494 research outputs found
P/2010 A2 LINEAR II: dynamical dust modelling
P/2010 A2 is an object on an asteroidal orbit that was observed to have an
extended tail or debris trail in January 2010. In this work, we fit the
outburst of P/2010 A2 with a conical burst model, and verify previous
suspicions that this was a one--time collisional event rather than an sustained
cometary outburst, implying that P/2010 A2 is not a new Main Belt Comet driven
by ice sublimation. We find that the best--fit cone opening angle is about 40
to 50 degrees, in agreement with numerical and laboratory simulations of
cratering events. Mapping debris orbits to sky positions suggests that the
distinctive arc features in the debris correspond to the same debris cone
inferred from the extended dust. From the velocity of the debris, and from the
presence of a velocity maximum at around 15 cm/s, we infer that the surface of
A2 probably has a very low strength (<1 kPa), comparable to lunar regolith.Comment: 14 pages, 25 figures; accepted by Astronomy and Astrophysic
Plausible home stars of the interstellar object 'Oumuamua found in Gaia DR2
The first detected interstellar object 'Oumuamua that passed within 0.25au of
the Sun on 2017 September 9 was presumably ejected from a stellar system. We
use its newly determined non-Keplerian trajectory together with the
reconstructed Galactic orbits of 7 million stars from Gaia DR2 to identify past
close encounters. Such an "encounter" could reveal the home system from which
'Oumuamua was ejected. The closest encounter, at 0.60pc (0.53-0.67pc, 90%
confidence interval), was with the M2.5 dwarf HIP 3757 at a relative velocity
of 24.7km/s, 1Myr ago. A more distant encounter (1.6pc) but with a lower
encounter (ejection) velocity of 10.7km/s was with the G5 dwarf HD 292249,
3.8Myr ago. Two more stars have encounter distances and velocities intermediate
to these. The encounter parameters are similar across six different
non-gravitational trajectories for 'Oumuamua. Ejection of 'Oumuamua by
scattering from a giant planet in one of the systems is plausible, but requires
a rather unlikely configuration to achieve the high velocities found. A binary
star system is more likely to produce the observed velocities. None of the four
home candidates have published exoplanets or are known to be binaries. Given
that the 7 million stars in Gaia DR2 with 6D phase space information is just a
small fraction of all stars for which we can eventually reconstruct orbits, it
is a priori unlikely that our current search would find 'Oumuamua's home star
system. As 'Oumuamua is expected to pass within 1pc of about 20 stars and brown
dwarfs every Myr, the plausibility of a home system depends also on an
appropriate (low) encounter velocity.Comment: Accepted to The Astronomical Journa
Multidisciplinary Control of a Sparse Interferometric Array Satellite Testbed
The MIT Adaptive Reconnaissance Golay-3 Optical Satellite (ARGOS) is a wide-angle Fizeau interferometer spacecraft testbed. Designing a space-based interferometer, which requires such high tolerances on pointing and alignment for its apertures, presents unique multidisciplinary challenges in the areas of structural dynamics, controls and multi-aperture phasing active optics. In meeting these challenges, emphasis is placed on modularity in spacecraft subsystems and optics as a means of allowing expandability and upgradeability. For the interferometer to function properly, unique methods of coherent wave front sensing are developed and used for error detection in control of the Fast Steering Mirrors (FSMs). The space environment is simulated by floating ARGOS on a frictionless air-bearing that allows it to track fast moving satellites such as the International Space Station (ISS), planets or point stars. A System Identification is performed on ARGOS to determine its dynamic properties and to design optimal controllers for
the Attitude Control System (ACS). ACS sensors include an electronic compass with a 2-axis tip-tilt sensor, a viewfinder camera with centroiding algorithm, and a 3-axis rate gyroscope. Nonlinear, quaternion-based control is employed using reaction wheels as the spacecraft's actuators
Discovery of the peculiar supernova 1998bw in the error box of GRB980425
The discovery of X-ray, optical and radio afterglows of gamma-ray bursts
(GRBs) and the measurements of the distances to some of them have established
that these events come from Gpc distances and are the most powerful photon
emitters known in the Universe, with peak luminosities up to 10^52 erg/s. We
here report the discovery of an optical transient, in the BeppoSAX Wide Field
Camera error box of GRB980425, which occurred within about a day of the
gamma-ray burst. Its optical light curve, spectrum and location in a spiral arm
of the galaxy ESO 184-G82, at a redshift z = 0.0085, show that the transient is
a very luminous type Ic supernova, SN1998bw. The peculiar nature of SN1998bw is
emphasized by its extraordinary radio properties which require that the radio
emitter expand at relativistical speed. Since SN1998bw is very different from
all previously observed afterglows of GRBs, our discovery raises the
possibility that very different mechanisms may give rise to GRBs, which differ
little in their gamma-ray properties.Comment: Under press embargo at Nature (submitted June 10, 1998
Galaxies in Southern Bright Star Fields I. Near-infrared imaging
As a prerequisite for cosmological studies using adaptive optics techniques,
we have begun to identify and characterize faint sources in the vicinity of
bright stars at high Galactic latitudes. The initial phase of this work has
been a program of K_s imaging conducted with SOFI at the ESO NTT. From
observations of 42 southern fields evenly divided between the spring and autumn
skies, we have identified 391 additional stars and 1589 galaxies lying at
separations 60" from candidate guide stars in the magnitude range 9.0 R 12.4.
When analyzed as a "discrete deep field" with 131 arcmin^2 area, our dataset
gives galaxy number counts that agree with those derived previously over the
range 16 K_s 20.5. This consistency indicates that in the aggregate, our fields
should be suitable for future statistical studies. We provide our source
catalogue as a resource for users of large telescopes in the southern
hemisphere.Comment: 10 pages, 7 figures, accepted by A&A; Table 3 is available at
http://www.rzg.mpg.de/~ajb/data.html pending upload to CD
The similarity of the interstellar comet 2I/Borisov to solar system comets from high resolution optical spectroscopy
Aims: 2I/Borisov (hereafter 2I) is the first visibly active interstellar comet observed in the Solar System, allowing us for the first time to sample the composition of a building block from another system. We report on the monitoring of 2I with the Ultraviolet-Visual Echelle Spectrograph, the high-resolution optical spectrograph of the ESO Very Large Telescope at Paranal, for four months from November 15, 2019 to March 16, 2020. Our goal is to characterise the activity and composition of 2I with respect to Solar System comets. Methods: We collected high-resolution spectra at 12 different epochs from 2.1 au pre-perihelion to 2.6 au post-perihelion. Results: On December 24 and 26, 2019, close to perihelion, we detected several OH lines of the 309 nm (0-0) band and derived a water production rate of 2.2 ± 0.2 × 10^26 molecules s^−1. The three [OI] forbidden oxygen lines were detected at different epochs and we derived a green-to-red doublet intensity ratio (G/R) of 0.31 ± 0.05 close to perihelion. The NH_2 ortho and para lines from various bands were measured and allowed us to derive an ortho-to-para abundance ratio (OPR) of 3.21 ± 0.15, corresponding to an OPR and spin temperature of ammonia of 1.11 ± 0.08 and 31 −5/+10 K, respectively. These values are consistent with the values usually measured for Solar System comets. Emission lines of the radicals NH (336 nm), CN (388 nm), CH (431 nm), and C2 (517 nm) were also detected. Several FeI and NiI lines were identified and their intensities were measured to provide a ratio of log (NiI/FeI) = 0.21 ± 0.18, which is in agreement with the value recently found in Solar System comets. Conclusions: Our high spectral resolution observations of 2I/Borisov and the associated measurements of the NH2 OPR and the Ni/Fe abundance ratio are remarkably similar to Solar System comets. Only the G/R ratio is unusually high, but it is consistent with the high abundance ratio of CO/H2O found by other investigators
An optical supernova associated with the X-ray flash XRF 060218
Long-duration gamma-ray bursts (GRBs) are associated with type Ic supernovae
that are more luminous than average and that eject material at very high
velocities. Less-luminous supernovae were not hitherto known to be associated
with GRBs, and therefore GRB-supernovae were thought to be rare events. Whether
X-ray flashes - analogues of GRBs, but with lower luminosities and fewer
gamma-rays - can also be associated with supernovae, and whether they are
intrinsically 'weak' events or typical GRBs viewed off the axis of the burst,
is unclear. Here we report the optical discovery and follow-up observations of
the type Ic supernova SN 2006aj associated with X-ray flash XRF 060218.
Supernova 2006aj is intrinsically less luminous than the GRB-supernovae, but
more luminous than many supernovae not accompanied by a GRB. The ejecta
velocities derived from our spectra are intermediate between these two groups,
which is consistent with the weakness of both the GRB output and the supernova
radio flux. Our data, combined with radio and X-ray observations, suggest that
XRF 060218 is an intrinsically weak and soft event, rather than a classical GRB
observed off-axis. This extends the GRB-supernova connection to X-ray flashes
and fainter supernovae, implying a common origin. Events such as XRF 060218 are
probably more numerous than GRB-supernovae.Comment: Final published versio
Reconfigurable photon localization by coherent drive and dissipation in photonic lattices
7 pags., 4 figs.The engineering of localized modes in photonic structures is one of the main targets of modern photonics. An efficient strategy to design these modes is to use the interplay of constructive and destructive interference in periodic photonic lattices. This mechanism is at the origin of the defect modes in photonic bandgaps, bound states in the continuum, and compact localized states in flat bands. Here, we show that in lattices of lossy resonators, the addition of external optical drives with a controlled phase enlarges the possibilities of manipulating interference effects and allows for the design of novel types of localized modes. Using a honeycomb lattice of coupled micropillars resonantly driven with several laser spots at energies within its photonic bands, we demonstrate the localization of light in at-will geometries down to a single site. These localized modes are fully reconfigurable and have the potentiality of enhancing nonlinear effects and of controlling light-matter interactions with single site resolution.Ministerio de Ciencia, Innovación y Universidades (PGC2018-094792-B-100); Consejo Superior de Investigaciones Científicas (PTI-001);
Comunidad de Madrid (CAM 2020 Y2020/TCS-6545); Narodowe Centrum Nauki (DEC-2019/32/T/ST3/00332); Agence Nationale de la Recherche
(ANR-11-LABX-0007, ANR-16-CE30-0021, ANR-16-IDEX-0004 ULNE, ANR-QUAN-0003-05); European Research Council (820392, 865151, 949730),
Région Hauts-de-France
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