Society for Popular Astronomy

PanSTARRS DR2 Temporal Photometry now available
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Author:  JohnM [ Thu Feb 07, 2019 9:55 pm ]
Post subject:  PanSTARRS DR2 Temporal Photometry now available

If you are interested in the light curves of variable start the PanSTARRS team have now released the temporal photometry in 5 bands on 'several' billion stars. The entire data set is around 1.6 petabytes so no chance of downloading it all !

However there are several tools that allow access to the photometry for specific stars. The servers also allow images to be downloaded. These are very deep going well into the 20th magnitude band.

There are some glitches in the access and analysis that I am currently trying to find work arounds for. I will write this up in due course and publish it on my website however I am waiting for some 'bugs' in the PanSTARRS data format and in Aladin to be fixed. Not sure when this will happen but they are working on it.

If you are interested in accessing this data in the meantime either respond to this thread or send me a private message.

John Murrell

Author:  JohnM [ Fri Feb 15, 2019 10:10 pm ]
Post subject:  Re: PanSTARRS DR2 Temporal Photometry now available

If you download the PanSTARRS DR2 photometry data as a Virtual Observatory .XML file rather than a CSV file there are two problems with the format of the .XML file you need to be aware of.

1: The data is stored in single element arrays - while not wrong I have been told this is unusual or even eccentric. Loading the data into TOpCat results in the data fields not showing in the drop down selection fields and you have to manually enter the values as RequiredFieldName[1]. [1] is the first element in the one element array RequiredFieldName. I have used RequiredField name as a generic for any field but you normally be using something like obsTime or PSFFlux.

2: The data types for some of the long numbers are wrongly described as ‘float’ in the XML file header. This results in some numbers with lots of significant figures being truncated – for instance the observation time is truncated to 0.01 MJD about 14.4 minutes ! The numbers should be described as double which allows all the digits in the values in the file to be read in.

Problem I was reported to the Space Telescope Science Institute (STSCI) by the author of TopCat following an email question from me.
The second one I reported to STSCI by me directly and they said that they were already aware of this problem.

In both cases they have promised a fix ‘shortly’.

Meanwhile either download the data as a CSV file which contains the full precision of the values in a format TopCat will read but does not load some additional information such as the measurement units.

An alternative is to edit the header of the .xml file either with a text editor or an XML file editor. You need to use a text editor such as Notepad++ that understands Linux line endings if you are using a windows computer.

You will find lines similar to the following:
<FIELD ID="psfFlux" arraysize="*" datatype="float" name="psfFlux">
To fix problem 1 delete ‘arraysize="*"’, the only thing to be aware of is that if the datatype = “char” do not delete the ‘arraysize=”*”’ as you will break the file ! However the temporal DR2 data has no “char” type data.

To fix problem 2 replace all the instances of “float” with “double”. It will use a bit more memory to load the file but should not be significant.

Save the file before exiting preferably with a different name in case you have broken it !

John Murrell

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