132,596 research outputs found
The VLA/ALMA Nascent Disk and Multiplicity (VANDAM) Survey of Perseus Protostars. VI. Characterizing the Formation Mechanism for Close Multiple Systems
We present Atacama Large Millimeter/submillimeter Array (ALMA) observations
of multiple protostar systems in the Perseus molecular cloud previously
detected by the Karl G. Jansky Very Large Array (VLA). We observed 17 close
(600~AU separation) multiple systems at 1.3~mm in continuum and five
molecular lines (i.e., \twco, \cateo, \thco, HCO, SO) to characterize the
circum-multiple environments in which these systems are forming. We detect at
least one component in the continuum for the 17 multiple systems. In three
systems, one companion is not detected, and for two systems the companions are
unresolved at our observed resolution. We also detect circum-multiple dust
emission toward 8 out of 9 Class 0 multiples. Circum-multiple dust emission is
not detected toward any of the 8 Class I multiples. Twelve systems are detected
in the dense gas tracers toward their disks/inner envelopes. For these 12
systems, we use the dense gas observations to characterize their formation
mechanism. The velocity gradients in the circum-multiple gas are clearly
orthogonal to the outflow directions in 8 out of the 12 systems, consistent
with disk fragmentation. Moreover, only two systems with separations 200~AU
are \textit{inconsistent} with disk fragmentation, in addition to the two
widest systems (500~AU). Our results suggest that disk fragmentation via
gravitational instability is an important formation mechanism for close
multiple systems, but further statistics are needed to better determine the
relative fraction formed via this method.Comment: 48 Pages, 26 Figures, 7 Tables, Accepted by Ap
Circumstellar Disks Around Binary Stars in Taurus
We have conducted a survey of 17 wide (> 100 AU) young binary systems in
Taurus with the Atacama Large Millimeter Array (ALMA) at two wavelengths. The
observations were designed to measure the masses of circumstellar disks in
these systems as an aid to understanding the role of multiplicity in star and
planet formation. The ALMA observations had sufficient resolution to localize
emission within the binary system. Disk emission was detected around all
primaries and ten secondaries, with disk masses as low as .
We compare the properties of our sample to the population of known disks in
Taurus and find that the disks from this binary sample match the scaling
between stellar mass and millimeter flux of
to within the scatter found in previous studies. We also compare the properties
of the primaries to those of the secondaries and find that the
secondary/primary stellar and disk mass ratios are not correlated; in three
systems, the circumsecondary disk is more massive than the circumprimary disk,
counter to some theoretical predictions.Comment: To appear in the Astrophysical Journal, 12 page
Resolved Young Binary Systems And Their Disks
We have conducted a survey of young single and multiple systems in the TaurusâAuriga star-forming region with the Atacama Large Millimeter Array (ALMA), substantially improving both the spatial resolution and sensitivity with which individual protoplanetary disks in these systems have been observed. These ALMA observations can resolve binary separations as small as 25â30 au and have an average 3Ï detection level of 0.35 mJy, equivalent to a disk mass of 4 Ă 10â5 M â for an M3 star. Our sample was constructed from stars that have an infrared excess and/or signs of accretion and have been classified as Class II. For the binary and higher-order multiple systems observed, we detect λ = 1.3 mm continuum emission from one or more stars in all of our target systems. Combined with previous surveys of Taurus, our 21 new detections increase the fraction of millimeter-detected disks to over 75% in all categories of stars (singles, primaries, and companions) earlier than spectral type M6 in the Class II sample. Given the wealth of other information available for these stars, this has allowed us to study the impact of multiplicity with a much larger sample. While millimeter flux and disk mass are related to stellar mass as seen in previous studies, we find that both primary and secondary stars in binary systems with separations of 30â4200 au have lower values of millimeter flux as a function of stellar mass than single stars. We also find that for these systems, the circumstellar disk around the primary star does not dominate the total disk mass in the system and contains on average 62% of the total mass
On the Observability of Giant Protoplanets in Circumstellar Disks
We investigate the possibility to detect giant planets that are still
embedded in young circumstellar disks. Based on models with different stellar,
planetary, and disk masses, and different radial positions of the planet we
analyze the resulting submillimeter appearance of these systems. We find that
the influence of the planet on the spectral energy distribution could not be
distinguished from that of other disk parameters. However, dust reemission
images of the disks show that the hot region in the proximity of a young
planet, along with the gap, could indeed be detected and mapped with the
Atacama Large Millimeter Array in the case of nearby circumstellar disks
(d<100pc) in approximate face-on orientation.Comment: ApJ, in pres
Resolved Young Binary Systems And Their Disks
We have conducted a survey of young single and multiple systems in the TaurusâAuriga star-forming region with the Atacama Large Millimeter Array (ALMA), substantially improving both the spatial resolution and sensitivity with which individual protoplanetary disks in these systems have been observed. These ALMA observations can resolve binary separations as small as 25â30 au and have an average 3Ï detection level of 0.35 mJy, equivalent to a disk mass of 4 Ă 10â5 M â for an M3 star. Our sample was constructed from stars that have an infrared excess and/or signs of accretion and have been classified as Class II. For the binary and higher-order multiple systems observed, we detect λ = 1.3 mm continuum emission from one or more stars in all of our target systems. Combined with previous surveys of Taurus, our 21 new detections increase the fraction of millimeter-detected disks to over 75% in all categories of stars (singles, primaries, and companions) earlier than spectral type M6 in the Class II sample. Given the wealth of other information available for these stars, this has allowed us to study the impact of multiplicity with a much larger sample. While millimeter flux and disk mass are related to stellar mass as seen in previous studies, we find that both primary and secondary stars in binary systems with separations of 30â4200 au have lower values of millimeter flux as a function of stellar mass than single stars. We also find that for these systems, the circumstellar disk around the primary star does not dominate the total disk mass in the system and contains on average 62% of the total mass
The Structure and X-ray Recombination Emission of a Centrally Illuminated Accretion Disk Atmosphere and Corona
We model an accretion disk atmosphere and corona photoionized by a central
X-ray continuum source. We calculate the opacity and radiation transfer for an
array of disk radii, to obtain the two-dimensional structure of the disk and
its X-ray recombination emission. The atmospheric structure is insensitive to
the viscosity alpha. We find a feedback mechanism between the disk structure
and the central illumination, which expands the disk and increases the solid
angle subtended by the atmosphere. We model the disk of a neutron star X-ray
binary. We map the temperature, density, and ionization structure of the disk,
and we simulate the high resolution spectra observable with the Chandra and
XMM-Newton grating spectrometers. The X-ray emission lines from the disk
atmosphere are detectable, especially for high-inclination binary systems. The
grating observations of two classes of X-ray binaries already reveal important
spectral similarities with our models. The line spectrum is very sensitive to
the structure of each atmospheric layer, and it probes the heating mechanisms
in the disk. The model spectrum is dominated by double-peaked lines of H-like
and He-like ions, plus weak Fe L. Species with a broad range of ionization
levels coexist at each radius: from Fe XXVI in the hot corona, to C VI at the
base of the atmosphere. The choice of stable solutions affects the spectrum,
since a thermal instability is present in the regime where the X-ray
recombination emission is most intense.Comment: 32 pages, incl. 26 figures, accepted for publication in Ap
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
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