251 research outputs found
Isotopic composition of gadolinium and neutron-capture effects in some meteorites
The isotopic composition of Gd in one chondrite, two achondrites, and the silicate inclusions of two iron meteorites has been determined. When corrected for mass discrimination, Gd in all samples except the Norton County achondrite shows the same relative isotopic abundances as terrestrial Gd. These results set an upper limit of 3×10^(15) neutrons per cm^2 on a differential integrated thermal neutron irradiation of the earth and these meteorites. Neutron-capture effects are present in Gd extracted from the Norton County achondrite. These most probably have been produced by secondary neutrons during the exceptionally long cosmic ray exposure of this large stone meteorite. The isotopic anomalies correspond to an integrated thermal neutron flux of (6.3±0.9)×10^(15) neutrons per cm^2. The percent abundances of terrestrial Gd found in our work for Gd^(160), Gd^(158), Gd^(157), Gd^(156), Gd^(155), Gd^(154), and Gd^(152) are 21.863, 24.835, 15.652, 20.466, 14.800, 2.1809, and 0.2029, respectively. Because of the higher precision, these abundances should replace the currently accepted values
Spitzer observations of the Hyades: Circumstellar debris disks at 625 Myr of age
We use the Spitzer Space Telescope to search for infrared excess at 24, 70,
and 160 micron due to debris disks around a sample of 45 FGK-type members of
the Hyades cluster. We supplement our observations with archival 24 and 70
micron Spitzer data of an additional 22 FGK-type and 11 A-type Hyades members
in order to provide robust statistics on the incidence of debris disks at 625
Myr of age an era corresponding to the late heavy bombardment in the Solar
System. We find that none of the 67 FGK-type stars in our sample show evidence
for a debris disk, while 2 out of the 11 A-type stars do so. This difference in
debris disk detection rate is likely to be due to a sensitivity bias in favor
of early-type stars. The fractional disk luminosity, L_dust/L*, of the disks
around the two A-type stars is ~4.0E-5, a level that is below the sensitivity
of our observations toward the FGK-type stars. However, our sensitivity limits
for FGK-type stars are able to exclude, at the 2-sigma level, frequencies
higher than 12% and 5% of disks with L_dust/L* > 1.0E-4 and L_dust/L* > 5.0E-4,
respectively. We also use our sensitivity limits and debris disk models to
constrain the maximum mass of dust, as a function of distance from the stars,
that could remain undetected around our targets.Comment: 33 pages, 11 figures, accepted by Ap
Isotopic analyses of barium in meteorites and in terrestrial samples
Isotopic composition and concentration of barium in six stone meteorites and the silicate inclusions of two iron meteorites and three terrestrial samples were measured by use of a ‘double spike’ isotopic dilution technique in order to correct for laboratory fractionation. Any differences between the abundances of the isotopes in meteoritic and terrestrial Ba were found to be less than 0.1% for all isotopes. The per cent abundances of Ba found in our work for Ba^(138), Ba^(137), Ba^(136), Ba^(135), Ba^(134), Ba^(132), and Ba^(130) are 71.699, 11.232, 7.853, 6.592, 2.417, 0.1012, and 0.1058, respectively. Because of the higher precision, these abundances should replace the currently accepted values. These results show the variations in the Ba isotopes reported by S. Umemoto (1962) to be unsubstantiated
TOI-3785 b: A Low-Density Neptune Orbiting an M2-Dwarf Star
Using both ground-based transit photometry and high-precision radial velocity
(RV) spectroscopy, we confirm the planetary nature of TOI-3785 b. This
transiting Neptune orbits an M2-Dwarf star with a period of ~4.67 days, a
planetary radius of 5.14 +/- 0.16 Earth Radii, a mass of 14.95 +4.10, -3.92
Earth Masses, and a density of 0.61 +0.18, -0.17 g/cm^3. TOI-3785 b belongs to
a rare population of Neptunes (4 Earth Radii < Rp < 7 Earth Radii) orbiting
cooler, smaller M-dwarf host stars, of which only ~10 have been confirmed. By
increasing the number of confirmed planets, TOI-3785 b offers an opportunity to
compare similar planets across varying planetary and stellar parameter spaces.
Moreover, with a high transmission spectroscopy metric (TSM) of ~150 combined
with a relatively cool equilibrium temperature of 582 +/- 16 K and an inactive
host star, TOI-3785 b is one of the more promising low-density M-dwarf Neptune
targets for atmospheric follow-up. Future investigation into atmospheric mass
loss rates of TOI-3785 b may yield new insights into the atmospheric evolution
of these low-mass gas planets around M-dwarfs.Comment: 22 pages, 6 figures, 6 tables, Submitted to A
TOI-5205b: A Jupiter transiting an M dwarf near the Convective Boundary
We present the discovery of TOI-5205b, a transiting Jovian planet orbiting a
solar metallicity M4V star, which was discovered using TESS photometry and then
confirmed using a combination of precise radial velocities, ground-based
photometry, spectra and speckle imaging. The host star TOI-5205 sits near the
eponymous `Jao gap', which is the transition region between partially and
fully-convective M dwarfs. TOI-5205b has one of the highest mass ratio for M
dwarf planets with a mass ratio of almost 0.3, as it orbits a host star
that is just . Its planetary radius is , while the mass is . Additionally, the large size
of the planet orbiting a small star results in a transit depth of ,
making it one of the deepest transits of a confirmed exoplanet orbiting a
main-sequence star. The large transit depth makes TOI-5205b a compelling target
to probe its atmospheric properties, as a means of tracing the potential
formation pathways. While there have been radial velocity-only discoveries of
giant planets around mid M dwarfs, this is the first transiting Jupiter with a
mass measurement discovered around such a low-mass host star. The high mass of
TOI-5205b stretches conventional theories of planet formation and disk scaling
relations that cannot easily recreate the conditions required to form such
planets.Comment: Submitted to ApJ. Comments are welcome. arXiv admin note: text
overlap with arXiv:2203.0717
The role of planetary formation and evolution in shaping the composition of exoplanetary atmospheres
Over the last twenty years, the search for extrasolar planets revealed us the
rich diversity of the outcomes of the formation and evolution of planetary
systems. In order to fully understand how these extrasolar planets came to be,
however, the orbital and physical data we possess are not enough, and they need
to be complemented with information on the composition of the exoplanets.
Ground-based and space-based observations provided the first data on the
atmospheric composition of a few extrasolar planets, but a larger and more
detailed sample is required before we can fully take advantage of it. The
primary goal of the Exoplanet Characterization Observatory (EChO) is to fill
this gap, expanding the limited data we possess by performing a systematic
survey of hundreds of extrasolar planets. The full exploitation of the data
that EChO and other space-based and ground-based facilities will provide in the
near future, however, requires the knowledge of what are the sources and sinks
of the chemical species and molecules that will be observed. Luckily, the study
of the past history of the Solar System provides several indications on the
effects of processes like migration, late accretion and secular impacts, and on
the time they occur in the life of planetary systems. In this work we will
review what is already known about the factors influencing the composition of
planetary atmospheres, focusing on the case of gaseous giant planets, and what
instead still need to be investigated.Comment: 26 pages, 9 figures, 1 table. Accepted for publication on
Experimental Astronomy, special issue on the M3 EChO mission candidat
The unusual M-dwarf Warm Jupiter TOI-1899~b: Refinement of orbital and planetary parameters
TOI-1899~b is a rare exoplanet, a temperate Warm Jupiter orbiting an M-dwarf,
first discovered by \citet{Canas2020_toi1899} from a TESS single-transit event.
Using new radial velocities (RVs) from the precision RV spectrographs HPF and
NEID, along with additional TESS photometry and ground-based transit follow-up,
we are able to derive a much more precise orbital period of ~d, along with a radius of ~\unit{R_{J}}. We have also improved the constraints on planet
mass, ~\unit{M_{J}}, and eccentricity, which is consistent
with a circular orbit at 2 (). TOI-1899~b
occupies a unique region of parameter space as the coolest known ( 380~K) Jovian-sized transiting planet around an M-dwarf; we show that
it has great potential to provide clues regarding the formation and migration
mechanisms of these rare gas giants through transmission spectroscopy with JWST
as well as studies of tidal evolution.Comment: 19 pages, 7 figures, 3 tables, submitted to AJ (comments welcome
The timing of basaltic volcanism at the Apollo landing sites
Precise crystallisation ages have been determined for a range of Apollo basalts from Pb-Pb isochrons generated using Secondary Ion Mass Spectrometry (SIMS) analyses of multiple accessory phases including K-feldspar, K-rich glass and phosphates. The samples analysed in this study include five Apollo 11 high-Ti basalts, one Apollo 14 high-Al basalt, seven Apollo 15 low-Ti basalts, and five Apollo 17 high-Ti basalts. Together with the samples analysed in two previous similar studies, Pb-Pb isochron ages have been determined for all of the major basaltic suites sampled during the Apollo missions. The accuracy of these ages has been assessed as part of a thorough review of existing age determinations for Apollo basalts, which reveals a good agreement with previous studies of the same samples, as well as with average ages that have been calculated for the emplacement of the different basaltic suites at the Apollo landing sites. Furthermore, the precision of the new age determinations helps to resolve distinctions between the ages of different basaltic suites in more detail than was previously possible. The proposed ages for the basaltic surface flows at the Apollo landing sites have been reviewed in light of these new sample ages. Finally, the data presented here have also been used to constrain the initial Pb isotopic compositions of the mare basalts, which indicate a significant degree of heterogeneity in the lunar mantle source regions, even among the basalts collected at individual landing sites
- …