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Register a new userConstraints on the presence of SiO gas in the debris disk of HD 172555
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We have carried out two sets of observations to quantify the properties of SiO gas in the unusual HD 172555 debris disk: (1) a search for the J=8-7 rotational transition from the vibrational ground state, carried out with the APEX sub-millimeter telescope and heterodyne receiver at 863 microns, and (2) a search at 8.3 microns for the P(17) ro-vibrational transition of gas phase SiO, carried out with VLT/VISIR with a resolution, $lambda/Deltalambda$, of 30000. The APEX measurement resulted in a 3 $sigma$ non-detection of an interstellar feature, but only an upper limit to emission at the radial velocity and linewidth expected from HD 172555. The VLT/VISIR result was also an upper limit. These were used to provide limits for the abundance of gas phase SiO, for a range of temperatures. The upper limit from our APEX detection, assuming an 8000 K primary star photospheric excitation, falls more than an order of magnitude below the self-shielding stability threshold derived by Johnson et al. (2012). Our results thus favor a solid-state origin for the 8.3 micron feature seen in the Spitzer IRS spectrum of the circumstellar excess emission, and the production of circumstellar O$^+$ and Si$^+$ by SiO UV photolysis. The implications of these estimates are explored in the framework of models of the HD 172555 circumstellar disk.
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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 present new $H$-band scattered light images of the HD 32297 edge-on debris disk obtained with the Gemini Planet Imager (GPI). The disk is detected in total and polarized intensity down to a projected angular separation of 0.15, or 20au. On the other hand, the large scale swept-back halo remains undetected, likely a consequence of its markedly blue color relative to the parent body belt. We analyze the curvature of the disk spine and estimate a radius of $approx$100au for the parent body belt, smaller than past scattered light studies but consistent with thermal emission maps of the system. We employ three different flux-preserving post-processing methods to suppress the residual starlight and evaluate the surface brightness and polarization profile along the disk spine. Unlike past studies of the system, our high fidelity images reveal the disk to be highly symmetric and devoid of morphological and surface brightness perturbations. We find the dust scattering properties of the system to be consistent with those observed in other debris disks, with the exception of HR 4796. Finally, we find no direct evidence for the presence of a planetary-mass object in the system.
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 sensitive observations carried out with the Atacama Large Millimeter/Submillimeter Array (ALMA) of the dusty debris disk HD 95086. These observations were made in bands 6 (223 GHz) and 7 (338 GHz) with an angular resolution of about 1$$ which allowed us to resolve well the debris disk with a deconvolved size of 7.0$$ $times$ 6.0$$ and with an inner depression of about 2$$. We do not detect emission from the star itself and the possible inner dusty belt. We also do not detect CO (J=2-1) and (J=3-2) emission, excluding the possibility of an evolved gaseous primordial disk as noted in previous studies of HD95086. We estimated a lower limit for the gas mass of $leq$0.01 M$_oplus$ for the debris disk of HD95086. From the mm. emission, we computed a dust mass for the debris disk HD95086 of 0.5$pm$0.2 M$_oplus$, resulting in a dust-to-gas ratio of $geq$50. Finally, we confirm the detection of a strong submillimeter source to the northwest of the disk (ALMA-SMM1) revealed by recent ALMA observations. This new source might be interpreted as a planet in formation on the periphery of the debris disk HD 95086 or as a strong impact between dwarf planets. However, given the absence of the proper motions of ALMA-SMM1 similar to those reported in the debris disk (estimated from these new ALMA observations) and for the optical star, this is more likely to be a submillimeter background galaxy.
We report here time domain infrared spectroscopy and optical photometry of the HD145263 silica-rich circumstellar disk system taken from 2003 through 2014. We find an F4V host star surrounded by a stable, massive 1e22 - 1e23 kg (M_Moon to M_Mars) dust disk. No disk gas was detected, and the primary star was seen rotating with a rapid ~1.75 day period. After resolving a problem with previously reported observations, we find the silica, Mg-olivine, and Fe-pyroxene mineralogy of the dust disk to be stable throughout, and very unusual compared to the ferromagnesian silicates typically found in primordial and debris disks. By comparison with mid-infrared spectral features of primitive solar system dust, we explore the possibility that HD 145263s circumstellar dust mineralogy occurred with preferential destruction of Fe-bearing olivines, metal sulfides, and water ice in an initially comet-like mineral mix and their replacement by Fe-bearing pyroxenes, amorphous pyroxene, and silica. We reject models based on vaporizing optical stellar megaflares, aqueous alteration, or giant hypervelocity impacts as unable to produce the observed mineralogy. Scenarios involving unusually high Si abundances are at odds with the normal stellar absorption near-infrared feature strengths for Mg, Fe, and Si. Models involving intense space weathering of a thin surface patina via moderate (T < 1300 K) heating and energetic ion sputtering due to a stellar superflare from the F4V primary are consistent with the observations. The space weathered patina should be reddened, contain copious amounts of nanophase Fe, and should be transient on timescales of decades unless replenished.
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