This paper provides a detailed comparison of the differences in parameters derived for a star cluster from its colormagnitude diagrams (CMDs) depending on the filters and models used. We examine the consistency and reliability of fitting three widely used stellar evolution models to 15 combinations of optical and near-IR photometry for the old open cluster NGC 188. The optical filter response curves match those of theoretical systems and are thus not the source of fit inconsistencies. NGC 188 is ideally suited to this study thanks to a wide variety of high-quality photometry and available proper motions and radial velocities that enable us to remove non-cluster members and many binaries. Our Bayesian fitting technique yields inferred values of age, metallicity, distance modulus, and absorption as a function of the photometric band combinations and stellar models. We show that the historically favored three-band combinations of UBV and VRI can be meaningfully inconsistent with each other and with longer baseline data sets such as UBVRIJHK S . Differences among model sets can also be substantial. .441 ± 0.007, 11.525 ± 0.005} mag, and A V = {0.162 ± 0.003, 0.236 ± 0.003} mag, respectively. Within the formal fitting errors, these two fits are substantially and statistically different. Such differences among fits using different filters and models are a cautionary tale regarding our current ability to fit star cluster CMDs. Additional modeling of this kind, with more models and star clusters, and future Gaia parallaxes are critical for isolating and quantifying the most relevant uncertainties in stellar evolutionary models.

Scintillators are widely used as particle detectors in particle physics. Scintillation at cryogenic temperatures can give rise to detectors with particle discrimination for rare-event searches such as dark matter detection. We present time-resolved scintillation studies of Caesium Iodide (CsI) under excitation of both α and γ particles over a long acquisition window of 1 ms to fully capture the scintillation decay between room temperature and 4 K. This allows a measurement of the light yield independent of any shaping time of the pulse. We find the light yield of CsI to increase up to two orders of magnitude from that of room temperature at cryogenic temperatures, and the ratio of α to γ excitation to vary significantly, exceeding 1 over a range of temperatures between 10 and 100 K. This property could be useful in separating α backgrounds from the low energy nuclear recoil signal region. We also find the time structure of the emitted light to follow similar exponential decay time constants between α and γ excitation, with the temperature behaviour consistent with a model of self-trapped exciton de-excitation. Based on these properties, undoped CsI is an interesting candidate for use in cryogenic particle detectors.