759 research outputs found
Differential Astrometry of Sub-arcsecond Scale Binaries at the Palomar Testbed Interferometer
We have used the Palomar Testbed Interferometer to perform very high
precision differential astrometry on the 0.25 arcsecond separation binary star
HD 171779. In 70 minutes of observation we achieve a measurement uncertainty of
approximately 9 micro-arcseconds in one axis, consistent with theoretical
expectations. Night-to-night repeatability over four nights is at the level of
16 micro-arcseconds. This method of very-narrow-angle astrometry may be
extremely useful for searching for planets with masses as small as 0.5 Jupiter
Masses around a previously neglected class of stars -- so-called ``speckle
binaries.'' It will also provide measurements of stellar parameters such as
masses and distances, useful for constraining stellar models at the 10^-3
level.Comment: 19 pages including 6 figures. Submitted to ApJ. Typos corrected,
several parts reworded for clarificatio
Swift X-ray Observations of Classical Novae
The new gamma-ray burst mission Swift has obtained pointed observations of
several classical novae in outburst. We analyzed all the observations of
classical novae from the Swift archive up to 30 June, 2006. We analyzed usable
observations of 12 classical novae and found 4 non-detections, 3 weak sources
and 5 strong sources. This includes detections of 2 novae exhibiting spectra
resembling those of Super Soft X-ray binary Source spectra (SSS) implying
ongoing nuclear burning on the white dwarf surface. With these new Swift data,
we add to the growing statistics of the X-ray duration and characteristics of
classical novae.Comment: Accepted for ApJ; this version contains additional material: 18
pages, 16 figure
Individual Dynamical Masses of Ultracool Dwarfs
We present the full results of our decade-long astrometric monitoring
programs targeting 31 ultracool binaries with component spectral types M7-T5.
Joint analysis of resolved imaging from Keck Observatory and Hubble Space
Telescope and unresolved astrometry from CFHT/WIRCam yields parallactic
distances for all systems, robust orbit determinations for 23 systems, and
photocenter orbits for 19 systems. As a result, we measure 38 precise
individual masses spanning 30-115 . We determine a
model-independent substellar boundary that is 70 in mass
(L4 in spectral type), and we validate Baraffe et al. (2015)
evolutionary model predictions for the lithium-depletion boundary (60 at field ages). Assuming each binary is coeval, we test models of the
substellar mass-luminosity relation and find that in the L/T transition, only
the Saumon & Marley (2008) "hybrid" models accounting for cloud clearing match
our data. We derive a precise, mass-calibrated spectral type-effective
temperature relation covering 1100-2800 K. Our masses enable a novel direct
determination of the age distribution of field brown dwarfs spanning L4-T5 and
30-70 . We determine a median age of 1.3 Gyr, and our population
synthesis modeling indicates our sample is consistent with a constant star
formation history modulated by dynamical heating in the Galactic disk. We
discover two triple-brown-dwarf systems, the first with directly measured
masses and eccentricities. We examine the eccentricity distribution, carefully
considering biases and completeness, and find that low-eccentricity orbits are
significantly more common among ultracool binaries than solar-type binaries,
possibly indicating the early influence of long-lived dissipative gas disks.
Overall, this work represents a major advance in the empirical view of very
low-mass stars and brown dwarfs.Comment: ApJS, in press. This arxiv posting contains all figures (111 pages)
and tables (107 pages). Updated version contains additional acknowledgments
and references and corrects typo
The Mass-Luminosity Relation in the L/T Transition:Individual Dynamical Masses for the New J-Band Flux Reversal Binary SDSSJ105213.51+442255.7AB
We have discovered that SDSSJ105213.51+442255.7 (T0.51.0) is a binary in
Keck laser guide star adaptive optics imaging, displaying a large J-to-K-band
flux reversal (J = -0.450.09 mag, K = 0.520.05 mag).
We determine a total dynamical mass from Keck orbital monitoring (885
) and a mass ratio by measuring the photocenter orbit from
CFHT/WIRCam absolute astrometry ( = 0.780.07). Combining these
provides the first individual dynamical masses for any field L or T dwarfs,
493 for the L6.51.5 primary and 393
for the T1.51.0 secondary. Such a low mass ratio for a nearly equal
luminosity binary implies a shallow massluminosity relation over the L/T
transition (log/log). This
provides the first observational support that cloud dispersal plays a
significant role in the luminosity evolution of substellar objects. Fully
cloudy models fail our coevality test for this binary, giving ages for the two
components that disagree by 0.2 dex (2.0). In contrast, our observed
masses and luminosities can be reproduced at a single age by "hybrid"
evolutionary tracks where a smooth change from a cloudy to cloudless
photosphere around 1300 K causes slowing of luminosity evolution. Remarkably,
such models also match our observed JHK flux ratios and colors well. Overall,
it seems that the distinguishing features SDSSJ1052+4422AB, like a J-band flux
reversal and high-amplitude variability, are normal for a field L/T binary
caught during the process of cloud dispersal, given that the age
(1.11 Gyr) and surface gravity (log = 5.05.2) of
SDSSJ1052+4422AB are typical for field ultracool dwarfs.Comment: Accepted to ApJ; 33 pages, 8 figures, 5 table
No Expanding Fireball: Resolving the Recurrent Nova RS Ophiuchi with Infrared Interferometry
Following the recent outburst of the recurrent nova RS Oph on 2006 Feb 12, we
measured its near-infrared size using the IOTA, Keck, and PTI Interferometers
at multiple epochs. The characteristic size of ~3 milliarcseconds hardly
changed over the first 60 days of the outburst, ruling out currently-popular
models whereby the near-infrared emission arises from hot gas in the expanding
shock. The emission was also found to be significantly asymmetric, evidenced by
non-zero closure phases detected by IOTA. The physical interpretation of these
data depend strongly on the adopted distance to RS Oph. Our data can be
interpreted as the first direct detection of the underlying RS Oph binary,
lending support to the recent ``reborn red giant'' models of Hachisu & Kato.
However, this result hinges on an RS Oph distance of ~< 540 pc, in strong
disagreement with the widely-adopted distance of ~1.6 kpc. At the farther
distance, our observations imply instead the existence of a non-expanding,
dense and ionized circumbinary gaseous disk or reservoir responsible for the
bulk of the near-infrared emission. Longer-baseline infrared interferometry is
uniquely suited to distinguish between these models and to ultimately determine
the distance, binary orbit, and component masses for RS Oph, one of the
closest-known (candidate) SNIa progenitor systems.Comment: Accepted by Astrophysical Journal Letter
Palomar Testbed Interferometer: update
The Palomar Testbed Interferometer is a long-baseline near- infrared interferometer operating at Palomar Observatory, CA. The interferometer has a maximum baseline of 110 m, 40-cm collecting apertures, and active fringe tracking. It also incorporates a dual-star architecture to enable cophasing and narrow-angle astrometry.
We will discuss recent system improvements and engineering results. These include upgrades to allow for longer coherent integration times, H band operation, and cophasing using delay line feedforward. Recent engineering tests of astrometry in dual-star mode have shown a night-to-night repeatability of 100 µas on a bright test target. Several new observation planning tools have been developed, and data reduction tools have been automated to allow fully pipelined nightly reductions and archiving
Palomar testbed interferometer status report
We discuss recent work from the Palomar Testbed Interferometer (PTI), including science results and system improvements. In the past two years PTI has been used to observe a wide range of scientifically interesting sources, including binaries, Cepheids and Miras. In addition PTI has been used to observe departures from spherical symmetry in several stars. Recent system improvements incude a new low read-noise camera based on a HAWAII infrared array, routine opteration in two baselines, and operation in the J band. Future developments include an upgrade to three-aperture combination and closure phase measurements, and double-Fourier interferometry
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