Examinando por Autor "Kuhn, M.A."
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Ítem New Galactic star clusters discovered in the disc area of the VVVX survey(Oxford University Press, 2018-12) Borissova, J.; Ivanov, V.D.; Lucas, P.W.; Kurtev, R.; Alonso-Garcia, J.; Ramírez Alegría, S.; Minniti, D.; Froebrich, D.; Hempel, M.; Medina, N.; Chené, A.-N.; Kuhn, M.A.The 'VISTA Variables in the Vía Láctea eXtended (VVVX)' ESO Public Survey is a nearinfrared photometric sky survey that covers nearly 1700 deg2 towards the Galactic disc and bulge. It is well-suited to search for newopen clusters, hidden behind dust and gas. The pipeline processed and calibrated KS-band tile images of 40 per cent of the disc area covered by VVVX was visually inspected for stellar overdensities. Then, we identified cluster candidates by examination of the composite JHKS colour images. The colour-magnitude diagrams of the cluster candidates are constructed. Whenever possible the Gaia DR2 parameters are used to calculate the mean proper motions, radial velocities, reddening and distances. We report the discovery of 120 new infrared clusters and stellar groups. Approximately half of them (47 per cent) are faint, compact, highly reddened, and they seem to be associated with other indicators of recent star formation, such as nearby Young Stellar Objects, Masers, HII regions or bubbles. The preliminary distance determinations allow us to trace the clusters up to 4.5 kpc, but most of the cluster candidates are centred at 2.2 kpc. The mean proper motions of the clusters show that in general they follow the disc motion of the Galaxy. © 2018 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society.Ítem The G305 Star-forming Region. I. Newly Classified Hot Stars(Astronomical Journal, 2019) Borissova, Juraa; Roman-Lopes, Alexandre; Covey, Kevin; Medina, Nicolas; Kurtev, Radostin; Roman-Zuniga, Carlos; Kuhn, M.A.; Contreras Pena, Carlos; Lucas, Philip; Ramirez Alegria, Sebastian; Minniti, Dante; Kounkel, MarinaThe relatively nearby star-forming complex G305 is one of the most luminous H ii regions in the Galaxy, and it contains several sites and epochs of star formation. Using a combination of near-infrared photometry from "Vista Variables in Via Lactea" ESO Large Public Survey, SDSS-IV APOGEE-2 spectra, and Gaia DR2 photometry and astrometry, we report on 29 OB type, Wolf-Rayet, and emission-line stars, 18 of which are newly classified. Most of these hot stars belongs to the main sequence, although some stars of class I are also proposed. The mean radial velocity is RV = -41.8 . The average spectroscopic distance is 3.2 +1.6 kpc, while the Gaia DR2 average distance is 3.7 +1.8 kpc. Eight objects show light-curve variations with amplitudes greater than 0.5 mag in the K S band. © 2019. The American Astronomical Society. All rights reserved.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.