27 research outputs found
Identification of Stellar Flares Using Differential Evolution Template Optimization
We explore methods for the identification of stellar flare events in
irregularly sampled data of ground-based time domain surveys. In particular, we
describe a new technique for identifying flaring stars, which we have
implemented in a publicly available Python module called "PyVAN". The approach
uses the Differential Evolution algorithm to optimize parameters of empirically
derived light-curve templates for different types of stars to fit a candidate
light-curve. The difference of the likelihoods that these best-fit templates
produced the observed data is then used to delineate targets that are well
explained by a flare template but simultaneously poorly explained by templates
of common contaminants. By testing on light-curves of known identity and
morphology, we show that our technique is capable of recovering flaring status
in of all light-curves containing a flare event above thresholds drawn
to include of any contaminant population. By applying to Palomar
Transient Factory data, we show consistency with prior samples of flaring
stars, and identify a small selection of candidate flaring G-type stars for
possible follow-up.Comment: 15 figures, 24 page
Identification of Stellar Flares Using Differential Evolution Template Optimization
We explore methods for the identification of stellar flare events in irregularly sampled data of ground-based time domain surveys. In particular, we describe a new technique for identifying flaring stars, which we have implemented in a publicly available Python module called "PyVAN." The approach uses the Differential Evolution algorithm to optimize parameters of empirically derived light curve templates for different types of stars to fit a candidate light curve. The difference of the likelihoods that these best-fit templates produced the observed data is then used to delineate targets that are well-explained by a flare template but simultaneously poorly explained by templates of common contaminants. By testing on light curves of known identity and morphology, we show that our technique is capable of recovering flaring status in 69% of all light curves containing a flare event above thresholds drawn to include <1% of any contaminant population. By applying to Palomar Transient Factory data, we show consistency with prior samples of flaring stars, and identify a small selection of candidate flaring G-type stars for possible follow-up
JWST/NIRCam Coronagraphy of the Young Planet-hosting Debris Disk AU Microscopii
High-contrast imaging of debris disk systems permits us to assess the
composition and size distribution of circumstellar dust, to probe recent
dynamical histories, and to directly detect and characterize embedded
exoplanets. Observations of these systems in the infrared beyond 2--3 m
promise access to both extremely favorable planet contrasts and numerous
scattered-light spectral features -- but have typically been inhibited by the
brightness of the sky at these wavelengths. We present coronagraphy of the AU
Microscopii (AU Mic) system using JWST's Near Infrared Camera (NIRCam) in two
filters spanning 3--5 m. These data provide the first images of the
system's famous debris disk at these wavelengths and permit additional
constraints on its properties and morphology. Conducting a deep search for
companions in these data, we do not identify any compelling candidates.
However, with sensitivity sufficient to recover planets as small as
Jupiter masses beyond ( au) with
confidence, these data place significant constraints on any massive companions
that might still remain at large separations and provide additional context for
the compact, multi-planet system orbiting very close-in. The observations
presented here highlight NIRCam's unique capabilities for probing similar disks
in this largely unexplored wavelength range, and provide the deepest direct
imaging constraints on wide-orbit giant planets in this very well studied
benchmark system.Comment: 27 pages, 14 figure
No Clear, Direct Evidence for Multiple Protoplanets Orbiting LkCa 15: LkCa 15 bcd are Likely Inner Disk Signals
Two studies utilizing sparse aperture-masking (SAM) interferometry and H-alpha differential imaging have reported multiple Jovian companions around the young solar-mass star, LkCa 15 (LkCa 15 bcd): the first claimed direct detection of infant, newly formed planets ("protoplanets"). We present new near-infrared direct imaging/spectroscopy from the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) system coupled with Coronagraphic High Angular Resolution Imaging Spectrograph (CHARIS) integral field spectrograph and multi-epoch thermal infrared imaging from Keck/NIRC2 of LkCa 15 at high Strehl ratios. These data provide the first direct imaging look at the same wavelengths and in the same locations where previous studies identified the LkCa 15 protoplanets, and thus offer the first decisive test of their existence. The data do not reveal these planets. Instead, we resolve extended emission tracing a dust disk with a brightness and location comparable to that claimed for LkCa 15 bcd. Forward-models attributing this signal to orbiting planets are inconsistent with the combined SCExAO/CHARIS and Keck/NIRC2 data. An inner disk provides a more compelling explanation for the SAM detections and perhaps also the claimed H-alpha detection of LkCa 15 b. We conclude that there is currently no clear, direct evidence for multiple protoplanets orbiting LkCa 15, although the system likely contains at least one unseen Jovian companion. To identify Jovian companions around LkCa 15 from future observations, the inner disk should be detected and its effect modeled, removed, and shown to be distinguishable from planets. Protoplanet candidates identified from similar systems should likewise be clearly distinguished from disk emission through modeling.NASA Senior Postdoctoral Fellowship; NASA/Keck grant [LK-2663-948181]; CONICYT-FONDECYT [1171246]; project CONICYT PAI/Concurso Nacional Insercion en la Academia, convocatoria 2015 [79150049]; JSPS KAKENHI [18H05442, 15H02063]; National Aeronautics and Space Administration; Subaru Time Allocation Committe; NASA/Keck Time Allocation CommitteThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]
Radial Velocity Discovery of an Eccentric Jovian World Orbiting at 18 au
Based on two decades of radial velocity (RV) observations using Keck/High Resolution Echelle Spectrometer (HIRES) and McDonald/Tull, and more recent observations using the Automated Planet Finder, we found that the nearby star HR 5183 (HD 120066) hosts a 3 minimum mass planet with an orbital period of yr. The orbit is highly eccentric (e ≃ 0.84), shuttling the planet from within the orbit of Jupiter to beyond the orbit of Neptune. Our careful survey design enabled high cadence observations before, during, and after the planet\u27s periastron passage, yielding precise orbital parameter constraints. We searched for stellar or planetary companions that could have excited the planet\u27s eccentricity, but found no candidates, potentially implying that the perturber was ejected from the system. We did identify a bound stellar companion more than 15,000 au from the primary, but reasoned that it is currently too widely separated to have an appreciable effect on HR 5183 b. Because HR 5183 b\u27s wide orbit takes it more than 30 au (1\u27\u27) from its star, we also explored the potential of complimentary studies with direct imaging or stellar astrometry. We found that a Gaia detection is very likely, and that imaging at 10 μm is a promising avenue. This discovery highlights the value of long-baseline RV surveys for discovering and characterizing long-period, eccentric Jovian planets. This population may offer important insights into the dynamical evolution of planetary systems containing multiple massive planets
Peter Pan Disks: Long-lived Accretion Disks Around Young M Stars
WISEA J080822.18-644357.3, an M star in the Carina association, exhibits
extreme infrared excess and accretion activity at an age greater than the
expected accretion disk lifetime. We consider J0808 as the prototypical example
of a class of M star accretion disks at ages Myr, which we call
``Peter Pan'' disks, since they apparently refuse to grow up. We present four
new Peter Pan disk candidates identified via the Disk Detective citizen science
project, coupled with \textit{Gaia} astrometry. We find that WISEA
J044634.16-262756.1 and WISEA J094900.65-713803.1 both exhibit significant
infrared excess after accounting for nearby stars within the 2MASS beams. The
J0446 system has likelihood of Columba membership. The J0949 system
shows likelihood of Carina membership. We present new GMOS optical
spectra of all four objects, showing possible accretion signatures on all four
stars. We present ground-based and \textit{TESS} lightcurves of J0808 and 2MASS
J0501-4337, including a large flare and aperiodic dipping activity on J0808,
and strong periodicity on J0501. We find Pa and Br emission
indicating ongoing accretion in near-IR spectroscopy of J0808. Using observed
characteristics of these systems, we discuss mechanisms that lead to accretion
disks at ages Myr, and find that these objects most plausibly
represent long-lived CO-poor primordial disks, or ``hybrid'' disks, exhibiting
both debris- and primordial-disk features. The question remains: why have
gas-rich disks persisted so long around these particular stars?Comment: 25 pages, 17 figures. Accepted for publication in the Astrophysical
Journa