54 research outputs found
The water trail from the cradle of a young Sun to Earth-like planets
El agua es un ingrediente crucial para la vida. Una de las áreas de investigación más fascinantes en el campo de la astrobiología y la astroquímica es la del origen del agua sobre la Tierra. Sabemos que nuestros océanos contienen una cantidad de agua igual a 3 diezmilésimas de la masa terrestre. Sin embargo, si consideramos también el agua presente bajo la costra terrestre, el total podría aumentar a entre 10 y 50 veces más. Existen muchas cuestiones por resolver, como por ejemplo: ¿Cuándo y cómo apareció el agua sobre la Tierra? ¿Nuestro planeta es un caso especial o hay agua, y posiblemente vida, en otros planetas de nuestra Galaxia? Con más de 1000 exoplanetas descubiertos y las estadísticas que indican que cada estrella alberga al menos un planeta, la búsqueda de agua en el universo es cada vez más urgente
T Tauri Jet Physics Resolved Near The Launching Region with the Hubble Space Telescope
We present an analysis of the gas physics at the base of jets from five T
Tauri stars based on high angular resolution optical spectra, using the Hubble
Space Telescope Imaging Spectrograph (HST/STIS). The spectra refer to a region
within 100 AU of the star, i.e. where the collimation of the jet has just taken
place. We form PV images of the line ratios to get a global picture of the flow
excitation. We then apply a specialised diagnostic technique to find the
electron density, ionisation fraction, electron temperature and total density.
Our results are in the form of PV maps of the obtained quantities, in which the
gas behaviour is resolved as a function of both radial velocity and distance
from the jet axis. They highlight a number of interesting physical features of
the jet collimation region, including regions of extremely high density,
asymmetries with respect to the axis, and possible shock signatures. Finally,
we estimate the jet mass and angular momentum outflow rates, both of which are
fundamental parameters in constraining models of accretion/ejection structures,
particularily if the parameters can be determined close to the jet footpoint.
Comparing mass flow rates for cases where the latter is available in the
literature (i.e. DG Tau, RW Aur and CW Tau) reveals a mass
ejection-to-accretion ratio of 0.01 - 0.07. Finally, where possible (i.e. DG
Tau and CW Tau), both mass and angular momentum outflow rates have been
resolved into higher and lower velocity jet material. For the clearer case of
DG Tau, this revealed that the more collimated higher velocity component plays
a dominant role in mass and angular momentum transport.Comment: 33 pages, 16 figures, accepted by Ap
The star formation history of RCW 36
Recent studies of massive-star forming regions indicate that they can contain
multiple generations of young stars. These observations suggest that star
formation in these regions is sequential and/or triggered by a previous
generation of (massive) stars. Here we present new observations of the star
forming region RCW 36 in the Vela Molecular Ridge, hosting a young cluster of
massive stars embedded in a molecular cloud complex. In the periphery of the
cluster several young stellar objects (YSOs) are detected which produce bipolar
jets (HH 1042 and HH 1043) demonstrating that these objects are still actively
accreting. The VLT/X-shooter spectrum of the jet structure of HH 1042 provides
detailed information on the physical conditions and kinematical properties of
the jet plasma. From this information the YSO's accretion history can be
derived. Combining the photometric and spectroscopic observations of RCW 36
gives insight into the formation process of individual stars and the star
formation history of this young massive-star forming region.Comment: 10 pages, 5 figures, to appear in the proceedings of the ESO workshop
"Circumstellar Dynamics at High Resolution", Foz do Iguacu (Br), Feb 2012,
eds. A. Carciofi and T. Riviniu
A proto-planetary disk revealed by the Herschel satellite
Herschel opened a new window on the study of the physical processes occurring when a star forms. Observations of the prototypical young star T Tau N revealed all the crucial ingredients known to be involved in star formation, namely: the parental cloud, the supersonic outflows driven by the forming star and the proto-planetary disk rotating around it. From the emission lines of the CN molecule we can estimate important disk properties, such as the disk size, inclination, and mass. The latter is roughly equal to the minimum mass of the solar nebula required to form the solar system, suggesting that the disk around T Tau N could form a planetary system like our own.Herschel ha aperto una nuova finestra per lo studio del processo di formazione delle stelle. Osservazioni della stella giovane T Tauri Nord rivelano tutti gli ingredienti che concorrono alla sua formazione: la nube molecolare da cui questa si forma, i getti di materia supersonici che si sviluppano mentre la stella accumula materia ed il disco proto-planetario in rotazione intorno ad essa. Dalle righe di emissione della molecola CN è possibile derivare importanti proprietà del disco, quali dimensione, inclinazione e massa. Quest’ultima risulta simile a quella minima necessaria alla formazione di un sistema di pianeti simile al nostro
Cloudlet Capture Model for the Accretion Streamer onto the disk of DG Tau
DG Tau is a nearby T Tauri star associated with a collimated jet, a
circumstellar disk and a streamer a few hundred au long. The streamer connects
to the disk at 50 au from DG Tau. At this location SO emission is
observed, likely due to the release of sulphur from dust grains caused by the
shock of the impact of the accretion streamer onto the disk. We investigate the
possibility that the DG Tau streamer was produced via cloudlet capture on the
basis of hydrodynamic simulations, considering a cloudlet initiating infall at
600 au from DG Tau with low angular momentum so that the centrifugal force is
smaller than the gravitational force, even at 50 au. The elongation of the
cloudlet into a streamer is caused by the tidal force when its initial velocity
is much less than the free-fall velocity. The elongated cloudlet reaches the
disk and forms a high density gas clump. Our hydrodynamic model reproduces the
morphology and line-of-sight velocity of CS () emission from the Northern
streamer observed with ALMA. We discuss the conditions for forming a streamer
based on the simulations. We also show that the streamer should perturb the
disk after impact for several thousands of years.Comment: 12 page, 11 figure
The protoplanetary disk of FT Tauri: multi-wavelength data analysis and modeling
Investigating the evolution of protoplanetary disks is crucial for our
understanding of star and planet formation. Several theoretical and
observational studies have been performed in the last decades to advance this
knowledge. FT Tauri is a young star in the Taurus star forming region that was
included in a number of spectroscopic and photometric surveys. We investigate
the properties of the star, the circumstellar disk, and the accretion and
ejection processes and propose a consistent gas and dust model also as a
reference for future observational studies. We performed a multi-wavelength
data analysis to derive the basic stellar and disk properties, as well as mass
accretion/outflow rate from TNG-Dolores, WHT-Liris, NOT-Notcam, Keck-Nirspec,
and Herschel-Pacs spectra. From the literature, we compiled a complete Spectral
Energy Distribution. We then performed detailed disk modeling using the MCFOST
and ProDiMo codes. Multi-wavelengths spectroscopic and photometric measurements
were compared with the reddened predictions of the codes in order to constrain
the disk properties. This object can serve as a benchmark for primordial disks
with significant mass accretion rate, high gas content and typical size.Comment: 16 pages, 9 figures, accepted for publication in A&
Hydrogen permitted lines in the first near-IR spectra of Th 28 microjet: accretion or ejection tracers?
We report the first near-infrared detection of the bipolar microjet from
TTauri star ThA 15-28 (aka Th 28). Spectra were obtained with VLT/ISAAC for the
slit both perpendicular and parallel to the flow to examine jet kinematics and
gas physics within the first arcsecond from the star. The jet was successfully
detected in both molecular and atomic lines. The H_2 component was found to be
entirely blueshifted around the base of the bipolar jet. It shows that only the
blue lobe is emitting in H_2 while light is scattered in the direction of the
red lobe, highlighting an asymmetric extinction and/or excitation between the
two lobes. Consistent with this view, the red lobe is brighter in all atomic
lines. Interestingly, the jet was detected not only in [Fe II], but also in Br
gamma and Pa beta lines. Though considered tracers mainly of accretion, we find
that these high excitation hydrogen permitted lines trace the jet as far as 150
AU from the star. This is confirmed in a number of ways: the presence of the
[Fe II] 2.13 micron line which is of similarly high excitation; H I velocities
which match the jet [Fe II] velocities in both the blue and red lobe; and high
electron density close to the source of >6x10^4 cm^-3 derived from the [Fe II]
1.64,1.60 micron ratio. These near-infrared data complement HST/STIS optical
and near-ultraviolet data for the same target which were used in a jet rotation
study, although no rotation signature could be identified here due to
insufficient angular resolution. The unpublished HST/STIS H alpha emission is
included here along side the other H I lines. Identifying Br gamma and Pa beta
as tracers of ejection is significant because of the importance of finding
strong near-infrared probes close to the star, where forbidden lines are
quenched, which will help understand accretion-ejection when observed with high
spatial resolution instruments such as VLTI/AMBER.Comment: 18 pages, 26 figures, Accepted by Ap
ALMA observations of polarized emission toward the CW Tau and DG Tau protoplanetary disks: constraints on dust grain growth and settling
We present polarimetric data of CW Tau and DG Tau, two well-known Class II
disk/jet systems, obtained with the Atacama Large Millimeter/submillimeter
Array at 870 m and 0."2 average resolution. In CW Tau, the total and
polarized emission are both smooth and symmetric, with polarization angles
almost parallel to the minor axis of the projected disk. In contrast, DG Tau
displays a structured polarized emission, with an elongated brighter region in
the disk's near side and a belt-like feature beyond about 0."3 from the source.
At the same time the total intensity is spatially smooth, with no features. The
polarization pattern, almost parallel to the minor axis in the inner region,
becomes azimuthal in the outer belt, possibly because of a drop in optical
depth. The polarization fraction has average values of 1.2% in CW Tau and 0.4%
in DG Tau. Our results are consistent with polarization from self-scattering of
the dust thermal emission. Under this hypothesis, the maximum size of the
grains contributing to polarization is in the range 100 - 150 m for CW Tau
and 50 - 70 m for DG Tau. The polarization maps combined with dust opacity
estimates indicate that these grains are distributed in a geometrically thin
layer in CW Tau, representing a settling in the disk midplane. Meanwhile, such
settling is not yet apparent for DG Tau. These results advocate polarization
studies as a fundamental complement to total emission observations, in
investigations of the structure and the evolution of protoplanetary disks.Comment: 8 pages, 5 figures. Accepted for publication in ApJ Letter
The near-UV: the true window on jet rotation
High resolution observations of jet rotation in newly forming stars have the potential to support theories of magneto-centrifugal jet launching. We report a detection of a radial velocity difference across the blue-shifted jet from RY Tau, the direction of which matches the CO disk rotation sense. Now, in 3 of 3 cases, the sense of the near-UV jet gradient matches the disk rotation sense, implying that we are indeed observing jet rotation. It seems the jet core, probed at near-UV wavelengths, is protected by the outer jet layers from kinematic contaminations, and thus represents the only true window on jet rotation
The two hot corinos of the SVS13-A protostellar binary system: counterposed siblings
We present ALMA high-angular resolution ( 50 au) observations of the
Class I binary system SVS13-A. We report images of SVS13-A in numerous
interstellar complex organic molecules: CHOH, CHOH,
CHCHO, CHOCH, and NHCHO. Two hot
corinos at different velocities are imaged in VLA4A (V= +7.7 km
s) and VLA4B (V= +8.5 km s). From a non-LTE analysis of
methanol lines we derive a gas density of 3 10 cm, and gas
temperatures of 140 K and 170 K for VLA4A and VLA4B, respectively. For the
other species the column densities are derived from a LTE analysis. Formamide,
which is the only N-bearing species detected in our observations, is more
prominent around VLA4A, while dimethyl ether, methanol and acetaldehyde are
associated with both VLA4A and VLA4B. We derive in the two hot corinos
abundance ratios of 1 for CHOH, CHOH, and
CHOCH, 2 for CHCHO, and 4 for
NHCHO. The present dataset supports a chemical segregation between
the different species inside the binary system. The emerging picture is that of
an onion-like structure of the two SVS13-A hot corinos, caused by the different
binding energies of the species, also supported by ad hoc quantum chemistry
calculations. In addition, the comparison between molecular and dust maps
suggests that the interstellar complex organic molecules emission originates
from slow shocks produced by accretion streamers impacting the VLA4A and VLA4B
disks and enriching the gas-phase component.Comment: 20 pages, 14 figure
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