Examinando por Autor "Lucas, Philip"

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    The extinction law in the inner 3 × 3 deg2of the Milky Way and the red clump absolute magnitude in the inner bar-bulge
    (Oxford University Press, 2022-08-01) Sanders, Jason L.; Smith, Leigh; González Fernández, Carlos; Lucas, Philip; Minniti, Dante
    The extinction law from 0.9 to 8 microns in the inner 3× 3° 2 of the Milky Way is measured using data from VISTA Variables in the Via Lactea, GLIMPSE, and WISE. Absolute extinction ratios are found by requiring that the observed red clump density peaks at the GRAVITY collaboration distance to the Galactic centre. When combined with selective extinction ratios measured from the bulge giant colour-colour diagrams, we find an extinction law of A Z:A Y:A J:A H:A K s:A W1:A [3.6]:A [4.5]:A W2:A [5.8]:A [8.0] =7.19(0.30):5.11(0.20):3.23(0.11):1.77(0.04):1:0.54(0.02):0.46(0.03):0.34(0.03):0.32(0.03):0.24(0.04):0.28(0.03) valid for low extinctions where non-linearities are unimportant. These results imply an extinction law from the Rayleigh Jeans colour excess method of A K_s=0.677(H-[4.5]-0.188). We find little evidence for significant selective extinction ratio variation over the inspected region (around 5\cent). Assuming the absolute extinction ratios do not vary across the inspected region gives an independent measurement of the absolute Ks magnitude of the red clump at the Galactic Centre of (-1.61± 0.07). This is very similar to the value measured for solar neighbourhood red clump stars giving confidence in the use of red clump stars as standard candles across the Galaxy. As part of our analysis, we inspect the completeness of PSF photometry from the VVV survey using artificial star tests, finding 90 cent completeness at K s 16\, (17) in high (low) density regions and good agreement with the number counts with respect to the GALACTICNUCLEUS and DECAPS catalogues over small regions of the survey. © 2022 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society.
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    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, Marina
    The 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.
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    Variable star classification across the Galactic bulge and disc with the VISTA Variables in the Vía Láctea survey
    (2022-01) Molnar, Thomas A; L. Sanders, Jason; Leigh C, Smith,; Belokurov, Vasily; Lucas, Philip; Minniti, Dante
    We present VIVACE, the VIrac VAriable Classification Ensemble, a catalogue of variable stars extracted from an automated classification pipeline for the Vista Variables in the Vía Láctea (VVV) infrared survey of the Galactic bar/bulge and southern disc. Our procedure utilizes a two-stage hierarchical classifier to first isolate likely variable sources using simple variability summary statistics and training sets of non-variable sources from the Gaia early third data release, and then classify candidate variables using more detailed light-curve statistics and training labels primarily from OGLE and VSX. The methodology is applied to point-spread-function photometry for 490 million light curves from the VIRAC v2 astrometric and photometric catalogue resulting in a catalogue of 1.4 million likely variable stars, of which 39 000 are high-confidence (classification probability >0.9) RR Lyrae ab stars, 8000 RR Lyrae c/d stars, 187, 000 detached/semi-detached eclipsing binaries, 18, 000 contact eclipsing binaries, 1400 classical Cepheid variables and 2200 Type II Cepheid variables. Comparison with OGLE-4 suggests a completeness of around $90, $ for RRab and $lesssim 60, $ for RRc/d, and a misclassification rate for known RR Lyrae stars of around $1, $ for the high confidence sample. We close with two science demonstrations of our new VIVACE catalogue: first, a brief investigation of the spatial and kinematic properties of the RR Lyrae stars within the disc/bulge, demonstrating the spatial elongation of bar-bulge RR Lyrae stars is in the same sense as the more metal-rich red giant population whilst having a slower rotation rate of $sim !40, {km, s}{-1}{kpc}{-1}$ and secondly, an investigation of the GaiaEDR3 parallax zero-point using contact eclipsing binaries across the Galactic disc plane and bulge. © 2021 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society.