110 research outputs found
Revealing Short-period Exoplanets and Brown Dwarfs in the Galactic Bulge using the Microlensing Xallarap Effect with the \textit{Nancy Grace Roman Space Telescope}
The \textit{Nancy Grace Roman Space Telescope} (\textit{ Roman}) will provide
an enormous number of microlensing light curves with much better photometric
precisions than ongoing ground-based observations. Such light curves will
enable us to observe high-order microlensing effects which have been previously
difficult to detect. In this paper, we investigate \textit{Roman}'s potential
to detect and characterize short-period planets and brown dwarfs (BDs) in
source systems using the orbital motion of source stars, the so-called xallarap
effect. We analytically estimate the measurement uncertainties of xallarap
parameters using the Fisher matrix analysis. We show that the \textit{Roman}
Galactic Exoplanet Survey (RGES) can detect warm Jupiters with masses down to
0.5 and orbital period of 30 days via the xallarap effect.
Assuming a planetary frequency function from \citet{Cumming+2008}, we find
\textit{Roman} will detect hot and warm Jupiters and close-in
BDs around microlensed source stars during the microlensing survey. These
detections are likely to be accompanied by the measurements of the companion's
masses and orbital elements, which will aid in the study of the physical
properties for close-in planet and BD populations in the Galactic bulge.Comment: Accepted for publication in The Astronomical Journa
Prediction of Planet Yields by the PRime-focus Infrared Microlensing Experiment Microlensing Survey
The PRime-focus Infrared Microlensing Experiment (PRIME) will be the first to
conduct a dedicated near infrared (NIR) microlensing survey by using a 1.8m
telescope with a wide field of view of 1.45 at the South
African Astronomical Observatory (SAAO). The major goals of the PRIME
microlensing survey are to measure the microlensing event rate in the inner
Galactic bulge to help design the observing strategy for the exoplanet
microlensing survey by the {\it Nancy Grace Roman Space Telescope} and to make
a first statistical measurement of exoplanet demographics in the central bulge
fields where optical observations are very difficult owing to the high
extinction in these fields. Here we conduct a simulation of the PRIME
microlensing survey to estimate its planet yields and determine the optimal
survey strategy, using a Galactic model optimized for the inner Galactic bulge.
In order to maximize the number of planet detections and the range of planet
mass, we compare the planet yields among four observation strategies. Assuming
{the \citet{2012Natur.481..167C} mass function as modified by
\citet{2019ApJS..241....3P}}, we predict that PRIME will detect planetary
signals for planets ( planets with ,
planets with mass , planets ), per year depending on the chosen
observation strategy.Comment: 25 pages, 17 figures, and 3 tables. Accept for publication in The
Astronomical Journa
Microlensing Results Challenge the Core Accretion Runaway Growth Scenario for Gas Giants
We compare the planet-to-star mass-ratio distribution measured by
gravitational microlensing to core accretion theory predictions from population
synthesis models. The core accretion theory's runaway gas accretion process
predicts a dearth of intermediate-mass giant planets that is not seen in the
microlensing results. In particular, the models predict fewer
planets at mass ratios of than inferred
from microlensing observations. This tension implies that gas giant formation
may involve processes that have hitherto been overlooked by existing core
accretion models or that the planet-forming environment varies considerably as
a function of host-star mass. Variation from the usual assumptions for the
protoplanetary disk viscosity and thickness could reduce this discrepancy, but
such changes might conflict with microlensing results at larger or smaller mass
ratios, or with other observations. The resolution of this discrepancy may have
important implications for planetary habitability because it has been suggested
that the runaway gas accretion process may have triggered the delivery of water
to our inner solar system. So, an understanding of giant planet formation may
help us to determine the occurrence rate of habitable planets.Comment: 12 pages, 2 figures, 1 table, accepted for publication in ApJ
Confirmation of Color Dependent Centroid Shift Measured After 1.8 years with HST
We measured precise masses of the host and planet in OGLE-2003-BLG-235
system, when the lens and source were resolving, with 2018 Keck high resolution
images. This measurement is in agreement with the observation taken in 2005
with the Hubble Space Telescope (HST). In 2005 data, the lens and sources were
not resolved and the measurement was made using color-dependent centroid shift
only. Nancy Grace Roman Space Telescope will measure masses using data
typically taken within 3-4 years of the peak of the event which is much shorter
baseline compared to most of the mass measurements to date. Hence, color
dependent centroid shift will be one of the primary method of mass measurements
for Roman. Yet, mass measurements of only two events (OGLE-2003-BLG-235 and
OGLE-2005-BLG-071) are done using the color dependent centroid shift method so
far. The accuracy of the measurements using this method are neither completely
known nor well studied. The agreement of Keck and HST results, shown in this
paper, is very important since this agreement confirms the accuracy of the mass
measurements determined at a small lens-source separation using the color
dependent centroid shift method. This also shows that with >100 high resolution
images, Roman telescope will be able to use color dependent centroid shift at
3-4 years time baseline and produce mass measurements. We find that
OGLE-2003-BLG-235 is a planetary system consists of a 2.34 +- 0.43M_Jup planet
orbiting a 0.56 +- 0.06M_Sun K-dwarf host star at a distance of 5.26 +- 0.71
kpc from the Sun.Comment: Submitted to AJ, under review. arXiv admin note: substantial text
overlap with arXiv:2009.0232
Subaru Hyper Suprime-Cam Survey for An Optical Counterpart of GW170817
We perform a -band survey for an optical counterpart of a binary neutron
star coalescence GW170817 with Subaru/Hyper Suprime-Cam. Our untargeted
transient search covers deg corresponding to the credible
region of GW170817 and reaches the completeness magnitude of mag
on average. As a result, we find 60 candidates of extragalactic transients,
including J-GEM17btc (a.k.a. SSS17a/DLT17ck). While J-GEM17btc is associated
with NGC 4993 that is firmly located inside the 3D skymap of GW170817, the
other 59 candidates do not have distance information in the GLADE v2 catalog or
NASA/IPAC Extragalactic Database (NED). Among 59 candidates, 58 are located at
the center of extended objects in the Pan-STARRS1 catalog, while one candidate
has an offset. We present location, -band apparent magnitude, and time
variability of the candidates and evaluate the probabilities that they are
located inside of the 3D skymap of GW170817. The probability for J-GEM17btc is
being much higher than those for the other 59 candidates
(). Furthermore, the possibility, that at
least one of the other 59 candidates is located within the 3D skymap, is only
. Therefore, we conclude that J-GEM17btc is the most-likely and
distinguished candidate as the optical counterpart of GW170817.Comment: 14 pages, 9 figures. Accepted for publication in PASJ (Publications
of the Astronomical Society of Japan
Keck Observations Confirm a Super-Jupiter Planet Orbiting M Dwarf OGLE-2005-BLG-071L
We present adaptive optics imaging from the NIRC2 instrument on the Keck II telescope that resolves the exoplanet host (and lens) star as it separates from the brighter source star. These observations yield the K-band brightness of the lens and planetary host star, as well as the lens-source relative proper motion, µ_(rel,H), in the heliocentric reference frame. The µ_(rel,H) measurement allows for the determination of the microlensing parallax vector, π_E, which had only a single component determined by the microlensing light curve. The combined measurements of µ_(rel,H) and K L provide the masses of the host star, M_(host) = 0.426 ± 0.037 M⊙, and planet, m_p = 3.27 ± 0.32M_(Jupiter) with a projected separation of 3.4 ± 0.5 au. This confirms the tentative conclusion of a previous paper that this super-Jupiter mass planet, OGLE-2005-BLG-071Lb, orbits an M dwarf. Such planets are predicted to be rare by the core accretion theory and have been difficult to find with other methods, but there are two such planets with firm mass measurements from microlensing, and an additional 11 planetary microlens events with host mass estimates <0.
0.5M⊙ and planet mass estimates >2 Jupiter masses that could be confirmed by high angular follow-up observations. We also point out that OGLE-2005-BLG-071L has separated far enough from its host star that it should be possible to measure the host-star metallicity with spectra from a high angular resolution telescope such as Keck, the Very Large Telescope, the Hubble Space Telescope, or the James Webb Space Telescope
Adaptive Optics Imaging Breaks the Central Caustic Cusp Approach Degeneracy in High Magnification Microlensing Events
We report new results for the gravitational microlensing target
OGLE-2011-BLG-0950 from adaptive optics (AO) images using the Keck observatory.
The original analysis by Choi et al. 2012 reports degenerate solutions between
planetary and stellar binary lens systems. This is due to a degeneracy in high
magnification events where the shape of the light curve peak can be explained
by a source approach to two different cusp geometries with different source
radius crossing times. This particular case is the most important type of
degeneracy for exoplanet demographics, because the distinction between a
planetary mass or stellar binary companion has direct consequences for
microlensing exoplanet statistics. The 8 and 10-year baselines between the
event and the Keck observations allow us to directly measure a relative proper
motion of mas/yr, which confirms the detection of the lens star
system and directly rules out the planetary companion models that predict a
smaller relative proper motion. The combination of the lens
brightness and close stellar binary light curve parameters yield primary and
secondary star masses of and at a distance of kpc, and a primary-secondary projected separation of
AU. Since this degeneracy is likely to be common, the
high resolution imaging method described here will be used to disentangle the
central caustic cusp approach degeneracy for events observed by the
\textit{Roman} exoplanet microlensing survey using the \textit{Roman} images
taken near the beginning or end of the survey.Comment: Revised version, 19 pages, 8 figures. AJ, 164, 21
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