{"id":168,"date":"2018-07-13T08:26:53","date_gmt":"2018-07-13T07:26:53","guid":{"rendered":"http:\/\/pht2.selfip.com\/?page_id=168"},"modified":"2018-07-13T08:26:53","modified_gmt":"2018-07-13T07:26:53","slug":"etc-help","status":"publish","type":"page","link":"https:\/\/cheops.unige.ch\/pht2\/etc-help\/","title":{"rendered":"ETC Help"},"content":{"rendered":"

\n\nThe CHEOPS ETC provides the expected photometric precision over several pre-defined time intervals as well as a time interval \nspecified by the user.
\n
\nIt also provides the estimates of both the maximum and the median observing efficiency (i.e. the fraction of time spent on target per orbit) \naccording to the target coordinates. It further computes the pixel filling factor (in % of the pixel full well capacity) at the PSF peak. \nThe user may choose to directly input the target expected flux in the CHEOPS passband (in electrons per second), \nrather than let the ETC evaluate it based on the target affective temperature and magnitude.
\n
\nA .pdf file summarising the results can be created.\n\n<\/a>\n

Input Parameters<\/h3>\nTarget G magnitude<\/b>
The apparent magnitude of the target in the Gaia G band.
\nTarget effective temperature<\/b>
The stellar effective temperature in Kelvin within the allowed range of 2300 to 40000 K.
\nSpectral type (stellar granulation)<\/b>
The spectral type of the target, selectable from a drop-down menu. This value \nwill be used to estimate the amplitude of noise due to stellar granulation.
\nExposure time<\/b>
The exposure time of the individual CHEOPS exposures.
\nRight Ascension<\/b>
The target right ascension in decimal degrees [dd.d], or sexagesimal format [hh:mm:ss.s].
\nDeclination<\/b>
The target declination in decimal degrees [dd.d], or sexagesimal format [hh:mm:ss.s].
\n\n<\/a>\n

Additional Parameters<\/h3>\nSpecify observation duration<\/b>
Ticking this box allows to specify the duration used for the calculation.
\nDefined time interval<\/b>
The duration (in hours) for which the calculation should be performed, \nbesides the pre-defined time intervals of 1, 10, 30, 60, 180 and 360 minutes.
\n
\nSpecify flux in CHEOPS passband<\/b>
Ticking this box allows to specify the flux in the CHEOPS passband.
\nIf not selected, the flux is computed based on the Gaia magnitude and the effective temperature (recommended).
\nFlux<\/b>
\nThe target flux measured by CHEOPS in electrons per second. This value is only used if the option \nSpecify flux in CHEOPS passband<\/i> is selected.
\n
\nSpecify visit\/observation efficiency<\/b>
Ticking this box allows to specify the observation efficiency. \nDo not select this option if the efficiency should be interpolated from the table as a function of (RA, DEC).
\nNote that the interpolation is approximate and gives the estimates of both the maximum and median efficiency that can be \nobtained for the specified target coordinates.
\nEfficiency<\/b>
The user specified observation efficiency in %.
\nEfficiency refers to the fraction of time spent on-target per orbit. This value is only used if the option \nSpecify visit\/observation efficiency<\/i> is selected.\n\n<\/a>\n

Calculation Results<\/h3>\nSaturation level at PSF peak [% FWC]<\/b>
The ratio of the electrons registered per pixel at the PSF peak and the pixel full well capacity (FWC).
\nValues between 10% and 85% are suggested, and values above 100% indicate saturation.
\n
\nTwo (or three) tables summarize the noise estimates computed over default time intervals (i.e. 1 min, 10 min, 30 min, 1 h, 3 h, and 6 h) \nplus a further time interval specified by the user (optional).
\nThe first table reports the noise estimates when assuming 100% efficiency and it may be followed either by:
\n(i) one further table reporting the noise estimates at the user-specified value of the efficiency; or
\n(ii) two further tables reporting the noise estimates when assuming the maximum and median efficiency values as extracted by the tool following (RA, DEC) interpolation.
\nOption (i) applies when the user ticks the optional box Specify visit\/observation efficiency<\/i>, otherwise option (ii) holds.
\n
\nStellar granulation noise <\/b>
Total stellar granulation noise expected for the measurement.
\nPhoton noise<\/b>
Total photon noise affecting the measurement.
\nTotal noise including stellar granulation<\/b>
Total noise affecting the measurement, including instrumental and observational noise \n(read-out, zodiacal light, self-smearing, dark current, quantisation, cosmic ray, hot pixel, stray light, and photon noise), \nplus the predicted noise due to stellar granulation.
\nTotal noise without stellar granulation<\/b>
Total noise affecting the measurement, including instrumental and observational noise\n(read-out, zodiacal light, self-smearing, dark current, quantisation, cosmic ray, hot pixel, stray light, and photon noise), \nbut excluding the predicted noise due to stellar granulation.
\n\n<\/a>\n

Export to PDF<\/h3>\nA PDF containing the details of the computation can be created via the button Export results<\/i>. \nOptionally, the user can add a comment to this PDF via the Comment on exported PDF<\/i> field. \n\n

Further notes<\/h2>\n\n<\/a>\n

Aperture Radius<\/h3>\nThe tool assumes the default aperture radius of 25 pixels.
\n\n<\/a>\n

Exposure Times<\/h3>\n\nThe user must specify the exposure time; that is, the time during which photons are collected to record an image \n(minimum allowed value is 0.001 s, maximum allowed value is 60 s).
\nThe user should always verify that the percentage of the full well capacity of a pixel filled by the highest \npeak of the PSF is below 100%. The suggested maximum exposure time<\/b> is the one where \nthe PSF peak fills 85% of the full well capacity (to provide enough margin to clearly avoid pixel \nsaturation). It is also recommended to select an exposure time close to this suggested maximum \nexposure time (or 60s if the 85% cannot be achieved), to keep the instrumental noise to a minimum.\nOn the other hand, the suggested minimum exposure time<\/b> is the one corresponding to the PSF peak \nfilling 10% of the full well capacity.
\nThe user is responsible for selecting the correct exposure time and may have reasons not to follow \nthe guidelines given above. For example, the user might be interested in shorter exposure times than \nrecommended to have a faster cadence of images or imagettes (see Observers Manual, Table 2).\n\n<\/a>\n

Observing Efficiency<\/h3>\nGaps in the light curves exist due to Earth occultations, passages of the satellite through the South Atlantic Anomaly and \nperiods during which the stray light exceeds observationally acceptable limits. Efficiency refers to the fraction of time \nspent on-target per orbit. Unless the Specify visit\/observation efficiency<\/i> option is activated, the observing efficiency \nis taken from a pre-computed table according to the target (RA, DEC). In detail, this table contains the maximum and median efficiencies \nat a given (RA, DEC) and on a daily grid for 'standard' visits defined as being 7 orbits (~11.5 hours) long and targeting a G = 6 magnitude star. \nSuch standard visit aim at averaging the contributed interruptions from Earth occultations, Earth straylight events and SAA crossings.\nPlease note that these values are to be understood as approximate and cannot replace a more thorough efficiency \ncalculation using the Feasibility Checker<\/b> tool.\n\n\n<\/span><\/p>\n","protected":false},"excerpt":{"rendered":"","protected":false},"author":1,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-168","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/cheops.unige.ch\/pht2\/wp-json\/wp\/v2\/pages\/168","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/cheops.unige.ch\/pht2\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/cheops.unige.ch\/pht2\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/cheops.unige.ch\/pht2\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/cheops.unige.ch\/pht2\/wp-json\/wp\/v2\/comments?post=168"}],"version-history":[{"count":1,"href":"https:\/\/cheops.unige.ch\/pht2\/wp-json\/wp\/v2\/pages\/168\/revisions"}],"predecessor-version":[{"id":169,"href":"https:\/\/cheops.unige.ch\/pht2\/wp-json\/wp\/v2\/pages\/168\/revisions\/169"}],"wp:attachment":[{"href":"https:\/\/cheops.unige.ch\/pht2\/wp-json\/wp\/v2\/media?parent=168"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}