526 research outputs found
Spectral variability in faint high frequency peakers
We present the analysis of simultaneous multi-frequency Very Large Array
(VLA) observations of 57 out of 61 sources from the ``faint'' high frequency
peaker (HFP) sample carried out in various epochs. Sloan Digital Sky Survey
(SDSS) data have been used to identify the optical counterpart of each radio
source. From the analysis of the multi-epoch spectra we find that 24 sources do
not show evidence of spectral variability, while 12 objects do not possess a
peaked spectrum anymore at least in one of the observing epochs. Among the
remaining 21 sources showing some degree of variability, we find that in 8
objects the spectral properties change consistently with the expectation for a
radio source undergoing adiabatic expansion. The comparison between the
variability and the optical identification suggests that the majority of radio
sources hosted in galaxies likely represent the young radio source population,
whereas the majority of those associated with quasars are part of a different
population similar to flat-spectrum objects, which possess peaked spectra
during short intervals of their life, as found in other samples of
high-frequency peaking objects. The analysis of the optical images from the
SDSS points out the presence of companions around 6 HFP hosted in galaxies,
suggesting that young radio sources resides in groups.Comment: 16 pages, 5 figures; accepted for publication in MNRA
Irrigation system performance assessment and diagnosis
Performance evaluation / Irrigation programs / Irrigation management / Irrigation systems / Case studies / Hydraulics / Management / Environmental effects / Asia / Africa / South America
Optical identifications of High Frequency Peakers
We present CCD observations of 13 objects from a complete sample of 55 bright
High Frequency Peaker (HFP) radio sources, and provide optical identification
for 12 of them. Images in R and V filters have been used to derive some
additional information concerning the host of the radio source. Three hosts are
likely to be galaxies, one resulted slightly extended, while the remaining 8
are likely distant quasars. Based on these identifications and those available
in the literature, we find that the fraction of quasars in our HFP sample is
significantly higher than in samples of Compact Steep-Spectrum and GHz-Peaked
Spectrum radio sources.Comment: 7 pages, A&A accepte
A Parkes half-Jansky sample of GPS galaxies
This paper describes the selection of a new southern/equatorial sample of
Gigahertz Peaked Spectrum (GPS) radio galaxies, and subsequent optical CCD
imaging and spectroscopic observations using the ESO 3.6m telescope. The sample
consists of 49 sources with -4020 degrees, and
S(2.7GHz)>0.5 Jy, selected from the Parkes PKSCAT90 survey. About 80% of the
sources are optically identified, and about half of the identifications have
available redshifts. The R-band Hubble diagram and evolution of the host
galaxies of GPS sources are reviewed.Comment: Latex, 12 pages, 8 figures, accepted for publication in MNRA
High Frequency Peakers: young radio sources or flaring blazars?
We present new, simultaneous, multifrequency observations of 45 out of the 55
candidate High Frequency Peakers (HFP) selected by Dallacasa et al. (2000),
carried out 3 to 4 years after a first set of observations. Our sub-sample
consists of 10 galaxies, 28 stellar objects (``quasars'') and 7 unidentified
sources. Both sets of observations are sensitive enough to allow the detection
of variability at the 10% level or lower. While galaxies do not show
significant variability, most quasars do. Seven of them no longer show the
convex spectrum which is the defining property of Gigahertz Peaked Spectrum
(GPS)/HFP sources and are interpreted as blazars caught by Dallacasa et al.
(2000) during a flare, when a highly self-absorbed component dominated the
emission. In general, the variability properties (amplitude, timescales,
correlation between peak luminosity and peak frequency of the flaring
component) of the quasar sub-sample resemble those of blazars. We thus conclude
that most HFP candidates identified with quasars may well be flaring blazars.Comment: 20 pages, 18 figures, accepted for publication in Astronomy &
Astrophysic
Molecule mapping of HR8799b using OSIRIS on Keck: Strong detection of water and carbon monoxide, but no methane
Context. In 2015, Barman et al. (ApJ, 804, 61) presented detections of
absorption from water, carbon monoxide, and methane in the atmosphere of the
directly imaged exoplanet HR8799b using integral field spectroscopy (IFS) with
OSIRIS on the Keck II telescope. We recently devised a new method to analyse
IFU data, called molecule mapping, searching for high-frequency signatures of
particular molecules in an IFU data cube.
Aims. The aim of this paper is to use the molecule mapping technique to
search for the previously detected spectral signatures in HR8799b using the
same data, allowing a comparison of molecule mapping with previous methods.
Methods. The medium-resolution H- and K-band pipeline-reduced archival data
were retrieved from the Keck archive facility. Telluric and stellar lines were
removed from each spectrum in the data cube, after which the residuals were
cross-correlated with model spectra of carbon monoxide, water, and methane.
Results. Both carbon monoxide and water are clearly detected at high
signal-to-noise, however, methane is not retrieved.
Conclusions. Molecule mapping works very well on the OSIRIS data of exoplanet
HR8799b. However, it is not evident why methane is detected in the original
analysis, but not with the molecule mapping technique. Possible causes could be
the presence of telluric residuals, different spectral filtering techniques, or
the use of different methane models. We do note that in the original analysis
methane was only detected in the K-band, while the H-band methane signal could
be expected to be comparably strong. More sensitive observations with the JWST
will be capable of confirming or disproving the presence of methane in this
planet at high confidence.Comment: 5 pages, 5 figures and 2 tables, accepted by A&
The spin axes orbital alignment of both stars within the eclipsing binary system V1143Cyg using the Rossiter-McLaughlin effect
Context: The Rossiter-McLaughlin (RM) effect, a rotational effect in
eclipsing systems, provides unique insight into the relative orientation of
stellar spin axes and orbital axes of eclipsing binary systems.
Aims: Our aim is to develop a robust method to analyze the RM effect in an
eclipsing system with two nearly equally bright components. This gives access
to the orientation of the stellar rotation axes and may shed light on questions
of binary formation and evolution.
Methods: High-resolution spectra have been obtained both out of eclipse and
during the primary and secondary eclipses in the V1143Cyg system, using the
high-resolution Hamilton Echelle Spectrograph at the Lick Observatory. The
Rossiter-McLaughlin effect is analyzed in two ways: (1) by measuring the shift
of the line center of gravity during different phases of the eclipses and (2)
by analysis of the line shape change of the rotational broadening function
during eclipses.
Results: The projected axes of both stars are aligned with the orbital spin
within the observational uncertainties, with the angle of the primary rotation
axis beta_p=0.3+-1.5 deg, and the angle of the secondary rotation axis
beta_s=-1.2+-1.6 deg, thereby showing that the remaining difference between the
theoretical and observed apsidal motion for this system is not due to a
misalignment of the stellar rotation axes. Both methods utilized in this paper
work very well, even at times when the broadening profiles of the two stars
overlap.[abridged]Comment: Accepted for publication in A&A; 11 pages, 9 figures, 3 tables ; a
typo in the abstract has been correcte
GPS radio sources: new optical observations and an updated master list
* Aims. Identify optical counterparts, address uncertain identifications and
measure previously unknown redshifts of the host galaxies of candidate GPS
radio sources, and study their stellar populations. * Methods. Long slit
spectroscopy and deep optical imaging in the B, V and R bands, obtained with
the Very Large Telescope. * Results. We obtain new redshifts for B0316+161,
B0407-658, B0904+039, B1433-040, and identify the optical counterparts of
B0008-421 and B0742+103. We confirm the previous identification for B0316+161,
B0407-658, B0554-026, and B0904+039, and find that the previous identification
for B0914+114 is incorrect. Using updated published radio spectral information
we classify as non GPS the following sources: B0407-658, B0437-454, B1648+015.
The optical colors of typical GPS sources are consistent with single
instantaneous burst stellar population models but do not yield useful
information on age or metallicity. A new master list of GPS sources is
presented.Comment: 10 pages + GPS master list. Accepeted for publication by A&
Massive galaxies with very young AGN
Gigahertz Peaked Spectrum (GPS) radio galaxies are generally thought to be
the young counterparts of classical extended radio sources and live in massive
ellipticals. GPS sources are vital for studying the early evolution of
radio-loud AGN, the trigger of their nuclear activity, and the importance of
feedback in galaxy evolution. We study the Parkes half-Jansky sample of GPS
radio galaxies of which now all host galaxies have been identified and 80% has
their redshifts determined (0.122 < z < 1.539). Analysis of the absolute
magnitudes of the GPS host galaxies show that at z > 1 they are on average a
magnitude fainter than classical 3C radio galaxies. This suggests that the AGN
in young radio galaxies have not yet much influenced the overall properties of
the host galaxy. However their restframe UV luminosities indicate that there is
a low level of excess as compared to passive evolution models.Comment: To appear in the proceedings of "Formation and Evolution of Galaxy
Bulges", IAUS 245; M. Bureau, E. Athanassoula & B. Barbuy, ed
Physical parameters in the hot spots and jets of Compact Symmetric Objects
We present a model to determine the physical parameters of jets and hot spots
of a sample of CSOs under very basic assumptions like synchrotron emission and
minimum energy conditions. Based on this model we propose a simple evolutionary
scenario for these sources assuming that they evolve in ram pressure
equilibrium with the external medium and constant jet power. The parameters of
our model are constrained from fits of observational data (radio luminosity,
hot spot radius and hot spot advance speed) versus projected linear size. From
these plots we conclude that CSOs evolve self-similarly and that their radio
luminosity increases with linear size along the first kiloparsec. Assuming that
the jets feeding CSOs are relativistic from both kinematical and
thermodynamical points of view, we use the values of the pressure and particle
number density within the hot spots to estimate the fluxes of momentum
(thrust), energy, and particles of these relativistic jets. The mean jet power
obtained in this way is within an order of magnitude that inferred for FRII
sources, which is consistent with CSOs being the possible precursors of large
doubles. The inferred flux of particles corresponds to, for a barionic jet,
about a 10% of the mass accreted by a black hole of at
the Eddington limit, pointing towards a very efficient conversion of accretion
flow into ejection, or to a leptonic composition of jets.Comment: 11 pages, 2 figures. Accepted for publication in Astrophysical
Journa
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