7 research outputs found
OGLE-2017-BLG-1186: first application of asteroseismology and Gaussian processes to microlensing
We present the analysis of the event OGLE-2017-BLG-1186 from the 2017 Spitzer microlensing campaign. This is a remarkable microlensing event because its source is photometrically bright and variable, which makes it possible to perform an asteroseismic analysis using ground-based data. We find that the source star is an oscillating red giant with average timescale of ∼9 days. The asteroseismic analysis also provides us source properties including the source angular size (∼27μas) and distance (∼11.5 kpc), which are essential for inferring the properties of the lens. When fitting the light curve, we test the feasibility of Gaussian Processes (GPs) in handling the correlated noise caused by the variable source. We find that the parameters from the GP model are generally more loosely constrained than those from the traditional χ2 minimization method. We note that this event is the first microlensing system for which asteroseismology and GPs have been used to account for the variable source. With both finite-source effect and microlens parallax measured, we find that the lens is likely a ∼0.045 M⊙ brown dwarf at distance ∼9.0 kpc, or a ∼0.073 M⊙ ultracool dwarf at distance ∼9.8 kpc. Combining the estimated lens properties with a Bayesian analysis using a Galactic model, we find a 35% probability for the lens to be a bulge object and 65% to be a background disk object
New results on long secondary periods in red giants
Original article can be found at: http://proceedings.aip.org/ Copyright 2009 American Institute of Physics. DOI: 10.1063/1.3246422 [Full text of this paper is not available in the UHRA]Approximately 30% of variable red giants have light curves which show a Long Secondary Period (LSP) in addition to their primary oscillation. No model has been proposed that can satisfactorily explain the LSPs. Here we present velocity curves obtained from VLT spectra for a large sample of LMC red giants exhibiting LSPs. We use the velocity data in addition to both MACHO and OGLE light curves to examine the properties of the stars, and to evaluate models for the cause of LSPs. Extant models generally involve either binarity or pulsation. We show that both of these have severe problems explaining the light and velocity variations. However, new mid-infrared observations of stars with LSPs indicate the presence of a significant amount of circumstellar dust, most likely in a disk-like configuration. This observation favours the presence of a binary companion.otherPeer reviewe
The Panchromatic View of the Magellanic Clouds from Classical Cepheids. I. Distance, Reddening, and Geometry of the Large Magellanic Cloud Disk
We present a detailed investigation of the Large Magellanic Cloud (LMC) disk
using classical Cepheids. Our analysis is based on optical (I,V; OGLE-IV),
near-infrared (NIR: J,H,Ks) and mid-infrared (MIR: w1; WISE) mean magnitudes.
By adopting new templates to estimate the NIR mean magnitudes from single-epoch
measurements, we build the currently most accurate, largest and homogeneous
multi-band dataset of LMC Cepheids. We determine Cepheid individual distances
using optical and NIR Period-Wesenheit relations (PWRs), to measure the
geometry of the LMC disk and its viewing angles. Cepheid distances based on
optical PWRs are precise at 3%, but accurate to 7, while the ones based on NIR
PWRs are more accurate (to 3%), but less precise (2%-15%), given the higher
photometric error on the observed magnitudes. We found an inclination i=25.05
0.02 (stat.) 0.55 (syst.) deg, and a position angle of the lines of
nodes P.A.=150.76 0.02(stat.) 0.07(syst.) deg. These values agree
well with estimates based either on young (Red Supergiants) or on
intermediate-age (Asymptotic Giant Branch, Red Clump) stellar tracers, but they
significantly differ from evaluations based on old (RR Lyrae) stellar tracers.
This indicates that young/intermediate and old stellar populations have
different spatial distributions. Finally, by using the reddening-law fitting
approach, we provide a reddening map of the LMC disk which is ten times more
accurate and two times larger than similar maps in the literature. We also
found an LMC true distance modulus of (stat. and
syst.) mag, in excellent agreement with the currently most accurate measurement
(Pietrzynski et al. 2013).Comment: 24 pages, 15 figures, to be published in Ap
The Panchromatic View of the Magellanic Clouds from Classical Cepheids. I. Distance, Reddening, and Geometry of the Large Magellanic Cloud Disk
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