70 research outputs found
Discovering habitable Earths, hot Jupiters and other close planets with microlensing
Searches for planets via gravitational lensing have focused on cases in which
the projected separation, a, between planet and star is comparable to the
Einstein radius, R_E. This paper considers smaller orbital separations and
demonstrates that evidence of close-orbit planets can be found in the
low-magnification portion of the light curves generated by the central star. We
develop a protocol to discover hot Jupiters as well as Neptune-mass and
Earth-mass planets in the stellar habitable zone. When planets are not
discovered, our method can be used to quantify the probability that the lens
star does not have planets within specified ranges of the orbital separation
and mass ratio. Nearby close-orbit planets discovered by lensing can be subject
to follow-up observations to study the newly-discovered planets or to discover
other planets orbiting the same star. Careful study of the low-magnification
portions of lensing light curves should produce, in addition to the discoveries
of close-orbit planets, definite detections of wide-orbit planets through the
discovery of "repeating" lensing events. We show that events exhibiting
extremely high magnification can effectively be probed for planets in close,
intermediate, and wide distance regimes simply by adding several-time-per-night
monitoring in the low-magnification wings, possibly leading to gravitational
lensing discoveries of multiple planets occupying a broad range of orbits, from
close to wide, in a single planetary system.Comment: 21 pages, 5 figures, submitted to the Astrophysical Journa
Mind your Ps and Qs: the Interrelation between Period (P) and Mass-ratio (Q) Distributions of Binary Stars
We compile observations of early-type binaries identified via spectroscopy,
eclipses, long-baseline interferometry, adaptive optics, common proper motion,
etc. Each observational technique is sensitive to companions across a narrow
parameter space of orbital periods P and mass ratios q = M_comp/M_1. After
combining the samples from the various surveys and correcting for their
respective selection effects, we find the properties of companions to O-type
and B-type main-sequence (MS) stars differ among three regimes. First, at short
orbital periods P < 20 days (separations a < 0.4 AU), the binaries have small
eccentricities e = 0.5, and exhibit a small
excess of twins q > 0.95. Second, the companion frequency peaks at intermediate
periods log P (days) = 3.5 (a = 10 AU), where the binaries have mass ratios
weighted toward small values q = 0.2-0.3 and follow a Maxwellian "thermal"
eccentricity distribution. Finally, companions with long orbital periods log P
(days) = 5.5-7.5 (a = 200-5,000 AU) are outer tertiary components in
hierarchical triples, and have a mass ratio distribution across q = 0.1-1.0
that is nearly consistent with random pairings drawn from the initial mass
function. We discuss these companion distributions and properties in the
context of binary star formation and evolution. We also reanalyze the binary
statistics of solar-type MS primaries, taking into account that (30+/-10)% of
single-lined spectroscopic binaries likely contain white dwarf companions
instead of low-mass stellar secondaries. The mean frequency of stellar
companions with q > 0.1 and log P (days) < 8.0 per primary increases from
0.50+/-0.04 for solar-type MS primaries to 2.1+/-0.3 for O-type MS primaries.
We fit joint probability density functions f(M_1,q,P,e) to the corrected
distributions, which can be incorporated into binary population synthesis
studies.Comment: Accepted in ApJS; this version includes the updated figures, text,
and equations as it appears in the accepted version; a Monte Carlo code that
generates a population of zero-age MS single stars and binaries according to
the corrected joint distribution f(M_1,q,P,e) is available upon request via
emai
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