Related papers: A Sample of HeII $\lambda$4686 "Changing-Look" Qua…

SBS0335-052E, one of the most metal-poor (Z ~ 3-4% Z$_{\odot}$) HeII-emitter starbursts known in the nearby universe, is studied using optical VLT/MUSE spectroscopic and Chandra X-ray observations. We spatially resolved the spectral map of…

Aims. Every 5.5 years eta Car's light curve and spectrum change remarkably across all observed wavelength bands. We compare the recent spectroscopic event in mid-2014 to the events in 2003 and 2009 and investigate long-term trends. Methods.…

Using a large sample of Type 1 AGN spectra, we investigated the complex structure of the Fe II emission region in order to understand the atomic processes responsible for the enhancement of the Fe II emission. We explored correlations…

We present the identification of changing-look active galactic nuclei (CL-AGNs) from the Dark Energy Spectroscopic Instrument First Data Release and Sloan Digital Sky Survey Data Release 16 at z \leq 0.9. To confirm the CL-AGNs, we utilize…

In a single optical spectrum, the quasar narrow-line region (NLR) reveals low density, photoionized gas in the host galaxy interstellar medium, while the immediate vicinity of the central engine generates the accretion disk continuum and…

Variable red- and blue-shifted absorption features observed in the Ca ii K line towards the A-type shell star $\phi$ Leo have been suggested by us in a previous work to be likely due to solid, comet-like bodies in the circumstellar (CS)…

We report the discovery of disappearance of Mg ii, Al iii, C iv, and Si iv broad absorption lines (BALs) at the same velocity, accompanied by a new Civ BAL emerging at a higher velocity, in the quasar J0827+4252 at z = 2.038. This is the…

Determining the frequency and duration of changing--look (CL) active galactic nuclei (AGNs) phenomena, where the optical broad emission lines appear or disappear, is crucial to understand the evolution of the accretion flow around…

Outflows in quasars during the early epochs of galaxy evolution are an important part of the feedback mechanisms potentially affecting the evolution of the host galaxy. However, systematic observations of outflows are only now becoming…

Changing-look active galactic nuclei (CLAGNs) show the disappearance and reappearance of broad emission lines in a few years, which challenges the orientation-based AGN unification model. We reduce the X-ray data for five well-studied…

In a sample of 60 quasars selected from Sloan Digital Sky Survey (SDSS) with at least six-epoch spectroscopy, we investigate the variability of emission lines and continuum luminosity at various aspects. A strong anti-correlation between…

We explore the properties of the H_beta emission line profile in a large, homogeneous and bright sample of N~470 low redshift quasars extracted from Sloan Digital Sky Survey (DR5). We approach the investigation from two complementary…

We report on a three-year program of coordinated X-ray and optical monitoring of the Narrow-Line Seyfert 1 galaxy NGC 4051. The rapid continuum variations observed in the X-ray spectra are not detected in the optical, although the X-ray and…

We present the first high resolution HeII 4686 images of the high excitation nebula around the WR star Brey 2 in the LMC. This nebula presents a striking morphology: a small arc-like feature some 3.6pc in radius is particularly prominent in…

Probing the structures of stellar winds is of prime importance for the understanding of massive stars. Based on their optical spectral morphology and variability, the stars of the Oef class have been suggested to feature large-scale…

Type II quasars are luminous AGNs whose central engines and broad-line regions are obscured by intervening material; such objects only recently have been discovered in appreciable numbers. We study the multiwavelength properties of 291 type…

A handful of active galactic nuclei (AGN) have shown strong spectral variations in the optical band between epochs that are years apart. The appearance or disappearance of broad emission lines in their spectra completely changes their…

We present VLT-SINFONI near infra-red spectra of 26 new heavily reddened quasar candidates selected from the UKIDSS-LAS, VISTA VHS and VIKING imaging surveys. This new sample extends our reddened quasar search to both brighter and fainter…

We monitored five high-luminosity quasars with lambda L_{3000A} > 10^45 erg s^-1 at 0.4 < z < 0.6 to measure flux variability of the MgII 2798 line and explore feasibility of reverberation mapping using MgII. Over the two year monitoring…

We analyze extensive spectroscopic and photometric data of the hypervariable quasar SDSS J131424+530527 (RMID 017) at z=0.456, an optical "changing look" quasar from the Sloan Digital Sky Survey Reverberation Mapping project that increased…