129 research outputs found
PAH emission in the proplyd HST10: what is the mechanism behind photoevaporation?
Proplyds are photodissociation region (PDR)-like cometary cocoons around
young stars which are thought to originate through photo-evaporation of the
central protoplanetary disk by external UV radiation from the nearby OB stars.
This letter presents spatially resolved mid-infrared imaging and spectroscopy
of the proplyd HST10 obtained with the VLT/VISIR instrument. These observations
allow us to detect Polycyclic Aromatic Hydrocarbons (PAH) emission in the
proplyd photodissociation region and to study the general properties of PAHs in
proplyds for the first time. We find that PAHs in HST10 are mostly neutral and
at least 50 times less abundant than typical values found for the diffuse ISM
or the nearby Orion Bar. With such a low PAH abundance, photoelectric heating
is significantly reduced. If this low abundance pertains also to the original
disk material, gas heating rates could be too low to efficiently drive
photoevaporation unless other processes can be identified. Alternatively, the
model behind the formation of proplyds as evaporating disks may have to be
revised.Comment: 5 pages, 3 figures, 1 tabl
Multi-wavelength observations of Galactic hard X-ray sources discovered by INTEGRAL. II. The environment of the companion star
Context: The INTEGRAL mission has led to the discovery of a new type of
supergiant X-ray binaries (SGXBs), whose physical properties differ from those
of previously known SGXBs. Those sources are in the course of being unveiled by
means of multi-wavelength X-rays, optical, near- and mid-infrared observations,
and two classes are appearing. The first class consists of obscured persistent
SGXBs and the second is populated by the so-called supergiant fast X-ray
transients (SFXTs). Aims: We report here mid-infrared (MIR) observations of the
companion stars of twelve SGXBs from these two classes in order to assess the
contribution of the star and the material enshrouding the system to the total
emission.} Methods: We used data from observations we carried out at ESO/VLT
with VISIR, as well as archival and published data, to perform broad-band
spectral energy distributions of the companion stars and fitted them with a
combination of two black bodies representing the star and a MIR excess due to
the absorbing material enshrouding the star, if there was any. Results: We
detect a MIR excess in the emission of IGR J16318-4848, IGR J16358-4726, and
perhaps IGR J16195-4945. The other sources do not exhibit any MIR excess even
when the intrinsic absorption is very high. (abridged)Comment: A&A in press, The official date of acceptance is 25/01/2008, 17
pages, 4 figures, 9 tables. New version with english language editing
required by editor, note added in proo
Mid-infrared astronomy with the E-ELT: Performance of METIS
We present results of performance modelling for METIS, the Mid-infrared
European Extremely Large Telescope (E-ELT) Imager and Spectrograph. Designed by
a consortium of NOVA (Netherlands), UK Astronomy Technology Centre (UK), MPIA
Heidelberg (Germany), CEA Saclay (France) and KU Leuven (Belgium), METIS will
cover the atmospheric windows in L, M and N-band and will offer imaging,
medium-resolution slit spectroscopy (R~1000-3000) and high-resolution integral
field spectroscopy (R~100,000). Our model uses a detailed set of input
parameters for site characteristics and atmospheric profiles, optical design,
thermal background and the most up-to-date IR detector specifications. We show
that METIS will bring an orders-of-magnitude level improvement in sensitivity
and resolution over current ground-based IR facilities, bringing mid-IR
sensitivities to the micro-Jansky regime. As the only proposed E-ELT instrument
to cover this entire spectral region, and the only mid-IR high-resolution
integral field unit planned on the ground or in space, METIS will open up a
huge discovery space in IR astronomy in the next decade.Comment: 13 pages, submitted to SPIE Proceedings vol. 7735, Ground-based and
Airborne Instrumentation for Astronomy III (2010). Simulation code available
at http://tinyurl.com/metis-sen
The QSO HE0450-2958: Scantily dressed or heavily robed? A normal quasar as part of an unusual ULIRG
(Abridged) The luminous z=0.286 quasar HE0450-2958 is interacting with a
companion galaxy at 6.5 kpc distance and the whole system is a ULIRG. A so far
undetected host galaxy triggered the hypothesis of a mostly "naked" black hole
(BH) ejected from the companion by three-body interaction. We present new
HST/NICMOS 1.6micron imaging data at 0.1" resolution and VLT/VISIR 11.3micron
images at 0.35" resolution that for the first time resolve the system in the
near- and mid-infrared. We combine these with existing optical HST and CO maps.
(i) At 1.6micron we find an extension N-E of the quasar nucleus that is
likely a part of the host galaxy, though not its main body. If true, this
places HE0450-2958 directly onto the M_BH-M_bulge-relation for nearby galaxies.
(ii) HE0450-2958 is consistent with lying at the high-luminosity end of
Narrow-Line Seyfert 1 Galaxies, and more exotic explanations like a "naked
quasar" are unlikely. (iii) All 11.3micron radiation in the system is emitted
by the quasar nucleus, which is radiating at super-Eddington rate,
L/L_Edd=6.2+3.8-1.8, or 12 M_sun/yr. (iv) The companion galaxy is covered in
optically thick dust and is not a collisional ring galaxy. It emits in the far
infrared at ULIRG strength, powered by Arp220-like star formation (strong
starburst-like). An M82-like SED is ruled out. (v) With its black hole
accretion rate HE0450-2958 produces not enough new stars to maintain its
position on the M_BH-M_bulge-relation, and star formation and black hole
accretion are spatially disjoint; the bulge has to grow by redistribution of
preexisting stars. (vi) Systems similar to HE0450-2958 with spatially disjoint
ULIRG-strength star formation and quasar activity are rare. At z<0.43 we only
find <4% (3/77) candidates for a similar configuration.Comment: 12 pages, 6 figures, accepted for publication in Ap
High-contrast imaging with METIS
The Mid-infrared E-ELT Imager and Spectrograph (METIS) for the European Extremely Large Telescope (E-ELT) consists of diffraction-limited imagers that cover 3 to 14 microns with medium resolution (R 5000) long slit spectroscopy, and an integral field spectrograph for high spectral resolution spectroscopy (R 100,000) over the L and M bands. One of the science cases that METIS addresses is the characterization of faint circumstellar material and exoplanet companions through imaging and spectroscopy. We present our approach for high contrast imaging with METIS, covering diffraction suppression with coronagraphs, the removal of slowly changing optical aberrations with focal plane wavefront sensing, interferometric imaging with sparse aperture masks, and observing strategies for both the imagers and IFU image slicers
Efficacy of Two Licensed Avian Influenza H5 Vaccines Against Challenge with a 2015 U.S. H5N2 clade 2.3.4.4 Highly Pathogenic Avian Influenza Virus in Domestic Ducks
Highly pathogenic avian influenza (HPAI) clade 2.3.4.4 viruses from the H5 goose/Guangdong lineage caused a major outbreak in poultry in the United States in 2015. Although the outbreak was controlled, vaccines were considered as an alternative control method, and new vaccines were approved and purchased by the U.S. Department of Agriculture National Veterinary Stockpile for emergency use. In this study, we evaluated the efficacy of two of these vaccines in protecting Pekin ducks (Anas platyrhynchos var. domestica) against challenge with a H5N2 HPAI poultry isolate. A recombinant alphavirus-based vaccine and an inactivated adjuvanted reverse genetics vaccine, both expressing the hemagglutinin gene of a U.S. H5 clade 2.3.4.4 isolate (A/Gyrfalcon/Washington/41088-6/2014 H5N8), were used to immunize the ducks. The vaccines were given either as single vaccination at 2 days of age or in a prime-boost strategy at 2 and 15 days of age. At 32 days of age, all ducks were challenged with A/turkey/Minnesota/12582/15 H5N2 HPAI virus clade 2.3.4.4. All ducks from the nonvaccinated challenge control group became infected and shed virus; one duck in this group presented mild ataxia, and a second duck died. No mortality or clinical signs were observed in vaccinated and challenged ducks, with the exception of one duck presenting with mild ataxia. Both vaccines, regardless of the vaccination strategy used, were immunogenic in ducks and reduced or prevented virus shedding after challenge. In conclusion, good protection against H5Nx infection was achieved in ducks vaccinated with the vaccines examined, which were homologous to the challenge virus, with prime-boost strategies conferring the best protection against infection.info:eu-repo/semantics/publishedVersio
ALMA Resolves CI Emission from the beta Pictoris Debris Disk
The debris disk around ~Pictoris is known to contain gas. Previous
ALMA observations revealed a CO belt at 85 au with a distinct clump,
interpreted as a location of enhanced gas production. Photodissociation
converts CO into C and O within 50 years. We resolve CI emission at 492
GHz using ALMA and study its spatial distribution. CI shows the same clump as
seen for CO. This is surprising, as C is expected to quickly spread in azimuth.
We derive a low C mass (between and
M), indicating that gas production started only recently (within
5000 years). No evidence is seen for an atomic accretion disk inwards of
the CO belt, perhaps because the gas did not yet have time to spread radially.
The fact that C and CO share the same asymmetry argues against a previously
proposed scenario where the clump is due to an outward migrating planet
trapping planetesimals in an resonance; nor can the observations be explained
by an eccentric planetesimal belt secularly forced by a planet. Instead, we
suggest that the dust and gas disks should be eccentric. Such a configuration,
we further speculate, might be produced by a recent tidal disruption event.
Assuming that the disrupted body has had a CO mass fraction of 10%, its total
mass would be 3 .Comment: 30 pages, 15 figures, accepted by Ap
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