane, Lind, Karin, Martell, Sarah L, and Ness, Melissa K
- Subjects
PHASE space ,ASTROMETRY ,CHEMISTRY ,DISK galaxies ,DISTRIBUTION of stars ,STELLAR dynamics - Abstract
We use the second data releases of the European Space Agency Gaia astrometric survey and the high-resolution Galactic Archaeology with HERMES (GALAH) spectroscopic survey to analyse the structure of our Galaxy's disc components. With GALAH, we separate the α-rich and α-poor discs (with respect to Fe), which are superposed in both position and velocity space, and examine their distributions in action space. We study the distribution of stars in the zV
|$\mathrm{ z}$| phase plane, for both Vϕ and VR , and recover the remarkable 'phase spiral' discovered by Gaia. We identify the anticipated quadrupole signature in zV|$\mathrm{ z}$| of a tilted velocity ellipsoid for stars above and below the Galactic plane. By connecting our work with earlier studies, we show that the phase spiral is likely to extend well beyond the narrow solar neighbourhood cylinder in which it was found. The phase spiral is a signature of corrugated waves that propagate through the disc, and the associated non-equilibrium phase mixing. The radially asymmetric distribution of stars involved in the phase spiral reveals that the corrugation, which is mostly confined to the α-poor disc, grows in z -amplitude with increasing radius. We present new simulations of tidal disturbance of the Galactic disc by the Sagittarius (Sgr) dwarf. The effect on the zV|$\mathrm{ z}$| phase plane lasts |${\gtrsim } 2\, \mathrm{Gyr}$|, but a subsequent disc crossing wipes out the coherent structure. We find that the phase spiral was excited |${\lesssim } 0.5\, \mathrm{Gyr}$| ago by an object like Sgr with total mass ∼3 × 1010 M⊙ (stripped down from ∼5 × 1010 M⊙ when it first entered the halo) passing through the plane. [ABSTRACT FROM AUTHOR]- Published
- 2019
- Full Text
- View/download PDF
48. The GALAH survey: co-orbiting stars and chemical tagging.
- Author
-
Simpson, Jeffrey D, Martell, Sarah L, Da Costa, Gary, Casey, Andrew R, Freeman, Ken C, Horner, Jonathan, Ting, Yuan-Sen, Nataf, David M, Lewis, Geraint F, Ness, Melissa K, Zucker, Daniel B, Cottrell, Peter L, Čotar, Klemen, Asplund, Martin, Bland-Hawthorn, Joss, Buder, Sven, D'Orazi, Valentina, De Silva, Gayandhi M, Duong, Ly, and Kos, Janez
- Subjects
STELLAR orbits ,STAR formation ,BINARY stars ,DISKS (Astrophysics) ,MILKY Way - Abstract
We present a study using the second data release of the GALAH survey of stellar parameters and elemental abundances of 15 pairs of stars identified by Oh et al. They identified these pairs as potentially co-moving pairs using proper motions and parallaxes from Gaia DR1. We find that 11 very wide (>1 pc) pairs of stars do in fact have similar Galactic orbits, while a further four claimed co-moving pairs are not truly co-orbiting. Eight of the 11 co-orbiting pairs have reliable stellar parameters and abundances, and we find that three of those are quite similar in their abundance patterns, while five have significant [Fe/H] differences. For the latter, this indicates that they could be co-orbiting because of the general dynamical coldness of the thin disc, or perhaps resonances induced by the Galaxy, rather than a shared formation site. Stars such as these, wide binaries, debris of past star formation episodes, and coincidental co-orbiters, are crucial for exploring the limits of chemical tagging in the Milky Way. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
49. The Gaia-ESO Survey: lithium depletion in the Gamma Velorum cluster and inflated radii in low-mass pre-main-sequence stars
- Author
-
Jeffries, R. D., primary, Jackson, R. J., additional, Franciosini, E., additional, Randich, S., additional, Barrado, D., additional, Frasca, A., additional, Klutsch, A., additional, Lanzafame, A. C., additional, Prisinzano, L., additional, Sacco, G. G., additional, Gilmore, G., additional, Vallenari, A., additional, Alfaro, E. J., additional, Koposov, S. E., additional, Pancino, E., additional, Bayo, A., additional, Casey, A. R., additional, Costado, M. T., additional, Damiani, F., additional, Hourihane, A., additional, Lewis, J., additional, Jofre, P., additional, Magrini, L., additional, Monaco, L., additional, Morbidelli, L., additional, Worley, C. C., additional, Zaggia, S., additional, and Zwitter, T., additional
- Published
- 2016
- Full Text
- View/download PDF
50. The GALAH survey: the data reduction pipeline
- Author
-
Kos, Janez, primary, Lin, Jane, additional, Zwitter, Tomaž, additional, Žerjal, Maruška, additional, Sharma, Sanjib, additional, Bland-Hawthorn, Joss, additional, Asplund, Martin, additional, Casey, Andrew R., additional, De Silva, Gayandhi M., additional, Freeman, Ken C., additional, Martell, Sarah L., additional, Simpson, Jeffrey D., additional, Schlesinger, Katharine J., additional, Zucker, Daniel, additional, Anguiano, Borja, additional, Bacigalupo, Carlos, additional, Bedding, Timothy R., additional, Betters, Christopher, additional, Da Costa, Gary, additional, Duong, Ly, additional, Hyde, Elaina, additional, Ireland, Michael, additional, Kafle, Prajwal R., additional, Leon-Saval, Sergio, additional, Lewis, Geraint F., additional, Munari, Ulisse, additional, Nataf, David, additional, Stello, Dennis, additional, Tinney, C. G., additional, Traven, Gregor, additional, Watson, Fred, additional, and Wittenmyer, Robert A., additional
- Published
- 2016
- Full Text
- View/download PDF
Catalog
Discovery Service for Jio Institute Digital Library
For full access to our library's resources, please sign in.