254 research outputs found
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
Is there a compact companion orbiting the late O-type binary star HD 164816?
We present a multi-wavelength (X-ray, -ray, optical and radio) study
of HD 194816, a late O-type X-ray detected spectroscopic binary. X-ray spectra
are analyzed and the X-ray photon arrival times are checked for pulsation. In
addition, newly obtained optical spectroscopic monitoring data on HD 164816 are
presented. They are complemented by available radio data from several large
scale surveys as well as the \emph{FERMI} -ray data from its
\emph{Large Area Telescope}. We report the detection of a low energy excess in
the X-ray spectrum that can be described by a simple absorbed blackbody model
with a temperature of 50 eV as well as a 9.78 s pulsation of the X-ray
source. The soft X-ray excess, the X-ray pulsation, and the kinematical age
would all be consistent with a compact object like a neutron star as companion
to HD 164816. The size of the soft X-ray excess emitting area is consistent
with a circular region with a radius of about 7 km, typical for neutron stars,
while the emission measure of the remaining harder emission is typical for late
O-type single or binary stars. If HD 164816 includes a neutron star born in a
supernova, this supernova should have been very recent and should have given
the system a kick, which is consistent with the observation that the star HD
164816 has a significantly different radial velocity than the cluster mean. In
addition we confirm the binarity of HD 164816 itself by obtaining an orbital
period of 3.82 d, projected masses = 2.355(69) M,
= 2.103(62) M apparently seen at low inclination
angle, determined from high-resolution optical spectra.Comment: Accepted for publication by MNRAS, 11 pages, 6 figures, 4 table
Using stable isotopes to assess surface water source dynamics and hydrological connectivity in a high-latitude wetland and permafrost influenced landscape
The research has been supported by the NERC/JPI SIWA project (NE/M019896/1); grant issued in accordance with Resolution of the Government of the Russian Federation No. 220 dated 9 April 2010, under Agreement No. 14.B25.31.0001 with Ministry of Education and Science of the Russian Federation dated 24 June 2013 (BIO-GEO-CLIM); grant RFBR No 17-05-00-348a; grant FCP “Kolmogorov” 14.587.21.0036, grant RNF No 15-17-1009, and grant RFBR No 17-55-16008. Stable water isotope data are available in the Natural Environment Research Council (NERC) Environmental Information Data Centre (EIDC) data repository (title: “Stable water isotopes in Western Siberian inland waters”, permanent identifier: https://doi.org/10.5285/ca17e364-638d-4949-befb-b18b3770aec6). We would like to acknowledge the Arctic-GRO and IAEA for their publicly available databases providing supporting data for our analyses. Stream flow data at Nikolskoe was provided by Sergey Vorobiev. Liliya Kovaleva is acknowledged for the artwork in Figure 9. We would like to thank the two anonymous reviewers and the handling editors for their constructive comments that improved the manuscript.Peer reviewedPublisher PD
High riverine CO2 emissions at the permafrost boundary of Western Siberia
Acknowledgements: The study was part of the JPI Climate initiative, financially supported by VR (the Swedish Research Council) grant no. 325-2014-6898 to J.K. Additional funding from RNF (RSCF) grant no. 18-17-00237, RFBR grant no. 17-55-16008 and RF Federal Target Program RFMEFI58717X0036 ‘Kolmogorov’ to O.S.P. and S.N.K. as well as NERC grant no. NE/M019896/1 to C.S. is acknowledged. The authors thank A. Sorochinskiy and A. Lim for assistance in the field, as well as M. Myrstener, M. Klaus and S. Monteux for advice on data analysis. L. Kovaleva is acknowledged for artwork.Peer reviewedPostprin
Astrometric confirmation of young low-mass binaries and multiple systems in the Chamaeleon star-forming regions
The star-forming regions in Chamaeleon are one of the nearest (distance ~165
pc) and youngest (age ~2 Myrs) conglomerates of recently formed stars and the
ideal target for population studies of star formation. We investigate a total
of 16 Cha targets, which have been suggested, but not confirmed as binaries or
multiple systems in previous literature. We used the adaptive optics instrument
Naos-Conica (NACO) at the Very Large Telescope Unit Telescope 4 of the Paranal
Observatory, at 2-5 different epochs, in order to obtain relative and absolute
astrometric measurements, as well as differential photometry in the J, H, and K
band. On the basis of known proper motions and these observations, we analyse
the astrometric results in our "Proper Motion Diagram" (PMD: angular separation
/ position angle versus time), to eliminate possible (non-moving) background
stars, establish co-moving binaries and multiples, and search for curvature as
indications for orbital motion. All previously suggested close components are
co-moving and no background stars are found. The angular separations range
between 0.07 and 9 arcseconds, corresponding to projected distances between the
components of 6-845 AU. Thirteen stars are at least binaries and the remaining
three (RX J0919.4-7738, RX J0952.7-7933, VW Cha) are confirmed high-order
multiple systems with up to four components. In 13 cases, we found significant
slopes in the PMDs, which are compatible with orbital motion whose periods
range from 60 to 550 years. However, in only four cases there are indications
of a curved orbit, the ultimate proof of a gravitational bond. Massive primary
components appear to avoid the simultaneous formation of equal-mass secondary
components. (abridged)Comment: 33 pages, 22 figures, accepted for publication in A&A, 2nd version:
typos and measurement unit added in Table
Multi-site campaign for transit timing variations of WASP-12 b: possible detection of a long-period signal of planetary origin
The transiting planet WASP-12 b was identified as a potential target for
transit timing studies because a departure from a linear ephemeris was reported
in the literature. Such deviations could be caused by an additional planet in
the system. We attempt to confirm the existence of claimed variations in
transit timing and interpret its origin. We organised a multi-site campaign to
observe transits by WASP-12 b in three observing seasons, using 0.5-2.6-metre
telescopes. We obtained 61 transit light curves, many of them with
sub-millimagnitude precision. The simultaneous analysis of the best-quality
datasets allowed us to obtain refined system parameters, which agree with
values reported in previous studies. The residuals versus a linear ephemeris
reveal a possible periodic signal that may be approximated by a sinusoid with
an amplitude of 0.00068+/-0.00013 d and period of 500+/-20 orbital periods of
WASP-12 b. The joint analysis of timing data and published radial velocity
measurements results in a two-planet model which better explains observations
than single-planet scenarios. We hypothesize that WASP-12 b might be not the
only planet in the system and there might be the additional 0.1 M_Jup body on a
3.6-d eccentric orbit. A dynamical analysis indicates that the proposed
two-planet system is stable over long timescales.Comment: Accepted for publication in A&
Diaspirin-crosslinked hemoglobin reduces blood transfusion in noncardiac surgery: a multicenter, randomized, controlled, double-blinded trial.
UNLABELLED: In this randomized, prospective, double-blinded clinical trial, we sought to investigate whether diaspirin-crosslinked hemoglobin (DCLHb) can reduce the perioperative use of allogeneic blood transfusion. One-hundred-eighty-one elective surgical patients were enrolled at 19 clinical sites from 1996 to 1998. Selection criteria included anticipated transfusion of 2-4 blood units, aortic repair, and major joint or abdomino-pelvic surgery. Once a decision to transfuse had been made, patients received initially up to 3 250-mL infusions of 10% DCLHb (n = 92) or 3 U of packed red blood cells (PRBCs) (n = 89). DCLHb was infused during a 36-h perioperative window. On the day of surgery, 58 of 92 (64%; confidence interval [CI], 54%-74%) DCLHb-treated patients received no allogeneic PRBC transfusions. On Day 1, this number was 44 of 92 (48%; CI, 37%-58%) and decreased further until Day 7, when it was 21 of 92 (23%; CI, 15%-33%). During the 7-day period, 2 (1-4) units of PRBC per patient were used in the DCLHb group compared with 3 (2-4) units in the control patients (P = 0.002; medians and 25th and 75th percentiles). Mortality (4% and 3%, respectively) and incidence of suffering at least one serious adverse event (21% and 15%, respectively) were similar in DCLHb and PRBC groups. The incidence of jaundice, urinary side effects, and pancreatitis were more frequent in DCLHb patients. The study was terminated early because of safety concerns. Whereas the side-effect profile of modified hemoglobin solutions needs to be improved, our data show that hemoglobin solutions can be effective at reducing exposure to allogeneic blood for elective surgery.
IMPLICATIONS: In a randomized, double-blinded red blood cell controlled, multicenter trial, diaspirin-crosslinked hemoglobin spared allogeneic transfusion in 23% of patients undergoing elective noncardiac surgery. The observed side-effect profile indicates a need for improvement in hemoglobin development
Accretion-related properties of Herbig Ae/Be stars. Comparison with T Tauris
We look for trends relating the mass accretion rate (Macc) and the stellar
ages (t), spectral energy distributions (SEDs), and disk masses (Mdisk) for a
sample of 38 HAeBe stars, comparing them to analogous correlations found for
classical T Tauri stars. Our goal is to shed light on the timescale and
physical processes that drive evolution of intermediate-mass pre-main sequence
objects.
Macc shows a dissipation timescale \tau = 1.3^{+1.0}_{-0.5} Myr from an
exponential law fit, while a power law yields Macc(t) \propto t^{-\eta}, with
\eta = 1.8^{+1.4}_{-0.7}. This result is based on our whole HAeBe sample (1-6
Msun), but the accretion rate decline most probably depends on smaller stellar
mass bins. The near-IR excess is higher and starts at shorter wavelengths (J
and H bands) for the strongest accretors. Active and passive disks are roughly
divided by 2 x 10^{-7} Msun/yr. The mid-IR excess and the SED shape from the
Meeus et al. classification are not correlated with Macc. We find Macc \propto
Mdisk^{1.1 +- 0.3}. Most stars in our sample with signs of inner dust
dissipation typically show accretion rates ten times lower and disk masses
three times smaller than the remaining objects.
The trends relating Macc with the near-IR excess and Mdisk extend those for T
Tauri stars, and are consistent with viscous disk models. The differences in
the inner gas dissipation timescale, and the relative position of the stars
with signs of inner dust clearing in the Macc-Mdisk plane, could be suggesting
a slightly faster evolution, and that a different process - such as
photoevaporation - plays a more relevant role in dissipating disks in the HAeBe
regime compared to T Tauri stars. Our conclusions must consider the mismatch
between the disk mass estimates from mm fluxes and the disk mass estimates from
accretion, which we also find in HAeBe stars.Comment: 11 pages, 7 figures, 1 appendix. Accepted in A&
Further deep imaging of HR 7329 A (eta Tel A) and its brown dwarf companion B
About 4" south of the young A0-type star HR 7329, a faint companion candidate
was found by Lowrance et al. (2000). Its spectral type of M7-8 is consistent
with a young brown dwarf companion. Here, we report ten new astrometric imaging
observations of the pair HR 7329 A and B, obtained with the Hubble Space
Telescope and the Very Large Telescope, aimed at showing common proper motion
with high significance and possible orbital motion of B around A. With 11 yrs
of epoch difference between the first and our last image, we can reject by more
than 21 sigma that B would be a non-moving background object unrelated to A. We
detect no change in position angle and small or no change in separation (2.91
+/- 2.41 mas/yr), so that the orbit of HR 7329 B around A is inclined and/or
eccentric and/or the orbital motion is currently only in radial direction. If
HR 7329 B is responsible for the outer radius of the debris disk around HR 7329
A being 24 AU, and if HR 7329 B currently is at its apastron at 200 AU (4.2" at
47.7 pc), we determine its pericenter distance to be 71 AU, its semi-major axis
to be 136 AU, and its eccentricity to be e=0.47. From the magnitude differences
between HR 7329 A and B and the 2MASS magnitudes for the HR 7329 A+B system, we
can estimate the magnitudes of HR 7329 B (J=12.06+/-0.19, H=11.75+/-0.10,
Ks=11.6+/-0.1, L=11.1+/-0.2 mag) and then, with a few otherwise known
parameters, its luminosity and mass (20-50 Jupiter masses). In the deepest
images available, we did not detect any additional companion candidates up to
<=9", but determine upper limits in the planetary mass regime.Comment: 7 pages, 3 figures, accepted for publication in MNRA
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