Keaton J. Bell
A5024343232- Stellar, planetary, and galactic studies
- Astronomy and Astrophysical Research
- Gamma-ray bursts and supernovae
- Astro and Planetary Science
- Astrophysics and Star Formation Studies
- Astronomical Observations and Instrumentation
- Astrophysical Phenomena and Observations
- Adaptive optics and wavefront sensing
- Solar and Space Plasma Dynamics
- Pulsars and Gravitational Waves Research
- Geophysics and Gravity Measurements
- History and Developments in Astronomy
- Space Exploration and Technology
- Geophysics and Sensor Technology
- High-pressure geophysics and materials
- Real-time simulation and control systems
- Radio Astronomy Observations and Technology
- Computational Physics and Python Applications
- Heat Transfer and Optimization
- Seismic Imaging and Inversion Techniques
- Advanced Frequency and Time Standards
- Heat Transfer and Boiling Studies
- Laser Design and Applications
- Inertial Sensor and Navigation
- Calibration and Measurement Techniques
Queens College, CUNY
2022-2024
City University of Seattle
2019-2023
University of Washington
2011-2023
Aarhus University
2018-2020
Max Planck Institute for Solar System Research
2017-2019
Max Planck Society
2018
The University of Texas at Austin
2013-2017
McDonald's (United States)
2013-2017
We present a spectroscopic catalog of 70,841 visually inspected M dwarfs from the seventh data release Sloan Digital Sky Survey. For each spectrum, we provide measurements spectral type, number molecular band heads, and Hα, Hβ, Hγ, Hδ, Ca ii K emission lines. In addition, calculate metallicity-sensitive parameter ζ identify relationship between g − r z colors dwarfs. assess precision our types (which were assigned by individual examination), review bulk attributes sample, examine magnetic...
Abstract In the third APOKASC catalog, we present data for complete sample of 15,808 evolved stars with APOGEE spectroscopic parameters and Kepler asteroseismology. We used 10 independent asteroseismic analysis techniques anchor our system on fundamental radii derived from Gaia L T eff . provide evolutionary state, surface gravity, mass, radius, age, to derive them 12,418 stars. This includes 10,036 exceptionally precise measurements, median fractional uncertainties in <mml:math...
We present photometry and spectroscopy for 27 pulsating hydrogen-atmosphere white dwarfs (DAVs; a.k.a. ZZ Ceti stars) observed by the Kepler space telescope up to K2 Campaign 8, an extensive compilation of observations with unprecedented duration (>75 days) duty cycle (>90%). The space-based reveals pulsation properties previously inaccessible ground-based observations. observe a sharp dichotomy in oscillation mode line widths at roughly 800 s, such that dwarf pulsations periods exceeding s...
The Large Synoptic Survey Telescope is designed to provide an unprecedented optical imaging dataset that will support investigations of our Solar System, Galaxy and Universe, across half the sky over ten years repeated observation. However, exactly how LSST observations be taken (the observing strategy or "cadence") not yet finalized. In this dynamically-evolving community white paper, we explore detailed performance anticipated science expected depend on small changes strategy. Using...
We present the discovery of TOI-197.01, first transiting planet identified by Transiting Exoplanet Survey Satellite (TESS) for which asteroseismology host star is possible. TOI-197 (HIP116158) a bright (V=8.2 mag), spectroscopically classified subgiant oscillates with an average frequency about 430 muHz and displays clear signature mixed modes. The oscillation amplitude confirms that redder TESS bandpass compared to Kepler has small effect on oscillations, supporting expected yield thousands...
We present a novel method to detect variable astrophysical objects and transient phenomena using anomalous excess scatter in repeated measurements from public catalogs of Gaia DR2 Zwicky Transient Facility (ZTF) DR3 photometry. first provide generalized, all-sky proxy for variability only photometry, calibrated white dwarf stars. To ensure more robust candidate detection, we further employ combining with ZTF photometry alerts. demonstrate the efficacy, apply this latter technique sample...
Abstract The Transiting Exoplanet Survey Satellite (TESS) has an exceptionally large plate scale of 21″ px −1 , causing most TESS light curves to record the blended multiple stars. This creates a danger misattributing variability observed by wrong source, which would invalidate any analysis. We developed method that can localize origin on sky better than one fifth pixel. Given measured frequencies (e.g., from periodogram analysis), we show best-fit sinusoid amplitudes raw extracted each...
We report the discovery of second and third pulsating extremely low mass (ELM) white dwarfs (WDs), SDSS J111215.82+111745.0 (hereafter J1112) J151826.68+065813.2 J1518). Both have masses < 0.25 M☉ effective temperatures below 10, 000 K, establishing these putatively He-core WDs as a cooler class hydrogen-atmosphere (DAVs, or ZZ Ceti stars). The short-period pulsations evidenced in light curve J1112 may also represent first observation acoustic (p-mode) any WD, which provide an exciting...
We report the discovery of two new pulsating extremely low-mass (ELM) white dwarfs (WDs), SDSS J161431.28+191219.4 (hereafter J1614) and J222859.93+362359.6 J2228). Both WDs have masses <0.25 Msun thus likely harbor helium cores. Spectral fits indicate these are coolest ever found. J1614 has Teff = 8880 +/- 170 K log g 6.66 0.14, which corresponds to a roughly 0.19 WD. J2228 is considerably cooler, with 7870 120 6.03 0.08, 0.16 WD, making it lowest-mass WD known. There multiple ELM effective...
Context. The study of stellar activity cycles is crucial to understand the underlying dynamo and how it causes magnetic signatures such as dark spots bright faculae. Having knowledge about dominant source surface might allow us draw conclusions age field topology, put solar cycle in context. Aims. We investigate process that by studying appearance contemporaneous photometric chromospheric time series. Methods. Lomb-Scargle periodograms are used search for periods present To emphasize...
Abstract We report the discovery of a white dwarf exhibiting deep, irregularly shaped transits, indicative circumstellar planetary debris. Using Zwicky Transient Facility DR2 photometry ZTF J013906.17+524536.89 and follow-up observations from Las Cumbres Observatory, we identify multiple transit events that recur every ≈107.2 days, much longer than 4.5–4.9 hr orbital periods observed in WD 1145+017, only other known with transiting The transits vary both depth duration, lasting 15–25 days...
We report the discovery of 74 new pulsating DA white dwarf stars, or ZZ Cetis, from data obtained by Transiting Exoplanet Survey Satellite (TESS) mission, Sectors 1 to 39, corresponding first 3 cycles. This includes objects Southern Hemisphere (Sectors 1-13 and 27-39) Northern 14-26), observed with 120 s- 20 s-cadence. Our sample likely 13 low-mass one extremely candidate, considering mass determinations fitting Gaia magnitudes parallax. In addition, we present follow-up time series...
Abstract The Vera C. Rubin Legacy Survey of Space and Time (LSST) holds the potential to revolutionize time domain astrophysics, reaching completely unexplored areas Universe mapping variability scales from minutes a decade. To prepare maximize LSST data for exploration transient variable Universe, one four pillars science, Transient Variable Stars Science Collaboration, eight Collaborations, has identified research interest requirements, paths enable them. While our roadmap is...
We present the Kepler light curve of KIC 4552982, first ZZ Ceti (hydrogen-atmosphere pulsating white dwarf star) discovered in field view. Our data span more than 1.5 years with a 86% duty cycle, making it longest pseudo-continuous ever recorded for Ceti. This extensive set provides most complete coverage to-date amplitude and frequency variations cool detect 20 independent frequencies variability that we compare asteroseismic models to demonstrate this star has mass M$_*$ > 0.6 M$_{\rm...
Using data from the extended Kepler mission in K2 Campaign 10 we identify two eclipsing binaries containing white dwarfs with cool companions that have extremely short orbital periods of only 71.2 min (SDSS J1205-0242, a.k.a. EPIC 201283111) and 72.5 J1231+0041, 248368963). Despite their periods, both systems are detached small, low-mass companions, one case a brown dwarf, other either dwarf or star. We present follow-up photometry spectroscopy binaries, as well phase-resolved brighter...
Since the onset of `space revolution' high-precision high-cadence photometry, asteroseismology has been demonstrated as a powerful tool for informing Galactic archaeology investigations. The launch NASA TESS mission enabled seismic-based inferences to go full sky -- providing clear advantage large ensemble studies different Milky Way components. Here we demonstrate its potential investigating Galaxy by carrying out first asteroseismic study red giant stars observed TESS. We use sample 25...
Abstract Given its large plate scale of 21″ pixel −1 , analyses data from the Transiting Exoplanet Survey Satellite (TESS) space telescope must be wary source confusion blended light curves, which creates potential to attribute observed photometric variability wrong astrophysical source. We explore impact curve contamination on detection fast yellow pulsating supergiant (FYPS) stars as a case study demonstrate importance confirming detected signals in TESS data. While some FYPS have already...
There are a few different mechanisms that can cause white dwarf stars to vary in brightness, providing opportunities probe the physics, structures, and formation of these compact stellar remnants. The observational characteristics three most common types variability summarized: pulsations, rotation, ellipsoidal variations from tidal distortion binary systems. Stellar pulsations emphasized as complex type variability, which also has greatest potential reveal conditions interiors.
We present optical and X-ray observations of two tidally distorted, extremely low-mass white dwarfs (WDs) with massive companions. There is no evidence neutron stars in our Chandra XMM these objects. SDSS J075141.18$-$014120.9 (J0751) an eclipsing double WD binary containing a 0.19 Msol 0.97 companion 1.9 h orbit. J0751 becomes the fifth system currently known. J174140.49+652638.7 (J1741) another 0.17 unseen M > 1.11 1.5 With mass ratio ~0.1, J1741 will have stable transfer through accretion...
We assess the photometric variability of nine stars with spectroscopic Teff and log(g) values from ELM Survey that locate them near empirical extremely low-mass (ELM) white dwarf instability strip. discover three new pulsating stars: SDSS J135512.34+195645.4, J173521.69+213440.6 J213907.42+222708.9. However, these are among few objects do not show radial velocity variations to confirm binary nature expected helium-core dwarfs. The dominant 4.31-hr pulsation in J135512.34+195645.4 far exceeds...
We report the discovery of sixth known eclipsing double white dwarf (WD) system, SDSS J1152+0248, with a 2.3968 ± 0.0003 h orbital period, in data from Kepler Mission's K2 continuation. Analysing and modelling together ground-based fast photometry, spectroscopy, radial-velocity measurements, we determine that primary is DA-type WD mass M1 = 0.47 0.11 M⊙, radius R1 0.0197 0.0035 R⊙, cooling age t1 52 36 Myr. No lines are detected, to within our sensitivity, secondary WD, but it likely also...
We present observations of a new phenomenon in pulsating white dwarf stars: large-amplitude outbursts at timescales much longer than the pulsation periods. The cool (Teff = 11,010 K), hydrogen-atmosphere PG 1149+057 was observed nearly continuously for more 78.8 d by extended Kepler mission K2 Campaign 1. target showed 10 outburst events, recurring roughly every 8 and lasting 15 hr, with maximum flux excursions up to 45% bandpass. demonstrate that affect pulsations therefore must come from...
We use ∼12,000 spectra of ∼3500 magnetically active M0–M9 dwarfs from the Sloan Digital Sky Survey taken at 10–15 minute intervals, together with ∼300 ∼60 M0–M8 stars obtained hourly Hydra multiobject spectrometer, to probe Hα variability on timescales minutes weeks. With multiple observations for every star examined, we are able characterize fluctuations in emission as a function activity strength and spectral type. Stars greater magnetic (as quantified by LHα/Lbol) found be less variable...
We present the discovery and asteroseismic analysis of a new g-mode hot B subdwarf (sdB) pulsator, EC 21494-7018 (TIC 278659026), monitored in TESS first sector using 120-second cadence. The light curve reveals that is sdB pulsator counting up to 20 frequencies associated with independent g-modes. seismic singles out an optimal model solution full agreement measurements provided by spectroscopy (atmospheric parameters derived from atmospheres) astrometry (distance evaluated Gaia DR2...