14 research outputs found
Library of flux-calibrated echelle spectra of southern late-type dwarfs with different activity levels
No full textWe present Echelle spectra of 91 late-type dwarfs, of spectral types from F to M and of different levels of chromospheric activity, obtained with the 2.15 m telescope of the CASLEO Observatory located in the Argentinean Andes. Our observations range from 3890 to 6690 Å at a spectral resolution from 0.141 to 0.249 Å per pixel (R = λ/δλ ≈ 26 400). The observations were flux calibrated with the aid of long slit spectra. A version of the calibrated spectra is available via the World Wide Web†.Fil: Cincunegui, Carolina Cecilia. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Mauas, Pablo Jacobo David. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentin
A possible activity cycle in Proxima Centauri
No full textContext.Several late-type stars present activity cycles resembling the Solar one. This fact has been observed mostly in stars ranging from F to K, i.e., in stars with a radiative core and an outer convective layer.
Aims.This work aims at studying whether an activity cycle can be detected in the dM5.5e star Proxima Centauri, which is supposed to be completely convective.
Methods.We present periodical medium-resolution echelle observations covering the complete visual range, which were taken at the CASLEO Argentinean Observatory. These observations are distributed over 7 years. We discarded the spectra that present flare activity, and analyze the remaining activity levels using four different statistical techniques to look for a period of activity.
Results.We find strong evidence of a cyclic activity, with a period of ~442 days. We also estimate that the Ca S index varies around 130% due to activity variations outside of flares.Fil: Cincunegui, Carolina Cecilia. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Diaz, Rodrigo Fernando. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Mauas, Pablo Jacobo David. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentin
Hα and the Ca II H and K lines as activity proxies for late-type stars
No full textContext.The main chromospheric activity indicator is the S index, which is the ratio of the flux in the core of the Ca II H and K lines to the continuum nearby, and is well studied for stars from F to K. Another chromospheric proxy is the Hα line, which is believed to be tightly correlated with the Ca II index. Aims.In this work we characterize both chromospheric activity indicators, the one associated with the H and K Ca II lines and the other with Hα, for the whole range of late type stars, from F to M. Methods.We present periodic medium-resolution echelle observations covering the complete visual range, taken at the CASLEO Argentinean Observatory over 7 years. We use a total of 917 flux-calibrated spectra for 109 stars that range from F6 to M5. We statistically study these two indicators for stars of different activity levels and spectral types. Results.We directly derive the conversion factor that translates the known S index to flux in the Ca II cores, and extend its calibration to a wider spectral range. We investigate the relation between the activity measurements in the calcium and hydrogen lines, and found that the usual correlation observed is the product of the dependence of each flux on stellar colour, and not the product of similar activity phenomena.Fil: Cincunegui, Carolina Cecilia. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Diaz, Rodrigo Fernando. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Mauas, Pablo Jacobo David. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentin
(Anti)-epistemology in Charles Taylor’s philosophical anthropology
No full textEste artículo aborda las fuentes de la (anti)-Epistemología en la obra del autor canadiense Charles Taylor. El punto de partida de su crítica a las
posiciones representacionalistas que caracterizan los trasfondos de signifi cación de nuestra cultura a partir del siglo XVII, son las obras de Hegel,
Heidegger, Wittgenstein y Merleau Ponty. De acuerdo con Taylor, estos fi lósofos nos han ofrecido recursos para enfrentarnos a la imagen de la agencia
desvinculada que promueven las fi losofías naturalistas, dándonos como alternativa una comprensión del anthropos como un sujeto encarnado, como un agente vinculado con una cultura y una forma de vida.This article discusses the sources of the (anti)-Epistemology in the work of the Canadian author Charles Taylor. The starting point of his critique to the
representationalist positions that characterize the backgrounds of signifi cance in our culture from the seventeenth century onward, are the works of
Hegel, Heidegger, Wittgenstein and Merleau Ponty. According to Taylor, these philosophers have given us resources to confront the image of disengaged
agency promoted by naturalistic philosophies, giving us an alternative understanding of the anthropos as an embodied subject, an agent linked to a culture and a way of [email protected]
Innovación y desarrollo territorial en aglomeraciones industriales periféricas: el caso del Polo Petroquímico de Bahía Blanca (Argentina)
No full textSince the 1980s, under a post-fordism scenery an “imagery” has been developed that represents regions as carriers of an opportunity for being more flexible and innovative than large national units. It has been emphasized also that foreign investments have an impact on innovation initiatives when an articulated social, economic and institutional context open to novelty and change exists. Regions, therefore, abandoned their position as “objects” of development to become “subjects” in charge of their own territorial development process. Under this new perspective, this article presents results of a study on innovation and territorial development in peripheral industrial agglomerations. This research analyses in the case of Bahía Blanca’s Petrochemical Pole. Investigates whether large enterprises activities have promoted territory’s competitiveness by pushing the advantages of proximity and located interaction.Bajo un escenario postfordista, se ha desarrollado desde la década de 1980 un “imaginario” que presenta a las regiones como portadoras de la oportunidad de actuar en forma más flexible e innovadora que las grandes unidades nacionales. Se ha enfatizado también el impacto de las inversiones extranjeras para el surgimiento de iniciativas innovadoras, siempre que exista un entorno social, económico e institucional articulado y receptivo a la novedad y al cambio. Así las regiones abandonan su pretérita situación de “objetos” de desarrollo para colocarse como “sujetos” encargados de reemprender su proceso de desarrollo territorial. Considerando este nuevo enfoque, el artículo expone los resultados de una investigación sobre innovación y desarrollo territorial en aglomeraciones industriales periféricas y analiza, para el caso del Polo Petroquímico de Bahía Blanca, si la actuación de las grandes empresas del Polo ha propiciado la competitividad del territorio al impulsar las ventajas de la proximidad y la interacción localizada
Chromospheric models of solar analogues with different activity levels
No full textWe computed chromospheric models of the Sun as a star and of nine solar
analogues. The atmospheric models were constructed to obtain the best possible match
with the Ca II K and Hβ lines, including the asymmetry of the lines due to
macroscopic velocity fields. The stars were chosen with
(the solar ) and have a wide variety of magnetic activity levels,
which allows us to study the differences in atmospheric
structures induced by activity.
For the less active stars we found that the changes with activity are in the region of
the temperature minimum, while the
most active stars show changes all along their
atmospheric structures, mainly in the upper chromosphere.
Regarding the macroscopic velocity fields, we can distinguish between the two groups.
The most active group has a velocity field in the temperature-minimum region, and the other
group in the chromospheric plateau. We also computed the net radiative losses
for each model, and found that they depend linearly on the usual index of
chromospheric activity, SCa II.
Hide and seek : radial-velocity searches for planets around active stars
No full textThe detection of low-mass extra-solar planets through radial-velocity searches is currently limited by the intrinsic magnetic activity of the host stars. The correlated noise that arises from their natural radial-velocity variability can easily mimic or conceal the orbital signals of super-Earth and Earth-mass extra-solar planets. I developed an intuitive and robust data analysis framework in which the activity-induced variations are modelled with a Gaussian process that has the frequency structure of the photometric variations of the star, thus allowing me to determine precise and reliable planetary masses.
I applied this technique to three recently discovered planetary systems: CoRoT-7,
Kepler-78 and Kepler-10. I determined the masses of the transiting super-Earth
CoRoT-7b and the small Neptune CoRoT-7c to be 4.73 ± 0.95 M⊕ and 13.56 ±
1.08 M⊕, respectively. The density of CoRoT-7b is 6.61 ± 1.72 g.cm⁻³, which is
compatible with a rocky composition. I carried out Bayesian model selection to
assess the nature of a previously identified signal at 9 days, and found that it is best
interpreted as stellar activity. Despite the high levels of activity of its host star, I
determined the mass of the Earth-sized planet Kepler-78b to be 1.76 ± 0.18 M⊕.
With a density of 6.2(+1.8:-1.4) g.cm⁻³, it is also a rocky planet. I found the masses of Kepler-10b and Kepler-10c to be 3.31 ± 0.32 M⊕ and 16.25 ± 3.66 M⊕, respectively. Their densities, of 6.4(+1.1:-0.7) g.cm⁻³ and 8.1 ± 1.8 g.cm⁻³, imply that they are both of rocky composition – even the 2 Earth-radius planet Kepler-10c!
In parallel, I deepened our understanding of the physical origin of stellar radial-velocity variability through the study of the Sun, which is the only star whose surface can be imaged at high resolution. I found that the full-disc magnetic flux is an excellent proxy for activity-induced radial-velocity variations; this result may become key to breaking the activity barrier in coming years.
I also found that in the case of CoRoT-7, the suppression of convective blueshift leads to radial-velocity variations with an rms of 1.82 m.s⁻¹, while the modulation induced by the presence of dark spots on the rotating stellar disc has an rms of 0.46 m.s⁻¹. For the Sun, I found these contributions to be 2.22 m.s⁻¹ and 0.14 m.s⁻¹, respectively. These results suggest that for slowly rotating stars, the suppression of convective blueshift is the dominant contributor to the activity-modulated radial-velocity signal, rather than the rotational Doppler shift of the flux blocked by starspots
The spectroscopic binary system Gl 375
No full textAims.We study the spectroscopic binary system Gl 375 to
characterise its orbit and the spectral types and chromospheric
activity levels of the components.
Methods.We employed medium-resolution echelle spectra obtained at the 2.15 m telescope at the
Argentinian observatory CASLEO and photometric observations obtained
from the ASAS database.
Results.We have separated the composite spectra
into those corresponding to both components. The separated spectra
allow us to confirm that the spectral types of both components are
similar (dMe3.5) and to obtain precise measurements of the orbital
period (P = 1.87844 days), minimum masses ( and ),
and other orbital parameters. The photometric observations exhibit a
sinusoidal variation with the same period as the orbital period. We
interpreted this as signs of active regions carried along with
rotation in a tidally synchronised system, and studied the evolution
of the amplitude of the modulation on longer timescales. Together
with the mean magnitude, the modulation exhibits a roughly cyclic
variation with a period of around 800 days. This periodicity is also
found in the flux of the Ca II K lines of both components, which
seem to be in phase.
Conclusions.The periodic changes in the three observables
are interpreted as a sign of a stellar activity cycle. Both
components appear to be in phase, which implies that they are
magnetically connected. The measured cycle of ≈2.2 years
(≈800 days) is consistent with previous determinations of
activity cycles in similar stars
The HARPS search for southern extra-solar planets : XXXVIII. Bayesian re-analysis of three systems. New super-Earths, unconfirmed signals, and magnetic cycles
No full textWe present the analysis of the entire HARPS observations of three stars that host planetary systems: HD 1461, HD 40307, and HD 204313. The data set spans eight years and contains more than 200 nightly averaged velocity measurements for each star. This means that it is sensitive to both long-period and low-mass planets and also to the effects induced by stellar activity cycles. We modelled the data using Keplerian functions that correspond to planetary candidates and included the short- and long-term effects of magnetic activity. A Bayesian approach was taken both for the data modelling, which allowed us to include information from activity proxies such as log R'HK in the velocity modelling, and for the model selection, which permitted determining the number of significant signals in the system. The Bayesian model comparison overcomes the limitations inherent to the traditional periodogram analysis. We report an additional super-Earth planet in the HD 1461 system. Four out of the six planets previously reported for HD 40307 are confirmed and characterised. We discuss the remaining two proposed signals. In particular, we show that when the systematic uncertainty associated with the techniques for estimating model probabilities are taken into account, the current data are not conclusive concerning the existence of the habitable-zone candidate HD 40307 g. We also fully characterise the Neptune-mass planet that orbits HD 204313 in 34.9 days.Peer reviewe
Flares on active M-type stars observed with XMM-Newton and Chandra.
No full textM-type red dwarfs are among the most active stars. Their light curves display random variability of rapid increase and gradual decrease in emission. It is believed that these large energy events, or flares, are the manifestation of the permanently reforming magnetic field of the stellar atmosphere. Stellar coronal flares are observed in the radio, optical, ultraviolet and X-rays. With the new generation of X-ray telescopes, XMM-Newton and Chandra, it has become possible to study these flares in much greater detail than ever before. This thesis focuses on three core issues about flares: (i) how their X-ray emission is correlated with the ultraviolet, (ii) using an oscillation to determine the loop length and the magnetic field strength of a particular flare, and (iii) investigating the change of density sensitive lines during flares using high-resolution X-ray spectra, (i) It is known that flare emission in different wavebands often correlate in time. However, here is the first time where data is presented which shows a correlation between emission from two different wavebands (soft X-rays and ultraviolet) over various sized flares and from five stars, which supports that the flare process is governed by common physical parameters scaling over a large range. (ii) As it is impossible to spatially resolve any but a very few giant stars, the only information on spatial dimensions as well as the magnetic field strength of stellar coronae has to come from indirect measurements. Using wavelet analysis, I isolated the first stellar X-ray flare oscillation. Interpreting it as a standing coronal flare loop oscillation, I derived a flare loop length as well as the magnetic field strength for this X-ray flare. (iii) The high-resolution soft X-ray spectra of Chandra and XMM-Newton allow us to determine temperatures, densities and abundances of the stellar coronae. De spite a low signal-to-noise ratio because of the relatively short duration of a flare, we find that, if adding up the photons of several flares, certain density sensitive spectral lines change significantly between quiescent and flaring states. This project led on to investigate the flaring spectrum further, and it is found that the plasma is no longer in collisional ionisation equilibrium, but that it is dominated by recombinations
