366 research outputs found
A Spitzer survey of mid-infrared molecular emission from protoplanetary disks I: Detection rates
We present a Spitzer InfraRed Spectrometer search for 10-36 micron molecular
emission from a large sample of protoplanetary disks, including lines from H2O,
OH, C2H2, HCN and CO2. This paper describes the sample and data processing and
derives the detection rate of mid-infrared molecular emission as a function of
stellar mass. The sample covers a range of spectral type from early M to A, and
is supplemented by archival spectra of disks around A and B stars. It is drawn
from a variety of nearby star forming regions, including Ophiuchus, Lupus and
Chamaeleon. In total, we identify 22 T Tauri stars with strong mid-infrared H2O
emission. Integrated water line luminosities, where water vapor is detected,
range from 5x10^-4 to 9x10^-3 Lsun, likely making water the dominant line
coolant of inner disk surfaces in classical T Tauri stars. None of the 5
transitional disks in the sample show detectable gaseous molecular emission
with Spitzer upper limits at the 1% level in terms of line-to-continuum ratios
(apart from H2). We find a strong dependence on detection rate with spectral
type; no disks around our sample of 25 A and B stars were found to exhibit
water emission, down to 1-2% line-to-continuum ratios, in the mid-infrared,
while almost 2/3 of the disks around K stars show sufficiently intense water
emission to be detected by Spitzer. Some Herbig Ae/Be stars show tentative
H2O/OH emission features beyond 20 micron at the 1-2 level, however, and one of
them shows CO2 in emission. We argue that the observed differences between T
Tauri disks and Herbig Ae/Be disks is due to a difference in excitation and/or
chemistry depending on spectral type and suggest that photochemistry may be
playing an important role in the observable characteristics of mid-infrared
molecular line emission from protoplanetary disks.Comment: 19 pages, accepted for publication in Ap
All-sky Search for High-Energy Neutrinos from Gravitational Wave Event GW170104 with the ANTARES Neutrino Telescope
Advanced LIGO detected a significant gravitational wave signal (GW170104)
originating from the coalescence of two black holes during the second
observation run on January 4, 2017. An all-sky high-energy
neutrino follow-up search has been made using data from the ANTARES neutrino
telescope, including both upgoing and downgoing events in two separate
analyses. No neutrino candidates were found within s around the GW
event time nor any time clustering of events over an extended time window of
months. The non-detection is used to constrain isotropic-equivalent
high-energy neutrino emission from GW170104 to less than
erg for a spectrum
The ANTARES Collaboration: Contributions to ICRC 2017 Part I: Neutrino astronomy (diffuse fluxes and point sources)
Papers on neutrino astronomy (diffuse fluxes and point sources, prepared for
the 35th International Cosmic Ray Conference (ICRC 2017, Busan, South Korea) by
the ANTARES Collaboratio
The ANTARES Collaboration: Contributions to ICRC 2017 Part II: The multi-messenger program
Papers on the ANTARES multi-messenger program, prepared for the 35th
International Cosmic Ray Conference (ICRC 2017, Busan, South Korea) by the
ANTARES Collaboratio
The ANTARES Collaboration: Contributions to ICRC 2017 Part III: Searches for dark matter and exotics, neutrino oscillations and detector calibration
Papers on the searches for dark matter and exotics, neutrino oscillations and
detector calibration, prepared for the 35th International Cosmic Ray Conference
(ICRC 2017, Busan, South Korea) by the ANTARES Collaboratio
The Antares Collaboration : Contributions to the 34th International Cosmic Ray Conference (ICRC 2015, The Hague)
The ANTARES detector, completed in 2008, is the largest neutrino telescope in the Northern hemisphere. Located at a depth of 2.5 km in the Mediterranean Sea, 40 km off the Toulon shore, its main goal is the search for astrophysical high energy neutrinos. In this paper we collect the 21 contributions of the ANTARES collaboration to the 34th International Cosmic Ray Conference (ICRC 2015). The scientific output is very rich and the contributions included in these proceedings cover the main physics results, ranging from steady point sources, diffuse searches, multi-messenger analyses to exotic physics
Status and Recent Results of the Acoustic Neutrino Detection Test System AMADEUS
The AMADEUS system is an integral part of the ANTARES neutrino telescope in
the Mediterranean Sea. The project aims at the investigation of techniques for
acoustic neutrino detection in the deep sea. Installed at a depth of more than
2000m, the acoustic sensors of AMADEUS are based on piezo-ceramics elements for
the broad-band recording of signals with frequencies ranging up to 125kHz.
AMADEUS was completed in May 2008 and comprises six "acoustic clusters", each
one holding six acoustic sensors that are arranged at distances of roughly 1m
from each other. The clusters are installed with inter-spacings ranging from
15m to 340m. Acoustic data are continuously acquired and processed at a
computer cluster where online filter algorithms are applied to select a
high-purity sample of neutrino-like signals. 1.6 TB of data were recorded in
2008 and 3.2 TB in 2009. In order to assess the background of neutrino-like
signals in the deep sea, the characteristics of ambient noise and transient
signals have been investigated. In this article, the AMADEUS system will be
described and recent results will be presented.Comment: 7 pages, 8 figures. Proceedings of ARENA 2010, the 4th International
Workshop on Acoustic and Radio EeV Neutrino Detection Activitie
Acoustic and optical variations during rapid downward motion episodes in the deep north-western Mediterranean Sea
An Acoustic Doppler Current Profiler (ADCP) was moored at the deep-sea site
of the ANTARES neutrino telescope near Toulon, France, thus providing a unique
opportunity to compare high-resolution acoustic and optical observations
between 70 and 170 m above the sea bed at 2475 m. The ADCP measured downward
vertical currents of magnitudes up to 0.03 m s-1 in late winter and early
spring 2006. In the same period, observations were made of enhanced levels of
acoustic reflection, interpreted as suspended particles including zooplankton,
by a factor of about 10 and of horizontal currents reaching 0.35 m s-1. These
observations coincided with high light levels detected by the telescope,
interpreted as increased bioluminescence. During winter 2006 deep dense-water
formation occurred in the Ligurian subbasin, thus providing a possible
explanation for these observations. However, the 10-20 days quasi-periodic
episodes of high levels of acoustic reflection, light and large vertical
currents continuing into the summer are not direct evidence of this process. It
is hypothesized that the main process allowing for suspended material to be
moved vertically later in the year is local advection, linked with topographic
boundary current instabilities along the rim of the 'Northern Current'.Comment: 30 pages, 7 figure
POISSON project - II - A multi-wavelength spectroscopic and photometric survey of young protostars in L 1641
Characterising stellar and circumstellar properties of embedded young stellar
objects (YSOs) is mandatory for understanding the early stages of the stellar
evolution. This task requires the combination of both spectroscopy and
photometry, covering the widest possible wavelength range, to disentangle the
various protostellar components and activities. As part of the POISSON project,
we present a multi-wavelength spectroscopic and photometric investigation of
embedded YSOs in L1641, aimed to derive the stellar parameters and evolutionary
stages and to infer their accretion properties. Our database includes
low-resolution optical-IR spectra from the NTT and Spitzer (0.6-40 um) and
photometric data covering a spectral range from 0.4 to 1100 um, which allow us
to construct the YSOs spectral energy distributions (SEDs) and to infer the
main stellar parameters. The SED analysis allows us to group our 27 YSOs into
nine Class I, eleven Flat, and seven Class II objects. However, on the basis of
the derived stellar properties, only six Class I YSOs have an age of ~10^5 yr,
while the others are older 5x10^5-10^6 yr), and, among the Flat sources, three
out of eleven are more evolved objects (5x10^6-10^7 yr), indicating that
geometrical effects can significantly modify the SED shapes. Inferred mass
accretion rates (Macc) show a wide range of values (3.6x10^-9 to 1.2x10^-5
M_sun yr^-1), which reflects the age spread observed in our sample. Average
values of mass accretion rates, extinction, and spectral indices decrease with
the YSO class. The youngest YSOs have the highest Macc, whereas the oldest YSOs
do not show any detectable jet activity in either images and spectra. We also
observe a clear correlation among the YSO Macc, M*, and age, consistent with
mass accretion evolution in viscous disc models.Comment: 61 pages, 16 figures; A&A in pres
The ANTARES Telescope Neutrino Alert System
The ANTARES telescope has the capability to detect neutrinos produced in
astrophysical transient sources. Potential sources include gamma-ray bursts,
core collapse supernovae, and flaring active galactic nuclei. To enhance the
sensitivity of ANTARES to such sources, a new detection method based on
coincident observations of neutrinos and optical signals has been developed. A
fast online muon track reconstruction is used to trigger a network of small
automatic optical telescopes. Such alerts are generated for special events,
such as two or more neutrinos, coincident in time and direction, or single
neutrinos of very high energy.Comment: 17 pages, 9 figures submitted to Astroparticle Physic
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