We present contemporaneous optical and infrared (IR) photometric observations of the Type IIn SN 1998S covering the period between 11 and 146 d after discovery. The IR data constitute the first ever ...IR light curves of a Type IIn supernova. We use blackbody and spline fits to the photometry to examine the luminosity evolution. During the first 2–3 months, the luminosity is dominated by the release of shock-deposited energy in the ejecta. After ∼100 d the luminosity is powered mostly by the deposition of radioactive decay energy from 0.15±0.05 M⊙ of 56Ni which was produced in the explosion. We also report the discovery of an astonishingly high IR excess, K−L′=2.5, that was present at day 130. We interpret this as being due to thermal emission from dust grains in the vicinity of the supernova. We argue that to produce such a high IR luminosity so soon after the explosion, the dust must be pre-existing and so is located in the circumstellar medium of the progenitor. The dust could be heated either by the UV/optical flash (IR echo) or by the X-rays from the interaction of the ejecta with the circumstellar material.
Context. Known Mars trojans could be primordial small bodies that have remained in their present-day orbits for the age of the Solar System. Their orbital distribution is strongly asymmetric; there ...are over a dozen objects at the L 5 point and just one at L 4 , (121514) 1999 UJ 7 . Most L 5 trojans appear to form a collision-induced asteroid cluster, known as the Eureka family. Asteroid 2023 FW 14 was recently discovered and it has a robust orbit determination that may be consistent with a Mars trojan status. Aims. Our aim is determine the nature and dynamical properties of 2023 FW 14 . Methods. We carried out an observational study of 2023 FW 14 to derive its spectral class using the OSIRIS camera spectrograph at the 10.4 m Gran Telescopio Canarias. We investigated its possible trojan resonance with Mars using direct N -body simulations. Results. The reflectance spectrum of 2023 FW 14 is not compatible with the olivine-rich composition of the Eureka family; it also does not resemble the composition of the Moon, although (101429) 1998 VF 31 does. The Eureka family and 101429 are at the L 5 point. The spectrum of 2023 FW 14 is also different from two out of the three spectra in the literature of the other known L 4 trojan, 121514, which are of C-type. The visible spectrum of 2023 FW 14 is consistent with that of an X-type asteroid, as is the third spectrum of 121514. Our calculations confirm that 2023 FW 14 is the second known L 4 Mars trojan although it is unlikely to be primordial; it may remain in its present-day “tadpole” path for several million years before transferring to a Mars-crossing orbit. It might be a fragment of 121514, but a capture scenario seems more likely. Conclusions. The discovery of 2023 FW 14 suggests that regular Mars-crossing asteroids can be captured as temporary Mars trojans.
Context.
The Arjuna asteroid belt is loosely defined as a diverse group of small asteroids that follow dynamically cold, Earth-like orbits. Most of them are not actively engaged in resonant, ...co-orbital behavior with Earth. Some of them experience temporary but recurrent horseshoe episodes. Objects in horseshoe paths tend to approach Earth at a low velocity, leading to captures as Earth’s temporary satellites or mini-moons. Four such objects have already been identified: 1991 VG, 2006 RH
120
, 2020 CD
3
, and 2022 NX
1
. Here, we focus on 2023 FY
3
, a recent finding, the trajectory of which might have a co-orbital status and perhaps lead to temporary captures.
Aims.
We want to determine the physical properties of 2023 FY
3
and explore its dynamical evolution.
Methods.
We carried out an observational study of 2023 FY
3
using the OSIRIS camera spectrograph at the 10.4 m Gran Telescopio Canarias, to derive its spectral class, and time-series photometry obtained with QHY411M cameras and two units of the Two-meter Twin Telescope to investigate its rotational state.
N
-body simulations were also performed to examine its possible resonant behavior.
Results.
The visible reflectance spectrum of 2023 FY
3
is consistent with that of an S-type asteroid; its light curve gives a rotation period of 9.3±0.6 min, with an amplitude of 0.48±0.13 mag. We confirm that 2023 FY
3
roams the edge of Earth’s co-orbital space.
Conclusions.
Arjuna 2023 FY
3
, an S-type asteroid and fast rotator, currently exhibits horseshoe-like resonant behavior and in the past experienced mini-moon engagements of the temporarily captured flyby type that may repeat in the future. The spectral type result further confirms that mini-moons are a diverse population in terms of surface composition.
Context.
The near-Earth orbital space is shared by natural objects and space debris that can be temporarily captured in geocentric orbits. Short-term natural satellites are often called mini-moons. ...Reflectance spectroscopy can determine the true nature of transient satellites because the spectral signatures of spacecraft materials and near-Earth asteroids (NEAs) are different. The recently discovered object 2022 NX
1
follows an Earth-like orbit that turns it into a recurrent but ephemeral Earth companion. It has been suggested that 2022 NX
1
could have an artificial origin or be lunar ejecta.
Aims.
Here, we use reflectance spectroscopy and
N
-body simulations to determine the nature and actual origin of 2022 NX
1
.
Methods.
We carried out an observational study of 2022 NX
1
, using the OSIRIS camera spectrograph at the 10.4 m Gran Telescopio Canarias, to derive its spectral class.
N
-body simulations were also performed to investigate how it reached NEA space.
Results.
The reflectance spectrum of 2022 NX
1
is neither compatible with an artificial origin nor lunar ejecta; it is also different from the V type of the only other mini-moon with available spectroscopy, 2020 CD
3
. The visible spectrum of 2022 NX
1
is consistent with that of a K-type asteroid, although it could also be classified as an Xk type. Considering typical values of the similar albedo of both K-type and Xk-type asteroids and its absolute magnitude, 2022 NX
1
may have a size range of 5 to 15 m. We confirm that 2022 NX
1
inhabits the rim of Earth’s co-orbital space, the 1:1 mean-motion resonance, and experiences recurrent co-orbital engagements of the horseshoe-type and mini-moon events.
Conclusions.
The discovery of 2022 NX
1
confirms that mini-moons can be larger than a few meters and also that they belong to a heterogeneous population in terms of surface composition.
We present visible and near-infrared spectra (0.5–2.4
μm) of 11 Near Earth Asteroids obtained with the telescopes at the “Observatorio del Roque de los Muchachos” in La Palma, Spain. A spectral ...analysis of the obtained data is performed in order to establish the taxonomical classification of the observed asteroids. We use the method outlined by Cloutis et al. Cloutis, E.A., Gaffey, M.J., Jackowski, T.L. Calibrations of phase abundance, composition, and particle size distribution for olivine-orthopyroxene mixtures from reflectance spectra. J. Geophys. Res. 91, B11, 11641–11653, 1986 and Gaffey et al. Gaffey, M.J., Bell, J.F., Brown, R.H. Mineralogical variations within the S-type asteroid class. Icarus 106, 573–602, 1993 to obtain spectral parameters that provide us with information about their surface composition. We found 2 V-type asteroids and 9 S-type asteroids, including several compositional subtypes.We also use the Modified Gaussian Model (MGM) method developed by Sunshine et al. Sunshine, J.M., Pieters, C.M., Pratt, S.F. Deconvolution of mineral absorption bands: an improved approach. J. Geophys. Res. 95, B5, 6955–6966, 1990 to extract further mineralogical information from the spectra of two of these asteroids, those classified as V-type. We obtain a surface compositional proportion of about 70% of orthopyroxene and 30% of clinopyroxene for both asteroids.
Context. The population of comets hosted by the Oort cloud is heterogeneous. Most studies in this area have 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 meaning that our current knowledge of the appearance of the average Oort cloud comet may not be accurate. Comet C/2018 F4 (PANSTARRS) is an object of interest in this regard. Aims. Here, we study the spectral properties in the visible region and the cometary activity of C/2018 F4, and 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. Methods. We present observations obtained with the 10.4 m Gran Telescopio Canarias (GTC) that we use to derive the spectral class and visible slope of C/2018 F4 as well as to characterise its level of cometary activity. Direct N-body simulations are carried out to explore its orbital evolution. Results. The absolute magnitude of C/2018 F4 is Hr > 13.62 ± 0.04 which puts a strong limit on its diameter, D < 10.4 km, assuming a pV = 0.04 cometary-like value of the albedo. 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 Å 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. Conclusions. Although the present-day heliocentric orbit of C/2018 F4 is slightly hyperbolic, both its observational properties and past orbital evolution are consistent with those of a typical dynamically old comet with an origin in the Oort cloud.
Context. Asteroid (6478) Gault was discovered to exhibit a comet-like tail in observations from December 2018, becoming a new member of the so-called active asteroid population in the main asteroid ...belt. Aims. We seek to investigate the grain properties of the dust ejected from asteroid (6478) Gault and to give insight into the activity mechanism(s). Methods. We use a Monte Carlo dust tail brightness code to retrieve the dates of dust ejection, the physical properties of the grains, and the total dust mass losses during each event. The code takes into account the brightness contribution of the asteroid itself. The model is applied to a large data set of images spanning the period from 2019 January 11 to 2019 March 13. In addition, we carried out both short- and long-term photometric measurements of the asteroid. Results. It is shown that, to date, asteroid (6478) Gault has experienced two episodes of impulsive dust ejection, which took place around 2018 November 5 and 2019 January 2. These two episodes released at least 1.4 × 107 kg and 1.6 × 106 kg of dust, respectively, at escape speeds. The size distribution, consisting of particles in the 1 μm–1 cm radius range, follows a broken power law with bending points near 15 μm and 870 μm. On the other hand, the photometric series indicate a nearly constant magnitude over several 5–7.3 h periods, which is a possible effect of the masking of a rotational light curve by the dust. Conclusions. The dust particles forming Gault’s tails were released from the asteroid at escape speeds, but the specific ejection mechanism is unclear until photometry of the dust-free asteroid are conducted to assess whether this was related to rotational disruption or to other possible causes.
The active centaur 2020 MK 4 de la Fuente Marcos, C.; de la Fuente Marcos, R.; Licandro, J. ...
Astronomy and astrophysics (Berlin),
5/2021, Letnik:
649
Journal Article
Recenzirano
Context.
Centaurs go around the Sun between the orbits of Jupiter and Neptune. Only a fraction of the known centaurs have been found to display comet-like features. Comet 29P/Schwassmann-Wachmann 1 ...is the most remarkable active centaur. It orbits the Sun just beyond Jupiter in a nearly circular path. Only a handful of known objects follow similar trajectories.
Aims.
We present photometric observations of 2020 MK
4
, a recently found centaur with an orbit not too different from that of 29P, and we perform a preliminary exploration of its dynamical evolution.
Methods.
We analyzed broadband Cousins
R
and Sloan
g
′,
r
′, and
i
′ images of 2020 MK
4
acquired with the
Jacobus Kapteyn
Telescope and the IAC80 telescope to search for cometary-like activity and to derive its surface colors and size. Its orbital evolution was studied using direct
N
-body simulations.
Results.
Centaur 2020 MK
4
is neutral-gray in color and has a faint, compact cometary-like coma. The values of its color indexes, (
g
′−
r
′) = 0.42 ± 0.04 and (
r
′−
i
′) = 0.17 ± 0.04, are similar to the solar ones. A lower limit for the absolute magnitude of the nucleus is
H
g
= 11.30 ± 0.03 mag which, for an albedo in the range of 0.1–0.04, gives an upper limit for its size in the interval (23, 37) km. Its orbital evolution is very chaotic and 2020 MK
4
may be ejected from the Solar System during the next 200 kyr. Comet 29P experienced relatively close flybys with 2020 MK
4
in the past, sometimes when they were temporary Jovian satellites.
Conclusions.
Based on the analysis of visible CCD images of 2020 MK
4
, we confirm the presence of a coma of material around a central nucleus. Its surface colors place this centaur among the most extreme members of the gray group. Although the past, present, and future dynamical evolution of 2020 MK
4
resembles that of 29P, more data are required to confirm or reject a possible connection between the two objects and perhaps others.
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