657 research outputs found
The Ever Changing Circumstellar Nebula Around UW Centauri
We present new images of the reflection nebula surrounding the R Coronae
Borealis Star, UW Cen. This nebula, first detected in 1990, has changed its
appearance significantly. At the estimated distance of UW Cen, this nebula is
approximately 0.6 ly in radius so the nebula cannot have physically altered in
only 8 years. Instead, the morphology of the nebula appears to change as
different parts are illuminated by light from the central star modulated by
shifting thick dust clouds near its surface. These dust clouds form and
dissipate at irregular intervals causing the well-known declines in the R
Coronae Borealis (RCB) stars. In this way, the central star acts like a
lighthouse shining through holes in the dust clouds and lighting up different
portions of the nebula. The existence of this nebula provides clues to the
evolutionary history of RCB stars possibly linking them to the Planetary
Nebulae and the final helium shell flash stars.Comment: To be published in ApJ Letters. 5 pages, 3 figures (2 in color
Study of the Fusion-Fission Process in the Reaction
Fusion-fission and fully energy-damped binary processes of the
Cl+Mg reaction were investigated using particle-particle
coincidence techniques at a Cl bombarding energy of E
8 MeV/nucleon. Inclusive data were also taken in order to determine the partial
wave distribution of the fusion process. The fragment-fragment correlation data
show that the majority of events arises from a binary-decay process with a
relatively large multiplicity of secondary light-charged particles emitted by
the two primary excited fragments in the exit channel. No evidence is observed
for ternary-breakup processes, as expected from the systematics recently
established for incident energies below 15 MeV/nucleon and for a large number
of reactions. The binary-process results are compared with predictions of
statistical-model calculations. The calculations were performed using the
Extended Hauser-Feshbach method, based on the available phase space at the
scission point of the compound nucleus. This new method uses
temperature-dependent level densities and its predictions are in good agreement
with the presented experimental data, thus consistent with the fusion-fission
origin of the binary fully-damped yields.Comment: 30 pages standard REVTeX file, 10 eps Figures; to be published at the
European Physical Journal A - Hadrons and Nucle
One, two, or three stars? An investigation of an unusual eclipsing binary candidate undergoing dramatic period changes
We report our investigation of 1SWASP J234401.81-212229.1, a variable with a 18 461.6 s period. After identification in a 2011 search of the SuperWASP archive for main-sequence eclipsing binary candidates near the distribution's short-period limit of ~0.20 d, it was measured to be undergoing rapid period decrease in our earlier work, though later observations supported a cyclic variation in period length. Spectroscopic data obtained in 2012 with the Southern African Large Telescope did not, however, support the interpretation of the object as a normal eclipsing binary. Here, we consider three possible explanations consistent with the data: a single-star oblique rotator model in which variability results from stable cool spots on opposite magnetic poles; a two-star model in which the secondary is a brown dwarf; and a three-star model involving a low-mass eclipsing binary in a hierarchical triple system. We conclude that the latter is the most likely model
The spin-orbit alignment of the transiting exoplanet WASP-3b from Rossiter-McLaughlin observations
We present an observation of the Rossiter-McLaughlin effect for the planetary
system WASP-3. Radial velocity measurements were made during transit using the
SOPHIE spectrograph at the 1.93m telescope at Haute-Provence Observatory. The
shape of the effect shows that the sky-projected angle between the stellar
rotation axis and planetary orbital axis (lambda) is small and consistent with
zero within 2 sigma; lambda = 15 +10/-9 deg. WASP-3b joins the ~two-thirds of
planets with measured spin-orbit angles that are well aligned and are thought
to have undergone a dynamically-gentle migration process such as planet-disc
interactions. We find a systematic effect which leads to an anomalously high
determination of the projected stellar rotational velocity (vsini = 19.6
+2.2/-2.1 km/s) compared to the value found from spectroscopic line broadening
(vsini = 13.4 +/- 1.5 km/s). This is thought to be caused by a discrepancy in
the assumptions made in the extraction and modelling of the data. Using a model
developed by Hirano et al. (2009) designed to address this issue, we find vsini
to be consistent with the value obtained from spectroscopic broadening
measurements (vsini = 15.7 +1.4/-1.3 km/s).Comment: 7 pages, 3 figures, published in MNRAS 405 (2010) 1867-1872. Update
includes discussion on differential rotaation and correction of typo
Qatar-1b: a hot Jupiter orbiting a metal-rich K dwarf star
We report the discovery and initial characterisation of Qatar-1b, a hot
Jupiter orbiting a metal-rich K dwarf star, the first planet discovered by the
Alsubai Project exoplanet transit survey. We describe the strategy used to
select candidate transiting planets from photometry generated by the Alsubai
Project instrument. We examine the rate of astrophysical and other false
positives found during the spectroscopic reconnaissance of the initial batch of
candidates. A simultaneous fit to the follow-up radial velocities and
photometry of Qatar-1b yield a planetary mass of 1.09+/-0.08 Mjup and a radius
of 1.16+/-0.05 Rjup. The orbital period and separation are 1.420033 days and
0.0234 AU for an orbit assumed to be circular. The stellar density, effective
temperature and rotation rate indicate an age greater than 4 Gyr for the
system.Comment: 8 pages, 5 figures, submitted to Monthly Notices of the Royal
Astronomical Societ
WASP-43b: The closest-orbiting hot Jupiter
We report the discovery of WASP-43b, a hot Jupiter transiting a K7V star
every 0.81 d. At 0.6-Msun the host star has the lowest mass of any star hosting
a hot Jupiter. It also shows a 15.6-d rotation period. The planet has a mass of
1.8 Mjup, a radius of 0.9 Rjup, and with a semi-major axis of only 0.014 AU has
the smallest orbital distance of any known hot Jupiter. The discovery of such a
planet around a K7V star shows that planets with apparently short remaining
lifetimes owing to tidal decay of the orbit are also found around stars with
deep convection zones.Comment: 4 page
WASP-44b, WASP-45b and WASP-46b: three short-period, transiting extrasolar planets
We report the discovery of three extrasolar planets that transit their
moderately bright (Vmag = 12-13) host stars. WASP-44b is a 0.89-MJup planet in
a 2.42-day orbit around a G8V star. WASP-45b is a 1.03-MJup planet which passes
in front of the limb of its K2V host star every 3.13 days. Weak Ca II H+K
emission seen in the spectra of WASP-45 suggests the star is chromospherically
active. WASP-46b is a 2.10-MJup planet in a 1.43-day orbit around a G6V star.
Rotational modulation of the light curves of WASP-46 and weak Ca II H+K
emission in its spectra show the star to be photospherically and
chromospherically active.
We imposed circular orbits in our analyses as the radial velocity data are
consistent with (near-)circular orbits, as could be expected from both
empirical and tidal-theory perspectives for such short-period, Jupiter-mass
planets. We discuss the impact of fitting for eccentric orbits for such planets
when not supported by the data. The derived planetary and stellar radii depend
on the fitted eccentricity and these parameters inform intense theoretical
efforts concerning tidal circularisation and heating, bulk planetary
composition and the observed systematic errors in planetary and stellar radii.
As such, we recommend exercising caution in fitting the orbits of short period,
Jupiter-mass planets with an eccentric model when there is no evidence of
non-circularity.Comment: 12 pages, 8 figures, 6 tables. As accepted for publication in MNRA
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