212 research outputs found
Long-term observations of Uranus and Neptune at 90 GHz with the IRAM 30m telescope - (1985 -- 2005)
The planets Uranus and Neptune with small apparent diameters are primary
calibration standards. We investigate their variability at ~90 GHz using
archived data taken at the IRAM 30m telescope during the 20 years period 1985
to 2005. We calibrate the planetary observations against non-variable secondary
standards (NGC7027, NGC7538, W3OH, K3-50A) observed almost simultaneously.
Between 1985 and 2005, the viewing angle of Uranus changed from south-pole to
equatorial. We find that the disk brightness temperature declines by almost 10%
(~2sigma) over this time span indicating that the south-pole region is
significantly brighter than average. Our finding is consistent with recent
long-term radio observations at 8.6 GHz by Klein & Hofstadter (2006). Both data
sets do moreover show a rapid decrease of the Uranus brightness temperature
during the year 1993, indicating a temporal, planetary scale change. We do not
find indications for a variation of Neptune's brightness temperature at the 8%
level. If Uranus is to be used as calibration source, and if accuracies better
than 10% are required, the Uranus sub-earth point latitude needs to be taken
into account.Comment: accepted for publication in A&
The First IRAM/PdBI Polarimetric Millimeter Survey of Active Galactic Nuclei. I. Global Properties of the Sample
We have studied the linear polarization of 86 active galactic nuclei (AGN) in
the observed frequency range 80-267 GHz (3.7-1.1mm in wavelength),
corresponding to rest-frame frequencies 82-738 GHz, with the IRAM Plateau de
Bure Interferometer (PdBI). The large number of measurements, 441, makes our
analysis the largest polarimetric AGN survey in this frequency range to date.
We extracted polarization parameters via earth rotation polarimetry with
unprecedented median precisions of ~0.1% in polarization fractions and ~1.2
degrees in polarization angles. For 73 of 86 sources we detect polarization at
least once. The degrees of polarization are as high as ~19%, with the median
over all sources being ~4%. Source fluxes and polarizations are typically
highly variable, with fractional variabilities up to ~60%. We find that BLLac
sources have on average the highest level of polarization. There appears to be
no correlation between degree of polarization and redshift, indicating that
there has been no substantial change of polarization properties since z~2.4.
Our polarization and spectral index distributions are in good agreement with
results found from various samples observed at cm/radio wavelengths; thus our
frequency range is likely tracing the signature of synchrotron radiation
without noticeable contributions from other emission mechanisms. The
"millimeter-break" located at frequencies >1 THz appears to be not detectable
in the frequency range covered by our survey.Comment: 19 pages, 9 figures, 2 long tables (p. 12-19). Accepted by A&A
Effects of severe water stress on partitioning of 14C-assimilates in tomato plants
Tomato plants (Lycopersicon esculentum Mill. cv Nikita) were grown hydroponically and subjected to severe water stress induced by addition of PEG-6000 to the nutrient solution. The PEG-treatment clearly impaired growth. Leaf photosynthesis decreased during the experiment. Moreover, the decrease in photosynthesis was associated with a decrease in dry weight of the shoot compared to the root. Also leaf area expansion, stomatal conductance and transpiration decreased. Water stress enhanced the transport of 14C-assimilates from the source leaf to the lower parts of the plant where the assimilates were incorporated in the lower stem, the leaves below the source leaf and the roots. It was observed that 14C was much more concentrated in the roots compared to the other plant parts
Two classes of radio flares in the blazar PKS 0420014
The two 5GHz VLBI (Very Long Baseline Interferometry) observations (1996 June
and 1997 November) presented in this paper, combined with several formerb VLBI
observations at 8.4GHz and 5GHz, suggest that the radio flares of the blazar
PKS 0420014 can be divided into two classes according to their geometric
origins in 5 or 8.4GHz VLBI maps and the properties of light curves. One class
of flares, which we call {\it core flares}, originate from the core. Core
flares have large lags between the light curves at different frequencies, and
will probably lead to the ejection of new jet components. The other class of
flares, which we call {\it jet flares}, come from jet components. Jet flares
vary simultaneously at different wavelengths, and may due to the Doppler
boosting effect of rotating knots moving along a helical jet. The radio flare
in 1991, accompanied by a simultaneous gamma-ray flare, was identified as a
core flare.Comment: 9 pages, 3 figure
The ISOPHOT-MAMBO survey of 3CR radio sources: Further evidence for the unified schemes
We present the complete set of ISOPHOT observations of 3CR radio galaxies and
quasars, which are contained in the ISO Data Archive, providing 75 mid- and
far-infrared spectral energy distributions (SEDs) between 5 and 200 micron. For
28 sources they are supplemented with MAMBO 1.2 mm observations and for 15
sources with new submillimetre data from the SCUBA archive.
We check the orientation-dependent unified scheme, in which the powerful FR2
narrow line galaxies are quasars viewed at high inclination, so that their
nuclei are hidden behind a dust torus intercepting the optical-ultraviolet AGN
radiation and reemitting it in the infrared. We find that (1) both the quasars
and the galaxies show a high mid- to far-infrared luminosity ratio typical for
powerful AGNs and (2) -- when matched in 178 MHz luminosity -- both show the
same ratio of isotropic far-infrared to isotropic 178 MHz lobe power.
Therefore, from our large sample investigated here we find strong evidence for
the orientation-dependent unification of the powerful FR2 galaxies with the
quasars.Comment: 16 pages, 7 figures, 3 tables, accepted by Astronomy & Astrophysic
Molecular Gas in the Powerful Radio Nucleus of the Ultraluminous Infrared Galaxy PKS 1345+12
Millimeter CO(1-0) interferometry and high resolution, Hubble Space Telescope
(HST) 1.1, 1.6, and 2.2 micron imaging of the radio compact galaxy PKS 1345+12
are presented. With an infrared luminosity of 2x10^{12} L_sun, PKS 1345+12 is a
prime candidate for studying the link between the ultraluminous infrared galaxy
phenomenon and radio galaxies. These new observations probe the molecular gas
distribution and obscured nuclear regions of PKS 1345+12 and provide
morphological support for the idea that the radio activity in powerful radio
galaxies is triggered by the merger of gas rich galaxies. Two nuclei separated
by 2" (4.0 kpc) are observed in the near-infrared; the extended southeastern
nucleus has colors consistent with reddened starlight, and the compact
northwestern nucleus has extremely red colors indicative of an optical quasar
with a warm dust component. Further, the molecular gas, 3mm continuum, and
radio emission are coincident with the redder nucleus, confirming that the
northwestern nucleus is the site of the AGN and that the molecular gas is the
likely fuel source.Comment: LaTex, 5 pages with 1 postscript and 1 jpg figure, ApJ Letters, in
press (August 20, 1999
The extragalactic radio-source population at 95 GHz
We have used the Australia Telescope Compact Array (ATCA) at 95GHz to carry
out continuum observations of 130 extragalactic radio sources selected from the
Australia Telescope 20GHz (AT20G) survey. Over 90% of these sources are
detected at 95 GHz, and we use a triple-correlation method to measure
simultaneous 20 and 95 GHz flux densities. We show that the ATCA can measure
95GHz flux densities to ~10% accuracy in a few minutes for sources above
~50mJy.
The median 20-95GHz spectral index does not vary significantly with flux
density for extragalactic sources with S20>150 mJy. This allows us to estimate
the extragalactic radio source counts at 95GHz by combining our observed
20-95GHz spectral-index distribution with the accurate 20GHz source counts
measured in the AT20G survey. The resulting 95GHz source counts down to 80 mJy
are significantly lower than those found by several previous studies. The main
reason is that most radio sources with flat or rising spectra in the frequency
range 5-20GHz show a spectral turnover between 20 and 95 GHz. As a result,
there are fewer 95GHz sources (by almost a factor of two at 0.1 Jy) than would
be predicted on the basis of extrapolation from the source populations seen in
lower-frequency surveys. We also derive the predicted confusion noise in CMB
surveys at 95GHz and find a value 20-30% lower than previous estimates.
The 95GHz source population at the flux levels probed by this study is
dominated by QSOs with a median redshift z~1. We find a correlation between
optical magnitude and 95GHz flux density which suggests that many of the
brightest 95 GHz sources are relativistically beamed, with both the optical and
millimetre continuum significantly brightened by Doppler boosting.Comment: Replaced with final version (MNRAS, in press), 15 pages plus two
landscape data table
Atmospheric drivers of storage water use in Scots pine
International audienceIn this study we determined the microclimatic drivers of storage water use in Scots pine (Pinus sylvestris L.) growing in a temperate climate. The storage water use was modeled using the ANAFORE model, integrating a dynamic water flow and ? storage model with a process-based transpiration model. The model was calibrated and validated with sap flow measurements for the growing season of 2000 (26 May?18 October). Because there was no severe soil drought during the study period, we were able to study atmospheric effects. Incoming radiation was the main driver of storage water use. The general trends of sap flow and storage water use are similar, and follow more or less the pattern of incoming radiation. Nevertheless, considerable differences in the day-to-day pattern of sap flow and storage water use were observed, mainly driven by vapour pressure deficit (VPD). During dry atmospheric conditions (high VPD) storage water use was reduced. This reduction was disproportionally higher than the reduction in measured sap flow. Our results suggest that the trees did not rely more on storage water during periods of atmospheric drought, without severe soil drought. A third important factor was the tree water deficit. When storage compartments were depleted beyond a threshold, storage water use was limited due to the low water potential in the storage compartments. The maximum relative contribution of storage water to daily transpiration was also constrained by an increasing tree water deficit
A tree-centered approach to assess impacts of extreme climatic events on forests
Ajut Marie Curie IF fellowship (No 659191); COST Action FP1106 STReES
Relation between millimeter wavelengths emission and high-energy emission for active galactic nuclei
After comparing the flux densities of a sample of active galactic nuclei
detected by energetic gamma-ray experiment telescope at 90 and 230 GHz with the
-ray emissions detected by Compton Gamma Ray Observatory and x-ray
emission, a strong correlation between the emissions at the millimeter
wavelength and the -ray emission is found. The average flux density of
x-ray is almost proportional to the average flux density at the millimeter
wavelength for quasars detected by energetic gamma-ray experiment telescope,
which strongly supports the previous idea that the x-ray emissions of this kind
sources are mainly produced by Synchrotron Self-Compton process.Comment: 6 pages, Chinese Physics Letters in pres
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