155 research outputs found
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 , 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&
Testing external photoevaporation in the -Orionis cluster with spectroscopy and disk mass measurements
The evolution of protoplanetary disks is regulated by an interplay of several
processes, either internal to the system or related to the environment. As most
of the stars and planets have formed in massive stellar clusters, studying the
effects of UV radiation on disk evolution is of paramount importance. Here we
test the impact of external photoevaporation on the evolution of disks in the
Orionis cluster by conducting the first combined large-scale UV to IR
spectroscopic and mm-continuum survey of this region. We study a sample of 50
targets located at increasing distances from the central, OB system
Ori. We combine new VLT/X-Shooter spectra with new and previously published
ALMA measurements of disk dust and gas fluxes and masses. We confirm the
previously found decrease of in the inner 0.5 pc of the
cluster. This is particularly evident when considering the disks around the
more massive stars ( 0.4 ), where those located in the inner
part ( 0.5 pc) have about an order of magnitude lower than
the more distant ones. About half of the sample is located in the region of the
vs expected by models of external
photoevaporation, namely showing shorter disk lifetimes. These are observed for
all targets with projected separation from Ori 0.5 pc, proving
that the presence of a massive stellar system affects disk evolution. External
photoevaporation is a viable mechanism to explain the observed shorter disk
lifetimes and lower in the inner 0.5 pc of the cluster.
Follow-up observations of the low stellar mass targets are crucial to confirm
the dependence of the external photoevaporation process with stellar host mass.
This work confirms that the effects of external photoevaporation are
significant down to impinging radiation as low as G.Comment: Accepted for publication on Astronomy & Astrophysics. 13 pages, 7
figures + appendix. Abstract abridged to meet arXiv requirement
A spectacular jet from the bright 244-440 Orion proplyd: the MUSE NFM view
In this work we present the highest spatial and spectral resolution integral
field observations to date of the bipolar jet from the Orion proplyd 244-440
using MUSE NFM) observations on the VLT. We observed a previously unreported
chain of six distinct knots in a roughly S-shaped pattern, and by comparing
them with HST images we estimated proper motions in the redshifted knots of 9.5
mas yr with an inclination angle of , though these
quantities could not be measured for the blueshifted lobe. Analysis of the
[FeII] and [NiII] lines suggests jet densities on the order of
cm. We propose that the observed S-shaped morphology originates from a
jet launched by a smaller source with M in orbital
motion around a larger companion of M at a
separation of 30-40 au. The measured luminosities of the knots using the
[OI] and [SII] lines were used to estimate a lower
limit to the mass-loss rate in the jet of M
yr and an upper limit of M yr, which is
typical for low-mass driving sources. While the brightness asymmetry between
the redshifted and blueshifted lobes is consistent with external irradiation,
further analysis of the [NiII] and [FeII] lines suggests that photoionization
of the jet is not likely to be a dominant factor, and that the emission is
dominated by collisional excitation. The dynamical age of the jet compared to
the anticipated survival time of the proplyd demonstrates that photoevaporation
of the proplyd occurred prior to jet launching, and that this is still an
active source. These two points suggest that the envelope of the proplyd may
shield the jet from the majority of external radiation, and that
photoionization of the proplyd does not appear to impact the ability of a star
to launch a jet.Comment: 30 pages, 20 figure
Spallative ablation of dielectrics by X-ray laser
Short laser pulse in wide range of wavelengths, from infrared to X-ray,
disturbs electron-ion equilibrium and rises pressure in a heated layer. The
case where pulse duration is shorter than acoustic relaxation time
is considered in the paper. It is shown that this short pulse may cause
thermomechanical phenomena such as spallative ablation regardless to
wavelength. While the physics of electron-ion relaxation on wavelength and
various electron spectra of substances: there are spectra with an energy gap in
semiconductors and dielectrics opposed to gapless continuous spectra in metals.
The paper describes entire sequence of thermomechanical processes from
expansion, nucleation, foaming, and nanostructuring to spallation with
particular attention to spallation by X-ray pulse
A dust and gas cavity in the disc around CQ Tau revealed by ALMA
The combination of high-resolution and sensitivity offered by ALMA is revolutionizing our understanding of protoplanetary discs, as their bulk gas and dust distributions can be studied independently. In this paper we present resolved ALMA observations of the continuum emission (\u3bb = 1.3 mm) and CO isotopologues (12CO, 13CO, C18O, J = 2 12 1) integrated intensity from the disc around the nearby (d = 162 pc), intermediate-mass (M = 1.67 M) pre-main-sequence star CQ Tau. The data show an inner depression in continuum and in both 13CO and C18O emission. We employ a thermo-chemical model of the disc reproducing both continuum and gas radial intensity profiles, together with the disc spectral energy distribution. The models show that a gas inner cavity with size between 15 and 25 au is needed to reproduce the data with a density depletion factor between 3c10 121 and 3c10 123. The radial profile of the distinct cavity in the dust continuum is described by a Gaussian ring centred at Rdust = 53 au and with a width of \u3c3 = 13 au. Three-dimensional gas and dust numerical simulations of a disc with an embedded planet at a separation from the central star of 3c20 au and with a mass of 3c6\u20139 MJup reproduce qualitatively the gas and dust profiles of the CQ Tau disc. However, a one-planet model appears not to be able to reproduce the dust Gaussian density profile predicted using the thermo-chemical modeling
Circumstellar discs: What will be next?
This prospective chapter gives our view on the evolution of the study of
circumstellar discs within the next 20 years from both observational and
theoretical sides. We first present the expected improvements in our knowledge
of protoplanetary discs as for their masses, sizes, chemistry, the presence of
planets as well as the evolutionary processes shaping these discs. We then
explore the older debris disc stage and explain what will be learnt concerning
their birth, the intrinsic links between these discs and planets, the hot dust
and the gas detected around main sequence stars as well as discs around white
dwarfs.Comment: invited review; comments welcome (32 pages
Production of nanoparticles from natural hydroxylapatite by laser ablation
Laser ablation of solids in liquids technique has been used to obtain colloidal nanoparticles from biological hydroxylapatite using pulsed as well as a continuous wave (CW) laser. Transmission electron microscopy (TEM) measurements revealed the formation of spherical particles with size distribution ranging from few nanometers to hundred nanometers and irregular submicronic particles. High resolution TEM showed that particles obtained by the use of pulsed laser were crystalline, while those obtained by the use of CW laser were amorphous. The shape and size of particles are consistent with the explosive ejection as formation mechanism
ALMA Survey of Lupus Protoplanetary Disks II: Gas Disk Radii
We present ALMA Band 6 observations of a complete sample of protoplanetary disks in the young (1-3 Myr) Lupus star-forming region, covering the 1.33 mm continuum and the 12CO, 13CO, and C18O J=2-1 lines. The spatial resolution is 0.25 arcsec with a medium 3-sigma continuum sensitivity of 0.30 mJy, corresponding to M_dust ~ 0.2 M_earth. We apply "Keplerian masking" to enhance the signal-to-noise ratios of our 12CO zero-moment maps, enabling measurements of gas disk radii for 22 Lupus disks; we find that gas disks are universally larger than mm dust disks by a factor of two on average, likely due to a combination of the optically thick gas emission as well as the growth and inward drift of the dust. Using the gas disk radii, we calculate the dimensionless viscosity parameter, alpha_visc, finding a broad distribution and no correlations with other disk or stellar parameters, suggesting that viscous processes have not yet established quasi-steady states in Lupus disks. By combining our 1.33 mm continuum fluxes with our previous 890 micron continuum observations, we also calculate the mm spectral index, alpha_mm, for 70 Lupus disks; we find an anti-correlation between alpha_mm and mm flux for low-mass disks (M_dust < 5), followed by a flattening as disks approach alpha_mm = 2, which could indicate faster grain growth in higher-mass disks, but may also reflect their larger optically thick components. In sum, this work demonstrates the continuous stream of new insights into disk evolution and planet formation that can be gleaned from unbiased ALMA disk surveys
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