39 research outputs found
The Araucaria Project: A study of the classical Cepheid in the eclipsing binary system OGLE LMC562.05.9009 in the Large Magellanic Cloud
We present a detailed study of the classical Cepheid in the double-lined,
highly eccentric eclipsing binary system OGLE-LMC562.05.9009. The Cepheid is a
fundamental mode pulsator with a period of 2.988 days. The orbital period of
the system is 1550 days. Using spectroscopic data from three 4-8-m telescopes
and photometry spanning 22 years, we were able to derive the dynamical masses
and radii of both stars with exquisite accuracy. Both stars in the system are
very similar in mass, radius and color, but the companion is a stable,
non-pulsating star. The Cepheid is slightly more massive and bigger (M_1 = 3.70
+/- 0.03M_sun, R_1 = 28.6 +/- 0.2R_sun) than its companion (M_2 = 3.60 +/-
0.03M_sun, R_2 = 26.6 +/- 0.2R_sun). Within the observational uncertainties
both stars have the same effective temperature of 6030 +/- 150K. Evolutionary
tracks place both stars inside the classical Cepheid instability strip, but it
is likely that future improved temperature estimates will move the stable giant
companion just beyond the red edge of the instability strip. Within current
observational and theoretical uncertainties, both stars fit on a 205 Myr
isochrone arguing for their common age. From our model, we determine a value of
the projection factor of p = 1.37 +/- 0.07 for the Cepheid in the
OGLE-LMC562.05.9009 system. This is the second Cepheid for which we could
measure its p-factor with high precision directly from the analysis of an
eclipsing binary system, which represents an important contribution towards a
better calibration of Baade-Wesselink methods of distance determination for
Cepheids.Comment: Accepted to be published in Ap
Microlensing optical depth and event rate in the OGLE-IV Galactic plane fields
Searches for gravitational microlensing events are traditionally concentrated
on the central regions of the Galactic bulge but many microlensing events are
expected to occur in the Galactic plane, far from the Galactic Center. Owing to
the difficulty in conducting high-cadence observations of the Galactic plane
over its vast area, which are necessary for the detection of microlensing
events, their global properties were hitherto unknown. Here, we present results
of the first comprehensive search for microlensing events in the Galactic
plane. We searched an area of almost 3000 square degrees along the Galactic
plane (|b|<7, 0<l<50, 190<l<360 deg) observed by the Optical Gravitational
Lensing Experiment (OGLE) during 2013-2019 and detected 630 events. We
demonstrate that the mean Einstein timescales of Galactic plane microlensing
events are on average three times longer than those of Galactic bulge events,
with little dependence on the Galactic longitude. We also measure the
microlensing optical depth and event rate as a function of Galactic longitude
and demonstrate that they exponentially decrease with the angular distance from
the Galactic Center (with the characteristic angular scale length of 32 deg).
The average optical depth decreases from at l=10 deg to
in the Galactic anticenter. We also find that the optical
depth in the longitude range 240<l<330 deg is asymmetric about the Galactic
equator, which we interpret as a signature of the Galactic warp.Comment: ApJS, in pres