Hasil untuk "astro-ph.EP"

Veronica Pratt, Jason R. Reeves, David V. Martin et al.

Most flares on the Sun occur at random, but there is a small percentage of "sympathetic flaring" -- the triggering of one flare by another. Previously there had been no widespread confirmation of sympathetic flares on other stars. In this work, we developed a new flare detection algorithm that is sensitive to closely-separated and overlapping stellar flares. We applied it to TESS data and discovered ~ 220,000 flares on ~ 16,000 stars, the majority of which are M-dwarfs. The wait time distribution between flares demonstrates an excess of closely-separated flares, relative to expectations from a Poisson process. We attribute this to sympathetic flares, occurring at a rate of between 4% and 9%, which matches the rate seen on the Sun. Our result is the first statistically robust detection of sympathetic flares on other stars, demonstrating a commonality between the Sun and low-mass stars.

Cole Mathis, Harrison B. Smith

Origins of life research is marred by ambiguous questions and goals, creating uncertainty about when research objectives have been achieved. Because of numerous unknowns and disagreements about definitions and theories, the field lacks clear markers of progress. We argue that the origins community should focus on goals that have agreed-upon meaning and can be consensually categorized as achieved or unachieved. The origins community needs these goals to maintain coherence amongst a federation of problems with the shared, but nebulous aspiration of understanding the origins of life. We propose a list of challenges with clear 'Finish Lines'--explicit descriptions of what will be achieved if each goal is reached--similar to the X-prize model. The intent is not to impose top-down research directions, but to compel the community to coalesce around explicit problems of the highest priority, as physics, astronomy, and planetary science communities do when setting science objectives for missions and megaprojects. Even if the generated phenomena are not unequivocally life-like, demonstrating systems that achieve these goals will sharpen the distinction between life itself and the constellation of phenomena that co-occur with life. This document was originally submitted as a whitepaper to the 2025 NASA-DARES (Decadal Astrobiology Research and Exploration Strategy) call for whitepapers (https://go.nasa.gov/ABStrategyRFI).

Casper Farret Jentink, Francesco Pepe, Christophe Lovis et al.

High-resolution spectroscopy (R>50,000) in astronomy typically uses echelle-type spectrographs, which excel for exoplanet detection via radial velocity but compromise throughput for atmospheric characterization. We propose and test a novel method to achieve very high spectral resolution with significantly higher throughput within a limited bandpass using a tuned, high fringe-density volume phase holographic (VPH) grating in double pass. Using a wavelength-tunable laser, we measured the dispersion and diffraction efficiency of this setup, finding that our tested VPH grating reaches a diffraction-limited resolving power >140,000 in double pass with a peak diffraction efficiency of 79% for unpolarized light. Based on current manufacturing capabilities, we estimate double-pass diffraction efficiencies >50% with resolving powers >200,000 are achievable from visible to near-infrared wavelengths, limited only by detector size.

Thayne Currie, Kellen Lawson, Erica Dykes et al.

For one of the first set of Roman Coronagraph project images, we propose to target AB Aurigae. AB Aurigae is a complex and visually stunning system, surrounded by a gas rich protoplanetary disk showing numerous spiral arms, an enigmatic embedded protoplanet (AB Aurigae b) at 0\farcs{}6 separation, and hints of potential additional sites of planet formation. Even a marginally-successful dark hole generation (e.g. 10$^{-5}$--10$^{-6}$ contrast) with CGI would yield a vastly improved view of AB Aur b at optical wavelengths where current ground-based and HST data struggle to yield a high SNR detection and parameters (astrometry, photometry) unbiased by processing artifacts. Total intensity imaging and polarimetry together will provide new constraints on the disk's dust properties and the range of emission sources for AB Aur b. AB Aur images with the Roman Coronagraph will provide a striking, inspiring demonstrations of the instrument's power and promise for detecting fainter planets and disks.

Ling Xuan Yao, Keaton J. Bell, Andrew Dublin

The measured rates of period change, $\dot{P}$, in the signals of pulsating white dwarf stars are often interpreted as direct detections of structural changes from secular cooling. Due to the intrinsic nature of this quantity, $\dot{P}$ analysis has been used to probe fundamental physics, such as constraining the mass of hypothetical axion particles. However, most white dwarfs are expected to host planets that could induce an external source of period change, caused by the light travel time variations from reflex motion about the system barycenter. Assuming a plausible distribution of planets that could orbit white dwarf stars, we quantify the amount of reflex motion expected from undiscovered planets as an important source of extrinsic error in $\dot{P}$ analyses. While the median error from reflex motion is $\sim10^{-15}$ ss$^{-1}$ (similar to the secular $\dot{P}$ rates expected for cool DAV pulsators), individual close-in planets could cause $\dot{P}$ errors as large as $10^{-11}$ ss$^{-1}$

Thayne Currie, Olivier Guyon, Ruslan Belikov et al.

The baseline contrast floor from the Roman Coronagraph's High-Order Wavefront Sensing and Control strategy likely degrades over the course of time, requiring periodic recalibration of the dark hole. Here, we propose to consider spatial linear dark field control (sLDFC) on a one-sided deep-contrast region of the focal plane as a potential test. Implementing sLDFC on CGI will likely require some unique data acquisition strategies given the EMCCD's high flux sensitivity in long exposures/high gain: we outline three possible approaches. However, if successful, sLDFC's advances are substantial: (1) enabling us to maintain a fainter, more temporally correlated dark hole which will improve CGI's contrast after post-processing and (2) efficiently providing a reliable signal (bright field) for accurate reconstruction of residual starlight in the dark field, further boosting CGI's detection limit for bright targets.

John Southworth

Limb darkening (LD) is typically parameterised using a range of functional "laws" in models of the light curves of eclipsing binary and transiting planetary systems. The two-coefficient LD laws all suffer from a strong correlation between their coefficients, preventing a reliable determination of both coefficients from high-quality light curves. We use numerical simulations to propose re-parameterisations of the quadratic, logarithmic, square-root and cubic LD laws that show much weaker correlations, and implement them into the JKTEBOP code. We recommend that these re-parameterisations are used whenever both LD coefficients are fitted. Conversely, when fitting for only one coefficient, the standard laws should be used to avoid problems with fixing coefficients at poor values. We find that these choices have little effect on the other fitted parameters of a light curve model. We also recommend that the power-2 LD law should be used as default because it provides a good fit to theoretical predictions, and that the quadratic and linear laws should be avoided because they do not.

Sumit Kumar, A. K. Meshram, A. Astro et al.

Technical advancements and experimental works for the integration of 5G and Non-Terrestrial Networks (NTN) have gained significant traction over the past few years. NTN components have been officially included in the 5G ecosystem by 3GPP in the latest Release-17. 5G-NTN research is ongoing and it is desirable to have a platform that facilitates quick prototyping of the proof-of-concept methods. OpenAirInterface(OAI) is an open-source experimental yet 3GPP standard-compliant Software Defined Radio (SDR) based protocol stack that has been widely known for implementing 4G/5G technologies. Due to its proven capabilities and flexibility, OAI is currently in the developmental process of integrating adaptations for the 5G-NTN. In this work, we discuss the peculiar features of OAI which are shaping it towards becoming a preferred tool for research and experimentation related to 5G-NTN. We provide details of completed/ongoing 5G-NTN projects leveraging OAI to achieve their objectives. In particular, we discuss 5G-GOA and 5G-LEO where critical adaptations in OAI are being done to support 5G-NTN use-cases. Such adaptations enable direct-access between UE and gNB via transparent payload Geostationary (5G-GOA) and Non-geostationary satellites (5G-LEO). Both projects have closely followed 3GPP discussions over 5G-NTN and the adaptations are compliant with the currently frozen 3GPP Release-17. OAI adaptations from both projects will be merged into the main development branch of OAI. We also provide a future roadmap of OAI towards 5G-NTN development. We believe that the pioneering steps taken in the course of the aforementioned projects will establish OAI as a preferred tool for 5G-NTN research and experimentations.

Afra Ashraf, Daniella C. Bardalez Gagliuffi, Elena Manjavacas et al.

We present a technique to identify spectrophotometrically variable L7-T3 brown dwarfs with single-epoch, low-resolution, near-infrared SpeX spectra. We calculated spectral indices on known variable brown dwarfs and used them to select 11 index-index parameter spaces where known variables can be distinguished from the rest of the general population of brown dwarfs. We find 62 candidate variables, 12 of which show significant variability amplitude in independent photometric monitoring surveys. This technique constitutes the first formal method to identify a time-dependent effect such as variability from peculiarities in their integrated light spectra. This technique will be a useful tool to prioritize targets for future photometric and spectroscopic monitoring in the era of JWST and 30m-class telescopes.

Laura Flagg, Christopher Johns-Krull, Kevin France et al.

Using HST-COS FUV spectra, we have discovered warm molecular hydrogen in the TWA 7 system. TWA 7, a $\sim$9 Myr old M2.5 star, has a cold debris disk and has previously shown no signs of accretion. Molecular hydrogen is expected to be extremely rare in a debris disk. While molecular hydrogen can be produced in star spots or the lower chromospheres of cool stars such as TWA 7, fluxes from progressions that get pumped by the wings of Ly$α$ indicate that this molecular hydrogen could be circumstellar and thus that TWA 7 is accreting at very low levels and may retain a reservoir of gas in the near circumstellar environment.

Saurabh Gore, Manuel Ntumba

Lunar hematite is formed by the oxidation of iron on the surface of the Moon by oxygen from the Earth's upper atmosphere. The Moon's surface is continuously affected by solar particles from the sun. However, Earth's magnetic tail blocks 99 % of the solar wind and provides windows of opportunity to transport oxygen from Earth's upper atmosphere to the Moon through magnetotail when it is in its full moon phase. Here, we propose to place a space weather observatory at the Earth-Moon L1 Lagrange point carrying a crucial payload onboard to study how Earth's magnetotail causes the Moon's surface to rust. The space weather observatory monitors the effect of Earth's magnetic field on the Moon using advanced spectroscopic sensors from Lagrange-based stations. Earth-moon L1 Lagrange point is the key location for space-weather observation as spacecraft near this point obtains a nearly unobstructed view of the moon. Numerical methods needed for a high-order analytical approximation have been implemented for more accurate predictions.

Beth Klein, Alexandra E. Doyle, B. Zuckerman et al.

The element beryllium is detected for the first time in white dwarf stars. This discovery in the spectra of two helium-atmosphere white dwarfs was made possible only because of the remarkable overabundance of Be relative to all other elements, heavier than He, observed in these stars. The measured Be abundances, relative to chondritic, are by far the largest ever seen in any astronomical object. We anticipate that the Be in these accreted planetary bodies was produced by spallation of one or more of O, C, and N in a region of high fluence of particles of MeV or greater energy.

Adam S. Jermyn, Shashikumar M. Chitre, Pierre Lesaffre et al.

Differential rotation is central to a great many mysteries in stars and planets. In Part I we predicted the order of magnitude and scaling of the differential rotation in both hydrodynamic and magnetohydrodynamic convection zones. Our results apply to both slowly- and rapidly-rotating systems, and provide a general picture of differential rotation in stars and fluid planets. We further calculated the scalings of the meridional circulation, entropy gradient and baroclinicity. In this companion paper we compare these predictions with a variety of observations and numerical simulations. With a few exceptions we find that these are consistent in both the slowly-rotating and rapidly-rotating limits. Our results help to localize core-envelope shear in red~giant stars, suggest a rotation-dependent frequency shift in the internal gravity waves of massive stars and potentially explain observed deviations from von Zeipel's gravity darkening in late-type stars.

M. Mugrauer, K. -U. Michel

The first results of a new survey are reported, which explores the 2nd data release of the ESA-Gaia mission, in order to search for stellar companions of (Community) TESS Objects of Interest and to characterize their properties. In total, 193 binary and 15 hierarchical triple star systems are presented, detected among 1391 target stars, which are located at distances closer than about 500pc around the Sun. The companions and the targets are equidistant and share a common proper motion, as it is expected for gravitationally bound stellar systems, proven with their accurate Gaia astrometry. The companions exhibit masses in the range between about 0.08$M_\odot$ and 3$M_\odot$ and are most frequently found in the mass range between 0.13 and 0.6$M_{\odot}$. The companions are separated from the targets by about 40 up to 9900au, and their frequency continually decreases with increasing separation. While most of the detected companions are late K to mid M dwarfs, also 5 white dwarf companions were identified in this survey, whose true nature is revealed by their photometric properties.

Andrei Tokovinin

HIP 45734 is a quadruple system of 2+2 architecture located at 68 pc from the Sun. The outer 9" system A,B has a period of ~10^4 yr. The pair Aa,Ab is a visual binary with a period of 20.1 years and an eccentricity of 0.78. Its periastron in 2019.1 was observed spectroscopically, yielding masses (1.10+-0.04 and 0.98+-0.03 M_sun) and orbital parallax, 14.90+-0.37 mas. The masses, luminosities, and colors approximately agree with evolutionary models of main sequence stars. The component Aa has a detectable lithium line, whereas in Ab it is absent. The pair Ba,Bb is a single-lined spectroscopic binary with a period of 0.55552 day and an orbital inclination of ~45 deg derived by modeling the rotationally broadened line profile with ``flat bottom''. The mass of Bb is ~0.4 M_sun. The star B is chromospherically active (an x-ray source); its flux is modulated with the orbital period by starspots, in addition to occasional flares. The system is probably older than ~600 Myr; it does not belong to any known moving group.

Christina Hedges, Ruth Angus, Geert Barentsen et al.

NASA's TESS mission \citep{tess} has produced high precision photometry of millions of stars to the community. The majority of TESS observations have a duration of $\approx$27 days, corresponding to a single observation during a TESS sector. A small subset of TESS targets are observed for multiple sectors, with approximately 1-2\% of targets falling in the Continuous Viewing Zone (CVZ) during the prime mission \citep{yield}, where targets are observed continuously for a year. These targets are highly valuable for extracting long period rotation rates, which can be linked to stellar ages. We present a pip installable Python tool for extracting long period rotation rates in the TESS CVZ, while simultaneously mitigating instrument systematics.

Luis Diego Pinto, Roberto Capuzzo-Dolcetta, Gianfranco Magni

The study of the stability of massive gaseous disks around a star in a non-isolated context is not a trivial issue and becomes a more complicated task for disks hosted by binary systems. The role of self-gravity is thought to be significant, whenever the ratio of the disk to the star mass is non-negligible. To tackle these issues we implemented, tested and applied our own Smoothed Particle Hydrodynamics (SPH) algorithm. The code (named GaSPH) passed various quality tests and shows good performances, so to be reliably applied to the study of disks around stars accounting for self-gravity. This work aims to introduce and describe the algorithm, making some performance and stability tests. It constitutes the first part of a series of studies in which self-gravitating disks in binary systems will be let evolve in larger environments such as Open Clusters.

Andrew Swan, Jay Farihi, Thomas G. Wilson

Archival data from the WISE satellite reveals infrared flux variations of tens of per cent around numerous dusty white dwarfs. Data spanning more than seven years reveal more than half of known systems are varying in the 3.4 micron band, while the 4.6 micron data are challenging to interpret due to lower signal-to-noise. The sparsely-sampled data limit interpretation, but the heterogeneous light curves suggest each source may be idiosyncratic, where there maybe competing processes operating on different time-scales. Collisions are likely driving the observed decays in flux, and this finding suggests that dust production is operating more often than indicated by previous observations. The observed variation is at odds with the canonical flat disc model in isolation, and underscores the need for infrared monitoring of these evolved planetary systems to inform the next generation of theoretical models.

Francisco Ocaña, Alejandro Sánchez de Miguel, ORISON team et al.

We investigate the observation of meteors with video cameras in stratospheric balloons, overcoming tropospheric handicaps like weather and extinction. We have studied the practical implementation of the idea, designed and tested instrumentation for balloon-borne missions. We have analysed the data of the Geminids 2016 campaign, determining the meteoroid flux just before the maximum. This text is an adaption of the work by the first author for his PhD Thesis: Techniques for near-Earth interplanetary matter detection and characterisation from optical ground-based observatories (Ocaña, 2017). Refer to his thesis for further detail. The lines here are a summary of the presentation given, for the sake of completeness of these proceedings of the IMC 2018 in Pezinok-Modra. The multimedia material shown during the presentation at IMC 2018 can be found in the Zenodo repository for the ORISON Project and Daedalus Project.

J. Landercasper, D. Attai, D. Atisha et al.

BackgroundMultiple recent reports have documented significant variability of reoperation rates after initial lumpectomy for breast cancer. To address this issue, a multidisciplinary consensus conference was convened during the American Society of Breast Surgeons 2015 annual meeting.MethodsThe conference mission statement was to “reduce the national reoperation rate in patients undergoing breast conserving surgery for cancer, without increasing mastectomy rates or adversely affecting cosmetic outcome, thereby improving value of care.” The goal was to develop a toolbox of recommendations to reduce the variability of reoperation rates and improve cosmetic outcomes. Conference participants included providers from multiple disciplines involved with breast cancer care, as well as a patient representative. Updated systematic reviews of the literature and invited presentations were sent to participants in advance. After topic presentations, voting occurred for choice of tools, level of evidence, and strength of recommendation.ResultsThe following tools were recommended with varied levels of evidence and strength of recommendation: compliance with the SSO-ASTRO Margin Guideline; needle biopsy for diagnosis before surgical excision of breast cancer; full-field digital diagnostic mammography with ultrasound as needed; use of oncoplastic techniques; image-guided lesion localization; specimen imaging for nonpalpable cancers; use of specialized techniques for intraoperative management, including excisional cavity shave biopsies and intraoperative pathology assessment; formal pre- and postoperative planning strategies; and patient-reported outcome measurement.ConclusionsA practical approach to performance improvement was used by the American Society of Breast Surgeons to create a toolbox of options to reduce lumpectomy reoperations and improve cosmetic outcomes.