ABSTRACT
High-velocity stars in the Milky Way are related to extreme astrophysical phenomena. In this work, we characterize 28 stars with Galactocentric velocities higher than 400 $\mathrm{km\, ...s^{-1}}$ observed in the Javalambre Photometric Local Universe Survey Data Release 2 (J-PLUS DR2) survey. We combine J-PLUS photometry with astrometric data from the Gaia DR3 catalogue to analyse the kinematics, dynamics, and fundamental stellar parameters of these stars. Our results indicate that most of the 28 stars have typical behaviour and properties of halo stars, and some of them could be related to the disk population. Some of the halo stars may belong to known structures that originated from mergers of other systems with the Milky Way.
Aims. We present a comparative analysis of the spectral slope and color distributions of Jupiter Trojans, with particular attention to asteroid families. We use a sample of data from the Moving ...Object Catalog of the Sloan Digital Sky Survey, together with spectra obtained from several surveys. Methods. We extracted a first sample of 349 observations, corresponding to 250 Trojan asteroids, from the Sloan Digital Sky Survey, and a second sample of 138 spectra, corresponding to 115 Trojans, from the literature. We computed the spectral slopes in the first sample by means of a least-squares fit to a straight line of the fluxes obtained from the Sloan observations, and in the second sample by means of a fit to the rebinned spectra. In both cases the reflectance fluxes/spectra were renormalized to 1 at 6230. Results. We found that the distribution of spectral slopes among Trojan asteroids shows a bimodality. About 2/3 of the objects have reddish slopes compatible with D-type asteroids, while the remaining bodies show less reddish colors compatible with the P-type and C-type classifications. The members of asteroid families also show a bimodal distribution with a very slight predominance of D-type asteroids, but the background is clearly dominated by the D-types. The L4 and L5 swarms show different distributions of spectral slopes, and bimodality is only observed in L4. These differences can be attributed to the asteroid families since the background asteroids show the same slope distributions in both swarms. The analysis of individual families indicates that the families in L5 are taxonomically homogeneous, but in L4 they show a mixture of taxonomic types. We discuss a few scenarios that might help to interpret these results.
Full text
Available for:
FMFMET, NUK, UL, UM, UPUK
We present a systematic method to identify possible basaltic (V-type) asteroids using the Moving Objects Catalog (MOC) of the SDSS. The method is based on the Principal Components Analysis of the MOC ...colors combined with some refined criteria of segregation of the taxonomic classes. We found several V-type candidates outside the Vesta family, most of them in the inner asteroid belt. We also identified a few candidates in the middle/outer belt. Notwithstanding, their basaltic nature still needs to be conformed by spectroscopy, and these candidates are potential targets for observation using large telescopes.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Abstract
Previous determinations of chemical abundances of the metal-poor red giant TYC 5619-109-1, derived via high-resolution near-infrared spectra from the Apache Point Observatory Galactic ...Evolution Experiment survey, indicate that this star is strongly enriched in the elements N and Al. Here, we obtain and analyse high-resolution optical spectra of TYC 5619-109-1 to verify these large N and Al overabundances and to measure abundances of a wider range of chemical elements. Our analysis confirms the N- and Al-rich nature of this star, and shows that the abundances of the s-process elements are also strongly enhanced, particularly in the heavy second s-process peak elements (Ba, La, Ce, Nd). Lighter s-process elements (Y, Zr) show smaller overabundances, and the ratio of the light-to-heavy s-process elements is consistent with the 13C(α, n)16O neutron source operating in a low-metallicity environment. The lack of Tc i lines and the abundance of Nb compared to Zr indicate that this red giant is probably not a thermally pulsing asymptotic giant branch (TP-AGB) star. Mass transfer from a former s-process-rich TP-AGB companion may produce the observed overabundances, but our radial velocity analysis provides no evidence that TYC 5619-109-1 is a binary with a white dwarf companion. We suggest that TYC 5619-109-1 formed from gas already strongly enriched in s-process elements, as found in many dwarf galaxies and globular clusters. A dynamical analysis reveals that there is only a small probability that TYC 5619-109-1 is an escaped member of a globular cluster, and in this case the most likely candidate would be ω Cen.
Abstract
We report on the analysis of high-resolution optical spectra of four symbiotic stars: AS 255, MWC 960, RW Hya, and StH
α
32. We employ the local-thermodynamic-equilibrium model atmospheres ...of Kurucz and the spectral analysis code
moog
to analyze the spectra. The abundance of barium and carbon was derived using the spectral synthesis technique. The chemical composition of the atmospheres of AS 255 and MWC 960 show that they are metal-poor K giants with metallicities of −1.2 and −1.7 respectively. StH
α
32 is a CH star and also a low-metallicity object (−1.4). AS 255 and MWC 960 are yellow symbiotic stars and, like other previously studied yellow symbiotics, are
s
-process enriched. StH
α
32, like other CH stars, is also an
s
-process and carbon-enriched object. RW Hya has a metallicity of −0.64, a value in accordance with previous determinations, and is not
s
-process enriched. Based on its position in the 2MASS diagram, we suggest that RW Hya is at an intermediate position between yellow symbiotics and classical S-type symbiotics. We also discuss whether the dilution effect was the mechanism responsible for the absence of the
s
-process elements overabundance in RW Hya. The luminosity obtained for StH
α
32 is below the luminosity of the asymptotic giant branch (AGB) stars that started helium burning (via thermal pulses) and became self-enriched in neutron-capture elements. Therefore, its abundance peculiarities are due to mass transfer from the previous thermally pulsing AGB star (now the white dwarf) that was overabundant in
s
-process elements. For the stars AS 255 and MWC 960, the determination of their luminosities was not possible due to uncertainties in their distance and interstellar absorption. AS 255 and MWC 960 have a low galactic latitude and could be bulge stars or members of the inner halo population. The heavy-element abundance distribution of AS 255 and MWC 960 is similar to that of the other yellow symbiotics previously analyzed. Their abundance patterns follow that of the thick disk population for RW Hya and of the halo population for AS 255, MWC 960, and StH
α
32. We also determined the rotational velocities of these four symbiotic stars and compare our results with those of single field stars.
•Elbow inlets of different radius are characterized in a turbocharger test rig.•Backflow is measured through the analysis of the temperature field.•Sound emission is captured by acoustic beamforming ...intensimetry.•Comparison with a straight baseline duct attests the effect of the radius.•Tighter radius is shown to promote whoosh and lower the efficiency.
While the influence of inlet geometry on turbocharger compressor behaviour has usually been investigated in terms of performance, surge margin and efficiency, data is scarce regarding the impact of the inlet flow field onto the noise emission. In many applications where tight packaging is required, a 90° elbow is placed just upstream of the compressor inducer. This can create a distortion of the incoming flow that affects the turbocharger operation; a distortion that is related to the radius of the elbow. In this experimental investigation three 90° elbow inlets are tested, measuring the in-duct sound intensity through acoustic beamforming, the spectral signature of the noise, and the distortion of the high temperature backflow typical of partially stalled conditions by means of thermocouple arrays. Results show that a tighter elbow radius not only impacts efficiency but also increases inlet noise at conditions close to surge. Spectral analysis shows that this increase is mainly produced in the form of a medium frequency broadband noise usually known as ‘whoosh’ in the literature. On the other hand, effect on the outlet is less noticeable. Measurements of the recirculated backflow distortion in terms of circumferential skewness show good correlation with whoosh noise increase, indicating that flow distortion caused by tighter elbows at marginal surge conditions facilitates the transmission of whoosh noise oscillations to the inlet duct, worsening the acoustic behaviour of the system.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
The identification of basaltic asteroids in the asteroid Main Belt and the description of their surface mineralogy is necessary to understand the diversity in the collection of basaltic meteorites. ...Basaltic asteroids can be identified from their visible reflectance spectra and are classified as V-type in the usual taxonomies. In this work, we report visible spectroscopic observations of two candidate V-type asteroids, (7472) Kumakiri and (10537) 1991 RY16, located in the outer Main Belt (
a
>
2.85
UA
). These candidates have been previously identified by Roig and Gil-Hutton 2006. Selecting candidate V-type asteroids from the analysis of the Sloan Digital Sky Survey colors. Icarus 183, 411 using the Sloan Digital Sky Survey colors. The spectroscopic observations have been obtained at the Calar Alto Observatory, Spain, during observational runs in November and December 2006. The spectra of these two asteroids show the steep slope shortwards of
0.70
μ
m
and the deep absorption feature longwards of
0.75
μ
m
that are characteristic of V-type asteroids. However, the presence of a shallow but conspicuous absorption band around
0.65
μ
m
opens some questions about the actual mineralogy of these two asteroids. Such band has never been observed before in basaltic asteroids with the intensity we detected it. We discuss the possibility for this shallow absorption feature to be caused by the presence of chromium on the asteroid surface. Our results indicate that, together with (1459) Magnya, asteroids (7472) Kumakiri and (10537) 1991 RY16 may be the only traces of basaltic material found up to now in the outer Main Belt.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The compilation of published results on the geography of the Monte Desert biome of Argentina that we present here offers a review of its boundaries and ecotones, and of its biophysical and ...socio-economic characteristics. In relation to socio-ecological issues, the focus is on a case study in the province of Mendoza. An analysis is presented about the ecological-economic issues and the sustainable investment policies in rangelands of the Patagonian Monte. In addition, this biome is compared with other South American arid biomes and their North American counterparts. We identified some gaps in the current knowledge, especially at a mesoscale level, where studies on Monte borders are deemed necessary as well as explicit boundary criteria for ecosystem differentiation. Also the ecological-economic relations and feedbacks between livestock herbivory, soil erosion and market behaviour should be considered within the framework of wider socio-ecological research.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Context. Close encounters with (1) Ceres and (4) Vesta, the two most massive bodies in the main belt, are known to be a mechanism of dynamical mobility able to significantly alter proper elements of ...minor bodies, and they are the main source of dynamical mobility for medium-sized and large asteroids (D > 20 km, approximately). Recently, it has been shown that drift rates caused by close encounters with massive asteroids may change significantly on timescales of 30 Myr when different models (i.e., different numbers of massive asteroids) are considered. Aims. So far, not much attention has been given to the case of diffusion caused by the other most massive bodies in the main belt: (2) Pallas, (10) Hygiea, and (31) Euphrosyne, the third, fourth, and one of the most massive highly inclined asteroids in the main belt, respectively. Since (2) Pallas is a highly inclined object, relative velocities at encounter with other asteroids tend to be high and changes in proper elements are therefore relatively small. It was thus believed that the scattering effect caused by highly inclined objects in general should be small. Can diffusion by close encounters with these asteroids be a significant mechanism of long-term dynamical mobility? Methods. By performing simulations with symplectic integrators, we studied the problem of scattering caused by close encounters with (2) Pallas, (10) Hygiea, and (31) Euphrosyne when only the massive asteroids (and the eight planets) are considered, and the other massive main belt asteroids and non-gravitational forces are also accounted for. Results. By finding relatively small values of drift rates for (2) Pallas, we confirm that orbital scattering by this highly inclined object is indeed a minor effect. Unexpectedly, however, we obtained values of drift rates for changes in proper semi-major axis a caused by (10) Hygiea and (31) Euphrosyne larger than what was previously found for scattering by (4) Vesta. These high rates may have repercussions on the orbital evolution and age estimate of their respective families.
Full text
Available for:
FMFMET, NUK, UL, UM, UPUK
V-type asteroids in the middle main belt Roig, F.; Nesvorný, D.; Gil-Hutton, R. ...
Icarus (New York, N.Y. 1962),
03/2008, Volume:
194, Issue:
1
Journal Article
Peer reviewed
Open access
V-type asteroids are bodies whose surfaces are constituted of basalt. In the Main Asteroid Belt, most of these asteroids are assumed to come from the basaltic crust of Asteroid (4) Vesta. This idea ...is mainly supported by (i) the fact that almost all the known V-type asteroids are in the same region of the belt as (4) Vesta, i.e., the inner belt (semi-major axis
2.1
<
a
<
2.5
AU), (ii) the existence of a dynamical asteroid family associated to (4) Vesta, and (iii) the observational evidence of at least one large craterization event on Vesta's surface. One V-type asteroid that is difficult to fit in this scenario is (1459) Magnya, located in the outer asteroid belt, i.e., too far away from (4) Vesta as to have a real possibility of coming from it. The recent discovery of the first V-type asteroid in the middle belt (
2.5
<
a
<
2.8
AU), (21238) 1995WV7 Binzel, R.P., Masi, G., Foglia, S., 2006. Bull. Am. Astron. Soc. 38, 627; Hammergren, M., Gyuk, G., Puckett, A., 2006. ArXiv e-print, astro-ph/0609420, located at ∼2.54 AU, raises the question of whether it came from (4) Vesta or not. In this paper, we present spectroscopic observations indicating the existence of another V-type asteroid at ∼2.53 AU, (40521) 1999RL95, and we investigate the possibility that these two asteroids evolved from the Vesta family to their present orbits by a semi-major axis drift due to the Yarkovsky effect. The main problem with this scenario is that the asteroids need to cross the 3/1 mean motion resonance with Jupiter, which is highly unstable. Combining
N-body numerical simulations of the orbital evolution, that include the Yarkovsky effect, with Monte Carlo models, we compute the probability that an asteroid of a given diameter
D evolves from the Vesta family and crosses over the 3/1 resonance, reaching a stable orbit in the middle belt. Our results indicate that an asteroid like (21238) 1995WV7 has a low probability (∼1%) of having evolved through this mechanism due to its large size (
D
∼
5
km
), because the Yarkovsky effect is not sufficiently efficient for such large asteroids. However, the mechanism might explain the orbits of smaller bodies like (40521) 1999RL95 (
D
∼
3
km
) with
∼
70
–
100
%
probability, provided that we assume that the Vesta family formed
≳
3.5
Gy
ago. We estimate the debiased population of V-type asteroids that might exist in the same region as (21238) and (40521) (
2.5
<
a
≲
2.62
AU
) and conclude that about 10 to 30% of the V-type bodies with
D
>
1
km
may come from the Vesta family by crossing over the 3/1 resonance. The remaining 70–90% must have a different origin.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
PDF
