Search for: All records

Abstract We present near-infrared Large Binocular Telescope LMIRCam imagery of the disk around the Herbig Ae/Be star AB Aurigae. A comparison of the surface brightness at K s (2.16 μ m), H 2 O narrowband (3.08 μ m), and L ′ (3.7 μ m) allows us to probe the presence of icy grains in this (pre)transitional disk environment. By applying reference differential imaging point-spread function subtraction, we detect the disk at high signal-to-noise ratios in all three bands. We find strong morphological differences between the bands, including asymmetries consistent with the observed spiral arms within 100 au in L ′ . An apparent deficit of scattered light at 3.08 μ m relative to the bracketing wavelengths ( K s and L ′ ) is evocative of ice absorption at the disk surface layer. However, the Δ( K s − H 2 O) color is consistent with grains with little to no ice (0%–5% by mass). The Δ ( H 2 O − L ′ ) color, conversely, suggests grains with a much higher ice mass fraction (∼0.68), and the two colors cannot be reconciled under a single grain population model. Additionally, we find that the extremely red Δ ( K s − L ′ ) disk color cannot be reproduced under conventional scattered light modeling with any combination of grain parameters or reasonable local extinction values. We hypothesize that the scattering surfaces at the three wavelengths are not colocated, and that the optical depth effects in each wavelength result from probing the grain population at different disk surface depths. The morphological similarity between K s and H 2 O suggests that their scattering surfaces are near one another, lending credence to the Δ( K s − H 2 O) disk color constraint of <5% ice mass fraction for the outermost scattering disk layer. 

Context. HD 113337 is a main-sequence F6V field star more massive than the Sun. This star hosts one confirmed giant planet and possibly a second candidate, detected by radial velocities (RVs). The star also hosts a cold debris disc detected through the presence of an infrared excess, making it an interesting system to explore. Aims. We aim to bring new constraints on the star’s fundamental parameters, debris disc properties, and planetary companion(s) by combining complementary techniques. Methods. We used the VEGA interferometer on the CHARA array to measure the angular diameter of HD 113337. We derived its linear radius using the parallax from the Gaia Second Data Release. We computed the bolometric flux to derive its effective temperature and luminosity, and we estimated its mass and age using evolutionary tracks. Then, we used Herschel images to partially resolve the outer debris disc and estimate its extension and inclination. Next, we acquired high-contrast images of HD 113337 with the LBTI to probe the ~10–80 au separation range. Finally, we combined the deduced contrast maps with previous RVs of the star using the MESS2 software to bring upper mass limits on possible companions at all separations up to 80 au. We took advantage of the constraints on the age and inclination brought by fundamental parameter analysis and disc imaging, respectively, for this analysis. Results. We derive a limb-darkened angular diameter of 0.386 ± 0.009 mas that converts into a linear radius of 1.50 ± 0.04 R ⊙ for HD 113337. The fundamental parameter analysis leads to an effective temperature of 6774 ± 125 K and to two possible age solutions: one young within 14–21 Myr and one old within 0.8–1.7 Gyr. We partially resolve the known outer debris disc and model its emission. Our best solution corresponds to a radius of 85 ± 20 au, an extension of 30 ± 20 au, and an inclination within 10–30° for the outer disc. The combination of imaging contrast limits, published RV, and age and inclination solutions allows us to derive a first possible estimation of the true masses of the planetary companions: ~7 −2 +4 M Jup for HD 113337 b (confirmed companion) and ~16 −3 +10 M Jup for HD 113337 c (candidate companion). We also constrain possible additional companions at larger separations. 

Abstract Tight relationships exist in the local Universe between the central stellar properties of galaxies and the mass of their supermassive black hole (SMBH)^1–3. These suggest that galaxies and black holes co-evolve, with the main regulation mechanism being energetic feedback from accretion onto the black hole during its quasar phase^4–6. A crucial question is how the relationship between black holes and galaxies evolves with time; a key epoch to examine this relationship is at the peaks of star formation and black hole growth 8–12 billion years ago (redshifts 1–3)⁷. Here we report a dynamical measurement of the mass of the black hole in a luminous quasar at a redshift of 2, with a look back in time of 11 billion years, by spatially resolving the broad-line region (BLR). We detect a 40-μas (0.31-pc) spatial offset between the red and blue photocentres of the Hα line that traces the velocity gradient of a rotating BLR. The flux and differential phase spectra are well reproduced by a thick, moderately inclined disk of gas clouds within the sphere of influence of a central black hole with a mass of 3.2 × 10⁸ solar masses. Molecular gas data reveal a dynamical mass for the host galaxy of 6 × 10¹¹ solar masses, which indicates an undermassive black hole accreting at a super-Eddington rate. This suggests a host galaxy that grew faster than the SMBH, indicating a delay between galaxy and black hole formation for some systems. 

Context.Since 2019, GRAVITY has provided direct observations of giant planets and brown dwarfs at separations of down to 95 mas from the host star. Some of these observations have provided the first direct confirmation of companions previously detected by indirect techniques (astrometry and radial velocities). Aims.We want to improve the observing strategy and data reduction in order to lower the inner working angle of GRAVITY in dual-field on-axis mode. We also want to determine the current limitations of the instrument when observing faint companions with separations in the 30–150 mas range. Methods.To improve the inner working angle, we propose a fiber off-pointing strategy during the observations to maximize the ratio of companion-light-to-star-light coupling in the science fiber. We also tested a lower-order model for speckles to decouple the companion light from the star light. We then evaluated the detection limits of GRAVITY using planet injection and retrieval in representative archival data. We compare our results to theoretical expectations. Results.We validate our observing and data-reduction strategy with on-sky observations; first in the context of brown dwarf follow-up on the auxiliary telescopes with HD 984 B, and second with the first confirmation of a substellar candidate around the starGaiaDR3 2728129004119806464. With synthetic companion injection, we demonstrate that the instrument can detect companions down to a contrast of 8 × 10⁻⁴(ΔΚ= 7.7 mag) at a separation of 35 mas, and a contrast of 3 × 10⁻⁵(ΔΚ= 11 mag) at 100 mas from a bright primary (K< 6.5), for 30 min exposure time. Conclusions.With its inner working angle and astrometric precision, GRAVITY has a unique reach in direct observation parameter space. This study demonstrates the promising synergies between GRAVITY andGaiafor the confirmation and characterization of substellar companions.