317 research outputs found
Monte-Carlo radiative transfer simulation of the circumstellar disk of the Herbig Ae star HD 144432
Studies of pre-transitional disks, with a gap region between the inner
infrared-emitting region and the outer disk, are important to improving our
understanding of disk evolution and planet formation. Previous infrared
interferometric observations have shown hints of a gap region in the
protoplanetary disk around the Herbig Ae star HD~144432. We study the dust
distribution around this star with two-dimensional radiative transfer modeling.
We compare the model predictions obtained via the Monte-Carlo radiative
transfer code RADMC-3D with infrared interferometric observations and the
{\SED} of HD~144432. The best-fit model that we found consists of an inner
optically thin component at 0.21\enDash0.32~\AU and an optically thick outer
disk at 1.4\enDash10~\AU. We also found an alternative model in which the
inner sub-AU region consists of an optically thin and an optically thick
component. Our modeling suggests an optically thin component exists in the
inner sub-AU region, although an optically thick component may coexist in the
same region. Our modeling also suggests a gap-like discontinuity in the disk of
HD~144432.Comment: 18 pages, 12 figure
GI2T/REGAIN spectro-interferometry with a new infrared beam combiner
We have built an infrared beam combiner for the GI2T/REGAIN interferometer of
the Observatoire de la Cote d'Azur. The beam combiner allows us to record
spectrally dispersed Michelson interference fringes in the near-infrared J-, H-
or K-bands. The beam combiner has the advantage that Michelson interferograms
can simultaneously be recorded in about 128 different spectral channels. The
tilt of the spectrally dispersed fringes is a measure of the instantaneous
optical path difference. We present the optical design of the beam combiner and
GI2T/REGAIN observations of the Mira star R Cas with this beam combiner in the
spectral range of 2.00 micron - 2.18 micron (observations on 22 and 25 August
1999; variability phase 0.08; V-magnitude approx. 6; seven baselines between
12m and 24m; reference stars Vega and Beta Peg). The spectrograph of the beam
combiner consists of an anamorphotic cylindrical lens system, an image plane
slit, and a grism. A system of digital signal processors calculates the
ensemble average power spectrum of the spectrally dispersed Michelson
interferograms and the instantaneous optical path difference error in real
time. From the observed R Cas visibilities at baselines 12.0m, 13.8m and 13.9m,
a 2.1 micron uniform-disk diameter of 25.3mas +/-3.3mas was derived. The
unusually high visibility values at baselines >16m show that the stellar
surface of R Cas is more complex than previously assumed. The visibility values
at baselines >16m can be explained by high-contrast surface structure on the
stellar surface of R Cas or other types of unexpected center-to-limb
variations. The R Cas observations were compared with theoretical Mira star
models yielding a linear Rosseland radius of 276Rsun +/-66Rsun and an effective
temperature of 2685K+/-238K for R Cas at phase 0.08.Comment: 10 pages, 6 figures, see also
http://www.mpifr-bonn.mpg.de/div/speckle, SPIE conf 4006 "Interferometry in
Optical Astronomy", in pres
Disks around massive young stellar objects: are they common?
We present K-band polarimetric images of several massive young stellar
objects at resolutions 0.1-0.5 arcsec. The polarization vectors around
these sources are nearly centro-symmetric, indicating they are dominating the
illumination of each field. Three out of the four sources show elongated
low-polarization structures passing through the centers, suggesting the
presence of polarization disks. These structures and their surrounding
reflection nebulae make up bipolar outflow/disk systems, supporting the
collapse/accretion scenario as their low-mass siblings. In particular, S140
IRS1 show well defined outflow cavity walls and a polarization disk which
matches the direction of previously observed equatorial disk wind, thus
confirming the polarization disk is actually the circumstellar disk. To date, a
dozen massive protostellar objects show evidence for the existence of disks;
our work add additional samples around MYSOs equivalent to early B-type stars.Comment: 9 pages, including 2 figures, 1 table, to appear on ApJ
Mineral inclusions in rutile: A novel recorder of HP-UHP metamorphism
The ability to accurately constrain the secular record of high- and ultra-high pressure metamorphism on Earth is potentially hampered as these rocks are metastable and prone to retrogression, particularly during exhumation. Rutile is among the most widespread and best preserved minerals in high- and ultra-high pressure rocks and a hitherto untested approach is to use mineral inclusions within rutile to record such conditions. In this study, rutiles from three different high- and ultrahigh-pressure massifs have been investigated for inclusions. Rutile is shown to contain inclusions of high-pressure minerals such as omphacite, garnet and high silica phengite, as well as diagnostic ultrahigh-pressure minerals, including the first reported occurrence of exceptionally preserved monomineralic coesite in rutile from the Dora–Maira massif. Chemical comparison of inclusion and matrix phases show that inclusions generally represent peak metamorphic assemblages; although rare prograde phases such as titanite, omphacite and corundum have also been identified implying that rutile grows continuously during prograde burial and traps mineralogic evidence of this evolution. Pressure estimates obtained from mineral inclusions, when used in conjunction with Zr-in-rutile thermometry, can provide additional constraints on the metamorphic conditions of the host rock. This study demonstrates that rutile is an excellent repository for high- and ultra-high pressure minerals and that the study of mineral inclusions in rutile may profoundly change the way we investigate and recover evidence of such events in both detrital populations and partially retrogressed samples
The inner circumstellar disk of the UX Ori star V1026 Sco
The UX Ori type variables (named after the prototype of their class) are
intermediate-mass pre-main sequence objects. One of the most likely causes of
their variability is the obscuration of the central star by orbiting dust
clouds. We investigate the structure of the circumstellar environment of the
UX~Ori star V1026 Sco (HD 142666) and test whether the disk inclination is
large enough to explain the UX Ori variability. We observed the object in the
low-resolution mode of the near-infrared interferometric VLTI/AMBER instrument
and derived H- and K-band visibilities and closure phases. We modeled our AMBER
observations, published Keck Interferometer observations, archival MIDI/VLTI
visibilities, and the spectral energy distribution using geometric and
temperature-gradient models. Employing a geometric inclined-ring disk model, we
find a ring radius of 0.15 +- 0.06 AU in the H band and 0.18 +- 0.06 AU in the
K band. The best-fit temperature-gradient model consists of a star and two
concentric, ring-shaped disks. The inner disk has a temperature of
1257^{+133}_{-53} K at the inner rim and extends from 0.19 +- 0.01 AU to 0.23
+- 0.02 AU. The outer disk begins at 1.35^{+0.19}_{-0.20} AU and has an inner
temperature of 334^{+35}_{-17} K. The derived inclination of
48.6^{+2.9}_{-3.6}deg approximately agrees with the inclination derived with
the geometric model (49 +- 5deg in the K band and 50 +- 11deg in the H band).
The position angle of the fitted geometric and temperature-gradient models are
163 +- 9deg (K band; 179 +- 17deg in the H band) and 169.3^{+4.2}_{-6.7}deg,
respectively. The narrow width of the inner ring-shaped model disk and the disk
gap might be an indication for a puffed-up inner rim shadowing outer parts of
the disk. The intermediate inclination of ~50deg is consistent with models of
UX Ori objects where dust clouds in the inclined disk obscure the central star
AMBER/VLTI observations of the B[e] star MWC 300
Aims. We study the enigmatic B[e] star MWC 300 to investigate its disk and
binary with milli-arcsecond-scale angular resolution. Methods. We observed MWC
300 with the VLTI/AMBER instrument in the H and K bands and compared these
observations with temperature-gradient models to derive model parameters.
Results. The measured low visibility values, wavelength dependence of the
visibilities, and wavelength dependence of the closure phase directly suggest
that MWC 300 consists of a resolved disk and a close binary. We present a model
consisting of a binary and a temperature-gradient disk that is able to
reproduce the visibilities, closure phases, and spectral energy distribution.
This model allows us to constrain the projected binary separation (~4.4 mas or
~7.9 AU), the flux ratio of the binary components (~2.2), the disk temperature
power-law index, and other parameters.Comment: 4 pages, 1 figure, accepted by A&
Bispectrum speckle interferometry of the massive protostellar outflow source IRAS 23151+5912
We present bispectrum speckle interferometry of the massive protostellar
object IRAS 23151+5912 in the near-infrared K' band. The reconstructed image
shows the diffuse nebulosity north-east of two point-like sources in
unprecedented detail. The comparison of our near-infrared image with mm
continuum and CO molecular line maps shows that the brighter of the two point
sources lies near the center of the mm peak, indicating that it is a high-mass
protostar. The nebulosity coincides with the blue-shifted molecular outflow
component. The most prominent feature in the nebulosity is a bow-shock-like
arc. We assume that this feature is associated with a precessing jet which has
created an inward-pointed cone in the swept-up material. We present numerical
jet simulations that reproduce this and several other features observed in our
speckle image of the nebulosity. Our data also reveal a linear structure
connecting the central point source to the extended diffuse nebulosity. This
feature may represent the innermost part of a jet that drives the strong
molecular outflow (PA ~80 degr) from IRAS 23151+5912. With the aid of radiative
transfer calculations, we demonstrate that, in general, the observed inner
structures of the circumstellar material surrounding high-mass stars are
strongly influenced by the orientation and symmetry of the bipolar cavity.Comment: accepted by Astronomy & Astrophysics; preprints with high-resolution
images can be obtained from
http://www.mpifr-bonn.mpg.de/staff/tpreibis/iras23151.htm
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
An equatorial wind from the massive young stellar object S140 IRS 1
The discovery of the second equatorial ionized stellar wind from a massive
young stellar object is reported. High resolution radio continuum maps of S140
IRS 1 reveal a highly elongated source that is perpendicular to the larger
scale bipolar molecular outflow. This picture is confirmed by location of a
small scale monopolar near-IR reflection nebula at the base of the blueshifted
lobe. A second epoch of observations over a five year baseline show little
ordered outward proper motion of clumps as would have been expected for a jet.
A third epoch, taken only 50 days after the second, did show significant
changes in the radio morphology. These radio properties can all be understood
in the context of an equatorial wind driven by radiation pressure from the
central star and inner disc acting on the gas in the surface layers of the disc
as proposed by Drew et al. (1998). This equatorial wind system is briefly
compared with the one in S106IR, and contrasted with other massive young
stellar objects that drive ionized jets.Comment: 19 pages, 5 figures, accepted by ApJ, minor changes in light of
referees repor
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