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Measuring the vertical age structure of the Galactic disc using asteroseismology and SAGA

Casagrande, L.; Aguirre, V. Silva; Schlesinger, K. J.; Stello, D.; Huber, D.; Serenelli, A. M.; Schoenrich, R.; Cassisi, S.; Pietrinferni, A. and Hodgkin, S., et al. (2016) In Monthly Notices of the Royal Astronomical Society 455(1). p.987-1007
Abstract
The existence of a vertical age gradient in the Milky Way disc has been indirectly known for long. Here, we measure it directly for the first time with seismic ages, using red giants observed by Kepler. We use Stromgren photometry to gauge the selection function of asteroseismic targets, and derive colour and magnitude limits where giants with measured oscillations are representative of the underlying population in the field. Limits in the 2MASS system are also derived. We lay out a method to assess and correct for target selection effects independent of Galaxy models. We find that low-mass, i. e. old red giants dominate at increasing Galactic heights, whereas closer to the Galactic plane they exhibit a wide range of ages and... (More)
The existence of a vertical age gradient in the Milky Way disc has been indirectly known for long. Here, we measure it directly for the first time with seismic ages, using red giants observed by Kepler. We use Stromgren photometry to gauge the selection function of asteroseismic targets, and derive colour and magnitude limits where giants with measured oscillations are representative of the underlying population in the field. Limits in the 2MASS system are also derived. We lay out a method to assess and correct for target selection effects independent of Galaxy models. We find that low-mass, i. e. old red giants dominate at increasing Galactic heights, whereas closer to the Galactic plane they exhibit a wide range of ages and metallicities. Parametrizing this as a vertical gradient returns approximately 4 Gyr kpc(-1) for the disc we probe, although with a large dispersion of ages at all heights. The ages of stars show a smooth distribution over the last similar or equal to 10 Gyr, consistent with a mostly quiescent evolution for the Milky Way disc since a redshift of about 2. We also find a flat age-metallicity relation for disc stars. Finally, we show how to use secondary clump stars to estimate the present-day intrinsic metallicity spread, and suggest using their number count as a new proxy for tracing the ageing of the disc. This work highlights the power of asteroseismology for Galactic studies; however, we also emphasize the need for better constraints on stellar mass-loss, which is a major source of systematic age uncertainties in red giant stars. (Less)
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keywords
asteroseismology, stars: distances, stars: fundamental parameters, stars: general, Galaxy: disc, Galaxy: evolution
in
Monthly Notices of the Royal Astronomical Society
volume
455
issue
1
pages
987 - 1007
publisher
Wiley-Blackwell
external identifiers
  • wos:000368005900099
  • scopus:84958193322
ISSN
1365-2966
DOI
10.1093/mnras/stv2320
language
English
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yes
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4f36e20c-eee7-40df-9eb2-7b09da80ec29 (old id 8748012)
date added to LUP
2016-02-23 09:22:16
date last changed
2017-09-03 03:17:36
@article{4f36e20c-eee7-40df-9eb2-7b09da80ec29,
  abstract     = {The existence of a vertical age gradient in the Milky Way disc has been indirectly known for long. Here, we measure it directly for the first time with seismic ages, using red giants observed by Kepler. We use Stromgren photometry to gauge the selection function of asteroseismic targets, and derive colour and magnitude limits where giants with measured oscillations are representative of the underlying population in the field. Limits in the 2MASS system are also derived. We lay out a method to assess and correct for target selection effects independent of Galaxy models. We find that low-mass, i. e. old red giants dominate at increasing Galactic heights, whereas closer to the Galactic plane they exhibit a wide range of ages and metallicities. Parametrizing this as a vertical gradient returns approximately 4 Gyr kpc(-1) for the disc we probe, although with a large dispersion of ages at all heights. The ages of stars show a smooth distribution over the last similar or equal to 10 Gyr, consistent with a mostly quiescent evolution for the Milky Way disc since a redshift of about 2. We also find a flat age-metallicity relation for disc stars. Finally, we show how to use secondary clump stars to estimate the present-day intrinsic metallicity spread, and suggest using their number count as a new proxy for tracing the ageing of the disc. This work highlights the power of asteroseismology for Galactic studies; however, we also emphasize the need for better constraints on stellar mass-loss, which is a major source of systematic age uncertainties in red giant stars.},
  author       = {Casagrande, L. and Aguirre, V. Silva and Schlesinger, K. J. and Stello, D. and Huber, D. and Serenelli, A. M. and Schoenrich, R. and Cassisi, S. and Pietrinferni, A. and Hodgkin, S. and Milone, A. P. and Feltzing, Sofia and Asplund, M.},
  issn         = {1365-2966},
  keyword      = {asteroseismology,stars: distances,stars: fundamental parameters,stars: general,Galaxy: disc,Galaxy: evolution},
  language     = {eng},
  number       = {1},
  pages        = {987--1007},
  publisher    = {Wiley-Blackwell},
  series       = {Monthly Notices of the Royal Astronomical Society},
  title        = {Measuring the vertical age structure of the Galactic disc using asteroseismology and SAGA},
  url          = {http://dx.doi.org/10.1093/mnras/stv2320},
  volume       = {455},
  year         = {2016},
}