Browsing Exact and Earth Sciences by Subject "Estrelas variaveis"

Now showing items 21-40 of 60

    • Evolutionary timescale of the pulsating white dwarf G117-B15A : the most stable optical clock known 

      Kepler, Souza Oliveira; Mukadam, Anjum Shagufta; Winget, Donald Earl; Nather, R. Edward; Metcalfe, Travis S.; Reed, M. D.; Kawaler, Steven D.; Bradley, Paul A. (2000) [Journal article]
      We observe G117-B15A, the most precise optical clock known, to measure the rate of change of the main pulsation period of this blue-edge DAV white dwarf. Even though the obtained value is only within 1 σ, P = (2.3±1.4) x ...

    • HST observations of the pulsating white dwarf GD 358 

      Castanheira, Bárbara Garcia; Nitta, Atsuko; Kepler, Souza Oliveira; Winget, Donald Earl; Koester, Detlev (2005) [Journal article]
      We used time-resolved ultraviolet spectroscopy obtained with the FOS and STIS spectrographs of the Hubble Space Telescope (HST), together with archival IUE observations to measure the effective temperature (Teff), surface ...

    • Identification of RR lyrae stars in multiband, sparsely sampled data from the dark energy survey using template fitting and random forest classification 

      Stringer, Katelyn M.; Santiago, Basilio Xavier; DES Collaboration (2019) [Journal article]
      Many studies have shown that RR Lyrae variable stars (RRL) are powerful stellar tracers of Galactic halo structure and satellite galaxies. The Dark Energy Survey (DES), with its deep and wide coverage (g ~ 23.5 mag in a ...

    • IUE temperatures for white dwarf stars in and around the ZZ ceti instability strip 

      Kepler, Souza Oliveira; Nelan, E.P. (1993) [Journal article]
      We have analyzed ali the archival IUE images of the DA4 and DAS white dwarfs with model atmosphere fluxes incorporating the quasimolecular opacities to obtain a consistent set of temperatures for both the variables and ...

    • Kepler and TESS observations of PG 1159-035 

      Rosa, Gabriela Oliveira da; Kepler, Souza Oliveira; Córsico, Alejandro Hugo; Costa, Jose Eduardo da Silveira; Hermes, James J.; Kawaler, Steven D.; Bell, Keaton; Montgomery, Michael Houston; Provencal, Judith L.; Winget, Donald Earl; Handler, Gerald; Dunlap, Bart; Clemens, J. Christopher; Uzundag, Murat (2022) [Journal article]
      PG 1159-035 is the prototype of the PG 1159 hot (pre-)white dwarf pulsators. This important object was observed during the Kepler satellite K2 mission for 69 days in 59 s cadence mode and by the TESS satellite for 25 days ...

    • Low-mass variable stars in the globular cluster NGC 6397 

      Martinazzi, Elizandra; Kepler, Souza Oliveira; Costa, Jose Eduardo da Silveira (2017) [Journal article]
      We have conducted a photometric survey of the globular cluster NGC 6397 in a search for variable stars. We obtained ∼11 h of time-resolved photometric images with one European Southern Observatory-Very Large Telescope using ...

    • Mass functions and structure of the young open cluster NGC 6611 

      Bonatto, Charles Jose; Santos Junior, Joao Francisco Coelho dos; Bica, Eduardo Luiz Damiani (2006) [Journal article]
      We use J, H and KS 2MASS photometry to study colour–magnitude (CMDs) and colour–colour diagrams, structure and mass distribution in the ionizing open cluster NGC 6611. Reddening variation throughout the cluster region is ...

    • Massive open star clusters using the VVV survey : I. Presentation of the data and description of the approach 

      Chené, André-Nicolas; Borissova, Jura; Clarke, J. R. A.; Bonatto, Charles Jose; Majaess, Daniel J.; Moni Bidin, Christian; Sale, Stuart E.; Mauro, Francesco; Kurtev, Radostin Georgiev; Baume, Gustavo Luis; Feinstein Baigorri, Carlos; Ivanov, Valentin D.; Geisler, Doug; Catelan, Márcio; Minniti, Dante; Lucas, Philip W.; Grijs, Richard de; Kumar, M. S. N. (2012) [Journal article]
      Context. The ESO Public Survey “VISTA Variables in the Vía Láctea” (VVV) provides deep multi-epoch infrared observations for unprecedented 562 sq. degrees of the Galactic bulge, and adjacent regions of the disk. Aims. The ...

    • Measuring the evolution of the most stable optical clock G 117-B15A 

      Kepler, Souza Oliveira; Costa, Jose Eduardo da Silveira; Castanheira, Bárbara Garcia; Winget, Donald Earl; Mullally, Fergal; Nather, R. Edward; Kilic, Mukremin; Von Hippel, Theodore A.; Mukadam, Anjum Shagufta; Sullivan, Denis J. (2005) [Journal article]
      We report our measurement of the rate of change of period with time (˙P ) for the 215 s periodicity in the pulsating white dwarf G 117-B15A, the most stable optical clock known. After 31 years of observations, we have ...

    • A method for simultaneous determination of A/sub v/ and R and applications 

      Ducati, Jorge Ricardo; Ribeiro, Daiana; Rembold, Sandro Barboza (2003) [Journal article]
      A method for the simultaneous determination of the interstellar extinction (AV) and of the ratio of total to selective extinction (R), derived from the 1989 Cardelli, Clayton, & Mathis fitting of the interstellar extinction ...

    • Mode identification of pulsating white dwarfs using the Hubble Space Telescope 

      Kepler, Souza Oliveira; Robinson, E.L.; Koester, Detlev; Clemens, J. Christopher; Nather, R. Edward; Jiang, Xiaojun (2000) [Journal article]
      We have obtained time-resolved ultraviolet spectroscopy for the pulsating DAV stars G226-29 and G185-32 and for the pulsating DBV star PG 1351+489 with the Hubble Space Telescope Faint Object Spectrograph to compare the ...

    • New developments of the ZZ Ceti instability strip : the discovery of 11 new variables 

      Castanheira, Bárbara Garcia; Kepler, Souza Oliveira; Kleinman, Scot James; Nitta, Atsuko; Fraga, Luciano (2010) [Journal article]
      Using the The SOuthern Astrophysical Research (SOAR) 4.1-m telescope, we report on the discovery of low amplitude pulsations for three stars previously reported as not-observed-tovary (NOV) by Mukadam et al. and Mullally ...

    • A new luminous blue variable : R143 in 30 Doradus 

      Parker, Joel Wm.; Clayton, Geoffrey C.; Winge, Claudia; Conti, Peter S. (1993) [Journal article]
      We have discovered that R143 in the Large Magellanic Cloud is a luminous blue variable (LBV), the first and perhaps the lone LBV in the central cluster of 30 Doradus, and only the sixth known LMC LBV. Photo­ metric and ...

    • New pulsating db white dwarf stars from the Sloan Digital Sky Survey 

      Nitta, Atsuko; Kleinman, Scot James; Krzesinski, Jerzy; Kepler, Souza Oliveira; Metcalfe, Travis S.; Mukadam, Anjum Shagufta; Mullally, Fergal; Nather, R. Edward; Sullivan, Denis J.; Thompson, S. E.; Winget, Donald Earl (2009) [Journal article]
      We are searching for new He atmosphere white dwarf pulsators (DBVs) based on the newly found white dwarf stars from the spectra obtained by the Sloan Digital Sky Survey. DBVs pulsate at hotter temperature ranges than their ...

    • New SX Phe variables in the globular cluster NGC 288 

      Martinazzi, Elizandra; Kepler, Souza Oliveira; Costa, Jose Eduardo da Silveira; Pieres, Adriano; Bonatto, Charles Jose; Bica, Eduardo Luiz Damiani; Fraga, Luciano (2015) [Journal article]
      We report the discovery of two new variable stars in the metal-poor globular cluster NGC 288, found by means of time series CCD photometry. We classified the new variables as SX Phoenicis (SX Phe) due to their characteristic ...

    • A new ZZ Ceti white dwarf pulsator : G30-20 

      Mukadam, Anjum Shagufta; Kepler, Souza Oliveira; Winget, Donald Earl; Bergeron, P. (2002) [Journal article]
      We report the discovery of a new hydrogen atmosphere variable white dwarf (DAV; ZZ Ceti), G30-20, a high-amplitude, long-period pulsator. The Fourier transform of its light curve shows power around 1050–1125 s. We suspect ...

    • NGC 6749 : a metal-poor halo globular in a disc field rich in mira variables 

      Rosino, L.; Ortolani, Sergio; Barbuy, Beatriz; Bica, Eduardo Luiz Damiani (1997) [Journal article]
      We present V, I photometry of the loose star cluster NGC 6749, and for the first time colour-magnitude diagrams are provided. We confirm that it is a globular cluster and its blue horizontal branch indicates that it is ...

    • Nonradial pulsation of the unevolved hot (gamma) scuti star cd-24 7599 discovered with the whole earth telescope 

      Handler, Gerald; Breger, M.; Sullivan, Denis J.; Peet, A.J. van der; Clemens, J. Christopher; O'Donoghue, Darragh; Chen, A.-L.; Kanaan Neto, Antonio Nemer; Sterken, C.; Claver, C.F.; Krisciunas, K.; Kleinman, Scot James; Wickramasinghe, D.T.; Wills, Beverley J.; Provencal, Judith L.; Nather, R. Edward; Winget, Donald Earl; Watson, Todd K.; Barstow, Martin A.; Buckley, David A.H. (1996) [Journal article]
      We report a frequency analysis of the δ Scuti star CD-24°7599 and the discovery that it pulsates nonradially with at least 7 frequencies between 27.01 and 38.11 cycles per day (312 to 441 μHz). These results are based on ...

    • Normal modes and discovery of high-order cross-frequencies in the DBV white dwarf GD 358 

      Vuille, F.; O'Donoghue, Darragh; Buckley, David A.H.; Massacand, C.N.; Solheim, Jan-Eric; Bard, S.; Vauclair, Gérard; Giovannini Junior, Odilon; Kepler, Souza Oliveira; Kanaan Neto, Antonio Nemer; Provencal, Judith L.; Wood, Matthew A.; Clemens, J. Christopher; Kleinman, Scot James; O'Brien, M. Sean; Nather, R. Edward; Winget, Donald Earl; Nitta, Atsuko; Klumpe, Eric W.; Montgomery, Michael Houston; Watson, Todd K.; Bradley, Paul A.; Sullivan, Denis J.; Wu, K.; Marar, T.M. Krishnan; Seetha, S.; Ashoka, B.N.; Mahra, H.S.; Bhat, B.C.; Babu, V.C.; Leibowitz, Elia M.; Hemar, Shirley; Ibbetson, Peter A.; Mashal, E.; Meistas, Edmundas G.; Moskalik, Pawel; Zola, Staszek; Krzesinski, Jerzy; Pajdosz, Gabriel (2000) [Journal article]
      We present a detailed mode identification performed on the 1994 Whole Earth Telescope (WET) run on GD 358. The results are compared with that obtained for the same star from the 1990 WET data. The two temporal spectra show ...

    • Observational limits on companions to g29-38 

      Kleinman, Scot James; Nather, R. Edward; Winget, Donald Earl; Clemens, J. Christopher; Bradley, Paul A.; Kanaan Neto, Antonio Nemer; Provencal, Judith L.; Claver, C.F.; Watson, Todd K.; Yanagida, K.; Dixson, James S.; Wood, Matthew A.; Sullivan, Denis J.; Meistas, Edmundas G.; Leibowitz, Elia M.; Moskalik, Pawel; Zola, Staszek; Pajdosz, Y.; Krzesinski, Jerzy; Solheim, Jan-Eric; Bruvold, A.; O'Donoghue, Darragh; Katz, M.; Vauclair, Gérard; Dolez, Noël; Chevreton, Michel; Barstow, Martin A.; Kepler, Souza Oliveira; Giovannini Junior, Odilon; Hansen, Carl J.; Kawaler, Steven D. (1994) [Journal article]
      Recent interest in the variable (DAV) white dwarf G29-38 has been stirred by a tentative report of a radial velocity variation that may be due to an unseen companion. Earlier evidence for a brown dwarf in the system has ...