Context . In the context of charge-coupled devices (CCDs), the ultraviolet (UV) region has mostly remained unexplored after the 1990s. Gaia DR3 offers the community a unique opportunity to explore ...tens of thousands of asteroids in the near-UV as a proxy of the UV absorption. This absorption has been proposed in previous works as a diagnostic of hydration, organics, and space weathering. Aims . In this work, we aim to explore the potential of the NUV as a diagnostic region for primitive asteroids using Gaia DR3. Methods . We used a corrective factor over the blue part of Gaia spectra to erase the solar analog selection effect. We identified an artificial relation between the band noise and slope and applied a signal-to-noise ratio (S/N) threshold for Gaia bands. Meeting the quality standards, we employed a Markov chain Monte Carlo (MCMC) algorithm to compute the albedo threshold, maximizing primitive asteroid inclusion. Utilizing one- and two-dimensional (1D and 2D) projections, along with dimensionality-reduction methods (such as PCA and UMAP), we identified primitive asteroid populations. Results . We uncovered: (a) the first observational evidence linking UV absorption to the 0.7 µm band, tied to hydrated iron-rich phyllosilicates; and (b) a 2D space revealing a split in C-type asteroids based on spectral features, including UV absorption. The computed average depth (3.5 ± 1.0 %) and center (0.70 ± 0.03 µm) of the 0.7 µm absorption band for primitive asteroids observed with Gaia is in agreement with the literature values. Conclusions . In this paper, we shed light on the importance of the UV absorption feature to discriminate among different mineralogies (i.e., iron-rich phyllosilicates vs. iron-poor) or to identify taxonomies that are conflated in the visible (i.e., F-types vs. B-types). We have shown that this is a promising region for diagnostic studies of the composition of primitive asteroids.
ABSTRACT
Potentially hazardous asteroids (PHAs) are objects that can have close encounters with Earth and are significantly large to cause significant regional damage in the event of impact. The ...mitigation strategy requires to understand their physical properties. We aim to investigate the physical nature of PHAs, using data obtained within the framework of the Visible NEOs Observations Survey (ViNOS). We analysed and characterized a sample comprised of 14 of these objects. To conduct this study, we obtained visible spectra of 14 PHAs in the 0.5–0.9-μm region using the 2.5 m Nordic Optical Telescope, located at the El Roque De Los Muchachos Observatory in La Palma (Spain). The resulting spectra were combined with their corresponding near-infrared counterparts, available in the literature from the Small Main-Belt Asteroid Spectroscopic Survey (SMASS). We performed a taxonomical classification, computed several diagnostic spectral parameters (slopes, band centres, and band area ratios), and provide completely new mineralogical information for 10 of these objects. We also compared the data with laboratory spectra of meteorites from the RELAB data base. Among the studied sample of PHAs, approximately 90 per cent of the objects (13 out of 14) were classified as silicaceous (S-types and subclasses). Only one object, 489 486, was classified as carbonaceous. Five of the studied PHAs did not have previous taxonomic classifications. The comparisons of the silicaceous PHAs with meteoritic spectra yielded, in all cases, ordinary chondrites as the best match for meteoritic analogues. The computed mineralogy of all of our targets is also consistent with this results.
Context.
Despite the observed signs of large impacts on the surface of Ceres, there is no confirmed collisional family associated with this dwarf planet. After a dynamical and photometric study, a ...sample of 156 asteroids were proposed as candidate members of a Ceres collisional family.
Aims.
Our main objective is to study the connection between Ceres and a total of 14 observed asteroids among the candidates sample to explore their genetic relationships with Ceres.
Methods.
We obtained visible spectra of these 14 asteroids using the OSIRIS spectrograph at the 10.4 m Gran Telescopio Canarias. We computed spectral slopes in two different wavelength ranges, from 0.49 to 0.80 μm and from 0.80 to 0.92 μm, to compare the values obtained with those on Ceres’ surface previously computed using the Visible and Infrared Spectrometer instrument on board the NASA Dawn spacecraft. We also calculated the spectral slopes in the same range for ground-based observations of Ceres collected from the literature.
Results.
We present the visible spectra and the taxonomy of 14 observed asteroids. We found that only two of the asteroids are spectrally compatible with Ceres’ surface. Further analysis of those two asteroids indicates that they are spectrally young and thus less likely to be members of the Ceres family.
Conclusions.
All in all, our results indicate that most of the 14 observed asteroids are not likely to belong to a Ceres collisional family. Despite two of them being spectrally compatible with the young surface of Ceres, further evaluation is needed to confirm or reject their origin from Ceres.
Social parasites usually rely on chemical cues (cuticular hydrocarbons) to successfully invade and coexist with their hosts. Most ants that are obligate social parasites (slave-makers) can parasitize ...several related host species with different levels of chemical similarity although there are few exceptions where there is only a single host species. An example of the latter is
Rossomyrmex minuchae
, which was known to be only associated with
Proformica longiseta
. However, a recent discovery of a new
R. minuchae
population revealed that it can parasitize
P. nasuta
, a species with a separate distribution to
P. longiseta
. Chemical analyses of cuticular hydrocarbons show local adaptation of the parasite to its host in this new population, being more similar to
P. nasuta
than to other
R. minuchae
populations. In addition, genetic analyses evidence differences from the other known populations, from which it split 1.21 Mya during glacial and interglacial periods of the Pleistocene and remained separated to the present day. This historical genetic isolation and the chemical differences found between parasite populations may evidence a speciation process and support the local host–parasite coevolution.
The aim of this paper is to describe the relationship between two ant species,
Formica frontalis
and
Iberoformica subrufa
, found together in shared nests. Therefore, we obtained data from dug nests ...and outdoor activity in two sympatric populations and investigated the cuticular hydrocarbons (CHCs) in both sympatric populations and in 10
I. subrufa
allopatric populations to unravel whether the relationship becomes tuned between both species. We also determined the CHCs of two sympatric
Serviformica
species (
F. cunicularia
and
F. lemani
). Our results showed that the ant
F. frontalis
is a temporary parasite of
I. subrufa
which facultatively forms mixed colonies complying with a loose form of the Emery’s rule. Alkanes and methylalkanes are the most abundant compounds found in
F. frontalis
and
I. subrufa
CHCs, respectively, but esters were only abundant in
I. subrufa
. As far as the CHC similarity is concerned, the sympatric free-living hosts were chemically closer to the parasite, albeit not identical, whereas the allopatric
I. subrufa
populations always maintained a separate CHC composition. We provide different potential hypotheses to explain this similarity of cuticular profiles only in the two geographically distant sympatric populations.
Context.
Spectrophotometry data of asteroids obtained in the 1980s showed that there are large variations in their near-ultraviolet (NUV) reflectance spectra. Reflectance spectra at NUV wavelengths ...are important because they help detect the presence of hydrated minerals and organics on the asteroid surfaces. However, the NUV wavelength region has not been fully investigated yet using spectroscopic data.
Aims.
The aim of our study is to obtain the near-ultraviolet to visible (NUV-VIS, 0.35–0.95 μm) reflectance spectra of primitive asteroids with a focus on members of the Themis and Polana-Eulalia complex families. This characterization allows us to discuss the origin of two recent sample return mission target asteroids, (162173) Ryugu and (101955) Bennu.
Methods.
We obtain low-resolution visible spectra of target asteroids down to 0.35 μm using the telescopes located at the Roque de los Muchachos Observatory (La Palma, Spain) and revisit spectroscopic data that have already been published. Using new spectroscopic and already published spectrophotometric and spectroscopic data, we study the characteristics of the NUV-VIS reflectance spectra of primitive asteroids, focusing on data of the Themis family and the Polana-Eulalia family complex. Finally, we compare the NUV characteristics of these families with (162173) Ryugu and (101955) Bennu. In this work, we also study systematic effects due to the use of the five commonly used stars in Landolt’s catalog as solar analogs to obtain the asteroid reflectance in the NUV wavelength range. We compare the spectra of five G-stars in Landolt’s catalog with the spectrum of the well-studied solar analog Hyades 64, also observed on the same nights.
Results.
We find that many widely used Landolt’s G-type stars are not solar analogs in the NUV wavelength spectral region and thus are not suitable for obtaining the reflectance spectra of asteroids. We also find that, even though the Themis family and the PolanaEulalia family complex show a similar blueness at visible wavelengths, the NUV absorption of the Themis family is much deeper than that of the Polana-Eulalia family complex. We did not find significant differences between the New Polana and Eulalia families in terms of the NUV-VIS slope. (162173) Ryugu’s and (101955) Bennu’s spectral characteristics in the NUV-VIS overlaps with those of the Polana-Eulalia family complex which implies that it is the most likely origin of these two near-Earth asteroids.
Three different isolated populations of the slave-making ant Rossomyrmex minuchae, sympatric with its obligate host Proformica longiseta, are known from the high mountains of southern Spain. To test ...the prediction that the slave-maker and its host represent a coevolutionary geographical mosaic, we studied the variation in the cuticular hydrocarbons (CHCs) as the trait most likely to show the selection mosaic, plus trait remixing by the gene flow in the populations of each species by means of microsatellites. We found within populations, host and parasite had more similar CHC profiles than between the populations or between parasites and allopatric hosts. The differences between the CHC profiles of the host and parasite, which may be responsible for the level of tolerance towards the parasite, varied between the populations suggesting the existence of a selection mosaic of coevolution. Furthermore, P. longiseta showed higher gene flow than R. minuchae, which would allow local variation in the coevolution of the host and parasite while allowing some trait remixing.
Context.
Hydrated minerals, such as phyllosilicates, on asteroids can provide constraints on the temperature or compositional distribution of the early Solar System. Previous studies pointed out the ...possibility that absorption in the near-ultraviolet (NUV, 0.35–0.5 μm) wavelength region is a proxy for hydrated minerals in primitive asteroids. However, the radial distribution of the NUV absorption among primitive asteroids was not revisited after the Eight Color Asteroid Survey (ECAS).
Aims.
Our objectives are first to evaluate the possibility of using the NUV absorption as diagnostics of hydrated minerals based on the recent datasets of primitive asteroids and hydrated carbonaceous chondrites, and second to investigate the reflectance spectrophotometry of the primitive asteroids in the NUV as functions of heliocentric distance and size.
Methods.
The NUV and visible reflectance spectrophotometry of more than 9000 primitive asteroids was investigated using two spectrophotometric surveys, ECAS and the Sloan Digital Sky Survey (SDSS), which cover wavelengths down to 0.32 μm and 0.36 μm, respectively. We classified asteroids from the main asteroid belt, the Cybele and Hilda zones, and Jupiter Trojans based on Tholen’s taxonomy and described the statistical distribution of primitive asteroid types. We also examined the relationship of the NUV, 0.7 μm, and 2.7 μm absorptions among primitive asteroids and hydrous carbonaceous chondrites CI and CM.
Results.
We find strong correlations between the NUV and the OH-band (2.7 μm) absorptions for primitive asteroids and hydrated meteorites, suggesting the NUV absorption can be indicative of hydrated silicates. Moreover, there is a great difference in the NUV absorption between the large asteroids (diameter
d >
50 km) and small asteroids (
d <
10 km) in the taxonomic distribution. The taxonomic distribution of asteroids differs between the inner main belt and middle-outer main belt. Notably, the C types are dominating large members through the main belt and the F types are dominating small asteroids of the inner main belt. The asteroids beyond the main belt consist mostly of P and D types, although P types are common everywhere in the main belt. The peculiar distribution of F types might indicate a different formation reservoir or a displacement process of F types in the early Solar System. The strongest absorptions of the NUV and 0.7 μm band were observed in G types, which likely comprise CM-like Fe-rich phyllosilicates. On the other hand, according to a recent sample return from an F-type asteroid (162173) Ryugu, the F types with the OH-band at 2.7 μm and the shallow NUV absorption could comprise CI-like Mg-rich phyllosilicates.
Context.
Observational and instrumental difficulties observing small bodies below 0.5 μm make this wavelength range poorly studied compared with the visible and near-infrared. Furthermore, the ...suitability of many commonly used solar analogues, essential in the computation of asteroid reflectances, is usually assessed only in visible wavelengths, while some of these objects show spectra that are quite different from the spectrum of the Sun at wavelengths below 0.55 μm. Stars HD 28099 (Hyades 64) and HD 186427 (16 Cyg B) are two well-studied solar analogues that instead present spectra that are also very similar to the spectrum of the Sun in the wavelength region between 0.36 and 0.55 μm.
Aims.
We aim to assess the suitability in the near-ultraviolet (NUV) region of the solar analogues selected by the team responsible for the asteroid reflectance included in
Gaia
Data Release 3 (DR3) and to suggest a correction (in the form of multiplicative factors) to be applied to the
Gaia
DR3 asteroid reflectance spectra to account for the differences with respect to the solar analogue Hyades 64.
Methods.
To compute the multiplicative factors, we calculated the ratio between the solar analogues used by
Gaia
DR3 and Hyades 64, and then we averaged and binned this ratio in the same way as the asteroid spectra in
Gaia
DR3. We also compared both the original and corrected
Gaia
asteroid spectra with observational data from the Eight Color Asteroid Survey (ECAS), one UV spectrum obtained with the
Hubble
Space Telescope (HST) and a set of blue-visible spectra obtained with the 3.6 m Telescopio Nazionale Galileo (TNG). By means of this comparison, we quantified the goodness of the obtained correction.
Results.
We find that the solar analogues selected for
Gaia
DR3 to compute the reflectance spectra of the asteroids of this data release have a systematically redder spectral slope at wavelengths shorter than 0.55 μm than Hyades 64. We find that no correction is needed in the red photometer (RP, between 0.7 and 1 μm), but a correction should be applied at wavelengths below 0.55 μm, that is in the blue photometer (BP). After applying the correction, we find a better agreement between
Gaia
DR3 spectra, ECAS, HST, and our set of ground-based observations with the TNG.
Conclusions.
Correcting the near-UV part of the asteroid reflectance spectra is very important for proper comparisons with laboratory spectra (minerals, meteorite samples, etc.) or to analyse quantitatively the UV absorption (which is particularly important to study hydration in primitive asteroids). The spectral behaviour at wavelengths below 0.5 μm of the selected solar analogues should be fully studied and taken into account for
Gaia
DR4.
The host-parasite genera Proformica-Rossomyrmex present four pairs of species with a very wide range of distribution from China to Southeastern Spain, from huge extended plains to the top of high ...mountains. Here we review (1) the published data on these pairs in comparison to other slave-makers; (2) the different dispersal ability in hosts and parasites inferred from genetics (chance of migration conditions the evolutionary potential of the species); (3) the evolutionary potential of host and parasite determining the coevolutionary process in each host-parasite system that we treat to define using cuticular chemical data. We find a lower evolutionary potential in parasites than in hosts in fragmented populations, where selective pressures give advantage to a limited female parasite migration due to uncertainty of locating a host nest. A similar evolutionary potential is detected for hosts and parasites when the finding of host nests is likely (i.e., in continuous and extended populations). Moreover, some level of local adaptation at CHC profiles between host and parasite exists independently of the kind of geographic distribution and the ability of dispersal of the different populations. Similarity at CHC profiles appears to be a trait imposed by natural selection for the interaction between hosts and slave-makers.
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