4,033 research outputs found
Infrared observations of the candidate double neutron star system PSR J1811-1736
PSR J1811-1736 (P=104 ms) is an old (~1.89 Gyrs) binary pulsar (P_orb=18.8 d)
in a highly eccentric orbit (e=0.828) with an unidentified companion.
Interestingly enough, the pulsar timing solution yields an estimated companion
mass 0.93 M_{\odot}<M_C<1.5 M_{\odot}, compatible with that of a neutron star.
As such, it is possible that PSR J1811-1736 is a double neutron star (DNS)
system, one of the very few discovered so far. This scenario can be
investigated through deep optical/infrared (IR) observations. We used J, H,
K-band images, obtained as part of the UK Infrared Telescope (UKIRT) Infrared
Deep Sky Survey (UKIDSS), and available in the recent Data Release 9 Plus, to
search for its undetected companion of the PSR J1811-1736 binary pulsar. We
detected a possible companion star to PSR J1811-1736 within the 3 sigma radio
position uncertainty (1.32 arcsec), with magnitudes J=18.61+/-0.07,
H=16.65+/-0.03, and K=15.46+/-0.02. The star colours are consistent with either
a main sequence (MS) star close to the turn-off or a lower red giant branch
(RGB) star, at a pulsar distance of ~5.5 kpc and with a reddening of
E(B-V)~4.9. The star mass and radius would be compatible with the constraints
on the masses and orbital inclination of the binary system inferred from the
mass function and the lack of radio eclipses near superior conjunction. Thus,
it is possible that it is the companion to PSR J1811-1736. However, based on
the star density in the field, we estimated a quite large chance coincidence
probability of ~0.27 between the pulsar and the star, which makes the
association unlikely. No other star is detected within the 3 sigma pulsar radio
position down to J~20.5, H~19.4$ and K~18.6, which would allow us to rule out a
MS companion star earlier than a mid-to-late M spectral type.Comment: 10 pages, 6 figures, accepted for publication on Monthly Notices of
the Royal Astronomical Societ
The optical companion to the binary millisecond pulsar J1824-2452H in the globular cluster M28
We report on the optical identification of the companion star to the
eclipsing millisecond pulsar PSR J1824-2452H in the galactic globular cluster
M28 (NGC 6626). This star is at only 0.2" from the nominal position of the
pulsar and it shows optical variability (~ 0.25 mag) that nicely correlates
with the pulsar orbital period. It is located on the blue side of the cluster
main sequence, ~1.5 mag fainter than the turn-off point. The observed light
curve shows two distinct and asymmetric minima, suggesting that the companion
star is suffering tidal distortion from the pulsar. This discovery increases
the number of non-degenerate MSP companions optically identified so far in
globular clusters (4 out of 7), suggesting that these systems could be a common
outcome of the pulsar recycling process, at least in dense environments where
they can be originated by exchange interactions.Comment: accepted for publication on ApJ, 17 pages, 5 figure
Gemini optical observations of binary millisecond-pulsars
Milli-second pulsars (MSPs) are rapidly spinning neutron stars, with spin
periods P_s <= 10 ms, which have been most likely spun up after a phase of
matter accretion from a companion star. In this work we present the results of
the search for the companion stars of four binary milli-second pulsars, carried
out with archival data from the Gemini South telescope. Based upon a very good
positional coincidence with the pulsar radio coordinates, we likely identified
the companion stars to three MSPs, namely PSRJ0614-3329 (g=21.95 +- 0.05),
J1231-1411 (g=25.40 +-0.23), and J2017+0603 (g=24.72 +- 0.28). For the last
pulsar (PSRJ0613-0200) the identification was hampered by the presence of a
bright star (g=16 +- 0.03) at \sim 2" from the pulsar radio coordinates and we
could only set 3-sigma upper limits of g=25.0, r= 24.3, and i= 24.2 on the
magnitudes of its companion star. The candidate companion stars to
PSRJ0614-3329, J1231-1411, and J2017+0603 can be tentatively identified as He
white dwarfs (WDs) on the basis of their optical colours and brightness and the
comparison with stellar model tracks. From the comparison of our multi-band
photometry with stellar model tracks we also obtained possible ranges on the
mass, temperature, and gravity of the candidate WD companions to these three
MSPs. Optical spectroscopy observations are needed to confirm their possible
classification as He WDs and accurately measure their stellar parameters.Comment: 17 pages, 7 figures, 6 tables, accepted for publication in MNRA
Real time decoherence of Landau and Levitov quasi-particles in quantum Hall edge channels
Quantum Hall edge channels at integer filling factor provide a unique
test-bench to understand decoherence and relaxation of single electronic
excitations in a ballistic quantum conductor. In this Letter, we obtain a full
visualization of the decoherence scenario of energy (Landau) and time (Levitov)
resolved single electron excitations at filling factor . We show that
the Landau excitation exhibits a fast relaxation followed by spin-charge
separation whereas the Levitov excitation only experiences spin-charge
separation. We finally suggest to use Hong-Ou-Mandel type experiments to probe
specific signatures of these different scenarios.Comment: 14 pages, 8 figure
Gauge invariance of parametrized systems and path integral quantization
Gauge invariance of systems whose Hamilton-Jacobi equation is separable is
improved by adding surface terms to the action fuctional. The general form of
these terms is given for some complete solutions of the Hamilton-Jacobi
equation. The procedure is applied to the relativistic particle and toy
universes, which are quantized by imposing canonical gauge conditions in the
path integral; in the case of empty models, we first quantize the parametrized
system called ``ideal clock'', and then we examine the possibility of obtaining
the amplitude for the minisuperspaces by matching them with the ideal clock.
The relation existing between the geometrical properties of the constraint
surface and the variables identifying the quantum states in the path integral
is discussed.Comment: 23 page
The giant, horizontal and asymptotic branches of galactic globular clusters. I. The catalog, photometric observables and features
A catalog including a set of the most recent Color Magnitude Diagrams (CMDs)
is presented for a sample of 61 Galactic Globular Clusters (GGCs). We used this
data-base to perform an homogeneous systematic analysis of the evolved
sequences (namely, Red Giant Branch (RGB), Horizontal Branch (HB) and
Asymptotic Giant Branch (AGB)). Based on this analysis, we present: (1) a new
procedure to measure the level of the ZAHB (V_ZAHB) and an homogeneous set of
distance moduli obtained adopting the HB as standard candle; (2) an independent
estimate for RGB metallicity indicators and new calibrations of these
parameters in terms of both spectroscopic ([Fe/H]_CG97) and global metallicity
([M/H], including also the alpha-elements enhancement). The set of equations
presented can be used to simultaneously derive a photometric estimate of the
metal abundance and the reddening from the morphology and the location of the
RGB in the (V,B-V)-CMD. (3) the location of the RGB-Bump (in 47 GGCs) and the
AGB-Bump (in 9 GGCs). The dependence of these features on the metallicity is
discussed. We find that by using the latest theoretical models and the new
metallicity scales the earlier discrepancy between theory and observations
(~0.4 mag) completely disappears.Comment: 51 pages, 23 figures, AAS Latex, macro rtrpp4.sty included, accepted
by A
Optical Identification of He White Dwarfs Orbiting Four Millisecond Pulsars in the Globular Cluster 47 Tucanae
We used ultra-deep UV observations obtained with the Hubble Space Telescope
to search for optical companions to binary millisecond pulsars (MSPs) in the
globular cluster 47 Tucanae. We identified four new counterparts (to MSPs
47TucQ, 47TucS, 47TucT and 47TucY) and confirmed those already known (to MSPs
47TucU and 47TucW). In the color magnitude diagram, the detected companions are
located in a region between the main sequence and the CO white dwarf cooling
sequences, consistent with the cooling tracks of He white dwarfs of mass
between 0.15 Msun and 0.20 Msun. For each identified companion, mass, cooling
age, temperature and pulsar mass (as a function of the inclination angle) have
been derived and discussed. For 47TucU we also found that the past accretion
history likely proceeded in a sub-Eddington rate. The companion to the redback
47TucW is confirmed to be a non degenerate star, with properties particularly
similar to those observed for black widow systems. Two stars have been
identified within the 2-sigma astrometric uncertainty from the radio positions
of 47TucH and 47TucI, but the available data prevent us from firmly assessing
whether they are the true companions of these two MSPs.Comment: 27 pages, 7 figures, Accepted for publication by Ap
HST Observations of the Central-Cusp Globular Cluster NGC 6752. The Effect of Binary Stars on the Luminosity Function in the Core
We consider the effect of binary stars on the main-sequence luminosity
functions observed in the core of globular clusters, with specific reference to
NGC 6752. We find that mass segregation results in an increased binary fraction
at fainter magnitudes along the main-sequence. If this effect is not taken into
account when analyzing luminosity functions, erroneous conclusions can be drawn
regarding the distribution of single stars, and the dynamical state of the
cluster. In the core of NGC 6752, our HST data reveal a flat luminosity
function, in agreement with previous results. However, when we correct for the
increasing binary fraction at faint magnitudes, the LF begins to fall
immediately below the turn-off. This effect appears to be confined to the inner
core radius of the cluster.Comment: 10 pages, 3 figures Accepted to ApJ Lett Vol 513 Number
Radio timing and optical photometry of the black widow system PSR J1518+0204C in the globular cluster M5
We report on the determination of astrometric, spin and orbital parameters
for PSR J1518+0204C, a "black widow" binary millisecond pulsar in the globular
cluster M5. The accurate position and orbital parameters obtained from radio
timing allowed us to search for the optical companion. By using WFC3/HST images
we identified a very faint variable star (m_F390W > 24.8, m_F606W > 24.3,
m_F814W > 23.1) located at only 0.25" from the pulsar's timing position. Due to
its strong variability, this star is visible only in a sub-sample of images.
However, the light curve obtained folding the available data with the orbital
parameters of the pulsar shows a maximum at the pulsar inferior conjunction and
a possible minimum at the pulsar superior conjunction. Furthermore, the shape
of the optical modulation indicates a heating process possibly due to the
pulsar wind. This is the first identification of an optical companion to a
black widow pulsar in the dense stellar environment of a globular cluster.Comment: Accepted for publication by ApJ; 24 Pages, 5 Figures, 1 Tabl
The identification of the optical companion to the binary millisecond pulsar J0610-2100 in the Galactic field
We have used deep V and R images acquired at the ESO Very Large Telescope to
identify the optical companion to the binary pulsar PSR J0610-2100, one of the
black-widow millisecond pulsars recently detected by the Fermi Gamma-ray
Telescope in the Galactic plane. We found a faint star (V~26.7) nearly
coincident (\delta r ~0".28) with the pulsar nominal position. This star is
visible only in half of the available images, while it disappears in the
deepest ones (those acquired under the best seeing conditions), thus indicating
that it is variable. Although our observations do not sample the entire orbital
period (P=0.28 d) of the pulsar, we found that the optical modulation of the
variable star nicely correlates with the pulsar orbital period and describes a
well defined peak (R~25.6) at \Phi=0.75, suggesting a modulation due to the
pulsar heating. We tentatively conclude that the companion to PSR J0610-2100 is
a heavily ablated very low mass star (~ 0.02Msun) that completely filled its
Roche Lobe.Comment: 17 pages, 5 figures - Accepted for pubblication in Ap
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