Distance and extinction determination for stars in LAMOST and APOGEE survey 王建岭 (LAMOST, References: NAOC) Wang et al. 2015a, MNRAS, submitted Wang et al. 2015b, In preparation
Outline Background: why distance and extinction are important Method: Bayesian method to determine d & Av Distance and extinction to stars in LAMOST survey Distance and extinction to stars in APOGEE survey Summery
Background There is no telescope which can compete with LAMOST now.
LAMOST is one of major community effort to reveal the evolution and present structure of Milky Way our knowledge on the formation and evolution of our Galaxy will be profoundly influenced. To fully exploit the dataset and make fully use the spectral information, we need to analyse the 6D phase-space distribution of stars. This is usually hampered by the lack of reliable estimation of distance.
Using Bayesian method derived accurate distance combining photometric & spectroscopic information LAMOST: ~20% APOGEE: ~15%
Why APOGEE? APOGEE is an important project on Milky Way 100,000 red giants stars. Complement to LAMOST Heavier extinction than LAMOST To further test accuracy of method on heavier extinction region Cross-check the results of LAMOST distance, Av Scientific results from different survey.
Theory: Bayesian method Why Bayesian method? Provide the full PDF of the derived parameters: provide a consistent stellar parameter measurement: opposed to permitting unphysical combinations of mass, radius, temperature, and metallicity; account for population effects: combining the likelihood of all possible solutions to provide a better weighted, and possibly more accurate solution. such as lifetime, SFR, IMF reconcile independent methods for inferring properties: such as the effective temperature.
Theory : Bayesian method Observed errors; Degeneracy: age vs. metal Distance vs. extinction.
To obtain precise results: improve accuracy of observables - limited by observation
Simulation results
Apply Bayesian method on LAMOST DR1: ~1M stars Compare with independent measurements
Compare with Hipparcos parallaxes
Other method to identify members From Xiang et al. 2014
Kinematic correction for dwarf and giants cv cv Our distance accurate to within 20% Proper motion of PPMXL is worse than UCAC4, even after corrected.
Compare extinction with that from RJCE
Compare extinction with that from RJCE Well recover the Temperature dependent feature of RJCE problematic
APOGEE LAMOST 100,000 red giant stars Stellar paramters calibrated in two steps: externally calibrated by star clusters & Kepler Comparison with Independent measurement check any systematical offset and random errors
1. Compare distance with Hipparcos parallaxes Accuracy of Hipparcos parallaxes is limited to 10% There is no systematical error observed. Individual dispersion less than 22%
2.Compare with APOGEE-RC catalogue Bovy et al. 2014
3. Compare with Rodrigues et al. 2014 spectroscopic constraints derived from the APOGEE asteroseismic parameters from Kepler individual uncertainties 1.8%
4.Compare distance with SAGA Claimed to have typical precision of a few percent.
Distance of APOGEE : ~15% Test extinction to APOGEE stars: Compare with extinction to individual star (RJCE: ea(ks)<0.11) Compare with 2D extinction map (Gonzale et al. 2012)
Compare extinction to individual star and 2D extinction map Clearly see the systematic effect of RJCE
Extinction difference as function of distance and A(Ks) Foreground RJCE underestimated
Different extinction law effects Derived from heavier extinction (toward galactic center) : Derived from low extinction (toward halo region ) : At present, there is no real consensus on the correct extinction law along all the direction of Galaxy Gonzalez et al. (2012) Little effect on distance Nishiyama et al.(2009) Yuan et al. 2013
Compare extinction from different extinction laws with RJCE
Summery With Bayesian method, we calculate distance and extinction to individual stars in LAMOST (2 millions) and APOGEE (100 K). LAMOST stars: distance uncertaities is better than 20%. output errors are correlated with true errors. APOGEE stars: distance indiividual uncertainties is better than 15% without obvious systematical offset being identified. Extinction are good for both of survey, and extinction law has marginal effect on the distance.
Thanks!