Recent Talks

Many stars are observed to belong to multiple systems. Interactions between binary stars may change the evolutionary track of a star, creating atypical stars like Blue Stragglers and explaining the existence of extreme horizontal branch (EHB) stars. Using evolutionary population synthesis models including binary star evolutionary tracks from Hurley et al. and including the two He white dwarfs merger channel, suggested by Han et al., for the formation of EHB stars we compute a series of isochrones which include these atypical stars. We derive the integrated spectral energy distributions and the colors corresponding to these populations. The predictions of this model are in good agreement with traditional population synthesis models, except when the spectrum of the stellar population is dominated by binary stars or their products, e.g., EHB stars in the ultraviolet (UV) of early-type galaxies (ETGs) (Hernández-Pérez and Bruzual 2013). Using this binary population synthesis model we reproduce successfully the observed colour-colour diagram of a sample of 3417 ETGs observed both in the optical (SDSS -DR8) and the UV (GALEX-GR6) (Hernández-Pérez and Bruzual 2014). I will show how important is to consider binary interactions in evolutionary synthesis models.

I will talk about how resolved stellar populations in the nearby Local Group dwarf galaxies have been used to study the detailed chemical, kinematic and star formation history of these systems and the link to the properties of the Milky Way. I will mainly discuss the results from the DART spectroscopic surveys of nearby dwarf spheroidal galaxies, determining detailed abundances, looking for CEMP stars and also combining spectroscopy with colour-magnitude diagram analysis to measure the time scale for star formation and chemical evolution.

Any successful model of galaxy formation needs to explain the low rate of star formation in the small progenitors of today’s galaxies. This inefficiency is necessary for reproducing the low stellar-to-virial mass fractions. A possible driver of this low efficiency is the radiation pressure exerted by ionizing photons from massive stars. The effect of radiation pressure in cosmological, zoom-in galaxy formation simulations is modelled as a non-thermal pressure that acts only in dense and optically thick star-forming regions. The main effect of radiation pressure is to regulate and limit the high values of gas density and the amount of gas available for star formation. By using these simulations, I will address the early formation of compact spheroids by violent disc instabilities (VDI). Due to the inefficiency of star formation, this process is gas rich, so the dissipation naturally leads to compact spheroids. These VDI-driven spheroids, much like merger-driven spheroids, have steep surface density profiles, consistent with a classical, de-Vaucouleurs profile at all times.

The Chromosphere and Prominence Magnetometer (ChroMag) is a synoptic  instrument with the goal of quantifying the intertwined dynamics and  magnetism of the solar chromosphere and in prominences through imaging  spectro-polarimetry of the full solar disk in a synoptic fashion. The  picture of chromospheric magnetism and dynamics is rapidly developing,  and a pressing need exists for breakthrough observations of  chromospheric vector magnetic field measurements at the true lower  boundary of the heliospheric system. ChroMag will provide measurements  that will enable scientists to study and better understand the  energetics of the solar atmosphere, how prominences are formed, how  energy is stored in the magnetic field structure of the atmosphere and  how it is released during space weather events like flares and coronal  mass ejections. An essential part of the ChroMag program is a commitment  to develop and provide community access to the `inversion' tools  necessary to interpret the measurements and derive the  magneto-hydrodynamic parameters of the plasma. Measurements of an  instrument like ChroMag provide critical physical context for the Solar  Dynamics Observatory (SDO) and Interface Region Imaging Spectrograph  (IRIS) as well as ground-based observatories such as the future Daniel  K. Inouye Solar Telescope (DKIST). A prototype is currently deployed in  Boulder, CO, USA. We will present an overview of instrument design and  capabilities, show some recent observations, and discuss the future of  the project.