We present the first comprehensive set of lunar exospheric line width and line width derived effective temperatures as a function of lunar phase (66° waxing phase to 79° waning phase). Data were collected between November 2013 and May 2014 during six observing runs at the National Solar Observatory McMath‐Pierce Solar Telescope by applying high‐resolution Fabry‐Perot spectroscopy (R ~ 180,000) to observe emission from exospheric sodium (5,889.9509 Å, D2 line). The 3‐arc min field of view of the instrument, corresponding to ~336 km at the mean lunar distance (384,400 km), was positioned at several locations off the lunar limb; only equatorial observations taken out to 950 km are presented here. We find the sodium effective temperature distribution to be approximately a symmetric function of lunar phase with respect to full Moon. Within magnetotail passage we find temperatures in the range of 2500–9000 K. For phase angles greater than 40° we find that temperatures flatten out to ~1700 K.
There have been several reports of a detection of an unexplained excess of X-ray emission at ≃ 3.5 keV in astrophysical systems. One interpretation of this excess is the decay of sterile neutrino dark matter. The most influential study to date analysed 73 clusters observed by the XMM-Newton satellite. We explore evidence for a ≃ 3.5 keV excess in the XMM-PN spectra of 117 redMaPPer galaxy clusters (0.1 < z < 0.6). In our analysis of individual spectra, we identify three systems with an excess of flux at ≃ 3.5 keV. In one case (XCS J0003.3+0204) this excess may result from a discrete emission line. None of these systems are the most dark matter dominated in our sample. We group the remaining 114 clusters into four temperature (TX) bins to search for an increase in ≃ 3.5 keV flux excess with TX - a reliable tracer of halo mass. However, we do not find evidence of a significant excess in flux at ≃ 3.5 keV in any TX bins. To maximise sensitivity to a potentially weak dark matter decay feature at ≃ 3.5 keV, we jointly fit 114 clusters. Again, no significant excess is found at ≃ 3.5 keV. We estimate the upper limit of an undetected emission line at ≃ 3.5 keV to be 2.41 × 10−6 photons cm−2 s−1, corresponding to a mixing angle of sin 2(2θ) = 4.4 × 10−11, lower than previous estimates from cluster studies (e.g. sin 2(2θ) ≃ 7 × 10−11, B14). We conclude that a flux excess at ≃ 3.5 keV is not a ubiquitous feature in clusters and therefore unlikely to originate from sterile neutrino dark matter decay.
We observed lunar exospheric potassium D1 (7,698.9646 Å) emissions using a high‐spectral resolution Fabry‐Perot spectrometer in 2014. We present the first potassium line profile measurements, which are representative of the potassium velocity distribution. Inferred temperatures are greater during the waxing gibbous phase, 1920±630 K and lower at waning gibbous phase, 980±200 K. Exosphere models suggest that the measured line widths are a combination of photon‐stimulated desorption and impact vaporization sources. The relative potassium emission intensity decreases by ∼2.5 between lunar phases 80° and 30° and is brightest off the northwest limb near the Aristarchus crater, which is a potassium‐rich surface region. Additionally, the emissions off the northern limb are brighter than the southern limb. The intensity decrease and the greater line width during the waxing gibbous versus the waning gibbous phase suggests a dawn‐dusk asymmetry.
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