341 research outputs found
Pupil stabilization for SPHERE's extreme AO and high performance coronagraph system
We propose a new concept of pupil motion sensor for astronomical adaptive
optics systems and present experimental results obtained during the first
laboratory validation of this concept. Pupil motion is an important issue in
the case of extreme adaptive optics, high contrast systems, such as the
proposed Planet Finder instruments for the ESO and Gemini 8-meter telescopes.
Such high contrast imaging instruments will definitively require pupil
stabilization to minimize the effect of quasi-static aberrations. The concept
for pupil stabilization we propose uses the flux information from the AO system
wave-front sensor to drive in closed loop a pupil tip-tilt mirror located in a
focal plane. A laboratory experiment validates this concept and demonstrates
its interest for high contrast imaging instrument.Comment: This paper was published in Optics Express and is made available as
an electronic reprint with the permission of OSA. The paper can be found at
http://www.opticsexpress.org/abstract.cfm?id=144687 on the OSA websit
DNA waves and water
Some bacterial and viral DNA sequences have been found to induce low
frequency electromagnetic waves in high aqueous dilutions. This phenomenon
appears to be triggered by the ambient electromagnetic background of very low
frequency. We discuss this phenomenon in the framework of quantum field theory.
A scheme able to account for the observations is proposed. The reported
phenomenon could allow to develop highly sensitive detection systems for
chronic bacterial and viral infections.Comment: Invited talk at the DICE2010 Conference, Castiglioncello, Italy
September 201
The very nearby M/T dwarf binary SCR 1845-6357
The recently discovered star SCR 1845-6357 is the first late M/T dwarf binary
discovered. SCR 1845 is a particular object due to its tight orbit (currently
around 4 AU) and its proximity to the Sun (3.85 pc). We present spatially
resolved VLT/NACO images and low resolution spectra of SCR 1845 in the J, H and
K near-infrared bands. Since the T dwarf companion, SCR 1845B, is so close to
the primary SCR 1845A, orbital motion is evident even within a year. Following
the orbital motion, the binary's mass can be measured accurately within a
decade, making SCR 1845B a key T-dwarf mass-luminosity calibrator. The NIR
spectra allow for accurate determination of spectral type and also for rough
estimates of the object's physical parameters. The spectral type of SCR 1845B
is determined by direct comparison of the flux calibrated JHK spectra with T
dwarf standard template spectra and also by NIR spectral indices obtained from
synthetic photometry. Constrained values for surface gravity, effective
temperature and metallicity are derived by comparison with model spectra. Our
data prove that SCR 1845B is a brown dwarf of spectral type T6 that is
co-moving with and therefore gravitationally bound to the M8.5 primary. Fitting
the NIR spectrum of SCR 1845B to model spectra yields an effective temperature
of about 950K and a surface gravity log(g)=5.1 (cgs) assuming solar
metallicity. Mass and age of SCR 1845B are in the range 40 to 50 Jupiter masses
and 1.8 to 3.1 Gyr.Comment: 5 pages, 4 figures, accepted for publication in Astronomy &
Astrophysic
Extrasolar planets and brown dwarfs around A--F type stars. VIII. A giant planet orbiting the young star HD113337
In the frame of the search for extrasolar planets and brown dwarfs around
early-type main-sequence stars, we present the detection of a giant planet
around the young F-type star HD113337. We estimated the age of the system to be
150 +100/-50 Myr. Interestingly, an IR excess attributed to a cold debris disk
was previously detected on this star. The SOPHIE spectrograph on the 1.93m
telescope at Observatoire de Haute-Provence was used to obtain ~300 spectra
over 6 years. We used our SAFIR tool, dedicated to the spectra analysis of A
and F stars, to derive the radial velocity variations. The data reveal a 324.0
+1.7/-3.3 days period that we attribute to a giant planet with a minimum mass
of 2.83 +- 0.24 Mjup in an eccentric orbit with e=0.46 +- 0.04. A long-term
quadratic drift, that we assign to be probably of stellar origin, is
superimposed to the Keplerian solution.Comment: 7 pages, 4 figure
A historical reflection on the discovery of human retroviruses
The discovery of HIV-1 as the cause of AIDS was one of the major scientific achievements during the last century. Here the events leading to this discovery are reviewed with particular attention to priority and actual contributions by those involved. Since I would argue that discovering HIV was dependent on the previous discovery of the first human retrovirus HTLV-I, the history of this discovery is also re-examined. The first human retroviruses (HTLV-I) was first reported by Robert C. Gallo and coworkers in 1980 and reconfirmed by Yorio Hinuma and coworkers in 1981. These discoveries were in turn dependent on the previous discovery by Gallo and coworkers in 1976 of interleukin 2 or T-cell growth factor as it was called then. HTLV-II was described by Gallo's group in 1982. A human retrovirus distinct from HTLV-I and HTLV-II in that it was shown to have the morphology of a lentivirus was in my mind described for the first time by Luc Montagnier in an oral presentation at Cold Spring Harbor in September of 1983. This virus was isolated from a patient with lymphadenopathy using the protocol previously described for HTLV by Gallo. The first peer reviewed paper by Montagnier's group of such a retrovirus, isolated from two siblings of whom one with AIDS, appeared in Lancet in April of 1984. However, the proof that a new human retrovirus (HIV-1) was the cause of AIDS was first established in four publications by Gallo's group in the May 4th issue of Science in 1984
The SOPHIE search for northern extrasolar planets: VI. Three new hot Jupiters in multi-planet extrasolar systems
We present high-precision radial-velocity measurements of three solar-type
stars: HD 13908, HD 159243, and HIP 91258. The observations were made with the
SOPHIE spectrograph at the 1.93-m telescope of Observatoire de Haute-Provence
(France). They show that these three bright stars host exoplanetary systems
composed of at least two companions. HD 13908 b is a planet with a minimum mass
of 0.865+-0.035 Mjup, on a circular orbit with a period of 19.382+-0.006 days.
There is an outer massive companion in the system with a period of 931+-17
days, e = 0.12+-0.02, and a minimum mass of 5.13+-0.25 Mjup. The star HD
159243, also has two detected companions with respective masses, periods, and
eccentricities of Mp = 1.13+-0.05 and 1.9+-0.13 Mjup, = 12.620+-0.004 and
248.4+-4.9 days, and e = 0.02+-0.02 and 0.075+-0.05. Finally, the star HIP
91258 has a planetary companion with a minimum mass of 1.068+-0.038 Mjup, an
orbital period of 5.0505+-0.0015 days, and a quadratic trend indicating an
outer planetary or stellar companion that is as yet uncharacterized. The
planet-hosting stars HD 13908, HD 159243, and HIP 91258 are main-sequence stars
of spectral types F8V, G0V, and G5V, respectively, with moderate activity
levels. HIP 91258 is slightly over-metallic, while the two other stars have
solar-like metallicity. The three systems are discussed in the frame of
formation and dynamical evolution models of systems composed of several giant
planets.Comment: accepted in A&
SOPHIE velocimetry of Kepler transit candidates XVII. The physical properties of giant exoplanets within 400 days of period
While giant extrasolar planets have been studied for more than two decades
now, there are still some open questions such as their dominant formation and
migration process, as well as their atmospheric evolution in different stellar
environments. In this paper, we study a sample of giant transiting exoplanets
detected by the Kepler telescope with orbital periods up to 400 days. We first
defined a sample of 129 giant-planet candidates that we followed up with the
SOPHIE spectrograph (OHP, France) in a 6-year radial velocity campaign. This
allow us to unveil the nature of these candidates and to measure a
false-positive rate of 54.6 +/- 6.5 % for giant-planet candidates orbiting
within 400 days of period. Based on a sample of confirmed or likely planets, we
then derive the occurrence rates of giant planets in different ranges of
orbital periods. The overall occurrence rate of giant planets within 400 days
is 4.6 +/- 0.6 %. We recover, for the first time in the Kepler data, the
different populations of giant planets reported by radial velocity surveys.
Comparing these rates with other yields, we find that the occurrence rate of
giant planets is lower only for hot jupiters but not for the longer period
planets. We also derive a first measurement on the occurrence rate of brown
dwarfs in the brown-dwarf desert with a value of 0.29 +/- 0.17 %. Finally, we
discuss the physical properties of the giant planets in our sample. We confirm
that giant planets receiving a moderate irradiation are not inflated but we
find that they are in average smaller than predicted by formation and evolution
models. In this regime of low-irradiated giant planets, we find a possible
correlation between their bulk density and the Iron abundance of the host star,
which needs more detections to be confirmed.Comment: To appear in Astronomy and Astrophysic
The SOPHIE search for northern extrasolar planets VIII. A warm Neptune orbiting HD164595
High-precision radial velocity surveys explore the population of low-mass
exoplanets orbiting bright stars. This allows accurately deriving their orbital
parameters such as their occurrence rate and the statistical distribution of
their properties. Based on this, models of planetary formation and evolution
can be constrained. The SOPHIE spectrograph has been continuously improved in
past years, and thanks to an appropriate correction of systematic instrumental
drift, it is now reaching 2 m/s precision in radial velocity measurements on
all timescales. As part of a dedicated radial velocity survey devoted to search
for low-mass planets around a sample of 190 bright solar-type stars in the
northern hemisphere, we report the detection of a warm Neptune with a minimum
mass of 16.1 +- 2.7 Mearth orbiting the solar analog HD164595 in 40 +- 0.24
days . We also revised the parameters of the multiplanetary system around
HD190360. We discuss this new detection in the context of the upcoming space
mission CHEOPS, which is devoted to a transit search of bright stars harboring
known exoplanets.Comment: 11 pages, 9 figure
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