• Pulsating low-mass white dwarfs in the frame of new evolutionary sequences : VI. Thin H-envelope sequences and asteroseismology of ELMV stars revisited 

      Calcaferro, Leila Magdalena; Córsico, Alejandro Hugo; Althaus, Leandro Gabriel; Romero, Alejandra Daniela; Kepler, Souza Oliveira (2018) [Artigo de periódico]
      Context. Some low-mass white-dwarf (WD) stars with H atmospheres currently being detected in our galaxy, show long-period g(gravity)-mode pulsations, and comprise the class of pulsating WDs called extremely low-mass variable ...
    • Pulsating white dwarfs 

      Kepler, Souza Oliveira; Romero, Alejandra Daniela (2017) [Artigo de periódico]
      The Sloan Digital Sky Survey has allowed us to increase the number of known white dwarfs by a factor of five and consequently the number of known pulsating white dwarfs also by a factor of five. It has also led to the ...
    • Pulsation in the white dwarf HE 1017−1352 

      Romero, Alejandra Daniela; Amaral, Larissa Antunes; Kepler, Souza Oliveira; Fraga, Luciano; Kurtz, Donald W.; Shibahashi, Hiromoto (2020) [Artigo de periódico]
      We report the detection of periodic variations on the Teff 32 000 K DA white dwarf star HE 1017−1352. We obtained time series photometry using the 4.1-m Southern Astrophysical Research telescope on three separate nights ...
    • Seismology of a massive pulsating hydrogen atmosphere white dwarf 

      Kepler, Souza Oliveira; Pelisoli, Ingrid Domingos; Antonio, Viviane Peçanha; Costa, Jose Eduardo da Silveira; Fraga, Luciano; Hermes, James J.; Winget, Donald Earl; Castanheira, Bárbara Garcia; Córsico, Alejandro Hugo; Romero, Alejandra Daniela; Althaus, Leandro Gabriel; Kleinman, Scot James; Nitta, Atsuko (2012) [Artigo de periódico]
      We report our observations of the new pulsating hydrogen atmosphere white dwarf SDSS J132350.28+010304.22. We discovered periodic photometric variations in frequency and amplitude that are commensurate with nonradial g-mode ...
    • A study of cool white dwarfs in the Sloan Digital Sky Survey Data Release 12 

      Ourique, Gustavo; Romero, Alejandra Daniela; Kepler, Souza Oliveira; Koester, Detlev; Amaral, Larissa Antunes (2019) [Artigo de periódico]
      In this work, we study white dwarfs where 30 000K > Teff > 5000K to compare the differences in the cooling of DAs and non-DAs and their formation channels. Our final sample is composed by nearly 13 000 DAs and more than 3 ...
    • The age-metallicity dependence for white dwarf stars 

      Romero, Alejandra Daniela; Campos, Fabíola; Kepler, Souza Oliveira (2015) [Artigo de periódico]
      We present a theoretical study on themetallicity dependence of the initial-to-final mass relation and its influence on white dwarf age determinations. We compute a grid of evolutionary sequences from the main sequence to ...
    • The impact of the uncertainties in the 12C(α, γ ) 16O reaction rate on the evolution of low- to intermediate-mass stars 

      Pepper, Ben Thomas; Istrate, Alina G.; Romero, Alejandra Daniela; Kepler, Souza Oliveira (2022) [Artigo de periódico]
      One of the largest uncertainties in stellar evolutionary computations is the accuracy of the considered reaction rates. The 12C(α, γ ) 16O reaction is particularly important for the study of low- and intermediate-mass stars ...
    • The rate of cooling of the pulsating white dwarf star G117−B15A : a new asteroseismological inference of the axion mass 

      Córsico, Alejandro Hugo; Althaus, Leandro Gabriel; Bertolami, Marcelo Miguel Miller; Romero, Alejandra Daniela; García-Berro, Enrique; Isern, J.; Kepler, Souza Oliveira (2012) [Artigo de periódico]
    • The sdA problem : II. Photometric and spectroscopic follow-up 

      Pelisoli, Ingrid Domingos; Kepler, Souza Oliveira; Koester, Detlev; Castanheira, Bárbara Garcia; Romero, Alejandra Daniela; Fraga, Luciano (2018) [Artigo de periódico]
      The spectral classification ‘subdwarfA’ (sdA) is given to stars showingH-rich spectra and submain- sequence surface gravities, but effective temperature lower than the zero-age horizontal branch. Their evolutionary origin ...
    • The white dwarf mass–radius relation and its dependence on the hydrogen envelope 

      Romero, Alejandra Daniela; Kepler, Souza Oliveira; Joyce, Simon R. G.; Ramos, Gabriel Lauffer; Córsico, Alejandro Hugo (2019) [Artigo de periódico]
      We present a study of the dependence of the mass–radius relation for DA white dwarf stars on the hydrogen envelope mass and the impact on the value of log g, and thus the determination of the stellar mass. We employ a set ...
    • Toward ensemble asteroseismology of ZZ Ceti stars with fully evolutionary models 

      Romero, Alejandra Daniela; Córsico, Alejandro Hugo; Althaus, Leandro Gabriel; Kepler, Souza Oliveira; Castanheira, Bárbara Garcia; Bertolami, Marcelo Miguel Miller (2012) [Artigo de periódico]
      ZZ Ceti stars form the most numerous group of degenerate variable stars. They are otherwise normal DA (H-rich atmospheres) white dwarfs that exhibit pulsations. Here, we present an asteroseismological analysis for 44 bright ...
    • Uncovering the chemical structure of the pulsating low-mass white dwarf SDSS J115219.99+024814.4 

      Romero, Alejandra Daniela; Ramos, Gabriel Lauffer; Istrate, Alina G.; Parsons, Steven (2022) [Artigo de periódico]
      Pulsating low-mass white dwarf (WD) stars are WDs with stellar masses between 0.30 and 0.45 M⊙ that show photometric variability due to gravity-mode pulsations. Within this mass range, they can harbour both a helium core ...
    • White dwarf and subdwarf stars in the Sloan Digital Sky Survey Data Release 14 

      Kepler, Souza Oliveira; Pelisoli, Ingrid Domingos; Koester, Detlev; Reindl, Nicole; Geier, Stephan; Romero, Alejandra Daniela; Ourique, Gustavo; Oliveira, Cristiane de Paula; Amaral, Larissa Antunes (2019) [Artigo de periódico]
      White dwarfs carry information on the structure and evolution of the Galaxy, especially through their luminosity function and initial-to-final mass relation. Very cool white dwarfs provide insight into the early ages of ...
    • White dwarf and subdwarf stars in the Sloan Digital Sky Survey Data Release 16 

      Kepler, Souza Oliveira; Koester, Detlev; Pelisoli, Ingrid Domingos; Romero, Alejandra Daniela; Ourique, Gustavo (2021) [Artigo de periódico]
      White dwarfs are the end state of the evolution of more than 97 per cent of all stars, and therefore carry information on the structure and evolution of the Galaxy through their luminosity function and initial-to-final ...
    • White dwarf variability with gPhoton : pulsators 

      Tucker, Michael A.; Fleming, S.W.; Pelisoli, Ingrid Domingos; Romero, Alejandra Daniela; Bell, Keaton; Kepler, Souza Oliveira; Caton, Daniel B.; Debes, John; Montgomery, Michael Houston; Thompson, S. E.; Koester, Detlev; Million, Chase; Shiao, Bernie (2018) [Artigo de periódico]
      We present results from a search for short time-scale white dwarf variability using gPhoton, a time-tagged data base of GALEX photon events and associated software package. We conducted a survey of 320 white dwarf stars ...