1,275 research outputs found
Can stellar activity make a planet seem misaligned?
Several studies have shown that the occultation of stellar active regions by
the transiting planet can generate anomalies in the high-precision transit
light curves, and these anomalies may lead to an inaccurate estimate of the
planetary parameters (e.g., the planet radius). Since the physics and geometry
behind the transit light curve and the Rossiter- McLaughlin effect
(spectroscopic transit) are the same, the Rossiter-McLaughlin observations are
expected to be affected by the occultation of stellar active regions in a
similar way. In this paper we perform a fundamental test on the spin-orbit
angles as derived by Rossiter-McLaughlin measurements, and we examine the
impact of the occultation of stellar active regions by the transiting planet on
the spin-orbit angle estimations. Our results show that the inaccurate
estimation on the spin-orbit angle due to stellar activity can be quite
significant (up to 30 degrees), particularly for the edge-on, aligned, and
small transiting planets. Therefore, our results suggest that the aligned
transiting planets are the ones that can be easily misinterpreted as misaligned
owing to the stellar activity. In other words, the biases introduced by
ignoring stellar activity are unlikely to be the culprit for the highly
misaligned systems.Comment: 8 pages, 8 figures, accepted for publication in Astronomy &
Astrophysic
Geometry Technology Module (GTM). Volume 1: Engineering description and utilization manual
The geometry technology module (GTM) is described as a system of computerized elements residing in the engineering design integration system library developed for the generation, manipulation, display, computation of mass properties, and data base management of panelled geometry. The GTM is composed of computer programs and associated data for performing configuration analysis on geometric shapes. The program can be operated in batch or demand mode and is designed for interactive use
Magnetic cycles of the planet-hosting star Tau Bootis: II. a second magnetic polarity reversal
In this paper, we present new spectropolarimetric observations of the
planet-hosting star Tau Bootis, using ESPaDOnS and Narval spectropolarimeters
at Canada-France-Hawaii Telescope (CFHT) and Telescope Bernard Lyot (TBL),
respectively. We detected the magnetic field of the star at three epochs in
2008. It is a weak magnetic field of only a few Gauss, oscillating between a
predominant toroidal component in January and a dominant poloidal component in
June and July. A magnetic polarity reversal was observed relative to the
magnetic topology in June 2007. This is the second such reversal observed in
two years on this star, suggesting that Tau Boo has a magnetic cycle of about 2
years. This is the first detection of a magnetic cycle for a star other than
the Sun. The role of the close-in massive planet in the short activity cycle of
the star is questioned.
Tau Boo has strong differential rotation, a common trend for stars with
shallow convective envelope. At latitude 40 deg., the surface layer of the star
rotates in 3.31 d, equal to the orbital period. Synchronization suggests that
the tidal effects induced by the planet may be strong enough to force at least
the thin convective envelope into corotation. Tau Boo shows variability in the
Ca H & K and Halpha throughout the night and on a night to night time scale. We
do not detect enhancement in the activity of the star that may be related to
the conjunction of the planet. Further data is needed to conclude about the
activity enhancement due to the planet.Comment: 9 pages, 5 figures, 3 tables Accepted to MNRA
Rapid magnetic flux variability on the flare star CN Leonis
We present UVES/VLT observations of the nearby flare star CN Leo covering the
Wing-Ford FeH band near 1mu with high spectral resolution. Some of the FeH
absorption lines in this band are magnetically sensitive and allow a
measurement of the mean magnetic flux on CN Leo. Our observations, covering
three nights separated by 48 hours each, allow a clear detection of a mean
magnetic field of Bf~2.2kG. The differential flux measurements show a
night-to-night variability with extremely high significance. Finally, our data
strongly suggest magnetic flux variability on time scales as low as 6 hours in
line with chromospheric variability.Comment: 4 pages, accepted for publication as A&A Lette
Multi-wavelength observations of Proxima Centauri
We report simultaneous observations of the nearby flare star Proxima Centauri
with VLT/UVES and XMM-Newton over three nights in March 2009. Our optical and
X-ray observations cover the star's quiescent state, as well as its flaring
activity and allow us to probe the stellar atmospheric conditions from the
photosphere into the chromosphere, and then the corona during its different
activity stages. Using the X-ray data, we investigate variations in coronal
densities and abundances and infer loop properties for an intermediate-sized
flare. The optical data are used to investigate the magnetic field and its
possible variability, to construct an emission line list for the chromosphere,
and use certain emission lines to construct physical models of Proxima
Centauri's chromosphere.
We report the discovery of a weak optical forbidden Fe xiii line at 3388 AA
during the more active states of Proxima Centauri. For the intermediate flare,
we find two secondary flare events that may originate in neighbouring loops,
and discuss the line asymmetries observed during this flare in H i, He i, and
Ca ii lines. The high time-resolution in the H alpha line highlights strong
temporal variations in the observed line asymmetries, which re-appear during a
secondary flare event. We also present theoretical modelling with the stellar
atmosphere code PHOENIX to construct flaring chromospheric models.Comment: 19 pages, 22 figures, accepted by A&
Chromospheric Variability in SDSS M Dwarfs. II. Short-Timescale H-alpha Variability
[Abridged] We present the first comprehensive study of short-timescale
chromospheric H-alpha variability in M dwarfs using the individual 15 min
spectroscopic exposures for 52,392 objects from the Sloan Digital Sky Survey.
Our sample contains about 10^3-10^4 objects per spectral type bin in the range
M0-M9, with a total of about 206,000 spectra and a typical number of 3
exposures per object (ranging up to a maximum of 30 exposures). Using this
extensive data set we find that about 16% of the sources exhibit H-alpha
emission in at least one exposure, and of those about 45% exhibit H-alpha
emission in all of the available exposures. Within the sample of objects with
H-alpha emission, only 26% are consistent with non-variable emission,
independent of spectral type. The H-alpha variability, quantified in terms of
the ratio of maximum to minimum H-alpha equivalent width (R_EW), and the ratio
of the standard deviation to the mean (sigma_EW/), exhibits a rapid rise
from M0 to M5, followed by a plateau and a possible decline in M9 objects. In
particular, R_EW increases from a median value of about 1.8 for M0-M3 to about
2.5 for M7-M9, and variability with R_EW>10 is only observed in objects later
than M5. For the combined sample we find that the R_EW values follow an
exponential distribution with N(R_EW) exp[-(R_EW-1)/2]; for M5-M9 objects the
characteristic scale is R_EW-1\approx 2.7, indicative of stronger variability.
In addition, we find that objects with persistent H-alpha emission exhibit
smaller values of R_EW than those with intermittent H-alpha emission. Based on
these results we conclude that H-alpha variability in M dwarfs on timescales of
15 min to 1 hr increases with later spectral type, and that the variability is
larger for intermittent sources.Comment: Submitted to ApJ; 20 pages, 15 figure
The engineering design integration (EDIN) system
A digital computer program complex for the evaluation of aerospace vehicle preliminary designs is described. The system consists of a Univac 1100 series computer and peripherals using the Exec 8 operating system, a set of demand access terminals of the alphanumeric and graphics types, and a library of independent computer programs. Modification of the partial run streams, data base maintenance and construction, and control of program sequencing are provided by a data manipulation program called the DLG processor. The executive control of library program execution is performed by the Univac Exec 8 operating system through a user established run stream. A combination of demand and batch operations is employed in the evaluation of preliminary designs. Applications accomplished with the EDIN system are described
Integrated aircraft scheduling problem: An auto-adapting algorithm to find robust aircraft assignments for large flight plans
The overall airline scheduling process involves hierarchical steps starting with the network design and ending with crew assignment. Aircraft routing is especially important with respect to timing and costs for an airline. In this contribution, we focus on aircraft routing where aircraft are assigned to flight legs further considering maintenance requirements. We developed and implemented algorithms that extend the aircraft routing problem (ARP) by including profit and robustness. The latter objective is important as the dependencies of flights and airlines increases and deviations to the original time plan as unexpected events like volcano eruptions or heavy weather-related issues are difficult to handle. A robust aircraft routing ensures that unforeseen events have less impact. The results are compared to current state-of-the-art solutions. We developed a test instance-generator to create specific problems and build a library for future benchmarking tests
Enterprise gamification systems and employment legislation: a systematic literature review
A recent innovation in employee motivation systems is the introduction of ‘gamification’, which refers to the use of game design mechanics and principles to influence behaviour to enhance staff motivation and engagement. Enterprise gamification systems aggravate the differences in information availability between employers and employees, and employees who may be forced to adopt such systems may be placed under stress, worsening employment relationships in the workplace. Therefore, this research examines the potential legal implications of gamified employee motivation systems. This study undertook a systematic review of enterprise gamification and then used thematic analysis coupled with a review of legislation to examine whether gamification in workplaces meets the legal obligations of employers under their ‘duty of good faith’ in the New Zealand context. We find that carefully designed enterprise gamification systems should provide sufficient information and clarity for employees and support positive employment relationships. Deployments of enterprise gamification systems should be carefully planned with employee consultation and feedback supporting the introduction of an enterprise gamification system. Future research should look beyond the ‘good faith’ obligation and examine the relationship between gamification systems and the law on personal grievances
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