914 research outputs found
Atmospheric Analysis of the M/L- and M/T-Dwarf Binary Systems LHS 102 and Gliese 229
We present 0.9-2.5um spectroscopy with R~800 and 1.12-1.22um spectroscopy
with R~5800 for the M dwarfs Gl 229A and LHS 102A, and for the L dwarf LHS
102B. We also report IZJHKL' photometry for both components of the LHS 102
system, and L' photometry for Gl 229A. The data are combined with previously
published spectroscopy and photometry to produce flux distributions for each
component of the kinematically old disk M/L-dwarf binary system LHS 102 and the
kinematically young disk M/T-dwarf binary system Gliese 229. The data are
analyzed using synthetic spectra generated by the latest "AMES-dusty" and
"AMES-cond" models by Allard & Hauschildt. Although the models are not able to
reproduce the overall slope of the infrared flux distribution of the L dwarf,
most likely due to the treatment of dust in the photosphere, the data for the M
dwarfs and the T dwarf are well matched. We find that the Gl 229 system is
metal-poor despite having kinematics of the young disk, and that the LHS 102
system has solar metallicity. The observed luminosities and derived
temperatures and gravities are consistent with evolutionary model predictions
if the Gl 229 system is very young (age ~30 Myr) with masses (A,B) of
(0.38,>0.007)M(sun), and the LHS 102 system is older, aged 1-10 Gyr with masses
(A,B) of (0.19,0.07)M(sun).Comment: 29 pages incl. 13 figures and 5 tables;; accepted for publication in
MNRA
Spectral Types of Planetary Host Star Candidates: Two New Transiting Planets?
Recently, 46 low-luminosity object transits were reported from the Optical
Gravitational Lensing Experiment. Our follow-up spectroscopy of the 16 most
promising candidates provides a spectral classification of the primary.
Together with the radius ratio from the transit measurements, we derived the
radii of the low-luminosity companions. This allows to examine the possible
sub-stellar nature of these objects. Fourteen of them can be clearly identified
as low-mass stars. Two objects, OGLE-TR-03 and OGLE-TR-10 have companions with
radii of 0.15 R_sun which is very similar to the radius of the transiting
planet HD209458B. The planetary nature of these two objects should therefore be
confirmed by dynamical mass determinations.Comment: 4 pages, 3 figures, accepted for publication by A&A Letter
Spectral Energy Distributions for Disk and Halo M--Dwarfs
We have obtained infrared (1 to 2.5 micron) spectroscopy for 42 halo and disk
dwarfs with spectral type M1 to M6.5. These data are compared to synthetic
spectra generated by the latest model atmospheres of Allard & Hauschildt.
Photospheric parameters metallicity, effective temperature and radius are
determined for the sample. We find good agreement between observation and
theory except for known problems due to incomplete molecular data for metal
hydrides and water. The metal-poor M subdwarfs are well matched by the models
as oxide opacity sources are less important in this case. The derived effective
temperatures for the sample range from 3600K to 2600K; at these temperatures
grain formation and extinction are not significant in the photosphere. The
derived metallicities range from solar to one-tenth solar. The radii and
effective temperatures derived agree well with recent models of low mass stars.Comment: 24 pages including 13 figures, 4 Tables; accepted by Ap
Spectral Modeling of SNe Ia Near Maximum Light: Probing the Characteristics of Hydro Models
We have performed detailed NLTE spectral synthesis modeling of 2 types of 1-D
hydro models: the very highly parameterized deflagration model W7, and two
delayed detonation models. We find that overall both models do about equally
well at fitting well observed SNe Ia near to maximum light. However, the Si II
6150 feature of W7 is systematically too fast, whereas for the delayed
detonation models it is also somewhat too fast, but significantly better than
that of W7. We find that a parameterized mixed model does the best job of
reproducing the Si II 6150 line near maximum light and we study the differences
in the models that lead to better fits to normal SNe Ia. We discuss what is
required of a hydro model to fit the spectra of observed SNe Ia near maximum
light.Comment: 29 pages, 14 figures, ApJ, in pres
Experimental Investigation of Phase Equilibria in the Ti—Al—Zr System at 1000–1300 °C
Four partial isothermal sections of the Ti—Al—Zr system up to 60 at. % Al and 30 at. % Zr were experimentally established between 1000–1300 °C. Six heat-treated alloys were analysed by scanning electron microscopy, transmission electron microscopy, electron probe microanalysis, conventional and high-energy X-ray diffraction, and differential thermal analysis. Phase equilibria were determined between B2-ordered (β0), βTi, Zr, αTi, Ti3Al, TiAl, and ZrAl2.This work is part of the ADVANCE project which has received funding from the Clean Sky 2 Joint Undertaking under the European Union's Horizon 2020 research and innovation programme under grant agreement No 820647
Solid-Solid Phase Transformations and Their Kinetics in Ti–Al–Nb Alloys
The application of light-weight intermetallic materials to address the growing interest and necessity for reduction of CO2 emissions and environmental concerns has led to intensive research into TiAl-based alloy systems. However, the knowledge about phase relations and transformations is still very incomplete. Therefore, the results presented here from systematic thermal analyses of phase transformations in 12 ternary Ti-Al-Nb alloys and one binary Ti-Al measured with 4–5 different heating rates (0.8 to 10 °C/min) give insights in the kinetics of the second-order type reaction of ordered (βTi)o to disordered (βTi) as well as the three first-order type transformations from Ti3Al to (αTi), ωo (Ti4NbAl3) to (βTi)o, and O (Ti2NbAl) to (βTi)o. The sometimes-strong heating rate dependence of the transformation temperatures is found to vary systematically in dependence on the complexity of the transformations. The dependence on heating rate is nonlinear in all cases and can be well described by a model for solid-solid phase transformations reported in the literature, which allows the determination of the equilibrium transformation temperatures
Phase Equilibria in the Ti-Rich Part of the Ti–Al–Nb System-Part II: High-Temperature Phase Equilibria Between 1000 and 1300 °C
Molecular line opacity of LiCl in the mid-infrared spectra of brown dwarfs
We present a complete line list for the X 1Sigma+ electronic ground state of
LiCl computed using fully quantum-mechanical techniques. This list includes
transition energies and oscillator strengths in the spectral region
0.3-39,640.7 cm-1 for all allowed rovibrational transitions in absorption
within the electronic ground state. The calculations were performed using an
accurate hybrid potential constructed from a spectral inversion fit of
experimental data and from recent multi-reference single- and double-excitation
configuration interaction calculations. The line list was incorporated into the
stellar atmosphere code PHOENIX to compute spectra for a range of young to old
T dwarf models. The possibility of observing a signature of LiCl in absorption
near 15.8 microns is addressed and the proposal to use this feature to estimate
the total lithium elemental abundance for these cool objects is discussed.Comment: 8 pages, 2 figures, 1 table. Accepted for publication in ApJ 613,
Sept. 20 200
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