594 research outputs found
Runaman tukuy: Language revitalization strategies for Runasimi heritage learners
The legacies of colonization remain a pervasive force in society and actively work against Indigenous communities and their right to their languages, knowledge systems, and cultural practices. More specifically, the colonial legacy of linguicide has endangered and marginalized thousands of Indigenous languages all over the world. This field project focuses on Quechua language revitalization and aims to better understand and contribute to Indigenous language and identity scholarship. This field project is informed by a brief qualitative study through participant interviews with six Quechua heritage learners and educators. The study explores the limitations and possibilities of formal Quechua language learning, reiterates the importance of informal learning strategies, and lays the foundation for an online virtual learning tool and community space for Quechua language heritage learners, Native speakers and educators. This field project culminates in a Quechua Learning Community server on Discord equipped with virtual learning and community building tools such as collaborative informal and formal learning resources, discussion boards, and study rooms
2MASS J154043.42-510135.7: a new addition to the 5 pc population
The aim of the project is to find the stars nearest to the Sun and to
contribute to the completion of the stellar and substellar census of the solar
neighbourhood. We identified a new late-M dwarf within 5 pc, looking for high
proper motion sources in the 2MASS-WISE cross-match. We collected astrometric
and photometric data available from public large-scale surveys. We complemented
this information with low-resolution optical and near-infrared spectroscopy
with instrumentation on the ESO NTT to confirm the nature of our candidate. We
also present a high-quality medium-resolution VLT/X-shooter spectrum covering
the 400 to 2500 nm wavelength range. We classify this new neighbour as an
M7.00.5 dwarf using spectral templates from the Sloan Digital Sky Survey
and spectral indices. Lithium absorption at 670.8 nm is not detected in the
X-shooter spectrum, indicating that the M7 dwarf is older than 600 Myr and more
massive than 0.06 M. We also derive a trigonometric distance of 4.4
pc, in agreement with the spectroscopic distance estimate, making
2MASS\,J154043.42510135.7 the nearest M7 dwarf to the Sun. This
trigonometric distance is somewhat closer than the 6 pc distance reported
by the ALLWISE team, who independently identified this object recently. This
discovery represents an increase of 25\% in the number of M7--M8 dwarfs already
known at distances closer than 8\,pc from our Sun. We derive a density of
\,=\,1.90.910\,pc for M7 dwarfs in the 8 pc
volume, a value similar to those quoted in the literature. This new ultracool
dwarf is among the 50 nearest systems to the Sun, demonstrating that our
current knowledge of the stellar census within the 5 pc sample remains
incomplete. 2M1540 represents a unique opportunity to search for extrasolar
planets around ultracool dwarfs due to its proximity and brightness.Comment: 8 pages, 5 figures. Acepted in Astronomy & Astrophysics (15/05/2005
Binary frequency of planet-host stars at wide separations: A new brown dwarf companion to a planet-host star
The aim of the project is to improve our knowledge on the multiplicity of
planet-host stars at wide physical separations.
We cross-matched approximately 6200 square degree area of the Southern sky
imaged by the Visible Infrared Survey Telescope for Astronomy (VISTA)
Hemisphere Survey (VHS) with the Two Micron All Sky Survey (2MASS) to look for
wide common proper motion companions to known planet-host stars. We
complemented our astrometric search with photometric criteria.
We confirmed spectroscopically the co-moving nature of seven sources out of
16 companion candidates and discarded eight, while the remaining one stays as a
candidate. Among these new wide companions to planet-host stars, we discovered
a T4.5 dwarf companion at 6.3 arcmin (~9000 au) from HIP70849, a K7V star which
hosts a 9 Jupiter mass planet with an eccentric orbit. We also report two new
stellar M dwarf companions to one G and one metal-rich K star. We infer stellar
and substellar binary frequencies for our complete sample of 37 targets of
5.4+/-3.8% and 2.7+/-2.7% (1 sigma confidence level), respectively, for
projected physical separations larger than ~60-160 au assuming the range of
distances of planet-host stars (24-75 pc). These values are comparable to the
frequencies of non planet-host stars. We find that the period-eccentricity
trend holds with a lack of multiple systems with planets at large
eccentricities (e > 0.2) for periods less than 40 days. However, the lack of
planets more massive than 2.5 Jupiter masses and short periods (<40 days)
orbiting single stars is not so obvious due to recent discoveries by
ground-based transit surveys and space missions.Comment: Accepted for publication in A&A, 13 pages, 5 figures, 3 tables,
optical spectra will be available at CDS Strasbour
UAV-Based Quantification of Dynamic Lahar Channel Morphology at Volcán de Fuego, Guatemala
This study quantified erosional and depositional processes for secondary lahars in Las Lajas drainage at Volcán de Fuego, Guatemala, during the rainy season from May to October 2021. Abundant pyroclastic material from ongoing eruptive activity is remobilized seasonally during heavy precipitation, which can impact infrastructure and populations living near Fuego. Our region of focus was in an agricultural zone 6 to 10 km from the summit, surveyed with an unoccupied aerial vehicle (UAV) quadcopter at monthly intervals. Imagery was processed into overlapping time-lapse structure from motion digital elevation models (DEMs). DEMs were differenced to find volumetric changes as a function of the channel flow path distance (quantified in 500 m sections) to track channel morphology changes over time. The largest measured volume changes were a 490 m3/day loss in the upper section (~6 km from summit) and a 440 m3/day gain in the lower sections (~10 km from summit). We discussed how the natural channel’s constriction and widening of Las Lajas in more distal sections control the behavior and stability of the stream evolution. Above the constriction, the channel is primarily downcutting and meandering within an old flood plain, which had been filled in by pyroclastic materials deposited by the June 2018 paroxysm
Electric dipole rovibrational transitions in HD molecule
The rovibrational electric dipole transitions in the ground electronic state
of the HD molecule are studied. A simple, yet rigorous formula is derived for
the transition rates in terms of the electric dipole moment function ,
which is calculated in a wide range of . Our numerical results for
transition rates are in moderate agreement with experiments and previous
calculations, but are at least an order of magnitude more accurate.Comment: 7 pages, 1 figur
High spatial resolution and high contrast optical speckle imaging with FASTCAM at the ORM
In this paper, we present an original observational approach, which combines,
for the first time, traditional speckle imaging with image post-processing to
obtain in the optical domain diffraction-limited images with high contrast
(1e-5) within 0.5 to 2 arcseconds around a bright star. The post-processing
step is based on wavelet filtering an has analogy with edge enhancement and
high-pass filtering. Our I-band on-sky results with the 2.5-m Nordic Telescope
(NOT) and the lucky imaging instrument FASTCAM show that we are able to detect
L-type brown dwarf companions around a solar-type star with a contrast DI~12 at
2" and with no use of any coronographic capability, which greatly simplifies
the instrumental and hardware approach. This object has been detected from the
ground in J and H bands so far only with AO-assisted 8-10 m class telescopes
(Gemini, Keck), although more recently detected with small-class telescopes in
the K band. Discussing the advantage and disadvantage of the optical regime for
the detection of faint intrinsic fluxes close to bright stars, we develop some
perspectives for other fields, including the study of dense cores in globular
clusters. To the best of our knowledge this is the first time that high
contrast considerations are included in optical speckle imaging approach.Comment: Proceedings of SPIE conference - Ground-based and Airborne
Instrumentation for Astronomy III (Conference 7735), San Diego 201
A practical approach for outdoors distributed target localization in wireless sensor networks
Wireless sensor networks are posed as the new communication paradigm where the use of small, low-complexity, and low-power devices is preferred over costly centralized systems. The spectra of potential applications of sensor networks is very wide, ranging from monitoring, surveillance, and localization, among others. Localization is a key application in sensor networks and the use of simple, efficient, and distributed algorithms is of paramount practical importance. Combining convex optimization tools with consensus algorithms we propose a distributed localization algorithm for scenarios where received signal strength indicator readings are used. We approach the localization problem by formulating an alternative problem that uses distance estimates locally computed at each node. The formulated problem is solved by a relaxed version using semidefinite relaxation technique. Conditions under which the relaxed problem yields to the same solution as the original problem are given and a distributed consensusbased implementation of the algorithm is proposed based on an augmented Lagrangian approach and primaldual decomposition methods. Although suboptimal, the proposed approach is very suitable for its implementation in real sensor networks, i.e., it is scalable, robust against node failures and requires only local communication among neighboring nodes. Simulation results show that running an additional local search around the found solution can yield performance close to the maximum likelihood estimate
A deep WISE search for very late type objects and the discovery of two halo/thick-disc T dwarfs : WISE 0013+0634 and WISE 0833+0052
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2013 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reservedA method is defined for identifying late-T and Y dwarfs in WISE down to low values of signal-to-noise. This requires a WISE detection only in the W2-band and uses the statistical properties of the WISE multiframe measurements and profile fit photometry to reject contamination resulting from non-point-like objects, variables and moving sources. To trace our desired parameter space, we use a control sample of isolated non-moving non-variable point sources from the Sloan Digital Sky Survey (SDSS), and identify a sample of 158 WISE W2-only candidates down to a signal-to-noise limit of eight. For signal-to-noise ranges >10 and 8-10, respectively, similar to 45 and similar to 90 per cent of our sample fall outside the selection criteria published by the WISE team, mainly due to the type of constraints placed on the number of individual W2 detections. We present follow-up of eight candidates and identify WISE 0013+0634 and WISE 0833+0052, T8 and T9 dwarfs with high proper motion (similar to 1.3 and similar to 1.8 arcsec yr(-1)). Both objects show a mid-infrared/near-infrared excess of similar to 1-1.5 mag and are K band suppressed. Distance estimates lead to space motion constraints that suggest halo (or at least thick disc) kinematics. We then assess the reduced proper motion diagram of WISE ultracool dwarfs, which suggests that late-T and Y dwarfs may have a higher thick-disc/halo population fraction than earlier objects.Peer reviewe
Space Velocities of L- and T-type Dwarfs
(Abridged) We have obtained radial velocities of a sample of 18 ultracool
dwarfs (M6.5-T8) using high-resolution, near-infrared spectra obtained with
NIRSPEC and the Keck II telescope. We have confirmed that the radial velocity
of Gl 570 D is coincident with that of the K-type primary star Gl 570 A, thus
providing additional support for their true companionship. The presence of
planetary-mass companions around 2MASS J05591914-1404488 (T4.5V) has been
analyzed using five NIRSPEC radial velocity measurements obtained over a period
of 4.37 yr. We have computed UVW space motions for a total of 21 L and T dwarfs
within 20 pc of the Sun. This population shows UVW velocities that nicely
overlap the typical kinematics of solar to M-type stars within the same spatial
volume. However, the mean Galactic (44.2 km/s) and tangential (36.5 km/s)
velocities of the L and T dwarfs appear to be smaller than those of G to M
stars. A significant fraction (~40%) of the L and T dwarfs lies near the Hyades
moving group (0.4-2 Gyr), which contrasts with the 10-12% found for
earlier-type stellar neighbors. Additionally, the distributions of all three
UVW components (sigma_{UVW} = 30.2, 16.5, 15.8 km/s) and the distributions of
the total Galactic (sigma_{v_tot} = 19.1 km/s) and tangential (sigma_{v_t} =
17.6 km/s) velocities derived for the L and T dwarf sample are narrower than
those measured for nearby G, K, and M-type stars, but similar to the
dispersions obtained for F stars. This suggests that, in the solar
neighborhood, the L- and T-type ultracool dwarfs in our sample (including brown
dwarfs) is kinematically younger than solar-type to early M stars with likely
ages in the interval 0.5-4 Gyr.Comment: Accepted for publication in Ap
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