Skip to content

Merged from: Exoplanet transit.md (stub) + Exoplanet Follow up.md (stub) + Exoplanet Spectroscopy.md (stub) + Exoplanet Transit Variation.md + Transit Photometry.md + Synthetic Aperture Photometry (Exoplanets).md All originals preserved. This is the canonical reference.

Exoplanet Science with a Distributed Network

"10000% a place we can put work." Three distinct science modes, each requiring a different approach.

Mode 1: Transit Photometry (Confirmation + Characterisation)

TESS finds thousands of candidates. Ground-based networks confirm them and refine parameters.

What We Actually Measure

  • Transit depth → planet radius ratio (Rp/R★)
  • Transit duration → semi-major axis estimate
  • Transit midtime → ephemeris refinement
  • Timing deviations → TTV signal (see Mode 2)

Hardware Requirements

Component Minimum Notes
Aperture 8"+ Smaller scopes limited by scintillation noise floor
Mount EQ (tracking) Alt-az usable only for short transits
Camera Mono CCD / cooled CMOS Color cameras add read noise; uncooled adds thermal drift
Bit depth 16-bit 8-bit compresses the dimming signal
Filter V or R Broadband "clear" works for hot Jupiters; V preferred

Critical Techniques

  • Intentional defocusing: Spread the star PSF across many pixels. Reduces flat-field errors and allows longer sub-exposures without saturation. Standard practice for precision photometry.
  • Calibration frames: Bias, darks, and flats are non-negotiable. Flat-field variation is the dominant systematic for faint transit depths.
  • Timing precision: UTC to ±5 seconds minimum; GPS-PPS to ±0.1s for high-precision work. NTP alone is insufficient for TTV science.
  • Comparison stars: Choose comparison stars of similar color and magnitude in the same FOV. Differential photometry cancels atmospheric systematics.

Software Workflow

  • AstroImageJ — standard tool for amateur transit photometry, differential aperture photometry, light curve fitting
  • NASA Exoplanet Watch — citizen science program; accepts and archives amateur transit data
  • AAVSO Exoplanet Database (AVDB) — submit light curves here
  • TFOP Working Group — formal TESS follow-up program that works with amateur networks

Precision Benchmarks

Setup Typical Precision Detectable Transit Depth
8" + CCD + V filter 5–10 mmag Hot Jupiters (1% = 10 mmag)
11" + cooled CMOS 3–5 mmag Sub-Saturns
16" + CCD + defocused 1–3 mmag Super-Earths around bright stars

Mode 2: Transit Timing Variations (TTVs)

The deep science. Deviations from a perfect period betray hidden planets. See dedicated note: TTV Reverse N-Body Inference.md.

Why This Requires a Network

  • Monitoring a single target requires observations every clear night for years
  • Target may be observable only 4–6 hours per night from any one longitude
  • Network provides 24h coverage; no transit missed to daylight
  • TTV signal requires 5–20 years of baseline — network persistence matters more than individual precision

Equipment Note

Same as Mode 1 but timing precision becomes critical: - GPS-PPS timing required for ±1 second midtime accuracy - Standard NTP (±50ms drift) is sufficient for initial detection but not refinement - At 5 mmag precision: ingress/egress duration limits midtime precision to ~30–60 seconds for a typical hot Jupiter

Mode 3: Transmission Spectroscopy During Transit

"Is this even possible from the ground?" — Yes, but hard.

The atmosphere of a transiting exoplanet absorbs specific wavelengths during transit. The transit depth varies slightly with wavelength, encoding atmospheric composition.

Feasibility Assessment

  • Space telescopes (JWST, Hubble): The standard. Achieves ppm precision.
  • Ground-based 8m telescopes: Possible for bright targets with careful systematics removal.
  • Amateur network: Marginal for hot Jupiter atmospheres around bright (V<8) stars. Water vapor and telluric contamination are the main enemies.

Distributed Network Advantage for Spectroscopy

Multiple simultaneous spectra from sites with different atmospheric conditions let you disentangle telluric contamination from the planetary signal. Each site sees different water column; the planetary signal is common to all; telluric is not. This is a real statistical advantage no single telescope has.

Minimum Equipment

  • Aperture: 30cm+ with spectrograph (Star Analyser 100 or slitless grating)
  • Or: simultaneous narrow-band photometry in multiple filters across the network (multi-band approach from This is of substance.md)

Connection to OpenAstro Pipeline

  1. Target selection: Pull TESS Objects of Interest (TOIs) + known TTV systems from literature
  2. Campaign assignment: Assign target to all sites that can observe it (longitude diversity)
  3. Data upload: Calibrated FITS + aperture photometry per frame
  4. Light curve assembly: Combine across sites with flux calibration (zero-point, color term correction)
  5. Midtime extraction: Fit transit model, extract midtime with uncertainty
  6. TTV analysis: Build timing residual time series → n-body inference pipeline