Mapping the Milky Way
The LSST is ideally suited to answering two basic questions about the Milky Way Galaxy:
- What is the structure and accretion history of the Milky Way?
- What are the fundamental properties of all the stars within 300 pc of the Sun?
LSST will produce a massive and exquisitely accurate photometric and astrometric data set. Compared to SDSS, the best currently available optical survey, LSST will cover an area more than twice as large, using hundreds of observations of the same region instead of one or two, and each observation will be about 2 magnitudes deeper. The coverage of the Galactic plane will yield data for numerous star-forming regions, and the y band data will penetrate through the interstellar dust layer. LSST will detect of the order 10 billion stars, with sufficient signal-to-noise ratio to enable accurate light curve, geometric parallax, and proper motion measurements for about a billion of these stars. LSST will obtain geometric parallaxes and proper motions with accuracy similar to Gaia's at its faint end (0.3 mas at r=20), and extend them to r=24 with an accuracy of 3 mas. Photometric metallicity measurements will be available for about 200 million main-sequence F/G stars that will sample the halo to distances of 100 kpc (Ivezic et al. 2008). The LSST in its standard surveying mode will be able to detect RR Lyrae variables (pulsating stars and standard candles) and classical novae (exploding stars and standard candles) at a distance of 400 kpc and hence explore the extent and structure of our own halo out to half the distance to the Andromeda galaxy. In summary, the LSST will enable studies of the distribution of numerous main-sequence stars beyond the presumed edge of the Galaxy's halo, of their metallicity distribution throughout most of the halo, and of their kinematics beyond the thick disk/halo boundary. It will also obtain direct distance measurements below the hydrogen-burning limit for a representative thin-disk sample.
- The faintest ever search for galaxy satellites and intergalactic stars over much of the Local Group.
- High-resolution studies of the distribution of stars in the outer halo in the six- dimensional space spanned by position, metallicity and proper motions. For example, a sample of about 200 milion F/G main-sequence stars will be detected to of 100 kpc, and will have metallicity and proper motion measurements.
- Deep and highly accurate color-magnitude diagrams for over half of the known globular clusters, including tangential velocities from proper motion measurements.
- Mapping the metallicity, kinematics and spatial profile of the Sgr dwarf tidal stream.
- Mapping the halo and Local Group to 400 kpc using RR Lyrae stars.
- Studies of the clumpiness of the gravitational potential in the Galaxy using fragile wide-angle binaries selected with the aid of trigonometric and photometric parallaxes, and common proper motion.
- Detailed studies of variable star populations using 2% or better accurate multicolor light curves for a sample of at least 50 million variable stars. (e.g. studies of cataclysmic variables, eclipsing binary systems, rare types of variables, etc.)
- Rare and faint high proper motion objects: probing the end of stellar mass function and search for free-floating planet candidates.
- Using trigonometric parallaxes to directly constrain the faint end of the stellar luminosity function. For example, LSST will deliver 10% or better distances for a sample of about 2,500 stars with 18<M_r<19. There are only a handful of such stars known today (and Gaia will detect fewer than 100).
- Using their rich molecular band structure, the LSST colors (especially the z-y color) and faint limit will permit the separation of halo M sub-dwarfs from disk M dwarfs.
- A complete census of the solar neighborhood to a distance of 100 pc based on trigonometric parallax measurements for objects as faint as M_r=17.
- Planetary transits: the data set may include a mini survey of 600 sq.deg. of sky which will collect about 40 hour-long sequences of 200 observations each over a 4-month period. There would be an additional 800 observations over 10 years of these same fields as part of the main survey. With about 10 million or more stars in the sample (depending on where the fields are placed), this would provide an excellent material to study the planet frequency as a function of stellar type and distance from the Galactic plane.
- A complete census of AGB stars by searching for resolved envelopes and optical identifications of IR counterparts, and by using color and variability selection.
- A complete census of faint populations in nearby star forming regions using color and variability selection.
- High-resolution three-dimensional studies of interstellar dust using 5-color SEDs of main sequence stars.
For a detailed description of how LSST data will impact Asymptotic Giant Branch Star Research, see Ivezic et al. 2006, The Impact of LSST on Asymptotic Giant Branch Star Research (astro-ph/0701507) [PDF].