Examinando por Autor "Lucas, P. W."

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    Near-infrared photometry and spectroscopy of the low Galactic latitude globular cluster 2MASS-GC 03
    (OXFORD UNIV PRESS, 2016-10) Carballo-Bello, Julio A.; Ramírez Alegría, S.; Borissova, J.; Smith, L. C.; Kurtev, R.; Lucas, P. W.; Moni Bidin, Ch.; Alonso-García, J.; Minniti, D.; Palma, T.; Dékány, I.; Medina, N.; Moyano, M.; Villanueva, V.; Kuhn, M. A.
    We present deep near-infrared photometry and spectroscopy of the globular cluster 2MASS-GC 03 projected in the Galactic disc using MMT and Magellan Infrared Spectrograph on the Clay Telescope (Las Campanas Observatory) and VISTA Variables in the Via Lactea Survey data. Most probable cluster member candidates were identified from near-infrared photometry. Out of 10 candidates that were followed-up spectroscopically, 5 have properties of cluster members, from which we calculate <[Fe/H]> = -0.9 +/- 0.2 and a radial velocity of = 78 +/- 12 km s(-1). A distance of 10.8 kpc is estimated from three likely RR Lyrae members. Given that the cluster is currently at a distance of 4.2 kpc from the Galactic Centre, the cluster's long survival time of an estimated 11.3 +/- 1.2 Gyr strengthens the case for its globular-cluster nature. The cluster has a hint of elongation in the direction of the Galactic Centre.
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    Short- and long-term near-infrared spectroscopic variability of eruptive protostars from VVV
    (Oxford University Press, 2020-02) Guo, Zhen; Lucas, P. W.; . Contreras Pena, C; Kurtev, R. G.; Smith, L. C.; Borissova, J.; Alonso-Garcia, J.; Minniti, D.; Caratti, A.; Froebrich, D.
    Numerous eruptive variable young stellar objects (YSOs), mostly Class I systems, were recently detected by the near-infrared Vista Variables in the Via Lactea (VVV) survey. We present an exploratory near-infrared spectroscopic variability study of 14 eruptive YSOs. The variations were sampled over one-day and one-to-two-year intervals and analysed in combination with VVV light curves. CO overtone absorption features are observed on three objects with FUor-like spectra: all show deeper absorption when they are brighter. This implies stronger emission from the circumstellar discwith a steeper vertical temperature gradient when the accretion rate is higher. This confirms the nature of fast VVV FUor-like events, in line with the accepted picture for classical FUors. The absence of Br? emission in a FUor-like object declining to pre-outburst brightness suggests that reconstruction of the stellar magnetic field is a slow process. Within the one-day time-scale, 60 per cent of H2-emitting YSOs show significant but modest variation, and 2/6 sources have large variations in Brγ. Over year-long time-scales, H2 flux variations remain modest despite up to 1.8 mag variation in Ks. This indicates that emission from the molecular outflow usually arises further from the protostar and is unaffected by relatively large changes in accretion rate on year-long time-scales. Two objects show signs of on/off magnetospheric accretion traced by Brγ emission. In addition, a 60 per cent inter-night brightening of the H2 outflow is detected in one YSO. © 2019 The Author(s).
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    YOUNG STELLAR CLUSTERS CONTAINING MASSIVE YOUNG STELLAR OBJECTS IN THE VVV SURVEY
    (IOP PUBLISHING, 2016-09) Borissova, J.; Ramírez Alegría, S.; Alonso, J.; Lucas, P. W.; Kurtev, R.; Medina, N.; Navarro, C.; Kuhn, M.; Gromadzki, M.; Retamales, G.; Fernandez, M. A.; Agurto-Gangas, C.; Chené, A.-N.; Minniti, D.; Contreras Pena, C.; Catelan, M.; Decany, I.; Thompson, M. A.; Morales, E. F. E.; Amigo, P.
    The purpose of this research is to study the connections of the global properties of eight young stellar clusters projected in the Vista Variables in the Via Lactea (VVV) ESO Large Public Survey disk area and their young stellar object (YSO) populations. The analysis is based on the combination of spectroscopic parallax-based reddening and distance determinations with main-sequence and pre-main-sequence ishochrone fitting to determine the basic parameters (reddening, age, distance) of the sample clusters. The lower mass limit estimations show that all clusters are low or intermediate mass (between 110 and 1800 M-circle dot), the slope Gamma of the obtained present-day mass functions of the clusters is close to the Kroupa initial mass function. The YSOs in the cluster's surrounding fields are classified using low resolution spectra, spectral energy distribution fits with theoretical predictions, and variability, taking advantage of multi-epoch VVV observations. All spectroscopically confirmed YSOs (except one) are found to be massive (more than 8 M-circle dot). Using VVV and GLIMPSE color-color cuts we have selected a large number of new YSO candidates, which are checked for variability and 57% are found to show at least low-amplitude variations. In few cases it was possible to distinguish between YSO and AGB classifications on the basis of light curves.