449 research outputs found
Short-timescale Fluctuations in the Difference Light Curves of QSO 0957+561A,B: Microlensing or Noise?
From optical R band data of the double quasar QSO 0957+561A,B, we made two
new difference light curves (about 330 days of overlap between the time-shifted
light curve for the A image and the magnitude-shifted light curve for the B
image). We observed noisy behaviours around the zero line and no
short-timescale events (with a duration of months), where the term event refers
to a prominent feature that may be due to microlensing or another source of
variability. Only one event lasting two weeks and rising - 33 mmag was found.
Measured constraints on the possible microlensing variability can be used to
obtain information on the granularity of the dark matter in the main lensing
galaxy and the size of the source. In addition, one can also test the ability
of the observational noise to cause the rms averages and the local features of
the difference signals. We focused on this last issue. The combined
photometries were related to a process consisting of an intrinsic signal plus a
Gaussian observational noise. The intrinsic signal has been assumed to be
either a smooth function (polynomial) or a smooth function plus a stationary
noise process or a correlated stationary process. Using these three pictures
without microlensing, we derived some models totally consistent with the
observations. We finally discussed the sensitivity of our telescope (at Teide
Observatory) to several classes of microlensing variability.Comment: MNRAS, in press (LaTeX, 14 pages, 22 eps figures
A Large Brightness Enhancement of the QSO 0957+561 A Component
We report an increase of more than 0.2 mag in the optical brightness of the
leading image (A) of the gravitational lens Q0957+561, detected during the
09/2000 -- 06/2001 monitoring campaign (2001 observing season). The brightening
is similar to or even greater than the largest change ever detected during the
20 years of monitoring of this system. We discuss two different provisional
explanations to this event: intrinsic source variability or microlensing
(either short timescale microlensing or cessation of the historical
microlensing). An exhaustive photometric monitoring of Q0957+561 is needed
until summer of 2002 and during 2003 to discriminate between these
possibilities.Comment: 13 pages including 3 figures and 1 table. Accepted for publication in
ApJ Let
El paleógeno del sector suroccidental de la Cuenca del Duero: nueva división estratigráfica y controles sobre su sedimentación
Como resultado de un detallado trabajo cartográfico, estratigráfico y
sedimentológico, se propone la división del Paleógeno del sector suroccidental
de la Cuenca del Duero en cuatro U.T.S. limitadas por discordancias. Estas
D.T.S., que abarcan desde el tránsito Cretácico superior-Paleoceno hasta el
Oligoceno, incluyen distintas unidades litoestratigráficas que sonreordenadas,
modificando la sucesión estratigrática propuesta por los autores anteriores.
Se asigna a la U.T.S. Me una edad Cretácico superior-Paleoceno. Se
individualiza el Eoceno inferior (U.T.S. PI) en la zona de Salamanca. Se
reinterpreta la relación existente entre los materiales del Eoceno mediosuperior
y los del Eoceno superior-Oligoceno considerándolos en tránsito
por lo que se asignan a una única U.T.S. (UT.S. P2, Eoceno medio Oligoceno
inferior). Se incluyen en la U.T.S. P3 (Oligoceno superior) los
sedimentos arcósicos anterionnente considerados como Vatlesienses. Así
mismo, se considera que gran parte de los materiales asignados al mioceno
inferior son sedimentos paleógenos afectados por un proceso de alteración
de edad Miocena, lo que implica una variación en la extensión y límites de
la cuenca neógena en su extremo SO.
Se analiza la evolución de las distintas U.T.S. deduciendo un carácter
tectónico para las megasecuencias propuestas relacionado con el progresivo
levantamiento de las áreas fuente. El clima muestra un tránsito desde
condiciones tropicales sin estaciones contrastadas (U,T.S. MC) hasta un
clima mediterráneo árido (U.T.S. P3) con una estación seca muy marcada
y una corta estación húmeda caracterizada por violentas avenidas.
[ABSTRACT]
A Paleogene four-fold stratigraphical division is proposed here
as result fram the detailed studies carried out during the elaboration
of 22 sheets of the Geological Map of Spain (E. 1 :50.000).
This units (T.S.U.) are limited by regional discordances and they
have a Upper Cretaceous to Oligocene ages.
The previous stratigraphical schemes are rearranged due to the
different stratigraphical relations observed between the lithostratigraphical
units proposed by other workers (Jiménez, 1970; Corrochano, 1977;
Alonso, 1981...).
An Upper Cretaceous-Paleocene age is assumed to T.S.U. MC
which is mainly composed by siliciclastic sediments strongly silicified
forming a FU megasequence. It is intcrpretated as braided streams
that flowed downslope filling paleovalleys erodcd onto Paleozoic
materiaIs. Mineralogical features point to a tropical climate.
Lower Eocene (T.S.U. P I ) is identified in the Salamanca area,
where ir was considered as lacking. It is composed by arkosic
sediments forming a CU megasequence. Fossil faunas of this T.S.U.
record a subtropical clima te. It is observed a transition from high
sinuosity streams to braided ones.
T.S.U. P2 (Middle Eocene-Lower Oligocene) is composed of
two lithostratigraphical units previously considered as bounded by
a discordance (Alonso, 1981).It has a subarkosic to lithic nature and
forms a CU megasequence. This unit records a subtropical climate
with short arid periods and is interpretated as braided streams
showing an increasing stability and enviromental energy to the topo
T.S. U. P3 (Upper Oligocene) is composed by arkosic sediments
previously considered of Vallesian (Middle to Upper Miocene) age.
They form a CU megasequence that records braided streams prograding
basinwardfrom higher arcas. Palinological associations and pedological
features indicate an arid mediterranean climate with long arid
periods and a short rainy season with strong floods.
We consider that most of Lower Miocene sediments are of
Paleogene age. They are afected by a widespread alteration profile
developed along Lower Miocene that masked its more significative
features.
Sedimentological analysis of T.S.U. shows that its megasequentiality
is related to the rates of tectonical uplift of source arcas whereas a
distensive regime developed in the sedimentation basin
New VR magnification ratios of QSO 0957+561
We present VR magnification ratios of QSO 0957+561, which are inferred from
the GLITP light curves of Q0957+561A and new frames taken with the 2.56m Nordic
Optical Telescope about 14 months after the GLITP monitoring. From two
photometric approaches and a reasonable range for the time delay in the system
(415-430 days), we do not obtain achromatic optical continuum ratios, but
ratios depending on the wavelength. These new measurements are consistent with
differential extinction in the lens galaxy, the Lyman limit system, the damped
Ly-alpha system, or the host galaxy of the QSO. The possible values for the
differential extinction and the ratio of total to selective extinction in the V
band are reasonable. Moreover, crude probability arguments suggest that the ray
paths of the two components cross a similar dusty environment, including a
network of compact dust clouds and compact dust voids. As an alternative (in
fact, the usual interpretation of the old ratios), we also try to explain the
new ratios as caused by gravitational microlensing in the deflector. From
magnification maps for each of the gravitationally lensed images, using
different fractions of the surface mass density represented by the microlenses,
as well as different sizes and profiles of the V-band and R-band sources,
several synthetic distributions of V-band and R-band ratios are derived. In
some gravitational scenarios, there is an apparent disagreement between the
observed pair of ratios and the simulated distributions. However, several
microlensing pictures work well. To decide between either extinction, or
microlensing, or a mixed scenario (extinction + microlensing), new
observational and interpretation efforts are required.Comment: PS and PDF versions are created from the LaTeX file and 5 EPS
figures, two additional figues (Figs. 6 and 7) in JPEG format, scheduled for
the ApJ 20 January 2005 issu
Scientific Basis for the Potential Use of Melatonin in Bone Diseases: Osteoporosis and Adolescent Idiopathic Scoliosis
The objective of this paper was to analyze the data supporting the possible role of melatonin on bone metabolism and its repercussion in the etiology and treatment of bone pathologies such as the osteoporosis and the adolescent idiopathic scoliosis (AIS). Melatonin may prevent bone degradation and promote bone formation through mechanisms involving both melatonin receptor-mediated and receptor-independent actions. The three principal mechanisms of melatonin effects on bone function could be: (a) the promotion of the osteoblast differentiation and activity; (b) an increase in the osteoprotegerin expression by osteoblasts, thereby preventing the differentiation of osteoclasts; (c) scavenging of free radicals generated by osteoclast activity and responsible for bone resorption. A variety of in vitro and in vivo experimental studies, although with some controversial results, point toward a possible role of melatonin deficits in the etiology of osteoporosis and AIS and open a new field related to the possible therapeutic use of melatonin in these bone diseases
Spectroscopy of the Lens Galaxy of Q0957+561A,B. Implications of a possible central massive dark object
We present new long-slit William Herschel Telescope spectroscopic
observations of the lens galaxy G1 associated with the double-imaged QSO
0957+561A,B. The obtained central stellar velocity dispersion, sigma_l = 310
+/- 20 km/s, is in reasonable agreement with other measurements of this
dynamical parameter. Using all updated measurements of the stellar velocity
dispersion in the internal region of the galaxy (at angular separations < 1".5)
and a simple isotropic model, we discuss the mass of a possible central massive
dark object. It is found that the data of Falco et al. (1997) suggest the
existence of an extremely massive object of (0.5-2.1) x 10E10/h M_\odot (80%
confidence level), whereas the inclusion of very recent data (Tonry & Franx
1998, and this paper) substantially changes the results: the compact central
mass must be 6 x10E9/h M_\odot at the 90% confidence level. We note that,
taking into account all the available dynamical data, a compact nucleus with a
mass of 10E9/h M_\odot (best fit) cannot be ruled out.Comment: 20 pages, 10 figures ApJ, in pres
QSO 2237+0305 VR light curves from Gravitational Lenses International Time Project optical monitoring
We present VR observations of QSO 2237+0305 conducted by the GLITP
collaboration from 1999 October 1 to 2000 February 3. The observations were
made with the 2.56 m Nordic Optical Telescope at Roque de los Muchachos
Observatory, La Palma (Spain). The PSF fitting method and an adapted version of
the ISIS subtraction method have been used to derive the VR light curves of the
four components (A-D) of the quasar. The mean errors range in the intervals
0.01-0.04 mag (PSF fitting) and 0.01-0.02 mag (ISIS subtraction), with the
faintest component (D) having the largest uncertainties. We address the
relatively good agreement between the A-D light curves derived using different
filters, photometric techniques, and telescopes. The new VR light curves of
component A extend the time coverage of a high magnification microlensing peak,
which was discovered by the OGLE team.Comment: 15 pages, 3 figures, ApJ accepted (Feb 19
Hidden Trigger for the Giant Starburst Arc in M 83?
The huge star formation events that occur at some galactic centers do not provide enough clues as to their origin, since the morphological signatures of the triggering mechanism are smeared out in the timescale of a few orbital revolutions of the galaxy core. Our high spatial resolution three-dimensional near-infrared spectroscopy for the first time reveals that a previously known hidden mass concentration is located exactly at the youngest end of a giant star-forming arc. This location, the inferred average cluster ages, and the dynamical times clearly indicate that the interloper has left behind a spur of violent star formation in M 83, in a transient event lasting less than one orbital revolution. The study of the origin (bar funneling or cannibalized satellite) and fate (black hole merging or giant stellar cluster) of this system could provide clues to the question of core growing and morphological evolution in grand-design spiral galaxies. In particular, our TreeSPH numerical modeling suggests that the two nuclei could coalesce, forming a single massive core in about 60 million years or less
Integral Field Spectroscopy of the Central Regions of 3C 120: Evidence of a Past Merging Event
IFS combined with HST WFPC imaging were used to characterize the central
regions of the Seyfert 1 radio galaxy 3C 120. We carried out the analysis of
the data, deriving intensity maps of different emission lines and the continua
at different wavelengths from the observed spectra. Applying a 2D modeling to
the HST images we decoupled the nucleus and the host galaxy, and analyzed the
host morphology. The host is a highly distorted bulge dominated galaxy, rich in
substructures. We developed a new technique to model the IFS data extending the
2D modeling. Using this technique we separated the Seyfert nucleus and the host
galaxy spectra, and derived a residual data cube with spectral and spatial
information of the different structures in 3C 120. Three continuum-dominated
structures (named A, B, and C) and other three extended emission line regions
(EELRs, named E1, E2 and E3) are found in 3C 120 which does not follow the
general behavior of a bulge dominated galaxy. We also found shells in the
central kpc that may be remnants of a past merging event in this galaxy. The
origin of E1 is most probably due to the interaction of the radio-jet of 3C 120
with the intergalactic medium. Structures A, B, and the shell at the southeast
of the nucleus seem to correspond to a larger morphological clumpy structure
that may be a tidal tail, consequence of the past merging event. We found a
bright EELR (E2) in the innermost part of this tidal tail, nearby the nucleus,
which shows a high ionization level. The kinematics of the E2 region and its
connection to the tidal tail suggest that the tail has channeled gas from the
outer regions to the center.Comment: 55 pages, 18 figures and 5 tables Accepted by AP
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