2,210 research outputs found
Observations of circumstellar disks with infrared interferometry
The structure and composition of circumstellar disks around young stars is one of the areas in which infrared interferometry has had a major impact. I will review the
observational progress in this field starting from the earliest observations of T Tauri, Herbig Ae/Be and FU Ori objects with smaller interferometers. Highlights of recent work include measurements of the inner disk size across 5 orders of magnitude in stellar luminosity, characterization of the dust composition as a function of radius in Herbig disks, high spectral resolution observations of gas emission and closure phase measurements of structure in disks. These observations have challenged models of disk structure and as the only direct probe on AU scales will continue to provide essential input in our understanding of the formation of stars and planets
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
Protoplanetary Disk Mass Distribution in Young Binaries
We present millimeter-wave continuum images of four wide (separations 210-800
AU) young stellar binary systems in the Taurus-Auriga star-forming region. For
all four sources, the resolution of our observations is sufficient to determine
the mm emission from each of the components. In all four systems, the primary
star's disk has stronger millimeter emission than the secondary and in three of
the four, the secondary is undetected; this is consistent with predictions of
recent models of binary formation by fragmentation. The primaries'
circumstellar disk masses inferred from these observations are comparable to
those found for young single stars, confirming that the presence of a wide
binary companion does not prevent the formation of a protoplanetary disk. Some
of the secondaries show signatures of accretion (H-alpha emission and K - L
excesses), yet their mm fluxes suggest that very little disk mass is present.Comment: Accepted by ApJ, to appear Feb. 2003; 9 pages, 5 postscript figures,
uses aastex, emulateapj5, and apjfonts style files. Also available at
http://astro.swarthmore.edu/~jensen/publications.htm
Interferometric science results on young stellar objects
Long-baseline interferometry at infrared wavelengths allows the innermost
regions around young stars to be observed. These observations directly probe
the location of the dust and gas in the disks. The characteristic sizes of
these regions found are larger than previously thought. These results have
motivated in part a new class of models of the inner disk structure, but the
precise understanding of the origin of these low visibilities is still in
debate. Mid-infrared observations probe disk emission over a larger range of
scales revealing mineralogy gradients in the disk. Recent spectrally resolved
observations allow the dust and gas to be studied separately showing that the
Brackett gamma emission can find its origin either in a wind or in a
magnetosphere and that there is probably no correlation between the location of
the Brackett gamma emission and accretion. In a certain number of cases, the
very high spatial resolution reveals very close companions and can determine
their masses. Overall, these results provide essential information on the
structure and the physical properties of close regions surrounding young stars
especially where planet formation is suspected to occur.Comment: 18 pages, 6 figures, invited lecture at the VLTI school on
"Astrometry and Imaging with the Very Large Telescope Interferometer", 2-13
June 2008, Keszthely, Hungary. v2: typos corrected; v3: reference adde
Science and technical progress at the Palomar Testbed Interferometer
The Palomar Testbed Interferometer (PTI) is a long-baseline, near-infrared interferometer located on Palomar Mountain. PTI has been in operation since 1997 and is used for extensive science observing as well as technical development. I will review the recent progress at PTI covering both science and instrumentation work. The science topics include fundamental stellar properties, novae, and an evaluation of all calibrator observations. The technical work includes the narrow-angle phase scanning mode and installation of the integrated optics combiner IONIC
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
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
A dim candidate companion to \epsilon Cephei
Using a vector vortex coronagraph behind the 1.5-m well-corrected subaperture
(WCS) at Palomar, we detected a second object very close to \epsilon Cephei, a
\delta Scuti F0 IV star. The candidate companion, ~50 times fainter than
\epsilon Cephei, if physically associated, is a late-type K or early M star,
and lies at an angular separation of 330 mas, or 1.1 \lambda/D for the WCS,
making it the smallest angle detection ever realized with a coronagraph in
terms of \lambda/D units. The projected separation of the putative companion is
~8.6 AU, most likely on a highly eccentric orbit. The recently detected
near-infrared excess is thus likely not due to hot dust. Moreover, we also show
that the previously reported IRAS 60 \mu m excess was due to source confusion
on the galactic plane.Comment: 5 pages, 3 figure
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