111 research outputs found
The impact of a large object with Jupiter in July 2009
On 2009 July 19, we observed a single, large impact on Jupiter at a
planetocentric latitude of 55^{\circ}S. This and the Shoemaker-Levy 9 (SL9)
impacts on Jupiter in 1994 are the only planetary-scale impacts ever observed.
The 2009 impact had an entry trajectory opposite and with a lower incidence
angle than that of SL9. Comparison of the initial aerosol cloud debris
properties, spanning 4,800 km east-west and 2,500 km north-south, with those
produced by the SL9 fragments, and dynamical calculations of pre-impact orbit,
indicate that the impactor was most probably an icy body with a size of 0.5-1
km. The collision rate of events of this magnitude may be five to ten times
more frequent than previously thought. The search for unpredicted impacts, such
as the current one, could be best performed in 890-nm and K (2.03-2.36 {\mu}m)
filters in strong gaseous absorption, where the high-altitude aerosols are more
reflective than Jupiter's primary cloud.Comment: 15 pages, 5 figure
Scientific design of skylights
This paper intends to present a critical reality in contemporary design, the astonishing coexistence of buildings in which daylighting has been carefully considered and simulated, and others in which this issue is treated with haphazard design gestures. Although initial simulation models in the daylighting field were very much distanced from the actual practicing architect, this is no longer the case in our opinion, and also, it is a fact, that the role of apertures in all the relevant thermal exchanges that occur in buildings has been thoroughly recognized. However, many types of designs or even bioclimatic designs do not consider lighting simulations from the beginning of the design-process, and they are presented as correct if only the thermal balance meets, even at the risk of later energy waste in lighting devices and visual or physical discomfort
An ingress and a complete transit of HD 80606 b
We have used four telescopes at different longitudes to obtain
near-continuous lightcurve coverage of the star HD 80606 as it was transited by
its \sim 4-MJup planet. The observations were performed during the predicted
transit windows around the 25th of October 2008 and the 14th of February 2009.
Our data set is unique in that it simultaneously constrains the duration of the
transit and the planet's period. Our Markov-Chain Monte Carlo analysis of the
light curves, combined with constraints from radial-velocity data, yields
system parameters consistent with previously reported values. We find a
planet-to-star radius ratio marginally smaller than previously reported,
corresponding to a planet radius of Rp = 0.921 \pm 0.036RJup .Comment: 6 pages, 2 figures, MNRAS accepte
A complex storm system in Saturn’s north polar atmosphere in 2018
Producción CientíficaSaturn’s convective storms usually fall in two categories. One consists of mid-sized storms ∼2,000 km wide, appearing as irregular bright cloud systems that evolve rapidly, on scales of a few days. The other includes the Great White Spots, planetary-scale giant storms ten times larger than the mid-sized ones, which disturb a full latitude band, enduring several months, and have been observed only seven times since 1876. Here we report a new intermediate type, observed in 2018 in the north polar region. Four large storms with east–west lengths ∼4,000–8,000 km (the first one lasting longer than 200 days) formed sequentially in close latitudes, experiencing mutual encounters and leading to zonal disturbances affecting a full latitude band ∼8,000 km wide, during at least eight months. Dynamical simulations indicate that each storm required energies around ten times larger than mid-sized storms but ∼100 times smaller than those necessary for a Great White Spot. This event occurred at about the same latitude and season as the Great White Spot in 1960, in close correspondence with the cycle of approximately 60 years hypothesized for equatorial Great White Spots.Ministerio de Economía, Industria y Competitividad - Fondo Europeo de Desarrollo Regional (project AYA2015-65041-P)Gobierno Vasco (project IT-366-19
The EBLM project. II. A very hot, low-mass M dwarf in an eccentric and long period eclipsing binary system from SuperWASP
In this paper, we derive the fundamental properties of
1SWASPJ011351.29+314909.7 (J0113+31), a metal-poor (-0.40 +/- 0.04 dex),
eclipsing binary in an eccentric orbit (~0.3) with an orbital period of ~14.277
d. Eclipsing M dwarfs orbiting solar-type stars (EBLMs), like J0113+31, have
been identified from WASP light curves and follow-up spectroscopy in the course
of the transiting planet search. We present the first binary of the EBLM sample
to be fully analysed, and thus, define here the methodology. The primary
component with a mass of 0.945 +/- 0.045 Msun has a large radius (1.378 +/-
0.058 Rsun) indicating that the system is quite old, ~9.5 Gyr. The M-dwarf
secondary mass of 0.186 +/- 0.010 Msun and radius of 0.209 +/- 0.011 Rsun are
fully consistent with stellar evolutionary models. However, from the
near-infrared secondary eclipse light curve, the M dwarf is found to have an
effective temperature of 3922 +/- 42 K, which is ~600 K hotter than predicted
by theoretical models. We discuss different scenarios to explain this
temperature discrepancy. The case of J0113+31 for which we can measure mass,
radius, temperature and metallicity, highlights the importance of deriving
mass, radius and temperature as a function of metallicity for M dwarfs to
better understand the lowest mass stars. The EBLM Project will define the
relationship between mass, radius, temperature and metallicity for M dwarfs
providing important empirical constraints at the bottom of the main sequence.Comment: 13 pages, 7 figures. Accepted for publication in A&
Multi-site, multi-year monitoring of the oscillating Algol-type eclipsing binary CT Her
We present the results of a multi-site photometric campaign carried out in
2004-2008 for the Algol-type eclipsing binary system CT Her, the primary
component of which shows Delta Scuti-type oscillations. Our data consist of
differential light curves collected in the filters B and V which have been
analysed using the method of Wilson-Devinney (PHOEBE). After identification of
an adequate binary model and removal of the best-matching light curve solution,
we performed a Fourier analysis of the residual B and V light curves to
investigate the pulsational behaviour. We confirm the presence of rapid
pulsations with a main period of 27.2 min. Up to eight significant frequencies
with semi-amplitudes in the range 3 to 1 mmag were detected, all of which
surprisingly lie in the frequency range 43.5-53.5 c\d. This result is
independent from the choice of the primary's effective temperature (8200 or
8700 K) since the light curve models for the binary are very similar in both
cases. This is yet another case of a complex frequency spectrum observed for an
accreting Delta Scuti-type star (after Y Cam). In addition, we demonstrate that
the amplitudes of several of these pulsation frequencies show evidence of
variability on time scales as short as 1-2 years, perhaps even less. Moreover,
our analysis takes into account some recently acquired spectra, from which we
obtained the corresponding radial velocities for the years 2007-2009.
Investigation of the O-C diagram shows that further monitoring of the epochs of
eclipse minima of CT Her will cast a new light on the evolution of its orbital
period.Comment: 13 pages, 13 encapsulated Postscript figures. Tables~3, 4, 9 and 12
will be available in electronic form only. Astronomy and Astrophysics, in
process (2011). Replaced the abstract with its final versio
Gas Giants
The gas giants (Jupiter and Saturn) and icy giants (Uranus and Neptune) are fluid planets with atmospheres primarily made of hydrogen and helium. The part of their atmospheres accessible to remote sensing occupies only a small fraction of their radii (0.05%). Clouds and hazes form around the 1 bar altitude pressure level and extend vertically, according to the thermochemical models, in a layer with a thickness of 200_500 km where temperature increases with depth (usually known as the "weather layer"). Clouds made of NH3, NH4SH, H2O (in Jupiter and Saturn), with the addition of CH4 (in Uranus and Neptune), cover the planet in stratified layers that are mixed with unknown hromophore agents. Dynamical phenomena in the weather layer shape different cloud patterns that define the visible appearance of these planets. In the thermal part of the spectrum clouds act as opacity sources providing brightness contrasts. The ensemble of cloud morphologies in terms of shapes, sizes and albedos allows their use as tracers of the atmospheric motions in the weather layer (Fig. 4.1). This is the main tool employed so far to study the winds on these fourplanets
NGC 1624-2: A slowly rotating, X-ray luminous Of?cp star with an extraordinarily strong magnetic field
This paper presents a first observational investigation of the faint Of?cp
star NGC 1624-2, yielding important new constraints on its spectral and
physical characteristics, rotation, magnetic field strength, X-ray emission and
magnetospheric properties. Modeling the spectrum and spectral energy
distribution, we conclude that NGC 1624-2 is a main sequence star of mass M
{\simeq} 30 M{\odot}, and infer an effective temperature of 35 {\pm} 2 kK and
log g = 4.0 {\pm} 0.2. Based on an extensive time series of optical spectral
observations we report significant variability of a large number of spectral
lines, and infer a unique period of 157.99 {\pm} 0.94 d which we interpret as
the rotational period of the star. We report the detection of a very strong -
5.35 {\pm} 0.5 kG - longitudinal magnetic field , coupled with probable
Zeeman splitting of Stokes I profiles of metal lines confirming a surface field
modulus of 14 {\pm} 1 kG, consistent with a surface dipole of polar
strength >~ 20 kG. This is the largest magnetic field ever detected in an
O-type star, and the first report of Zeeman splitting of Stokes I profiles in
such an object. We also report the detection of reversed Stokes V profiles
associated with weak, high-excitation emission lines of O iii, which we propose
may form in the close magnetosphere of the star. We analyze archival Chandra
ACIS-I X-ray data, inferring a very hard spectrum with an X-ray efficiency log
Lx/Lbol = -6.4, a factor of 4 larger than the canonical value for O-type stars
and comparable to that of the young magnetic O-type star {\theta}1 Ori C and
other Of?p stars. Finally, we examine the probable magnetospheric properties of
the star, reporting in particular very strong magnetic confinement of the
stellar wind, with {\eta}* {\simeq} 1.5 {\times} 10^4, and a very large Alfven
radius, RAlf = 11.4 R*.Comment: 17 pages, MNRAS accepted and in pres
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