108 research outputs found
Early evolution of disrupted asteroid P/2016 G1 (PANSTARRS)
We present deep imaging observations of activated asteroid P/2016 G1
(PANSTARRS) using the 10.4m Gran Telescopio Canarias (GTC) from late April to
early June 2016. The images are best interpreted as the result of a relatively
short-duration event with onset about days before
perihelion (i.e., around 10th February, 2016), starting sharply and decreasing
with a days (Half-width at half-maximum, HWHM). The
results of the modeling imply the emission of 1.710 kg of
dust, if composed of particles of 1 micrometer to 1 cm in radius, distributed
following a power-law of index --3, and having a geometric albedo of 0.15. A
detailed fitting of a conspicuous westward feature in the head of the
comet-like object indicates that a significant fraction of the dust was ejected
along a privileged direction right at the beginning of the event, which
suggests that the parent body has possibly suffered an impact followed by a
partial or total disruption. From the limiting magnitude reachable with the
instrumental setup, and assuming a geometric albedo of 0.15 for the parent
body, an upper limit for the size of possible fragment debris of 50 m in
radius is derived.Comment: Accepted by ApJ Letter
The dust environment of Main-Belt Comet P/2012 T1 (PANSTARRS)
Main-Belt Comet P/2012 T1 (PANSTARRS) has been imaged using the 10.4m Gran
Telescopio Canarias (GTC) and the 4.2m William Herschel Telescope (WHT) at six
epochs in the period from November 2012 to February 2013, with the aim of
monitoring its dust environment. The dust tails brightness and morphology are
best interpreted in terms of a model of sustained dust emission spanning 4 to 6
months. The total dust mass ejected is estimated at 6--25 kg.
We assume a time-independent power-law size distribution function, with
particles in the micrometer to centimeter size range. Based on the quality of
the fits to the isophote fields, an anisotropic emission pattern is favored
against an isotropic one, in which the particle ejection is concentrated toward
high latitudes ( to ) in a high obliquity object
(=80). This seasonally-driven ejection behavior, along with the
modeled particle ejection velocities, are in remarkable agreement to those we
found for P/2010 R2 (La Sagra) \citep{Moreno11a}.Comment: Accepted for publication in The Astrophysical Journal Letter
The Measurement of Growth under Embodied Technical Change
New U.S. evidence from NIPA contradicts some of the well-known Kaldor stylized facts, and call for a reformulation of the modem theory of economic growth. Among these new facts, two must be stressed : A permanent decline in the relative price of durable goods, and a permanent increase in the real equipment to real GDP ratio. To be consistent with these new facts, growth models must include at least two sectors and address the problem of defining aggregate output. In this paper, the economic theory of index numbers is used to define the growth rate of real output in a growth model with embodied technical change. The main findings are : (i) NIPA's methodology measures growth in accordance with the economic theory on index numbers, and (ii) when the growth rate is measured as in NIPA, the contribution of embodied technical change to per capital GDP growth in the U.S. is 69%, which reinforce the claim that embodied technical change is important for growth.Embodied technical change, Growth facts, Growth accounting, Index number theory
Compositional study of asteroids in the Erigone collisional family using visible spectroscopy at the 10.4 m GTC
Two primitive near Earth asteroids, (101955) Bennu and (162173) Ryugu, will
be visited by a spacecraft with the aim of returning samples back to Earth.
Since these objects are believed to originate in the inner main belt primitive
collisional families (Erigone, Polana, Clarissa, and Sulamitis) or in the
background of asteroids outside these families, the characterization of these
primitive populations will enhance the scientific return of the missions. The
main goal of this work is to shed light on the composition of the Erigone
collisional family by means of visible spectroscopy. Asteroid (163) Erigone has
been classified as a primitive object, and we expect the members of this family
to be consistent with the spectral type of the parent body. We have obtained
visible spectra (0.5 to 0.9 microns) for 101 members of the Erigone family,
using the OSIRIS instrument at the 10.4 m Gran Telescopio Canarias. We found
that 87 percent of the objects have typically primitive visible spectra
consistent with that of (163) Erigone. In addition, we found that a significant
fraction of these objects (approximately 50 percent) present evidence of
aqueous alteration
Spectroscopic and dynamical properties of comet C/2018 F4, likely a true average former member of the Oort cloud
The population of comets hosted by the Oort cloud is heterogeneous. Most
studies in this area focused on highly active objects, those with small
perihelion distances or examples of objects with peculiar physical properties
and/or unusual chemical compositions. This may have produced a biased sample of
Oort cloud comets in which the most common objects may be rare, particularly
those with perihelia well beyond the orbit of the Earth. Within this context,
the known Oort cloud comets may not be representative of the full sample. Here,
we study the spectral properties in the visible region and the cometary
activity of Comet C/2018 F4 (PANSTARRS). We also explore its orbital evolution
with the aim of understanding its origin within the context of known minor
bodies moving along nearly parabolic or hyperbolic paths. We present
observations obtained with the 10.4 m Gran Telescopio Canarias (GTC), derive
the spectral class and visible slope of C/2018 F4 and characterise its level of
cometary activity. Direct N-body simulations are carried out to explore its
orbital evolution. The absolute magnitude of C/2018 F4 is Hr=13.62+/-0.04.
Assuming a pV=0.04 its diameter is D<10.4 km. The object presents a conspicuous
coma, with a level of activity comparable to those of other comets observed at
similar heliocentric distances. Comet C/2018 F4 has a visible spectrum
consistent with that of an X-type asteroid, and has a spectral slope
S'=4.0+/-1.0 %/1000\AA and no evidence of hydration. The spectrum matches those
of well-studied primitive asteroids and comets. The analysis of its dynamical
evolution prior to discovery suggests that C/2018 F4 is not of extrasolar
origin. Although the present-day heliocentric orbit of C/2018 F4 is slightly
hyperbolic, its observational properties and past orbital evolution are
consistent with those of a dynamically old comet with an origin in the Oort
cloud.Comment: 6 pages, 5 figures. In pres
- …