2,043 research outputs found
Near-Infrared Spectroscopy of McNeil's Nebula Object
We present 0.8-5.2 micron spectroscopy of the compact source at the base of a
variable nebula (McNeil's Nebula Object) in the Lynds 1630 dark cloud that went
into outburst in late 2003. The spectrum of this object reveals an extremely
red continuum, CO bands at 2.3-2.5 microns in emission, a deep 3.0 micron ice
absorption feature, and a solid state CO absorption feature at 4.7 microns. In
addition, emission lines of H, Ca II, Mg I, and Na I are present. The Paschen
lines exhibit P Cygni profiles, as do two lines of He I, although the emission
features are very weak in the latter. The Brackett lines, however, are seen to
be purely in emission. The P Cygni profiles clearly indicate that mass outflow
is occurring in a wind with a velocity of ~400 km/s. The H line ratios do not
yield consistent estimates of the reddening, nor do they agree with the
extinction estimated from the ice feature (A_V ~ 11). We propose that these
lines are optically thick and are produced in a dense, ionized wind. The
near-infrared spectrum does not appear similar to any known FUor or EXor
object. However, all evidence suggests that McNeil's Nebula Object is a
heavily-embedded low-mass Class I protostar, surrounded by a disk, whose
brightening is due to a recent accretion event.Comment: 11 pages, 2 ps figures, accepted for publication in ApJ Letter
I Componenti azotati del latte della capra sarda
The Authors, in a study on the Sardinian goat milk, have found the following milk percentual composition:
fats 5.02, nitrogen compounds 4.03, proteins 3.61, casein 2.86, soluble proteins 0.75, coagulable proteins
2.65, non coagulable proteins 0.96, non proteic compounds 0,42, urea 386 mg/kg, uric acid 35 mg/kg, creatinine
39 mg/kg
Vacuum energy and spectral function sum rules
We reformulate the problem of the cancellation of the ultraviolet
divergencies of the vacuum energy, particularly important at the cosmological
level, in terms of a saturation of spectral function sum rules which leads to a
set of conditions on the spectrum of the fundamental theory. We specialize the
approach to both Minkowski and de Sitter space-times and investigate some
examples.Comment: 11 pages, revtex4, no figures, version to be published on PR
Comment on Mie Scattering from a Sonoluminescing Bubble with High Spatial and Temporal Resolution [Physical Review E 61, 5253 (2000)]
A key parameter underlying the existence of sonoluminescence (SL)is the time
relative to SL at which acoustic energy is radiated from the collapsed bubble.
Light scattering is one route to this quantity. We disagree with the statement
of Gompf and Pecha that -highly compressed water causes the minimum in
scattered light to occur 700ps before SL- and that this effect leads to an
overestimate of the bubble wall velocity. We discuss potential artifacts in
their experimental arrangement and correct their description of previous
experiments on Mie scattering.Comment: 10 pages, 2 figure
STIS ultraviolet/optical spectroscopy of `warm' ultraluminous infrared galaxies
(Abridged) We present high spatial resolution ultraviolet and optical
spectroscopy, obtained using the Space Telescope Imaging Spectrograph on board
the Hubble Space Telescope, of nuclear structures within four `warm'
Ultraluminous Infrared Galaxies (ULIRGs). We find an AGN in at least three, and
probably all four of our sample, hosted in a compact, optically luminous
`knot'. In three cases these knots were previously identified as a putative AGN
nucleus from multiband optical imaging. Three of the sample also harbor a
starburst in one or more knots, suggesting that the optically luminous knots
seen in local ULIRGs are the most likely sites of the dust-shrouded starburst
and AGN activity that power the infrared emission. The four AGN have a diverse
range of properties; two are classical narrow line AGN, one shows both broad
and narrow lines and evidence for lines of sight from the narrow through to the
broad line regions, and one is plausibly a FeLoBAL AGN. The probable presence
in one object of an FeLoBAL AGN, which are extremely rare in the QSO
population, supports the idea that LoBAL AGN may be youthful systems shrouded
in gas and dust rather than AGN viewed along a certain line of sight. The three
starbursts for which detailed constraints are possible show a smaller range in
properties; all three bursts are young with two having ages of ~4Myr and the
third having an age of 20Myr, suggesting that ULIRGs undergo several bursts of
star formation during their lifetimes. None of the starbursts show evidence for
Initial Mass Function slopes steeper than about 3.3. The metallicities of the
knots for which metallicities can be derived are all at least 1.5 times the
Solar value. The properties of one further starburst knot are consistent with
it being the forming core of an elliptical galaxy.Comment: ApJ, accepte
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