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  • 1
    Electronic Resource
    Electronic Resource
    Cooling of White Dwarfs (1990)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Astronomy and Astrophysics 28 (1990), S. 139-181 
    Details
    ISSN: 0066-4146
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.aa.28.090190.001035
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  • 2
    Electronic Resource
    Electronic Resource
    A possible observational constraint on the production of lithium by galactic novae (1985)
    Springer
    Astrophysics and space science 112 (1985), S. 361-365 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Recent computations (D'Antona and Mazzitelli, 1982), together with the general scheme of evolution of cataclysmic binaries (CBs), lead to conclude that the secondaries in those CBs having periods shorter than ∼4.5 hr have a large3He content in the envelope, ranging from 10−4 (P=4.5 hr) to 〉2×10−3 (P=3 hr) in mass fraction, if the nova systems have an age of some billion years. The consequence on the frequency of novae outbursts is shortly examined. If lithium is produced by galactic novae, the7Li content of old disk stars should be very close to the Population II content.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00653518
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  • 3
    Electronic Resource
    Electronic Resource
    The structure of late type stars and the Hayashi track (1974)
    Springer
    Astrophysics and space science 28 (1974), S. 303-324 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A topological approach in the HR diagram is given for the occurrence and the characteristics of convective envelopes in population II stars. The location of the Hayashi track and of the Red Giants branch are both investigated for various assumed masses of the stars and chemical compositions of the convective layers. An analysis is performed on the influence of the assumed mixing length. The observational consequences of a possible mass loss is discussed for both the Red Giants and the Asymptotic branches. Possible causes for separation between these two branches are briefly examined. The case of the globular cluster ω Cen is investigated, in order to give some suggestions for a large dispersion in colours observed among the giants belonging to this cluster.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00641930
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  • 4
    Electronic Resource
    Electronic Resource
    Search for variability in hydrogen-poor stars (1982)
    Springer
    Astrophysics and space science 83 (1982), S. 287-310 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The evolutionary status of hydrogen-poor stars is analyzed. Photoelectric observations of six objects are reported as a first step of a long-term project devoted to search for variability of a large sample of hydrogen-poor stars. The observed stars show phenomena of microvariability with an amplitude of the order of 0m. 1 or less. Two extreme helium stars have been examined: a period in the range of 0d.162-0d.164 has been found for BD+ 1002179, andP=0d.1079962 for BD+1303324. The mass-losing O subdwarf (sdO) BD+370 443 presents short-term fluctuations with a time-scale of several minutes and long-term variations on a scale of months. The ‘standard’ sdO BD+750325 is probably non-variable, although light variations of very small amplitude (Δm≃0.03) with a time-scale of about 1 hr might be present. The high gravity sdO BD+2504655, which is very close to the white dwarf stage, also presents variability on a time-scale of about 13 minutes, and might be an analog of the recently discovered pulsating sdO, or ‘hot’ white dwarf, PG 1159-035. The variability of the intermediate helium star HD 37776 is finally confirmed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00648561
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  • 5
    Electronic Resource
    Electronic Resource
    Photometric information on globular cluster stars from the Palomar Sky Survey prints (1973)
    Springer
    Astrophysics and space science 22 (1973), S. 71-78 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Photometric information that can be taken from the Palomar Sky Survey prints can be used to discriminate among the various evolutionary stages of stars that are members of globular clusters, as well as to obtain some idea of the HR diagram for vary faint stars. For a test case, it is shown that in a check analysis forM3 the known turn-off luminosity is given to within about 0.5 mag. The globular cluster NGC 5466 is examined and it is concluded that no turn-off occurs beforeP≈20 mag.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00642823
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  • 6
    Electronic Resource
    Electronic Resource
    Cooling sequence of a pure helium white dwarf of 0.15 solar masses (1972)
    Springer
    Astrophysics and space science 19 (1972), S. 151-158 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Description / Table of Contents: Riassunto E' stato elaborato un nuovo metodo di integrazione numerica, ed applicato al calcolo della sequenza evolutiva di raffreddamento di una nana bianca di puro elio di 0.15M ⊙. I risultati vengono discussi e confrontati con i precedenti modelli ottenuti da altri autori.
    Notes: Abstract A new method of integration has been performed and applied to the computation of the cooling sequence of a 0.15M ⊙ white dwarf consisting of helium. The results are discussed and compared with the previous ones obtained by other authors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00643172
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  • 7
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    The extended main-sequence turn-off cluster NGC 1856: rotational evolution in a coeval stellar ensemble (2015)
    Oxford University Press
    Details
    Publication Date: 2015-09-27
    Description: Multiple or extended turn-offs in young clusters in the Magellanic Clouds have recently received large attention. A number of studies have shown that they may be interpreted as the result of a significant age spread (several 10 8  yr in clusters aged 1–2 Gyr), while others attribute them to a spread in stellar rotation. We focus on the cluster NGC 1856, showing a splitting in the upper part of the main sequence, well visible in the colour m F336W – m F555W , and a very wide turn-off region. Using population synthesis available from the Geneva stellar models, we show that the cluster data can be interpreted as superposition of two main populations having the same age (~350 Myr), composed for 2/3 of very rapidly rotating stars, defining the upper turn-off region and the redder main sequence, and for 1/3 of slowly/non-rotating stars. Since rapid rotation is a common property of the B-A type stars, the main question raised by this model concerns the origin of the slowly/non-rotating component. Binary synchronization is a possible process behind the slowly/non-rotating population; in this case, many slowly/non-rotating stars should still be part of binary systems with orbital periods in the range from 4 to 500 d. For these orbital periods, Roche lobe overflow occurs during the evolution of the primary off the main sequence, so most primaries may not be able to ignite core helium burning, consistently why the lack of a red clump progeny of the slowly rotating population.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 8
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    The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters - IV. Helium content and relative age of multiple stellar populations within NGC 6352 (2015)
    Oxford University Press
    Details
    Publication Date: 2015-05-30
    Description: In this paper, we combine Wide Field Camera3/UVIS F 275 W , F 336 W , and F 438 W data from the ‘UV Legacy Survey of Galactic Globular Clusters: Shedding Light on Their Populations and Formation’ (GO 13297) Hubble Space Telescope Treasury programme with F 606 W , F 625 W , F 658 N , and F 814 W Advanced Camera for Surveys archive data for a multiwavelength study of the globular cluster NGC 6352. In the colour–magnitude and two-colour diagrams obtained with appropriate combination of the photometry in the different bands, we separate two distinct stellar populations and trace them from the main sequence to the subgiant, red giant, horizontal and asymptotic giant branches. We infer that the two populations differ in He by Y  = 0.029 ± 0.006. With a new method, we also estimate the age difference between the two sequences. Assuming no difference in [Fe/H] and [α/Fe], and the uncertainties on Y , we found a difference in age between the two populations of 10 ± 120 Myr. If we assume [Fe/H] and [α/Fe] differences of 0.02 dex (well within the uncertainties of spectroscopic measurements), the total uncertainty in the relative age rises to ~300 Myr.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 9
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    Accretion of pristine gas and dilution during the formation of multiple-population globular clusters (2016)
    Oxford University Press
    Details
    Publication Date: 2016-07-29
    Description: We study the interaction of the early spherical GC wind powered by Type II supernovae (SNe II) with the surrounding ambient medium consisting of the gaseous disc of a star-forming galaxy at redshift z 2. The bubble formed by the wind eventually breaks out of the disc, and most of the wind moves directly out of the galaxy and is definitively lost. The fraction of the wind moving nearly parallel to the galactic plane carves a hole in the disc which will contract after the end of the SN activity. During the interval of time between the end of the SN explosions and the ‘closure’ of the hole, very O-poor stars (the Extreme population) can form out of the super-AGB (asymptotic giant branch) ejecta collected in the GC centre. Once the hole contracts, the AGB ejecta mix with the pristine gas, allowing the formation of stars with an oxygen abundance intermediate between that of the very O-poor stars and that of the pristine gas. We show that this mechanism may explain why Extreme populations are present only in massive clusters, and can also produce a correlation between the spread in helium and the cluster mass. Finally, we also explore the possibility that our proposed mechanism can be extended to the case of multiple populations showing bimodality in the iron content, with the presence of two populations characterized by a small difference in [Fe/H]. Such a result can be obtained taking into account the contribution of delayed SN II.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 10
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    Evolution of binary stars in multiple-population globular clusters - II. Compact binaries (2016)
    Oxford University Press
    Details
    Publication Date: 2016-03-08
    Description: We present the results of a survey of N -body simulations aimed at exploring the evolution of compact binaries in multiple-population globular clusters. We show that as a consequence of the initial differences in the structural properties of the first-generation (FG) and the second-generation (SG) populations and the effects of dynamical processes on binary stars, the SG binary fraction decreases more rapidly than that of the FG population. The difference between the FG and SG binary fraction is qualitatively similar to but quantitatively smaller than that found for wider binaries in our previous investigations. The evolution of the radial variation of the binary fraction is driven by the interplay between binary segregation, ionization and ejection. Ionization and ejection counteract in part the effects of mass segregation but for compact binaries the effects of segregation dominate and the inner binary fraction increases during the cluster evolution. We explore the variation of the difference between the FG and the SG binary fraction with the distance from the cluster centre and its dependence on the binary binding energy and cluster structural parameters. The difference between the binary fraction in the FG and the SG populations found in our simulations is consistent with the results of observational studies finding a smaller binary fraction in the SG population.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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