scholarly journals The Luminosity Function of White Dwarfs in the Local Disk and Halo

1989 ◽  
Vol 114 ◽  
pp. 15-23 ◽  
Author(s):  
James Liebert ◽  
Conard C. Dahn ◽  
David G. Monet
Keyword(s):  
White Dwarfs ◽  
Luminosity Function ◽  
Solar Neighborhood ◽  
Star Formation History ◽  
Empirical Estimates ◽  
Formation History ◽  
History Of ◽  
Cool White Dwarfs ◽  
Local Disk

The luminosity function (LF) and total space density of white dwarfs in the solar neighborhood contain important information about the star formation history of the stellar population, and provide an independent method of measuring its age. The first empirical estimates of the LF for degenerate stars were those of Weidemann (1967), Kovetz and Shaviv (1976) and Sion and Liebert (1977). The follow-up investigations made possible by the huge Luyten Palomar proper motion surveys, however, added many more faint white dwarfs to the known sample. While the number of known cool white dwarfs grew to nearly one hundred, these did not include any that were much fainter intrinsically than the coolest degenerates found from the early Luyten, van Biesbroeck and Eggen-Greenstein lists.

scholarly journals The Star Formation History of Leo I

1999 ◽  
Vol 192 ◽  
pp. 151-157
Author(s):  
C. Gallart ◽  
W. L. Freedman
Keyword(s):  
Star Formation ◽  
Binary Stars ◽  
Large Fraction ◽  
Solar Neighborhood ◽  
Star Formation History ◽  
Formation History ◽  
Magnitude Diagram ◽  
History Of ◽  
The One ◽  
Low Rate

We advance some results of our study of the star formation history of the Local Group dSph galaxy Leo I, obtained through the analysis of its deep HST color-magnitude diagram (CMD) using model CMDs computed from stellar evolutionary models. We conclude that most star formation (≃ 90%) took place in Leo I between 7 and 1 Gyr ago. It seems to have started at a very low rate ≃ 15 Gyr ago and continued, also at a very low rate, from 1 Gyr ago until the present time. A constant Z=0.0004 and a large fraction of binary stars are required to obtain the best agreement with both the distribution of stars across the CMD and with its morphology. An IMF like the one obtained by Kroupa et al. (1993) for the solar neighborhood, or steeper, is compatible with the data.

scholarly journals Pixel Lensing: The Key to the Universe

1996 ◽  
Vol 173 ◽  
pp. 365-370
Author(s):  
Andrew Gould
Keyword(s):  
Event Rate ◽  
Virgo Cluster ◽  
Star Formation History ◽  
Powerful Method ◽  
Suppression Factor ◽  
Photon Detection ◽  
Formation History ◽  
History Of ◽  
The Universe

Pixel lensing, the gravitational microlensing of unresolved stars, is potentially a powerful method for detecting and measuring microlensing events. Two groups are currently refining this method in observations toward M31. I show that the technique has wide application, from searching for intra-cluster Machos in the Virgo cluster, to improving the accuracy of follow-up observations of Galactic microlensing events, to measuring the star-formation history of the universe. I derive the equation for the pixel lensing event rate where Qmin is the minimum signal to noise for detection, τ is the optical depth, Nres is the number of telescope resolution elements in the field, is the photon detection rate from a fluctuation magnitude star, and ξ is a suppression factor.

scholarly journals Two distinct halo populations in the solar neighborhood: evidence from stellar abundance of beryllium

2013 ◽  
Vol 9 (S298) ◽  
pp. 83-85
Author(s):  
Kefeng Tan ◽  
Gang Zhao
Keyword(s):  
Star Formation ◽  
Galactic Halo ◽  
Formation Rate ◽  
Solar Neighborhood ◽  
Elemental Abundance ◽  
Star Formation History ◽  
Dwarf Stars ◽  
Formation History ◽  
The Galaxy ◽  
History Of

AbstractIt is now generally believed that the Galaxy was formed through hierarchical merging, which means that different components of the Galaxy may have experienced different chemical evolution histories. Since alpha elements are mainly produced by core collapse supernovae, they are closely associated with the star formation history of the Galaxy. In this regard, Galactic components with different alpha elemental abundance patterns may show different behaviors in beryllium abundances since the production of beryllium is correlated with the cosmic rays and thus the supernovae. A recent study by Nissen & Schuster (2010) has revealed the existence of two distinct halo populations in the solar neighborhood based on the alpha elemental abundances and kinematics of 94 dwarf stars. We determined beryllium abundances for some of these stars and find systematic differences in beryllium abundances between these two halo populations. Our results consolidate the conclusion of two distinct halo populations in the solar neighborhood. Our results also show that beryllium abundance is a very good indicator of star formation rate, and could be used to trace the substructures of the Galactic halo.

scholarly journals Identification of Cool White Dwarfs in the Sloan Digital Sky Survey

2000 ◽  
Vol 176 ◽  
pp. 514-514 ◽  
Author(s):  
T. S. Metcalfe ◽  
A. Mukadam ◽  
D. E. Winget ◽  
X. Fan ◽  
M. A. Strauss ◽  
...  
Keyword(s):  
White Dwarf ◽  
White Dwarfs ◽  
Luminosity Function ◽  
Galactic Disk ◽  
Sloan Digital Sky Survey ◽  
Dwarf Stars ◽  
White Dwarf Stars ◽  
The Galaxy ◽  
History Of ◽  
Cool White Dwarfs

AbstractWe are searching for the coolest white dwarf stars in the galactic disk and halo. The Sloan survey, in due course, will identify an enormous number of new white dwarf stars which will better define the white dwarf luminosity function—an important tool for understanding the age and history of the stellar population of the galaxy. The broadband filter data obtained in the digital photometry phase of the survey will not permit identification of the most interesting of these, the coolest white dwarf stars. This is because the cool main sequence and subdwarf stars become indistinguishable from the white dwarfs in the various colorcolor diagrams. We have interference filters designed to separate out these classes of objects. We have obtained photometry of test fields to complement the Sloan data and identify the population of cool white dwarf stars. These data will ultimately resolve the controversies, based for the most part on small-number statistics, of the location of the turndown in the white dwarf luminosity function for the disk. If the halo is significantly older than the disk, we will find a second peak in the white dwarf luminosity function, at lower luminosities than the disk turndown. Our data will provide the first meaningful constraints on the location of the turndown in the halo white dwarf luminosity function.

scholarly journals The Luminosity Function and Evolution of Cool White Dwarfs

1979 ◽  
Vol 53 ◽  
pp. 146-164 ◽  
Author(s):  
James Liebert
Keyword(s):  
Star Formation ◽  
White Dwarf ◽  
White Dwarfs ◽  
Luminosity Function ◽  
List Type ◽  
Type Number ◽  
Atmospheric Parameters ◽  
Theoretical Interest ◽  
History Of ◽  
Cool White Dwarfs

In the review, I attempt to focus on what we have recently learned from the observations about three general topics of great theoretical interest: 1. evidence for evolution of white dwarf surface abundances,2. the special problems of determining atmospheric parameters and abundances at the cool end of the sequence, and3. evidence for a peaking of the white dwarf luminosity function at Mbol = + 15 ± 1, with possible implications for cooling theory and the history of galactic star formation.

scholarly journals The Gaia DR2 halo white dwarf population: the luminosity function, mass distribution, and its star formation history

2021 ◽  
Vol 502 (2) ◽  
pp. 1753-1767
Author(s):  
Santiago Torres ◽  
Alberto Rebassa-Mansergas ◽  
María E Camisassa ◽  
Roberto Raddi
Keyword(s):  
Star Formation ◽  
Mass Distribution ◽  
White Dwarf ◽  
High Speed ◽  
White Dwarfs ◽  
Luminosity Function ◽  
Age Distribution ◽  
Star Formation History ◽  
Formation History ◽  
The Individual

ABSTRACT We analyse the volume-limited nearly complete 100 pc sample of 95 halo white dwarf candidates identified by the second data release of Gaia. Based on a detailed population synthesis model, we apply a method that relies on Gaia astrometry and photometry to accurately derive the individual white dwarf parameters. This method is tested with 25 white dwarfs of our sample for which we took optical spectra and performed spectroscopic analysis. We build and analyse the halo white dwarf luminosity function, for which we find for the first time possible evidences of the cut-off, leading to an age estimate of ${\simeq}12\pm 0.5$ Gyr. The mass distribution of the sample peaks at $0.589\, \mathrm{ M}_{\odot }$, with $71{{\ \rm per\ cent}}$ of the white dwarf masses below $0.6\, \mathrm{ M}_{\odot }$ and just two massive white dwarfs of more than $0.8\, \mathrm{ M}_{\odot }$. From the age distribution, we find three white dwarfs with total ages above 12 Gyr, of which J1312−4728 is the oldest white dwarf known with an age of $12.41\pm 0.22\,$ Gyr. We prove that the star formation history is mainly characterized by a burst of star formation that occurred from 10 to 12 Gyr in the past, but extended up to 8 Gyr. We also find that the peak of the star formation history is centred at around 11 Gyr, which is compatible with the current age of the Gaia-Enceladus encounter. Finally, $13{{\ \rm per\ cent}}$ of our halo sample is contaminated by high-speed young objects (total age <7 Gyr). The origin of these white dwarfs is unclear but their age distribution may be compatible with the encounter with the Sagittarius galaxy.

scholarly journals White dwarfs as advanced physics laboratories. The axion case

2019 ◽  
Vol 15 (S357) ◽  
pp. 138-153
Author(s):  
Jordi Isern
Keyword(s):  
Star Formation ◽  
Physical Properties ◽  
White Dwarfs ◽  
Luminosity Function ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Star Formation History ◽  
Formation History ◽  
The Galaxy ◽  
Physics Laboratories

AbstractThe shape of the luminosity function of white dwarfs (WDLF) is sensitive to the characteristic cooling time and, therefore, it can be used to test the existence of additional sources or sinks of energy such as those predicted by alternative physical theories. However, because of the degeneracy between the physical properties of white dwarfs and the properties of the Galaxy, the star formation history (SFH) and the IMF, it is almost always possible to explain any anomaly as an artifact introduced by the star formation rate. To circumvent this problem there are at least two possibilities, the analysis of the WDLF in populations with different stories, like disc and halo, and the search of effects not correlated with the SFH. These procedures are illustrated with the case of axions.

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