An absolute stellar luminosity atlas

State of the art

Gaia satellite will have a dramatic impact on the definition of the cosmic distance scale (DS), providing the direct measure via parallaxes, of the local primary distance indicators, and, in turn, a direct re-calibration of the secondary distance indicators. From the observational and the theoretical points of view, Gaia era will allow us to connect different distance indicators and to identify the principal sources of uncertainties still affecting the calibration of primary and secondary indicators.

Description of the work and training:

The key training will exploit the Gaia data by concentrating efforts on the derivation of stellar absolute luminosities using high precision parallaxes, kinematics, photometry and spectroscopic data (The full set of Gaia Data). This work tracks back to the exploitation of the Hipparcos data (Luri et al., 1996; Brown et al., 1997). In astrophysical applications, derived quantities like distances, absolute magnitudes and velocities are used instead of the observed quantities, such as parallaxes and proper motions. As the observed values are affected by random errors and selection effects, the estimates of the astrophysical quantities can be biased if a correct statistical treatment is not used. Work to be done involves several activities:

  • Development of statistical tools for the correct and full exploitation of Gaia data
  • Development of tools for the treatment and analysis of large data samples (data mining)
  • Calibration of luminosities: from normal stars to standard candles
  • Re-evaluation of the distance scale

We first propose a rigorous evaluation of the expected Gaia systematic and random errors, in particular small-scale correlations, at least what we know at present. We will deeply study how to get unbiased estimates of absolute magnitudes and distances, using either Bayesian or non-parametrical methods. These methods may be applied to get either mean quantities or individual estimates. Methods previously being used when treating Hipparcos data will need a critical re-evaluation: we propose to use methods that simultaneously take into account the effects of the selection of the sample, the observational errors, the galactic rotation and the interstellar absorption, all as an intrinsic part of the formulation (as opposed to external corrections). Furthermore, the method shall be able to identify and characterize physically distinct groups in inhomogeneous samples, thus avoiding biases due to unidentified components. Moreover, the proposed methods and their implementation will need to make an extensive use of numerical methods, so avoiding the need for simplification of the equations and thus the bias they could introduce.

All these areas of activity need to be updated in preparation of the arrival of the Gaia data in order to fully exploit its much higher precision and the much larger volume of data. For this reason the UB, in the frame of this ITN, intends to devote a PhD to specifically work on them, complemented by the proposed school “AstroStatistics on Massive Data Sets”.


The ESR will be for 3 years at the Universitat de Barcelona

Mobility within the GREAT/ITN:

The ESR will spend:

* 6 months at the Observatoire de Paris-Meudon to work on a detailed astrometry error modelling and impact on distance accuracies

* 4 months at the INAF - Astronomical Observatory of Bologna working on the calibration of extragalactic distance scale and the statistical analysis of Gaia data in terms of calibration of distance indicators.

Topic revision: r2 - 2010-11-09 - FrancescaFigueras
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