Context. Emission lines that are indicative of active accretion have been observed for a number of low-mass companions (M < 30 MJup) to stars. Line variability is ubiquitous on stellar accretors, but ...it has never been characterized in detail for low-mass companions. Such characterizations can offer insights into the accretion mechanism at play.Aims. We aim to characterize the short-to-long-term H I Paschen β emission line variability of two 10 to 30 MJup companions on wide orbits: GQ Lup b and GSC 06214-00210 b. We also aim to clarify their accretion mechanisms. Methods. We used J-band observations at R = 1800-2360, obtained with VLT/SINFONI in 2017, to record time-series investigations of the hours-to-weeks variability of the H I Paschen β emission line (1.282 μm). Contrary to HI, it should be less affected by chromospheric activity contamination. The photospheric emission was analyzed at each epoch and removed with the ForMoSA forward-modeling tool, using new grids of ATMO models exploring different C/O and M/H values. The time series of line profiles and intensities were compared to those of more massive accretors and to predictions from the latest magnetospheric accretion and shock models. To complement these results, we also re-investigated archival spectroscopic observations at near-infrared wavelengths of each target to increase the time frame up to a decade and to build a more comprehensive understanding of the variability processes at play.Results. For GQ Lup b, we find line variability on timescales of several months to decades, whereas it is within the acceptable noise levels on shorter timescales. For GSC 06214-00210 b, we find line variability on timescales of tens of minutes all the way up to a decade. The line profiles of GSC 06214-00210 b are partially resolved in at least one epoch. Both objects show H I Paschen β flux variability that is moderate (<50%), on timescales that are below their rotation period, and that is more significant on longer timescales (up to ~1000% on decade-long timescales). This behavior resembles that of classical T Tauri stars. The line profiles of GQ Lup b are blue-shifted and can only be reproduced by magnetospheric accretion models, while those of GSC 06214-00210 b are fairly well reproduced by both magnetospheric accretion and shock models, except for one epoch for which the shock model is highly favored. The companions have C/O values broadly consistent with solar values.Conclusions. While magnetospheric accretion is favored for GQ Lup b, higher resolution (R > 10 000) observations are required to disentangle the two (non-exclusive) emitting mechanisms. The similar variability behavior observed in these low mass companions and in classical T Tauri stars may support similar accretion mechanisms. The high amplitude of variability on timescales of over a month and longer that is found for both objects could be key to explaining the low yield of Hi imaging campaigns.
We present JWST Early Release Science coronagraphic observations of the super-Jupiter exoplanet, HIP 65426b, with the Near-Infrared Camera (NIRCam) from 2 to 5 μ m, and with the Mid-Infrared ...Instrument (MIRI) from 11 to 16 μ m. At a separation of ∼0.″82 (87 − 31 + 108 au), HIP 65426b 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 μ 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 σ contrast limits of ∼1 × 10 −5 and ∼2 × 10 −4 at 1″ for NIRCam at 4.4 μ m and MIRI at 11.3 μ m, respectively. These contrast limits provide sensitivity to sub-Jupiter companions with masses as low as 0.3 M Jup beyond separations of ∼100 au. Together with existing ground-based near-infrared data, the JWST photometry are fit well by a BT-SETTL atmospheric model from 1 to 16 μ m, and they span ∼97% of HIP 65426b's luminous range. Independent of the choice of model atmosphere, we measure an empirical bolometric luminosity that is tightly constrained between log L bol / L ⊙ = −4.31 and −4.14, which in turn provides a robust mass constraint of 7.1 ± 1.2 M Jup . In totality, these observations confirm that JWST presents a powerful and exciting opportunity to characterize the population of exoplanets amenable to high-contrast imaging in greater detail.
Emission lines indicative of active accretion have been seen on a handful of low-mass companions (M < 30 MJup) to stars. Line variability is ubiquitous on stellar accretors but has never been ...characterized in detail on low-mass companions and can give insights on the accretion mechanism at play. We investigate the emission line variability of two low-mass companions (M<30 MJup) to stars to understand their accretion mechanisms. Using J-band observations, we analyze the short to long-term variability of the HI Paschen {\beta} emission line (1.282 {\mu}m) for GQ Lup b and GSC 06214-00210 b. Archival spectroscopic observations are also examined to extend the time span. We compare their line profiles and intensities to more massive accretors and magnetospheric accretion and shock models. Both objects have HI Paschen {\beta} flux variability that is moderate at short timescales (< 50 %) and increases at longer timescales (~1000 % on decade timescales), resembling classical T Tauri stars. GQ Lup b's line profiles are compatible with magnetospheric accretion. GSC 06214-00210 b's profiles are reproduced by both magnetospheric accretion and shock models, except for the brightest epoch for which the shock model is highly favored. Both companions have C/O values broadly consistent with solar values. While magnetospheric accretion is favored for GQ Lup b, higher resolution (R > 10000) observations are required to disentangle the two (non-exclusive) line formation mechanisms. The similarity in variability behavior may support similar accretion mechanisms between these low-mass companions and classical T Tauri stars. The significant variability observed at months and longer timescales could explain the low yield of H{\alpha} imaging campaigns.
The discovery of planets orbiting at less than 1 au from their host star and less massive than Saturn in various exoplanetary systems revolutionized our theories of planetary formation. The ...fundamental question is whether these close-in low-mass planets could have formed in the inner disk interior to 1 au, or whether they formed further out in the planet-forming disk and migrated inward. Exploring the role of additional giant planets in these systems may help us to pinpoint their global formation and evolution. We searched for additional substellar companions by using direct imaging in systems known to host close-in small planets. The use of direct imaging complemented by radial velocity and astrometric detection limits enabled us to explore the giant planet and brown dwarf demographics around these hosts to investigate the potential connection between both populations. We carried out a direct imaging survey with VLT/SPHERE to look for outer giant planets and brown dwarf companions in 27 systems hosting close-in low-mass planets discovered by radial velocity. Our sample is composed of very nearby (<20pc) planetary systems, orbiting G-, K-, and M-type mature (0.5-10Gyr) stellar hosts. We performed homogeneous direct imaging data reduction and analysis to search for and characterize point sources, and derived robust statistical detection limits. Of 337 point-source detections, we do not find any new bound companions. We recovered the emblematic very cool T-type brown dwarf GJ229B. Our typical sensitivities in direct imaging range from 5 to 30 MJup beyond 2 au. The non-detection of massive companions is consistent with predictions based on models of planet formation by core accretion. Our pilot study opens the way to a multi-technique approach for the exploration of very nearby exoplanetary systems with future ground-based and space observatories.
A&A 670, L9 (2023) We present simultaneous 0.65-2.5 microns medium resolution (3300 < R < 8100)
VLT/X-Shooter spectra of the young low-mass (19+/-5MJup) L-T transition object
VHS 1256-1257 b, a known ...spectroscopic analogue of HR8799d. The companion is a
prime target for the JWST Early Release Science (ERS) and one of the
highest-amplitude variable brown-dwarf known to date. We compare the spectrum
to the custom grids of cloudless ATMO models exploring different atmospheric
composition with the Bayesian inference tool ForMoSA. We also re-analyze
low-resolution HST/WFC3 1.10-1.67 microns spectra at minimum and maximum
variability to contextualize the X-Shooter data interpretation. The models
reproduce the slope and most molecular absorption from 1.10 to 2.48 microns
self-consistently but fail to provide a radius consistent with evolutionary
model predictions. They do not reproduce consistently the optical spectrum and
the depth of the K I doublets in the J-band. We derive Teff = 1380+/-54 K,
log(g) = 3.97+/-0.48 dex, M/H = 0.21+/-0.29, and C/O > 0.63. Our inversion of
the HST/WFC3 spectra suggests a relative change of 27+6-5 K of the
disk-integrated Teff correlated with the near-infrared brightness. Our data
anchor the characterization of that object in the near-infrared and could be
used jointly to the ERS mid-infrared data to provide the most detailed
characterization of an ultracool dwarf to date.
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 simultaneous 0.65-2.5 microns medium resolution (3300 < R < 8100) VLT/X-Shooter spectra of the young low-mass (19+/-5MJup) L-T transition object VHS 1256-1257 b, a known spectroscopic ...analogue of HR8799d. The companion is a prime target for the JWST Early Release Science (ERS) and one of the highest-amplitude variable brown-dwarf known to date. We compare the spectrum to the custom grids of cloudless ATMO models exploring different atmospheric composition with the Bayesian inference tool ForMoSA. We also re-analyze low-resolution HST/WFC3 1.10-1.67 microns spectra at minimum and maximum variability to contextualize the X-Shooter data interpretation. The models reproduce the slope and most molecular absorption from 1.10 to 2.48 microns self-consistently but fail to provide a radius consistent with evolutionary model predictions. They do not reproduce consistently the optical spectrum and the depth of the K I doublets in the J-band. We derive Teff = 1380+/-54 K, log(g) = 3.97+/-0.48 dex, M/H = 0.21+/-0.29, and C/O > 0.63. Our inversion of the HST/WFC3 spectra suggests a relative change of 27+6-5 K of the disk-integrated Teff correlated with the near-infrared brightness. Our data anchor the characterization of that object in the near-infrared and could be used jointly to the ERS mid-infrared data to provide the most detailed characterization of an ultracool dwarf to date.
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.
