We present initial results on a survey of high-mass X-ray binaries (HMXBs) in the nearby, star-forming spiral galaxy M33. The HMXB population in M33 is identified and characterized using a combination of deep Chandra X-ray imaging and archival Hubble Space Telescope (HST) observations. We determine ages for the HMXBs to ~5 Myr precision from fits to the color-magnitude diagrams (CMDs) of the surrounding stars and the resultant star formation histories (SFHs). The HMXBs in our M33 sample have measured ages, as well as candidate optical counterparts identified from HST photometry.

I find high turbulent shearing in a neutron-rich accretion disk surrounding a proto-neutron star formed at the collapse of a rapidly-rotating MZAMS = 54M⊙ star. These might be features of superluminous supernovae powered by jets and/or magnetar spin-down.

In the frame of radiation driven wind theory (Castor et al.1975), we present self-consistent hydrodynamical solutions to the line-force parameters (k, α, δ) under LTE conditions. Hydrodynamic models are provided by HydWind (Curé 2004). We evaluate these results with those ones previously found in literature, focusing in different regions of the optical depth to be used to perform the calculations. The values for mass-loss rate and terminal velocity obtained from our calculations are also presented.

We also examine the line-force parameters for the case when large changes in ionization throughout the wind occurs (δ-slow solutions, Curé et al.2011).

We present here a modern study of the radial velocity curve and of the photometric light curve of the very interesting supergiant O7.5If + O9I(f) binary system HD 166734. The physical parameters of the stars and the orbital parameters are carefully determined. We also perform the analysis of the observed X-ray light curve of this colliding-wind binary.

We present a pilot study of using the Atacama Large Millimeter/sub-millimeter Array (ALMA) continuum observations to constrain the density structure in the intermediate wind zone of massive stars, in which the wind is extremely sensitive to clumping.

The origin of red supergiant mass loss still remains to be unveiled. Characterising the formation loci and the dust distribution in the first stellar radii above the surface is key to understand the initiation of the mass loss phenomenon. Polarimetric interferometry observations in the near-infrared allowed us to detect an inner dust atmosphere located only 0.5 stellar radius above the photosphere of Betelgeuse. We modelled these observations and compare them with visible polarimetric measurements to discuss the dust distribution properties.

MASGOMAS (MAssive Stars in Galactic Obscured MAssive clusterS) is a project aiming at discovering OB stars in Galactic, dust enshrouded, star-forming massive clusters (Marín-Franch et al. 2009, A&A 502, 559). The project has gone through different phases of increasing automatization, that have allowed us to discover massive clusters like MASGOMAS-1 (Ramírez Alegría et al. 2012, A&A 541, A75) (with M≈20,000 M⊙).

We present the results from the quantitative spectroscopic analysis of ~280 likely single O stars targeted by the IACOB and OWN surveys. This implies the largest sample of Galactic O-type stars analyzed homogeneously to date. We used the iacob-broad and iacob-gbat tools (see Simón-Díaz et al. 2011,2015) to obtain the complete set of spectroscopic parameters which can be determined from the optical spectrum of O-type stars: projected rotational velocity (v sin i), macroturbulence velocity (vmac), effective temperature (Teff), gravity (logg), wind-strength (logQ), helium abundance (YHe), microturbulence (ξt), and the exponent of the wind-law (β).

SNe of Type IIn are among the brightest supernova explosions due to strong circumstellar interaction. Examining the geometric and optical properties of the circumstellar material (CSM) can help to identify the progenitors of individual IIn SNe. Polarimetry is the optimal method for constraining CSM characteristics, as polarimetric signals both depend upon and preserve geometric information from unresolved sources. I present the results of fitting an ensemble of simulated polarized Hα emission-line profiles of interacting SNe, created using a three-dimensional Monte Carlo radiative transfer code called SLIP, to the multi-epoch observed polarized spectra of the Type IIn SN 1997eg. Further study of this model ensemble will allow us to investigate relationships among SNe IIn based on viewing angle and consider how the category should be subdivided based on physical properties of the CSM and/or progenitor.

We build a 2D model of the radiative envelope of main sequence massive stars. We set a dynamical boundary condition at the bottom of the radiative envelope at η = rC/R (where rC is the core size and R the radius of the star) to account for the differential rotation of the convective core as computed in 3D simulations (e.g. Browning et al. (2004, IAUS, 224, 149). We seek the differential rotation and associated meridional circulation induced by such a shear competing with the baroclinic flow of the stably stratified radiative envelope using the Boussinesq approximation.

The Swift satellite allows us to use gamma-ray bursts (GRBs) to peer through the hearts of star forming galaxies through cosmic time. Our open collaboration, representing most of the active European researchers in this field, builds a public legacy sample of GRB X-shooter spectroscopy while Swift continues to fly. To date, our spectroscopy of more than 100 GRB afterglows covers a redshift range from 0.059 to about 8 (Tanvir et al. 2009, Nature 461, 1254), with more than 20 robust afterglow-based metallicity measurements (over a redshift range from 1.7 to 5.9). With afterglow spectroscopy (throughout the electromagnetic spectrum from X-rays to the sub-mm) we can hence characterize the properties of star-forming galaxies over cosmic history in terms of redshift, metallicity, molecular content, ISM temperature, UV-flux density, etc.. These observations provide key information on the final evolution of the most massive stars collapsing into black holes, with the potential of probing the epoch of the formation of the first (very massive) stars.

VLT/X-shooter (Vernet et al. 2011, A&A 536, A105) is in many ways the ideal GRB follow-up instrument and indeed GRB follow-up was one of the primary science cases behind the instrument design and implementation. Due to the wide wavelength coverage of X-shooter, in the same observation one can detect molecular H2 absorption near the atmospheric cut-off and many strong emission lines from the host galaxy in the near-infrared (e.g., Friis et al. 2015, MNRAS 451, 167). For example, we have measured a metallicity of 0.1 Z⊙ for GRB 100219A at z = 4.67 (Thöne et al. 2013, MNRAS 428, 3590), 0.02 Z⊙ for GRB 111008A at z = 4.99 (Sparre et al. 2014, ApJ 785, 150) and 0.05 Z⊙ for GRB 130606A at z = 5.91 (Hartoog et al. 2015, A&A 580, 139). In the latter, the very high value of [Al/Fe]=2.40 ± 0.78 might be due to a proton capture process and may be a signature of a previous generation of massive (perhaps even the first) stars. Reconciling the abundance patterns of GRB absorbers, other types of absorbers (in particular QSO DLAs), and old stars in the Local Group is an important long-term goal of this program (see Sparre et al. 2014, ApJ 785, 150). Metallicities are also measured from host emission lines (Krühler et al. 2015, A&A 581, A125). GRB spectroscopy also allows us to determine the dust content of their environments, both through analysis of the depletion pattern and the measurement of the associated extinction (Japelj et al. 2015, A&A 451, 2050). This way one can quantify the dust-to-metals ratio and its evolution with redshift. The detection of GRBs at z > 6 shows that GRBs have become competitive as a tool to identifying galaxies at the highest redshifts and unsurpassed in providing detailed abundance information via absorption line spectroscopy.

In order to investigate the distinguishability about the progenitors of FeCCSNe and ECSNe, we calculate the luminosities and spectra of their pre-SN neutrinos and estimate the number of events at neutrino detectors.

Mass is a key parameter in understanding the evolution and eventual fate of hot, luminous stars. Mass loss through a wind driven by UV-scattering forces is already known to reduce the mass of such stars by 10−10 − 10−4 M⊙/yr over the course of their lifetimes. However, high-mass stars already drive such strong winds while they are still in their accretion epoch. Therefore, stellar UV-scattering forces will efficiently ablate material off the surface of their circumstellar disks, perhaps even shutting off the final accretion through the last several stellar radii and onto a massive protostar. By using a three-dimensional UV-scattering prescription, we here quantify the role of radiative ablation in controlling the disk’s accretion rate onto forming high-mass stars. Particular emphasis is given to the potential impact of this process on the stellar upper mass limit.

η Carinae, the most extreme luminous blue variable in our Galaxy, underwent a Great Eruption in the 1800s and ejected significant mass into the well-known bipolar Homunculus. But η Car's outer ejecta, a spread of dense, nitrogen-rich knots outside the Homunculus, have led to suspicion that the Great Eruption was not this star's first major mass-loss event. We have measured proper motions for nearly 800 distinct features in the outer ejecta using 21 years of HST WFPC2 and ACS imaging. With motions measured across sixteen baselines, we find that the outer ejecta are expanding ballistically and belong to three age groups: one dating to the mid-1200s, another to the mid-1500s, and a third to the early 1800s, associated with but perhaps predating the peak of the Great Eruption. These three age groups are separated in space and radial velocity. There is no evidence for interaction between the dense ejecta that could be powering η Car's soft X-ray shell, which is instead likely driven by fast, rarefied ejecta from the Great Eruption striking the older dense ejecta. The thirteenth-century event was strikingly asymmetric, ejecting mass almost entirely to one side of the star. The sixteenth-century event displays bipolar symmetry, but along a different axis than the current Homunculus. These observations provide constraints on theoretical models of η Car's behavior, as viable models must explain the repetition, timescale, and asymmetry of these major mass-loss events. For more details, see Kiminki, Reiter, & Smith (2016, MNRAS, 463, 845).

To this date ψ Per is the only classical Be star that was angularly resolved in radio (by the VLA at λ = 2 cm). Gaussian fit to the azimuthally averaged visibility data indicates a disk size (FWHM) of ~500 stellar radii (Dougherty & Taylor 1992). Recently, we obtained new multi-band cm flux density measurements of ψ Per from the enhanced VLA. We modeled the observed spectral energy distribution (SED) covering the interval from ultraviolet to radio using the Monte Carlo radiative transfer code HDUST (Carciofi & Bjorkman 2006). An SED turndown, that occurs between far-IR and radio wavelengths, is explained by a truncated viscous decretion disk (VDD), although the shallow slope of the radio SED suggests that the disk is not simply cut off, as is assumed in our model. The best-fit size of a truncated disk derived from the modeling of the radio SED is 100+5−15 stellar radii, which is in striking contrast with the result of Dougherty & Taylor (1992). The reasons for this discrepancy are under investigation.

On the basis of long-term UBV observations of P Cygni, which were made by Eugene Kharadze and Nino Magalashvili between 1951-1983, is evident that P Cygni undergone reddening during those observations. P cygni is a LBV and a supernova impostor. Corrected on the reddening B-V color has values between about -0.4 (at the beginning of 1950-ies) and -0.1 (for the 1980-ies). It means that the star probably had earlier spectral type at the beginning of 20-th century and accordingly, we are witnesses of its evolutionary changes. It means also that on the HR diagram the star moves gradually to the instability strip of LBVs in Outburst. So, if the rate of the reddening of the P Cygni will the same in near future then the star will have the next eruption (or even supernova explosion) after approximately 80-120 years.

The long (approximately 1500 d, 1160 d, 760 d, 580 d) quasi-periods and the shorter ones (approximatelly 130 d, 68 d and 15-18 days) were revealed using the above observations.

We observed P Cygni on July 23 - October 20, 2014 with the 48 cm Cassegrain telescope and standard B,V,R,I filters. HD 228793 has been used as a comparison star. We revealed that during our observations the star underwent light variations with the mean amplitude of approximately 0.1 magnitudes in all pass-bands and the period of this change was approximately 68 days. There is also a relation between brightness and the Hα EW variability. Therefore, we think that the cause of this behavior may be a variability of rate of the stellar wind that is very strong in this star. Changes in the rate of the stellar wind, on the other hand, maybe due to the pulsation of the star. It seems that quasi-periods of the brightness variability are almost the exact multiples of each other which probably also indicates on pulsation of the star. According to the new photometric observations of 2014 the star continues reddening.

A substantial number of core-collapse supernovae (CCSNe) are expected to be hosted by starbursting luminous infrared galaxies (LIRGs). However, so far very few CCSNe have been discovered in LIRGs, most likely as a result of dust extinction and lack of contrast in their typically luminous and complex nuclear regions. We present the first results of Project SUNBIRD (Supernovae UNmasked By InfraRed Detection), where we aim to uncover dust-obscured nuclear supernovae by monitoring over 30 LIRGs, using near-infrared state-of-the-art Laser Guide Star Adaptive Optics (LGSAO) imaging on the Gemini South and Keck telescopes. Such discoveries are vital for determining the fraction of supernovae which will be missed as a result of dust obscuration by current and future optical surveys.

Winds of hot massive stars are driven radiatively by light absorption in the lines of heavier elements. Therefore, the radiative force depends on the wind ionization. That is the reason why the accretion powered X-ray emission of high-mass X-ray binaries influences the radiative force and may even lead to wind inhibition. We model the effect of X-ray irradiation on the stellar wind in high-mass X-ray binaries. The influence of X-rays is given by the X-ray luminosity, by the optical depth between a given point and the X-ray source, and by the distance to the X-ray source. The influence of X-rays is stronger for higher X-ray luminosities and in closer proximity of the X-ray source. There is a forbidden area in the diagrams of X-ray luminosity vs. the optical depth parameter. The observations agree with theoretical predictions, because all wind-powered high-mass X-ray binary primaries lie outside the forbidden area. The positions of real binaries in the diagram indicate that their X-ray luminosities are self-regulated.

We are using light curves from the KELT exoplanet transit survey (Pepper et al. 2007) to study the variability of hundreds of Be stars. Combining these light curves with simultaneous time-series spectra from the APOGEE survey (Majewski et al. 2015) provides a glimpse into how changes in the circumstellar environment are correlated to brightness variations.

Massive stars are intrinsically rare and therefore present a challenge to understand from a statistical perspective, especially within the Milky Way. We recently conducted follow-up observations to the Panchromatic Hubble Andromeda Treasury (PHAT) survey that were designed to detect more than 10,000 emission line stars, including WRs, by targeting regions in M31 previously known to host large numbers of young, massive clusters and very young stellar populations. Because of the existing PHAT data, we are able to derive an effective temperature, bolarimetric luminosity, and extinction for each of our detected stars. We report on preliminary results of the massive star population of our dataset and discuss how our results compare to previous studies of massive stars in M31.