The Palomar QUEST Variability Survey
Charles BaltayYale University
- JPL
Palomar-QUEST Collaboration
Yale Peter Andrews, Charles Baltay, Anne Bauer, Nan Ellman, Will Emmet, Nick Morgan, David Rabinowitz, Jeff Snyder, Kathy Vivas, Bob Zinn
Indiana Bryce Adams, Mark Gebhard, Kent Honeycutt, Jim Musser
Cal Tech Richard Ellis, George Djorgovski, Shri Kulkarni, Ashish Mahabal, Mike Brown, Lynn Hillenbrand, John Carpenter, Avishay Gal-Yam, Matthew Graham, Roy Williams
JPL Ray Bradbury, Steve Pravdo
Berkeley Saul Perlmutter, Greg Aldering, Peter Nugent, Michael Woods-Vasey, et al.
Large Area CCD Camera for the 48” Palomar Schmidt Telescope
25.0 cm4.60
19.3 cm3.60
5.40 DiameterClear Field of ViewOf the Telescope
14” Window Diameter
4 Rows of 28 CCD’s each 112 CCD’s totalEach CCD – 2400 x 600 13 μ x 13 μ pixelsArray 16, 800 x 9,600 pixels 161 Megapixels tot.
Drift Scanning• Keep telescope stationary• Align CCD’s with columns along line of motion of star images• Synchronize clock rate to motion of star
Issues to worry about:
• Clock rate– Precision– Variability
• Exposure time fixed by star image motion• Resolution broadening due to curvature of star tracks on CCD
– Sagitta– Clock rate variation across CCD
These considerations limit CCD array size to ~ 4000 x 1000, 7.5 to 25 µ pixels
Star Image
CCDFinger (28 CCD’s)Return Spring
Spiral CAM
Base Plate
Pivot Point
StarImage
Fig. 11 Design for the CCD rotating mechanism
CameraBody
Shutter
Filter Tray
UVBlueVisRed
• Up to 4 colors per Drift Scan Pass• Easily Changeable
Star Image
Data Rates in Drift Scan ModePixels/CCD 1.44 x 106
CCD’s in Camera 112
Total Pixels 161 x 106
Total Bytes at 2 bytes/pixel 322 x 106
Megabytes/139 seconds 322
Data Rate 2.3 Megabytes/sec
Data Per Night 66 Gigabytes/night
In Point and Track Mode
Data/Night Depends on Exposure Time
Data/Night = GigabytesxTimeExp
66
sec 140
Current Observing PatternAllocate nights about evenly between Drift Scanning and Point and
Track
Drift Scan Nights• We do a strip 4.6o wide (in N-S direction) by 8 hours x 15o/hour =
120o in RA• ~ 550 square degrees/night
in 4 colors “simultaneously” using one of two filter sets: Johnson UBRI, or Gunn rizz
• Effective exposure time ~ 140 seconds on each CCD
Point and Track Nights• Use single broad Red Filter on whole array,λ> 6000 Å
• Typically take one minute exposures, ~ 30/hour, 9.4 square degrees each
• Take 3 shots of the same area of sky at ~ ½ hour spacing• So in a clear 8 hour night cover ~ 750 square degrees, 3 times
each, one color
~
Palomar/QUEST Data – Fall 2003Region C – RA from ~ 20 hrs to ~ 5 hrs
Declination UBRI rizz
22½o Nov. 6Nov. 7
Dec. 29
18 Sept. 27Nov. 26
Oct. 2Oct. 3
13½ Aug. 31Dec. 2
Aug. 8Sept. 3
9 Aug. 2Sept. 5
Sept. 2Sept. 28
4½ Aug. 30Sept. 4
Aug. 10Sept. 29
0 Sept. 1Sept. 6Sept. 7
Sept. 30Oct. 1
-4½ Sept. 8Dec. 3
Oct. 4Oct. 5
-9 Oct. 6
-13½ Jan. 1
-18 Jan 4
-22½ Jan. 5
Variability Time Scales
Repeated observations on time scales from minutes to years:
• In drift scan mode, 4 repeated observations (in different colors) on the 4 rows of CCD’s spaced by ~ 4 minutes
• In point and track mode repeat same area of sky (in the same color) at ~ ½ hour spacing then repeat again in ~ a month
• In any given lunation repeat drift scan of same area of sky 4 times (2 with UBRI, 2 with rizz) at interval of a few days to weeks or a month
• In both point and track and in drift scan plan to cover 10,000 to 15,000 square degrees each year, repeat same area year after year for yearly variability up to ~ 5 years
Callibration and Limiting Magnitudes
1. Calibrate Magnitudes in each color filter using Stetson Standard Stars
2. Define Limiting Magnitude at Signal/Noise = 10/1. Estimate Lim Mag from plot of
mag error vs. calib. mag for each
color.
15
10
5
0-2.2 -2.4 -2.6 -2.8
Mag
Err
or
No.
of
Sta
nd
ard
Sta
rs
Calibrated Magnitude
R
R
M (instrum) – m (Standard Star)
3. Using Col 13 from Sept. 1, 2003 data, obtain
Color Seeing
FWHM
Sky Level
e/pixel
Limiting Magnitude
U 2.3” 20 19.9
B 2.2” 300 21.7
R 2.0” 1500 20.9
I 1.7” 2300 20.2
Supernova StudiesFour Distinct Projects:
1. Low Red Shift (Z ≤ 0.1) Type Ia’sAnchor Hubble Diagram for high Z SNe studies (Cosmology)Perlmutter, Aldering, Nugent, Woods-Vasey, Yale Group (Supernova
Factory)
2. Type II (Core Collapse) SupernovaeCan these be used as Standard Candles?R. Ellis, Avishay Gal-Yam, Yale Group
3. Intermediate Red Shift (0.1 ≤ Z ≤ 0.3) Type Ia’sMeasure of w in Dark Energy Equation of state P = wρPerlmutter, Aldering, Yale Group
4. Type Ib,c SNe’sS. Kulkarni, et al.
Expected Numbers of Supernovae
Type Ia SNEUse Rate from R. Pain, et al. (APJ 577, 120, 2002)
Type II SNE• Typically 2 mags fainter than Ia’s
(Hamuy & Pinto APJ 566, L63, 2002)
• About twice as numerous per unit volume as Ia’s(Capellaro, et al., AA 351, 459, 1999)
Estimate numbers of SNe’s for 1000 square degrees, 15 day time window
Up to Z Peak m No/1000 sq deg
Peak m No/1000 sq deg
0.05 17.5 2 19.5 6
0.10 19.0 12 21.0 24
0.20 20.5 100 22.5 200
0.30 21.5 300 23.5 600
0.40 22.0 650 24.0 1300
Type Ia SNe’s Type II SNe’s
Study of Type Ia Supernovae
1. Low Red Shift (Z < 0.1)• Need to calibrate Hubble Diagram for high Z
SNe studies; systematic studies of nearby Ia’s• Rare, bright events
m < 18.5~ 10 SNe/1000 square degrees/15 day windowPalomar-QUEST is an ideal instrument for this(Supernova Factory)
• Need to look all year, both in drift scan and point and track *Discovery with 3 repeated QUEST scans*Photometric follow-up to get light curves
McDonald lm, SMART
• Spectroscopic Follow-upHawaii 2.2 m (Supernova Factory)
2. Study of Type II Supernovae
• Question – Can Type II supernovae be used as Standard Candles?
• Indication by Hamuy & Pinto (ApJ 566, L63 (2002) of a correlation between SNe absolute magnitude and expansion velocity of photosphere at mid plateau
• Palomar-QUEST plan to collect a sample of low red shift (Z < 0.1) Type II’s to establish (or otherwise) this
correlation
– Discovery of Type II’s on QUEST drift scan in UBRI colors*m peak < 21*~ 20 SNe’s/1000 square degrees/15 day window
– Devote one lunation per year Scan 1000 square degrees 5 times each on 2 day
intervals– Use colors to separate Type II’s from Type Ia’s a la Peter
Nugent– Photometric follow-up on Palomar 60” to get light curve– Spectroscopic follow-up on Palomar 200” or KECK to
measure Photosphere expansion velocity (using Fe 5169 Å line?)
– Measure magnitude spread after correlation correctionType Ia spread m ~ 0.17
~
3. Intermediate Red Shift (0.1 < Z < 0.4)
• Goal – measurement of w in p = wρ
w < -1/3 Dark Energy, w = -1 Cosmological Const.
• Fainter, more frequent events19 < m <22~ 1 SNe/square degree/15 day window
• Dedicated 1 month search on QUEST ~ 5 repeated scans of ~ 1000 sq. degrees get light curves near peak from QUESTAlso good for search for Type II SNE’s and Bob Zinn’s RR
Lyrae study
• Need follow-up photometry for tails of light curves (Palomar 60”?)
• Need spectroscopic follow-up of faint objects (m < 22!)This is a problem - ….
*Suggested by Spergel & Starkman astro-ph/0204089
Palomar-QUEST Science Projects1. Quasar Variability Survey (~ 15000 sq degrees)
Yale Group2. Gravitational Lensing of Quasars
Yale Group3. High Red Shift Quasars Z ≥ 6
G. Djorgovski, et al., and Yale Group4. Type Ia Supernova
Perlmutter, Aldering, Nugent, Woods-Vasey, et al., with Yale Group (Supernova Factory)
5. Type II SupernovaR. Ellis, Avishay Gl-Yam and Yale Group
6. GRB’s, Tlype Ib,c Supernovae, Unusual TransientsS. Kulkarni, et al., and G. Djorkovski, et at.
7. Variation of with timeYale Group with Yale Atomic Physics Group & U of Connecticut
8. Minor Planet/Kuyper Belt Object SurveyMike Brown, et al., and D. Rabinowitz, Yale
9. RR Lyrae StarsYale (Bob Zin, Kathy Vivas, et al.)
10. Near Earth Asteroid TrackingJPL NEAT Project
11. T-Tauri StarsLynn Hillenbrand, John Carpenter, et al.
12. Young Star FormationKent Honeycutt, et al.