409 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 &
AMBER and CRIRES observations of the binary sgB[e] star HD 327083: evidence of a gaseous disc traced by CO bandhead emission
HD 327083 is a sgB[e] star that forms a binary system with an orbital
semi-major axis of ~1.7 AU. Our previous observations using the VLTI and AMBER
in the medium resolution K-band mode spatially resolved the environment of HD
327083. The continuum visibilities obtained indicate the presence of a
circumbinary disc. CO bandhead emission was also observed. However, due to the
limited spectral resolution of the previous observations, the kinematic
structure of the emitting material was not constrained. In this paper, we
address this and probe the source of the CO emission with high spectral
resolution and spatial precision. We have observed HD 327083 with high spectral
resolution (25 & 6 km/s) using AMBER and CRIRES. The observations are compared
to kinematical models to constrain the source of the emission. It is shown that
the CO bandhead emission can be reproduced using a model of a Keplerian disc
with an inclination and size consistent with our previous VLTI observations.
The model is compared to AMBER differential phase measurements, which have a
precision as high as 30-micro-arcseconds. A differential phase signal
corresponding to 0.15 milli-arcseconds (~5 sigma) is seen over the bandhead
emission, which is in excellent agreement with the model that fits the CRIRES
observations. In comparison, a model of an equatorial outflow, as envisaged in
the standard sgB[e] scenario, does not reproduce the observations well. The
excellent agreement between the disc model and observations in the spatial and
spectral domains is compelling evidence that the CO bandhead emission of HD
327083 originates in a circumbinary Keplerian disc. In contrast, the model of
an equatorial outflow cannot reproduce the observations well. This suggests
that the standard sgB[e] scenario is not applicable to HD 327083, which
supports the hypothesis that the B[e] behaviour of HD 327083 is due to binarity
(ABRIDGED).Comment: Accepted for publication in A&
Probing discs around massive young stellar objects with CO first overtone emission
We present high resolution (R~50,000) spectroastrometry over the CO 1st
overtone bandhead of a sample of seven intermediate/massive young stellar
objects. These are primarily drawn from the red MSX source (RMS) survey, a
systematic search for young massive stars which has returned a large, well
selected sample of such objects. The mean luminosity of the sample is
approximately 5 times 10^4 L_\odot, indicating the objects typically have a
mass of ~15 solar masses. We fit the observed bandhead profiles with a model of
a circumstellar disc, and find good agreement between the models and
observations for all but one object. We compare the high angular precision
(0.2-0.8 mas) spectroastrometric data to the spatial distribution of the
emitting material in the best-fitting models. No spatial signatures of discs
are detected, which is entirely consistent with the properties of the
best-fitting models. Therefore, the observations suggest that the CO bandhead
emission of massive young stellar objects originates in small-scale disks, in
agreement with previous work. This provides further evidence that massive stars
form via disc accretion, as suggested by recent simulations.Comment: Accepted for publication in MNRA
Tracers of Discs and Winds around Intermediate and High Mass Young Stellar Objects
We present a study of the kinematical properties of a small sample of nearby
near-infrared bright massive and intermediate mass young stellar objects using
emission lines sensitive to discs and winds. We show for the first time that
the broad (kms) symmetric line wings on the HI Brackett series
lines are due to Stark broadening or electron scattering, rather than pure
Doppler broadening due to high speed motion. The results are consistent with
the presence of a very dense circumstellar environment. In addition, many of
these lines show evidence for weak line self-absorption, suggestive of a wind
or disc-wind origin for that part of the absorbing material. The weakness of
the self-absorption suggests a large opening angle for such an outflow. We also
study the fluorescent 1.688m FeII line, which is sensitive to dense
material. We fitted a Keplerian disc model to this line, and find reasonable
fits in all bar one case, in agreement with previous finding for classical Be
stars that fluorescent iron transitions are reasonable disc tracers. Overall
the picture is one in which these stars still have accretion discs, with a very
dense inner circumstellar environment which may be tracing either the inner
regions of a disc, or of a stellar wind, and in which ionised outflow is also
present. The similarity with lower mass stars is striking, suggesting that at
least in this mass range they form in a similar fashion.Comment: 20 pages, 7 figures, accepted for publication in MNRA
VLTI/AMBER observations of the binary B[e] supergiant HD 327083
HD 327083 is a luminous B type star which exhibits emission lines and an
infrared excess and is therefore classified as a supergiant B[e] star. In
addition, the star is the primary of a close binary system. It is not clear
whether the B[e] behaviour of HD 327083 is related to its binarity or its
evolutionary state. Here we address this issue by studying its circumstellar
environment with high spatial resolution. To this end, we have observed HD
327083 with the VLTI and AMBER in the medium resolution K-band setting. 13CO
bandhead emission is detected, confirming HD 327083 is a post-main sequence
object. The observations spatially resolve the source of the NIR continuum and
the Br-gamma and CO line emission. In addition, differential phase measurements
allow us to probe the origin of the observed Br-gamma emission with sub-mas
precision. Using geometrical models, we find that the visibilities and closure
phases suggest that the close binary system is surrounded by a circum-binary
disk. We also find that in the case of the binary HD 327083, the relative sizes
of the continuum and Br-gamma emitting regions are different to those of a
single supergiant B[e] star where the standard dual outflow scenario is thought
to apply. These findings are consistent with the hypothesis that the mass loss
of HD 327083 is related to its binary nature.Comment: Accepted in A&
Probing the properties of Be star discs with spectroastrometry and NLTE radiative transfer modelling: beta CMi
While the presence of discs around classical Be stars is well established,
their origin is still uncertain. To understand what processes result in the
creation of these discs and how angular momentum is transported within them,
their physical properties must be constrained. This requires comparing high
spatial and spectral resolution data with detailed radiative transfer
modelling. We present a high spectral resolution, R~80,000, sub milli-arcsecond
precision, spectroastrometric study of the circumstellar disc around the Be
star beta CMi. The data are confronted with three-dimensional, NLTE radiative
transfer calculations to directly constrain the properties of the disc.
Furthermore, we compare the data to disc models featuring two velocity laws;
Keperian, the prediction of the viscous disc model, and angular momentum
conserving rotation. It is shown that the observations of beta CMi can only be
reproduced using Keplerian rotation. The agreement between the model and the
observed SED, polarisation and spectroastrometric signature of beta CMi
confirms that the discs around Be stars are well modelled as viscous decretion
discs.Comment: Accepted for publication in MNRA
Pollinator Limitation, Autogamy and Minimal Inbreeding Depression in Insect-pollinated Plants on a Boreal Island
CO bandhead emission of massive young stellar objects: determining disc properties
Massive stars play an important role in many areas of astrophysics, but numerous details regarding their formation remain unclear. In this paper we present and analyse high-resolution (R~30 000) near-infrared 2.3 μm spectra of 20 massive young stellar objects (MYSOs) from the Red MSX Source (RMS) data base, in the largest such study of CO first overtone bandhead emission to date. We fit the emission under the assumption it originates from a circumstellar disc in Keplerian rotation. We explore three approaches to modelling the physical conditions within the disc-a disc heated mainly via irradiation from the central star, a disc heated mainly via viscosity, and a disc in which the temperature and density are described analytically. We find that the models described by heating mechanisms are inappropriate because they do not provide good fits to the CO emission spectra. We therefore restrict our analysis to the analytic model, and obtain good fits to all objects that possess sufficiently strong CO emission, suggesting circumstellar discs are the source of this emission. On average, the temperature and density structure of the discs correspond to geometrically thin discs, spread across a wide range of inclinations. Essentially all the discs are located within the dust sublimation radius, providing strong evidence that the CO emission originates close to the central protostar, on astronomical unit scales. In addition, we show that the objects in our sample appear no different to the general population of MYSOs in the RMS data base, based on their near- and mid-infrared colours. The combination of observations of a large sample of MYSOs with CO bandhead emission and our detailed modelling provide compelling evidence of the presence of small-scale gaseous discs around such objects, supporting the scenario in which massive stars form via disc accretion. © 2013 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society
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A behavioral comparison of male and female adults with high functioning autism spectrum conditions
Autism spectrum conditions (ASC) affect more males than females in the general population. However, within ASC it is unclear if there are phenotypic sex differences. Testing for similarities and differences between the sexes is important not only for clinical assessment but also has implications for theories of typical sex differences and of autism. Using cognitive and behavioral measures, we investigated similarities and differences between the sexes in age- and IQ-matched adults with ASC (high-functioning autism or Asperger syndrome). Of the 83 (45 males and 38 females) participants, 62 (33 males and 29 females) met Autism Diagnostic Interview-Revised (ADI-R) cut-off criteria for autism in childhood and were included in all subsequent analyses. The severity of childhood core autism symptoms did not differ between the sexes. Males and females also did not differ in self-reported empathy, systemizing, anxiety, depression, and obsessive-compulsive traits/symptoms or mentalizing performance. However, adult females with ASC showed more lifetime sensory symptoms (p = 0.036), fewer current socio-communication difficulties (p = 0.001), and more self-reported autistic traits (p = 0.012) than males. In addition, females with ASC who also had developmental language delay had lower current performance IQ than those without developmental language delay (p<0.001), a pattern not seen in males. The absence of typical sex differences in empathizing-systemizing profiles within the autism spectrum confirms a prediction from the extreme male brain theory. Behavioral sex differences within ASC may also reflect different developmental mechanisms between males and females with ASC. We discuss the importance of the superficially better socio-communication ability in adult females with ASC in terms of why females with ASC may more often go under-recognized, and receive their diagnosis later, than males
Blinded by the light: on the relationship between CO first overtone emission and mass accretion rate in massive young stellar objects
To date, there is no explanation as to why disc-tracing CO first overtone (or ‘bandhead’) emission is not a ubiquitous feature in low- to medium-resolution spectra of massive young stellar objects (MYSOs), but instead is only detected towards approximately 25 per cent of their spectra. In this paper, we investigate the hypothesis that only certain mass accretion rates result in detectable bandhead emission in the near-infrared spectra of MYSOs. Using an analytic disc model combined with an LTE model of the CO emission, we find that high accretion rates (≳10⁻⁴ M⊙ yr⁻¹) result in large dust sublimation radii, a larger contribution to the K-band continuum from hot dust at the dust sublimation radius, and therefore correspondingly lower CO emission with respect to the continuum. On the other hand, low accretion rates (≲10⁻⁶ M⊙ yr⁻¹) result in smaller dust sublimation radii, a correspondingly smaller emitting area of CO, and thus also lower CO emission with respect to the continuum. In general, moderate accretion rates produce the most prominent, and therefore detectable, CO first overtone emission. We compare our findings to a recent near-infrared spectroscopic survey of MYSOs, finding results consistent with our hypothesis. We conclude that the detection rate of CO bandhead emission in the spectra of MYSOs could be the result of MYSOs exhibiting a range of mass accretion rates, perhaps due to the variable accretion suggested by recent multi-epoch observations of these objects
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