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Dipping Variables

Dipping Variables (dip)

Dipping variables are objects that exhibit transient fading events — decreases in brightness that are not caused by eclipses from a stellar companion. The fading is typically caused by obscuration from circumstellar material such as dust in a disk, warped inner disk edges, or dust clouds in the line of sight.

Classification and numbers

  • Supertypes
  • variable
  • irregular
  • Occurrence rate: uncommon as a primary classification; most dippers are young stellar objects or evolved dusty systems

Description

Dipping is distinguished from eclipsing by the mechanism and light curve morphology. Eclipses are caused by a companion star or planet passing in front of the primary, producing repeatable, symmetric dips at a fixed orbital period. Dipping, by contrast, arises from circumstellar dust or gas structures and tends to produce:

  • Irregular depths: successive dips vary in depth, unlike the repeatable depths of eclipses
  • Asymmetric profiles: ingress and egress may differ in duration
  • Variable recurrence: dips may be quasi-periodic (if tied to orbital dust structures) or fully aperiodic

Light curve characteristics

  • Fading events ranging from a few percent to several magnitudes
  • Timescales from hours to weeks (individual dips) or months to years (faders)
  • Flat or mildly variable baseline between dipping events
  • Color-dependent depth: dips caused by dust extinction are typically deeper in bluer bands
  • May appear quasi-periodic if the obscuring material co-rotates with the star (quasi-periodic dippers)

Astrophysical sources of dipping

  • AA Tau-type dippers: warped inner disk edges co-rotating with the YSO, producing quasi-periodic dips on the stellar rotation period (typically 3-10 days)
  • Aperiodic dippers: dust structures at varying disk radii causing random occultation events
  • UX Ori / UXOR variables: Herbig Ae/Be stars with large (1-3 mag) fading episodes from circumstellar dust clouds
  • R Coronae Borealis stars: carbon-rich evolved stars forming dust in their atmospheres, causing deep (up to 8 mag) irregular fading
  • Disintegrating planets: rare cases of transiting rocky planets shedding dusty tails (e.g., KIC 12557548)

Distinguishing dipping from eclipsing

Feature Eclipsing Dipping
Cause Companion star/planet Circumstellar dust/gas
Depth consistency Repeatable Variable
Period Strict orbital period Quasi-periodic or aperiodic
Symmetry Usually symmetric Often asymmetric
Color dependence Achromatic (stellar occultation) Chromatic (dust reddening)

References and further reading:

  • Bodman et al., 2017, MNRAS 470 202, Variable Stars in One Field of K2 Supernova Experiment arxiv:1705.04710
  • Cody et al., 2014, AJ 147 82, CSI 2264: Simultaneous Optical and Infrared Light Curves of Young Disk-bearing Stars arxiv:1401.6582
  • Ansdell et al., 2016, ApJ 816 69, Young "Dipper" Stars in Upper Sco and Oph arxiv:1510.08853