The planetary nebula NGC 1514 and its binary central star, the orbital period of which was found to be more than nine years
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Dormant black holes in X-ray transients can be identified by the presence of broad Hα emission lines from quiescent accretion discs. Unfortunately, short-period cataclysmic variables can also produce broad Hα lines, especially when viewed at high inclinations, and are thus a major source of contamination. Here we compare the full width at half maximum (FWHM) and equivalent width (EW) of the Hα line in a sample of 20 quiescent black hole transients and 354 cataclysmic variables (305 from SDSS I to IV) with secure orbital periods (Porb) and find that: (1) FWHM and EW values decrease with PorbAdvertised on -
Nuclear star clusters are dense and compact stellar systems, with sizes of a few parsecs, found at the centers of many galaxies. Their formation is thought to be closely connected to the assembly history of their host galaxies, and astronomers think that these clusters contain important clues about how galaxies formed and evolved over cosmic time. Recent studies suggest that different formation pathways may operate in late- and early-type galaxies, but the dominant mechanisms and their dependence on galaxy morphology remain unclear. While most observational studies have focused on early-typeAdvertised on -
H II regions are clouds of glowing, ionised gas associated with regions of recent star formation. By studying the light emitted by these regions, we can learn about their physical conditions and chemical composition, providing important clues about how stars and galaxies form and evolve. One of the key properties we need to know is the temperature of the gas. We can measure it from the emission lines of different chemical elements, which probe different parts of an H II region. However, it is not always possible to measure all these temperatures directly. In these cases, we need to estimateAdvertised on