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J. A. Caballero

Publications and source records attributed to J. A. Caballero.

At least 271 records · Page 15Linked to original sources
arXiv2012

Cool dwarfs in wide multiple systems. Paper 4: a common-proper-motion pair of two identical mid-M dwarfs separated by about 10000 AU

LSPM J0651+1843 and LSPM J0651+1845 are two high-proper-motion stars recently claimed to form a binary system, FMR 83, by Rica (2012). Here we characterize the system in detail, using astrometric and photometric data, and find that the pair consists of two M4+/-1 dwarfs separated by 9500^(+6200)_(-3800) AU. With these results, FMR 83 becomes one of the very few 'ultrafragile' systems (i.e., systems with very low total masses and very wide physical separations), many of which have been identified in this series of papers.

astro-ph.GA↗
arXiv2012

Cool dwarfs in wide multiple systems. Paper 3: Two common-proper-motion, late-type stars separated by over 11 arcmin

LP 209-28 and LP 209-27 have similar proper motions as tabulated by several catalogues. Using seven astrometric epochs spanning 59 years, we confirm a common tangential velocity by measuring a constant angular separation of rho = 666.62+/-0.09 arcsec. Accurate SDSS and 2MASS photometry indicates that they are normal dwarfs of approximate spectral types K7 V and M3 V. However, from their apparent magnitudes, both LP 209-28 and LP 209-27 are located at 200-250 pc, from where one can deduce an astonishing projected physical separation of 0.6-0.8 pc. The system Koenigstuhl 6 AB represents another world record among the least-bound systems with low-mass star components.

astro-ph.GA↗
arXiv2012

Superscaling predictions for neutrino-induced charged-current charged pion production at MiniBooNE

Superscaling approximation (SuSA) predictions to neutrino-induced charged-current charged pion production in the Δ-resonance region are explored under MiniBooNE experimental conditions. The results obtained within SuSA for the flux-averaged double-differential cross sections of the π+ production for the ν_μ+CH_2 reaction as a function of the muon kinetic energy and of the scattering angle, the cross sections averaged over the angle, the total cross section for the π+ production, as well as CC1π+ to CCQE cross section ratio are compared with the corresponding MiniBooNE experimental data. The SuSA predictions are in good agreement with data on neutrino flux average cross-sections, but a somewhat different dependence on the neutrino energy is predicted than the one resulting from the experimental analysis.

nucl-th↗
arXiv2012

Cool dwarfs in wide multiple systems: Paper 2: A distant M8.5V companion to HD 212168 AB

DENIS J222644.3-750342 is a nearby, very-low-mass, M8.5 V-type star that has been repeatedly targeted by kinematic and activity studies. Thought to be an isolated star, it is actually a wide common-proper-companion at 265 arcsec from the bright G0 V Hipparcos star HD 212168. The third member in the trio is CD-75 1242, a poorly investigated K dwarf. We confirm the physical binding of the triple system, to which we call Koenigstuhl 5, by compiling common radial velocities and proper-motions and measuring constant angular separations and position angles between components A, B and C over very long time baselines (A-B: 114 yr; A-C: 22 yr). With about 0.095 Msol, the M8.5 V star at 6090 AU to the G0 V primary is one of the least-bound, ultracool dwarfs in multiple systems.

astro-ph.SR↗
arXiv2012

Meson-exchange currents and quasielastic antineutrino cross sections in the SuperScaling Approximation

We evaluate quasielastic double-differential antineutrino cross sections obtained in a phenomenological model based on the superscaling behavior of electron scattering data and estimate the contribution of the vector meson-exchange currents in the 2p-2h sector. We show that the impact of meson-exchange currents for charge-changing antineutrino reactions is much larger than in the neutrino case.

nucl-th↗
arXiv2012

Identification of red high proper-motion objects in Tycho-2 and 2MASS catalogues using Virtual Observatory tools

Aims: With available Virtual Observatory tools, we looked for new M dwarfs in the solar neighbourhood and M giants with high tangential velocities. Methods: From an all-sky cross-match between the optical Tycho-2 and the near-infrared 2MASS catalogues, we selected objects with proper motions >50mas/yr and very red V-Ks colours. For the most interesting targets, we collected multi-wavelength photometry, constructed spectral energy distributions, estimated effective temperatures and surface gravities from fits to atmospheric models, performed time-series analysis of ASAS V-band light curves, and assigned spectral types from low-resolution spectroscopy obtained with CAFOS at the 2.2m Calar Alto telescope. Results: We got a sample of 59 bright red high proper-motion objects, including fifty red giants, four red dwarfs, and five objects reported in this work for the first time. The five new stars have magnitudes V~10.8-11.3mag, reduced proper motions midway between known dwarfs and giants, near-infrared colours typical of giants, and effective temperatures Teff~2900-3400K. From our time-series analysis, we discovered a long secondary period in Ruber 4 and an extremely long primary period in Ruber 6. With the CAFOS spectra, we confirmed the red giant nature of Ruber 7 and 8, the last of which seems to be one of the brightest metal-poor M giants ever identified.

astro-ph.SR↗
arXiv2012

An Aladin-based search for proper-motion companions to young stars in the Local Association, Tucana-Horologium and beta Pictoris

We have used the Aladin sky atlas of the Virtual Observatory to look for new common proper-motion pairs in three young stellar kinematic groups: Local Association (~10-120 Ma), Tucana-Horologium (~30 Ma) and ? Pictoris (~12 Ma). We have found 9 new and 14 known common proper-motion companions to the 210 investigated stars. With the CAFOS instrument at the 2.2m Calar Alto telescope, we have investigated in detail one of the new pairs, the HD 143809 AB system, which is formed by a bright G0V primary star and a previously unknown young M1.0-1.5Ve star.

astro-ph.SR↗
arXiv2011

The substellar population of Sigma Orionis: A deep wide survey

We present a deep I,Z photometric survey covering a total area of 1.12 deg^{2} of the Sigma Orionis cluster (Icompl=22 and Zcompl=21.5mag). From I, I-Z color-magnitude diagrams we have selected 153 candidates that fit the previously known sequence of the cluster. Using J-band photometry, we find that 124 of the 151 candidates follow the previously known infrared photometric sequence of the cluster and are probably members. We have studied the spatial distribution of these candidates and found that there are objects located at distances greater than 30 arcmin to the north and west of Sigma Orionis that probably belong to different populations of the Orion's Belt. For the 102 bona fide Sigma Orionis cluster member candidates, we find that the radial surface density can be represented by a decreasing exponential function (sigma = sigma_0 e^{-r/r_0}) with a central density of sigma_0=0.23+/-0.03 object/arcmin^{2} and a characteristic radius of r_0=9.5+/-0.7 arcmin. From a statistical comparison with Monte Carlo simulations, we conclude that the spatial distribution of the cluster member candidates is compatible with a Poissonian distribution and, hence, they are not mainly forming aggregations or sub-clustering. Using near-infrared JHK-band data from 2MASS and UKIDSS and mid-infrared data from IRAC/Spitzer, we find that 5-9 % of the brown dwarf candidates in the Sigma Orionis cluster have K-band excesses and 31+/-7 % of them show mid-infrared excesses at wavelengths longer than 5.8 microns, which are probably related to the presence of disks. We have also calculated the initial mass spectrum (dN/dm) of Sigma Orionis from very low mass stars (0.10 Msol) to the deuterium-burning mass limit (0.012-0.013 Msol). This is a rising function toward lower masses and can be represented by a power-law distribution (dN/dm = m^{-alpha}) with an exponent alpha of 0.7+/-0.3 for an age of 3 Myr.

astro-ph.SR↗
arXiv2011

Relativistic Models for Quasi-Elastic Neutrino-Nucleus Scattering

Two relativistic approaches to charged-current quasielastic neutrino-nucleus scattering are illustrated and compared: one is phenomenological and based on the superscaling behavior of electron scattering data and the other relies on the microscopic description of nuclear dynamics in relativistic mean field theory. The role of meson exchange currents in the two-particle two-hole sector is explored. The predictions of the models for differential and total cross sections are presented and compared with the MiniBooNE data.

nucl-th↗
arXiv2011

A third massive star component in the σ Orionis AB system

We report on the detection of a third massive star component in the σ Orionis AB system, traditionally considered as a binary system. The system has been monitored by the IACOB spectroscopic survey of Northern Massive stars program, obtaining 23 high-resolution FIES@NOT spectra with a time-span of ~2.5 years. The analysis of the radial velocity curves of the two spectroscopic components observed in the spectra has allowed us obtain the orbital parameters of the system, resulting in a high eccentric orbit (e~0.78) with an orbital period of 143.5 +/- 0.5 d. This result implies the actual presence of three stars in the σ Orionis AB system when combined with previous results obtained from the study of the astrometric orbit (with an estimated period of ~157 yr).

astro-ph.SR↗
arXiv2011

Relativistic descriptions of final-state interactions in charged-current quasielastic neutrino-nucleus scattering at MiniBooNE kinematics

The results of two relativistic models with different descriptions of the final-state interactions are compared with the MiniBooNE data of charged-current quasielastic cross sections. The relativistic mean field model uses the same potential for the bound and ejected nucleon wave functions. In the relativistic Green's function (RGF) model the final-state interactions are described in the inclusive scattering consistently with the exclusive scattering using the same complex optical potential. The RGF results describe the experimental data for total cross-sections without the need to modify the nucleon axial mass.

nucl-th↗
arXiv2011

Near-infrared Linear Polarization of Ultracool Dwarfs

We report on near-infrared J- and H-band linear polarimetric photometry of eight ultracool dwarfs (two late-M, five L0-L7.5, and one T2.5) with known evidence for photometric variability due to dust clouds, anomalous red infrared colors, or low-gravity atmospheres. The polarimetric data were acquired with the LIRIS instrument on the William Herschel Telescope. We also provide mid-infrared photometry in the interval 3.4-24 micron for some targets obtained with Spitzer and WISE, which has allowed us to confirm the peculiar red colors of five sources in the sample. We can impose modest upper limits of 0.9% and 1.8% on the linear polarization degree for seven targets with a confidence of 99%. Only one source, 2MAS, J02411151-0326587 (L0), appears to be strongly polarized (P ~ 3%) in the J-band with a significance level of P/sigma_P ~ 10. The likely origin of its linearly polarized light and rather red infrared colors may reside in a surrounding disk with an asymmetric distribution of grains. Given its proximity (66 +/- 8 pc), this object becomes an excellent target for the direct detection of the disk.

astro-ph.SR↗
arXiv2011

Identification of blue high proper motion objects in the Tycho-2 and 2MASS catalogues using Virtual Observatory tools

With available Virtual Observatory tools, we looked for new bright blue high proper motion objects in the entire sky: white dwarfs, hot subdwarfs, runaway OB stars, and early-type stars in nearby young moving groups. We performed an all-sky cross-match between the optical Tycho-2 and near-infrared 2MASS catalogues with Aladin, and selected objects with proper motions >50mas/yr and colours Vt-Ks<-0.5mag with TOPCAT. We also collected multi-wavelength photometry, constructed the spectral energy distributions and estimated effective temperatures from fits to atmospheric models with VOSA for the most interesting targets. We assembled a sample of 32 bright blue high proper motion objects, including ten sdO/B subdwarfs, nine DA white dwarfs, five young early-type stars (two of which are runaway stars), two blue horizontal branch stars, one star with poor information, and five objects reported for the first time in this work. These last five objects have magnitudes Bt~11.0-11.6mag, effective temperatures ~24,000-30,000K, and are located in the region of known white dwarfs and hot subdwarfs in a reduced proper motion-colour diagram. We confirmed the hot subdwarf nature of one of the new objects, Albus 5, with public far-ultraviolet spectroscopic data obtained with FUSE.

astro-ph.SR↗
arXiv2011

Relativistic descriptions of quasielastic charged-current neutrino-nucleus scattering: application to scaling and superscaling ideas

The analysis of the recent experimental data on charged-current neutrino-nucleus scattering cross sections measured at MiniBooNE requires fully relativistic theoretical descriptions also accounting for the role of final state interactions. In this work we evaluate inclusive quasielastic differential neutrino cross sections within the framework of the relativistic impulse approximation. Results based on the relativistic mean field potential are compared with the ones corresponding to the relativistic Green function approach. An analysis of scaling and superscaling properties provided by both models is also presented.

nucl-th↗
arXiv2011

Relativistic analyses of quasielastic neutrino cross sections at MiniBooNE kinematics

Two relativistic approaches are considered to evaluate the quasielastic double-differential and integrated neutrino-nucleus cross sections. One, based on the relativistic impulse approximation, relies on the microscopic description of nuclear dynamics using relativistic mean field theory, and incorporates a description of the final-state interactions. The second is based on the superscaling behavior exhibited by electron scattering data and its applicability, due to the universal character of the scaling function, to the analysis of neutrino scattering reactions. The role played by the vector meson-exchange currents in the two-particle two-hole sector is also incorporated and the results obtained are compared with the recent data for neutrinos measured by the MiniBooNE Collaboration.

nucl-th↗
arXiv2011

Scaling Function, Spectral Function and Nucleon Momentum Distribution in Nuclei

The link between the scaling function extracted from the analysis of (e,e') cross sections and the spectral function/momentum distribution in nuclei is revisited. Several descriptions of the spectral function based on the independent particle model are employed, together with the inclusion of nucleon correlations, and effects of the energy dependence arising from the width of the hole states are investigated. Although some of these approaches provide rough overall agreement with data, they are not found to be capable of reproducing one of the distinctive features of the experimental scaling function, namely its asymmetry. However, the addition of final-state interactions, incorporated in the present study using either relativistic mean field theory or via a complex optical potential, does lead to asymmetric scaling functions in accordance with data. The present analysis seems to indicate that final-state interactions constitute an essential ingredient and are required to provide a proper description of the experimental scaling function.

nucl-th↗
arXiv2010

Superscaling predictions for NC and CC quasi-elastic neutrino-nucleus scattering

Quasielastic double differential neutrino cross sections can be obtained in a phenomenological model based on the superscaling behavior of electron scattering data. In this talk the superscaling approach (SuSA) is reviewed and its validity is tested in a relativistic shell model. Results including meson exchange currents for the kinematics of the MiniBoone experiment are presented.

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