5,746 research outputs found
New candidate planetary nebulae in M81
A 34 x 34 arcmin field centred on the spiral galaxy M81 has been searched for
emission-line objects using the prime focus wide field camera (WFC) of the 2.54
m Isaac Newton Telescope (La Palma, Spain). A total of 171 candidate planetary
nebulae (PNe) are found, 54 of which are in common with the ones detected by
Jacoby et al. (1989). The behaviour of PNe excitation as a function of
galactocentric distance is examined, and no significant variations are found.
The PNe luminosity function is built for the disk and bulge of M81, separately.
A distance modulus of 27.92+-0.23 mag is found for disk PNe, in good agreement
with previous distance measurements for M81 (Jacoby et al. 1989; Huterer et al.
1995).Comment: 7 pages including 2 tables. A&A accepted; also available at
http://www.iac.es/publicaciones/preprints.htm
A deep narrowband survey for planetary nebulae at the outskirts of M33
Context: Planetary nebulae (PNe) are excellent tracers of stellar populations
with low surface brightness, and therefore provide a powerful method to detect
and explore the rich system of substructures discovered around the main spiral
galaxies of the Local Group. Aims: We searched the outskirts of the Local Group
spiral galaxy M33 (the Triangulum) for PNe to gain new insights into the
extended stellar substructure on the northern side of the disc and to study the
existence of a faint classical halo. Methods: The search is based on wide field
imaging covering a 4.5 square degree area out to a maximum projected distance
of about 40 kpc from the centre of the galaxy. The PN candidates are detected
by the combination of images obtained in narrowband filters selecting the
[OIII] and H + [NII] nebular lines and in the continuum
g' and r' broadband filters. Results:Inside the bright optical disc of M33,
eight new PN candidates were identified, three of which were spectroscopically
confirmed. No PN candidates were found outside the limits of the disc. Fourteen
additional sources showing [OIII] excess were also discovered. Conclusions:The
absence of bright PN candidates in the area outside the galaxy disc covered by
this survey sets an upper limit to the luminosity of the underlying population
of , suggesting the lack of a massive
classical halo, which is in agreement with the results obtained using the RGB
population.Comment: 13 pages, 18 figure
High-velocity collimated outflows in planetary nebulae: NGC 6337, He 2-186, and K 4-47
We have obtained narrow-band images and high-resolution spectra of the
planetary nebulae NGC 6337, He 2-186, and K 4-47, with the aim of investigating
the relation between their main morphological components and several
low-ionization features present in these nebulae. The data suggest that NGC
6337 is a bipolar PN seen almost pole on, with polar velocities higher than 200
km/s. The bright inner ring of the nebula is interpreted to be the "equatorial"
density enhancement. It contains a number of low-ionization knots and outward
tails that we ascribe to dynamical instabilities leading to fragmentation of
the ring or transient density enhancements due to the interaction of the
ionization front with previous density fluctuations in the ISM. The lobes show
a pronounced point-symmetric morphology and two peculiar low-ionization
filaments whose nature remains unclear. The most notable characteristic of He
2-186 is the presence of two high-velocity (higher than 135 km/s) knots from
which an S-shaped lane of emission departs toward the central star. K 4-47 is
composed of a compact core and two high-velocity, low-ionization blobs. We
interpret the substantial broadening of line emission from the blobs as a
signature of bow shocks, and using the modeling of Hartigan, Raymond, & Hartman
(1987), we derive a shock velocity of 150 km/s and a mild inclination of the
outflow on the plane of the sky. We discuss possible scenarios for the
formation of these nebulae and their low-ionization features. In particular,
the morphology of K 4-47 hardly fits into any of the usually adopted mass-loss
geometries for single AGB stars. Finally, we discuss the possibility that
point-symmetric morphologies in the lobes of NGC 6337 and the knots of He 2-186
are the result of precessing outflows from the central stars.Comment: 16 pages plus 7 figures, ApJ accepted. Also available at
http://www.iac.es/publicaciones/preprints.htm
K 3-22: a D-type symbiotic star
A goal of the IPHAS survey is to determine the frequency and nature of
emission-line sources in the Galactic plane. According to our selection
criteria, K 3-22 is a candidate symbiotic star, but it was previously
classified as a planetary nebula. To determine its nature, we acquired a
low-resolution optical spectrum of K 3-22. Our analysis of our spectroscopy
demonstrates that K 3-22 is indeed a D-type symbiotic star, because of its high
excitation nebular spectrum and the simultaneous presence of Raman-scattered O
VI emission at 6825 and 7082 angstrom, which is detected primarily in symbiotic
stars.Comment: 3 pages, 1 figure. Accepted for publication on Astronomy and
Astrophysic
Spatially resolved physical and chemical properties of the planetary nebula NGC 3242
Optical integral-field spectroscopy was used to investigate the planetary
nebula NGC 3242. We analysed the main morphological components of this source,
including its knots, but not the halo. In addition to revealing the properties
ofthe physical and chemical nature of this nebula, we also provided reliable
spatially resolved constraints that can be used for future photoionisation
modelling of the nebula. The latter is ultimately necessary to obtain a fully
self-consistent 3D picture of the physical and chemical properties of the
object. The observations were obtained with the VIMOS instrument attached to
VLT-UT3. Maps and values for specific morphological zones for the detected
emission-lines were obtained and analysed with routines developed by the
authors to derive physical and chemical conditions of the ionised gas in a 2D
fashion. We obtained spatially resolved maps and mean values of the electron
densities, temperatures, and chemical abundances, for specific morphological
structures in NGC 3242. These results show the pixel-to-pixel variations of the
the small- and large-scale structures of the source. These diagnostic maps
provide information free from the biases introduced by traditional single
long-slit observations. In general, our results are consistent with a uniform
abundance distribution for the object, whether we look at abundance maps or
integrated fluxes from specified morphological structures. The results indicate
that special care should be taken with the calibration of the data and that
only data with extremely good signal-to-noise ratio and spectral coverage
should be used to ensure the detection of possible spatial variations.Comment: 11 pages, 8 figures accepted for publication in Astronomy &
Astrophysic
Kinematic and morphological modeling of the bipolar nebula Sa2-237
We present [OIII]500.7nm and Halpha+[NII] images and long-slit, high
resolution echelle spectra in the same spectral regions of Sa2--237, a possible
bipolar planetary nebula. The image shows a bipolar nebula of about 34" extent,
with a narrow waist, and showing strong point symmetry about the central
object, indicating it's likely binary nature. The long slit spectra were taken
over the long axis of the nebula, and show a distinct ``eight'' shaped pattern
in the velocity--space plot, and a maximum projected outflow velocity of
V=106km/s, both typical of expanding bipolar planetary nebulae. By model
fitting the shape and spectrum of the nebula simultaneously, we derive the
inclination of the long axis to be 70 degrees, and the maximum space velocity
of expansion to be 308 km/s. Due to asymmetries in the velocities we adopt a
new value for the system's heliocentric radial velocity of -30km/s. We use the
IRAS and 21cm radio fluxes, the energy distribution, and the projected size of
Sa2-237 to estimate it's distance to be 2.1+-0.37kpc. At this distance Sa2-237
has a luminosity of 340 Lsun, a size of 0.37pc, and -- assuming constant
expansion velocity -- a nebular age of 624 years. The above radial velocity and
distance place Sa2--237 in the disk of the Galaxy at z=255pc, albeit with
somewhat peculiar kinematics.Comment: 10pp, 4 fig
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