Related papers: New theoretical Fe II templates for bright quasars
The detection of a HeII absorption trough in the spectra of three high-redshift quasars provides new constraints on the spectral shape of the UV extragalactic background. The relative strengths of the observed flux decrements at the…
Recent observations of quasars, Mrk 335 and the HST quasar composite spectrum, have indicated that many of them have remarkably soft ionizing continua (fnu ~ nu^-2.0, 13.6 eV -- 100 eV). We point out that the number of E > 54.4 eV photons…
Broad-band images of the solar chromosphere in the Ca II H&K line cores around active regions are covered with fine bright elongated structures called bright fibrils. The mechanisms that form these structures and cause them to appear bright…
A non-local-thermodynamic-equilibrium (NLTE) level population model of the first and second ionisation stages of iron, nickel and cobalt is used to fit a sample of XShooter optical + near-infrared (NIR) spectra of Type Ia supernovae (SNe…
We have compared the optical emission line ratios of type 2 quasars from Zakamska et al. with standard AGN photoionization model predictions, Seyfert 2s, HII galaxies, and narrow line FRII radio galaxies. Moderate to high ionization narrow…
We present a new self-consistent and versatile method that derives photospheric radius and temperature variations of Type II-Plateau supernovae based on their expansion velocities and photometric measurements. We apply the method to a…
Type Ia supernova (SN Ia) light curves have a secondary maximum that exists in the $r$, $i$, and near-infrared filters. The secondary maximum is relatively weak in the $r$ band, but holds the advantage that it is accessible, even at high…
We investigate the effect of Fe II equivalent width ($W_{2600}$) and fibre size on the average luminosity of [O II]$\lambda\lambda$3727,3729 nebular emission associated with Mg II absorbers (at $0.55 \le z \le 1.3$) in the composite spectra…
Star-forming galaxies with nebular HeII emission contain very energetic ionizing sources of radiation, which can be considered as analogs to the major contributors of the reionization of the Universe in early epochs. It is therefore of…
We assume a distribution of clouds optically thick for electron scattering (OTCM) which are moderately optically thin for absorption and we consider them as a model of the mean quasar spectrum of Laor et al. (1997). We show that the model…
Recent atomic physics calculations for Si II are employed within the Cloudy modelling code to analyse Hubble Space Telescope (HST) STIS ultraviolet spectra of three cool stars, Beta-Geminorum, Alpha-Centauri A and B, as well as previously…
Wavelengths of absorption lines in the spectra of galaxies along the line-of-sight to distant quasars can be used to probe the variablility of the fine structure constant, $\alpha$, at high redshifts, provided that the laboratory…
A deep narrow-band survey for Ly-alpha emission carried out on the VLT-FORS2 has revealed 98 Ly-alpha candidates down to a flux limit of 4.e-18 erg/s/cm^2 in a volume of 5500 comoving Mpc^3 at z=2.4 centered on the hyperluminous quasar…
The variability of quasars across multiple wavelengths is a useful probe of physical conditions in active galactic nuclei. In particular, variable accretion rates, instabilities, and reverberation effects in the accretion disk of a…
We present moderate and high-dispersion 1-2.5 micron spectra of the 10 arcsec nebula around P Cygni, dominated by bright emission lines of [Fe II]. Observed [Fe II] line ratios disagree with theoretical transition rates in the literature,…
Type 2 quasars are luminous active galactic nuclei (AGN) whose central regions are obscured by large amounts of gas and dust. In this paper, we present a catalog of type 2 quasars from the Sloan Digital Sky Survey (SDSS), selected based on…
Theories unifying gravity and other interactions suggest the possibility of spatial and temporal variation of physical ``constants'' in the Universe. Detection of high-redshift absorption systems intersecting the sight lines towards distant…
We introduce a new physical parameter, the optical variability amplitude, to the well-established Eigenvector 1 space of quasars and test a sample of long-term B-band light curves of 42 PG quasars monitored by Giveon et al. (1999). We find…
Ca II absorbers, characterized by dusty and metal-rich environments, provide unique insights into the interstellar medium of galaxies. However, their rarity and weak absorption features have hindered comprehensive studies. In this work, we…
We measure the differential microlensing of the UV Fe II and Fe III emission line blends between 14 quasar image pairs in 13 gravitational lenses. We find that the UV iron emission is strongly microlensed in 4 cases with amplitudes…