1,007 research outputs found
The Thresher : lucky imaging without the waste
JAH acknowledges funding from the Science and Technology Facilities Council of the United Kingdom.In traditional lucky imaging (TLI), many consecutive images of the same scene are taken with a high frame-rate camera, and all but the sharpest images are discarded before constructing the final shift-and-add image. Here, we present an alternative image analysis pipeline – The Thresher – for these kinds of data, based on online multi-frame blind deconvolution. It makes use of all available data to obtain the best estimate of the astronomical scene in the context of reasonable computational limits; it does not require prior estimates of the point-spread functions in the images, or knowledge of point sources in the scene that could provide such estimates. Most importantly, the scene it aims to return is the optimum of a justified scalar objective based on the likelihood function. Because it uses the full set of images in the stack, The Thresher outperforms TLI in signal-to-noise ratio; as it accounts for the individual-frame PSFs, it does this without loss of angular resolution. We demonstrate the effectiveness of our algorithm on both simulated data and real Electron-Multiplying CCD images obtained at the Danish 1.54-m telescope (hosted by ESO, La Silla). We also explore the current limitations of the algorithm, and find that for the choice of image model presented here, non-linearities in flux are introduced into the returned scene. Ongoing development of the software can be viewed at https://github.com/jah1994/TheThresher.Publisher PDFPeer reviewe
First Impressions: Early-Time Classification of Supernovae using Host Galaxy Information and Shallow Learning
Substantial effort has been devoted to the characterization of transient
phenomena from photometric information. Automated approaches to this problem
have taken advantage of complete phase-coverage of an event, limiting their use
for triggering rapid follow-up of ongoing phenomena. In this work, we introduce
a neural network with a single recurrent layer designed explicitly for early
photometric classification of supernovae. Our algorithm leverages transfer
learning to account for model misspecification, host galaxy photometry to solve
the data scarcity problem soon after discovery, and a custom weighted loss to
prioritize accurate early classification. We first train our algorithm using
state-of-the-art transient and host galaxy simulations, then adapt its weights
and validate it on the spectroscopically-confirmed SNe Ia, SNe II, and SNe Ib/c
from the Zwicky Transient Facility Bright Transient Survey. On observed data,
our method achieves an overall accuracy of % within 3 days of an
event's discovery, and an accuracy of % within 30 days of discovery.
At both early and late phases, our method achieves comparable or superior
results to the leading classification algorithms with a simpler network
architecture. These results help pave the way for rapid photometric and
spectroscopic follow-up of scientifically-valuable transients discovered in
massive synoptic surveys.Comment: 24 pages, 8 figures. Accepted to Ap
Radial Velocity Observations and Light Curve Noise Modeling Confirm That Kepler-91b is a Giant Planet Orbiting a Giant Star
Kepler-91b is a rare example of a transiting hot Jupiter around a red giant
star, providing the possibility to study the formation and composition of hot
Jupiters under different conditions compared to main-sequence stars. However,
the planetary nature of Kepler-91b, which was confirmed using phase-curve
variations by Lillo-Box et al., was recently called into question based on a
re-analysis of Kepler data. We have obtained ground-based radial velocity
observations from the Hobby-Eberly Telescope and unambiguously confirm the
planetary nature of Kepler-91b by simultaneously modeling the Kepler and radial
velocity data. The star exhibits temporally correlated noise due to stellar
granulation which we model as a Gaussian Process. We hypothesize that it is
this noise component that led previous studies to suspect Kepler-91b to be a
false positive. Our work confirms the conclusions presented by Lillo-Box et al.
that Kepler-91b is a 0.73+/-0.13 Mjup planet orbiting a red giant star.Comment: Published in Ap
Stellar and Planetary Properties of K2 Campaign 1 Candidates and Validation of 17 Planets, Including a Planet Receiving Earth-like Insolation
The extended Kepler mission, K2, is now providing photometry of new fields
every three months in a search for transiting planets. In a recent study,
Foreman-Mackey and collaborators presented a list of 36 planet candidates
orbiting 31 stars in K2 Campaign 1. In this contribution, we present stellar
and planetary properties for all systems. We combine ground-based
seeing-limited survey data and adaptive optics imaging with an automated
transit analysis scheme to validate 21 candidates as planets, 17 for the first
time, and identify 6 candidates as likely false positives. Of particular
interest is K2-18 (EPIC 201912552), a bright (K=8.9) M2.8 dwarf hosting a 2.23
\pm 0.25 R_Earth planet with T_eq = 272 \pm 15 K and an orbital period of 33
days. We also present two new open-source software packages which enable this
analysis. The first, isochrones, is a flexible tool for fitting theoretical
stellar models to observational data to determine stellar properties using a
nested sampling scheme to capture the multimodal nature of the posterior
distributions of the physical parameters of stars that may plausibly be
evolved. The second is vespa, a new general-purpose procedure to calculate
false positive probabilities and statistically validate transiting exoplanets.Comment: 17 pages, 5 figures, 5 tables, accepted for publication in the
Astrophysical Journal. Updated to closely reflect published version in ApJ
(2015, 809, 25
eleanor: An open-source tool for extracting light curves from the TESS Full-Frame Images
During its two year prime mission the Transiting Exoplanet Survey Satellite
(TESS) will perform a time-series photometric survey covering over 80% of the
sky. This survey comprises observations of 26 24 x 96 degree sectors that are
each monitored continuously for approximately 27 days. The main goal of TESS is
to find transiting planets around 200,000 pre-selected stars for which fixed
aperture photometry is recorded every two minutes. However, TESS is also
recording and delivering Full-Frame Images (FFIs) of each detector at a 30
minute cadence. We have created an open-source tool, eleanor, to produce light
curves for objects in the TESS FFIs. Here, we describe the methods used in
eleanor to produce light curves that are optimized for planet searches. The
tool performs background subtraction, aperture and PSF photometry,
decorrelation of instrument systematics, and cotrending using principal
component analysis. We recover known transiting exoplanets in the FFIs to
validate the pipeline and perform a limited search for new planet candidates in
Sector 1. Our tests indicate that eleanor produces light curves with
significantly less scatter than other tools that have been used in the
literature. Cadence-stacked images, and raw and detrended eleanor light curves
for each analyzed star will be hosted on MAST, with planet candidates on
ExoFOP-TESS as Community TESS Objects of Interest (CTOIs). This work confirms
the promise that the TESS FFIs will enable the detection of thousands of new
exoplanets and a broad range of time domain astrophysics.Comment: 21 pages, 13 figures, 2 tables, Accepted to PAS
The three-dimensional structure of Galactic molecular cloud complexes out to 2.5 kpc
Knowledge of the three-dimensional structure of Galactic molecular clouds is
important for understanding how clouds are affected by processes such as
turbulence and magnetic fields and how this structure effects star formation
within them. Great progress has been made in this field with the arrival of the
Gaia mission, which provides accurate distances to stars.
Combining these distances with extinctions inferred from optical-IR, we recover
the three-dimensional structure of 16 Galactic molecular cloud complexes at
pc resolution using our novel three-dimensional dust mapping algorithm
\texttt{Dustribution}. Using \texttt{astrodendro} we derive a catalogue of
physical parameters for each complex. We recover structures with aspect ratios
between 1 and 11, i.e.\ everything from near-spherical to very elongated
shapes. We find a large variation in cloud environments that is not apparent
when studying them in two-dimensions. For example, the nearby California and
Orion A clouds look similar on-sky, but we find California to be more
sheet-like, and massive, which could explain their different star-formation
rates. In Carina, our most distant complex, we observe evidence for dust
sputtering, which explains its measured low dust mass. By calculating the total
mass of these individual clouds, we demonstrate that it is necessary to define
cloud boundaries in three-dimensions in order to obtain an accurate mass;
simply integrating the extinction overestimates masses. We find that Larson's
relationship on mass vs radius holds true whether you assume a spherical shape
for the cloud or take their true extents.Comment: accepted for publication by MNRAS, 23 pages, 9 figures, 3 table
An Efficient Automated Validation Procedure for Exoplanet Transit Candidates
Surveys searching for transiting exoplanets have found many more candidates
than they have been able to confirm as true planets. This situation is
especially acute with the Kepler survey, which has found over 2300 candidates
but has confirmed only 77 planets to date. I present here a general procedure
that can quickly be applied to any planet candidate to calculate its false
positive probability. This procedure takes into account the period, depth,
duration, and shape of the signal; the colors of the target star; arbitrary
spectroscopic or imaging follow-up observations; and informed assumptions about
the populations and distributions of field stars and multiple-star properties.
I also introduce the concept of the "specific occurrence rate," which allows
for the calculation of the FPP without relying on an assumed planet radius
function. Applying these methods to a sample of known Kepler planets, I
demonstrate that many signals can be validated with very limited follow-up
observations: in most cases with only a spectrum and an AO image. Additionally,
I demonstrate that this procedure can reliably identify false positive signals.
Because of the computational efficiency of this analysis, it is feasible to
apply it to all Kepler planet candidates in the near future, and it will
streamline the follow-up efforts for Kepler and other current and future
transit surveys.Comment: accepted to Ap
V1298 Tau with TESS: Updated Ephemerides, Radii, and Period Constraints from a Second Transit of V1298 Tau e
V1298 Tau is a young (20-30 Myr) solar-mass K star hosting four transiting exoplanets with sizes between 0.5 and 0.9 R J. Given the system's youth, it provides a unique opportunity to understand the evolution of planetary radii at different separations in the same stellar environment. V1298 Tau was originally observed 6 yr ago during K2 Campaign 4. Now, V1298 Tau has been re-observed during the extended mission of NASA's Transiting Exoplanet Survey Satellite (TESS). Here, we present new photometric observations of V1298 Tau from TESS. We use the TESS data to update the ephemerides for V1298 Tau bcde as well as compare newly observed radii to those measured from the K2 light curve, finding shallower transits for V1298 Tau bcd in the redder TESS bandpass at the 1-2σ level. We suspect the difference in radii is due to starspot crossing events or contamination from nearby faint stars on the same pixels as V1298 Tau. Additionally, we catch a second transit of V1298 Tau e and present a new method for deriving the marginalized posterior probability of a planet's period from two transits observed years apart. We find the highest probability period for V1298 Tau e to be in a near 2:1 mean motion resonance with V1298 Tau b which, if confirmed, could make V1298 Tau bcde a four-planet resonant chain. V1298 Tau is the target of several ongoing and future observations. These updated ephemerides will be crucial for scheduling future transit observations and interpreting future Doppler tomographic or transmission spectroscopy signals
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