分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: 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.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: Extrasolar analogues of the Solar System's Kuiper belt offer unique constraints on outer planetary system architecture. Radial features such as the sharpness of disk edges and substructures such as gaps may be indicative of embedded planets within a disk. Vertically, the height of a disk can constrain the mass of embedded bodies. Edge-on debris disks offer a unique opportunity to simultaneously access the radial and vertical distribution of material, however recovering either distribution in an unbiased way is challenging. In this study, we present a non-parametric method to recover the surface brightness profile (face-on surface brightness as a function of radius) and height profile (scale height as a function of radius) of azimuthally symmetric, edge-on debris disks. The method is primarily designed for observations at thermal emission wavelengths, but is also applicable to scattered light observations under the assumption of isotropic scattering. By removing assumptions on underlying functional forms, this algorithm provides more realistic constraints on disk structures. We also apply this technique to ALMA observations of the AU Mic debris disk and derive a surface brightness profile consistent with estimates from parametric approaches, but with a more realistic range of possible models that is independent of parametrisation assumptions. Our results are consistent with a uniform scale height of 0.8 au, but a scale height that increases linearly with radius is also possible.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: The edge-on debris disk of the nearby young star Beta Pictoris shows an unusual brightness asymmetry in the form of a clump. The clump has been detected in both the mid-IR and CO and its origin has so far remained uncertain. Here we present new mid-IR observations of Beta Pic to track any motion of the dust clump. Together with previous observations, the data span a period of 12 years. We measured any projected displacement of the dust clump over the 12-yr period to be $0.2^{+1.3}_{-1.4}$ au away from the star based on the median and 1$\sigma$ uncertainty, and constrain this displacement to be <11 au at the 3$\sigma$ level. This implies that the observed motion is incompatible with Keplerian motion at the 2.8$\sigma$ level. It has been posited that a planet migrating outwards may trap planetesimals into a 2:1 resonance, resulting in the observed clump at pericentre of their orbits that trails the planet. The observed motion is also incompatible with such resonant motion at the 2.6$\sigma$ level. While Keplerian motion and resonant motion is still possible, the data suggest that the dust clump is more likely stationary. Such a stationary dust clump could originate from the collision or tidal disruption of a planet-sized body, or from secular perturbations due to a planet that create regions with enhanced densities in the disk.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: 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$0.82" (87$^{+108}_{-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, with measured 5$\sigma$ contrast limits of $\sim$4$\times10^{-6}$ ($\sim$2.4 $\mu$Jy) and $\sim$2$\times10^{-4}$ ($\sim$10 $\mu$Jy) at 1" for NIRCam at 3.6 $\mu$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 forward model atmosphere we measure an empirical bolometric luminosity that is tightly constrained between $\mathrm{log}\!\left(L_\mathrm{bol}/L_{\odot}\right)$=-4.35 to -4.21, which in turn provides a robust mass constraint of 7.1$\pm$1.1 $M_\mathrm{Jup}$. In totality, these observations confirm that JWST presents a powerful and exciting opportunity to characterise the population of exoplanets amenable to direct imaging in greater detail.