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Ultraviolet (UV) emission from galaxies is associated with hot components, whether from stellar sources or not. By making use of colour-colour diagrams, early-type galaxies (ETGs) can be classified in terms of their UV emission in mainly…
We present the time evolution of viscously accreting circumstellar disks as they are irradiated by ultraviolet and X-ray photons from a low-mass central star. Our model is a hybrid of a 1D time-dependent viscous disk model coupled to a 1+1D…
We present the results from the analysis of optical spectra of 31 Halpha-selected regions in the extended UV (XUV) disks of M83 (NGC5236) and NGC4625 recently discovered by GALEX. The spectra were obtained using IMACS at Las Campanas…
The extended ultraviolet (XUV) disk galaxies are one of the most interesting objects studied in the last few years. The UV emission, revealed by GALEX, extends well beyond the optical disk, after the drop of H$\alpha$ emission, the usual…
We present the ultraviolet (UV) color-color relation of early-type galaxies (ETGs) in the nearby universe (0.05 < z < 0.12) to investigate the properties of hot stellar populations responsible for the UV excess (UVX). The initial sample of…
We present new X-ray and Far Ultraviolet (FUV) observations of T Tauri stars covering the age range 1 to 10 Myr. Our goals are to observationally constrain the intensity of radiation fields responsible for evaporating gas from the…
Stellar population studies of early-type galaxies (ETGs) based on their optical stellar continuum suggest that these are quiescent systems. However, emission lines and ultraviolet photometry reveal a diverse population. We use a new version…
Ultraviolet imaging with the Galaxy Evolution Explorer (GALEX) has revealed an extensive sample of UV-bright stellar complexes in the extreme outer disk of M83, extending to about four times the radius where the majority of HII regions are…
GALEX detected a significant fraction of early-type galaxies showing Far-UV bright structures. These features suggest the occurrence of recent star formation episodes. We aim at understanding their evolutionary path[s] and the mechanisms at…
Breaks in the surface brightness profiles in the outer regions of galactic discs are thought to have formed by various internal and external processes, and by studying the breaks we aim to better understand what processes are responsible…
The extreme outer regions of disk galaxies, lying at or beyond the classical optical radius defined by R25, present an opportunity to study star formation and chemical evolution under unique physical conditions, possibly reminscent of those…
We present ultraviolet integrated and azimuthally-averaged surface photometric properties of a sample of 44 dIm, BCD, and Sm galaxies measured from archival NUV and FUV images obtained with GALEX. We compare the UV to Halpha and V-band…
We combine GALEX (ultra-violet; UV) and SDSS (optical) photometry to study the recent star formation histories of ~100 field galaxies on the optical red sequence, a large fraction of which exhibit widespread signs of disturbed morphologies…
We report on intriguing photometric properties of Galactic stars observed in the GALEX satellite's far-UV and near-UV bandbasses as well as from the SDSS survey and the Kepler Input Catalog. First, the FUV-NUV color distribution of stars in…
Studying star formation beyond the optical radius of galaxies allows us to test empirical relations in extreme conditions with low average gas density and low molecular fraction. Previous studies discovered galaxies with extended…
We analyzed the deconvolved surface brightness profiles of 247 massive and angularly large disk galaxies at $1\leq z\leq 3$ to study high-redshift disk breaks, using F356W-band images from the Cosmic Evolution Early Release Science survey…
Hierarchical assembly of early-type galaxies (Es and S0s) over an extended period of time will result in mixed-generation stellar populations. Here we look for signatures of composite populations in broad-band, near-ultraviolet (2500-3400…
Context. Planets are thought to eventually form from the mostly gaseous (~99% of the mass) disks around young stars. The density structure and chemical composition of protoplanetary disks are affected by the incident radiation field at…
New deep optical and near-infrared imaging is combined with archival ultraviolet and infrared data for fifteen nearby galaxies mapped in the Spitzer Extended Disk Galaxy Exploration Science survey. These images are particularly deep and…
We present an ultra-violet (UV) study of the galaxy NGC~300 using GALEX far-UV (FUV) and near-UV (NUV) observations. We studied the nature of UV emission in the galaxy and correlated it with optical, H~I and mid-infrared (3.6 $\mu$m)…