The Planetary Nebula Population of the Sagittarius Dwarf Spheroidal Galaxy
Zijlstra A.A., Gesicki K., Walsh J.R., Péquignot D.,van Hoof P.A.M., Minniti D.
published in: MNRAS, 369, 875 (2006)
The identification of two new Planetary Nebulae in the Sagittarius Dwarf
Spheroidal Galaxy (Sgr) is presented. This brings the total number to four.
Both new PNe were previously classified as Galactic objects. The first, StWr
2-21, belongs to the main body of Sgr, from its velocity and location. The
second, the halo PN BoBn 1, has a location, distance and velocity in agreement
with the leading tidal tail of Sgr. We estimate that 10 per cent of the
Galactic halo consists of Sgr debris. The specific frequency of PNe indicate a
total luminosity of Sgr, including its tidal tails, of MV = -14.1.
StWr 2-21 shows a high abundance of [O/H] = -0.23, which confirms the
high-metallicity population in Sgr uncovered by Bonaficio et al. (2004). The
steep metallicity-age gradient is due to ISM removal during the Galactic plane
passages, ISM reformation due to stellar mass loss, and possibly accretion of
metal-enriched gas from our Galaxy. The ISM re-formation rate of Sgr, from
stellar mass loss, is 5 x 10-4 Msol yr-1, amounting to
approximately 106 Msol per orbital period.
HST images of three of the PNe reveal well-developed bipolar morphologies, and
provide clear detections of the central stars. All three stars with deep
spectra show WR-lines, suggesting that the progenitor mass and metallicity
determines whether a PN central star develops a WR spectrum. We show that the
temperature of the WR central stars is higher at lower metallicity. Expansion
velocities are determined for three nebulae. Comparison with hydrodynamical
models indicates an initial density profile of ρ proportional to
r-3. This is evidence for increasing mass-loss rates on the AGB.
Peak mass-loss rates are indicated of approximately 10-4 Msol
yr-1. One of the Sgr PNe, He 2-436, provides the sole direct
detection of dust in a dwarf spheroidal galaxy, to date.
Back to the list of refereed publications
Peter van Hoof
Royal Observatory of Belgium
Ringlaan 3
1180 Brussel
Belgium
email: p DOT vanhoof AT oma DOT be
