Transiting Exoplanet Working Group

Nikole K. LewisSTScI

10/20/2015

Science Case: Transiting Exoplanets

Signal Strengths

Less Than Eclipse Depth

Transiting Exoplanets: Requirements

• Exposures on the order of hours to days

• Stable pointing (no dithers, no parallels)

• Brightest host stars generally present best SNR

Time-Series Observations (TSOs)Other use cases with similar operational and pipeline processing requirements include:• Solar system stellar

occultations, eclipses, mutual events

• Eclipsing cataclysmic variables

• Brown Dwarf Variability

• Non-transiting exoplanet phase curves

Time-series Observations (TSO) Req’s

Exposures longer than 10,000 sec Phase Constraints in APT ([-1,1])

Visits exceeding 24 hours Minimum number of guide stars required (mitigate failure during long stares)

Uninterruptible observations > 48 hours BJD_TDB time standard (HJD and BJD_UTC)

Slew to science target ASAP and wait (allows for thermal settling)

Time-tagging of integrations

Timing of target acquisition relative to slew and start of science data collection

FITS file format for TSO exposures

Disable Dithers in TSO observations Flag integrations acquired during HGA moves

Avoid electronic and mechanical disturbances (NO_PARALLEL)

Cross-instrument TSO functionality (APT, pipeline, etc.)

Open, development in progress

Nearly Closed

Closed

Time Tagging of Integrations• What sets limits on accuracy/precision of time tags?

– 10 μs precision on frame time– Onboard time tags (UTC) are generated when the last pixel of “science

image” is read– Onboard clock sampled at a rate of 64 ms, which sets the precision limit

for the time tags of SSR science data files– Corrections to the onboard clock can be updated on 12hr contact interval.

Linear correction is applied on 1.024 s intervals (with 0.5 ms accuracy), with steps on the order of a few microseconds. Clock will not be allowed to drift more than 1 s away from the true UTC time over a 24 hour period. Clock performance can be estimated starting in 2016 (EMTB, OTB facilities).

• Bottom line: 64 ms clock sampling rate is limiter to time-tag accuracy.

Time Tagging of Integrations• What is a “science image”?

• Packet of data equivalent to one full frame (2048x2048).• Subarray data will stacked frame-by-frame (group-by-group)

until it meets this size. For example 64 256x256 subarrays would be included in one science image.

• This means timestamps are generated every 10.7/42.2 seconds (accurate to 64 ms).

• Bottom line/Take Away: Don’t panic!• Very similar to subarray stacking and timestamp cadence used

by Spitzer (64 frames per image with one timestamp)• Frame times are precise and allow extrapolation between

timestamps • Reformatting of data will take care of timestamp propagation

(discussion on next slide).

Fits File Formatting for TSO• Original Plan: one fits file per exopsure with a

timestamp(s) propagated from last pixel read.• Suggested Plan: A new pipeline processing module

created that will repackage all TSO data products (raw frames, calibrated ramps, etc.) and include time tags with each frame.– Time tags will be generated in multiple flavors including

BJD_TT, BJD_UTC, HJD_UTC– HST/Spitzer include time tags in header, Kepler as a table

extension (I’ve been told the latter is more computationally efficient).

– Work continues on one fits file per exopsure vs. one fits file per integration. Need solution that will work in context of current pipeline/archive architecture.

TSO Version of Pipeline

• Standard pipeline design would require TSO users to work with raw integrations

• TSO pipeline minimizes corrections that could introduce unwanted errors (less is more).

• TSO pipeline provides high-level data products in temporal space as opposed to stacking integrations.

• Currently working Calibration and Pipeline WGs to enable TSO science.

Tracking Data ‘Features’• Persistence/Latent

Images• Saturation/Linearity• Pointing Jitter/Settling• IPSV, IPC• Background • Noise (white, 1/f, red)• Flat-Fielding Errors• On orbit calibration

High-Precision Time Series Observation w/JWST Website Coming Online at the end of October! SSC

HAT-P-2, 8 μm

Enabling Transiting Exoplanet Science with JWST

A STScI Mini-Workshop

November 16th-18th, 2015

Goals of the Workshop• Inform the community about JWST’s capabilities for

transiting exoplanet observations, so that they can start thinking about good science cases now.

• Inform both STScI and the broader community about some of the cutting edge exoplanet science that can be enabled with JWST through invited science talks.

• Facilitate discussions in the transiting exoplanet community about wants/needs for early release science programs and support from STScI (clearing house for data reduction tools, data challenges, etc.)

Currently ~60 in person participants. Workshop Link