2,426 research outputs found
Keck Observatory Laser Guide Star Adaptive Optics Discovery and Characterization of a Satellite to the Large Kuiper Belt Object 2003 EL_(61)
The newly commissioned laser guide star adaptive optics system at Keck Observatory has been used to discover and characterize the orbit of a satellite to the bright Kuiper Belt object 2003 EL_(61). Observations over a 6 month period show that the satellite has a semimajor axis of 49,500 ± 400 km, an orbital period of 49.12 ± 0.03 days, and an eccentricity of 0.050 ± 0.003. The inferred mass of the system is (4.2 ± 0.1) × 10^(21) kg, or ~32% of the mass of Pluto and 28.6% ± 0.7% of the mass of the Pluto-Charon system. Mutual occultations occurred in 1999 and will not occur again until 2138. The orbit is fully consistent neither with one tidally evolved from an earlier closer configuration nor with one evolved inward by dynamical friction from an earlier more distant configuration
Short-term variability of a sample of 29 trans-Neptunian objects and Centaurs
We present results of 6 years of observations, reduced and analyzed with the
same tools in a systematic way. We report completely new data for 15 objects,
for 5 objects we present a new analysis of previously published results plus
additional data and for 9 objects we present a new analysis of data already
published. Lightcurves, possible rotation periods and photometric amplitudes
are reported for all of them. The photometric variability is smaller than
previously thought: the mean amplitude of our sample is 0.1mag and only around
15% of our sample has a larger variability than 0.15mag. The smaller
variability than previously thought seems to be a bias of previous
observations. We find a very weak trend of faster spinning objects towards
smaller sizes, which appears to be consistent with the fact that the smaller
objects are more collisionally evolved, but could also be a specific feature of
the Centaurs, the smallest objects in our sample. We also find that the smaller
the objects, the larger their amplitude, which is also consistent with the idea
that small objects are more collisionally evolved and thus more deformed.
Average rotation rates from our work are 7.5h for the whole sample, 7.6h for
the TNOs alone and 7.3h for the Centaurs. All of them appear to be somewhat
faster than what one can derive from a compilation of the scientific literature
and our own results. Maxwellian fits to the rotation rate distribution give
mean values of 7.5h (for the whole sample) and 7.3h (for the TNOs only).
Assuming hydrostatic equilibrium we can determine densities from our sample
under the additional assumption that the lightcurves are dominated by shape
effects, which is likely not realistic. The resulting average density is
0.92g/cm^3 which is not far from the density constraint that one can derive
from the apparent spin barrier that we observe.Comment: Accepted for publication in A&
Initial Hubble Diagram Results from the Nearby Supernova Factory
The use of Type Ia supernovae as distance indicators led to the discovery of
the accelerating expansion of the universe a decade ago. Now that large second
generation surveys have significantly increased the size and quality of the
high-redshift sample, the cosmological constraints are limited by the currently
available sample of ~50 cosmologically useful nearby supernovae. The Nearby
Supernova Factory addresses this problem by discovering nearby supernovae and
observing their spectrophotometric time development. Our data sample includes
over 2400 spectra from spectral timeseries of 185 supernovae. This talk
presents results from a portion of this sample including a Hubble diagram
(relative distance vs. redshift) and a description of some analyses using this
rich dataset.Comment: Short version of proceedings for ICHEP08, Philadelphia PA, July 2008;
see v1 for full-length versio
The Rising Light Curves of Type Ia Supernovae
We present an analysis of the early, rising light curves of 18 Type Ia
supernovae (SNe Ia) discovered by the Palomar Transient Factory (PTF) and the
La Silla-QUEST variability survey (LSQ). We fit these early data flux using a
simple power-law to determine the time of first
light , and hence the rise-time from first light to
peak luminosity, and the exponent of the power-law rise (). We find a mean
uncorrected rise time of days, with individual SN rise-times
ranging from to days. The exponent n shows significant
departures from the simple 'fireball model' of (or ) usually assumed in the literature. With a mean value of , our data also show significant diversity from event to event. This
deviation has implications for the distribution of 56Ni throughout the SN
ejecta, with a higher index suggesting a lesser degree of 56Ni mixing. The
range of n found also confirms that the 56Ni distribution is not standard
throughout the population of SNe Ia, in agreement with earlier work measuring
such abundances through spectral modelling. We also show that the duration of
the very early light curve, before the luminosity has reached half of its
maximal value, does not correlate with the light curve shape or stretch used to
standardise SNe Ia in cosmological applications. This has implications for the
cosmological fitting of SN Ia light curves.Comment: 19 pages, 19 figures, accepted for publication in MNRA
Time Domain Explorations With Digital Sky Surveys
One of the new frontiers of astronomical research is the exploration of time
variability on the sky at different wavelengths and flux levels. We have
carried out a pilot project using DPOSS data to study strong variables and
transients, and are now extending it to the new Palomar-QUEST synoptic sky
survey. We report on our early findings and outline the methodology to be
implemented in preparation for a real-time transient detection pipeline. In
addition to large numbers of known types of highly variable sources (e.g., SNe,
CVs, OVV QSOs, etc.), we expect to find numerous transients whose nature may be
established by a rapid follow-up. Whereas we will make all detected variables
publicly available through the web, we anticipate that email alerts would be
issued in the real time for a subset of events deemed to be the most
interesting. This real-time process entails many challenges, in an effort to
maintain a high completeness while keeping the contamination low. We will
utilize distributed Grid services developed by the GRIST project, and implement
a variety of advanced statistical and machine learning techniques.Comment: 5 pages, 2 postscript figures, uses adassconf.sty. To be published
in: "ADASS XIV (2004)", Eds. Patrick Shopbell, Matthew Britton and Rick
Ebert, ASP Conference Serie
The QUEST large area CCD camera
We have designed, constructed, and put into operation a very large area CCD camera that covers the field of view of the 1.2 m Samuel Oschin Schmidt Telescope at the Palomar Observatory. The camera consists of 112 CCDs arranged in a mosaic of four rows with 28 CCDs each. The CCDs are 600 x 2400 pixel Sarnoff thinned, back-illuminated devices with 13 µm x 13 µm pixels. The camera covers an area of 4.6° x 3.6° on the sky with an active area of 9.6 deg_2. This camera has been installed at the prime focus of the telescope and commissioned, and scientific-quality observations on the Palomar-QUEST Variability Sky Survey were started in 2003 September. The design considerations, construction features, and performance parameters of this camera are described in this paper
Basic Connection between Superconductivity and Superfluidity
A basic and inherently simple connection is shown to exist between
superconductivity and superfluidity. It is shown here that the author's
previously derived general equation which agrees well with the superconducting
transition temperatures for the heavy-electron superconductors, metallic
superconductors, oxide supercon- ductors, metallic hydrogen, and neutron stars,
also works well for the superfluid transition temperature of 2.6 mK for liquid
3He. Reasonable estimates are made from 10^-3 K to 10^9K -- a range of 12
orders of magnitude. The same paradigm applies to the superfluid transition
temperature of liquid 4He, but results in a slightly different equation. The
superfluid transition temperature for dilute solutions of 3He in superfluid 4He
is estimated to be ~ 1 to 10mK. This paradigm works well in detail for
metallic, cuprate, and organic superconductors.Comment: 16 pages, 2 figure
Satellites of the largest Kuiper Belt objects
We have searched the four brightest objects in the Kuiper Belt for the presence of satellites using the newly commissioned Keck Observatory Laser Guide Star Adaptive Optics system. Satellites are seen around three of the four objects: Pluto (whose satellite Charon is well-known and whose recently discovered smaller satellites are too faint to be detected), 2003 EL61 (where a second satellite is seen in addition to the previously known satellite), and 2003 UB313 (where a satellite is seen for the first time). The object 2005 FY9, the brightest Kuiper Belt object (KBO) after Pluto, does not have a satellite detectable within 0".4 with a brightness of more than 1% of the primary. The presence of satellites around three of the four brightest KBOs is inconsistent with the fraction of satellites in the Kuiper Belt at large at the 99.2% confidence level, suggesting a different formation mechanism for these largest KBO satellites. The two satellites of 2003 EL61, and the one satellite of 2003 UB313, with fractional brightnesses of 5% and 1.5%, and 2%, of their primaries, respectively, are significantly fainter relative to their primaries than other known KBO satellites, again pointing to possible differences in their origin
Transneptunian objects and Centaurs from light curves
We analyze a vast light curve database by obtaining mean rotational
properties of the entire sample, determining the spin frequency distribution
and comparing those data with a simple model based on hydrostatic equilibrium.
For the rotation periods, the mean value obtained is 6.95 h for the whole
sample, 6.88 h for the Trans-neptunian objects (TNOs) alone and 6.75 h for the
Centaurs. From Maxwellian fits to the rotational frequencies distribution the
mean rotation rates are 7.35 h for the entire sample, 7.71 h for the TNOs alone
and 8.95 h for the Centaurs. These results are obtained by taking into account
the criteria of considering a single-peak light curve for objects with
amplitudes lower than 0.15 mag and a double-peak light curve for objects with
variability >0.15mag. The best Maxwellian fits were obtained with the threshold
between 0.10 and 0.15mag. The mean light-curve amplitude for the entire sample
is 0.26 mag, 0.25mag for TNOs only, and 0.26mag for the Centaurs. The amplitude
versus Hv correlation clearly indicates that the smaller (and collisionally
evolved) objects are more elongated than the bigger ones. From the model
results, it appears that hydrostatic equilibrium can explain the statistical
results of almost the entire sample, which means hydrostatic equilibrium is
probably reached by almost all TNOs in the H range [-1,7]. This implies that
for plausible albedos of 0.04 to 0.20, objects with diameters from 300km to
even 100km would likely be in equilibrium. Thus, the great majority of objects
would qualify as being dwarf planets because they would meet the hydrostatic
equilibrium condition. The best model density corresponds to 1100 kg/m3.Comment: 21 pages, 8 figures. Astronomy & Astrophysics, in pres
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