385 research outputs found
A highly inclined orbit for the 110-day period M-dwarf companion KOI-368.01
We report the detection of asymmetry in the transit light curves of the
110-day period companion to KOI-368, a rapidly rotating A-dwarf. The
significant distortion in the transit light curve is attributed to spin-orbit
misalignment between the transiting companion and the gravity darkened host
star. Our analysis was based on 11 Long Cadence and 2 Short Cadence transits of
KOI-368.01 from the Kepler mission, as well as stellar parameters determined
from our follow-up spectroscopic observation. We measured the true obliquity
between the orbit normal and the stellar rotation axis to be 69 +9/-10 deg. We
also find a secondary eclipse event with depth 29 +/- 3 ppm at phase 0.59, from
which the temperature of the companion is constrained to 3060 +/- 50 K,
indicating that KOI-368.01 is a late M-dwarf. The eccentricity is also
calculated from the eclipse to be 0.1429 +/- 0.0007. The long period, high
obliquity, and low eccentricity of KOI-368.01 allow us to limit a number of
proposed theories for the misalignment of binary systems.Comment: 7 pages, 4 figures, 1 table, accepted for publication in ApJ
Bayesian Ages for Early-Type Stars from Isochrones Including Rotation, and a Possible Old Age for the Hyades
We combine recently computed models of stellar evolution using a new
treatment of rotation with a Bayesian statistical framework to constrain the
ages and other properties of early-type stars. We find good agreement for
early-type stars and clusters with known young ages, including beta Pictoris,
the Pleiades, and the Ursa Majoris Moving Group. However, we derive a
substantially older age for the Hyades open cluster (750+/-100 Myr compared to
625+/-50 Myr). This older age results from both the increase in main-sequence
lifetime with stellar rotation and from the fact that rotating models near the
main-sequence turnoff are more luminous, overlapping with slightly more massive
(and shorter-lived) nonrotating ones. Our method uses a large grid of
nonrotating models to interpolate between a much sparser rotating grid, and
also includes a detailed calculation of synthetic magnitudes as a function of
orientation. We provide a web interface at www.bayesianstellarparameters.info
where the results of our analysis may be downloaded for individual early-type
(B-V<~0.25) Hipparcos stars. The web interface accepts user-supplied parameters
for a Gaussian metallicity prior and returns posterior probability
distributions on mass, age, and orientation.Comment: 11 pages, 6 figures, ApJ accepted. Error fixed: ages -> ~15% younger.
bayesianstellarparameters.info update
Testing the Titius-Bode law predictions for Kepler multi-planet systems
We use three and half years of Kepler Long Cadence data to search for the 97
predicted planets of Bovaird & Lineweaver (2013) in 56 of the multi-planet
systems, based on a general Titius-Bode relation. Our search yields null
results in the majority of systems. We detect five planetary candidates around
their predicted periods. We also find an additional transit signal beyond those
predicted in these systems. We discuss the possibility that the remaining
predicted planets are not detected in the Kepler data due to their
non-coplanarity or small sizes. We find that the detection rate is beyond the
lower boundary of the expected number of detections, which indicates that the
prediction power of the TB relation in general extra solar planetary systems is
questionable. Our analysis of the distribution of the adjacent period ratios of
the systems suggests that the general Titius-Bode relation may over-predict the
presence of planet pairs near the 3:2 resonance.Comment: Accepted by MNRA
Rotating Stellar Models Can Account for the Extended Main Sequence Turnoffs in Intermediate Age Clusters
We show that the extended main sequence turnoffs seen in intermediate age
Large Magellanic Cloud (LMC) clusters, often attributed to age spreads of
several hundred Myr, may be easily accounted for by variable stellar rotation
in a coeval population. We compute synthetic photometry for grids of rotating
stellar evolution models and interpolate them to produce isochrones at a
variety of rotation rates and orientations. An extended main sequence turnoff
naturally appears in color-magnitude diagrams at ages just under 1 Gyr, peaks
in extent between ~1 and 1.5 Gyr, and gradually disappears by around 2 Gyr in
age. We then fit our interpolated isochrones by eye to four LMC clusters with
very extended main sequence turnoffs: NGC 1783, 1806, 1846, and 1987. In each
case, stellar populations with a single age and metallicity can comfortably
account for the observed extent of the turnoff region. The new stellar models
predict almost no correlation of turnoff color with rotational vsini: the red
edge of the turnoff is populated by a combination of slow rotators and edge-on
rapid rotators.Comment: 7 pages, 4 figures, 1 table, ApJ accepted. Conclusions unchange
The Age and Age Spread of the Praesepe and Hyades Clusters: a Consistent, ~800 Myr Picture from Rotating Stellar Models
We fit the upper main sequence of the Praesepe and Hyades open clusters using
stellar models with and without rotation. When neglecting rotation, we find
that no single isochrone can fit the entire upper main sequence at the
clusters' spectroscopic metallicity: more massive stars appear, at high
significance, to be younger than less massive stars. This discrepancy is
consistent with earlier studies, but vanishes when including stellar rotation.
The entire upper main sequence of both clusters is very well-fit by a
distribution of 800 Myr-old stars with the spectroscopically measured
[Fe/H]=0.12. The increase over the consensus age of ~600-650 Myr is due both to
the revised Solar metallicity (from to ) and to the lengthening of main sequence lifetimes and increase in
luminosities with rapid rotation. Our results show that rotation can remove the
need for large age spreads in intermediate age clusters, and that these
clusters may be significantly older than is commonly accepted. A
Hyades/Praesepe age of ~800 Myr would also require a recalibration of
rotation/activity age indicators.Comment: 6 pages, 4 figures, ApJ accepted. Replaced with accepted version,
conclusions unchange
Warm Jupiters are less lonely than hot Jupiters: close neighbours
Exploiting the Kepler transit data, we uncover a dramatic distinction in the
prevalence of sub-Jovian companions, between systems that contain hot Jupiters
(periods inward of 10 days) and those that host warm Jupiters (periods between
10 and 200 days). Hot Jupiters, with the singular exception of WASP-47b, do not
have any detectable inner or outer planetary companions (with periods inward of
50 days and sizes down to ). Restricting ourselves to inner
companions, our limits reach down to . In stark contrast, half
of the warm Jupiters are closely flanked by small companions. Statistically,
the companion fractions for hot and warm Jupiters are mutually exclusive,
particularly in regard to inner companions.
The high companion fraction of warm Jupiters also yields clues to their
formation. The warm Jupiters that have close-by siblings should have low
orbital eccentricities and low mutual inclinations. The orbital configurations
of these systems are reminiscent of those of the low-mass, close-in planetary
systems abundantly discovered by the Kepler mission. This, and other arguments,
lead us to propose that these warm Jupiters are formed in-situ. There are
indications that there may be a second population of warm Jupiters with
different characteristics. In this picture, WASP-47b could be regarded as the
extending tail of the in-situ warm Jupiters into the hot Jupiter region, and
does not represent the generic formation route for hot Jupiters.Comment: 12 pages, 7 figures, accepted by Ap
On the IMF in a Triggered Star Formation Context
The origin of the stellar initial mass function (IMF) is a fundamental issue
in the theory of star formation. It is generally fit with a composite power
law. Some clues on the progenitors can be found in dense starless cores that
have a core mass function (CMF) with a similar shape. In the low-mass end,
these mass functions increase with mass, albeit the sample may be somewhat
incomplete; in the high-mass end, the mass functions decrease with mass. There
is an offset in the turn-over mass between the two mass distributions. The
stellar mass for the IMF peak is lower than the corresponding core mass for the
CMF peak in the Pipe Nebula by about a factor of three. Smaller offsets are
found between the IMF and the CMFs in other nebulae. We suggest that the offset
is likely induced during a starburst episode of global star formation which is
triggered by the formation of a few O/B stars in the multi-phase media, which
naturally emerged through the onset of thermal instability in the cloud-core
formation process. We consider the scenario that the ignition of a few massive
stars photoionizes the warm medium between the cores, increases the external
pressure, reduces their Bonnor?Ebert mass, and triggers the collapse of some
previously stable cores. We quantitatively reproduce the IMF in the low-mass
end with the assumption of additional rotational fragmentation.Comment: 3 figure
TESS Discovery of a Transiting Super-Earth in the pi Mensae System
We report the detection of a transiting planet around Ï Men (HD 39091), using data from the Transiting Exoplanet Survey Satellite (TESS). The solar-type host star is unusually bright (V = 5.7) and was already known to host a Jovian planet on a highly eccentric, 5.7 yr orbit. The newly discovered planet has a size of 2.04 ± 0.05 Râ and an orbital period of 6.27 days. Radial-velocity data from the High-Accuracy Radial-velocity Planet Searcher and Anglo-Australian Telescope/University College London Echelle Spectrograph archives also displays a 6.27 day periodicity, confirming the existence of the planet and leading to a mass determination of 4.82 ± 0.85 Mâ. The star's proximity and brightness will facilitate further investigations, such as atmospheric spectroscopy, asteroseismology, the RossiterâMcLaughlin effect, astrometry, and direct imaging
Universal quantum semigroupoids
We introduce the concept of a universal quantum linear semigroupoid (UQSGd),
which is a weak bialgebra that coacts on a (not necessarily connected) graded
algebra universally while preserving grading. We restrict our attention to
algebraic structures with a commutative base so that the UQSGds under
investigation are face algebras (due to Hayashi). The UQSGd construction
generalizes the universal quantum linear semigroups introduced by Manin in
1988, which are bialgebras that coact on a connected graded algebra universally
while preserving grading. Our main result is that when is the path algebra
of a finite quiver , each of the various UQSGds introduced here is
isomorphic to the face algebra attached to . The UQSGds of preprojective
algebras and of other algebras attached to quivers are also investigated.Comment: v2: 34 pages. Minor edits. Added Question 3.12. Submitte
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