574 research outputs found
Prime agricultural land monitoring and assessment component of the California Integrated Remote Sensing System
The use of digital LANDSAT techniques for monitoring agricultural land use conversions was studied. Two study areas were investigated: one in Ventura County and the other in Fresno County (California). Ventura test site investigations included the use of three dates of LANDSAT data to improve classification performance beyond that previously obtained using single data techniques. The 9% improvement is considered highly significant. Also developed and demonstrated using Ventura County data is an automated cluster labeling procedure, considered a useful example of vertical data integration. Fresno County results for a single data LANDSAT classification paralleled those found in Ventura, demonstrating that the urban/rural fringe zone of most interest is a difficult environment to classify using LANDSAT data. A general raster to vector conversion program was developed to allow LANDSAT classification products to be transferred to an operational county level geographic information system in Fresno
Extragalactic archeology with the GHOSTS Survey I. - Age-resolved disk structure of nearby low-mass galaxies
We study the individual evolution histories of three nearby low-mass edge-on
galaxies (IC 5052, NGC4244, and NGC5023). Using resolved stellar populations,
we constructed star count density maps for populations of different ages and
analyzed the change of structural parameters with stellar age within each
galaxy.
We do not detect a separate thick disk in any of the three galaxies, even
though our observations cover a wider range in equivalent surface brightness
than any integrated light study. While scale heights increase with age, each
population can be well described by a single disk. Two of the galaxies contain
a very weak additional component, which we identify as the faint halo. The mass
of these faint halos is lower than 1% of the mass of the disk. The three
galaxies show low vertical heating rates, which are much lower than the heating
rate of the Milky Way. This indicates that heating agents, such as giant
molecular clouds and spiral structure, are weak in low-mass galaxies. All
populations in the three galaxies exhibit no or only little flaring. While this
finding is consistent with previous integrated light studies, it poses strong
constraints on galaxy simulations, where strong flaring is often found as a
result of interactions or radial migration.Comment: Accepted for publication in A&
Future Prospects: Deep Imaging of Galaxy Outskirts using Telescopes Large and Small
The Universe is almost totally unexplored at low surface brightness levels.
In spite of great progress in the construction of large telescopes and
improvements in the sensitivity of detectors, the limiting surface brightness
of imaging observations has remained static for about forty years. Recent
technical advances have at last begun to erode the barriers preventing
progress. In this Chapter we describe the technical challenges to low surface
brightness imaging, describe some solutions, and highlight some relevant
observations that have been undertaken recently with both large and small
telescopes. Our main focus will be on discoveries made with the Dragonfly
Telephoto Array (Dragonfly), which is a new telescope concept designed to probe
the Universe down to hitherto unprecedented low surface brightness levels. We
conclude by arguing that these discoveries are probably only scratching the
surface of interesting phenomena that are observable when the Universe is
explored at low surface brightness levels.Comment: 27 pages, 10 figures, Invited review, Book chapter in "Outskirts of
Galaxies", Eds. J. H. Knapen, J. C. Lee and A. Gil de Paz, Astrophysics and
Space Science Library, Springer, in pres
Constraining the age of the NGC 4565 HI Disk Warp: Determining the Origin of Gas Warps
We have mapped the distribution of young and old stars in the gaseous HI warp
of NGC 4565. We find a clear correlation of young stars (<600 Myr) with the
warp, but no coincident old stars (>1 Gyr), which places an upper limit on the
age of the structure. The formation rate of the young stars, which increased
~300 Myr ago relative to the surrounding regions, is (6.3 +2.5/-1.5) x 10^-5
M_sol/yr/kpc^2. This implies a ~60+/-20 Gyr depletion time of the HI warp,
similar to the timescales calculated for the outer HI disks of nearby spiral
galaxies. While some stars associated with the warp fall into the asymptotic
giant branch (AGB) region of the color magnitude diagram, where stars could be
as old as 1 Gyr, further investigation suggests that they may be interlopers
rather than real AGB stars. We discuss the implications of these age
constraints for the formation of HI warps, and the gas fueling of disk
galaxies.Comment: 12 pages, 9 figures. Accepted for publication in Ap
Testing galaxy formation models with the GHOSTS survey: The color profile of M81's stellar halo
We study the properties of the stellar populations in M81's outermost part,
which hereafter we will term the stellar halo, using HST ACS/WFC observations
of 19 fields from the GHOSTS survey. The observed fields probe the stellar halo
out to a projected distance of ~ 50 kpc from the galactic center. Each field
was observed in both F606W and F814W filters. The 50% completeness levels of
the color magnitude diagrams (CMDs) are typically at 2 mag below the tip of the
red giant branch (TRGB). Fields at distances closer than 15 kpc show evidence
of disk-dominated populations whereas fields at larger distances are mostly
populated by halo stars. The RGB of the M81's halo CMDs is well matched with
isochrones of ~ 10 Gyr and metallicities [Fe/H] ~ -1.2 dex, suggesting that the
dominant stellar population of M81's halo has a similar age and metallicity.
The halo of M81 is characterized by a color distribution of width ~ 0.4 mag and
an approximately constant median value of (F606W - F814W) ~ 1 mag measured
using stars within the magnitude range 23.7 < F814W < 25.5. When considering
only fields located at galactocentric radius R > 15 kpc, we detect no color
gradient in the stellar halo of M81. We place a limit of 0.03+/-0.11 mag
difference between the median color of RGB M81 halo stars at ~ 15 and at 50
kpc, corresponding to a metallicity difference of 0.08+/-0.35 dex over that
radial range for an assumed constant age of 10 Gyr. We compare these results
with model predictions for the colors of stellar halos formed purely via
accretion of satellite galaxies. When we analyze the cosmologically motivated
models in the same way as the HST data, we find that they predict no color
gradient for the stellar halos, in good agreement with the observations.Comment: 16 pages, 7 figures. Accepted to Ap
Habitat Characteristics of Eastern Wild Turkey Nest and Ground-roost Sites in 2 Longleaf Pine Forests
Managing and restoring longleaf pine forests throughout the Southeast is a conservation priority. Prescribed fire is an integral part of these activities, as it is the primary means of controlling hardwood encroachment and maintaining native groundcover. Nest site and preflight brood groundroost site selection of eastern wild turkeys (Meleagris gallopavo silvestris) has not been well studied in longleaf pine systems. Therefore, we determined habitat characteristics associated with wild turkey nests and ground-roosts in 2 longleaf pine forests in southwestern Georgia. We radio-tagged 45 female turkeys and evaluated habitat characteristics associated with 84 nests and 51 ground-roosts during the 2011–2013 nesting seasons. Nests were located farther from mature pine and mature pine-hardwood stands and closer to shrub/scrub habitats than expected. Nests were also negatively associated with percent canopy closure and positively associated with percent woody ground cover and vegetation height. Ground-roosts were closer to mature pine-hardwood stands and open water than were random sites. We suggest that management of longleaf pine forests should focus on maintaining open-canopied forests with adequate understory vegetation to serve as nesting and brood-rearing cover. Our findings suggest that frequent prescribed fire (≤ 2 years), when the management goal is to optimize restoration of longleaf ecosystems, is conducive to maintaining wild turkey populations
GHOSTS I: A New Faint very Isolated Dwarf Galaxy at D = 12 +/- 2 Mpc
We report the discovery of a new faint dwarf galaxy, GHOSTS I, using HST/ACS
data from one of our GHOSTS (Galaxy Halos, Outer disks, Substructure, Thick
disk, and Star clusters) fields. Its detected individual stars populate an
approximately one magnitude range of its luminosity function (LF). Using
synthetic color-magnitude diagrams (CMDs) to compare with the galaxy's CMD, we
find that the colors and magnitudes of GHOSTS I's individual stars are most
consistent with being young helium-burning and asymptotic giant branch stars at
a distance of 12 +/- 2 Mpc. Morphologically, GHOSTS I appears to be actively
forming stars, so we tentatively classify it as a dwarf irregular (dIrr)
galaxy, although future HST observations deep enough to resolve a larger
magnitude range in its LF are required to make a more secure classification.
GHOSTS I's absolute magnitude is , making it one
of the least luminous dIrr galaxies known, and its metallicity is lower than
[Fe/H] =-1.5 dex. The half-light radius of GHOSTS I is 226 +/- 38 pc and its
ellipticity is 0.47 +/- 0.07, similar to Milky Way and M31 dwarf satellites at
comparable luminosity. There are no luminous massive galaxies or galaxy
clusters within ~ 4 Mpc from GHOSTS I that could be considered as its host,
making it a very isolated dwarf galaxy in the Local Universe.Comment: 8 pages, 7 figures. Accepted for publication in Ap
Elacestrant (oral selective estrogen receptor degrader) Versus Standard Endocrine Therapy for Estrogen Receptor–Positive, Human Epidermal Growth Factor Receptor 2–Negative Advanced Breast Cancer: Results From the Randomized Phase III EMERALD Trial
Elacestrant; Cà ncer de mamaElacestrant; Cáncer de mamaElacestrant; Breast cancerPURPOSE
Patients with pretreated estrogen receptor (ER)–positive/human epidermal growth factor receptor 2 (HER2)–negative advanced breast cancer have poor prognosis. Elacestrant is a novel, oral selective ER degrader that demonstrated activity in early studies.
METHODS
This randomized, open-label, phase III trial enrolled patients with ER-positive/HER2-negative advanced breast cancer who had one-two lines of endocrine therapy, required pretreatment with a cyclin-dependent kinase 4/6 inhibitor, and ≤ 1 chemotherapy. Patients were randomly assigned to elacestrant 400 mg orally once daily or standard-of-care (SOC) endocrine monotherapy. Primary end points were progression-free survival (PFS) by blinded independent central review in all patients and patients with detectable ESR1 mutations.
RESULTS
Patients were randomly assigned to elacestrant (n = 239) or SOC (n = 238). ESR1 mutation was detected in 47.8% of patients, and 43.4% received two prior endocrine therapies. PFS was prolonged in all patients (hazard ratio = 0.70; 95% CI, 0.55 to 0.88; P = .002) and patients with ESR1 mutation (hazard ratio = 0.55; 95% CI, 0.39 to 0.77; P = .0005). Treatment-related grade 3/4 adverse events occurred in 7.2% receiving elacestrant and 3.1% receiving SOC. Treatment-related adverse events leading to treatment discontinuations were 3.4% in the elacestrant arm versus 0.9% in SOC. Nausea of any grade occurred in 35.0% receiving elacestrant and 18.8% receiving SOC (grade 3/4, 2.5% and 0.9%, respectively).
CONCLUSION
Elacestrant is the first oral selective ER degrader demonstrating a significant PFS improvement versus SOC both in the overall population and in patients with ESR1 mutations with manageable safety in a phase III trial for patients with ER-positive/HER2-negative advanced breast cancer
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