arXiv subjects

A. Peimbert

Publications and source records attributed to A. Peimbert.

At least 19 recordsLinked to original sources

arXiv2026

On the Influence of Pluto on Twotino Dynamics Through Their Mutual 4:3 Mean Motion Resonance

Context: The role of Pluto contributing to the long-term evolution of the trans-Neptunian region has been considered significant only over its neighboring Plutinos. However, it has recently been found that the long-term stability of the Twotino population is strongly affected when including Pluto as a massive object in simulations, while Eris, with a similar mass, has a negligible effect. Aims: We hypothesize that the effect of Pluto on Twotinos results from the latter being trapped in a 4:3 mean motion resonance (MMR) with Pluto. In this work, we aim to demonstrate the resonant behavior of Twotinos within Pluto's 4:3 MMR and the significance of this resonance for the long-term evolution of the population. Methods: We run high-resolution, 10 Myr REBOUND simulations of the observed Twotino population in the Kuiper belt, under the perturbations of the Sun, the four giant planets, and Pluto, as massive objects. Results: We find that all objects trapped in the 2:1 MMR with Neptune are locked in a weak 4:3 MMR with Pluto. The 4:3 resonant angles of most objects trapped in the leading and trailing islands of the 2:1 MMR, librate with amplitudes lower than $360^\circ$. Objects in the symmetric islands of the 2:1 MMR librate in the 4:3 MMR with amplitudes greater than $360^\circ$, but, contrary to circulating objects, will oscillate by up to $840^\circ$ visiting preferred angles on Pluto's co-rotating frame, indicating a diluted resonant effect that may also perturb their orbits on secular timescales. Conclusions: The importance of Pluto in shaping the structure of the trans-Neptunian region should be reconsidered, specifically for resonant populations. Moreover, with current computational power, its exclusion from simulations can not be justified.

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arXiv2021

Long-term Dynamical Stability in the Outer Solar System I: The Regular and Chaotic Evolution of the 34 Largest Trans-Neptunian Objects

We carried out an extensive analysis of the stability of the outer solar system, making use of the frequency analysis technique over short-term integrations of nearly a hundred thousand test particles, as well as a statistical analysis of 200, 1 Gyr long numerical simulations, which consider the mutual perturbations of the giant planets and the 34 largest trans-Neptunian objects (we have called all 34 objects ``dwarf planets'', DPs, even if probably only the largest of them are true DPs). From the frequency analysis we produced statistical diffusion maps for a wide region of the $a$-$e$ phase-space plane; we also present the average diffusion time for orbits as a function of perihelion. We later turned our attention to the 34 DPs making an individualized analysis for each of them and producing a first approximation of their future stability. From the 200 distinct realizations of the orbital evolution of the 34 DPs, we classified the sample into three categories including 17 Stable, 11 Unstable, and 6 Resonant objects each; we also found that statistically, 2 objects from the sample will leave the trans-Neptunian region within the next Gyr, most likely being ejected from the solar system, but with a non-negligible probability of going inside the orbit of Neptune, either to collide with a giant planet or even falling to the inner solar system, where our simulations are no longer able to resolve their continuous evolution.

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arXiv2020

The ADF and the t$^2$ formalism in H II regions based on the upper mass limit of the IMF for the MW

We study in depth the abundance discrepancy problem in H II regions, this time from a different perspective than the usual one: by studying the effect of the upper mass limit (M$_{\rm up}$) of the initial mass function (IMF) on the O, C, and He predicted by chemical evolution models for the Milky Way. We use abundances determined with the direct method (DM) and with the temperature independent method (TIM). We compare the predicted abundances at the present time with observations of Orion, M17, and M8 to determine the M$_{\rm up}$ value of the galactic IMF. From the DM abundances, the models predict an M$_{\rm up}$ = 25-45 M$_{\odot}$, while from the TIM, CEMs derive an M$_{\rm up}$ = 70-110 M$_{\odot}$. Spiral galaxies with the stellar mass and star formation rate of the MW are predicted to have an M$_{\rm up} \sim100$ M$_{\odot}$. These results support that abundances derived from the TIM are better than those derived from the DM.

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arXiv2019

Chemical evolution models for the Galactic disk based on H II region abundances derived from a direct method and a temperature independent method

We present two chemical evolution models of our galaxy, both models are built to fit the O/H ratios derived from H II regions, using two different methods. One model is based on abundances obtained from the [O III] 4363/5007 temperatures (direct method, DM) and the other on abundances obtained from the recombination line ratios of [O II/H I] (temperature independent method, TIM). The differences between the O/H values obtained from these two methods are about 0.25 dex. We find that the model based on the TIM values produces an excellent fit to the observational stellar constraints (B-stars, Cepheids, and the Sun), while the model based on the DM fails to reproduce each of them. Moreover, the TIM model can explain the flattening of the O/H gradient observed in the inner disk due to the assumption of an inside-out star formation quenching, in the 3 - 6 kpc galactocentric range, starting ~ 9 Gyr ago.

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arXiv2017

Dynamics and Morphology of the Milky Way Spiral Arms from the Metallicity Distribution and Radial Mixing

Albeit radial migration must be a ubiquitous process in disc galaxies, its significance in the evolution of stellar discs is not always reflected through global trends. However, there are other key observables, such as the metallicity distribution function (MDF), that may shed some light in this matter. We argue that the shape of the MDF not only tells us whether the stellar disc experienced radial migration, but it also contains important clues on the structure that triggered it. Specifically, the MDF contains information about the dynamics and morphology of the spiral pattern. To constrain the spiral parameters, we have included a detailed chemical tagging in our simulations; this allows us to produce a restriction of the structural parameters of the spiral arms in the Milky Way as well as a method to constrain chemical evolution models towards the center of the Galactic disc, where no chemical model provides information. We also found that it is unlikely that the Sun was formed near its current galactocentric position, therefore it might be inaccurate to consider the Sun as representative of the chemical abundances in the solar neighborhood. We also show that a stellar disc of the Milky Way, after evolving dynamically and chemically for 5 Gyr, preserves 80% of its original global metallicity gradient despite having suffered important heating and radial migration; this means that the presence of a metallicity gradient in a given galaxy, does not guarantee that radial mixing has not played a role in its evolution.

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arXiv2016

On the Survival of High-Altitude Open Clusters within the Milky Way Galaxy Tides

It is a common assumption that high-altitude open clusters live longer compared with clusters moving close to the Galactic plane. This is because at high altitudes, open clusters are far from the disruptive effects of in-plane substructures, such as spiral arms, molecular clouds and the bar. However, an important aspect to consider in this scenario is that orbits of high-altitude open clusters will eventually cross the Galactic plane, where the vertical tidal field of the disk is strong. In this work we simulate the interaction of open clusters with the tidal field of a detailed Milky Way Galactic model at different average altitudes and galactocentric radii. We find that the life expectancy of clusters decreases as the maximum orbital altitude increases and reaches a minimum at altitudes of approximately 600 pc. Clusters near the Galactic plane live longer because they do not experience strong vertical tidal shocks from the Galactic disk; then, for orbital altitudes higher than 600 pc, clusters start again to live longer due to the decrease in the number of encounters with the disk. With our study, we find that the compressive nature of the tides in the arms region and the bar have an important role on the survival of small clusters by protecting them from disruption: clusters inside the arms can live up to twice as long as those outside the arms at similar galactocentric distance.

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arXiv2016

Revealing the spiral arms through radial migration and the shape of the Metallicity Distribution Function

Recent observations show that the Milky Way's metallicity distribution function (MDF) changes its shape as a function of radius. This new evidence of radial migration within the stellar disc sets additional constraints on Galactic models. By performing controlled test particle simulations in a very detailed, observationally motivated model of the Milky Way, we demonstrate that, in the inner region of the disc, the MDF is shaped by the joint action of the bar and spiral arms, while at outer radii the MDF is mainly shaped by the spiral arms. We show that the spiral arms are able to imprint their signature in the radial migration, shaping the MDF in the outskirts of the Galactic disc with a minimal participation of the bar. Conversely, this work has the potential to characterise some structural and dynamical parameters of the spiral arms based on radial migration and the shape of the MDF. Finally, the resemblance obtained with this approximation to the MDF curves of the Galaxy as seen by APOGEE, show that a fundamental factor influencing their shape is the Galactic potential.

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arXiv2016

On the Origin of High-Altitude Open Clusters in the Milky Way

We present a dynamical study of the effect of the bar and spiral arms on the simulated orbits of open clusters in the Galaxy. Specifically, this work is devoted to the puzzling presence of high-altitude open clusters in the Galaxy. For this purpose we employ a very detailed observationally motivated potential model for the Milky Way and a careful set of initial conditions representing the newly born open clusters in the thin disk. We find that the spiral arms are able to raise an important percentage of open clusters (about one-sixth of the total employed in our simulations, depending on the structural parameters of the arms) above the Galactic plane to heights beyond 200 pc, producing a bulge-shaped structure toward the center of the Galaxy. Contrary to what was expected, the spiral arms produce a much greater vertical effect on the clusters than the bar, both in quantity and height; this is due to the sharper concentration of the mass on the spiral arms, when compared to the bar. When a bar and spiral arms are included, spiral arms are still capable of raising an important percentage of the simulated open clusters through chaotic diffusion (as tested from classification analysis of the resultant high-z orbits), but the bar seems to restrain them, diminishing the elevation above the plane by a factor of about two.

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arXiv2009

'Chemical abundances in H II regions and their implications -- Retrospective on: M. Peimbert & R. Costero, Boletin de los Observatorios de Tonantzintla y Tacubaya, Vol. 5, 3, 1969'

We present a review about the relevance of the paper by Peimbert and Costero (1969), on the chemical abundance determinations of H II regions. We analize the observational evidence in favor of the presence of temperature variations inside gaseous nebulae. We make a brief mention of the methods used to estimate the contribution of the unobserved ions to the total chemical abundances.

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arXiv2009

Measurements of 4He in Metal-Poor Extragalactic HII Regions: the Primordial Helium Abundance and the Delta Y / Delta O Ratio

We present a review on the determination of the primordial helium abundance Yp, based on the study of hydrogen and helium recombination lines in extragalactic HII regions. We also discuss the observational determinations of the increase of helium to the increase of oxygen by mass Delta Y / Delta O, and compare them with predictions based on models of galactic chemical evolution.

astro-ph.CO↗

arXiv2009

Keck HIRES Spectroscopy of Extragalactic HII Regions: C and O Abundances from Recombination Lines

We present very deep spectrophotometry of 14 bright extragalactic HII regions belonging to spiral, irregular, and blue compact galaxies. The data for 13 objects were taken with the HIRES echelle spectrograph on the Keck I telescope. We have measured CII recombination lines in 10 of the objects and OII recombination lines in 8 of them. We have determined electron temperatures from line ratios of several ions, specially of low ionization potential ones. We have found a rather tight linear empirical relation between Te([NII]) and Te([OIII]). We have found that OII lines give always larger abundances than [OIII] lines. Moreover, the difference of both O++ abundance determinations --the so-called abundance discrepancy factor-- is very similar in all the objects, with a mean value of 0.26+/-0.09 dex, independently of the properties of the HII region and of the parent galaxy. Using the observed recombination lines, we have determined the O, C, and C/O radial abundance gradients for 3 spiral galaxies: M33, M101, and NGC2403, finding that C abundance gradients are always steeper than those of O, producing negative C/O gradients accross the galactic disks. This result is similar to that found in the Milky Way and has important implications for chemical evolution models and the nucleosynthesis of C.

astro-ph.CO↗

arXiv2008

NLTE Model of NGC 6543's Central Star and its Relation with the Surrounding Planetary Nebula

We analyze the chemical composition of the central star of the planetary nebula NGC 6543 based upon a detailed NLTE model of its stellar wind. The logarithmic abundances by number are H=12.00, He=11.00, C=9.03, N=8.36, O=9.02, Si=8.19, P=5.53, S=7.57 and Fe=7.24. Compared with the solar abundances, most of the elements have solar composition with respect to hydrogen except C which is overabundant by 0.28 dex and Fe which is depleted by $\sim 0.2$ dex. Contrary to most previous work, we find that the star is not H-poor and has a normal He composition. These abundances are compared with those found in the diffuse X-ray plasma and the nebular gas. Compared to the plasma emitting in diffuse X-rays, the stellar wind is much less depleted in iron. Since the iron depletions in the nebular gas and X-ray plasma are similar, we conclude that the plasma emitting diffuse X-rays is derived from the nebular gas rather than the stellar wind. Excellent agreement is obtained between the abundances in the stellar wind and the nebular recombination line abundances for He, C, and O relative to H. On the other hand, the derived stellar N abundance is smaller than the nebular N abundance derived from recombination lines and agrees with the abundance found from collisionally-excited lines. The mean temperature variation determined by five different methods indicates that the difference in the nebular abundances between the recombination lines and collisionally excited lines can be explained as due to the temperature variations in a chemically homogeneous medium.

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arXiv2007

Revised Primordial Helium Abundance Based on New Atomic Data

We have derived a primordial helium abundance of Yp = 0.2477 +- 0.0029, based on new atomic physics computations of the recombination coefficients of He I and of the collisional excitation of the H I Balmer lines together with observations and photoionization models of metal-poor extragalactic H II regions. The new atomic data increase our previous determination of Yp by 0.0086, a very significant amount. By combining our Yp result with the predictions made by the standard Big Bang nucleosynthesis model, we find a baryon-to-photon ratio, η, in excellent agreement both with the ηvalue derived by the primordial deuterium abundance value observed in damped Lyman-αsystems and with the one obtained from the WMAP observations.

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arXiv2007

Diffuse Ionized Gas inside the dwarf irregular galaxy NGC 6822

We have studied the differences between the diffuse ionized gas (DIG) and the HII regions along a slit position in the local dwarf irregular galaxy NGC 6822. The slit position passes through the two most prominent HII regions: Hubble V and Hubble X. Important differences have been found in the excitation, ionization, and [NII]6584/Ha and [SII]6717/Ha line ratios between the DIG and the HII locations. Moreover, the values of all the line ratios are not similar to those in the DIG locations of spiral galaxies but are very similar to the values in other irregular galaxies, such as IC 10. We also determined the rate of recombination using the HeI5875 line. Finally, we obtained a picture of the ionization sources of the DIG. We consider that the leakage of photons from the HII regions might explain most of the line ratios, except [NII]/Ha, which might be explained by turbulence.

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arXiv2007

On the Primordial Helium Abundance and the DeltaY/DeltaO Ratio

We present a review on the determination of the primordial helium abundance, Yp, based on the study of hydrogen and helium recombination lines in extragalactic H II regions. We also discuss the observational determinations of the increase of helium to the increase of oxygen by mass Delta Y/Delta O, and compare them with predictions based on models of galactic chemical evolution.

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arXiv2006

The chemical composition of the Galactic regions M8 and M17. A revision based on deep VLT echelle spectrophotometry

We present new echelle spectrophotometry of the Galactic H II regions M8 and M17. The data have been taken with the VLT UVES echelle spectrograph in the 3100 to 10400 angstroms range. We have measured the intensities of 375 and 260 emission lines in M8 and M17 respectively, increasing significatively the number of emission lines measured in previous spectrophotometric studies of these nebulae. Most of the detected lines are permitted lines. Electron temperatures and densities have been determined using different diagnostics. We have derived He+, C++, O+ and O++ ionic abundances from pure recombination lines. We have also derived abundances from collisionally excited lines for a large number of ions of different elements. Highly consistent estimations of t2 have been obtained by using different independent indicators, the values are moderate and very similar to those obtained in other Galactic H II regions. We report the detection of deuterium Balmer emission lines, up to D$ε$, in M8 and show that their intensities are consistent with continuum fluorescence as their main excitation mechanism.

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arXiv2006

The Calibration of the O/H Abundance Indicators for Extragalactic H II Regions Based on O II Recombination Lines

Based on O II recombination lines we present a new calibration (called O II[RL]) of Pagel's O23 indicator to determine the O/H abundance ratio in extragalactic H II regions and emission line galaxies. The O II(RL) calibration produces O/H abundances about a factor of two higher than those derived from the T(4363) method with t2 = 0.00. The O II(RL) calibration has implications for the study of different properties of emission line galaxies such as their metallicity, star formation rate, and initial mass function. The O II(RL) calibration also affects the abundance determinations based on other O/H indicators, that include collisionally excited lines, like those known as O3N2, N2, S23, Ar3O3, and S3O3. We argue that the controversy between the T(4363) method and the photoionization models method to derive O/H values is mainly due to temperature variations inside the observed H II regions.

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arXiv2006

Faint emission lines in the Galactic H II regions M16, M20 and NGC 3603

We present deep echelle spectrophotometry of the Galactic {\hii} regions M16, M20 and NGC 3603. The data have been taken with the Very Large Telescope Ultraviolet-Visual Echelle Spectrograph in the 3100 to 10400 Årange. We have detected more than 200 emission lines in each region. Physical conditions have been derived using different continuum and line intensity ratios. We have derived He$^{+}$, C$^{++}$ and O$^{++}$ abundances from pure recombination lines as well as abundances from collisionally excited lines for a large number of ions of different elements. We have obtained consistent estimations of the temperature fluctuation parameter, {\ts}, using different methods. We also report the detection of deuterium Balmer lines up to D$δ$ (M16) and to D$γ$ (M20) in the blue wings of the hydrogen lines, which excitation mechanism seems to be continuum fluorescence. The temperature fluctuations paradigm agree with the results obtained from optical CELs and the more uncertain ones from far IR fine structure CELs in NGC 3603, although, more observations covering the same volume of the nebula are necessary to obtain solid conclusions.

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