308 research outputs found
A collision-induced satellite in the Lyman Beta profile due to H-H collisions
We present a theoretical profile of the Lyman Beta line of atomic hydrogen
perturbed by collisions with neutral hydrogen atoms and protons. We use a
general unified theory in which the electric dipole moment varies during a
collision. A collision-induced satellite appears on Lyman Beta, correlated to
the B''\barB 1Sigma+u - X 1Sigma+g asymptotically forbidden transition of H_2.
As a consequence, the appearance of the line wing between Lyman Alpha and Lyman
Beta is shown to be sensitive to the relative abundance of hydrogen ions and
neutral atoms, and thereby to provide a temperature diagnostic for stellar
atmospheres and laboratory plasmas.Comment: 8 pages, 4 figures, acc.f.publ.European Physical Journal
Theoretical profiles of the Mg + resonance lines perturbed by collisions with He
International audienceThe effects of collision broadening by He are central to understanding the opacity of cool stellar atmospheres. Aims. DZ white dwarfs show metal lines which are, in many cases, believed to come from some rocky material, a remnant of a former exoplanetary system. The analysis of the Mg + resonance lines is a valuable method to determine the chemical abundances in these systems. Methods. Unified profiles of the strongest of the UV lines of Mg + have been calculated in the semi-classical approach using very recent ab initio potential energies. Results. We present the first theoretical line profile calculations of the resonance lines of Mg + that have been perturbed by helium in physical conditions of atmospheres in helium-rich white dwarfs with metal traces
FUSE observations of G226-29: First detection of the H_2 quasi-molecular satellite at 1150A
We present new FUV observations of the pulsating DA white dwarf G226-29
obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE). This ZZ Ceti
star is the brightest one of its class and the coolest white dwarf observed by
FUSE. We report the first detection of the broad quasi-molecular
collision-induced satellite of Ly-beta at 1150 A, an absorption feature that is
due to transitions which take place during close collisions of hydrogen atoms.
The physical interpretation of this feature is based on recent progress of the
line broadening theory of the far wing of Ly-beta. This predicted feature had
never been observed before, even in laboratory spectra.Comment: Accepted for publication in ApJ Letters; 6 pages, 3 figure
A Young Solar Twin in the Rosette Cluster NGC 2244 Line of Sight
Based on prior precision photometry and cluster age analysis, the bright star GSC 00154â01819 is a possible young pre-main sequence member of the Rosette cluster, NGC 2244. As part of a comprehensive study of the large-scale structure of the Rosette and its excitation by the cluster stars, we noted this star as a potential backlight for a probe of the interstellar medium and extinction along the sight line towards a distinctive nebular feature projected on to the cluster centre. New high-resolution spectra of the star were taken with the University College London Echelle Spectrograph of the AAT. They reveal that rather than being a reddened spectral type B or A star within the Mon OB2 association, it is a nearby, largely unreddened, solar twin of spectral type G2V less than 180 Myr old. It is about 219 pc from the Sun with a barycentric radial velocity of +14.35 ± 1.99âkmâsâ1. The spectrum of the Rosette behind it and along this line of sight shows a barycentric radial velocity of +26.0 ± 2.4âkmâsâ1 in Hâα, and a full width at half-maximum velocity dispersion of 61.94 ± 1.38âkmâsâ1
Spitzer and z' Secondary Eclipse Observations of the Highly Irradiated Transiting Brown Dwarf KELT-1b
We present secondary eclipse observations of the highly irradiated transiting
brown dwarf KELT-1b. These observations represent the first constraints on the
atmospheric dynamics of a highly irradiated brown dwarf, and the atmospheres of
irradiated giant planets at high surface gravity. Using the Spitzer Space
Telescope, we measure secondary eclipse depths of 0.195+/-0.010% at 3.6um and
0.200+/-0.012% at 4.5um. We also find tentative evidence for the secondary
eclipse in the z' band with a depth of 0.049+/-0.023%. These measured eclipse
depths are most consistent with an atmosphere model in which there is a strong
substellar hotspot, implying that heat redistribution in the atmosphere of
KELT-1b is low. While models with a more mild hotspot or even with dayside heat
redistribution are only marginally disfavored, models with complete heat
redistribution are strongly ruled out. The eclipse depths also prefer an
atmosphere with no TiO inversion layer, although a model with TiO inversion is
permitted in the dayside heat redistribution case, and we consider the
possibility of a day-night TiO cold trap in this object. For the first time, we
compare the IRAC colors of brown dwarfs and hot Jupiters as a function of
effective temperature. Importantly, our measurements reveal that KELT-1b has a
[3.6]-[4.5] color of 0.07+/-0.11, identical to that of isolated brown dwarfs of
similarly high temperature. In contrast, hot Jupiters generally show redder
[3.6]-[4.5] colors of ~0.4, with a very large range from ~0 to ~1. Evidently,
despite being more similar to hot Jupiters than to isolated brown dwarfs in
terms of external forcing of the atmosphere by stellar insolation, KELT-1b has
an atmosphere most like that of other brown dwarfs. This suggests that surface
gravity is very important in controlling the atmospheric systems of substellar
mass bodies.Comment: 14 pages, 3 tables, 11 figures. Accepted by ApJ. Updated to reflect
the accepted versio
Modulation of NF-ÎșB-dependent gene transcription using programmable DNA minor groove binders
Nuclear factor ÎșB (NF-ÎșB) is a transcription factor that regulates various aspects of immune response, cell death, and differentiation as well as cancer. In this study we introduce the Py-Im polyamide 1 that binds preferentially to the sequences 5âČ-WGGWWW-3âČ and 5âČGGGWWW-3âČ. The compound is capable of binding to ÎșB sites and reducing the expression of various NF-ÎșBâdriven genes including IL6 and IL8 by qRT-PCR. Chromatin immunoprecipitation experiments demonstrate a reduction of p65 occupancy within the proximal promoters of those genes. Genome-wide expression analysis by RNA-seq compares the DNA-binding polyamide with the well-characterized NF-ÎșB inhibitor PS1145, identifies overlaps and differences in affected gene groups, and shows that both affect comparable numbers of TNF-αâinducible genes. Inhibition of NF-ÎșB DNA binding via direct displacement of the transcription factor is a potential alternative to the existing antagonists
Modeling of the Lyman gamma satellites in FUSE spectra of DA white dwarfs
We present new theoretical calculations of the line profile of Lyman gamma
that include transitions in which a photon is absorbed by a neutral hydrogen
atom while it interacts with a proton. Models show that two absorption features
located near 992 A and 996 A are due to H-H^+ collisions. These quasi-molecular
satellites are similar to those that were identified in the wings of Lyman
alpha and Lyman beta lines of hydrogen-rich white dwarfs. We compute synthetic
spectra that take account of these new theoretical profiles and compare them to
the spectra of four DA white dwarfs that were observed with FUSE. The models
predict the absorption features that are observed in the wing of Lyman gamma
near 995 A, and confirm that these features are quasi-molecular satellites.Comment: 5 pages, 3 figures, accepted for publication in Astronomy and
Astrophysic
K-H_2 Quasi-molecular absorption detected in the T-dwarf epsilon Indi Ba
T-type dwarfs present a broad and shallow absorption feature centred around
6950 A in the blue wing of the K doublet at 0.77 micron which resembles in
depth and shape the satellite absorption predicted by detailed collisional
broadening profiles. In our previous work, the predicted line satellite
position was however somewhat too blue compared to the observed feature. In
this paper we investigate whether new calculations of the energy surfaces of
the potentials in the K-H_2 system, including spin-orbit coupling, result in a
closer coincidence of the satellite with the observed position. We also
investigate the extent to which CaH absorption bands contribute to the feature.
We present model atmospheres and synthetic spectra, including gravitational
settling for an improved description of depth-dependent abundances of
refractory elements, and based on new K-H_2 line profiles using improved
interaction potentials. By comparison with a high signal-to-noise optical
spectrum of the T1 dwarf epsilon Indi Ba, we find that these new models do
reproduce the observed feature, while CaH does not contribute for the
atmospheric parameters considered. We also find that CaH is settled out so deep
into the atmosphere that even turbulent vertical mixing would appear
insufficient to bring significant amounts of CaH to the photosphere in dwarfs
later than ~L5. We conclude that previous identification of the feature at this
location in T and late L dwarf spectra with CaH was erroneous, as expected on
physical grounds: calcium condenses onto grains in early L dwarfs and thus
should have settled out of the photosphere in cooler brown dwarfs. This finding
revokes one observational verification for the cloud-clearing theory: a gradual
clearing of the cloud cover in early T dwarfs.Comment: accepted for publication by Astronomy & Astrophysics Letters, 4
pages, 3 colour figure
KELT-3b: A Hot Jupiter Transiting A V=9.8 Late-F Star
We report the discovery of KELT-3b, a moderately inflated transiting hot Jupiter with a mass of 1.477(-0.067)(+0.066) M-J, radius of 1.345 +/- 0.072 R-J, and an orbital period of 2.7033904 +/- 0.000010 days. The host star, KELT-3, is a V = 9.8 late F star with M-* = 1.278(-0.061)(+0.063) M-circle dot, R-* = 1.472(-0.067)(+0.065) R-circle dot, T-eff = 6306(-49)(+50) K, log(g) = 4.209(-0.031)(+0.033), and [Fe/H] = 0.044(-0.082)(+0.080), and has a likely proper motion companion. KELT-3b is the third transiting exoplanet discovered by the KELT survey, and is orbiting one of the 20 brightest known transiting planet host stars, making it a promising candidate for detailed characterization studies. Although we infer that KELT-3 is significantly evolved, a preliminary analysis of the stellar and orbital evolution of the system suggests that the planet has likely always received a level of incident flux above the empirically identified threshold for radius inflation suggested by Demory & Seager
Molecular basis of FIR-mediated c-myc transcriptional control
The far upstream element (FUSE) regulatory system promotes a peak in the concentration of c-Myc during cell cycle. First, the FBP transcriptional activator binds to the FUSE DNA element upstream of the c-myc promoter. Then, FBP recruits its specific repressor (FIR), which acts as an on/off transcriptional switch. Here we describe the molecular basis of FIR recruitment, showing that the tandem RNA recognition motifs of FIR provide a platform for independent FUSE DNA and FBP protein binding and explaining the structural basis of the reversibility of the FBP-FIR interaction. We also show that the physical coupling between FBP and FIR is modulated by a flexible linker positioned sequentially to the recruiting element. Our data explain how the FUSE system precisely regulates c-myc transcription and suggest that a small change in FBP-FIR affinity leads to a substantial effect on c-Myc concentration.MRC Grant-in-aid U11757455
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