92 research outputs found
NICMOS and VLA Observations of the Gravitatonally Lensed Ultraluminous BAL Quasar APM~08279+5255: Detection of a Third Image
We present a suite of observations of the recently identified ultraluminous
BAL quasar APM 08279+5255, taken both in the infra-red with the NICMOS high
resolution camera on board the Hubble Space Telescope, and at 3.5cm with the
Very Large Array. With an inferred luminosity of ~5x10^15 Solar luminosities,
APM 08279+5255 is apparently the most luminous system known. Extant
ground-based images show that APM 08279+5255 is not point-like, but is instead
separated into two components, indicative of gravitational lensing. The much
higher resolution images presented here also reveal two point sources, A and B,
of almost equal brightness (f_B/f_A=0.782 +/- 0.010), separated by 0."378 +/-
0."001, as well as a third, previously unknown, fainter image, C, seen between
the brighter images. While the nature of C is not fully determined, several
lines of evidence point to it being a third gravitationally lensed image of the
quasar, rather than being the lensing galaxy. Simple models which recover the
relative image configuration and brightnesses are presented. While proving to
be substantially amplified, APM 08279+5255 possesses an intrinsic bolometric
luminosity of ~10^14 to 10^15 Solar luminosities and remains amongst the most
luminous objects known.Comment: 21 pages, 5 figures (2 as GIF files); accepted for publication in the
Astronomical Journa
Discovery of Irradiation Induced Variations in the Light Curve of the Classical Nova Cygni 2001 No.2 (V2275 Cyg)
We present the CCD photometry, light curve and time series analysis of the
classical nova V2275 Cyg (N Cyg 2001 No.2). The source was observed for 14
nights in total using an R filter in 2002 and 2003 with the 1.5 m
Russian-Turkish joint telescope (RTT150) at the TUBITAK (The Scientific and
Technical Research Council of Turkey) National Observatory in Antalya Turkey,
as part of a large program on the CCD photometry of Cataclysmic Variables
(CVs). We report the detection of two distinct periodicities in the light curve
of the nova : a) P_1=0.31449(15) d -- 7.6 h, b) P_2=0.017079(17) d -- 24.6 min.
The first period is evident in both 2002 and 2003 whereas the second period is
only detected in the 2003 data set. We interpret the first period as the
orbital period of the system and attribute the orbital variations to aspect
changes of the secondary irradiated by the hot WD. We suggest that the nova was
a Super Soft X-ray source in 2002 and, perhaps, in 2003. The second period
could be a QPO originating from the oscillation of the ionization front (due to
a hot WD) below the inner Lagrange point as predicted by King (1989) or a beat
frequency in the system as a result of the magnetic nature of the WD if steady
accretion has already been re-established.Comment: 6 pages and 8 figures. Accepted to be published in MNRAS main Journal
as it stand
A Search for Period Changes in Delta Scuti Stars with the Super-LOTIS Sky Patrol System
We have observed a sample of Delta Scuti stars discovered by the ROTSE
collaboration in 1999 with Super-LOTIS in order to characterize changes in
their pulsation periods over a time baseline of roughly three years. Achieving
these goals required the creation of an automated astrometric and photometric
data reduction pipeline for the Super-LOTIS camera. Applying this pipeline to
data from a June 2002 observing campaign, we detect pulsations in 18 objects,
and find that in two cases the periods have changed significantly over the
three years between the ROTSE and Super-LOTIS observations. Since theory
predicts that evolutionary period changes should be quite small, sources of
non-evolutionary period changes due to the interactions of pulsations modes are
discussed.Comment: 9 pages, 3 figures, 2 tables. Accepted for publication in A&
Central kinematics of the globular cluster NGC 2808: Upper limit on the mass of an intermediate-mass black hole
Globular clusters are an excellent laboratory for stellar population and
dynamical research. Recent studies have shown that these stellar systems are
not as simple as previously assumed. With multiple stellar populations as well
as outer rotation and mass segregation they turn out to exhibit high
complexity. This includes intermediate-mass black holes which are proposed to
sit at the centers of some massive globular clusters. Today's high angular
resolution ground based spectrographs allow velocity-dispersion measurements at
a spatial resolution comparable to the radius of influence for plausible IMBH
masses, and to detect changes in the inner velocity-dispersion profile.
Together with high quality photometric data from HST, it is possible to
constrain black-hole masses by their kinematic signatures. We determine the
central velocity-dispersion profile of the globular cluster NGC 2808 using
VLT/FLAMES spectroscopy. In combination with HST/ACS data our goal is to probe
whether this massive cluster hosts an intermediate-mass black hole at its
center and constrain the cluster mass to light ratio as well as its total mass.
We derive a velocity-dispersion profile from integral field spectroscopy in the
center and Fabry Perot data for larger radii. High resolution HST data are used
to obtain the surface brightness profile. Together, these data sets are
compared to dynamical models with varying parameters such as mass to light
ratio profiles and black-hole masses. Using analytical Jeans models in
combination with variable M/L profiles from N-body simulations we find that the
best fit model is a no black hole solution. After applying various Monte Carlo
simulations to estimate the uncertainties, we derive an upper limit of the back
hole mass of M_BH < 1 x 10^4 M_SUN (with 95 % confidence limits) and a global
mass-to-light ratio of M/L_V = (2.1 +- 0.2) M_SUN/L_SUN.Comment: 12 pages, 9 figures, 2 tables, accepted for publication in A&
How voluntary actions modulate time perception
Distortions of time perception are generally explained either by variations in the rate of pacing signals of an âinternal clockâ, or by lag-adaptation mechanisms that recalibrate the perceived time of one event relative to another. This study compares these accounts directly for one temporal illusion: the subjective compression of the interval between voluntary actions and their effects, known as âintentional bindingâ. Participants discriminated whether two cutaneous stimuli presented after voluntary or passive movements were simultaneous or successive. In other trials, they judged the temporal interval between their movement and an ensuing tone. Temporal discrimination was impaired following voluntary movements compared to passive movements early in the action-tone interval. In a control experiment, active movements without subsequent tones produced no impairment in temporal discrimination. These results suggest that voluntary actions transiently slow down an internal clock during the action-effect interval. This in turn leads to intentional binding, and links the effects of voluntary actions to the self
Combined Analysis of the Binary-Lens Caustic-Crossing Event MACHO 98-SMC-1
We fit the data for the binary-lens microlensing event MACHO 98-SMC-1 from 5
different microlensing collaborations and find two distinct solutions
characterized by binary separation d and mass ratio q: (d,q)=(0.54,0.50) and
(d,q)=(3.65,0.36), where d is in units of the Einstein radius. However, the
relative proper motion of the lens is very similar in the two solutions, 1.30
km/s/kpc and 1.48 km/s/kpc, thus confirming that the lens is in the Small
Magellanic Cloud. The close binary can be either rotating or approximately
static but the wide binary must be rotating at close its maximum allowed rate
to be consistent with all the data. We measure limb-darkening coefficients for
five bands ranging from I to V. As expected, these progressively decrease with
rising wavelength. This is the first measurement of limb darkening for a
metal-poor A star.Comment: 29 pages + 9 figures + 2 tables, submitted to Ap
The first two transient supersoft X-ray sources in M 31 globular clusters and the connection to classical novae
Classical novae (CNe) have been found to represent the major class of
supersoft X-ray sources (SSS) in our neighbour galaxy M 31. We determine
properties and evolution of the two first SSSs ever discovered in the M 31
globular cluster (GC) system. We have used XMM-Newton, Chandra and Swift
observations of the centre region of M 31 to discover both SSS and to determine
their X-ray light curves and spectra. We performed detailed analysis of
XMM-Newton EPIC PN spectra of the source in Bol 111 (SS1) using blackbody and
NLTE white dwarf (WD) atmosphere models. For the SSS in Bol 194 (SS2) we used
optical monitoring data to search for an optical counterpart. Both GC X-ray
sources were classified as SSS. We identify SS1 with the CN M31N 2007-06b
recently discovered in the M 31 GC Bol 111. For SS2 we did not find evidence
for a recent nova outburst and can only provide useful constraints on the time
of the outburst of a hypothetical nova. The only known CN in a M 31 GC can be
identified with the first SSS found in a M31 GC. We discuss the impact of our
observations on the nova rate for the M 31 GC system.Comment: 11 pages, 9 figures, 4 tables, submitted to A&A; v2: accepted versio
Horizontal Branch Stars: The Interplay between Observations and Theory, and Insights into the Formation of the Galaxy
We review HB stars in a broad astrophysical context, including both variable
and non-variable stars. A reassessment of the Oosterhoff dichotomy is
presented, which provides unprecedented detail regarding its origin and
systematics. We show that the Oosterhoff dichotomy and the distribution of
globular clusters (GCs) in the HB morphology-metallicity plane both exclude,
with high statistical significance, the possibility that the Galactic halo may
have formed from the accretion of dwarf galaxies resembling present-day Milky
Way satellites such as Fornax, Sagittarius, and the LMC. A rediscussion of the
second-parameter problem is presented. A technique is proposed to estimate the
HB types of extragalactic GCs on the basis of integrated far-UV photometry. The
relationship between the absolute V magnitude of the HB at the RR Lyrae level
and metallicity, as obtained on the basis of trigonometric parallax
measurements for the star RR Lyrae, is also revisited, giving a distance
modulus to the LMC of (m-M)_0 = 18.44+/-0.11. RR Lyrae period change rates are
studied. Finally, the conductive opacities used in evolutionary calculations of
low-mass stars are investigated. [ABRIDGED]Comment: 56 pages, 22 figures. Invited review, to appear in Astrophysics and
Space Scienc
Asymmetric recurrent laryngeal nerve conduction velocities and dorsal cricoarytenoid muscle electromyographic characteristics in clinically normal horses
The dorsal cricoarytenoid (DCA) muscles, are a fundamental component of the athletic horseâs respiratory system: as the sole abductors of the airways, they maintain the size of the rima glottis which is essential for enabling maximal air intake during intense exercise. Dysfunction of the DCA muscle leads to arytenoid collapse during exercise, resulting in poor performance. An electrodiagnostic study including electromyography of the dorsal cricoarytenoid muscles and conduction velocity testing of the innervating recurrent laryngeal nerves (RLn) was conducted in horses with normal laryngeal function. We detected reduced nerve conduction velocity of the left RLn, compared to the right, and pathologic spontaneous activity (PSA) of myoelectrical activity within the left DCA muscle in half of this horse population and the horses with the slowest nerve conduction velocities. The findings in this group of horses are consistent with left sided demyelination and axonal loss, consistent with Recurrent Laryngeal Neuropathy (RLN), a highly prevalent degenerative disorder of the RLn in horses that predominantly affects the left side. The detection of electromyographic changes compatible with RLN in clinically unaffected horses is consistent with previous studies that identified âsubclinicalâ subjects, presenting normal laryngeal function despite neuropathologic changes within nerve and muscle confirmed histologically
Estimating the parameters of globular cluster M 30 (NGC 7099) from time-series photometry
Aims: We present the analysis of 26 nights of V and I time-series observations from 2011 and 2012 of the globular cluster M 30 (NGC 7099). We used our data to search for variable stars in this cluster and refine the periods of known variables; we then used our variable star light curves to derive values for the cluster's parameters. Methods: We used difference image analysis to reduce our data to obtain high-precision light curves of variable stars. We then estimated the cluster parameters by performing a Fourier decomposition of the light curves of RR Lyrae stars for which a good period estimate was possible. We also derived an estimate for the age of the cluster by fitting theoretical isochrones to our colour-magnitude diagram (CMD). Results: Out of 13 stars previously catalogued as variables, we find that only 4 are bona fide variables. We detect two new RR Lyrae variables, and confirm two additional RR Lyrae candidates from the literature. We also detect four other new variables, including an eclipsing blue straggler system, and an SX Phoenicis star. This amounts to a total number of confirmed variable stars in M 30 of 12. We perform Fourier decomposition of the light curves of the RR Lyrae stars to derive cluster parameters using empirical relations. We find a cluster metallicity [Fe/H][SUB]ZW[/SUB] = -2.01 ± 0.04, or [Fe/H][SUB]UVES[/SUB] = -2.11 ± 0.06, and a distance of 8.32 ± 0.20 kpc (using RR0 variables), 8.10 kpc (using one RR1 variable), and 8.35 ± 0.42 kpc (using our SX Phoenicis star detection in M 30). Fitting isochrones to the CMD, we estimate an age of 13.0 ± 1.0 Gyr for M 30. This work is based on data collected by MiNDSTEp with the Danish 1.54 m telescope at the ESO La Silla Observatory.The full light curves, an extract of which is shown in Table 2 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/555/A36Tables 8-10, and Figs. 6 and 9 are available in electronic form at http://www.aanda.org</A
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