334 research outputs found
The Rotation Period of the Planet-Hosting Star HD 189733
We present synoptic optical photometry of HD 189733, the chromospherically
active parent star of one of the most intensively studied exoplanets. We have
significantly extended the timespan of our previously reported observations and
refined the estimate of the stellar rotation period by more than an order of
magnitude: days. We derive a lower limit on the
inclination of the stellar rotation axis of 56\arcdeg (with 95% confidence),
corroborating earlier evidence that the stellar spin axis and planetary orbital
axis are well aligned.Comment: To appear in A
Orbital Orientations of Exoplanets: HAT-P-4b is Prograde and HAT-P-14b is Retrograde
We present observations of the Rossiter-McLaughlin effect for two
exoplanetary systems, revealing the orientations of their orbits relative to
the rotation axes of their parent stars. HAT-P-4b is prograde, with a
sky-projected spin-orbit angle of lambda = -4.9 +/- 11.9 degrees. In contrast,
HAT-P-14b is retrograde, with lambda = 189.1 +/- 5.1 degrees. These results
conform with a previously noted pattern among the stellar hosts of close-in
giant planets: hotter stars have a wide range of obliquities and cooler stars
have low obliquities. This, in turn, suggests that three-body dynamics and
tidal dissipation are responsible for the short-period orbits of many
exoplanets. In addition, our data revealed a third body in the HAT-P-4 system,
which could be a second planet or a companion star.Comment: AJ, in press [8 pages
Aircraft System and Product Development: Teaching the Conceptual Phase
This paper reports the first offering of a graduate level subject covering the conceptual phase of aircraft product development. The output of the conceptual phase is a system level specification that usually serves as the input for a traditional undergraduate capstone subject on aircraft design. Of critical importance in the conceptual phase is addressing the business case for the candidate product. The conceptual phase spans a much wider range of topics than the technical issues which dominate preliminary design. These include user needs, investment and business requirements, market analysis, operational issues, exogenous constraints (certification, regulation, political, etc.), as well as engineering and manufacturing requirements.
Students in the subject were required to Prepare for the Board of Directors of a large aerospace company a compelling business case and specification for a large jet transport product. Three student teams produced original responses to the challenge and have reported their findings in a companion AIAA paper. This paper addresses the pedagogical approaches and outcomes. These encompass the use of distance learning technology and techniques for several off-campus practicing engineering students. Overall, the outcome was very gratifying. The class will be offered in the spring of 2001, focusing on a supersonic business jet
Obliquities of Hot Jupiter host stars: Evidence for tidal interactions and primordial misalignments
We provide evidence that the obliquities of stars with close-in giant planets
were initially nearly random, and that the low obliquities that are often
observed are a consequence of star-planet tidal interactions. The evidence is
based on 14 new measurements of the Rossiter-McLaughlin effect (for the systems
HAT-P-6, HAT-P-7, HAT-P-16, HAT-P-24, HAT-P-32, HAT-P-34, WASP-12, WASP-16,
WASP-18, WASP-19, WASP-26, WASP-31, Gl 436, and Kepler-8), as well as a
critical review of previous observations. The low-obliquity (well-aligned)
systems are those for which the expected tidal timescale is short, and likewise
the high-obliquity (misaligned and retrograde) systems are those for which the
expected timescale is long. At face value, this finding indicates that the
origin of hot Jupiters involves dynamical interactions like planet-planet
interactions or the Kozai effect that tilt their orbits, rather than
inspiraling due to interaction with a protoplanetary disk. We discuss the
status of this hypothesis and the observations that are needed for a more
definitive conclusion.Comment: Accepted for publication in ApJ; typos corrected, 2 broken references
fixed, 26 pages, 25 figure
The architecture of the hierarchical triple star KOI 928 from eclipse timing variations seen in Kepler photometry
We present a hierarchical triple star system (KIC 9140402) where a low mass
eclipsing binary orbits a more massive third star. The orbital period of the
binary (4.98829 Days) is determined by the eclipse times seen in photometry
from NASA's Kepler spacecraft. The periodically changing tidal field, due to
the eccentric orbit of the binary about the tertiary, causes a change in the
orbital period of the binary. The resulting eclipse timing variations provide
insight into the dynamics and architecture of this system and allow the
inference of the total mass of the binary ()
and the orbital parameters of the binary about the central star.Comment: Submitted to MNRAS Letters. Additional tables with eclipse times are
included here. The Kepler data that was used for the analysis of this system
(Q1 through Q6) will be available on MAST after June 27, 201
The orbits of the quadruple star system 88 Tau A from PHASES differential astrometry and radial velocity
We have used high precision differential astrometry from the Palomar
High-precision Astrometric Search for Exoplanet Systems (PHASES) project and
radial velocity measurements covering a time-span of 20 years to determine the
orbital parameters of the 88 Tau A system. 88 Tau is a complex hierarchical
multiple system comprising a total of six stars; we have studied the brightest
4, consisting of two short-period pairs orbiting each other with an 18-year
period. We present the first orbital solution for one of the short-period
pairs, and determine the masses of the components and distance to the system to
the level of a few percent. In addition, our astrometric measurements allow us
to make the first determination of the mutual inclinations of the orbits. We
find that the sub-systems are not coplanar.Comment: Corrected Author Ordering; 12 Pages, Accepted for publication in Ap
The Transit Ingress and the Tilted Orbit of the Extraordinarily Eccentric Exoplanet HD 80606b
We present the results of a transcontinental campaign to observe the 2009
June 5 transit of the exoplanet HD 80606b. We report the first detection of the
transit ingress, revealing the transit duration to be 11.64 +/- 0.25 hr and
allowing more robust determinations of the system parameters. Keck spectra
obtained at midtransit exhibit an anomalous blueshift, giving definitive
evidence that the stellar spin axis and planetary orbital axis are misaligned.
The Keck data show that the projected spin-orbit angle is between 32-87 deg
with 68.3% confidence and between 14-142 deg with 99.73% confidence. Thus the
orbit of this planet is not only highly eccentric (e=0.93), but is also tilted
away from the equatorial plane of its parent star. A large tilt had been
predicted, based on the idea that the planet's eccentric orbit was caused by
the Kozai mechanism. Independently of the theory, it is noteworthy that all 3
exoplanetary systems with known spin-orbit misalignments have massive planets
on eccentric orbits, suggesting that those systems migrate differently than
lower-mass planets on circular orbits.Comment: ApJ, in press [13 pg
The Photoeccentric Effect and Proto-Hot Jupiters II. KOI-1474.01, a candidate eccentric planet perturbed by an unseen companion
The exoplanets known as hot Jupiters---Jupiter-sized planets with periods
less than 10 days---likely are relics of dynamical processes that shape all
planetary system architectures. Socrates et al. (2012) argued that high
eccentricity migration (HEM) mechanisms proposed for situating these close-in
planets should produce an observable population of highly eccentric proto-hot
Jupiters that have not yet tidally circularized. HEM should also create
failed-hot Jupiters, with periapses just beyond the influence of fast
circularization. Using the technique we previously presented for measuring
eccentricities from photometry (the "photoeccentric effect"), we are distilling
a collection of eccentric proto- and failed-hot Jupiters from the Kepler
Objects of Interest (KOI). Here we present the first, KOI-1474.01, which has a
long orbital period (69.7340 days) and a large eccentricity e =
0.81+0.10/-0.07, skirting the proto-hot Jupiter boundary. Combining Kepler
photometry, ground-based spectroscopy, and stellar evolution models, we
characterize host KOI-1474 as a rapidly-rotating F-star. Statistical arguments
reveal that the transiting candidate has a low false-positive probability of
3.1%. KOI-1474.01 also exhibits transit timing variations of order an hour. We
explore characteristics of the third-body perturber, which is possibly the
"smoking-gun" cause of KOI-1474.01's large eccentricity. Using the host-star's
rotation period, radius, and projected rotational velocity, we find
KOI-1474.01's orbit is marginally consistent with aligned with the stellar spin
axis, although a reanalysis is warranted with future additional data. Finally,
we discuss how the number and existence of proto-hot Jupiters will not only
demonstrate that hot Jupiters migrate via HEM, but also shed light on the
typical timescale for the mechanism.Comment: ApJ, in press. Received 2012 July 7; accepted 2012 October 1
All Six Planets Known to Orbit Kepler-11 Have Low Densities
The Kepler-11 planetary system contains six transiting planets ranging in
size from 1.8 to 4.2 times the radius of Earth. Five of these planets orbit in
a tightly-packed configuration with periods between 10 and 47 days. We perform
a dynamical analysis of the system based upon transit timing variations
observed in more than three years of \ik photometric data. Stellar parameters
are derived using a combination of spectral classification and constraints on
the star's density derived from transit profiles together with planetary
eccentricity vectors provided by our dynamical study. Combining masses of the
planets relative to the star from our dynamical study and radii of the planets
relative to the star from transit depths together with deduced stellar
properties yields measurements of the radii of all six planets, masses of the
five inner planets, and an upper bound to the mass of the outermost planet,
whose orbital period is 118 days. We find mass-radius combinations for all six
planets that imply that substantial fractions of their volumes are occupied by
constituents that are less dense than rock. The Kepler-11 system contains the
lowest mass exoplanets for which both mass and radius have been measured.Comment: 39 pages, 10 figure
Revised Masses and Densities of the Planets around Kepler-10
Determining which small exoplanets have stony-iron compositions is necessary for quantifying the occurrence of such planets and for understanding the physics of planet formation. Kepler-10 hosts the stony-iron world Kepler-10b, and also contains what has been reported to be the largest solid silicate-ice planet, Kepler-10c. Using 220 radial velocities (RVs), including 72 precise RVs from Keck-HIRES of which 20 are new from 2014 to 2015, and 17 quarters of Kepler photometry, we obtain the most complete picture of the Kepler-10 system to date. We find that Kepler-10b (R_p = 1.47 R_â) has mass 3.72 ± 0.42 M_â and density 6.46 ± 0.73 g cm^(-3). Modeling the interior of Kepler-10b as an iron core overlaid with a silicate mantle, we find that the iron core constitutes 0.17 ± 0.11 of the planet mass. For Kepler-10c (R_p = 2.35 R_â) we measure mass 13.98 ± 1.79 M_â and density 5.94 ± 0.76 g cm^(-3), significantly lower than the mass computed in Dumusque et al. (17.2 ± 1.9 M_â). Our mass measurement of Kepler-10c rules out a pure stony-iron composition. Internal compositional modeling reveals that at least 10% of the radius of Kepler-10c is a volatile envelope composed of hydrogenâhelium (0.2% of the mass, 16% of the radius) or super-ionic water (28% of the mass, 29% of the radius). However, we note that analysis of only HIRES data yields a higher mass for planet b and a lower mass for planet c than does analysis of the HARPS-N data alone, with the mass estimates for Kepler-10 c being formally inconsistent at the 3Ï level. Moreover, dividing the data for each instrument into two parts also leads to somewhat inconsistent measurements for the mass of planet c derived from each observatory. Together, this suggests that time-correlated noise is present and that the uncertainties in the masses of the planets (especially planet c) likely exceed our formal estimates. Transit timing variations (TTVs) of Kepler-10c indicate the likely presence of a third planet in the system, KOI-72.X. The TTVs and RVs are consistent with KOI-72.X having an orbital period of 24, 71, or 101 days, and a mass from 1 to 7 M_â
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