1,183 research outputs found
The [O III] Veil: Astropause of Eta Carinae's Wind?
We present narrowband images of eta Carinae in the light of [O III] 5007
obtained with HST/WFPC2, as well as a ground-based image in the same emission
line with a larger field of view. These images show a thin veil of [O III]
emission around eta Car and its ejecta, confirming the existence of an
oxygen-bearing ``cocoon'' inferred from spectra. This [O III] veil may be the
remnant of the pre-outburst wind of eta Car, and its outer edge probably marks
the interface where eta Car's ejecta meet the stellar wind of the nearby O4
V((f)) star HD303308 or other ambient material -- i.e., it marks the
``astropause'' in eta Car's wind. This veil is part of a more extensive [O III]
shell that appears to be shaped and ionized by HD303308. A pair of HST images
with a 10 yr baseline shows no proper motion, limiting the expansion speed away
from eta Car to 12pm13 km/s, or an expansion age of a few times 10^4 yr. Thus,
this is probably the decelerated pre-outburst LBV wind of eta Car. The [O III]
morphology is very different from that seen in [N II], which traces young knots
of CNO-processed material; this represents a dramatic shift in the chemical
makeup of material recently ejected by eta Car. This change in the chemical
abundances may have resulted from the sudden removal of the star's outer
envelope during eta Car's 19th century outburst or an earlier but similar
event.Comment: 11 pages, 4 figs. Figs 1 and 3 in color. Accepted to AJ, October 200
Spectroscopy and Time Variability of Absorption Lines in the Direction of the Vela Supernova Remnant
We present high resolution (R~75,000), high signal-to-noise (S/N~100) Ca II
3933.663 and Na I 5889.951, 5895.924 spectra of 68
stars in the direction of the Vela supernova remnant. The spectra comprise the
most complete high resolution, high S/N, optical survey of early type stars in
this region of the sky. A subset of the sight lines has been observed at
multiple epochs, 1993/1994 and 1996. Of the thirteen stars observed twice,
seven have spectra revealing changes in the equivalent width and/or velocity
structure of lines, most of which arise from remnant gas. Such time variability
has been reported previously for the sight lines towards HD 72089 and HD 72997
by Danks & Sembach (1995) and for HD 72127 by Hobbs et al. (1991). We have
confirmed the ongoing time variability of these spectra and present new
evidence of variability in the spectra of HD 73658, HD 74455, HD 75309 and HD
75821. We have tabulated Na I and Ca II absorption line information for the
sight lines in our sample to serve as a benchmark for further investigations of
the dynamics and evolution of the Vela SNR.Comment: 8 pages of text, 4 tables, 16 pages of figures Accepted and to be
published in ApJ
Variability in shape of the dental arcade of Homo sapiens in Late Pleistocene and modern samples from southern Africa
Mandibles are among the most common skeletal elements of Late Pleistocene specimens of Homo sapiens from southern African sites (notably Klasies River Mouth and Border Cave). For this reason mandibles have been selected for study to compare with samples drawn from modem populations (including South African negroes, Khoisanoid "Bushmen" and caucasoids). An analysis of shape of the dental arcade, based on the spatial distribution of molars, premolars and canines, indicates that several of the Late Pleistocene samples (including KRM 41815) are outside the range of variation found in modem African and caucasoid populations, and in this respect, cannot be described as "anatomically modem", sensu strictu. There appears to be a trend in the process of modernisation, from very flared dental arcades (notably in the case of the Kabwe skull, representing "archaic" H. sapiens), through moderately flared arcades (as found in Late Pleistocene "nearly modem" samples) towards a less flared condition which is found in modern Africans and caucasoids.Foundation for Research Developmen
Nautilus, Inc.: Dealing With a Lone Wolf in the Sales Team
Headquartered in Vancouver, Washington, Nautilus Inc. is a global fitness products company providing innovative, quality solutions to help people achieve a healthy lifestyle. With a brand portfolio including Nautilus®, Bowflex®, Schwinn®, and Universal®, Nautilus markets innovative fitness products through direct and retail channels (Bean 2013).”
Nautilus, Inc. has a strong sales organization with remarkably low turnover of salespeople. They take a consultative approach to sales. Among the group, however, is a “lone wolf” who generally makes transactional sales rather than being consultative and focuses on her individual results rather than the objectives of the company. At the same time, she has the top sales results of the group. She also has an outstanding work ethic and works very hard. She is good at multi-tasking and never takes breaks between calls to rest or socialize with co-workers.
There are several potential issues in this case. The objective is to determine how to optimize the effectiveness of the sales organization. Part of that is determining how to deal with the lone wolf. How do her methods and results affect the rest of the sales team? Do her results justify her methods, or is it more important to have everyone following the company direction of consultative selling
Pourbaix-like phase diagram for lithium manganese spinels in acid
Calculations are performed on the free energies for proton-promoted reactions of the lithium-ion-battery electrode material LiMn_(2)O_4 spinel in acid, as a function of lithium excess and lithium deficiency relative to stoichiometry. In particular, we consider the dissolution reaction proposed by Hunter (J. Solid State Chem., 1981, 39, 142), in which protons react with lithium manganate spinel to form λ-MnO2, Li^+, and Mn^(2+) products. The calculations employ a hybrid method developed in previous work in which first principles total energy calculations are applied for the solid phases and free atom energies, and tabulated ionization and hydration energies for the aqueous species. A correction to the atomic energies, derived from analysis of binary oxide dissolution reactions, improves the accuracy of the results. A Pourbaix-like dissolution/stability phase diagram is constructed from the resultant reaction free energies
Fe VII lines in the spectrum of RR Telescopii
Thirteen transitions within the ground 3d^2 configuration of Fe VII are
identified in ultraviolet and optical spectra of the symbiotic star RR
Telescopii obtained with the STIS instrument of the Hubble Space Telescope. The
line fluxes are compared with theoretical data computed with the recent atomic
data of K.A. Berrington et al., and high resolution optical spectra from
VLT/UVES are used to identify blends. Seven branching ratios are measured, with
three in good agreement with theory and one affected by blending. The
lambda5277/lambda4943 branching ratio is discrepant by > 3 sigma, indicating
errors in the atomic data for the lambda5277 line. A least-squares minimization
scheme is used to simultaneously derive the temperature, T, and density, N_e,
of the RR Tel nebula, and the interstellar extinction, E(B-V), towards RR Tel
from the complete set of emission lines. The derived values are: log T/K = 4.50
+/- 0.23, log N_e/cm^-3=7.25 +/- 0.05, and E(B-V)<0.27. The extinction is not
well-constrained by the Fe VII lines, but is consistent with the more accurate
value E(B-V)=0.109^{+0.052}_{-0.059} derived here from the Ne V
lambda2974/lambda1574 ratio in the STIS spectrum. Large differences between the
K.A. Berrington et al. electron excitation data and the earlier F.P. Keenan &
P.H. Norrington data-set are demonstrated, and the latter is shown to give
worse agreement with observations.Comment: To be published in Astronomy & Astrophysics; 7 pages, 4 figure
Accretion onto the Companion of Eta Carinae During the Spectroscopic Event: III. the He II 4686 Line
We continue to explore the accretion model of the massive binary system eta
Carinae by studying the anomalously high He II 4686 line. The line appears just
before periastron and disappears immediately thereafter. Based on the He II
4686 line emission from O-stars and their modeling in the literature, we
postulate that the He II 4686 line comes from the acceleration zone of the
secondary stellar wind. We attribute the large increase in the line intensity
to a slight increase in the density of the secondary stellar wind in its
acceleration zone. The increase in density could be due to the ionization and
subsequent deceleration of the wind by the enhanced X-ray emission arising from
the shocked secondary wind further downstream or to accretion of the primary
stellar wind. Accretion around the secondary equatorial plane gives rise to
collimation of the secondary wind, which increases its density, hence enhancing
the He II 4686 emission line. In contrast with previous explanations, the
presently proposed model does not require a prohibitively high X-ray flux to
directly photoionize the He.Comment: ApJ, in pres
Characterisation of the magnetic field of the Herbig Be star HD 200775
After our recent discovery of four magnetic Herbig stars, we have decided to
study in detail one of them, HD 200775, to determine if its magnetic topology
is similar to that of the main sequence magnetic stars. With this aim, we
monitored this star in Stokes I and V over more than two years, using the new
spectropolarimeters ESPaDOnS at CFHT, and Narval at TBL. Using our data, we
find that HD 200775 is a double-lined spectroscopic binary system, whose
secondary seems similar, in temperature, to the primary. We determine the
luminosity ratio of the system, and using the luminosity of the system found in
literature, we derive the luminosity of both stars. From our measurements of
the radial velocities of both stars we determine the ephemeris and the orbital
parameters of the system. We have fitted 30 Stokes V profiles simultaneously,
using a chi2 minimisation method, with a decentered-dipole model. The best-fit
model provides a rotation period of 4.3281 d an inclination angle of 60
degrees, and a magnetic obliquity angle of 125 degrees. The polar strength of
the magnetic dipole field is 1000 G, which is decentered by 0.05 R* from the
center of the star. The derived magnetic field model is qualitatively identical
to those commonly observed in the Ap/Bp stars, which bring strong argument in
favour of the fossil field hypothesis, to explain the origin of the magnetic
fields in the main sequence Ap/Bp stars. Our determination of the inclination
of the rotation axis leads to a radius of the primary which is smaller than
that derived from the HR diagram position. This can be explained by a larger
intrinsic luminosity of the secondary relative to the primary, due to a larger
circumstellar extinction of the secondary relative to the primary.Comment: Accepted for publication in MNRAS, 14 pages, 10 figure
On the He II Emission In Eta Carinae and the Origin of Its Spectroscopic Events
We describe and analyze Hubble Space Telescope (HST) observations of
transient emission near 4680 {\AA} in Eta Car, reported earlier by Steiner &
Damineli (2004). If, as seems probable, this is He II 4687, then it is
a unique clue to Eta Car's 5.5-year cycle. According to our analysis, several
aspects of this feature support a mass-ejection model of the observed
spectroscopic events, and not an eclipse model. The He II emission appeared in
early 2003, grew to a brief maximum during the 2003.5 spectroscopic event, and
then abruptly disappeared. It did not appear in any other HST spectra before or
after the event. The peak brightness was larger than previously reported, and
is difficult to explain even if one allows for an uncertainty factor of order
3. The stellar wind must provide a temporary larger-than-normal energy supply,
and we describe a special form of radiative amplification that may also be
needed. These characteristics are consistent with a class of mass-ejection or
wind-disturbance scenarios, which have implications for the physical structure
and stability of Eta Car.Comment: 47 pages (including all appendices, tabs, & figs), 9 figures, 3
tables; submitted to Astrophysical Journal (2005 March 29), accepted for
publication in Ap
- …