Abstract
Wide-field and deep DECam multiband photometry, combined with HST data for the core of the Galactic globular cluster NGC 2808, allowed us to study the distribution of various stellar ...subpopulations and stars in different evolutionary phases out to the cluster tidal radius. We used the
C
ugi
= (
u
−
g
) − (
g
−
i
) index to identify three chemically distinct subpopulations along the red giant branch and compared their spatial distributions. The most light-element-enriched subpopulation (P3) is more centrally concentrated; however, it shows a more extended distribution in the external regions of the cluster compared to the primordial (P1) and intermediate (P2) composition populations. Furthermore, the P3 subpopulation centroid is off-center relative to those of the P1 and P2 groups. We also analyzed the spatial distribution of horizontal branch stars and found that the relative fraction of red horizontal branch stars increases for radial distances larger than ≈1.′5, while that of the blue and hotter stars decreases. These new observations, combined with literature spectroscopic measurements, suggest that the red horizontal branch stars are the progeny of all the stellar subpopulations in NGC 2808, i.e., primordial and light-element enhanced, while the blue stars are possibly the result of a combination of the “hot-flasher” and the “helium-enhanced” scenarios. A similar distribution of different red giant branch subpopulations and horizontal branch stars was also found for the most massive Galactic globular cluster,
ω
Cen, based on combined DECam and HST data, which suggests that the two may share a similar origin.
Abstract
We present wide-field, high resolution maps of the color excess for 14 globular clusters toward the Southern Galactic bulge. The maps were derived using Gaia EDR3 astrometry and stellar ...photometry from the Blanco DECam Bulge Survey, which is a deep, wide-field
ugriz
Y photometric survey of the southern Galactic bulge. Comparisons with WISE 12
μ
m images of thermal continuum emission demonstrate that the maps presented here trace interstellar extinction by dust down to 5″ scales. We use the reddening-corrected photometry of proper motion-selected cluster stars to build color–magnitude diagrams for the target globular clusters, which show residual broadening in excess of that expected from the photometric errors alone. This residual broadening is likely to be driven by star-to-star elemental abundance variations.
Abstract
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 (
ugriz
Y) 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.
Abstract
We present the detection of a very broad (FWHM = 670 ± 17 km s
−1
), low-intensity H
α
emission line component near the center of DDO 53, a star-forming dwarf irregular galaxy located in the ...M81 group. The broad component is found at the base of a bright and narrow (FWHM = 38 ± 2 km s
−1
) component. Using WIYN/Sparsepak optical spectroscopy of the region in addition to multiwavelength archival data, we evaluate the plausibility of several candidate sources, and find that stellar winds from embedded young stars are the most likely origin. However, this result is surprising for such a faint H
ii
region.
Abstract We present new JWST NIRSpec integral field spectroscopy (IFS) data for the luminous infrared galaxy NGC 7469, a nearby (70.6 Mpc) active galaxy with a Seyfert 1.5 nucleus that drives a ...highly ionized gas outflow and a prominent nuclear star-forming ring. Using the superb sensitivity and high spatial resolution of the JWST instrument NIRSpec IFS, we investigate the role of the Seyfert nucleus in the excitation and dynamics of the circumnuclear gas. Our analysis focuses on the Fe ii , H 2 , and hydrogen recombination lines that trace the radiation/shocked-excited molecular and ionized interstellar medium around the active galactic nucleus (AGN). We investigate gas excitation through H 2 /Br γ and Fe ii /Pa β emission line ratios and find that photoionization by the AGN dominates within the central 300 pc of the galaxy except in a small region that shows signatures of shock-heated gas; these shock-heated regions are likely associated with a compact radio jet. In addition, the velocity field and velocity dispersion maps reveal complex gas kinematics. Rotation is the dominant feature, but we also identify noncircular motions consistent with gas inflows as traced by the velocity residuals and the spiral pattern in the Pa α velocity dispersion map. The inflow is 2 orders of magnitude higher than the AGN accretion rate. The compact nuclear radio jet has enough power to drive the highly ionized outflow. This scenario suggests that the inflow and outflow are in a self-regulating feeding–feedback process, with a contribution from the radio jet helping to drive the outflow.
Abstract
We present James Webb Space Telescope (JWST) Near Infrared Spectrograph (NIRSpec) integral field spectroscopy of the nearby luminous infrared galaxy NGC 7469. We take advantage of the high ...spatial/spectral resolution and wavelength coverage of JWST/NIRSpec to study the 3.3
μ
m neutral polycyclic aromatic hydrocarbon (PAH) grain emission on ∼200 pc scales. A clear change in the average grain properties between the star-forming ring and the central AGN is found. Regions in the vicinity of the AGN, with Ne
iii
/Ne
ii
> 0.25, tend to have larger grain sizes and lower aliphatic-to-aromatic (3.4/3.3) ratios, indicating that smaller grains are preferentially removed by photodestruction in the vicinity of the AGN. PAH emission at the nucleus is weak and shows a low 11.3/3.3 PAH ratio. We find an overall suppression of the total PAH emission relative to the ionized gas in the central 1 kpc region of the AGN in NGC 7469 compared to what has been observed with Spitzer on 3 kpc scales. However, the fractional 3.3
μ
m–to–total PAH power is enhanced in the starburst ring, possibly due to a variety of physical effects on subkiloparsec scales, including recurrent fluorescence of small grains or multiple photon absorption by large grains. Finally, the IFU data show that while the 3.3
μ
m PAH-derived star formation rate (SFR) in the ring is 27% higher than that inferred from the Ne
ii
and Ne
iii
emission lines, the integrated SFR derived from the 3.3
μ
m feature would be underestimated by a factor of 2 due to the deficit of PAHs around the AGN, as might occur if a composite system like NGC 7469 were to be observed at high redshift.
Phosphatidylinositol (PtdIns) synthase 1 from the plant
Arabidopsis thaliana has been expressed in
Escherichia coli in order to study the synthetic capacities of the enzyme. Analysis of the total ...fatty acid content of the bacteria shows that PtdIns synthase activity does not have a profound effect on the proportions of the different fatty acids produced, even if the presence of an extra acidic phospholipid leads to a global reduction of the lipid content. A closer analysis carried out on individual phospholipids reveals a global fatty acid composition almost unchanged in the two major bacterial lipids phosphatidylethanolamine (PtdEtn) and phosphatidylglycerol (PtdGro). Phosphatidylinositol has a very unusual composition that shows the ability of the plant enzyme to use CDP-diacylglycerol molecular species absent from plants. We identified the various PtdIns molecular species. They represent a pool of the major molecular species of PtdEtn and PtdGro. These results, together with the determination of the apparent affinity constants of AtPIS1 for
myo-inositol and CDP-diacylglycerol, allow us to discuss some of the constraints of PtdIns synthesis in plants in terms of specificity, which will depend on the subcellular localization of the protein.
Phosphatidylinositol synthase is the enzyme responsible for the synthesis of phosphatidylinositol, a key phospholipid component of all eukaryotic membranes and the precursor of messenger molecules ...involved in signal transduction pathways for calcium‐dependent responses in the cell. Using the amino acid sequence of the yeast enzyme as a probe, we identified an Arabidopsis expressed sequence tag potentially encoding the plant enzyme. Sequencing the entire cDNA confirmed the homology between the two proteins. Functional assays, performed by overexpression of the plant cDNA in Escherichia coli, a bacteria which lacks phosphatidylinositol and phosphatidylinositol synthase activity, showed that the plant protein induced the accumulation of phosphatidylinositol in the bacterial cells. Analysis of the enzymatic activity in vitro showed that synthesis of phosphatidylinositol occurs when CDP‐diacylglycerol and myo‐inositol only are provided as substrates, that it requires manganese or magnesium ions for activity, and that it is at least in part located to the bacterial membrane fraction. These data allowed us to conclude that the Arabidopsis cDNA codes for a phosphatidylinositol synthase. A single AtPIS genetic locus was found, which we mapped to Arabidopsis chromosome 1.
Wide-field and deep DECam multi-band photometry, combined with HST data for the core of the Galactic globular cluster NGC 2808, allowed us to study the distribution of various stellar sub-populations ...and stars in different evolutionary phases out to the cluster tidal radius. We used the C_ugi = (u-g)-(g-i) index to identify three chemically distinct sub-populations along the red giant branch and compared their spatial distributions. The most light-element enriched sub-population (P3) is more centrally concentrated; however, it shows a more extended distribution in the external regions of the cluster compared to the primordial (P1) and intermediate (P2) composition populations. Furthermore, the P3 sub-population centroid is off-center relative to those of the P1 and P2 groups. We also analyzed the spatial distribution of horizontal branch stars and found that the relative fraction of red horizontal branch stars increases for radial distances larger than ~ 1.5' while that of the blue and hotter stars decreases. These new observations, combined with literature spectroscopic measurements, suggest that the red horizontal branch stars are the progeny of all the stellar sub-populations in NGC 2808, i.e. primordial and light-element enhanced, while the blue stars are possibly the result of a combination of the "hot-flasher" and the "helium-enhanced" scenarios. A similar distribution of different red giant branch sub-populations and horizontal branch stars was also found for the most massive Galactic globular cluster, omega Cen, based on combined DECam and HST data, which suggests the two may share a similar origin.
This article explains how each of the six phases of Appreciative Advising can be applied to study abroad through individual advising. It also identifies collaborative approaches and broader ...applications of an Appreciative mindset to support and empower students in their study‐abroad journeys.
PDF
