38 research outputs found
Open Issues on the Synthesis of Evolved Stellar Populations at Ultraviolet Wavelengths
In this paper we briefly review three topics that have motivated our (and
others') investigations in recent years within the context of evolutionary
population synthesis techniques. These are: The origin of the FUV up-turn in
elliptical galaxies, the age-metallicity degeneracy, and the study of the
mid-UV rest-frame spectra of distant red galaxies. We summarize some of our
results and present a very preliminary application of a UV grid of theoretical
spectra in the analysis of integrated properties of aged stellar populations.
At the end, we concisely suggest how these topics can be tackled once the World
Space Observatory enters into operation in the midst of this decade.Comment: 8 pages, 4 figures, accepted for publication in Astrophysics & Space
Science, UV Universe special issu
Stability analysis of agegraphic dark energy in Brans-Dicke cosmology
Stability analysis of agegraphic dark energy in Brans-Dicke theory is
presented in this paper. We constrain the model parameters with the
observational data and thus the results become broadly consistent with those
expected from experiment. Stability analysis of the model without best fitting
shows that universe may begin from an unstable state passing a saddle point and
finally become stable in future. However, with the best fitted model, There is
no saddle intermediate state. The agegraphic dark energy in the model by itself
exhibits a phantom behavior. However, contribution of cold dark matter on the
effective energy density modifies the state of teh universe from phantom phase
to quintessence one. The statefinder diagnosis also indicates that the universe
leaves an unstable state in the past, passes the LCDM state and finally
approaches the sable state in future.Comment: 15 pages, 12 figure
The Relationship between Globular Cluster Mass, Metallicity, and Light-element Abundance Variations
We investigate aluminum abundance variations in the stellar populations of globular clusters using both literature measurements of sodium and aluminum and APOGEE measurements of nitrogen and aluminum abundances. For the latter, we show that the Payne is the most suitable of the five available abundance pipelines for our purposes. Our combined sample of 42 globular clusters spans approximately 2 dex in [Fe/H] and 1.5 dex in {log}{M}GC}/{M}â . We find no fewer than five globular clusters with significant internal variations in nitrogen and/or sodium with little to no corresponding variation in aluminum, and that the minimum present-day cluster mass for aluminum enrichment in metal-rich systems is {log}{M}GC}/{M}â â 4.50+2.17([{Fe}/{{H}}]+1.30). We demonstrate that the slopes of the [Al/Fe] versus [Na/Fe] and [Al/Fe] versus [N/Fe] relations for stars without field-like abundances are approximately log-linearly dependent on both the metallicity and the stellar mass of the globular clusters. In contrast, the relationship between [Na/Fe] and [N/Fe] shows no evidence of such dependencies. This suggests that there were (at least) two classes of non-supernova chemical polluters that were common in the early universe, and that their relative contributions within globular clusters somehow scaled with the metallicity and mass of globular clusters. The first of these classes is predominantly responsible for the CNO and NeNa abundance variations, and likewise the second for the MgAl abundance variations. Particularly striking examples of this dichotomy include 47 Tuc and M4. As an auxiliary finding, we argue that abundance variations among Terzan 5 stars are consistent with it being a normal globular cluster.D.M.N. was supported by the Allan C. and Dorothy H. Davis
Fellowship. D.M. is supported by the BASAL Center for
Astrophysics and Associated Technologies (CATA) through
grant AFB 170002; the Programa Iniciativa Cientifica Milenio
grant IC120009, awarded to the Millennium Institute of
Astrophysics (MAS); and Proyecto FONDECYT No. 1170121.
J.G.F.-T. is supported by FONDECYT No. 3180210 and
European COST Action CA16117 (ChETEC) project No.
41736. Sz.M. has been supported by the Premium Postdoctoral
Research Program of the Hungarian Academy of Sciences and the
Hungarian NKFI grants K-119517 and GINOP-2.3.2-15-2016-
00003 of the Hungarian National Research, Development and
Innovation Office. D.G. gratefully acknowledges support from the
Chilean Centro de Excelencia en AstrofĂsica y TecnologĂas Afines
(CATA) BASAL grant AFB-170002. D.G. also acknowledges
financial support from the DirecciĂłn de InvestigaciĂłn y Desarrollo
de la Universidad de La Serena through the Programa de
Incentivo a la Investigación de Académicos (PIA-DIDULS). D.A.
G.H. acknowledges support provided by the Spanish Ministry of
Economy and Competitiveness (MINECO) under grant AYA2017-88254-P. D.A.G.H. acknowledge support provided by the
Spanish Ministry of Economy and Competitiveness (MINECO)
under grant AYA-2017-88254-P. P.M.F. acknowledge support for
this research from the National Science Foundation (AST1311835 and AST-1715662
Horizontal Branch Stars: The Interplay between Observations and Theory, and Insights into the Formation of the Galaxy
We review HB stars in a broad astrophysical context, including both variable
and non-variable stars. A reassessment of the Oosterhoff dichotomy is
presented, which provides unprecedented detail regarding its origin and
systematics. We show that the Oosterhoff dichotomy and the distribution of
globular clusters (GCs) in the HB morphology-metallicity plane both exclude,
with high statistical significance, the possibility that the Galactic halo may
have formed from the accretion of dwarf galaxies resembling present-day Milky
Way satellites such as Fornax, Sagittarius, and the LMC. A rediscussion of the
second-parameter problem is presented. A technique is proposed to estimate the
HB types of extragalactic GCs on the basis of integrated far-UV photometry. The
relationship between the absolute V magnitude of the HB at the RR Lyrae level
and metallicity, as obtained on the basis of trigonometric parallax
measurements for the star RR Lyrae, is also revisited, giving a distance
modulus to the LMC of (m-M)_0 = 18.44+/-0.11. RR Lyrae period change rates are
studied. Finally, the conductive opacities used in evolutionary calculations of
low-mass stars are investigated. [ABRIDGED]Comment: 56 pages, 22 figures. Invited review, to appear in Astrophysics and
Space Scienc
Measurement of azimuthal hadron asymmetries in semi-inclusive deep inelastic scattering off unpolarised nucleons
Adolph C, Akhunzyanov R, Alexeev MG, et al. Measurement of azimuthal hadron asymmetries in semi-inclusive deep inelastic scattering off unpolarised nucleons. Nuclear Physics B. 2014;886:1046-1077.Spin-averaged asymmetries in the azimuthal distributions of positive and negative hadrons produced in deep inelastic scattering were measured using the CERN SPS muon beam at GeV/c and a LiD target. The amplitudes of the three azimuthal modulations , and were obtained binning the data separately in each of the relevant kinematic variables , or and binning in a three-dimensional grid of these three variables. The amplitudes of the and modulations show strong kinematic dependencies both for positive and negative hadrons