300 research outputs found
Planetary nebulae in M32 and the bulge of M31: Line intensities and oxygen abundances
We present spectroscopy of planetary nebulae in M32 and in the bulge of M31
that we obtained with the MOS spectrograph at the Canada-France-Hawaii
Telescope. Our sample includes 30 planetary nebulae in M31 and 9 planetary
nebulae in M32. We also observed one H II region in the disk of M31. We
detected [O III]4363 in 18 of the planetary nebulae, 4 in M32 and 14
in the bulge of M31. We use our line intensities to derive electron
temperatures and oxygen abundances for the planetary nebulae.Comment: 17 pages, 12 figures, accepted by Astronomy & Astrophysics Supplement
Serie
Polarization in the Lagoon nebula
A V-band polarimetric survey of stars associated with the Lagoon nebula was conducted. The data were combined with existing photometric and spectroscopic observations in order to investigate the alignment of magnetic field lines with identifiable symmetry axes and to evaluate the nature of dust in the immediate vicinity. Although stars are not in general highly polarized, electric vectors align with the minor axis of the Lagoon nebula, perpendicular to the major axis of the spatial distribution of massive stars. The observations indicate that the collapse of the molecular cloud progenitor was inhibited along directions perpendicular to magnetic field lines. Considering the low polarization efficiency and the high ratio of total to selective extinction, smaller grains of intranebular dust appear to have been destroyed
The Spectral Types of White Dwarfs in Messier 4
We present the spectra of 24 white dwarfs in the direction of the globular
cluster Messier 4 obtained with the Keck/LRIS and Gemini/GMOS spectrographs.
Determining the spectral types of the stars in this sample, we find 24 type DA
and 0 type DB (i.e., atmospheres dominated by hydrogen and helium
respectively). Assuming the ratio of DA/DB observed in the field with effective
temperature between 15,000 - 25,000 K, i.e., 4.2:1, holds for the cluster
environment, the chance of finding no DBs in our sample due simply to
statistical fluctuations is only 6 X 10^(-3). The spectral types of the ~100
white dwarfs previously identified in open clusters indicate that DB formation
is strongly suppressed in that environment. Furthermore, all the ~10 white
dwarfs previously identified in other globular clusters are exclusively type
DA. In the context of these two facts, this finding suggests that DB formation
is suppressed in the cluster environment in general. Though no satisfactory
explanation for this phenomenon exists, we discuss several possibilities.Comment: Accepted for Publication in Astrophys. J. 11 pages including 4
figures and 2 tables (journal format
The Evolution of the Kinematics of Nebular Shells in Planetary Nebulae in the Milky Way Bulge
We study the line widths in the [\ion{O}{3}]5007 and H lines
for two groups of planetary nebulae in the Milky Way bulge based upon
spectroscopy obtained at the Observatorio Astron\'omico Nacional in the Sierra
San Pedro M\'artir (OAN-SPM) using the Manchester Echelle Spectrograph. The
first sample includes objects early in their evolution, having high H
luminosities, but [\ion{O}{3}]. The second
sample comprises objects late in their evolution, with \ion{He}{2} . These planetary nebulae represent evolutionary
phases preceeding and following those of the objects studied by Richer et al.
(2008). Our sample of planetary nebulae with weak [\ion{O}{3}]5007 has
a line width distribution similar to that of the expansion velocities of the
envelopes of AGB stars, and shifted to systematically lower values as compared
to the less evolved objects studied by Richer et al. (2008). The sample with
strong \ion{He}{2} has a line width distribution
indistinguishable from that of the more evolved objects from Richer et al.
(2008), but a distribution in angular size that is systematically larger and so
they are clearly more evolved. These data and those of Richer et al. (2008)
form a homogeneous sample from a single Galactic population of planetary
nebulae, from the earliest evolutionary stages until the cessation of nuclear
burning in the central star. They confirm the long-standing predictions of
hydrodynamical models of planetary nebulae, where the kinematics of the nebular
shell are driven by the evolution of the central star.Comment: accepted for publication in the Astrophysical Journa
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