README web version of /home/usg/OPS/MTS/readme_xml/readme_80500300
Principal Investigator Email Address
Estimated Total Execution Time (hours, including overheads)
General Description
The OBs introduced here are for the observation of 2 photometric transits
for the new planets WASP4 and WASP5. The goal is to benefit from the very high-standard
quality of the VLT FORS2 instrument and the Paranal site to reach sub-mmag sub-minute
transit light curves. We choose to observe in the z band to decrease the impact
of the limb-darkening on the precision of the obtained planetary and stellar parameters.
To reach this ambitious goal, the night has to be clear and a special observationnal
strategy has to be used (special at least for the VLT): a very large defocus with
the BAD CAL mode is needed that will lead fortunately to awfull stellar images but
very high precision light curves. This strategy has demonstrated its potential for
many transiting planets and should lead to very nice results here.
Waiver Requests
Critical Observing Condition Constraints
Each one of the proposed windows for the observation of the transit of
WASP4 and 5 has a maximal airmass lower or equal to 2. Larger airmass conditions
would increase the influence of the color differences and small transparency variations
and bring the obtained photometric quality below the desired level. The night has
to be clear. A photometric night is better, but small transparency variations should
not be a major problem for relative photometry. Lunar phase should not be a concern.
Time-Critical Aspects
We introduced in the OBs the remaining good observation windows for this
year for the transits of WASP4 and WASP5.
For both planets, priority should be given to the first window, than to the second
one. Indeed, the stars are slighty setting down and the airmass conditions are better
in the first window than in the second, and in the second than in the third.
Special Execution Requirements
To reach the ambitious goal of this project, i.e. reaching with the VLT
sub-mmag sub-minute differential photometry for two V=12 stars, several special
conditions have to be fullfiled:
(1) Despite the fact that this does not comply with the instrument-specific requirements
of the Phase 2 web page, all the observations for a transit have of course to be
performed continuously. This is why we introduce here OBs larger than 1 hour.
(2) The night has to be clear, leading to a low-level of atmospheric red noise (low
frequency noise).
(3) The photon and scintillation noise (and all other high frequency noises) have
to be minimized. To fullfil this condition, the duty cycle has to be optimized and
the exposure time large enough. Defocus is thus clearly needed in this case with
the BAD CAL mode. A 29s exposure time should lead to a good time sampling while
allowing for very low levels of scintillation and photon noise. The increase of
the sky and read-out noise is not a problem for such a bright star. The ugly PSF
shape that should be obtained is no more a problem: the flux will be measured by
aperture photometry as these bright stars are well isolated.
For each target, the joined finding chart shows the 2 main reference stars and the
target within the choosen field of view. These finding charts are from DSS images
in a red filter. We observed both targets with the Euler Swiss telescope in the
RG filter and one of the reference star revealed to be brigther than the target
for each case (this star is denoted R1 in the finding charts). For WASP4, R1 is
1.8 times brighter in RG than WASP4, while for WASP5, R2 is 1.2 times brighter than
WASP5. The choosen strategy takes into account this fact, and each pixel of the
images of the R1 reference stars must stay here in the linearity range: the observer
will have to check their flux at the beginning of the run and change the defocus
or the exposure time if needed. In other words, the R1 stars will be in fact the
actual targets, as all the other stars should be fainter. Of course, the other stars
should also be checked: we know the color of WASP4 and 5, but not of the other stars
whithin the FOV.
If the color of the R1 star or the shape of the very defocused PSF leads to saturated
or nonlinear regime for some pixels of any of the stars within the FOV in the first
frames, the observer will have to decrease the exposure time accordingly to fix
the problem. Of course, if the exposure time is decreased, the number of exposures
should be increased accordingly to cover the whole observation window.
Special Calibration Information
ToO Information
ToO Activators List
Is this a Pre-imaging run ?
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 ?
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 ?
Have you included OBs for any calibrations that you need but which are
not part of the Calibration Plan ?
If you are observing Moving Targets, have you attached suitable ephemeris
files to your OBs?
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 ?
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 ?
Last creation of page: Tue Oct 6 15:40:22 2009
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