538 research outputs found
Back to the Future: Surveying the Northern Hemisphere and Reprocessing the Southern TESS Data Set
TESS launched 18 April 2018 to conduct a two-year, near all-sky survey for at least 50 small, nearby exoplanets for which masses can be ascertained and whose atmospheres can be characterized by ground- and space-based follow-on observations. TESS has completed its survey of the southern hemisphere and begun its survey of the northern hemisphere, identifying >1000 candidate exoplanets and unveiling a plethora of exciting non-exoplanet astrophysics results, such as asteroseismology, asteroids, and supernova. The TESS Science Processing Operations Center (SPOC) processes the data downlinked every two weeks to generate a range of data products hosted at the Mikulski Archive for Space Telescopes (MAST). For each sector (~1 month) of observations, the SPOC calibrates the image data for both 30-min Full Frame Images (FFIs) and up to 20,000 pre-selected 2-min target star postage stamps. Data products for the 2-min targets include simple aperture photometry and systematic error-corrected flux time series. The SPOC also conducts searches for transiting exoplanets in the 2-min data for each sector and generates Data Validation time series and associated reports for each transit-like feature identified in the search. Multi-sector searches for exoplanets are conducted periodically to discover longer period planets, including those in the James Webb Continuous Viewing Zone (CVZ), which are observed for up to one year. Starting with Sector 8, scattered light from the Earth and Moon contaminated significant portions of the data in each orbit. We have developed algorithms for automated identification of the scattered light features at the individual target level. Previously, data for all stars on a CCD affected by scattered light were manually excluded. The automated flagging will allow us to retain significantly more data for stars that are not affected by the scattered light even though it is occurring elsewhere on the CCD. We also discuss enhancements to the SPOC pipeline and the newly available FFI light curves. The TESS Mission is funded by NASA's Science Mission Directorate as an Astrophysics Explorer Mission
Wormholes and Ringholes in a Dark-Energy Universe
The effects that the present accelerating expansion of the universe has on
the size and shape of Lorentzian wormholes and ringholes are considered. It is
shown that, quite similarly to how it occurs for inflating wormholes, relative
to the initial embedding-space coordinate system, whereas the shape of the
considered holes is always preserved with time, their size is driven by the
expansion to increase by a factor which is proportional to the scale factor of
the universe. In the case that dark energy is phantom energy, which is not
excluded by present constraints on the dark-energy equation of state, that size
increase with time becomes quite more remarkable, and a rather speculative
scenario is here presented where the big rip can be circumvented by future
advanced civilizations by utilizing sufficiently grown up wormholes and
ringholes as time machines that shortcut the big-rip singularity.Comment: 11 pages, RevTex, to appear in Phys. Rev.
Jerk, snap, and the cosmological equation of state
Taylor expanding the cosmological equation of state around the current epoch
is the simplest model one can consider that does not make any a priori
restrictions on the nature of the cosmological fluid. Most popular cosmological
models attempt to be ``predictive'', in the sense that once somea priori
equation of state is chosen the Friedmann equations are used to determine the
evolution of the FRW scale factor a(t). In contrast, a retrodictive approach
might usefully take observational dataconcerning the scale factor, and use the
Friedmann equations to infer an observed cosmological equation of state. In
particular, the value and derivatives of the scale factor determined at the
current epoch place constraints on the value and derivatives of the
cosmological equation of state at the current epoch. Determining the first
three Taylor coefficients of the equation of state at the current epoch
requires a measurement of the deceleration, jerk, and snap -- the second,
third, and fourth derivatives of the scale factor with respect to time.
Higher-order Taylor coefficients in the equation of state are related to
higher-order time derivatives of the scale factor. Since the jerk and snap are
rather difficult to measure, being related to the third and fourth terms in the
Taylor series expansion of the Hubble law, it becomes clear why direct
observational constraints on the cosmological equation of state are so
relatively weak; and are likely to remain weak for the foreseeable future.Comment: V1: 10 pages; uses iopart.cls setstack.sty V2: six additional
references, some clarifying comments and discussion, no physics changes. V3:
significant additions based on community feedback; explicit calculations now
carried out to fourth order in redshift. V4: Discussion of current
observational situation added. This version accepted for publication in
Classical and Quantum Gravity. Now 15 page
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