Variability class

δ Scuti stars

δ Scuti stars sit where the instability strip meets the main sequence — hot, ordinary stars rippling with pressure-mode pulsations, with periods from half an hour to a few hours. Their γ Doradus cousins pulsate in gravity modes over days.

747,748 starsDSCT · HADS · GDOR

Phaseφ 0.00 · Δm 0.00

the star at this phase

Low amplitude, periods of a few hours; hard to resolve with nightly cadence.

What it is

A star of roughly 1.5–2.5 solar masses on or just above the main sequence, pulsating in pressure (p) modes with periods of about 0.02 to 0.3 days — sometimes under an hour. Amplitudes are usually small, a few hundredths to a few tenths of a magnitude, and many stars pulsate in several modes at once.

The physics

The same helium κ-mechanism drives acoustic (pressure) standing waves through the star's envelope. High-amplitude δ Scuti (HADS) pulsate dominantly in a radial mode and look almost like miniature RR Lyrae; the metal-poor Population II analogs are the SX Phoenicis stars. Their pulsation frequencies are a direct probe of stellar structure (asteroseismology).

VSX types

Subtypes

δ Scuti

DSCT

Low-amplitude, often multiperiodic p-mode pulsators on or near the main sequence. Periods ~0.5–7 hours.

High-amplitude

HADS

Radial-mode, large-amplitude, asymmetric — RR-Lyrae-like but much shorter period.

SX Phoenicis

SXPHE

Population II, metal-poor subdwarf cousins; common in globular clusters.

γ Doradus

GDOR

F-type gravity-mode (g-mode) pulsators with periods of ~0.3–3 d, often multiperiodic; δ Scuti–γ Doradus hybrids exist.

Method

Finding the period

The shape is easy; the cadence is the enemy. A one-hour period sampled roughly once per night is badly undersampled, so the periodogram is a thicket of daily aliases and the real peak must be picked out of the lattice. And because the period is so short, it must be right to about P²/baseline or the fold smears over years of data. Camera zero-point conditioning matters here too, since the amplitudes are small.

Pitfalls

Severe daily aliasing: the strongest periodogram peak is frequently a one-day beat of the true frequency.
Multiperiodic stars don't fold to a single clean light curve — a residual scatter after folding is real, not noise.
Low amplitude means the Stetson J variability index, not eyeballing, is what flags these against the noise floor.

Archive stars

Examples

YZ UMi

DSCT · a 2.3-hour p-mode pulsator

#10000000117710 →

V2013 Aql

HADS · a high-amplitude δ Scuti, RR-Lyrae-like at 2.1 h

#10000000101998 →

V1139 Her

SXPHE · a 1.6-hour SX Phoenicis pulsator

#10000000124588 →

Browse δ Scuti stars

747,748 stars in search →Populations