We present new Hubble Space Telescope (HST)/WFPC2 imagery and STIS long‐slit spectroscopy of the planetary nebula NGC 7009. The primary goal was to obtain high spatial resolution of the intrinsic line ratio [O iii] 4364/5008 and thereby evaluate the electron temperature (Te) and the fractional mean‐square Te variation (tA2)across the nebula. The WFPC2 Te map is rather uniform; almost all values are between 9000–11 000 K, with the higher Te values closely coinciding with the inner He++ zone. The results indicate very small values–≲0.01– for tA2 throughout. Our STIS data allow an even more direct determination of Te and tA2, albeit for a much smaller area than with WFPC2. We present results from binning the data along the slit into tiles that are 0.5‐arcsec square (matching the slit width). The average [O iii] temperature using 45 tiles (excluding the central star and STIS fiducial bars) is 10 139 K; tA2 is 0.0035. The measurements of Te reported here are an average along each line of sight. Therefore, despite finding remarkably low tA2, we cannot completely rule out temperature fluctuations along the line of sight as the cause of the large abundance discrepancy between heavy element abundances inferred from collisionally excited emission lines compared to those derived from recombination lines.

We present a laser frequency stabilization system that uses a transfer interferometer to stabilize slave lasers to a reference laser. Our implementation uses off-the-shelf optical components along with microcontroller-based digital feedback, and offers a simple, flexible, and robust way to stabilize multiple laser frequencies to better than 1 MHz.

We produce cold and dense clouds of atomic ions (Ca + , Dy + ) by laser ablation of metal targets and cryogenic buffer gas cooling of the resulting plasma. We measure the temperature and density of the ion clouds using laser absorption spectroscopy. We find that large ion densities ( 10 9 cm −3 ) can be obtained at temperatures as low as 6 K. Our method opens up new ways to study cold neutral plasmas, and to perform survey spectroscopy of ions that cannot be laser-cooled easily.

We obtained new HST/STIS long-slit spectra and WFPC2 imagery of the planetary nebula NGC 7009 in order to obtain high spatial resolution of the intrinsic flux ratio [O III] 4364/5008, which is a well-known diagnostic for electron temperature (Te). Our primary purpose was to quantify Te variations across the nebula. We address whether the observational data support the possibility that the [fractional] mean-square Te variation (t2) (Peimbert 1967) in NGC 7009 may be as large as ~0.1. Such large values are required to reconcile the “abundance dichotomy” by Te variations alone. The abundance dichotomy (discussed by Liu at greater length elsewhere in this volume) refers to the significantly higher heavy element abundances derived from optical recombination lines (e.g., a factor of ~5 for NGC 7009, Liu et al. 1995) compared with the corresponding values deduced from collisionally-excited lines.

We report measurements of the isotope shifts of two transitions (4f 4 6s → [25044.7] • 7/2 and 4f 4 6s → [25138.6] • 7/2 ) in neodymium ions (Nd + ) with hundredfold improved accuracy, using laser spectroscopy of a cryogenically-cooled neutral plasma. The isotope shifts were measured across a set of five spin-zero isotopes that spans a nuclear shape transition. We discuss the prospects for further improvements to the accuracy of Nd + isotope shifts using optical clock transitions, which could enable higher precision tests of King plot linearity for new physics searches.