Dec 12 2008 C. Liu@KIAA-Cambridge Joint Workshop on Near-Field Cosmology and Galactic Archeology LAMOST Sky Survey LAMOST Sky Survey -- -- Site limitations and survey planning Site limitations and survey planning Chao Liu, Licai Deng National Astronomical Observatories, CAS Heidi Newberg Rensselaer Polytechnic Institute
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Dec 12 2008 C. Liu@KIAA-Cambridge Joint Workshop on Near-Field Cosmology and Galactic Archeology
LAMOST Sky SurveyLAMOST Sky Survey ----Site limitations and survey planningSite limitations and survey planning
Chao Liu, Licai DengNational Astronomical Observatories, CAS
Heidi NewbergRensselaer Polytechnic Institute
Dec 12 2008 C. Liu@KIAA-Cambridge Joint Workshop on Near-Field Cosmology and Galactic Archeology
Overview
• Site limitations that strictly constrain the survey and subsequently scientific goals of LAMOST– weather and sky brightness
• Proposal of Milky Way stellar survey with LAMOST (LEGUE)– c.f. a previous talk of Heidi Newberg
Dec 12 2008 C. Liu@KIAA-Cambridge Joint Workshop on Near-Field Cosmology and Galactic Archeology
LAMOST optics
Dec 12 2008 C. Liu@KIAA-Cambridge Joint Workshop on Near-Field Cosmology and Galactic Archeology
LAMOST Facts
• Aperture: ~4m• Type: Schmidt, Alt-Az, Meridian• Focal length: 20m• Field of view: 5 degree diameter• Size of focus plane: 1.75m• Sky coverage: Dec>-10degrees, 1.5hours
around meridian• Wavelength: 370~900nm, R=1000/2000• Number of fibers: 4000, 16 spectrographs with
250 fibers each
Dec 12 2008 C. Liu@KIAA-Cambridge Joint Workshop on Near-Field Cosmology and Galactic Archeology
Location
• Location: – E117◦34’ N40◦23’
• Elevation: – ~900m
Dec 12 2008 C. Liu@KIAA-Cambridge Joint Workshop on Near-Field Cosmology and Galactic Archeology
BATC weather logs from 2004.1 to 2007.9The redder dots representsthe better weather nights
Dec 12 2008 C. Liu@KIAA-Cambridge Joint Workshop on Near-Field Cosmology and Galactic Archeology
Footprint of the planningLAMOST Survey of Milky Way stars
24000 sqdegs in total (blue area are double counted)
Dec 12 2008 C. Liu@KIAA-Cambridge Joint Workshop on Near-Field Cosmology and Galactic Archeology
Extinction Coefficient
Y. Liu et al. 2003
k=0.3
BATC historical data from 1995-2001
Dec 12 2008 C. Liu@KIAA-Cambridge Joint Workshop on Near-Field Cosmology and Galactic Archeology
Seeing
Y. Liu et al. 2003
BATC is a Schmidt telescope with CCDimage resolution of1.7arcsec/pixel
A small telescope isbeing used to monitorthe seeing for LAMOST
Dec 12 2008 C. Liu@KIAA-Cambridge Joint Workshop on Near-Field Cosmology and Galactic Archeology
Sky Brightness
• Moon• Light pollution from nearby cities
– turning worse due to economy development• Climate factors• Air pollutions• Scattering
– surrounding ground of MA
Dec 12 2008 C. Liu@KIAA-Cambridge Joint Workshop on Near-Field Cosmology and Galactic Archeology
Moon contribution in sky brightness
Y. Liu et al. 2003
BATC monitor data pointing to the North pole from 1995-2001
In order to estimate the sky brightness for any position of the sky at any time, we needa model to describe the sky brightness as a function ofmoon phase and angular separation between moon and sky position etc.
Dec 12 2008 C. Liu@KIAA-Cambridge Joint Workshop on Near-Field Cosmology and Galactic Archeology
Modeling the sky brightness
• Krisciunas & Schaefer 1991– based on observation at Mauna Kea
where αis the phase angle of the moon, ρ is the angular separation betweenthe observation sky position and the moon, f(ρ) is the atmospheric scattering function, which is the sum of Rayleigh and Mie scattering, Z is the zenith distance of the sky position. k is the extinction coeffecient, and Bmoon is the model surface brightness contributed of the moon
Dec 12 2008 C. Liu@KIAA-Cambridge Joint Workshop on Near-Field Cosmology and Galactic Archeology
Testing the model with sky brightness data at the north pole in Xinglong observed by BATC from 1995-2004. The data includes bad weather which is not suitable for observation as well.
The model sky brightness is ~0.3mag deeperthan the data.
Limited mag with 90min exposure at 550nm (Xue Y. 2008)
Dec 12 2008 C. Liu@KIAA-Cambridge Joint Workshop on Near-Field Cosmology and Galactic Archeology
Sky CoverageDEC=-10~70degs (vignetting is significant when DEC>70deg )902 plates, each of which is ~20sqdegs: 605 in higher Galactic latitude (|b|>20) and 297 in lower Galactic latitude (|b|<20)
The strategy of the survey is to assign the dark and grey nights to fainter objects at high latitude and assign the bright nights to brighter objects at low latitude
Dec 12 2008 C. Liu@KIAA-Cambridge Joint Workshop on Near-Field Cosmology and Galactic Archeology
Observe high latitude at grey/dark nights
580 of 605 plates will be observed from 2010-2014;totally 2609 observed platesAverage repeat times:~4.5
Sky brightness
Repeat times
Dec 12 2008 C. Liu@KIAA-Cambridge Joint Workshop on Near-Field Cosmology and Galactic Archeology
Observe low latitude at bright nights
204 of 297 plates will be observed from 2010-2014;totally 609 observed platesAverag repeat times~3
Sky brightness
Repeat times
Dec 12 2008 C. Liu@KIAA-Cambridge Joint Workshop on Near-Field Cosmology and Galactic Archeology
LAMOST is a meridian telescope and cannot point to any position, thus the sky footprint of one-year survey is discontinuous. The following plots are survey footprints in 2010
Dec 12 2008 C. Liu@KIAA-Cambridge Joint Workshop on Near-Field Cosmology and Galactic Archeology
Maximum number of spectra (5-year plan)• Total observed plates: ~3218
– High latitude(|b|>20, g<20): ~2609– Low latitude(|b|<20, B<16):~609
• Total number of spectra/year– High latitude: 2609/5*3500~1.8 x 106
– Low Latitude: 609/5*3500*2.5~1.1 x 106
– Totally ~1.9 x 106
• A 5-year plan: ~1.45 x 107 spectra– 9 x 106 in high latitude (stars, QSOs and Galaxies)– 5.5 x 106 in low latitude (stars, HI, HII, CO, ...)
Dec 12 2008 C. Liu@KIAA-Cambridge Joint Workshop on Near-Field Cosmology and Galactic Archeology
The LAMOST Survey of Milky Way Stars(LEGUE)• Basics
– 2.5 million stellar spectra in 5 years• 17<g<20 at high latitude• B<16 at low latitude
– use dark/grey nights at high latitude with a quarter of the fibers pointing to stellar objects
– bright nights at low latitude with most fibers pointing to stellar objects
– R=5000 grating used at low latitude
Dec 12 2008 C. Liu@KIAA-Cambridge Joint Workshop on Near-Field Cosmology and Galactic Archeology
The LAMOST Survey of Milky Way Stars(LEGUE)• Scientific goals
– Substructure, formation and evolution of the Galactic stellar halo
– kinematics, formation history, chemical and dynamical evolution of the disk population
Dec 12 2008 C. Liu@KIAA-Cambridge Joint Workshop on Near-Field Cosmology and Galactic Archeology
Substructure of the Milky Way
Dec 12 2008 C. Liu@KIAA-Cambridge Joint Workshop on Near-Field Cosmology and Galactic Archeology
Dec 12 2008 C. Liu@KIAA-Cambridge Joint Workshop on Near-Field Cosmology and Galactic ArcheologyIvezic et al. 2008
Dec 12 2008 C. Liu@KIAA-Cambridge Joint Workshop on Near-Field Cosmology and Galactic Archeology
Dec 12 2008 C. Liu@KIAA-Cambridge Joint Workshop on Near-Field Cosmology and Galactic Archeology
Dec 12 2008 C. Liu@KIAA-Cambridge Joint Workshop on Near-Field Cosmology and Galactic Archeology
Outstanding problems• The observation data is more complicated than models, how do we
compare them?• What the dark matter potential of the Milky Way looks like?• How many stellar components are there in the Milky Way, and how
to describe them?• What is the detail structure of the Milky Way’s disks? How is it
related to Monoceros/Canis Major?• How many dwarf galaxies are merged to create the Milky Way, and
when?• Study the frequency of metallicity as a function of position in the
Milky Way, favoring detection of rare, low metallicity stars.• Disentangle the components of the Galactic disks and possible tidal
debris therein• Describe the chemical evolution of the Galactic disks.• How do we utilize all of the partial chemical, kinematical, and spatial
information at the same time?
Dec 12 2008 C. Liu@KIAA-Cambridge Joint Workshop on Near-Field Cosmology and Galactic Archeology
Suggestions for target selection
• Understand the limitation of the telescope: instrument, site and time allocation
• Identify the grand challenge science goals that can be accomplished, and design a grand survey that can be analyzed statistically.
• How to consistently select target objects from both SDSS footprint and non-SDSS
Dec 12 2008 C. Liu@KIAA-Cambridge Joint Workshop on Near-Field Cosmology and Galactic Archeology