90 research outputs found
Quantum Uncertainty Considerations for Gravitational Lens Interferometry
The measurement of the gravitational lens delay time between light paths has
relied, to date, on the source having sufficient variability to allow
photometric variations from each path to be compared. However, the delay times
of many gravitational lenses cannot be measured because the intrinsic source
amplitude variations are too small to be detectable. At the fundamental quantum
mechanical level, such photometric time stamps allow which-path knowledge,
removing the ability to obtain an interference pattern. However, if the two
paths can be made equal (zero time delay) then interference can occur. We
describe an interferometric approach to measuring gravitational lens delay
times using a quantum-eraser/restorer approach, whereby the time travel along
the two paths may be rendered measurably equal. Energy and time being
non-commuting observables, constraints on the photon energy in the energy-time
uncertainty principle, via adjustments of the width of the radio bandpass,
dictate the uncertainty of the time delay and therefore whether the path taken
along one or the other gravitational lens geodesic is knowable. If one starts
with interference, for example, which-path information returns when the
bandpass is broadened (constraints on the energy are relaxed) to the point
where the uncertainty principle allows a knowledge of the arrival time to
better than the gravitational lens delay time itself, at which point the
interference will disappear. We discuss the near-term feasibility of such
measurements in light of current narrow-band radio detectors and known short
time-delay gravitational lenses.Comment: 22 page
Transit of Extrasolar Planets
During the past five years we have pursued the detection of extrasolar planets by the photometric transit method, i.e. the detection of a planet by watching for a drop in the brightness of the light as it crosses in front of a star. The planetary orbit must cross the line-of-sight and so most systems will not be lined up for such a transit to ever occur. However, we have looked at eclipsing binary systems which are already edge-on. Such systems must be very small in size as this makes the differential light change due to a transit much greater for a given planet size (the brightness difference will be proportional to the area of the transiting planet to the disc area of the star). Also, the planet forming region should be closer to the star as small stars are generally less luminous (that is, if the same thermal regime for planet formation applies as in the solar system). This led to studies of the habitable zone around other stars, as well. Finally, we discovered that our data could be used to detect giant planets without transits as we had been carefully timing the eclipses of the stars (using a GPS antenna for time) and this will drift by being offset by any giant planets orbiting around the system, as well. The best summary of our work may be to just summarize the 21 refereed papers produced during the time of this grant. This will be done is chronological order and in each section separately
Detecting Reflected Light from Close-In Extrasolar Giant Planets with the Kepler Photometer
NASA's Kepler Mission promises to detect transiting Earth-sized planets in
the habitable zones of solar-like stars. In addition, it will be poised to
detect the reflected light component from close-in extrasolar giant planets
(CEGPs) similar to 51 Peg b. Here we use the DIARAD/SOHO time series along with
models for the reflected light signatures of CEGPs to evaluate Kepler's ability
to detect such planets. We examine the detectability as a function of stellar
brightness, stellar rotation period, planetary orbital inclination angle, and
planetary orbital period, and then estimate the total number of CEGPs that
Kepler will detect over its four year mission. The analysis shows that
intrinsic stellar variability of solar-like stars is a major obstacle to
detecting the reflected light from CEGPs. Monte Carlo trials are used to
estimate the detection threshold required to limit the total number of expected
false alarms to no more than one for a survey of 100,000 stellar light curves.
Kepler will likely detect 100-760 51 Peg b-like planets by reflected light with
orbital periods up to 7 days.Comment: 43 pages, 6 figures, 9 tables, accepted for publication by ApJ May
200
Origins of planetary systems: Observations and analysis
This cooperative agreement was established with the scientific goal of understanding the conditions of early solar-type planetary systems. We investigated two facets of young solar systems: The effects on planetary bodies of young solar-type stellar mass loss, and photo-production of various organic materials due to radiation under comet-like conditions
Observational Limits on Terrestrial-sized Inner Planets around the CM Draconis System Using the Photometric Transit Method with a Matched-Filter Algorithm
A lightcurve of the eclipsing binary CM Draconis has been analyzed for the presence of transits of planets of size \u3e= 2.5 Earth-radii (Re), with periods of 60 days or less, and in co-planar orbits around the binary system. About 400 million model lightcurves, representing transits from planets with periods ranging from 7 to 60 days, have been matched/correlated against these data. This process we call the \u22transit detection algorithm\u22 or TDA. The resulting `transit-statistics\u27 for each planet candidate allow the quantification of detection probabilities, and of false alarm rates. Our current lightcurve of CM Dra has a coverage of 1014 hours with 26,043 individual points, at a photometric precision between 0.2% and 0.7%. Planets significantly larger then 3Re would constitute a `supra-noise\u27 detection, and for periods of 60 days or less, they would have been detected with a probability of 90%. `Subnoise\u27 detections of smaller planets are more constrained. For example, 2.5 Re planets with 10-day periods or less would have been detected with an 80% probability. The necessity for predicted observations is illustrated with the nine top planet candidates that emerged from our TDA analysis. They are the planet candidates with the highest transit-statistics from the 1994-1998 observing seasons and, for them, transits for the 1999 observing season were predicted. Of the seven candidates that were then observationally tested in 1999, all were ruled out except one, which needs further observational confirmation. We conclude that the photometric transit method is a viable way to search for relatively small, inner extrasolar planets with moderate-sized telescopes using CCD photometry with a matching-filter analysis. (Refer to PDF file for exact formulas)
An All-Sky Survey for the Detection of Transiting Extrasolar Planets and for Permanent Variable Star Tracking
An overview is given of the Permanent All Sky Survey (PASS) project. The
primary goal of PASS is the detection of all transiting giant planets in the
entire sky, complete for stellar systems of magnitudes ~ 5.5-10.5. Since the
sample stars are fairly bright and relatively close, planets detected by PASS
would be ideally suited for any follow-up study with ground- or space-based
instrumentation. The survey would also allow the pursuit of a variety of work
on temporal astronomical phenomena of any kind, and is intended to lead to a
permanent all-sky tracking of variable stars with high temporal resolution. The
instrument consists of arrays of CCD cameras with wide-field optics that cover
the entire sky visible from their observing locations. Calculations of the
instrument's noise sources and subsequent simulations indicate that the
proposed design is able to achieve the prime objective of a full-sky survey for
transits. An equation for the signal-to-noise ratio from photometry of unguided
stellar images is given in the appendix, together with equations for the
detection probability of planetary transits based on the observational coverage
and the instrument's duty cycle.Comment: 25 pages, 8 figures, accepted by PAS
Optical Light Curve of the Type Ia Supernova 1998bu in M96 and the Supernova Calibration of the Hubble Constant
We present the UBVRI light curves of the Type Ia supernova SN 1998bu which
appeared in the nearby galaxy M96 (NGC 3368). M96 is a spiral galaxy in the Leo
I group which has a Cepheid-based distance. Our photometry allows us to
calculate the absolute magnitude and reddening of this supernova. These data,
when combined with measurements of the four other well-observed supernovae with
Cepheid based distances, allow us to calculate the Hubble constant with respect
to the Hubble flow defined by the distant Calan/Tololo Type Ia sample. We find
a Hubble constant of 64.0 +/- 2.2(internal) +/- 3.5(external) km/s/Mpc,
consistent with most previous estimates based on Type Ia supernovae. We note
that the two well-observed Type Ia supernovae in Fornax, if placed at the
Cepheid distance to the possible Fornax spiral NGC 1365, are apparently too
faint with respect to the Calan/Tololo sample calibrated with the five Type Ia
supernovae with Cepheid distances to the host galaxies.Comment: AAS LaTeX, 20 pages, 4 figures, 6 tables, accepted for publication in
the Astronomical Journal. Figure 1 (finding chart) not include
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