1,122 research outputs found
Progress with micro-pattern gas detectors
Abstract Micro-pattern gas detectors are position-sensitive proportional counters whose sense electrodes are constructed using micro-electronics, thin-film or advanced PCB techniques. The feature size attainable using these methods is of the order of a few microns and the detectors demonstrate excellent spatial resolution and fast charge collection. We review recent progress on micro-pattern gas detectors for tracking and other cross-disciplinary applications, focussing on design principles, performance and limitations. A short list of interesting applications is discussed
The Red Giant Branch Tip and Bump of the Leo II dwarf spheroidal galaxy
We present V and I photometry of a 9.4' X 9.4' field centered on the dwarf
spheroidal galaxy Leo II. The Tip of the Red Giant Branch is identified at
I^{TRGB}=17.83 +/- 0.03 and adopting = -1.53 +/- 0.2 from the
comparison of RGB stars with Galactic templates, we obtain a distance modulus
(m-M)_0=21.84 +/- 0.13, corresponding to a distance D=233 +/- 15 Kpc. Two
significant bumps have been detected in the Luminosity Function of the Red
Giant Branch. The fainter bump (B1, at V=21.76 +/- 0.05) is the RGB bump of the
dominant stellar population, while the actual nature of the brightest one (B2,
at V=21.35 +/- 0.05) cannot be firmly assessed on the basis of the available
data, it can be due to the Asymptotic Giant Branch Clump of the main population
or it may be a secondary RGB bump. The luminosity of the main RGB bump (B1)
suggests that the majority of RGB stars in Leo II belongs to a population that
is ~4 gyr younger than the classical Galactic globular clusters. The stars
belonging to the He-burning Red Clump are shown to be significantly more
centrally concentrated than RR Lyrae and Blue Horizontal Branch stars, probing
the existence of an age/metallicity radial gradient in this remote dwarf
spheroidal.Comment: Accepted for publication by MNRAS. Latex, 10 pages, 8 .ps figure
The distance to the Leo I dwarf spheroidal galaxy from the Red Giant Branch Tip
We present V and I photometry of a 9.4 arcmin X 9.4 arcmin field centered on
the dwarf spheroidal galaxy Leo I. The I magnitude of the tip of the Red Giant
Branch is robustly estimated from two different datasets (I^{TRGB}=17.97
+0.05/-0.03). From this estimate, adopting [M/H]=-1.2 from the comparison of
RGB stars with Galactic templates, we obtain a distance modulus (m-M)_0=22.02
+/- 0.13, corresponding to a distance D=254 +16/-19 Kpc.Comment: 6 pages, 5 figures, Fig. 1 and 2 provided in low resolution version.
Latex. Accepted for publication by MNRA
A dwarf galaxy remnant in Canis Major: the fossil of an in-plane accretion onto the Milky Way
We present an analysis of the asymmetries in the population of Galactic
M-giant stars present in the 2MASS All Sky catalogue. Several large-scale
asymmetries are detected, the most significant of which is a strong
elliptical-shaped stellar over-density, close to the Galactic plane at (l=240,
b=-8), in the constellation of Canis Major. A small grouping of globular
clusters (NGC 1851, NGC 1904, NGC 2298, and NGC 2808), coincident in position
and radial velocity, surround this structure, as do a number of open clusters.
The population of M-giant stars in this over-density is similar in number to
that in the core of the Sagittarius dwarf galaxy. We argue that this object is
the likely dwarf galaxy progenitor of the ring-like structure that has recently
been found at the edge of the Galactic disk. A numerical study of the tidal
disruption of an accreted dwarf galaxy is presented. The simulated debris fits
well the extant position, distance and velocity information on the ``Galactic
Ring'', as well as that of the M-giant over-densities, suggesting that all
these structures are the consequence of a single accretion event. The disrupted
dwarf galaxy stream orbits close to the Galactic Plane, with a pericentre at
approximately the Solar circle, an orbital eccentricity similar to that of
stars in the Galactic thick disk, as well as a vertical scale height similar to
that of the thick disk. This finding strongly suggests that the Canis Major
dwarf galaxy is a building block of the Galactic thick disk, that the thick
disk is continually growing, even up to the present time, and that thick disk
globular clusters were accreted onto the Milky Way from dwarf galaxies in
co-planar orbits.Comment: 13 pages, 18 figures (2 in colour), accepted for publication in MNRA
The StEllar Counterparts of COmpact high velocity clouds (SECCO) survey. II. Sensitivity of the survey and an Atlas of Synthetic Dwarf Galaxies
SECCO is a survey devoted to the search for stellar counterparts within Ultra
Compact High Velocity Clouds. In this contribution we present the results of a
set of simulations aimed at the quantitative estimate of the sensitivity of the
survey as a function of the total luminosity, size and distance of the stellar
systems we are looking for. For all our synthetic galaxies we assumed an
exponential surface brightness profile and an old and metal-poor population.
The synthetic galaxies are simulated both on the images and on the photometric
catalogs, taking into account all the observational effects. In the fields
where the available observational material is of the top quality we detect
synthetic galaxies as >=5 sigma over-densities of resolved stars down to
muV,h=30.0 mag/arcsec2, for D<=1.5 Mpc, and down to muV,h~29.5 mag/arcsec2, for
D<=2.5 Mpc. In the field with the worst observational material of the whole
survey we detect synthetic galaxies with muV,h<=28.8 mag/arcsec2 out to D<=1.0
Mpc, and those with muV,h<=27.5 mag/arcsec2 out to D<=2.5 Mpc. Dwarf galaxies
with MV=-10, with sizes in the range spanned by known dwarfs, are detected by
visual inspection of the images up to D=5 Mpc independently of the image
quality. In the best quality images dwarfs are partially resolved into stars up
to D=3.0 Mpc, and completely unresolved at D=5 Mpc. As an independent test of
the sensitivity of our images to low surface brightness galaxies we report on
the detection of several dwarf spheroidal galaxies probably located in the
Virgo cluster with MV<=-8.0 and muV,h<=26.8 mag/arcsec2. The nature of the
previously discovered SECCO 1 stellar system, also likely located in the Virgo
cluster, is re-discussed in comparison with these dwarfs. While specific for
the SECCO survey, our study may also provide general guidelines for detection
of faint stellar systems with 8m class telescopes.Comment: accepted for publication on A&
The fine-tuning price of the early LHC
LHC already probed and excluded half of the parameter space of the
Constrained Minimal Supersymmetric Standard Model allowed by previous
experiments. Only about 0.3% of the CMSSM parameter space survives. This
fraction rises to about 0.9% if the bound on the Higgs mass can be
circumvented.Comment: 7 pages. v3: updated with new bounds from ATLAS and CMS at 1.1/fb
presented at the EPS-HEP-2011 conferenc
Grassmann-Gaussian integrals and generalized star products
In quantum scattering on networks there is a non-linear composition rule for
on-shell scattering matrices which serves as a replacement for the
multiplicative rule of transfer matrices valid in other physical contexts. In
this article, we show how this composition rule is obtained using Berezin
integration theory with Grassmann variables.Comment: 14 pages, 2 figures. In memory of Al.B. Zamolodichiko
Goldstone Fermion Dark Matter
We propose that the fermionic superpartner of a weak-scale Goldstone boson
can be a natural WIMP candidate. The p-wave annihilation of this `Goldstone
fermion' into pairs of Goldstone bosons automatically generates the correct
relic abundance, whereas the XENON100 direct detection bounds are evaded due to
suppressed couplings to the Standard Model. Further, it is able to avoid
indirect detection constraints because the relevant s-wave annihilations are
small. The interactions of the Goldstone supermultiplet can induce non-standard
Higgs decays and novel collider phenomenology.Comment: 25 pages, 6 figures. References added, minor typos corrected.
Submitted to JHE
The Rotation of Sub-Populations in omega Centauri
We present the first result of the Ital-FLAMES survey of red giant branch
(RGB) stars in omega Cen. Radial velocities with a precision of ~0.5 km/s are
presented for 650 members of omega Cen observed with FLAMES-Giraffe at the Very
Large Telescope. We found that stars belonging to the metal -poor (RGB-MP),
metal-intemediate (RGB-MInt) and metal-rich (RGB-a) sub -populations of Omega
Cen are all compatible with having the same rotational pattern. Our results
appear to contradict past findings by Norris et al., who could not detect any
rotational signature for metal -rich stars. The slightly higher precision of
the present measurements and the much larger sample size, especially for the
metal-richer stars, appear as the most likely explanation for this discrepancy.
The result presented here weakens the body of evidence in favour of a merger
event in the past history of omega Cen.Comment: 5 pages, 3 fiures, electronic table can be obtained from E. Pancino.
Accepted for publication in ApJ Letter
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