Stars of the Draco dwarf spheroidal galaxy beyond its measured tidal boundary

Slawomir Piatek, Carlton Pryor, Taft E. Armandroff, Edward W Olszewski

Research output: Contribution to journalArticle

20 Scopus citations


We report R-and V-band photometry derived from CCD imaging for objects in nine fields in and around the Draco dwarf spheroidal galaxy. The most distant fields are about 1°.3 from the center. We use these data to search for Draco stars outside of its measured tidal boundary. The search involves three methods: (1) plotting color-magnitude diagrams for individual fields, for sections of fields, and for combined fields and sections - a colour-magnitude diagram can reveal a population of Draco stars by the presence of the expected principal sequences; (2) measuring field-to-field fluctuations in the surface density of objects located near the Draco principal sequences in the color-magnitude diagram; (3) measuring intrafield fluctuations in the surface density of those objects. We find evidence for the presence of Draco stars immediately beyond the measured tidal boundary of Draco and place an upper limit on the number of such stars in more distant fields that lie close to the extension of its major axis. The best evidence is the presence of the Draco principal sequences in the color-magnitude diagram for some combined fields and sections of fields. The measurements of the field-to-field fluctuations in the stellar surface density confirm this result.

Original languageEnglish (US)
Pages (from-to)841-860
Number of pages20
JournalAstronomical Journal
Issue number2
Publication statusPublished - Feb 2001



  • Galaxies: dwarf
  • Galaxies: individual (Draco)
  • Galaxies: stellar content
  • Galaxies: structure
  • Local group

ASJC Scopus subject areas

  • Space and Planetary Science
  • Astronomy and Astrophysics

Cite this