Related papers: Ultraviolet Flux Decrease Under a Grand Minimum fr…

We studied new simultaneous observations of the flux variations of the photospheric and chromospheric emissions of 33 solar-type stars and Sun during the HK-project that were conducted over the past 20 years. In addition to the known cyclic…

We present ultraviolet (UV) spectroscopy and photometry of four Type Ia supernovae (SNe 2004dt, 2004ef, 2005M, and 2005cf) obtained with the UV prism of the Advanced Camera for Surveys on the Hubble Space Telescope. This dataset provides…

Context: Ultraviolet (UV) emission-line spectra are used to spectroscopically confirm high-z galaxies and increasingly also to determine their physical properties. Aims: To interpret the observed UV spectra of distant galaxies in terms of…

We present the results of a spectroscopic survey of the Ca II H & K core strengths in a sample of 60 solar-type stars that are members of the solar-age and solar-metallicity open cluster M67. We adopt the HK index, defined as the summed H+K…

A collection of spectral energy distributions (SEDs) is available in the Hubble Space Telescope (HST) CALSPEC database that is based on calculated model atmospheres for pure hydrogen white dwarfs (WDs). A much larger set (~100,000) of UV…

M dwarf stars are excellent candidates around which to search for exoplanets, including temperate, Earth-sized planets. To evaluate the photochemistry of the planetary atmosphere, it is essential to characterize the UV spectral energy…

We have assembled a UV-flux selected sample of 82 early-type galaxies and collected additional information at other wavelengths. These data confirm a large spread of the UV-V color in the range 2 to 5. The spread in UV-V is accompanied by a…

We examine whether the spectral energy distribution of UV continuum emission of active galactic nuclei changes during flux variation. We used multi-epoch photometric data of QSOs in the Stripe 82 observed by the SDSS Legacy Survey and…

Efforts to discover and characterize habitable zone planets have primarily focused on Sun-like stars and M dwarfs. K stars, however, provide an appealing compromise between these two alternatives that has been relatively unexplored.…

Measurements of maximum magnetic flux, minimum intensity, and size are presented for 12 967 sunspot umbrae detected on the NASA/NSO spectromagnetograms between 1993 and 2004 to study umbral structure and strength during the solar cycle. The…

Using a phenomenological approach, we self-consistently model the redshift evolution of the ultraviolet (UV) and infrared (IR) luminosity functions across cosmic time, as well as a range of observed IR properties of UV-selected galaxy…

Transits of hot Jupiters in X-rays and the ultraviolet have been shown to be both deeper and more variable than the corresponding optical transits. This variability has been attributed to hot Jupiters having extended atmospheres at these…

The relation between the ratio of infrared (IR) and ultraviolet (UV) flux densities (the infrared excess: IRX) and the slope of the UV spectrum (\beta) of galaxies plays a fundamental role in the evaluation of the dust attenuation of star…

The spectral energy distribution, variability and evolution of the high-energy radiation from an M dwarf planet host is crucial in understanding the planet's atmospheric evolution and habitability and in interpreting the planet's spectrum.…

M-type stars are crucial for stellar activity studies since they cover two types of magnetic dynamos and particularly intriguing for habitability studies due to their abundance and long lifespans during the main-sequence stage. In this…

If magnetic activity in outer stellar atmospheres is due to an interplay between rotation and subsurface convection, as is generally presumed, then one would not expect to observe indicators of activity in stars with T_eff > 8300 K. Any…

An echelle spectrogram (R = 30,000) of the 2300-3100 A region in the ultraviolet spectrum of the F8V star 9 Comae is presented. The observation is used to calibrate features in the mid-ultraviolet spectra of similar stars according to age…

Determining the properties of old stellar systems using evolutionary population synthesis requires a library of reliable model stellar fluxes. Empirical libraries are limited to spectra of stars in the solar neighborhood, with nearly solar…

Stars with very low levels of magnetic activity provide an opportunity for a more quantitative comparison with the Sun during its Maunder minimum. We employ spectra from the RAVE survey in a search for particularly low-activity stars with…

Mini-EUSO is a telescope observing the Earth in the ultraviolet band (290-430 nm) since 2019, through a nadir-facing UV-transparent window in the Russian Zvezda module of the International Space Station. The main camera has an optical…