Southern Observatory for Astrophysical Research

La Serena, Chile

Southern Observatory for Astrophysical Research

La Serena, Chile
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Bullock E.,University of Washington | Szkody P.,University of Washington | Mukadam A.S.,University of Washington | Borges B.W.,Federal University of Grande Dourados | And 15 more authors.
Astronomical Journal | Year: 2011

The prototype of accreting, pulsating white dwarfs (GW Lib) underwent a large amplitude dwarf nova outburst in 2007. We used ultraviolet data from Galaxy Evolution Explorer and ground-based optical photometry and spectroscopy to follow GW Lib for three years following this outburst. Several variations are apparent during this interval. The optical shows a superhump modulation in the months following outburst, while a 19 minute quasi-periodic modulation lasting for several months is apparent in the year after outburst. A long timescale (about 4 hr) modulation first appears in the UV a year after outburst and increases in amplitude in the following years. This variation also appears in the optical two years after outburst but is not in phase with the UV. The pre-outburst pulsations are not yet visible after three years, likely indicating the white dwarf has not returned to its quiescent state. © 2011. The American Astronomical Society. All rights reserved..


Romero A.D.,Federal University of Rio Grande do Sul | Kepler S.O.,Federal University of Rio Grande do Sul | Corsico A.H.,National University of La Plata | Corsico A.H.,CONICET | And 4 more authors.
Revista Mexicana de Astronomia y Astrofisica: Serie de Conferencias | Year: 2014

We performed the first asteroseismological study for 42 massive DA variable white dwarf, or ZZ Ceti stars, based on detailed and fully evolutionary models representative of these stars.


Paunzen E.,Masaryk University | Iliev I.K.,Bulgarian Academy of Science | Pintado O.I.,Instituto Superior Of Correlacion Geologica | Baum H.,University of Vienna | And 7 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2014

Globular clusters are main astrophysical laboratories to test and modify evolutionary models. Thought to be rather homogeneous in their local elemental distribution of members, results suggest a wide variety of chemical peculiarities. Besides different main sequences, believed to be caused by different helium abundances, peculiarities of blue horizontal-branch stars and on the red giant branch were found. This whole zoo of peculiar objects has to be explained in the context of stellar formation and evolution. The tool of Δ photometry is employed in order to detect peculiar stars in the whole spectral range. This three filter narrowband system measures the flux distribution in the region from 4900 to 5600 Å in order to find any peculiarities around 5200 Å. It is highly efficient to detect classical chemically peculiar stars of the upper main sequence, Be/Ae, shell and metal-weak objects in the Milky Way and Magellanic Clouds. We present Δa photometry of 2266 stars from 109 individual frames for three globular clusters (NGC 104, NGC 6205, and NGC 7099). A comparison with published abundances, for three horizontal-branch stars, only, yields an excellent agreement. According to the 3s detection limit of each globular cluster, about 3 per cent of the stars lie in abnormal regions in the diagnostic diagrams. The first observations of three widely different aggregates give very promising results, which will serve as a solid basis for follow-up observations including photometric as well as spectroscopic studies. © 2014 The Authors.Published by Oxford University Press on behalf of the Royal Astronomical Society.


Castanheira B.G.,Federal University of Rio Grande do Sul | Castanheira B.G.,Institute For Astronomie | Kepler S.O.,Federal University of Rio Grande do Sul | Kleinman S.J.,Gemini Observatory | And 2 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2010

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-to-vary (NOV) by Mukadam et al. and Mullally et al., which are inside the ZZ Ceti instability strip. With the two pulsators discovered by Castanheira et al., we have now found variability in a total of five stars previously reported as NOVs. We also report the variability of eight new pulsating stars, not previously observed, bringing the total number of known ZZ Ceti stars to 148. In addition, we lowered the detection limit for 10 NOVs located near the edges of the ZZ Ceti instability strip. Our results are consistent with a pure mass-dependent ZZ Ceti instability strip. © 2010 The Authors. Journal compilation © 2010 RAS.


Castanheira B.G.,Institute For Astronomie | Kepler S.O.,Federal University of Rio Grande do Sul | Kleinman S.J.,Gemini Observatory | Nitta A.,Gemini Observatory | Fraga L.,Southern Observatory for Astrophysical Research
Monthly Notices of the Royal Astronomical Society | Year: 2013

Using the SOuthern Astrophysical Research telescope (SOAR) Optical Imager at the SOAR 4.1 m telescope, we report on the discovery of five new massive pulsating white dwarf stars. Our results represent an increase of about 20 per cent in the number of massive pulsators. We have detected both short and long periods, low and high amplitude pulsation modes, covering the whole range of the ZZ Ceti instability strip. In this paper, we present a first seismological study of the new massive pulsators based on the few frequencies detected. Our analysis indicates that these stars have masses higher than average, in agreement with the spectroscopic determinations. In addition, we study for the first time the ensemble properties of the pulsating white dwarf stars with masses above 0.8 M⊙. We found a bimodal distribution of the main pulsation period with the effective temperature for the massive DAVs, which indicates mode selection mechanisms. © 2013 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.


Dalessio J.,University of Delaware | Dalessio J.,Delaware Asteroseismology Research Center | Sullivan D.J.,Victoria University of Wellington | Provencal J.L.,University of Delaware | And 7 more authors.
Astrophysical Journal | Year: 2013

Variations in the pulsation arrival time of five independent pulsation frequencies of the DB white dwarf EC 20058-5234 individually imitate the effects of reflex motion induced by a planet or companion but are inconsistent when considered in unison. The pulsation frequencies vary periodically in a 12.9 year cycle and undergo secular changes that are inconsistent with simple neutrino plus photon-cooling models. The magnitude of the periodic and secular variations increases with the period of the pulsations, possibly hinting that the corresponding physical mechanism is located near the surface of the star. The phase of the periodic variations appears coupled to the sign of the secular variations. The standards for pulsation-timing-based detection of planetary companions around pulsating white dwarfs, and possibly other variables such as subdwarf B stars, should be re-evaluated. The physical mechanism responsible for this surprising result may involve a redistribution of angular momentum or a magnetic cycle. Additionally, variations in a supposed combination frequency are shown to match the sum of the variations of the parent frequencies to remarkable precision, an expected but unprecedented confirmation of theoretical predictions. © 2013. The American Astronomical Society. All rights reserved..


Romero A.D.,Federal University of Rio Grande do Sul | Kepler S.O.,Federal University of Rio Grande do Sul | Corsico A.H.,National University of La Plata | Corsico A.H.,CONICET | And 4 more authors.
Astrophysical Journal | Year: 2013

We present the first asteroseismological study for 42 massive ZZ Ceti stars based on a large set of fully evolutionary carbon-oxygen core DA white dwarf models characterized by a detailed and consistent chemical inner profile for the core and the envelope. Our sample comprises all of the ZZ Ceti stars with spectroscopic stellar masses between 0.72 and 1.05 M known to date. The asteroseismological analysis of a set of 42 stars enables study of the ensemble properties of the massive, pulsating white dwarf stars with carbon-oxygen cores, in particular the thickness of the hydrogen envelope and the stellar mass. A significant fraction of stars in our sample have stellar mass that is high enough to crystallize at the effective temperatures of the ZZ Ceti instability strip, which enables us to study the effects of crystallization on the pulsation properties of these stars. Our results show that the phase diagram presented in Horowitz et al. seems to be a good representation of the crystallization process inside white dwarf stars, in agreement with the results from white dwarf luminosity function in globular clusters. © 2013. The American Astronomical Society. All rights reserved..


Kepler S.O.,Federal University of Rio Grande do Sul | Pelisoli I.,Federal University of Rio Grande do Sul | Pecanha V.,Federal University of Rio Grande do Sul | Costa J.E.S.,Federal University of Rio Grande do Sul | And 14 more authors.
Astrophysical Journal | Year: 2012

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 pulsations in ZZ Ceti stars. This, along with estimates for the star's temperature and gravity, establishes it as a massive ZZ Ceti star. We used time-series photometric observations with the 4.1m SOAR Telescope, complemented by contemporary McDonald Observatory 2.1m data, to discover the photometric variability. The light curve of SDSS J132350.28+010304.22 shows at least nine detectable frequencies. We used these frequencies to make an asteroseismic determination of the total mass and effective temperature of the star: M= 0.88 ± 0.02 M and T eff = 12, 100 ± 140 K. These values are consistent with those derived from the optical spectra and photometric colors. © 2012. The American Astronomical Society. All rights reserved.


Fraga L.,Southern Observatory for Astrophysical Research | Fraga L.,Laboratorio Nacional Of Astrofisica Mcti | Kunder A.,Cerro Tololo Inter American Observatory | Tokovinin A.,Cerro Tololo Inter American Observatory
Astronomical Journal | Year: 2013

We present high-quality BVRI photometric data in the field of globular cluster NGC 6496 obtained with the SOAR Telescope Adaptive Module (SAM). Our observations were collected as part of the ongoing SAM commissioning. The distance modulus and cluster color excess as found from the red clump are (m-M)V = 15.71 ± 0.02 mag and E(V-I) = 0.28 ± 0.02 mag. An age of 10.5 ± 0.5 Gyr is determined from the difference in magnitude between the red clump and the subgiant branch. These parameters are in excellent agreement with the values derived from isochrone fitting. From the color-magnitude diagram we find a metallicity of [Fe/H] = -0.65 dex and hence support a disk classification for NGC 6496. The complete BVRI data set for NGC 6469 is made available in the electronic edition of the Journal. © 2013. The American Astronomical Society. All rights reserved.


Paunzen E.,Bulgarian Academy of Science | Paunzen E.,University of Vienna | Heiter U.,Uppsala University | Fraga L.,Southern Observatory for Astrophysical Research | Pintado O.,Instituto Superior Of Correlacion Geologica
Monthly Notices of the Royal Astronomical Society | Year: 2012

The small group of λ Bootis stars comprises late B- to early F-type stars, with moderate to extreme (up to a factor of 100) surface underabundances of most Fe-peak elements and solar abundances of lighter elements (C, N, O and S). The main mechanisms responsible for this phenomenon are atmospheric diffusion, meridional mixing and accretion of material from their surroundings. In particular, spectroscopic binary (SB) systems with λ Bootis-type components are very important to investigate the evolutionary status and accretion process in more detail. For HD 210111, δ Scuti-type pulsation was also found, which gives the opportunity to use the tools of asteroseismology for further investigations. The latter could result in strict constraints for the amount of diffusion for this star. Together with models for the accretion and its source, this provides a unique opportunity to shed more light on these important processes. We present classification and high-resolution spectra for HD 210111. A detailed investigation of the most likely combinations of single star components was performed. For this, composite spectra with different stellar astrophysical parameters were calculated and compared to the observations to find the best-fitting combination. HD 210111 comprises two equal (within the estimated errors) stars with T eff= 7400K, logg= 3.8dex, [M/H] =-1.0dex and vsini= 30kms -1. This result is in line with other strict observational facts published so far for this object. This is only the third detailed investigation of the λ Bootis-type SB system, but the first one with a known infrared excess. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.

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