291 research outputs found
Discovery of a high-redshift Einstein ring
We report the discovery of a partial Einstein ring of radius 1.48arcsec
produced by a massive (and seemingly isolated) elliptical galaxy. The
spectroscopic follow-up at the VLT reveals a 2L* galaxy at z=0.986, which is
lensing a post-starburst galaxy at z=3.773. This unique configuration yields a
very precise measure of the mass of the lens within the Einstein radius,
(8.3e11 +- 0.4)/h70 Msolar. The fundamental plane relation indicates an
evolution rate of d [log (M/L)B] / dz = -0.57+-0.04, similar to other massive
ellipticals at this redshift. The source galaxy shows strong interstellar
absorption lines indicative of large gas-phase metallicities, with fading
stellar populations after a burst. Higher resolution spectra and imaging will
allow the detailed study of an unbiased representative of the galaxy population
when the universe was just 12% of its current age.Comment: 5 pages, 3 figures, accepted in A&A Le
A narrow-band search for Ly alpha emitting galaxies at z = 8.8
Aims: The first star forming galaxies in the early universe should be copious
Ly alpha emitters, and may play a significant role in ionizing the
intergalactic medium (IGM). It has been proposed that the luminosity function
of Lya emitting galaxies beyond z~6 may be used to constrain the neutral
fraction of the IGM during this epoch. In this work we report on a search for
Ly alpha emitters at redshift 8.8.
Methods: We performed a narrow band imaging programme using ISAAC at the ESO
VLT. Seven fields, covering a total area of 31sq. arcmin and for which optical
and broad band infra-red images have been obtained in the GOODS survey, were
imaged to a limiting flux (respectively luminosity) of ~ 1.3 x 10^{-17}
ergs.s^{-1}.cm^{-2} (respectively ~ 1.3 x 10^{43} ergs.s^{-1} in a narrow band
filter centered in a region of low OH sky emission at 1.19 micron. Candidate
Lyman alpha emitters are objects that are detected in the ISAAC NB images and
undetected in the visible broad band images.
Results: No z=8.8 Ly alpha emitting galaxies were detected to a limit
approaching recent estimates of the luminosity function at z ~ 6. Our results
do suggest, however, that detections or substantial constraints could be
achieved by this method in the near future with larger field instruments
planned for various telescopes.Comment: 7 pages, accepted for publication in A&
An exploratory study of phosphorus release from biomass by carbothermic reduction reactions
Phosphorus (P) from biomass can cause operational problems in thermal conversion processes. In order to explore the release mechanism of P to the gas phase, carbothermic reduction of meta-, pyro-, and orthophosphates of ash elements commonly found in biomass; sodium, potassium, magnesium, and calcium was investigated. Mixtures of each phosphate and activated carbon were heated to 1135 \ub0C in a laboratory-scale reactor, with the CO and CO2 evolving from the sample monitored, and the chemical composition of selected residues analyzed to quantify the release of P. Thermal gravimetric analysis was also performed on selected samples. The alkaline earth phosphates were reduced in steps, following the sequence meta → pyro → ortho → alkaline earth oxide. However, the alkali metaphosphates appear to be reduced in one step, in which both alkali and P are released. Alkali pyro- and orthophosphate appear to undergo a two-step process. In the first step, mainly alkali is released and in the second step both alkali and P. An intermediate is produced in the first step, which has a K:P:O atomic ratio of about 2:1:2.7, indicating it might be a phosphite with the overall stoichiometry; K4P2O5. The reduction of alkaline earth phosphates could be interpreted using available thermodynamic data, whereas thermodynamic equilibrium calculations for the alkali phosphates did not correspond well to the experimental observations. Kinetics were derived for the different reduction reactions, and can be used to compare the reactivity of the phosphates. The work suggests that carbothermic reduction reactions are important for the release of P in the temperature range 850-1135 \ub0C and relevant for biomass combustion, pyrolysis and gasification
Time delay measurement of the lensed quasar HE1104-1805
We have measured the time delay between the two images of the gravitationally
lensed quasar HE1104-1805 by combining observations made with the Wise
Observatory 1m telescope and published observations of this system by Schechter
et al., spanning a total of five years, from 1997 to 2002. Based on a variety
of techniques, we find that the best fit time delay is -161 (+/-7)(+34 -11)
days. The 68% and 95% confidence intervals include the systematic errors due to
an observed component of uncorrelated variability between images. The delay is
shorter than predicted by simple models and may indicate a large external shear
or a large value of the Hubble parameter, h>0.75 (95% confidence). The residual
light curve between the two images shows a longterm trend of ~0.04 mag/yr,
presumably the result of microlensing by stars in the lens galaxy, but also
short timescale (~1 month) variability with a mean amplitude of about 0.07 mag.Comment: 7 pages, ApJ, in pres
Ground-based follow-up observations of TRAPPIST-1 transits in the near-infrared
The TRAPPIST-1 planetary system is a favorable target for the atmospheric
characterization of temperate earth-sized exoplanets by means of transmission
spectroscopy with the forthcoming James Webb Space Telescope (JWST). A possible
obstacle to this technique could come from the photospheric heterogeneity of
the host star that could affect planetary signatures in the transit
transmission spectra. To constrain further this possibility, we gathered an
extensive photometric data set of 25 TRAPPIST-1 transits observed in the
near-IR J band (1.2 m) with the UKIRT and the AAT, and in the NB2090 band
(2.1 m) with the VLT during the period 2015-2018. In our analysis of these
data, we used a special strategy aiming to ensure uniformity in our
measurements and robustness in our conclusions. We reach a photometric
precision of (RMS of the residuals), and we detect no significant
temporal variations of transit depths of TRAPPIST-1 b, c, e, and g over the
period of three years. The few transit depths measured for planets d and f hint
towards some level of variability, but more measurements will be required for
confirmation. Our depth measurements for planets b and c disagree with the
stellar contamination spectra originating from the possible existence of bright
spots of temperature 4500 K. We report updated transmission spectra for the six
inner planets of the system which are globally flat for planets b and g and
some structures are seen for planets c, d, e, and f.Comment: accepted for publication in MNRA
An Optical Time-Delay for the Lensed BAL Quasar HE2149-2745
We present optical V and i-band light curves of the gravitationally lensed
BAL quasar HE2149-2745. The data, obtained with the 1.5m Danish Telescope
(ESO-La Silla) between October 1998 and December 2000, are the first from a
long-term project aimed at monitoring selected lensed quasars in the Southern
Hemisphere. A time delay of 103+/-12 days is determined from the light curves.
In addition, VLT/FORS1 spectra of HE2149-2745 are deconvolved in order to
obtain the spectrum of the faint lensing galaxy, free of any contamination by
the bright nearby two quasar images. By cross-correlating the spectrum with
galaxy-templates we obtain a tentative redshift estimate of z=0.495+/-0.01.
Adopting this redshift, a Omega=0.3, Lambda=0.7 cosmology, and a chosen
analytical lens model, our time-delay measurement yields a Hubble constant of
H_0=66+/-8 km/s/Mpc with an estimated systematic error of +/-3 km/s/Mpc. Using
non-parametric models yields H_0=65+/-8 km/s/Mpc and confirms that the lens
exhibits a very dense/concentrated mass profile.Comment: 11 pages, accepted for publication in Astronomy & Astrophysic
Microlensing of Relativistic Knots in the Quasar HE1104-1805
We present 3 years of photometry of the ``Double Hamburger'' lensed quasar,
HE1104-1805, obtained on 102 separate nights using the OGLE 1.3-m telescope.
Both the A and B images show variations, but with substantial differences in
the lighcurves at all time delays. At the 310 day delay reported by Wisotzki
and collaborators the difference lightcurve has an rms amplitude of 0.060 mag.
The structure functions for the A and B images are quite different, with image
A more than twice as variable as image B (a factor of 4 in structure function)
on timescales of less than a month. Adopting microlensing as a working
hypothesis for the uncorrelated variability, the short timescale argues for the
relativistic motion of one or more components of the source. We argue that the
small amplitude of the fluctuations is due to the finite size of the source
with respect to the microlenses.Comment: As accepted for publication in ApJ. 22 pages. The discussion of
microlensing at high optical depth has been shortened and a few minor points
have been clarifie
Release of phosphorus from thermal conversion of phosphorus-rich biomass chars – Evidence for carbothermic reduction of phosphates
Biomass can be used to generate heat, power, or biofuels in thermal conversion processes such as combustion, gasification and pyrolysis. However, some types of biomass contain high levels of phosphorus, which can be released to the gas phase and cause operational or environmental problems. The mechanism(s) responsible for phosphorus release has not been convincingly established. Understanding the high-temperature phosphorus chemistry is also important in order to enable efficient recovery of phosphorus in residues from thermal conversion of biomass. In this work, the release of phosphorus from wheat bran char and sunflower seed char in different gas environments (100 % N2, 1–20 % O2, and 10 % CO2) and temperatures (900–1100 \ub0C) was studied. The chars were converted in a horizontal tube reactor and characterized using ICP-OES, XRD, SEM-EDS, and 31P NMR. The release of ash-forming elements was determined using ICP-OES analysis of the char and sample residues, whereas the release of carbon was determined using CO and CO2 gas analysis. In both chars, phosphorus was present primarily together with potassium and magnesium, mainly as pyrophosphates in the wheat bran char, and largely as orthophosphates in the sunflower seed char. For wheat bran char, the release of phosphorus increased from 27 % at 900 \ub0C to 71 % at 1100 \ub0C in N2, whereas the release was at least 20 % lower in the oxidizing atmospheres (1–20 % O2, or 10 % CO2). The sunflower seed char reached a maximum release of 55 % at 1100 \ub0C in N2. For wheat bran char, the molar ratio of released carbon/phosphorus was close to 2.5, which fits well with the theoretical value for carbothermic reduction of phosphates (P2O5(s, l) + 5C(s) → P2(g) + 5CO(g)). At 1100 \ub0C, in N2, the release of phosphorus, potassium and sodium occurred mainly during the first 10 min. It was shown that KMgPO4, used as a model compound, could be reduced by carbon starting from 950 \ub0C, but that some of the phosphorus remained in the condensed phase. The work provides a better understanding of phosphorus release and presents evidence showing that carbothermic reduction reactions can be an important phosphorus release mechanism for seed- and grain-based biomass char
The extinction law in high redshift galaxies
We estimate the dust extinction laws in two intermediate redshift galaxies.
The dust in the lens galaxy of LBQS1009-0252, which has an estimated lens
redshift of zl~0.88, appears to be similar to that of the SMC with no
significant feature at 2175 A. Only if the lens galaxy is at a redshift of
zl~0.3, completely inconsistent with the galaxy colors, luminosity or location
on the fundamental plane, can the data be fit with a normal Galactic extinction
curve. The dust in the zl=0.68 lens galaxy for B0218+357, whose reddened image
lies behind a molecular cloud, requires a very flat ultraviolet extinction
curve with (formally) R(V)=12 +- 2. Both lens systems seem to have unusual
extinction curves by Galactic standards.Comment: 15 pages, 3 figures. ApJ in pres
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