162 research outputs found
Long-lived protoplanetary disks in multiple systems: the VLA view of HD 98800
The conditions and evolution of protoplanetary disks in multiple systems can
be considerably different from those around single stars, which may have
important consequences for planet formation. We present Very Large Array (VLA)
8.8 mm (34 GHz) and 5 cm (6 GHz) observations of the quadruple system HD 98800,
which consists of two spectroscopic binary systems (Aa-Ab, Ba-Bb). The Ba-Bb
pair is surrounded by a circumbinary disk, usually assumed to be a debris disk
given its 10 Myr age and lack of near infrared excess. The VLA 8.8 mm
observations resolve the disk size (5-5.5 au) and its inner cavity (3
au) for the first time, making it one of the smallest disks known. Its small
size, large fractional luminosity, and millimeter spectral index consistent
with blackbody emission support the idea that HD 98800 B is a massive,
optically thick ring which may still retain significant amounts of gas. The
disk detection at 5 cm is compatible with free-free emission from photoionized
material. The diskless HD 98800 A component is also detected, showing partial
polarization at 5 cm compatible with non-thermal chromospheric activity. We
propose that tidal torques from Ba-Bb and A-B have stopped the viscous
evolution of the inner and outer disk radii, and the disk is evolving via mass
loss through photoevaporative winds. This scenario can explain the properties
and longevity of HD 98800 B as well as the lack of a disk around HD 98800 A,
suggesting that planet formation could have more time to proceed in multiple
systems than around single stars in certain system configurations.Comment: 14 pages, 4 figures, 3 tables; Submitted to ApJ May 14 2018; Accepted
to ApJ August 3 2018. This version fixes a mistake in the reported position
angle. The order of the figures has been changed to match that of the
references in the tex
Resolving The Moth at Millimeter Wavelengths
HD 61005, also known as "The Moth," is one of only a handful of debris disks
that exhibit swept-back "wings" thought to be caused by interaction with the
ambient interstellar medium (ISM). We present 1.3 mm Submillimeter Array (SMA)
observations of the debris disk around HD 61005 at a spatial resolution of 1.9
arcsec that resolve the emission from large grains for the first time. The disk
exhibits a double-peaked morphology at millimeter wavelengths, consistent with
an optically thin ring viewed close to edge-on. To investigate the disk
structure and the properties of the dust grains we simultaneously model the
spatially resolved 1.3 mm visibilities and the unresolved spectral energy
distribution. The temperatures indicated by the SED are consistent with
expected temperatures for grains close to the blowout size located at radii
commensurate with the millimeter and scattered light data. We also perform a
visibility-domain analysis of the spatial distribution of millimeter-wavelength
flux, incorporating constraints on the disk geometry from scattered light
imaging, and find suggestive evidence of wavelength-dependent structure. The
millimeter-wavelength emission apparently originates predominantly from the
thin ring component rather than tracing the "wings" observed in scattered
light. The implied segregation of large dust grains in the ring is consistent
with an ISM-driven origin for the scattered light wings.Comment: 10 pages, 6 figure
Discovery of an equal-mass "twin" binary population reaching 1000+ AU separations
We use a homogeneous catalog of 42,000 main-sequence wide binaries identified
by Gaia to measure the mass ratio distribution, p(q), of binaries with primary
masses , mass ratios , and separations
. A well-understood selection function allows us to
constrain p(q) in 35 independent bins of primary mass and separation, with
hundreds to thousands of binaries in each bin. Our investigation reveals a
sharp excess of equal-mass "twin" binaries that is statistically significant
out to separations of 1,000 to 10,000 AU, depending on primary mass. The excess
is narrow: a steep increase in p(q) at , with no significant
excess at . A range of tests confirm the signal is real, not a
data artifact or selection effect. Combining the Gaia constraints with those
from close binaries, we show that the twin excess decreases with increasing
separation, but its width () is constant over . The wide twin population would be difficult to explain if the
components of all wide binaries formed via core fragmentation, which is not
expected to produce strongly correlated component masses. We conjecture that
wide twins formed at closer separations ( AU), likely via
accretion from circumbinary disks, and were subsequently widened by dynamical
interactions in their birth environments. The separation-dependence of the twin
excess then constrains the efficiency of dynamical widening and disruption of
binaries in young clusters. We also constrain p(q) across .
Besides changes in the twin fraction, p(q) is independent of separation at
fixed primary mass over . It is flatter than
expected for random pairings from the IMF but more bottom-heavy for wide
binaries than for binaries with 100 AU.Comment: 24 pages, 17 figures, plus appendices. Accepted to MNRAS. Fig 17 and
Appendix F are new since v
A coplanar circumbinary protoplanetary disk in the TWA 3 triple M dwarf system
Funding: This project has received funding from the European Unionâs Horizon 2020 research and innovation program under the Marie SkĆodowska-Curie grant agreement No 210021. E.C. acknowledges NASA grants 80NSSC19K0506 and NNX15AD95G/NEXSS.We present sensitive ALMA observations of TWA 3, a nearby, young (âŒ10 Myr) hierarchical system composed of three pre-main-sequence M3âM4.5 stars. For the first time, we detected 12CO and 13CO J = 2â1 emissions from the circumbinary protoplanetary disk around TWA 3A. We jointly fit the protoplanetary disk velocity field, stellar astrometric positions, and stellar radial velocities to infer the architecture of the system. The Aa and Ab stars (0.29 ± 0.01 Mâ and 0.24 ± 0.01 Mâ, respectively) comprising the tight (P = 35 days) eccentric (e = 0.63 ± 0.01) spectroscopic binary are coplanar with their circumbinary disk (misalignment <6° with 68% confidence), similar to other short-period binary systems. From models of the spectral energy distribution, we found the inner radius of the circumbinary disk (rinner = 0.50â0.75 au) to be consistent with theoretical predictions of dynamical truncation rcav/ainner â 3. The outer orbit of the tertiary star B (0.40 ± 0.28 Mâ, a ⌠65 ± 18 au, e = 0.3 ± 0.2) is not as well constrained as the inner orbit; however, orbits coplanar with the A system are still preferred (misalignment < 20°). To better understand the influence of the B orbit on the TWA 3A circumbinary disk, we performed SPH simulations of the system and found that the outer edge of the gas disk (router = 8.5 ± 0.2 au) is most consistent with truncation from a coplanar, circular, or moderately eccentric orbit, supporting the preference from the joint orbital fit.Publisher PDFPeer reviewe
A coplanar circumbinary protoplanetary disk in the TWA 3 triple M dwarf system
We present sensitive ALMA observations of TWA 3, a nearby, young (10
Myr) hierarchical system composed of three pre-main sequence M3--M4.5 stars.
For the first time, we detected CO and CO =2-1 emission
from the circumbinary protoplanetary disk around TWA 3A. We jointly fit the
protoplanetary disk velocity field, stellar astrometric positions, and stellar
radial velocities to infer the architecture of the system. The Aa and Ab stars
( and , respectively) comprising
the tight ( days) eccentric () spectroscopic binary are
coplanar with their circumbinary disk (misalignment with 68%
confidence), similar to other short-period binary systems. From models of the
spectral energy distribution, we found the inner radius of the circumbinary
disk ( au) to be consistent with theoretical
predictions of dynamical truncation . The outer orbit of the tertiary star B (, au, ) is not as well constrained as the inner orbit,
however, orbits coplanar with the A system are still preferred (misalignment ). To better understand the influence of the B orbit on the TWA 3A
circumbinary disk, we performed SPH simulations of the system and found that
the outer edge of the gas disk ( au) is most
consistent with truncation from a coplanar, circular or moderately eccentric
orbit, supporting the preference from the joint orbital fit.Comment: 19 pages, 9 figures, accepted to Ap
Keck Adaptive Optics Observations of the Protostellar Disk around Radio Source I in the Orion Kleinmann-Low Nebula
We have made the first detection of a near-infrared counterpart associated
with the disk around Radio Source "I," a massive protostar in the Kleinmann-Low
Nebula in Orion using imaging with laser guide star adaptive optics on the Keck
II telescope. The infrared emission is evident in images acquired using L' (3.8
microns) and Ms (4.7 microns) filters and is not detectable at K' (2.1
microns). The observed morphology strongly suggests that we are seeing some
combination of scattered and thermal light emanating from the disk. The disk is
also manifest in the L'/Ms flux ratio image. We interpret the near-infrared
emission as the illuminated surface of a nearly edge-on disk, oriented so that
only the northern face is visible; the opposite surface remains hidden by the
disk. We do not see infrared radiation associated directly with the star
proposed to be associated with Source "I." The data also suggest that there is
a cavity above and below the disk that is oriented perpendicular to the disk,
and is sculpted by the known, strong outflow from the inner disk of Source I.
We compare our data to models of a protostar with a surrounding disk, envelope,
and wind-blown cavity in order to elucidate the nature of the disk around Radio
Source I.Comment: 22 pages, 7 figures. Accepted for publication to Ap
Resolved Debris Discs Around A Stars in the Herschel DEBRIS Survey
The majority of debris discs discovered so far have only been detected
through infrared excess emission above stellar photospheres. While disc
properties can be inferred from unresolved photometry alone under various
assumptions for the physical properties of dust grains, there is a degeneracy
between disc radius and dust temperature that depends on the grain size
distribution and optical properties. By resolving the disc we can measure the
actual location of the dust. The launch of Herschel, with an angular resolution
superior to previous far-infrared telescopes, allows us to spatially resolve
more discs and locate the dust directly. Here we present the nine resolved
discs around A stars between 20 and 40 pc observed by the DEBRIS survey. We use
these data to investigate the disc radii by fitting narrow ring models to
images at 70, 100 and 160 {\mu}m and by fitting blackbodies to full spectral
energy distributions. We do this with the aim of finding an improved way of
estimating disc radii for unresolved systems. The ratio between the resolved
and blackbody radii varies between 1 and 2.5. This ratio is inversely
correlated with luminosity and any remaining discrepancies are most likely
explained by differences to the minimum size of grain in the size distribution
or differences in composition. We find that three of the systems are well fit
by a narrow ring, two systems are borderline cases and the other four likely
require wider or multiple rings to fully explain the observations, reflecting
the diversity of planetary systems.Comment: 19 pages, 13 figures, 6 tables. Accepted for publication in MNRA
The VLTI / PIONIER near-infrared interferometric survey of southern T Tauri stars. I. First results
Context : The properties of the inner disks of bright Herbig AeBe stars have
been studied with near infrared (NIR) interferometry and high resolution
spectroscopy. The continuum and a few molecular gas species have been studied
close to the central star; however, sensitivity problems limit direct
information about the inner disks of the fainter T Tauri stars.
Aims : Our aim is to measure some of the properties of the inner regions of
disks surrounding southern T Tauri stars.
Methods : We performed a survey with the PIONIER recombiner instrument at
H-band of 21 T Tauri stars. The baselines used ranged from 11 m to 129 m,
corresponding to a maximum resolution of 3mas (0.45 au at 150 pc).
Results : Thirteen disks are resolved well and the visibility curves are
fully sampled as a function of baseline in the range 45-130 m for these 13
objects. A simple qualitative examination of visibility profiles allows us to
identify a rapid drop-off in the visibilities at short baselines in 8 resolved
disks. This is indicative of a significant contribution from an extended
contribution of light from the disk. We demonstrate that this component is
compatible with scattered light, providing strong support to a prediction made
by Pinte et al. (2008). The amplitude of the drop-off and the amount of dust
thermal emission changes from source to source suggesting that each disk is
different. A by-product of the survey is the identification of a new
milli-arcsec separation binary: WW Cha. Spectroscopic and interferometric data
of AK Sco have also been fitted with a binary and disk model.
Conclusions : Visibility data are reproduced well when thermal emission and
scattering form dust are fully considered. The inner radii measured are
consistent with the expected dust sublimation radii. Modelling of AK Sco
suggests a likely coplanarity between the disk and the binary's orbital planeComment: 19 pages, 11 figure
On the universal outcome of star-formation: Is there a link between stars and brown-dwarfs?
(abridged) The recent evidence obtained by Briceno et al. that star-formation
in Taurus-Auriga (TA) may be producing significantly fewer brown dwarfs (BDs)
per star than the ONC is investigated by setting up a realistic model stellar
plus BD population and explicitly taking into account a high binary proportion
and dynamical evolution in the TA groups and the ONC. The Briceno result is
reproduced almost exactly despite an identical IMF in both systems because many
BD-BD and star-BD binaries are disrupted in the ONC thus freeing BDs, while the
TA groups remain unevolved dynamically. However, the resulting populations do
not have the correct star-star, star-BD and expecially BD-BD binary properties,
even if a variable BD IMF is allowed for. The conclusion is therefore that BDs
need to be added as a separate population which has its own binary properties.
Such an extra population can have various origins which are briefly discussed
in this contribution but more fully in an associated paper.Comment: MNRAS, accepted, 23 pages, 14 figures, LaTeX, two references adde
Disk and Envelope Structure in Class 0 Protostars: I. The Resolved Massive Disk in Serpens FIRS 1
We present the first results of a program to characterize the disk and
envelope structure of typical Class 0 protostars in nearby low-mass star
forming regions. We use Spitzer IRS mid-infrared spectra, high resolution CARMA
230 GHz continuum imaging, and 2-D radiative transfer models to constrain the
envelope structure, as well as the size and mass of the circum-protostellar
disk in Serpens FIRS 1. The primary envelope parameters (centrifugal radius,
outer radius, outflow opening angle, and inclination) are well constrained by
the spectral energy distribution (SED), including Spitzer IRAC and MIPS
photometry, IRS spectra, and 1.1 mm Bolocam photometry. These together with the
excellent uv-coverage (4.5-500 klam) of multiple antenna configurations with
CARMA allow for a robust separation of the envelope and a resolved disk. The
SED of Serpens FIRS 1 is best fit by an envelope with the density profile of a
rotating, collapsing spheroid with an inner (centrifugal) radius of
approximately 600 AU, and the millimeter data by a large resolved disk with
Mdisk~1.0 Msun and Rdisk~300 AU. These results suggest that large, massive
disks can be present early in the main accretion phase. Results for the larger,
unbiased sample of Class~0 sources in the Perseus, Serpens, and Ophiuchus
molecular clouds are needed to determine if relatively massive disks are
typical in the Class 0 stage.Comment: Comments: 13 pages, 8 figures, 3 tables; accepted for publication in
the Ap
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