19 research outputs found
Limits on the Mass and Initial Entropy of 51 Eri b from Gaia EDR3 Astrometry
51 Eri b is one of the only young planets consistent with a wide range of
possible initial entropy states, including the cold-start scenario associated
with some models of planet formation by core accretion. The most direct way to
constrain the initial entropy of a planet is by measuring its luminosity and
mass at a sufficiently young age that the initial conditions still matter. We
present the tightest upper limit on 51 Eri b's mass yet (M < 11 Mjup at
2) using a cross-calibration of Hipparcos and Gaia EDR3 astrometry and
the orbit-fitting code orvara. We also reassess its luminosity using a direct,
photometric approach, finding log(Lbol/Lsun) = -5.50.2 dex. Combining this
luminosity with the 243 Myr age of the Pic moving group, of which
51 Eri is a member, we derive mass distributions from a grid of evolutionary
models that spans a wide range of initial entropies. We find that 51 Eri b is
inconsistent with the coldest-start scenarios, requiring an initial entropy of
>8 /baryon at 97% confidence. This result represents the first
observational constraint on the initial entropy of a potentially cold-start
planet, and it continues the trend of dynamical masses for directly imaged
planets pointing to warm- or hot-start formation scenarios.Comment: Accepted for publication in MNRAS (9 pages, 6 figures
The First Dynamical Mass Measurement in the HR 8799 System
HR 8799 hosts four directly imaged giant planets, but none has a mass
measured from first principles. We present the first dynamical mass measurement
in this planetary system, finding that the innermost planet HR~8799~e has a
mass of . This mass results from combining
the well-characterized orbits of all four planets with a new astrometric
acceleration detection (5) from the Gaia EDR3 version of the
Hipparcos-Gaia Catalog of Accelerations. We find with 95\% confidence that
HR~8799~e is below , the deuterium-fusing mass limit. We
derive a hot-start cooling age of \,Myr for HR~8799~e that
agrees well with its hypothesized membership in the Columba association but is
also consistent with an alternative suggested membership in the
~Pictoris moving group. We exclude the presence of any additional
5- planets interior to HR~8799~e with semi-major axes
between 3-16\,au. We provide proper motion anomalies and a matrix
equation to solve for the mass of any of the planets of HR~8799 using only mass
ratios between the planets.Comment: Accepted to ApJ Letter
htof::A New Open-source Tool for Analyzing Hipparcos, Gaia, and Future Astrometric Missions
We present htof, an open-source tool for interpreting and fitting the
intermediate astrometric data (IAD) from both the 1997 and 2007 reductions of
Hipparcos, the scanning-law of Gaia, and future missions such as the Nancy
Grace Roman Space Telescope (NGRST). htof solves for the astrometric parameters
of any system for any arbitrary combination of absolute astrometric missions.
In preparation for later Gaia data releases, htof supports arbitrarily
high-order astrometric solutions (e.g. five-, seven-, nine-parameter fits).
Using htof, we find that the IAD of 6617 sources in Hipparcos 2007 might have
been affected by a data corruption issue. htof integrates an ad-hoc correction
that reconciles the IAD of these sources with their published catalog
solutions. We developed htof to study masses and orbital parameters of
sub-stellar companions, and we outline its implementation in one orbit fitting
code (orvara, https://github.com/t-brandt/orvara). We use htof to predict a
range of hypothetical additional planets in the ~Pic system, which could
be detected by coupling NGRST astrometry with Gaia and Hipparcos. htof is pip
installable and available at https://github.com/gmbrandt/htof .Comment: Accepted to AJ. References updated in version 2. The Hipparcos 2007
Re-reduction Java Tool Intermediate Astrometric Data are available at , via
the "zip file" link at https://www.cosmos.esa.int/web/hipparcos/hipparcos-2 :
"...human readable version of the IAD of the Java tool in a zip file
[warning: ~350 MB]...
orvara::An Efficient Code to Fit Orbits using Radial Velocity, Absolute, and/or Relative Astrometry
We present an open-source Python package, Orbits from Radial Velocity,
Absolute, and/or Relative Astrometry (orvara), to fit Keplerian orbits to any
combination of radial velocity, relative astrometry, and absolute astrometry
data from the Hipparcos-Gaia Catalog of Accelerations. By combining these three
data types, one can measure precise masses and sometimes orbital parameters
even when the observations cover a small fraction of an orbit. orvara achieves
its computational performance with an eccentric anomaly solver five to ten
times faster than commonly used approaches, low-level memory management to
avoid python overheads, and by analytically marginalizing out parallax,
barycenter proper motion, and the instrument-specific radial velocity zero
points. Through its integration with the Hipparcos and Gaia intermediate
astrometry package htof, orvara can properly account for the epoch astrometry
measurements of Hipparcos and the measurement times and scan angles of
individual Gaia epochs. We configure orvara with modifiable .ini configuration
files tailored to any specific stellar or planetary system. We demonstrate
orvara with a case study application to a recently discovered white dwarf/main
sequence (WD/MS) system, HD 159062. By adding absolute astrometry to literature
RV and relative astrometry data, our comprehensive MCMC analysis improves the
precision of HD 159062B's mass by more than an order of magnitude to
. We also derive a low eccentricity and
large semimajor axis, establishing HD 159062AB as a system that did not
experience Roche lobe overflow.Comment: 24 pages, 5 figures, 5 tables. AJ accepted with minor changes. orvara
is available at https://github.com/t-brandt/orvar
Precise Masses and Orbits for Nine Radial Velocity Exoplanets
Radial velocity (RV) surveys have discovered hundreds of exoplanetary systems
but suffer from a fundamental degeneracy between planet mass and orbital
inclination . In this paper we break this degeneracy by combining RVs with
complementary absolute astrometry taken from the Gaia EDR3 version of the
cross-calibrated Hipparcos-Gaia Catalog of Accelerations (HGCA). We use the
Markov Chain Monte Carlo orbit code to simultaneously fit
literature RVs and absolute astrometry from the HGCA. We constrain the orbits,
masses, and inclinations of nine single and massive RV companions orbiting
nearby G and K stars. We confirm the planetary nature of six companions: HD
29021 b (), HD 81040 b
(), HD 87883 b (), HD 98649 b (), HD 106252 b
(), and HD 171238 b
(). We place one companion, HD 196067 b
() on the planet-brown dwarf boundary, and two
companions in the low mass brown dwarf regime: HD 106515 Ab
(), and HD 221420 b
(). The brown dwarf HD 221420 b, with a
semi-major axis of AU, a period of
years, and an eccentricity of
represents a promising target for high-contrast imaging. The RV orbits of HD
87883 b, HD 98649 b, HD 171238 b, and HD 196067 b are not fully constrained yet
because of insufficient RV data. We find two possible inclinations for each of
these orbits due to difficulty in separating prograde from retrograde orbits,
but we expect this will change decisively with future Gaia data releases
Improved Dynamical Masses for Six Brown Dwarf Companions Using Hipparcos and Gaia EDR3
We present comprehensive orbital analyses and dynamical masses for the
substellar companions Gl~229~B, Gl~758~B, HD~13724~B, HD~19467~B, HD~33632~Ab,
and HD~72946~B. Our dynamical fits incorporate radial velocities, relative
astrometry, and most importantly calibrated Hipparcos-Gaia EDR3 accelerations.
For HD~33632~A and HD~72946 we perform three-body fits that account for their
outer stellar companions. We present new relative astrometry of Gl~229~B with
Keck/NIRC2, extending its observed baseline to 25 years. We obtain a 1\%
mass measurement of for the first T dwarf Gl~229~B
and a 1.2\% mass measurement of its host star ()
that agrees with the high-mass-end of the M dwarf mass-luminosity relation. We
perform a homogeneous analysis of the host stars' ages and use them, along with
the companions' measured masses and luminosities, to test substellar
evolutionary models. Gl~229~B is the most discrepant, as models predict that an
object this massive cannot cool to such a low luminosity within a Hubble time,
implying that it may be an unresolved binary. The other companions are
generally consistent with models, except for HD~13724~B that has a host-star
activity age 3.8 older than its substellar cooling age. Examining our
results in context with other mass-age-luminosity benchmarks, we find no trend
with spectral type but instead note that younger or lower-mass brown dwarfs are
over-luminous compared to models, while older or higher-mass brown dwarfs are
under-luminous. The presented mass measurements for some companions are so
precise that the stellar host ages, not the masses, limit the analysis.Comment: Accepted for publication in AJ. References updated in version 2. See
the journal version for the full quality figures. Figure sets and the MCMC
chains (reduced to just 1000 samples however) are included with the journal
version of the article, and pre-publication at
https://drive.google.com/drive/folders/1_A8QYn9NyPgmGqJaY5sMHyT_wAS3uRRK?usp=sharin
The Gliese 86 Binary System: A Warm Jupiter Formed in a Disk Truncated at ≈2 au
© 2022. The Author(s). Published by the American Astronomical Society. This is an open access article distributed under the Creative Commons Attribution License, to view a copy of the license, see: https://creativecommons.org/licenses/by/4.0/Gliese 86 is a nearby K dwarf hosting a giant planet on a ≈16 day orbit and an outer white dwarf companion on a ≈century-long orbit. In this study we combine radial velocity data (including new measurements spanning more than a decade) with high angular resolution imaging and absolute astrometry from Hipparcos and Gaia to measure the current orbits and masses of both companions. We then simulate the evolution of the Gl 86 system to constrain its primordial orbit when both stars were on the main sequence; the closest approach between the two stars was then about 9 au. Such a close separation limited the size of the protoplanetary disk of Gl 86 A and dynamically hindered the formation of the giant planet around it. Our measurements of Gl 86 B and Gl 86 Ab’s orbits reveal Gl 86 as a system in which giant planet formation took place in a disk truncated at ≈2 au. Such a disk would be just big enough to harbor the dust mass and total mass needed to assemble Gl 86 Ab’s core and envelope, assuming a high disk accretion rate and a low viscosity. Inefficient accretion of the disk onto Gl 86 Ab, however, would require a disk massive enough to approach the Toomre stability limit at its outer truncation radius. The orbital architecture of the Gl 86 system shows that giant planets can form even in severely truncated disks and provides an important benchmark for planet formation theory.Peer reviewe
The Gliese 86 Binary System: A Warm Jupiter Formed in a Disk Truncated at approximate to 2 au
Gliese 86 is a nearby K dwarf hosting a giant planet on a ≈16 day orbit and an outer white dwarf companion on a ≈century-long orbit. In this study we combine radial velocity data (including new measurements spanning more than a decade) with high angular resolution imaging and absolute astrometry from Hipparcos and Gaia to measure the current orbits and masses of both companions. We then simulate the evolution of the Gl 86 system to constrain its primordial orbit when both stars were on the main sequence; the closest approach between the two stars was then about 9 au. Such a close separation limited the size of the protoplanetary disk of Gl 86 A and dynamically hindered the formation of the giant planet around it. Our measurements of Gl 86 B and Gl 86 Ab’s orbits reveal Gl 86 as a system in which giant planet formation took place in a disk truncated at ≈2 au. Such a disk would be just big enough to harbor the dust mass and total mass needed to assemble Gl 86 Ab’s core and envelope, assuming a high disk accretion rate and a low viscosity. Inefficient accretion of the disk onto Gl 86 Ab, however, would require a disk massive enough to approach the Toomre stability limit at its outer truncation radius. The orbital architecture of the Gl 86 system shows that giant planets can form even in severely truncated disks and provides an important benchmark for planet formation theory
Ultrabroadband Density of States of Amorphous In-Ga-Zn-O
The sub-gap density of states of amorphous indium gallium zinc oxide
(-IGZO) is obtained using the ultrabroadband photoconduction (UBPC) response
of thin-film transistors (TFTs). Density functional theory simulations classify
the origin of the measured sub-gap density of states peaks as a series of
donor-like oxygen vacancy states and acceptor-like Zn vacancy states. Donor
peaks are found both near the conduction band and deep in the sub-gap, with
peak densities of cmeV. Two deep acceptor-like
metal vacancy peaks with peak densities in the range of
cmeV and lie adjacent to the valance band Urbach tail region at
2.0 to 2.5 eV below the conduction band edge. By applying detailed charge
balance, we show increasing the density of metal vacancy deep-acceptors
strongly shifts the -IGZO TFT threshold voltage to more positive values.
Photoionization (h > 2.0 eV) of metal vacancy acceptors is one cause of
transfer curve hysteresis in -IGZO TFTs owing to longer recombination
lifetimes as they get captured into acceptor-like vacancies.Comment: 31 pages, 5 figures, supplementary section include