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We report observations of the nova RS Ophiuchi (RS Oph) using the Keck Interferometer Nuller (KIN), approximately 3.8 days following the most recent outburst that occurred on 2006 February 12. These observations represent the first scientific results from the KIN, which operates in N-band from 8 to 12.5 microns in a nulling mode. By fitting the unique KIN 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 and atomic metals including silicon located in the inner spatial regime near the white dwarf (WD) relative to the outer regime. There are also nebular emission lines and evidence of hot silicate dust in the outer spatial region, centered at ! 17 AU from the WD, that are not found in the inner regime. Our evidence suggests that these features have been excited by the nova flash in the outer spatial regime before the blast wave reached these regions. These identifications support a model in which the dust appears to be present between outbursts and is not created during the outburst event. We further 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., 41 pages, 10 figures

The Keck Interferometer Nuller (KIN) is one of the major scientific and technical precursors to the Terrestrial Planet Finder Interferometer (TPF-I) mission. KIN's primary objective is to measure the level of exo-zodiacal mid-infrared emission around nearby main sequence stars, which requires deep broad-band nulling of astronomical sources of a few Janskys at 10 microns. A number of new capabilities are needed in order to reach that goal with the Keck telescopes: mid-infrared coherent recombination, interferometric operation in 'split pupil' mode, N-band optical path stabilization using K-band fringe tracking and internal metrology, and eventually, active atmospheric dispersion correction. We report here on the progress made implementing these new functionalities, and discuss the initial levels of extinction achieved on the sky.

Water vapor, while usually a small contributor to the atmospheric refractive index for astronomical observations at IR wavelengths, is highly dispersive and can introduce optical path length errors affecting high‐precision interferometer observing modes. The refractive index of atmospheric water vapor can be computed from a summation over the various IR resonances, and we present values over a range of 1.2–13.5 μm. The dispersion of water vapor introduces phase errors across the instrument passband and produces excess noise in interferometer group delay, residual errors in cophasing using a different source wavelength, and coherence loss over broad optical bandwidths. We quantify these effects for the J through N bands, discuss means of amelioration, and consider their implications for differential phase and nulling observing modes.

We obtained low resolution (R = 100) mid-infrared (8-13 micron wavelengths) spectra of 8 nearby young main sequence stars with the Keck 1 telescope and Long-Wavelength Spectrometer (LWS) to search for 10 micron silicate (Si-O stretch) emission from circumstellar dust. No stars exhibited readily apparent emission: Spectra were then analyzed by least-squares fitting of a template based on a spectrum of Comet Hale-Bopp. Using this technique, we were able to constrain the level of silicate emission to a threshold ten times below what was previously possible from space. We found one star, HD 17925, with a spectrum statistically different from its calibrator and consistent with a silicate emission peak of 7% of the photosphere at a wavelength of 10 microns. Excess emission at 60 microns from this star has already been reported., 19 total pages, 5 Postscript figures, 2 tables, Latex

We examine several theories that describe how stellar magnetic fields on classical T Tauri stars (CTTSs) interact with their surrounding accretion disks. We demonstrate that these theories require magnetic field strengths ranging from a few hundred to several thousand gauss, depending on which model is used and more importantly on the properties of individual systems. For example, the CTTS BP Tau is predicted to have a relatively strong magnetic field (1.4-4.1 kG), which should be detectable. We present infrared (IR) and optical echelle spectra of BP Tau and several reference stars of similar spectral class. Using detailed spectrum synthesis and the latest model atmospheres, we fitted 12 absorption features in the optical spectrum, including the strong titanium oxide (TiO) band head at 7055 A. For BP Tau we determine key stellar parameters: effective temperature (Teff=4055 ± 112 K), gravity (log g=3.67 ± 0.50), metallicity ([M/H]=0.18 ± 0.11), projected rotational velocity (v sin i=10.2 ± 1.8 km s-1), and optical veiling (r=0.00-0.15). A similar analysis of 61 Cyg B (K7 V) is used to validate the methodology. We then use the IR spectra to look for Zeeman broadening, which has a more pronounced effect at longer wavelengths. A Zeeman sensitive Ti I line at 2.2233 μm appears significantly broadened in BP Tau, relative to several rotationally broadened standard stars. The observed line is also significantly broader than predictions based on our optical analysis. Interpreting this excess broadening as Zeeman splitting of the Ti I line, we fitted the spectrum and find a distribution of field strengths whose surface averaged mean is =2.6 ± 0.3 kG. We did not use the Zeeman sensitive Fe I line at 8468.4 A when determining stellar or magnetic parameters for BP Tau, so this line provides a test of our results. The observed line profile is indeed broader than the nonmagnetic prediction, but the 8468.4 A line gives a magnetic flux lower than what was obtained in the IR, perhaps indicating that strong fields are concentrated into cool spots. Finally, we investigate an ad hoc model in which the IR line is assumed to form in the accretion disk itself. We discuss several reasons why the magnetic model is preferred, but the disk atmosphere example illustrates that our magnetic field measurement must still be tested using several IR lines with a range of Zeeman sensitivities.

Afterglow, or long-lived emission, has now been detected from about a dozen well-positioned gamma-ray bursts. Distance determinations made by measuring optical emission lines from the host galaxy, or absorption lines in the afterglow spectrum, place the burst sources at significant cosmological distances, with redshifts ranging from ~1--3. The energy required to produce the bright gamma-ray flashes is enormous: up to ~10^{53} erg or 10 percent of the rest mass energy of a neutron star, if the emission is isotropic. Here we present the discovery of the optical afterglow and the redshift of GRB 990123, the brightest well-localized GRB to date. With our measured redshift of >1.6, the inferred isotropic energy release exceeds the rest mass of a neutron star thereby challenging current theoretical models for the origin of GRBs. We argue that the optical and IR afterglow measurements reported here may provide the first observational evidence of beaming in a GRB, thereby reducing the required energetics to a level where stellar death models are still tenable.

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-e

The discovery of fading but relatively long-lived X-ray emission accompanying γ-ray bursts has revolutionized the study of these objects. This 'afterglow' is most easily explained by models similar to those describing supernovae, but with relativistic ejecta. And as with supernovae, afterglow measurements should in principle provide important constraints on burst properties, permitting, for example, estimates of the amount of energy released, the geometry of the emitting surface and the density of the ambient medium. Here we report infrared observations of the fading optical transient associated with the burst of 14 December 1997 (GRB971214). We detect a 'break' in the broad-band spectrum, as predicted by afterglow models, which constrains the total energy in the burst to be >10^(51) erg. Combining the fluence of optical afterglow with the redshift (z = 3.42), we estimate that the energy released in the afterglow alone was 2 x 10^(51) erg. Estimates of afterglow energetics are less likely to be subject to geometric effects—such as beaming—that render uncertain estimates of the total burst energy, but it nevertheless appears from our measurements that γ-ray bursts may be much more energetic than the 10^(51) erg usually assumed.

The Keck Interferometer (KI) combined the two 10 m W. M. Keck Observatory telescopes on Mauna Kea, Hawaii, as a long-baseline near- and mid-infrared interferometer. Funded by NASA, it operated from 2001 until 2012. KI used adaptive optics on the two Keck telescopes to correct the individual wavefronts, as well as active fringe tracking in all modes for path-length control, including the implementation of cophasing to provide long coherent integration times. KI implemented high sensitivity fringe-visibility measurements at H (1.6 μm), K (2.2 μm), and L (3.8 μm) bands, and nulling measurements at N band (10 μm), which were used to address a broad range of science topics. Supporting these capabilities was an extensive interferometer infrastructure and unique instrumentation, including some additional functionality added as part of the NSF-funded ASTRA program. This paper provides an overview of the instrument architecture and some of the key design and implementation decisions, as well as a description of all of the key elements and their configuration at the end of the project. The objective is to provide a view of KI as an integrated system, and to provide adequate technical detail to assess the implementation. Included is a discussion of the operational aspects of the system, as well as of the achieved system performance. Finally, details on V^2 calibration in the presence of detector nonlinearities as applied in the data pipeline are provided.

We describe the Keck Interferometer nuller theory of operation, data reduction, and on-sky performance, particularly as it applies to the nuller exozodiacal dust key science program that was carried out between 2008 February and 2009 January. We review the nuller implementation, including the detailed phasor processing involved in implementing the null-peak mode used for science data and the sequencing used for science observing. We then describe the Level 1 reduction to convert the instrument telemetry streams to raw null leakages, and the Level 2 reduction to provide calibrated null leakages. The Level 1 reduction uses conservative, primarily linear processing, implemented consistently for science and calibrator stars. The Level 2 processing is more flexible, and uses diameters for the calibrator stars measured contemporaneously with the interferometer’s K-band cophasing system in order to provide the requisite accuracy. Using the key science data set of 462 total scans, we assess the instrument performance for sensitivity and systematic error. At 2.0 Jy we achieve a photometrically-limited null leakage uncertainty of 0.25% rms per 10 minutes of integration time in our broadband channel. From analysis of the Level 2 reductions, we estimate a systematic noise floor for bright stars of ~0.2% rms null leakage uncertainty per observing cluster in the broadband channel. A similar analysis is performed for the narrowband channels. We also provide additional information needed for science reduction, including details on the instrument beam pattern and the basic astrophysical response of the system, and references to the data reduction and modeling tools.

The Keck Interferometer combines the two 10m diameter Ke ck 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 ev olved 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. Keywords: stellar interferometry, visibility measurements, operational efficiency, spectro-interferometry, phase referencing, pre-main sequence binaries

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.

We report observations of the nova RS Ophiuchi using the Keck Interferometer Nuller (KIN) taken approximately 3.8 days following the most recent outburst that occurred on 2006 February 12. The KIN operates in N-band from 8 to 12.5 μm in a nulling mode. In this mode the stellar light is suppressed by a destructive fringe, effectively enhancing the contrast of the circumstellar material located near the star. In a second, constructive-fringe mode, the instrument detects primarily the light from the central, bright source. These are the outer and inner spatial regimes, respectively. We will describe the capabilities of the KIN, including these unique modes, and outline how they were key in our discovery that dust was created between nova events. We also show how these first results from the KIN are consistent with Spitzer data. The KIN data show evidence of enhanced neutral atomic hydrogen emission and atomic metals including silicon located in the inner spatial regime (< 4 AU from theWD) relative to the outer regime. There are also nebular emission lines and evidence of hot silicate dust in the outer spatial region, centered at approximately ~ 17 AU from the WD, that are not found in the inner regime. The KIN and Spitzer data suggest that these emissions were excited in the outer spatial regime before the blast wave reached these regions. We describe the present results in terms of a new model for dust creation in recurrent novae 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.

We report the detection of the 1.5 and 2.0 μm absorption bands due to water ice in the near-infrared reflection spectrum of the Centaur 1997 CU_(26), which is currently located just outside the heliocentric distance of Saturn. The water ice bands are weaker than those detected on the surface of any other solar system body; the spectrum is well fit with a model surface consisting predominantly of a neutral dark absorbing substance with only ~3% areal coverage of water ice. The spectrum thus appears very different from that of the Centaur 5140 Pholus, although both objects are of similar brightness and are at similar heliocentric distances.

The Keck Interferometer Nuller (KIN) is now largely in place at the Keck Observatory, and functionalities and performance are increasing with time. The main goal of the KIN is to examine nearby stars for the presence of exozodiacal emission, but other sources of circumstellar emission, such as disks around young stars, and hot exoplanets are also potential targets. To observe with the KIN in nulling mode, knowledge of the intrinsic source spectrum is essential, because of the wide variety of wavelengths involved in the various control loops - the AO system operates at visible wavelengths, the pointing loops use the J-band, the high-speed fringe tracker operates in the K-band, and the nulling observations take place in the N-band. Thus, brightness constraints apply at all of these wavelengths. In addition, source structure plays a role at both K-band and N-band, through the visibility. In this talk, the operation of the KIN is first briefly described, and then the sensitivity and performance of the KIN is summarized, with the aim of presenting an overview of the parameter space accessible to the nuller. Finally, some of the initial observations obtained with the KIN are described.

The Keck Interferometer Nuller (KIN) will be used to examine nearby stellar systems for the presence of circumstellar exozodiacal emission. A successful pre-ship review was held for the KIN in June 2004, after which the KIN was shipped to the Keck Observatory. The integration of the KIN's many sub-systems on the summit of Mauna Kea, and initial on-sky testing of the system, has occupied the better part of the past year. This paper describes the KIN system- level configuration, from both the hardware and control points of view, as well as the current state of integration of the system and the measurement approach to be used. During the most recent on-sky engineering runs, all of the sub- systems necessary to measure a narrowband null were installed and operational, and the full nulling measurement cycle was carried out on stellar targets for the first time.

The first high-dynamic-range interferometric mode planned to come on line at the Keck Observatory is mid-infrared nulling. This observational mode, which is based on the cancellation of the on-axis starlight arriving at the win Keck telescopes, will be used to examine nearby stellar systems for the presence of circumstellar exozodiacal emission. This paper describes the system level layout of the Keck Interferometer Nuller (KIN), as well as the final performance levels demonstrated in the laboratory integration and test phase at the Jet Propulsion Laboratory prior to shipment of the nuller hardware to the Keck Observatory in mid-June 2004. On-sky testing and observation with the mid-infrared nuller are slated to begin in August 2004.

The control of longitudinal dispersion, which determines the position of the null fringe as a function of wavelength, is central to the problem of producing deep broadband interferometric nulls. The dispersion is the sum of terms due to environmental factors such as the dry-air and water-vapor atmospheric seeing, the unbalanced air column due to the unequal delay-line paths between the telescopes the combiner, and to the distance from the central fringe. The difference between an achromatic nuller and a normal constructive combiner operating at its first (chromatic) null can be thought of as an added longitudinal dispersion, which for the case of the Keck Interferometer is smaller than the environmental terms. We demonstrate that the sum of these effects can be adequately compensated by an appropriate thickness of ZnSe combined with an additional achromatic pathlength. The Keck Interferometer nulling combiners take advantage of this result. They are intrinsically constructive combiners made to produce achromatic nulls by inserting a ZnSe dispersion corrector into each of the four input beams. We describe the null fringe stabilization control algorithm and present calculations of the required loop bandwidth and precision. A potentially important advantage of the present approach is that the system will be able to function as either a destructive or constructive combiner, depending on the value of a single control-loop parameter (the target fringe phase).

We simulate the actions of a coronagraph matched to diffraction-limited adaptive optics (AO) systems on the Calypso 1.2 m, Palomar Hale 5 m and Gemini 8.1 m telescopes, and identify useful parameter ranges for AO coronagraphy on these systems. We model the action of adaptive wavefront correction with a tapered, high-pass filter in spatial frequency rather than a hard low frequency cutoff, and estimate the minimum number of AO channels required to produce sufficient image quality for coronagraphic suppression within a few diffraction widths of a central bright object (as is relevant to e.g., brown dwarf searches near late-type dwarf stars). We explore the effect of varying the occulting image- plane stop size and shape, and examine the trade-off between throughput and suppression of the image halo and Airy rings. We discuss our simulations in the context of results from the 241-channel Palomar Hale AO coronagraph system, and suggest approaches for future AO coronagraphic instruments on large telescopes.

The white dwarf Giclas 29-38 has attracted much attention due to its large infrared excess and the suggestion that excess might be due to a companion brown dwarf. We observed this object using speckle interferometry at the Keck telescope, obtaining diffraction-limited resolution (55 milliarcseconds) at K band, and found it unresolved. Assuming the entire K band excess is due to a single point-like companion, we place an upper limit on the binary separation of 30 milliarcseconds, or 0.42 AU at the star's distance of 14.1 pc. This result, combined with astroseismological data and other images of G29-38, supports the hypothesis that the source of the near-infrared excess is not a cool companion but a dust cloud., Comment: 7 pages, 2 figures

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".101$\pm$0".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 $\sim$0.5 magnitudes in the J, H and K' bands. Thus, both objects have similarly red colors and very likely constitute a very low-mass binary system. For reasonable assumptions about the age (0.12~Gyr--1.0~Gyr) and total mass of the system (0.09~M$_\odot$--0.15~M$_\odot$), we estimate that the orbital period is $\sim$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.

We report the detection of the 1.5 and 2.0 micrometers absorption bands of water ice in the near-infrared reflection spectrum of Neptune's distant irregular satellite Nereid. The spectrum and albedo of Nereid appear intermediate between those of the Uranian satellites Umbriel and Oberon, suggesting a surface composed of a combination of water ice frost and a dark and spectrally neutral material. In contrast, the surface of Nereid appears dissimilar to those of the outer solar system minor planets Chiron, Pholus, and 1997 CU26. The spectrum thus provides support for the hypothesis that Nereid is a regular satellite formed in a circumplanetary environment rather than a captured object.

The Palomar Testbed Interferometer (PTI) is an infrared, phase-tracking interferometer in operation at Palomar Mountain since July 1995. It was funded by NASA for the purpose of developing techniques and methodologies for doing narrowangle astrometry for the purpose of detecting extrasolar planets. The instrument employs active fringe trackingin the infrared (2.0-2.4 μm) to monitor fringe phase. It is a dual-star interferometer; it is able to measure fringes on two separate stars simultaneously. An end-to-end heterodyne laser metrology system is used to monitor the optical path length of the starlight. Recently completed engineering upgrades have improved the initial instrument performance. These upgrades are:extended wavelength coverage, a single mode fiber for spatial filtering, vacuum pipes to relay the beams, accelerometers on the siderostat mirrors and a new baseline. Results of recent astrometry data indicate the instrument is approaching the astrometric limit as set by the atmosphere.

High-resolution images of T Tau and its infrared companion have been reconstructed from near- and mid-infrared data collected at the Hale 5 m telescope. The near-infrared ( 1-5 µm) results were obtained by two dimensional speckle imaging and the mid-infrared (10-20 µm) results were derived from shift and add procedures applied to slit scans. The spectral energy distributions of the separated components were constructed from 1 to 20 µm data collected in less than half a year (1990 September to 1991 January). The spectral energy distribution of the optical component (T Tau N) is interpreted as containing two distinct constituents, a photosphere and a surrounding disk of circumstellar material. Measurements at a number of infrared wavelengths over the period 1985 December to 1991 January show a 2 mag color-independent change in the brightness of the infrared component (T Tau S). We propose that this may have been caused by an increase in accretion onto T Tau S and model the spectral energy distribution of T Tau S as being dominated by an accretion disk.

International audience; Because of an error at the Press, the received date for this paper was incorrectly given as 2004 January 5. The correct received date is 2004 December 5. The Press sincerely regrets this error.

Diffraction-limited IR images of the protostellar system Mon R2 IRS 3 reveal a bright conical nebula which extends about 0.5 arcsec south from the southern component of the previously known star pair. The bright nebula is probably dust scattering the starlight which emerges along the polar axis of a large (greater than 500 AU) circumstellar disk. We estimate a lower limit to the disk mass of 3 X 10 exp -2 solar masses. A faint, previously unknown pointlike source lies 0.37 arcsec east of the northern star.

A two-dimensional image of HL Tauri at 2.2 microns with 0.4-arcsec resolution is constructed from one-dimensional speckle-interferometric scans by means of tomographic back projection. The light distribution is dominated by scattered starlight above and below the midplane of the circumstellar disk of gas and dust. It is suggested that the scattering material is not associated directly with the disk but rather represents particles entrained in gas accreting onto the disk and star. The estimated mass accretion rate of 2 x 10 to the -6th solar mass/yr is in excellent accord with that expected from residual infall associated with the formation of the star. 27 refs.