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Register a new userFrom scattered-light to millimeter emission: A comprehensive view of the Gyr-old system of HD 202628 and its eccentric debris ring
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We present here new observations of the eccentric debris ring surrounding the Gyr-old solar-type star HD 202628: at millimeter wavelengths with ALMA, at far-infrared wavelengths with textit{Herschel}, and in scattered light with textit{HST}. The ring inner edge is found to be consistent between ALMA and textit{HST} data. As radiation pressure affects small grains seen in scattered-light, the ring appears broader at optical than at millimeter wavelengths. The best fit to the ring seen with ALMA has inner and outer edges at $143.1 pm 1.7$ AU and $165.5 pm 1.4$, respectively, and an inclination of $57.4^circ pm 0.4$ from face-on. The offset of the ring centre of symmetry from the star allows us to quantify its eccentricity to be $e=0.09_{-0.01}^{+0.02}$. This eccentric feature is also detected in low resolution textit{Herschel}/PACS observations, under the form of a pericenter-glow. Combining the infrared and millimeter photometry, we retrieve a disk grain size distribution index of $sim -3.4$, and therefore exclude in-situ formation of the inferred belt-shaping perturber, for which we provide new dynamical constraints. Finally, ALMA images show four point-like sources that exceed 100$,mu$Jy, one of them being just interior to the ring. Although the presence of a background object cannot be excluded, we cannot exclude either that this source is circumplanetary material surrounding the belt-shaper, in which case degeneracies between its mass and orbital parameters could be lifted, allowing us to fully characterize such a distant planet in this mass and age regime for the very first time.
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We performed observations of the Sco-Cen F star HD 117214 aiming at a search for planetary companions and the characterization of the debris disk structure. HD 117214 was observed with the SPHERE subsystems IRDIS, IFS and ZIMPOL at optical and near-IR wavelengths using angular and polarimetric differential imaging techniques. This provided the first images of scattered light from the debris disk with a spatial resolution reaching 25 mas and an inner working angle $< 0.1$. With the observations with IRDIS and IFS we derive detection limits for substellar companions. The geometrical parameters of the detected disk are constrained by fitting 3D models for the scattering of an optically thin dust disk. Investigating the possible origin of the disk gap, we introduced putative planets therein and modeled the planet-disk and planet-planet dynamical interactions. The obtained planetary architectures are compared with the detection limit curves. The debris disk has an axisymmetric ring structure with a radius of $0.42(pm 0.01)$ or $sim45$ au and an inclination of $71(pm 2.5)^circ$ and exhibits a $0.4$ ($sim40$ au) wide inner cavity. From the polarimetric data, we derive a polarized flux contrast for the disk of $(F_{rm pol})_{rm disk}/F_{rm ast}> (3.1 pm 1.2)cdot 10^{-4}$ in the RI band. The fractional scattered polarized flux of the disk is eight times smaller than the fractional infrared flux excess. This ratio is similar to the one obtained for the debris disk HIP 79977 indicating that dust radiation properties are not very different between these two disks. Inside the disk cavity we achieve the high sensitivity limits on planetary companions with a mass down to $sim 4 M_{rm J}$ at projected radial separations between $0.2$ and $0.4$. We can exclude the stellar companions at a radial separation larger than 75 mas from the star.
We have used the Submillimeter Array (SMA) to make 1.3 millimeter observations of the debris disk surrounding HD 15115, an F-type star with a putative membership in the beta Pictoris moving group. This nearly edge-on debris disk shows an extreme asymmetry in optical scattered light, with an extent almost two times larger to the west of the star than to the east (originally dubbed the Blue Needle). The SMA observations reveal resolved emission that we model as a circumstellar belt of thermal dust emission. This belt extends to a radius of ~110 AU, coincident with the break in the scattered light profile convincingly seen on the western side of the disk. This outer edge location is consistent with the presence of an underlying population of dust-producing planetesimals undergoing a collisional cascade, as hypothesized in birth ring theory. In addition, the millimeter emission shows a ~3 sigma feature aligned with the asymmetric western extension of the scattered light disk. If this millimeter extension is real, then mechanisms for asymmetry that affect only small grains, such as interactions with interstellar gas, are disfavored. This tentative feature might be explained by secular perturbations to grain orbits introduced by neutral gas drag, as previously invoked to explain asymmetric morphologies of other, similar debris disks.
We present observations of the HD 15115 debris disk from ALMA at 1.3 mm that capture this intriguing system with the highest resolution ($0.!!^{primeprime}6$ or $29$ AU) at millimeter wavelengths to date. This new ALMA image shows evidence for two rings in the disk separated by a cleared gap. By fitting models directly to the observed visibilities within a MCMC framework, we are able to characterize the millimeter continuum emission and place robust constraints on the disk structure and geometry. In the best-fit model of a power law disk with a Gaussian gap, the disk inner and outer edges are at $43.9pm5.8$ AU ($0.!!^{primeprime}89pm0.!!^{primeprime}12$) and $92.2pm2.4$ AU ($1.!!^{primeprime}88pm0.!!^{primeprime}49$), respectively, with a gap located at $58.9pm4.5$~AU ($1.!!^{primeprime}2pm0.!!^{primeprime}10$) with a fractional depth of $0.88pm0.10$ and a width of $13.8pm5.6$ AU ($0.!!^{primeprime}28pm0.!!^{primeprime}11$). Since we do not see any evidence at millimeter wavelengths for the dramatic east-west asymmetry seen in scattered light, we conclude that this feature most likely results from a mechanism that only affects small grains. Using dynamical modeling and our constraints on the gap properties, we are able to estimate a mass for the possible planet sculpting the gap to be $0.16pm0.06$ $M_text{Jup}$.
We present the first scattered-light images of two debris disks around the F8 star HD 104860 and the F0V star HD 192758, respectively $sim45$ and $sim67$ pc away. We detected these systems in the F110W and F160W filters through our re-analysis of archival Hubble Space Telescope NICMOS data with modern starlight subtraction techniques. Our image of HD 104860 confirms the morphology previously observed by Herschel in thermal emission with a well-defined ring at radius $sim114$ au inclined $sim58$ degrees. Although the outer edge profile is consistent with dynamical evolution models, the sharp inner edge suggests sculpting by unseen perturbers. Our images of HD 192758 reveal a disk at radius $sim95$ au inclined by $sim59$ degrees, never resolved so far. These disks have low scattering albedos of 10% and 13% respectively, inconsistent with water ice grain compositions. They are reminiscent of several other disks with similar inclination and scattering albedos: Fomalhaut, HD 92945, HD 202628, and HD 207129. They are also very distinct from brighter disks in the same inclination bin, which point to different compositions between these two populations. Varying scattering albedo values can be explained by different grain porosities, chemical compositions, or grain size distributions, which may indicate distinct formation mechanisms or dynamical processes at work in these systems. Finally, these faint disks with large infrared excesses may be representative of an underlying population of systems with low albedo values. Searches with more sensitive instruments on HST or on the James Webb Space Telescope and using state-of-the art starlight-subtraction methods may help discover more of such faint systems.
We present the first scattered light image of the debris disk around HD 129590, a ~1.3 M$_odot$ G1V member of the Scorpius Centaurus association with age ~10-16 Myr. The debris disk is imaged with the high contrast imaging instrument SPHERE at the Very Large Telescope, and is revealed by both the IRDIS and IFS subsytems, operating in the H and YJ bands respectively. The disk has a high infrared luminosity of $L_{textrm{IR}}/L_{textrm{star}}$~5$times$10$^{-3}$, and has been resolved in other studies using ALMA. We detect a nearly edge on ring, with evidence of an inner clearing. We fit the debris disk using a model characterized by a single bright ring, with radius ~60-70 AU, in broad agreement with previous analysis of the target SED. The disk is vertically thin, and has an inclination angle of ~75$^circ$. Along with other previously imaged edge-on disks in the Sco-Cen association such as HD 110058, HD 115600, and HD 111520, this disk image will allow of the structure and morphology of very young debris disks, shortly after the epoch of planet formation has ceased.
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