7 research outputs found
Dynamical Masses and Ages of Sirius-like Systems
We measure precise orbits and dynamical masses and derive age constraints for
six confirmed and one candidate Sirius-like systems, including the Hyades
member HD 27483. Our orbital analysis incorporates radial velocities, relative
astrometry, and Hipparcos-Gaia astrometric accelerations. We constrain the
main-sequence lifetime of a white dwarf's progenitor from the remnant's
dynamical mass and semi-empirical initial-final mass relations and infer the
cooling age from mass and effective temperature. We present new relative
astrometry of HD 27483 B from Keck/NIRC2 observations and archival HST data,
and obtain the first dynamical mass of ,
and an age of Myr, consistent with previous age estimates
of Hyades. We also measure precise dynamical masses for HD 114174 B ( ) and HD 169889 B ( ),
but their age precisions are limited by their uncertain temperatures. For HD
27786 B, the unusually small mass of suggests a
history of rapid mass loss, possibly due to binary interaction in its
progenitor's AGB phase. The orbits of HD 118475 and HD 136138 from our RV
fitting are overall in good agreement with Gaia DR3 astrometric two-body
solutions, despite moderate differences in the eccentricity and period of HD
136138. The mass of for HD 118475 B and
a speckle imaging non-detection confirms that the companion is a white dwarf.
Our analysis shows examples of a rich number of precise WD dynamical mass
measurements enabled by Gaia DR3 and later releases, which will improve
empirical calibrations of the white dwarf initial-final mass relation.Comment: 21 pages, 7 figures. Submitted to MNRA
The channel capacity of the ribosome
Translation is one of the most fundamental processes in the biological cell.
Because of the central role that translation plays across all domains of life,
the enzyme that carries out this process, the ribosome, is required to process
information with high accuracy. This accuracy often approaches values near
unity experimentally. In this paper, we model the ribosome as an information
channel and demonstrate mathematically that this biological machine has
information-processing capabilities that have not been recognized previously.
In particular, we calculate bounds on the ribosome's theoretical Shannon
capacity and numerically approximate this capacity. Finally, by incorporating
estimates on the ribosome's operation time, we show that the ribosome operates
at speeds safely below its capacity, allowing the ribosome to process
information with an arbitrary degree of error. Our results show that the
ribosome achieves a high accuracy in line with purely information-theoretic
means.Comment: 7 pages, 5 figure
Surveying Nearby Brown Dwarfs with HGCA: Direct Imaging Discovery of a Faint, High-Mass Brown Dwarf Orbiting HD 176535 A
Brown dwarfs with well-measured masses, ages and luminosities provide direct
benchmark tests of substellar formation and evolutionary models. We report the
first results from a direct imaging survey aiming to find and characterize
substellar companions to nearby accelerating stars with the assistance of the
Hipparcos-Gaia Catalog of Accelerations (HGCA). In this paper, we present a
joint high-contrast imaging and astrometric discovery of a substellar companion
to HD 176535 A, a K3.5V main-sequence star aged approximately
Gyrs at a distance of pc. In advance of
our high-contrast imaging observations, we combined precision HARPS RVs and
HGCA astrometry to predict the potential companion's location and mass. We
thereafter acquired two nights of KeckAO/NIRC2 direct imaging observations in
the band, which revealed a companion with a contrast of mag at a projected separation of 0.\!\!''35
(13 AU) from the host star. We revise our orbital fit by incorporating
our dual-epoch relative astrometry using the open-source MCMC orbit fitting
code . HD 176535 B is a new benchmark dwarf useful for constraining
the evolutionary and atmospheric models of high-mass brown dwarfs. We found a
luminosity of and a model-dependent
effective temperature of K for HD 176535 B. Our dynamical mass
suggests that some substellar evolutionary models may be underestimating
luminosity for high-mass T dwarfs. Given its angular separation and luminosity,
HD 176535 B would make a promising candidate for Aperture Masking
Interferometry with JWST and GRAVITY/KPIC, and further spectroscopic
characterization with instruments like the CHARIS/SCExAO/Subaru integral field
spectrograph