A Mid-infrared Study of Directly Imaged Planetary-mass Companions Using Archival Spitzer/IRAC Images

The atmospheres and accretion disks of planetary-mass and substellar companions provide an unprecedented look into planet and moon formation processes, most notably the frequency and lifetime of circumplanetary disks. In our ongoing effort to leverage the extraordinary sensitivity of the Spitzer/Infrared Array Camera (IRAC) at 3.6, 4.5, 5.8, and 8.0 μm to study wide planetary-mass and substellar companions near the diffraction limit, we present point-spread function fitting photometry of archival Spitzer/IRAC images for nine stars (G0 to M4+M7) in nearby star-forming regions or stellar associations that host companions at separations of ρ = 1.″17–12.″33. We detect all system primaries in all four IRAC channels and recover eight low-mass companions in at least one IRAC channel for our sample, five of which have not been resolved previously in IRAC images. We measure nonphotospheric [3.6]–[8.0] colors for four of the system companions (DH Tau B, 2M0441 B, SR 12 c, and ROXs 42B b), confirming or discovering the presence of circumstellar or circum(sub)stellar disks. We detect fluxes consistent with photospheric emission for four other companions (AB Pic b, CHXR 73 b, 1RXS J1609 b, and HD 203030 b) that are unlikely to host disks. Combined with past detections of accretion or disk indicators, we determine the global disk frequency of young (<15 Myr) wide companions with masses near the deuterium-burning limit to be 56% ± 12%.

V488 Per Revisited: No Strong Mid-infrared Emission Features and No Evidence for Stellar/substellar Companions

We present characterization of the planetary system architecture for V488 Per, the dustiest main-sequence star known with a fractional infrared luminosity of ≈16%. Far-infrared imaging photometry confirms the existence of an outer planetary system dust population with a blackbody-fit temperature of ≈130 K. Mid-infrared spectroscopy probing the previously identified ≈800 K inner planetary system dust population does not detect any obvious solid-state emission features, suggesting either large grain sizes that mute such emission and/or grain compositions dominated by species like amorphous carbon and metallic iron, which do not produce such features. In the latter case, the presence of significant quantities of iron-rich material could be indicative of the active formation of a Mercury-like planet around V488 Per. In any event, the absence of solid-state emission features is very unusual among main-sequence stars with copious amounts of warm orbiting dust particles; we know of no other such star whose mid-infrared spectrum lacks such features. Combined radial velocity monitoring and adaptive optics imaging find no evidence for stellar/substellar companions within several hundred astronomical units of V488 Per.

The search for disks or planetary objects around directly imaged companions: a candidate around DH Tauri B

Context. In recent decades, thousands of substellar companions have been discovered with both indirect and direct methods of detection. While the majority of the sample is populated by objects discovered using radial velocity and transit techniques, an increasing number have been directly imaged. These planets and brown dwarfs are extraordinary sources of information that help in rounding out our understanding of planetary systems. Aims. In this paper, we focus our attention on substellar companions detected with the latter technique, with the primary goal of investigating their close surroundings and looking for additional companions and satellites, as well as disks and rings. Any such discovery would shed light on many unresolved questions, particularly with regard to their possible formation mechanisms. Methods. To reveal bound features of directly imaged companions, whether for point-like or extended sources, we need to suppress the contribution from the source itself. Therefore, we developed a method based on the negative fake companion technique that first estimates the position in the field of view (FoV) and the flux of the imaged companion with high precision, then subtracts a rescaled model point spread function (PSF) from the imaged companion, using either an image of the central star or another PSF in the FoV. Next it performs techniques, such as angular differential imaging, to further remove quasi-static patterns of the star (i.e., speckle contaminants) that affect the residuals of close-in companions. Results. After testing our tools on simulated companions and disks and on systems that were chosen ad hoc, we applied the method to the sample of substellar objects observed with SPHERE during the SHINE GTO survey. Among the 27 planets and brown dwarfs we analyzed, most objects did not show remarkable features, which was as expected, with the possible exception of a point source close to DH Tau B. This candidate companion was detected in four different SPHERE observations, with an estimated mass of ~1MJup, and a mass ratio with respect to the brown dwarf of 1∕10. This binary system, if confirmed, would be the first of its kind, opening up interesting questions for the formation mechanism, evolution, and frequency of such pairs. In order to address the latter, the residuals and contrasts reached for 25 companions in the sample of substellar objects observed with SPHERE were derived. If the DH Tau Bb companion is real, the binary fraction obtained is ~7%, which is in good agreement with the results obtained for field brown dwarfs. Conclusions. While there may currently be many limitations affecting the exploration of bound features to directly imaged exoplanets and brown dwarfs, next-generation instruments from the ground and space (i.e., JWST, ELT, and LUVOIR) will be able to image fainter objects and, thus, drive the application of this technique in upcoming searches for exo-moons and circumplanetary disks.

Characterizing brown dwarf companions with IRDIS long-slit spectroscopy: HD 1160 B and HD 19467 B

ABSTRACT The determination of the fundamental properties (mass, separation, age, gravity, and atmospheric properties) of brown dwarf companions allows us to infer crucial informations on their formation and evolution mechanisms. Spectroscopy of substellar companions is available to date only for a limited number of objects (and mostly at very low resolution, R &lt; 50) because of technical limitations, i.e. contrast and angular resolution. We present medium resolution (R = 350), coronagraphic long-slit spectroscopic observations with SPHERE of two substellar companions, HD 1160 B and HD 19467 B. We found that HD 1160 B has a peculiar spectrum that cannot be fitted by spectra in current spectral libraries. A good fit is possible only considering separately the Y+J and the H spectral band. The spectral type is between M5 and M7. We also estimated a Teff of 2800–2900 K and a log g of 3.5–4.0 dex. The low surface gravity seems to favour young age (10–20 Myr) and low mass (∼20 MJup ) for this object. HD 19467 B is instead a fully evolved object with a Teff of ∼1000 K and log g of ∼5.0 dex. Its spectral type is T6 ± 1.

MIRACLES: atmospheric characterization of directly imaged planets and substellar companions at 4–5 μm

Context. Directly imaged planets and substellar companions are key targets for the characterization of self-luminous atmospheres. Their photometric appearance at 4–5 μm is sensitive to the chemical composition and cloud content of their atmosphere. Aims. We aim to systematically characterize the atmospheres of directly imaged low-mass companions at 4–5 μm. We want to homogeneously process the data, provide robust flux measurements, and compile a photometric library at thermal wavelengths of these mostly young, low-gravity objects. In this way, we want to find trends related to their spectral type and surface gravity by comparing with isolated brown dwarfs and predictions from atmospheric models. Methods. We used the high-resolution, high-contrast capabilities of NACO at the Very Large Telescope (VLT) to directly image the companions of HIP 65426, PZ Tel, and HD 206893 in the NB4.05 and/or M′ filters. For the same targets, and additionally β Pic, we also analyzed six archival VLT/NACO datasets which were taken with the NB3.74, L′, NB4.05, and M′ filters. The data processing and photometric extraction of the companions was done with PynPoint while the species toolkit was used to further analyze and interpret the fluxes and colors. Results. We detect for the first time HIP 65426 b, PZ Tel B, and HD 206893 B in the NB4.05 filter, PZ Tel B and HD 206893 B in the M′ filter, and β Pic b in the NB3.74 filter. We provide calibrated magnitudes and fluxes with a careful analysis of the error budget, both for the new and archival datasets. The L′–NB4.05 and L′–M′ colors of the studied sample are all red while the NB4.05–M′ color is blue for β Pic b, gray for PZ Tel B, and red for HIP 65426 b and HD 206893 B (although typically with low significance). The absolute NB4.05 and M′ fluxes of our sample are all larger than those of field dwarfs with similar spectral types. Finally, the surface gravity of β Pic b has been constrained to log g = 4.17−0.13+0.10 dex from its photometry and dynamical mass. Conclusions. A red color at 3–4 μm and a blue color at 4–5 μm might be (partially) caused by H2O and CO absorption, respectively, which are expected to be the most dominant gaseous opacities in hot (Teff ≳ 1300 K) atmospheres. The red characteristics of β Pic b, HIP 65426 b, and HD 206893 B at 3–5μm, as well as their higher fluxes in NB4.05 and M′ compared to field dwarfs, indicate that cloud densities are enhanced close to the photosphere as a result of their low surface gravity.

2MASS J15491331-3539118: a new low-mass wide companion of the GQ Lup system

Substellar companions at wide separation around stars hosting planets or brown dwarfs (BDs) yet close enough for their formation in the circumstellar disc are of special interest. In this Letter we report the discovery of a wide (projected separation ∼16″​​.0, or 2400 AU, and position angle 114.61°) companion of the GQ Lup A-B system, most likely gravitationally bound to it. A VLT/X-shooter spectrum shows that this star, 2MASS J15491331-3539118, is a bonafide low-mass (∼0.15 M⊙) young stellar object (YSO) with stellar and accretion/ejection properties typical of Lupus YSOs of similar mass, and with kinematics consistent with that of the GQ Lup A-B system. A possible scenario for the formation of the triple system is that GQ Lup A and 2MASS J15491331-3539118 formed by fragmentation of a turbulent core in the Lup I filament, while GQ Lup B, the BD companion of GQ Lup A at 0″​​.7, formed in situ by the fragmentation of the circumprimary disc. The recent discoveries that stars form along cloud filaments would favour the scenario of turbulent fragmentation for the formation of GQ Lup A and 2MASS J15491331-3539118.