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12. Science Variable Stars
The Science section hosts VSTarget, a first-party plugin for AAVSO variable-star planning and photometry. It is aimed at observers who contribute variable-star brightness measurements to the American Association of Variable Star Observers (AAVSO) database.
Pre-alpha note: VSTarget's screens are under active development. Some features shown below may be placeholders in the current build. Check the README status section for what is built today.
Click Science in the left sidebar, then choose Variable Stars in the secondary panel.
The planning tab helps you decide which variable stars to observe tonight and schedules them into a session.
| Control | Effect |
|---|---|
| AAVSO VSP | Opens the AAVSO Variable Star Planner in a panel — search by name or coordinates |
| Observable tonight | Filter to stars that are above your minimum altitude during darkness at your Observatory |
| Magnitude range | Show only stars within a brightness range suited to your equipment |
| Program stars | Your personal AAVSO observing program (imported from AAVSO My Observations) |
Select a star from the list and click Add to Session. This appends a Variable Star Observation block to the current session in Planning > Sessions. The block carries the star's name, recommended filters (from the AAVSO VSP) and exposure parameters.
After an imaging run against a variable-star field, the Photometry tab measures the variable star's brightness using comparison stars from the AAVSO comparison-star catalog.
- Load the FITS frame (or pick it from Library > Images).
- VSTarget identifies comparison and check stars from the AAVSO VSP chart for this star.
- Aperture photometry is run on the variable and all comparison stars.
- The variable's instrumental magnitude is differenced against the comparison stars to produce a calibrated magnitude.
- The result is shown with its uncertainty and any quality flags.
VSTarget uses photutils (a dedicated aperture photometry library) for all measurement — separate from SEP, which Galileo's core uses for star detection and HFR. Both coexist deliberately; SEP is optimized for fast detection and HFR, while photutils gives the precise flux measurements aperture photometry requires.
Aperture parameters:
| Parameter | Meaning |
|---|---|
| Aperture radius | Radius of the measurement aperture in pixels |
| Inner / outer sky annulus | Sky background is measured in this annulus and subtracted from the aperture sum |
| Gain | Camera gain in e⁻/ADU, used for Poisson noise estimation |
After measuring a variable, click Submit to AAVSO to generate an AAVSO-format observation report (Extended File Format). You can:
-
Save as file: writes a
.txtreport for manual upload to the AAVSO WebObs portal. - Submit directly: submits the observation via the AAVSO WebObs API (requires your AAVSO observer credentials configured under Options > Science).
Each submitted observation includes: star name, Julian date, magnitude, filter, comparison-star IDs, transformation flag, chart ID, and any notes.