arXiv subjects

M. A. Bautista

Publications and source records attributed to M. A. Bautista.

At least 19 recordsLinked to original sources

arXiv2024

PROJECT-J: JWST observations of HH46~IRS and its outflow. Overview and first results

We present the first results of the JWST program PROJECT-J (PROtostellar JEts Cradle Tested with JWST ), designed to study the Class I source HH46 IRS and its outflow through NIRSpec and MIRI spectroscopy (1.66 to 28 micron). The data provide line-images (~ 6.6" in length with NIRSpec, and up to 20" with MIRI) revealing unprecedented details within the jet, the molecular outflow and the cavity. We detect, for the first time, the red-shifted jet within ~ 90 au from the source. Dozens of shock-excited forbidden lines are observed, including highly ionized species such as [Ne III] 15.5 micron, suggesting that the gas is excited by high velocity (> 80 km/s) shocks in a relatively high density medium. Images of H2 lines at different excitations outline a complex molecular flow, where a bright cavity, molecular shells, and a jet-driven bow-shock interact with and are shaped by the ambient conditions. Additional NIRCam 2 micron images resolve the HH46 IRS ~ 110 au binary system and suggest that the large asymmetries observed between the jet and the H2 wide angle emission could be due to two separate outflows being driven by the two sources. The spectra of the unresolved binary show deep ice bands and plenty of gaseous lines in absorption, likely originating in a cold envelope or disk. In conclusion, JWST has unraveled for the first time the origin of the HH46 IRS complex outflow demonstrating its capability to investigate embedded regions around young stars, which remain elusive even at near-IR wavelengths.

astro-ph.GA↗

arXiv2021

Plasma environment effects on K lines of astrophysical interest. V. Universal formulae for ionization potential and K-threshold shifts

Aims. We calculate the plasma environment effects on the ionization potentials (IPs) and K-thresholds used in the modeling of K lines for all the ions belonging to the isonuclear sequences of abundant elements apart from oxygen and iron, namely: carbon, silicon, calcium, chromium, and nickel. These calculations are used to extend the data points for the fits of the universal formulae, first proposed in our fourth paper of this series, to predict the IP and K-threshold lowerings in any elemental ion. Methods. We used the fully relativistic multi-configuration Dirac-Fock (MCDF) method and approximated the plasma electron-nucleus and electron-electron screenings with a time-averaged Debye-Huckel potential. Results. We report the modified ionization potentials and K-threshold energies for plasmas characterized by electron temperatures and densities in the ranges of 10^5-10^7 K and 10^18-10^22 cm^-3 . In addition, the improved universal fitting formulae are obtained. Conclusions. We conclude that since explicit calculations of the atomic structures for each ion of each element under different plasma conditions is impractical, the use of these universal formulae for predicting the IP and K-threshold lowerings in plasma modeling codes is still recommended. However, their comparatively moderate to low accuracies may affect the predicted opacities with regard to certain cases under extreme plasma conditions that are characterized by a plasma screening parameter of μ> 0.2 a.u., especially for the K-thresholds.

physics.atom-ph↗

arXiv2020

On the changes in the physical properties of the ionized region around the Weigelt structures in Eta Carinae over the 5.54-yr spectroscopic cycle

We present HST/STIS observations and analysis of two prominent nebular structures around the central source of Eta Carinae, the knots C and D. The former is brighter than the latter for emission lines from intermediate or high ionization potential ions. The brightness of lines from intermediate and high ionization potential ions significantly decreases at phases around periastron. We do not see conspicuous changes in the brightness of lines from low ionization potential (<13.6 eV) that the total extinction towards the Weigelt structures is that the total extinction towards the Weigelt structures is AsubV =2/0. that the total extinction towards the Weigelt structures is AV = 2.0. Weigelt C and D are characterized by an electron density of that the total extinction towards the Weigelt structures is AV = 2.0. Weigelt C and D are characterized by an electron density of 10exp6.9 cm-3 that does not significantly change throughout the orbital cycle. The electron temperature varies from 5500 K (around periastron) to 7200 K (around apastron). The relative changes in the brightness of He I lines are well reproduced by the variations in the electron temperature alone. We found that, at phases around periastron, the electron temperature seems to be higher for Weigelt C than that of D. The Weigelt structures are located close to the Homunculus equatorial plane, at a distance of about 1240 AU from the central source. From the analysis of proper motion and age, the Weigelt complex can be associated with the equatorial structure called the Butterfly Nebula surrounding the central binary system.

astro-ph.SR↗

arXiv2020

Plasma-environment effects on K lines of astrophysical interest III. IPs, K thresholds, radiative rates, and Auger widths in Fe ix - Fe xvi

Aims. In the context of black-hole accretion disks, we aim to compute the plasma-environment effects on the atomic parameters used to model the decay of K-vacancy states in moderately charged iron ions, namely Fe ix - Fe xvi. Methods. We used the fully relativistic multiconfiguration Dirac-Fock (MCDF) method approximating the plasma electron-nucleus and electron-electron screenings with a time-averaged Debye-Huckel potential. Results. We report modified ionization potentials, K-threshold energies, wavelengths, radiative emission rates, and Auger widths for plasmas characterized by electron temperatures and densities in the ranges $10^5$ - $10^7$ K and $10^{18}$ - $10^{22}$ cm$^{-3}$. Conclusions. This study confirms that the high-resolution X-ray spectrometers onboard the future XRISM and ATHENA space missions will be capable of detecting the lowering of the K edges of these ions due to the extreme plasma conditions occurring in accretion disks around compact objects.

physics.atom-ph↗

arXiv2019

Plasma environment effects on K lines of astrophysical interest. II. Ionization potentials, K thresholds, radiative rates and Auger widths in Ne- through He-like iron ions (Fe xvii - Fe xxv)

Aims. In the context of accretion disks around black holes, we estimate plasma-environment effects on the atomic parameters associated with the decay of K-vacancy states in highly charged iron ions, namely Fe xvii - Fe xxv. Methods. Within the relativistic multiconfiguration Dirac-Fock (MCDF) framework, the electron-nucleus and electron-electron plasma screenings are approximated with a time-averaged Debye-Huckel potential. Results. Modified ionization potentials, K thresholds, wavelengths, radiative emission rates and Auger widths are reported for astrophysical plasmas characterized by electron temperatures and densities respectively in the ranges 1E5 - 1E7 K and 1E18 - 1E22 cm-3 . Conclusions. We conclude that the high-resolution micro-calorimeters onboard future X-ray missions such as XRISM and ATHENA are expected to be sensitive to the lowering of the iron K edge due to the extreme plasma conditions occurring in accretion disks around compact objects.

physics.atom-ph↗

arXiv2018

Current State of Astrophysical Opacities: A White Paper

Availability of reliable atomic and molecular opacity tables is essential in a wide variety of astronomical modeling: the solar and stellar interiors, stellar and planetary atmospheres, stellar evolution, pulsating stars, and protoplanetary disks, to name a few. With the advancement of powerful research techniques such as helio-seismology and asteroseismology, solar neutrino-flux measurements, exoplanet survey satellites, three-dimensional hydrodynamic atmospheric simulations (including non-LTE and granulation effects), high-performance computing of atomic and molecular data, and innovative plasma experiments the accuracy and completeness of opacity tables is being taken to an unprecedented level. The goal of the second Workshop on Astrophysical Opacities was to gather opacity data producers and consumers from both the atomic and molecular sectors to contribute to solving outstanding problems and to develop more effective and integrated interfaces. In this review we attempt to summa- rize the discussion at the workshop and propose future directions for opacity research.

astro-ph.SR↗

arXiv2017

K-shell photoabsorption and photoionization of trace elements. II. Isoelectronic sequences with electron number $12\leq N \leq 18$

We are concerned with improving the diagnostic potential of the K lines and edges of elements with low cosmic abundances that are observed in the X-ray spectra of supernova remnants, galaxy clusters and accreting black holes and neutron stars. Since accurate photoabsorption and photoionization cross sections are needed in their spectral models, they have been computed for isoelectronic sequences with electron number $12\leq N\leq 18$ using a multi-channel method. Target representations are obtained with the atomic structure code AUTOSTRUCTURE, and ground-state cross sections are computed with the Breit--Pauli $R$-matrix method (BPRM) in intermediate coupling, including damping (radiative and Auger) effects. The contributions from channels associated with the 2s-hole $[2{\rm s}]μ$ target configurations and those containing 3d orbitals are studied in the Mg and Ar isoelectronic sequences. Cross sections for the latter ions are also calculated in the isolated-resonance approximation as implemented in AUTOSTRUCTURE and compared with BPRM to test their accuracy. It is confirmed that the collisional channels associated with the $[2{\rm s}]μ$ target configurations must be taken into account owing to significant increases in the monotonic background cross section between the L and K edges. Target configurations with 3d orbitals give rise to fairly conspicuous unresolved transition arrays in the L-edge region, but to a much lesser extent in the K-edge which is our main concern; therefore, they have been neglected throughout owing to their computationally intractable channel inventory, thus allowing the computation of cross sections for all the ions with $12\leq N\leq 18$ in intermediate coupling with BPRM. We find that the isolated-resonance approximations performs satisfactorily.

astro-ph.IM↗

arXiv2016

A benchmark of the He-like triplet for ions with $6\leq Z\leq 14$ in Maxwellian and non-Maxwellian plasmas

After an extensive assessment of the effective collision strengths available to model the He-like triplet of C V, N VI, O VII, Ne IX, Mg XI and Si XIII in collisionally dominated plasmas, new accurate effective collision strengths are reported for Ne IX. The uncertainty intervals of the density and temperature diagnostics due to the atomic data errors are also determined for both Maxwell-Boltzmann and $κ$ electron-energy distributions. It is shown that these uncertainty bands limit the temperature range where the temperature line-ratio diagnostic can be applied and its effectiveness to discern the electron-energy distribution type. These findings are benchmarked with Chandra and XMM-Newton spectra of stellar coronae and with tokamak measurements.

astro-ph.IM↗

arXiv2014

Physical properties of the interstellar medium using high-resolution Chandra spectra: O K-edge absorption

Chandra high-resolution spectra toward eight low-mass Galactic binaries have been analyzed with a photoionization model that is capable of determining the physical state of the interstellar medium. Particular attention is given to the accuracy of the atomic data. Hydrogen column densities are derived with a broadband fit that takes into account pileup effects, and in general are in good agreement with previous results. The dominant features in the oxygen-edge region are O I and O II K$α$ absorption lines whose simultaneous fits lead to average values of the ionization parameter of $\logξ=-2.90$ and oxygen abundance of $A_{\rm O}=0.70$. The latter is relative to the standard by Grevesse & Sauval (1998), but a rescaling with the revision by Asplund et al. (2009) would lead to an average abundance value fairly close to solar. The low average oxygen column density ($N_{\rm O}=9.2 \times 10^{17}$ cm$^{-2}$) suggests a correlation with the low ionization parameters, the latter also being in evidence in the column density ratios OII/OI and OIII/OI that are estimated to be less than 0.1. We do not find conclusive evidence for absorption by any other compound but atomic oxygen.

astro-ph.IM↗

arXiv2014

Testing the existence of non-Maxwellian electron distributions in H II regions after assessing atomic data accuracy

The classic optical nebular diagnostics [N II], [O II], [O III], [S II], [S III], and [Ar III] are employed to search for evidence of non-Maxwellian electron distributions, namely $κ$ distributions, in a sample of well-observed Galactic H II regions. By computing new effective collision strengths for all these systems and A-values when necessary (e.g. S II), and by comparing with previous collisional and radiative datasets, we have been able to obtain realistic estimates of the electron-temperature dispersion caused by the atomic data, which in most cases are not larger than $\sim 10$%. If the uncertainties due to both observation and atomic data are then taken into account, it is plausible to determine for some nebulae a representative average temperature while in others there are at least two plasma excitation regions. For the latter, it is found that the diagnostic temperature differences in the high-excitation region, e.g. $T_e$(O III), $T_e$(S III), and $T_e$(Ar III), cannot be conciliated by invoking $κ$ distributions. For the low excitation region, it is possible in some, but not all, cases to arrive at a common, lower temperature for [N II], [O II], and [S II] with $κ\approx 10$, which would then lead to significant abundance enhancements for these ions. An analytic formula is proposed to generate accurate $κ$-averaged excitation rate coefficients (better than 10% for $κ\geq 5$) from temperature tabulations of the Maxwell-Boltzmann effective collision strengths.

astro-ph.IM↗

arXiv2013

A Comprehensive X-ray Absorption Model for Atomic Oxygen

An analytical formula is developed to represent accurately the photoabsorption cross section of O I for all energies of interest in X-ray spectral modeling. In the vicinity of the Kedge, a Rydberg series expression is used to fit R-matrix results, including important orbital relaxation effects, that accurately predict the absorption oscillator strengths below threshold and merge consistently and continuously to the above-threshold cross section. Further minor adjustments are made to the threshold energies in order to reliably align the atomic Rydberg resonances after consideration of both experimental and observed line positions. At energies far below or above the K-edge region, the formulation is based on both outer- and inner-shell direct photoionization, including significant shake-up and shake-off processes that result in photoionization-excitation and double photoionization contributions to the total cross section. The ultimate purpose for developing a definitive model for oxygen absorption is to resolve standing discrepancies between the astronomically observed and laboratory measured line positions, and between the inferred atomic and molecular oxygen abundances in the interstellar medium from XSTAR and SPEX spectral models.

astro-ph.IM↗

arXiv2013

Time-dependent Photoionization of Gaseous Nebulae: the Pure Hydrogen Case

We study the problem of time-dependent photoionization of low density gaseous nebulae subjected to sudden changes in the intensity of ionizing radiation. To this end, we write a computer code that solves the full time-dependent energy balance, ionization balance, and radiation transfer equations in a self-consistent fashion for a simplified pure hydrogen case. It is shown that changes in the ionizing radiation yield ionization/thermal fronts that propagate through the cloud, but the propagation times and response times to such fronts vary widely and non-linearly from the illuminated face of the cloud to the ionization front (IF). Ionization/thermal fronts are often supersonic, and in slabs initially in pressure equilibrium such fronts yield large pressure imbalances that are likely to produce important dynamical effects in the cloud. Further, we studied the case of periodic variations in the ionizing flux. It is found that the physical conditions of the plasma have complex behaviors that differ from any steady-state solutions. Moreover, even the time average ionization and temperature is different from any steady-state case. This time average is characterized by over-ionization and a broader IF with respect to the steady-state solution for a mean value of the radiation flux. Around the time average of physical conditions there is large dispersion in instantaneous conditions, particularly across the IF, which increases with the period of radiation flux variations. Moreover, the variations in physical conditions are asynchronous along the slab due to the combination of non-linear propagation times for thermal/ionization fronts and equilibration times.

astro-ph.HE↗

arXiv2013

Photoionization modeling of oxygen K absorption in the interstellar medium:the Chandra grating spectra of XTE J1817-330

We present detailed analyses of oxygen K absorption in the interstellar medium (ISM) using four high-resolution Chandra spectra towards the X-ray low-mass binary XTE J1817-330. The 11-25 A broadband is described with a simple absorption model that takes into account the pileup effect and results in an estimate of the hydrogen column density. The oxygen K-edge region (21-25 A) is fitted with the physical warmabs model, which is based on a photoionization model grid generated with the xstar code with the most up-to-date atomic database. This approach allows a benchmark of the atomic data which involves wavelength shifts of both the K lines and photoionization cross sections in order to fit the observed spectra accurately. As a result we obtain: a column density of N(H)=1.38+/-0.01\times 10^21 cm^-2; ionization parameter of log(xi)=-2.70+/-0.023; oxygen abundance of A(O)= 0.689^{+0.015}_{-0.010}; and ionization fractions of OI/O = 0.911, OII/O = 0.077, and OIII/O = 0.012 that are in good agreement with previous studies. Since the oxygen abundance in warmabs is given relative to the solar standard of Grevesse et al. (1998), a rescaling with the revision by Asplund et al. (2009) yields A(O)=0.952^{+0.020}_{-0.013}, a value close to solar that reinforces the new standard. We identify several atomic absorption lines Kalpha, Kbeta, and Kgamma in OI and OII; and Kalpha in OIII, OVI, and OVII - last two probably residing in the neighborhood of the source rather than in the ISM. This is the first firm detection of oxygen K resonances with principal quantum numbers n>2 associated to ISM cold absorption.

astro-ph.HE↗

arXiv2012

Radiation Damping in the Photoionization of Fe^{14+}

A theoretical investigation of photoabsorption and photoionization of Fe^{14+} extending beyond an earlier frame transformation R-matrix implementation is performed using a fully-correlated, Breit-Pauli R-matrix formulation including both fine-structure splitting of strongly-bound resonances and radiation damping. The radiation damping of $2p\rightarrow nd$ resonances gives rise to a resonant photoionization cross section that is significantly lower than the total photoabsorption cross section. Furthermore, the radiation-damped photoionization cross section is found to be in good agreement with recent experimental results once a global shift in energy of $\approx -3.5$ eV is applied. These findings have important implications. Firstly, the presently available synchrotron experimental data are applicable only to photoionization processes and not to photoabsorption; the latter is required in opacity calculations. Secondly, our computed cross section, for which the L-shell ionization threshold is aligned with the NIST value, shows a series of $2p \rightarrow nd$ Rydberg resonances that are uniformly 3-4 eV higher in energy than the corresponding experimental profiles, indicating that the L-shell threshold energy values currently recommended by NIST are likely in error.

physics.atom-ph↗

arXiv2011

K-shell photoionization of Nickel ions using R-matrix

We present R-matrix calculations of photoabsorption and photoionization cross sections across the K edge of the Li-like to Ca-like ions stages of Ni. Level-resolved, Breit-Pauli calculations were performed for the Li-like to Na-like stages. Term-resolved calculations, which include the mass-velocity and Darwin relativistic corrections, were performed for the Mg-like to Ca-like ion stages. This data set is extended up to Fe-like Ni using the distorted wave approximation as implemented by AUTOSTRUCTURE. The R-matrix calculations include the effects of radiative and Auger dampings by means of an optical potential. The damping processes affect the absorption resonances converging to the K thresholds causing them to display symmetric profiles of constant width that smear the otherwise sharp edge at the K-shell photoionization threshold. These data are important for the modeling of features found in photoionized plasmas.

astro-ph.HE↗

arXiv2011

Modeling the oxygen K absorption in the interstellar medium: an {\it XMM}-Newton view of Sco X-1

We investigate the absorption structure of the oxygen in the interstellar medium by analyzing {\it XMM}-Newton observations of the low mass X-ray binary Sco X-1. We use simple models based on the O {\sc i} atomic cross section from different sources to fit the data and evaluate the impact of the atomic data in the interpretation of astrophysical observations. We show that relatively small differences in the atomic calculations can yield spurious results. We also show that the most complete and accurate set of atomic cross sections successfully reproduce the observed data in the $21-24.5$ Å wavelength region of the spectrum. Our fits indicate that the absorption is mainly due to neutral gas with an ionization parameter of $ξ=10^{-4}$ erg cm s$^{-1}$, and an oxygen column density of $N_{\mathrm{O}}\approx 8-10\times 10^{17}$ cm$^{-2}$. Our models are able to reproduce both the K edge and the K$α$ absorption line from O {\sc i}, which are the two main features in this region. We find no conclusive evidence for absorption by other than atomic oxygen.

astro-ph.HE↗

arXiv2010

K-shell photoionization of Na-like to Cl-like ions of Mg, Si, S, Ar, and Ca

We present $R$-matrix calculations of photoabsorption and photoionization cross sections across the K-edge of Mg, Si, S, Ar, and Ca ions with more than 10 electrons. The calculations include the effects of radiative and Auger damping by means of an optical potential. The wave functions are constructed from single-electron orbital bases obtained using a Thomas--Fermi--Dirac statistical model potential. Configuration interaction is considered among all states up to $n=3$. The damping processes affect the resonances converging to the K-thresholds causing them to display symmetric profiles of constant width that smear the otherwise sharp edge at the photoionization threshold. These data are important for modeling of features found in photoionized plasmas.

physics.atom-ph↗

arXiv2010

Distance to Multiple Kinematic Components of Quasar Outflows: VLT Observations of QSO 2359-1241 and SDSS J0318-0600

Using high resolution VLT spectra, we study the multi-component outflow systems of two quasars exhibiting intrinsic Fe II absorption (QSO 2359-1241 and SDSS J0318-0600). From the extracted ionic column densities and using photoionization modeling we determine the gas density, total column density, and ionization parameter for several of the components. For each object the largest column density component is also the densest, and all other components have densities of roughly 1/4 of that of the main component. We demonstrate that all the absorbers lie roughly at the same distance from the source. Further, we calculate the total kinetic luminosities and mass outflow rates of all components and show that these quantities are dominated by the main absorption component.

astro-ph.CO↗