157 research outputs found
VHF discharges in storm cells producing microbursts
An experiment was carried out in which 3-D mapping of VHF sources was compared to a 3-D description of the reflectivity and dynamics of associated cloud cells observed by a radar network. Data from 61 microbursts were analyzed and it was found that, in 93 pct. of the cases, electrical activity precedes outflow development. The results confirm that the peak in intracloud activity precedes the maximum value of the outflow
Workplace bullying policies, higher education and the First Amendment: Building bridges not walls
The purpose of this article is to demonstrate that higher education institutions should change their Faculty Codes of Conduct to reflect workplace bullying as a form of unacceptable harassment. The article first provides a definition for workplace bullying; secondly, it offers an analysis of how the First Amendment is not an absolute, especially in the workplace; thirdly, it examines the scant legislative and judicial attention that is given to this issue; and finally, an argument is made to show how colleges and universities are not providing clear enough policies and procedures to address workplace bullying. That argument focuses on results of our thematic analysis of 276 Faculty Codes of Conduct from a variety of universities and colleges across the United States. That analysis revealed two primary themes: the Harassment Hang-up and Employee Engagement. Based on this analysis, we conclude that higher education institutions should change their Faculty Codes of Conduct so bullying is defined as a distinctive form of harassment, provide faculty and staff clear communications regarding how to define bullying, and offer guidance for both targets and bystanders of workplace bullying
On Echo Outbursts and ER UMa Supercycles in SU UMa-type Cataclysmic Variables
I present a variation on Osaki's tidal-thermal-instability model for SU UMa
behavior. I suggest that in systems with the lowest mass ratios, the
angular-momentum dissipation in an eccentric disk is unable to sustain the disk
on the hot side of the thermal instability. This decoupling of the tidal and
thermal instabilities in systems with q < 0.07 allows a better explanation of
the `echo' outbursts of EG Cnc and the short supercycles of RZ LMi and DI UMa.
The idea might also apply to the soft X-ray transients.Comment: To appear in PASP, April 2001 (6 pages, 4 figs
Transiting hot Jupiters from WASP-South, Euler and TRAPPIST : WASP-95b to WASP-101b
We report the discovery of the transiting exoplanets WASP-95b, WASP-96b, WASP-97b, WASP-98b, WASP-99b, WASP-100b andWASP-101b. All are hot Jupiters with orbital periods in the range 2.1-5.7 d, masses of 0.5-2.8 MJup and radii of 1.1-1.4 RJup. The orbits of all the planets are compatible with zero eccentricity. WASP-99b produces the shallowest transit yet found by WASP-South, at 0.4 per cent. The host stars are of spectral type F2-G8. Five have metallicities of [Fe/H] from -0.03 to +0.23, while WASP-98 has a metallicity of -0.60, exceptionally low for a star with a transiting exoplanet. Five of the host stars are brighter than V = 10.8, which significantly extends the number of bright transiting systems available for follow-up studies. WASP-95 shows a possible rotational modulation at a period of 20.7 d. We discuss the completeness of WASP survey techniques by comparing to the HATnet project.Publisher PDFPeer reviewe
WASP-29b: A Saturn-sized transiting exoplanet
We report the discovery of a Saturn-sized planet transiting a V = 11.3, K4
dwarf star every 3.9 d. WASP-29b has a mass of 0.24+/-0.02 M_Jup and a radius
of 0.79+/-0.05 R_Jup, making it the smallest planet so far discovered by the
WASP survey, and the exoplanet most similar in mass and radius to Saturn. The
host star WASP-29 has an above-Solar metallicity and fits a possible
correlation for Saturn-mass planets such that planets with higher-metallicity
host stars have higher core masses and thus smaller radii.Comment: 6 pages, submitted to ApJ
The phase 0.5 absorption in SW Sextantis-type cataclysmic variables
The SW Sextantis stars are a group of cataclysmic variables with distinctive
observational characteristics, including absorption features in the emission
line cores at phases 0.2-0.6. Hellier and Robinson have proposed that these
features are caused by the accretion stream flowing over the accretion disk.
However, in a simple model the absorption occurred at all orbital phases, which
is contradicted by the data. I show that invoking a flared accretion disk
resolves this problem.Comment: 4 pages, 3 figures, LaTeX, To appear in PASP. Also at
http://www.astro.keele.ac.uk/~ch
Why do some intermediate polars show soft X-ray emission? A survey of XMM-Newton spectra
We make a systematic analysis of the XMM-Newton X-ray spectra of intermediate
polars (IPs) and find that, contrary to the traditional picture, most show a
soft blackbody component. We compare the results with those from AM Her stars
and deduce that the blackbody emission arises from reprocessing of hard X-rays,
rather than from the blobby accretion sometimes seen in AM Hers. Whether an IP
shows a blackbody component appears to depend primarily on geometric factors: a
blackbody is not seen in those that have accretion footprints that are always
obscured by accretion curtains or are only visible when foreshortened on the
white-dwarf limb. Thus we argue against previous suggestions that the blackbody
emission characterises a separate sub-group of IPs which are more akin to AM
Hers, and develop a unified picture of the blackbody emission in these stars.Comment: 9 pages, 6 figures. Accepted for publication in Ap
WASP-80b has a dayside within the T-dwarf range
AHMJT is a Swiss National Science Foundation (SNSF) fellow under grant number P300P2-147773. MG and EJ are Research Associates at the F.R.S-FNRS; LD received the support the support of the F.R.I.A. fund of the FNRS. DE, KH, and SU acknowledge the financial support of the SNSF in the frame of the National Centre for Competence in Research ‘PlanetS’. EH and IR acknowledge support from the Spanish Ministry of Economy and Competitiveness (MINECO) and the ‘Fondo Europeo de Desarrollo Regional’ (FEDER) through grants AYA2012-39612-C03-01 and ESP2013-48391-C4-1-R.WASP-80b is a missing link in the study of exo-atmospheres. It falls between the warm Neptunes and the hot Jupiters and is amenable for characterisation, thanks to its host star's properties. We observed the planet through transit and during occultation with Warm Spitzer. Combining our mid-infrared transits with optical time series, we find that the planet presents a transmission spectrum indistinguishable from a horizontal line. In emission, WASP-80b is the intrinsically faintest planet whose dayside flux has been detected in both the 3.6 and 4.5 m Spitzer channels. The depths of the occultations reveal that WASP-80b is as bright and as red as a T4 dwarf, but that its temperature is cooler. If planets go through the equivalent of an L-T transition, our results would imply this happens at cooler temperatures than for brown dwarfs. Placing WASP-80b's dayside into a colour-magnitude diagram, it falls exactly at the junction between a blackbody model and the T-dwarf sequence; we cannot discern which of those two interpretations is the more likely. Flux measurements on other planets with similar equilibrium temperatures are required to establish whether irradiated gas giants, like brown dwarfs, transition between two spectral classes. An eventual detection of methane absorption in transmission would also help lift that degeneracy. We obtained a second series of high-resolution spectra during transit, using HARPS. We reanalyse the Rossiter-McLaughlin effect. The data now favour an aligned orbital solution and a stellar rotation nearly three times slower than stellar line broadening implies. A contribution to stellar line broadening, maybe macroturbulence, is likely to have been underestimated for cool stars, whose rotations have therefore been systematically overestimated. [abridged]Publisher PDFPeer reviewe
Outbursts of EX Hydrae: mass-transfer events or disc instabilities?
We present the 45-yr record of EX Hya's lightcurve and discuss the
characteristics of its 15 observed outbursts. We then concentrate on the 1998
outburst, reporting the first outburst X-ray observations. We discover an X-ray
beat-cycle modulation, indicating that an enhanced accretion stream couples
directly with the magnetosphere in outburst, confirming our previous
prediction. Optical eclipse profiles late in outburst show that the visible
light is dominated by an enhanced mass-transfer stream overflowing the
accretion disc. We are uncertain whether the enhanced mass transfer is
triggered by a disc instability, or by some other cause. While in outburst, EX
Hya shows some of the characteristics of SW Sex stars.Comment: To appear in MNRAS (8 pages; 9 figs
The thermal emission of the exoplanets WASP-1b and WASP-2b
We present a comparative study of the thermal emission of the transiting
exoplanets WASP-1b and WASP-2b using the Spitzer Space Telescope. The two
planets have very similar masses but suffer different levels of irradiation and
are predicted to fall either side of a sharp transition between planets with
and without hot stratospheres. WASP-1b is one of the most highly irradiated
planets studied to date. We measure planet/star contrast ratios in all four of
the IRAC bands for both planets (3.6-8.0um), and our results indicate the
presence of a strong temperature inversion in the atmosphere of WASP-1b,
particularly apparent at 8um, and no inversion in WASP-2b. In both cases the
measured eclipse depths favor models in which incident energy is not
redistributed efficiently from the day side to the night side of the planet. We
fit the Spitzer light curves simultaneously with the best available radial
velocity curves and transit photometry in order to provide updated measurements
of system parameters. We do not find significant eccentricity in the orbit of
either planet, suggesting that the inflated radius of WASP-1b is unlikely to be
the result of tidal heating. Finally, by plotting ratios of secondary eclipse
depths at 8um and 4.5um against irradiation for all available planets, we find
evidence for a sharp transition in the emission spectra of hot Jupiters at an
irradiation level of 2 x 10^9 erg/s/cm^2. We suggest this transition may be due
to the presence of TiO in the upper atmospheres of the most strongly irradiated
hot Jupiters.Comment: 10 pages, submitted to Ap
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