38 research outputs found
Where Are the Binaries? Results of a Long-Term Search for Radial Velocity Binaries in Proto-Planetary Nebulae
We present the results of an expanded, long-term radial velocity search (25
yrs) for evidence of binarity in a sample of seven bright proto-planetary
nebulae (PPNe). The goal is to investigate the widely-held view that the
bipolar or point-symmetric shapes of planetary nebulae (PNe) and PPNe are due
to binary interactions. Observations from three observatories were combined
from 2007-2015 to search for variations on the order of a few years and then
combined with earlier observations from 1991-1995 to search for variations on
the order of decades. All seven show velocity variations due to periodic
pulsation in the range of 35-135 days. However, in only one PPN, IRAS
22272+5435, did we find even marginal evidence found for multi-year variations
that might be due to a binary companion. This object shows
marginally-significant evidence of a two-year period of low semi-amplitude
which could be due to a low-mass companion, and it also displays some evidence
of a much longer period of >30 years. The absence of evidence in the other six
objects for long-period radial velocity variations due to a binary companion
sets significant constraints on the properties of any undetected binary
companions: they must be of low mass, 30 years.
Thus the present observations do not provide direct support for the binary
hypothesis to explain the shapes of PNe and PPNe and severely constrains the
properties of any such undetected companions.Comment: 28 pages, 5 figure
A Herschel study of Planetary Nebulae
We present Herschel PACS and SPIRE images of the dust shells around the
planetary nebulae NGC 650, NGC 6853, and NGC 6720, as well as images showing
the dust temperature in their shells. The latter shows a rich structure, which
indicates that internal extinction in the UV is important despite the highly
evolved status of the nebulae.Comment: 2 pages, 1 figure, 2012, proceedings IAU Symposium 283 Planetary
Nebulae: An Eye to the Futur
The heart of Sakurai's Object revealed by ALMA
We present high angular-resolution observations of Sakurai's object using the
Atacama Large Millimeter Array, shedding new light on its morpho-kinematical
structure. The millimetre continuum emission, observed at an angular resolution
of 20 milliarcsec (corresponding to 70 AU), reveals a bright compact central
component whose spectral index indicates that it composed of amorphous carbon
dust. Based on these findings, we conclude that this emission traces the
previously suggested dust disc observed in mid-infrared observations.
Therefore, our observations provide the first direct imaging of such a disc.
The HCN(=43) line emission, observed at an angular
resolution of 300 milliarcsec (corresponding to 1000 AU), displays bipolar
structure with a north-south velocity gradient. From the position-velocity
diagram of this emission we identify the presence of an expanding disc and a
bipolar molecular outflow. The inclination of the disc is determined to be
=72. The derived values for the de-projected expansion velocity and
the radius of the disc are =53 km s and =277 AU,
respectively. On the other hand, the de-projected expansion velocity of the
bipolar outflow detected in the HCN(=43) emission of
approximately 1000 km s. We propose that the molecular outflow has an
hourglass morphology with an opening angle of around 60. Our
observations unambiguously show that an equatorial disc and bipolar outflows
formed in Sakurai's object in less than 30 years after the born-again event
occurred, providing important constraints for future modelling efforts of this
phenomenon.Comment: 9 pages, 5 figures. Accepted for publication as a Letter in Astronomy
and Astrophysic
JWST observations of the Ring Nebula (NGC 6720): I. Imaging of the rings, globules, and arcs
We present JWST images of the well-known planetary nebula NGC 6720 (the Ring
Nebula), covering wavelengths from 1.6m to 25 m. The bright shell is
strongly fragmented with some 20 000 dense globules, bright in H, with a
characteristic diameter of 0.2 arcsec and density -
cm. The shell contains a thin ring of polycyclic aromatic hydrocarbon
(PAH) emission. H is found throughout the shell and in the halo. H in
the halo may be located on the swept-up walls of a biconal polar flow. The
central cavity is shown to be filled with high ionization gas and shows two
linear structures. The central star is located 2 arcsec from the emission
centroid of the cavity and shell. Linear features (`spikes') extend outward
from the ring, pointing away from the central star. Hydrodynamical simulations
are shown which reproduce the clumping and possibly the spikes. Around ten
low-contrast, regularly spaced concentric arc-like features are present; they
suggest orbital modulation by a low-mass companion with a period of about 280
yr. A previously known much wider companion is located at a projected
separation of about 15 000 au; we show that it is an M2-M4 dwarf. The system is
therefore a triple star. These features, including the multiplicity, are
similar to those seen in the Southern Ring Nebula (NGC 3132) and may be a
common aspect of such nebulae.Comment: 25 pages, 23 figures. Submitted to Monthly Notices of the Royal
Astronomical Society. Corrected typos in metadat
A stubbornly large mass of cold dust in the ejecta of Supernova 1987A
We present new Herschel photometric and spectroscopic observations of
Supernova 1987A, carried out in 2012. Our dedicated photometric measurements
provide new 70 micron data and improved imaging quality at 100 and 160 micron
compared to previous observations in 2010. Our Herschel spectra show only weak
CO line emission, and provide an upper limit for the 63 micron [O I] line flux,
eliminating the possibility that line contaminations distort the previously
estimated dust mass. The far-infrared spectral energy distribution (SED) is
well fitted by thermal emission from cold dust. The newly measured 70 micron
flux constrains the dust temperature, limiting it to nearly a single
temperature. The far-infrared emission can be fitted by 0.5+-0.1 Msun of
amorphous carbon, about a factor of two larger than the current nucleosynthetic
mass prediction for carbon. The observation of SiO molecules at early and late
phases suggests that silicates may also have formed and we could fit the SED
with a combination of 0.3 Msun of amorphous carbon and 0.5 Msun of silicates,
totalling 0.8 Msun of dust. Our analysis thus supports the presence of a large
dust reservoir in the ejecta of SN 1987A. The inferred dust mass suggests that
supernovae can be an important source of dust in the interstellar medium, from
local to high-redshift galaxies.Comment: ApJ accepted, 8 page
<i>JWST</i> observations of the Ring Nebula (NGC 6720): I. Imaging of the rings, globules, and arcs
We present images of the well-known planetary nebula NGC 6720 (the Ring Nebula), covering wavelengths from 1.6m to 25m. The bright shell is strongly fragmented with some 20 000 dense globules, bright in , with a characteristic diameter of 0.2 arcsec and density ∼ – . The shell contains a narrow ring of polycyclic aromatic hydrocarbon (PAH) emission. is found throughout the shell and also in the halo. in the halo may be located on the swept-up walls of a biconal polar flow. The central cavity is filled with high ionization gas and shows two linear structures which we suggest are the edges of a biconal flow, seen in projection against the cavity. The central star is located 2 arcsec from the emission centroid of the cavity and shell. Linear features (‘spikes’) extend outward from the ring, pointing away from the central star. Hydrodynamical simulations reproduce the clumping and possibly the spikes. Around ten low-contrast, regularly spaced concentric arc-like features are present; they suggest orbital modulation by a low-mass companion with a period of about 280 yr. A previously known much wider companion is located at a projected separation of about 15 000 au; we show that it is an M2–M4 dwarf. NGC 6720 is therefore a triple star system. These features, including the multiplicity, are similar to those seen in the Southern Ring Nebula (NGC 3132) and may be a common aspect of such nebulae