245,302 research outputs found
Synthetic spectra of H Balmer and HeI absorption lines. II: Evolutionary synthesis models for starburst and post-starburst galaxies
We present evolutionary stellar population synthesis models to predict the
spectrum of a single-metallicity stellar population, with a spectral sampling
of 0.3 A in five spectral regions between 3700 and 5000 A. The models, which
are optimized for galaxies with active star formation, synthesize the profiles
of the hydrogen Balmer series (Hb, Hg, Hd, H8, H9, H10, H11, H12 and H13) and
the neutral helium absorption lines (HeI 4922, HeI 4471, HeI 4388, HeI 4144,
HeI 4121, HeI 4026, HeI 4009 and HeI 3819) for a burst with an age ranging from
1 to 1000 Myr, and different assumptions about the stellar initial mass
function. Continuous star formation models lasting for 1 Gyr are also
presented. The input stellar library includes NLTE absorption profiles for
stars hotter than 25000 K and LTE profiles for lower temperatures. The
temperature and gravity coverage is 4000 K <Teff< 50000 K and 0.0< log g$< 5.0,
respectively.
The models can be used to date starburst and post-starburst galaxies until 1
Gyr. They have been tested on data for clusters in the LMC, the super-star
cluster B in the starburst galaxy NGC 1569, the nucleus of the dwarf elliptical
NGC 205 and a luminous "E+A" galaxy. The full data set is available for
retrieval at http://www.iaa.es/ae/e2.html and at
http://www.stsci.edu/science/starburst/, or on request from the authors at
[email protected]: To be published in ApJS. 48 pages and 20 figure
Christian Higher Education and Students with Diverse Beliefs: Impacts and Challenges
The ethos, mission, and values of Christian Higher Education Institutions (HEIs) are usually grounded in a biblical worldview. Increasingly, Christian HEIs are attracting students who do not share the faith espoused by the institutions they attend. This qualitative case study explored the perceptions of six final-year education students with different belief frameworks to those of the Christian HEI they attended. They were interviewed to determine their perceptions of the transparency of the ethos, mission, and values of the HEI, the impact of the HEI on their lives, and the challenges they faced as students. The data revealed some positive impacts and some challenges for both the students and the Christian HEI and identified an overarching factor that moderated the identified tensions. Introductio
On the sensitivity of HeI singlet lines to the FeIV model atom in O stars
Recent calculations and analyses of O star spectra have revealed
discrepancies between theory and observations, and between different
theoretical calculations, for the strength of optical HeI singlet
transitions.We investigate the source of these discrepancies. Using a non-LTE
radiative transfer code we have undertaken detailed test calculations for a
range of O star properties. Our principal test model has parameters similar to
those of the O9V star, 10 Lac. We show that the discrepancies arise from
uncertainties in the radiation field in the HeI resonance transition near
584Angs. The radiation field at 584Angs. is influenced by model assumptions,
such as the treatment of line-blanketing and the adopted turbulent velocity,
and by the FeIV atomic data. It isshown that two FeIV transitions near 584Angs
can have a substantial influence on the strength of the HeI singlet
transitions. Because of the difficulty of modeling the HeI singlet lines,
particularly in stars with solar metalicity, the HeI triplet lines should be
preferred in spectral analyses. These lines are much less sensitive to model
assumptions.Comment: 7 pages, 9 figures, accepted for publication in A&
A non-LTE spectral analysis of the 3He and 4He isotopes in the HgMn star kappa Cancri
We present a pilot study on non-local thermodynamic equilibrium (NLTE)
line-formation computations for the isotopes 3He and 4He in the
mercury-manganese star kappa Cancri. The impact of NLTE effects on the
determination of isotopic abundances and the vertical stratification of helium
in the atmosphere is investigated. Modern NLTE line-formation computations were
employed to analyse a high-resolution and high signal-to-noise ratio
ESO-VLT/UVES spectrum of kap Cnc. The atmospheric parameters were determined
from fitting the hydrogen Balmer lines and the spectral energy distribution.
Multiple HeI lines were investigated, including HeI 4921A and 6678A, which show
the widest isotopic splits. Half of the observed HeI lines in the spectrum of
kap Cnc show significant NLTE strengthening, the effects are strongest in the
red lines HeI 5875A and HeI 6678A. NLTE abundances from individual HeI lines
are up to a factor of about 3 lower than LTE values. Helium is found to be
stratified in the atmosphere of kap Cnc. While the LTE analysis indicates a
step-like profile of the helium abundance, a gradual decrease with height is
indicated by the NLTE analysis. A 3He/4He ratio of about 0.25-0.30 is found.
With the available data it cannot be decided whether the two isotopes follow
the same stratification profile, or not. This work implies that NLTE effects
may be ubiquitous in the atmospheres of HgMn stars and may have a significant
impact on abundance determinations and the interpretation of the vertical
abundance stratification of elements.Comment: 7 pages, 9 figure
Analisys of the education market trends development in Ukraine
The report is devoted to some forecasting aspects of the HEI development, on the basis of methods of econometrical modeling that allow revealing the common trends for improving marketing policy of the HEI. In order to analyze the development of the education market and to forecast the market environment condition the adapting forecasting methods are implemented in this research
The GAPS programme at TNG XXII. The GIARPS view of the extended helium atmosphere of HD189733 b accounting for stellar activity
Exoplanets orbiting very close to their host star are strongly irradiated.
This can lead the upper atmospheric layers to expand and evaporate into space.
The metastable helium (HeI) triplet at 1083.3nm has recently been shown to be a
powerful diagnostic to probe extended and escaping exoplanetary atmosphere. We
perform high-resolution transmission spectroscopy of the transiting hot Jupiter
HD189733b with the GIARPS (GIANO-B + HARPS-N) observing mode of the Telescopio
Nazionale Galileo, taking advantage of the simultaneous optical+near infrared
spectral coverage to detect HeI in the planet's extended atmosphere and to
gauge the impact of stellar magnetic activity on the planetary absorption
signal. Observations were performed during five transit events of HD189733b. By
comparison of the in- and out-of-transit GIANO-B observations we compute
high-resolution transmission spectra, on which we perform equivalent width
measurements and light-curves analyses to gauge the excess in-transit
absorption in the HeI triplet. We detect an absorption signal during all five
transits. The mean in-transit absorption depth amounts to 0.75+/-0.03%. We
detect night-to-night variations in the HeI absorption signal likely due to the
transit events occurring in presence of stellar surface inhomogeneities. We
evaluate the impact of stellar-activity pseudo-signals on the true planetary
absorption using a comparative analysis of the HeI and the H lines. We
interpret the time-series of the HeI absorption lines in the three nights not
affected by stellar contamination -exhibiting a mean in-transit absorption
depth of 0.77+/-0.04%- using a 3-d atmospheric code. Our simulations suggest
that the helium layers only fill part of the Roche lobe. Observations can be
explained with a thermosphere heated to 12000 K, expanding up to
1.2 planetary radii, and losing 1 g/s of metastable helium.Comment: 17 pages, 17 figures, accepted for publication in A&
Establishing a student satisfaction index - A Malaysian case study
The paper provides an insight on student satisfaction in a higher education institution (HEI) within the context of a quasi-government environment. Students’ opinions about factors related to academic life are sought in the form of a satisfaction feedback questionnaire. This survey aims to investigate issues viewed as important to students by seeking their opinion on a number of factors related to teaching, assessment and support provided by the HEI and its courses. A new model that is based on SERVQUAL framework is proposed that suited the quasi-government environment. The case study was conducted at a quasi-government HEI located in Pahang on the East Coast of Malaysia. Based on the results of this comprehensive study, it is clear that many of the physical aspects of the HEI services were viewed as important relating to student satisfaction. Student feedback confirms that they do receive high quality teaching from staff with high levels of expertise in their various academic disciplines. The lecture and tutorial are considered as the core service provided by the HEI. Students are prepared to tolerate largely deficiencies in the physical aspects of the facilities as long as the teaching they receive is perceived to be at the acceptable level. The concept of the service-product bundle is a valid and reliable tool for the design of a satisfaction survey and segments a HEI's service offering in such a way as to allow management to target resources at those areas that are perceived to be low satisfaction and high importance. This research model can be utilized in most HEIs establishments
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