76 research outputs found
The frequency and infrared brightness of circumstellar discs at white dwarfs
White dwarfs whose atmospheres are polluted by terrestrial-like planetary
debris have become a powerful and unique tool to study evolved planetary
systems. This paper presents results for an unbiased Spitzer IRAC search for
circumstellar dust orbiting a homogeneous and well-defined sample of 134 single
white dwarfs. The stars were selected without regard to atmospheric metal
content but were chosen to have 1) hydrogen rich atmospheres, 2) 17 000 K <
T_eff < 25 000 K and correspondingly young post main-sequence ages of
15-270Myr, and 3) sufficient far-ultraviolet brightness for a corresponding
Hubble Space Telescope COS Snapshot. Five white dwarfs were found to host an
infrared bright dust disc, three previously known, and two reported here for
the first time, yielding a nominal 3.7% of white dwarfs in this post-main
sequence age range with detectable circumstellar dust. Remarkably,
complementary HST observations indicate that a fraction of 27% show metals in
their photosphere that can only be explained with ongoing accretion from
circumstellar material, indicating that nearly 90% of discs escape detection in
the infrared, likely due to small emitting surface area. This paper also
presents the distribution of disc fractional luminosity as a function of
cooling age for all known dusty white dwarfs, suggesting possible disc
evolution scenarios and indicating an undetected population of circumstellar
discs.Comment: 17 pages, 5 figures and 4 tables. Accepted for publication in MNRA
Uniqueness and Non-uniqueness in the Einstein Constraints
The conformal thin sandwich (CTS) equations are a set of four of the Einstein
equations, which generalize the Laplace-Poisson equation of Newton's theory. We
examine numerically solutions of the CTS equations describing perturbed
Minkowski space, and find only one solution. However, we find {\em two}
distinct solutions, one even containing a black hole, when the lapse is
determined by a fifth elliptic equation through specification of the mean
curvature. While the relationship of the two systems and their solutions is a
fundamental property of general relativity, this fairly simple example of an
elliptic system with non-unique solutions is also of broader interest.Comment: 4 pages, 4 figures; abstract and introduction rewritte
Characterization of the Benchmark Binary NLTT 33370
We report the confirmation of the binary nature of the nearby, very low-mass
system NLTT 33370 with adaptive optics imaging and present resolved
near-infrared photometry and integrated light optical and near-infrared
spectroscopy to characterize the system. VLT-NaCo and LBTI-LMIRCam images show
significant orbital motion between 2013 February and 2013 April. Optical
spectra reveal weak, gravity sensitive alkali lines and strong lithium 6708
Angstrom absorption that indicate the system is younger than field age.
VLT-SINFONI near-IR spectra also show weak, gravity sensitive features and
spectral morphology that is consistent with other young, very low-mass dwarfs.
We combine the constraints from all age diagnostics to estimate a system age of
~30-200 Myr. The 1.2-4.7 micron spectral energy distribution of the components
point toward T_eff=3200 +/- 500 K and T_eff=3100 +/- 500 K for NLTT 33370 A and
B, respectively. The observed spectra, derived temperatures, and estimated age
combine to constrain the component spectral types to the range M6-M8.
Evolutionary models predict masses of 113 +/- 8 M_Jup and 106 +/- 7 M_Jup from
the estimated luminosities of the components. KPNO-Phoenix spectra allow us to
estimate the systemic radial velocity of the binary. The Galactic kinematics of
NLTT 33370AB are broadly consistent with other young stars in the Solar
neighborhood. However, definitive membership in a young, kinematic group cannot
be assigned at this time and further follow-up observations are necessary to
fully constrain the system's kinematics. The proximity, age, and late-spectral
type of this binary make it very novel and an ideal target for rapid, complete
orbit determination. The system is one of only a few model calibration
benchmarks at young ages and very low-masses.Comment: 25 pages, 3 tables, 13 figures, accepted for publication in The
Astrophysical Journa
Binarity of Transit Host Stars - Implications on Planetary Parameters
Straight-forward derivation of planetary parameters can only be achieved in
transiting planetary systems. However, planetary attributes such as radius and
mass strongly depend on stellar host parameters. Discovering a transit host
star to be multiple leads to a necessary revision of the derived stellar and
planetary parameters. Based on our observations of 14 transiting exoplanet
hosts, we derive parameters of the individual components of three transit host
stars (WASP-2, TrES-2, and TrES-4) which we detected to be binaries. Two of
these have not been known to be multiple before. Parameters of the
corresponding exoplanets are revised. High-resolution "Lucky Imaging" with
AstraLux at the 2.2m Calar Alto telescope provided near diffraction limited
images in i' and z' passbands. These results have been combined with existing
planetary data in order to recalibrate planetary attributes. Despite the
faintness (delta mag ~ 4) of the discovered stellar companions to TrES-2,
TrES-4, and WASP-2, light-curve deduced parameters change by up to more than
1sigma. We discuss a possible relation between binary separation and planetary
properties, which - if confirmed - could hint at the influence of binarity on
the planet formation process.Comment: 9 pages, 3 Figures. Accepted by A&
Heat Treatment Process Energy Efficient Design and Optimisation
AbstractEnergy efficiency optimization ICT (Information and Communication Technology) solutions are currently being developed for energy saving in buildings and, to some ex-tent, also for the manufacturing domain. This paper describes an approach and ICT tool developed for manufacturing process energy efficiency optimization, in particular focused on the heat treatment process of steel casting parts. Traditionally this manufacturing process is designed based on experts experience selecting a predefined temperature-time curve provided customer specifications for the resulting steel parts. However this curve can actually be optimised in terms of energy consumption while keeping required mechanical properties. This improved design is what the tool here described provides, using knowledge based approach for process design and multivariate optimisation and simulation techniques for process optimisation
Lucky Imaging survey for southern M dwarf binaries
While M dwarfs are the most abundant stars in the Milky Way, there is still
large uncertainty about their basic physical properties (mass, luminosity,
radius, etc.) as well as their formation environment. Precise knowledge of
multiplicity characteristics and how they change in this transitional mass
region, between Sun-like stars on the one side and very low mass stars and
brown dwarfs on the other, provide constraints on low mass star and brown dwarf
formation. In the largest M dwarf binary survey to date, we search for
companions to active, and thus preferentially young, M dwarfs in the solar
neighbourhood. We study their binary/multiple properties, such as the
multiplicity frequency and distributions of mass ratio and separation, and
identify short period visual binaries, for which orbital parameters and hence
dynamical mass estimates can be derived in the near future. The observations
are carried out in the SDSS i' and z' band using the Lucky Imaging camera
AstraLux Sur at the ESO 3.5 m New Technology Telescope. In the first part of
the survey, we observed 124 M dwarfs of integrated spectral types M0-M6 and
identified 34 new and 17 previously known companions to 44 stars. We derived
relative astrometry and component photometry for these systems. More than half
of the binaries have separations smaller than 1 arcsec and would have been
missed in a simply seeing-limited survey. Correcting our sample for selection
effects yields a multiplicity fraction of 32+/-6% for 108 M dwarfs within 52 pc
and with angular separations of 0.1-6.0 arcsec, corresponding to projected
separation 3-180 AU at median distance 30 pc. Compared to early-type M dwarfs
(M>0.3M_Sun), later type (and hence lower mass) M dwarf binaries appear to have
closer separations, and more similar masses.Comment: 18 pages, 9 figures. Minor corrections and changes. Revised to match
accepted A&A versio
Recommended from our members
Characterization of the Benchmark Binary Nltt 33370
We report the confirmation of the binary nature of the nearby, very low-mass system NLTT 33370 with adaptive optics imaging and present resolved near-infrared photometry and integrated light optical and near-infrared spectroscopy to characterize the system. VLT-NaCo and LBTI-LMIRCam images show significant orbital motion between 2013 February and 2013 April. Optical spectra reveal weak, gravity sensitive alkali lines and strong lithium 6708 ËA absorption that indicate the system is younger than field age. VLT-SINFONI near-IR spectra also show weak, gravity sensitive features and spectral morphology that is consistent with other young, very low-mass dwarfs. We combine the constraints from all age diagnostics to estimate a system age of âŒ30-200 Myr. The 1.2-4.7 ”m spectral energy distribution of the components point toward Teff = 3200 ± 500 K and Teff = 3100 ± 500 K for NLTT 33370 A and B, respectively. The observed spectra, derived temperatures, and estimated age combine to constrain the component spectral types to the range M6-M8. Evolutionary models predict masses of 113 ±8 MJup and 106±7 MJup from the estimated luminosities of the components. KPNO-Phoenix spectra allow us to estimate the systemic radial velocity of the binary. The Galactic kinematics of NLTT 33370AB are broadly consistent with other young stars in the Solar neighborhood. However, definitive membership in a young, kinematic group cannot be assigned at this time and further follow-up observations are necessary to fully constrain the systemâs kinematics. The proximity,
age, and late-spectral type of this binary make it very novel and an ideal target for rapid, complete orbit determination. The system is one of only a few model calibration benchmarks at young ages and very low-masses.Astronom
Differential Expression of Alpha 4 Integrins on Effector Memory T Helper Cells during Bordetella Infections. Delayed Responses in Bordetella pertussis
Bordetella pertussis (B. pertussis) is the causative agent of whooping cough, a respiratory disease that is reemerging worldwide. Mechanisms of selective lymphocyte trafficking to the airways are likely to be critical in the immune response to this pathogen. We compared murine infection by B. pertussis, B. parapertussis, and a pertussis toxin-deleted B. pertussis mutant (BpÎPTX) to test the hypothesis that effector memory T-helper cells (emTh) display an altered pattern of trafficking receptor expression in B. pertussis infection due to a defect in imprinting. Increased cell recruitment to the lungs at 5 days post infection (p.i.) with B. parapertussis, and to a lesser extent with BpÎPTX, coincided with an increased frequency of circulating emTh cells expressing the mucosal-associated trafficking receptors α4ÎČ7 and α4ÎČ1 while a reduced population of these cells was observed in B. pertussis infection. These cells were highly evident in the blood and lungs in B. pertussis infection only at 25 days p.i. when B. parapertussis and BpÎPTX infections were resolved. Although at 5 days p.i., an equally high percentage of lung dendritic cells (DCs) from all infections expressed maturation markers, this expression persisted only in B. pertussis infection at 25 days p.i. Furthermore, at 5 days p.i with B. pertussis, lung DCs migration to draining lymph nodes may be compromised as evidenced by decreased frequency of CCR7+ DCs, inhibited CCR7-mediated in vitro migration, and fewer DCs in lung draining lymph nodes. Lastly, a reduced frequency of allogeneic CD4+ cells expressing α4ÎČ1 was detected following co-culture with lung DCs from B. pertussis-infected mice, suggesting a defect in DC imprinting in comparison to the other infection groups. The findings in this study suggest that B. pertussis may interfere with imprinting of lung-associated trafficking receptors on T lymphocytes leading to extended survival in the host and a prolonged course of disease
Dynamical masses of M-dwarf binaries in young moving groups:I. The case of TWA 22 and GJ 2060
Evolutionary models are widely used to infer the mass of stars, brown dwarfs,
and giant planets. Their predictions are thought to be less reliable at young
ages ( 200 Myr) and in the low-mass regime (). GJ
2060 AB and TWA 22 AB are two rare astrometric M-dwarf binaries respectively
members of the AB Doradus and Beta Pictoris moving groups. As their dynamical
mass can be measured within a few years, they can be used to calibrate the
evolutionary tracks and set new constraints on the age of young moving groups.
We find a total mass of for TWA 22. That mass
is in good agreement with model predictions at the age of the Beta Pic moving
group. We obtain a total mass of for GJ
2060. We estimate a spectral type of M,
dex, and K
for GJ 2060 A. The B component is a M dwarf with
dex and K.
The dynamical mass of GJ 2060 AB is inconsistent with the most recent models
predictions (BCAH15, PARSEC) for an ABDor age in the range 50-150 Myr. It is 10
to 20\% (1-2 sigma, depending on the assumed age) above the models predictions,
corresponding to an underestimation of to .
Coevality suggests a young age for the system ( 50 Myr) according to most
evolutionary models. TWA 22 validates the predictions of recent evolutionary
tracks at 20 Myr. On the other hand, we evidence a 1-2 sigma mismatch
between the predicted and observed mass of GJ 2060 AB. This slight departure
may indicate that one of the star hosts a tight companion. Alternatively, this
would confirm the models tendency to underestimate the mass of young low-mass
stars.Comment: Accepted for publication in A&A. 26 pages, 22 figures, 12 table
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