arXiv subjects

R. V. Ibañez Bustos

Publications and source records attributed to R. V. Ibañez Bustos.

9 recordsLinked to original sources

arXiv2026

Interferometric Survey of Stellar Parameters: Limb darkening study with the "Pipeline for Interferometric Measurements of Stars"

Accurate and unbiased determination of stellar parameters is of importance in many astrophysical domains. We therefore present an improved method to estimate stellar parameters, based on interferometric observations and stellar atmosphere models, as well as spectroscopic and photometric data. The fundamental stellar parameters were estimated by fitting a model of intensity profiles to interferometric data over a large spectral window and combining them with spectroscopic and photometric observations as an additional constraint on the fitting. Based on stellar atmosphere models, we have developed an algorithm that trains artificial neural networks (ANNs) to estimate the spectrum and intensity profile of a star over three bands: R, H, and K. The ANNs cover effective temperatures (Teff) ranging from 4500-7000 K for dwarf stars and 2500-8000 K for giant stars, with surface gravities (log g) ranging from 3.0-5.0 dex and -0.5-3.5 dex, respectively, and 12 viewing angles. As a result, consistent and precise stellar parameters, such as Teff, log g, and angular diameter ($θ$), can be estimated. We fitted $ι$ Psc (F7V) and $δ$ Ari (G9.5IIIb) observed with SPICA, MIRC-X, and MYSTIC at the CHARA Array, and archival data of $α$ Cen A and B (G2V and K1V) from VLTI/PIONIER with PIMS. For angular diameter estimations, when fitting with a one-dimensional stellar atmosphere model, we reached a precision of 0.5%. For Teff and radius, we obtained a precision of approximately 1%, while we obtained a precision of 5% for log g. Through evolutionary models, we further show how these constraints can improve the mass and age determination, as they attain a precision of approximately 2% for mass and 5-10% for age.

astro-ph.SR↗

arXiv2026

Multi-chromatic observations of classical Cepheids using the CHARA Array interferometer: Surface brightness-colour relation, projection factor, and limb-darkening

The Baade-Wesselink (BW) method compares the linear and angular variations of Cepheids to derive their distance. This method is limited, however, by the projection factor, which relates the observed radial velocity to the true pulsation velocity of the star. Using simultaneous observations from the CHARA Array interferometer in the K, H, and R bands with the MYSTIC, MIRC-X, and SPICA combiners, respectively, we aim to understand the physics of Cepheid atmospheres better. Applying a specific method to multi-chromatic simultaneous interferometric observations of Cepheids, we derived robust limb-darkened angular diameters that were then used to calibrate the SBCR and study the projection factor. We also developed a strategy to measure the limb-darkening of Cepheids in R, H, and K bands. These measurements were then used to constrain the geometrical component of the projection factor. From the limb-darkened angular diameter curves of three Cepheids, we decreased the scatter of the SBCR in $V-K$ colour to 0.0011 magnitude and to 0.0040 for the SBCR in $G_{BP}-G_{RP}$. These SBCRs are particularly robust because they are based on multi-chromatic diameters and are homogeneous, which previous calibrations for Cepheids were not. For the very first time, we derived the limb-darkening of Cepheids in R, H, and K bands. For $δ$ Cep, we derived an R-based projection factor of $1.275 \pm 0.051$, and the geometrical part obtained from the measured limb-darkening coefficient in R band was estimated to $1.420 \pm 0.016$ (on average), as expected from stellar static and hydrodynamical atmosphere models. The limb-darkening coefficients obtained in H and K band are consistent with models. These results demonstrate that multi-chromatic interferometry can improve the accuracy of the BW method. It is therefore essential to continue the CHARA survey of Cepheids in the coming years.

astro-ph.SR↗

arXiv2026

CHARA/SPICA: The six-telescope visible combiner and near-infrared fringe tracker for the CHARA Array

The suite called Stellar Parameters and Images with a Cophased Array (SPICA) has two interferometric instruments installed at the focus of the CHARA Array located at Mount Wilson, CA. SPICA is made of SPICA-VIS, a fiber-fed six-beam visible spectrograph with three spectral resolutions, and SPICA-FT, a six-beam near-infrared fringe tracker for the fast stabilization of the fringes. SPICA is opening access to imaging in the visible domain with an unprecedented angular resolution down to 0.2 milliarcseconds. It has been designed around a large survey of fundamental parameters of stars over the Hertzsprung- Russell diagram, aiming at understanding the deviations from the standard empirical relations of stellar physics as a function of activity: limb darkening, multiplicity, rotation, winds, and environments. SPICA makes use of the advanced technologies in electron multiplying detectors in the visible and electron- avalanche photodiode arrays in the near-infrared. It benefits from the newly commissioned adaptive optics on the one-meter telescopes of the array. The modules of the visible instrument, SPICA-VIS, optimize the injection of light into single-mode fibers for spatial filtering before spectral dispersion in the image plane. The fringe tracker, SPICA-FT, performs group-delay and phase-delay tracking for six beams in the H band. SPICA-FT can use an all-in-one or ABCD encoding of the fringe signals. SPICA is operational on sky and is close to reaching the expected performance in low spectral resolution, in particular, for the Interferometric Survey of Stellar Parameters (ISSP). More work is still needed to achieve the ultimate performance in terms of sensitivity and to allow operations with higher spectral resolutions.

astro-ph.IM↗

arXiv2025

Characterisation of magnetic activity of M dwarfs. Possible impact on the surface brightness

Context. M dwarfs are an ideal laboratory for hunting Earth-like planets, and the study of chromospheric activity is an important part of this task. On the one hand, its short-term activity show high levels of magnetic activity that can affect habitability and make it difficult to detect exoplanets orbiting around them. But on the other hand, long-term activity studies can show whether these stars exhibit cyclical behavior or not in their activity, facilitating the detection of planets in those periods of low magnetic activity. Aims. The long-term cyclical behavior of magnetic activity can be detected studying several spectral lines and explained by different stellar dynamo models. In this work, we studied the Mount Wilson $S$-index to search for evidence of activity cycles possibly driven by a solar-type dynamo. Methods. We studied a sample of 35 dM with spectral classes ranging from dM0 to dM6. To perform this, we used 2965 spectra in the optical range to build time series with extensions of up to 21 years. We have analysed thesm with different time-domain techniques to detect cyclical patterns. In addition, we have also studied the potential impact of chromospheric activity on the surface brightness. Results. Using the color index (V-Ks), we have computed the chromospheric emission levels and we found that the majority of the stars in the sample have low emission levels. In this work, we have detected 13 potential activity cycles with a duration between 3 and 19 years and with false alarm probabilities (FAPs) less than 0.1%. For stars with non-cyclic behaviour, we have found that the mean value of the $S$-Index varies between 0.350 and 1.765 and its mean variability and chromospheric emission level are around 12% and -5.110 dex, respectively. We do not find any impact of chromospheric activity on the surface brightness in the domain of -5.6 < log $R'_{HK}$ < -4.5.

astro-ph.SR↗

arXiv2023

Elemental abundances differences in the massive planet-hosting wide binary HD 196067-68

It has been suggested that small chemical anomalies observed in planet-hosting wide binary systems could be due to planet signatures, where the role of the planetary mass is still unknown. We search for a possible planet signature by analyzing the Tc trends in the remarkable binary system HD196067-HD196068. At the moment, only HD196067 is known to host a planet which is near the brown dwarf regime. We take advantage of the strong physical similarity between both stars, which is crucial to achieving the highest possible precision in stellar parameters and elemental chemical abundances. This system gives us a unique opportunity to explore if a possible depletion of refractories in a binary system could be inhibited by the presence of a massive planet. We performed a line-by-line chemical differential study, employing the non-solar-scaled opacities, in order to reach the highest precision in the calculations. After differentially comparing both stars, HD196067 displays a clear deficiency in refractory elements in the Tc plane, a lower iron content (0.051 dex) and also a lower Li I content (0.14 dex) than its companion. In addition, the differential abundances reveal a Tc trend. These targets represent the first cases of an abundance difference around a binary system hosting a super-Jupiter. Although we explored several scenarios to explain the chemical anomalies, none of them can be entirely ruled out. Additional monitoring of the system as well as studies of larger sample of wide binary systems hosting massive planets, are needed to better understand the chemical abundance trend observed in HD196067-68.

astro-ph.SR↗

arXiv2023

Correlation between activity indicators: H$α$ and Ca II lines in M-dwarf stars

Different approaches have been adopted to study short- and long-term stellar magnetic activity, and although the mechanisms by which low-mass stars generate large-scale magnetic fields are not well understood, it is known that stellar rotation plays a key role. There are stars that show a cyclical behaviour in their activity which can be explained by solar dynamo or $αΩ$ dynamo models. However, when studying late-type dwarf stars, it is necessary to implement other indicators to analyse their magnetic activity. In the present work, we perform a comparative study between the best-known activity indicators so far defined from the Ca II and H$α$ lines to analyse M-dwarf stars. We studied a sample of 29 M stars with different chromospheric activity levels and spectral classes ranging from dM0 to dM6. To do so, we employed 1796 wide range spectra from different instruments with a median time span of observations of 21 yr. In addition, we complemented our data with photometric observations from the TESS space mission for better stellar characterisation and short-term analysis. We obtained a good and significant correlation ($rho = 0.91$) between the indexes defined from the two lines for the whole set of stars in the sample. However, we found that there is a deviation for faster rotators (with $P_{rot} < 4$ days) and higher flare activity (at least one flare per day). There is an overall positive correlation between Ca II and H$α$ emission in dM stars, except during flare events. In particular, we found that low-energy high-frequency flares could be responsible for the deviation in the linear trend in fast-rotator M dwarfs. This implies that the rotation period could be a fundamental parameter to study the stellar activity and that the rotation could drive the magnetic dynamo in low-mass active stars.

astro-ph.SR↗

arXiv2020

Detecting prolonged activity minima in binary stars. The case of $ζ^{2}$ Ret

Context. It is well known that from 1645 to 1715 solar activity was notably low and the number of sunspots was extremely reduced. This epoch is known as the Maunder Minimum (MM). The study of stars in prolonged activity minima like the MM could help to shed light on this enigmatic epoch. Aims. To explore if the star $ζ^{2}$ Ret, which belongs to a binary system, is in a state similar to the MM. We have collected more than 430 spectra acquired between 2000 and 2019 with the HARPS, REOSC, UVES, and FEROS spectrographs. Methods. We performed a detailed long-term activity study of both components using the Mount Wilson index, which is obtained from the Ca II H\&K lines. To search for signs of an activity cycle, we analyzed the resulting time-series with the Generalized Lomb-Scargle and CLEAN periodograms. Results. Our spectroscopic analysis shows a high activity level for zet01 Ret and a significant decrease in the magnetic activity cycle amplitude of $ζ^{2}$ Ret. Thus, the activity difference between both components has been slightly increased ($Δ$log (RHK) $\sim$0.24 dex), when compared to the previously reported value. The long series analyzed here allowed us to recalculate and constrain the period of $ζ^{2}$ Ret to $\sim$7.9 yr. We also detected a long-term activity cycle of $\sim$4.2 yr in $ζ^{1}$ Ret. Conclusions. By analogy with the scenario that proposes a weak solar cycle during the MM, we suggest that activity signatures showed by $ζ^{2}$ Ret, i.e., a very low activity level when compared to its stellar companion, a notably decreasing amplitude ($\sim$47%), and a cyclic behaviour, are possible evidence that this star could be in a MM state. It is, to our knowledge, the first MM candidate star detected through a highly discrepant activity behaviour in a binary system.

astro-ph.SR↗

arXiv2020

Activity-rotation in the dM4 star Gl 729. A possible chromospheric cycle

Recently, new debates about the role of layers of strong shear have emerged in stellar dynamo theory. Further information on the long-term magnetic activity of fully convective stars could help determine whether their underlying dynamo could sustain activity cycles similar to the solar one. We performed a thorough study of the short- and long-term magnetic activity of the young active dM4 star Gl 729. First, we analyzed long-cadence $K2$ photometry to characterize its transient events (e.g., flares) and global and surface differential rotation. Then, from the Mount Wilson $S$-indexes derived from CASLEO spectra and other public observations, we analyzed its long-term activity between 1998 and 2020 with four different time-domain techniques to detect cyclic patterns. Finally, we explored the chromospheric activity at different heights with simultaneous measurements of the H$α$ and the Na I D indexes, and we analyzed their relations with the $S$-Index. We found that the cumulative flare frequency follows a power-law distribution with slope $\sim- 0.73$ for the range $10^{32}$ to $10^{34}$ erg. We obtained $P_{rot} = (2.848 \pm 0.001)$ days, and we found no evidence of differential rotation. We also found that this young active star presents a long-term activity cycle with a length of $\text{about four}$ years; there is less significant evidence of a shorter cycle of $0.8$ year. The star also shows a broad activity minimum between 1998 and 2004. We found a correlation between the S index, on the one hand, and the H$α$ the Na I D indexes, on the other hand, although the saturation level of these last two indexes is not observed in the Ca lines. Because the maximum-entropy spot model does not reflect migration between active longitudes, this activity cycle cannot be explained by a solar-type dynamo. It is probably caused by an $α^2$-dynamo.

astro-ph.SR↗

arXiv2018

Design and implementation of a micro-coil induction magnetometer

We present a micron-sized induction magnetometer designed to measure the magnetic response of superconducting mesoscopic samples. The device is manufactured using the Memscap PolyMUMPs process and consists of two octagonal planar parallel micro-coils covering an area of 240 microns X 240 microns, which are separated by only 2.75 microns. We show that this design is sufficiently sensitive to detect the Meissner transition at zero dc field, of a high-Tc superconductor Bi2Sr2CaCu2O8 disk of 40 microns in diameter and 1 micron in thicknesses.

cond-mat.supr-con↗