Search

Solar eclipses provide an excellent opportunity to study the effects of a sudden localized change in photoionization flux in the Earth's ionosphere and its consequent repercussion in the Geomagnetic field. We have focused on a subset of the data available from the North American 2017 eclipse in order to study VTEC measurements from GNSS data and geomagnetic field estimations from INTERMAGNET observatories near the eclipse path. Our simultaneous analysis of both datasets allowed us to quantify the ionosphere and magnetic field reaction to the eclipse event with which allowed us to compare how differently these take place in time. We found that studying the behaviour of VTEC differences with respect to reference values provides better insight of the actual eclipse effect and were able to characterize the dependence of parameters such as time delay of maximum depletion and recovery phase. We were also able to test models that link the ionospheric variations in a quantitative manner. Total electron content depletion measured from GNSS were fed into an approximation of Ashour-Chapman model at the locations of geomagnetic observatories and its predictions match the behaviour of magnetic field components in time and magnitude strikingly accurately., Comment: Accepted for publication in Advances in Space Research

We present a detailed study of the physical properties of the nebular material in four star-forming knots of the blue compact dwarf galaxy Haro 15. Using long-slit and echelle spectroscopy obtained at Las Campanas Observatory, we study the physical conditions (electron density and temperatures), ionic and total chemical abundances of several atoms, reddening and ionization structure, for the global flux and for the different kinematical components. The latter was derived by comparing the oxygen and sulphur ionic ratios to their corresponding observed emission line ratios (the $\eta$ and $\eta$' plots) in different regions of the galaxy. Applying the direct method or empirical relationships for abundance determination, we perform a comparative analysis between these regions. The similarities found in the ionization structure of the different kinematical components implies that the effective temperatures of the ionizing radiation fields are very similar in spite of some small differences in the ionization state of the different elements. Therefore the different gaseous kinematical components identified in each star forming knot are probably ionized by the same star cluster. However, the difference in the ionizing structure of the two knots with knot A showing a lower effective temperature than knot B, suggests a different evolutionary stage for them consistent with the presence of an older and more evolved stellar population in the first.

Using echelle spectroscopy, obtained at Las Campanas Observatory, we present a detailed study of the internal kinematics of the nebular material in multiple knots of the blue compact dwarf galaxy Haro 15. A detailed analysis of the complex emission line profiles show the presence of an underlying broad component in almost all knots, and the brightest star-forming region shows unmistakable signs for the presence of two distinct narrow kinematical components. We also study the information that our analysis provides regarding the motion of the individual knots in the Haro 15 galaxy potential, confirming that they follow galactic rotation. Finally, we examine the relation between their velocity dispersion and luminosity, finding that almost all knots follow the relation for virialised systems. This holds for the strong narrow components identified in complex fits and for single profile fits, although the latter show a flatter slope. In agreement with previous findings, in this paper we show that the existence of multiple kinematical components among massive starbursts cannot be overlooked, as it has a noticeable effect on any subsequent analysis that relies on basic parameters.

We have analysed spectra obtained with the Gemini Multi Object Spectrograph (GMOS) for more than 50 stars in the ionising cluster of 30Doradus during a seven epochs observing campaign at Gemini South. We derive a binary candidate rate of about 50%, which is however consistent with an intrinsic 100% binary rate among massive stars. After decontaminating the sample from the stars that show binary orbital motions, we were able to calculate the "true" cluster velocity dispersion and found it to be about 8 km s-1. This value implies a virial mass of about 4.5 × 10M⊙ which is consistent with previous photometric mass determinations therefore suggesting that NGC 2070 is a firm candidate for a future globular cluster., Facultad de Ciencias Astronómicas y Geofísicas

We present results of a search for giant H II regions in southern galaxies. Using high-resolution spectra, obtained with the Magellan Inamori Kyocera Echelle (MIKE) at the Las Campanas Magellan II telescope, we were able to resolve the emission-line profiles and determine the intrinsic velocity dispersion of the ionized gas. Out of four observed regions, selected from previous CCD narrow-band photometry, we detected three H II regions showing supersonic velocity dispersion, characteristic of giant H II regions, and their location in diagnostic diagrams suggests that a powerful starburst is the source of ionization energy., Facultad de Ciencias Astronómicas y Geofísicas

We present spectral types for 175 stars in the ionising cluster of 30 Doradus derived from multislit observations of 231 stars. Comparison with published classifications for 70 stars in common with other authors reveals excellent agreement with the exception of a few cases which are discussed in detail. Our new observations raise to 261 the total number of stars in 30 Dor with known spectral types, outside R136. We analyse the spatial distribution of these stars according to their spectral types, and find evidence for mass segregation.

We present new results from our search for Giant H\,{\sc ii} Regions in galaxies visible from the southern hemisphere. In this work we study two galaxies: NGC\,7479 and NGC\,6070. Using high-resolution spectra, obtained with different instruments at Las Campanas Observatory, we are able to resolve the emission-line profile widths and determine the intrinsic velocity dispersion of the ionised gas. We detect profile widths corresponding to supersonic velocity dispersions in the six observed H\,{\sc ii} regions. We find that all of them show at least two distinct kinematical components: a relatively narrow feature (between ~11 and ~22\kms) and a broader (between ~31 and ~77\kms) component. Two of the regions show a complex narrow profile in all ion lines, which can be further split into two components with different radial velocities. Whereas the wing broadening of the overall profile can be fitted with a low-intensity broad component for almost all profiles, in one region it was better reproduced by two separate shell-like wings. We have analysed the impact that the presence of multiple components has on the location of the H{\sc ii} regions in the $\log(L) - \log(\sigma)$ plane. Although the overall distribution confirms the presence of a regression, the precise location of the regions in the plane is strongly dependent on the components derived from the profile fitting.

We present a detailed study of the physical properties of the nebular material in multiple knots of the blue compact dwarf galaxy Haro 15. Using long slit and echelle spectroscopy, obtained at Las Campanas Observatory, we study the physical conditions (electron density and temperature), ionic and total chemical abundances of several atoms, reddening and ionization structure. The latter was derived by comparing the oxygen and sulphur ionic ratios to their corresponding observed emission line ratios (the eta and eta' plots) in different regions of the galaxy. Applying direct and empirical methods for abundance determination, we perform a comparative analysis between these regions., Comment: (Poster paper) 2 pages, 2 figures

We have obtained accurate CCD narrow band H_beta and H_alpha photometry of Giant HII Regions in M 33, NGC 6822 and M 101. Comparison with previous determinations of emission line fluxes show large discrepancies; their probable origins are discussed. Combining our new photometric data with global velocity dispersion (sigma) derived from emission line widths we have reviewed the L(H_beta)-sigma relation. A reanalysis of the properties of the GEHRs included in our sample shows that age spread and the superposition of components in multiple regions introduce a considerable spread in the regression. Combining the information available in the literature regarding ages of the associated clusters, evolutionary footprints on the interstellar medium, and kinematical properties of the knots that build up the multiple GEHRs, we have found that a subsample - which we refer to as young and single GEHRs - do follow a tight relation in the L-sigma plane., Comment: Accepted for publication in MNRAS, large figures available on a separate tarfile

A new method is used to determine masses, ages, and reddening for the stars of the starburst cluster NGC 2070 in 30 Doradus. The data are consistent with a star-formation rate which increases exponentially with a characteristic rise time of 1.7 Myr, independent of mass, starting 7 Myr ago. The IMF is consistent with a single power law IMF with Salpeter slope over the whole 3 M⊙ < M < 120 M⊙ range investigated, with evidence for flattening for the innermost radial bin.