Examinando por Autor "Smith, L.C."
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Ítem An Automated Tool to Detect Variable Sources in the Vista Variables in the Vía Láctea Survey: The VVV Variables (V4) Catalog of Tiles d001 and d002(Institute of Physics Publishing, 2018-09) Medina, N.; Borissova, J.; Bayo, A.; Kurtev, R.; Navarro Molina, C.; Kuhn, M.; Kumar, N.; Lucas, P.W.; Catelan, M.; Minniti, D.; Smith, L.C.Time-varying phenomena are one of the most substantial sources of astrophysical information, and their study has led to many fundamental discoveries in modern astronomy. We have developed an automated tool to search for and analyze variable sources in the near-infrared K s band using the data from the VISTA Variables in the Vía Láctea (VVV) ESO Public Large Survey. This process relies on the characterization of variable sources using different variability indices calculated from time series generated with point-spread function (PSF) photometry of sources under analysis. In particular, we used two main indices, the total amplitude and the eta index η, to identify variable sources. Once the variable objects are identified, periods are determined with generalized Lomb-Scargle periodograms and the information potential metric. Variability classes are assigned according to a compromise between comparisons with VVV templates and the period of the variability. The automated tool is applied on VVV tiles d001 and d002 and led to the discovery of 200 variable sources. We detected 70 irregular variable sources and 130 periodic ones. In addition, nine open-cluster candidates projected in the region are analyzed, and the infrared variable candidates found around these clusters are further scrutinized by cross-matching their locations against emission star candidates from VPHAS+ survey Hα color cuts. © 2018. The American Astronomical Society. All rights reserved.Ítem Discovery of a brown dwarf companion to the A3V star β Circini(Oxford University Press, 2015-12) Smith, L.C.; Lucas, P.W.; Contreras Peña, C.; Kurtev, R.; Marocco, F.; Jones, H.R.A.; Beamin, J.C.; Napiwotzki, R.; Borissova, J.; Burningham, B.; Faherty, J.; Pinfield, D.J.; Gromadzki, M.; Ivanov, V.D.; Minniti, D.; Stimson, W.; Villanueva, V.We report the discovery of an L dwarf companion to the A3V star β Circini. VVV J151721.49−585131.5, or β Cir B, was identified in a proper motion and parallax catalogue of the VISTA Variables in the Vía Láctea survey as having near-infrared luminosity and colour indicative of an early L dwarf, and a proper motion and parallax consistent with that of β Cir. The projected separation of ∼3.6 arcmin corresponds to 6656 au, which is unusually wide. The most recent published estimate of the age of the primary combined with our own estimate based on newer isochrones yields an age of 370–500 Myr. The system therefore serves as a useful benchmark at an age greater than that of the Pleiades brown dwarfs and most other young L dwarf benchmarks. We have obtained a medium resolution echelle spectrum of the companion which indicates a spectral type of L1.0 ± 0.5 and lacks the typical signatures of low-surface gravity seen in younger brown dwarfs. This suggests that signs of low-surface gravity disappear from the spectra of early L dwarfs by an age of ∼370–500 Myr, as expected from theoretical isochrones. The mass of β Cir B is estimated from the BHAC15 isochrones as 0.056 ± 0.007 M⊙.Ítem Large-amplitude periodic outbursts and long-period variables in the VVV VIRAC2-β data base(Oxford University Press, 2022-06-01) Guo, Zhen; Lucas, P.W.; Smith, L.C.; Clarke, C.; Contreras, Penã C.; Bayo, A.; Bricenõ, C.; Elias, J.; Kurtev, R.G.; Borissova, J.; Alonso-Garciá, J.; Minniti, D.; Catelan, M.; Nikzat, F.; Morris, C.; Miller, N.The VISTA Variables in the Via Lactea (VVV) survey obtained near-infrared photometry towards the Galactic bulge and the southern disc plane for a decade (2010-2019). We designed a modified Lomb-Scargle method to search for large-amplitude (Δ Ks, 2-98 per cent > 1.5 mag) mid to long-term periodic variables (P> 10 d) in the 2nd version of VVV Infrared Astrometric Catalogue (VIRAC2-β). In total, 1520 periodic sources were discovered, including 59 candidate periodic outbursting young stellar objects (YSOs), based on the unique morphology of the phase-folded light curves, proximity to Galactic H ii regions and mid-infrared colours. Five sources are spectroscopically confirmed as accreting YSOs. Both fast-rise/slow-decay and slow-rise/fast-decay periodic outbursts were found, but fast-rise/slow-decay outbursts predominate at the highest amplitudes. The multiwavelength colour variations are consistent with a variable mass accretion process, as opposed to variable extinction. The cycles are likely to be caused by dynamical perturbations from stellar or planetary companions within the circumstellar disc. An additional search for periodic variability amongst YSO candidates in published Spitzer-based catalogues yielded a further 71 candidate periodic accretors, mostly with lower amplitudes. These resemble cases of pulsed accretion but with unusually long periods and greater regularity. The majority of other long-period variables are pulsating dusty Miras with smooth and symmetric light curves. We find that some Miras have redder W3-W4 colours than previously thought, most likely due to their surface chemical compositions. © 2022 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society.Ítem The VVV open cluster project - II. Near-infrared sequences of 37 open clusters on eight-dimensional parameter space(Oxford University Press, 2022-07-01) Ramírez, K. Pena; Smith, L.C.; Alegría, S. Ramírez; Chené, A.-N.; González Fernández, C.; Lucas, P.W.; Minniti, D.Open clusters are key coeval structures that help us understand star formation, stellar evolution and trace the physical properties of our Galaxy. In the past years, the isolation of open clusters from the field has been heavily alleviated by the access to accurate large-scale stellar parallaxes and proper motions along a determined line of sight. Still, there are limitations regarding their completeness since large-scale studies rely on optical wavelengths. Here, we extend the open clusters sequences towards fainter magnitudes complementing the Gaia photometric and astrometric information with near-infrared data from the VVV survey. We performed a homogeneous analysis on 37 open clusters implementing two coarse-to-fine characterization methods: extreme deconvolution Gaussian mixture models coupled with an unsupervised machine learning method on eight-dimensional parameter space. The process allowed us to separate the clusters from the field at near-infrared wavelengths. We report an increase of ∼47 per cent new member candidates on average in our sample (considering only sources with high membership probability p ≳ 0.9). This study is the second in a series intended to reveal open cluster near-infrared sequences homogeneously. © 2022 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society.Ítem VIRAC: The VVV Infrared Astrometric Catalogue(Oxford University Press, 2018) Smith, L.C.; Lucas, P.W.; Kurtev, R.; Smart, R.; Minniti, D.; Borissova, J.; Jones, H.R.A.; Zhang, Z.H.; Marocco, F.; Contreras Peña, C.; Gromadzki, M.; Kuhn, M.A.; Drew, J.E.; Pinfield, D.J.; Bedin, L.R.We present VIRAC version 1, a near-infrared proper motion and parallax catalogue of the VISTA Variables in the Via Lactea (VVV) survey for 312 587 642 unique sources averaged across all overlapping pawprint and tile images covering 560 deg2 of the bulge of the MilkyWay and southern disc. The catalogue includes 119 million high-quality proper motion measurements, of which 47 million have statistical uncertainties below 1 mas yr-1. In the 11 < Ks < 14 magnitude range, the high-quality motions have a median uncertainty of 0.67 mas yr-1. The catalogue also includes 6935 sources with quality-controlled 5s parallaxes with a median uncertainty of 1.1 mas. The parallaxes show reasonable agreement with the Tycho- Gaia Astrometric Solution, though caution is advised for data with modest significance. The SQL data base housing the data is made available via the web. We give example applications for studies of Galactic structure, nearby objects (low-mass stars and brown dwarfs, subdwarfs, white dwarfs) and kinematic distance measurements of young stellar objects. Nearby objects discovered include LTT 7251 B, an L7 benchmark companion to a G dwarf with over 20 published elemental abundances, a bright L subdwarf, VVV 1256-6202, with extremely blue colours and nine new members of the 25 pc sample. We also demonstrate why this catalogue remains useful in the era of Gaia. Future versions will be based on profile fitting photometry, use the Gaia absolute reference frame and incorporate the longer time baseline of the VVV extended survey.Ítem VVV high proper motion stars – I. The catalogue of bright KS ≤ 13.5 stars(OXFORD UNIV PRESS, 2016-09) Kurtev, R.; Gromadzki, M.; Beamín, J.C.; Folkes, S.L.; Pena Ramirez, K.; Ivanov, V.D.; Borissova, J.; Villanueva, V.; Minniti, D.; Mendez, R.; Lucas, P.W.; Smith, L.C.; Pinfield, D.J.; Kuhn, M.A.; Jones, H.R.A.; Antonova, A.; Yip, A.K.P.Knowledge of the stellar content near the Sun is important for a broad range of topics ranging from the search for planets to the study of Milky Way (MW) structure. The most powerful method for identifying potentially nearby stars is proper motion (PM) surveys. All old optical surveys avoid, or are at least substantially incomplete, near the Galactic plane. The depth and breadth of the 'VISTA Variables in Vía Láctea' (VVV) near-IR survey significantly improves this situation. Taking advantage of the VVV survey data base, we have measured PMs in the densest regions of the MW bulge and southern plane in order to complete the census of nearby objects. We have developed a custom PM pipeline based on VVV catalogues from the Cambridge Astronomy Survey Unit, by comparing the first epoch of JHKS with the multiepoch KS bands acquired later. Taking advantage of the large time baseline between the Two Micron All Sky Survey (2MASS) and the VVV observations, we also obtained 2MASS-VVV PMs.We present a near-IR PMcatalogue for the whole area of theVVVsurvey, which includes 3003 moving stellar sources. All of these have been visually inspected and are real PM objects. Our catalogue is in very good agreement with the PM data supplied in IR catalogues outside the densest zone of the MW. The majority of the PM objects in our catalogue are nearby M-dwarfs, as expected. This new data base allows us to identify 57 common PM binary candidates, among which are two new systems within 30 pc of the Sun.