820 research outputs found
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
The mid-infrared spectrum of the transiting exoplanet HD 209458b
We report the spectroscopic detection of mid-infrared emission from the
transiting exoplanet HD 209458b. Using archive data taken with the Spitzer/IRS
instrument, we have determined the spectrum of HD 209458b between 7.46 and
15.25 microns. We have used two independent methods to determine the planet
spectrum, one differential in wavelength and one absolute, and find the results
are in good agreement. Over much of this spectral range, the planet spectrum is
consistent with featureless thermal emission. Between 7.5 and 8.5 microns, we
find evidence for an unidentified spectral feature. If this spectral modulation
is due to absorption, it implies that the dayside vertical temperature profile
of the planetary atmosphere is not entirely isothermal. Using the IRS data, we
have determined the broad-band eclipse depth to be 0.00315 +/- 0.000315,
implying significant redistribution of heat from the dayside to the nightside.
This work required development of improved methods for Spitzer/IRS data
calibration that increase the achievable absolute calibration precision and
dynamic range for observations of bright point sources.Comment: 35 pages, 12 figures, revised version accepted by the Astrophysical
Journa
Misaligned Protoplanetary Disks In A Young Binary Star System
Many extrasolar planets follow orbits that differ from the nearly coplanar and circular orbits found in our Solar System; their orbits may be eccentric or inclined with respect to the host star\u27s equator, and the population of giant planets orbiting close to their host stars suggests appreciable orbital migration. There is at present no consensus on what produces such orbits. Theoretical explanations often invoke interactions with a binary companion star in an orbit that is inclined relative to the planet\u27s orbital plane. Such mechanisms require significant mutual inclinations between the planetary and binary star orbital planes. The protoplanetary disks in a few young binaries are misaligned, but often the measurements of these misalignments are sensitive only to a small portion of the inner disk, and the three-dimensional misalignment of the bulk of the planet-forming disk mass has hitherto not been determined. Here we report that the protoplanetary disks in the young binary system HK Tauri are misaligned by 60 to 68 degrees, such that one or both of the disks are significantly inclined to the binary orbital plane. Our results demonstrate that the necessary conditions exist for misalignment-driven mechanisms to modify planetary orbits, and that these conditions are present at the time of planet formation, apparently because of the binary formation process
Pulsed Accretion in the T Tauri Binary TWA 3A
TWA 3A is the most recent addition to a small group of young binary systems
that both actively accrete from a circumbinary disk and have spectroscopic
orbital solutions. As such, it provides a unique opportunity to test binary
accretion theory in a well-constrained setting. To examine TWA 3A's
time-variable accretion behavior, we have conducted a two-year, optical
photometric monitoring campaign, obtaining dense orbital phase coverage (~20
observations per orbit) for ~15 orbital periods. From U-band measurements we
derive the time-dependent binary mass accretion rate, finding bursts of
accretion near each periastron passage. On average, these enhanced accretion
events evolve over orbital phases 0.85 to 1.05, reaching their peak at
periastron. The specific accretion rate increases above the quiescent value by
a factor of ~4 on average but the peak can be as high as an order of magnitude
in a given orbit. The phase dependence and amplitude of TWA 3A accretion is in
good agreement with numerical simulations of binary accretion with similar
orbital parameters. In these simulations, periastron accretion bursts are
fueled by periodic streams of material from the circumbinary disk that are
driven by the binary orbit. We find that TWA 3A's average accretion behavior is
remarkably similar to DQ Tau, another T Tauri binary with similar orbital
parameters, but with significantly less variability from orbit to orbit. This
is only the second clear case of orbital-phase-dependent accretion in a T Tauri
binary.Comment: 6 pages, 4 figure
Interferometric Evidence for Resolved Warm Dust in the DQ Tau System
We report on near-infrared (IR) interferometric observations of the
double-lined pre-main sequence (PMS) binary system DQ Tau. We model these data
with a visual orbit for DQ Tau supported by the spectroscopic orbit & analysis
of \citet{Mathieu1997}. Further, DQ Tau exhibits significant near-IR excess;
modeling our data requires inclusion of near-IR light from an 'excess' source.
Remarkably the excess source is resolved in our data, similar in scale to the
binary itself ( 0.2 AU at apastron), rather than the larger circumbinary
disk ( 0.4 AU radius). Our observations support the \citet{Mathieu1997}
and \citet{Carr2001} inference of significant warm material near the DQ Tau
binary.Comment: 14 pgs, 3 figures, ApJL in pres
The circumbinary disk of HD 98800B: Evidence for disk warping
The quadruple young stellar system HD 98800 consists of two spectroscopic binary pairs with a circumbinary disk around the B component. Recent work by Boden and collaborators using infrared interferometry and radial velocity data resulted in a determination of the physical orbit for HD 98800B. We use the resulting inclination of the binary and the measured extinction toward the B component stars to constrain the distribution of circumbinary material. Although a standard optically and geometrically thick disk model can reproduce the spectral energy distribution, it cannot account for the observed extinction if the binary and the disk are coplanar. We next constructed a dynamical model to investigate the influence of the A component, which is not in the Ba‐Bb orbital plane, on the B disk. We find that these interactions have a substantial impact on the inclination of the B circumbinary disk with respect to the Ba‐Bb orbital plane. The resulting warp would be sufficient to place material into the line of sight and the noncoplanar disk orientation may also cause the upper layers of the disk to intersect the line of sight if the disk is geometrically thick. These simulations also support that the dynamics of the Ba‐Bb orbit clear the inner region to a radius of~3 AU. We then discuss whether the somewhat unusual properties of the HD 98800B disk are consistent with material remnant from the star formation process or with more recent creation by collisions from larger bodies
Stellar and Molecular Radii of a Mira Star: First Observations with the Keck Interferometer Grism
Using a new grism at the Keck Interferometer, we obtained spectrally
dispersed (R ~ 230) interferometric measurements of the Mira star R Vir. These
data show that the measured radius of the emission varies substantially from
2.0-2.4 microns. Simple models can reproduce these wavelength-dependent
variations using extended molecular layers, which absorb stellar radiation and
re-emit it at longer wavelengths. Because we observe spectral regions with and
without substantial molecular opacity, we determine the stellar photospheric
radius, uncontaminated by molecular emission. We infer that most of the
molecular opacity arises at approximately twice the radius of the stellar
photosphere.Comment: 12 pages, including 3 figures. Accepted by ApJ
Spatially and Spectrally Resolved Hydrogen Gas within 0.1 AU of T Tauri and Herbig Ae/Be Stars
We present near-infrared observations of T Tauri and Herbig Ae/Be stars with
a spatial resolution of a few milli-arcseconds and a spectral resolution of
~2000. Our observations spatially resolve gas and dust in the inner regions of
protoplanetary disks, and spectrally resolve broad-linewidth emission from the
Brackett gamma transition of hydrogen gas. We use the technique of
spectro-astrometry to determine centroids of different velocity components of
this gaseous emission at a precision orders of magnitude better than the
angular resolution. In all sources, we find the gaseous emission to be more
compact than or distributed on similar spatial scales to the dust emission. We
attempt to fit the data with models including both dust and Brackett
gamma-emitting gas, and we consider both disk and infall/outflow morphologies
for the gaseous matter. In most cases where we can distinguish between these
two models, the data show a preference for infall/outflow models. In all cases,
our data appear consistent with the presence of some gas at stellocentric radii
of ~0.01 AU. Our findings support the hypothesis that Brackett gamma emission
generally traces magnetospherically driven accretion and/or outflows in young
star/disk systems.Comment: 48 pages, including 17 figures. Accepted for publication by Ap
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