Fire is a major selective force on arid grassland communities, favoring traits such as the smoke‐induced seed germination response seen in a wide variety of plant species. However, little is known ...about the relevance of smoke as a cue for plants beyond the seedling stage.
We exposed a fire‐adapted savanna tree, Vachellia (=Acacia) drepanolobium, to smoke and compared nutrient concentrations in leaf and root tissues to unexposed controls. Experiments were performed on three age cohorts: 2‐year‐old, 9‐month‐old, and 3‐month‐old plants.
For the 2‐year‐old plants exposed to smoke, carbon and nitrogen concentrations were lower in the leaves and higher in the roots than controls. Less pronounced trends were found for boron and magnesium.
In contrast, smoke‐exposed 3‐month‐old plants had lower root nitrogen concentrations than controls. No significant differences were found in the 9‐month‐old plants, and no significant shifts in other nutrient concentrations were observed between plant tissues for any of the three age cohorts.
Synthesis: Our findings are consistent with smoke‐induced translocation of nutrients from leaves to roots in 2‐year‐old V. drepanolobium. This could represent a novel form of fire adaptation, with variation over the course of plant development. The translocation differences between age cohorts highlight the need to investigate smoke response in older plants of other species. Accounting for this adaptation could better inform our understanding of savanna community structure and nutrient flows under fire regimes altered by anthropogenic land use and climate change.
We exposed a fire‐adapted savanna tree, Vachellia (=Acacia) drepanolobium, to smoke and compared nutrient concentrations in leaf and root tissues to unexposed controls. Our findings suggest trees may detect smoke and respond by translocating nutrients from leaves to roots, a potential mechanism for improving survival and post‐fire resprouting.
We present the highest fidelity spectrum to date of a planetary-mass object. VHS 1256 b is a <20 MJup widely separated (∼8'', a = 150 au), young, planetary-mass companion that shares photometric ...colors and spectroscopic features with the directly imaged exoplanets HR 8799c, d, and e. As an L-to-T transition object, VHS 1256 b exists along the region of the color–magnitude diagram where substellar atmospheres transition from cloudy to clear. We observed VHS 1256 b with JWST's NIRSpec IFU and MIRI MRS modes for coverage from 1 to 20 μm at resolutions of ∼1000–3700. Water, methane, carbon monoxide, carbon dioxide, sodium, and potassium are observed in several portions of the JWST spectrum based on comparisons from template brown dwarf spectra, molecular opacities, and atmospheric models. The spectral shape of VHS 1256 b is influenced by disequilibrium chemistry and clouds. We directly detect silicate clouds, the first such detection reported for a planetary-mass companion.
We present the highest fidelity spectrum to date of a planetary-mass object. VHS 1256 b is a \(<\)20 M\(_\mathrm{Jup}\) widely separated (\(\sim\)8\arcsec, a = 150 au), young, planetary-mass ...companion that shares photometric colors and spectroscopic features with the directly imaged exoplanets HR 8799 c, d, and e. As an L-to-T transition object, VHS 1256 b exists along the region of the color-magnitude diagram where substellar atmospheres transition from cloudy to clear. We observed VHS 1256~b with \textit{JWST}'s NIRSpec IFU and MIRI MRS modes for coverage from 1 \(\mu\)m to 20 \(\mu\)m at resolutions of \(\sim\)1,000 - 3,700. Water, methane, carbon monoxide, carbon dioxide, sodium, and potassium are observed in several portions of the \textit{JWST} spectrum based on comparisons from template brown dwarf spectra, molecular opacities, and atmospheric models. The spectral shape of VHS 1256 b is influenced by disequilibrium chemistry and clouds. We directly detect silicate clouds, the first such detection reported for a planetary-mass companion.
We present JWST Early Release Science (ERS) coronagraphic observations of the
super-Jupiter exoplanet, HIP 65426 b, with the Near-Infrared Camera (NIRCam)
from 2-5 $\mu$m, and with the Mid-Infrared ...Instrument (MIRI) from 11-16 $\mu$m.
At a separation of $\sim$0.82" (86$^{+116}_{-31}$ au), HIP 65426 b is clearly
detected in all seven of our observational filters, representing the first
images of an exoplanet to be obtained by JWST, and the first ever direct
detection of an exoplanet beyond 5 $\mu$m. These observations demonstrate that
JWST is exceeding its nominal predicted performance by up to a factor of 10,
depending on separation and subtraction method, with measured 5$\sigma$
contrast limits of $\sim$1$\times10^{-5}$ and $\sim$2$\times10^{-4}$ at 1" for
NIRCam at 4.4 $\mu$m and MIRI at 11.3 $\mu$m, respectively. These contrast
limits provide sensitivity to sub-Jupiter companions with masses as low as
0.3$M_\mathrm{Jup}$ beyond separations of $\sim$100 au. Together with existing
ground-based near-infrared data, the JWST photometry are well fit by a BT-SETTL
atmospheric model from 1-16 $\mu$m, and span $\sim$97% of HIP 65426 b's
luminous range. Independent of the choice of model atmosphere we measure an
empirical bolometric luminosity that is tightly constrained between
$\mathrm{log}\!\left(L_\mathrm{bol}/L_{\odot}\right)$=-4.31 to $-$4.14, which
in turn provides a robust mass constraint of 7.1$\pm$1.2 $M_\mathrm{Jup}$. In
totality, these observations confirm that JWST presents a powerful and exciting
opportunity to characterise the population of exoplanets amenable to
high-contrast imaging in greater detail.
We present aperture masking interferometry (AMI) observations of the star HIP 65426 at \(3.8\,\rm{\mu m}\) as a part of the \textit{JWST} Direct Imaging Early Release Science (ERS) program obtained ...using the Near Infrared Imager and Slitless Spectrograph (NIRISS) instrument. This mode provides access to very small inner working angles (even separations slightly below the Michelson limit of \({}0.5\lambda/D\) for an interferometer), which are inaccessible with the classical inner working angles of the \textit{JWST} coronagraphs. When combined with \textit{JWST}'s unprecedented infrared sensitivity, this mode has the potential to probe a new portion of parameter space across a wide array of astronomical observations. Using this mode, we are able to achieve a contrast of \(\Delta m_{F380M}{\sim }7.8\)\,mag relative to the host star at a separation of \({\sim}0.07\arcsec\) but detect no additional companions interior to the known companion HIP\,65426\,b. Our observations thus rule out companions more massive than \(10{-}12\,\rm{M\textsubscript{Jup}}\) at separations \({\sim}10{-}20\,\rm{au}\) from HIP\,65426, a region out of reach of ground or space-based coronagraphic imaging. These observations confirm that the AMI mode on \textit{JWST} is sensitive to planetary mass companions orbiting at the water frost line, even for more distant stars at \(\sim\)100\,pc. This result will allow the planning and successful execution of future observations to probe the inner regions of nearby stellar systems, opening essentially unexplored parameter space.
We present JWST Early Release Science (ERS) coronagraphic observations of the super-Jupiter exoplanet, HIP 65426 b, with the Near-Infrared Camera (NIRCam) from 2-5 \(\mu\)m, and with the Mid-Infrared ...Instrument (MIRI) from 11-16 \(\mu\)m. At a separation of \(\sim\)0.82" (86\(^{+116}_{-31}\) au), HIP 65426 b is clearly detected in all seven of our observational filters, representing the first images of an exoplanet to be obtained by JWST, and the first ever direct detection of an exoplanet beyond 5 \(\mu\)m. These observations demonstrate that JWST is exceeding its nominal predicted performance by up to a factor of 10, depending on separation and subtraction method, with measured 5\(\sigma\) contrast limits of \(\sim\)1\(\times10^{-5}\) and \(\sim\)2\(\times10^{-4}\) at 1" for NIRCam at 4.4 \(\mu\)m and MIRI at 11.3 \(\mu\)m, respectively. These contrast limits provide sensitivity to sub-Jupiter companions with masses as low as 0.3\(M_\mathrm{Jup}\) beyond separations of \(\sim\)100 au. Together with existing ground-based near-infrared data, the JWST photometry are well fit by a BT-SETTL atmospheric model from 1-16 \(\mu\)m, and span \(\sim\)97% of HIP 65426 b's luminous range. Independent of the choice of model atmosphere we measure an empirical bolometric luminosity that is tightly constrained between \(\mathrm{log}\!\left(L_\mathrm{bol}/L_{\odot}\right)\)=-4.31 to \(-\)4.14, which in turn provides a robust mass constraint of 7.1\(\pm\)1.2 \(M_\mathrm{Jup}\). In totality, these observations confirm that JWST presents a powerful and exciting opportunity to characterise the population of exoplanets amenable to high-contrast imaging in greater detail.
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