710 research outputs found
Identification of WISE J000100.45+065259.6 as an M8.5+T5 Spectral Binary Candidate
[not part of RNAAS note] We report the discovery of WISE J000100.45+065259.6
as a very low mass star/brown dwarf spectral binary candidate, on the basis of
low resolution near-infrared spectroscopy obtained with IRTF/SpeX.
Decomposition of the spectrum indicates component types of M8.5+T5 with a
predicted = 3.5. As the majority of confirmed spectral binary
candidates to date are very closely-separated systems ( 3 AU;
15~yr), this source may provide mass measurements across the
hydrogen burning limit within the decade.Comment: 3 pages, 1 figure, accepted to Research Notes of the AA
Single and Composite Hot Subdwarf Stars in the Light of 2MASS Photometry
Utilizing the Two Micron All Sky Survey (2MASS) Second Incremental Data
Release Catalog, we have retrieved near-IR magnitudes for several hundred hot
subdwarfs (sdO and sdB stars) drawn from the "Catalogue of Spectroscopically
Identified Hot Subdwarfs" (Kilkenny, Heber, & Drilling 1988, 1992). This sample
size greatly exceeds that of previous studies of hot subdwarfs. Examining 2MASS
photometry alone or in combination with visual photometry (Johnson BV or
Stromgren uvby) available in the literature, we show that it is possible to
identify hot subdwarf stars that exhibit atypically red IR colors that can be
attributed to the presence of an unresolved late type companion. Utilizing this
large sample, we attempt for the first time to define an approximately volume
limited sample of hot subdwarfs. We discuss the considerations, biases, and
difficulties in defining such a sample.
We find that, of the hot subdwarfs in Kilkenny et al., about 40% in a
magnitude limited sample have colors that are consistent with the presence of
an unresolved late type companion. Binary stars are over-represented in a
magnitude limited sample. In an approximately volume limited sample the
fraction of composite-color binaries is about 30%.Comment: to appear in Sept 2003 AJ, 41 pages total, 12 figures, 2 tables are
truncated (full tables to appear in electronic journal or available by
request
Radial velocities and kinematic ages of nearby T dwarfs from Keck/NIRSPEC high-resolution spectroscopy
Stars and planetary system
The Perkins INfrared Exosatellite Survey (PINES) II. Transit Candidates and Implications for Planet Occurrence around L and T Dwarfs
We describe a new transit detection algorithm designed to detect single
transit events in discontinuous Perkins INfrared Exosatellite Survey (PINES)
observations of L and T dwarfs. We use this algorithm to search for transits in
131 PINES light curves and identify two transit candidates: 2MASS
J18212815+1414010 (2MASS J1821+1414) and 2MASS J08350622+1953050 (2MASS
J0835+1953). We disfavor 2MASS J1821+1414 as a genuine transit candidate due to
the known variability properties of the source. We cannot rule out the
planetary nature of 2MASS J0835+1953's candidate event and perform follow-up
observations in an attempt to recover a second transit. A repeat event has yet
to be observed, but these observations suggest that target variability is an
unlikely cause of the candidate transit. We perform a Markov chain Monte Carlo
simulation of the light curve and estimate a planet radius ranging from
to , depending on the
host's age. Finally, we perform an injection and recovery simulation on our
light curve sample. We inject planets into our data using measured M dwarf
planet occurrence rates and attempt to recover them using our transit search
algorithm. Our detection rates suggest that, assuming M dwarf planet occurrence
rates, we should have roughly a 1 chance of detecting a candidate that
could cause the transit depth we observe for 2MASS J0835+1953. If 2MASS
J0835+1953 b is confirmed, it would suggest an enhancement in the occurrence of
short-period planets around L and T dwarfs in comparison to M dwarfs, which
would challenge predictions from planet formation models.Comment: 23 pages, 15 figures, accepted to A
Fluctuations of elastic interfaces in fluids: Theory and simulation
We study the dynamics of elastic interfaces-membranes-immersed in thermally
excited fluids. The work contains three components: the development of a
numerical method, a purely theoretical approach, and numerical simulation. In
developing a numerical method, we first discuss the dynamical coupling between
the interface and the surrounding fluids. An argument is then presented that
generalizes the single-relaxation time lattice-Boltzmann method for the
simulation of hydrodynamic interfaces to include the elastic properties of the
boundary. The implementation of the new method is outlined and it is tested by
simulating the static behavior of spherical bubbles and the dynamics of bending
waves. By means of the fluctuation-dissipation theorem we recover analytically
the equilibrium frequency power spectrum of thermally fluctuating membranes and
the correlation function of the excitations. Also, the non-equilibrium scaling
properties of the membrane roughening are deduced, leading us to formulate a
scaling law describing the interface growth, W^2(L,T)=L^3 g[t/L^(5/2)], where
W, L and T are the width of the interface, the linear size of the system and
the temperature respectively, and g is a scaling function. Finally, the
phenomenology of thermally fluctuating membranes is simulated and the frequency
power spectrum is recovered, confirming the decay of the correlation function
of the fluctuations. As a further numerical study of fluctuating elastic
interfaces, the non-equilibrium regime is reproduced by initializing the system
as an interface immersed in thermally pre-excited fluids.Comment: 15 pages, 11 figure
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