Examinando por Autor "Sanders, Jason L."
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Ítem Mira variables in the Milky Way's nuclear stellar disc: Discovery and classification(Oxford University Press, 2022-11) Sanders, Jason L.; Matsunaga, Noriyuki; Kawata, Daisuke; Smith, Leigh C.; Minniti, Dante; Lucas, Philip W.The properties of the Milky Way's nuclear stellar disc give crucial information on the epoch of bar formation. Mira variables are promising bright candidates to study the nuclear stellar disc, and through their period-age relation dissect its star formation history. We report on a sample of 1782 Mira variable candidates across the central $3\times 3\, \mathrm{deg}2$ of the Galaxy using the multi-epoch infrared VISTA Variables in Via Lactea (VVV) survey. We describe the algorithms employed to select candidate variable stars and then model their light curves using periodogram and Gaussian process methods. By combining with WISE, 2MASS, and other archival photometry, we model the multiband light curves to refine the periods and inspect the amplitude variation between different photometric bands. The infrared brightness of the Mira variables means many are too bright and missed by VVV. However, our sample follows a well-defined selection function as expected from artificial star tests. The multiband photometry is modelled using stellar models with circumstellar dust that characterize the mass-loss rates. We demonstrate how 90 per cent of our sample is consistent with O-rich chemistry. Comparison to period-luminosity relations demonstrates that the bulk of the short period stars are situated at the Galactic Centre distance. Many of the longer period variables are very dusty, falling significantly under the O-rich Magellanic Cloud and solar neighbourhood period-luminosity relations and exhibit high mass-loss rates of. The period distribution appears consistent with the nuclear stellar disc forming ago, although it is not possible to disentangle the relative contributions of the nuclear stellar disc and the contaminating bulge. © 2022 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society.Ítem 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, DanteThe 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.Ítem Variable stars in the VVV globular clusters III. RR Lyrae stars in the inner Galactic globular clusters(EDP Sciences, 0025-03) Alonso-García, Javier; Smith, Leigh C.; Sanders, Jason L.; Minniti, Dante; Catelan, Márcio; Rojas, Gonzalo Aravena; Carballo-Bello, Julio A.; Fernández-Trincado, José G; Ferreira Lopes, Carlos E; Garro, Elisa R.; Guo, Zhen; Hempel, Maren. High reddening near the Galactic plane hampers observations and proper characterization of the globular clusters (GCs) located toward the inner regions of the Milky Way. Aims. The VISTA Variables in the Vía Láctea (VVV) survey observed the Galactic bulge and adjacent disk for several years, providing multi-epoch, near-infrared images for 41 Galactic GCs. Detecting RR Lyrae variable stars belonging to these GCs will aid in their accurate parameterization. Methods. By fully leveraging the astrometric, photometric, and variability VVV catalogs, we searched for RR Lyrae stars associated with GCs. Our selection criteria, based on proper motions, proximity to the cluster centers, and distances inferred from their period-luminosity-metallicity relations, enable us to accurately identify the RR Lyrae population in these GCs and determine color excesses and distances to these poorly studied GCs in a homogeneous manner. Since the VVV catalogs cover from the innermost regions of the GCs to their outskirts, we can provide a comprehensive picture of the entire RR Lyrae population in these GCs. Results. We have discovered significant RR Lyrae populations in two highly reddened Galactic GCs: UKS 1 and VVV-CL160, previously unknown to host RR Lyrae stars. Additionally, we have detected one RR Lyrae candidate in each of Terzan 4 and Terzan 9, also new to RR Lyrae detection. We further confirm and increase the number of RR Lyrae stars detected in 22 other low-latitude Galactic GCs. The RR Lyrae distances place most of these GCs within the Galactic bulge, aligning well with the few GCs in our sample with reliable Gaia or Hubble Space Telescope measurements. However, most of the VVV GCs lack accurate Gaia distances, and literature distances are generally significantly smaller than those derived in this work. As a byproduct of our analysis, we have obtained the proper motions for all the VVV GCs, independently confirming Gaia results, except for two of the most reddened GCs: UKS 1 and 2MASS-GC02. © The Authors 2025.