Siriusly, a newly identified intermediate-age Milky Way stellar cluster: a spectroscopic study of Gaia 1

Simpson, Jeffrey D.; Silva, G. M. De; Martell, Sarah L.; Zucker, D. B.; Ferguson, Annette M. N.; Bernard, Edouard J.; Irwin, M. J.; Peñarrubia, Jorge; Tolstoy, Eline

doi:10.1093/mnras/stx1892

Cited by 12 publications

(24 citation statements)

References 57 publications

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“…Subsequently, Mucciarelli et al (2017) measured chemical abundances of six stars in Gaia 1, suggesting an equally high metallicity, but based on their abundance study, the suggestion of an extragalactic origin was revoked. While a more metal-rich nature found by the latter authors conformed with the results by Simpson et al (2017), the evolutionary diagrams of both studies are very dissimilar and could not be explained by one simple isochrone fit. In particular, it was noted that "the Simpson et al (2017) stars do not define a red giant branch in the theoretical plane, suggesting that their parameters are not correct" (Fig.…”

Section: Introductionsupporting

confidence: 83%

“…While a more metal-rich nature found by the latter authors conformed with the results by Simpson et al (2017), the evolutionary diagrams of both studies are very dissimilar and could not be explained by one simple isochrone fit. In particular, it was noted that "the Simpson et al (2017) stars do not define a red giant branch in the theoretical plane, suggesting that their parameters are not correct" (Fig. 1 of Mucciarelli et al 2017).…”

Section: Introductionsupporting

confidence: 83%

“…Thence, this object was characterized by Koposov et al (2017) as a star cluster, most likely of the globular confession. Further investigation of Gaia 1 found a metallicity higher by more than 0.5 dex, which challenged the previous age measurement and rather characterized it as a young (3 Gyr), metalrich (−0.1 dex) object, possibly of extragalactic origin given its orbit that leads it up to ∼1.7 kpc above the disk (Simpson et al 2017). Subsequently, Mucciarelli et al (2017) measured chemical abundances of six stars in Gaia 1, suggesting an equally high metallicity, but based on their abundance study, the suggestion of an extragalactic origin was revoked.…”

Section: Introductionmentioning

confidence: 62%

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Detailed chemical abundance analysis of the thick disk star cluster Gaia 1

Koch

Hansen

Kunder

2017

A&A

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Star clusters, particularly those objects in the disk-bulge-halo interface are as of yet poorly charted, albeit carrying important information about the formation and the structure of the Milky Way. Here, we present a detailed chemical abundance study of the recently discovered object Gaia 1. Photometry has previously suggested it as an intermediate-age, moderately metal-rich system, although the exact values for its age and metallicity remained ambiguous in the literature. We measured detailed chemical abundances of 14 elements in four red giant members, from high-resolution (R=25000) spectra that firmly establish Gaia 1 as an object associated with the thick disk. The resulting mean Fe abundance is −0.62±0.03(stat.)±0.10(sys.) dex, which is more metal-poor than indicated by previous spectroscopy from the literature, but it is fully in line with values from isochrone fitting. We find that Gaia 1 is moderately enhanced in the α-elements, which allowed us to consolidate its membership with the thick disk via chemical tagging. The cluster's Fe-peak and neutron-capture elements are similar to those found across the metal-rich disks, where the latter indicate some level of s-process activity. No significant spread in iron nor in other heavy elements was detected, whereas we find evidence of light-element variations in Na, Mg, and Al. Nonetheless, the traditional Na-O and Mg-Al (anti-)correlations, typically seen in old globular clusters, are not seen in our data. This confirms that Gaia 1 is rather a massive and luminous open cluster than a low-mass globular cluster. Finally, orbital computations of the target stars bolster our chemical findings of Gaia 1's present-day membership with the thick disk, even though it remains unclear, which mechanisms put it in that place.

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Section: Introductionsupporting

confidence: 83%

Section: Introductionsupporting

confidence: 83%

Section: Introductionmentioning

confidence: 62%

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Detailed chemical abundance analysis of the thick disk star cluster Gaia 1

Koch

Hansen

Kunder

2017

A&A

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“…The O M software developed by the team is used to select a field that will be near the meridian at the time of observation. This field is required to be at least 30 degrees from the Moon, to have a relatively small change in airmass over the exposure time, and to have no Solar System planets within it at the time of observation (as bright sources such as Jupiter have caused trouble with scattered light contaminating spectra in previous 2dF survey observations, though HERMES has been found to suffer much less from this than AAOmega; see Simpson et al 2017). Fiducial targets, used for field acquisition and guiding, are chosen from the stars with 11 V 12 in the input catalogue that are located in the field.…”

Section: Observationsmentioning

confidence: 99%

The GALAH Survey: second data release

Buder

Asplund

Duong

et al. 2018

Monthly Notices of the Royal Astronomical Society

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370

447

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The Galactic Archaeology with HERMES (GALAH) survey is a large-scale stellar spectroscopic survey of the Milky Way and designed to deliver chemical information complementary to a large number of stars covered by the Gaia mission. We present the GALAH second public data release (GALAH DR2) containing 342,682 stars. For these stars, the GALAH collaboration provides stellar parameters and abundances for up to 23 elements to the community. Here we present the target selection, observation, data reduction and detailed explanation of how the spectra were analysed to estimate stellar parameters and element abundances. For the stellar analysis, we have used a multi-step approach. We use the physics-driven spectrum synthesis of Spectroscopy Made Easy (SME) to derive stellar labels (T eff , log g, [Fe/H], [X/Fe], v mic , v sin i, A K S ) for a representative training set of stars. This information is then propagated to the whole survey with the data-driven method of The Cannon. Special care has been exercised in the spectral synthesis to only consider spectral lines that have reliable atomic input data and are little affected by blending lines. Departures from local thermodynamic equilibrium (LTE) are considered for several key elements, including Li, O, Na, Mg, Al, Si, and Fe, using 1D stellar atmosphere models. Validation tests including repeat observations, Gaia benchmark stars, open and globular clusters, and K2 asteroseismic targets lend confidence to our methods and results. Combining the GALAH DR2 catalogue with the kinematic information from Gaia will enable a wide range of Galactic Archaeology studies, with unprecedented detail, dimensionality, and scope.

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“…The second data release of the Gaia mission (Prusti et al 2016;Brown et al 2018) has revolutionized our view of the Milky Way Galaxy. Among its many results, it has proven very useful for investigating purported stellar clusters, in many cases confirming their existence (e.g., Simpson et al 2017b;Soubiran et al 2018;Cantat-Gaudin et al 2018), but in some cases showing they are not real physical associations (e.g., Kos et al 2018). The precise proper motions are especially helpful in the Milky Way bulge, where imaging surveys are hampered by the large and differential reddening and extinction, resulting in clusters hidden from easy view.…”

Section: Introductionmentioning

confidence: 99%

The retrograde orbit of the globular cluster FSR1758 revealed with Gaia DR2

Simpson

2019

Monthly Notices of the Royal Astronomical Society

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We report the first radial velocity measurements of the recently identified globular cluster FSR1758. From the two member stars with radial velocities from the Gaia Radial Velocity Spectrograph reported in Gaia DR2, we find FSR1758 has a radial velocity of 227 ± 1km s −1 . We also find potential extra-tidal star lost from the cluster in the surrounding 1 deg. Combined with Gaia proper motions and photometric distance estimates, this shows that FSR1758 is on a relatively retrograde, radial orbit with an pericentre of 3.8 +0.9 −0.9 kpc, an apocentre of 16 +8 −5 kpc, and eccentricity of 0.62 +0.05 −0.04 . Although it is currently at a Galactocentric distance of 3.8 +0.9 −0.9 kpc -at the edge of the bulge -it is an intruder from the halo. We investigate whether a reported 'halo' of stars around FSR1758 is related to the cluster, and find that most of these stars are likely foreground dwarf stars. We conclude that FSR1758 is not a dwarf galaxy, but rather a globular cluster.

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Siriusly, a newly identified intermediate-age Milky Way stellar cluster: a spectroscopic study of Gaia 1

Cited by 12 publications

References 57 publications

Detailed chemical abundance analysis of the thick disk star cluster Gaia 1

Detailed chemical abundance analysis of the thick disk star cluster Gaia 1

The GALAH Survey: second data release

The retrograde orbit of the globular cluster FSR1758 revealed with Gaia DR2

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