135 research outputs found
Master of Science
thesisThe early to middle Eocene Green River Formation consists of continental strata deposited in Laramide ponded basins in Utah, Colorado, and Wyoming. This study (1) documents fluvial and lacustrine strata from the Douglas Creek and Parachute Creek Members of the middle Green River Formation, southeastern Uinta Basin, Utah, and (2) uses new interpretations of the link between climate and fluvial sedimentary expression to interpret the terrestrial evolution of early Eocene climate. The stratigraphy was analyzed via outcrops along a 10 km transect in Main Canyon on the Tavaputs Plateau, and is divided into three distinct, stratigraphically separated depositional settings: (1) the lowermost Interval 1 is dominated by amalgamated sandstone channels that contain 70-100% upper flow regime sedimentary structures. The channels are interpreted to represent fluvial deposits controlled by a highly seasonal climate, where most deposition was limited to seasonal flooding events. (2) Interval 2 is dominated by alternating siliciclastic and carbonate lacustrine deposits, interpreted as local pulsed fluvial siliciclastic input into shallow Lake Uinta, and periods of fluvial quiescence represented by littoral carbonate deposition. (3) The uppermost Interval 3 is dominated by erosively-based, trough cross bedded sandstone channels interbedded with littoral lacustrine and deltaic deposits. The Interval 3 sandstone channels are interpreted as perennial fluvial deposits with relatively little variation in annual discharge, akin to modern humid-temperate fluvial systems. The stratigraphic transition from seasonally-controlled (Interval 1) to perennial (Interval 3) fluvial deposits is interpreted to represent a fundamental shift in Eocene climate, from the peak hyperthermal regime of the Early Eocene Climatic Optimum (EECO) to a more stable post-EECO climate
A Cool and Inflated Progenitor Candidate for the Type Ib Supernova 2019yvr at 2.6 Years Before Explosion
We present Hubble Space Telescope imaging of a pre-explosion counterpart to
SN 2019yvr obtained 2.6 years before its explosion as a type Ib supernova (SN
Ib). Aligning to a post-explosion Gemini-S/GSAOI image, we demonstrate that
there is a single source consistent with being the SN 2019yvr progenitor
system, the second SN Ib progenitor candidate after iPTF13bvn. We also analyzed
pre-explosion Spitzer/IRAC imaging, but we do not detect any counterparts at
the SN location. SN 2019yvr was highly reddened, and comparing its spectra and
photometry to those of other, less extinguished SNe Ib we derive
mag for SN 2019yvr. Correcting photometry
of the pre-explosion source for dust reddening, we determine that this source
is consistent with a and K star. This relatively cool photospheric
temperature implies a radius of 320, much larger
than expectations for SN Ib progenitor stars with trace amounts of hydrogen but
in agreement with previously identified SN IIb progenitor systems. The
photometry of the system is also consistent with binary star models that
undergo common envelope evolution, leading to a primary star hydrogen envelope
mass that is mostly depleted but seemingly in conflict with the SN Ib
classification of SN 2019yvr. SN 2019yvr had signatures of strong circumstellar
interaction in late-time (150 day) spectra and imaging, and so we consider
eruptive mass loss and common envelope evolution scenarios that explain the SN
Ib spectroscopic class, pre-explosion counterpart, and dense circumstellar
material. We also hypothesize that the apparent inflation could be caused by a
quasi-photosphere formed in an extended, low-density envelope or circumstellar
matter around the primary star.Comment: 22 pages, 9 figures, submitted to MNRA
The Star Formation Rate Density and Dust Attenuation Evolution over 12 Gyr with the VVDS Surveys
[Abridged] We investigate the global galaxy evolution over 12 Gyr
(0.05<z<4.5), from the star formation rate density (SFRD), combining the VVDS
Deep (17.5<=I<=24.0) and Ultra-Deep (23.00<=i<=24.75) surveys. We obtain a
single homogeneous spectroscopic redshift sample, totalizing about 11000
galaxies. We estimate the rest-frame FUV luminosity function (LF) and
luminosity density (LD), extract the dust attenuation of the FUV radiation
using SED fitting, and derive the dust-corrected SFRD. We find a constant and
flat faint-end slope alpha in the FUV LF at z1.7, we set alpha
steepening with (1+z). The absolute magnitude M*_FUV brightens in the entire
range 02 it is on average brighter than in the literature,
while phi* is smaller. Our total LD shows a peak at z=2, present also when
considering all sources of uncertainty. The SFRD history peaks as well at z=2.
It rises by a factor of 6 during 2 Gyr (from z=4.5 to z=2), and then decreases
by a factor of 12 during 10 Gyr down to z=0.05. This peak is mainly produced by
a similar peak within the population of galaxies with -21.5<=M_FUV<=-19.5 mag.
As times goes by, the total SFRD is dominated by fainter and fainter galaxies.
The presence of a clear peak at z=2 and a fast rise at z>2 of the SFRD is
compelling for models of galaxy formation. The mean dust attenuation A_FUV of
the global galaxy population rises by 1 mag during 2 Gyr from z=4.5 to z=2,
reaches its maximum at z=1 (A_FUV=2.2 mag), and then decreases by 1.1 mag
during 7 Gyr down to z=0. The dust attenuation maximum is reached 2 Gyr after
the SFRD peak, implying a contribution from the intermediate-mass stars to the
dust production at z<2.Comment: 23 pages, 15 figures, accepted for publication in A&
Orbit size and estimated eye size in dinosaurs and other archosaurs and their implications for the evolution of visual capabilities
Vision is one of the most important senses for animals, allowing them to interact with their environment and with further implications for evolutionary histories. However, relevant soft tissues, such as the eye and associated structures, are not preserved in fossil vertebrates, limiting our knowledge of their visual capabilities. Here, we quantified absolute and relative orbit size for 400 species of dinosaurs and other extinct archosaurs using linear measurements of the preserved skeletal elements as a proxy for visual capabilities. Our results demonstrate that the orbit makes up on average 20% of skull size with a strong and consistent correlation across all sampled groups. This trend is largely independent of temporal distribution, species richness, and phylogeny. In fact, relative orbit size is narrowly constrained and did not surpass 45% of skull size, suggesting physiological and functional controls. Estimated eye size was found to be absolutely larger in herbivores, whereas carnivores tended to have smaller eyes absolutely and compared with skull size. Relatively large eyes only occurred in small-bodied species and vice versa. However, eye size alone was not sufficient to discriminate between different activity patterns or to characterize visual capabilities in detail.</p
Flight of the Bumblebee: the Early Excess Flux of Type Ia Supernova 2023bee revealed by , and Young Supernova Experiment Observations
We present high-cadence ultraviolet through near-infrared observations of the
Type Ia supernova (SN Ia) 2023bee in NGC~2708 ( Mpc), finding
excess flux in the first days after explosion relative to the expected
power-law rise from an expanding fireball. This deviation from typical behavior
for SNe Ia is particularly obvious in our 10-minute cadence light curve
and UV data. Compared to a few other normal SNe Ia with detected early
excess flux, the excess flux in SN 2023bee is redder in the UV and less
luminous. We present optical spectra of SN 2023bee, including two spectra
during the period where the flux excess is dominant. At this time, the spectra
are similar to those of other SNe Ia but with weaker Si II, C II and Ca II
absorption lines, perhaps because the excess flux creates a stronger continuum.
We compare the data to several theoretical models that have been proposed to
explain the early flux excess in SNe Ia. Interaction with either a nearby
companion star or close-in circumstellar material is expected to produce a
faster evolution than seen in the data. Radioactive material in the outer
layers of the ejecta, either from a double detonation explosion or simply an
explosion with a Ni clump near the surface, can not fully reproduce the
evolution either, likely due to the sensitivity of early UV observable to the
treatment of the outer part of ejecta in simulation. We conclude that no
current model can adequately explain the full set of observations. We find that
a relatively large fraction of nearby, bright SNe Ia with high-cadence
observations have some amount of excess flux within a few days of explosion.
Considering potential asymmetric emission, the physical cause of this excess
flux may be ubiquitous in normal SNe Ia.Comment: 21 pages, 12 figures. Accepted by the astrophysical journa
Systemic iron reduction by venesection alters the gut microbiome in patients with haemochromatosis
Background & Aims: Iron reduction by venesection has been the cornerstone of treatment for haemochromatosis for decades, and its reported health benefits are many. Repeated phlebotomy can lead to a compensatory increase in intestinal iron absorption, reducing intestinal iron availability. Given that most gut bacteria are highly dependent on iron for survival, we postulated that, by reducing gut iron levels, venesection could alter the gut microbiota. Methods: Clinical parameters, faecal bacterial composition and metabolomes were assessed before and during treatment in a group of patients with haemochromatosis undergoing iron reduction therapy. Results: Systemic iron reduction was associated with an alteration of the gut microbiome, with changes evident in those who experienced reduced faecal iron availability with venesection. For example, levels of Faecalibacterium prausnitzii, a bacterium associated with improved colonic health, were increased in response to faecal iron reduction. Similarly, metabolomic changes were seen in association with reduced faecal iron levels. Conclusion: These findings highlight a significant shift in the gut microbiome of patients who experience reduced colonic iron during venesection. Targeted depletion of faecal iron could represent a novel therapy for metabolic and inflammatory diseases, meriting further investigation. Lay summary: Iron depletion by repeated venesection is the mainstay of treatment for haemochromatosis, an iron-overload disorder. Venesection has been associated with several health benefits, including improvements in liver function tests, reversal of liver scarring, and reduced risk of liver cancer. During iron depletion, iron absorption from the gastrointestinal (GI) tract increases to compensate for iron lost with treatment. Iron availability is limited in the GI tract and is crucial to the growth and function of many gut bacteria. In this study we show that reduced iron availability in the colon following venesection treatment leads to a change in the composition of the gut bacteria, a finding that, to date, has not been studied in patients with haemochromatosis
Protein Architecture of the Human Kinetochore Microtubule Attachment Site
Centromeric chromatin – spindle microtubule interactions mediated by kinetochores drive chromosome segregation. We have developed a two-color fluorescence light microscopy method that measures average label separation, Delta, at < 5 nm accuracy — to elucidate the protein architecture of human metaphase kinetochores. Delta analysis, when correlated with tension states of spindle-attached sister kinetochore pairs, provided information on mechanical properties of protein linkages within kinetochores. Treatment with taxol—which suppresses microtubule dynamics, eliminates tension at kinetochores, and activates the spindle checkpoint—resulted in specific large-scale changes in kinetochore architecture. Cumulatively, Delta analysis revealed compliant linkages close to the centromeric chromatin, suggests a model for how the KMN (KNL1/Mis12 complex/Ndc80 complex) network provides microtubule attachment and generates pulling forces from depolymerization, and reveals architectural changes induced by taxol treatment. The methods described here should also be applicable to other intermediate-scale biological machines in cells
SN2023ixf in Messier 101: the twilight years of the progenitor as seen by Pan-STARRS
The nearby type II supernova, SN2023ixf in M101 exhibits signatures of
early-time interaction with circumstellar material in the first week
post-explosion. This material may be the consequence of prior mass loss
suffered by the progenitor which possibly manifested in the form of a
detectable pre-supernova outburst. We present an analysis of the long-baseline
pre-explosion photometric data in , , , , and filters from
Pan-STARRS as part of the Young Supernova Experiment, spanning 5,000
days. We find no significant detections in the Pan-STARRS pre-explosion light
curve. We train a multilayer perceptron neural network to classify
pre-supernova outbursts. We find no evidence of eruptive pre-supernova activity
to a limiting absolute magnitude of . The limiting magnitudes from the full
set of (average absolute magnitude -8) data are consistent
with previous pre-explosion studies. We use deep photometry from the literature
to constrain the progenitor of SN2023ixf, finding that these data are
consistent with a dusty red supergiant (RSG) progenitor with luminosity
5.12 and temperature 3950K,
corresponding to a mass of 14-20 MComment: 19 pages, 8 figures, 1 tabl
SN 2022oqm: A Multi-peaked Calcium-rich Transient from a White Dwarf Binary Progenitor System
We present the photometric and spectroscopic evolution of SN 2022oqm, a
nearby multi-peaked hydrogen- and helium-weak calcium-rich transient (CaRT). SN
2022oqm was detected 19.9 kpc from its host galaxy, the face-on spiral galaxy
NGC 5875. Extensive spectroscopic coverage reveals a hot (T >= 40,000 K)
continuum and carbon features observed ~1 day after discovery, SN Ic-like
photospheric-phase spectra, and strong forbidden calcium emission starting 38
days after discovery. SN 2022oqm has a relatively high peak luminosity (MB =
-17 mag) for CaRTs, making it an outlier in the population. We determine that
three power sources are necessary to explain SN 2022oqm's light curve, with
each power source corresponding to a distinct peak in its light curve. The
first peak of the light curve is powered by an expanding blackbody with a power
law luminosity, consistent with shock cooling by circumstellar material.
Subsequent peaks are powered by a double radioactive decay model, consistent
with two separate sources of photons diffusing through an optically thick
ejecta. From the optical light curve, we derive an ejecta mass and 56Ni mass of
~0.89 solar masses and ~0.09 solar masses, respectively. Detailed spectroscopic
modeling reveals ejecta that is dominated by intermediate-mass elements, with
signs that Fe-peak elements have been well-mixed. We discuss several physical
origins for SN 2022oqm and favor a white dwarf progenitor model. The inferred
ejecta mass points to a surprisingly massive white dwarf, challenging models of
CaRT progenitors.Comment: 33 pages, 17 figures, 5 tables, Submitted to Ap
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