Deep SAGE Sky Survey

Introduction

The Stromgren-Crawford (SC) intermediate-band photometric system was invoked in the 1960s, and was originally designed to study early-type stars. After almost three decades of development, this system has been proven to be extremely powerful in the study of atmospheric parameters of various types of stars. The parameters like effective temperature, gravity and metallicity, yielded from the SC system is much more accurate than those from widely-used broad band photometric system or low-resolution specta, and are comparable to those from high-resolution spectra. This system is also useful for the determination of extinction, stellar distance, radius, and stellar evolutionary phases. However, limited by previous filters, detectors and telescopes, and the only sky survey is the GCS survey, with a depth of 8.5 mag in V, mainly the stars in the solar neighbourhood. In this situation, we propose a northern deep sky survey in the SC system wit the 1-m wide-field telescope at Nanshan Site of XinJiang Astronomical Observatories. We plan to cover the four Stromgren filters uvby and the pair of Crawford Hbeta filters, to a completeness depth of 20mag in y (the same in V) in about 4 years, detecting ~0.5 billion stars. This survey will not only provide accurate input catalogue for the LAMOST survey, but also greatly prompt the research of stellar astrophysics, the formation and evolution of the Milky Way and its components and neighbours, especially when combined with the LAMOST spectroscopic survey and the GAIA mission.


Fig.1 The footprint of the survey (Dec.>-10 deg).

The observations may start from the year of 2013 and it may last for ten years. The main aim is to provide an unprecedented detailed information of 0.5 billion stars in in the Galaxy, as well as serving as an input catalog for LAMOST telescope. Six filters will be used in our survey: u (3425 Å), v (4100 Å), b (4675 Å), y (5480 Å), beta_n (4858 Å) and beta_w (4850 Å) with the footprint of 22,000 deg2 for all the north sky Dec >-10 deg.


Fig.2 Stromgren-Crawford uvbybeta filter response functions

Science

  1. Determine the foreground extinction of the all the stars, evolutionary stage, stellar atmosphere parameters, distances, etc with the 4 color indices.
  2. Search and identify the solar system nearby faint objects, including white dwarfs and brown dwarfs; determine the stellar mass function; solve the problems of the G-dwarfs, dark matter and local formation scales.
  3. Study the fine structure of the Milky Way, including dividing thin disk and thick disk, the nature and morphology, star streams, substructures and searching the dwarf galaxies which are falling into our Milky way.
  4. Search and study the metal-poor and extreme metal-poor stars; stellar early-formation, nuclear fusion processes, stellar evolution.
  5. Study the metallicity of the Milky Way, including the radial or vertical distributions of the thin disk and thick disk; age metallicity relation (AMR); metallicity evolution.
  6. Study the Galactic open clusters and globular clusters, including the member star identification, foreground stars excluding, mass function, age, abundance, etc., the radial density distribution of stars with different mass; search the super massive stars, brown stars, even free planets.
  7. Study the nearby galaxies, including search and identify the giant broach stars in the dwarf galaxies and search the planetary nebular and then study the age metallicity relation (AMR), metallicity gradient and galaxy structures.
  8. Combining this photometry catalogue with the LAMOST spectroscopy survey and GAIA project data, the five-dimension of the Milky Way (R.A., Dec., distances, proper motion and radial velocities) can be determined.