Principal Investigator Email Address
mattila@cc.helsinki.fi
Estimated Total Execution Time (hours, including overheads)
18.5h
General Description
We measure the Extragalactic Background Light using the shadowing effect of a galactic dark cloud. This is done using long slit spectroscopy at positions on and off the cloud. Operationally this is a simple LSS program. However, since spectroscopy is done of essentially blank sky, there are no stars to center the slits on and HIGHLY ACCURATE IN ADVANCE KNOWLEDGE OF THE SLIT POSITION IS NOT NECESSARY. Slit positions have been selected from Far Infrared based extinction maps, and avoid stars to DSS magnitude limits. Acquisition images are nevertheless needed for registering the de facto position of the slit which we need to know afterwards. THEREFORE, RE-CENTERING OR OTHER TELESCOPE POSITION CHANGES ARE NOT ALLOWED AFTER THE ACQUISITION IMAGE EXPOSURE! (other than involving specified offsets within the OBs.) Pointing accuracy should be fine. Only if the target field position is grossly wrong should a recentering be done and then a NEW ACQUISITION IMAGE TAKEN BEFORE STARTING THE LONG-SLIT EXPOSURE. Please see 'Special Execution Requirements' for some further critical instructions for different OBs.
Waiver Requests
Waiver ID: 082.A-0421A.01WAV We have requested that we are allowed to structure our observations in such such a way that up to five OBs are concatenated leading to a total time required for each such sequence of ca. 1 hour 40 minutes. The program includes 7 such sequences of OBs, of ca. 1h 40m duration. We have requested and been granted the waiver (31.7.2008 Palle Moeller) for having three OBs (Pos10-I, Pos10-II, and Pos10-III) of duration of ca. 1h40m each. TargetChangeRequest for SM 082.A-0421(A):Our request has been approved (29.7.2008 Francesca Primas) to measure off-axis straylight contribution from stars outside the instrument field of view up to ~0.5 deg. This is done near Sirius with the three-OB sequence of Straylight-1/2/3.
Critical Observing Condition Constraints
We are measuring an extremely weak signal. It is critical that the conditions are photometric and also that the airmass constraint (1.2) is strictly observed. Otherwise the sky brightness will change too much during the OBs and the science can not be achieved.
Time-Critical Aspects
Some OBs have to be observed in immediate sequence. See waiver and Special Execution Requirements.
Special Execution Requirements
OBs for Pos-18 and Pos-20: -------------------------- These consist of GROUPS OF FIVE (18a-1-ON, 18a-2-OFF, 18a-3-ON, 18a-4-OFF, 18a-5-ON) and (20a-1-ON, 20a-2-OFF, 20a-3-ON, 20a-4-OFF,20a-5-ON) WHICH SHOULD BE OBSERVED IN IMMEDIATE SEQUENCE IN THIS ORDER !! The second and fourth OB in every group comes back to the darkest position of the cloud, which is used as the standard reference point. The first, third and fifth measure the program points outside the cloud. Difference spectra are calculated, and for the science to succeed it is essential that airglow variations are minimised. Since the airglow changes in a time scale of tens of minutes, performing the differences from spectra taken at different times is pointless. Note also that the FIRST OB includes a LONG 10 min acquisition image used to exclude sections of faint galaxies from spectra. The sequences take ca. 1h 40m. Since we have no constraints for seeing, this should pose no problems for short term scheduling. OBs for Pos-9 and Pos-42: ------------------------- These consist of GROUPS OF FOUR (e.g. 9-I-1, 9-I-2, 9-I-3, 9-I-4 and 42-I-1, 42-I-2, 42-I-3, 42-I-4) WHICH SHOULD BE OBSERVED IN IMMEDIATE SEQUENCE !! Each of the individual OBs consists of on ON-OFF pair, where the OFF position is defined by a large offset along the slit (614 arcsec for Pos 9 and 489 arcsec for Pos 42). The OFF position is in both cases in the opaque cloud core. The FCs provide the direction of the offset which may help the Operator to select a suitable guide star to serve both positions - it is however not required that such a star is found, the accuracy of slit-position at the off-position is not critical. However, minimizing the overhead time for the offset is an advantage for our science. Again, difference spectra are calculated, and for the science to succeed it is essential that airglow variations, changing in timescale of tens of minutes, are minimised and pairs taken at different times are pointless. Two groups of four OBs are to be performed for Pos 9 and three for Pos 42. It would be a further advantage for the airglow elimination if more than one of these groups-of-4-OBs could be observed immediataly one after the other, if possible. Again one OB of each position includes a long 10 min acquisiton image. OBs for Pos-10: --------------- Here we have selected a guide star which should serve both ON and OFF positions, so the OB is constructed to switch between the ON and OFF positions automatically during a single OB. There are three of these OBs, the first of which again includes a long 10 min acquisition image. Straylight-1/2/3 OBs: --------------------- These three OBs should also be observed in immediate sequence!! The reasons are the same as given for target positions 18, 20, 9, and 42 above.
Special Calibration Information
ToO Information
ToO Activators List
Is this a Pre-imaging run ?
false
Pre-imaging Requirements
Source(s) of Pre-imaging
Pre-imaging sources not listed above
Do all your OBs comply with the instrument-specific requirements listed on the instrument-specific Phase 2 web page ?
If this is a pre-imaging run, did you select PRE-IMAGING for the Observing Category for each Observing Template ?
N/A
Do all your finding charts comply with both the general and instrument-specific Phase 2 Web Pages ?
If you submitted OBs for standard stars, did you specify the magnitude and spectral type of all standard stars in the OBs ?
N/A
Have you included OBs for any calibrations that you need but which are not part of the Calibration Plan ?
N/A
If you are observing Moving Targets, have you attached suitable ephemeris files to your OBs?
N/A
If you have preferences which OBs should be executed first, did you make use of the User Priority field in the OBs ?
If this is a run that requires coordinated observations with other facilities, did you give proper instructions in the Time-Critical Aspects Section ?
N/A
If you have prepared your finding charts with tools other than FIMS, do they comply with the specifications on the FORS1 Phase 2 web page ?
N/A