Grain growth in the envelopes and disks of Class I protostars

We present new 3 mm ATCA data of two Class I Young Stellar Objects in the Ophiucus star forming region: Elias29 and WL12. For our analysis we compare them with archival 1.1 mm SMA data. In the (u,v) plane the two sources present a similar behavior: a nearly constant non-zero emission at long baselines, which suggests the presence of an unresolved component and an increase of the fluxes at short baselines, related to the presence of an extended envelope. Our data analysis leads to unusually low values of the spectral index $\alpha_{\rm 1.1-3mm}$, which may indicate that mm-sized dust grains have already formed both in the envelopes and in the disk-like structures at such early stages. To explore the possible scenarios for the interpretation of the sources we perform a radiative transfer modeling using a Monte Carlo code, in order to take into account possible deviations from the Rayleigh-Jeans and optically thin regimes. Comparison between the model outputs and the observations indicates that dust grains may form aggregates up to millimeter size already in the inner regions of the envelopes of Class I YSOs. Moreover, we conclude that the embedded disk-like structures in our two Class Is are probably very compact, in particular in the case of WL12, with outer radii down to tens of AU.Comment: 12 pages, 8 figures, Accepted for publication in A&

Spectral line profiles changed by dust scattering in heavily obscured young stellar objects

It is known that scattering of radiation by circumstellar dust can strongly change the line profiles in stellar spectra. This hampers the analysis of spectral lines originating in the emitting regions of heavily obscured young stars. To calculate the line profile of the scattered radiation, we suggest to use the approximation of remote scattering particles. This approximation assumes that the scattering dust grains are at a distance from the star that is much larger than the characteristic size of the emitting region. Using this method, we calculated the line profiles of several simple models. They show the H alpha line profiles of Herbig AeBe stars in the presence and absence of motionless or moving dust

On the gas content of transitional disks: a VLT/X-Shooter study of accretion and winds

Transitional disks (TDs) are thought to be a late evolutionary stage of protoplanetary disks with dust depleted inner regions. The mechanism responsible for this depletion is still under debate. To constrain the models it is mandatory to have a good understanding of the properties of the gas content of the inner disk. Using X-Shooter broad band -UV to NIR- medium resolution spectroscopy we derive the stellar, accretion, and wind properties of a sample of 22 TDs. The analysis of these properties allows us to put strong constraints on the gas content in a region very close to the star (<0.2 AU) which is not accessible with any other observational technique. We fit the spectra with a self-consistent procedure to derive simultaneously SpT,Av,and mass accretion rates (Macc) of the targets. From forbidden emission lines we derive the wind properties of the targets. Comparing our findings to values for cTTs, we find that Macc and wind properties of 80% of the TDs in our sample, which is strongly biased towards strongly accreting objects, are comparable to those of cTTs. Thus, there are (at least) some TDs with Macc compatible with those of cTTs, irrespective of the size of the dust inner hole.Only in 2 cases Macc are much lower, while the wind properties are similar. We do not see any strong trend of Macc with the size of the dust depleted cavity, nor with the presence of a dusty optically thick disk close to the star. In the TDs in our sample there is a gas rich inner disk with density similar to that of cTTs disks. At least for some TDs, the process responsible of the inner disk clearing should allow for a transfer of gas from the outer disk to the inner region. This should proceed at a rate that does not depend on the physical mechanism producing the gap seen in the dust emission and results in a gas density in the inner disk similar to that of unperturbed disks around stars of similar mass.Comment: Accepted on Astronomy & Astrophysics. Abstract shortened to fit arXiv constraint

Vertical structure models of T Tauri and Herbig Ae/Be disks

In this paper we present detailed models of the vertical structure (temperature and density) of passive irradiated circumstellar disks around T Tauri and Herbig Ae/Be stars. In contrast to earlier work, we use full frequency- and angle-dependent radiative transfer instead of the usual moment equations. We find that this improvement of the radiative transfer has strong influence on the resulting vertical structure of the disk, with differences in temperature as large as 70 %. However, the spectral energy distribution (SED) is only mildly affected by this change. In fact, the SED compares reasonably well with that of improved versions of the Chiang & Goldreich (CG) model. This shows that the latter is a reasonable model for the SED, in spite of its simplicity. It also shows that from the SED alone, little can be learned about the vertical structure of a passive circumstellar disk. The molecular line emission from these disks is more sensitive to the vertical temperature and density structure, and we show as an example how the intensity and profiles of various CO lines depend on the adopted disk model. The models presented in this paper can also serve as the basis of theoretical studies of e.g. dust coagulation and settling in disks.Comment: 12 pages, 15 figures, accepted for publication in A&

KH15D: a star eclipsed by a large scale dusty vortex?

We propose that the large photometric variations of KH15D are due to an eclipsing swarm of solid particles trapped in giant gaseous vortex rotating at \~0.2 AU from the star. The efficiency of the capture-in-vortex mechanism easily explains the observed large optical depth. The weaker opacity at mid-eclipse is consistent with a size segregation of the particles toward the center of the vortex. This dusty structure must extend over ~1/3 of an orbit to account for the long eclipse duration. The estimated size of the trapped particles is found to range from 1 to 10cm, consistent with the gray extinction of the star. The observations of KH15D support the idea that giant vortices can grow in circumstellar disks and play a central role in planet formation.Comment: Accepted in ApJ Letters - 4 pages - 2 figure

Accretion properties of T Tauri stars in sigma Ori

Accretion disks around young stars evolve in time with time scales of few million years. We present here a study of the accretion properties of a sample of 35 stars in the ~3 million year old star-forming region sigma Ori. Of these, 31 are objects with evidence of disks, based on their IR excess emission. We use near-IR hydrogen recombination lines (Pa_gamma) to measure their mass accretion rate. We find that the accretion rates are significantly lower in sigma Ori than in younger regions, such as rho-Oph, consistently with viscous disk evolution. The He I 1.083 micron line is detected (either in absorption or in emission) in 72% of the stars with disks, providing evidence of accretion-powered activity also in very low accretors, where other accretion indicators dissapear.Comment: Astronomy and Astrophysics, accepte

Determination of the Physical Conditions of the Knots in the Helix Nebula from Optical and Infrared Observations

[Abridged] We use new HST and archived images to clarify the nature of the knots in the Helix Nebula. We employ published far infrared spectrophotometry and existing 2.12 micron images to establish that the population distribution of the lowest ro-vibrational states of H2 is close to the distribution of a gas in LTE at 988 +- 119 K. We derive a total flux from the nebula in H2 lines and compare this with the power available from the central star for producing this radiation. We establish that neither soft X-rays nor FUV radiation has enough energy to power the H2 radiation, only the stellar EUV radiation shortward of 912 Angstrom does. Advection of material from the cold regions of the knots produces an extensive zone where both atomic and molecular hydrogen are found, allowing the H2 to directly be heated by Lyman continuum radiation, thus providing a mechanism that can explain the excitation temperature and surface brightness of the cusps and tails. New images of the knot 378-801 reveal that the 2.12 micron cusp and tail lie immediately inside the ionized atomic gas zone. This firmly establishes that the "tail" structure is an ionization bounded radiation shadow behind the optically thick core of the knot. A unique new image in the HeII 4686 Angstrom line fails to show any emission from knots that might have been found in the He++ core of the nebula. We also re-examined high signal-to-noise ratio ground-based telescope images of this same inner region and found no evidence of structures that could be related to knots.Comment: Astronomical Journal, in press. Some figures are shown at reduced resolution. A full resolution version is available at http://www.ifront.org/wiki/Helix_Nebula_2007_Pape

Verbal communication disorders in brain damaged post-stroke patients in Benin

AbstractIn Western countries, progress has lessened the severity of numerous sequels of verbal communication disorders (VCD). For Africa and more particularly Benin, few data on the subject are presently available.ObjectiveTo analyze the occurrence and development of post-stroke VCD in Benin.MethodA retrospective, descriptive and analytical study focused on 563 post-stroke patients treated in rehabilitation department of the National university hospital of Cotonou (CNHU) from January 2006 through December 2010.ResultsVCD prevalence was 42.10%. Average age was 57.17±12.62years, sex ratio was 1.75, and 74.69% were right-handed. VCD affected oral expression (95.78%), written expression (2.11%), oral comprehension (13.08%) and written comprehension or reading (0.84%). Type of stroke, sex and age had no impact on VCD occurrence following stroke. Only 5.91% of the patients underwent speech therapy. Progression was favorable in 21.09% of the cases studied.ConclusionIn Benin, post-stroke VCD is exceedingly common and occasions major social difficulties. Prevalence of VCD in a predominantly oral culture underscores the need for speech therapists to develop a more broadly ecological approach toward treatment

A Multicenter, Prospective, Randomized, Contralateral Study of Tissue Liquefaction Liposuction vs Suction-Assisted Liposuction

Tissue liquefaction liposuction (TLL) deploys a novel energy source utilizing a stream of warmed, low-pressurized, and pulsed saline to extract fat tissue. Objectives: Compare TLL to suction-assisted liposuction (SAL) to determine which device is more efficient for surgeons and provides better recovery for patients. Methods: Thirty-one adult female patients were followed prospectively in a contralateral study design comparing differences in bruising, swelling, tenderness, and incision appearance ratings between TLL and SAL procedures. Surgical efficiency and appearance of the lipoaspirate were also compared. Results: All 31 patients successfully completed the study. For TLL and SAL procedures, the average volumes of infusion (1.242 vs 1.276 L) and aspirated supernatant fat (704 vs 649 mL) were statistically similar. TLL median fat extraction rate was faster than SAL (35.6 vs 25 mL/min; P < 0.0001), and stroke rate was reduced in TLL vs SAL procedures (48 vs 120 strokes/min; P < 0.0001), and both were statistically significant. The mean total scores for bruising, swelling, treatment site tenderness, and incision appearance were lower, indicating improved patient recovery on the TLL side. Conclusions: TLL and SAL techniques produced comparable volume of fat aspirate. TLL demonstrated a 42% faster fat extraction rate and a 68% reduction in arm movements needed to complete the procedure compared to SAL, both of these differences are statistically significant. The TLL side was noted to have reduced bruising and swelling and improved incision site appearance with less tenderness compared to the SAL side

The circumstellar disc around the Herbig AeBe star HD169142

We present 7 mm and 3.5 cm wavelength continuum observations toward the Herbig AeBe star HD169142 performed with the Very Large Array (VLA) with an angular resolution of ~1". We find that this object exhibits strong (~4.4 mJy), unresolved (~1") 7 mm continuum emission, being one of the brightest isolated Herbig AeBe stars ever detected with the VLA at this wavelength. No emission is detected at 3.5 cm continuum, with a 3 sigma upper limit of ~0.08 mJy. From these values, we obtain a spectral index of ~2.5 in the 3.5 cm to 7 mm wavelength range, indicating that the observed flux density at 7mm is most likely dominated by thermal dust emission coming from a circumstellar disc. We use available photometric data from the literature to model the spectral energy distribution (SED) of this object from radio to near-ultraviolet frequencies. The observed SED can be understood in terms of an irradiated accretion disc with low mass accretion rate, 10^{-8} solar masses per year, surrounding a star with an age of ~10 Myr. We infer that the mass of the disc is ~0.04 solar masses, and is populated by dust grains that have grown to a maximum size of 1 mm everywhere, consistent with the lack of silicate emission at 10 microns. These features, as well as indications of settling in the wall at the dust destruction radius, led us to speculate the disc of HD169142 is in an advanced stage of dust evolution, particularly in its inner regions.Comment: 13 pages, 2 figures. Accepted by MNRA