183 research outputs found
Prenatal management of disorders of Sex development
Disorders of sex development (DSD) rarely present prenatally but, as they are very complex conditions, management should be directed by highly specialised medical teams to allow consideration of all aspects of diagnosis, treatment and ethical issues. In this brief review, we present an overview of the prenatal presentation and management of DSD, including the sonographic appearance of normal genitalia and methods of determining genetic sex, the prenatal management of pregnancies with the unexpected finding of genital ambiguity on prenatal ultrasound and a review of the prenatal management of pregnancies at high risk of DSD. As this is a rapidly developing field, management options will change over time, making the involvement of clinical geneticists, paediatric endocrinologists and urologists, as well as fetal medicine specialists, essential in the care of these complex pregnancies. The reader should also bear in mind that local social, ethical and legal aspects may also influence management
Stellar activity and rotation of the planet host Kepler-17 from long-term space-borne photometry
The study of young Sun-like stars is of fundamental importance to understand
the magnetic activity and rotational evolution of the Sun. Space-borne
photometry by the Kepler telescope provides unprecedented datasets to
investigate these phenomena in Sun-like stars. We present a new analysis of the
entire Kepler photometric time series of the moderately young Sun-like star
Kepler-17 that is accompanied by a transiting hot Jupiter. We applied a
maximum-entropy spot model to the long-cadence out-of-transit photometry of the
target to derive maps of the starspot filling factor versus the longitude and
the time. These maps are compared to the spots occulted during transits to
validate our reconstruction and derive information on the latitudes of the
starspots. We find two main active longitudes on the photosphere of Kepler-17,
one of which has a lifetime of at least days, although with a
varying level of activity. The latitudinal differential rotation is of solar
type, that is, with the equator rotating faster than the poles. We estimate a
minimum relative amplitude between
and , our determination being affected by the finite lifetime of
individual starspots and depending on the adopted spot model parameters. We
find marginal evidence of a short-term intermittent activity cycle of
days and an indication of a longer cycle of days characterized by an
equatorward migration of the mean latitude of the spots as in the Sun. The
rotation of Kepler-17 is likely to be significantly affected by the tides
raised by its massive close-by planet. We confirm the reliability of
maximum-entropy spot models to map starspots in young active stars and
characterize the activity and differential rotation of this young Sun-like
planetary host.Comment: Accepted by Astronomy and Astrophysics - 22 pages, 29 figure, 1
table, 2 appendixe
Detection of Neptune-size planetary candidates with CoRoT data. Comparison with the planet occurrence rate derived from Kepler
[Abridged] Context. The CoRoT space mission has been searching for transiting
planets since the end of December 2006. Aims. We aim to investigate the
capability of CoRoT to detect small-size transiting planets in short-period
orbits, and to compare the number of CoRoT planets with 2 \leq R_p \leq 4
Rearth with the occurrence rate of small-size planets provided by the
distribution of Kepler planetary candidates (Howard et al. 2012). Methods. We
performed a test that simulates transits of super-Earths and Neptunes in real
CoRoT light curves and searches for them blindly by using the LAM transit
detection pipeline. Results. The CoRoT detection rate of planets with radius
between 2 and 4 Rearth and orbital period P \leq 20 days is 59% (31%) around
stars brighter than r'=14.0 (15.5). By properly taking the CoRoT detection rate
for Neptune-size planets and the transit probability into account, we found
that according to the Kepler planet occurrence rate, CoRoT should have
discovered 12 \pm 2 Neptunes orbiting G and K dwarfs with P \leq 17 days in six
observational runs. This estimate must be compared with the validated Neptune
CoRoT-24b and five CoRoT planetary candidates in the considered range of
planetary radii. We thus found a disagreement with expectations from Kepler at
3 \sigma or 5 \sigma, assuming a blend fraction of 0% (six Neptunes) and 100%
(one Neptune) for these candidates. Conclusions. This underabundance of CoRoT
Neptunes with respect to Kepler may be due to several reasons. Regardless of
the origin of the disagreement, which needs to be investigated in more detail,
the noticeable deficiency of CoRoT Neptunes at short orbital periods seems to
indirectly support the general trend found in Kepler data, i.e. that the
frequency of small-size planets increases with increasing orbital periods and
decreasing planet radii.Comment: 10 pages, 7 figures. Accepted for publication in A&
The secondary eclipses of WASP-19b as seen by the ASTEP 400 telescope from Antarctica
The ASTEP (Antarctica Search for Transiting ExoPlanets) program was
originally aimed at probing the quality of the Dome C, Antarctica for the
discovery and characterization of exoplanets by photometry. In the first year
of operation of the 40 cm ASTEP 400 telescope (austral winter 2010), we
targeted the known transiting planet WASP-19b in order to try to detect its
secondary transits in the visible. This is made possible by the excellent
sub-millimagnitude precision of the binned data. The WASP-19 system was
observed during 24 nights in May 2010. The photometric variability level due to
starspots is about 1.8% (peak-to-peak), in line with the SuperWASP data from
2007 (1.4%) and larger than in 2008 (0.07%). We find a rotation period of
WASP-19 of 10.7 +/- 0.5 days, in agreement with the SuperWASP determination of
10.5 +/- 0.2 days. Theoretical models show that this can only be explained if
tidal dissipation in the star is weak, i.e. the tidal dissipation factor Q'star
> 3.10^7. Separately, we find evidence for a secondary eclipse of depth 390 +/-
190 ppm with a 2.0 sigma significance, a phase consistent with a circular orbit
and a 3% false positive probability. Given the wavelength range of the
observations (420 to 950 nm), the secondary transit depth translates into a day
side brightness temperature of 2690(-220/+150) K, in line with measurements in
the z' and K bands. The day side emission observed in the visible could be due
either to thermal emission of an extremely hot day side with very little
redistribution of heat to the night side, or to direct reflection of stellar
light with a maximum geometrical albedo Ag=0.27 +/- 0.13. We also report a
low-frequency oscillation well in phase at the planet orbital period, but with
a lower-limit amplitude that could not be attributed to the planet phase alone,
and possibly contaminated with residual lightcurve trends.Comment: Accepted for publication in Astronomy and Astrophysics, 13 pages, 13
figure
BVRIJHK photometry and proper motion analysis of NGC 6253 and the surrounding field
Context. We present a photometric and astrometric catalog of 187963 stars
located in the field around the old super-metal-rich Galactic open cluster NGC
6253. The total field-of-view covered by the catalog is 34' x 33'. In this
field, we provide CCD BVRI photometry. For a smaller region close to the
cluster's center, we also provide near-infrared JHK photometry. Aims. We
analyze the properties of NGC 6253 by using our new photometric data and
astrometric membership. Methods. In June 2004, we targeted the cluster during a
10 day multi-site campaign, which involved the MPG/ESO 2.2m telescope with its
wide-field imager and the Anglo-Australian 3.9m telescope, equipped with the
IRIS2 near-infrared imager. Archival CCD images of NGC 6253 were used to derive
relative proper motions and to calculate the cluster membership probabilities.
Results. We have refined the cluster's fundamental parameters, deriving
(V_0-M_v)=11.15, E(B - V)=0.15, E(V - I)=0.25, E(V - J)=0.50, and E(V -
H)=0.55. The color excess ratios obtained using both the optical and near
infrared colors indicate a normal reddening law in the direction of NGC 6253.
The age of NGC 6253 at 3.5 Gyr, determined from our best-fitting isochrone
appears to be slightly older than the previous estimates. Finally, we estimated
the binary fraction among the cluster members to be \sim20%-30% and identified
11 blue straggler candidates.Comment: 16 pages, 13 figures, 11 tables. Accepted for publication in A&A.
Catalog avaiable via CD
Modelling the Autocovariance of the Power Spectrum of a Solar-Type Oscillator
Asteroseismology is able to conduct studies on the interiors of solar-type
stars from the analysis of stellar acoustic spectra. However, such an analysis
process often has to rely upon subjective choices made throughout. A recurring
problem is to determine whether a signal in the acoustic spectrum originates
from a radial or a dipolar oscillation mode. In order to overcome this problem,
we present a procedure for modelling and fitting the autocovariance of the
power spectrum which can be used to obtain global seismic parameters of
solar-type stars, doing so in an automated fashion without the need to make
subjective choices. From the set of retrievable global seismic parameters we
emphasize the mean small frequency separation and, depending on the intrinsic
characteristics of the power spectrum, the mean rotational frequency splitting.
Since this procedure is automated, it can serve as a useful tool in the
analysis of the more than one thousand solar-type stars expected to be observed
as part of the Kepler Asteroseismic Investigation (KAI). We apply the
aforementioned procedure to simulations of the Sun. Assuming different apparent
magnitudes, we address the issues of how accurately and how precisely we can
retrieve the several global seismic parameters were the Sun to be observed as
part of the KAI.Comment: 10 pages, 8 figures, accepted for publication in MNRA
ASTEP South: An Antarctic Search for Transiting ExoPlanets around the celestial South pole
ASTEP South is the first phase of the ASTEP project (Antarctic Search for
Transiting ExoPlanets). The instrument is a fixed 10 cm refractor with a 4kx4k
CCD camera in a thermalized box, pointing continuously a 3.88 degree x 3.88
degree field of view centered on the celestial South pole. ASTEP South became
fully functional in June 2008 and obtained 1592 hours of data during the 2008
Antarctic winter. The data are of good quality but the analysis has to account
for changes in the point spread function due to rapid ground seeing variations
and instrumental effects. The pointing direction is stable within 10 arcseconds
on a daily timescale and drifts by only 34 arcseconds in 50 days. A truly
continuous photometry of bright stars is possible in June (the noon sky
background peaks at a magnitude R=15 arcsec-2 on June 22), but becomes
challenging in July (the noon sky background magnitude is R=12.5 arcsec?2 on
July 20). The weather conditions are estimated from the number of stars
detected in the field. For the 2008 winter, the statistics are between 56.3 %
and 68.4 % of excellent weather, 17.9 % to 30 % of veiled weather and 13.7 % of
bad weather. Using these results in a probabilistic analysis of transit
detection, we show that the detection efficiency of transiting exoplanets in
one given field is improved at Dome C compared to a temperate site such as La
Silla. For example we estimate that a year-long campaign of 10 cm refractor
could reach an efficiency of 69 % at Dome C versus 45 % at La Silla for
detecting 2-day period giant planets around target stars from magnitude 10 to
15. This shows the high potential of Dome C for photometry and future planet
discoveries. [Short abstract
Sounding stellar cycles with Kepler - I. Strategy for selecting targets
The long-term monitoring and high photometric precision of the Kepler
satellite will provide a unique opportunity to sound the stellar cycles of many
solar-type stars using asteroseismology. This can be achieved by studying
periodic changes in the amplitudes and frequencies of the oscillation modes
observed in these stars. By comparing these measurements with conventional
ground-based chromospheric activity indices, we can improve our understanding
of the relationship between chromospheric changes and those taking place deep
in the interior throughout the stellar activity cycle. In addition,
asteroseismic measurements of the convection zone depth and differential
rotation may help us determine whether stellar cycles are driven at the top or
at the base of the convection zone. In this paper, we analyze the precision
that will be possible using Kepler to measure stellar cycles, convection zone
depths, and differential rotation. Based on this analysis, we describe a
strategy for selecting specific targets to be observed by the Kepler
Asteroseismic Investigation for the full length of the mission, to optimize
their suitability for probing stellar cycles in a wide variety of solar-type
stars.Comment: accepted for publication in MNRA
A new search for planet transits in NGC 6791
Context. Searching for planets in open clusters allows us to study the
effects of dynamical environment on planet formation and evolution.
Aims. Considering the strong dependence of planet frequency on stellar
metallicity, we studied the metal rich old open cluster NGC 6791 and searched
for close-in planets using the transit technique.
Methods. A ten-night observational campaign was performed using the
Canada-France-Hawaii Telescope (3.6m), the San Pedro M\'artir telescope (2.1m),
and the Loiano telescope (1.5m). To increase the transit detection probability
we also made use of the Bruntt et al. (2003) eight-nights observational
campaign. Adequate photometric precision for the detection of planetary
transits was achieved.
Results. Should the frequency and properties of close-in planets in NGC 6791
be similar to those orbiting field stars of similar metallicity, then detailed
simulations foresee the presence of 2-3 transiting planets. Instead, we do not
confirm the transit candidates proposed by Bruntt et al. (2003). The
probability that the null detection is simply due to chance coincidence is
estimated to be 3%-10%, depending on the metallicity assumed for the cluster.
Conclusions. Possible explanations of the null-detection of transits include:
(i) a lower frequency of close-in planets in star clusters; (ii) a smaller
planetary radius for planets orbiting super metal rich stars; or (iii)
limitations in the basic assumptions. More extensive photometry with 3-4m class
telescopes is required to allow conclusive inferences about the frequency of
planets in NGC 6791.Comment: 23 pages, 23 figures, A&A accepte
Discovery and characterisation of detached M-dwarf eclipsing binaries in the WFCAM Transit Survey
We report the discovery of 16 detached M-dwarf eclipsing binaries with J<16
mag and provide a detailed characterisation of three of them, using
high-precision infrared light curves from the WFCAM Transit Survey (WTS). Such
systems provide the most accurate and model-independent method for measuring
the fundamental parameters of these poorly understood yet numerous stars, which
currently lack sufficient observations to precisely calibrate stellar evolution
models. We fully solve for the masses and radii of three of the systems,
finding orbital periods in the range 1.5<P<4.9 days, with masses spanning
0.35-0.50 Msun and radii between 0.38-0.50 Rsun, with uncertainties of
~3.5-6.4% in mass and ~2.7-5.5% in radius. Close-companions in short-period
binaries are expected to be tidally-locked into fast rotational velocities,
resulting in high levels of magnetic activity. This is predicted to inflate
their radii by inhibiting convective flow and increasing star spot coverage.
The radii of the WTS systems are inflated above model predictions by ~3-12%, in
agreement with the observed trend, despite an expected lower systematic
contribution from star spots signals at infrared wavelengths. We searched for
correlation between the orbital period and radius inflation by combining our
results with all existing M-dwarf radius measurements of comparable precision,
but we found no statistically significant evidence for a decrease in radius
inflation for longer period, less active systems. Radius inflation continues to
exists in non-synchronised systems indicating that the problem remains even for
very low activity M-dwarfs. Resolving this issue is vital not only for
understanding the most populous stars in the Universe, but also for
characterising their planetary companions, which hold the best prospects for
finding Earth-like planets in the traditional habitable zone.Comment: 30 pages, 14 figures, 16 tables, Accepted for publication in MNRA
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