1,151 research outputs found
The loss of material from the cathode of metal arcs
A study was made of the effect of arc length, cathode thickness, current strength, gas pressure and the chemical nature of the cathode material and filling gases upon the material loss from Cu, Fe, and Ag cathodes in arcs. The results show that the analysis of the phenomenon is complex and the energy balance is difficult to formulate
Constraining the Distribution of L- & T-Dwarfs in the Galaxy
We estimate the thin disk scale height of the Galactic population of L- &
T-dwarfs based on star counts from 15 deep parallel fields from the Hubble
Space Telescope. From these observations, we have identified 28 candidate L- &
T- dwarfs based on their (i'-z') color and morphology. By comparing these star
counts to a simple Galactic model, we estimate the scale height to be 350+-50
pc that is consistent with the increase in vertical scale with decreasing
stellar mass and is independent of reddening, color-magnitude limits, and other
Galactic parameters. With this refined measure, we predict that less than 10^9
M_{sol} of the Milky Way can be in the form L- & T- dwarfs, and confirm that
high-latitude, z~6 galaxy surveys which use the i'-band dropout technique are
97-100% free of L- & T- dwarf interlopers.Comment: 4 pages, 4 figures, accepted to ApJ
No variations in transit times for Qatar-1 b
The transiting hot Jupiter planet Qatar-1 b was presented to exhibit
variations in transit times that could be of perturbative nature. A hot Jupiter
with a planetary companion on a nearby orbit would constitute an unprecedented
planetary configuration, important for theories of formation and evolution of
planetary systems. We performed a photometric follow-up campaign to confirm or
refute transit timing variations. We extend the baseline of transit
observations by acquiring 18 new transit light curves acquired with 0.6-2.0 m
telescopes. These photometric time series, together with data available in the
literature, were analyzed in a homogenous way to derive reliable transit
parameters and their uncertainties. We show that the dataset of transit times
is consistent with a linear ephemeris leaving no hint for any periodic
variations with a range of 1 min. We find no compelling evidence for the
existence of a close-in planetary companion to Qatar-1 b. This finding is in
line with a paradigm that hot Jupiters are not components of compact
multi-planetary systems. Based on dynamical simulations, we place tighter
constraints on a mass of any fictitious nearby planet in the system.
Furthermore, new transit light curves allowed us to redetermine system
parameters with the precision better than that reported in previous studies.
Our values generally agree with previous determinations.Comment: Accepted for publication in A&
New transit observations for HAT-P-30 b, HAT-P-37 b, TrES-5 b, WASP-28 b, WASP-36 b, and WASP-39 b
We present new transit light curves for planets in six extrasolar planetary
systems. They were acquired with 0.4-2.2 m telescopes located in west Asia,
Europe, and South America. When combined with literature data, they allowed us
to redetermine system parameters in a homogeneous way. Our results for
individual systems are in agreement with values reported in previous studies.
We refined transit ephemerides and reduced uncertainties of orbital periods by
a factor between 2 and 7. No sign of any variations in transit times was
detected for the planets studied.Comment: Submitted to Acta Astronomic
cGMP-Dependent Protein Kinase II Modulates mPer1 and mPer2 Gene Induction and Influences Phase Shifts of the Circadian Clock
High-precision photometry of WASP-12 b transits
The transiting extrasolar planet WASP-12 b was found to be one of the most
intensely irradiated exoplanets. It is unexpectedly bloated and is losing mass
that may accrete into the host star. Our aim was to refine the parameters of
this intriguing system and search for signs of transit timing variations. We
gathered high-precision light curves for two transits of WASP-12 b. Assuming
various limb-darkening laws, we generated best-fitting models and redetermined
parameters of the system. Error estimates were derived by the prayer bead
method and Monte Carlo simulations. System parameters obtained by us are found
to agree with previous studies within one sigma. Use of the non-linear
limb-darkening laws results in the best-fitting models. With two new
mid-transit times, the ephemeris was refined to BJD(TDB)=(2454508.97682 +/-
0.00020) + (1.09142245 +/- 0.00000033) E. Interestingly, indications of transit
timing variation are detected at the level of 3.4 sigma. This signal can be
induced by an additional planet in the system. Simplified numerical simulations
shows that a perturber could be a terrestrial-type planet if both planets are
in a low-order orbital resonance. However, we emphasise that further
observations are needed to confirm variation and to constrain properties of the
perturber.Comment: 5 pages, 3 figures, accepted for publication in A&
Towards the Rosetta Stone of planet formation
Transiting exoplanets (TEPs) observed just about 10 Myrs after formation of
their host systems may serve as the Rosetta Stone for planet formation
theories. They would give strong constraints on several aspects of planet
formation, e.g. time-scales (planet formation would then be possible within 10
Myrs), the radius of the planet could indicate whether planets form by
gravitational collapse (being larger when young) or accretion growth (being
smaller when young). We present a survey, the main goal of which is to find and
then characterise TEPs in very young open clusters.Comment: Poster contribution to Detection and Dynamics of Transiting
Exoplanets (Haute Provence Observatory Colloquium, 23-27 August 2010
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