Pixel level decorrelation in service of the Spitzer microlens parallax survey

Microlens parallax measurements combining space-based and ground-based observatories can be used to study planetary demographics. In recent years, the Spitzer Space Telescope was used as a microlens parallax satellite. Meanwhile, Spitzer IRAC has been employed to study short-period exoplanets and their atmospheres. As these investigations require exquisite photometry, they motivated the development of numerous self-calibration techniques now widely used in the exoplanet atmosphere community. Specifically, pixel level decorrelation (PLD) was developed for starring-mode observations in uncrowded fields. We adapt and extend PLD to make it suitable for observations obtained as part of the Spitzer Microlens Parallax Campaign. We apply our method to two previously published microlensing events, OGLE-2017-BLG-1140 and OGLE-2015-BLG-0448, and compare its performance to the state-of-the-art pipeline used to analyses Spitzer microlensing observation. We find that our method yields photometry 1.5–6 times as precise as previously published. In addition to being useful for Spitzer, a similar approach could improve microlensing photometry with the forthcoming Nancy Grace Roman Space Telescope

Pixel level decorrelation in service of the Spitzer microlens parallax survey

Microlens parallax measurements combining space-based and ground-based observatories can be used to study planetary demographics. In recent years, the Spitzer Space Telescope was used as a microlens parallax satellite. Meanwhile, Spitzer IRAC has been employed to study short-period exoplanets and their atmospheres. As these investigations require exquisite photometry, they motivated the development of numerous self-calibration techniques now widely used in the exoplanet atmosphere community. Specifically, pixel level decorrelation (PLD) was developed for starring-mode observations in uncrowded fields. We adapt and extend PLD to make it suitable for observations obtained as part of the Spitzer Microlens Parallax Campaign. We apply our method to two previously published microlensing events, OGLE-2017-BLG-1140 and OGLE-2015-BLG-0448, and compare its performance to the state-of-the-art pipeline used to analyses Spitzer microlensing observation. We find that our method yields photometry 1.5–6 times as precise as previously published. In addition to being useful for Spitzer, a similar approach could improve microlensing photometry with the forthcoming Nancy Grace Roman Space Telescope

Medienpraktiken: situieren, erforschen, reflektieren; eine Einleitung

Mit dem Fokus auf Medienpraktiken bündelt dieses Heft aktuelle Positionen zur empirischen Erforschung von Medien. Die Beiträge gehen davon aus, dass Medien erst durch ihren Gebrauch zu Medien werden. Medienpraktiken zu erforschen, bedeutet jedoch nicht nur herauszufinden, was Menschen mit Medien tun, sondern auch was Medien mit Menschen machen. Diese für die Medienpraktikenforschung zentrale Einsicht lösen die interdisziplinären Beiträge des Bandes ein, indem sie aus den jeweiligen Positionen und Konstellationen verdeutlichen, wie Medien und Praktiken sich gegenseitig bedingen. Medienpraktikenforschung erfordert erstens, medienpraktische Phänomene in einem hohen Detailgrad zu fassen, um die Relation der beteiligten menschlichen und medialen Akteure zueinander in situ und in actu nachzuvollziehen. Erst durch die analytische Durchdringung dieser situativen Vollzugsmomente lässt sich zweitens der Status von Medien klären: was durch Praktiken zu einem Medium wird und wie die Praktiken unter Berücksichtigung der an ihnen konstitutiv beteiligten Medien beschaffen sind. Dadurch lassen sich ebenso übersituative Bezüge zur Praxis herstellen, durch die die Praktiken zur situativen Entfaltung kommen. Drittens muss dabei berücksichtigt werden, inwiefern die eigenen Medienpraktiken der Erforschung in ihren jeweiligen situativen Stadien die (Analyse der) Medienpraktik zurichten. Die Beiträge dieses Bandes lösen diese Forderungen in unterschiedlicher Gewichtung ein. Sie befassen sich aus medienethnologischer, kultursoziologischer, literaturwissenschaftlicher, historischer, soziologischer und medienwissenschaftlicher Perspektive damit, was jeweils als situierte Medienpraktik verstanden werden kann. Gemeinsam ist damit allen Beiträgen, dass sie erst aus ihren jeweiligen Untersuchungen und Perspektiven heraus bestimmen, was genau als Medienpraktik und Medien, die in ihnen zum Tragen kommen, gefasst werden kann

Detection of a Westward Hotspot Offset in the Atmosphere of a Hot Gas Giant CoRoT-2b

Short-period planets exhibit day-night temperature contrasts of hundreds to thousands of degrees K. They also exhibit eastward hotspot offsets whereby the hottest region on the planet is east of the substellar point; this has been widely interpreted as advection of heat due to eastward winds. We present thermal phase observations of the hot Jupiter CoRoT-2b obtained with the IRAC instrument on the Spitzer Space Telescope. These measurements show the most robust detection to date of a westward hotspot offset of 23 $\pm$ 4 degrees, in contrast with the nine other planets with equivalent measurements. The peculiar infrared flux map of CoRoT-2b may result from westward winds due to non-synchronous rotation magnetic effects, or partial cloud coverage, that obscures the emergent flux from the planet's eastern hemisphere. Non-synchronous rotation and magnetic effects may also explain the planet's anomalously large radius. On the other hand, partial cloud coverage could explain the featureless dayside emission spectrum of the planet. If CoRoT-2b is not tidally locked, then it means that our understanding of star-planet tidal interaction is incomplete. If the westward offset is due to magnetic effects, our result represents an opportunity to study an exoplanet's magnetic field. If it has Eastern clouds, then it means that our understanding of large-scale circulation on tidally locked planets is incomplete.Comment: 30 pages, 4 figures, 15 supplementary figure

ATOCA: an algorithm to treat order contamination. Application to the NIRISS SOSS mode

After a successful launch, the James Webb Space Telescope is preparing to undertake one of its principal missions, the characterization of the atmospheres of exoplanets. The Single Object Slitless Spectroscopy (SOSS) mode of the Near Infrared Imager and Slitless Spectrograph (NIRISS) is the only observing mode that has been specifically designed for this objective. It features a wide simultaneous spectral range (0.6--2.8\,\micron) through two spectral diffraction orders. However, due to mechanical constraints, these two orders overlap slightly over a short range, potentially introducing a ``contamination'' signal in the extracted spectrum. We show that for a typical box extraction, this contaminating signal amounts to 1\% or less over the 1.6--2.8\,\micron\ range (order 1), and up to 1\% over the 0.85--0.95\,\micron\ range (order 2). For observations of exoplanet atmospheres (transits, eclipses or phase curves) where only temporal variations in flux matter, the contamination signal typically biases the results by order of 1\% of the planetary atmosphere spectral features strength. To address this problem, we developed the Algorithm to Treat Order ContAmination (ATOCA). By constructing a linear model of each pixel on the detector, treating the underlying incident spectrum as a free variable, ATOCA is able to perform a simultaneous extraction of both orders. We show that, given appropriate estimates of the spatial trace profiles, the throughputs, the wavelength solutions, as well as the spectral resolution kernels for each order, it is possible to obtain an extracted spectrum accurate to within 10\,ppm over the full spectral range.Comment: Submitted to PASP. 22 pages, 12 figure