Astronomical Time Series Analysis. I. A Search for Periodicity Using Information Entropy

Cincotta, Pablo Miguel; Méndez, Mariano; Núñez, Josué A.

doi:10.1086/176050

Cited by 52 publications

(56 citation statements)

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“…m 05 in V J . In spite of many attempts to detect periodicities in the V J -band fluxes and UV emission-line fluxes with both Fourier-methods and information-entropy minimalisation methods (Cincotta et al 1995), no significant periodicity could be found. We were also not able no find any direct correlation between the flux variations in the UV and visual.…”

Section: +463mentioning

confidence: 96%

Modeling of PMS Ae/Fe stars using UV spectra

Blondel

Djie²

2006

A&A

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Context. Spectral classification of PMS Ae/Fe stars, based on visual observations, may lead to ambiguous conclusions. Aims. We aim to reduce these ambiguities by using UV spectra for the classification of these stars, because the rise of the continuum in the UV is highly sensitive to the stellar spectral type of A/F-type stars. Methods. We analyse the low-resolution UV spectra in terms of a 3-component model, that consists of spectra of a central star, of an optically-thick accretion disc, and of a boundary-layer between the disc and star. The disc-component was calculated as a juxtaposition of Planck spectra, while the 2 other components were simulated by the low-resolution UV spectra of well-classified standard stars (taken from the IUE spectral atlases). The hot boundary-layer shows strong similarities to the spectra of late-B type supergiants (see Appendix A). Results. We modeled the low-resolution UV spectra of 37 PMS Ae/Fe stars. Each spectral match provides 8 model parameters: spectral type and luminosity-class of photosphere and boundary-layer, temperature and width of the boundary-layer, disc-inclination and circumstellar extinction. From the results of these analyses, combined with available theoretical PMS evolutionary tracks, we could estimate their masses and ages and derive their mass-accretion rates. For a number of analysed PMS stars we calculated the corresponding SEDs and compared these with the observed SEDs. Conclusions. All stars (except β Pic) show indications of accretion, that affect the resulting spectral type of the stellar photosphere. Formerly this led to ambiguities in classificaton of PMS stars as the boundary-layer was not taken into consideration. We give evidence for an increase of the mass-accretion rate with stellar mass and for a decreases of this rate with stellar age.

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Section: +463mentioning

confidence: 96%

Modeling of PMS Ae/Fe stars using UV spectra

Blondel

Djie²

2006

A&A

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“…The initial period search was conducted using an IDL implementation of the information entropy algorithm of Cincotta et al (1995). The orbit fitting itself (including the final period calculation) was done independently by two of us: J.M.A.…”

Section: Spectroscopic Orbit Of Ls III +46 11mentioning

confidence: 99%

The little-studied cluster Berkeley 90

Apellániz

Negueruela

Barbá

et al. 2015

A&A

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Context. It appears that most (if not all) massive stars are born in multiple systems. At the same time, the most massive binaries are hard to find owing to their low numbers throughout the Galaxy and the implied large distances and extinctions. Aims. We want to study LS III +46 11, identified in this paper as a very massive binary; another nearby massive system, LS III +46 12; and the surrounding stellar cluster, Berkeley 90. Methods. Most of the data used in this paper are multi-epoch high S/N optical spectra, although we also use Lucky Imaging and archival photometry. The spectra are reduced with dedicated pipelines and processed with our own software, such as a spectroscopicorbit code, CHORIZOS, and MGB. Results. LS III +46 11 is identified as a new very early O-type spectroscopic binary [O3.5 If* + O3.5 If*] and LS III +46 12 as another early O-type system [O4.5 V((f))]. We measure a 97.2-day period for LS III +46 11 and derive minimum masses of 38.80 ± 0.83 M and 35.60 ± 0.77 M for its two stars. We measure the extinction to both stars, estimate the distance, search for optical companions, and study the surrounding cluster. In doing so, a variable extinction is found as well as discrepant results for the distance. We discuss possible explanations and suggest that LS III +46 12 may be a hidden binary system where the companion is currently undetected.

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“…In the three cases, we chose a partition of two bins, due to the small number of data points. (Cincotta et al 1995), for the data of Table 2.…”

Section: Behavior Of Hα With Timementioning

confidence: 99%

A possible activity cycle in Proxima Centauri

Cincunegui¹,

Díaz²,

Mauas³

2006

A&A

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Context. 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 II S index varies around 130% due to activity variations outside of flares.

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Astronomical Time Series Analysis. I. A Search for Periodicity Using Information Entropy

Cited by 52 publications

References 0 publications

Modeling of PMS Ae/Fe stars using UV spectra

Modeling of PMS Ae/Fe stars using UV spectra

The little-studied cluster Berkeley 90

A possible activity cycle in Proxima Centauri

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