Overview
The Universe is an ever-changing place. My research involves understanding
and characterizing the past, current, and future of astronomical sources
by observing 100's of millions of sources using synoptic astronomical surveys.
For more than two decades I have undertaken work on a wide variety of such
"time-domain" projects with the aim of understanding the dynamic nature
of astrophysical objects. My investigations have ranged from working on
explosive transients, such as supernovae, to sources exhibiting repeated
variablity, such as RR Lyrae.
Transient Event Astronomy
Transient event astronomy involves study of the occurance and nature of unpredictable
astronomical events. Large optical surveys for transients began in the 1990's
with microlensing surveys such as Macho
and OGLE. Larger
and more general surveys began in the 2000's with
Palomar Quest,
CRTS,
PTF and
Pan-STARRs.
Current very large scale transient and variabilty surveys include
ZTF and
LSST.
In the past I worked on the Macho project, Palomar Quest, and CRTS.
I currently work on ZTF.
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The Zwicky Transient Facility (ZTF)
is a time-domain survey that began at Palomar Observatory in 2017.
ZTF uses a camera with a 47 square degree field of view mounted on the
Oschin 48-inch Schmidt telescope. ZTF scans more than 3750 square degrees an
hour to a depth of 20.5 mag to discover young supernovae, rare and exotic transients,
and variable stars.
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I was co-PI of the CRTS and CRTS-II surveys which ran
from Nov. 2007 to Feb. 2019.
These two projects discovered of more than 15,000 transient astronomical sources, including ~4000 Supernovae.
CRTS was the first
large scale optical transient survey to both discover and publish transient detections
within minutes of observation, as well as make all discoveries public for the benefit of the
astronomical community.
Variable Stars and Exoplanets
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For the past twenty years I have worked on variable stars. Recently, using CRTS
data I have produced catalogs containing over 100,000 periodic variable star within an
area 30,000 sq. deg. of the northern and southern sky.
Halo RR Lyrae
RR Lyrae are standard candles that can be used as probes to the Galactic
evolution and structure. Some of my recent
work has involved
using these sources to trace the shape and extent of the outer halo of our Galaxy.
Short Period Binaries
Main sequence stars in binaries exhibit an orbitial period minimum of around 0.22 days.
The exact cause for this minimum period remains unknown, but is likely related
to the separation between where convection and conduction dominate in stars.
I recently used data for tens of thousands of binaries discovered in CRTS to
investigate the nature of the
few stars with period below the minimum.
White Dwarf Exoplanets
Over the last 20 years the search for planets like our own has grown to become
a major research area in astronomy with hundreds of planets now known.
However, ground-based surveys are generally not sensitive to Earth-size
planets. In 2008 I theorized
that it would be possible to discover Earth-size or smaller planets by observing
white dwarf stars. Although no candidates were found, the first clear detections
of planets in such systems have recently been
detected.