arXiv subjects

E. Bertone

Publications and source records attributed to E. Bertone.

At least 19 recordsLinked to original sources

arXiv2020

Do instabilities in high-multiplicity systems explain the existence of close-in white dwarf planets?

We investigate the origin of close-in planets and related phenomena orbiting white dwarfs (WDs), which are thought to originate from orbits more distant from the star. We use the planetary architectures of the 75 multiple-planet systems (four, five and six planets) detected orbiting main-sequence stars to build 750 dynamically analogous templates that we evolve to the WD phase. Our exploration of parameter space, although not exhaustive, is guided and restricted by observations and we find that the higher the multiplicity of the planetary system, the more likely it is to have a dynamical instability (losing planets, orbit crossing and scattering), that eventually will send a planet (or small object) through a close periastron passage. Indeed, the fraction of unstable four- to six-planet simulations is comparable to the 25-50$\%$ fraction of WDs having atmospheric pollution. Additionally, the onset of instability in the four- to six-planet configurations peaks in the first Gyr of the WD cooling time, decreasing thereafter. Planetary multiplicity is a natural condition to explain the presence of close-in planets to WDs, without having to invoke the specific architectures of the system or their migration through the von Zeipel-Lidov-Kozai (ZLK) effects from binary companions or their survival through the common envelope phase.

astro-ph.EP↗

arXiv2020

Understanding the origin of white dwarf atmospheric pollution by dynamical simulations based on detected three-planet systems

Between 25-50 % of white dwarfs (WD) present atmospheric pollution by metals, mainly by rocky material, which has been detected as gas/dust discs, or in the form of photometric transits in some WDs. Planets might be responsible for scattering minor bodies that can reach stargazing orbits, where the tidal forces of the WD can disrupt them and enhance the chances of debris to fall onto the WD surface. The planet-planet scattering process can be triggered by the stellar mass-loss during the post main-sequence evolution of planetary systems. In this work, we continue the exploration of the dynamical instabilities that can lead to WD pollution. In a previous work we explored two-planet systems found around main-sequence (MS) stars and here we extend the study to three-planet system architectures. We evolved 135 detected three-planet systems orbiting MS stars to the WD phase by scaling their orbital architectures in a way that their dynamical properties are preserved by using the $N$-body integrator package Mercury. We find that 100 simulations (8.6 %) are dynamically active (having planet losses, orbit crossing and scattering) on the WD phase, where low mass planets (1-100 $\mathrm{M}_\oplus$) tend to have instabilities in Gyr timescales while high mass planets ($>100~\mathrm{M}_\oplus$) decrease the dynamical events more rapidly as the WD ages. Besides, 19 simulations (1.6 %) were found to have planets crossing the Roche radius of the WD, where 9 of them had planet-star collisions. Our three-planet simulations have an slight increase percentage of simulations that may contribute to the WD pollution than the previous study involving two-planet systems and have shown that planet-planet scattering is responsible of sending planets close to the WD, where they may collide directly to the WD, become tidally disrupted or circularize their orbits, hence producing pollution on the WD atmosphere.

astro-ph.EP↗

arXiv2020

Dynamical evolution of two-planet systems and its connection with white dwarf atmospheric pollution

Asteroid material is detected in white dwarfs (WDs) as atmospheric pollution by metals, in the form of gas/dust discs, or in photometric transits. Within the current paradigm, minor bodies need to be scattered, most likely by planets, into highly eccentric orbits where the material gets disrupted by tidal forces and then accreted onto the star. This can occur through a planet-planet scattering process triggered by the stellar mass loss during the post main-sequence evolution of planetary systems. So far, studies of the $N$-body dynamics of this process have used artificial planetary system architectures built ad hoc. In this work, we attempt to go a step further and study the dynamical instability provided by more restrictive systems, that, at the same time allow us an exploration of a wider parameter space: the hundreds of multiple planetary systems found around main-sequence (MS) stars. We find that most of our simulated systems remain stable during the MS, Red and Asymptotic Giant Branch and for several Gyr into the WD phases of the host star. Overall, only $\approx$ 2.3$\%$ of the simulated systems lose a planet on the WD as a result of dynamical instability. If the instabilities take place during the WD phase most of them result in planet ejections with just 5 planetary configurations ending as a collision of a planet with the WD. Finally 3.2$\%$ of the simulated systems experience some form of orbital scattering or orbit crossing that could contribute to the pollution at a sustained rate if planetesimals are present in the same system.

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arXiv2018

Wandering near the red edge: photometric observations of three cool ZZ Ceti stars

We summarize our findings on three cool ZZ Ceti type pulsating white dwarfs. We determined eight independent modes in HS 0733+4119, of which seven are new findings. For GD 154, we detected two new eigenmodes, and the recurrence of the pulsational behaviour first observed in 1977. We discuss that GD 154 does not only vary its pulsations between a multiperiodic and a quasi-monoperiodic phase, but there are also differences between the relative amplitudes of the near-subharmonics observed in the latter phase. In the complex pulsator, Ross 808, we compared the pre- and post Whole Earth Telescope campaign measurements, and determined two new frequencies besides the ones observed during the campaign. Studying these stars can contribute to better understanding of pulsations close to the empirical ZZ Ceti red edge. All three targets are in that regime of the ZZ Ceti instability strip where short-term amplitude variations or even outbursts are likely to occur, which are not well-understood theoretically.

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arXiv2017

Asteroseismology of the ZZ Ceti star KUV 08368+4026

Asteroseismology is a unique tool to explore the internal structure of stars through both observational and theoretical research. The internal structure of pulsating hydrogen shell white dwarfs (ZZ Ceti stars) detected by asteroseismology is regarded as the representative of all DA white dwarfs. Observations for KUV~08368+4026, which locates in the middle of the ZZ Ceti instability strip, have been carried out in 1999 and from 2009 to 2012 with either single-site runs or multisite campaigns. Time-series photometric data of about 300 hours were collected in total. Through data reduction and analysis, 30 frequencies were extracted, including four triplets, two doublets, one single mode and further signals. The independent modes are identified as either l=1 or l=2 modes. Hence, a rotation period of $5.52\pm 0.22$ days was deduced from the period spacing in the multiplets. Theoretical static models were built and a best fit model for KUV~08368+4026 was obtained with $0.692\pm0.002$ solar mass, $(2.92\pm0.02)\times 10^{-3}$ solar luminosity and the hydrogen mass fraction of $10^{-4}$ stellar mass.

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arXiv2016

ALMA's view of the Sun's nearest neighbours: The submm/mm SEDs of the alpha Centauri binary and a new source

The precise mechanisms that provide the non-radiative energy for heating the chromosphere and the corona of the Sun and other stars are at the focus of intense contemporary research. Observations at submm/mm wavelengths are particularly useful to obtain information about the run of the temperature in the upper atmosphere of Sun-like stars. We used ALMA to study the chromospheric emission of the aCen binary system in all six available frequency bands during Cycle2 in 2014/15. Since ALMA is an interferometer, the multi-telescope array is particularly suited for the observation of point sources. With its large collecting area, the sensitivity is high enough to allow the observation of nearby main-sequence stars at submm/mm wavelengths for the first time. The comparison of the observed spectral energy distributions with theoretical model computations provides the chromospheric structure in terms of temperature and density above the stellar photosphere and the quantitative understanding of the primary emission processes. Both stars were detected and resolved at all ALMA frequencies. For both aCenA and B, the existence and location of the temperature minima, firstly detected from space with Herschel, are well reproduced by the theoretical models of this paper. For aCenB, the temperature minimum is deeper than for A and occurs at a lower height in the atmosphere, but for both stars, Tmin/Teff is consistently lower than what is derived from optical and UV data. The submm/mm emission of the aCen stars is indeed very well reproduced by modified chromospheric models of the Quiet Sun. This most likely means that the non-radiative heating mechanisms of the upper atmosphere that are at work in the Sun are operating also in other solar-type stars.

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arXiv2016

Deep LMT/AzTEC millimeter observations of Epsilon Eridani and its surroundings

Epsilon Eridani is a nearby, young Sun-like star that hosts a ring of cool debris analogous to the solar system's Edgeworth-Kuiper belt. Early observations at (sub-)mm wavelengths gave tentative evidence of the presence of inhomogeneities in the ring, which have been ascribed to the effect of a putative low eccentricity planet, orbiting close to the ring. The existence of these structures have been recently challenged by high resolution interferometric millimeter observations. Here we present the deepest single-dish image of Epsilon Eridani at millimeter wavelengths, obtained with the Large Millimeter Telescope Alfonso Serrano (LMT). The main goal of these LMT observations is to confirm (or refute) the presence of non-axisymmetric structure in the disk. The dusty ring is detected for the first time along its full projected elliptical shape. The radial extent of the ring is not spatially resolved and shows no evidence, to within the uncertainties, of dust density enhancements. Additional features of the 1.1 mm map are: (i) the presence of significant flux in the gap between the ring and the star, probably providing the first exo-solar evidence of Poynting-Robertson drag, (ii) an unambiguous detection of emission at the stellar position with a flux significantly above that expected from Epsilon Eridani's photosphere, and (iii) the identification of numerous unresolved sources which could correspond to background dusty star-forming galaxies.

astro-ph.EP↗

arXiv2015

A new submm source within a few arcseconds of $α$ Centauri: ALMA discovers the most distant object of the solar system

We recently announced the detection of an unknown submillimeter source in our ALMA observations of alpha Cen AB. The source was detected in two epochs, a strong detection at 445~GHz and one at lower significance at 343.5~GHz. After valuable feedback of the community, it turns out that the detection at 343.5~GHz could not be reproduced with a different reduction software nor with fitting within the $(u,v)$-plane. The detection at 445~GHz has been further confirmed with modeling of the $(u,v)$-data and was shown to be robust at $>12σ$, confirming our detection of this unknown source. However, based on only one epoch, further analysis and preferably new data are needed, before publication of an article in which the nature of the new source can be discussed. The analysis has indicated the importance of both $(u,v)$-plane fitting and alternative data reduction when dealing with low signal to noise source detections.

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arXiv2015

Lithium abundance in a sample of solar-like stars

We report on the determination of the lithium abundance [A(Li)] of 52 solar-like stars. For 41 objects the A(Li) here presented corresponds to the first measurement. We have measured the equivalent widths of the 6708Å lithium feature in high-resolution spectroscopic images ($R \sim 80\,000$), obtained at the Observatorio Astrofísico Guillermo Haro (Sonora, Mexico), as part of the first scientific observations of the revitalized Lunar and Planetary Laboratory (LPL) Echelle Spectrograph, now known as the Cananea High-resolution Spectrograph (CanHiS). Lithium abundances were derived with the Fortran code MOOG, using as fundamental input a set of atmospheric parameters recently obtained by our group. With the help of an additional small sample with previous A(Li) determinations, we demonstrate that our lithium abundances are in agreement, to within uncertainties, with other works. Two target objects stand out from the rest of the sample. The star BD+47 3218 ($T_{\rm eff}$ = 6050$\pm$52 K, A(Li) = 1.86$\pm$ 0.07 dex) lies inside the so-called lithium desert in the the A(Li)--$T_{\rm eff}$ plane. The other object, BD+28 4515, has an A(Li) = 3.05$\pm$0.07 dex, which is the highest of our sample and compatible with the expected abundances of relatively young stars.

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arXiv2014

ALMA observations of alpha Centauri: First detection of main-sequence stars at 3mm wavelength

The precise mechanisms that provide the non-radiative energy for heating the chromosphere and the corona of the Sun and those of other stars constitute an active field of research. By studying stellar chromospheres one aims at identifying the relevant physical processes. Defining the permittable extent of the parameter space can also serve as a template for the Sun-as-a-star. Earlier observations with Herschel and APEX have revealed the temperature minimum of alpha Cen, but these were unable to spatially resolve the binary into individual components. With the data reported here, we aim at remedying this shortcoming. Furthermore, these earlier data were limited to the wavelength region between 100 and 870mu. In the present context, we intend to extend the spectral mapping to longer wavelengths, where the contrast between stellar photospheric and chromospheric emission becomes increasingly evident. ALMA is particularly suited to point sources, such as unresolved stars. ALMA provides the means to achieve our objectives with both its high sensitivity of the collecting area for the detection of weak signals and the high spatial resolving power of its adaptable interferometer for imaging close multiple stars. This is the first detection of main-sequence stars at a wavelength of 3mm. Furthermore, the individual components of the binary alpha CenAB are clearly detected and spatially well resolved at all ALMA wavelengths. The high S/N of these data permit accurate determination of their relative flux ratios. The previously obtained flux ratio of 0.44, which was based on measurements in the optical and at 70mu, is consistent with the present ALMA results, albeit with a large error bar. Given the distinct difference in their cyclic activity, the similarity of their submm SEDs appears surprising.

astro-ph.SR↗

arXiv2014

Supersolar metallicity in G0-G3 main sequence stars with V<15

The basic stellar atmospheric parameters (effective temperature, surface gravity and global metallicity) were simultaneously determined for a sample of 233 stars, limited in magnitude ($V<15$) with spectral types between G0 and G3 and luminosity class V (main sequence). The analysis was based on spectroscopic observations collected at the Observatorio Astrofísico Guillermo Haro and using a set of Lick-like indices defined in the spectral range of 3800-4800 $Å$. An extensive set of indices computed in a grid of theoretical spectra was used as a comparison tool in order to determine the photospheric parameters. The method was validated by matching the results from spectra of the asteroids Vesta and Ceres with the Sun parameters. The main results were: i) the photospheric parameters were determined for the first time for 213 objects in our sample; ii) a sample of 20 new super metal-rich stars candidates was found.

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arXiv2013

UB CCD photometry of the old, metal rich, open clusters NGC 6791, NGC 6819 and NGC 7142

We report on a UV-oriented imaging survey in the fields of the old, metal-rich open clusters, NGC 6791, NGC 6819 and NGC 7142. These three clusters represent both very near and ideal stellar aggregates to match the distinctive properties of the evolved stellar populations, as in elliptical galaxies and bulges of spirals. The CMD of the three clusters is analyzed in detail, with special emphasis to the hot stellar component. We report, in this regard, one new extreme horizontal-branch star candidate in NGC 6791. For NGC 6819 and 7142, the stellar luminosity function points to a looser radial distribution of faint lower Main Sequence stars, either as a consequence of cluster dynamical interaction with the Galaxy or as an effect of an increasing fraction of binary stars toward the cluster core, as actually observed in NGC 6791 too.

astro-ph.GA↗

arXiv2012

Flux calibrated emission line imaging of extended sources using GTC/OSIRIS Tunable Filters

We investigate the utility of the Tunable Filters (TFs) for obtaining flux calibrated emission line maps of extended objects such as galactic nebulae and nearby galaxies, using the OSIRIS instrument at the 10.4-m GTC. Despite a relatively large field of view of OSIRIS (8'x8'), the change in the wavelength across the field (~80 Ang) and the long-tail of Tunable Filter (TF) spectral response function, are hindrances for obtaining accurate flux calibrated emission-line maps of extended sources. The purpose of this article is to demonstrate that emission-line maps useful for diagnostics of nebula can be generated over the entire field of view of OSIRIS, if we make use of theoretically well-understood characteristics of TFs. We have successfully generated the flux-calibrated images of the nearby, large late-type spiral galaxy M101 in the emission lines of Halpha, [NII]6583, [SII]6716 and [SII]6731. We find that the present uncertainty in setting the central wavelength of TFs (~1 Ang), is the biggest source of error in the emission-line fluxes. By comparing the Halpha fluxes of HII regions in our images with the fluxes derived from Halpha images obtained using narrow-band filters, we estimate an error of ~11% in our fluxes. The flux calibration of the images was carried out by fitting the SDSS griz magnitudes of in-frame stars with the stellar spectra from the SDSS spectral database. This method resulted in an accuracy of 3% in flux calibration of any narrow-band image, which is as good as, if not better, to that is feasible using the observations of spectrophotometric standard stars. Thus time-consuming calibration images need not be taken. A user-friendly script under the IRAF environment was developed and is available on request.

astro-ph.IM↗

arXiv2011

Wavelength calibration for OSIRIS/GTC* tunable filters

OSIRIS (Optical System for Imaging and low Resolution Integrated Spectroscopy) is the first light instrument of the Gran Telescopio Canarias (GTC). It provides a flexible and competitive tunable filter (TF). Since it is based on a Fabry-Perot interferometer working in collimated beam, the TF transmission wavelength depends on the position of the target with respect to the optical axis. This effect is non-negligible and must be accounted for in the data reduction. Our paper establishes a wavelength calibration for OSIRIS TF with the accuracy required for spectrophotometric measurements using the full field of view (FOV) of the instrument. The variation of the transmission wavelength $λ(R)$ across the FOV is well described by $λ(R)=λ(0)/\sqrt{1+(R/f_2)^2}$, where $λ(0)$ is the central wavelength, $R$ represents the physical distance from the optical axis, and $f_2=185.70\pm0.17\,$mm is the effective focal length of the camera lens. This new empirical calibration yields an accuracy better than 1\,Å across the entire OSIRIS FOV ($\sim$8\arcmin$\times$8\arcmin), provided that the position of the optical axis is known within 45 $μ$m ($\equiv$ 1.5 binned pixels). We suggest a calibration protocol to grant such precision over long periods, upon re-alignment of OSIRIS optics, and in different wavelength ranges. This calibration differs from the calibration in OSIRIS manual which, nonetheless, provides an accuracy $\lesssim1$Å\, for $R\lesssim 2\arcmin$.

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arXiv2011

The underlying stellar absorption contribution to the primordial helium abundance determination

We carried out an exploratory analysis of the contribution of the underlying stellar absorption to the total uncertainty of the abundance of primordial helium using simple stellar populations models and observational data from the Sloan Digital Sky Survey. Results indicate that our analysis yields a lower limit to the error on the helium abundance determination if the stellar absorption is neglected.

astro-ph.CO↗

arXiv2008

A spectroscopic study of the blue stragglers in M67

Based on spectrophotometric observations from the Guillermo Haro Observatory (Cananea, Mexico), a study of the spectral properties of the complete sample of 24 blue straggler stars (BSs) in the old Galactic open cluster M67 (NGC 2682) is presented. All spectra, calibrated using spectral standards, were recalibrated by means of photometric magnitudes in the Beijing-Arizona-Taipei-Connecticut system, which includes fluxes in 11 bands covering ~3500-10000 A. The set of parameters was obtained using two complementary approaches that rely on a comparison of the spectra with (i) an empirical sample of stars with well-established spectral types and (ii) a theoretical grid of optical spectra computed at both low and high resolution. The overall results indicate that the BSs in M67 span a wide range in Teff(~ 5600 -12600 K) and surface gravities that are fully compatible with those expected for main-sequence objects (log g = 3.5 -5.0 dex).

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arXiv2007

New Model Atmospheres: Testing the Solar Spectrum in the UV

We present preliminary results on the calculation of synthetic spectra obtained with the stellar model atmospheres developed by Cardona, Crivellari, and Simonneau. These new models have been used as input within the SYNTHE series of codes developed by Kurucz. As a first step we have tested if SYNTHE is able to handle these models which go down to log tau(Ross)= -13. We have successfully calculated a synthetic solar spectrum in the wavelength region 2000--4500 A at high resolution (R=522,000). Within this initial test we have found that layers at optical depths with log tau(Ross) < -7 significantly affect the mid-UV properties of a synthetic spectrum computed from a solar model. We anticipate that these new extended models will be a valuable tool for the analysis of UV stellar light arising from the outermost layers of the atmospheres.

astro-ph↗

arXiv2007

Population synthesis at short wavelengths and spectrophotometric diagnostic tools for galaxy evolution

Taking advantage of recent important advances in the calculation of high-resolution spectral grids of stellar atmospheres at short wavelengths, and their implementation for population synthesis models, we briefly review here some special properties of ultraviolet emission in SSPs, and discuss their potential applications for identifying and tuning up effective diagnostic tools to probe distinctive evolutionary properties of early-type galaxies and other evolved stellar systems.

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