Click on the figure to download a Postscript version.
Contents:
We propose to use the WIYN 0.9m telescope and S2KB camera to carry out these tasks in a series of observing runs over the next few years.
The Northern SNAP field is a rectangle roughly 6.5 degrees wide and 1.2 degrees high, centered at (RA = 16:21, Dec = +55:35). It is located some fifteen degrees away from the North Ecliptic Pole to avoid dust and gas in the Milky Way. Below is a schematic outline of the field and the focal plane of the SNAP camera; the yellow, green and blue areas represent optical CCDs, and the larger red squares represent near-IR detectors.
Click on the figure to download a Postscript version.
The SNAP field spreads over more than 7 square degrees. Since the S2KB camera acquires an image only 0.34 degrees on a side, it take a very large number of images (roughly 90, allowing for some overlap) to cover the entire field. We propose initially to concentrate on six Selected Areas instead, shown in the figure above with labels A through F. Each Selected Area is composed of four overlapping pointings of the S2KB camera, yielding a square half a degree on a side. Each area is large enough to swallow one entire block of optical CCDs, or one entire block of near-IR detectors, in the SNAP focal plane. After measuring the stars in these Selected Areas, we can quickly calibrate the SNAP telescope by pointing it so that two blocks of detectors at a time fall on two of the Selected Areas.
We will increase the number of Selected Areas as the years pass so that the survey eventually covers most or all of the SNAP field.
The northern SNAP field is visible from Kitt Peak for more than 5 hours a night during the months of April, May and June. We propose to restrict all SNAP work on the WIYN 0.9m to these months.
The SNAP camera and spectrograph will be able to measure stars as bright as V=14. Some of the fundamental flux standards may be slightly brighter. The main SNAP survey work -- searching for supernovae -- requires careful measurements of sources at V=25. It will be necessary to transfer the calibration of the fundamental standards from one end of this range to the other, over at least ten magnitudes. We suggest using the WIYN 0.9m telescope to study the bright half of this range: from V=14 (or slightly brighter) to V=19. Larger telescopes will be necessary for the fainter portion of the range.
We can divide the observations into two types:
The broad-band observations will at first require additional images of Landolt standard stars to create a photometric solution for the night, so that we can put the V and I magnitudes onto the standard system. However, after we have set up local standards in each Selected Area (based on one or two good nights), we can then use the local standards to adjust zeropoints from one run to the next as we search for variability. The narrow-band observations require no additional calibration data, since we use them differentially.
We have calculated exposure times required to reach stars at V=19 with sufficient signal-to-noise to identify variables and distinguish dwarfs from giants. The sky is assumed to be relatively bright (V=19 per square arcsecond), corresponding to moonlit conditions.
Required times for each pointing
exposure readout repetitions total
Broad-band: ( 300 s + 130 s ) x 3 1290 s
Narrow-band: ( 1000 s + 130 s ) x 3 3390 s
The first set of broad-band measurements taken on a clear night will require accompanying observations of Landolt standards. Based on the experience from our May, 2002, we estimate that we can acquire one full pointing set (V and I) plus calibration frames per hour. We could then cover a single Selected Area in two broadband filters in a single night, plus have time left over for cross-checks with other Selected Areas. The entire set of 6 Selected Areas could be covered in 6 good, clear nights.
Similar calculations suggest that we could cover the entire set of 6 Selected Areas in the narrow DDO51 passband over 4 nights. We can take these images through thin clouds, since we do not need to compare them to measurements of standard stars.
Thus, we estimate that we can cover the Selected Areas in 10 decent nights.
After the initial measurements through one narrowband and two broadband filters, we then plan to concentrate on a single broadband filter (with occasional observations through a second broadband filter to measure the color evolution of variable stars). We will plan several runs to detect variability on a range of timescales. Photometric conditions are not necessary for any of this work.
Three-night run night 1: A B C D
night 2: E F A B
night 3: C D E F
Seven-night run night 1: A B C D
night 2: E F A B
night 3: A B A C
night 4: D A E A
night 5: A F C A
night 6: B C B D
night 7: C E F C
Another option for future years is to expand the number of Selected Areas, so that we cover a larger and larger fraction of the entire field. One possibility is to choose Areas which lie near the "top" and "bottom" edges of the entire SNAP field:
With the proper choice of new Areas, we can cover all four optical (or near-IR) detectors in the focal plane with a single pointing of the spacecraft.
The observing plan for each of these extensions would follow that of the initial set. We do not include any time for these extensions in the detailed plan below for simplicity.
It is possible, of course, to mix followup observations of the initial Areas together with new observations of the extended Areas in a single run at the WIYN 0.9m.
We suggest a long-term project extending at least three years into the future, starting next summer (April, 2004).
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Year One: 1. Initial coverage
(2004) broadband 6 nights
narrowband 4 nights 10
2. one or two weeks later
broadband 3 nights 3
3. one month later
broadband 3 nights 3
4. one month later
broadband 3 nights 3
total = 19 nights
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Year Two: 5. Long-term variability
(2005) broadband 6 nights 6
6. one month later
broadband 3 nights 3
total = 9 nights
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Year Three: 7. Long-term variability
(2006) broadband 3 nights 3
6. one month later
broadband 3 nights 3
total = 6 nights
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Some of the time in Years Two and Three will be spent gradually covering each of the Selected Areas intensively for a single night, or filling gaps in the initial coverage missed in Year One.
As mentioned above, one could also begin adding new Selected Areas in these years, given additional time. In theory, one could extend this observing program from 2004 to 2009 and
We estimate roughly the cost of carrying out the observations, reducing and analyzing the data, publishing and publicizing the results as follows.
The following assumes, for simplicity, that there is a single person (MWR) performing all the work. It is, of course, possible (and perhaps preferable) to split the project between a number of persons and institutions. To a rough approximation, the total cost is likely to be similar.Note that I include the cost of an undergraduate student on one of the trips to KPNO, and for a portion of one summer. We anticipate two publications: one based on the first season's work, and a smaller followup paper describing long-term variables two years later.
Cost of the program
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Year One: Travel to KPNO 3 trips @ $1050 each (1 person) $ 3,150
and lodging 1 trip @ $1900 (2 persons) $ 1,900
Summer salary (MWR) $ 6,000
Summer salary (student) $ 3,000
Travel to AAS meeting $ 1,200
to present poster
Travel to SNAP collaboration meeting $ 1,000
Page charges for publication $ 1,000
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subtotal $ 17,250
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Year Two: Travel to KPNO 2 trips @ $1050 each (1 person) $ 2,100
and lodging
Summer salary (MWR) $ 6,100
Travel to SNAP collaboration meeting $ 1,000
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subtotal $ 9,200
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Year Three: Travel to KPNO 2 trips @ $1050 each (1 person) $ 2,100
and lodging
Summer salary (MWR) $ 6,200
Travel to AAS meeting $ 1,200
to present poster
Travel to SNAP collaboration meeting $ 1,000
Page charges for publication $ 500
------------
subtotal $ 11,000
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Grand total $ 37,450
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Note that this is only a rough estimate. A detailed budget would include overhead and benefits on the salaries.
If we chose to expand the number of Selected Areas in future years, the cost would increase approximately linearly with increasing area; that is, going from 6 to 12 Selected Areas would double the cost, from 6 to 18 would triple the cost, and so on.