9,136 research outputs found
Stellar Populations and Ages of M82 Super Star Clusters
We present high signal-to-noise optical spectra of two luminous super star
clusters in the starburst galaxy M82. The data for cluster F and the nearby,
highly reddened cluster L were obtained with the William Herschel Telescope
(WHT) at a resolution of 1.6A. The blue spectrum (3250-5540A) of cluster F
shows features typical of mid-B stars. The red spectra (5730-8790A) of clusters
F and L show the Ca II triplet and numerous F and G-type absorption features.
Strong Ca II and Na I interstellar absorption lines arising in M82 are also
detected, and the 6283A diffuse interstellar band appears to be present. The
quality of the WHT spectra allows us to considerably improve previous age
estimates for cluster F. By comparing the blue spectrum with theoretical model
cluster spectra using the PEGASE spectral synthesis code (Fioc &
Rocca-Volmerange 1997), we derive an age of 60+/-20 Myr. The strength of the Ca
II triplet is also in accord with this age. Cluster L appears to have a similar
age, although this is much less certain. The measured radial velocities for the
two clusters differ substantially, indicating that they are located in
different regions of the M82 disk. Cluster F appears to be deep in M82,
slightly beyond the main starburst region while the highly obscured cluster L
lies near the outer edges of the disk. We derive an absolute V magnitude of
-16.5 for F indicating that it is an extremely massive cluster. The presence of
such a luminous super star cluster suggests that the M82 starburst experienced
an episode of intense star formation approximately 60 Myr ago.Comment: 10 pages and 5 figures for publication in MNRA
Expansion of epicyclic gear dynamic analysis program
The multiple mesh/single stage dynamics program is a gear tooth analysis program which determines detailed geometry, dynamic loads, stresses, and surface damage factors. The program can analyze a variety of both epicyclic and single mesh systems with spur or helical gear teeth including internal, external, and buttress tooth forms. The modifications refine the options for the flexible carrier and flexible ring gear rim and adds three options: a floating Sun gear option; a natural frequency option; and a finite element compliance formulation for helical gear teeth. The option for a floating Sun incorporates two additional degrees of freedom at the Sun center. The natural frequency option evaluates the frequencies of planetary, star, or differential systems as well as the effect of additional springs at the Sun center and those due to a flexible carrier and/or ring gear rim. The helical tooth pair finite element calculated compliance is obtained from an automated element breakup of the helical teeth and then is used with the basic gear dynamic solution and stress postprocessing routines. The flexible carrier or ring gear rim option for planetary and star spur gear systems allows the output torque per carrier and ring gear rim segment to vary based on the dynamic response of the entire system, while the total output torque remains constant
Oral History Interview: Linda Smith
This interview is one of a series conducted with former employees of the Huntington Owens-Illinois, Inc. glass bottle factory. Linda Smith worked at the Owens-Illinois glass plant for 23 years, and talks about her experiences at the factory, including subjects such as race relations and woman in business. She also comments on the factory going from high ranking to low when new management stepped in, discusses medical insurance/benefits, and discusses her fear over her lack of employment opportunities after the plant closed.https://mds.marshall.edu/oral_history/1525/thumbnail.jp
Realistic Ionizing Fluxes for Young Stellar Populations from 0.05 to twice solar metallicity
We present a new grid of ionizing fluxes for O and Wolf-Rayet stars for use
with evolutionary synthesis codes and single star H II region analyses. A total
of 230 expanding, non-LTE, line-blanketed model atmospheres have been
calculated for five metallicities (0.05, 0.2, 0.4, 1 and 2 solar) using the
WM-basic code of Pauldrach et al. (2001) and the CMFGEN code of Hillier &
Miller (1998). The stellar wind parameters are scaled with metallicity for both
O and W-R stars. We incorporate the new models into Starburst99 (Leitherer et
al. 1999) and compare the ionizing outputs with Schaerer & Vacca (1998) and
Leitherer et al. (1999). The changes in the output ionizing fluxes are
dramatic, particularly below 228 A. We also find lower fluxes in the He I
continuum for Z > 0.4 solar and ages < 7 Myr because of the increased line
blanketing. We test the accuracy of the new models by constructing
photoionization models. We show that for the dwarf O star grid, He I 5876/H
beta decreases between Z = 1 and twice solar in a similar manner to
observations (e.g. Bresolin et al. 1999) due to the increased effect of line
blanketing. We therefore suggest that a lowering of the upper mass limit at
high abundances is not required to explain the observations. For the case of an
instantaneous burst, we plot the softness parameter "eta prime" against the
abundance indicator R_23. The new models are coincident with the data of
Bresolin et al. (1999), particularly during the W-R phase, unlike previous
models which over-predict the hardness of the ionizing radiation.Comment: 21 pages, 15 postscript colour figures, includes mn2e.cls. To be
published in MNRAS. Revised version containing modifications to Tables 1-
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