- Select New in the File menu (or click on in the main Toolbar) to open a new Observations Window (ObsWin). This brings up an empty ObsWin in the Peranso Desktop.
- The toolbar of the ObsWin contains several buttons. Click on (Add Internet light curve). This brings up a menu. Select the TESS light curve entry to display the below dialog box.
- This dialog box contains 2 sections: Star name and Additional fields:
- In the Star name section, there's an empty field labeled Star name. You can enter Star names in 4 ways:
- If you know the TESS TIC (TESS Input Catalog) name of the object, you can enter it here. An example TIC name is 261136679.
- You can also enter the AAVSO VSX or SIMBAD name of the object. We enter Pi Mensae or Pi Men for this tutorial.
- Or you can enter (J2000.0) RA and Decl coordinates. Both values have to be separated with a semi-colon. RA and Decl need to be in sexagesimal format with values separated by spaces. So, a valid entry would be: 04 59 13.57; -69 35 43.3
- Or you can enter (J2000.0) RA and Decl coordinates, expressed in degrees and separated with a semi-colon. Example: 76.80654; -69.595361
The field Used star names recalls the Star name you entered for each successful TESS search. It makes it more convenient to repeat searches in the future. Click the Clear button to erase all entries in the Used star names field.
- The Additional fields section has 4 fields:
- Photometry type: TESS light curve files contain photometric data in two versions. The first is Simple Aperture Photometry (SAP), the second one is "Pre-search Data Conditioning Simple Aperture Photometry (PDCSAP).
The SAP light curve is calculated by summing together the brightness of pixels that fall within an aperture set by the TESS mission. This is often referred to as the optimal aperture, but in spite of its name can sometimes be improved upon. Because the SAP light curve is a sum of the brightness in chosen pixels, it is still subject to systematic artifacts of the mission.
The PDCSAP light curve is subject to more treatment than the SAP light curve, and is specifically intended for detecting planets. The PDCSAP pipeline attempts to remove systematic artifacts while keeping planetary transits intact. Sometimes, however, PDCSAP data are overcorrected, looking worse than raw SAP data. For most analyses, a PDCSAP light curve is what you want to use, but when looking at astronomical phenomena that aren’t planets (e.g. long-term variability), the SAP flux may be preferred.
Peranso offers the capability to select Corrected (PDCSAP) or Raw (SAP) data. We will use Corrected (PDCSAP) in this tutorial.
- Brightness as: TESS obtains flux time series of individual targets, expressed in units of electrons per second. Peranso allows to convert flux values to the magnitude system, or to present them as normalized flux using the median flux (across the selected sector) for normalization. In this tutorial we will use Normalized flux.
- Show brightness-error bars: when selected, Peranso will display the error value of the brightness (flux or magnitude).
- Finally, the Marker size defines the size of the dots used for drawing the observations. Each dot represents one observation.
- Using the above values, we click the Plot button. Peranso subsequently connects to the TESS survey database and retrieves all Datasets (light curve descriptions) whose coordinates match the coordinates of Star name, within the given search radius (expressed in arcsec), collected during the life span of the TESS mission.
The matching Datasets are visualized in the above TESS datasets selector form. It contains one row for each matching dataset, and following columns:
- TIC Id: the unique TESS Input Catalog (TIC) identification of the target for which data are present in the dataset. If you click with the mouse on the TIC id, a small dialog box appears showing the cross-matches of the TIC Id in other catalogues such as UCAC4, Gaia DR2 and so on, in addition to the J2000.0 RA and Decl position values (degrees) of the target.
- The Median magnitude and Median mag error value: calculated by TESS on the entire dataset.
- The TESS Sector number. TESS observes the sky in sectors measuring 24° x 96°. Each sector is observed for two orbits of the satellite around the Earth, or about 27 days on average. Each sector has a unique sector number.
- The Cadence type and approximate Number of Observations. TESS has two data modes: short cadence (2 minutes or 20 seconds) postage stamps, and full-frame images FFIs (10 minutes or 30 minutes cadence). Peranso supports TESS short cadence data, so the Cadence type is either 2 minutes or 20 seconds.
The Number of Observations field provides information about the size of the dataset. Note that the number of observations is an approximation for the exact number of observations in the dataset.
- The Start date and End date between which the observations in the dataset were collected. You can sort datasets by start (or end) date by clicking the resp. column header.
- Import: click the checkbox to select the corresponding dataset for import in the ObsWin. You can select multiple datasets. The approx. total number of observations that will be imported is displayed at the bottom right corner.
Next, there are 4 buttons in the TESS datasets selector:
- Apply: clicking this button will download all datasets marked in the Import column and display them in the ObsWin. If TESS datasets were present in the ObsWin prior to clicking the Apply button (e.g., from a previous Apply operation), the contents of the ObsWin will be updated such that only datasets with a corresponding checkbox selection in the Import column are shown.
Each dataset is imported in a separate Observation set. Using the navigation bar buttons of the ObsWin toolbar makes it very convenient to step through the TESS datasets in an ObsWin.
IMPORTANT: the time of a TESS observation is expressed in the TESS Barycentric Julian Day (BTJD), this is a Julian day minus 2457000.0 and corrected to the arrival times at the barycenter of the solar system. Upon importing the observations in an ObsWin, Peranso converts the time from BTJD to (Geocentric) Julian Day.
- Cancel: closes the dialog box without further action.
- Import all: selects all checkboxes in the Import column.
- Import none: deselects all checkboxes in the Import column.
- For this tutorial, we will select the same Dataset as used by D. Gandolfi et. al. in their Astronomy & Astrophysics paper. It's the first dataset in the TESS datasets selector, with Start date 2018-07-25 and End date 2018-08-22, covering 28 days. It is a dataset with approx. 18000 observations of 2 minutes cadence. Click the checkbox in the Import column and then press the Apply button. The ObsWin will look as follows: