689 research outputs found
Orbits and Masses in the multiple system LHS 1070
We present a study of the orbits of the triple system LHS1070, with the aim
to determine individual masses of its components.
Sixteen new relative astrometric positions of the three components in the K
band were obtained with NACO at the VLT, Omega CASS at the 3.5m telescope on
Calar Alto, and other high-spatial-resolution instruments. We combine them with
data from the literature and fit orbit models to the dataset. We derive an
improved fit for the orbit of LHS1070B and C around each other, and an estimate
for the orbit of B and C around A.
The orbits are nearly coplanar, with a misalignment angle of less than
10{\deg}. The masses of the three components are M_A = 0.13 - 0.16 Msun, M_B =
0.077+/-0.005 Msun, and M_C = 0.071+/-0.004 Msun. Therefore, LHS1070C is
certainly, and LHS1070B probably a brown dwarf. Comparison with theoretical
isochrones shows that LHS1070A is either fainter or more massive than expected.
One possible explanation would be that it is a binary. However, the close
companion reported previously could not be confirmed.Comment: 9 pages, 8 figures, accepted by Astronomy and Astrophysic
Sistemas de trabajo y estructura social: una comparación República Federal de Alemania - España.
Sin resume
Orbital motion in T Tauri binary systems
Using speckle-interferometry we have carried out repeated measurements of
relative positions for the components of 34 T Tauri binary systems. The
projected separation of these components is low enough that orbital motion is
expected to be observable within a few years. In most cases orbital motion has
indeed been detected. The observational data is discussed in a manner similar
to Ghez et al. (1995). However, we extend their study to a larger number of
objects and a much longer timespan. The database presented in this paper is
valuable for future visible orbit determinations. It will yield empirical
masses for T Tauri stars that now are only poorly known. The available data is
however not sufficient to do this at the present time. Instead, we use short
series of orbital data and statistical distributions of orbital parameters to
derive an average system mass that is independent of theoretical assumptions
about the physics of PMS stars. For our sample this mass is 2.0 solar masses
and thus in the order of magnitude one expects for the mass sum of two T Tauri
stars. It is also comparable to mass estimates obtained for the same systems
using theoretical PMS evolutionary models.Comment: Accepted by Astronomy and Astrophysic
Mid-infrared interferometry with K band fringe-tracking I. The VLTI MIDI+FSU experiment
Context: A turbulent atmosphere causes atmospheric piston variations leading
to rapid changes in the optical path difference of an interferometer, which
causes correlated flux losses. This leads to decreased sensitivity and accuracy
in the correlated flux measurement. Aims: To stabilize the N band
interferometric signal in MIDI (MID-infrared Interferometric instrument), we
use an external fringe tracker working in K band, the so-called FSU-A (fringe
sensor unit) of the PRIMA (Phase-Referenced Imaging and Micro-arcsecond
Astrometry) facility at VLTI. We present measurements obtained using the newly
commissioned and publicly offered MIDI+FSU-A mode. A first characterization of
the fringe-tracking performance and resulting gains in the N band are
presented. In addition, we demonstrate the possibility of using the FSU-A to
measure visibilities in the K band. Methods: We analyzed FSU-A fringe track
data of 43 individual observations covering different baselines and object K
band magnitudes with respect to the fringe-tracking performance. The N band
group delay and phase delay values could be predicted by computing the relative
change in the differential water vapor column density from FSU-A data.
Visibility measurements in the K band were carried out using a scanning mode of
the FSU-A. Results: Using the FSU-A K band group delay and phase delay
measurements, we were able to predict the corresponding N band values with high
accuracy with residuals of less than 1 micrometer. This allows the coherent
integration of the MIDI fringes of faint or resolved N band targets,
respectively. With that method we could decrease the detection limit of
correlated fluxes of MIDI down to 0.5 Jy (vs. 5 Jy without FSU-A) and 0.05 Jy
(vs. 0.2 Jy without FSU-A) using the ATs and UTs, respectively. The K band
visibilities could be measured with a precision down to ~2%.Comment: 11 pages, 13 figures, Accepted for publication in A&
Visual orbit for the low-mass binary Gliese 22 AC from speckle interferometry
Based on 14 data points obtained with near-infrared speckle interferometry
and covering an almost entire revolution, we present a first visual orbit for
the low-mass binary system Gliese 22 AC. The quality of the orbit is largely
improved with respect to previous astrometric solutions. The dynamical system
mass is 0.592 +- 0.065 solar masses, where the largest part of the error is due
to the Hipparcos parallax. A comparison of this dynamical mass with
mass-luminosity relations on the lower main sequence and theoretical
evolutionary models for low-mass objects shows that both probably underestimate
the masses of M dwarfs. A mass estimate for the companion Gliese 22 C indicates
that this object is a very low-mass star with a mass close to the hydrogen
burning mass limit.Comment: Accepted by Astronomy and Astrophysics, 6 pages, 2 figure
Spatially resolved mid-infrared observations of the triple system T Tauri
To enhance our knowledge of the characteristics and distribution of the
circumstellar dust associated with the individual components of the young
hierarchical triple system T Tau, observations in the N-band with MIDI at the
VLTI were performed. Our study is based on both the interferometric and the
spectrophotometric measurements and is supplemented by new visual and infrared
photometry. Also, the phases were investigated to determine the dominating
mid-infrared source in the close southern binary. The data were fit with the
help of a sophisticated physical disc model. This model utilises the radiative
transfer code MC3D that is based on the Monte-Carlo method. Extended
mid-infrared emission is found around all three components of the system.
Simultaneous fits to the photometric and interferometric data confirm the
picture of an almost face-on circumstellar disc around T Tau N. Towards this
star, the silicate band is seen in emission. This emission feature is used to
model the dust content of the circumstellar disc. Clear signs of dust
processing are found. Towards T Tau S, the silicate band is seen in absorption.
This absorption is strongly pronounced towards the infrared companion T Tau Sa
as can be seen from the first individual N-band spectra for the two southern
components. Our fits support the previous suggestion that an almost edge-on
disc is present around T Tau Sa. This disc is thus misaligned with respect to
the circumstellar disc around T Tau N. The interferometric data indicate that
the disc around T Tau Sa is oriented in the north-south direction, which
favours this source as launching site for the east-western jet. We further
determine from the interferometric data the relative positions of the
components of the southern binary.Comment: 24 pages, 19 figures, accepted for publication in A&
Electrically Switchable Photonic Molecule Laser
We have studied the coherent intercavity coupling of the evanescent fields of
the whispering gallery modes of two terahertz quantum-cascade lasers
implemented as microdisk cavities. The electrically pumped single-mode
operating microcavities allow to electrically control the coherent mode
coupling for proximity distances of the cavities up to 30-40 \mu\m. The optical
emission of the strongest coupled photonic molecule can be perfectly switched
by the electrical modulation of only one of the coupled microdisks. The
threshold characteristics of the strongest coupled photonic molecule
demonstrates the linear dependence of the gain of a quantum-cascade laser on
the applied electric field.Comment: 4 pages, 4 figure
Size- and density-controlled deposition of Ag nanoparticle films by a novel low-temperature spray chemical vapour deposition method—research into mechanism, particle growth and optical simulation
Ag nanoparticles have attracted interest for plasmonic absorption enhancement of solar cells. For this purpose, well-defined particle sizes and densities as well as very low deposition temperatures are required. Thus, we report here a new spray chemical vapour deposition method for producing Ag NP films with independent size and density control at substrate temperatures even below 100 °C, which is much lower than for many other techniques. This method can be used on different substrates to deposit Ag NP films. It is a reproducible, low-cost process which uses trimethylphosphine (hexafluoroacetylacetonato) silver as a precursor in alcoholic solution. By systematic variation of deposition parameters and classic experiments, mechanisms of particle growth and of deposition processes as well as the low decomposition temperature of the precursor could be explained. Using the 3D finite element method, absorption spectra of selected samples were simulated, which fitted well with the measured results. Hence, further applications of such Ag NP films for generating plasmonic near field can be predicted by the simulation
Mass ratios of the components in T Tauri binary systems and implications for multiple star formation
Using near-infrared speckle interferometry we have obtained resolved
JHK-photometry for the components of 58 young binary systems. From these
measurements, combined with other data taken from literature, we derive masses
and particularly mass ratios of the components. We use the J-magnitude as an
indicator for the stellar luminosity and assign the optical spectral type of
the system to the primary. On the assumption that the components within a
binary are coeval we can then place also the secondaries into the HRD and
derive masses and mass ratios for both components by comparison with different
sets of current theoretical pre-main sequence evolutionary tracks. The
resulting distribution of mass ratios is comparatively flat for M(2)/M(1) >
0.2, but depends on assumed evolutionary tracks. The mass ratio is neither
correlated with the primary's mass or the components' separation. These
findings are in line with the assumption that for most multiple systems in T
associations the components' masses are principally determined by fragmentation
during formation and not by the following accretion processes. Only very few
unusually red objects were newly found among the detected companions. This
finding shows that the observed overabundance of binaries in the Taurus-Auriga
association compared to nearby main sequence stars should be real and not the
outcome of observational biases related to infrared observing.Comment: accepted by Astronomy and Astrophysics, contains extensive tables and
figures that will only be published electronically at CDS (in total: 34
pages, 11 figures
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