6,703 research outputs found
Effect of Zn2+ on photosynthetic oxygen evolution and chloroplast manganese
AbstractTreatment of thylakoid suspensions with Zn2+ causes the appearance of an EPR signal due to Mn2+. The size of the signal was linearly correlated with the inhibition of oxygen evolution. Full inhibition appeared to correspond to the release of 2 Mn atoms/reaction centre of photosystem II. The released Mn2+ remained associated with the chloroplast pellet on centrifugation and took several hours to equilibrate with the surrounding medium. The sequestered Mn2+ does not appear to be in the thylakoid interior but in a more restricted hydrophilic compartment
Modeling magnetohydrodynamics and non equilibrium SoHO/UVCS line emission of CME shocks
We provide a guideline to interpret the UVCS emission lines (in particular O
VI and Si XII) during shock wave propagation in the outer solar corona. We use
a numerical MHD model performing a set of simulations of shock waves generated
in the corona and from the result we compute the plasma emission for the O VI
and Si XII including the effects of NEI. We analyze the radiative and spectral
properties of our model with the support of a detailed radiation model
including Doppler dimming and an analytical model for shocks, and, finally, we
synthesize the expected O VI 1032A line profile. We explain several spectral
features of the observations like the absence of discontinuities in the O VI
emission during the shock passage, the brightening of Si XII emission and the
width of the lines. We use our model also to give very simple and general
predictions for the strength of the line wings due to the ions shock heating
and on the line shape for Limb CMEs or Halo CMEs. The emission coming from
post-shock region in the solar corona roughly agrees with the emission from a
simple planar and adiabatic shock, but the effect of thermal conduction and the
magnetic field may be important depending on the event parameters. Doppler
dimming significantly influences the O VI emission while Si XII line brightens
mainly because of the shock compression. Significant shock heating is
responsible for the wide and faint component of the O VI line usually observed
which may be taken as a shock signature in the solar corona.Comment: 11 pages, 12 figures, 2 appendixe
The faint supernova remnant G 34.7-0.4 (W44)
Flux calibrated images of the known supernova remnant G 34.7-0.4 in basic
optical emission lines are presented. The low ionization images show a
relatively flat flux distribution. The diffuse and patchy morphology of the
detected optical emission may indicate the presence of turbulent magnetic
fields. Typical observed Halpha+[N II] fluxes are ~8 x 10^{-17} erg s^{-1}
cm^{-2} arcsec^{-2}, while the [S II] fluxes are lower around 4 x 10^{-17} erg
s^{-1} cm^{-2} arcsec^{-2}. Emission in the medium ionization line of [O III]
5007 A is not detected within our sensitivity limits, probably due to the heavy
extinction towards the remnant. The long-slit spectra reveal strong [S II] and
[N II] emission relative to Halpha and moderate [O I] 6300 A emission. Shock
velocities in the range of 110-150 km/s and low electron densities are
estimated. Archival MSX infrared data show emission in the south and west areas
of the remnant matching rather well the optical and radio emission.Comment: 6 pages, 4 figures, accepted for publication in A&
Stellar wind bubbles around WR and [WR] stars
We study the dynamics of stellar wind bubbles around hydrogen-deficient stars
using numerical simulations with time- and ion dependent cooling. We consider
two types of hydrogen-deficient stars, massive WR stars, producing Ring
Nebulae, and low mass [WR] stars, producing Planetary Nebulae. We show that for
the Planetary Nebulae, the different cooling properties of the
hydrogen-deficient wind lead to a later transition from momentum- to
energy-driven flow, which could explain the observed turbulence of these
nebulae. We find that Ring Nebulae should all be energy-driven, and show how
comparing the bubble's momentum and kinetic energy to the input wind momentum
and kinetic energy, can give misleading information about the dynamics of the
bubble.Comment: 9 pages, 3 figures, to be published in A&
Optical Imaging and Spectroscopic Observation of the Galactic Supernova Remnant G85.9-0.6
Optical CCD imaging with H and [SII] filters and spectroscopic
observations of the galactic supernova remnant G85.9-0.6 have been performed
for the first time. The CCD image data are taken with the 1.5m Russian-Turkish
Telescope (RTT150) at TUBITAK National Observatory (TUG) and spectral data are
taken with the Bok 2.3 m telescope on Kitt Peak, AZ.
The images are taken with narrow-band interference filters H, [SII]
and their continuum. [SII]/H ratio image is performed. The ratio
obtained from [SII]/H is found to be 0.42, indicating that the
remnant interacts with HII regions. G85.9-0.6 shows diffuse-shell morphology.
[SII] average flux ratio is calculated from the
spectra, and the electron density is obtained to be 395 . From
[OIII]/H ratio, shock velocity has been estimated, pre-shock density of
, explosion energy of ergs,
interstellar extinction of , and neutral hydrogen column density
of are reported.Comment: 20 pages, 4 tables, 4 figures. Accepted for publication in
Astrophysics & Space Scienc
Dominance of a clonal green sulfur bacterial population in a stratified lake
For many years, the chemocline of the meromictic Lake Cadagno, Switzerland, was dominated by purple sulfur bacteria. However, following a major community shift in recent years, green sulfur bacteria (GSB) have come to dominate. We investigated this community by performing microbial diversity surveys using FISH cell counting and population multilocus sequence typing [clone library sequence analysis of the small subunit (SSU) rRNA locus and two loci involved in photosynthesis in GSB: fmoA and csmCA]. All bacterial populations clearly stratified according to water column chemistry. The GSB population peaked in the chemocline (c. 8 × 106 GSB cells mL−1) and constituted about 50% of all cells in the anoxic zones of the water column. At least 99.5% of these GSB cells had SSU rRNA, fmoA, and csmCA sequences essentially identical to that of the previously isolated and genome-sequenced GSB Chlorobium clathratiforme strain BU-1 (DSM 5477). This ribotype was not detected in Lake Cadagno before the bloom of GSB. These observations suggest that the C. clathratiforme population that has stabilized in Lake Cadagno is clonal. We speculate that such a clonal bloom could be caused by environmental disturbance, mutational adaptation, or invasio
Could we identify hot Ocean-Planets with CoRoT, Kepler and Doppler velocimetry?
Planets less massive than about 10 MEarth are expected to have no massive
H-He atmosphere and a cometary composition (50% rocks, 50% water, by mass)
provided they formed beyond the snowline of protoplanetary disks. Due to inward
migration, such planets could be found at any distance between their formation
site and the star. If migration stops within the habitable zone, this will
produce a new kind of planets, called Ocean-Planets. Ocean-planets typically
consist in a silicate core, surrounded by a thick ice mantle, itself covered by
a 100 km deep ocean. The existence of ocean-planets raises important
astrobiological questions: Can life originate on such body, in the absence of
continent and ocean-silicate interfaces? What would be the nature of the
atmosphere and the geochemical cycles ?
In this work, we address the fate of Hot Ocean-Planets produced when
migration ends at a closer distance. In this case the liquid/gas interface can
disappear, and the hot H2O envelope is made of a supercritical fluid. Although
we do not expect these bodies to harbor life, their detection and
identification as water-rich planets would give us insight as to the abundance
of hot and, by extrapolation, cool Ocean-Planets.Comment: 47 pages, 6 Fugures, regular paper. Submitted to Icaru
First optical detection from the supernova remnant G 15.1-1.6
Deep optical CCD images of the supernova remnant G 15.1-1.6 were obtained and
filamentary and diffuse emission has been discovered. The images, taken in the
emission lines of Halpha+[N II], [S II] and [O III], reveal filamentary and
diffuse structures all around the remnant. The radio emission at 4850 MHz in
the same area is found to be well correlated with the brightest optical
filaments. The IRAS 60 micron emission may also be correlated with the optical
emission but to a lesser extent. The flux calibrated images suggest that the
optical emission originates from shock-heated gas ([S II]/Halpha > 0.4), while
there is a possible HII region ([S II]/Halpha ~0.3) contaminating the supernova
remnant's emission to the east. Furthermore, deep long-slit spectra were taken
at two bright filaments and also show that the emission originates from shock
heated gas. An [O III] filamentary structure has also been detected further to
the west but it lies outside the remnant's boundaries and possibly is not
associated to it. The [O III] flux suggests shock velocities into the
interstellar "clouds" ~100 km/s, while the [S II] 6716/6731 ratio indicates
electron densities up to ~250 cm^{-3}. Finally, the Halpha emission has been
measured to be between 2 to 7 x 10^{-16} erg/s/cm^2/arcsec^2, while the lower
limit to the distance is estimated at 2.2 kpc.Comment: 12 pages, 6 figures, 3 tables. Accepted for pubication in A&
The Mass of HD 38529 c from Hubble Space Telescope Astrometry and High-Precision Radial Velocities
(Abridged) Hubble Space Telescope (HST) Fine Guidance Sensor astrometric
observations of the G4 IV star HD 38529 are combined with the results of the
analysis of extensive ground-based radial velocity data to determine the mass
of the outermost of two previously known companions. Our new radial velocities
obtained with the Hobby-Eberly Telescope and velocities from the
Carnegie-California group now span over eleven years. With these data we obtain
improved RV orbital elements for both the inner companion, HD 38529 b and the
outer companion, HD 38529 c. We identify a rotational period of HD 38529
(P_{rot}=31.65 +/- 0.17 d) with FGS photometry. We model the combined
astrometric and RV measurements to obtain the parallax, proper motion,
perturbation period, perturbation inclination, and perturbation size due to HD
38529 c. For HD 38529 c we find P = 2136.1 +/- 0.3 d, perturbation semi-major
axis \alpha =1.05 +/-0.06i_{Jup}) companion at
P~194 days. Additional observations (radial velocities and/or Gaia astrometry)
are required to validate an interpretation of HD 38529 d as a planetary-mass
companion. If confirmed, the resulting HD 38529 planetary system may be an
example of a "Packed Planetary System".Comment: Accepted by The Astronomical Journa
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