Champlane Observation: CTIO 4m/MosaicII June 7-11, 2005

ChaMPlane Observation with CTIO 4m MosaicII

June 7-11, 2005

Target List
Exposure Sequence
Observation Plan
Biases, Flats etc.

I. Target List

Following is the 15 selected target fields for this run, sorted by increasing RA. The RA and Dec in the list are the telescope pointings, i.e. the center of the Mosaic (not the Chandra coordinates), based on the overlay of Mosaic on ACIS. NO MORE OFFSET IS NEEDED.

Priorities are sorted by ACIS-I over ACIS-S, lower NH, and longer Exposure time. 1 is the highest priority, 15 is the lowest priority.

                       Champlane CTIO 4m/MosaicII Target list   June 7-11, 2005

                                    Telescope pointing
                                    Center of Mosaic II                                               Chandra
Pri  Field        Observed?     RA            Dec        RAd         Decd         l          b        NHe22   ACIS  Exp
---  ------------ ---------  -----------  -----------  ----------  ----------  ----------  ---------  ------  ----  ---
8    PSRB1046-58      Y      10 48 00.00  -58 28 48.0  162.000000  -58.480000  287.376203   0.613344   0.638  S      36
6    MYCN18           Y      13 39 57.60  -67 20 24.0  204.990000  -67.340000  307.592717  -4.908352   0.427  S      40
13   PSRB1509-58             15 13 49.39  -59 07 56.6  228.455792  -59.132389  320.311155  -1.152022   2.948  I     209
12   G327.1-1.1              15 54 40.80  -55 02 29.3  238.670000  -55.041472  327.194516  -1.046133   1.486  I      50
2    Abell3627        Y      16 13 45.60  -60 48 36.0  243.440000  -60.810000  325.242022  -7.033822   0.115  I      45
15   SGR1627-41              16 35 50.40  -47 35 24.0  248.960000  -47.590000  336.973207  -0.108577  26.660  S      75
3    MXB1659-298             17 02 04.80  -29 58 48.0  255.520000  -29.980000  353.795603   7.249799   0.216  S      80
10   XTEJ1723-376            17 23 52.80  -37 42 00.0  260.970000  -37.700000  350.178104  -0.934813   1.330  I      30
11   X1724-307               17 27 31.20  -30 49 12.0  261.880000  -30.820000  356.300847   2.294058   1.381  I      25
7    4U1730-22               17 34 00.00  -21 58 48.0  263.500000  -21.980000    4.520228   5.907118   0.471  S      40
9    KS1731-260              17 34 24.00  -26 03 00.0  263.600000  -26.050000    1.126753   3.640217   1.064  S     110
1    LW               Y      17 51 48.00  -29 34 12.0  267.950000  -29.570000    0.151600  -1.481712   0.675  I     100
14   SGR1806-20              18 08 55.20  -20 32 05.2  272.230000  -20.534778    9.917686  -0.355983  10.703  I,S    53
4    V4641Sgr         Y      18 19 21.38  -25 27 00.0  274.839083  -25.450000    6.735457  -4.808124   0.277  S      95
5    1H1905+000       Y      19 08 36.00  +00 11 24.0  287.150000    0.190000   35.060535  -3.730803   0.367  S      25
-----------------------------------------------------------------------------------------------------------------------

Click a object name to see the Mosaic & ACIS overlay on DSS image. This should help to identify the field. Note that the DSS images are E-left & N-up. But the Mosaic display at the CTIO is E-up & N-right.

II. Exposure Sequence

For each field, do the following Exposure Sequence to achieve the project goal - reaching 24th mag.

           Exposure sequence for each field

N  Filter  Frame         Exp   Exp+readout Total Timeline
                        (sec)  (min/frame) (min)   (min)
---------------------------------------------------------
1  R       single image     2       1.7     1.7     1.7
2  Ha      single image    60       2.7     2.7     4.4
3  R       dither 1x5     240       5.7    28.5    32.9
4  Ha      dither 1x5    1500      26.7   133.5   166.4
5  V       single image     2       1.7     1.7   168.0
6  I       single image     2       1.7     1.7   169.8
7  V       dither 1x5     180       4.7    23.5   193.3
8  I       dither 1x5     180       4.7    23.5   216.8
---------------------------------------------------------
1. N is the exposure sequence number.
2. Exp is the exposure time for each image in seconds.
3. Exp+readout is the exposure plus 1.7min readout time for each image.
4. Total is the total time ((Exp+readout) x dither) for each filter.
5. Timeline is the accumulated time for each field.

Under Frame: 

A. single image: take one short exposure for each filter.  No dither.

B. dither 1x5: Use command "mosdither" to do one set of standard dither pattern 
   of 5 positions for R, Ha and V filters.  Take one image at each position. 
   The standard dither pattern is at "ditherdb$todd.dat".

It looks like this:
===========
# Tod Lauer's canned dither scheme for the NOAO mosaic 

# Offset relative to current telescope position 

# RA (pixels) Dec (pixels) 

0 0 

160 -240 

-160 240 

80 120 

-80 -120 
==============

C. When short of time, dither 1x3 can be used for filters I and V: 
   Use command "mosdither" to do one set of dither pattern of 3.  Take
   one image at each position. Create and use a "ditherdb$dither3.dat"
   file like this:

===========
# Dither 3 positions.

# Offset relative to current telescope position

# RA (pixels) Dec (pixels)

0 0

160 -240

-160 240
===========

OR, simply use the standard dither pattern and stop it after 3 exposures.

III. Observation Plan

The astronomical twilight on June 7-11, 2005 ends at around 7:15pm local time and the duration is 10:55 (655min). Above exposure sequence requires 216.8 min (3h36.8m, including readout time) for each field. Three fields need 650.4 min (10h50.4m). This doesn't even include the time to slew the telescope and locate the new field. Therefore careful planing is needed.

A. Try to start 10-15 min before and to end 10-15 after the astronomical twilight zone to get a little more observing time.

B. When time is running short, do the following to save time:

a. First reduce the number of I images to dither 1x3. (save 9.4 min)

a. Then reduce the number of V images to dither 1x3. (save 9.4 min)

b. Skip V and I short (2 sec) images. (save 1.7 min each)

c. Reduce one or two more I deep images, then V deep images. (save 4.7 min each) But keep at least one V and one I images.

When take only one deep V and one deep I images, the total time needed for a field is reduced to 175.8 min - a total saving of 41.0 min.

C. Don't need to take the standard (not enough time). We will apply for time on CTIO 1.3m telescope for the calibration.

Here is an observing elevation chart showing the locus of these 15 objects during the night.

postscript

Here is an observing almanac made for this run.

Here is the CTIO 2005 Ephemeris.

Here is a suggested observation plan for the 5 nights.

Night               Do
----------------------------------------
6/7     MYCN18      LW         V4641Sgr
6/8     PSRB1046    Abell362   1H1905
6/9     G327        MXB1659    4U1730
6/10    PSRB1509    XTEJ1723   KS1731
6/11    SGR1627     X1724      SGR1806
----------------------------------------

IV. Biases, Flats etc.

Biases and Domeflats: Take biases and domeflats in the afternoon before dinner.
Skyflats: Take twilight skyflats starting shortly after sunset at around 6:00pm.
Pointing and Focus: Do telescope pointing and focus after the skyflats at around 6:40pm.

1. Biases and Domeflats

Take 15 biases and 7 domeflats each (V R I & Ha) in each afternoon before observing. Dark is not necessary.

2. Skyflats

Take some skyflats in the evening or morning twilight if possible. I filter skyflats are probably the most needed in order to correct the fringes. Ideally, dark skyflats made from object fields (or blank skys) are the best. But there are too many stars in the Galactic plane which makes this impossible (and we don't have time to spend on taking blank skys). So we need to take some twilight skyflats. Timing is very crucial for this. Here are some simple steps for doing evening twilight skyflats:

Point the telescope to zenith at sunset at 6:05pm.
Turn the tracking on during the skyflat exposures and turn the tracking off during the readouts so there will be an offset between exposures.
Do the Ha filter skyflats first, then do the I filter skyflats.
Start at about 6:10pm, take a 2 seconds Ha skyflats. Examine the image and make the adjustment of the exposure time so the flat has about 10000 counts.
Take the first Ha skyflats with adjusted exposure time (remember to turn the tracking on during exposure and off during readout).
Take the second Ha skyflats with exposure time twice as long as the first exposure (e.g.: first is 5sec, second one should be 10sec). The sky gets darker during the 1.7 min readout. To double the exposure time is just about to compensate the change in the sky.
Take at least 3 Ha skyflats.
Take at least 3 Ha skyflats.
If the exposure time is still under 30sec, continue to take the Ha skyflats until the the exposure time is over 30sec.
Take the first I filter skyflat with exposure time equal to 1/10 of the last Ha skyflat exposure. Examine the image to make sure it gets about 10000 counts. Adjust exposure time if needed.
Take the second I filter skyflat with exposure twice as long as the first.
Take at least 3 I skyflats.

3. Pointing and Focus:

Stop the skyflats at around 6:40pm.
Do the pointing and focus at around 6:40pm.
Start to observe the first ChaMplane field at about 7:00pm.

Call me anytime if there are questions: 617-496-7582 (office), 781-646-0611(home)

THANKS!

Ping Zhao: zhao@cfa.harvard.edu