We propose a set of standard assumptions for the modelling of Class II and III protoplanetary disks, which includes detailed continuum radiative transfer, thermo-chemical modelling of gas and ice, and line radiative transfer from optical to cm wavelengths. The first paper of this series focuses on the assumptions about the shape of the disk, the dust opacities, dust settling, and polycyclic aromatic hydrocarbons (PAHs). In particular, we propose new standard dust opacities for disk models, we present a simplified treatment of PAHs in radiative equilibrium which is sufficient to reproduce the PAH emission features, and we suggest using a simple yet physically justified treatment of dust settling. We roughly adjust parameters to obtain a model that predicts continuum and line observations that resemble typical multi-wavelength continuum and line observations of Class II T Tauri stars. We systematically study the impact of each model parameter (disk mass, disk extension and shape, dust settling, dust size and opacity, gas/dust ratio, etc.) on all mainstream continuum and line observables, in particular on the SED, mm-slope, continuum visibilities, and emission lines including [OI] 63 μm, high-J CO lines, (sub-)mm CO isotopologue lines, and CO fundamental ro-vibrational lines. We find that evolved dust properties, i.e. large grains, often needed to fit the SED, have important consequences for disk chemistry and heating/cooling balance, leading to stronger near-to far-IR emission lines in general. Strong dust settling and missing disk flaring have similar effects on continuum observations, but opposite effects on far-IR gas emission lines. PAH molecules can efficiently shield the gas from stellar UV radiation because of their strong absorption and negligible scattering opacities in comparison to evolved dust. The observable millimetre-slope of the SED can become significantly more gentle in the case of cold disk midplanes, which we find regularly in our T Tauri models. We propose to use line observations of robust chemical tracers of the gas, such as O, CO, and H 2 , as additional constraints to determine a number of key properties of the disks, such as disk shape and mass, opacities, and the dust/gas ratio, by simultaneously fitting continuum and line observations.

We report on the properties of pre-main-sequence objects in the Taurus molecular clouds as observed in 7 mid-and far-infrared bands with the Spitzer Space Telescope. There are 215 previously-identified members of the Taurus star-forming region in our ∼44 square degree map; these members exhibit a range of Spitzer colors that we take to define young stars still surrounded by circumstellar dust (noting that ∼20% of the bonafide Taurus members exhibit no detectable dust excesses). We looked for new objects in the survey field with similar Spitzer properties, aided -2by extensive optical, X-ray, and ultraviolet imaging, and found 148 candidate new members of Taurus. We have obtained follow-up spectroscopy for about half the candidate sample, thus far confirming 34 new members, 3 probable new members, and 10 possible new members, an increase of 15-20% in Taurus members. Of the objects for which we have spectroscopy, 7 are now confirmed extragalactic objects, and one is a background Be star. The remaining 93 candidate objects await additional analysis and/or data to be confirmed or rejected as Taurus members. Most of the new members are Class II M stars and are located along the same cloud filaments as the previously-identified Taurus members. Among non-members with Spitzer colors similar to young, dusty stars are evolved Be stars, planetary nebulae, carbon stars, galaxies, and AGN.Subject headings: stars: formation -stars: circumstellar matter -stars: pre-main sequenceinfrared: starswhere m is the reported magnitude (and F ν the flux density) for a given object, Z = 18.259, 17.204, and 14.837, and f = 1.94×10 −16 , 4.76×10 −16 , and 5.71×10 −15 ergs cm −2 s −1Å−1 counts −1 sec for U , UVW1, and UVW2 (respectively). In the equation, λ is in units ofÅ, and c is 3×10 18Å s −1 The effective wavelengths are 0.344, 0.291, and 0.212 µm for U , UVW1, and UVW2. There are ∼1600 objects with XMM-Newton OM flux densities in our catalog (0.2% of the entire catalog).We note that many of the X-ray detected XEST sources are likely background galaxies (see Güdel et al. 2007) and that XEST included regions not covered by our map, such as L1551.The XEST team assembled a catalog of supporting data from the literature, such as optical photometric measurements, for all of the previously-identified Taurus members (see §3.1.1 below); we have included these photometric points in our database, converting Johnson magnitudes to flux densities using zero-points available in the literature (e.g., Cox 2001 and references therein).The SEDs presented in this paper use all of these supporting data where available (except for the X-ray fluxes), and are presented as λF λ in cgs units (erg s −1 cm −2 ), against λ in microns.2 In SDSS, a "maggy" is the ratio of the flux density of the object to a standard flux density. The Sloan magnitudes are AB magnitudes, as opposed to Vega magnitudes. In the AB system, a flat spectrum object with 3631 Jy at each band should have every magnitude equal to zero, and all maggies equal to one. Flux densities returned by th...

Context. The accretion history of low-mass young stars is not smooth but shows spikes of accretion that can last from months and years to decades and centuries. Aims. Observations of young stars in outbursts can help us understand the temporal evolution of accreting stars and the interplay between the accretion disk and the stellar magnetosphere. Methods. The young late-type star V1118 Orionis was in outburst from 2005 to 2006. We followed the outburst with optical and near-infrared photometry. The X-ray emission was further probed with observations taken with XMM-Newton and Chandra during and after the outburst. In addition, we obtained mid-infrared photometry and spectroscopy with Spitzer at the peak of the outburst and in the post-outburst phase. Results. The spectral energy distribution of V1118 Ori varied significantly over the course of the outburst. The optical flux showed the largest variations, most likely caused by enhanced emission by a hot spot. The hot spot dominated the optical and near-infrared emission at the peak of the outburst, while the disk emission dominated in the mid-infrared. The emission silicate feature in V1118 Ori is flat and does not vary in shape, but was slightly brighter at the peak of the outburst compared to the post-outburst spectrum. The X-ray flux correlated with the optical and infrared fluxes, indicating that accretion affected the magnetically active corona and the stellar magnetosphere. The thermal structure of the corona was variable with some indication of a cooling of the coronal temperature in the early phase of the outburst with a gradual return to normal values. Color-color diagrams in the optical and infrared showed variations during the outburst, with no obvious signature of reddening caused by circumstellar matter. Using Monte-Carlo realizations of star+disk+hotspot models to fit the spectral energy distributions in "quiescence" and at the peak of the outburst, we determined that the mass accretion rate varied from about 2.5 × 10 −7 M yr −1 to 1.0 × 10 −6 M yr −1 ; in addition, the fractional area of the hotspot increased significantly. Conclusions. The multi-wavelength study of the V1118 Ori outburst helped us to understand the variations in spectral energy distributions and demonstrated the interplay between the disk and the stellar magnetosphere in a young, strongly accreting star.

Context. The [Ne II] line 12.81 μm was proposed to be a good tracer of gas in the environments of proto-planetary disks; its origin is explained by different mechanisms: jets in outflows, photo-evaporative disk winds driven by stellar X-rays/EUV or by the X-ray irradiated proto-planetary disk atmosphere. Previous Spitzer studies gave hints toward the neon emitting mechanism by exploring correlations between the line luminosity and properties of the star-disk system. These studies concluded that the origin of the emission is likely related to accretion and outflows, with some influence from X-rays. Aims. We provide direct constraints on the origin of the [Ne II] emission using high-spatial and spectral resolution observations that allow us to study the kinematics of the emitting gas. In addition we compare the [Ne II] line with optical forbidden lines. Methods. We obtained high-resolution ground-based observations with VISIR-VLT for 15 stars and UVES-VLT for three of them. The stars were chosen for having bright neon emission lines detected with Spitzer/IRS. The velocity shifts and profiles are used to disentangle the different emitting mechanisms producing the [Ne II] line. A comparison between results from this study and previous high-resolution studies is also presented. Results. The [Ne II] line was detected in seven stars, among them the first confirmed detection of [Ne II] in a Herbig Be star, V892 Tau. In four cases, the large blueshifted lines indicate an origin in a jet. In two stars, the small shifts and asymmetric profiles indicate an origin in a photo-evaporative wind. CoKu Tau 1, seen close to edge-on, shows a spatially unresolved line centered at the stellar rest velocity, although cross-dispersion centroids move within 10 AU from one side of the star to the other as a function of wavelength. The line profile is symmetric with wings extending up to ∼±80 km s −1 . The origin of the [Ne II] line is unclear and could either be due to the bipolar jet or to the disk. For the stars with VLT-UVES observations, in several cases, the optical forbidden line profiles and shifts are very similar to the profile of the [Ne II] line, suggesting that the lines are emitted in the same region. A general trend observed with VISIR is a lower line flux when compared with the fluxes obtained with Spitzer. We found no correlation between the line full-width at half maximum and the line peak velocity. The [Ne II] line remains undetected in a large part of the sample, an indication that the emission detected with Spitzer in those stars is likely extended.

Context. Quantifying the gas surface density inside the dust cavities and gaps of transition disks is important to establish their origin. Aims. We seek to constrain the surface density of warm gas in the inner disk of HD 139614, an accreting 9 Myr Herbig Ae star with a (pre-)transition disk exhibiting a dust gap from 2.3±0.1 to 5.3±0.3 AU. Methods. We observed HD 139614 with ESO/VLT CRIRES and obtained high-resolution (R∼90 000) spectra of CO ro-vibrational emission at 4.7 µm. We derived constraints on the disk's structure by modeling the CO isotopolog line-profiles, the spectroastrometric signal, and the rotational diagrams using grids of flat Keplerian disk models. Results. We detected υ = 1 → 0 12 CO, 2→1 12 CO, 1→0 13 CO, 1→0 C 18 O, and 1→0 C 17 O ro-vibrational lines. Lines are consistent with disk emission and thermal excitation. 12 CO υ = 1 → 0 lines have an average width of 14 km s −1 , T gas of 450 K and an emitting region from 1 to 15 AU. 13 CO and C 18 O lines are on average 70 and 100 K colder, 1 and 4 km s −1 narrower than 12 CO υ = 1 → 0, and are dominated by emission at R≥ 6 AU. The 12 CO υ = 1 → 0 composite line-profile indicates that if there is a gap devoid of gas it must have a width narrower than 2 AU. We find that a drop in the gas surface density (δ gas ) at R < 5 − 6 AU is required to be able to simultaneously reproduce the line-profiles and rotational diagrams of the three CO isotopologs. Models without a gas density drop generate 13 CO and C 18 O emission lines that are too broad and warm. The value of δ gas can range from 10 −2 to 10 −4 depending on the gas-to-dust ratio of the outer disk. We find that the gas surface density profile at 1 < R < 6 AU is flat or increases with radius. We derive a gas column density at 1 < R < 6 AU of N H = 3 × 10 19 − 10 21 cm −2 (7 × 10 −5 − 2.4 × 10 −3 g cm −2 ) assuming N CO = 10 −4 N H . We find a 5σ upper limit on the CO column density N CO at R≤1 AU of 5 × 10 15 cm −2 (N H ≤ 5 × 10 19 cm −2 ). Conclusions. The dust gap in the disk of HD 139614 has molecular gas. The distribution and amount of gas at R≤ 6 AU in HD 139614 is very different from that of a primordial disk. The gas surface density in the disk at R ≤ 1 AU and at 1 < R < 6 AU is significantly lower than the surface density that would be expected from the accretion rate of HD 139614 (10 −8 M yr −1 ) assuming a standard viscous α-disk model. The gas density drop, the non-negative density gradient in the gas inside 6 AU, and the absence of a wide (> 2 AU) gas gap, suggest the presence of an embedded < 2 M J planet at around 4 AU. A. Carmona et al.: CO ro-vibrational emission in the transition disk HD 139614. 12 CO 1-0 P(6) 12 CO 1-0 P(7) 12 CO 1-0 P(9) 2.0 2.2 2.4 2.6 12 CO 1-0 P(10) -40 -20 0 20 40 0.2 0.6 1.0 12 CO 1-0 P(11) 12 CO 1-0 P(12) 12 CO 1-0 P(13) 12 CO 1-0 P(15) 13 CO 1-0 R(6) 13 CO 1-0 R(5) 13 CO 1-0 R(4) 2.0 2.2 13 CO 1-0 R(2) -40 -20 0 20 40 0.2 0.6 1.0 13 CO 1-0 R(0) 13 CO 1-0 P(1) 13 CO 1-0 P(2) 13 CO1-0P4 12 CO2-1P9 C 18 O 1-0 R(7) C 18 O 1-0 R(6) C 18 O 1-0 R(5)