Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>We are undertaking the first systematic infrared (IR) census of R Coronae Borealis (RCB) stars in the Milky Way, beginning with IR light curves from the Palomar Gattini IR (PGIR) survey. The PGIR is a 30 cm <jats:italic>J</jats:italic>-band telescope with a 25 deg<jats:sup>2</jats:sup> camera that is surveying 18,000 deg<jats:sup>2</jats:sup> of the northern sky (<jats:italic>δ</jats:italic> &gt; −28°) at a cadence of 2 days. We present PGIR light curves for 922 RCB candidates selected from a mid-IR color-based catalog. Of these 922, 149 are promising RCB candidates, as they show pulsations or declines similar to RCB stars. The majority of the candidates that are not RCB stars are either long-period variables (LPVs) or RV Tauri stars. We identify IR color-based criteria to better distinguish between RCB stars and LPVs. As part of a pilot spectroscopic run, we obtain NIR spectra for 26 of the 149 promising candidates and spectroscopically confirm 11 new RCB stars. We detect strong He <jats:sc>i</jats:sc> <jats:italic>λ</jats:italic>10830 features in the spectra of all RCB stars, likely originating within high-velocity (200–400 km s<jats:sup>−1</jats:sup>) winds in their atmospheres. Nine of these RCB stars show <jats:sup>12</jats:sup>C<jats:sup>16</jats:sup>O and <jats:sup>12</jats:sup>C<jats:sup>18</jats:sup>O molecular absorption features, suggesting that they are formed through a white dwarf merger. We detect quasiperiodic pulsations in the light curves of five RCB stars. The periods range between 30 and 125 days and likely originate from the strange-mode instability in these stars. Our pilot run results motivate a dedicated IR spectroscopic campaign to classify all RCB candidates.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>A current sheet, where magnetic energy is liberated through reconnection and converted to other forms, is thought to play the central role in solar flares, the most intense explosions in the heliosphere. However, the evolution of a current sheet and its subsequent role in flare-related phenomena such as particle acceleration is poorly understood. Here we report observations obtained with NASA’s Solar Dynamics Observatory that reveal a multiphase evolution of a current sheet in the early stages of a solar flare, from its formation to quasi-stable evolution and disruption. Our observations have implications for the understanding of the onset and evolution of reconnection in the early stages of eruptive solar flares.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>As many as 10% of OB-type stars have global magnetic fields, which is surprising given that their internal structure is radiative near the surface. A direct probe of internal structure is pulsations, and some OB-type stars exhibit pressure modes (<jats:italic>β</jats:italic> Cep pulsators) or gravity modes (slowly pulsating B-type stars; SPBs); a few rare cases of hybrid <jats:italic>β</jats:italic> Cep/SPBs occupy a narrow instability strip in the H-R diagram. The most precise fundamental properties of stars are obtained from eclipsing binaries (EBs), and those in clusters with known ages and metallicities provide the most stringent constraints on theory. Here we report the discovery that HD 149834 in the ∼5 Myr cluster NGC 6193 is an EB comprising a hybrid <jats:italic>β</jats:italic> Cep/SPB pulsator and a highly irradiated low-mass companion. We determine the masses, radii, and temperatures of both stars; the ∼9.7 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> primary resides in the instability strip where hybrid pulsations are theoretically predicted. The presence of both SPB and <jats:italic>β</jats:italic> Cep pulsations indicates that the system has a near-solar metallicity, and is in the second half of the main-sequence lifetime. The radius of the ∼1.2 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> companion is consistent with theoretical pre-main-sequence isochrones at 5 Myr, but its temperature is much higher than expected, perhaps due to irradiation by the primary. The radius of the primary is larger than expected, unless its metallicity is super-solar. Finally, the light curve shows residual modulation consistent with the rotation of the primary, and Chandra observations reveal a flare, both of which suggest the presence of starspots and thus magnetism on the primary.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present a study of 41 dwarf galaxies hosting active massive black holes (BHs) using Hubble Space Telescope observations. The host galaxies have stellar masses in the range of <jats:italic>M</jats:italic> <jats:sub>⋆</jats:sub> ∼ 10<jats:sup>8.5</jats:sup>–10<jats:sup>9.5</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> and were selected to host active galactic nuclei (AGNs) based on narrow emission line ratios derived from Sloan Digital Sky Survey spectroscopy. We find a wide range of morphologies in our sample including both regular and irregular dwarf galaxies. We fit the HST images of the regular galaxies using GALFIT and find that the majority are disk-dominated with small pseudobulges, although we do find a handful of bulge-like/elliptical dwarf galaxies. We also find an unresolved source of light in all of the regular galaxies, which may indicate the presence of a nuclear star cluster and/or the detection of AGN continuum. Three of the galaxies in our sample appear to be Magellanic-type dwarf irregulars and two galaxies exhibit clear signatures of interactions/mergers. This work demonstrates the diverse nature of dwarf galaxies hosting optically selected AGNs. It also has implications for constraining the origin of the first BH seeds using the local BH occupation fraction at low masses—we must account for the various types of dwarf galaxies that may host BHs.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The detection of GeV <jats:italic>γ</jats:italic>-ray emission from Galactic novae by the Fermi-Large Area Telescope has become routine since 2010, and is generally associated with shocks internal to the nova ejecta. These shocks are also expected to heat plasma to ∼10<jats:sup>7</jats:sup> K, resulting in detectable X-ray emission. In this paper, we investigate 13 <jats:italic>γ</jats:italic>-ray emitting novae observed with the Neil Gehrels Swift Observatory, searching for 1–10 keV X-ray emission concurrent with <jats:italic>γ</jats:italic>-ray detections. We also analyze <jats:italic>γ</jats:italic>-ray observations of novae V407 Lup (2016) and V357 Mus (2018). We find that most novae do eventually show X-ray evidence of hot shocked plasma, but not until the <jats:italic>γ</jats:italic>-rays have faded below detectability. We suggest that the delayed rise of the X-ray emission is due to large absorbing columns and/or X-ray suppression by corrugated shock fronts. The only nova in our sample with a concurrent X-ray/<jats:italic>γ</jats:italic>-ray detection is also the only embedded nova (V407 Cyg). This exception supports a scenario where novae with giant companions produce shocks with external circumbinary material and are characterized by lower density environments, in comparison with novae with dwarf companions where shocks occur internal to the dense ejecta.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In this paper we analyze the implications of gravitational waves (GWs) as standard sirens on the modified gravity models by using the third-generation GW detector, i.e., the Einstein Telescope. Two viable models in <jats:italic>f</jats:italic>(<jats:italic>R</jats:italic>) theories within the Palatini formalism are considered in our analysis (<jats:inline-formula> <jats:tex-math> <?CDATA ${f}_{1}({ \mathcal R })={ \mathcal R }-\tfrac{\beta }{{{ \mathcal R }}^{n}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabebe0ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> and <jats:inline-formula> <jats:tex-math> <?CDATA ${f}_{2}({ \mathcal R })={ \mathcal R }+\alpha \mathrm{ln}{ \mathcal R }-\beta $?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabebe0ieqn2.gif" xlink:type="simple" /> </jats:inline-formula>), with the combination of simulated GW data and the latest electromagnetic (EM) observational data (including the recently released Pantheon type Ia supernovae sample, the cosmic chronometer data, and baryon acoustic oscillation distance measurements). Our analysis reveals that the standard siren GWs, which provide an independent and complementary alternative to current experiments, could effectively eliminate the degeneracies among parameters in the two modified gravity models. In addition, we thoroughly investigate the nature of geometrical dark energy in the modified gravity theories with the assistance of <jats:italic>Om</jats:italic>(<jats:italic>z</jats:italic>) and statefinder diagnostic analysis. The present analysis makes it clear-cut that the simplest cosmological constant model is still the most preferred by the current data. However, the combination of future naturally improved GW data and the most recent EM observations will reveal the consistency or acknowledge the tension between the ΛCDM model and modified gravity theories.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present constraints on the physical properties (including stellar mass, age, and star formation rate) of 207 6 ≲ <jats:italic>z</jats:italic> ≲ 8 galaxy candidates from the Reionization Lensing Cluster Survey (RELICS) and Spitzer-RELICS surveys. We measure photometry using T-PHOT and perform spectral energy distribution fitting using EA<jats:italic>z</jats:italic>Y and BAGPIPES. Of the 207 candidates for which we could successfully measure (or place limits on) Spitzer fluxes, 23 were demoted to likely <jats:italic>z</jats:italic> &lt; 4. Among the high-<jats:italic>z</jats:italic> candidates, we find intrinsic stellar masses between 1 × 10<jats:sup>6</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> and 4 × 10<jats:sup>9</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>, and rest-frame UV absolute magnitudes between −22.6 and −14.5 mag. While our sample is mostly comprised of <jats:inline-formula> <jats:tex-math> <?CDATA ${L}_{m\mathrm{UV}}/{L}_{m\mathrm{UV}}^{* }\lt 1$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabe533ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> galaxies, it extends to <jats:inline-formula> <jats:tex-math> <?CDATA ${L}_{m\mathrm{UV}}/{L}_{m\mathrm{UV}}^{* }\sim 2$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabe533ieqn2.gif" xlink:type="simple" /> </jats:inline-formula>. Our sample spans ∼4 orders of magnitude in stellar mass and star formation rates, and exhibits ages that range from maximally young to maximally old. We highlight 11 <jats:italic>z</jats:italic> ≥ 6.5 galaxies with detections in Spitzer/IRAC imaging, several of which show evidence for some combination of evolved stellar populations, large contributions of nebular emission lines, and/or dust. Among these is PLCKG287+32-2013, one of the brightest <jats:italic>z</jats:italic> ∼ 7 candidates known (AB mag 24.9 at 1.6 <jats:italic>μ</jats:italic>m) with a Spitzer 3.6 <jats:italic>μ</jats:italic>m flux excess suggesting strong [O <jats:sc>iii</jats:sc>] + H-<jats:italic>β</jats:italic> emission (∼1000 Å rest-frame equivalent width). We discuss the possible uses and limits of our sample and present a public catalog of Hubble + Spitzer photometry along with physical property estimates for all objects in the sample. Because of their apparent brightnesses, high redshifts, and variety of stellar populations, these objects are excellent targets for follow-up with the James Webb Space Telescope.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present the direct detection of the splashback feature using the sample of massive galaxy clusters from the Local Cluster Substructure Survey (LoCuSS). This feature is clearly detected (above 5<jats:italic>σ</jats:italic>) in the stacked luminosity density profile obtained using the <jats:italic>K</jats:italic>-band magnitudes of spectroscopically confirmed cluster members. We obtained the best-fit model by means of Bayesian inference, which ranked models including the splashback feature as more descriptive of the data with respect to models that do not allow for this transition. In addition, we have assessed the impact of the cluster dynamical state on the occurrence of the splashback feature. We exploited the extensive multiwavelength LoCuSS data set to test a wide range of proxies for the cluster formation history, finding the most significant dependence of the splashback feature location and scale according to the presence or absence of X-ray emitting galaxy groups in the cluster infall regions. In particular, we report for the first time that clusters that do not show massive infalling groups present the splashback feature at a smaller clustercentric radius <jats:italic>r</jats:italic> <jats:sub>sp</jats:sub>/<jats:italic>r</jats:italic> <jats:sub>200,<jats:italic>m</jats:italic> </jats:sub> = 1.158 ± 0.071 than clusters that are actively accreting groups <jats:italic>r</jats:italic> <jats:sub>sp</jats:sub>/<jats:italic>r</jats:italic> <jats:sub>200,<jats:italic>m</jats:italic> </jats:sub> = 1.291 ± 0.062. The difference between these two subsamples is significant at 4.2<jats:italic>σ</jats:italic>, suggesting a correlation between the properties of the cluster potential and its accretion rate and merger history. Similarly, clusters that are classified as old and dynamically inactive present stronger signatures of the splashback feature, with respect to younger, more active clusters. We are directly observing how fundamental dynamical properties of clusters reverberate across vastly different physical scales.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present a new generation of model calculations for cosmogenic production rates in various types of solar system bodies. The model is based on the spectra for primary and secondary particles calculated using the INCL++6 code, which is the most reliable and most sophisticated code available for spallation reactions. Thanks to the recent improvements (extending the code to lower and higher energies and considering light charged particles as ejectiles and projectiles), we can for the first time directly consider primary and secondary Galactic <jats:italic>α</jats:italic> particles. We calculate production rates for <jats:sup>22</jats:sup>Na, <jats:sup>10</jats:sup>Be, and <jats:sup>26</jats:sup>Al in an L-chondrite with a radius of 45 cm and in the Apollo 15 drill core, and we determine the long-term average Galactic cosmic-ray (GCR) spectrum (represented by the solar modulation potential Φ) in the meteoroid orbits at ∼3 au of Φ = 600 MV and at 1 au, i.e., for Earth and Moon of Φ = 660 MV. From this, we calculate a long-term average GCR gradient in the inner solar system of ∼5% au<jats:sup>−1</jats:sup>. Finally, we discuss the possibility of studying temporal GCR variations and meteoroid orbits using production rate ratios of short- and long-lived radionuclides.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>While observations of many high-precision radio pulsars of order ≲1 <jats:italic>μ</jats:italic>s across the sky are needed for the detection and characterization of a stochastic background of low-frequency gravitational waves (GWs), sensitivity to single sources of GWs requires even higher timing precision. The Argentine Institute of Radio Astronomy (IAR; Instituto Argentino de Radioastronomía) has begun observations of the brightest known millisecond pulsar, J0437−4715. Even though the two antennas are smaller than other single-dish telescopes previously used for pulsar timing array (PTA) science, the IAR’s capability to monitor this pulsar daily, coupled with the pulsar’s brightness, allows for high-precision measurements of pulse-arrival time. While upgrades of the facility are currently underway, we show that modest improvements beyond current plans will provide IAR with unparalleled sensitivity to this pulsar. The most stringent upper limits on single GW sources come from the North American Nanohertz Observatory for Gravitational Waves (NANOGrav). Observations of PSR J0437−4715 will provide a significant sensitivity increase in NANOGrav’s “blind spot” in the sky where fewer pulsars are currently being observed. With state-of-the-art instrumentation installed, we estimate the array’s sensitivity will improve by a factor of ≈2–4 over 10 yr for 20% of the sky with the inclusion of this pulsar, as compared to a static version of the PTA used in NANOGrav’s most recent limits. More modest instrumentation results in factors of ≈1.4–3. We identify four other candidate pulsars as suitable for inclusion in PTA efforts. International PTA efforts will also benefit from inclusion of these data, given the potential achievable sensitivity.</jats:p>