Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>We apply a novel statistical analysis to measurements of 16 elemental abundances in 34,410 Milky Way disk stars from the final data release (DR17) of APOGEE-2. Building on recent work, we fit median abundance ratio trends [X/Mg] versus [Mg/H] with a 2-process model, which decomposes abundance patterns into a “prompt” component tracing core-collapse supernovae and a “delayed” component tracing Type Ia supernovae. For each sample star, we fit the amplitudes of these two components, then compute the residuals Δ[X/H] from this two-parameter fit. The rms residuals range from ∼0.01–0.03 dex for the most precisely measured APOGEE abundances to ∼0.1 dex for Na, V, and Ce. The <jats:italic>correlations</jats:italic> of residuals reveal a complex underlying structure, including a correlated element group comprised of Ca, Na, Al, K, Cr, and Ce and a separate group comprised of Ni, V, Mn, and Co. Selecting stars poorly fit by the 2-process model reveals a rich variety of physical outliers and sometimes subtle measurement errors. Residual abundances allow for the comparison of populations controlled for differences in metallicity and [<jats:italic>α</jats:italic>/Fe]. Relative to the main disk (<jats:italic>R</jats:italic> = 3–13 kpc), we find nearly identical abundance patterns in the outer disk (<jats:italic>R</jats:italic> = 15–17 kpc), 0.05–0.2 dex depressions of multiple elements in LMC and Gaia Sausage/Enceladus stars, and wild deviations (0.4–1 dex) of multiple elements in <jats:italic>ω</jats:italic> Cen. The residual abundance analysis opens new opportunities for discovering chemically distinctive stars and stellar populations, for empirically constraining nucleosynthetic yields, and for testing chemical evolution models that include stochasticity in the production and redistribution of elements.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Despite their importance for astrometry and navigation, the active galactic nuclei (AGNs) that comprise the International Celestial Reference Frame (ICRF) are relatively poorly understood, with key information such as their spectroscopic redshifts, AGN spectral type, and emission-/absorption-line properties generally missing from the literature. Using an updated, publicly available, state-of-the-art spectroscopic fitting code optimized for the spectra of AGNs from low to high redshift, we present a catalog of emission-line and spectral continuum parameters for 1014 unique ICRF3 objects with single-fiber spectra from the Sloan Digital Sky Survey DR16. We additionally present black hole virial mass scaling relationships that use H<jats:italic>α</jats:italic>-, H<jats:italic>β</jats:italic>-, Mg <jats:sc>ii</jats:sc>-, and C <jats:sc>iv</jats:sc>-based line widths, all consistent with each other, which can be used in studies of radio-loud objects across a wide range of redshifts, and we use these scaling relationships to provide derived properties such as black hole masses and bolometric luminosities for the catalog. We briefly comment on these properties for the ICRF objects, as well as their overall spectroscopic characteristics.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>A four-epoch monitoring program spanning ∼three months (from 2020 January 8 to April 7) for ammonia, water, and methanol transitions toward the high-mass star-forming region W51 IRS2 was conducted using the Shanghai 65 m Tianma Radio Telescope with its <jats:italic>K</jats:italic>-band (18–26.5 GHz) receiver. In total, 33 ammonia transitions and 16 methanol transitions were detected toward the target at least once during this monitoring program. Among them, 14 ammonia and 4 methanol transitions show maser emission characteristics. Rapid variabilities (including both increases and decreases) in the ammonia and methanol transitions were detected from both maser and thermal emissions during the three months of the monitoring. In addition, H<jats:sub>2</jats:sub>O masers with obvious variability were also detected. The results of the rotation diagram analysis for the ammonia and methanol quasi-thermal transitions show the variations in their rotational temperatures during the monitoring. The derived temperatures from the transitions with larger upper energies (<jats:italic>E</jats:italic> <jats:sub> <jats:italic>u</jats:italic> </jats:sub>/<jats:italic>κ</jats:italic>) generally decreased over the whole monitoring period, from January 8 to April 7, but those with smaller <jats:italic>E</jats:italic> <jats:sub> <jats:italic>u</jats:italic> </jats:sub>/<jats:italic>κ</jats:italic> first increased from January 8 to April 1, then rapidly decreased from April 1 to April 7. These findings support the suggestion that an inside-out heatwave propagation in W51 IRS2 was involved with the accretion burst over a short duration (only on the order of months) and caused the drastic variability behaviors of the different line transitions during high-mass star formation.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Be stars are B-type main-sequence stars that display broad Balmer emission lines in their spectra. Identification of the Be population is essential to further examine the formation and evolutionary models. We report the detection of classical Be (CBe) stars from observations with the Large sky Area Multi-Object fiber Spectroscopic Telescope Medium Resolution Survey Data Release 7 (LAMOST MRS DR7). We used a deep convolutional neural network, <jats:monospace>ResNet</jats:monospace>, with an 18 layer module to examine the morphology of the H<jats:italic>α</jats:italic> profile. We identified 1162 candidate Be stars from the collection of 2,260,387 spectra for 789,918 stars in the database. The <jats:monospace>ResNet</jats:monospace> network achieves a Be-star classification accuracy of 99.5%. Among the detections, 151 of these are prior known Be stars crossmatched from the literature. By applying a three-step test, we identified 183 new CBe stars. We find that 41 CBe stars are members of known open clusters. Based on an investigation of the kinematics of the identified CBe stars from the Gaia EDR3 astrometric solutions, we identified 16 new runaways. These new identifications will provide a reference for future follow-ups to further investigate their physical properties.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Coronal mass ejections (CMEs) are the largest-scale eruptive phenomena in the solar system. Associated with enormous plasma ejections and energy releases, CMEs have an important impact on the solar–terrestrial environment. Accurate predictions of the arrival times of CMEs at the Earth depend on precise measurements of their 3D velocities, which can be achieved by using simultaneous line-of-sight (LOS) and plane-of-sky (POS) observations. Besides the POS information from routine coronagraph and extreme-ultraviolet (EUV) imaging observations, spectroscopic observations could unveil the physical properties of CMEs, including their LOS velocities. We propose that spectral line asymmetries measured by Sun-as-a-star spectrographs can be used for routine detections of CMEs and estimations of their LOS velocities during their early propagation phases. Such observations can also provide important clues for the detection of CMEs on other solar-like stars. However, few studies have concentrated on whether we can detect CME signals and accurately diagnose CME properties through Sun-as-a-star spectral observations. In this work, we construct a geometric CME model and derive the analytical expressions for full disk-integrated EUV line profiles during CMEs. For different CME properties and instrumental configurations, the full disk-integrated line profiles are synthesized. We further evaluate the detectability and diagnostic potential of CMEs from the synthetic line profiles. Our investigations provide important constraints on the future design of Sun-as-a-star spectrographs for CME detections through EUV line asymmetries.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>A spectroscopic study of atomic oxygen (O <jats:sc>i</jats:sc>) is performed using the Fourier-transform vacuum ultraviolet (VUV) spectrometer at the Dichroïsme Et Spectroscopie par Interaction avec le Rayonnement Synchrotron beamline of the SOLEIL synchrotron. Transition frequencies of O <jats:sc>i</jats:sc> lines in the range between 76,000 and 151,000 cm<jats:sup>−1</jats:sup>, corresponding to wavelengths between 665 and 1306 Å, are presented. In the wavelength window a data set of 208 lines is obtained for which line centers were determined at an accuracy of ≤0.035 cm<jats:sup>−1</jats:sup>, verified through a comparison with previous VUV-laser spectroscopy at an accuracy of 0.008 cm<jats:sup>−1</jats:sup>. Transitions to upper states belonging to several <jats:italic>ns</jats:italic> and <jats:italic>nd</jats:italic> Rydberg series that converge to the <jats:sup>4</jats:sup>S<jats:sub>3/2</jats:sub>, <jats:sup>2</jats:sup>D, and <jats:sup>2</jats:sup>P ionization limits are presented. Besides studies on the main <jats:sup>16</jats:sup>O isotope, measurements of the <jats:sup>18</jats:sup>O isotope are also performed, for which an enriched sample of <jats:sup>18</jats:sup>O<jats:sub>2</jats:sub> gas is used. A least-squares optimization analysis is performed after merging the present new data set with some relevant accurate literature data to extract a list of level energies at high accuracy. When comparing with the database of the National Institute of Standards and Technology, good agreement is found for levels with low principal quantum numbers <jats:italic>n</jats:italic> ≤ 7 or below excitation energies of 108,000 cm<jats:sup>−1</jats:sup>; however, significant deviations were found for levels with <jats:italic>n</jats:italic> &gt; 7. The main result of the present study is the realization of an improved data set of transition frequencies and level energies for O <jats:sc>i</jats:sc>, with its usefulness demonstrated in a comparison with high-resolution astronomical spectra showing absorption in the line of sight to distant quasars.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Luminosity, which is the total amount of radiant energy emitted by an object, is one of the most critical quantities in astrophysics for characterizing stars. Equally important is the temporal evolution of a star’s luminosity because of its intimate connection with the stellar energy budget, large-scale convective motion, and heat storage in the stellar interior. The Sun’s luminosity and its variation have not been measured to date because current observations of the solar radiative output have been restricted to vantage points near the Earth. Here, we model the solar luminosity by extending a semiempirical total solar irradiance (TSI) model that uses solar-surface magnetism to reconstruct solar irradiance over the entire 4<jats:italic>π</jats:italic> solid angle around the Sun. This model was constrained by comparing its output to the irradiance in the Earth’s direction with the measured TSI. Comparing the solar luminosity to the TSI on timescales from days to solar cycles for cycles 23 and 24, we find poor agreement on short timescales (&lt;solar rotation). This is not unexpected due to the Earth-centric viewing geometry and short-term irradiance dependence on surface features on the Earth-facing solar disk. On longer timescales, however, we find good agreement between the luminosity model and the TSI, which suggests that the extrapolation of luminosities to multicycle timescales based on TSI reconstructions may be possible. We show that the solar luminosity is not constant but varies in phase with the solar cycle. This variation has an amplitude of 0.14% from minimum to maximum for Solar Cycle 23. Considering the energetics in the solar convection zone, it is therefore obvious that a steady-state input from the radiative zone at the solar minimum level would lead to a gradual reduction in the energy content in the convection zone over multicentury timescales. We show that the luminosity at the base of the convection zone should be approximately 0.032% higher than that at the solar surface during solar minimum to maintain net energy equilibrium through the solar cycle. These different energy-input scenarios place constraints on the long-term evolution of the TSI and its impact on the solar forcing of climate variability. These results highlight the convection zone’s role as an energy reservoir on solar-cycle timescales and set constraints for dynamo models intending to understand the long-term evolution of the Sun and solar analogs.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present the most extensive and well-sampled long-term multiband near-infrared (NIR) temporal and spectral variability study of OJ 287, considered to be the best candidate binary supermassive black hole blazar. These observations were made between 2007 December and 2021 November. The source underwent ∼2–2.5 mag variations in the <jats:italic>J</jats:italic>, <jats:italic>H</jats:italic>, and <jats:italic>Ks</jats:italic> NIR bands. Over these long-term timescales there were no systematic trends in either flux or spectral evolution with time or with the source’s flux states. However, on shorter timescales, there are significant variations in flux and spectra indicative of strong changes during different activity states. The NIR spectral energy distributions show diverse facets at each flux state, from the lowest to the highest. The spectra are, in general, consistent with a power-law spectral profile (within 10%) and many of them indicate minor changes (observationally insignificant) in the shift of the peak. The NIR spectra generally steepen during bright phases. We briefly discuss these behaviors in the context of blazar emission scenarios/mechanisms, OJ 287's well-known traditional behavior, and implications for models of the source central engine invoked for its long-term optical semiperiodic variations.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present an improved background model for the Large Area X-ray Proportional Counter (LAXPC) detectors on board AstroSat. Because of the large collecting area and high pressure, the LAXPC instrument has a large background count rate, which varies during the orbit. Apart from the variation with latitude and longitude during the orbit there is a prominent quasi-diurnal variation which has not been previously modeled. Using over 5 yr of background observations, we determined the period of the quasi-diurnal variation to be 84,495 s and using this period it is possible to account for the variation and also identify time intervals where the fit is not good. These lead to a significant improvement in the background model. The quasi-diurnal variation can be ascribed to the changes in charged particle flux in the near-Earth orbit.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The dust extinction curves toward individual sight lines in M33 are derived for the first time with a sample of reddened O-type and B-type supergiants obtained from the Local Group Galaxies Survey (LGGS). The observed photometric data are obtained from the LGGS, PS1 Survey, UKIRT, PHATTER Survey, Galaxy Evolution Explorer, Swift/UVOT, and XMM-SUSS. We combine the intrinsic spectral energy distributions (SEDs) obtained from the ATLAS9 and Tlusty stellar model atmosphere extinguished by the model extinction curves from the silicate-graphite dust model to construct model SEDs. The extinction traces are distributed along the arms in M33, and the derived extinction curves cover a wide range of shapes (<jats:italic>R</jats:italic> <jats:sub> <jats:italic>V</jats:italic> </jats:sub> ≈ 2–6), indicating the complexity of the interstellar environment and the inhomogeneous distribution of interstellar dust in M33. The average extinction curve with <jats:italic>R</jats:italic> <jats:sub> <jats:italic>V</jats:italic> </jats:sub> ≈ 3.39 and dust size distribution <jats:inline-formula> <jats:tex-math> <?CDATA ${dn}/{da}\sim {a}^{-3.45}\exp (-a/0.25)$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="italic">dn</mml:mi> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:mi mathvariant="italic">da</mml:mi> <mml:mo>∼</mml:mo> <mml:msup> <mml:mrow> <mml:mi>a</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>3.45</mml:mn> </mml:mrow> </mml:msup> <mml:mi>exp</mml:mi> <mml:mo stretchy="false">(</mml:mo> <mml:mo>−</mml:mo> <mml:mi>a</mml:mi> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:mn>0.25</mml:mn> <mml:mo stretchy="false">)</mml:mo> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjsac63c1ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> is similar to that of the Milky Way but with a weaker 2175 Å bump and a slightly steeper rise in the far-UV band. The extinction in the <jats:italic>V</jats:italic> band of M33 is up to 2 mag, with a median value of <jats:italic>A</jats:italic> <jats:sub> <jats:italic>V</jats:italic> </jats:sub> ≈ 0.43 mag. The multiband extinction values from the UV to IR bands are also predicted for M33, which will provide extinction corrections for future works. The method adopted in this work is also applied to other star-resolved galaxies (NGC 6822 and WLM), but only a few extinction curves can be derived because of the limited observations.</jats:p>