Randy Campbell

The W. M. Keck Observatory Laser Guide Star Adaptive Optics System: Overview

The Keck Observatory began science observations with a laser guide star adaptive optics system, the first such system on an 8-10 m class telescope, in late 2004. This new capability greatly extends the scientific potential of the Keck II Telescope, allowing near-diffraction-limited observations in the near-infrared using natural guide stars as faint as 19th magnitude. This paper describes the conceptual approach and technical implementation followed for this system, including lessons learned, and provides an overview of the early science capabilities.

The W. M. Keck Observatory Laser Guide Star Adaptive Optics System: Performance Characterization

The Keck II Telescope is the first 8-10 m class telescope equipped with a laser guide star adaptive optics (LGS AO) system. Under normal seeing conditions, the LGS AO system produces K-band Strehl ratios between 30% and 40% using bright tip-tilt guide stars, and it works well with tip-tilt guide stars as faint as , with partial correction for stars up to a magnitude fainter. This paper presents the algorithms implemented m p 18 R in the LGS AO system, as well as experimental performance results. A detailed error budget shows excellent agreement between the measured and expected image quality for both bright and faint guide stars.

The first laser guide star adaptive optics observations of the galactic center : Sgr A*'S infrared color and the extended red emission in its vicinity

We present the first Laser Guide Star Adaptive Optics (LGS-AO ) observations of the Galactic center. LGSAO has dramatically improved the quality and robustness with which high angular resolution infrared images of the Galactic center can be obtained with the W. M. Keck II 10-meter telescope. Specifically, Strehl ratios of 0.7 and 0.3 at L’[3.8 µm] and K’[2.1 µm], respectively, are achieved in these LGS-AO images; these are at least a factor of two higher and a factor of four to five more stable ag ainst atmospheric fluctuations than the Strehl ratios delivered thus far with the Keck Natural Guide Star AO system on the Galactic center. Furthermore, these observations are the first that cover a large area (76 ′′ × 76 ′′ ) surrounding the central black hole at diffractionlimited resolution for an 8-10 meter class telescope. Durin g our observations, the infrared counterpart to the central supermassive black hole, Sgr A*-IR, showed signific ant infrared intensity variations, with observed L’ magnitudes ranging from 12.6 to 14.5 mag and a decrease in fl ux density of a factor of two over an 8 minute interval. The faintest end of our L’ detections, 1.3 m Jy (dereddened), is the lowest level of emission yet observed for this source by a factor of 3. No significant varia tion in the location of SgrA*-IR is detected as a function of either wavelength or intensity. Previous claim s of such positional variations are easily attributable to a nearby (0. 09 or 720 AU, projected), extended, very red source, which we suggest arises from a locally heated dust feature. Near a peak in its intensity, we obtaine d the first measurement of SgrA*-IR’s K’-L’ color; its K’-L’ of 3.0 ± 0.2 mag (observed) or 1.4 ± 0.2 (dereddened) corresponds to an intrinsic spectral index of � -0.5 ± 0.3 for F� � � � . This is significantly bluer than other recent infrared meas urements from the literature, which suggest � = -4 ± 1. Because our measurement was taken at a time when Sgr A* was�6 times brighter in the infrared than the other measurements, we posit that the spectral index of the emission arising from the vicinity of our Galaxy’s central black hole may depend on the strength of the flare, with stronger flares giving rise to a higher fraction of high energy electrons in the emit ting region. Subject headings:black hole physics ‐ Galaxy:center — infrared:stars ‐ techniques:high angular resolution

The Discovery and Broadband Follow-Up of the Transient Afterglow of GRB 980703

We report on the discovery of the radio, infrared, and optical transient coincident with an X-ray transient proposed to be the afterglow of GRB 980703. At later times when the transient has faded below detection, we see an underlying galaxy with R=22.6; this galaxy is the brightest host galaxy (by nearly 2 mag) of any cosmological gamma-ray burst (GRB) thus far. In keeping with an established trend, the GRB is not significantly offset from the host galaxy. Interpreting the multiwavelength data in the framework of the popular fireball model requires that the synchrotron cooling break was between the optical and X-ray bands on 1998 July 8.5 UT and that the intrinsic extinction of the transient is A -->V=0.9. This is somewhat higher than the extinction for the galaxy as a whole, as estimated from spectroscopy.

Keck-I MOSFIRE Spectroscopy of Compact Star- Forming Galaxies at z≳ 2: High Velocity Dispersions in Progenitors of Compact Quiescent Galaxies

We present Keck-I MOSFIRE near-infrared spectroscopy for a sample of 13 compact star-forming galaxies (SFGs) at redshift 2 ≤ z ≤ 2.5 with star formation rates of SFR ~ 100 M_☉ yr^(–1) and masses of log(M/M_☉) ~10.8. Their high integrated gas velocity dispersions of σ_(int_ =230^(+40)_(-30) km s^(–1), as measured from emission lines of Hα and [O III], and the resultant M_* -σ_(int) relation and M_*-M_(dyn) all match well to those of compact quiescent galaxies at z ~ 2, as measured from stellar absorption lines. Since log(M*/M_(dyn)) =–0.06 ± 0.2 dex, these compact SFGs appear to be dynamically relaxed and evolved, i.e., depleted in gas and dark matter (<13^(+17)_(-13)%), and present larger σ_(int) than their non-compact SFG counterparts at the same epoch. Without infusion of external gas, depletion timescales are short, less than ~300 Myr. This discovery adds another link to our new dynamical chain of evidence that compact SFGs at z ≳ 2 are already losing gas to become the immediate progenitors of compact quiescent galaxies by z ~ 2.

Keck Observatory Laser Guide Star Adaptive Optics Discovery and Characterization of a Satellite to the Large Kuiper Belt Object 2003 EL61

The newly commissioned laser guide star adaptive optics system at Keck Observatory has been used to discover and characterize the orbit of a satellite to the bright Kuiper Belt object 2003 EL_(61). Observations over a 6 month period show that the satellite has a semimajor axis of 49,500 ± 400 km, an orbital period of 49.12 ± 0.03 days, and an eccentricity of 0.050 ± 0.003. The inferred mass of the system is (4.2 ± 0.1) × 10^(21) kg, or ~32% of the mass of Pluto and 28.6% ± 0.7% of the mass of the Pluto-Charon system. Mutual occultations occurred in 1999 and will not occur again until 2138. The orbit is fully consistent neither with one tidally evolved from an earlier closer configuration nor with one evolved inward by dynamical friction from an earlier more distant configuration.

Excess mid-infrared emission in cataclysmic variables

We present a search for excess mid-IR emission due to circumbinary material in the orbital plane of cataclysmic variables (CVs). Our motivation stems from the fact that the strong braking exerted by a circumbinary (CB) disc on the binary system could explain several puzzles in our current understanding of CV evolution. Since theoretical estimates predict that the emission from a CB disc can dominate the spectral energy distribution (SED) of the system at λ > 5 � m, we obtained simultaneous visible to mid-IR SEDs for eight systems. We report detections of SS Cyg at 11.7 � m and AE Aqr at 17.6 � m, both in excess of the contribution from the secondary star. In AE Aqr, the IR likely originates from synchrotron-emitting clouds propelled by the white dwarf. In SS Cyg, we argue that the observed mid-IR variability is difficult to reconcile with simple models of CB discs and we consider free-free emission from a wind. In the other systems, our mid-IR upper limits place strong constraints on the maximum temperature of a putative CB disc. The results show that if any sizeable CB disc are present in these systems, they must be self-shadowed or perhaps dust-free, with the peak thermal emission shifted to far-IR wavelengths.

Episodic mass loss in binary evolution to the Wolf-Rayet phase: Keck and HST proper motions of RY Scuti's nebula

Binary mass transfer via -Roche lobe overflow (RLOF) is a key channel for producing stripped-envelope Wolf–Rayet (WR) stars and may be critical to account for Type Ib/c supernova progenitors. RY Scuti is an extremely rare example of a massive binary star caught in this brief but important phase. Its unusual toroidal nebula indicates equatorial mass loss during RLOF, while the mass-gaining star is apparently embedded in an opaque accretion disc. RY Scuti’s toroidal nebula has two components: an inner ionized double-ring system, and an outer dust torus that is roughly twice the size of the ionized rings. We present two epochs of L-band Keck natural guide star adaptive optics (NGS-AO) images of the dust torus, plus three epochs of Hubble Space Telescope (HST) images of the ionized gas rings. Proper motions show that the inner ionized rings and the outer dust torus, while having similar geometry, came from two separate ejection events roughly 130 and 250 yr ago. This suggests that WR star formation via RLOF in massive contact binaries can be accompanied by eruptive and episodic bursts of mass loss, reminiscent of luminous blue variables (LBVs). We speculate that the repeating outbursts may arise in the mass gainer from instabilities associated with a high accretion rate. In the case of RY Scuti, we know of no historical evidence that either of its mass-loss events were observed as luminous outbursts, but if discrete mass-loss episodes in other RLOF binaries are accompanied by luminous outbursts, they might contribute to the population of extragalactic optical transients. When RLOF ends for RY Scuti, the overluminous mass gainer, currently surrounded by an accretion disc, will probably become a B[e] supergiant and may outshine the hotter stripped-envelope mass-donor star that should die as a Type Ib/c supernova.

Sculpting a Pre-Planetary Nebula with a Precessing Jet: IRAS 16342-3814

We have imaged the bipolar pre-planetary nebula IRAS 16342-3814 with the Keck adaptive optics (AO) system in four near-infrared bands in the 1.6-4.7 μm range. The lobes, which showed smoothly varying brightness distributions in previous optical images taken with the Hubble Space Telescope, have a limb-brightened appearance in the AO images, with a remarkable corkscrew structure inscribed on the lobe walls. A well-collimated, precessing jet with a diameter 100 AU and a precession period 50 yr, interacting with ambient circumstellar material, is most likely responsible for the corkscrew structure and the lobes, as indicated by a detailed comparison of our observations with published numerical simulations. The very red colors of the lobes in the near-infrared, coupled with their visibility at optical wavelengths, require that at least half, but not all, of the light of the central star be trapped by a compact circumstellar dust cloud heated to ~600-700 K and reradiated in the infrared. The lobes are thus illuminated both by the infrared light from this dust cloud as well as by the optical light from the central star.

A New Distortion Solution for NIRC2 on the Keck II Telescope

We present a new geometric distortion model for the narrow-field mode of the near-infrared camera (NIRC2) fed by the adaptive optics system on the W. M. Keck II telescope. The adaptive optics system and NIRC2 camera were realigned on 2015 April 13. Observations of the crowded globular cluster, M53, were obtained before and after the realignment to characterize the geometric field distortion. The distorted NIRC2 positions of M53 stars were compared with precise astrometry of this cluster from Hubble Space Telescope observations. The resulting distortion map constructed just before the realignment is consistent with the previous solution derived using data from 2007 to 2009, indicating that the distortion has been stable to ~0.5 mas. The distortion map changed significantly after a realignment of 4.5 mas (75%) rms, and the new distortion model for post-realignment observations have a total accuracy of ~1.1 mas.