239 research outputs found
A Search For Light Hydrides In The Envelopes Of Evolved Stars
Hydrides are important molecular constituents of the interstellar and circumstellar media, but there are still many questions regarding their variety and formation. In the envelopes of asymptotic giant branch and red supergiant stars, hydrides like silane \chem{SiH_4}, phosphine \chem{PH_3}, ammonia \chem{NH_3}, and water \chem{H_2O} are known to form, but have been observed in stark overabundance relative to predictions of chemical equilibrium models\footnote{Agundez et al., A\&A 637, A59 (2020)}. Diatomic hydrides (species with the form XH) are natural precursors to their more hydrogenated counterparts, and could therefore be crucial in constraining this puzzling chemistry. In this talk, I will present our search for the hydrides silicon monohydride (\chem{SiH}), phosphinidene (\chem{PH}), and iron hydride (\chem{FeH}) using the Stratospheric Observatory for Infrared Astronomy (SOFIA). We used the German Receiver for Astronomy at Terahertz Frequencies (GREAT) instrument to search for rotational emission lines of these molecules along the line of sight toward the chemically rich circumstellar envelopes of the evolved stars IRC+10216 and VY Canis Majoris. In these spectra we detected high-energy ro-vibrational lines from over a dozen molecules, though no significant emission from our target molecules was found. We derive upper limits on their abundances in each source, discuss how these findings influence our understanding of hydride chemistry in circumstellar envelopes, and outline the observational steps needed to further constrain this chemistry
Spiral and bar driven peculiar velocities in Milky Way sized galaxy simulations
We investigate the kinematic signatures induced by spiral and bar structure
in a set of simulations of Milky Way-sized spiral disc galaxies. The set
includes test particle simulations that follow a quasi-stationary density
wave-like scenario with rigidly rotating spiral arms, and -body simulations
that host a bar and transient, co-rotating spiral arms. From a location similar
to that of the Sun, we calculate the radial, tangential and line-of-sight
peculiar velocity fields of a patch of the disc and quantify the fluctuations
by computing the power spectrum from a two-dimensional Fourier transform. We
find that the peculiar velocity power spectrum of the simulation with a bar and
transient, co-rotating spiral arms fits very well to that of APOGEE red clump
star data, while the quasi-stationary density wave spiral model without a bar
does not. We determine that the power spectrum is sensitive to the number of
spiral arms, spiral arm pitch angle and position with respect to the spiral
arm. However, it is necessary to go beyond the line of sight velocity field in
order to distinguish fully between the various spiral models with this method.
We compute the power spectrum for different regions of the spiral discs, and
discuss the application of this analysis technique to external galaxies.Comment: 14 pages, 11 figures. Improved and MNRAS Accepte
Investigating Anomalous Photochemistry in the Inner Wind of IRC+10216 Through ALMA Observations of HCN
In recent years, many questions have arisen regarding the chemistry of
photochemical products in the carbon-rich winds of evolved stars. To address
them, it is imperative to constrain the distributions of such species through
high angular resolution interferometric observations covering multiple
rotational transitions. We used archival ALMA observations to map rotational
lines involving high energy levels of cyanoacetylene (HCN) toward the inner
envelope (radius <8"/1000 AU) of the carbon star IRC+10216. The observed lines
include the J=28-27, J=30-29, and J=38-37, transitions of HCN in its ground
vibrational state. In contrast to previous observations of linear carbon chains
toward this AGB star which show extended, hollow emission at 15"-20" radii
(e.g. CH, CH, HCN), the maps of the HCN lines here show compact
morphologies comprising various arcs and density enhancements, with significant
emission from gas clumps at an angular distance of ~3" (350 AU) from the
central AGB star. We compared visibility sampled non-LTE radiative transfer
models with the observed brightness distributions, and derive a fractional
abundance with respect to H of for HCN at the radii probed by
these lines. These results are consistent with enhanced photochemistry
occurring in warm (~200 K) regions of the circumstellar envelope. After
application of a specialized chemical model for IRC+10216, we find evidence
that the enhanced HCN abundances in the inner wind are most likely due to a
solar-type binary companion initiating photochemistry in this region.Comment: 17 pages, 9 figures, 2 tables. Accepted for publication in Ap
Ultra-high foraging rates of harbor porpoises make them vulnerable to anthropogenic disturbance
This study was partly funded by the German Federal Agency for Nature Conservation (BfN) under the contract Z1.2-5330/2010/14 and the BfN-Cluster 7 “Effects of underwater noise on marine vertebrates.” D.M.W. and P.T.M. were also supported by the Danish National Research Foundation (FNU) and the Carlsberg Foundation, and M.J. was also supported by the Marine Alliance for Science and Technology Scotland (MASTS) and by a Marie Curie-Sklodowska award.The question of how individuals acquire and allocate resources to maximize fitness is central in evolutionary ecology. Basic information on prey selection, search effort, and capture rates are critical for understanding a predator’s role in its ecosystem and for predicting its response to natural and anthropogenic disturbance. Yet, for most marine species, foraging interactions cannot be observed directly. The high costs of thermoregulation in water require that small marine mammals have elevated energy intakes compared to similar-sized terrestrial mammals [1]. The combination of high food requirements and their position at the apex of most marine food webs may make small marine mammals particularly vulnerable to changes within the ecosystem [2–4], but the lack of detailed information about their foraging behavior often precludes an informed conservation effort. Here, we use high-resolution movement and prey echo recording tags on five wild harbor porpoises to examine foraging interactions in one of the most metabolically challenged cetacean species. We report that porpoises forage nearly continuously day and night, attempting to capture up to 550 small (3–10 cm) fish prey per hour with a remarkable prey capture success rate of >90%. Porpoises therefore target fish that are smaller than those of commercial interest, but must forage almost continually to meet their metabolic demands with such small prey, leaving little margin for compensation. Thus, for these “aquatic shrews,” even a moderate level of anthropogenic disturbance in the busy shallow waters they share with humans may have severe fitness consequences at individual and population levels.PostprintPeer reviewe
Dynamics of Warm-Absorbing Gas in Seyfert Galaxies: NGC 5548
A hydromagnetic (MHD) wind from a clumpy molecular accretion disk is invoked
to explain observations of warm absorbing (WA) gas in UVX from Sy galaxies.
This paper focuses on two issues: (1) compatibility of kinematics and dynamics
of MHD wind with the observed properties of WAs; and (2) relationship between
the UVX absorptions. We provide an in-depth comparison between the MHD model
and the Sy 1 galaxy NGC 5548, which at high spectral resolution exhibits a
number of discrete UV absorption components. We find that: (1) the total column
densities of Ovii, Oviii and H, are reproduced by constraining the UV ion
column densities of Civ and Nv in each component to lie within a factor of 2 of
their observed values and optimizing over the possible sets of component
ionization states and Civ column densities; (2) the WA exists in the outer part
of the wind and is not a continuation of the flow in the BLR; and (3) the WA
extends in radial and polar directions and is ionization-stratified. X-ray
absorption is found to be heavily biased towards smaller r, and UV absorption
originates at larger distances from the central continuum source. We show that
the discrete absorption components along the line-of-sight are intrinsically
clumpy. Density differences between kinematic components result in a range of
ionization and recombination timescales. We further test the applicability of
the MHD wind to WAs in general, by constructing a quasi-continuous flow model,
and extending it to arbitrary aspect angles. We estimate the fraction of Sy 1s
having detectable WAs with larger Ovii column density than Oviii, and the range
of total H column densities. We also find that the ratio of Ovii to Oviii
optical depths can serve as a new diagnostic of AGN aspect angle.Comment: Latex, 8 postscript figures. Astrophysical Journal, 536, June 10, in
pres
A Search for Light Hydrides in the Envelopes of Evolved Stars
We report a search for the diatomic hydrides SiH, PH, and FeH along the line
of sight toward the chemically rich circumstellar envelopes of IRC+10216 and VY
Canis Majoris. These molecules are thought to form in high temperature regions
near the photospheres of these stars, and may then further react via gas-phase
and dust-grain interactions leading to more complex species, but have yet to be
constrained by observation. We used the GREAT spectrometer on SOFIA to search
for rotational emission lines of these molecules in four spectral windows
ranging from 600 GHz to 1500 GHz. Though none of the targeted species were
detected in our search, we report their upper limit abundances in each source
and discuss how they influence the current understanding of hydride chemistry
in dense circumstellar media. We attribute the non-detections of these hydrides
to their compact source sizes, high barriers of formation, and proclivity to
react with other molecules in the winds.Comment: Accepted for publication in ApJ. 14 pages, 4 figures, 3 table
Protective effect of anti-SUAM antibodies on \u3cem\u3eStreptococcus uberis\u3c/em\u3e mastitis
In the present study, the effect of anti-recombinant Streptococcus uberis adhesion molecule (SUAM) antibodies against S. uberis intramammary infections (IMI) was evaluated using a passive protection model. Mammary quarters of healthy cows were infused with S. uberis UT888 opsonized with affinity purified anti-rSUAM antibodies or hyperimmune sera. Non-opsonized S. uberis UT888 were used as a control. Mammary quarters infused with opsonized S. uberis showed mild-to undetectable clinical symptoms of mastitis, lower milk bacterial counts, and less infected mammary quarters as compared to mammary quarters infused with non-opsonized S. uberis. These findings suggest that anti-rSUAM antibodies interfered with infection of mammary gland by S. uberis which might be through preventing adherence to and internalization into mammary gland cells, thus facilitating clearance of S. uberis, reducing colonization, and causing less IMI
Dynamics and energetics of the mammalian phosphatidylinositol transfer protein phospholipid exchange cycle
Phosphatidylinositol-transfer proteins (PITPs) regulate phosphoinositide signaling in eukaryotic cells. The defining feature of PITPs is their ability to exchange phosphatidylinositol (PtdIns) molecules between membranes, and this property is central to PITP-mediated regulation of lipid signaling. However, the details of the PITP-mediated lipid exchange cycle remain entirely obscure. Here, all-atom molecular dynamics simulations of the mammalian StART-like PtdIns/phosphatidylcholine (PtdCho) transfer protein PITP alpha, both on membrane bilayers and in solvated systems, informed downstream biochemical analyses that tested key aspects of the hypotheses generated by the molecular dynamics simulations. These studies provided five key insights into the PITP alpha lipid exchange cycle: (i) interaction of PITP alpha with the membrane is spontaneous and mediated by four specific protein substructures; (ii) the ability of PITP alpha to initiate closure around the PtdCho ligand is accompanied by loss of flexibility of two helix/loop regions, as well as of the C-terminal helix; (iii) the energy barrier of phospholipid extraction from the membrane is lowered by a network of hydrogen bonds between the lipid molecule and PITP alpha; (iv) the trajectory of PtdIns or PtdCho into and through the lipidbinding pocket is chaperoned by sets of PITP alpha residues conserved throughout the StART-like PITP family; and (v) conformational transitions in the C-terminal helix have specific functional involvements in PtdIns transfer activity. Taken together, these findings provide the first mechanistic description of key aspects of the PITP alpha PtdIns/PtdCho exchange cycle and offer a rationale for the high conservation of particular sets of residues across evolutionarily distant members of the metazoan StART-like PITP family.Peer reviewe
Detection of Two Interstellar Polycyclic Aromatic Hydrocarbons via Spectral Matched Filtering
Ubiquitous unidentified infrared emission bands are seen in many astronomical
sources. Although these bands are widely, if not unanimously, attributed to the
collective emission from polycyclic aromatic hydrocarbons, no single species
from this class has been detected in space. We present the discovery of two -CN
functionalized polycyclic aromatic hydrocarbons, 1- and 2-cyanonaphthalene, in
the interstellar medium aided by spectral matched filtering. Using radio
observations with the Green Bank Telescope, we observe both bi-cyclic ring
molecules in the molecular cloud TMC-1. We discuss potential in situ gas-phase
formation pathways from smaller organic precursor molecules
ALMA Observations of the DART Impact: Characterizing the Ejecta at Sub-Millimeter Wavelengths
We report observations of the Didymos-Dimorphos binary asteroid system using
the Atacama Large Millimeter/Submillimeter Array (ALMA) and the Atacama Compact
Array (ACA) in support of the Double Asteroid Redirection Test (DART) mission.
Our observations on UT 2022 September 15 provided a pre-impact baseline and the
first measure of Didymos-Dimorphos' spectral emissivity at mm,
which was consistent with the handful of siliceous and carbonaceous asteroids
measured at millimeter wavelengths. Our post-impact observations were conducted
using four consecutive executions each of ALMA and the ACA spanning from
T3.52 to T8.60 hours post-impact, sampling thermal emission from the
asteroids and the impact ejecta. We scaled our pre-impact baseline measurement
and subtracted it from the post-impact observations to isolate the flux density
of mm-sized grains in the ejecta. Ejecta dust masses were calculated for a
range of materials that may be representative of Dimorphos' S-type asteroid
material. The average ejecta mass over our observations is consistent with
1.3--6.4 kg, with the lower and higher values calculated for
amorphous silicates and for crystalline silicates, respectively. Owing to the
likely crystalline nature of S-type asteroid material, the higher value is
favored. These ejecta masses represent 0.3--1.5\% of Dimorphos' total mass and
are in agreement with lower limits on the ejecta mass based on measurements at
optical wavelengths. Our results provide the most sensitive measure of mm-sized
material in the ejecta and demonstrate the power of ALMA for providing
supporting observations to spaceflight missions
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