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News Article | April 10, 2017
Site: www.scientificcomputing.com

Recently, astronomers announced the discovery that a star called TRAPPIST-1 is orbited by seven Earth-size planets. Three of the planets reside in the "habitable zone," the region around a star where liquid water is most likely to exist on the surface of a rocky planet. Other potentially habitable worlds have also been discovered in recent years, leaving many people wondering: How do we find out if these planets actually host life? At Caltech, in the Exoplanet Technology Laboratory, or ET Lab, of Associate Professor of Astronomy Dimitri Mawet, researchers have been busy developing a new strategy for scanning exoplanets for biosignatures—signs of life such as oxygen molecules and methane. These chemicals—which don't naturally stick around for long because they bind with other chemicals—are abundant on Earth largely thanks to the living creatures that expel them. Finding both of these chemicals around another planet would be a strong indicator of the presence of life. In two new papers to be published in The Astrophysical Journal and The Astronomical Journal, Mawet's team demonstrates how this new technique, called high-dispersion coronagraphy, could be used to look for extraterrestrial biosignatures with the planned Thirty Meter Telescope (TMT), which, when completed by the late 2020s, will be the world's largest optical telescope. Using theoretical and laboratory models, the researchers show that this technique could detect biosignatures on Earth-like planets around M-dwarf stars, which are smaller and cooler than our sun and the most common type of star in the galaxy. The strategy could also be used on stars like our own sun, using future space telescopes such as NASA's proposed Habitable Exoplanet Imaging Mission (HabEx) and Large UV/Optical/IR Surveyor (LUVOIR). "We've shown this technique works in theory and in the lab, so our next step is to show it works on the sky," says Ji Wang, one of the lead authors on the two new papers and a postdoctoral scholar in the Mawet lab. The team will test the instrumentation on the W. M. Keck Observatory in Hawaii this year or next. The new technique involves three main components: a coronagraph, a set of optical fibers, and a high-resolution spectrometer. Coronagraphs are devices used in telescopes to block or remove starlight so that planets can be imaged. Stars outshine their planets by a few thousand to a few billion times, making the planets difficult to see. Many different types of coronagraphs are in development; for example, Mawet's group recently installed and took initial images with its new vortex coronagraph on the Keck Observatory. Once an image of a planet has been obtained, the next step is to study the planet's atmosphere using a spectrometer, an instrument that breaks apart the planet's light to reveal "fingerprints" of chemicals, such as oxygen and methane. Most coronagraphs work in conjunction with low-resolution spectrometers. Mawet's new technique incorporates a high-resolution spectrometer, which has several advantages. One main advantage is in helping to further sift out the unwanted starlight. With high-resolution spectrometers, the spectral features of a planet are more detailed, making it easier to distinguish and separate the planet's light from the lurking starlight. What this means is that, in Mawet's method, the coronagraph does not have to be as good at sifting out starlight as was thought necessary to characterize Earth-like worlds. "This new technique doesn't require the coronagraph to work as hard, and that's important because we can use current technologies that are already available," says Mawet, who is also a research scientist at the Jet Propulsion Laboratory (JPL), which is managed by Caltech for NASA. "With a high-resolution spectrometer, we can improve the sensitivity of our system by a factor of 100 to 1,000 over current ground-based methods." Another advantage of using high-resolution spectrometers lies in the richness of the data. In addition to providing more detail about the molecular constituents of a planet's atmosphere, these instruments should be able to reveal a planet's rotation rate and provide rough maps of surface features and weather patterns. "It's a long shot, but we might even have the ability to look for continents on candidate Earth-like planets," says Mawet. In the team's design, the coronagraph is connected to the high-resolution spectrometer using a set of optical fibers. Surprisingly, laboratory experiments revealed that the fibers also filter out starlight. "This was completely serendipitous," says Garreth Ruane, co-author on the two new papers and a National Science Foundation postdoctoral fellow in Mawet's group. "It's icing on the cake." Next, the researchers will demonstrate their technique at the Keck Observatory. Although the instrumentation cannot yet study potential Earth-like planets—that will require the larger Thirty Meter Telescope—the system should be able to reveal new details about the atmospheres of larger gas exoplanets, including exotic varieties that are nothing like those in our own solar system. "This new innovation of combining the coronagraph with a high-res spectrometer gives us a clear pathway to ultimately search for life beyond Earth." The first study, titled "Observing Exoplanets with High-Dispersion Coronagraphy. I. The Scientific Potential of Current and Next-Generation Large Ground and Space Telescopes," led by Wang and appearing in The Astronomical Journal, includes Caltech co-authors Mawet, Ruane visiting associate Renyu Hu, and postdoctoral scholar Bjoern Benneke. The second study, titled, "Observing Exoplanets with High-Dispersion Coronagraphy. II. Demonstration of an Active Single-Mode Fiber Injection Unit," led by Mawet and appearing in The Astrophysical Journal, includes Caltech co-authors Ruane and Wang; Caltech summer students Wenhao Xuan, Daniel Echeverri, and Michael Randolph; graduate student Nikita Klimovich; postdoctoral scholar Jacques-Robert Delorme; assistant research engineer Jason Fucik; and Associate Director for Development of Caltech Optical Observatories


News Article | April 10, 2017
Site: www.scientificcomputing.com

Recently, astronomers announced the discovery that a star called TRAPPIST-1 is orbited by seven Earth-size planets. Three of the planets reside in the "habitable zone," the region around a star where liquid water is most likely to exist on the surface of a rocky planet. Other potentially habitable worlds have also been discovered in recent years, leaving many people wondering: How do we find out if these planets actually host life? At Caltech, in the Exoplanet Technology Laboratory, or ET Lab, of Associate Professor of Astronomy Dimitri Mawet, researchers have been busy developing a new strategy for scanning exoplanets for biosignatures—signs of life such as oxygen molecules and methane. These chemicals—which don't naturally stick around for long because they bind with other chemicals—are abundant on Earth largely thanks to the living creatures that expel them. Finding both of these chemicals around another planet would be a strong indicator of the presence of life. In two new papers to be published in The Astrophysical Journal and The Astronomical Journal, Mawet's team demonstrates how this new technique, called high-dispersion coronagraphy, could be used to look for extraterrestrial biosignatures with the planned Thirty Meter Telescope (TMT), which, when completed by the late 2020s, will be the world's largest optical telescope. Using theoretical and laboratory models, the researchers show that this technique could detect biosignatures on Earth-like planets around M-dwarf stars, which are smaller and cooler than our sun and the most common type of star in the galaxy. The strategy could also be used on stars like our own sun, using future space telescopes such as NASA's proposed Habitable Exoplanet Imaging Mission (HabEx) and Large UV/Optical/IR Surveyor (LUVOIR). "We've shown this technique works in theory and in the lab, so our next step is to show it works on the sky," says Ji Wang, one of the lead authors on the two new papers and a postdoctoral scholar in the Mawet lab. The team will test the instrumentation on the W. M. Keck Observatory in Hawaii this year or next. The new technique involves three main components: a coronagraph, a set of optical fibers, and a high-resolution spectrometer. Coronagraphs are devices used in telescopes to block or remove starlight so that planets can be imaged. Stars outshine their planets by a few thousand to a few billion times, making the planets difficult to see. Many different types of coronagraphs are in development; for example, Mawet's group recently installed and took initial images with its new vortex coronagraph on the Keck Observatory. Once an image of a planet has been obtained, the next step is to study the planet's atmosphere using a spectrometer, an instrument that breaks apart the planet's light to reveal "fingerprints" of chemicals, such as oxygen and methane. Most coronagraphs work in conjunction with low-resolution spectrometers. Mawet's new technique incorporates a high-resolution spectrometer, which has several advantages. One main advantage is in helping to further sift out the unwanted starlight. With high-resolution spectrometers, the spectral features of a planet are more detailed, making it easier to distinguish and separate the planet's light from the lurking starlight. What this means is that, in Mawet's method, the coronagraph does not have to be as good at sifting out starlight as was thought necessary to characterize Earth-like worlds. "This new technique doesn't require the coronagraph to work as hard, and that's important because we can use current technologies that are already available," says Mawet, who is also a research scientist at the Jet Propulsion Laboratory (JPL), which is managed by Caltech for NASA. "With a high-resolution spectrometer, we can improve the sensitivity of our system by a factor of 100 to 1,000 over current ground-based methods." Another advantage of using high-resolution spectrometers lies in the richness of the data. In addition to providing more detail about the molecular constituents of a planet's atmosphere, these instruments should be able to reveal a planet's rotation rate and provide rough maps of surface features and weather patterns. "It's a long shot, but we might even have the ability to look for continents on candidate Earth-like planets," says Mawet. In the team's design, the coronagraph is connected to the high-resolution spectrometer using a set of optical fibers. Surprisingly, laboratory experiments revealed that the fibers also filter out starlight. "This was completely serendipitous," says Garreth Ruane, co-author on the two new papers and a National Science Foundation postdoctoral fellow in Mawet's group. "It's icing on the cake." Next, the researchers will demonstrate their technique at the Keck Observatory. Although the instrumentation cannot yet study potential Earth-like planets—that will require the larger Thirty Meter Telescope—the system should be able to reveal new details about the atmospheres of larger gas exoplanets, including exotic varieties that are nothing like those in our own solar system. "This new innovation of combining the coronagraph with a high-res spectrometer gives us a clear pathway to ultimately search for life beyond Earth." The first study, titled "Observing Exoplanets with High-Dispersion Coronagraphy. I. The Scientific Potential of Current and Next-Generation Large Ground and Space Telescopes," led by Wang and appearing in The Astronomical Journal, includes Caltech co-authors Mawet, Ruane visiting associate Renyu Hu, and postdoctoral scholar Bjoern Benneke. The second study, titled, "Observing Exoplanets with High-Dispersion Coronagraphy. II. Demonstration of an Active Single-Mode Fiber Injection Unit," led by Mawet and appearing in The Astrophysical Journal, includes Caltech co-authors Ruane and Wang; Caltech summer students Wenhao Xuan, Daniel Echeverri, and Michael Randolph; graduate student Nikita Klimovich; postdoctoral scholar Jacques-Robert Delorme; assistant research engineer Jason Fucik; and Associate Director for Development of Caltech Optical Observatories


Phillips A.C.,University of California at Santa Cruz | Bauman B.J.,Lawrence Livermore National Laboratory | Larkin J.E.,University of California at Los Angeles | Moore A.M.,Caltech Optical Observatories | And 3 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2010

We present a conceptual design for the atmospheric dispersion corrector (ADC) for TMT's Infrared Imaging Spectrograph (IRIS). The severe requirements of this ADC are reviewed, as are limitations to observing caused by uncorrectable atmospheric effects. The requirement of residual dispersion less than 1 milliarcsecond can be met with certain glass combinations. The design decisions are discussed and the performance of the design ADC is described. Alternative options and their performance tradeoffs are also presented. © 2010 Copyright SPIE - The International Society for Optical Engineering.


Beerman L.C.,University of Washington | Johnson L.C.,University of Washington | Fouesneau M.,University of Washington | Dalcanton J.J.,University of Washington | And 14 more authors.
Astrophysical Journal | Year: 2012

The apparent age and mass of a stellar cluster can be strongly affected by stochastic sampling of the stellar initial mass function (IMF), when inferred from the integrated color of low-mass clusters (≲104 M). We use simulated star clusters to show that these effects are minimized when the brightest, rapidly evolving stars in a cluster can be resolved, and the light of the fainter, more numerous unresolved stars can be analyzed separately. When comparing the light from the less luminous cluster members to models of unresolved light, more accurate age estimates can be obtained than when analyzing the integrated light from the entire cluster under the assumption that the IMF is fully populated. We show the success of this technique first using simulated clusters, and then with a stellar cluster in M31. This method represents one way of accounting for the discrete, stochastic sampling of the stellar IMF in less massive clusters and can be leveraged in studies of clusters throughout the Local Group and other nearby galaxies. © 2012. The American Astronomical Society. All rights reserved.


Fisher C.D.,Jet Propulsion Laboratory | Braun D.F.,Jet Propulsion Laboratory | Kaluzny J.V.,Jet Propulsion Laboratory | Seiffert M.D.,Jet Propulsion Laboratory | And 3 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2012

The Prime Focus Spectrograph (PFS) is a fiber fed multi-object spectrometer for the Subaru Telescope that will conduct a variety of targeted surveys for studies of dark energy, galaxy evolution, and galactic archaeology. The key to the instrument is a high density array of fiber positioners placed at the prime focus of the Subaru Telescope. The system, nicknamed "Cobra", will be capable of rapidly reconfiguring the array of 2394 optical fibers to the image positions of astronomical targets in the focal plane with high accuracy. The system uses 2394 individual "SCARA robot" mechanisms that are 7.7mm in diameter and use 2 piezo-electric rotary motors to individually position each of the optical fibers within its patrol region. Testing demonstrates that the Cobra positioner can be moved to within 5μm of an astronomical target in 6 move iterations with a success rate of 95%. The Cobra system is a key aspect of PFS that will enable its unprecedented combination of high-multiplex factor and observing efficiency on the Subaru telescope. The requirements, design, and prototyping efforts for the fiber positioner system for the PFS are described here as are the plans for modular construction, assembly, integration, functional testing, and performance validation. © 2012 SPIE.


Travouillon T.,TMT Observatory Corporation | Schock M.,TMT Observatory Corporation | Schock M.,Herzberg Institute for Astrophysics | Els S.,TMT Observatory Corporation | And 2 more authors.
Boundary-Layer Meteorology | Year: 2011

In the second part of this study, we compare both the wind speed and turbulence given by the Sodars with independent sets of measurements. In the case of the wind speed we compare the lowest Sodar data bin with a sonic anemometer located on a 7-m tower. The agreement between the two instruments was convincing with a regression slope near unity. The integrated turbulence measurements of the Sodars are compared with those obtained with a combined multi-aperture scintillation sensor and differential image motion monitor (MASS/DIMM) unit. It was found that the Sodars are indeed capable of quantitatively measuring optical turbulence, and agree with the MASS/DIMM measurements with a correlation coefficient of approximately 80% and a regression slope within 10% of unity. Additional acoustic noise in the Sodar data was identified using this comparison and removed from the data. © 2011 Springer Science+Business Media B.V.


Travouillon T.,TMT Observatory Corporation | Schock M.,TMT Observatory Corporation | Schock M.,Herzberg Institute for Astrophysics | Els S.,TMT Observatory Corporation | And 2 more authors.
Boundary-Layer Meteorology | Year: 2011

In this two-part study, we investigate the usefulness of Sodars as part of a large instrument suite for the study of high mountains in the site selection process of the Thirty Meter Telescope (TMT). In this first part, we describe the reproducibility of the measurements and the comparability of results from different sites for data taken with two complementary Sodar models: the XFAS and SFAS models manufactured by Scintec Inc. To this end, a cross-calibration campaign was conducted on two of the sites comparing both the wind speeds and the optical turbulence measurements of the different units. The specific set-up conditions and the low atmospheric pressure require us to make a compromise between the amount of data available for statistics and the quality of the data. For the comparison of the wind speed, results from the same models show a systematic difference of 12 and 9% for the XFAS and SFAS, respectively. The scatter between individual measurements, which includes instrumental, set-up and statistical fluctuation contributions, was found to be 21 and 23%. For optical turbulence, the respective values are 6 and 3% for the systematic difference and 46 and 67% for the scatter. These results show that Sodars can be useful tools for astronomical site testing for projects such as the TMT. © 2011 Springer Science+Business Media B.V.


Smith R.M.,Caltech Optical Observatories | Hale D.,Caltech Optical Observatories | Wizinowich P.,Wm Keck Observatory
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2014

Bad pixels are generally treated as a loss of useable area and then excluded from averaged performance metrics. The definition and detection of "bad pixels" or "cosmetic defects" are seldom discussed, perhaps because they are considered self-evident or of minor consequence for any scientific grade detector, however the ramifications can be more serious than generally appreciated. While the definition of pixel performance is generally understood, the classification of pixels as useable is highly application-specific, as are the consequences of ignoring or interpolating over such pixels. CMOS sensors (including NIR detectors) exhibit less compact distributions of pixel properties than CCDs. The extended tails in these distributions result in a steeper increase in bad pixel counts as performance thresholds are tightened which comes as a surprise to many users. To illustrate how some applications are much more sensitive to bad pixels than others, we present a bad pixel mapping exercise for the Teledyne H2RG used as the NIR tip-tilt sensor in the Keck-1 Adaptive Optics system. We use this example to illustrate the wide range of metrics by which a pixel might be judged inadequate. These include pixel bump bond connectivity, vignetting, addressing faults in the mux, severe sensitivity deficiency of some pixels, non linearity, poor signal linearity, low full well, poor mean-variance linearity, excessive noise and high dark current. Some pixels appear bad by multiple metrics. We also discuss the importance of distinguishing true performance outliers from measurement errors. We note how the complexity of these issues has ramifications for sensor procurement and acceptance testing strategies. © 2014 SPIE.


Dekany R.,Caltech Optical Observatories
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2010

Experience with the current generation of astronomical single laser guide star (LGS) adaptive optics (AO) systems has demonstrated system performance that is often limited by residual tip-tilt errors induced by the paucity of bright tip-tilt natural guide stars (NGS). To overcome this limitation, we are developing a new generation of tip-tilt sensors that will operate at near-infrared wavelengths where the NGS is sharpened to the diffraction limit. To optimize performance, single LGS AO systems utilizing sharpened tip-tilt NGS should generally not point their LGS directly toward their science target. Rather, optimal performance for wide sky coverage is obtained by offsetting LGS pointing along a radius connecting the science target and the tip-tilt NGS. We demonstrate that determination of the jointly optimized LGS pointing angle and tip-tilt wavefront sensor (WFS) integration time can improve performance metrics by factors of several, particularly for faintest NGS operation. We find the LGS offset should be as much as 1/2 the distance to the NGS to maximize Strehl ratio at near-infrared wavelengths and ≈ 1/4 the distance to the NGS to maximize ensquared energy, with lesser off-pointing for brighter NGS. Future AO systems may benefit from predictive determination of optimal LGS offsetting, based upon changing atmospheric conditions and observational geometries. © 2010 SPIE.


Kulkarni S.R.,Caltech Optical Observatories
Proceedings of the International Astronomical Union | Year: 2011

One of the principal motivations of wide-field and synoptic surveys is the search for, and study of, transients. By transients I mean those sources that arise from the background, are detectable for some time, and then fade away to oblivion. Transients in distant galaxies need to be sufficiently bright as to be detectable, and in almost all cases those transients are catastrophic events, marking the deaths of stars. Exemplars include supernovæ and gamma-ray bursts. In our own Galaxy, the transients are strongly variable stars, and in almost all cases are at best cataclysmic rather than catastrophic. Exemplars include flares from M dwarfs, novæ of all sorts (dwarf novæ, recurrent novæ, classical novæ, X-ray novæ) and instabilities in the surface layers of stars such as S Dor or η Carina. In the nearby Universe (say out to the Virgo cluster) we have sufficient sensitivity to see novæ. In 1 I review the history of transients (which is intimately related to the advent of wide-field telescopic imaging). In 2 I summarize wide-field imaging projects, and I then review the motivations that led to the design of the Palomar Transient Factory (PTF). Next comes a summary of the astronomical returns from PTF (3), and that is followed by lessons that I have learnt from PTF (4). I conclude that, during this decade, the study of optical transients will continue to flourish (and may even accelerate as surveys at other wavelengths - notably radio, UV and X-ray - come on-line). Furthermore, it is highly likely that there will be a proliferation of highly-specialized searches for transients. Those searches may well remain active even in the era of LSST (5). I end the article by discussing the importance of follow-up telescopes for transient object studies - a topical issue, given the Portfolio Review that is being undertaken in the US. © 2012 International Astronomical Union.

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