Related papers: The Wind of Variable C in M33

Spectroscopic monitoring with Mercator-HERMES over the past two years reveals that MWC 314 is a massive binary system composed of an early B-type primary LBV star and a less-luminous supergiant companion. We determine an orbital period Porb…

Our recent progress on time-dependent modeling of the multiwavelength spectra and variability of blazars with leptonic and hadronic jet models is reviewed. Special emphasis is placed on X-ray spectral variability of low-frequency peaked…

The luminous blue variable (LBV) phase is a poorly understood stage in the evolution of high mass stars, characterized for its brevity and instability. The surroundings of LBV stars are excellent test beds to study their dense stellar winds…

In a recent paper we have calculated the power density spectrum of Gamma-Ray Bursts arising from multiple shocks in a relativistic wind. The wind optical thickness is one of the factors to which the power spectrum is most sensitive,…

Luminous Blue Variables (LBVs) oftentimes show double-troughed absorption in their strong Halpha lines, which are as yet not understood. Intriguingly, the feature has also been seen in the interacting supernova SN 2005gj, which was for this…

In a recent paper, Smith and Tombleson (2015) state that the Luminous Blue Variables (LBVs) in the Milky Way and the Magellanic Clouds are isolated; that they are not spatially associated with young O-type stars. They propose a novel…

Brown dwarfs of a variety of spectral types have been observed to be photometrically variable. Previous studies have focused on objects at the L/T transition, where the iron and silicate clouds in L dwarfs break up or dissipate. However,…

Despite a resurgence of effort over the last decade in the area of massive stars there is still ambiguity over their evolutionary path, contamination of their surface abundances and the behaviour of their stellar winds. Here 10 SMC B-type…

We report on the preliminary results of a three-year monitoring campaign of Galactic and Magellanic LBVs with both moderate and high resolution spectroscopy. We have collected more than 500 moderate-resolution spectra of 20 stars in the red…

Due to its peculiar and highly variable nature, the blazar 3C 454.3 has been extensively monitored by the WEBT team. Here, we present for the first time these long-term optical flux and color variability results using data acquired in B, V,…

We performed spectroscopy of five Luminous Blue Variable (LBV) candidates and two known LBV stars (AE And and Var A-1) in M31. We obtained the same-epoch near-infrared (NIR) and optical spectra of these stars. The NIR spectra were taken…

Luminous blue variables (LBVs) are evolved massive stars close to the Eddington limit, with a distinct spectroscopic and photometric variability having unsteady mass-loss rates. These stars show a considerable change in their surface…

We call attention to the fact that one of the brightest red supergiants in the SMC has recently changed its spectral type from K0-1 I (December 2004) to M4 I (December 2005) and back to K0-1 I (September 2006). An archival spectrum from the…

Using CCD photometry obtained by the EROS collaboration in 1991-1993, we have discovered an LMC variable star with a light curve that is oscillating with a mean period of $\sim 14$ days and an amplitude of $\sim$ 0.3 mag. The oscillations…

We evaluate the place of Eta Carinae amongst the class of luminous blue variables (LBVs) and show that the LBV phenomenon is not restricted to extremely luminous objects like Eta Car, but extends luminosities as low as log(L/Lsun) = 5.4 -…

Blazars are known to show periods of quiescence followed by outbursts visible throughout the electromagnetic spectrum. We present a novel maximum likelihood approach to capture this bimodal behavior by examining blazar radio variability in…

We study the kinematics of luminous blue variables (LBVs) in the Large Magellanic Cloud (LMC). Using high-resolution spectra, we measure the systemic radial velocities for a sample of 16 LBVs and LBV candidates. In order to measure the net…

We have investigated the stellar and wind properties of a sample of five late-type O dwarfs in order to address the weak wind problem. A grid of TLUSTY models was used to obtain the stellar parameters, and the wind parameters were…

The emission from blazars is known to be variable at all wavelengths. The flux variability is often accompanied by spectral changes. Spectral energy distribution (SED) changes must be associated with changes in the spectra of emitting…

We obtained high spectral resolution spectra ($\Delta v$ $\sim$ 2.5 km s$^{-1}$) for DG Tau A from 4800 \r{A} to 7500 \r{A} using Subaru High Dispersion Spectrograph (HDS) for the first time. The low-velocity components (LVCs, |$v$| < 100…