88 research outputs found
A Third Star in the T Tauri System
New speckle-holographic images of the T Tauri Infrared Companion (T Tauri
IRC; T Tauri S) reveal it to be a double system with a sky-projected separation
of 0".05, corresponding to a linear distance of 7 AU. The presence of this
third star may account for the relative paucity of dust surrounding the IRC.Comment: 5 pages in AASTeX preprint form, including one grayscale figur
An 11.6 Micron Keck Search For Exozodiacal Dust
We have begun an observational program to search nearby stars for dust disks
that are analogous to the disk of zodiacal dust that fills the interior of our
solar system. We imaged six nearby main-sequence stars with the Keck telescope
at 11.6 microns, correcting for atmosphere-induced wavefront aberrations and
deconvolving the point spread function via classical speckle analysis. We
compare our data to a simple model of the zodiacal dust in our own system based
on COBE/DIRBE observations and place upper limits on the density of exozodiacal
dust in these systems.Comment: 10 pages, figure1, figure2, figure3, and figures 4a-
The Discovery of a Companion to the Very Cool Dwarf Gl~569~B with the Keck Adaptive Optics Facility
We report observations obtained with the Keck adaptive optics facility of the
nearby (d=9.8 pc) binary Gl~569. The system was known to be composed of a cool
primary (dM2) and a very cool secondary (dM8.5) with a separation of 5" (49
Astronomical Units). We have found that Gl~569~B is itself double with a
separation of only 0".1010".002 (1 Astronomical Unit). This detection
demonstrates the superb spatial resolution that can be achieved with adaptive
optics at Keck. The difference in brightness between Gl~569~B and the companion
is 0.5 magnitudes in the J, H and K' bands. Thus, both objects have
similarly red colors and very likely constitute a very low-mass binary system.
For reasonable assumptions about the age (0.12~Gyr--1.0~Gyr) and total mass of
the system (0.09~M--0.15~M), we estimate that the orbital
period is 3 years. Follow-up observations will allow us to obtain an
astrometric orbit solution and will yield direct dynamical masses that can
constrain evolutionary models of very low-mass stars and brown dwarfs
Keck Interferometer nuller update
The Keck Interferometer combines the two 10 m Keck telescopes as a long baseline interferometer, funded by NASA, as a joint development among the Jet Propulsion Laboratory, the W. M. Keck Observatory, and the Michelson Science Center. Since 2004, it has offered an H- and K-band fringe visibility mode through the Keck TAC process. Recently this mode has been upgraded with the addition of a grism for higher spectral resolution. The 10 um nulling mode, for which first nulling data were collected in 2005, completed the bulk of its engineering development in 2007. At the end of 2007, three teams were chosen in response to a nuller key science call to perform a survey of nearby stars for exozodiacal dust. This key science observation program began in Feb. 2008. Under NSF funding, Keck Observatory is leading development of ASTRA, a project to add dual-star capability for high sensitivity observations and dual-star astrometry. We review recent activity at the Keck Interferometer, with an emphasis on the nuller development
Recent progress at the Keck Interferometer: operations and V^2 science
The Keck Interferometer combines the two 10m diameter Keck telescopes for near-infrared fringe visibility, and mid-infrared nulling observations. We report on recent progress with an emphasis on new visibility observing capabilities, operations improvements for visibility and nulling, and on recent visibility science. New visibility observing capabilities include a grism spectrometer for higher spectral resolution. Recent improvements include a new AO output dichroic for increased infrared light throughput, and the installation of new wave-front controllers on both Keck telescopes. We also report on recent visibility results in several areas including (1) young stars and their circumstellar disks, (2) pre-main sequence star masses, and (3) Circumstellar environment of evolved stars. Details on nuller instrument and nuller science results, and the ASTRA phase referencing and astrometry upgrade, are presented in more detail elsewhere in this conference
FU Orionis resolved by infrared long baseline interferometry at a 2-AU scale
We present the first infrared interferometric observations of a young stellar
object with a spatial projected resolution better than 2 AU. The observations
were obtained with the Palomar Testbed Interferometer. FU Ori exhibits a
visibility of V^2 =0.72 +/- 0.07 for a 103 +/- 5 m projected baseline at lambda
= 2.2 microns. The data are consistent on the spatial scale probed by PTI both
with a binary system scenario (maximum magnitude difference of 2.7 +/- 0.5 mag
and smallest separation of 0.35 +/- 0.05 AU) and a standard luminous accretion
disk model (approx. accretion rate of 6e-5 Mo/yr) where the thermal emission
dominates the stellar scattering, and inconsistent with a single stellar
photosphere.Comment: 13 pages, 4 figures, accepted for publication in ApJ
High-Resolution N-Band Observations of the Nova RS Ophiuchi with the Keck Interferometer Nuller
We report new observations of the nova RS Ophiuchi (RS Oph) using the Keck Interferometer Nulling Instrument, approximately 3.8 days following the most recent outburst that occurred on 2006 February 12. The Keck Interferometer Nuller (KIN) operates in K-band from 8 to 12.5 pm in a nulling mode, which means that the central broad-band interference fringe is a dark fringe - with an angular width of 25 mas at mid band - rather than the bright fringe used ill a conventional optical interferometer. In this mode the stellar light itself is suppressed by the destructive fringe, effectively enhancing the contrast of the circumstellar material located near the star. By subsequently shifting the neighboring bright fringe onto the center of the source brightness distribution and integrating, a second spatial regime dominated by light from the central portion of the source is almost simultaneously sampled. The nulling technique is the sparse aperture equivalent of the conventional corongraphic technique used in filled aperture telescopes. By fitting the unique KIK inner and outer spatial regime data, we have obtained an angular size of the mid-infrared continuum of 6.2, 4.0. or 5.4 mas for a disk profile, gaussian profile (fwhm), and shell profile respectively. The data show evidence of enhanced neutral atomic hydrogen emission located in the inner spatial regime relative to the outer regime. There is also evidence of a 9.7 micron silicate feature seen outside of this region. Importantly, we see spectral lines excited by the nova flash in the outer region before the blast wave reaches these regions. These lines are from neutral, weakly excited atoms which support the following interpretation. We discuss the present results in terms of a unifying model of the system that includes an increase in density in the plane of the orbit of the two stars created by a spiral shock wave caused by the motion of the stars through the cool wind of the red giant star. These data show the power and potential of the nulling technique which has been developed for the detection of Earth-like planets around nearby stars for the Terrestrial Planet Finder Mission and Darwin missions
Multi-wavelength observations of the young binary system Haro 6-10: The case of misaligned discs
Context. We present a multi-wavelength, high-resolution observational survey
of the young binary system Haro 6-10 (GV Tau, IRAS 04263+2426), which is
harbouring one of the few known infrared companions. Aims. The primary goal of
this project is to determine the physical and geometrical properties of the
circumstellar and circumbinary material in the Haro 6-10 system. Methods.
High-resolution optical (HST/WFPC2) and near-infrared (VLT/NACO) images in
different bands were analysed to investigate the large-scale structures of the
material around the binary.Mid-infrared interferometry (VLTI/MIDI) and
spectroscopy (TIMMI2 at the 3.6m ESO telescope) were carried out to determine
the structure and optical depth of the circumstellar material around the
individual components. Results. The multi-wavelength observations suggest that
both components of the binary system Haro 6-10 are embedded in a common
envelope. The measured extinction indicates a dust composition of the envelope
similar to that of the interstellar medium. Each component of the system has a
circumstellar disc-like structure typical of young stars. The discs are highly
misaligned: the northern component is seen almost edge-on and the southern
component is an almost face-on disc. Conclusions. The two main formation
scenarios of binary systems with misaligned discs are the gravitational capture
of a passing object in a dense environment, and the fragmentation of the
collapsing molecular cloud. Given the low-density environment of the
Taurus-Aurigae star-forming region, the first scenario is unlikely for Haro
6-10. The binary system most probably formed via fragmentation of two different
parts of the collapsing molecular cloud combined with other dynamical processes
related to the cloud and/or the protostars. This can be the explanation also
for other binary systems with an infrared companion.Comment: accepted for publication in A&A on July 15, 201
The Host Galaxy of GRB 990123
We present deep images of the field of gamma-ray burst (GRB) 990123 obtained
in a broad-band UV/visible bandpass with the Hubble Space Telescope, and deep
near-infrared images obtained with the Keck-I 10-m telescope. Both the HST and
Keck images show that the optical transient (OT) is clearly offset by 0.6
arcsec from an extended object, presumably the host galaxy. This galaxy is the
most likely source of the metallic-line absorption at z = 1.6004 seen in the
spectrum of the OT. With magnitudes V_{C} ~ 24.6 +/- 0.2 and K = 21.65 +/- 0.30
mag this corresponds to an L ~ 0.7 L_* galaxy, assuming that it is located at z
= 1.6. The estimated unobscured star formation rate is SFR ~ 6 M_sun/yr, which
is not unusually high for normal galaxies at comparable redshifts. The strength
of the observed metallic absorption lines is suggestive of a relatively high
metallicity of the gas, and thus of a chemically evolved system which may be
associated with a massive galaxy. It is also indicative of a high column
density of the gas, typical of damped Ly-alpha systems at high redshifts. We
conclude that this is the host galaxy of GRB 990123. No other obvious galaxies
are detected within the same projected radius from the OT. There is thus no
evidence for strong gravitational lensing magnification of this burst, and some
alternative explanation for its remarkable energetics may be required. The
observed offset of the OT from the center of its apparent host galaxy, 5.5 +/-
0.9 proper kpc (projected) in the galaxy's rest-frame, both refutes the
possibility that GRBs are related to galactic nuclear activity and supports
models of GRBs which involve the death and/or merger of massive stars. Further,
the HST image suggests an intimate connection of GRB 990123 and a star-forming
region.Comment: Updated references. 12 pages including 3 Postscript figures. Camera-
ready reproductions of the figures can be found at
http://astro.caltech.edu/~jsb/GRB/grb990123.htm
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