PHOTOMETRIC REDUCTION PROCEDUREWITH TJO OBSERVATIONS FOR GAIA

SCIENCE ALERTS

Umut BURGAZ

burgaz.umut@gmail.com

University of Barcelona

04/2015

Revision Sheet

Release No. Date Revision DescriptionRev. 0 18/04/2015 Creation of Template & First Draft

TABLE OF CONTENTS

1.0 GENERAL INFORMATION...............................................................................................

1.1 System Overview........................................................................................................

1.2 Installation Notes........................................................................................................ 1.2.1 Python............................................................................................................... 1.2.2 Astropy............................................................................................................. 1.2.3 CCDProc........................................................................................................... 1.2.4 Astrometry.net................................................................................................. 1.2.5 Sextractor..........................................................................................................

2.0 TARGET SELETIONN.........................................................................................................

3.0 PHOTOMETRIC REDUCTION.........................................................................................

3.1 Cleaning the Data.......................................................................................................

3.2 Applying the Astrometry..........................................................................................

3.3 Applying the Sextractor.............................................................................................

3.4 Uploading the Data to the Calibration Server......................................................

1.0 GENERAL INFORMATION

1.0 GENERAL INFORMATION

This manual explains the photometric reduction of the data received from JoanOró Telescope(TJO) at Observatori Astronòmic del Montsec(OAdM) step by step withall the priori installations for future usage. In this manual photometric reduction will bedone by Astropy.

1.1 System Overview

Before starting the reduction procedure, one should have all the listed programsand packages installed and ready. If you have already some of the packages installed,the current versions of python packages can be checked after opening and importing theone by the command : packagename.__version__

Python 2.6.5 , 2.7.x , 3.3.x or 3.4.x

Astropy 1.0

Numpy 1.6.0 or later

Matplotlib 1.4.3

Ccdproc 0.3

Astrometry.net 0.5

Scipy 0.13.3 or later

Sextractor 2.19.5

For all astronomers, Python 2.7 is the most useful and recommended languageversion. It is also known that Astropy has bugs and more difficulties with Python 3versions. All the process that will be explained in this manual is done with Python 2.7.5.

1.2 Installation Notes

For the first time installers for everything, Python 2.6,2.7,3.3,3.4 and around 270packages(including Astropy, Numpy, Matplotlib, Scipy, ccdproc) that Python uses canbe gained by a simple installation of Anaconda Scientific Python Distribution.

1.2.1 Python

Python can be installed for all the environments with ease. All the versions ofPython for specific installations are available on the official site of Python downloadspage.

Most recommended one for scientific usage is the version 2.7.

1.2.2 Astropy

Astropy is the main package our reduction process requires. Before installingAstropy, one should already have installed Numpy, Matplotlib and Scipy which can beeasily done from a terminal in Ubuntu & Debian with the following command :

$ sudo apt-get install python-numpy python-scipy python-matplotlib

Upon successful installation of the packages on top, one can install Astropy usingpip with simply calling :

$ pip install --no-deps astropy

Pip is a general easy install tool for python packages. If you don't have pip, it canbe installed before calling the astropy installation by :

$ python get-pip.py

Also make sure that you have the installing compilers such as gcc. This can bechecked and obtained by :

$ sudo apt-get update$ sudo apt-get upgrade$ sudo apt-get install build-essential$ gcc -v$ make -v

If any permission errors occurs during the installation of Astropy, sudo commandcan be used to bypass that permission errors.

Astropy can also be installed from the binary installers by downloading therelated version from the page : astropy and then simply using the build and installcommands from the root of the source directory :

$ python setup.py build$ python setup.py install

If you have installed Anaconda package all you have to do is just run :

$ conda update astropy

1.2.3 CCDProc

To install with pip we simply run :

$ pip install --no-deps ccdproc

Also can be installed from the binary installers by downloading the latest versionfrom the page : ccdproc and then simply using the build and install commands from theroot of the source directory :

$ python setup.py build$ python setup.py install

1.2.4 Astrometry.net

Astrometry is what we use to give our data(from OAdM), astronomic coordinatescompared with 2MASS data fits we have(previusly downloaded index files). This is afast and automatic procedure. It basically compares two fields and gives the coordinatesfor the matched targets.

Installing Astrometry.net is quite easy. There are more than one way to get theprogram but simply all we have to do is write these commands on the terminal :

$ wget http://astrometry.net/downloads/astrometry.net-0.46.tar.bz2$ tar xjf astrometry.net-0.46.tar.bz2$ cd astrometry.net-0.46$ make$ make py$ make extra

$ make install

In order to have full functionality, we will have to check or get if we have all therequired packages ;

GNU build tools (gcc/clang, make, etc.)

cairo

netpbm

libpng

libjpeg

libz

bzip2

python

numpy

We can acquire all this packages by the following command :

$ sudo apt-get install libcairo2-dev libnetpbm10-dev netpbm libpng12-dev libjpeg-devpython-numpy python-pyfits python-dev zlib1g-dev libbz2-dev swig cfitsio-dev

In order to use Astrometry.net, we have to download several fields that we willbe using. This can be done through the web page : Astrometry

One has to download all between index-4202-00.fits and index-4202-47.fits

After downloading all the index files, we need to put them into thecorresponding folder. Which can be checked from “cfg” file of the program. If we wantto change the current location of the data or need to keep it on some other places otherthan the default path, we can change the add_path to the desired location such as :

add_path /home/USERNAME/astrometry/dataautoindex

1.2.5 Sextractor

Sextractor is a software for source extraction. It creates a catalog of objects froman astronomical image. To obtain Sextractor(for Ubuntu 14.04 or higher) :

$ sudo apt-get install sextractor

Sextractor can also be downloaded from the official web page : Sextractor.

After downloading the Source file we uncompress the tar.gz file and go to thatdirectory and :

$ ./configure$ make$ sudo make install

If we get an error on the part ./configure , we can try using :

$ ./configure --disable-model-fitting

In order to be able to use the Sextractor for our purposes we need theconfiguration and parameter files called (default.param and default.sex) and we need tomodify the default.param to :

MAG_AUTO

MAGERR_AUTO

ALPHA_J2000

DELTA_J2000

Also we will need to change the configuration file(default.sex) with :

CATALOG_NAME to TJOtest.catCATALOG_TYPE to ASCII_HEADPARAMETERS_NAME to /home/umutt/default.param #wherever our

param file is

We can specifically put our file to any location we want in my case I use homefolder and we can call the program while using such as :

sex -c /home/umutt/default.sex IMAGENAME.new

2.0 TARGET SELECTION

2.0 TARGET SELECTION

Target selection for TJO observations are done by daily controlling of the GaiaScience Alerts web page. Not all the alerts are published as the same date when Gaiadetected the alerts. Generally, alerts come within 5 to 10 days after the alert detectiondate since all this process is still manually done by the Gaia Photometric Science AlertsTeam. Also not all the detected alerts are published via the web page. At first ScienceAlerts Team performs some criteria to the alerts and the chosen ones are published inthe web page.

Before starting to observe any target I would suggest to go the CambridgePhotometry Calibration Server and check for the target if any observations were done byother observatories and etc. This might give some ideas about the current state of thealert.

Selection of the target is based on 3 steps. First and the most important one is themagnitude limit. As a starting point anything brighter than V<17.5 magnitude is goodenough to do follow-ups since day by day the target will loose its brightness, thebrighter the starting magnitude the more time we will have to observe the target.

Another important condition is the alert publication date since these transientsloose their magnitudes very quickly, the sooner we start the observations, the morepossibly we will be able to catch a maximum and we will have the opportunity toobserve the target for a longer period of time and will end up with a more completelight curve.

Last but not least, another important point is the star altitude, we must haveenough time to observe the target during the night. This condition must be checkedconsidering an airmass below 1.55 (above 40 degrees) in order to keep the atmosphericair turbulence minimum. In general we use 4 filters and for each filter we ask for 3exposures each having 300 seconds of exposure time. Therefore, a minimum of 1 hourand 5 minutes of time is required for these conditions.

After the first observation we would have some ideas about the current state ofthe alert like if it is still in the magnitude reach and etc. After a few days of observationseach target must be checked to see if the light curves are stable or not. Stable light curvewould most probably mean that the alert is missed (recovered its original state by thetime our observations started). Also if we start to get very faint results with big errors,we must stop observing as well. Day by day checking the CPCS page can give moreideas about each target and how our light curve is getting built. There might be otherobservatories contributing for the same target so we might see more data points.

3.0 PHOTOMETRIC REDUCTION

3.0 PHOTOMETRIC REDUCTION

In this part of the manual, I will describe the photometric reduction that we needto do before submitting the data to the Gaia Consortium. What we will do is basically,first clean the observation data of TJO from the effects of bias, dark and flats.

After that we will use Astrometry.net to give the astronomic coordinates to thesources in the images we have. Then, we will use Sextractor to create the final catalogfile that we will submit to the Cambridge Calibration Server page.

3.1 Cleaning the Data

Our first step to start the reduction process is to clean the data we receive fromOAdM. In order to do that we use Astropy and CCDProc. What we basically do iscombine the flats, combine the bias and apply the darks to our scientific rawimages(imr.fits) on the folder.

In order to do that, we will use a python code that can be obtained from here. Weput this code to the folder where our data is. Then we open a terminal and go to thatdirectory and call ; python clean_data.py

Successful trials always end up with new files named “imc.fits” created. Thesefiles are the cleaned files we need. After having these files, we can delete all the otheroutcomes and everything else.

3.2 Applying the Astrometry.net

Upon cleaning the data what we have to do is first call the Astrometry inorder to give the coordinates to the stars we have on our images. This process isautomatically done by comparing the index files we have downloaded and thenew images we have.

We will be using the command solve-field in order to do that. An exampleof the full code that we need is :

$ solve-field --use-sextractor --overwrite TJO2456957.61754_R_imc.fits--ra 43.7 --dec -6.46 --radius 1 --no-plots

The code we have includes the followings :

ra : Right Ascension(ICRS, decimal degrees)dec : Declination (ICRS, decimal degrees)use-sextractor : Sextractor can be called and used to extract the sourcesoverwrite : Uses our image to create a same named file with .new formatradius 1 : Matching radius is 1 by defaultno-plots : After the process no plots will appear We have to use this code to each image we have separately because in one

folder there may be more than one targets and for each target we will have tomodify our RA and DEC in our code.

Successful completion of the process will end up with the creation of 8 newfiles. What we will need is the one with the format “.new”

Our code will end up something similar like this upon successfulcompletion :

Fig.1 : Astrometry result on terminal

We can delete all the files created during this process except “imc.new”

If there are any errors, make sure you have entered the correct ra and decfor the target you are using at that moment. That is essential to do thecomparison purposes with the index files.

3.3 Applying the Sextractor

After successfully obtaining the “imc.new” file with Astrometry.net we need toextract the sources from that image with the Sextractor in order to create a catalog. Thiscan simply be done with the terminal by calling :

$ sex -c /home/umutt/default.sex TJO2457127.55590_U_imc.new

or depending on the installation method it can be :

$ sextractor -c /home/umutt/default.sex TJO2457127.55590_U_imc.new

Upon successful completion we will receive a catalog file named TJOtest.cat andour terminal will look like something similar to the image below :

Fig.2 : Sextractor result on terminal

3.4 Uploading the Data to the Calibration Server

Once we have the catalog file created by the Sextractor, what we need to do is toupload it to the Cambridge Photometry Calibration Server (CPCS). The main purpose ofthe CPCS is to provide homogeneous photometric follow ups within the astronomersworking with Gaia Science Alerts. Our aim is to provide informations and build a lightcurve with the targets we observe. For that purposes we should clean and upload thedata we have received within 24 hours.

In order to be able to upload any data to the CPCS we need a hastag to login thesystem. Which can be obtained from Dr. Lukasz Wyrzykowski.

After logging in, we click on Upload new followup data. There we will have someinformations to be filled :

Event ID : The name of the target we have observed, must begin withivo:// such as ivo://Gaia15adb , In case our target does not exist we can create it fromthe main page of the CPCS by clicking Enter new event and filling all the necessaryinformations

MJD OBS : Modified Julien Data of the observation. Julien Date of theobservation can be obtained from the Header of the image with ds9 or some otherimaging program. Then, MJD = JD - 2400000.5

Exposure time(sec) : Can also be obtained from the Header of the image ifunknown.

Comment(optional) : If we have any comment about uploading the data

Sextractor catalog : We need to upload the TJOtest.cat data here

Matching radius : We choose 1 arcsec

Force filter : The filter of the image we are uploading, can be obtainedfrom the Header of the image. In case we do not know, No (automatic determination)can be chosen. When clicked we will see options such as SDSS, APASS, VSTATLAS,OGLE3 and so on. We will be uploading our data in APASS form for all the bands( B-V-R-I). Using the automatic determination is not encouraged.

Dry Run : This is a mode that will not store the data on the serverupon uploading. We can use this mode to see which filter we have in case we don'tknow it. We can also check how it behaves with other filters and so on.

In case of uploading the data somehow wrong, the data point can be deletedfrom the system by going the Delete a followup point from the system from the homepage.

We can access any data uploaded to the server including our data and light curvefrom the Lists of alerts page from the home page.

Upon successful upload we can see our data point in the system both from thelist of follow-up data page and from the light curve such as in case of Gaia15adb :

Light curve will be currently updated upon uploading new data, not only by usbut also everyone else. There we will be seeing the apparent magnitude of our target wehave uploaded. Which is automatically determined by the field stars upon uploadingthe server.

We can also obtain the apparent magnitude of our data by going to the catalogfile and searching for the coordinates of our target and identifying it. There we will beseeing the instrumental magnitude of our target. What we need to do now is thedifferential photometry. We can check the coordinates of the known stars from Vizierand get their apparent magnitude to determine the factor between our instrumentalmagnitude and the apparent magnitude. Then we can apply this factor to our target andobtain the apparent magnitude of our target.