493 research outputs found
Purity control of the XENON1T gas inventory prior to initial filling and studies of mixing properties of impurities in gaseous xenon
Dark matter composes 27% of the universe but its presence is inferred only from gravitational phenomena. Direct detection experiments, such as Xenon1T, attempt to detect the scattering of dark matter particles with the detector target, in this case xenon nuclei. The experiment Xenon1T employs 3.3 tonnes of liquid xenon in a Time Projection Chamber (TPC). The TPC is a detector that employs electromagnetic fields in a sensitive volume for 3-d position reconstruction and particle identification. Since dark matter scattering is a rare event, it is necessary to reduce the background to improve the sensitivity of the detector. It is necessary to monitor two kind of impurities in liquid xenon: radioactive impurities such as krypton (present in commercially available xenon at ppb level), since it increases the background, and electronegative molecules such as oxygen and water, since they lower the electron life-time and disrupts the well functioning of the TPC. In this work, the measurements of the xenon inventory prior to filling is presented using the technique of gas chromatography. Some of the bottles measurements are presented and the total purity is summarized. In the second part, a study of gas mixing as solution of inconsistency measurements in the previous part is presented, and different solutions to speed up the gas diffusion are tested. Finally, since gas chromatography is not sensitive to helium, a measurement of the helium concentration in the full xenon inventory is presented using the technique of mass spectrometry
Sub-ppb xenon purity control and study of PTFE surface contamination towards the first results of XENONnT
The XenonnT experiment, successor of Xenon1T, aims at probing the cross sections of the interaction between a WIMP, a well-motivated dark matter candidate, and a xenon nucleus down to 1.4 x 1048 cm2; in addition, it will allow to distinguish if the electronic event excess observed by Xenon1T was due to new physics or a new standard model background. XenonnT employs 8.5 tonnes of xenon in a dual-phase Time Projection Chamber (TPC) and it needs both ultra-pure xenon and an ultralow background for increasing the sensitivity. Some of the impurities of concern are: radioactive impurities such as 85Kr, 222Rn and its progenies, and -3H, since they increase the background rate; electronegative impurities such as oxygen, since they reduce the amount of electrons in the TPC. In the first part of this thesis, we present an offline purity monitor, able to detect trace impurities at sub-ppb level. The setup uses a combination of Atmospheric Pressure Ionization Mass Spectrometry (APIMS), with a commercial APIX dQ from ThermoFisher, and a custom-made gas chromatography setup. The setup is used to measure xenon samples from the start of the science run of XenonnT. First results are given on oxygen and hydrogen contamination of the gaseous phase. In the second part, a study of deposition of 222Rn daughters on Polytetrafluoroethylene (PTFE) is presented. The study was conducted in the framework of the assembly of the XenonnT TPC, as PTFE is the most abundant material. Results are given for several PTFE samples that were deployed during the Xenon1T TPC construction phase
SN1987A: Revisiting the Data and the Correlation between Neutrino and Gravitational Detectors
We re-examine the data taken by the neutrino detectors during the supernova
SN1987A. It is found that the Kamiokande data, in addition to the well known
burst at 7:35 hours UT, show another one at 7:54 hours, with seven pulses in
6.2 seconds. This second burst supports the idea that the duration of the
collapse was much longer than a few seconds, as already suggested by the LSD
detection at 2:56 hours the same day, i.e. four and a half hours earlier. The
correlations between the gravitational wave detectors (Rome and Maryland) and
the neutrino detectors are also revisited. It is shown that the g.w. detectors
exhibit significant correlations with both the LSD and the Kamiokande detectors
over periods of one-two hours that are centered, in both cases, at the LSD
time.Comment: Presented at the VULCANO WOKSHOP 2008, Frontier Objects in
Astrophysics and Particle Physics, May 26-3
The Infrared Telescope Facility (IRTF) spectral library: spectral diagnostics for cool stars
The near-infrared (NIR) wavelength range offers some unique spectral
features, and it is less prone to the extinction than the optical one.
Recently, the first flux calibrated NIR library of cool stars from the NASA
Infrared Telescope Facility (IRTF) have become available, and it has not been
fully exploited yet. We want to develop spectroscopic diagnostics for stellar
physical parameters based on features in the wavelength range 1-5 micron. In
this work we test the technique in the I and K bands. The study of the Y, J, H,
and L bands will be presented in the following paper. An objective method for
semi-empirical definition of spectral features sensitive to various physical
parameters is applied to the spectra. It is based on sensitivity map--i.e.,
derivative of the flux in the spectra with respect to the stellar parameters at
a fixed wavelength. New optimized indices are defined and their equivalent
widths (EWs) are measured. A number of sensitive features to the effective
temperature and surface gravity are re-identified or newly identified clearly
showing the reliability of the sensitivity map analysis. The sensitivity map
allows to identify the best bandpass limits for the line and nearby continuum.
It reliably predicts the trends of spectral features with respect to a given
physical parameter but not their absolute strengths. Line blends are easy to
recognize when blended features have different behavior with respect to some
physical stellar parameter. The use of sensitivity map is therefore
complementary to the use of indices. We give the EWs of the new indices
measured for the IRTF star sample. This new and homogeneous set of EWs will be
useful for stellar population synthesis models and can be used to get
element-by-element abundances for unresolved stellar population studies in
galaxies.Comment: 46 pages, 27 figures, accepted for publication on Astronomy and
Astrophysic
Peanut-shaped bulges in face-on disk galaxies
We present high resolution absorption-line spectroscopy of 3 face-on
galaxies, NGC 98, NGC 600, and NGC 1703 with the aim of searching for
box/peanut (B/P)-shaped bulges. These observations test and confirm the
prediction of Debattista et al. (2005) that face-on B/P-shaped bulges can be
recognized by a double minimum in the profile of the fourth-order Gauss-Hermite
moment h_4. In NGC 1703, which is an unbarred control galaxy, we found no
evidence of a B/P bulge. In NGC 98, a clear double minimum in h_4 is present
along the major axis of the bar and before the end of the bar, as predicted. In
contrast, in NGC 600, which is also a barred galaxy but lacks a substantial
bulge, we do not find a significant B/P shape.Comment: 4 pages, 1 figure. To appear in "Tumbling, twisting, and winding
galaxies: Pattern speeds along the Hubble sequence", E. M. Corsini and V. P.
Debattista (eds.), Memorie della Societa` Astronomica Italian
Near-infrared spectroscopic indices for unresolved stellar populations: I. Template galaxy spectra
Context. A new generation of spectral synthesis models has been developed in recent years, but there is no matching set of template galaxy spectra, in terms of quality and resolution, for testing and refining the new models.
Aims: Our main goal is to find and calibrate new near-infrared spectral indices along the Hubble sequence of galaxies which will be used to obtain additional constraints to the population analysis based on medium-resolution integrated spectra of galaxies.
Methods: Spectra of previously studied and well-understood galaxies with relatively simple stellar populations (e.g., ellipticals or bulge dominated galaxies) are needed to provide a baseline data set for spectral synthesis models.
Results: X-shooter spectra spanning the optical and infrared wavelengths (350-2400 nm) of bright nearby elliptical galaxies with a resolving power of R \u2dc 4000-5400 were obtained. Heliocentric systemic velocity, velocity dispersion, and Mg, Fe, and H\u3b2 line-strength indices are presented.
Conclusions: We present a library of very-high-quality spectra of galaxies covering a large range of age, metallicity, and morphological type. Such a dataset of spectra will be crucial to addressing important questions of the modern investigation concerning galaxy formation and evolution
Upper limits on the mass of supermassive black holes from HST/STIS archival data
The growth of supermassive black holes (SBHs) appears to be closely linked
with the formation of spheroids. There is a pressing need to acquire better
statistics on SBH masses, since the existing samples are preferentially
weighted toward early-type galaxies with very massive SBHs. With this
motivation we started a project aimed at measuring upper limits on the mass of
the SBHs in the center of all the nearby galaxies (D<100 Mpc) for which
STIS/G750M spectra are available in the HST archive. These upper limits will be
derived by modeling the central emission-line widths observed in the Halpha
region over an aperture of ~0.1''. Here we present our results for a subsample
of 20 S0-Sb galaxies within 20 Mpc.Comment: 2 pages, 1 figure. To appear in the proceedings of "Black Holes: from
Stars to Galaxies", IAU Symp. No. 238, V. Karas & G. Matt (eds.), Cambridge
University Pres
Dark Matter searches using gravitational wave bar detectors: quark nuggets and newtorites
Many experiments have searched for supersymmetric WIMP dark matter, with null
results. This may suggest to look for more exotic possibilities, for example
compact ultra-dense quark nuggets, widely discussed in literature with several
different names. Nuclearites are an example of candidate compact objects with
atomic size cross section. After a short discussion on nuclearites, the result
of a nuclearite search with the gravitational wave bar detectors Nautilus and
Explorer is reported. The geometrical acceptance of the bar detectors is 19.5
sr, that is smaller than that of other detectors used for similar
searches. However, the detection mechanism is completely different and is more
straightforward than in other detectors. The experimental limits we obtain are
of interest because, for nuclearites of mass less than g, we find a
flux smaller than that one predicted considering nuclearites as dark matter
candidates. Particles with gravitational only interactions (newtorites) are
another example. In this case the sensitivity is quite poor and a short
discussion is reported on possible improvements.Comment: published on Astroparticle Physics Sept 25th 2016 replaced fig 1
Kinematic and stellar population properties of the counter-rotating components in the S0 galaxy NGC 1366
Context. Many disk galaxies host two extended stellar components that rotate in opposite directions. The analysis of the stellar populations of the counter-rotating components provides constraints on the environmental and internal processes that drive their formation. Aims. The S0 NGC 1366 in the Fornax cluster is known to host a stellar component that is kinematically decoupled from the main body of the galaxy. Here we successfully separated the two counter-rotating stellar components to independently measure the kinematics and properties of their stellar populations. Methods. We performed a spectroscopic decomposition of the spectrum obtained along the galaxy major axis and separated the relative contribution of the two counter-rotating stellar components and of the ionized-gas component. We measured the line-strength indices of the two counter-rotating stellar components and modeled each of them with single stellar population models that account for the \u3b1/Fe overabundance. Results. We found that the counter-rotating stellar component is younger, has nearly the same metallicity, and is less \u3b1/Fe enhanced than the corotating component. Unlike most of the counter-rotating galaxies, the ionized gas detected in NGC 1366 is neither associated with the counter-rotating stellar component nor with the main galaxy body. On the contrary, it has a disordered distribution and a disturbed kinematics with multiple velocity components observed along the minor axis of the galaxy. Conclusions. The different properties of the counter-rotating stellar components and the kinematic peculiarities of the ionized gas suggest that NGC 1366 is at an intermediate stage of the acquisition process, building the counter-rotating components with some gas clouds still falling onto the galaxy. \ua9 ESO 2017
Quark nuggets search using 2350 Kg gravitational waves aluminum bar detectors
The gravitational wave resonant detectors can be used as detectors of quark
nuggets, like nuclearites (nuclear matter with a strange quark). This search
has been carried out using data from two 2350 Kg, 2 K cooled, aluminum bar
detectors: NAUTILUS, located in Frascati (Italy), and EXPLORER, that was
located in CERN Geneva (CH). Both antennas are equipped with cosmic ray shower
detectors: signals in the bar due to showers are continuously detected and used
to characterize the antenna performances. The bar excitation mechanism is based
on the so called thermo-acoustic effect, studied on dedicated experiments that
use particle beams. This mechanism predicts that vibrations of bars are induced
by the heat deposited in the bar from the particle. The geometrical acceptance
of the bar detectors is 19.5 sr, that is smaller than that of other
detectors used for similar searches. However, the detection mechanism is
completely different and is more straightforward than in other detectors. We
will show the results of ten years of data from NAUTILUS (2003-2012) and 7
years from EXPLORER (2003-2009). The experimental limits we obtain are of
interest because, for nuclearites of mass less than grams, we find a
flux smaller than that one predicted considering nuclearites as dark matter
candidates.Comment: presented to the 33rd International Cosmic Ray Conference Rio de
Janeiro 201
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