Search for: All records

ABSTRACT We search a sample of 9361 613 isolated sources with 13<g<14.5 mag for slowly varying sources. We select sources with brightness changes larger than $$\sim 0.03$$ mag yr−1 over 10 yr, removing false positives due to, for example, nearby bright stars or high proper motions. After a thorough visual inspection, we find 782 slowly varying systems. Of these systems, 433 are identified as variables for the first time, 349 are previously classified as variables, and there are roughly equal numbers of sources becoming brighter and fainter. Previously classified systems were mostly identified as semiregular variables (SR), slow irregular variables (L), spotted stars (ROT), or unknown (MISC or VAR), as long time-scale variability does not fit into a standard class. The sources are scattered across the CMD and can be placed into five groups that exhibit distinct behaviours. The largest groups are very red subgiants and lower main sequence stars. There are also eight AGNs. There are 551 candidates ($$\sim$$ 70 per cent) that also show shorter time-scale periodic variability, mostly with periods longer than 10 d. The variability of 191 of these candidates may be related to dust. 

ABSTRACT Most ultra-hot Jupiters (UHJs) show evidence of temperature inversions, in which temperature increases with altitude over a range of pressures. Temperature inversions can occur when there is a species that absorbs the stellar irradiation at a relatively high level of the atmospheres. However, the species responsible for this absorption remains unidentified. In particular, the UHJ KELT-20b is known to have a temperature inversion. Using high resolution emission spectroscopy from LBT/PEPSI we investigate the atomic and molecular opacity sources that may cause the inversion in KELT-20b, as well as explore its atmospheric chemistry. We confirm the presence of Fe i with a significance of 17σ. We also report a tentative 4.3σ detection of Ni i. A nominally 4.5σ detection of Mg i emission in the PEPSI blue arm is likely in fact due to aliasing between the Mg i cross-correlation template and the Fe i lines present in the spectrum. We cannot reproduce a recent detection of Cr i, while we do not have the wavelength coverage to robustly test past detections of Fe ii and Si i. Together with non-detections of molecular species like TiO, this suggests that Fe i is likely to be the dominant optical opacity source in the dayside atmosphere of KELT-20b and may be responsible for the temperature inversion. We explore ways to reconcile the differences between our results and those in literature and point to future paths to understand atmospheric variability.