scholarly journals Evidence of spectral evolution on the white dwarf sample from the Gaia mission

2020 ◽  
Vol 492 (4) ◽  
pp. 5003-5010 ◽  
Author(s):  
G Ourique ◽  
S O Kepler ◽  
A D Romero ◽  
T S Klippel ◽  
D Koester
Keyword(s):  
White Dwarf ◽  
White Dwarfs ◽  
Mass Function ◽  
Initial Mass Function ◽  
Star Formation History ◽  
Initial Mass ◽  
Spectral Evolution ◽  
Formation History ◽  
Magnitude Diagram ◽  
Double Population

ABSTRACT Since the Gaia data release 2, several works have been published describing a bifurcation in the observed white dwarf colour−magnitude diagram for ${G_{\mathrm{BP}}}{}-{G_{\mathrm{RP}}}{} \gt 0$. Some possible explanations in the literature include the existence of a double population with different initial mass functions or two distinct populations, one formed by hydrogen-envelope and one formed by helium-envelope white dwarfs. We propose instead spectral evolution to explain the bifurcation. From a population synthesis approach, we find that spectral evolution occurs for effective temperatures below ${\simeq }11\, 000\, \mathrm{K}$ and masses mainly between $0.64\, \mathrm{M}_\odot$ and $0.74\, \mathrm{M}_\odot$, which correspond to around 16 per cent of all DA white dwarfs. We also find that the Gaia white dwarf colour–magnitude diagram indicates a star formation history that decreases abruptly for objects younger than $1.4\, \mathrm{Gyr}$ and a top-heavy initial mass function for the white dwarf progenitors.

scholarly journals Photometric Properties of White Dwarf Dominated Halos

2004 ◽  
Vol 21 (2) ◽  
pp. 153-156 ◽  
Author(s):  
Hyun-chul Lee ◽  
Brad K. Gibson ◽  
Yeshe Fenner ◽  
Chris B. Brook ◽  
Daisuke Kawata ◽  
...  
Keyword(s):  
White Dwarf ◽  
White Dwarfs ◽  
High Redshift ◽  
Mass Function ◽  
Large Magellanic Cloud ◽  
Initial Mass Function ◽  
Initial Mass ◽  
Galactic Halos ◽  
Dark Halo ◽  
Dynamical Mass

AbstractUsing stellar population synthesis techniques, we explore the photometric signatures of white dwarf progenitor dominated galactic halos, in order to constrain the fraction of halo mass that may be locked up in white dwarf stellar remnants. We first construct a 109 M⊙ stellar halo using the canonical Salpeter initial stellar mass distribution, and then allow for an additional component of low- and intermediate-mass stars, which ultimately give rise to white dwarf remnants. Microlensing observations towards the Large Magellanic Cloud, coupled with several ground-based proper motion surveys, have led to claims that in excess of 20% of the dynamical mass of the halo (1012 M⊙) might be found in white dwarfs. Our results indicate that (1) even if only 1% of the dynamical mass of the dark halo today could be attributed to white dwarfs, their main sequence progenitors at high redshift (z ≈ 3) would have resulted in halos more than 100 times more luminous than those expected from conventional initial mass functions alone, and (2) any putative halo white dwarf progenitor dominated initial mass function component, regardless of its dynamical importance, would be virtually impossible to detect at the present day, due to its extremely faint surface brightness.

scholarly journals PROBING THE STAR FORMATION HISTORY AND INITIAL MASS FUNCTION OF THEz∼ 2.5 LENSED GALAXY SMM J163554.2+661225 WITHHERSCHEL

2011 ◽  
Vol 742 (2) ◽  
pp. 108 ◽  
Author(s):  
Keely D. Finkelstein ◽  
Casey Papovich ◽  
Steven L. Finkelstein ◽  
Christopher N. A. Willmer ◽  
Jane R. Rigby ◽  
...  
Keyword(s):  
Star Formation ◽  
Mass Function ◽  
Initial Mass Function ◽  
Star Formation History ◽  
Initial Mass ◽  
Formation History

scholarly journals Binary White Dwarfs in the Galactic Halo

2013 ◽  
Vol 9 (S298) ◽  
pp. 431-431
Author(s):  
Pim van Oirschot ◽  
Gijs Nelemans ◽  
Amina Helmi ◽  
Else Starkenburg ◽  
Onno Pols ◽  
...  
Keyword(s):  
Star Formation ◽  
Galaxy Formation ◽  
White Dwarf ◽  
White Dwarfs ◽  
Galactic Halo ◽  
Mass Function ◽  
Initial Mass Function ◽  
Star Formation History ◽  
Population Synthesis ◽  
Two Parameters

We use the stellar population synthesis code SeBa (Portegies Zwart & Verbunt (1996), Toonen, Nelemans & Portegies Zwart (2012)) to study the halo white dwarf population. Here we assume a Kroupa initial mass function and compare 4 models, varying two parameters: the star formation (SF) history of the halo (either continuous SF during 2.5 Gyr, which started 13.2 Gyr ago, or a SF burst during 360 Myr, which started 12.9 Gyr ago – see the left panel of the figure) and the binary fraction of the halo (either 100% single stars, or 100% binaries). White dwarf cooling models (Althaus et al. (2009) and Renedo et al. (2010)) allow us to plot the halo white dwarf luminosity function for these 4 models, as is done in the right panel of the figure. Combined with an assumption about the density distribution of halo stars, we will study which of these white dwarfs Gaia can see, and what that can tell us about the initial parameter distributions in the halo. In the near future, we plan to use the Munich-Groningen semi-analytical galaxy formation model (Starkenburg et al. (2013)), to obtain key ingredients for the population synthesis modeling, such as a realistic star formation history (see the left panel of the figure).

scholarly journals The stellar initial mass function of the solar neighbourhood revealed by Gaia

2019 ◽  
Vol 489 (2) ◽  
pp. 2377-2394 ◽  
Author(s):  
A Sollima
Keyword(s):  
Star Formation ◽  
Mass Function ◽  
Initial Mass Function ◽  
Star Formation History ◽  
Solar Neighbourhood ◽  
Initial Mass ◽  
Galactic Disc ◽  
Formation History ◽  
Stellar Initial Mass Function ◽  
Metallicity Distribution

Abstract I use a sample of more than 120 000 stars in the solar neighbourhood, with parallaxes, magnitudes and colours estimated with unprecedented accuracy by the second data release of the Gaia mission, to derive the initial mass function of the Galactic disc. A full-forward technique is used to take into account, for the population of unresolved binaries, the metallicity distribution and the star formation history, including their variation across the Galactic disc, as well as all the observational effects. The shape of the initial mass function is well represented by a segmented power law with two breaks at characteristic masses. It has a maximum at M ∼ 0.15 M⊙ with significant flattening (possibly a depletion) at lower masses and a slope of α = −1.34 ± 0.07 in the range 0.25 < M/M⊙ < 1. Above 1 M⊙, the initial mass function shows an abrupt decline with a slope ranging from α = −2.68 ± 0.09 to α = −2.41 ± 0.11, depending on the adopted resolution of the star formation history.

scholarly journals The Star Formation History and IMF in the LMC and SMC from Deep HST Imaging

1999 ◽  
Vol 190 ◽  
pp. 351-353
Author(s):  
J. Holtzman ◽  
J. R. Mould ◽  
J. S. Gallagher
Keyword(s):  
Star Formation ◽  
Mass Function ◽  
Initial Mass Function ◽  
Solar Neighborhood ◽  
Star Formation History ◽  
Initial Mass ◽  
Luminosity Functions ◽  
Formation History

We present deep photometry to V ~ 27.5 obtained with the HST in several fields in the LMC and the SMC. We derive luminosity functions for the faintest stars which are consistent with an initial mass function similar to that of the solar neighborhood, although moderate variations are not excluded. We discuss implications of these observations for the star formation history in these regions of the LMC and SMC.

Recovering the star formation history of galaxies through spectral fitting: Current challenges

2019 ◽  
Vol 15 (S359) ◽  
pp. 386-390
Author(s):  
Lucimara P. Martins
Keyword(s):  
Star Formation ◽  
Mass Function ◽  
Initial Mass Function ◽  
Star Formation History ◽  
Stellar Spectra ◽  
Spectral Fitting ◽  
Formation History ◽  
History Of ◽  
Nearby Galaxies ◽  
Extract Information

AbstractWith the exception of some nearby galaxies, we cannot resolve stars individually. To recover the galaxies star formation history (SFH), the challenge is to extract information from their integrated spectrum. A widely used tool is the full spectral fitting technique. This consists of combining simple stellar populations (SSPs) of different ages and metallicities to match the integrated spectrum. This technique works well for optical spectra, for metallicities near solar and chemical histories not much different from our Galaxy. For everything else there is room for improvement. With telescopes being able to explore further and further away, and beyond the optical, the improvement of this type of tool is crucial. SSPs use as ingredients isochrones, an initial mass function, and a library of stellar spectra. My focus are the stellar libraries, key ingredient for SSPs. Here I talk about the latest developments of stellar libraries, how they influence the SSPs and how to improve them.

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