Blanco DECam Bulge Survey (BDBS)

Marchetti, Tommaso; Johnson, Christian I.; Joyce, Meridith; Rich, R. Michael; Simion, Iulia T.; Young, Michael D.; Clarkson, W. I.; Pilachowksi, C. A.; Michael, S.; Kunder, Andrea; Koch-Hansen, A. J.

doi:10.1051/0004-6361/202243921

Cited by 10 publications

(10 citation statements)

References 134 publications

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“…Hasselquist et al (2020) use a large sample of APOGEE data to argue that a large fraction of the bulge-at least half their sample-is old (>8 Gyr), and that the population of young (2-5 Gyr) stars they do find is strongly constrained to the Galactic plane. The present work, along with Marchetti et al (2022), do not confirm the presence of such young stars. However, we note that Marchetti et al (2022) does not sample inside b ∼ −3°.5, where young stars may be more prevalent.…”

Section: Implications Of Our Derived Agescontrasting

confidence: 87%

“…The present work, along with Marchetti et al (2022), do not confirm the presence of such young stars. However, we note that Marchetti et al (2022) does not sample inside b ∼ −3°.5, where young stars may be more prevalent. On the other hand, the B17 sample analyzed here shows no significant correlation between age and Galactic latitude.…”

Section: Implications Of Our Derived Agescontrasting

confidence: 87%

“…However, the most luminous late-type stars are extremely concentrated to the Galactic center (Blommaert & Groenewegen 2007). This work and our foreground cleaning of disk stars from the Galactic bulge (Marchetti et al 2022) argue strongly against a significant population of main-sequence progenitors younger than 3 Gyr. Considering the lack of main-sequence progenitor candidates, we conclude that no substantial population of massive, evolved AGB stars is present in large numbers in the bulge.…”

Section: Implications Of Our Derived Agesmentioning

confidence: 63%

“…For each of the five stars, we compute its probability to belong kinematically to the bulge based on its Galactic proper motions (μ ℓ* , μ b ), which we determine by fitting the distribution in proper motion for all the stars within 0°. 5 from the center of the fields presented in Marchetti et al (2022). By this metric, we find OGLE-2013-BLG-0692S to be the only star with a probability marginally lower than 50% of belonging to the bulge, P bulge = 0.48.…”

Section: A2 Gaia Photometrymentioning

confidence: 69%

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The Ages of Galactic Bulge Stars with Realistic Uncertainties

Joyce

Johnson

Marchetti

et al. 2023

ApJ

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Using modern isochrones with customized physics and carefully considered statistical techniques, we recompute the age distribution for a sample of 91 microlensed dwarfs in the Galactic bulge presented by Bensby et al. and do not produce an age distribution consistent with their results. In particular, our analysis finds that only 15 of 91 stars have ages younger than 7 Gyr, compared to their finding of 42 young stars in the same sample. While we do not find a constituency of very young stars, our results do suggest the presence of an ∼8 Gyr population at the highest metallicities, thus contributing to the long-standing debate about the age–metallicity distribution of the Galactic bulge. We supplement this with attempts at independent age determinations from two sources of photometry, BDBS and Gaia, but find that the imprecision of photometric measurements prevents reliable age and age uncertainty determinations. Lastly, we present age uncertainties derived using a first-order consideration of global modeling uncertainties in addition to standard observational uncertainties. The theoretical uncertainties are based on the known variance of free parameters in the 1D stellar evolution models used to generate isochrones, and when included, result in age uncertainties of 2–5 Gyr for this spectroscopically well-constrained sample. These error bars, which are roughly twice as large as typical literature values, constitute realistic lower limits on the true age uncertainties.

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Section: Implications Of Our Derived Agescontrasting

confidence: 87%

Section: Implications Of Our Derived Agescontrasting

confidence: 87%

Section: Implications Of Our Derived Agesmentioning

confidence: 63%

Section: A2 Gaia Photometrymentioning

confidence: 69%

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The Ages of Galactic Bulge Stars with Realistic Uncertainties

Joyce

Johnson

Marchetti

et al. 2023

ApJ

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“…The BDBS point-source photometry used in this project is from the most recent BDBS-Gaia EDR3 (Gaia Collaboration et al 2018 crossmatched catalog (Marchetti et al 2022). We start by collecting BDBS-Gaia EDR3 crossmatched point sources from within 10 half-light radii (r h ) of each cluster center.…”

Section: Gaia Matching and Pm Cluster Membership Criterionmentioning

confidence: 99%

Blanco DECam Bulge Survey (BDBS). VII. Multiple Populations in Globular Clusters of the Galactic Bulge

Kader

Pilachowski

Johnson

et al. 2022

ApJ

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We present photometric evidence for multiple stellar populations (MPs) in 14 globular clusters (GCs) toward the southern Galactic bulge. The photometric data come as part of the Blanco DECam Bulge Survey, which is a deep, wide-field near-UV-near-IR (ugrizY) survey of the southern Galactic bulge. Here, we present the first systematic study of bulge GC multiple populations with deep photometry including the u band, which is a crucial indicator of the abundance of CNO-bearing molecules in stellar atmospheres. We identify cluster members using Gaia EDR3 proper motion measurements, and then isolate red giant branch stars using r versus u − r color–magnitude diagrams. We find evidence suggesting all 14 clusters host at least two populations, and NGC 6441, NGC 6626, and NGC 6656 appear to have at least three populations. Many of these clusters are not part of the Hubble Space Telescope (HST) surveys nor do they have comprehensive spectroscopic analyses so we are presenting the first evidence of MPs in several clusters. Not only do we find a strong anticorrelation between the fraction of first-generation stars and cluster absolute V magnitude, but the correlation coefficient and cluster-to-cluster scatter are similar to the results obtained from HST. Our ground-based data extend to much larger radial distances than similar HST observations, enabling a reliable estimate of the global fraction of first-generation stars in each cluster. This study demonstrates that ground-based u-band photometry as provided by DECam will prove powerful in the study of multiple populations in resolved GCs.

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Astrometry in crowded fields towards the Galactic bulge

Luna¹,

Marchetti²,

Rejkuba³

et al. 2023

A&A

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Context. The astrometry towards the Galactic bulge is hampered by high stellar crowding and patchy extinction. This effect is particularly severe for optical surveys such as the European Space Agency satellite Gala. Aims. In this study, we assess the consistency of proper motion measurements between optical (Gaia DR3) and near-infrared (VIRAC2) catalogues in comparison with proper motions measured with the Hubble Space Telescope (HST) observations in several crowded fields towards the Galactic bulge and in Galactic globular clusters. Methods. Assuming that the proper motion measurements are well characterised, the uncertainty-normalised proper motion differences between pairs of catalogues are expected to follow a normal distribution. A deviation from a normal distribution defines the inflation factor r. By multiplying the proper motion uncertainties with the appropriate inflation factor values, the Gaia (VIRAC2) proper motion measurements are brought into a 1σ agreement with the HST proper motions. Results. The inflation factor (r) depends on stellar surface density. For the brightest stars in our sample (G < 18), the dependence on G-band magnitude is strong, corresponding to the most precise Gaia DR3 proper motions. We used the number of observed Gaia DR3 sources as a proxy for the stellar surface density. Assuming that the HST proper motion measurements are well determined and free from systematic errors, we find that Gaia DR3 proper motion uncertainties are better characterised, having r < 1.5 in fields with a stellar number density with fewer than 200 Gaia DR3 sources per arcmin2, and are underestimated by up to a factor of 4 in fields with stellar densities higher than 300 sources per arcmin2. For the most crowded fields in VIRAC2, the proper motion uncertainties are underestimated by a factor of 1.1 up to 1.5, with a dependence on J-band magnitude. In all fields, the brighter sources have the higher r value. At the faint end (G > 19), the inflation factor is close to 1, meaning that the proper motions already fully agree with the HST measurements within 1σ. Conclusions. In the crowded fields common to both catalogues, VIRAC2 proper motions agree with HST proper motions and do not need an inflation factor for their uncertainties. Because of the depth and completeness of VIRAC2 in these fields, it is an ideal complement to Gaia DR3 for proper motion studies towards the Galactic bulge.

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Blanco DECam Bulge Survey (BDBS)

Cited by 10 publications

References 134 publications

The Ages of Galactic Bulge Stars with Realistic Uncertainties

The Ages of Galactic Bulge Stars with Realistic Uncertainties

Blanco DECam Bulge Survey (BDBS). VII. Multiple Populations in Globular Clusters of the Galactic Bulge

Astrometry in crowded fields towards the Galactic bulge

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