70 research outputs found
Studying The Properties Of SF6 Gas Mixtures For Directional Dark Matter Detection
Although dark matter comprises approximately 85\% of the matter content of the universe, direct detection of dark matter remains elusive. As the available parameter space for dark matter candidates is pushed to lower and lower limits, the demand for larger, more sensitive detectors continues to grow. Although upscaling the detector improves the sensitivity, it greatly increases the cost and complexity of the experiment. Even after a dark matter signal is detected, there remains the possibility that an unknown background mimics the dark matter signal. Consequently, verifying the dark matter origin of a detection signal is an issue for any dark matter experiment. The solution is to search for the so-called ``smoking gun signatures for dark matter. There is the annual modulation of the event rate, and the modulation of the recoil direction over a sidereal day. The directional modulation is the more robust signal. It would not only unambiguously confirm the existence of dark matter, but pave the way for characterizing the properties of dark matter.
This thesis describes research toward advancing low pressure gas Time Projection Chamber (TPC) technology for directional dark matter detection. It begins by measuring the thermal negative ion behavior of the novel TPC gas, SF6, and thereby confirming SF6 as an ideal gas for directional dark matter experiments. The disadvantage of SF6 is the low fiducialization efficiency due to the relatively small secondary drift species, SF5-. This motivated studies of CF4-SF6 gas mixtures that led to the discovery of a new negative ion species hypothesized to be CF3-. We show that the relative production of the new species can be tuned by adjusting the SF6 concentration and the drift field. We also propose a model for CF3- production in CF4-SF6 gas mixtures that makes qualitative predictions, which are consistent with our measurements. Our studies show that a 20-3 CF4-SF6 mixture results in low thermal diffusion and a factor two enhancement of the fiducialization efficiency relative to that measured for pure SF6. Using this mixture our measurements demonstrate gamma/electron discrimination down to 15 keVee and head-tail directionality down to 30 keVee. These are the first such measurements in TPCs with SF6-based gases, and the first utilizing a 1D readout in any gas
Discovery of a Variable Star Population in NGC 2808
We have applied the image subtraction method to images of the peculiar,
bimodal-horizontal branch globular cluster NGC 2808, taken over a total of six
nights over a range of five months. As a result, we have found, for the first
time, a sizeable population of variable stars in the crowded inner regions of
the cluster, thus raising the known RR Lyrae population in the cluster to a
total of 18 stars. In addition, an eclipsing binary and two other variables
with periods longer than 1 day were also found. Periods, positions and
(differential) light curves are provided for all the detected variables. The
Oosterhoff classification of NGC 2808, which has recently been associated with
a previously unknown dwarf galaxy in Canis Major, is briefly discussed.Comment: 8 pages, 4 figures. A&A, in pres
Two-Way Quantum Time Transfer: A Method for Daytime Space-Earth Links
Remote clock synchronization is crucial for many classical and quantum
network applications. Current state-of-the-art remote clock synchronization
techniques achieve femtosecond-scale clock stability utilizing frequency combs,
which are supplementary to quantum-networking hardware. Demonstrating an
alternative, we synchronize two remote clocks across our freespace testbed
using a method called two-way quantum time transfer (QTT). In one second we
reach picosecond-scale timing precision under very lossy and noisy channel
conditions representative of daytime space-Earth links with commercial
off-the-shelf quantum-photon sources and detection equipment. This work
demonstrates how QTT is potentially relevant for daytime space-Earth quantum
networking and/or providing high-precision secure timing in GPS-denied
environments.Comment: arXiv admin note: text overlap with arXiv:2211.0073
Four-colour photometry of eclipsing binaries. XL, uvby light curves for the B-type systems DW Carinae, BF Centauri, AC Velorum, and NSV 5783
Aims. In order to increase the limited number of B-stars with accurately known dimensions, and also the number of well studied eclipsing binaries in open clusters, we have undertaken observations and studies of four southern double-lined eclipsing B-type binaries; DWCar, BF Cen, ACVel, and NSV 5783.
Methods. Complete uvby light curves were observed between January 1982 and April 1991 at the Danish 0.5 m telescope at ESO La Silla, since 1985 known as the Strömgren Automatic Telescope (SAT). Standard indices for the systems and the comparison stars,as well as additional minima observations for ACVel, have been obtained later at SAT. For DWCar and ACVel, high-resolution spectra for definitive spectroscopic orbits have also been obtained; they are presented as part of the detailed analyses of these systems.
A few spectra of NSV 5783 are included in the present paper.
Results. For all four systems, the first modern accurate light curves have been established. DWCar is a detached system consisting of two nearly identical components. It is member of the young open cluster Cr228. A detailed analysis, based on the new light curves and 29 high-resolution spectra, is published separately. BFCen is semidetached and is member of NGC 3766. Modern spectra are
needed for a detailed study. ACVel is a detached system with at least one more star. A full analysis, based on the new light curves and 18 high-resolution spectra, is published separately. NSV 5783 is discovered to be an eclipsing binary consisting of two well-detached
components in an 11-day period eccentric (e = 0.18) orbit. Secondary eclipse is practically total. From the light curves and a few high-resolution spectra, accurate photometric elements and preliminary absolute dimensions have been determined. The quite similar components have masses of about 5 M and radii of about 3.5 R, and they seem to have evolved just slightly off the ZAMS. The
measured rotational velocities (â150 km sâ1) are about 6 times those corresponding to pseudosynchronization
Multiresolution approach for period determination on unevenly sampled data
In this paper we present a multiresolution-based method for period
determination that is able to deal with unevenly sampled data. This method
allows us to detect superimposed periodic signals with lower signal-to-noise
ratios than in classical methods. This multiresolution-based method is a
generalization of the wavelet-based method for period detection that is unable
to deal with unevenly sampled data, presented by the authors in Otazu et al.
(2002). This new method is a useful tool for the analysis of real data and, in
particular, for the analysis of astronomical data.Comment: 6 pages, 3 figures, LaTeX, uses mn2e.cls. Accepted for publication in
MNRA
Four-colour photometry of eclipsing binaries. XLI uvby light curves for AD Bootis, HW Canis Majoris, SW Canis Majoris, V636 Centauri, VZ Hydrae, and WZ Ophiuchi
CONTEXT: Accurate mass, radius, and abundance determinations from binaries
provide important information on stellar evolution, fundamental to central
fields in modern astrophysics and cosmology.
AIMS: Within the long-term Copenhagen Binary Project, we aim to obtain
high-quality light curves and standard photometry for double-lined detached
eclipsing binaries with late A, F, and G type main-sequence components, needed
for the determination of accurate absolute dimensions and abundances, and for
detailed comparisons with results from recent stellar evolutionary models.
METHODS: Between March 1985 and July 2007, we carried out photometric
observations of AD Boo, HW CMA, SW CMa, V636 Cen, VZ Hya, and WZ Oph at the
Str"omgren Automatic Telescope at ESO, La Silla.
RESULTS: We obtained complete uvby light curves, ephemerides, and standard
uvby\beta indices for all six systems.For V636 Cen and HW CMa, we present the
first modern light curves, whereas for AD Boo, SW CMa, VZ Hya, and WZ Oph, they
are both more accurate and more complete than earlier data. Due to a high
orbital eccentricity (e = 0.50), combined with a low orbital inclination (i =
84.7), only one eclipse, close to periastron, occurs for HW CMa. For the two
other eccentric systems, V636 Cen (e = 0.134) and SW CMa (e = 0.316), apsidal
motion has been detected with periods of 5270 +/- 335 and 14900 +/- 3600 years,
respectively.Comment: Only change is: Bottom lines (hopefully) not truncated anymore.
Accepted for publication in Astonomy & Astrophysic
Background Assay and Rejection in DRIFT
The DRIFT-IId dark matter detector is a m3-scale low-pressure TPC with directional sensitivity to WIMP-induced nuclear recoils. Its primary backgrounds were due to alpha decays from contamination on the central cathode. Efforts to reduce these backgrounds led to replacing the 20 ÎŒm wire central cathode with one constructed from 0.9 ÎŒm aluminized mylar, which is almost totally transparent to alpha particles. Detailed modeling of the nature and origin of the remaining backgrounds led to an in-situ, ppt-sensitive assay of alpha decay backgrounds from the central cathode. This led to further improvements in the thin-film cathode resulting in over 2 orders of magnitude reduction in backgrounds compared to the wire cathode. Finally, the addition of O2 to CS2 gas was found to produce multiple species of electronegative charge carriers, providing a method to determine the absolute position of nuclear recoils and reject all known remaining backgrounds while retaining a high efficiency for nuclear recoil detection
Substructure revealed by RR Lyraes in SDSS Stripe 82
We present an analysis of the substructure revealed by 407 RR Lyraes in Sloan
Digital Sky Survey (SDSS) Stripe 82. Period estimates are determined to high
accuracy using a string-length method. A subset of 178 RR Lyraes with
spectrally derived metallicities are employed to derive
metallicity-period-amplitude relations, which are then used to find
metallicities and distances for the entire sample. The RR Lyraes lie between 5
and 115 kpc from the Galactic center. They are divided into subsets of 316 RRab
types and 91 RRc types based on their period, colour and metallicity. The
density distribution is not smooth, but dominated by clumps and substructure.
Samples of 55 and 237 RR Lyraes associated with the Sagittarius Stream and the
Hercules-Aquila Cloud respectively are identified. Hence, ~ 70 % of the RR
Lyraes in Stripe 82 belong to known substructure. There is a sharp break in the
density distribution at Galactocentric radii of 40 kpc, reflecting the fact
that the dominant substructure in Stripe 82 - the Hercules-Aquila Cloud and the
Sagittarius Stream - lies within 40 kpc. In fact, almost 60 % of all the RR
Lyraes in Stripe 82 are associated with the Hercules-Aquila Cloud alone, which
emphasises its pre-eminence. Additionally, evidence of a new and distant
substructure - the Pisces Overdensity - is found, consisting of 28 faint RR
Lyraes centered on Galactic coordinates (80 deg, -55 deg) and with distances of
~ 80 kpc. The total stellar mass in the Pisces Overdensity is ~10000 solar
masses and its metallicity is [Fe/H] ~ -1.5.Comment: 15 pages, submitted to MNRA
The First Known Mira-type Variable Star in IC 1613
King, Modjaz, & Li (1999) discovered Nova 1999 in IC1613 at Lick Observatory.
Both Fugazza et al. (2000) and Borissova et al. (2000) questioned this
classification, because they were able to detect the star on images obtained in
previous years. In infrared frames taken on Oct. 15, 1998, the Nova 1999 has
(J-K) = 1.14 and K = 14.69 mag. Our light curve study, based primarily on 92
unfiltered Lick images, suggested that the object could be a Mira-type variable
with a period of 640.7 days. This period is very close to that obtained by
Fugazza et al. (2000) - 631 days. The star is overluminous with respect to the
period-luminosity (PL) relation derived by Feast et al. (1989) for Mira
variables in the LMC. At longer periods (P > 400 ~ days), many LMC Miras show
such behavior and the PL relation appears to break down. It is possible that
the situation in IC1613 is similar. An optical spectrum obtained with the
Keck-II telescope shows features typical of M3Ie or M3IIIe stars. We conclude
that the star is a normal long-period M-type Mira variable, the first such star
confirmed in IC1613.Comment: 5 pages, 5 figures, accepted in A&
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