Related papers: Active cool stars and He I 10830 \AA: the coronal …

We report on observations of a solar prominence obtained on 26 April 2007 using the Extreme Ultraviolet Imaging Spectrometer on Hinode. Several regions within the prominence are identified for further analysis. Selected profiles for lines…

Aims. We aim to explain line formation of He I D3 and He I 10830 {\AA} in small-scale reconnection events. Methods. We make use of a simulated Ellerman bomb (EB), present in a Bifrost-generated radiative Magnetohydrodynamics (rMHD)…

Solar jets are well-collimated plasma ejections in the solar atmosphere. They are prevalent in active regions, the quiet Sun, and even coronal holes. They display a range of temperatures, yet the nature of the cool components has not been…

We propose new diagnostics for circumstellar interaction in Type IIP supernovae by the detection of high velocity (HV) absorption features in Halpha and He I 10830 A lines during the photospheric stage. To demonstrate the method, we compute…

We present new spectroscopic observations of the He I $\lambda$10830 line in R Coronae Borealis (RCB) stars which provide the first strong evidence that most, if not all, RCB stars have winds. It has long been suggested that when dust forms…

We present an analysis of ten cool stars (Algol, Capella, Procyon, Eps Eri, Alpha Cen A&B, UX Ari, AD Leo, YY Gem, and HR1099) observed with the Low Energy Transmission Grating Spectrometer (LETGS) on board the Chandra X-ray Observatory.…

Mysteries about the origin of high-energy cosmic neutrinos have deepened by the recent IceCube measurement of a large diffuse flux in the 10-100 TeV range. Based on the standard disk-corona picture of active galactic nuclei (AGN), we…

Context: Recently, the He I triplet at 10830 \r{A} has been rediscovered as an excellent probe of the extended and possibly evaporating atmospheres of close-in transiting planets. This has already resulted in detections of this triplet in…

We present a study of correlations between high Li abundances and strong chromospheric He I 10830 \AA\ absorption line strengths in Kepler field giant stars. Our sample includes 84 giants with detectable solar-like oscillations in their…

This thesis strives to improve our understanding of solar activity, specifically the behaviour of solar flares and coronal mass ejections. An investigation into the hydrodynamic evolution of a confined solar flare was carried out using…

He I 10830 profiles acquired with Keck's NIRSPEC for 6 young low mass stars with high disk accretion rates (AS 353A, DG Tau, DL Tau, DR Tau, HL Tau and SVS 13) provide new insight into accretion-driven winds. In 4 stars the profiles have…

FUSE ultraviolet spectra of 8 giant and supergiant stars reveal that high temperature (3 X 10^5 K) atmospheres are common in luminous cool stars and extend across the color-magnitude diagram from Alpha Car (F0 II) to the cool giant Alpha…

Using high resolution cosmological simulations, we study hydrogen and helium gravitational cooling radiation. We focus on the HeII cooling lines, which arise from gas with a different temperature history (T_max ~ 10^5K) than HI line…

We present a digital atlas of peculiar, high-luminosity massive stars in the near-infrared region (10470-11000 A) at medium resolution (R~7000). The spectra are centered around He I 10830 A, which is formed in the wind of those stars, and…

The profiles of emission lines formed in the corona contain information on the dynamics and the heating of the hot plasma. Only recently has data with sufficiently high spectral resolution become available for investigating the details of…

We present new collisional-radiative models (CRMs) for helium in the quiescent solar corona, and predict the emissivities of the He and He$^+$ lines to be observed by DKIST, Solar Orbiter, and Proba-3. We discuss in detail the rates we…

Two properties of Messier 13 are pertinent to the study of mass loss among metal-poor stars and the chemical evolution of globular clusters: (i) an extended blue horizontal branch, which seems to demand mass loss from red giant progenitor…

We present a survey of coronal forbidden lines detected in Far Ultraviolet Spectroscopic Explorer (FUSE) spectra of nearby stars. Two strong coronal features, Fe XVIII 974 A and Fe XIX 1118 A, are observed in 10 of the 26 stars in our…

Spectra of the He I 10830 line have been obtained for 23 metal-poor stars, the majority of which are dwarfs ranging in metallicity from [Fe/H] = -2.1 to -0.8. The data were acquired with the NIRSPEC spectrograph on the Keck 2 telescope.…

The helium absorption line at 10830 {\AA}, originating from the metastable triplet state 2$^3$S, has been suggested as an excellent probe for the extended atmospheres of hot Jupiters and their hydrodynamic escape processes, and has recently…