23 research outputs found
Radio and IR interferometry of SiO maser stars
Radio and infrared interferometry of SiO maser stars provide complementary
information on the atmosphere and circumstellar environment at comparable
spatial resolution. Here, we present the latest results on the atmospheric
structure and the dust condensation region of AGB stars based on our recent
infrared spectro-interferometric observations, which represent the environment
of SiO masers. We discuss, as an example, new results from simultaneous VLTI
and VLBA observations of the Mira variable AGB star R Cnc, including VLTI near-
and mid-infrared interferometry, as well as VLBA observations of the SiO maser
emission toward this source. We present preliminary results from a monitoring
campaign of high-frequency SiO maser emission toward evolved stars obtained
with the APEX telescope, which also serves as a precursor of ALMA images of the
SiO emitting region. We speculate that large-scale long-period chaotic motion
in the extended molecular atmosphere may be the physical reason for observed
deviations from point symmetry of atmospheric molecular layers, and for the
observed erratic variability of high-frequency SiO maser emissionComment: 8 pages, 4 figures, submitted to Proc. IAU Symp. 287 "Cosmic masers -
from OH to H_0", R.S. Booth, E.M.L. Humphreys, W.H.T. Vlemmings (eds.),
invited pape
The Environmental Dependence of the Evolving S0 Fraction
We reinvestigate the dramatic rise in the S0 fraction, f_S0, within clusters
since z ~ 0.5. In particular, we focus on the role of the global galaxy
environment on f_S0 by compiling, either from our own observations or the
literature, robust line-of-sight velocity dispersions, sigma's, for a sample of
galaxy groups and clusters at 0.1 < z < 0.8 that have uniformly determined,
published morphological fractions. We find that the trend of f_S0 with redshift
is twice as strong for sigma < 750 km/s groups/poor clusters than for
higher-sigma, rich clusters. From this result, we infer that over this redshift
range galaxy-galaxy interactions, which are more effective in lower-sigma
environments, are more responsible for transforming spiral galaxies into S0's
than galaxy-environment processes, which are more effective in higher-sigma
environments. The rapid, recent growth of the S0 population in groups and poor
clusters implies that large numbers of progenitors exist in low-sigma systems
at modest redshifts (~ 0.5), where morphologies and internal kinematics are
within the measurement range of current technology.Comment: Accepted for publication in The Astrophysical Journal. 13 pages, 6
figure
Structural properties of discs and bulges of early-type galaxies
We have used the EFAR sample of galaxies to study the light distributions of
early-type galaxies. We decompose the 2D light distribution of the galaxies in
a flattened spheroidal component with a Sersic radial light profile and an
inclined disc component with an exponential light profile. We show that the
brightest, bulge dominated elliptical galaxies have a fairly broad distribution
in the Sersic profile shape parameter n_B, with a median of about 3.7 and a
sigma of ~0.9. Other galaxies have smaller n_B values, meaning that spheroids
are in general less concentrated than the n_B=4 de Vaucouleurs-law profile.
The results of our light decompositions are robust, even though without
kinematic information we cannot prove that the spheroids and discs are really
pressure- and rotation-supported stellar systems. If we assume that the
detected spheroids and discs are indeed separate components, we can draw the
following conclusions: 1) the spheroid and disc scale sizes are correlated; 2)
bulge-to-total luminosity ratios, bulge effective radii, and bulge n_B values
are all positively correlated; 3) the bivariate space density distribution of
elliptical galaxies in the (luminosity, scale size)-plane is well described by
a Schechter luminosity function in and a log-normal scale-size distribution at
a given luminosity; 4) at the brightest luminosities, the scale size
distribution of elliptical galaxies is similar to those of bright spiral
galaxies; at fainter luminosities the elliptical scale size distribution peaks
at distinctly smaller sizes than the spiral galaxy distribution; and 5) bulge
components of early-type galaxies are typically a factor 1.5 to 2.5 smaller
than the disks of spiral galaxies, while disc components of early-type galaxies
are typically twice as large as the discs of spiral galaxies. [abridged]Comment: 16 pages, 18 figures. Accepted for publication in the MNRA
The environmental dependence of the structure of galactic discs in STAGES S0 galaxies: implications for S0 formation
We present an analysis of V-band radial surface brightness ÎŒ(r) profiles for S0 galaxies in different environments using Hubble Space Telescope/Advanced Camera for Surveys imaging and data from the Space Telescope A901/2 Galaxy Evolution Survey. Using a large sample of âŒ280 field and cluster S0s, we find that in both environments, âŒ25 per cent have a pure exponential disc (type I) and âŒ50 per cent exhibit an up-bending disc break (antitruncation, type III). However, we find hardly any (<5 per cent) down-bending disc breaks (truncations, type II) in our S0s and many cases (âŒ20 per cent) where no discernible exponential component was observed (i.e. general curvature). We also find no evidence for an environmental dependence on the disc scalelength h or break strength T (outer-to-inner scalelength ratio), implying that the galaxy environment does not affect the stellar distribution in S0 stellar discs. Comparing disc structure (e.g. h, T) between these S0s and the spiral galaxies from our previous studies, we find: (i) no evidence for the type I scalelength h being dependent on morphology; and (ii) some evidence to suggest that the type II/III break strength T is smaller (weaker) in S0s compared to spiral galaxies. Taken together, these results suggest that the stellar distribution in S0s is not drastically affected by the galaxy environment. However, some process inherent to the morphological transformation of spiral galaxies into S0s does affect stellar disc structure causing a weakening of ÎŒ(r) breaks and may even eliminate truncations from S0 galaxies. In further tests, we perform analytical bulgeâdisc decompositions on our S0s and compare the results to those for spiral galaxies from our previous studies. For type III galaxies, we find that bulge light can account for the excess light at large radii in up to âŒ50 per cent of S0s but in only âŒ15 per cent of spirals. We propose that this result is consistent with a fading stellar disc (evolving bulge-to-disc ratio) being an inherent process in the transformation of spiral galaxies into S0s
A Search for Extended Ultraviolet Disk (XUV-disk) Galaxies in the Local Universe
We have initiated a search for extended ultraviolet disk (XUV-disk) galaxies
in the local universe. Herein, we compare GALEX UV and visible--NIR images of
189 nearby (D40 Mpc) S0--Sm galaxies included in the GALEX Atlas of Nearby
Galaxies and present the first catalogue of XUV-disk galaxies. We find that
XUV-disk galaxies are surprisingly common but have varied relative (UV/optical)
extent and morphology. Type~1 objects (\ga20% incidence) have structured,
UV-bright/optically-faint emission features in the outer disk, beyond the
traditional star formation threshold. Type~2 XUV-disk galaxies (10%
incidence) exhibit an exceptionally large,
UV-bright/optically-low-surface-brightness (LSB) zone having blue
outside the effective extent of the inner, older stellar population, but not
reaching extreme galactocentric distance. If the activity occuring in XUV-disks
is episodic, a higher fraction of present-day spirals could be influenced by
such outer disk star formation. Type~1 disks are associated with spirals of all
types, whereas Type~2 XUV-disks are predominantly found in late-type spirals.
Type~2 XUV-disks are forming stars quickly enough to double their [presently
low] stellar mass in the next Gyr (assuming a constant SF rate). XUV-disk
galaxies of both types are systematically more gas-rich than the general galaxy
population. Minor external perturbation may stimulate XUV-disk incidence, at
least for Type~1 objects. XUV-disks are the most actively evolving galaxies
growing via inside-out disk formation in the current epoch, and may constitute
a segment of the galaxy population experiencing significant, continued gas
accretion from the intergalactic medium or neighboring objects.Comment: 83 pages, 16 figures, 2 tables. Appearing in the GALEX special issue
of ApJS. (A version with high quality figures and proof corrections can be
found at http://www.journals.uchicago.edu/toc/apjs/173/2
The 3--D ionization structure of NGC 6818: a Planetary Nebula threatened by recombination
Long-slit NTT+EMMI echellograms of NGC 6818 (the Little Gem) at nine equally
spaced position angles, reduced according to the 3-D methodology introduced by
Sabbadin et al. (2000a,b), allowed us to derive: the expansion law, the
diagnostics and ionic radial profiles, the distance and the central star
parameters, the nebular photo-ionization model, the 3-D reconstruction in He
II, [O III] and [N II], the multicolor projection and a series of movies. The
Little Gem results to be a young (3500 years), optically thin (quasi-thin in
some directions) double shell (Mion~0.13 Msun) at a distance of 1.7 kpc, seen
almost equatorial on: a tenuous and patchy spherical envelope (r~0.090 pc)
encircles a dense and inhomogeneous tri-axial ellipsoid (a/2~0.077 pc,
a/b~1.25, b/c~1.15) characterized by a hole along the major axis and a pair of
equatorial, thick moustaches. NGC 6818 is at the start of the recombination
phase following the luminosity decline of the 0.625 Msun central star, which
has recently exhausted the hydrogen shell nuclear burning and is rapidly moving
toward the white dwarf domain (log T*~5.22 K; log(L*/Lsun)~3.1). The nebula is
destined to become thicker and thicker, with an increasing fraction of neutral,
dusty gas in the outermost layers. Only over some hundreds of years the plasma
rarefaction due to the expansion will prevail against the slower and slower
stellar decline, leading to a gradual re-growing of the ionization front. The
exciting star of NGC 6818 (mV~17.06) is a visual binary: a faint, red companion
(mV~17.73) appears at 0.09 arcsec in PA=190deg, corresponding to a separation
>=150 AU and to an orbital period >=1500 yearsComment: 23 pages, 18 figures, A&A accepted. 12 movies of NGC 6818 are
available at http://web.pd.astro.it/sabbadin The paper may also be retrivied
at http://web.pd.astro.it/supern/preprints.htm
The Emergence of Conspirituality
The female-dominated New Age (with its positive focus on self) and the male-dominated realm of conspiracy theory (with its negative focus on global politics) may seem antithetical. There is a synthesis of the two, however, that we call âconspiritualityâ. We define, describe, and analyse this hybrid system of belief; it has been noticed before without receiving much scholarly attention. Conspirituality is a rapidly growing web movement expressing an ideology fuelled by political disillusionment and the popularity of alternative worldviews. It has international celebrities, bestsellers, radio and TV stations. It offers a broad politico-spiritual philosophy based on two core convictions, the first traditional to conspiracy theory, the second rooted in the New Age: 1) a secret group covertly controls, or is trying to control, the political and social order, and 2) humanity is undergoing a âparadigm shiftâ in consciousness. Proponents believe that the best strategy for dealing with the threat of a totalitarian ânew world orderâ is to act in accordance with an awakened ânew paradigmâ worldview