25 research outputs found
Asteroseismology of the GW Virginis stars SDSS J0349-0059 and VV 47
We present an asteroseismological study of SDSS J0349-0059 and VV 47 aimed
mainly at deriving their total mass on the basis of state-of-the-art PG 1159
evolutionary models. We compute adiabatic nonradial -mode pulsation periods
for PG 1159 evolutionary models with stellar masses ranging from to
0.741\ M_{\sun}, that take into account the complete evolution of the
progenitor stars. We first estimate a mean period spacing for both SDSS
J0349-0059 and VV 47. By comparing the observed period spacing with the
asymptotic period spacing we obtain M_{\star}\sim 0.569\ M_{\sun} for SDSS
J0349-0059 and M_{\star}\sim 0.523\ M_{\sun} for VV 47. If we compare the
observed period spacing with the average of the computed period spacings we
found M_{\star}\sim 0.535\ M_{\sun} for SDSS J0349-0059 and M_{\star}\sim
0.528 M_{\sun} for VV 47. Searching for the best period fit we found, in the
case of SDSS J0349-0059, an asteroseismological model with $M_{\star}= 0.542\
M_{\sun}T_{\rm eff}= 91\, 255\ P_{\rm rot}= 1/\Omega \sim 0.407$
days. The results presented in this work constitute a further step in the study
of GW Vir stars through asteroseismology in the frame of fully evolutionary
models of PG 1159 stars. In particular, once again it is shown the potential of
asteroseismology to derive stellar masses of PG 1159 stars with an
unprecedented precision.Comment: 13 pages, 16 figures, 6 tables. To be published in Astronomy and
Astrophysic
Exploring the internal rotation of the extremely low-mass He-core white dwarf GD 278 with TESS asteroseismology
(Abridged) We present an exploration of the internal rotation of GD 278, the
first pulsating extremely low-mass white dwarf that shows rotational splittings
within its periodogram. We assess the theoretical frequency splittings expected
for different rotation profiles and compare them to the observed frequency
splittings of GD 278. To this aim, we employ an asteroseismological model
representative of the pulsations of this star, obtained by using the LPCODE
stellar evolution code. We also derive a rotation profile that results from
detailed evolutionary calculations carried out with the MESA stellar evolution
code and use it to infer the expected theoretical frequency splittings. We
found that the best-fitting solution when assuming linear profiles for the
rotation of GD 278 leads to values of the angular velocity at the surface and
the center that are only slightly differential, and still compatible with rigid
rotation. The values of the angular velocity at the surface and the center for
the simple linear rotation profiles and for the rotation profile derived from
evolutionary calculations are in very good agreement. Also, the resulting
theoretical frequency splittings are compatible with the observed frequency
splittings, in general, for both cases. The results obtained from the different
approaches followed in this work to derive the internal rotation of GD 278
agree. The fact that they were obtained employing two independent stellar
evolution codes gives robustness to our results. Our results suggest only a
marginally differential behavior for the internal rotation in GD 278, and
considering the uncertainties involved, very compatible with the rigid case, as
has been observed previously for white dwarfs and pre-white dwarfs. The
rotation periods derived for this star are also in line with the values
determined asteroseismologically for white dwarfs and pre-white dwarfs in
general.Comment: 9 pages, 6 figures. Accepted for publication in Astronomy &
Astrophysic
White dwarf-main-sequence binaries from Gaia EDR3: The unresolved 100 pc volume-limited sample
We use the data provided by the Gaia Early Data Release 3 to search for a highly-complete volume-limited sample of unresolved binaries consisting of a white dwarf and a main sequence companion (i.e. WDMS binaries) within 100 pc. We select 112 objects based on their location within the Hertzsprung-Russell diagram, of which 97 are new identifications. We fit their spectral energy distributions (SED) with a two-body fitting algorithm implemented in VOSA (Virtual Observatory SED Analyser) to derive the effective temperatures, luminosities and radii (hence surface gravities and masses) of both componentsARM acknowledges financial support from the MINECO under the
Ramón y Cajal program (RYC-2016-20254). ST and ARM acknowledge support from the MINECO under the AYA2017-86274-P grant,
and the AGAUR grant SGR-661/2017. ESM and FJE acknowledge
financial support from the MINECO under the AYA2017-86274-P
grant. FJE acknowledges support from the H2020 ESCAPE project
(Grant Agreement no. 824064). LMC, LGA and AHC acknowledge
support from AGENCIA through the Programa de Modernización
Tecnológica BID 1728/OC-AR, and from CONICET through the
PIP 2017-2019 GI grant. This publication makes use of VOSA
and SVO DiscTool, developed under the Spanish Virtual Observatory project supported from the Spanish MINECO through grant
AyA2017-84089. This research has made use of Aladin sky atlas
developed at CDS, Strasbourg Observatory, France (Bonnarel et al.
2000; Boch & Fernique 2014). TOPCAT (Taylor 2005) and STILTS
(Taylor 2006) have also been widely used in this paper.
We thank the anonymous referee for the helpful suggestions. The
authors are greatly indebted to Detlev Koester for sharing his grid
of model atmosphere white dwarf spectra. The authors also thank
Roberto Raddi for sharing the grid of white dwarf absolute magnitudes calculated for the Gaia EDR3 bandpasses.
This work has made use of data from the European Space
Agency (ESA) mission Gaia (https://www.cosmos.esa.int/
gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, https://www.cosmos.esa.int/web/gaia/dpac/
consortium). Funding for the DPAC has been provided by national
institutions, in particular the institutions participating in the Gaia
Multilateral AgreementPostprint (updated version
A refined search for pulsations in white dwarf companions to millisecond pulsars
We present optical high-speed photometry of three millisecond pulsars with low-mass (< 0.3M⊙) white dwarf companions, bringing the total number of such systemswith follow-up time-series photometry to five. We confirm the detection of pulsations in one system, the white dwarf companion to PSR J1738+0333, and show that the pulsation frequencies and amplitudes are variable over many months. A full asteroseismic analysis for this star is underconstrained, but the mode periods we observe are consistent with expectations for an M⁎ = 0.16-0.19 M⊙ white dwarf, as suggested from spectroscopy. We also present the empirical boundaries of the instability strip for low-mass white dwarfs based on the full sample of white dwarfs, and discuss the distinction between pulsating low-mass white dwarfs and subdwarf A/F stars.Instituto de Astrofísica de La PlataFacultad de Ciencias Astronómicas y Geofísica
White dwarf-main sequence binaries from Gaia EDR3 : the unresolved 100 pc volume-limited sample
We use the data provided by the Gaia Early Data Release 3 to search for a highly-complete volume-limited sample of unresolved binaries consisting of a white dwarf and a main sequence companion (i.e. WDMS binaries) within 100 pc. We select 112 objects based on their location within the Hertzsprung-Russell diagram, of which 97 are new identifications. We fit their spectral energy distributions (SED) with a two-body fitting algorithm implemented in VOSA (Virtual Observatory SED Analyser) to derive the effective temperatures, luminosities and radii (hence surface gravities and masses) of both components. The stellar parameters are compared to those from the currently largest catalogue of close WDMS binaries, from the Sloan Digital Sky Survey (SDSS). We find important differences between the properties of the Gaia and SDSS samples. In particular, the Gaia sample contains WDMS binaries with considerably cooler white dwarfs and main sequence companions (some expected to be brown dwarfs). The Gaia sample also shows an important population of systems consisting of cool and extremely low-mass white dwarfs, not present in the SDSS sample. Finally, using a Monte Carlo population synthesis code, we find that the volume-limited sample of systems identified here seems to be highly complete (≃ 80 ± 9 per cent), however it only represents ≃9 per cent of the total underlying population. The missing ≃91 per cent includes systems in which the main sequence companions entirely dominate the SEDs. We also estimate an upper limit to the total space density of close WDMS binaries of ≃ (3.7 ± 1.9) × 10-4 pc-3.Fil: Rebassa Mansergas, A. Universidad Politécnica de Catalunya. Departament de Física Enginyeria; EspañaFil: Solano, E.. CSIC-INTA. Centro de Astrobiología; EspañaFil: Jiménez Esteban, F. M.. CSIC-INTA. Centro de Astrobiología; EspañaFil: Torres, S.. Universidad Politécnica de Catalunya. Departament de Física Enginyeria; EspañaFil: Rodrigo, C.. CSIC-INTA. Centro de Astrobiología; EspañaFil: Ferrer Burjachs, A. Universidad Politécnica de Catalunya. Departament de Física Enginyeria; EspañaFil: Calcaferro, Leila Magdalena. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; ArgentinaFil: Althaus, Leandro Gabriel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; ArgentinaFil: Córsico, Francisco Armando. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; Argentin
A refined search for pulsations in white dwarf companions to millisecond pulsars
We present optical high-speed photometry of three millisecond pulsars with low-mass (< 0.3M⊙) white dwarf companions, bringing the total number of such systemswith follow-up time-series photometry to five. We confirm the detection of pulsations in one system, the white dwarf companion to PSR J1738+0333, and show that the pulsation frequencies and amplitudes are variable over many months. A full asteroseismic analysis for this star is underconstrained, but the mode periods we observe are consistent with expectations for an M⁎ = 0.16-0.19 M⊙ white dwarf, as suggested from spectroscopy. We also present the empirical boundaries of the instability strip for low-mass white dwarfs based on the full sample of white dwarfs, and discuss the distinction between pulsating low-mass white dwarfs and subdwarf A/F stars.Instituto de Astrofísica de La PlataFacultad de Ciencias Astronómicas y Geofísica
La Universidad contribuye a revalorizar la Ciencia en la Escuela Primaria.
A partir de la crisis económica del año 2002, un grupo de docentes, estudiantes e investigadores de distintas Unidades Académicas de la UNLP, nos acercamos a las Escuelas Públicas y Estatales con la intención de contribuir y fomentar la enseñanza de las Ciencias Naturales a través de la experimentación, en el marco del proyecto de Extensión "La Facultad va a la Escuela del Barrio". Un objetivo del proyecto es crear vínculos dinámicos y horizontales con Escuelas Primarias de la provincia de Buenos Aires. La estrategia de intervención se centra en la realización, con los docentes, de talleres basados en la currícula escolar e incluye tanto una planificación como una evaluación conjunta, dando un rol activo a los docentes en todas las instancias. Los talleres constituyen un dispositivo analizador, no sólo de conocimientos teóricos, sino también de las prácticas áulicas. Se parte de los conocimientos previos de las maestras, se busca problematizar e hipotetizar diferentes fenómenos naturales y, a partir de los resultados de una secuencia de experiencias, arribar a las conclusiones, discutiendo, además, su implementación en el aula. La planificación conjunta permite la incorporación del trabajo realizado al proceso de enseñanza-aprendizaje en forma natural. La intervención no se reduce a unos pocos encuentros y a un grupo definido de personas sino que apuesta a que el docente se apropie de metodologías científicas y revalorice el conocimiento científico como significativo, principalmente en instituciones cuya comunidad se encuentra inmersa en una dura realidad socio-económica. La interacción dentro del ámbito escolar nos interioriza de la realidad institucional, lo cuál no sólo permite analizar las variables institucionales para definir la estrategia de articulación sino que enriquece nuestra formación docente-profesional. La constitución interdisciplinaria del grupo (ver que pertenecemos a distintas facultades y/o carreras) permite garantizar respuestas a las inquietudes de las maestras, las cuales suelen abarcar diferentes temas, consecuencia de que su conocimiento proviene de múltiples recortes disciplinares. El Proyecto realiza una autoevaluación continua, analizando la pertinencia de la estrategia de intervención y los resultados obtenidos. Al finalizar el ciclo lectivo realizamos una evaluación conjunta con cada colegio. De ambas evaluaciones rescatamos los siguientes indicadores: el impacto positivo que conlleva la implementación en el aula; la adquisición de equipamiento de laboratorio por parte de las escuelas; la creación de nuevos talleres surgidos de las inquietudes de las docentes; el efecto multiplicador hacia otras instituciones, todo ello consecuencia de la movilidad docente y/o del interés de las sedes de inspección y nuestra incorporación al Proyecto Institucional.
Pulsating low-mass white dwarfs in the frame of new evolutionary sequences
Context. Many pulsating low-mass white dwarf stars have been detected in the past years in the field of our Galaxy. Some of them exhibit multiperiodic brightness variation, therefore it is possible to probe their interiors through asteroseismology.
Aims. We present a detailed asteroseismological study of all the known low-mass variable white dwarf stars based on a complete set of fully evolutionary models that are representative of low-mass He-core white dwarf stars.
Methods. We employed adiabatic radial and nonradial pulsation periods for low-mass white dwarf models with stellar masses ranging from 0.1554 to 0.4352 M⊙ that were derived by simulating the nonconservative evolution of a binary system consisting of an initially 1 M⊙ zero-age main-sequence (ZAMS) star and a 1.4 M⊙ neutron star companion. We estimated the mean period spacing for the stars under study (where this was possible), and then we constrained the stellar mass by comparing the observed period spacing with the average of the computed period spacings for our grid of models. We also employed the individual observed periods of every known pulsating low-mass white dwarf star to search for a representative seismological model.
Results. We found that even though the stars under analysis exhibit few periods and the period fits show multiplicity of solutions, it is possible to find seismological models whose mass and effective temperature are in agreement with the values given by spectroscopy for most of the cases. Unfortunately, we were not able to constrain the stellar masses by employing the observed period spacing because, in general, only few periods are exhibited by these stars. In the two cases where we were able to extract the period spacing from the set of observed periods, this method led to stellar mass values that were substantially higher than expected for this type of stars.
Conclusions. The results presented in this work show the need for further photometric searches, on the one hand, and that some improvements of the theoretical models are required on the other hand in order to place the asteroseismological results on a firmer ground
Pulsating low-mass white dwarfs in the frame of new evolutionary sequences
Context. An increasing number of low-mass (M⋆/M⊙ ≲ 0.45) and extremely low-mass (ELM, M⋆/M⊙ ≲ 0.18−0.20) white-dwarf stars are being discovered in the field of the Milky Way. Some of these stars exhibit long-period g-mode pulsations, and are called ELMV variable stars. Also, some low-mass pre-white dwarf stars show short-period p-mode (and likely radial-mode) photometric variations, and are designated as pre-ELMV variable stars. The existence of these new classes of pulsating white dwarfs and pre-white dwarfs opens the prospect of exploring the binary formation channels of these low-mass white dwarfs through asteroseismology.
Aims. We aim to present a theoretical assessment of the expected temporal rates of change of periods (\hbox{}) for such stars, based on fully evolutionary low-mass He-core white dwarf and pre-white dwarf models.
Methods. Our analysis is based on a large set of adiabatic periods of radial and nonradial pulsation modes computed on a suite of low-mass He-core white dwarf and pre-white dwarf models with masses ranging from 0.1554 to 0.4352 M⊙, which were derived by computing the non-conservative evolution of a binary system consisting of an initially 1 M⊙ ZAMS star and a 1.4 M⊙ neutron star companion.
Results. We computed the secular rates of period change of radial (ℓ = 0) and nonradial (ℓ = 1,2) g and p modes for stellar models representative of ELMV and pre-ELMV stars, as well as for stellar objects that are evolving just before the occurrence of CNO flashes at the early cooling branches. We find that the theoretically expected magnitude of \hbox{} of g modes for pre-ELMVs is by far larger than for ELMVs. In turn, \hbox{} of g modes for models evolving before the occurrence of CNO flashes are larger than the maximum values of the rates of period change predicted for pre-ELMV stars. Regarding p and radial modes, we find that the larger absolute values of \hbox{} correspond to pre-ELMV models.
Conclusions. We conclude that any eventual measurement of a rate of period change for a given pulsating low-mass pre-white dwarf or white dwarf star could shed light about its evolutionary status. Also, in view of the systematic difficulties in the spectroscopic classification of stars of the ELM Survey, an eventual measurement of \hbox{} could help to confirm that a given pulsating star is an authentic low-mass white dwarf and not a star from another stellar population