arXiv subjects

F. Moreno

Publications and source records attributed to F. Moreno.

29 records · Page 2Linked to original sources

arXiv2015

Spectrophotometric properties of the nucleus of comet 67P/Churyumov-Gerasimenko from the OSIRIS instrument onboard the ROSETTA spacecraft

The Rosetta mission of the European Space Agency has been orbiting the comet 67P/Churyumov-Gerasimenko (67P) since August 2014 and is now in its escort phase. A large complement of scientific experiments designed to complete the most detailed study of a comet ever attempted are onboard Rosetta. We present results for the photometric and spectrophotometric properties of the nucleus of 67P derived from the OSIRIS imaging system, which consists of a Wide Angle Camera (WAC) and a Narrow Angle Camera (NAC). The disk-averaged phase function of the nucleus of 67P shows a strong opposition surge with a G parameter value of -0.13$\pm$0.01 in the HG system formalism and an absolute magnitude $H_v(1,1,0)$ = 15.74$\pm$0.02 mag. The integrated spectrophotometry in 20 filters covering the 250-1000 nm wavelength range shows a red spectral behavior, without clear absorption bands except for a potential absorption centered at $\sim$ 290 nm that is possibly due to SO$_2$ ice. The nucleus shows strong phase reddening, with disk-averaged spectral slopes increasing from 11\%/(100 nm) to 16\%/(100 nm) in the 1.3$^{\circ}$--54$^{\circ}$ phase angle range. The geometric albedo of the comet is 6.5$\pm$0.2\% at 649 nm, with local variations of up to $\sim$ 16\% in the Hapi region. From the disk-resolved images we computed the spectral slope together with local spectrophotometry and identified three distinct groups of regions (blue, moderately red, and red). The Hapi region is the brightest, the bluest in term of spectral slope, and the most active surface on the comet. Local spectrophotometry shows an enhancement of the flux in the 700-750 nm that is associated with coma emissions.

astro-ph.EP↗

arXiv2015

On the dust environment of Main-Belt Comet 313P/Gibbs

We present observations carried out using the 10.4 m Gran Telescopio Canarias and an interpretative model of the dust environment of activated asteroid 313P/Gibbs. We discuss three different models relating to different values of the dust parameters, i.e, dust loss rate, maximum and minimum sizes of particles, power index of the size distribution, and emission pattern. The best model corresponds with an isotropic emission of particles which started on August 1st. The size of grains were in the range of $0.1-2000$ $μ$m, with velocities for 100 $μ$m particles between $0.4-1.9$ m$~$s$^{-1}$, with a dust production rate in the range of $0.2-0.8$ kg$~$s$^{-1}$. The dust tails' brightness and morphology are best interpreted in terms of a model of sustained and low dust emission driven by water-ice sublimation, spanning since 2014 August 1st, and triggered by a short impulsive event. This event produced an emission of small particles of about 0.1 $μ$m with velocities of $\sim$4 m$~$s$^{-1}$. From our model we deduce that the activity of this Main-Belt Comet continued for, at least, four months, since activation.

astro-ph.EP↗

arXiv2014

Dust environment and dynamical history of a sample of short period comets

Aims. In this work, we present an extended study of the dust environment of a sample of short period comets and their dynamical history. With this aim, we characterized the dust tails when the comets are active, and we made a statistical study to determine their dynamical evolution. The targets selected were 22P/Kopff, 30P/Reinmuth 1, 78P/Gehrels 2, 115P/Maury, 118P/Shoemaker-Levy 4, 123P/West-Hartley, 157P/Tritton, 185/Petriew, and P/2011 W2 (Rinner). Methods. We use two different observational data: a set of images taken at the Observatorio de Sierra Nevada and the Afrho curves provided by the amateur astronomical association Cometas-Obs. To model these observations, we use our Monte Carlo dust tail code. From this analysis, we derive the dust parameters, which best describe the dust environment: dust loss rates, ejection velocities, and size distribution of particles. On the other hand, we use a numerical integrator to study the dynamical history of the comets, which allows us to determine with a 90% of confidence level the time spent by these objects in the region of Jupiter Family Comets. Results. From the Monte Carlo dust tail code, we derived three categories attending to the amount of dust emitted: Weakly active (115P, 157P, and Rinner), moderately active (30P, 123P, and 185P), and highly active (22P, 78P, and 118P). The dynamical studies showed that the comets of this sample are young in the Jupiter Family region, where the youngest ones are 22P (100 yr), 78P (500 yr), and 118P (600 yr). The study points to a certain correlation between comet activity and time spent in the Jupiter Family region, although this trend is not always fulfilled. The largest particle sizes are not tightly constrained, so that the total dust mass derived should be regarded as lower limits.}

astro-ph.EP↗

arXiv2012

Exploring the nature of new main-belt comets with the 10.4m GTC telescope: (300163) 2006 VW139

We aim to study the dust ejected by main-belt comet (MBC) (300163) 2006 VW139 to obtain information on the ejection mechanism and the spectral properties of the object, to see if they are compatible with those of "normal" comets. Images in the g and r band and a low-resolution spectrum in the 0.35-0.9 micron region were obtained with the GTC telescope (La Palma, Spain). Images were analyzed to produce a color map and derive a lower limit of the absolute magnitude. A Monte Carlo (MC) scattering model was used to derive dust properties such as mass loss rates and ejection velocities as a function of time. The spectrum was compared to that of MBC 133P/Elst-Pizarro and used to search for CN emission. The spectrum of 2006 VW139 is typical of a C-class asteroid, with a spectral slope S=0.5+/-1.0%/1000A. It is similar to the spectrum of 133P and other MBCs. No CN emission is detected. A CN production rate upper limit of 3.76e23 1/s is derived. The MBC present a narrow almost linear tail that extends up to 40.000 km in the anti-solar direction and more than 80.000 km in the direction of the object's orbital plane. The color of the tail is slightly redder than the Sun (S=3 to 6%/1000A). The MC dust tail model derived the mass loss rates and ejection velocity as a function of time, and the results show that the activity onset occurs shortly after perihelion, and lasts about 100 days; the total ejected mass is about 2e6 kg. The spectrum of VW139 suggests that it is not a "normal" comet. It is typical of the other observed MBCs. Even if no CN emission is detected, the more likely activation mechanism is water-ice sublimation. Like other well studied MBCs, VW139 is likely a primitive C-class asteroid that has a water-ice subsurface depth reservoir that has recently been exposed to sunlight or to temperatures that produce enough heat to sublime the ice.

astro-ph.EP↗

arXiv2010

Water-ice driven activity on Main-Belt Comet P/2010 A2 (LINEAR) ?

The dust ejecta of Main-Belt Comet P/2010 A2 (LINEAR) have been observed with several telescopes at the at the Observatorio del Roque de los Muchachos on La Palma, Spain. Application of an inverse dust tail Monte Carlo method to the images of the dust ejecta from the object indicates that a sustained, likely water-ice driven, activity over some eight months is the mechanism responsible for the formation of the observed tail. The total amount of dust released is estimated to be 5E7 kg, which represents about 0.3% of the nucleus mass. While the event could have been triggered by a collision, this cannot be decided from the currently available data.

astro-ph.EP↗

arXiv2009

The Impact of Uncertainties in Reaction Q-values on Nucleosynthesis in Type I X-Ray Bursts

Nucleosynthesis in Type I X-ray bursts may involve up to several thousand nuclear processes. The majority of these processes have only been determined theoretically due to the lack of sufficient experimental information. Accurate reaction Q-values are essential for reliable theoretical estimates of reaction-rates. Those reactions with small Q-values (< 1 MeV) are of particular interest in these environments as they may represent waiting points for a continuous abundance flow towards heavier-mass nuclei. To explore the nature of these waiting points, we have performed a comprehensive series of post-processing calculations which examine the sensitivity of nucleosynthesis in Type I X-ray bursts to uncertainties in reaction Q-values. We discuss and list the relatively few critical masses for which measurements could better constrain the results of our studies. In particular, we stress the importance of measuring the mass of 65As to obtain an experimental Q-value for the 64Ge(p,gamma)65As reaction.

astro-ph↗

arXiv2007

Symmetry breaking and clustering in a vibrated granular gas with several macroscopically connected compartments

The spontaneous symmetry breaking in a vibro-fluidized low-density granular gas in three connected compartments is investigated. When the total number of particles in the system becomes large enough, particles distribute themselves unequally among the three compartments. Particles tend to concentrate in one of the compartments, the other two having the (relatively small) same average number of particles. A hydrodynamical model that accurately predicts the bifurcation diagram of the system is presented. The theory can be easily extended to the case of an arbitrary number of connected compartments.

cond-mat.stat-mech↗

arXiv2006

Hydrodynamic profiles for an impurity in a open vibrated granular gas

The hydrodynamic state of an impurity immersed in a low density granular gas is analyzed. Explicit expressions for the temperature and density fields of the impurity in terms of the hydrodynamic fields of the gas are derived. It is shown that the ratio between the temperatures of the two components, measuring the departure from energy equipartition, only depends on the mechanical properties of the particles, being therefore constant in the bulk of the system. This ratio plays an important role in determining the density profile of the intruder and its position with respect to the gas, since it determines the sign of the pressure diffusion coefficient. The theoretical predictions are compared with molecular dynamics simulation results for the particular case of the steady state of an open vibrated granular system in absence of macroscopic fluxes, and a satisfactory agreement is found.

cond-mat.stat-mech↗

arXiv2005

Energy partition and segregation for an intruder in a vibrated granular system under gravity

The difference of temperatures between an impurity and the surrounding gas in an open vibrated granular system is studied. It is shown that, in spite of the high inhomogeneity of the state, the temperature ratio remains constant in the bulk of the system. The lack of energy equipartition is associated to the change of sign of the pressure diffusion coefficient for the impurity at certain values of the parameters of the system, leading to a segregation criterium. The theoretical predictions are consistent with previous experimental results, and also in agreement with molecular dynamics simulation results reported in this paper.

cond-mat.stat-mech↗

arXiv2003

Steady state representation of the homogeneous cooling state of a granular gas

The properties of a dilute granular gas in the homogeneous cooling state are mapped to those of a stationary state by means of a change in the time scale that does not involve any internal property of the system. The new representation is closely related with a general property of the granular temperature in the long time limit. The physical and practical implications of the mapping are discussed. In particular, simulation results obtained by the direct simulation Monte Carlo method applied to the scaled dynamics are reported. This includes ensemble averages and also the velocity autocorrelation function, as well as the self-diffusion coefficient obtained from the latter by means of the Green-Kubo representation. In all cases, the obtained results are compared with theoretical predictions.

cond-mat.stat-mech↗

arXiv2002

Transversal inhomogeneities in dilute vibrofluidized granular fluids

The spontaneous symmetry breaking taking place in the direction perpendicular to the energy flux in a dilute vibrofluidized granular system is investigated, using both a hydrodynamic description and simulation methods. The latter include molecular dynamics and direct Monte Carlo simulation of the Boltzmann equation. A marginal stability analysis of the hydrodynamic equations, carried out in the WKB approximation, is shown to be in good agreement with the simulation results. The shape of the hydrodynamic profiles beyond the bifurcation is discussed.

cond-mat.stat-mech↗