32 research outputs found
Dominadora.
Praga dominante entre os insetos que atacam a macieira, a mosca-das-frutas (Anastrepha fraterculus) ultrapassa 90% das espécies coletadas nas armadilhas de monitoramento instaladas nos pomares da cultura. Por isso, o acompanhamento do nível populacional é técnica imprescindível para evitar depreciação dos frutos e altas perdas na colheita
Evidence of Compton cooling during an X-ray flare supports a neutron star nature of the compact object in 4U1700-37
Based on new Chandra X-ray telescope data, we present empirical evidence of
plasma Compton cooling during a flare in the non pulsating massive X-ray binary
4U1700-37. This behaviour might be explained by quasispherical accretion onto a
slowly rotating magnetised neutron star. In quiescence, the neutron star in
4U1700-37 is surrounded by a hot radiatively cooling shell. Its presence is
supported by the detection of mHz quasi periodic oscillations likely produced
by its convection cells. The high plasma temperature and the relatively low
X-ray luminosity observed during the quiescence, point to a small emitting area
about 1 km, compatible with a hot spot on a NS surface. The sudden transition
from a radiative to a significantly more efficient Compton cooling regime
triggers an episode of enhanced accretion resulting in a flare. During the
flare, the plasma temperature drops quickly. The predicted luminosity for such
transitions, Lx = 3 x 10^35 erg s-1, is very close to the luminosity of
4U1700-37 during quiescence. The transition may be caused by the accretion of a
clump in the stellar wind of the donor star. Thus, a magnetised NS nature of
the compact object is strongly favoured.Comment: Accepted for publication in MNRA
The Ultraviolet Spectrum and Physical Properties of the Mass Donor Star in HD 226868 = Cygnus X-1
We present an examination of high resolution, ultraviolet spectroscopy from
Hubble Space Telescope of the photospheric spectrum of the O-supergiant in the
massive X-ray binary HD 226868 = Cyg X-1. We analyzed this and ground-based
optical spectra to determine the effective temperature and gravity of the O9.7
Iab supergiant. Using non-local thermodynamic equilibrium (non-LTE), line
blanketed, plane parallel models from the TLUSTY grid, we obtain T_eff = 28.0
+/- 2.5kK and log g > 3.00 +/- 0.25, both lower than in previous studies. The
optical spectrum is best fit with models that have enriched He and N
abundances. We fit the model spectral energy distribution for this temperature
and gravity to the UV, optical, and IR fluxes to determine the angular size of
and extinction towards the binary. The angular size then yields relations for
the stellar radius and luminosity as a function of distance. By assuming that
the supergiant rotates synchronously with the orbit, we can use the radius -
distance relation to find mass estimates for both the supergiant and black hole
as a function of the distance and the ratio of stellar to Roche radius. Fits of
the orbital light curve yield an additional constraint that limits the
solutions in the mass plane. Our results indicate masses of 23^{+8}_{-6} M_sun
for the supergiant and 11^{+5}_{-3} M_sun for the black hole.Comment: ApJ in pres
A search for interstellar anthracene toward the Perseus anomalous microwave emission region
We report the discovery of a new broad interstellar (or circumstellar) band
at 7088.8 +- 2.0 \AA coincident to within the measurement uncertainties with
the strongest band of the anthracene cation (CH) as measured
in gas-phase laboratory spectroscopy at low temperatures (Sukhorukov et
al.2004). The band is detected in the line of sight of star Cernis 52, a likely
member of the very young star cluster IC 348, and is probably associated with
cold absorbing material in a intervening molecular cloud of the Perseus star
forming region where various experiments have recently detected anomalous
microwave emission. From the measured intensity and available oscillator
strength we find a column density of N= 1.1(+-0.4) x 10
cm implying that ~0.008% of the carbon in the cloud could be in the form
of CH. A similar abundance has been recently claimed for the
naphthalene cation (Iglesias-Groth et al. 2008) in this cloud. This is the
first location outside the Solar System where specific PAHs are identified. We
report observations of interstellar lines of CH and CH that support a
rather high column density for these species and for molecular hydrogen. The
strength ratio of the two prominent diffuse interstellar bands at 5780 and 5797
\AA suggests the presence of a ``zeta'' type cloud in the line of sight
(consistent with steep far-UV extinction and high molecular content). The
presence of PAH cations and other related hydrogenated carbon molecules which
are likely to occur in this type of clouds reinforce the suggestion that
electric dipole radiation from fast spinning PAHs is responsible of the
anomalous microwave emission detected toward Perseus.Comment: Accepted for publication in Monthly Notices of the Royal Astronomical
Societ
Detection of diffuse interstellar bands in M31
We investigate the diffuse interstellar band (DIB) spectrum in the
interstellar medium of M31. The DEIMOS spectrograph of the W. M. Keck
observatory was used to make optical spectroscopic observations of two
supergiant stars, MAG 63885 and MAG 70817, in the vicinity of the OB78
association in M31 where the metallicity is approximately equal to solar. The
5780, 5797, 6203, 6283 and 6613 DIBs are detected in both sightlines at
velocities matching the M31 interstellar Na I absorption. The spectra are
classified and interstellar reddenings are derived for both stars. Diffuse
interstellar band (DIB) equivalent widths and radial velocities are presented.
The spectrum of DIBs observed in M31 towards MAG 63885 is found to be similar
to that observed in the Milky Way. Towards MAG 70817 the DIB equivalent widths
per unit reddening are about three times the Galactic average. Compared to
observations elsewhere in the Universe, relative to reddening the M31 ISM in
the vicinity of OB78 is apparently a highly favourable environment for the
formation of DIB carriers
Cloud Structure and Physical Conditions in Star-Forming Regions from Optical Observations. II. Analysis
To complement the optical absorption-line survey of diffuse molecular gas in
Paper I, we obtained and analyzed far ultraviolet H and CO data on lines of
sight toward stars in Cep OB2 and Cep OB3. Possible correlations between column
densities of different species for individual velocity components, not total
columns along a line of sight as in the past, were examined and were
interpreted in terms of cloud structure. The analysis reveals that there are
two kinds of CH in diffuse molecular gas: CN-like CH and CH-like CH.
Evidence is provided that CO is also associated with CN in diffuse molecular
clouds. Different species are distributed according to gas density in the
diffuse molecular gas. Both calcium and potassium may be depleted onto grains
in high density gas, but with different dependences on local gas density. Gas
densities for components where CN was detected were inferred from a chemical
model. Analysis of cloud structure indicates that our data are generally
consistent with the large-scale structure suggested by maps of CO
millimeter-wave emission. On small scales, the gas density is seen to vary by
factors greater than 5.0 over scales of 10,000 AU. The relationships
between column densities of CO and CH with that of H along a line of sight
show similar slopes for the gas toward Cep OB2 and OB3, but the CO/H and
CH/H ratios tend to differ which we ascribe to variation in average density
along the line of sight.Comment: 49 pages, 9 figures, accepted by Ap
A search for diffuse bands in the circumstellar envelopes of post-AGB stars
In this work we present the results of a systematic search for diffuse bands
(DBs, hereafter) in the circumstellar envelopes of a carefully selected sample
of post-AGB stars. We concentrated on the analysis of 9 of the DBs most
commonly found in the interstellar medium. The strength of these features is
determined using high resolution optical spectroscopy and the results obtained
are compared with literature data on field stars affected only by interstellar
reddening. Based on the weak features observed in the subsample of post-AGB
stars dominated by circumstellar reddening we conclude that the carrier(s) of
these DBs must not be present in the circumstellar environment of these
sources, or at least not under the excitation conditions in which DBs are
formed. The conclusion is applicable to all the post-AGB stars studied,
irrespective of the dominant chemistry or the spectral type of the star
considered. A detailed radial velocity analysis of the features observed in
individual sources confirms this result, as the Doppler shifts measured are
found to be consistent with an interstellar origin.Comment: Accepted for A&
Improvements in the determination of ISS Ca II K parameters
Measurements of the ionized Ca II K line are one of the major resources for
long-term studies of solar and stellar activity. They also play a critical role
in many studies related to solar irradiance variability, particularly as a
ground-based proxy to model the solar ultraviolet flux variation that may
influence the Earth's climate. Full disk images of the Sun in Ca II K have been
available from various observatories for more than 100 years and latter
synoptic Sun-as-a-star observations in Ca II K began in the early 1970s. One of
these instruments, the Integrated Sunlight Spectrometer (ISS) has been in
operation at Kitt Peak (Arizona) since late 2006. The ISS takes daily
observations of solar spectra in nine spectra bands, including the Ca II K and
H line s. We describe recent improvements in data reduction of Ca II K
observations, and present time variations of nine parameters derived from the
profile of this spectral line
Conceptual Framework for Desertification Monitoring in the Mediterranean Using Earth Observation Satellite Data
Abstract not availableJRC.(IRSA)-Institute For Remote Sensing Application
The interstellar Ca II distance scale
Aims. We attempt to extend the relation between the strengths of the interstellar \ion{Ca}{ii} lines and the distances to early-type stars to
objects beyond 1 kiloparsec, with the line saturation taken
into account.
Methods. We measure the \ion{Ca}{ii} K and \ion{Ca}{ii} H equivalent widths, and compute \ion{Ca}{ii} column densities for 262 lines of sight
towards early-type stars with available Hipparcos parallaxes (π). The targets are located within a few hundred parsecs of the Galactic
plane, and span all the range of Galactic longitudes. We fit the N_{\ion{Ca}{ii}} – parallax relation with a function of the form
\pi = 1 / (a \cdot N_{\ion{Ca}{ii}} + b), using a maximum-likelihood approach to take account of errors in both variables. We use the
resultant formula to estimate distances to stars in OB associations and clusters, and compare them to those found in the literature, usually
estimated by spectrophotometric methods.
Results. For lines of sight with , we obtain the following approximate formula for the distance: D_{\ion{Ca}{ii}} = 77 +
(2.78 + \frac{2.60}{\frac{EW(K)}{EW(H)} - 0.932}) EW(H), where the equivalent widths and are in mÅ, and the
distance D_{\ion{Ca}{ii}} in parsecs. The errors in D_{\ion{Ca}{ii}}, resulting from the uncertainty in the fit parameters
and errors in the equivalent widths, are typically about 15% of the distance. We can also expect the equation not to hold for objects
situated farther than a few hundred parsecs from the Galactic plane. We find several cases of significant column density differences between
association or cluster members, especially notable in the Trumpler 1