The hypothesis of a universal initial mass function (IMF) - motivated by observations in nearby stellar systems - has been recently challenged by the discovery of a systematic variation of the IMF with the centralvelocity dispersion, σ, of early-type galaxies (ETGs), towards an excessof low-mass stars in high-σ galaxies. This trend has been derived so farfrom integrated spectra, and remains unexplained at present. To testwhether such trend depends on the local properties within a galaxy, we have obtained new, extremely deep, spectroscopic data, for three nearby ETGs, two galaxies with high σ (~300 km/s), and one lower mass system, with σ ~100 km/s. From the analysis of IMF-sensitive spectral features, we find that the IMF depends significantly ongalactocentric distance in the massive ETGs, with the enhanced fraction of low-mass stars mostly confined to their central regions. In contrast, the low-σ galaxy does not show any significant radial gradient in the IMF, well described by a shallower distribution, relative to the innermost regions of massive galaxies, at all radii. Such a result indicates that the IMF should be regarded as a local (rather than global) property, and suggests a significant difference between the formation process of the core and the outer regions ofmassive ETGs
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An international team of researchers led by the Instituto de Astrofísica de Canarias (IAC) and the Universidad de La Laguna (ULL), has unveiled a breakthrough explanation for the origin of tiny, jet-like plasma ejections in the solar atmosphere, known as “nanojets.” These elusive events which are recently discovered by the NASA’s solar telescopes are thought to play an important role in heating and sustaining the solar corona at temperatures above one million Kelvin. Why Study Nanojets? For decades, solar physicists have been puzzled by the so-called “coronal heating problem.” While the SunAdvertised on -
Low-mass X-ray binaries are systems in which a star transfers matter onto a compact object—either a black hole or a neutron star—producing energetic outbursts. During these events, their optical spectra provide a way to study extreme processes of accretion and matter ejection. While some spectroscopic features have been analysed in detail (e.g., revealing disc expansion and the presence of optical winds), the appearance of broad absorptions in the optical regime has traditionally been neglected. In this work, we present the first systematic study of these broad absorptions. We carry out theAdvertised on -
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