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Register a new userThe Tierras Observatory: An ultra-precise photometer to characterize nearby terrestrial exoplanets
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Juliana Garc\\'ia-Mej\\'ia
Publication date
2020
fields
Physics
and research's language is
English
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We report on the status of the Tierras Observatory, a refurbished 1.3-m ultra-precise fully-automated photometer located at the F. L. Whipple Observatory atop Mt. Hopkins, Arizona. Tierras is designed to limit systematic errors, notably precipitable water vapor (PWV), to 250 ppm, enabling the characterization of terrestrial planet transits orbiting $< 0.3 , R_{odot}$ stars, as well as the potential discovery of exo-moons and exo-rings. The design choices that will enable our science goals include: a four-lens focal reducer and field-flattener to increase the field-of-view of the telescope from a $11.94$ to a $0.48^{circ}$ side; a custom narrow bandpass ($40.2$ nm FWHM) filter centered around $863.5$ nm to minimize PWV errors known to limit ground-based photometry of red dwarfs; and a deep-depletion $4K times 4K$ CCD with a 300ke-full well and QE$>85%$ in our bandpass, operating in frame transfer mode. We are also pursuing the design of a set of baffles to minimize the significant amount of scattered light reaching the image plane. Tierras will begin science operations in early 2021.
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Combining adaptive optics and interferometric observations results in a considerable contrast gain compared to single-telescope, extreme AO systems. Taking advantage of this, the ExoGRAVITY project is a survey of known young giant exoplanets located in the range of 0.1 to 2 from their stars. The observations provide astrometric data of unprecedented accuracy, being crucial for refining the orbital parameters of planets and illuminating their dynamical histories. Furthermore, GRAVITY will measure non-Keplerian perturbations due to planet-planet interactions in multi-planet systems and measure dynamical masses. Over time, repetitive observations of the exoplanets at medium resolution ($R=500$) will provide a catalogue of K-band spectra of unprecedented quality, for a number of exoplanets. The K-band has the unique properties that it contains many molecular signatures (CO, H$_2$O, CH$_4$, CO$_2$). This allows constraining precisely surface gravity, metallicity, and temperature, if used in conjunction with self-consistent models like Exo-REM. Further, we will use the parameter-retrieval algorithm petitRADTRANS to constrain the C/O ratio of the planets. Ultimately, we plan to produce the first C/O survey of exoplanets, kick-starting the difficult process of linking planetary formation with measured atomic abundances.
Recent results have strongly confirmed that multiple supernovae happened at distances ~100 pc consisting of two main events: one at 1.7 to 3.2 million years ago, and the other at 6.5 to 8.7 million years ago. These events are said to be responsible for excavating the Local Bubble in the interstellar medium and depositing 60Fe on Earth and the Moon. Other events are indicated by effects in the local cosmic ray (CR) spectrum. Given this updated and refined picture, we ask whether such supernovae are expected to have had substantial effects on the terrestrial atmosphere and biota. In a first cut at the most probable cases, combining photon and cosmic ray effects, we find that a supernova at 100 pc can have only a small effect on terrestrial organisms from visible light and that chemical changes such as ozone depletion are weak. However, tropospheric ionization right down to the ground due to the penetration of $geq$TeV cosmic rays will increase by nearly an order of magnitude for thousands of years, and irradiation by muons on the ground and in the upper ocean will increase 20-fold, which will approximately triple the overall radiation load on terrestrial organisms. Such irradiation has been linked to possible changes in climate and increased cancer and mutation rates. This may be related to a minor mass extinction around the Pliocene-Pleistocene boundary, and further research on the effects is needed.
ImageJ is a graphical user interface (GUI) driven, public domain, Java-based, software package for general image processing traditionally used mainly in life sciences fields. The image processing capabilities of ImageJ are useful and extendable to other scientific fields. Here we present AstroImageJ (AIJ), which provides an astronomy specific image display environment and tools for astronomy specific image calibration and data reduction. Although AIJ maintains the general purpose image processing capabilities of ImageJ, AIJ is streamlined for time-series differential photometry, light curve detrending and fitting, and light curve plotting, especially for applications requiring ultra-precise light curves (e.g., exoplanet transits). AIJ reads and writes standard FITS files, as well as other common image formats, provides FITS header viewing and editing, and is World Coordinate System (WCS) aware, including an automated interface to the astrometry.net web portal for plate solving images. AIJ provides research grade image calibration and analysis tools with a GUI driven approach, and easily installed cross-platform compatibility. It enables new users, even at the level of undergraduate student, high school student, or amateur astronomer, to quickly start processing, modeling, and plotting astronomical image data with one tightly integrated software package.
The NEAT (Nearby Earth Astrometric Telescope) mission is a proposition submitted to ESA for its 2010 call for M-size mission. The main scientific goal is to detect and characterize planetary systems in an exhaustive way down to 1 Earth mass in the habitable zone and further away, around nearby stars for F, G, and K spectral types. This survey would provide the actual planetary masses, the full characterization of the orbits including their inclination, for all the components of the planetary system down to that mass limit. Extremely- high-precision astrometry, in space, can detect the dynamical effect due to even low mass orbiting planets on their central star, reaching those scientific goals. NEAT will continue the work performed by Hipparcos (1mas precision) and Gaia (7{mu}as aimed) by reaching a precision that is improved by two orders of magnitude (0.05{mu}as, 1{sigma} accuracy). The two modules of the payload, the telescope and the focal plane, must be placed 40m away leading to a formation flying option studied as the reference mission. NEAT will operate at L2 for 5 years, the telescope satellite moving around the focal plane one to point different targets and allowing whole sky coverage in less than 20 days. The payload is made of 3 subsystems: primary mirror and its dynamic support, the focal plane with the detectors, and the metrology. The principle is to measure the angles between the target star, usually bright (R leq 6), and fainter reference stars (R leq 11) using a metrology system that projects dynamical Youngs fringes onto the focal plane. The proposed architecture relies on two satellites of about 700 kg, offering a capability of more than 20,000 reconfigurations. The two satellites are launched in a stacked configuration using a Soyuz ST launch, and are deployed after launch to individually perform cruise to their operational Lissajous orbit.
Wong et al. (2018) recently performed an encouraging criticism to our paper Gravitational waves from ultra-short period exoplanets (Cunha, Silva, Lima 2018) exploring the potentialities of a subset of exoplanets with extremely short periods (less than 80 min) as a possible scientific target to the planned space-based LISA observatory. Here we call attention to some subtleties and limitations underlying the basic criticism which in our view were not properly stressed in their comment. Particularly, simple estimates show that a sphere encircling the Earth with a radius of 250 pc may accommodate a population $ sim 10^{4}$ ultra-short period exoplanets with characteristic strain of the same order or higher than the ones analyzed in our paper. This means that the question related to the gravitational wave pattern of ultra-short period exoplanets may be surpassed near future by the LISA instrument with new and more definitive data.
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