D. Fedele

The structure of the protoplanetary disk surrounding three young intermediate mass stars II. Spatially resolved dust and gas distribution

Aims. We present the first direct comparison of the distribution of the gas, as traced by the [O i] 6300 A emission, and the dust, as traced by the 10 μm emission, in the planet-forming region of proto-planetary disks around three intermediate-mass stars: HD 101412, HD 135344 B and HD 179218. Methods. N-band visibilities were obtained with VLTI/MIDI. Simple geometrical models are used to compare the dust emission to high-resolution optical spectra in the 6300 A [O i] line of the same targets. Results. HD 101412 and HD 135344 B show compact (< 2A U) 10μm emission while the [O i] brightness profile shows a double peaked structure. The inner peak is strongest and is consistent with the location of the dust, the outer peak is fainter and is located at 5–10 AU. In both systems, spatially extended PAH emission is found. HD 179218 shows a double ring-like 10 μm emission with the first ring peaking at ∼1 AU and the second at ∼20 AU. The [O i] emitting region is more compact, peaking between 3–6 AU. Conclusions. The disks around HD 101412 and HD 135344 B appear strongly flared in the gas, but self-shadowed in the dust beyond ∼ 2A U. The difference in the gas and dust vertical structure beyond 2 AU might be the first observational evidence of gas-dust decoupling in protoplanetary disks. The disk around HD 179218 is flared in the dust. The 10 μm emission emerges from the inner rim and from the flared surface of the disk at larger radii. No dust emission is detected between ∼3–15 AU. The oxygen emission seems also to come from a flared structure, however, the bulk of this emission is produced between ∼1–10 AU. This could indicate a lack of gas in the outer disk or could be due to chemical effects which reduce the abundance of OH – the parent molecule of the observed [O i] emission – further away from the star. It may also be a contrast effect if the [O i] emission is much stronger in the inner disk. We suggest that the three systems, HD 179218, HD 135344 B and HD 101412, may form an evolutionary sequence: the disk initially flared becomes flat under the combined action of gas-dust decoupling, grain growth and dust settling.

The Structure of Protoplanetary Disks Surrounding Three Young Intermediate Mass Stars ⋆ I. Resolving the disk rotation in the (OI) 6300 Å line

We present high-spectral-resolution, optical spectra of three young, intermediate-mass stars, in all of which we spectrally resolve the 6300 A [OI] emission line. Two of these have a double-peaked line-profile. We attempt to fit these data using a simple model of [OI] emission, which is generated by photo-dissociation of OH molecules, in the upper layer of a circumstellar disk, by stellar UV radiation. We translate the Doppler-broadened [OI] emission line profile, into a measure of emission, as a function of distance from the central star. The resulting spectra are in agreement with the expected disk shapes derived from their spectral energy distribution. We find evidence for shadowing by an inner rim in the disk surrounding HD 101412, and observe a flaring disk structure in HD 179218, while the [OI] spectrum of HD 135344 B is more complex. The [OI] emission starts for all three targets at velocities corresponding to their dust sublimation radius and extends up to radii of 10–90 AU. This shows that this method can be a valuable tool in the future investigation of circumstellar disks.

Optical and infrared properties of V1647 Orionis during the 2003–2006 outburst - II. Temporal evolution of the eruptive source

Aims. The occurrence of new FU Orionis-like objects is fundamental to understand the outburst mechanism in young stars and their role in star formation and disk evolution. Our work is aimed at investigating the properties of the recent outburst of V1647 Ori. Methods. Using optical and mid infrared long slit spectroscopy we monitored V1647 Orionis in outburst between February 2004 and January 2006. Results. The optical spectrum is characterized by Hα and Hβ in P-Cygni profile and by many weak Fe i and Fe ii emission lines. Short timescale variability was measured in the continuum and line emission. In January 2006 we detected for the first time forbidden emission lines ([O i], [S ii ]a nd [Feii]). These lines are likely produced by a Herbig-Haro object driven by V1647 Ori. The mid infrared spectrum of V1647 Ori is flat and featureless at all epochs. The SED changed drastically: the source was much redder in the early outburst than in the final phase. The magnitude rise and the SED of V1647 Ori resembles that of a FUor while the duration and recurrence of the outburst resemble that of a EXor. The optical spectrum is clearly distinct from either the absorption line spectrum of a FUor or the T Tauri-like spectrum of an EXor. Conclusions. Our data are consistent with a disk instability event which led to an increase of the mass accretion rate. The data also suggest the presence of a circumstellar envelope around the star+disk system. The peculiar N band spectrum might be explained by dust sublimation in the outer layers of the disk. The presence of the envelope and the outburst statistics suggest that these instability events occur only in a specific stage of a Class I source (e.g. in the transition phase to an optically visible star surrounded by a protoplanetary disk). We discuss the outburst mechanisms in term of the thermal instability model.

A search for near-infrared molecular hydrogen emission in the CTTS LkHα 264 and the debris disk 49 Ceti

We report on the first results of a search for molecular hydrogen emission from protoplanetary disks using CRIRES, ESO’s new VLT Adaptive Optics high resolution near-infrared spectrograph. We observed the classical T Tauri star LkHα 264 and the debris disk 49 Cet, and searched for υ = 1− 0S (1) H 2 emission at 2.1218 µm, υ = 1− 0S (0) H 2 emission at 2.2233 µ ma ndυ = 2− 1S (1) H2 emission at 2.2477 µm. The H2 line at 2.1218 µm is detected in LkHα 264 confirming the previous observations by Itoh et al. (2003). In addition, our CRIRES spectra reveal the previously observed but not detected H2 line at 2.2233 µ mi n LkHα 264. An upper limit of 5.3 ×10 −16 erg s −1 cm −2 on the υ = 2− 1S (1) H 2 line flux in LkHα 264 is derived. The detected lines coincide with the rest velocity of LkHα 264. They have a FWHM of ∼20 km s −1 . This is strongly suggestive of a disk origin for the lines. These observations are the first simultaneous detection of υ = 1− 0S (1) andυ = 1− 0S (0) H 2 emission from a protoplanetary disk. 49 Cet does not exhibit H2 emission in any of the three observed lines. We derive the mass of optically thin H2 at T ∼ 1500 K in the inner disk of LkHα 264 and derive stringent limits in the case of 49 Cet at the same temperature. There are a few lunar masses of optically thin hot H2 in the inner disk (∼0.1 AU) of LkHα 264, and less than a tenth of a lunar mass of hot H2 in the inner disk of 49 Cet. The measured 1− 0S (0)/1− 0S (1) and 2− 1S (1)/1−0 S(1) line ratios in LkHα 264 indicate that the H2 emitting gas is at a temperature lower than 1500 K and that the H2 is most likely thermally excited by UV photons. The υ = 1− 0S (1) H 2 line in LkHα 264 is single peaked and spatially unresolved. Modeling of the shape of the line suggests that the disk should be seen close to face-on (i < 35 ◦ ) and that the line is emitted within a few AU of the LkHα 264 disk. A comparative analysis of the physical properties of classical T Tauri stars in which the H2 υ = 1−0 S(1) line has been detected and non-detected indicates that the presence of H2 emission is correlated with the magnitude of the UV excess and the strength of the Hα line. The lack of H2 emission in the NIR spectra of 49 Cet and the absence of Hα emission suggest that the gas in the inner disk of 49 Cet has dissipated. These results combined with previous detections of 12 CO emission at sub-mm wavelengths indicate that the disk surrounding 49 Cet should have an inner hole. We favor inner disk dissipation by inside-out photoevaporation, or the presence of an unseen low-mass companion as the most likely explanations for the lack of gas in the inner disk of 49 Cet.

Optical and infrared properties of V1647 Orionis during the 2003-2006 outburst I. The reflection nebula

Aims. The recent outburst of the young eruptive star V1647 Orionis has produced a spectacular appearance of a new reflection nebula in Orion (McNeil’s nebula). We present an optical/near infrared investigation of McNeil’s nebula. This analysis is aimed at determining the morphology, temporal evolution and nature of the nebula and its connection to the outburst. Methods. We performed multi epoch B, V, RC, IC, zgunn ,a ndKS imaging of McNeil’s nebula and V1647 Ori as well as KS imaging polarimetry. The multiband imaging allows us to reconstruct the extinction map inside the nebula. Through polarimetric observations we attempt to disentangle the emission from the nebula from that of the accretion disk around V1647 Ori. We also attempt to resolve the small spatial scale structure of the illuminating source. Results. The energy distribution and temporal evolution of McNeil’s nebula mimic that of the illuminating source. The extinction map reveals a region of higher extinction in the direction of V1647 Ori. Excluding foreground extinction, the optical extinction due to McNeil’s nebula in the direction of V1647 Ori is AV ∼ 6.5 mag. The polarimetric measurement shows a compact high polarization emission around V1647 Ori. The percentage of KS band linear polarization goes from 10–20%. The vectors are all well aligned with a position angle of 90 ◦ ± 9 ◦ East of North. This may correspond to the orientation of a possible accretion disk around V1647 Ori. These findings suggest that the appearance of McNeil’s nebula is due to reflection of light by pre-existing material in the surroundings of V1647 Ori. We also report on the discovery of a new candidate brown dwarf or protostar in the vicinity of V1647 Ori as well as the presence of clumpy structure within HH 22A.