7,931 research outputs found
Resolving the terrestrial planet forming regions of HD113766 and HD172555 with MIDI
We present new MIDI interferometric and VISIR spectroscopic observations of
HD113766 and HD172555. Additionally we present VISIR 11um and 18um imaging
observations of HD113766. These sources represent the youngest (16Myr and 12Myr
old respectively) debris disc hosts with emission on <<10AU scales. We find
that the disc of HD113766 is partially resolved on baselines of 42-102m, with
variations in resolution with baseline length consistent with a Gaussian model
for the disc with FWHM of 1.2-1.6AU (9-12mas). This is consistent with the
VISIR observations which place an upper limit of 0."14 (17AU) on the emission,
with no evidence for extended emission at larger distances. For HD172555 the
MIDI observations are consistent with complete resolution of the disc emission
on all baselines of lengths 56-93m, putting the dust at a distance of >1AU
(>35mas). When combined with limits from TReCS imaging the dust at ~10um is
constrained to lie somewhere in the region 1-8AU. Observations at ~18um reveal
extended disc emission which could originate from the outer edge of a broad
disc, the inner parts of which are also detected but not resolved at 10um, or
from a spatially distinct component. These observations provide the most
accurate direct measurements of the location of dust at 1-8AU that might
originate from the collisions expected during terrestrial planet formation.
These observations provide valuable constraints for models of the composition
of discs at this epoch and provide a foundation for future studies to examine
in more detail the morphology of debris discs.Comment: 22 pages, 19 figures, accepted for publication in MNRA
Resolved Imaging of the HD191089 Debris Disc
Two thirds of the F star members of the 12 Myr old Beta Pictoris Moving Group
(BPMG) show significant excess emission in the mid-infrared, several million
years after the expected dispersal of the protoplanetary disc. Theoretical
models of planet formation suggest that this peak in the mid-infrared emission
could be due to the formation of Pluto-sized bodies in the disc, which ignite
the collisional cascade and enhance the production of small dust. Here we
present resolved mid-infrared imaging of the disc of HD191089 (F5V in the BPMG)
and consider its implications for the state of planet formation in this system.
HD191089 was observed at 18.3 microns using T-ReCS on Gemini South and the
images were compared to models of the disc to constrain the radial distribution
of the dust. The emission observed at 18.3 microns is shown to be significantly
extended beyond the PSF at a position angle of 80 degrees. This is the first
time dust emission has been resolved around HD191089. Modelling indicates that
the emission arises from a dust belt from 28-90 AU, inclined at 35 degrees from
edge on with very little emission from the inner 28AU of the disc, indicating
the presence of an inner cavity. The steep slope of the inner edge is more
consistent with truncation by a planet than with ongoing stirring. A tentative
brightness asymmetry F(W)/F(E)=0.80+/-0.12 (1.8 sigma) between the two sides of
the disc could be evidence for perturbations from a massive body on an
eccentric orbit in the system.Comment: 11 Pages Accepted to MNRA
Impacts of Small Intestinal Enzyme Activity and Varying Corn Grain Processing Types on Feeding Behavior, and Growth Performance of Finishing Beef Steers
The objective of this study was to quantify the differences in activity of jejunal maltase and isomaltase between 2 groups of steers with average dry matter intake (DMI) and differing average daily gain (ADG). Dry matter intake and ADG were measured in crossbred steers (n = 69). Jejunal mucosal samples were collected from 8 steers with the greatest (high) or least (low) ADG and average DMI (± 0.55 standard deviation). Homogenates of jejunal mucosa were incubated with increasing amounts of maltose and isomaltose to determine the disaccharidase kinetics. Neither the Km of isomaltase (P = 0.15) or maltase (P = 0.43) differed between group. The isomaltase Vmax expressed per gram of protein (P = 0.11) or tissue (P = 0.18), respectively, did not differ between groups of steers. While previous studies have indicated that disaccharidase expression is associated with differences in ADG, data presented here indicate that differences in enzyme activity at the end of a feeding period are minimal. The objective of the second study was to evaluate the impact of corn-grain processing on feeding behavior and growth performance. There were 3 diets fed which differed in grain processing; wholeshelled corn-based diet (WSC); a blended corn-based diet containing a 50:50 wholeshelled corn and high-moisture corn (BLD); and a high-moisture corn-based diet (HMC). Meal duration, average meal size, and number of meals differed across treatments (P \u3c 0.01). For meal duration, HMC was greater (P \u3c 0.01) than WSC and BLD which did not differ (P \u3e 0.13). The average meal size was greatest for WSC which tended to differ (P = 0.07) from BLD, and differed (P \u3c 0.01) from HMC which had the least kg of intake at each meal. The HMC treatment consumed the greatest number of meals and differed from WSC and BLD (P \u3c 0.01); whereas, WSC had the least number of meals and tended to differ from BLD (P = 0.09). Though the growth performance resembled previous work, no differences in steer growth performance or DMI were detected in the current experiment
SB30-15/16: Amending Bylaws on KBGA
SB30-15/16: Amending Bylaws on KBGA. This resolution was passed by unanimous consent at the December 9, 2015 meeting of the Associated Students of the University of Montana (ASUM)
SB38-15/16: Resolution Amending Bylaws, KBGA
SB38-15/16: Amending Bylaws, KBGA. This resolution was passed by unanimous consent at the March 9, 2016 meeting of the Associated Students of the University of Montana (ASUM)
Warm dusty discs: Exploring the A star 24um debris population
(Abridged) Studies of debris discs have shown that most systems are analogous
to the EKB. In this study we aim to determine how many IRAS 25um excesses
towards A stars are real, and investigate where the dust lies. We observe with
TIMMI2, VISIR, Michelle and TReCS a sample of A and B-type main sequence stars
reported as having mid-IR excess. We constrain the location of the debris
through combined modelling of the emission spectrum and a modelling technique
designed to constrain the radial extent of emission in mid-IR imaging. We
independently confirm the presence of warm dust around 3 of the candidates:
HD3003, HD80950 and eta Tel. For the binary HD3003 a stability analysis
indicates the dust is either circumstellar and lying at ~4 AU with the binary
orbiting at >14AU, or the dust lies in an unstable location; there is some
evidence for temporal evolution of its excess emission on a ~20 year timescale.
For 7 of the targets we present quantitative limits on the location of dust
around the star. We demonstrate that the disc around HD71155 must have
spatially distinct components at 2 and 60AU. We model the limits of current
instrumentation and show that most of the known A star debris discs which could
be readily resolved at 18um on 8m instruments have been resolved. Limits from
unresolved imaging can help distinguish between competing models of the disc
emission, but resolved imaging is key to the determination of the disc
location. Modelling of the detection limits for extended emission can be useful
for targeting future observational campaigns. MIRI on the JWST will be able to
resolve most of the known A star debris disc population. METIS on the E-ELT
will provide the opportunity to explore the hot disc population more thoroughly
by detecting extended emission where calibration accuracy limits disc detection
through photometry, reaching levels below 1 zodi for stars at <10pc.Comment: Accepted for publication in Astronomy and Astrophysic
Relationships Between Undigested And Physically Effective Fiber In Lactating Dairy Cow Diets
In recent years, economic, social, and environmental factors have encouraged higher forage diets to be fed to dairy cows. Consequently, a better understanding of both the chemical and physical properties of dietary forage fiber is needed. Undigested neutral detergent fiber after 240 hours of fermentation (uNDF240) is the fiber residue remaining after 240 hours of in vitro fermentation and has only recently been defined. Physically effective neutral detergent fiber (peNDF) was defined about two decades ago and is the fraction of dietary fiber with a particle size (i.e., ≥1.18-mm screen) that stimulates chewing behavior, forms the rumen digesta mat, and is resistant to passage from the rumen. To-date, the relationship between these two dietary fiber measurements has not been evaluated. The overall goal of this thesis research was to quantitate the relationship between dietary uNDF240 and peNDF on feed intake, lactational performance, chewing behavior, and the ruminal environment of lactating Holstein dairy cows.
The focal study (Chapter 2) investigated the effects of dietary uNDF240 (low or high) and peNDF (low or high) on lactating dairy cows. The four treatments were: 1) low uNDF240, low peNDF (8.8%, 20.1%; LULP; 2) low uNDF240, high peNDF (8.9%, 21.8%; LUHP); 3) high uNDF240, low peNDF (11.4%, 18.6%; HULP); and 4) high uNDF240, high peNDF (11.6%, 22.0%; HUHP). Additionally, a new descriptive term, physically effective uNDF240 (peuNDF240) was calculated as the product of the dietary physical effectiveness factor (pef; % of particles retained on ≥1.18-mm screen with dry sieving) and uNDF240 as a percentage of dry matter (DM). This new descriptive term aimed to integrate the effects of dietary particle size and NDF (in)digestibility. The dietary peuNDF240 concentrations were 5.4% (LULP), 5.8% (LUHP), 5.9% (HULP), and 7.1% (HUHP). The LULP treatment resulted in greater dry matter intake (DMI) and energy corrected milk (ECM), as well as more favorable chewing behavior (i.e., no effect on rumination but less time spent eating) in comparison to the HUHP diet. When comparing the same two treatments, total volatile fatty acid concentration was greater, mean ruminal pH was lower, and NDF turnover rate tended to be greater for the LULP treatment. Milk fat percentage was influenced by dietary uNDF240 with the high uNDF240 diets having an elevated percentage. The LUHP and HULP treatments often did not differ in animal response variables, such as DMI, ECM, mean ruminal pH, and chewing behavior, reflecting their similar dietary peuNDF240 concentration. Importantly, by reducing peNDF of the high uNDF240 treatments, DMI increased to an amount similar to the low uNDF240 treatments.
Animal responses were consistently different between the LULP and HUHP treatments as expected: the low uNDF240 diet, chopped more finely, encouraged greater DMI than the high uNDF240 diet chopped coarsely. However, the LUHP and HULP diets with similar peuNDF240 often resulted in similar cow responses, even though the peuNDF240 was obtained differently for each diet. With these diets fed to high-producing cows, it appears that the integration of particle size and indigestibility of fiber using a peuNDF240 measurement is highly related to DMI, ECM yield, chewing behavior, and ruminal environment. In the future, this relationship may prove useful in predicting DMI of lactating dairy cows fed a range of diets differing in uNDF240 and particle size
Estimating the mass of the debris disc in HD 69830
We present a method to estimate the mass of the debris disc in the HD 69830
system, which also hosts three exoplanets with Neptune-like minimum masses. By
considering the range of published stellar ages, we interpret the infrared
emission from the debris disc as originating from a steady state, collisional
cascade of dust grains. Using dynamical survival models subjected to
observational constraints, we estimate the allowed range of disc masses. If the
disc has an age of about 1 Gyr, then its mass is several times that of our
asteroid belt. The maximum allowed age for the disc and the number of
planetesimals it contains are determined by the assumed value for the binding
energy of the planetesimals. If one insists on interpreting the disc as being
transient, then this mass estimate becomes an upper limit.Comment: Accepted by MNRAS. 4 pages, 2 figures. No changes from previous
version, except for corrections of typographical errors and to British
English (e.g., "disc"
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