409 research outputs found
Correlated radial velocity and X-ray variations in HD 154791/4U 1700+24
We present evidence for approximately 400-d variations in the radial velocity
of HD 154791 (V934 Her), the suggested optical counterpart of 4U 1700+24. The
variations are correlated with the previously reported approximately 400 d
variations in the X-ray flux of 4U 1700+24, which supports the association of
these two objects, as well as the identification of this system as the second
known X-ray binary in which a neutron star accretes from the wind of a red
giant. The HD 154791 radial velocity variations can be fit with an eccentric
orbit with period 404 +/- 3 d, amplitude K=0.75 +/- 0.12 km/s and eccentricity
e=0.26 +/- 0.15. There are also indications of variations on longer time scales
>~ 2000 d. We have re-examined all available ASM data following an unusually
large X-ray outburst in 1997-98, and confirm that the 1-d averaged 2-10 keV
X-ray flux from 4U 1700+24 is modulated with a period of 400 +/- 20 d. The mean
profile of the persistent X-ray variations was approximately sinusoidal, with
an amplitude of 0.108 +/- 0.012 ASM count/s (corresponding to 31% rms). The
epoch of X-ray maximum was approximately 40 d after the time of periastron
according to the eccentric orbital fit. If the 400 d oscillations from HD
154791/4U 1700+24 are due to orbital motion, then the system parameters are
probably close to those of the only other neutron-star symbiotic-like binary,
GX 1+4. We discuss the similarities and differences between these two systems.Comment: 6 pages, 2 figures; accepted by Ap
Water and chemical budgets at the catchment scale from intact forests and disturbed landscapes.
Poster 262
Adjusting a simple crop model to predict maize and sorghum yield in the northeast Brazil.
A agricultura de sequeiro no Nordeste do Brasil tem sido frequentemente afetada pelas condiçÔes adversas de tempo e clima. Para antecipar a ocorrĂȘncia de um colapso na produção agrĂcola o presente trabalho objetivou ajustar um modelo agrometeorolĂłgico para as culturas de milho e sorgo nos municĂpios de Serra Talhada e Araripina, ambos no estado de Pernambuco. Foi utilizado o modelo de balanço hĂdrico do CPTEC/INPE, incluindo informaçÔes para estimar colapso de safra, como proposto por Doorenbos e Kassan (1979). A anĂĄlise apresentou um Ăndice de concordĂąncia de 80%, classificado como muito bom, e um erro menor que 30%, classificado como aceitĂĄvel, o que sugere que o modelo ajustado possa tambĂ©m produzir estimativas satisfatĂłrias pra toda regiĂŁo Nordeste
Biodegradability of diesel and biodiesel blends
The biodegradability of pure diesel and biodiesel and blends with different proportions of biodiesel (2%(commercial); 5% and 20%) was evaluated employing the respirometric method and the redox indicator2,6-dichlorophenol indophenol (DCPIP) test. In the former, experiments simulating the contamination of natural environments (soil from a petrol station or water from a river) were carried out in Bartha biometer flasks (250 ml), and used to measure the microbial CO2 production. With the DCPIP test, the capability of three inocula to biodegrade the blends was tested. Results show that although biodiesel is more easily and faster biodegraded than diesel oil, among the blends evaluated (2%, 5% and 20%), only the blend with higher concentration of biodiesel presented biodegradability significantly different from diesel and it was not verified an improvement on the biodegradation of the diesel by means of cometabolism
Supernova 2012ec: Identification of the progenitor and early monitoring with PESSTO
We present the identification of the progenitor of the Type IIP SN 2012ec in
archival pre-explosion HST WFPC2 and ACS/WFC F814W images. The properties of
the progenitor are further constrained by non-detections in pre-explosion WFPC2
F450W and F606W images. We report a series of early photometric and
spectroscopic observations of SN 2012ec. The r'-band light curve shows a
plateau with M(r')=-17.0. The early spectrum is similar to the Type IIP SN
1999em, with the expansion velocity measured at Halpha absorption minimum of
-11,700 km/s (at 1 day post-discovery). The photometric and spectroscopic
evolution of SN 2012ec shows it to be a Type IIP SN, discovered only a few days
post-explosion (<6d). We derive a luminosity for the progenitor, in comparison
with MARCS model SEDs, of log L/Lsun = 5.15+/-0.19, from which we infer an
initial mass range of 14-22Msun. This is the first SN with an identified
progenitor to be followed by the Public ESO Spectroscopic Survey of Transient
Objects (PESSTO).Comment: 6 pages, 3 figures, MNRAS accepte
Secondary forest as a counterbalance on the deforestation effects: its role on evapotranspiration and water use efficiency.
Published in 19th EGU General Assembly, EGU2017
A Motivating Exploration on Lunar Craters and Low-Energy Dynamics in the Earth -- Moon System
It is known that most of the craters on the surface of the Moon were created
by the collision of minor bodies of the Solar System. Main Belt Asteroids,
which can approach the terrestrial planets as a consequence of different types
of resonance, are actually the main responsible for this phenomenon. Our aim is
to investigate the impact distributions on the lunar surface that low-energy
dynamics can provide. As a first approximation, we exploit the hyberbolic
invariant manifolds associated with the central invariant manifold around the
equilibrium point L_2 of the Earth - Moon system within the framework of the
Circular Restricted Three - Body Problem. Taking transit trajectories at
several energy levels, we look for orbits intersecting the surface of the Moon
and we attempt to define a relationship between longitude and latitude of
arrival and lunar craters density. Then, we add the gravitational effect of the
Sun by considering the Bicircular Restricted Four - Body Problem. As further
exploration, we assume an uniform density of impact on the lunar surface,
looking for the regions in the Earth - Moon neighbourhood these colliding
trajectories have to come from. It turns out that low-energy ejecta originated
from high-energy impacts are also responsible of the phenomenon we are
considering.Comment: The paper is being published in Celestial Mechanics and Dynamical
Astronomy, vol. 107 (2010
Evaluating GAIA performances on eclipsing binaries. I. Orbits and stellar parameters for V505 Per, V570 Per and OO Peg
The orbits and physical parameters of three detached, double-lined A-F
eclipsing binaries have been derived combining H_P, V_T, B_T photometry from
the Hipparcos/Tycho mission with 8500-8750 Ang ground-based spectroscopy,
mimicking the photometric+spectroscopic observations that should be obtained by
GAIA, the approved Cornerstone 6 mission by ESA. This study has two main
objectives, namely (a) to derive reasonable orbits for a number of new
eclipsing binaries and (b) to evaluate the expected performances by GAIA on
eclipsing binaries and the accuracy achievable on the determination of
fundamental stellar parameters like masses and radii. It is shown that a 1%
precision in the basic stellar parameters can be achieved by GAIA on well
observed detached eclipsing binaries provided that the spectroscopic
observations are performed at high enough resolution. Other types of eclipsing
binaries (including semi-detached and contact types) and different spectral
types will be investigated in following papers along this series.Comment: A&A, 11 pages, 5 figures, 5 table
Optical and near infrared observations of SN 2014ck: an outlier among the Type Iax supernovae
We present a comprehensive set of optical and near-infrared photometric and
spectroscopic observations for SN 2014ck, extending from pre-maximum to six
months later. These data indicate that SN 2014ck is photometrically nearly
identical to SN 2002cx, which is the prototype of the class of peculiar
transients named SNe Iax. Similar to SN 2002cx, SN 2014ck reached a peak
brightness mag, with a post-maximum decline-rate mag. However, the spectroscopic sequence shows
similarities with SN 2008ha, which was three magnitudes fainter and faster
declining. In particular, SN 2014ck exhibits extremely low ejecta velocities,
km s at maximum, which are close to the value measured for
SN 2008ha and half the value inferred for SN 2002cx. The bolometric light curve
of SN 2014ck is consistent with the production of of Ni. The spectral identification of several iron-peak
features, in particular Co II lines in the NIR, provides a clear link to SNe
Ia. Also, the detection of narrow Si, S and C features in the pre-maximum
spectra suggests a thermonuclear explosion mechanism. The late-phase spectra
show a complex overlap of both permitted and forbidden Fe, Ca and Co lines. The
appearance of strong [Ca~II] 7292, 7324 again mirrors the
late-time spectra of SN 2008ha and SN 2002cx. The photometric resemblance to SN
2002cx and the spectral similarities to SN 2008ha highlight the peculiarity of
SN 2014ck, and the complexity and heterogeneity of the SNe Iax class.Comment: MNRAS Accepted 2016 March 22. Received 2016 March
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