2,335 research outputs found
ALMA data suggest the presence of a spiral structure in the inner wind of CW Leo
(abbreviated) We aim to study the inner wind of the well-known AGB star CW
Leo. Different diagnostics probing different geometrical scales have pointed
toward a non-homogeneous mass-loss process: dust clumps are observed at
milli-arcsec scale, a bipolar structure is seen at arcsecond-scale and
multi-concentric shells are detected beyond 1". We present the first ALMA Cycle
0 band 9 data around 650 GHz. The full-resolution data have a spatial
resolution of 0".42x0".24, allowing us to study the morpho-kinematical
structure within ~6". Results: We have detected 25 molecular lines. The
emission of all but one line is spatially resolved. The dust and molecular
lines are centered around the continuum peak position. The dust emission has an
asymmetric distribution with a central peak flux density of ~2 Jy. The
molecular emission lines trace different regions in the wind acceleration
region and suggest that the wind velocity increases rapidly from about 5 R*
almost reaching the terminal velocity at ~11 R*. The channel maps for the
brighter lines show a complex structure; specifically for the 13CO J=6-5 line
different arcs are detected within the first few arcseconds. The curved
structure present in the PV map of the 13CO J=6-5 line can be explained by a
spiral structure in the inner wind, probably induced by a binary companion.
From modeling the ALMA data, we deduce that the potential orbital axis for the
binary system lies at a position angle of ~10-20 deg to the North-East and that
the spiral structure is seen almost edge-on. We infer an orbital period of 55
yr and a binary separation of 25 au (or ~8.2 R*). We tentatively estimate that
the companion is an unevolved low-mass main-sequence star. The ALMA data hence
provide us for the first time with the crucial kinematical link between the
dust clumps seen at milli-arcsecond scale and the almost concentric arcs seen
at arcsecond scale.Comment: 22 pages, 18 Figures, Astronomy & Astrophysic
SBS 0335-052W: The Lowest-Metallicity Star-Forming Galaxy Known
We present 4-meter Kitt Peak telescope and 6.5-meter MMT spectrophotometry of
the extremely low-metallicity galaxy SBS 0335-052W, the western companion of
the blue compact dwarf galaxy SBS 0335-052E. These observations have been
combined with published 10-meter Keck data to derive for the brightest region
of SBS 0335-052W an oxygen abundance 12+logO/H=7.12+/-0.03. This makes SBS
0335-052W the lowest metallicity star-forming galaxy known in the local
universe. Using a Monte Carlo technique, we fit the spectral energy
distribution of SBS 0335-052W to derive the age of the oldest stars
contributing to its optical light. We find that star formation in SBS 0335-052W
began less than 500 Myr ago, making it a likely nearby young dwarf galaxy.Comment: 13 pages, 3 figures, accepted for publication in the Astrophysical
Journa
Evidence of Substructure in the Cluster of Galaxies A3558
We investigate the dynamical properties of the cluster of galaxies A3558
(Shapley 8). Studying a region of one square degree ( 3 Mpc) centered
on the cluster cD galaxy, we have obtained a statistically complete photometric
catalog with positions and magnitudes of 1421 galaxies (down to a limiting
magnitude of ). This catalog has been matched to the recent velocity
data obtained by Mazure et al. (1997) and from the literature, yielding a
radial velocity catalog containing 322 galaxies. Our analysis shows that the
position/velocity space distribution of galaxies shows significant
substructure. A central bimodal core detected previously in preliminary studies
is confirmed by using the Adaptive Kernel Technique and Wavelet Analysis. We
show that this central bimodal subtructure is nevertheless composed of a
projected feature, kinematically unrelated to the cluster, plus a group of
galaxies probably in its initial merging phase into a relaxed core. The cD
velocity offset with respect to the average cluster redshift, reported earlier
by several authors, is completely eliminated as a result of our dynamical
analysis. The untangling of the relaxed core component also allows a better,
more reliable determination of the central velocity dispersion, which in turn
eliminates the ``-problem'' for A3558. The cluster also shows a
``preferential'' distribution of subclumps coinciding with the direction of the
major axis position angle of the cD galaxy and of the central X-ray emission
ellipsoidal distribution, in agreement with an anisotropic merger scenario.Comment: 35 pages in latex, 17 figures in Postscript, accepted for publication
in the Astrophysical Journa
Arp 302: Non-starburst Luminous Infrared Galaxies
Arp 302, a luminous infrared source (L_{IR} = 4.2x10^{11} Lsun), consisting
of two spiral galaxies (VV340A and VV340B) with nuclear separation of 40'', has
the highest CO luminosity known. Observations with the BIMA array at 5'' X 7''
resolution reveal that the CO emission is extended over 23.0 kpc in the edge-on
spiral galaxy, VV340A, corresponding to 6.7x10^{10} Msun of H_2. In the
companion face-on galaxy, VV340B, the CO emission is extended over ~10.0 kpc,
with 1.1x10^{10} Msun of H_2. The large CO extent is in strong contrast to
starburst systems, such as Arp 220, in which the CO extent is typically 1
kpc. Furthermore, (H_2) is found to be 6.0 Lsun/Msun throughout
both galaxies. Thus the high IR luminosity of Arp 302 is apparently not due to
starbursts in the nuclear regions, but is due to its unusually large amount of
molecular gas forming stars at a rate similar to giant molecular clouds in the
Milky Way disk. Arp 302 consists of a pair of very gas-rich spiral galaxies
that may be interacting and in a phase before a likely onset of starbursts.Comment: AAS Latex plus two postscript figures. ApJ Letters (accepted
ASCA Observation of an X-Ray-Luminous Active Nucleus in Markarian 231
We have obtained a moderately long (100 kilosecond) ASCA observation of the
Seyfert 1 galaxy Markarian 231, the most luminous of the local ultraluminous
infrared galaxy (ULIRG) population. In the best-fitting model we do not see the
X-ray source directly; the spectrum consists of a scattered power-law component
and a reflection component, both of which have been absorbed by a column N_H
\approx 3 X 10^(22)/cm^2. About 3/4 of the observed hard X-rays arise from the
scattered component, reducing the equivalent width of the iron K alpha line.
The implied ratio of 1-10 keV X-ray luminosity to bolometric luminosity,
L_x/L_bol \sim 2%, is typical of Sy 1 galaxies and radio-quiet QSOs of
comparable bolometric luminosities, and indicates that the bolometric
luminosity is dominated by the AGN. Our estimate of the X-ray luminosity also
moves Mrk 231 in line with the correlations found for AGN with extremely strong
Fe II emission. A second source separated by about 2 arcminutes is also clearly
detected, and contributes about 25% of the total flux.Comment: 11 pages, 3 figures; to appear in ApJ Letter
Observations of Stripped Edge-on Virgo Cluster Galaxies
We present observations of highly inclined, HI deficient, Virgo cluster
spiral galaxies. Our high-resolution VLA HI observations of edge-on galaxies
allow us to distinguish extraplanar gas from disk gas. All of our galaxies have
truncated H-alpha disks, with little or no disk gas beyond a truncation radius.
While all the gas disks are truncated, the observations show evidence for a
continuum of stripping states: symmetric, undisturbed truncated gas disks
indicate galaxies that were stripped long ago, while more asymmetric disks
suggest ongoing or more recent stripping. We compare these timescale estimates
with results obtained from two-dimensional stellar spectroscopy of the outer
disks of galaxies in our sample. One of the galaxies in our sample, NGC 4522 is
a clear example of active ram-pressure stripping, with 40% of its detected HI
being extraplanar. As expected, the outer disk stellar populations of this
galaxy show clear signs of recent (and, in fact, ongoing) stripping. Somewhat
less expected, however, is the fact that the spectrum of the outer disk of this
galaxy, with very strong Balmer absorption and no observable emission, would be
classified as ``k+a'' if observed at higher redshift. Our observations of NGC
4522 and other galaxies at a range of cluster radii allow us to better
understand the role that clusters play in the structure and evolution of disk
galaxies.Comment: 4 pages, 2 figures, to appear in the proceedings of the Island
Universes conference held in Terschelling, Netherlands, July 2005, ed. R. de
Jong, version with high resolution figures can be downloaded from
ftp://ftp.astro.yale.edu/pub/hugh/papers/iu_crowl_h.ps.g
Polarisation Observations of HO 620.701 GHz Maser Emission with Herschel/HIFI in Orion KL
Context. The high intensities and narrow bandwidths exhibited by some
astronomical masers make them ideal tools for studying star-forming giant
molecular clouds. The water maser transition at
620.701 GHz can only be observed from above Earth's strongly absorbing
atmosphere; its emission has recently been detected from space. Aims. We sought
to further characterize the star-forming environment of Orion KL by
investigating the linear polarisation of a source emitting a narrow 620.701 GHz
maser feature with the heterodyne spectrometer HIFI on board the Herschel Space
Observatory. Methods. High-resolution spectral datasets were collected over a
thirteen month period beginning in 2011 March, to establish not only the linear
polarisation but also the temporal variability of the source. Results. Within a
uncertainty, no polarisation was detected to an upper limit of
approximately 2%. These results are compared with coeval linear polarisation
measurements of the 22.235 GHz maser line from
the Effelsberg 100-m radio telescope, typically a much stronger maser
transition. Although strongly polarised emission is observed for one component
of the 22.235 GHz maser at 7.2 km s, a weaker component at the same
velocity as the 620.701 GHz maser at 11.7 km s is much less polarised.Comment: Accepted for publication in A&
GGD 37: An Extreme Protostellar Outflow
We present the first Spitzer-IRS spectral maps of the Herbig-Haro flow GGD 37 detected in lines of [Ne III], [O IV], [Ar III], and [Ne v]. The detection of extended [O IV] (55 eV) and some extended emission in [Ne v] (97 eV) indicates a shock temperature in excess of 100,000 K, in agreement with X-ray observations, and a shock speed in excess of 200 km s(-1). The presence of an extended photoionization or collisional ionization region indicates that GGD 37 is a highly unusual protostellar outflow.Jet Propulsion Laboratory, under NASA 1407NASA 1257184Jet Propulsion Laboratory (JPL) 960803University of Rochester 31419-5714Astronom
Water vapor emission from IRC+10216 and other carbon-rich stars: model predictions and prospects for multitransition observations
We have modeled the emission of H2O rotational lines from the extreme C-rich
star IRC+10216. Our treatment of the excitation of H2O emissions takes into
account the excitation of H2O both through collisions, and through the pumping
of the nu2 and nu3 vibrational states by dust emission and subsequent decay to
the ground state. Regardless of the spatial distribution of the water
molecules, the H2O 1_{10}-1_{01} line at 557 GHz observed by the Submillimeter
Wave Astronomy Satellite (SWAS) is found to be pumped primarily through the
absorption of dust-emitted photons at 6 m in the nu2 band. As noted by
previous authors, the inclusion of radiative pumping lowers the ortho-H2O
abundance required to account for the 557 GHz emission, which is found to be
(0.5-1)x10^{-7} if the presence of H2O is a consequence of vaporization of
orbiting comets or Fischer-Tropsch catalysis. Predictions for other
submillimeter H2O lines that can be observed by the Herschel Space Observatory
(HSO) are reported. Multitransition HSO observations promise to reveal the
spatial distribution of the circumstellar water vapor, discriminating among the
several hypotheses that have been proposed for the origin of the H2O vapor in
the envelope of IRC+10216. We also show that, for observations with HSO, the
H2O 1_{10}-1_{01} 557 GHz line affords the greatest sensitivity in searching
for H2O in other C-rich AGB stars.Comment: 35 pages, 12 figures, to be published in The Astrophysical Journa
The renormalization of the energy-momentum tensor for an effective initial state
An effective description of an initial state is a method for representing the
signatures of new physics in the short-distance structure of a quantum state.
The expectation value of the energy-momentum tensor for a field in such a state
contains new divergences that arise when summing over this new structure. These
divergences occur only at the initial time at which the state is defined and
therefore can be cancelled by including a set of purely geometric counterterms
that also are confined to this initial surface. We describe this gravitational
renormalization of the divergences in the energy-momentum tensor for a free
scalar field in an isotropically expanding inflationary background. We also
show that the back-reaction from these new short-distance features of the state
is small when compared with the leading vacuum energy contained in the field.Comment: 18 pages, uses RevTeX, references adde
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