We report Gemini Planet Imager H band high-contrast imaging/integral field spectroscopy and polarimetry of the HD 100546, a 10 M yr-old early-type star recently confirmed to host a thermal infrared bright (super)jovian protoplanet at wide separation, HD 100546 b. We resolve the inner disk cavity in polarized light, recover the thermal-infrared (IR) bright arm, and identify one additional spiral arm. We easily recover HD 100546 b and show that much of its emission plausibly originates from an unresolved, point source. The point source component of HD 100546 b has extremely red infrared colors compared to field brown dwarfs, qualitatively similar to young cloudy superjovian planets; however, these colors may instead indicate that HD 100546 b is still accreting material from a circumplanetary disk. Additionally, we identify a second point source-like peak at r proj ∼ 14 AU, located just interior to or at inner disk wall consistent with being a 10-20 M J candidate second protoplanet-"HD 100546 c" -and lying within a weakly polarized region of the disk but along an extension of the thermal IR bright spiral arm. Alternatively, it is equally plausible that this feature is a weakly polarized but locally bright region of the inner disk wall. Astrometric monitoring of this feature over the next 2 years and emission line measurements could confirm its status as a protoplanet, rotating disk hot spot that is possibly a signpost of a protoplanet, or a stationary emission source from within the disk.

The characterization of gas in the inner disks around young stars is of particular interest because of its connection to planet formation. In order to study the gas in inner disks, we have obtained high-resolution K-band and M-band spectroscopy of 14 intermediate mass young stars. In sources that have optically thick inner disks, i.e. E(K-L)>1, our detection rate of the rovibrational CO transitions is 100% and the gas is thermally excited. Of the five sources that do not have optically thick inner disks, we only detect the ro-vibrational CO transitions from HD 141569. In this case, we show that the gas is excited by UV fluorescence and that the inner disk is devoid of gas and dust. We discuss the plausibility of the various scenarios for forming this inner hole. Our modeling of the UV fluoresced gas suggests an additional method by which to search for and/or place stringent limits on gas in dust depleted regions in disks around Herbig Ae/Be stars.Subject headings: accretion, accretion disks ---circumstellar matter---line: profiles---molecular processes---planetary systems: protoplanetary disks---stars: pre-main sequence 1 Michelson Postdoctoral Fellow A complementary diagnostic of gas in the inner disk are the ro-vibrational transitions of CO. Previous work has shown that the ro-vibrational lines of CO are sensitive probes of circumstellar gas and are well suited to exploring conditions within the inner, planet-forming regions of disks These lines can be excited thermally or by UV fluorescence. Infrared observations can detect an amount of CO much smaller than an Earth mass, well below the threshold necessary to circularize the orbits of terrestrial planets. Although CO is not a useful probe of the total mass of circumstellar gas at large column densities, its presence can be used to trace the "skin" of the gas disk.An observational clarification of how the gas evolves in the inner disks of young stars is central to an understanding of early planet formation. If planets form by a two-step process where grains first agglomerate into a large rocky core followed by the accretion of a gaseous envelope (e.g. Lissauer 1993), then the disk should go through a gas-rich/dust-poor stage. Alternatively, if planets form by a gravitational instability (e.g. Boss 1998), then the gas and dust ObservationsWe have observed a heterogeneous sample of 14 young intermediate mass stars (2-10 M  ) to measure the emission from H I (Br γ) and CO (Δv=1) ( Table 1). The targets include two intermediate mass T Tauri stars (IMTTS), seven Herbig AeBe (HAeBe) stars, four transitional

We observed a sample of 20 representative Herbig Ae/Be stars and 5 A-type debris discs with PACS onboard Herschel, as part of the GAS in Protoplanetary Systems (GASPS) project. The observations were done in spectroscopic mode, and cover the far-infrared line is only detected in 25% and CO J = 18-17 in 45% (and fewer cases for higher J transitions) of the Herbig Ae/Be stars, while for [C ii] 157 μm, we often find spatially variable background contamination. We show the first detection of water in a Herbig Ae disc, HD 163296, which has a settled disc. Hydroxyl is detected as well in this disc. First seen in HD 100546, CH + emission is now detected for the second time in a Herbig Ae star, HD 97048. We report fluxes for each line and use the observations as line diagnostics of the gas properties. Furthermore, we look for correlations between the strength of the emission lines and either the stellar or disc parameters, such as stellar luminosity, ultraviolet and X-ray flux, accretion rate, polycyclic aromatic hydrocarbon (PAH) band strength, and flaring. We find that the stellar ultraviolet flux is the dominant excitation mechanism

The accretion rate of young stars is a fundamental characteristic of these systems. While accretion onto T Tauri stars has been studied extensively, little work has been done on measuring the accretion rate of their intermediate-mass analogs, the Herbig Ae/Be stars. Measuring the stellar accretion rate of Herbig Ae/Bes is not straightforward both because of the dearth of metal absorption lines available for veiling measurements and the intrinsic brightness of Herbig Ae/Be stars at ultraviolet wavelengths where the brightness of the accretion shock peaks. Alternative approaches to measuring the accretion rate of young stars by measuring the luminosity of proxies such as the Br γ emission line have not been calibrated. A promising approach is the measurement of the veiling of the Balmer discontinuity. We present measurements of this veiling as well as the luminosity of Br γ. We show that the relationship between the luminosity of Br γ and the stellar accretion rate for classical T Tauri stars is consistent with Herbig Ae stars but not Herbig Be stars. We discuss the implications of this finding for understanding the interaction of the star and disk for Herbig Ae/Be stars.

In this paper we present high-resolution 4.7 μm spectra of the isolated Herbig Be star HD 100546. HD 100546 has been the subject of intense scrutiny because it is a young nearby star with a transitional disk. We observe the Δv = 1 rovibrational CO transitions in order to clarify the distribution of warm gas in the inner disk. Modeling of the CO spectrum indicates that the gas is vibrationally excited by collisions and UV fluorescence. The observed emission extends from 13 to 100 AU. The inner edge of the molecular gas emission is consistent with the inner edge of the optically thick dust disk indicating that the inner hole is not simply a hole in the dust opacity but is likely cleared of gas as well. The rotational temperature of the CO is ∼1000 K-much hotter than the ∼200 K CO in the otherwise similar transitional disk surrounding HD 141569. The origin of this discrepancy is likely linked to the brighter polycyclic aromatic hydrocarbon emission observed toward HD 100546. We use the excitation of the CO to constrain the geometry of the inner disk and comment on the evolutionary state of the system.