Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>The recent detection of GW190521 stimulated ideas on how to populate the predicted black hole (BH) pair-instability (PI) mass gap. One proposal is the dynamical merger of two stars below the PI regime forming a star with a small core and an oversized envelope. We outline the main challenges this scenario faces to form one BH in the gap. In particular, the core needs to avoid growing during the merger, and the merger product needs to retain enough mass, including in the subsequent evolution, and at core collapse (CC). We explore this scenario with detailed stellar evolution calculations, starting with ad hoc initial conditions enforcing no core growth during the merger. We find that these massive merger products are likely to be helium-rich and spend most of their remaining lifetime within regions of instabilities in the Herzsprung–Russell diagram, such as luminous blue variable eruptions. An energetic estimate of the amount of mass loss neglecting the back reaction of the star suggests that the total amount of mass that can be removed at low metallicity is ≲1 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>. This is small enough that at CC our models are retaining sufficient mass to form BHs in the PI gap similar to the recent ones detected by LIGO/Virgo. However, mass loss at the time of merger, the resulting core structure, and the mass loss at CC still need to be quantified for these models to confirm the viability of this scenario.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The recently discovered object P/2019 LD2 (by the Asteroid Terrestrial-impact Last Alert System) was initially thought to be a Jupiter Trojan asteroid, until dynamical studies and the appearance of persistent cometary activity revealed that this object is actually an active Centaur. However, the dynamical history, thermal environment, and impact of such environments on the activity of 2019 LD2 are poorly understood. Here we conduct dynamical simulations to constrain its orbital history and resulting thermal environment over the past 3000 yr. We find that 2019 LD2 is currently in the vicinity of a dynamical “Gateway” that facilitates the majority of transitions from the Centaur population into the Jupiter Family of Comets (JFC population). Our calculations show that it is unlikely to have spent significant amounts of time in the inner solar system, suggesting that its nucleus is relatively pristine in terms of physical, chemical, and thermal processing through its history. This could explain its relatively high level of distant activity as a recently activated primordial body. Finally, we find that the median frequency of transition from the Gateway population into the JFC population varies from once every ∼3 yr to less than once every 70 yr, if 2019 LD2's nucleus is ∼1 km in radius or greater than 3 km in radius. Forward modeling of 2019 LD2 shows that it will transition into the JFC population in 2063, representing the first known opportunity to observe the evolution of an active Centaur nucleus as it experiences this population-defining transition.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report on NICER observations of the magnetar SGR 1935+2154, covering its 2020 burst storm and long-term persistent emission evolution up to ∼90 days postoutburst. During the first 1120 s taken on April 28 00:40:58 UTC, we detect over 217 bursts, corresponding to a burst rate of &gt;0.2 bursts s<jats:sup>−1</jats:sup>. Three hours later, the rate was 0.008 bursts s<jats:sup>−1</jats:sup>, remaining at a comparatively low level thereafter. The <jats:italic>T</jats:italic> <jats:sub>90</jats:sub> burst duration distribution peaks at 840 ms; the distribution of waiting times to the next burst is fit with a lognormal with an average of 2.1 s. The 1–10 keV burst spectra are well fit by a blackbody, with an average temperature and area of <jats:italic>kT</jats:italic> = 1.7 keV and <jats:italic>R</jats:italic> <jats:sup>2</jats:sup> = 53 km<jats:sup>2</jats:sup>. The differential burst fluence distribution over ∼3 orders of magnitude is well modeled with a power-law form <jats:italic>dN</jats:italic>/<jats:italic>dF</jats:italic> ∝ <jats:italic>F</jats:italic> <jats:sup>−1.5±0.1</jats:sup>. The source persistent emission pulse profile is double-peaked hours after the burst storm. We find that the burst peak arrival times follow a uniform distribution in pulse phase, though the fast radio burst associated with the source aligns in phase with the brighter peak. We measure the source spin-down from heavy-cadence observations covering days 21–39 postoutburst, <jats:inline-formula> <jats:tex-math> <?CDATA $\dot{\nu }=-3.72(3)\times {10}^{-12}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlabc94cieqn1.gif" xlink:type="simple" /> </jats:inline-formula> Hz s<jats:sup>−1</jats:sup>, a factor of 2.7 larger than the value measured after the 2014 outburst. Finally, the persistent emission flux and blackbody temperature decrease rapidly in the early stages of the outburst, reaching quiescence 40 days later, while the size of the emitting area remains unchanged.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>CK Vulpeculae (CK Vul), which erupted in AD 1670–71, was long considered to be a nova outburst; however, recent observations have required that alternative scenarios be considered. Long-slit infrared spectroscopy of a forbidden line of iron reported here has revealed high line-of-sight velocities (∼±900 km s<jats:sup>−1</jats:sup>) of the ansae at the tips of the bipolar lobes imaged in H<jats:italic>α</jats:italic> in 2010. The deprojected velocities of the tips are approximately ±2130 km s<jats:sup>−1</jats:sup> assuming the previously derived inclination angle of 65° for the axis of cylindrical symmetry of the bipolar nebula. Such high velocities are in stark contrast to previous reports of much lower expansion velocities in CK Vul. Based on the deprojected velocities of the tips and their angular expansion measured over a 10 yr baseline, we derive a revised estimate, with estimated uncertainties, of <jats:inline-formula> <jats:tex-math> <?CDATA ${3.2}_{-0.6}^{+0.9}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlabc885ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> kpc for the distance to CK Vul. This implies that the absolute visual magnitude at the peak of the 1670 explosion was <jats:inline-formula> <jats:tex-math> <?CDATA ${M}_{V}=-{12.4}_{-2.4}^{+1.3}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlabc885ieqn2.gif" xlink:type="simple" /> </jats:inline-formula>, indicating that the 1670 event was far more luminous than previous estimates and brighter than any classical nova or any Galactic stellar merger. We propose that CK Vul belongs to the class of intermediate-luminosity optical transients (ILOTs), objects which bridge the luminosity gap between novae and supernovae. While eruptions in lower luminosity ILOTs are attributed to merger events, the origin of the highly luminous ILOT outbursts is currently not known.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present the direct imaging discovery of a substellar companion to the nearby Sun-like star, HD 33632 Aa, at a projected separation of ∼20 au, obtained with SCExAO/CHARIS integral field spectroscopy complemented by Keck/NIRC2 thermal infrared imaging. The companion, HD 33632 Ab, induces a 10.5<jats:italic>σ</jats:italic> astrometric acceleration on the star as detected with the Gaia and Hipparcos satellites. SCExAO/CHARIS <jats:italic>JHK</jats:italic> (1.1–2.4 <jats:italic>μ</jats:italic>m) spectra and Keck/NIRC2 <jats:italic>L</jats:italic> <jats:sub>p</jats:sub> (3.78 <jats:italic>μ</jats:italic>m) photometry are best matched by a field L/T transition object: an older, higher-gravity, and less dusty counterpart to HR 8799 cde. Combining our astrometry with Gaia/Hipparcos data and archival Lick Observatory radial velocities, we measure a dynamical mass of 46.4 ± 8 <jats:italic>M</jats:italic> <jats:sub>J</jats:sub> and an eccentricity of <jats:italic>e</jats:italic> &lt; 0.46 at 95% confidence. HD 33632 Ab’s mass and mass ratio (4.0% ± 0.7%) are comparable to the low-mass brown dwarf GJ 758 B and intermediate between the more massive brown dwarf HD 19467 B and the (near-)planet-mass companions to HR 2562 and GJ 504. Using Gaia to select for direct imaging observations with the newest extreme adaptive optics systems can reveal substellar or even planet-mass companions on solar system–like scales at an increased frequency compared to blind surveys.</jats:p>