31 research outputs found
Angular dimensions of planetary nebulae
We have measured angular dimensions of 312 planetary nebulae from their
images obtained in Halpha (or Halpha + [NII]). We have applied three methods of
measurements: direct measurements at the 10% level of the peak surface
brightness, Gaussian deconvolution and second-moment deconvolution. The results
from the three methods are compared and analysed. We propose a simple
deconvolution of the 10% level measurements which significantly improves the
reliability of these measurements for compact and partially resolved nebulae.
Gaussian deconvolution gives consistent but somewhat underestimated diameters
compared to the 10% measurements. Second-moment deconvolution gives results in
poor agreement with those from the other two methods, especially for poorly
resolved nebulae. From the results of measurements and using the conclusions of
our analysis we derive the final nebular diameters which should be free from
systematic differences between small (partially resolved) and extended (well
resolved) objects in our sample.Comment: 10 figures, 2 table
Survey of Planetary Nebulae at 30 GHz with OCRA-p
We report the results of a survey of 442 planetary nebulae at 30 GHz. The
purpose of the survey is to develop a list of planetary nebulae as calibration
sources which could be used for high frequency calibration in future. For 41
PNe with sufficient data, we test the emission mechanisms in order to evaluate
whether or not spinning dust plays an important role in their spectra at 30
GHz.
The 30-GHz data were obtained with a twin-beam differencing radiometer,
OCRA-p, which is in operation on the Torun 32-m telescope. Sources were scanned
both in right ascension and declination. We estimated flux densities at 30 GHz
using a free-free emission model and compared it with our data.
The primary result is a catalogue containing the flux densities of 93
planetary nebulae at 30 GHz. Sources with sufficient data were compared with a
spectral model of free-free emission. The model shows that free-free emission
can generally explain the observed flux densities at 30 GHz thus no other
emission mechanism is needed to account for the high frequency spectra.Comment: 10 pages, 7 Postscript figures, to be published in A&
An evolutionary catalogue of Galactic post-AGB and related objects
With the ongoing AKARI infrared sky survey, of much greater sensitivity than
IRAS, a wealth of post-AGB objects may be discovered. It is thus time to
organize our present knowledge of known post-AGB stars in th galaxy with a view
to using it to search for new post-AGB objects among AKARI sources. We searched
the literature available on the NASA Astrophysics Data System up to 1 October
2006, and defined criteria for classifying sources into three categories: "very
likely", "possible" and "disqualified" post-AGB objects. The category of "very
likely" post-AGB objects is made up of several classes. We have created an
evolutionary, on-line catalogue of Galactic post-AGB objects, to be referred to
as "The Torun catalogue of Galactic post-AGB and related objects". The present
version of the catalogue contains 326 "very likely", 107 "possible" and 64
"disqualified" objects. For the very likely post-AGB objects, the catalogue
gives the available optical and infrared photometry, infrared spectroscopy and
spectral types, and links to finding charts and bibliography.Comment: 9 pages, 6 figures, accepted for publication in A&
The Herschel Planetary Nebula Survey (HerPlaNS) I. Data Overview and Analysis Demonstration with NGC 6781
This is the first of a series of investigations into far-IR characteristics
of 11 planetary nebulae (PNs) under the Herschel Space Observatory Open Time 1
program, Herschel Planetary Nebula Survey (HerPlaNS). Using the HerPlaNS data
set, we look into the PN energetics and variations of the physical conditions
within the target nebulae. In the present work, we provide an overview of the
survey, data acquisition and processing, and resulting data products. We
perform (1) PACS/SPIRE broadband imaging to determine the spatial distribution
of the cold dust component in the target PNs and (2) PACS/SPIRE
spectral-energy-distribution (SED) and line spectroscopy to determine the
spatial distribution of the gas component in the target PNs. For the case of
NGC 6781, the broadband maps confirm the nearly pole-on barrel structure of the
amorphous carbon-richdust shell and the surrounding halo having temperatures of
26-40 K. The PACS/SPIRE multi-position spectra show spatial variations of
far-IR lines that reflect the physical stratification of the nebula. We
demonstrate that spatially-resolved far-IR line diagnostics yield the (T_e,
n_e) profiles, from which distributions of ionized, atomic, and molecular gases
can be determined. Direct comparison of the dust and gas column mass maps
constrained by the HerPlaNS data allows to construct an empirical gas-to-dust
mass ratio map, which shows a range of ratios with the median of 195+-110. The
present analysis yields estimates of the total mass of the shell to be 0.86
M_sun, consisting of 0.54 M_sun of ionized gas, 0.12 M_sun of atomic gas, 0.2
M_sun of molecular gas, and 4 x 10^-3 M_sun of dust grains. These estimates
also suggest that the central star of about 1.5 M_sun initial mass is
terminating its PN evolution onto the white dwarf cooling track.Comment: 27 pages, 16 figures, accepted for publication in A&
Time resolved spectroscopy of BD+46 442: gas streams and jet creation in a newly discovered evolved binary with a disk
Previous studies have shown that many post-AGB stars with dusty disks are
associated with single-lined binary stars. To verify the binarity hypothesis on
a larger sample, we started a high-resolution spectral monitoring of about 40
field giants, whose binarity was suspected based on either a light curve, an
infrared excess, or a peculiar chemical composition. Here we report on the
discovery of the periodic RV variations in BD+46 442, a high-latitude F giant
with a disk. We interpret the variations due to the motion around a faint
companion, and deduce the following orbital parameters: Porb = 140.77 d, e =
0.083, asini=0.31 AU. We find it to be a moderately metal-poor star
([M/H]=-0.7) without a strong depletion pattern in the photospheric abundances.
Interestingly, many lines show periodic changes with the orbital phase: Halpha
switches between a double-peak emission and a PCyg-like profiles, while strong
metal lines appear split during the maximum redshift. Similar effects are
likely visible in the spectra of other post-AGB binaries, but their regularity
is not always realized due to sporadic observations. We propose that these
features result from an ongoing mass transfer from the evolved giant to the
companion. In particular, the blue-shifted absorption in Halpha, which occurs
only at superior conjunction, may result from a jet originating in the
accretion disk around the companion and seen in absorption towards the luminous
primary.Comment: 16 pages, accepted in A&
The Planetary Nebula Luminosity Function at the Dawn of Gaia
The [O III] 5007 Planetary Nebula Luminosity Function (PNLF) is an excellent
extragalactic standard candle. In theory, the PNLF method should not work at
all, since the luminosities of the brightest planetary nebulae (PNe) should be
highly sensitive to the age of their host stellar population. Yet the method
appears robust, as it consistently produces < 10% distances to galaxies of all
Hubble types, from the earliest ellipticals to the latest-type spirals and
irregulars. It is therefore uniquely suited for cross-checking the results of
other techniques and finding small offsets between the Population I and
Population II distance ladders. We review the calibration of the method and
show that the zero points provided by Cepheids and the Tip of the Red Giant
Branch are in excellent agreement. We then compare the results of the PNLF with
those from Surface Brightness Fluctuation measurements, and show that, although
both techniques agree in a relative sense, the latter method yields distances
that are ~15% larger than those from the PNLF. We trace this discrepancy back
to the calibration galaxies and argue that, due to a small systematic error
associated with internal reddening, the true distance scale likely falls
between the extremes of the two methods. We also demonstrate how PNLF
measurements in the early-type galaxies that have hosted Type Ia supernovae can
help calibrate the SN Ia maximum magnitude-rate of decline relation. Finally,
we discuss how the results from space missions such as Kepler and Gaia can help
our understanding of the PNLF phenomenon and improve our knowledge of the
physics of local planetary nebulae.Comment: 12 pages, invited review at the conference "The Fundamental Cosmic
Distance Scale: State of the Art and Gaia Perspective", to appear in
Astrophysics and Space Scienc
An analysis of the observed radio emission from planetary nebulae
We have analysed the radio fluxes for 264 planetary nebulae for which
reliable measurements of fluxes at 1.4 and 5 GHz, and of nebular diameters are
available. For many of the investigated nebulae the optical thickness is
important, especially at 1.4 GHz. Simple models like the one specified only by
a single optical thickness or spherical, constant density shells do not account
satisfactorily for the observations. Also an r^{-2} density distribution is
ruled out. A reasonable representation of the observations can be obtained by a
two-component model having regions of two different values of optical
thickness. We show that the nebular diameters smaller than 10 arcsec are
uncertain, particularly if they come from photographic plates or gaussian
fitting to the radio profile. While determining the interstellar extinction
from an optical to radio flux ratio caution should be paid to optical thickness
effects in the radio. We have developed a method for estimating the value of
self absorption. At 1.4 GHz self absorption of the flux is usually important
and can exceed a factor of 10. At 5 GHz self absorption is negligible for most
of the objects although in some cases it can reach a factor of 2. The Galactic
bulge planetary nebulae when used to calibrate the Shklovsky method give the
mean nebular mass of 0.14 solar mass. The statistical uncertainty of the
Shklovsky distances is smaller than factor 1.5.Comment: 17 pages, 14 figures, latex2
Planetary Nebula dust haloes revealed by Herschel
Herschel Planetary Nebula Survey (HerPlaNS) is a far-IR imaging and spectroscopic survey of planetary nebulae, performedwith the Herschel Space Observatory, aiming at (1) establishing the spatially-resolved far-IR characteristics of the target nebulae and (2) understanding the energetics and shaping history of the circumstellar nebulae. Below we briefly demonstrate the breadth and depth of the HerPlaNS data set using one of the targets, NGC6781, as an example, and explore expectations in the era of SPICA, the next-generation far-IR mission