215 research outputs found
HD 85567: A Herbig B[e] star or an interacting B[e] binary
Context. HD 85567 is an enigmatic object exhibiting the B[e] phenomenon, i.e.
an infrared excess and forbidden emission lines in the optical. The object's
evolutionary status is uncertain and there are conflicting claims that it is
either a young stellar object or an evolved, interacting binary.
Aims. To elucidate the reason for the B[e] behaviour of HD 85567, we have
observed it with the VLTI and AMBER.
Methods. Our observations were conducted in the K-band with moderate spectral
resolution (R~1500, i.e. 200 km/s). The spectrum of HD 85567 exhibits Br gamma
and CO overtone bandhead emission. The interferometric data obtained consist of
spectrally dispersed visibilities, closure phases and differential phases
across these spectral features and the K-band continuum.
Results. The closure phase observations do not reveal evidence of asymmetry.
The apparent size of HD 85567 in the K-band was determined by fitting the
visibilities with a ring model. The best fitting radius, 0.8 +/- 0.3 AU, is
relatively small making HD 85567 undersized in comparison to the
size-luminosity relationship based on YSOs of low and intermediate luminosity.
This has previously been found to be the case for luminous YSOs, and it has
been proposed that this is due to the presence of an optically thick gaseous
disc. We demonstrate that the differential phase observations over the CO
bandhead emission are indeed consistent with the presence of a compact (~1 AU)
gaseous disc interior to the dust sublimation radius.
Conclusions. The observations reveal no sign of binarity. However, the data
do indicate the presence of a gaseous disc interior to the dust sublimation
radius. We conclude that the data are consistent with the hypothesis that HD
85567 is a YSO with an optically thick gaseous disc within a larger dust disc
that is being photo-evaporated from the outer edge.Comment: Accepted for publication in A &
Spatially resolved H_2 emission from a very low-mass star
Molecular outflows from very low-mass stars (VLMSs) and brown dwarfs have
been studied very little. So far, only a few CO outflows have been observed,
allowing us to map the immediate circumstellar environment. We present the
first spatially resolved H2 emission around IRS54 (YLW52), a ~0.1-0.2 Msun
Class I source. By means of VLT SINFONI K-band observations, we probed the H2
emission down to the first ~50 AU from the source. The molecular emission shows
a complex structure delineating a large outflow cavity and an asymmetric
molecular jet. Thanks to the detection of several H2 transitions, we are able
to estimate average values along the jet-like structure (from source position
to knot D) of Av~28 mag, T~2000-3000 K, and H2 column density N(H2)~1.7x10^17
cm^-2. This allows us to estimate a mass loss rate of ~2x10^-10 Msun/yr for the
warm H2 component . In addition, from the total flux of the Br Gamma line, we
infer an accretion luminosity and mass accretion rate of 0.64 Lsun and ~3x10^-7
Msun/yr, respectively. The outflow structure is similar to those found in
low-mass Class I and CTTS. However, the Lacc/Lbol ratio is very high (~80%),
and the mass accretion rate is about one order of magnitude higher when
compared to objects of roughly the same mass, pointing to the young nature of
the investigated source.Comment: accepted as a Letter in A&
Velocity and magnetic fields within 1000 AU from a massive YSO
We want to study the velocity and magnetic field morphology in the vicinity
(<1000 AU) of a massive young stellar object (YSO), at very high spatial
resolution (10-100 AU). We performed milli-arcsecond polarimetric observations
of the strong CH3OH maser emission observed in the vicinity of an O-type YSO,
in G023.01-00.41. We have combined this information with the velocity field of
the CH3OH masing gas previously measured at the same angular resolution. We
analyse the velocity and magnetic fields in the reference system defined by the
direction of the molecular outflow and the equatorial plane of the hot
molecular core at its base, as recently observed on sub-arcsecond scales. We
provide a first detailed picture of the gas dynamics and magnetic field
configuration within a radius of 2000 AU from a massive YSO. We have been able
to reproduce the magnetic field lines for the outer regions (>600 AU) of the
molecular envelope, where the magnetic field orientation shows a smooth change
with the maser cloudlets position (0.2 degree/AU). Overall, the velocity field
vectors well accommodate with the local, magnetic field direction, but still
show an average misalignment of 30 degrees. We interpret this finding as the
contribution of a turbulent velocity field of about 3.5 km/s, responsible for
braking up the alignment between the velocity and magnetic field vectors. We do
resolve different gas flows which develop both along the outflow axis and
across the disk plane, with an average speed of 7 km/s. In the direction of the
outflow axis, we establish a collimation of the gas flow, at a distance of
about 1000 AU from the disk plane. In the disk region, gas appears to stream
outward along the disk plane for radii greater than 500-600 AU, and inward for
shorter radii.Comment: 7 pages, 4 figures, 1 table, accepted by Astronomy & Astrophysic
Augmented visualization by computer vision and chromatographic fingerprinting on comprehensive two-dimensional gas chromatographic patterns: Unraveling diagnostic signatures in food volatilome
Accretion bursts in high-mass protostars: a new testbed for models of episodic accretion
It is well known that low mass young stellar objects (LMYSOs) gain a
significant portion of their final mass through episodes of very rapid
accretion, with mass accretion rates up to ~yr. Recent observations of high mass young stellar objects
(HMYSO) with masses uncovered outbursts with
accretion rates exceeding ~yr. Here we
examine which scenarios proposed in the literature so far to explain accretion
bursts of LMYSOs can apply to the episodic accretion in HMYSOs. We utilise a 1D
time dependent models of protoplanetary discs around HMYSOs to study burst
properties. We find that discs around HMYSOs are much hotter than those around
their low mass cousins. As a result, much more extended regions of the disc are
prone to the thermal hydrogen ionisation and MRI activation instabilities. The
former in particular is found to be ubiquitous in a very wide range of
accretion rates and disc viscosity parameters. The outbursts triggered by these
instabilities, however, always have too low , and are one to several
orders of magnitude too long compared to those observed from HMYSOs so far. On
the other hand, bursts generated by tidal disruptions of gaseous giant planets
formed by the gravitational instability of the protoplanetary discs yield
properties commensurate with observations, provided that the clumps are in the
post-collapse configuration with planet radius Jupiter
radii. Furthermore, if observed bursts are caused by disc ionisation
instabilities then they should be periodic phenomena with the duration of the
quiescent phase comparable to that of the bursts. This may yield potentially
observable burst periodicity signatures in the jets, the outer disc, or the
surrounding diffuse material of massive HMYSOs. (abridged)Comment: 8 pages, 6 figures, Accepted to A&A Letter
Discovery of the heavily obscured supernova 2002cv
On the 13th of May 2002, supernova 2002cv was discovered using a
near-infrared camera working at the AZT-24 1.1m telescope at Campo Imperatore
(AQ-Italy). After the infrared detection a simultaneous photometric follow-up
was started at optical wavelengths. The preliminary results confirm a heavily
obscured object with a V-K color not lower than 6 magnitudes, making SN 2002cv
the most reddened supernova ever observed. This finding, along with the recent
discovery of another obscured supernova, suggests a critical revision of the
rates known to date. The estimate of the visual extinction and the light curves
are provided here. These latter indicate that our SN 2002cv observations are
the earliest available for a type-Ia supernova at IR wavelengths.Comment: 4 page
Corrections to Einstein's relation for Brownian motion in a tilted periodic potential
In this paper we revisit the problem of Brownian motion in a tilted periodic
potential. We use homogenization theory to derive general formulas for the
effective velocity and the effective diffusion tensor that are valid for
arbitrary tilts. Furthermore, we obtain power series expansions for the
velocity and the diffusion coefficient as functions of the external forcing.
Thus, we provide systematic corrections to Einstein's formula and to linear
response theory. Our theoretical results are supported by extensive numerical
simulations. For our numerical experiments we use a novel spectral numerical
method that leads to a very efficient and accurate calculation of the effective
velocity and the effective diffusion tensor.Comment: 29 pages, 7 figures, submitted to the Journal of Statistical Physic
AMBER/VLTI high spectral resolution observations of the Br emitting region in HD 98922. A compact disc wind launched from the inner disc region
We analyse the main physical parameters and the circumstellar environment of
the young Herbig Be star HD 98922. We present AMBER/VLTI high spectral
resolution (R =12000) interferometric observations across the Br line,
accompanied by UVES high-resolution spectroscopy and SINFONI-AO assisted
near-infrared integral field spectroscopic data. To interpret our observations,
we develop a magneto-centrifugally driven disc-wind model. Our analysis of the
UVES spectrum shows that HD 98922 is a young (~5x10^5 yr) Herbig Be star
(SpT=B9V), located at a distance of 440(+60-50) pc, with a mass accretion rate
of ~9+/-3x10^(-7) M_sun yr^(-1). SINFONI K-band AO-assisted imaging shows a
spatially resolved circumstellar disc-like region (~140 AU in diameter) with
asymmetric brightness distribution. Our AMBER/VLTI UT observations indicate
that the Br emitting region (radius ~0.31+/-0.04 AU) is smaller than
the continuum emitting region (inner dust radius ~0.7+/-0.2 AU), showing
significant non-zero V-shaped differential phases (i.e. non S-shaped, as
expected for a rotating disc). The value of the continuum-corrected pure
Br line visibility at the longest baseline (89 m) is ~0.8+/-0.1, i.e.
the Br emitting region is partially resolved. Our modelling suggests
that the observed Br line-emitting region mainly originates from a disc
wind with a half opening angle of 30deg, and with a mass-loss rate of ~2x10(-7)
M_sun yr^(-1). The observed V-shaped differential phases are reliably
reproduced by combining a simple asymmetric continuum disc model with our
Br disc-wind model. The Br emission of HD 98922 can be modelled
with a disc wind that is able to approximately reproduce all interferometric
observations if we assume that the intensity distribution of the dust continuum
disc is asymmetric.Comment: Accepted for publication on Astronomy \& Astrophysics. High
resolution figures published on the main journal (see Astronomy &
Astrophysics: Forthcoming) or at
www.researchgate.net/profile/Alessio_Caratti_o_Garatti/publication
LBT/LUCIFER near-infrared spectroscopy of PV Cephei. An outbursting young stellar object with an asymmetric jet
We present a detailed spectroscopic investigation of the young eruptive star
PV Cep, to improve our understanding of its nature and characterise its
circumstellar environment after its last outburst in 2004. The analysis of our
medium-resolution spectroscopy in the near-IR (0.9-2.35 um), collected in 2012
at the Large Binocular Telescope with the IR spectrograph LUCIFER, allows us to
infer the main stellar parameters (visual extinction, accretion luminosity,
mass accretion and ejection rates), and model the inner disc, jet, and wind.
The NIR spectrum displays several strong emission lines associated with
accretion/ejection activity and circumstellar environment. Our analysis shows
that the brightness of PV Cep is fading, as well as the mass accretion rate
(2x10^-7 Msun/yr^-1 in 2012 vs ~5x10^-6 Msun/yr^-1 in 2004), which is more than
one order of magnitude lower than in the outburst phase. Among the several
emission lines, only the [FeII] intensity increased after the outburst. The
observed [FeII] emission delineates blue- and red-shifted lobes, both with
high- and low-velocity components, which trace an asymmetric jet and wind,
respectively. The observed emission in the jet has a dynamical age of ~8 years,
indicating that it was produced during the last outburst. The mass ejection
rate in both lobes is 1.5x10^-7 Msun/yr^-1, approximately matching the high
accretion rate observed during and immediately after the outburst . The
observed jet/outflow asymmetries are consistent with an inhomogeneous medium.
Our modelling of the CO emission hints at a small-scale gaseous disc ring,
extending from ~0.2-0.4 AU to ~3 AU from the source, with an inner temperature
of ~3000 K. Our HI lines modelling indicates that most of the observed emission
comes from an expanding disc wind at Te=10000 K. The line profiles are strongly
affected by scattering, disc screening, and outflow self-absorption.Comment: To be published in A&
YSO jets in the Galactic Plane from UWISH2: II - Outflow Luminosity and Length distributions in Serpens and Aquila
Jets and outflows accompany the mass accretion process in protostars and
young stellar objects. Using a large and unbiased sample, they can be used to
study statistically the local feedback they provide and the typical mass
accretion history. Here we analyse such a sample of Molecular Hydrogen emission
line Objects in the Serpens and Aquila part of the Galactic Plane. Distances
are measured by foreground star counts with an accuracy of 25%. The resulting
spacial distribution and outflow luminosities indicate that our objects sample
the formation of intermediate mass objects. The outflows are unable to provide
a sizeable fraction of energy and momentum to support, even locally, the
turbulence levels in their surrounding molecular clouds. The fraction of parsec
scale flows is one quarter and the typical dynamical jet age of the order of
1E4yrs. Groups of emission knots are ejected every 1E3yrs. This might indicate
that low level accretion rate fluctuations and not FU-Ori type events are
responsible for the episodic ejection of material. Better observational
estimates of the FU-Ori duty cycle are needed.Comment: 16pages, 3tables, 10figures, accepted for publication by MNRAS, a
version with higher resolution figures can be found at
http://astro.kent.ac.uk/~df
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