290 research outputs found
An ingress and a complete transit of HD 80606 b
We have used four telescopes at different longitudes to obtain
near-continuous lightcurve coverage of the star HD 80606 as it was transited by
its \sim 4-MJup planet. The observations were performed during the predicted
transit windows around the 25th of October 2008 and the 14th of February 2009.
Our data set is unique in that it simultaneously constrains the duration of the
transit and the planet's period. Our Markov-Chain Monte Carlo analysis of the
light curves, combined with constraints from radial-velocity data, yields
system parameters consistent with previously reported values. We find a
planet-to-star radius ratio marginally smaller than previously reported,
corresponding to a planet radius of Rp = 0.921 \pm 0.036RJup .Comment: 6 pages, 2 figures, MNRAS accepte
Observation of the full 12-hour-long transit of the exoplanet HD80606b. Warm-Spitzer photometry and SOPHIE spectroscopy
We present new observations of a transit of the 111-day-period exoplanet
HD80606b. Using the Spitzer Space Telescope and its IRAC camera on the
post-cryogenic mission, we performed a 19-hour-long photometric observation of
HD80606 that covers the full transit of 13-14 January 2010. We complement this
photometric data by new spectroscopic observations that we simultaneously
performed with SOPHIE at Haute-Provence Observatory. This provides radial
velocity measurements of the first half of the transit that was previously
uncovered with spectroscopy. This new data set allows the parameters of this
singular planetary system to be significantly refined. We obtained a
planet-to-star radius ratio R_p/R_* = 0.1001 +/- 0.0006 that is slightly lower
than the one measured from previous ground observations. We detected a feature
in the Spitzer light curve that could be due to a stellar spot. We also found a
transit timing about 20 minutes earlier than the ephemeris prediction; this
could be caused by actual TTVs due to an additional body in the system or by
underestimated systematic uncertainties. The sky-projected angle between the
spin-axis of HD80606 and the normal to the planetary orbital plane is found to
be lambda = 42 +/- 8 degrees thanks to the fit of the Rossiter-McLaughlin
anomaly. This allows scenarios with aligned spin-orbit to be definitively
rejected. Over the twenty planetary systems with measured spin-orbit angles, a
few of them are misaligned; this is probably the signature of two different
evolution scenarios for misaligned and aligned systems, depending if they
experienced or not gravitational interaction with a third body. As in the case
of HD80606b, most of the planetary systems including a massive planet are
tilted; this could be the signature of a separate evolution scenario for
massive planets in comparison with Jupiter-mass planets.Comment: 14 pages, 9 figures, 2 tables, accepted for publication in A&
Evolutionary calculations of phase separation in crystallizing white dwarf stars
We present an exploration of the significance of Carbon/Oxygen phase
separation in white dwarf stars in the context of self-consistent evolutionary
calculations. Because phase separation can potentially increase the calculated
ages of the oldest white dwarfs, it can affect the age of the Galactic disk as
derived from the downturn in the white dwarf luminosity function. We find that
the largest possible increase in ages due to phase separation is 1.5 Gyr, with
a most likely value of approximately 0.6 Gyr, depending on the parameters of
our white dwarf models.
The most important factors influencing the size of this delay are the total
stellar mass, the initial composition profile, and the phase diagram assumed
for crystallization. We find a maximum age delay in models with masses of 0.6
solar masses, which is near the peak in the observed white dwarf mass
distribution. We find that varying the opacities (via the metallicity) has
little effect on the calculated age delays.
In the context of Galactic evolution, age estimates for the oldest Galactic
globular clusters range from 11.5 to 16 Gyr, and depend on a variety of
parameters. In addition, a 4 to 6 Gyr delay is expected between the formation
of the globular clusters and that of the Galactic thin disk, while the observed
white dwarf luminosity function gives an age estimate for the thin disk of 9.5
+/-1.0 Gyr, without including the effect of phase separation. Using the above
numbers, we see that phase separation could add between 0 to 3 Gyr to the white
dwarf ages and still be consistent with the overall picture of Galaxy
formation. Our calculated maximum value of 1.5 Gyr fits within these bounds, as
does our best guess value of 0.6 Gyr.Comment: 13 total pages, 8 figures, 3 tables, accepted for publication in the
Astrophysical Journal on May 25, 199
Recommended from our members
SEIS: Insight's Seismic Experiment for Internal Structure of Mars.
By the end of 2018, 42 years after the landing of the two Viking seismometers on Mars, InSight will deploy onto Mars' surface the SEIS (Seismic Experiment for Internal Structure) instrument; a six-axes seismometer equipped with both a long-period three-axes Very Broad Band (VBB) instrument and a three-axes short-period (SP) instrument. These six sensors will cover a broad range of the seismic bandwidth, from 0.01 Hz to 50 Hz, with possible extension to longer periods. Data will be transmitted in the form of three continuous VBB components at 2 sample per second (sps), an estimation of the short period energy content from the SP at 1 sps and a continuous compound VBB/SP vertical axis at 10 sps. The continuous streams will be augmented by requested event data with sample rates from 20 to 100 sps. SEIS will improve upon the existing resolution of Viking's Mars seismic monitoring by a factor of ∼ 2500 at 1 Hz and ∼ 200 000 at 0.1 Hz. An additional major improvement is that, contrary to Viking, the seismometers will be deployed via a robotic arm directly onto Mars' surface and will be protected against temperature and wind by highly efficient thermal and wind shielding. Based on existing knowledge of Mars, it is reasonable to infer a moment magnitude detection threshold of M w ∼ 3 at 40 ∘ epicentral distance and a potential to detect several tens of quakes and about five impacts per year. In this paper, we first describe the science goals of the experiment and the rationale used to define its requirements. We then provide a detailed description of the hardware, from the sensors to the deployment system and associated performance, including transfer functions of the seismic sensors and temperature sensors. We conclude by describing the experiment ground segment, including data processing services, outreach and education networks and provide a description of the format to be used for future data distribution.Electronic supplementary materialThe online version of this article (10.1007/s11214-018-0574-6) contains supplementary material, which is available to authorized users
Habitable Zones in the Universe
Habitability varies dramatically with location and time in the universe. This
was recognized centuries ago, but it was only in the last few decades that
astronomers began to systematize the study of habitability. The introduction of
the concept of the habitable zone was key to progress in this area. The
habitable zone concept was first applied to the space around a star, now called
the Circumstellar Habitable Zone. Recently, other, vastly broader, habitable
zones have been proposed. We review the historical development of the concept
of habitable zones and the present state of the research. We also suggest ways
to make progress on each of the habitable zones and to unify them into a single
concept encompassing the entire universe.Comment: 71 pages, 3 figures, 1 table; to be published in Origins of Life and
Evolution of Biospheres; table slightly revise
The Problem of Hipparcos Distances to Open Clusters: I. Constraints from Multicolor Main Sequence Fitting
Parallax data from the Hipparcos mission allow the direct distance to open
clusters to be compared with the distance inferred from main sequence (MS)
fitting. There are surprising differences between the two distance
measurements, which could lead to consequences of significant astrophysical
importance. We examine the different possibilities, focusing on MS fitting in
both metallicity-sensitive B-V and metallicity-insensitive V-I for five
well-studied systems (the Hyades, Pleiades, Alpha Per, Praesepe, and Coma Ber).
The Hipparcos distances to the Hyades and Alpha Per agree with the MS fitting
distances in both colors; there is a possible conflict for Praesepe and Coma
Ber. The Hipparcos distance to the Pleiades disagrees with the MS fitting
distance in both colors at more than the three sigma level. Changes in the
cluster metal abundance, helium abundance, reddening and age-related effects
are all shown to be unlikely to explain the puzzling behavior for the Pleiades.
We present evidence for spatially dependent systematic errors at the 1 mas
level in the parallaxes of Pleiades stars. The implications of this result are
discussed.Comment: 52 pages, 24 figures. To appear in ApJ. Figures also available by ftp
at ftp://ftp.astronomy.ohio-state.edu/pub/pinsono/hipparco
uvby(-) photometry of high-velocity and metal-poor stars X. Stars of very low metal abundance: observations, reddenings, metallicities, classifications, distances, and relative ages
uvby(--) photometry has been obtained for an additional 411 very
metal-poor stars selected from the HK survey, and used to derive basic
parameters such as interstellar reddenings, metallicities, photometric
classifications, distances, and relative ages... These very metal-poor stars
are compared to M92 in the c_0,(b-y)_0 diagram, and evidence is seen for field
stars 1-3 Gyrs younger than this globular cluster. The significance of these
younger very metal-poor stars is discussed in the context of Galactic
evolution, mentioning such possibilities as hierarchical
star-formation/mass-infall of very metal-poor material and/or accretion events
whereby this material has been acquired from other (dwarf) galaxies with
different formation and chemical-enrichment historiesComment: 20 pages, 11 figures, and 9 table
A transiting giant planet with a temperature between 250 K and 430 K
Of the over 400 known exoplanets, there are about 70 planets that transit their central star, a situation that permits the derivation of their basic parameters and facilitates investigations of their atmospheres. Some short-period planets, including the first terrestrial exoplanet (CoRoT-7b), have been discovered using a space mission designed to find smaller and more distant planets than can be seen from the ground. Here we report transit observations of CoRoT-9b, which orbits with a period of 95.274 days on a low eccentricity of 0.11 ± 0.04 around a solar-like star. Its periastron distance of 0.36 astronomical units is by far the largest of all transiting planets, yielding a ‘temperate’ photospheric temperature estimated to be between 250 and 430 K. Unlike previously known transiting planets, the present size of CoRoT-9b should not have been affected by tidal heat dissipation processes. Indeed, the planet is found to be well described by standard evolution models with an inferred interior composition consistent with that of Jupiter and Saturn
Role of Kv1 Potassium Channels in Regulating Dopamine Release and Presynaptic D2 Receptor Function
Dopamine (DA) release in the CNS is critical for motor control and motivated behaviors. Dysfunction of its regulation is thought to be implicated in drug abuse and in diseases such as schizophrenia and Parkinson's. Although various potassium channels located in the somatodendritic compartment of DA neurons such as G-protein-gated inward rectifying potassium channels (GIRK) have been shown to regulate cell firing and DA release, little is presently known about the role of potassium channels localized in the axon terminals of these neurons. Here we used fast-scan cyclic voltammetry to study electrically-evoked DA release in rat dorsal striatal brain slices. We find that although G-protein-gated inward rectifying (GIRK) and ATP-gated (KATP) potassium channels play only a minor role, voltage-gated potassium channels of the Kv1 family play a major role in regulating DA release. The use of Kv subtype-selective blockers confirmed a role for Kv1.2, 1.3 and 1.6, but not Kv1.1, 3.1, 3.2, 3.4 and 4.2. Interestingly, Kv1 blockers also reduced the ability of quinpirole, a D2 receptor agonist, to inhibit evoked DA overflow, thus suggesting that Kv1 channels also regulate presynaptic D2 receptor function. Our work identifies Kv1 potassium channels as key regulators of DA release in the striatum
The depth of the shower maximum of air showers measured with AERA
The Auger Engineering Radio Array (AERA) is currently the largest array of radio antennas for the detection of cosmic rays, spanning an area of 17 km2 with 153 radio antennas, measuring in the energy range from 1017.0 to 1019.0 eV. It detects the radio emission of extensive air showers produced by cosmic rays in the 30 − 80 MHz band. The cosmic-ray mass composition is a crucial piece of information in determining the sources of cosmic rays and their acceleration mechanisms. The depth of the shower maximum, Xmax, a probe for mass composition can be determined with a likelihood analysis that compares the measured radio-emission footprint on the ground to an ensemble of footprints from CORSIKA/CoREAS Monte-Carlo air shower simulations. These simulations are also used to determine the resolution of the method and to validate the reconstruction by identifying and correcting for systematic uncertainties. We will present the method for the reconstruction of the depth of the shower maximum, achieving a resolution of up to 15 g/cm2, show compatibility with the independent fluorescence detector reconstruction measured on an event-by-event basis, and show that the data taken over the past seven years with AERA shows a light cosmic-ray mass composition reconstruction in the energy range from 1017.5 to 1018.8 eV
- …