The Open Cluster Chemical Abundances and Mapping (OCCAM) survey aims to constrain key Galactic dynamical and chemical evolution parameters by the construction of a large, comprehensive, uniform, ...infrared-based spectroscopic data set of hundreds of open clusters. This fourth contribution from the OCCAM survey presents analysis using Sloan Digital Sky Survey/APOGEE DR16 of a sample of 128 open clusters, 71 of which we designate to be "high quality" based on the appearance of their color-magnitude diagram. We find the APOGEE DR16 derived Fe/H abundances to be in good agreement with previous high-resolution spectroscopic open cluster abundance studies. Using the high-quality sample, we measure Galactic abundance gradients in 16 elements, and find evolution of some of the X/Fe gradients as a function of age. We find an overall Galactic Fe/H versus RGC gradient of −0.068 0.001 dex kpc−1 over the range of 6 < RGC < 13.9 kpc; however, we note that this result is sensitive to the distance catalog used, varying as much as 15%. We formally derive the location of a break in the Fe/H abundance gradient as a free parameter in the gradient fit for the first time. We also measure significant Galactic gradients in O, Mg, S, Ca, Mn, Cr, Cu, Na, Al, and K, some of which are measured for the first time. Our large sample allows us to examine four well-populated age bins in order to explore the time evolution of gradients for a large number of elements and comment on possible implications for Galactic chemical evolution and radial migration.
ABSTRACT
Metal-poor stars are important tools for tracing the early history of the Milky Way, and for learning about the first generations of stars. Simulations suggest that the oldest metal-poor ...stars are to be found in the inner Galaxy. Typical bulge surveys, however, lack low metallicity ($\rm {Fe/H} \lt -1.0$) stars because the inner Galaxy is predominantly metal-rich. The aim of the Pristine Inner Galaxy Survey (PIGS) is to study the metal-poor and very metal-poor (VMP, $\rm {Fe/H} \lt -2.0$) stars in this region. In PIGS, metal-poor targets for spectroscopic follow-up are selected from metallicity-sensitive CaHK photometry from the CFHT. This work presents the ∼250 deg2 photometric survey as well as intermediate-resolution spectroscopic follow-up observations for ∼8000 stars using AAOmega on the AAT. The spectra are analysed using two independent tools: ULySS with an empirical spectral library, and FERRE with a library of synthetic spectra. The comparison between the two methods enables a robust determination of the stellar parameters and their uncertainties. We present a sample of 1300 VMP stars – the largest sample of VMP stars in the inner Galaxy to date. Additionally, our spectroscopic data set includes ∼1700 horizontal branch stars, which are useful metal-poor standard candles. We furthermore show that PIGS photometry selects VMP stars with unprecedented efficiency: 86 per cent/80 per cent (lower/higher extinction) of the best candidates satisfy $\rm {Fe/H} \lt -2.0$, as do 80 per cent/63 per cent of a larger, less strictly selected sample. We discuss future applications of this unique data set that will further our understanding of the chemical and dynamical evolution of the innermost regions of our Galaxy.
Abstract
APOGEE is a high-resolution (
R
∼ 22,000), near-infrared, multi-epoch, spectroscopic survey of the Milky Way. The second generation of the APOGEE project, APOGEE-2, includes an expansion of ...the survey to the Southern Hemisphere called APOGEE-2S. This expansion enabled APOGEE to perform a fully panoramic mapping of all of the main regions of the Milky Way; in particular, by operating in the
H
band, APOGEE is uniquely able to probe the dust-hidden inner regions of the Milky Way that are best accessed from the Southern Hemisphere. In this paper we present the targeting strategy of APOGEE-2S, with special attention to documenting modifications to the original, previously published plan. The motivation for these changes is explained as well as an assessment of their effectiveness in achieving their intended scientific objective. In anticipation of this being the last paper detailing APOGEE targeting, we present an accounting of all such information complete through the end of the APOGEE-2S project; this includes several main survey programs dedicated to exploration of major stellar populations and regions of the Milky Way, as well as a full list of programs contributing to the APOGEE database through allocations of observing time by the Chilean National Time Allocation Committee and the Carnegie Institution for Science. This work was presented along with a companion article, Beaton et al. (2021), presenting the final target selection strategy adopted for APOGEE-2 in the Northern Hemisphere.
We present chemical abundances of Al and several Fe-Peak and neutron-capture elements for 13 red giant branch stars in the Galactic globular cluster NGC 6171 (M107). The abundances were determined ...using equivalent width and spectrum synthesis analyses of moderate-resolution (
R ∼ 15,000
R
∼
15
,
000
), moderate signal-to-noise ratio (〈S/N〉 ∼ 80
〈
S
/
N
〉
∼
80
) spectra obtained with the WIYN telescope and Hydra multifiber spectrograph. A comparison between photometric and spectroscopic effective temperature estimates seems to indicate that a reddening value of
E(B - V) = 0.46
E
(
B
-
V
)
=
0.46
may be more appropriate for this cluster than the more commonly used value of
E(B - V) = 0.33
E
(
B
-
V
)
=
0.33
. Similarly, we found that a distance modulus of(m - M)V ≈ 13.7
(
m
-
M
)
V
≈
13.7
provided reasonable surface gravity estimates for the stars in our sample. Our spectroscopic analysis finds M107 to be moderately metal-poor with〈Fe/H〉 = -0.93
〈
Fe
/
H
〉
=
-
0.93
and also exhibits a small star-to-star metallicity dispersion (σ = 0.04
σ
=
0.04
). These results are consistent with previous photometric and spectroscopic studies. Aluminum appears to be moderately enhanced in all program stars (〈Al/Fe〉 = +0.39
〈
Al
/
Fe
〉
=
+
0.39
,σ = 0.11
σ
=
0.11
). The relatively small star-to-star scatter in Al/Fe differs from the trend found in more metal-poor globular clusters, and is more similar to what is found in clusters withFe/H ≳ -1
Fe
/
H
≳
-
1
. The cluster also appears to be moderately
r
r
-process-enriched with〈Eu/La〉 = +0.32
〈
Eu
/
La
〉
=
+
0.32
(σ = 0.17
σ
=
0.17
).
Acute myeloid leukemia (AML) is composed of a heterogeneous blast population that exhibits characteristics of normal myeloid cells, including immature, HSC-like cells and differentiated, ...monocyte-like cells. The balance of immature and differentiated blasts within a patient is important clinically, as immature AML blasts are acutely sensitive to treatment with venetoclax, a BH3 mimetic that blocks the anti-apoptotic activity of BCL2. BCL2-inhibitor-based therapeutic strategies are the standard of care among elderly patients with untreated or relapsed/refractory AML. While these strategies result in a remission rate of nearly 70%, the majority of patients who do achieve remission ultimately relapse. Frequently, the relapsed disease is composed of differentiated, monocyte-like blasts. Given the importance of BCL2 inhibitors to the clinical management of AML, it is critical to understand the mechanisms by which BCL2 inhibitors result in monocytic relapse. Disease relapse has been traditionally thought to emerge from intrinsically resistant cells that confer a survival advantage under therapeutic pressure. Several studies have suggested that differentiated AML blasts have a survival advantage in the presence of BCL2 inhibition due to a reliance on anti-apoptotic proteins other than BCL2. Immature AML blasts express high levels of BCL2, whereas blasts that are primed for lympho-myeloid or granulocytic-monocytic progenitor cell fates express high levels of MCL-1 and BCL-XL, respectively. However, these studies do not explain why patients with dominant, differentiated subclones frequently achieve long-lasting remission with BCL2-inhibitor-based strategies. Therefore, simple selection of differentiated blasts appears to be an insufficient model to describe BCL2 inhibitor resistance. Alternative models of therapeutic resistance have been identified where cancer cells adapt to a resistant phenotype and acquire a survival advantage under therapeutic pressure. In the context of BCL2 inhibitor resistance, it is unclear the extent to which the emergence of differentiated blasts is the result of selective pressure or blast differentiation state plasticity in response to BCL2 inhibition. In our work, we have investigated the adaptive mechanism of BCL2 inhibition resistance in AML. We have explored this mechanism using an AML cell line model in which immature AML cells continuously generate differentiated AML cells (OCI-AML8227). We used fluorescence-activated cell sorting to isolate immature CD34+/CD38- OCI-AML8227 cells. After 72 hours in liquid culture, we observed that these cells recapitulated a pool of differentiated CD34-/CD38+/CD14+ cells. Furthermore, we used single cell ATAC sequencing to confirm that the unfractionated pool of OCI-AML8227 cells display chromatin accessibility profiles resembling cells across the continuum of myeloid differentiation. To understand whether this model is appropriate to investigate the differentiation-state-specific differences in sensitivity to BLC2 inhibition, we measured the viability of immature CD34+ and differentiated CD34- OCI-AML8227 cells following BCL2 inhibition. Consistent with previous studies, immature CD34+ cells were significantly more sensitive to BCL2 inhibition than differentiated CD34- cells. In addition, BLC2 inhibition of unfractionated OCI-AML8227 cells resulted in an 82% increase in the number of differentiated CD34-/CD38+ cells. While the number of immature CD34+/CD38- cells was reduced following BCL2 inhibition, it was only reduced by 27%. Furthermore, there was no change in the apoptosis marker Annexin V among immature CD34+/CD38- cells. These results support an adaptive resistance model where AML cells acquire resistance through differentiation state plasticity. We will explore this mechanism by following the temporal dynamics of immature and differentiated blasts following BCL2 inhibition. Using single cell barcoding, we will not only be able to trace the trajectories of these populations but also investigate transcriptional adaptation of the immature and differentiated populations. With an understanding of the adaptive mechanism of resistance to BCL2 inhibition, we can nominate alternative targets to prevent the outgrowth of resistance populations and design more effective, rational BLC2-inhibitor-based therapeutic strategies.
Abstract
The Apache Point Observatory Galactic Evolution Experiment 2 (APOGEE-2) is a dual-hemisphere, near-infrared (NIR), spectroscopic survey with the goal of producing a chemodynamical mapping of ...the Milky Way. The targeting for APOGEE-2 is complex and has evolved with time. In this paper, we present the updates and additions to the initial targeting strategy for APOGEE-2N presented in Zasowski et al. (2017). These modifications come in two implementation modes: (i) “Ancillary Science Programs” competitively awarded to Sloan Digital Sky Survey IV PIs through proposal calls in 2015 and 2017 for the pursuit of new scientific avenues outside the main survey, and (ii) an effective 1.5 yr expansion of the survey, known as the Bright Time Extension (BTX), made possible through accrued efficiency gains over the first years of the APOGEE-2N project. For the 23 distinct ancillary programs, we provide descriptions of the scientific aims, target selection, and how to identify these targets within the APOGEE-2 sample. The BTX permitted changes to the main survey strategy, the inclusion of new programs in response to scientific discoveries or to exploit major new data sets not available at the outset of the survey design, and expansions of existing programs to enhance their scientific success and reach. After describing the motivations, implementation, and assessment of these programs, we also leave a summary of lessons learned from nearly a decade of APOGEE-1 and APOGEE-2 survey operations. A companion paper, F. Santana et al. (submitted; AAS29036), provides a complementary presentation of targeting modifications relevant to APOGEE-2 operations in the Southern Hemisphere.
The evolution of elements as a function or age throughout the Milky Way disk provides strong constraints for galaxy evolution models, and on star formation epochs. In an effort to provide such ...constraints, we conducted an investigation into r- and s-process elemental abundances for a large sample of open clusters as part of an optical follow-up to the SDSS-III/APOGEE-1 near infrared survey. To obtain data for neutron capture abundance analysis, we conducted a long-term observing campaign spanning three years (2013-2016) using the McDonald Observatory Otto Struve 2.1-meter telescope and Sandiford Cass Echelle Spectrograph (SES, R(λ/Δλ) ∼60,000). The SES provides a wavelength range of ∼1400 Å, making it uniquely suited to investigate a number of other important chemical abundances as well as the neutron capture elements. For this study, we derive abundances for 18 elements covering four nucleosynthetic families– light, iron-peak, neutron capture and α-elements– for ∼30 open clusters within 6 kpc of the Sun with ages ranging from ∼80 Myr to ∼10 Gyr. Both equivalent width (EW) measurements and spectral synthesis methods were employed to derive abundances for all elements. Initial estimates for model stellar atmospheres– effective temperature and surface gravity– were provided by the APOGEE data set, and then re-derived for our optical spectra by removing abundance trends as a function of excitation potential and reduced width log(EW/λ). With the exception of Ba II and Zr I, abundance analyses for all neutron capture elements were performed by generating synthetic spectra from the new stellar parameters. In order to remove molecular contamination, or blending from nearby atomic features, the synthetic spectra were modeled by a best-fit Gaussian to the observed data. Nd II shows a slight enhancement in all cluster stars, while other neutron capture elements follow solar abundance trends. Ba II shows a large cluster-to-cluster abundance spread, consistent with other open cluster abundance studies. From log(Age) ∼8.5, this large spread as a function of age appears to replicate the findings from an earlier, much debated study by Orazi et al. (2009) which found a linear trend of decreasing barium abundance with increasing age.
Context. Bulge globular clusters (BGCs) are exceptional tracers of the formation and chemodynamical evolution of this oldest Galactic component. However, until now, observational difficulties have ...prevented us from taking full advantage of these powerful Galactic archeological tools. Aims. CAPOS, the bulge Cluster APOgee Survey, addresses this key topic by observing a large number of BGCs, most of which have only been poorly studied previously. Even their most basic parameters, such as metallicity, {\alpha}/Fe, and radial velocity, are generally very uncertain. We aim to obtain accurate mean values for these parameters, as well as abundances for a number of other elements, and explore multiple populations. In this first paper, we describe the CAPOS project and present initial results for seven BGCs. Methods. CAPOS uses the APOGEE-2S spectrograph observing in the H band to penetrate obscuring dust toward the bulge. For this initial paper, we use abundances derived from ASPCAP, the APOGEE pipeline. Results. We derive mean Fe/H values of \(-\)0.85\(\pm\)0.04 (Terzan 2), \(-\)1.40\(\pm\)0.05 (Terzan 4), \(-\)1.20\(\pm\)0.10 (HP 1), \(-\)1.40\(\pm\)0.07 (Terzan 9), \(-\)1.07\(\pm\)0.09 (Djorg 2), \(-\)1.06\(\pm\)0.06 (NGC 6540), and \(-\)1.11\(\pm\)0.04 (NGC 6642) from three to ten stars per cluster. We determine mean abundances for eleven other elements plus the mean \(\alpha\)/Fe and radial velocity. CAPOS clusters significantly increase the sample of well-studied Main Bulge globular clusters (GCs) and also extend them to lower metallicity. We reinforce the finding that Main Bulge and Main Disk GCs, formed in situ, have Si/Fe abundances slightly higher than their accreted counterparts at the same metallicity. We investigate multiple populations and find our clusters generally follow the light-element (anti)correlation trends of previous studies of GCs of similar metallicity. We finally explore the abundances ...
APOGEE-2 is a dual-hemisphere, near-infrared (NIR), spectroscopic survey with the goal of producing a chemo-dynamical mapping of the Milky Way Galaxy. The targeting for APOGEE-2 is complex and has ...evolved with time. In this paper, we present the updates and additions to the initial targeting strategy for APOGEE-2N presented in Zasowski et al. (2017). These modifications come in two implementation modes: (i) "Ancillary Science Programs" competitively awarded to SDSS-IV PIs through proposal calls in 2015 and 2017 for the pursuit of new scientific avenues outside the main survey, and (ii) an effective 1.5-year expansion of the survey, known as the Bright Time Extension, made possible through accrued efficiency gains over the first years of the APOGEE-2N project. For the 23 distinct ancillary programs, we provide descriptions of the scientific aims, target selection, and how to identify these targets within the APOGEE-2 sample. The Bright Time Extension permitted changes to the main survey strategy, the inclusion of new programs in response to scientific discoveries or to exploit major new datasets not available at the outset of the survey design, and expansions of existing programs to enhance their scientific success and reach. After describing the motivations, implementation, and assessment of these programs, we also leave a summary of lessons learned from nearly a decade of APOGEE-1 and APOGEE-2 survey operations. A companion paper, Santana et al. (submitted), provides a complementary presentation of targeting modifications relevant to APOGEE-2 operations in the Southern Hemisphere.
Metal-poor stars are important tools for tracing the early history of the Milky Way, and for learning about the first generations of stars. Simulations suggest that the oldest metal-poor stars are to ...be found in the inner Galaxy. Typical bulge surveys, however, lack low metallicity (Fe/H < -1.0) stars because the inner Galaxy is predominantly metal-rich. The aim of the Pristine Inner Galaxy Survey (PIGS) is to study the metal-poor and very metal-poor (VMP, Fe/H < -2.0) stars in this region. In PIGS, metal-poor targets for spectroscopic follow-up are selected from metallicity-sensitive CaHK photometry from the CFHT. This work presents the ~250 deg^2 photometric survey as well as intermediate-resolution spectroscopic follow-up observations for ~8000 stars using AAOmega on the AAT. The spectra are analysed using two independent tools: ULySS with an empirical spectral library, and FERRE with a library of synthetic spectra. The comparison between the two methods enables a robust determination of the stellar parameters and their uncertainties. We present a sample of 1300 VMP stars -- the largest sample of VMP stars in the inner Galaxy to date. Additionally, our spectroscopic dataset includes ~1700 horizontal branch stars, which are useful metal-poor standard candles. We furthermore show that PIGS photometry selects VMP stars with unprecedented efficiency: 86%/80% (lower/higher extinction) of the best candidates satisfy Fe/H < -2.0, as do 80%/63% of a larger, less strictly selected sample. We discuss future applications of this unique dataset that will further our understanding of the chemical and dynamical evolution of the innermost regions of our Galaxy.
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