An official website of the United States government
We present a reanalysis of the K2-106 transiting planetary system, with a focus on the composition of K2-106b, an ultra-short-period, super-Mercury candidate. We globally model existing photometric and radial velocity data and derive a planetary mass and radius for K2-106b of Mp = 8.53 ± 1.02 M⊕ and = - + Rp 1.71 0.057 RÅ 0.069 , which leads to a density of r = - + 9.4 p 1.5 1.6 g cm−3 , a significantly lower value than previously reported in the literature. We use planet interior models that assume a two-layer planet comprised of a liquid, pure Fe core and an iron-free, MgSiO3 mantle, and we determine that the range of the core mass fractions are consistent with the observed mass and radius. We use existing high-resolution spectra of the host star to derive the Fe/Mg/Si abundances ([Fe/ H] = −0.03 ± 0.01, [Mg/H] = 0.04 ± 0.02, [Si/H] = 0.03 ± 0.06) to infer the composition of K2-106b. We find that K2-106b has a density and core mass fraction ( - + 44 %15 12 ) consistent with that of Earth (CMF⊕ = 32%). Furthermore, its composition is consistent with what is expected, assuming that it reflects the relative refractory abundances of its host star. K2-106b is therefore unlikely to be a super-Mercury, as has been suggested in previous literature.
more »
« less
Cloud busting: enstatite and quartz clouds in the atmosphere of 2M2224-0158
ABSTRACT We present the most detailed data-driven exploration of cloud opacity in a substellar object to-date. We have tested over 60 combinations of cloud composition and structure, particle-size distribution, scattering model, and gas phase composition assumptions against archival 1–15 μm spectroscopy for the unusually red L4.5 dwarf 2MASSW J2224438-015852 using the Brewster retrieval framework. We find that, within our framework, a model that includes enstatite and quartz cloud layers at shallow pressures, combined with a deep iron cloud deck fits the data best. This model assumes a Hansen distribution for particle sizes for each cloud, and Mie scattering. We retrieved particle effective radii of $$\log _{10} a {\rm (\mu m)} = -1.41^{+0.18}_{-0.17}$$ for enstatite, $$-0.44^{+0.04}_{-0.20}$$ for quartz, and $$-0.77^{+0.05}_{-0.06}$$ for iron. Our inferred cloud column densities suggest $${\rm (Mg/Si)} = 0.69^{+0.06}_{-0.08}$$ if there are no other sinks for magnesium or silicon. Models that include forsterite alongside, or in place of, these cloud species are strongly rejected in favour of the above combination. We estimate a radius of 0.75 ± 0.02 RJup, which is considerably smaller than predicted by evolutionary models for a field age object with the luminosity of 2M2224-0158. Models which assume vertically constant gas fractions are consistently preferred over models that assume thermochemical equilibrium. From our retrieved gas fractions, we infer $${\rm [M/H]} = +0.38^{+0.07}_{-0.06}$$ and $${\rm C/O} = 0.83^{+0.06}_{-0.07}$$. Both these values are towards the upper end of the stellar distribution in the Solar neighbourhood, and are mutually consistent in this context. A composition towards the extremes of the local distribution is consistent with this target being an outlier in the ultracool dwarf population.
more »
« less
- Award ID(s):
- 1909776
- PAR ID:
- 10294138
- Date Published:
- Journal Name:
- Monthly Notices of the Royal Astronomical Society
- Volume:
- 506
- Issue:
- 2
- ISSN:
- 0035-8711
- Page Range / eLocation ID:
- 1944 to 1961
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
null (Ed.)ABSTRACT Advanced LIGO and Advanced Virgo are detecting a large number of binary stellar origin black hole (BH) mergers. A promising channel for accelerated BH merger lies in active galactic nucleus (AGN) discs of gas around supermasssive BHs. Here, we investigate the relative number of compact object (CO) mergers in AGN disc models, including BH, neutron stars (NS), and white dwarfs, via Monte Carlo simulations. We find the number of all merger types in the bulk disc grows ∝ t1/3 which is driven by the Hill sphere of the more massive merger component. Median mass ratios of NS–BH mergers in AGN discs are $$\tilde{q}=0.07\pm 0.06(0.14\pm 0.07)$$ for mass functions (MF) M−1(− 2). If a fraction fAGN of the observed rate of BH–BH mergers (RBH–BH) come from AGN, the rate of NS–BH (NS–NS) mergers in the AGN channel is $${R}_{\mathrm{ BH}\!-\!\mathrm{ NS}} \sim f_{\mathrm{ AGN}}[10,300]\, \rm {Gpc}^{-3}\, \rm {yr}^{-1},({\mathit{ R}}_{NS\!-\!NS} \le \mathit{ f}_{AGN}400\, \rm {Gpc}^{-3}\, \rm {yr}^{-1}$$). Given the ratio of NS–NS/BH–BH LIGO search volumes, from preliminary O3 results the AGN channel is not the dominant contribution to observed NS–NS mergers. The number of lower mass gap events expected is a strong function of the nuclear MF and mass segregation efficiency. CO merger ratios derived from LIGO can restrict models of MF, mass segregation, and populations embedded in AGN discs. The expected number of electromagnetic (EM) counterparts to NS–BH mergers in AGN discs at z < 1 is $$\sim [30,900]\, {\rm {yr}}^{-1}(f_{\mathrm{ AGN}}/0.1)$$. EM searches for flaring events in large AGN surveys will complement LIGO constraints on AGN models and the embedded populations that must live in them.more » « less
-
null (Ed.)ABSTRACT Planets and stars ultimately form out of the collapse of the same cloud of gas. Whilst planets, and planetary bodies, readily loose volatiles, a common hypothesis is that they retain the same refractory composition as their host star. This is true within the Solar system. The refractory composition of chondritic meteorites, Earth, and other rocky planetary bodies are consistent with solar, within the observational errors. This work aims to investigate whether this hypothesis holds for exoplanetary systems. If true, the internal structure of observed rocky exoplanets can be better constrained using their host star abundances. In this paper, we analyse the abundances of the K-dwarf, G200-40, and compare them to its polluted white dwarf companion, WD 1425+540. The white dwarf has accreted planetary material, most probably a Kuiper belt-like object, from an outer planetary system surviving the star’s evolution to the white dwarf phase. Given that binary pairs are chemically homogeneous, we use the binary companion, G200-40, as a proxy for the composition of the progenitor to WD 1425+540. We show that the elemental abundances of the companion star and the planetary material accreted by WD 1425+540 are consistent with the hypothesis that planet and host-stars have the same true abundances, taking into account the observational errors.more » « less
-
ABSTRACT Interstellar chemistry is important for galaxy formation, as it determines the rate at which gas can cool, and enables us to make predictions for observable spectroscopic lines from ions and molecules. We explore two central aspects of modelling the chemistry of the interstellar medium (ISM): (1) the effects of local stellar radiation, which ionizes and heats the gas, and (2) the depletion of metals on to dust grains, which reduces the abundance of metals in the gas phase. We run high-resolution (400 M⊙ per baryonic particle) simulations of isolated disc galaxies, from dwarfs to Milky Way-mass, using the fire galaxy formation models together with the chimes non-equilibrium chemistry and cooling module. In our fiducial model, we couple the chemistry to the stellar fluxes calculated from star particles using an approximate radiative transfer scheme; and we implement an empirical density-dependent prescription for metal depletion. For comparison, we also run simulations with a spatially uniform radiation field, and without metal depletion. Our fiducial model broadly reproduces observed trends in H i and H2 mass with stellar mass, and in line luminosity versus star formation rate for [C ii]$$_{158 \rm {\mu m}}$$, [O i]$$_{63 \rm {\mu m}}$$, [O iii]$$_{88 \rm {\mu m}}$$, [N ii]$$_{122 \rm {\mu m}}$$, and H α6563Å. Our simulations with a uniform radiation field predict fainter luminosities, by up to an order of magnitude for [O iii]$$_{88 \rm {\mu m}}$$ and H α6563Å, while ignoring metal depletion increases the luminosity of carbon and oxygen lines by a factor ≈ 2. However, the overall evolution of the galaxy is not strongly affected by local stellar fluxes or metal depletion, except in dwarf galaxies where the inclusion of local fluxes leads to weaker outflows and hence higher gas fractions.more » « less
-
ABSTRACT We perform cosmological hydrodynamical simulations to study the formation of proto-globular cluster candidates in progenitors of present-day dwarf galaxies $$(M_{\rm vir} \approx 10^{10}\, {\rm M}_\odot$$ at z = 0) as part of the ‘Feedback in Realistic Environment’ (FIRE) project. Compact (r1/2 < 30 pc), relatively massive (0.5 × 105 ≲ M⋆/M⊙ ≲ 5 × 105), self-bound stellar clusters form at 11 ≳ z ≳ 5 in progenitors with $$M_{\rm vir} \approx 10^9\, \mathrm{M}_{\odot }$$. Cluster formation is triggered when at least $$10^7\, \mathrm{M}_{\odot }$$ of dense, turbulent gas reaches $$\Sigma _{\rm gas} \approx 10^4\, {\rm M}_\odot \, {\rm pc}^{-2}$$ as a result of the compressive effects of supernova feedback or from cloud–cloud collisions. The clusters can survive for $$2-3\, {\rm Gyr}$$; absent numerical effects, they could possibly survive substantially longer, perhaps to z = 0. The longest lived clusters are those that form at significant distance – several hundreds of pc – from their host galaxy. We therefore predict that globular clusters forming in progenitors of present-day dwarf galaxies will be offset from any pre-existing stars within their host dark matter haloes as opposed to deeply embedded within a well-defined galaxy. Properties of the nascent clusters are consistent with observations of some of the faintest and most compact high-redshift sources in Hubble Space Telescope lensing fields and are at the edge of what will be detectable as point sources in deep imaging of non-lensed fields with JWST. By contrast, the star clusters’ host galaxies will remain undetectable.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1093/mnras/stab1361
