2,399 research outputs found
Core level photoelectron spectroscopy of heterogeneous reactions at liquid-vapor interfaces: Current status, challenges, and prospects
Liquid–vapor interfaces, particularly those between aqueous solutions and air, drive numerous important chemical and physical processes in the atmosphere and in the environment. X-ray photoelectron spectroscopy is an excellent method for the investigation of these interfaces due to its surface sensitivity, elemental and chemical specificity, and the possibility to obtain information on the depth distribution of solute and solvent species in the interfacial region. In this Perspective, we review the progress that was made in this field over the past decades and discuss the challenges that need to be overcome for investigations of heterogeneous reactions at liquid–vapor interfaces under close-torealistic environmental conditions. We close with an outlook on where some of the most exciting and promising developments might lie in this fiel
Gravity in the Local Universe : density and velocity fields using CosmicFlows-4
This article publicly releases three-dimensional reconstructions of the local
Universe gravitational field below z=0.8 that were computed using the
CosmicFlows-4 catalog of 56,000 galaxy distances and its sub-sample of 1,008
type Ia supernovae distances. The article also provides measurements of the
growth rate of structure using the pairwise correlation of radial peculiar
velocities f sigma8 = 0.38(+/-0.04) (ungrouped CF4), f sigma8 = 0.36(+/-0.05)
(grouped CF4), f sigma8 = 0.30(+/-0.06) (SNIa) and of the bulk flow in the 3D
reconstructed Local Universe of 230 +/- 136 km s-1 at 300 Mpc of distance from
the observer. The exploration of 10,000 reconstructions gives that the
distances delivered by the Cosmicflows-4 catalog are compatible with a Hubble
constant of H0 = 74.5 +/- 0.1 (grouped CF4), H0 = 75.0 +/- 0.35 (ungrouped CF4)
and H0 = 75.5 +/- 0.95 (CF4 SNIa subsample).Comment: Submitted A&A Oct 31st, 2022 / (AA/2022/45331) / Accepted January
2023 All Figures and values updated after the december 2022 major correction
in CF4 catalo
Structural and mutational analyses of the Leptospira interrogans virulence-related heme oxygenase provide insights into its catalytic mechanism
© 2017 Soldano et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Heme oxygenase from Leptospira interrogans is an important virulence factor. During catalysis, redox equivalents are provided to this enzyme by the plastidic-type ferredoxin-NADP+ reductase also found in L. interrogans. This process may have evolved to aid this bacterial pathogen to obtain heme-iron from their host and enable successful colonization. Herein we report the crystal structure of the heme oxygenase-heme complex at 1.73 Å resolution. The structure reveals several distinctive features related to its function. A hydrogen bonded network of structural water molecules that extends from the catalytic site to the protein surface was cleared observed. A depression on the surface appears to be the H+ network entrance from the aqueous environment to the catalytic site for O2 activation, a key step in the heme oxygenase reaction. We have performed a mutational analysis of the F157, located at the above-mentioned depression. The mutant enzymes were unable to carry out the complete degradation of heme to biliverdin since the reaction was arrested at the verdoheme stage. We also observed that the stability of the oxyferrous complex, the efficiency of heme hydroxylation and the subsequent conversion to verdoheme was adversely affected. These findings underscore a long-range communication between the outer fringes of the hydrogen-bonded network of structural waters and the heme active site during catalysis. Finally, by analyzing the crystal structures of ferredoxin-NADP+ reductase and heme oxygenase, we propose a model for the productive association of these proteins
The discovery of a T6.5 subdwarf
We report the discovery of ULAS J131610.28+075553.0, an sdT6.5 dwarf in the UKIDSS Large Area Survey 2 epoch proper motion catalogue. This object displays significant spectral peculiarity, with the largest yet seen deviations from T6 and T7 templates in the Y and K bands for this subtype. Its large, similar to 1 arcsec yr(-1), proper motion suggests a large tangential velocity of V-tan approximate to 240-340 km s(-1), if we assume its M-J lies within the typical range for T6.5 dwarfs. This makes it a candidate for membership of the Galactic halo population. However, other metal-poor T dwarfs exhibit significant under luminosity both in specific bands and bolometrically. As a result, it is likely that its velocity is somewhat smaller, and we conclude it is a likely thick disc or halo member. This object represents the only T dwarf earlier than T8 to be classified as a subdwarf, and is a significant addition to the currently small number of known unambiguously substellar subdwarfs.Peer reviewe
HIP 38939B: A New Benchmark T Dwarf in the Galactic Plane Discovered with Pan-STARRS1
We report the discovery of a wide brown dwarf companion to the mildly
metal-poor ([Fe/H]=-0.24), low galactic latitude (b = 1.88 deg) K4V star HIP
38939. The companion was discovered by its common proper motion with the
primary and its red optical (Pan-STARRS1) and blue infrared (2MASS) colors. It
has a projected separation of 1630 AU and a near-infrared spectral type of
T4.5. As such it is one of only three known companions to a main sequence star
which have early/mid-T spectral types (the others being HN Peg B and eps Indi
B). Using chromospheric activity we estimate an age for the primary of
900{+1900,-600} Myr. This value is also in agreement with the age derived from
the star's weak ROSAT detection. Comparison with evolutionary models for this
age range indicates that HIP 38939B falls in the mass range 38+/-20 Mjup with
an effective temperature range of 1090+/-60 K. Fitting our spectrum with
atmospheric models gives a best fitting temperature of 1100 K. We include our
object in an analysis of the population of benchmark T dwarfs and find that
while older atmospheric models appeared to over-predict the temperature of the
coolest objects compared to evolutionary models, more recent atmospheric models
provide better agreement.Comment: ApJ, in press. Tiny changes incorporated into final version: added
analysis of likelihood of companionship, clarified the fitting proceedure,
and updated the benchmark analysis to highlight when the quoted evolutionary
models use the atmospheric model they are being compared to as a boundary
conditio
Parallaxes of southern extremely cool objects (PARSEC). II : Spectroscopic follow-up and parallaxes of 52 targets
We present near-infrared spectroscopy for 52 ultracool dwarfs, including two newly discovered late-M dwarfs, one new late-M subdwarf candidate, three new L, and four new T dwarfs. We also present parallaxes and proper motions for 21 of them. Four of the targets presented here have previous parallax measurements, while all the others are new values. This allow us to populate further the spectral sequence at early types (L0-L4). Combining the astrometric parameters with the new near-infrared spectroscopy presented here, we are able to investigate further the nature of some of the objects. In particular, we find that the peculiar blue L1 dwarf SDSS J133148.92-011651.4 is a metal-poor object, likely a member of the galactic thick disk. We discover a new M subdwarf candidate, 2MASS J20115649-6201127. We confirm the low-gravity nature of EROS-MP J0032-4405, DENIS-P J035726.9-441730, and 2MASS J22134491-2136079. We present two new metal-poor dwarfs: the L4pec 2MASS J19285196-4356256 and the M7pec SIPS2346-5928. We also determine the effective temperature and bolometric luminosity of the 21 targets with astrometric measurements, and we obtain a new polynomial relation between effective temperature and near-infrared spectral type. The new fit suggests a flattening of the sequence at the transition between M and L spectral types. This could be an effect of dust formation, which causes a more rapid evolution of the spectral features as a function of the effective temperature.Peer reviewe
ADAPTIVE OPTICS IMAGING OF VHS 1256-1257: A LOW MASS COMPANION TO A BROWN DWARF BINARY SYSTEM
Recently, Gauza et al. (2015) reported the discovery of a companion to the
late M-dwarf, VHS J125601.92-125723.9 (VHS 1256-1257). The companion's absolute
photometry suggests its mass and atmosphere are similar to the HR 8799 planets.
However, as a wide companion to a late-type star, it is more accessible to
spectroscopic characterization. We discovered that the primary of this system
is an equal-magnitude binary. For an age Myr the A and B components
each have a mass of , and the b component
has a mass of , making VHS 1256-1257 only the third brown
dwarf triple system. There exists some tension between the spectrophotometric
distance of pc and the parallax distance of pc. At
12.7 pc VHS1256-1257 A and B would be the faintest known M7.5 objects, and are
even faint outliers among M8 types. If the larger spectrophotmetric distance is
more accurate than the parallax, then the mass of each component increases. In
particular, the mass of the b component increases well above the deuterium
burning limit to and the mass of each binary
component increases to . At 17.1 pc, the UVW
kinematics of the system are consistent with membership in the AB~Dor moving
group. The architecture of the system resembles a hierarchical stellar multiple
suggesting it formed via an extension of the star-formation process to low
masses. Continued astrometric monitoring will resolve this distance uncertainty
and will provide dynamical masses for a new benchmark system.Comment: Accepted to ApJ
A focus on L dwarfs with trigonometric parallaxes
This is an author-created, un-copyedited version of an article published in Publications of the Astronomical Society of the Pacific. Under embargo until 14 May 2019. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at https://doi.org/10.1088/1538-3873/aaacc5.We report new parallax measurements for ten L and early T type dwarfs, five of which have no previous published values, using observations over 3 years at the robotic Liverpool Telescope. The resulting parallaxes and proper motions have median errors of 2\,mas and 1.5\,mas/year respectively. Their space motions indicate they are all Galactic disk members. We combined this sample with other objects with astrometry from the Liverpool Telescope and with published literature astrometry to construct a sample of 260 L and early T type dwarfs with measured parallaxes, designated the Astrometry Sample. We study the kinematics of the Astrometry Sample, and derived a solar motion of \,\kms~ with respect to the local standard of rest, in agreement with recent literature. We derive a kinematic age of 1.5-1.7\,Gyr for the Astrometry Sample assuming the age increases monotonically with the total velocity for a given disk sample. This kinematic age is less than half literature values for other low mass dwarf samples. We believe this difference arises for two reasons (1) the sample is mainly composed of mid to late L dwarfs which are expected to be relatively young and (2) the requirement that objects have a measured parallax biases the sample to the brighter examples which tend to be younger.Peer reviewedFinal Accepted Versio
Growing the Grassroots or Backing Bandits? Dilemmas of Donor Support for Haiti’s (UN)Civil Society
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