703 research outputs found
Ground-based detection of sodium in the transmission spectrum of exoplanet HD209458b
[Context] The first detection of an atmosphere around an extrasolar planet
was presented by Charbonneau and collaborators in 2002. In the optical
transmission spectrum of the transiting exoplanet HD209458b, an absorption
signal from sodium was measured at a level of 0.023+-0.006%, using the STIS
spectrograph on the Hubble Space Telescope. Despite several attempts, so far
only upper limits to the Na D absorption have been obtained using telescopes
from the ground, and the HST result has yet to be confirmed.
[Aims] The aims of this paper are to re-analyse data taken with the High
Dispersion Spectrograph on the Subaru telescope, to correct for systematic
effects dominating the data quality, and to improve on previous results
presented in the literature.
[Methods] The data reduction process was altered in several places, most
importantly allowing for small shifts in the wavelength solution. The relative
depth of all lines in the spectra, including the two sodium D lines, are found
to correlate strongly with the continuum count level in the spectra. These
variations are attributed to non-linearity effects in the CCDs. After removal
of this empirical relation the uncertainties in the line depths are only a
fraction above that expected from photon statistics.
[Results] The sodium absorption due to the planet's atmosphere is detected at
>5 sigma, at a level of 0.056+-0.007% (2x3.0 Ang band), 0.070+-0.011% (2x1.5
Ang band), and 0.135+-0.017% (2x0.75 Ang band). There is no evidence that the
planetary absorption signal is shifted with respect to the stellar absorption,
as recently claimed for HD189733b. The measurements in the two most narrow
bands indicate that some signal is being resolved.[abridged]Comment: Latex, 7 pages: accepted for publication in Astronomy & Astrophysic
Structure and Evolution of Nearby OB Associations
We present the first results of a comprehensive census of the stellar content
of the nearby OB associations based on Hipparcos positions, proper motions and
parallaxes for 12842 candidate member stars distributed over 21 fields on the
sky. We use a new method to identify moving groups in these fields (see de
Bruijne et al., these proceedings). Previously, astrometric membership in
nearly all the nearby OB associations was known only for stars with spectral
types earlier than B5. The Hipparcos measurements now allow us to identify
members down to late F. This census provides a firm basis for studies of
galactic and extragalactic star forming regions.Comment: 6 pages, 4 Postscript figures, LaTeX using venice97.sty,
twocolumn.sty; to appear in Proceedings of the Hipparcos Venice '97
Symposium, ESA-SP 40
GW190814 follow-up with the optical telescope MeerLICHT
The Advanced LIGO and Virgo gravitational wave observatories detected a
signal on 2019 August 14 during their third observing run, named GW190814. A
large number of electromagnetic facilities conducted follow-up campaigns in the
search for a possible counterpart to the gravitational wave event, which was
made especially promising given the early source classification of a neutron
star-black hole merger.We present the results of the GW follow-up campaign
taken with the wide-field optical telescope MeerLICHT, located at the South
African Astronomical Observatory Sutherland site. We use our results to
constrain possible kilonova models. MeerLICHT observed more than 95% of the
probability localisation each night for over a week in three optical bands
(u,q,i) with our initial observations beginning almost 2 hours after the GW
detection. We describe the search for new transients in MeerLICHT data and
investigate how our limiting magnitudes can be used to constrain an
AT2017gfo-like kilonova. A single new transient was found in our analysis of
MeerLICHT data, which we exclude from being the electromagnetic counterpart to
GW190814 due to the existence of a spatially unresolved source at the
transient's coordinates in archival data. Using our limiting magnitudes, the
confidence with which we can exclude the presence of an AT2017gfo-like kilonova
at the distance of GW190814 was low ().Comment: 19 pages, 6 figures, accepted by A&
Calculations of the dynamical critical exponent using the asymptotic series summation method
We consider how the Pad'e-Borel, Pad'e-Borel-Leroy, and conformal mapping
summation methods for asymptotic series can be used to calculate the dynamical
critical exponent for homogeneous and disordered Ising-like systems.Comment: 21 RevTeX pages, 2 figure
The transcriptional repressor protein NsrR senses nitric oxide directly via a [2Fe-2S] cluster
The regulatory protein NsrR, a member of the Rrf2 family of transcription repressors, is specifically dedicated to sensing nitric oxide (NO) in a variety of pathogenic and non-pathogenic bacteria. It has been proposed that NO directly modulates NsrR activity by interacting with a predicted [Fe-S] cluster in the NsrR protein, but no experimental evidence has been published to support this hypothesis. Here we report the purification of NsrR from the obligate aerobe Streptomyces coelicolor. We demonstrate using UV-visible, near UV CD and EPR spectroscopy that the protein contains an NO-sensitive [2Fe-2S] cluster when purified from E. coli. Upon exposure of NsrR to NO, the cluster is nitrosylated, which results in the loss of DNA binding activity as detected by bandshift assays. Removal of the [2Fe-2S] cluster to generate apo-NsrR also resulted in loss of DNA binding activity. This is the first demonstration that NsrR contains an NO-sensitive [2Fe-2S] cluster that is required for DNA binding activity
Solution structure of a repeated unit of the ABA-1 nematode polyprotein allergen of ascaris reveals a novel fold and two discrete lipid-binding sites
Parasitic nematode worms cause serious health problems in humans and other animals. They can induce allergic-type immune responses, which can be harmful but may at the same time protect against the infections. Allergens are proteins that trigger allergic reactions and these parasites produce a type that is confined to nematodes, the nematode polyprotein allergens (NPAs). These are synthesized as large precursor proteins comprising repeating units of similar amino acid sequence that are subsequently cleaved into multiple copies of the allergen protein. NPAs bind small lipids such as fatty acids and retinol (Vitamin A) and probably transport these sensitive and insoluble compounds between the tissues of the worms. Nematodes cannot synthesize these lipids, so NPAs may also be crucial for extracting nutrients from their hosts. They may also be involved in altering immune responses by controlling the lipids by which the immune and inflammatory cells communicate. We describe the molecular structure of one unit of an NPA, the well-known ABA-1 allergen of Ascaris and find its structure to be of a type not previously found for lipid-binding proteins, and we describe the unusual sites where lipids bind within this structur
Gravitational Waves From Known Pulsars: Results From The Initial Detector Era
We present the results of searches for gravitational waves from a large selection of pulsars using data from the most recent science runs (S6, VSR2 and VSR4) of the initial generation of interferometric gravitational wave detectors LIGO (Laser Interferometric Gravitational-wave Observatory) and Virgo. We do not see evidence for gravitational wave emission from any of the targeted sources but produce upper limits on the emission amplitude. We highlight the results from seven young pulsars with large spin-down luminosities. We reach within a factor of five of the canonical spin-down limit for all seven of these, whilst for the Crab and Vela pulsars we further surpass their spin-down limits. We present new or updated limits for 172 other pulsars (including both young and millisecond pulsars). Now that the detectors are undergoing major upgrades, and, for completeness, we bring together all of the most up-to-date results from all pulsars searched for during the operations of the first-generation LIGO, Virgo and GEO600 detectors. This gives a total of 195 pulsars including the most recent results described in this paper.United States National Science FoundationScience and Technology Facilities Council of the United KingdomMax-Planck-SocietyState of Niedersachsen/GermanyAustralian Research CouncilInternational Science Linkages program of the Commonwealth of AustraliaCouncil of Scientific and Industrial Research of IndiaIstituto Nazionale di Fisica Nucleare of ItalySpanish Ministerio de Economia y CompetitividadConselleria d'Economia Hisenda i Innovacio of the Govern de les Illes BalearsNetherlands Organisation for Scientific ResearchPolish Ministry of Science and Higher EducationFOCUS Programme of Foundation for Polish ScienceRoyal SocietyScottish Funding CouncilScottish Universities Physics AllianceNational Aeronautics and Space AdministrationOTKA of HungaryLyon Institute of Origins (LIO)National Research Foundation of KoreaIndustry CanadaProvince of Ontario through the Ministry of Economic Development and InnovationNational Science and Engineering Research Council CanadaCarnegie TrustLeverhulme TrustDavid and Lucile Packard FoundationResearch CorporationAlfred P. Sloan FoundationAstronom
Microdevices for extensional rheometry of low viscosity elastic liquids : a review
Extensional flows and the underlying stability/instability mechanisms are of extreme relevance to the efficient operation of inkjet printing, coating processes and drug delivery systems, as well as for the generation of micro droplets. The development of an extensional rheometer to characterize the extensional properties of low viscosity fluids has therefore stimulated great interest of researchers, particularly in the last decade. Microfluidics has proven to be an extraordinary working platform and different configurations of potential extensional microrheometers have been proposed. In this review, we present an overview of several successful designs, together with a critical assessment of their capabilities and limitations
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